GB2248004A

GB2248004A - Device for inspecting internal screw threads

Info

Publication number: GB2248004A
Application number: GB9017737A
Authority: GB
Inventors: Thomas Sidney Peat; Philip Ian Durie; Ronald William Calder Bain; Peter Richard John Hardyman; Alan Forbes Mcleod
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1990-08-11
Filing date: 1990-08-11
Publication date: 1992-03-18
Also published as: GB9017737D0

Abstract

An assembly including a camera 48, a reflecting prism 50 and light fibres 54 for illumination is disposed within a thread 12 to be inspected; the assembly may be stepped along the longitudinal axis of the thread by motor 38 and lead screw 36, and may be rotated by 360 DEG by worm 26 between steps. the rotation sense being reversed for successive rotations. <IMAGE>

Description

An Inspection Device This invention relates to an inspection device for the inspection of an internal cylindrical surface, and more particularly but not exclusively to the inspection of internally screw-threaded surfaces.

According to the present invention, there is provided an inspection device for inspecting an internal cylindrical surface, the device comprising, camera means for obtaining images of the surface, light means for illuminating the surface, means for moving the camera means and the light means longitudinally with respect to the cylindrical surface, and means for rotating the camera means and the light means, the longitudinal means and the rotating means being arranged to cooperate to provide that the camera means obtains images of a predetermined helical path on the surface.

In a preferred aspect of the invention, the helical path is defined by a screw thread defined by the surface.

The cooperation of the camera means and the longitudinal means may be arranged by stepping motor means.

The invention will now be further described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a perspective representation of an inspection device; Figure la shows a modification of the device of Figure 1; Figure 2 shows a diagrammatic representation of an inspection system; Figure 3 shows part of a modification of the device of Figure 1, and Figures 4 and 4a show a position identification system for the device of Figure 1.

Referring now to Figure 1, a device 10 is shown for inspecting a screw-threaded hole 12 in a body 13. The device 10 comprises a housing 14 having an upper screw thread guide 16 and a lower screw thread guide 18 that locate the housing 14 in the hole 12. Three unequally spaced lugs 20 (only two are shown) locate the housing 14 uniquely in corresponding slots 22 in an inner rotary portion 23 of a rotary table 24 which is attached to the body 13. The rotary table 24 is arranged to be driven by a worm gear assembly 26 which is itself driven by an electric motor (not shown).

A camera assembly 30 comprises two spaced support plates 32, 34 respectively which locate in screw threaded engagement with a lead screw 36. The lead screw 36 is arranged to be driven by an electric motor 38 mounted at 40 to the upper end of the housing 14. Four equi-spaced pegs 42 (only two are shown) locate in corresponding longitudinal slots 44 (only one is shown) to guide the camera assembly 30 as it is raised or lowered by the lead screw 36. A camera 48 with a control and signal cable 49 is mounted longitudinally between the support plates 32, 34 above a 45O glass prism 50 which is aligned with a slot 51 in the housing 14. A light unit 52 adjacent to the prism 50 is supplied from a fibre optic cable 54 from an external source (not shown).

In operation, the worm gear assembly 26 is driven so as to rotate the inner portion 23 and thereby the housing 14 through 360O in one direction at a speed such that the prism 50 reflects to the camera 48 the image of the screw thread 12 and follows the helix of the screw thread 12.

The lead screw 36 is then rotated by the electric motor 38 to raise the camera 48 by one or more thread pitches.

The worm gear assembly 26 then reverses through 360" and the sequence continues until a complete image is taken of the screw thread 12. The control and signal cable 49 as shown in Figure 2 may be connected to a monitor 60 which is itself connected to a video cassette recorder 62, and the operating sequence is controlled by a programmable logic controller 64.

As an alternative to the use of the light unit 52, in a modified arrangement as shown in Figure la, a transparent tubular light guide 55 having a flared inlet end 56 is concentric with and is a relatively close fit inside the housing 14. A circular tubular light source 57 is disposed at the flared inlet end 56. A lower end 58 of the light guide 55 terminates in the vicinity of the prism 30.

Appropriate indicia may be associated with the rotary table 24 and the lead screw 36 to provide data on the relative positions. Stepping motors may be used as the electric motors in the device 10.

In a modified device as shown in Figure 3, a mounting 68 supports a camera assembly 70 and a prism 71 and is guided by two rods 72, 74 in parallel relationship instead of by the pegs 42 in the slots 44 of Figure 1. A lead screw 76 extends through the mounting 68, parallel and between the rods 72, 74, and locates in a cross-piece 78 which is clamped to the ends of the rods 72, 74. The other ends of the rods 72, 74 and the lead screw are supported in a similar manner. A light unit 80 is supported from the mounting 68, and in other respects the modified device of Figure 3 operates in a similar manner to the device of Figure 1.

An example of a position identification system for providing information on camera orientation and vertical position is shown in Figure 4 to which reference is made.

A light source 84 is mounted on and fixed to the rotary table 24 of Figure 1, and carries an opaque coded pattern 86 on one continuous surface. Light from the light source 84 is transmitted by a number of individual fibre optic guides 88 (three are shown) which rotate together with the camera 48 to the front of the prism 50. The camera 48 views the ends 89 of the light guides 88 through the prism 50 and their image 90 is seen on the screen of the monitor 60 - see Figure 4a. The combination of the light guides 88 illuminated, changes in accordance with the coded pattern 86 as the camera 48 and prism 50 are rotated. The code of the coded pattern 86 which may be binary or otherwise indicates to the user the sector 'k' to which the camera 48 points. A scale 92 placed adjacent to the slot 51 in the housing 14 of Figure 1 is viewed via the prism 50 by the camera 48.

The scale 92 is not moved when the camera 48 is raised by operation of the lead screw 36, and the scale 92 is seen at the edge of the monitor 60 to identify individual screw threads. For example, in Figure 4a the numeral 6 identifies the screw thread which the camera 48 is examining and which appears in the centre of the screen 61 of the monitor 60.

Claims

1. An inspection device for inspecting an internal cylindrical surface comprising camera means for obtaining images of the surface, light means for illuminating the surface, means for moving the camera means and the light means longitudinally with respect to the cylindrical surface and means for rotating the camera means and the light means, the longitudinal means and rotating means being arranged to cooperate to provide that the camera means obtains images of a predetermined helical path on the surface.

2. An inspection devices as claimed in Claim 1 in which the helical path comprises a screw thread on the surface.

3. An inspection device as claimed in Claim 1 or 2 including stepping motors for effecting longitudinal and rotational movements.

4. An inspection device for inspecting an internal cylindrical surface constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.