Open-loop d.c. motor of printer carriage speed

Abstract

Open-loop means for controlling the speed of a d.c. motor controlled print head moving across a document. A switch couples a first voltage to the d.c. motor to accelerate the print head in a first direction. When the print head reaches the desired velocity, the first voltage is decoupled from the motor and a highly regulated voltage is coupled to the d.c. motor to move the print head at the desired velocity. The switch reverses the voltage polarity at the input terminals of the d.c. motor to decelerate the print head, accelerate it in the opposite direction and maintain the desired velocity as it moves in the reverse direction. Logic means detects the direction of carriage movement and connects the first voltage to the d.c. motor for an interval sufficient to bring the d.c. motor to the desired speed in the shortest practical interval. The second voltage maintains the constant speed until the print head reaches the end of the line. At the end of a line, the logic means reverses the polarity to the motor and reapplies the first voltage for the same interval initially required for acceleration, decelerate and halt the print head, or alternatively applies the opposite polarity first voltage for twice said time interval to being the motor to constant speed in the reverse direction in the shortest practical interval. The acceleration voltage for carriage return is applied for a shorter interval if less than a full line is printed, to prevent damage due to excessive acceleration.