Machine Design

Tiny-coil winders work better with vision

Double Vision coil winders handle mandrels from 0.001 to 0.188-in. diameter, 65-in. long (different mandrel lengths are optional), metal or plastic filaments from 0.0004 to 0.025-in. round solid or tube, or ribbon, filament tensions from 0 to 80 gm (±0.1 gm), mandrel tensions between 75 gm and 4 kg, (±2 gm), coil angles of ±3° at ±0.02° resolution (with vision) and greater angles at lower resolution without vision. The winders program through a color touchscreen display and are Ethernet ready. Two independent machines stack on one frame to double production for a given floor space.

A miniature coil and a human hair sit atop a penny. Applications for miniature coils include coil stents, catheters, motor coils, and heating elements.

Machine vision in Double Vision coil winders from Engineering by Design, San Jose, detects wind angles, without physical contact, to 0.02°. Previous measurement techniques used a mechanical arm fitted with an angle sensor. But as wires get smaller, contact with the mechanical sensor arm changes the wind angle and introduces errors up to 2°.

"Machine vision eliminates the error and boosts control accuracy by a factor of 100, which equates to more consistent product and less waste," says EBD President, Dale Henson. "Maintaining a steady tension of 0.2 gm and a wind angle of 0.1° makes it possible to produce coils from 0.0004-in.-diameter platinum wire."

Automatic mandrel and filament tensioning and variablepitch control let the machine wind coils with multiple and repeating combinations of pitch, direction, and length. Closed-loopfilament tension and slack control maintain programmed tension at speeds to 6,000-mandrel rpm and faster. Brushless servomotors drive the traverse mechanism and both mandrel ends, eliminating a back shaft. The control system records statistical data for each wind including the mean and standard deviation of all measured variables to verify product quality and refine the process.

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