JP3517764B2 - Linear scale - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear scale, and more particularly to an optical linear scale.

[0002]

2. Description of the Related Art As an optical linear scale, "Servo sensor basics and applications" published by Ohmsha, for example.
(Kojiro Oshima and Yuji Akiyama) [Published February 20, 1988] is known. The technology described in this publication will be described with reference to FIGS.

Here, a position scale is taken as an example of the linear scale 100. As shown in FIG. 12, the linear scale 100 given as an example includes a glass scale 103 including a pair of main scales 101 and index scales 102, each having a bright and dark grid of exactly the same pitch, and the scale 103. A light source 104 including an LED that illuminates, a mirror 106 that guides the light emitted from the light source 104 to the scale 102 side, a collimator lens 107, and a photodiode 105 that detects the light that has passed through the scale 103. Although the scale 102 is fixed and the main scale 101 moves, the output of the photodiode 105 changes as the scale moves.

As shown in FIG. 13 (a), the output becomes maximum when the transmissive parts of the two sheets of glass coincide with each other, and when the transmissive part and the opaque chrome-coated part overlap, the output is 0 in the ideal state. Becomes Therefore, the output waveform ideally has the light amount change as shown in FIG.
Actually, since the grating pitch of light and dark is as small as 8 μm, there is an influence of light diffraction and an influence of reflection on the chrome-bonded surface.
It is output in the form of an approximate sine wave as in the output waveform shown in (c). Since the interval between the peaks of this output waveform corresponds to the pitch of the scale, the amount of movement can be known by counting the number of peaks. This is the basic principle of the position scale, but in reality, the photodiode A of FIG.
B, / A, / B105 (“/” indicates inversion.)
Various processes are performed by using the four.

The grids of the index scale 102 corresponding to A, B, / A, and / B are 0 °, 90 °,
The phase relationship is 180 ° and 270 °. This is A
, / A, B, and / B are combined to detect by a differential method, and the scale is set to be strong against dirt and a change in light amount, thereby improving reliability. The signals thus obtained are respectively referred to as A and B, and the electrically inverted signals are referred to as / A and / B, respectively. Then, a process for reading even finer dimensions using these signals is executed.

The moving direction of the scale 102 can be determined by knowing which of the A signal and the B signal the phase is advanced as shown in FIG. As a method of reading finer than the pitch of the scale 102, when only the A signal is used, it is possible to read in units of 4 μm by catching both when the reference level is crossed from below and when it is crossed from above. Further, when the B signal is used, it can be read up to 2 μm. A, B for more detailed reading
It is necessary to generate a signal having a 45 ° phase difference using the signal of (1) and a signal having a 135 ° phase difference from the signals of B and / A.

[0007]

By the way, in the above-mentioned linear scale, the light emitted from the light source (LED) is converted into parallel rays by the collimating lens, and the light passing through the overlap between the main scale and the index scale is received by the light receiving element. Since it is detected by the method, a fine and highly accurate main scale, index scale, and precise collimator lens are required, resulting in high cost. In addition, some linear scales of this type have an origin mark and have a function that outputs a position signal based on that origin. A scale was desired.

The present invention has been made in view of such a background, and a first object thereof is to provide a linear scale capable of obtaining an origin position with high accuracy with a simple structure.

A second object is to provide a linear scale in which the origin position can be easily changed and the origin position accuracy is high.

[0010]

In order to achieve the above object, the first means is to form a pattern of lines formed by inclining a plurality of straight lines in parallel with the longitudinal direction of the scale at a constant interval. In the main scanning direction and the sub scanning direction
The area formed by the × n pixels is set in the main scanning direction and
Scanning with a line sensor while moving in the sub-scanning direction ,
In a linear scale for calculating the position of the straight line in the region each time the region is set to detect at least one of the reading error, the reading speed, and the reading position, a specific straight line outside the region where the line pattern is formed. Mark indicating the position of the mark and the reading data of the mark.
The value of the center of gravity of the specific straight line specified by
Of each pixel read in the area containing a specific straight line
The sum of the moments from a certain position within the region of concentration is 0
As the position that corresponds to the calculated value of the center of gravity
Means for determining the origin position based on the position of the clock . The second means is the first means.
On a linear scale similar to
Holding an address that specifies one of the straight lines that make up the
A row and a straight line specified by the held address
Value of the center of gravity of the inside of the area including the specified straight line
From a position in the area of the density of each pixel read
Is calculated as the position where the sum of the moments of
Origin based on the position of the clock corresponding to the value of the center of gravity
And means for determining the position. Third
Means determines the origin position in the first means.
The means to measure the center of gravity of the straight line under the condition that the mark exists
When calculating, the direction of movement of the line sensor
The value of the center of gravity in the intersecting direction and the center of gravity of the set area
Is calculated by interpolating the values of the center of gravity before and after the value of the center of gravity is exceeded.
Characterized by determining the position of the center of gravity of the set region
To do. A fourth means is the same as the origin position according to the second means.
The means for determining the location is the direct address specified by the address.
When calculating the center of gravity of the line, move the line sensor
The value of the center of gravity in the direction orthogonal to the moving direction and the set area
Compensate for the values of the center of gravity before and after the center of gravity of the area exceeds the value of the center of gravity.
And determining the position of the center of gravity of the set region
Is characterized by.

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1. Structure of Linear Scale FIG. 1 shows a scale 1 which is a premise of the present invention in which a diagonal pattern 4 is formed by repeating opaque diagonal lines 3 on a transparent glass 2. The repetition of the hatched line 3 is repeated in "3. As described in “Measurement Principles”, continuous positions or speeds can be measured even if a window of a predetermined size jumps between the diagonal lines 3 so that the line sensor has an overlap when viewed in the length direction of the line sensor described later. I am trying. The inclination of the slanted line 3 can be measured arbitrarily, but 45 ° or 135 ° is convenient for simplifying the calculation on the measurement. The width of the slanted line is set to a predetermined motion in the bitmap data read by the line sensor to obtain the center of gravity of the slanted line 3 in the window. . By reading a relatively large pattern like this, you can read minute changes in position,
It is not necessary to increase the resolution of the lens that constitutes the device so much, and the requirement for the smoothness of the edges of the pattern is not high because the influence is reduced in the process of calculating the center of gravity.

Further, an origin mark 5 is also formed so as to output a position signal based on the origin. Since the origin mark 5 also has the origin at the position of the center of gravity of the read data similarly to the diagonal line 3, a fine mark is provided to improve the accuracy of the origin, and a high-resolution lens and a light receiving unit are provided to read the fine mark. It is not necessary to provide an element. The origin mark 5 is provided at a position where the line sensor does not read the oblique line 3, as shown in FIG. Therefore, it is not necessary to provide a special sensor for the origin, and the line sensor for reading the diagonal line 3 can be used as it is as a sensor for obtaining the position of the origin.

FIG. 2 is an explanatory view showing a cross section of the linear sensor. The scale 1 in the figure corresponds to a cross section with the short side of the scale 1 in FIG. 1 in the foreground, and the unit 8 in which the light source 6, the lens 7, the line sensor and the control board are integrated with the scale 1 in between is a scale 1. It can be moved in the longitudinal direction. Usually, the scale 1 is fixed, and an object whose position or velocity is desired to be obtained is combined with the unit 8 and integrated, and measurement is performed. In this example, since the image of the scale 1 is read by the line sensor, the diffusion plate 9 is provided between the scale 1 and the light source 6.
Is provided to make the amount of light uniform. Instead of providing the diffusing plate 9, the pattern of the diagonal lines 3 may be formed on the diffusing plate 9. Further, the diffusion plate 9 can be provided on the side of the moving unit 8. The line sensor extends in the vertical direction in FIG. 2, and the lens 7 reads the image of the pattern of diagonal lines 3 formed on the sensor. The line sensor and unit 8 perform shading correction in order to correct a decrease in the peripheral light amount of the lens due to the cosine fourth law of the lens, a variation in the illumination light amount depending on the position of the sensor, a variation in the sensitivity between the light receiving elements of the line sensor, and the like. In the shading correction, the data when the line sensor is reading a portion of the scale 1 without the oblique lines 3 is stored in the memory, and the sensitivity of each pixel is corrected so that the data at that time becomes uniform. This data is read in a predetermined mode and stored in a non-volatile memory, and is always used when performing correction.

2. System Configuration of Signal Processing Unit FIG. 3 is a block diagram showing the system configuration of the signal processing unit. In the photoelectric conversion device, the line CCD 20 converts the image of the original image formed on the light receiving portion of the CCD and the image of the measurement pattern 4 into electric signals. The image converted into an electric signal is converted into digital multi-valued image data by the A / D converter 21. The converted data is subjected to shading correction for correcting unevenness of illumination, reduction of the amount of light around the lens, difference in sensitivity between pixels of the photoelectric conversion device, and the like. The data of the reference density plate read by the photoelectric conversion device is used for the shading correction. The shading-corrected image data is input to the position error calculation circuit 24 via the memory 23, and will be described in “4. The position error between lines is measured for each reading line in the sub-scanning direction by the process described in "Position error measurement process".
The measurement result is output to the position error calculator. The position error calculation unit 24 receives the position error signal together with the image data (video signal), causes the memory 23 to sequentially hold the predetermined number of lines of image data necessary for correction, and the error signal between the adjacent lines, and the memory 23 By using the data of No. 23, the image data before and after the line to be corrected and the error data, the value of each pixel on the line by the interpolation method based on the value of the image read the image data at the original position. And the corrected image data of the line is output as a video signal for each line. The memory 23, which has been processed and no longer requires data, holds the next data, and processes the image on the entire surface of the original by sequentially repeating the process to output the image. The control unit 25 controls the timing of each functional block, sets operating conditions, etc., and operates in relation to each other. In the figure, reference numeral 26 is an external interface described later.

Although the CCD 20 is used in this embodiment, a photodiode array or the like may be used instead. The advantage of using the CCD 20 is that it is cheap. The photodiode array is preferable in terms of high speed and S / N.

3. Measurement Principle FIG. 4 is a diagram for explaining the measurement principle assuming a typical case. In the figure, the arrow 31 written as main scanning indicates the arrangement of the pixels of the image of one line that is simultaneously read by the device that reads the image in line order, and the sequence on the time axis when this parallel data is converted into linear data. . An arrow 32 written as sub-scan in the drawing indicates the direction of reading while sequentially moving the reading range of one column of main scanning. As means for moving, a mirror for projecting an image of a document on a photoelectric conversion element, a device for mechanically moving an illumination lamp, a device for moving a document, or a photoelectric conversion device and its imaging optical system are moved integrally. There are things. Here, each quadrangle surrounded by a line parallel to the main scanning direction and the sub scanning direction is referred to as a pixel. The plane formed by the pixels can be regarded as an image in which the data obtained by converting the image of the document into an electric signal is directly aligned with the map of the image of the document, and is sometimes called a bitmap. When it is output from the reading device in real time, the main scanning direction and the sub-scanning direction show the temporal order, but when the output data is stored in the memory, it is possible to access each pixel arbitrarily. Yes, the main scan, the sub-scan, and the handling regardless of the order of time become possible.

FIG. 4 shows the case where the pixel sizes of the main scanning and the sub-scanning are equal, and when the scanning speed in the sub-scanning direction fluctuates and when the oblique line of 45 ° is read at a constant speed, it is projected on the photoelectric conversion device. , An image corresponding to a bitmap without any deterioration. That is, a indicates that the image at 45 ° is formed on the bitmap when scanning is performed at a predetermined constant speed corresponding to the clock that controls the reading timing in the sub-scanning direction. b is an image when the speed changes, and the inclination changes depending on the speed. That is, AB
Indicates that when the scanning speed in the sub-scanning direction is 0, the position at which the document is read does not change even if the bit map address in the sub-scanning direction advances by the clock that controls the reading timing in the sub-scanning direction. It becomes a line parallel to. In BC, when the scanning speed in the sub-scanning direction is 1/2 of the predetermined speed, even if the address of the bitmap advances, it means that the image is read at a position where only half of the address is read. The angle with the direction line is tan θ =
From 0.5 to about 26.57 °. CD is when scanning at a predetermined speed, and the inclination is 45 °. Similarly, after D-, when the scanning speed is 1.5 times, the angle is about 56.31 °. That is, the inclination of the image is different depending on the scanning speed, in other words, the moving speed of the slanted line 3 in the main scanning direction corresponds to the moving speed in the sub scanning direction. The position error of the pixel of the bitmap image caused by the vibration of the lens, the photoelectric conversion device, or the like is measured.

Although the above description has been made in the case where the pixel has square pixels and a line of 45 ° is used, the pixel is not a square pixel. For example, the resolution of main scanning is 400 dpi and the resolution of sub-scanning is 60.
It can also be applied to image data of a reading device such as 0 dpi. Similarly, even if the slanted line 3 other than 45 ° is used, the movement amount of the slanted line 3 in the main scanning direction depends on the speed in the reading direction in the sub-scanning direction. Since the relationship of doing is established,
The position error of the pixel can be measured.

4. Position error measurement process FIG. 5 shows a bit map similar to that shown in FIG.
It is for explaining the processing when measuring the position error when there is. W1 is an 11 × 3 window for performing calculation for obtaining the position of the image data. To find the position of the data in the window, the center of gravity in the main scanning direction is calculated. In this calculation, the center of gravity is obtained by sequentially moving the positions of the windows to W2, W3, .... In the case where the position of the center of gravity in the main scanning direction is a line of 45 °, if the position of the pixel does not move due to some error factor, if the window is moved as shown in the figure, it moves by one pixel in the main scanning direction. Should do. If the amount of movement of the pixel is different from that of one pixel, it means that the position of the pixel has changed for some reason, and the position error can be obtained. When it is known that the main cause of the position error is the unevenness of the scanning speed in the sub-scanning direction, it is easy to convert the data of the position error into the speed unevenness data.

Since a large number of pixel data including the data of peripheral pixels are used to obtain the center of gravity, various noises including CCD-specific noise are included in the image data. The impact is reduced,
High S / N measurement is possible. Generally, the larger the number of pixels in the window, the higher the S / N.

The shape of the window is preferably large on the main scanning side because the center of gravity in the main scanning direction is obtained. It is possible to measure even if the sub-scanning direction is 1.

FIG. 6 illustrates the movement of the window and the processing associated therewith when the position error is measured using a plurality of slanted lines. Similar to the example in FIG. 5, when the windows are sequentially moved to reach the preset Wn, Wn + 1 is set as the next window.
Move to. Patterns a1 and a of diagonal lines before and after moving
The interval of 2 is decided at the stage of creating the measurement chart, and the value of the interval is corrected when the movement of the center of gravity in the main scanning direction is calculated. Wn + 1, Wn + 2, Wn + 3 ... If the interval between patterns is set to an integral multiple of the pixel size, the correction when the window is jumped is easy, and it is also convenient when inputting this correction amount to the measuring device prior to measurement.

Although the window is moved pixel by pixel in this example, the window may be moved by two pixels or more when the frequency band such as vibration that causes a pixel position error is low. By doing so, the time required for measurement can be shortened.

Further, if the position error is measured using a plurality of diagonal lines, it is possible to measure the entire position in the sub-scanning direction even if the reading range of the reading device is vertically long. Further, if the measurement is performed only within the narrow width in the main scanning direction, it becomes possible to measure the position error separately in the central portion, the front side, or the back side in the main scanning direction.

As is clear from these figures, even if the position error is measured with high resolution in the present application, it is not necessary to make the slanted line pattern thin accordingly, and there is no influence of the restriction of the MTF of the system. The feature is that a wide pattern can be used. If a wide pattern is used, the window will be correspondingly larger, resulting in higher measurement accuracy. When processing speed and real-time processing are performed, the width of the pattern may be set in balance with the size of the buffer, the economy of the circuit scale, and the like.

5. Calculation of Window Data and Center of Gravity FIG. 7 shows the relationship between the window data and the hatched pattern. In each pixel of the window, the value of the image data obtained by reading the hatched pattern is entered. The image data value is 8-bit digital data and is 1
When expressed in the 0-ary system, it can take a value of 0 to 255. The values in the figure are values in which the image data is expressed in decimal notation.

To calculate the center of gravity in the main scanning direction, the sum of data is obtained for each column. From the right side, h0, h1, ...
・ Assuming h10 is 14, 37, 150, 34, respectively
5, 562, 590, 427, 202, 50, 18, 1
It is 3. The coordinates of the center of each pixel in the main scanning direction are set from 0 to 10 in order from the right, and the position of the center of gravity in the main scanning direction is m and slut, and the moment around m is 0, so h0 (m-0) + h1 ( m-1) + ... h10 (m-1
0) = 0 holds, and when a numerical value is entered and calculation is performed, m = 4.667 is obtained.

Obtaining the center of gravity does not require preprocessing such as interpolation and is useful for simplifying and speeding up the calculation. The position of the image is obtained from the sequence of the sum of the data in each column.
It is also possible to use a method in which a data string having a predetermined resolution is obtained by interpolation and the position where the peak value exists is obtained from the data.

6. When calculating the center of gravity for the width of the diagonal line, the width of the diagonal line does not matter as long as the data can be read properly, but the pixel is square,
When the angle of the slanted line is 45 ° and the slight deviation of the image scanning speed from the predetermined target speed is measured with higher accuracy, if the width of the slanted line in the main scanning direction is set to an integral multiple of the pixel, the window Even if is moved diagonally, the relationship between the diagonal line and the pixel is the same on both sides of the diagonal line, the error factors of the image data are balanced, and the accuracy of calculating the image position can be improved.

7. Relationship between movement amount of image in diagonal line in main scanning direction and positional error of pixel in sub-scanning direction In this embodiment, in order to measure positional error of pixel in sub-scanning direction, the diagonal line is moved in the main scanning direction. You are watching the movement of the image position. When a square pixel is measured using a diagonal line of 45 °, as is clear from the above description, the deviation between the windows of the movement amount in the main scanning direction becomes the position error in the sub scanning direction as it is. If the pixel is not square, or if the diagonal angle is not 45 °,
It is necessary to perform conversion to obtain the position error in the sub-scanning direction.

8. Since the diagonal line for determining the moving direction is used, the moving direction of the position of the center of gravity of the image of the diagonal pattern differs depending on the relative moving direction of the line sensor and the scale. For example, if the line sensor moves to the right with respect to the scale shown in FIG. 1, the diagonal barycenter moves upward. If you move it to the left, the center of gravity of the diagonal line will move downward. This can be easily identified by looking at the code when moving the center of gravity of the front and rear windows. This code differs depending on whether or not the inclination of the oblique line exceeds 90 °, but if it is determined to be one by design, the relationship between the code and the moving direction is uniquely determined. Therefore, a special light receiving element or the like for discriminating the direction unlike the above-mentioned conventional example is unnecessary.

9. Mark of Origin and Center of Gravity FIG. 8 is a perspective view showing a pattern of the linear scale according to the embodiment of the present invention. In this embodiment, a mark 5 indicating a region having an origin is provided beside the diagonal line 3. As the origin itself, A is given as shown in the figure as the value of the center of gravity when a predetermined area is set for the data obtained by reading the diagonal lines 3 and the center of gravity is obtained. A is just a value, not a position entity. The position where the value of the center of gravity is A exists in each of the slanted lines 3 that are repeated, but to specify which of these is the origin position is the position of the origin provided outside the formation region of the slanted line 3. It is mark 5 shown. This mark 5 gives a condition for indicating that it is the origin, and it is sufficient if the condition can be detected. Therefore, the accuracy of the mark 5 may be poor. Further, there is no need for processing such as calculating the center of gravity for the read data. The position of the origin can be easily changed by changing the position of the mark 5. For example, it is also possible to first create a pattern in which only the shaded lines 3 are repeated and then write or paste the mark 5 according to the desired origin position because the mark 5 does not require positional accuracy.

FIG. 9 is a flowchart showing a processing procedure for determining the position of the given center of gravity A. In this process,
First, it is checked whether or not there is an image of the mark 5 indicating the area where the origin exists (step 901), and if there is, the processing for determining the position of the origin is performed. Calculating the center of gravity by setting a predetermined area for the shaded image in order to obtain the velocity or position of the linear scale The value of the center of gravity obtained by the above-described processing is checked, and the value is set in advance.
Is detected (step 902), and the values of the center of gravity before and after the center of gravity A is held in the register (memory). The value of the center of gravity immediately before exceeding A is gn-1, the clock at that time is n-1, the value of the center of gravity immediately after exceeding A is gn, and the clock at that time is n. The center of gravity is plotted on the vertical axis in FIG.

As can be seen from FIG. 10, the position a of the clock corresponding to A is obtained by linear approximation from the positions of the center of gravity before and after the value of the center of gravity A. This a is the origin on the clock,
Let A be the origin of the position. Therefore, the scanning speed at this time can be determined from the fact that the distance has moved by gn -A in the time of na. Therefore, the position of the origin can be obtained with high accuracy without providing a dedicated sensor or processing system for obtaining the origin.

10. Address of diagonal line and center of gravity [9. In the section of “Mark of origin and center of gravity”, the mark 5 indicating the position or range of the origin is provided, and the position of the origin is determined on the condition that the mark 5 exists, but in this example, instead of the mark 5, An address is provided on each of the diagonal lines 3 forming the pattern.

That is, as shown in FIG. 11, by assigning a number from 0 to n to each diagonal line 3 and designating that number, the center of gravity of the diagonal line 3 designated by that number is calculated. From the values of the center of gravity before and after A, the position of the center of gravity is determined in the same manner as in the previous item 9. When the area is set and the center of gravity is calculated, the area is jumped to move to the diagonal line next. Therefore, by counting the number of times of the jump, the diagonal line 3 designated by the number is detected. By doing so, it becomes possible to change the position of the origin by setting a logical value without providing the mark 5 described above.

At this time, an interface 26 is provided on the linear scale (two-dot chain line in FIG. 3), and the interface 2
If the hatched number 3 can be set from the outside via 6, the origin position can be changed very easily. If the setting is held in the non-volatile memory, the specified setting is maintained even when the power is turned off, which is very convenient for use.

When the origin can be set by designating the address through the interface, if the origin is not set, the end is often the origin when using a normal linear sensor. , The default is the diagonal line at the end. In this embodiment, since the address "0" is assigned to the diagonal line at the end, the origin position is determined by setting "0" as the default diagonal line by setting it to 0 when no specific data is written. can do.

Further, in this embodiment, it is possible to set the value A giving the center of gravity, in addition to the number indicating the address of the diagonal line, via the interface 26. The value of the center of gravity set via the interface 26 in this way is held in a non-volatile memory like the address of the diagonal line. The origin position can be changed only with the accuracy of repeating the slanted line by setting only the address of the slanted line, but if both the address of the slanted line and the value A of the center of gravity can be set in this way, the origin position can be It is possible to set the origin. The value of the center of gravity and the address of the diagonal line are held in a non-volatile memory here, but the above value and address are set by a switch or the like provided in the device, and the data is held as the state of the switch. You can also do so.

[0048]

As is apparent from the above description, according to the present invention configured as described above, (1) the origin position can be obtained with high precision by a simple structure.
It (2) Origin position without degrading the origin position accuracy
Can be changed. (3) The origin position can be determined with high accuracy. And the like .

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[Brief description of drawings]

FIG. 1 is a perspective view of a scale which is a premise of the present invention.

FIG. 2 is a schematic configuration diagram of a linear scale according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a system configuration of a signal processing unit of the image reading apparatus according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a measurement principle of the line sensor according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram showing the measurement principle of the position error measurement processing according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing movement of a window and a process associated with the movement when there are a plurality of diagonal lines and a position error is measured using the plurality of diagonal lines.

FIG. 7 is an explanatory diagram for explaining the principle of calculation of window data and center of gravity.

FIG. 8 is a perspective view showing a state of an origin mark and a diagonal line pattern of the linear scale according to the embodiment of the present invention.

9 is a flowchart showing a processing procedure for detecting a center of gravity position using the pattern of FIG.

10 is an explanatory diagram showing a detection principle of the processing procedure of FIG.

FIG. 11 is a perspective view showing a pattern of a linear scale according to another embodiment in which hatched numbers are assigned.

FIG. 12 is a schematic configuration diagram showing a configuration of a linear scale according to a conventional example.

FIG. 13 is an explanatory diagram showing a measurement principle of a linear scale encoder according to a conventional example.

FIG. 14 is a diagram showing a principle of determining a moving direction of a linear scale according to a conventional example.

[Explanation of symbols]

1 scale 2 glass 3 diagonal lines 4 diagonal pattern 5 origin mark 6 light source 7 lenses 8 units 9 Diffuser 20 CCD 21 A / D converter 22 Shading correction section 23 memory 24 Position error calculation circuit 25 Control unit 26 External Interface

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-4-32714 (JP, A) JP-A-5-317956 (JP, A) JP-A-4-366718 (JP, A) JP-A-57- 6994 (JP, A) Actual development Sho 63-27817 (JP, U) Actual development Sho 63-167217 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01D 5/26-5 / 38 G01B 11/00-11/30

Claims (4)

(57) [Claims] 1. A pattern of lines formed by inclining a plurality of straight lines in parallel to the longitudinal direction of the scale and forming a parallel pattern in a main scanning direction and a sub-scanning direction at preset constant intervals by m × n.
Direction and sub-scanning read main scanning region formed by the pixel
In a linear scale for reading with a line sensor while moving in the scanning direction, calculating the position of the straight line in the area every time the area is set, and detecting at least one of a reading error, a reading speed and a reading position, A mark indicating a position where a specific straight line exists outside the area where the line pattern is formed, and the specific straight line specified by the read data of the mark.
Read the barycentric value of the line in the area containing the specific straight line.
From a position in the region of the density of each pixel taken
Calculated as the position where the sum of moments becomes 0
And a means for determining the origin position based on the position of the clock corresponding to the value of the center of gravity . 2. A pattern of lines formed by inclining a plurality of straight lines in parallel to the longitudinal direction of the scale and forming parallel patterns in a main scanning direction and a sub scanning direction at preset constant intervals.
Direction and sub-scanning read main scanning region formed by the pixel
In a linear scale for reading with a line sensor while moving in the scanning direction, calculating the position of the straight line in the area every time the area is set, and detecting at least one of a reading error, a reading speed and a reading position, Means for holding an address designating one of the straight lines forming the pattern, and the center of gravity of the straight line designated by the held address
Reading the value of within the area containing the specified straight line
Mode of the density of each of the recorded pixels from a position in the area.
The center of gravity calculated as the position where the sum of the ment is 0
Means for determining the origin position based on the position of the clock corresponding to the value of . Wherein means for determining the home position, when the mark is calculating the center of gravity of the straight line conditions under present, the value of the direction of the center of gravity perpendicular to the moving direction of said line sensor, wherein the center of gravity of the set area is two rear scale claim 1 Symbol mounting and determining the position of the center of gravity of the area that is the setting value by interpolating the center of gravity before and after exceeding the value of the center of gravity. 4. The means for determining the origin position is the
When calculating the center of gravity of the straight line specified by the dress
The center of gravity in the direction orthogonal to the moving direction of the line sensor
And the center of gravity of the set area, the value of the center of gravity
Interpolate the value of the center of gravity before and after exceeding the
The position of the center of gravity is determined, according to claim 2 .
Linear A scale.