Angle measuring device

In a measuring device for the non-contact detection of the absolute angle of rotation of a shaft, such as a steering column, at multiple revolutions, magnetic, optical or magneto-optical structures are arranged on the shaft or a part connected therewith. The shaft carries a thread which is in engagement with a rider or index finger. At least one sensor is provided to detect the magnetic, optical or magneto-optical structures as well as the displaced position of the rider or index finger.

In FIG. 1, a partial section of a shaft, e.g. the steering column of a motor vehicle, is denoted by 1. About the circumference of the shaft 1 are arranged magnetic structures 2 which, as is more clearly apparent from the developed view of the cylinder according to FIG. 2 , are comprised of several regions 3 , 4 and 5 mutually adjoining in the axial direction of the shaft. The magnetic structure 3 is comprised of several structural patterns recurring in the circumferential direction, with a total of four segments 6 being arranged about the circumference of the shaft 1 . These magnetic structures 3 comprise simply detectable field or magnetizing changes which, at a rotation of the shaft, exhibit a distance a to the reference structure 5 monotonously growing along the generating line of the shaft 1 , thus enabling the unambiguous allocation of an angle value to a distance value. The measurement of the absolute angle becomes thereby feasible by means of a sensor system comprising a sensor array 7 , whereby an unambiguous value may be detected within a segment 6 in the configuration illustrated in FIG. 2 . In order to enable the respective allocation to the respective segment, a reference structure 4 is provided, which is formed by a helical transition line between regions of different magnetic properties. The helical line in this case extends about the total circumference such that an unambiguous allocation to the respective segment is feasible. Due to lower demands on the angular resolution, region 4 may have a smaller axial height than region 3 . From FIG. 3 the overall measuring system is apparent, wherein, in addition to the magnetic structure illustrated in FIG. 1 , also a cylindrical sleeve 8 is visible, whose internal thread engages in the external thread 9 of the shaft 1 . A rotation of the shaft in the sense of arrow 10 causes the cylindrical sleeve 8 to be axially displaced in the sense of double arrow 11 in a manner so as to enable the detection of this axial movement by the sensor system 7 . To this end, a magnetic ring structure 12 is attached to the cylindrical sleeve 8 . The measurement of the displaced position of the cylindrical sleeve 8 gives a coarse information on the number of revolutions of the shaft 1 such that, in combination with the precise and absolute angle detection in a range of between 0 and 360°, i.e., within the range of a single revolution, also the overall revolution angle can be absolutely measured over several revolutions. The reference structure 4 may be omitted, if the overall system according to FIG. 3 , which comprises a movable cylindrical sleeve, allows the determination of the number of revolutions to precisely 360°/n, where n is the number of segments for the absolute angle measurement in the range of 0 to 360°. FIG. 4 depicts an alternative embodiment of the measuring system, in which the external thread 9 of the shaft 1 cooperates with a rider or index finger or a carrier 13 for the sensor array 7 . There, the revolution-dependent vertical displacement of the sensor array is detected by determining the position of the reference ring 5 relative to a zero point defined anywhere on the sensor array 7 , and is calculated back to the respective angular position via the pitch of the thread. FIG. 5 depicts an alternative embodiment in which the magnetic structure may be arranged on a cylinder dish 14 . In such a configuration, the magnetic structure 2 applied on the cylinder dish 14 may, for instance, be arranged spirally.