How Does a Linear Actuator Work?by Pauline Gill
Linear Actuators Intro
Linear actuators are motors that provide push and pull motive force in a straight line. Linear actuators move work tables on industrial machines, modulate control valves, drive material handling equipment and robotics, and move printer and scanner heads back and forth on computer equipment. They drive shovels and lifts on construction equipment and provide the oscillatory motion of audio loudspeakers.
Many Power and Operational Options
There are many linear actuator driving force options. Manual mechanical methods include the lead screw systems of vises and clamps, and levers found in manual juicers or can crushers. Cylinders with pistons powered by compressed air are used to move parts of machines. Hydraulic cylinders with pistons provide large forces and strokes for construction equipment such as shovels, lifts and jacks, and short throw cylinders for braking systems. Solenoid coils, which are short throw electromagnetic linear actuators, turn switches and valves on and off as well as lock and unlock car doors. Linear progressions of electromagnetic motor poles are used for trams, people movers and material conveyors.
Rotary to Linear Motion
Some linear actuators use straight sections of cogged belt or roller drive chain in a lengthwise circuit between two pulleys or sprockets. These are widely used in garage door openers. Other linear actuators also use standard rotational electric motors with mechanical conversion employing sector gears for steering systems or crankshafts in sewing machines.
Highly specialized linear actuators are used in critical applications such as hydraulically actuated flight control surfaces on large aircraft, in precise positioning to tenths of thousandths of an inch in ultra fine machining equipment with tiny servo motors and cog belts, and for minute movements in medical procedures such as eye surgery. Even the inexpensive stepper motor driven linear actuators used in home computer printers have resolution down to single pixel size.
Motion, Position, Velocity, Force, or a Combination
Designers integrating linear actuators into equipment examine applications to determine whether motion, force, position, or velocity is the primary operational requirement or whether the application requires some combination of all of them. Printer head skewing systems must be able to position the heads precisely across a long stroke, while braking cylinders provide very large forces through relatively short strokes against the brake discs that limit their motion. The hydraulic cylinders on large excavators used in construction must be able to provide tens of thousands of pounds of force over many feet of stroke, with a degree of precision of an inch or two being considered adequate. Electronically controlled linear positioners used in circuit board assembly move at blinding speed as microchips are inserted into precise positions. Therefore, complex linear actuator applications will often incorporate position, force and velocity feedback sensors connected into programmable machine control systems to assure that all linear actuator performance is achieved consistently.