Actuator Interfaces
Actuators turn control commands into physical action; the interface must convert, amplify, and safely drive them while confirming what actually happened.
The Output Side of Control
An actuator interface carries the controller's commands out to the devices that act on the physical world: motors, valves, heaters, power supplies, and magnet coils. It is the mirror of the sensor interface. The controller computes a desired action as a number; the interface converts that number into the electrical drive the actuator needs and does so with the timing the control loop assumes.
Command Conversion
- Digital-to-analog conversion for analog drive levels
- Pulse-width modulation to control average power efficiently
- Digital protocols for smart drives and power converters
- Power stages that amplify low-level commands to actuator drive levels
Timing of Output
When a command reaches the actuator matters as much as its value. Output jitter makes the actuator see a noisy command even when the computed value is correct. As with sampling, the tightest designs latch the output from a hardware timer so the update instant is precise, rather than depending on when the software happens to write it. The delay from computation to physical action is part of the loop's total latency and directly affects stability.
Feedback and Confirmation
A robust actuator interface does not assume commands take effect. It reads back the actual state, position, current, or valve status, so the controller and safety logic know what physically happened. This closes the loop on the actuator itself and lets the system detect a stuck valve, a saturated drive, or a failed power stage rather than commanding blindly.
Safe States and Limits
Because actuators move energy and mass, their interfaces enforce limits: maximum drive, rate-of-change limits, and defined safe states on fault or loss of communication. A well-designed interface fails to a known safe condition, for example de-energizing a coil or closing a valve, rather than holding the last command or drifting. This behavior is coordinated with the system's interlocks so that protection can override normal control and command a safe state directly.