DEVICE FOR DERIVING LIMITED RECIPROCATING MOTION FROM ROTATIONAL MOTION

A device for deriving limited reciprocating motion from a bi-directional electric motor. The device is employed, for example, to reciprocate the plunger of a liquid dispensing pipet to dispense a measured amount of liquid with each reciprocation. The motor drives the plunger upwardly, drawing liquid reagent into the pipet, until an adjustable stop carried by the plunger engages the top flange of the pipet barrel. This causes the motor to reverse and move the plunger downwardly to its bottom limiting position, discharging the measured amount of reagent into a collection receptacle.