JP2008170407A - Scale reading system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove a parallax when reading both scales, in calipers or the like using a scale reading method using overlapping of a main scale and a vernier scale. <P>SOLUTION: The present invention discloses constitution for removing the parallax when reading the scales, in a scale reading system of detection-reading the other scale positioned in the center of a scale clearance in one side of the respective scales by overlapping the main scale and the vernier scale. The problem to be solved is solved by contact-sliding a vernier scale plate with the vernier scale engraved as a slit, with respect to a main scale face. The parallax when reading the both scales is removed to allow precise, quick and sure reading. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method in which the reading accuracy of a scale reading method using a vernier used in a vernier caliper is increased. Specifically, a conventional vernier caliper or the like is a method in which the main scale and the sub-scale are made to face each other and the coincidence position is read. On the other hand, the present invention relates to an improvement of a scale reading method using a moire fringe generated by superimposing a main scale and a sub scale, with the scale width and the scale gap width being substantially equal.

  2. Description of the Related Art Conventionally, in a semiconductor device manufacturing process, as a method for detecting an overlay deviation amount of a composite pattern formed on a substrate by lithography, a moire formed by superimposing a main scale pattern and a vernier pattern formed on the substrate. A method for detecting the amount of misalignment from the density of stripes is known (Patent Document 1). The present invention relates to a configuration for applying this known method to calipers and the like.

  In the method using the moire fringes, the coincidence position between the main scale and the minor scale is the position of the minor scale at the center position of the main scale gap. The scale is located at the densest part of the moire fringes. Furthermore, it is known that the minimum read value can be halved compared to a normal case by detecting and reading the main scale at the center position of the vernier scale gap (Patent Document 1).

  In the scale reading method using a vernier, the minimum reading value is the main metric unit by using a vernier obtained by dividing n by the length of (n-1) main metric unit, where n is an integer of 2 or more. A 1 / n reading system can be realized. If the minimum reading value can be halved while keeping the value of n as it is, reading with high accuracy can be performed with a short vernier scale. The scale reading method using the vernier scale enables high-precision reading because the movement of the coincidence position between the main scale and the vernier scale is expanded to n times the movement of the vernier itself by the moire principle. I would like to point out that it is derived from this.

Further, by increasing the identification sensitivity when detecting the coincidence position between the main scale and the minor scale, it is possible to reduce the probability of misreading and perform reliable reading. If the identification sensitivity is high, reliable reading is possible even if sufficient illumination is not obtained during reading operation. Depending on the purpose of use, reliable reading is possible even from a position away from the clear vision distance. Furthermore, when detecting the coincidence position between the main scale and the sub-scale, if the coincidence position can be easily narrowed down, reading can be speeded up.
Patent application publication number JP-A-7-120221

  The present invention solves a problem in applying a scale reading method using a vernier having the above-described features to calipers and the like. In order to realize a caliper with high reading accuracy, the product is required to have high processing accuracy and high stability. Furthermore, when the above reading method is applied, the parallax generated when the main scale and the vernier scale are superimposed directly affects the accuracy, so that it is an important issue to remove them. Here, a vernier method is provided in which the main scale surface and the vernier scale surface are slid in contact with each other.

  1 and 2 are explanatory views of the principle of the scale reading method applied to the present invention. The scale width and the scale gap width are almost equal for both the main scale and the sub-scale, and the scale is indicated by a black line. In the drawing, the main scale is shown on the upper side, and the sub-scale is shown on the lower side, and these are arranged so that parts of them overlap each other at the center. The main scale and the sub-scale are overlapped, and it is shown that a striped pattern due to average shading or moire fringes generated by black lines having different widths.

  The main scale gaps are numbered 0, 1, 2,..., 20 and 20 from the left, indicating the first part of the main scale. In addition, the 21 scales of the vernier are also numbered with 0, 2, 4,. Here, 19 units of the main scale unit (the length obtained by adding the main scale graduation width and the main scale graduation gap width) are 20 vernier units (the length obtained by adding the sub-scale graduation width and the minor scale graduation gap width). It corresponds to the unit. That is, an example of a vernier whose minimum reading value is 1/20 of the main scale unit is shown. This can be confirmed on the diagram as follows. That is, the distance from the right end of the main scale gap 0 to the right end of the main scale gap 19 is equal to the distance from the left end of the sub scale 0 to the left end of the sub scale 40.

  It should be noted that the main scale is numbered not on the main scale but on the main scale gap. This means that the main scale gap serves as a main scale in the conventional method. Therefore, the coincidence position of the main scale and the minor scale is the position where the center line of the minor scale and the center line of the main scale gap coincide, and it is sandwiched between adjacent major scales. It is located in the center. In other words, gaps of equal width are formed on both sides of the sandwiched vernier scale. This is the same as the condition of the graduation method for aligning the target graduation at the center of the two graduations, and the determination of the center position of the graduations can be performed with high sensitivity. Further, the vernier scale with a gap of equal width on both sides is limited to this vernier scale. Further, the vernier scale indicating the coincidence position is located at the center of the moire fringe dark portion, and the coincidence position can be easily narrowed down. Therefore, the coincidence position can be read quickly and reliably.

  This situation is shown in FIG. In the figure, a vernier scale 20 is sandwiched between two main scales. FIG. 1 shows that the vernier scale is in the 0 position (the position where the main scale gap 0 and the vernier scale 0 coincide with each other, so that the vernier scale 0 coincides with the scale between the main scale graduations 0 and 1. ) To the right half of the main scale unit. The movement distance can be obtained as 20/40 using the maximum value 40 of the vernier scale and 20 of the coincidence scale.

  Next, in contrast to the above, consider a case where the main scale graduation and the minor scale graduation coincide. FIG. 2 shows a state in which the main scale between the main scale gaps 10 and 11 is sandwiched between the minor scales 20 and 22. This is realized by further moving the vernier from the state of FIG. 1 to the right of 1/40 of the main scale unit. 1 indicates half ½ of the main scale unit, and arrow 2 of FIG. 2 indicates half ½-1 / 40 of the vernier unit. The difference 1/40 is shown in FIG. It becomes the movement distance to the state of 2. The movement distance from the 0 position of the vernier can be obtained as 21/40 using a value 21 (not shown) between the vernier scales 20 and 22. As in the case of FIG. 1, a gap having the same width is formed on both sides of the sandwiched scale, and the position is located at the center of the moire fringe dark portion. Can be read. In this way, a minimum read value of 1/40 can be realized by using a vernier whose minimum read value is 1/20.

  Next, in order for the effect of the present invention to appear, the conditions that the scale width and the scale gap width of the main scale and the sub scale must be satisfied are obtained. FIG. 3 is an explanatory diagram showing the main scale unit as a rectangular wave. A portion having a height represents a scale, and a portion having no height represents a gap. The horizontal arrow 3 represents the major scale width, and 4 represents the major scale gap width. If the former value is a, the latter value is 1-a, and the sum is 1 in main scale units and is indicated by an arrow 5. FIG. 4 is an explanatory diagram showing a vernier unit of a vernier whose minimum reading value is 1 / n, in the same manner as FIG. Assuming that the vernier scale width (indicated by arrow 6) is the same as that of the main scale, the vernier gap width (indicated by arrow 7) is (1-a) -1 / n, which is the unit of the vernier (indicated by arrow 8). ) Is a total of 1-1 / n thereof.

  The condition for creating a gap at both ends of the sandwiched scale is that the minor scale gap is smaller than the major scale gap, so the case where the major scale is sandwiched between two adjacent minor scales may be considered. . That is, the width a of the main scale should be smaller than the vernier gap width (1-a) -1 / n. From this condition, the formula a <1 / 2-1 / 2n giving the upper limit of a is obtained. Further, from the condition that the sum of the gaps on both sides is suppressed to b% or less of the vernier gap width, an expression (1-1 / n) (100−b) / (200−b) <a that gives the lower limit of a is obtained. . In the above description, it is assumed that the major scale width and the minor scale width are equal, but it is clear that the same result can be obtained even in a general case where they are not equal.

  Next, a configuration method for applying the principle of the scale reading method described above by superimposing the main scale and the subscale to the caliper will be considered. To superimpose the main scale and the minor scale, either the main scale or the minor scale is engraved on the transparent scale plate, and the scale surfaces are overlapped and visually observed from the transparent scale plate side. A method of optically superimposing both graduations using a beam splitter such as a translucent mirror is conceivable. Here, by overlaying the main scale scale surface on the surface of the main scale scale, the main scale scale and the sub-scale scale that can be seen through the slit are overlapped. Consider a method without parallax.

  FIG. 5 is an explanatory diagram of the scale reading system based on the present invention. A scale such as 9 indicates a main scale scale inscribed on the main scale, and a gap such as 10 indicates a main scale scale gap. The main scale graduations are numbered 0, 1, 2,..., And number 0 corresponds to the origin. 11 is a vernier scale plate in which slits such as 13 are formed in an opaque plate, and slides in contact with the left and right on the main scale. A slit gap such as 12 corresponds to a vernier scale, and is assigned with even numbers of 0, 2, 4,..., And 0 corresponds to the origin. A slit such as 13 corresponds to a vernier scale gap. This figure shows a state where the origins of the main scale and the vernier coincide. A minor scale 0 is sandwiched between the main scales 0.

  FIG. 6 shows a state in which the vernier scale plate is moved to the right by 1 / 2n unit from the state of FIG. The main scale between the main scale gaps 0 and 1 is sandwiched between the center of the minor scales 0 and 2.

  FIG. 7 shows a state where the vernier scale plate has moved to the right by 2 / 2n units from the state of FIG. The minor scale 2 is sandwiched between the center of the main scale 1

  As described above in detail, in the scale reading method using the vernier scale, the scale width of the main scale and the vernier scale and the scale gap width are substantially equal, and the coincidence position can be read by overlapping both scales. The coincidence position between the main scale and the minor scale is a position where the minor scale is sandwiched between the centers of the adjacent major scales. Moreover, the minimum reading value can be halved as compared with the conventional method by adding a position where the main scale is sandwiched between the centers of the adjacent minor scales as the matching position.

  At this time, the recognition sensitivity at the time of reading the coincidence position is increased, for example, a gap having an equal width is formed on both sides of the sandwiched scale. Further, since the coincidence position is located at the center of the dark portion of the moire fringes generated by the superposition of the main scale and the sub-scale, the coincidence position can be easily narrowed down. For the reasons described above, a vernier caliper to which this method is applied enables quick and reliable scale reading with high accuracy.

  The caliper using the scale reading method according to the present invention has features such that the vernier scale plate can be made of a metal and can have a robust structure, and the vernier scale plate and the slider can be integrated. The scale reading method according to the present invention can be applied not only to the long vernier method widely used in calipers in recent years, but also to the reading of the rotational position of a micrometer or the like.

  By applying the scale reading method by superimposing the main scale and the sub-scale scale to calipers, etc., the scale can be read quickly and reliably, and at the same time, high-precision calipers with a minimum reading value halved compared to the conventional method. It can be realized.

  Read from the overlap of the main scale and the vernier scale that can be seen through the slit by attaching a vernier scale plate with the vernier scale as a slit to the slider window and sliding the vernier scale plate in contact with the main scale surface. Calipers to do.

  In a scale reading method using a main scale unit of 1 mm and a scale which is divided into 50 equal parts of 49 mm, the main scale and the minor scale width are 0.48 mm, the main scale gap width is 0.52 mm, and the minor scale gap width is 0. By setting the thickness to 5 mm, a caliper with a minimum reading value of 1/100 can be realized.

Explanatory drawing of the principle of the scale reading method applied to the present invention Explanatory drawing of the principle of the scale reading method applied to the present invention Explanatory drawing which shows the main scale unit applied to the present invention as a rectangular wave Explanatory drawing which shows a vernier scale unit applied to the present invention by a rectangular wave Explanatory drawing of the scale reading system of the present invention (when the zero point of the main and vernier coincides) Explanatory drawing of the scale reading system of the present invention (when the vernier moves to the right of the main scale by 1 / 2n unit) Explanatory drawing of the scale reading system of the present invention (when the vernier moves to the right by 2 / 2n units with respect to the main scale)

Explanation of symbols

1 Half width of main scale unit: 1/2
2 Half width of vernier unit: 1 / 2-1 / 40
3 Main scale width: a
4 Main scale graduation gap width: 1-a
5 Main scale unit: 1
6 Major scale width: a
7 Minor scale gap width: (1-a) -1 / n
8 Vernier scale unit: 1-1 / n
9 Main scale 10 Main scale graduation 11 Sub-scale scale 12 Sub-scale scale slit slit (equivalent to minor scale)
13 Sub-scale plate slit (equivalent to the sub-scale scale gap)

Claims (1)

  Graduation reading characterized in that the graduation gap of the minor graduation plate that contacts and slides on the main graduation scale surface is a slit, and the other graduation at the center position of one graduation gap of each of the graduations is detected and read. method.

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