Copley Controls: New linear motors include lower cost

Linear motors—of the direct-drive type—come in various styles, but share the common attribute of eliminating the need for belts, ballscrews, or other rotary-to-linear motion-converting devices between the motor and driven load.

By Control Engineering Staff March 24, 2005
ServoTube motors eliminate deep channels of conventional U-channel linear motors that accumulate dirt and debris. They also withstand regular wash down and run quietly.

Linear motors—of the direct-drive type—come in various styles, but share the common attribute of eliminating the need for belts, ballscrews, or other rotary-to-linear motion-converting devices between the motor and driven load. As a result true linear motors are inherently faster and generate higher acceleration than the just-mentioned alternatives, including pneumatic actuators.

Copley Controls Corp . has “tuned in” on the productivity advantages offered by direct-drive linear (DDL) motion technology, with its recent introduction of ServoTube linear motors, and complemented the design with low-cost features. In the past, higher cost and difficulty of integrating linear motors into automated systems has been a major barrier to their adoption in large numbers, says the company.

ServoTube motors have simple, intrinsically robust construction, made up of two basic components: thrust rod and forcer . The motor’s symmetrical design configuration exposes all outside surfaces of the electrically powered forcer to air-cooling. There is no need for water or forced air-cooling. A further ServoTube advancement is replacement of the delicate, costly, and difficult-to-align optical encoder with an integral Hall-effect position sensor. Eliminating the encoder—the weak link of previous DDL motors—makes the new design more rugged and enables it to meet IP67 environmental seal rating.

Multiple forcer options

ServoTube allows the use of two or three forcers on one thrust tube, thereby increasing drive force. Moreover, the two forcers are autonomous. They can be independently controlled, travel in opposite directions, and carry different loads. For example, while forcer A loads, forcer B unloads. Depending on the controls, multiple forcers can also be operated in unison to double or triple the motor’s drive force. This alternative benefits applications where space is tight. Copley suggests that even four forcers could be operated on a single linear motor.

Eight ServoTube models offer a wide range of force, acceleration, and travel. Four models with 25-mm (2 in.) diameter thrust rods output 11.5-23 lb continuous thrust force (70-175 lb, peak). These motors have 8.7 m/s (28.5 ft/s) maximum velocity and 256 m/ss.

ServoTube motors work with any servo amplifier that accepts analog encoder input, and they are optimally compatible with Copley’s Xenus servo amplifier. ServoTube motors are available from stock-4 weeks after receipt of order, priced from $897 (depending on motor model) for quantities of one to nine.

—Frank J. Bartos, executive editor, Control Engineering, fbartos@reedbusiness.com