Actuators & motors

In one line

An actuator turns electrical energy into motion or force. Sensors let a device sense; actuators let it act on the world — pushing a plunger, turning a joint, opening a valve.

The common types

• DC motor — simple, spins fast; pair with a gearbox for torque. Cheap pumps, fans.
• Stepper motor — moves in exact, countable steps. Drives the lead-screw of an infusion or syringe pump, so every step delivers a precise micro-dose.
• Servo — a motor plus a position sensor and controller, so you command an angle and it holds it. Robot joints, camera/scope positioning, prosthetic fingers.
• Solenoid / valve — an electromagnet that snaps open or shut. Gas and fluid control in ventilators and analysers.

A controller pin can't supply enough current to move a motor, so it switches a transistor / MOSFET (often an H-bridge, which also reverses direction) that powers the motor.

Where it shows up in digital health

• Infusion & syringe pumps — a stepper turning a lead-screw; step count = volume delivered. Safety hinges on detecting a stall or an occlusion.
• Surgical & assistive robots — servos at each joint, commanded by the control loop.
• Prosthetics & exoskeletons — motors driven by muscle (EMG) signals.
• Lab automation — steppers and solenoids moving samples and reagents.

Watch for

Anything that moves can harm. Medical actuators pair with sensors that close the loop (measure current, position, force) and with hard limits so a runaway motor is caught — a pump must know when it has actually delivered the dose, not just assume it.

Key takeaways

• An actuator converts electricity into motion/force — how a device acts.
• Types: DC motor (speed), stepper (countable steps — pump dosing), servo (commanded angle — robot joints), solenoid/valve (open/shut).
• A controller switches a transistor/MOSFET (often an H-bridge) to power the motor.
• Safety requires closed-loop sensing (current, position, force) and hard limits — know the dose was delivered.