(57) An impact printer is described which includes a shock wave generator means (10),
a print hammer (30), and a solid wave guide (28) interposed between the shock wave
generator and print hammer (30). The solid wave guide (28) acts to transmit a shock
wave from the shock wave generator to the print hammer (30) to cause its movement
towards a substrate upon which printing is to occur. In a preferred embodiment, the
shock wave generator comprises a piezoelectric or electrostrictive actuator, which
actuator is held in compression by a frame (12, 26) that prevents any substantial
longitudinal movement thereof. In a further preferred embodiment, circuitry is connected
to the actuator for detecting, after an actuation, the return of the hammer (30) into
contact with the solid wave guide (28). In response to that detection, the circuitry
provides a signal (80) which enables operation of the shock wave generator.
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