Recording Images of a Three-Dimensional Surface by Focusing on a Plane of Light Irradiating the Surface

In copying or reproducing three-dimensional surfaces, heretofore, the conventional technique involves the recording of images of sections of the surface, which are illuminated by a plane of light directed against the surface. The images are recorded of the sections where the plane of light intersects the surface. The plane of light is produced by a projector which directs the light against the surface.

In carrying out the conventional methods for reproducing three-dimensional surfaces, the camera which views the surface and records the intersections of the plane of light and surface sections, is displaced from the projector or the light plane. In practice, the camera is at a substantial angle to the light plane.

When the optical axis of the camera is substantially perpendicular to the light plane, it is possible to locate a surface point and record it on the camera film with particularly high accuracy. However, when that angle is substantially small, substantially poor accuracy is incurred in locating a point on the surface of the object to be reproduced.

Copying systems for reproducing three-dimensional surfaces are conventionally constructed so that small angles prevail between the optical axis of the camera and the light plane, because hidden areas or holes cannot be viewed by the camera when large angles prevail. Thus, shadow effects are present when the reproduction system possesses large angles between the optical axis of the camera and the light plane.

When using such small angles in conventional systems, the camera focus is not suitable for all points of the three-dimensional object surface. Thus, if the camera focus is set for one given point of this surface, the focus cannot be expected to be properly set for other points of a general three-dimensional surface. As a result, the focus is required to be continuously adjusted in conventional systems.

Accordingly, it is an object of the present invention to provide an arrangement in which the camera focus may be set so that it is in proper focus for substantially all points of the surface to be recorded, without having to readjust the setting of the focus for differently located points on the surface.

Another object of the present invention is to provide an arrangement of the foregoing character which is substantially simple in construction and may be economically fabricated.

A further object of the present invention is to provide an arrangement as described, which may be readily maintained in service with substantially long operating life.

The objects of the present invention are achieved by providing an arrangement in which the camera is focused on the light plane in a region about or encompassing the object surface to be viewed.

In accordance with the present invention, planes passed through the film of the camera, the camera lens, and the light plane, all meet along a common line. As a result of this arrangement the camera is in focus with respect to all intersections of the light plane with the object surface, so that images of surface sections illuminated by the light plane appear in focus on the thin plane of the camera.

The construction in accordance with the present invention is achieved by inclining the camera lens plane with respect to the film plane so that these two planes intersect along a line which lies in the light plane transmitted by the projector.

In another embodiment of the present invention, the effect resulting from inclining the lens plane with respect to the film plane of the camera is produced by providing a wedgeshaped coherent fiber optic bundle between the lens and film of the camera. By the use of such a fiber optic bundle, it is possible to use conventional camera structure in which the lens plane and film plane of the camera are parallel to each other.

In a further embodiment of the present invention, the accuracy of the information recorded from the object surface is increased by repeating the entire procedure with a thinner plane of light projected against the object surface. The information obtained from the use of the first plane of light, which is a thicker plane, is stored in a computer. This stored information is then used as a guide for applying a thinner light plane against the object surface for the purpose of locating more precisely a point, for example, on the surface. The procedure can be used, furthermore, successively with thinner planes of light to result in a final predetermined accuracy of points located on the object surface.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

FIG. 1 is a schematic elevational view and shows an arrangement for viewing an object with a camera so as to avoid shadowing effects;

FIG. 2 is a schematic view and shows the relationships among the camera lens plane, camera film plane, and light plane directed against the object surface by a projector, in accordance with the present invention;

FIG. 3 is a schematic view of another embodiment of the arrangement of FIG. 2, using a coherent fiber bundle;

FIG. 4 is a schematic view of an arrangement used to position the object with respect to projector and camera, and to increase the accuracy of the recorded data;

FIG. 5 is a diagrammatic view and shows the relationship between a thicker and thinner light plane for locating a point within them;

FIG. 6 is a diagrammatic view and shows the relationship between a thicker and thinner light plane and the required depth of field.

Referring to FIG. 1, the projector 12 directs a plane of light against an object surface 10. When viewing FIG. 1, the plane of light passes through the optical axis of the projector (x-axis) and is perpendicular to the plane of the drawing. A camera 14 may be angularly displaced from the projector by an angle .theta.. This angle .theta. represents the angle between the plane of light and the optical axis of the camera. The plane of light may be generated by the projector 12 by known techniques using, for example, apertures with slits.

When a camera 16 is positioned so that its optical axis is substantially perpendicular to the light plane, whereby .theta.=.sub.1 =90.degree., the accuracy of locating a point on the object surface 10 is substantially high. The high accuracy condition prevails because a change in the camera ray angle, and therefore the movement of an illuminated point on the camera film plane 18 for a given depth change .DELTA.x on the surface is maximized. When, on the other hand, a camera 14 is located at an angle .theta. which is substantially less than 90.degree., substantially low accuracy is obtained because a large change in depth causes only a small angular change which, in turn, causes only a small movement at the film plane 20. The relationship in accuracies of cameras 14 and 16 placed at different angles with respect to the light plane of the projector 12, may be observed in FIG. 1.

Thus, it may be seen that .DELTA.d.sub.1 /.DELTA.d is much larger than .DELTA.d.sub.2 /.DELTA.d because .theta..sub.1 is much larger than .theta..sub.2. However, although camera 16, in the position shown, provides more favorable accuracies, the camera 14 is more used in practice at a substantially smaller angle with respect to the light plane 22, because the camera 16 experiences difficulties in viewing hidden areas or holes. For example, if the object surface 10 is advanced in increments sequentially in the y direction as pictures are taken by the camera, all surface features on the right-hand side of the object surface 10 shown in FIG. 1 will become eventually illuminated, but only camera 14 will be able to view images of point P and contour C. This results from the condition that the internal curve of contour is hidden from camera 16 because ledge F is in the line of sight from the camera 16. Similarly, ledge B hides point P from camera 16. To avoid such problems in which the camera 16 cannot see all points on the object surface, the camera 14 is used in practice. The camera 14, in the position shown in the drawing, makes it possible to see a large selection of object features without experiencing the shadowing effects encountered by the camera 16.

Camera 14, however, has the disadvantage that when in the position shown in the drawing, where the angle .theta. is substantially less than 90.degree., the camera is not suitable for focusing on all points of the object shown. For example, if the camera 14 is focused along the plane r--r, as in common practice, it may be seen that the lower portion of the object will not be in focus. Similarly, whereas the upper portion of the object may be initially in focus, sections of the surface illuminated by the light plane will not remain in focus, as the object surface is advanced in increments in the y direction. Thus, it may be seen from FIG. 1, that as the object surface 10 is traversed in the y direction, the camera is required to focus from x.sub.1 to x.sub.2. In accordance with this condition, the aperture of the camera 14 must be decreased to maintain adequate depth of field over the required depth range. However, decreasing the aperture limits, in turn, the resolvable camera spot size due to diffraction, and this decreases the accuracy and resolution obtainable since .DELTA.d.sub.2 /.DELTA.d is small. Thus, the resolvable spot size on the surface .DELTA.d suffers because the spot size on the film increases due to the diffraction effects of the stopped-down aperture. The stopping-down of the aperture is common to all reproduction systems in which the camera focuses on the object, as best as possible.

In accordance with the practice of the present invention, the camera focuses on the light plane itself, instead of focusing on the object surface. Since the intersection of the light plane with the surface of the object must necessarily always be in this light plane, it may be seen that the intersection will always be in focus, regardless of the shape of the object surface. Since focus is from object plane to image plane, a negligible depth of field is required. As a result, a wide-open aperture may be used.

In order to practice the present invention, the standard conventional camera cannot be used to focus on the light plane, because the light plane is not orthogonal to the camera axis. It can be shown, however, that by arranging the camera film plane, camera lens plane, and light plane so that they all meet along a common line of intersection, the focusing of the light plane on the film plane can be achieved. The resulting arrangement and interrelationships of the planes are shown in FIG. 2. Thus, the film plane 20 is inclined with respect to the lens plane 24 so that these two planes intersect the light plane 22 along a common line 26. It is essential to note that along any camera ray, the local camera magnification is still given by the ratio of distances from the lens; i.e., image size is to object size, as lens to film distance d.sub.o.sup.1 is to lens to object distance d.sub.o (when viewed along the ray). However, this ratio varies across the field of the image, in contrast to the constant magnification between object plane and image plane when the planes of the lens, film and object are all parallel to each other.

In an alternate embodiment shown in FIG. 3, a wedge-shaped coherent fiber optic bundle 28 is placed between the lens and the film planes so that the fiber optic bundle receives the image plane where it is in substantially perfect focus and transmits it to the normal film plane location 30. In the embodiment of FIG. 3 the camera 32 is arranged so that the planes of the film 30 and the lens 34 are parallel to each other. Thus, by using the wedge-shaped fiber optic bundle 28, the effect in FIG. 2 is obtained with standard camera construction in which the lens and film planes are parallel.

To minimize lens aberrations caused by off-axis rays, it is preferred, but not required, that the lens plane be orthogonal to the line of sight directed to the center of the portion of the light plane being used.

When using a plane of light that is projected with a predetermined thickness against the object surface 10, a predetermined accuracy is obtained with regard to the location of points on the surface within the light plane. Thus, a point on the surface will be sensed to be at any location within the thickness of the light plane. To increase the accuracy by which the location of a point on the surface may be specified, a thinner plane of light needs to be projected. With a thinner plane of light, the uncertainty of the location of a point will be reduced, because the location will be specified within a narrower distance corresponding to the thickness of the thinner light plane. This may be seen from FIG. 5 where the location of a point P on the object surface has an uncertainty associated with it by the amount TA, corresponding to the thickness of the thicker plane 40. If a thinner plane 42 is used, the location of the point P has an uncertainty associated with it, which is only TB. It may be seen from this analysis that by using successively thinner planes of light projected onto the object, greater accuracy may be realized.

To benefit from the greater accuracy which is possible through the use of thinner light planes, it is necessary that the depth of field of the camera be reduced for the thinner planes. Such reduction in the depth of field, however, is not a disadvantage when using the procedure of first scanning the object surface with a relatively thicker plane and using the information obtained therefrom as a reference guide when scanning the object surface with thinner planes of light. The smaller depth of field associated with the thinner light planes will also not result in loss of data due to curvature of the object surface. This may be seen by referring to FIG. 6 in which the thicker plane 40 is seen to intersect the object surface 10 along the curved portion R-S-U. The thinner plane 42 intersects the object surface along the curved portion R-S. It may be seen that, in general, the requirement for the depth of field for the thinner plane will be less than for the thicker plane, due to the usual character of curved surfaces, whereby the amount of curvature over the larger area is greater than over a smaller area.

In operation of the system to obtain increased accuracy, the object surface 10 is placed on the folding unit for support 34 which makes it possible to move the object surface 10 in the three space coordinates, X, Y, Z, and to also rotate the object surface about the Z and X axes. This is accomplished, for example, by lead screws 46, 48, and 50, in the conventional manner. Motion devices such as the unit 44 are well known in the art for moving objects in the space coordinate directions, and for this reason, the unit 44 is not described in further detail here. The coordinate diagram below the unit 44 shown in FIG. 4, indicates the directions in which the object may be moved towards to show the entire surface to both the projector 12 and camera 14.

After the object surface 10 has been scanned using a relatively thick light plane projected from the projector 12, the surface data sensed by the camera 14 is inserted into a computer 54. An intermediate unit 52 serves to convert the video signals from the camera 14 into corresponding electrical signals suitable for processing by the computer 54. Thus, the unit 52 is an interface unit which serves to modify the signals from the camera 14 for insertion into the computer 54. Such interface units 52 are well-known in the art, and are not described in further detail here.

The computer 54 also serves to operate the unit 44 by means of suitable motors with encoders 64. Thus, the lead screws 46, 48, and 50 are rotated by motors which are shown schematically by the unit 64. These motors are operated in accordance with signals received from the computer through another interface unit 62. This unit 62 converts the signals transmitted from the computer 54 into signals usable for driving the motors 64. Encoders may be provided in conjunction with the motors to further code signals from the computer so that they are acceptable by the motors, as may be required. In practice, it is possible to have the computer 54 carry out also the functions of the unit 62 and the encoders, so that a separate unit 62 and encoders may not be necessary.

The computer 54 coordinates the operations of the projector 12, camera 14, and motors 64 of the unit 44, so that after the desired data within a light plane on the object surface has been reported, for example, the unit 44 is set into motion by respective motors 64 for the purpose of exposing another planar area of the object surface to the projector 12 and camera 14. p After the preceding procedure has been carried out with a relatively thick plane, the procedure may be repeated with a thinner light plane projected onto the object surface 10. The scanning of the object surface with the relatively thinner plane is accomplished by using the data obtained from the thicker plane, as a reference guide. Thus, the positional information stored or recorded by the computer 54 is used as a reference for positioning the object surface 10 with respect to the projector 12 by the unit 44. To aid the computer 54 in storing a large quantity of information, auxiliary storage devices such as the disc drive 58 and tape drive 60 may be used in conjunction with the computer 54. A visual display, such as on a cathode-ray-tube terminal 56 may also be used in conjunction with the computer to enable operating personnel to observe data visually. The auxiliary units 56, 58, and 60 are well-known in the art and are optional units in the operation of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention, and therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.