A dual drive system for rack and pinion applications requiring very precise positioning and repeatability, system clearance can be eliminated by using two gears - one to drive the axle and the other to "preload" the axle to remove play. Positioning accuracy is maintained during acceleration and deceleration, as well as when changing direction. There are several different solutions to achieve a zero clearance drive system:
The simplest drive system with zero clearance uses a split pinion, which consists of two halves of the pinion and an axial spring packet. The gear halves mesh with the opposite sides of the teeth on the same gear, eliminating play.
One half pinion drives the axle and the other half pinion is "preloaded" to remove slack. The pre-setting of the second half pinion is fully adjustable on the machine by rotating the axial spring packet at the end of the pinion shaft.
The split-pinion shafts mount directly into a High-Torque (HT) & High-Performance (HP) Servo-Worm Reducers.
Another method to remove the backlash at the rack & pinion is to use two motor/reducer assemblies with dual pinions operating on the same rack in a master/slave setup.
One pinion drives the axis (the "master") while the second pinion is "preloaded" to remove the backlash (the "slave"). The preload is created electronically with a special motor controller; these systems can also be set up to drive together during cycle times when backlash is not critical. Dual-pinion gearboxes using only one motor are also possible.
An Automatic Lubrication System is highly recommended for use with these drives, providing continuous grease lubrication to the rack & pinion tooth flanks to preserve the quality and lifetime of the gearing.
These drives are ideal for precise positioning applications such as overhead cranes and columns, milling machines, CNC routers and axial drives. You can also use two reducers / motors to eliminate axial play by electric preload.
In fact, ball screws often provide adequate performance for axle drives that require accurate positioning and repeatability - thanks to low backlash and pitch errors. If necessary, zero clearance can be achieved by using pre-loaded nuts.
The gear and pinions can also provide precise positioning and repeatability. Thanks to the use of hardened and ground tooth sides, low play and pitch error can be achieved; zero clearance can be achieved by using split or double pinion drives.
For drives with long and heavy axles, such as those used in machine tools and the aerospace industry, gears and gears can actually outperform ball screws because their stroke length may be limited by their buckling and whip strength. In high-speed applications, rack and pinion drives can also support higher linear speeds (up to six meters per second) than ball screws.
Gear wheels are a system that uses rollers instead of teeth to attach a rack. These discs are advertised for zero play because multiple rollers are on at the same time. However, these drives require pre-loading of rollers into the cabinet to ensure optimal engagement. This preload can vary up and down depending on the accuracy of mounting the cabinet. If pre-charging is lost, slack may occur; if the preload is excessive, the pinion can generate vibration and noise, and lead to premature failure.
As mentioned, dual drive rack and pinion drives can achieve zero clearance by using a split pinion or a double pinion to preload the axle. The preload is set mechanically (split pinion) or electrically (double pinion) and is always present, regardless of the accuracy of the rack assembly. In addition, in heavy-duty applications, rack and pinion drives may outperform roller drives because they can exhibit lower load capacity and rigidity.
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