What is an encoder? What is its function? How should open-loop and closed-loop control be understood?

An encoder is a feedback device used to detect the actual motion status of a motor or mechanical system. It can measure parameters such as position, speed, and direction, and convert this motion information into electrical signals that can be recognized by the control system.

In motor systems, the primary function of an encoder is to provide real-time feedback to the driver or controller, allowing the system to monitor the motor’s actual operating condition more accurately. This helps improve positioning accuracy, speed stability, dynamic response, and overall operational reliability.

From a control perspective, motor systems are commonly divided into open-loop control and closed-loop control:

Open-loop control: After the controller sends a command, it does not receive feedback about the motor’s actual motion. The system operates according to the preset pulses or command signals, but it cannot automatically determine whether the motor has lost steps, stalled, or deviated from the target position. The main advantages of open-loop control are simpler system architecture and lower cost.

Closed-loop control: The system uses feedback devices such as encoders to continuously monitor the motor’s actual position, speed, or direction, and compares the actual value with the commanded value. Based on this comparison, the controller can automatically adjust the output in real time. This significantly reduces the risk of step loss and positioning error, while improving control accuracy, response performance, and operating stability.

In simple terms, the role of an encoder is to let the system know how far the motor has actually moved, how fast it is moving, and where it is at any given moment. Closed-loop control uses this feedback to correct errors in real time, while open-loop control operates without such correction.

For applications with higher requirements for precision, stability, and anti-step-loss performance, a closed-loop solution with encoder feedback is generally more suitable. For applications where cost sensitivity and basic motion control are the primary considerations, open-loop systems remain a common and practical choice.