MOTION SYSTEMS HANDBOOK
NUMERIK JENA’s LIKgo linear encoders are designed for the demands of production and inspection machines in the semiconductor industry. A new two-field scanning principle ensures that signals are produced free of offset errors and phase errors. The measuring standard is a SINGLEFLEX steel scale tape 8 mm wide with a grating period of 20 µm, making possible measuring steps down to 78.125 nm.
Encoders — the basics In automation and control systems using closed-loop control, speed and position are two critical variables. And the most common way to acquire position information is using an encoder. Encoders can be classified in a number of different ways – whether they are rotary (the more common) or linear, by the sensing technique, whether the output is absolute or incremental, as well as by some common performance parameters.
SENSING TECHNIQUES Common sensing techniques include optical, magnetic, and capacitive sensing. While optical encoders have historically been the only option for resolutions below 5 microns, improvements in magnetic scale technology now allow them to achieve resolutions down to 1 micron. Optical encoders use a light source and a photo-detector to determine position, but their use of light makes them sensitive to dirt and debris, which can disrupt the signal.
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The performance of optical encoders is influenced by the gap between the sensor and the scale, which must be properly set and maintained to ensure that signal integrity isn’t compromised. This means that mounting must be done carefully, and shocks and vibrations should be avoided. Magnetic encoders use a magnetic reader head and a magnetic scale to determine position. Unlike optical encoders, magnetic encoders are mostly unaffected by dirt, debris, or liquid contamination. Shock and vibration are also less likely to affect magnetic encoders. They are, however, sensitive to magnetic chips, such as steel or iron, as they may interfere with the magnetic field. Capacitive encoders, a relatively new technology, offer resolution comparable to optical devices, with the ruggedness of magnetic encoders. The basic principle behind capacitive encoders is that they detect changes in capacitance using a high-frequency reference signal. This is accomplished with the three main parts—a stationary transmitter, a rotor, and a stationary receiver. (Capacitive encoders can also be provided in a “two-part” configuration, with a
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8/20/19 1:53 PM
