What should we consider when applying rack and pinion systems?

●Operation environment

It is important to determine the environment,in which the rack and pinion will operate to determine if any protective measures or other precautions are needed.Since the inherent design is an open gear system,any contaminants that may accumulate in the gear teeth should be considered and avoided if possible.

●Axis travel length

The nearly unlimited travel means that the rack and pinion set is limited only by the manufacturer's ability to mount and align the rack and accompanying guide rail. The use of longer rack pieces,many of which are up to 2 m in length,reduces installation time and provides greater accuracy and easier alignment over long distances. For shorter runs,standard 1-m,0.5-m and custom cut lengths are also readily available.

●Axis weight being moved

In a fixed -rack system,carriage or gantries usually move along the rack and carry the load with them.Both the structural weight and the load weight(if combined)need to be determined to calculate the torque required to move the load.

●Axis orientation

Innon-horizontal applications,the additional force caused by gravity must be considered.In horizontal applications,friction is a necessary additional factor.In some cases,whether the tooth connection is at the top,bottom,or side of the mounting rack is also a relevant consideration.

●Load support

Up to a third of the linear force can be seen when helical cutting rack is used.The guide system must be able to accommodate this.Therefore,linear guides should be specified not only to withstand the weight of the load,but also to resist the side force of the gear connection reaction.When using a straight rack,there is no side force.This may allow other guide systems,such as rollers,to be acceptable.The helical cutting rack has several advantages,such as higher force capacity and quieter operation.Therefore,consider the application requirements before choosing a rack type.After the guide type is selected for the selected rack,the guide friction coefficient is conveyed.This is necessary to calculate the required driving torque.

Special rack designs allow direct mounting of linear rails for precise alignment.

●Acceleration and speed

Like all motion applications,faster inertial acceleration and deceleration requires more torque,which can lead to larger systems.Slower acceleration rates,while requiring less torque,may require faster running speeds to get into place in time.Optimizing the acceleration and running speed of the motion curve can reduce the size and cost of the input driver.One of the outstanding advantages of the rack and pinion is that it can cover distances quickly.This provides a great deal of flexibility in configuring the motion profile.

●Axis duty cycle

This is the number of operations or movements of the system,usually measured in hours per hour and hours per day.While there are certainly service factors to consider when choosing rack and pinion sizes,it is even more important for lubrication intervals and drive kits,especially where gearboxes are involved.All rack selection assumes proper lubrication.In applications where pinion gears are moved and placed for long periods of time,regular manual lubrication may be sufficient.But as the number of cycles increases,so does the frequency of lubrication required.

Refillable automatic "smart" lubrication systems are readily available to measure grease at appropriate amounts and intervals for each application.Gearhead life is more sensitive to start and stop torques.The period is the key factor in choosing the period.

Automatic lubrication systems are available to minimize maintenance intervals.

●Position accuracy

This is related to the required positional accuracy or allowable deviations at various points along the length of the stroke.The drive system is excluded,which is mainly affected by the pitch error of the rack and pinion teeth.Higher pitch errors lead to lower predictability of position control.A lower pitch error will increase predictability.

●The input drive system

This involves how to drive the rack and pinion.In most automation systems,servo motors will be chosen because of their controllability.To increase mechanical advantage and reduce load inertia reflected back to the motor,some kind of gear box is usually added.This can be a planetary inline design or a right angle servo worm.Each has its advantages.In either case,choosing the right gear ratio can have a significant impact on the cost and performance of the motor and drive.A high gearbox transmission ratio will slow down the system speed.Too low a ratio would require larger,more expensive motors and drives.

Click to select ALM high quality linear motion components for your application:

www.autolinearmotion.com/products.html