Absolute incremental hybrid shaft position encoder

Claim 1

Shaft position encoder means comprising: a. first means including a first coded track and an associated first sensor means between which relative movement is caused by rotation of said shaft, said first sensor means being arranged so as to be sensitive only to said first track, and said first sensor means generating, in response to said relative movement within said first means, a first signal at each of substantially regular angular intervals α of rotation of said shaft, b. second means including a second coded track and an associated second sensor means between which relative movement is also caused by rotation of said shaft, said second sensor means being arranged so as to be sensitive only to said second track, and said second sensor means generating, in response to said relative movement within said second means, a second signal at each of substantially regular angular intervals β of rotation of said shaft, where β=M/N×α, and M and N are positive intergers >1 which contain no prime factor, other than the prime number one, which is common to both, and c. third means including a third coded track and an associated third sensor means between which relative movement is also caused by rotation of said shaft, said third sensor means being arranged so as to be sensitive only to said third track, and said third sensor means generating, in response to said relative movement within said third means, a voltage or current transition at each of substantially regular angular intervals β/M/k of rotation of said shaft where k is a positive integer, whereby for a predetermined direction and amount of shaft rotation each positionally different first signal has associated therewith a corresponding and identifying electrical signature comprising a predetermined number of said transitions occurring between the associated first signal and the second signal last occurring prior to the associated first signal, each said electrical signature being different from all the other electrical signatures within said predetermined amount of shaft rotation in that each said electrical signature comprises a different number of said transitions.