GB2436618A

GB2436618A - Hole inspection method and apparatus

Info

Publication number: GB2436618A
Application number: GB0606329A
Authority: GB
Inventors: John Corry
Original assignee: Advanced Analysis and Integration Ltd
Current assignee: Advanced Analysis and Integration Ltd
Priority date: 2006-03-30
Filing date: 2006-03-30
Publication date: 2007-10-03
Also published as: GB0606329D0

Abstract

A method and apparatus for inspecting a hole, particularly a drilled hole, for example for rivets in aircraft construction includes an annular measuring head 15 having a plurality of resiliently mounted, radically extending wall contact probes 16, which head is passed through the drilled hole 11. Each probe 16 passes through the head to the lumen 17 of the head annulus. The position of the inner ends of the probes 16 within the lumen 17 is measured. The measurement may be conducted using imaging by use of a backlight and a digital camera or a CCD array.

Description

Measuring Instrument This invention relates to measuring

instruments.

In certain applications, notably in fabrication from carbon-based composite materials, drilling accurate holes is problematic. This is, to some extent, because of drill wear, which can be so rapid that a drill bit might be useful only for drilling six or seven holes

before it is Out of specification.

If a hole is drilled inaccurately, the cost can be high, involving the scrapping of an expensive workpiece.

Checking the accuracy with which a hole has been drilled is also problematic, especially where fine holes are concerned, with diameters as little as 4.5mm. Inaccuracies involve size and departure from circularity.

The present invention provides apparatus and methods for checking the accuracy of fine holes in workpieces, which methods arid apparatus can be integrated in a production process to monitor drill wear and reduce the incidence of inaccurately drilled holes.

The invention comprises a method for inspecting a hole, comprising passing through the hole an annular measuring head having a plurality of resiliently mounted, radially-extending wall contact probes, each probe extending through the annular head to the lumen of the annulus, and measuring the positions of the inner ends of the probes within the lumen.

The invention, in another aspect, comprises a method for inspecting a hole, comprising passing through the hole probe means adapted to respond to one or more aspects of hole configuration in a manner that can be imaged, and imaging said probe means to produce an image of the probe means from which said one or more aspects may be deduced.

The positions of the inner ends of the probes may be measured optically. They may be illuminated, as by backlighting, for example, and imaged. The image may be taken through a fibre optic arrangement to a camera, which may be a digital camera. The image made by the camera may be examined electronically. Data from such electronic examination may be used in a production monitoring and/or control arrangement to pass or fail a drilled hole, to pass or fail a drill bit for further drilling operations, and, if desired, to schedule and effect a change of drill bit before it goes out of specification.

The invention comprises, in another aspect, apparatus for inspecting a hole, comprising probe means adapted to be passed through the hole and respond to one or more aspects of hole configuration in a manner that can be imaged, and imaging means adapted to produce an image of the probe means from which said one or more aspects may be deduced.

The probe means may comprise an annular measuring head, smaller in diameter than the hole to be measured, having a plurality of resiliently mounted, radially-extending wall contact probes each extending through the annular head to the lumen of the annulus, and measuring means for measuring the positions of the inner ends of the probes within the lumen.

The measuring means may comprise optical measuring means. The apparatus may comprise illuminating means illuminating the inner ends of the probes. The illuminating means may comprise backlighting. The apparatus may comprise imaging means adapted to image the inner ends of the probes. The imaging means may comprise digital camera means. The apparatus may comprise a fibre optic arrangement taking the image to the imaging means. The fibre optic arrangement may be flexible.

Methods and apparatus for inspecting a hole according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross section through a workpiece with a series of drilled holes, showing how the hole configuration may depart from a specified configuration: Figure 2 is a cross section through a workpiece with a drilled hole and, in it, apparatus according to the invention; Figure 3 is a side elevation of the apparatus illustrated in Figure 3; Figure 4 is a schematic drawing showing a control arrangement involving apparatus as shown in Figures 2 and 3.

The drawings illustrate method and apparatus for inspecting a hole I I, comprising probe means 12 adapted to be passed through the hole 11 and respond to one or more aspects of hole configuration in a manner that can be imaged, and imaging means 13 adapted to produce an image of the probe means 12 from which said one or more aspects may be deduced.

Figure I comprises a cross section through a workpiece 14 having a three drilled holes 1 IA, lID, 11 C. The actual boundary of each hole is shown in solid line, the specified boundary limits in broken line. It will be seen that holes can be drilled off-centre or to the wrong diameter or with considerable departure from circularity. Only hole II A is within specification. Where holes are used to receive rivets, for example, in aircraft construction, tolerances can be very tight.

When, moreover, carbon composites and other high specification materials are involved, drill bits are subject to rapid wear.

The probe means 12 comprise annular measuring head, smaller in diameter than the hole to be measured, having a plurality of resiliently mounted, radially-extending wall contact probes each extending through the annular head to the lumen of the annulus, and measuring means for measuring the positions of the inner ends of the probes within the lumen.

Usually, a drill bit will be able to drill only six or seven holes before wearing beyond the point where it can drill an in-specification hole. By measuring the hole according to the invention, the drill bit can be changed before it wears so far that it is likely to drill an out-

of-specification hole.

The probe means 12 comprise an annular measuring head 15, smaller in diameter than the hole 11, having a plurality of resiliently mounted, radially-extending wall contact probes 16, each extending through the annular head 15 to the lumen 17 of the annulus, and measuring means for measuring the positions of the inner ends of the probes 16 within the lumen 17.

A typical diameter for the measuring head lumen is from 0.1mm up to several millimetres, with probes 16 of 0.01mm to one or two millimetre cross section. Springs 18 acting between the outer surface of the head 15 and abutments 19 on the probes 16 urge the probes, tipped with ball ends 21, outwardly into contact with the wall 22 of the hole 11. The furthermost extension of the probes 16 is such that their outer radius is greater than the radius of the hole that is to be examined, but only by less than the diameter of the ball ends, so that the edge of the hole pushes the ball ends inwardly. The furthermost extension is controlled by abutments 16a on the probes 16.

Moving the head 15 through the hole 11 pushes the probes 16 inwardly so that their inner ends project more or less into the lumen 17 of the annular head 15. The lumen 17 with its intruding probe inner ends is backlit, as by illuminating the remote end of the hole -see arrows -or by incorporating a lamp, e.g. and led in the probe itself, and imaged via a fibre optic rod 22 which carries the head 15. At the end of the rod 22 is a digital imaging device 13 which images the positions of the probe ends in the lumen. A ccd array of low resolution, imaging the lumen area, will give substantially 1% accuracy locating the ends of the probes. The rod 22 is shown as a rigid rod, but, of course, a flexible optical fibre could be used.

The head 15 can be moved through the hole 11 manually, of course, but a mechanical drive is provided, Figure 4, comprising a workpiece contactor 31 placed over the backlit hole I I and adjusted using the imaging device to locate the head centrally over the hole 11 and a motor-driven plunger 32 to move the head 15 through the hole. A control arrangement 33 operates the imaging device 23 to image the lumen at desired locations along the hole II. The images are examined using software adapted to locate the ends of the probes and check for circularity and dimensions.

The apparatus is used in conjunction with a drill which is drilling the holes II, to examiner each hole as soon as it is drilled. It may be expected that a drill bit will be able to drill, say, seven holes before it is worn too far. Drill bits vary, however, in resistance to wear, and, of course, there may be variations in the material of the workpiece. The rate of bit wear can be monitored on this hole-by-hole inspection routine, and an instruction given to change the bit just before it is expected to drill an out-of-specification hole. Drill bit exchange can be enforced by locking the drill, and can, in more advanced robotics applications, be carried out automatically.

Because the head 15 and its component probes are necessarily very small, they will be made by micromachining methods. Variations in probe length can be accommodated by calibration using a standard hole. V. 5

Claims

Claims: A method for inspecting a hole, comprising passing through the

hole an annular measuring head having a plurality of resiliently mounted, radially-extending wall contact probes, each probe extending through the annular head to the lumen of the annulus, and measuring the positions of the inner ends of the probes within the lumen.

2 A method for inspecting a hole, comprising passing through the hole probe means adapted to respond to one or more aspects of hole configuration in a manner that can be imaged, and imaging said probe means to produce an image of the probe means from which said one or more aspects may be deduced.

3 A method according to claim I or claim 2, in which the positions of the inner ends of the probes are measured optically 4 A method according to claim 3, in which the inner ends of the probes are illuminated and imaged.

A method according to claim 4, in which the inner ends of the probes are backlit.

6 A method according to claim 4 or claim 5, in which the image us taken through a fibre optic arrangement to a camera.

7 A method according to claim 6, in which the camera comprises a digital camera.

8 A method according to any one of claims 4 to 7, in which the image is examined electronically.

9 A method according to claim 8, in which data from electronic examination is used in a production monitoring andlor control arrangement to pass or fail a drilled hole.

A method according to claim 8 or claim 9, in which data from electronic examination is used to pass or fail a drill bit for further drilling operations.

11 A method according to any one of claims 7 to 10, in which data from electronic examination is used to schedule and effect a change of drill bit before it goes out of

specification.

12 Apparatus for inspecting a hole, comprising probe means adapted to be passed through the hole and respond to one or more aspects of hole configuration in a manner that can be imaged, and imaging means adapted to produce an image of the probe means from which said one or more aspects may be deduced.

13 Apparatus according to claim 12, in which the probe means comprise an annular measuring head having a plurality of resiliently mounted, radially-extending wall contact probes, each probe extending through the annular head to the lumen of the annulus, and measuring means for measuring the positions of the inner ends of the probes within the lumen.

14 Apparatus according to claim 13, in which the probes comprise wall-contacting baIl ends.

Apparatus according to claim 13 or claim 14, in which the probes have abutments outside the annular head and springs acting between the head and the abutments.

16 Apparatus according to any one of claims 13 to 15, in which the probes have abutments on their inner ends limiting extension out of the annular head.

17 Apparatus according to claim 12, in which the imaging means comprise a camera.

18 Apparatus according to claim 17, in which the camera comprises a digital camera.

19 Apparatus according to claim 18, in which the camera comprises a low resolution ccd.