Linear motion systems are used in almost every robotic work cell.
The type of system used can be defined by the type of linear motion bearing used.
There are basically three types of bearings utilized-
Plain bearings are generally cylindrical in shape and can be straight or flanged. Friction is generally higher than rolling element bearings but cost is lower. I like to consider two types in my automation projects-
Photo shows the Bost-Bronze oil impregnated bronze bearings. Please click here to visit the Boston Gear website for further information.
As the name suggests, these bearings are self lubricating and in light load applications can make a perfectly sound linear motion system.
This photo depicts the BostonE® plastic sleeve bearing.
With Teflon as their major ingredient, glass-filled bearings are self-lubricating and offer a low coefficient of friction. They withstand extreme temperatures from -400° to +550° F, handle high loads at moderate speeds, and have excellent wear and corrosion resistance. In addition, BostonE® F-1 bearings are machined from extruded rods and held to close tolerances.
As long as the loads are relatively light and if two shafts are used close together, then these bearings can be an inexpensive solution. Stick/slip is high and if two shafts are far apart, then jamming can result.
These bearings consist of an outer ring and several rows of balls retained by cages. Some advantages are-smooth motion, low friction, high rigidity and long life. They are low cost and easy to maintain and replace. Thomson is usually given credit for first producing what is now known as a linear ball bearing. Click here to visit the Thomson Website.
Linear motion systems can benefit from the rolling element bearing, they are more expensive than plain bearings, but friction and stick/slip is low. If the budget will allow, rolling element bearings are a step up from the plain bearing.
Once considered to be expensive, the crossed roller slide is now very economical and available in a wide range of sizes. I have used this bearings in many linear motion systems applications that would be impossible with other types of bearings. When a wide span is required between bearings, the crossed roller bearing is possibly the only choice. It's tolerance to "stick/slip" is very high.
The photo at left shows THK linear cross roller bearings and rails. Please click here to visit their website.
Roller slides offer line contact as compared to point contact when using ball bearing slides. Thus greater loads can be tolerated.
Many pick and place modules use crossed roller bearings.
We are all familiar with the type of slide used in the typical filing cabinet. This style of linear motion system is very compact and can solve some problems in certain applications.
As an example-Accuride International offers a wide range of Drawer Slides.
Photo shows a Schock Metall slide. Visit their site for full information.
Applications can include-
The Dovetail slide has been around for a long time. Generally manufactured from cast iron, they can absorb high loads and can be manually operated or powered.
The photo shows the Setco Dovetail Slide. Visit their website, where full details can be found.
Rather than designing a slide from scratch, I prefer to purchase a ready made module and Setco offer a wide range of units that can generally be adapted to many applications.
We will conclude by mentioning a company that manufactures a very good modular system that is very simple and can have many applications in robotics engineering. This system is particularly suited for the manufacture of gantry robots and linear motion systems.
The photo here shows the Bishop Wisecarver Dual Vee System. Visit their web site, for full information.