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Chain code encoder

  • US 4,628,298 A
  • Filed: 06/22/1984
  • Issued: 12/09/1986
  • Est. Priority Date: 06/22/1984
  • Status: Expired due to Term
First Claim
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1. An apparatus providing information of the position of a rotating member having an axis of rotation, comprisingcode means positioned for rotation with the rotating member for providing a code sequence of code cycles arranged circumferentially about the axis of rotation of the rotating member, wherein each code cycle is associated with a unique position of the rotating member and provides position data, and further wherein the position data from each code cycle, in combination with the position data from adjacent N-1 consecutive code cycles, defines a pattern which is unique from the pattern formed by the position data from any other N consecutive code cycles in the code sequence, so that each N consecutive code cycles identify a unique position of the rotating member wherein the code sequence comprises a series of bits formed by the bits occupying a selected bit position in each of the words in a sequence of N-bit code words the sequence of N-bit code words being formed according to the steps of:

  • a. beginning with all N-bits of a first N-bit code word in a first logic state;

    b. shifting the bits in the first N-bit code word by one bit position so that a bit position is vacated;

    c. setting the vacated bit position to a second logic state, different from the first logic state, to form a new N-bit code word and assigning the new N-bit code word to the sequence of N-bit code words if the new N-bit code word does not match any of the other N-bit code words in the sequence of N-bit code words;

    d. setting the vacated bit position to the first logic state to form an alternate N-bit code word and assigning the alternate N-bit code word to the sequence of N-bit code words if the new N-bit code word of step "c" matches any of the other N-bit code words in the sequence of N-bit code words; and

    e. repeating steps "b" through "d" until 2N N-bit code words are present in the sequence of N-bit code words, wherein in step "b" the "first N-bit code word" is replaced by the N-bit code word that was assigned to the sequence of N-bit code words in steps "c" and "d";

    means for reading the code cycles of the code sequence which are brought into instantaneous registration with a monitoring point as the rotating member is rotated, wherein the monitoring point is fixed in position relative to the rotating member;

    means coupled to the reading means for extracting the position data from the code cycles being read by the reading means and for temporarily storing the position data in the order received; and

    means coupled to the extracting and storing means for converting the consecutive sequence of the N most recently received position data into positional information.

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