A tooth rack and pinion are a type of linear actuator that contains a pair of gears that are transforming rotary motion in a linear motion. A gear wheel called "pinion" meshes with the teeth on a linear "rack" rod called "rack". The rotary movement applied to the pinion causes rack to move relative to the pinion, thus translating the rotational movement of the pinion to linear motion.
Rack and pinion drives are widely used in large portal robots and material transport systems because of their ability to achieve fast movements at long travels. The most common rack and pinion systems in industrial automation consist of a linear gear rack (also known as a "linear gearbox"), a pinion gear (also known as a "gear wheel"), and a gearbox.
The tooth rack or pinion system consists of a linear rack, pinion and gear.
Although the rack and pinion can use straight or helical teeth, helical teeth are often the preferred choice because they provide higher load capacity and quieter operation. Helical gearboxes also have very small tooth pitch errors - in terms of single microns - for very low clearance.
The gear wheel is a proven and true technology that offers reasonable performance over unlimited distances at a low cost. However, it is limited in accuracy, play, noise and vibration; tooth fatigue, maintenance requirements and particle emissions are other problems. Using split or dual rack mechanisms can work around some problems, but this solves problems with increasing system costs and makes other problems worse.
A better solution that solves these problems directly replaces a traditional toothed rack or helical rack with a rotary rack with a drive element consisting of rollers mounted on bearings that engage the linear rack with a modified tooth profile. The gear shaft system thus shaped operates without mechanical clearance and ensures that two or more shafts are always loaded as opposed to eliminating backlash. And by minimizing friction, it converts rotary motion into linear motion with greater than 99% efficiency.
Two words explain how rack and pinion drive systems contribute to productivity - speed and precision. Rack and pinion drives can reach linear speeds of 1000 feet/min. with simple grease lubrication, and this speed can be maintained on any axis length. Gears and pinions are made of different materials and quality levels, offering the optimal balance of power, precision and price in most applications. A complete drive system consists of a rack and pinion, speed reducer, servomotor, and an automatic lubrication system that extends rack life. Since more racks can be added to an existing axis, this modular design allows for simple changes in machine lengths and configurations.
For systems requiring zero backlash, drive gears must be mechanically or electrically preloaded. Achieving precision, in general, demands high stiffness, which minimizes torsional and radial pinion deflections as well as subsequent position errors and vibration. The optimum solution is to cut the pinion into the motor shaft, creating a solid drive element. This allows for the smallest pinion pitch diameter while providing maximum stiffness and minimum deflection.
Rack and pinion drives are available in a variety of materials, tooth arrangements and pitch types (including metric) and in modular packages. One of the most common types uses helical teeth to transfer high pressure forces at relatively low noise levels. Rack and pinion drives are usually used in applications requiring long strokes and high speeds. Linear guides with a ball rail are the basic choice for linear guiding where and when required. Lubrication is usually done by a matching felt shaft, in which grease is metered through the felt and applied to the gears.
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