DE102008039333A1 - Rotating structure i.e. rotary disk, rotating angle measuring method for e.g. aircraft, involves determining arc tangent of division in analog manner using specific function, where determined arc tangent corresponds to angle of structure - Google Patents

Abstract

The method involves measuring an X-component and a Y-component of magnetic field in an analog manner using a magneto resistive bridge circuit. The X-component and the Y-component are divided. An offset (psi 0) of a rotating angle (psi) of a rotating structure is corrected. An arc tangent of the division is determined in analog manner using a specific function by an analog multiplier, an adder and an operation amplifier. The determined arc tangent corresponds to the angle. A coefficient (a1) is adapted such that an average error is controlled at a measuring interval. An independent claim is also included for a device for measuring an angle of a rotating structure using measurement of X-component and a Y-component of magnetic field.

Description

Field of the invention

The This invention relates to the field of metrology, more specifically to angle measurement. In particular, the invention relates to a method and a device for analogue angle signal evaluation by measuring the X and Y component a magnetic field, which is the angle to be measured clearly assigned.

State of the art and disadvantages

method and devices for angle measurement are sufficient known in the art. For measurement come next to purely mechanical Method in particular also electromechanical method used or those that give the angle a certain number of electro-optical Assign impulses, for example by using them accordingly encoded turntables. Accordingly, incremental can be different from continuous measuring methods.

ever according to application rotary encoder are needed, the can capture multiple, even very fast turns, or even those only for a limited Angular range or slow angle change speeds can be used. It is obvious that for the The latter range of usable devices is generally more cost effective can be produced than for the former.

One known method for determining a rotation angle consists in the coupling of the rotatable object, for example a ventilation flap, with a trained as a bar magnet field generator, the one (in its strength constant) generates magnetic field. The magnetic field whose orientation depends on the position of the rotatable Subject matter is preferably proportional depends is can be dismantled into an X and Y component. These individual components are then for example by means of a magnetoresistive bridge circuit detected.

At the output of the bridge circuit, the voltage is then obtained U x = U = + ΔU · cos (2 · Φ) Eq. 1 U y = U = + ΔU · sin (2 · Φ) Eq. 2

These voltages contain a DC component U ₌ , which can be eliminated for example by a balance. By dividing the voltages you get (U y - U = ) / (U x - U = ) = tan (2 · Φ), Eq. 3 wherein the variations of the amplitude .DELTA.U are eliminated. From the inverse function arctangent (atan) the desired angle can be formed: Φ = 1/2 · atan [(U y - U = ) / (U x - U = )]. Eq. 4

Due to manufacturing tolerances or due to the often difficult to determine precise orientation of the above-mentioned bar magnet angle Φ often an offset Φ _{0 is} superimposed, which is to be eliminated.

The Calculation of the functions described is usually done by digitizing the two bridge signals by means of two A / D converter channels and using a digital Signal processor. In this way it is possible to do the calculations very accurately and with a high clock rate (signal bandwidth). However, starting at clock rates of a few kilohertz, however, expensive Circuits needed, which cause correspondingly high costs.

Such an angle measuring device of the prior art shows, for example, the document DE 202 105 48 U1 , The device is constructed so that it comprises a bridge circuit in which the bridge voltage varies depending on the position of an adjustment along an adjustment path, wherein the outputs of the bridge circuit are connected to a differential amplifier having an analog gain stage and a digital differentiator. The adjusting device is coupled to a bar magnet, which he present in the form of a changing magnetic field signal witnesses, if the bar magnet moves along the adjustment path. In particular, the digital part of the circuit is, as mentioned above, feasible only with appropriate costs. In addition, the device of the publication is used in the context of the adjustment of motor vehicle seats, ie in an area in which the achievable by means of the proposed circuit high frequencies do not occur at all.

Object of the invention and solution

The The object of the invention is therefore a method and a device which overcomes the disadvantages of the prior art. In particular, the invention is a method and an apparatus provide, with which or with which the measurement of a rotation angle for both low and high bandwidths possible and feasible at the lowest possible cost is.

The The object is achieved by the features of the invention A method according to claim 1 and the features of the invention Device solved according to claim 11.

Further preferred embodiments are dependent Claims and the following detailed description and to take the figures.

description

The inventive method will be detailed below explained.

• (a) Analoge Messung der X- und Y-Komponente des magnetischen Feldes mit einer magnetoresistiven Brückenschaltung;
• (b) Analoge Division der beiden Komponenten des magnetischen Feldes;
• (c) Analoge Ermittlung des Arcustangens der Division;

The angle measurement of a rotating structure is carried out according to the invention by means of a measurement of the X and Y component of a magnetic field which is uniquely associated with the angle. The magnetic field can be provided by any field generator. The method according to the invention comprises the following steps:

• (a) Analog measurement of the X and Y component of the magnetic field with a magnetoresistive bridge circuit;
• (b) analogous division of the two components of the magnetic field;
• (c) analog determination of the arctangent of the division;

The Calculation result of step (c) corresponds to the searched Angle Φ. For measuring the X and Y component of the magnetic Field and components needed to perform the calculations be later in the context of the invention Device described in more detail. According to the invention provided that all calculation operations be carried out by means of analog circuits. By The use of analog components can on the one hand a high processing speed on the other hand, the cost of the corresponding Components are significantly lower than for components, which perform a signal processing on a digital basis.

To A preferred embodiment is between the steps (a) and (b) a step inserted in which a any existing DC component is eliminated. This will be special preferably achieved by a balance.

To Another preferred embodiment is between a step is added to steps (b) and (c), in which any existing offset of the angle is eliminated. An offset of the angle corresponds to a rotation of the coordinate system around the zero point (0, 0), which is determined by suitable arithmetic operations, as shown later, can be eliminated.

According to a further preferred embodiment, the analog determination of the arctangent mentioned in step (c) is approximated (approximated). For small angles, namely, the exact calculation, to the correspondingly complex calculation facilities such. B. microcontroller are necessary to be approximated by the following term, which is particularly easy represented by an analog circuit: atan (x) ≈ a 1 · X + a 3 .x 3 Eq. 5

Especially the analog determination of the arctangent is preferred by means of analogous Multilplierierer, adder and operational amplifier performed.

The coefficients a ₁ and a ₃ must first be determined separately.

Particularly preferred is the goal of determining that the mean error F = [atan (x) - (a 1 · X + a 3 .x 3 )] 2 Eq. 6 over the measuring interval, so the area in which the angle Φ is to be measured, is minimal.

Particularly preferably, the adaptation of the coefficients a ₁ and a _{3 takes place} by means of simulation. Alternatively, the adaptation can also be carried out by experiments or by analytical investigations.

beseitigt werden.To minimize the error F, due to the point symmetry of the arctangent function to the origin (x, y) = (0, 0), it is necessary to minimize the offset Φ ₀ , or to make the input signal offset-free. The offset in the form of the above-mentioned rotation of the coordinate system by an angle Φ ₀ offset can be achieved by an inverse transformation of the form

be eliminated.

erreicht werden, die ohne die aufwändige Berechnung der Sinus- und Cosinusterme auskommt und die bekannte Annäherung nutzt, dass für kleine Winkel der Cosinus in etwa 1 ist und der Sinus eines Winkels in etwa dem Winkel selber entspricht.In the case of small angles, it is possible to approximate the inverse transformation by an approximation solution. This can be done, for example, by means of the function

can be achieved without the elaborate calculation of the sine and cosine pattern and uses the well-known approach that for small angles of the cosine is about 1 and the sine of an angle corresponds approximately to the angle itself.

Especially are preferred for circuit implementation of the above mentioned arithmetic operations op amp and analog Used multiplier. According to another embodiment is therefore the division necessary for normalization by a multiplier in the feedback branch of an operational amplifier realized.

The inventive method is in particular to Measurement of rotation angles suitable, which covers a range of some 10 degrees. Accordingly, the maximum measurement angle at unidirectional deviation from a zero position about 90 degrees, and with a bidirectional deviation from a zero position approx. ± 45 Degrees.

• – einen Feldgenerator zur Erzeugung eines magnetischen Feldes in Abhängigkeit des zu messenden Winkels;
• – eine Feldmesseinrichtung zur Messung der X- und Y-Komponente des magnetischen Feldes;
• – eine Berechnungseinrichtung zur Berechnung des Winkels aus den X- und Y-Komponente des magnetischen Feldes.

The invention further discloses a device for measuring the angle of a rotating structure with a magnetic field for measuring the X and Y component of the magnetic field, which is uniquely associated with the angle of the structure to be measured. The device according to the invention comprises the following components:

• A field generator for generating a magnetic field as a function of the angle to be measured;
• - A field measuring device for measuring the X and Y component of the magnetic field;
• - A calculation device for calculating the angle of the X and Y component of the magnetic field.

According to the invention provided that the calculation device substantially is constructed of analog circuit components.

Of the Field generator can preferably be a bar magnet. This bar magnet can particularly preferably have the shape of a disc of one half the south pole and the other half forms the north pole. Alternatively, the bar magnet also another Have shape that is capable of a magnetic field between the two To transform Poland, whose turn to a change the magnetic field strength or their orientation leads.

It is further preferred that the device for measuring the X and Y component of the magneti field comprises two magnetoresitive bridges. Alternatively, of course, any other measurement technique known in the art may be used to measure the X and Y components of the changing magnetic field.

The Inventive calculation device, with the corresponding method of the invention Calculations are particularly preferred essentially opamps and analog multipliers. It is clear that beside it necessarily also elements like electrical Lines, a power supply, etc. must be present. By using only analog circuit elements This ensures that the costs of the calculation unit are low Stay tuned for more expensive digital components can be waived. Furthermore, the analog circuits provide a very high calculation speed, so that too fast Angle changes or large signal bandwidths be covered by the circuit.

In this connection, it is particularly preferred that the operational amplifiers and analog multipliers used in the calculation device approximate the function atan (x) ≈ a ₁ * x + a ₃ * x ³ . In this context, be on the 2 and the corresponding description.

Especially the device according to the invention is preferred used in the aerospace industry. In this area In particular, the reliability is simpler analog Circuits versus complex and often error prone Digital circuits of particular importance.

The The invention provides a method and an apparatus with which or with which the measurement of a rotation angle for both low as well as high bandwidths possible is. Compared to digital circuits, the inventive Device using the invention Process can also be realized at low cost.

LIST OF FIGURES

1 shows a schematic representation of the measuring principle.

2 shows the structure of a preferred embodiment of the analog circuit according to the invention.

figure description

The 1 shows a schematic representation of the measuring principle, as it uses the inventive device, but also the prior art. Shown is field generator 1 in the form of a disc-shaped bar magnet whose left half is formed as north pole N and the right half as south pole S. The dashed line indicates that the field generator is slightly tilted, ie, in total, its field lines do not extend exactly in the horizontal, but are tilted by an angle Φ. This tilting occurs through a mechanical connection (not shown) between the field generator 1 and a (also not shown) rotatable object whose tilting is to be measured, concluded.

Laterally next to the field generator 1 is the field measuring device 2 arranged to measure the X and Y component of the magnetic field. In the illustrated embodiment, this comprises two magnetoresistive bridges 3A and 3B , These two bridges 3A and 3B are responsible for measuring the X or Y component of the magnetic field. At the outputs of the two bridges, the voltages U _x and U _y are available, which correspond to the respective field components.

The 2 shows the structure of a preferred embodiment of the analog circuit according to the invention.

At the inputs shown on the left are superimposed with the offset Φ ₀ voltages U _x 'and U _y ' on. In addition, the DC component U _{= is} on.

The remaining part of the left half of the circuit is used to implement the inverse transformation of the rotated by Φ ₀ coordinate system, as well as the implementation of the quotient formation according to Eq. 3. At the output of this part of the circuit according to the invention is the result of Eq. 3 on.

The right half of the circuit is used to implement the in Eq. 5 illustrated replacement function for the Arc tangent, which approximates the calculation of the arctangent and offers sufficient accuracy, especially for small angles (a few tens of degrees). By using the replacement coefficient b ₁ according to the formula b 1 = a 3 / a 1 Eq. 9 This part of the circuit can be realized in a particularly advantageous manner and with analog circuit components. Finally, at the output of this part of the circuit is a voltage value which is proportional to the desired angle Φ.

All Components of the two parts of the overall circuit consist of simple Operational amplifiers and analog multipliers. Digital working components such. B. A / D converter, however, are not necessary. In this way, a particularly cost-effective implementation the circuit is done. At the same time provide the analog components a high processing speed, so that also high signal bandwidths can be processed without relying on expensive, digitally working To have to resort to components.

1

field generator

2

Field measuring device

3A, 3B

magnetoresistive bridge

Φ

angle

Φ ₀

offset

F

error

a ₁ , a ₃

coefficients

b ₁

replacement coefficient

U _x

X component the tension

U _y

Y component the tension

N

North Pole

S

South Pole

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 20210548 U1 [0009]

Claims (17)

Method for measuring the angle of a rotating structure by measuring the X and Y component of a magnetic field, which is uniquely associated with the angle (Φ) the following steps: (a) Analogous measurement of the X and Y components the magnetic field with a magnetoresistive bridge circuit; (B) Analogous division of the two components of the magnetic field; (C) Analogous determination of the arctangent of the division; the Calculation result of step (c) the searched angle (Φ) equivalent. The method according to claim 1, wherein between step (a) and step (b) the following step is performed: - eliminating a DC component (U ₌ ); and / or between step (b) and step (c), the following step is performed: removing an offset (Φ ₀ ) of the angle (Φ). A method according to claim 2, characterized in that the elimination of the DC component (U ₌ ) is done by means of adjustment. Method according to one of the preceding claims, characterized in that the analog determination of the arctangent is approximated by the function atan (x) ≈ a ₁ · x + a ₃ · x ³ . Method according to claim 4, characterized in that that the analog determination of the arctangent by means of analog multiplier, Adder and operational amplifier performed becomes. A method according to claim 4 or 5, characterized in that the coefficients (a ₁ ) and (a ₃ ) are adjusted such that the average error (F) over the measurement interval is minimal. Method according to claim 6, wherein the adaptation by means of Simulation is done. Method according to one of claims 2 to 7, wherein the offset (Φ ₀ ) is eliminated by inverse transformation. The method of claim 8, wherein the back propagation is approximated for small angles. Method according to one of the preceding claims, wherein the division necessary for normalization by a multiplier realized in the feedback branch of an amplifier becomes. Method according to one of the preceding claims, where the angle (Φ) does not exceed ± 20 degrees deviates from a zero position. Device for angle measurement of a rotating structure with a magnetic field for measuring the X and Y component of the magnetic field, which is uniquely associated with the angle (Φ) of the structure, the device comprising - a field generator ( 1 ) for generating a magnetic field as a function of the angle (Φ) to be measured; - a field-measuring device ( 2 ) for measuring the X and Y component of the magnetic field; A calculating means for calculating the angle (Φ) from the X and Y components of the magnetic field; characterized in that the calculating means is constructed of analog circuit components. Device according to claim 12, characterized in that it can be used as a field generator ( 1 ) comprises a bar magnet. Apparatus according to claim 12 or 13, characterized in that it comprises two magnetoresistive bridges (X, Y) for measuring the magnetic field. 3A . 3B ). Device according to one of claims 12 to 14, characterized in that the calculation direction ( 3 ) substantially comprises operational amplifiers and analog multipliers. Device according to one of Claims 12 to 15, characterized in that the operational amplifiers and analogue multipliers approximate the function atan (x) ≈ a ₁ · x + a ₃ · x ³ . Use of a device or a method according to one of the above claims in an air or spacecraft.