GB2224444A

GB2224444A - Syringe infusion pump

Info

Publication number: GB2224444A
Application number: GB8909154A
Authority: GB
Inventors: Bernard Ching Bing Lim; Peter Lloyd; Paul Wadham
Original assignee: Welmed Ltd
Current assignee: Welmed Ltd
Priority date: 1988-04-21
Filing date: 1989-04-21
Publication date: 1990-05-09
Anticipated expiration: 2009-04-21
Also published as: GB8809410D0; GB8909154D0; GB2224444B

Abstract

A syringe infusion pump transmission comprises (a) a fixedly mountable transfer plate (7) having an aperture (6) therein; (b) an externally screw-threaded leadscrew (4) engaged at one end region (5) with the aperture in the transfer plate so that one end projects through the transfer plate for connection at the said one end to said motor so that, in use, the motor can rotate the leadscrew about its axis; (c) carriage means (11) mounted in engagement with the leadscrew for achieving linear sliding displacement as the leadscrew is driven through the transfer plate and including a surface intended to act on the plunger of a syringe and drive it forward towards said aperture; (d) a fixedly mountable cantilever arm (1) in which the other end of the leadscrew is bearing mounted for free rotation while being subject to the axial stresses of the leadscrew; (e) strain measuring means (15) operatively connected to the cantilever arm (1) to measure the strain exerted on the cantilever arm by the leadscrew as a measure of pumping pressure as operation of said motor takes place and the carriage means (11) acts in use against the plunger of the syringe to expel fluid from the syringe; (f) means (16 and 17) for sensing directly or indirectly the position of said surface of the carriage means with respect to an end of said drive rod; (g) a microprocessor arranged to receive input signals from said strain measuring means (15), said carriage means (11) and also from motor control means (18) associated with the motor (8) and to derive therefrom, when the syringe infusion pump is in use, firstly the fluid delivery rate and secondly the fluid delivery pressure; and (h) a control system acting through said microprocessor to input operating commands to the syringe infusion pump. <IMAGE>

Description

SYRINGE INFUSION PUMP This invention reLates to an intrusion device, and more particularly to a syringe intusion pump to be used tor ettecting precise operation ot a syringe.

Such intrusion devices are widely used in health care where it is necessary to achieve accurate control ot delivery ot fluid to a patient in a reliable and safe manner.

One mechanism tor controlling the operation or syringe intusion pumps is described in EP-A-229450 and is ot a type in which a carriage acting as a syringe plunger mover is coupled to a rotary driven leadscrew tor converting the rotary motion ot a D.C. driven motor to the required linear motion of the plunger parallel to the axis of the leadscrew. The pumping pressure at any particular instant is identified through the agency of a strain gauge connected up so that the torque reaction created, as the motor drives the carriage and hence the syringe plunger to expel fluid from the syringe, is measured.

Such an arrangement is not entirely satistactory.

Firstly the arrangement is relatively complicated and moreover the sensing ot position ot the plunger via a strain gauge takes place using a considerable number of mechanical stages from the pressure source which is being monitored. Such an indirect measuring method involving several conversions of forces involved will lead to relatively inaccurate results, Lack ot reproducibility and some potential for delay before the true pressure in the IV (intravenous) line is identitied.

It is an object of this invention to provide an accurate and reliable means tor measuring variable pumping pressures in syringe infusion pumps, more particularly those utilised in supply of fluid to patients via intravenous, intraarterial or subcutaneous delivery lines.

According to one aspect of the present invention, there is provided a transmission for a syringe infusion pump which comprises, for positioning in a casing additionally housing a motor; (a) a tixedly mountable transfer plate having an aperture therein; (b) an externally screw-threaded leadscrew engaged at one end region with the aperture in the transfer plate so that one end projects through the transfer plate for connection at the said one end to said motor so that, in use, the motor can rotate the leadscrew about its axis; (c) carriage means mounted in engagement with the leadscrew for achieving linear sliding dispLacement as the leadscrew is driven through the transfer plate and including a surface intended to act on the plunger of a syringe and drive it forward towards said aperture;; (d) a fixedly mountable cantilever arm in which the other end of the leadscrew is bearing mounted tor free rotation while being subject to the axial stresses of the leadscrew; (e) strain measuring means operatively connected to the cantilever arm to measure the strain exerted on the cantilever ev er arm by the leadscrew as a measure ot pumping pressure as operation of said motor takes place and the carriage means acts in use against the plunger or the syringe to expel fluid from the syringe; (f) means for sensing directly or indirectly the position of said surface of the carriage means with respect to an end ot said drive rod;; (g) a microprocessor arranged to receive input signals from said strain measuring means, from said carriage means and also from motor control means associated with the motor and to derive therefrom, when the syringe infusion pump is in use, firstly the fluid delivery rate and secondly the fluid delivery pressure; and (h) a control system acting through said microprocessor to input operating commands to the syringe infusion pump.

In a second aspect of the invention, this syringe infusion pump transmission is utiLised in a syringe infusion pump, for which purpose it is housed in a casing which additionally contains a motor and gear means tor transmitting the drive of said motor to the leadscrew.

In a preferred arrangement, the carriage means includes a sleeve extending along the leadscrew to terminate in a nut attached to the leadscrew. The nut is housed in a body member which rides on one additional rod which is fixed and thereby, through being guided by this fixed rod, is not susceptible to torque reaction.

Furthermore, the nut is preferably of split nut type thereby enabling ready disengagement of the carriage means from the drive which can be imparted to the leadscrew when it is desired to reset the carriage means to a new position when, for example, a fresh syringe is provided for use with the pump. Means located externally of the main body of the casing will act to hold the syringe in position against the drive plate of the carriage. It is possible for this declutch arrangement to be supported on more than one fixed rod.

Preferably the syringe infusion pump further includes a display system driven by the microprocessor to display a predetermined set of parameters relating to the operating condition of the syringe infusion pump.

The means for sensing the position of the carriage may be of the type described in EP-A-229450, comprising a reader unit attached to the carriage or to split nut-housing body member and positioned so as to read a position code carried, for example, by a bar coded member. This may be a two-channel linear encoder located in the syringe infusion pump casing alongside the carriage or body member respectively. However such coding is difficult to incorporate and may not be sufficiently accurate. Thus it is conceivable that the determination of absolute position as in EP-A-229450 be dispensed with and incremental movement only be determined, for which purpose a single channeL linear encoder means mounted similarly can be used.

The casing of the syringe infusion pump is in two parts, an upper part and a lower part; the motor and associated drive parts along with the microprocessor and display/control elements are located in the upper casing part.

The output from the motor and gear means when utilised together with the output from a single channeL linear encoder enables the movement of the carriage means and hence movement of the syringe to be calculated at any given time. This information together with the information from the strain measuring means provides a plurality of usefuL parameters relating to the amount of fluid delivered and the pumping pressure obtaining at any time. While such a system is analogous to that of EP-A-22#45U, there is a particular advantage in that the strain measuring means provides a direct measurement of the force applied to the plunger of the syringe which is a more accurate indication of the fLuid delivery conditions prevailing. This direct force, which is variable, is transmitted to the cantiLever and the compression and strain to which it is subject can be determined by means of a mechanical or an electrical strain gauge or, indirectly, by the movement of the plate.

The control and display system operates with the microprocessor in a preselected manner to control the motor and to give displays of parameters associated with pump operation. The microprocessor wilL also generally be programmed to generate one or more alarm indications in the event that one or more predetermined safety parameters are violated.

For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made by way of exampLe, to the accompanying drawing which is a perspective view of a syringe pump transmission embodying this invention.

Referring to the drawing, the syringe infusion pump transmission mechanism is to be used in a casing with transmission mechanism gear means and control and display means of the type disclosed in EP-A-2294#0.

These features although essential for the operation of the syringe infusion pump transmission of this invention are not part of the present invention as such and for a fuller indication of their construction and interaction, reference is made to EP-A-22945U.

Thus the drawing shows only the features of a syringe infusion pump transmission which are provided by the present invention. Fixed in the casing are a cantiLever arm I carried on a fixedly mounted support 2 and through which passes one end 3 of a leadscrew 4 whose other end is externally screw-threaded at 5 and engages with a corresponding aperture 6 in a transfer plate V on which is mounted a small DC motor 8 with associated gear box and transmission means to the leadscrew. The latter are not visible in the drawing. Although fixed to the cantilever, tne end 3 of the leadscrew is of reduced diameter and is able to rotate in an opening 9 in the cantilever arm 1 in which it is bearing mounted.Over the remainder of its length, the leadscrew is of the same diameter (subject to variation therein caused by the screw-threading). Over a portion of its length, the leadscrew carries a sleeve 10 on which is mounted a carriage 11 acting as a drive plate for the plunger of a syringe which is to be driven towards the transfer plate 7. The drive plate 11 acts with clamping means for the toot of the syringe plunger to Locate the forward end of the plunger.

The opposite end of the sleeve 10 carrying the drive plate 11 enters a carriage body 12 wherein there is housed a decLutch arrangement for controlling engagement and disengagement of the drive plate li from the leadscrew 4. Thus the carriage body 12 houses a halt-nut arrangement provided for coupling the sleeve to the leadscrew so that the rotational motion of the leadscrew as it is driven through the transfer plate 7 is transmitted via the sLeeve and hence via the drive plate 11 to the toot of the syringe plunger, so expeLling fluid from the syringe. Torque reaction in the system is prevented by having the carriage body 12 additionally engage at a channel 13 therein a fixed rod 14 shown also to pass through the transfer pLate 7.The carriage body 12 not only keeps the nut therein in contact with the leadscrew 4 to provide drive but can easily be temporarily dismantled to aLLow repositioning of the carriage IZ, sleeve 10 and hence the drive plate 11 when a fresh syringe is to be operated.# For this purpose, the drive plate II is attached to an outer tube fixed to the carriage, while the halt-nut arrangement is acted on by an intermediate tube such that the half-nut may be disengaged by the clutch mechanism as described above.

The cantilever arm I carries a strain gauge 15 which is responsive to strains imparted to the cantilever arm through the end of the full sized part of the leadscrew abutting thereon and which wiLl be indicative of the pressure which it is exerting on the plunger via the drive plate means in achieving intravenous administration of a fluid from a syringe. Alongside the carriage body 12 is located a reader unit 16 which includes a single optical switch arrangement. This cooperates with a single-channel linear encoder 1l which is fixed to the part of the casing in which the transmission is housed.A light beam from the reader is directed at the channeL of the linear encoder 17, the markings of which indicate incrementaL movement and when coupLed with information generated by the rotary encoder means 18 which acts as motor control means and which is attached to the rear output shaft of the motor 8 allows a microprocessor to process the output signals thus created and determine inter alia (i) the amount of fluid delivered from a syringe held between the drive plate 11 and an abutment surface at which it is clamped; and (it) the fluid delivery from said syringe as corroboration of the input commands from control buttons and information so derived.

The microprocessor also generates signals, activates displays and monitors the performance of the syringe infusion pump so that if any predetermined safety parameters are violated, an alarm signaL is generated.

When a preset delivery rate is keyed into the syringe infusion pump unit, the microprocessor converts this rate into a numerical code which corresponds to a pulse rate which in turn is applied by a control means 18 to motor 8. The microprocessor counts the number of "on" pulses and so is able to determine (I) the position of the syringe relative to its start position and (2) the rate of infusion of this volume with respect to time.

The former allows the quantity of infusion liquid to be displayed, removing the need for measurement or for calculation of figures derived from the body of the syringe.

Preferably, when the unit is completing delivery from a syringe, the microprocessor is arranged to slow down motor 8 so that the last few millilitres of infusion liquid are delivered at a reduced rate which is independent of the preset delivery rate. When this condition is reached, the microprocessor can actuate an alarm to warn an operative that the end of infusion is approaching. This reduced rate delivery towards the end of the infusion also avoids problems which can arise at the end of an infusion cycLe when air may be injected to a vein or when a vein may tend to cLose.

Claims

Claims:

1. A transmission for a syringe infusion pump which comprises, for positioning in a casing additionally housing a motor; (a) a fixedly mountable transfer plate having an aperture therein; (b) an externally screw-threaded leadscrew engaged at one end region with the aperture in the transfer plate so that one end projects through the transfer plate for connection at the said one end to said motor so that, in use, the motor can rotate the leadscrew about its axis; (c) carriage means mounted in engagement with the leadscrew for achieving linear sliding displacement as the leadscrew is driven through the transfer plate and including a surface intended to act on the plunger of a syringe and drive it forward towards said aperture;; (d) a fixedly mountable cantilever arm in which the other end of the leadscrew is bearing mounted for tree rotation while being subject to the axial stresses of the leadscrew; (e) strain measuring means operatively connected to the cantilever arm to measure the strain exerted on the cantilever arm by the leadscrew as a measure of pumping pressure as operation of said motor takes place and the carriage means acts in use against the plunger of the syringe to expel fluid from the syringe; (f) means for sensing directly or indirectly the position of said surface of the carriage means with respect to an end of said drive rod;; (g) a microprocessor arranged to receive input signals from said strain measuring means, from said carriage means and also from motor control means associated with the motor and to derive therefrom, when the syringe infusion pump is in use, firstly the fluid delivery rate and secondly the fluid delivery pressure; and (h) a control system acting through said microprocessor to input operating commands to the syringe infusion pump.

2. A transmission as claimed in claim 1, wherein a declutch arrangement is provided to control the engagement and disengagement of the carriage means from the leadscrew.

3. A transmission as claimed in claim 2, wherein the declutch arrangement is supported on one or more fixed rods.

4. A transmission as claimed in any preceding claim which further comprises a display system driven by said microprocessor to display a predetermined set of parameters relating to the operating condition of the syringe infusion pump.

5. A transmission as claimed in any preceding claim, wherein said means for sensing the position of said surface of the carriage means comprises a reader unit attached to said body member and positioned so as to read an incremental code providing information relating to movement.

6. A transmission as claimed in claim 5, wherein said code is carried by a bar-coded member.

7. A transmission for a syringe infusion pump substantially as hereinbefore described with reference to the accompanying drawings.

8. A syringe infusion pump which comprises a transmission as claimed in any preceding claim and in addition: (i) a casing; (j) within said casing; a motor and associated means for transmitting drive of said motor to the leadscrew.

Y. A syringe infusion pump as claimed in claim 8, wherein the casing comprises an upper part and a lower part, the upper part accommodating said motor and associated means and the microprocessor.

10. A syringe infusion pump substantially as hereinbefore described with reference to the accompanying drawings.