Method for controlling delivery pressure of a feed pump
The method addresses the challenges of pressure control in viscous material delivery systems by employing a pressure buffer and control unit to stabilize delivery pressure, improving reliability, accuracy, and handling of abrasive materials.
Patent Information
- Application Number
- JP2024551554
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-03-02
- Filing Date
- 2023-03-02
- Publication Date
- 2025-04-18
AI Technical Summary
Existing methods for controlling the delivery pressure of supply pumps in systems for delivering and metering viscous materials are prone to reliability issues, accuracy problems, and wear due to high pressure fluctuations and abrasive materials, and are often costly and bulky.
A method utilizing a pressure buffer with a variable buffer volume pre-pressurized to a pretension pressure, coupled with a control unit that adjusts the supply pump pressure based on actual pressure values and the operating state of the metering pump, to mitigate pressure fluctuations and maintain a constant supply pressure.
This method enhances the reliability and accuracy of viscous material delivery and metering by reducing extreme pressure fluctuations, allowing for the processing of materials with abrasive fillers, and providing a cost-effective and compact solution.
Smart Images
Figure 2025512616000001_ABST
Abstract
Description
[Technical field]
[0001] The present invention relates to a method for controlling the delivery pressure of a feed pump in a system for delivering and metering a viscous material. [Background technology]
[0002] When processing viscous materials, the plastic components are usually pumped directly from a container, for example from a hobbock, to a metering pump via a delivery line using a feed pump. The feed pump is often several meters away from the metering pump, which must build up a sufficiently high delivery pressure to pump the viscous material from the feed pump to the metering pump. During the metering process, i.e. during the operation of the metering pump, a pressure drop occurs in the delivery line due to the outflow of material. To compensate for this pressure loss, a high delivery pressure is required, which is built up by the feed pump. At the same time, however, this results in a rapid increase in pressure on the inlet side of the metering pump between the individual metering processes, as soon as the metering pump is stopped and the pressure loss in the delivery line becomes significantly lower.
[0003] Very high supply pressure at the inlet of the metering pump is a decisive factor in causing wear to the metering pump, especially the shaft seal. Moreover, excessive pressure fluctuations at the inlet of the metering pump have a negative effect on the metering accuracy. Finally, a supply pressure that is too low even for a short time can cause serious problems with the metering accuracy and even wear to the metering pump.
[0004] To remedy this, it is known to use a material pressure reducing valve near the metering pump inlet. With such a valve, the delivery pressure of the feed pump is set at a pressure significantly higher than the pressure actually required to supply the metering pump. The material pressure reducing valve reduces the pressure just before the metering pump to the required metering pump inlet pressure.
[0005] However, the use of material pressure reducing valves has several disadvantages: they are very prone to failure. Even a small air bubble in the valve can lead to a so-called pressure "breakthrough" and the metering pump can be damaged or even destroyed by the momentary very high inlet pressure. Furthermore, material pressure reducing valves are not suitable when processing materials that contain large or abrasive filler particles, because the particles cause rapid and strong wear of the mechanical parts of the valve, thereby undermining the reliability of the valve. Finally, material pressure control valves have the disadvantages of a relatively large weight and a relatively high price.
[0006] Another solution is active pressure control of the feed pump. For this purpose, a pressure sensor is attached to the inlet of the metering pump and, depending on the pressure detected at the inlet of the metering pump, adjusts the delivery pressure or the performance of the feed pump via a control circuit. The disadvantage of this method is the inertia of the system, i.e. the fact that a pressure that is too high or too low must first be measured at the inlet of the metering pump before the feed pump can react accordingly. This, combined with the very stiff delivery lines required for high material pressures, usually results in undesirably low or undesirably high pressures at the inlet side of the metering pump at the start and stop of metering. Moreover, the scoop piston pumps usually used as feed pumps do not allow the backflow of material and therefore cannot reduce the pressure without leakage during the stop of the metering pump.
[0007] From WO 2017 / 004635 A1, an apparatus is known which comprises a supply source for at least one liquid plastic component and a metering device, with a buffer device having a variable buffer volume being arranged between said supply source and said metering device, whereby it is possible to supply liquid plastic component to the metering device without interruption and the pressure in the liquid plastic component between said buffer device and said metering device can be controlled by said buffer device.
[0008] It is an object of the present invention to provide a method for controlling the delivery pressure of a feed pump in a system for delivering and metering a viscous material, which method can be operated more reliably and accurately than known methods. Summary of the Invention
[0009] This object is achieved by a method having the features of claim 1.
[0010] Advantageous embodiments and further developments of the method are the subject of the dependent claims.
[0011] According to claim 1, the invention relates to a method for controlling a delivery pressure of a feed pump in a system for delivering and metering a viscous material, comprising: The system includes a feed pump, a metering pump, and a delivery line extending between the feed pump and the metering pump, the feed pump using a delivery pressure D to deliver the viscous material from a material store through the delivery line to an inlet of the metering pump; Further, a pressure buffer, pre-pressurized to a pretension pressure P and having a variable buffer volume, is connected upstream of the inlet of the metering pump; the buffer volume is capable of receiving viscous material from the delivery line when the delivery pressure in the delivery line in the region of the pressure buffer is higher than the pretension pressure P of the pressure buffer; When the delivery pressure in the delivery line in the region of the pressure buffer is lower than a pretension pressure P of the pressure buffer, viscous material may be discharged from the buffer volume into the delivery line; The system further comprises a pressure sensor coupled upstream of the inlet of the metering pump for detecting an actual pressure value in the delivery line, and a control unit; The control unit is coupled to the pressure sensor, the feed pump, and the metering pump. The method according to the invention is characterized in that the control unit sends a command value to the supply pump based on the deviation between a predetermined target pressure value and the actual pressure value in the delivery line and on the operating state of the metering pump.
[0012] In other words, the method according to the invention uses a pressure buffer with a variable buffer volume upstream of the inlet of the metering pump, which is pre-pressurized to a pretension pressure P, whereby viscous material is taken into the buffer volume from the delivery line or expelled from the buffer volume into the delivery line in order to buffer pressure fluctuations in the delivery line, the pretension pressure P varying depending on the filling level of the buffer volume.
[0013] The method according to the invention further provides that not only the actual pressure value detected in the delivery line but also information on the operating state of the metering pump is used to regulate the delivery pressure of the feed pump. To determine the command value for the feed pump, the control unit also processes information on whether the metering pump has started and thus started the metering process or whether the metering pump has stopped and thus ended. Taking into account information on the operating state of the metering pump allows faster and more accurate tracking of the delivery pressure provided by the feed pump, since changes in the operating state of the metering pump are responded to immediately, without first having to wait for an increase or decrease in pressure at the inlet side of the metering pump, which is associated with the change in operating state, to be detected by a pressure sensor arranged there. By using a pressure buffer with a variable buffer volume provided according to the invention on the one hand and taking into account the operating state of the metering pump when adjusting the delivery pressure of the supply pump on the other hand, extreme pressure fluctuations at the inlet side of the metering pump and the associated disadvantages can be effectively reduced and a very constant supply pressure can be set at the inlet of the metering pump.
[0014] The control unit preferably comprises a PI or PID controller, which operates with a given target pressure value and an actual pressure value detected by the pressure sensor at the inlet side of the metering pump. The operating state of the metering pump can be substantially taken into account when regulating the delivery pressure of the feed pump in such a way that the command value sent by the control unit to the feed pump is given a correction value depending on the operating state of the metering pump. As soon as the metering process is stopped, the value of the I component in the PI or PID control can be multiplied by a factor less than 1, for example a factor of 0.5, compared to the last value of the I component during the immediately preceding metering process. As a result, when metering is stopped, the command value sent to the feed pump suddenly drops to a significantly lower value. Thus, a strong pressure increase expected at the inlet side of the metering pump due to a changing disturbance variable "pressure loss in the line" is compensated for before a deviation in the measured value detected by the pressure sensor is registered. This means that the delivery pressure can be tracked much more quickly and efficiently than if reacting solely to a signal from a pressure sensor which detects a pressure rise on the inlet side of the metering pump for a period of time after the metering pump has stopped.
[0015] As soon as metering is resumed, 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 metering process. As a result, it is possible to prevent a sharp increase in the command value transmitted to the supply pump, which would cause a strong pressure drop at the inlet side of the metering pump when metering is resumed. In this way, a relatively constant pressure can be achieved at the inlet side of the metering pump, regardless of the stop time of the metering pump between two meters.
[0016] The use of pressure buffers in systems for delivering and metering viscous materials has several advantages. In contrast to solutions known from the prior art, when using pressure buffers, even highly loaded materials or media containing abrasive fillers can be easily handled. The method according to the invention can therefore be used in a wide variety of applications and is therefore very flexible to use. The material density of the delivered material is about 0.5 g / cm 3 ~5g / cm 3 in the range of about 1 g / cm 3 ~3g / cm 3 The delivery speed can be in the range of about 0.05 cm 3 / s~150cm 3 / s, preferably about 0.5 cm 3 / s~20cm 3 / s.
[0017] Such pressure buffers also have the advantage of being relatively small in size and significantly lighter in weight than material pressure reducing valves, so that they can be mounted on the robot, for example together with a metering pump.
[0018] Finally, the use of a pressure buffer is more cost effective than the use of a material pressure reducing valve.
[0019] The pretensioning force of the pressure buffer, which gives rise to the pretensioning pressure P, can be applied, for example, via air pressure, spring force or hydraulic pressure. In order to avoid unintentional full or empty filling of the buffer, it is advantageous if the pretensioning force depends on the filling level of the buffer, i.e. it is advantageous if the pretensioning force increases as the volume of the buffer is filled.
[0020] An embodiment of the method according to the invention provides for the use of at least one steel spring designed as a wave spring for the pretensioning of said pressure buffer. Compared to conventional spiral springs, wave springs have a spring height up to 50% lower for the same spring force and therefore occupy a significantly smaller space. This allows for a smaller installation size and a simpler design of the buffer compared to the use of conventional spiral springs.
[0021] According to a further embodiment of the invention, the pressure buffer comprises a rolling membrane for sealing and isolating the variable buffer volume. The rolling membrane is a very flexible, thin-walled, fiber-reinforced membrane made of a rubber-elastic material, such as silicone, polyurethane, fluororubber, ethylene-propylene-diene rubber or acrylonitrile-butadiene rubber. The rolling membrane has the advantage of excellent sealing properties, which is particularly important in applications using viscous adhesives. Otherwise, even a small leak would cause the adhesive to leak out of the buffer volume and harden, impairing the function of the buffer or rendering it unusable. Furthermore, the rolling diaphragm allows the buffer to operate virtually friction-free and hysteresis-free.
[0022] According to the present invention, the variable buffer volume is 100 mm 3 ~10,000mm 3 , preferably 500 mm 3 ~5,000mm 3 For example, the variable buffer volume may include a volume of 1,500 mm available as a compensation volume. 3 The volume of the suction pipe may include:
[0023] According to an embodiment variant of the method according to the invention, in addition to the signal from the pressure sensor and information about the operating state from the metering pump, information about the current filling level in the buffer volume can be included in the control. In this case, the delivery pressure of the feed pump is also adjusted depending on how much viscous material can be discharged from the buffer volume into the delivery line to compensate for pressure fluctuations, or how much can be taken from the delivery line into the buffer volume. This allows the control precision to be further improved.
[0024] It is provided that the pressure buffer comprises a plunger, which protrudes from a housing of the pressure buffer, via which the filling level of the buffer volume can be determined. In other words, the plunger moves up and down depending on the filling level of the buffer volume, whereby the filling level of the buffer volume can be inferred from the length of the part of the plunger that protrudes from the housing of the pressure buffer. This length can be determined optically or with the aid of other suitable sensors. A corresponding signal can be supplied to the control unit as an additional input signal.
[0025] Alternatively or additionally, when using means for pretensioning the pressure buffer that are suitable for enabling an at least approximately linear spring behavior, the filling level of the buffer volume can also be deduced on the basis of the measured pressure. In particular, when the pressure buffer exhibits an approximately linear pressure-volume behavior, the use of a wave spring may be considered.
[0026] According to an embodiment variant of the present invention, the pressure sensor and / or pressure protection element can be accommodated in the housing of the pressure buffer. In other words, the pressure sensor upstream of the inlet of the metering pump can be accommodated directly in the housing of the pressure buffer, where any pressure fluctuations can be detected early. Additionally or alternatively, a pressure protection element such as a burst disk or a pressure relief valve can be accommodated in the housing of the pressure buffer, whereby in the event of a sudden excessive pressure rise in the delivery line, pressure can be effectively reduced to protect the downstream metering pump.
[0027] In one embodiment of the invention, the change in viscosity of the viscous material over time is taken into account when determining the command value to be sent to the feed pump. For this purpose, a profile of the viscosity of the viscous material over time can be stored in the control unit, and the change in the viscosity of the viscous material over time can be taken into account when controlling the feed pump based on the PT1 element. In particular, in this way it is possible to influence the pressure at the inlet of the metering pump, the strength or length of a short pressure pulse at the start of the next metering, and a combination of the above options, depending on the time that has passed since the last metering.
[0028] Alternatively, between two meters while the metering pump is stopped, a slightly higher target pressure can be specified at the inlet of the metering pump than during metering, which prevents the pressure at the inlet of the metering pump from briefly dropping below a critical threshold when metering resumes.
[0029] When using a scoop piston pump as a supply pump, undesired pressure changes, such as pressure drops or pressure rises in the delivery lines, can occur at the switching points of the pump. According to an embodiment of the present invention, a displacement sensor can be provided, which detects the position and the speed of the movable piston of said supply pump and transmits information about the expected switching points of said supply pump to said control unit for further processing. In this way, by suitable pre-control of the air pressure applied to the pneumatic supply pump, said pressure drop at said switching points of the supply pump can be significantly adjusted. A further advantage of such a displacement sensor is that leaks in the hydraulic system can be reliably detected.
[0030] By means 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 when a pressure of up to 300 bar, preferably 10 to 80 bar, is applied by the feed pump. The distance between the feed pump and the metering pump can be about 1 m to 20 m, preferably 2 m to 10 m.
[0031] As viscous materials, in particular silicones, polyols, isocyanates, MS polymers, polyacrylates, epoxies, butyls, polysulfides, dispersions or prepolymers of one of the aforementioned groups of substances can be delivered and metered.
[0032] Preferably, viscous materials having a viscosity in the range of 10,000 mPas to 2,000,000 mPas, preferably in the range of 20,000 mPas to 500,000 mPas, are delivered and metered. [Brief description of the drawings]
[0033] The invention will now be explained in more detail by way of an exemplary embodiment and with reference to the accompanying drawings, in which: [Figure 1] FIG. 2 shows a schematic diagram of a system for delivering and metering a viscous material for use in the method according to the invention; [Diagram 2] 1 shows a cross-sectional view of an exemplary embodiment of a pressure buffer for use in a method according to the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] FIG. 1 shows a schematic diagram of a system, generally designated 1, for delivering and metering a viscous material (e.g. a plastic component for a sealant). The system 1 comprises a feed pump 2, designed as a pneumatic scoop piston pump, which delivers the viscous material from a material store 5 to a delivery line 4. Due to the delivery pressure by the feed pump 2, the viscous material is sent through the delivery line 4 to the inlet 6 of a metering pump 3. The viscous material is discharged via the metering pump 3 to a mixhead 10. In the mixhead 10, the viscous material is mixed with one or more other components (not specified here) before the mixture (indicated by arrow 11) is discharged from the mixhead 10, for example in the form of a sealing bead. As an alternative to the mixhead 10 shown here, a component valve (not shown) can be used if the viscous material is not mixed with other components but is instead discharged directly.
[0035] The feed pump 2 and the metering pump 3 are controlled via a control unit 9 which includes a PID controller. As the feed pump 2 is a pneumatic piston pump, the system 1 comprises a proportional pressure control valve 12 located between the control unit 9 and the feed pump 2, which converts an electrical signal from the control unit 9 into an air pressure acting on the feed pump 2.
[0036] To detect the actual pressure value in the delivery line 4, the system 1 comprises a pressure sensor 8 accommodated in a housing 13 of the pressure buffer 7. The pressure sensor 8 is connected via a signal line 14 to an input of a control unit 9, which stores a predetermined target pressure value and compares it with the actual pressure value. Depending on the result of this comparison, a corresponding command value is sent via a signal line 15 to the supply pump 2 or to the proportional pressure control valve 12.
[0037] The metering 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 about the operating state of the metering pump 3 is also taken into account by the control unit 9 when determining the command value for the feed pump 2. That is, in addition to the pressure value detected by the pressure sensor 8, the control unit 9 also processes information about the metering start or metering stop of the metering pump and takes this information into account when determining the command value to be sent to the feed pump 2. In this way, a very rapid reaction to changes in the operating state of the metering pump 3 can be made and strong increases or decreases in 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 when regulating the delivery pressure of the feed pump 2 in such a way that the command value sent from the control unit 9 to the feed pump 2 or to the proportional pressure control valve 12 is corrected depending on the operating state of the metering pump 3. As soon as the metering is stopped, the value of the I component of the PID control is multiplied by 0.5 with respect to the value of the I component at the immediately preceding metering. As a result, the command value sent to the feed pump 2 suddenly drops to a significantly lower value at the metering stop. As soon as metering is started again, the value of the I component is reset to the last value of the I component during the previous metering process, so that the command value sent to the feed pump 2 rises again sharply, preventing a strong pressure drop at the inlet of the metering pump 3 when metering is restarted.
[0038] 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 further comprises a pressure buffer 7 connected upstream of the metering pump 3. The pressure buffer 7 has a variable buffer volume which is able to absorb viscous material from the delivery line 4 or to expel viscous material therefrom into the delivery line 4.
[0039] The structure and function of the pressure buffer 7 will be explained in more detail with reference to FIG. 2. The pressure buffer 7 is connected to a delivery line 4 through which the viscous material is delivered from the feed pump 2 to the metering pump 3 in the direction indicated by the arrow. The pressure buffer 7 comprises a housing 13 and a plunger 17 which is movable in a smooth bushing 23 in the direction indicated by the arrow S. The plunger 17 protrudes at least partially from the housing 13. At the end of the plunger 17 facing the delivery line 4, a rolling diaphragm 18 is arranged, which limits a variable buffer volume 19 which acts as a compensation volume. The buffer volume 19 is sealed by the rolling diaphragm 18 next to the plunger 17 and is open next to the delivery line 4 where it abuts. The rolling diaphragm 18 allows the pressure buffer 7 to operate substantially without friction.
[0040] The pressure buffer 7 is pre-pressurized to a pretension pressure P, which depends on the filling level of the buffer volume 19. The pretension pressure P is applied by a steel spring designed as a wave spring 20, arranged between the 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, which is upstream of the metering pump 3 in the area of the pressure buffer 7, becomes higher than the pretension pressure P of the pressure buffer 7, the viscous material from the delivery line 4 enters the buffer volume 19 and presses the plunger 17 via the rolling diaphragm 18, which causes the plunger 17 to move upwards away from the delivery line 4 and compresses the wave spring 20. The variable buffer volume 19 increases accordingly, and the pretension pressure P of the pressure buffer 7 increases. This process continues until a pressure equilibrium is established or, as shown in FIG. 2, until the plunger 17 hits the housing 13 with its shoulder 22. If the delivery pressure in the delivery line 4 falls again below the currently prevailing pretension pressure P of the pressure buffer, the restoring force of the wave spring 20 causes the plunger 17 to move in the opposite direction towards the delivery line 4, thereby reducing the buffer volume 19 and discharging the viscous material from the buffer volume 19 into the delivery line 4 to be supplied to the metering pump 3. In this way, the pressure buffer 7 can buffer pressure fluctuations in the delivery line 4 and thereby contribute to a more constant pressure on the inlet side of the metering pump 3. By using the wave spring 20, the pressure buffer 7 shows an approximately linear pressure-volume behavior. To prevent overloading of the pressure buffer 7, the variable buffer volume 19 can expand in a pressure range of approximately 2 bar to 20 bar. Above or below these values, the movement of the plunger 17 is limited by a mechanical stop.
[0041] 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 adjust the delivery pressure of the feed pump 2, whereby a substantially constant feed pressure can be provided on the inlet side of the metering pump 3 regardless of the stop time of the metering pump 3.
[0042] In a variant method not shown, additional information regarding the filling level of the buffer volume 19 can be included in the control. For this purpose, the filling level of the buffer volume 19 can be determined indirectly based on the length of the part of the plunger 17 protruding from the housing 13 of the pressure buffer 7. For this purpose, preferably an optical sensor can be provided, which detects the position of the plunger 17 and sends a corresponding signal to the control unit 9 for further processing.
Claims
1. 1. A method for controlling a delivery pressure of a feed pump (2) in a system (1) for delivering and metering a viscous material, comprising: The system (1) comprises a feed pump (2), a metering pump (3), and a delivery line (4) extending between the feed pump (2) and the metering pump (3); The feed pump (2) delivers the viscous material from the material storage (5) through the delivery line (4) to the inlet (6) of the metering pump (3) using a delivery pressure D; Furthermore, a pressure buffer (7) pre-pressurized to a pretension pressure P and having a variable buffer volume (19) is connected upstream of the inlet (6) of the metering pump (3), said buffer volume (19) being capable of receiving viscous material from said delivery line (4) when the delivery pressure in said delivery line (4) in the region of said pressure buffer (7) is higher than said pretension pressure P of said pressure buffer (7), When the delivery pressure in the delivery line (4) in the region of the pressure buffer (7) is lower than the pretension pressure P of the pressure buffer (7), viscous material can be discharged from the buffer volume into the delivery line (4), The system (1) further comprises a pressure sensor (8) connected upstream of the inlet (6) of the metering pump (3) for detecting an actual pressure value in the delivery line (4), and a control unit (9), The method, wherein the control unit (9) is connected to the pressure sensor (8), the feed pump (2) and the metering pump (3), The control unit (9) sends a command value to the supply pump (2) based on the deviation between a predetermined target pressure value and the actual pressure value in the delivery line (4) and on the operating state of the metering pump (3). A method comprising:
2. 10. The method of claim 1 , The command value transmitted from the control unit (9) to the supply pump (2) is provided with a correction value according to the operating state of the metering pump (3). A method comprising:
3. The method according to claim 1 or 2, The pretension pressure P of the pressure buffer (7) is applied by at least one steel spring designed as a wave spring (20). A method comprising:
4. The method according to any one of claims 1 to 3, The pressure buffer (7) includes a rolling membrane (18) for sealing and isolating the variable buffer volume (19). A method comprising:
5. The method according to any one of claims 1 to 4, The variable buffer volume (19) is 500 mm ３ From 5000mm ３ With a volume of up to A method comprising:
6. The method according to any one of claims 1 to 5, In addition to the signal from the pressure sensor (8) and the signal from the metering pump (3) regarding the operating state, information regarding the filling level in the buffer volume (19) is included in the control. A method comprising:
7. 7. The method of claim 6, 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. A method comprising:
8. The method according to any one of claims 1 to 7, The pressure sensor (8) and / or the pressure protection element are accommodated in a housing (13) of the pressure buffer (7). A method comprising:
9. The method according to any one of claims 1 to 8, A profile of the viscosity of the viscous material over time is stored in a control unit (9); The change in the viscosity of the viscous material over time is taken into account when determining the command value sent to the feed pump (2). A method comprising: