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Selecting the Optimum Motion Technology for your Application: Duty Cycle

December 4, 2019

The next factor to review is the duty cycle for the motion solution in the application.  The duty cycle is defined as the ratio of the time the motor operates divided by the amount of total time for the cycle.  Typically, the motor does not run continuously but rather operates for a period (on-time) and then rests for a period (off-time).  The duty cycle affects the selection of the optimum motion solution, so it is important to understand the details and factors to consider.

The main consideration with the duty cycle is the temperature rise of the motor.  All motors have a maximum rated temperature, operating the motor above that temperature can lead to damage to internal components.  The amount of current drawn or supplied to the motor will dictate the temperature rise, the higher the current the faster the temperature will rise.  Since current is proportional to the torque output of the motor, it can be desired to get increased torque out of the motor via increased current, keeping the overall size of the motor as small as possible.  This is where the duty cycle comes in.  The on-time requirements for the cycle must be balanced with the current drawn or supplied to the motor, to keep the motor from overheating.  For example, stepper motors are typically supplied with higher than their rated current, to maximize the torque output.  But the on-time must be such that the temperature reached at the end of the on-time does not exceed the maximum operating temperature of the motor.  During the off-time, the motor temperature will reduce.

Environmental factors also need to be considered in addition to the duty cycle, as these will impact the temperature rise of the motor.  For example, is the motor mounted to an aluminum base (which is a good conductor of heat) or to a plastic base (which is a poor conductor of heat)?  Is there air flow around the motor which will help by cooling the motor?  Is the motor in an enclosure where other components are generating heat, raising the ambient temperature?

Every application will be different for both duty cycle and environmental factors.  The goal is to use the proper technology occupying the smallest space while providing the necessary output.  The Portescap application engineers can review your application requirements, duty cycle and environmental factors to determine the optimum solution.