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WO2024261679A1 - System and method for detecting defects in a bottom wall of plastic caps - Google Patents

System and method for detecting defects in a bottom wall of plastic caps Download PDF

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Publication number
WO2024261679A1
WO2024261679A1 PCT/IB2024/056018 IB2024056018W WO2024261679A1 WO 2024261679 A1 WO2024261679 A1 WO 2024261679A1 IB 2024056018 W IB2024056018 W IB 2024056018W WO 2024261679 A1 WO2024261679 A1 WO 2024261679A1
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WO
WIPO (PCT)
Prior art keywords
value
voltage
cap
testing position
humidity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/IB2024/056018
Other languages
French (fr)
Inventor
Carlo Cassani
Paolo GASPERONI
Antonio GUADAGNINI
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sacmi Imola SC
Original Assignee
Sacmi Imola SC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sacmi Imola SC filed Critical Sacmi Imola SC
Publication of WO2024261679A1 publication Critical patent/WO2024261679A1/en
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/60—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrostatic variables, e.g. electrographic flaw testing
    • G01N27/61—Investigating the presence of flaws
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
    • B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
    • B07C5/34—Sorting according to other particular properties
    • B07C5/3404—Sorting according to other particular properties according to properties of containers or receptacles, e.g. rigidity, leaks, fill-level
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
    • B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
    • B07C5/34—Sorting according to other particular properties
    • B07C5/344—Sorting according to other particular properties according to electric or electromagnetic properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M3/00—Investigating fluid-tightness of structures
    • G01M3/40—Investigating fluid-tightness of structures by using electric means, e.g. by observing electric discharges
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0078—Testing material properties on manufactured objects
    • G01N33/0081—Containers; Packages; Bottles

Definitions

  • This invention relates to a system and a method for detecting defects in a bottom wall of plastic caps.
  • micro-holes or cracks may form in the bottom wall of the caps.
  • Micro holes make the caps unfit for use and it is therefore very important to detect and discard any defective caps which have micro holes in them. These holes are not visible to the human eye or to a camera.
  • one of the known methods of detecting defective caps with micro holes in them involves the use of an electrical field. In particular, a voltage is applied across two electrodes and the cap to be inspected is placed between the two electrodes.
  • an electric discharge occurs between the electrodes only if the cap has a hole in it; that is because the cap acts as a dielectric and the presence of the micro holes in the cap changes the dielectric rigidity of the cap.
  • the hole is usually formed at the point of injection and, in particular, at the centre of the bottom wall of the cap.
  • patent document DE102013014473 describes a device which uses high voltage to detect plastic caps with holes in the bottom wall and which comprises a star wheel with a plurality of arms acting as an upper electrode and a lower electrode located under the star wheel, wherein a voltage is applied across the electrodes.
  • the caps are transported along a feeding direction and the arms of the star wheel are immersed one after the other in the respective caps so that the bottom walls of the caps are interposed one after the other between the electrodes.
  • the choice of the correct voltage should be such as not to exceed the dielectric rigidity of the cap if the cap does not have any holes in it.
  • Patent document EP3204762B1 also describes a method for testing plastic caps to detect the presence of holes or cracks in their bottom surface.
  • each cap is placed between an upper electrode, connected to a first voltage generator, and a lower electrode, connected to a second voltage generator, where the two voltage generators are electrically connected in series.
  • the first and the second voltage generator are such that the first voltage generator generates a voltage only when there is a cap between the upper electrode and the lower electrode, whilst the second voltage generator generates a voltage continuously. Furthermore, the voltages generated by the two voltage generators are monitored so that the sum of the two voltages is greater than or equal to the breakdown voltage across the electrodes in air and less than the breakdown voltage across the electrodes through a cap without holes in it, and when a dielectric breakdown across the electrodes is detected, the cap is identified as defective.
  • patent document JP2006084362 concerns a machine for inspecting the quality of a sealing portion of a liquid container.
  • This document provides for a first electrode positioned to face a predetermined surface of the subject and a second electrode positioned to face the sealing portion of the subject.
  • the document provides for the application of an electrical voltage between the first and second electrodes, adjustable based on a detected value for the ambient humidity or the ambient temperature.
  • the aim of this invention is to provide an apparatus and a method for detecting defects in a bottom wall of plastic caps to overcome the above mentioned disadvantages of the prior art.
  • this disclosure provides a system for detecting defects in a bottom wall of plastic caps (closures).
  • the system for detecting defects in a bottom wall of plastic caps may be used to inspect different types of plastic closures and, generally speaking, plastic items made by injection moulding.
  • the system might be a stand-alone system or it may be integrated in another machine, for example, a plastic cap cutting machine where the injection- moulded caps are processed.
  • the system for detecting defects in a bottom wall of plastic caps (or the system, for short) comprises a conveyor.
  • the conveyor is used for transporting a succession of plastic caps along a feeding path. In particular, there is a testing position on the feeding path.
  • the system comprises an electrode arrangement.
  • the electrode arrangement includes an upper electrode.
  • the upper electrode is situated above the bottom wall of the plastic cap located at the testing position.
  • the electrode arrangement also includes a lower electrode.
  • the lower electrode is situated under the bottom wall of the plastic cap located at the testing position.
  • the upper electrode and the lower electrode are positioned in such a way that each cap at the testing position is interposed between the upper electrode and the lower electrode.
  • the system also includes a voltage generator.
  • the voltage generator is connected to the electrode arrangement.
  • the voltage generator is configured to apply an operating electric potential difference (that is to say, voltage) between the upper and the lower electrode.
  • the generator applies the operating electric potential difference between the upper and the lower electrode continuously.
  • the generator may apply the operating voltage discontinuously, for example, only when the cap is located at the testing position.
  • the system includes a control unit.
  • the control unit is configured to detect whether the cap is defective.
  • the control unit is configured to detect whether the cap is defective responsive to detection of an electric discharge occurring between the upper and lower electrodes through the plastic cap located at the testing position.
  • the system includes a humidity detection device.
  • the humidity detection device is configured to detect a control parameter.
  • the control parameter is representative of an environmental humidity value at the testing position.
  • the expression "environmental humidity value at the testing position" is used to mean the humidity of the environment surrounding the cap located at the testing position.
  • the control unit is connected to the voltage generator.
  • the control unit is also connected to the humidity detection device.
  • the control unit is configured to adjust the operating electric potential difference generated by the voltage generator in response to the environmental humidity value at the testing position.
  • the operating voltage generated by the generator is set as a function of the humidity of the environment in which the caps are tested.
  • the value of the voltage to be applied between the electrodes to check for the presence of holes in the plastic cap is influenced by several different parameters; of these parameters, the environmental humidity has a considerable influence on the optimum voltage value. For example, the drier the air, the higher the optimum value of the voltage.
  • adjusting the operating voltage in response to the humidity detected allows providing a system for detecting defects in plastic caps with a particularly high level of reliability.
  • the control unit can be configured to adjust the operating electric potential difference generated by the electric voltage generator in response to the speed at which the conveyor moves and consequently the speed at which the capsules are transported along the feed path. Therefore, the voltage can be adjusted based on a control parameter that is representative of an ambient humidity value and/or based on a speed parameter that is representative of a conveyor speed value. If the conveyor speed increases, there is less time for discharge and thus a higher electric field is required to allow the air to ionize more quickly, which can lead to a voltage adjustment based on the speed at which the capsules are transported.
  • the system includes a speed detection device.
  • the speed detection device is configured to detect a speed parameter representative of the speed value of the conveyor movement.
  • the control unit is programmed to adjust the operating electric potential difference generated by the electric voltage generator in response to the conveyor movement speed value detected by the speed detection device.
  • the speed device includes a speed sensor.
  • the solution where the control parameter is representative of the ambient humidity value (e.g., relative humidity) or the conveyor speed, as well as the solution where the control parameter is representative of both the ambient humidity value (e.g., relative humidity) and the conveyor speed can be combined with one or more aspects of the present description.
  • the voltage is adjusted based on both humidity (or specifically relative humidity) and conveyor speed
  • it may be provided to have a plurality of reference data.
  • Such reference data can be obtained from prior knowledge or calibrations.
  • These reference data can be matrix data. Additionally or alternatively to using such matrix data, it is possible to derive the correct operating voltage value by performing an automatic search procedure with a voltage ramp. Using the voltage ramp may require time and examples of defective caps.
  • a memory can be provided with a plurality of values for the control parameter (humidity), the speed parameter, and a corresponding plurality of reference voltage values.
  • the control unit is programmed to select a voltage setpoint value based on the control parameter value and the speed parameter value detected by the humidity detection device and the speed detection device, respectively, and the plurality of reference voltage values.
  • the humidity detection device includes a humidity sensor.
  • the humidity sensor is configured to detect the relative humidity of the testing environment (the environment surrounding the testing position).
  • the humidity detection device also includes a temperature sensor.
  • the temperature sensor is configured to detect the temperature of the testing environment.
  • the humidity detection device is configured to calculate a volumetric humidity value of the testing environment.
  • the humidity detection device is configured to calculate the volumetric humidity value of the testing environment based on the relative humidity and the temperature detected by the humidity sensor and the temperature sensor.
  • the control parameter represents the volumetric humidity.
  • This configuration allows the operating voltage to be adjusted on the basis of the quantity (mg) of water in one cubic metre of the environment, to obtain a more precise adjustment.
  • the system also includes a memory.
  • the memory contains a voltage setpoint value.
  • the voltage generator is configured to generate the operating electric potential difference between the upper and the lower electrode in response to the voltage setpoint value.
  • the control unit is also configured to update the voltage setpoint value in response to detection of that control parameter.
  • the memory may comprise a plurality of values for the control parameter.
  • the memory also comprises a plurality of reference voltage values.
  • the control unit is programmed to select a value for the voltage setpoint as a function of the value of the control parameter detected by the humidity detection device and of the plurality of voltage reference values.
  • This configuration can match a plurality of reference values for the voltage with a plurality of values for the control parameter (humidity) which can be used to select the optimum setpoint value effectively and precisely.
  • control unit is configured to check the value of the control parameter.
  • the control unit is also configured to select the voltage setpoint value.
  • the setpoint value is calculated using the verified control parameter and the plurality of voltage reference values.
  • the control unit is also configured to detect an update value of the operating electric potential difference.
  • the update value of the operating electric potential difference is the value of the voltage detected in real time.
  • the term "update value” is used to mean a value of the operating electric potential difference detected while the system is in operation and detection can be performed after a predetermined length of time has elapsed from the moment the system started operating.
  • the control unit is programmed to compare the update value of the operating electric potential difference to the selected voltage setpoint value.
  • the control unit is also programmed to adjust the update value of the operating electric potential difference to the selected voltage setpoint value if the difference between the update value of the operating electric potential difference and the selected voltage setpoint value exceeds a predetermined threshold.
  • the value of the control parameter and the value of the operating voltage can be detected one or more times during system operation, and the voltage value at the moment of detection in real time (that is to say, update value of the operating electric potential difference) is compared to the selected setpoint, using the plurality of voltage reference values and the plurality of values for the control parameter, for the value of control parameter detected in real time; if the difference between the two values exceeds a predetermined threshold, the operating voltage value is updated.
  • This control allows the precision and reliability of the system to be considerably increased.
  • the term “real time” is used with reference to a data analysis process by which input data are analysed as soon as they enter a data processing system.
  • the feedback control could be performed automatically and, for example, at predetermined time intervals.
  • the feedback control might be in response to a control request entered by the operator.
  • the conveyor comprises a carousel.
  • the carousel has a plurality of housings.
  • the housings are distributed along the periphery of the carousel.
  • the housings are used to accommodate the respective plurality of caps.
  • the carousel rotates around a first rotation axis.
  • the carousel rotates around the first rotation axis to transport the caps to the testing position.
  • the electrode arrangement may include a star unit.
  • the star unit is configured to rotate about a second rotation axis.
  • the second rotation axis is perpendicular to the first rotation axis.
  • the star unit may be provided with a plurality of arms. The arms protrude radially with respect to the second rotation axis. The arms are uniformly distributed around the second rotation axis.
  • the electrode arrangement includes a plurality of upper electrodes.
  • the upper electrodes of the plurality of upper electrodes may be provided at the tips of the arms.
  • the electrode arrangement may also include an actuator.
  • the actuator is connected to the star unit.
  • the actuator is configured to rotate the star unit in synchrony with the movement of the carousel.
  • the actuator is configured to rotate the star unit in such a way that each of the plurality of upper electrodes engages a respective cap in the respective housings, one at a time at the testing position.
  • the system may have a camera to detect the presence of the caps in the carousel housings.
  • the camera detects that there is no cap in the housing, the presence of a defective cap is not detected and consequently the cap is not discarded.
  • the feeding path comprises a groove.
  • the groove is configured to house the caps.
  • the groove houses the caps in such a way that the caps move in a row along a feeding direction.
  • the electrode arrangement includes a star unit.
  • the star unit is configured to rotate around a rotation axis.
  • the rotation axis is perpendicular to the feeding direction.
  • the star unit is provided with a plurality of arms. The plurality of arms protrude radially with respect to the rotation axis. The plurality of arms are uniformly distributed around the rotation axis.
  • the electrode arrangement includes a plurality of upper electrodes.
  • each of the plurality of arms is provided with a respective upper electrode.
  • the star unit is configured to rotate around the rotation axis in response to each of the plurality of upper electrodes engaging a respective cap at the testing position and to the cap moving along the feeding direction.
  • the conveyor may comprise a belt.
  • the belt may extend longitudinally.
  • the system comprises an idle star unit which moves freely when one of the plurality of arms is inserted into a respective cap and the cap moves along the conveyor in the feeding direction.
  • This solution allows feeding the caps in a row one after the other along the feeding path and having a relatively low voltage across the electrodes continuously.
  • This embodiment does not require an actuator because the star is entrained by the caps; it is therefore possible to obtain a particularly efficient system that is at once lower in cost and less complicated in structure.
  • the upper electrode and the lower electrode may be located at a fixed position above the conveyor and at a position below the conveyor, respectively; thus, the generator applies operating voltage only when the cap is between the upper electrode and the lower electrode at the testing position.
  • the conveyor includes a belt. The belt may extend along a horizontal direction. This example, therefore, does not require movable upper electrodes.
  • the electrode arrangement comprises a plurality of lower electrodes.
  • the conveyor might include lower electrode housings.
  • each of the plurality of lower electrode housings is configured to receive a respective lower electrode.
  • the lower electrode housings may be spaced from each other along the conveyor.
  • the lower electrode housings are located on the conveyor and each cap is positioned on the respective lower electrode so that the lower electrode is inserted into the cap. The caps therefore face down in such a way that the lower electrode comes into contact with the bottom wall of the cap.
  • the electrode arrangement includes only one upper electrode, fixed at the testing position; when the cap, with the lower electrode in it, reaches the testing position, the generator applies the test voltage.
  • the conveyor may include a belt. The belt extends longitudinally. The solution of the example in which the conveyor is provided with lower electrode housings allows having a relatively low voltage continuously.
  • the voltage generator comprises a plurality of capacitors.
  • the capacitors are configured to generate the operating voltage.
  • the capacitors generate the operating voltage, starting from an input voltage.
  • the input voltage is lower than the operating voltage.
  • the capacitors undertake an electrical discharge transient.
  • the system also includes an electrical resistor. The electrical resistor is connected to the plurality of capacitors, so that the electrical discharge transient is slower than it would be without the electrical resistor.
  • Providing the generator with a plurality of capacitors allows having a smaller, less cumbersome generator.
  • Providing the generator with an electrical resistor allows having a slower electrical discharge transient so that the generator generates the voltage more rapidly after the discharge; it is therefore possible to feed the caps at a higher speed along the feeding path, thus enhancing the efficiency of the system.
  • this solution increases the readiness of the system for subsequent detection or discharge.
  • a possible alternative to the capacitive generator described herein is an inductive generator, which would not require resistance.
  • the inductive generator would have the disadvantage of being bulkier and more expensive, and it would make the detection of the discharge event more difficult, thus potentially making the system less reliable/robust.
  • this disclosure provides a method for detecting defects in a bottom wall of plastic caps.
  • the method comprises a step of transporting a succession of plastic caps along a feeding path.
  • the method comprises a step of positioning the cap at a testing position.
  • the testing position is located on the feeding path.
  • the method comprises a step of providing an electrode arrangement.
  • the method comprises a step of providing the electrode arrangement with an upper electrode.
  • the upper electrode is situated above the bottom wall of the plastic cap.
  • the method also comprises a step of providing the electrode arrangement with a lower electrode.
  • the lower electrode is situated under the bottom wall of the plastic cap at the testing position.
  • the method comprises a step of positioning the cap between the upper electrode and the lower electrode.
  • the method comprises a step of generating an operating electric potential difference (that is, a voltage) across the upper electrode and the lower electrode.
  • the operating voltage is applied across the lower electrode and the upper electrode by a voltage generator.
  • the method comprises a step of verifying that the cap is defective when an electric discharge occurs between the upper and lower electrodes through the plastic cap located at the testing position.
  • the method also comprises a step of detecting a control parameter.
  • the control parameter is representative of an environmental humidity value at the testing position.
  • the method comprises a step of adjusting the operating electric potential difference generated by the voltage generator as a function of the humidity value of the testing environment.
  • the method comprises a step of detecting the relative humidity of the testing environment.
  • the method also comprises a step of detecting the temperature of the testing environment.
  • the method comprises a step of calculating a volumetric humidity value of the testing environment based on the detected relative humidity and temperature.
  • the control parameter represents the volumetric humidity.
  • the method comprises a step of saving a voltage setpoint value.
  • the method comprises a step of generating the operating electric potential difference between the upper and the lower electrode in response to the voltage setpoint value.
  • the method also comprises a step of updating the voltage setpoint value in response to detection of the control parameter.
  • the method comprises a step of saving a plurality of values for the control parameter and a corresponding plurality of voltage reference values.
  • the method comprises a step of selecting the value for the voltage setpoint as a function of the detected value of the control parameter and of the plurality of voltage reference values.
  • the method comprises a step of checking the value of the control parameter.
  • the method comprises a step of selecting the voltage setpoint value.
  • the method comprises a step of detecting an update value of the operating electric potential difference.
  • the method comprises a step of comparing the update value of the operating electric potential difference to the selected voltage setpoint value.
  • the method comprises a step of adjusting the operating electric potential difference update value to the selected voltage setpoint value if the difference between the operating electric potential difference update value and the selected voltage setpoint value exceeds a predetermined threshold.
  • the method comprises a step of providing a carousel.
  • the carousel has a plurality of housings. The housings are distributed along the periphery of the carousel.
  • the method comprises a step of accommodating the caps in the respective housings.
  • the method also comprises a step of rotating the carousel around a first rotation axis to transport the caps to the testing position.
  • the method comprises a step of providing the electrode arrangement with a star unit.
  • the star unit rotates about a second rotation axis.
  • the second rotation axis is perpendicular to the first rotation axis.
  • the star unit is provided with a plurality of arms. The arms protrude radially with respect to the second rotation axis. The arms are uniformly distributed around the second rotation axis.
  • the method comprises a step of providing the electrode arrangement with a plurality of upper electrodes.
  • the upper electrodes may be provided at the tips of the arms.
  • the method comprises a step of rotating the star unit by means of an actuator.
  • the star unit is rotated in a synchronized way with respect to the movement of the carousel, so that each of the plurality of upper electrodes engages a respective cap in the respective housings, one at a time at the testing position.
  • the method comprises a step of providing the voltage generator with a plurality of capacitors.
  • the capacitors generate the operating voltage, starting from an input voltage.
  • the input voltage is lower than the operating voltage.
  • the capacitors undertake an electrical discharge transient.
  • the method comprises a step of connecting an electrical resistor to the plurality of capacitors, so that the electrical discharge transient is slower than it would be without the electrical resistor.
  • FIGS. 1 -3 illustrate a system for detecting defects in a bottom wall of plastic caps according to this disclosure, in a first embodiment, where the caps are transported by a carousel;
  • the numeral 1 denotes a system for detecting defects in a bottom wall BW of plastic caps C.
  • the system 1 comprises a conveyor 2 for transporting a succession of plastic caps C along a feeding path F. On the feeding path there is a testing position T.
  • the system 1 also comprises an electrode arrangement 3.
  • the electrode arrangement includes an upper electrode 301 , located above the bottom wall BW of the plastic cap C located at the testing position T, and a lower electrode 302, located beneath the bottom wall BW of the plastic cap C located at the testing position T.
  • each cap when it is located at the testing position T, is interposed between the upper electrode 301 and the lower electrode 302.
  • the system 1 includes a voltage generator 5.
  • the voltage generator (or generator, for short) is connected to the electrode arrangement 3 and is configured to apply an operating electric potential difference between the upper electrode 301 and the lower electrode 302.
  • the system 1 includes a control unit 6.
  • the control unit 6 is configured to detect whether the cap C is defective.
  • the cap is identified as defective when an electric discharge occurs between the upper and lower electrodes through the plastic cap while the cap is at the testing position T.
  • the system also has a humidity detection device 7 for detecting a control parameter.
  • the control parameter is the environmental humidity value at the testing position T.
  • the humidity value of the environment surrounding the caps at the testing position is detected and the operating electric potential difference across the electrodes 301 , 302 is adjusted responsive to the detected humidity value of the environment.
  • system may also include a speed detection device to detect the speed value of the conveyor movement.
  • control unit is programmed to adjust the operating electric potential difference generated by the electric voltage generator in response to the speed value of the conveyor movement.
  • the caps are transported along the feeding path F and the operating voltage is applied to the electrodes.
  • the caps are placed at the testing position T (interposed between the upper electrode and the lower electrode) individually (one at a time).
  • the upper electrode 301 and the lower electrode 302 are placed in the cap, in contact with the bottom wall BW of the cap.
  • the upper electrode and the lower electrode are aligned along a vertical direction.
  • the electrode that is placed inside the cap is inserted into the cap C at a central point of the bottom wall BW thereof.
  • the voltage generator comprises a plurality of capacitors for generating the operating voltage, starting from an input voltage that is lower than the operating voltage. Further, when the discharge occurs across the upper electrode 301 and the lower electrode 302 at the testing position T, the capacitors undertake an electrical discharge transient.
  • the system 1 also includes an electrical resistor, connected to the plurality of capacitors, so that the electrical discharge transient is slower than it would be without the electrical resistor.
  • the resistor is electrically connected in series to the plurality of capacitors.
  • the humidity detection device includes a humidity sensor to detect the relative humidity of the testing environment, and a temperature sensor to detect the temperature of the testing environment.
  • a volumetric humidity value of the testing environment is calculated on the basis of the relative humidity and temperature detected by the humidity sensor and the temperature sensor.
  • the volumetric humidity value may be calculated by a processing unit connected to the humidity and temperature sensors to receive data relating to the relative humidity and the temperature.
  • the operating voltage is adjusted in response to the calculated value for the volumetric humidity of the environment at the testing position T.
  • the system 1 also includes a memory.
  • the memory is used to store a voltage setpoint value.
  • the operating electric potential difference between the upper and the lower electrode is generated in response to the voltage setpoint value.
  • the operating voltage is therefore set on the basis of the setpoint stored.
  • the setpoint value depends on the value of the control parameter (that is, the humidity of the environment). In effect, the setpoint value is updated each time the value of the control parameter is detected.
  • a plurality of values for the control parameter and a corresponding plurality of voltage reference values are stored.
  • the value for the voltage setpoint is selected as a function of the detected value of the control parameter and of the plurality of voltage reference values.
  • the control unit selects the operating voltage setpoint value, which corresponds to the detected value for the control parameter using the plurality of values for the control parameter and the corresponding plurality of voltage reference values.
  • the plurality of values for the control parameter and the corresponding plurality of voltage reference values may be stored in the form of a table or they may form a characteristic curve.
  • Figure 7 shows the curve that describes the relation between the voltage generated across the electrodes and the relative humidity value of the environment.
  • the curve shows an inverse relation between the voltage and the relative humidity and thus, the two parameters change in opposite directions.
  • the characteristic curve is obtained before the system comes into operation; the characteristic curve may, however, be updated by the operator at a later stage. If the plurality of values for the control parameter and the corresponding plurality of voltage reference values are stored in a table, any values not available in the table are obtained by interpolation.
  • the memory can also include a plurality of values for the control parameter, the speed parameter, and a corresponding plurality of reference voltage values.
  • the control unit is programmed to select the voltage setpoint value based on the relative humidity value, conveyor speed value, and corresponding reference voltage value.
  • the plurality of values for ambient humidity at the test position and the plurality of values for conveyor speed, along with the corresponding plurality of reference voltage values can be stored in the form of a table or can form a characterization curve.
  • Such data can be in the form of a data matrix.
  • Figure 9 is a graph depicting the relationship between the reference voltage value, ambient relative humidity value, and conveyor speed value. Therefore, once the ambient relative humidity value and conveyor speed value are detected, these curves can be used to determine the voltage value. This curve is preferably obtained before the system starts operating; however, the characterization curve can be updated later by the operator.
  • the voltage setpoint value depends on the conveyor speed value. For instance, a plurality of values for conveyor speed and a corresponding plurality of reference voltage values are stored. Additionally, the voltage setpoint value is selected based on the speed value and the plurality of reference voltage values. Therefore, when the conveyor speed value is detected, the control unit selects the operational voltage setpoint value corresponding to the detected conveyor speed value using the plurality of values for conveyor speed and the corresponding plurality of reference voltage values.
  • the plurality of values for conveyor speed and the corresponding plurality of reference voltage values can be stored in the form of a table or can form a characterization curve.
  • Figure 8 illustrates the curve describing the relationship between the voltage generated between the electrodes and the conveyor speed value.
  • a feedback control may be performed on the value of the operating voltage across the electrodes.
  • the voltage value is detected in real time (this value may be called the "update value").
  • the humidity value is detected in real time and the voltage setpoint value is detected using the plurality of humidity values and the corresponding plurality of voltage reference values stored. If the voltage value detected in real time does not correspond to the selected setpoint value, and in particular, if the difference between these two values exceeds a predetermined threshold, the operating voltage value is updated so it does correspond to the selected setpoint value.
  • This feedback control may be performed automatically. For example, the control may be performed automatically and periodically at preset time intervals. The control might also be performed directly by the user.
  • the conveyor 2 comprises a carousel 4.
  • the carousel 4 includes a plurality of housings 401.
  • the housings are distributed along the periphery of the carousel 4 and each housing accommodates a respective cap of the plurality of caps C.
  • the housings are spaced from each other.
  • the carousel rotates around a first rotation axis RA1 and transports the caps to the testing position T.
  • the carousel is illustrated in Figures 1 -3.
  • the electrode arrangement 3 includes a star unit S.
  • the star unit rotates around a second rotation axis RA2, perpendicular to the first rotation axis RA1 .
  • the star unit includes a plurality of arms A which protrude radially with respect to the second rotation axis and which are uniformly distributed around the second rotation axis RA2.
  • a plurality of upper electrodes 301 are provided at the tips of the arms A.
  • the star unit S is rotated by an actuator synchronously with respect to the movement of the carousel 4.
  • the carousel rotates and when a cap in the respective housing reaches the testing position T, one of the arms A of the star unit is inserted into the cap so that the cap is interposed between the lower electrode 302 and the upper electrode 301.
  • the lower electrode 302 is located under the bottom wall BW of the cap at a fixed location.
  • the conveyor 2 may comprise a belt.
  • the belt extends along a horizontal direction.
  • the caps to be inspected are fed along the feeding path in a single row along a feeding direction FD.
  • the caps are placed in a row close to each other and are transported towards the testing position T.
  • the caps are placed at the testing position T individually (one at a time).
  • the belt includes a groove G which houses the caps along the feeding direction.
  • the electrode arrangement 3 includes the star unit S.
  • the configuration of the star unit is similar to that described for the first embodiment (described above).
  • the star unit S in this embodiment is not rotated by an actuator.
  • the star unit S is an idle wheel. In this embodiment, therefore, the star unit S rotates freely around a rotation axis RA.
  • the rotation axis RA is perpendicular to the feeding direction.
  • the upper electrodes 301 are located on the respective arms of the star unit S.
  • the upper part of each arm A (the tip of the arm, further from the rotation axis RA) is provided with the respective upper electrode 301.

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Abstract

A system (1) for detecting defects in a bottom wall (BW) of plastic caps (C), comprises: a conveyor (2) for transporting a succession of plastic caps (C) along a feeding path (F) on which a testing position is located; an electrode arrangement (3) having an upper electrode (301) and a lower electrode (302), so that each capsule located at the testing position is interposed between the electrodes; a voltage generator (5) for applying an operating electric potential difference between the electrodes; a control unit (6) for detecting whether the cap (C) is defective responsive to detection of an electric discharge occurring between the electrodes through the plastic cap located at the testing position; a humidity detection device (7) configured to detect a control parameter representative of an environmental humidity value at the testing position (T). The control unit is configured to adjust the operating electric potential difference in response to the environmental humidity value at the testing position.

Description

DESCRIPTION
SYSTEM AND METHOD FOR DETECTING DEFECTS IN A BOTTOM WALL OF PLASTIC CAPS
Technical field
This invention relates to a system and a method for detecting defects in a bottom wall of plastic caps.
Background art
During the production of plastic caps, especially when made by injection moulding, micro-holes or cracks may form in the bottom wall of the caps. Micro holes make the caps unfit for use and it is therefore very important to detect and discard any defective caps which have micro holes in them. These holes are not visible to the human eye or to a camera. There are various different methods for detecting defective caps that have micro holes in them. For example, one of the known methods of detecting defective caps with micro holes in them involves the use of an electrical field. In particular, a voltage is applied across two electrodes and the cap to be inspected is placed between the two electrodes. Generally speaking, in the presence of an electrical field, an electric discharge occurs between the electrodes only if the cap has a hole in it; that is because the cap acts as a dielectric and the presence of the micro holes in the cap changes the dielectric rigidity of the cap.
The hole is usually formed at the point of injection and, in particular, at the centre of the bottom wall of the cap.
In this context, patent document DE102013014473 describes a device which uses high voltage to detect plastic caps with holes in the bottom wall and which comprises a star wheel with a plurality of arms acting as an upper electrode and a lower electrode located under the star wheel, wherein a voltage is applied across the electrodes. According to the solution disclosed in that document, the caps are transported along a feeding direction and the arms of the star wheel are immersed one after the other in the respective caps so that the bottom walls of the caps are interposed one after the other between the electrodes.
One of the important parameters to be considered during detection of the defect in the plastic caps by application of an electric field is the choice of the correct voltage. In particular, the voltage chosen should be such as not to exceed the dielectric rigidity of the cap if the cap does not have any holes in it.
Patent document EP3204762B1 also describes a method for testing plastic caps to detect the presence of holes or cracks in their bottom surface. In that solution, each cap is placed between an upper electrode, connected to a first voltage generator, and a lower electrode, connected to a second voltage generator, where the two voltage generators are electrically connected in series.
According to that document, the first and the second voltage generator are such that the first voltage generator generates a voltage only when there is a cap between the upper electrode and the lower electrode, whilst the second voltage generator generates a voltage continuously. Furthermore, the voltages generated by the two voltage generators are monitored so that the sum of the two voltages is greater than or equal to the breakdown voltage across the electrodes in air and less than the breakdown voltage across the electrodes through a cap without holes in it, and when a dielectric breakdown across the electrodes is detected, the cap is identified as defective.
An additional example of known methods for detecting the presence of holes in a container is described in the patent document JPH09222378. This document concerns a system for detecting the presence of pinholes in a sealed packaging container having a first electrode and a second electrode. It provides for an embodiment where an upper electrode is in contact with the upper surface of the container, and a lower electrode is in contact with the lower surface of the container, allowing a voltage to be applied simultaneously to both surfaces of the container tube. A detection control circuit is provided to detect the current flowing through the container placed between the electrodes to determine whether the container is defective or not (when there is no defect in the seam portion of the container, the container functions as a complete insulator). Additionally, the document describes an adjustment of the electrical voltage based on a detected value for the ambient humidity or, alternatively, the ambient temperature.
Furthermore, patent document JP2006084362 concerns a machine for inspecting the quality of a sealing portion of a liquid container. This document provides for a first electrode positioned to face a predetermined surface of the subject and a second electrode positioned to face the sealing portion of the subject. The document provides for the application of an electrical voltage between the first and second electrodes, adjustable based on a detected value for the ambient humidity or the ambient temperature.
However, the prior art methods have some disadvantages and can be improved. In effect, in this field, there is a growing need for a more efficient method of detecting defects in a bottom wall of plastic caps. Another need is to provide an apparatus and a method for detecting defects in a bottom wall of plastic caps where the voltage across the electrodes can be set in a precise and reliable manner. Another need felt in this field is to reduce costs and complexity of the defect detection process.
Disclosure of the invention
The aim of this invention is to provide an apparatus and a method for detecting defects in a bottom wall of plastic caps to overcome the above mentioned disadvantages of the prior art.
This aim is fully achieved by the system and method of this disclosure as characterized in the appended claims.
According to an aspect of it, this disclosure provides a system for detecting defects in a bottom wall of plastic caps (closures). It should be noted that the system for detecting defects in a bottom wall of plastic caps according to this disclosure may be used to inspect different types of plastic closures and, generally speaking, plastic items made by injection moulding. The system might be a stand-alone system or it may be integrated in another machine, for example, a plastic cap cutting machine where the injection- moulded caps are processed. The system for detecting defects in a bottom wall of plastic caps (or the system, for short) comprises a conveyor. The conveyor is used for transporting a succession of plastic caps along a feeding path. In particular, there is a testing position on the feeding path. The system comprises an electrode arrangement. The electrode arrangement includes an upper electrode. The upper electrode is situated above the bottom wall of the plastic cap located at the testing position. The electrode arrangement also includes a lower electrode. The lower electrode is situated under the bottom wall of the plastic cap located at the testing position. In particular, the upper electrode and the lower electrode are positioned in such a way that each cap at the testing position is interposed between the upper electrode and the lower electrode. The system also includes a voltage generator. The voltage generator is connected to the electrode arrangement. The voltage generator is configured to apply an operating electric potential difference (that is to say, voltage) between the upper and the lower electrode.
In an example, the generator applies the operating electric potential difference between the upper and the lower electrode continuously. Alternatively, the generator may apply the operating voltage discontinuously, for example, only when the cap is located at the testing position.
The system includes a control unit. The control unit is configured to detect whether the cap is defective. The control unit is configured to detect whether the cap is defective responsive to detection of an electric discharge occurring between the upper and lower electrodes through the plastic cap located at the testing position. The system includes a humidity detection device. The humidity detection device is configured to detect a control parameter. The control parameter is representative of an environmental humidity value at the testing position. The expression "environmental humidity value at the testing position" is used to mean the humidity of the environment surrounding the cap located at the testing position.
The control unit is connected to the voltage generator. The control unit is also connected to the humidity detection device. The control unit is configured to adjust the operating electric potential difference generated by the voltage generator in response to the environmental humidity value at the testing position.
According to an aspect of this disclosure, therefore, the operating voltage generated by the generator is set as a function of the humidity of the environment in which the caps are tested. The value of the voltage to be applied between the electrodes to check for the presence of holes in the plastic cap is influenced by several different parameters; of these parameters, the environmental humidity has a considerable influence on the optimum voltage value. For example, the drier the air, the higher the optimum value of the voltage. Thus, adjusting the operating voltage in response to the humidity detected allows providing a system for detecting defects in plastic caps with a particularly high level of reliability.
Alternatively, or in combination with the solution described above, the control unit can be configured to adjust the operating electric potential difference generated by the electric voltage generator in response to the speed at which the conveyor moves and consequently the speed at which the capsules are transported along the feed path. Therefore, the voltage can be adjusted based on a control parameter that is representative of an ambient humidity value and/or based on a speed parameter that is representative of a conveyor speed value. If the conveyor speed increases, there is less time for discharge and thus a higher electric field is required to allow the air to ionize more quickly, which can lead to a voltage adjustment based on the speed at which the capsules are transported. In this solution, the system includes a speed detection device. The speed detection device is configured to detect a speed parameter representative of the speed value of the conveyor movement. The control unit is programmed to adjust the operating electric potential difference generated by the electric voltage generator in response to the conveyor movement speed value detected by the speed detection device. The speed device includes a speed sensor.
It is to be noted that the solution where the control parameter is representative of the ambient humidity value (e.g., relative humidity) or the conveyor speed, as well as the solution where the control parameter is representative of both the ambient humidity value (e.g., relative humidity) and the conveyor speed, can be combined with one or more aspects of the present description. In the case where the voltage is adjusted based on both humidity (or specifically relative humidity) and conveyor speed, it may be provided to have a plurality of reference data. Such reference data can be obtained from prior knowledge or calibrations. These reference data can be matrix data. Additionally or alternatively to using such matrix data, it is possible to derive the correct operating voltage value by performing an automatic search procedure with a voltage ramp. Using the voltage ramp may require time and examples of defective caps.
In particular, a memory can be provided with a plurality of values for the control parameter (humidity), the speed parameter, and a corresponding plurality of reference voltage values. In this example, the control unit is programmed to select a voltage setpoint value based on the control parameter value and the speed parameter value detected by the humidity detection device and the speed detection device, respectively, and the plurality of reference voltage values.
In an example, the humidity detection device includes a humidity sensor. The humidity sensor is configured to detect the relative humidity of the testing environment (the environment surrounding the testing position). The humidity detection device also includes a temperature sensor. The temperature sensor is configured to detect the temperature of the testing environment. The humidity detection device is configured to calculate a volumetric humidity value of the testing environment. The humidity detection device is configured to calculate the volumetric humidity value of the testing environment based on the relative humidity and the temperature detected by the humidity sensor and the temperature sensor. In an example, the control parameter represents the volumetric humidity.
This configuration allows the operating voltage to be adjusted on the basis of the quantity (mg) of water in one cubic metre of the environment, to obtain a more precise adjustment.
In an example, the system also includes a memory. The memory contains a voltage setpoint value. The voltage generator is configured to generate the operating electric potential difference between the upper and the lower electrode in response to the voltage setpoint value. The control unit is also configured to update the voltage setpoint value in response to detection of that control parameter.
According to this aspect of the disclosure, therefore, each time the humidity value is identified, the voltage setpoint is updated for the humidity value identified. This solution enhances the precision of the system.
The memory may comprise a plurality of values for the control parameter. The memory also comprises a plurality of reference voltage values. In this example, the control unit is programmed to select a value for the voltage setpoint as a function of the value of the control parameter detected by the humidity detection device and of the plurality of voltage reference values.
This configuration can match a plurality of reference values for the voltage with a plurality of values for the control parameter (humidity) which can be used to select the optimum setpoint value effectively and precisely.
In an example, the control unit is configured to check the value of the control parameter. The control unit is also configured to select the voltage setpoint value. The setpoint value is calculated using the verified control parameter and the plurality of voltage reference values.
The control unit is also configured to detect an update value of the operating electric potential difference. The update value of the operating electric potential difference is the value of the voltage detected in real time. In particular, the term "update value" is used to mean a value of the operating electric potential difference detected while the system is in operation and detection can be performed after a predetermined length of time has elapsed from the moment the system started operating.
The control unit is programmed to compare the update value of the operating electric potential difference to the selected voltage setpoint value. The control unit is also programmed to adjust the update value of the operating electric potential difference to the selected voltage setpoint value if the difference between the update value of the operating electric potential difference and the selected voltage setpoint value exceeds a predetermined threshold.
According to an aspect of this disclosure, therefore, it is possible to perform a feedback control on the operating voltage value across the electrodes. In particular, the value of the control parameter and the value of the operating voltage can be detected one or more times during system operation, and the voltage value at the moment of detection in real time (that is to say, update value of the operating electric potential difference) is compared to the selected setpoint, using the plurality of voltage reference values and the plurality of values for the control parameter, for the value of control parameter detected in real time; if the difference between the two values exceeds a predetermined threshold, the operating voltage value is updated. This control allows the precision and reliability of the system to be considerably increased. The term “real time” is used with reference to a data analysis process by which input data are analysed as soon as they enter a data processing system.
In an example, the feedback control could be performed automatically and, for example, at predetermined time intervals. In another example, the feedback control might be in response to a control request entered by the operator.
In an embodiment, the conveyor comprises a carousel. The carousel has a plurality of housings. The housings are distributed along the periphery of the carousel. The housings are used to accommodate the respective plurality of caps. In an example, the carousel rotates around a first rotation axis. The carousel rotates around the first rotation axis to transport the caps to the testing position.
In the example where the conveyor includes the carousel, the electrode arrangement may include a star unit. The star unit is configured to rotate about a second rotation axis. The second rotation axis is perpendicular to the first rotation axis. The star unit may be provided with a plurality of arms. The arms protrude radially with respect to the second rotation axis. The arms are uniformly distributed around the second rotation axis.
Also, in this example, the electrode arrangement includes a plurality of upper electrodes. The upper electrodes of the plurality of upper electrodes may be provided at the tips of the arms.
The electrode arrangement may also include an actuator.
The actuator is connected to the star unit. The actuator is configured to rotate the star unit in synchrony with the movement of the carousel. In particular, the actuator is configured to rotate the star unit in such a way that each of the plurality of upper electrodes engages a respective cap in the respective housings, one at a time at the testing position.
In the solution with the carousel, it is possible to provide a relatively low voltage continuously, since the electrodes, at the testing position, are at a minimum distance, substantially corresponding to the thickness of the bottom wall of the cap and the distance between the electrodes, which defines the electrical field, is variable because the electrodes reach the minimum distance only when the electrode of the star unit (which moves in synchrony with the carousel) is inserted into the cap at the testing position. In an example, the system may have a camera to detect the presence of the caps in the carousel housings. In this example, when a housing is empty and the upper electrode is inserted into the housing, an electrical discharge occurs across the electrodes. In this example, since the camera detects that there is no cap in the housing, the presence of a defective cap is not detected and consequently the cap is not discarded. This solution enhances the precision and efficiency of the system.
In another embodiment, the feeding path comprises a groove. The groove is configured to house the caps. In particular, the groove houses the caps in such a way that the caps move in a row along a feeding direction. In this example, the electrode arrangement includes a star unit. The star unit is configured to rotate around a rotation axis. The rotation axis is perpendicular to the feeding direction. Furthermore, the star unit is provided with a plurality of arms. The plurality of arms protrude radially with respect to the rotation axis. The plurality of arms are uniformly distributed around the rotation axis.
Furthermore, the electrode arrangement includes a plurality of upper electrodes. In particular, each of the plurality of arms is provided with a respective upper electrode. The star unit is configured to rotate around the rotation axis in response to each of the plurality of upper electrodes engaging a respective cap at the testing position and to the cap moving along the feeding direction. In this example, the conveyor may comprise a belt. The belt may extend longitudinally.
According to an aspect of this disclosure, therefore, the system comprises an idle star unit which moves freely when one of the plurality of arms is inserted into a respective cap and the cap moves along the conveyor in the feeding direction. This solution allows feeding the caps in a row one after the other along the feeding path and having a relatively low voltage across the electrodes continuously. This embodiment does not require an actuator because the star is entrained by the caps; it is therefore possible to obtain a particularly efficient system that is at once lower in cost and less complicated in structure. Alternatively, in another example, the upper electrode and the lower electrode may be located at a fixed position above the conveyor and at a position below the conveyor, respectively; thus, the generator applies operating voltage only when the cap is between the upper electrode and the lower electrode at the testing position. In this example, the conveyor includes a belt. The belt may extend along a horizontal direction. This example, therefore, does not require movable upper electrodes.
In another embodiment, the electrode arrangement comprises a plurality of lower electrodes. In this example, the conveyor might include lower electrode housings. In particular, each of the plurality of lower electrode housings is configured to receive a respective lower electrode. The lower electrode housings may be spaced from each other along the conveyor. In this example, the lower electrode housings are located on the conveyor and each cap is positioned on the respective lower electrode so that the lower electrode is inserted into the cap. The caps therefore face down in such a way that the lower electrode comes into contact with the bottom wall of the cap. In this example, the electrode arrangement includes only one upper electrode, fixed at the testing position; when the cap, with the lower electrode in it, reaches the testing position, the generator applies the test voltage. In this example, the conveyor may include a belt. The belt extends longitudinally. The solution of the example in which the conveyor is provided with lower electrode housings allows having a relatively low voltage continuously.
In an example, the voltage generator comprises a plurality of capacitors. The capacitors are configured to generate the operating voltage. The capacitors generate the operating voltage, starting from an input voltage. The input voltage is lower than the operating voltage. Further, responsive to the discharge that occurs across the upper electrode and the lower electrode at the testing position, the capacitors undertake an electrical discharge transient. In an example, the system also includes an electrical resistor. The electrical resistor is connected to the plurality of capacitors, so that the electrical discharge transient is slower than it would be without the electrical resistor.
Providing the generator with a plurality of capacitors allows having a smaller, less cumbersome generator. Providing the generator with an electrical resistor allows having a slower electrical discharge transient so that the generator generates the voltage more rapidly after the discharge; it is therefore possible to feed the caps at a higher speed along the feeding path, thus enhancing the efficiency of the system.
In particular, this solution increases the readiness of the system for subsequent detection or discharge. A possible alternative to the capacitive generator described herein is an inductive generator, which would not require resistance. However, the inductive generator would have the disadvantage of being bulkier and more expensive, and it would make the detection of the discharge event more difficult, thus potentially making the system less reliable/robust.
According to an aspect of it, this disclosure provides a method for detecting defects in a bottom wall of plastic caps. The method comprises a step of transporting a succession of plastic caps along a feeding path. The method comprises a step of positioning the cap at a testing position. The testing position is located on the feeding path.
The method comprises a step of providing an electrode arrangement. The method comprises a step of providing the electrode arrangement with an upper electrode. The upper electrode is situated above the bottom wall of the plastic cap. The method also comprises a step of providing the electrode arrangement with a lower electrode. The lower electrode is situated under the bottom wall of the plastic cap at the testing position.
The method comprises a step of positioning the cap between the upper electrode and the lower electrode. The method comprises a step of generating an operating electric potential difference (that is, a voltage) across the upper electrode and the lower electrode. The operating voltage is applied across the lower electrode and the upper electrode by a voltage generator.
The method comprises a step of verifying that the cap is defective when an electric discharge occurs between the upper and lower electrodes through the plastic cap located at the testing position. The method also comprises a step of detecting a control parameter. In an example, the control parameter is representative of an environmental humidity value at the testing position.
The method comprises a step of adjusting the operating electric potential difference generated by the voltage generator as a function of the humidity value of the testing environment.
In an example, the method comprises a step of detecting the relative humidity of the testing environment.
The method also comprises a step of detecting the temperature of the testing environment. The method comprises a step of calculating a volumetric humidity value of the testing environment based on the detected relative humidity and temperature. In an example, the control parameter represents the volumetric humidity.
In an example, the method comprises a step of saving a voltage setpoint value. The method comprises a step of generating the operating electric potential difference between the upper and the lower electrode in response to the voltage setpoint value. The method also comprises a step of updating the voltage setpoint value in response to detection of the control parameter.
The method comprises a step of saving a plurality of values for the control parameter and a corresponding plurality of voltage reference values.
The method comprises a step of selecting the value for the voltage setpoint as a function of the detected value of the control parameter and of the plurality of voltage reference values.
The method comprises a step of checking the value of the control parameter. The method comprises a step of selecting the voltage setpoint value. The method comprises a step of detecting an update value of the operating electric potential difference. The method comprises a step of comparing the update value of the operating electric potential difference to the selected voltage setpoint value. The method comprises a step of adjusting the operating electric potential difference update value to the selected voltage setpoint value if the difference between the operating electric potential difference update value and the selected voltage setpoint value exceeds a predetermined threshold.
In an example, the method comprises a step of providing a carousel. The carousel has a plurality of housings. The housings are distributed along the periphery of the carousel.
The method comprises a step of accommodating the caps in the respective housings. The method also comprises a step of rotating the carousel around a first rotation axis to transport the caps to the testing position. The method comprises a step of providing the electrode arrangement with a star unit. The star unit rotates about a second rotation axis. The second rotation axis is perpendicular to the first rotation axis. The star unit is provided with a plurality of arms. The arms protrude radially with respect to the second rotation axis. The arms are uniformly distributed around the second rotation axis.
The method comprises a step of providing the electrode arrangement with a plurality of upper electrodes. The upper electrodes may be provided at the tips of the arms. The method comprises a step of rotating the star unit by means of an actuator. The star unit is rotated in a synchronized way with respect to the movement of the carousel, so that each of the plurality of upper electrodes engages a respective cap in the respective housings, one at a time at the testing position.
The method comprises a step of providing the voltage generator with a plurality of capacitors. The capacitors generate the operating voltage, starting from an input voltage. The input voltage is lower than the operating voltage. Further, responsive to the discharge that occurs across the upper electrode and the lower electrode at the testing position, the capacitors undertake an electrical discharge transient.
The method comprises a step of connecting an electrical resistor to the plurality of capacitors, so that the electrical discharge transient is slower than it would be without the electrical resistor.
Brief description of drawings
These and other features will become more apparent from the following description of a preferred embodiment, illustrated by way of non-limiting example in the accompanying drawings, in which:
- Figures 1 -3 illustrate a system for detecting defects in a bottom wall of plastic caps according to this disclosure, in a first embodiment, where the caps are transported by a carousel;
- Figures 4-5 illustrate a second embodiment of the system;
- Figure 6 illustrates the electrode arrangement and the cap at the testing position;
- Figure 7 illustrates the relation between environmental relative humidity and voltage across the electrodes,
- Figure 8 illustrates the relation between the velocity of the conveyor and voltage across the electrodes;
- Figure 9 illustrates the relation between environmental relative humidity, the velocity of the conveyor and voltage across the electrodes.
Detailed description of preferred embodiments of the invention
With reference to the accompanying drawings, the numeral 1 denotes a system for detecting defects in a bottom wall BW of plastic caps C. The system 1 comprises a conveyor 2 for transporting a succession of plastic caps C along a feeding path F. On the feeding path there is a testing position T.
The system 1 also comprises an electrode arrangement 3. The electrode arrangement includes an upper electrode 301 , located above the bottom wall BW of the plastic cap C located at the testing position T, and a lower electrode 302, located beneath the bottom wall BW of the plastic cap C located at the testing position T. Thus, each cap, when it is located at the testing position T, is interposed between the upper electrode 301 and the lower electrode 302. The system 1 includes a voltage generator 5. The voltage generator (or generator, for short) is connected to the electrode arrangement 3 and is configured to apply an operating electric potential difference between the upper electrode 301 and the lower electrode 302. The system 1 includes a control unit 6. The control unit 6 is configured to detect whether the cap C is defective. In particular, the cap is identified as defective when an electric discharge occurs between the upper and lower electrodes through the plastic cap while the cap is at the testing position T. The system also has a humidity detection device 7 for detecting a control parameter. In an example, the control parameter is the environmental humidity value at the testing position T. Thus, the humidity value of the environment surrounding the caps at the testing position is detected and the operating electric potential difference across the electrodes 301 , 302 is adjusted responsive to the detected humidity value of the environment.
Additionally, the system may also include a speed detection device to detect the speed value of the conveyor movement. In this example, the control unit is programmed to adjust the operating electric potential difference generated by the electric voltage generator in response to the speed value of the conveyor movement.
Generally speaking, the caps are transported along the feeding path F and the operating voltage is applied to the electrodes. The caps are placed at the testing position T (interposed between the upper electrode and the lower electrode) individually (one at a time). At the testing position T, the upper electrode 301 and the lower electrode 302 are placed in the cap, in contact with the bottom wall BW of the cap. Also, at the testing position T, the upper electrode and the lower electrode are aligned along a vertical direction. Preferably, the electrode that is placed inside the cap is inserted into the cap C at a central point of the bottom wall BW thereof. When a cap C with a hole in its bottom wall BW is placed at the testing position T, an electrical discharge occurs across the electrodes and when such a discharge is detected, the cap is identified as defective. Next, the inspected cap is transported towards an outlet of the conveyor 2. If the cap has been identified as defective, it is discarded; otherwise it is collected among the non-defective caps.
The voltage generator comprises a plurality of capacitors for generating the operating voltage, starting from an input voltage that is lower than the operating voltage. Further, when the discharge occurs across the upper electrode 301 and the lower electrode 302 at the testing position T, the capacitors undertake an electrical discharge transient. The system 1 also includes an electrical resistor, connected to the plurality of capacitors, so that the electrical discharge transient is slower than it would be without the electrical resistor. The resistor is electrically connected in series to the plurality of capacitors.
Preferably, the humidity detection device includes a humidity sensor to detect the relative humidity of the testing environment, and a temperature sensor to detect the temperature of the testing environment. In an example, therefore, a volumetric humidity value of the testing environment is calculated on the basis of the relative humidity and temperature detected by the humidity sensor and the temperature sensor. For example, the volumetric humidity value may be calculated by a processing unit connected to the humidity and temperature sensors to receive data relating to the relative humidity and the temperature. Preferably, the operating voltage is adjusted in response to the calculated value for the volumetric humidity of the environment at the testing position T.
The system 1 also includes a memory. The memory is used to store a voltage setpoint value. Generally speaking, the operating electric potential difference between the upper and the lower electrode is generated in response to the voltage setpoint value. The operating voltage is therefore set on the basis of the setpoint stored. The setpoint value depends on the value of the control parameter (that is, the humidity of the environment). In effect, the setpoint value is updated each time the value of the control parameter is detected.
In an example, a plurality of values for the control parameter and a corresponding plurality of voltage reference values are stored. Also, the value for the voltage setpoint is selected as a function of the detected value of the control parameter and of the plurality of voltage reference values. Thus, when the value of the control parameter is detected, the control unit selects the operating voltage setpoint value, which corresponds to the detected value for the control parameter using the plurality of values for the control parameter and the corresponding plurality of voltage reference values. The plurality of values for the control parameter and the corresponding plurality of voltage reference values may be stored in the form of a table or they may form a characteristic curve. Figure 7 shows the curve that describes the relation between the voltage generated across the electrodes and the relative humidity value of the environment. It is noted that the curve shows an inverse relation between the voltage and the relative humidity and thus, the two parameters change in opposite directions. The characteristic curve is obtained before the system comes into operation; the characteristic curve may, however, be updated by the operator at a later stage. If the plurality of values for the control parameter and the corresponding plurality of voltage reference values are stored in a table, any values not available in the table are obtained by interpolation.
In the case where the voltage is adjusted based on both relative humidity and conveyor speed, the memory can also include a plurality of values for the control parameter, the speed parameter, and a corresponding plurality of reference voltage values. The control unit is programmed to select the voltage setpoint value based on the relative humidity value, conveyor speed value, and corresponding reference voltage value. Specifically, the plurality of values for ambient humidity at the test position and the plurality of values for conveyor speed, along with the corresponding plurality of reference voltage values, can be stored in the form of a table or can form a characterization curve. Such data can be in the form of a data matrix. Figure 9 is a graph depicting the relationship between the reference voltage value, ambient relative humidity value, and conveyor speed value. Therefore, once the ambient relative humidity value and conveyor speed value are detected, these curves can be used to determine the voltage value. This curve is preferably obtained before the system starts operating; however, the characterization curve can be updated later by the operator.
It may be provided to adjust the voltage solely based on conveyor speed. In this example, the voltage setpoint value depends on the conveyor speed value. For instance, a plurality of values for conveyor speed and a corresponding plurality of reference voltage values are stored. Additionally, the voltage setpoint value is selected based on the speed value and the plurality of reference voltage values. Therefore, when the conveyor speed value is detected, the control unit selects the operational voltage setpoint value corresponding to the detected conveyor speed value using the plurality of values for conveyor speed and the corresponding plurality of reference voltage values. The plurality of values for conveyor speed and the corresponding plurality of reference voltage values can be stored in the form of a table or can form a characterization curve. Figure 8 illustrates the curve describing the relationship between the voltage generated between the electrodes and the conveyor speed value.
Moreover, a feedback control may be performed on the value of the operating voltage across the electrodes. In particular, during such a control, the voltage value is detected in real time (this value may be called the "update value"). Furthermore, the humidity value is detected in real time and the voltage setpoint value is detected using the plurality of humidity values and the corresponding plurality of voltage reference values stored. If the voltage value detected in real time does not correspond to the selected setpoint value, and in particular, if the difference between these two values exceeds a predetermined threshold, the operating voltage value is updated so it does correspond to the selected setpoint value. This feedback control may be performed automatically. For example, the control may be performed automatically and periodically at preset time intervals. The control might also be performed directly by the user.
In an embodiment, the conveyor 2 comprises a carousel 4. The carousel 4 includes a plurality of housings 401. The housings are distributed along the periphery of the carousel 4 and each housing accommodates a respective cap of the plurality of caps C. The housings are spaced from each other. In particular, the carousel rotates around a first rotation axis RA1 and transports the caps to the testing position T. The carousel is illustrated in Figures 1 -3. Thus, the caps are transported towards the carousel in a row and, at an entrance to the carousel 4, each cap is loaded onto the respective housing 401. In this embodiment, the electrode arrangement 3 includes a star unit S. The star unit rotates around a second rotation axis RA2, perpendicular to the first rotation axis RA1 . The star unit includes a plurality of arms A which protrude radially with respect to the second rotation axis and which are uniformly distributed around the second rotation axis RA2. In addition, a plurality of upper electrodes 301 are provided at the tips of the arms A. In particular, the star unit S is rotated by an actuator synchronously with respect to the movement of the carousel 4. Thus, the carousel rotates and when a cap in the respective housing reaches the testing position T, one of the arms A of the star unit is inserted into the cap so that the cap is interposed between the lower electrode 302 and the upper electrode 301. In this configuration, the lower electrode 302 is located under the bottom wall BW of the cap at a fixed location. When defect detection is over, the inspected cap that was at the testing position is transported towards the outlet of the conveyor 2 and the cap in the adjacent housing is transported to the testing position T; consequently, the same is rotated synchronously so that the respective arm is inserted into the next cap.
In another embodiment, the conveyor 2 may comprise a belt. The belt extends along a horizontal direction. In this configuration, the caps to be inspected are fed along the feeding path in a single row along a feeding direction FD. The caps are placed in a row close to each other and are transported towards the testing position T. The caps are placed at the testing position T individually (one at a time). In particular, the belt includes a groove G which houses the caps along the feeding direction. In this configuration, the electrode arrangement 3 includes the star unit S. The configuration of the star unit is similar to that described for the first embodiment (described above). The star unit S in this embodiment is not rotated by an actuator. The star unit S is an idle wheel. In this embodiment, therefore, the star unit S rotates freely around a rotation axis RA. The rotation axis RA is perpendicular to the feeding direction. Further, the upper electrodes 301 are located on the respective arms of the star unit S. In particular, the upper part of each arm A (the tip of the arm, further from the rotation axis RA) is provided with the respective upper electrode 301. In particular, when a cap C moves close to the star unit S, the cap comes into contact with the respective arm A and the movement of the cap C along the feeding direction FD entrains the arm, causing the star unit S to rotate around the rotation axis RA and the arm to be inserted into the cap when the cap is at the testing position T. After being inspected, the cap is transported towards the outlet of the conveyor 2.

Claims

1. A system (1 ) for detecting defects in a bottom wall (BW) of plastic caps (C), comprising:
- a conveyor (2) for transporting a succession of plastic caps (C) along a feeding path (F) wherein a testing position (T) is located on the feeding path;
- an electrode arrangement (3) having an upper electrode (301 ), located above the bottom wall (BW) of the plastic cap (C) located at the testing position (T), and a lower electrode (302), located beneath the bottom wall (BW) of the plastic cap (C) located at the testing position (T), so that each cap located at the testing position is interposed between the upper and the lower electrode;
- a voltage generator (5), connected to the electrode arrangement (3) and configured to apply an operating electric potential difference between the upper and the lower electrode;
- a control unit (6) configured to detect whether the cap (C) is defective responsive to detection of an electric discharge occurring between the upper and lower electrodes through the plastic cap located at the testing position;
- a humidity detection device (7) configured to detect a control parameter representative of an environmental humidity value at the testing position (T), wherein the control unit is connected to the voltage generator and to the humidity detection device and configured to adjust the operating electric potential difference generated by the voltage generator in response to the environmental humidity value at the testing position.
2. The system (1 ) according to claim 1 , wherein the humidity detection device includes a humidity sensor configured to detect the relative humidity of the testing environment and a temperature sensor configured to detect the temperature of the testing environment and wherein the humidity detection device is configured to calculate a volumetric humidity value of the testing environment based on the relative humidity and the temperature detected by the humidity sensor and the temperature sensor, and wherein the control parameter represents said volumetric humidity.
3. The system (1 ) according to claim 1 or 2, further comprising a memory having a voltage setpoint value, wherein the voltage generator is configured to generate the operating electric potential difference between the upper and the lower electrode in response to the voltage setpoint value and the control unit is configured to update the voltage setpoint value in response to detection of said control parameter.
4. The system (1 ) according to claim 3, wherein the memory includes a plurality of values for the control parameter and a corresponding plurality of voltage reference values, the control unit being programmed to select a value for the voltage setpoint as a function of the value of the control parameter detected by the humidity detection device and of the plurality of voltage reference values.
5. The system (1 ) according to claim 4, wherein the control unit is configured to:
- check the value of the control parameter;
- select the voltage setpoint value;
- detect an update value of the operating electric potential difference;
- compare the update value of the operating electric potential difference to the selected voltage setpoint value;
- adjust the update value of the operating electric potential difference to the selected voltage setpoint value if the difference between the update value of the operating electric potential difference and the selected voltage setpoint value exceeds a predetermined threshold.
6. The system (1 ) according to any of the previous claims, wherein the conveyor (2) includes a carousel (4) having a plurality of housings (401 ), distributed along the periphery of the carousel, to accommodate the respective plurality of caps (C), wherein the carousel rotates around a first rotation axis (RA1 ) to transport the caps to the testing position (T).
7. The system (1 ) according to claim 6, wherein the electrode arrangement (3) includes
- a star unit (S) rotating around a second rotation axis (RA2), perpendicular to the first rotation axis (RA1 ), and provided with a plurality of arms (A) protruding radially with respect to the second rotation axis, uniformly distributed around the second rotation axis,
- a plurality of upper electrodes (301 ), provided at the tips of the arms (A),
- an actuator, connected to the star unit (S) to rotate the star unit in a synchronized way with respect to the movement of the carousel, so that each of the plurality of upper electrodes (301 ) engages a respective cap (C) in the respective housings (401 ), one at a time at the testing position (T).
8. The system (1 ) according to any of the previous claims from 1 to 5, wherein the feeding path (F) includes a groove (G) configured to house the caps (C) so that the caps move in a row along a feeding direction (FD), wherein the electrode arrangement (3) includes
- a star unit (S) rotating around a rotation axis (RA), perpendicular to the feeding direction (FD), and provided with a plurality of arms (A) protruding radially with respect to the rotation axis, uniformly distributed around the rotation axis,
- a plurality of upper electrodes (301 ), wherein each arm is provided with a respective upper electrode, wherein the star unit is configured to rotate around the rotation axis in response to each of the plurality of upper electrodes engaging a respective cap (C) at the testing position (T) and to the cap moving along the feeding direction.
9. The system (1 ) according to any of the previous claims, wherein the voltage generator includes a plurality of capacitors configured to generate the operating voltage, starting from an input voltage, lower than the operating voltage, responsive to the discharge occurring between the upper and lower electrodes at the testing position (T), the capacitors undertake an electrical discharge transient, wherein the system (1 ) further includes an electrical resistor, connected to the plurality of capacitors, so that the electrical discharge transient is slower than it would be without the electrical resistor.
10. The system according to any one of the preceding claims comprising a speed detection device configured to detect a speed parameter representative of a value of the conveyor movement speed, wherein the control unit is programmed to adjust the operating electric potential difference generated by the electric voltage generator in response to the conveyor movement speed value.
11. The system according to any one of the preceding claims further comprising a memory having a plurality of values for the control parameter, the speed parameter, and a corresponding plurality of reference voltage values, the control unit being programmed to select a voltage setpoint value based on the control parameter value and the speed parameter detected by the humidity detection device and the speed detection device, respectively, and the plurality of reference voltage values
12. A method for detecting defects in a bottom wall (BW) of plastic caps (C), the method comprising the following steps:
- transporting a succession of plastic caps (C) along a feeding path (F);
- positioning the cap (C) at a testing position (T), located on the feeding path;
- providing an electrode arrangement (3) with an upper electrode (301 ), located above the bottom wall of the plastic cap, and a lower electrode (302), located beneath the bottom wall of the plastic cap at the testing position;
- placing the cap between the upper electrode (301 ) and the lower electrode;
- adjusting an operating electric potential difference generated by the voltage generator in response to the testing environment humidity value;
- generating the operating electric potential difference between the upper and the lower electrode through a voltage generator (5);
- verifying that the cap is defective when an electric discharge occurs between the upper and lower electrodes through the plastic cap located at the testing position;
- detecting a control parameter representative of an environmental humidity value at the testing position.
13. The method according to claim 12, wherein the step of detecting a control parameter comprises the following steps:
- detecting the relative humidity of the testing environment;
- detecting the temperature of the testing environment;
- calculating a volumetric humidity value of the testing environment based on the detected relative humidity and temperature, wherein the control parameter represents said volumetric humidity.
14. The method according to claim 12 or 13, comprising the following steps:
- saving a voltage setpoint value;
- generating the operating electric potential difference between the upper and the lower electrode in response to the voltage setpoint value,
- updating the voltage setpoint value in response to detection of said control parameter;
- saving a plurality of values for the control parameter and a corresponding plurality of voltage reference values;
- selecting a value for the voltage setpoint as a function of the detected value of the control parameter and of the plurality of voltage reference values.
15. The method according to claim 14, further comprising the following steps:
- checking the value of the control parameter;
- selecting the voltage setpoint value;
- detecting an update value of the operating electric potential difference;
- comparing the update value of the operating electric potential difference to the selected voltage setpoint value;
- adjusting the update value of the operating electric potential difference to the selected voltage setpoint value if the difference between the update value of the operating electric potential difference and the selected voltage setpoint value exceeds a predetermined threshold.
16. The method according to any of the previous claims from 12 to 15 comprising the following steps:
- providing a carousel (4) having a plurality of housings (401 ) distributed along the periphery of the carousel;
- accommodating the caps (C) in the respective housings,
- rotating the carousel around a first rotation axis (RA1 ) to transport the caps to the testing position (T);
- providing the electrode arrangement (3) with a star unit (S) rotating around a second rotation axis (RA2), perpendicular to the first rotation axis (RA1 ), and having a plurality of arms (A) protruding radially with respect to the second rotation axis, uniformly distributed around the second rotation axis; a plurality of upper electrodes (301 ), provided at the tips of the arms (A);
- rotating the star unit (S), through an actuator, in a synchronized way with respect to the movement of the carousel, so that each of the plurality of upper electrodes (301 ) engages a respective cap (C) in the respective housings (401 ), one at a time at the testing position (T).
17. The method according to any of the previous claims from 12 to 16, comprising the following steps:
- providing the voltage generator with a plurality of capacitors that generate the operating voltage, starting from an input voltage, lower than the operating voltage, wherein, responsive to the discharge occurring between the upper and lower electrodes at the testing position (T), the capacitors undertake an electrical discharge transient,
- connecting an electrical resistor to the plurality of capacitors, so that the electrical discharge transient is slower than it would be without the electrical resistor.
PCT/IB2024/056018 2023-06-22 2024-06-20 System and method for detecting defects in a bottom wall of plastic caps Pending WO2024261679A1 (en)

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IT102023000012924A IT202300012924A1 (en) 2023-06-22 2023-06-22 SYSTEM AND METHOD FOR DETECTING DEFECTS IN THE BOTTOM WALL OF PLASTIC CAPSULES.

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JPH09222378A (en) * 1996-02-19 1997-08-26 Pola Chem Ind Inc Pin hole inspection device
US7168223B2 (en) * 2002-05-28 2007-01-30 Ecocap's S.R.L. Capsule-sealing machine for food or drink containers
JP2006084362A (en) * 2004-09-17 2006-03-30 Nihon Tetra Pak Kk Seal condition inspection device
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