Position detection apparatus
This invention provides a position detection apparatus that improves the position detection accuracy. A position detection apparatus includes an absolute track in which when N is an integer of not less than 2, a recording binary sequence created based on a position detection binary sequence in which identical sequences do not exist no matter which N continuous terms are extracted is recorded, and an absolute sensor unit that reads the recording binary sequence from the absolute track, wherein a plurality of terms included in the recording binary sequence consist of two binary values, and when the two binary values are assumed to be 1 and 0, the recording binary sequence is a sequence obtained by replacing one of two values included in the position detection binary sequence with 10 and the other value in the position detection binary sequence with 01.
1. A position detection apparatus comprising:
an absolute track in which a first binary sequence generated from a second binary sequence is recorded; and
an absolute sensor unit that reads the first binary sequence from said absolute track,
wherein the first binary sequence consists of 0s and 1s and is generated by replacing 0 in the second binary sequence with 10 and 1 in the second binary sequence with 01, or by replacing 0 in the second binary sequence with 01 and 1 in the second binary sequence with 10,
wherein when reading, values in the second binary sequence are replaced with 1s and 0s in accordance with not a positive/negative of magnetism but a direction of inversion from positive to negative or from negative to positive, and
wherein said absolute sensor unit includes two sensor elements arranged at an interval of λ/2 or less than λ/2 of a recording pitch λ of the first binary sequence,
the apparatus further comprising:
an incremental track communicating with an incremental sensor unit that detects fore and rear positions of the absolute sensor unit;
an inverter that generates an inverted sequence by bit-inverting a detected sequence detected by said absolute sensor unit;
a discriminator that discriminates, based on the fore and rear positions detected by the incremental sensor unit, which one of the detected sequence and the inverted sequence should be searched for;
a searcher that searches the second binary sequence for the detected sequence or the inverted sequence discriminated by the discriminator; and
a position detector that detects a position of said absolute sensor unit based on a position of the detected sequence or the inverted sequence found by said searcher in the second binary sequence and the fore and rear positions detected by the incremental sensor unit.
2. The apparatus according to claim 1 , wherein said absolute sensor unit includes a sensor that senses a sequence of at least (N+1) terms by measuring every other term from the first binary sequence.
3. The apparatus according to claim 1 , wherein the discriminator discriminates, based on whether the detected sequence or the inverted sequence is found by said searcher, which one of the two values of the first binary sequence, which is replaced from one value of the second binary sequence, is detected by said absolute sensor unit.
4. A position detection apparatus according to claim 1 , comprising:
an absolute track in which a first binary sequence generated from a second binary sequence is recorded; and
an absolute sensor unit that reads the first binary sequence from said absolute track,
wherein the first binary sequence consists of 0s and 1s and is generated by replacing 0 in the second binary sequence with 10 and 1 in the second binary sequence with 01, or by replacing 0 in the second binary sequence with 01 and 1 in the second binary sequence with 10,
wherein when reading, values in the second binary sequence are replaced with 1s and 0s in accordance with not a positive/negative of magnetism but a direction of inversion from positive to negative or from negative to positive,
wherein said absolute sensor unit includes two sensor elements arranged at an interval of λ/2 or less than λ/2 of a recording pitch λ, of the first binary sequence, and
wherein said absolute sensor unit detects every other term of a sequence of at least N terms from the first binary sequence, and
the apparatus further comprises:
an incremental track communicating with an incremental sensor unit operating as a fore and rear detector that detects which one of the two values of the first binary sequence corresponds to the position that said absolute sensor unit faces;
an inverter that generates an inverted sequence by bit-inverting a detected sequence detected by said absolute sensor unit;
a discriminator that discriminates, based on fore and rear positions detected by the fore and rear detector, which one of the detected sequence and the inverted sequence should be searched for;
a searcher that searches the second binary sequence for the detected sequence or the inverted sequence discriminated by the discriminator; and
a position detector that converts, based on a correspondence relationship between the first binary sequence and the second binary sequence, the sequence detected by said absolute sensor unit, and detects a position of said absolute sensor unit based on the position of the detected sequence or the inverted sequence found by said searcher in the second binary sequence after the conversion and the fore and rear positions detected by said fore and rear detector.
5. A position detection method comprising:
recording, in an absolute track, a first binary sequence generated from a second binary sequence; and
reading, by an absolute sensor unit, the first binary sequence from said absolute track,
wherein the first binary sequence consists of 0s and 1s and is generated by replacing 0 in the second binary sequence with 10 and 1 in the second binary sequence with 01, or by replacing 0 in the second binary sequence with 01 and 1 in the second binary sequence with 10,
wherein when reading, values in the second binary sequence are replaced with 1s and 0s in accordance with not a positive/negative of magnetism but a direction of inversion from positive to negative or from negative to positive, and
wherein said absolute sensor unit includes two sensor elements arranged at an interval of λ/2 or less than λ/2 of a recording pitch λ of the first binary sequence,
the method further comprising:
communicating, by an incremental track, with an incremental sensor unit that detects fore and rear positions of the absolute sensor unit;
generating, by an inverter, an inverted sequence by bit-inverting a detected sequence detected by said absolute sensor unit;
discriminating, by a discriminator, based on the fore and rear positions detected by the incremental sensor unit, which one of the detected sequence and the inverted sequence should be searched for;
searching, by a searcher, the second binary sequence for the detected sequence or the inverted sequence discriminated by the discriminator; and
detecting, by a position detector, a position of said absolute sensor unit based on a position of the detected sequence or the inverted sequence found by said searcher in the second binary sequence and the fore and rear positions detected by the incremental sensor unit.
6. The method according to claim 5 , further comprising discriminating, by the discriminator, based on whether the detected sequence or the inverted sequence is found by said searcher, which one of the two values of the first binary sequence, which is replaced from one value of the second binary sequence, is detected by said absolute sensor unit.