GB2133173A - Rotatable optical projection comparator - Google Patents

Abstract

An image 102 is projected onto e.g. a fillet 12B and rotated about the axis, 33 to thereby scan along the surface of the fillet. In an embodiment, the image is received and focused generally toward the axis, and then generally upward, by a mirror 91 intersecting the axis, to a display screen 94 which rotates along with the image. A template 118 containing a reference image 121 rotates along the display screen 94. In this manner, the entire fillet can be scanned (including portions hidden from view by the boss 9B) and images obtained for comparison with the reference images. The images do not translocate through space, but only rotate on the display screen about the axis for convenience of comparison with the similarly rotating reference image. <IMAGE>

Description

SPECIFICATION Optical comparator The present invention relates to optical comparators, and more particularly, to comparators of this type used for measuring a radius of curvature.

Background of the Invention When materials are joined together, such as two metals when they are welded, sharp angles are sought to be avoided at the junction because such angles tend to concentrate mechanical stresses and strains. Instead, it is preferred that sharp angles be milled into smooth, gently curving shapes, sometimes termed fillets. The fillets serve to reduce the concentration of stress otherwise present in a sharply angled junction.

In many applications, the particular dimensions and configuration of a fillet are important. In order to determine whether a fillet conforms to the correct dimensions and configuration, a procedure commonly used is to place a reference contour gauge into contact with the fillet and to shine a flashlight onto one side of the gauge while visually searching on the other side for light escaping between any cracks present between the fillet and the gauge. The cracks indicate a lack of conformity. This examination task is timeconsuming and can become more difficult if the fillets are located in inaccessible positions.

It is an object of the present invention to provide a new and improved optical comparator for comparing a structural configuration with a reference.

One form of the invention comprises a rotatable projector for projecting an image onto selected rotational positions of an object to be examined and other means for comparing the image as reflected by the object with a reference image.

In the drawings: FIGURE 1 illustrates one form of the optical comparator of the present invention positioned atop a gas turbine engine rotor.

FIGURE 1A illustrates schematically a portion of a gas turbine engine rotor.

FIGURE 2 is a schematic side view of some of the optical paths in the form of the present invention depicted in Figure 1.

FIGURE 3 is a schematic top view of some of the optical paths in the form of the present invention depicted in Figure 1.

FIGURE 4 depicts a side view of a lens 11 2B in a different position than lens 1 12 in Figure 2.

One form of the optical comparator of the present invention is shown in Figure 1 in which a portion of a gas turbine engine rotor 3 in one stage of manufacture has a surface 6 from which extends a plurality of bosses, some of which are shown as bosses 9A-D. The bosses 9A-D will, in later manufacturing stages, be drilled to provide mounting holes for other engine components.

Each boss 9A-D has along its surface a respective annular fillet 1 2A-D at the region of connection to the surface 6. As shown in Figure 1A, the bosses 9A-D as well as additional bosses 9E-T are identical and uniformly spaced in a circular array.

In Figure 1 is shown a base assembly 1 5 of the present invention adjacent the bosses 9A-D. The base assembly 1 5 comprises an outer, annular, movable bracket 1 8 together with a rotatable disc 21 supported by the bracket 1 8. The bracket 1 8 contains an annular channel 25 in an annular wall 26. The outer edge of the disc 21 is fitted into the channel 25 so that the disc 21 is fixed in position as to translation with respect to the bracket 1 8, although the disc 21 is free to be manually rotated within the bracket 18 about an axis 33 and to thereby slide its outer edge along the channel 25.

A tape 27, comprising a low friction plastic such as the one commonly designated by the trade name Teflon, is affixed to at least one surface of the channel 25 to act as a bearing between the bracket 1 8 and the disc 21. The closeness with which the disc 21 fits into the channel 25 is made as precise as economically possible in order to assure that the disc 21 rotates about the axis 33 with as little lash and looseness as feasible. Thus, the disc 21 is rotatable about an axis 33 for scanning later to be described and the position of the axis 33 with respect to the bosses 9A-D is determined by the position of the bracket 18.

There is a series of spaces 36 defined between the bosses 9A-D and a circular wall 39 of the rotor 3. This is more clearly shown in Figure 1 A.

These spaces 36, when viewed together, provide a circular path shown as dotted lines 38 in Figures 1 and 1 A along which an elongated guide 45 in Figures 1 and 1 A can travel. The guide 45 is affixed to the underside of the bracket 1 8 and the dimensions of guide 45 are such that it closely fits between the wall 39 and the bosses 9AD. The close fit is required in order to assure that the guide 45, as well as the bracket 1 8 to which it is attached, follows the circular path 38 as closely as possible. As shown in Figure 1 A, the guide 45 contains an indented region 45A to prevent interference with scanning of the boss 9B.

An indexing means 51A is attached to the bracket 18 and includes an outrigger 51 which is rotatable about a pivot 54 so that the outrigger 51 can be moved to occupy the position shown by phantom outline 57. Rotation allows the indexing means 51 A to disengage from the boss 9C to allow the bracket 1 8 to move along the circular path 38. The outrigger 51 is preferentially biased by a spring 60 so that the outrigger 51 normally occupies the position as shown in solid outline in Figure 1. The outrigger 51 supports an indexing block 63 which has a surface 66 which is preferentially conformal in shape to the curved surfaces of the bosses 9A-D. The conformality of the surface 66 serves to precisely locate the indexing block 63 when the surface 66 is positioned against a boss 9C.

The precise location of the indexing block 63, together with the fact that the distance between the indexing surface 66 and the axis 33 of the disc 21 is known in advance, means that the axis 33 is located in a predetermined position with respect to the boss 9C which is in contact with the indexing block 63. If the boss 9B under inspection is cylindrical, then the axis 33 of the disc is preferably located so as to be co-axial with the center axis (not separately shown) of the boss 9B.

If the inspected boss 9B is not cylindrical, then a suitable position at which to locate the axis 33 must of course be selected according to the region of the fillet 1 2B which is to be scanned in the manner later described. The principle selection criterion will be that the distance between the lens 101 and the fillet 1 2B change as little as possible during the scanning to minimize the changes in focus at which the linear image (described later) is projected to the fillet 12B.

Therefore, as shown in Figure 1 A, the bracket 1 8 is constrained to travel along the circular path 38 on a gas turbine rotor 3. The disc 21 travels along with the bracket 1 8 and its axis 33 of rotation follows a second circular path 40 which intersects each of the bosses as described in the paragraph above. From one point of view, if the disc 21 is viewed as continually rotating as the bracket 1 8 follows the first circular path 38, then a point 40A on the rotating disc 21 describes a path resembling a trochoid. The indexing means serves to position the disc's axis 33 at predetermined selected positions along the second circular path 40 and these positions are determined by reference to a surface of a nearby boss.

As shown in Figure 1, a projection means 73 which preferably comprises a fiber optic light source 76 and power supply 79, available as Model No. ILK--IV, from Olympus Corp., New Hyde Park, New York, is fastened to the disc 21.

The projection means 73 projects a light beam 82 through a port 70 in the disc 21 onto fillet 1 2B in a generally radial direction of the boss 9B (that is, toward the axis 33). The light beam 82 is reflected as a reflected beam 85A to a first mirror 88, thence as a beam 85B to a second mirror 91, and thence as a beam 85C parallel to the axis 33 (but shown as a ray coincident with the axis 33) to a frosted glass display screen 94 which intersects the axis 33 and on which an image 95 is formed.

An elongated, opaque object such as a wire 97 is stretched across the path of the light beam 82 to eclipse a linear portion of the light beam 82 to thereby create a linear image as the shadow of the wire 97. The linear image is focused onto the fillet 12B by a lens 101 and shown as an image 102.

The shape of the image 102 will in part depend upon the alignment of the wire 97 with the fillet 12B. Preferably, the wire 97 is aligned to be coplanar with the axis 33.

The lens 101 is preferably positioned midway between the wire 97 and the fillet 1 2B and preferably has a focal length equal to half the distance between the wire 97 and the fillet 12B.

The shape of the image 102 on the fillet 1 2B derived from the linear image will also depend upon the shape of the fillet 12B. This image 102 is contained in the reflected light beam 85A and is focused by a second lens 112 so that the image 95 projected onto the display screen 94 will be in focus. The display screen 94 is supported by a mount 11 5. A template 11 8 is positioned upon (or near) the display screen 94 and it bears a predetermined image 121.The predetermined image 121 represents the curved image which would be projected to the display screen 94 by a fillet 128 having a known curvature.

Rotation of the disc 21 about its axis 33 allows the linear image to be scanned along the fillet 1 2B for examination of the entire fillet surface. The mirror 91 is preferably located above the boss 9B so that the axis 33 of rotation intersects the mirror 91. Thus, rotation of the disc 21 results in the rotation of the mirror 91 about the axis 33 so that the image 95 projected upon the display screen 94 does not move across the screen 94 but only rotates with respect to the bracket 1 8. Of course, the display scree 94 and the template 11 8, in being supported by the mount 11 5, rotate along with the disc 21 so that the relative rotational positions of the image 95 and the template remain unchanged.Thus, the user can conveniently compare the image 95 with the predetermined image 121 on the template 11 8 at all times during rotation of the disc 21 because the image 95 does not translocate, it only rotates. In addition, the user, who will more likely be positioned on one side of the'bosks 9B, can examine fillet portions on the side of the boss 9B opposite to the user which portions are obstructed from direct view by the boss 9B itself. Rotation of the display screen 94 (which occurs because of its attachment to the rotatable disc 21 by mount 115) is not seen as strictly necessary since the screen 94 provides an imaging surface and rotation of the imaging surface is not necessary for image formation.

However, rotation of the template is seen as convenient to the user for comparing the images 95 and 121.

Figures 2 and 3 show greater detail concerning the geometric arrangement of the components described above. Figure 2 is a side view of the light beam 82 striking boss 9B. The angle 130 between the light beam 82 and the surface 6 in Figure 1 is 790. Preferably, the lens 112 (shown in solid outline) directs the light reflected by the boss 9B along a path that intersects this surface 6 (herein treated as a horizontal surface) at an angle of 450, which is angle 136. If distance 141 equals distance 1 44 (the distances are not shown as equal in Figure 2), then positioning mirror 88 at an angle of 22.50 (angle 145) with respect to a vertical line 1 47 results in the projection of the light beam 85B parallel with the surface 6 and toward the second mirror 91. If the angle that second mirror 91 makes with the disc 21 is 450 (angle 148), then light beam 85C will then travel parallel to vertical line 147 to the display screen 94.

Figure 3 shows a top view of the embodiment discussed above. Light beam 82 is projected normal (that is, perpendicular to a tangent, which projection, in the case of a boss of circular cross section, would be projection in the radial direction) to the boss 9B. The lens 11 2 directs the light beam 85A such that the path followed by light beam 85A to the first mirror 88 makes a 45" angle (angle 151) with the light beam 82. The first mirror 88 reflects the light beam 85B back to the second mirror 91.

Mirror 88 is positioned so that light beam 85B is directed to the axis 33, shown as a point 33 in Figure 3. Accordingly, if dimensions 1 52 plus 1 54 equal dimension 1 56 and if angle 1 57 is a right angle, then angle 1 61A is 450. Line 164 is normal to first mirror 88, meaning that angles 1 64A plus 164B equal 900. Application of simple trigonometry to Figure 3 allows computation of the value of angle 1 64A needed to cause light beam 85B to intersect axis 33.

The first mirror 88 can be supported by adjusting screws 1 50 shown in Figures 2 and 3 to adjust the position of the light beam 85B. The second mirror 91 and the projection means 73 can be similarly supported. It is possible that manual adjustment of the mirrors 88 and 91 and the projection means 73 using the adjusting screws 1 50 for proper image projection may be less time-consuming than undertaking the geometric calculations, the conclusions of which are given in the angles connected with Figures 2 and 3.

As shown in Figures 2 and 3, the focal plane of the lens 112, as positioned in those Figures, is depicted as dashed lines 1 20. The focal plane 120 does not contain both the top and bottom region 121A and 121 B of the image 102 in Figure 2 and thus these regions are focused differently by the lens 112. One reason for this positioning of the focal plane 120 is that, in actual practice, space limitations prevent lowering and rotation of the lens 112 to occupy the dashed outline 11 2A.

Such positioning would increase the alignment of the top and bottom regions 121 A and 121 B with the focal plane 120 (which would then be rotated clockwise) and would reduce the difference in focus.

As a preferred way to reduce the differential focus of the top and bottom regions 1 21 A and 1 21 B under these space limitations, a wide angle lens 11 2B (dashed outline in Figures 2-3, solid outline in Figure 4) such as a 38 mm, f 4.5 enlarging lens is positioned as shown and used as the lens 112. The wide angle lens 11 2B has the feature that, despite the fact that its optical axis 126 in Figure 4 does not coincide with the light beam 85A reflected from the fillet 12B, the wide angle lens 11 2B can nevertheless be positioned as shown so that its focal plane 128 is substantially coplanar with the top and bottom regions 121 A and 121 B, thereby reducing the difference in focus between these regions.The wide angle characteristics of the wide angle lens 11 2B assist in capturing the image 102 even though this image is positioned off the optical axis 126. This positioning requires the rotation of the wide angle lens 11 2B to occupy the dashed outline in Figure 2 and the relocation of the wide angle lens 11 2B to occupy the dashed outline near the tangent 85D in Figure 3.

However, positioning the lens 11 2B near the tangent 85D presents a new problem in image capture due to specular (as opposed to diffuse) reflection. That is, with reference to Figure 3, it is known that an observer sighting along light beam 82 will see a different view of the image 102 on the fillet 1 2B than an observer sighting along light beam 85A. The former observer will see the image 102 as a straight line, and the latter observer will see it as a curved line. It is also known that an observer sighting along the tangent 85D to the boss 9B at the location of the image 102 would see the image 102 as the true cross-sectional shape of the fillet 12B. However, in practice, if the surface of the boss 9B is specularly reflective, it will be practically impossible to see image 102 by sighting along the tangent 85D.If the specularly reflective boss 9B is rendered more diffusely reflective by, for example, etching, sandblasting or the application of a coating of a fine powder such as talc, then the image 102 can be viewed by mirror 88A along a line which approaches the tangent 85D. The sprinkling of talc powder onto a fillet 11 2B by the inventor has allowed the positioning of the optical axis 1 26 of the wide angle lens 112 in Figure 3 along a line which falls eight degrees (angle 1 90) short of the tangent 85D. As is known, the correspondence of the image 102 viewed along line 126 changes, broadly speaking, with the cosine of angle 190.

Thus, since the cosine of eight degrees hardly differs from the cosine of zero degrees, the image seen along line 126 using talc hardly differs from the actual image 102 in Figure 1 seen along the tangent 85D in Figure 3.

The employment of a human operator to compare the image 95 on display screen 94 with the template image 121 has been assumed.

However, this function can be automated and the use of optical pattern recognition equipment is contemplated. This equipment is schematically shown by a camera means 1 55 in Figure 1 which captures the image 95 and generates signals indicative thereof which are transmitted to processing circuitry (not shown).

The predetermined image 121 contained on template 11 8 can be generated by trigonometric calculations which take into account the curve of the fillet 12B, the geometrical path followed by the various light beams, and any magnification introduced by lenses, such as lens 112. However, it is preferred that the template be generated from the invention actually to be used. In this latter manner of template generation, a reference fillet (not shown) is precisely manufactured to a desired configuration and dimensions. The reference fillet is scanned in the manner described above and the image which the reference fillet generates on the display screen 94 is recorded, such as by photographing. From the photograph, the template image 121 can be generated.

It is to be noted that the boss 9C is a boss other than a boss currently under inspection, but the boss under inspection could be in contact with the indexing block 63, provided that the indexing block 63 does not interfere with the scanning procedure later described. Thus, a boss 9C used for indexing (i.e., an indexing boss) and a boss 9B under inspection (i.e., an inspected boss) have been described and these may be the same boss in some cases.

The use of a tape such as Teflon tape has been described as providing a bearing surface for the disc 21. Other kinds of bearing apparatus can be used, such as ball bearings or roller bearings.

Further, projection of the image 95 is not limited to projection onto the display screen 94, but the image 95 can be projected by a photographic projector (not shown) onto a ceiling or wall for greater magnification if desired. In this connection, it is possible that the motion of the invention along the circle 38 in Figure 2 may not be desired, so that the invention can be held stationary and the turbine rotor 3 be moved instead to provide relative motion between the two indicated by circle 38.

An invention has been described which provides an optical comparator for comparison of curved surfaces with a reference and which provides the noncontact measurement of fillet radii configuration. In particular, measurement of the fillets on bosses on a gas turbine engine rotor has been described.

While one form of the present invention has been described, it is clear that numerous substitutions and modifications can be undertaken without departing from the true spirit and scope of the present invention as defined by the following

Claims (14)

claims. CLAIMS

1. Optical comparator for examination of configurations located at selected rotational positions with respect to an axis, comprising: (a) projection means rotatable about the axis for projecting a predetermined first image to the selected rotational positions for modification into respective second images depending upon the configurations located at the selected rotational positions, (b) focusing means for viewing the second images, and (c) display means for receiving at least some of the second images and for comparing with a reference image.

2. Optical comparator according to claim 1 in which the predetermined first image comprises a shadow of an elongated, opaque object.

3. Optical comparator for examination of an annular surface surrounding an axis, comprising: (a) means for projecting a light beam to the annular surface, (b) means for generating an image in the light beam for projection onto the annular surface, (c) a display screen which intersects the axis, (d) means for scanning the image along the annular surface, and (e) means for focusing the image of (d) onto the display screen.

4. Optical comparator according to claim 3 in which the image of (b) comprises a shadow of an elongated, opaque object.

5. Optical comparator for examination of an annular surface surrounding an axis, comprising: (a) a projector rotatable about the axis for projecting a predetermined image onto selected portions of the annular surface, (b) a display screen intersecting the axis, and (c) optical processing means rotatable about the axis in fixed relationship with respect to the rotatable projector for receiving a reflection of the image from the annular surface and for focusing the reflection to the display screen as an image which rotates about the axis.

6. Optical comparator according to claim 5 in which the predetermined moving image of (a) comprises a shadow of an elongated, opaque object.

7. Optical comparator for examination of fillets located at the bases of bosses in a turbine rotor and comprising: (a) a bracket having an annular channel, (b) a disc supported by the annular channel and rotatable about an axis, (c) a bearing for contacting the disc and for reducing forces due to friction during rotation of the disc, (d) a guide fastened to the bracket for guiding the bracket along the bosses, (e) indexing means for positioning the axis of (b) at a predetermined position with respect to a selected first boss, (f) projection means fastened to the disc for projecting a beam of light onto the fillet of a predetermined second boss, (g) eclipsing means fastened to the projection means for eclipsing a substantially linear portion of the light beam of (f) for generating an image on the fillet of (f) which image contains information as to the configuration of the fillet, (h) a first lens means fastened to the disc for bringing the image of (g) into a selected degree of focus on the fillet, (i) a first mirror fastened to the disc for receiving the image and for reflecting the image generally toward the axis of (b), (j) a second mirror fastened to the disc and intersecting the axis of (b) for receiving the image reflected by the first mirror and for reflecting the image along the axis, (k) display means fastened to the disc and intersecting the axis of (b) for receiving the image reflected by the second mirror and for displaying the image received, and (I) a second lens fastened to the disc for bringing the image on the display means to a selected degree of focus, (m) reference means positioned near the display means for comparing the image displayed in (k) with a reference image.

8. Optical comparator according to claim 7 in which the eclipsing means of (g) comprises a wire.

9. Optical comparator according to claim 7 in which the second lens of (I) is positioned such that (n) a focal plane of the second lens is substantially coplanar with the image on the fillet.

1 0. Optical comparator according to claim 9 in which the second lens of (I) is positioned such that (o) the optical axis of the second lens makes an angle of less than ten degrees with the tangent which intersects the image on the fillet.

11. Optical comparator according to claim 10 in which the second lens of (I) comprises a wide angle, 38 mm, f 4.8 enlarging lens.

12. A method of optical comparison of an annular surface surrounding an axis, comprising the steps of: (a) scanning a predetermined image about the axis along the annular surface, (b) capturing a reflection of the predetermined image during scanning and focusing the reflection such that the reflection (i) appears as an image in the region of the axis, and (ii) rotates about the axis during the scanning of (a).

13. A method according to claim 12 and further comprising the step of increasing the diffuse reflecting characteristics of the annular surface.

14. A method according to claim 13 in which the predetermined image is captured along a path which makes an angle of less than ten degrees with the tangent at the location of the predetermined image on the annular surface.

1 5. A method of inspecting a cylindrical object having an axis, comprising the steps of: (a) projecting a linear image toward the axis and onto the object; (b) rotating the linear image about the axis and along a surface of the object; (c) focusing a reflection of the linear image captured from the surface of the object (i) toward a first mirror, (ii) from the first mirror, toward the axis, to a second mirror, (iii) from the second mirror, parallel with the axis and to a display screen; and (d) rotating the first mirror and the second mirror along with the linear image for rotating the image focused on the display screen about the axis.

1 6. An optical comparator substantially as hereinbefore described with reference to an as illustrated in the drawings.

1 7. A method of optical comparison substantailly as hereinbefore described with reference to the drawings.