Abstract: In a drive circuit for an electromagnetic printing element of an impact printer, a drive pulse drives the printing element from a backstop toward a record medium to print indicia. A voltage comparator senses the change in the induced voltage in the printing element when it impacts on the backstop for triggering a single shot circuit to apply to the printing element a damping pulse of a polarity such as to oppose its rebound from the backstop. A latch circuit is responsive to the damping pulse to disable the single shot circuit until the end of the next drive pulse. The drive and damping pulses are applied to the printing element through a bidirectional current source.

Abstract: An impact printer is described having a control circuit for varying the location at which the printing elements of a printhead are actuated in order to compensate for flight time of the elements and other mechanical characteristics of the printer.

Abstract: A regulator for a two phase shaft encoder used in sensing irregular body movements which determines when the light transmission of a photocoupler is maximum and corrects the photocoupler output to agree with a reference value.

Abstract: A photoelectric detection system for a printer that is particularly useful for accurately detecting the position of type bearing or printing elements of known width and spacing as they pass a predetermined location. An output signal is generated that substantially corresponds to the light and dark periods created as the elements pass between a light source and detector. This output signal is integrated and compared with a reference signal that represents the ratio of the width of the elements to the spacing therebetween and the error is used to modify the light source and thereby adjust the output signal to accurately correspond with the dimensional criteria of the elements.