Encoder Resolves to within 5 arc-sec

Dec. 12, 2002
Motion Control Reference Guide
The Dignalizer absolute optical rotary encoder has 18-bit resolution in single-turn configuration and 36-bit in a multiturn version.

A general trend in manufacturing is for machines to perform precise, high-resolution movements. This means the systems that control these processes must track ever-smaller movements: submicron, nanometer, and beyond. Encoders are keeping pace with this demand by getting smaller and adding more functions to handle the accuracy and resolution demanded from industry.

An example of advances in encoder technology comes from Baumer Electric Ltd., Southington, Conn. (www.baumerelectric.com). The Dignalizer is an absolute optical rotary encoder with 36-bit resolution in a multiturn configuration. It can measure 262,144 pulses (218) per revolution over 262,144 revolutions, allowing the encoder to track over 68 billion pulses (236) with unique binary codes, amounting to a resolution of 5 arc-sec.

A clever operating principle eliminates the bulky and breakage-prone traditional gear system used to track revolutions. One physical disk contains two tracks: a digital track that generates a proprietary pseudo-random code, and an analog track that resembles an incremental encoder disk. A small sampling window moves across the pseudo-random code track producing a distinct position increment with each move.

Other encoders produce two signals, an analog and binary signal, which are output and combined in a separate external circuit. The Dignalizer combines these signals inside the encoder and puts out one signal. This is less costly because there is no external piece of equipment to buy, plus it simplifies wiring. The other benefit is that by not putting the signals outside, there is no concern about susceptibility to noise and EMI.

The Dignalizer supports most major bus system outputs, including SSI, CANopen, DeviceNet, and Profibus, as well as RS-485 outputs. It offers both cable and radial-connector configurations and has 12-mm hollow-shaft and various industry-standard shaft sizes. It also features 50 g shock protection and IP 64 sealing. It can operate in temperatures from -20 to 85°C. The encoder has a diameter of 58 mm, a depth of 55 mm, and weighs 370 gm. Internal monitoring electronics decrease output lag, allowing accurate monitoring of rotation down to 6,000 rpm.

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