Terminology and Difference from Rotary Bearings 

A linear guide is a machine element that utilizes bearings, which were developed for rotary motion, in order to move heavy objects easily in a straight line. It is referred to as a “recirculating linear ball bearing” by ISO and JIS, and “linear guideway” by the Japan Machine Tool Builders’ Association. THK CO., LTD. calls this the LM Guide (Linear Motion Guide). Other names like “linear motion ball guide” exist, and it is even referred to as a “linear bearing” in the sense that it is a bearing for linear motion as opposed to rotary motion. 

Structure of the LM Guide 

The linear guide largely comprises three components: a mobile carriage, a rail that supports the movements of the carriage, and balls. Linear motion is enabled by attaching a mechanism for recirculating the balls.

THK's LM Guide refers to these parts as the LM block and LM rail.

History of the LM Guide

The history of the linear guide goes back to 1944, when the ball bushing was developed in the United States as the first linear motion rolling guide. The ball bushing contains balls as rolling elements between a cylindrical shaft and sleeve type nut. The balls recirculate with the movement of the nut, which enables infinite linear motion. A problem with the ball bushing was that the load capacity was low because the balls make point contact with the shaft and nut, and the contact surface area is small. In addition, the nut rotates when a moment (torque) acts on the shaft, which means two or more shafts become necessary to keep it from moving out of the travel direction. This presented an obstacle to compact machine design.

The ball spline was developed to overcome these challenges, featuring arc-shaped raceways ground into the shaft and nut. This changed the point contact between the balls and raceways into surface contact, which enables the ball spline to bear larger loads than the ball bushing. In addition, because the balls are contained between the raceway surfaces on the shaft and nut, the nut is prevented from rotating on the shaft. This meant only one shaft was needed to guide linear motion, and it could transmit torque.

The first ball spline had a problem with clearance occurring, and it was the search for a solution that led Hiroshi Teramachi (the founder of THK CO., LTD.) to develop the angular ball spline in 1971. The angular ball spline features protrusions on the nut and shaft raceways to provide angles that press on the balls, which eliminate the clearance that occurred with the conventional ball spline.

Compared to the ball bushing, the ball spline drastically increased the load capacity and provided smoother, clearance-free motion. However, because it was used with the shaft fixed on both ends, there were times when the ball spline could not support its true potential capacity during practical use, so its applications were limited. Then in 1972, Hiroshi Teramachi cut the ball spline nut and used that freed-up space to mount the shaft on a base, thus creating the linear motion ball guide. The world's first linear motion ball guide (linear guide) was the Model LSR. By attaching a base, the ball spline shaft that used to float in the air when both ends were secured was now integrated with the mounting surface as a rail, which eliminated the loss in precision caused by deflection. In addition, the creation of a single block by fixing a housing onto the nut made handling easier because mounting from the top became possible just like it was with the rail. This became the basic form of the modern linear guide. ​

Later in 1973, THK developed the Model NSR-BC by combining the spline shaft and mounting base into the LM rail. Further improvements and combining the spline nut and housing into the LM block led to the development of the Model NSR-BA in 1975.

• 1944 Ball bushing (USA)
• 1971 Angular ball spline (Hiroshi Teramachi, founder of THK CO., LTD.) 
• 1972 Model LSR, the world's first LM Guide (Linear Motion Guide) linear guide (developed by THK CO., LTD.) 
• 1973 Model NSR-BC with combined rail (developed by THK CO., LTD.)
• 1975 Model NSR-BA with combined block (developed by THK CO., LTD.)

Learn More: “LSR Registered in National Museum of Nature and Science’s Database of Materials on the History of Industrial Technology”

Linear Guide Applications

Linear guides play the role of easily and smoothly guiding linear motion while bearing loads in order for machines to operate precisely and efficiently. They are an indispensable part of linear components in devices such as machine tools and semiconductor manufacturing equipment. Recently, they have also been used in railway vehicles, buses, automatic doors, seismic isolation systems, and other consumer fields. ​

Industrial Applications

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  Machine tools

  THK’s linear motion systems contribute to the guide portions that determine the machining accuracy of machine tools.

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  Semiconductor and LCD manufacturing equipment

  THK products are also suited for computers, cell phones, flat-screen TVs, and other cutting-edge technology.

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  Industrial robots

  THK products grant robot joints superior precision, rigidity, and high-speed performance.

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  Transportation equipment

  THK products have been widely adopted in railway vehicles and automobiles, including in critical vehicle components.

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  Construction

  THK products are also used to support heavy loads in outdoor environments covered in water and mud.

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  Aerospace

  THK products designed for use in special environments have been used in everything from fuselage manufacturing equipment to seating mechanisms.

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  Medical and nursing care

  THK products meet the high standard of reliability needed for medical devices with advanced electronics.

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  Other

Everyday Applications 

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  Residences and buildings

  Products that protect lives, property, and livelihoods from the threat of earthquakes

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  Daily life

  Home kitchens that adapt to just the right height

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  Vehicles

  Faster turns around tighter curves

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  Entertainment

  Producing thrills and excitement with both intensity and precision

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  Science

  National Astronomical Observatory of Japan

Linear Guide Mechanism (Linear Motion System)

Linear guide mechanisms (linear motion systems) are used to move or position objects along a straight line with precision. Their main functions are split between guiding and driving elements. In particular, they refer to a system made up of machine elements that utilize rolling technology to move objects accurately in a straight line. The linear guide is one machine component that can be used for the guiding element.

Some of the many other possibilities include ball splines, linear bushings, slide rails, and cross-roller guides.

The driving element can be a machine element that converts torque from a motor into linear thrust, such as a ball screw or belt, or it could be hydraulics, pneumatics, or a linear motor. These components are combined in the mechanism design to achieve the precision, speed, and load requirements for the application. These mechanisms were developed around machine tools in particular, and they have been adopted for use in other types of industrial machinery as well as linear motion parts in consumer fields. "Linear motion system” is a registered trademark of THK CO., LTD. We also provide a lineup of machine elements that utilize the linear motion system to enable other types of motion such as arcs, or to combine linear and curved motion. ​ ​

Linear Guide Characteristics

・Light movement with no clearance

As linear guides are rolling guides, they have no clearance and lighter movements than sliding guides.

・Infinite linear motion is possible

Rolling guides such as cross-roller guides and ball guides have finite strokes, but the linear guide’s balls recirculate endlessly, which means that the stroke can extend to however long the rail is made.

・High permissible load

The linear guide's raceways are curved grooves, which provide surface contact between the balls and raceways. This makes the permissible load about 13 times greater than that of guide components with point contact, such as the linear bushing. As a result, a linear guide can achieve a similar permissible load as a point-contact type through a more compact design.

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