JP2015225215A - Optical system and image measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system having coaxial illumination that suppresses doubling of an image and aberrations caused by insertion of a beam splitter in a path of non-parallel light rays.SOLUTION: An optical system includes a light source unit that emits diffusive light rays, a thin film that reflects the diffusive light rays from the light source unit, and a first lens group that irradiates the light reflected by the thin film as parallel light. The optical system may preferably include a filter that is to be located between the light source unit and the thin film to make uniform irradiation by reducing light intensity of a portion of the diffusive light rays emitted by the light source unit relative to light intensity of the remaining portion thereof.

Description

  The present invention relates to an optical system and an image measurement apparatus that include coaxial epi-illumination.

  In recent years, various image measuring apparatuses have been commercialized against the background of development of image processing technology. The work (measuring object) has also been diversified and complicated, and there is a need to measure relatively large and thick mechanical parts, blade tools, electronic parts, and the like with an image measuring apparatus. In order to meet these needs, the object has a wide field of view, a depth of focus that enables measurement of thick and stepped workpieces, and telecentricity (parallelism between the principal ray of the off-axis light beam and the optical axis) is well corrected. As an optical system, for example, a double-sided telecentric objective lens as shown in FIG. 9 has been proposed (see, for example, Patent Document 1 for details).

When building a coaxial incident illumination optical system using such an optical system, the parallel light beam portion between the front group lenses G _F and the lens rear gun G _R (d ₈₎ to insert a beam splitter in the usual is there. However, when the magnification of the optical system is low, flare light is likely to be generated. However, when a beam splitter is inserted into the parallel light beam portion (d ₈ ), the surface reflected light from the lenses L _{1 to} L ₅ is not reflected. It becomes flare and deteriorates the quality of the observed image.

The can best reduce flare is a structure for inserting the beam splitter to the left of the cemented lens G ₁ in FIG. 9, resulting a disadvantage that the working distance in this configuration is shortened.

Therefore, a sufficient distance for inserting the beam splitter BS between the cemented lens G ₁ and the lens group G ₂ (d ₃ ) is secured, and this position (d ₃ ) is set to this position (d ₃ ) to suppress flare. It is conceivable to arrange the beam splitter BS as indicated by a broken line inside. According to such a configuration, the surface reflected light contributing to the flare is only due to the lenses L ₁ and L _2, so that the flare can be reduced while ensuring the working distance.

Japanese Patent No. 3708845

  However, in the configuration in which the beam splitter BS is inserted in such a portion that is not a parallel light beam, the reflection and the thickness on the back surface of the beam splitter BS cause double images and aberrations as shown in FIG. Sometimes.

  An object of the present invention is to provide an optical system provided with a coaxial illumination that can suppress the generation of double images and aberrations by inserting a beam splitter into a non-parallel light beam portion.

(1) The optical system of the present invention includes a light source unit that emits diffused light, a thin film that reflects diffused light from the light source, and a first lens group that irradiates light reflected by the thin film as parallel light. Is provided. With such a configuration, it is possible to prevent generation of a double image due to insertion of a beam splitter in a portion that is not a parallel light flux while preventing flare and ensuring a working distance.

(2) In this invention, it is good to further provide the filter which is distribute | arranged between the light source part and the thin film film, and reduces the light quantity in one part of the light beam of the diffused light which a light source part radiate | emits from the light quantity in another part. (3) The filter may be a diffusion filter that diffuses part of light from the light source, for example. (4) As another example, the filter may be a filter provided with a coating whose optical density continuously changes. (5) The filter may be formed in an oval shape. (6) For example, the filter may be formed in an oval shape. With the configuration including such a filter, it is possible to realize coaxial epi-illumination with less unevenness in illuminance while suppressing flare and ensuring a working distance.

(7) In the present invention, the first lens group may constitute a double-sided telecentric optical system together with other lens groups. In this case, in the double-sided telecentric optical system, the first lens group is closest to the measurement object (workpiece). It is good to use a lens group arranged in With such a configuration, it is possible to introduce coaxial epi-illumination with less unevenness in illuminance into a bilateral telecentric optical system while suppressing flare and ensuring a working distance.

(8) An image measurement apparatus according to the present invention includes any one of the optical systems described above, a stage on which a measurement object is arranged, and an imaging element that captures an image of the measurement object formed by the optical system. With such a configuration, it is possible to provide an image measuring apparatus including coaxial illumination while suppressing flare and ensuring a working distance.

It is a perspective view which shows the structure of the image measuring apparatus 1 incorporating the optical system which concerns on 1st Embodiment. 2 shows a configuration of an optical system 120 and an image sensor 130 included in a housing 110. The structure of the optical system 120 and the image pick-up element 130 which the illumination light from the light source part 122 diffuses is shown. 2 is a block diagram illustrating a configuration of a computer main body 141. FIG. In the structure of the optical system 120 of 1st Embodiment, it is a schematic diagram which shows illumination light quantity distribution in case the reflection characteristic of the thin film film 128 has incident angle dependence. The structure of the optical system 120 which concerns on 2nd Embodiment is shown. An appearance of the light amount adjustment filter 125 is schematically shown. Another example of the light amount adjustment filter 125 is schematically shown. The structure of the conventional both-side telecentric objective lens is shown. It is a typical optical path diagram which shows the principle which a double image produces with beam splitter BS.

[First Embodiment]
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings.

  FIG. 1 is a perspective view showing a configuration of an image measuring apparatus 1 in which an optical system according to the first embodiment is incorporated. The image measurement apparatus 1 includes a stage 100, a housing 110, and a computer system 140.

  The stage 100 is arranged such that the upper surface thereof coincides with a horizontal plane, and a workpiece (measuring object) W is placed on the upper surface. The stage 100 can be moved in the X-axis direction and the Y-axis direction by rotating the handles 101 and 102. The housing 110 includes the optical system 120 and the image sensor 130, and enables the housing 110 itself to move along with the optical system 120 and the image sensor 130 in the Z-axis direction by rotating the handle 112.

FIG. 2 shows a configuration of the optical system 120 and the image sensor 130 included in the housing 110. The optical system 120 irradiates the work W placed on the stage 100 with illumination light and forms an image of the work W on the light receiving surface of the image sensor 130. As shown in FIG. 2, the optical system 120 includes a lens group G with a rear group G _R having a positive refractive index as G _F and the entire front unit having positive refractive index as a whole, the light source unit 122, a thin film Film 128.

Each lens in the lens group G includes a front focal point of the rear focal and the rear group G _R a front group G _F are arranged to coincide. That is, the optical system 120 including the lens group G constitutes a double-sided telecentric optical system.

Front group _{G F} comprises a first group _{G 1} and second group _{G 2} Prefecture. The first group G ₁ is composed of a cemented lens convex L ₁ and a concave lens L _2, having a positive refractive power as a whole. The second group G ₂ is composed of a cemented lens and a concave lens L ₅ Metropolitan convex lens L ₃ and a concave lens L ₄ in the order of distance from the object side, having positive refractive power overall.

The rear group _{G R} consists third group _{G 3} and the fourth group _{G 4} Prefecture. Third group G ₃ is composed of a cemented lens of a concave lens L ₆ and a concave lens L ₇ and a convex lens L _8, with an overall positive refractive power. The fourth group _{G 4} is composed of a cemented lens of a concave lens _{L 9} and a convex lens _{L 10,} with an overall positive refractive power.

  In the optical system 120 of this embodiment, coaxial epi-illumination is introduced into the lens group G as described above by the light source unit 122 and the thin film 128.

  The light source unit 122 may be configured by combining, for example, a light emitting element 123 such as a light emitting diode and a lens 124 for limiting the diffusion direction of diffused light emitted from the light emitting element 123. The diffused light emitted from the light emitting element 123 enters the thin film 128 through the lens 124.

Thin film 128 is disposed between the first group _{G 1} in the front group _{G F} of the second group _{G 2,} and functions as a beam splitter. That is, as shown in FIG. 3, the thin film 128 reflects the light from the light source unit 122 along the optical axis of the lens group G in the direction of the stage 100 on which the workpiece W is disposed. Further, a thin film 128 is transmitted through the light incident through the first group _{G 1} from the stage 100 side, to be incident on the second group _{G 2.} As the thin film 128, for example, a polyester film or the like having appropriate transmittance and reflectance may be used.

  The image sensor 130 is a two-dimensional image sensor such as a CCD or CMOS. An image of the workpiece W is formed on the light receiving surface of the image sensor 130 by the optical system 120. The image sensor 130 captures the image that has been formed and outputs an image signal. The image signal output from the image sensor 130 is taken into the computer system 140.

  Returning to FIG. 1, the computer system 140 includes a computer main body 141, a keyboard 142, a mouse 143, and a display 144. FIG. 4 is a block diagram illustrating a configuration of the computer main body 141. As shown in FIG. 3, the computer main body 141 includes a CPU 40, a storage unit 41, a work memory 42, interfaces (shown as “IF” in FIG. 3) 43, 44, and a display 144, which are the main control elements. And a display control unit 45 for controlling the display of.

  Operator instruction information input from the keyboard 142 or the mouse 143 is input to the CPU 30 via the interface 43. The interface 44 is connected to the optical system 120 and the image sensor 130, supplies various control signals from the CPU 40 to the optical system 120 and the image sensor 130, and receives various status information and measurement results from the optical system 120 and the image sensor 130. Receive and input to CPU 40.

  The display control unit 45 displays an image based on the image signal supplied from the image sensor 130 on the display 144. In addition to the image captured by the image sensor 130, the display control unit 45 displays an interface for inputting a control instruction to the image measurement apparatus 1, a tool interface for analyzing the captured image, and the like on the display 144. To do.

  The work memory 42 provides a work area for various processes of the CPU 40. The storage unit 41 includes, for example, a hard disk drive, a RAM, and the like, and stores a program executed by the CPU 40, image data obtained by imaging by the imaging element 130, and the like.

  The CPU 40 controls the light source unit 122 and the image sensor 130, captures a two-dimensional image by the image sensor 130, and images based on various input information via each interface, an operator instruction, and a program stored in the storage unit 41. Various processes such as analysis of image data obtained in this way are executed.

  With the configuration described above, it is possible to prevent generation of a double image by inserting a beam splitter in a portion that is not a parallel light flux while preventing flare and ensuring a working distance.

[Second Embodiment]
FIG. 5A is a schematic diagram showing that the angle at which the diffused light from the light source unit 122 enters the thin film 128 varies depending on the position. The thin film 128 may have reflection characteristics depending on the incident angle depending on the characteristics of the material. In the present embodiment, it is assumed that a film is used as the thin film 128 in which the intensity of reflected light is increased (the reflectance is higher) as the incident angle is larger. When the thin film 128 has such a reflection characteristic depending on the incident angle, in the configuration of the optical system 120 of the first embodiment, the illumination light of the coaxial epi-illumination irradiated on the workpiece W on the stage 100 is as shown in FIG. As shown in FIG. 5B, the position where the incident angle / reflection angle at the thin film 128 is larger is brighter (in the order of positions C, B, and A in FIG. 5B) and uniform with respect to the workpiece W. Can not get the right illumination. As a result, spots (unevenness) appear in the brightness of the image of the workpiece W photographed by the image measuring device 1.

  The optical system according to the second embodiment of the present invention is characterized in that the light amount adjustment filter 125 is provided in the light source unit in order to solve the problem caused by the uneven intensity of the illumination light. Other than that, the optical system is the same as that of the first embodiment. For example, the optical system is incorporated into the image measurement apparatus 1 described in the first embodiment. In order to avoid redundant description, description of common parts with the first embodiment is omitted here.

FIGS. 6 (a) shows the optical system 120 according to the second embodiment, the light source unit 122, a thin film 128, and the first group _{G 1} configuration of the lens group G. The light amount adjustment filter 125 is disposed in the optical path from the light emitting element 123 to the thin film 128. In the present embodiment, the light amount adjustment filter 125 is disposed between the light emitting element 123 and the lens 124. The light amount adjustment filter 125 causes a difference in light amount according to the position of the light beam in the optical path from the light emitting element 123 to the thin film film 128. The light from the light source unit 122 is reflected by the thin film 128 and applied to the workpiece W on the stage 100.

  FIG. 7 is a schematic diagram showing the appearance of the light amount adjustment filter 125. The light quantity adjustment filter 125 of the present embodiment is constituted by a diffusion film having a circular shape (that is, a shape obtained by cutting a circle by a straight line connecting two points on an arc). For example, the light amount adjustment filter 125 is formed in a semicircular shape as shown in FIG. The light amount adjustment filter 125 of the present embodiment is inserted into a region in the light beam where the incident angle to the thin film 128 is larger than the angle formed by the optical axis direction and the thin film 128, and passes through the region (that is, FIG. 6 (a), the light quantity of the left half of the light emitted from the light emitting element 123 is based on the light quantity of the light in other regions (that is, the right half of the light emitted from the light emitting element 123 in FIG. 6 (a)). Also reduce.

  By providing the light quantity adjustment filter 125 as described above, the illumination light incident on the thin film film 128 has a relatively small amount of light in a portion where the incident angle is relatively large compared to other portions. On the other hand, the thin film 128 has a reflection characteristic in which the intensity of the reflected light increases as the incident angle increases, so that the difference in incident light is canceled by the reflection characteristic. Thereby, as shown in FIG.6 (b), the illumination light intensity irradiated to the workpiece | work W on the stage 100 can be made substantially uniform. As described above, in the optical system according to the second embodiment of the present invention, it is possible to construct an image system with less unevenness in illuminance even in the coaxial illumination after suppressing flare and ensuring a working distance.

[Modification of Embodiment]
It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the second embodiment, the case where a diffusion film is used as the light amount adjustment filter 125 has been described as an example. Instead, a diffusion plate or a filter with a coating whose optical density continuously changes is used. May be. For example, as shown in FIG. 8, as a filter having a continuously changing coating, the coating is applied so that the optical density increases as the distance from the semicircular chord (straight line portion) in the semicircular transparent glass substrate increases. It is recommended to use the filter. In addition, in the second embodiment described above, the case where the shape of the light amount adjustment filter 125 is semicircular has been described as an example. However, the shape of the light amount adjustment filter 125 is not limited to a non-circular shape or a semicircular shape. It may be a rectangle or the like.

  As described above, the optical system according to the present invention can be suitably used for an image measuring device, but can also be applied to other optical devices using coaxial epi-illumination.

DESCRIPTION OF SYMBOLS 1 Image measuring apparatus 100 Stage 110 Case 120 Optical system 122 Light source part 125 Light quantity adjustment filter 128 Thin film 130 Image pick-up element 140 Computer system G Lens group W Workpiece (measuring object)

Claims (8)

A light source that emits diffused light;
A thin film that reflects diffused light from the light source, and
An optical system comprising: a first lens group that irradiates light reflected by the thin film as parallel light.   2. The filter according to claim 1, further comprising a filter that is disposed between the light source unit and the thin film film and reduces a light amount in a part of a luminous flux of diffused light emitted from the light source unit as compared with a light amount in another part. The optical system described in 1.   The optical system according to claim 2, wherein the filter is a diffusion filter that diffuses a part of light from the light source.   The optical system according to claim 2, wherein the filter is a filter provided with a coating whose optical density continuously changes.   The optical system according to any one of claims 2 to 4, wherein the filter is formed in an oval shape.   The optical system according to claim 5, wherein the filter is formed in a semicircular shape. The first lens group constitutes a both-side telecentric optical system together with other lens groups,
7. The optical system according to claim 1, wherein in the double-sided telecentric optical system, the first lens group is a lens group disposed at a position closest to an object to be measured. The optical system according to any one of claims 1 to 7,
A stage for placing an object to be measured;
An image measurement apparatus comprising: an image pickup device that picks up an image of the measurement object formed by the optical system.

Images