“Closed-loop” refers to a control principle in which the actual position of a drive is continuously measured, compared to the target position, and automatically adjusted if there is a deviation. This is based on a feedback system—such as a position measurement system or encoder—that reports the actual position back to the controller.
Distinction from Open Loop
- Open-loop operation works without feedback: The setpoint is converted directly into motion without checking whether the position has actually been reached. This is typical for simple stepper motor drives.
- Closed-loop operation continuously measures the actual position and actively compensates for deviations.
Pros and Cons
- Higher positioning accuracy, even with varying loads, temperature changes, or friction
- Detects and corrects step losses or deviations that would go unnoticed in open-loop systems
- Higher costs due to the additional measurement system and control technology
- If the controller is operating under unfavorable conditions, there is a risk of control-loop instability
Practical Applications in Thread Technology
Closed-loop control is used with ball screws and trapezoidal screws when the application requires the highest positioning accuracy and repeatability, such as in machine tools, measurement and testing technology, or semiconductor manufacturing. A position-measuring system mounted directly on the spindle or the moving slide also compensates for elastic deflections in the drive train that pure motor feedback would not detect.