JP2632534B2 - Rotary encoder - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary encoder suitable for use in, for example, an angle measuring device for detecting a relative rotation angle between two objects.

[Summary of the Invention]

The present invention is, for example, a rotary encoder suitable for use in an angle measuring device for detecting a relative rotation angle between two objects, and has a grating formed at a pitch angle λ by equally dividing one cycle T. A lattice disk, and a detection unit having a pair of detection elements for outputting an electric signal in response to the rotation of the lattice.
に お い て In a rotary encoder that outputs two-phase detection signals having different phases, a pair of detection elements is (m + 1/4) λ
(M is a positive integer) and a simple configuration using two detection elements, such that the sum signal and the difference signal of the output signals of these detection elements are used as the two-phase detection signals. In this method, the detection error can be averaged and reduced.

[Conventional technology]

A rotary encoder for detecting a relative rotation angle between two objects is widely used as a feedback element of a servomotor, a detection element of an angle measuring device, and the like. FIG. 7 shows an example of a conventional rotary encoder. In FIG. 7, (1) shows an input axis, and this input axis (1) has a light-dark pattern grid (2) formed at a pitch angle λ by equally dividing one period T (360 °). The lattice disk (3) is fixed. The input shaft (1) is usually connected to a spindle or the like of an external motor and held rotatably in the θ direction, and the rotation of the input shaft (1) causes the lattice disk (3) to rotate.

Further, (9) shows a detecting portion for reading the grating (2), and the detecting portion (9) is formed with the same pattern graduation as that of the grating (2) in two sections with a phase shift of 90 ° from each other. A reference scale (5) having a reference grating (4) and a light emitting element (6) illuminating these gratings (2) and (4).
a) and (6b), and a photoelectric element (7) that photoelectrically converts illumination light passing through these grating (2) and reference grating (4).
a) and (7b), and buffer amplifiers (8a) and (8b) for receiving the outputs of these photoelectric elements. Here, the lattice disk (3) will be described with reference to FIG. 8 in which the positional relationship between the photoelectric elements (7a) and (7b) is expressed with a large pitch angle λ of the lattice (2). (4) is divided into two sections having phases different from each other by 90 ° (λ / 4 at an angle), so that the photoelectric elements (7a) and (7b) corresponding to them have an angle of (n + 1/4) λ (n is (Positive integers) apart, and the resulting signals U _A and U _B are 90 ° out of phase, so the detection signals φ differ from the buffers (8a) and (8b) by 90 ° from each other. _A and phi _B is obtained. The detection signal phi _A and phi _B for rotation in the θ direction of the grating disc (3), one cycle has a sine wave of lambda.

These detection signals phi _A and phi _B in Figure 7 is inputted to the further interpolation circuits (10), the direction discrimination and 1 cycle λ subdivision pulses generated is performed, up from the interpolation circuit (10) A count pulse UP and a down count pulse DN corresponding to the reverse rotation are output, respectively. Reference numeral (11) denotes a reversible counter for integrating and counting these pulses and displaying the rotation angle of the lattice disk (3). In this way, direction discrimination and 1
Since interpolation is performed within the period λ, two signals having phases different by 90 ° are required as detection signals.

[Problems to be solved by the invention]

High precision is required in the rotary encoder, but the angular position error E _theta is the rotary encoder by the pitch error or the like at the time of production of eccentricity and the grating of the grating disc, which is a component of (3) (2) Exists. The error _Eθ is, for example, a master rotary encoder (not shown) in which the count value of the reversible counter (11) in FIG. 7 when the amount of rotation of the lattice disk (3) is θ is connected to the input shaft (1) without eccentricity. ) Can be obtained by processing the detection signal and comparing it with the count value obtained by processing.

Here, in the rotary encoder, since one rotation is 360 ° and the displacement is periodic, the angular position error _Eθ is shown in FIG.
As shown in the figure, the period T is a 360 ° periodic function.
Therefore, if the error E _θ is Fourier analysis, Can be expressed as In equation (1), F _K sin (K
θ + α _K ) is a K-order component of the error E _θ , and F _K and α _K are constants, respectively. Furthermore, the output U _iota photoelectric elements at angular position θ _U ι = Asin [N _(θ + E θ)], (N = 360 ° / lambda) can be expressed as ...... (2), A in formula (2) Is the amplitude, and N is the number of patterns in one rotation. For example, the error E in FIG.
_θ can be represented by the sum of a primary component as shown in FIG. 9B and a secondary component as shown in FIG. 9C.

However, since the conventional rotary encoder shown in FIG. 8 does not have an error correction function, the angular position error _{Eθ in} FIG. 9A is not corrected, and for example, the reversible counter (11) in FIG.
Has a disadvantage in that a value obtained by adding the error _Eθ to the true value is counted and displayed.

Therefore, in order to correct the error _Eθ , a rotary encoder as shown in FIG. 10 has been conventionally proposed. Tenth
In the figure, (7a) and (7b) show photoelectric elements having the same positional relationship as in FIG. 8, and further, photoelectric elements (7c) and (7d) are arranged at positions 180 ° away from those photoelectric elements. It is set up. Also, the output signals U _{A of the} photoelectric elements (7a) and (7c)
And U _B are next to be added by the add unit (12a) A phase signal phi _A, the output signal U _B and U _D of the photoelectric element (7b) and (7d) are added by the sum calculator (12b) B-phase signal the φ _B. At this time, the 2-phase signals phi _A and phi _B are each _{φ A = U A + U C} = Asin [N _(θ + E θ)] + Asin _{[N (θ + E θ + π} ) ] = 2Acos _(Nα θ) sin [N _(θ + ε θ )] ......
_{(3) φ B = 2Acos (} Nα θ) cos [N _(θ + ε θ)] ......
(4) However, an _{α θ = (E θ -E θ} + π) / 2, ε θ (E θ + E θ + π) / 2 ...... (5), has placed the convenience 180゜Wo [pi in subscript E _theta. Here, when substituting equation (1) into equation (5), From the error ε _θ , it can be seen that the odd-order Fourier components in the angular position error E _θ are removed. Therefore,
In the conventional rotary encoder shown in FIG. 10, the odd-order errors are removed. However, this echo system requires at least four photoelectric elements (7a), (7b), (7c) and (7d). However, there is a disadvantage that the size is increased and the price is increased.

The present invention has been made in view of such problems, and an object is to provide a rotary encoder with a simple structure having a function of correcting the angular position error E _theta.

[Means for solving the problem]

A rotary encoder according to the present invention comprises a grating disk (3) having a grating (2) formed at a pitch angle λ by equally dividing one period T (360 °), as shown in FIG. grating pair of detection elements for outputting in response to rotation respectively electric signals V _a and V _B of (2) (13a) and become more detector having (13b) and (9), the grid disc (3) In a rotary encoder that outputs two-phase detection signals φ _A and φ _B having a phase difference of 90 ° in accordance with the relative rotation between the detection elements (9), the pair of detection elements (13a) and (13b) are set to (m +
1/4) lambda (with m places a positive integer) apart, and the sum signal and the difference signal of the output signal V _A and V _B of the detection element and a detection signal phi _A and phi _B of the two-phase Things.

The rotary encoder of the present invention includes a pair of detecting elements (13a) and (13b) as shown in FIG. They are arranged apart.

[Action]

According to the present invention, the pair of detecting elements (13a) and (13a) spaced apart from each other by (m + 1/4) λ (= W).
The angular position error in the output signal V _A and V _B of b) the angle theta E _theta
Assuming that T / λ (360 ° / λ) is N, V _A = Asin [N (θ + E _θ )] and V _B = Asin [θ + w + E _θ + w)]. Therefore, the two-phase detection signals φ _A and φ _{B which} are the sum signal and the difference signal thereof are It is expressed as Here, A ₁ and A ₂ have amplitudes of | A ₁ || A ₂ |. These have an angular position error of (E _θ + E _θ +
w) / 2 means that the angular position error is reduced by the effect of averaging.

Also, a pair of detecting elements (13a) and (13b) If you place them apart, From the equations (7) and (8), the angular position error is φ _A and φ
_{B is} (E _θ + E _θ + π) / 2. The angular position error becomes the same as the angular phase error epsilon _theta contained in the detection signals of two phases of a conventional rotary encoder of FIG. 10 of formula (3) and (4), apparent from equation (6) In this manner, the odd-order error components in the angular position error _Eθ are removed.

[Embodiment] Hereinafter, an embodiment of the rotary encoder of the present invention will be described as a first
This will be described with reference to the drawings. In the drawings, portions corresponding to FIGS. 7 and 8 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, (3) is a grid disk which is held rotatably in the θ direction. On the outer periphery of the lattice disk (3), 36
The pitch angle λ (N = 360) obtained by dividing 0 ゜ (one cycle T) into N equal parts
A grid (2) having a light / dark pattern of (゜ / λ) is formed. Also, (9) denotes a detection unit that outputs a detection signal phi _A and phi _B of two phases in accordance with rotation of the grating (2), a pair of detector elements in the detector (9) (13a) and ( 13b) is disposed in the vicinity of the lattice disk (3) and separated by (m + 1/4) λ (m is a positive integer). The detection elements (13a) and (13
b) may be considered as elements corresponding to the photoelectric elements (7a) and (7b) in FIG. 7, but when the division number N increases,
Further, it can be considered as an element including a reference scale (5) forming a conventional reference grating (4). Thus, the grating (2) is from detector elements correspondingly rotates in the θ direction (13a) and (13b) to obtain an output signal V _A and V _B,
The angular position error E _theta, When W a (m + 1/4) λ , using the constants A V _A = Asin [N _(θ + E θ)], V _B = Asin _{[N (θ + W + E θ} + w) ] ...... ( 9) can be expressed.

Also, in FIG. 1, the output signal V _A and V _B are inputted together add unit (14a) and a difference calculator to (15a). OR calculator (14a) outputs an A-phase signal phi _A and calculates the sum of the two input signals, a difference calculator (15a) output a B-phase signal phi _B by calculating the difference between the two input signals I do. From equation (9), φ _A
And φ _B are respectively , And the detection signals are 90 ° out of phase with each other. However, A ₁ and A ₂ indicate the amplitude, And ignoring E _θ + E _θ + w, Holds. These two-phase signals φ _A and φ _B are supplied from terminals (16) and (17) of FIG. 1 to an external circuit such as an interpolation circuit (10) shown in FIG.

Next, the operation of the present embodiment will be described. In the present embodiment, the angular position error of the finally obtained two-phase detection signals φ _A and φ _B is given by the following equation
( _Eθ + _Eθ + w) / 2 as shown in (0) and (11).
Included in the form. Accordingly, since the error at the angular position θ and the error at the angular position (θ + W) are averaged, the errors cancel each other out and become smaller. Moreover, the number of detection elements is two, which is the same as the conventional example shown in FIG. 8, and error correction is performed with an extremely simple structure.

Here, the case where the value of m is selected so that mλ becomes T / 2, that is, 180 ° in the rotary encoder of FIG. 1 will be described with reference to FIG.

In FIG. 2, two detection elements (13a) and (13
The configuration is the same as that of FIG. 1 except that b) is arranged 180 ° + λ / 4 apart. This is mλ = T / 2 (= 180 °)
It means that the value of m was selected such that In this case, considering a general case where the number of divisions N is sufficiently large (pitch angle λ << 180 °), Holds, the detection signal φ _{A is obtained} from Expressions (10) and (11).
And φ _B are respectively Is represented by However, the error ε _θ is the same as the equation (5) (E _θ
+ E _θ + π) / 2. This error is epsilon _theta is the same as the error of the detection signal obtained by the Fig. 10 of the rotary encoder of the formula (3) and (4), since the equation (6) is applied as it is, the mechanical initial Angular position error E _θ
The odd-order components therein have been removed.

Generally the largest component in the angular position error E _theta is the primary component due to the eccentricity of the grating disk (3), since an error of odd words primary components are removed, according to the encoder of the second illustrated example The effect is great.

Here, FIGS. 4 and 5 show the measurement results of the angular position error of the encoder of FIG.

FIG. 4 shows the results obtained by using a commercially available rotary encoder having a grid division number N of 5,000, changing the arrangement of the detection elements and the processing circuit, and comparing the error with that of the master rotary encoder. The encoder is calibrated by a method as disclosed in, for example, Journal of Precision Engineering, Vol. 52, 10 (1986) P1732. 4A shows the error when the configuration of the conventional rotary encoder shown in FIG. 8 is used, and FIG. 4B shows the error when the configuration of the rotary encoder shown in FIG. 2 is used. In FIG. 4B, it can be seen that the primary error component has been removed, but the secondary error component remains.

FIG. 5 shows the measurement results of a rotary encoder having a grid division number N of 5400, and FIG. 5A shows the conventional method of FIG.
FIG. B shows errors when the configuration of the system shown in FIG. 2 is used. In FIG. 5B, the secondary component remains as in FIG. 4B. In this way, it was experimentally confirmed that the rotary encoder of FIG. 2 can remove odd-order error components.

As described above, the rotary encoder of this embodiment can remove odd-order error components in the same manner as the conventional rotary encoder of FIG. 10, but its configuration requires only two detection elements.
Compared to the case shown in the figure, the encoder can be downsized and the cost can be further reduced.

Next, another embodiment of the rotary encoder of the present invention will be described with reference to FIG.

In FIG. 3, the detecting elements (13c) and (13d) are arranged at T / 4, that is, 90 ° apart from the detecting elements of FIG. 2, respectively. Further, the processing circuit includes a sum calculator (14a), (1
4b), (18a) and (18b) are converted to difference arithmetic units (15a) and (15
b) is provided. Here, each detection element (13a), (13
b), (13c) and (13d) as V _A , V _B , V _C and V _D , respectively, and the sum operation units (14a) and (14b) and the difference operation units (15a) and (15b) Assuming outputs W _A , W _C , W _B, and W _D , respectively, the wirings in FIG. 3 are: W _A = V _A + V _B , W _B = V _A −V _B W _C = V _C + V _D , W _D = V _C −V _D is established. Furthermore, the signal W _A and W _C is the sum calculator (18a) at is added A-phase signal phi _A, and the signal W _B
And W _D is formed by adding the B-phase signal phi _B by the sum calculator (18b). When calculating in the same manner as the first illustrated _{example, φ A = W A + W} C = 4AK A sin [N _(θ + ε θ + Φ] _{... (15) φ B = W} B + W D = 4AK B cos [N] θ ₊ ε θ + Φ] (16) where Φ = 90 ° and ε _θ = E _θ + E _{θ + π / 2} + E _{θ + π} + E _{θ + 3π / 2} ) / 4
... (17) K _A = cos (Nb _θ ) cos (NC _θ- φ) K _B = cos (Nb _θ ) sin (NC _θ- φ) b _θ = (E _θ- E _{θ + π / 2} ) / 2 C _{θ = (E θ + E θ +} π / 2 -E θ + π -E θ + 3π / 2)
/ 4. These are in subscript angular position error E _theta formula represents convenience 180 ° is [pi. At this time, ε _{θ in} equation (17)
Substituting equation (1) for the error E _θ in And errors of higher-order components other than a multiple of 4 have been removed.

The rotary encoder of FIG. 3 is constructed by modifying a commercially available rotary encoder, and the results of error measurement are shown in FIGS. 4C and 5C. FIG. 4C shows the number of divisions N =
In this case, 5000 grids were used, and the error was almost the same as the result of the example in FIG. 2 (FIG. 4B) except that the secondary component was removed.
Furthermore, the correctness of the theoretical analysis is supported from the place where the fourth-order component remains. Similarly, FIG. 5C shows a case in which a grid having a division number N = 5400 is used. However, an error curve from which the secondary component has been further removed is obtained as compared with FIG. 5B, and the fourth-order component remains. ing.

As described above, in the rotary encoder of the third illustrated example, not only the odd order components of the mechanical initial angular position error E _theta, even even-order components except multiples next 4 Since it has been removed, more accurate angle detection is possible.

Next, an example in which the rotary encoder of the present invention is applied to a magnetic encoder will be described with reference to FIG.

In FIG. 6, reference numeral (20) denotes a magnetic disk. The magnetic disk (20) is rotatable in the .theta. Direction, and has a magnetic graduation having a pitch angle .lamda. (21) is formed. (19) shows the detection unit as a whole, in which (22a) and (22b) The magnetic heads are spaced apart from each other, and the pair of magnetic heads (22a) and (22b) correspond to the detecting element in the example of FIG. The magnetic heads (22a) and (22b) have oscillators (2
Exciting signal f ₀ output from 5) is supplied via the V / I converter (26). The signal f ₀ has an amplitude I and an angular frequency ω, Can be expressed as

The output signal obtained from the magnetic head (22a) and (22b) is supplied to the respective band-pass filter (23a) and (23b), 2 times the high-frequency component P _A and P _B are filtered. P _A and P _B
Is expressed by the following equation using a constant P ₀ and an angular position error E _θ .

P _A = P ₀ cosωt sin [N (θ + E _θ )] These signals P _A and P _B are taken by the A-phase signal phi _{A 'added} by the add unit (14a). On the other hand, the signal P _A and P _B is 90 ° phase shifter (24a) and are respectively supplied to the (24b) signal P _A represented by the following formula 'and P _B'.

P _A '= P ₀ sinωt sin [N (θ + E _θ )] The difference between these signals P _A ′ and P _B ′ is calculated by a difference calculator (15a) to become a B-phase signal φ _B ′. Equations (10) and (1
By the same operation as 1) | P ₁ || P ₂ | holds. Signal phi _{A 'and} phi _B' are added in the mixing circuit (27) a phase-modulated signal f _theta. Here, if P ₁ P ₂ Thereafter, the angular displacement is obtained as a count value by the method disclosed in, for example, Japanese Patent Publication No. 52-17427.

In the rotary encoder of FIG. 6, the second
As in the illustrated example, the odd-order component of the angular position error _Eθ is removed.

In the embodiment, an example is shown in which the rotary encoder of the present invention is applied to a photoelectric encoder and a magnetic encoder. However, it is apparent that the present invention can be applied to, for example, a capacitive encoder or an electromagnetic induction encoder.

[Effect of the Invention] In the rotary encoder of the present invention, a pair of detection elements are arranged at a distance of (m + 1/4) λ, and a sum signal and a difference signal of output signals of these detection elements are two-phase detection signals. Therefore, the angular position error _Eθ is averaged and reduced.
Further, the configuration is simple, and the size of the detector can be reduced to further reduce the cost.

Further, one cycle is T, and a pair of detecting elements is T / 2 + λ / 4.
If they are arranged apart, it is possible to remove odd-order error components of the angular position error _Eθ .

[Brief description of the drawings]

1 is a block diagram showing an embodiment of the rotary encoder of the present invention, FIG. 2 is a block diagram showing a case where mλ = 180 ° in FIG. 1, and FIG. 3 is another practical example of the rotary encoder of the present invention. FIG. 4 and FIG. 5 are error curve diagrams showing measurement results of detection errors of the conventional and present rotary encoders, and FIG. 6 is a diagram showing an example in which the present rotary encoder is applied to a magnetic encoder. FIG. 7 is a block diagram including a partial perspective view showing a conventional rotary encoder, and FIG.
The figure shows the rotating disk (3) and the photoelectric elements (7a) and (7) in FIG.
configuration diagram for explaining the positional relationship between b), the Figure 9 graph showing an example of the angular position error E _theta rotary encoder,
FIG. 10 is a configuration diagram showing another example of a conventional rotary encoder. (2) is a lattice, (3) is a lattice disk, (9) is a detection unit,
(13a), (13b), (13c) and (13) are detection elements respectively, (14a), (14b), (18a) and (18b) are sum arithmetic units, respectively, and (15a) and (15b) are each It is a difference calculator.

Claims (2)

(57) [Claims] 1. A grating disk having a grating formed at a pitch angle λ by equally dividing one period T, and a detecting unit having a pair of detecting elements for outputting an electric signal in response to rotation of the grating. A rotary encoder that outputs two-phase detection signals having a phase difference of 90 ° in accordance with the relative rotation between the lattice disk and the detection unit, wherein the pair of detection elements are connected to each other by T / 2 + (m + 1 / 4) λ (m is zero or a positive integer at which mλ is a sufficiently small value compared to T / 2), and the sum signal and difference signal of the output signals of the detection element are detected in the two phases. A rotary encoder characterized in that the signal is a signal. 2. A detecting section having a grating disk having a grating formed at a pitch angle λ by equally dividing one period T, and two pairs of pair detecting elements for outputting an electric signal corresponding to the rotation of the grating. And a rotary encoder that outputs two-phase detection signals having a phase difference of 90 ° according to the relative rotation between the lattice disk and the detection unit, wherein two of each of the two pairs of detection elements are provided. T /
2+ (m + 1/4) λ (m is zero or a positive integer where mλ is a sufficiently small value compared to T / 2), and the two pairs of detecting elements are disposed at a distance of T / 4 from each other. Adding the sum signal of the output signals of the first pair of detection elements and the sum signal of the output signals of the second pair of detection elements to obtain a difference signal between the output signal of the first pair of detection elements and A rotary encoder characterized in that the two-phase detection signal is obtained by adding a difference signal between the output signals of the second pair of detection elements.