Open-Loop Control

Open-loop control is a control method in which a controller sends unidirectional signals to a motor without receiving feedback on actual movement, such as position or speed. Because it requires no feedback sensors or complex processing circuits, it offers clear advantages: lower cost, high reliability with fewer potential failure points, and no micro-vibrations (hunting) while at a standstill. On the other hand, its primary limitation is that any deviation between the command signal and actual movement cannot be detected or corrected.

Motors used in open-loop control are not equipped with position sensors (encoders). For example, with a stepping motor that rotates 1.8° per pulse, the system assumes the motor has reached its target position (180°) as soon as the controller finishes sending 100 pulses. Even if an external load causes the motor to move only 99 pulses’ worth (178.2°), the controller has no way of detecting the error and simply proceeds to the next process. The opposite approach—where a sensor monitors actual movement and automatically corrects any positional deviation—is known as "Closed-Loop Control."

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