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Rolling-ring drives are friction drives that convert the constant rotary motion of a plain shaft into a traversing action that moves an attached carriage. Used in positioning and reciprocating linear-motion applications, rolling-ring linear drives are mechanical alternatives to electronically controlled linear-motion drive systems.
Rolling-ring drives run on a smooth, unthreaded shaft. The rotary input of the motor-driven shaft is converted into linear output by the action of specially machined rolling-ring bearings. The mechanism generating the linear output is friction between the rolling-ring bearings and the shaft.
Rolling-ring drives come in both fixed-pitch and variable-pitch models. Fixed-pitch versions operate more or less as threadless screws. These drives handle incremental positioning and PLC-controlled operations such as in metrology machines. The required controls are similar to those in conventional screw-based drive systems.
For many applications, however, variable-pitch rolling-ring linear drives eliminate the need for electronic controls, as pitch can be precisely adjusted and even set to zero. Travel direction and linear speed are mechanically controlled independently of the motor. This simplifies both design and operation of the linear-motion system. Variable-pitch rolling-ring drives are used in reciprocating linear-motion applications such as ejecting, cutting, spraying, and winding.
Rolling-ring drives hold several advantages when used in appropriate applications. These include:
Long lifespan (10 years or more) when load is properly supported and coupled to the drive unit.
Automatic reciprocating linear motion without complex controls.
Variable traversing speeds ranging from 0 to 4.2 m/sec. Speeds can also be separately set for each direction, even though shaft-rotation speed is constant.
Variable traverse length and position.
Near-instantaneous, automatic reversal without changing drive-motor direction.
Low operating and maintenance costs.
HOW THEY WORK
In either fixed or variable-pitch rolling-ring linear drives, the drive unit sits on a smooth, unthreaded shaft. High-quality drives use only induction-hardened, ground, and finished steel shafts with minimum surface hardness of 50 Rc, diametral tolerance of h6, concentricity tolerance (ISO 1101) <0.1 mm/m, and surface roughness Ra...