The design analysis of the slewing bearings for industrial robots

Small slewing bearings are indispensable as one of the key components of the industrial robots. Currently, according to the development trend of the robots, modern robots become more and more light-weight, precise and intelligent. This thus require the corresponding slewing bearings have more light-weight structure and more advanced assembling processes. Under usual circumstances, industrial robots have very limited assembling space for slewing bearings. The slewing bearings have to satisfy the functionality needs of the robot host for slewing bearing load rating, stiffness, precision, friction torque,etc. Standard slewing bearings are hard to meet those requirements, whereas light-weight slewing bearings can solve this problem easily.

The features of light-weight slewing bearings

Light-weight four point contact ball slewing bearings are widely applicable in the joints of the industrial robots. Industrial robots slewing bearings usually have two structural types: sealed and unsealed structures. Their steel balls are of large quantity and small diameters, thus can withstand radial load, bi-directional axial load and overturning moments.

The analysis of main parameters

Light-weight slewing bearings use dynamic load rating as the objective function to determine the main parameters. Usually we get the main parameters under certain restraints by optimization. For the industrial robots light-weight slewing bearings, not only the relatively large dynamic load rating is necessary, but also require sufficient stiffness to ensure the positioning precision of the robot host and a relatively small friction torque to guarantee the flexible operation. This thus need the mufti-objective optimization design based on the dynamic load rating, stiffness and friction torque as objective function. We have to find the optimal structure type to match the ball diameter and the ball quantity.

The Analysis of key structural parameters

For the industrial robots light-weight slewing bearings, ring groove curvature radius coefficient, groove position, flange height are main structural parameters. Those parameters need to be considered carefully when designing. Light-weight slewing bearing have very small radial dimensions. Thus to strengthen the support block, it is necessary the width of the support block. Due to the restraints of the seal ring position, to enlarge the width of the support block, this slewing bearing adopt the asymmetric groove position design.

Deformation and stiffness

When the inner diameters are equal, light-weight slewing bearings contain more steel balls than ordinary slewing bearings, thus improve the internal stress distribution, reduce the elastic deformation between the steel balls and the groove,enhance the stiffness of the slewing bearings. Because the light-weight slewing bearings are usually very sensitive to the stiffness of the bearing seat, when designing the bearing we have to carry out a systemic analysis about the shafting of slewing bearing and bearing seat to ensure the functionality of the light-weight slewing bearing.