The use of a source of light such as a laser, combined with a camera, to monitor railway vehicles is known for example from US 5 808 906 (Talgo Patentes). In this example the train rolls along a specially designed support. Another example is described in US 5 636 026 (Mian et al. ) in which laser scanners are mounted on a solid steel plate that is located beneath a sleeper (a rail tie), so that the support is unaffected by rail vibrations; this system is further characterized in requiring a slot cut through the rail head so that a light beam can be incident orthogonally onto the wheel tread. In each example the equipment is complex and cannot be simply and cheaply installed.

According to the present invention there is provided an apparatus for inspection of railway vehicles, the apparatus comprising a light source and a camera located within a support box connected to the underside of the rails.

The box is preferably of similar size to a sleeper, and consequently installation is very considerably simplified. No excavation of ballast from below the existing sleepers is required, so that the track does not have to be closed for a long period during the installation procedure; the box merely has to be slid under the rails and clamped or bolted to the underside of the rails. Having the optical components within the box and not protruding above it simplifies this operation,

and also ensures they are well protected from damage during use. It may however be desirable to have other components that protrude slightly above the top of the box, for example a vehicle speed detector.

The light source and the camera are preferably attached to the box by vibration-suppressing resilient mounting. The camera preferably incorporates means to perform image analysis. The apparatus preferably also comprises a data analysis unit such as a computer, which may be installed in a cabinet adjacent to the track.

Signals are transmitted between the data analysis unit and the components within the support box, for example using a cable.

The apparatus may comprise more than one such light source and more than one such camera. For example one light source may be a laser, which in combination with a camera may be used to monitor the shape of a wheel tread, while another light source may be a flash, which in combination with a camera may be used to monitor the shape or thickness of brake pads, or other components that may be subject to wear such as electric current pickup shoes. Since the region between the rails is likely to be dusty and dirty, each optical component preferably is provided with an air knife to ensure all optical windows or lenses are kept clean.

The apparatus must also comprise a wheel detector to trigger operation of the light source and camera. To avoid problems from wear this wheel detector is preferably a non-contact detector. The wheel detector may for example be a radar proximity detector, arranged to detect radar signals reflected by the wheel. An alternative wheel detector comprises a radar transmitter on one side of a rail and a radar detector on the other

side, each arranged below the top of the rail, so that transmission from one to the other depends upon diffraction over the top of the rail, and is obstructed when a wheel is present. The apparatus may also comprise other sensors, for example a vibration sensor may be attached to the rail for example to detect the approach of a train. A vibration sensor may also be used to detect repeated bangs due to wheel flats or out-of-round wheels, and for this purpose it would be preferable to provide vibration sensors on each of the rails, so such defects in any wheel can be detected. Preferably the apparatus also comprises means to measure the speed of an approaching train, as this permits the time delay between detection of a wheel and triggering of the light source to be set to a suitable value.

The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of an inspection apparatus; Figure 2 shows an end view of the support box of the apparatus of figure 1, partly broken away, on arrow A of figure 1 ; and Figure 3 shows an electronic circuit diagram of the inspection apparatus of figure 1.

Referring to figures 1 and 2, an inspection apparatus 10 comprises a steel box 12 consisting of a trough 13 with sleeper plates 14 welded along each side; the box 12 may also include bulk heads (not shown) at intermediate positions along its length. The box 12 is installed beneath the rails 16 on a railway track 18.

The track 18 is conventional, consisting of rails 16 attached by clips 20 to sleepers 22, with ballast 24 below and between the sleepers 22, so that before installing the box 12 it may be necessary to rake out some of the ballast 24 from between two adjacent sleepers 22. The box 12 is then slid under the rails 16, a rubber plate 26 (shown in figure 2) is placed between each rail 16 and each sleeper plate 14, and clips 20 are used to secure the sleeper plates 14 to the rails 16 (these clips 20 being provided with electrical insulation where they contact the rails 16 so that the box 12 does not provide an electrical connection between the rails 16). The ballast 24 can then be repacked around the box 12. At each end of the box 12 is attached an end plate 28. The end plate 28 at one end defines an aperture 29 for an electrical cable 30 connecting components within the box 12 to other components of the apparatus 10 installed in a lineside cabinet 32.

Referring now to figure 2 (in which the clips 20 are not shown), the box 12 encloses electronic modules 34, camera modules 36, light source modules 38 and radar modules 40. These modules are all mounted onto the trough 13 by means of vibration-damping rubber mounts 42 (each mount consisting two aligned bolts connected together by a flexible rubber ring). In addition a vibration sensor 44 is fixed to the underside of one rail 16, connected by a cable to one of the electronic modules 34. The box 12 may also be provided with cover plates (not shown) with apertures for the cameras, light sources and radar modules. Such cover plates prevent ballast 24 or large items of rubbish falling into the box 12. Each optical component (e. g. camera module 36 and light source module 38) has an air knife (not shown) arranged to keep the optical windows or lenses clean from dust and small items of litter or leaves.

Although the box 12 and all the sensors and electronic components within it will move with the rails 16 as a train passes over the box 12, and are therefore subjected to considerable vibrations, the shock loadings are considerably reduced both by the rubber plates 26, and by the rubber mounts 42.

Referring now to figure 3, in which the end plate 28 is represented diagrammatically by a broken line, the power supply and control signals for the components within the box 12 are supplied by the cable 30 to an input/output interface unit 50. This transmits electrical power to each of the other components, and performs some signal filtration. The interface unit 50 receives signals from a radar wheel-detector 40a and from the vibration detector 44, and also from a radar train speed detector 40b. It supplies control signals to lasers 38a and thereby to cameras 36a that are arranged to view wheels on each rail 16, one laser 38a and camera 36a for each rail 16. The cameras 36a incorporate image recognition software, and provide data representing the recognized image to a network node 52. The node 52 transmits data from several different sources along the cable 30 to a processor 54 within the lineside cabinet 32.

In operation, when a train travels along the track 18, signals from the vibration sensor 44 initiate operation of the other components. When a signal from the wheel detector 40a indicates that a wheel is passing over the box 12, the interface 50 causes each laser 38a to provide a line scan across the wheel tread and the camera 36a to view this line. The camera 36a is set up to look forwards (i. e. in the direction of train travel) along the track 18, and to take an image when the wheel

is at a fixed distance beyond the box 12 (for example 300 mm), and the time delay between detection of a wheel by the wheel detector 40a and the operation of the camera 36a is set (by an integrated circuit 56) in accordance with the train speed as detected by the train speed radar 40b (as explained below).

The box 12 also contains cameras 36b with associated flash units 38b (only one is shown in figure 3), the flash units 38b being operated in a similar fashion to the lasers 38a but enabling the camera 36b to obtain an image of, for example, brake pads. There may also be a second vibration detector 44 attached to the other rail 16, the signals from the vibration detectors 44 being analyzed for regularly repeated bangs that would indicate wheel flats.

The programmable integrated circuit 56 is also enclosed in the lineside cabinet 32, and its primary role is to determine timings. The integrated circuit 56 receives data signals from the train sensors (i. e. the vibration sensor 44, the radar speed sensor 40b and the wheel detector 40a) via the interface 50, determines the appropriate timings for operation of the cameras 36a and 36b and of the lasers 38a and the flash units 38b, and sends timing signals to these components via the interface unit 50.

The computer processor 54 is linked to a computer bus 58, and for example can store data as obtained by the cameras 36a and 36b in a data store 60 (such as a hard disk). Data can also be transferred between the bus 58 and the integrated circuit 56 via sixteen optically isolated inputs 62 and sixteen optically isolated outputs 63. The processor 54 is linked directly by a line 64 to the integrated circuit 56, so that the processor 54 can

set parameter values for use by the integrated circuit 56 in its determination of timings. The processor 54 is also connected to a modem 66 so that the data from the cameras 36a and 36b (and indeed from other sensors such as the vibration sensors 44) can be transmitted to a remote station for example by telephone line.

The processor 54 provides high-level control over operation of the inspection apparatus 10, for example determining which image analysis program a camera 36 should follow, or adjusting the image analysis parameters. The processor 54 can send control signals to the cameras 36 for this purpose via the bus 58 and the outputs 63, the control signals passing unaffected through the integrated circuit 56, and being directed by the interface unit 50 to the appropriate camera 36.

Similarly the cameras 36 can send data (for example identifying which image analysis program it is following) back to the processor 54 via the interface 50 and the integrated circuit 56, or via the node 52.

It will be appreciated that system control might be achieved in a different way from that described above, for example using analogue electronic circuits. It will also be understood that other sensors may be incorporated in the inspection apparatus 10, for example infrared sensors to detect any components (such as bearings) that are overheating, or an optical sensor to detect any component that is hanging below that train (such as loose cables).