WO2025187080A1 - Abnormality detection device and position detector - Google Patents

Abstract

this abnormality detection device, in one embodiment, comprises a voltage detector for detecting a voltage corresponding to a resistance value of a thermistor. The abnormality detection device comprises: an acquisition unit that acquires a temperature-related variable on the basis of a signal from the voltage detector; and a determination unit that determines an abnormality in a thermistor circuit on the basis of a change in the variable. The acquisition unit acquires the variable at predetermined time intervals, and calculates, as a first measurement value, a slope of the variable with respect to time. The determination unit determines that an abnormality has occurred in the thermistor circuit if the first measurement value deviates from a predetermined first determination range.

Description

Anomaly detection device and position detector

This disclosure relates to an anomaly detection device and a position detector.

It has long been known to use thermistor circuits containing thermistors to measure the temperature of devices. A thermistor is a semiconductor element whose resistance value changes with temperature. A thermistor circuit can estimate the temperature based on changes in the thermistor's resistance value. For example, if the temperature of a device detected by a thermistor circuit becomes too high, the device's operation can be restricted or an alarm can be issued. Monitoring the device's temperature with a thermistor circuit can help prevent device failure. However, thermistor circuits can also fail. For example, a short circuit can occur in the thermistor circuit, or the conductors can be damaged.

As a method of detecting an abnormality in the thermistor circuit, if the temperature detected by the thermistor circuit is very high or very low, it can be determined that the thermistor circuit is abnormal. For example, if the temperature detected by the thermistor circuit significantly deviates from the temperature range at which the device operates, it can be determined that the thermistor circuit is abnormal.

Japanese Patent Application Publication No. 4-95986 Japanese Unexamined Patent Publication No. 2-104994

In the control for detecting abnormalities in the thermistor circuit, for example, a temperature judgment value can be set that is lower than the temperature range when the device is operating. Then, if the temperature detected by the thermistor circuit is below the temperature judgment value, it can be determined that the thermistor circuit is abnormal. Alternatively, a temperature judgment value can be set that is higher than the temperature range when the device is operating. Then, if the temperature detected by the thermistor circuit is higher than the temperature judgment value, it can be determined that the thermistor circuit is abnormal.

However, even if an abnormality occurs in the thermistor circuit, the detected temperature may still be within the temperature range at which the device operates. For example, even if the actual temperature of the device is not high, an abnormality in the thermistor circuit may cause the detected temperature to be in the overheating range. As such, when an abnormal temperature is detected by the thermistor circuit, it is difficult to determine whether the abnormality is in the actual device temperature or whether the abnormality is in the thermistor circuit.

Furthermore, even if the temperature detected by the thermistor circuit is within the operating temperature range of the device, an abnormality in the thermistor circuit may cause the detected temperature to be higher or lower than the actual temperature. In this case, there is a problem in that the device's temperature cannot be properly controlled.

A first aspect of the present disclosure is an abnormality detection device that detects an abnormality in a thermistor circuit. The abnormality detection device includes a voltage detector that detects a voltage corresponding to the resistance value of the thermistor. The abnormality detection device includes an acquisition unit that acquires a temperature-related variable based on a signal from the voltage detector, and a judgment unit that judges an abnormality in the thermistor circuit based on a change in the variable. The acquisition unit acquires the variable at predetermined time intervals and calculates the slope of the variable with respect to time as a first measurement value. The judgment unit judges that an abnormality has occurred in the thermistor circuit when the first measurement value deviates from a predetermined first judgment range.

A second aspect of the present disclosure is an abnormality detection device that detects an abnormality in a thermistor circuit. The abnormality detection device includes a voltage detector that detects a voltage corresponding to the resistance value of the thermistor. The abnormality detection device includes an acquisition unit that acquires a temperature-related variable based on a signal from the voltage detector, and a judgment unit that judges an abnormality in the thermistor circuit based on changes in the variable. The acquisition unit acquires the variable at predetermined time intervals and calculates a measured value by second-order differentiation of the variable with respect to time. The judgment unit judges that an abnormality has occurred in the thermistor circuit if the measured value deviates from a predetermined judgment range.

A third aspect of the present disclosure is a rotational position detector that includes the aforementioned abnormality detection device and an angle calculation unit that detects the rotational position of the rotation shaft.

FIG. 1 is a block diagram of a machine tool according to an embodiment. FIG. 2 is a block diagram of a rotational position detector according to the embodiment. 1 shows a thermistor circuit according to an embodiment. 10 is a graph of the voltage detected in the thermistor circuit when the device overheats. 10 is a graph of the voltage detected in the thermistor circuit when the device is no longer overheating. 10 is a graph showing the voltage detected when cutting fluid adheres to the thermistor. 10 is a graph of the voltage detected when a fixed resistor is broken. 10 is a graph showing the voltage detected when the thermistor circuit is normal. 6 is a graph illustrating control for determining an abnormality in the thermistor circuit when cutting fluid adheres to the thermistor in the first embodiment. 6 is a graph illustrating control for determining an abnormality in the thermistor circuit when a fixed resistor is broken in the first embodiment. 5 is a flowchart of control for detecting an abnormality in a thermistor circuit in the first embodiment. 10 is a graph showing voltage when cutting fluid adheres to a thermistor in a comparative example. 10 is a graph showing the voltage when the fixed resistor in the comparative example is broken. 10 is a graph showing the relationship between the temperature of a thermistor and the detected voltage in the second embodiment. 10 is a graph illustrating control for determining an abnormality in the thermistor circuit when cutting fluid adheres to the thermistor in the second embodiment. 10 is a graph illustrating control for determining an abnormality in the thermistor circuit when a fixed resistor is broken in the second embodiment. 10 is a flowchart of a control for detecting an abnormality in a thermistor circuit according to a second embodiment.

(First embodiment)
An abnormality detection device and a position detector according to a first embodiment will be described with reference to Figures 1 to 13. The abnormality detection device of this embodiment detects an abnormality in a thermistor circuit equipped with a thermistor. In this embodiment, a rotational position detector that detects the rotational position of a rotating shaft will be described as an example of a device equipped with a thermistor circuit. Furthermore, a machine tool will be described as an example of a device equipped with a rotational position detector.

FIG. 1 is a block diagram of a machine tool in this embodiment. Machine tool 1 is a device that cuts a workpiece based on a machining program 45 as an operating program. Machine tool 1 is equipped with an electric motor 9 that drives the components of machine tool 1. Examples of electric motor 9 include a spindle motor that rotates a spindle that holds a tool, or a feed axis motor that moves a table that holds a workpiece or a spindle head including a spindle along a predetermined coordinate axis.

A rotational position detector 10 is attached to the electric motor 9 to detect the rotational position or rotational speed of the output shaft. In this embodiment, the rotational position detector 10 is configured as an encoder. The rotational position signal output from the rotational position detector 10 is input to the machine control device 41. Note that devices equipped with a rotational position detector are not limited to electric motors of machine tools, and any device can be used.

The machine tool 1 in this embodiment is a numerically controlled device. The machine tool 1 is equipped with a machine control device 41 that controls the operation of its components. The machine control device 41 in this embodiment includes an arithmetic processing device (computer). The machine control device 41 includes a CPU (Central Processing Unit) as a processor. The machine control device 41 has RAM (Random Access Memory), ROM (Read Only Memory), etc. connected to the CPU via a bus.

The machine tool 1 is driven based on command statements written in a machining program 45 created in advance. The machine control device 41 includes a memory unit 42 that stores information about the machine tool 1, and an operation control unit 43 that generates operation commands for the electric motor 9 based on the machining program 45. The machine tool 1 includes a drive unit 46 that includes an electrical circuit that supplies electricity to the electric motor 9 based on the operation commands generated by the operation control unit 43. The electric motor 9 is driven by the electricity supplied by the drive unit 46.

The operation control unit 43 corresponds to a processor that operates in accordance with the machining program 45. The processor that functions as the operation control unit 43 is configured to be able to read information stored in the memory unit 42. The processor reads the machining program 45 stored in the memory unit 42 and performs the control defined in the machining program 45, thereby functioning as the operation control unit 43.

The storage unit 42 can be configured as a non-transitory storage medium capable of storing information. For example, the storage unit 42 can be configured as a storage medium such as volatile memory, non-volatile memory, magnetic storage medium, or optical storage medium.

The machine control device 41 includes a display unit 44 that displays information related to the machine tool 1. The display unit 44 can be configured with any display panel, such as a liquid crystal display panel or an organic EL (Electro Luminescence) display panel.

Figure 2 shows a block diagram of the rotational position detector in this embodiment. The rotational position detector 10 can be attached to any rotating shaft, such as a drive shaft. In this embodiment, the rotational position detector 10 is attached to the output shaft of the electric motor 9.

The rotational position detector 10 of this embodiment is an optical detector. It includes a light-emitting element 11 composed of an LED (Light Emitting Diode), and a light-receiving element 12 that receives light from the LED. The rotational position detector 10 includes a rotating plate that is arranged between the light-emitting element 11 and the light-receiving element 12. The rotating plate has a plurality of small holes formed along its circumferential direction. The rotating plate is connected to the output shaft of the electric motor 9.

As the output shaft of the electric motor 9 and the rotating plate rotate, holes in the rotating plate allow or block light from the light-emitting element 11. The light-receiving element 12 receives the light that passes through the holes.

The rotational position detector 10 includes a circuit board 13 on which an electric circuit is formed. The rotational position detector 10 includes a microcomputer disposed on the circuit board as an arithmetic processing device. The microcomputer in this embodiment includes a CPU as a processor. Note that the processor is not limited to a CPU, and any element capable of arithmetic processing, such as an LSI (Large Scale Integration), IC (Integrated Circuit), or ASIC (Application Specific Integrated Circuit), can be used.

The microcomputer includes an angle calculation unit 21. The angle calculation unit 21 can calculate the rotational position (rotation angle) of the rotating plate based on the pattern of light received by the light receiving element 12. The angle calculation unit 21 can also detect the rotational speed based on the rotational position and time. The angle calculation unit 21 corresponds to a processor that performs predetermined processing. The processor performs predetermined control, thereby functioning as the angle calculation unit 21.

The microcomputer includes a memory unit 14 that stores information related to the rotational position detector 10. The memory unit 14 can be configured as a non-transitory storage medium capable of storing information. The memory unit 14 can be configured as a storage medium such as volatile memory, non-volatile memory, magnetic storage medium, or optical storage medium. The processor stores information in the memory unit 14 and reads information stored in the memory unit 14. Note that the rotational position detector is not limited to the optical detector described above, and any type, such as a magnetic type, can be used.

Figure 3 shows the thermistor circuit of this embodiment. With reference to Figures 2 and 3, the rotational position detector 10 of this embodiment includes a thermistor circuit 19 that detects the temperature of the circuit board 13. The thermistor circuit 19 can be formed on the circuit board 13 of the rotational position detector 10. In this embodiment, the thermistor circuit 19 is arranged to detect the temperature of the circuit board 13.

In this embodiment, the explanation will be given taking as an example a thermistor circuit 19 including an NTC (Negative Temperature Coefficient) thermistor, whose resistance value decreases as the temperature rises. However, the abnormality detection device of this embodiment can be applied to a thermistor circuit including any thermistor. For example, control similar to that of this embodiment can also be implemented for a thermistor circuit including a PTC (Positive Temperature Coefficient) thermistor, whose resistance value increases as the temperature rises.

Thermistor circuit 19 includes a thermistor 15, which is a semiconductor whose resistance value changes with temperature. The thermistor circuit 19 also includes a fixed resistor 16 that maintains a predetermined resistance value. In the thermistor circuit 19 of this embodiment, the thermistor 15 and fixed resistor 16 are connected in series. The fixed resistor 16 is grounded. A predetermined supply voltage Vcc is applied to the thermistor 15 from a power supply. The supply voltage Vcc is, for example, 5 V. The thermistor circuit 19 also includes a voltage detector 17 for detecting the voltage between the thermistor 15 and fixed resistor 16.

The thermistor circuit 19 includes an acquisition unit 22 that acquires temperature-related variables based on a signal from the voltage detector 17. The variables include, for example, the voltage detected by the voltage detector 17, or the temperature of the thermistor 15 calculated from the voltage detected by the voltage detector 17. In this embodiment, the voltage detected by the voltage detector 17 is referred to as the "detected voltage."

The relationship between the detected voltage V detected by the voltage detector 17, the resistance value Rth of the thermistor 15, the resistance value R of the fixed resistor 16, and the supply voltage Vcc supplied by the power supply is expressed by the following equation (1):

V=R/(Rth+R)×Vcc...(1)

The resistance value Rth changes depending on the temperature of the thermistor. The acquisition unit 22 can calculate the resistance value Rth of the thermistor 15 from the detected voltage V detected by the voltage detector 17 based on the above formula (1).

The relationship between the resistance value Rth of the thermistor 15 and the temperature of the thermistor 15 can be determined in advance and stored in the memory unit 14. The acquisition unit 22 can then detect the temperature of the thermistor 15 based on the resistance value Rth of the thermistor 15.

Note that the tendency for resistance to change in response to temperature changes may differ depending on the type of thermistor. However, the thermistor circuit shown in Figure 3 can be used for any thermistor. The temperature of the thermistor can be estimated based on the detected voltage.

The rotational position detector 10 of this embodiment includes an abnormality detection device that detects abnormalities in the thermistor circuit 19. The abnormality detection device includes a voltage detector 17 that detects a voltage corresponding to the resistance value of the thermistor 15. The abnormality detection device also includes an acquisition unit 22 that acquires a temperature-related variable based on a signal from the voltage detector 17. In this embodiment, the detection voltage detected by the voltage detector 17 will be used as an example of the variable acquired by the acquisition unit 22. The temperature-related variable is not limited to the detection voltage, and the temperature detected from the detection voltage may also be used. Furthermore, the abnormality detection device includes a determination unit 23 that determines an abnormality in the thermistor circuit 19 based on a change in the variable acquired by the acquisition unit 22.

The anomaly detection device of this embodiment includes the microcomputer described above. The acquisition unit 22 and determination unit 23 correspond to processors that perform predetermined processing. The processors perform predetermined control, thereby functioning as the respective units.

Figure 4 shows a graph illustrating the change in detection voltage when the temperature of the circuit board rises. Referring to Figures 3 and 4, in this embodiment, the resistance value of the thermistor 15 decreases as the temperature increases. As the temperature of the thermistor 15 increases over the operating time of the rotational position detector 10 and the resistance value of the thermistor 15 decreases, the detection voltage increases as indicated by arrow 61. In this example, at time t1, the detection voltage exceeds the alarm generation threshold at which an alarm is issued.

In this embodiment, the alarm generation judgment value is a judgment value that determines whether the temperature of the circuit board 13 is too high. A temperature higher than the normal temperature range of the circuit board 13 can be set as the alarm generation judgment value. The alarm generation judgment value is predetermined and stored in the memory unit 14. If the detected voltage exceeds the alarm generation judgment value, the judgment unit 23 can determine that the temperature of the circuit board 13 is too high. In other words, the judgment unit 23 can determine that overheating of the circuit board 13 has occurred.

The judgment unit 23 notifies the machine control device 41 that the temperature of the circuit board 13 has exceeded the alarm judgment value. The display unit 44 can then display an alarm that the temperature of the circuit board 13 has exceeded the alarm judgment value. Alternatively, the operation control unit 43 can limit the operation of the electric motor 9 to suppress the operation of the rotational position detector 10. Note that in addition to the judgment value that triggers an alarm on the high temperature side, a judgment value that triggers an alarm on the low temperature side may also be set. In this case, the judgment unit can determine that the temperature of the circuit board is too low when the temperature of the circuit board is lower than the judgment value on the low temperature side.

Figure 5 shows a graph illustrating the change in detection voltage over time when the alarm is canceled. In the graph in Figure 5, the temperature of the circuit board 13, which was in an overheated state, drops. When the temperature of the thermistor 15 drops, the detection voltage drops, as indicated by arrow 62. At time t2, the detection voltage becomes smaller than the alarm generation threshold.

The judgment unit 23 notifies the machine control device 41 that the temperature of the circuit board 13 has fallen below the alarm generation judgment value. The display unit 44 can display that the temperature of the circuit board 13 has returned to the normal temperature range. Alternatively, the operation control unit 43 can release restrictions on the operation of the electric motor 9.

In this way, the thermistor circuit 19 in this embodiment detects the temperature of the device to which the thermistor 15 is attached, and can issue an alarm if the detected temperature deviates from a predetermined normal temperature range.

However, if an abnormality occurs in the thermistor circuit 19, the thermistor circuit 19 may not be able to accurately detect the temperature. Next, we will explain the abnormality detection device that detects abnormalities in the thermistor circuit 19.

Figure 6 shows a graph of the detected voltage when liquid adheres to the thermistor of the thermistor circuit. In this example, cutting fluid adheres to the thermistor 15 when machining a workpiece with the machine tool 1. At time t3, the resistance value of the thermistor drops sharply as cutting fluid adheres to the thermistor. The detected voltage rises sharply, as indicated by arrow 63. In this example, the detected voltage rises above the alarm generation threshold.

In addition to when cutting fluid or other liquid adheres to the thermistor, the detection voltage also increases when liquid adheres to the fixed resistor. Alternatively, the detection voltage increases when the solder pad to which the thermistor is fixed shorts out. Alternatively, the detection voltage increases when a conductive foreign object such as metal comes into contact with the thermistor.

Figure 7 shows a graph of the change in detection voltage over time when a crack occurs in the fixed resistor. At time t4, a crack occurs in the fixed resistor 16, causing the resistance value of the fixed resistor 16 to increase. The detection voltage drops sharply, as indicated by arrow 64. In this example, the detection voltage, which was higher than the alarm generation threshold, drops to below the alarm generation threshold. This phenomenon of a drop in detection voltage occurs when, for example, the lead wire in the thermistor circuit is damaged or the fixed resistor becomes detached from the solder pad.

By the way, referring to Figure 6, even if the actual circuit board temperature has not risen, if the detected voltage rises and exceeds the alarm threshold, a circuit board temperature alarm will be issued. Alternatively, referring to Figure 7, even if the actual circuit board temperature has not fallen, if the detected voltage falls and becomes smaller than the alarm threshold, the circuit board temperature alarm will be canceled. In this way, if there is an abnormality in the thermistor circuit, an inaccurate judgment may be made about the device temperature.

Alternatively, when the detection voltage changes from lower to higher than the alarm threshold, or from higher to lower than the alarm threshold, it can be difficult to determine whether the temperature of the circuit board has changed or whether an abnormality has occurred in the thermistor circuit.

In the abnormality detection device of this embodiment, the acquisition unit 22 acquires a temperature-related variable based on a signal from the voltage detector 17 at predetermined time intervals. Here, the acquisition unit 22 acquires the detected voltage. The acquisition unit 22 calculates the slope of the detected voltage over time as a first measurement value. The determination unit 23 then determines that an abnormality has occurred in the thermistor circuit if the first measurement value deviates from a predetermined first determination range. In other words, the abnormality detection device of this embodiment monitors the continuity of the variable value, and determines that an abnormality has occurred in the thermistor circuit if the variable value changes suddenly.

Figure 8 shows a graph of the detected voltage when the temperature of the circuit board is approximately constant within the normal temperature range and the thermistor circuit is normal. The acquisition unit 22 acquires the detected voltage at predetermined time intervals. The acquisition unit 22 can detect the detected voltage, for example, approximately every 1 msec. The acquisition unit 22 can then adopt a variable at an appropriate time interval from the detected variables. In the example shown in Figure 8, the acquisition unit 22 acquires the detected voltage every 1 second. The detected voltage detected by the voltage detector 17 is approximately constant. The determination unit 23 determines that the thermistor circuit is normal.

Figure 9 shows a graph of the detected voltage when cutting fluid adheres to the thermistor. In addition to measurement points MP1 to MP6, the actual voltage is shown by a solid line. At time t3, cutting fluid adheres, and the detected voltage rises sharply, as indicated by arrow 63. In this example, the acquisition unit 22 acquires the detected voltage at measurement points MP1 to MP6 at one-second intervals. The actual detected voltage rises sharply between measurement points MP3 and MP4. The acquisition unit 22 calculates the slope of the detected voltage between measurement points MP1 to MP4 as the first measurement value.

In this example, the slope of the detected voltage per unit time is calculated as the first measurement value based on measurement points at predetermined time intervals. The acquisition unit 22 calculates the slope between adjacent measurement points as the first measurement value. For example, the acquisition unit 22 calculates the slope between measurement points MP1 and MP2, the slope between measurement points MP2 and MP3, and the slope between measurement points MP3 and MP4. A first judgment range is set in advance for the first measurement value. The judgment unit 23 judges that an abnormality has occurred in the thermistor circuit 19 if each first measurement value deviates from the first judgment range.

Here, upper and lower limit values for the slope are predetermined as the first judgment range. The upper limit value can be set to a large upward slope that cannot occur when the device is driven. The lower limit value can be set to a large downward slope with an absolute value that cannot occur when the device is driven. For example, if the variable rises slowly, it can be determined that the thermistor circuit is normal and the temperature of the device is rising.

In this example, the slope from measurement point MP1 to measurement point MP2 and the slope from measurement point MP2 to measurement point MP3 are almost zero, which are within the first judgment range. The judgment unit 23 judges that the thermistor circuit 19 is normal. In contrast, the slope between measurement point MP3 and measurement point MP4, indicated by arrow 65, exceeds the upper limit of the first judgment range. In this case, the judgment unit 23 judges that an abnormality has occurred in the thermistor circuit 19. Furthermore, the slope from measurement point MP4 onwards is almost zero, which is within the first judgment range. However, the judgment unit 23 maintains its judgment that an abnormality has occurred in the thermistor circuit 19 until the occurrence of the abnormality is reset by an operator or the like.

Figure 10 shows a graph of the detected voltage when a crack occurs in the fixed resistor and causes it to break. At time t4, a crack occurs in the fixed resistor 16, causing the detected voltage to drop sharply, as indicated by arrow 64. The slope between the measurement points up to measurement point MP13 is almost zero, which is within the first judgment range. The judgment unit 23 determines that the thermistor circuit 19 is normal. In contrast, the slope between measurement point MP13 and measurement point MP14, as indicated by arrow 66, is less than the lower limit of the first judgment range. In this case, the judgment unit 23 determines that an abnormality has occurred in the thermistor circuit 19. The slope from measurement point MP14 onwards is within the first judgment range. However, the judgment unit 23 maintains its determination that an abnormality has occurred in the thermistor circuit 19 until the occurrence of the abnormality is reset by an operator or other user.

In this manner, in this embodiment, it is possible to determine whether or not an abnormality has occurred in the thermistor circuit 19 based on the slope of the temperature-related variable and the first determination range. The memory unit 14 of the abnormality detection device in this embodiment can store information related to an abnormality in the thermistor circuit 19. When the determination unit 23 determines that an abnormality has occurred in the thermistor circuit 19, the memory unit 14 stores information related to the time the abnormality occurred and the first measurement value. Examples of information related to the first measurement value include the detected voltage at the measurement point where the abnormality occurred and the slope of the detected voltage.

Furthermore, if the determination unit 23 determines that an abnormality has occurred in the thermistor circuit 19, the display unit 44 can display a warning that an abnormality has occurred in the thermistor circuit 19. Alternatively, the display unit 44 may display information related to the first measurement value, such as the time, the detected voltage, and the slope of the detected voltage.

The determination unit 23 can also determine whether the slope of the variable as the first measurement value is positive or negative. Referring to FIG. 9, if the first measurement value is a positive value, the determination unit 23 can infer the cause of the abnormality, such as adhesion of cutting fluid to the thermistor or fixed resistor, contact with a conductive foreign object such as metal, or a short circuit between the thermistor pads. Referring to FIG. 10, if the first measurement value is a negative value, the determination unit 23 can infer the cause of the abnormality, such as damage to the fixed resistor, such as cracks in the fixed resistor, or damage to the lead wires of the thermistor circuit.

The memory unit 14 can store whether the first measurement value is a positive or negative value, along with the time when the abnormality occurred. The memory unit 14 may also store the estimated cause of the abnormality. The display unit 44 can also display whether the first measurement value is a positive or negative value, along with the time. The display unit 44 may also display the estimated cause of the abnormality.

Figure 11 shows a control flowchart for detecting an abnormality in the thermistor circuit in this embodiment. In step 71, the acquisition unit 22 acquires the time and the detected voltage obtained from the voltage detector 17. Here, the detected voltage is acquired at predetermined time intervals. Next, in step 72, the memory unit 42 stores the time and the detected voltage.

In step 73, the acquisition unit 22 calculates the slope of the detected voltage as a first measurement value based on the detected voltage acquired previously and the detected voltage acquired this time. Here, the amount of change in the detected voltage per unit time is calculated as the slope of the detected voltage.

Next, in step 74, the determination unit 23 determines whether the slope of the detected voltage is within a first determination range. If the slope of the detected voltage deviates from the first determination range in step 74, the determination unit 23 can determine that an abnormality has occurred in the thermistor circuit. In this case, control proceeds to step 76.

In step 76, the display unit 44 of the machine control device 41 displays an alarm indicating that an abnormality has occurred in the thermistor circuit 19. In step 77, the memory unit 14 of the rotational position detector 10 can store information related to the alarm. For example, the memory unit 14 can store information related to the first measurement value, such as the time the alarm occurred and the value of the detected voltage at the measurement point when the alarm occurred and the slope of the detected voltage. Then, control to detect the abnormality ends.

On the other hand, if the slope of the detected voltage is within the first judgment range in step 74, control proceeds to step 75. In this case, the judgment unit 23 can judge that the thermistor circuit is normal. In step 75, the abnormality detection device judges whether or not it has received an end signal for control to detect an abnormality in the thermistor circuit 19. The control to detect an abnormality ends, for example, when the electric motor 9 stops. If a signal to end abnormality monitoring has not been received, control returns to step 71, and the control from step 71 to step 75 is repeated. On the other hand, if a signal to end control to monitor an abnormality has been received in step 75, this control ends.

If the determination unit 23 determines in step 74 that an abnormality has occurred in the thermistor circuit, the machine control device 41 can perform any control action. For example, the machine control device 41 can stop the machine tool 1 or restrict the operation of the electric motor 9.

As a comparative example, Figure 12 shows a graph of the detected voltage when cutting fluid adheres to the thermistor. In the example shown in Figure 12, cutting fluid adheres to the thermistor at time t5, causing the detected voltage to rise sharply, as indicated by arrow 63. However, although the detected voltage has risen, it does not reach the alarm generation threshold. For this reason, it is difficult for the operator to notice an abnormality in the thermistor circuit.

As a comparative example, Figure 13 shows a graph of the detected voltage when a crack occurs in the fixed resistor. In the example shown in Figure 13, a crack occurs in the fixed resistor at time t6, causing a sudden drop in the detected voltage, as indicated by arrow 64. However, because the detected voltage before the crack occurs in the fixed resistor is smaller than the alarm generation threshold, no alarm is generated. This makes it difficult for the operator to notice an abnormality in the thermistor circuit.

In addition to false alarms being generated or canceled, as mentioned above, there are cases where operators fail to notice an abnormality in the thermistor circuit. As a result, control may continue at the temperature detected by the abnormal thermistor circuit.

In contrast, the anomaly detection device of this embodiment determines an anomaly in the thermistor circuit based on the slope of a variable related to temperature, making it possible to detect an anomaly in the thermistor circuit without relying on the magnitude of the variable or the alarm generation threshold. This allows for accurate detection of an anomaly in the thermistor circuit, improving the reliability of the temperature detected by the thermistor circuit.

The rotational position detector in this embodiment can be attached to the spindle motor of the spindle head of a machine tool. Because the spindle motor is placed inside a machining chamber where cutting fluid splashes, there is a risk of cutting fluid adhering to it. Even in this case, the abnormality detection device of this embodiment can accurately detect abnormalities in the thermistor circuit.

Second Embodiment
The abnormality detection device and position detector according to the second embodiment will be described with reference to Figures 14 to 17. The configuration of the machine tool and the configuration of the rotational position detector according to this embodiment are the same as those of the first embodiment (see Figures 1 and 2). The abnormality detection device according to this embodiment differs from the first embodiment in the control for detecting an abnormality in the thermistor circuit.

Figure 14 shows a graph of the detection voltage versus temperature for an NTC thermistor. The horizontal axis represents the thermistor temperature, and the vertical axis represents the detection voltage output from the thermistor circuit. In the low temperature range, the increase in detection voltage relative to an increase in temperature is small. In other words, on the low temperature side, the change in detection voltage relative to a change in temperature is small. In contrast, in the high temperature range, the increase in detection voltage relative to an increase in temperature is large.

For example, in the range below 80°C, the slope of the detection voltage relative to temperature is small, but in the range above 80°C, the slope of the detection voltage relative to temperature is large. For this reason, in the control for detecting abnormalities in the first embodiment, the detection sensitivity for abnormalities is high in the high temperature range, but in the low temperature range, the slope of the detection voltage relative to temperature change is small, so the detection sensitivity is low. In other words, in the low temperature range, there is a risk that the accuracy of determining whether or not an abnormality has occurred in the thermistor circuit will decrease.

Referring to FIG. 2, the acquisition unit 22 in this embodiment acquires a variable at predetermined time intervals. The acquisition unit 22 calculates a value obtained by second-order time differentiation of the variable as a second measurement value. The determination unit 23 then determines that an abnormality has occurred in the thermistor circuit if the second measurement value deviates from a predetermined second determination range. The second determination range can be set such that a large value that cannot occur when the device is operated is set as the upper limit. Also, a small value that cannot occur when the device is operated is set as the lower limit.

Figure 15 shows a graph of the detected voltage when cutting fluid adheres to the thermistor. At time t3, cutting fluid adheres, and the detected voltage rises sharply, as indicated by arrow 63. The time intervals and detected voltages for measurement points MP1 to MP6 are the same as those in Figure 9 for the first embodiment. In this example, the acquisition unit 22 acquires the detected voltage at one-second time intervals.

In this embodiment, the acquisition unit 22 selects three consecutive measurement points. Then, the acquisition unit 22 acquires the slope of the detected voltage from two consecutive measurement points. The acquisition unit 22 calculates the second measurement value by second-order differentiation of the detected voltage based on the slope of the adjacent detected voltages. Then, the determination unit 23 determines that an abnormality has occurred in the thermistor circuit if the second measurement value deviates from a predetermined second determination range.

For example, the acquisition unit 22 calculates a first slope from measurement point MP1 to measurement point MP2, and a second slope from measurement point MP2 to measurement point MP3. Then, the acquisition unit 22 subtracts the first slope from the second slope, divides the result by the time from measurement point MP1 to measurement point MP3, and calculates the second derivative. The second derivative corresponds to the second measurement value. In this example, the second measurement value is approximately zero. Because the second measurement value is within the second determination range, the determination unit 23 determines that the thermistor circuit 19 is normal.

Next, the acquisition unit 22 calculates the second derivative at measurement point MP3. The acquisition unit 22 acquires the detected voltages at measurement points MP2, MP3, and MP4. The acquisition unit 22 then calculates a first slope from measurement point MP2 to measurement point MP3, as indicated by arrow 67a, and a second slope from measurement point MP3 to measurement point MP4, as indicated by arrow 67b. The acquisition unit 22 then subtracts the first slope from the second slope, divides the result by the time ts1 from measurement point MP2 to measurement point MP4, and calculates the second derivative as the second measurement value. In this case, because the second measurement value exceeds the upper limit of the second judgment range, the judgment unit 23 judges that the thermistor circuit is abnormal.

After the judgment unit 23 detects an abnormality in the thermistor circuit, control to detect the abnormality can be suspended until the abnormality alarm is reset. Alternatively, the acquisition unit 22 acquires the detected voltages at measurement points MP3, MP4, and MP5. In this case, the second measurement value will be smaller than the lower limit of the second judgment range. However, because it has just exceeded the upper limit of the second judgment range, the judgment unit 23 may determine that the increase in the detected voltage has completed.

Figure 16 shows a graph of the detected voltage when a crack occurs in the fixed resistor. At time t4, a crack occurs in the fixed resistor 16, and the detected voltage drops sharply, as indicated by arrow 64. The acquisition unit 22 selects three consecutive measurement points. The acquisition unit 22 acquires the slope of the detected voltage from two consecutive measurement points. The acquisition unit 22 calculates the second-order time derivative of the detected voltage from the slope of adjacent detected voltages, as the second measurement value.

The change in the slope of the detected voltage up to measurement point MP13 is small. For example, the value of the second-order derivative of the detected voltage at measurement point MP12 is almost zero, so it is within the second judgment range. The judgment unit 23 determines that the thermistor circuit 19 is normal.

Next, the acquisition unit 22 calculates the second-order differential value at measurement point MP13. The acquisition unit 22 subtracts the slope between measurement points MP12 and MP13, indicated by arrow 68a, from the slope between measurement points MP13 and MP14, indicated by arrow 68b, and divides this value by the time ts2 from measurement point MP12 to measurement point MP14 to calculate a second measurement value. Because the second measurement value is less than the lower limit of the second judgment range, the judgment unit 23 judges that an abnormality has occurred in the thermistor circuit 19. After the judgment unit 23 judges that an abnormality has occurred in the thermistor circuit, control to detect the abnormality can be suspended until the abnormality alarm is reset.

In this way, if the value of the second-order derivative of the temperature-related variable falls outside the second judgment range, it can be determined that an abnormality has occurred in the thermistor circuit. In other words, if the slope of the temperature-related variable changes suddenly, it can be determined that an abnormality has occurred in the thermistor circuit.

Furthermore, the determination unit 23 can determine whether the second measurement value is a positive value or a negative value. Then, the same control as in the first embodiment can be implemented. Referring to FIG. 15, if the second measurement value is a positive value, the determination unit 23 can infer the cause in the same way as when the first measurement value is a positive value. For example, the determination unit 23 can infer that cutting fluid has adhered to the thermistor or fixed resistor. Referring to FIG. 16, if the second measurement value is a negative value, the determination unit 23 can infer the cause in the same way as when the first measurement value is a negative value. For example, the determination unit 23 can infer that a crack has occurred in the fixed resistor.

Furthermore, as in the first embodiment, the display unit 44 may display the time of occurrence of the abnormality, the second measurement value, and an alarm, display whether the second measurement value is positive or negative, and display the estimated cause of the abnormality. Further, as in the first embodiment, the memory unit 42 may store the second measurement value, the alarm, and the estimated cause of the abnormality along with the time of occurrence of the abnormality.

Figure 17 shows a flowchart of the control for detecting an abnormality in the thermistor circuit in this embodiment. Steps 71 and 72 are the same as steps 71 and 72 of the control in the first embodiment (see Figure 11).

Next, in step 81, the acquisition unit 22 calculates the second-order derivative of the detected voltage with respect to time as a second measurement value based on the previously detected detected voltage and the currently detected detected voltage. In step 82, the determination unit 23 determines whether the second-order derivative of the detected voltage is within a second determination range. If the second-order derivative of the detected voltage is not within the second determination range in step 82, the determination unit 23 determines that an abnormality has occurred in the thermistor circuit. In this case, control proceeds to steps 84 and 85.

Steps 84 and 85 are similar to steps 76 and 77 in the control of the first embodiment (see Figure 11). That is, the display unit 44 displays information related to the alarm, and the memory unit 42 stores information related to the alarm. This control then ends.

On the other hand, if the value of the second-order derivative of the detected voltage is within the second determination range in step 82, the determination unit 23 determines that the thermistor circuit is normal. In this case, control proceeds to step 83.

The control of step 83 is the same as step 75 in the control of the first embodiment (see Figure 11). That is, the control of steps 71 to 83 is repeated until a signal is input to terminate the control that determines whether the thermistor circuit is normal.

The control for detecting abnormalities in the thermistor circuit in this embodiment can accurately detect abnormalities in the thermistor circuit without relying on the temperature of the thermistor. In particular, even when the change in detection voltage with respect to temperature is small (when the sensitivity of detection voltage to temperature is low), abnormalities in the thermistor circuit can be detected with high accuracy. For example, in the case of the NTC thermistor shown in Figure 14, abnormalities in the thermistor circuit can be accurately determined even in the low temperature range below 80°C.

It should be noted that the control for detecting an abnormality in the first embodiment and the control for detecting an abnormality in the second embodiment may be performed simultaneously. For example, if the thermistor circuit is determined to be abnormal in either the control in the first embodiment or the control in the second embodiment, it may ultimately be determined that the thermistor circuit is abnormal. Alternatively, the control for detecting an abnormality in the first embodiment and the control for detecting an abnormality in the second embodiment may be performed independently, with information regarding the alarm being displayed or stored separately.

At least one of the embodiments described above can provide an abnormality detection device that can accurately detect abnormalities in a thermistor circuit.

Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible to these embodiments without departing from the gist of the present disclosure, or the spirit of the present disclosure as derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values or formulas are used to explain the above-described embodiments.

The following notes are provided regarding the above embodiments and variations.

(Appendix 1)
An abnormality detection device for detecting an abnormality in a thermistor circuit,
a voltage detector that detects a voltage corresponding to the resistance value of the thermistor;
an acquisition unit that acquires a variable related to temperature based on a signal from the voltage detector;
a determination unit that determines whether there is an abnormality in the thermistor circuit based on a change in the variable,
The acquisition unit acquires a variable at a predetermined time interval and calculates a slope of the variable with respect to time as a first measurement value;
The determination unit determines that an abnormality has occurred in the thermistor circuit when the first measurement value deviates from a predetermined first determination range.

(Appendix 2)
2. The abnormality detection device according to claim 1, wherein the determination unit determines whether the first measurement value is a positive value or a negative value and displays the determination result on the display unit.

(Appendix 3)
a storage unit for storing information relating to an abnormality in the thermistor circuit;
3. The abnormality detection device according to claim 1, wherein, when the determination unit determines that an abnormality has occurred in the thermistor circuit, the memory unit stores information regarding the time when the abnormality occurred and the first measurement value.

(Appendix 4)
The acquisition unit calculates a second measurement value by differentiating the variable twice with respect to time;
4. The abnormality detection device according to claim 1, wherein the judgment unit judges that an abnormality has occurred in the thermistor circuit when the second measurement value deviates from a predetermined second judgment range.

(Appendix 5)
an anomaly detection device according to claim 1;
and an angle calculation unit that detects the rotation position of the rotation shaft.

(Appendix 6)
An abnormality detection device for detecting an abnormality in a thermistor circuit,
a voltage detector that detects a voltage corresponding to the resistance value of the thermistor;
an acquisition unit that acquires a variable related to temperature based on a signal from the voltage detector;
a determination unit that determines whether there is an abnormality in the thermistor circuit based on a change in the variable,
The acquisition unit acquires a variable at a predetermined time interval and calculates a second-order derivative of the variable with respect to time as a measurement value;
The determination unit determines that an abnormality has occurred in the thermistor circuit when the measured value deviates from a predetermined determination range.

(Appendix 7)
7. The abnormality detection device according to claim 6, wherein the determination unit determines whether the measurement value is a positive value or a negative value and displays the determination result on the display unit.

10 Rotational position detector 13 Circuit board 14 Memory unit 17 Voltage detector 19 Thermistor circuit 22 Acquisition unit 23 Determination unit 41 Machine control device 42 Memory unit 44 Display unit

Claims (7)

An abnormality detection device for detecting an abnormality in a thermistor circuit,
a voltage detector that detects a voltage corresponding to the resistance value of the thermistor;
an acquisition unit that acquires a variable related to temperature based on a signal from the voltage detector;
a determination unit that determines an abnormality in the thermistor circuit based on a change in the variable,
the acquisition unit acquires the variable at a predetermined time interval and calculates a slope of the variable with respect to time as a first measurement value;
The abnormality detection device, wherein the determination unit determines that an abnormality has occurred in the thermistor circuit when the first measurement value deviates from a predetermined first determination range. The anomaly detection device of claim 1, wherein the determination unit determines whether the first measurement value is a positive value or a negative value and displays the determination result on a display unit. a storage unit that stores information regarding an abnormality in the thermistor circuit;
3. The abnormality detection device according to claim 1, wherein when the determination unit determines that an abnormality has occurred in the thermistor circuit, the storage unit stores information about the time when the abnormality occurred and the first measurement value. the acquisition unit calculates a second measurement value by differentiating the variable with respect to time,
4. The abnormality detection device according to claim 1, wherein the determination unit determines that an abnormality has occurred in the thermistor circuit when the second measurement value deviates from a predetermined second determination range. The abnormality detection device according to claim 1;
and an angle calculation unit that detects the rotation position of the rotation shaft. An abnormality detection device for detecting an abnormality in a thermistor circuit,
a voltage detector that detects a voltage corresponding to the resistance value of the thermistor;
an acquisition unit that acquires a variable related to temperature based on a signal from the voltage detector;
a determination unit that determines an abnormality in the thermistor circuit based on a change in the variable,
the acquisition unit acquires the variable at a predetermined time interval and calculates a second-order derivative of the variable with respect to time as a measurement value;
The determination unit determines that an abnormality has occurred in the thermistor circuit when the measured value deviates from a predetermined determination range. The anomaly detection device of claim 6, wherein the determination unit determines whether the measurement value is a positive value or a negative value and displays the determination result on a display unit.