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Accurate low cost method of home/zero Axis setting

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As much as I like to disagree with Hanermo, his figures are probably not far off, given my experience of slot sensors.

Looking at the datasheet for the current version of the slot sensor I used (Panasonic PM-45 series), it lists hysteresis as 0.05mm or better, and repeatability as 0.01mm or better.
Given I never noticed any variance on a DTI gauge with 0.01mm intervals, I'd put repeatability at better than 0.005mm. However due to the stepping nature of stepper motors, the stepping probably contributes to the repeatability.

Would those 2 microns possibly be the travel of the ball screw when located by the sensor. So linear travel of screw related to angular travel of opto sensor  :scratch:


--- Quote from: awemawson on March 30, 2019, 11:11:45 AM ---Heidenhain encoders do a similar thing as implemented on Bridgeport Interacts and indeed also on my Beaver Partsmaster.

They drive to the limit switch then look for a 'once per rev' index on the encoder.

--- End quote ---

Yes I found this out the hard way on my Partsmaster. After removing the Z axis encoder for repair I pranged the tool change carousel as the Z axis tool change position had changed by around 3mm! Luckily I got away without any damage  :doh:   

Typically, the linear sensor acts as a trigger for locating a rotation sensor  , either a motor encoder pulse or a separate lead screw sensor.


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