Posted to News on 21st Nov 2009, 21:36
Absolute optical encoder with BiSS-C communications
Renishaw's new RESOLUTE absolute optical encoder is now available with BiSS-C high-speed serial communications, an open protocol that is available on a range of industry-standard servo drives, controllers, counter cards and encoders. With pure serial high-speed communications at up to 10MHz, BiSS-C allows motion system developers to take full advantage of the RESOLUTE encoders' resolution of 1 nanometre at up to 100m/s for both linear encoder and angle encoder applications.
Modern absolute encoders communicate using pure serial digital signals that facilitate combinations of very high speeds and super-fine resolutions while ensuring excellent immunity to electromagnetic interference. Absolute encoders also eliminate the need for reference returns and provide instant commutation for direct-drive linear or rotary motors.
However, historically absolute encoders had a hidden down-side: several industry-standard serial communications protocols were developed by encoder manufacturers with the intention of locking out competitors; furthermore, the lack of alternatives meant that some of these protocols were adopted by controller manufacturers. This situation was compounded by the uncompetitive open protocols (such as SSI), which Renishaw describes as 'outdated and outperformed' when it came to precision motion control. Overall it was not the ideal environment in which motion system designers could achieve their performance specifications at competitive prices.
Technical benefits
This was the market situation that led IC-Haus to develop the BiSS high-speed serial communications open protocol, which can be licensed freely by encoder and controller manufacturers. The result is said to be healthier competition between encoder manufacturers, plus technical benefits such as high data rates of up to 10MHz, low latency, fast repetition rates and data propagation delay compensation. Such is the appeal of BiSS that currently over 150 device manufacturers have licensed the BiSS Interface Intellectual Property, services and tools.
Renishaw identified BiSS as a suitable open protocol for use with its RESOLUTE absolute encoder, a patented non-contact absolute encoder that has an advanced optical scheme that reads from a fine-pitch single-track scale. Not only does this endow the encoder with greater set-up tolerances, but it also delivers excellent immunity to dirt, scratches and light oils.
With speeds up to 100m/s and 1nm resolution, only a pure serial interface such as BiSS could match RESOLUTE's performance. Furthermore, the high-speed serial protocol enables users to reap the full benefits of RESOLUTE's low sub-divisional error (SDE) of +/-40nm and low jitter (noise) of 7nm RMS for superior motion control performance, especially on dynamic axes that require high speed, high acceleration, smooth velocity control and positional stability.
Options
The absolute linear encoder version of RESOLUTE is available with a comprehensive range of scale options. RELA Invar spars offer thermal expansion and +/-1um accuracy on lengths up to 1130mm. For high performance on long axes and significantly more robustness than glass scales, RSLA stainless steel spars have a total accuracy of +/-4um over 5m, with lengths up to 10m available. Plus, for the quickest and easiest installation the new FASTRACK linear encoder scale system with low-profile RTLA tape scale offering +/-5 um/m accuracy.
Absolute angle encoder options are also well catered for; RESA rings are bolt-hole compatible with Renishaw's leading SiGNUM RESM angle encoder rings and are offered in a standard range of diameters from 52mm to 550mm, with even larger size options available to order. Like the SiGNUM RESM, RESA angle encoder rings feature large through-holes for easy design-in and a patented taper mount for quick, easy and precise adjustment of eccentricity, whilst minimising shaft preparation costs.
Absolute linear encoder versions of RESOLUTE with the BiSS protocol have resolution options of 1, 5 and 50nm, while RESOLUTE absolute angle encoders with the BiSS protocol have resolution options of 18 bits (4.94 arc seconds), 26 bits (0.02 arc seconds) and 32 bits (0.0003 arc seconds). In all cases, the maximum speed is 100m/s.
The RESOLUTE absolute encoder range is also available with other protocols and, like all Renishaw encoders, is backed by a global sales and support network. Furthermore the product satisfies the highest environmental standards, with both WEEE and RoHS compliance.
Follow the link for more information about the RESOLUTE absolute optical linear and absolute optical rotary (angle) encoder system
