Linear Thrusters

Linear thrusters use double-acting pneumatic, hydraulic, or electrohydraulic cylinders mated to plates and shafts to provide cyclical linear motion. They are used in conveying, positioning and inspection systems. The integral stages of linear thrusters are mounted vertically or horizontally and include features such as position switches, end stops and cushions, and corrosion resistant coatings and treatments. There are several common drive configurations. ACME screws are square-topped and have a very specific thread geometry that directly contacts the nut and provides linear motion through direct sliding friction between the nut and lead screw. Ball screws are lead screw and ball nut combinations in which the balls in the nut circulate when in motion. Belt drives connect the motor to the actuator with a belt. By contrast, geared drives connect the motor to the actuator through a set of gears. Others specialized and proprietary drive configurations for linear thrusters are also available. 

Selecting linear thrusters requires an analysis of performance specifications, body materials, and bearing types. Maximum stroke is the maximum distance that the shaft travels from the fully retracted position to the fully extended position. Maximum speed is rated at low or no load conditions. Operating pressure and operating temperature are full-required ranges. Bore size and shaft diameter are usually measured in inches (in). For linear thrusters with multiple guide shafts, suppliers specify the diameter of the largest shaft. Most devices use aluminum, steel, stainless steel, or plastic as the body material. Several bearing types are commonly available. Balls or rollers are used in applications that require recirculating linear motion. Solid metal bushings use materials such as oil-impregnated bronze. Continuous-surface composite bearings are often recommended for their anti-corrosive properties and tolerance to debris.  

Many linear thrusters include features such as bumpers or cushions, pneumatic or hydraulic shock absorbers, protective boots, integral position sensors, and self-locking mechanisms that engage automatically when a signal is disrupted. Water-resistant devices block the ingress of moisture and prevent corrosion. Intrinsically safe (IS) linear thrusters will not produce sparks, electrical energy or other thermal effects that would cause an explosion under normal or fault conditions. Devices with thermal overload circuitry trip a switch when a preset temperature is exceeded. Closed loop controls and magnetic switches are used to indicate whether the thruster is retracted or extended. Integral flow valves limit the amount of air of fluid that enters the cylinder. Devices with adjustable stroke and double-ended rods are commonly available.

• Pneumatic linear guides lighten loads
  Air-powered motion systems combine economy, speed, and cleanliness. Linear thrusters from Bimba Mfg. Co. come in seven bore sizes. They are said to ensure smooth, guided motion because a durable...
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• 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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• Choosing the Best Lead Screw for a Linear Motion Application
  Getting the best lead screw for the job Knowing the details of a linear-motion application increases the odds of choosing the right ball screw. Before engineers can specify the type and size of...
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Part Numbers for Linear Thrusters