Method for operating a piston pump, piston pump and coating system

Abstract

The invention relates to a method for operating a dual-action piston pump of a coating system for coating a flowable medium onto a substrate, wherein the piston pump has a piston which can be moved between a first reversal point and a second reversal point, wherein a reversal of the movement direction of the piston takes place upon reaching the respective reversal point, wherein the coating system has an output device, wherein the output of the flowable medium takes place by means of the output device during an output period and the process of outputting the flowable medium by means of the output device is interrupted during an interruption period, wherein a reversal of the movement direction of the piston takes place during at least one of the interruption periods, wherein the piston is in an intermediate position between the first reversal point and the second reversal point when reversing the movement direction during at least one of the interruption periods. Furthermore, the invention relates to a dual-action piston pump and to a coating system.

Description

Technical Field

[0001] The present invention relates to a method for operating a dual-action, preferably pneumatically driven or drivable, piston pump of a coating system for applying a flowable medium, in particular a heated adhesive, to a substrate, wherein the piston pump has a piston that can move between a first reversal point and a second reversal point for conveying the flowable medium. The direction of movement of the piston is reversed upon reaching the respective reversal point. The coating system has a discharge device for intermittently discharging the flowable medium supplied to the discharge device by means of the piston pump. The present invention also relates to a dual-action piston pump for conveying the flowable medium to the discharge device. The present invention also relates to a coating system for applying a flowable medium to a substrate. Background Art

[0002] A piston pump for conveying a flowable medium is known, for example, from EP 2 732 884 A2.

[0003] In the field of applying flowable media, particularly adhesives, there is a desire to achieve the most precise coating pattern possible. In this regard, there is a particular need to minimize the influence of adhesive delivery devices, such as dual-action piston pumps, on the coating pattern. In particular, with dual-action, pneumatically driven piston pumps, the use of dual-action piston pumps presents the following problem: a pressure drop in the flowable medium delivered by the piston pump occurs at the reversal point, where the direction of motion of the piston reverses upon reaching the reversal point. This pressure drop and its temporal profile depend particularly on the viscosity and flow properties of the flowable medium, such as the heated adhesive being delivered. Furthermore, this pressure drop and its temporal profile are strongly dependent on the design of the piston pump and its components. For example, the reversal of the stroke direction of pneumatically driven piston pumps with a pneumatic piston is accomplished via an electrically actuated pneumatic switching valve. The switching process of this valve requires a certain amount of time. Similarly, during switching, the elimination of the existing air pressure on one side of the pneumatic piston and the buildup of air pressure on the other side require a certain amount of time. Dual-action piston pumps often have two check valves, typically of different designs. These two check valves are typically constructed in the form of movable balls that alternately seal above and below the piston in the vertical direction of travel to prevent the flow of the fluid medium to be conveyed. During the switching process, the ball of one check valve moves from a sealing position to a free position, and the ball of the other check valve moves from a free position to a sealing position, and vice versa. This movement of the balls also takes some time. During the reversal process at the first and second reversal points of the piston, and thus during the actuation of the check valves, a slight loss in the volume flow of the fluid medium occurs. This loss, or pressure drop, is typically not the same at the two reversal points. For dual-action piston pumps, the following problem arises: when the piston's direction of movement is reversed, the pressure of the delivered flowable medium drops within a limited time, or a certain time is required until the pressure of the flowable medium returns to a nearly constant value. The pressure drop at the reversal point negatively affects the quality of the flowable medium applied to the substrate or the coating pattern. When the flowable medium is continuously applied to the substrate by means of a dispensing device, the reversal of the piston's direction of movement and the resulting pressure drop result in a time-limited reduction in the output of the flowable medium. Accordingly, for coating systems with dual-action piston pumps, a reduction in the output of the flowable medium occurs at the reversal point of the piston pump, which negatively affects the coating pattern.For example, when a flowing medium is continuously dispensed in the form of a strip, also known as an application strip or strip, a distinct constriction appears in the cross section of the applied strip, which is temporally associated with the reversal point in the direction of movement of the piston of the adhesive pump. The so-called application pattern then shows a distinct, regular constriction.

[0004] Various possibilities are known from the prior art for avoiding or reducing the pressure drop when reversing the direction of movement of the piston of a piston pump or for minimizing the influence of this pressure drop on the coating pattern.

[0005] 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 a flowable medium. The two pumps are operated in such a way that the pressure drop when one of the pumps conveys the fluid is compensated by the other pump. In addition, the prior art ES2 064 183 A2 discloses the use of a pressure accumulator, wherein the pressure accumulator compensates for the pressure drop as much as possible when the direction of movement of the piston of the piston pump is reversed. The disadvantage of this solution is that the pressure accumulator can only be designed optimally for one operating state. The compensation for the pressure drop is satisfactory only for a specific pressure regulation and only for a specific viscosity of the flowable medium. The greater the deviation from the optimal operating point, the worse the compensation for the pressure drop by the pressure accumulator. Summary of the Invention

[0006] The present invention is based on the object of specifying a method for operating a dual-action piston pump of a coating system for applying a flowable medium, in particular a heated adhesive, to a substrate, in such a way that the pressure drop during reversal of the direction of movement, the influence on the coating pattern, in particular the constriction of the coating strip, is avoided or at least reduced. Furthermore, the present invention is based on the object of specifying a dual-action piston pump for supplying a flowable medium to a dispensing device, with which constrictions can be avoided during the application of the flowable medium. Furthermore, the present invention is based on the object of specifying a coating system for applying a flowable medium, which coating system is able to avoid or at least reduce constrictions during the application of the flowable medium.

[0007] These objects are achieved by a method according to the invention, a dual-action piston pump according to the invention, and a coating system according to the invention.

[0008] The method according to the invention is a method for operating a dual-action piston pump of a coating system for applying a flowable medium. The flowable medium is, in particular, a heated adhesive and / or a viscous melt. The piston pump is a dual-action piston pump, and thus a piston pump that delivers the flowable medium in both stroke directions of the piston. The coating system is used to apply the flowable medium to a substrate, wherein the substrate is, for example, paper, cardboard or film. The substrate can consist of a variety of separate structures, for example, a variety of strip-shaped elements, such as paper strips, cardboard strips or film strips, which are arranged in a spaced-apart manner and are guided successively past a coating head for dispensing the medium.

[0009] The piston pump has a piston that can move between a first reversal point and a second reversal point for conveying a flowable medium, wherein the direction of movement of the piston is reversed when the corresponding reversal point is reached. The coating system also has a discharge device, such as one or more spray heads, for intermittently discharging the flowable medium that is supplied to the discharge device by means of the piston pump. In the method according to the invention, provision is made for the discharge of the flowable medium by means of the discharge device during a discharge time period and for the discharge of the flowable medium by means of the discharge device to be interrupted during an interruption time period. In the method according to the invention, provision is made for the direction of movement of the piston to be reversed during at least one of the interruption time periods, wherein the piston is in an intermediate position between the first reversal point and the second reversal point during the reversal of the direction of movement during the at least one interruption time period. Since the reversal of the direction of movement of the piston occurs during at least one of the interruption time periods, at least this reversal of the direction of movement occurs during a time period in which the reversal of the direction of movement of the piston and the resulting pressure drop have no or only a slight effect on the application pattern of the flowable medium to the substrate, since no flowable medium is being dispensed via the dispensing device during the interruption time period. In particular, the reversal of the direction of movement of the piston occurs during at least one of the interruption time periods in such a way that the dispensing time period immediately following the at least one interruption time period is sufficient to restore the setpoint pressure value by the beginning of the following dispensing time period, in which case the time-limited pressure drop caused by the reversal has already elapsed at the beginning of the following dispensing time period.

[0010] With conventional piston pumps or methods for operating piston pumps, the direction of motion of the piston is reversed only upon reaching a corresponding reversal point. Consequently, with such methods or piston pumps, there is no temporal coordination between the reversal of the direction of motion of the piston and the interruption period. However, with the solution according to the present invention, the direction of motion of the piston of the piston pump is reversed during at least one of the interruption periods in an intermediate position, thus before reaching a reversal point in the direction of motion.

[0011] It is entirely conceivable that the reversal of the movement direction of the piston of the piston pump is carried out in an intermediate position between the two reversal points during at least one of the interruption time periods and that the reversal of the movement direction of the piston of the piston pump is carried out in another intermediate position between the two reversal points during another of the interruption time periods.

[0012] It is entirely conceivable that during the method the piston also reaches the first and / or second reversal point.

[0013] It is also entirely conceivable that during one or more further interruption periods the piston reaches the first or second reversal point anyway, so that no premature reversal of the movement direction of the piston occurs in the intermediate position.

[0014] The flowable medium is preferably discharged intermittently in such a way that a temporally recurring pattern of the discharged flowable medium is produced during the intermittent discharge, in particular if a plurality of similar substrates are provided with the flowable medium.

[0015] Preferably, the piston pump has a delivery region and a drive region. The piston is arranged in the delivery region and is used to deliver the flowable medium. The components for driving the movement of the piston are at least partially, preferably completely, arranged in the drive region.

[0016] Preferably, the piston pump is a pneumatically drivable piston pump. The piston pump preferably includes a pneumatic piston operatively connected to a piston for conveying a flowable medium, the pneumatic piston being used to drive the movement of the piston. For the reciprocating movement of the piston toward a first reversal point or a second reversal point, compressed air is preferably applied to the corresponding side of the pneumatic piston, while the other side is ventilated. The reversal of the piston's movement direction is preferably accomplished via a pneumatic switching valve that can be actuated electrically or magnetically.

[0017] In particular, the piston pump has a pneumatic part, also referred to as the pneumatic area, and a delivery area, wherein the pneumatic piston is arranged in the pneumatic part and the piston for conveying the flowable medium is arranged in the delivery area.

[0018] Drives other than pneumatic drives are also conceivable, which cause an alternating movement of the piston, such as hydraulic drives, in particular with hydraulic pistons, or electric drives, in particular in the form of linear motors.

[0019] Preferably, the first reversal point and the second reversal point are not designed to be variable, so that the first reversal point and the second reversal point are fixed when operating a dual-action piston pump. Preferably, the two reversal points are immutable, in particular for design reasons.

[0020] Preferably, the first reversal point and the second reversal point refer to the bottom dead center or the top dead center of the piston.

[0021] It is considered particularly advantageous to only, or at least mostly, perform a reversal of the direction of motion of the piston during the interruption period. This results in a particularly small negative impact of a corresponding reversal of the direction of motion on the coating pattern. Of course, the reversal of the direction of motion of the piston does not necessarily have to occur during every interruption period.

[0022] It is particularly preferred that the amount of the flowable medium dispensed by the dispensing device during the respective dispensing time period is less than the amount of the medium delivered to the dispensing device by the piston pump during the piston stroke from the first reversal point to the second reversal point and / or vice versa from the second reversal point to the first reversal point. In such an embodiment, the flowable medium can be dispensed during the dispensing time period 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.

[0023] If the amount of fluid medium delivered by the delivery device during one of the delivery time periods is greater than the amount of fluid medium delivered to the delivery device over the complete stroke length of the piston pump or the amount delivered during one of the delivery time periods at the time of reaching one of the reversal points, it is entirely conceivable to compensate for the pressure drop during the reversal of the direction of movement of the piston of the piston pump. For this purpose, it is conceivable to activate the pressure accumulator in a controlled manner to compensate for the pressure drop during the switching process. Possible pressure accumulators include spring accumulators or pressure accumulators based on the principle of a single-acting, pneumatically actuated piston pump.

[0024] 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 reversals of the direction of movement occur primarily in the intermediate positions of the piston between the first reversal point and the second reversal point.

[0025] It is entirely conceivable that during operation, the direction of movement is only reversed in an intermediate position, as long as a reversal point has not been reached. The reversal point is only reached if, for example, a malfunction of the pump causes the direction of movement to be reversed unintentionally in an intermediate position while carrying out the method or a control system for carrying out the method. Since the direction of movement is then reversed with respect to the movement of the piston in the direction of one of the reversal points at the latest when this reversal point is reached, damage to components of the piston pump is avoided.

[0026] It is considered particularly advantageous if the piston speed of the piston during the interruption period is reduced relative to the piston speed during the output period, wherein the piston speed refers to the magnitude of the piston speed, and in particular, the piston speed during the interruption period is zero. Accordingly, the temporal evolution of the piston speed is correlated with the output period and the interruption period. Accordingly, by detecting the piston speed, it is possible to determine whether an output period or an interruption period is present. Consequently, a higher-level control system is not necessary to detect whether the output device is outputting a medium or the output is interrupted. Instead, the reversal of the movement direction can be performed independently of a higher-level control system or knowledge of the operating state of the output device (output or interruption of output), solely based on the measured piston speed. This allows for substantially autonomous operation of the piston pump, thereby eliminating the need for a higher-level control system. Because the piston speed is correlated with the output period and the interruption period, the reversal of the movement direction of the piston can be performed based on the piston speed, and the reversal of the movement direction can be performed during the at least one interruption period based on knowledge of the piston speed.

[0027] For recurring coating patterns, the recurring coating pattern can be identified by measuring the piston speed. This allows the predicted piston stroke length to be determined at the start of one interruption period until the start of the next interruption period. Alternatively, it is conceivable to use a programmed or predefined coating pattern of a higher-level coating control system to determine the temporal profile of the interruption periods and, therefore, the predicted piston position relative to the interruption periods. This improves the operational reliability of the present invention, as unexpected changes in the coating pattern can be taken into account.

[0028] It is considered particularly advantageous if the piston pump has leakage with respect to the flowable medium to be conveyed, so that during the interruption period the piston speed of the piston is reduced compared to the piston speed during the delivery period. A piston pump with leakage should also be considered advantageous with regard to minimizing wear on the piston pump, avoiding maintenance work, and maximizing its service life. It is considered particularly advantageous if the leakage occurs between the piston and the cylinder. This leakage depends primarily on the viscosity and flow properties of the flowable medium, the size of the gap around the piston, and the pressure built up by the piston pump. For a piston pump with leakage, the piston speed of the piston during the interruption period is reduced compared to the piston speed during the delivery period because the resistance to the piston movement during the interruption period is increased compared to the resistance to the piston movement when delivering the flowable medium.

[0029] Preferably, the piston of the piston pump is designed not to be sealed relative to the cylinder and / or the piston pump has a piston rod that is designed not to be sealed relative to a guide.

[0030] The piston pump preferably has two check valves, one of which is open and the other closed depending on the direction of piston movement. The two check valves are generally designed as movable balls that alternately seal at the top and bottom relative to the vertical direction of piston movement to prevent the flow of the fluid medium to be conveyed. During a switching operation, the ball of one check valve moves from a sealing position to a pass position, and the ball of the other check valve moves from the pass position to a sealing position, and in the subsequent switching operation, the movements are inversely proportional.

[0031] In a preferred embodiment of the method, the piston speed is measured, and if the piston speed is equal to a specific value, in particular, the specific value corresponds to the piston speed during the interruption period, the direction of movement of the piston is reversed outside of the reversal point. The aforementioned condition, namely that the piston speed is less than or equal to the specific value, should be understood as a necessary condition for reversing the direction of movement of the piston, but not necessarily a sufficient condition. However, it is entirely conceivable that it is a sufficient condition for reversing the direction of movement of the piston.

[0032] In an advantageous refinement of the method, it is provided that the distance of the piston from a reversal point existing along the direction of movement of the piston is determined, wherein if the distance of the piston from the reversal point existing along the direction of movement of the piston is lower than a specific value, the reversal of the direction of movement of the piston is carried out during the corresponding interruption time period before reaching the reversal point existing along the direction of movement of the piston, and / or the distance of the piston from a reversal point existing opposite to the direction of movement of the piston is determined, wherein if the distance of the piston from the reversal point existing opposite to the direction of movement of the piston exceeds a specific value, the reversal of the direction of movement of the piston is carried out during the corresponding interruption time period before reaching the reversal point existing along the direction of movement of the piston.

[0033] It is entirely conceivable to permanently measure the piston position.

[0034] Preferably, at the beginning of the respective interruption period, the distance of the piston from the respective reversal point is determined for comparison with a specific value.

[0035] The specific value for the reversal point present along the direction of movement of the piston preferably corresponds to the expected travel of the piston along the direction of movement of the piston until the start of the next interruption period.

[0036] The specific value for the reversal point, which is located opposite to the direction of movement of the piston, preferably corresponds to the expected travel of the piston opposite to its direction of movement until the start of the next interruption period.

[0037] It is considered particularly advantageous to measure the piston speed and determine the distance of the piston from a reversal point along the direction of movement of the piston, wherein the direction of movement of the piston is reversed if the piston speed is below a specific value and the distance of the piston from a reversal point along the direction of movement of the piston is below a specific value, and / or to measure the piston speed and determine the distance of the piston from a reversal point opposite to the direction of movement of the piston, wherein the direction of movement of the movable piston is reversed if the piston speed is below a specific value and the distance of the piston from a reversal point opposite to the direction of movement of the piston exceeds a specific value.

[0038] The advantage of the aforementioned embodiment of the method is that the piston speed is a criterion for whether an interruption period exists. Because if the direction of movement of the piston is to be reversed during an interruption period, the reversal of the direction of movement of the piston should only be carried out during a period with a reduced piston speed. Therefore, the reduced piston speed is the first criterion for switching. The distance between the pistons from the corresponding reversal points is used as another criterion to determine whether the reversal of the direction of movement should be carried out. This is against the background that if the distance between the pistons from the reversal points that exist opposite to the direction of movement of the piston is too small, there is the risk that when the direction of movement of the piston is reversed, the piston reaches this reversal point in the next output period, so that the reversal of the direction of movement occurs in this output period and the corresponding pressure drop during the output medium occurs with a corresponding negative impact on the coating pattern.

[0039] It is entirely conceivable to determine the piston position or the distance value of the piston from the corresponding reversal point if the piston speed falls below a specific value. To this end, a check is first performed to determine whether a first criterion, i.e., whether the piston speed falls below a specific speed value, exists. Only if the first criterion exists is the second criterion, i.e., the distance, checked. This reduces the measurement and evaluation effort.

[0040] It is considered particularly advantageous if the piston pump has a sensor for measuring the piston position and / or the 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 effect sensor. In conjunction with the Hall effect sensor, it is considered particularly advantageous if the piston pump has a magnet, preferably a ring magnet, which is movable with the piston. It is entirely conceivable for the piston pump to have multiple Hall effect sensors, preferably at least four Hall effect sensors, in particular exactly four Hall effect sensors.

[0041] The concept of "distance" should be understood in a broad sense in the context mentioned above. For example, it is conceivable that the section of the piston from one reversal point to the other reversal point is divided into at least two sections, wherein "distance" then refers to the section in which the piston is located. For example, the section can be divided into a first section and a second section, wherein the first section includes the first reversal point and the second section includes the second reversal point. As a distance criterion or distance, it can then be considered which section the piston is in. Therefore, 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. Therefore, the knowledge of which section the piston is in can be used as a criterion for judging whether a distance value is not exceeded or exceeded.

[0042] In principle, it is conceivable that for a coating system having two dual-acting piston pumps, the reversal of the movement direction of the pistons of the corresponding piston pumps is controlled in a similar manner so that the reversal of the movement direction of the pistons of the two piston pumps does not take place simultaneously, but rather the movement direction of the piston of one of the piston pumps is changed in advance if it is foreseeable that the reversal of the movement direction of one of the piston pumps at the first or second reversal point will coincide with the reversal of the movement direction of the piston of the other pump at the first or second reversal point.

[0043] The dual-action piston pump according to the invention is used to convey a flowable medium to an output device. In particular, the dual-action piston pump is used to convey a heated adhesive, in particular a viscous melt, to an output device. The output device can be, in particular, a spray head. The piston pump has a piston that can move between a first reversal point and a second reversal point, which is used to convey the flowable medium. In addition, the piston pump has a control device for controlling the direction of movement of the piston, wherein the control device is designed to reverse the direction of movement of the piston when the corresponding reversal point is reached. In addition, the piston pump has a measuring device for measuring the piston speed, wherein the control device is designed to reverse the direction of movement of the piston when the speed value of the measured piston speed falls below a specific value.

[0044] Since the speed of the piston generally depends on whether the outlet device is discharging a flowable medium, the piston speed serves as a measure of whether the outlet device is discharging a flowable medium or whether the process of discharging a flowable medium by means of the outlet device is interrupted. The dual-action piston pump is therefore suitable for carrying out the method according to the invention with corresponding advantages.

[0045] It is considered particularly advantageous if the piston pump has leakage with respect to the flowable medium to be conveyed. In this regard, it is considered particularly advantageous if the piston is designed to be leak-tight relative to the cylinder and / or if the piston pump has a piston rod that is designed to be leak-tight in its guide. A leaking piston pump has the advantage, on the one hand, of reduced wear on the piston pump and, in addition, with respect to the method, the advantage that the speed of the piston during the interruption period is reduced relative to its speed during the delivery period.

[0046] Preferably, the piston pump has two non-return valves, wherein one non-return valve is open and the other non-return valve is closed depending on the direction of movement of the piston, in particular the non-return valves are designed differently. The two non-return valves are assigned to the part of the piston pump in which the flowable medium is conveyed, thus to the delivery region.

[0047] The dual-action piston pump is preferably designed as a pneumatically drivable piston pump. In particular, the piston pump has a pneumatic part, also referred to as the pneumatic area, and a delivery area, wherein the pneumatic piston is arranged in the pneumatic part and the piston for conveying the flowable medium is arranged in the delivery area.

[0048] Preferably, the piston pump has a measuring device for measuring the distance of the piston position of the piston from a reversal point existing along the movement direction of the piston, wherein the control device is set up to reverse the movement direction of the piston when the speed is below a specific speed value of the measured piston speed and below a specific distance value of the measured distance, or the piston pump has a measuring device for measuring the distance of the piston position of the piston from a reversal point existing in the opposite direction to the movement direction of the piston, wherein the control device is set up to reverse the movement direction of the piston when the speed is below a specific speed value of the measured piston speed and exceeds a specific distance value of the measured distance.

[0049] The piston pump preferably has one magnet or multiple magnets, preferably one or more ring magnets, wherein the magnet or the multiple magnets are movable 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. The piston pump preferably has at least three Hall sensors, in particular at least four Hall sensors. If the piston pump has multiple Hall sensors, it preferably also has multiple magnets. In particular, one magnet is associated with each Hall sensor. The control device preferably has an evaluation device for evaluating the magnetic flux density measured by means of one or more Hall sensors, wherein the evaluation device is particularly configured to determine first and second derivatives of the measured magnetic flux density. The piston position, piston velocity, and piston acceleration can be inferred from the measured magnetic flux density, the first derivative of the magnetic flux density, and the second derivative of the magnetic flux density.

[0050] The piston pump preferably has at least two Hall sensors, wherein the distance of the piston from one reversal point to the other reversal point is divided into at least two sections for measuring the piston speed and / or the piston position, wherein one of the at least two sensors can be assigned to each section. In particular, the distance is divided and the Hall sensors are assigned such that, for a Hall sensor that can be assigned to a respective section, when the piston is in the section assigned to the Hall sensor, there is a nearly linear correlation between the magnetic flux density detected by the Hall sensor and the piston position of the piston.

[0051] Based on the measurement of the piston position and / or piston speed by Hall sensors as a function of the magnetic flux density, it is considered advantageous to perform an adjustment process, in particular to compensate for manufacturing tolerances of the individual components. This adjustment process can be performed automatically when the piston pump is started. To this end, the piston can be moved at a low speed without adhesive over a number of cycles. A reference value for the magnetic flux density can be learned.

[0052] Furthermore, the alignment process allows the polarity of the magnet to be determined during the alignment process. Reference values ​​can be automatically adapted; in particular, the digital electronics can be programmed to analyze the Hall effect sensor based on the magnet's installation position. This eliminates the need to adhere to a specific orientation of the magnet during installation. Disassembly to correct an incorrect installation position of the magnet is also unnecessary.

[0053] By determining the speed and / or acceleration of the piston, its oscillation characteristics or vibrations can be measured. This oscillation characteristic can be used as an indicator of wear and possible imminent failure of piston pump components. This allows for preventive maintenance or replacement of components, thus avoiding costly production interruptions for the customer.

[0054] It is considered particularly advantageous if the piston pump is designed as a pneumatically drivable piston pump having a pneumatic piston operatively connected to the piston, wherein the control device has an actuatable valve or an actuatable valve arrangement, wherein the direction of the pressure acting on the pneumatic piston is changed when the valve or valve arrangement is actuated. Thus, the direction of movement of the piston can be reversed in a simple manner by actuating the valve or valve arrangement.

[0055] The coating system according to the invention for applying a flowable medium, in particular a heated adhesive, to a substrate comprises a dual-acting piston pump according to the invention and an output device for intermittently outputting the flowable medium supplied to the output device by means of the dual-acting piston pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The invention is explained in more detail in the following drawings using an exemplary embodiment without being restricted to this exemplary embodiment.

[0057] Figure 1 A coating system for applying a flowable medium is shown, which has a dual-action piston pump and a dispensing device;

[0058] Figure 2 Shown according to Figure 1 A piston pump with a piston in a first reversal point;

[0059] Figure 3 Shown according to Figure 1 A piston pump with a piston in an intermediate position;

[0060] Figure 4 Shown according to Figure 1 A piston pump with a piston in a second reversal point;

[0061] Figure 5 A diagram illustrating the temporal profile of the piston position of a piston pump, the output quantity per time unit of a flowable medium, and a schematic diagram of a coating strip resulting therefrom, a piston pump, and a method for operating the piston pump, wherein the reversal of the movement direction of the piston occurs only at fixed reversal points;

[0062] Figure 6A diagram is shown for illustrating the temporal profile of the piston position, the output quantity per time unit of the flowable medium, and a schematic diagram of a coating strip produced therefrom with the piston pump according to the invention or the method according to the invention for operating a piston pump. DETAILED DESCRIPTION

[0063] Figure 1 The present invention shows 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, paper or cardboard. The application system 2 comprises a dual-action piston pump 1. As it is a dual-action piston pump 1, it acts in both directions of reciprocation of the piston 4. The flowable medium is supplied to a dispensing device 5 from a storage container (not shown), which can be connected to the piston pump 1. The dispensing device 5 is fluidically connected to the piston pump 1, i.e., its cylinder bore 12, by means of a heating hose 11. When the piston pump is in operation, the adhesive flows from the storage container into a suction chamber 13 for the adhesive. From there, the adhesive is sucked into the cylinder bore 12 and supplied under pressure to the dispensing device 5 via a pressure connection 14, to which the heating hose 11 is connected.

[0064] The dispensing device 5 is suitable for dispensing the adhesive fed to it intermittently, so that during the dispensing time period the adhesive is dispensed by means of the dispensing device 5 and the dispensing of the adhesive by means of the dispensing device 5 is interrupted during the interruption time period. This is advantageous, for example, if, as in Figure 1 As schematically shown in FIG, adhesive is to be applied to substrates 3, which are arranged spaced apart from one another on a conveyor belt 15 and, by means of this conveyor belt 15, are passed, in particular continuously, in the direction of arrow 16 past a discharge device 5, wherein the discharge device 5 applies a strip 17 of adhesive 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 process of discharging the adhesive by means of the discharge device 5, in particular at a time when no substrate 3 is arranged below the discharge device 5.

[0065] 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 points 24, 25 are reached, the direction of movement of the piston 4 is reversed. When the direction of movement of the piston 4 is reversed, a time-limited drop in the pressure of the delivered adhesive occurs. If adhesive is delivered during this limited time period by means of the delivery device 5, this pressure drop has a negative impact on the adhesive delivery quantity and thus on the so-called application pattern. During the switching process of the piston pump 1 and thus during the drop in the adhesive pressure, significantly less adhesive is applied, as during the continuous movement of the piston 4 of the piston pump 1. A clear constriction 18 can then be seen in the applied adhesive strip 17. The influence of the switching process of the piston pump 4 on the adhesive delivery quantity per time unit 23 and on the adhesive pattern or adhesive strip 17 can be seen from the Figure 5 It can be seen in.

[0066] Generally speaking, in piston pumps 1 or methods for operating such piston pumps 1 as are known from the prior art, the direction of movement of the piston 4 is changed continuously and only at fixed positions, namely, at two fixed reversal points 24, 25, which typically coincide with the dead center of the piston pump 1. After a complete stroke of the piston 4, the switching process begins, and the piston 4 then completes a complete stroke in the opposite direction until reaching the other of the reversal points 24, 25. Generally, the switching process, and thus the reversal of the direction of movement of the piston 4, is actuated purely mechanically or by actuating an electrical or electronic switch. There is no temporal coordination between the direction of movement of the piston 4 of the piston pump 1 and the switching process of the adhesive application delivery and interruption periods.

[0067] exist Figure 6 In the exemplary embodiment according to the invention shown, it is provided that the reversal of the movement direction of the piston 4 takes place only during the interruption period. The temporal evolution of the piston position 26 and the output quantity of adhesive per time unit 23 is schematically shown in FIG. Figure 6 As shown in Figure 5 and 6 As can be seen from the comparison of Figure 6 In the output time period, no decrease in the output quantity of adhesive per time unit 23 occurs, because the reversal of the movement direction of the piston 4 is only performed during the interruption time period. Figure 6 The adhesive strip 17 shown in FIG. Figure 5 The adhesive strip 17 shown in FIG. 1 has no constriction 18 .

[0068] As can also be obtained from Figure 6As can be seen in FIG, upon reversal of the direction of movement, the piston 4 is in each case in an intermediate position between a first reversal point 24 and a second reversal point 25, wherein the intermediate positions are different.

[0069] As can also be obtained from Figure 6 As can be seen in FIG, the amount of adhesive delivered by means of the delivery device 5 during the corresponding delivery time period is less than the amount of medium delivered to the delivery device 5 by means of the piston pump 1 during the piston stroke of the piston 4 from one reversal point 24, 25 to the other reversal point 24, 25.

[0070] exist Figures 1 to 4 The piston pump 1 shown in FIG is a piston pump 1 with leakage with respect to the adhesive to be conveyed, so that during the interruption period the piston speed of the piston 4 is reduced compared to the piston speed during the delivery period. This can also be seen from the piston position 26 of the piston 4, as in FIG. Figure 5 and 6 The leakage is caused by the fact that the piston 4 is not sealed relative to the cylinder bore 12 , wherein the cylinder bore 12 is hollowed out in the housing 19 of the piston pump 1 .

[0071] 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 a piston 4 for conveying adhesive. Furthermore, in the pneumatic area of ​​the piston pump 1, an annular magnet 9 is connected to the pneumatic piston 20 and, therefore, to the piston rod 6. Furthermore, an electronic print 21 is provided adjacent to the pneumatic piston 20 or the annular magnet 9, with three Hall sensors 10 connected to the electronic print 21. The Hall sensors 10 are designed to measure the magnetic flux density in the horizontal direction. During the stroke of the pneumatic piston 20 or the piston 4, which are connected to each other via the piston rod 6, the annular magnet 9 moves according to the movement of the piston rod 6, causing the magnetic flux density detected by the corresponding Hall sensors 10 to change due to the change in the position of the annular magnet 9. The piston position 26 and piston speed can then be determined using the output signals of the Hall sensors 10. Furthermore, the direction of movement of the piston 4 or the pneumatic piston 20 can also be determined.

[0072] In principle, not only the piston position 26 and the piston speed of the piston 4 but also the direction of movement of the piston 4 can be determined by means of a single Hall sensor 10. However, it is preferred to use at least three Hall sensors 10, since this increases the accuracy on the one hand and the redundancy on the other hand, thereby increasing the fault tolerance, functional reliability, and operational reliability of the piston pump 1.

[0073] Outside the pneumatic part of the piston pump 1 , thus in the adhesive conveying region of the piston pump 1 , the piston pump has a widening in the region of the end of the piston rod 6 facing away from the pneumatic piston 20 , which widening forms a double-acting piston 4 .

[0074] The piston 4 is provided with an axial passage, in the region of which a non-return valve 7 with an associated valve seat is arranged. The piston 4 is guided in a leak-tight manner in a cylinder bore 12 formed in the housing 19. A second non-return valve 8 is formed in the cylinder bore 12. This non-return valve 8 is associated with the suction chamber 13 so that adhesive can flow from the suction chamber 13 into the adhesive delivery chamber of the piston pump 1 when the non-return valve 8 is in a defined position. If the non-return valve 7 is in the defined position, the adhesive can reach the pressure connection 14 and from there via the heated hose 11 to the dispensing device 5.

[0075] A dynamic seal 22 without a pressure difference is provided between the pneumatic part and the part of the piston pump 1 that conveys the adhesive.

[0076] During the stroke of the piston rod 6 from the first reversal point 24 in the direction of the second reversal point 25, adhesive is simultaneously supplied to the dispensing device 5 and adhesive is drawn from a 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 moves in the opposite direction, and thus when the piston rod 6 moves from the second reversal point 25 in the direction of the first reversal point 24, no adhesive is drawn in, but adhesive is only supplied to the dispensing device 5.

[0077] The piston pump 1 also includes a control mechanism (not shown) for controlling the direction of movement of the piston 4 , wherein the control mechanism is configured to reverse the direction of movement of the piston 4 upon reaching the respective reversal points 24 , 25 . Furthermore, the piston pump 1 includes a measuring mechanism for measuring the piston speed, wherein the control mechanism 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 includes a measuring mechanism for measuring the distance of the piston position 26 of the piston 4 from the reversal point located along the direction of movement of the piston 4 . The Hall sensor 10 forms a component of the measuring mechanism for measuring the piston speed, piston position 26 , or distance, and direction of movement of the piston 4 . The control mechanism is configured to reverse the direction of movement of the piston 4 upon falling below a specific speed value of the measured piston speed and below a specific distance value of the measured distance. Such a design of the piston pump 1 has the advantage that the switching process of the direction of movement of the piston 4 is performed solely based on knowledge of internal measurement data or measured variables of the piston pump 1 . Consequently, it is not necessary to acquire data regarding the state of the output device 5 and transmit it to the control mechanism 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 method described above. This allows the piston pump 1 to be used universally. In particular, existing coating systems 2 can be retrofitted by replacing the piston pump 1 so that they can carry out the method described above.

[0078] Reference Signs List

[0079] 1 piston pump

[0080] 2 Coating system

[0081] 3 base

[0082] 4 pistons

[0083] 5 Output device

[0084] 6 Piston rod

[0085] 7 Check valve

[0086] 8 Check valve

[0087] 9 Ring magnet

[0088] 10 Hall effect sensors

[0089] 11 Heating hose

[0090] 12 cylinder bores

[0091] 13 Suction Chamber

[0092] 14 Pressure connector

[0093] 15 Conveyor belt

[0094] 16 Arrows

[0095] 17 Adhesive Strips

[0096] 18 Contraction

[0097] 19 Housing

[0098] 20 pneumatic piston

[0099] 21 Electronic Printing

[0100] 22 Dynamic seals

[0101] 23 Output per time unit

[0102] 24 First Turning Point

[0103] 25 Second Turning Point

[0104] 26 Piston position.

Claims

1. A method for operating a dual-action piston pump (1) of a coating system (2) for applying a flowable medium to a substrate (3), wherein the piston pump (1) has a piston (4) movable between a first reversal point (24) and a second reversal point (25) for conveying the flowable medium, wherein the direction of movement of the piston (4) is reversed upon reaching the respective reversal points (24, 25), wherein the coating system (2) has a discharge device (5) for intermittently discharging the flowable medium supplied to the discharge device (5) by means of the piston pump (1), wherein the discharge of the flowable medium is carried out by means of the discharge device (5) during discharge time periods, and the discharge of the flowable medium by means of the discharge device (5) is interrupted during interruption time periods, wherein the direction of movement of the piston (4) is reversed during at least one of the interruption time periods, wherein the piston (4) is in an intermediate position between the first reversal point (24) and the second reversal point (25) during the reversal of the direction of movement during at least one interruption time period.

2. The method according to claim 1, wherein the reversal of the movement direction of the piston (4) is mostly performed during the interruption period.

3. The method according to claim 1, wherein the reversal of the movement direction of the piston (4) is performed only during the interruption period.

4. The method according to claim 1, wherein The flowable medium is a heated adhesive.

5. A method according to claim 1, wherein the number of reversals of the direction of movement performed in an intermediate position of the piston (4) between the first reversal point (24) and the second reversal point (25) is greater than the number of reversals of the direction of movement performed in the reversal points (24, 25).

6. The method according to any one of claims 1 to 5, wherein the piston speed of the piston (4) during the interruption period is reduced relative to the piston speed during the output period.

7. A method according to any one of claims 1 to 5, wherein the piston pump (1) has a leak with respect to the flowable medium to be conveyed, whereby the piston speed of the piston (4) during the interruption time period is reduced relative to the piston speed during the output time period.

8. The method according to any one of claims 1 to 5, wherein the piston speed is measured and, if the piston speed is less than or equal to a specific value, a reversal of the direction of movement of the piston (4) is performed.

9. The method according to claim 8, wherein The specific value corresponds to the piston speed of the piston (4) during the interruption period.

10. The method according to claim 1 , wherein the distance of the piston ( 4 ) from a reversal point ( 24 , 25 ) present along the direction of movement of the piston ( 4 ) is determined, wherein if the distance of the piston ( 4 ) from the reversal point ( 24 , 25 ) present along the direction of movement of the piston ( 4 ) is below a specific value, the reversal of the direction of movement of the piston ( 4 ) is carried out during the corresponding interruption period before reaching the reversal point ( 24 , 25 ) present along the direction of movement of the piston ( 4 ), and / or The distance between the piston (4) and the reversal point (24, 25) located opposite to the direction of movement of the piston (4) is determined, wherein if the distance between the piston (4) and the reversal point (24, 25) located opposite to the direction of movement of the piston (4) exceeds a specific value, the reversal of the direction of movement of the piston (4) is carried out during the corresponding interruption time period before reaching the reversal point (24, 25) located along the direction of movement of the piston (4).

11. The method according to claim 1 , wherein the piston speed is measured and the distance of the piston (4) from the reversal point (24, 25) present along the direction of movement of the piston (4) is determined, wherein the direction of movement of the piston (4) is reversed if the piston speed is below a specific value and the distance of the piston (4) from the reversal point (24, 25) present along the direction of movement of the piston (4) is below a specific value, and / or The piston speed is measured and the distance between the piston (4) and the reversal point (24, 25) opposite to the direction of movement of the piston (4) is determined, wherein the direction of movement of the piston (4) is reversed if the piston speed falls below a specific value and the distance between the reversal point (24, 25) opposite to the direction of movement of the piston (4) exceeds a specific value.

12. A dual-action piston pump for conveying a flowable medium to an output device (5), wherein the piston pump (1) has a piston (4) that can move between a first reversal point (24) and a second reversal point (25) for conveying the flowable medium, wherein the piston pump (1) has a control mechanism for controlling the movement direction of the piston (4), wherein the control mechanism is designed to reverse the movement direction of the piston (4) when the corresponding reversal points (24, 25) are reached, wherein the piston pump (1) has a measuring mechanism for measuring the piston speed, wherein the control mechanism is designed to reverse the movement direction of the piston (4) when the speed value of the measured piston speed is lower than a specific speed value.

13. The dual-action piston pump according to claim 12, wherein the piston pump (1) has leakage with respect to the flowable medium to be conveyed and / or the piston pump (1) has a piston rod (6) which is designed to be leak-tight in the guide.

14. The double-acting piston pump according to claim 12, wherein the piston (4) is designed to be leak-tight relative to the cylinder and / or the piston pump (1) has a piston rod (6) designed to be leak-tight in a guide.

15. A dual-action piston pump according to claim 12, wherein the piston pump (1) has two non-return valves (7, 8), wherein, depending on the direction of movement of the piston (4), one of the non-return valves (7, 8) is open and the other of the non-return valves (7, 8) is closed.

16. The dual-action piston pump according to claim 12, wherein the piston pump (1) comprises two non-return valves (7, 8), wherein the non-return valves (7, 8) are designed differently.

17. A dual-action piston pump according to any one of claims 12 to 16, wherein the piston pump (1) has a measuring device for measuring the distance of the piston position (26) of the piston (4) from a reversal point (24, 25) located along the direction of movement of the piston (4), wherein the control device is designed to reverse the direction of movement of the piston (4) below a specific speed value of the measured piston speed and below a specific distance value of the measured distance, and / or The piston pump (1) has a measuring device for measuring the distance of the piston position (26) of the piston (4) from a reversal point (24, 25) located opposite to the movement direction of the piston (4), wherein the control device is designed to reverse the movement direction of the piston (4) when the speed value of the measured piston speed is lower than a specific speed value and the distance value of the measured distance is exceeded.

18. A dual-action piston pump according to any one of claims 12 to 16, wherein the piston pump (1) has one or more magnets, wherein the one or more magnets can move together 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 distance of the piston position (26) of the piston (4) from a reversal point (24, 25) located along the movement direction of the piston (4) has at least one Hall sensor (10), and / or the measuring device for measuring the distance of the piston position (26) of the piston (4) from a reversal point (24, 25) located opposite to the movement direction of the piston (4) has at least one Hall sensor (10).

19. A dual-action piston pump according to any one of claims 12 to 16, wherein the piston pump (1) has one or more annular magnets (9), wherein the one or more annular magnets (9) are movable together with the piston (4), wherein a measuring device for measuring the piston speed has at least one Hall sensor (10) and / or a measuring device for measuring the distance of the piston position (26) of the piston (4) from a reversal point (24, 25) located along the direction of movement of the piston (4) has at least one Hall sensor (10), and / or a measuring device for measuring the distance of the piston position (26) of the piston (4) from a reversal point (24, 25) located opposite to the direction of movement of the piston (4) has at least one Hall sensor (10).

20. A dual-action piston pump according to claim 18, wherein the piston pump (1) has at least two Hall sensors (10), wherein the distance of the piston (4) from one reversal point (24, 25) to the other reversal point (24, 25) is divided into at least two sections with respect to the measurement of the piston speed and / or the measurement of the piston position (26), wherein one of the at least two sensors (10) can be assigned to the corresponding section.

21. A dual-action piston pump according to claim 18, wherein the piston pump (1) has at least four Hall sensors (10), wherein the distance of the piston (4) from one reversal point (24, 25) to the other reversal point (24, 25) is divided into at least two sections with respect to the measurement of the piston speed and / or the measurement of the piston position (26), wherein one of the at least two sensors (10) can be assigned to the corresponding section, and for the Hall sensor (10) that can be assigned to the corresponding section, when the piston (4) is in the section assigned to this Hall sensor (10), there is an almost linear correlation between the magnetic flux density detected by this Hall sensor (10) and the piston position (26) of the piston (4).

22. A dual-acting piston pump according to any one of claims 12 to 16, wherein the piston pump (1) is constructed as a piston pump (1) that can be driven pneumatically, wherein the control mechanism has a controllable valve or a controllable valve device, wherein the direction of the pressure loading of the pneumatic piston (20) is changed when the valve or valve device is actuated, and wherein the pneumatic piston (20) is operatively connected to the piston (4).

23. A coating system for applying a flowable medium to a substrate (3), the coating system having a dual-acting piston pump (1) according to any one of claims 12 to 22 and having an output device (5), the output device being used to intermittently output the flowable medium delivered to the output device (5) by means of the dual-acting piston pump (1).

24. The coating system for applying a flowable medium to a substrate (3) according to claim 23, wherein: The flowable medium is a heated adhesive.

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