High resolution shaft position encoder

Shaft position encoder means comprising:

• first means for generating a signal .sigma..sub.1 as said shaft rotates an angle .alpha..sub.1, said first means including a coded track CDT.sub.1 and an associated sensor means SEN.sub.1 between which relative movement is caused as said shaft rotates, said first means requiring, as a condition for generating a signal .sigma..sub.1, an appropriate alignment between the sensor means SEN.sub.1 and a predetermined part of said track CDT.sub.1, said first means further including controlling means, responsive to rotation of said shaft, for allowing one or more predetermined occurrences of said alignment, but less than all occurrences of said alignment, to result in the generation of a signal .sigma..sub.1,
• second means for generating a signal .sigma..sub.2 as said shaft rotates an angle .alpha..sub.2, where .alpha..sub.2 .noteq..alpha..sub.1, said second means including a coded track CDT.sub.2 and an associated sensor means SEN.sub.2 between which relative movement is caused as said shaft rotates, and
• third means for generating a signal .sigma..sub.3 as said shaft rotates an angle .alpha..sub.3, said third means including a coded track CDT.sub.3 and an associated sensor means SEN.sub.3 between which relative movement is caused as said shaft rotates,
• each of sensor means SEN.sub.1, SEN.sub.2, and SEN.sub.3, (a) being sensitive to the associated one of the three numerically subscripted tracks CDT.sub.1, CDT.sub.2, and CDT.sub.3 and (b) being insensitive to the other two of the three numerically subscripted tracks,
• .alpha..sub.3 being related to .alpha..sub.1 and .alpha..sub.2 so that (i) between the Uth occurrence of signal .sigma..sub.1 and a nearby occurrence of signal .sigma..sub.2 there occurs a number V of signals .sigma..sub.3, the number V permitting identification of the number U, and (ii) between the Wth occurrence of signal .sigma..sub.1 and a nearby occurrence of signal .sigma..sub.2 there occurs a number Y of signals .sigma..sub.3, the number Y permitting identification of the number W, W being .noteq.U and Y being .noteq.V, whereby, each one of a plurality of signals .sigma..sub.1 is absolutely identifiable and distinguishable from all the other ones of said plurality of signals .sigma..sub.1 because between each signal .sigma..sub.1, of said plurality, and a nearby signal .sigma..sub.2 there occurs a different number of signals .sigma..sub.3 which thereby permits identification of the particular signal .sigma..sub.1.