Photoelectric measuring methods
Photoelectric measuring methods are the most important and most widely used measuring systems that supply the coordinates for controlling the work processes of machine tools . A distinction is made between incident and transmitted light methods.
Transmitted light method
The transmitted light method essentially consists
- from a light source - usually an LED because of the longer service life and lower heat emission
- a condenser - that directs the light evenly
- a scanning plate - which specifies the pattern to be scanned through recesses
- an exact scale - mostly glass because of lower thermal expansion and higher accuracy
- and the photo elements - their arrangement corresponds to the pattern of the scanning plate.
The function corresponds to that of a light barrier . The aligned light falls over the pattern of the scanning plate through the graduations and reference marks of the scale onto the photo elements. The light is interrupted again and again by a relative movement of the scale, causing light fluctuations on the photo elements, which are processed electrically.
Incident light method
It is similar with the incident light method. The main difference is that the light rays that hit the scale are reflected and directed to the photo elements via the scanning plate and condenser. The advantage of the incident light method is a more compact design and a lower price.
properties
The advantages of photoelectric measuring systems are high accuracy and low cost. A disadvantage is the sensitivity to dirt and vibration.
The methods achieve a relatively high accuracy of 0.1 µm . The glass scales are used for machines with the highest accuracy requirements such as B. Measuring machines manufactured with a graduation period of 10 µm. With steady movement, the resulting signal is a sinusoid. By dividing this known curve into a hundred sections, a total resolution of 0.1 µm is achieved.