Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1991-03-07
1992-05-26
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
341 13, G01D 534
Patent
active
051171058
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an absolute encoder employing recurring decimal codes.
DESCRIPTION OF THE PRIOR ART
Heretofore, general absolute encoders have used a code plate having a plurality of tracks having different numbers of slits and arranged radially to produce binary codes or gray codes having the desired number of bits. With such an arrangement, however, it is difficult to provide a compact high-resolution absolute encoder since the number of tracks increases as the number of bits increases.
One solution to the above problem is an absolute encoder which employs M-series random numbers.
As is well known in the art, the M-series random numbers are the longest sequence of numbers that can be produced using a shift register A k-bit shift register can generate recurring patterns of 2.sup.k -1 codes other than 0. For exmaple, a 4-bit shift register as shown in FIG. 7 produces codes given in Table 1, below, on the condition that R0 through R3 in FIG. 7 do not become 0 at the same time.
TABLE 1 ______________________________________
No. R.sub.3
R.sub.2 R.sub.1
R.sub.0
______________________________________
1 0 0 0 1
2 0 0 1 1
3 0 1 1 1
4 1 1 1 1
5 1 1 1 0
6 1 1 0 1
7 1 0 1 0
8 0 1 0 1
9 1 0 1 1
10 0 1 1 0
11 1 1 0 0
12 1 0 0 1
13 0 0 1 0
14 0 1 0 0
15 1 0 0 0
______________________________________
The M-series random numbers thus produced are composed of recurring patterns of different 2.sup.k -1 codes. If a code disc has a circumferential array of opaque areas representing "0" and transparent areas representing "1" and a pattern of adjacent k bits representing opaque and transparent areas is read from the array, then an absolute circumferential position on the disc can be determined since there is only one such pattern on the circumference of the disc.
SUMMARY OF THE INVENTION
General absolute encoders are of the resolution of 2.sup.k using binary codes or gray codes. The above absolute encoder with the M-series random numbers can achieve a resolution of only 2.sup.k -1 and is not compatible with the general value encoders.
It is an object of the present invention to provide an absolute value encoder having a particular resolution.
A first absolute encoder according to the present invention comprises a code plate divided into N equal slits each coded 0 or 1 for producing a sequence of recurring random numbers whose binary codes (B.sub.1 -B.sub.N) composed of successive P slits are different from each other and a detector device for reading the codes of successive P slits of the code plate so that the absolute angle of the code disc within one revolution can be detected.
FIG. 1 is a flowchart of the process for generating recurring random number codes with the first absolute encoder.
First, the first P-bit code B'.sub.1 composed of 0 or 1 is established in step 1. The P bits serve as the first P numbers of a sequence of random numbers. Then, the initial code B'.sub.1 is shifted one bit to the right (or the left) in step 2. If the initial code B'.sub.1 is shifted to the left, then the processing is executed as indicated in the parentheses below. The MSB (most significant bit)) (or LSB (least significant bit)) of the initial code B'.sub.1 after it has been shifted to the right (or the left) is set at 0. This bit serves as the (P+1)th number of a sequence of random numbers. A newly generated P-bit code B'.sub.2 and the initial code B'.sub.1 are compared with each other in step 3. If the two codes differ from each other, control goes to step 4, and if the two codes are equal, control goes to step 5. Step 4 determines whether the new code is an Nth code or not. If the new code is an Nth code, control goes to step 6, and if the new code is not an Nth code, control returns to step 2. It is now assumed that at an ith code B'.sub.i is generated, and control goes from step 4 back to step 2. In step 2, this code is shifted one bit to the right (or the left), and the MSB (or the LSB) is set at 0, producing a new code B'.sub.i+1. Step 3 the
REFERENCES:
patent: 4720699 (1988-01-01), Smith
patent: 5038243 (1991-08-01), Gordon
IEEE Tr. On Instr. and Measurement; vol. IM-36, No. 4, Dec. 1987, N.Y., USA pp. 950-955; Emil M. Petriu: "Absolute-Type Position Transducers Using a Pseudorandom Encoding" FIG. 1; Tables 1, 2.
Higashi Kouichi
Nagase Takashi
Davenport T.
Kabushiki Kaisha Yaskawa Denki Seisakusho
Nelms David C.
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