A pump

Abstract

A pump comprising a dosing mechanism, at least one valve, at least one actuator, and a controller. The dosing mechanism comprises a fluid chamber configured to hold a volume of fluid and a movable element configured to move to change the volume of the fluid chamber. The valve controls fluid flow into or out of the fluid chamber. The actuator moves the dosing mechanism movable element. The controller supplies drive signals to the actuator in response to a first parameter indicative of a position of the dosing mechanism movable element to control the position of the dosing mechanism movable element within a range of movement.

Description

[0001] A PUMP

[0002] Field

[0003] The present application relates to a pump. The pump may be used as a drug delivery device. The pump has a particular application for accurately pumping relatively small amounts of fluid, for example a therapeutic product, for delivery to a human or animal body.

[0004] Background

[0005] Infusion pumps are medical devices used to administer a predetermined amount of a therapeutic liquid (for example, insulin) to a human or animal body (for example, into 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 desired levels.

[0006] For an infusion pump worn on the body of a patient it is desirable to make the infusion pump as small as possible in order to make it more comfortable for the patient, interfere less with their daily activities including interference with clothing worn over the pump, and be less conspicuous. An infusion pump may connect to an external tube, in turn connected to an infusion site on the patient's body. An alternative type of infusion, known as a patch pump, has no external tube: a patch pump uses a flexible tube (cannula) extending under the patient's skin, and is self-contained with a reservoir for a therapeutic liquid and a pump mechanism contained within a single housing that is secured to a patient's skin with an adhesive patch. Examples of the present invention are presented in the context of a patch pump but apply equally to other types of infusion pumps.

[0007] A patch pump may typically comprise a reservoir for a therapeutic liquid, such as insulin, a dosing mechanism, one or more valves, one or more actuators for controlling the dosing mechanism and the valves, a power supply, a cannula, and a control system to control the various parts. The term "dosing mechanism" is used in the present specification to refer to a device that when actuated doses or displaces a fluid from a fluid chamber and so may instead be referred to as a displacer. In the context of an infusion pump the term "dosing mechanism" indicates its function in terms of dosing a therapeutic liquid to a patient and so could also be referred to as a dispenser. In the following description an example of a dosing mechanism is presented comprising a fluid chamber and a diaphragm or other movable portion defining a portion of the fluid chamber and configured to be moved by an actuator assembly to change the volume of the fluid chamber and so displace fluid into or out of the fluid chamber. Other suitable dosing mechanism mechanisms will be well known to the skilled person, for instance a piston or syringe. The combination of a dosing mechanism and one or more valves(particularly, an inlet valve and an outlet valve or a combined valve mechanism) to control fluid flow into and out of the fluid chamber comprises a pump or pumping mechanism. In the present patent specification, a pump is also referred to as a microdoser, indicating the capability to repeatedly and accurately deliver small volumes of therapeutic liquids to a patient, through control of the dosing mechanism and the valves.

[0008] 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.

[0009] Certain embodiments of the present invention seeks to address this, and other problems encountered in the prior art. In particular, certain embodiments of the present invention seek to provide a pump capable of accurately pumping or dispensing variable volumes of liquid from a fluid chamber.

[0010] Summary

[0011] According to a first aspect of the present invention there is provided a pump comprising: a dosing mechanism comprising a fluid chamber configured to hold a volume of fluid and a movable element configured to move to change the volume of the fluid chamber; at least one valve configured to control fluid flow into or out of the fluid chamber; at least one actuator coupled to and configured to move the dosing mechanism movable element; and a controller configured to supply drive signals to the at least one actuator in response to a first parameter indicative of a position of the dosing mechanism movable element to control the position of the dosing mechanism movable element within a range of movement.

[0012] The dosing mechanism movable element is thus drivable to and can be held at any position within its range of movement according to a closed feedback loop based on measured or inferred position. From any position (other than the extremes of the range of movement) the dosing mechanism movable element can be driven in either direction. This provides a range of benefits, including that in one embodiment the controller may be configured to supply drive signals to the at least one actuator in response to the first parameter so as to move the dosing mechanism movable element to pump a determined volume of fluid from the chamber. That is, the dose volume dispensed from the chamber may be any size, including dosing the whole pumpable volume of the fluid chamber or a partial volume of the chamber. Where less than the whole volume is dispensed, the chamber may be refilled after each dispense stroke or the pump may be configured to sequentially doses smaller volumes of liquid and periodically refill the chamber. The ability to accurately control the position of the dosing mechanism movable element permits the rate of movement to be controlled, for instance allowing the speed of dispensing a volume of fluid from the chamber to be adjusted.The at least one actuator may comprise: a first actuator coupled to and configured to move the dosing mechanism movable element; and at least one further actuator coupled to and configured to control the at least one valve. That is, a single actuator may control the movement of all controllable elements of the pump or separate actuators may control the dosing mechanism and the at least one valve.

[0013] Where, as discussed below, the at least one valve comprises an inlet valve and an outlet valve, there may be a common actuator responsible for controlling both valves. Alternatively, the valves may be controlled by separate actuators.

[0014] The dosing mechanism movable element may comprise a movable diaphragm configured to move to change the volume of the fluid chamber. The diaphragm may close an aperture formed in a portion of the chamber. As an example, the diaphragm may be defined by a flexible membrane affixed about the periphery of the aperture and having a portion (for instance, a central portion) that may be moved by the actuator to change the volume of the chamber. As an example, the actuator may drive movement of a push rod or piston which is coupled to the membrane so as to distort the membrane thereby changing the chamber volume.

[0015] The at least one valve may comprise: an inlet valve configured to be coupled to a reservoir of fluid and to control fluid flow from the fluid reservoir into the fluid chamber; and an outlet valve configured to control fluid flow from the fluid chamber. That is, they may be separate valves. However, the present invention is more broadly applicable to any suitable valve arrangement for controlling fluid flow into and out of a fluid chamber.

[0016] The at least one actuator may be further configured open and close at least one of, or both, the inlet and outlet valves in response to drive signals from the controller. That is one or both valves (or the single valve if a single valve controls both fluid flow) may be an active valve in the sense that it is driven to open and close.

[0017] The inlet valve may comprise a movable element configured to move to permit or restrict the flow of fluid. Similarly, the outlet valve may comprise a movable element configured to move to permit or restrict the flow of fluid. Either or both of the inlet valve movable element and the outlet valve movable element may comprise a diaphragm that is movable to control the flow of fluid through the valve. Such a diaphragm may be configured similarly to the dosing mechanism diaphragm discussed above, except that the diaphragm may be drive towards or away from a valve seat to close or open the valve to fluid flow.The controller may be further configured to supply drive signals to the at least one actuator in response to at least a second parameter indicative of a position of at least one valve movable element so as to control the position of the valve movable element within a range of movement to vary the flow of fluid into or out of the fluid chamber. That is, the pump may be configured to measure or infer the position of one or both valve movable elements and supply drive signals to the appropriate actuator to move the valve to a variable position within a range of movement. Such a valve is not just active (driven to open or close) but also able to adopt or move to any given position within its range of movement. This permits the flow of fluid through the valve to be adjusted, including controlling the rate of opening or closing.

[0018] The pump may further comprise a position detection mechanism configured to generate the first parameter indicative of a position of the dosing mechanism movable element. The position detection mechanism or a further position detection mechanism may be configured to generate the at least a second parameter indicative of a position of the at least one valve movable element. Where there are separate inlet and outlet valves separate parameters indicative of the positions of the inlet valve movable element and the outlet valve movable element may be measured or inferred.

[0019] The at least one actuator may include at least one shape memory alloy, SMA, element. Where separate actuators control the dosing mechanism and the valves, each actuator may include at least one SMA element, optionally at least two SMA element for controlling movement of a movable element (for instance a dosing mechanism diaphragm or a valve diaphragm) in opposed directions.

[0020] The position detection mechanism and / or the further position detection mechanism may comprise at least one of: a resistance measurement circuit configured to measure the resistance of an SMA element; a power measurement circuit configured to measure a parameter indicative of the power drawn by the SMA element; or a temperature measurement circuit configured to measure the temperature of the SMA element. As discussed in the following description of particular embodiments, an SMA based actuator allows for a position of a connected movable element (for instance, a diaphragm) to be inferred from a sensed parameter of the SMA element which is indicative of its length.

[0021] As well or instead, the position detection mechanism may comprise or further comprise a Hall sensor, a capacitive sensor, or any other position sensor. That is, the position of a dosing mechanism or valve movable element may be directly measured. In some embodiments more than one technique may be used to detect the position of a movable element, allowing for increased accuracy and / or redundancy.A pump may further comprise a pressure measurement mechanism configured to measure the pressure of the fluid in the pump. Measuring pressure may be used to further control the drive signals generated by the controller so that a pump rate may be adjusted according to sensed system pressure so as to pump a determined volume of fluid from the chamber. As an example, if pressure downstream of the pump increases then the pump rate may be increased to ensure that the flow rate of liquid from the pump remains the same (or that the dispensed volume remains the same).

[0022] Similarly, a pump may further comprise a flow rate measurement mechanism configured to measure the flow rate of the fluid in the pump, and the controller may be further configured such that the drive signals are further in response to the measured flow rate so as to pump a determined volume of fluid from the chamber.

[0023] According to a second aspect of the present invention there is provided a method of controlling a pump, the pump comprising: a dosing mechanism comprising a fluid chamber configured to hold a volume of fluid and a movable element configured to move to change the volume of the fluid chamber; a least one valve configured to control fluid flow into or out of the fluid chamber; and at least one actuator coupled to and configured to move the dosing mechanism movable element; wherein the method comprises driving the at least one actuator in response to a first parameter indicative of a position of the dosing mechanism movable element to control the position of the dosing mechanism movable element within a range of movement.

[0024] The controlled pump may be according the first aspect of the present invention.

[0025] The method may further comprise driving the at least one actuator in response to the first parameter so as to move the dosing mechanism movable element to pump a determined volume of fluid from the chamber.

[0026] The method may further comprise driving the at least one actuator in response to at least a second parameter indicative of a position of a movable element forming part of the at least one valve so as to control the position of the valve movable element within a range of movement to vary the flow of fluid into or out of the fluid chamber.

[0027] The at least one actuator may include at least one shape memory alloy, SMA, element. The method may further comprise detecting a position of a dosing mechanism movable element or a valve movable element according to one of: measuring the resistance of an SMA element; measuring a parameter indicative of the power drawn by the SMA element; or measuring the temperature of the SMA element.The method may further comprise measuring detecting a position of a dosing mechanism movable element or a valve movable element using a Hall sensor, a capacitive sensor, or any other position sensor.

[0028] Each movable element may comprise a movable portion of a dosing mechanism or a valve. For instance, a dosing mechanism movable element may comprise a diaphragm for which a portion (for instance, a central portion) is movable under the control of an actuator to change the volume of a fluid chamber. Similarly, for a valve, a movable element may comprise a valve closure element, for instance a movable portion of a valve diaphragm that may be moved away from or towards a valve seat to open or close the valve.

[0029] In an alternative, that falls within the scope of the present disclosure, the controller may be configured to supply drive signals to the at least one actuator in response to a first parameter indicative of a position of a movable element forming part of a valve so as to control the position of the valve movable element within a range of movement. That is, a valve may comprise a movable element, such as a diaphragm which can be moved to any position within a range of movement using closed loop feedback control. This may be desirable to control the rate or amount by which the valve opens. This position controllable valve may be in combination with a position controllable dosing mechanism movable element, or in combination with a dosing mechanism movable element which is more simply controlled (such as to always deliver the same volume of liquid).

[0030] According to a further embodiment there is provided a pump comprising: a dosing mechanism comprising a fluid chamber configured to hold a volume of fluid and a movable element arranged to pump fluid from the fluid chamber; an inlet valve comprising a movable element and configured 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 configured to control fluid flow from the fluid chamber; at least one actuator coupled to and configured to move at least one of the inlet valve movable element, the outlet valve movable element and the dosing mechanism movable element; a position detection mechanism configured to detect a position of at least one 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 at least one actuator, 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.In some embodiments the pump comprises: 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.

[0031] 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 may control the drive signals in response to the measured pressure so as to pump a determined volume of fluid from the chamber.

[0032] Pressure measurement may be used in conjunction with the dosing mechanism movable element and / or the inlet valve movable element, and / or the outlet movable membrane position to calculate a measure of flow rate. The pump may further include a flow rate measurement mechanism arranged to measure the flow rate of the fluid in the pump, and the control system may control the drive signals in response to the measured flow rate so as to control the fluid flow within the chamber.

[0033] The actuator may may include at least one shape memory alloy, SMA, element. 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.

[0034] The position detection mechanism may include a resistance measurement circuit configured to measure the resistance of an SMA element. The control system may be configured to control the drive signals in response to the measured resistance to verify that a 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.A power measurement circuit may be arranged to measure the power supplied to an actuator controlling the inlet valve and / or outlet valve movable elements and / or dosing mechanism movable element, and the control system may be configured to control 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.

[0035] 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 .

[0036] 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).

[0037] The position detection mechanism may be a Hall sensor. Other position sensors can be used such as capacitive sensors.

[0038] The pump may further comprise a fluid reservoir. The fluid reservoir may be pressurised.

[0039] 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.

[0040] According to a further embodiment there is provided a method of controlling a pump, the pump comprising: a dosing mechanism comprising a fluid chamber configured to hold a volume of fluid and a movable element arranged to pump fluid from the fluid chamber; an inlet valve comprising a movable element and configured to be coupled to a reservoir of fluid; an outlet valve comprising a movable element configured to control fluid flow from the fluid chamber; at least one actuator coupled to and configured to move at least one of the inlet valve movable element, the outlet valve movable element,and the dosing mechanism movable element; and a position detection mechanism configured to detect a position of at least one of the inlet valve movable element, the outlet valve movable element, and the dosing mechanism movable element; wherein the method comprises: detecting the position of at least one of the inlet valve movable element, the outlet valve movable element, and the dosing mechanism movable element; and supplying drive signals to the at least one actuator in response to the detected position so as to pump a determined volume of fluid from the chamber.

[0041] The method may comprise 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.

[0042] The actuator may comprise at least one SMA element, and 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.

[0043] Alternatively, the actuator may comprise at least one SMA element, 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 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.

[0044] 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.

[0045] The step of detecting the position of the movable element may comprise using a Hall sensor, capacitive sensor, or other suitable position sensors.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The dosing mechanism movable element may be moved in incremental steps to provide a partial dispense of the fluid in the fluid chamber.

[0050] 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.

[0051] According to a further embodiment 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] The control system may be arranged to output a warning signal in response to detecting abnormal operation of the pumping arrangement.

[0056] 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.

[0057] 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 toverify 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] The inlet valve may comprise a chamber coupled to the inlet. The outlet valve may comprise a chamber coupled to the outlet.

[0063] The inlet valve chamber of the pump, the outlet valve chamber and the fluid chamber may comprise a single chamber.

[0064] The movable elements of the inlet valve, the outlet valve and the dose control mechanism may each comprise a flexible diaphragm.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] The control system may be configured to measure the flow rate of the fluid.

[0069] 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.

[0070] 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.

[0071] According to a further embodiment 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 thedrive signals in response to the detected position so as to pump a determined volume of fluid from the pump.

[0072] The determined volume of fluid may be continually variable.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 outletvalve 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.

[0079] 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.

[0080] 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.

[0081] Brief description of the drawings

[0082] Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0083] Figure 1 is a schematic representation of a pump comprising an inlet valve coupled to a fluid reservoir, a dosing mechanism, and an outlet valve;

[0084] Figure 2 is schematic representation of an example of an actuation assembly for the pump of figure 1;

[0085] Figure 3 is a schematic representation of a control system for the pump of figure 1; and

[0086] Figure 4 is a schematic representation of a second embodiment of a control system for the pump of figure 1.

[0087] Detailed description

[0088] Certain example devices will now be described. Where similar or identical components are used in the different examples, they will be given the same reference numerals. For efficiency, description of similar or identical elements may not be repeated between the examples and characteristics and features of elements are to be understood as applying to those elements in all examples unless the description indicates otherwise.

[0089] Pump Overview

[0090] Figure 1 illustrates a drug delivery device which may incorporate or implement the present invention. It may suitably be a patch pump as described above, however it may be any other form of infusion pump for delivery a therapeutic substance to a human or animal body. More generally still, the present invention is applicable to other medical or non-medical types of pumps, particularly miniature pumps,where the capacity to accurate dispense small and optionally variable small volumes of liquids is required.

[0091] Certain embodiments of the present invention provide a miniature pump that uses two active valves and a dosing mechanism comprising a diaphragm defining a portion of a fluid chamber (also referred to as a displacement chamber) which uses variable position control to achieve a high flow rate and a low minimum dose in the same product. When the dosing mechanism diaphragm moves, the volume of the fluid chamber changes so that liquid is drawn in or pushed out of the fluid chamber. However, the present invention is not restricted to the use of active valves. The ability to accurately control the position of a movable element that changes the volume of a fluid chamber, in combination with any form of valves including passive valves (for instance, check valves) is within the scope of the present invention. In one described embodiment, high flow rate may be achieved by continuously cycling the dosing mechanism diaphragm through its full displacement, for instance at a controlled frequency. Low minimum dose rate may be achieved by performing partial displacement of the dosing mechanism diaphragm in a single cycle, which may then be repeated. The pump may wait for an indefinite period before delivering the next dose. The precise pumping cycle implemented is outside of the scope of the present invention, for which the focus is the ability to accurately control the movement of a movable element in a dosing mechanism in order to pump a determined volume of liquid.

[0092] Advantageously, active valves (meaning that the valve is actively driven in both the opening and closing directions) provide precision opening and closing plus variable displacement, which allows optimisation of valve openings to suit high and low flow rate requirements. As well as increasing efficiency and improving accuracy of pumped volume, this also reduces the pressure differentials experienced by the fluid, which can cause destabilisation of complex fluids like drugs, causing crystallisation, fibrilization or breakdown of the molecules, or the release of absorbed gases from the fluid due to negative pressure.

[0093] Precisely controlled valve opening also means that the fluid displacement generated by the displacement of the valve components can be compensated by synchronising the movement of the dosing mechanism diaphragm to balance the flow, preventing or reducing reverse flow in the outlet, minimising pressure changes in the fluid within the pump and increasing accuracy.

[0094] In some embodiments, controlling the rate of valve opening also reduces the rate of pressure change in the fluid, thereby reducing pressure spikes, which helps maintain fluid stability.Additionally, active valves also enable a minimum dose to be unconstrained by the hysteresis of opening and closing a passive valve which requires a certain minimum pressure differential before they open or close. Using active valves can also decouple internal pressure from external back pressure.

[0095] For certain embodiments described herein the dosing mechanism diaphragm and the diaphragms of the valves are controlled with high precision, and high-resolution feedback to provide closed loop control and monitoring necessary for safety critical applications. This, in some embodiments, is implemented using shape memory alloy, SMA, actuators with resistance feedback control or external sensors, for instance Hall sensors or capacitive sensors to provide controlled actuation. In other embodiments different types of actuator, such as voice coil motor, VCM, motors and other types of precision-controlled actuator technology can be used. The present invention is not limited to any particular dosing mechanism or actuator technology so long as the dosing mechanism includes a fluid chamber and a movable element which when moved changes the volume of the fluid chamber such that liquid is drawn in or pushed out of the fluid chamber (through an appropriate valve arrangement). The ability to determine a parameter indicative of the position of the movable element, for instance through a position detection mechanism, allows the actuator to be controlled with appropriate drive signals so that the movable element can be accurately moved to any position within its range of movement. This control of the position of the movable element allows the volume of liquid drawn into or dispensed from the fluid chamber to be variable (certain conventional pump technologies only allow a fixed volume to be drawn in or dispensed). In some examples described below, the position detection mechanism may comprise measuring a parameter of the actuator itself, for instance where the actuator is based on SMA.

[0096] Pump

[0097] There is disclosed herein a pump suitable for drug delivery applications that comprises an SMA actuated inlet valve, a dosing mechanism comprising an SMA actuated movable element (for instance, a diaphragm) for dosing control, and an SMA actuated outlet valve. The inlet valve and outlet valve may also comprise SMA actuated diaphragms. However, as previously noted this is only one example pump to which the present invention is applicable. Each diaphragm comprises a movable element which is actuated by a respective SMA actuator. In particular, for each movable element (diaphragm) a portion of the diaphragm is moved (up and down in the view of figure 1) to change the volume of a dosing chamber (for the dosing mechanism) or to move towards or away from a valve seat (for the input and output valves). Particularly, the portion of each movable element (diaphragm) which is operated on by an actuator may be a point contact or an area of the diaphragm smaller than the full diaphragm which extends across an aperture defined by the fluid (dosing) chamber or a valve housing. In some examples an SMA element may be coupled directly to a diaphragm (or via a crimp connection). In other examplesthe actuator may include a plunger element, also referred to as a push rod, along with the SMA element and the plunger may be coupled to the diaphragm (and may define the area of the diaphragm which is moved). In some examples the actuator may push on the diaphragm to effect movement in one direction without being coupled to the diaphragm, with a return force provided by a separate biasing mechanism or the resilience of the diaphragm itself. It will be understood that where in the following description reference is made to a movable element or diaphragm moving, this corresponds to movement of the portion of the diaphragm that is coupled to the actuator. A remainder of the diaphragm extending from that portion to a periphery of the diaphragm where it is coupled to the dosing chamber or valve housing (defining an aperture) may stretch or otherwise deform to accommodate this movement.

[0098] In one embodiment of the invention, the SMA actuated diaphragm of the dosing mechanism 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 delivered amount of fluid may comprise a maximum volume corresponding to the full range of motion of the movable element, or a partial dose. The inlet and outlet valves may also be SMA actuated diaphragms enabling variable position control using resistance feedback. This use of SMA actuated valves and dosing mechanism offers finer resolution control of the fluid, by minimising the orifice when pumping small volumes and / or balancing the movement of the valves with equivalent movement of the diaphragm of the dosing mechanism so that, as the valve generates a suction from its displacement, the diaphragm of the dosing mechanism 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.

[0099] This variable displacement of the dosing mechanism diaphragm, enabled by the closed loop control of the position of the dosing mechanism diaphragm through position measurement, allows a pump to deliver a range of doses from high volume "bolus" type doses (for instance, of the order of 500 nl or larger) at relatively high speed, to very small and accurate micro doses in small increments for "basal" type doses (for instance, of the order of 50 nl or smaller). This is also useful when working in conjunction with a patient feedback sensor such as a Continuous Glucose Monitor (CGM), wherein the dispensed drug is insulin, which measures the varying condition of the patient and can be used to trigger the delivery of finely adjusted doses.

[0100] 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 anoutlet 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 198 that stores a liquid 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.

[0101] The diaphragm 144 of the dosing mechanism can move between different positions (that is, up and down as illustrated in figure 1 and indicated by the dashed lines). Moving diaphragm 144 upwards in the view of figure 1 draws fluid from the reservoir 198 into a fluid chamber 146 of the dosing mechanism 140. The diaphragm 144 is also movable downwards in the view of figure 1 in order to discharge fluid through the outlet 170. It will be understood that in some embodiments the inlet valve 120 and the outlet valve 160 may be controlled synchronously with the dosing mechanism 140 in order to ensure fluid flow through the pump 100 as indicated by the arrows. However, in other embodiments, passive valves such as one-way check valves may be used in order to ensure fluid flows in the direction indicated. The dosing mechanism diaphragm 144 may be moved to any position within a range of movement, for instance by being 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.

[0102] The arrows in figure 1 indicate the direction of flow of a liquid through the pump 100. Liquid is received (for example, from the reservoir 198) 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 (for example, 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.

[0103] It is also possible, where active valves are used, to operate the pump 100 in the reverse direction if required. For example, this may facilitate filling the reservoir 198 using the pump 100. It will be appreciated that to enable fluid flow in the reverse direction the roles of the inlet valve 120 and the outlet valve 160 are essentially reversed.

[0104] Inlet Valve

[0105] Considering the inlet valve 120 in more detail, an embodiment of an active inlet valve 120 comprises one or more SMA elements 122 forming an actuator connected to a flexible diaphragm 124 (directly, orfor instance via a push rod). In this embodiment a single SMA element 122 is coupled between the diaphragm 124 and a support structure (not shown) via coupling arrangements 132. As illustrated, the SMA element is connected at each end to a support structure and at an intermediate point is coupled to a portion of the diaphragm 124. In an alternative, the arrangement may be two separate SMA elements extending from the support structure to the diaphragm 124 (or there may only be a single SMA element connected between the support structure and the diaphragm). Further arrangements of SMA elements will be apparent to the skilled person. 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). Further actuator arrangements will be appropriate to the skilled person, including actuator arrangements that do not make use of SMA, for instance those based on VCM.

[0106] 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 (that is, by passing electrical 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.

[0107] The SMA element 122 therefore controls the operation of the inlet valve 120 through its 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.

[0108] 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 therate at which it is opened. For a high flow rate, the diaphragm 124 is fully opened and for a low flow rate the diaphragm 124 may only be partially opened to improve accuracy and minimise pressure changes in the fluid that may damage or change the viscosity of some drugs.

[0109] 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 mechanism 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 position may in principle be continuously variable within a range of movement. 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.

[0110] Outlet Valve

[0111] 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. Other opposed SMA actuator arrangements will be apparent to the skilled person. 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 outlet valve 160 is further shown including a plunger element 163 (also referred to as a push rod) connecting the SMA elements to the diaphragm 164 (or pushing against the diaphragm 164 in the event that the actuator is not attached to the diaphragm 164, as noted above).

[0112] 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 outlet valve 160.In an alternative, the spring can be replaced by other forms of biasing control (or, as for any of the diaphragms, the bias force may be provided by the resilience of the diaphragm itself). In another embodiment, the outlet valve 160 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).

[0113] 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.

[0114] 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. Both the inlet valve 120 and the outlet valve 160 may be substantially identical in at least their actuator arrangement (and may take either form illustrated in figure 1). In a further option, both the inlet valve 120 and the outlet valve 160 may be controlled by a single actuator arranged such that only a single valve can be open at a time, to guard against uncontrolled flow of the liquid drug from reservoir 198 to the patient in the event of pump failure.

[0115] Dosing Mechanism

[0116] The dosing mechanism 140 positioned in between the inlet valve 120 and outlet valve 160 also comprises an actuator comprising one or more SMA elements 142, a flexible diaphragm 144 and a fluid chamber 146. The dosing mechanism actuator may be generally the same as that of the inlet valve 120 or the outlet valve 160 or may take other forms. 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.

[0117] 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.

[0118] 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. The dosing diaphragm 144 may be moved through control of the actuator to any position within a range of motion.

[0119] In figure 1, the diaphragm 144 shows flexed positions extending inwardly of the chamber 146.

[0120] However, the diaphragm may be flexed outwardly that is, outside or above the chamber 146 as well or instead if required. This may be desirable when drawing in fluid from the inlet 110 via the inlet valve 120 in the event that a subsequent large dose of fluid is to be expelled. Similarly, the diaphragms for the inlet and outlet valves can be configured so that they also flex outwardly as well as inwardly.

[0121] 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.

[0122] In general, and as already described, the inlet valve diaphragm 124, the dosing diaphragm 144 and the outlet valve 164 can each 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), as well as its primary role in pumping fluid from the inlet 110 to the outlet 170. As well, and as previously noted, actuators not based on SMA may be used.

[0123] Figure 1 further illustrates a controller 199 (also referred to herein as a control system) shown coupled via dotted lines to each actuator controlling each one of the valves and the dosing mechanism. The controller 199 is also coupled via dashed lines to position detection mechanisms 196 associated with each valve and the dosing mechanism. Where passive valves are used it will be understood that the controller 199 is only connected to the dosing mechanism actuator and a position detection mechanism for the dosing mechanism. Each position detection mechanism 196 is configured to measure, detect, or receive a parameter indicative of a movable element (in this embodiment, a valve diaphragm, or the dosing diaphragm). As is described in greater detail below, a position detection mechanism may be a separate position directly measuring the position of a respective movable element. In some embodiments the position detection mechanism may comprise or incorporate the actuator such that aparameter indicative of a position of a movable element is measured or provided by the actuator which also moves that movable element.

[0124] Example Pump

[0125] The pump may suitably be constructed from a layered structure of rigid and flexible components that are bonded or clamped together to create the fluidic system. Actuators comprising SMA elements may be attached to the assembly and structurally anchored to the rigid components with connections to the flexible components of the dosing mechanism diaphragm and the valve diaphragms so that they can be pushed and pulled by the SMA elements.

[0126] The valves may consist of two ports joined by a chamber, with a flexible diaphragm resting across at least one of the ports so as to seal the port. An SMA actuator may be mounted to generate a positive force on the sealing diaphragm, creating a "normally closed" valve. Powering the SMA element may cause the SMA element to phase change, causing it to contract to open the valve. A partial operation of the actuator will cause a partial opening of the valve. The position of each valve closure element (such as a valve diaphragm) can be measured, either by resistance feedback from the SMA element, or by an external sensor, for example a Hall sensor or a capacitive sensor. For an external sensor, a sensing element may be directly coupled to a movable element (for instance, a diaphragm) or it may be coupled to a connected part (for instance, a push rod driving movement of a diaphragm) and the measured position corrected for the difference in position.

[0127] The diaphragm chamber may have ports connected to the inlet and outlet valves, and a flexible diaphragm across one face of the chamber. The flexible diaphragm may be connected to an opposing SMA element actuator arrangement which when powered causes the diaphragm to displace in and out, changing the internal volume of the chamber.

[0128] The opposing wire SMA actuator may consist of two or more SMA elements, arranged so that when one SMA element is heated and contracts, it causes the other to stretch out. Unpowered, the diaphragm may rest approximately in a neutral position. Accordingly, the available stroke may be both positive and negative relative to the unpowered position. The actuator may have end-stops at one or both ends, to limit travel of the diaphragm and to allow calibration of the travel range. Control of power to the SMA elements allows the diaphragm to be moved to any position within limits of end-stops or SMA element extension. A position of the diaphragm may be measured either via resistance measurement, or by an external sensor, for example a hall sensor or a capacitive sensor.The diaphragm actuator may in some examples feature a spring in series with one (or more) of the opposing SMA elements that compress the fluid, whilst at least one opposing SMA element is connected directly between the valve and the base structure.

[0129] Pump Operation

[0130] The operation of the pump 100 will now be described with reference to figure 1. It will be appreciated that this operation is achieved through the supply of appropriate drive signals to each actuator from the controller 199. 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 (that is, 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 and into the dosing mechanism chamber 146) under the force of the pressurised reservoir. It will be understood that in some embodiments the reservoir is not pressurised. In other examples where the reservoir connected to the pump 100 is not pressurised or the pressure is lower, 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.

[0131] 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.

[0132] 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 effected using the force of the spring 128 and / or opposing SMA elements.

[0133] Once the inlet valve 120 has closed, the outlet valve 160 is opened using SMA elements 162. It will be appreciated that there may be a delay between filling the fluid chamber and dispensing the liquid drug through the outlet valve 160. 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 the outlet 170. This is achieved by moving the flexible diaphragm 144 downwards (using the SMA elements142), which decreases the volume of the chamber 146 and pushes the fluid in the pump out through the outlet.

[0134] 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 (that is, 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 (that is, basal dosage), by repeated administrations of smaller amounts of the fluid. For example, if 1 ml 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.

[0135] 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 operation from the chamber 146 via the outlet 170.

[0136] 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.

[0137] Once the outlet valve 160 has closed, the process may be repeated again (starting from opening the inlet valve 120). A further alternative is to completely fill the fluid chamber 146 and then perform two or more partial dispense operations before the fluid chamber is partially or fully filled again. Further pump cycles will be apparent to the skilled person.

[0138] 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.

[0139] 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 (for example, by1

[0140] 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). Delivery of a basal dose may comprise repeated discrete doses, or for certain periods of time the dosing mechanism may operate by continuously moving the diaphragm 144 at a slow speed for continuous discharge of fluid through the outlet 170. 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.

[0141] This variable displacement and hence variable dosing is particularly advantageous 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 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.

[0142] Position Control

[0143] 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. For this example, the position detection mechanism 196 for each controlled movable element comprises the actuator itself.

[0144] 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. The measured SMA resistance or consumed power comprises a parameter indicative of the position of the associated movable element (for instance, a valve or dosing diaphragm). It will be understood that in order to control the movement of the movable element the actual position of the movable element may not actually need to be determined: a measured resistance or power may comprise an input to a control algorithm implemented by the controller 199, along with a required position of the movable element, with the controller 199 supplying drive signals to the actuator in order to reduce the error between a current position and the required position. However, in some embodiments the current position of the movable element can be calculated or inferred from the measured resistance or power. For instance, given knowledge of the mechanical arrangement of the SMA element and any intermediate parts between the SMA element and the movable element, the resistance of the SMA element (or a pair of opposed SMA elements) can be converted to a length of the or each SMA element, and that translated to a position of the movable element via an appropriate equation governing the arrangement of the actuator. Or, through a process of calibration, a measured parameter derived from the actuator (for instance, resistance or power) may be mapped to position of the movable element using a look up table.

[0145] In another alternative, the position detection mechanism 196 may comprise one or more separate position sensors, such as a Hall Sensor, capacitive sensor, or other suitable sensor allowing the position of the respective diaphragms to be directly detected. The output signal from a Hall sensor, a capacitive sensor, or another similar sensor may, for instance, comprise a voltage which is indicative of the position of the associated movable element. Similarly, a measured resistance or power of a SMA element forming part of an actuator for a movable element may be indicative of the connected movable element.

[0146] 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, the controller 199 may calculate the length of the at least one of the one or more shape memory alloy elements from the measured resistance.

[0147] In some examples, the position of one or more of the diaphragms may be measured using one or more of the techniques described above. This may allow for increased accuracy and / or redundancy. For instance, the position of the dosing diaphragm may be measured or inferred using one or more parameter obtained from an SMA element forming part of the dosing diaphragm actuator. As well, the position of the dosing diaphragm may be directly measured using a position sensor such as a Hall sensoror capacitive sensor. Alternatively, two different types of position sensor may be used. This dual position measurement may be used equally with one or both of the valves.

[0148] 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.

[0149] Actuator Assembly

[0150] 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 an intermediate moveable part, wherein the intermediate moveable part is moveable relative to the support structure in at least one linear direction. The intermediate moveable part is connected to the flexible diaphragm such that movement of the intermediate 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 intermediate moveable part and the support structure, the selective actuation of which drives the movement of intermediate the moveable part.

[0151] 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.

[0152] 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.

[0153] Each of the SMA elements 208a, 208b are also connected to an intermediate movable part 210. The support structure 204 is fixed with respect to the moveable part 210.

[0154] The intermediate moveable part 210 comprises a first connection portion 206 connected to a portion of a flexible diaphragm 212 (a movable element) and a second connection 214 connected to a spring 202. In other examples, the intermediate movable part 210 may bear against the diaphragm 212 at point 206 without being connected to it (with the resilience of the diaphragm 212 itself providing a return force,or a separate biasing mechanism applied to the diaphragm 212). In some examples the intermediate part 210 may comprise or be connected to a plunger element acting on the diaphragm 212.

[0155] 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.

[0156] The SMA elements 208a, 208b receive control signals from drive circuitry (not shown in figure 2) to control the length of the SMA elements 208a, 208b so as to control the flexible diaphragm 212.

[0157] 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.

[0158] 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 figure 2. By varying the temperature of the element that is, 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.

[0159] 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 downwards (which for a valve may comprise a closed position and for the dosing mechanism may comprise a relatively smaller dosing chamber volume).

[0160] As already indicated above, other arrangements of SMA elements and springs (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.

[0161] 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

[0162] The actuator assembly 200 may be controlled by a control system 300. A schematic illustration of a control system 300 is shown in figure 3. This control system 300 may comprise or form part of controller 199 shown in figure 1.

[0163] 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.

[0164] For clarity, figure 3 shows a single SMA element 308. In practice, and as described above, the pump 100 may have a number of SMA elements depending upon the configuration of the pump 100.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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 respectiveconnection 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.

[0170] In an alternative springless actuator assembly, in which first and second SMA elements are used, the resistances of the individual elements are 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.

[0171] 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.

[0172] 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.

[0173] Figure 4 describes an illustration of feedback control example of SMA actuator elements in the pump 100.

[0174] In figure 4, the actuator SMA elements 308 are indicated by the reference numbers SMA0 to SMA7. that is, for control of up to eight SMA elements 308. In one example, where each of the inlet valve, the outlet valve and the dosing mechanism are operated using the actuator arrangement of figure 2, up to six of the SMA elements may 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 for example, control of other mechanisms.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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 intermediate moveable part 210 (and thus themovable elements - the flexible diaphragm(s) 124, 144, 164) relative to the support structure 204. Where there is no intermediate movable part, for instance as illustrated in figure 1, and the SMA elements are coupled directly to or act directly against the flexible diaphragms, the measure resistance is directly determinative of the position of the diaphragms. 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.

[0182] 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.

[0183] The measures of resistance of each SMA actuator element 308 derived by the detection circuits 306 are supplied to the PID controller 314.

[0184] 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.

[0185] The feedback difference measure is used as a feedback signal in the closed-loop control of the SMA actuator elements 308 as follows.

[0186] 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.

[0187] 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 (that is, 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.

[0188] 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, that is, reduces the difference between the feedback difference measure and the target difference measure.

[0189] 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.

[0190] 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.

[0191] Control and Measurement SignalsThe 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.

[0192] 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).

[0193] 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.

[0194] Each time slot is divided into a plurality of sub-slots. Each time slot consists of the plurality of sub-slots. Each PWM pulse is provided in a sub-slot.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] 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.

[0201] 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.

[0202] 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 (for example, a constant current source). The measurement pulse and the PWM control signals may be of a different type (for example, one a current pulse, the other a voltage pulse) or may be of the same type (for example, both current pulses, or both voltage pulses).

[0203] Position Control Measurement

[0204] Being able to accurately determine the position of the flexible diaphragms 124, 144, 164 provides a number of advantages.

[0205] 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.

[0206] 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 (that is, 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.

[0207] Pressure Measurement

[0208] 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.

[0209] Measuring the fluid pressure and detecting changes in fluid pressure within the fluid in the pump 100, for instance within the dosing mechanism chamber 146, can be used to more accurately control the delivery of the fluid.

[0210] Changes to the measurement pulse due to changes in fluid flow can be detected and measured.

[0211] 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.

[0212] 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 (that is, the pump rate), 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.

[0213] 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 304 may 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.

[0214] 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. For example, the stroke of the closing 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.

[0215] 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. For example, as previously described, movement of the dosing mechanism movable element changes the volume of the fluid chamber. Knowledge of a first position of the movable element at a first time and a second position of the movable element at a second time allows for the change in volume of the fluid chamber between the first and second times to be determined. The flow rate may be determined based on change in volume of the fluid chamber and the time duration. Measurement of pressure during this time period may be used to correct for the effect of changing pressure on dispensed fluid volume.

[0216] In particular, the pump may include a flow rate measurement mechanism (based on the above analysis of movable element position) arranged to measure the flow rate of the fluid in the pump. The controller or control system may control the drive signals in response to the measured flow rate so as to control the fluid flow within the chamber.

[0217] Other variations

[0218] In alternative embodiments to the invention, here may be many other variations of the above-described examples.

[0219] 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 WO 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 may comprise a parameter indicative of the position of a movable element coupled to the SMA elements on the basis that temperature of an SMA element is indicative of how much the SMA element has contracted (given knowledge of the martensite finish temperature for the SMA elements). Thus, SMA temperature can be measured and used to control the diaphragms. Alternatively, the power consumed in the SMA elements can be used as a position sensor.

[0220] 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.

[0221] 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 or capacitive sensors could be used to directly determine the position of a diaphragm.

[0222] The inlet and outlet valves could be passive valves that is, not SMA actuated but may be opened and closed in response to fluid flow.

[0223] 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.

[0224] Dynamic Range

[0225] The above-described ability to control the position of a dosing mechanism movable element to variable positions within its range of motion (based on knowledge of a parameter indicative of the position of the movable element) allows for different volumes to be pumped from the fluid chamber in each pump cycle. That is, in each pump cycle either the whole pumpable volume of the fluid chamber may be dispensed, or a proportion of the volume can be dispensed. This may allow the dynamic range of deliverable volumes of liquid over a period to time to be significantly increased. As a simplified example, assuming that a pump is capable of operating at 1 Hz, then over 5 minutes there is a maximum of 300 available dosing cycles. If in each dosing cycle a dose corresponding to multiples of a tenth of the pumpable volume of the chamber can be delivered, then 10 times more different pumped volumes can be delivered in each cycle. For the example of an insulin pump, this allows for smoother delivery of insulin for a basal dose over time while still providing the capacity to rapidly deliver a bolus dose.Position Control of Valves

[0226] The above description has focused on the determination of parameters indicative of position for a dosing mechanism in order to control the delivery of a determined volume of liquid from the fluid chamber. The valves may be passive or may be actively controlled to be either fully open or fully shut. However, as noted above, the inlet and outlet valves may be active and the position of the movable element for each valve (the valve closure member, for instance a valve diaphragm) may be determined in the same way as described previously in connection with the dosing mechanism movable element. Accordingly, the position of each valve closure member may be determined and so controlled to any position within a range from fully closed to fully open. Controlling the degree to which each valve is open can allow for greater control over fluid flow into and out of the fluid chamber. That is, determining the position of the movable elements of each valve and the dosing mechanism allows for each to be controlled in order to deliver a determined volume of liquid from the fluid chamber (by moving the movable element of the dosing mechanism to displace an appropriate volume of liquid and appropriately timing the opening and closing of each valve). However, in a simpler embodiment of the invention only the movable element of the dosing mechanism may be controlled based on its detected position, with the valves being more simply controlled, or being based on passive valves. In a further embodiment a single valve may be provided, coupled to the fluid chamber, and configured to direct liquid to either the inlet or the outlet depending on whether the fluid chamber is aspirating or dispensing.

[0227] Additionally, the determination of a parameter indicative of a position of a valve closure member can allow valve failure to be detected. Valve failure may comprise the valve not correctly moving to the required position, and so corrective action may include increase the force applied to the valve to force it to the correct position. Or a detected valve failure may result in alarm signal provided to the user.

[0228] In a further variant, in place of an inlet valve and an outlet valve, the pump may include a single valve that selectively connects the fluid chamber to an inlet, an outlet, or disconnects the fluid chamber from both inlet and outlet. Such a valve may be actively controlled such that the valve is fully closed, fully connected to the inlet, or fully connected to the outlet. Or the valve may be actively controlled such that the degree to which the fluid chamber is connected to the inlet or outlet is variable, for instance by detecting a parameter indicative of the position of a movable element of the valve and using this to control the position of the movable element, as described above.

[0229] Fixed Volume Pumping

[0230] In a further embodiment a pump may comprise a dosing mechanism including a movable element for drawing liquid into or out of a fluid chamber coupled with at least one valve for controlling the flow offluid into or out of the fluid chamber. The dosing mechanism may comprise a fluid chamber and a diaphragm similar to the dosing mechanism described above. The dosing mechanism is controlled by an actuator for moving the diaphragm, which may include one or more SMA elements (though other actuator types may be used). The at least one valve may comprise a single valve for coupling the fluid chamber to an inlet or an outlet (or optionally also disconnecting the fluid chamber from both the inlet and the outlet). Alternatively, the at least one valve may comprise an inlet valve for selectively connecting the fluid chamber to an inlet (which may in turn be coupled to a reservoir) and an outlet valve for selectively connecting the fluid chamber to an outlet (which may in turn be coupled to a cannula or similar mechanism for supplying a liquid drug to a patient). In a mode of operation, the single valve or the pair of inlet and outlet valves may be actively controlled so as to open or close the valve to the flow of fluid. For the single valve, the active control may comprise the fluid chamber being connected to the inlet, the outlet, or closed, but without the ability to control the degree to which the valve is open to either the inlet or the outlet. For the pair of inlet and outlet valves the active control may comprise each valve being controlled to be fully open or fully closed. The dosing mechanism is controlled such that the movable element (for instance, the diaphragm) is moved from one end of its range of motion to the other. Accordingly, on an aspirate stroke, the at least one valve connects the fluid chamber to the inlet, and the movable element is driven to completely fill the fluid chamber. The movable element is driven to its position corresponding to the maximum fluid chamber volume. On a dispense stroke the at least one valve connects the fluid chamber to the outlet, and the movable element is driven to completely discharge the pumpable volume of the fluid chamber. By pumpable volume it is meant the volume of liquid that can be dispensed by driving the movable element to its position in which the volume of liquid in the fluid chamber is at a minimum. Accordingly, the volume dispensed on each pump cycle is fixed. An advantage of this embodiment is that the at least one valve and the dosing mechanism may be more simply controlled, without the requirement to be able to drive each movable element to intermediate positions.

[0231] Such a fixed volume pump may comprise: a dosing mechanism comprising a fluid chamber configured to hold a volume of fluid and a movable diaphragm configured to move to change the volume of the fluid chamber; an inlet valve configured to be coupled to a reservoir of fluid and to control fluid flow from the fluid reservoir into the fluid chamber; an outlet valve configured to control fluid flow from the fluid chamber (or a single valve as noted above); and at least one actuator coupled to and configured to move the movable diaphragm to draw fluid in and pump fluid out of the fluid chamber and to control the opening and closing of the inlet and outlet valves.Interpretation

[0232] Throughout this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to" and they are not intended to (and do not) exclude other components, integers, or steps. Throughout this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Throughout this specification, the term "about" is used to provide flexibility to a range endpoint by providing that a given value may be "a little above" or "a little below" the endpoint. The degree of flexibility of this term can be dictated by the particular variable and can be determined based on experience and the associated description herein.

[0233] Features, integers, or characteristics described in conjunction with a particular aspect or example of the invention are to be understood to be applicable to any other aspect or example described herein unless incompatible therewith. All of the features disclosed in this specification, and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing examples. The invention extends to any novel feature or combination of features disclosed in this specification.

[0234] Each feature disclosed in this specification may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0235] The phrase 'normal operation of the assembly' is intended to refer to a state in which the assembly is functioning as intended and excludes e.g. a user dropping the device in which the assembly is embodied.

[0236] SMA

[0237] The above-described SMA actuator assemblies may comprise at least one SMA element. The term 'shape memory alloy (SMA) element' may refer to any element comprising SMA. One suitable SMA material is a nickel-titanium alloy (for instance, Nitinol) but may also contain tertiary components such as copper. 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 (for instance, non-tensile) forces to elements.

[0238] 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. The coating may be an electrically insulating layer, for instance an SMA oxide layer increased through thermal or chemical treatment to an insulating thickness (for instance, 1 pm or more). Alternatively, the electrically insulating coating may a material applied to the SMA core on top of an oxide layer or after removal of the oxide layer. Suitable materials include, without limitation, polyimide, polyamide, polyurethane, Parylene, polytetrafluoroethylene (PTFE) or any combination thereof. Portions of an SMA element where an electrical connection is to be made may be uncoated, for instance by masking prior to a coating process, or by later removal by mechanical abrasion, or other chemical or physical means such as focussed laser or plasma ablation.

[0239] 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 wire, 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.

[0240] The SMA element may exhibit any shape memory effect, for instance, a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable way, for instance, by Joule heating, another heating technique or by applying a magnetic field. The heating of the SMA element may be achieved in a number of ways. In one arrangement, the material could be heated by passing a current through the SMA element. This current might come from a local or external power supply. Alternatively, the current might be induced in the SMA element by inductive coupling with an external alternating field. Where there are two actuators, the two actuators might be designed so that theycouple to two different frequencies of the inductive power source, thus allowing the two actuators to be heated differentially. In another arrangement, the material could be heated by external radiation such as a visible or infra-red laser. The external radiation could be focussed so that one actuator is heated preferentially over another actuator, thus allowing differential actuation. Alternatively, or additionally, different actuators, or portions of the actuators, could be treated (for example with a surface coating) so that the different actuators heat at different rates depending on the nature (for instance, the frequency) of the incident radiation.

[0241] "Smart" materials

[0242] SMA is an example of a "smart" material. By "smart" material it is meant a heat-activated material which may be used as part of an actuator to control movement of components of a device. Other examples of heat-activated material that may be used as well as or in place of SMA include:

[0243] Physically crosslinked SMP (Shape Memory Polymer); representative shape memory polymers include polyurethanes, polyurethanes with ionic or mesogenic components made by a prepolymer method. Other block copolymers also show the shape-memory effect, including: a block copolymer of polyethylene terephthalate (PET) and polyethyleneoxide (PEO), block copolymers containing polystyrene and poly(l,4-butadiene), and an ABA triblock copolymer made from poly(2-methyl-2-oxazoline) and polytetrahydrofuran.

[0244] Chemically crosslinked SMPs; examples include crosslinked polyurethane or PEO-based crosslinked SMPs. The network polymer can be synthesized by either polymerization with multifunctional (3 or more) crosslinker or by subsequent crosslinking of a linear or branched polymer.

[0245] These alternative heat-activated materials may be heated in the same or analogous ways to as described above in connection with SMA. In devices having two or more actuators, different actuators may be made from different heat-activated materials (or from two different materials of the same type). This may be useful to achieve an arrangement in which the actuators have different properties, either in terms of their mechanical properties or how they are actuated.

Claims

P612-GB03 46CLAIMS:

1. A pump comprising:a dosing mechanism comprising a fluid chamber configured to hold a volume of fluid and a movable element configured to move to change the volume of the fluid chamber;at least one valve configured to control fluid flow into or out of the fluid chamber;at least one actuator coupled to and configured to move the dosing mechanism movable element; anda controller configured to supply drive signals to the at least one actuator in response to a first parameter indicative of a position of the dosing mechanism movable element to control the position of the dosing mechanism movable element within a range of movement.

2. A pump according to claim 1, wherein the controller is configured to supply drive signals to the at least one actuator in response to the first parameter so as to move the dosing mechanism movable element to pump a determined volume of fluid from the chamber.

3. A pump according to claim 1 or claim 1, wherein the at least one actuator comprises:a first actuator coupled to and configured to move the dosing mechanism movable element; andat least one further actuator coupled to and configured to control the at least one valve.

4. A pump according to any one of the preceding claims, wherein the dosing mechanism movable element comprises a movable diaphragm configured to move to change the volume of the fluid chamber.

5. A pump according to any one of the preceding claims, wherein the at least one valve comprises:an inlet valve configured to be coupled to a reservoir of fluid and to control fluid flow from the fluid reservoir into the fluid chamber; andan outlet valve configured to control fluid flow from the fluid chamber; andwherein the at least one actuator is further configured open and close at least one of, or both, the inlet and outlet valves in response to drive signals from the controller.

6. A pump according to claim 5, wherein the inlet valve comprises a movable element configured to move to permit or restrict the flow of fluid;wherein the outlet valve comprises a movable element configured to move to permit or restrict the flow of fluid; andP612-GB03 47optionally wherein one or both of the inlet valve movable element and the outlet valve movable element comprises a diaphragm that is movable to control the flow of fluid through the valve.

7. A pump according to claim 6, wherein the controller is further configured to supply drive signals to the at least one actuator in response to at least a second parameter indicative of a position of at least one valve movable element so as to control the position of the valve movable element within a range of movement to vary the flow of fluid into or out of the fluid chamber.

8. A pump according to any one of the preceding claims, further comprising a position detection mechanism configured to generate the first parameter indicative of a position of the dosing mechanism movable element.

9. A pump according to claim 7 or claim 8 when dependent on claim 7 , wherein the position detection mechanism or a further position detection mechanism is configured to generate the at least a second parameter indicative of a position of the at least one valve movable element.

10. A pump according to any one of the preceding claims, wherein the at least one actuator includes at least one shape memory alloy, SMA, element.

11. A pump according to claim 10 when dependent on claim 8 or claim 9, wherein the position detection mechanism and / or the further position detection mechanism comprises at least one of: a resistance measurement circuit configured to measure the resistance of an SMA element; a power measurement circuit configured to measure a parameter indicative of the power drawn by the SMA element; ora temperature measurement circuit configured to measure the temperature of the SMA element.

12. A pump according to any one of claims 8 to 11, wherein the position detection mechanism comprises or further comprises a Hall sensor, a capacitive sensor, or any other position sensor.

13. A pump according to any one of the preceding claims, further comprising a pressure measurement mechanism configured to measure the pressure of the fluid in the pump, and wherein the controller is further configured such that the drive signals are further in response to the measured pressure so as to pump a determined volume of fluid from the chamber.P612-GB03 4814. A pump according to any one of the preceding claims, further comprising a flow rate measurement mechanism configured to measure the flow rate of the fluid in the pump, and wherein the controller is further configured such that the drive signals are further in response to the measured flow rate so as to pump a determined volume of fluid from the chamber.

15. A method of controlling a pump, the pump comprising:a dosing mechanism comprising a fluid chamber configured to hold a volume of fluid and a movable element configured to move to change the volume of the fluid chamber;at least one valve configured to control fluid flow into or out of the fluid chamber; and at least one actuator coupled to and configured to move the dosing mechanism movable element;wherein the method comprises driving the at least one actuator in response to a first parameter indicative of a position of the dosing mechanism movable element to control the position of the dosing mechanism movable element within a range of movement.

16. A method according to claim 15, wherein the method further comprises driving the at least one actuator in response to the first parameter so as to move the dosing mechanism movable element to pump a determined volume of fluid from the chamber.

17. A method according to claim 15 or claim 16, wherein the method further comprises driving the at least one actuator in response to at least a second parameter indicative of a position of a movable element forming part of the at least one valve so as to control the position of the valve movable element within a range of movement to vary the flow of fluid into or out of the fluid chamber.

18. A method according to any one of claims 15 to 17, wherein the at least one actuator includes at least one shape memory alloy, SMA, element; andwherein the method further comprises detecting a position of a dosing mechanism movable element or a valve movable element according to one of:measuring the resistance of an SMA element;measuring a parameter indicative of the power drawn by the SMA element; or measuring the temperature of the SMA element.

19. A method according to any one of claims 15 to 18, further comprising measuring detecting a position of a dosing mechanism movable element or a valve movable element using a Hall sensor, a capacitive sensor, or any other position sensor.

Images