An expanded series of angle encoders works on slew bearings and provides higher accuracies than previous models. Hollow-shaft ERA circular encoders from Heidenhain Inc., Shaumburg, Ill, (heidenhain.com) are said to come with high accuracy, several mounting methods, and reference marks that can be coded for semi-absolute positioning.

The newest addition, the ERA 4×80, mounts using a centering collar. The manufacturer says this low-profile encoder does not require complex centering methods because a centering collar mates with a precision-machined shaft of the motion system. A 20µm grating period on seven diameters provides system accuracies from ±6.1 arc-sec on the smallest diameter to ±2.8 arc-sec on the largest.

The T-profile ERA 4×81 is light weight and mounts using three-point centering. Three centering marks on the ring at 120° intervals point to the exact center of the ring. Accuracies of ±8.6 arc-sec are possible with the smallest diameter and ±2.8 arc-sec for the largest. A third and larger encoder also uses the three-point centering and has accuracies from ±5.1 to ±2 arc sec.

All three use the same scanning unit and a movable faceplate which maintains position despite machine vibrations.