JPH01174916A - Encoder - Google Patents

Abstract

PURPOSE:To accurately perform the detection of a positional change, by detecting the positional change on the basis of the positional change of a center line of a binary stripe pattern. CONSTITUTION:The light emitted from a light emitting diode passes through a code plate to be received by a CCD image sensing element 2. The stripe like scale pattern formed to the code plate is projected on the element 2. The element 2 is arranged so as to be inclined by a predetermined angle theta with respect to the stripe like scale pattern and positional change is detected from the binary stripe pattern formed from the output signal of said element 2. At this time, the middle point C is detected from the points L, R in the imaging data of the element 2 stored in a RAM 7 by a middle point detection part 16' and position data within pitch accuracy is calculated from the change of the middle point C by a position operation part 18'. This data is set to a position operating and result output part 13. By this method, since data of accuracy is calculated from the change of the middle point C, that is, the positional change of the center line of a binary stripe pattern, detection can be performed accurately regardless of the change of the quantity of light and the change of sensitivity.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an encoder suitable for use, for example, in detecting the angle of an arm of an industrial robot or detecting the feeding position of a table of a machine tool. [Summary of the Invention] In the present invention, a solid-state image sensor is arranged at a predetermined angle with respect to a striped scale pattern, and a position change is detected from a binarized stripe pattern formed from an output signal of the solid-state image sensor. By detecting position changes based on changes in the position of the center line of the binarized stripe pattern, the encoder detects position changes based on changes in the center line of the binarized stripe pattern. This allows for accurate detection. [Prior Art] Conventionally, a solid-state image sensor is arranged tilted at a predetermined angle with respect to a striped scale pattern, and positional changes can be detected with high precision using a binarized stripe pattern formed from the output signal of this solid-state image sensor. An encoder has been proposed to detect. FIG. 6 shows an example. In the same figure, (1) is the encoder board, (2) is the CCD
The image sensor (3) is a light emitting diode. The code plate (1) is configured to move linearly in the direction of the arrow. As shown in FIG. 7, this code plate (1) is provided with a gray code pattern area (4) and a striped pattern area (5). In the gray code pattern area (4), a pattern indicating a gray code is formed, and in the striped pattern area (5), a plurality of striped patterns are formed in parallel and at equal intervals. This striped pattern is arranged around the edge of the pattern indicating the gray code SB. The width of this striped pattern is, for example, 50 μm. A Gray code is one of the codes that expresses a binary number, and unlike a binary code, a Gray code has the characteristic that only one bit among all digits changes each time the number changes by one. In addition, a CCD image sensor (2) is provided facing the code plate (1).
) will be placed. When attaching this CCD image sensor (2), as shown in FIG. 8, a slight inclination angle is given to the striped pattern of the code plate (1). This inclination angle is, for example, 1 of the CCD image sensor (2).
It is considered as the pitch. The CCD image sensor (2) has, for example, (500x500) pixels and a pitch of, for example, 10μ.
m is used. In FIG. 6, light is emitted from a light emitting diode [3], this light passes through a code plate (1), and is received by a CCD image sensor (2). As a result, as shown in FIG. 9, a pattern representing a gray code and a striped pattern formed on the code plate (1) are displayed on the CCD image sensor (2). The image projected on this CCD image sensor (2) is binarized by the binarization circuit (6) and stored in the RAM.
It is stored in (7). Then, necessary data is extracted from the data stored in the RAM (7), and position data of the code plate (1) is determined by the microprocessor (8). That is, the code plate (1) is processed by the microprocessor (8).
) Coarse position data is obtained from the gray code pattern formed in the stripe pattern, and precise position data is obtained from the striped pattern. In order to obtain coarse-accuracy position data, a CCD image sensor (
Of the data obtained from 2), in Figure 9 H1r
The horizontal line at the bottom indicated by is extracted. And this lower end horizontal line Htl. Gray code pattern is read. This results in
Position data up to Gray code accuracy is obtained. Furthermore, positional data of the CCD image sensor (2) with an accuracy of up to one pitch can be obtained from the vertical address of the horizontal line H12 at the bottom of the lowest stripe pattern that is completely projected. That is, as shown in FIG. 1O, striped patterns Pi, P2.・
... are formed in parallel and at equal intervals. Then, this Gray code pattern P1°P2. ... are arranged with the edge of the pattern indicating the LSB of the Gray code pattern as the center position. Therefore, the center position between each striped pattern corresponds to the point of change of the Gray code. For example, if the horizontal line Hfl at the lower end of the CCD image sensor (2) is at the position shown by the dashed line in FIG. 10, the striped pattern projected at the bottom is pattern P2,
The horizontal line H12 at the lower end of this pattern P2 comes to the position shown in FIG. 1θ. From the vertical address of the horizontal line HN2, the distance a1 between the horizontal line H11 and the horizontal line H1t is determined with an accuracy of one pitch of the CCD image sensor (2). The point of change in the gray code is the distance (1/2) as 172 of the distance a2 between each striped pattern.
Therefore, if you know the distance a, you can find the horizontal line H1r
The distance a= from to the point of change in the Gray code can be determined with an accuracy of one pitch of the CCD image sensor (2). Position data with an accuracy of one pitch or less is obtained using a striped pattern. As described above, the CCD image sensor (2) has a slight inclination angle with respect to the striped pattern. For this reason, as shown in FIG. 9, a CCD image sensor (
In the striped pattern shown in 2), the vertical lines at both ends of each pattern are interrupted midway. That is, FIG. 11 shows a striped pattern P.
This is a schematic representation of the positional relationship between n and each pixel of the CCD image sensor (2), and H and V are
), Z is the orthogonal coordinate axis representing the pixel center position of the pattern P
This is an axis parallel to the moving direction of pattern Pn, and the center line of pattern Pn and the Z axis are perpendicular to each other. Also, θ is the angle formed by the V axis and the Z axis, and as mentioned above, for the pattern Pn,
If the CCD image sensor [2] is tilted by one pitch in the vertical direction, then the number of pixels in the horizontal direction required to display one pattern is equal to the pitch in the vertical direction of the CCD image sensor (2). pv and the pitch in the horizontal direction is pH, then θ=jan-'□p. Furthermore, when the pattern Pn and each pixel of the CCD image sensor (2) are in the positional relationship as shown in the figure, the binarized stripe pattern will cause each pixel of the CCD image sensor (2) to
It becomes a pattern divided by "mouth" or "■". That is, the parts of "口" and "謹" are high level "1" and low level "0" parts, respectively. The L point and the R point are the first points that change from "mouth" to "■" in the same horizontal line row of the CCD tlil image element (2), respectively. When the pattern Pn moves in the Z-axis direction, the L point and R point move in the horizontal direction. If the coordinate values of the L point and R point on the H and V coordinate axes are (Lu, Lv) and (RH, RV), respectively, then the projected positions ZL and Z of each point on the Z axis are, respectively. It becomes as follows. ZL=LVCOS θ+l,, sin θZa=
Rvcos θ+RHsin θThese projection positions Z
,,Zl similarly moves in the Z-axis direction when the pattern Pn moves slightly in the Z-axis direction. Therefore, if the change in point L or point R is known, position data with an accuracy of 1 pitch or less can be obtained. 112 The figure shows the operation of the microprocessor (8) using functional blocks. In Figure 12, CC stored in RAM (7)
Among the image data of the D image sensor (2), the data of the gray code pattern area (4) of the lower end horizontal line H1 is detected by the gray code detection unit (11), and the gray code of the lower end horizontal line HfB is detected. Gray code decoding part (1
2). The Gray code is decoded by the Gray code decoding section (12), and position data with coarse accuracy is obtained. This coarse-accuracy position data is used by the position calculation and result output section (13
) will be sent to. In addition, the CCD image sensor (
Among the imaging data in 2), the horizontal line Hβ2 at the lower end of the striped pattern that is located at the bottom and is completely projected.
is detected by the lower end vertical address detection section (14), and the vertical address is sent to the position calculation section (15). A position calculation unit (15) obtains position data up to pitch accuracy. This position data is sent to the position calculation and result output section (13). In addition, the CCD image sensor (
Among the imaging data of 2), the change point detection unit (16) detects the L point or the R point. Then, based on the change in the L point or R point, position data within the pitch accuracy is determined by the position calculation section (18), and this position data is sent to the position calculation and result output section (13). The position calculation and result output unit (13) is given the required accuracy from the required accuracy generation unit (19). Depending on the required accuracy, a Gray code decoder (12),
Position data from the position calculation unit (15) and position calculation unit (18) are added. [Problems to be solved by the invention] As described above, according to the encoder shown in the example in FIG. Even if the pattern Pn' does not move in the Z-axis direction, the mesh point or R point may change due to changes in the amount of light from the light emitting diode (3), changes in the sensitivity of the CCD image sensor (2), etc. Therefore, the position may change. There was a risk of errors in detection. The present invention takes these points into consideration and aims to enable accurate detection of positional changes. [Means for Solving the Problems] The present invention provides a solid-state image sensor (2) that is arranged at a predetermined angle θ with respect to a striped scale pattern Pn.

[2] An encoder that detects positional changes from a binary stripe pattern formed from the output signal of
The positional change is detected based on the change in the point (0 point). [Operation] The position of the center line of the binarized stripe pattern remains unchanged even with changes in the amount of light from the light source and changes in sensitivity of the solid-state image sensor (2). Therefore, in the above configuration, even if there is a change in the light amount of the light source, a change in the sensitivity of the solid-state image sensor, etc., the position change can be accurately detected. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. This example is basically configured in the same way as the example in FIG. 6, but position data with an accuracy less than the pitch accuracy is obtained based on positional changes in the center line position of the binarized stripe pattern. . FIG. 1 schematically represents the positional relationship between the striped pattern Pn and each pixel of the CCD image sensor (2), similar to FIG. 11 described above, but in this example, L The midpoint C is determined from the point and the R point. This midpoint C is the center line position of the binarized stripe pattern. Then, from the change in the horizontal position of the midpoint C, position data with an accuracy of 1 pitch or less can be obtained. here,
For example, when the light intensity of the light emitting diode (3) changes, L
Although the points L and R move, the midpoint C remains stationary because the L and R points change in opposite directions. Therefore, the midpoint C changes only when the pattern Pn moves in the Z-axis direction. So, if we know the change in midpoint C, we can get
It is possible to obtain position data with an accuracy of l pitch or less. By the way, if the pixel pitch in the horizontal direction of the CCD image sensor (2) is Pi, since the θΦ value is small, Pu5i
The resolution of n θ Zc is □. Therefore, in this example, a finer value Zc' of Zc is obtained. That is, in this example, the amount of light emitted by the light emitting diode (3), and therefore the amount of exposure of the CCD image sensor (2), can be changed by a constant amount. The amount of light received by the CCD image sensor (2) is IXT!, as shown in FIG. It is. Here, ■ is the intensity of the light emitting diode (3), T2 is the exposure time, and T is the cycle time of the CCD image sensor (2). When the intensity (2) is constant, the exposure time Tt can be changed in order to change the exposure amount. In the case of this example, the exposure time Tt is set as T, = n Tc where n is the control amount and Tc is the clock cycle, and the control amount n is monotonically increased by +1 from no. FIG. 3 shows the imaging position ZL, 21. It is a diagram illustrating the relationship between ZC. From this figure, the finer value Z of Zc
c' is determined by n3 n+ 2. When ns n+=10, the resolution is improved by one order of magnitude. Here, Zc+ is the control ZL
+Zm (2c=□ when fin is n. Similarly, a finer value zc' of Zc is.Here, ZC3 is A large amount of data can be obtained, and more reliable position results can be obtained from these data, increasing accuracy. Figure 5 shows the operation of the microprocessor (3) in this example using functional blocks. , parts corresponding to those in FIG. 12 are indicated with the same reference numerals. In this example,
Among the imaging data of the CCD image sensor (2) stored in the RAM (7), the midpoint detection section (16') detects the midpoint C from the L point and the R point. Then, based on the change in the midpoint C, the position calculation section (18') calculates position data within pitch accuracy. In this case, a finer value Zc' of ze is obtained, and position data is obtained from this. This position data is then transferred to the position calculation and result output section (
13). The rest is the same as that shown in FIG. 12. In this way, according to this example, position data with an accuracy of 1 pitch or less is obtained from the change in the center line position C of the binarized stripe pattern, so the change in the light amount of the light emitting diode (3), the CCD image sensor Even if there is a sensitivity change in (2),
Position changes can be detected accurately. Further, since the exposure amount is sequentially changed by a fixed amount to obtain a finer value Zc' of Zc, position detection can be performed with even higher precision. In this case, since a large amount of Zc' is required, defects in the edge line of pattern Pn and CC
Abnormal values due to defective pixels of the D image sensor (2) can be deleted, and reliability can be improved. In addition, since highly accurate position detection can be performed, CCD image pickup devices (2
) pixels with at least high resolution can be realized. In addition, according to the above-mentioned embodiment, the finer value Zc of Zc
′, the exposure amount of the CCD image sensor (2) can be changed, but even if the threshold level of the binary 11-way (Q) can be changed by a fixed amount, the same result can be obtained. Effects can be obtained. Further, in order to obtain a value Zc' finer than Zc, the position of the light emitting diode (3) may be displaced minutely by a piezoelectric element or the like in a direction parallel to the Z axis. Here, the displacement amount Dg is D!, where s5 is the control amount and DC is the minute amount. =SDC, and the control amount S is monotonically increased by +1 from 80. FIG. 4 illustrates the relationship between photographing positions ZL, ZR, and ZC. From this figure, the finer value Zc' of Zc
is found by . Here, by increasing the control amount S of the control ms sl in the ZCI, a large amount of data can be obtained and a more reliable position result can be obtained. Further, in the above-mentioned embodiment, the solid-state image sensor is
Although it uses a CCD image sensor (2), MO3
A type image sensor may also be used. [Effects of the Invention] According to the present invention described above, the positional change is detected based on the positional change of the center line of the binarized stripe pattern, so that the change in the light amount of the light source and the sensitivity change of the solid-state image sensor are detected. Even if such a situation occurs, position changes can be detected accurately.

[Brief explanation of the drawing]

1 to 5 are diagrams for explaining one embodiment of the present invention,
6 to 12 are diagrams for explaining conventional examples. (1) is a code board, (2) is a CCD image sensor, (3) is a light emitting diode, (6) is a binarization circuit, and (7) is a RAM.
, (8) is a microprocessor. Figure 2 shows the relationship between light leakage and IL, zR, Zc and Φ. Figure 10 is an explanatory diagram of O detection up to the angle of the wound, and Figure 11 is a diagram showing the date and time of the O detection under the γ-te

Claims (1)

[Claims] In an encoder in which a solid-state image sensor is arranged inclined at a predetermined angle with respect to a striped scale pattern, and a position change is detected from a binary stripe pattern formed from an output signal of the solid-state image sensor. , An encoder characterized in that a positional change is detected based on a positional change of a center line of the binarized stripe pattern.