Print head and drive circuit

Claim 1

Wire printing apparatus comprising: a print head including a plurality of print wires and a plurality of electromagnetic actuators, one for each printing wire repectively; each actuator comprising a magnetic core, at least one coil electromagnetically coupled to the core and an armature mounted for movement relative to the core between an unoperated position and an operated position, the armature being operative during movement from the unoperated to the operated position to engage the corresponding print wire and thereby propel the print wire towards its printing position; a plurality of drive circuits, one for each electromagnetic actuator respectively, each comprising a capacitor; a charging path for the capacitor including an inductor and a first semiconductor switch; a discharge path for the capacitor including said coil of the actuator and a second semiconductor switch, said second semiconductor switch being operative during a switching period defined by the duration of a control pulse to cause the capacitor to discharge and produce an electric current through the coil effective to move the armature from its unoperated position to its operated position, first means responsive to the electric current to maintain the first switch non-conductive and second means operative to render the first switch non-conductive in response to the capacitor charging to a predetermined voltage; and the capacitor and coil having values of capacitance and inductance respectively such that the current rises to a peak value and then decreases during said switching period.