08-10-2011, 11:32 AM
[quote name='miro' timestamp='1312966079' post='10569']
Ooops,
The current Imatest target is reflective while encoders base is transluctive.
Target has dark and white areas.The targhet is with high contrast. While most optical encoders are transluctive – metal grid over glas or trans[perant plastic.
Back illuminating is not an option. Since another side effects will occures – scattering, refraction etc. The encoder manufactures do a lot of trics to acheve resonacble sharp images. remember the encoder head is looking for 0 and 1 while we must look for nuaces of light
SinCos encoder is exection of 0s rule, but high end manufacures guaranties 1% THD by perfectly aligned encoder
[/quote]
miro, I am not sure but I think you made the wrong assumptions.
The optical encoder I used needed a reflective surface. This was achieved the traditional way by sputtering the wafer with chrome after the lithography process. So this requirement of Imatest can be served.
Concerning the sensor signal, I might misunderstand you. The sensor does not look for 0 and 1, thats the microcontroler input. The sensor measures level of light sensivity, which are transformed into digital outputs by the quadrature encoder via A and B channels. I think this is what you meant when talking about the SinCos encoder function and zero points. But then, what influence does this fact have on what we need? Is it sharpness of the pattern you are concerned about? The lithography mask we used was created without optical processes involved. The optical errors that can lead to low contrast edges on the final pattern on the wafer during lithography, yes. But this is a problem in general and the magnitude of the error is related to the structure size we need.
Klaus suggestion of 20k lines per inch calculates back to ~1.27µm distance from line to line, making it ~0,63µm line width. I have to confess, this is probably out of reach for the capabilities I could provide. But in these dimensions, structure contrast should still not be a problem.
Christian
Ooops,
The current Imatest target is reflective while encoders base is transluctive.
Target has dark and white areas.The targhet is with high contrast. While most optical encoders are transluctive – metal grid over glas or trans[perant plastic.
Back illuminating is not an option. Since another side effects will occures – scattering, refraction etc. The encoder manufactures do a lot of trics to acheve resonacble sharp images. remember the encoder head is looking for 0 and 1 while we must look for nuaces of light
SinCos encoder is exection of 0s rule, but high end manufacures guaranties 1% THD by perfectly aligned encoder
[/quote]
miro, I am not sure but I think you made the wrong assumptions.
The optical encoder I used needed a reflective surface. This was achieved the traditional way by sputtering the wafer with chrome after the lithography process. So this requirement of Imatest can be served.
Concerning the sensor signal, I might misunderstand you. The sensor does not look for 0 and 1, thats the microcontroler input. The sensor measures level of light sensivity, which are transformed into digital outputs by the quadrature encoder via A and B channels. I think this is what you meant when talking about the SinCos encoder function and zero points. But then, what influence does this fact have on what we need? Is it sharpness of the pattern you are concerned about? The lithography mask we used was created without optical processes involved. The optical errors that can lead to low contrast edges on the final pattern on the wafer during lithography, yes. But this is a problem in general and the magnitude of the error is related to the structure size we need.
Klaus suggestion of 20k lines per inch calculates back to ~1.27µm distance from line to line, making it ~0,63µm line width. I have to confess, this is probably out of reach for the capabilities I could provide. But in these dimensions, structure contrast should still not be a problem.
Christian