A linear actuator is a machine element that turns energy into straight line motion. In robotics, it lets a mechanism push, pull, lift, clamp, tilt, or extend with controlled position and force. Electric linear actuators are common because they are compact, clean, and easy to control with sensors and motor drivers.
Understanding their parts helps you predict speed, load capacity, accuracy, and safe operating limits.
A typical electric linear actuator uses a motor, gearbox, screw, traveling nut, and extension rod inside a rigid housing. The motor spins, the gearbox changes torque and speed, and the lead screw or ball screw converts rotation into linear motion. The screw pitch, motor torque, friction, and duty cycle determine how much force the actuator can produce and how long it can run without overheating.
Limit switches, encoders, and current sensing are often used to stop motion safely and measure position.
Key Facts
- Linear motion distance is the stroke, measured from fully retracted to fully extended.
- For a screw actuator with no losses, linear speed is v = pN, where p is screw pitch and N is rotation rate in revolutions per second.
- Mechanical power is P = Fv, where F is linear force and v is linear speed.
- For an ideal screw, F = 2πT / p, where T is screw torque and p is screw pitch.
- Real actuators have efficiency less than 100 percent, so useful output power is Pout = ηPin.
- Duty cycle = run time / total cycle time × 100 percent, and exceeding it can overheat the motor.
Vocabulary
- Linear actuator
- A device that produces controlled straight line motion from electrical, hydraulic, pneumatic, or mechanical energy.
- Lead screw
- A threaded shaft that converts rotational motion into linear motion as a nut travels along its threads.
- Ball screw
- A screw mechanism that uses recirculating balls to reduce friction and improve efficiency compared with a basic lead screw.
- Stroke
- The maximum linear distance an actuator rod can travel between its retracted and extended positions.
- Duty cycle
- The fraction of a repeated operating period during which the actuator is allowed to run under load.
Common Mistakes to Avoid
- Confusing stroke with total actuator length is wrong because stroke is only the rod travel distance, not the full physical length of the device.
- Ignoring duty cycle is wrong because an actuator that can lift a load briefly may overheat if it is run continuously.
- Using ideal force equations without efficiency is wrong because friction in gears, bearings, and screw threads reduces the actual output force.
- Assuming higher speed always improves performance is wrong because faster screw motion usually reduces available force for a given motor power.
Practice Questions
- 1 A lead screw has a pitch of 5 mm per revolution and rotates at 120 revolutions per minute. What is the actuator rod speed in mm/s?
- 2 An actuator lifts a 300 N load at a speed of 0.020 m/s. What mechanical output power is delivered to the load?
- 3 A robot gripper needs to hold a heavy object for long periods without overheating. Explain why duty cycle, screw type, and holding method matter when choosing a linear actuator.