GB2311866A

GB2311866A - Test apparatus for a syringe driver

Info

Publication number: GB2311866A
Application number: GB9706739A
Authority: GB
Inventors: David Williams
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-04-03
Filing date: 1997-04-03
Publication date: 1997-10-08
Anticipated expiration: 2017-04-03
Also published as: GB2311866B; GB9706739D0; GB9607100D0

Abstract

A test apparatus for a syringe driver, intended to be placed on a driver under test in place of a syringe, comprises a current sensor 12 to sample the current drawn by the driver, linear motion and driving force sensors 16,13 to measure the corresponding movement of and force applied by the driver, and an interface 10 whereby the measured values may be shown by a display 21. The apparatus may be operable to display motor pulse interval, percentage interval error, linear accuracy, and thrust level. A dryness test may also be applied, based on quiescent current. Two constructional forms are described.

Description

TEST APPARATUS FOR A SYRINGE DRIVER The present invention relates to an apparatus for testing a device known as a syringe driver.

A syringe driver is a medical device for driving a plunger down a syringe at a predetermined rate. The contents of the syringe are thereby delivered at a known rate over a predetermined period such as one hour, three hours or twenty four hours. A motor is energised for a short period at known intervals to rotate a lead screw and drive a drive element along the screw. The delivery rate is determined by the mechanical characteristics of the drive train and the mark-space ratio of the motor drive signal.

A problem arises in that correct operation of the syringe driver is difficult to verify. The motor drive pulse is usually of the order of one or two seconds, and the interval between pulses is usually relatively long such as around 5 minutes. It is desired to check not only that the motor operates, but that it is driven correctly and consistently over a long period. Testing may be done by manually monitoring the apparatus for an extended period, such as three hours, but a manual test procedure is labour intensive and subject to human error. It is desired to provide an apparatus that assists human monitoring.

According to the present invention there is provided a test apparatus for a syringe driver, comprising: current sense means for sensing current drawn by a syringe driver under test and producing a current signal; movement sense means for sensing linear movement of a driven portion of a syringe driver under test and producing a movement signal; force sense means for sensing force of a driven portion of a syringe driver under test and producing a force signal; and interface means for interfacing said current signal, said movement signal and said force signal to a human readable output.

The current sense means may produce a two-state output (high or low) dependent upon whether the current drawn is above or below a predetermined threshold. For example, the output may go "high" whenever current is drawn above a predetermined level. The current sensor may have a low pass filter to inhibit switching noise from a DC motor in the syringe driver.

In a preferred embodiment, the interface means includes an A/D converter for providing an 8-bit digital quantizisation of the sensed current, which gives 256 discrete current levels that may be directly proportional to the sensed current, or may be assigned a non-linear relationship such as by a look-up table.

The interface means preferably comprises means for determining the length of "high" current pulses caused by operation of the DC motor in the syringe driver, and the interval between pulses. Further, the interface means may comprise means for recording the pulse length and pulse interval for a desired time period or a desired number of cycles. Comparison means may be employed to determine whether the pulse length or pulse interval are set to a predetermined level, preferably within a predetermined error margin.

Commonly, a syringe driver is regulated by an internal clock. To give a visual indication of the clock speed, an LED on the syringe driver is driven at a set relationship to the clock speed of the driver. The test apparatus also senses the current drawn by the LED. The interface means may comprise means for distinguishing between current pulses of a long duration which relate to the motor and current pulses of a short duration which relate to the LED. The pulse interval of the LED can be monitored and compared with an expected interval to give a further indication of correct functioning of the syringe driver.

Preferably, the movement sense means comprises a body member mounted on the syringe driver in place of a syringe, and a plunger driven into the body member. Conveniently, a slide arm of a slide potentiometer mounted on the body member is moved by the plunger to give an output proportional to movement.

The force sense means comprises a strain gauge such as a thrust beam for monitoring the level of thrust exerted on the driven plunger by the syringe driver. Alternatively, a biasing means of known resistance opposes the plunger such that the output of the slide potentiometer is also proportional to force.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is an overview of a test apparatus; Fig. 2 is a side view of a first sensor; Fig. 3 is a plan view of the first sensor; and Fig. 4 is a side view of a second sensor.

As shown in Fig. 1, the preferred embodiment senses three main characteristics of a syringe driver and these are used for performance verification. The elements are current, linear movement and force.

A syringe driver under test 1 is coupled to power supply 11 via a current sensing circuit 12 that is coupled to an interface circuit 10. Digitised current levels from the current sensing circuit 12 are processed by computer 20 and results are output to display 21.

Syringe drivers often fail due to immersion in water.

A dryness test is performed by examining current drawn in a quiescent state, on a scale such as 0-50 mA, and a quiescent current of less than say 5mA is acceptable.

The current signal is normally at a quiescent level with long pulses relating to the motor and short pulses relating to an LED. A trace representing the current signal is drawn on display 21 on a scale such as 0-500 mA.

The current signal is monitored and pulse length and pulse interval are determined by computer 20. These may be compared with expected levels and error margins.

An output in the form of a graph on display 21 allows a human operator to monitor the syringe driver under test.

The height of each bar may be proportional to an interval between motor pulses. Preferably, the height of each bar above or below a zero line is proportional to an error signal being the difference between successive pulse intervals. The graph allows an efficient visual check of correct and consistent operation of the syringe driver. For example, it has been discovered that every sixth interval is slightly longer due to the mechanical construction of the drive train. The test may be repeated with the syringe driver set to different rates.

With reference to Figures 2 and 3, a sensing apparatus is used to determine linear movement and force.

The sensor is placed on the syringe driver with body 18 in a position normally occupied by a driven syringe. A stainless steel rod engages with a driven part of the syringe driver. The rod is coupled via spring 19 to slide potentiometer 16. Thus, a sliding portion of slide potentiometer 16 is moved relative to movement of the rod.

The output of the slide potentiometer is converted from analog to digital such as by using an 8-bit ADC 17. The digital output is coupled to interface 10 and processed by computer 20.

Upon installing the sense apparatus, backlash of around 1 mm is taken up and the output of the slide potentiometer 16 monitored over time. This allows verification that, not only is the motor being driven correctly, but also that the drive train functions correctly to move the plunger at the correct rate.

Samples of the slide potentiometer may be taken, for example, every minute or on each motor current pulse.

Again, a visual display is generated.

Further, it is desired not only to verify that the drive element is being driven along at the correct rate, but that it has sufficient force to operate correctly.

For example, the drive element may in some circumstances slip on the drive thread. The drive element is driven against a strain gauge mounted on thrust beam 13. The output of the strain gauge is amplified using strain gauge amplifier 14 and subject to analog to digital conversion using ADC 15. The strain test may be repeated with the power supply unit set, for example, to 7 volts and then 9 volts to simulate different battery conditions. The interface unit 10 provides the output of ADC 15 to computer 20. The ADC output is compared with a calibrated look-up table and a visual output produced.

A second embodiment of the movement and load sensor 40 is shown in Figure 4. The body 41 rests on the syringe driver in place of a syringe with the plunger 42 driven against a compression spring 43. A slide potentiometer 44 coupled to the plunger 42 reflects linear movement. Also, the range of the slide potentiometer, such as 50mm, is calibrated to the resistance of the spring 43 to give an indication of load such as 0-5 Kg.

The movement measurement is plotted against time and should show a generally linear gradient. The corresponding force measurement is taken as a proportion of the travel of the potentiometer against the substantially linearly increasing resistance of spring 43. Of particular interest is the point where the driver 'thrusts out', i.e. the spring force equals that of the motor and drive train.

The test apparatus prompts, via a visual and/or audible signal, a human operator to change settings on a syringe driver under test. The settings are changed in a logical sequence to perform all of the desired tests.

Thus, even an inexperienced person may operate the test apparatus reliably.

In the preferred embodiment, the test apparatus is operated to measure and display motor pulse interval, percentage interval error, LED interval, linear accuracy, and thrust level at both 7 volts and 9 volts. A continuous IT trace shows the current drawn by the syringe driver and a magnified section is used to show operation of a 'boost' control that gives an additional 8-second motor drive pulse. The syringe driver under test is monitored over an extended period, such as three hours. Also, a zero-rate test is performed where the apparatus is monitored for a long period to check that there is no movement when in a stand-by mode. A further motor pulse interval display confirms that a 'fast-run' link of the syringe driver used to accelerate the testing procedure has been returned to a normal setting. The results of these tests may be stored in a software database, and a hard copy produced.

Claims

1. A test apparatus for a syringe driver, comprising: current sense means for sensing current drawn by a syringe driver under test and producing a current signal; movement sense means for sensing movement of a driven portion of a syringe driver under test and producing a movement signal; force sense means for sensing force of a driven portion of a syringe driver under test and producing a force signal; and interface means for interfacing said current signal, said movement signal and said force signal to a human readable output.

2. A test apparatus as claimed in claim 1, wherein: said movement sense means and said force sense means together comprise: a body member locatable in use on a syringe driver in place of a syringe; a plunger linearly movable with respect to said body member, said plunger arranged to be operatively moved in place of a syringe plunger; biasing means for operatively biasing said plunger against movement toward said body member, said biasing means having a known biasing force; monitoring means for monitoring linear movement of said plunger with respect to said body member and producing a monitor signal being said movement signal and said force signal, said monitor signal being proportional to said movement and said biasing force.

3. A test apparatus as claimed in claim 2, wherein said monitoring means comprises a slide potentiometer having a housing coupled to said body member and a slide arm coupled to said plunger.

4. A test apparatus as claimed in claim 3, wherein said biasing means comprises a spring means acting against said plunger to provide a biasing force proportional to movement of said plunger with respect to said body member.

5. A test apparatus as claimed in claims 2, 3 or 4 wherein said interface means comprises: means for converting said monitor signal and said current signal to digital quantizisation; and computer means for storing and processing said monitor signal and said current signal, and producing a graphic output.

6. A test apparatus as claimed in any preceding claim, comprising: means for determining motor pulses and LED pulses of said current signal by comparison with level and length thresholds; means for determining a pulse interval between successive motor pulses; means for determining and displaying a pulse error signal representing the difference between successive pulse intervals.