Two heads are better than one for rotary position

Renishaw's new DSi combines two Signum SR readheads on a RESM ring and outputs a customer located, angularly repeatable propoZ reference (index) position.

Renishaw's new DSi combines two Signum SR readheads on a RESM ring and outputs a customer located, angularly repeatable propoZ reference (index) position, which is completely unaffected by bearing wander or power cycling.

Precision rotary axes often demand very high accuracy without calibration or error-map compensation.

As a modular solution, DSi allows a second readhead to be added, which eliminates odd error harmonics including eccentricity and compensates for the effect of bearing wander.

The result is total installed error of typically +/-2.5arc-secd (200mm diameter RESM).

For ultimate precision, DSi combined with the new ultra-high accuracy REXM ring offers better than +/-1arc-sec total installed accuracy.

DSi provides the customer located and angularly repeatable propoZ reference (index) output, which is completely unaffected by bearing wander or power cycling.

The customer selects the desired propoZ reference position by driving the axis to the chosen angle and simply pressing a button.

This feature makes alignment of the encoder's reference position to the T-slots on a machine tool rotary table, for example, faster and more precise.

The selected angle is then stored in the DSi's memory so the patented propoZ reference (index) is locked to that angle, ensuring perfect angular repeatability - even if the centre of rotation of the axis moves whilst the DSi is switched off.

DSi makes adding a second SR readhead very easy.

By combining the incremental signals from the two readheads and using patented reference mark processing, the DSi appears to the controller as a single very high accuracy encoder.

Furthermore, DSi maintains the dynamic advantages of Signum encoders.

As a noncontact system, Signum RESM rings are taper locked to the rotor shaft, ensuring a compact axis design and the elimination of coupling losses, oscillation, shaft torsion and other hysteresis errors that plague enclosed encoders.

Like the rest of the Renishaw Signum encoder range, DSi is capable of operating at speeds up to 4500rev/min and temperatures up to 85C.

Signum also benefits from rugged IP64 sealed readheads, dynamic signal processing for excellent reliability, and ultra-low cyclic error (less then +/-40nm).

In addition, comprehensive Signum software enables optimum setup and real-time diagnostics via a PC's USB port.

As with all Renishaw products, the Signum range is backed up by a worldwide team offering truly responsive global support.

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