EP4239194A1 - Method for controlling the delivery pressure of a supply pump - Google Patents

Abstract

The invention relates to a method for controlling the delivery pressure of a supply pump (2) in a system (1) for delivering and metering a viscous material, the system (1) having a supply pump (2), a metering pump (3) and a supply pump (2) and the metering pump (3) and the supply pump (2) transports the viscous material from a material supply (5) at a delivery pressure D through the delivery line (4) to an inlet (6) of the metering pump (3) conveys, with the inlet (6) of the dosing pump (3) also being preceded by a pressure buffer (7) pretensioned to a pretensioning pressure P and comprising a variable buffer volume (19), the buffer volume (19) receiving viscous material from the feed line ( 4) when the delivery pressure in the delivery line (4) in the area of the pressure buffer (7) is higher than the preload pressure P of the pressure buffer (7), and from which viscous material can be discharged into the delivery line (4) when the Delivery pressure in the delivery line (4) in the area of the pressure buffer (7) is lower than the preload pressure P of the pressure buffer (7), the system (1) also having a pressure sensor (8) upstream of the input (6) of the metering pump (3) for detection of an actual pressure value in the delivery line (4) and a control unit (9), the control unit (9) being connected to the pressure sensor (8) and to the supply pump (2) and the dosing pump (3), the control unit (9) transmits a default value to the supply pump (2) depending on a deviation between a specified target pressure value and the actual pressure value in the delivery line (4) and on the operating state of the metering pump (3).

Description

The invention relates to a method for controlling the delivery pressure of a supply pump in a system for delivering and dosing a viscous material.

When processing viscous materials, the plastic component is usually conveyed directly from the container, for example from a hobbock, via a conveying line to a dosing pump with the aid of a supply pump. The supply pump is often located several meters away from the dosing pump, so that the supply pump must build up a sufficiently high delivery pressure in order to convey the viscous material from the supply pump to the dosing pump. During a dosing process, i.e. during operation of the dosing pump, there is a pressure drop in the delivery line due to the material discharge. In order to compensate for this pressure loss, a high delivery pressure built up by the supply pump is all the more necessary. At the same time, however, this has the consequence that between individual dosing processes, as soon as the dosing pump is at a standstill and the pressure loss in the delivery line is significantly lower, the pressure on the inlet side of the dosing pump rises sharply.

Very high supply pressures on the inlet side of the dosing pump are a decisive factor in the wear of the dosing pump, especially the shaft seal. In addition, excessive pressure fluctuations on the inlet side of the dosing pump have a negative impact on the dosing accuracy. After all, a supply pressure that is only briefly too low can lead to considerable problems with the dosing accuracy or to wear on the dosing pump

In order to remedy this, it is known to use material pressure reducing valves near the metering pump inlet. When using such a valve, the feed pressure of the supply pump is set to a significantly higher pressure than would actually be necessary to supply the metering pump. The material pressure reducing valve reduces the pressure just before the dosing pump to the required dosing pump inlet pressure.

However, the use of material pressure reducing valves has various disadvantages. So the reducing valves are very prone to failure. Even small air bubbles in the valve can cause the pressure to "break through" and the dosing pump can be damaged or even destroyed by the very high inlet pressure for a short time. In addition, material pressure reducing valves are not suitable when processing materials with large or abrasive filler particles, as the particles cause rapid and severe wear of the valve's mechanical components, thereby affecting their reliability. Finally material pressure control valves have a relatively high dead weight and a comparatively high price, both of which are considered disadvantageous.

An alternative solution is to actively regulate the pressure of the supply pump. For this purpose, a pressure sensor is attached to the inlet of the dosing pump, which regulates the delivery pressure or the output of the supply pump via a control circuit depending on the pressure recorded at the inlet of the dosing pump. The disadvantage of this method is the inertia of the system, ie the fact that the pressure at the inlet of the dosing pump must first be measured too high or too low before the supply pump reacts accordingly. In combination with the very rigid delivery lines required due to the high material pressure, this regularly leads to an undesirably low or undesirably high pressure on the inlet side of the metering pump when metering is started and stopped. In addition, scoop piston pumps, which are usually used as supply pumps, do not allow any backflow of material, which makes it impossible to subsequently reduce the pressure when the dosing pump is at a standstill without a leak.

From the WO 2017/004635 A1 a device with a source for at least one liquid plastic component and a dosing device is known, wherein a buffer device with a variable buffer volume is arranged between the source and the dosing device. This makes it possible to make the liquid plastic component available to the dosing device without interruption, the pressure prevailing in the liquid plastic component between the buffer device and the dosing device being controllable by the buffer device.

The object of the present invention is to provide a method for controlling the delivery pressure of a supply pump in a system for delivering and dosing a viscous material, which method can be operated more reliably and with greater accuracy than known methods.

This object is achieved by a method having the features of patent claim 1.

Advantageous refinements and developments of the method are the subject matter of the dependent claims.

According to patent claim 1, the invention is a method for controlling the delivery pressure of a supply pump in a system for delivering and metering a viscous material, the system having a supply pump, a metering pump and a delivery line extending between the supply pump and the metering pump, and wherein the supply pump delivers the viscous material from a supply of material at a delivery pressure D through the delivery line to an inlet of the metering pump, the inlet the dosing pump is preceded by a pressure buffer that is preloaded to a preload pressure P and has a variable buffer volume, with the buffer volume being able to absorb viscous material from the delivery line if the delivery pressure in the delivery line in the area of the pressure buffer is higher than the preload pressure P of the pressure buffer, and from which viscous material can be discharged into the delivery line if the delivery pressure in the delivery line in the area of the pressure buffer is lower than the preload pressure P of the pressure buffer, with the system also having a pressure sensor connected upstream of the metering pump input for recording an actual pressure value in the delivery line and a Has control unit, wherein the control unit is connected to the pressure sensor and to the supply pump and to the dosing pump. The method according to the invention is characterized in that the control unit transmits a default value to the supply pump as a function of a deviation between a specified target pressure value and the actual pressure value in the delivery line and on the operating state of the metering pump.

In other words, the method according to the invention provides that a pressure buffer with a variable buffer volume, which is connected upstream of the inlet of the metering pump and is preloaded to a preload pressure P, is used, with viscous material being taken up or removed from the delivery line in the buffer volume in order to mitigate pressure fluctuations in the delivery line the buffer volume can be released into the delivery line. The preload pressure P changes depending on the filling level of the buffer volume.

The method according to the invention also provides that not only the actual pressure value recorded in the delivery line is used to control the delivery pressure of the supply pump, but also information regarding the operating state of the metering pump. In order to determine the default value for the supply pump, the control unit also processes information about whether the metering pump starts up and a metering process starts or whether the metering pump is switched off and the metering process ends. Taking into account the information regarding the operating state of the metering pump enables the delivery pressure to be built up by the supply pump to be tracked more quickly and therefore more precisely, since changes in the operating state of the metering pump can be reacted to immediately and one does not have to wait until the change in operating state increases or a drop in pressure on the input side of the metering pump is detected by the pressure sensor arranged there. The use of a pressure buffer with a variable buffer volume provided according to the invention, on the one hand, and the consideration of the operating state of the metering pump when regulating the delivery pressure of the supply pump, on the other hand, can effectively reduce extreme pressure fluctuations on the inlet side of the metering pump and the disadvantages associated with them, and a very constant Supply pressure can be set at the inlet of the dosing pump.

The control unit preferably comprises a PI or a PID controller. This acts on the input side of the dosing pump with the specified setpoint pressure value and the actual pressure value recorded by the pressure sensor. The operating state of the metering pump can be taken into account when regulating the delivery pressure of the supply pump in such a way that the default value transmitted from the control unit to the supply pump is provided with a correction value depending on the operating state of the metering pump. Thus, as soon as the dosing process is stopped, the value of the I component in a PI or PID control can be reduced by a factor of <1, for example by a factor of 0.5, compared to the last value of the I component during the previous dosing process , to be multiplied. As a result, the default value transmitted to the supply pump drops suddenly to a significantly lower value when dosing is stopped. An expected strong increase in pressure on the inlet side of the dosing pump due to the changing interference variable "pressure loss in the line" is already compensated for before a deviation in the measured value recorded by the pressure sensor is registered. This means that the delivery pressure can be tracked much faster and more efficiently than would be possible if the pressure sensor only reacted to the signal, which would only detect an increase in pressure on the inlet side of the metering pump a certain time after the metering pump had been switched off.

As soon as dosing starts again, the value of the I component of the PI or PID control is reset to the last value of the I component during the previous dosing process. As a result, the default value transmitted to the supply pump rises abruptly and a sharp drop in pressure on the inlet side of the dosing pump when dosing restarts can be prevented. In this way, a relatively constant pressure can be achieved on the inlet side of the metering pump between two meterings, regardless of the idle time of the metering pump.

The use of a pressure buffer within a system for conveying and metering a viscous material has several advantages. In contrast to the solutions known from the prior art, when using a pressure buffer, heavily filled materials and media with abrasive fillers can also be processed without any problems. The method according to the invention is therefore available for a wide variety of application areas and can therefore be used very flexibly. The material density of the conveyed material can be in a range of about 0.5 to 5 g/cm ³ , preferably in a range of about 1 to 3 g/cm ³ . The flow rate can be about 0.05 cm3/s to 150 cm3/s, preferably about 0.5 cm3/s to 20 cm3/s.

Such pressure buffers also have the advantage of comparatively small dimensions and a significantly lower weight compared to material pressure reducing valves, so that they can, for example, be carried on a robot together with the dosing pump.

After all, using a pressure buffer is cheaper than using a material pressure reducing valve.

The prestressing force of the pressure buffer that causes the prestressing pressure P can be applied, for example, via a pneumatic force or a spring force or a hydraulic force. It is advantageous if the prestressing force is dependent on the fill level of the buffer, ie if the prestressing force is greater the more the buffer volume is filled, in order to avoid accidental complete filling or complete emptying of the buffer.

One embodiment of the method according to the invention provides for the use of at least one steel spring designed as a wave spring for prestressing the pressure buffer. Compared to conventional spiral springs, wave springs have a spring height that is up to 50% lower with the same spring force and therefore take up significantly less space. Compared to the use of conventional coil springs, this enables the buffer to be smaller and simpler to construct.

According to a further embodiment of the invention, the pressure buffer comprises a rolling membrane for the hermetic separation of the variable buffer volume. This is a highly flexible, thin-walled, fabric-reinforced membrane made from a rubber-elastic material such as silicone, polyurethane, fluorine rubber, ethylene-propylene-diene rubber or acrylonitrile-butadiene rubber. A rolling diaphragm has the advantage of excellent tightness, which is particularly important for applications with viscous adhesives. The smallest leaks would otherwise result in the adhesive escaping from the buffer volume and hardening, thus impairing the function of the buffer or even rendering it unusable. In addition, a rolling diaphragm enables the buffer to work practically without friction and almost without hysteresis.

According to the invention, the variable buffer volume can have a volume of 100 to 10000 mm ³ , preferably a volume of 500 to 5000 mm ³ . For example, the variable buffer volume can include a volume of 1500 mm ³ which is available as a compensation volume.

According to one embodiment of the method according to the invention, in addition to the signal from the pressure sensor and information regarding the operating state of the dosing pump, information regarding the current fill level in the buffer volume can also be included in the control. In this case, the delivery pressure of the supply pump is also adjusted depending on how much viscous material can be discharged from the buffer volume into the delivery line or out of the delivery line to compensate for pressure fluctuations can be accommodated with the buffer volume. As a result, the control accuracy can be further improved.

It can be provided that the buffer comprises a plunger which protrudes from a housing of the pressure buffer and via which the fill level of the buffer volume can be determined. In other words, the plunger moves up and down depending on the fill level of the buffer volume, so that the fill level of the buffer volume can be inferred from the length of the portion of the plunger protruding from the housing of the pressure buffer. This length can be determined, for example, optically or with the aid of another suitable sensor. The corresponding signal can be fed to the control unit as a further input signal.

Alternatively or additionally, when using a means for prestressing the pressure buffer, which is suitable for enabling an at least approximately linear spring behavior, the fill level of the buffer volume can also be inferred from the measured pressure. In particular, the use of wave springs would be conceivable here, in which the pressure buffer has an approximately linear pressure-volume behavior.

According to an embodiment variant of the invention, the pressure sensor and/or a pressure-protecting element is accommodated in a housing of the pressure buffer. In other words, the pressure sensor upstream of the inlet of the metering pump can be accommodated directly inside the housing of the pressure buffer and can detect any pressure fluctuations here at an early stage. Additionally or alternatively, a pressure-protecting element, for example a bursting disc or a pressure relief valve, can be accommodated in the housing of the pressure buffer, so that in the event of a pressure in the delivery line suddenly rising too high, the pressure can be effectively reduced in order to protect the downstream metering pump .

In one embodiment of the invention, it can be provided that the time-dependent change in the viscosity of the viscous material is taken into account when determining the default value transmitted to the supply pump. For this purpose, a time-dependent viscosity profile of the viscous material can be stored in the control unit and this viscosity development over time can be taken into account in the control of the supply pump based on a PT1 element. In particular, it is possible in this way to influence the pressure at the inlet of the metering pump, the strength or the length of a short pressure pulse at the start of a next metering, and combinations of the options mentioned, depending on the time that has elapsed since the last metering.

Alternatively, between two dosing while the dosing pump is at a standstill, a slightly higher setpoint pressure can be specified at the inlet of the dosing pump than during the dosage is the case. This prevents the pressure at the inlet of the metering pump from briefly falling below a critical threshold when metering is restarted.

When using a scoop piston pump as a supply pump, an undesirable pressure change, such as a pressure drop or a pressure increase in the delivery line, can occur at the switchover point of the pump. According to one embodiment of the invention, a travel sensor can be provided, which detects the position and the speed of the movable piston of the supply pump and transmits information regarding the expected switching point of the supply pump to the control unit for further processing. Thus, by appropriate pre-control of the air pressure, with which a pneumatic supply pump is acted upon, an extensive adjustment of the pressure drop at the switchover point of the supply pump can be achieved. Another advantage of such a displacement sensor is that a leak in the hydraulic system could be reliably detected.

With the aid of the method according to the invention, a relatively constant pressure of up to 40 bar, preferably 2 to 10 bar, can be set at the inlet of the metering pump at a pressure applied by the supply pump of up to 300 bar, preferably 10 to 80 bar. The distance between the supply pump and metering pump can be about 1 to 20 m, preferably 2 to 10 m.

In particular, a silicone, a polyol, an isocyanate, an MS polymer, a polyacrylate, an epoxy, a butyl, a polysulfide, a dispersion or a prepolymer of one of the groups of substances mentioned can be conveyed and metered as viscous material.

Such a viscous material is preferably conveyed and metered, the viscosity of which is in a range from 10,000 mPas to 2,000,000 mPas, preferably in a range from 20,000 mPas to 500,000 mPas.

Figur 1:

ein System zur Förderung und Dosierung eines viskosen Materials, wie es in dem erfindungsgemäßen Verfahren eingesetzt wird, in schematischer Darstellung;

Figur 2:

ein Ausführungsbeispiel eines Druckpuffers, der in dem erfindungsgemäßen Verfahren eingesetzt wird, in einer Schnittdarstellung.

The invention is explained in more detail below using an exemplary embodiment and with reference to the attached drawings. Show it:

Figure 1:

a system for conveying and dosing a viscous material, as used in the method according to the invention, in a schematic representation;

Figure 2:

an embodiment of a pressure buffer, which is used in the method according to the invention, in a sectional view.

figure 1 1 shows a schematic representation of a system, denoted as a whole by 1, for conveying and dosing a viscous material, for example a plastic component for a sealing material. The system 1 comprises a supply pump 2 designed as a pneumatic scoop piston pump, which conveys the viscous material from a material supply 5 into a delivery line 4 . Because of the delivery pressure built up by the supply pump 2 , the viscous material is delivered through the delivery line 4 to the input 6 of a metering pump 3 . The viscous material is delivered to a mixing head 10 via the metering pump 3 . In the mixing head 10, the viscous material is mixed with one or more other components, not specified here, before the mixture, indicated by the arrow 11, is discharged from the mixing head 10, for example in the form of a sealing bead. As an alternative to the mixing head 10 shown here, a component valve (not shown) can also be used if the viscous material is not to be mixed with another component, but instead is to be dispensed directly.

The supply pump 2 and the dosing pump 3 are controlled by a control unit 9 which includes a PID controller. Since the supply pump 2 is a pneumatic scoop piston pump, the system 1 has a proportional pressure control valve 12 which is arranged between the control unit 9 and the supply pump 2 and which converts an electrical signal from the control unit 9 into a pneumatic pressure which is applied to the supply pump 2 becomes.

In order to detect an actual pressure value in the delivery line 4, the system 1 includes a pressure sensor 8, which is accommodated in a housing 13 of a pressure buffer 7, which will be described in detail later. The pressure sensor 8 is connected to an input of the control unit 9 via a signal line 14 . A predetermined desired pressure value is stored in the control unit 9, with which the actual pressure value is compared. Depending on the result of this comparison, a corresponding default value is transmitted to the supply pump 2 or to the proportional pressure control valve 12 via a signal line 15 .

The dosing pump 3 is controlled by the control unit 9 via a further signal line 16 . In addition to the signal from the pressure sensor, information regarding the operating state of the metering pump 3 is also taken into account by the control unit 9 when determining the default value for the supply pump 2 . In other words, in addition to the pressure value detected by the pressure sensor 8 , the control unit 9 also processes information regarding a start or stop of dosing of the dosing pump and takes this information into account when determining the default value transmitted to the supply pump 2 . In this way it is possible to react particularly quickly to changes in the operating state of the metering pump 3 and a sharp increase or drop in the pressure at the inlet 6 of the metering pump 3 can be prevented. In practice, the operating state of the metering pump 3 is taken into account in the Regulation of the feed pressure of the supply pump 2 in such a way that the default value transmitted from the control unit 9 to the supply pump 2 or the proportional pressure control valve 12 is corrected depending on the operating state of the metering pump 3 . As soon as dosing is stopped, the value of the I component of the PID control is multiplied by a factor of 0.5 compared to the last value of the I component during the previous dosing process. As a result, the default value transmitted to the supply pump 2 drops abruptly to a significantly lower value when dosing is stopped. As soon as dosing starts again, the value of the I-component is reset to the last value of the I-component during the previous dosing process. As a result, the default value transmitted to the supply pump 2 rises abruptly again and a sharp drop in pressure on the input side of the metering pump 3 when metering restarts can be prevented.

In order to influence the pressure in the delivery line 4 , in particular at the inlet 6 of the metering pump 3 , the system 1 additionally has a pressure buffer 7 connected upstream of the metering pump 3 . The pressure buffer 7 includes a variable buffer volume which can absorb viscous material from the delivery line 4 or from which viscous material can be discharged into the delivery line 4 .

The structure and operation of the print buffer 7 are based on figure 2 explained in more detail. The pressure buffer 7 is connected to the delivery line 4, through which viscous material is delivered in the direction indicated by the arrows from the supply pump 2 to the metering pump 3. The pressure buffer 7 comprises a housing 13 and a plunger 17 which is movable in sliding bushes 23 in a direction indicated by the arrow S. The plunger 17 protrudes at least partially out of the housing 13 . A rolling diaphragm 18 is arranged on the end of the plunger 17 facing the delivery line 4, by means of which a variable buffer volume 19 acting as a compensation volume is limited. The buffer volume 19 is hermetically sealed adjacent to the plunger 17 by the rolling diaphragm 18, while adjacent to the delivery line 4 it is open and in contact with it. The rolling diaphragm 18 enables the pressure buffer 7 to work practically without friction.

The pressure buffer 7 is preloaded to a preload pressure P, which depends on the fill level of the buffer volume 19 . The preload pressure P is applied by a steel spring designed as a wave spring 20 which is arranged between a shoulder 21 of the plunger 17 and the inner wall of the housing 13 . As soon as the delivery pressure in the delivery line 4 in the area of the pressure buffer 7 and in front of the dosing pump 3 is higher than the preload pressure P of the pressure buffer 7, viscous material enters the delivery line 4 into the buffer volume 19 and presses on the plunger 17 via the rolling diaphragm 18, so that it moves upward away from the conveying line 4 and the wave springs 20 are compressed. The variable buffer volume 19 increases accordingly and the preload pressure P of the pressure buffer 7 increases. This process lasts until a pressure equilibrium is established or until the plunger 17 with its shoulder 22 on the Housing 13 strikes, as is the figure 2 shows. If the delivery pressure in the delivery line 4 falls below the now prevailing preload pressure P of the pressure buffer, the restoring force of the wave springs 20 causes the plunger 17 to move in the opposite direction towards the delivery line 4, as a result of which the buffer volume 19 is reduced and viscous material is removed from the buffer volume 19 is discharged into the feed line 4 to supply the metering pump 3. In this way, the pressure buffer 7 can mitigate pressure fluctuations in the delivery line 7 and thus contribute to a more constant pressure on the inlet side of the metering pump 3 . Through the use of wave springs 20, the pressure buffer 7 has an approximately linear pressure-volume behavior. In order to prevent the pressure buffer 7 from being overloaded, the variable buffer volume 19 can expand in a pressure range of approximately 2 to 20 bar. If these values fall below or are exceeded, the movement of the plunger 17 is limited by a mechanical stop.

By providing a variable buffer volume on the one hand and taking into account the operating state of the metering pump 3 on the other hand, the method according to the invention makes it possible to control the feed pressure of the supply pump 2 in such a way that a substantially constant Supply pressure can be provided.

In a variant of the method that is not shown in the figures, additional information regarding the filling level of the buffer volume 19 can be included in the regulation. For this purpose, the filling level of the buffer volume 19 can be determined indirectly based on the length of the portion of the plunger 17 protruding from the housing 13 of the pressure buffer 7 . For this purpose, a preferably optical sensor can be provided, which detects the position of the ram 17 and sends a corresponding signal to the control unit 9 for further processing.

Claims (9)

A method for controlling the delivery pressure of a supply pump (2) in a system (1) for delivering and dosing a viscous material, the system (1) having a supply pump (2), a dosing pump (3) and a pump located between the supply pump (2) and the metering pump (3) and the supply pump (2) conveys the viscous material from a material supply (5) at a delivery pressure D through the delivery line (4) to an inlet (6) of the metering pump (3). , wherein the inlet (6) of the dosing pump (3) is preceded by a pressure buffer (7) preloaded to a preload pressure P and comprising a variable buffer volume (19), the buffer volume (19) being able to absorb viscous material from the delivery line (4). , when the delivery pressure in the delivery line (4) in the area of the pressure buffer (7) is higher than the preload pressure P of the pressure buffer (7), and from which viscous material can be discharged into the delivery line (4) when the delivery pressure in the delivery line (4) in the area of the pressure buffer (7) is lower than the preload pressure P of the pressure buffer (7), the system (1) furthermore having a pressure sensor (8) connected upstream of the input (6) of the metering pump (3) for detecting an actual pressure value in the delivery line (4) and a control unit (9), the control unit (9) being connected to the pressure sensor (8) and to the supply pump (2) and to the dosing pump (3), characterized in that the control unit (9) transmits a default value to the supply pump (2) depending on a deviation between a specified target pressure value and the actual pressure value in the delivery line (4) and on the operating state of the metering pump (3). Method according to Claim 1, characterized in that the default value transmitted from the control unit (9) to the supply pump (2) is provided with a correction value depending on the operating state of the metering pump (3). Method according to Claim 1 or 2, characterized in that the prestressing pressure P of the pressure buffer (7) is applied by at least one steel spring designed as a wave spring (20). Method according to one of Claims 1 to 3, characterized in that the pressure buffer (7) comprises a rolling membrane (18) for the hermetic separation of the variable buffer volume (19). Method according to one of Claims 1 to 4, characterized in that the variable buffer volume (19) has a volume of 500 to 5000 mm ³ . Method according to one of Claims 1 to 5, characterized in that in addition to the signal from the pressure sensor (8) and the signal from the metering pump (3) with regard to its operating state, information relating to the fill level in the buffer volume (19) is also included in the control. Method according to Claim 6, characterized in that the pressure buffer (7) comprises a plunger (17) which protrudes from a housing (13) of the pressure buffer (7) and via which the filling level of the buffer volume (19) can be determined. Method according to one of Claims 1 to 7, characterized in that the pressure sensor (8) and/or a pressure-protecting element is accommodated in a housing (13) of the pressure buffer (7). Method according to one of Claims 1 to 8, characterized in that a time-dependent viscosity profile of the viscous material is stored in the control unit (9) and the time-dependent change in the viscosity of the viscous material is taken into account when determining the default value transmitted to the supply pump (2). .

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