JPH063164A - Rotational position detector - Google Patents

Abstract

PURPOSE:To obtain an absolute encoder having high resolution at low cost. CONSTITUTION:Two polarizing plates 40, 50 are set confronting to each other and one is used as a rotor. Polarizing parts 31, 32, 33 shifted every pi/3, a transparent part 70, and gray scales 81, 82 are provided in one polarizing plate. When the light penetrating each part of the polarizing plate is detected, the level of the light is detected. An inverse cosine is calculated from the ratio of the intensity of the detected light between the polarizing part and the transparent part, thereby to obtain the angle. A signal which is always in the middle level is selected among the three signals obtained by the three polarizing parts and utilized for the calculation to enhance the accuracy. The two gray scales are shifted 90 deg.. The state (high, middle, low) of each signal obtained from the light passing thorough the gray scales is detected and the range of the angle is identified.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the detection of rotational position.

[0002]

2. Description of the Related Art A device for detecting a rotation angle, that is, a rotary encoder is roughly classified into the following two types. That is, one of them outputs a pulse signal for each minute rotation, which is called an incremental type, and the other outputs an absolute angle signal, which is called an absolute type.

The incremental type encoder can provide a device with high resolution for detecting the rotation amount at a low cost, but since the absolute rotation position is not known, it is generally used in applications requiring the detection of the absolute position. , Two sets of encoders whose phases are shifted from each other for detecting the rotation direction are provided, and further combined with a position detection sensor, the signals output by them are
The absolute position is obtained by electronically processing by a device including a counter, a memory, a comparator and the like.

Further, the absolute type encoder has an advantage that the signal processing is easy because it outputs an absolute rotational position signal, but the structure is complicated and high mechanical accuracy is required. Therefore, it is difficult to increase the resolution.

As a prior art of an incremental type encoder, Japanese Patent Laid-Open No. 1-282424 is known. In this technique, a deflection plate is used to separate the phases of the diffraction grating.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a rotary position detecting device, which has a high resolution and can be used as an absolute type encoder, at a low cost.

[0007]

In order to solve the above-mentioned problems, the rotational position detecting device of the present invention comprises a light source (10); at least one light-receiving element (2) arranged facing the light source.
1, 22, 23); arranged between the light source and the light receiving element, each of which has at least one polarizing means (31,
32, 33, 34), arranged opposite each other,
At least one of the first and second polarizing plates (4
0, 50); and signal processing means (60) for processing the signal output from the light receiving element and generating a signal corresponding to the relative rotational position of the first polarizing plate and the second polarizing plate. Equipped with.

According to a second aspect of the invention, the first and second aspects are
One of the two polarizing plates is placed in a different polarization state from each other.
It is provided with three or more light receiving elements (21, 22, 23) including the above-mentioned polarizing means (31, 32, 33) and simultaneously receiving light which has passed through each of these polarizing means.

According to a third aspect of the invention, the first and second aspects are
At least one of the polarizing plates includes a transparent portion (70) arranged at a position different from that of the polarizing means, and includes a reference light detecting means (75) for receiving light passing through the transparent portion, and the signal processing means. Is configured to generate a signal corresponding to the rotational position based on the signal level output by the reference light detecting means.

According to a fourth aspect of the invention, the first and second aspects are
One of the polarizing plates of the three polarizing means (31, 32, 33) arranged in a polarized state having a phase difference of π / 3 with each other.
And a transparent part (7) arranged at a position different from that of the polarizing means.
0), and three light receiving elements (21, 22, 23) that simultaneously receive light that has passed through each of the polarization means, and reference light detection means (75) that receives light that has passed through the transparent portion.
The signal processing means is configured to generate a signal according to the rotational position based on the signal level output by the reference light detection means and the signals output by the three light receiving elements.

Further, in the fifth invention, the first and second
One of the polarizing plates includes two or more gray scale means (81, 82) which are arranged out of phase with each other and whose light transmittance changes continuously, and each of the gray scale means passes through the gray scale means. Two or more gray light detecting means for receiving light (9
1, 92), and the signal processing means is configured to generate a signal according to the rotational position based on the signal output by the gray light detecting means.

The symbols shown in parentheses are reference numerals of corresponding elements in the embodiments described later, but each constituent element of the present invention is a concrete element in the embodiments. It is not limited to only.

[0013]

In the present invention, since the first and second polarizing plates arranged between the light source and the light receiving element each include the polarizing means, both of the first and second polarizing plates are included. The intensity of light that passes through and reaches the light receiving element from the light source continuously changes according to the relative rotational position of the first polarizing plate and the second polarizing plate. Therefore, the absolute rotational position can be identified by the level of the signal output by the light receiving element. Also,
Since the level of the signal output from the light receiving element is an analog amount, the resolution can be increased by using, for example, a highly accurate A / D converter.

The intensity of the light reaching the light receiving element from the light source shows a change in the rotation angle according to the cosine function. For this reason, in the vicinity of each angle of 0, π, and 2π [rad], the change in the received light intensity with respect to the change in the angle becomes small, and the resolution of position detection deteriorates. However, in the second aspect of the invention, one or more of the first and second polarizing plates is provided with three or more polarizing means arranged in mutually different polarization states, and light passing through each of these polarizing means is simultaneously irradiated. Since three or more light receiving elements for receiving light are provided, three or more signals having mutually different intensity change patterns in phase can be obtained at the same time. That is, the resolution of position detection can be constantly maintained high by selecting and using a signal having a large change in received light intensity with respect to a change in angle among the plurality of signals.

The intensity of the light reaching the light receiving element from the light source changes in accordance with the change in the emission intensity of the light source. Therefore, if the rotational position is obtained only based on the intensity of the light reaching the light receiving element, a detection error will occur. May occur. But the third
In the invention of No. 2, at least one of the first and second polarizing plates includes a transparent portion arranged at a position different from that of the polarizing means, and includes reference light detecting means for receiving light passing through the transparent portion. Therefore, based on the signal level output by the reference light detecting means, it is possible to compensate the change in the received light intensity according to the change in the emitted light intensity of the light source and to accurately obtain the rotational position.

The intensity of the light reaching the light receiving element from the light source shows a change according to the cosine function with respect to the rotation angle. Therefore, the same level appears for a plurality of rotational positions with only a single signal, and the absolute position in a wide rotational range cannot be identified. However, in the fourth invention, one of the first and second polarizing plates includes three polarizing means arranged in a polarized state having a phase difference of π / 3 with each other, and each of the polarizing means is provided. Since three light receiving elements that simultaneously receive the light passing therethrough are provided, the combinations of the three types of signal levels output by the three light receiving elements are not the same for a plurality of rotational positions, and based on them, The absolute position in a wide rotation range can be identified. Moreover, since at least one of the first and second polarizing plates includes a transparent portion arranged at a position different from that of the polarizing means, and the reference light detecting means for receiving light passing through the transparent portion is provided, the reference light Based on the signal level output by the detecting means, it is possible to compensate for the change in the received light intensity according to the change in the emitted light intensity of the light source and to accurately obtain the rotational position.

Although the intensity of the light reaching the light receiving element from the light source shows a change according to the cosine function with respect to the rotation angle, the level of the signal actually output from the light receiving element is in the range of 0 to π and π to 2π. It is the same as the range. Therefore, the rotational position in the range of 0 to π can be detected but the rotational position in the range of 0 to 2π cannot be identified only by using the signal level output from the light receiving element. However, in the fifth invention, the first
One of the second polarizing plate and the second polarizing plate includes two or more gray scale means which are arranged out of phase with each other and whose light transmittance changes continuously, and each of the light passing through the gray scale means is Since two or more gray light detecting means for receiving light are provided, it is possible to discriminate the range of 0 to π and the range of π to 2π of the rotational position based on the signal output by the gray light detecting means. , 0 to 2π can be identified.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the physical construction of an absolute rotary encoder which is an embodiment of the present invention. The drive shaft 3 of the electric motor M to be detected is rotatably supported by the frame 1 via a bearing 4. Drive shaft 3
A disc-shaped polarizing plate 40 is fixed to the tip of the polarizing plate 40, and the polarizing plate 40 rotates together with the drive shaft 3. Another polarizing plate 50 fixed to the frame 1 is provided near the polarizing plate 40.
Is arranged, and the diffusion plate 2 fixed to the frame 1 is arranged at a position adjacent to the polarizing plate 50. Further, the lamp 10 is installed at a position adjacent to the diffusion plate 2.

The diffusing plate 2 diffuses the light transmitted therethrough. Therefore, the light emitted from the lamp 10 passes through the diffusion plate 2 and becomes light of uniform intensity and enters the polarizing plate 50. The polarizing plate 50 is configured by sticking a polarizing material 34 having a predetermined polarization characteristic on transparent glass. Therefore, the light that has entered the polarizing plate 50 passes through it, is polarized, and enters the next polarizing plate 40.

The polarizing plate 40 is composed of various parts formed in a ring shape as shown in FIG. That is, the ring-shaped polarization portions 31, 32, 33, the transparent portion 70, and the gray scales 81 and 82 are concentrically arranged in order from the outermost peripheral side of the polarizing plate 40 toward the inside. Three
The two polarization parts 31, 32 and 33 have polarization directions of π with respect to each other.
It is shifted by / 3 [radian] (see FIG. 3). Transparent part 70
Indicates a transparent portion having a high light transmittance and does not generate polarized light. The gray scales 81 and 82 are optical patterns whose light transmittances (brightness and darkness) change smoothly depending on the difference in position in the same circumferential direction. In this example, 90 degrees are provided between the two gray scales 81 and 82. The positions in the rotation direction are displaced by 90 degrees from each other so as to have a phase difference of 90 degrees.

Polarizing portions 31, 32, 33 on the polarizing plate 40,
In order to detect the light transmitted through the transparent portion 70 and the gray scales 81 and 82, in order to detect the light transmitted through those portions,
Light receiving elements (photodiodes) 21, 22, 23, 75, 91 and 92 fixed to the frame 1 are arranged respectively. That is, the light emitted from the lamp 10 passes through the diffusion plate 2 and the polarizing plate 50, and the polarizing portions 31, 32, 33, the transparent portion 70, and the gray scale 8 on the polarizing plate 40.
1 or 82 to transmit the light receiving elements 21, 22, 22 respectively.
The light is received at 23, 75, 91 or 92.

As can be seen by referring to FIG. 3, the polarization unit 3
The intensity Va of light entering the light receiving element 21 through 1 and the intensity Vb of light entering the light receiving element 22 through the polarization unit 32,
And the intensity Vc of the light that enters the light receiving element 23 through the polarization unit 33 is affected by the polarization, and is calculated as follows.

Va = (V / α) · Cos θ (1) Vb = (V / β) · Cos (θ−π / 3) (2) Vc = (V / γ) · Cos (θ-2π / 3) (3) where α, β and γ are coefficients corresponding to the characteristics of the light receiving system.

The intensity V of the light incident on the polarizing plate 40 is
Since the light amount of the lamp 10 changes in accordance with the light amount of the lamp 10, when the light amount of the lamp 10 changes, the light receiving amounts Va, Vb, and Vc change in addition to the rotation angle. A light receiving element 75 is provided to compensate for this change. That is, since the light emitted from the lamp 10 passes through the diffusion plate 2, the polarizing plate 50, the transparent portion 70 of the polarizing plate 40 and enters the light receiving element 75, the incident light amount of the light receiving element 75 is rotated. It is independent of position and changes depending on the intensity of light emitted from the lamp 10. That is, the intensity Vr of the light incident on the light receiving element 75 is as follows.

Vr = V / ε (4) However, ε is greater than 1 and almost equal to 1.

Therefore, for example, the following equation is obtained from the equations (1) and (4).

Va / (ε · Vr / α) = Cos θ (5) θ = arcCos ((Va / Vr) (α / ε)) (6) In other words, rotation from Va and Vr The angle θ can be obtained. In this embodiment, there are two reasons for detecting the light reception amounts Va, Vb and Vc of three systems having different polarization directions. That is, since the angle θ is obtained from the cosine function as in the equation (6), the parameter can be set by using only one function.
In the region where ((Va / Vr) (α / ε)) is close to 1, the change in the parameter becomes small with respect to the change in the angle θ, and the detection error is likely to occur. Further, although a plurality of types of angles are obtained by calculation for one type of detected value, it cannot be determined which result is true.

FIG. 4 shows the configuration of a signal processing unit for processing the signals output from the above light receiving elements. Referring to FIG. 4, the electric signals output from the light receiving elements 21, 22, 23, 75, 91 and 92 are amplifiers A1, A2, A, respectively.
3, A4, A5 and A6 are applied and amplified to become signals Sa, Sb, Sc, Sr, Sp and Sq, respectively.
In this example, the amplification factors of the amplifiers A1, A2, A3, and A4 are k · α / ε, k · β / ε, k · γ / ε, and k (k: constant), and the amplifiers A5 and A6 is set to a predetermined amplification factor. Therefore, the signals Sa, Sb,
There is no difference between the levels of Sc and Sr due to the difference in the light receiving system, and they can be treated under the equal condition.
That is, for example, the equation (6) can be modified as follows.

Θ = arcCos (Sa / Sr) (7) The waveforms of the signals Sa, Sb, Sc, Sp and Sq are shown in FIG. Signals Sa, Sb and S
c is input to the comparison circuit 61 and the A / D converter 63, the signal Sr is applied to the A / D converter 63 and the comparison circuit 62, and the signals Sp and Sq are applied to the comparison circuit 62.

The structure of the comparison circuit 61 is shown in FIG. 6, and the structure of the comparison circuit 62 is shown in FIG. First, the comparison circuit 61 will be described with reference to FIG. This circuit has three signals Sa, S
The levels of b and Sc are discriminated from each other using three comparators, and four signals A are identified based on the comparison result.
Generate cnv, Bcnv, Ccnv and Gr. In this embodiment, as the signal used for the calculation of the angle θ, of the three signals Sa, Sb and Sc, the one having the intermediate level at that time is always selected. The signals Acnv, Bcnv and Ccnv output by the comparator circuit 61 indicate that the signals Sa, Sb and Sc are the ones to be selected (intermediate level ones) when they are at the high level H.

Please refer to the waveform of the signal selected by the signals Acnv, Bcnv and Ccnv, that is, the intermediate level signal Sabc obtained by combining the signals Sa, Sb and Sc, as shown in FIG. Further, the signal Gr becomes a high level H when the level of the signal Sabc monotonically increases, and becomes a low level L when the level of the signal Sabc monotonically decreases. CLK is a clock pulse that determines the timing of the latch. The signals Acnv, Bcnv, Ccnv and Gr output by the comparison circuit 61 are A / D.
It is applied to the converter 63 and the control circuit 64. That is, A /
The D converter 63 normally has three signals Sa, Sb and Sc.
Among them, the level at that time is intermediate, that is, the signal Sab
The level of c is sampled and converted into a digital quantity.
The level of the signal Sr is sometimes sampled as needed and converted to a digital quantity.

Next, the comparison circuit 62 will be described with reference to FIG. This circuit outputs the signal Sp to two threshold levels P
Signals P1 and P2 indicating the result of comparison with H and PL
, And P3, and comparing the signal Sq with two threshold levels QH and QL, and showing the result signal Q1,
Outputs Q2 and Q3. That is, when the signals P1, P2, and P3 are at the high level H, the levels of Sp are higher than PH, between PH and PL, and lower than PL, respectively, and the signals Q1, Q2, and Q3 are high. When it is a level, it shows a state in which the level of Sq is higher than QH, between QH and QL, and lower than QL, respectively.

In this embodiment, the level of the signal Sr is divided by the variable resistors and the threshold levels PH,
PL, QH and QL are created. Therefore, when the light amount of the lamp 10 changes and the levels of the signals Sp and Sq change, the threshold level PH,
PL, QH and QL are corrected. That is, the change in the light amount of the lamp 10 does not affect the phases of the signals P1 to P3 and Q1 to Q3. The signals P1 to P output by the comparison circuit 62
3 and Q1 to Q3 are input to the control circuit 64.

Three signals Sa, S that change with polarization
Whether each of b and Sc is in the selected state (active),
As Ca, Cb and Cc respectively, and gray scale
It is shown in FIG. 5 as Cp and Cq indicating which of the three kinds of states the signal Sp and Sq of the signal are in, respectively, so please refer to them.

The control circuit 64 shown in FIG. 4 is constituted by a microcomputer in this example, and the comparison circuit 6 described above is used.
1, 62 and the information output from the A / D converter 63 are input, the information is processed to obtain the rotation angle θ at that time, and the information of the angle θ is transmitted via the interface 65 as necessary. Output to the outside. The control circuit 64 obtains the rotation angle θ as follows.

First, θs is obtained by the following equation.

Θs = arcCos (Sabc / Sr) (8) Next, θc is determined under the following conditions. That is, the signal Acnv output from the comparison circuit 61 is at the high level H (active).
Then θc = 0, and if the signal Bcnv is at high level H, then θc =
π / 3, and if the signal Ccnv is at high level H, θc = 2π /
Set to 3.

Then, θn is obtained. Comparison circuit 61
The output signal Gr is referred to, and if Gr is a high level H, θn = θc + θs, and (9) If Gr is a low level L, θn = θc−θs. (10) In the processing up to this point, the range of 0 to π and the range of π to 2π cannot be distinguished, and the absolute angle θ can be detected only in the range of half rotation. Therefore, in order to widen the detectable range, the processing is further continued with reference to the gray scale signals P1 to P3 and Q1 to Q3.

That is, the signal Acnv output from the comparison circuit 61
Is high level H (Ca is active), the comparator circuit 6
If the signal Q3 output by 2 is at a high level H (Cq is in a low state), the following condition is applied.

When Gr is H: θ = θn (11) When Gr is L: θ = π + θn (12) Further, the signal Acnv output from the comparison circuit 61 is at the high level H.
If the signal Q1 output from the comparison circuit 62 is at a high level H (Cq is in a high state) when (Ca is active), the following condition is applied.

When Gr is H: θ = θn + π (13) When Gr is L: θ = 2π + θn (14) Further, the signal Bcnv output from the comparison circuit 61 is at the high level H.
If the signal Q2 output from the comparison circuit 62 is at a high level H (Cq is in an intermediate level state) while Cb is active, and P3 is at a low level L (Cp is not Low), the following condition is applied. To do.

Θ = θn (15) Further, the signal Bcnv output from the comparison circuit 61 is at the high level H.
When (Cb is active), the signal Q2 output from the comparison circuit 62 is at a low level L (Cq is not an intermediate level),
Alternatively, if P3 is at a high level H (Cp is Low), the following conditions apply.

Θ = π + θn (16) Further, the signal Ccnv output from the comparison circuit 61 is at the high level H.
When (Cc is active), the signal Q1 output from the comparison circuit 62 is at a low level L (Cq is not High), P1 is at a high level H (Cp is High), and Q2 is at a low level L ( If Cq is not an intermediate level),
The following conditions apply:

Θ = θn (17) Further, the signal Ccnv output from the comparison circuit 61 is at the high level H.
When (Cc is active), the signal Q1 output from the comparison circuit 62 is at a high level H (Cq is High), or P1.
If is a low level L (Cp is not High) or Q2 is a high level H (Cq is an intermediate level) then the following conditions apply.

Θ = π + θn (18) The above-mentioned determination condition can be applied when a signal as shown in FIG. 5 is obtained, but it must be changed if the position of each gray scale or the like changes. .

In the above embodiment, the control circuit 64 uses the microcomputer. However, the processing required therefor is only comparatively simple judgment processing and arithmetic processing, and therefore this is used as a general logic circuit. It is easy to replace. Further, in the above embodiment, the difference in the characteristics of the plurality of light receiving systems is compensated by adjusting the amplification degree of the amplifiers A1 to A4. This compensation is performed, for example, by the arithmetic processing inside the microcomputer of the control circuit 64. Good.

Further, in the above-mentioned embodiment, the encoder which can detect the absolute angles of all the positions of 0 to 2π has been shown, but depending on the application, it may be necessary to detect only the range of 0 to π. In such a case, the gray scale 81,8
2 and various components associated therewith may be omitted. Further, in an application requiring only detection of a narrower angle range, the polarizing plate 40 may be provided with at least one polarizing section, and the other polarizing sections and constituent elements related thereto may be omitted.

[0048]

As described above, according to the present invention, the first and second polarizing plates arranged between the light source and the light receiving element each include the polarizing means, and therefore the first and second polarizing plates are provided. The intensity of light that passes through both polarizing plates and reaches the light receiving element from the light source continuously changes according to the relative rotational position of the first polarizing plate and the second polarizing plate. Therefore, the absolute rotational position can be identified by the level of the signal output by the light receiving element. Further, since the level of the signal output from the light receiving element is an analog amount, the resolution can be increased by using, for example, a highly accurate A / D converter.

In the second aspect of the invention, the resolution of position detection can be constantly kept high by always selecting and using the signal having a large change in the received light intensity with respect to the angle change.

According to the third aspect of the invention, the rotational position can be accurately obtained by compensating for the change in the received light intensity according to the change in the emitted light intensity of the light source.

In the fourth aspect of the invention, the combination of the three types of signal levels output by the three light receiving elements is not the same for a plurality of rotational positions, and based on these combinations, a wide rotational range can be obtained. Absolute position can be identified. Moreover, the rotational position can be accurately obtained by compensating for the change in the received light intensity according to the change in the emitted light intensity of the light source.

According to the fifth aspect of the invention, the range of 0 to π and the range of π to 2π of the rotational position can be discriminated based on the signal output from the gray light detecting means, and by utilizing this. , 0 to 2π can be identified.

[Brief description of drawings]

FIG. 1 is a front view showing a mechanical portion of a rotary encoder of an embodiment.

FIG. 2 is a plan view showing a polarizing plate 40 included in the device of FIG.

FIG. 3 shows the light incident on the polarizing plate 40 and the light transmitted through it.
It is a vector diagram which shows a kind of light.

4 is a block diagram showing an electric circuit of the apparatus of FIG. 1. FIG.

5 is a waveform diagram showing signal waveforms and signal states of respective parts of the circuit of FIG.

6 is a block diagram showing a configuration of a comparison circuit 61 of FIG.

7 is a block diagram showing a configuration of a comparison circuit 62 in FIG.

[Explanation of symbols]

1: Frame 2: Diffusion plate 3: Drive shaft 4: Bearing 10: Lamp 21, 22, 23, 75, 91, 92: Light receiving element 31, 32, 33: Polarizing part 40: Polarizing plate 50: Polarizing plate 60 : Signal processing unit 61, 62: Comparison circuit 63: A / D converter 64: Control circuit 65: Interface 70: Transparent part 81, 82: Gray scale A1-A6: Amplifier PH, PL, QH, QL: Threshold level

Claims (5)

[Claims] 1. A light source; at least one light-receiving element arranged to face the light source; arranged between the light source and the light-receiving element, each including at least one polarizing means, and arranged to face each other. And at least one of the first and second polarizing plates is rotatable; and a signal output from the light receiving element is processed so that a relative rotational position of the first and second polarizing plates is obtained. A rotational position detection device comprising: a signal processing unit that generates a corresponding signal. 2. One of the first and second polarizing plates includes three or more polarizing means arranged in mutually different polarization states, and simultaneously receives light passing through each of the polarizing means. The rotational position detecting device according to claim 1, comprising the above light receiving element. 3. At least one of the first and second polarizing plates includes a transparent portion arranged at a position different from that of the polarizing means, and includes a reference light detecting means for receiving light passing through the transparent portion. 2. The rotational position detecting device according to claim 1, wherein the signal processing unit generates a signal corresponding to a rotational position based on a signal level output by the reference light detecting unit. 4. One of the first and second polarizing plates is provided with three polarizing means arranged in a polarized state having a phase difference of π / 3 with each other, and arranged at a position different from that of the polarizing means. The signal processing means includes three light receiving elements that include a transparent portion and simultaneously receive light that has passed through each of the polarizing means, and reference light detection means that receives light that has passed through the transparent portion. The rotational position detecting device according to claim 1, wherein a signal corresponding to a rotational position is generated based on a signal level output by the light detecting means and a signal output by each of the three light receiving elements. 5. One of the first and second polarizing plates includes two or more gray scale means which are arranged out of phase with each other and whose light transmittance continuously changes, and the gray scale is provided. Said two or more gray light detecting means for receiving each light passing through said means, wherein said signal processing means generates a signal corresponding to a rotational position based on the signal output by said gray light detecting means. Item 1. A rotational position detection device according to item 1.