Tool table bearings integrate angle sensors

A high precision combined radial, thrust bearing designed for machine tool rotary tables and spindle heads has been developed with an integrated angle measuring system by bearing manufacturer Unitec. Available in the UK from factory representative, RA Rodriguez, the new Unitec RTB AMS bearings use an inductive detecting principle. As a result no magnetic field, nor the presence of lubricating fluid or grease, interferes or influences measurement accuracy and the system is therefore understood to be more accurate than others currently available. The system includes a graduated stainless steel scale that fits precisely onto the bearing's washer ring and two sensor heads on the outer ring, sited at 180 degrees to the centreline. During rotation, the sensors detect the slots on the scale and generate a 1V peak-peak output signal to the machine's CNC enabling the angle to be continuously monitored. The scale slots - set at intervals of 1mm - are protected from dirt ingress by a metal cover. This new bearing is available in seven sizes with bores from 150 to 460mm. One reference point is provided as standard but on request several distance-coded reference marks can be specified at any angle from 40 to 15 degrees, depending on bearing sise. The absolute position may be determined by detecting during rotation, the single reference point or alternatively two distance-coded marks. Total accuracy of the system is up to +/-3arc-sec (460mm bore size). With a few exceptions, these new angle measuring bearings are interchangeable with the majority of the Unitec RTB range, as well as some competitor systems