JPH08145621A - Edge detector - Google Patents

Abstract

PURPOSE: To realize a highly accurate edge detection by inputting an enlarged edge image through a pair of beam splitters into three light receiving means, operating the output of received light and determining inflection point. CONSTITUTION: The edge image of a graduation line on a standard scale 1 is enlarged by means of an objective lens 2 and passed sequentially through beam splitters 3, 4 which deliver a transmission image from the splitter 4, a reflection image from the splitter 3 and a reflection image from the splitter 4, respectively, to light receiving elements 5a-5c. In front of the elements 5a-5c, slits 6a-6c are disposed so that the edge image of a graduation line on the scale 1 is received sequentially by the elements 5a-5c when the scale 1 is shifted perpendicularly to the graduation line thus determining the position of respective linear light receiving faces. The outputs A-C of received light are fed from the elements 5a-5c through amplifiers 7a-7c to a processing circuit 8 where an operation of A+C-B is performed and a point where A+C-B goes zero is detected as an inflection point (edge position).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge detecting device for optically detecting an edge of a scale line used in a standard scale calibration device having a plurality of parallel scale lines arranged therein.

[0002]

2. Description of the Related Art Conventionally, as a method of optically detecting the scale line edge of this type of standard scale, it is roughly divided into an inflection point method for measuring the light and dark inflection points of the scale line edge image, and
There is a light relative intensity method in which the light relative intensity of the scale line edge image is sliced at a predetermined level to obtain the edge position. The former is a vibration slit method that obtains an inflection point from a received light signal obtained by vibrating a slit arranged in front of the light receiving element, and an inflection point is obtained from the differential signals by processing the output signals of two light receiving elements. There is a two-way arrangement sensor method. The latter also includes a pinhole method, a slit method, an image processing method and the like.

[0003]

The conventional edge detection method has advantages and disadvantages. For example, the inflection point method has good reproducibility and excellent operability, and the edge interval of the scale line can be measured with high accuracy, but accurate detection of the edge position is difficult. The optical relative intensity method can measure the edge position with high accuracy, but on the other hand, it is necessary to set the slice level in accordance with 100% and 0% light and dark matching.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an edge detecting device capable of highly accurate edge position detection with relatively low illumination.

[0005]

The present invention is, firstly, an apparatus for optically detecting a scale line edge of a scale in which a plurality of parallel scale lines are formed in an array. An objective lens that magnifies the edge image, a first beam splitter that half-transmits and half-reflects the edge image magnified by this objective lens, and a second beam-half that half-transmits and half-reflects the transmission image of the first beam splitter. Beam splitter, first light receiving means having a linear light receiving surface parallel to the scale line edge for detecting the transmission image of the second beam splitter, and the reflection image of the first beam splitter Second light receiving means having a linear light receiving surface parallel to the scale line edge, and linear light receiving surface parallel to the scale line edge for detecting a reflected image of the second beam splitter. A third light receiving means, wherein the first, second and third light receiving means receive the scale line edge images sequentially when the scale is moved in a direction orthogonal to the scale line, It is characterized in that the positions of these linear light receiving surfaces are set.

In the first invention, it is preferable that each of the first, second and third light receiving means has a linear light receiving surface position by arranging a slit on the front surface of the light receiving element. It has a feature.

Secondly, the present invention is an apparatus for optically detecting a scale line edge of a scale in which a plurality of parallel scale lines are formed and arranged, and an objective for enlarging an edge image of the scale line of the scale. It is characterized by having a lens and a light-receiving element array in which three linear light-receiving surfaces parallel to the scale line edges are arranged at equal intervals in order to detect an edge image magnified by this objective lens.

[0008]

The principle of the edge detecting apparatus according to the present invention is to apply the inflection point method by receiving an enlarged edge image using three linear light receiving surfaces arranged in parallel with the edge image. First
In the above invention, two half-transmission and half-reflection beam splitters are used. The first light receiving means detects the transmission image of the second beam splitter, and the second light receiving means is the first light receiving means.
The reflected image of the beam splitter is detected, and the third light receiving means detects the reflected image of the second beam splitter. At this time, the first, second and third light receiving means set their linear light receiving surface positions so that the scale line edge images are sequentially received when the scale is moved in the direction orthogonal to the scale line. Has been done. The light receiving outputs A, B, and C of the first, second, and third light receiving means are 1/4, 1/2, and 1/4, respectively, as compared with the case where they are not provided, by the beam splitter. The inflection point can be obtained by performing the operation A + CB.

In the second invention, a beam splitter is not used, but a light receiving element array in which three linear light receiving surfaces parallel to the scale line edges are arranged at equal intervals is used. At this time, if the light receiving outputs on the respective light receiving surfaces when the scale is moved in the direction orthogonal to the scale line are A, B, and C, A +
By the calculation of C-2B, a point at which this becomes 0 is obtained as an inflection point. In both the first and second inventions, the edge image is enlarged by the objective lens, the enlarged edge image is received by using the three linear light receiving surfaces which are arranged substantially in parallel, and the received light output is obtained. As a result of the processing, highly accurate edge detection is possible.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an edge detection device according to an embodiment of the present invention. A large number of parallel scale lines are formed on the standard scale 1. The standard scale 1 is, for example, one having a scale formed by vapor-depositing a metal film on glass, or one having a scale engraved on a metal. The scale width is 2 to 20 μm.

An edge image of the graduation line of the standard scale 1 due to transmitted illumination from the back surface, for example, is magnified by the objective lens 2 and is incident on the first beam splitter 3. The transmission image of the first beam splitter 3 is further incident on the second beam splitter 4. These beam splitters 3, 4
Have the same characteristics of transmission / reflection = 50/50. The specific mold may be a prism type or a plate type.

The transmission image of the second beam splitter 4 is detected by the first light receiving element 5a having the slit 6a arranged on the front surface and the linear light receiving surface position being set. The reflected image of the first beam splitter 3 is the second light receiving element 5b in which the slit 6b is arranged on the front surface and the linear light receiving surface position is set.
Is detected by Similarly, the reflected image of the second beam splitter 4 is detected by the third light receiving element 5c in which the slit 6c is arranged on the front surface and the linear light receiving surface position is set.

Here, the slits 6a, 6b, and 6c are such that when the standard scale 1 is moved in a direction orthogonal to the scale line, the scale line edge image shows the first light receiving element 5a,
The second light receiving element 5b and the third light receiving element 5c are arranged in this order so as to receive light, and the position of each linear light receiving surface is determined. Specifically, the openings of the slits 6a, 6b, 6c are, for example, 10 μm wide and 5 mm long, and the intervals are 10 to 20 μm.

FIG. 2 specifically shows the positional relationship between the first, second and third light receiving elements 5a, 5b and 5c and the slits 6a, 6b and 6c. In FIG. 2, the shaded portion on the right side of the scale line edge 9 indicates the dark portion, and the left side indicates the bright portion. Now, at an arbitrary position on the scale 1, the second light receiving element 5
Assuming that the scale line edge 9 is located exactly in the center of the slit 6b with respect to b, the slit 6a is formed in the first light receiving element 5a.
Of the slits 6c in the third light receiving element 5c are all dark, and conversely all the openings of the slits 6c are dark.
Reference numerals a, 6b and 6c determine the linear light receiving surface of each light receiving element.

The light receiving outputs A, B, C of the respective light receiving elements 5a, 5b, 5c are sent to the arithmetic processing circuit 8 via preamplifiers 7a, 7b, 7c including current-voltage conversion.
In the arithmetic processing circuit 8, for each light reception output, A + C−B
Then, the point at which this becomes zero is detected as the inflection point, that is, the edge position of the scale line.

FIG. 3 shows the principle of edge detection in this embodiment in an easy-to-understand manner. As shown in the figure, when the edge 9 of the enlarged image of the scale line of the scale 1 moves, the three light receiving elements 5a, 5 having linear light receiving surfaces arranged along the moving direction.
The outputs A0, B0, C0 of b, 5c change sequentially as shown in the figure. For these outputs, A0 + C0 -2B0
When the left edge 9 is located at the position of the light receiving element 5b, the value becomes exactly zero when the left edge 9 is located, and the edge can be detected. Further, the scale interval is obtained from the edge positions of two adjacent scales. Further, if the left and right edges of the scale are detected, the central position of the scale line can be calculated.

In the configuration of FIG. 1, since the two beam splitters 3 and 4 are used, the first light receiving element 5a
And the intensity of the incident light entering the third light receiving element 5c is 1
/ 4, and the intensity of the incident light entering the second light receiving element 5b is 1
/ 2. Therefore, as described above, the same result can be obtained by the operation of A + CB.

FIG. 4 shows the structure of an edge detecting apparatus according to another embodiment of the present invention. In this embodiment, as shown in FIG. 4A, the scale line edge image of the standard scale 1 is magnified by the objective lens and directly detected by the light receiving element array 10. The light receiving element array 10 is, as shown in FIG.
The three linear light-receiving surfaces 10a, 10b, 10c are arranged in parallel with each other in parallel with the scale line edges of the scale 1. These linear light-receiving surfaces 10a, 10b, 10c are, for example, photodiodes integrally formed on a single semiconductor substrate, and their outputs A, B, C are independently taken out, and similar to the previous embodiment. It is processed. However, the arithmetic processing is A + C-2B according to the principle of FIG.

The present invention is not limited to the above embodiment. For example, in the embodiment shown in FIG. 1, the slits 6a, 6b and 6c are omitted, and the light receiving elements 5a, 5b and 5c are elements having linear light receiving surfaces set by the slits 6a, 6b and 6c, respectively. You can also do it. Further, in the embodiment shown in FIG. 4, the three linear light-receiving surfaces may not be photodiodes each having an output terminal independently, but may be CCDs.

[0020]

As described above, according to the edge detecting apparatus of the present invention, the edge image magnified by the objective lens is received by using the three linear light receiving surfaces arranged in parallel with the edge image and the inflection point is received. By applying the method, the edge of the scale line of the scale can be detected with high accuracy even with relatively low illumination.

[Brief description of drawings]

FIG. 1 shows a configuration of an edge detection device according to an embodiment of the present invention.

FIG. 2 shows an arrangement relationship between a light receiving element and a slit of the same embodiment.

FIG. 3 is a diagram illustrating an edge detection principle of the embodiment.

FIG. 4 shows a configuration of an edge detection device according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Standard scale, 2 ... Objective lens, 3 ... 1st beam splitter, 4 ... 2nd beam splitter, 5a ... 1st
Light receiving element, 5b ... second light receiving element, 5c ... third light receiving element, 6a, 6b, 6c ... slit, 7a, 7b, 7c
... Preamplifier, 8 ... Arithmetic processing circuit, 9 ... Edge, 10 ...
Light receiving element array, 10a, 10b, 10c ... Linear light receiving surface.

Claims (3)

[Claims] 1. An apparatus for optically detecting a scale line edge of a scale in which a plurality of parallel scale lines are formed and arranged, wherein the objective lens enlarges an edge image of the scale line of the scale, and the objective lens. A first beam splitter that half-transmits and half-reflects the edge image enlarged by, a second beam splitter that half-transmits and half-reflects the transmission image of the first beam splitter, and a second beam splitter of the second beam splitter. A first light receiving means having a linear light receiving surface parallel to the scale line edge for detecting a transmission image; and a linear light receiving surface parallel to the scale line edge for detecting a reflected image of the first beam splitter. A second light receiving means; and a third light receiving means having a linear light receiving surface parallel to the scale line edge for detecting a reflected image of the second beam splitter, The first, second and third light receiving means have their linear light receiving surface positions set so that the scale line edge images are sequentially received when the scale is moved in a direction orthogonal to the scale line. An edge detection device characterized in that 2. The first, second and third light receiving means,
The edge detecting device according to claim 1, wherein slits are arranged on the front surface of each light receiving element to set a linear light receiving surface position. 3. An apparatus for optically detecting a scale line edge of a scale in which a plurality of parallel scale lines are formed and arranged, wherein the objective lens enlarges an edge image of the scale line of the scale, and the objective lens. 2. An edge detecting device, comprising: a light-receiving element array in which three linear light-receiving surfaces parallel to the scale line edges are arranged at equal intervals in order to detect the edge image magnified in 1.