Rack and Pinion Drives

Rack and pinion drives use a rotational motor to affect linear motion via a rack and pinion combination. They are used frequently in long-travel applications, such as machine tool table positioning, that require high stiffness and accuracy. There are two gearing configurations for rack and pinion drives: straight tooth and helical tooth. Straight tooth gears contain teeth that run parallel to the axis of the gear. Load movement or transfer is manual or walk-behind. Helical tooth gears provide continuous engagement along the tooth length and are often quieter and more efficient than straight tooth gears. Helical tooth gears resemble spur gears in the plane of rotation, but include teeth that are twisted along a helical path in the axial direction. The American Gear Manufacturers Association (AGMA) publishes quality-level standards for gears based on pitch variation, profile error, and tooth alignment accuracy. Quality levels are defined in the AGMA 2000-A88 Gear Classification and Inspection Hand Book. In general, higher quality levels indicate higher quality gears. For example, AGMA 8 and 9 describe lapped gear teeth. AGMA 10 describes automotive-quality gears with high degrees of strength and dimensional refinement. AGMA 11 describes gears with hardened and ground teeth that are particularly well-suited for rack and pinion drives.  

Selecting rack and pinion drives requires an analysis of performance specifications, preload configurations, and special features. Axis drive force is the maximum drive force for which devices are rated. The rating represents the torque of the motor transmitted through the pinion to the rack. Axis weight rating, another important performance specification, is the rated weight for the driven axis. There are three preload configurations for rack and pinion drives. Split pinions contain a torsion spring or other anti-backlash mechanism that enables the pinion to load both sides of the rack simultaneously. Mechanical preloading consists of a drive pinion and a second preload pinion and gearbox. To maintain preloading and eliminate backlash, the preload assembly applies an opposing force to the drive assembly. Electrical preloading consists of a drive pinion and motor, as well as a second pinion/motor assembly that applies an opposing or braking force. The opposing motor can take over during deceleration, smoothing carriage stops and reversals. In terms of special features, rack and pinion drives with an integral rack and rail include teeth that are machined or ground directly onto the moving element to increase power transmission efficiency. With ground teeth, the gearing features hardened teeth that provide a precise fit and smoother operation.

• Basics of Configuring Drives
  The key to many motion applications is in sizing the drive components lying between the motor and load. Here are the basics. • The overall design determines basic drive mechanisms....
  (read more)
• A Better Belt Drive
  If you think belt drives have too much slop for your precision linear motion applications, think again. Bell-Everman Inc., a specialist in high-accuracy motion systems, has come up with a new kind of...
  (read more)
• Nexen Roller Pinion System -- A White Paper
  Competitive market pressures are pushing machine builders to design machines that are faster, more precise, and require less maintenance so they are more productive for their end users. In pursuit of...
  (read more)

Pages: 1 - 3 of 200