LIDA linear encoders operate according to the imaging scanning principle. Imaging scanning principle

Photoelectric Scanning

To put it simply, the imaging scanning principle functions by means of projected- light signal generation: two scale gratings with equal grating periods are moved relative to each other—the scale and the scanning reticle. The carrier material of the scanning reticle is transparent, whereas the graduation on the measuring standard may be applied to a transparent or refl ective surface.When parallel light passes through a grating, light and dark surfaces are projected at a certain distance. An index grating with the same grating period is located here. When the two gratings move in relation to each other, the incident light is modulated: if the gaps are aligned, light passes through. If the lines of one grating coincide with the gaps of the other, no light passes through. Photovoltaic cells convert these variations in light intensity into electrical signals. The specially structured grating of the scanning reticle fi lters the light current to generate nearly sinusoidal output signals. The smaller the period of the grating structure is, the closer and more tightly toleranced the gap must be between the scanning reticle and scale. Practical mounting tolerances for encoders with the imaging scanning principle are achieved with grating periods of 10 µm and larger. Most HEIDENHAIN encoders operate using the principle of photoelectric scanning. The photoelectric scanning of a measuring standard is contact-free, and therefore without wear. This method detects even very fi ne lines, no more than a few microns wide, and generates output signals with very small signal periods.The fi ner the grating period of a measuring standard is, the greater the effect of diffraction on photoelectric scanning. HEIDENHAIN uses two scanning principles with linear encoders:The
Signal period360° elec. 90° elec.Phase shift imaging scanning principle interferential scanning principle for grating periods from 10 µm to 200 µm. The for very fi ne graduations with grating periods of 4 µm and smaller.••
ScaleWindowStructured detector Scanning reticleIndex gratingCondenser lensLight sourceLED Photoelectric scanning in accordance with the imaging scanning principle with steel scale and single-fi eld scanning (LIDA 400)

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