# Rack and Pinion Drive

A rack and pinion drive is a linear actuator that includes a circular gear as a helical pinion gear that meshes with a linear gear as a rack gear and converts rotary motion into linear motion. Racks are simple but profiles pieces and the move of racks is used in a various ways. This is the transition of the power source mechanism, driving the helical pinions to rotate and causing the rack to be driven linearly. The pitch of the racks is one of the important parameters.

Mechanically, the linear drives of the rack will cause the helical pinions to be driven and rotated. Rack and pinion drives can use both spur and helical gears. The helical gear was preferred because it runs quieter and has a higher load bearing capacity. The maximum force that can be transmitted in a rack and pinion mechanism depends on the pitch and the size of the helical pinions gear in the structure. Here is an example, in rack railway, the rotation of the helical pinions mounted on the locomotive meshes with the rack placed between the tracks and helps to move the train along steep slopes. Generally, the basic rack is the contour of a conjugate gear with an infinite pitch radius. Racks’ pitch is the mechanical variable that shall be taken into considerations.

## Rack Railway

Rack and pinion drive can be divided into several parts for further discussion. The drives are based on specific conditions such as the pitch of racks. Speaking of the structure of the rack railway, this is the mountain railway, which uses the rack built in the center of the track and the helical pinions gear on the locomotive as its mechanism. With this configuration, in contrast to conventional railways that rely solely on friction for movement, this allows them to work on steep slopes up to 45 degrees. In addition, the addition of racks and helical pinions provides controlled braking for these trains, and reduces the impact of snow or ice on the rails, thereby enhancing safety and power usages.

In addition, a rack and pinion mechanism with two racks and a helical pinion is used in the actuator unit and the pitch of racks is important. For example, pneumatic rack and helical pinion actuators that can be used to control valves in pipeline transportation. The drives of the machines are designed based on the racks’ specifications such as shapes and pitches. The design of pinions is also related since pinions are the smaller one with specific pitch values. Some actuators are used to control the valves of large water pipelines. In the top actuator, you can see the gray control signal wire connected to the solenoid valve, which is a small black box connected to the back of the top actuator, which used as a pilot for the actuator. The solenoid valve controls the air pressure from the input air line, and the output air of the solenoid valve is fed to the chamber in the middle of the actuator, thereby increasing the pressure as designed.

Regarding valves, for the fluid mechanics industry, the use of pneumatics is a method in engineering that uses gas or pressurized air for further usages.Pneumatic systems used in industry are usually powered by compressed air or compressed inert gas. In terms of machinery, the centrally located electric compressor can be power cylinders, air motors, and other pneumatic equipment. At the time of purchase, the pneumatic system controlled by manual or automatic solenoid valve is selected, usually based on its lower cost, better flexibility or safer structure than electric motor.

## Industrial Applications

Like gearboxes, motors, and pumps, many power transmission units are widely used to facilitate precise movements in industrial operations. The combination of rack and pinion is commonly used as part of a simple linear actuator in which the rotation of a shaft driven by hand or electric motor is converted into a corresponding linear motion as is designed.

In addition, the rack directly carries the full load of the actuator, so driving pinion is usually small in size. As a result, the gear transmission ratio reduces the torque which is required, but in fact, the force and torque may still be very large. Therefore, a very common solution is to use a reduction gear unit immediately before this, in either gear or worm gear reduction mechanism. As far as applications are concerned, racks have a higher transmission ratio, so under normal circumstances they require a greater driving torque than screw actuators.

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