USE OF ONE OR MORE METRICS TO TRIGGER ELECTRIC PULSE INITIATION AND/OR TERMINATION DURING CONTROL OF ACTUATION OF A MEDICAMENT DELIVERY PUMP

Exemplary embodiments may terminate application of an electric pulse to a shape memory alloy (SMA) element that causes actuation of a medicament pump based on resistance values unlike conventional approaches that rely on a mechanical mechanisms to trigger termination of the application of the electric pulse. The magnitude of the resistance values, the rate of change (RoC) of the resistance values, the temperature of the SMA element, the time that has passed since initial application of the electric pulse to the SMA element, or combinations thereof may be used to trigger the termination of the application of the electric pulse to the SMA element in exemplary embodiments. The monitoring of the resistance of an unactuated SMA element may be used to determine when to initiate and when to terminate application of an electrical pulse to the other SMA element.

BACKGROUND

Certain conventional medicament delivery devices may employ shape memory alloy (SMA) elements. SMA elements transition between shapes as the temperatures of the elements change. SMA elements “remember” their original shapes when the temperature of the elements reaches a transition temperature. For example, an SMA wire may shorten to an original shorter shape when the SMA wire warms. This characteristic may be exploited within a device to actuate a component.

In one medicament delivery device provided by Insulet Corporation of Acton, Massachusetts, an SMA wire is used to drive the actuation of the medicament delivery pump of the device to deliver medicament. Specifically, an electric pulse of a predetermined duration is applied to the SMA wire in the device. The application of the electric pulse causes the SMA wire to heat and shorten. The shortening of the SMA wire causes a component to be moved that drives actuation of the medicament delivery pump. The termination of the application of the electric pulse to the SMA wire is caused by a mechanical termination mechanism that relies on overshoot of the component that drives actuation.

SUMMARY

In accordance with an inventive facet, a medicament delivery device for delivering medicament to a user includes a medicament reservoir for storing the medicament and a medicament pump for pumping the medicament from the medicament reservoir for delivery to the user. The device also includes a power source and a shape memory alloy (SMA) element for causing actuation of the medicament pump to deliver the medicament. The device further includes a processor configured to initiate application of an electric pulse from the power source to the SMA element to cause the medicament pump to deliver the medicament from the medicament reservoir. The processor also is configured to determine resistance of the SMA element over time and based on the determined resistance of the SMA element over time, to determine whether the application of the electric pulse should be terminated. The processor additionally is configured to cause the application of the electric pulse to the SMA element to be terminated responsive to the determining that the application of the electric pulse should be terminated.

The processor may be configured to determine a rate of change (RoC) of the resistance and to compare the RoC to a threshold in the determining that the application of the electric pulse should be terminated. The processor may be configured to determine a magnitude of change of the resistance of the SMA element, to compare the determined magnitude of change of the resistance to a threshold, and to cause the electric pulse to terminate in part based on the comparing to the threshold. The processor may be configured to collect voltage readings and current readings for the SMA element over time, and the determining of the resistance of the SMA element over time may entail the processor calculating the resistance of the SMA over time from the collected voltage readings and current readings. The processor may cause the application of the electric pulse to the SMA element to be terminated by determining moving average values of subsets of the resistance values, determining at least one derivative or approximation of the derivative of the determined moving average values, and comparing the at least one derivative or the approximation of the derivative of the determined moving average values to a threshold as part of the determining that the application of the electric pulse should be terminated. The SMA element may be an SMA wire. The determining that the application of the electric pulse should be terminated may include determining a second derivative or an approximation of a second derivative of one of the resistance values or averages of successive ones of the resistance values and based on the second derivative or the approximation of the second derivative, determining that the application of the electric pulse should be terminated.

In accordance with another inventive facet, a medicament delivery device includes a medicament reservoir for storing medicament, a pump for pumping medicament from the medicament reservoir, a SMA element for actuating the pump, and a power source. The device also includes a processor configured to cause an electric pulse from the power source to be applied to the SMA element to cause actuation of the medicament pump to output medicament from the medicament reservoir, to monitor resistance values of the SMA element, and to terminate the application of the pulse to the SMA based on a metric reflective of the resistance values.

The medicament delivery device may be a wearable insulin pump, and the medicament may be insulin. The processor may be configured to perform filtering of the resistance values. The power source may be a battery and/or a capacitor. The SMA element may be coupled to a component that drives actuation of the medicament pump. The SMA element may shrink in length responsive to application of the electric pulse. The metric reflective of the resistance values may be a metric of a RoC over time concerning the resistance values or of averages of the resistance values. The metric of the RoC over time concerning the resistance values may be a derivative of the resistance values or averages of the resistance values. The metric of a RoC over time concerning the resistance values may be a second derivative of the resistance values or averages of the resistance values.

In accordance with an additional inventive aspect, a medicament delivery device includes a medicament reservoir for storing medicament, a pump for pumping medicament from the medicament reservoir, an SMA element for actuating the pump, a power source, and may further include a temperature sensor for sensing temperature of the SMA element, and a clock for outputting an indication of time. The device further includes a processor configured to cause an electric pulse from the power source to be initially applied to the SMA element to actuate the medicament pump to output medicament from the medicament reservoir. The processor may also be configured to monitor temperature values of the SMA element that were measured by the temperature sensor and to terminate the application of the pulse to the SMA element based on the temperature of the SMA element and time since the initial application of the electric pulse to the SMA element.

The SMA element may be one or more SMA wires. Multiple successive temperature values may be used to determine that a threshold has been exceeded before terminating the application of the pulse to the SMA element. The medicament delivery device may be an insulin delivery device.

In accordance with a further inventive aspect, a medicament delivery system may include a medicament reservoir for storing medicament and a pump for pumping medicament from the medicament reservoir. The system may include a first SMA element and a second SMA element for actuating the pump. The first and second SMA elements may be configured to be opposed and to be actuated in alternating fashion to drive the pump. The system may include a power source and a processor. The processor may be configured to monitor a resistance of the first SMA element. An electrical pulse from the power source may have been applied to the first SMA element more recently than the second SMA element. The processor may be further configured to identify when the resistance of the first SMA element reaches a threshold level and based on the identifying, to cause an electrical pulse to be applied to the second SMA element to activate the second SMA element in order to drive the pump to deliver medicament from the reservoir to a user.

The system may include one or more drive wheels coupled to the pump that are driven by the first SMA element and the second SMA element responsive to application of electrical pulses to the first and second SMA elements. The first SMA element and the second SMA element may be SMA wires. Application of the electrical pulse to the first SMA element may cause the first SMA element to transition from a current state to a more fully austenite state. The threshold level of resistance may be associated with a state where the second SMA element has not fully cooled to ambient temperature and is still partially in an austenite state. The monitoring of the resistance of the first SMA element may include measuring the voltage of the first SMA element and determining the resistance of the first SMA element from the measured voltage. The system may include a current sensor for measuring current at the first SMA element, and the measured current also may be used in determining the resistance of the first SMA element. The medicament may include at least one of insulin, a glucagon-like peptide (GLP)-1 receptor agonist, or a gastric inhibitory peptide (GIP), or a dual GIP-GLP receptor agonist.

In accordance with a still further inventive facet, a medicament delivery system may include a medicament reservoir for storing medicament and a pump for pumping medicament from the medicament reservoir. The system also may include a first SMA element and a second SMA element for actuating the pump. The first and second SMA elements may be configured to be opposed and actuated in alternating fashion to drive the pump. The system may include a power source and a processor. The processor may be configured to initiate application of an electrical pulse from the power source to the second SMA element to cause actuation of the second SMA element by transitioning from a current state to a more fully austenite state that results in actuation of the pump to deliver the medicament from the reservoir to the user. The processor also may be configured to monitor resistance of the second SMA element as the electrical pulse is applied to the second SMA element and based on the monitoring, to terminate application of the electrical pulse to the second SMA element.

The monitoring of the resistance of the second SMA element may include measuring a voltage of the second SMA element and a current of the second SMA element and determining the resistance from the measured voltage and the measured current. The application of the electrical pulse to the second SMA element may be terminated while a temperature of the second SMA element is higher than an ambient temperature. The first and second SMA elements may be SMA wires. The device may include a switch under control of the processor for the initiating of the application of the electrical pulse to the second SMA element. The switch also may be configurable to terminate the application of the electrical pulse to the second SMA element. The device may include an additional switch for controlling application of electricity to the first SMA element.

In accordance with yet another inventive facet, a method may include monitoring with a processor the resistances of a first SMA element and a second SMA element that are arranged in an opposing arrangement and are actuated in alternating fashion in a medical device. Per the method, based on the measured resistances, with the processor one of the following may be determined: that a crimp for one of the SMA elements has a problem, that one of the SMA elements overheated during application of an electrical stimulus, or that there is a problem with a ground for an element of the medical device.

The medical device may be a medicament delivery device. The SMA elements may act as actuators for a pump to cause delivery of medicament from the pump. The SMA elements may be SMA wires. The opposing arrangement may be configured to cause a selected one of the SMA elements to stretch the other SMA element as the other SMA element cools. The method may include obtaining voltage and current values to calculate the resistances of the SMA elements.

DETAILED DESCRIPTION

Exemplary embodiments may terminate application of an electric pulse to an SMA element that causes actuation of a medicament pump based on resistance values unlike conventional approaches that rely on mechanical mechanisms (including mechanical-electrical switch mechanisms) to trigger termination of the application of the electric pulse. The magnitude of the resistance values, the rate of change (RoC) concerning the resistance values, the temperature of the SMA element, the time that has passed since initial application of the electric pulse to the SMA element, or combinations thereof may be used to trigger the termination of the application of the electric pulse to the SMA element in exemplary embodiments, as will be described below. It should be appreciated that RoC concerning the resistance of the SMA element may be captured by the first or second derivative of resistance values relative to time as described below. The RoC concerning the resistance values may be a more robust and reliable metric for accurately triggering termination of application of the electric pulse at a desired time than merely relying on resistance value magnitudes.

More accurate timing (i.e., earlier) termination of application of the electric pulse to the SMA element in the exemplary embodiments results in less energy use during operation of the medicament delivery device. This may be especially beneficial when the medicament delivery device is powered by a finite power source, like batteries and/or a charged capacitor, where the lower energy requirements can extend the time period before the power source needs to be recharged or replaced. The earlier termination may also result in less mechanical fatigue on the SMA element due to the shortened excitation time of the wire resulting from the earlier termination of application of electric pulses relative to the conventional termination approach.

In some exemplary embodiments, the resistance of the unactuated SMA element (i.e., the SMA element that was most recently actuated but is not currently actuated) may be monitored. This monitoring may be used to determine when to initiate application of an electrical pulse to the other SMA element. Further, the monitoring of the resistance of the unactuated SMA element may be used to decide when to terminate application of the electrical pulse to the other SMA element. The initiation of the pulse may occur before the unactuated SMA element is fully cooled, and the termination of the electrical pulse may be chosen to be as soon as possible to save energy and extend the lifetime of the SMA elements.

The monitoring of the resistances of the SMA elements may also identify issues within the device. For instance, the monitoring of the resistances may be used to identify overheating of an SMA element or problems with a crimp or a ground of a component. More generally, the monitoring of the resistances of the SMA elements may provide useful information regarding the states of the SMA elements.

FIG.1depicts a block diagram of an illustrative medicament delivery system100that is suitable for delivering a medicament to a user108in accordance with the exemplary embodiments. The medicament delivery system100includes a medicament delivery device102. The medicament delivery device102may be a wearable device that is worn on the body of the user108or carried by the user. The medicament delivery device102may be directly coupled to a user (e.g., directly attached to a body part and/or skin of the user108via an adhesive or the like) with no tubes and an infusion location directly under the medicament delivery device102, or carried by the user (e.g., on a belt or in a pocket) with the medicament delivery device102connected to an infusion site where the medicament is injected using a needle and/or cannula. A surface of the medicament delivery device102may include an adhesive to facilitate attachment to the user108.

The medicament delivery device102may include a processor110. The processor110may be, for example, a microprocessor, a logic circuit, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC) or a microcontroller. The processor110may maintain a date and time as well as other functions (e.g., calculations or the like). The processor110may be operable to execute a control application116encoded in computer programming instructions stored in the storage114that enables the processor110to direct operation of the medicament delivery device102. The control application116may be a single program, multiple programs, modules, libraries or the like. The processor110also may execute computer programming instructions stored in the storage114for a user interface (UI)117that may include one or more display screens shown on display127. The display127may display information to the user108and, in some instances, may receive input from the user108, such as when the display127is a touchscreen.

The control application116may control delivery of a medicament to the user108per a control approach like that described herein. In exemplary embodiments, the control application116may control the termination of the electric pulse to an SMA element as described below. The storage114may hold histories111for the device and/or user, such as a history of resistance values, resistance RoC values, or a history of basal deliveries, a history of bolus deliveries, and/or other histories, such as a meal event history, exercise event history, glucose level history, and/or the like. In addition, the processor110may be operable to receive data or information. The storage114may include both primary memory and secondary memory. The storage114may include random access memory (RAM), read only memory (ROM), optical storage, magnetic storage, removable storage media, solid state storage or the like.

The medicament delivery device102may include a tray or cradle and/or one or more housings for housing its various components including a pump113, a power source (not shown), and a reservoir112for storing a medicament for delivery to the user108. A fluid path to the user108may be provided, and the medicament delivery device102may expel the medicament from the reservoir112to deliver the medicament to the user108using the pump113via the fluid path. The fluid path may, for example, include tubing coupling the medicament delivery device102to the user108(e.g., tubing coupling a cannula to the reservoir112), and may include a conduit to a separate infusion site. The medicament delivery device102may have operational cycles, such as every 5 minutes, in which basal doses of medicament are calculated and delivered as needed. These steps are repeated for each cycle.

There may be one or more elements for enabling communications links with one or more devices physically separated from the medicament delivery device102including, for example, a management device104of the user and/or a caregiver of the user, sensor(s)106, a smartwatch130, a fitness monitor132and/or another variety of device134. The communication links may include any wired or wireless communication links operating according to any known communications protocol or standard, such as Bluetooth®, Wi-Fi, a near-field communication standard, a cellular standard, or any other wireless protocol.

The medicament delivery device102may interface with a network122via a wired or wireless communications link. The network122may include a local area network (LAN), a wide area network (WAN) or a combination therein. A computing device126may be interfaced with the network122, and the computing device may communicate with the medicament delivery device102.

The medicament delivery system100may include one or more sensor(s)106for sensing the levels of one or more analytes. The sensor(s)106may be coupled to the user108by, for example, adhesive or the like and may provide information or data on one or more medical conditions and/or physical attributes of the user108. The sensor(s)106may be physically separate from the medicament delivery device102or may be an integrated component thereof. The sensor(s)106may include, for example, glucose monitors, such as continuous glucose monitors (CGM's) and/or non-invasive glucose monitors. The sensor(s)106may include ketone sensors, analyte sensors, heart rate monitors, breathing rate monitors, motion sensors, temperature sensors, perspiration sensors, blood pressure sensors, alcohol sensors, or the like. Some sensors106may also detect characteristics of components of the medicament delivery device102. For instance, the sensors106in the medicament delivery device may include voltage sensors, current sensors, temperature sensors and the like.

The medicament delivery system100may or may not also include a management device104. In some embodiments, no management device is needed as the medicament delivery device102may manage itself. The management device104may be a special purpose device, such as a dedicated personal diabetes manager (PDM) device. The management device104may be a programmed general-purpose device, such as any portable electronic device including, for example, a dedicated controller, such as a processor, a micro-controller, or the like. The management device104may be used to program or adjust operation of the medicament delivery device102and/or the sensor(s)106. The management device104may be any portable electronic device including, for example, a dedicated device, a smartphone, a smartwatch, or a tablet. In the depicted example, the management device104may include a processor119and a storage118. The processor119may execute processes to manage a user's glucose levels and to control the delivery of the medicament to the user108. The medicament delivery device102may provide data from the sensors106and other data to the management device104. The data may be stored in the storage118. The processor119may also be operable to execute programming code stored in the storage118. For example, the storage118may be operable to store one or more control applications120for execution by the processor119. The control application120may be responsible for controlling the medicament delivery device102, such as by controlling the automated insulin delivery (AID) of insulin to the user108. In some exemplary embodiments, the control application120provides the adaptability described herein. The storage118may store the control application120, histories121like those described above for the medicament delivery device102, and other data and/or programs.

A display140, such as a touchscreen, may be provided for displaying information. The display140may display user interface (UI)123. The display140also may be used to receive input, such as when it is a touchscreen. The management device104may further include input elements125, such as a keyboard, button, knobs, or the like, for receiving input form the user108.

The management device104may interface with a network124, such as a LAN or WAN or combination of such networks, via wired or wireless communication links. The management device104may communicate over network124with one or more servers or cloud services128. Data, such as sensor values, may be sent, in some embodiments, for storage and processing from the medicament delivery device102directly to the cloud services/server(s)128or instead from the management device104to the cloud services/server(s)128.

Other devices, like smartwatch130, fitness monitor132and device134may be part of the medicament delivery system100. These devices130,132and134may communicate with the medicament delivery device102and/or management device104to receive information and/or issue commands to the medicament delivery device102. These devices130,132and134may execute computer programming instructions to perform some of the control functions otherwise performed by processor110or processor119, such as via control applications116and120. These devices130,132and134may include displays for displaying information. The displays may show a user interface for providing input by the user, such as to request a change or pause in dosage, or to request, initiate, or confirm delivery of a bolus of a medicament, or for displaying output, such as a change in dosage (e.g., of a basal delivery amount) as determined by processor110or management device104. These devices130,132and134may also have wireless communication connections with the sensor106to directly receive analyte measurement data. Another delivery device105, such as a medicament delivery pen, may be accounted for or may be provided for also delivering medicament to the user108.

A wide variety of medicaments may be delivered by the medicament delivery device102and delivery device105. The medicament may be insulin for treating diabetes. The medicament may be glucagon for raising a user's glucose level. The medicament may also be a glucagon-like peptide (GLP)-1 receptor agonists for lowering glucose or slowing gastric emptying, thereby delaying spikes in glucose after a meal. Alternatively, the medicament delivered by the medicament delivery device102may be one of a pain relief agent, a chemotherapy agent, an antibiotic, a blood thinning agent, a hormone, a blood pressure lowering agent, an antidepressant, an antipsychotic, a statin, an anticoagulant, an anticonvulsant, an antihistamine, an anti-inflammatory, a steroid, an immunosuppressive agent, an antianxiety agent, an antiviral agent, a nutritional supplement or a vitamin. The medicament may be a coformulation of two or more of those medicaments listed above.

The functionality described herein for the exemplary embodiments may be under the control of or performed by the control application116of the medicament delivery device102or the control application120of the management device104. In some embodiments, the functionality wholly or partially may be under the control of or performed by the cloud services/servers128, the computing device126or by the other enumerated devices, including smartwatch130, fitness monitor132or another wearable device13

In the closed loop mode, the control application116,120determines the medicament delivery amount for the user108on an ongoing basis based on a feedback loop. For an insulin delivery device, the aim of the closed loop mode is to have the user's glucose level at a target glucose level or within a target glucose range.

FIG.2depicts exemplary components found inside the housing202of an exemplary medicament delivery device200. The components may include a reservoir204in which medicament is stored for delivery to the user108, batteries206to serve as a power source for the medicament delivery device200, SMA wire208(formed of a wire208A and a second wire208B that are collectively referred to as208) for causing actuation of a medicament pump209. The SMA wires208may be wrapped around SMA pulleys210. A drive wheel212is coupled to the medicament pump209and includes one or more toothed wheels214and216. A pivotable drive engaging member218has one or more arms220and222for engaging the toothed wheel214and216, respectively. The SMA wire208is coupled to the pivotable drive engaging member218by integral connector230to cause the pivotable drive engaging member218to pivot back and forth and drive the drive wheel212as described below. The medicament pump209pumps the medicament from the reservoir204. The medicament pump209includes a plunger224that actuates to expel medicament from the reservoir204. The drive wheel212may be connected to tube nut226. The tube nut226may be positioned on a leadscrew (not shown) on the plunger224, and movement of the drive wheel212may cause the leadscrew to rotate, which in turn causes linear displacement of the plunger224.

To actuate the exemplary medicament pump209, an electric pulse is applied to SMA wire208A to energize the SMA wire208A. When charged, the first portion of the SMA wire208contracts and pulls the pivotable drive engaging member218in a first direction. When the pivotable drive engaging member218pivots in the first direction, the arm220engages a tooth on the toothed wheel214causing the drive wheel212to rotate one increment. The pivotable drive engaging member262pivots in the first direction. Generally speaking, one of the arms220and222is alternatively engaged by the toothed wheels214and216of the drive wheel212. The engaged arm220and222, therefore prevent reverse rotation of the drive eliminating the need for a separate pawl element.

To initiate another pulse, the control circuitry applies current to SMA wire208B. When charged, the SMA wire208B contracts and pulls the pivotable drive engaging member218in a second direction that is the opposite of the first direction. When the pivotable drive engaging member218pivots in the second direction, the arm222engages a tooth on the toothed wheel216causing the drive wheel212to rotate one increment. The pivotable drive engaging member218pivots in the second direction.

Each incremental rotation of the drive wheel212advances the plunger in the reservoir204to cause a discrete amount of fluid to be dispensed. The discrete amount of fluid to be dispensed is a function of the lead screw pitch of the (i.e., threads/inch), toothed wheel tooth size and the diameter of the fluid reservoir. In a preferred embodiment, for delivering U100 insulin for treatment of Type I diabetes, the discrete amount of fluid to be dispensed is between about 0.025 ul and about 0.05 ul. The control circuitry alternates energizing the SMA wires s208A and208B until a desired amount of fluid has been dispensed.

The depiction of the exemplary medicament delivery device200inFIG.2shows the mechanical overshoot components in place. Nevertheless, those components may be removed or may remain in the exemplary embodiments.

The optimal time for terminating the application of the electric pulse to the SMA wires208A and208B corresponds to the point in time where the active arm220or222of the pivotable drive engaging member218falls off the corresponding toothed wheel214or216of the drive wheel212of the medicament pump209. The exemplary embodiments may determine and use a termination time that is closer to the optimal termination time than a conventional approach that relies upon a mechanical overshoot mechanism.

As was mentioned above, in exemplary embodiments a resistance metric (e.g., resistance values, RoC of resistance values, etc.) may be used in triggering the termination of an electric pulse that drives actuation of a medicament pump113in the medicament delivery device102.FIG.3depicts a flowchart of illustrative steps that may be performed in exemplary embodiments to use resistance values in triggering the termination of the electric pulse. The termination in the electric pulse to the SMA element (like SMA wires208) causes the medicament pump113to no longer actuate and thus to cease delivery of medicament to the user108. At302, the electric pulse is applied to the SMA element, such as the SMA wire208A or208B, to cause actuation of the medicament pump113resulting in delivery of medicament to the user108from the medicament delivery device102. At304, the resistance values of the SMA element are monitored to determine the resistance of the SMA element over time. Based on the determined resistance values, at306, a determination is made that the electric pulse should be terminated so that the electric pulse is no longer applied to the SMA element. At308, based on the determination, application of the electric pulse to the SMA element is terminated.

FIG.4depicts an illustrative plot400of resistance expressed in ohms of the SMA element over time during application of an electric pulse of 0.25 seconds. In this instance the SMA element is one of the SMA wires208A or208B. When the electric pulse is initially applied at402, the resistance is at its highest level of approximately 16 ohms. As the electricity flows through the SMA wire208responsive to the electric pulse, the SMA wire208A or208B heats, and the resistance of the SMA wire208A or208B slowly begins to drop. Hence, at404, the resistance has dropped relative to402. As the SMA wire208A or208B continues to heat, the SMA wire208A or208B approaches and then undergoes a state transition from a martensite state to an austenite state. The SMA wire208A or208B shortens as the transition progresses and the resistance decreases more quickly at406in the plot400as the transition temperature where the state transition occurs is reached. Due to the arrangement of the actuation components of the medicament pump (e.g., toothed wheels214,216, arms220,222, pivotable drive engaging member218, and the SMA wire(s) connected thereto), it is during this time that the actuation of the toothed wheel214and216by the arm220or222is completed responsive to movement of the SMA wire208A or208B. Once the transition is complete, the resistance stays largely flat since the SMA wire208A or208B is no longer shortening as indicated by the flat region at408in the plot400.

FIG.5depicts a plot500that illustrates the earlier or more accurate termination on the plot of resistance values versus time. This plot500is derived based on resistance values and termination points triggered based on use of a conventional mechanical overshoot termination mechanism on the one hand and, on the other hand, use of the termination approach based on resistance values on the same device as described herein. At504, the application of the electric pulse to the SMA wire is terminated based on resistance values, such as in the exemplary embodiments. As a safety factor, there is some latency between the detection and the termination so that the termination is not at the true optimal termination point. Later, at506, application of the electric pulse to the SMA wire is terminated by the mechanical overshoot mechanism employed in the conventional system.

FIG.5also shows plot502, which depicts the RoC in resistance over time. Point510corresponds to the time of termination based on resistance values and point512corresponds to the time of termination based on the conventional mechanical overshoot termination mechanism.

The earlier termination of application of the electric pulse to the SMA element in the exemplary embodiments results in less energy use during operation of the medicament delivery device102. This may be especially beneficial when the medicament delivery device102is powered by batteries, where the lower energy requirements can extend the battery life. The earlier termination may also result in less mechanical fatigue on the SMA element due to the shortened excitation time of the wire resulting from the earlier termination of application of electric pulses relative to the conventional termination approach.

The resistance values of the SMA element, such as the SMA wires208A or208B, may be obtained from a resistance measuring component. Alternatively, the resistance values may be obtained by determining the voltage applied to the SMA element and measuring the current flowing through the SMA element. Ohm's law states that I=V/R, where I is current, V is voltage, and R is resistance. Thus, resistance can be calculated as R=VA. Hence, once the voltage and current are obtained, the resistance for the SMA element may be determined.

A first approach that may be adopted to trigger termination of the electric pulse to the SMA element is to examine a RoC concerning the resistance of the SMA element (e.g., the SMA wire). In this context, the RoC may refer to the difference in resistance between successively sampled resistance values or averages of resistance values, such as determined from a first derivative or an approximation of a first derivative relative to time of resistance values or averages of resistance values, or deceleration of change in resistance values, such as determined from a second derivative of resistance values. The resistance values may be sampled at predetermined sample times. As detailed below, the RoC may, in some exemplary embodiments, be one of multiple factors that are reviewed in deciding whether to terminate application of the electric pulse to the SMA element.

FIG.6depicts a flowchart600of illustrative steps that may be performed in exemplary embodiments in using the RoC concerning resistance values to trigger termination of the application of the electric pulse to the SMA element that causes actuation of the medicament pump113. At602, the RoC concerning the resistance values may be determined. A number of illustrative approaches for determining the RoC are detailed below. At604, the determined RoC is compared to a threshold to determine if should the application of the electric pulse should be terminated. If not, at606, the application of the electric pulse is not terminated. If so, at608, the application of the electric pulse to the SMA element is terminated.

FIG.7depicts a flowchart700of illustrative steps that may be performed in exemplary embodiments to determine the RoC (see602) in accordance with a first approach. In this first approach, at702, the differences between resistance values at successive times or between averages, such as rolling averages, at successive times is determined. At704, the RoC is calculated from the difference, such as being set equal to the difference. Where the RoC is determined by determining the difference between resistance values or the difference between averages of resistance values at successive times (such as rolling averages of several successive resistance values), the comparison at604may be whether the RoC is below a threshold value (which may be determined empirically). This is because the resistance of the SMA element does not continue to drop and may actually rise slightly after actuation responsive to the electric pulse is complete as shown inFIG.4.

Another approach to determining the RoC value is to determine a first derivative or an approximation of the first derivative of the resistance values as the RoC.FIG.8depicts a flowchart800of illustrative steps that may be performed in exemplary embodiments. At802, the first derivative of resistance relative to time (i.e., dR/dt) is calculated or an approximation of the first derivative is calculated. In some embodiments, a curve may be constructed from the obtained resistance values and interpolation may be used between values to complete the curve. At804, the calculated or approximated first derivative may be used as the RoC value.

An additional approach to determining the RoC value is to use a second derivative of the resistance values as the RoC. The second derivative determines the RoC of the RoC of the resistance values.FIG.9depicts a flowchart900of illustrative steps that may be performed in exemplary embodiments to use the second derivative. At902, a second derivative of the resistance values is determined. At904, a check of whether the second derivative is less than a threshold is performed. At the inflection point where the state transition is complete and the resistance has stopped decelerating, the acceleration or deceleration of the change in resistance values should zero or near zero, since the RoC of the resistance values does not change a great deal at the inflection point. If not, at906, the application of the electric pulse to the SMA element is not terminated and recalculated at the next sample time. If so, at908, application of the electric pulse to the SMA element is terminated.

In some exemplary embodiments, the RoC concerning the resistance values and the magnitude of change in resistance since a last sampling time are used in conjunction to determine whether to trigger termination of application of the electric pulse to the SMA element. Looking at the magnitude of change in the resistance values helps avoid triggering termination early due to noise or other factors.FIG.10depicts a flowchart1000of illustrative steps that may be performed in exemplary embodiments to trigger termination of application of the electric pulse based on RoC of the resistance values and the percentage of change in the resistance values. At1002, the RoC of the resistance values is determined, such as described above. If the RoC of the resistance values does not indicate that the application of the electric pulse should be terminated at1004, then the application of the electric pulse is not terminated at1006and the process repeats at1002. If the RoC of the resistance values indicates that there should be termination at1004, then additional steps are performed. At1008, the percentage of the change in resistance between samples is determined, and at1010, the percentage is compared to a threshold. If the percentage is not less than the threshold, the application of the electric pulse is not terminated at1006and the process repeats at1002. If the percentage of the change in resistance values is less than the threshold, at1012, the application of the electric pulse to the SMA element is terminated. It should be appreciated that measures of magnitude of change other than percentages of change may be used in some embodiments.

As a stop gap measure or as an alternate approach, the time that has elapsed since application of the electric pulse to the SMA element may be used as a metric to terminate application of the electric pulse to the SMA element in some exemplary embodiments.FIG.11depicts a flowchart1100of illustrative steps that may be performed in exemplary embodiments to use time to trigger termination of application of the electric pulse to the SMA element. At1102, the time since the initiation of the application of the electric pulse to the SMA element is determined using a timer or based on a clock that is accessible to or incorporated in the processor110. At1104, a check is made whether the time has exceeded a maximum threshold. The maximum threshold may be a time close to the optimal termination time or may be fail safe time to terminate application of the pulse that otherwise would continue longer than desired. If the maximum time is exceeded, at1106, application of the electric pulse to the SMA element is terminated. If not, the process repeats beginning at1102.

As was mentioned above, different combinations of metrics and possibly other values may be used to trigger termination of application of the electric pulse to the SMA element in exemplary embodiments.FIG.12depicts a flowchart1200of illustrative steps that may be performed in exemplary embodiments where the derivative of resistance values at a point in time and the resistance percentage change are used in conjunction to trigger termination of application of the electric pulse to the SMA element. At1202, the voltage drop across the SMA element and the current are collected. These values are used at1204to calculate the resistance value at1204. An exemplary three point rolling average filter may be applied at1206to output a three point moving average of the latest resistance value and the previous two resistance values. The first derivative is approximated based on the three point moving average at1208. An exponentially weighted moving average filter is applied to the derivative at1210to determine an exponentially weighted moving average of the derivative values. The resulting derivative average is compared to a first threshold at1212. The percentage change in resistance is determined and compared to a second threshold at1214. If the derivative and the percentage change of the resistance are below the thresholds to which they are compared as checked at1216, the application of the electric pulse to the SMA element is terminated at1218. Otherwise, the process is repeated at the next sample time.

Another alternate factor that may be examined in deciding whether to trigger termination of the application of the electric pulse to the SMA element is temperature of the SMA element. As electricity is applied to the SMA element, the temperature of the SMA element rises. A signature temperature value or range may be associated with the inflection point where the actuation of the medicament pump113is completed. That signature temperature may be used as a trigger for the termination of the application of the electric pulse to the SMA element.FIG.13depicts a flowchart1300of illustrative steps that may be performed in exemplary embodiments to use temperature as a trigger. At1302, one or more temperature readings of the SMA element are obtained from a temperature sensor. Multiple successive temperature readings may be obtained in some exemplary embodiments. At1304, a check is made whether the one or more temperature readings are at or above a value indicative of the optimal termination point, which value may be based on a transition temperature of the SMA element and/or simple experimentation. The check may, for instance, compare an average of the last three temperature readings to the threshold value, may compare each of the temperature values to the threshold value, or may compare a single temperature value to the threshold. If the one or more temperature values (or an average thereof) are at or above the threshold, the application of the electric pulse to the SMA element is terminated at1306. Otherwise, the steps are repeated at1302.

In other exemplary embodiments, both time and temperature may be examined to determine whether to terminate application of the electric pulse to the SMA elements. At1402, one or more temperature readings are obtained from a temperature sensor. At1404, if the one or more temperature reading(s) are not greater than or equal to the threshold temperature, the steps are repeated for a next sample time at1402. If the one or more temperature reading(s) are greater than or equal to the threshold, the time since application of the electric pulse is referenced. Specifically, at1406, the time since application of the electric pulse to the SMA element is determined. If the time is greater than the minimum time as checked at1408, the application of the electrical pulse to the SMA element is terminated at1410. Otherwise, the steps are repeated for the next sample time at1402.

In some exemplary embodiments, multiple factors may be examined to determine whether to terminate application of the electric pulse to an SMA element. Confidence intervals may be defined based on values for the factors. The decision to terminate may be based on whether the values for the factors fall within a specified confidence interval in some embodiments.

In some exemplary embodiments, the unactuated SMA element may be monitored to control when a pulse is initiated.FIG.15depicts a flowchart1500depicting illustrative steps that may be performed in exemplary embodiments to determine the state of an SMA element, such as an SMA wire. It is assumed that the SMA elements are in an opposing relationship such that they actuate against each other and that the SMA elements are alternately actuated. At1502, the resistance of the unactuated SMA element is measured, such as by measuring the current and voltage and calculating resistance from those measured values.

At1504, the state of the unactuated SMA element may be determined from the resistance measurement.FIG.16, depicts what sort of state information1600regarding the unactuated SMA element may be determined from the resistance. First, the state1602of the SMA element may be determined. For instance, the resistance may identify whether the SMA element is in an austenite phase, a martensite phase, or a mixture thereof. When the SMA element is in a mixed phase, the resistance may identify where the SMA element is in the transition between the phases. The resistance may also identify the length1604of the SMA element. The length1604is related to the phase because the SMA element shortens in the austenite phase and returns to its original length when it returns to the martensite phase. The temperature1606of the SMA element may also be determined from the resistance.

FIG.17depicts an illustrative depiction of the electrical pulses being applied to a first SMA wire1702and to a second SMA wire1704. In the depiction, electrical pulses1706and1708are applied to SMA wire1702. In between these electrical pulses1706and1708, an electrical pulse1710may be applied to the other opposing SMA wire1704. The pulse widths (PWs) of the electrical pulses1706,1708, and1710are shown. The pulse width represents the time between when an electrical pulse is initiated (e.g.,1712for pulse1710) and when the electrical pulse is terminated (1714). The pulse to pulse (PP) length is shown. The PP length (see the PP labelled arrows) represents the length of time between termination of an electrical pulse on one SMA wire and the initiation of an electrical pulse on the other SMA wire.

FIG.18depicts a flowchart1800of illustrative steps that may be performed in exemplary embodiments to decide when to trigger the initiation of an electrical pulse to an unactuated SMA element. The choice of when to trigger the initiation of the electrical pulses determines the PP timing. The aim of the choice of this timing in some exemplary embodiments is to minimize energy loss. Cooling an SMA element all the way down to ambient temperature is not efficient and results in wasted energy application. In these exemplary embodiments, the initiation of the application of an electrical pulse to the unactuated SMA element takes place when the unactuated SMA element has sufficiently cooled (or sufficiently transitioned to the martensite phase from the austenite phase, or sufficiently lengthened from its contracted length to return to its uncontracted or original length) but not all the way to ambient temperature. These embodiments may choose to apply the electrical pulse to the unactuated SMA element when the cooling is enough to stretch or de-twin the SMA element. Thus, the pulse widths are shorter and energy is saved. On the other hand, however, actuating before the SMA element has sufficiently relaxed will waste energy. This ideal window in which to initiate the application of an electrical pulse to the unactuated SMA element(s) will vary among SMA elements and may depend upon the materials (e.g., the alloys) that make up the SMA element, the length of the SMA element, the age of the SMA element, etc.

With reference again toFIG.18, at1802, the resistance of the unactuated SMA element is determined, such as has been described above, from voltage and current measurements, for example. The measuring of the resistance occurs after the last applied pulse to the other opposing SMA element is terminated. In some instances, a delay may be built in before resistance measurements are gathered. At1804, the measured resistance is compared to a first threshold. The first threshold may be an empirically derived value that indicates that the unactuated SMA element (2002in this case) has sufficiently cooled so that there is detwinning. If the measured resistance is above a threshold value (e.g., above a first threshold value since the last pulse was terminated), the process repeats at1802. There may be a built-in delay between successive measurements at1802. If the measured resistance is above the first threshold, it is an indication that there is sufficient cooling, and at1806, the triggering of an electrical pulse occurs so that an electrical pulse is applied to the previously unactuated SMA element (i.e.,2004or1704in this case).

FIG.20depicts an example of the resistance values2000for the pulse pattern previously shown inFIG.17. At the end of pulse2006for the SMA element2002(“wire1”), the SMA element2002begins to cool because the electrical pulse is no longer applied. The resistance during this period2008stays changes only minimally. When the cooling is sufficient, the SMA element begins the transition back to the martensite phase, so the resistance begins to increase rapidly (i.e., more than at other periods) as can be seen at2010. When the resistance surpasses the first threshold (see2012), the electrical pulse is applied to the opposing SMA element2004. The first threshold may be an empirically derived value that is known to represent a state as described above. In other embodiments, the threshold instead may be a rate of change in resistance or a derivative value over time.

The exemplary embodiments may also determine when to terminate an electrical pulse that is applied to an SMA element. In general, one wants to terminate the electrical pulse as soon as possible in order to save energy. The strategy of these exemplary embodiments described herein is to terminate the electrical pulse when the unactuated SMA element is still warm but no longer mostly austenite but before the phase transition to the martensite phase is complete.

FIG.19depicts a flowchart1900of illustrative steps that may be performed in exemplary embodiments to decide when to terminate application of an electrical pulse to an SMA element based on the ROC of the resistance of the SMA element. The approach is like that described above inFIG.6for the single wire case. At1902, the resistance of the SMA element is measured. At1904, a check is made of whether the resistance is above a threshold. The threshold is an empirically derived value at which the electrical pulse should be terminated. If not, the process repeats beginning at1902. In some instances, a delay may be added between1904and1902. If so, the application of the electrical pulse to the SMA element is terminated at1906. It should be appreciated that other approaches such as using the derivative (seeFIG.8) or the second derivative (seeFIG.9) may be used as well. Further, magnitude of resistance and ROC maybe used (seeFIG.10) or an approach like inFIG.12may be used.

FIG.21depicts an illustrative electrical circuit2100of exemplary embodiments for measuring the resistance of the unactuated SMA elements (e.g., SMA22104), which in this case is an SMA wire arranged in an opposing configuration, like that described above, with another SMA wire (e.g., SMA12102). A power source2106provides power for the circuit2100. Four switches2108, designated as S1, S2, S3, and S4are provided. The resistance values of the SMA wires are represented as resistors Rsma12110and Rsma22112. The circuit is connected to ground2114as shown.

The application of a voltage to the SMA wires2102and2104causes current to flow through the SMA wires2102and2104. Closure of switch S1applies current to SMA12102, and closure of switch S4applies power to SMA22104. Closure of switches S1and S3allows a current to be delivered to SMA12102and SMA22104, respectively. The delivered current is set to a low level to conserve power and prevent the SMA wires2102and2104from being activated to undergo a phase change. The voltage of SMA12102may be measured at V1, and the voltage of SMA22104may be measured at V2. To measure the resistance of SMA22104(the unactuated wire), the switch S3may be closed so that current I flows through SMA22104. The resistance of SMA22104may be calculated as V2/I.

The voltage created by the large current of the driven SMA wire through the ground connection may create a voltage offset error due to ground impedance that may affect the calculated resistance of SMA22104.FIG.22Adepicts a flowchart2200of illustrative steps that may be performed in exemplary embodiments to account for the offset error. Initially, at2202, switch S1may be closed to drive SMA12102. At2204, switch S3may be opened, and the voltage offset may be measured at V2. At2206, switch S3is closed to direct current I to flow through SMA22104. At2208, the resistance Rsma22112may be calculated as (V2-voltage offset)/I.

The voltage offset alternatively may be taken into account as shown in the flowchart2210ofFIG.22B. At2212, switch S1is closed to cause current to flow through SMA12102. At2214, switch S3is closed to cause current I to flow through SMA22104. At2216, switch S1is opened to cause a brief pause in the driving of SMA12102, and the resistance of SMA22104is calculated as the voltage at V2divided by I. At2218, switch S1is closed again to drive SMA12102.

Another alternative to address the voltage offset problem is to add electrical connections to the electrical circuit as shown in electrical circuit2300ofFIG.23. The electrical circuit2300includes a voltage source2302, a ground2304, switches2306and SMA wires2308and2310as found in the electrical circuit2100. However, a reference voltage VREF2312is used in a high impedance differential amplifier arrangement to remove the voltage offset while measuring V1and V2.

FIG.24depicts another alternative electrical circuit2400for measuring the resistance of SMA22404. The electrical circuit is similar to the electrical circuit2300shown inFIG.23with some notable differences. A large resistor2406crosses over between the SMA wires2402and2406. The resistor2406provides a path for current to go through the SMA wire that is not driven (or that is not activated). This approach reduces the number of switches so that only two switches S1and S2are needed and also eliminates a current source. The VREF2408arrangement is like that depicted inFIG.23.

As was mentioned above, the resistance of the unactuated SMA element may be monitored to determine if the SMA element overheated by determining how long it takes for the SMA element to cool down as reflected in the resistance values.FIG.25depicts a flowchart2500of illustrative steps that may be performed in exemplary embodiments to identify overheating. At2502, the resistance of the SMA element is monitored after it has had an electrical pulse applied to it. At2504, based on the resistance, the temperature of the wire is determined, and the time it takes for the wire to cool to a specified temperature is determined. At2506, a determination may be made to determine whether the time has been sufficient or whether the time was excessive. If the time was longer than anticipated given the ambient temperature, at2508, a conclusion that the SMA element overheated may be reached. The cause of the overheating may be investigated and addressed.

As was mentioned above, the monitoring of the resistance of the SMA elements may help identify problems with crimps, aging, lengthening, or other factors.FIG.26depicts a flowchart2600of illustrative steps that may be performed in exemplary embodiments to identify such problems. At2602, the baseline resistance of both SMA elements may be determined. At2604, the resistance of both SMA wires may be measured after the SMA elements have fully cooled. At2606, a check is made to determine whether the resistance is above a baseline or a threshold resistance. If the resistance is above a baseline or a threshold resistance from both SMA elements, at2608, it is concluded that there is an issue with the crimp or hook ground. If not, at2610, a check is made to determine if one of the SMA elements has a resistance above the baseline or threshold resistance. If so, at2612, it is concluded that the crimp for the offending SMA element with the elevated resistance has an issue or that another issue has arisen that significantly increased the circuit impedance. Otherwise, there is no issue identified.

While the exemplary embodiments have been described herein, it should be appreciated that various changes in form and detail may be made without departing from the scope of the appended claims.