GB2493205A

GB2493205A - Non-contact measuring device

Info

Publication number: GB2493205A
Application number: GB1113074.7A
Authority: GB
Inventors: Jonathan Victor Watson; Christopher Andrew Thompson; Richard John Reynolds; Daniel James Williams
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2011-07-29
Filing date: 2011-07-29
Publication date: 2013-01-30
Also published as: GB201113074D0

Abstract

A non-contact measuring device is provided which allows measurements to be made in confined spaces. The device 2 comprises: a lens 8 having a field of view 12; a laser source 4 operable to produce a laser beam 14 for illuminating a target 16 within the field of view 12, the laser source 4 being configured such that the laser beam 14 intersects the field of view between the lens 8 and the target 16; and an optical relay 10 coupled to the lens 8. In use, the lens 8 and at least a portion of the optical relay 10 are received within a cavity through an aperture and wherein the lens 8 produces an image of the target 16 within the cavity which is transmitted by the optical relay 10 from the lens 8 at one end of the optical relay, out of the cavity and to the other end of the optical relay 10 for analysis. The position of the laser beam 14 in the image corresponds to the distance / range x of the target 16 from the lens 8. The optical relay 10 and lens 8 may form part of a borescope. The device may further comprise a camera which is coupled to the optical relay 10 and captures the image from the lens 8 via the optical relay 10.

Description

A NON-CONTACT MEASURING DEVICE AND METHOD

The present invention relates to a non-contact measuring device and method, and particularly, but not exclusively, to such a device and method which allows measurements to be made in confined spaces.

Background

Various non-contact measurement techniques and devices are known, which are able to measure properties such as distances, shapes, contours, etc. For example, Figure 1 shows a known measuring device 1 which uses laser triangulation to measure distance. The device 1 comprises a laser emitter 3 and a laser receiverS which are separated from one another by a known distance d. In use, the laser emitter 3 emits a beam of light 7 which is incident on a target 9. The incident beam 7 is reflected by the target 9 and the reflected beam 11 is received by the laser receiver 5. The position of the reflected beam 11 at the laser receiver 5 may be used to calculate the distance from the device 1 to the target 9.

For the measurement of small distances, the required separation between the laser emitter and laser receiver may lead to the device being prohibitively large, particularly for applications in confined spaces.

It is therefore desirable to provide a non-contact measurement device and method which allows measurements to be made in confined spaces.

Statements of Invention

In accordance with an aspect of the invention, there is provided a non-contact measuring device comprising: a lens having a field of view; a laser source operable to produce a laser beam for illuminating a target within the field of view, the laser source being configured such that the laser beam intersects the field of view between the lens and the target; and an optical relay coupled to the lens; wherein, in use, the lens and at least a portion of the optical relay are received within a cavity through an aperture and wherein the lens produces an image of the target within the cavity which is transmitted by the optical relay from the lens at one end of the optical relay, out of the cavity and to the other end of the optical relay for analysis, and wherein the position of the laser beam in the image corresponds to the distance of the target from the lens.

The optical relay and lens may form part of a borescope.

The device may further comprise an adjusting means configured to adjust the lens and/or laser beam to maximise the sensitivity of the measurement.

is The adjusting means may be configured to maximise the sensitivity of the measurement by reducing the distance between the lens and the target.

The adjusting means may be configured to maximise the sensitivity of the device by moving the position of the laser beam in the image towards a perimeter of the image.

The adjusting means may be operable to adjust the field of view of the lens and/or to move the laser beam and lens relative to one another such that the laser beam impinges on the target towards the perimeter of the field of view.

The adjusting means may adjust the lens and/or laser beam such that the laser beam is at the perimeter of the image The laser source may be offset from the axis of the lens. The laser source may also be angled so that the laser beam intersects the field of view between the lens and the target.

The optical relay may be an optical fibre.

A proximal portion of the optical relay may be enclosed within a probe and a distal portion of the optical relay including the lens may protrude from the probe.

The device may further comprise a spacer member which is adjustable and allows the length of the distal portion of the optical relay to be varied. This may allow the distance between the lens and the target to be adjusted.

The device may further comprise a camera for capturing the image from the lens. The camera may, for example, be a digital camera, such as a CCD camera. The camera may also acquire video images.

The device may further comprise measuring means for measuring the distance of the is laser beam from the centre of the image. For example, the measuring means may count the number of pixels between the laser beam and the centre of the image. This process may be automated using digital image processing.

The laser source may be connected to an optical fibre which transmits the laser beam towards the target.

The optical fibre which transmits the laser beam may terminate in a collimating lens.

The laser source may be a laser diode.

The laser source, optical fibre and/or collimating lens may be housed within the probe.

The device may be attached to an end of a borescope, particularly a flexible borescope.

In accordance with another aspect of the invention there is provided a non-contact measuring method, the method comprising: introducing a lens and a laser beam into a cavity through an aperture; positioning a target within a field of view of the lens inside the cavity; illuminating the target with the laser beam, the laser beam being arranged such that it intersects the field of view between the lens and the target; producing an image of the target using the lens; wherein the position of the laser beam in the image corresponds to the distance of the target from the lens; transmitting the image from the lens along an optical relay and out of the cavity for analysis; and measuring the distance of the target based on the position of the laser beam in the image.

The method may further comprise adjusting the lens and/or laser beam to maximise the sensitivity of the measurement.

The sensitivity of the measurement may be maximised by reducing the distance between the lens and the target.

is The sensitivity of the measurement may be maximised by moving the position of the laser beam in the image towards a perimeter of the image.

Adjusting the lens and/or laser beam may comprise adjusting the field of view of the lens and/or moving the laser beam and lens relative to one another such that the laser beam impinges on the target towards the perimeter of the field of view.

The lens and/or laser beam may be adjusted so that the laser beam is at the perimeter of the image.

The cavity may be within an engine or other mechanical unit used in the Aerospace, Automotive, Marine or other industry.

In accordance with another aspect of the invention there is provided a non-contact measuring device comprising: a lens having a field of view; and a laser source operable to produce a laser beam for illuminating a target within the field of view, the laser source being configured such that the laser beam bypasses the lens; wherein, in use, the lens produces an image of the target and wherein the position of the laser beam in the image corresponds to the distance of the target from the lens.

In accordance with another aspect of the invention there is provided a non-contact measuring method, the method comprising: positioning a target within a field of view of a lens; illuminating the target with a laser beam; producing an image of the target using the lens; wherein the position of the laser beam in the image corresponds to the distance of the target from the lens; and measuring the distance of the target based on the position of the laser beam in the image.

Brief Description of the Drawings

For a better understanding of the present invention, and to show more clearly how it is may be carried into effect, reference will now be made by way of example, to the following drawings, in which: Figure 1 is a schematic view of a prior art device which uses laser triangulation; Figure 2 is a schematic view of a non-contact measuring device according to an embodiment of the invention; Figure 3 is a graph of fractional laser height versus target distance; Figure 4 is a detailed perspective view of the measuring device; Figure 5 is a cross-sectional view of the measuring device shown in Figure 4; Figure 6 is a cross-sectional view of a measuring device according to another embodiment of the invention; and Figure 7 is a more detailed view of the measuring device shown in Figure 6.

Detailed Description

With reference to Figure 2, a non-contact measuring device 2 in accordance with an embodiment of the invention comprises a laser source 4 and a borescope 6. The borescope 6 comprises a lens 8 and an optical relay 10 which transmits an image from the lens 8 at one end of the optical relay 10 to the other end of the optical relay 10. The lens 8 has a height and a divergence angle 0. The divergence angle Odefines the field of view of the lens 8 which is indicated by diverging lines 12. The field of view defines the horizontal and vertical extent of the image that can be captured by the lens 8 at the working distance.

The laser source 4 is offset from the lens axis by an offset distance & The offset distance Sis greater than /1/2. Accordingly, a collimated laser beam 14 produced by the laser source 4 bypasses the lens 8.

In use, a target 16 is positioned within the field of view of the lens 8. The device 2 is used to measure the distance x between the target 16 and the lens 8. As a result of the offset distance 8 the laser beam 14 (of visible spectrum wavelength) enters the field of view of the lens 8 between the lens 8 and the target 16. The laser beam 14 illuminates the target 16 at a point P on the surface of the target.

The lens 8 collects light from the target 16 and forms an image of the target 16 on the lens 8. The laser beam 14 is projected on to the lens 8 at a distance yfrom the lens axis (i.e. the centre of the image).

The distance y as a fraction of the lens height S (herein referred to as the fractional laser height y/S) is a monotonic function of the target distance x. In other words, as the target distance x increases, the fractional laser height y/S decreases.

If a simplification regarding the lens properties is made, it can be shown that the fractional laser height y/S is related to the target distance x by the following equation: 1 [1] A A+2xtanO Equation 1 is plotted in Figure 3 for a set of nominal values and illustrates the monotonic relationship between the fractional laser height y/A and the target distance x.

Equation 1 will not necessarily hold with a real lens, however the equation allows the effect of changing various system parameters to be determined. With a real lens the function relating fractional laser height y/A to target distance x will be empirical and determined through a calibration procedure, however the shape will approximately follow the curve shown in Figure 3.

The maximum fractional height y/A corresponds to a condition where the laser beam 14 is projected on to the lens 8 at its outer extremities. This is achieved when the laser beam 14 illuminates the target 16 at the edge of the field of view of the lens 8. This represents a minimum target distance x, since the laser beam 14 will not impinge on the field of view at smaller distances. As the distance increases from this minimum, the fractional height decreases.

The fractional laser height y/A can therefore be used to measure the distance x of the target 16 from the lens 8.

As is shown in Figure 3, the rate of change of the fractional laser height y/A decreases with target distance x. The rate of change of the fractional laser height y/a defines the accuracy of the measurements. In other words, if the rate of change is increased the measurement device 2 will be more sensitive to changes in target distance x. As shown in Figure 3, if it is assumed that the fractional laser height y/A can be measured with a constant uncertainty e, the uncertainty tx1 at smaller distances is lower than the uncertainty u2 at larger distances. Accordingly, the uncertainty in the target distance x increases with target distance x.

Furthermore, for any given working distance, the sensitivity of the device 2 may be increased by increasing the laser offset distance Sor decreasing the field of view divergence 9. Both of these alterations act to move the laser beam 14 towards the edge of the field of view, thus increasing rate of change of the fractional laser height y1tA.

Accordingly, the device 2 may be provided with an adjusting means (not shown) which is configured to maximise the sensitivity of the device 2. The adjusting means is configured to maximise the sensitivity of the device 2 by minimising the target distance x, maximising the laser offset distance b' and/or minimising the field of view divergence a The laser offset distance 5and/or field of view divergence Gmay be controlled such that the laser beam 14 illuminates the target 16 at the perimeter of the field of view of the lens 8.

The image may be captured using a camera. The captured image can be digitally processed to measure the distance y between the laser beam and the centre of the image. Accordingly, for a given image resolution of the camera, a higher measurement resolution can be obtained by maximising the rate of change, as described above.

Figs. 4 and 5 show a practical implementation of this concept. In this embodiment, a laser source 4, borescope 6 and a digital camera 18 are integrated into a single unit.

As described previously, the borescope 6 comprises a lens 8 and an optical relay 10 which transmits an image from the lens 8 at one end of the optical relay 10 to an eyepiece 20 at the other end of the optical relay 10. The borescope 6 and digital camera 18 are held within a housing 22. The housing 22 fixes the relative positions of the borescope 6 and the digital camera 18 such that the eyepiece 20 of the borescope 6 is adjacent to a lens 24 of the digital camera 18. This allows the digital camera 18 to capture the image from the eyepiece 20 of the borescope 6. In this regard, the lens 24 of the digital camera 18 is captured by a pair of half rings 21 which are attached to the housing 22.

The optical relay 10 has a diameter of 5mm and extends from the housing 22 and through a mounting collar 24 and probe 26. The probe 26 supports the optical relay 10 along part of its length. However, a distal portion of the optical relay 10, which comprises the lens 8, protrudes from the probe 26.

The laser source 4, for example a laser diode, is attached to the exterior of the housing 22. An optical fibre 28 is connected to the laser source 4 and passes into the housing 22 and to the mounting collar 24, where the optical fibre 28 terminates. A collimating lens 30 is provided at the end of the optical fibre 28 to focus the laser beam 14. The collimating lens 30 is preferably 2.5mm in diameter and produces a laser beam of approximately 0.6mm. It is desirable to position the collimating lens 30 close to the front of the device in order to minimise the measurement error due to deflection and bending of the device.

is The mounting collar 24 and probe 26 are coupled to the housing 22 by an adapter plate 32. The adapter plate 32 is keyed to prevent relative rotation. The adapter plate 32 is separated from the housing 22 by a spacing member 34, which has a thickness a. The spacing member 34 may be selected to have any thickness a, and thus to vary the distance between the adapter plate 32 and the housing 22. This has the effect of changing the length b of the distal portion of the optical relay 10 which protrudes from the probe 26. The length b may be controlled in order to minimise the distance between the lens 8 and the target and thus to maximise the sensitivity of the device.

The laser source 4 is slidably mounted to the exterior of the housing 22 to allow the laser source 4, optical fibre 28 and collimating lens 30 to translate with the adapter plate 32.

The collimating lens 30 is secured in the probe 26 by an insert 36. The insert 36 also supports the optical relay 10 of the borescope 6 and thus increases the resistance of the optical relay 10 to bending.

Two diametrically opposed dowel pins 38 are provided on the adaptor plate 32. The dowel pins 38 extend through corresponding holes in the spacing member 34 and into bores in the housing 22. The dowel pins 38 therefore align and support the housing 22, spacing member 34 and adapter plate 32 while the optical fibre 28 and insert 36 are installed.

In use, the device is introduced into a cavity of a gas turbine engine through a 7mm diameter circular aperture. The probe 26 and the protruding portion of the optical relay pass into the gas turbine engine, with the mounting collar 24 abutting an external surface of the gas turbine engine surrounding the aperture. The mounting collar 24 may also be used to attach the device to the engine.

As described previously, a collimated laser beam is emitted by the collimating lens 30.

The laser beam is incident of a target within the engine cavity. The lens 8 collects light from the target and forms an image of the target on the lens 8. This is transmitted along the optical relay 10 to the eyepiece 20 and the lens 24 of the digital camera 18.

is Here the image is captured and analysed to determine the fractional laser height y/a, and from this value the distance of the target from the lens 8. This process may be automated using digital image processing.

The device allows measurements to be made without contacting the target, hence the engine's shafts can be rotated with the probe 26 in situ.

The borescope 6 may further comprise a high intensity light source which illuminates the field of view of the lens 8. For example, a number of optical fibres may be provided around the optical relay 10 to transmit light from a light source to the target. This may be used to illuminate the inside of the engine. The capturing of illuminated photos of the target inside the engine is an additional benefit of this device.

Figs. 6 and 7 show another embodiment of the invention, where the device is formed as a module 40 for attachment to a flexible borescope.

The borescope comprises a flexible optical relay 10, formed, for example, by a plurality of optical fibres. The module 40 may be threadably attached to the optical relay 10.

The module 40 comprises a lens 8 defining a field of view of the borescope and a CCD camera 18 for capturing the image from lens 8. The module 40 further comprises a collimating lens 30. A laser source (not shown) supplies a laser beam through an optical fibre of the optical relay 10 to the collimating lens 30. The laser beam 14 is emitted from the collimating lens and is incident on a target.

The image is transmitted trom the camera 18 along another optical fibre of the optical relay. As described previously, the image may then be processing to determine the fractional laser height y/A, which can in turn be used to calculate the distance of the target from the lens 8.

The target may be a fan or turbine blade. Specifically, the distance to the tip of the is blade may be measured to determine the clearance between the tip and the casing.

The device may be orientated to look at the tip of a blade from above. The device may also capture video images to enable live monitoring of the distance to the target. A recording device may also be provided to log the distance measurements over time.

The same technique could be used for monitoring the movement of rotational parts such as gears, where the displacement of the teeth could be measured using the invention. The invention is ideal for performing measurement through a small hole, and could be performed inside mechanical units in the Aerospace, Automotive, Marine or other industries. The invention may remove the need to disassemble a unit to measure the displacement of moving parts inside the unit.

The device could also be used in manufacturing, where the system could measure distances directly or become part of a feedback loop for machining. This could be particularly useful in the alignment of components or during assembly, and could be integrated into various tooling hardware.

Furthermore, the invention could be applied to the field of medicine for measuring the distance to objects during keyhole surgery or endoscopy, particularly using the module described previously in conjunction with a flexible borescope (endoscope).

The invention could also be implemented to measure distances inside pipes, tubes or containment vessels. This could be applicable to water, gas or other areas in order to gauge distances to blockages or to gauge fluid levels.

The invention may also be used in geology to measure the depth of a crack or of a drilled hole (for example during oil drilling).

Although the target has been described as being within the field of view of the lens, it is not necessary for the whole of the target be within the field of view, only a portion which is illuminated by the laser beam.

Although the device has been described as measuring the distance of the target from the lens, alternative measurements which derive from this distance may be made. For example, the device may measure speed, shape, contours, etc. To avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the invention may also be used with any other aspect or embodiment of the invention.

Claims

<claim-text>CLAIMSA non-contact measuring device comprising:a lens having a field of view;a laser source operable to produce a laser beam for illuminating a target within the field of view, the laser source being configured such that the laser beam intersects the field of view between the lens and the target; and an optical relay coupled to the lens; wherein, in use, the lens and at least a portion of the optical relay are received within a cavity through an aperture and wherein the lens produces an image of the target within the cavity which is transmitted by the optical relay from the lens at one end of the optical relay, out of the cavity and to the other end of the optical relay for analysis; the position of the laser beam in the image corresponding to the distance of the target from the lens.</claim-text> <claim-text>2 A device as claimed in claim 1, wherein the optical relay and lens form part of a borescope.</claim-text> <claim-text>3 A device as claimed in any preceding claim, further comprising an adjusting means configured to adjust the lens and/or laser beam to maximise the sensitivity of the measurement.</claim-text> <claim-text>4 A device as claimed in claim 3, wherein the adjusting means is configured to maximise the sensitivity of the measurement by reducing the distance between the lens and the target.</claim-text> <claim-text>A device as claimed in claim 3 or 4, wherein the adjusting means is configured to maximise the sensitivity of the device by moving the position of the laser beam in the image towards a perimeter of the image.</claim-text> <claim-text>6 A device as claimed in claim 5, wherein the adjusting means is operable to adjust the field of view of the lens and/or to move the laser beam and lens relative to one another such that the laser beam impinges on the target towardsthe perimeter of the field of view.</claim-text> <claim-text>7 A device as claimed in claim 5 or 6, wherein the adjusting means adjusts the lens and/or laser beam such that the laser beam is at the perimeter of the image 8 A device as claimed in any preceding claim, wherein a proximal portion of the optical relay is enclosed within a probe and wherein a distal portion of the optical relay including the lens protrudes from the probe.9 A device as claimed in claim 8, wherein the device further comprises a spacer member which is adjustable and allows the length of the distal portion of the optical relay to be varied.A device as claimed in any preceding claim, further comprising a camera which is coupled to the optical relay and captures the image from the lens via the optical relay.11 A device as claimed in any preceding claim, further comprising measuring means for measuring the distance of the laser beam from the centre of the image.12 A non-contact measuring device substantially as described herein with reference to and as shown in the accompanying drawings.13 A non-contact measuring method, the method comprising: introducing a lens and a laser beam into a cavity through an aperture; positioning a target within a field of view of the lens inside the cavity; illuminating the target with the laser beam, the laser beam being arranged such that it intersects the field of view between the lens and the target; producing an image of the target using the lens; wherein the position of the laser beam in the image corresponds to the distance of the target from the lens; transmitting the image from the lens along an optical relay and out of the cavity for analysis; and measuring the distance of the target based on the position of the laser beam in the image.14 A method as claimed in claim 13, further comprising adjusting the lens and/or laser beam to maximise the sensitivity of the measurement.A method as claimed in claim 14, wherein the sensitivity of the measurement is maximised by reducing the distance between the lens and the target.16 A method as claimed in claim 14 or 15, wherein the sensitivity of the measurement is maximised by moving the position of the laser beam in the image towards a perimeter of the image.17 A method as claimed in claim 16, wherein adjusting the lens and/or laser beam comprises adjusting the field of view of the lens and/or moving the laser beam and lens relative to one another such that the laser beam impinges on the targettowards the perimeter of the field of view.18 A method as claimed in claim 16 or 17, wherein the lens and/or laser beam are adjusted so that the laser beam is at the perimeter of the image.19 A non-contact measuring method substantially as described herein with reference to and as shown in the accompanying drawings.</claim-text>