High speeds and accelerations, uneven loads, or vertical orientations in crossed-roller rail-guide applications can cause "cage creep," or cage and roller assembly migration. In most cases, as the cage shifts toward one end of the travel, it gradually moves from its centered position until it hits an end stop. As system friction increases at the stroke limits, the rollers tend to skid during operation.
A centered pinion gear rotates during operation as it meshes with internal rack gears on each rail, positively controlling roller cage-position.
To solve the problem, a machine typically must be shut down for a recalibration stroke, which may require larger than necessary motors, with enough power to reset the cage to the centered position. External type rack-and-pinion systems and internal wire and pulley techniques have been used with limited success to prevent cage migration. However, wire-based solutions can slip or succumb to fatigue, while external pinion wheels have a size penalty.
The patented Anti-Creeping System (ACS) positively controls roller-cage position without a size or cost penalty compared to other techniques, although there is a cost premium compared to a standard cross-roller system. Designed as an internal drop-in component, it uses a rack-and-pinion mechanism that fits within the existing design envelope of a standard crossed-roller system.
Wayne Greer, SKF Motion Technologies, 1530 Valley Center Pkwy., Bethlehem, PA 18017-2226; Tel: (800) 541-3624; Fax: (610) 861-4811; E-mail: [email protected].
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