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Motion System Design

Wedging out shock

Well-designed stops make machines agile, in turn boosting production. Where brakes and electronics are overkill for deceleration, using a simple shock absorber is one option. But traditional absorbers can reflect shock back into machines: Their mechanism of operation (typically via damping oil that squirts out of a series of outlets) effectively stops machinery, but not without huge initial deceleration.

Now a new design of shock absorber decelerates components at a constant rate for a sufficiently controlled halt. For more compliance at initial impact, it includes a progressively reduced channel cut into its piston. In summary: Oil sits in a chamber at the end of the unit. When the shock absorber is struck with a moving object, the oil floods into the piston's spiraling channels, starting at the fat openings and quickly squeezing to the narrow ends, to finally dribble out to an exhaust chamber. Because the oil's forces about the piston cancel, operation is more balanced. But more importantly, initial deceleration is lowered.

The buck stops here

Moving objects possess kinetic energy; the heavier the object or the faster it travels, the more energy it has. Because kinetic energy increases exponentially with velocity, free-falling vertical components and other fast applications are particularly challenging for shocks. On traditional units, the resulting forces break down the oil, causing vibrations within the shock absorber that shorten useful life.

Designed by Zimmer GmbH (with North American operations at Intercon Automation Parts, Inc., Ontario, Canada) the spiral-cut shock absorber's laminar flow makes for smoother damping. A uniform, hydrostatic slide bearing is formed between the piston and tube, keeping mechanical strain on the oil low. The sliding film, as it symmetrically separates the moving elements, increases the operating life of the shock. The diminishing groove lowers the required braking power, with quick damping cycles produced over short strokes. The space between piston and bore governs the shock absorber's response rate and damping behavior.

Called the PowerStop, the shock absorbs up to 300% more energy than a conventional shock. This makes it suitable where space constraints are an issue — for example, in pneumatic pressure chambers. Offered are diameters of M6 to M45, strokes to 50 mm, and energy absorption to 3,000 Nm. Units designed for emergency stops are not suited for constantly recurring loads, but provide high energy absorption at optimal damping behavior — from low speeds at big masses to quick speeds at small masses.

For more information, visit, call (705) 727-7801 or e-mail the editor at [email protected].

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