Posted to News on 7th Oct 2007, 18:27
Why thin-section bearings suit robot applications
RA Rodriguez explains why Kaydon Reali-Slim thin-section bearings are suitable for use in robots, offering considerable advantages over conventional bearing types.
Bearing selection can make a significant difference to robot performance, affecting total robot weight, compactness, cost, payload, reach, power requirements, positioning repeatability and responsiveness.
The inherent design and performance benefits of the Kaydon Reali-Slim thin-section bearings make them a popular choice for robot applications. Aside from their space- and weight-saving potential, other distinguishing features are high bearing stiffness and a large internal diameter to accommodate electrical, hydraulic and pneumatic services.
A single four-point contact bearing is suitable for shoulder, elbow and wrist joints; the bearings are also available with integral gears and mounting holes to reduce the component count and tolerance build-up. This results in maximum accuracy and a simplified design.
Gothic arch
The bearings can accept combinations of radial, thrust and moment loads due to the Gothic arch geometry of the raceways. The ball raceway in each race has two radii that are larger than the ball radius and their centres are offset from the centre of the ball radius; this generates the Gothic arch configuration in each of the raceways grooves, giving rise to the four-point contact on the balls.
Kaydon Reali-Slim thin-section bearings have a radial cross-section that remains constant with bore diameter. As bore diameter increases, they therefore become considerably lighter in weight than bearings with conventional cross-sections.
As a 'rule of thumb', every kilo saved by bearing weight is usually accompanied by almost ten kilos less structural weight. Such weight reductions in mechanical assemblies provide material and drive power economies that can significantly reduce the cost of a robot.
The bearings are available with bore diameters of 20mm to 1m. In comparison, conventional bearings are generally limited to bores less than 200mm in standard sizes. Also, for a given precision class, they are said to be more accurate in large diameter sizes than standard-section bearings because tolerances do not increase as much with diameter.
Turntable bearings
Kaydon Reali-Slim bearings are widely used for light to medium loads at all robot joints, including the waist. When robot payloads exceed 113kg, a Kaydon turntable bearing is a good choice, as it can handle combined loads at the waist without the need for pairs of standard-section bearings. Turntable bearings are suitable for supporting the intermittent rotating loads that occur at the waist of most robots.
A useful option is the Kaydon Reali-Slim TT series of miniature thin-section turntable bearings. These are significantly smaller than conventional alternatives and offer performance advantages; for example, they are significantly smaller, allowing greater design versatility. The smallest bore is 39mm, the largest 152mm and the height only 6mm. Yet, despite their small size, they offer great accuracy. The extended radial bearing cross-section increases rigidity and optional preload or clearances meet application torque or deflection requirements.
