Abstract:
In method and an arrangement for detecting parameters in displacement or angle sensors, in a test procedure sensor signals in a stationary sensor are evaluated, which signals are generated by scanning a plurality of code elements located side by side, perpendicular to a direction of motion, on a transducer element as a moving component; and the test procedure is performed with a transducer element that has a predetermined variation of geometrical variables of the code elements.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a method and an arrangement for detecting parameters, in particular the air gap in magnetic sensor arrangements, in displacement or angle sensors.  
         [0002]     It is known per se that for detecting rotary speeds or rotational angle changes, for instance in motor vehicles, rpm sensors are used for measuring the rotary speed of wheels, for electronic stability control systems, or in engine control. These sensors can evaluate an angular position, for instance, on the basis of pulses generated optically, magnetically, or otherwise, by the rotation and detected by suitable means.  
         [0003]     Particularly in magnetic measuring methods, knowledge of the maximum allowable air gap between the transducer element and the sensor is very important, if a reliable measurement method is to be obtained. The maximum allowable air gap, in the applications described above, is the air gap at which it is assured that under all operating conditions, every mechanical or magnetic flank, for instance of a transducer wheel provided with tooth flanks, is detected and output by the sensor.  
         [0004]     In the manufacture of such rpm sensors, typically a defined test air gap is established between the transducer wheel and the sensor for every sensor produced. If the sensor correctly reflects all the flanks of the transducer wheel, the outcome of the test is positive. The test air gap is selected such that in the ensuing operation, the function is assured under all peripheral conditions.  
         [0005]     This test is typically designed as a so-called go/no-go test and furnishes no quantitative information whatever about the air gap actually attainable with the particular sensor. The go/no-go test method, however, is in no way appropriate for the importance of the air gap as a parameter in production, since with it, static detection and if needed correction of the production process, for instance, is not possible.  
       SUMMARY OF THE INVENTION  
       [0006]     It is therefore an object of the present invention to provide a method and arrangement for detecting parameters in displacement or angle sensors which avoid the disadvantages of the prior art.  
         [0007]     In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a method for detecting parameters in displacement or angle sensors, comprising the steps of evaluating in a test procedure, sensor signals in a stationary sensor, which signals are generated by scanning a plurality of code elements located side by side, perpendicular to a direction of motion, on a transducer element as a moving component; and performing the test procedure with the transducer element that has a predetermined variation of geometrical variables of the code elements.  
         [0008]     When the method is performed in accordance with the present invention, a test procedure is advantageously performed in which sensor signals are evaluated in a stationary sensor, which signals are generated by scanning of a plurality of code elements, located side by side, perpendicular to the direction of motion, on a transducer element as a moving component. The test procedure is performed with a transducer element that has a predetermined variation of the geometric variables of the code elements.  
         [0009]     Preferably, the proposed method serves to detect the air gap that occurs between a magnetic-field-sensitive sensor and a tooth-gap contour on the transducer element as a parameter, and the tooth height and/or gap height is varied in a predetermined order.  
         [0010]     With the invention, a test method can advantageously be implemented which makes a quantitative determination of the attainable air gap possible for each sensor manufactured. The test procedure is not lengthened in duration by this. In this way, it is thus possible at minimal additional expense to detect the attainable air gap statistically during production and use it for both controlling and optimizing the production processes.  
         [0011]     In an advantageous embodiment of the invention, the transducer element is a transducer wheel, and the test procedure is effected during one wheel revolution, identified by means of an index marking.  
         [0012]     A variant of the invention may be designed in such a way that the variation in the tooth height and/or gap depth is embodied such that during the test procedure, a continuous enlargement of the air gap occurs. However, it is especially advantageous if the variation in the tooth height and/or gap depth is embodied such that during the test procedure, a groupwise enlargement of the air gap takes place; for instance, four groups, each with tooth heights and/or gap heights that repeat four times, may be located on the circumference of the transducer wheel during the test procedure.  
         [0013]     In an advantageous arrangement for performing the above-described method, there is a test apparatus which uses a metal transducer wheel, produced for the test procedure, which has the varied tooth-gap contour on its circumference. The tooth-gap contour is located across the air gap opposite an rpm sensor, and the beginning of the test procedure can be defined via an index hole, as an index marking.  
         [0014]     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims the invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  shows a basic arrangement of a magnetic field sensitive rpm sensor, which is diametrically opposite, across an air gap, from a tooth-gap contour of a transducer wheel;  
         [0016]      FIGS. 2 and 3  each show a transducer wheel for a test procedure, with a groupwise variation in the tooth-gap contour of the transducer wheel;  
         [0017]      FIG. 4  shows the course of measurement and sensor signals during a test procedure, or one revolution of the transducer wheel of  FIG. 2 ; and  
         [0018]      FIG. 5  shows the course of the magnetic differential field during the test procedure.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     In  FIG. 1 , in a schematic view, part of a transducer wheel  1  is shown, which is provided on its circumference with a tooth-gap contour Z, L. There is also a magnetic-field- sensitive sensor  2 , as an rpm sensor, which is diametrically opposite the tooth-gap contour Z, L across an air gap  3 . As the transducer wheel  1  below the sensor  2  rotates past it, the switching edges that are tripped by the field variation on the part of the tooth-gap contour Z, L, can be evaluated, if the size of the air gap  3  permits the generation of a sensor output signal.  
         [0020]     In a test apparatus, a qualitative effect of the air gap  3  is now to be performed by measurement with a transducer wheel  1  of  FIG. 2  and  FIG. 3 ; this measurement can be achieved with an arbitrary sensor configuration. To that end, the transducer wheel  1  of  FIG. 2  has a variation in the tooth-gap contour in terms of the height of both the teeth Z and the gaps L. In this transducer wheel  1 , there are four periods  4 ,  5 ,  6  and  7 , each with four approximately equal teeth and tooth-gap heights Z 1 , L 1 ; Z 2 , L 2 ; Z 3 , L 3 ; Z 4 , L 4  located on the circumference. Moreover, via an index hole  8 , an index marking or reference position is set for the beginning of a test procedure or of a revolution. The beginning of the test procedure can then be detected, for instance by a light gate.  
         [0021]     From  FIG. 3 , one tooth-gap group with Z 1  and L 1  and one group with tooth-gap heights Z 2  and L 2  differing from it can also be seen in detail.  
         [0022]     In  FIG. 4 , the magnetic field  10 , the index signal  11 , and the output signal  12  of the sensor are shown over the rpm a and a revolution of the transducer wheel  1 . The variation in the tooth-gap contour Z, L, in the exemplary embodiment shown, is emphasized in such a way that after the traversal through the index marking  8  (index signal  11 ), initially a slight air gap  3  with a tooth-gap height Z 1 , L 1  is established between the sensor  2  and the transducer wheel  1 . In the rotation of the transducer wheel  1  past the sensor, by reducing the tooth-gap height from Z 2 , L 2  after the index position through Z 3 , L 3  to Z 4 , L 4 , an increasing air gap  3  is established, and decreasing field fluctuations in the course  10  are generated.  
         [0023]     In the process, the output signals of the sensor  2  are evaluated by means of the pulses  12 . As soon as a flank or a pulse is missing as an output signal of the sensor  2  is missing, then either the time since the passage past the index marking  8  or alternatively the rotational angle α is stored in memory. On the condition that the rotational speed of the transducer wheel  1  is constant, an unambiguous association with the air gap  3  and thus with the magnetic amplitude  10  is thus possible.  
         [0024]     In designing the variation in the tooth-gap contour of the transducer wheel  1  over its circumference, calibration algorithms internal to the sensor may be taken into account. In the exemplary embodiment of  FIG. 2 , with four periods, each with four identical tooth-gap pairs, the sensor  2  can adapt by internal adaptation to the magnetic stimulation before the air gap  3  is artificially increased still further. Moreover, the conclusiveness of the measurement is improved by the repetition of identical tooth-gap pairs.  
         [0025]     In the test procedure of  FIG. 4 , the sensor  2  furnishes correct signals up to the angular position α=150° and does not fail until at an air gap  3  corresponding to Z 2 , L 2 , while Z 1 , L 1  is still evaluated correctly.  
         [0026]     In  FIG. 5 , the simulated course  13  of the differential magnetic field Delta B is shown for a differential magnetic field sensor  2  with air gap heights of 4.1 mm, 4.3 mm, 4.5 mm, and 4.7 mm. From this, the influence can be seen that is exerted by the nonideal periodicity of the transducer wheel  1  at the beginning and end of each of the four groups. This can be suitably taken into account in the design of the transducer wheel  1  constructed for the testing. By changing the tooth-gap contour Z, L at the transition between groups, the overswings and underswings apparent here can be minimized in their amplitude.  
         [0027]     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of methods and constructions differing from the types described above.  
         [0028]     While the invention has been illustrated and described as embodied in method nd arrangement for detecting parameters in displacement or angle sensors, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0029]     Without further analysis, the foregoing will reveal fully revela the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of the invention.