CA2003734A1 - Inspection apparatus - Google Patents
Inspection apparatusInfo
- Publication number
- CA2003734A1 CA2003734A1 CA 2003734 CA2003734A CA2003734A1 CA 2003734 A1 CA2003734 A1 CA 2003734A1 CA 2003734 CA2003734 CA 2003734 CA 2003734 A CA2003734 A CA 2003734A CA 2003734 A1 CA2003734 A1 CA 2003734A1
- Authority
- CA
- Canada
- Prior art keywords
- optical
- focusing
- radiation
- optical axis
- optical apparatus
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
- G01N21/9515—Objects of complex shape, e.g. examined with use of a surface follower device
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
- G02B7/28—Systems for automatic generation of focusing signals
- G02B7/30—Systems for automatic generation of focusing signals using parallactic triangle with a base line
- G02B7/305—Systems for automatic generation of focusing signals using parallactic triangle with a base line using a scanner
Abstract
ABSTRACT
An optical apparatus including focusing means (41), an optical axis, an object point (31) and an image point on said optical axis, said object point being movable along the optical axis with respect to the focusing means, means being provided to change the effective optical distance between either the object point and the focusing means or between the image point and the focusing means to maintain the object point at a fixed point even if the image point moves.
An optical apparatus including focusing means (41), an optical axis, an object point (31) and an image point on said optical axis, said object point being movable along the optical axis with respect to the focusing means, means being provided to change the effective optical distance between either the object point and the focusing means or between the image point and the focusing means to maintain the object point at a fixed point even if the image point moves.
Description
i-- 200;~,734 - 1 - , .
." " ::, -, I N~; P ECT ~ O N A P PA RATU S
The present inventioll relates to an optical apparatus, preferably an inspection apparatus. The inspection apparatus which will be described as a preferred embodiment of the invention is an apparatus for inspecting a surface of, for example, a panel of an article such as a motor car but is not restricted thereto.
There is a considerable requirement for the inspection -;~
of surfaces, and in particular, the surfaces of articles. Many articles require inspecting, for -~
example domestic goods and motor cars in particular.
There are a number of difficulties to be overcome in ~ ;
properly inspecting the surface of such articles. ;-~
- ... .,:, , One Oe the problems is that, particularly in the case -i ot motor cars, they are irregularly shaped and on a production line a variety of different shaped motor cars may succeed each other down the production line.
The inspection apparatus should be able to cope with such changes.
:
It is necessary usually to move the optical system close tol!the sur,racejto be inspected, and any m~vement of the optical system away from that surface causes problems of focusing or the beam of radiation. ; ;
Through the specirication we will refer to "light", "optical" and like expressions which refer to radiation of visible wavelengths. It will be understood that the , :
apparatus may be suitably modified to deal with radiation of other wavelengths such as ultra violet or infra red and such apparatus is included in the scope , - -- 200373~ ~
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The present inventioll relates to an optical apparatus, preferably an inspection apparatus. The inspection apparatus which will be described as a preferred embodiment of the invention is an apparatus for inspecting a surface of, for example, a panel of an article such as a motor car but is not restricted thereto.
There is a considerable requirement for the inspection -;~
of surfaces, and in particular, the surfaces of articles. Many articles require inspecting, for -~
example domestic goods and motor cars in particular.
There are a number of difficulties to be overcome in ~ ;
properly inspecting the surface of such articles. ;-~
- ... .,:, , One Oe the problems is that, particularly in the case -i ot motor cars, they are irregularly shaped and on a production line a variety of different shaped motor cars may succeed each other down the production line.
The inspection apparatus should be able to cope with such changes.
:
It is necessary usually to move the optical system close tol!the sur,racejto be inspected, and any m~vement of the optical system away from that surface causes problems of focusing or the beam of radiation. ; ;
Through the specirication we will refer to "light", "optical" and like expressions which refer to radiation of visible wavelengths. It will be understood that the , :
apparatus may be suitably modified to deal with radiation of other wavelengths such as ultra violet or infra red and such apparatus is included in the scope , - -- 200373~ ~
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of the invention.
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According to a first aspect, the present invention ~-provides an optical apparatus including focusing means, an optical axis, an object point and an image point on said optical axis, said object point being ~ovable along the optical axis with respect to the focusing means, means being provided to change the effective optical distance between either the object point and the focusing means or between the image point and the focusing means to maintain the object point at a fixed point even if the image point moves. Preferably the focusing means remains stationary, and the means for ~-changing the effective optical distance comprises a movable non-focusing element. Preferably means may be provided to move said movable non-focusing element in such a way that continuous changes in the continuous movement of the object point is compensated so that the image point remains stationery at all times.
Preferably said means may comprise a movable mirror means, the mirror means being in the form of two `~
mirrors at an angle to one another and being rotatable togetheF about an axis to one side of the optical axis.
According to a second aspect of thè invention, there is plrovi!ded,anloptliqal appara~tus (which need not be an `
inspection apparatus), including optical means for ~ ~ ;
varying the~focusl~ng effect of a focusing component, sa~id optical~appa;rat~us including a main optical axis, the~focusing component being on said main optical axis and~having~an~ optlcal axis, the focusing component being tilted so that the two optical axes are tilted ~ X;
with respect to each other and means being provided to pass a bèam of radiation through said focusing ,~ .f ~ ,?` - ",","
component at a variable transverse position with ~= `
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According to a first aspect, the present invention ~-provides an optical apparatus including focusing means, an optical axis, an object point and an image point on said optical axis, said object point being ~ovable along the optical axis with respect to the focusing means, means being provided to change the effective optical distance between either the object point and the focusing means or between the image point and the focusing means to maintain the object point at a fixed point even if the image point moves. Preferably the focusing means remains stationary, and the means for ~-changing the effective optical distance comprises a movable non-focusing element. Preferably means may be provided to move said movable non-focusing element in such a way that continuous changes in the continuous movement of the object point is compensated so that the image point remains stationery at all times.
Preferably said means may comprise a movable mirror means, the mirror means being in the form of two `~
mirrors at an angle to one another and being rotatable togetheF about an axis to one side of the optical axis.
According to a second aspect of thè invention, there is plrovi!ded,anloptliqal appara~tus (which need not be an `
inspection apparatus), including optical means for ~ ~ ;
varying the~focusl~ng effect of a focusing component, sa~id optical~appa;rat~us including a main optical axis, the~focusing component being on said main optical axis and~having~an~ optlcal axis, the focusing component being tilted so that the two optical axes are tilted ~ X;
with respect to each other and means being provided to pass a bèam of radiation through said focusing ,~ .f ~ ,?` - ",","
component at a variable transverse position with ~= `
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respect to the main optical axis to thereby vary the focusing eLfect OL said focusing component.
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The means to move the beam may comprise a tiltable mirror.
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According to a third aspect, the invention may comprise an inspection apparatus, including means to pass a beam ~ -of radiation across a surface to be inspected beam shaping means being provided whereby, different points during said movement, the cross section of the beam of radiation is`changed by beam shaping means so as to -detect different types of fault. Thus, if the beam of radiation is scanned across the surface in two opposite directions, whilst scanning in one diretion, the cross section of the beam at the surface may be of a first shape, and when scanning in the opposite direction, the cross section may be of a different shape. Typically, one of these shapes may be circular, and the other slot shaped. ~ -According to a fourth aspect, the invention may comprise an optical apparatus in which a composite beam comprising a plurality of beams of separate, distinct wavelengths is provided, whereby some optical components in the apparatus sensitive to wavelength may a~féct thie differe~nt beams in a different manner, and other optical components not sensitive to wavelength ;
may afect all of the beams in a similar manner.
The invention may also provide according to a fifth aspect an inspection apparatus in which means is provided to pass a beam of radiation to a surface to be inspected, means is provided to collect the beam from the surface, and means is provided to determine the - ~. ~: .- . . .
. ., ~ ~, z0037~4 sharpness of the cross-section of the beam collected from the surface under inspection. Thus, said collected beam may be passed over an opaque edge, and then to a radiation detector, and means being provided to determine the shape of the beam cross section from the output of the signal detector. Thus a fuzzy ~eam cross section will be detected as providing a different change of signal level from a sharp beam.
An apparatus for inspecting the panels of a motor car will now be desccibed as an example of apparatus according to t11e invention and with reference to the accompanying drawings in which ~ :;
Figure 1 is a diagrammatic side view of an inspection apparatus of the invention in the form of inspection ~;
apparatus, Figure 2 is a diagrammatic perspective view of the apparatus of F ~ure 1, Figure 3 is a diagram showing the optical components of the apparatus of Figure 1, Figures 4A and 4B diagrammatic are side and plan views respectiv!e,ly offa~first par~t (first dynamic focusing means) of the optical apparatus of Figure 3, , ~ ~ . - : : ~ .
Figure 5 is a view similar to Figure 4A sh~wing diagrammatically the operation of the optical apparatus of Figures 4A and 4B, Figure 6 is a diagrammatic side view of the principle of operation of another part (the second dynamic focusing means~ of the optical apparatus, : ., : ::: ::,, - 5 - - ~
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Figure 7 i5 a more detailed diagrammatic side view of the second dynamic focusing means of the optical apparatus of Figure 3, - ~-,,,, :- -::
Figures 8A, B and C which are vertically aligned with one another show, respectively, a grating with two types of light beams passing through the grating, the output signals corresponding to the two light beams, and the threshold signals corre~ponding to the light beams.
Figure 9 is a diagrammatic view of part oE the apparatus which shows a further dynamic focusing effect.
The apparatus of the present invention is intended amongst other things to detect defects such as dents, so called distinctiveness of image (DOI) and diffuse reflectancy defects and surface colour changes.
Figure 1 illustrates an inspection apparatus 10 according to the invention. The inspection apparatus is arranged to inspect the front, rear and upper painted panels of a motor car 11 on a production line.
The side,su~rfaces~may beiinspected by two generally less mobile inspection means (not shown but utilising ~the~same principles as the apparatus to be described) on each side OL the car as the car moves past. ~he inspection apparatus 10 comprises a frame 12 mounted so as to be movable up and down and forwardly and rearwardly with respect to the axis of the motor car 11, and to tilt about a transverse axis H. These degrees of motion are shown by the arrows 13 and the moveLent may be controlled by hyoraulic ram~ or by a robot arm (not shown). When inspecting the rear of the car, the apparatus may carry out a more complex movement. Instead of the frame 12 sloping rearwardly as shown in Figure 1, the frame may slope forwardly.
The frame 12 ~ounts a first upper housing 14 housing the majority of the optical cpmponents~ and a lower member 16. As is clear rrom Figure 2 which shows a perspective front view, the lower member 16 comprises an extended grating 17 which extends generally across the width of the car, and slightly downwardly on each side of the car. The lines 20 of the grating 17 are shown in Figure 2 grossly exaggerated in width for clarity. Behind the grating 17 (behind, in the sense that it is behind the grating 17 from the point of view of an incident light beam) and in contact therewith is a generally coextending retro reflective screen 18 and in front of the grating 17 is a generally coextending filter wedge 19 (18 and 19 not being shown in Figure 2 for clarity). The filter wedge 19 is of a pink colour and its optical density increases from its upper edge l9A to the lower edge l9B. The increase in density may be provided by having a thicker lower edge 19B, the material of the wedge 19 having the same optical density per cubic mm, or alternatively the "wedge" 19 may be of the same thickness throughout but produced in such a way that its optical density~ increases~from~ its top edge l9A to its lower edge l9B.
. .,, ~ ., ~rom Figures 1 and 2 it will be seen that the optical components within the upper housing 14 provide an outgoing beam 22 of radiation (details of which will be given hereafter) which is scanned (see Figure 2) along a scan line 21 across the surface of the upper panels of the car 11. The beam is specularly reflected to . :.: ,.: ::: .
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pass through the filter wedge 19, through the grating 17, (the beam being scanned perpendicularly to the grating lines 2-~) to the retro reflective 5creen 18, is then retro reflected from that screen back through the grating 17, wedge 19 and is rereflected from the car panel to the optical apparatus within the upper housing 14. It is well known that retro reflective material reflects an incident beam back along the incident path with a small degree of scatter.
Figure 3 shows i n diagrammatic form the optical components within the upper housing 14. The optical apparatus includes a first laser 23A providing a beam at a first wavelength (633 nm), the beam being passed to a first beam combining mirror 24. Also passed to mirrorS (24B, 24C) are two further beams from two further lasers (23B, 23C), via a single mode polarisation preserving optical fibre 26, the two further laser beams being of 458 nm and 514 nm wavelength respectively.
The combined beam is reflected onto an optical axis 27 by a mirror 28. ~he combined beam passes to a first dynamic focusing means 25 to maintain the beam in focus as it scans across the car. As is also illustrated in Figures 4A and 4B, the dynamic focusing means 25 cludes; ,a rota,table tilt mirror 29, comprising a mirror arranged at an angle to the optical axis 27 so as to deflect the incoming beam. The mirror 29 being arranged so as to be tiltable about an axis 31 which is in~ the plane~of the mirror surface, the optical axis 27 also passing through the axis 31. Thus, by varying the tilt of the mirror 29, the beam path reflected from the mirror 29 may be reflected by an angle between A and B
(see Figure 4A).
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The beam re~lected rrom mirror 29 is passed to a tilted lens 32 and tllence along a beam path to a pair OL 9~
roo~ mirrors 33. When the tilt mirror 29 is at a position such that the angle of re~lection o~ the beam is A then the reflected beam passing between the tilted lens 32 and the mirrors 33 also passes througll a pair of lenses 36,37.
The beam passing back t~lroug~l the tilted lens 32 is reflected from the mirror 29 along an axis 3U at an angle to axis 27 (one lies behind the other in the view of Figure 3 but see Figure 4B) and passes through lens 20, and past mirror 28. The beam continues to a scanning mirror 3~ which oscillates about an axis J
which is in the plane of the mirror 38 and also passes through the optical axis 3~. The outgoing beam 22 is thereby passed down to the surface of the car as shown in Figures , and 2 and is scanned thereacross by the mirror 38. The beam is reflected from the surface oc the motor car to the grating 17 as already described and back by the retroreflector 18. The return beam 42 is received by the oscillating mirror scanner 38 where it is descanned.
Unlike the outgoing beam 22 which i9 a narrow-rocused (combined) laser beam, the returning beam 42 includes i:mlage fo~'r~ing inifo'rm'ation a's will be clear lateriand is of greater width than outgoing beam 22. Thus, the oscillating scanner mirror 38 has relatively large t~ransverse dimensions. The Ini rror 3~ reflects the incoming beam 39 back to a mirror 39, the mirror 3~
having a central hole 34 through which the optical a~is 30 passes, the majority of the beam striking the mirror 39 which reflects it to a lens 41 which focuses the : , ,:
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incoming beam 42 to a point behind the surface of a mirror 45A of mirror pair 45A,45B.
The mirror pair 45A, 45B rorm a second dynamic focusing means 43, whicll is illustrated in more detail in Figure 7. Effectively,~lowever, the second dynamic focusing means 43 causes tlle incoming beam to focus at a fixed image point P (shown in Figure 7) and lens 46 focuses the image point P onto a mirror 47. The mirror 47 is a mirror with a central hole. The lenses 41 and 46, together with the second dynamic focusing means 43 combine to image onto (or in fact just behind) the plane of the mirror 47 the surface of the panel of the motor car being inspected. This means that light which originates from the panel of the motor car (scattered light only)is focused down to a narrow cone and passes through the central hole to an optical fibre 48. The remaining component of the incoming light beam, which is in fact specularly reflected light from the panel, because it does not have a point of origin on the surface of the panel of the motor car, will not be tightly focused at that point and will therefore effectively form a circular shaped cross section at the mirror 47, thereby effectively apparently forming a halo around the central cone of scattered light. Thus the specular component of the incoming beam 42 will be reflected by the mirror 47 to a lens 49, beam splitters 51!,52 beinglpr!ovided to split theIbeam into ibs blue (48~ nm) component and green (514 nm) component. The blue and green components are collected by respective lenses 53,54 and passed to respective optical fibres 56,57. The remaining red part of the beam (633 nm) passes through the second beam splitter 52 and is ; coIlected by lens 58 and passed to an optical fibres 59 (the centre of tlle beam) and 60 (the outer ring of the .: : ~
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To the end OL each of fibre 48,56,57,59 60 there i5 attached a respective light sensitive detector 63 to 67 for detecting light passing along the respective fibre.
Outputs from eacll Ot the detectors (~3) to (67) are passed to a central computer processor (72) to process the infromation and produce outputs.
The mode of operation of the apparatus will now be described.
On a production line the motor car moves in the ;
direction of the arrow 15 and the frame 12 is moved by, for example, a motion system eg a robot so as to be swept over the upper, front and rear surfaces of the motor car 11. Because of its configuration it is not necessary for the apparatus 10 to closely follow the ;i`~
surface of the motor car 11 as with our earlier arrangement shown in our earlier PCT patent application number PCT/GB86/00399, but the lower housing 16 of the apparatus 10 may be spaced some reasonable distance, typically 200-500 mm from the surface of the panel of the car. ~;
It will be understood that the beam which is scanned across the,surfacelo~f the motor car 11 along scan line 21 comprises three colours, (633 nm, 488 nm, and 514 nm). ~
The red (633 nm) and green (514 nm) laser beam components will pass through the grating 17 without any variable modulation, because of the colour, (yellow) of ~ -the grating. - ~
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Tlle ~lue (4~ nm) beam will be affected by the gratingbecause the yellow g~ating acts as ic it were a black and white grating. Tl~us, as the laser beam scans over the car body, the returned blue laser beam will be modulated by the effect of the grating.
This modulated (blue) signal, the specular component of which is detected by light sensitive detector 64, can be used to detect dents and distinctiveness of image (DOI). The dents are detected by comparing the modulated signal received by the detector 64 with that expected for that part of the body.
Thus the outgoing beam 22 is reflected from the surface of the panel of the car. Iî the surface of the car was exactly flat, then as the outgoing beam 22 is scanned across the flat surface it would strike the lines 20 or the grating 17 at regular intervals and the return signal would be modulated in a regular rashion.
However, because the surface of the car body is not flat (eg: includes dents or i~ naturally curved) the ~outgolng beam~is reclected at an angle which varies ~depending upon the curvature of the car surface and this affcects~the modulation of the beam by the grating 17. Thus, if the outgoing beam scans across an area of car panel ura¢e which; is convex then the ray reflected from the body surface to the grating 17 will move across the grating 17 more rapidly than if the car panel surfa~ce~was flat, and the modulation of the signal will be at a greater frequency than otherwise.
Similarly, if the outgoing beam scans across a concave part~of -the car panel's surface, then the rerlected beam will move across the grating 17 more slowly than if the car panel surface was flat and so the modulated signal be at a lower frequency. A perfect panel which :: ~ :
, ~ ' ~ , includes natural curves will produce a modulated signal where the fre~uency varies with time in a known way.
Thus to detect dents (or waviness of panels) the frequency of the modulated signal is compared with that expected ror a per~ect panel.The size of dents which can be detected depends upon the spatial fre~uency of the grating 17. A fine grating will allow smaller dents to be detected. The pitch of the grating may ~e in the range lmm'- 20mm, typically 12mm. This pitch is small enough to detect dents and waviness. The blue (488 nm)beam may also be utilised to provide a measure of the distinctiveness of image. The term "distinctiveness of image" (DOI) is a well known term in the art and effectively measures the "shinyness of ....
the surface". The manner in which this is measured is ~
shown in Figures 8A-8C. ~ ~ -The three figures, Figures 8A-8C are aligned vertically. Thus, considering the left hand sides OL
the figures, if we assume that the paint surface of the vehicle is very shiny, then it will produce a very ;
sharp distinct image of the blue beam and this sharp ;
beam cross section 70 (which is typically OL
approximately 0.25 mm diameter at the car surrace and 2-3mm where it strikes the grating 17) is shown in Figure 8A. The output signal of detector 64 is shown inFigure 8B for a beam of beam cros's section 70 passes from a transparent part 68 to yellow line 69 of the grating 17. ~
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In Figure 8A, a beam cross section 71 is shown for a beam reflected from a less shiny surface. It will be seen that the central area 71A of the cross section is surrounded by a "llalo" outer area 71B. As a result, :, , ~.: ' ::: : ::
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- 2003~34 the detected signal shown on the right hand side of Figure 8B changes from a peak value to the lower value by means of a less steep slope compared with the signal to the left o~ Figure 8A. By providing threshold values at A, B, C and D it is possible to provide a measure of the slope and hence the "halo" effect. In this way, therefore, it is possible to measure the degree to which the beam cross section is sharp and hence the "distinctiveness of image". More thresholds may be used.
The green(514 nm) laserbeam will also not be affected by the grating, as it scans across the grating, but will be attenuated by the pink perspex wedge 19. The pink perspex wedge is used to measure the vertical position at which the green beam strikes the retro reflective screen 18. Referring to Figure 1 the wedge 19 is increasingly opaque to the green laser beam as one moves from the upper l9A to the lower l9B edge, Clearly, if the beam strikes the pink wedge towards its lower edge, then the beam will be attenuated to a greater extent than if it strikes the wedge near its upper edge. Thus, the signal output of light sensitive detector 65 which effectively measures the amplitude of the specularly reflected component of the green laser beam will vary depending upon the position in which the g~een l~ase,c ~eam,s,trlikes th~q pink wedge 19 and this is in turn, as is clear from Figures 1 and 2, a measure of the angle at which ;the incoming beam is reflected from the surface of the vertical body 11. The normal position in which the beam strikes the pink wedge 19 ;will be known (from, for example, a computer memory) and changes, particularly rapid changes, from that known position and hence known value of the output signal of detector 65 will be a further measure of 200373~
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defects SUCIl as dents in the body surface.
As has already been described, the red (633 nm) laser beam will not be affected by the grating nor indeed by the pink wedge 19 and so, the specular component of the returning red beam which is detected by the detectors 66,67 is also to be used to provide information about ;
discrete defects such as dirt inclusion in the paint ~ ~
and scattering type defects such as scratches or ;
sanding marks. ;;
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The arrangement of the optics is such as to focus onto the front end of the optical fibres 59 and 60 an image of the retroreElector 18. Thus, the central fibre 59 will pick up the specular light and the surrounding optical fibre 60 will pick up light which has been scattered.
As already described, the diffuse light in the three coLours from the car body surface is collected separately by the fibre optic 48. In order to obtain relevant colour information it is necessary to separate the three colours by optical means, such as beam splitters like the beam splitters 51,52. The three-beams may then be separately detected and the colour of the body surface determined from those three separate beams. If, howéver, it is only desired to look atithe combined beam, then the fibre optic 48 is arranged to pass the combined beam to the light sensitive detector 63 and the light sensitive detector 63 may be used to provide information regarding gross surface defects in highly curved areas where the specular beam may be deflected so much that it does not come into contact with a retro reflective screen.
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. ~ . , -As already discussed, the apparatus also provides twodynamic focusing systems. As the upper housing 14 is at some distance from the position where the beam strikes the sur~ace of the motor car 11, as the depth of focus of the beam at the surface of the car panel is only about 62 mm it is necessary to provide a first focusing means 25 to focus the outgoing beam onto the surface and a second focusing means 43 to focus the returning beam onto parts of the optical apparatus.
The first dynamic focusing means 25 for focusing the outgoing beam comprises, as already describied, the rotatable tilt mirror 29, the tilted lens 32, and roof mirrors 33.
: ': ' It will be understood that by tilting the mirror 31 the beam (which is a laser beam of very small transverse dimensions) is swept from one edge (the lower edge in figure 4A) of the lens 32 to the opposite (upper) edge.
As is clear, the beam passes from the lens 32 to the roof mirrors 33 and:back to the lens 32. Thus, if the beam is adjacent the lower edge of the lens 32 (and ignoring for the moment the lenses 36,37) then the distance from the lens 32 to the.roof mirrors 33 and back to the lens 32 is much less than if the beam is adjacent the upper edge of the lens 32. The effect of this i's shown ih Figure S in which the~'roof,~ir~rors have been omitted and the optical system opened out showing the beam passing from the lens 32 back to the lens 32. In fact, we show two beams Bl and B2 which although narrow (their widths are much exaggerated in the Figure for clarity) are not collimated and show the focusing effect of the lens 32. The input field or object plane which is curved is indicated as O and the image plane is indicated as I(which is also curved but .
: , -` 2003734 ' ' ~ ' '' is predominantly at an angle to the optical axis). -The mirror 31 may be tilted in accordance with a predetermined program, which may be held in the memory of a computer, for a particular motor vehicle. Thus, the mirror 31 may be tilted at varying angles to maintain the surface of the car body 11 in focus throughout the scanning of the beam 22 across the surface of the body of the motor car 11.
Apart from utilising a computer memory of the body shape to change the focus, one may use the signals obtained from the optical head itself. If the relationship between the optical head 14 and the retro reflective screen 18 is fixed then the position of the specularly reflected spot on the retro reflective screen 18 can be measured by interpreting the signals - - ~ -~
from the blue and green beams. This, together with the knowledge of the scanning geometry is enough to predict the focus position.
:' " :' At this point, it would be useful to refer to Figure 9. -In this arrangement, a lens 35 corrsponding to lens 32 is not tilted, but its optical axis coincides with the :,: "., : ,- ":" , optical axis of the apparatus. The lens 35 has effectively a curved input field or object plane 0.
The èffecit of t~ib`curved object plane O is t!o make a i -i curved image plane I which effectively varies the focus. As in Figure 5 we show two beams which although narrow (they are muc7l wider in the figure for clarity) are not collimated and shows the focusing effect of ;~
lens 35. A combination of the effect of Figure 9, together with that of Figures ~A and 4B can produce a dynamic focusing means. ~- -, ,: :, ::
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In some circumstances, the arrangement of Figure 9 may be sufficient without the arrangement of Figures 4A and 4B.
We will now describe the second dynamic focusing means 43 for focusing ti-e incoming beam onto the optical components.
Whilst it is theoreticaly possible to use, as a second dynamic focusing system, a system similar to the first dynamic focusing system, in practice the syste~ would need to be able to cope with much larger beam widths and a greater range of change of focus. Thus the system would need to be very large and require special lenses. Figures 6 and 7 show a preferred second dynamic focus system as already described.
Referring firstly to Figure 6, which shows a simplified version of the path over which the incoming beam 42 passes from the panel 21 to the mirror 47. Panel 21 is shown in two alternative positions 21A,21B which illustrates the change of distance from the optical apparatus within the housing 14 to the panel 21 as the beam is scanned across the panel surface. The incoming beam 42 passes through mirror 41 which focuses an image of the panel 21 to an image point P, and this image ;`
point P is relayed via lens 46 onto the mirror'47. The second dynamic focusing means 43 is provided to vary -~-the optical distance between the lens 41 and the image point P so that the image point P and the panel 21 remain at conjugate points with respect to the lens 41 even as the panel 21 moves with respect to the lens 41 between positions 21A and 21B.
Figure 7 shows the apparatus 43 for carrying this out.
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The incoming beam 42 which is to be focused is reflected twice at the two mirrors 45A,45B. There are shown two focal points FB and FA which corre~pond to the points at which the lens 41 would focus an image of the panel surface 21 when at respective positions 21B
and 21A. It will be seen from Figure 7 that rotation of the mirror pair 45A, 45B about the axis 61 enables the incoming beam to be focused to the point P in both cases. Thus, considering the panel being positioned in panel position 21A in which case the image would be brought to focus at point FA, thenif the mirrorsystem is in position X3 then the optical path length R.FB
must equal the optical path length R.S.T.U.V.P. ~ -Similarly, when the panel is in position 21A, the mirror pair is in the position Xl and the optical path length T.FA must equal path length T.U.V.P.
', ,. .:';' ,': ,; :~, By a suitable choice of angle between the mirror surfaces of the two mirrors 42A, 42B, the incoming beam 42, the distance between the axis of rotation 61 and the mirrors 45A, 45B the point P may be maintained stationary, as the mirrors 45A, 45B are rotated about the axis~61 to compensate for changes in the distance between the lens 41 and the panel 21. ;~
Referring back to Figure 3, the rotable mirror 31 may ;;
also rotate the beam` to the angle A,when the beam will pass through the lens 32, and then through the lenses 37,36 before being reflected at the roof mirrors 33 back through the lens system 36,37 and lens 32. The `~
effect of the lenses 36,37 is to spread the beam so as to provide a slot shaped cross section beam (the axis ~of the slot being arranged to be transverse the line of scan). In the apparatus described, as the beam 22 is scanned in a first direction (say left to right in ;~
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Figure 2) then a beam of the circular cross section shown in Figure 8A is provided by the mirror 31 being tilted between angles A and B and when the beam is scanned in tlle other direction, from right to left as shown in Figure 2, thenthe beam is switched by tilting the mirror 31 to angle A whereby the beam passes through the lenses 36,37 to provide a slot shaped cross section beam. This slot shape has advantages for detecting the extent of a defect as will now be described.
With a small spot as shown in Figure 8A, defects such as distinctness of image (DOI) dents, orange peel and scratches can be detected as has already been described. A slot shaped laser spot can be used to detect discrete defects such as dirt inclusions and colour defects.
It also allows one to inspect the whole body ofthe car by means of the slit whilst only inspecting part of the body with the spot as shown in Figure 8A, which means that the scan can be slower, which produces a lower electronic band width with better signal to noise ratio, or else the body may be scanned in a shorter time.
T~e'size~of~ the !slot shaped cross section!beam is approximately 3mm long and 0.6mm wide. The size of small dirt inclusions may be measured by determining the extent to which they reduce the signal. Thus, if the slot is'larger than the dirt inclusions, then not all of the signal will be attenuated and'the degree of attenuation gives some measure of the extent of the dirt inclusion. Small dirt inclusions may be acceptable but larger ones may be unacceptable.
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- 2~ -The invention is not restricted to the details of the foregoing example.
We have chosen a particular set of colours: blue, green and red for the beam, yellow for the grating and pink for the wedge. Other combinations of colours, particularly for the grating and wedge may be used and ;
the particulars are given as examples only.
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The second focusing means has been provided between the ;
lens 41 and the point P. However, it could be provided between the point P and the lens 46 or, indeed, between ~- -the lens 46 and mirror 47. - ;-Many parts of the apparatus may be used in other types of apparatus. Thus, for example, both the first and . .. . .. .
second dynamic focusing means (referred to in the introduction as the first and second aspects of the invention) may usefully be used to focus dynamically from moving object planes onto a fixed image place (or vice versa).
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Similarly the use or a beam of different cross-sections ~ ;
(the third aspect of the invention) at different points ;~ -~
in the beam has widespread application in other (usually inspection) apparatus.
Also the use of a composite beam comprising a plurality of beams of separate, distinct wavelengths (the fourth aspéct of the invention) has many uses in other apparatus. ;~
The means for analysing the sharpness of a beam cross~
ection (the ~ifth aspect of the invention) may also be ,,, ~ , ~:
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used in other inspection apparatus.
Although the apparatus has been described in terms of inspecting a surface, the principle of the apparatus may be applied to inspecting, for example, article such transparent articles such as film whereby the radiation passes through the article. In this case, where the radiation is transmitted through the material, in addition to detecting defects on the surface of the material, bulk defects, that is defects within the bulk of the material, :. :. .:-:, . ~
may also be detected. :~
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The means to move the beam may comprise a tiltable mirror.
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According to a third aspect, the invention may comprise an inspection apparatus, including means to pass a beam ~ -of radiation across a surface to be inspected beam shaping means being provided whereby, different points during said movement, the cross section of the beam of radiation is`changed by beam shaping means so as to -detect different types of fault. Thus, if the beam of radiation is scanned across the surface in two opposite directions, whilst scanning in one diretion, the cross section of the beam at the surface may be of a first shape, and when scanning in the opposite direction, the cross section may be of a different shape. Typically, one of these shapes may be circular, and the other slot shaped. ~ -According to a fourth aspect, the invention may comprise an optical apparatus in which a composite beam comprising a plurality of beams of separate, distinct wavelengths is provided, whereby some optical components in the apparatus sensitive to wavelength may a~féct thie differe~nt beams in a different manner, and other optical components not sensitive to wavelength ;
may afect all of the beams in a similar manner.
The invention may also provide according to a fifth aspect an inspection apparatus in which means is provided to pass a beam of radiation to a surface to be inspected, means is provided to collect the beam from the surface, and means is provided to determine the - ~. ~: .- . . .
. ., ~ ~, z0037~4 sharpness of the cross-section of the beam collected from the surface under inspection. Thus, said collected beam may be passed over an opaque edge, and then to a radiation detector, and means being provided to determine the shape of the beam cross section from the output of the signal detector. Thus a fuzzy ~eam cross section will be detected as providing a different change of signal level from a sharp beam.
An apparatus for inspecting the panels of a motor car will now be desccibed as an example of apparatus according to t11e invention and with reference to the accompanying drawings in which ~ :;
Figure 1 is a diagrammatic side view of an inspection apparatus of the invention in the form of inspection ~;
apparatus, Figure 2 is a diagrammatic perspective view of the apparatus of F ~ure 1, Figure 3 is a diagram showing the optical components of the apparatus of Figure 1, Figures 4A and 4B diagrammatic are side and plan views respectiv!e,ly offa~first par~t (first dynamic focusing means) of the optical apparatus of Figure 3, , ~ ~ . - : : ~ .
Figure 5 is a view similar to Figure 4A sh~wing diagrammatically the operation of the optical apparatus of Figures 4A and 4B, Figure 6 is a diagrammatic side view of the principle of operation of another part (the second dynamic focusing means~ of the optical apparatus, : ., : ::: ::,, - 5 - - ~
, . . .
Figure 7 i5 a more detailed diagrammatic side view of the second dynamic focusing means of the optical apparatus of Figure 3, - ~-,,,, :- -::
Figures 8A, B and C which are vertically aligned with one another show, respectively, a grating with two types of light beams passing through the grating, the output signals corresponding to the two light beams, and the threshold signals corre~ponding to the light beams.
Figure 9 is a diagrammatic view of part oE the apparatus which shows a further dynamic focusing effect.
The apparatus of the present invention is intended amongst other things to detect defects such as dents, so called distinctiveness of image (DOI) and diffuse reflectancy defects and surface colour changes.
Figure 1 illustrates an inspection apparatus 10 according to the invention. The inspection apparatus is arranged to inspect the front, rear and upper painted panels of a motor car 11 on a production line.
The side,su~rfaces~may beiinspected by two generally less mobile inspection means (not shown but utilising ~the~same principles as the apparatus to be described) on each side OL the car as the car moves past. ~he inspection apparatus 10 comprises a frame 12 mounted so as to be movable up and down and forwardly and rearwardly with respect to the axis of the motor car 11, and to tilt about a transverse axis H. These degrees of motion are shown by the arrows 13 and the moveLent may be controlled by hyoraulic ram~ or by a robot arm (not shown). When inspecting the rear of the car, the apparatus may carry out a more complex movement. Instead of the frame 12 sloping rearwardly as shown in Figure 1, the frame may slope forwardly.
The frame 12 ~ounts a first upper housing 14 housing the majority of the optical cpmponents~ and a lower member 16. As is clear rrom Figure 2 which shows a perspective front view, the lower member 16 comprises an extended grating 17 which extends generally across the width of the car, and slightly downwardly on each side of the car. The lines 20 of the grating 17 are shown in Figure 2 grossly exaggerated in width for clarity. Behind the grating 17 (behind, in the sense that it is behind the grating 17 from the point of view of an incident light beam) and in contact therewith is a generally coextending retro reflective screen 18 and in front of the grating 17 is a generally coextending filter wedge 19 (18 and 19 not being shown in Figure 2 for clarity). The filter wedge 19 is of a pink colour and its optical density increases from its upper edge l9A to the lower edge l9B. The increase in density may be provided by having a thicker lower edge 19B, the material of the wedge 19 having the same optical density per cubic mm, or alternatively the "wedge" 19 may be of the same thickness throughout but produced in such a way that its optical density~ increases~from~ its top edge l9A to its lower edge l9B.
. .,, ~ ., ~rom Figures 1 and 2 it will be seen that the optical components within the upper housing 14 provide an outgoing beam 22 of radiation (details of which will be given hereafter) which is scanned (see Figure 2) along a scan line 21 across the surface of the upper panels of the car 11. The beam is specularly reflected to . :.: ,.: ::: .
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pass through the filter wedge 19, through the grating 17, (the beam being scanned perpendicularly to the grating lines 2-~) to the retro reflective 5creen 18, is then retro reflected from that screen back through the grating 17, wedge 19 and is rereflected from the car panel to the optical apparatus within the upper housing 14. It is well known that retro reflective material reflects an incident beam back along the incident path with a small degree of scatter.
Figure 3 shows i n diagrammatic form the optical components within the upper housing 14. The optical apparatus includes a first laser 23A providing a beam at a first wavelength (633 nm), the beam being passed to a first beam combining mirror 24. Also passed to mirrorS (24B, 24C) are two further beams from two further lasers (23B, 23C), via a single mode polarisation preserving optical fibre 26, the two further laser beams being of 458 nm and 514 nm wavelength respectively.
The combined beam is reflected onto an optical axis 27 by a mirror 28. ~he combined beam passes to a first dynamic focusing means 25 to maintain the beam in focus as it scans across the car. As is also illustrated in Figures 4A and 4B, the dynamic focusing means 25 cludes; ,a rota,table tilt mirror 29, comprising a mirror arranged at an angle to the optical axis 27 so as to deflect the incoming beam. The mirror 29 being arranged so as to be tiltable about an axis 31 which is in~ the plane~of the mirror surface, the optical axis 27 also passing through the axis 31. Thus, by varying the tilt of the mirror 29, the beam path reflected from the mirror 29 may be reflected by an angle between A and B
(see Figure 4A).
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The beam re~lected rrom mirror 29 is passed to a tilted lens 32 and tllence along a beam path to a pair OL 9~
roo~ mirrors 33. When the tilt mirror 29 is at a position such that the angle of re~lection o~ the beam is A then the reflected beam passing between the tilted lens 32 and the mirrors 33 also passes througll a pair of lenses 36,37.
The beam passing back t~lroug~l the tilted lens 32 is reflected from the mirror 29 along an axis 3U at an angle to axis 27 (one lies behind the other in the view of Figure 3 but see Figure 4B) and passes through lens 20, and past mirror 28. The beam continues to a scanning mirror 3~ which oscillates about an axis J
which is in the plane of the mirror 38 and also passes through the optical axis 3~. The outgoing beam 22 is thereby passed down to the surface of the car as shown in Figures , and 2 and is scanned thereacross by the mirror 38. The beam is reflected from the surface oc the motor car to the grating 17 as already described and back by the retroreflector 18. The return beam 42 is received by the oscillating mirror scanner 38 where it is descanned.
Unlike the outgoing beam 22 which i9 a narrow-rocused (combined) laser beam, the returning beam 42 includes i:mlage fo~'r~ing inifo'rm'ation a's will be clear lateriand is of greater width than outgoing beam 22. Thus, the oscillating scanner mirror 38 has relatively large t~ransverse dimensions. The Ini rror 3~ reflects the incoming beam 39 back to a mirror 39, the mirror 3~
having a central hole 34 through which the optical a~is 30 passes, the majority of the beam striking the mirror 39 which reflects it to a lens 41 which focuses the : , ,:
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incoming beam 42 to a point behind the surface of a mirror 45A of mirror pair 45A,45B.
The mirror pair 45A, 45B rorm a second dynamic focusing means 43, whicll is illustrated in more detail in Figure 7. Effectively,~lowever, the second dynamic focusing means 43 causes tlle incoming beam to focus at a fixed image point P (shown in Figure 7) and lens 46 focuses the image point P onto a mirror 47. The mirror 47 is a mirror with a central hole. The lenses 41 and 46, together with the second dynamic focusing means 43 combine to image onto (or in fact just behind) the plane of the mirror 47 the surface of the panel of the motor car being inspected. This means that light which originates from the panel of the motor car (scattered light only)is focused down to a narrow cone and passes through the central hole to an optical fibre 48. The remaining component of the incoming light beam, which is in fact specularly reflected light from the panel, because it does not have a point of origin on the surface of the panel of the motor car, will not be tightly focused at that point and will therefore effectively form a circular shaped cross section at the mirror 47, thereby effectively apparently forming a halo around the central cone of scattered light. Thus the specular component of the incoming beam 42 will be reflected by the mirror 47 to a lens 49, beam splitters 51!,52 beinglpr!ovided to split theIbeam into ibs blue (48~ nm) component and green (514 nm) component. The blue and green components are collected by respective lenses 53,54 and passed to respective optical fibres 56,57. The remaining red part of the beam (633 nm) passes through the second beam splitter 52 and is ; coIlected by lens 58 and passed to an optical fibres 59 (the centre of tlle beam) and 60 (the outer ring of the .: : ~
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To the end OL each of fibre 48,56,57,59 60 there i5 attached a respective light sensitive detector 63 to 67 for detecting light passing along the respective fibre.
Outputs from eacll Ot the detectors (~3) to (67) are passed to a central computer processor (72) to process the infromation and produce outputs.
The mode of operation of the apparatus will now be described.
On a production line the motor car moves in the ;
direction of the arrow 15 and the frame 12 is moved by, for example, a motion system eg a robot so as to be swept over the upper, front and rear surfaces of the motor car 11. Because of its configuration it is not necessary for the apparatus 10 to closely follow the ;i`~
surface of the motor car 11 as with our earlier arrangement shown in our earlier PCT patent application number PCT/GB86/00399, but the lower housing 16 of the apparatus 10 may be spaced some reasonable distance, typically 200-500 mm from the surface of the panel of the car. ~;
It will be understood that the beam which is scanned across the,surfacelo~f the motor car 11 along scan line 21 comprises three colours, (633 nm, 488 nm, and 514 nm). ~
The red (633 nm) and green (514 nm) laser beam components will pass through the grating 17 without any variable modulation, because of the colour, (yellow) of ~ -the grating. - ~
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Tlle ~lue (4~ nm) beam will be affected by the gratingbecause the yellow g~ating acts as ic it were a black and white grating. Tl~us, as the laser beam scans over the car body, the returned blue laser beam will be modulated by the effect of the grating.
This modulated (blue) signal, the specular component of which is detected by light sensitive detector 64, can be used to detect dents and distinctiveness of image (DOI). The dents are detected by comparing the modulated signal received by the detector 64 with that expected for that part of the body.
Thus the outgoing beam 22 is reflected from the surface of the panel of the car. Iî the surface of the car was exactly flat, then as the outgoing beam 22 is scanned across the flat surface it would strike the lines 20 or the grating 17 at regular intervals and the return signal would be modulated in a regular rashion.
However, because the surface of the car body is not flat (eg: includes dents or i~ naturally curved) the ~outgolng beam~is reclected at an angle which varies ~depending upon the curvature of the car surface and this affcects~the modulation of the beam by the grating 17. Thus, if the outgoing beam scans across an area of car panel ura¢e which; is convex then the ray reflected from the body surface to the grating 17 will move across the grating 17 more rapidly than if the car panel surfa~ce~was flat, and the modulation of the signal will be at a greater frequency than otherwise.
Similarly, if the outgoing beam scans across a concave part~of -the car panel's surface, then the rerlected beam will move across the grating 17 more slowly than if the car panel surface was flat and so the modulated signal be at a lower frequency. A perfect panel which :: ~ :
, ~ ' ~ , includes natural curves will produce a modulated signal where the fre~uency varies with time in a known way.
Thus to detect dents (or waviness of panels) the frequency of the modulated signal is compared with that expected ror a per~ect panel.The size of dents which can be detected depends upon the spatial fre~uency of the grating 17. A fine grating will allow smaller dents to be detected. The pitch of the grating may ~e in the range lmm'- 20mm, typically 12mm. This pitch is small enough to detect dents and waviness. The blue (488 nm)beam may also be utilised to provide a measure of the distinctiveness of image. The term "distinctiveness of image" (DOI) is a well known term in the art and effectively measures the "shinyness of ....
the surface". The manner in which this is measured is ~
shown in Figures 8A-8C. ~ ~ -The three figures, Figures 8A-8C are aligned vertically. Thus, considering the left hand sides OL
the figures, if we assume that the paint surface of the vehicle is very shiny, then it will produce a very ;
sharp distinct image of the blue beam and this sharp ;
beam cross section 70 (which is typically OL
approximately 0.25 mm diameter at the car surrace and 2-3mm where it strikes the grating 17) is shown in Figure 8A. The output signal of detector 64 is shown inFigure 8B for a beam of beam cros's section 70 passes from a transparent part 68 to yellow line 69 of the grating 17. ~
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In Figure 8A, a beam cross section 71 is shown for a beam reflected from a less shiny surface. It will be seen that the central area 71A of the cross section is surrounded by a "llalo" outer area 71B. As a result, :, , ~.: ' ::: : ::
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- 2003~34 the detected signal shown on the right hand side of Figure 8B changes from a peak value to the lower value by means of a less steep slope compared with the signal to the left o~ Figure 8A. By providing threshold values at A, B, C and D it is possible to provide a measure of the slope and hence the "halo" effect. In this way, therefore, it is possible to measure the degree to which the beam cross section is sharp and hence the "distinctiveness of image". More thresholds may be used.
The green(514 nm) laserbeam will also not be affected by the grating, as it scans across the grating, but will be attenuated by the pink perspex wedge 19. The pink perspex wedge is used to measure the vertical position at which the green beam strikes the retro reflective screen 18. Referring to Figure 1 the wedge 19 is increasingly opaque to the green laser beam as one moves from the upper l9A to the lower l9B edge, Clearly, if the beam strikes the pink wedge towards its lower edge, then the beam will be attenuated to a greater extent than if it strikes the wedge near its upper edge. Thus, the signal output of light sensitive detector 65 which effectively measures the amplitude of the specularly reflected component of the green laser beam will vary depending upon the position in which the g~een l~ase,c ~eam,s,trlikes th~q pink wedge 19 and this is in turn, as is clear from Figures 1 and 2, a measure of the angle at which ;the incoming beam is reflected from the surface of the vertical body 11. The normal position in which the beam strikes the pink wedge 19 ;will be known (from, for example, a computer memory) and changes, particularly rapid changes, from that known position and hence known value of the output signal of detector 65 will be a further measure of 200373~
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defects SUCIl as dents in the body surface.
As has already been described, the red (633 nm) laser beam will not be affected by the grating nor indeed by the pink wedge 19 and so, the specular component of the returning red beam which is detected by the detectors 66,67 is also to be used to provide information about ;
discrete defects such as dirt inclusion in the paint ~ ~
and scattering type defects such as scratches or ;
sanding marks. ;;
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The arrangement of the optics is such as to focus onto the front end of the optical fibres 59 and 60 an image of the retroreElector 18. Thus, the central fibre 59 will pick up the specular light and the surrounding optical fibre 60 will pick up light which has been scattered.
As already described, the diffuse light in the three coLours from the car body surface is collected separately by the fibre optic 48. In order to obtain relevant colour information it is necessary to separate the three colours by optical means, such as beam splitters like the beam splitters 51,52. The three-beams may then be separately detected and the colour of the body surface determined from those three separate beams. If, howéver, it is only desired to look atithe combined beam, then the fibre optic 48 is arranged to pass the combined beam to the light sensitive detector 63 and the light sensitive detector 63 may be used to provide information regarding gross surface defects in highly curved areas where the specular beam may be deflected so much that it does not come into contact with a retro reflective screen.
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. ~ . , -As already discussed, the apparatus also provides twodynamic focusing systems. As the upper housing 14 is at some distance from the position where the beam strikes the sur~ace of the motor car 11, as the depth of focus of the beam at the surface of the car panel is only about 62 mm it is necessary to provide a first focusing means 25 to focus the outgoing beam onto the surface and a second focusing means 43 to focus the returning beam onto parts of the optical apparatus.
The first dynamic focusing means 25 for focusing the outgoing beam comprises, as already describied, the rotatable tilt mirror 29, the tilted lens 32, and roof mirrors 33.
: ': ' It will be understood that by tilting the mirror 31 the beam (which is a laser beam of very small transverse dimensions) is swept from one edge (the lower edge in figure 4A) of the lens 32 to the opposite (upper) edge.
As is clear, the beam passes from the lens 32 to the roof mirrors 33 and:back to the lens 32. Thus, if the beam is adjacent the lower edge of the lens 32 (and ignoring for the moment the lenses 36,37) then the distance from the lens 32 to the.roof mirrors 33 and back to the lens 32 is much less than if the beam is adjacent the upper edge of the lens 32. The effect of this i's shown ih Figure S in which the~'roof,~ir~rors have been omitted and the optical system opened out showing the beam passing from the lens 32 back to the lens 32. In fact, we show two beams Bl and B2 which although narrow (their widths are much exaggerated in the Figure for clarity) are not collimated and show the focusing effect of the lens 32. The input field or object plane which is curved is indicated as O and the image plane is indicated as I(which is also curved but .
: , -` 2003734 ' ' ~ ' '' is predominantly at an angle to the optical axis). -The mirror 31 may be tilted in accordance with a predetermined program, which may be held in the memory of a computer, for a particular motor vehicle. Thus, the mirror 31 may be tilted at varying angles to maintain the surface of the car body 11 in focus throughout the scanning of the beam 22 across the surface of the body of the motor car 11.
Apart from utilising a computer memory of the body shape to change the focus, one may use the signals obtained from the optical head itself. If the relationship between the optical head 14 and the retro reflective screen 18 is fixed then the position of the specularly reflected spot on the retro reflective screen 18 can be measured by interpreting the signals - - ~ -~
from the blue and green beams. This, together with the knowledge of the scanning geometry is enough to predict the focus position.
:' " :' At this point, it would be useful to refer to Figure 9. -In this arrangement, a lens 35 corrsponding to lens 32 is not tilted, but its optical axis coincides with the :,: "., : ,- ":" , optical axis of the apparatus. The lens 35 has effectively a curved input field or object plane 0.
The èffecit of t~ib`curved object plane O is t!o make a i -i curved image plane I which effectively varies the focus. As in Figure 5 we show two beams which although narrow (they are muc7l wider in the figure for clarity) are not collimated and shows the focusing effect of ;~
lens 35. A combination of the effect of Figure 9, together with that of Figures ~A and 4B can produce a dynamic focusing means. ~- -, ,: :, ::
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In some circumstances, the arrangement of Figure 9 may be sufficient without the arrangement of Figures 4A and 4B.
We will now describe the second dynamic focusing means 43 for focusing ti-e incoming beam onto the optical components.
Whilst it is theoreticaly possible to use, as a second dynamic focusing system, a system similar to the first dynamic focusing system, in practice the syste~ would need to be able to cope with much larger beam widths and a greater range of change of focus. Thus the system would need to be very large and require special lenses. Figures 6 and 7 show a preferred second dynamic focus system as already described.
Referring firstly to Figure 6, which shows a simplified version of the path over which the incoming beam 42 passes from the panel 21 to the mirror 47. Panel 21 is shown in two alternative positions 21A,21B which illustrates the change of distance from the optical apparatus within the housing 14 to the panel 21 as the beam is scanned across the panel surface. The incoming beam 42 passes through mirror 41 which focuses an image of the panel 21 to an image point P, and this image ;`
point P is relayed via lens 46 onto the mirror'47. The second dynamic focusing means 43 is provided to vary -~-the optical distance between the lens 41 and the image point P so that the image point P and the panel 21 remain at conjugate points with respect to the lens 41 even as the panel 21 moves with respect to the lens 41 between positions 21A and 21B.
Figure 7 shows the apparatus 43 for carrying this out.
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The incoming beam 42 which is to be focused is reflected twice at the two mirrors 45A,45B. There are shown two focal points FB and FA which corre~pond to the points at which the lens 41 would focus an image of the panel surface 21 when at respective positions 21B
and 21A. It will be seen from Figure 7 that rotation of the mirror pair 45A, 45B about the axis 61 enables the incoming beam to be focused to the point P in both cases. Thus, considering the panel being positioned in panel position 21A in which case the image would be brought to focus at point FA, thenif the mirrorsystem is in position X3 then the optical path length R.FB
must equal the optical path length R.S.T.U.V.P. ~ -Similarly, when the panel is in position 21A, the mirror pair is in the position Xl and the optical path length T.FA must equal path length T.U.V.P.
', ,. .:';' ,': ,; :~, By a suitable choice of angle between the mirror surfaces of the two mirrors 42A, 42B, the incoming beam 42, the distance between the axis of rotation 61 and the mirrors 45A, 45B the point P may be maintained stationary, as the mirrors 45A, 45B are rotated about the axis~61 to compensate for changes in the distance between the lens 41 and the panel 21. ;~
Referring back to Figure 3, the rotable mirror 31 may ;;
also rotate the beam` to the angle A,when the beam will pass through the lens 32, and then through the lenses 37,36 before being reflected at the roof mirrors 33 back through the lens system 36,37 and lens 32. The `~
effect of the lenses 36,37 is to spread the beam so as to provide a slot shaped cross section beam (the axis ~of the slot being arranged to be transverse the line of scan). In the apparatus described, as the beam 22 is scanned in a first direction (say left to right in ;~
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Figure 2) then a beam of the circular cross section shown in Figure 8A is provided by the mirror 31 being tilted between angles A and B and when the beam is scanned in tlle other direction, from right to left as shown in Figure 2, thenthe beam is switched by tilting the mirror 31 to angle A whereby the beam passes through the lenses 36,37 to provide a slot shaped cross section beam. This slot shape has advantages for detecting the extent of a defect as will now be described.
With a small spot as shown in Figure 8A, defects such as distinctness of image (DOI) dents, orange peel and scratches can be detected as has already been described. A slot shaped laser spot can be used to detect discrete defects such as dirt inclusions and colour defects.
It also allows one to inspect the whole body ofthe car by means of the slit whilst only inspecting part of the body with the spot as shown in Figure 8A, which means that the scan can be slower, which produces a lower electronic band width with better signal to noise ratio, or else the body may be scanned in a shorter time.
T~e'size~of~ the !slot shaped cross section!beam is approximately 3mm long and 0.6mm wide. The size of small dirt inclusions may be measured by determining the extent to which they reduce the signal. Thus, if the slot is'larger than the dirt inclusions, then not all of the signal will be attenuated and'the degree of attenuation gives some measure of the extent of the dirt inclusion. Small dirt inclusions may be acceptable but larger ones may be unacceptable.
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- 2~ -The invention is not restricted to the details of the foregoing example.
We have chosen a particular set of colours: blue, green and red for the beam, yellow for the grating and pink for the wedge. Other combinations of colours, particularly for the grating and wedge may be used and ;
the particulars are given as examples only.
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The second focusing means has been provided between the ;
lens 41 and the point P. However, it could be provided between the point P and the lens 46 or, indeed, between ~- -the lens 46 and mirror 47. - ;-Many parts of the apparatus may be used in other types of apparatus. Thus, for example, both the first and . .. . .. .
second dynamic focusing means (referred to in the introduction as the first and second aspects of the invention) may usefully be used to focus dynamically from moving object planes onto a fixed image place (or vice versa).
: ",. ~ " ~ "
Similarly the use or a beam of different cross-sections ~ ;
(the third aspect of the invention) at different points ;~ -~
in the beam has widespread application in other (usually inspection) apparatus.
Also the use of a composite beam comprising a plurality of beams of separate, distinct wavelengths (the fourth aspéct of the invention) has many uses in other apparatus. ;~
The means for analysing the sharpness of a beam cross~
ection (the ~ifth aspect of the invention) may also be ,,, ~ , ~:
' ; :`.' ':
used in other inspection apparatus.
Although the apparatus has been described in terms of inspecting a surface, the principle of the apparatus may be applied to inspecting, for example, article such transparent articles such as film whereby the radiation passes through the article. In this case, where the radiation is transmitted through the material, in addition to detecting defects on the surface of the material, bulk defects, that is defects within the bulk of the material, :. :. .:-:, . ~
may also be detected. :~
: , .- ~ ,:. ,::
:, : . .:
.
:. ,: : . .
~: ~' '', ; ~
' ~ ~
:' ~' ~' ~ ' ,',', ' ' '; " ~ ' . ~
" ' :~' " ": '.:' ',' ' ' ,', ~' ' '' ~`. ' " ~ '', "' ~.
,' ~
Claims (19)
1. An optical apparatus including focusing means (41), an optical axis, an object point (31) and an image point on said optical axis, said object point being movable along the optical axis with respect to the focusing means, means being provided to change the effective optical distance between either the object point and the focusing means or between the image point and the focusing means to maintain the object point at a fixed point even if the image point moves.
2. An optical apparatus as claimed in claim 1, characterised in that the focusing means remains stationary, and the means for changing the effective optical distance comprises a movable non-focusing element.
3. An optical apparatus as claimed in claim 1 or 2 characterised in that means is provided to move said movable non-focusing element in such a way that continuous changes in the continuous movement of the object point is compensated so that the image point remains stationary at all times.
4. An optical apparatus as claimed in claim 3 characterised in that said means comprises a movable mirror.
5. An optical apparatus as claimed in claim 4 characterised in that the movable mirror (43) comprises two mirrors (45A, 45B) at an angle to one another and being rotatable together about an axis to one side of the optical axis.
6. An optical apparatus as claimed in claim 5 characterised in that the two mirrors (45A, 45B) are at right angles to one another to form a corner cube.
7. Optical apparatus as claimed in any of claims 1 to 6 further characterised by means to pass a beam of radiation across a surface to be inspected, beam shaping means (36, 37) being provided whereby at different points during said movement, the cross section of the beam of radiation is changed so as to detect different types of fault.
8. Optical apparatus as claimed in claim 7 further characterised by means to scan a beam of radiation back and forth across a surface to be inspected, said beam shpaing means (36, 37) being operable to provide one cross section of beam whilst the beam is scanning across the surface in one direction, and a second cross section whilst the beam is scanning across the surface in the opposite direction.
9. Optical apparatus as claimed in claim 7 or 8 characterised in that one of the cross section shapes is circular, and the other slot shaped.
10. Optical apparatus as claimed in any of claims 7 to 9 characterised in that said beam shaping means (36, 37) comprises optical components to change the shape of the beam, and means (29) to selectively pass said beam through said optical components.
11. An optical apparatus as claimed in any of claims 1 to 10 characterised in that there is provided a composite beam comprising a plurality of beams of separate, distinct wavelengths, whereby some optical components (17) in the apparatus sensitive to wavelength affect the different beams in a different manner, and other optical components not sensitive to wavelength affect all of the beams in a similar manner.
12. An optical apparatus as claimed in any of claims 1 to 11 characterised in that means (38) is provided to pass a beam of radiation to a surface to be inspected, means (38) is provided to collect the beam from the surface, and means (36, 37) is provided to determine the sharpness of the cross-section of the beam collected from the surface under inspection.
13. An optical apparatus as claimed in claim 12 characterised in that said collected beam (70) is passed over an opaque edge (20), and then to a radiation detector (64), and means (72, 70) being provided to determine the shape of the beam cross section from the output of the signal detector.
14. An optical apparatus as claimed in any of claims 1 to 13 characterised by optical means (25) for varying the focusing effect of a focusing component (32), said optical means (25) including a main optical axis (27), the focusing component (32) being on said main optical axis (27) and having an optical axis (35), the focusing component (32) being tilted so that the two optical axes (35, 27) are tilted with respect to each other and means (29) being provided to pass a beam of radiation through said focusing component (32) at a variable transverse position with respect to the main optical axis (27) to thereby vary the focusing effect of said focusing component (32).
15. An optical apparatus as claimed in claim 14 characterised in that the means (29) to move the beam comprises a tiltable mirror (29).
16. An optical apparatus, including optical means (25) for varying the focusing effect of a focusing component (32), said optical means (25) including a main optical axis (27), the focusing component (32) being on said main optical axis (27) and having an optical axis (35), the focusing component (32) being tilted so that the two optical axes (35, 27) are tilted with respect to each other and means (29) being provided to pass a beam of radiation through said focusing component (32) at a variable transverse position with respect to the main optical axis (27) to thereby vary the focusing effect of said focusing component (32).
17. An inspection apparatus including means to pass a beam of radiation across a surface to be inspected, beam shaping means (36, 37) being provided, whereby at different points during said movement, the cross section of the beam of radiation is changed so as to detect different types of fault.
18. An optical apparatus including means (23A, 23B, 23C) to provide a composite beam comprising a plurality of beams of separate, distinct wavelengths, whereby some optical components (17) in the apparatus sensitive to wavelength affect the different beams in a different manner, and other optical components not sensitive to wavelength affect all of the beams in a similar manner.
19. An inspection apparatus in which means (38) is provided to pass a beam of radiation to a surface to be inspected, means (38) is provided to collect the beam from the surface, and means (36, 37) is provided to determine the sharpness of the cross-section of the beam collected from the surface under inspection.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8827297.6 | 1988-11-23 | ||
| GB888827297A GB8827297D0 (en) | 1988-11-23 | 1988-11-23 | Inspection apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2003734A1 true CA2003734A1 (en) | 1990-05-23 |
Family
ID=10647279
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2003734 Abandoned CA2003734A1 (en) | 1988-11-23 | 1989-11-23 | Inspection apparatus |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA2003734A1 (en) |
| GB (1) | GB8827297D0 (en) |
| WO (1) | WO1990005907A2 (en) |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2053017A1 (en) * | 1970-10-29 | 1972-05-04 | Grundig Emv | Method for contactless distance measurement |
| NL7206376A (en) * | 1972-05-11 | 1973-11-13 | ||
| GB1403911A (en) * | 1972-07-26 | 1975-08-28 | Sira Institute | Method and apparatus for testing optical components |
| JPS5343303B2 (en) * | 1973-02-28 | 1978-11-18 | ||
| JPS59148025A (en) * | 1983-02-14 | 1984-08-24 | Victor Co Of Japan Ltd | Focus adjusting method |
| GB8424084D0 (en) * | 1984-09-24 | 1984-10-31 | Sira Ltd | Inspection apparatus |
-
1988
- 1988-11-23 GB GB888827297A patent/GB8827297D0/en active Pending
-
1989
- 1989-11-17 WO PCT/GB1989/001372 patent/WO1990005907A2/en unknown
- 1989-11-23 CA CA 2003734 patent/CA2003734A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO1990005907A3 (en) | 1990-07-12 |
| WO1990005907A2 (en) | 1990-05-31 |
| GB8827297D0 (en) | 1988-12-29 |
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| Date | Code | Title | Description |
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| FZDE | Dead |