Abstract: A serial impact printer including a platen mounted for rotation upon a support frame, a print element having character imprinting portions disposed thereon and a print element selector for moving the print element to position a selected character imprinting portion at a printing position. A high effective mass hammer, driven toward and away from the platen in a timed manner, drives each selected character imprinting portion for deforming the platen with a printing force. A carriage mounted for reciprocating movement generally parallel to the platen, supports thereon the print element, the print element selector, the hammer and the hammer driver, and a stationary reaction bar secured to the support frame is spaced from and extends parallel to the platen. The reaction bar incudes a reaction surface against which the carriage is urged for developing the printing force as the hammer deforms the platen.

Abstract: Apparatus for adapting a common dc motor for use in a typewriter to drive the ribbon lift and advance functions. The motor is coupled by means of a set of gears to a shaft on which are mounted the ribbon advance gear and ribbon lift cams. Also mounted on the shaft is a slotted disk. As the motor and disk rotate, an optical sensor outputs a signal for each slot. A processor then computes the motor speed from the slot timing and issues modulated pulses to the motor to regulate its speed.

Abstract: A stepper motor controller circuit is described. The circuit comprises four power transistors configured to drive current in either direction through a stepper motor winding. A series resistor senses instantaneous current and a chopper is used to limit this current to some predetermined maximum value. Eight diodes protect the circuit against reverse, current surges, and a flip-flop guarantees a minimum duty cycle.