|The inner race of a "rolling ring" bearing is specially contoured to form a central "ridge" which runs around the entire inner race surface of the bearing.|
When mounted on a shaft of rolling ring drive, a rolling ring bearing contacts the shaft only on the apex of this central ridge. The bearing may be "pivoted" left or right on the shaft, and still maintain point contact with the shaft.
In a rolling ring linear drive, an assembly of three or four rolling ring bearings is fixed and compressed within a housing. A smooth, threadless shaft is inserted through the housing, and through the rolling ring bearing assembly.
When the rolling ring bearing assembly is angled on the smooth shaft, and the shaft is rotated, compression against the central ridge surface is generated causing the bearings to "roll" along the length of the shaft.
The rotary motion input provided by the motor-driven shaft is thereby converted to linear motion output. The housing, which bears the payload, moves along with the rolling ring bearing assembly.
The angle of the rolling ring bearing assembly, relative to the shaft, determines travel direction and pitch (distance traveled per shaft revolution).
No backlash -- Advantage over precision ball screws
Backlash is inherent to ball screw design. It results from the amount of clearance between the ball bearing and the threads.
|Backlash is caused by clearance or "play" between contacting surfaces in ball screws, gears, belt drives and other linear motion devices.|
To overcome backlash, ball screw users typically preload the nut to keep the balls under steady pressure. Other methods for fighting backlash include active cam mechanisms, shims and other devices which load the geartrain. These methods can be expensive. And their performance level deteriorates over time due to wear and tear.
Okcoil rolling ring drives require no preload to eliminate backlash. Rolling ring engineering assures continuous point-contact between the rolling ring bearing surface and the shaft. There is no "play" and virtually zero backlash - even during reversal. Additionally, rolling ring drives ( trvaverse units) have built-in overload protection. If the system is overloaded, the nut will slip, not jam.
Ball screws can't match these features. And ball screws require a significant, up front investment to reduce of backlash before the system can be used for precision linear motion control work.