METHOD AND APPARATUS FOR ABRADING IRREGULAR SURFACES

Abstract

A system for abrading irregular surfaces includes a bracket that can be attached to a shop aid. The bracket carries two motors to which abrasive pads are attached, and the positions of the motors are controlled to move abrasive elements over the surface to be abraded. The abrasive pads are attached to abrasive-pad backing of different configurations. Disclosed configurations are generally flat, triangular, and U-shaped.

Description

TECHNICAL FIELD

This invention relates to the abrading of irregularly shaped surfaces.

BACKGROUND ART

It is often necessary to abrade surfaces to prepare them for a variety of uses. The surfaces are typically abraded by attaching an abrasive pad to a motor that moves the abrasive pad in a circular or linear motion. One such motor that is commercially available is an orbital motor, which oscillates the abrasive pad in a circular motion.

When the surface to be abraded is flat or essentially flat in that its radius of curvature is large, the abrasive pad can also be essentially flat. Complications arise, however, when the surface to be treated includes such features as stringers, such as a blade or vent that protrude from an essentially flat surface for added strength, ventilation, etc. In this situation, a simple flat pad attached to an orbital motor cannot effectively engage the various surfaces of a stringer to abrade them properly. It is particularly difficult to abrade irregular surfaces efficiently with known surface-abrading pads that are directed by known shop aids such as that sold by Temple Allen Industries of Rockville, Md. under the trademark EMMA.

A particular problem addressed by the present invention is the abrading of an aircraft wing panel that presents essentially flat surfaces but also includes stringers of varying geometry that run the length of the wing. These features extend outward from flat portions of the wing, which is toward the interior of a completed wing, to present surfaces that cannot be abraded with known equipment.

SUMMARY OF THE INVENTION

In accordance with the invention a set of abrasive-pad supports cooperate with a shop aid to hold a known abrasive pad to abrade irregular surfaces, such as stringers. An abrasive-pad backing is mounted on an end effector that is attached to a known shop aid that moves the end effector along the surface to be abraded. The end effectors carry one or more motors that move the abrasive pads with respect to the surfaces to abrade them uniformly as the shop aid moves the end effector along the surface to be abraded. The motors can be orbital motors that drive an abrasive-pad backing in a circular motion.

In one embodiment an abrasive-pad backing is configured to abrade upper and lower surfaces of a stringer that extends away from a generally flat surface. The upper and lower web surfaces of the stringer are typically not parallel, and each of the upper or lower web surfaces intersects the generally flat surface at a respective curved surface of small radius. The abrasive-pad backing in this embodiment can be a triangular prism where two faces of the pad backing are angularly oriented to match the angle between the flat portion of the article to be abraded and a respective web face of the stringer. Thus, one of the abrasive-pad supports matches the angular relationship between the flat portion of the article and one of the web surfaces and another of the abrasive-pad supports matches the relationship between the flat portion and the other of the web surfaces of the stringer. An abrasive pad is attached to each of two backings, and the two abrasive-pad backings are mounted on an end effector that holds an abrasive pad on each side of the stringer against the surfaces to be abraded.

An abrasive pad can be attached to an abrasive-pad backing in a variety of ways. For example, a known abrasive pad includes one part of a hook-and-loop (e.g., VELCRO®) fastener, and the abrasive-pad support can have the matching part of such a fastener. Other fastening mechanisms, such as adhesives, snaps, elastic bands, and the like could be used.

In one embodiment, an abrasive pad is applied to one surface of the backing and folded over the edge of the backing to engage an adjacent side of the backing. It has been found, however, that the abrasive pad is often too thick to form an edge of the abrasive pad that is sharp enough to fit into and abrade the concave portion formed at the intersection of the flat main surface with the surface of the flange. In that case, the edge of the abrasive-pad backing is provided with a thin ridge that extends along the length of the backing to force the folded-over abrasive pad to form a thinner edge that engages the concave intersection.

Another feature of the invention is an end effector that is designed to control the position and motion of the abrasive-pad backings to abrade a stringer. This end effector includes a bracket to which two motors are mounted for motion toward and away from each other. An abrasive-pad backing is attached to each of the motors, and the mechanism that moves the motors toward or away from each other is controlled to maintain a predetermined force of the abrasive pads on the two opposed surfaces of the stringer.

Other end effectors are configured to control the operation of abrasive-pad backings used to abrade features having a plurality of surfaces that are themselves essentially flat but are oriented with respect to each other to form a more complex object. For example, such an object might be a stringer formed by three intersecting surfaces in a box-like configuration, such as a vent. The end effectors in this embodiment are designed to hold essentially flat abrasive-pad backings in either a coplanar arrangement or a parallel facing arrangement to abrade selected surfaces. Yet another end effector is designed to control an abrasive-pad support designed to abrade an outer end of the box-like object.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of an end effector in accordance with a first embodiment of the invention for abrading a Stringer.

FIG. 2a is a side view of the end effector of FIG. 1.

FIG. 2b is a side view of the end effector showing abrasive-pad supports closer than shown in FIG. 2a.

FIG. 3 is a perspective of an abrasive-pad backing.

FIG. 4 is a vertical cross-section of abrasive-pad backing of FIG. 3.

FIG. 5 is a perspective of an end effector for holding abrasive-pad supports in a coplanar arrangement on opposite sides of a box-like feature.

FIG. 6a is a side view of the end effector of FIG. 5.

FIG. 6b is a side view of the end effector of FIG. 5 with the spacing of the abrasive-pad supports being less than in FIG. 6a.

FIG. 7 is a perspective of an end effector for operating two abrasive-pad supports facing each other.

FIG. 8 is a side view of the embodiment of FIG. 7 for abrading upper and lower surfaces of a box-like feature.

FIGS. 9a and 9b illustrate the embodiment of FIG. 7 with the upper and lower abrasive-pad supports in different positions.

FIG. 10 is a perspective of an end effector holding an abrasive-pad support designed to abrade an end of a box-like feature.

FIG. 11 is a side view of the embodiment shown in FIG. 10.

FIG. 12 is a perspective of an abrasive-pad backing used with the end effector of FIG. 10.

FIG. 13 is a side view of the abrasive-pad support of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, an end effector 2 is shown positioned to abrade upper and lower web surfaces of a stringer 4. The stringer, for example, can be a strengthening stringer for an aircraft wing panel 6. The upper web surface 8 of the stringer is not necessarily parallel to the lower web surface 10, and the edge 12 is in many instances narrow enough that it does not require separate abrading.

The end effector includes a bracket 14 with a connector 16 for connecting the end effector 2 to a known shop aid (not shown) for controlling the motion of the end effector. The end effector 2 includes two spaced pneumatic orbital motors 18, each of which operates an abrasive-pad backing 20. The upper motor 18 is mounted directly to the bracket 14, while the lower motor 18 is mounted to a movable plate 22 that is movably attached to the bracket 14 to provide control of the spacing between the upper and lower abrasive-pad supports 20. Movement of the plate 22 can be provided by pneumatic cylinder 24, which is in turn controlled by an operator or automatically by a central control (not shown). FIGS. 2a and 2b illustrate operation of the pneumatic cylinder 24 to adjust the spacing of the motors.

FIGS. 3 and 4 show an embodiment of the abrasive-pad backing 20 found in the end effector of FIGS. 1 and 2 with an abrasive pad 30 attached. The backing includes a generally triangular prismatic core 26 and outer foam layers 28 and 36 for supporting the abrasive pad 30. The backing 20 also includes a narrow, flat ridge 32 (see FIG. 4) that is placed at the peak, or intersection of two surfaces of the backing and extends above the two surfaces to engage a central portion of the abrasive pad 30. This provides the abrasive pad 30 with a rounded edge 34 of small radius of curvature. This small radius has been found to be effective in allowing the abrasive pad to contact the respective radius intersections of the upper and lower web surfaces 8, 10 of the stringer 4 with the wing flange 6.

Another end effector in accordance with the invention is shown in FIGS. 5 and 6. The end effector 38 is designed to abrade generally flat surfaces such as surfaces 40 of a flange as shown in FIG. 6a. End effector 38 support two motors 18 to which are attached generally flat abrasive-pad backings 42. In this embodiment the backings 42 are nominally coplanar, but could be at a small angle relative to each other, for abrading generally flat surfaces 40. The end effector in this embodiment includes a first bracket 44 that has connector 16 for connecting the end effector 38 to a shop aid (not shown). A second bracket 46 pivotally attached to the first bracket 44 supports a motor mount 48. The motor mount includes one or more mounting shafts 50 that engage bushings 52 on the motors for allowing motion of the motors toward or away from each other. A pneumatic cylinder 54 is mounted between the motor mount 48 and one of the motors to move that motor along the mounting shafts toward or away from the other motor, which is fixed in position on the motor mount. Alternatively, the pneumatic cylinder 54 can be mounted between the motors and both motors allowed to move along the shafts 50. One or more gas springs 56 are arranged between the motors to dampen vibrations. A handle 58 is provided to facilitate manual movement of the end effector 38.

FIG. 6a illustrates the end effector 38 positioned with respect to a box-like stringer 60 to abrade essentially flat surfaces of a flange 40. Foam bumpers 62 are provided on the pad backings to absorb vibrations and allow the abrasive pads 30 to abrade the flange 40 very close to the upper and lower surfaces of the stringer 60. The foam bumpers 62 are in contact with the web surfaces. As the width of a stringer web changes, the pneumatic cylinder extends or retracts to accommodate the changing width of the stringer.

FIG. 6b illustrates the position of the motors 18 after the lower motor has been moved close to the upper motor.

FIGS. 7 through 9 show an end effector 64 configured to abrade upper and lower surfaces of a box-like stringer 60. In this embodiment, the motors 18 are mounted to a motor mount 66 by a motor mount bracket 67, the mount 66 being pivotally attached to the bracket 46 at a bearing 68. The arrangement of the connector 16, the pivot axis of the bracket 46 with respect to the bracket 44, and the rotation of the motor mount provide three axes of motion, for this end effector. (The other end effectors described herein also have three degrees of rotational motion, e.g., roll, pitch, and yaw.)

The upper motor 18 in the embodiment of FIGS. 7 through 9 is rigidly attached to the mount 66. Bars 70 are also rigidly attached and extend forwardly from the mount 66. Shafts 72 connect the bars 70 to plates 74. The shafts 72 can move vertically through bushings in plates 74. This allows a known portion of the weight of the end effector assembly to be supported by the force of springs 76.

The lower motor 18 is connected to the mount 66 by a shaft 78, which carries the motor on a bearing 80. The vertical motion of the lower motor is controlled by a pneumatic cylinder. The lower motor is also mounted to horizontal pins 82 for lateral movement with respect to the upper motor. This lateral offset motion is caused by contact of the lower backing with the flange, and the lower motor is urged outward by gas spring 84.

The offset structure described above allows the two backings to adjust automatically for offsets in the positions of the flanges above and below the stringer. In the embodiment illustrated, the lower backing 42 is provided with a foam pad 62. The plate 74 is provided with a tapered bumper 86. The plate 74 allows the end effector 64 to index the upper backing relative to the upper part of the flange, while the lower backing is urged against the lower part of the flange. This feature is illustrated in FIG. 9b and provides more complete coverage of the upper and lower surfaces of the stringer.

FIGS. 10-13 show an embodiment configured to abrade the end of a box-like stringer. In this embodiment, a single motor 18 is pivotally mounted to a bracket 88, which is pivotally mounted to bracket 44 at bearings 90. The motor is pivotally mounted to the bracket 88, the connector 16, bearings 90, and pivot mounting of the motor provide three degrees of freedom. An abrasive-pad backing 92 is attached to the motor so that it can engage the end of a box-like stringer 60. The abrasive-pad backing 92 is generally U-shaped to hold an abrasive pad in a similar shape. A flat part 94 of the backing 92 engages a flat part of the end of the stringer 60, while a curved portion 96 on each side on the flat part 94 engages the corners of the end surface of the stringer 60.

The backings disclosed herein, such as backing 92, can be made of foam or other resilient materials. Moreover, a backing can be made of materials such as those shown in FIG. 12 at 98, 100.

Modifications will be apparent to those of skill in the art.

Claims

1. Apparatus for abrading an irregular surface comprising a bracket supporting two spaced motors, an abrasive-pad backing on each motor, and means for moving said motors toward and away from each other.

2. Apparatus according to claim 1 wherein said spaced motors are orbital motors.

3. Apparatus according to claim 1 further comprising a connector for connecting said bracket to a shop aid.

4. Apparatus according to claim 3 wherein one of said spaced motors is mounted to said bracket and another of said two spaced motors is mounted to a movable plate that is movably attached to said bracket.

5. Apparatus according to claim 4 wherein said means for moving said motors toward an away from each other comprises a pneumatic cylinder connected to said bracket and to said movable plate.

6. Apparatus according to claim 1 wherein said abrasive-pad backing is triangular in cross section.

7. Apparatus according to claim 6 wherein said abrasive-pad backing further comprises a flat ridge between two adjacent generally flat surfaces.

8. Apparatus according to claim 1 wherein each said abrasive-pad is are generally flat.

9. Apparatus according to claim 8 wherein said spaced motors are supported on mounting shafts to allow said spaced motors to move toward and away from each other.

10. A method for abrading irregular surfaces comprising the use of the apparatus of claim 1 to move abrasive elements across said irregular surfaces.

11. An abrasive-pad backing comprising a generally flat part between first and second curved parts at respective opposed ends of said generally flat part.