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'Pistonless' actuator speeds paper punch
Flexible tube replaces articulated lever
By Roy OConner, European Bureau Chief, Global Design News -- Design News, March 26, 2001
Schlierbach, Germany —Despite the proliferation of PCs, laptops, and personal organizers, a tremendous amount of information is still held in paper-based files and a significant demand for conventional filing systems remains. Karl Widmann Schweissmaschinen GmbH produces machines for processing paper and plastic film in polypropylene and PVC. The machine range includes punching and imprinting equipment for file cards and registers.
To increase throughput on its new Model TA-R5 index tab punching machine, the company designed out the conventional cylinder/articulated lever used to punch holes, and designed in a "fluidic muscle." Result: 250 vs 180 sheets per minute, an almost 40% gain in performance.
In contrast to conventional actuators based on pneumatic cylinders, the fluidic muscle pneumatic actuator has no piston. Circumferential expansion and contraction of the cylinder generates the required movement or change in actuator length.
Developed and marketed by Festo AG, the fluidic muscle features a flexible tube made of fibers woven in a hash-type pattern, forming a three-dimensional grid structure. Applying pressure to the cylinder expands the cylinder circumference. This, in turn, produces a tensile force in the axial direction, shortening the muscle.
One advantage of this actuator, essential for the high dynamic performance of the index tab punching mechanism, is its light weight—approximately one-tenth that of an equivalent conventional cylinder. In addition, the muscle can produce very slow movements free of stick and slip. Fast movements are also possible with integral end-position damping. Strokes of approximately 25% of the nominal length can be obtained.
Direct driving of the load is not possible with the fluidic muscle, so Widmann's designers included compression springs to pull the muscle back to its nominal length during the punch cycle. The punch stroke, in which the muscle contracts under pneumatic pressure, takes 15 msec, while the return stroke under spring tension takes 30 msec.
The company intends to implement the fluidic muscle throughout its punching and imprinting machines.
Additional Details
Contact FESTO, 395 Moreland Rd., Hauppauge, NY11788; Tel/FAX: (800) 963-3786
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