JP2012042254A - Method for inspecting lens defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a defect inspection method utilizing an illumination transition region capable of visualizing a defect at high sensitivity and utilizing the illumination transition region for the whole surface of a lens.SOLUTION: A lens to be inspected is transparently illuminated by pattern illumination composed of a bright part and a dark part. An imaging means is arranged on the opposite side of an illumination about the lens to be inspected, and the lens to be inspected is focused. A projected pattern shape is symmetrical about a lens power center axis or a power center face and is composed of at least one bright part and one dark part. A plurality of different patterns are projected to the lens to be inspected while maintaining symmetry about the center axis or the center face to form an illumination transition region on the whole surface of the lens, and images are acquired for each of the plurality of projected patterns.

Description

  The present invention relates to a lens defect inspection method, and more particularly to an inspection method using transmitted illumination using pattern illumination.

  For defects such as scratches, cracks, and foreign matter adhering in the lens manufacturing process, an automatic inspection device using a sensing means such as a camera has been devised. There exists what was described in patent document 1 as such an inspection apparatus.

  According to the technique of Patent Document 1, the target lens is illuminated by the diffusion plate that diffuses the illumination light, and the target lens is rotated around the optical axis. The target lens is imaged by the line sensor, and at that time, the entire width of the target lens on the licensor is hidden with a strip-shaped light shielding member on the diffusion plate so that the diffuse illumination light does not directly enter the line sensor. Is arranged. By adopting such a prior art arrangement, a so-called dark field illumination state is realized, and when the illumination light is scattered at the defect portion, the image is photographed brighter than the background, and the lens is rotated around the entire circumference of the lens. Images can be acquired.

  In addition, there are methods described in Patent Document 2 and Patent Document 3 as inspection methods using pattern illumination.

  According to the technique of Patent Document 2, a diffuser plate that diffuses illumination light is provided with a portion that is mainly transparent in a stripe shape and a portion that is not transparent, and the diffused light from this diffuser plate is inspected. Irradiate the subject. The phase of the pattern light is changed by changing the position of the diffusion plate, and an image is acquired with a camera or the like each time. Here, if there is a defect in the bright part and dark part of the pattern, it is detected dark in the bright part and bright in the dark part. This signal is acquired using a camera or the like to perform defect inspection.

  According to the technique of Patent Document 3, a diffused light source is formed using a plurality of LED arrays, and striped pattern illumination is formed by lighting / non-lighting of each array. These LED arrays can be rotated for each block, and the angle is changed according to the shape of the object to be inspected. The illumination projected in this way is composed of a bright part and a dark part and its transition area on the surface to be inspected, and the defect signal from the bright part and the dark part and its transition area is detected by scanning this pattern, respectively. The defect determination is performed with high accuracy by comparing the signal intensities at the positions.

Japanese Patent Laid-Open No. 10-246706 JP 2000-18932 A JP-A-11-281582

However, the above-described prior art has the following problems.
That is, in Patent Document 1 relating to lens inspection, auxiliary illumination is required when the defect has a dependency on the illumination incident angle. Further, in order to inspect the entire lens area, it is necessary to rotate the inspected lens. These lead to complication of the apparatus configuration.

  Further, in Patent Documents 2 and 3 as inspection methods using pattern illumination, when a defect has an illumination incident angle dependency, the defect is likely to be overlooked. In addition, when a stripe pattern is applied to the lens inspection, it is difficult to maintain the same illumination state over the entire lens surface.

In particular, in Patent Document 3, although the illumination transition region is used, the detection sensitivity is not sufficient with respect to a defect having an illumination incident angle dependency, and there is a fear of overlooking.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lens defect inspection method capable of inspecting the entire lens surface using an illumination transition region with high defect detection sensitivity and maintaining detection sensitivity even for a defect depending on the illumination incident angle. There is.

In the lens inspection method,
Irradiating the lens to be inspected with light, and detecting the generated light with an imaging means;
Inspecting the lens based on the detected image;
Have
A lens inspection method, wherein the pattern light is concentric, and the lens is inspected only from an image corresponding to an illumination transition region formed in the vicinity of a boundary between a bright part and a dark part of the irradiated pattern light.

  In order to effectively use the illumination transition area with high detection sensitivity, it is possible to detect defects that depend on the incident angle of illumination such as scratches on the surface of the inspected lens, which were often overlooked by conventional inspection methods. Sensitivity can be maintained.

Overall configuration diagram of the present invention The figure which shows the projection pattern and phase shift of this invention The schematic diagram which shows the illumination incident angle by the pattern illumination of this invention Overall configuration diagram using a reflective diffuser with pattern illumination of the present invention The figure which shows the projection pattern of a fixed period in the projection pattern of this invention The figure which shows the pattern at the time of targeting a cylindrical lens in this invention Diagram showing scattered light intensity distribution from defects The figure which shows the background signal and the defect signal when the pattern interval is wide The figure which shows the background signal and the defect signal when the pattern interval is appropriate

Example 1
FIG. 1 shows the overall configuration of a defect inspection apparatus according to the present invention.
In this embodiment, the inspected lens 103 is described as a general circular lens.
Illumination light emitted from the pattern projection light source 101 is diffused by the transmission type diffusion plate 102 and irradiated onto the lens 103 to be inspected. Thus, in a state where the illumination light is incident on the lens 103 to be inspected, the imaging lens of the imaging means 104 is focused on the lens 103 to be inspected, and an image of the lens to be inspected in a state where the illumination light of pattern illumination is irradiated. Can be obtained. The pattern projection light source 101 is constituted by a liquid crystal projector so that the pattern shape can be changed sequentially.

  In such a configuration, the pattern to be projected is a concentric pattern as an axis object with respect to the power center axis (or optical axis) of the lens to be inspected as shown in FIG. This pattern is formed by changing the period in the orthogonal direction from the central axis, and the illumination incident angle with respect to the principal ray of the imaging lens that has passed through the lens to be inspected in the dark portion is “0 ° <incident angle ≦ 4 °”. It is comprised so that the component which becomes may be included.

  As shown in FIG. 7, with respect to defects that exhibit light scattering properties, the scattered light intensity is generally the strongest in the light incident direction. That is, the signal intensity from the defect becomes stronger as the illumination incident angle 705 on the defect is smaller. In other words, it is important for the projected concentric pattern to appropriately set the illumination incident angle 705 to the defect.

  Therefore, the projection pattern is considered with reference to the principal ray of the imaging lens (broken line in the figure). The chief ray is a ray that comes out of an object point and passes through the aperture center of the lens system.

  In the following description, the description will be made in the reverse ray tracing state for convenience. The incident direction of the illumination light with respect to the lens 103 to be inspected is an angle formed with the principal ray.

  FIG. 3 is a schematic view showing an illumination incident angle by the pattern illumination of the present invention. In the figure, a part of a concentric light and dark pattern projected on the diffusion plate is cut out and drawn.

  The principal ray emitted from the point P on the imaging lens image plane 305 that is the light receiving surface of the imaging element in the imaging unit 104 of FIG. 3 is directed to the object plane P ′ on the lens 103 to be inspected that is conjugate to the imaging lens 302. It will be incident.

  Then, the principal ray incident on the lens 103 to be inspected is connected to the transmissive diffusion plate 102 at an emission angle corresponding to the power of the lens 103 to be inspected. Of course, this principal ray represents a certain virtual light path, and does not represent an actual light traveling path. Here, for the sake of explanation, a case will be described in which a defect exists at the position P ′ on the lens 103 to be inspected. It can be seen that the direction of the illumination incident angle of 0 ° at which the signal intensity from the defect is maximized is the direction from the point P ″ to the point P ′ (the direction of the principal ray).

  Next, a concentric pattern to be projected is determined based on this point P ″. As described above, the signal intensity from the defect increases as the illumination incident angle decreases. Therefore, considering that the position P ′ on the inspected lens 103 is inspected, in order to maximize the signal intensity from the defect, the pattern projected at the point P ″ on the diffusion plate 102 is a bright part. There must be. However, when the point P ″ is a bright portion, the signal intensity from the defect is maximized, but at the same time, the signal intensity of the background signal other than the defect is also maximized. In such a case, since the defect signal is extremely small compared to the background signal, it is impossible to separate the background signal and the defect signal, which is not suitable for inspection. Therefore, an optimum angle as the illumination incident angle 304 will be described.

  FIG. 8 and FIG. 9 are schematic diagrams comparing the case where the illumination incident angle is large and the optimum case, respectively. However, although a concentric pattern is originally used in this embodiment, FIG. 8 and FIG. 9 are described in a striped pattern in which a part thereof is cut out for simplification of description.

  FIG. 8 is a schematic diagram corresponding to a case where the pitch of the light / dark pattern is increased, that is, the illumination incident angle 304 in FIG. 3 includes 0 ° or is larger than 4 °. A bright pattern portion 107 and a dark pattern portion 108 are formed on the transmissive diffusion plate 102. In addition, a background signal 801 corresponding to a bright pattern area and a dark area exists on the imaging lens image plane, and a defect signal intensity 802 at the image plane position is shown. Since the background signal is large at the position on the image plane corresponding to the bright pattern portion, the defect signal cannot be confirmed. On the other hand, in the illumination transition region 803 formed near the boundary between the bright part and the dark part, the defect signal becomes strong because the illumination incident angle is small. When the illumination transition region 803 further moves to the dark pattern side, the illumination incident angle increases, and the defect signal becomes weak. For this reason, when the illumination incident angle 304 of FIG. 3 is set large, an area having a weak defect detection capability is also included in the inspection area.

  On the other hand, FIG. 9 is a schematic view corresponding to the case where the pitch of the light / dark pattern is appropriately determined and the illumination incident angle 304 in FIG. 3 is appropriately given. In the case of this embodiment, the illumination incident angle 304 is set to be 2 ° with respect to the position P ′ on the lens to be inspected, and relative to the point on the lens to be inspected corresponding to the dark part on the image plane. In this case, the incident angle is set to “0 ° <incident angle ≦ 4 °”. With such a configuration, the inspection can be performed in the illumination transition region 803 having a high defect detection capability in which the defect signal becomes strong on the imaging lens image plane 305.

  Thus, the pattern projected in the present embodiment is axially symmetric with respect to the power central axis of the lens 103 to be inspected, and the period changes from the central axis to the diameter direction so that the illumination incident angle 304 satisfies the above-described conditions. I am letting. By setting it as such a structure and pattern shape, the ratio of the illumination transition area | region in the lens whole surface can be maximized.

Next, the inspection method in the present embodiment will be described.
In the above-described configuration, when inspecting the defect of the lens to be inspected, the illumination transition region is changed with respect to the surface of the lens to be inspected by changing the phase of the concentric pattern light in order to generate the illumination transition region over the entire surface of the lens. To scan. In this embodiment, imaging is performed so that the phase change is 0 to 2π so as to be divided into three. However, any number of divisions may be used as long as the illumination incident angle to the illumination transition region described above can be satisfied. Alternatively, the pattern may be scanned and scanned.

  FIGS. 2A to 2C show a state in which the concentric pattern is step-scanned with respect to the diffusion plate. First, a concentric pattern as shown in FIG. 2A is projected onto the diffusion plate using the pattern control device 106 and the pattern projection light source 101. FIG. 2B shows the period of this pattern. An image in this state is acquired by the imaging unit 104 and held in the processing device 105. Next, the pattern control device 106 changes the phase of the above-mentioned concentric pattern as shown in FIG. 2C, and similarly acquires and holds an image. Further, the pattern control device changes the phase of the concentric pattern as shown in FIG. 2D, and similarly acquires and holds an image. In the case of the concentric pattern depicted in FIG. 2, an illumination transition area is projected on the surface of the lens to be inspected, corresponding to the area between “bright” and “bright”. The illumination transition area is acquired by the imaging means by using a series of images obtained in this way, and only the illumination transition area is cut out by image processing or a representative value of each pixel is calculated to obtain an inspection image over the entire lens surface. can do.

  In the image acquired in this way, if there is a defect on the lens, the illumination light is scattered by the defect, so the defective part has a pixel value different from the background on the image, so detecting this will detect the defect. Can be performed. As described above, unlike conventional defect inspection methods, defects are inspected using only the illumination transition region with high detection sensitivity, so defects that depend on the illumination incident angle such as scratches on the surface of the object to be inspected, etc. In contrast, detection sensitivity can be maintained.

  In the above embodiment, a liquid crystal projector is shown as the pattern projection light source 101. However, the present invention is not particularly limited to the above-described configuration as long as a bright and dark pattern can be formed. For this reason, a mask projection light source for projecting a mask or the like in which a transmissive / opaque portion is arranged may be used, and a configuration in which these masks are replaced in accordance with a phase shift may be used.

  From the above, detection sensitivity to scratches and cracks by scanning the surface of the lens to be inspected in the illumination transition area, such as scratches and cracks that occurred on the lens surface, which was often overlooked by conventional defect inspection methods A defect inspection can be performed based on an image obtained by imaging a high illumination transition region.

  Furthermore, detection sensitivity can be further improved by performing image processing on the captured image of the lens to be inspected and performing defect inspection based on image data obtained by cutting out an image corresponding to the illumination transition region.

(Example 2)
As a second embodiment of the present invention, as shown in FIG. 4, reflected light is used instead of transmitted light from a diffuser.

  By adopting such a configuration, a reduction in illumination efficiency due to absorption generated in the transmission type diffusion plate does not occur, and the use efficiency of illumination can be improved.

(Example 3)
A third embodiment of the present invention will be described in which a pattern projected as shown in FIG. 5 uses a concentric pattern having a fixed period in a direction orthogonal to the lens power central axis of the lens to be inspected.

  Such a concentric pattern having a constant period can be calculated using a simple paraxial ray theory, and therefore, parameter setting is facilitated in a variety of lens inspection.

  Such a concentric pattern can be suitably applied to inspection of a cylindrical lens as a lens to be inspected. The apparatus configuration is the same as in the first embodiment. Also for the cylindrical lens 602 as shown in FIGS. 6A and 6B, the diffused light from the concentric pattern illumination FIG. 6C as a target is transmitted through the power center plane 601.

  With such a configuration, it is possible to detect a strong defect signal from the illumination transition region for the cylindrical lens as well as the circular lens described above. As described above, when a concentric pattern is appropriately set in accordance with the shape of the lens to be inspected and defect inspection is performed, a more sensitive and simple lens inspection can be realized.

  It can be suitably applied to an automatic inspection process of optical elements such as a circular lens and a cylindrical lens.

DESCRIPTION OF SYMBOLS 101 Pattern projection light source 102 Transmission type diffuser plate 103 Lens to be inspected 104 Image pickup means 105 Processing device 106 Pattern control device 107 Pattern bright part 108 Pattern dark part 301 Imaging lens principal ray 302 Imaging lens 303 Imaging lens main plane 304 Illumination incident angle 305 Lens image surface 601 Cylindrical lens power center 602 Cylindrical lens 701 Work 702 Illumination incident direction 703 Defect 704 Scattered light intensity distribution 705 Illumination incident angle 801 Background signal 802 Defect signal 803 Illumination transition region

Claims (6)

In the lens inspection method,
Irradiating the lens to be inspected with light, and detecting the generated light with an imaging means;
Inspecting the lens based on the detected image;
Have
The pattern light is concentric, scans an illumination transition area formed in the vicinity of a boundary between a bright part and a dark part of the irradiated pattern light, and inspects a lens from an image corresponding to the illumination transition area. Lens inspection method.   2. The lens inspection method according to claim 1, wherein the pattern light is composed of concentric bright portions and dark portions having a constant period in a direction orthogonal to a lens power central axis or a power central plane.   3. The lens inspection method according to claim 1, wherein the pattern light is projected onto a diffusion plate, and reflected light from the diffusion plate is irradiated onto a lens to be inspected.   2. The lens inspection method according to claim 1, wherein a period of a pattern of a bright part and a dark part is configured so that the pattern light irradiated to the lens to be inspected includes only a bright part and an illumination transition region.   2. The lens according to claim 1, wherein the inspected lens is imaged by scanning the illumination transition region over the entire lens surface by changing the phases of the concentric bright part and dark part, and the inspection is performed based on the acquired image. Inspection method.   The said pattern is comprised so that the illumination incident angle with respect to the chief ray of the imaging lens in the said imaging means may be included so that it may be 0 degree <incidence angle <= 4 degree. The lens inspection method described in 1.

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