MEASUREMENT SYSTEMS

Abstract: A laser beam (14, 32) is projected on to a plurality of aligned screens (11, 30a-d), each of which is partially opaque. The position at which the laser beam impinges on each screen is determined and measurement calculations carried out form the information thereby obtained.

Description: 1 MEASUREMENT SYSTEMS Field of the Invention This invention relates to measurement systems of the kind which include means for projecting a laser beam on to a screen, means for determining the position at which the laser beam impinges on the screen and means for carrying out a measurement calculation from the information thereby obtained. Such a system is hereinafter referred to for convenience as "a measurement system of the kind specified". The invention also relates to a method of measuring which includes projecting a laser beam on to a screen, determining the position at which the laser impinges on the screen and carrying out a measurement calculation from the information thereby obtained. Such a method is hereinafter for convenience referred to as "a method of measuring of the kind specified". One example of a measurement system of the kind specified, for use as a structure movement monitoring and emergency alarm system, is described in US Patent Specification No. 5,657,003, which also discloses a method of measuring of the kind specified.. It is an object of the present invention to provide an improved measurement system of the kind specified. It is also an object of 2 the present invention to provide an improved method of measuring of the kind specified. Summary of the Invention According to a first aspect of the present invention there is provided a measurement system of the kind specified characterised in that a plurality of screens are provided, at least a first of which is partially opaque and that a single laser beam is caused to impinge on each of said plurality of screens. According to a second aspect of the present invention there is provided a method of measuring of the kind specified which includes the use of a plurality of screens, at least a first of which is partially opaque, and that a single laser beam is caused to impinge on said plurality of screens. There is preferably a plurality of partially opaque screens, each of which is incorporated in a target. Each target may include a single screen, but at least one of the targets preferably includes two screens. Each target is preferably of tubular form, of either rectangular or circular cross-section and, in the case of a target which includes two screens, will contain two oppositely directed video cameras linked to a computer for carrying out the necessary computations relating to the position at which the laser beam impinges on the two screens. 3 The system may be used for guiding operating of a tunnelling machine when carrying out a tunnelling operation, the laser beam being set on the course which the tunnelling machine is required to adopt and computations being carried out to indicate any variations of the tunnelling machine from that course. Alternatively, the system may be used for monitoring movements of part of a structure, for example, a lift shaft, a bridge or a tunnel lining, and providing an indication of the extent of movement of such parts. Brief Descriptions of the Drawings Figures 1 (a) and 1 (b) are perspective views of double screen target transducers specifically designed for use as guidance transducers in tunnelling machines, Figure 2 is a sectional view of a guidance transducer, Figure 3 shows the layout of a computer management system for a tunnelling machine, Figure 4 shows the use of a plurality of single screen alignment transducers to monitor movements of a structure, Figure 5 shows the use of a plurality of double screen alignment transducers incorporated within a structure position monitoring system, Figure 6 shows a multi-transducer structure position monitoring system which also includes strain gauges, Figure 7 shows the use of a plurality of double screen alignment transducers in combination with a prism to provide a second referencing line whose position can be measured by a target transducer mounted on the laser generator, and Figure 8 is a block diagram showing the information flow for a system employing these transducers. Description of the Preferred Embodiments The target 10 shown in Figure 1 (a) is of a welded steel construction and is of square cross-section, typically 180 mm. X 180 mm., with a length of 420 mm. It has a screen 11 at each end, with a typical screen area of 165 mm. X 130 mm. The target 12 shown in Figure 1 (b) is also of a welded steel construction, and is of circular cross-section, with a typical external diameter of 205 mm. It also has a screen 11 at each end, with a typical screen diameter of 160 mm. As shown in Figure 2, each target 10, 12 contains two CCD video cameras 13 which are arranged facing in opposite directions so as to obtain images of the two screens 11 and, in particular, images showing the positions at which a laser beam 14 impinges on the two screens 11. The two CCD video cameras 13 are connected, as described below, to a computer which carries out calculations concerning the positions at which the laser beam 14 impinges on the screens 11. Each target 10, 12 is provided with feet 15 which are adjustable to enable any required initial setting operations to be carried out. Each screen 11 is made of a material which is such that a proportion of the energy of the laser beam 14 is absorbed by the screen 11 and results in random reflection indicating a spot where the laser light travels through. Such a material is referred to herein as being partially opaque and may be glass, polymethylmethacrylate or other translucent or semi-translucent material. The position of the spot created by the laser beam 14 is very accurately registered using the appropriate video camera 13, whose signal can then be corrected using a calibration table. The target 10, 12 shown in Figure 2 can be considered as having a first screen 11 (a) and a second screen 11 (b). The proportion of the light that passes through the first screen 11 (a) can then pass through the second screen 11 (b) and a third, and so on, until the absorbed and reflected energy is so small as not to register on its adjacent video camera. Where only two screens are in use, the second screen may be opaque and is mechanically connected to the first screen so that yaw and look-up positions of the two interconnected screens can be measured accurately relative to the line of the laser beam 14. Figure 3 shows a typical layout of a computer management system for a tunnelling machine. A laser generator 16 is connected to a power supply 17 and to controls 18, being movable relative to a stable mounting by means of an alignment slider 19. A single target 10, 12 having two screens 11 is mounted on the tunnelling machine and the video cameras 13 within the target 10, 12 are connected to a PC module 20 which is connected, as shown, to an accessories module 21 , to primary articulation means 22 of the tunnelling machine, to secondary articulation means 23 of the tunnelling machine, to solenoids 24 and to an LCD readout 25. A central management unit 26 is connected to the PC module 20 and receives information from an FMCM functions controller 27. The system shown in Figure 3 provides for laser detection resolution on line and level of ± 0.1 mm., gradient and roll resolution of ± 0.1 ° and extensometer resolution of ± 0.1 mm. Figure 4 shows an arrangement which includes a plurality of single screen transducers 30 (a) to (e) connected to a structure 31 and a single laser generator (not shown) which generates a laser beam 32 which impinges on (and passes through) the screens of 7 transducers 30 (a) to 30 (d) and impinges on the screen of transducer 30 (e). Figure 5 shows a similar arrangement, but with three double screen transducers 33 (a) to (e) mounted on a structure 34 and arranged to register with a laser beam 32. In the cases shown in Figures 4 and 5, an indication is obtained of any movement of the structure 31 or 34 by monitoring the positions at which the laser beam 32 impinges on the screens. As five or six screens are being used, an indication is obtained not only of the fact that some movement has occurred, but the particular part or parts of the structure which has or have moved is or are immediately identified. Figure 6 shows an arrangement which includes three laser generators 40, 41 and 42. Laser generator 40 generates a beam 43 which impinges on three single screen transducers 44, 45 and 46. Laser generator 41 generates a beam 47 which impinges on four double screen transducers 48, 49, 50 and 51 , and laser generator 42 generates a beam 52 which impinges on three single screen transducers 53, 54 and 55. The video cameras within the transducers are connected to a PC module 56 which is connected to a modem and hard drive 57. Strain gauges 58, 59, 60 and 61 are mounted on appropriate parts of the structure (not shown) being monitored so that a read-out can be obtained of the strains in the structure and any resulting movements, either by means of a laptop computer 62 or via a telecommunications link 63. 8 The structure being monitored may be, for example, a bridge, the linings of a tunnel, such as a railway tunnel, or the lift shaft of a multi-storey building. The benefits obtained by being able to arrange a plurality of transducers in line with a single laser generator will be apparent. Each partially opaque screen will typically absorb less than 10% of the incident radiation, i.e. at least 90% of the radiation incident on each screen will be transmitted. Figure 7 shows an arrangement which includes a laser generator 70, a pair of double screen transducers 71 , each of which contains two video cameras 72, and a prism unit 73. The prism unit 73 includes a partially opaque screen 74, through which passes the laser beam 75, a video camera 76 for obtaining an image of the spot on the screen 74, and a prism 77 which returns the laser beam 75 along a path parallel to the original so that it impinges on (and passes through) a partially opaque screen 78 of a further transducer 79. The further transducer 79 is mounted on the laser generator 70 and contains a video camera 80. The various video cameras 72, 76 and 80 are connected to a processor module 81 , which is connected to a remote data logger 82, a monitor 83 and a modem link 84. Figure 8 is a block diagram showing the information flow for a system as outlined above. It includes the following stages 85 to 92 as follows:- SUBST1TUTE SHEET (RULE 26) 9 85 - "Multiplex CCD Signals", 86 - "Sample Next Incoming" 87 - "Scan Whole Area", 88 - "Laser Detected ?" 89 - "Scan Small Area", 90 - "Compare With Video Map", 91 - "Process Correction", and 92 - "Transmit Data". As applied to a system for measuring movement of parts of a structure, the processor module may include information as to what are regarded as excessive or dangerous movements and alarm means may then be provided which is actuated in response to detection or determination of such excessive or dangerous movements.

Claims: 10 Claims:- 1. A measurement system of the kind which includes means for projecting a laser beam on to a screen, means for determining the position at which the laser beam impinges on the screen and means for carrying out a measurement calculation from the information thereby obtained, characterised in that a plurality of screens are provided, at least a first of which is partially opaque and that a single laser beam is caused to impinge on each of said plurality of screens. 2. A system as claimed in Claim 1 , in which each of said screens is incorporated in a target. 3. A system as claimed in Claim 2, in which at least one of the targets includes two screens. 4. A system as claimed in Claim 2 or Claim 3, in which each target is of tubular form and is of either rectangular or circular cross-section. 5. A system as claimed in Claim 3, which contains two oppositely directed video cameras linked to a computer. 6. A system as claimed in Claim 3, which includes a plurality of targets arranged in line with a prism arranged to reflect the laser beam on to a screen mounted on the laser generator. 1 1 7. A method of measuring which includes projecting a laser beam on to a screen, determining the position at which the laser beam impinges on the screen and carrying out a measurement calculation from the information thereby obtained, characterised by the use of a plurality of screens, at least a first of which is partially opaque and that a single laser beam is caused to impinge on said plurality of screens. 8. A method as claimed in Claim 7, which includes incorporating the screens in targets, some at least of which have two screens. 9. A method as claimed in Claim 8, which includes the use of a laser generator on which a screen is mounted, a plurality of aligned targets and a prism arranged to reflect the laser beam on to the screen mounted on the laser generator.

Inventors: MOSS ARTHUR F, MOSS, ARTHUR, F.
Applicants: MOSS ARTHUR F, TUNNEL MANAGEMENT SYSTEMS LIMI, MOSS, ARTHUR, F., TUNNEL MANAGEMENT SYSTEMS LIMITED
Application year: 1999
Main classification: G01C15
IPC codes: E21D9, G01C15