Engineering Productivity Kit Motion Control

By: 
January 04, 1999

Dual-axis linear drive adds a new twist to pick-and-place

by John Lewis, Northeast Technical Editor

Hauppauge, NY --Imagine a direct-linear drive that moves in two axes. That's essentially what Anorad Corp. came up with to simplify multi-axis stage design. Called PSM (Planar Servo Motor) technology, the design consists of a motorized forcer that glides over a platen or defined work area.

Linear motors, air bearings, and encoders--mounted on the forcer's underside--work with a magnetic array embedded in the platen's surface. Together, these devices propel and position the forcer as it glides on a cushion of air over the platen. The design eliminates mechanical guides commonly used in stacked or planar X-Y systems, and allows more than one forcer to perform coordinated motion over a single defined work area.

Although developed in a planar form, PSM technology will make its commercial debut as a rotary device called the Cyclone Z-Theta stage. "Anorad gained its fame by essentially flattening out the traditional rotary motor to create a direct linear drive," says Anorad's Founder and CEO Anwar Chitayat. "Now we've taken a two-axis, planar version of our linear motor and inverted the forcer and platen function so that the motors, encoders, and air bearings are stationary, and the magnetic array is buried within the moving forcer. Then we rolled it back up into a cylinder to achieve rotary and linear motion."

Compact stacking. Cyclone is only 31-mm wide, and has flat sides for compact "ganging" or "stacking" in high-throughput, pick-and-place applications. A hollow-shaft forcer allows centerline vision for positioning correction without offsets. It lets engineers minimize space requirements by routing control wiring and pneumatic tubing for tool sensors and pickup hardware through the forcer for a neat package.

"Cyclone acts like an air cylinder, but its design offers much higher performance," says Chitayat. Capable of 1.0-m/sec velocities in the z direction and 60 rad/sec in theta; 2.0-g acceleration in z and 600 rad/sec 2 in theta; the Cyclone 50 (50-mm stroke) provides 0.15-m positioning resolution in z and 0.0007 degree resolution in theta--at a rated payload of 100 gm.

The Cyclone series is totally non-contact. Coated air-bearings resist damage in the event of air loss. "Without wearing surfaces, position performance won't degrade," says Chitayat. "The design eliminates lubrication, and reduces maintenance. Moreover, the encoder's read head averages feedback from a large patch of the scale. This means that even large scratches or surface defects in the forcer won't affect accuracy."

Vacuum counterbalance. To neutralize vacuum force so the motor doesn't have to fight it during actuation, Anorad designed a "leaky" seal or filter for the vacuum generator. "It breathes to achieve higher forces, and so that the motor doesn't have to pull extra current and generate extra heat," explains Chitayat.

The design allows the Cyclone 50 to act as a pneumatic cylinder that produces 27 lb of downward force. While Cyclone's construction gives work-cell designers another option, customization is also available to meet additional requirements.


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