GB2330470A

GB2330470A - Rail measurement system

Info

Publication number: GB2330470A
Application number: GB9822240A
Authority: GB
Inventors: Romuald Pojda
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1997-10-20
Filing date: 1998-10-12
Publication date: 1999-04-21
Anticipated expiration: 2018-10-12
Also published as: ITMI982201A1; DE19747872C2; IT1302662B1; FR2769976A1; GB2330470B; FR2769976B1; ITMI982201A0; DE19747872A1; GB9822240D0

Abstract

A system for measuring rails 1, (in particular running rails for cranes, storage/retrieval machines or running-wheel blocks) comprises; a transmitter unit 2 located on a rail 1 (which has a laser with at least one laser beam 4 which extends in the longitudinal direction of the rail) and a drivable receiver unit 3 (which can be moved longitudinally along rail 1 and has at least one photo detector 6 facing the laser beam 4). The photo detector 6 (which has a rectangular matrix of sensor elements) generates an electrical output signal in response to the impinging laser beam which allows the location of the laser beam 4 in a measuring surface 5 to be determined. A distance sensor is also provided for detecting the change in distance between the transmitter unit 2 and the receiver unit 3.

Description

RAIL MEASUREMENT SYSTEM 2330470 The invention relates to a system for

measuring the surfaces of rails, in particular running rails for cranes, storage/retrieval machines or running-wheel blocks.

A measuring system for monitoring rails is known from German Patent No. 212 931. The system comprises a laser transmitter unit located in use on the rail with a laser alignment apparatus. In this arrangement, the laser beam serves as a spatially fixed measuring axis for the rail. The measuring arrangement consists of a car with a travelling mechanism comprising two horizontally arranged running rollers and two lateral guidance rollers on each side. To detect the position of the car in relation to the measuring axis, a photosensor is provided facing the laser beam. The photosensor is in the form of a fourquadrant photodiode. The electrical signal produced when the laser beams strikes the photodiode is sent to evaluation electronics which activate a vertical tracking means and a horizontal turning mechanism to displace or turn the photodiode such that the four quadrants of the photodiode always adopt the same position in relation to the laser beam.

A disadvantage of this known measuring arrangement is the mechanical tracking of the photodiode, since this determines the accuracy of detection of the rail, i.e. in particular the change of position of the running surface of the rail. A further disadvantage is the long measuring times owing to the mechanical resetting of the photodiode in the measuring plane (X and Z directions).

It is an object of the invention to provide a system for measuring rails which can travel to individual positions on the rail with high tracking accuracy to allow determination of the change of position of the running surface of the rail relative to the laser beam, but without displacement of the photosensor being necessary.

According to the invention there is provided a 1 system for measuring rails comprising a transmitter unit located in use on a rail which transmits at least one laser beam in the longitudinal direction of the rail, a drivable receiver unit which can be moved on the same rail in the longitudinal direction thereof and has at least one photodetector facing the laser beam, the photodetector generating an electrical output signal in response to the impinging laser beam, and an electronic evaluation means for determining from the signal the location of the laser beam in a vertical measuring surface oriented transversely to the longitudinal direction of the rails wherein the photodetector has a plurality of pixels arranged next to each other in a rectangular matrix, the output signals of the pixels being fed to the electronic evaluation means such that the determination of the point of incidence of the laser beam in the measuring surface is effected purely electronically by evaluation of the output signals, and wherein a distance sensor is provided for detecting a change in distance between the transmitter unit and the receiver unit.

The invention provides for the photodetector to have a rectangular matrix with a plurality of pixels (optical sensor elements) arranged immediately next to one another. The electrical output signals of the pixels are fed to evaluation means which determine the point of incidence of the laser beam in the measuring surface purely electronically by evaluation of the pixel output signals. A distance sensor is provided for detecting the change in distance between the transmitter unit and the receiver unit. The system allows determination of the change in position of the running surface in relation to the laser beam, which is fixed in space, for each point along the length of the rail. The configuration of the photodetector as a rectangular matrix makes it possible to measure the intensity distribution of the laser beam in two dimensions, which permits accurate determination of the point of incidence of the main beam direction or of the laser beam 2 axis on the preset measuring surface. Advantageously, the measuring surface no longer has to be displaced. Adjustment of the zero point (reference point) is necessary only once, which shortens the duration of the measurements and furthermore increases the measuring accuracy.

The photodetector may be CCD camera, in front of which a transparent diffusion disc is arranged as the measuring surface, which is optically imaged on the matrix of the CCD camera. This results in a system for measuring rails which is very simple to construct.

More accurate determination of the point of incidence of the laser beam on the measuring surface is achieved by so-called subpixel resolution. The point of incidence of the laser beam on the diffusion disc can be determined by adapting the measured subpixel position of the beam image of the diffusion disc to the matrix. To this end, first of all, each scanning line and each scanning column is individually evaluated in a square region around the beam image, and the results are then summed. The exact position (subpixel position) of the beam within the camera image is yielded as a result. The difference from the initial position (reference point) is thus a measurement for the deviation of the receiver unit from the ideal line.

Expediently, the adaptation is effected by means of a computer program.

It is further proposed that the electronic evaluation means comprise a microprocessor which ensures the complicated calculations and control processes are carried out at low cost.

In order to determine the position of the running surface of the rail as a function of distance, the distance sensor may have a friction wheel which rolls on the running surface of the rail.

A high distance accuracy is achieved if the friction wheel is connected to an incremental transducer for detecting the length travelled.

3 In order to monitor the correct performance of the measurement, the motion state of the receiver unit can be detected by means of the friction wheel.

Advantageously, the receiver unit is designed to be remotely-controllable, so that even rails which are difficult to access can be measured under poor visibility conditions and under adverse environmental conditions (toxic gases, vapours, etc.).

The position of the laser beam is preferably stabilised. The stabilisation is advantageously effected by means of an electronic "spirit level", which produces high positional stability at relatively low cost.

Expediently, the position stability is mm deviation per 100 m rail length.

Exact travel to the measuring positions is achieved for a rail crosssection which includes flange and web parts if the receiver unit is guided by at least two guide rollers which are vertically rotationally mounted, spaced apart in the longitudinal direction of the rails and are biassed against the side faces of the rail and at least two running rollers, with an axis of rotation oriented transversely to the longitudinal direction of the rails, the running rollers being horizontally rotationally mounted and spaced apart in the longitudinal direction of the rails and rolling on the running surface of the rail. At least one of the running rollers is driven.

The system also permits the measurement of greatly worn rails, if the vertical height of the guide rollers is individually adjustable.

The tracking properties are particularly good if, viewed in the longitudinal direction of the rails, each front running roller is located behind the front guide rollers.

The tracking stability is improved if the distance between the axes of the running roller and of the closest guide roller is between one and three times the diameter of the guide roller.

4 The movement precision of the receiver unit can be improved if the guide rollers on one side of the rail have a f ixed axis of rotation and those on the other side are biassed against the rail side face.

Expediently, the guide rollers are acted upon by spring force.

In order that the guide rollers can adapt better to inclined rails, the guide rollers may be mounted in self aligning ball-bearings.

To allow transversal of expansion joints and broken rails, the guide rollers may be arranged in pairs each on a common longeron which extends in the longitudinal direction of the rails, and connected in articulated manner to the receiver unit. This also distributes the horizontal forces upon acceleration and braking over a plurality of contact points, which results in more stable guidance.

A radial groove may be centrally formed in the running surface of the running rollers. Better stability in relation to lateral inclinations is achieved through the consequent two-point contact on the rail surface.

A security system may be provided to protect the receiver unit.

The safety system can detect defective rails or areas of rail which may result in the receiver unit crashing if it has at least one distance sensor for detecting the distance of a reference point of the receiver unit from the rail.

In order to measure at least two rails located in one plane, the laser beam may be separated into two horizontal partial laser beams extending at right-angles to each other, for determining the difference in height of the two rails in relation to a horizontal straight line located in a vertical plane. This makes it possible, in particular, accurately to measure the parallelism of the two rails relative to each other in space at low cost.

Expediently, one partial laser beam extends transversely to the two rails and lies in a vertical plane, i.e. the vertical plane is clearly defined by this partial laser beam.

Advantageously, the reference line may be the horizontal straight line which lies in the vertical plane defined by the partial laser beam extending transversely to the two rails.

The invention will now be described by way of example and with reference to the accompanying drawings in which:

Fig. 1 shows a system for measuring rails in a three-dimensional schematic representation; Fig. 2 is a cross-section through a worn rail showing the position of the guide rollers and the running roller; Fig. 3 is a top view of the receiver unit; Fig. 4 is a longitudinal section through the receiver unit of Fig. 3, and, Fig. 5 is a top view of the receiver unit of Fig. 3 with pairs of guide rollers.

Fig. 1 is a three-dimensional view of a system for measuring rails 1, with a transmitter unit 2 arranged on a rail 1 and a receiver unit 3 at a distance therefrom which is located on the same rail. The transmitter unit 2 is equipped with a laser, the laser beam 4 of which is directed in the longitudinal direction of the rails. The laser beam 4 strikes a transparent diffusion disc 5a of the receiver unit 3; the diffusion disc 5a serves as a given measuring surface 5. Behind the diffusion disc 5a there is a photodetector 6, designed as a CCD camera 6a, facing the laser beam 4. The CCD camera 6a has a rectangular matrix 6b with a plurality of pixels which are arranged immediately next to one another. The pixels are formed by light-sensitive sensor elements. The light spot of the laser beam 4 on the diffusion disc 5a is imaged on the matrix 6b by means of an imaging optics system 6c, so that the point of incidence or location of the laser beam 4 in the vertical measuring surface 5 oriented transversely to 6 the longitudinal direction of the rail 1 can be determined solely electronically by the electrical output signals of the individual pixels produced by the impinging laser beam 4. All electrical and mechanical components of the receiver unit 3 are located on a solid baseplate 3a.

In order to improve the sensitivity, a narrow-band interference filter is placed in the beam path of the CCD camera 6a. The image of the laser beam 4 then stands out with a high contrast in the video image of the CCE) camera 6a.

The measuring of the rail 1 is effected by moving the receiver unit 3, provided with two drivable running rollers 7, in the longitudinal direction of the rails and each time detecting the point of incidence of the laser beam 4 which is displaced on the measuring surface 5 upon a change in position of the running surface 8 of the rail. Since the photodetector 6 is mounted in a fixed position on the baseplate 3a, the position of the beam 4 at any position along the rail 1 relative to a position at the beginning of the rail 1 is an accurate reflection of the deviation of the rail 1 in the horizontal and vertical direction at the respective measuring position.

A method of subpixel resolution is used for more accurate evaluation of the beam image on the matrix 6b. In this case, in a square region around the beam image each scanning line and each scanning column is evaluated individually and the results are averaged. The result is the 11 subpixel accurate" position of the beam image within the matrix 6b, which corresponds to or can be converted to the location of the laser beam 4 in the vertical measuring surface 5 oriented transversely to the longitudinal direction of the rail 1, namely on the basis of the linear connection existing between the subject and the image. The point of incidence of the laser beam 4 on the diffusion disc 5a can be determined very accurately by adapting the measured subpixel position of the beam image of the diffusion disc 5a on the matrix 6b.

7 The difference from the initial position is a measurement of the deviation of the car of the receiver unit 3 from the ideal line.

"Change in position,' here is understood to mean the change in the position of the highest horizontal point of the running surface 8 of the rail. As Fig. 2 (and Fig. 3) shows, the horizontally rotationally mounted running rollers 7 are in the form of cylinders, which ensures that the receiver unit 3 is supported by means of its two running rollers 7 on two spaced-apart measuring points in each case at the highest horizontal contact points 9 of the running surface 8 of the rail 1. Thus, dependent on the path of the running surface 8 along the rail 1, the receiver unit 3 and consequently of the measuring surface 5 is raised or lowered. The laser beam 4 is spatially positionally stabilised, i.e. it maintains its position in space with high accuracy and thus represents the reference line of the system. The positional stabilisation of the laser beam 4 is effected electronically, preferably by means of an "electronic spirit level,,; in the example of embodiment it is +/- 1 mm deviation per 100 m length of the laser beam 4.

The measuring surface 5 is connected to evaluation electronics 10, which comprise a microprocessor and can be controlled by means of computer programs. The evaluation electronics 10 read out the position of the beam image detected by the CCE) camera dependent on location, and in this manner determines the exact position of the laser beam 4 on the measuring surface 5. In order to determine the point of incidence of the main direction of the laser beam 4, the evaluation electronics 10 have a special computer program, which individually evaluates each line and column in a square region around the beam image, and averages the results (0.2 mm per pixel). In order to obtain sufficient linearity and to increase the measuring accuracy, a measuring camera with pixels which are square in shape must be used.

8 In order to determine the distance between the transmitter unit 2 and the receiver unit 3, the receiver unit 3 is provided with a distance sensor 11. The distance sensor 11 consists of a friction wheel 12 which rolls on the running surface 8 of the rail 1 and is connected to an incremental transducer which is in turn connected to the evaluation electronics 10 for detecting the length travelled. In this manner, the distance and/or the change in distance between the receiver unit 3 and transmitter unit 2 can be detected with high accuracy. Furthermore, the friction wheel 12 also serves to detect the motion state of the receiver unit 3 by means of the evaluation electronics 10 and to switch off the drive motor 13 of the receiver unit in emergencies. Fig. 3 shows that the drive motor 13 drives the running rollers 7 synchronously by means of a toothed belt 14 and deflecting rolls 15.

Figures 2, 3 and 4 show two running rollers 7 which are spaced apart in the longitudinal direction of the rails and roll on the running surface of the rail 1, which rollers have an axis of rotation oriented horizontally transversely to the longitudinal direction of the rails and guide rollers 17, 18 which lie, acted upon by force, against the side faces 16 of the rail 1 for guiding the receiver unit 3 on either side of the rail and which are vertically rotationally mounted. For better adaptation to the respective rail cross-section, the vertical height of the guide rollers 17 is individually adjustable in each case. In the embodiment of Fig. 3, the running rollers 7 are arranged between the guide rollers 17, is. The distance of the axes of the running rollers 7 and the immediately adjacent guide rollers 17, 18 is expediently between one and three times the diameter of the guide rollers 17, 18.

The guide rollers 17, 18 on one side of the rail have a fixed axis of rotation, and on the other side of the rail 1 are pressed against the side face 16 by a spring force. The guide rollers 17, 18 are mounted in self- 9 aligning ball bearings.

An alternative embodiment is shown in Figure 5, where the guide rollers are arranged in pairs 17a, 18a in each case on a common longeron which extends in the longitudinal direction of the rails and is fastened to the baseplate 3a. The pairs 17a, 18a of guide rollers each also have fixed vertical axes of rotation on one side of the rail, and on the other side of the rail 1 are pressed against the associated side face 16 by a spring force.

The running surface 19 for the running rollers, as Figure 5 shows, alternatively has a radial groove 20 approximately in the centre of the running roller 7, which ensures more stable two-point contact.

In order to prevent crashes of the system in the event of greatly worn rails, the receiver unit 3 is provided with a safety system which is integrated in the evaluation electronics 10. The safety system comprises an additional horizontal distance sensor which detects the distance of a reference point of the receiver unit 3 from the running surface 8 of the rail 1, and switches off the drive motor 13 if a limit value is exceeded.

In order to measure two rails located next to each other approximately in one plane, the laser beam 4 is separated into two horizontal partial laser beams (4a, 4b) extending at right-angles to one another, which are used for determining the difference in height of the two rails 1. This is done in relation to a horizontal straight line located in a vertical plane, which is defined by the partial laser beam (4b) extending transversely to the two rails 1.

Claims

1. A system for measuring rails comprising a transmitter unit located in use on a rail which transmits at least one laser beam in the longitudinal direction of the rail, a drivable receiver unit which can be moved on the same rail in the longitudinal direction thereof and has at least one photodetector facing the laser beam, the photodetector generating an electrical output signal in response to the impinging laser beam, and an electronic evaluation means for determining from the signal the location of the laser beam in a vertical measuring surface oriented transversely to the longitudinal direction of the rails wherein the photodetector has a plurality of pixels arranged next to each other in a rectangular matrix, the output signals of the pixels being fed to the electronic evaluation means such that the determination of the point of incidence of the laser beam in the measuring surface is effected purely electronically by evaluation of the output signals, and wherein a distance sensor is provided for detecting a change in distance between the transmitter unit and the receiver unit.

2. A system as claimed in Claim 1 wherein the photodetector is a CCD camera and wherein a transparent diffusion disc is arranged in front of the CCD camera as the measuring surface and is optically imaged on the matrix of the CCD camera.

A system as claimed in Claim 2 wherein the point of incidence of the laser beam on the diffusion disc can be determined by adapting the measured subpixel position of the beam image of the diffusion disc to the matrix.

4. A system as claimed in Claim 3 wherein the adaptation is effected by means of a computer program.

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5. A system as claimed in any preceding claim wherein the evaluation means comprises a microprocessor.

6. A system as claimed in any preceding claim wherein the distance sensor has a friction wheel which rolls on the running surface of the rail.

7. A system as claimed in Claim 6 wherein the friction wheel is connected to an incremental transducer for detecting the length travelled.

8. A system as claimed in either Claim 6 or Claim 7 wherein the movement of the receiver unit can be detected by means of the friction wheel.

9. A system as claimed in any preceding claim wherein the receiver unit is remote-controllable.

10. A system as claimed in any preceding claim wherein the spacial position of the laser beam is stabilised.

11. A system as claimed in Claim 10 wherein the stabilisation of the position of the laser beam is effected by means of an electronic level.

12. A system as claimed in either Claim 10 or Claim 11 wherein the positional stability is +/- 1 mm deviation per 100 m rail length.

13.

A system as claimed in any preceding claim further comprising at least two guide rollers for guiding the receiver unit which are rotatable about a vertical axis, the guide rollers being spaced apart in the longitudinal direction of the rail and running against the two side faces of the rail and at least two running rollers, with an axis of rotation oriented transversely to the longitudinal direction of the rails, the running rollers being spaced 12 apart in the longitudinal direction of the rail and rolling on the running surface of the rail, at least one of the running rollers being driven and so driving the receiver unit.

14. A system as claimed in Claim 13 wherein the vertical height of the guide rollers is individually adjustable.

15. A system as claimed in either Claim 13 or Claim 14 wherein, viewed in the longitudinal direction of the rails, the front running roller is located behind the front guide rollers.

16. A system as claimed in any one of Claims 13 to 15 wherein the distance between the axes of each running roller and of the closest guide roller is between one and three times the diameter of the guide roller.

17. A system as claimed in any one of Claims 13 to 16 wherein the guide rollers on one side of the rail have a fixed axis of rotation and the guide rollers on the other side are biassed towards the side face.

18. A system as claimed in Claim 17 wherein the guide rollers are biassed by means of spring force.

19- A system as claimed in any one of Claims 13 to 18 wherein the guide rollers are mounted in self-aligning ball-bearings.

20. A system as claimed in any one of Claims 13 to 19 wherein the guide rollers are arranged in pairs in each case on a common longeron which extends in the longitudinal direction of the rails and which is located on the receiver unit.

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21. A system as claimed in any one of Claims 13 to 20 wherein a central radial groove is formed in the running surface of the running rollers.

22. A system as claimed in any preceding claim wherein the receiver unit is provided with a security system.

23. A system as claimed in Claim 22 wherein the safety system has at least one distance sensor for detecting the distance of a reference point of the receiver unit from the rail.

24. A system as claimed in any preceding claim wherein, for measurement of at least two rails located in a common plane, the laser beam is separated into two horizontal partial laser beams extending at right- angles to each other, whereby the difference in height of the rails can be determined.

25. A system for measuring rails substantially as hereinbefore described and illustrated in the accompanying drawings.

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