was capable of high rotational speeds. Although they contained fewer balls in the bearings, they also had excellent running life. 

The history of the needle bearing also reveals how the quality improved through the use of retainers. Balls at their point of contact slip against each other in opposite directions. This contact slip is at twice the speed of each balls rotation. The slip results in severe wear, louder noise, and a shorter running life.  The massive pressures and metal-to-metal slip between the balls will also break down the oil film which breaks down at 3kg/mm² of surface pressure.

Alternatively, retainers and balls contact each other, which prevents the break down of oil and provides for quieter operation, high rotational speeds, and longer running life.

Full Ball Type vs. Present Bearing with Ball Retainers

In the first stage of development 

(Full ball type)

Full Ball Type 

• Adjacent balls contact each other at a point. As a result, the contact stress is large and the oil film breaks down due to friction.

• The life becomes shorter.

Present bearing
(with ball retainers)

Present bearing with ball retainers

• The life is extended due to the absence of friction.

• Heat generation during high-speed rotation is limited due to the absence of the friction between adjacent balls.

• The balls do not contact each other. Noise does not arise from the metal to metal contact.

• Balls move smoothly because they are positioned evenly.

• The lubricating oil retained between the balls provides excellent lubrication and long life.

Conventional, Full Ball LM Guide

The Revolutionary Ball cage Design

Advantages of THK's Caged Ball

Low Noise: The balls, retained by the ball cage, do not contact each other.  Thus, the guide runs without metallic noise, which provides for low running sound levels: less overall noise.

Type SHS has ball-circulating sections made of resin molded in the block. This structure eliminates metallic noise caused by balls contacting the block. The employment of ball retainers has also eliminated metallic noise produced by balls hitting each other. Thus, type SHS operate quietly even at high speeds. In addition, the ball retainers are effective in preventing balls from rubbing against each other, resulting in low heat generation and a super high speed performance.

Maintenance-Free Operation: Adjacent balls, retained by the ball cage, do not rub against each other and produce friction.  As a result, the balls are not subject to wear and particle generation.  In addition, the grease retention has been enhanced, providing long-term, maintenance-free operation.

In fact, tests have been run in which the new bearing design has lasted 28,000 Km on the initial shot of grease.  Compare this to the lubrication interval of a convention linear guide which is 100 km.  In most cases, this eliminates the need for lubrication or forced lubrication systems.  This results in a tremendous reduction in machine building costs and a positive environmental effect as well.

Non-Caged (Ball to Ball Contact)

Non-Caged:  Subject to high bearing stress due to point contact.  This high stress breaks down the grease film and generates particle as the balls wear against each other.

Caged Ball: Extremely low bearing stress due to the contact between the ball cage and the balls means the grease film does not degrade and there is no particle generation.  The ball cage also forms a grease pocket, further increasing the life of the lubrication.

Higher Speed and Longer Life: The ball retainers exhibit excellent high-speed performance though reduced heat generation due to lower bearing stress and the 50% reduction in ball contact velocity.  The life of the balls is prolonged due to the elimination of friction and particle generation due to wear between adjacent balls.  Since the balls are separated, there is less of a tendency for the balls to jam up in the block during higher acceleration.  This means that higher velocities and higher accelerations are possible.  While conventionally designed bearings are generally limited to 2.5 G's of acceleration, and 5.0 m/s of velocity,  there are applications running now with caged ball technology at well over 5 G's and 8 m/s.

Low Dusting: Dusting tests have shown that Caged Ball LM Guides generate much lower amounts of dust during use as a results of the elimination of the ball to ball contact.   When ball to ball point contact occurs, high stress occurs in the grease film used to lubricate the balls.  This stress will break down the lube film and steel to steel contact contact will occur.  This contact creates debris as the surfaces move against each other.  The double lip seal that is used on all caged ball LM Guides to retain the grease within the block also provides another level of protection from particles that are generated within the block.  The lower dust generating characteristic makes these types of LM Guides especially suitable for clean room applications. 

Dusting with Non-Caged Type

Dusting with Caged Type

Rolling Resistance and variation reduced by 90%: Metallic noise is suppressed due to the elimination of friction between the balls. Smoother movement with less variation of torque can be obtained since the balls are lined uniformly and circulated without jamming.  This reduction in torque variation results in less overshoot and much more precise movements.

For more information on cage ball technology call Techmaster, Inc. or THK.

Note: The majority of the information on the caged ball technology above was taken from THK's web site.

Convention Bearing 
Rolling Resistance Variation

Ball Cage Design 
Rolling Resistance Variation