Technical field

The present disclosure is related to the technical field of drive control units for ambulatory infusion devices, to drive units for ambulatory infusion devices, to ambulatory infusion devices, and to methods for controlling a motor of ambulatory infusion devices. Embodiments in accordance with the present disclosure may, for example, be used in the context of insulin pumps.

Background

A state-of-the art therapy of diabetes mellitus is often based on Continuous Subcutaneous Insulin Infusion (CSII). In this therapy, a person with Diabetes (PwD) carries an insulin pump substantially continuous night and day. The insulin pump is a typically computer-controlled micro dosing device that administers small doses of a liquid insulin formulation substantially continuous according to a time-variable personal basal administration schedule via a subcutaneous cannula and additionally administers larger insulin boli on demand. Those devices are typically designed to be carried substantially continuously over an extended time period of several months or even ears, e.g., 4 years, in a discrete way and concealed from view. Reference is made to WO 2003053498 A2 and WO2000025844 A1 for typical designs and characteristics of such pumps, as well as to the ACCU-CHEK ^® Spirit infusion device, as manufactured by Roche Diabetes Care AG, Burgdorf, Switzerland. In the following, the phrases "ambulatory infusion device" or "ambulatory infusion system" generally refer to devices and systems that are suited and typically used for the application in CSII. Those devices, however, may also be used in the context of further therapies, such as pain therapy or cancer therapy, with no or minor modification. The present disclosure is accordingly not limited to a specific medical field.

Ambulatory infusion devices may include a typically cylindrical and user-replaceable drug cartridge with a piston. The cartridge is hold in a cartridge compartment of the device. Metered infusion is achieved by displacing the piston in a precisely controlled way, thus forcing liquid drug out of the cartridge into a catheter or directly into a cannula. For displacing the piston, the device may include a drive unit with a spindle drive, the spindle drive typically including an electronically controlled motor, a reduction gear, as well as piston rod that engages, during operation, the piston of the drug cartridge. In typical devices, the drive unit is fully reusable and designed for long-term application. It may, however, also be partly or fully disposable and be fully or partly integral with the cartridge.

For expelling drug out of the cartridge, a corresponding displacement direction of the piston rod and the plunger as well as the typically rotational motion direction of the motor are referred to as "forward direction". The corresponding mode of operation is referred to as "forward operation".

After emptying a drug cartridge which typically takes a time of some days to some weeks, the cartridge needs to be replaced by a new cartridge. This procedure is typically carried out by activating a corresponding function of the device, e.g. via a menu structure.

Cartridge replacement includes retracting the piston rod from an extended to a retraced position after removing the empty cartridge.

For retracting the piston rod, the motion direction of the motor may be reversed in typical state of the art devices. A motion direction for retraction is referred to as "backward direction" and is a motion direction against the forward direction. The corresponding mode of operation is referred to as "backward operation". For this procedure, the ambulatory infusion device is not connected to the patient and no drug is infused.

The time for retracting the piston rod is typically in a range of minutes. Besides retracting the piston rod, replacing the drug cartridge can involve further time- consuming steps such as filling a new drug cartridge, e.g. from a larger vial, removing air bubbles from the cartridge, loading the new cartridge into the device, connecting a fresh tubing, filling the fresh tubing with drug (priming), removing an old subcutaneous cannula from the tissue and placing a new subcutaneous cannula into the tissue. The single steps add up to a considerable amount of time which is known to be annoying for many users, thus reducing the acceptance of and compliance with the therapy as a whole. Especially waiting times, such as the time for retracting the piston rod as explained above, have been found to be particularly disliked.

For reducing the amount of time that is required for retracting the piston rod, gear boxes with mechanically switchable reduction rate have been proposed in the application EP 2165722 A1. Those gear boxes, however, are complex in design, bulky and potentially susceptible to mechanical defects, thus contradicting the general aim of providing cost-efficient, discrete and reliable devices.

Summary of the Disclosure

When designing a drive unit of the spindle-drive type for an ambulatory infusion device, a number of constraints must be met, some major of which are discussed in the following. First, forward operation is considered.

Ambulatory infusion devices are typically powered by one or more batteries as primary electric power supply. Typical current devices may be powered, for example, by a single rechargeable or non-rechargeable and user-replaceable round cell of the AA or AAA type of various electro-chemical designs. Other types of batteries, special-purpose power packs or built-in rechargeable batteries, high-energy condensers, fuel cells or the like may be used as well.

The battery is limited with respect to the maximum current that can be drawn at a required minimum voltage as well as with respect to its maximum output power P _Um it- In a simplified model, corresponding values can be computed from the battery's off- circuit voltage and internal resistance. Values can further be obtained from more complex mathematical modes, experimentally and from battery manufacturer's data sheets. If the motor is operated at a voltage above the battery voltage via a DC/DC step-up converter, the efficiency and operational limits of the converter must be considered in addition. For the moment, the motor is assumed to be a standard DC motor for illustrative purposes. Other motor designs will be discussed below.

For a typical spindle drive, a threaded spindle is coupled to the motor via a reduction gear of reduction rate i. The gear may, for example, be a helical gear box, a planetary gear in axial arrangement with the motor, a gear belt arrangement, or a combination of those. The reduction rate i is constrained in various ways. The rotational motor resolution, referred to as step angle, the reduction rate i, the pitch of the spindle thread, and the cross sectional area of the cartridge, in combination, define the minimum drug volume that can be infused. In dependence of the motor design and the motor control, the step angle, may be a fraction of a full revolution such as 180°, 120° or 60°. Alternatively, however, the step angle may be larger than a full revolution and be a whole-number multiple of 360°. For typical CSII devices, the smallest infusion amounts typically occur during basal infusion and are in the sub-micro liter range. The infusion rate may, in dependence of the device design and the patient-specific programming, change e.g., hourly, half- hourly or quasi-continuously.

Basal infusion is typically characterized by the infusion rate as the total volume that is infused per time as lU/h (International Units per hour), with 100 lU/ml (100IU per ml of liquid drug) being the currently most common concentration for insulin formulations, while lower and especially higher concentrations are possible as well.

Some ambulatory infusion devices carry out quasi-continuous infusion by infusing a fractional amount of the hourly amount with a fixed infusion time interval, such as 1/20th of the total hourly volume every 3 min, with the infusion rate varying according to a time-variable schedule, typically according to a circadian profile. For such devices, the minimum drug volume that can be infused has to be identical to the minimum fractional amount according to the infusion time interval and may, e.g., correspond to 0.05 IU of liquid U100 insulin formulation, or even less. If the other variables are fixed, the required reduction rate i is given. Generally, the smallest fractional volume, that is infused in a single fractional infusion according to the lowest basal infusion rate defines a lower limit for the reduction rate i.

Some other devices, however, carry out basal infusion by infusing a design-given and typically somewhat larger and constant fractional amount of, e.g., 0.1 IU with an infusion time interval that is adjusted and varied in accordance with the infusion schedule. For those devices, the constraints for the minimum fractional volume that can be infused, and accordingly, the design constraints for reduction rate i, are less strict due to the somewhat higher volume that is infused per fractional infusion. Mixtures of both approaches are also possible.

If the reduction gear is, at least partly, a commercial component that is typically supplied in combination with the motor, only a limited number of different reduction rates may be available and the reduction rate i is further constrained by geometric and manufacturability limits. Overall, the reduction rate i may, in addition to an upper limit as discussed above, have a lower limit that can not be fallen below. Typical reduction rates are somewhere in a range of, e.g., 1 :200 to 1 :4000. For devices which vary the time interval between infusing fractional amounts as described above, this lower limit is typically of particular relevance. For displacing the cartridge plunger, the plunger friction force has to be overcome by providing a corresponding driving force via the drive unit. The plunger friction force is known to show considerable variation from cartridge to cartridge, from batch to batch, with temperature, the cartridge storing time prior to use, etc. The maximum plunger friction force may be determined by estimation via statistically evaluated experiments and may be, e.g. in a range of 20N to 30N. This driving force is provided by the motor in form of a corresponding driving torque. In addition, the motor must provide the torque for covering all drive-internal losses. The corresponding total torque is referred to as nominal torque T _nom as the maximum torque to be provided by the motor according to the drive design. Due to typically occurring wear and/or dirt entering the drive system over its lifetime, the drive-internal losses increase, and the degree of efficiency η is accordingly reduced. The efficiency reduction over time as well as any uncertainty with respect to the plunger friction force may be considered via a safety factor SF as the ratio of the maximum torque that can be provided by the drive to the nominal torque T _n0 m- Typical values for SF may be, e.g., in a range of 1.5 ...3.

Either of the safet factor SF or the gear reduction rate can be determined as

SF * T nom (1 b)

^ - / ₀ \ * ΚΜ * η

R

with the other one being given. In these equations, U and R are the motor voltage and the ohmic motor resistance, respectively. I ₀ is the non-load current and KM the torque constant of the motor.

Figure 1 a and Figure 1 b illustrate the relations as described above for an exemplary design. The diagram of Figure 1 a shows the reduction rate i according to (1 b) as a function of the motor voltage U for different values of the safety factor SF. Figure 1 b indicates the maximum electric power P _max of the motor according to ^ρ ^ = (2)· This maximum electric power occurs both if the motor spindle is blocked and as initial power consumption for each start-up of the motor, since the motor is represented by a ohmic resistor of resistance R in both cases.

The bold lines 1 , 2, in the upper left corner further illustrate two of the constraints as discussed above. Horizontal line 1 represents a reduction rate constraint i > i _min , that is, the reduction rate i must be above the line. Vertical line 2 represents an electric power consumption constraint P _max < Pumit, that is, the maximum power P _max must be left of the line.

It can be seen from Figure 1a that only a rather small section of the diagram is actually available for a drive design in accordance with the constraints.

A further constraint is given by the required safety factor SF. That is, within the box shown in Figure 1 a, the point of design must be on or above a curve which represents the required safety factor.

For operating the drive in the backward direction when retracting the piston rod, the situation is different. Here, the drive is operated in an idle-state where only a power resulting from drive-internal losses is consumed.

For convenience and user-acceptance reasons as discussed above, it is generally desirable to carry out the piston rod retraction in a short time. Since the displacement speed of the piston rod increases with decreasing reduction rate i, a small reduction rate i is favorable for carrying out the piston rod retraction. However, the required safety factor SF and in particular the continuing demand for infusing smaller and smaller basal infusion rates, and/or drug formulations of higher and higher concentration, call for a high reduction rate i according to the previously discussed relationships.

To solve this dilemma, the motor may be powered with a higher voltage for backward operation as compared to forward operation, thus increasing the motor speed for piston rod retraction. As explained above, however, a voltage-dependent maximum power P _max according to (2) is consumed for each motor start-up. Increasing the motor voltage may therefore cause the power limit Pumit to be exceeded.

To overcome this problem, a drive control unit of an ambulatory infusion device in accordance with the present disclosure may therefore modify the drive voltage or the drive current during piston rod retraction. In this way, a piston rod retraction can be carried out considerably faster as compared to powering the motor with the same voltage as for drug infusion, without exceeding an operational limit of the power supply and in particular meeting the power consumption constrains.

According to one aspect, the present disclosure is directed towards a drive control unit for a motor of an ambulatory infusion device. The drive control unit is designed to power the motor for forward operation in a forward direction and to alternatively power the motor for backward operation in an opposite backward direction. The drive control unit is further designed to modify, in a start-up phase of backward operation, a backup drive voltage or a backup drive current supplied to the motor, thus increasing a motor speed. The start-up phase starts at a motor speed of zero, that is, with the beginning of the motor operation.

Increasing the motor speed is carried out such that an operational limit of a power supply is not exceeded. This operational limit may be a maximum power that can be provided by a device battery and/or the drive control circuitry. It may, however, also be somewhat smaller threshold power consumption if significant power consumption by additional loads, such as a display backlight or an RF communication module, needs to be considered at the same time. The operational limit may further be a maximum current that can be drawn from the power supply, or a maximum power or maximum current that can be provided by a DC/DC converter powering the motor, or the like.

In the context of the present disclosure, the motor is generally assumed to be a rotary motor and a piston rod, typically including a spindle drive, is used to generate a linear displacement motion. Alternatively, however, the motor may directly generate a translational motion and be designed, e.g., as linear motor.

Powering the motor may be done either continuously or in a pulsed way with a high frequency, typically in the kHz range. In the first case, adjustment may be carried out by adjusting the absolute value of the drive voltage and/or drive current. In the latter way, adjustment may be carried out by pulse width modulation (PWM). For PWM, the motor is powered in a switched way, i.e., wit a square wave voltage. By adjusting the duty cycle, i.e., the relative duration of the switched-on time per cycle, the effective value of the drive voltage is adjusted. The absolute value of the drive voltage in the switched-on state may be adjusted additionally. In some embodiments, the drive control unit is designed to operate the motor such that a power consumption of the motor during backward operation does not exceed a power consumption in a range of 200 mW to 500 mW.

A maximum power consumption as operational limit of the power supply in this range is typical for a single AAA powering the device. Higher or lower threshold values may alternatively be used.

In some embodiments, the drive control unit is designed, in the starting phase of backward operation, to increase the backward drive voltage. For a rotational motor, the motor speed is typically the rotational speed of the motor shaft, measured as number of full or fractional revolutions per time. For a DC motor, the motor speed increases linearly with the drive voltage for a constant load torque. Controlling the drive voltage and controlling the motor speed are therefore equivalent as long as the load torque is constant. Alternatively to directly increasing the drive voltage, controlling the motor to increase the motor speed may be achieved by powering the motor with a constant backward drive current, as will be discussed below. Increasing the backward drive voltage or increasing the motor speed is favorably carried out monotonically.

By starting with a low initial backward drive voltage and increasing the voltage after beginning of the motor operation, the initial power consumption when starting the backward operation is limited in accordance with (2). Once the motor is in operation, the motor voltage can be increased while simultaneously meeting the power consumption constraint.

In some embodiments, the drive control unit is designed, subsequent to the starting phase, to power the motor with a constant backward drive voltage or to operate the motor at a constant motor speed. Such a phase of operation is also referred to as "steady phase".

In some embodiments, the duration of the starting phase does not exceed a value of 1 sec and may not exceed a value 0.5 sec. Longer or shorter durations, however, may also be used in dependence of further boundary conditions and/or design constraints. The duration of the start-up phase is typically short as compared to the total rewind time. The A typical total rewind time is in the range of about 30 sec to 1 min. Typically, the start-up time is further long as compared to a mechanical time constant of the drive.

In some embodiments, the drive control unit is designed to power the motor, following the starting phase, with the backward drive voltage having a value which would, as initial value of the backward drive voltage when starting backward operation, result in the power consumption of motor exceeding an operational limit of a power supply.

In some embodiments, the drive control unit is designed to power the motor, in the starting phase, with a constant backward drive current.

If a DC motor is powered with a constant drive current I, the initial power consumption at each start-up of the motor is given by

With the resistance R being known, a current I can accordingly be selected such that the initial power consumption P _max does not exceed the operational limits of the power supply, in particular a power consumption threshold. While powering the motor with a constant drive current, the motor speed continuously increases. Upon the motor speed assuming the desired value for backward operation, the power supply may be changed to power the motor with a constant backward drive voltage. Alternatively, the motor may be powered with a constant nominal voltage corresponding to the steady phase from beginning on, with a current limitation according to (3) being simultaneously active, as will be discussed below in the context of exemplary embodiments.

In some embodiments, the drive control unit is configured to increase the backward drive voltage in the starting phase in a time-controlled way. Alternatively, the backward drive voltage may be increased in dependence of the motor speed, based on a feedback signal provided by the motor or an encoder that is coupled to the motor. For increasing the backward drive voltage in a time-controlled way, a corresponding timer is favorably provided in the drive control unit. A relationship between time or motor speed and corresponding backward drive voltage is favorably stored by the drive control unit in form of a table, as interpolation function or the like.

In some embodiments, the drive control unit is designed to increase the backward supply voltage in a number of discreet steps. Alternatively, the motor backward supply voltage may be increased in a steady or continuous way, e.g. according to a linear ramp or a ramp of increasing or decreasing slope. In further embodiments where the motor speed is controlled, the drive control unit may be designed to increase the motor speed in a number of discrete steps or continuously.

In some embodiments, the drive control unit is designed to supply the motor with a constant forward drive voltage or to operate the motor with a constant motor speed during forward operation. For forward operation, in particular, drug infusion, the drive voltage may be switched from zero to a constant value which is subsequently maintained such that forward drive voltage is constant from beginning on. This value is selected such that the power consumption threshold is not exceeded. Alternatively, an adjustment may be carried out in a similar way as for backward operation. In an exemplary embodiment, a constant forward drive voltage of the same value as the initial backward drive voltage may be used. When switching the forward drive voltage from zero to a constant voltage, the motor speed will increase within a short time period in according to the mechanical time constant of the drive and subsequently stay constant for a constant load. Alternatively to the forward drive voltage, the forward motor speed may be controlled by the drive control unit.

In some embodiments, the drive control unit further includes a DC/DC step-up converter, the DC/DC step-up converter powering the motor for backward operation. Powering the motor via a DC/DC step-up converter generally allows powering the infusion device at a low voltage and accordingly using a small battery, such as a single AA or AAA cell. For the backward operation, step-up conversion is particularly favorable for a device in accordance with the present disclosure because of the higher supply voltage. For forward operation, the motor may be powered directly or via the same or a further converter.

In some embodiments, the drive control unit is designed to control a brushless DC motor (also referred to as electronically commutated DC motor, EC motor). In contrast to a standard DC motor, a brushless DC motor comprises a rotor with a permanent magnet coupled to the motor shaft and a set of typically three stationary coils which must be cyclically powered according to a well-defined powering scheme for the motor to run. Because powering of the coils must be synchronized with the rotational angle of the rotor, a turning angle encoder is typically coupled to the motor shaft which provides corresponding trigger signals. Evaluation of the encoder signal and powering of the coils may be carried out by the drive control unit, by further independent circuitry or a micro controller running corresponding firmware code. While requiring a somewhat higher powering and control effort, brushless DC motors are advantageous with respect to robustness, lifetime and safety.

If the motor is a standard DC motor, selecting the motion direction of the motor, and, thus, selecting between forward and backward operation, is carried out via the polarity of the motor supply voltage. For a brushless DC motor, selecting the motion direction is carried out be selecting a corresponding cyclic powering scheme for the coils, the powering scheme defining both the polarity and the timing of the voltage or current supplied to the motor.

Some other characteristics apply for a standard and a brushless DC motor in the same way or in analogous ways. In particular, the motor speed increases linearly with the motor supply voltage in both cases. Where the motor is a brushless DC motor, phrases like "drive voltage" or "drive current" refer to powering each of the coils according to the cyclic powering scheme.

Terms like "increasing" or "adjusting", refer, in the context of powering the motor, generally to a change in the effective value, which is, in case of a non-pulsed DC voltage or current, identical to the absolute value, if not explicitly stated differently.

The drive control unit may be designed to couple to a battery, the battery having a nominal voltage in a range of 1 V to 2 V, the battery serving, during operation, as power supply for the motor. A battery voltage in the indicated range is favorable in so far as it is typical for small and sufficiently powerful battery cells, such as rechargeable and non-rechargeable general-purpose AA or AAA cells which are widely available with various electro-chemical designs.

The drive control unit may be designed to evaluate a motor feedback signal by corresponding circuitry and/or software code. The motor feedback signal may especially be an encoder signal as provided by an optical or magnetic rotation encoder or turning angle encoder. During forward operation, in particular drug infusion, the feedback signal may favorably be used for supervising and controlling the infused drug amount. In some embodiments, the motor speed, as derived from the feedback signal, may be used for controlling the drive voltage or the drive current in dependence of the motor speed as described above either or both of for forward and backward operation. For general power management reasons, the drive control unit may be designed to power the motor in a pulsed or switched way rather than continuously, typically by repeatedly switching the drive voltage. A phase where the motor is powered for such embodiments is referred to as a "burst".

A burst may, e.g., correspond to 20 ... 50, e.g. about 30, steps of motor 345. The step angle is determined by the motor design and the motor control strategy as discussed above. One burst may correspond to a fixed burst volume of drug, e.g. 0.1 IU. During a burst, the motor may be powered continuously or in a pulsed way and controlled via PWM. In this latter case, the PW frequency, typically in the kHz range, is high as compared to the burst frequency. That is, during each burst, the drive voltage is switched multiple times according to the PWM frequency. If the ambulatory infusion device is designed to alternatively receive different types of cartridges of different cross sectional areas, such as cylindrical cartridges of different diameters, the number of steps per burst may be varied such that the burst volume is kept constant.

For embodiments where the motor is powered in bursts, adjusting the drive voltage or drive current refers to an adjustment of the switched-on value. A voltage or current adjustment may be carried out from burst to burst, such that the voltage or current is constant during a single burst, or may, at least partly, be carried out during the bursts.

Between consecutive bursts, a somewhat longer delay allows a battery recovery and prevents a battery breakdown. A typical burst frequency may, e.g., about 2 Hz, with the duration of a burst being, e.g., 100 msec. For the infusion of a fractional basal volume and/or for the infusion of small boli, the motor may be activated only for a few bursts or a few motor steps, corresponding to a burst fraction. For the infusion of larger boli and for piston rod retraction, the motor is operated continuously for a large number of bursts.

According to a further aspect, the present disclosure is related to a drive unit for an ambulatory infusion device, the drive unit including a drive control unit as discussed above and further below in the context of exemplary embodiments, and a motor.

In some embodiments, the drive unit includes a reduction gear, the reduction gear having a reduction rate of 1 :200 or more.

In some embodiments, the drive unit further includes a linearly displaceable piston rod. The piston rod is coupled or coupable to the motor for forcing a liquid drug, e.g. an insulin formulation, out of a drug cartridge.

According to a still further aspect, the present disclosure is related to an ambulatory infusion device. The ambulatory infusion device is designed to be carried by a patient over an extended time period and concealed from view and is further designed for a substantially continuous drug administration according to a time- variable administration schedule. The ambulatory infusion device includes a power supply or a receptacle for a power supply, and a drive unit as discussed above and further below. The power supply serves especially as primary power source for powering the motor. Further circuitry and components of the ambulatory infusion device may be powered by the same and/or further power supplies.

According to a still further aspect, the present disclosure is related to a method of controlling a motor of an ambulatory infusion device. The method may include powering the motor for forward operation in a forward direction and alternatively powering the motor for backward operation in an opposite backward direction: The method may further include, modifying, in a starting phase of backward operation, modifying a backward drive voltage or a backward drive current supplied to the motor, thus increasing a motor speed.

According to a still further aspect, the present disclosure is directed towards a method of controlling a piston rod retraction in an ambulatory infusion device. The method may include powering a motor of the ambulatory infusion device for backward operation in backward direction, thus retracting a piston rod of the ambulatory infusion device against a forward direction. The method may further include modifying, in a starting phase of backward operation, modifying a backward drive voltage or a backward drive current supplied to the motor, thus increasing a motor speed.

A method according to the present disclosure may be carried out using drive control units and/or drive units according to the present disclosure and using ambulatory infusion devices according to the present disclosure. Vice versa, drive control units, drive units and ambulatory infusion devices in accordance with the present disclosure may be used to carry out a method in accordance to the present disclosure. Therefore, disclosed embodiments of drive control units, drive units and ambulatory infusion devices, also define corresponding method embodiments and vice versa. Similarly, definitions and explanations that are provided in the context of a specific aspect also refer to other aspects of the present disclosure, where not explicitly stated differently.

Exemplary Embodiments

In the following, exemplary embodiments are discussed greater detail with reference to the figures.

Figure 1 a and Figure 1 b exemplarily illustrate major constraints for a drive unit of an ambulatory infusion device (discussed above).

Figure 2 shows an outside view of an exemplary ambulatory infusion device.

Figure 3 shows an exemplary drive unit in a schematic structural view.

Figure 4 shows an exemplary drive unit in a schematic structural view.

Figure 5a to Figure 5d illustrate the backward drive voltage (Figure 5a), the resulting motor current (Figure 5b), the power consumption (Figure 5c), and the motor speed (Figure 5d) for an exemplary backward operation.

Figure 6a to Figure 6c illustrate the backward drive voltage (Figure 6a), the motor current (Figure 6b), and the motor speed (Figure 6c) for a further exemplary backward operation.

Figure 2 shows an outside view of an exemplary ambulatory infusion device 100 in accordance with the present disclosure. The device 100 includes a housing 105 of a size and shape that allows carrying the device 100, e.g., in a trouser's pocket or at a belt with a belt clip. In an operable state, the device 100 may be water-protected or water tight.

The device 100 includes a user interface that is exemplarily realized by a display 1 10, such as a graphical LCD or OLED display, a number of push buttons 115a, 1 15b, 115c, 1 15d, as well as an audio transducer, such as a buzzer, and a tactile indication unit, such as a pager vibrator (not visible). Among others, the user interface is used for commanding the on-demand infusion of drug boli and for retracting a piston rod of the drive unit (discussed below). A remote controller may be provided additionally or alternatively to the user interface of the device 100, thus allowing control of some or all functionality of device 100 without direct physical access, with the device 100 being carried concealed from view.

The device 100 further includes a battery compartment (not visible) to receive a typically user-replaceable battery, such as a single rechargeable or non- rechargeable AA or AAA cell of 1.5 V nominal voltage.

In the operable state, a drug container, typically realized as cylindrical cartridge, is inserted in a cartridge compartment 120 and may be visible without removal via a transparent window. The cartridge has a typical filling volume of 1 ml..3 ml with an inner diameter in a typical range of about 0.5 cm ... 2 cm. The corresponding displacement range of a cartridge plunger between full and empty cartridge is in the cm range. The cartridge may be a special-purpose cartridge that is especially designed for use in device 100 and typically filled with drug by the user immediately prior to insertion into cartridge compartment 120. Alternatively or additionally, cartridge compartment 120 may receive readily filled cartridges, such as cylindrical glass cartridges as typically used in pen-type injection devices.

In the operable state, a catheter with coupler 130 is coupled to the drug container via a removable adapter 125 which also supports the drug cartridge axially against the displacement direction of the plunger. Both for the adapter 125 as well as the coupler 130 a number of designs may be used. The adapter 125 and/or the coupler 130 may include further components and functions, such as a check valve and/or a fluidic pressure sensor.

The drug cartridge may further be, fully or in part, integral with the adapter 125 and/or the catheter. In a further variant, the device 100 may be designed to be directly attached to the user's skin via an adhesive layer directly or via an intermediate cradle. In such an embodiment, a catheter may not be required and an infusion cannula may be directly coupled to the drug cartridge.

Figure 3 shows an exemplary drive unit 300 of ambulatory infusion device in accordance with the present disclosure, such as device 100, together with a battery 310, in a schematic structural view. Figure 4 shows a corresponding electromechanical arrangement. The battery 310 also powers the further electronic components of the ambulatory infusion device.

Major components of the drive unit 300 are a drive control unit 320 and a motor 345 with attached gear box 355 and telescopic piston rod 360. Motor 345 is exemplarily realized as brushless DC motor but may also be a standard DC motor. An exemplary gear box 355 includes a multi-stage planetary gear 355a inline with motor 345 and a further helical gear which simultaneously realizes a 180° direction change, thus allowing a side-by-side parallel arrangement of motor 345 and piston rod 360. The helical gear includes a toothed wheel 355b that is coupled to a shaft of planetary gear 355a, an intermediate toothed wheel 355c and an output side toothed gear 355d that is coupled to piston rod 360. The resulting overall reduction rate i is about 450.

Piston rod 360 is realized in form of a telescopic spindle drive which is designed, e.g., according to the disclosure of EP 0991440 A1. A telescopic arrangement allows the total length in the retracted state to be shorter than the travel range between fully retracted and fully extended state, thus reducing the overall device dimensions. Piston rod 360 includes the telescopic spindle section 360a that is coupled to output side wheel 355d and plunger coupler 360b that is designed to couple to a cartridge plunger, typically via a releasable threaded engagement or a bayonet.

Inline with the motor 345 is a typically magnetic turning angle encoder 350. Encoder 350 provides the trigger signals that are required for correct powering of the three coils of motor 345. In addition, the signals provided by encoder 350 are used for counting the motor revolutions during drug infusion and for general operation monitoring. In alternative embodiments where the motor 345 is a standard DC motor, encoder 350 is provided only for the latter purposes or may be omitted.

A number of variants may be used for the electro-mechanical arrangement. For example, piston rod 360 may not be realized in a telescopic way, motor 345 with encoder 350 and planetary gear box 355a may be arranged in-line with rather than parallel to piston rod 360, a multi-stage helical gear may be used rather than a combination of a planetary gear and a helical gear, etc.

Drive control unit 320 includes control circuitry 325, voltage converter 335 in form of a DC/DC step-up converter, and power circuitry 340. Control circuitry 325 may be realized fully or partly integral with the general circuitry of the ambulatory infusion device, typically including components such as micro-controllers, ASICS, memory components, display circuitry, communication interfaces, an input unit with a keyboard, a touch screen, or the like, and supplementary circuitry. Control circuitry 325 may be realized in hardware, firmware, embedded software, or any combination of those.

Voltage converter 335 is designed to supply a number of different voltages to power circuitry 340 in accordance with a corresponding voltage control signal provided by control circuitry 325. Power circuitry 340 is typically based on a number of FET transistors for individually powering the coils of motor 345 with reversible polarity. Motor 345 is accordingly powered by battery 310 via voltage converter 335 and power circuitry 340.

The drive control unit 320 may power motor 345, during operation, continuously or in a series of pulses and/or bursts as described above. For an exemplary EC motor, the step angle may be 60°. The burst frequency may, e.g., be in a range of 0.5 Hz to 4 Hz.

For powering motor 345, control circuitry 325 provides a control signal to converter 335. Control circuitry 325 further provides cyclic signals to power circuitry 340 for cyclically powering the coils of motor 345 in accordance with a cyclic scheme. Control circuitry 325 further receives and evaluates the trigger signals provided by encoder 350, such that powering of the coils is switched at the correct rotational angels of the motor shaft.

In the exemplary embodiment of Figure 3, power circuitry 340 is designed to selectively power the three coils of brushless DC motor 345 with selectable polarity. In alternative embodiments where motor 345 is a standard DC motor, the motor 345 typically comprises a single coil and power circuitry 340 is designed to power the single coil with selectable polarity.

For forward operation, in particular for basal drug infusion and bolus infusion, as well as for initially filling a fresh catheter (priming), control circuitry 325 controls converter 335 to provide a constant forward drive voltage of, e.g., 1.8 V. The forward drive voltage is selected such that the initial power consumption of motor 345 for foreward operation does not exceed the threshold power consumption P _Limi t of, e.g., 300mW.

For backward operation, in particular for retracting piston rod 360, control circuitry 325 controls converter 335 to increase the backward drive voltage in a time- controlled way. For this purpose, control circuitry 325 includes voltage control unit 330 which is coupled to converter 335. The control signal that is generated by voltage control unit 330 may be an analogue or digital signal and controls converter 335 to increase the backward drive voltage in a number of discrete steps to a maximum value which is subsequently maintained during backward operation.

Figure 5 shows exemplary time diagrams for the backward drive voltage (Figure 5a), the resulting backward drive current (Figure 5b), the power consumption (Figure 5c) and the motor speed (Figure 5d) in a numeric simulation.

The backward drive voltage is controlled to assume, in the starting phase starting from 0, values of 1.8 V as initial backward drive voltage, 2.2 V, 2.6 V, and finally 3.0 V as maximum value which is subsequently maintained in the steady phase. The duration of each step is 100msec, resulting in a total start-up time of 0.3 sec. Figure 5b and Figure 5c show that each step of the backward drive voltage is associated with a corresponding peak in the backward drive current and, accordingly, in the power consumption. The highest peak occurs at t=0.2 sec as initial power consumption of the backward operation, with the power consumption being given by (2). With approximately 250 mW for an exemplary and typical resistance of R = 13.2 Ohm for the motor coils, this peak does not exceed the threshold power consumption of P _L imit ⁼ 300 mW. The subsequent peaks are lower because of the motor rotation.

Figure 5d shows a steady motor speed of 7.5*10 ³ RPM (rounds per minute). For a typical reduction rate of the gear 355 and a typical spindle thread of piston rod 360, the total duration of the rewind process is typically in the range of a minute. The duration of the starting phase is accordingly negligible and substantially the whole rewind process is carried out at maximum speed.

Figure 5d further shows a motor speed of 4.2*10 ³ RPM for a voltage of 1.8 V (steady state motor speed after first step). Since the total rewind time is - neglecting the starting phase - proportional to the motor speed, the total rewind time would be about 1.8 times longer if using a constant backward drive voltage of 1.8 V in order not to exceed the power consumption threshold.

If a constant backward drive voltage of 3 V was used for the rewind process from the beginning on, the above-given resistance R would, according to (2), result in a power consumption of about 680 mW, thus by far exceeding the power consumption threshold. For a device in accordance with the present disclosure, the rewind process can accordingly be carried out at a high motor speed, corresponding to a high drive voltage, without violating the power consumption constraints.

It should be noted that variables such as the number of steps, the voltage increase per step, the time duration of each step, the maximum value of the backward drive voltage, etc., are exemplary and may be selected differently for different drive designs and/or for further optimization.

Figure 4d, for example, shows that the motor 345 assumes a stationary state with substantially constant motor speed in a time interval that is substantially shorter as compared to the time interval between consecutive steps of the backward drive voltage. The time interval between consecutive steps may accordingly be further reduced, thus reducing the overall duration of the starting phase.

In further variants, the backward drive voltage is increased in a continuous ramp rather than in a number of discrete steps.

In still further variants, voltage control unit 330 controls the backward drive voltage in dependence of the motor speed based on encoder signals provided by encoder 350. In such an embodiment, the backward drive voltage may be increased with increasing motor speed.

Figure 6a to Figure 6c illustrate the backward drive voltage U, the backward drive current I and the motor speed n in a schematic view for an alternative design in accordance with the present disclosure.

For this type of embodiment, drive control circuitry 325 controls voltage converter 335 and power circuitry 340 to power motor 345, with beginning of backward operation at time , with a constant nominal backward drive voltage U ₀ which would, as initial-start-up voltage, result in the power consumption constraint to be violated.

Therefore, current limiting circuitry is provided in drive control unit 320 which limits the current drawn by motor 345 to a threshold current l ₀ by reducing the drive voltage U if the current exceeds the threshold current ^.Threshold current l ₀ is chosen in accordance with (3). As a consequence, backward drive current I equals threshold current l ₀ in the starting phase, with the actual backward drive voltage U being below the nominal value U ₀ . As the motor speed increases, the backward drive voltage U and the motor speed n increase in a substantially linear way. When the actual backward drive voltage U assumes the nominal value U ₀ at time t ₂ , the backward drive voltage will not further increase but is maintained at this value. Consequently, the backward drive current I starts decreasing and the backward drive voltage U is accordingly not further determined by the current limiting circuitry, thus ending the starting phase. The motor speed consequently assumes, following a short transition period (not referenced), a constant value in accordance with backward drive voltage Uo in the following steady phase.

In a variant of this type of embodiment, drive control circuitry 325 directly controls motor 345 in the ramp up-phase, that is, from to t ₂ , to power motor 345 with a constant drive current l ₀ in accordance with (3). At time t ₂ , drive control circuitry 325 is switched to powering motor 345 with constant backward drive voltage U ₀ . Switching from current control to voltage control is favorably carried out such that the backward drive voltage is steady and does not "jump" at the moment of switching, that is, when the backward drive voltage U for I = l ₀ equals U ₀ (time t ₂ in Figure 6).