VIEWING APPARATUS

Abstract: Viewing apparatus comprises an array of mirrors surrounding an object under examination with the mirrors disposed relative to the object and to one another in such a way as to be able to present, in a single plane, a composite representation of the object derived from a series of images seen from a variety of viewpoints spaced around the object. The invention also includes a quality control system using the viewing apparatus as the primary sensor.

Description: VIEWING APPARATUS The present invention relates to viewing apparatus. Quality control processes are increasingly being automated due to the expanding capabilities of available sensing systems, especially those using machine vision techniques. Within the machine vision industry, the sensors used are predominantly focal plane array charge-coupled device (CCD) cameras, although electron tube cameras can still be useful for some tasks. These cameras operate by transferring a scene of interest by optical means to form an image on a two-dimensional grid array of sensing elements or a photosensitive surface which provide electronic capture of the scene for subsequent processing bv a dedicated computer. If the surface of the object under investigation is essentially three-dimensional in form (as compared to the surface of a fabric, for example, which is essentially two- dimensional), then a minimum of two cameras will be required to view the whole surface and, in practice, three are usually employed. This incurs considerable expense and. in addition, a relatively sophisticated computer program will be required to enable the computer to correlate the information it receives from the three different cameras and to take account of the fact that some of this information may be in part duplicated, owing to the fact that some regions of the object surface will be seen by more than one camera. A further drawback is that the high cost of some cameras dictates that economical usage limits the number of viewpoints to 2 or 3 to view the entire object. Each of these cameras will be accepting light over a relatively large included angle so that the intensity of at least some of the incident light will almost certainly have been augmented by specular reflectance at the object surface due to the position of direct light sources. This will tend to result in the occurrence of spurious "bright spots" at the associated camera. This problem is exacerbated when in addition to being three-dimensional, the object surfaces are also significantly non-uniform, as will be the case with many agricultural products for example. In its broadest aspect the present invention comprises viewing apparatus operative to transpose the views of an object or object surface seen from two or more different viewpoints into a single two-dimensional representation. In preferred embodiments, there will be at least five said viewpoints circumferentially spaced about the object or object surface so as to give different views of the object or object surface. Conveniently, the apparatus includes a circumferential arrangement of reflecting surfaces disposed to present said different views side-by-side in said two-dimensional representation. The principal advantage of taking multiple viewpoints around an object is that the distonion when transferring a viewed object to a single plane is reduced as the number of radial viewpoints increases. This is important as a minimum feature on the surface of the subject may otherwise not be resolved to its full extent. For example, if one considers the three viewpoint systems of the prior art systems mutually positioned at 120° to each other, then it is possible, when viewing an object of circular cross section, to transfer an area, say a rectangular area on the curved surface with length twice the breadth, to a square on the transferred plane. The distortion maximum with a ten viewpoint system, however, is a maximum of 1.07 as a fraction of length/breadth. Conveniently, the viewing apparatus of the present invention also includes an array of reflecting surfaces disposed to present the different views side-by-side in said two- dimensional plane. Conveniently, the reflecting surfaces of the circumferential arrangement are disposed to present said side-by-side views in the same sequence as occurs in the object or object surface viewed. Conveniently, the reflecting surfaces of the circumferential arrangement are disposed to present each of said side-by-side views with the same reversed or non-reversed and the same inverted or no-inverted format as one another when compared with the object or object surface viewed. Conveniently, where the apparatus is operative to present side-by-side views in the same sequence and reversed/non-reversed, inverted/non-inverted characteristics as one another when compared with the object or object surface being viewed, then the apparatus includes a viewing point for direct observation by a manual operator. Conveniently, the apparatus of the present invention also includes a convener which responds to the visual information in said two dimensional representation to produce and feed a corresponding electric signal into a computer or like monitoring device e.g. a microprocessor. Conveniently, the monitoring device is operative to monitor said side-by-side views in the same sequence as occurs in the object or object surface viewed and/or to correct for any differences in format as regards reversal/non-reversal or inversion/non-inversion of the side-by-side views so as in effect to monitor the side-by-side views as though they had the same reversed or non-reversed and the same inverted or non-inverted format as one another when compared with the object or object surface viewed. According to another aspect, the invention comprises a quality control system comprising apparatus as claimed in any preceding claim operative to actuate a selector to divide objects leaving the apparatus into objects which satisfy predetermined criteria and objects which fail to satisfy said criteria. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic and part-diagrammatic drawings, in which: Figure 1 is a simplified perspective view of the general construction of a viewing apparatus according to a first embodiment of the invention; Figure 2 is a perspective view of a test object to be viewed in the apparatus; Figure 3 is a side view of a ten viewpoint central mirror system used in said first embodiment, the path of the light through that system being also indicated in the Figure: Figures 4A, 4B and 4C. collectively referred to as Figure 4, are perspective views illustrating one of the two side mirror systems used in the first embodiment, the path of the light through that system being also indicated in Figure 4A; Figure 5 shows the two side mirror systems as they will appear when viewing the apparatus in plan view, the paths of the light through those systems being also indicated in the Figure: Figure 6 shows the two dimensional representation of the test object as it would be seen by the human eye when the test object is in place in the apparatus of Figure 1 : - Figures 7A. 7B. 7C and 7D, collectively referred to as Figure 7. are side views of four different designs of eight viewpoint central mirror systems for use in the first embodiment of the invention, the path of the light through the system being also indicated in the Figure: Figures 8 and 9 are side views of a twelve viewpoint and twenty viewpoint central mirror system respectively, the path of the light through that system being indicated in each case: Figures 10A, 10B and IOC. collectively referred to as Figure 10. are respective side, plan and end views of a horizontal feed system for use with the apparatus of Figure 1 : Figure 1 1 is a side view of a gravity feed system for use with the apparatus of Figure 1 when re-orientated so as to have a vertical rather than a horizontal feed passage: Figure 12 is a side view of Figure 3 modified to produce viewing axis which converge to allow complete imaging of the views by a lens system, in place of the parallel viewing axis shown in Figure 3; Figure 13 illustrates a multi-spectral sensor unit for "waveband imaging" of objects within the viewing apparatus; Figures 14A and 14B. collectively referred to as Figure 14. show a schematic of a conversion unit operative to convert optical information received from the multispectral sensor unit into an electric signal output to a processing unit: Figure 15 shows a quality control system incorporating the viewing apparatus of Figure 1. the multispectral sensor unit of Figure 13 and the conversion unit of Figure 12; Figures 16A and 16B. collectively referred to as Figure 16. show the operating characteristics and spectral sensitivity of two types of camera used in a preferred embodiment of the invention namely typical characteristics for an electron-tube camera (Figure 16A) and typical sensor characteristics for a CCD sensor (Figure 16B); and Figure 17 illustrates a narrow-width ten viewpoint central mirror system according to vet another embodiment of the invention. Thus referring first to Figure 1 of the drawings, a viewer 12 according to the present invention comprises a box 14 to the floor of which are secured a central support structure 16 for a central mirror system 18 (Figure 3) and the respective side support structures 20.21 for the two side mirror systems 23.24 (Figure 5). Four "light- folding" mirrors 26.27,28,29 are secured in the box 14 as shown to span the width of the three support structures 16,20.21. The walls of these latter are apertured. as are the side walls of box 12. to provide a feed passage or viewing chamber 31 extending from one side of the apparatus to the other. If desired, a transparent cylindrical tube may be secured within the apertures to protect the mirror system from any dust or dirt falling off the objects under examination. One example of this is identified by reference numeral 33 in Figure I OC. A suitable material for the feed tube would be polycarbonate flexible sheeting, for example or toughened glass, provided the transmission characteristics of the chosen material was compatible with the wavebands imaged in the multi-spectral sensor unit. As already indicated. Figure 2 shows a test object 35 which may be used in checking that the various mirrors in systems 18.23 and 24 are all at the required setting. This same object will also be referred to in explaining the manner in which the mirror systems operate. The test object shown in Figure 2 comprises a decagon core section 37 with a right-angled prism 39,40 either end. The core section facets of the object 35 are sequentially numbered from "1 " to " 10" with the "bottom" of each facet number adjacent to the "top" of the following facet number. The upright faces of the end prisms 39,40 bear upright numbers "1 ". "2" (prism 39) and "3"."4" (prism 40). Figure 3 shows a side view of a ten-viewpoint central mirror system with the test object in place in the viewing chamber. It will be noted that the top and bottom facets of the object are reflected seven times before viewing at the viewing port 42 while those of the middle facets, for example, are reflected ten times. It will be noted that the image of the numbers on the longitudinal faces of the test object is reversed (left to right and vice versa ) on each reflection. Inversion (top to bottom and vice versa) occurs after reflections in mirrors which are convergent in the vertical plane ( as is the case with mirrors 26 and 27. say) but not when the mirrors are parallel in that plane (as is the case with mirrors 28 and 29, say). It will also be observed from Figure 3 that the optical path length from the viewing point to the surface for each facet of the test object does vary, so it is desirable to set a long viewing distance such that the error in focus for a viewing sensor is minimal. This is done by increasing the overall path length in the system which is at the same time kept reasonably compact by "folding" the light path in the way shown in Figure 3. This allows direct viewing by an observer or camera system at a point adjacent to the viewing apparatus. In all embodiments, the reflecting elements preferably have the reflective coating applied to their front surfaces, thereby minimising light attenuation through the glass substrates as in common mirror type systems. Figure 4A shows the mirror arrangement in the more remote mirror system 23 of the two side systems 23.24. This Figure also illustrates how the light from the furthest end (40) of the test object is reflected around that system. Both the side mirror systems 23.24 are shown in the plan view of Figure 5. In both these systems, the final beam of light is discharged horizontally from the system towards "light-folding" mirror 26 but. for clarity, only the centre line of the top beams (e.g. beam 44 in Figure 4A) is shown in full line while the outer limits of the bottom beams (e.g. beam 45 in Figure 4A) are shown in broken line. Regarding the orientation and inclination of the reflecting surfaces of the various mirrors, mirror pairs 46.48 and 47.49 have vertical reflecting surfaces inclined at 45° to the axis of the feed passage 31. the reflecting surfaces of mirrors 51,52 lie parallel to the feed passage axis but inclined at 45° to the vertical, and the reflecting surfaces of mirrors (54,55 lie at 45° to the axis of feed passage axis and at 45° to the vertical. The dispositions of mirrors 54,55 are further clarified in the enlarged views of Figures 4B and 4C where the right-angles 90° have been marked as such. The remaining angles marked are all 45°. In both these Figures upper surfaces Η of the items concerned, lie in the horizontal plane. To summarise then, in the embodiment of Figures 1 to 5. in the central mirror system, there are ten separate viewpoints, that is the lines-of-sight of the views are radially disposed around the object at intervals of thirty-six degrees whilst the side mirror systems allow transposition on the same total view of another set of views taken at forty-five degrees to the previous set and oriented such that the ends or apices of an object can be viewed, with two views taken at each end. With the test object lying parallel to the feed passage axis as shown in Figure 2 and orientated so as to have its facet number " 1 " uppermost, the composite image produced in a single vertical plane to an observer at the viewing port 42 will be as depicted in Figure 6. the four separate displays in that Figure corresponding to the vertical faces of the end prisms 39.40 of the test object. It should also be noted that image inversion of the numbers on the facets of the test object will occur when, for the images concerned, reflections have taken place at an odd number of converging mirror pairs ( as already explained above with reference to Figure 3). Lastly, it will also be noted that the images of the prism faces "1 " to "4" are inclined at 45° as shown in Figure 6. In one particular form, the test object of Figure 2 might, for example, have a body portion in the form of a decagon with pre-defined facet dimensions of 25 mm x 160 mm and four facets of size 57 mm x 80 mm disposed at forty-five degrees to the viewing axis at each end of the decagon. This represents the maximum sized object that could be viewed with the apparatus of Figures 1 to 5. Objects which are significantly under this size will, when viewed, show commensurate overlap in each segment of surface features seen from a particular viewpoint. For example, objects which have a maximum dimension less than one half of the maximum described will only require one half of the available viewpoint (alternate viewpoints) to fully view the surface. Turning now to Figure 7A. this shows the reflection that will occur within the central mirror system of an eight-viewpoint arrangement. Reference numerals 57 in this (and subsequent) Figures indicate tungsten-halogen lamps mounted adjacent to the feed path 31 on the internal faces of support constructions (20.21) for evenly illuminating the object under investigation while it moves through the feed passage. Similar lamps will also be mounted in a similar fashion between the reflected beams in the arrangement of Figure 3 to give a total often in all but these lamps have been omitted from Figure 3 for clarity. By having a series of tungsten-halogen lamps to provide illumination point sources radially disposed around the viewing chamber as shown, adequate illumination of the chamber is achieved without the intrusion of the lamps themselves within the required field of view. Because the lamps are at either end of the feed path, the angle of illumination to a typical body under investigation is oblique with respect to the viewing axii and this ensures that specular (or mirror-like) reflections from the body are minimised. This is important where, as is usually the case, diffuse reflectance is being investigated. The only specular reflected light rays viewed will be those which are incident upon a particular pan of the body that allows the reflected rays to transmit through the viewing chamber. substantially perpendicular with the feed passage axis. Returning now to Figure 7 A. the images of the numbers on the eight sides of a i now eight-faceted) test object(not shown) have been indicated at various points along the path of the light through the central mirror system. It will be noted that in the composite single- plane representation produced in this embodiment, the images of the numbers on two of the sides ("3" and "7") are neither inverted nor reversed while the remainder of the images are both inverted and reversed. It is also to be noted that in the single plane representation, the image numbers do not run sequentially as they do in the test object. Both these discrepancies can be corrected by appropriate image processing in a dedicated computer . This will "convert" all the images in the representation so as to "see" them with the same inversion/non-inversion and reversal/non-reversal characteristics and sequentially arranged. In this latter respect, it will be appreciated that it makes no difference whether in the single plane representation, the image numbers run from " 1 " to "8" or in the order ("2" to "8"." 1 ") or ("3" to "8". " 1 ", "2") etc. as long as they are sequential (on the test object, the highest and lowest numbers are of course adjacent). Figure 7B shows another eight-viewpoint design of central mirror system in which two of the beams are split by split-mirrors 59,60 and are either recombined again in the middle of the single plane representation (left hand vertical face of the test object) or are disposed at opposite ends of the representation (right hand vertical face of the test object). In this arrangement, the image numbers of the faces run sequentially but. once again, some are inverted and reversed while others are neither.. Figure 7C shows yet another eight viewpoint design in which the image numbers can be made to run sequentially by means of an appropriate mirror arrangement 62,63,64 in place of the beam-splitter 59 and mirror 66 etc. in place of beam-splitter 60. Once again the image numbers run sequentially and the images as they will appear at various points in the system are indicated. It will be noted that the images of facet numbers "3" and "7" are "correct" while those of the remaining facet numbers are inverted and reversed. Figure 7D shows a modification of the Figure 7C embodiment in which mirrors 62 and 63 in the Figure 7C embodiment have been replaced by mirrors 62A. 62B. 62C and 63A. 63B respectively in the Figure 7D embodiment. Since the image of vertical facet number "3" is now reflected by an odd number of mirrors and the vertical orientation of the mirrors is such as to produce image inversion, it follows that the image of facet number "3" will now be inverted and reversed in the single plane representation in the same way as those of object facets " 1 ","2","4"",5","6" and "8". A similar optical system (not shown) can be used to reverse and invert the image of facet "7". This has the result that the final display in the single plane representation will have all the images sequential and with the same reversed/non-reversed and inverted/non-inverted characteristic. Thus in this case there is no need of a computer to reverse or invert any of the images as a consistent representation is already in place. Figures 8 and 9 show the light paths for 12-viewpoint and 20-viewpoint systems, respectively. Once again, unless modified in accordance with the teaching of Figure 7D. the various images will not run sequentially and some of them will have different reversal/non-reversal and inversion/non-inversion characteristics to others. Although in the most basic form of the viewing apparatus, the objects to be scanned may be placed one by one within the viewing chamber with the object in a preferred longitudinal orientation and its longitudinal axis preferentially coincident with the centre axis of the chamber, in the more sophisticated versions, a convenient transport means may be employed for passing objects sequentially through the chamber. Figure 10 shows a convenient form of horizontal feeder for this purpose comprising an array of differently tensioned horizontal wires 68. Each of these wires has a horizontal run which passes through the transparent cylindrical tube 33 secured within the apertured walls of item 14.16.20,21 to define the viewing chamber in this embodiment. As will be clear from Figure 10B. the resiliently sprung tension adjusters 70 have been set so that the tensions of the wires are graduated to produce a tension "profile" with the tension of the wires increasing as one passes from the most highly tensioned outer wires of the array to the least tensioned middle wire. When an object is being carried by the wires, this difference in tension controls the degree of sagging in such a way as to keep that object fairly centrally located within the tube 33 as is best seen from Figure IOC where reference numeral 72 indicates an irregular object, such as a potato, being transported through the system. The loading of objects on to the feeder wires prior to their passage through the apparatus may be accomplished using any suitable means, for example, using the flighted conveyor 74 shown in Figure 10A. In an alternative arrangement shown in Figure 1 1. the viewing apparatus is re¬ orientated to have a vertical viewing chamber and the objects to be viewed, such as potato 76. are dropped into the upper end of tube 33 using a pair of horizontal transporter belts 78.79 disposed relative to one another in a V-formation. A snapshot of the object as represented in the single plane composite representation produced by the apparatus can then be taken by an appropriately activated camera as each object passes a predetermined point in the viewing chamber e.g. as detected by sensor 81 in Figure 1 1. As already indicated, according to another aspect, the invention includes the combination of a viewing/scaruύng apparatus with a conversion unit adapted to change the information displayed in the single plane composite representation from an optical format into a corresponding series of electrical signals e.g. for processing by a dedicated computer or microprocessor. One such arrangement is shown representatively in Figure 14 and diagramma ically in Figure 15A where the image acquisition unit (100) and processing unit (101 ) are linked to the multispectral sensor (85). In Figure 14A, reference numerals 104.105.106 and 107 respectively indicate a signal timing extraction unit (104). an analogue to digital conversion unit (105), an image pre-processing unit ( 106) and a memory unit (107). The same reference numerals have been used to indicate the same elements in the conversion unit of Figure 14B which shows, by way of example, how a typical image (that produced in the Figure 7a system) can be transported by appropriate data-handling steps in the software to the correct orientation and sequence in the memory store 107. In yet another aspect, the invention comprises a quality control system including the optical viewing/scanning apparatus, a conversion unit, a computer comparing the signal received from the conversion unit with a predetermined standard indicative of an object in acceptable condition and an actuator responsive to a signal from the computer to activate a reject mechanism which will remove from any objects leaving the viewing apparatus, those which have been shown not to satisfy the predetermined criteria required. One such arrangement is shown in Figure 15 where the objects are transported from the viewing chamber (12) by the wire transport mechanism (69) and a two way grading mechanism is realised by a moving deflector arm (102) passing objects to either conveyor (103). With the embodiments so far described, the field of view issuing at the viewing port 42 will, in a commercial automatic viewing system, be fitted with a converging lens system to focus the light on the objective lens of a camera system or the like which will convert the optical input into an electric signal output e.g. for feeding into a computer. For a simpler system, it may be more convenient to minimise or avoid the transfers of the Figure 14 arrangement by setting the geometry of the mirrors more appropriately, and this would be certainly more convenient if a human inspector was involved. Thus, in modifications and further embodiments, viewing apparatus in accordance with the present invention may be used as an aid to direct observation by a manual operator, with the viewing position optimised for the human eye. Observations of the whole of the surface of an object can be made. This may have an application in some quality control areas of industry where inspection is performed manually and it is important to inspect the whole surface at optimal speeds. Examples may be in the examination of the quality of extrusion processes and products, pipe-drawing, products which are currently inspected over a conveyor etc. This last example, if the product and conveying system are inherently clean. may be embodied into the viewing system by the use of a transparent material as the conveyor material, thus allowing all-round viewing. One such apparatus is illustrated by way of example, in Figure 12 which shows an inspector's eye position and the viewing paths for two adjacent segments of an object's surface. This apparatus uses a system of staggered mirrors 83 arranged to produce a field of view that converges as shown. The internal mirror system is identical with that shown in Figure 7d. Returning now to apparatus incorporating an automatic viewing system, a staggered mirror system identical to system 83 can once again be employed to converge the light, but this time on to the imaging objective lens of a multi-spectral sensor analyser. The basic requirements of the multi-spectral sensor show that eight wavebands are required. These view a common field-of-view by the use of beam-splitters (special coatings applied to a glass substrate which allow some radiation to be transmitted and some reflected). Narrow-bandpass filters are situated adjacent to the cameras which restrict the incident radiation to the wavebands desired. One such sensor is shown in more detail in Figure 13 and comprises an objective lens 87, filters (as indicated by way of example at 89), CCD (charge coupled device) silicon based cameras (as indicated by way of example at 91 ), eyepiece lenses (as indicated by way of example at 93), beam-splitters (as indicated by way of example at 95) and a special infra-red camera 97. In a scanner adapted for use with agricultural produce, the multi-spectral sensor has to include both the CCD silicon based cameras as well as a special infra-red camera because although most of the required wavebands for the application of disease/defect detection occur below 1 100 nanometres, the operating limit for CCD cameras, one waveband occurs at around 1660 nanometres, which requires a sensor to be sensitive to that part of the spectrum. An infra-red vidicon tube camera is conveniently used in this case for camera 97 but there are alterative solid-state cameras that may perform the function equally well. Details on the operating characteristics and spectral sensitivity of the CCD and infra¬ red cameras are reproduced in Figures 16A and 16B, respectively. From the above description in relation to Figure 13. it will be appreciated that throughout the specification and in the accompanying claims, the term 'light' is to be interpreted not only visible radiation but also radiation which is invisible to the human eye e.g. radiation in the infra-red spectrum. Turning lastly to Figure 17. this illustrates a ten viewpoint central mirror system operative to transpose ten individual views to a horizontal plane above the viewing chamber in the manner described in respect of the earlier embodiments illustrated. The resulting narrow-width configuration of the system makes it particularly suited to multi-chamber arrays where the chambers lie side-by-side to provide a multi-lane device in which the width of the device is the minimum consistent with the successful operation of the device. - 1 J-

Claims: CLAIMS 1. Viewing apparatus operative to transpose the views of an object or object surface seen from two or more different viewpoints into a single two-dimensional representation. 2. Apparatus as claimed in Claim 1 in which there are at least e said viewpoints circumferentially spaced about the object or object surface so as to give different views of the object or object surface. 3. Apparatus as claimed in Claim 1 or Claim 2 including a circumferential arrangement of reflecting surfaces disposed to present said different view s side-by-side in said two-dimensional representation. 4. Apparatus as claimed in Claim 3 including an array of reflecting surfaces disposed to present end views of the object or object surface in said two dimensional plane. 5. Apparatus as claimed in Claim 3 or Claim 4 in which the reflecting surfaces of the circumferential arrangement are disposed to present said side-by-side \ lews in the same sequence as occurs in the object or object surface viewed. 6. Apparatus as claimed in any of Claims 3 to 5 in which the reflecting surfaces of the circumferential arrangement are disposed to present each of said side-b> -side views with the same reversed or non-reversed and the same inverted or non-invened format as one another w hen compared with the object or object surface viewed. 7. Apparatus as claimed in any of Claims 3 to 6 including a convener which responds to the visual information in said two-dimensional representation to produce and feed a corresponding electric signal into a computer or like monitoring device. 8. Apparatus as claimed in Claim 7 in which the monitoring device is operative to monitor said side-by-side views in the same sequence as occurs in the object or object surface viewed and /or to correct for any differences in format as regards reversal/non- reversal or inversion/non-inversion of the side-by-side views so as in effect to monitor the side-by-side views as though they had the same reversed or non-reversed and the same inverted or non-inverted format as one another when compared with the object or object surface viewed. 9. Apparatus as claimed in Claim 6 when including the limitations of Claim 5. the apparatus including a viewing point for direct observation by a manual operator. 10. A quality control system comprising apparatus as claimed in any preceding claim operative to actuate a selector to divide objects leaving the apparatus into objects which satisfy predetermined criteria and objects which fail to satisfy said criteria. 1 1. An apparatus or quality control system substantially as hereinbefore described with reference to, and/or as illustrated in. the accompanying drawings.

Inventors: ROSS DAVID WILLIAM, ROSS, DAVID, WILLIAM
Applicants: BRITISH TECH GROUP, ROSS DAVID WILLIAM, BRITISH TECHNOLOGY GROUP LIMITED, ROSS, DAVID, WILLIAM
Application year: 1996
Main classification: G02B27
IPC codes: G01N21, G02B27