Akhtar Ali Khan, Age 913670 Peacock Ct UNIT 4, Santa Clara, CA 95051

5274229, Dec 28, 1993

Jun 11, 1991

7/713718

Akhtar R. Khan - San Jose CA

Hewlett-Packard Company - Palo Alto CA

G01D 534

25023118

An optical shaft angle encoder has a circumferentially extending data track having alternating windows and opaque spaces or spokes between the windows. Each window and space between windows has substantially the same width along the track. An array of photodetectors is provided adjacent to the data track, with each photodetector having substantially the same width as a space or window. An LED illuminates the photodetectors through the windows. The lengths of each window transverse to the data track, and hence the area of each window, is selected from a limited set which preferably has lengths varying by powers of 2. The areas of successive windows along the track are in a predetermined sequence which does not repeat around the track. The photo current due to illuminating the photodetectors in the array provides a unique indication of the angular position of the code wheel. To assure a reading of the angular position at essentially all times, including immediately upon startup of the encoder, there are interleaved arrays of odd and even numbered photodetectors.