Open-loop control refers to a control principle in which a drive directly converts a specified setpoint into motion without measuring or reporting the actual position reached. There is no feedback between the actual and setpoint states; the drive “trusts” that it is executing the specified steps correctly.
Principle of Operation
Typically, open-loop systems use stepper motors that execute a defined number of steps. The system does not verify whether the target position has actually been reached, unless an additional position-measuring system is retrofitted to convert the system into a closed-loop control system.
Pros and Cons
- Simpler and more cost-effective setup, since no measurement system or control technology is required
- Resistant to external disturbances within the normal operating range
- Lower positioning accuracy, as deviations are not detected
- Risk of lost steps due to overload, high acceleration, or obstructions that are not detected or corrected by the system
Practical Applications in Thread Technology
For ball screws and trapezoidal screws, open-loop control is suitable for applications with moderate accuracy requirements and known, consistent load conditions, where it reduces costs and complexity compared to a closed-loop solution. However, when high positioning accuracy, varying loads, or monitoring for missed steps are required, closed-loop control with a position measurement system is the more suitable choice.