Drug delivery pump

Abstract

A drug delivery pump comprising a fluid chamber 146, an inlet valve 120 comprising a moveable element, an outlet valve 160 comprising a movable element and a dosing mechanism 140 comprising a movable

Description

Field The present application relates to a pump as a drug delivery device. The pump has a particular application for the pumping of relatively small amounts of fluid, for example a therapeutic product that may be delivered to the human body. Background Drugs in a liquid formation can require high forces to move the drug from a storage reservoir through to the patient. This is particularly true where the fluid has a high viscosity. This makes it difficult to dispense small volumes with a high accuracy. The present disclosure seeks to address this, and other problems encountered in the prior art. By way of example, infusion pumps are medical devices used to administer a predetermined amount of therapeutic product (e.g. insulin) to the human body (e.g. in the subcutaneous tissue) in a controlled manner. In the case of insulin infusion pumps, the delivered volume of insulin at a basal rate (background) and at a bolus rate (an increased dose for a mealtime) should be of sufficient accuracy to ensure that the glucose concentration in the bloodstream is maintained within the desired levels. Summary According to a first aspect of the present invention, there is provided a pump comprising: a fluid chamber arranged to hold a volume of fluid; an inlet valve comprising a movable element and arranged to be coupled to a reservoir of fluid and to control fluid flow from the fluid reservoir into the fluid chamber; an outlet valve comprising a movable element and arranged to control fluid flow from the pump. The pump may also comprise a dosing mechanism arranged comprising a movable element arranged to pump fluid. The pump may also comprise one or more actuation elements coupled to at least one of the inlet valve, and / or the outlet valve and / or the dosing mechanism movable elements for moving the respective at least one of the inlet valve, and / or the outlet valve and / or dosing mechanism movable elements. The pump may also comprise a position detection mechanism configured to detect the positions of the at least one inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element. The pump may also comprise a control system arranged to supply drive signals to the inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element, wherein the control system controls the drive signals in response to the detected positions of the inlet valve movable element, the outlet valve movable element and the dosing mechanism movable element so as to pump a determined volume of fluid from the chamber. The pump may further include a pressure measurement mechanism arranged to measure the pressure of the fluid in the pump, and wherein the control system controls the drive signals in response to the measured pressure so as to pump a determined volume of fluid from the chamber. Pressure measurement may be used in conjunction with dosing mechanism movable element and / or inlet valve movable element, and / or outlet movable membrane position to calculate a measure of flow rate. In particular, the pump may include a flow rate measurement mechanism arranged to measure the flow rate of the fluid in the pump, and wherein the control system controls the drive signals in response to the measured flow rate so as to control the fluid flow within the chamber. The actuation elements may be SMA elements. The SMA elements may be coupled to at least one of the inlet valve movable element, the outlet valve movable element and the dosing mechanism movable element for moving the respective inlet valve movable element, the outlet valve movable element and / or the dosing mechanism movable element. The resistance measurement circuit may be arranged to measure the resistance of the inlet valve and / or outlet valve movable elements, and / or the dosing mechanism movable element; and wherein an inlet valve control system and / or an outlet valve control system and / or a dosing mechanism control system controls the drive signals in response to the measured resistance to verify that the respective inlet valve and / or outlet valve and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid. The power measurement circuit may be arranged to measure the power supplied to the inlet valve and / or outlet valve movable elements and / or dosing mechanism movable element, and wherein an inlet valve control system and / or an outlet valve control system and / or a dosing mechanism control system controls the drive signals in response to the measured power to verify that the respective inlet valve and / or outlet valve movable element and / or dosing mechanism control system moves the required extent so as to pump the determined volume of fluid . The position detection mechanism may be arranged to measure the temperature of the SMA elements of the inlet valve movable element and / or outlet valve movable element and / or dosing mechanism movable element; and wherein an inlet valve control system and / or an outlet valve control system and / or a dosing control system controls the drive signals in response to the measured temperature to verify that the respective inlet valve movable element and / or outlet valve movable element and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid . The inlet valve control system, outlet valve control system and dosing control system may be configured as a single control system or can be provided as dedicated control system for each of inlet valve, outlet valve and dosing mechanism (or a combination). The position detection mechanism may be a Hall sensor. Other position sensors can be used such as capacitive sensors. The pump may further comprise a fluid reservoir. The fluid reservoir may be pressurised. The movable element is arranged to deliver the determined volume of fluid on each stroke, and the control system is arranged to detect the position of the dosing mechanism movable element to verify that the respective dosing mechanism element moves the required extent of the stroke to deliver the determined volume of fluid. The stroke may be variable to deliver different volumes of fluid. According to a second aspect of the invention, there is provided a method of controlling a pump, the pump comprising a fluid chamber arranged to hold a volume of fluid; an inlet valve comprising a movable element and arranged to be coupled to a reservoir of fluid; an outlet valve comprising a movable element; and a dosing mechanism arranged comprising a movable element arranged to pump fluid; one or more actuation elements coupled to at least one of the inlet valve, outlet valve and dosing mechanism movable elements for moving the respective inlet valve, outlet valve and dosing mechanism movable element; and a position detection mechanism configured to detect the positions of the inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element; the method comprising: detecting the positions of at least one of the inlet valve, outlet valve and dosing mechanism movable elements; and supplying drive signals to the at least one of the inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element in response to the detected positions of the respective inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element so as to pump a determined volume of fluid from the chamber. The actuation elements may be SMA elements, and wherein the detection of the position of the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element may comprise measuring the resistance of at least one of the one or more SMA elements; and wherein the drive signals are controlled in response to the measured resistance to verify that the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid. Alternatively, the actuation elements may be SMA elements, and wherein the detection of the position of the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element may comprise measuring the power of the drive signals, and wherein the drive signals are controlled in response to the measured power to verify that the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid. In a further alternative, the actuation elements may be SMA elements, and wherein the detection of position of the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element may comprise measuring the temperature of at least one of the one or more SMA elements; and wherein the drive signals are controlled in response to the measured temperature to verify that the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid. The inlet valve control system and / or outlet valve control system and / or dosing mechanism control element may be arranged to detect abnormal operation of the respective inlet valve movable element and / or outlet valve movable element on the basis of the measured resistance, power, or temperature. The step of detecting the position of the movable element may comprise using a Hall sensor or other suitable position sensors. The method may further comprise the step measuring the flow rate of the fluid. Pressure measurement may be used in conjunction with dosing mechanism movable element and / or inlet valve movable element, and / or outlet movable membrane position to calculate a measure of flow rate. In particular, the pump may include a flow rate measurement mechanism arranged to measure the flow rate of the fluid in the pump, and wherein the control system controls the drive signals in response to the measured flow rate so as to control the fluid flow within the chamber. The method may further comprise the step of detecting abnormal operation of the respective inlet valve movable element and / or outlet valve movable element and / or dosing mechanism movable element. The method may comprise the steps of: closing the inlet and outlet valves using the respective inlet valve movable element and outlet valve movable element; opening the inlet valve using the inlet valve movable element; moving the dosing mechanism movable element to aspirate fluid into the fluid chamber; closing the inlet valve using the inlet valve movable element; opening the outlet valve using the outlet valve movable element; moving the dosing mechanism movable element to dispense the determined volume of fluid; and closing the outlet valve using the outlet valve movable element. The dosing mechanism movable element may be moved in incremental steps to provide a partial dispense of the fluid in the fluid chamber. The fluid may be aspirated into the fluid chamber in incremental amounts. The dosing mechanism movable element and / or the inlet valve movable element and / or outlet valve movable mechanism may be moved synchronously. According to a third aspect of the present disclosure, there is provided a pump comprising: a fluid chamber arranged to hold a volume of fluid; an inlet valve arranged to be coupled to a reservoir of fluid and to control fluid flow from the fluid reservoir into the fluid chamber; an outlet valve arranged to control fluid flow from the pump; a pumping arrangement comprising a movable element arranged to pump fluid; one or more SMA elements coupled to the movable element for moving the movable element; a position detection mechanism configured to detect the position of the movable element; and a control system arranged to supply drive signals to the one or more SMA elements, wherein the control system controls the drive signals in response to the detected position so as to pump a determined volume of fluid from the chamber. The position detection mechanism may comprise a resistance measurement circuit arranged to measure the resistance of at least one of the one or more SMA elements; and the control system may control the drive signals in response to the measured resistance to verify that the movable element moves the required extent so as to pump a determined volume of fluid. The position detection mechanism may comprise a power measurement circuit, and the control system may control the drive signals in response to the measured power to verify that the movable element moves the required extent so as to pump a determined volume of fluid. The position detection mechanism may be arranged to measure the temperature of at least one of the one or more SMA elements; and the control system may control the drive signals in response to the measured temperature to verify that the movable element moves the required extent so as to pump a determined volume of fluid. The control system may be arranged to output a warning signal in response to detecting abnormal operation of the pumping arrangement. The control system may be arranged to detect abnormal operation of the pumping arrangement on the basis of the measured resistance, and / or power, and / or temperature. The movable element may have a stroke and is arranged to deliver the determined volume of fluid on each stroke, and the control system may be arranged to detect the position of the movable element to verify that the movable element moves the required extent of the stroke to deliver the determined volume of fluid. The stroke may be variable to deliver different volumes of fluid. The stroke may be a reciprocating stroke, and the control system may be arranged to detect the position of the movable element to verify that the movable element moves the required extent of the stroke. The inlet valve may comprise a inlet valve movable element and one or more inlet valve SMA elements coupled to the inlet valve movable element for moving the inlet valve movable element; an inlet valve position detection mechanism configured to detect the position of the inlet valve movable element; and an inlet valve control system arranged to supply drive signals to the one or more inlet valve SMA elements, wherein the inlet valve control system may control the drive signals in response to the detected position so as to control fluid flow in to the chamber. The outlet valve may comprise a outlet valve movable element and one or more outlet valve SMA elements coupled to the outlet valve movable element for moving the outlet valve movable element; an outlet valve position detection mechanism configured to detect the position of the inlet valve movable element; and an outlet valve control system arranged to supply drive signals to the one or more outlet valve SMA elements, wherein the outlet valve control system may control the drive signals in response to the detected position so as to control fluid flow out of the chamber. As such, the inlet valve and the outlet valve are therefore active valve mechanisms which can be independently controllable. As an alternative, the inlet valve and outlet valve may be passive. The inlet valve may comprise a chamber coupled to the inlet. The outlet valve may comprise a chamber coupled to the outlet. The inlet valve chamber of the pump, the outlet valve chamber and the fluid chamber may comprise a single chamber. The movable elements of the inlet valve, the outlet valve and the dose control mechanism may each comprise a flexible diaphragm. In an alternative, the pump may comprise a single flexible diaphragm comprising the inlet valve movable element, the outlet valve movable element and the dosing control movable element. The position detection mechanism of the inlet valve and / or the outlet valve and / or dosing mechanism may comprise a resistance measurement circuit arranged to measure the resistance of the respective at least one of the one or more inlet valve and outlet valve SMA elements; and wherein the control system controls the drive signals in response to the measured resistance to verify that the respective inlet valve and / or outlet valve movable element moves the required extent so as to pump a determined volume of fluid. The position detection mechanism of the inlet valve and / or the outlet valve and / or dosing mechanism may comprise a power measurement circuit, and wherein the respective inlet valve / outlet valve and dosing control system controls the drive signals in response to the measured power to verify that the respective inlet valve and / or outlet valve movable element and / or dosing control movable element moves the required extent so as to control the flow of fluid into or out of the chamber. The position detection mechanism of the inlet valve and / or the outlet valve and / or dosing mechanism valve may be arranged to measure the temperature of the one or more SMA elements of the at least one of the respective inlet valve and / or outlet valve and / or dosing mechanism; and wherein the respective inlet valve / outlet valve and / or dosing mechanism control system controls the drive signals in response to the measured temperature to verify that the respective inlet valve / outlet valve and / or dosing control movable elements moves the required extent so as to control the flow of fluid into or out of the chamber. The control system may be configured to measure the flow rate of the fluid. The inlet valve control system and / or outlet valve control system may be arranged to detect abnormal operation of the respective inlet valve movable element and / or outlet valve movable element on the basis of the measured resistance, power, or temperature. The control system may be arranged to output a warning signal in response to detecting abnormal operation of the respective inlet valve movable element and / or outlet valve movable element. According to a fourth aspect of the present disclosure, there is provided a method of controlling a pump, the pump comprising a movable element that is movable relative to a support structure and one or more SMA elements arranged to control movement of the movable element, wherein the movable element is actuated using the one or more SMA elements, the method comprising: controlling the one or more SMA elements using drive signals to drive movement of a movable element relative to a support structure to dispense a volume of fluid; detecting the position of the movable element; controlling the drive signals in response to the detected position so as to pump a determined volume of fluid from the pump. The determined volume of fluid may be continually variable. The detection of the position of the movable element may comprise measuring the resistance of at least one of the one or more SMA elements; and wherein the drive signals are controlled in response to the measured resistance to verify that the movable element moves the required extent so as to pump the determined volume of fluid. The detection of the position of the movable element may comprise measuring the power of the drive signals, and wherein the drive signals are controlled in response to the measured power to verify that the movable element moves the required extent so as to pump the determined volume of fluid. The detection of position of the movable element may comprise measuring the temperature of at least one of the one or more SMA elements; and wherein the drive signals are controlled in response to the measured temperature to verify that the movable element moves the required extent so as to pump a determined volume of fluid. The pump may further include an inlet valve to control flow of fluid into the pump, wherein the inlet valve may comprise a inlet valve movable element and one or more inlet valve SMA elements coupled to the inlet valve movable element, and the method further comprises: moving the inlet valve movable element using one or more inlet valve SMA elements; detecting the position of the inlet valve movable element; supplying drive signals to the one or more inlet valve SMA elements, and controlling the drive signals in response to the detected position so as to control fluid flow in to the chamber. The pump may further include an outlet valve to control flow of fluid into out of the pump The outlet valve may comprise a outlet valve movable element and one or more outlet valve SMA elements coupled to the outlet valve movable element, and the method further comprises: moving the outlet valve movable element using one or more outlet valve SMA elements; detecting the position of the outlet valve movable element; supplying drive signals to the one or more outlet valve SMA elements, and controlling the drive signals in response to the detected position so as to control fluid flow out of the pump. The step of detecting the position of the inlet valve and / or the outlet valve may comprise measuring the resistance, power or temperature of the respective at least one of the one or more inlet valve and outlet valve SMA elements; and wherein the drive signals are controlled in response to the measured resistance, power or temperature to verify that the respective inlet valve and / or outlet valve movable element moves the required extent so as to pump the determined volume of fluid. The method may further include the step of measuring the pressure of the fluid in the pump, and wherein the inlet valve and / or outlet valve control system controls the drive signals in response to the measured pressure so as to control the flow of fluid into or out of the chamber. With the present invention it is possible to achieve very highly accurate feedback on the contraction of SMA wires, by directly measuring the resistance, power or temperature of the SMA elements. Brief description of the drawings Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic of a pump according to an embodiment of the present disclosure; Figure 2 is schematic illustration of an example of an actuation assembly for the pump of Figure 1; Figure 3 is a schematic of a control system for the pump of Figure 1; and Figure 4 is a schematic of a second embodiment of a control system for the pump of Figure 1. Detailed description Pump There is disclosed a pump suitable for drug delivery applications that features an SMA actuated inlet valve, a dosing mechanism comprising an SMA actuated diaphragm for dosing control and an SMA actuated outlet valve. The inlet valve and outlet valve may comprise SMA actuated diaphragms. In one embodiment of the invention, the SMA actuated diaphragm is controlled by resistance feedback to provide fine resolution displacement control, allowing a variable output dose, by varying the aspiration and or dispensing stroke. Thus, the pump is configured to adjust the stroke to deliver a determined amount of fluid. The inlet and outlet valves are also variable position controlled using resistance feedback, which offers finer resolution of control of the fluid, both by minimising the orifice when pumping small volumes and / or balancing the movement of the valve with equivalent movement of the diaphragm so that, as the valve generates a suction from its displacement, the diaphragm compensates for this, which avoids unwanted pressure variation in the fluid in the pump and or sucking fluid back out of the patient. In alternative embodiments, the inlet and outlet valves can be controlled by other control methods, as can the dosing mechanism. This variable displacement of the dosing control diaphragm allows a pump to deliver a range of doses from high volume "bolus" type doses at relatively high speed, to very small and accurate micro doses in small increments for "basal" type doses. This is also useful when working in conjunction with a patient feedback sensor such as a Continuous Glucose Monitor (CGM) which measure the varying condition of the patient and can be used to trigger the delivery of finely adjusted doses. Figure 1 illustrates a pump 100 according to the present disclosure. The pump 100 may be suitable for drug delivery to a patient. The pump 100 comprises an inlet valve 120, a dosing mechanism 140 and an outlet valve 160, the details of which will be described below. The pump 100 may further comprise an inlet 110 and an outlet 170, as well as connecting tubes 180,190 between the inlet valve 120 and the dosing mechanism 140, and between the dosing mechanism 140 and the outlet valve 160. The inlet 110 may be connected to a reservoir 300 that stores a drug, for example insulin, ready for administering to a patient. In general, the inlet 110 is connected to any suitable entity that is capable of holding a drug in fluid form. The dosing mechanism diaphragm 144 of the dosing mechanism can move between different positions to an open position (i.e. from down to up as in Figure 1) so as to draw fluid from the reservoir 300 into a chamber 146 of the dosing mechanism 140. The diaphragm 144 is also configured to be moved in small incremental steps in order to control the volume of fluid that can be dispensed by the pump 100 as will be described in further detail below. The arrows in Figure 1 indicate the direction of flow of a liquid through the pump 100. Liquid is received (e.g. from the reservoir 300) at the inlet 110, passes through the inlet valve 120 (when the inlet 120 is open) to the dosing mechanism 140 and then to the outlet valve 160. The outlet 170 may be connected to an implement suitable for passing a drug into a patient's body. For example, when in use, the outlet 170 may be connected to a cannula (not shown) that is suitable to be inserted into a patient's body (e.g. into a subcutaneous layer when delivering insulin, or a blood vessel for example, for other drugs where intravenous delivery is required). The connection may be direct to the cannula or the connection between the outlet 170 and cannula maybe via flexible tubing of various lengths. It is also possible to operate the pump 100 in the reverse direction if required. For example, this may facilitate filling the reservoir 300 using the pump 100. Inlet valve Considering the inlet valve 120 in more detail, the inlet valve 120 comprises one or more SMA elements 122 connected to a flexible diaphragm 124. In this embodiment a single SMA element is coupled between the diaphragm 124 and a support structure (not shown) via coupling arrangements 132. The flexible diaphragm 124 is positioned in a chamber 126 of the inlet valve 120 and is configured to be driven by the SMA element 122 to open or close the inlet valve 120. The inlet valve 120 further comprises a spring 128 which biases the flexible diaphragm 124 into the "closed" position - in which the flexible diaphragm 124 is extended downwards to seal off a port of the inlet valve 120, for example by sealing of the exit or the inlet of the valve 120. In an alternative, the spring can be replaced by other forms of biasing control. In a further alternative, two opposing SMA elements could be used, which may also include a biasing spring (see the description of the outlet valve 160, below). In the closed position, the SMA element 122 may be in tension and the tensile force of the SMA elements 122 is less than the spring force that is forcing the flexible diaphragm 124 into the closed position. On actuation of the SMA element 122 (i.e. by passing current through the SMA elements 122 to cause the SMA element 122 to heat up), the SMA element 122 contracts and provide a net upwards actuation force which overcomes the downward biasing force of the spring 128 and lifts the flexible diaphragm 124 away from the exit 130 of the inlet valve 120, thereby opening the inlet valve 120 by creating a flow path through the inlet valve 120. In an alternative, the SMA elements 122 may not be in tension when unpowered and can be biased to a closed position using a suitable biasing mechanism. The SMA element 122 therefore controls the operation of the inlet valve 120 through their contraction and extension In this example, the spring 128 biases the inlet valve 120 closed. By biasing the diaphragm 124 in a closed position, the diaphragm is only powered when being actuated to an open position by the SMA element 122. This improves battery life as power is only required when being used to open the inlet valve 120. In addition, if the diaphragm 124 is biased to the closed position, in the event of failure or malfunction of the SMA elements 122, the inlet valve 120 will remain closed and no accidental drug delivery can take place. In use, the inlet valve 120 serves to control the amount and flow of fluid into the pump 100, from the reservoir). The flow can be controlled by controlling the amount the diaphragm 124 is opened, and the rate at which it is opened. For a high flow rate, the diaphragm 124 is fully opened and partially opened for low flow rate to improve accuracy and minimise pressure changes in the fluid that may damage or change viscosity of some drugs. Figure 1 illustrates using dashed lines at least two positions of the flexible diaphragm 124 in the open position. In general, it is possible to control to a high degree of precision and accuracy the amount of contraction of the SMA elements 122 - for example by controlling the amount of power to the SMA elements 122. As mentioned above, and as with the outlet valve diaphragm 164 and the dosing diaphragm 144 described below, resistance feedback can be used to provide very fine resolution control over the SMA elements 122. In turn it is possible to provide fine-tuned control over the flexible diaphragm 124, meaning that the flexible diaphragm 124 can be accurately positioned at any one of a plurality of open positions (for example the two open positions shown by the dashed lines) and the closed position. For example, the SMA element 122 may be able to position the flexible diaphragm 124 at any one of a plurality of positions, for example 10, or 20 or 100, or 500 or even more different open positions The diaphragm 124 can be controlled using input values of up to 0.1 of a micron so as to move the diaphragm 124 in 1 micron steps with a total range of greater than 400 microns. It is envisaged that an even greater range of positions could be possible depending upon the length of the SMA elements and or drive electronics optimisation and or control systems optimisation. Outlet valve Figure 1 further illustrates outlet valve 160, which comprises one or more SMA elements 162, a flexible diaphragm 164, chamber 166 and spring 168. In this embodiment a pair of opposing SMA elements 162a; 162b is used and coupled to between the diaphragm 164 and a support structure (not shown) via coupling arrangements 161. The flexible diaphragm 164 is positioned in the chamber 166 of the outlet valve 160 and is configured to be driven by the SMA elements 162 to open or close the outlet valve 160. The spring 168 biases the flexible diaphragm 164 into the "closed" position - in which the flexible diaphragm 164 is extended downwards to seal off a port of the outlet valve 160, for example by sealing of the exit or the inlet of the valve 160. In an alternative, the spring can be replaced by other forms of biasing control. In another embodiment, the valve can have a single SMA element with a biasing spring as described herein in relation to the inlet valve 120, or have no spring (or other biasing element) The operation of the outlet valve 160 can be the same as that of inlet valve 120 and is also shown in the closed position in Figure 1. Two of the plurality of open positions are indicated using dotted lines. In Figure 1, the flexible diaphragm 164 of the outlet valve 160 is controlled using an arrangement of SMA elements similar to that of the dosing mechanism described in more detail below. However, an arrangement similar to that described in relation to the inlet valve may also be used. Dosing mechanism The dosing mechanism 140 positioned in between the inlet valve 120 and outlet valve 160 also comprises one or more SMA elements 142, a flexible diaphragm 144 and a chamber 146. In the embodiment described herein, a pair of opposing SMA elements 142a; 142b is used and coupled to between the diaphragm 144 and a support structure (not shown) via coupling arrangements 148. The flexible diaphragm 144 is positioned in the chamber 146 of the dosing mechanism 140 and is configured to be driven by the SMA elements 142. In the present embodiment, the flexible diaphragm 144 is not biased by a spring (or other biasing mechanism). However, in other examples, a spring / biasing force may act on the diaphragm 144 of the dosing mechanism 140. Similar to the inlet and outlet valves, the pair of opposing SMA elements 142a, 142b are in tension and control the position of the diaphragm. In particular, the pair of opposing SMA elements 142a, 142b comprise at least one SMA element in tension that applies a downwards force on the flexible diaphragm 144, and at least one other SMA element in tension that applies an opposite, upwards force on the diaphragm. Therefore, upwards and downwards movement of the flexible diaphragm 144 can be achieved by selectively controlling the contractions of both of the SMA elements 142a, 142b. As with the inlet and outlet valves, the SMA elements 142 are able to position the flexible diaphragm 144 at any one of a plurality of positions, as indicated by the dashed lines representing the flexible diaphragm 144. The SMA elements 142 may be able to position the flexible diaphragm 144 at any one of a plurality of positions, for example 10, 20,100, or 500 different open positions. The diaphragm 144 can be controlled using input values of up to 0.1 of a micron so as to move the diaphragm 144 in lmicron steps with a total range of greater than 400 microns. In Figure 1, the diaphragm 144 is showing flexed positions extending inwardly of the chamber 146. However, the diaphragm may be flexed outwardly i.e. outside or above the chamber 146 if required. Similarly, the diaphragms for the inlet and outlet valves can be configured so that they also flex outwardly as well as inwardly. In the embodiment described herein, the dosing diaphragm 144 does not block fluid flow from the connecting tube 180 to the connecting tube 190. However, in an alternative embodiment, the flexible diaphragm could be used to interrupt fluid flow between the inlet valve 120 and the outlet valve 160. In general, and as already described, the inlet valve diaphragm 124, the dosing diaphragm 144 and the outlet valve 164 can be actuated using a single SMA element with a biasing spring (or other biasing element) or using one or more SMA actuating elements with or without a biasing spring (or other biasing element). Pump operation The operation of the pump 100 will now be described with reference to Figure 1. Initially, the inlet and outlet valves are both closed. The inlet valve 120 is opened by actuating SMA elements 122 which causes the flexible diaphragm 124 to open (i.e. move upwards against the force of the biasing spring 128). In some examples where the inlet 110 of the pump 100 is connected to a pressurised reservoir, opening of the inlet valve 120 allows fluid to flow into the pump 100 (past the inlet valve 120) under the force of the pressurised reservoir. In other examples where the reservoir connected to the pump 100 is not pressurised, the fluid may be drawn into the pump 100 by moving the flexible dosing diaphragm 144 of the dosing mechanism 140 upwards. This increases the volume of the chamber 146 which in turn lowers the pressure, creating a suction that draws the fluid in from the reservoir. In either case, the diaphragm 144 is controlled to achieve the dosing required, as will be described in further detail below. In an alternative, the pump may have a pressurised reservoir, and the dosing chamber is filled by moving the dosing diaphragm 144 to allow the fluid to be pushed into the dosing chamber 146 by the pressure. A predefined amount of fluid can be drawn into the chamber 146 according to the amount that the flexible diaphragm 144 moves. Thus, it is possible to control the amount of fluid entering the pump 100 by controlling the SMA elements 142 which in turn controls the movement of the flexible diaphragm 144. The predefined amount of fluid may correspond to the total drug dosage to be delivered to the patient. For example, the amount of fluid drawn into the pump may be 1 microlitre, 10 microlitres, lOOmicrolitres, 1 millilitre or 10 millilitres. Other volumes are also possible. Once the predefined amount of fluid has been drawn into the pump 100, the inlet valve 120 closes under control of the actuating SMA elements 122 to cause the flexible diaphragm 124 to be moved to the closed position (as shown in Figure 1). Closure can also be affected using the force of the spring 128 and / or opposing SMA elements. Once the inlet valve 120 has closed, the outlet valve 160 is opened using SMA elements 162. The fluid that has been drawn into the pump 100 can then be administered to the patient by forcing the fluid in the pump 100 out via the outlet valve 160 and outlet 170. This is achieved by moving the flexible diaphragm 144 downwards (using the SMA elements 142), which decreases the volume of the chamber 146 and pushes the fluid in the pump out through the outlet. A predefined amount of fluid can be administered to the patient according to the amount that the diaphragm 144 moves downwards. Thus, it is possible to control the amount of fluid exiting the pump 100 via the outlet 170 by controlling the SMA elements 142 which in turn controls the movement of the flexible diaphragm 144. The predefined amount of fluid may correspond to the total drug dosage to be delivered to the patient (i.e. all of the fluid that entered the pump 100 in the first step that is to be delivered as a bolus dose) or may be less. For example, the total drug dosage that entered the pump 100 may then be gradually provided to the patient over a period of time (i.e. basal dosage), by repeated administrations of smaller amounts of the fluid. For example, if 1ml of fluid enters the pump, this may be delivered to the patient in incremental stages, such as 10, 20 or 100 incremental stages. Generally speaking, the number of incremental stages in which the fluid in the pump 100 can be delivered to the patient corresponds to the number of different positions that the SMA elements can position the flexible diaphragm 144 in. The pump 100 can also be operated in a mode in which each dose consists of refilling the chamber 146 and then dispensing a single partial volume. Alternatively, each dosing cycle comprises a partial aspiration from the reservoir into the chamber 146 and then a partial dispense from the chamber 146 via the outlet 170. Once the fluid that was initially drawn into the pump 100 has been delivered to the patient (in a single dose or in incremental stages), the outlet valve 160 closes by actuating SMA elements 162 to cause the flexible diaphragm 164 to be moved to the closed position (as shown in Figure 1), either by actuation of the SMA elements 162, and / or under the force of the spring 168. Once the outlet valve 160 has closed, the process may be repeated again (starting from opening the inlet valve 120). The outlet valve 160 can be configured to close between dispensing steps as the spring 168 prevents fluid from leaving the pump 100. This has the advantage of conserving power. In general, the variable displacement of the flexible diaphragm 144 of the dosing mechanism 140 allows the pump 100 to deliver high volume "bolus" type doses at relatively high speed (e.g. by delivering all of the fluid drawn into the pump in a single dose), or alternatively delivering very small and accurate micro doses in small increments for "basal" type doses (by repeatedly delivering a small amount of the total fluid drawn into the pump over a longer period of time). As described above, and as an example, the SMA elements 142 are able to position the flexible diaphragm 144 at any one of a plurality of positions. The SMA elements 142 may be able to position the flexible diaphragm 144 at any one of a plurality of positions, for example 10, 20, 100, or 500 different open positions. The diaphragm 144 can be controlled using input values of up to 0.1 of a micron so as to move the diaphragm 144 in 1 micron steps with a total range of greater than 400 microns. This is particularly advantageous when working in conjunction with a patient feedback sensor such as a Continuous Glucose Monitor which measure the varying condition of the patient and can be used to trigger the delivery of finely adjusted doses of insulin. Dosage regimes can also be controlled by selectively controlling the amount of displacement of the inlet valve and outlet valve diaphragms, which is enabled by the fact that the diaphragms are SMA element actuated. For example, for high speed and high-volume treatments, the diaphragms 124 and 164 of the inlet valve and outlet valve respectively, may be fully opened at the appropriate times for higher flow rates allowing for faster delivery. Alternatively, for micro doses, the diaphragms 124 and 164 may only open a small amount, leaving a small orifice in the inlet and outlet vales 120 and 160 which improves the accuracy of the dosing. The use of SMA elements enables direct feedback from the SMA elements themselves to be used to control the SMA elements. This is achieved by determining the position of the respective diaphragm to a high degree of accuracy. This feedback control can take the form of a resistance measurement, taken from the SMA elements as power is applied to them using a constant voltage or constant current drive mechanism, to cause them to contract and using a control loop as described in further detail below. Thus, it is possible to monitor the measured resistance and verify that the diaphragms are moving the correct amount for a given dosage regime. The control system may control drive signals in response to the measured resistance so as to pump a determined amount of fluid that is required to be dispensed. Alternatively, the power consumed in the SMA element can be measured. In another alternative, the position of the respective diaphragms can be detected by using alternative position sensors, such as a Hall Sensor or other suitable sensor. Measuring the resistance or power consumed provides an accurate measure of the length of the SMA element, which also allows accurate verification of the proper operation of each valve and the pump as a whole, without requiring any additional sensor elements. For example, a control system connected to the SMA elements may calculate the length of the at least one of the one or more shape memory alloy elements from the measured resistance. The control system may also detect abnormal operation of the pumping arrangement on the basis of the measured resistance indicating that the diaphragms are not moving the correct amount and may output a warning signal in response to detecting abnormal operation of the pumping arrangement. This can be done using the outlet valve 160 or the diaphragm 144 of the dosing mechanism 140 as the indicators, by measuring the resistances in the respective SMA elements 142 or 162. A control system may output a warning signal in response to detecting abnormal resistance to movement of the movable element. Actuator assembly Generally speaking, the SMA elements in the form of SMA wires of any of the inlet, outlet and dosing mechanism may be connected to the corresponding diaphragm via a connection portion. In some examples, the SMA elements may form part of an actuator assembly. The actuator assembly may have a support structure and a moveable part, wherein the moveable part is moveable relative to the support structure in at least one linear direction. The moveable part is connected to the flexible diaphragm such that movement of the moveable part in the linear direction causes the movement of the diaphragm between the various positions. The actuator assembly comprises a plurality of SMA elements connected between the moveable part and the support structure, the selective actuation of which drives the movement of the moveable part. Figure 2 is a schematic illustration of an actuator assembly 200 as may be used with any one of the inlet valve 120, outlet valve 160 and dosing mechanism 140. Figure 2 describes an actuator mechanism using a pair of opposing SMA elements 208a, 208b. Each SMA element 208a, 208b is coupled at their ends to a support structure 204 by means of connection portions 220, for example crimps or other suitable means of connection. Each of the SMA elements 208a, 208b are also connected to a movable part 210. The support structure 204 is fixed with respect to the moveable part 210. The moveable part 210 comprises a first connection portion 206 connected to a flexible diaphragm 212 and a second connection 214 connected to a spring 202. One of the SMA elements 208a is connected to the first connection portion 206 and the other of the SMA elements 208b is connected to the second connection 214. The SMA elements 208a, 208b receive control signals from drive circuitry (not shown in Fig. 2) to control the length of the SMA elements 208a, 208b so as to control the flexible diaphragm 212. This control is affected by supplying a drive current to one or both of the SMA elements 208a, 208b as will be described further below. When the temperature of the SMA element 208a, 208b is increased by supplying it with an electrical current, the increase in temperature causes the length of the respective SMA element to decrease. In turn, the respective connection portion 206, 214 to which the SMA element 208a, 208b is connected, is pulled either downwards or upwards as viewed in Fig. 2. By varying the temperature of the element i.e. by varying the power / current / voltage supplied, the diaphragm 212 can be moved upwards or downwards in the direction of the double-headed arrow A in Figure 2. In the example shown in Figure 2, a spring 202 is arranged coupled to the movable part 210 so as to apply a biasing force to the movable part 210 (and to the diaphragm 212) to bias the diaphragm 212 to a closed position i.e. down in Figure 2. As already indicated above, other arrangements of SMA elements and spring (or other suitable biasing mechanism) can be used. For example, a similar opposing SMA element actuation arrangement can be used without a spring (or other suitable biasing mechanism) or a single SMA element can be used with a spring (or other suitable biasing mechanism). In any pump, the actuating arrangement can be the same for the inlet and outlet valves and dosing mechanism, or different actuator arrangements can be used for each. As such, the inlet and outlet valves and the dosing mechanism can be provided with a combination of SMA elements, biasing mechanisms such as a spring, along with drive and control circuitry as will be described in further detail below. Actuator assembly control The actuator assembly 200 may be controlled by a control system 300. A schematic illustration of a control system 300 is shown in Fig. 3. As is conventional, a length of an SMA element 308 of the actuator assembly 200 is varied by varying the temperature by regulating the power of the drive signals supplied to the SMA elements. Heating is provided directly by the drive signals. Cooling is provided by reducing or ceasing the power of the drive signals to allow the SMA element to cool by conduction, convection and radiation to its surroundings. For clarity. Figure 3 shows a single SMA element 308. In practice, and as described above, the pump 100 will have a number of SMA elements depending upon the configuration of the pump 100. The control system 300 is connected to the SMA element 308 and supplies drive signals thereto. The control system 300 may be implemented in any suitable manner, for example in an integrated circuit chip. The control system 300 includes a drive circuit 302 arranged to generate the drive signals, and a control unit 304 that is arranged to control the drive circuit 302. The drive circuit 302 may be implemented by suitable electronic components. The control unit 304 may be implemented by a processor executing an appropriate program. The control system 300 also includes a power supply 316. The control unit 304 controls the power of the drive signals supplied by the drive circuit 302. For example, the drive signals may be pulse width modulated signals whose pulse-width is controlled by the control unit 304 to vary the power of the drive signals and thereby control the SMA element 308 The control system 300 further includes a resistance measurement circuit 306 that is connected to the SMA element 308 and measures the electrical resistance of the SMA element 308. A measure of the resistance output from the resistance measurement circuit 306 is supplied to control unit 304 which uses it as a feedback signal to control the power of the drive signals under closed loop control. The control unit 304 of the control system 300 monitors the measured resistance to provide position detection of the respective diaphragm which is actuated by the SMA element(s) and to control the drive of the SMA elements to move the flexible diaphragm to which it is coupled. The resistance of the SMA element 308 is related to its length, and so the control unit 304 calculates the length of the SMA element 308 from the measured resistances, and hence the position of the flexible diaphragm 212. The length of the SMA element 308 is directly related to the position of the respective connection portion 206, 214 to which the SMA element 308 is coupled and hence the position of the flexible diaphragm. Therefore, the measured resistance of the SMA element 308 is used to calculate its length which, in turn, is used to detect the position of connection portion 210 and flexible diaphragm 212 to which it is attached. In an alternative springless actuator assembly, in which first and second SMA elements are used, the resistances of the individual elements is directly related to the position of connection portion 210 and hence the flexible diaphragm 212. Therefore, the measured resistances of both the first and second SMA elements are used to calculate their lengths which are used to detect the position of connection portion 210 to verify that the flexible diaphragm 212 is in the required position. The control unit 304 can also detect abnormal operation of the actuator assembly 200 on the basis of the measured resistance, and outputs a warning signal in response to detecting abnormal operation of the actuator assembly 200. The warning signal may be of any suitable type, for example an electrical signal, a visible signal or an audible signal or a haptic event. Figure 4 describes an illustration of feedback control example of SMA actuator elements in the pump 100. In Figure 4, the actuator SMA elements 308 are indicated by the reference numbers SMA0 to SMA7. i.e. for control of up to eight SMA elements 308. In practice, up to six of the SMA elements would be used in the pump for actuation of the respective valves (two for each of the inlet valve, outlet valve and dosing mechanism) with the additional two channels being available for other functions e.g. control of other mechanisms. As described above, the control of the SMA actuator elements is affected by the control unit 304 which generates drive signals for each of the SMA actuator elements 308 by means of the drive circuit 3O2.The movement of the flexible diaphragms of the respective valves is controlled by selectively varying the temperature of the SMA actuator elements 308 using selective drive signals. Heating is provided directly by the drive signals. Cooling is provided by reducing or ceasing the power of the drive signals to allow the SMA actuator elements 308 to cool by conduction, convection and radiation to its surroundings. The control system 300 has the following arrangement and operation. Each of the SMA elements 308, receives power from the power supply 316 and is connected to a common ground 312 via the drive circuit 302. The drive circuit 302 is connected to the SMA actuator element and supplies a drive signal to one or more of the SMA actuator elements 308. The power supply 316 may be a constant-voltage current source or a constant-current current source. For example, in the latter case the constant current might be of the order of 30 to 100mA. The drive circuit 302 receives power from the power supply 316. The drive signal generated by the drive circuit 302 is a pulse-width modulation (PWM) signal. The PWM duty cycle of the drive signal is varied by the drive circuit 302 to vary the power in accordance with a control signal supplied thereto. Signals from the drive circuit are coupled via FETs 310. The FETs 310 act as a switch to control power supplied to the SMA elements 308. The drive circuit 302 controls the average power by controlling the power source 316 to vary the power supplied to the SMA elements 308. In particular, the FETs 310 deliver the power into the into the SMA actuator elements 308 at the proportion requested by the drive circuit 302. In this way, the control unit 304 controls the average power of the drive signals to achieve predetermined tensions in the SMA actuator elements 308. The average power may be kept constant during an actuation operation but may be varied between actuations, for example in response to a measure of the ambient temperature. The measure of ambient temperature may be determined by a temperature sensor (not shown). Alternatively, if the temperature sensor is omitted, the measure of ambient temperature may be a measure of an electrical characteristic of the SMA elements 308 that is representative of ambient temperature, for example determined as disclosed in WO 2009 / 0741898. Typically, the average power is controlled to decrease as the ambient temperature increases, although at relatively high ambient temperatures, the average power is controlled to decrease by a smaller amount or to remain constant with further ambient temperature increases. For example, the average power may be controlled to remain constant above a threshold of say 50°C. These settings provide good operating efficiency and protection against element damage. As already described, the length of an SMA element is a function of the resistance of the SMA element. Measuring resistance may thus provide a measure of the length of a respective SMA element, and so ultimately allows determination of the position of the moveable part 210 (and thus the flexible diaphragm(s) 124,144, 164) relative to the support structure 204. The determined position of the movable part 210 relative to the support structure 204 may be compared to a desired position of the movable part 210 relative to the support structure 204, and a pulse width modulation (PWM) control signal may be adjusted to bring the movable part 210 closer to the desired position. So, the control unit 304 may comprise closed loop control. In the embodiment described herein, this closed loop control is provided by a Proportional-lntegral-Derivative (PID) controller 314 to generate the PWM control signals. The measured resistance may be fed back to the PID controller 314. The resistance detection circuit 306 is connected across the SMA actuator elements 308 and is arranged to detect the measure of the resistance of the SMA actuator element 308. In the case that the power supply 316 is a constant-current current source, the detection circuit 306 may be a voltage detection circuit operable to detect the voltage across the SMA actuator element 308 which is a measure of the resistance of the SMA actuator element 308. In the case that the power supply 316is a constant-voltage current source, the detection circuit 306 may be a current detection circuit. For a higher degree of accuracy, the detection circuit 306 may comprise a voltage detection circuit and a current detection circuit operable to detect both the voltage and current across the SMA actuator and to derive a measure of resistance as the ratio thereof. The measures of resistance of each SMA actuator element 308 derived by the detection circuits 306 are supplied to the PID controller 314. The PID controller 314 derives a feedback difference measure. The feedback difference measure is the sum of the measures of resistance of each SMA actuator element 308 scaled relative to each other by factors. The magnitude of the factors represents the component of the force applied to the flexible diaphragm so as to move the diaphragm to reach its requested position. The sign of the factors represents the direction in which the respective SMA actuator wire applies said component of force. The feedback difference measure is used as a feedback signal in the closed-loop control of the SMA actuator elements 308 as follows. A position signal represents the desired position of the flexible diaphragm and is supplied to an offset subtractor that subtracts an offset to derive a target difference measure. The offset has a fixed value and represents a difference between characteristic resistances for the SMA actuator elements 308. These characteristic resistances could be measured, calculated or stored on the control unit 304. For example, the characteristic resistance of each SMA actuator element 308 could be (a) the resistance of the respective SMA actuator element when an equal power is applied to all the SMA actuator elements 308, (b) a resistance associated with a position at the centre of the range of movement of the flexible diaphragm, or (c) related to the maximum resistance of the SMA actuator element 308 when changing length under a fixed tension. The offset may arise due to differences in the environment of the pump 100 or properties of the SMA actuator elements 308. The offset is optional but when used gives improved control where the change in resistance with power applied to an SMA element 308 approaches zero (i.e. at the maximum resistance or minimum resistance as the power is changed at a fixed tension), because even if the resistance of one of the SMA actuator elements 308 is invariant with changing power, so long as the resistance of the other of the SMA actuator elements 308 still varies with applied power, then the difference in the resistances will still vary. The feedback difference measure and the target difference measure are supplied to an error detector which derives an error signal representing the difference therebetween. The control unit 304 generates a control signal for each of the SMA actuator elements 308 on the basis of the error signal E using a closed-loop control algorithm that reduces the error signal, i.e. reduces the difference between the feedback difference measure and the target difference measure. The closed-loop control may be proportional or may include differential and / or integral terms. The control unit 304 supplies the control signals to the drive circuits 302. Since the feedback control is performed on the basis of the feedback difference measure, effectively the tension and temperature of the SMA actuator elements 308 may be performed independently of the positional control by varying the average power supplied to the SMA actuator elements 308. Thus, the control signals for each of the SMA actuator elements 308 may represent the relative power of the respective drive signal and are selected so as to reduce the error signal. The drive circuits 302 then supply a drive signal that has a power equal to the average power supplied to each of the SMA actuator elements 308 multiplied by the relative power represented by the control signal. This has the effect of adjusting the relative amounts by which the powers of the drive signals vary from an average power in accordance with the control signals. Control and Measurement Signals The control unit 304 generates and supplies drive signals to the drive circuit 302 that modulates power through the SMA elements 308. As already mentioned, the drive signals are pulse width modulated (PWM) drive signals. The control unit 304 may generate and supply a respective PWM drive signal to each SMA element. The PWM control signals each comprise a series of PWM pulses. The frequency of the pulses is the PWM frequency f(PWM). The period between starts of adjacent pulses in the PWM control signals is the PWM period t(PWM). The PWM period t(PWM) corresponds to the reciprocal of the PWM frequency f(PWM). The control unit 304 schedules the PWM pulses in a series of time slots which are defined by a PWM frequency f(PWM). The duration of each time slot TS is equal to the PWM period t(PWM). Each SMA element 308 is supplied with a respective PWM pulse once (or not at all, if no power is to be provided to an SMA element) per time slot. Each time slot is divided into a plurality of sub-slots. Each time slot consists of the plurality of subslots. Each PWM pulse is provided in a sub-slot. The control unit 304 operates at a servo frame frequency. The control unit 304 updates the PWM control signals at most at the servo frame frequency, so once per servo frame. The pulse width of the PWM pulses may be updated once per servo frame. So, the PWM control signals generally remain the same within a servo frame, although some predetermined deviation within some time slots may be allowed for the purpose of scheduling measurement pulses, for example. The pulses of the PWM control signals may comprise voltage pulses or current pulses. In general, the pulses may be any pulses capable of supplying electrical energy to the SMA elements 308. The pulses of the PWM control signals are preferably square pulses, although in general pulses with other shapes may also be used. Switching the PWM control signals thus gives rise to rising or falling edges in the PWM control signals. The amplitude of the pulses of the PWM control signal is preferably constant, such that the power applied to the SMA elements is controlled solely or at least primarily by adjusting the width of the pulses of the PWM control signals. The amplitude of the PWM control signals may also be adjusted so as to provide additional control of the power provided to the SMA elements 308. The control unit 304 may determine the measured resistance during a respective sensing interval. During the sensing interval, the control unit 304 may generate a measurement pulse. The PWM control signals that are used to drive the SMA elements may be suspended during this interval. In general, specifically the PWM control signal of the SMA element to which the measurement pulse is to be applied may be suspended, or all PWM control signals may be suspended. The control unit 304 may determine the electrical characteristics of each SMA element once per servo frame, for example. Each measurement pulse may be applied to a different SMA element so as to determine the resistance in each SMA element. The measurement pulse may be square voltage pulse. However, the measurement pulse may in general be any other pulse (for example a current pulse) that allows measuring of the electrical characteristic of the SMA element. The measurement pulse is not necessarily a square pulse but may be a pulse with a slower or gradual onset and a slower or gradual descent. The measurement pulse and the PWM control signals may be generated by different sources. For example, the PWM control signals may be generated by a voltage source, and the measurement pulse may be generated by a current source (e.g. a constant current source). The measurement pulse and the PWM control signals may be of a different type (e.g. one a current pulse, the other a voltage pulse), or may be of the same type (e.g. both current pulses, or both voltage pulses). Position Control Measurement Being able to accurately determine the position of the flexible diaphragms 124, 144,164 provides a number of advantages. Knowing the positions of the flexible diaphragms enables correct operation of the pump. It also confirms correct operation of the pump and so prevents undetected loss of drug delivery which may be required under regulatory requirements. If the diaphragm is determined to be in an incorrect position, then the controller can be operable to provide an alarm and, if necessary, stop operation of the pump. The position of the inlet valve membrane 124 and outlet valve membrane are adjusted relative to the dosing mechanism 140 to balance the fluid volume within the pump 100 volume so as to prevent large pressure variations. The advantage in this case is to reduce pressure changes on the fluid which may cause damage to active ingredients in the fluid (i.e. to the medication itself), and or high flow rates between chambers of the pump 100 which can cause high shear forces on the fluid, and which can cause also cause damage to the ingredients in the fluid and maybe damage to the pump 100. This allows the actuation of the diaphragms to take place at a faster rate because there is less constraint imposed by the control system to limit damage to the drug. Pressure Measurement Fluid pressure is a measurement of the force per unit area within a fluid. In a container, the pressure can be the result of gravity, acceleration, or other forces. In a fluid pressure applies in all directions. Fluid pressure changes with the velocity of the fluid. Measuring the fluid pressure and detecting changes in fluid pressure within the fluid in the pump 100 can be used to more accurately control the delivery of the fluid. Changes to the measurement pulse due to changes in fluid flow can be detected and measured. Changes in fluid pressure can give rise to changes in resistance, power or temperature changes measured during the control process described above. In particular, such changes may be unexpected or outside usual limits which may indicate a malfunction or sub-optimal operation of the pump. Detecting pressure within the pump 100, for example within the chambers 126, 146, 166 or in the connecting tubes 180,190 will help maximise pumping accuracy, by enabling the stroke of the dosing diaphragm 144, or the frequency of the stroke, to be adjusted to take account of variations in pressure. Controlling the position of the diaphragm 144 also enables the flow rate of the fluid within the pump 100 to be controlled. As an example, the controller 304 may be operable to monitor the power of the drive signals to detect if the power of the drive signals is abnormally high, this being indicative of a change in the fluid flow. Similarly, the controller 304may be operable to monitor the resistance measurement signals to detect if they are outside of normal operating parameters and to control the dosing of the fluid. Change in the fluid flow which could be the result of, for example, a leak within the pump. Detection of a loss of pressure is indicative a of a leak. This may typically be detected during downward actuation of the dosing diaphragm 144 when the outlet valve 170 is closed. Detecting the pressure within the pump 100, for example within the chambers 126, 146, 166 or in the connecting tubes 180, 190 will also help maximise pumping accuracy, by adjusting the stroke of the dosing diaphragm 144, or the frequency of the stroke, can be adjusted to take account of variations in pressure. Controlling the position of the diaphragm 144 also enables the flow rate of the fluid within the pump 100 to be controlled as measuring the positions of the diaphragm 144 as it moves to deliver the required dose can be used to monitor and control the flow rate. Pressure measurement may be used in conjunction with dosing mechanism movable element and / or inlet valve movable element, and / or outlet movable membrane position to calculate a measure of flow rate. In particular, the pump may include a flow rate measurement mechanism arranged to measure the flow rate of the fluid in the pump, and wherein the control system controls the drive signals in response to the measured flow rate so as to control the fluid flow within the chamber. Other variations In alternative embodiments to the invention, here may be many other variations of the abovedescribed examples. For example, the actuator assembly may include different types of actuating units to those described above. Examples of such actuating units include a folded SMA element arrangement as disclosed in WO 2021 / 111131 Al, a V-shaped SMA element with a compliant connector as disclosed in \N0 2013 / 121225 Al, a scissor jack arrangement as disclosed in WO 2021 / 156458 Al, a two-stage arrangement as disclosed in WO 2021 / 111181 Al. The documents referred to in the preceding sentence are each herein incorporated by reference. The actuator assembly may have any number of different types of actuating units and may have any suitable number of actuating units of each type. Other position sensing arrangements can be used. For example, the temperature of the SMA elements can be measured and used to control the diaphragms. Alternatively, the power consumed in the SMA elements can be used as a position to sensor. The control systems describe above can be configured as a single control system for all of the inlet valve, outlet valve and diaphragm valve or as individual control systems for each valve In alternative configurations, the pump 100 can use other means of detecting the position of the movable element and therefore the diaphragm. For example, Hall Effect sensors could be used to determine the position. The inlet and outlet valves could be passive valves i.e. not SMA actuated but may be opened and closed in response to fluid flow. In another embodiment, instead of separate chambers for each of the inlet and outlet valves and the dosing mechanism, a single chamber can be provided in which the inlet 110, outlet 170 are in fluid communication. In this embodiment, instead of separate diaphragms for each of the inlet and outlet valves and the dosing mechanism, a single diaphragm can be used which can be actuated at variations regions to perform the functions described above. SMA The above-described SMA actuator assemblies comprise at least one SMA element. The term 'shape memory alloy (SMA) element' may refer to any element comprising SMA. The SMA element may be described as an SMA element. The SMA element may have any shape that is suitable for the purposes described herein. The SMA element may be elongate and may have a round cross section or any other shape cross section. The cross section may vary along the length of the SMA element. The SMA element might have a relatively complex shape such as a helical spring. It is also possible that the length of the SMA element (however defined) may be similar to one or more of its other dimensions. The SMA element may be sheet-like, and such a sheet may be planar or non-planar. The SMA element may be pliant or, in other words, flexible. In some examples, when connected in a straight line between two components, the SMA element can apply only a tensile force which urges the two components together. In other examples, the SMA element may be bent around a component and can apply a force to the component as the SMA element tends to straighten under tension. The SMA element may be beam-like or rigid and may be able to apply different (e.g. non-tensile) forces to elements. The SMA element may or may not include material(s) and / or component(s) that are not SMA. For example, the SMA element may comprise a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term 'SMA element' may refer to any configuration of SMA material acting as a single actuating element which, for example, can be individually controlled to produce a force on an element. For example, the SMA element may comprise two or more portions of SMA material that are arranged mechanically in parallel and / or in series. In some arrangements, the SMA element may be part of a larger SMA element. Such a larger SMA element might comprise two or more parts that are individually controllable, thereby forming two or more SMA elements. The SMA element may comprise an SMA element, SMA foil, SMA film or any other configuration of SMA material. The SMA element may be manufactured using any suitable method, for example by a method involving drawing, rolling, deposition, sintering or powder fusion. The SMA element may exhibit any shape memory effect, e.g. a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, e.g. by Joule heating, another heating technique or by applying a magnetic field.

Claims

1. A pump comprising: a fluid chamber arranged to hold a volume of fluid; an inlet valve comprising a movable element and arranged to be coupled to a reservoir of fluid and to control fluid flow from the fluid reservoir into the fluid chamber; an outlet valve comprising a movable element and arranged to control fluid flow from the pump; a dosing mechanism arranged comprising a movable element arranged to pump fluid; one or more actuation elements coupled to the at least one of the respective inlet valve, and / or the outlet valve and / or the dosing mechanism movable elements for moving the respective inlet valve, outlet valve and dosing mechanism movable element; a position detection mechanism configured to detect the positions of the inlet valve movable element, the outlet valve movable element and the dosing mechanism movable element; and a control system arranged to supply drive signals to the inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element, wherein the control system controls the drive signals in response to the detected positions of the inlet valve movable element, the outlet valve movable element and the dosing mechanism movable element so as to pump a determined volume of fluid from the chamber.

2. A pump according to claim 1, further including a pressure measurement mechanism arranged to measure the pressure of the fluid in the pump, and wherein the control system controls the drive signals in response to the measured pressure so as to control the fluid flow within the chamber.

3. A pump according to claim 1 or claim 2, further including a flow rate measurement mechanism arranged to measure the flow rate of the fluid in the pump, and wherein the control system controls the drive signals in response to the measured flow rate so as to control the fluid flow within the chamber.

4. A pump according to any of claims 1 to 3, wherein the actuation elements are SMA elements.

5. A pump according to claim 4, wherein the SMA elements are coupled to at least one of the inlet valve movable element, the outlet valve movable element and / or the dosing mechanism movable element for moving the respective inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element.

6. A pump according to claim 4, wherein the position detection mechanism comprises a resistance measurement circuit arranged to measure the resistance of at least one of the one or more SMA elements; and wherein the control system controls the drive signals in response to the measured resistance to verify that the respective movable element moves the required extent so as to pump the determined volume of fluid.

7. A pump according to claim 4, wherein the position detection mechanism comprises a power measurement circuit, and wherein the control system controls the drive signals in response to the measured power to verify that the respective movable element moves the required extent so as to pump the determined volume of fluid.

8. A pump according to claim 5, wherein the position detection mechanism is arranged to measure the temperature of at least one of the one or more SMA elements; and wherein the control system controls the drive signals in response to the measured temperature to verify that the respective movable element moves the required extent so as to pump the determined volume of fluid.

9. A pump according to claim 1 or claim 2 wherein the position detection mechanism is a Hall sensor or any other position sensor.

10. A pump according to any preceding claim, including a fluid reservoir.

11. A pump according to claim 10 wherein the reservoir is a pressurised reservoir.

12. A pump according to any preceding claim, wherein the dosing mechanism movable element is arranged to deliver the determined volume of fluid on each stroke, and the control system is arranged to detect the position of the dosing mechanism movable element to verify that the movable element moves the required extent of the stroke to deliver the determined volume of fluid.

13. A pump according to any of claims 6, wherein the resistance measurement circuit is arranged to measure the resistance of the inlet valve and / or outlet valve movable elements, and / or dosing mechanism movable element; and wherein an inlet valve control system and / or an outlet valve control system and / or a dosing mechanism control system controls the drive signals in response to the measured resistance to verify that the respective inlet valve and / or outlet valve and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid.

14. A pump according to any of claims 7, wherein the wherein the power measurement circuit is arranged to measure the power supplied to the inlet valve and / or outlet valve movable elements and / or dosing mechanism movable element, and wherein an inlet valve control system and / or an outlet valve control system and / or a dosing mechanism control system controls the drive signals in response to the measured power to verify that the respective inlet valve and / or outlet valve movable element and / or dosing mechanism control system moves the required extent so as to pump the determined volume of fluid .

15. A pump according to any of claims 8, wherein the position detection mechanism is arranged to measure the temperature of the SMA elements of the inlet valve movable element and / or outlet valve movable element and / or dosing mechanism movable element; and wherein an inlet valve control system and / or an outlet valve control system and / or a dosing control system controls the drive signals in response to the measured temperature to verify that the respective inlet valve movable element and / or outlet valve movable element and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid .

16. A pump according to any preceding claim, wherein the control system is arranged to detect abnormal operation of the respective inlet valve movable element and / or outlet valve movable element and / or dosing mechanism movable element.

17. A method of controlling a pump, the pump comprising a fluid chamber arranged to hold a volume of fluid; an inlet valve comprising a movable element and arranged to be coupled to a reservoir of fluid; an outlet valve comprising a movable element; and a dosing mechanism arranged comprising a movable element arranged to pump fluid; one or more actuation elements coupled to at least one of the inlet valve, outlet valve and dosing mechanism movable elements for moving the respective inlet valve, outlet valve and dosing mechanism movable element; and a position detection mechanism configured to detect the positions of at least one of the inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element; the method comprising: detecting the positions of the at least one of the inlet valve, outlet valve and dosing mechanism movable elements; and supplying drive signals to the at least one inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element in response to the detected positions of the respective inlet valve movable element, and / or the outlet valve movable element and / or the dosing mechanism movable element so as to pump a determined volume of fluid from the chamber.

18. The method of claim 17, wherein the actuation elements are SMA elements, and wherein the detection of the position of the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element comprises measuring the resistance of at least one of the one or more SMA elements; and wherein the drive signals are controlled in response to the measured resistance to verify that the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid.

19. The method of claim 17, wherein the actuation elements are SMA elements, and wherein the detection of the position of respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element comprises measuring the power of the drive signals, and wherein the drive signals are controlled in response to the measured power to verify that the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid.

20. The method of claim 17, wherein the actuation elements are SMA elements, and wherein the detection of position of respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element comprises measuring the temperature of at least one of the one or more SMA elements; and wherein the drive signals are controlled in response to the measured temperature to verify that the respective inlet valve movable element, and / or outlet valve movable element and / or dosing mechanism movable element moves the required extent so as to pump the determined volume of fluid.

21. The method of any of claims 17 to 20, wherein the inlet valve control system and / or outlet valve control system may be arranged to detect abnormal operation of the respective inlet valve movable element and / or outlet valve movable element on the basis of the measured resistance, power, or temperature.

22. The method of claim 17, wherein the step of detecting the position of the movable element comprises using a Hall sensor or other position sensor.

23. The method of any of claims 17 to 22 further comprising the step measuring the flow rate of the fluid and controlling the drive signals in response to the measured flow rate so as to control the fluid flow within the chamber.

24. The method of any of claims 17 to 23 further comprising the step of detecting abnormal operation of the respective inlet valve movable element and / or outlet valve movable element and / or dosing mechanism movable element.

25. The method of any of claims 17 to 24, further comprising the steps of: closing the inlet and outlet valves using the respective inlet valve movable element and outlet valve movable element; opening the inlet valve using the inlet valve movable element; moving the dosing mechanism movable element to aspirate fluid into the fluid chamber; closing the inlet valve using the inlet valve movable element; opening the outlet valve using the outlet valve movable element; and moving the dosing mechanism movable element to dispense the determined volume of fluid; and closing the outlet valve using the outlet valve movable element.s

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