Machine tools are used for machining parts of automobiles, aircrafts, and construction equipment. Therefore, machine tools are called “mother machines,” and are under constant pressure to increase machining efficiency and improve quality of machined products. In order to improve machining efficiency, increase of rotational speed of the main spindles is effective. However, when the bearings run in high speed, the centrifugal force on the rolling elements will increase. Therefore, lightweight ceramics are used for rolling elements to reduce this centrifugal force. 1) Also, for quality improvement of machined products, bearings are required to improve rotational precision and increase shaft rigidity. For improving rotational precision, it is effective to increase the number of rolling elements and improve dimensional precision for inner/outer rings. On the other hand, for higher rigidity of bearings, it is effective to increase the size of rolling elements and raise the pressurized amount. These improvements tend to increase temperature in the bearings; therefore, it is difficult to achieve high speed and high rigidity at the same time. However, for recent machining centers and field-assisted machining, both high speed and high rigidity are desired for space saving and process integration. Technology for fulfilling high speed and high rigidity has been realized by supplying coolant in the spindle (core-cooling main spindle) and a device to adjust running bearing pressurization; however, these methods require complex main spindle designs. 2) To cope with this issue, NTN is developing air cooling spacer technology , which will be able to decrease the operating temperature of bearings by applying cooling air onto the outside diameter of inner ring spacer . This technology can be used to achieve high speed or high rigidity of machine tools, or both, without complicating the main spindle design. In this paper, the performance of this air cooling spacer is introduced.
To satisfy these requirements, particularly from a functionality standpoint, robot arms use technology to determine various conditions in addition to high rigidity, broad operational range and easy operation. Therefore, bearings supporting the robot arms are required to be designed to conform to these technology trends. In this paper, we briefly discuss industrial robots and present the lightweight bearings for robots developed by NTN-SNR.
