Linear Actuators

Electric linear actuators provide linear motion via a motor-driven ball screw, lead screw, or acme screw assembly. The load is attached to the end of the screw and is unsupported. Acme screws are lead screws with matching threads on both the screw and nut. Ball screws are lead screw and ball nut combinations that enable the balls in the nut to circulate when the actuator is in motion. Electric linear actuators with belt drives, geared drives, and direct drives are also available. Belt drives connect the motor to the actuator with a belt. Geared drives connect the motor to the actuator with a set of gears. With direct drives, the motor is connected directly to the electric linear actuator. In terms of performance, important specifications include stroke, rated force or load, system backlash, and rated speed. Stroke is the maximum distance that the shaft travels from a fully extended position to a fully retracted position. Backlash is the position error due to directional change. The maximum rated speed is typically a low or no load amount. 

Electric linear actuators vary in terms of motor type, power, and features. DC brush motors feature built-in commutation so that as the motor rotates, mechanical brushes automatically actuate coils on the rotor. By contrast, brushless DC motors use an external power drive that allows commutation of the coils on the stator. DC servomotors have an output shaft that is positioned when a coded signal is sent to the motor. Electric linear actuators also use a variety of AC motors. Common types include single, multiphase, universal, induction, gear, and synchronous motors. AC servomotors are permanent magnet synchronous motors that have low torque-to-inertia ratios for high acceleration ratings. AC stepper motors use a magnetic field to move a rotor in small angular steps or fractions of steps. Motor voltage and continuous power are important performance specifications for both AC and DC motors. Motor features include motor encoder feedback, linear position feedback, position switches, and integral brakes.  

There are several mounting options for electric linear actuators. Some cylinders are equipped with a clevis or eye attachment that connects to the extended end of the piston. Others are equipped with a mounting flange or bracket, a floating mount bracket, tapped holes, or threaded holes. Foot brackets are flanges that rest underneath the cylinder. Lugs are short blocks with holes that attach to the side of the cylinder and allow mounting to another surface. Cylinders equipped with trunnion mounts feature specially designed mounting blocks that are located at the cylinder cap or head. Face mount, nose mount, and rear mount electric linear actuators are also available.  

Electric linear actuators provide many optional features. Some devices provide adjustable stroke, holding brakes, or shock absorbers. Other devices include double-ended rods, a multi-position endplate, an integrated overload slip clutch or torque limiter, and a protective boot. Integral sensors monitor position and proximity. Integral flow control incorporates a valve that limits the amount of air of fluid that enters the cylinder. Magnetic switches indicate the thruster’s position. Thermal overload protection trips a switch when a preset temperature is exceeded. Bumpers or cushions soften the impact at the ends of a stroke. Intrinsically safe electric linear actuators can be used in hazardous environments such as chemical processing facilities. Water resistant devices are sealed to prevent corrosion. Typically, body materials consist of aluminum, steel, plastic, or stainless steel.

• Linear actuators get a servo look
  New actuators borrow ideas from linear motors to provide controlled displacement on a budget. Vice President Copley Controls Corp. Canton, Mass. Historically, industry has depended on ball screws,...
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• Back Driving Forces on Linear Actuators
  Back driving force refers to the force value, that when applied to the leadscrew on a linear actuator that is not energized will result in linear travel of the leadscrew. Several factors are...
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• Hybrid Linear Actuators: Technical Overview
  Converting the rotary motion of a stepping motor into linear motion can be accomplished by several mechanical means, including rack and pinion, belts and pulleys and other mechanical linkages. All of...
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Part Numbers for Linear Actuators