Users of step motors will praise their simplicity, excellent positioning skills, and economy. They may also lament certain characteristics of step motor performance. For example, traditional step motor systems run open loop which means the drive electronics supply constant current to the motor whether there is a demand for torque from the load or not. What happens to that current when there’s no torque demand? It is lost as heat.
Open Loop is Inefficient
This situation of lost power classifies open loop step motors as pretty inefficient devices. Step motor systems are great when they’re producing torque, but pretty darn inefficient when they’re not. So how do we make a greener, more efficient step motor system? We close the current loop.
A Power Saving Solution
By employing a common feedback device to monitor commanded shaft position versus actual position, closed loop step motor drives automatically reduce current to the motor when no torque is being demanded by the load. This saves power when the torque demand is low. This simple change to the stepper system is extremely powerful and greatly improves the efficiency of the step motor system.
A closed loop stepper system will consume as little as 1/3 the power of a traditional step motor system, as shown in the diagram below and explained in greater detail in the white paper Comparing Open Loop and StepSERVO™ Closed Loop Stepper Systems. You can download the white paper here.
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