Fluid dose delivery apparatus

Abstract

A fluid delivery apparatus comprises a chamber 12 for containing a volume of liquid, an outlet (20, Figure 5) connected to a valve arrangement 22, and a clamp (60, Figure 7) that restricts the outlet

Description

FIELD OF THE INVENTION The present invention relates to the delivery of fluid doses, in particular dose in small volumes, and provides an apparatus for doing so. BACKGROUND ART The accurate delivery of small-volume doses is a challenging problem. Existing solutions involve careful measurement of the dose by a skilled and trained operator using accurate equipment, with self-evident associated costs. Less highly-skilled operators and non-precision equipment can be used if the fluid being delivered is first diluted, but this creates inefficiencies in the storage and delivery processes since a much larger volume and weight of fluid needs to be handled. Automated solutions to this problem tend to be complex and therefore expensive and / or temperamental. The need for such measured delivery systems exists across a wide range of applications extending from scientific and medical applications to more day-to-day scenarios such as the delivery of flavourings to beverages and colour to dyes such as hair dyes, fabric dyes and the like. In the beverage context, concentrated flavours are available for which a 1,000:1 dilution ratio is correct, i.e. 0.5ml of flavour is needed for a 500ml drink. Generally, serving staff in a retail context have a degree of accuracy suitable for delivering a 10:1 dilution which is unsuited to a 1,000:1 dilution. At that dilution level, accuracy is important since a small absolute variation in the amount of flavouring delivered will result in a substantial change to the dilution ratio. SUMMARY OF THE INVENTION In its first aspect, the present invention provides a fluid delivery apparatus comprising a fluid chamber defined by a reciprocating piston within a cylinder, the chamber being supplied with fluid under pressure from a peristaltic pump and having a selectively closeable outlet, including a position sensor for the piston adapted to stop the pump when the piston has moved to accommodate a predetermined volume of fluid within the chamber. A biassing means can be provided, to urge the piston toward an empty state of the chamber. This will allow the chamber to be filled by the pressure exerted by the pump and then, once an outlet is opened, the fluid will be ejected by the pressure exerted by the biassing means. The piston can include a shaft projecting from a rear face thereof, in which case the position sensor can be a switch that the shaft actuates when the piston has moved to accommodate the predetermined volume of fluid within the chamber. In that case, the biassing means can be a helical spring disposed around the shaft. This provides a simple and efficient delivery apparatus. When the outlet is closed, the chamber is filled by the pump. When the outlet opens, the peristaltic pump will by its nature prevent backflow of the fluid which will therefore be ejected exclusively via the outlet. When the outlet is closed again, the chamber will re-fill with a predetermined volume of fluid set by the dimensions of the piston and cylinder, thus delivering a repeatable defined volume of fluid. In its second aspect, the present invention provides a fluid delivery apparatus comprising a chamber for containing a volume of fluid to be dispensed, an outlet from the chamber which comprises a flexible conduit, a valve arrangement for controlling flow through the conduit, a selectively actuatable clamp around the conduit able to partially constrict the conduit, linked to the valve arrangement such that the clamp partially constricts the conduit to a first degree when the valve arrangement is open and partially constricts the conduit to a second and lesser degree when the valve closes. The partial constriction of the outlet conduit can be mild enough to not disturb delivery of the fluid. However, by lifting the constriction on closing the valve arrangement, a suction effect is created which draws the fluid in the conduit back and prevents drips from escaping. This both creates a cleaner environment around the apparatus and also improves the consistency of the fluid volumes delivered by eliminating a variable error of + / - 1 droplet volume. The valve arrangement can be in the form of, or include, a second clamp moveable so as to wholly constrict the conduit. As the conduit is flexible, this provides a convenient way to close the outlet without contaminating the fluid and without leakage. We prefer that the apparatus comprising a cam element moveable from an open position to a closed position and having at least one cam surface, wherein in the closed position the (or a) cam surface contacts the second clamp thereby to cause it to wholly constrict the conduit, and in the open position the (or a) cam surface contacts the selectively adjustable clamp to cause it to partially constrict the conduit. In this way, movement of a single cam element causes both steps to happen in a coordinated manner, thus ensuring reliability of operation in a simple manner. Of course, normally it will be the case that in the open position, the (or a) cam surface will allow the second clamp to release the conduit, and in the closed position the (or a) cam surface will allow the selectively adjustable clamp to relax its constriction of the conduit. The second and lesser degree of constriction of the conduit is, preferably, substantially no constriction of the conduit. Features of the above two aspects can of course be combined within a single implementation. Thus, the chamber of the second aspect can be supplied with fluid from a reservoir by a pump, such as a peristaltic pump. A sensor can be provided, to detecting the state of the valve arrangement and trigger activation of the pump when the valve arrangement is closed. Likewise, the chamber can be defined by a reciprocating piston within a cylinder. A position sensor can be provided for the piston, to cause the pump to stop when the piston has moved to accommodate a predetermined volume of fluid within the chamber. As in the first aspect, a biassing means can be provided to urge the piston toward an empty state of the chamber. The piston can include a shaft projecting from a rear face thereof and the position sensor can then be in the form of a switch which the shaft actuates when the piston has moved to accommodate the predetermined volume of fluid within the chamber. In that case, the biassing means can be in the form of a helical spring disposed around the shaft. The fluid can be a liquid, such as a flavour concentrate, a sauce, or a dye composition. BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which; Figure 1 shows the apparatus of the present invention from the front; Figure 2 shows the apparatus of the present invention from the rear; Figure 3 shows the fluid plunger of the present invention in an initial empty state; Figure 4 shows the fluid plunger of the present invention in a filled and ready state; Figure 5 shows the outlet valve of the present invention in a ready state; Figure 6 shows the outlet valve of the present invention in a delivering state; Figure 7 shows a sectional view of the internal parts of the outlet valve in a delivering state Figure 8 shows the sectional view of figure 7, after delivery is complete; Figure 9 shows the constricting levers in more detail; and Figure 10 shows adjustment of the fluid dose amount. DETAILED DESCRIPTION OF THE EMBODIMENTS A micro-dispenser able to reliably and consistently deliver small fluid doses, of generally less than 1ml, would be of great value in a number of fields. In the beverage and dying fields mentioned above, it would allow the ex tempore provision of a desired beverage or dye made up from dilution of a concentrated flavouring or dyestuff with a suitable solvent such as water. However, at a dilution ratio of 1,000:1, great accuracy and repeatability is needed since a small absolute error (e.g. of 0.5ml) will double the concentration of a delivery into (for example) 500ml of solvent. Referring to figures 1 and 2, the apparatus 10 of the present invention comprises a fluid chamber in the form of a syringe arrangement defined by a cylinder and piston (not visible). This is fed with a supply of fluid from a delivery conduit 14, supplied via a peristaltic pump 16 which is fed via a conduit 18 from a reservoir (not shown). If desired, a sensor can be included in the conduit 18 to detect a change in pressure, flow and / or vacuum (or any other indicator) to detect when the reservoir is empty or nearly so. Fluid is dispensed from the chamber via an outlet 20 which leads to an outlet valve 22. An operating lever 24 causes the outlet valve 22 to open and close as required. Referring also to figures 3, 4 et seq, the operation of the apparatus will now be described. With the outlet valve 22 closed (as will be described), the peristaltic pump 16 pushes fluid into the empty chamber 12 (fig 3) which pushes the internal piston 24 of the syringe 12 upwards (fig 4) against a spring-loading, compressing the spring 26 further as the syringe 12 fills and the plunger 24 rises. The plunger 24 has a guide rod or shaft 28 of a pre-determined length and thus as the syringe 12 fills and the plunger 24 rises, the upper end 30 of the guide shaft 28 will eventually reach a the limit switch 32. This limit switch 32 is held in a pre-determined location relative to the syringe 12 by a supporting frame 34 which will be described later. When the limit switch 32 is triggered, this cuts off power to the peristaltic pump 16, which ceases turning. With the syringe 12 full, it is held in this position under the pressure exerted by the spring 26 since the outlet valve 22 is closed and the peristaltic pump 16 will (by its nature) act as a one-way valve. Of course, a different form of pump, perhaps paired with an actual one-way valve, would also suffice. Similarly, other biassing mechanisms could act as an alternative or a supplement to the spring 26, other temporary fluid storage arrangements could be provided in lieu of the syringe 12, and other mechanisms for detecting a "full" state of the fluid storage could be employed. However, the above-described arrangement is simple and compact. It will be apparent that the use of the syringe 12 as described (or an equivalent structure) together with detection of when it is full will ensure that a consistent and accurate volume of fluid is drawn from the reservoir. It only now remains to dispense this fluid in a consistent and repeatable manner, and to cause it to re-fill once dispensed. To dispense the fluid, the operating lever 24 is moved downwards against an upward bias, provided in this example by a pair of springs 36 either side of the operating lever 24. More or fewer springs could be provided, or a different biassing arrangement could be employed. This movement takes the operating lever from the closed position shown in figure 5 to the open position shown in figure 6, and opens the liquid path from the syringe as shown in figure 7. The operating lever 24 comprises a knob 38 extending forwardly from a vertical plate 40, from the rear of which extend a pair of walls 42, 44 either side of a flexible-walled conduit or hose 46. This hose 46 leads from the outlet 20 of the syringe 12 to a nozzle 48 at the base of the outlet valve 22. The internal walls 42, 44 each have an outwardly-directed shoulder 50, 52 which contacts the upper end of each spring 36 to compress them against a base 54 and provide the desired upward bias against which the operating lever 24 is depressed. On their internal surfaces, the internal walls 42, 44 have upper cam surfaces 58 and lower cam surfaces 54. The cam surfaces operate a pair of symmetrical constricting levers 60 disposed either side of the hose 46 between it and the cam surfaces of the internal walls 42, 44. In this example, each internal wall 42, 44 is symmetrical with the other, either side of the hose 46, as are the constricting levers 60. Other arrangements are possible, such as a constricting lever on one side of the conduit 46 only, moving correspondingly further. However, a symmetrical arrangement is generally more reliable. The constricting levers 60 are shown in more detail in figure 9, which shows the lever adjacent the internal wall 42; the other constricting lever 60 is a mirror-image of the one shown. They each have a central fixing point 62 at which they are held fixed to a mounting point 64; either side of the fixing point 62 is a thinner flexible section 63 that acts as a living hinge allowing the thicker, rigid upper and lower sections 66, 68 to flex back and forth, away from and towards the flexible hose 46, under the influence of the cam surfaces 54, 58 of the internal walls 42, 44. Those cam surfaces 54, 58 are profiled so as to urge the lower section 68 towards the flexible hose 46 when the operating lever 24 is depressed, and to urge the upper section 66 towards the flexible hose 46 when the operating lever 24 is in its upper, rest position. The natural position of the flexible sections 63 is a gentle arc away from the flexible hose 46, so that the upper and lower sections 66, 68 are moved away from the flexible hose 46 unless positively urged toward it by the action of the cam surfaces 56, 58. The upper section 66 has a pinch arm 70 on its side facing the flexible hose 46. This is sized so that, when the cam surface 58 engages the upper section 66 and urges it toward the hose 46, it and its corresponding pinch arm 70 on the opposing constricting lever 60 completely close the hose 46 by pinching it shut. The lower section 68 is sized to slightly constrict the hose 46 but not to close it completely. The aim is to allow fluid flow from the syringe 12, subject to the action of the upper section 66, but when the lower section 66 is released and draws back from the hose 46 under the influence of the associated flexible section 63, to allow the hose 46 to open up fully again. As noted above, the upper and lower sections 66, 68 of the constricting arms 60 are controlled by the cam surfaces 56, 58 of the internal walls 42, 44 which move up and down with the knob 38. Thus, with the knob 38 in its upper (rest) position, to which it is urged to return by the springs 36, the upper cam surfaces 58 act on the upper sections 66 of the constricting arms 60 and the pinch arms 70 close the hose 46, preventing outflow from the syringe 12. Then the knob 38 is moved to its lower position and held there by a user against the pressure of the springs 36, the upper cam surfaces 58 release the upper sections 66 of the constricting arms 60 and allow fluid to flow through the hose 46. Meanwhile, the lower cam surfaces 56 engage with the lower sections 68 of the constricting arms 60 and slightly constrict the hose 46, but not enough to prevent flow. A projection 72 from one of the internal walls 44 extends upwardly so that it contacts a microswitch 74 when the internal walls 42, 44 are in their upper position. In that state, the microswitch 74 allows power to the peristaltic pump 16, subject to the limit switch 32. When the knob 38 is depressed and the internal walls 42, 44 move to their lower position, the microswitch 74 is released, cutting off power to the peristaltic pump 16. The net result of this arrangement is an operating procedure as follows. First, in its quiescent state with the operating lever in its upwards biassed position, power is present to the peristaltic pump 16 until the syringe 12 is full of fluid and the limit switch 32 is triggered to cut power to the pump. Fluid is then held in the syringe under pressure exerted by the spring-loading 26. The pinch arms 70 close the flexible hose 46 and prevent release. When the knob 38 is depressed, the pinch arms 70 of the upper sections 66 are released and the lower sections 68 move to slightly constrict the hose 46, but not enough to prevent flow. The microswitch 74 is released, cutting power to the peristaltic pump 16 and preventing further fluid from being pumped in. Fluid will be expelled via the outlet 20, the flexible hose 46, and the nozzle 48 into a receptacle (not shown) placed below the nozzle 48. Once the syringe 12 is empty and the fluid flow ceases, the user can release the knob 38. Under the influence of the pair of springs 36, the operating lever 24 will move back to its upper position. The upper cam surfaces 58 will act on the upper parts 66 of the constricting arms 60 to urge the pinch arms 70 into place, closing off the flexible hose 46. At the same time, the lower cam surfaces 56 will move upwards and release the lower sections 68 of the constricting arms 60, releasing their slight constriction of the hose 46 in its lower part, just above the nozzle 48. This release will pull back any remaining fluid in the hose 46 as a result of the slight suction created by the de-constriction of the hose 46, preventing drips from being released into the receptacle or onto surfaces below once the receptacle has been removed. This non-drip feature also contributes to the accuracy of dispensing since variability caused by the presence or absence of the volume of an additional drip is eliminated. The lengths and vertical locations of the cam surfaces 56, 58 can be selected so that the pinch arms 70 close just prior to release of the lower sections 68 and activation of the microswitch 74, ensuring that no new fluid is pumped into the syringe until the outlet is closed, and the non-drip function draws fluid back from the nozzle 48 rather from above. Once the operating lever 24 has moved back to its upper position under the bias of the pair of springs 36, the microswitch 74 will be engaged again, restoring power to the peristaltic pump 16. With the syringe 12 now empty, the limit switch 32 will not be engaged and therefore the pump will run, sending fluid into the syringe 12. As the pinch arms 70 are closed, fluid cannot escape via the hose 46 and the syringe 12 will fill until the limit switch 32 is triggered and the pump 16 stops. The process is then complete and ready to repeat. In this way, a precisely metered volume of fluid is drawn into the syringe 12 since the internal volume of the syringe is known and the limit switch 32 stops filling at a predetermined position. The outlet mechanism (when open) delivers only the internal contents of the syringe 12, and prevents any further delivery of fluid to the syringe until the dispensing process is complete. Figure 10 shows how the dispensed volume can be made adjustable in the abovedescribed apparatus. As noted above, the syringe 12 is surrounded by a supporting frame 34 which carries the limit switch 32 and which is connected to the syringe 12 via a ratchet mechanism 76. The syringe 12 has shoulders 78 on either lateral side which hold the ratchet mechanism 76 fixed relative to syringe 12, whilst the ratchet mechanism 76 is slidably connected to the supporting frame 34 in an adjustable manner. In this example, the ratchet mechanism 76 engages with a linear toothed rack formation 78 on the inner faces of the supporting frame 34, but other forms of adjustable positioning are feasible. Thus, by adjustment of the position of the ratchet mechanism 76 along the length of the supporting frame 34, the position of the limit switch 32 relative to the syringe 12 is adjusted. As a result, the degree to which the syringe 12 is filled is adjusted, thereby varying the volume dispensed by the apparatus. The increments set (in this case) by the pitch of the teeth of the rack formation 78 and the dimensions of the syringe 12 can be set at whatever is required by the application in question. Of course, the position of the limit switch 32 could be adjusted in a different manner, but we find that the above-described structure is convenient, accurate and repeatable. Alternatively, if the apparatus is only required to dispense a single predetermined volume then the adjustment mechanism can be omitted entirely. It will of course be understood that many variations may be made to the abovedescribed embodiment without departing from the scope of the present invention.

Claims

1. A fluid delivery apparatus comprising;a chamber for containing a volume of fluid to be dispensed;an outlet from the chamber which comprises a flexible conduit;a valve arrangement for controlling flow through the conduita selectively actuatable clamp around the conduit able to partially constrict the conduit, linked to the valve arrangement such that the clamp partially constricts the conduit to a first degree when the valve arrangement is open and partially constricts the conduit to a second and lesser degree when the valve closes.

2. A fluid delivery apparatus according to claim 1 in which the valve arrangement includes a second clamp moveable so as to wholly constrict the conduit.

3. A fluid delivery apparatus according to claim 2 comprising a cam element moveable from an open position to a closed position and having at least one cam surface wherein in the closed position the or a cam surface contacts the second clamp thereby to cause it to wholly constrict the conduit and in the open position the or a cam surface contacts the selectively adjustable clamp to cause it to partially constrict the conduit.

4. A fluid delivery apparatus according to any one of the preceding claims in which the chamber is supplied with fluid from a reservoir by a pump.

5. A fluid delivery apparatus according to claim 4 in which the pump is a peristaltic pump.

6. A fluid delivery apparatus according to claim 4 or claim 5 further comprising a sensor for detecting the state of the valve arrangement and adapted to activate the pump when the valve arrangement is closed.

7. A fluid delivery apparatus according to any one of the preceding claims in which the second and lesser degree of constriction of the conduit is substantially no constriction of the conduit.

8. A fluid delivery apparatus according to any one of the preceding claims in which the chamber is defined by a reciprocating piston within a cylinder.

9. A fluid delivery apparatus according to claim 8 as dependent on any one of claims 4 to 6, including a position sensor for the piston adapted to stop the pump when the piston has moved to accommodate a predetermined volume of fluid within the chamber.

10. A fluid delivery apparatus comprising a fluid chamber defined by a reciprocating piston within a cylinder, the chamber being supplied with fluid under pressure from a peristaltic pump and having a selectively closeable outlet, including a position sensor for the piston adapted to stop the pump when the piston has moved to accommodate a predetermined volume of fluid within the chamber.

11. A fluid delivery apparatus according to claim 9 or claim 10 including a biassing means urging the piston toward an empty state of the chamber.

12. A fluid delivery apparatus according to claim 9 or claim 10 in which the piston includes a shaft projecting from a rear face thereof and the position sensor is a switch which the shaft actuates when the piston has moved to accommodate the predetermined volume of fluid within the chamber.

13. A fluid delivery apparatus according to claim 12 including a biassing means urging the piston toward an empty state of the chamber in the form of a helical spring disposed around the shaft.

14. A fluid delivery apparatus according to any one of the preceding claims in which the fluid is a liquid.

15. A fluid delivery apparatus according to claim 14 in which the liquid is a flavour concentrate.

16. A fluid delivery apparatus according to claim 14 in which the liquid is a dye composition.

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