DE19818799C2 - Method and device for measuring angles - Google Patents

Description

The invention relates to a method and a device for measuring angles of rotation an axis of rotation with a magnetic scale and the sensor unit assigned to the scale according to the preamble of the independent claims.

WO 89/11 080 A1 discloses an apparatus and a method for determining the Distance between two mutually movable parts. Using two sensors, two Scanned tracks, each generating a sinusoidal signal pair with one at any time defined phase position. The relative distance is then the difference between the two Phases. In WO 89/11 080 A1 at least two signal pairs must be recorded so there are at least four sensors for determining the relative phase position of the sinusoidal signals necessary.

A generic device for measuring angles of rotation is from DE 44 40 214 C2 known. A magnetic scale with two coaxial on a rotatable axis arranged magnetic coded rings is by an associated sensor unit consisting of 4 Hall sensors.

The device according to the invention and the method according to the invention differ from the previously known systems through the combination of magnetoresistive sensors and Hall sensors and by reducing the necessary sensors to three. Magnetoresistive sensors have an improved sensitivity compared to Hall sensors on, but have the disadvantage of the direction and thus the sign of the magnetic field not being able to recognize. The device according to the invention and the invention Processes combine the advantages of both types of sensors and also ensure a reduction the necessary sensors. The reduction in the number of sensors enables production cost-effective systems and also ensures a reduction  possible sources of error, which is particularly the case in safety-relevant systems such. B. Automobiles is of great importance.

With regard to new concepts with so-called x-by-wire devices for vehicles and other mobile systems in which mechanical transmission means such. B. for steering and / or braking are largely replaced by electronic modules increasingly the requirement for the accuracy of the position determination of those to be controlled Components. Knowledge of the absolute position is essential. So z. B. handlebars of a vehicle requires knowledge of angles of rotation from 0 ° to over 360 °. It is Detection of absolute angles with conventional sensors, e.g. B. inductive sensors, Potentiometer sensors or optical sensors with gray code possible, but that is The resolution of such sensors is too low and is not suitable for use with x-by-wire systems suitable. Magnetoresistive angle sensors are more sensitive to the angular resolution, they are, however, for principle reasons only for the detection of absolute angles of less suitable as 180 °.

The invention is therefore based on the object of a method and an apparatus for Detection of rotation angles indicate the advantages of magnetoresistive sensors and Hall sensors combined, thus reducing the number of sensors at the same time an improved angular resolution.  

The object is solved by the features of the independent claims. Further and advantageous embodiments are to the further claims and the description remove.

The invention is based on a device for measuring angles, the front direction an angle sensor system with a magnetic scale and a sensor unit comprises and the sensor device has at least one magnetoresistive sensor. The Invention is that the device as a magnetic scale at least two has coaxial, magnetically coded rings on a rotatable axis. The number of Magnetic poles on the half circumference of each of the rings is not prime. The sensor unit points two magnetoresistive sensors, which are operated in the saturated state. Invention a hall sensor is additionally provided which is assigned to a coded ring which has an odd number of poles on half the circumference of the ring.

In a preferred embodiment, the rings are concentric with respect to the rotatable one Axis adjacent in the radial direction, arranged. The advantage is that the two rings only require a minimal overall height so that the axis length can be small. Another The advantage is that the arrangement is insensitive to vibrations of the axis, since the Distance between sensor and ring changes much less than with axially offset and rings firmly connected to the axle.

In a further preferred embodiment, the rings are in relation to the rotatable axis arranged axially adjacent. The rings are preferably fixed with the axis connected. The advantage is that this arrangement is mechanically very robust.

It is useful that a ring is formed in one piece. The advantage is simple and safe re mounting on the axis. Another convenient arrangement is a ring from several to assemble the ring segments. The advantage is that it can be retrofitted of an angle sensor system according to the invention is possible on one axis. More advantageous the ring segments are arranged one above the other or axially offset and can preferably overlap in the circumferential direction.  

In a favorable embodiment of the angle sensor arrangement according to the invention, a ma gnetoresistive sensor and a Hall sensor separately from each other on a magnetic coded ring arranged.

A magnetoresistive sensor and a Hall are in a further preferred embodiment sensor combined in a single component. The component is preferably a microelek tronic component, particularly preferably the component is a monolithic integrator t component, which has an integrated magnetoresistive sensor and an integrated Hall sensor has.

In a method according to the invention for operating a device for determining The phase offset between the output signals of two magnetoresis is given by angles stiver sensors determined and with the sign of the output signal of a Hall sensor connected. This means that the angle of rotation can be absolutely between 0 and 360 ° with high accuracy speed and high resolution.

In the following the features, insofar as they are essential for the invention, are detailed explained and described in more detail with reference to figures. Show it

Fig. 1 shows an arrangement according to the invention with angle sensors and coaxial rings,

Fig. 2 shows an arrangement according to the invention with concentric rings,

Fig. 3 is a detailed representation of angle sensors according to the invention and

Fig. 4 signal-angle relationships of an angle sensor arrangement according to the invention.

An angle sensor system according to the invention is shown schematically in FIG. 1. On egg ner axis 3 , e.g. B. a steering wheel in a motor vehicle, a first ring 1 and a second ring 2 are arranged axially adjacent to each other coaxially. Each ring 1 , 2 is radially adjacent to a magnetoresistive sensor S1 or S2 assigned. Magnetoresistive sensors have an advantageous high resolution of better than 0.05 ° down to 0.01 ° and are therefore suitable for these high-resolution angle measurements. Another sensor S3 is assigned to one of the rings 1 , 2 . This is shown schematically in the figure.

The two rings 1 , 2 form the magnetic scale of the angle sensor system according to the invention and are magnetically coded, so that the north poles and south poles are alternately strung together on the circumference of each ring 1 , 2 . The magnetic coding is not shown in detail in the figure. In this embodiment, the magnetic scale 1 , 2 is not housed, but is arranged on the outside of the axis 3 . It is advantageous that the distance between the scale and the sensor is minimal here. It is also possible to arrange the magnetic scale inside a non-magnetic tube, preferably made of an austenitic steel with a very high nitrogen content. The advantage is that the scale is protected from dirt, corrosion and wear. A tube made of the preferred material has the particular advantage that the material is very strong and stable and can be processed, in particular formed and / or polished, without forming magnetic martensite components.

Another advantageous arrangement of the rings 1 , 2 and sensors S1, S2 is shown in Fig. 2 Darge. Another sensor S3 is not shown separately. The two coaxial rings 1 , 2 are arranged concentrically in a plane perpendicular to an axis 3 . The rings 1 , 2 are preferably connected to a carrier which is fixed to the axis 3 . The carrier can be very thin, so that the installation height of the entire arrangement is low. The sensors S1 and S2 assigned to the rings detect the magnetic signal of the respective ring 1 , 2 . If the axis 3 vibrates, the rings move relative to the sensors in the radial direction perpendicular to the axis 3 , but the distance between the rings and sensors hardly changes. The measurement signal is therefore only slightly influenced by a change in distance. This is advantageous for use in the vehicle in which steering movements are to be detected with the aid of the arrangement according to the invention, since vibrations, for example of the steering spindle, cannot be avoided during driving operation.

At the circumference of each ring 1 , 2 north poles and south poles are alternately lined up one after the other. This is shown in FIG. 3. For the sake of clarity, the two magnetic scale rings 1 , 2 are not drawn one above the other, but next to each other in the figure. The individual poles have the pole length P, preferably the pole length P is the same for all poles. The number of poles of a semicircle is 1 n1 in the first ring and 2 n2 in the second ring. The total number of magnetic poles in each ring is 2. n1 or 2. n2. Each ring 1 , 2 is scanned by a magnetoresistive sensor element S1, S2, the output signal of which is correlated with the scanned coding. The sensor elements are equipped with usual measuring bridges, which are not shown.

Each magnetoresistive sensor S1, S2 is operated in the saturated state, ie the local magnetic field strength at the sensor S is large enough so that the sensor S is saturated. Before preferably the magnetic encodings are seen with a corresponding field strength. Typical saturation field strengths for magnetoresistive sensors are e.g. B. above about 10-20 mT. It is particularly favorable to choose the distance between magnetic scale 1 , 2 and sensor S1, S2 so small that the highest possible field strength is reached at the location of the sensor, in particular above the saturation field strength, but the sensor signal is still largely sinusoidal or cosine-shaped is. If the distance is too small, the signal distorts and deviates greatly from the sine or cosine shape which is advantageous for evaluation, while the magnetic field strength advantageously increases. If the distance is too large, the signal shape approaches the sine or cosine shape better, but the magnetic field strength decreases and is ultimately too low to control a magnetoresistive sensor. In the controlled, so-called. saturated state, a magnetoresistive sensor is no longer sensitive to the field strength, but to the angle θ of the sensor or the magnetic field-sensitive sensor part to the magnetic field. In principle, an angle θ between the field and the sensor produces the same signal as an angle θ + π. It follows from this that with magnetoresistive sensor elements in this arrangement an absolute measurement of the angle is only possible in the range from 0 ° to a maximum of 180 °. There are several reasons for this limitation.

The absolute angle of rotation α in the range from 0 ° to 180 ° of axis 3 is determined from the phase offset Δϕ [0.2π] of the sensor signals S1 and S2. The assignment of the sensor signals from α to Δϕ must therefore be clear. The sensor signals of magnetoresistive sensors are periodic with the pole length P of the magnetic scale and not with the periodicity 2 P of the scale itself.

Since the number of poles of a half ring is n, a magnetic ring scale must always have an even number of poles 2 n. If for the first ring 1 n = n1 and for the second ring 2 n = n2, then for a half turn by 180 ° the phase shift Δϕ [0.2π] can be clearly assigned to the angle of rotation α [0.180 °], if n1 and n2 are prime.

What applies to a half ring cannot apply to the entire ring α [0.360 °], since the number of poles on the rings have the common divider 2 . This leads to the limitation of the absolute measurement of the angle of rotation with magnetoresistive sensors operated in the saturation to angles between 0 ° and 180 °.

According to the invention, the range of the absolute angle measurement can be from the interval of Expand [0, π] to [0.2π] if at least one further sensor element S3 is provided, the further sensor element S3, in contrast to a magnetoresistive sensor S1, S2 the field direction, d. H. can recognize the polarity of a detected magnetic pole. A special the preferred sensor element is a Hall sensor. Other sensors are also suitable whose output signal is dependent on the polarity of a detected magnetic pole.

Since the number of poles n1, n2 in each half ring of rings 1 , 2 must be prime, n1 and n2 in particular cannot both be even numbers, but either n1 is even and n2 odd or n2 is even and n1 odd or both, n1 and n2, are odd. In Fig. 3, an axis A is drawn in each of the two rings 1 , 2 , which is intended to illustrate the situation in the ring when the axis 3 is rotated by 180 °. Is a magnetic pole at 0 °, e.g. B. a south pole is assigned to a sensor S1, S2, so if the number of poles in the semicircle is even after a rotation of the axis by 180 ° there is a magnetic pole (south pole), if the number of poles in the semicircle is not equal, there is an opposite magnetic pole (north pole) on sensor S1, S2.

The Hall sensor 53 is to be installed on a ring which has an odd number of poles in the half ring. In the example in FIG. 3, this is ring 2 . In this case, there is a reversal of the field direction of the magnetic coding at the location of the Hall sensor at a rotation of 180 °, which provides the signal which distinguishes the two semicircles from 0 ° -180 ° and from 180 ° to 360 °. If the angle of rotation α = 180 ° is exceeded, ie the first semicircle has been scanned, any further angular value up to 360 ° can be recognized as belonging to the second semicircle. In particular, the output signal of the Hall sensor 3 differs in sign. The absolute value of the Hall signal is not necessary for evaluation.

According to the invention, the phase offset Δϕ is determined from the output signal of the first and second magnetoresistive sensors S1, S2. At the same time, the sign of the output signal from the Hall sensor is determined. The sign of the output signal of the Hall sensor S3 is, for. B. positive if axis 3 is in the 0 ° position. The Hall sensor is e.g. B. opposite a south pole, as shown in Fig. 3. If axis 3 is rotated, the sign of the Hall signal changes as soon as a north pole is detected. If the axis 3 continues to rotate, the sign changes again when the Hall sensor S3 detects the next south pole. After a rotation of 180 °, ring 1 , which has an odd number of poles with n1 = 3 in the semicircle, comes to lie in front of the Hall sensor S3 at the north pole opposite the initial state at 0 °. Since the number of poles in the ring is known, the respective absolute angle between 0 ° and 360 ° can be determined unambiguously and with high accuracy from the sequence of the change of sign of the Hall signal and the phase shift Δϕ of the signals of the magnetoresistive sensors S1, S2.

A magnetoresistive sensor element S1 or S2 generates when it is over the periodically ma gnetized scale is performed, two analog voltage signals U1, U2 connected to one Bridge circuit in which commercially available magnetoresistive resistance elements are usually switched, can be removed.

A period of the scale corresponds to a side-by-side pair of magnetic poles, a north and a south pole. With 2 n poles, the ring-shaped scale bears n periods. A period then corresponds to an angular range of Δϕ = 2π / n degrees. The analog voltage signals of the sensor elements S1, S2 are also periodic, but with the period π / n. It follows that a full signal period is obtained over a single pole of the scale. This is shown in FIG. 4. The phase of the sine or cosine Si gnals the sensors S1, S1 accordingly changes from 0 ° -360 ° within a single pole length P1, P2.

The two analog voltage signals U1, U2, each a sensor element S1 or S2 as the output signal, have the same form, but are mutually ver by π / 2 pushed. Ideally, their shape is that of an exact sine or cosine curve. Your real Shape depends on the magnetization of the scale 1, 2 and the distance of the sensor element mentes S1, S2 to scale 1, 2. The sinusoidal shape of the signal improves with increasing distance between sensor and scale. When evaluating, idea len sine or cosine curves of the signals U1 (α), U2 (α) depending on the Angle of rotation α assumed.

A preferred evaluation has the following sequence: The axis of rotation, in particular a steering wheel of a motor vehicle, with the scale 1 and 2 is at a certain starting position, which can be characterized by the angle α in the range from 0 to 180 °. This corresponds to a specific phase ϕ _{1 of} the sine or cosine signal of sensor S1. For the deflection of the axis of rotation, the values apply with the signal phase ϕ ₁ in the angular range [0, π]

α _k = ϕ ₁ / 2n ₁ + kπ / n ₁ with k = 0, 1, 2, ...., n ₁ - 1

The combination with the sensor signal, in particular the phase ϕ ₂ , of the second sensor S2 results in a unique angle value β for the position of the axis of rotation in the range between 0 ° and 180 °.

A preferred method for determining the phase from the analog voltage signals the sensors S1, S2 is described below. The evaluation for the second Senso Relement S2 is completely analogous to the evaluation of the signals from the first sensor S1.

The analog sensor signals U1, U2 of sensor S1 are first Digitized digital converter. Further processing is preferably carried out with a Mi croprocessor. The range of the phase signal ϕ in the interval between 0 and 360 ° (ϕ range [0,2π]) is broken down into several, preferably 8, sub-segments. Preferably, the  Sub-segments of the same length. Each sub-segment suitably corresponds to one Pole length P. The microprocessor uses the sign of the signals U1 and through Comparison of the size U1 of the signal determines which segment you are in. Dependent of which phase ϕ is affected by evaluating the sine or cosine function in the ϕ segment determined. This is preferably done by comparing the measured value with values in a stored table.

This table includes pairs of values of the sine function in the angular range [0, π / 4], the angular range in each case corresponding to a sub-segment. It can be used for evaluation in all 8 areas because the curve, apart from the sign and direction, is the same for all functions. In FIG. 4, each of the steep flanks of the sine and cosine functions. A small change in the phase advantageously leads to a large signal change here, so that this angle determination is fundamentally highly accurate. The further explanations therefore relate to the first range ϕ∈ [0, π / 4].

The table shows the relationships between the signs of the sine and / or cosi nus-shaped sensor voltage signal, the amount of the sine and / or cosine Sensor voltage signal and the phase range shown.  

By comparison, the two pairs of values (ϕ _k , sinϕ _k ), (ϕ _{k + 1} , sinϕ _{k + 1} ) of the table are determined, for which the following applies:

sinϕ _k <sinϕ <sinϕ _{k + 1}

The searched phase ϕ then lies between ϕ _k and ϕ _{k + 1} . Linear interpolation determines 9 more precisely. The phase ϕ thus determined is included in the formula

α _k = ϕ ₁ / 2n ₁ + kπ / n ₁ k = 0,1,2, ...., n ₁ - 1

used, with which α is determined. It is not yet clear whether α is between 0 and 180 ° or is between 180 ° and 360 °. However, because at α + 180 ° the Hall sensor S3 is on the sensible magnetic pole sees as at α, the Hall signal at α + 180 ° shows another signs as at α. According to the output signal with the sign of Hall signal linked, and the angle of rotation α is a clearly defined angle between between 0 and 360 °.

The high resolution of the arrangement can be demonstrated in a numerical example. A ring typically carries 2 n = 30 poles. A pole therefore corresponds to an angular range of 360 ° / 30 = 12 °. This angular range corresponds to a signal period, ie a signal phase of 360 °. This area is divided into 8 sub-segments. Such a sub-segment then corresponds to an angle of 12 ° / 8 = 1.5 °. If 128 value pairs are stored in the table, then the equidistant distance between two value pairs corresponds to an angular range of 1.5 ° / 128 = 0.0117 °. Within this range, linear interpolation can preferably be carried out. The angular resolution is significantly better than 0.5 ° and shows that the sensor system according to the invention for use in so-called. X-by-wire facilities is suitable.

In a further preferred evaluation method, the digitized sine signal is carried out the digitized cosine signal divided and the phase ϕ by the microprocessor as arctan certainly. Again, the clear assignment of the phase in the pole segment is within a semicircle by evaluating the signals of a second magnetoresistive sensor Sors reached, which is assigned to a second magnetic scale. The clear Zu order whether the signal has an angle of rotation α from the first (0-180 °) or the second Semicircle (180-360 °) can be assigned, provides the sign of the Hall voltage of the Hall sors S3.

In a further preferred evaluation method, the arcsin formation is calculated determined and not by comparing values that are stored in a table. Again, the clear assignment of the phase in the pole segment is within a semicircle by evaluating the signals of a second magnetoresistive sensor Sors reached, which is assigned a second magnetic scale, as well as the one clear assignment whether the signal from the first (0-180 °) or the second semicircle (180-360 °) comes from the sign of the Hall voltage of Hall sensor S3 becomes.

An expedient arrangement of the magnetoresistive sensors S1, S2 and the Hall sensor S3 according to the invention consists in arranging them separately from one another, with a first magnetoresistive sensor and a Hall sensor a single coded ring with an un Rader number of poles n in a semicircle and a second magnetoresistive sensor a second ring is assigned with an even or odd number of poles in the semicircle. In this arrangement commercially available sensors with the usual evaluation circuits be applied.  

Another preferred embodiment of a sensor element is a magnetoresistive sensor to combine sensor and a Hall sensor in one component, this particularly preferably has Sensor element on a carrier a monolithically integrated Hall sensor and magnetore sistive sensor. This training takes advantage of the fact that semiconductor material lien can have both a Hall effect and magnetoresistive properties. Different materials, each of which is optimal magneto, can also be preferred have resistive properties and an optimal Hall effect on a microelek integrate tronic chip. The arrangement is very compact and robust and has a ho hey resolution.

Other evaluation methods can also be used to evaluate the sensor signals be in which the modulation of the output signal of the magnetoresistive sensors with the polarity of a detected magnetic pole can be suitably linked.

The invention can advantageously be used for measuring absolute angles of rotation from 0 to 360 °. The previously known solutions are due to a lack of integration with the mechanics special of a motor vehicle, and their low resolution marked. You are ver susceptible to wear and have a large volume. The solution according to the invention on the other hand, allows a compact and robust design that is also wear-resistant and can be integrated into vehicles.

A preferred embodiment is the arrangement of the rings 1 , 2 of the magnetic scale in a tube, the material of which is magnetically transparent on the outer wall. It is very particularly preferred to use an austenitic steel which has a very high nitrogen content of more than 0.3 percent by weight, in particular the nitrogen content is between 0.3 and 1 percent by weight. In contrast to conventional austenitic steels, such steels have the great advantage that they do not form a martensite component which has undesirable magnetic properties, even in the case of deformation and stress. The preferred type of steel can therefore be deformed without special aftertreatment, and in particular can be ground and polished in particular, and remains extremely hard and tough. This enables the use as a heavy-duty construction element, e.g. B. as a steering column ge with an integrated magnetic sensor, very simple and reliable. The magnetic scale is largely protected from damage and contamination.

Claims (18)

1. Device for measuring angles of rotation of an axis of rotation with a magnetic scale and the sensor unit assigned to the scale, the device as a magnetic scale having at least two magnetically coded rings ( 1 , 2 ) coaxially arranged at least indirectly on a rotatable axis ( 3 ), the number the magnetic poles on half the circumference of one ring ( 1 ) is relatively prime to the number of magnetic poles on the half circumference of the other ring ( 2 ), the sensor unit has a first and a second sensor (S1, S2), the output signals of which are detected with a Magnetic field of the rings ( 1 , 2 ) are correlated, and in addition a third sensor (S3) is provided which is assigned to a ring ( 1 , 2 ) which has an odd number of poles on half the circumference, characterized in that at least the first and the second sensor (S1, S2) assigned to the rings ( 1 , 2 ) is a magnetoresistive sensor and that the third pulls the rings ( 1 , 2 ) ordered sensor (S3) is a Hall sensor. 2. Device according to claim 1, characterized in that the rings ( 1 , 2 ) assigned magnetoresistive sensors (S1, S2) are operated in the saturated state. 3. Device according to one of claims 1 to 2, characterized in that the rings ( 1 , 2 ) with respect to the rotatable axis ( 3 ) are arranged adjacent in the axial direction. 4. Device according to one of claims 1 to 3, characterized in that the rings ( 1 , 2 ) with respect to the rotatable axis ( 3 ) are arranged concentrically. 5. Device according to one of claims 1 to 4, characterized in that at least one ring ( 1 , 2 ) is formed in one piece. 6. Device according to one of claims 1 to 5, characterized in that at least one ring ( 1 , 2 ) is composed of several ring segments. 7. The device according to claim 6, characterized in that the ring segments ( 1 , 2 ) are arcuate. 8. Apparatus according to claim 6 or 7, characterized in that the ring segments ( 1 , 2 ) are arranged one above the other or axially next to one another. 9. Device according to one of claims 1 to 8, characterized in that a magnetoresistive sensor (S1) and a Hall sensor (S3) separately from each other are individually assigned a magnetically coded ring ( 1 ). 10. The device according to one of claims 1 to 9, characterized, that a magnetoresistive sensor (S1) and a Hall sensor (S3) in one component are united. 11. The device according to claim 10, characterized, that the component is a microelectronic component. 12. The apparatus of claim 10 or 11, characterized,  that the component is a monolithically integrated component, which one integrated magnetoresistive sensor (S1) and an integrated Hall sensor (S3) having. 13. A method of operating a device according to claim 1, characterized in that in each case a sensor (S1, S2) is assigned a magnetically coded ring ( 1 , 2 ) of a magnetic scale, that a first ring ( 1 ), the number of magnetic poles on half the circumference is prime to the number of magnetic poles on the half circumference of a second ring ( 2 ), from which the sensor (S1) assigned to the first ring ( 1 ) is scanned and the second ring ( 2 ) from the second ring ( 2 ) assigned sensor (S2) is scanned and magnetic field signals of the rings ( 1 , 2 ) are detected, that output-side sensor voltage signals (U1, U2) of the sensors (S1, S2) are digitized, that a phase value from the sensor voltage signals (U1, U2) (ϕ) and a phase shift (Δϕ) it is determined that an output value is determined from the phase shift (Δϕ) and the absolute values of the sensor voltage signals (U1, U2), and that this output value has a sign of an Au output signal of a third sensor (S3) is linked to a signed output value and the signed output value is assigned an angle value (α) between 0 ° and 360 °. 14. The method according to claim 13, characterized, that at least one magnetoresistive sensor (S1, S2) operated in the saturated state becomes, 15. The method according to claim 13, or 14, characterized, that the first and second sensors have sinusoidal and cosine voltage signals (U1, U2) are output. 16. The method according to any one of claims 13 to 15, characterized in that two value pairs (ϕ _k , sinϕ _k ) are formed from sine and cosine-shaped sensor voltage signals (U1, U2) for each phase value (ϕ) and compared with a table. 17. The method according to any one of claims 13 to 16, characterized, that the phase value (ϕ) is determined by linear interpolation. 18. The method according to any one of claims 13 to 17, characterized, that the phase value (ϕ) by dividing sine and cosine Sensor voltage signals (U1, U2) is determined.