BACKGROUND INFORMATIONThe present invention relates to a method and an apparatus for measuring the angle of a first rotatable body which coacts with two further rotatable bodies, the angle of the two further bodies being measured and the angle of the first body being determined therefrom.[0001]
A method and an apparatus of this kind are known from German Unexamined Patent Application 195 06 938 A1, in which a first gear which is equipped with a number of teeth and is rotatably through more than 360° is provided as the first rotatable body. The two further rotatable bodies are also gears, which are in engagement with the first gear and whose numbers of teeth is less than the number for the first gear. In addition, the numbers of teeth of the two further bodies differ, for example, by one tooth.[0002]
Associated with each of the two further bodies is a sensor with which the angle of the body can be measured absolutely, i.e. even when the body is stationary. The angle of the first body can be determined from the measured angles of the two further bodies.[0003]
The accuracy of the angle determined for the first body can be influenced by an appropriate selection of the number of teeth of the first body and of the two further bodies. It has been found, however, that even after optimization in this regard, the angle determined for the first body still exhibits inaccuracies.[0004]
Proceeding therefrom, it is the object of the invention to develop a method and an apparatus of the kind cited initially in such a way that exact determination of the angle of the first rotatable body is possible.[0005]
In the case of a method and an apparatus of the kind cited initially, this object is achieved according to the present invention in that the angle of the two further bodies is measured simultaneously.[0006]
Simultaneous measurement ensures that even when the angles of the two further bodies are measured during rotation of the bodies, an exact determination of the angle of the first body is possible. If the angles of the two further bodies were not measured simultaneously, the result, especially in the event of rotation of the bodies, could be that the body measured later would already have rotated further by a slight “delta.” This delta is in itself very small, but can nevertheless means that the requisite accuracy can no longer be obtained in the subsequent determination of the angle of the first body. This is reliably avoided by simultaneous measurement of the angles of the two further bodies. Measurement of the angles of the two further bodies is thus synchronized, with the substantial advantage that the accuracy of the determination of the angle of the first body is thereby improved.[0007]
Because of the synchronization, the angles of the two other bodies are measured at a single sampling time, i.e. simultaneously. Synchronization and definition of the single sampling time, and thus simultaneous measurement, are achieved with the aid of a signal with which measurement of the two angles is started.[0008]
In an advantageous embodiment of the invention, the measured angles of the two further bodies are stored. The result of this is that determination of the angle of the first rotatable body is independent of measurement of the angles of the two further bodies. It is thus unnecessary to process the measured angles of the two further bodies immediately; rather it is possible, because the measured angles are stored, to process these measured angles regardless of the time at which measurement occurred.[0009]
It is particularly useful if each of the two further bodies is equipped with a magnet, associated with which is an AMR sensor that is provided for measuring the angle of the associated further body; and if an analysis circuit is provided which is coupled to the two AMR sensors and is provided for analyzing and optionally for transforming the measured angles of the two further bodies. The aforesaid AMR sensors are suitable for making an absolute measurement of the angles of the two further bodies. The angles can thus be measures with no need to impart any rotation to the two bodies. The analysis circuit associated with the two AMR sensors is provided in order to process the measured angles further in a first step. In particular, it is possible for the analysis circuit to transform the measured angles, for example, into pulse-length modulated signals or other digital signals.[0010]
In an advantageous development of the invention, the analysis circuit is equipped with means, in particular with sample-and-hold elements, for storing the measured angles of the two further bodies. The aforesaid decoupling of the measurement of the angles of the two further bodies from the determination of the angle of the first body is thereby accomplished in simple fashion.[0011]
It is particularly useful if a calculation device, in particular a programmable microprocessor, is provided for determining the angle of the first body. This makes it possible, in particularly simple fashion, to adapt the determination of the angle of the first body, for example, to the geometry of the two further bodies. All that is necessary in this context is to modify the corresponding values in the program of the microprocessor.[0012]
In an advantageous embodiment of the invention, the calculation device can generate a start signal with which simultaneous measurement of the angles of the two further bodies by the two AMR sensors can be triggered. The calculation device is thus responsible for the simultaneous measurement of the angles of the two further bodies. The calculation device triggers this simultaneous measurement by generating a single start signal which brings about measurements at both AMR sensors. This represents a reliable but nevertheless very simple possibility for achieving simultaneous measurement of the angles of the two further bodies.[0013]
The result of this common start signal is that the angles of the two further bodies are measured at a single sampling time, i.e. simultaneously. The single sampling time is defined by the start signal.[0014]
In an advantageous development of the invention, a line is provided with which the calculation device is connected to the analysis circuit, and on which the start signal can be delivered to the analysis circuit. The analysis circuit is acted upon by the start signal by way of this line.[0015]
Further features, potential applications, and advantages of the invention are evident from the description below and from exemplary embodiments of the invention which are depicted in the Figures of the drawings. In this context, all features described or depicted constitute, of themselves or in any combination, the subject matter of the present invention, regardless of their summarization in the claims or references thereto, and regardless of their wording or depiction in the description or the drawings.[0016]
BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 shows a schematic depiction of an exemplary embodiment of an apparatus according to the present invention for determining the angle of a first rotatable body;[0017]
FIG. 2 shows a schematic block diagram of an electrical circuit for the apparatus of FIG. 1; and[0018]
FIG. 3 shows a schematic diagram of two signals occurring in the circuit of FIG. 2.[0019]
DETAILED DESCRIPTIONFIG. 1 depicts an[0020]apparatus1 which has a first rotatable body and two further rotatable bodies. Agear2 having a number of teeth n is provided as the first rotatable body. The two further rotatable bodies are also configured asgears3,4, gear3 having a number of teeth m, and gear4 a number of teeth m+1.
Gear[0021]2 is, for example, coupled to a steering wheel of a motor vehicle. In particular,gear2 is mounted on ashaft5 which constitutes a component of the aforesaid steering wheel.
Each of the two[0022]gears3,4 is equipped with a magnet6, each of magnets6 generating a magnetic field oriented in a specific direction.
The two[0023]gears3,4 andgear2 are in engagement, so that a rotation ofgear2 causes corresponding rotations ofgears3,4. Because of the different numbers of teeth ongears2,3,4, the rotation angles ofgears2,3,4 upon rotation are different.
The rotation angle of[0024]gear2 can be less than 360°. Especially whenapparatus1 is used for a steering wheel of a motor vehicle,gear2 can perform multiple rotations. In particular, the rotation angle ofgear2 is, for example, 1440°. The rotation angles of the twogears3,4 are preferably not limited.
FIG. 2 depicts a[0025]circuit7 which is associated withapparatus1 of FIG. 1.Circuit7 of FIG. 2 has two so-calledAMR sensors8,9, which are elements having a variable resistance (AMR =anisotropic magnetic resistance). AMR sensors are sensors whose resistance changes depending on how the sensor is oriented in an external magnetic field. AMR sensors are therefore suitable for sensing the rotation angles of bodies on which, for example, a magnet is mounted. The twoAMR sensors8,9 are connected to ananalysis circuit10 which is made up of twoblocks11,12;first AMR sensor8 acts onblock11, andsecond AMR sensor9 onblock12.Analysis circuit10 is connected to acalculation device13, in particular to a microprocessor. Aclock14 and amemory15 are connected tocalculation device13. Apower supply16 generates a supply voltage VCC which is supplied tocalculation device13,clock14,memory15, the twoblocks11,12 ofanalysis circuit10, and to the twoAMR sensors8,9. When the circuit is used in a motor vehicle, the aforesaid supply voltage VCC is generated from the battery voltage of the motor vehicle.
The calculation device is connected to other devices via a plurality of further lines. When[0026]circuit7 is used in a motor vehicle,calculation device13 is connected by way of the aforesaid lines, in particular, to a control device for controlling and/or regulating the functions of the motor vehicle.
The two[0027]AMR sensors8,9 are associated with the two magnets6 of the twogears3,4. Each of magnets6 generates in the associatedstationary AMR sensor8,9 a voltage which depends on the angle of the associatedgear3,4. Rotation of therespective gear3,4 causes a voltage profile which rises over an angle of approximately 180°, and then declines again over an angle of approximately 180°. After one revolution ofgear3,4, i.e. after 360°, this voltage profile repeats.
FIG. 3 depicts the voltage profile generated by the two[0028]AMR sensors8,9 when gears3,4 rotate. The rotation ofgear2, which extends over a range from 0° to 1440°, is plotted on the horizontal axis. A rotation of this kind ofgear2 brings about a plurality of rotations ofgears3,4. This plurality of rotations ofgears3,4 in turn causes the voltages generated by theAMR sensors8,9 to change. This is plotted on the horizontal axis of the diagram of FIG. 3. A rise in the voltage profile means a180-degree rotation of the associatedgear3,4.
Because of the differing numbers of teeth on[0029]gears3,4, different voltage profiles occur for the twoAMR sensors8,9. As depicted in FIG. 3, the voltage for the twoAMR sensors8,9 whengear2 is at an angle of 0° is also 0°. Whengear2 then rotates, the voltage of the twoAMR sensors8,9 rises. Because of the differing numbers of teeth on the twogears3,4, this rise occurs with differing slopes. The consequence is that the two voltage profiles generated byAMR sensors8,9 are not identical. This is evident from FIG. 3 in particular at somewhat greater angles forgear2, at which the two voltage profiles ofAMR sensors8,9 differ substantially from one another.
When[0030]apparatus1 andcircuit7 are in operation, the voltage of the twoAMR sensors8,9 is measured. This voltage is equivalent to the angles of the twogears3,4.
From these two measured angles of[0031]gears3 and4, and in particular from the difference between the two aforesaid angles, conclusions can be drawn as to the angle ofgear2. This calculation of the angle ofgear2 involves the numbers n, m, and m+1 forgears2,3, and4. The correlation described above is plotted in FIG. 3, as an example, for an angle W.
As is evident from FIG. 2, a[0032]line17 is provided which connectscalculation device13 to each of the twoblocks11,12 and thus toanalysis circuit10. Online17 it is possible to deliver, toanalysis circuit10 and in particular to the twoblocks11,12, a start signal S with which simultaneous measurement of the angles of the twogears3,4, can be achieved. These simultaneously measured angles of the twogears3,4 are then stored.
For this purpose, the two[0033]blocks11,12 each contain, in particular, a sample-and-hold element which is connected to the respectively associatedAMR sensor8,9. The sample-and-hold element is also acted upon by start signal S.
When[0034]calculation device13 then generates start signal S, for example by transferring on line17 a binary signal from a “low” to a “high” potential, the result is that the two sample-and-hold elements in the twoblocks11,12 simultaneously read in and store the voltages supplied by the twoAMR sensors8,9. This means that the angles measured by the two AMR sensors for the twogears3,4 are stored synchronously in the sample-and-hold elements.
It is possible thereafter for the calculation device, with the aid of further activation signals, to read the stored angles of the two[0035]gears3,4 out of the sample-and-hold elements of the twoblocks11,12, and read them via correspondinglines18,19 intocalculation device13 for further processing.
Start signal S present on[0036]line17 thus results in a synchronization of the twoblocks11,12, and thus ultimately in a synchronization of the measurement of the angles of the twogears3,4. This ensures an identical time reference for the measurement of the angles of the twogears3,4. The consequence is that because of the aforesaid identical time reference, a higher accuracy can be achieved in the subsequent calculation of the angle ofgear2.
The identical time reference for measuring the angles of the two[0037]gears3 and4 is achieved with the aid of start signal S. The sampling time, and thus the identical time reference, for the measure of said angles is defined by way of the transition, already mentioned above, in start signal S from a lower to a higher potential. On the basis of start signal S, a common time reference is created which results in a synchronization of the measurement of the two angles and thus in a simultaneous measurement, i.e. a measurement of the two angles at one sampling time. It is entirely possible, in this context, for the sampling time to be identical to a time generated byclock14.