Sliding contact linear motion bearings
This type is the oldest, simplest, least expensive way, and it still has wide range of applications. In general all sliding contact bearings have greater friction coefficient than other types described hereunder, and because of this, they are considered to be inferior to these guides for precise positioning applications. With lubricant forcibly maintained between two relatively moving objects, a relative speed helps to pull in lubricant, and thereby, a thin film is formed.
Rolling element linear motion bearings
This type decreases friction utilizing rolling contact via rolling elements (balls, rollers, etc.) that are placed between two relatively moving objects. There are many specialized manufacturers and each manufacturer provides wide variety of products. Because of its superiority over the sliding contact linear motion bearings as described hereunder and because of its availability, this type has won the position as an essential component for the equipment that requires highly accurate positioning operation.
Hydrostatic or aerostatic linear motion bearings
When extremely accurate and quiet operation must be attained, a guide without mechanical contact between its elements is often chosen. With pressurized fluid forcibly supplied between two relatively moving objects, one of them is kept floating by the fluid. Depending upon the fluid in use, it is classified in aerostatic and hydrostatic linear motion bearings. Although this type of guides is very advantageous for particular purposes, it is usually costly, difficult in manufacturing, and requires expensive auxiliary apparatus. Yet, this type is sometimes used for ultra-precision machines.
Magnetic linear motion bearings
By means of magnetic force, either repelling or attracting, one of the two relatively moving objects is kept afloat. Use of electromagnet makes it costly and ineffective in energy consumption. This type has very limited applications. Although numerous sliding contact linear motion bearings have long been used, their positions are being quickly replaced by the rolling element linear motion bearings. This is because the sliding contact bearings have the following disadvantages for today’s needs for high speed, high precision, high quality and long term maintenance-free operation
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