MEDICAL DEVICE WITH POWER-UP ROUTINE

Abstract

The present disclosure relates to a method for powering up a medical device powered by a battery. The method includes executing an initial battery test. In the initial battery test, a difference voltage between a battery voltage measured without and with a test load is determined. The test load is favorably dimensioned not to significantly stress the battery. The difference voltage is compared with a difference voltage threshold, the difference voltage threshold being predefined in dependence of the no-test-load voltage. The method further includes providing an alarm if the difference voltage is above the difference voltage threshold. The present disclosure further concerns a medical device that implements the method and a method for determining the relation between the difference voltage and the difference voltage threshold. The disclosure can be used to ensure that an alarm is provided if a newly inserted battery is too weak to power the medical device.

Claims

1. A method for powering up a medical device powered by a battery, comprising: a) determining a no-test-load voltage (U.sub.NoTestLoad) of the battery without a test load (R.sub.Test) being connected to the battery; b) providing an alarm when the U.sub.NoTestLoad is below a predetermined no-test-load voltage threshold (U.sub.Threshold,NoTestLoad) and terminating the method; c) when the U.sub.NoTestLoad is above the U.sub.Threshold,NoTestLoad executing the steps of: c1) determining a test-load voltage (U.sub.TestLoad) of the battery with the R.sub.Test being connected to the battery; c2) comparing a difference voltage (ΔU) between the U.sub.NoTestLoad and the U.sub.TestLoad with a difference voltage threshold (ΔU.sub.Threshold), the ΔU.sub.Threshold being predefined in dependence of the U.sub.NoTestLoad; c3) when the ΔU is above the ΔU.sub.Threshold, providing an alarm; and d) when ΔU is below ΔU.sub.Threshold, completing the powering up of the medical device.

2. The method according to claim 1, wherein the ΔU.sub.Threshold is a linear function of the U.sub.NoTestLoad.

3. The method according to claim 1, wherein the R.sub.Test is a constant resistance test load.

4. The method according to claim 1, wherein the initial battery test includes storing a result of the initial battery test in a history memory of the medical device.

5. The method according to claim 1, wherein, when it is determined in step (c2) that the ΔU is below the ΔU.sub.Threshold, executing a further battery test, wherein the further battery test includes drawing a further test load current, thereby stressing the battery to a limit that is expected to occur during regular operation of the medical device and providing an alarm if it is determined that the battery is not capable of powering the medical device.

6. The method according to claim 1, wherein the method includes before step a), turning on the power of the medical device.

7. The method according to claim 1, wherein the subsequent steps include at least one of the following: memory checks, communication controller checks, medical device circuitry checks, sensor checks, electrode checks, checking of a communication controller, tests of acoustic indication devices, checks of tactile indication devices, and initializing steps of the medical device.

8. A battery-powered medical device, comprising: a battery compartment configured to removably hold a battery and contact elements for electrically contacting the battery; a test load (R.sub.Test) selectively coupleable to the battery; and a control circuit configured to execute the method according to claim 1.

9. The battery-powered medical device according to claim 8, further comprising one or more DC/DC step-up converters powering at least some functional units of the medical device, wherein the R.sub.Test is electrically arranged between the contact elements and an input side of the DC/DC step-up converter.

10. The battery-powered medical device according to claim 8, wherein a relation between the ΔU.sub.Threshold and the U.sub.NoTestLoad is stored in a memory of the control circuit.

11. The battery-powered medical device according to claim 8, wherein the medical device is an extracorporeal insulin pump configured to be carried by a user for an extended time period under clothing and/or attached to the body.

12. The method according to claim 1, further comprising: (1) experimentally determining a functional relation between values of an effective internal resistance (R.sub.i) and values of an open-circuit voltage (U.sub.0) for which the battery is capable of powering-up the medical device; (2) determining a minimum no-test-load voltage (U.sub.NoTestLoad,min) of the battery for powering up the medical device without the R.sub.Test being connected to the battery as a function of the open-circuit voltage U.sub.0 based on the functional relation determined in step (1); (3) determining a minimum test-load voltage (U.sub.TestLoad,min) of the battery for powering up the medical device (1) with the R.sub.Test being connected to the battery as a function of the open-circuit voltage U.sub.0 based on the functional relation as determined in step (1); (4) computing the ΔU.sub.Threshold from the difference between the U.sub.NoTestLoad,min and the U.sub.TestLoad,min in dependence of the U.sub.NoTestLoad,min with the U.sub.0 as parameter.

13. The method according to claim 12, including determining the functional relation between values of the R.sub.i and values of the U.sub.0 as an approximated linear functional relation.

14. The method according to claim 12, including computing the ΔU.sub.Threshold as a linear approximation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0056] FIG. 1 schematically shows an exemplary battery-powered medical device with a battery;

[0057] FIG. 2 shows an exemplary operational flow for powering up a medical device; and

[0058] FIG. 3 shows exemplary graphs for a threshold difference voltage in dependence of a no-test-load voltage.

DESCRIPTION

[0059] The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.

[0060] FIG. 1 shows a battery-powered medical device 1 which is exemplarily an insulin pump together with a battery 2 in a schematic functional view. The battery 2 is removably arranged inside a battery compartment 11 of the medical device 1. Further, the battery 2, for example a rechargeable or non-rechargeable AA cell or AAA cell, is modelled as ideal battery 21 with open-circuit voltage U.sub.0 and an internal resistance R.sub.i,1. The battery 2 is contacted and connected with the further components of the medical device 1 via battery contacts 11a. The battery contacts 11a have a transition resistance R.sub.i,2 in series with the internal resistance R.sub.i,1 of the battery 2. In combination, the internal resistance R.sub.i,1 of the battery 2 and the transition resistance R.sub.i,2 form the effective internal resistance R.sub.i. The terminal voltage of the battery 2 is referred to as U.

[0061] The medical device 1 further includes a DC/DC step-up converter 14 that is connected to the battery contacts 11a. The medical device 1 further includes a control circuit 15 that is connected to the output side of the DC/DC step-up converter. The control circuit 15 as well as further components as explained below are accordingly powered from the battery 2 via the DC/DC step-up converter 14.

[0062] The control circuit 15 includes a processor 151 with corresponding software in particular firmware code, memory 152 and a voltage measurement circuit 153 for measuring the terminal voltage U of the battery 2. Memory 151 may include both program storage that stores firmware code for processor 151 as well as Random Access Memory RAM as data memory. Further, control circuit 15 controls opening and closing of switch 13. Via switch 13, a constant resistance test load R.sub.Test test load that is implemented as can be connected to the battery in parallel to the contact elements 11a.

[0063] The current that is drawn by the test load R.sub.Test if switch 13 is closed is the test load current I.sub.Test. The current I that is drawn by the medical device 1 apart from the test load current I.sub.Test is referred to as I. During an initial battery test as explained further below, it is the baseline current I.sub.B.

[0064] Processor 151, memory 152, and voltage measurement circuit 153 may also be integrated, e.g., in form of a microcontroller as core element of control circuit 15. The control circuit 15 may and typically does further comprise a variety of further components and functional units as generally known in the art.

[0065] The battery-powered medical device 1 in the form of an extracorporeal insulin further includes an actuator 16 in form of an electric motor, a display 17 and at least one acoustic and/or tactile indication device 18, all of which operate under control of the control circuit 15.

[0066] It is noted that the design as shown in FIG. 1 is schematic and simplified for the sake of clarity and conciseness and in order to focus on aspects of particular relevance in the context of this disclosure. By way of example, more than one DC/DC step-up converters may be present that supply different functional components shown DC/DC step-up converter may be omitted. Further, the test load R.sub.Test may be arranged on the output side of the DC/DC step-up converter 14. Further, the test load R.sub.Test is not necessarily realized by a standard constant resistor, but may be realized by other circuitry such as a FET to form a controlled resistor.

[0067] The control circuit 15 implements a method for powering up the medical device 1, which is explained in more detail with additional reference to FIG. 2. The operational flow starts in step S where battery 2 is placed into the battery compartment 11, resulting in the medical device 1 and in particular the control circuit 15 being supplied with power. In step S01, the voltage U is measured via the voltage measurement circuit 153. In this state, the switch 13 is open, and the measured voltage is accordingly the no-test-load voltage, U=U.sub.NoTestLoad, with I=I.sub.B as baseline current.

[0068] In subsequent step S02, the no-test-load voltage U.sub.NoTestLoad is compared with a no-test-load voltage threshold U.sub.Threshold,NoTestLoad that is stored in memory 152 and the operational flow branches in dependence of the result. If the no-test-load voltage U.sub.NoTestLoad is below the no-test-load voltage threshold U.sub.Threshold,NoTestLoad, the operational flow proceeds with step S03. In Step S03 an alarm is generated and indicated via display 17 and indication devices 18. Further, a corresponding entry is written into a history memory which is part of memory 152. Subsequently, the operational flow ends with step E and the powering up is terminated. The alarm may be indicated until the battery 2 is fully emptied respectively removed. In an exemplary realization where the battery 2 is an ordinary, commercially available standard cell and the no-test-load voltage threshold U.sub.Threshold,NoTestLoad may be, for example 1000 mV respectively 1 V.

[0069] If it is determined in step S02 that the no-test-load voltage U.sub.NoTestLoad is above the no-test-load voltage threshold U.sub.Threshold,NoTestLoad, the operational flow proceeds with step S04. In step S04, the voltage U is measured via the voltage measurement circuit 153 with switch 13 being temporarily closed. The measured voltage is accordingly the test-load voltage, U=U.sub.TestLoad, and the current that is drawn from the battery 2 corresponds to the sum of the baseline current I.sub.B and the test current I.sub.Test.

[0070] In subsequent step S05, the difference voltage ΔU=U.sub.NoTestLoad−U.sub.TestLoad is determined and compared with a difference voltage threshold ΔU.sub.Threshold which is predefined in dependence of the no-test-load voltage U.sub.NoTestLoad. The relation between the difference voltage threshold ΔU.sub.Threshold and the no-test-load voltage U.sub.NoTestLoad may be stored in and retrieved from memory 152 in form of a look-up table or may be provided in form of an equation ΔU.sub.Threshold=f(U.sub.NoTestLoad) which may especially be a linear equation and is evaluated by control circuit 15, in particular processor 151. This aspect is also discussed further below.

[0071] If it is determined in step S05 that the difference voltage ΔU is above the difference voltage threshold ΔU.sub.Threshold, the operational flow proceeds with step S06. In Step S06 an alarm is generated and indicated as explained before in the context of step S03 and a corresponding entry is again written into the history memory. Also like in step S03, the operational flow ends with step E and the powering up is terminated.

[0072] If it is determined in step S05 that the difference voltage ΔU is below the difference voltage threshold ΔU.sub.Threshold, the operational flow proceeds with step S07 where the powering up is continued and completed. Step S07 may include executing a further battery test as explained before in the general description.

[0073] In the following, the functional relation between the difference voltage threshold ΔU.sub.Threshold and the no-test-load voltage U.sub.NoTestLoad is discussed in more detail.

[0074] In investigating the start-up behavior of a battery-powered medical device and in particular an extracorporeal insulin pump as explained before, it is found that correct start-up is in any case possible if the effective internal resistance R.sub.i meets the condition

R.sub.i<r.sub.i(U.sub.0)=k.sub.1.Math.U.sub.0+k.sub.2  (1a).

[0075] Consequently, for the effective internal resistance R.sub.i being given, the open-circuit voltage U.sub.0 needs to meet the condition

[00001]$\begin{array}{cc}{U}_0>u_0\left(R_i\right)=\frac{R_i-k_2}{k1}.& \left(1b\right)\end{array}$

[0076] Further, it can be seen from FIG. 1 that the following applies:

[00002]$\begin{array}{cc}{U}_0=R_i.Math.I_B+U_{\mathrm{NoTestLoad}},& \left(2a\right)\\ U_0=R_i.Math.\left(I_B+\frac{U_{\mathrm{TestLoad}}}{R_{\mathrm{Test}}}\right)I_B+U_{\mathrm{NoTestLoaad}},& \left(2b\right)\end{array}$

with Eqn. (2a) applying during the initial battery test with switch 13 being open and Eqn. (2b) applying during the initial battery test with switch 13 being closed.

[0077] In the following, a voltage on the output side of the DC/DC step-up converter 14 (i.e., the supply voltage of control circuit 15) is referred to as U′. Further, the (virtual) load resistance that is seen by the battery 2 as drawing the baseline current I.sub.B is referred to as R.sub.B. Eqn. (2a), (2b) can accordingly be re-written as

[00003]$\begin{array}{cc}{U}_0=\frac{R_i}{R_B}\frac{U^{\mathrm{\prime 2}}}{U_{\mathrm{NoTestLoad}}}+U_{\mathrm{NoTestLoad}},& \left(3a\right)\\ U_0=\frac{R_i}{R_B}.Math.\frac{U^{\mathrm{\prime 2}}}{U_{\mathrm{TestLoad}}}+\left(\frac{R_i}{R_{\mathrm{Test}}}+1\right).Math.U_{\mathrm{TestLoad}}.& \left(3b\right)\end{array}$

[0078] By re-arranging Eqn. (3a), (3b) for U.sub.NoTestLoad and U.sub.TestLoad, respectively and solving the resulting quadratic equations, the following is obtained:

[00004]$\begin{array}{cc}{U}_{\mathrm{NoTestLoad}}\left(U_0,R_i\right)=\frac{U_0}{2}+\sqrt{{\left(\frac{U_0}{2}\right)}^2-\frac{R_i}{R_B}.Math.U^{\mathrm{\prime 2}}}& \left(4a\right)\\ U_{\mathrm{TestLoad}}\left(U_0,R_i\right)=\frac{U_0}{2}.Math.\frac{R_{\mathrm{Test}}}{R_{\mathrm{Test}}+R_i}+\sqrt{{\left(\frac{R_{\mathrm{Test}}}{R_{\mathrm{Test}}+R_i}.Math.\frac{U_0}{2}\right)}^2-\frac{R_{\mathrm{Test}}}{R_{\mathrm{Test}}+R_i}\frac{R_i}{R_B}.Math.U^{\mathrm{\prime 2}}}.& \left(4b\right)\end{array}$

[0079] Eqn. (4a, 4b) accordingly express the voltages U.sub.NoTestLoad, U.sub.TestLoad for the battery 2 that can be measured in the medical device 1 in operation as function of the generally unknown open-circuit voltage U.sub.0 and effective internal resistance R.sub.i.

[0080] In Eqn. (4a, 4b), the effective internal resistance may be substituted by its threshold value for which a powering-up is possible according to Eqn. (1a), resulting in equations for the minimum no-test-load voltage U.sub.NoTestLoad,min and the minimum test load voltage U.sub.TestLoad,min with the open-circuit voltage U.sub.0 as sole parameter.

[0081] The graph of FIG. 3 schematically shows the difference voltage ΔU=U.sub.NoTestLoad−U.sub.TestLoad when plotted over the no-test-load voltage U.sub.NoTestLoad with the open-circuit voltage U.sub.0 as parameter. Curve A is obtained from directly applying Eqn. (4a), (4b). In a region II above curve, a powering up the medical device 1 is not possible, while in the area I below the curve, powering up is possible. Curve A accordingly defines the difference voltage threshold ΔU.sub.Threshold as a function respectively in dependence of the no-test-load voltage U.sub.NoTestLoad−Curve A may be implemented in the control circuit 151 by way of a mathematical function that is evaluated by the processor 151 or may be implemented as look-up table in the memory 152.

[0082] A further computational simplification as explained in the following may be used in a further embodiment. Instead of curve A, the linear approximation of curve B is used. Curve B may be obtained as tangent to curve A at a reference value ΔU.sub.0. Like curve A, Curve B may be implemented in the control circuit 151 by way of a (linear) mathematical function that is evaluated by the processor 151 or may be implemented as look-up table in the memory 152. In an exemplary implementation, the reference value may be in the range of 1 mV.

[0083] While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

LIST OF DESIGNATIONS

[0084] 1 battery-powered medical device/extracorporeal insulin pump [0085] 11 battery compartment [0086] 11a contact element [0087] 13 switch [0088] 14 DC/DC step-up converter [0089] 15 control circuit [0090] 151 processor [0091] 152 memory [0092] 153 voltage measurement circuit [0093] 16 actuator/motor [0094] 17 display [0095] 18 indication device [0096] 2 battery [0097] 21 ideal battery [0098] U.sub.0 open-circuit voltage [0099] U terminal voltage [0100] U′ voltage at output side of step-up converter [0101] R.sub.i,1 internal resistance of battery [0102] R.sub.i,2 transition resistance of contact elements [0103] R.sub.Test test load resistance [0104] R.sub.B virtual resistance drawing baseline current [0105] ΔU difference voltage [0106] ΔU.sub.0 reference value for difference voltage [0107] U.sub.NoTestLoad no-test-load voltage [0108] U.sub.TestLoad test-load voltage [0109] U.sub.Threshold,NoTestLoad threshold voltage without test load [0110] ΔU.sub.Threshold difference voltage threshold [0111] I current [0112] I.sub.B baseline current [0113] I.sub.Test test load current [0114] k.sub.1, k.sub.1 constants [0115] A, B curves