Renishaw: REXM Ultra-high Accuracy Angle Encoder REXM20USA104

For applications that require the highest angular accuracy, the REXM angle encoder offers new levels of angular metrology - better than ±1 arc second total installed accuracy, zero coupling losses and exceptional repeatability.

Like the RESM, the REXM stainless steel ring has graduations marked directly onto the periphery. However, it features a thicker cross-section designed to minimise all installation errors except eccentricity.

The remaining eccentricity is easily corrected using the combined output of two readheads. Renishaw's new DSi (Dual SiGNUM™ Interface) blends the output of two readheads whilst providing a repeatable and customer programmable reference mark propoZ™ position. Once the DSi has eliminated eccentricity, the only other errors remaining are graduation and cyclic error (sub-divisional error - SDE) both of which are exceedingly small.

When REXM is used with the DSi, it is possible to achieve a total installed accuracy of better than ±1 arc second. Tests on a 183mm REXM ring have achieved an impressive total installed accuracy of ±0.22 arc seconds.

Furthermore, REXM maintains the dynamic performance advantages of SIGNUM™ encoders. As a non-contact system, REXM rings are directly locked to the rotor, eliminating coupling losses, oscillation, shaft torsion and other hysteresis errors that plague enclosed encoders.

The total installed accuracy of a typical REXM system is ±0.22 arc second, determined by analysis of sequentially rotated installations.

REXM20 has a thicker cross-section, to ensure that the only significant installation error is eccentricity. Eccentricity is easily removed using two readheads, either with Renishaw’s DSi (Dual Signal interface), or by combining the signals inside the host controller. The only errors remaining are graduation errors and readhead SDE, both of which are so small they are often negligible. As a non-contact encoder, REXM20 offers dynamic performance advantages, eliminating coupling losses, oscillation, shaft torsion and other hysteresis errors that plague enclosed encoders. Combining two readheads is easy with the DSi, which also offers an angularly repeatable reference position (propoZ ™) which is unaffected by bearing wander or power cycling.

REXM20 total installed accuracy grades:

Designed for axes that are limited to partial rotation, REXT20 rings have two reference marks, oriented diametrically opposed, for use with partial arc versions of DSi. DSi processes these reference marks to give a single, angularly repeatable propoZ reference output.

Features

With zero coupling losses and exceptional repeatability, the REXM/REXT ultra-high accuracy angle encoder achieves better than ±1 arc second total installed accuracy.

• Use with two VIONiC™, TONiC™ or SiGNUM™ encoders, combined with DSi to give ultra-high accuracy

• Installed accuracy to ±1 arc second with dual readheads

• Wide range of standard sizes from 52 mm to 417 mm

• Large internal diameter for ease of integration

• Flange mounted with easy 4-point adjustment method

• Angularly repeatable propoZ reference position is unaffected by bearing wander or power cycling

Supporting Links

RENISHAW: REXM/REXT ultra-high accuracy angle encoder