DE102008063118B4 - Improved device with a field mirror for optical inspection of a surface - Google Patents

Abstract

Device for optically testing an examination region (3) of a specular or diffusely reflecting surface (2) of an object (1),
With a field mirror (4), which reflects a light bundle standing vertically on the surface (2) with a light bundle axis (5) into a light bundle with a light bundle axis (5 ') at a reflection angle α (9) and its projection surface on the one to be examined Surface (2) covers the examination area (3) at least straight,
With at least one light source (21) arranged on the optical axis (7) of the illumination beam path in the region of the focal plane (20) of the field mirror (4) for bright field illumination, which is imaged onto the examination region (3) by means of a telecentric beam path;
• with at least one light source (22, 22 ') arranged outside the optical axis (7) of the illumination beam path in the region of the focal plane (20) of the field mirror (4) for near-field dark field illumination,
With an electronic camera (11) with objective whose entrance pupil (13) in the focal plane (10) of the field mirror (4) on the camera-side optical ...

Description

The The invention relates to a device for optically testing a Surface.

From the German patent application DE 10 2007 022 831 A1 The applicant is a device for optically testing a surface with a telecentric beam path for illumination and image recording with a field mirror is known in which between the axis of the object-side beam and the axis of the field mirror reflected beam is an angle of about 90 ° is included. In such an imaging geometry, and in particular when using a field focus with a short focal length, an aspherically corrected field mirror is to be provided in order to reduce aberrations to an extent that is acceptable for the test task.

From the US Pat. No. 4,547,073 A is in 7 discloses a device for optically examining an object surface with a concave mirror arrangement which has different beam paths for illumination and image recording, wherein the reflection angles of the beam axes at the concave mirror have a significantly greater angle than 90 °; in the example of 7 the angle is about 120 °.

task The invention is one of a few, standard available optical Components existing, compact and inexpensive to manufacture device for optical testing a substantially rectangular region of a diffusely reflecting or reflective surface with a telecentric beam path for light of different wavelengths to create in particular in the direction perpendicular to the device examining surface one possible low altitude should have. In particular, should under the optical testing both Qualitative recognition of surface structures and / or defects as well as the recognition of characters and / or encodings understood become.

The The object of the invention is an arrangement with a for lighting and image acquisition identical telecentric beam path with a Field mirror solved, the focal length for limiting the opening angle of the beam at least 2 times the maximum extent of the examination area is. The reflection angle at the field mirror will limit the aberrations greater than 120 ° selected.

Around when using a long-range field mirror a compact To achieve arrangement of the individual components, the beam path between the field mirror and the camera or the lighting device reflected at least one plane mirror and a semi-transparent mirror into the entrance pupil of the lens of an electronic camera whereby, to illuminate the surface, a brightfield or a dark field illumination arrangement is used and the Light sources in the focal plane of the field mirror in the field of optical Axis of the field mirror (bright field illumination) or at a short distance from the optical axis of the field mirror (near-axis dark field illumination) are arranged.

The The invention will be explained in more detail with reference to the figures.

In 1 is the beam path according to the invention in a view perpendicular to the optical axis of the camera ( 8th ) and the light beam axis ( 5 ) shown schematically. The field mirror shown in section ( 4 ) points in the direction of the projection on the surface ( 2 ) of the object to be examined ( 1 ) vertical light bundle axis ( 5 ) has a cross-section, the outer contour of the examination area ( 3 ) of the surface ( 2 ) of the object to be examined ( 1 ). A peculiarity of a telecentric beam path is that the field mirror ( 4 ) on the side of the examination area ( 3 ) has a parallel beam path and thus the projection of the field mirror ( 4 ) in the direction of the light bundle axis ( 5 ) must contain the examination area. The telecentric image gives the structures of the examination area ( 3 ) regardless of the distance of the field mirror ( 4 ) from the surface ( 2 ) with always the same magnification. The unillustrated optical axis of the field mirror ( 4 ) is opposite the light beam axis ( 5 ) so far tilted, that the field mirror ( 4 ) reflected light bundles with the light bundle axis ( 5 ' ) to an outside of the incident light bundle with the light bundle axis ( 5 ) arranged plane mirror ( 40 ) and in the direction of a beam splitter ( 6 ) is reflected. Behind the beam splitter ( 6 ) is in the camera-side focal plane ( 20 ) of the field mirror ( 4 ) the entrance pupil ( 13 ) of the lens of the camera ( 11 ) with an imaging sensor ( 12 ) arranged. At the camera ( 11 ) is preferably an electronic camera with an imaging sensor ( 12 ), for example a CCD or a CMOS imager, which is arranged on a camera board, not shown. The camera board preferably carries an electronic circuit for controlling the camera ( 11 ), particularly for controlling the image pick-up and read operation.

When Field mirror is a parabolic or spherical mirror of mirrored Glass or plastic or metal.

On the light bundle axis ( 5 '' ) is by means of the beam splitter ( 6 ) Light from in the illumination-side focal plane ( 10 ) of the field mirror ( 4 ) arranged lighting sources reflected.

On the optical axis of the illumination beam path ( 7 ) in the focal plane ( 10 ) of the field mirror ( 4 ) is a light source ( 21 ) for the bright field illumination of the examination area ( 3 ) arranged. Light of this as an approximately punctiform bright field light source ( 21 ) meets as a parallel light bundle with a light bundle axis ( 5 ) perpendicular to the surface ( 2 ) of the object to be examined ( 1 ) on.

At a distance from the optical axis of the illumination beam path ( 7 ) are other light sources ( 22 . 22 ' ) in the focal plane ( 20 ) provided and selectively operable individually or in groups by means of a lighting control, not shown. The light sources ( 22 . 22 ' ) allow an achsnahe dark field illumination of the examination area ( 2 ) of the object to be examined ( 1 ),

It is provided in the context of the invention, the light source ( 21 ) and the light source ( 22 . 22 ' ) into a programmable surface light source. Such a programmable surface light source can be made of a controllable micromirror array illuminated by a light source, an LED array whose LEDs can be activated individually or in groups, or a surface light source covered by a mask with controllable selective transmission, preferably a controllable liquid crystal mask (LCD mask) be formed.

All optical components are housed in a light and dust-tight housing ( 15 ), which in the figures only in the area of the transparent windscreen ( fourteen ) indicated schematically. The windscreen ( fourteen ) is opposite the light beam axis ( 5 ) to reflect reflections of the light sources ( 21 . 22 . 22 ' ) on the front or rear optical surface of the windscreen ( fourteen ) from the light beam axis ( 5 ), thereby injecting these reflections into the camera ( 11 ) to prevent. In the housing ( 15 ) are in the vicinity of the windscreen ( fourteen ) Additional light sources ( 44 . 44 ' ) arranged for a non-telecentric dark field illumination. These additional light sources ( 44 . 44 ' ), of which only two are shown schematically, are preferably in the form of a line pair, annular or in the form of a rectangle around the input window (FIG. fourteen ) and can be selectively controlled by a lighting controller individually or in groups to realize sectoral dark field lighting.

In 2 is an alternative beam path of the arrangement according to the invention with a plane mirror ( 40 ) to the in 1 represented known beam path.

3 shows a schematic beam path in the same sectional plane as in the 1 and 2 with the difference that the camera-side beam path with the light bundle axes ( 5 ' . 5 '' . 5 ''' ) on two flat mirrors ( 40 . 41 ) is reflected. As a result, the focal length of the field mirror ( 4 ) folded twice on the camera side, whereby a compact design is made possible even with long focal lengths.

The light source ( 21 ) can be designed to achieve a bright field illumination as a point light source, which in the focal plane ( 20 ) on the optical axis ( 8th ) out 1 lies. The invention provides for further light sources or an extended light source in the focal plane (FIG. 20 ) or near them. Depending on the examination task and the surface condition of the surface to be examined ( 2 ) can be a point-like light source in the focal plane ( 20 ) by a slightly extended area light source near the focal plane ( 20 ) be replaced. It is planned to use the light source ( 21 ) or the arrangement of multiple light sources by means of an unspecified lighting control in their intensity, in the mixed color of the emitted light and in the spatial distribution of the intensities and wavelengths.

List of pictures

1 : Schematic view of the beam path with a plane mirror in a plane perpendicular to the optical axis of the camera ( 8th ) and the light beam axis ( 5 ),

2 : Schematic view of an alternative beam path with a plane mirror in a plane perpendicular to the optical axes of the camera ( 8th ) and the light beam axis ( 5 ) of the incoming bundle.

3 : Schematic view of the beam path as in 1 and 2 , but with two plane mirrors.

LIST OF REFERENCE NUMBERS

1

object

2

surface

3

study area

4, 4 ', 4' '

field mirror

5, 5 ', 5' ', 5' ''

Beam axis

6

beamsplitter

7

optical Axis of the illumination beam path

8th

optical Axis of the camera beam path

9

Reflection angle α

10

illumination-side Focal plane of the field mirror

11

camera

12

imaging sensor

13

entrance pupil

14

windscreen

15

casing

20

camera mounted Focal plane of the field mirror

21

Bright field light source

22 22 '

Darkfield light source

40

plane mirror

41

plane mirror

44 44 '

Additional light source

• DE 10 2007 022 831 A1
• US 4,547,073 A

Patent documents cited in the application:

• DE 10 2007 022 831 A1
• US 4,547,073 A

Claims (11)

Device for optically testing an examination area ( 3 ) of a specular or diffusely reflecting surface ( 2 ) of an object ( 1 ), • with a field mirror ( 4 ), one on the surface ( 2 ) vertical light bundle with a light bundle axis ( 5 ) into a light bundle with a light bundle axis ( 5 ' ) by a reflection angle α ( 9 ) and its projection surface on the surface to be examined ( 2 ) the examination area ( 3 ) at least just covered, • with at least one on the optical axis ( 7 ) of the illumination beam path in the region of the focal plane ( 20 ) of the field mirror ( 4 ) arranged light source ( 21 ) to the bright field illumination, which by means of a telecentric beam path to the examination area ( 3 ) with at least one outside the optical axis ( 7 ) of the illumination beam path in the region of the focal plane ( 20 ) of the field mirror ( 4 ) arranged light source ( 22 . 22 ' ) to near-dark field illumination, • with an electronic camera ( 11 ) with objective, whose entrance pupil ( 13 ) in the focal plane ( 10 ) of the field mirror ( 4 ) on the camera-side optical axis ( 8th ) and which part of the surface ( 2 ) in the examination area ( 3 ) receives light emitted via a telecentric beam path and transmits the images obtained to an evaluation device, as well as • with a steel divider ( 6 ), which optionally the optical axis of the camera beam path ( 8th ) or the optical axis of the illumination beam path ( 7 ) by 90 ° to the light beam axis ( 5 '' . 5 ''' ). characterized in that the field mirror ( 4 ) a concave mirror surface having a focal length of at least 2 times the maximum extent of the examination area ( 3 ), and in such a way to the light bundle axis ( 5 ), that the reflection angle α ( 9 ) is at least 120 ° and that the beam path between the field mirror ( 4 ) and the focal planes ( 10 . 20 ) on at least one plane mirror ( 40 ) is reflected. Device for optically testing a surface according to Claim 1, characterized in that the field mirror ( 4 ) is a parabolic mirror. Device for optically testing a surface according to Claim 1, characterized in that the field mirror ( 4 ) is a spherical mirror. Device for optically testing a surface according to one of claims 1-3, characterized in that the beam path between the field mirror ( 4 ) and the focal planes ( 10 . 20 ) is reflected at least twice at two opposite and parallel to each other arranged plan mirrors. Device for optically testing a surface according to one of Claims 1-4, characterized in that the light source ( 21 ) in the light source ( 22 . 22 ' ) is integrated and is designed as a programmable surface light source. Device for optical testing of a surface according to Claim 5, characterized in that the programmable surface light source from a controllable, illuminated by a light source, micromirror array is formed. Device for optical testing of a surface according to Claim 5, characterized in that the programmable surface light source consists of a LED array whose LEDs are individually or in groups can be activated. Device for optical testing of a surface according to Claim 5, characterized in that the programmable surface light source from one of a mask with controllable selective transmission covered area light source is formed. Device for optical testing of a surface according to Claim 8, characterized in that the mask with controllable selective permeability a controllable liquid crystal (LCD) mask is. Device for optically testing a surface according to one of Claims 1-9, characterized in that the field mirror ( 4 ) is designed as a Fresnel mirror. Device for optically testing a surface according to one of Claims 1-10, characterized in that an additional light source ( 44 . 44 ' ) for illuminating the examination area ( 3 ) outside the telecentric beam between the examination area ( 3 ) and the field mirror ( 4 ) is arranged and that the additional light source ( 44 . 44 ' ) individually or together with other light sources ( 21 . 22 . 22 ' ) is controllable by means of a lighting control.

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