DRIVE MECHANISM
A lead screw drive comprises a lead screw (10) which is rotated by a motor. A traveller (40) is clamped at one end to a rod (14) parallel to the lead screw, the rod in turn engaging the plunger of a medical syringe. The other end of the traveller (40) has a U-shaped engaging element (42) with the two parallel arms (44, 46) thereof having grooves on their inner surfaces for engaging with the lead screw thread. The grooves also extend upwardly and downwardly of the region of engagement with the lead screw thread, and radial movement of the engaging element (42) therefore moves the region of contact with the lead screw without causing disengagement. The device is particularly suitable for use with a medical syringe pump, to prevent inadvertent disengagement of the engaging element from the lead screw.