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Linear actuator challenges pneumatics

01 March, 2004

Linear actuator challenges pneumatics

Linear actuator specialist Copley Motion Controls has launched a range of linear servomotors which, it says, combine the speed and ruggedness of pneumatics, with the controllability of ballscrews and the reliability of linear motors, at an "unprecedented" price. The ServoTube range is based the company`s ThrustTube technology but uses the motor itself to generate a feedback signal, thus avoiding the cost of a separate encoder.

This patented feedback development, combined with improved manufacturing techniques at the company`s Basildon plant, will allow the new motors to compete with controlled pneumatics. "Our twin aims were simplicity and affordability," says Copley`s sales director, Bill Luckins. "We`ve met these aims and can now deliver a sophisticated linear servo-electric actuator with integrated feedback at keener prices - typically 5-10% less - than our standard products."

There are two versions of the new device: the ServoTube Actuator, with integrated full-length bearings for push, pull and lift applications; and the simpler, cheaper ServoTube Component, which does not include the bearing and acts as a conventional moving-forcer system with a fixed thrust rod.

The embedded sin-cos encoder eliminates the problems of conventional encoders being degraded by dirt or damage. It also avoids the problems of aligning tight-tolerance encoders and is said to make the ServoTube as easy install as a pneumatic cylinder. The actuators can be driven by Copley`s own amplifiers or third-party controllers.

The actuators use a patented 25mm-diameter thrust rod consisting of a sealed stainless steel tube containing rare-earth magnets. Different lengths of forcer interact with the magnets to deliver continuous forces from 51-104N, and peak forces up to 959N. Acceleration can exceed 574m/s˛ and velocities can exceed 13m/s, with resolutions down to ±6µm.

The ThrustTube range, which uses and external encoder, will still be available for applications requiring higher accuracy.

Luckins expects the ServoTube actuators to open up new markets. "Although we are not going to compete with basic push-me, pull-you pneumatics," he says, "we will be extremely competitive with controlled pneumatics". The devices have been designed for volume manufacturing, he adds.

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