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THK Co., Ltd.: Linear Motion Guide

Outline

With machine tools, where one object is required to move in a straight line above another object, it was common practice until now to use lubricant between the two objects to allow them to slide over one another. However, this method results in a layer of lubricant between the two objects, thereby creating a gap. The gap can then cause misalignment during processing, resulting in a decline in accuracy.

The LM Guide, developed by THK in 1972, was a revolutionary piece of technology that improved accuracy in linear motion processing. Key to the LM Guide is the use of a rolling motion to facilitate linear motion.

This mechanism has significantly improved the functionality of mechatronics equipment, facilitating enhancements in accuracy, speed, and low power. It is now used in many products that are part of our everyday lives: liquid crystal production lines, train carriages, vehicles for disabled persons, medical devices, high-rise buildings, and home, and amusement equipment.


Toward the Realization of Commercially Viable Rolling Technology

You may well have seen murals, the remains of ancient civilizations, which depict people carrying heavy loads by rolling them on rollers placed under the load. The principle behind the LM Guide is much the same, only considerably more precise.

Machine technology using this rolling principle was developed for rotary motion well before it was applied to linear motion; namely the bearing, developed about 100 years ago. But for linear motion, although the potential benefits of using rolling technology for linear motion was understood, the development and commercial launch of any such technology showed little progress.

Problems related to the use of linear motion in machinery mechanisms included difficulty in expressing rolling motion in linear rather than rotary motion, and the need to account for motion in every direction rather than just one. There were many other issues to consider: cost, product lifetime, ease of maintenance, and low energy.

Since its establishment in 1971, THK has worked to develop unique technology that has allowed it to produce and commercialize rolling technology for linear motion; in 1972 it succeeded in developing the LM Guide, which maximizes the benefits of using rolling in linear motion. This was the first such product anywhere in the world. Utilization of the LM Guide in industrial machinery makes it possible to achieve extremely precise processing; in semi-conductor production equipment, processing can be carried out at the sub-micron level. This kind of figure is revolutionary compared to the level of accuracy achievable by conventional machine processing.

Today, linear motion bearings are being produced by other manufacturers, but the LM Guide is a THK registered trademark and its position as the pioneer in this field is undisputable. The company continues to develop and produce; as of March 2011 it holds 759 Japanese patents, and 1251 overseas patents (including patents pending). The world share for THK’s LM Guide is estimated to be around 70% in Japan, and 60% worldwide.


Caged Ball LM Guide: SPR/SPS Models

In Caged Ball LM Guides, the balls (which perform the rolling function) are contained within a ball retainer, in which they rotate. The retainer, or ball cage, prevents the balls from touching each other, thereby eliminated friction between the balls. This allows the guide to function uniformly and in alignment.

Moreover, the space (grease pocket), between the ball rotator and the ball retainer, in which lubricant becomes collected is drawn onto the contact face, thereby forming a layer of lubricant on the surface of the balls. For this reason, the risk of the lubricant layer drying up is significantly reduced, helping to maintain smooth rolling operation and lessen friction.

The SPR/SPS models, developed in 2010, are high-precision guides with low waving, at just one tenth that of previous LM Guides. The deformation volume of the balls has been minimized, and ultra-high rigidity has been achieved. These models have a larger number of rolling rows than previous models, and the balls are extremely small, enabling an increase in the number of effective balls and facilitating smooth operation. 

It is no simple task to develop and manufacture products to this level of precision. It should be clear just how special THK’s technology actually is. Special enough, indeed, to command an impressive 60% share in the global market.

The name THK comes from three key words: Durability (Toughness), High Quality, and Know-how. Machine equipment must be precise, rigid, and quick. The durability and high quality of the machine equipment that supports the world’s industries is down to the application of many years of know-how, as well as the pursuit and provision of ever better technological solutions. It is doubtless that THK will continue to be at the forefront of innovation in this industry.

16 March, 2012

About the author
Hiromi Jitsukata is a reporter for Japanest NIPPON



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(THK Co., Ltd.)