GB2420719A - A syringe pump and pusher mechanism - Google Patents

Abstract

A syringe pump has a plunger pusher mechanism 86 moved by a leadscrew 88. A half nut 151 in the pusher 86 can disengaged from the leadscrew 88 by a thumb lever 158 and is latched in the disengaged position by a latch lever 143 so that the pusher can be slid manually along the leads crew towards or away from the syringe plunger 81. The latch lever 143 is urged forwardly by a spring 146 and has a projection 142 arranged to contact the plunger head 85 so that the latch lever is displaced rearwardly to unlatch the half-nut 151 when the pusher 86 contacts the plunger 81. The leadscrew 88 is rotated by a dc motor 89 and its speed is controlled by varying the width of pulses supplied to the motor. The drive mechanism is electrically isolated from other electrically-conductive components in the pump to prevent the user being exposed to electrical hazard.

Description

SYRINGE PUMPS

This invention relates to syringe pumps.

Syringe pumps are used to administer liquid medication to a patient at a precisely controlled rate. A syringe is filled with medication and is connected to a catheter. The syringe is then loaded into the pump and its plunger is gripped by a pusher mechanism, which is moved forwardly to push in the plunger and dispense the medication. Usually, the pusher is moved forwardly by means of a Ieadscrew rotated by a motor.

It is known in such pumps to have some arrangement for measuring the diameter of the syringe barrel so that the size of the syringe can be determined. The pump displays an indication of the syringe size for the user to confirm that this is correct. This information is then used in controlling the rate at which medication is dispensed. An example of a syringe barrel size measuring arrangement is described in GB2350062 where a strip coupled with an arm that bears on the syringe barrel moves along a CCD array of over a hundred elements.

The strip has apertures of different lengths and, by measuring the position and length of the apertures, it is possible to obtain a very accurate indication of the diameter of the syringe barrel. Although this arrangement is very accurate it is relatively expensive and requires calibration, which does not make it suitable for low cost pumps. Alternative, low cost, arrangements involve a flag moving along a row of typically three sensors so that an increasing number of 1, 2 or 3 sensors are obscured as the flag moves. This arrangement gives an approximate indication of size but it does not enable the pump to distinguish between many different syringes.

Syringe pumps also commonly have some arrangement for detecting that the head of the plunger has been correctly retained by the pusher. This is important because, if the plunger is not retained, it is possible that it could move forwardly along the barrel and allow medication to siphon out of the syringe. The usual arrangement for detecting the presence of the plunger head is some form of electrical switch or pressure sensor in the pusher, such as described in GB2368288. Although this arrangement can function satisfactorily, it involves electrical connection being made to the movable pusher, which can cause problems, especially because the pusher may be exposed to liquid.

Some syringe pumps are used primarily at the bedside where they can be mounted on a pole and connected to a main power supply. The size, weight and power consumption of these pumps is not critical. Where, however, the pump is of the ambulatory kind, adapted to be carried by the patient, it is important that its size and weight be as small as possible. It is also important that its battery life be as long as possible without the need for large batteries, which would increase the size and weight of the pump.

It is an object of the present invention to provide an alternative syringe pump.

According to the present invention there is provided a syringe pump including a motor, a leadscrew coupled with the motor to be rotated about its axis and a plunger pusher mechanism including an engagement member engageable with the leadscrew so that the pusher member displaces the plunger of a syringe forwardly to dispense medication to a patient when the leadscrew is rotated, the pusher mechanism including a manuallydisplaceable member operable to disengage the engagement member from the leadscrew such as to enable the pusher mechanism to be displaced manually longitudinally of the leadscrew, the manually-engageable member being displaceable to a latched position in which the engagement member is held disengaged from the leadscrew, the pusher mechanism including an actuator member adapted to be contacted by the plunger, and the actuator member being coupled with the manually-displaceable member such that displacement of the actuator member on contact with the plunger releases the latch and allows the engagement member to engage the leadscrew.

The manually-engageable member is preferably a lever pivoted about an axis parallel to the axis of the leadscrew. The lever is preferably coupled with the engagement member such that displacement of the lever causes lateral displacement of the engagement member.

The actuator member may be urged away from the pusher mechanism by a spring. The pump may include a motor control unit arranged to control the speed of the motor, the motor being a dc motor and the motor control unit being arranged to energise the motor in a pulsed fashion, and the control unit being arranged to control the speed of the motor by varying the width of the pulses and, at low speeds, by varying the interval between pulses. The control unit may be arranged to vary the interval between pulses by omitting pulses at low speeds.

The pump may include a cover having a lock mechanism for securing the cover in a closed position protecting the syringe, manually-engageable control means on the housing for controlling operation of the pusher mechanism, and a lock sensor for sensing whether or not the cover is locked closed, the lock sensor providing an output to inhibit programming of the pump via the manually-engageable control means unless the cover is unlocked and to prevent the pusher mechanism moving the plunger to dispense medication unless the cover is locked closed. The pump preferably includes an elongate housing supporting the syringe and an elongate cover mounted at one end on the housing by a hinge mechanism, the hinge mechanism including a first pivot connecting the cover with one end of a coupling link and a second pivot connecting the other end of the coupling link with the housing. The pump may have a housing of a non- conductive material and a user-accessible drive mechanism including exposed metal components, the drive mechanism being electrically isolated from other conductive components within the pump such that a fault condition leading to excess voltage on the other components does not cause excess voltage on the drive mechanism. The pump may include a communications module secured with and supported by the pump. The pump may include ambulatory support means by which the pump can be supported by a patient receiving medication from the pump. The leadscrew is preferably mounted to allow limited axial displacement when there is an obstruction to movement of the pusher mechanism, the pump including a sensor responsive to axial displacement of the leadscrew to provide an output indicative of an obstruction, and a rotary encoder mechanism comprising an encoder disc and an encoder sensor, and both the encoder disc and the encoder sensor being mounted on the leadscrew such that both are displaced axially with the leadscrew when an obstruction occurs, such that the disc is rotated with the leadscrew and the sensor is restrained from rotation.

A syringe pump according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an elevation view of the front of the pump; Figure 2 is perspective view of the rear of the pump with a part of its casing removed; Figure 3 is a perspective view from the rear showing parts of the pump pusher mechanism; Figure 4 is an elevation view of the rear of the barrel size sensor mechanism; Figure 5 is a perspective view of the barrel size sensor mechanism; Figure 6 is a perspective view of the forward side of the plunger pusher mechanism; Figure 7 is a perspective view of the rear of the plunger pusher mechanism with its rear cover removed; Figure 8 is a side perspective view of a latch lever and half nut within the pusher mechanism; Figure 9 is an exploded view of the plunger pusher mechanism; Figure 10 is a perspective view of the forward side of a part of the pusher mechanism with the front cover removed; Figure 11 shows a communications module for the pump and shows schematically how the cover of the pump can be opened; and Figure 12 is an enlarged elevation view of a part of the leadscrew; With reference first to Figures 1 and 2, the pump has a generally rectangular shape with a substantially flat front face 1 supporting various controls 2 and a display 3. The rear surface 4 is also substantially flat and may have formations (not shown) for supporting the pump in a horizontal attitude.

The upper surface 61 of the casing 7 supports a conventional syringe 8 beneath a cover 5 secured at its right-hand end 6 on the casing by means of an articulated hinge 50, shown most clearly in Figure 11. The hinge 50 comprises a first pivot 51 with a transverse axis connecting the cover 5 with one end of a short coupling link 52. The other end of the coupling link 52 has a second pivot 53 with a parallel, transverse axis and is connected with the casing 7. When the cover 5 is closed, the coupling link 52 extends vertically upwards.

When the cover 5 is opened, it can rotate about both pivots 51 and 53, thereby enabling the cover to be swung open through a large angle, as illustrated in Figure 11.

Approximately midway along the length of the pump, the cover 5 and the upper surface 61 of the pump casing 7 have a lock mechanism 54 of the kind described in W00400715. A lock sensor 55 adjacent the lock mechanism 54 provides an electrical output to the pump control unit 56 indicative of whether the cover 5 is locked and closed or is unlocked and open. The pump control unit 56 is arranged to inhibit operation of the controls 2 so that the pump cannot be progranm-ied unless the lock sensor 55 indicates that the cover 5 is unlocked. Further, the control unit 56 prevents the pump being started to dispense medication until the lock sensor 55 indicates that the cover 5 is locked and closed.

The syringe 8 is shown in Figure 2 with its plunger 81 in an extended position relative to the barrel 82, that is, with the syringe full of medication. The head 85 of the plunger 81 is gripped by a plunger pusher mechanism indicated generally by the numeral 86 and shown in more detail in Figures 6 to 10. The pusher mechanism 86 is moved by a leadscrew 88 extending lengthwise of the casing 7 and rotated axially by means of a motor 89 via a universal coupling joint 90, as shown in Figure 12. The pusher 86 has an aperture 91 through which a guide rod 102 (Figure 3) extends parallel to the leadscrew 88. The guide rod 102 prevents rotation of the pusher 86 and ensures that rotation of the leadscrew 88 is translated entirely into axial movement of the plunger 81, thereby ensuring accurate medication delivery.

The leadscrew 88, guide rod 102 and pusher 86 comprise the mechanical drive mechanism of the pump and are exposed for access by the user. Some of these components are formed of metal, so they are electrically conductive. The entire drive mechanism is electrically isolated from any other conductive component within the pump. In this way, there is no need for the pump to have electrical protection at its inlet connections since, even if there were a fault causing the circuit components within the pump to develop a high voltage, any such voltage could not be transferred to any metallic component to which the user has access, so there is no hazard to the user. By avoiding electrical protection at the inlet connections the cost, size and weight of these components can be avoided.

The motor 89 is controlled by a drive unit 92 as shown in Fig 12. In contrast to previous stepper motors used in syringe pumps, the present motor 89 is a dc motor. The drive unit 92 generates voltage pulses at regular intervals, typically once every three seconds. An encoder disc 100 mounted on the leadscrew 88 is used to produce a feedback signal to the drive unit 92 for motor speed control purposes. The leadscrew 88 is mounted resiliently to allow limited movement along its length when an excess force is applied, such as when flow of medication out of the syringe is obstructed and the pusher 86 is prevented from moving forwards. A force sensor (not shown) mounted at the end of the leadscrew 88 measures such an excess force and provides an output to the control unit 56 to generate an alarm and stop further rotation of the motor 89. Because the leadscrew 88 can move axially, the encoder disc will also move. The encoder sensor 101 (which may be a Hall effect sensor where the disc 100 is of a magnetic material) is also mounted on the leadscrew 88 adjacent the disc so that it moves axially with the leadscrew. The sensor 101 is rotationally mounted on the leadscrew 88, so that the leadscrew can rotate relative to the sensor, and the sensor is prevented from rotation by engagement with a longitudinally-extending slot or other formation 103 formed with the pump casing that enables longitudinal movement of the sensor but prevents rotation.

The drive unit 92 varies the speed of the motor 89 by altering the length of the pulses so that the speed is increased by increasing the length of the pulse and is reduced by shortening the length of the pulses. With larger syringes required to dispense at a higher rate, the drive unit 92 can insert an additional pulse periodically, between the regular pulses, such as an additional pulse after every fourth pulse. When the pump needs to dispense at very low rates such as around 0.1 mi/hour the drive unit 92 omits pulses. Typically, it might omit one pulse every twelve seconds. By using a dc motor 89 in this way the power consumption of the pump is reduced, thereby enabling a longer battery life or enabling a smaller battery to be used, so that the size and weight of the pump can be minimized As shown in Figure 6, the pusher 86 has a retaining plate 140 spaced a short distance forwardly of a pusher surface 141 to form a gap in which the head 85 of the plunger 81 can be located. Projecting forwardly from the surface 141, towards its lower end adjacent the plate 140 is an actuator member in the form of an inclined projection 142 formed towards the lower end of a latch lever 143, most clearly seen in Figure 8. The latch lever 143 has a pivot 144 at its upper end and has an inclined latch tooth 145 on one side at its lower end. As shown in Figure 10, the latch lever 143 is urged forwardly by a curved metal strip spring 146 extending laterally across the pusher behind the latch lever. The spring 146 is fixed at its lefi- hand end 147 but its opposite end is joined with a laterally-projecting finger 148, which is displaced outwardly of the pusher 86 when the latch lever 143 is pressed rearwardly. The finger 148 has two lugs 163 and 164, one spaced above the other.

The leadscrew 88 extends through an aperture 149 at the lower end of the pusher 86 and its upper surface is engaged in meshing engagement by a half nut 150 formed at the lower end of a vertical bar 151. The half-nut bar 151 is urged downwardly by a spring (not shown) and has an inclined latch tooth 152 (Figure 9) on its right-hand side towards its upper end. A short stub 153 projects rearwardly at the upper end of the bar 151 and this locates in a notch 154 at the end of a short camming lever 155. The lower edge of the lever 155 has a cam profile 156, which is, in turn, engaged by a cam 157 protruding from the forward surface of a thumb lever 158 extending up the rear face of the pusher 86. The thumb lever 158 is generally of L shape having a lower horizontal limb 159 pivoted towards the right-hand side of the pusher about an axis parallel with the guide rod 102 and leadscrew 88. The vertical limb 160 of the lever 158 is formed at its upper end with a forwardly-projecting, curved, ribbed thumb plate 161. The upper end of the thumb lever 158 is urged outwardly by the spring acting on the half nut bar 151, acting through the cam surfaces 156 and 157. The right- hand, upper part of the casing of the pusher 86 is moulded with ribs 162 similar to those on the thumb plate 161.

When the user wishes to move the pusher 86 forwardly towards the plunger 81 of the syringe 8, he grips the ribs 162 and the thumb plate 161 between the thumb and forefinger so as to move the thumb lever 158 to the left (as viewed from the rear, in Figure 7). The cam 157 on the lever 158 moves to the left and slides along the cam profile 156 of the camming lever 155, thereby displacing its left-hand end upwards. This, in turn, moves the stub 153 and hence the half-nut bar 151 laterally upwardly sufficient for the half nut 150 to unmesh from the thread of the leadscrew 88. As the half-nut bar 151 moves up, the latch tooth 152 on its side rides along the inclined surface of the cooperating latch tooth 145 on the latch lever 143.

This causes the latch lever 143 to move rearwardly against the force of the spring 146 until the lower edge of the latch tooth 152 on the bar 151 clears the upper edge of the latch tooth on the lever. This allows the lever 143 to move forwardly into a latching position where the bar 151 is held up, with the half nut 150 out of engagement with the leadscrew 88. The thumb lever 158 can now be released and the pusher 86 will still be free to slide along the leadscrew 88. When the pusher 86 is pushed close to the head 85 of the plunger 81, it can be slotted into the gap between the retaining plate 140 and the pusher surface 141. As the plunger head 85 is pushed down into this gap it engages the inclined projection 142 on the latch lever 143 thereby displacing this rearwardly. This causes the latch tooth 145 on the latch lever 143 also to move rearwardly and clear the tooth 152 on the half-nut arm 151, thereby allowing the arm to be moved down by its spring and engage the leadscrew 88. The latch lever 143 is held in this rear position as long as the plunger head 85 is captured by the pusher 86. The rear position of the latch lever 143 flattens the strip spring 146 and, because it is fixed at its left- hand end, this causes the finger 148 at its right-hand end to be displaced outwardly.

The side of the pusher mechanism 86 moves along a panel 126 extending along the inside of the front face 1 of the pump. The inner surface 127 of the panel 126, that is, the surface adjacent the pusher mechanism 86, supports two membrane switches 128 and 129.

The first membrane switch 128 takes the form of an elongate narrow strip of constant width extending horizontally parallel to the direction of travel of the pusher mechanism 86. The first switch 128 is positioned vertically so that it aligns with the upper lug 163 on the finger 148. The second switch 129 is located below the first 128 towards its right-hand, forward end. The second switch 129 has an operative contact region 130 about three times the width of the first switch 128 and a length of about 20mm. The contact region 130 connects with a thinner track 131 extending rearwardly and spaced below the first switch 128. The dispositions of the first and second switches 128 and 129 are such that the first switch will be contacted at any point along its length by the upper lug 163 when the finger 148 is pushed out by engagement with the plunger 81. The force with which the finger 148 is pushed out is sufficient to ensure that the switch 128 is turned on. The contacting surfaces of the finger 148 and switch 128 have a low friction so there is little resistance to forward movement of the plunger mechanism 86. As the pusher mechanism 86 moves forwardly, the finger 148 slides along the switch 128 keeping it on for as long as the plunger 8lis correctly engaged with the pusher mechanism. The lower lug 164 of the finger 148 is spaced above the track 131 of the second switch 129 for all rear positions of the pusher mechanism 86 so that the second switch remains off. When the pusher mechanism 86 approaches close to the limit of its forward travel, the lower lug 164 contacts the rear end of the enlarged contact region 130 of the second switch 129, thereby turning it on and providing an output indicating that the syringe 8 is nearly empty. The second switch 129 remains on as the pusher mechanism 86 moves forwardly along the length of the contact region 130.

This arrangement enables an output indication to be provided indicative of both plunger capture and a neax empty syringe without the need for any electrical connection to the moving components. The membrane switches 128 and 129 are completely enclosed electrically so are not damaged by contact with fluid. The membrane switch arrangement is described in greater detail in W005004952.

With reference now also to Figures 4 and 5, the pump has a syringe size sensor 200 including an arm 201 extending upwardly at an angle and hinged towards its lower end 202 about a horizontal axis. The arm 201 extends up the rear side of the syringe 8 and has a transverse finger 203 at its upper end extending forwardly above the barrel 82 at least across half the diameter of the barrel. An overcentre spring arrangement 204 urges the arm 201 anticlockwise, as viewed in Figures 2, 4 and 5, so that the finger 203 is urged down on the syringe barrel 82. The overcentre action enables the arm 201 to be retained in an open position by rotating it clockwise past a vertical position. The lower end 202 of the arm 201 is coupled with a sector plate 205, on the opposite side of the axis of rotation, which has a curved lower surface 206 supporting three flags 207, 208 and 209 spaced from one another along the lower surface. The flags 207 to 209 are provided by forwardly-projecting curved plates formed from the sector plate 205, which is of an opaque material. The two outer flags 207 and 209 are at the same radial distance from the upper, pivoted end of the sector plate 205 whereas the middle flag 208 is spaced radially outwardly by a short distance. The three flags are arranged to cooperate with three sensors 217, 218 and 219 respectively which are optical transmission sensors each having a slot 220 between an emitter and receiver. The flags 207 to 209 are located to pass through the slot 220 of respective sensors 217 to 219 as the arm 201 rotates, thereby interrupting the optical path and changing the output of the sensor. The length of the flags 207 to 209 and their positions are such that the arm 201 is initially in a first position where at least one sensor is exposed on one side of a flag. Then the arm moves through a second position where the flag is aligned with and obscures the sensor, thereby changing its output. Continued movement of the arm moves it to a third position where the sensor is exposed on an opposite side of the flag. This thereby causes at least one of the sensors 217 to 219 to change state from an initial, to a second and then back to an initial state as the arm moves in one direction.

In particular, if the sensors 217, 218 and 219 are designated A, B and C respectively, as the arm 201 rotates clockwise when viewed from the rear of the pump, from the smallest syringe diameter to the largest, their outputs will be as follows:

A B C 1 0 0 1 1 0 1 1 1 o 1 1 o 0 1 o 0 0

It can be seen that both sensors B and C change from "0" to "1" and then back to "0" as the arm moves in one direction. This arrangement enables discrimination between six different angles of the arm 201. It will be appreciated, however, that it would be possible with three sensors and three flags to have up to nine different sensor outputs, that is, 32* general, where n flags and sensors are used it would be possible to provide a maximum of n2 different outputs. The control unit of the pump readily converts the sensor outputs into an angle measurement and hence into a measurement of the diameter of the syringe barrel 82.

This arrangement enables the pump to distinguish between a greater number of diameters of syringe than would be possible using the same number of sensors in a conventional fashion. The arrangement, however, is low cost and does not require calibration.

The sensors need not be optical sensors but could, for example, be of a magnetic or any other suitable form.

The pump also includes an alarm sounder arrangement 300 (Figure 2) that generates an audible warning when a fault is detected or when the user needs to be alerted to some other situation such as the end, or near end, of infusion. The sounder arrangement 300 includes a single sounder device such as a buzzer 301 connected to a driver unit 302. The driver unit 302 is arranged to monitor the current flowing through the sounder 301 to ensure that it is functioning correctly. The driver 302 activates the sounder 301 briefly before the pump is run and its current flow is measured. If the current flow is not within predetermined limits the driver unit 302 causes a visible warning to be generated on the display 3. Because this visible warning is given while the user is setting up the pump, it is readily apparent. It will be appreciated that, if the sounder on a pump should fail during use, the user might not be alerted adequately to a fault, thereby presenting a risk to the patient. Previous arrangements for reducing this risk have employed two sounders, in the manner described in US5 103214. The present arrangement, by using only a single sounder has a smaller size, thereby enabling the pump to be more compact. It also enables the weight and cost of the pump to be minimized.

The pump has an optional communications module 400 (Figure 11), which can be clipped onto the bottom of the pump so that it is supported and carried with the pump. The rear surface of the pump casing has formations (not shown) that enable the pump to be secured to a belt, harness or the like for ambulatory use. The module 400 is smaller than the pump and is lightweight so is easily portable. The module 400 includes a connector 401 on its upper surface located to mate with a cooperating connector 402 on the lower surface of the pump. The module 400 typically includes a radio frequency wireless communications circuit 403 that converts data from the pump into a suitable protocol for wireless transmission to a nearby transceiver 404, such as in a hospital or the like. The communications module 400 also receives data transmitted to it from the transceiver, such as to control or modify operation of the pump. Other wireless systems could be used such as involving an infra-red link. Alternatively, the module 400 could include an output connector adapted to couple with a cooperating connector, the circuit within the module being arranged to convert the pump data into a form suitable for transmission along a wire. The module 400 may also include a supplementary battery pack 405 for providing additional power to the pump and the module itself. Because the communications module is sufficiently compact to be carried by the pump it does not significantly affect its portability. Housing the communications circuits in a separate module enables the pump itself to be kept as small as possible and reduces power consumption. The communications module can be secured on the pump as and when needed.

Claims (14)

1. A syringe pump including a motor, a leadscrew coupled with the motor to be rotated about its axis and a plunger pusher mechanism including an engagement member engageable with the leadscrew so that the pusher member displaces the plunger of a syringe forwardly to dispense medication to a patient when the leadscrew is rotated, wherein the pusher mechanism includes a manually-displaceable member operable to disengage the engagement member from the leadscrew such as to enable the pusher mechanism to be displaced manually longitudinally of the leadscrew, wherein the manually-engageable member is displaceable to a latched position in which the engagement member is held disengaged from the leadscrew, wherein the pusher mechanism includes an actuator member adapted to be contacted by the plunger, and wherein the actuator member is coupled with the manually-displaceable member such that displacement of the actuator member on contact with the plunger releases the latch and allows the engagement member to engage the leadscrew.
2. 2. A syringe pump according to Claim 1, wherein the manually-engageable member is a lever pivoted about an axis parallel to the axis of the leadscrew.
3. 3. A syringe pump according to Claim 2, wherein the lever is coupled with the engagement member such that displacement of the lever causes lateral displacement of the engagement member.
4. 4. A syringe pump according to any one of the preceding claims, wherein the actuator member is urged away from the pusher mechanism by a spring.
5. 5. A syringe pump according to any one of the preceding claims including a motor control unit arranged to control the speed of the motor, wherein the motor is a dc motor and the motor control unit is arranged to energise the motor in a pulsed fashion, and wherein the control unit is arranged to control the speed of the motor by varying the width of the pulses and, at low speeds, by varying the interval between pulses.
6. 6. A syringe pump according to Claim 5, wherein the control unit is arranged to vary the interval between pulses by omitting pulses at low speeds.
7. 7. A syringe pump according to any one of the preceding claims including a cover having a lock mechanism for securing the cover in a closed position protecting the syringe, manually-engageable control means on the housing for controlling operation of the pusher mechanism, and a lock sensor for sensing whether or not the cover is locked closed, wherein the lock sensor provides an output to inhibit programming of the pump via the manually-engageable control means unless the cover is unlocked and to prevent the pusher mechanism moving the plunger to dispense medication unless the cover is locked closed.
8. 8. A syringe pump according to any one of the preceding claims including an elongate housing supporting the syringe and an elongate cover mounted at one end on the housing by a hinge mechanism, wherein the hinge mechanism includes a first pivot connecting the cover with one end of a coupling link and a second pivot connecting the other end of the coupling link with the housing.
9. 9. A syringe pump according to any one of the preceding claims including a housing of a non-conductive material and a user-accessible drive mechanism including exposed metal components, wherein the drive mechanism is electrically isolated from other conductive components within the pump such that a fault condition leading to excess voltage on the other components does not cause excess voltage on the drive mechanism.
10. 10. A syringe pump according to any one of the preceding claims, wherein the pump includes a communications module secured with and supported by the pump.
11. 11. A syringe pump according to any one of the preceding claims, wherein the pump includes ambulatory support means by which the pump can be supported by a patient receiving medication from the pump.
12. 12. A syringe pump according to any one of the preceding claims, wherein the leadscrew is mounted to allow limited axial displacement when there is an obstruction to movement of the pusher mechanism, wherein the pump includes a sensor responsive to axial displacement of the leadscrew to provide an output indicative of an obstruction, and a rotary encoder mechanism comprising an encoder disc and an encoder sensor, and wherein both the encoder disc and the encoder sensor are mounted on the leadscrew such that both are displaced axially with the leadscrew when an obstruction occurs, such that the disc is rotated with the leadscrew and the sensor is restrained from rotation.
13. 13. A syringe pump substantially as hereinbefore described with reference to the accompanying drawings.
14. 14. Any novel and inventive feature or combination of features as hereinbefore described.