Syringe drivers that automatically apply force to move a syringe plunger through a syringe barrel to effect dispensing of fluid from the syringe barrel are known in the art. However, it is important to provide a device that dispenses a desired volume of drug extremely accurately. Additionally, the device should be sensitive to the presence of an occlusion in the line. Whilst prior art devices have included means for such detection, for example a pressure sensor, such detectors may be slow to respond to such an occlusion and may require wires to move with the reciprocal movement of the plunger which is undesirable.

It is an object of the present invention to provide an improved syringe driver assembly that aims to overcome the abovementioned drawbacks.

It is a further object of the present invention to provide a portable syringe driver assembly that has the necessary safety features to enable a patient to operate the device without medical assistance.

Accordingly, the present invention provides a syringe driver assembly comprising driver means for imparting controlled translational movement to a syringe plunger to drive the plunger through a syringe barrel and means for detecting an increase in resistance to the movement of the plunger, the driver means including a motor that causes rotation of a shaft which is linked to an actuator for contacting the

plunger, rotation of the shaft effecting linear movement of the actuator wherein at least part of the driver means is fixedly secured such that any resistance to rotation of the shaft causes a deformation of said driver means, said deformation being detected by a sensor.

Movement of the actuator by rotation of the shaft causes a corresponding movement in the plunger head thereby forcing the plunger through the syringe barrel to dispense fluid therefrom.

Suitable control means, for example in the form of a micro-processor, are preferably provided for controlling the output of the motor.

Preferably, a stepping motor is provided to drive the shaft. In the context of this disclosure, a stepping motor is a motor whose rotor moves through a fixed angle in response to a pulse from the control means. This enables the plunger of the syringe to be moved in small, accurate amounts. For example, a single step of the motor may move the shaft and drive the plunger by 0.001mm.

In a preferred embodiment of the present invention, the motor itself is fixedly secured in position such that any resistance to the rotation of the shaft that causes forward movement of the plunger creates a twist or bend in the motor. Such resistance may be created when an occlusion occurs in the fluid line. This deformation of the motor may be detected by any appropriate sensor. Preferably, the sensor comprises a strain gauge linked to the motor wherein deformation of the motor causes flexing of the strain gauge. A strain gauge consists of a metal or semiconductor filament which, when subjected to strain, experiences a change in its electrical properties which may be used as a basis for measurement.

Alternatively, the sensor may comprise a pressure pad wherein deformation of the motor causes compression of the pad. The motor may be linked to the pressure pad by means of a flange attached to the motor wherein twisting of the motor causes the flange to press against the pad.

Preferably, detection of deformation of the driver means beyond a predetermined threshold (for example, by the measurement of the degree of bending of a strain gauge or the pressure exerted on a pressure pad) stops the motor and/or activates an alarm status.

The driver means may further comprise a series of gears that are connected to a threaded shaft. Preferably, the motor causes rotation of a first gear which engages with a second gear which engages with the threaded shaft. The arrangement of the gears may be such that a change in rotation of the shaft causes flexing or twisting of the gears which may be detected by a sensor. For example, a strain gauge comprising a thin metallic strip may be attached to a gear, more preferably being supported on a lever that is fixedly secured to a gear. More preferably, the threaded shaft and lever are fixedly secured in position. In this manner, when an imbalance occurs between said first and second gears as a result of the shaft rotating more slowly than the motor, the lever flexes due to the threaded shaft and gears being fixedly secured in position.

Minute tensions in the lever alter the electrical properties of the strain gauge which may be detected by suitable means.

Alternatively, the strain gauge or other type of sensor may be fixed elsewhere to detect a strain on a component of the driver means.

Preferably, the components of the syringe driver are contained within a casing, the casing preferably having a lockable lid. The casing is provided with a

compartment for receiving the barrel of the syringe. Preferably clamps or brackets are provided for securing the barrel within the compartment.

The syringe driver assembly preferably includes means for measuring the size and position of the syringe, for example in form of potentiometers and/or optical encoders.

Preferably, means is provided for detecting air in a line of the syringe. For example, a beam of infra red light may be transmitted across the line and a detector may be provided to receive the transmitted light. Detection of the edge of any bubbles that pass through the line may be obtained using interference techniques.

Alternatively, other suitable means may be provided, such as measuring the absorption spectra of the water or fluid that passes through the line.

The assembly is preferably powered by a rechargeable battery provided within the casing but also has a power input socket for connection to an external power supply. Preferably, the assembly includes a low battery indicator, such as a LED, which lights up when a predetermined percentage of the battery has been used up.

Other indicators may be provided for indicating different types of alarm conditions, such as a system or syringe fault. The alarms may be audible and/or visual.

Furthermore, the assembly is preferably provided with a flash memory data storage and may have a real time clock and calendar to log all operations of the syringe driver assembly.

Preferably, the assembly is provided with a selection of operating modes, such as a run mode when the syringe is dispensing, a hold mode, a configuration mode and an alarm mode.

It is preferable for a set of user controls to be provided for operation of the assembly. More preferably, the majority of the controls are within the casing and are not accessible during dispensing of the syringe, being locked in by means of the lockable lid. The assembly preferably includes a display screen, such as a LCD, which may show details of the operating mode of the device and/or a set-up menu.

Whilst the majority of control switches are preferably contained within the casing, some may be required outside of the casing, such as a RUN/HOLD switch to start and stop the dispensing of fluid from the syringe and a BOLUS switch which enables a pre-selected bolus dose to be administered to the patient.

In a preferred embodiment of the present invention, the assembly includes a barcode reader on the syringe identifying the syringe type, volume and/or drug type.

Preferably, the control means has means for a cross-check of the syringe type, volume and/or drug type prior to enabling dispensing of the fluid.

The control means preferably receives inputs in the form of feedback from a variety of sources to enable it to monitor and configure the syringe driver and generate outputs to the motor, LCD display, indicators and/or alarms.

The assembly may be provided with a USB port for connection to various external peripherals, such as a personal computer and/or a GSM modem interface.

For a better understanding and to show more clearly how the invention may be carried into effect reference will now be made by way of example only to the accompanying drawings in which: Figure 1 is a perspective front view of one type of casing for a syringe driver assembly according to one embodiment of the present invention;

Figure 2 is a schematic perspective view of the interior of a casing for a syringe driver according to one embodiment of the present invention showing the drive chamber and syringe holder, the member that engages with the plunger head of the syringe being shown in the withdrawn position; Figure 3 is a schematic perspective view of the interior of the casing shown in Figure 2, the member that engages with the plunger head of the syringe being shown fully forward corresponding to the plunger being fully inserted within the barrel of the syringe ; Figure 4 illustrates the syringe driver components of Figures 2 and 3 free from the casing ; Figure 5 is a top plan view of a syringe driver assembly according to another embodiment of the present invention; Figure 6 is side view of the syringe driver assembly shown in Figure 5; Figure 7 is a perspective view of the syringe driver assembly shown in Figure 5; Figure 8 is a schematic diagram illustrating the major electronic components for a syringe driver assembly according to one embodiment of the present invention; Figure 9 is a flow chart illustrating the main operations of a syringe driver assembly according to an embodiment of the present invention; and Figure 10 is a schematic diagram of the driver means of a syringe driver assembly according to a further embodiment of the present invention, illustrating an alternative mechanism for sensing a build up in back pressure on the syringe plunger.

Referring to Figures 1 to 5 of the accompanying drawings, an automatic portable syringe driver assembly 1 is provided according to one embodiment of the

present invention. The unit is designed to accept many common syringe types and be easily configured to deliver a constant dose rate to the patient. The mechanical and electrical components of the syringe driver assembly are contained within a casing 2 (see Figure 1) which has an integral hinged cover 3 that provides access to the interior of the housing containing the various components, including the drive chamber 5 for receiving the plunger of a syringe (not shown) and having a compartment 7 for receiving the syringe barrel, the barrel being supported between a barrel clamp and an end clamp (not shown). The drive chamber 5 contains a controlled stepper motor 20 that operates via a series of gears 22,24 to turn a threaded shaft 26. The end of the shaft 26 is provided with a member 28 at right angles to the shaft which moves with rotation of the shaft. The rear surface of the plunger head of the syringe engages with the forward facing surface 30a of the member to effect movement of the plunger in a forward direction, thereby enabling the stepper motor to impart controlled translational movement to the plunger of the syringe to drive it into the barrel and thereby effect dispensing of fluid from the interior cavity of the barrel.

The stepper motor 20 moves the syringe plunger at a predetermined rate to dispense the required dosage of medication in ml/hour. Single steps of the stepper motor moves the threaded shaft driving the plunger by 0. 001mm. The step rate is calculated linearly from the overall syringe volume fitted within the device and the dispense rate desired. For example, for a syringe volume of 20ml, the stepper motor dispenses a theoretical dispense volume of 0. 00025ml per motor step. This provides for dispensing of extremely accurate measures of a drug.

It is to be appreciated that any suitable design of casing may be used to house the components of the syringe driver assembly. However, it is preferable for the casing to be as small as possible.

The syringe driver is also provided with means for detecting an occlusion in the line that results in a back pressure acting against the forward movement of the syringe plunger. It is important that such a build up is detected extremely quickly.

The present invention provides a superior, more sensitive mechanism for detecting such an occurrence by the provision of means for deformation of the driver means which is brought about by resistance being applied to the normal rotation of the shaft causing its rotation to be hindered. At least part of the driver means is fixed in some manner such that when rotation of the shaft is hindered, a build up of torque against the driver means causes the driver means to deform or twist which is detected by an appropriate sensor. In the embodiment illustrated in Figures 1 to 5, the sensor comprises a strain gauge 41 supported on a lever which measures the torque on the drive mechanism. The rotatable threaded shaft 26 and lever 40 are fixedly secured in position with the lever 40 being connected to the gears in a direction transverse to the motor. A build up of back pressure causes the speed of rotation of the gear 24 that engages with the threaded shaft to slow down. However, the motor is still driving its gear 22 at a predetermined speed causing an imbalance between the two gears. As the lever and shaft are fixed in position, a strain is exerted on the lever 40 causing it to flex. This results in the electrical properties of the strain gauge 41 being altered which can be monitored to quickly and accurately indicate when an occlusion occurs.

Figures 5 to 7 of the accompanying drawings also illustrate the positioning of the strain gauge in a syringe driver assembly according to another embodiment of the

present invention. Identical features already described in relation to Figures 2 to 4 are given the same reference numerals and only the differences will be discussed in detail.

The components are mounted on a printed circuit board (PCB) 100 and comprise a motor 20, gearbox 22, shaft 26 and a flexible metal strip 102 that is anchored to the PCB at point X. The shaft carries a member 104 that extends into the syringe carriage 106. Additionally, a linear potentiometer 108 is provided to for measuring the travel of the shaft. The motor and gearbox rotate around the pivot point P when a load is applied to the shaft due to back pressure in the system. As the motor and gearbox rotate, the thin metallic strip 102 which is attached to the PCB at its far end is bent.

The bending of the strip denotes the degree of torque being created in the system.

The torque is measured by a strain gauge on the thin strip. In this manner, it is possible to detect an increase in torque due to back pressure on the shaft.

The drive chamber may also include an optical encoder (not shown) to measure the syringe position. This will require the plunger of the syringe to be driven back to an end stop at power on and for loading of the syringe. This will provide an automatic calibration of the syringe and will also improve the measurement accuracy of the syringe length. If such an encoder is included, a linear potentiometer for measurement of the syringe length may not be required. Furthermore, an optical encoder may also be included in the stepper motor to provide feedback on the position of the motor.

The syringe driver assembly contained within the casing is also provided with the necessary electrical components to control and monitor the dispensing of medication from a syringe that is loaded into the casing, see Figure 8. A rechargeable battery 50 is provided within the casing and a power input socket 52 is provided on

one side of the casing for connecting to an external power supply. A supply monitor 54 manages re-charging of the battery when power is supplied from an external power source and provides power to operate the motor of the driver. When powered from the internal battery source, the supply monitor continuously measures the voltage and provides a low battery warning at an appropriate time when a predetermined percentage of the power of the battery has been used up, for example when there is 15% of the expected life of the battery remaining.

The casing also contains means for automatically measuring the syringe diameter 60 and syringe length 62, being in the form of potentiometers. The unit is able to measure syringes varying in diameter from 10 to 30mm. Additionally, a pressure sensitive resistor 63 is mounted in the end block of the syringe clamp for measuring the overall pressure of the syringe drive. A further resistive potentiometer (not shown) may also be provided to indicate the linear position of the syringe plunger. A miniature micro-switch (not shown) is also provided in the drive clamp to indicate the end position of the plunger of the syringe. Further components include a flash memory data storage 64 to allow a log of the syringe operation to be recorded, all actions carried out of the device being recorded to the memory with the date and time of occurrence. The data logged will include changes made to operating set-up, the loading of the syringe with the drug type and dispense times for the patient, patient identification information, any alarm conditions and bolus dosages. This memory will also contain the configuration set-up parameters for the device and the operational code. This will allow the data to be stored in a non volatile memory which will not be lost even in the event of complete battery discharge. The status of the syringe is monitored by a number of methods to provide feedback. A real time

clock and calendar 66 is also provided within the casing to keep the current time and date. This is powered from the main battery but a separate rechargeable battery, such as a lithium cell, is provided to keep the clock running in the event of a complete main battery discharge.

Additionally, a set of user controls including an LCD graphics display 70 and a set of switch keys 72a, 72b are provided on the front of the driver within the casing.

These allow programming and control of the device and are locked within the casing by means of the cover 3 to prevent access to the syringe during the dispensing operation. Programming and setting up of the unit will only be possible with the cover open. When the cover is closed, the LCD will be activated to indicate the current status of the dispense by means of two multi-coloured LED 74 indicators or to indicate an alarm condition. Additionally, switches are provided"Run/Hold"76 and "Bolus"76 to allow the dispense process to be controlled when the cover is closed.

When the HOLD switch is activated the syringe driver is not dispensing and the dispense functions may be set by opening the lid of the casing. In the RUN mode, the syringe is dispensing and the lid most be closed. When the unit is in this mode, all programming and set-up functions are disabled. A buzzer 79 is also provided as an audible alarm indicator.

A USB port 80 allows connection of the syringe driver assembly to various external peripherals. Generally, the assembly will be connected to a PC to allow operating data to be loaded to the unit. A further option may be to provide a GSM modem interface (not shown) to allow remote polling of the driver for home operation by a patient. The interface may be used for servicing and configuring the unit and downloading the operational code of the unit.

Additionally, a barcode reader 86, such as a standard OEM barcode reader element utilising laser scanner technology, may be incorporated into the unit to identify the syringe type, volume and/or drug type that is loaded into the assembly. A window (not shown) is provided in the front of the casing through which the scanner will read. This enables the user of the device to swipe the syringe past the reader.

The patient's and/or medical staff's identification barcode tag may also be read. The unit will have an internal database of syringe types and sizes and drug types and uses this information to configure the unit. The bar coder reader is only activated when the user starts a new process from the menu buttons (see further details below), prior to a new syringe being inserted into the device thereby conserving battery power.

Scanning of the syringe may result in details of the syringe being displayed on the LCD 70 and the syringe must then be inserted into the casing within a preset time.

The syringe driver may check the size of syringe from the barrel feedback and, if this agrees with the scanned value, display information to the user to confirm that the details are correct. Instructions concerning scanning and loading of the syringe may be displayed on the LCD, such as"LOAD SYRINGE", "SCAN SYRINGE","SCAN PATIENT ID TAG"and so on.

All the main controls for the system functions of the unit are provided by a micro-processor controller 90 contained within the casing, receiving inputs from feedback circuits, data port, the barcode reader, clock and user interfaces. The micro- processor then uses these inputs to generate control outputs to the stepper motor, LCD display, indicators and visual/audible alarms.

As mentioned above, the assembly is provided with a number of operating modes, namely OFF, ON, HOLD, CONFIGURATION, RUN, ALARM and

TECHNICAL. The set-up, programming and operation of a unit according to one embodiment of the present invention are shown in Figure 9 of the accompanying drawings. When the unit is in the OFF mode, power to the unit is off and the only functional switch is the Power Off/On switch 72a. If this is switched to the ON mode, power is supplied to the unit and the user has access to all operational modes of the device. The HOLD mode is when the syringe is not dispensing. In this mode, the dispense functions including the dispense rate and programming of patient details can be carried out when the cover of the casing is open. In the CONFIGURATION mode the unit is being configured for its operating mode. The configuration may be made via a barcode interface and the LCD display menu and switches (see further details below). The RUN mode is when the syringe is actually dispensing. This mode is only allowed when the cover of the casing is closed and all programming and set-up functions are disabled by means of a software lock. The unit will enter the ALARM mode if an incorrect operation or action is detected or there is a detectable failure within the unit. The device will also switch to the ALARM mode from the RUN mode if the cover of the casing is opened. The ALARM mode always halts infusion of the drug from the syringe. The device reverts back to the RUN/HOLD mode upon cancellation of the alarm. Finally, a TECHNICAL mode allows a technician to program syringe parameters not accessible during normal operation. During this mode, upload and download of data can be made via the USB interface.

The majority of control switches 72b are located within the casing 2 and are not therefore accessible when the unit is running. However, two switches are provided on the outside of the casing, namely the RUN/HOLD switch 74 and the BOLUS switch 76. A single press of the RUN/HOLD switch starts the syringe

dispense at the pre-selected feed rate. The dispense will stop upon a single press of the switch to return the unit to the HOLD mode. If, whilst during operation, the casing is opened, the dispense will stop and the unit will go into ALARM mode. The unit will also go into ALARM mode if an incorrect signal is received from one of the syringe position sensors 60,62, 63 or a system fault is detected by the control processor 90.

The BOLUS switch 78 enables a pre-determined"bolus"dose to be administered to a patient. Preferably, a single press of this switch causes a sounder 79 provided within the unit to emit a short beep and a further press of the switch has to be made within a given period of time, say 2 seconds, to result in the administration of a pre-determined"bolus"dose of between 0.01 to 5ml to the patient, either at the maximum delivery rate for the syringe or over a fixed period of 1 to 15 minutes. The bolus dose is set up whilst in the TECHNICIAN mode and is cancelled if the RUN/HOLD button is pressed or an alarm condition occurs.

The LCD display 70 which is visible from the exterior of the casing is used to show the operating mode of the syringe driver assembly and to display the set-up menu. The display has an LED back-light to allow the display to be viewed at low ambient light conditions. This back-light is activated for a predetermined period of time, for example 10 seconds, when any active menu key or the power on/off key is pressed.

Menu keys are used in conjunction with screen messages on the LCD display to define the system operation and programming. Additionally, scroll keys are provided to enable the user to scroll up or down thought the menu messages on display or to make changes to values when the unit is in the programming mode.

Display screen information may include, for example, pre-set options (such as a selection of different volumes to be administered), bolus details, a new patient selection (to clear previous settings) or a repeat prescription setting (to allow previous setting to be used again) and so on.

Additionally, a power status indicator 74 consisting of a three colour LED is provided to indicate the power of the unit when in the ON mode. This is visible on the outer casing even when the cover is closed. The power status indicator is capable of flashing green, indicating that the battery power is adequate or emitting a continuous green light indicating that the unit is being powered from an external power supply. An amber flashing light indicates that the battery supply is low. A red flashing light is an alarm warning, for example indicating that the syringe is near the end of its dispense and a continuous red light is an alarm condition, indicating a system or syringe fault.

An audible indicator 79 may also be provided within the assembly, such as a piezo-electric sounder. Different alarm tones are sounded to indicate different conditions. For example, the sounder will give a continuous alarm sound when the syringe is within 10% of being empty from its full volume. This alarm will not cause the dispense to stop. The alarm may be silenced by pressing the run/hold or bolus buttons. The sounder will give a further audible beep warning each time the volume that is remaining falls by a further 1% and a continuous alarm sound when the syringe is empty if the unit is in RUN mode. Additionally, the sounder may give a pulsed alarm sound for any system or syringe fault detected. The volume of the sounder output is adjustable through an alarm option provided on the set-up menu.

Figure 10 of the accompanying drawings illustrates an alternative mechanism according to the present invention for detecting a build up in back pressure on the syringe plunger which hinders the rotation of the shaft. The motor 200 that drives rotation of the shaft is itself fixedly secured in position and has a push rod 202 attached to it which is in line with a pressure sensor 204 mounted on a printed circuit board 206. In this manner, when the shaft is prevented from rotating due to a build up in back pressure, the motor is forced to twist or flex due to a build up in torque, as illustrated by the arrow in Figure 10. This results in the push rod pressing on to the pressure sensor. The sensor is connected to a control unit which shuts down the motor to prevent dispensing of the fluid from the syringe. An alternative type of sensor may be employed to detect the deformation of the motor, such as a strain gauge being attached to a bar that is fixedly secured to the motor. It is to be appreciated that the motor would only be shut down when a back pressure above a certain predetermined threshold is detected.