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Scanning principle MS 20, MS 21

The MS 20, MS 21 incremental Linear Encoders work with the imaging, photoelectric measuring principle and a singlefield reflective scanning method. A scale graduation pattern on a steel tape (with gold grating) or a glass scale (with chrome grating) with 40 µm grating pitch is used.

Scanning principle

The light from an infrared LED with a small light emitting surface is collimated parallel by a condenser lens and directed through the scanning reticle to the scale. When the scale is moved relative to the encoder head, the light is modulated by the scale gratings and produces a periodic intensity signal that is converted into electrical signals by photo elements back in the encoder head.The scanning reticle is designed to allow for a large mounting gap and liberal mounting tolerances. This system is insensitive to waviness of the steel tape due to poor mounting conditions. Any minor differences in the grating period of the scale or the scanning reticle will not cause a measuring problem due to the large continuous pattern reflected onto the structured sensor. This sensor consists of multiple photo elements connected in a pattern to generate four sinusoidal signals, each shifted by 90°. All four signals are generated from one scanning field and all four signals are equally influenced by any contamination simultaneously. When all four signals are influenced at the same time by the same amount, interpolation error is eliminated.

Effect of contamination on the quality and size of the measuring signal Clean steel tape scale -optimal conditionContaminated steel tape scale -unfavorable condition