Method for operating double-acting piston pump of application system

Abstract

A method for operating a double-action piston pump of an application system for applying a fluid medium to a substrate, wherein the piston pump has a piston which is movable between a first reversal point and a second reversal point for delivering the fluid medium, wherein on reaching the first reversal point and the second reversal point, the movement direction of the piston is reversed, wherein during an output period, the fluid medium is output by means of an output device, and during an interruption period, an output of the fluid medium by means of the output device is interrupted, wherein during the interruption period, the movement direction of the piston is reversed, wherein on reversal of the movement direction during the interruption period, the piston is situated at an intermediate position between the first reversal point and the second reversal point.

Claims

1. A method for operating a double-action piston pump of an application system for applying a fluid medium to a substrate, wherein the piston pump has a piston which is movable between a first reversal point and a second reversal point for delivering the fluid medium, wherein on reaching the respective reversal point, a movement direction of the piston is reversed, wherein the application system has an output device for intermittent output of the fluid medium delivered by means of the piston pump to the output device, wherein during an output period, the fluid medium is output by means of the output device and during an interruption period, an output of the fluid medium by means of the output device is interrupted, wherein during at least one interruption period, the movement direction of the piston is reversed, wherein on the reversal of movement direction during the at least one interruption period, the piston is situated at an intermediate position between the first reversal point and the second reversal point.

2. The method as claimed in claim 1, wherein the reversal of the movement direction of the piston takes place exclusively during the interruption period.

3. The method as claimed in claim 1, wherein a number of reversals of the movement direction, which take place at intermediate positions of the piston between the first reversal point and the second reversal point, is greater than a number of reversals of the movement direction which take place at the first and second reversal points.

4. The method as claimed in claim 1, wherein during the interruption period, a piston speed of the piston is reduced in comparison with a piston speed during the output period.

5. The method as claimed in claim 1, wherein a piston speed is measured and the movement direction of the piston is reversed if the piston speed is less than or equal to a specific speed value.

6. The method as claimed in claim 1, wherein a distance of the piston from the first reversal point or the second reversal point lying in the movement direction of the piston is determined, wherein a reversal of the movement direction of the piston during the interruption period takes place before reaching the first reversal point or the second reversal point lying in the movement direction of the piston if the distance of the piston from the first reversal point or the second reversal point lying in the movement direction of the piston is less than a specific distance value.

7. The method as claimed in claim 1, wherein a distance of the piston from the first reversal point or the second reversal point lying opposite the movement direction of the piston is determined, wherein a reversal of the movement direction of the piston during the interruption period takes place before reaching the first reversal point or the second reversal point lying in the movement direction of the piston if the distance of the piston from the first reversal point or the second reversal point lying opposite the movement direction of the piston exceeds a specific distance value.

8. The method as claimed in claim 1, wherein a piston speed is measured and a distance of the piston from the first reversal point or the second reversal point lying in the movement direction of the piston is determined, wherein the movement direction of the piston is reversed if the piston speed is less than a specific speed value and the distance of the piston from the first reversal point or the second reversal point lying in the movement direction of the piston is less than a specific distance value.

9. The method as claimed in claim 1, wherein a piston speed is measured and a distance of the piston from the first reversal point or the second reversal point lying opposite the movement direction of the piston is determined, wherein the movement direction of the piston is reversed if the piston speed is less than a specific speed value and the distance of the piston from the first reversal point or the second reversal point lying opposite the movement direction of the piston exceeds a specific distance value.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) In the figures which follow, the invention is explained in more detail with reference to one or more exemplary embodiments, without being restricted thereto.

(2) FIG. 1 shows an application system for applying a fluid medium, having a double-action piston pump and an output device.

(3) FIG. 2 shows the piston pump from FIG. 1 with a piston at a first reversal point.

(4) FIG. 3 shows the piston pump from FIG. 1 with the piston at an intermediate position.

(5) FIG. 4 shows the piston pump from FIG. 1 with the piston at a second reversal point.

(6) FIG. 5 is a diagram to illustrate a temporal development of a piston position of a piston pump, an output quantity of the fluid medium per time unit and a schematic illustration of the resulting application bead, of a piston pump or a method for operating the piston pump in which a reversal of the movement direction of the piston takes place exclusively at fixed reversal points.

(7) FIG. 6 is a diagram to illustrate the temporal development of the piston position, the output quantity of the fluid medium per time unit and a schematic illustration of the resulting application bead, in a piston pump according to the invention or with a method according to the invention for operating a piston pump.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

(8) FIG. 1 shows an application system 2 for application of a fluid medium, in the present case a heated adhesive, to a substrate 3. The substrate 3 may for example be a paper sheet or cardboard sheet. The application system 2 has a double-action piston pump 1. Since this is a double-action piston pump 1, the piston pump 1 is active in both stroke directions of the piston 4. By means of the piston pump 1, the fluid medium is delivered from a storage device (not shown), which can be connected to the piston pump 1, to an output device 5. The output device 5 is fluidically connected to the piston pump 1, namely to a cylinder bore 12 of the piston pump, by means of a heating hose 11. During operation of the piston pump, the adhesive is conducted from the storage container to an intake chamber 13 for adhesive. From there, the adhesive is drawn into the cylinder bore 12 and delivered to the output device 5 under pressure via a pressure port 14 which is connected to the heating hose 11.

(9) In the present case, the output device 5 is suitable for intermittent output of the adhesive delivered to the output device 5, so that during output periods, adhesive is output by means of the output device 5, and during interruption periods, an output of the adhesive by means of the output device 5 is interrupted. This is advantageous for example if, as shown schematically in FIG. 1, the adhesive is to be applied to substrates 3 which are arranged spaced apart from one another on a conveyor belt 15 and moved, in particular continuously, by means of this conveyor belt 15 in the direction of the arrow 16 past the output device 5, wherein the output device 5 in each case applies an adhesive bead 17 to the respective substrate 3. To guarantee a clean application of adhesive to the substrate 3, it is useful to interrupt the output of adhesive by means of the output device 5 from time to time, in particular at times at which no substrate 3 is arranged below the output device 5.

(10) The piston 4 of the piston pump 1 is movable between a first reversal point 24 and a second reversal point 25 (see FIG. 5 and FIG. 6). The movement direction of the piston 4 is reversed on reaching the respective reversal point 24, 25. On a reversal of the movement direction of the piston 4, there is a temporally limited fall in the pressure of the delivered adhesive. If adhesive is output by means of the output device 5 during this limited period, this pressure fall has a negative effect on the output quantity of the adhesive and hence a negative effect on the so-called application pattern. During the changeover process of the piston pump 1 and hence during the fall in adhesive pressure, there is a significantly smaller application of adhesive 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 changeover processes of the piston pump 4 on the output quantity of adhesive per time unit 23 and on the adhesive pattern or adhesive bead 17, are evident from FIG. 5.

(11) Usually, the movement direction of the piston 4 in a piston pump 1 or in the methods for operating a piston pump 1 as known from the prior art, changes always and exclusively 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, the changeover process is initiated and then a complete stroke is carried out in the opposite direction as far as the respective other reversal point of the reversal points 24, 25. Usually, activation of the changeover process and hence the reversal of the movement direction of the piston 4 takes place purely mechanically or by actuation of an electrical or electronic switch. There is no temporal coordination of the process of changing the movement direction of the piston 4 of the piston pump 1 with the output periods and interruption periods of the adhesive application.

(12) In the exemplary embodiment according to the invention as shown in FIG. 6, it is provided that the movement direction of the piston 4 is reversed exclusively during the interruption periods. The temporal development of the piston position 26 and the output quantity of the adhesive per time unit 23 are depicted schematically in FIG. 6. It is clear from a comparison of FIG. 5 and FIG. 6 that, in FIG. 6, there is no fall in output quantity of adhesive per time unit 23 during the output periods, since the movement direction of the piston 4 is reversed exclusively during the interruption periods. Accordingly, the adhesive beads 17 shown in FIG. 6, in contrast to the adhesive beads 17 shown in FIG. 5, have no constrictions 18.

(13) As also evident from FIG. 6, on a reversal of the movement direction, the piston 4 is each time at an intermediate position between the first reversal point 24 and the second reversal point 25, wherein the intermediate positions are different.

(14) As also evident in FIG. 6, an output quantity of the adhesive output by means of the output device 5 during the respective output period is smaller than a delivery quantity of the medium delivered to the output device 5 by means of the piston pump 1 on a piston stroke of the piston 4 from the one reversal point 24, 25 to the other reversal point 24, 25.

(15) The piston pump 1 shown in FIGS. 1 to 4 is a piston pump 1 which has leakages with respect to the adhesive to be delivered, so that during the interruption periods, a piston speed of the piston 4 is reduced in comparison with a piston speed during the output periods. This is also evident from the temporal development of the piston position 26 of the piston 4, as shown in FIG. 5 and FIG. 6. The leakage is achieved in that the piston 4 is not designed to seal with respect to a cylinder bore 12, wherein the cylinder bore 12 is made in a housing 19 of the piston pump 1.

(16) The piston pump 1 has an upper pneumatic part with a pneumatic piston 20 for its drive. The pneumatic piston 20 is fixedly connected to a piston rod 6 which is in turn connected to the piston 4 serving for delivery of the adhesive. In the pneumatic region of the piston pump 1, furthermore a ring magnet 9 is connected to the pneumatic piston 20 and hence to the piston rod 6. Furthermore, an electronic printed circuit board 21 is arranged next to the pneumatic piston 20 or ring magnet 9, wherein three Hall sensors 10 are connected to the electronic printed circuit board 21. The Hall sensors 10 are configured such that they measure the magnetic flux density in the horizontal direction. On a travel of the pneumatic piston 20 or piston 4, which are connected together by means of the piston rod 6, the ring magnet 9 moves correspondingly to the movement of the piston rod 6, so because of the change in position of the ring magnet 9, the magnetic flux density detected by the respective Hall sensor 10 also changes. By means of the output signals from the Hall sensors 10, the piston position 26 and the piston speed can thus be determined. Furthermore, the movement direction of the piston 4 or pneumatic piston 20 can also be determined.

(17) In principle, the piston position 26, the piston speed and also the movement direction of the piston 4 can be determined by means of a single Hall sensor 10. Preferably however, at least three Hall sensors 10 are used, since this firstly increases the accuracy and secondly raises the redundancy level, thus increasing the security against failure and the function and operating reliability of the piston pump 1.

(18) Outside the pneumatic part of the piston pump 1, i.e. in the adhesive delivery region of the piston pump 1, this has a widening in the region of the end of the piston rod 6 facing away from the pneumatic piston 20, forming the double-action piston 4.

(19) The piston 4 has an axial passage, in the region of which a check valve 7 with associated valve seat is arranged. The piston 4 is guided without sealing in the cylinder bore 12 formed on the housing 19. A second check valve 8 is formed in the cylinder bore 12. The check valve 8 is assigned to the intake chamber 13, so that adhesive from the intake chamber 13 can enter the adhesive delivery chamber of the piston pump 1 when the check valve 8 is in a defined position. If the check valve 7 is in a defined position, adhesive can be delivered to the pressure port 14 and from there reach the output device 5 via the heating hose 11.

(20) A dynamic seal 22 without differential pressure is provided between the pneumatic part and the adhesive delivery part of the piston pump 1.

(21) On a travel of the piston rod 6 from the first reversal point 24 in the direction of the second reversal point 25, at the same time adhesive is delivered to the output device 5 and adhesive is drawn in to the intake chamber 13 from the storage container (not shown). Leakage losses occur between the piston rod 6 and the housing 19, and between the piston 4 and the housing 19. On travel of the piston rod 6 in the opposite direction, i.e. on movement of the piston rod 6 from the second reversal point 25 in the direction of the first reversal point 24, no adhesive is drawn in but adhesive is merely delivered to the output device 5.

(22) The piston pump 1 furthermore has a control device for controlling the movement direction of the piston 4, wherein the control device is configured to reverse the movement direction of the piston 4 on reaching the first reversal point 24 and the second reversal point 25. The piston pump 1 furthermore has a measuring device for measuring the piston speed, wherein the control device is configured to reverse the movement direction of the piston 4 if the measured piston speed is less than a specific speed value. Furthermore, the piston pump 1 has a measuring device for measuring a distance of the piston position 26 of the piston 4 from the reversal point lying in the movement direction of the piston 4. The Hall sensors 10 here form constituents of the measuring device for measuring the piston speed, the piston position 26, the distance and the movement direction of the piston 4. The control device is configured to reverse the movement direction of the piston 4 if the measured piston speed is less than a specific speed value, and the measured distance is less than a specific distance value. Such a design of the piston pump 1 has the advantage that the process of changing the movement direction of the piston 4 may take place solely from knowledge of the internal measurement data or measurement values of the piston pump 1. It is therefore not necessary to detect data on the state of the output device 5 and transmit this to the control device of the piston pump 1. The piston pump 1 may thus be used completely independently of the actual output device 5 used, and execute the method described above. Thus the piston pump 1 can be used universally. In particular, existing application systems 2 may be upgraded by replacement of the piston pump 1, so that these application systems 2 can execute the method described above.