JPH04301713A - Angle measuring method - Google Patents

Abstract

PURPOSE:To enable measurement of a slit angle without being affected by an eccentricity by obtaining the distance between an edge outside an area to be measured and a fixed point by taking advantage that the characteristic of the rotational angle vs. the eccentricity of a circumferential ring is sinusoidal. CONSTITUTION:The distance in the Y direction between an edge of a circumferential ring 52 and a fixed point is measured, and the characteristic of the rotational angle theta2 vs. eccentricity is measured. When the edge falls outside an area to be measured 6, the curve of the eccentricity is regarded as sinusoidal and the eccentricity at the angle theta2 is calculated. Then, a table of the rotational angle theta1 vs. eccentricity is prepared when the angle theta is shifted by 90 deg.. A code plate 5 is rotated and the distance X between the edge of a slit 51 and the fixed point is measured. When the edge of the slit 51 falls outside the area 6, an arrangement is made so that the edge of the slit 51 may fall within the area 6 by rotating the plate 5, and the distance in the X direction is measured. The eccentricity corresponding to the rotational angle of the plate 5 is read out of the table, and this value is deducted from the distance in the X direction to calculate a correct slit angle.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting the slit pattern of a code plate used in a rotary encoder. More specifically, the present invention relates to a method of measuring the arrangement angle of a slit pattern provided along the edge of a circular code plate.

0002

[Prior Art] Light is irradiated from a light source onto a circular code plate in which a large number of slits are provided at regular angles along the edge.
There is a rotary encoder that measures the rotation angle of a code plate by receiving light passing through a slit with a photoelectric conversion element. FIG. 6 shows a code plate used in such a rotary encoder.

[0003] The code plate is attached to, for example, the rotating shaft of a motor, and the accuracy of measuring the rotation angle by the rotary encoder is influenced by the arrangement "angle" of the slits provided at regular angle intervals. Therefore, in order to realize an encoder that can measure the rotation angle with high precision, it is necessary to manufacture the slit arrangement angle of the code plate with high precision. For this reason, conventionally, an angle measuring device as shown in FIG. 7 has been used to measure the arrangement angle of the slits in a manufactured code plate to determine the quality of the code plate.

The conventional device shown in FIG. 7 will be explained. The apparatus shown in the figure is composed of a line width measuring device 1, a rotary stepper 2, and a controller (not shown).

The line width measuring device 1 includes an optical microscope 11 that can magnify and view the slit portion of the code plate 5, an autofocus mechanism 12 that automatically focuses the microscope 11, and a The CCD camera 13 converts the image into an electrical signal, recognizes the shading of the line image based on this electrical signal, and uses the shading threshold to automatically align two cursors with the shading edges that form the line. The line width measuring device control system 3 automatically measures the line width x from the cursor spacing.

The rotary stepper 2 has a high-resolution drive mechanism 2 that can finely rotate a rotating shaft with very high resolution.
1 and a high-resolution encoder 22 that detects its rotational position.
, a static pressure air bearing 23 that supports the rotating shaft, and a code plate 5 that is attached to the upper end of the rotating shaft of the rotary stepper to hold the measurement target thereon, and aligns the center of the code plate 5 with the center of the rotating shaft. XY stage 2 for removing eccentricity, which can perform positioning by sliding in the X and Y directions as if
4 and the output of the high-resolution encoder 22 (rotational position information)
The rotary stepper control system 4 controls the high-resolution drive mechanism 21 based on the rotational speed of the rotary stepper and rotates the rotary shaft (that is, the code plate 5) of the rotary stepper by an angle instructed by a controller (not shown). Here, the high-resolution encoder 22 is used, for example, with a resolution of 3.6 million pulses/rotation, and the high-resolution drive mechanism 21 is used, for example, with an order of magnitude higher resolution, 36 million pulses/rotation. The rotational resolution of the code plate rotated by the action of the high-resolution encoder 22 and the high-resolution drive mechanism 21 is as follows:
The resolution is sufficient to inspect the acceptability of the slit arrangement angle.

The operation of the conventional angle measuring device shown in FIG. 7 will be explained. First, the code plate 5 is fixed to the rotary stepper 2 by the action of the XY stage 24 so that the center of the rotation axis of the rotary stepper 2 and the rotation center of the code plate 5 coincide (that is, with eccentricity removed).

The ideal equal dividing angle (360 /
N) is calculated in advance by a controller (not shown). Then, the controller controls the rotary stepper control system 4 so as to rotate the code plate 5 at this ideal angle step.
instruct. As a result, the code plate 5 sequentially rotates in ideal angular steps starting from the angular position that is its origin.

FIG. 8 is a diagram showing the code plate 5 and a measurement area 6, which is a portion of the code plate 5 to be observed with a microscope 11. That is, the area around the edges of the slits 51 that sequentially enter the measurement area 6 (within the field of view of the microscope 11) is
The image is enlarged by a CCD camera 13 and converted into electrical information (image data). Based on this image data, the line width length measuring device control system 3 applies a control signal to the autofocus mechanism 12, and sends a control signal to the microscope 11 through the slit 51 of the code plate 5.
automatically focuses.

FIG. 9 is a diagram showing an example of a microscopic image of the measurement area 6 in FIG. 8. In the figure, at position Po, the angular arrangement of the slits 51 is ideally manufactured;
It also shows the position where the edge of each slit 51 stops when the code plate 5 is shifted by the ideal angle step by the rotary stepper 2. In other words, Po indicates the reference position. However, in reality, the slit 51 is not manufactured ideally, and the edges of the slit 51 that appear sequentially in the measurement area 6 are located at distances X1, X2, . . . from the reference position Po.
It is observed with variations in the positions P1, P2, . . .

FIG. 10 is a diagram illustrating the measurement operation of the line width length measuring device 1. The line width measuring device control system 3 inputs the line image data shown in FIG. 10(A) from the CCD camera 13, and selects the line 6 to be measured using the grayscale threshold a (see FIG. 10(B)).
The two cursors 64 and 65 are automatically aligned with the edges 62 and 63 of 1 (FIG. 10(A)). That is, the line width length measuring device control system 3 moves the cursor 64 so that the center of the cursor 64 is located on the edge 62. Similarly, so that the center of the cursor 65 is located on the edge 63,
Move the cursor 65. Then, the line width x is automatically measured from the interval. However, although this method is possible in a line width measurement range of 0.5 to 20 .mu.m, it cannot be applied directly to a line width of about 400 .mu.m, such as a slit in a code plate, since the line width exceeds the measurement area 6. Therefore, the present applicant disclosed an apparatus capable of measuring a relatively wide width in Utility Application No. 01-82614 "Angle Measuring Apparatus".

FIG. 11 is a diagram illustrating the operation of the line width length measuring device 1 in the angle measuring device filed in Utility Application No. 01-82614 (hereinafter referred to as the prior application). In the prior application, for example, the position of the left cursor 65 is fixed, and only the right cursor 64 is automatically moved as described above to match one edge of the slit 51. Then, the distance x between the cursors 65 and 64 is read by the line width length measuring device control system 3. That is, the left cursor 65 is at a fixed position because its position is fixed. When the code plate 5 is rotated by the ideal angle step described above with respect to this fixed point position, if each slit 51 is ideally manufactured at a predetermined angle position, the distance x shown in FIG. , always constant. However, in reality, since there are manufacturing errors in the formation of each slit, the distance x shown in FIG. 11 varies from slit to slit (when the code plate 5 is sequentially rotated in steps by the rotary stepper). The angular error of the code plate 5 can be determined by converting the variation of the distance x from the fixed point PA shown in FIG. 11, Δx1, Δx2, .

[0013]

In the above description, it is assumed that the center of the code plate 5 and the center of the rotation axis of the rotary stepper 2 are adjusted by the XY stage so that they completely coincide with each other. That is, it was assumed that the amount of eccentricity was 0. However, in reality, the amount of eccentricity cannot be adjusted to zero, and some amount of eccentricity exists. Because of this amount of eccentricity,
The angle measurement of the slit 51 includes an error.

The reason why an error occurs in the measured value of the slit angle due to the amount of eccentricity will be explained with reference to FIG. FIG. 5 is a diagram showing the rotation center O1 of the rotary stepper 2 and the center O2 of the code plate 5. The distance between the two centers 01 and O2 is r
shall be. Here, if the two center positions match (r=0)
, if each slit of the code plate 5 is formed at an ideal arrangement angle (perfectly equal intervals), when the code plate 5 is rotated in ideal angle steps by the rotary stepper 2, the slits at each rotation step are as follows. It stops at the dotted line SA in FIG.

However, if r≠0, even if each slit of the code plate 5 is formed at an ideal arrangement angle, the slits at the position (SB) deviated from the line L by the eccentric amount WX as shown in FIG. Stop. Furthermore, the eccentricity WX changes in a sinusoidal manner with an amplitude r as shown in FIG. 3, depending on the rotation angle of the code plate 5 by the rotary stepper 2. As described above, the line width length measuring device control system 3 measures, for example, the distance between the line L in FIG. 5 and the edge of the slit (that is, the eccentricity WX in FIG. 5), resulting in a measurement error.

Furthermore, when the amount of eccentricity WX is large, the amplitude of the waveform shown in FIG.
When rotated in ideal angle steps, the edge position of each slit 51 that stops at each step is the measurement area 6 (Fig. 1
(See 1). In other words, if the amount of eccentricity is large, the edge no longer exists within the measurement area 6, so there is a problem that x (angle) cannot be measured.

An object of the present invention is to provide an angle measuring method that can accurately measure the slit angle without causing the edge to protrude from within the measurement area 6 and without being affected by the amount of eccentricity WX.

[0018]

[Means for Solving the Problems] In order to solve the above problems, the present invention includes a rotary stepper (2) that rotates a code plate (5) in a stepwise manner at an angle corresponding to an applied control signal (S3); The camera (13) converts the image of the measurement area (6) set on the code board into an electrical signal, and also sets a fixed point position anywhere in the image of this camera, and from this fixed point position, the camera Line width measuring device (1) that outputs the distance to the edge of the image that exists in the image
In a method of measuring the arrangement angle of slits provided at equal intervals along the edge of a code plate provided with a so-called circumferential ring (52), a control signal for rotating the code plate at a certain angle ( S3) to the rotary stepper (2)
At the same time, the line width measuring device (1) measures the image of the edge of the circumferential ring (52) at the angle and the distance in the y direction to the fixed point position, and calculates the rotation angle (θ2).
In the first step of measuring the characteristics of eccentricity, if the image of the edge of the circumferential ring deviates from the measurement area (6) at a certain rotation angle of the rotary stepper during the first step, the first step has already been performed. A second step of extending the obtained curve of rotation angle (θ2) versus eccentricity as part of a sine wave and calculating the value of the sine wave corresponding to the rotation angle as the eccentricity at the rotation angle; , the third step is to create a table of rotation angle (θ1) vs. eccentricity by shifting the characteristic rotation angle (θ2) obtained in the first and second steps by 90 degrees, and to correspond to the ideal spacing of each slit. A control signal is applied to the rotary stepper to rotate the code plate at a certain angle step, and the line width length measuring device (1)
The image of the edge of the slit and x to the fixed point position are
During the fourth step, if the image of the edge of the slit deviates from the measurement area (6) at a certain rotation angle of the rotary stepper, the step angle (6) corresponding to the ideal interval is The code plate is rotated to a composite angle obtained by adding the correction angle θA to θ11) and controlled so that the image of the edge of the slit enters the measurement area (6). Measure the distance in the x direction between the image of the edge of the slit and the fixed point position, and
The fifth step is to set x+θA) as the measurement angle of the slit at the rotation angle (θ11), read out the eccentricity corresponding to the rotation angle (θ11) from the table, and calculate this from the measured distance in the x direction (x+θA). 6th to subtract
The method is designed to include a process.

[0019]

[Operation] In the first step, the characteristics of rotation angle (θ2) versus eccentricity are measured. If the amount of eccentricity is large, the edge of the circumferential ring will move out of the measurement area at a certain rotation angle, making it impossible to measure the amount of eccentricity. Therefore, in the second step, the curve of rotation angle θ2 vs. eccentricity obtained in the first step is regarded as a part of the sine wave and is extended (θP in Fig. 3).
~θQ), the value of the sine wave corresponding to the rotation angle is taken as the amount of eccentricity at the rotation angle. The amount of eccentricity obtained in the first and second steps is the component in the y direction (Fig.
), and the eccentricity of the slit, which is the component in the x direction (
In order to correct WX), it is necessary to shift the rotation angle, that is, the phase, of characteristic (2) by 90°. Therefore, in the third step, a table of rotation angle (θ1) versus eccentricity is created by shifting the rotation angle (θ2) of characteristic (■) by 90°. In the fourth step, the distance in the x direction between the edge of the slit image and the fixed point position, that is, the eccentricity (WX...Figure 5
Reference) The value corresponding to the arrangement angle of the included slits is measured. However, if the amount of eccentricity is large, the edge of the slit will move out of the measurement area at a certain rotation angle, making it impossible to measure the angle of the slit. Therefore, in the fifth step, the code plate is rotated to a composite angle obtained by adding the correction angle θA to the step angle (θ11) so that the edge of the slit enters the measurement area. Then, the distance in the x direction between the edge of the slit and the fixed point position is measured, and (x+θA) is defined as the measurement angle of the slit at the rotation angle θ11. However, this measurement angle (x + θA) has an eccentricity amount (eccentricity error)
It is included. In the sixth step, a signal corresponding to the true arrangement angle of the slit is obtained by subtracting the amount of eccentricity included in the measured value (x+θA).

[0020]

[Example] Fig. 1 is a diagram showing the angle measurement method according to the present invention.
FIG. 2 is a diagram showing an apparatus for carrying out the method of FIG. 1, FIG. 3 is a diagram showing the characteristics of rotation angle versus eccentricity, FIG. FIG. 6 is a diagram illustrating measurement errors in certain cases, and is a diagram illustrating an example of the configuration of an actual code plate.

The operation of the present invention will be explained with reference to FIGS. 1 to 4. The present invention provides a so-called circumferential ring 52 (see FIG. 6).
This is a method of measuring the arrangement angle of slits 51 provided at equal intervals along the edge of a code plate provided with slits 51. The hardware configuration of the angle measuring device using the present invention is the same as that shown in FIG. 7, but the control method of the controller, which is not shown in FIG. 7, is different from the conventional one.

To explain the outline of the present invention, first, the rotation angle θ2 (to be described later) versus the amount of eccentricity is measured (
1st step). Here, if the amount of eccentricity is large, the edge of the circumferential ring will protrude from the measurement area 6. Therefore, the rotation angle θ
2. Utilizing the fact that the characteristic of the amount of eccentricity is a sine wave, the distance between the edge protruding from the measurement area 6 and the fixed point is determined by calculation (second step). Next, the amount of eccentricity is x
It is converted into a direction value and written in the memory as a table (third step). This completes the measurement of eccentricity. Next, the rotary stepper is rotated in constant angular steps corresponding to the ideal spacing between the slits, and the distance in the x direction between the edge of the slit and the fixed point position is measured. In this case, similarly to the measurement of the amount of eccentricity, if the amount of eccentricity is large, the edge of the slit will protrude from the measurement area 6. Therefore, the rotation angle of the rotary stepper is slightly changed so that the edge of the slit falls within the measurement area 6. To explain with a specific example,
Assume that when the rotary stepper is at a certain angle θ11, the edge 51a of the slit protrudes from the measurement area 6 (see FIG. 4(A)). Therefore, the CPU 7 calculates the minute angle θ
By rotating the rotary stepper 2 by A, the edge 51a of the slit can be moved to the distance x shown in FIG. 4(A). Therefore, the slit 5 at a certain angle θ11
The distance of 1a from the fixed point PC can be (x+θA). The above is the fifth step. Since this measured distance (x+θA) includes the amount of eccentricity, the amount of eccentricity corresponding to the rotation angle θ11 is read from the table and subtracted from the distance (x+θA) to measure the correct angle. ing.

In FIG. 2, the CPU 7 is provided in the controller and calculates an ideal equal dividing angle (360/N) determined by the number N of slits 51 provided at equal intervals on the code plate 5. Calculate it in advance and have this data.

(A) Characteristic measurement of rotation angle θ2 versus eccentricity (first step) The CPU 7 instructs the rotary stepper 2 to rotate the code plate 5, for example, in minute angular steps. More precisely, a control signal S3 is applied to the rotary stepper control system 4 (see FIG. 7) to rotate the code plate in minute angular steps. Further, the CPU 7 instructs the line width length measuring device 1 to measure the distance in the y direction between the edge of the image of the circumferential ring 52 of the code plate 5 and the fixed point position by applying a control signal S1. As a result, the CPU 7 can measure the characteristics of the rotation angle θ2 versus the amount of eccentricity, as shown in FIG.

[0025] This will be explained in detail. When the line width length measuring device 1 receives the control signal S1 from the CPU 7,
Two designated cursors 64 and 65 are arranged along the Y direction as shown in FIG. 4(B). Then, in FIG. 5, the measurement area 6 is moved up and down along the Y axis (L line), and as shown in FIG.
The circumferential ring 52 of the code plate 5 (see FIG. 6) is C
CD Make it possible to capture it as an image. The line width length measuring device 1 fixes the designated cursor 65 as a fixed point position (for example, PB position) and detects the edge of the image (that is, the edge of the circumferential ring 52) existing in the CCD image (FIG. 4(B)).
Move the cursor 64 so that it is at the center of the designated cursor 64.
, and measure the distance y between the two cursors (see Figure 4(B)).

Here, the rotation center of the rotary stepper 2 is 0.
1 and the center 02 of the code plate 5 are at a distance r as shown in FIG.
(that is, there is eccentricity). In this state, when the code plate 5 is rotated by, for example, minute angle steps under the control of the CPU 7, the two centers 01 and 02 do not coincide, so the edge of the circumferential ring 52 is rotated as shown in FIG. 4(B). As shown in △y2~
It fluctuates as △y3. If this variation is accurately shown in a diagram in association with the rotation angle of the rotary stepper 2, it will be as shown in FIG.

FIG. 3 will be explained. Assuming that the rotation angle of the rotary stepper 2 is θ2, when θ2 = 0°, Fig. 4 (B
) is assumed to be y1. This distance y
1 changes sinusoidally as shown in FIG. 3, as is clear from the relationship in FIG. 5, when the rotary stepper 2 is rotated. Here, the amplitude of this sine wave is the distance r between the two center points 01 and 02 shown in FIG.

(B) Amount of eccentricity that cannot be measured in the first step
Measurement (second step) Here, if the eccentricity shown in FIG. 5 is large, during the first step, at a certain rotation angle of the rotary stepper,
The image of the edge of the circumferential ring 52 deviates from the measurement area 6. Therefore, the rotation angle (θ2) already obtained in the first step
The eccentricity curve is regarded as a part of a sine wave and is extended, and the value of the sine wave corresponding to the rotation angle is calculated as the eccentricity at the rotation angle. This is shown in Figures 3 and 4.
This will be explained with reference to (B). As shown in Fig. 4(B), the measurement range of eccentricity (measurement range in the y direction) is ymax
It is. Here, if the amount of eccentricity is large, for example, θP
In the rotation angle section of ~θQ, the measurement range ymax is exceeded, so the amount of eccentricity at this rotation angle cannot be measured.

On the other hand, as mentioned above, the relationship between the rotation angle and the amount of eccentricity is that of a phase and a sine wave. This is regarded as a part of the wave and is extended (dotted line section in FIG. 3), and the value of the sine wave corresponding to the rotation angle is calculated as the amount of eccentricity at the rotation angle. Since such calculations can be easily performed by a known program in the CPU 7 of FIG. 2, a description of the specific operational steps will be omitted.

The CPU 7 controls the rotation angle θ2 of the rotary stepper 2, and also controls the line width length measuring device 1.
Since the measured value data of the distance in the Y direction shown in FIG. 4(B) is introduced, it is possible to measure the characteristic of rotation angle θ2 versus eccentricity shown in FIG. 3. In addition, Figure 3
has two types on the vertical axis: the distance in the Y direction and the amount of eccentricity. The distance in the Y direction is the distance from the fixed point PB to the designated cursor 64 in Fig. 4(B), but the eccentricity is the amount obtained by setting the center of fluctuation to 0 and capturing the amplitude from this center as shown in Fig. 3. be.

(C) Creating a table of rotation angle θ1 versus eccentricity (third step) Through the first and second steps, the characteristics of rotation angle θ2 versus eccentricity were obtained. This eccentricity characteristic is data based on the Y-axis direction, as shown in FIG. 4(B). However, what is now a problem as an error in measuring the arrangement angle of the slit is the amount of eccentricity WX in the X direction, as shown in FIG. 5 (the eccentricity in the Y direction does not cause a measurement error). That is, it is necessary to convert the eccentricity measured on the Y-axis to the X-axis. This conversion is easy. In other words, the Y-axis and the X-axis are exactly 90 degrees out of phase, and the rotation angle θ1 in FIG.
It is sufficient to replace it with =θ2 +90°. The CPU 7 performs this conversion, creates a table of rotation angle θ1 vs. eccentricity by shifting rotation angle θ2 by 90°, and calculates C
Write to memory 7a built into PU 7 (see Figure 2)
. In this table, θ1 and the eccentricity corresponding to the angle (for example, dxj, -dXi...see FIG. 3) are written.

(D) Distance measurement in the X direction (fourth step) Next, the CPU 7 applies, for example, a control signal S3 to the rotary stepper 2 to rotate the code plate 5 by the ideal angle step of each slit 51, and also applies a control signal S3 to the rotary stepper 2. A control signal S instructing to measure the distance in the x direction between the edge of the image of the slit 51 captured by the camera 13 and the fixed point position
2 is output by the line width measuring device 1.

[0033] This will be explained in detail. When the line width length measuring device 1 receives the control signal S2 from the CPU 7,
Two designated cursors 64 and 65 are arranged in the X direction as shown in FIG. 4(A). In FIG. 5, measurement area 6
is moved up and down along the Y axis (L line) so that the slit 51 (see FIG. 6) of the code plate 5 can be captured as a CCD image as shown in FIG. 4(A). Then, the line width length measuring device 1 fixes the specified cursor 65 as a fixed point position (for example, PC position), and sets the edge of the image existing in the CCD image (FIG. 4(A)) to the center of the specified cursor 64. Move the cursor 64 to the distance x between the two cursors.
(See Figure 4(A)).

(E) Measurement of the distance in the X direction that cannot be measured in the fourth step (fifth step) Here, if the amount of eccentricity shown in FIG. 5 is large, at a certain rotation angle of the rotary stepper during the fourth step , Figure 4(A)
The image of the edge deviates from the measurement area 6 as shown in the slit 51a shown in FIG. The slit 51 shown in FIG. 4(A)
It is assumed that the position a is the stop position of the slit when the code plate 5 is rotated by a certain angle θ11 in an ideal angle step. If the image of the edge is removed from the measurement area 6 in this way, the arrangement angle of the slit 51a cannot be measured. Therefore, the CPU 7 uses the control signal S
3, a small correction angle Δθ is added to the current angle θ11 of the rotary stepper 2 to slightly change the rotation angle of the code plate 5. As a result, the edge of the slit 51a finally enters the measurement area 6. Let the minute correction angle at this time be θA (Fig. 4 (A
) reference). Then, the line width length measuring device 1 measures the image of the edge of the slit and the distance in the x direction to the fixed point position, and (x+θA) is taken as the measurement angle of the slit at the rotation angle θ11. Note that θA shown in FIG. 4 is a distance converted into a rotation angle.

[0035] The distance in the x direction obtained in this way (
x+θA) includes the eccentricity WX as an error, as explained in the conventional example. Therefore, in the present invention, the table created in the third step is used to remove this eccentricity WX in the next sixth step.

(D) Removal of the influence of eccentricity error (6th step)
The CPU 7 reads the eccentricity corresponding to the rotation angle (for example, θ11) from the table stored in the memory 7a, and subtracts it from the measured distance in the x direction (x+θA) obtained in the fifth step. In addition, in the first step, the amount of eccentricity is measured in fine rotation angle steps, so the amount of eccentricity corresponding to the rotation angle obtained in the fifth step is shown in table 7a.
can be easily found from. However, if the corresponding rotation angle does not exist in the table 7a, the eccentricity of the rotation angle can also be calculated by linear proportionality, for example, based on the eccentricity of the rotation angles before and after the rotation angle. In other words, when the CPU 7 obtains distance data in the x direction from the line width length measuring device 1 (see Figure 2), it corresponds to the rotation angle of the rotary stepper 2 when this measured distance x (or x + θA) is obtained. Since the amount of eccentricity is read from the memory 7a and subtracted by the subtracter 7b, a measured angle value from which the influence of the eccentricity error has been removed is obtained as the output of the subtracter 7b.

[0037]

As explained above, according to the present invention, the edge of the slit does not protrude from the measurement area 6, and measurement errors due to eccentricity are eliminated, and the angle of the slit can be accurately measured. An encoder that can measure angles with high precision can be realized.

[Brief explanation of drawings]

[Fig. 1] A diagram showing the angle measurement method according to the present invention.

FIG. 2 is a diagram showing an apparatus for carrying out the method of FIG. 1;

[Figure 3] Rotation angle
Diagram showing the characteristics of eccentricity vs.

[Fig. 4] Diagram explaining the operation of the line width length measuring device 1

[Figure 5] Diagram explaining measurement error when there is eccentricity

[Figure 6] Diagram showing an example of the configuration of an actual code board

FIG. 7 is a configuration diagram of an angle measuring device to which the conventional method and the present invention are applied.

[Figure 8] Diagram showing the relationship between the code plate and the measurement area

[Figure 9] Diagram showing the relationship between the reference position and edges in the measurement area

[Figure 10] Diagram explaining line width measurement operation

[Figure 11] Diagram showing the relationship between fixed point positions and edges in the measurement area

[Explanation of symbols]

1 Line width measuring device 2 Rotary stepper 5 Code board 52 Circumferential ring 7 CPU 7a Memory

Claims (1)

[Claims] [Claim 1] A rotary stepper (2) that rotates the code plate (5) stepwise at an angle according to an applied control signal (S3) and a camera (13) for measurement set on the code plate. Converts the image of area (6) into an electrical signal, sets a fixed point position anywhere in the camera image, and outputs the distance from this fixed point position to the edge of the video that exists in the camera image. Line width measuring device (1)
In a method of measuring the arrangement angle of slits provided at equal intervals along the edge of a code plate provided with a so-called circumferential ring (52), a control signal for rotating the code plate at a certain angle ( S3) to the rotary stepper (2)
At the same time, the line width measuring device (1) measures the image of the edge of the circumferential ring (52) at the angle and the distance in the y direction to the fixed point position, and calculates the rotation angle (θ2).
In the first step of measuring the characteristics of eccentricity, if the image of the edge of the circumferential ring deviates from the measurement area (6) at a certain rotation angle of the rotary stepper during the first step, the first step has already been performed. A second step of extending the obtained curve of rotation angle (θ2) versus eccentricity as part of a sine wave and calculating the value of the sine wave corresponding to the rotation angle as the eccentricity at the rotation angle; , the third step is to create a table of rotation angle (θ1) vs. eccentricity by shifting the characteristic rotation angle (θ2) obtained in the first and second steps by 90 degrees, and to correspond to the ideal spacing of each slit. A control signal is applied to the rotary stepper to rotate the code plate at a certain angle step, and the line width length measuring device (1)
The image of the edge of the slit and x to the fixed point position are
During the fourth step, if the image of the edge of the slit deviates from the measurement area (6) at a certain rotation angle of the rotary stepper, the step angle (6) corresponding to the ideal interval is The code plate is rotated to a composite angle obtained by adding the correction angle θA to θ11) and controlled so that the image of the edge of the slit enters the measurement area (6). Measure the distance in the x direction between the image of the edge of the slit and the fixed point position, and
The fifth step is to set x+θA) as the measurement angle of the slit at the rotation angle (θ11), read out the eccentricity corresponding to the rotation angle (θ11) from the table, and calculate this from the measured distance in the x direction (x+θA). 6th to subtract
An angle measurement method comprising a process and.