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Machine Design

Electric actuators provide precise positioning

It is difficult to get intelligent motion control with flexibility and precision out of low-cost pneumatic cylinders. You could use servos, but that adds cost and complexity.

An alternative, the Ternary intelligent actuator system from alpha gear drives Inc., Elk Grove Village, Ill.(, is a low-cost actuator that provides up to 16 precise positions over a travel length of up to 300 mm. The Ternary, an integrated closed-loop system, consists of an amplifier, controller, incremental encoder, brushless motor, ball screw, and optional brake in a single package. It controls position, velocity, acceleration, and thrust, and handles changes in midmove velocities.

Users download positioning data into the controller from alpha's proTern Ternary Digital Assistant software. The software runs on PCs and PDAs and is used for set up, diagnostics, and an OEM project manager that can revise, track, archive, and document applications.

A PC or PLC controls the actuator, which can position up to 16 points with 0.0075-mm resolution. With a standard serial interface to their PCs, users can store point tables and send position changes, creating a virtually infinite number of points.

Models are available with strokes from 25 to 300 mm, thrust to 600 N (135 lbf), and velocities to 900 mm/sec with repeatability of ±0.018 mm. In addition to the linear Ternary, a rotary version is also available, with optional reducers from 5:1 to 100:1.

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