Increasingly competitive markets make efficient and accurate processes more critical than ever before. To meet the demands of manufacturers, machine builders are constantly searching for new methods to design faster, more precise, and longer-lasting systems that will facilitate increased productivity.
For many motion control applications, this often includes a linear drive system based on ball screw, belt drive, linear motor, or traditional rack and pinion technology. While these systems offer unique features and advantages, they are susceptible to limitations, including low accuracy, speed and efficiency, as well as high noise, vibration and maintenance.
For high-precision applications, a roller pinion system can be used to provide linear positioning boasting accuracy within half the diameter of a single human hair — and no backlash. Featuring a unique roller pinion/rack combination, these systems can be simply installed in a broad range of motion control applications, delivering superior accuracy and longer life than most alternative linear drive systems.
Teeth and Rollers
Traditional rack and pinion systems comprise a toothed circular pinion that engages teeth on a flat rail, referred to as the rack, to convert rotary to linear motion. Roller pinion systems replace the teeth of the circular pinions with bearing supported rollers that engage a unique rack tooth profile — a partnership which allows smooth rotary-to-linear motion conversion at greater than 99 percent efficiency. The reduced friction results in near-silent operation, unparalleled smoothness and significantly less wear on the system, delivering longer functional life — even at extremely fast speeds.
The system also differs from traditional rack and pinion systems in that two or more rollers are in contact with the opposing rack teeth at all times, resulting in zero backlash. The rollers approach the tooth face in a tangent path, smoothly rolling down the face to minimize tooth slap that causes noise, vibration, or tooth fatigue in alternate linear drive systems.
High Accuracy, Stiffness
The innovative meshing action of roller pinion systems provides positional accuracy of up to ± 30 μm (±0.00118 in.) at speeds up to 11 m/s (32 ft/s), with backlash of less than 3.2 μm (0.00013 in). Each tooth profile is precisely measured relative to the first to maintain high positional accuracy and eliminate cumulative error. A robust tooth profile and large bearing surfaces contribute to excellent system stiffness, surpassing that of ground ball and roller screws.
Roller pinion systems additionally reduce wear due to their durable construction. The rolling action of the mesh ensures that, as the pinion engages the rack, the bearing supported pins smoothly roll across the face of the teeth. This highly efficient design minimizes impact on the conjugate surfaces.
Additionally, the roller pinion system may include a Raydent® surface treatment that permeates the metal surface and molecularly bonds with the steel, forming a ceramic chrome layer with minimal surface buildup. The resulting surface is highly durable and provides excellent resistance to corrosion. This surface treatment, combined with the efficient rolling motion, allows for minimal or no system lubrication at speeds below 0.5 m/s.
The low lubrication requirements lend to low particle emissions, delivering an ideal solution for clean room, food processing, pharmaceutical and additional applications. It also means that contaminants are less likely to bond to the rack, reducing the system wear the contaminants could potentially cause — especially in dirty environments common to cutting, milling, routing and other applications.
The smooth engagement of the rack teeth by the rollers allows nearly silent operation at low speeds and less than 75 db at full speed. This noise level is much lower than ball screws that feature re-circulating ball paths, as well as traditional rack and pinions, which are subjected to loud tooth slap. In addition to improving work environments for personnel in the area, the lower noise and vibration levels reduce interference that could negatively affect the accuracy of sensitive sensors and encoders.
Segmented racks are available in varying lengths, allowing for simple integration and unlimited linear travel. Standard lengths may be cut to accommodate custom requirements.
A flange mount pinion and pinion preloader can be used to simplify the integration of the roller pinion system into a machine design and give superior pinion preload and meshing geometry results. High precision surfaces and an adjuster allow the pinion to be positioned up or down into the rack, while maintaining proper pinion orientation to the rack. This feature significantly reduces the tendency of the servo drive to tip when moving the pinion into the rack.
With flexible and simple mounting options and an innovative roller/rack design, roller pinion systems can be simply integrated into linear motion control applications to provide greater system efficiency and reliable operation.
This article was written by Al Conway, RPS Product Manager for Nexen Group, Vadnais Heights, MN. For more information, please contact Mr. Conway at