Fluid pump

Abstract

A fluid pump 100 having an inlet valve 106, an outlet valve 108 and a compressible fluid conduit 202 between the inlet valve and the outlet valve, the conduit has a flow axis, and a pump actuator has

Description

Technical Field [0001 ] The present invention relates to a fluid pump. More specifically, the present invention relates to a positive displacement pump comprising a flexible fluid chamber which is deformed to convert mechanical energy to hydraulic energy of the fluid. Background Art

[0002] Positive displacement pumps are used in a variety of applications. One such application is the pumping of medical fluids. By "medical fluids" we mean fluids used in the practice of medicine. These may be, for example, biological fluids (those from the human body) as well as fluids used in treatment of the human body such as medicines. Such fluids may contain delicate elements such as biological cells or similar structures that may be damaged by application of excessive shear within the fluid.

[0003] Peristaltic pumps are common in the prior art. Peristaltic pumps comprise a flexible tube, typically disposed on part of a circular path. At least one shoe is connected to a rotor which compresses the tube, and as it does so rotates to move along the flexible tube. The force of the shoe acts to at least partially, and usually fully, compress or flatten the tube. Movement of the shoe moves the site of this compression along the length of the tube. This acts to, ahead of the shoe, increase the fluid pressure, and behind the shoe to decrease fluid pressure, thus advancing the fluid along the tube.

[0004] There are several problems with this type of peristaltic pump. In applications where specific amounts of fluid are to be pumped, they have limited accuracy, due to pulsatile flow. Movement of the compression along the tube can cause damage to sensitive materials (e.g. proteins, biologies, cells) within the fluid. The constant combined radial compression and axial compression and tension on the tube can cause wear, causing drift in performance. The flexible tubes are often constructed from a silicone material, and as such silicone shedding into the fluid path may occur. They have a limited viscosity range. There is limited cleanability of the pump head (crevices). Multiple pumps can also take up a lot of space.

[0005] An alternative type of pump is the piston pump. In such a pump, the fluid to be pumped flows into a metal (or ceramic) cylinder, and a metal (or ceramic) piston is inserted to pressurise the fluid and cause it to flow. During the intake stroke, an inlet valve is opened (with an outlet valve closed) to draw fluid into the cylinder. During the exhaust stroke, the inlet valve is closed and an outlet valve is opened. The valving is often achieved by having relieved sections of the cylinder and by rotating the cylinder 180 degrees between intake and output strokes.

[0006] While being very accurate, there are several problems with this type of pump. They are expensive. They are also non disposable (due to their cost), and as such between uses autoclaving and cleaning validation is needed. They must be assembled aseptically inside containment (due to being not fully sealed). Leakage can occur (due to being not fully sealed). They induce high shear in the fluid, which can cause severe damage to fluid components. Metals can react with some materials. Ceramics on the other hand are expensive and are easily damaged. They can also seize due to tight tolerances / build up on surfaces particularly between the piston and cylinder.

[0007] It is an aim of the present invention to overcome, or at least mitigate, some of the above disadvantages of the prior art devices. Summary of Invention

[0008] According to a first aspect of the present invention there is provided a fluid pump comprising: an inlet valve; an outlet valve; a compressible fluid conduit between the inlet valve and the outlet valve, the conduit having a flow axis; a pump actuator comprising a head configured to compress the fluid conduit in a direction substantially perpendicular to the flow axis; a controller configured to control the inlet valve, the outlet valve and the pump actuator to undertake a plurality of cycles comprising: an inlet step in which the inlet valve is open, the outlet valve is closed, and the pump actuator head moves to facilitate an increase in volume of the fluid conduit; and; an outlet step in which the inlet valve is closed, the outlet valve is open, and the pump actuator head moves to facilitate a decrease in volume of the fluid conduit..

[0009] Such an arrangement has the following advantages: • Low shear - the motion differs from the high shear rolling method of the peristaltic pumps of the prior art. • High accuracy - the present invention is able to dose very accurately due to lack of pulsatile flow. • Capability of higher viscosities than prior art devices. • The device has a closed fluid path. • The device can use non-reactive contact materials. • The motion minimises or eliminates material shedding. • The invention can be constructed for reasonable cost. • The invention has comparable hold up volume compared to the prior art. • The invention is able to support "zero loss prime" in which no fluid is lost in the priming operation. • Compact - the invention allows for a compact device to be constructed.

[0010] Preferably, the pump actuator head acts to compress the fluid conduit during the outlet step. [0011 ] Preferably, the pump actuator head is controlled to compress the fluid conduit to a position prior to contact between the internal sidewalls thereof.

[0012] Preferably, the pump actuator head is controlled to limit compression of the fluid conduit to a level above 10% of its uncompressed width. More preferably, the pump actuator head is controlled to limit compression of the fluid conduitto a level between 20% - 30% of its uncompressed width. For example the limit may be 25%.

[0013] Preferably, the pump actuator head acts to allow the fluid conduit to decompress during the outlet step.

[0014] Preferably, the pump actuator head is controlled to prohibit the fluid conduit from achieving full decompression. [001 5] Preferably, the pump actuator head is controlled to limit decompression of the fluid conduit to a level below 90% of its uncompressed width. More preferably, the pump actuator head is controlled to limit decompression of the fluid conduit to a level between 70 - 80% of its uncompressed width. For example the limit may be 75%.

[0016] Preferably, the pump actuator is configured to compress the fluid conduit between two surfaces.

[0017] Preferably, the two surfaces are the pump actuator head and a static reaction surface.

[0018] Preferably, wherein the fluid conduit comprises: a central section acted on by the valve actuator head; an inlet section acted on by the inlet valve; an outlet section acted on by the outlet valve; wherein the central section has a cross sectional area higher than the inlet section and outlet section.

[0019] Preferably, the fluid conduit is configured to be replaceable.

[0020] Preferably, the inlet section, outlet section and central section are removeable as a single assembly. [0021 ] Preferably, the inlet valve, outlet valve and pump actuator each have an opening for insertion and removal of the fluid conduit, which openings face in a common insertion / removal direction.

[0022] Preferably, the pump actuator comprises a rotary drive connected to a ball screw to advance and retract the pump actuator head.

[0023] Preferably, the ball screw comprises a ball screw shaft having a ball screw shaft axis, and a ball screw nut that can be advanced along the ball screw shaft by rotation of the ball screw shaft by the rotary drive, wherein the ball screw nut is connected to a pump actuator head pusher, the pump actuator head pusher being moveable along a pusher axis parallel to, but offset from, the ball screw axis.

[0024] Preferably, the inlet valve, outlet valve and valve actuator head each has an axis of actuation, the axes of actuation being parallel.

[0025] Preferably, the fluid conduit extends along a straight line between the inlet valve, pump actuator and the outlet valve.

[0026] According to a second aspect, there is provided a method of operating a fluid pump comprising the steps of: providing a compressible fluid conduit having an inlet and an outlet; undertaking an inlet step in which the inlet valve is open, the outlet valve is closed, and causing an increase in volume of the fluid conduit; and; undertaking an outlet step in which the inlet valve is closed, the outlet valve is open, and causing a decrease in volume of the fluid conduit.

[0027] Preferably, the inlet and outlet steps are repeated over a plurality of cycles to pump a fluid from the inlet to the outlet Brief Description of Drawings

[0028] An embodiment of the present invention will now be described with reference to the following figure in which: FIGURE 1 is a side view of a first pump in accordance with the present invention; FIGURE 2 is a perspective view of the pump of Figure 1; FIGURE 3 is a side view of the pump of Figure 1 with a component removed; FIGURE 4 is a perspective detail view of a part of the pump of Figure 1; FIGURE 5 is a perspective detail view of a part of the pump of Figure 1; FIGURE 6 is a side detail view of a part of the pump of Figure 1; FIGURE 7 is a perspective detail view of a part of the pump of Figure 1; FIGURES 8a to 8f are schematic views of a sequence of operation of the pump of Figure 1 (from a reverse angle compared to Figure 7); and, FIGURES 9a to 9d are section views of a part of the pump of Figure 1. Description of the embodiment

[0029] Figures 1 to 9d show various views of a pump 1 00 in accordance with the present invention. Configuration

[0030] The pump 100 comprising a housing 102, a pump actuator 104, a first valve assembly 106, a second valve assembly 108 and a tube assembly 11 0. Housing

[0031] The housing 102 comprises a generally cuboidal case 112 having two opposing open ends 114, 116. The housing further comprises a rear pump plate 118 and a main pump plate 120. The rear pump plate 118 closes the first open end 114, and the main pump plate 120 closes the second open end delimiting a cuboidal internal volume ofthe housing 102. Pump actuator

[0032] Referring to Figure 5, the pump actuator 104 comprises a servomotor 122 having a rotary output shaft 124 connected via a coupling 126 to a ballscrew shaft 128. A ball assembly 130 is provided on the shaft 128 and is configured to move linearly along the shaft upon rotation ofthe shaft 128.

[0033] An actuator brace 132 comprises a plate-like flange 134 having a ballscrew opening 136 and a pusher opening 138. At one edge ofthe flange 134 a carriage 140 extends normal thereto. The carriage 140 also delimits the pusher opening 138. A ballscrew clamp 166 is provided to clamp the ball assembly 130 to the flange 134 ofthe actuator brace 132.

[0034] A rail 142 is provided having an external form received within a channel of a slider 144. The slider 144 is attached to the carriage 140.

[0035] Referring to Figure 3, an actuator casing 146 is provided attached to the main pump plate 120. The actuator casing 146 supports the rail 142 and the servomotor 122, fixing them to the housing 102.

[0036] A compression spring 148 is provided, at a first end 150 abutting the actuator casing 146 and at a second end 1 52 extending into the carriage 140 end of the pusher opening 138 to bear against the actuator brace and eliminate backlash. As such, the compression spring 148 acts to urge the actuator casing 146 in a first, outward direction D1.

[0037] A pump pusher 1 54 is mounted to the actuator brace 132 opposite the spring 148. The pump pusher has a shaft 1 56 connected to a pusher head 158. The pusher head 158 is generally cuboidal having a rectangular pusher face 160 with a central, semi-cylindrical groove 162 running centrally therealong. The pusher 154 extends through a linear sealing assembly 164 mounted in the main pump plate 120.

[0038] Attached to the outside of the main pump plate 120 there is provided a guarding 188 (visible in Figures 2 and 7). The guarding defines a recess 190 delimited by a reaction surface 192 facing the outside of the main pump plate 120. The reaction surface 192 is elongate and flat.

[0039] First and second axial tube positioners 194, 196 are provided at either end of the recess, inboard ofthe respective valve assemblies 1 06, 108. Each axial tube positioner 194, 196 is attached to the main pump plate 120 and defines a central through-bore 198, 200 respectively. First valve assembly

[0040] The first valve assembly 106 is shown in more detail in Figure 4. It comprises a linear actuator 168 having a splined output shaft 1 70 connected to a valve pincher 1 72 at a free end. The valve pincher 1 72 has is shaped as a disc with a central, radially extending rib 174 having a tip 1 76 with a thin, rectangular flat surface 1 78 and two, opposed curved edges 180, 182. [0041 ] The first valve assembly 106 further comprises a housing 184 contains the actuator 168 and pincher 172. The housing 184 defines an internal volume and has an internal end surface 1 86 opposing the pincher 1 72. The end surface comprises an opposing pincher rib 187. The pincher 172 can move towards and away from the end surface 1 86 and the rib 187. Second valve assembly

[0042] The second valve assembly 1 08 is substantially identical to the first valve assembly 106 and as such will not be described here. Tube assembly

[0043] The tube assembly 110 comprises a first, central tube section 202, an inlet tube 204, an outlet tube 206, a first tube adaptor 208 and a second tube adaptor 21 0.

[0044] The first tube section 202 is constructed from an elastically deformable material, is circular in cross-section having a sidewall 212 and has open ends 214, 216. It has an internal diameter D1 and an external diameter D2. It has a main, longitudinal, flow axis X.

[0045] The inlet tube 202 and outlet tube 204 have much smaller inlet and outlet diameters (which are the same for both tubes). They are also constructed from an elastically deformable material.

[0046] The first and second tube adaptors 208, 210 are identical. Each comprises a first tubular portion 218 and a second tubular portion 220. Each has a bore running therethrough. The first tubular portion 218 is configured to receive the inlet or outlet tube. The second tubular portion 220 has ridges 224 on the outer surface, the inner surface being tapered to form a frustoconical surface 222. Use

[0047] Referring to Figures 8a to 9d, operation of the pump 100 is shown. Figures 8a to 8f show various consecutive stages of pump operation S900 - S910. The tube assembly 110 is shown installed in the pump 1 00 and containing a fluid to be pumped 1 0.

[0048] At stage S900, the inlet tube 202 is closed by the first valve assembly 106-specifically by compression between the valve pincher rib 174 and end surface opposing pincher rib 1 87. Because the ribs 1 74, 187 extend the width of the tube 202, they are able to completely close the lumen within the tube 202 under such compression. In stage S900, the outlet tube 204 is also closed by the second valve assembly 108.

[0049] At stage S902, the second valve assembly is opened by retraction of the pincher.

[0050] At stage S904, the servomotor 122 is activated, rotating the shaft 124 which rotates the ballscrew shaft. This rotation motion is translated into a linear motion of the ballscrew nut (ball assembly 130). This moves the actuator brace and the carriage 140 to advance the pump pusher 154 towards the tube assembly 110. Referring to Figure 8c, the central tube section 202 is compressed between the pusher face 160 and the reaction surface 192 to compress it, thereby reducing internal volume and pressurising the fluid 10. Due to the face that the second valve assembly 108 is open, fluid passes into the outlet tube 206 under pressure. [0051 ] At step S906, the second valve assembly 108 is closed.

[0052] At step S908, the first valve assembly 1 06 is opened.

[0053] At step S910, the servomotor is reversed, pulling the pusher face 160 away from the reaction face 192. The resilience of the central tube section 202 means that its volume increases, reducing pressure and drawing fluid 10 through the first valve assembly 106.

[0054] Referring to Figures 9a to 9c, stages of compression of the central tube section 202 are shown. In Figure 9a the tube 202 is uncompressed. In Figure 9b it is 25% compressed (the minimum distance between the outer surfaces is reduced to 75%). In Figure 9c it is 50% compressed (the minimum distance between the outer surfaces is reduced to 50%). In Figure 9d it is 100% compressed (the minimum distance between the outer surfaces is reduced such that the lumen is closed).

[0055] According to the present invention, the central section is held in the working range of 25% to 75% compression. In other words, it only opens to 75% of its relaxed width (Figs. 8a, 8b, 8f) and only doses to 25% (8c, 8d, 8e). This reduces wear and excessive strain on the tube material. It is noted that the central tube section 202 is not fully evacuated for each pumping cycle as a result.

Claims

1. A fluid pump comprising:an inlet valve;an outlet valve;a compressible fluid conduit between the inlet valve and the outlet valve, the conduit having a flow axis;a pump actuator comprising a head configured to compress the fluid conduit in a direction substantially perpendicular to the flow axis;a controller configured to control the inlet valve, the outlet valve and the pump actuator to undertake a plurality of cycles comprising:an inlet step in which the inlet valve is open, the outlet valve is closed, and the pump actuator head moves to facilitate an increase in volume of the fluid conduit; and;an outlet step in which the inlet valve is closed, the outlet valve is open, and the pump actuator head moves to facilitate a decrease in volume of the fluid conduit.

2. A fluid pump according to claim 1, wherein the pump actuator head acts to compress the fluid conduit during the outlet step.

3. Afluid pump according to claim 2, wherein the pump actuator head is controlled to compress the fluid conduit to a position prior to contact between the internal sidewalls thereof.

4. Afluid pump according to claim 3, wherein the pump actuator head is controlled to limit compression of the fluid conduit to a level above 10% of its uncompressed width.

5. Afluid pump according to claim 4, wherein the pump actuator head is controlled to limit compression of the fluid conduit to a level between 20% - 30% of its uncompressed width.

6. Afluid pump according to any of claims 1 to 5, wherein the pump actuator head acts to allow the fluid conduit to decompress during the outlet step.

7. Afluid pump according to claim 6, wherein the pump actuator head is controlled to prohibit the fluid conduit from achieving full decompression.

8. A fluid pump according to claim 7, wherein the pump actuator head is controlled to limit decompression of the fluid conduitto a level below 90% of its uncompressed width.

9. Afluid pump according to claim 8, wherein the pump actuator head is controlled to limit decompression of the fluid conduitto a level between 70 - 80% of its uncompressed width.

10. A fluid pump according to any preceding claim, wherein the pump actuator is configured to compress the fluid conduit between two surfaces.

11. Afluid pump according to claim 10, wherein the two surfaces are the pump actuator head and a static reaction surface.

12. A fluid pump according to any preceding claim, wherein the fluid conduit comprises:a central section acted on by the valve actuator head;an inlet section acted on by the inlet valve;an outlet section acted on by the outlet valve;wherein the central section has a cross sectional area higher than the inlet section and outlet section.

13. A fluid pump according to any preceding claim, wherein the fluid conduit is configured to be replaceable.

14. A fluid pump according to claim 13, dependent on claim 12, wherein the inlet section, outlet section and central section are removeable as a single assembly.

15. A fluid pump according to claim 14, wherein the inlet valve, outlet valve and pump actuator each have an opening for insertion and removal of the fluid conduit, which openings face in a common insertion / removal direction.

16. A fluid pump according to any preceding claim, wherein the pump actuator comprises a rotary drive connected to a ball screw to advance and retract the pump actuator head.1 7. A fluid pump according to claim 16, wherein the ball screw comprises a ball screw shaft having a ball screw shaft axis, and a ball screw nut that can be advanced along the ball screw shaft by rotation of the ball screw shaft by the rotary drive, wherein the ball screw nutis connected to a pump actuator head pusher, the pump actuator head pusher being moveable along a pusher axis parallel to, but offset from, the ball screw axis.

18. A fluid pump according to any preceding claim, wherein the inlet valve, outlet valve and valve actuator head each has an axis of actuation, the axes of actuation being parallel.

19. A fluid pump according to any preceding claim, wherein the fluid conduit extends along a straight line between the inlet valve, pump actuator and the outlet valve.

20. A method of operating a fluid pump comprising the steps of:providing a compressible fluid conduit having an inlet and an outlet;undertaking an inlet step in which the inlet valve is open, the outlet valve is closed, and causing an increase in volume of the fluid conduit; and;undertaking an outlet step in which the inlet valve is closed, the outlet valve is open, and causing a decrease in volume of the fluid conduit.

21. A method of operating a fluid pump according to claim 20, wherein the inlet and outlet steps are repeated over a plurality of cycles to pump a fluid from the inlet to the outlet.13

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