THK Linear motion guides have progressed significantly since the 1950s and development closely followed increasing automation of industrial processes to meet demands for accurate and repeatable movements and cost-efficient operation.
Linear motion guides are, in essence, transport mechanisms on which machinery and components can be moved or positioned to perform specified tasks. THK guides have a minimal operational footprint and can be configured to meet different criteria to provide high levels of rigidity. A variety of possible options allow utilisation on level surfaces, vertical planes, inverted positions and inclines.
Linear motion systems are available in miniature, rotary, high-load, caged-ball, caged-roller and ballspline type guides and are engineered for smooth, efficient movements for accuracy with adaptability, versatility, high-speed performance, low-noise and compact designs for machining centres, medical equipment, measuring instrumentation and industrial robots.
Control technology advances have encouraged dramatic development in linear motion technology and the modern circular-arc design centres on a two-point contact construction between the carriage and the raceway.
Quite different from the gothic-arch principle, or the ball-bushing technology of some early linear motion devices, the later design is capable of self-adjustment, high capacities and consistently low friction. As the design compensates for the elastic deformation of the balls, deviations in the installation's surface can be absorbed ensuring smooth movement without excessive forces.
This design also significantly reduces differential slip, which equates to the differential between the circumferences of the inner and outer surfaces of the ball in contact with the raceway. With the conventional gothic-arch design, each ball was in contact with the raceway at four points, circumferential differences were generally larger, causing increased slippage. The circular-arch design, with only two contact points in the loading direction, reduces differential slip, thereby increasing possible load ratings, facilitating a smoother rolling motion.
Load ratings are determined through extensive testing on life-test machines, during which products undergo thorough dynamic load trials. These tests reveal how linear motion guides perform over extended periods and provide an indication of expected life-cycle maintenance requirements. THKs' investment in life-test facilities paid dividends and recent trials by THK in Japan established that THK's Caged Ball system has a greater dynamic capacity than initially estimated.
Factors such as noise reduction and compliance with EU directives are fuelling new engineering solutions and near-silent guides have been developed, many with THK's Caged Ball technology, which incorporates a flexible ball retainer that prevents ball-on-ball contact for significant noise reduction.
This concept guarantees that the linear guide's rolling elements are equally spaced and that the system's lubricating grease is retained between them. This enables smooth, high-speed ball circulation with significantly reduced heat generation and minimal wear. The impact of modern linear motion designs has been apparent in a number of sectors, especially in the expanding food-processing industry, where speed and accuracy are prerequisites.
By incorporating a non-contact mechanism that eliminates ball-to-ball impact, the Caged Ball design offers the potential for near maintenance-free performance as each ball is held in a position equidistant to its neighbour by a retainer. A grease pocket is formed in the space between the ball and the retainer, ensuring that the ball is subjected to a continuous film of lubricant. This configuration not only reduces ball-to-ball contact and therefore ball wear, but extends maintenance intervals by reducing lubricant usage.
This is an important feature of many modern linear motion systems as it has a direct impact on long-term maintenance costs, downtime and ultimately, profits. SKF South Africa is the sole distributor for THK's range of Linear Guides throughout sub Saharan Africa and is also responsible for after sales service and technical support.
For more information contact Graham O'Donoghue, SKF South Africa, +27 (0) 82 565 3189, [email protected], www.thk.com
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