Rotary coding disc and method for designing the same

Abstract

A rotary coding disc and a method for designing the same is applied to an optical encoder. N-bit De Bruijn sequences include 1 and 0. The N-bit De Bruijn sequence has the maximum binary code and the minimum binary code. When a binary code having M bits is located between the maximum binary code and the minimum binary code, the corresponding N-bit De Bruijn sequences are selected as diagonal De Bruijn sequences, wherein $\frac{2^N-2N}{2}-\frac{N}{2}<M<\frac{2^N-2N}{2}+\frac{N}{2}.$
The De Bruijn sequence may be converted into a De Bruijn energy level. The total number of 1 consecutively neighboring 0 and (N−1) consecutively neighboring N of the De Bruijn energy level is calculated. The transparent areas and the opaque areas are located based on the De Bruijn sequence or the De Bruijn energy level that corresponds to the total number less than or equal to N.

Claims

1. A rotary coding disc, applied to an optical encoder, comprising: a plurality of transparent areas; and a plurality of opaque areas; wherein the plurality of transparent areas and the plurality of opaque areas are circularly distributed; wherein the number of N-bit De Bruijn sequences is 2.sup.[2.sup.(N-1).sup.−N], the N-bit De Bruijn sequences include 1 and 0, N is a natural number larger than or equal to 3, and each of the N-bit De Bruijn sequences has a length of 2.sup.N, a maximum binary, code with a length of N bits, and a minimum binary code with a length of N bits; wherein when a binary code with a length of M bits is located between the maximum binary code and the minimum binary code, the corresponding N-bit De Bruijn sequences are selected as diagonal De Bruijn sequences, M is a positive integer, and $\frac{2^N-2N}{2}-\frac{N}{2}<M<\frac{2^N-2N}{2}+\frac{N}{2};$ wherein positions of the plurality of transparent areas and the plurality of opaque areas are arranged based on the diagonal De Bruijn sequences.

2. The rotary coding disc according to claim 1, wherein a first number of each bit of the diagonal De Bruijn sequence is added to second numbers of (N−1) bits consecutively neighboring the first number to obtain a value of an energy level, the value of the energy level replaces a corresponding the first number to convert the De Bruijn sequence into a De Bruijn energy level, the De Bruijn energy level includes the value of the energy level, the value of the energy level is a non-negative integer less than or equal to N, the total number of 1 consecutively neighboring 0 and (N−1) consecutively neighboring N of the De Bruijn energy level is calculated, and the positions of the plurality of transparent areas and the plurality of opaque areas are arranged based on the De Bruijn energy level that corresponds to the total number less than or equal to N.

3. The rotary coding disc according to claim 1, wherein positions of 1 and 0 of the diagonal De Bruijn sequence respectively correspond to the positions of each of the plurality of transparent areas and each of the plurality of opaque areas.

4. The rotary coding disc according to claim 1, wherein positions of 0 and 1 of the diagonal De Bruijn sequence respectively correspond to the positions of each of the plurality of transparent areas and each of the plurality of opaque areas.

5. The rotary coding disc according to claim 1, wherein a number of each bit of the maximum binary code is 1 and a number of each bit of the minimum binary code is 0.

6. A method for designing a rotary coding disc, applied to an optical encoder with transparent areas and opaque areas, comprising: forming N-bit De Bruijn sequences with 1 and 0, wherein the number of the N-bit De Bruijn sequences is 2.sup.[2.sup.(N-1).sup.−N], N is a natural number larger than or equal to 3, and each of the N-bit De Bruijn sequences has a length of 2.sup.N, a maximum binary code with a length of N bits, and a minimum binary code with a length of N bits; when a binary code with a length of M bits is located between the maximum binary code and the minimum binary code, the corresponding N-bit De Bruijn sequences are selected as diagonal De Bruijn sequences, M is a positive integer, and $\frac{2^N-2N}{2}-\frac{N}{2}<M<\frac{2^N-2N}{2}+\frac{N}{2};$ and arranging positions of the transparent areas and the opaque areas based on the diagonal De Bruijn sequences, wherein the transparent areas and the opaque areas are circularly distributed.

7. The method for designing a rotary coding disc according to claim 6, wherein after the step of selecting the diagonal De Bruijn sequences, the method further comprising: adding a first number of each bit of the diagonal De Bruijn sequence to second numbers of (N−1) bits consecutively neighboring the first number to obtain a value of an energy level, and replacing a corresponding the first number with the value of the energy level to convert the diagonal De Bruijn sequence into a De Bruijn energy level, wherein the De Bruijn energy level includes the value of the energy level, and the value of the energy level is a non-negative integer less than or equal to N; and calculating a total number of 1 consecutively neighboring 0 and (N−1) consecutively neighboring N of the De Bruijn energy level, and arranging the positions of the transparent areas and the opaque areas based on the De Bruijn energy level that corresponds to the total number less than or equal to N.

8. The method for designing a rotary coding disc according to claim 6, wherein positions of 1 and 0 of the diagonal De Bruijn sequence respectively correspond to the positions of the transparent area and the opaque area.

9. The method for designing a rotary coding disc according to claim 6, wherein positions of 0 and 1 of the diagonal De Bruijn sequence respectively correspond to the positions of the transparent area and the opaque area.

10. The method for designing a rotary coding disc according to claim 6, wherein a number of each bit of the maximum binary code is 1 and a number of each bit of the minimum binary code is 0.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram schematically illustrating a conventional optical encoder;

(2) FIG. 2 is a diagram schematically illustrating a conventional coding disc;

(3) FIG. 3 is a diagram schematically illustrating the intensity of the waveform of a conventional voltage signal;

(4) FIG. 4 is a diagram illustrating Table 1;

(5) FIG. 5 is a diagram schematically illustrating a rotary coding disc according to an embodiment of the present invention;

(6) FIG. 6 is a diagram schematically illustrating the intensity of the waveform of a voltage signal of the present invention;

(7) FIG. 7 is a diagram schematically illustrating the intensity of the waveform of voltage signals corresponding to Table 1 and Table 2 of the present invention;

(8) FIG. 8 is a diagram illustrating Table 2;

(9) FIGS. 9(a)-9(c) are diagrams illustrating Table 3;

(10) FIGS. 10(a)-10(c) are diagrams illustrating Table 4; and

(11) FIG. 11 is a diagram schematically illustrating the energy levels of five-bit De Bruijn sequences of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(12) FIG. 5 is a diagram schematically illustrating a rotary coding disc according to an embodiment of the present invention. FIG. 6 is a diagram schematically illustrating the intensity of the waveform of a voltage signal of the present invention. Referring to FIG. 5 and FIG. 6, an embodiment of the method for designing a rotary coding disc 20 is introduced as follows. The rotary coding disc 20 is applied to an optical encoder. The rotary coding disc 20 includes a plurality of transparent areas and a plurality of opaque areas. The plurality of transparent areas and the plurality of opaque areas are circularly distributed. In the method, N-bit De Bruijn sequences with 1 and 0 are used, wherein the number of the N-bit De Bruijn sequences is 2.sup.[2.sup.(N-1).sup.−N], N is a natural number larger than or equal to 3. Each N-bit De Bruijn sequence updates one bit within one cycle to represent 2.sup.N different N-bit sequences. For example, a three-bit De Bruijn sequence may be 00010111. The three-bit De Bruijn sequence represents 8 different three-bit subsequences, namely 000, 001, 010, 101, 011, 111, 110, and 100. Each N-bit De Bruijn sequence has a length of 2.sup.N, the maximum binary code with a length of N bits, and the minimum binary code with a length of N bits. For example, the positions of the transparent areas and the opaque areas of the rotary coding disc 20 are arranged based on the N-bit De Bruijn sequences including 0 and 1. In an embodiment, the positions of 1 and 0 respectively correspond to the positions of the transparent area and the opaque area. In another embodiment, the positions of 0 and 1 respectively correspond to the positions of the transparent area and the opaque area. In some embodiment of the present invention, a number of each bit of the maximum binary code is 1 and a number of each bit of the minimum binary code is 0, but the present invention is not limited thereto.

(13) If N=9, the positions of transparent areas and opaque areas of the rotary coding disc 20 are arranged based on nine-bit De Bruijn sequences formed of 1 and 0, wherein 1 and 0 respectively represent the positions of transparent areas and opaque areas. The rotary coding disc 20 is divided into 512 positions. The nine-bit De Bruijn sequences include 2.sup.247 De Bruijn sequences. Take Table 2 as an example. Table 2 shows one of the nine-bit De Bruijn sequences. From Table 2 of FIG. 8 and FIG. 5, 111111111 and 000000000 are located in diagonal positions of the rotary coding disc 20. In other words, the maximum binary code and the minimum binary code are located in the diagonal positions of the rotary coding disc 20. In an optical encoder, a photosensor receives a light signal through the rotary coding disc 20 to generate a current signal. The photosensor converts the current signal into a voltage signal through the resistances. The intensity of the voltage signal is illustrated in FIG. 6 during the rotary coding disc 20 rotates one cycle. FIG. 7 is a diagram schematically illustrating the intensity of the waveform of voltage signals corresponding to Table 1 and Table 2 of the present invention. Compared with the voltage signal corresponding to Table 1, the voltage signal corresponding to Table 2 can effectively reduce the variation of the voltage level of a periodic signal and the burden of the processing circuit in the back end.

(14) If N=5, the positions of transparent areas and opaque areas of the rotary coding disc 20 are arranged based on five-bit De Bruijn sequences formed of 1 and 0, wherein 1 and 0 respectively represent the positions of transparent areas and opaque areas. The rotary coding disc 20 is divided into 32 positions, wherein position 1, position 2, . . . , position 31, and position 32 respectively represent the first bit, the second bit, . . . , the 31st bit, and the 32nd bit. The five-bit De Bruijn sequences include 2.sup.[2.sup.(5-1).sup.−5]=2048 different De Bruijn sequences. Take Table 3 as an example. Table 3 shows 64 five-bit De Bruijn sequences. FIGS. 9(a)-9(c) are diagrams illustrating Table 3. FIGS. 9(a)-9(c) belong to the same table. From Table 3, it is known that 11111 and 00000 are located in the diagonal positions of the rotary coding disc 20.

(15) According to Table 2 and Table 3, when a binary code with a length of M bits is located between the maximum binary code and the minimum binary code, the corresponding N-bit De Bruijn sequences are selected as diagonal De Bruijn sequences. M is a positive integer, and

(16) $\frac{2^N-2N}{2}-\frac{N}{2}<M<\frac{2^N-2N}{2}+\frac{N}{2}.$
Table 2 shows the diagonal De Bruijn sequence. Finally, the positions of the plurality of transparent areas and the plurality of opaque areas of the rotary coding disc 20 are arranged based on the diagonal De Bruijn sequences. For example, the positions of 1 and 0 of the diagonal De Bruijn sequence respectively correspond to the positions of the transparent area and the opaque area. The transparent areas and the opaque areas may be circularly distributed.

(17) In order to further reduce the variation of the voltage level of the periodic signal, the following steps may be performed after selecting the diagonal De Bruijn sequences.

(18) The first number of each bit of the diagonal De Bruijn sequence is added to the second numbers of (N−1) bits consecutively neighboring the first number to obtain the value of the energy level. The value of the energy level replaces the corresponding first number to convert the diagonal De Bruijn sequence into a De Bruijn energy level. The De Bruijn energy level includes the value of the energy level. The value of the energy level is a non-negative integer less than or equal to N. Take N=5 as an example. FIGS. 10(a)-10(c) are diagrams illustrating Table 4. FIGS. 10(a)-10(c) belong to the same table. Table 4 shows the De Bruijn energy level. Take the first diagonal De Bruijn sequence in Table 3 as an example. The first number of the third bit is 0. The second numbers of four bits, being located at the left and right sides of the first number of the third bit and consecutively neighboring the first number of the third bit, are 0. Thus, the corresponding value of the energy level is 0. Alternatively, the second numbers of four bits, being located at the right side of the first number of the third bit and consecutively neighboring the first number of the third bit, are 0, 0, 1, and 0. Thus, the corresponding value of the energy level is 1. All the diagonal De Bruijn sequences are converted into the De Bruijn energy levels based on the same rule. In addition, if the second numbers of four bits being located at the left side of the first number of the first bit and consecutively neighboring the first number of the first bit are selected, the second numbers of the 29th, the 30th, the 31st, and 32nd bits are selected. This is because the De Bruijn sequence is a cyclic sequence. The 32nd bit neighbors the first bit.

(19) In Table 4, the rightmost column represents the total number of 1 consecutively neighboring 0 and (N−1) consecutively neighboring N of the De Bruijn energy level. The fourth De Bruijn energy level corresponds to the highest total number. The 25.sup.th De Bruijn energy level corresponds to the lowest total number. FIG. 11 is a diagram schematically illustrating the energy levels of the fourth and 25.sup.th De Bruijn energy levels of the present invention. From FIG. 11, it is known that the value of the energy level of the 25.sup.th De Bruijn energy level more frequently varies but has small variations. In the conventional technology, the value of the energy level of the De Bruijn energy level has a higher variation such that the voltage signal suddenly drops, which is different from the 25.sup.th De Bruijn energy level. As a result, the total number of 1 consecutively neighboring 0 and (N−1) consecutively neighboring N of the De Bruijn energy level is calculated. The positions of the plurality of transparent areas and the plurality of opaque areas are arranged based on the De Bruijn energy level that corresponds to the total number less than or equal to N.

(20) According to the embodiments provided above, the maximum binary code and the minimum binary code of the De Bruijn sequence are located in the diagonal positions of the rotary coding disc in order to effectively reduce the variation of the voltage level of a periodic signal and the burden of the processing circuit in the back end.

(21) The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Therefore, any equivalent modification or variation according to the shapes, structures, features, or spirit disclosed by the present invention is to be also included within the scope of the present invention.