Rotation angle sensor or length sensor

This application is a National Stage completion of PCT/EP2008/053736 filed Mar. 28, 2008, which claims priority from German patent application serial no. 10 2007 015 195.2 filed Mar. 29, 2007.

The invention relates to a rotation angle sensor with two or more oscillators according to Claim 1 , and to a length sensor with two or more.

From the prior art as described in DE 690 13 170 T2 a proximity sensor is known, which works with so-termed striplines. Striplines are a particular class of electric waveguides which consist of one or more conductive strips fixed on a dielectric support. Stripline structures can consist for example of conductive strips arranged in one plane. They are often arranged, insulated, in or on a metallic surface. Their field of use is in high-frequency technology and, in that context, within the microwave range. They provide defined impedances in circuits for the transmission, coupling and filtering of high signal frequencies.

Often they are referred to using the English term ‘stripline’ and in many cases also the English term ‘microstrip’, although the latter denotes a particular structural form. In any event striplines are only conducting paths on printed circuits (printed-circuit boards) which are of a size to act as waveguides, and are operated as such. The electric and magnetic fields extend almost exclusively perpendicularly to the propagation direction, as is also the case in coaxial, or two-wire leads. In contrast, however, striplines are only used for short distances within structural groups.

The proximity sensor according to the document DE 690 13 170 T2 makes use of this technology. A proximity sensor is disclosed, which has just one oscillator and just one actuating element, not a rotation angle sensor or a length sensor with two or more oscillators. Correspondingly, in this prior art only the distance of this actuating element from the oscillator is evaluated, but not anything such as a relative movement of a plurality of oscillators around a curve or along a line. The known stripline is either linear (FIGS. 5 / 6 ) or of spiral shape (FIGS. 7 / 8 ). The purpose of the present invention is to put to use the technology of the known proximity switch for rotation angle sensors and length sensors.

The solution, which includes the aforesaid technical prerequisite (a plurality of oscillators), consists in shaping the striplines of the sensor elements in such manner that an actuating element covers more than one oscillator, or a plurality of actuating elements cover more than one oscillator.

In particular, the assembly of striplines can be nested in a curve one inside another; if the associated actuating element has the shape of a slender rod, then in any position it covers two to three sensor elements. Analogously, the configuration of the striplines can also be straight whereas the actuating element is curved in a sickle shape, or is orientated obliquely. Then too, in any measurement position two or three sensor elements will be covered. A comparable effect is achieved when two mechanically coupled actuating elements cover more than one oscillator.

Other features and advantages of the invention emerge from the following description of figures, which show:

FIG. 1 : An example embodiment of a rotation angle sensor with four curved stripline structures nested one inside another and with two straight actuating elements positioned approximately radially

FIG. 2 : Circuit diagram of a known stripline (microstrip) having three connection terminals, and whose frequency range can be tuned with the help of a capacitor

FIG. 3 : A linear, overlapping array of striplines, overlapping in relation to a straight actuating element

FIG. 4 : Circular-arc-shaped array of striplines, with two coupled actuating elements according to the invention, and

FIG. 5 : A straight (linear) array of striplines, with two coupled actuating elements according to the invention

In the example embodiment shown in FIG. 1 exact rotation angles (or, in other arrangements, also a torque) are determined with no contact by stripline oscillators arranged in a circle. This can begin, for example, from the U-shaped stripline oscillator shown in FIG. 2 or from the linear structure or from the spiral structure according to the DE 690 13 170 T2 prior art. The stripline is usually made by removing (by etching or milling) the top layer of metallization on the support. To measure a rotation angle larger than 360 degrees using the known oscillator geometries, a plurality of such microstrips must be arranged in a circle. However, if no special provisions are made, the disadvantage exists that the desired rotation angle measurement cannot be continuously made with constantly high accuracy. In contrast, with the solution shown in FIG. 1 not only can the rotation angle be measured dynamically with high angular resolution, but it is also possible, with relatively little additional effort and expense, to determine a torque. The no-contact determination of the rotation angle takes place by virtue of the oscillators, which oscillate at high frequencies (GHz range), with an angular resolution of 0.01 degree over a radius of a few centimeters.

Starting from the prior art cited, the shape of the known striplines is changed to give circular segments and in a certain sense—namely in relation to the actuating element—they are arranged with an overlap. In FIG. 1 four individual striplines can be seen, identifiable by their black outlines; however, different numbers of striplines can also be used. The striplines can be electrically separate from one another; however, they can also consist of a copper surface (high-frequency principle). With both variants the function would remain the same; only the frequencies would change.

In FIG. 1 actuation is effected for example by a metal rod, which is passed over the oscillators. On each respective stripline the indexes S 1 to S 4 denote the corresponding connection point for the oscillator circuit. To save space, the connection points S 1 to S 4 can also be arranged on the back of the circuit board. Furthermore, the oscillator signal decoupling points are indexed A 1 to A 4 . Corresponding to the overlapping, twisted configuration shown in FIG. 1 , the striplines can also be twisted in the opposite direction or they can be arranged in mirror-image inversion. In such a case the connection points S 1 to S 4 for the oscillator circuit and the decoupling points A 1 to A 4 of the oscillator signals then have to be adapted accordingly.

FIG. 1 shows the sense in which the above-described overlapping is to be understood. The striplines are shaped so that an actuating element (or even a plurality of actuating elements) always cover(s) more than one oscillator. Thanks to this overlap, uninterruptedly continuous detection of the position is possible. In theory, with only two coils an entire revolution can be detected without any break. If, in addition to rotation angle determination, it is also desired to determine a torque, then the number of oscillators can be increased correspondingly.

As the damping elements B 1 and B 2 of the striplines, various materials and geometries can be used (for example small metal plates, ferrite, etc.); however, it is preferable to use a metal rod.

Owing to the high frequencies of the oscillators, despite the short measurement time very high dynamics are achieved. To facilitate the evaluation of the signal, a frequency shift (for example by a multiplier) to a lower frequency range is recommended. The signals, which are measured with no contact, can then be evaluated for example with the help of digital technology.

By uniform distribution of the temperature, the invention favors the compensation of temperature variations over time, i.e. a fluctuation compensation which takes place during the digital evaluation. Thus, the sensor array shown in FIG. 1 contributes toward a temperature-stable system. A further advantage worth mentioning is that the electromagnetic tolerance (EMT) is substantially less critical than with known rotation angle sensors, since owing to the high frequencies screening is easier and by means of an evaluation step of integration (by virtue of the frequency measurement method) interferences are averaged out. By comparison with known rotation angle sensors, there is also a saving of active components.

FIG. 3 shows a linear array of striplines, which can be thought of as a straightening out of the curved array shown in FIG. 1 . Accordingly, this is a length sensor which determines the position of the straight actuating element. In the measurement range of the arrangement, the actuating element—owing to the “overlapping”, oblique configuration of the striplines—covers more than one oscillating stripline. In other respects the explanations relate to those for FIGS. 1 and 2 .

FIGS. 4 and 5 show arrangements (again, curved for angle measurement and straight for length measurement, respectively), which differ from the corresponding structures shown in FIGS. 1 and 3 in that the overlap is produced in other ways. In the configurations of FIGS. 4 and 5 the stripline oscillators are not sickle-shaped and nested obliquely one in another in relation to a radial or transverse actuating element. Rather, two radial actuating elements ( FIG. 4 ) or two transverse actuating elements are mechanically coupled to one another. Either the two actuating elements are on a common support, or two individually supported actuating elements are used, which always move with a predetermined, fixed distance between them. With such an arrangement too, the principle according to the invention is realized since at every point within the measurement range more than one stripline oscillator is covered.