Actuator
How it works
An actuator receives a control signal (e.g. voltage, current, fluid or air pressure) and uses its energy source to produce mechanical work. In an electric actuator, current through the motor windings creates a magnetic field and torque; a gearbox can trade speed for torque, and a conversion element (e.g. a ball screw) turns rotary motion into linear motion. In a hydraulic actuator, pressurized fluid drives a piston inside a cylinder to produce large linear forces; a pneumatic actuator uses compressed air for the same purpose. In closed-loop systems, the actuator works with position, velocity, or force sensors (encoders, torque sensors) that close the feedback loop and enable precise motion control.
Problem solved
Control systems and AI models produce decisions and signals that, on their own, cause no physical effect in the world. The actuator solves the problem of translating those signals into real motion — it delivers the force and displacement needed for a robot to move its joints, grasp objects, or locomote, closing the loop between perception, decision, and action.
Components
The electric, hydraulic, or pneumatic energy that powers the actuator.
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A motor, cylinder, or other element that converts the input energy into mechanical motion.
Gearboxes, ball screws, or linkages that adjust speed, torque, and the type of motion (rotary or linear).
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A controller and position/velocity/force sensors (encoders, torque sensors) that close the control loop.
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Implementation
Play in the gearbox introduces nonlinearity and position uncertainty, degrading control accuracy, especially on motion reversal.
Sustained high load heats the windings and magnets, limiting continuous torque and risking motor damage.
High gear ratios boost torque but reduce backdrivability and force control, making safe physical interaction harder.
Evolution
Gill Pratt and Matthew Williamson (MIT) introduce the series elastic actuator, placing an elastic element between the motor and the load to enable accurate force control and compliance in robots.
The MIT Cheetah team describes a proprioceptive actuator design with high-bandwidth force control and impact robustness, enabling dynamic legged locomotion without dedicated force sensors.
Hyperparameters (configurable axes)
The type of energy driving the actuator; determines power density, speed, and applications.
Whether the actuator produces rotary or linear motion.
Gear reduction ratio; increases torque at the cost of speed and affects backdrivability.
The quantity regulated in the feedback loop: position, velocity, or torque/force.
The actuator's ability to yield to external force; key for safe interaction and force control.
Hardware requirements
An actuator is a physical component, not a compute workload — the concept itself is not tied to any specific AI compute hardware.
High-frequency actuator control loops are often implemented on FPGAs or microcontrollers for timing determinism.