Zero reference generating method and apparatus for optical encoders

Abstract From the Canadian patent

Improved Zero Reference Generating Method And Apparatus For Optical Encoders An encoder for providing positional information about a moveable member comprising code member means couplable to the moveable member for movement with the moveable member, reference means positioned to be stationary relative to the code member an index, sequence positioned on the code member a mask sequence, positioned on the reference member means and means for, detecting the degree of registration between the index sequence and the mask sequence, wherein the index sequence and the mask sequence include a plurality of building block patterns that are separated by predetermined spacings.