Hi, I've worked with these type of sensors for a lot of years. If you haven't really committed to the type of sensor I really advise changing to electronic hall sensors.
Myself and others have put a lot of work into the open-source hall sensors thread;http://www.cnczone.com/forums/open_s...made_easy.html (Electronic home switches made easy!)
The reasons the hall sensors are better are;
1. the opto ones are affected by ambient light, affecting their accuracy
2. the optos age over time, affecting their accuracy
3. the optos can be problematic with dust/grit etc
4. the optos are not temperature compensated
5. the opto's won't give the 0.01mm accuracy you can get easily from the hall sensors
Besides being temperature compensated, the hall sensors are a much better design having 4 tiny sensors in the one little package as a "bridge" which cancels out effects like ageing and most external noise.
I can provide suggestions re whatever sensor you choose, but if this is for your big machine I would go with the hall sensors, they are a step up from opto-interruptors and you may as well do it right.