Rotary print drum having an intermittent drive

Claim 1

A printing mechanism comprising: a rotatable print drum containing around the periphery thereof a plurality of circumferentially spaced-apart sets of print type; drive means responsive to a succession pulse signals for rotationally driving said print drum in an intermittent manner through a succession of angular increments each corresponding to one pulse signal, said drive means comprising a ratchet wheel connected to said print drum for rotational movement therewith, a pawl coacting with said ratchet wheel to effect intermittent stepwise rotation of said ratchet wheel in response to recoprocatory movement of said pawl, and pviotal driving lever connected to said pawl, an armature affixed to said driving lever, and a electromagnet responsive to each pulse signal to create therearound a magnetic field having sufficient strength to attract said armature towards said electromagnet accompanied by pivotal movement of said driving lever and pawl to effect angular movement of said print drum through one angular increment; detecting means for detecting when said drum has been angularly driven to a predetermined angular start position during each rotational cycle and providing a corresponding output signal; and a control circuit operative to develop a succession of pulse signals and apply same to said electromagnet to effect intermittent rotation of said print drum and inclding means responsive to said output signal for terminating the application of the pulse signal to said electromagnet after said print drum has been driven through a prescribed nubmer of angular increments and returned to said start position, said control circuit comprising a gate circuit receptive of said succession of pulse signals and operative when in a gating state to gate the pulse signals to said electromagnet and operative when in a blocking state to block application of the pulse signals to said electromagnet, and counting means receptive of the pulse signals applied to said electromagnet and operative in response to said output signal for counting a predetermined number of pulse signals and then delivering a reset signal to said gate circuit to place same in said blocking state.