Glossary · Motion control and drives
Current loop
Also known as: Current control loop, Torque loop
German: Stromregelkreis
In drive control, the current loop is the innermost control loop of a servo or vector drive: it compares the commanded motor current, which is proportional to torque, with the measured current and adjusts the output voltage accordingly.
- Motion control
In one sentence
The current loop is a drive's innermost control loop; it regulates motor current and thus torque, beneath the velocity and position loops.
Example
In a cascaded servo drive, the current loop runs at a much higher rate than the velocity loop, which in turn runs faster than the position loop.
How it applies
- Engineering: In the cascade structure, the Position loop feeds the Velocity loop, which commands the current loop. Current limits in this loop cap the motor's torque.
- Commissioning: The current loop is usually tuned automatically from motor data. Wrong motor data can cause noise, overheating or instability in all outer loops.
- Operation: Current limits protect the motor and mechanics and can be used for torque-limited tasks such as pressing or clamping.
- Documentation: When a manual tells users to change current limits, explain the effect on force and on the mechanics. A current limit is a control function, not a safety function unless it is implemented and validated as one (for example as a safety-rated torque monitoring function).
Current loop vs. current loop signal
In instrumentation, "current loop" also means the 4–20 mA signal transmission. In drives, it means the torque control loop. Qualify the term where both appear in one document.