Electric linear actuators provide precision linear motion control through converting rotary motion from a drive motor into accurate linear displacement of payloads. A deeper examination of each subsystem is needed to understand their function.
There are several common motor choices. AC servo motors offer resolver or encoder feedback loops enabling precise open or closed loop speed control from 0 to over 10,000 RPM. This high resolution drives other systems. DC gearmotors supply continuous torque at lower speeds from 0-3000 RPM. They require less complex controls. Stepper motors increment rotation in small steps enabling motion without encoders but provide limited torque at higher speeds. All convert controlled rotational motion.
Ball screws are precision ground steel shafts with raceway grooves enabling balls to roll between the screw and a matching nut component. This converts rotations into smooth linear motion with backlash below 25 microns. Lead screws provide lower accuracy with backlash up to 150 microns but at low cost. Rack and pinion gears mesh cut teeth to change rotation into translation best for short strokes to 250mm where precision is not critical. Toothed belts couple pulleys well for intermittent lower precision applications.
On ball screw systems, the ball nut attaches to the moving carriage. It has inner raceways matching the screw's which enable precision ground steel balls to roll between generating minimal friction. During rotation, the balls circulate within the nut's raceways and between the screw and nut. This precisely converts screw turns into linear displacement of the nut. Lead screw nuts apply pressure directly rather than through balls.
As the electric motor precisely rotates the drive screw or belt at controlled velocities, the corresponding nut is forced to travel linearly along the screw's axis. This high resolution reciprocal motion transfers to connected payloads which can range from less than a kilogram to hundreds of kilograms.
Optical encoders provide feedback to control systems. Encoders mount inside the linear actuator while motor-mounted resolvers or encoders enable closed loop velocity and position control to an accuracy of less than 1/10,000th of an inch. Additional switches prevent over-extension of the moving platens.
Programmable logic controllers, computers or motion controllers command actuators. Communications profiles connect actuators as addressed nodes for synchronized multi-axis automation scenarios. Machines benefit from each actuator's high speed, stiffness and micron resolution.