Motion control is essential for the digitization and automation of high-tech equipment, but bearings remain basic to frictionless movement. Bearing Engineers, a bearing distributor, recently changed its name to Motion Solutions (Aliso Viejo, CA) to better reflect their evolution into a custom designer of motion solutions for high-tech electromechanical systems. Developing custom solutions has lead to developing lines of proprietary products that the company manufactures in-house.
A company came to Motion Solutions seeking a better linear motor table for positioning laser surgery equipment. The customer’s Lasik eye surgery equipment was not performing smoothly enough, and its running parallelism was not up to their standards. The problem was being caused by linear bearing cage slippage. Though positioned horizontally, at full operating speed, the bearing retainer would creep as the momentum of the bearing movement was transferred to the cage (also called the retainer). An anti-cage creep mechanism was the logical solution.
The term “anti-creep” is used to describe the method of eliminating any slippage of the retainer holding the crossed rollers between the two V-grooved rails of the slideway. In addition to maintaining precise movement, without creepage, downtime is reduced, lowering the cost of maintenance.
An anti-creep device eliminates this creeping of the retainer so the slideway can be used in any mounting direction and with lower-momentum motors such as linear motors. Several complex anti-creep devices have been developed. To prevent cage creep/ slippage, manufacturers have used a few different approaches such as a rack and pinion mechanism, an external attachment made of plastic gears outside of the rail, and a metal gear inside of the rail. Some of these devices are quite expensive.
After comparison tests, one mechanism was chosen that does not use a gear. The STUDROLLER™ anti-cage creep mechanism from NB Corporation of America (Hanover Park, IL) uses a roller with round balls studded around its surface. It has the smoothest tracking motion and therefore is quieter than an externally attached toothed-gear anti-creep device. In this mechanism, creep is prevented because the raceway has depressions that track the studs or nodules, preventing slippage in any position.
By placing studs in the center roller and machining a path along the rail, the retainer will never slip. It is suitable for high acceleration, vertical or horizontal mounting, and uneven load distribution.
Motion Solutions saw that the improved linear motor table held promise as a proprietary product. However, they had commercial concerns, including cost, which varied for crossed roller bearings with anti-creep mechanisms depending on the complexity of the design and whether the application has to be custom-designed to accommodate them. Since the NB device uses a studded roller, as opposed to a gear or exterior control, the cost is almost the same as a standard slideway — almost half the cost of other anti-creep devices, and there are no redesign costs to replace a standard slideway.
The product lowered the customer’s cost by 17 percent, and Motion Solutions was able to establish processes that would shorten the lead time to between two and three weeks. The linear motor table — which initially was incorporated into Lasik eye surgery systems focusing optics and lasers on the eye — has a demonstrated level of precision that can be used for other applications. It’s suitable for any positioning equipment that demands high tolerance and repeatability in the medical, life sciences, and semiconductor manufacturing industries. Successfully meeting the challenge has led to the development of a proprietary line of precision positioning tables that also meets the demanding requirements of liquid crystal-related equipment, measuring instruments, assembling systems, and material transfer equipment.
The Motion Solutions Linear Motor Table is powered by an iron-less core linear motor. The smooth, non-contact drive system prevents force ripple (attraction force or cogging). Designed for high-speed positioning, the linear motor tables allow speeds up to 2,550 mm/second. A compact, lightweight aluminum alloy enclosure houses a linear encoder that positions down to 10-nanometer resolution. Each encoder is customized per a client’s needs. They can choose from four motor sizes, three base length options (84, 168, or 210 mm), and encoder resolutions from 5 microns to 10 nanometers.
This article was contributed by NB Corporation of America. For more information, Click Here .