LIMITING STEPPER MOTOR HEATING.

To prevent overheating of the paper advance stepper motor in a printer, a timer is used to introduce a delay between uses of the motor. This reduces the duty cycle to a level which does not generate excessive heat. For most normal use, this delay occurs during printing time and throughput is not degraded. For applications with much spacing and little printing, printing may be delayed, and throughput is somewhat degraded. Other known techniques for temperature control, i. e. , large heat sinks, fans, bigger motor, reduction of motor speed, etc. , are generally more expensive, require more space, or degrade throughput for all applications. In the present embodiment, prior tests have determined that a stepper motor that overheats when operated at 100% duty cycle does not exceed a safe operating temperature at a two-thirds duty cycle. This desired duty cycle is achieved by inhibiting a succeeding motor operation for a time interval equal to one half of the preceding motor usage time. Regardless of motor on time for each usage, the average usage time does not exceed two thirds.