The present invention relates to a system for surveying rails, in particular running rails for cranes, shelf handling units, running wheel blocks.
A measuring arrangement for monitoring railway tracks is known from DD 212 931 and includes a transmitter unit arranged on the track and having a laser alignment unit. The laser beam is so aligned hereby as to serve as measuring axis, fixed in space, for the track rail. The measuring arrangement includes a measuring vehicle having a traveling mechanism which has two horizontal running rollers as well as two side guide rollers on the right side and two side guide rollers on the left side. The position of the measuring vehicle in relation to the measuring axis is determined by providing a photosensor which confronts the laser beam and is configured as four-quadrant photodiode. Upon incident laser beam, the photodiode generates an electric signal which is delivered to an electronic evaluation device which controls a vertical tracing device as well as a horizontal rotary mechanism for shifting and turning the photodiode. The control is so implemented that each of the four-quadrants of the photodiode occupies in relation to the laser beam the same position. In view of the high sensibility of the photodiode, the positional determination is limited in such a measuring arrangement only by the accuracy of the mechanical adjustment.
The drawback of this conventional measuring arrangement resides in the mechanical tracing of the photodiode, which is determinative for the accuracy with respect to positional determination of the rail, i.e. in particular the positional change of the running surface of the rail. Moreover, the long measuring times as a result of the mechanical readjustment of the photodiode in the measuring plane (X-direction and Z-direction) are disadvantageous.
It is thus an object of the present invention to provide an improved system for surveying rails, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved system for surveying rails, which is capable of approaching individual positions at great accuracy in order to determine the positional change of the running surface of the rail relative to the laser beam, without requiring a shift of the photosensor.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a transmitter unit arranged on the rail and emitting a laser beam which is aligned longitudinally in the direction of a rail and is incident on a measuring surface; a detector unit designed for mobility along the rail and having a photodetector which confronts the laser beam and has a matrix in the form of a plurality of neighboring optical sensor elements for generating electric output signals in response to the incident laser beam on the measuring surface; an electronic evaluation unit receiving the output signals from the sensor elements for determining the point of impact and thereby the position of the laser beam on the measuring surface; and a proximity sensor for determining a change in distance between the transmitter unit and the detector unit.
In accordance with the present invention, the photodetector may include a matrix of rectangular configuration with a plurality of immediately neighboring pixels (optical sensor elements) for generating the electric output signals which are delivered to the electronic evaluation unit by which the point of impact of the spatially, positionally stabilized laser beam in the measuring surface is determined solely through electronic means by evaluating the output signals of the pixels. The photodetector may be an opto-electronic camera which has arranged in front thereof a transparent diffusion screen as measuring surface which is optically projected onto the matrix of the camera. In this fashion, it is possible to determine for each spot in relation to the length of the rail the positional change of the running surface with respect to the laser beam which is fixed in space. The configuration of the photodetector in the form of a rectangular matrix permits a two-dimensional measurement of the intensity distribution (Gaussian distribution) of the laser beam, thereby realizing a precise determination of the point of impact of the principal beam direction or of the laser beam axis upon the preset measuring surface. Thus, there is no longer any need to shift the measuring surface. The adjustment of the zero point (point of reference) is necessary only once, thereby shortening the duration of the measurements and, moreover, enhancing the measuring accuracy.
Suitably, the photodetector may be configured as CCD camera. This results in a rail surveying system which is very easy to compile.
A more precise determination of the point of impact of the laser beam upon the measuring surface can be realized by a so-called subpixel resolution, through determination of the point of impact of the laser beam upon the diffusion screen by conforming the measured subpixel position of the beam image of the diffusion screen upon the matrix. This is attained by initially evaluating each image line and each image column separately in a square zone about the beam image, and subsequently averaging the outcomes. The result provides the precise position (subpixel position) of the beam within the camera image. The difference between the inputted starting position (reference point) is thus a measure for the deviation of the mobile detector unit from the ideal line. Suitably, the conformation is implemented by a computer program.
According to another feature of the present invention, the electronic evaluation unit includes a microprocessor to implement in a simple manner complex computations and control processes.
In order to determine the position of the running surface of the rail in dependence on distance, the proximity sensor may include a friction wheel which rolls on the running surface of the rail. Suitably, the friction wheel is connected with an incremental shaft encoder for determination of the travel distance of the detector unit, thereby realizing a high distance precision. The friction wheel may also be utilized to register a state of motion of the detector unit to thereby ensure a correct execution of the survey.
Suitably, the detector unit can be remote-controlled so that rails which are difficult to access can be surveyed even under adverse conditions of visibility and unfavorable conditions of the surrounding (toxic gases, vapors etc.).
The positional stabilization of the laser can be realized by an electronic level which accomplishes a high positional stability in a fairly simple manner. Suitably, the positional stability amounts to +/xe2x88x921 mm deviation over 100 m rail length.
The precise approach of the measuring positions can be realized for a running rail cross section composed of flange parts and web parts, by providing at least two vertically rotatably supported guide rollers which are arranged in spaced-apart relation longitudinally in the direction of the rail, and which are forced against both side surfaces of the rail for guiding the detector unit, and by providing at least two running rollers which are arranged in spaced-apart relation longitudinally in the direction of the rail and rolling on the running surface of the rail and which are horizontally supported for rotation about pivot axes aligned transversely to the longitudinal rail direction, with at least one of the running rollers being driven.
Suitably, the vertical height of each of the guide rollers can be individually adjusted so that a survey of heavily worn rails can be implemented.
The traveling behavior of the detector unit on the rail can be enhanced, when, as viewed in longitudinal rail direction, the leading running roller is arranged behind the leading guide rollers. Also, the stability of travel can be improved, when the distance between the axis of the running roller and the axis of the immediately neighboring guide roller is one time to three times the guide roller diameter.
In order to ensure a precise movement of the detector unit, the guide rollers on one side of the rail have a fixed pivot axis and the guide rollers on the other side of the rail are forced, e.g. by a spring force, upon the side surface of the rail. The guide rollers may be supported in ball bearing, in particular, self-aligning ball bearings, to better conform the guide rollers to inclined rails.
In order to be able to travel over expansion joints and cracked rails, the guide rollers are arranged in pairs on a common transverse carrier which extends longitudinally in the direction of the rail and is articulated to the detector unit. At the same time, horizontal forces, which act during acceleration and deceleration, are thereby spread over more contact points so that a more stable guiding behavior is realized.
According to another feature of the present invention, the running rollers have a running surface which is formed in mid-section with a radial groove to realize a better stability with respect to lateral inclination as a consequence of the attained two-point contact upon the rail surface.
A safeguard of the detector unit can be implemented by providing a safety system. Defective rails or rail sections, which can lead to a crash of the detector unit, are registered in particular by providing the safety system with at least one proximity sensor for determining the distance of a reference point of the detector unit relative to the rail.
A survey of at least two rails extending in one plane can be realized by splitting the laser beam into two horizontal partial laser beams extending perpendicular to one another, for determination of the height difference of both rails with respect to a horizontal straight line extending in a vertical plane. This enables a precise measurement of the parallelism of both rails relative to one another in space in a simple manner. Suitably, the partial laser beam, which extends transversely to both rails, is positioned in the vertical plane, i.e. the vertical plane is unambiguously defined by this partial laser beam. Advantageously, one of the options for defining the reference line permits the use of the partial laser beam, which extends transversely to both rails, for formation of the horizontal straight line which is oriented in a vertical plane.