Skin Contour Inspection System

It is standard practice to check the contour of large skin panels such as are used in aircraft wing assemblies by use of a horizontal fixture containing headers shaped to the proper contour. The skin is draped over the headers, a limited load is applied on the skin, and the deviation measured between the skin and the headers. A separate check fixture is required for upper and lower skin panels and it requires a difficult header reorientation procedure or the use of an additional pair of fixtures to accommodate skin panels for an opposite wing. It is desirable to have a single fixture that can accommodate all of the wing skin panels for a particular aircraft model and it was found that such a fixture can be prepared that furthermore suspends the formed skin in the vertical position in which skins are normally conveyed.

A series of probes extend horizontally to define a selected skin contour. A formed skin is suspended in a vertical position adjacent to the skin defining probes. A series of matching probes extend horizontally to force the formed skin against the contour defining probes with a predetermined force and the deviation is measured between the skin and the skin defining probes.

It is an object of this invention to provide a fixture for checking a compound contour of a skin in a vertical position.

It is another object of this invention to provide a single fixture for checking various skins of compound contour.

FIG. 1 is a perspective view of the contour checking apparatus of this invention.

FIG. 2 is a side elevation sectional view from inside the checking fixture of the checking apparatus and looking toward a positioned skin.

FIG. 3 is a fragmented sectional view taken along line 3--3 of FIG. 2.

FIG. 4 is an end view of a hanger used in this invention.

FIG. 5 is a side view of the hanger of FIG. 4.

FIG. 6 is a schematic of the controls for this invention.

A skin contour verification apparatus 10, has a checking fixture 12, and a systems control unit 14. The fixture has a U-shaped construction with a base 16, spaced apart vertically extending leg structures 18 and 20, and the legs are topped with horizontally extending upper members 22 and 24, respectively. Connected to leg structures 18 are a series of measuring probes 26 that extend horizontally and laterally toward the opposite leg structure. There are many of these probes, and they all are controlled to be separately extended and locked in place so that the ends of the probes define the contour of a skin to be checked. These probes can be positioned to define any desired skin contour. A set of axially aligned pressure inducing probes 28 are joined to the leg structures 20 and extend toward the first set of probes.

A formed skin 30 is suspended in the checking fixture in an essentially vertical position. The skin is brought to the fixture on an overhead rail 32. The rail is supported through rods 34 to an overhead conveyor (not shown). The skin is supported along an upper edge 36 through a series of spaced apart supporting tabs 38, and a series of quick connect hangers 40 join the tabs to the rail. Each hanger has a pin 42 that extends through hole 44, in a tab, to secure the fastener to the tab and each hanger has a quick connect/disconnect fastener 46 with pin 48 to quickly secure the hanger to the overhead rail and to quickly release the hanger from the rail. The rail has a horizontal slot 50 and the hanger has a vertical slot 52 to assist in alignment. Each hanger also has a rod 54 and a rod 56 to extend horizontally and longitudinally outward. These rods are used to support the skins during the checking process. A series of skin support units 58 that provide support to the rods on the hangers are made up of pneumatic cylinders 60 that are mounted to the upper horizontal member 22 of the checking fixture 12. These cylinders are each located to advance and retract a laterally extending support rod 62. These support rods provide point of contact support to the rods 54 and 56 of the hangers.

Various types of probes may be used to check the skins. In a preferred embodiment, as is best shown in FIG. 3, the measuring probes 26 use an electromechanical transducer probe of the linear variable transformer type and the pressure inducing probes 28 use pressure controlled pneumatic cylinders. The measuring probes have a cylindrical housing with an outer surface 64 of helical grooves shaped to handle ball bearings. The housing is mounted in a nut 66 that is rotatably secured to the vertical leg structures 18. As the nut rotates, a series of balls 68 move the probe in or out depending on the direction of rotation of the nut. A gear 70 is located on the nut to mesh with a gear 72 on a reversible drive motor 74. This permits accurate control of movement of the probe in either direction, and when the motor is stopped the balls lock the probe into position. A self-aligning joint 76 is located on the end of shaft 78 of the probe; a magnetic core 80 on the shaft provides a path for magnetic flux linking the core position to the three coils 82. An encoder 84 registers the location or position of the measuring probe. The position of the pressure inducing force of probes 28 is controlled by the pressure in line 86.

In operation, all the information for controlling the checking of a skin of a particular contour is initially fed into a disk drive 88. The disk drive then sends the required information into a central processor 90 which in turn feeds information through two-way lines 92 to several local processors 94. The local processors send signals through two-way lines 96 to the series of measuring probes 26 where each probe is first advanced and then locked in position with the ends of the self aligning joints 76 located to define the particular compound contour. Next, the formed skin 30, which is suspended vertically by hangers 40 from overhead rail 32, is brought into position adjacent to the measuring probes. A signal from local processors is sent from the local processors over pneumatic line 98 to the skin support unit 58 where the cylinder 60 is actuated to advance piston rod 62 to a position under hanger rods 54 and 56. Then, disconnect fasteners 46 are actuated to release the hangers from the overhead rail and leave the skin suspended on the rods 62. The local processors then send compressed air to pressure inducing probes 28, through lines 86 and rods 100, with self-aligning joints 102 on the end, force the skin against the contour defining probes. The pressure in lines 86 is set to provide the correct pressure acting against the skins. The electromechanical transducer feature on the measuring probes then sends a signal of any out of tolerance condition of the skin, along with that location, back through the local processors. The central processors then send the signals over line 104 into a read out and print out unit 106 which converts the signal to show the location and amount of any out of tolerance part of the contour of the skin. The hangers are again joined to the overhead rail 32, the support rods 62 removed, the rods on the pressure inducing probes retracted and the skin moved out of the checking fixture to make way for a new skin to be checked.