The development of modern robots tends to be lighter. For bearings to be installed in a limited space, they must be small and light, that is, lightweight. But at the same time, the high load, high rotation accuracy, high running stability, high positioning speed, high repeat positioning accuracy, long life, and high reliability of the robot require the supporting robot bearings must have high load capacity, high precision, high Stiffness, low friction torque, long life, high reliability performance.