Method and measuring system for registering a fixed point adjacent a track

Abstract

A method of determining the actual position of a track relative to a fixed point located in a lateral vicinity of the track by using a registering device being mobile on the track includes surveying the position of the fixed point relative to the track. The registering device is moved along the track, image pairs of the lateral vicinity of the track are continuously recorded by a stereo camera system on the registering device and the fixed point is searched for in the image pairs by pattern recognition carried out in an evaluation device. Upon recognition of the fixed point, the position of the fixed point relative to the track is determined by evaluating at least one image pair. This creates the possibility of surveying fixed points in passing with the configuration of the fixed point not being bound to any special form. A measuring system is also provided.

Claims

1. A method of determining the actual position of a track relative to a fixed point located in a lateral vicinity of the track, the method comprising the following steps: providing a registering device being mobile on the track for surveying the position of the fixed point relative to the track; moving the registering device along the track while continuously recording image pairs of the lateral vicinity of the track by using a stereo camera system disposed on the registering device; searching for the fixed point in the image pairs by pattern recognition carried out in an evaluation device; and upon identification of the fixed point, determining the position of the fixed point relative to the track by evaluation of at least one of the image pairs.

2. The method according to claim 1, which further comprises using an inertial measuring unit to continuously register a position of the registering device relative to a stationary reference system, and correcting a resulting drift by using the determined position of the fixed point.

3. The method according to claim 1, which further comprises measuring a super-elevation position of the registering device and including the super-elevation position in determining the position of the fixed point.

4. The method according to claim 1, which further comprises recording and evaluating an identification affixed next to the fixed point.

5. The method according to claim 1, which further comprises recording image pairs of the fixed point from a plurality of recording positions while passing by, and evaluating the position of the fixed point relative to the track in a plurality of image pairs.

6. The method according to claim 5, which further comprises establishing coordinates of a plurality of recording positions in a common coordinate system, and transforming position coordinates of the fixed point determined in the respective recording position into the common coordinate system.

7. The method according to claim 6, which further comprises calculating an averaged coordinate value for each axis of the common coordinate system from a plurality of transformed coordinate values for indicating the position of the fixed point.

8. The method according to claim 1, which further comprises using flanged rollers to move the registering device on rails of the track while pressing the flanged rollers laterally against the rails.

9. The method according to claim 1, which further comprises using a measuring device to continuously measure a position of the registering device relative to a rail of the track.

10. The method according to claim 1, which further comprises using an infrared spotlight to illuminate the lateral vicinity of the track, and using an infrared filter to record the image pairs.

11. A measuring system for determining the actual position of a track, the measuring system comprising: a fixed point positioned in a lateral vicinity of the track; a registering device being mobile on the track for surveying a position of said fixed point relative to the track; a stereo camera system disposed on said registering device for recording image pairs of the lateral vicinity of the track; and an evaluation device connected to said stereo camera system for determining the position of said fixed point relative to the track based on at least one of the image pairs.

12. The measuring system according to claim 11, which further comprises an inertial measuring unit disposed on said registering device.

13. The measuring system according to claim 11, wherein the registering device is a component of a track maintenance machine or a measuring car.

14. The measuring system according to claim 13, which further comprises a displacement transducer for measuring a distance travelled by the track maintenance machine or the measuring car on the track.

15. The measuring system according to claim 11, wherein said fixed point includes redundant elements.

Description

DESCRIPTION OF THE INVENTION

(1) The invention will be described by example below with reference to the attached figures. There is shown in schematic representation in:

(2) FIG. 1 a side view of a measuring car with a registering device

(3) FIG. 2 a sectional view of the measuring car with registering device

(4) FIG. 3 a fixed point with a redundant element

(5) FIG. 4 a registering device in three recording positions

DESCRIPTION OF THE EMBODIMENTS

(6) The measuring car 1 comprises a car body 3, built on a machine frame 2, which is supported on two undercarriages 4. By means of these undercarriages 4, the measuring car 1 is mobile on a track 5. The track 5 consists of two rails 7 fastened to sleepers 6 and is supported in a ballast bed 8.

(7) A registering device 10 is fastened to the machine frame 2 by means of a movable suspension 9. For a measuring operation, the registering device 10 is lowered upon the track 5, as shown. During transfer travel, it is pulled up and locked.

(8) At the front of the measuring car 1, as seen in the travelling direction 11, a displacement transducer 12 designed as a measuring wheel is installed to record a distance covered. Alternatively, a wheel of an undercarriage 4 could also be equipped with a displacement transducer 12 (Distance Measurement Indicator DMI). The displacement transducer 12 emits impulses representing fractions of the wheel revolutions.

(9) In the embodiment shown, the registering device 10 includes flanged rollers 13 which are pressed laterally against the rails 7 by means of a pressing device 14. In this, a coordinate system having three axes x, y, z is specified as a reference system for the evaluation of the position of a fixed point 15, with the origin 16 of the coordinate system lying in the wheel flange contact point of the left front flanged roller 13 (as seen in the travelling direction 11). Due to the flanged roller 13 being pressed laterally against the rail 7, this point 16 is always precisely defined.

(10) In a different embodiment, the registering device 10 is mounted on an undercarriage 4 (shown in FIG. 1 in dashed lines at the front undercarriage 4) and oscillates sinusoidal transversely to the travelling direction 11 relative to the rail 7. A defined wheel flange contact point serves here as origin 16 of a reference system. Usually, the same is assumed as the point of intersection of the inner rail contour and a horizontal straight line extending 14 mm below the rail upper edge. With this kind of arrangement, it is possible to realize higher working speeds as compared to an embodiment with pressed-on flanged rollers.

(11) Arranged on the registering device 10 or on the undercarriage 4 is a measuring device which continuously measures the movement of the registering device 10 relative to a rail 7. This is, for example, an optical gauge measurement system (Optical Gauge Measurement System, OGMS). A measured relative displacement of the registering device 10 versus the defined rail contact point is included in the calculation of the position of the registered fixed point 15.

(12) Favorably also, the travelled path to be documented is correlated to the coordinate system with the wheel flange contact point as origin 16. In this, a value measured by the displacement transducer 12 is reduced by a constant distance x between displacement transducer 12 and the coordinate origin 16.

(13) Arranged as a picture-taking component of the registering device 10 is a stereo camera system 17. The latter comprises two cameras 18 which are precisely aligned with one another, wherein an axis of symmetry of the stereo camera system 17 favorably extends through the coordinate origin 16. Specifically, the optical axes 19 of the two cameras 18 are aligned parallel to one another in the direction of the lateral vicinity of the track 5.

(14) The method according to the invention uses the stereo camera system 17 to continuously record image pairs of the lateral vicinity while traveling past. For evaluation of the image pairs, the stereo camera system 17 is connected to an evaluation device 20. This is, for example, an industrial computer which has been set up particularly for this purpose.

(15) In the evaluation device 20, an automated pattern recognition process takes place in order to recognize a fixed point 15 in the recorded image pairs. For such matching, algorithms are known which deliver reliable results in real time. Usually, the fixed point 15 is positioned as a marking bolt 21 on a stationary installation 22 beside the track, for example a utility pole.

(16) In order to avoid interference by sunlight or lighting fixtures, it is useful if the lateral environment of the track 4 to be registered is illuminated by means of an infrared beam 23. The cameras 18 are then provided with infrared filters for filtering the light from other sources.

(17) For reliably registering the fixed point 15, it is further helpful if the latter is equipped with redundant elements, as shown FIG. 3. Located in the center of the geometrical figure is the marking bolt 21 shown in a front view. In this, the position of the fixed point 15 is defined by the center point of the visible face side of the marking bolt 21. Redundant elements are provided on a panel 24 at the base of the marking bolt 21. In the present example, the corner points of the squares form redundant reference points for the position of the fixed point 15. Even if parts of the panel 24 are obscured by dirt or plants, enough reference points remain for an evaluation, as a rule.

(18) As soon as the fixed point 15 has been recognized in an image pair, in a next method step the evaluation of position informations of the fixed point 15 takes place by means of photogrammetry. In this, a two-image evaluation ensues on the basis of the parallaxes and a known base distance between the cameras 18. Here again, algorithms are known which enable an evaluation in real time.

(19) As a rule, at first coordinates are determined in a camera-internal reference system, and subsequently a transformation to the specified coordinate system takes place. Shown in FIG. 2 as a result are the y-coordinate y.sub.p and the z-coordinate z.sub.p of the fixed point 15. If the track 5 has a super-elevation, the same is to be taken into account when calculating the coordinates y.sub.p, z.sub.p. Advantageously, the super-elevation is determined by means of an inertial measuring unit 25 (IMU) mounted on the registering device 10.

(20) In order to increase the precision of this evaluation step, a high resolution of the cameras 18 is useful. Additionally, short shutter speeds should be selected, wherein this stipulation depends on the travel speed of the registering device 10. This also influences the frame rate of the cameras 18. At a speed of 80 km/h, experiments with frame rates of 140 image pairs per second have delivered very good results.

(21) As shown in FIG. 4, several image pairs of the fixed point 15 are recorded and evaluated during a passing-by. Thus, several position information data from different recording positions 26, 27, 28 are known for the fixed point 15. A merging of these position information data by transformation to a common coordinate system enhances the precision of the result.

(22) Such a transformation of the z-coordinate of the fixed point 15 is explained by means of the coordinates x.sub.1, z.sub.1, z.sub.2, x.sub.32, z.sub.32, z.sub.3, x.sub.3 shown in FIG. 4. In this, for example, the wheel flange contact point of the left front flanged roller 13 at the time of the shown middle recording position 27 is defined as origin 16 of the common coordinate system. The x-coordinate of the fixed point 15 here equals zero.

(23) To transform the z-coordinate z.sub.3 of the fixed point 15 relative to the next recording position 28 into the common coordinate system, the position of the recording position 28 in relation to said coordinate system must first be determined. This takes place, for example, by means of the inertial measuring unit 25 and results in a corresponding x-coordinate x.sub.32 and a z-coordinate z.sub.32. If the track 5 has a gradient or a super-elevation ramp, a corresponding y-value results also.

(24) If the coordinates are interpreted as vectors, the following relationship ensues as transformed z-coordinate z.sub.t3 of the fixed point 15:
{right arrow over (Z.sub.t3)}={right arrow over (X.sub.32)}+{right arrow over (Z.sub.32)}+{right arrow over (Z.sub.3)}+{right arrow over (X.sub.3)}

(25) In the evaluation device 20, a corresponding algorithm for coordinate transformation is set up. A transformed z-coordinate z.sub.t1 results also for the z-coordinate z.sub.1 of the fixed point 15 with regard to the previous recording position 26.

(26) By forming a mean value of all transformed z-coordinates z.sub.t1, z.sub.t3 and the z-coordinate z.sub.2 registered in the common coordinate system, a precise z-coordinate z.sub.p of the fixed point 15 results. Individual faulty recordings due to, for instance, a pixel jump, dirt particles or insufficient lighting are compensated in this way. In practice, far more than 3 image pairs of the fixed point 15 are recorded at a high frame rate, as a result of which a sufficient number of position data for forming a mean value are available.

(27) In an optional further method step, the registered position of the fixed point 15 is used to synchronize the position of the measuring car 1 which is continuously determined by means of the inertial measuring unit 25 and the displacement transducer 12. Specifically, at the start of a measuring run, the position of the measuring car 1 relative to a stationary reference system is defined. Starting from this original position, the inertial measuring unit 25 and the displacement transducer 12 register the relative position changes of the measuring car 1, wherein according to experience a drift occurs.

(28) Since a fixed point 15 also represents a stationary reference point, said drift is determined and eliminated by the automatized surveying of the fixed point 15 during the measuring run. Usually several fixed points 15 are installed along a measuring path, so that, due to recurring matching, precise position data of the measuring car 1 are available over the entire measuring path.

(29) The same method is intended for track maintenance machines such as tamping machines, for example. Here, the actual position of the track 5 is measured before it is brought into its target position by lifting, lining and tamping.