servoing

Servoing is a closed-loop control technique used to drive a system along a desired trajectory or to reach a specified target state by continuously reacting to feedback. A servoing system compares a reference signal with sensor measurements that quantify the current state, producing corrective actions through actuators. The approach is central to automation and robotics, where precise motion and positioning are required. Typical components include sensors (such as encoders, potentiometers, or cameras), a controller (often PID or more advanced algorithms), actuators (electric motors, hydraulic or pneumatic cylinders), and the mechanical transmission that converts actuator commands into motion.

Servoing can be implemented in several modes. Position servoing aims to reach and hold a chosen pose or position by regulating the actuated joints to match a reference value. Velocity servoing controls motion speed along a path, often using a velocity reference rather than a position target. Torque or force servoing directly regulates actuator torques or forces, which can be advantageous for compliant or interactive tasks. Impedance or interaction servoing adjusts the system dynamics to respond to external forces in a controlled manner.

A major subfield is visual servoing, which uses camera data to guide motion. In image-based visual servoing (IBVS), control is driven by image features, while pose-based visual servoing (PBVS) relies on estimated scene geometry and camera pose. Visual servoing faces challenges such as sensor noise, latency, feature tracking, and model precision.

Applications span robotics, CNC machining, flight and automotive systems, and prosthetics. Servoing remains foundational for precise, responsive automation in environments requiring high precision or safe interaction with humans and objects.