Double-acting piston pump and application system for applying a flowable medium to a substrate

Description

[0001] The invention relates to a double-acting piston pump for conveying a flowable medium to a dispensing device. Furthermore, the invention relates to an application system for applying a flowable medium to a substrate.

[0002] A piston pump for conveying a flowable medium is known, for example, from EP 2 732 884 A2. EP 2 732 884 A2 discloses a piston pump having the features of the preamble of patent claim 1.

[0003] In the field of applying flowable media, particularly in the field of adhesive application, there is a desire to achieve the most precise application pattern possible. In this respect, there is particular interest in minimizing the influence of an adhesive delivery device, for example a double-acting piston pump, on the application pattern. When using double-acting piston pumps, particularly double-acting, pneumatically driven piston pumps, the problem arises that at the reversal points, at which the direction of movement of the piston reverses, there is a drop in pressure in the flowable medium delivered by the piston pump. This pressure drop and its temporal progression depend in particular on the viscosity and flow properties of the flowable medium, for example the heated adhesive being delivered.Furthermore, the pressure drop and its temporal progression depend heavily on the design and construction of certain components of the piston pump. For example, the stroke direction of a pneumatically driven piston pump with a pneumatic piston is reversed using an electrically operated pneumatic changeover valve. The changeover process of this valve requires a certain amount of time. Likewise, during changeover, the reduction of the existing air pressure on one side of the pneumatic piston and the buildup of air pressure on the other side of the pneumatic piston require a certain amount of time. Double-acting piston pumps often have two check valves, which are usually not identical in design. The two check valves are usually designed in the form of movable balls, which, when the piston is operating vertically, alternately seal off the flow of the fluid medium to be pumped at the top and bottom.During the switching process, the ball of one check valve moves from a sealing position to a passing position, and the ball of the other check valve moves from a passing position to a sealing position and vice versa. This movement of the balls also takes some time. During the reversal process at the first reversal point and the second reversal point of the piston, i.e., during the actuation of the check valves, a slight loss of volume flow of the flowable medium occurs. This loss, or pressure drop, is typically different at the two reversal points.

[0004] With a double-acting piston pump, the problem arises that the pressure of the pumped, flowable medium drops for a limited time when the direction of movement of the piston is reversed, or it takes a certain amount of time until the pressure of the flowable medium returns to an approximately constant value. The pressure drop at the reversal points has a negative impact on the quality of the flowable medium applied to the substrate and the application pattern. With continuous application of the flowable medium to the substrate using the dispensing device, a reversal of the direction of movement of the piston and the associated pressure drop lead to a temporarily reduced output of flowable medium. Accordingly, in an application system with a double-acting piston pump, the output of flowable medium is reduced at the reversal points of the piston pump, which has a negative impact on the application pattern.For example, when the flowable medium is continuously dispensed in the form of a stripe, also known as an application bead or bead, the applied bead will exhibit distinct constrictions in its cross-section, which correlate in time with the reversal points of the direction of movement of the adhesive pump's piston. The so-called application pattern then shows distinct, regular constrictions.

[0005] Various possibilities are known from the state of the art to avoid or reduce the pressure drop when reversing the direction of movement of the piston of the piston pump or to minimize the effects of this pressure drop on the application pattern.

[0006] For example, EP 2 107 241 A2 proposes a piston pump for this purpose, wherein the piston pump has at least two piston-cylinder units for conveying the flowable medium. The two pumps are operated in such a way that a pressure drop when conveying the fluid from one pump is compensated by the other pump. Furthermore, the use of a pressure accumulator is known from prior art ES 2 064 183 A2, wherein when the direction of movement of the piston of the piston pump is reversed, the pressure accumulator largely compensates for the falling pressure. The disadvantage of this solution is that a pressure accumulator can only be optimally designed for one operating state. Compensation for the falling pressure is only satisfactory for a specific pressure setting and only for a specific viscosity of the flowable medium.The greater the deviation from the optimal operating point, the worse the pressure drop compensation by the pressure accumulator is.

[0007] The object of the present invention is to further develop a double-acting piston pump for conveying a flowable medium to a dispensing device, which has the features of the preamble of patent claim 1, such that it can prevent constrictions during the application of the flowable medium. Furthermore, the object of the present invention is to provide an application system for applying a flowable medium that makes it possible to avoid or at least reduce constrictions during the application of the flowable medium.

[0008] These objects are solved by the subject matter of patent claims 1 and 8.

[0009] The flowable medium is in particular a heated adhesive and / or a viscous hot melt adhesive. The piston pump is a double-acting piston pump, i.e. a piston pump that pumps the flowable medium in both stroke directions of the piston. The application system is used to apply the flowable medium to a substrate, which can be, for example, a sheet of paper, cardboard or film. A substrate can certainly consist of a large number of separate structures, for example the substrate can be a large number of strip-like elements, e.g. paper strips, cardboard strips or film strips, which are arranged at a distance from one another and are guided one after the other past an application head which serves to dispense the medium.

[0010] The piston pump has a piston movable between a first reversal point and a second reversal point for conveying the flowable medium, wherein the direction of movement of the piston reverses upon reaching the respective reversal point. The application system further has a dispensing device, for example one or more spray heads, for intermittently dispensing the flowable medium conveyed to the dispensing device by means of the piston pump. An aspect not covered by the scope of protection of the patent claims relates to a method, wherein the method provides that during dispensing periods, dispensing of the flowable medium by means of the dispensing device takes place and during interruption periods, dispensing of the flowable medium by means of the dispensing device is interrupted.The method provides that during at least one interruption period of the interruption periods, a reversal of the direction of movement of the piston takes place, wherein the piston is in an intermediate position between the first reversal point and the second reversal point when the direction of movement is reversed during the at least one interruption period.

[0011] Since a reversal of the direction of movement of the piston occurs during at least one interruption period of the interruption periods, at least this reversal of the direction of movement occurs during a period in which the reversal of the direction of movement of the piston and the associated pressure drop have no or only a slight effect on the application pattern of the flowable medium onto the substrate, since during the interruption period no discharge of the flowable medium is carried out by the discharge device.In particular, the reversal of the direction of movement of the piston during the at least one interruption period of the interruption periods takes place in such a way that the time until the dispensing period following the at least one interruption period is sufficient to rebuild a target value of the pressure until the beginning of the subsequent dispensing period, insofar as the reversal-related, time-limited pressure drop is over at the beginning of the subsequent dispensing period.

[0012] In conventional piston pumps or methods for operating a piston pump, the direction of movement of the piston is reversed only upon reaching the respective reversal point. Thus, in such methods or piston pumps, there is no temporal coordination between the reversal of the direction of movement of the piston and the interruption period(s). In contrast, in the solution according to the invention, the direction of movement of the piston of the piston pump occurs during at least one of the interruption periods in an intermediate position, thus before reaching the reversal point in the direction of movement.

[0013] It is quite conceivable that a reversal of the direction of movement of the piston of the piston pump occurs during one interruption period of the interruption periods in an intermediate position between the two reversal points and a reversal of the direction of movement of the piston of the piston pump occurs during another interruption period of the interruption periods in another intermediate position between the two reversal points.

[0014] It is quite conceivable that during this process the piston also reaches the first and / or second reversal point.

[0015] It is also quite conceivable that during one or more other interruption periods the piston reaches the first reversal point or the second reversal point anyway, so that no reversal of the direction of movement of the piston in an intermediate position occurs in advance.

[0016] Preferably, the intermittent dispensing of the flowable medium is carried out in such a way that the intermittent dispensing results in a temporally recurring pattern of dispensed flowable medium, in particular when a plurality of similar substrates are provided with the flowable medium.

[0017] The piston pump preferably has a delivery area and a drive area. The piston is arranged in the delivery area and serves to convey the flowable medium. The components that drive the movement of the piston are arranged at least partially, preferably entirely, in the drive area.

[0018] The piston pump is preferably a pneumatically driven piston pump. The piston pump preferably has a pneumatic piston operatively connected to the piston used to convey the flowable medium, which serves to drive the movement of the piston. For the stroke movement of the piston toward the first reversal point or the second reversal point, one side of the pneumatic piston is preferably pressurized with compressed air, while the other side is vented. The reversal of the piston's direction of movement is preferably achieved via an electrically or magnetically actuated pneumatic changeover valve.

[0019] In particular, the piston pump has a pneumatic part, also referred to as pneumatic area, and a delivery area, wherein the pneumatic piston is arranged in the pneumatic part and the piston which serves to convey the flowable medium is arranged in the delivery area.

[0020] Drives other than pneumatic drives that cause alternating movement of the piston are also conceivable. For example, a hydraulic drive, particularly with a hydraulic piston, or an electric drive, particularly in the form of a linear motor.

[0021] Preferably, the first reversal point and the second reversal point are not variable, so that the first reversal point and the second reversal point are fixed during operation of the double-acting piston pump. Preferably, the two reversal points are fixed, particularly due to their design.

[0022] Preferably, the first reversal point and the second reversal point are respectively a bottom dead center and a top dead center of the piston.

[0023] It is considered particularly advantageous if the piston's direction of movement is reversed exclusively, or at least predominantly, during the interruption periods. This minimizes the negative impact of the respective reversal of the direction of movement on the application pattern. However, the piston's direction of movement does not necessarily reverse during every interruption period.

[0024] It is considered particularly preferred if the dispensing quantity of the flowable medium dispensed by the dispensing device during the respective dispensing period is smaller than the delivery quantity of the medium conveyed by the piston pump during one piston stroke of the piston pump from the first reversal point to the second reversal point and / or vice versa to the dispensing device. In such an embodiment, the flowable medium can be dispensed during the dispensing periods without reversing the direction of movement of the piston. This has a particularly advantageous effect on the quality of the application of the flowable medium to the substrate.

[0025] In the event that the output quantity of the flowable medium dispensed by the dispensing device during one of the dispensing periods is greater than the medium conveyed to the dispensing device during a complete stroke of the piston pump or when one of the reversal points is reached during one of the dispensing periods, it is certainly conceivable to compensate for the pressure drop when the direction of movement of the piston pump's piston is reversed. For this purpose, it is conceivable to activate a pressure accumulator in a controlled manner so that the pressure drop during the switching process is compensated. A spring-loaded accumulator or a pressure accumulator based on the principle of a single-acting, pneumatically actuated piston pump can be used as the pressure accumulator.

[0026] During operation of the piston pump, the number of reversals of the direction of movement that occur in intermediate positions of the piston between the first reversal point and the second reversal point is preferably greater than the number of reversals of the direction of movement that occur at the reversal points. Thus, the reversal of the direction of movement occurs predominantly in intermediate positions of the piston between the first reversal point and the second reversal point.

[0027] It is entirely conceivable that during operation, a reversal of the direction of movement occurs exclusively in intermediate positions, provided the reversal points are not reached. The reversal points would then only be reached if, for example, due to a malfunction of the pump during execution of the process or a control system used to carry out the process, a reversal of the direction of movement in the intermediate position inadvertently did not occur. Since a reversal of the direction of movement with respect to a movement of the piston towards one of the reversal points then occurs at the latest when this reversal point is reached, damage to components of the piston pump is avoided.

[0028] It is considered particularly advantageous if the piston speed (where piston speed is understood to be the absolute value of the piston speed) of the piston is reduced during the interruption periods compared to the piston speed during the dispensing periods, in particular if the piston speed is zero during the interruption periods. Accordingly, the temporal development of the piston speed correlates with the dispensing periods and the interruption periods. Accordingly, by detecting the piston speed, it can be determined whether a dispensing period or an interruption period is present. Accordingly, it is not necessary to provide a higher-level control system which detects whether the dispensing device is dispensing the medium or whether the dispensing is interrupted; instead, the reversal of the direction of movement can be carried out independently of the higher-level control system.The operating state of the dispensing device (dispensing or interruption of dispensing) can be determined solely from the measured piston speed, allowing the piston pump to operate virtually autonomously, eliminating the need for a higher-level control system. Since the piston speed correlates with the dispensing periods and interruption periods, the direction of piston movement can be reversed depending on the piston speed, and knowledge of the piston speed can be used to reverse the direction of movement during at least one interruption period.

[0029] In the case of a recurring application pattern, the recurring application pattern can be detected by measuring the piston speed. This allows the expected stroke of the piston at the beginning of one interruption period until the beginning of the next interruption period to be determined. Alternatively, it is conceivable that the programmed or predefined application pattern of a higher-level application control system could be used to determine the temporal progression of the interruption periods to determine the expected piston positions with respect to the interruption periods. This can improve the operational reliability of the invention, as unexpected changes in the application pattern can be taken into account.

[0030] It is considered particularly advantageous if the piston pump is subject to leakage with respect to the fluid to be pumped, so that during the interrupted periods the piston speed is reduced compared to the piston speed during the discharge periods. A leakage-prone piston pump is also advantageous in terms of minimizing wear, avoiding maintenance work, and ensuring the longest possible service life for the piston pump. It is considered particularly advantageous if the leakage occurs between the piston and the cylinder. This leakage depends primarily on the viscosity and flow behavior of the fluid, the size of the gap around the piston, and the pressure built up by the piston pump.In a leaky piston pump, the piston speed is reduced during the interruption periods compared to the piston speed during the dispensing periods, since the resistance of the piston movement is increased during the interruption periods compared to the resistance of the piston movement when the flowable medium is dispensed.

[0031] Preferably, the piston of the piston pump is not designed to be sealed with respect to a cylinder and / or the piston pump has a piston rod that is not designed to be sealed with respect to a guide.

[0032] The piston pump preferably has two check valves, with one check valve being open and the other closed depending on the direction of piston movement. The two check valves are typically designed as movable balls that, in vertical operating direction, alternately seal the top and bottom of the piston against the flow of the fluid to be pumped. During the switching process, the ball of one check valve moves from a sealing position to a flow position, and the ball of the other check valve moves from a flow position to a sealing position, and vice versa during a subsequent switching process.

[0033] In a preferred embodiment of the method, the piston speed is measured, and a reversal of the piston's direction of movement outside the reversal points occurs when the piston speed is equal to a specific value, in particular when the specific value corresponds to the piston speed of the piston during the interruption periods. The aforementioned condition, namely that the piston speed is less than or equal to a specific value, is to be understood as a necessary but not necessarily sufficient condition for reversing the direction of movement of the piston. However, it is certainly conceivable that it is a sufficient condition for reversing the direction of movement of the piston.

[0034] In an advantageous development of the method, it is provided that a distance of the piston from the reversal point lying in the direction of movement of the piston is determined, wherein a reversal of the direction of movement of the piston occurs during the respective interruption period before reaching the reversal point lying in the direction of movement of the piston if the distance of the piston from the reversal point lying in the direction of movement of the piston falls below a certain value, and / or wherein a distance of the piston from the reversal point lying opposite to the direction of movement of the piston is determined, wherein a reversal of the direction of movement of the piston occurs during the respective interruption period before reaching the reversal point lying in the direction of movement of the piston if the distance of the piston from the reversal point lying opposite to the direction of movement of the piston exceeds a certain value.

[0035] It is quite conceivable that the piston position is measured permanently.

[0036] The distance of the piston from the respective reversal point used for comparison with the determined value is preferably determined at the beginning of the respective interruption period.

[0037] The determined value with respect to the reversal point in the direction of movement of the piston preferably corresponds to an expected stroke of the piston in the direction of movement of the piston until the beginning of the next interruption period.

[0038] The determined value with respect to the reversal point opposite to the direction of movement of the piston preferably corresponds to an expected stroke of the piston opposite to the direction of movement of the piston until the beginning of the next interruption period.

[0039] It is considered particularly advantageous if the piston speed is measured and a distance of the piston from the reversal point in the direction of movement of the piston is determined, wherein a reversal of the direction of movement of the piston occurs when the piston speed falls below a certain value and the distance of the piston from the reversal point in the direction of movement of the piston falls below a certain value, and / or if the piston speed is measured and a distance of the piston from the reversal point opposite to the direction of movement of the piston is determined, wherein a reversal of the direction of movement of the movable piston occurs when the piston speed falls below a certain value and the distance of the piston from the reversal point opposite to the direction of movement of the piston exceeds a certain value.

[0040] The advantage of the aforementioned method design is that the piston speed is a criterion for determining whether an interruption period is present. Since a reversal of the piston's direction of movement should occur during an interruption period, a reversal of the piston's direction of movement should only occur during a period with reduced piston speed. Therefore, the reduced piston speed is a first criterion for switching. The distance of the piston from the respective reversal point is used as a further criterion to determine whether a reversal of the direction of movement should occur.This is against the background that if the distance between the piston and the reversal point opposite to the direction of movement of the piston is too small, there is a risk that if the direction of movement of the piston is reversed, the piston will reach this reversal point in the subsequent dispensing period, consequently a reversal of the direction of movement occurs in this dispensing period and accordingly a pressure drop occurs during the dispensing of the medium with the corresponding negative effects on the application pattern.

[0041] It is entirely conceivable that the piston position is used to determine the distance value of the piston from the respective reversal point, or that the distance value of the piston from the respective reversal point is determined when the piston speed falls below a certain value. Therefore, the first criterion, namely the piston speed falling below a certain value, is checked first. Only when the first criterion is met is the second criterion, namely the distance, checked. This reduces the measurement and evaluation effort.

[0042] It is considered particularly advantageous if the piston pump has sensors for measuring a piston position and / or a distance of the piston from the first reversal point or the second reversal point and / or for measuring the direction of movement of the piston and / or for measuring the speed of the piston. It is considered particularly advantageous if the sensor is designed as a Hall sensor. In connection with a Hall sensor, it is considered particularly advantageous if the piston pump has a magnet, preferably a ring magnet, wherein the magnet is movable together with the piston. It is certainly conceivable for the piston pump to have a plurality of Hall sensors, preferably at least four Hall sensors, in particular exactly four Hall sensors.

[0043] The term "distance" is to be understood broadly in the aforementioned contexts. For example, it is conceivable that the distance traveled by the piston from one reversal point to the other is divided into at least two sections, with "distance" then being understood as the section in which the piston is located. For example, the distance can be divided into a first section and a second section, with the first section containing the first reversal point and the second section containing the second reversal point. The section in which the piston is currently located can then be used as the distance criterion or distance. For example, the distance of the piston from the first reversal point is smaller when the piston is in the first section than when the piston is in the second section. Knowing the section in which the piston is located can therefore be used as a criterion for falling below or exceeding the specified value.Exceeding a distance value.

[0044] In principle, it is conceivable, in an application system with two double-acting piston pumps, to control the reversal of the direction of movement of the piston of the respective piston pump in a similar manner, so that a reversal of the direction of movement of the pistons of the two piston pumps does not occur simultaneously, but to change the direction of movement of the piston of one piston pump prematurely if it is foreseeable that a reversal of the direction of movement of one piston pump at the first or second reversal point would coincide with a reversal of the direction of movement of the piston of the other pump at the first reversal point or the second reversal point.

[0045] The double-acting piston pump according to the invention serves to convey a flowable medium to a dispensing device. In particular, the double-acting piston pump serves to convey a heated adhesive, in particular a viscous hot-melt adhesive, to a dispensing device. The dispensing device can in particular be a spray head. The piston pump has a piston movable between a first reversal point and a second reversal point, which serves to convey the flowable medium. Furthermore, the piston pump has a control device for controlling the direction of movement of the piston, wherein the control device is configured to reverse the direction of movement of the piston upon reaching the respective reversal point.Furthermore, the piston pump has a measuring device for measuring a piston speed, wherein the control device is designed to reverse the direction of movement of the piston when the measured piston speed falls below a certain speed value.

[0046] Since the piston speed generally depends on whether the dispensing device is dispensing flowable medium or not, the piston speed is a measure of whether the dispensing device is dispensing flowable medium or whether the dispensing of flowable medium by the dispensing device is interrupted. The double-acting piston pump is thus suitable for implementing the method according to the invention with the corresponding advantages.

[0047] It is considered particularly advantageous if the piston pump is designed to be leak-proof with respect to the fluid medium to be pumped. In this context, it is considered particularly advantageous if the piston is not designed to be sealed with respect to a cylinder and / or if the piston pump has a piston rod that is not designed to be sealed in a guide. A leak-proof piston pump has the advantage of reducing wear on the piston pump and, with respect to the process, the advantage that the piston speed during the interruption periods is reduced compared to the speed of the piston during the discharge periods.

[0048] The piston pump preferably has two check valves, one of which is open and the other closed depending on the direction of piston movement. In particular, the check valves are designed differently. The two check valves are assigned to the part of the piston pump in which the flowable medium is pumped, thus the delivery area.

[0049] The double-acting piston pump is preferably designed as a pneumatically driven piston pump. In particular, the piston pump comprises a pneumatic part, also referred to as the pneumatic section, and a delivery section, with the pneumatic piston being arranged in the pneumatic part and the piston used to deliver the flowable medium being arranged in the delivery section.

[0050] Preferably, the piston pump has a measuring device for measuring a distance of the piston position of the piston from the reversal point lying in the direction of movement of the piston, wherein the control device is configured to reverse the direction of movement of the piston when the measured piston speed falls below a certain speed value and the measured distance falls below a certain distance value, and / or the piston pump has a measuring device for measuring a distance of the piston position of the piston from the reversal point lying opposite the direction of movement of the piston, wherein the control device is configured to reverse the direction of movement of the piston when the measured piston speed falls below a certain speed value and the measured distance exceeds a certain distance value.

[0051] The piston pump preferably has one or more magnets, preferably one or more ring magnets, wherein the magnet is movable together with the piston or the magnets are movable together with the piston, wherein the measuring device for measuring the piston speed has at least one Hall sensor and / or the measuring device for measuring the distance has at least one Hall sensor. In particular, the measuring device for measuring the distance of the piston position of the piston from the reversal point lying in the direction of movement of the piston has at least one Hall sensor and / or the measuring device for measuring the distance of the piston position of the piston from the reversal point lying opposite to the direction of movement of the piston has at least one Hall sensor. The piston pump preferably has at least three Hall sensors, in particular at least four Hall sensors.If there are multiple Hall sensors, the piston pump preferably also has multiple magnets. In particular, each Hall sensor is assigned a magnet. The control device preferably has an evaluation device for evaluating the magnetic flux density measured by the one or more Hall sensors, wherein the evaluation device is particularly configured to determine the first and second derivatives of the measured magnetic flux density. Conclusions about the piston position, piston speed, and piston acceleration can be drawn from the measured magnetic flux density, the first derivative of the flux density, and the second derivative of the flux density.

[0052] The piston pump preferably has at least two Hall sensors, preferably four Hall sensors, wherein a path of the piston from one reversal point to the other reversal point with respect to the measurement of the piston speed and / or a measurement of the piston position is divided into at least two sections, wherein one of the at least two sensors can be assigned to the respective section. In particular, the division of the path and the assignment of the Hall sensors is such that, for the Hall sensor assignable to the respective section, there is an almost linear relationship between the magnetic flux density detected by this Hall sensor and the piston position of the piston when the piston is located in the section assigned to this Hall sensor.

[0053] With regard to measuring the piston position and / or piston speed based on the magnetic flux density by the Hall sensors, it is considered advantageous to perform a calibration process, especially to compensate for manufacturing tolerances of the individual parts. This calibration process can be performed automatically when the piston pump is started up. For this purpose, the piston can be moved at low speed for several cycles without adhesive. The reference values ​​of the flux densities can be learned during this process.

[0054] The alignment process also makes it possible to determine the magnet's polarity during the alignment process. The reference values ​​can be adjusted automatically, and in particular, digital electronics for evaluating the Hall sensors can be programmed according to the magnet's installation position. This eliminates the need to maintain a specific magnet orientation during installation. Disassembly to correct an incorrect magnet installation position is therefore unnecessary.

[0055] By determining the speed and / or acceleration of the piston, it is possible to measure the piston's oscillation behavior or vibration. This oscillation behavior can serve as an indication of wear and possible imminent failure of piston pump components. This can be used to initiate preventative maintenance or replace components, thus avoiding costly production downtime for the customer.

[0056] It is considered particularly advantageous if the piston pump is designed as a pneumatically driven piston pump with a pneumatic piston operatively connected to the piston, wherein the control device comprises an actuatable valve or an actuatable valve arrangement, wherein the direction of pressure applied to the pneumatic piston changes upon actuation of the valve or valve arrangement. Thus, by actuating the valve or valve arrangement, the direction of movement of the piston can be reversed in a simple manner.

[0057] The application system according to the invention for applying a flowable medium, in particular a heated adhesive, to a substrate comprises the above-described double-acting piston pump or one of the above-described embodiments of the double-acting piston pump and a dispensing device for intermittently dispensing the flowable medium conveyed to the dispensing device by means of the double-acting piston pump.

[0058] In the following figures, the invention is explained in more detail using an exemplary embodiment, without being limited thereto.

[0059] They show: Fig. 1 an application system for applying a flowable medium comprising a double-acting piston pump and comprising a dispensing device, Fig. 2 the piston pump according to Fig. 1 with a piston in a first reversal point, Fig. 3the piston pump according to Fig. 1 with the piston in an intermediate position, Fig. 4the piston pump according to Fig. 1 with the piston at a second reversal point, Fig. 5 a diagram to illustrate a time course of a piston position of a piston pump, an output quantity of the flowable medium per unit of time and a schematic representation of the resulting application bead, a piston pump or a method for operating the piston pump in which a reversal of the direction of movement of the piston takes place exclusively at fixed reversal points, Fig. 6 a diagram to illustrate the time course of the piston position, the output quantity of the flowable medium per unit of time and a schematic representation of the resulting application bead, in a piston pump according to the invention or a method for operating a piston pump.

[0060] The Fig. 1shows an application system 2 for applying a flowable medium, in this case a heated adhesive, to a substrate 3. The substrate 3 can be, for example, sheets of paper or cardboard. The application system 2 has a double-acting piston pump 1. Since it is a double-acting piston pump 1, the piston pump 1 is effective in both stroke directions of the piston 4. By means of the piston pump 1, the flowable medium is conveyed from a storage container (not shown) that can be connected to the piston pump 1 to a dispensing device 5. The dispensing device 5 is fluidly connected to the piston pump 1, namely to a cylinder bore 12 of the piston pump, by means of a heating hose 11. When the piston pump is in operation, the adhesive passes from the storage container into an adhesive suction chamber 13.From there, the adhesive is sucked into the cylinder bore 12 and conveyed under pressure to the dispensing device 5 via a pressure connection 14 to which the heating hose 11 is connected.

[0061] The dispensing device 5 is suitable in the present case for intermittently dispensing the adhesive conveyed to the dispensing device 5, so that during dispensing periods, the adhesive is dispensed by means of the dispensing device 5 and during interruption periods, the adhesive is dispensed by means of the dispensing device 5. This is advantageous, for example, when, as in the Fig. 1schematically shown, the adhesive is to be applied to substrates 3 which are arranged at a distance from one another on a conveyor belt 15 and are moved past the dispensing device 5, in particular continuously, in the direction of the arrow 16 by means of this conveyor belt 15, wherein the dispensing device 5 applies a bead of adhesive 17 to the respective substrate 3. In order to ensure a clean application of the adhesive to the substrates 3, it is expedient to temporarily interrupt the dispensing of the adhesive by means of the dispensing device 5, in particular at times when no substrate 3 is arranged below the dispensing device 5.

[0062] The piston 4 of the piston pump 1 is movable between a first reversal point 24 and a second reversal point 25. When the respective reversal point 24, 25 is reached, the direction of movement of the piston 4 reverses. When the direction of movement of the piston 4 is reversed, the pressure of the pumped adhesive drops for a limited time. If adhesive is dispensed by means of the dispensing device 5 during this limited period, this pressure drop has a negative effect on the dispensed quantity of adhesive and thus on the so-called application pattern. During the switching process of the piston pump 1 and thus during the drop in adhesive pressure, significantly less adhesive is applied than during a continuous movement of the piston 4 of the piston pump 1. A clear constriction 18 is then visible in the applied adhesive bead 17.The effects of the switching operations of the piston pump 4 on the output quantity of the adhesive per unit of time 23 and the adhesive pattern or the adhesive beads 17 can be seen from the . Fig. 5 visible.

[0063] Typically, the change in the direction of movement of the piston 4 in piston pumps 1 or in methods for operating a piston pump 1, as are known from the prior art, always and exclusively occurs at fixed positions, namely at the two fixed reversal points 24, 25, which typically coincide with the dead centers of the piston pump 1: After a complete stroke of the piston 4 has occurred, the switching process is initiated and then a complete stroke takes place in the opposite direction up to the other reversal point of the reversal points 24, 25. Typically, the actuation of the switching process, thus reversing the direction of movement of the piston 4, occurs purely mechanically or by actuating an electrical or electronic switch. There is no temporal coordination between the switching process of the direction of movement of the piston 4 of the piston pump 1 and the dispensing periods and interruption periods of the adhesive application.

[0064] In the Figure 6 In the exemplary embodiment according to the invention shown, it is provided that the direction of movement of the piston 4 is reversed only during the interruption periods. The temporal development of the piston position 26 and the output quantity of the adhesive per unit of time 23 are shown schematically in the Fig. 6 As can be seen from a comparison of the Figs. 5 and 6 As can be seen, the Fig. 6 does not lead to a decrease in the dispensed quantity of adhesive per unit of time 23 during the dispensing periods, since a reversal of the direction of movement of the piston 4 occurs exclusively during the interruption periods. Accordingly, the Fig. 6 adhesive beads 17 shown in contrast to the Fig. 5 The adhesive beads 17 shown do not have any constrictions 18.

[0065] As also from the Fig. 6As can be seen, when the direction of movement is reversed, the piston 4 is in an intermediate position between the first reversal point 24 and the second reversal point 25, whereby the intermediate positions are different.

[0066] As from the Fig. 6 As can also be seen, a dispensing quantity of the adhesive dispensed by means of the dispensing device 5 during the respective dispensing period is smaller than a delivery quantity of the medium conveyed by means of the piston pump 1 during one piston stroke of the piston 4 from one reversal point 24, 25 to the other reversal point 24, 25 to the dispensing device 5.

[0067] In the Fig. 1 to 4The piston pump 1 shown is a piston pump 1 that is subject to leakage with respect to the adhesive to be pumped, so that during the interruption periods, the piston speed of the piston 4 is reduced compared to the piston speed during the dispensing periods. This is also evident from the temporal development of the piston position 26 of the piston 4, as shown in the Figs. 5 and 6 The leakage is achieved by the fact that the piston 4 is not designed to seal with respect to a cylinder bore 12, wherein the cylinder bore 12 is incorporated into a housing 19 of the piston pump 1.

[0068] The piston pump 1 has an upper pneumatic part with a pneumatic piston 20 for the drive. The pneumatic piston 20 is fixedly connected to a piston rod 6, which in turn is connected to the piston 4, which serves to convey the adhesive. In the pneumatic area of ​​the piston pump 1, a ring magnet 9 is also connected to the pneumatic piston 20 and thus to the piston rod 6. Adjacent to the pneumatic piston 20 or the ring magnet 9, an electronics print 21 is also formed, with three Hall sensors 10 connected to the electronics print 21. The Hall sensors 10 are designed such that they measure the magnetic flux density in the horizontal direction. When the pneumatic piston 20 orof the piston 4, which are connected to each other by the piston rod 6, the ring magnet 9 moves in accordance with the movement of the piston rod 6, so that the change in the position of the ring magnet 9 changes the magnetic flux density detected by the respective Hall sensor 10. Using the output signals of the Hall sensors 10, the piston position 26 and the piston speed can then be determined. Furthermore, the direction of movement of the piston 4 or the pneumatic piston 20 can also be determined.

[0069] In principle, both the piston position 26, the piston speed, and the direction of movement of the piston 4 can be determined using a single Hall sensor 10. However, at least three Hall sensors 10 are preferably used, as this increases accuracy and redundancy, thereby increasing the reliability, functionality, and operational safety of the piston pump 1.

[0070] Outside the pneumatic part of the piston pump 1, thus in the adhesive delivery area of ​​the piston pump 1, the latter has an extension in the area of ​​the end of the piston rod 6 facing away from the pneumatic piston 20, which forms the double-acting piston 4.

[0071] The piston 4 is provided with an axial passage, in the region of which a check valve 7 with an associated valve seat is arranged. The piston 4 is guided in a non-sealing manner in the cylinder bore 12 formed in the housing 19. A second check valve 8 is formed in the cylinder bore 12. The check valve 8 is assigned to the suction chamber 13, so that adhesive can enter the adhesive delivery chamber of the piston pump 1 from the suction chamber 13 when the check valve 8 is in a defined position. If the check valve 7 is in a defined position, adhesive can reach the pressure connection 14 and from there via the heating hose 11 to the dispensing device 5.

[0072] A dynamic seal 22 without differential pressure is provided between the pneumatic part and the adhesive-feeding part of the piston pump 1.

[0073] When the piston rod 6 is stroked from the first reversal point 24 toward the second reversal point 25, adhesive is simultaneously conveyed to the dispensing device 5 and adhesive is sucked from the storage container (not shown) into the suction chamber 13. Leakage losses occur between the piston rod 6 and the housing 19 and between the piston 4 and the housing 19. When the piston rod 6 is moved in the opposite direction, thus when the piston rod 6 is moved from the second reversal point 25 toward the first reversal point 24, no adhesive is sucked in, but rather adhesive is merely conveyed to the dispensing device 5.

[0074] The piston pump 1 further comprises a control device (not shown) for controlling the direction of movement of the piston 4. The control device is configured to reverse the direction of movement of the piston 4 upon reaching the respective reversal point 24, 25. The piston pump 1 further comprises a measuring device for measuring the piston speed. The control device is configured to reverse the direction of movement of the piston 4 upon falling below a specific speed value of the measured piston speed. Furthermore, the piston pump 1 comprises a measuring device for measuring a distance between the piston position 26 of the piston 4 and the reversal point located in the direction of movement of the piston 4. The Hall sensors 10 form components of the measuring device for measuring the piston speed, the piston position 26, or the distance and the direction of movement of the piston 4.The control device is configured to reverse the direction of movement of the piston 4 when the measured piston speed falls below a specific value and the measured distance falls below a specific value. This design of the piston pump 1 has the advantage that the switching process for the direction of movement of the piston 4 occurs solely based on knowledge of internal measurement data or measured variables of the piston pump 1. It is therefore not necessary to record data on the status of the dispensing device 5 and transmit it to the control device of the piston pump 1. The piston pump 1 can thus be used completely independently of the specific dispensing device 5 used and can carry out the previously described method. The piston pump 1 is therefore universally applicable.In particular, existing application systems 2 can be converted by replacing the piston pump 1 in such a way that these application systems 2 can carry out the previously described process. List of reference symbols

[0075] 1Piston pump 2Application system 3Substrate 4Piston 5Dispensing device 6Piston rod 7Check valve 8Check valve 9Ring magnet 10Hall sensors 11Heating hose 12Cylinder bore 13Suction chamber 14Pressure connection 15Conveyor belt 16Arrow 17Adhesive bead 18Constriction 19Housing 20Pneumatic piston 21Electronic board 22Dynamic seal 23Dispensing quantity per unit of time 24First reversal point 25Second reversal point 26Piston position

Claims

1. Double-action piston pump for conveying a fluid medium to an output device (5), wherein the piston pump (1) has a piston (4) which, for conveying the fluid medium, is movable between a first reversal point (24) and a second reversal point (25), wherein the piston pump (1) has a control device for controlling the direction of movement of the piston (4), wherein the control device, when reaching the respective reversal point (24, 25), is specified to reverse the direction of movement of the piston (4), characterized in that the piston pump (1) has a measuring device for measuring a piston speed, wherein the control device, when the measured piston speed falls short of a specific speed value, is specified to reverse the direction of movement of the piston (4).

2. Double-action piston pump according to Claim 1, wherein the piston pump (1) is prone to leakage in terms of the fluid medium to be conveyed, preferably the piston (4) not being embodied to seal in relation to a cylinder, and / or the piston pump (1) has a piston rod (6) which is embodied so as not to seal in relation to a guide.

3. Double-action piston pump according to Claim 1 or 2, wherein the piston pump (1) has two check valves (7, 8), wherein, depending on the direction of movement of the piston (4), the one check valve of the check valves (7, 8) is open and the other check valve of the check valves (7, 8) is closed, the check valves (7, 8) in particular being of different designs.

4. Double-action piston pump according to one of Claims 1 to 3, wherein the piston pump (1) has a measuring device for measuring a spacing of the piston position (26) of the piston (4) from the reversal point (24, 25) that lies in the direction of movement of the piston (4), wherein the control device, when the measured piston speed falls short of a specific speed value, and the measured spacing falls short of a specific spacing value, is specified to reverse the direction of movement of the piston (4); and / or wherein the piston pump (1) has a measuring device for measuring a spacing of the piston position (26) of the piston (4) from the reversal point (24, 25) that lies counter to the direction of movement of the piston (4), wherein the control device, when the measured piston speed falls short of a specific speed value, and the measured spacing exceeds a specific spacing value, is specified to reverse the direction of movement of the piston (4).

5. Double-action piston pump according to one of Claims 1 to 4, wherein the piston pump (1) has one magnet or a plurality of magnets, preferably one or a plurality of ring magnets (9), wherein the magnet or the magnets is / are movable conjointly with the piston (4), wherein the measuring device for measuring the piston speed has at least one Hall sensor (10), and / or the measuring device for measuring the spacing of the piston position (26) of the piston (4) from the reversal point (24, 25) that lies in the direction of movement of the piston (4) has at least one Hall sensor (10), and / or the measuring device for measuring the spacing of the piston position (26) of the piston (4) from the reversal point (24, 25) that lies counter to the direction of movement of the piston (4) has at least one Hall sensor (10).

6. Double-action piston pump according to Claim 5, wherein the piston pump (1) has at least two Hall sensors (10), preferably four Hall sensors (10), wherein a distance of travel of the piston (4) from the one reversal point (24, 25) to the other reversal point (24, 25) in terms of measuring the piston speed and / or measuring the piston position (26) is divided into at least two portions, wherein the respective portion is able to be assigned one of the at least two sensors (10), there being in particular for the Hall sensor (10) assignable to the respective portion an almost linear correlation between the magnetic flux density and piston position (26) of the piston (4) detected by this Hall sensor (10) when the piston (4) is located in the portion assigned to this Hall sensor (10).

7. Double-action piston pump according to one of Claims 1 to 6, wherein the piston pump (1) is designed as a piston pump (1) which is able to be pneumatically driven, wherein the control device has an activatable valve or an activatable valve assembly, wherein a direction of pressurization of a pneumatic piston (20) changes when the valve or the valve assembly is activated, wherein the pneumatic piston (20) is operatively connected to the piston (4).

8. Application system for applying a fluid medium, in particular a heated adhesive, to a substrate (3), having a double-action piston pump (1) according to one of Claims 1 to 7, and having an output device (5) for intermittently outputting the fluid medium which has been conveyed to the output device (5) by means of the double-action piston pump (1).