JP2005043228A - Digital angle measurement system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve high-precision angular resolution and high angular precision without using an expensive analog to digital converter. <P>SOLUTION: By controlling each amplitude to be supplied to analog to digital converters 8, 9 so as to be constant, each resolution of the converters 8, 9 necessary for making their errors within their permissible values can be made larger. Accordingly, the errors of the converters 8, 9 can be corrected, and a circuit can be miniaturized. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a digital angle measurement system, and more specifically, a digital angle measurement system that outputs information about the position of a magnetic sensor by using a plurality of magnetic sensors and calculating their outputs. The present invention relates to a digital angle measurement system that can be miniaturized and can perform highly accurate measurement.

  FIG. 1 is a diagram for explaining the principle of operation of a rotation angle sensor as a conventional digital angle measuring device, in which a magnetic field generated from a magnet rotates in accordance with the rotation of a rotating body, with respect to the rotation center of the rotating body. When the angle formed by the two magnetic sensors is 90 degrees, the relationship between the signals (Vx, Vy) output by the two magnetic sensors and the rotation angle (indicated by the arrows) of the rotating body is shown. is there. The angle formed by the two magnetic sensors may not necessarily be 90 degrees, but here, as one preferred example, a case where the angle formed by the two magnetic sensors is 90 degrees will be described. FIG. 2 shows how the signals (Vx, Vy) change with respect to the rotation angle of the rotating body. FIG. 2 shows an output signal of the magnetic sensor in an ideal case where the rotation center of the magnetic field coincides with the rotation center of the rotating body and there is no deviation in the magnetization of the magnet. In this case, the output signals of the two magnetic sensors are sine waves whose phases are shifted from each other by 90 degrees (see, for example, Patent Document 1).

JP-A-54-18768

  When the rotation angle sensor is actually manufactured, the rotation center of the magnetic field is shifted from the rotation center of the rotating body due to an error during assembly. Magnets are also misaligned, and the two magnetic sensors do not have the same sensitivity to magnetic fields. FIG. 3 shows an example of signals output from two magnetic sensors when there is such an assembly error, magnet magnetization deviation, magnetic sensor sensitivity variation, and the like. In this case, as long as the output angle from the magnetic sensor is regarded as a sine wave whose phases are shifted by 90 degrees and the rotation angle is calculated, the detected rotation angle includes an error that cannot be ignored. In order to prevent the above errors, it is necessary to use high-precision assembly technology in the assembly process of the rotation angle sensor, and it is necessary to use a magnet with no magnetization deviation for the magnet to be used. Must use a pre-screened magnetic sensor so that the two magnetic sensors have the same sensitivity. As a result, it is difficult to reduce the manufacturing cost of the rotation angle sensor.

  Accordingly, an object of the present invention is to provide a digital angle measurement system that can solve the above-described problems and can calibrate the influence of the above-described various error factors in manufacturing a rotation angle sensor.

  The invention according to claim 1 outputs at least a value corresponding to the rotational angular displacement from the reference position in the magnetic field, and at least two magnetic sensors in which the magnetosensitive axes representing the magnetic flux detection directions hold a predetermined angle; Storage means for storing rotational angular displacement data of the magnetic sensor with respect to the magnetic field corresponding to a relationship between the output values of the at least two magnetic sensors, and amplitudes of output signals of the at least two magnetic sensors. Automatic gain control means for controlling within a certain range, AD conversion means for converting the output signals of the at least two magnetic sensors whose amplitudes are controlled by the automatic gain control means into digital data, and from the AD conversion means Based on the digital data, rotational angular displacement data in the storage means corresponding to the relationship between the output values of the at least two magnetic sensors is extracted and output. Characterized by comprising an output means for.

  According to a second aspect of the present invention, in the first aspect, the automatic gain control circuit executes the control based on data of a sum of squares of an output signal of the magnetic sensor from the AD converter. .

  According to a third aspect of the present invention, in the first aspect, the rotational angle displacement data stored in the storage means is a deviation between the measured value of the angle formed by the magnetosensitive axes of the at least two magnetic sensors and the predetermined angle. It is a value which compensates.

  According to a fourth aspect of the present invention, in the first aspect, the rotational angular displacement data stored in the storage means is a value obtained based on output values from the at least two magnetic sensors. .

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the predetermined angle held by the magnetosensitive axes of the at least two magnetic sensors is substantially a right angle.

  According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the at least two magnetic sensors are attached to one of a fixed portion and a moving portion that relatively rotate, and the other is a magnet. Or the magnetic body which changes the surrounding magnetic field is attached, It is characterized by the above-mentioned.

  A seventh aspect of the present invention provides the method according to any one of the first to sixth aspects, wherein the output unit extracts at least two rotation angle displacement data from the storage unit, and the at least two rotation angle displacement data are extracted. It is characterized by complementing.

  In the digital angle measurement system of the present invention, highly accurate angle resolution and angle accuracy can be achieved without using an expensive AD converter.

  4A and 4B are diagrams showing an example of the arrangement of two magnetic sensors, where FIG. 4A is a perspective view and FIG. 4B is a front view. In FIG. 4, a white arrow indicates a direction in which the magnet 401 and the yoke can rotate. The support member 400 is fixed inside the magnetic field generated by the magnet 401. Reference numerals 101 and 111 denote magnetic sensors (Hall elements), which measure magnetic fields orthogonal to each other, and support members so that axes indicating the directions of magnetic flux detected by each of the magnetic sensors (hereinafter referred to as “magnetic sensitive axes”) are orthogonal to each other. 400 is attached.

  In the digital angle measurement system to which the present invention is applied, a magnetic sensor is attached to one of a fixed part and a moving part that relatively rotate, and a magnet or a magnetic body that changes a surrounding magnetic field is attached to the other. As a result, it can be put to practical use. Therefore, the example shown in FIG. 4 shows an example of a magnetic sensor that can rotate a magnetic field and is attached to a member fixed inside the magnetic field. On the contrary, a magnet is fixed. Alternatively, a magnetic sensor may be attached to a support member that can rotate within the magnetic field.

  FIG. 5 shows an example of a rotation angle sensor (IC structure) to which the present invention is applied. The rotation angle sensor 1 receives the output signals (Hall electromotive force signals) of the two magnetic sensors (Hall elements) 101 and 111, processes the input signals as described later, and outputs digital angle measurement data. Reference numeral 13 denotes an external rotation angle sensor calibration device, which can be configured by a computer system, for example. In the rotation angle sensor 1, output signals from the two magnetic sensors 101 and 111 are input to the chopper switches 2 and 3. The chopper switch 2.3 is used for the purpose of removing the offset of the magnetic sensor (Hall element), and switches the direction in which the magnetic sensor is electrically driven between the vertical direction and the horizontal direction. Due to the action of the chopper switches 2 and 3, the output signals (Hall electromotive force signals) from the magnetic sensors 101 and 111 are modulated at an AC frequency for operating the chopper switch. The modulated Hall electromotive force signal is amplified by variable amplifiers 4 and 5, demodulated by chopper demodulators 6 and 7, and input to AD converters 8 and 9.

  Outputs of the AD converters 8 and 9 are supplied to the rotation angle sensor calibration device 13, the amplitude calculation gain control circuit 10, and the rotation angle calculation digital circuit 11. The rotation angle calculation digital circuit 11 converts the output data from the AD converters 8 and 9 into calibrated rotation angle detection data with reference to an angle calculation table (details will be described later) in the nonvolatile memory 12 and outputs the data. To do.

  The operations of the rotation angle sensor calibration device 13 and the amplitude calculation gain control circuit 10 will be described later.

  FIG. 6 shows a flow of a calibration procedure for the rotation angle sensor of the present invention.

  This procedure consists of S1 to S7, and details will be sequentially described below. First, for example, after assembling the rotation angle sensor including the magnet, the magnetic sensor, and the IC as shown in FIG. 5 for performing the rotation angle calculation signal processing as shown in FIG. , S1), the rotating body is rotated for the purpose of calibrating the rotation angle sensor (FIG. 6, S2). The rotation range at this time is a range including a predetermined rotation range of the rotation angle sensor.

  During the rotation operation, the magnetic sensor output signals (Vx (n), Vy (n)) converted by the AD are rotated in the rotation angle sensor when the rotation angle is an integral multiple of the predetermined rotation angle step size θSTEP. Read out to the angle sensor calibration device 13.

  The rotation angle sensor calibration device 13 performs quadrant division on the measured (Vx (n), Vy (n)) as follows, and calculates table data in each quadrant. As a result, when the rotation range of the rotation angle sensor is 360 °, four tables are created corresponding to the four quadrants (FIG. 6, S5).

  Here, when the offset of the magnetic sensor and the offset of a series of signal processing circuits until the AD conversion of the magnetic sensor output signal is known in advance, change the quadrant judgment conditions and the table data calculation formula in Table 1 to Table data may be created as shown in Table 2.

  After the calculation of the table data is completed in the rotation angle sensor calibration device 13, the table data is written from the rotation angle sensor calibration device 13 to the nonvolatile memory 12 built in the rotation angle sensor (FIG. 6, S6).

  As described above, by calculating the table data Q (n) based on the measured (Vx (n), Vy (n)), all the absolute values of Q (n) should be 1 or less. I can do it.

  In the definition of the table data given in Tables 1 and 2, the sign of Q (n) in quadrant numbers 2 and 4 is inverted. FIG. 7 shows the table data in the case where the table is created without reversing the sign in the quadrants 2 and 4 as described above.

  As can be seen from FIG. 7, in this case, the table data monotonically increases with respect to the rotation angle in the quadrants 1 and 3, and the table data monotonously decreases with respect to the rotation angle in the quadrants 2 and 4. Thus, when the table data monotonously increases or decreases monotonically depending on the quadrant, the rotation angle calculation digital circuit 11 in the rotation angle sensor compares the table data stored in the nonvolatile memory 12 with reference to the table data. The operation becomes complicated, and as a result, the scale of the digital circuit 11 increases.

  In the present invention, since the sign of Q (n) is inverted in quadrants 2 and 4 as shown in Tables 1 and 2, the interior of the table corresponding to each quadrant as shown in FIG. Increase function.

  Next, a method of calculating the rotation angle based on the output signals from the two magnetic sensors in the rotation angle sensor that has been calibrated by the calibration procedure of the present invention will be described (S7 in FIG. 6).

  The offset value that is measured in advance from the X and Y components of the Hall electromotive force signal that has been AD converted and stored in the nonvolatile memory 12 is subtracted.

  Whether the quotient Q = Y / X or the quotient Q = X / Y is calculated is determined based on the magnitude relationship between the absolute values of the X and Y components.

  The corresponding quadrant is selected from the four quadrants based on the magnitude relationship between the sign of Vx and Vy and the absolute value. Within each quadrant, a Q value is stored for each constant angle θSTEP. For the selected quadrant, refer to the table and find Q1 and Q2 that satisfy the following relationship. Here, the angle values θn and θn−1 correspond to the two quotient values Qn and Qn−1, respectively.

  The angle θ is calculated by linear interpolation based on Q1 and Q2 obtained as a result of the table reference. The state of linear interpolation is shown in FIG. At this time, the angle θQUAD at the start of the selected quadrant is added.

  In the method of storing the ratio of Vx and Vy measured at a constant angular interval in the nonvolatile memory device, | Vx | = | Vy | (tan θ = cot θ) is not necessarily obtained at the angle at which quadrant switching occurs. Therefore, as shown in FIG. 10, by extending the table of each quadrant area to the adjacent quadrant area at the boundary of the quadrant area, it is possible to perform angle calculation by linear interpolation up to an angular position where | Vx | = | Vy |. .

  The present invention has realized a high-accuracy rotational angle sensor having an angular resolution exceeding 0.1 degrees by using the rotational angle calculation method described above. Hereinafter, the configuration will be described.

  In order to realize a high-precision rotation angle sensor with an angular resolution exceeding 0.1 degrees using the rotation angle calculation method, the AD converter needs to have a high precision of 10 bits or more. Generally, when realizing an AD converter with 10 or more bits in a semiconductor integrated circuit, the solid-state difference is calibrated after the semiconductor is manufactured as a method to make the AD converter's integral nonlinearity error (INL) less than 0.5LSB. For example, a method of preparing a means for performing the above, a method of providing an AD converter with a self-calibration function, a method of using a ΔΣ method using oversampling, and the like are used. Although it is possible to suppress the INL of the AD converter by such a method, this method increases the cost of the AD converter, and as a result, inexpensively manufactures a rotation angle sensor using a high-precision AD converter. Becomes difficult. (The Philips KMZ41 and UZZ9000, which are rotational angle sensors using MR elements, use a 128-bit oversampling ΔΣ 14-bit AD converter.)

  In the present invention, highly accurate rotation angle detection is realized while avoiding an increase in cost due to the preparation of a high-bit AD converter in the rotation angle calculation method described above.

  In the rotation angle calculation method described above, the results of a computer simulation performed to see the effect of the INL error of the AD converter on the angle detection accuracy are shown below. In this computer simulation, a 12-bit AD converter having the INL characteristic shown in FIG. 11 was assumed. In this computer simulation, the rotation angle sensor was calibrated (an angle calculation table was created) when the amplitude of the signal-amplified magnetic sensor was 70% of the AD converter input signal level full scale.

When the rotation angle detection performance was computer simulated using the above AD converter INL error model, the rotation angle was calculated using table data obtained by dividing the 360 degree range into 128 points. In this case, the step width Q _STEP of the table data is 2.8125 ° (360 ° / 128).

  FIG. 12 shows the result of computer simulation of the rotation angle detection error when the magnetic sensor output signal level after signal amplification is 70% of the AD converter full scale level. As can be seen from this result, the INL error of the AD converter is stored in the nonvolatile memory as long as the magnetic sensor output signal level input to the AD converter at the time of rotation angle detection is the same level as when calibration was performed. Is corrected by the calculated angle calculation table. As a result, the INL error of the AD converter does not affect the rotation angle detection accuracy.

  The simulation results of the rotation angle detection error shown in FIGS. 13 and 14 are obtained when the magnetic sensor output signal level input to the AD converter is attenuated to 60% and 50%, respectively. Such attenuation of the output level of the magnetic sensor actually occurs as the magnetic field sensitivity of the magnetic sensor decreases and the magnetic force of the magnet decreases as the temperature increases. FIG. 15 is a simulation result when the magnetic sensor output signal level input to the AD converter becomes 90% of the AD converter full-scale level, and is compared with the level when the magnetic sensor output level is calibrated. It can be seen that the rotational angle detection accuracy decreases due to the influence of the INL error of the AD converter.

  Therefore, in the present invention, as shown in FIG. 5, the gains of the variable amplifiers 4 and 5 are determined based on the Hall electromotive force signals of the X and Y components output from the AD converter by the amplitude calculation amplification factor control circuit 10. Control is performed so that the amplitude level calculated in the above is within a certain range. As a result, the magnetic sensor output signal level input to the AD converters 8 and 9 can be kept within a certain range regardless of the temperature change, as shown in the computer simulation results of FIGS. The rotation angle detection error can be eliminated.

  FIG. 16 shows another example of the rotation angle sensor, in which the outputs of the two magnetic sensors 101 and 111 are time-division processed. That is, the outputs of the two magnetic sensors 101 and 111 are input to the two chopper switches 2 and 3, and the outputs of the two chopper switches 2 and 3 are switched by the X and Y changeover switches 14 and alternately output. The processing from processing this output signal to obtaining the sensor output from the digital circuit 11 is the same as that of FIG. 5, but each processing is one variable amplifier 15, one chopper demodulator 16, one AD converter. 17 is supplied to the rotation angle sensor calibration device 13, the rotation angle calculation digital circuit 11, and the amplitude calculation gain control circuit 10.

  For the automatic gain control as described above, it is necessary to calculate the amplitude of the Hall electromotive force signal (the sum of squares of X and Y components), but calculating the amplitude of the Hall electromotive force signal is Since this is a useful operation for self-diagnosis of a failure by the sensor itself, the circuit scale of the rotation angle sensor IC is not increased by realizing the automatic gain control of the present invention.

  In this way, by using automatic gain control that keeps the signal level input to the AD converter at a constant value, the AD converter used in the rotation angle sensor of the present invention only needs to be monotonous. Thus, the self-calibration circuit of the AD converter or the laser trimming adjustment process is not necessary. Therefore, in the rotation angle sensor of the present invention, highly accurate angle resolution and angle accuracy can be achieved without using an expensive AD converter.

It is a figure explaining the principle of operation of the rotation angle sensor as the conventional digital angle measuring device. It is the figure which showed a mode that signal (Vx, Vy) changed with respect to the rotation angle of a rotary body. It is a figure which shows an example of the signal output from two magnetic sensors. It is a figure which shows an example of arrangement | positioning of two magnetic sensors, (a) is a perspective view, (b) is a front view. It is a figure which shows an example of the rotation angle sensor concerning this invention. It is a figure which shows the flow of the calibration procedure with respect to the rotation angle sensor of this invention. It is a figure which shows the table data at the time of producing without performing inversion of the code | symbol in quadrants 2 and 4. It is a figure which shows the table data at the time of creating by inverting the sign in quadrants 2 and 4. It is a figure which shows the mode of linear interpolation. It is a figure which shows the mode of the linear interpolation in the boundary of a quadrant area | region. It is a figure which shows the INL model of the 12-bit AD converter used in the simulation It is a figure which shows the angle detection error when an amplitude is 70% of full scale. It is a figure which shows the angle detection error when an amplitude is 60% of full scale. It is a figure which shows the angle detection error when an amplitude is 50% of full scale. It is a figure which shows the angle detection error when an amplitude is 90% of full scale. It is a figure which shows another example of the rotation angle sensor concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotation angle sensor 2, 3 Chopper switch 4, 5 Variable amplifier 6, 7 Chopper demodulator 8, 9 AD converter 10 Amplitude calculation gain control circuit 12 Non-volatile memory 13 Rotation angle sensor calibration circuit

Claims (7)

A value corresponding to the rotational angular displacement from the reference position in the magnetic field, and at least two magnetic sensors in which the magnetosensitive axes representing the magnetic flux detection direction hold a predetermined angle;
Storage means for storing rotational angular displacement data of the magnetic sensor with respect to the magnetic field corresponding to the relationship between the output values of the at least two magnetic sensors;
Automatic gain control means for controlling the amplitude of output signals of the at least two magnetic sensors within a certain range;
AD conversion means for converting output signals of the at least two magnetic sensors whose amplitudes are controlled by the automatic gain control means into digital data;
Output means for extracting and outputting rotational angular displacement data in the storage means corresponding to the relationship between the output values of the at least two magnetic sensors based on the digital data from the AD conversion means. A digital angle measurement system characterized by that.   2. The digital angle measurement system according to claim 1, wherein the automatic gain control circuit executes the control based on data of a square sum of an output signal of the magnetic sensor from the AD converter.   The rotation angle displacement data stored in the storage means is a value that compensates for a deviation between an actual measurement value of an angle formed by magnetosensitive axes of the at least two magnetic sensors and the predetermined angle. Item 2. The digital angle measurement system according to Item 1.   2. The digital angle measurement system according to claim 1, wherein the rotational angle displacement data stored in the storage means is a value obtained based on output values from the at least two magnetic sensors.   The digital angle measurement system according to any one of claims 1 to 4, wherein the predetermined angle held by the magnetosensitive axes of the at least two magnetic sensors is substantially a right angle.   The at least two magnetic sensors are attached to one of a fixed part and a moving part that relatively rotate, and a magnet or a magnetic body that changes a surrounding magnetic field is attached to the other. The digital angle measurement system according to any one of claims 1 to 5. The output means extracts at least two rotation angle displacement data from the storage means, and complements between the extracted at least two rotation angle displacement data. The described digital angle measurement system.

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