Piston Pump And Method For Determining Volume Delivered By Piston Pump

Abstract

A piston pump and a method for determining a volume V.sub.eff of a liquid medium delivered to a consumer by a double acting, pneumatically driven piston pump, wherein the piston pump is subject to leakage when a constant pressure is acting on a drive of the piston pump and at least one double stroke of a piston pump from one dead center position thereof to the other dead center position thereof and back to the first dead center position is carried out includes: a. without the piston pump being able to deliver the medium to the consumer, a leakage time t.sub.L auf for one stroke of the piston pump from the bottom dead center position thereof to the top dead center position thereof is measured, b. without the piston pump being able to deliver the medium to the consumer, a leakage time t.sub.L ab for one stroke of the piston pump from the top dead center position thereof to the bottom dead center position thereof is measured, c. a quotient of a volume of the medium V.sub.auf theoretically delivered by the piston pump without leakage and of the leakage time t.sub.L auf is determined for the stroke of the piston pump from the bottom dead center position to the top dead center position, d. a quotient of a volume V.sub.ab theoretically delivered by the piston pump without leakage and of the leakage time t.sub.L ab is determined for the stroke of the piston pump from the top dead center position to the bottom dead center position, e. the time t.sub.auf for the stroke of the piston pump from the bottom dead center position to the top dead center position and the time t.sub.ab for the stroke of the piston pump from the top dead center position to the bottom dead center position is measured as the medium is delivered to the consumer, f. the effectively delivered volume V.sub.eff is multiplied by the number of double strokes in accordance with

[00001]$V_{\mathrm{eff}}=\left(V_{\mathrm{auf}}-\frac{V_{\mathrm{auf}}}{t_{L.Math..Math.\mathrm{auf}}}{t}_{\mathrm{auf}}\right)+\left(V_{\mathrm{ab}}-\frac{V_{\mathrm{ab}}}{t_{L.Math..Math.\mathrm{ab}}}{t}_{\mathrm{ab}}\right).$

Claims

1. A method for determining a volume V.sub.eff of a liquid medium delivered to a consumer by a double acting, pneumatically driven piston pump, wherein the piston pump is subject to leakage when a constant pressure is acting on a drive of the piston pump and at least one double stroke of a piston pump from one dead center position thereof to the other dead center position thereof and back to the first dead center position is carried out, comprising: a. without the piston pump being able to deliver the medium to the consumer, a leakage time t.sub.L auf for one stroke of the piston pump from the bottom dead center position thereof to the top dead center position thereof is measured; b. without the piston pump being able to deliver the medium to the consumer, a leakage time t.sub.L ab for one stroke of the piston pump from the top dead center position thereof to the bottom dead center position thereof is measured; c. a quotient of a volume of the medium V.sub.auf theoretically delivered by the piston pump without leakage and of the leakage time t.sub.L auf is determined for the stroke of the piston pump from the bottom dead center position to the top dead center position; d. a quotient of a volume V.sub.ab theoretically delivered by the piston pump without leakage and of the leakage time t.sub.L ab is determined for the stroke of the piston pump from the top dead center position to the bottom dead center position; e. the time t.sub.auf for the stroke of the piston pump from the bottom dead center position to the top dead center position and the time t.sub.ab for the stroke of the piston pump from the top dead center position to the bottom dead center position is measured as the medium is delivered to the consumer; and f. the effectively delivered volume V.sub.eff is multiplied by the number of double strokes in accordance with $V_{\mathrm{eff}}=\left(V_{\mathrm{auf}}-\frac{V_{\mathrm{auf}}}{t_{L.Math..Math.\mathrm{auf}}}{t}_{\mathrm{auf}}\right)+\left(V_{\mathrm{ab}}-\frac{V_{\mathrm{ab}}}{t_{L.Math..Math.\mathrm{ab}}}{t}_{\mathrm{ab}}\right).$

2. The method as claimed in claim 1, wherein the volume V.sub.eff of the medium delivered is determined in terms of its mass m, and the density D of the medium is calculated in accordance with $D=\frac{m}{V_{\mathrm{eff}}}.$

3. The method as claimed in claim 2, wherein, as the medium is being delivered to the consumer, the delivered mass of the medium is calculated continuously by multiplying the calculated delivered volume V.sub.eff by the density D.

4. The method as claimed in claim 1, wherein the steps are repeated after each change of the temperature settings of the medium to be delivered to the consumer and/or after each change of the medium and/or after each change of the pressure acting on the drive of the piston pump.

5. The method as claimed in claim 1, wherein the leakage times t.sub.L auf and t.sub.L ab and/or a total leakage time t.sub.Leck are/is measured before the beginning of production.

6. The method as claimed in claim 1, wherein the leakage times and/or the densities are stored for each type of medium and temperature, for the purpose of use in subsequent production processes under comparable conditions without the need for redetermination.

7. The method as claimed in claim 1, wherein the leakage times t.sub.L auf and t.sub.L ab and/or a total leakage time t.sub.Leck thereof measured for the output pressure are/is corrected by means of a calculation model based on tests if there is a change in the pressure on the drive of the piston pump.

8. The method as claimed in claim 1, wherein a message relating to wear of the piston pump is output if a large deviation in a currently measured leakage time from a stored value of the leakage times is detected.

9. The method as claimed in claim 1, wherein reversal positions of a piston of the piston pump and/or intermediate positions of the piston between the reversal points thereof are detected by means of Hall effect sensors.

10. The method as claimed in claim 9, wherein the delivered volume and/or the delivered mass are/is calculated on the basis of a knowledge of the position of the piston.

11. A double acting, pneumatically drivable piston pump for carrying out the method as claimed in claim 1, having a piston configured in such a way that it does not form a seal with respect to a cylinder, having a piston rod configured in such a way that it does not form a seal with respect to a guide, and having two check valves, wherein one check valve is open and the other check valve is closed, depending on the direction of movement of the piston.

12. The piston pump as claimed in claim 11, wherein the check valves are of different designs.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0048] The invention is illustrated in the accompanying drawing figures by means of exemplary embodiments without being restricted thereto.

[0049] FIG. 1 shows an application unit for hot melt adhesive, having an adhesive tank and an adhesive pump installed in said tank.

[0050] FIG. 2 shows the adhesive pump shown in FIG. 1 in a sectional illustration, having an overflow channel.

[0051] FIG. 3 shows the illustration of the partial area of the piston pump during an upward piston stroke.

[0052] FIG. 4 shows the illustration of the partial area of the piston pump during a downward piston stroke.

[0053] FIG. 5 shows a diagram intended to illustrate the leakage behavior of the double acting, pneumatically driven piston pump as the piston moves from the bottom dead center position into the top dead center position and from the top dead center position into the bottom dead center position (leakage volume as a function of the stroke time).

[0054] FIG. 6 shows a diagram intended to illustrate the measured leakage times as a function of the pressure acting on the drive of the piston pump, illustrated for different heated adhesives, and thus different viscosities of the liquid medium, wherein curves are calculated from the measured points.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0055] FIG. 1 shows an adhesive tank 1 for holding a viscous hot melt adhesive, e.g. one based on EVA. Heating elements 2 of the adhesive tank 1 serve to heat up the adhesive, causing it to melt and allowing it to be brought to its processing temperature. A piston pump 3 is inserted into the adhesive tank 1 and secured thereto. The piston pump 3 is a double acting pump, and thus a pump which acts in both stroke directions of the piston. The piston pump 3 is driven pneumatically. Arranged in the inflow region of the adhesive from the adhesive tank 1 to the piston pump 3 there is a perforated plate 4 to retain incompletely melted solid adhesive. The adhesive passes through the holes in the perforated plate 4 into an intake chamber 5 for adhesive below the piston pump 3. From there, the adhesive is drawn into the piston pump 3 and discharged under pressure via a pressure port 6. Downstream of the pressure port 6 there is an adhesive filter 7. From there, adhesive passes into a pressure distributor 8 leading to outlets 9 for adhesive consumers. As used herein, the term consumers is intended to refer generically to adhesive application equipment that receives the adhesive, for example, an adhesive applicator module, adhesive dispenser, applicator nozzle or the like.

[0056] FIG. 2 shows the design of the piston pump 3. This has an upper pneumatic part having a piston 10 for the drive. The piston 10 is connected in a fixed manner to a piston rod 11, which forms the active element for delivering the adhesive under pressure. This pneumatic region of the piston pump 3 furthermore has a pressure distributor 36 for pneumatics for driving the pump, a manually adjustable pressure regulator 12, a manometer 13, a solenoid valve 14, an annular magnet 38 and a pressure sensor 39. The pressure sensor 39 is used to measure the air pressure P acting on the drive of the piston pump 3. The pressure sensor 39 is installed downstream of the pressure regulator 12. The pressure sensor 39 is required for automatic correction calculation in the case of a change in the air pressure P. Two Hall effect sensors 16, 17 are used to determine the piston position at the reversal points of the piston and the intermediate positions thereof. With the aid of the piston position, it is possible to calculate the volume delivered by the piston pump and the mass delivered, to increase the accuracy or resolution of the calculation.

[0057] An electronic system of the piston pump 3 furthermore has an electronic print 15 without a processor.

[0058] Outside the pneumatic part of the piston pump 3 and thus in the adhesive delivery region of the piston pump 3, this has a widened portion in the region of the end of the piston rod 11 remote from the piston 10, said widened portion forming a double acting piston 18. The piston 18 is provided with an axial passage 28, in the region of which the check valve 20 with associated valve seat is arranged. Furthermore, passage openings 30 for adhesive are provided at the transition of the piston 18 to the reduced-diameter region of the piston rod 11. The piston 18 is guided without forming a seal in a cylinder bore 22 formed in a housing 19 or cylinder of the adhesive delivery region. In this region, the piston pump 3 furthermore has an upper check valve 20 and a lower check valve 21. The lower check valve 21 is arranged in the intake chamber 5, with the result that adhesive can enter the adhesive delivery chamber of the piston pump 3 from the intake chamber 5, past the check valve 21, when the check valve 21 is in a defined position. If the upper check valve 20 is in a defined position, adhesive can pass the check valve 20 to the pressure port 6 and, from there, can reach the outlets 9 for the adhesive consumers.

[0059] A dynamic seal 33 is provided without differential pressure between the pneumatic part and the adhesive-delivering part of the piston pump 3.

[0060] FIG. 3 shows the situation as the piston 10 is transferred from the bottom dead center position to the top dead center position. Owing to the force and flow conditions, a ball 23 of the lower check valve 21 has risen from the ball seat thereof, and a ball 24 of the other check valve 20 is in contact with the ball seat associated with this ball 24. Consequently, adhesive can be drawn out of the adhesive tank 1 in the direction of the arrows 25 and passes through the check valve 21, which is in the open position, into the cylinder chamber of the adhesive delivery region of the piston pump 3, while, owing to the upward stroke movement of the piston 18, adhesive is discharged in accordance with arrows 35 through a laterally arranged pressure channel 34 and the pressure port 6 following the latter in the flow direction. During this upward movement of the piston 18, a leakage flow in accordance with the arrows 26 forms in the annular gap between the piston 18 and the housing 19 because of the non-sealing arrangement of the piston 18 and the wall interacting therewith in the region of the cylinder bore 22. In the outflowing region of the adhesive, leakage furthermore arises between the piston rod 11 and the housing 19 as illustrated by the arrows 27 into a chamber 31 of the housing 19 further up, in which ambient pressure prevails. This chamber 31 is connected to an overflow channel 29, which thus serves to allow the overflow of leakage between the piston rod 11 and the housing 19. This leakage is returned to the adhesive tank 1 via the overflow channel 29.

[0061] During the stroke of the piston rod 11 and hence of the pistons 10 and 18 from the bottom dead center position to the top dead center position, adhesive is thus simultaneously delivered to the outlets 9 and adhesive is drawn in from the adhesive tank 1. Leakage losses occur between the piston rod 11 and the housing 19 and between the piston 18 and the housing 19.

[0062] FIG. 4 illustrates the conditions during the movement of the piston rod 11 in the opposite direction and thus during the movement of the piston rod 11 and hence of the pistons 10 and 18 from the top dead center position to the bottom dead center position. During this process, only adhesive delivery occurs. No adhesive is drawn in from the adhesive tank 1. The adhesive flows upward through the passage 28 of the piston 18 in accordance with arrow 37, through the passage openings 30 into the annular chamber between the piston rod 11 and the housing 19 and, from there, through the pressure channel 34 to the outlets 9 in accordance with arrow 35. Leakage losses occur only between the piston rod 11 and the housing 19. The flow between the pistons 18 and the housing 19 has no effect on the quantity of adhesive delivered.

[0063] More specifically, the ball 23 is in its lower position on contact with the ball seat during this movement of the piston rod 11 from the top down, and therefore inflow from the adhesive tank 1 is not possible. The adhesive flows upward on the inside of the piston 18. The ball 24 of the upper check valve 20 is raised from the ball seat, with the result that adhesive is delivered to the pressure port 6 through the passage openings 30. Leakage in accordance with the arrows 27 occurs between the piston rod 11 and the housing 19 and thus between the pressure chamber and chamber 31, in which ambient pressure prevails.

[0064] Reference numeral 32 indicates a closure plug.

[0065] After each change in the temperature setting and after each change of adhesive, the following procedure is repeated in accordance with a preferred approach. In this case, the following process is carried out at constant pressure, which acts on the pneumatic drive of the piston pump. [0066] 1. Without the piston pump being able to supply adhesive to the consumer, the time t.sub.L auf for one complete stroke of the piston pump from the bottom dead center position to the top dead center position is measured. This time t.sub.L auf is referred to as the leakage time for the upward movement of the piston. [0067] 2. Without the piston pump being able to supply adhesive to the consumer, the time t.sub.L ab for one complete stroke of the piston pump from the top dead center position to the bottom dead center position is measured. This time t.sub.L ab is referred to as the leakage time for the downward movement of the piston. [0068] 3. The total leakage time t.sub.Leck for one complete double stroke of the piston is obtained by adding the two leakage times for the upward stroke t.sub.L auf and the downward stroke t.sub.L ab. [0069] 4. For the upward stroke, the ratio m.sub.auf of the volume delivered to the time for one complete stroke movement from the bottom dead center position to the top dead center position is determined. For this purpose, the volume V.sub.auf theoretically delivered without leakage is divided by the leakage time t.sub.L auf. [0070] 5. For the downward stroke, the ratio m.sub.ab of the volume delivered to the time for one complete stroke movement from the top dead center position to the bottom dead center position is determined. For this purpose, the volume V.sub.ab theoretically delivered without leakage is divided by the leakage time t.sub.L ab. [0071] 6. During operation and thus during the delivery of the medium to the consumer, the elapsed time is measured for each complete stroke movement of the piston pump. For the stroke from the bottom dead center position to the top dead center position, the time t.sub.auf is determined. For the stroke from the top dead center position to the bottom dead center position, the time t.sub.ab is determined. [0072] 7. The effectively delivered volume V.sub.eff is calculated by subtracting the ratio m.sub.auf multiplied by the time t.sub.auf from the theoretical delivery volume V.sub.auf for each upward stroke and by subtracting the ratio m.sub.ab multiplied by the time t.sub.ab from the theoretical delivery volume V.sub.ab for each downward stroke. [0073] 8. During any time period t, adhesive is delivered and collected in a collecting container. During this time period t, the effectively delivered adhesive volume V.sub.eff is calculated in accordance with the above method. The mass m of adhesive collected is measured on a balance. From this, the density D is determined by dividing the mass m delivered by the effectively delivered volume V.sub.eff. [0074] 9. During the operation of the piston pump, the mass delivered is calculated continuously by multiplying the volume V.sub.eff calculated in accordance with the above method by the density D.

[0075] It is possible to store the values determined from the calibration procedures in a data matrix relative to the temperature settings, the type of adhesive and the viscosity of the adhesive to avoid the need to carry out a recalibration process after each change.

[0076] FIG. 5 shows how the leakage time for the double stroke is divided between the time for the upward stroke and the time for the downward stroke in the case of the piston pump used. The times for the two stroke movements are different in magnitude. The effectively delivered volume for each stroke direction can be calculated in a simple manner by means of linear relationships, using these two times. In the left-hand, steeper graph, FIG. 5 shows the measurement points for the upward movement of the piston. For the movement from the bottom dead center position to the top dead center position, the piston requires about 5 seconds at a leakage volume of somewhat more than forty units. For the movement from the top dead center position to the bottom dead center position, a significantly longer time is required, namely almost 30 seconds, as illustrated by the measurement points situated along the less steeply sloping line.

[0077] FIG. 6 shows various curves for measurements when using adhesives of different viscosities, wherein each curve signifies one viscosity. The lowermost curve illustrates the conditions at the lowest viscosity, and the respective curves situated above it illustrate adhesives of higher viscosity. For each curve, the leakage time is indicated in seconds as a function of the pressure P acting on the piston 10 of the drive. The points shown in FIG. 6 are measured, while the curves are calculated.

[0078] Taking into account the above steps 1 to 9, a calculation model can be used when the pressure P acting on the piston pump is changed. The calculation process compensates the effect of the pressure P on the quantity of adhesive delivered. For this purpose, the measured leakage times t.sub.L auf and t.sub.L ab are corrected. The new corrected leakage times, in turn, are used as input values for the above calculation method. The calculation model can be developed on the basis of a large number of tests and is tailored to a particular piston pump. Different specific values apply for other pumps.

[0079] The mass of adhesive is thus determined in two steps. First of all, the calculated leakage is used to determine the volume of adhesive delivered per unit time and the number of products processed. In a second step, the mass is determined with a previously determined density of the adhesive. It is thus necessary to determine information on the leakage and density before the mass delivered can be calculated. This approach enables the user to know the mass of adhesive applied per product.