Patent ID: 8358124

Claim:
A magnetic absolute encoder comprising: first to third rotation detectors each including a gear fixed to a rotary shaft and having a predetermined number of teeth and one or more magnetic detecting elements for detecting magnetic flux passing through the predetermined number of teeth, each capable of detecting a rotational position of the gear, the gears of the first to third rotation detectors respectively having N1 to N3 teeth, N1 being an integer of m×n where m and n are each an integer of 2 or more, N2 being an integer of N1+1, and N3 being an integer of m×(n−1); an A/D conversion section for converting an electrical signal output from each of the first to third rotation detectors into a digital value and outputting first to third angle data each having a predetermined number of cycles which is equivalent to the number of the teeth of the corresponding gear, wherein one cycle is represented by a predetermined digital value; and an absolute position computing section for detecting an absolute position of the rotary shaft in one rotation, based on outputs from the A/D conversion section, by: preliminarily computing fourth angle data having m cycles, wherein one cycle is represented by a predetermined digital value, based on a difference between the first angle data having N1 cycles and the third angle data having N3 cycles while the rotary shaft makes one rotation, and also computing fifth angle data having one cycle, wherein one cycle is represented by a predetermined digital value, based on a difference between the first angle data having N1 cycles and the second angle data having N2 cycles while the rotary shaft makes one rotation, and then storing the fourth angle data and the fifth angle data; determining in which cycle of the m cycles of the fourth angle data, newly computed fifth angle data occurs and defining the thus determined cycle as a first determined cycle, and then determining in which cycle of n cycles of the first angle data that occur in the first determined cycle, the newly computed fifth angle data occurs and defining the thus determined cycle as a second determined cycle; determining in which cycle of the N1 cycles of the first angle data, newly output first angle data occurs based on the first determined cycle and the second determined cycle, and defining the thus determined cycle as a third determined cycle; and determining the absolute position based on the third determined cycle and the digital value of the newly output first angle data.