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| Solenoids Used in Pinch Rollers |
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To print text on a flexible steel tape, a manufacturer needs to move pinch rollers into position to advance the tape through the printing head. This is typically accomplished by mounting each of the many rubberized pinch rollers on a small air cylinder. By use of small electrically actuated valve assemblies, the rollers are extended or retracted as required. A flow restricting device is also used for each cylinder to slow the rod actuation speed.
When a decision was made to convert the equipment to exclusively electrical operation, different actuation devices were needed. Motors and their controllers were costly and hard to apply. Solenoids held promise but there were several challenges. Solenoids actuated very rapidly, sometimes crimping the thin steel tapes. In addition, common linear types did not offer rigid support of the rollers due to built in armature side play.
A solution was soon suggested using a rotary device, the BTA. It had several advantages. First, the ball bearing mounted output shaft did present a very rigid axis to rotate the roller about. The ball bearings also promised very long running life. Of equal importance was the low shock clamping force the BTA could deliver by ramping the coil current. The BTA lends itself to velocity control, thus the crimping problem could be eliminated. Since the pinch rollers actually clamped against drive rollers, there might have been some difficulty with a standard rotary solenoid if the stroke was restricted. This is not a problem with the BTA and even helps extend unit life. The BTA is also expected to dramatically reduce machine noise levels, as the thumping and hissing of pneumatics will be replaced with solenoids actuating under controlled velocity conditions.
This application demonstrates how well the BTA fits applications that extend beyond the capabilities of standard linear or rotary solenoids. Again offering a complete solution; actuation, bearings, and return spring in a single package.
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