Measuring device for track building machines
BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention relates to a measuring device for track building machines, which comprises an optical receiver device for receiving light waves emitted by light sources situated on both sides of and at a distance from the measuring device, and an evaluation device. 
     B. Description of the Prior Art 
     In the construction of new track installations or the restoration of existing track installations, particularly for railways, measuring devices are required to enable the course of the track to be accurately determined and, in particular, to be adapted to requirements or corrected. Measuring devices of this kind conventionally consist of an optical measuring system utilising three reference points at a distance from one another on the path of the track for the purpose of determining the course of the latter. For straight horizontal stretches these three points must lie in one line, but on curves, for example, these three reference points must be offset to a certain extent in relation to one another. This offset is measured and evaluated. The layout of the track must if necessary be corrected in accordance with the evaluation. 
     OBJECTIVES AND SUMMARY OF THE INVENTION 
     Conventional optical measuring devices have motor-driven lens discs which at the middle reference point project onto appropriately disposed sensors the light waves radiated by means of lamps in the two outer reference points. The relative positions of the two outer reference points in relation to the optical axis of the measuring device are in this case conventionally ascertained and evaluated by time measurement. 
     The object of the present invention thus consisted in finding a measuring device which does not need movable parts and thus eliminates wear and the consequent increasing inaccuracy of measurement. 
     According to the invention this object is achieved in that two lenses are provided which are disposed at a distance from one another in one axis, and that between the two lenses at least one sensor having a plurality of light-sensitive points is in each case disposed in such a manner that light rays entering through the respective lens are projected, in accordance with their entry angle onto the lens, onto the corresponding zone of the sensor, and that an evaluation logic circuit is provided which brings together and evaluates the signals produced by the sensors. 
     Preferred embodiments of the invention are described in Claims 2 to 12. 
     The measuring device according to the invention has the advantage of having no moving parts, so that constant accuracy of measurement is ensured throughout the useful life of the device, since there is no wear on moving parts of the optical system to reduce the accuracy of measurement in dependence on the length of time during which the device is used. Moreover, the measuring device can be of very compact construction and is insensitive to shocks and rough transport conditions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One exemplary embodiment of the invention is explained more fully below with reference to the drawings, in which: 
     FIG. 1 shows the arrangement according to the invention of the measuring optical system with sensor strips, and 
     FIGS. 2a and 2b show schematically the sensor strips with different positions of the light sources. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A sensor strip 4, 5 is disposed in the middle of the optical axis 3 formed by each of two lenses 1, 2 of semicircular cross-section. These strips are so disposed that the light rays collected by the lenses are, in dependence on the position of the corresponding light sources, projected, focused as a fine line of light, along the sensor strips. In the example the light source A lying on the optical axis 3 is projected onto the point A&#39; of the sensor strip 5. A light source B lying outside the optical axis 3 is correspondingly projected onto the point B&#39; of the sensor strip 5. The distance between the projected point on the sensor strip and the point of the optical axis on the sensor strip is a measure of the angle β of the light source relative to the optical axis at that point. In order to filter out stray light, according to the invention a colour filter 6 and polarisation filters 7, 8 are in addition disposed in front of the lens 2. It can thus be ensured that only light from a particular light source will fall on the sensor strips and that an unambiguous signal can be produced. In particular when use is made of highly sensitive CCD (charge coupled device) sensors, only a relatively small amount of light should fall on the sensors. By adjusting the two polarisation filters 7, 8 so that they are turned at about 90° to one another, a very large proportion of the incident light is absorbed. If very powerful light sources are now used, only a small part of these light rays will be allowed through onto the sensors and all other extraneous light sources will be filtered out. By disposing one lens and one sensor strip on each side of the optical axis, the angles of each one or more light sources on both sides of the measuring arrangement relative to the optical axis can be determined and evaluated. In the embodiment illustrated the optical axis is actually a plane, and for complete measurement of the angle of the light source relative to two optical planes, two of the measuring devices described will correspondingly be required, their optical planes being so disposed as to be turned at a certain angle, preferably 90°, to one another. However, it is also conceivable to use only one measuring device, which is mounted in a casing for rotation about its optical axis, and to determine the two angles by two measurements spaced apart in time in each case, or to use square sensors which, with an appropriate optical system, for example a biconvex lens, simultaneously measures both axes through the light focused to point form. 
     In an embodiment which is likewise conceivable, provision is made for the duplication of the measuring device described, with in each case two pairs of cylindrical lenses, turned at preferably 90° to one another, together with the correspondingly allocated pairs of sensor strips, for the purpose of determining the angle of incidence of the light in two optical planes, the measuring device thus duplicated being disposed so as to be turned about its longitudinal optical axis at a certain angle, preferably 45°, relative to a plane, for example a horizontal plane. With this embodiment the effect is achieved that a plurality of light sources lying in the same plane can be distinguishably detected and evaluated by the sensor strips. 
     The nature of the evaluation will be explained with reference to FIG. 2. For the sake of greater clarity the two sensor strips are there shown with their operative faces side by side. A sensor strip consists here, for example, of 2000 individual light-sensitive cells. All the cells are scanned in respect of their state cyclically from cell 0 to cell 2000 by means of a pulse generator logic circuit. The first cell 0 is in this arrangement disposed in the sensor strips 4, 5, which are arranged one behind the other, at respective opposite ends of the sensor strip. In accordance with the intensity of the light falling on each individual cell a certain voltage value is produced as said state. In the example illustrated in FIG. 2a the two light sources A and C lie on the optical axis of the measuring device. The light ray collected in each case by the optical system illuminates the cell 1000 on both sensor strips. This means that in the cyclical scanning of their state the cells 0 to 999 and 1001 to 2000 of both sensor strips 4, 5 produce no voltage in each case, while each of the cells 1000 produces a certain voltage value. The scanning cycles of the two sensor strips are now synchronised, and at the same time a count module is provided, which at a first positive signal of a cell of the one sensor strip in accordance with the scanning cycle starts the counting process, and on the second arrival of a signal of a cell of the other sensor strip interrupts the counting process. The direction of counting, that is to say the sign of the counter, is fixed by the respective sensor strip. For example, a signal from the sensor strip 4 causes the counter to count forwards, and a signal from the sensor strip 5 causes the counter to count backwards. The counter is so constructed that in the event of the simultaneous arrival of a signal from both the sensor strips the signal is suppressed. Thus the reading of the counter after a complete scanning cycle corresponds to the differential angle between the two relative angles of the light sources A and C of the optical axis, the sign determining the applicable side of the angle, that is to say in the upward or downward direction. Before the commencement of a scanning cycle the reading of the counter is always set to zero. In accordance with the number and spacing of the cells on the sensor strip and the design of the lenses a direct relationship between the counter reading and the relative angle can be established in degrees and displayed with the aid of appropriate means or processed in another evaluation logic circuit. The advantage of direct measurement of the relative angle consists in particular in that any offset of the optical axis is thereby compensated. If in fact the two light sources lie on an axis which passes through the optical centre of the mesuring device, the differential angle is correctly given as 0. 
     With an arrangement of the light sources relative to the measuring device in accordance with FIG. 2b, after 500 pulses of each scanning cycle the counter will start forward counting on a signal from the sensor strip 5. After 500 more pulses, at the pulse number 1000, the counting process is stopped by a signal from the sensor strip 4. The count of the counter accordingly amounts to 500 units, which corresponds to a certain angle value in degrees in the upward direction between the connection of the light source C to the measuring device and the connection of the light source A to the measuring device. This value is finally used for checking the measurement points and if necessary for correcting the linearity of the tracks. 
     Instead of CCD sensors it is also possible to use other sensors, for example PSD (position-sensitive detector) sensors.