. Introduction

　　This guide will explain a number of phenomena that occur when using angle encoders andtherefore explain the benefits of the RESR encoder ring.

　　The RESR offers high accuracy combined with ease of use. Specifically， the modular formatof the RESR with no contact between the readhead and encoder ring， results in a friction-freesystem that does not suffer from the various mechanical hystereses that affect sealed

　　encoders with integral bearings. The RESR is fitted directly to the machine shaft， so couplinglosses， backlash and shaft wind-up （torsion） are eliminated. The non-contact arrangementenables the RESR to be mounted much closer to the measuring surface， read the machineshaft‘s motion directly and provide positional feedback that offers repeatability to 0.01 arcsecond.

　　The RESR can offer considerable metrological advantages over traditional sealed encoders，especially in applications involving acceleration， deceleration， stopping and reversing underhigh loads， or where small incremental moves are required.

　　RESR is ideally suited to direct-drive rotary （DDR） motors. Here， the non-contact formatprovides the perfect match to the direct-drive， resulting in a very “stiff” servo loop. It alsoeliminates problems associated with sealed encoders （with integral bearings） acting as

　　sprung vibrating masses， which can cause poor positional stability. In a direct-drive system，only a non-contact encoder， such as the RESR， can provide the direct encoding of angularmotion without adding undesirable hysteresis and friction.

　　The RESR is designed for installation using the taper mount. This patented feature enablesthe ring to be adjusted; simply tightening a screw will pull that section of the ring down thetaper and therefore increase the radial displacement in that region. This method is used tominimise repeatable eccentricity， and therefore maximise accuracy