Collaboration produces angle encoder for GEO space applications

Its readhead is designed to survive harsh environments, with 150g vibration resistance and wide operating temperature range, combined with a robust optical detection principle. Particular attention has been paid to radiation hardness, resulting in the encoder achieving qualification for 15 years' use in GEO space conditions. The readhead has a mass of only 300g and power consumption is typically less than 1W.

The scale comprises a stainless steel ring with graduations marked directly onto the periphery, thus eliminating shock / vibration-induced breakages associated with traditional glass discs. The graduations include IN-TRAC reference marks that are directly embedded into the incremental channel, arranged in a distance-coded pattern so that the distance between any two adjacent reference marks is unique. This means that only a small rotation is required before absolute position is determined by the on-board FPGA (field-programmable gate array). The ring format enables easy integration into rotary axes, with a large through-hole to allow easy routing of supplies.

The ring is mounted directly to the rotor, with the head mounted to the stator. There is no contact between the two parts, so there is no need for separate bearings or flexible couplings. This arrangement improves reliability and eliminates backlash, shaft wind-up (torsion) and other irregular metrology effects that plague traditional enclosed encoders.

High accuracy has been achieved, with short-range error less than 0.5urad RMS and long-range error less than 5urad (without mechanical errors). Combined with resolution of less than 0.5urad, the system is well suited to applications demanding precision metrology.

Enquiries for this space-qualified encoder should be directed to [email protected] at Tesat-Spacecom GmbH. For further information about Renishaw products please go to www.renishaw.com.