WO1993014375A1

WO1993014375A1 - Gauging apparatus

Info

Publication number: WO1993014375A1
Application number: PCT/GB1993/000128
Authority: WO
Inventors: Eric Ireland; Geoffrey Kaniuk
Original assignee: VERNON GAUGING SYSTEMS Ltd; MS Instruments Ltd
Current assignee: VERNON GAUGING SYSTEMS Ltd; MS Instruments Ltd
Priority date: 1992-01-20
Filing date: 1993-01-20
Publication date: 1993-07-22
Anticipated expiration: 1994-07-20
Also published as: GB9201123D0

Abstract

Gauging apparatus includes a probe (10) with a contact element for contacting a surface of an object to be measured. An indicator (12) such as a mirror is positioned on the probe at a point near the contact point of the contact element and emits, transmits or reflects a signal which indicates the position and/or orientation of the contact element in the field of view of a camera (15). A processor determines the positions of the contact element from the signals picked up by one or more such cameras from one or more such indicators as the contact element moves across the surface of the object.

Description

Gauging Apparatus

The present invention relates to gauging apparatus and more particularly to a probe for such apparatus and which is arranged to contact a surface of a solid object.

Gauging apparatus including a probe is already known and such apparatus is used to compare the geometry of test surfaces with a predetermined datum in order to determine manufacturing quality.

The present invention provides gauging apparatus comprising a probe for contacting a surface of an object under test and means for optically monitoring the probe in order to derive signals representative of probe movement.

The monitoring means may take the form of one or more targets on the probe or probes and means for detecting movement of the targets. Preferably the detecting means comprises a camera.

In order that the present invention be more readily understood embodiments thereof will now be described by way of example with reference to the accompanying drawings which:-

Fig. 1 shows a first embodiment of apparatus according to the present invention;

Fig. 2 shows a second embodiment according to the present invention;

Fig. 3 shows a third embodiment according to the present invention;

Fig. 4 shows a fourth embodiment according to the present invention; and

Fig. 5 shows a modification to the probe as shown in the previous figures.

Gauging apparatus comprises a probe having a contact element and at least one target provided at a location and in an orientation on the probe which is known with respect to the contact element. The targets may be self luminous, illuminated, electrically powered or excited with energy so as to emit light. In these examples they are illuminated by a light source and are viewed by a camera(s). The camera(s) may, however, be replaced by any other optical information processing system including direct observation by an operator.

In the embodiment of the invention shown in Figure 1 the gauging apparatus has a probe 10 associated with a light source 14. Two reflective targets 12 are mounted on a contact element 11 of the probe, each target reflecting the light from the light source 14 as the contact element 11 moves in relation to the surface 16 of an object being gauged. Associated with each target 12 is a camera 15. Each camera is thus able to provide to a processor 17 a signal in which the position in two dimensions of one of the targets at a given time is indicated. By processing the signals from each camera at a given time, a vector representing the position and/or the orientation of the contact element may be determined by the processor 17. This vector, in combination with sufficient knowledge of the probe design, allows the actual contact point of the contact element 11 to the surface 16 to be determined. By carrying out this determination at several points on the surface, the characteristics of the complete surface may be measured to a desired resolution.

Preferably the target or targets should be placed as close to the point of contact with the surface as possible so as to minimize errors associated with the support and positioning of the contact element.

For accuracy of measurement, it is also preferable for the cameras to be a sufficient distance away as to minimize parallax errors. Alternatively, the cameras may be tracked together with the probe, thus allowing the target to remain at or near to the centre of the field of view of each camera even for measurements over a large surface.

Embodiments of the invention in which the camera is a long distance from the target allow gauging to be carried out of the insides of long tubes or cavities.

Where the measurements being made require a finer resolution than is possible with the standard field of view, the system can be locally zoomed in to provide a magnified result. It may be necessary to zoom in on some portions but not others of a complex surface.

The number of targets and/or optical monitoring means can be varied depending of the number of dimensions which it is desired to gauge. In simple cases it may be possible to use only one target.

The source may be any source of suitable radiation such as white light, infra-red light, or microwaves, and may be produced in any convenient manner, for example by an LED or a laser. The energy may be directed from the source to the target by a variety of means such as light-guides, fibre-optics, mirrors, wave-guides or conductors as well as by direct illumination.

The probe may be a cross-head or combinations of individual probes. Optical fibres may be used. The principal above can also be used in multiple target situations on the same probe to determine the position of the probe in the number of places as there are targets and is particularly useful where a geometric angular component is present, as for example in turbine blade measurement.

SUBSTITUTESHEET In Figure 1 the light source 14 is located distant from the tip 11 which is provided with transmissive apertures forming the targets 12. This is shown more clearly in Figure 2 where it is assumed that there is only one target and the periphery of the tip 11 is of larger diameter than the stem. The light source 14 can be part of the probe 10 and the light from the source 12 can be transmitted up the stem to the light transmissive aperture in any convenient way including the use of one or more optical fibres. The advantage of this arrangement is that the stem can be very long and if the stem bends there is no loss of accuracy as the light transmissive window is viewed directly and is directly related to the tip diameter.

An alternative probe design is shown in Figure 3 where the probe 10 is provided with a conventional tip 11. However, the probe 10 is pivotally mounted in a frame 20 by means of a ball and socket joint, the ball element 21 forming the base of the probe. The ball is provided with a target 12 again in the form of a light transmissive window for emitting light from a light source such as an LED within the ball element. Movement of the target 12 within the field of view of the camera or other light sensitive device then indicates the profile of the object 16 under test. Equally the camera or other light sensitive device could track movement of the target as it pivots and this movement could be translated by the processor into appropriate signals.

Figure 4 shows that the probe tip can be of any convenient predetermined shape such as a cross with a target 12 located at a convenient position depending on the shape. In this case the convenient position is at the centre of the cross. Turning now to Figure 5, This shows diagrammatically two arrangements for a plurality of probes. In Figure 5a there are four probes mounted at the centres of each side of a rectangle. The exact disposition is not important as long as it is known and either remains unchanged or is changed under the control of a processor which can feed appropriate signals to the main processor. An alternative arrangement is shown in Figure 5b, where the four probes are regularly arranged in rows and columns. All probes can be viewed by one camera if desired or each probe can be viewed individually.

It will be appreciated that other probe dispositions can be used depending on the object to be tested.

In all the embodiments described above, it is assumed that the probe will be hollow and transmit light through the probe to the target. It is possible, however, to envisage reflective targets where the area of the test piece under test is illuminated by an external source of light and the camera simply views totally reflected light. It is also possible for the target to be coloured or to filter light so that the camera sensitivity and accuracy can be increased.

Generally the apparatus is able to provide more accurate data if the probe is stationary at each of a number of points while measurements are made. The apparatus can however, be adapted to measure results dynamically as the probe is traced across the surface of an objection. The reduction of the resulting surface measurements would then be limited only by the processing power of the apparatus and the optical resolution of the cameras.

Claims

CLAIMS :

1. Gauging apparatus comprising a probe for contacting a surface of an object and monitoring means for optically monitoring the probe in order to derive signals representative of the position and/or the orientation of the probe.

2. Gauging apparatus according to claim 1 wherein the monitoring means comprises indicating means positioned on the probe and detecting means for detecting the position and/or orientation of the indicating means.

3. Gauging apparatus according to claim 2 wherein the indicating means is a reflector or is luminous.

4. Gauging apparatus according to claim 3 wherein the indicating means comprises a transmissive element and a light source.

5. Gauging apparatus according to claim 4 wherein the light source is located within the probe.

6. Gauging apparatus according to any of claims 2 to 5 wherein the detecting means comprises a camera.

7. Gauging apparatus according to any one of the preceding claims wherein the monitoring means includes a plurality of indicating means.

8. Gauging apparatus according to any of the preceding claims wherein the monitoring means includes a plurality of detecting means.