Precision bearing manufacturer Schaeffler has developed an angular measuring system suitable for direct-driven, highly dynamic, high precision rotary axes in machine tools. The system incorporates an inductive (absolute) angular measuring system integrated in a rotary table bearing.

The principle of integrating the SRM measuring system into a rotary table bearing was successfully implemented in Schaeffler’s YRTM range of bearings, but has now been developed further. The SRM measuring system combines high measuring speed and measurement accuracy with a reduced design envelope and increased robustness. The system is insensitive to contamination (e.g. lubricants and coolants), offers a rotary axis with an open centre (freeing up space in the centre of the machine) and reduces alignment errors. With fewer mechanical components, the system is also easy to replace and maintain.

The new YRTSMA bearings from Schaeffler can be fitted to the rotary axes as an alternative to optical angular measuring systems. YRTSMA bearings are available with bore diameters from 150 mm up to 1030 mm.

High measurement accuracy

By fitting the YRTSMA bearing to the rotary axis, information about the absolute angle is available immediately after switching on the machine. With an incremental measuring system, the absolute position cannot be found until a reference run is carried out after switching on the machine. Knowledge of the absolute position is critical if there is a risk of collision between the tool and the workpiece (e.g. collision of projecting edges) during the reference run. This system is therefore typically used in milling head applications.

The measuring scale of the YRTSMA series is positioned directly on the inner ring. Due to the excellent radial runout of the measuring scale, which is manufactured in high precision bearing steel, a second measuring head is not required. By using only one measuring head, the overall design envelope is significantly reduced, without adversely affecting system performance.

Due to the inductive measuring principle, YRTSMA bearings are even less sensitive to rolling bearing grease and contaminants that are normally present in harsh machine tool rotary table applications. The free space in the centre of the axis can still be used for mounting other machine ancillary components. The electronic evaluation system is integrated into the measuring head so that the system can be connected directly to the machine tool control system. The measuring head is effectively sealed off from the adjacent construction and is designed to be screw mounted to the bearing, which means it is positioned at the correct distance from the measuring scale at all times, without requiring any adjustments. The measuring head is easily accessible and can be replaced without additional setup if required.