EVOLUTE™ absolute encoder system with RTLA50 linear scale
- Protocols: BiSS®, Mitsubishi, Yaskawa
- Readhead size: 36 x 16.5 x 17.2 mm
- Resolutions to 50 nm at 100 m/s
- ±10 µm/m accuracy at 20 °C
- Scale coefficient of thermal expansion at 20 °C: 10.1 ±0.2 µm/m/°C
- Side cable outlet version available
- Very high dirt immunity
- Wide set-up tolerances for quick and easy installation
- Excellent motion control performance
- Less than 10 nm RMS jitter for improved positional stability
- ±150 nm Sub-Divisional Error for smooth velocity control
- Side mounting option and reversible readhead for flexible mounting
What is EVOLUTE?
Based on Renishaw's industry-proven absolute technology, the EVOLUTE series is a true-absolute non-contact optical encoder with a 50 µm scale period, bringing superb installation tolerances and greater dirt immunity for applications that demand not only the highest operational integrity, but where fast installation is critical.
Resolutions down to 50 nm along with low SDE and jitter from cutting edge optical design and high-speed signal processing give the EVOLUTE encoder the targeted performance to meet the needs of the most demanding OEM applications.
What is RTLA50 scale?
RTLA50 incorporates the same stainless steel tape scale as RTLA, but this time with a 50 µm pitch version of our absolute scale code. It is accurate to ±10 µm/m and available in lengths up to 10.02 metres. Two mounting options are available, both of which allow independent scale thermal expansion and the convenience of tape scale.
- RTLA50 can be used with the revolutionary FASTRACK™ scale carrier system. This system allows a track to be laid quickly and easily with no need for fixing holes. A sacrificial spacer is removed and the tape scale is then fed into the track.
- RTLA50-S is laid onto the substrate with self-adhesive backing tape. The self-adhesive is formulated in such a way that it allows the scale to expand independently of the substrate.
To complete the installation, both types of scale are clamped at one point to provide a datum position.
Why choose this encoder system?
Fast and easy installation
Machine build time is critical in OEM applications as time saved in component installation allows shorter manufacturing lead times and ultimately higher profitability. The large rideheight and tolerance offered by the EVOLUTE readhead (rideheight of 0.8 mm, tolerance ±0.25 mm) ensures fast and simple installation with instant validation from the integral set‑up LED, eliminating the need for time consuming fine adjustment. This superior set-up tolerance is enabled through advanced optics and by not following the conventional absolute measurement technique of using dual tracks side-by-side (one incremental, one absolute) which inherently suffer de-phasing problems when small amounts of angular misalignment are introduced.
Minimising down-time is a top priority for end-users of production machinery. The EVOLUTE encoder ensures up-time through multiple mechanisms that enable high dirt immunity for an optical system: a Digital Signal Processor (DSP) is used to analyse captured data from the custom image sensor and work with the optical imaging system to overcome light scattering effects of oily or greasy smears that may cause other encoders to fail; the custom point-source LED changes its flash duration to provide the best signal integrity for all traversing speeds; and finally, substantial redundancy is built into the absolute code pattern, allowing the EVOLUTE readhead to function over parts of the scale that are partially obscured by particulate contamination.
When a customer installs outsourced components on their product, their reputation is dependent on the quality of those components. Renishaw has a long established and trusted reputation for producing high quality and capable encoder products that reliably meet the demands of the most challenging industrial applications.
|Protocol||Description||Data sheet||Compatible products|
Renishaw supports the BiSS C (unidirectional) open protocol for absolute encoders. BiSS is a high-speed serial protocol, perfect for dynamic axes that require high acceleration, silky-smooth velocity control, excellent bi-directional repeatability and rock-solid positional stability.
The BiSS protocol is compatible with a wide range of industry-standard controllers, drives, DROs and PC counter cards.
The Mitsubishi serial communications interface is compatible with the J4 series of servo drives and the MDS-D2/DH2/DM2/DJ drives for machine tool applications.
The Yaskawa serial communications interface is compatible with Sigma-5 and Sigma-7 SERVOPACKs.
FASTRACK RTLA50: stainless steel tape scale with carrier system
RTLA50-S: stainless steel absolute coded tape scale with self-adhesive backing tape, for mounting directly to a substrate without the FASTRACK guide rails
Readhead size (LxWxH)
36 mm x 16.5 mm x 17.2 mm
Nominal 50 μm
Coefficient of thermal expansion at 20 °C
10.1 ±0.2 μm/m/°C
Accuracy grade at 20 °C
Some BiSS C® protocol variants have limited maximum length (See data sheet for details)
FASTRACK: 100 mm to 10.02 m
RTLA50/RTLA50-S: up to 10.02 m
(See data sheet for details)
Up to 100 m/s
BiSS C, Mitsubishi, Yaskawa
500 nm, 100 nm and 50 nm resolutions
Sub-Divisional Error (SDE)
0.5, 1, 1.5 or 3 m cable lengths with 9-way D-type connector
5 V ±10%, max 250 mA @ 5 V (terminated)
300 m/s2 max @ 55 Hz to 2 000, 3 axes
1 000 m/s2, 6 ms, ½ sine, 3 axes
0 °C to +80 °C
Refer to data sheets for full details.
*Other protocols are continually being added.
- Data sheet: EVOLUTE™ absolute optical encoder with Yaskawa serial communications
- Data sheet: EVOLUTE™ absolute optical encoder with Mitsubishi serial communications
- Data sheet: EVOLUTE™ absolute optical encoder with BiSS serial communications
- Data sheet: RTLA50 absolute linear encoder scale system for EVOLUTE™
- Data sheet: BiSS® C-mode (unidirectional) for EVOLUTE™ encoders
How it works
The EVOLUTE encoder communicates bi-directionally in purely serial format, using a variety of industry-standard protocols, of both proprietary and open standard.
The process begins...
The controller initiates operation by sending a demand message to the readhead, instructing it to capture the absolute position on the linear scale at that instant. The head responds by flashing a high-power LED source to illuminate the scale. The flash duration is as brief as 100 ns to minimise image blur on moving axes. Crucially its timing is controlled within a few nanoseconds to preserve the relationship between demanded and reported position, making the EVOLUTE series ideally suited for high specification motion systems.
Single track scale
The scale is essentially a single track of full-width contrasting lines, based on a nominal period of 50 µm. The absence of multiple parallel tracks gives important immunity from yaw errors and a higher lateral tolerance in head position.
The scale is imaged, via an aspheric lens which minimises distortion, onto a custom detector array. The optical arrangement, with a folded illumination path but direct imaging, is highly compact yet stable thus assuring the fidelity essential for excellent metrology.
Data decoding and analysis
Once captured by the detector, the image is transferred via an analogue-to-digital converter to a powerful Digital Signal Processor (DSP). Specially developed algorithms then obtain a true absolute, but relatively coarse position from the code embedded in the scale. This process is checked, and corrections are made by further algorithms in the DSP which exploit redundancy and intentional restrictions in the scale code. Meanwhile other routines calculate a very high resolution fine position, which is then combined with the coarse position to provide a truly absolute and very high resolution location.
Final checks and data output
After final error checking procedures, position information is uploaded in the appropriate protocol to the controller as a pure serial word. Protection against electrical noise disturbance is provided by addition of a Cyclic Redundancy Check (CRC). The entire process can take as little as a few microseconds and be repeated up to 25 000 times per second. By a variety of techniques, including adjusting the light flash duration to the axis speed, this performance can be achieved at up to 100 m/s while preserving exceptionally low positional jitter at lower operating speeds.
And the result is...
The EVOLUTE encoder offers generous installation tolerances of ±0.75° in yaw, and ±0.5° in pitch and roll, along with an impressive ±250 µm in rideheight. Meanwhile the generous optical footprint and advanced error correction procedures provide excellent immunity to optical contamination, including both particulate and greasy smears, while maintaining 50 nm resolution of up to 100 m/s.