Syringe pump mechanisms must. translate motor rotational movement into linear movement of the disposable syringe plunger. In addition, they must enable the easy installation of the syringe and hold the syringe in a secure manner to prevent accidental removal whilst still providing for precision linear movement of the plunger plate of the syringe. These requirements mean that syringe pump mechanisms are complex, incorporating a mechanical clutch mechanism to disengage drive from the syringe to facilitate installation of the syringe.

An object of this invention is to provide a syringe pump mechanism which achieves all the necessary functions of accuracy of linear movement, security against accidental removal, and ease of location of syringe, in a design which uses few moving parts and no mechanical clutch mechanism.

Accordingly, this invention provides a syringe pump mechanism which includes a single drive screw of square-cut thread with a pitch of sufficient magnitude to allow the introduction of the disposable syringe plunger plate in between adjacent screw threads. The syringe plunger plate is held securely in contact with the drive screw by the action of a closing door piece. Apart from the motor drive an infusion pump, utilising such a mechanism would comprise of only two moving parts.

A preferred embodiment of the invention will be described with reference to the accompanying drawings in which: Figure 1 shows a side view of the complete mechanism.

Figure 2 shows the end-on view of the mechanism showing the drive screw (6) engaging the syringe plunger plate (8) which is held in position by the retaining door lever (2) As shown in Figure 1, the mechanism comprises a syringe support (1) and an end block (7) between which is located a rotational broad gauge square-cut thread drive screw (6). A plastic disposable syringe (3) is held in position by syringe support (1). The plunger plate (8) of the disposable syringe locates into the gap between adjacent screw threads such that, as the drive screw (6) is rotated by the action of motor drive unit (4) and gear train (5), the plunger plate (8) is moved forward along the length axis of the syringe. A securing door lever (2) allows for the syringe to be installed or removed when open, but retains the syringe securely when closed.

Figure 2 shows, end-on, the relative positions of drive screw (6), syringe plunger plate (8) and retaining door (2). No lateral movement of the syringe plunger plate (8) is possible since it is held in position by contact with the drive screw (6), the syringe pump casing (9) and the door (2).