Patent ID: 9689986
Date: 2017-06-27
CPC Classifications: G01C,G01D,G01S,G02B

Claim:
1. A method for obtaining a reference correction value for an angular encoder, the method comprising: providing the angular encoder having an encoder disk and a read head assembly, the read head assembly including a first read head and a second read head separated by 180 degrees, the encoder disk including a plurality of incremental marks forming a periodic pattern and an index mark; providing a processor; generating, in a first instance, a relative rotation between the encoder disk and the read head assembly about a first axis and obtaining, in response, first incremental readings, second incremental readings, and a first index reading, the first incremental readings including a plurality of readings of the incremental marks by the first read head, the second incremental readings including a plurality of readings of the incremental marks by the second read head, and the first index reading including a reading of the index mark by the first read head; determining with the processor a first reference position, the first reference position based at least in part on the first index reading and a first incremental angle based at least in part on differences between the first incremental readings and the second incremental readings; generating, in a second instance, a relative rotation between the encoder disk and the read head assembly about the first axis and obtaining, in response, third incremental readings, fourth incremental readings, and a second index reading, the third incremental readings including a plurality of readings of the incremental marks by the first read head, the fourth incremental readings including a plurality of readings of the incremental marks by the second read head, and the second index reading including a reading of the index mark by the first read head; determining with the processor a second reference position, the second reference position based at least in part on the second index reading and a second incremental angle, the second incremental angle based at least in part on differences between the third incremental readings and the fourth incremental readings; and determining with the processor the reference correction value based at least in part on the first reference position and the second reference position.