Piston membrane pump for pumping a liquid

Abstract

A piston membrane pump (100) for pumping a liquid, comprising: housing (101) with a chamber (106) having an inlet (107) and outlet (108); a piston (102) in the housing, reciprocating along a longitudinal axis (111) to pump liquid by changing the chamber's volume; a membrane element (103a) sealing the piston (102) to the housing 5 (101); and an actuator (104) driving the piston (102) between a rear (R1) and front end position (F1); and a control unit (105) configured to: control the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of multiple, different sets of end positions (R1,F1; R2,F2; Rn,Fn) for the piston along the longitudinal axis, wherein each set of end positions comprises a rear end position (R1-10 Rn) and a front end position (F1-Fn) where the distance (L) between the rear end position and the front end position of each set corresponds to a predetermined, full stroke length (L) of the piston. 1 15

Description

[0001] PISTON MEMBRANE PUMP FOR PUMPING A LIQUID

[0002] Technical Field

[0003] The invention relates to a piston membrane pump for pumping a liquid. The invention also relates to a filling machine, and to method of controlling a piston membrane pump.

[0004] Background

[0005] A known piston membrane pump for pumping a liquid comprises a housing defining a chamber. The chamber has an inlet and an outlet for the liquid. The known piston membrane pump further comprises a piston arranged within the housing. The piston is configured to reciprocate along a longitudinal axis to pump the liquid through the inlet and the outlet by repeatedly decreasing and increasing the volume of the chamber. The known piston membrane pump further comprises a membrane element connected to both the piston and the housing. The membrane element forms a seal between the piston and the housing. The known piston membrane pump further comprises an actuator operatively connected to the piston to drive the reciprocating motion of the piston between a rear end position and a front end position along the longitudinal axis.

[0006] Summary

[0007] In the piston membrane pump, after start-up, the actuator drives the reciprocating motion of the piston between the same rear end position and the same front end position along the longitudinal axis throughout operation of the pump. It has been found that this may cause stress on the regions of the membrane element that “bend” or turn” when the piston is in the end positions, as will be explained in detail further on. This stress can eventually lead to a rupture of the membrane element. Every time a rupture occurs, for example, in a filling machine that comprises the piston membrane pump, the machine needs to be cleaned and sterilized, which can take a significant amount of time.

[0008] It is an object of the invention to at least partly overcome one or more of the above-identified limitations of the piston membrane pump. In particular, it is an object to achieve fewer ruptures of the membrane element of the piston membrane pump.

[0009] To solve these objects, according to a first aspect, a piston membrane pump for pumping a liquid is provided. The piston membrane pump comprises a housing defining a chamber, the chamber having an inlet and an outlet for the liquid; a piston arranged within the housing and configured to reciprocate along a longitudinal axis to pump the liquid through the inlet and the outlet by repeatedly decreasing and increasing the volume of the chamber; a membrane element connected to both the piston and the housing, forming a seal between the piston and the housing; an actuator operatively connected to the piston to drive the reciprocating motion of the piston between a rear end position and a front end position along the longitudinal axis; and a control unit configured to: control the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of multiple, different sets of end positions for the piston along the longitudinal axis, wherein each set of end positions comprises a rear end position and a front end position where the distance between the rear end position and the front end position of each set corresponds to a predetermined, full stroke length of the piston. For the multiple, different sets of end positions, the distance between the rear end position and the front end position (the full stroke length) may thus be the same for each set in the different sets. It may be said that each set of end positions comprises a rear end position and a front end position where the distance between the rear end position and the front end position of each set corresponds to the same, predetermined, full stroke length of the piston. It may also be said that each set of end positions may define the same predetermined full stroke length, even though the rear and front end positions in the respective set vary along the longitudinal axis.

[0010] By controlling the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of multiple, different sets of end positions for the piston along the longitudinal axis, the stress on the membrane element is not always applied to the same region of the membrane element throughout operation of the piston membrane pump, which in turn will make the membrane element less prone to ruptures. In other words, stress fractures on the membrane element may be decreased, and / or the lifetime of the membrane element may be extended. Moreover, since the distance between the rear end position and the front end position of each set corresponds to a predetermined, full stroke length of the piston, the filling volume of the liquid may remain constant regardless of which set is used.

[0011] In further detail, it has been observed that the operational lifetime of the membrane is significantly extended by using the described piston membrane pump. Specifically, because the membrane is connected to the piston, it follows the reciprocating motion of the piston as it moves between the rear end and front end positions of each set of end positions. During this motion, the membrane undergoes continuous “folding” or “bending”. This folding or bending propagates along a length of the membrane as the piston reciprocates, and the direction of the folding or bending changes at the respective end positions.

[0012] It has been found that the membrane is subjected to the highest levels of mechanical stress at the regions of the membrane where the folding or bending changes direction. This stress may be referred to as “end region stress”. By utilizing multiple, different sets of end positions for the piston, the regions of the membrane experiencing those high stress levels (end region stress) are shifted, thus distributing the mechanical load across different sections of the membrane. As a result, this distribution of end region stress reduces premature membrane fatigue and rupture, resulting in an increased operational lifetime of the membrane. The different points in time may be determined by predetermined time intervals and / or receiving a signal indicative of an interruption in an operational cycle of the piston membrane pump.

[0013] The multiple, different sets of end positions may differ from each other by their respective set of end positions shifted by an offset distance value along the longitudinal axis. The offset distance value may for example be in the range of 2 mm to 10 mm

[0014] The control unit may be configured to: record a value representing the number of reciprocating motions the actuator drives the piston at each of the respective different sets of end positions. The recorded value may be used to ensure that the sets of end positions are evenly utilized, effectively distributing the end region stress across different sections of the membrane element.

[0015] The control unit may be configured to: distribute the number of reciprocating motions evenly across the multiple, different sets of end positions. In this way, stress may be distributed equally in different positions on the membrane element. “Evenly” may be defined as at most ± 25% difference between the sets, over a given time or a given total number of reciprocating motions.

[0016] The control unit may be configured to: (control the actuator to) set the piston in a reset position, defined by an abutment surface of the housing that prevents further movement of the piston in one direction of the longitudinal axis, before controlling the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of said multiple, different sets of end positions. The control unit may for example be configured to set the piston in the reset position at start-up.

[0017] The membrane element may comprise, between its connection points to the housing and the piston, a 180-degree fold that moves along a length of the membrane element when the piston reciprocates between the rear end position and the front end position. The membrane element may be connected to a first end of the piston, wherein the piston membrane pump further comprises: a further membrane element connected to both the piston and the housing, at a second end of the piston opposite the first end, forming an additional seal between the piston and the housing, such that a sealed space is formed between the housing, the piston and the membranes; and a vacuum connection leading to the sealed space.

[0018] The housing may comprise: a first end section that comprises the inlet and the outlet; a second end section configured to accommodate a coupling arrangement to couple the piston to the actuator; and an intermediate section connected to both end sections, thereby forming a hollow space that accommodates the piston. The membrane element may be attached to the housing via a flange located at the connection between the first end section and the intermediate section. The further membrane element may be attached to the housing via a flange located at the connection between the second end section and the intermediate section.

[0019] The inlet may be arranged to cooperate with an inlet valve, and the outlet may be arranged to cooperate with an outlet valve, such that liquid is pumped through the housing when the actuator drives the piston.

[0020] The control unit may be configured to transmit a control signal to the inlet valve to set it in an open state when the actuator is controlled to switch between different sets of end positions used to drive the piston.

[0021] This control signal transmission is done because, when the end positions are shifted (either to the left or right), the volume in the pump chamber changes accordingly. As the volume changes, liquid either escape from the chamber (if the volume decreases) or enter into the chamber (if the volume increases) to maintain proper operation. Opening the inlet valve allows the system to effectively accommodate this shift in volume, ensuring a smooth transition between different sets of end positions without creating pressure imbalances or operational inefficiencies.

[0022] The control unit may be configured to: control the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of said multiple, different sets of end positions such that the rear and front end positions first monotonically increase over time and then monotonically decrease over time. That the rear and front end positions increase / decrease may for example mean that the actuator is being more / less extended. As used herein, "monotonically increase over time and then monotonically decrease over time" means that the rear and front end positions are consistently shifted in a first direction during a first period of time, and then, during a subsequent second period of time, are consistently shifted in a second, opposite direction, without any reversal to the first direction during the second period of time.

[0023] According to a second aspect, there is provided a filling machine for filling liquid product in packages, wherein the liquid is dispensed by pumping with a piston membrane pump according to the first aspect. The same features and advantages presented above with respect to the first aspect also apply for this second aspect.

[0024] According to a third aspect, there is provided a method of controlling a piston membrane pump, the piston membrane pump comprising: a housing defining a chamber with an inlet and an outlet for the liquid; a piston configured to reciprocate along a longitudinal axis to pump the liquid by changing the volume of the chamber; a membrane element forming a seal between the piston and the housing; and an actuator operatively connected to the piston to drive its reciprocating motion, the method comprising: controlling the actuator to drive the reciprocating motion of the piston by using, at different points in time, each of multiple, different sets of end positions for the piston along the longitudinal axis, wherein each set of end positions comprises a rear end position and a front end position where the distance between the rear end position and the front end position of each set corresponds to a predetermined, full stroke length of the piston. The same features and advantages presented above with respect to the first aspect also apply for this third aspect.

[0025] Still other objectives, features, aspects and advantages of the invention will appear from the following detailed description as well as from the drawings.

[0026] Drawings

[0027] Embodiments of the invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which

[0028] Fig. 1 is a side view of a piston membrane pump.

[0029] Figs. 2a-b illustrate a piston membrane pump with the piston in a rear end position and a front end position, respectively.

[0030] Figs. 3a-b illustrate a piston membrane pump with the piston in a different rear end position and front end position, respectively.

[0031] Fig. 4 is a flowchart of a method of controlling a piston membrane pump.

[0032] Fig. 5 is a schematic view of a filling machine.

[0033] With reference to Fig. 1 a piston membrane pump 100 for pumping a liquid is illustrated. The pump 100 could also be referred to as a volumetric fill pump. The liquid may for example be dairy and non-dairy beverages such as milk, including ultra-high temperature (UHT) treated milk, plant-based milk alternatives (such as almond, soy, and oat milk), and fruit juices. Other examples of liquid are broths, soups, cooking creams, whipping creams, coconut water, pre-mixed smoothies, protein shakes, nectar drinks, and wines. The piston membrane pump 100 comprises a housing 101 , a piston 102, a membrane element 103a, an actuator 104, and a control unit 105. Parts of the piston membrane pump 100 are also illustrated in Figs. 2a-b and 3a-b.

[0034] The housing 101 defines a chamber 106. The chamber 106 may have an inlet 107 and an outlet 108 for the liquid. The inlet 107 and outlet 108 may be arranged (and aligned) along a vertical axis 109. The inlet 107 may be arranged above the outlet 108. The inlet 107 and the outlet 108 may be comprised in a first end section 101a of the housing 101. The housing 101 may further comprise a second end section 101 b and an intermediate section 101c.

[0035] The piston 102 is arranged within the housing 101. Moreover, the piston 102 is configured to reciprocate, as schematically indicated by arrow 110, along a longitudinal axis 111 to pump the liquid through the inlet 107 and the outlet 108 by repeatedly decreasing and increasing the volume of the chamber 106. Specifically, liquid may be drawn in through the inlet 107 when the piston 102 moves to the left in Fig. 1 , and liquid may be pushed out through the outlet 108 when the piston 102 is moved to the right in Fig .1 . The longitudinal axis 111 may be horizontal.

[0036] The piston 102 may have a (generally) cylindrical shape. The piston 102 may have a first (base) end 102a and a second (base) end 102b opposite the first end 102a. The first end 102a of the piston 102 may face the chamber 106 of the housing 101. The piston 102 may be hollow.

[0037] The aforementioned intermediate section 101c of the housing 101 may be mechanically connected to the first end section 101a and the section end section 101 b, thereby forming a hollow space 112 that accommodates the piston 102. The intermediate section 101c may be a cylinder. Centering plugs 113 may serve to center the piston 102 with respect to the intermediate section 101 c of the housing 101.

[0038] The membrane element 103a is connected to both the piston 102 and the housing 101 , forming a seal between the piston 102 and the housing 101. The membrane element 103a may be connected to the first end 102a of the piston 102. The membrane element 103a may for example be connected to (the first end 102a of) the piston 102 by vacuum suction. The membrane element 103a may be connected or attached to the housing 101 via a flange 114a (of the membrane element 103a) located at the connection between the first end section 101a and the intermediate section 101c of the housing 101.

[0039] The membrane element 103a may comprise, between its connection points to the housing 101 and the piston 102, a 180-degree fold 115a (see Fig. 2a). The connection point to the housing 101 may be the aforementioned flange 114a. A connection point 116 to the piston 102 may for example be at an opening 117 in the first end 102a of the piston 102 where the membrane element 103a is connected by vacuum suction. The 180-degree fold 115a may move along a length L2 of the membrane element 103a when the piston 102 reciprocates.

[0040] The membrane element 103a in the piston membrane pump 100 may generally be shaped as a cylindrical bucket with the “bottom” folded up towards and sometimes beyond the flange 114a. The membrane element 103a may be made of any suitable and commonly available food grade elastomeric material. Some examples include silicone rubber, ethylene propylene diene monomer, nitrile rubber and thermoplastic elastomers. The membrane element 103a may also be referred to as a diaphragm 103a. The membrane element 103a may be a first membrane element 103a.

[0041] The actuator 104 is operatively connected to the piston 102 to drive the reciprocating motion of the piston 102 generally between a rear end position (such as rear end position R1) and a front end position (such as front end position F1) along the longitudinal axis 111. The rear end position could also be referred to as a first position. The front end position could also be referred to as a second position. The rear and front end positions such as R1 ,F1 may for example be illustrated (and / or defined) with reference to the first end 102a of the piston 102, as in Figs. 2a-b and 3a-b.

[0042] The actuator 104 may be a linear actuator. The actuator 104 may for example comprise a servo motor. The aforementioned second end section 101b of the housing 101 may be configured to accommodate a coupling arrangement 118 to couple (the second end 102b of) the piston 102 to the actuator 104.

[0043] The piston membrane pump 100 may further comprise a further membrane element 103b. The further membrane element 103b will in the following be referred to as a second membrane element 103b.

[0044] The second membrane element 103b may be connected to both the piston 102 and the housing 101 , at the second end 102b of the piston 102, forming an additional seal between the piston 102 and the housing 101 , such that a sealed space 119 is formed between the housing 101 , the piston 102 and the first and second membrane elements 103a-b. The second membrane element 103b may be connected or attached to the housing 101 via a flange 114b (of the second membrane element 103b) located at the connection between the second end section 101 b and the intermediate section 101c of the housing 101.

[0045] The second membrane element 103b may comprise, between its connection points to the housing 101 and the piston 102, a 180-degree fold 115b. The connection point to the housing 101 may be the aforementioned flange 114b. A connection point to the piston 102 may for example be at a clamp 120 mechanically connecting the second membrane element 103b to the second end 102b of the piston 102.

[0046] The second membrane element 103b in the piston membrane pump 100 may generally be shaped as a cylindrical bucket with the “bottom” folded up towards and sometimes beyond the flange 114b, wherein the bottom has a central aperture for the coupling arrangement 118. The second membrane element 103b may be made of the same type of material as the first membrane element 103 is made ofa. The second membrane element 103b may also be referred to as a second diaphragm 103b.

[0047] The piston membrane pump 100 may have a vacuum connection 121 leading to the aforementioned sealed space 119. The vacuum connection 120 may comprise a non-return valve 122. A vacuum generating unit (not shown) is connected to the vacuum connection 121 to create a vacuum, or sub-atmospheric pressure, in the sealed space 119. The piston 102, which in the illustrated embodiment is hollow, contains an internal cavity 140, with openings 141 that lead from the sealed space 119 to the internal cavity 140. Additionally, the piston 102 has several openings, such as opening 117, that lead from the internal cavity 140 to the first end 102a of the piston 102, where the membrane element 103a is connected. Thus, by applying vacuum to the vacuum connection 121 , the membrane element 103a is held in place on the first end 102a of the piston 102 by vacuum suction.

[0048] The piston membrane pump 100 may further comprise an inlet valve 123 and an outlet valve 124. The piston 102 cooperates with the inlet valve 123 and the outlet valve 124, which may be check valves, to pump liquid through the housing 101. During the piston’s suction stroke, as the piston 102 moves away from the chamber 106, the inlet valve 123 opens to allow liquid to enter the chamber 106 while the outlet valve 124 remains closed, preventing backflow. During the discharge stroke, as the piston 102 moves toward the chamber 106, the inlet valve 123 closes to prevent backflow, and the outlet valve 124 opens, allowing the liquid to be expelled through the outlet 108. This alternating action of the inlet valve 123 and outlet valve 124 ensures unidirectional flow of liquid through the housing 101 during the reciprocating motion of the piston 102. This operation is previously known per se. The piston membrane pump 100 may further comprise one or more of: an fluid reservoir 125 for the actuator 104, a shaft seal 126, and leveling adjustment 127.

[0049] Turning to the control unit 105, the control unit 105 is configured to control the actuator 104. To this end, the control unit 105 may be connected to the actuator 104, e.g. via a wired or wireless connection 130. The control unit 105 may i.a. comprise processing circuitry 131 for controlling the actuator 104.

[0050] The control unit 105 may or may not be part of the membrane pump 100. The control unit 105 may be implemented by hardware or a combination of software and hardware. In the illustrated example, the control unit 105 comprises the processor circuitry 131 , a computer memory (memory or data storage) 132 and a signal interface. The processor circuitry 131 may, for example include one or more of a CPU ("Central Processing Unit"), a DSP ("Digital Signal Processor"), a microprocessor, a microcontroller, an ASIC ("Application-Specific Integrated Circuit"), a combination of discrete analog and / or digital components, or some other programmable logical device, such as an FPGA ("Field Programmable Gate Array"). A control program comprising computer instructions may be stored in the computer memory 132 and executed by the processor circuitry 131 to perform methods and procedures as described in herein. The control program may be supplied to the control unit 102 on a computer-readable medium, which may be a tangible (non-transitory) product (e.g. magnetic medium, optical disk, read-only memory, flash memory, etc.) or a propagating signal. The signal interface may be configured in accordance with conventional practice to receive input signals and provide output signals.

[0051] Specifically, the control unit 105 is configured to control the actuator 104 to drive the reciprocating motion of the piston 102 by using, at different points in time, each of multiple, different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn for the piston 102 along the longitudinal axis 111. Each set of end positions comprises a rear end position R1 - Rn and a front end position F1 - Fn, where the distance L between the rear end position R1 - Rn and the front end position F1 - Fn of each set corresponds to a predetermined, full stroke length L of the piston 102.

[0052] That is, the control unit 105 adjusts the movement of the piston 102 in such a way that: a) At different moments (points in time), the control unit 105 switches between various sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn (where the piston 102 starts and stops its motion along the longitudinal axis 111). b) Each of these end positions is part of a (predetermined, or dynamically determined based on defined rules) set that includes a rear end position (starting point, for example R1) and a front end position (ending point, for example F1). c) While the piston 102 moves between different rear and front positions, the stroke length L remains constant; it is just the end positions of the piston 102 that shift along the longitudinal axis 111 over time.

[0053] In other words: the piston 102 moves back and forth (reciprocating motion) between different pairs of rear and front end positions R1 ,F1 ; R2,F2; .... Rn,Fn, and at different times, the control unit 105 will shift to a new set of end positions, but the distance the piston 102 travels (the stroke length L) stays the same.

[0054] For example, for a certain time period, the piston 102 might move between rear end position R1 and front end position F1 (as in Figs. 2a-b). At a later time, the control unit 105 switches the piston 102 to move between rear end position R2 and front end position F2 (as in Figs. 3a-b). In both cases, the distance L between the rear and front positions remains the same (i.e., the piston stroke length L), but the specific rear and front end positions of the piston stroke change.

[0055] By controlling the actuator 104 to drive the reciprocating motion of the piston 105 by using, at different points in time, each of the multiple, different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn for the piston 102 along the longitudinal axis 111 , any stress on the membrane element 103a (and the second membrane element 103b) is not always in the same region throughout operation of the piston membrane pump 100, especially where the folding or bending changes direction (at the end pistons), which in turn will make the membrane elements 103a-b less prone to ruptures. For example, the 180-degree fold 115a of the membrane element 103a is in a different position between its connection points 114a, 116 in Fig. 3a compared to Fig. 2a and likewise in a different position in Fig. 3b compared to Fig. 2b. The same applies to the 180-degree fold 115b of the second membrane element 103b.

[0056] As mentioned, a membrane element is subjected to the highest levels of mechanical stress at the regions of the membrane element where the folding or bending of the membrane element changes direction. This is particularly true when the folding or bending takes the form of a 180-degree fold. By utilizing multiple, different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn for the piston 102, the regions of the membrane elements 103a-b where the 180-degree folds change direction are shifted and distributed across different areas of the membrane elements 103a-b. As a result, an increased operational lifetime of the membrane elements 103a-b is obtained.

[0057] Moreover, since the distance L between the rear end position and the front end position of each set corresponds to a predetermined, full stroke length of the piston 102, the filling volume of the liquid will remain constant regardless of which set is used.

[0058] The multiple, different sets of end positions R1 ,F1 ; R2,F2; ... Rn,Fn may be predetermined, or they may be determined by the control unit 105, for example according to a defined scheme, and / or randomly within a defined selection interval for the end positions. Moreover, the number of different sets of end positions R1 ,F1; R2,F2; ... Rn,Fn may for example be in the range of 2-200, preferably in the range of 50-150, such as 100.

[0059] The different points in time when the control unit 105 uses the multiple, different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn may be predetermined time intervals. For example, the control unit 105 may use rear and front end positions R1 ,F1 for, say, 5 minutes, and then rear and front end positions R2,F2 for the next five minutes, and so on. Alternatively or complementary, the control unit 105 may be configured to determine the different points in time by receiving a signal indicative of an interruption in an operational cycle of the piston membrane pump 100. Such a signal may be received, for example, from a processing system that controls a liquid filling machine using the piston membrane pump for dispensing liquid into packages. When the operation of the filling machine is stopped or otherwise interrupted, the operational cycle of the piston membrane pump may be interrupted simultaneously.

[0060] The multiple, different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn may differ from each other by their respective set of end positions shifted by an offset distance value Ax along the longitudinal axis 111. The offset distance value Ax may for example be in the range of 2 mm to 10 mm.

[0061] The control unit 105 may be configured to record a value representing the number of reciprocating motions the actuator 104 drives the piston 102 at each of the respective different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn. The values may for example be recorded in a memory or data storage 132 of the control unit 105.

[0062] The control unit 105 may be configured to distribute the number of reciprocating motions evenly across the multiple, different sets of end positions. “Evenly” may be defined as at most ± 25% difference between the sets, over a given time or a given total number of reciprocating motions. For example, the control unit 105 may use rear and front end positions R1 ,F1 for, say, 100 reciprocating motions of the piston 102, and rear and front end positions R2,F2 for another 100 reciprocating motions, and so on.

[0063] The control unit 105 may be configured to control the actuator 104 to set the piston 102 in a reset position, defined by an abutment surface 133 of the housing 101 that prevents further movement of the piston 102 in one direction (to the left in Fig. 1) of the longitudinal axis 111 , before controlling the actuator 104 to drive the reciprocating motion of the piston 102 by using, at different points in time, each of the multiple, different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn. The control unit 105 may for example be configured to set the piston 102 in the reset position at start-up of the piston membrane pump 100. The piston 102 in the reset position is illustrated in Fig. 1.

[0064] The control unit 105 may be configured to control the actuator 104 to drive the reciprocating motion of the piston 102 by using, at different points in time, each of said multiple, different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn such that the rear and front end positions first monotonically increase over time and then monotonically decrease over time. That the rear and front end positions increase / decrease may be construed as the actuator 104 being more / less extended. The rear and front end positions may for example increase / decrease along the longitudinal axis 111 relative to the above-mentioned abutment surface 133. For example, the control unit 105 may control the actuator 104 to drive the reciprocating motion of the piston 102 by first using end positions R1 ,F1 , and then using end positions R2,F2, wherein R2=R1+Ax and F2=F1+Ax. The control unit 105 may be configured to keep adding Ax until Rn,Fn is reached, and then retract Ax from every pump stroke until the piston 102 is back at R1 ,F1. The control unit 105 may be configured to continue or repeat this sequence (of incremental / decremental change in the rear and front end positions) until operation of the piston membrane pump 100 is stopped. Ax may be constant, such as 3 mm, throughout production / operation of the piston membrane pump 100.

[0065] The control unit 105 may be configured to transmit a control signal to the inlet valve 123 to set the inlet valve 123 in an open state when the actuator 104 is controlled to switch between different sets of end positions R1 ,F1 ; R2,F2; .... Rn,Fn used to drive the piston 102.

[0066] T urning to Fig. 4, Fig. 4 is a flow chart of a method of controlling the piston membrane pump 100. The method may correspond to operation of the piston membrane pump 100.

[0067] At start SO, the piston 102 may be set in a reset position, defined by the abutment surface 133 of the housing 101 that prevents further movement of the piston 102 in one direction of the longitudinal axis 111. SO may also signify production start.

[0068] At S1 , the method comprises controlling, e.g. by the control unit 105, the actuator 104 to drive the reciprocating motion of the piston 102 by using, at different points in time, each of the multiple, different sets of end positions R1 ,F1 ; R2,F2; ... Rn,Fn for the piston 102 along the longitudinal axis 111 , wherein each set of end positions R1 ,F1 ; R2,F2; ... Rn,Fn comprises a rear end position R1 - Rn and a front end position F1 - Fn where the distance L between the rear end position R1 - Rn and the front end position F1 - Fn of each set corresponds to a predetermined, full stroke length L of the piston 102. When the piston 102 moves from a front end position (such as F1 in Fig. 2b) to a rear end position (such as R1 in Fig. 2b), the inlet valve 123 is open and liquid is drawn in through the inlet 107 (then the outlet valve 124 is closed). And when the piston 102 moves from a rear end position (such as R1 in Fig. 2b) to a front end position (such as F1 in Fig. 2b), the outlet valve 124 is open and liquid may be pushed out through the outlet 108 (then the inlet valve 123 is closed). Thus, liquid is pumped through the housing 101 when the actuator 104 drives the piston 102.

[0069] The step of controlling S1 may comprise recording S2, e.g. by the control unit 105, a value representing the number of reciprocating motions the actuator 104 drives the piston 102 at each of the respective different sets of end positions R1 ,F1 ; R2,F2; ... Rn,Fn. The step of controlling S1 may further comprise distributing S3 the number of reciprocating motions evenly across the multiple, different sets of end positions R1 ,F1 ; R2,F2; ... Rn,Fn.

[0070] Alternatively or complementary, the step of controlling S1 may comprise controlling S4 the actuator 104 to drive the reciprocating motion of the piston 102 by using, at different points in time, each of the multiple, different sets of end positions R1 ,F1 ; R2,F2; ... Rn,Fn such that the rear and front end positions first monotonically increase over time and then monotonically decrease over time. For example, the actuator 104 may be controlled to drive the reciprocating motion of the piston 102 by first using end positions R1 ,F1 , and then using end positions R2,F2, wherein R2=R1+Ax and F2=F1+Ax. The control unit 105 may keep adding Ax until Rn,Fn is reached, and then retract Ax from every pump stroke until the piston 102 is back at R1 ,F1. This sequence may be repeated until production and operation of the piston membrane pump 100 is stopped at S5.

[0071] Fig. 5 is a schematic view of a filling machine 200 for filling liquid product 201 in packages 202, wherein the liquid (product) 201 is dispensed by pumping with the piston membrane pump 100 installed in the filling machine 200. The packages 202 may for example be food packages. The liquid (product) may, for example, be dairy and non-dairy beverages such as milk, including ultra-high temperature (UHT) treated milk, plant-based milk alternatives (such as almond, soy, and oat milk), and fruit juices. Other examples of liquid (product) are broths, soups, cooking creams, whipping creams, coconut water, pre-mixed smoothies, protein shakes, nectar drinks, and wines. The liquid product 201 may be supplied from a tank 203 of the filling machine 200. The filling machine 200, aside from incorporating the piston membrane pump 100, may otherwise be a conventional filling machine. From the description above follows that, although various embodiments of the invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims.

Claims

CLAIMS1 . A piston membrane pump (100) for pumping a liquid, the piston membrane pump (100) comprising: a housing (101) defining a chamber (106), the chamber (106) having an inlet(107) and an outlet (108) for the liquid; a piston (102) arranged within the housing (101) and configured to reciprocate along a longitudinal axis (111) to pump the liquid through the inlet (107) and the outlet(108) by repeatedly decreasing and increasing the volume of the chamber (106); a membrane element (103a) connected to both the piston (102) and the housing (101), forming a seal between the piston (102) and the housing (101); an actuator (104) operatively connected to the piston (102) to drive the reciprocating motion of the piston (102) between a rear end position (R1) and a front end position (F1) along the longitudinal axis (111); characterized by a control unit (105) configured to:- control the actuator (104) to drive the reciprocating motion of the piston (102) by using, at different points in time, each of multiple, different sets of end positions (R1 ,F1 ; R2,F2; Rn,Fn) for the piston (102) along the longitudinal axis (111), wherein each set of end positions comprises a rear end position (R1 - Rn) and a front end position (F1 - Fn) where the distance (L) between the rear end position (R1 - Rn) and the front end position (F1 - Fn) of each set corresponds to a predetermined, full stroke length (L) of the piston (102).

2. The piston membrane pump (100) according to claim 1 , wherein the different points in time are determined by predetermined time intervals and / or receiving a signal indicative of an interruption in an operational cycle of the piston membrane pump (100).

3. The piston membrane pump (100) according to any preceding claim, wherein the multiple, different sets of end positions (R1 ,F1 ; R2,F2; Rn,Fn) differ from each other by their respective set of end positions (R1 ,F1 ; R2,F2; Rn,Fn) shifted by an offset distance value (Ax) along the longitudinal axis (111).

4. The piston membrane pump (100) according to claim 3, wherein the offset distance value (Ax) is in the range of 2 mm to 10 mm.

5. The piston membrane pump (100) according to any preceding claim, wherein the control unit (105) is configured to: record a value representing the number of reciprocating motions the actuator(104) drives the piston (102) at each of the respective different sets of end positions (R1.F1 ; R2,F2; Rn.Fn).

6. The piston membrane pump (100) according to claim 5, wherein the control unit(105) is configured to: distribute the number of reciprocating motions evenly across the multiple, different sets of end positions (R1 ,F1 ; R2,F2; Rn,Fn).

7. The piston membrane pump (100) according to any preceding claim, wherein the control unit (105) is configured to: set the piston (102) in a reset position, defined by an abutment surface (133) of the housing (101) that prevents further movement of the piston (102) in one direction of the longitudinal axis (111), before controlling the actuator (104) to drive the reciprocating motion of the piston (102) by using, at different points in time, each of said multiple, different sets of end positions (R1 ,F1 ; R2,F2; Rn,Fn).

8. The piston membrane pump (100) according to any preceding claim, wherein the membrane element (103a) comprises, between its connection points (114a, 116) to the housing (101) and the piston (102), a 180-degree fold (115a) that moves along a length (L2) of the membrane element (103a) when the piston (102) reciprocates between the rear end position (R1) and the front end position (F1).

9. The piston membrane pump (100) according to any preceding claim, wherein the membrane element (103a) is connected to a first end (102a) of the piston (102), and wherein the piston membrane pump (100) further comprises: a further membrane element (103b) connected to both the piston (102) and the housing (101), at a second end (102b) of the piston (102) opposite the first end (102a), forming an additional seal between the piston (102) and the housing (101), such that a sealed space (119) is formed between the housing (101), the piston (102) and the membrane elements (103a, 103b); and17 a vacuum connection (121) leading to the sealed space (119).

10. The piston membrane pump (100) according to claim 9, wherein the housing (101) comprises: a first end section (101a) that comprises the inlet (107) and the outlet (108); a second end section (101 b) configured to accommodate a coupling arrangement (118) to couple the piston (102) to the actuator (104); and an intermediate section (101c) connected to both end sections (101a-b), thereby forming a hollow space (112) that accommodates the piston (102), wherein the membrane element (103a) is attached to the housing (101) via a flange (114a) located at the connection between the first end section (101a) and the intermediate section (101 b); and the further membrane element (103b) is attached to the housing (101) via a flange (114b) located at the connection between the second end section (101 b) and the intermediate section (101c).11 . The piston membrane pump (100) according to any preceding claim, wherein the inlet (111) is arranged to cooperate with an inlet valve (123), and the outlet (112) is arranged to cooperate with an outlet valve (124), such that liquid is pumped through the housing (101) when the actuator (104) drives the piston (102).

12. The piston membrane pump (100) according to claim 11 , wherein the control unit (105) is configured to: transmit a control signal to the inlet valve (123) to set it in an open state when the actuator (104) is controlled to switch between the different sets of end positions (R1 ,F1 ; R2,F2; Rn,Fn) used to drive the piston (102).

13. The piston membrane pump (100) according to any preceding claim, wherein the control unit (105) is configured to: control the actuator (104) to drive the reciprocating motion of the piston (102) by using, at different points in time, each of said multiple, different sets of end positions (R1 ,F1 ; R2,F2; Rn,Fn) such that the rear and front end positions first monotonically increase over time and then monotonically decrease over time.1814. A filling machine (200) for filling liquid product (201) in packages (202), wherein the liquid is dispensed by pumping with a piston membrane pump (100) according to any preceding claim.

15. A method of controlling a piston membrane pump (100), the piston membrane pump (100) comprising: a housing (101) defining a chamber (106) with an inlet (107) and an outlet (108) for the liquid; a piston (102) configured to reciprocate along a longitudinal axis (111) to pump the liquid by changing the volume of the chamber (106); a membrane element (103a) forming a seal between the piston (102) and the housing (101); and an actuator (104) operatively connected to the piston (102) to drive its reciprocating motion, the method comprising:- controlling (S1) the actuator (104) to drive the reciprocating motion of the piston (102) by using, at different points in time, each of multiple, different sets of end positions (R1 ,F1 ; R2,F2; Rn,Fn) for the piston (102) along the longitudinal axis (111), wherein each set of end positions (R1 ,F1 ; R2,F2; Rn,Fn) comprises a rear end position (R1 - Rn) and a front end position (F1 - Fn) where the distance (L) between the rear end position (R1 - Rn) and the front end position (F1 - Fn) of each set corresponds to a predetermined, full stroke length (L) of the piston (102).

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