GB2168155A

GB2168155A - Apparatus for thickness measurement of re-entrant structures

Info

Publication number: GB2168155A
Application number: GB08120017A
Authority: GB
Inventors: Evan Samuel Thomas
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1980-07-01
Filing date: 1981-06-29
Publication date: 1986-06-11

Abstract

A wall thickness measuring apparatus for a re-entrant component such as a conical radome 2 and comprising a template 21 and a template follower 4 having a caliper 30 carrying internal 31 and external 33 transducers mounted to read variations of corresponding wall surfaces, the follower being traversable over the template to a plurality of defined longitudinal stations on the component. The component is also mounted within a supporting bearing so that the transducers are notionally rotatable to any circumferential position. <IMAGE>

Description

SPECIFICATION Apparatus for thickness measurement of re-entrant structures This invention relates to the thickness measurement of re-entrant structures and in particular to the thickness measurement of conical radomes.

A conical radome is an example of a component the wall thickness of which at various stations both longitudinally and circumferentially can be critical to the performance of the component , and may be required to vary as between stations. The present invention provides apparatus for measuring the wall thickness and of such a component at numerous co-ordinates. The apparatus may also be arranged to provide a shape indication.

According to the present invention apparatus for measuring the wall thickness of a reentrant component of substantially annular cross-section comprises rotation means for rotating the component about the polar axis of the component, a template with a profile corresponding to the profile of the component in the plane of the polarçaxis, and a template follower having an internal and an external transducer, the internal and external transducers being operable to provide in use signals in respect of variation of the component interior and exterior surfaces respectively, the said interior and exterior surfaces being opposite one another.

According to a feature of the present invention the apparatus may include circumferential reader means for establishing the rotational position of the component relative to the transducers. This may comprise a striated collar locatable within the mouth of the component and means reading the striations for recording the said relative circumferential position. The template may also include recorder means for establishing the axial position of the transducers relative to the component. For this the template may carry striations indexing the axial profile of the shell and the template follower means reading the striations for recording the said relative axial position.

According to a further feature of the present invention the apparatus may include rotation drive means for rotating the component about its polar axis to a required position. Traverse drive means may also be included to traverse the transducers to a required position. Preferably the drive means are associated with the recorder means so that the drive means bring consecutive stations of the component to the attention of the transducers. The transducers may have sensing heads for contacting the component surface. These may be retractable, for example by vacuum means, to prevent wear thereof during relative component/transducer motion. A relaying lever, perhaps cranked, may be included to convey internal surface variation to the internal transducer, to minimise the component internal diameter below which measurements cannot be taken.

Measuring apparatus in accordance with the present invention will now be described by way of example with reference to Fig. 1 which shows the apparatus with a conical shell in situ.

The apparatus includes a circumferential positioning assembly 1 for indexing the conical shell 2 to a definable circumferential position when the shell is mounted upon a support assembly 3. A template assembly 4 is used to traverse a measuring heads to a definable axial position on the shell.

The positioning assembly 1 includes a motor drive unit 6 pivotably mounted upon an overhead arm 7. The drive unit 6 has a drive wheel 8 extending therefrom, the drive wheel having an elastomeric edge to ensure drivable contact with the conical shell 2. Collar 9 is threaded within the mouth of the shell 2 the collar having alternate black and white striations radially disposed on its upper surface.

The positioning assembly 1 includes a circumferential position reader 10 which projects an infra-red beam onto the striations and registers the returning beams which are reflected on passage of the white striations thereunder, signalling the circumferential station and controlling the drive unit 6.

The shell 2 is supported within the support assembly 3 which comprises a housing 11 having a thrust bearing 12 which supports the shell vertically and three equi-spaced rollers 13 which support the shell laterally.

The template assembly 4 comprises a support frame 20 and a template 21 having a profile 22 corresponding to the inner cone profile of the shell 2. A template follower 23 is supported on rolling contact bearings 24 and is traversible on the template 21 by means of a belt 25 linked with a motorised pulley 26. A series of alternate black and white striations 27 extend over a required length of the template 21 an axial position reader 28, as described for the positioning assembly 2, is mounted on the follower 23 to count the number of white striations which pass thereunder, signalling the axial station and controlling the motorised pulley 26.

The measuring head 5 comprises a caliper 30 rigidly attached to the follower 23. The caliper 30 has an internal pressure transducer 31 mounted thereon. The internal transducer 31 is of a type used to record precise dimensional changes and is associated with the internal surface of the shell 2. It incorporates a retractable sensor head 31a. A lever 32 is pivotally mounted towards the free end of the caliper 30. On he end of the lever 32 co-acts with the sensor head 31 a and the other end projects beyond the caliper 30 and carries a repeater sensor head 31b for contact with the inner surfaces of the shell 2. An external transducer 33 is oppositely positioned from the internal transducer 31 and rigidly mounted on the caliper 30. It has a retractable sensor head 33a.

The weight of the follower 23 and the measuring head 5 are off-set by a counterbalance weight 34 linked by the belt 25 passing over a freely rotatable pulley 35. The template assembly 4 and measuring head 5 are radially arranged with respect to the shell 2 such that they avoid the equi-spaced rollers 13.

A reading programme control and printout unit 40 is connected to the motors 6 and 26 and the transducers 31 and 33.

When the thickness dimensions of the shell are to be ascertained the collar 9 is secured to the mouth of the shell 2. The drive unit 6 is raised on the overhead arm 7 so that the shell 2 can be inserted into the support assembly 3 to be freely rotatable on the bearing 12 and the wheels 13. The drive unit 6 is then lowered to place the drive wheel 8 in contact with the shell 2, and the follower 23 arranged at a reading programme start station under the control of the unit 40 the drive unit 6 rotates the shell 2 stopping at each striation on the collar 9, as described by the reader 10, the drive unit 26 dropping the follower 23 by a striation 27, as detected by the reader 28, at the completion profile the internal transducer 31 and external transducer 33 of each revolution of the shell. At each station the transducer heads 31b and 33a are allowed to bear on the shell's internal and external surfaces respectively. Their positions are sensed by the transducers and signalled to the unit 40 which prints out a thickness value for each station. The unit 40 then orders the retraction of the sensor heads 31a and 33a and the advance of the shell to the preceeding station.

In an alternative form of the invention the wheel 8 constitutes the third positioning wheel 13, and the unit 1 is swingable toward and away from the shell to permit shell installation rotation and removable. A trippable weight may be used alternately to hold the unit 1 clear from, or to urge it into driving contact with, the shell 2.

Claims

CLAIMS Superseded claims 1-12 New or amended claims 1 to 8: 1. Apparatus for measuring the wall thickness of a conical re-entrant component and comprising rotation means for rotating the component about the polar axis of the component, a template with a profile arranged to be similar to the external profile of the component in a plane including the said polar axis, a template follower having an internal and an external transducer, and traverse drive means for driving the template follower, circumferential reader means for establishing the rotational position of the component with respect to the transducers, and axial reader means for establishing the axial position of the transducers with respect to the component the internal and external transducer being operable to provide in use signals in respect of variation of the component interior and exterior surfaces respectively, at opposite points across the component wall, and the internal transducer having repeater means including a relaying lever adapted for bearing on a surface inaccessible to the transducer alone. 2. Apparatus as claimed in claim 1 and wherein the circumferential reader means comprises a striated collar attachable to the component and means for reading the collar striations. 3. Apparatus as claimed in claim 1 or claim 2 and wherein the axial reader means comprises striations on the template indexing the said external profile of the shell and a reader on the template follower for reading the striations and recording the said relative axial position. 4. Apparatus as claimed in any one of claims 1 to 3 and wherein drive means are associated with the reader means so that the drive means bring consecutive stations of the component to the attention of the transducers. 5. Apparatus as claimed in any one of the preceding claims and wherein the transducers have retractable sensing heads. 6. Apparatus as claimed in any one of the preceding claims having measurement programme control means. 7. Apparatus as claimed in any one of the preceding claims and having print out means for recording thickness measurements for each component station. 8. Apparatus substantially as hereinbefore described with reference to the accompanying drawing. CLAIMS

1. Apparatus for measuring the wall thickness of a re-entrant component of substantially annular cross-section and comprising rotation means for rotating the component about the polar axis of the component, a template with a profile corresponding to the profile of the component in the plane of the polar axis, and a template follower having an internal and an external transducer, the internal and external transducer being operable to provide in use signals in respect of variation of the component interior and exterior surfaces respectively, the said interior and exterior surfaces opposite one another.

2. Apparatus as claimed in claim 1 and including circumferential reader means for establishing the rotational position of the component relative to the transducers.

3. Apparatus as claimed in claim 2 and wherein the circumferential reader means comprises a striated collar attachable to the component and means for reading the collar striations.

4. Apparatus as claimed in any one of claims 1 to 3 and wherein the template carries striations indexing the axial profile of the shell and the template follower means reading the striations for recording the said relative axial position.

5. Apparatus as claimed in any one of the preceding claims and having rotation drive means for rotating the component about its polar axis to a required position.

6. Apparatus as claimed in any one of the preceding claims and having traverse drive means.

7. Apparatus as claimed in claim 5 or claim 6 and wherein drive means are associated with the recorder means so that the drive means bring consecutive stations of the component to the attention of the transducers.

8. Apparatus as claimed in any one of the preceding claims and wherein the transducers have retractable sensing heads.

9. Apparatus as claimed in any one of the preceding claims and wherein the internal transducer has repeater means including a relaying lever.

10. Apparatus as claimed in any one of the preceding claims having measurement programme control means.

11. Apparatus as claimed in any one of the preceding claims and having print out means for recording thickness measurements for each component station.

12. Apparatus substantially hereinbefore described with reference to the accompanying drawing.