JP2012230021A - Rotation angle measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rotation angle measuring device having a circuit configuration dispensing with a differential amplifier circuit and an analog/digital conversion circuit, for reducing a circuit cost.SOLUTION: The rotation angle measuring device includes: a rotation angle sensor 2 having sensor element sections 211, 212, 221, 222, 231, 232, 241, and 242 for outputting a magnetic field direction generated by magnetic field generating means rotating synchronously with a rotary shaft, as electric signals having at least two or more different phases; a signal generating circuit 35 for outputting a periodic waveform for driving the sensor element sections to the rotation angle sensor; comparators 31, 32, 33, and 34 in which the outputs obtained from the sensor element sections are input; and an arithmetic circuit 40 in which the output from the comparator is input. The arithmetic circuit has a pulse input terminal for importing a pulse waveform output from the comparator as a digital value and is configured to calculate and output the magnetic field direction that is equivalent to the rotation angle of the rotary shaft on the basis of the value imported by the pulse input terminal.

Description

  The present invention relates to detection of a rotation angle of a rotating body, and more particularly to a rotation angle measurement device that detects non-contact.

  A device that uses a wheel or magnet that rotates in synchronization with a rotating body such as a shaft and an element that detects a physical quantity according to the rotation angle as one of measuring devices for the rotation angle of a shaft such as a motor or a steering wheel of an automobile. There is. Among these, a rotation angle measuring device constituted by a magnet and a spin valve giant magnetoresistive element (Spin Valve Giant Magnetoresistive element, hereinafter referred to as SVGMR element) can reduce power consumption from the characteristics of the element. In addition, it is attracting attention because it can be configured to reduce temperature dependence in principle. As a rotation angle measuring device having such a configuration, for example, there are techniques disclosed in Patent Documents 1 and 2 below.

WO2008 / 062778 JP 2009-150795 A

  The techniques disclosed in Patent Documents 1 and 2 have the following configuration. The SVGMR element is an element whose resistance value changes in accordance with the direction (rotation angle) of the magnetic field when a magnetic field having a certain intensity or more is applied. A bridge circuit is configured by connecting two sets of serially connected circuits in which two SVGMR elements differing in the direction of the zero point of the detected magnetic field by 180 ° in series are connected in parallel in opposite directions. When a constant voltage is applied to the bridge circuit and a magnetic field is applied from the outside, the differential voltage of the bridge circuit output becomes a sine wave waveform corresponding to the rotation angle β of the magnetic field. Two bridge circuits are used and arranged so as to face each other by 90 ° so that the outputs correspond to cos β and sin β. Each of the two bridge circuit outputs is differentially amplified, converted from analog to digital, and taken into an arithmetic circuit. The arithmetic circuit performs arctan calculation, corrects the angle error, and outputs the rotation angle. However, the above circuit configuration requires a large number of differential amplifier circuits and analog-digital conversion circuits, which increases the cost of the entire circuit.

  In view of the above problems, an object of the present invention is to provide a circuit configuration that does not require a differential amplifier circuit or an analog / digital conversion circuit in order to reduce circuit cost.

  In order to achieve the above object, in the present invention, a rotation angle sensor having a sensor element unit that outputs a magnetic field direction generated by a magnetic field generation unit rotating in synchronization with a rotation axis as an electrical signal having at least two or more phases. A signal generation circuit that outputs a periodic waveform for driving the sensor element unit to the rotation angle sensor, a comparator that receives an output obtained from the sensor element unit, and an arithmetic circuit that receives an output from the comparator The arithmetic circuit has a pulse input terminal that captures the pulse waveform output from the comparator as a digital value, and is equivalent to the rotation angle of the rotating shaft based on the value captured at the pulse input terminal. The magnetic field direction is calculated and output.

  Other objects and features of the present invention will be made clear in the embodiments described below.

  According to the present invention, in a rotation angle measurement device using a rotation angle sensor using an SVGMR element, a circuit for processing a signal output from the rotation angle sensor can be realized with a relatively inexpensive configuration.

An example of the circuit structure of the rotation angle measuring device which concerns on this invention. An example of the mounting structure of the rotation angle measuring device which concerns on this invention. An example of the signal waveform in the circuit structure of the rotation angle measuring device which concerns on this invention. An example of the digital value taken in the arithmetic circuit of the rotation angle measuring device which concerns on this invention, a rotation angle calculation result, and a detection error. Another example of the circuit structure of the rotation angle measuring device which concerns on this invention. Another example of the circuit structure of the rotation angle measuring device which concerns on this invention.

  Hereinafter, the configuration of a rotation angle measuring apparatus according to an embodiment of the present invention will be described with reference to FIGS.

  1 and 2 are diagrams showing an example of a circuit configuration of the rotation angle measuring device 1 according to the present invention and an example of a mounting configuration of the rotation angle measuring device 1, respectively.

  The rotation angle measuring device 1 is mainly composed of a rotation angle sensor 2, a peripheral circuit 3, and a magnet 8 that rotates in synchronization with the rotation shaft 9, and rotates in synchronization with the direction of the magnetic field generated by the magnet 8, that is, the magnet 8. This is a device for measuring the rotation angle of the rotary shaft 9.

  Specifically, the rotation angle sensor 2 is composed of eight SVGMR elements 211, 212, 221, 222, 231, 232, 241, 242 and a pinned magnetic layer (pinned magnetic layer) whose magnetization direction is not changed mainly by an external magnetic field. , A non-magnetic conductive layer, and an element having a multilayer structure of a free magnetic layer whose magnetization direction is changed by an external magnetic field. When a magnetic field having a certain intensity or higher and a vector in the plane of the multilayer structure is applied to the element from the outside, the magnetization direction of the free magnetic layer rotates in the direction of the magnetic field applied from the outside, and the resistance value of the nonmagnetic conductive layer is reduced. Change. When a magnetic field generating means such as a magnet is arranged so that the direction of rotation of the magnetic field is in the plane of the multilayer structure, and the angle between the magnetization direction of the pinned magnetic layer and the direction of the magnetic field applied from the outside is α, non-magnetic The change in resistance value of the conductive layer is proportional to (1-cos α). The resistance value is the smallest when the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer are the same, that is, when the magnetic field direction is the same as the magnetization direction of the pinned magnetic layer (α = 0 °), and the magnetic field direction is pinned magnetic The maximum value is obtained when the direction is opposite to the magnetization direction of the layer (α = 180 °). Note that the magnitude of this resistance value change takes a value of around 10%.

  Here, when two SVGMR elements are connected in series so that the magnetization direction of the pinned magnetic layer is opposite to each other and the magnetic field B is applied, the change in resistance value of each GMR element depending on the direction of the magnetic field is opposite. It becomes. Therefore, when a constant voltage is applied to both ends of this series connection circuit, the voltage at the midpoint changes according to the rotation angle of the magnetic field.

  The rotation angle sensor 2 is configured by arranging four sets of series connection circuits 21, 22, 23, 24 each comprising 90 SVGMR elements 211, 212, 221, 222, 231, 232, 241, 242 every 90 °. Is done. Here, the respective arrows on the eight SVGMR elements 211, 212, 221, 222, 231, 232, 241, 242 indicate the magnetization direction of the fixed magnetic layer, and the angle θ is the magnetic field generated from the magnet 8. The direction (rotation angle) is indicated.

  The peripheral circuit 3 mainly includes a triangular wave generation circuit 35, comparators 31, 32, 33 and 34, and an arithmetic circuit 40. These peripheral circuits 3 are arranged on the substrate 5 together with the rotation angle sensor 2.

  The angle measurement principle and circuit operation of the rotation angle measuring apparatus 1 according to the present invention will be described below.

  First, focusing on the series connection circuit 21, an example of the relationship between the applied voltage and the output voltage V (cos θ) at the midpoint 213 is shown in FIG. The output voltage V (cos θ) at the midpoint 213 is a voltage proportional to the applied voltage. Since the resistance values of the two SVGMR elements 211 and 212 change in opposite directions depending on the angle θ, the slope of the output change due to the applied voltage changes depending on the angle θ. The voltage at the midpoint 213 is input to the comparator 31 having a threshold value Vth. Here, when a triangular wave voltage is applied to the series connection circuit 21 by the triangular wave generation circuit 35, the output waveform f (cos θ) of the comparator 31 becomes a pulse waveform as in the example shown in FIG. 3B. As shown in FIG. 3B, when the angle θ is changed, the duty ratio of the pulse waveform changes.

  Similarly, when the comparators 32, 33, and 34 are connected to the midpoints 223, 233, and 243 with respect to the other series connection circuits 22, 23, and 24, and the angle θ is changed, the output f ( Similarly, the duty ratio of sin θ), f (−cos θ), and f (−sin θ) also changes. FIG. 4A shows an example of a change in output duty ratio in the comparators 31, 32, 33, and 34 due to a change in the angle θ. Each duty ratio change has a phase difference every 90 °. The outputs of these comparators 31, 32, 33, 34 are connected to the pulse input terminals duty1, duty2, duty3, duty4 of the arithmetic circuit 40, the respective duty ratios are taken in as digital values, and x = f in the arithmetic circuit 40. When the calculation of (cos θ) −f (−cos θ), y = f (sin θ) −f (−sin θ) is performed, the waveforms are almost sinusoidal and cosine waves as shown in FIG. 4B. . Further, when arctan (y / x) is calculated, as shown in FIG. 4C, an angle measured and calculated by this method can be obtained by changing the angle θ. In this method, the theoretical measurement error cannot be set to zero as shown in FIG. 4 (d). However, since it is a periodic and reproducible error characteristic, It is also possible to correct the error. The angle obtained by the arithmetic circuit 40 is output to the outside as the output of the rotation angle measuring device 1.

  Each comparator 31, 32, 33, 34 may be a Schmitt trigger input. In addition, the same method can be used even if a sawtooth wave generation circuit is used instead of the triangular wave generation circuit 35. Further, as in the rotation angle measuring device 11 shown in FIG. 5, in place of the triangular wave generating circuit 35 shown in FIG. 1, a triangular wave / square wave generating circuit 351 capable of outputting a triangular wave voltage and a square wave voltage is used. A square wave may be input to the trigger terminal “in” of the arithmetic circuit 41 and used as a trigger signal for taking in the duty ratio.

  The oscillation frequency of the triangular wave generating circuit 35 is appropriately set according to the maximum rotational speed of the rotating shaft 9, the required resolution for angle measurement, and the calculation speed of the calculation circuit 40. Further, the output amplitude and offset voltage of the triangular wave generation circuit 35 and the threshold voltage Vth of each of the comparators 31, 32, 33, 34 may be appropriately changed.

  Further, since the change in the resistance value of the SVGMR element due to the angle θ has temperature dependence, the temperature of the rotation angle sensor 2 is determined from the amplitude of the duty ratio change and the value of (x squared) + (y squared). Is also possible. Using this temperature information, it is also possible to correct a temperature-dependent error by a known correction means.

  By the above method, a rotation angle measuring device having a low-cost circuit configuration that does not require a differential amplifier circuit or an analog / digital conversion circuit can be realized.

  Next, another example of the circuit configuration in the rotation angle measuring device according to the present invention will be described with reference to FIG. The rotation angle measuring device 12 according to this configuration includes the voltage V (cos θ) and the voltage V (−cos θ) at the midpoints 213 and 233 of the series connection circuits 21 and 23 and the midpoints 223 and 243 of the series connection circuits 22 and 24. Voltage V (sin θ) and voltage V (−sin θ) are respectively input to the differential amplifier circuits 36 and 37, and V (cos θ) −V (−cos θ) and V (sin θ) −V (−sin θ) are obtained. After detection, the respective outputs are input to comparators 38 and 39 having a threshold value Vth. The outputs of the comparators 38 and 39 are pulse waveforms, and the duty ratio changes depending on the angle θ. The outputs of the comparators 38 and 39 are connected to the pulse input terminals duty5 and duty6 of the arithmetic circuit 41, and the respective duty ratios are taken in as digital values x 'and y'. Further, when arctan (y ′ / x ′) is calculated, the angle measured and calculated by this method can be obtained by the change of the angle θ.

  Although this method requires a differential amplifier circuit, the number of pulse input terminals in the arithmetic circuit can be reduced, and the number of operations in the arithmetic circuit can be reduced.

2 Rotational angle sensor 3 Peripheral circuit 5 Substrate 8 Magnet 9 Rotating shaft 31, 32, 33, 34, 38, 39 Comparator 40 Arithmetic circuit 211, 212, 221, 222, 231, 232, 241, 242 SVGMR element

Claims (8)

A rotation angle sensor having a sensor element unit that outputs a magnetic field direction generated by a magnetic field generation unit that rotates in synchronization with a rotation axis as at least two electrical signals having different phases;
A signal generation circuit for outputting a periodic waveform for driving the sensor element unit to the rotation angle sensor;
A comparator to which an output obtained from the sensor element unit is input;
An arithmetic circuit to which the output from the comparator is input,
The arithmetic circuit has a pulse input terminal that captures a pulse waveform output from the comparator as a digital value, and the magnetic field direction that is equivalent to the rotation angle of the rotating shaft based on the value captured at the pulse input terminal. A rotation angle measuring device characterized by calculating and outputting. In the rotation angle measuring device according to claim 1,
The number of outputs of the sensor element section is 4, and the rotation angle measuring device outputs electrical signals having different phases every 90 degrees. In the rotation angle measuring device according to claim 1 or 2,
An output of the signal generating circuit is a triangular wave or a sawtooth wave, the rotation angle measuring device. In the rotation angle measuring device according to any one of claims 1 to 3,
The rotation angle measuring device characterized in that the arithmetic circuit has a function of measuring a duty ratio of the pulse waveform and converting it into a digital value. In the rotation angle measuring device according to any one of claims 1 to 4,
The signal generation circuit is configured to output a trigger signal synchronized with the periodic waveform in addition to the periodic waveform and input to the arithmetic circuit,
The rotation angle measuring device, wherein the arithmetic circuit has a function of using the trigger signal as a trigger for capturing the pulse waveform. A rotation angle sensor having a sensor element unit that outputs the magnetic field direction generated by the magnetic field generating means rotating in synchronization with the rotation axis as an even number of electrical signals having different phases;
A signal generation circuit for outputting a periodic waveform for driving the sensor element unit to the rotation angle sensor;
A differential circuit to which an output obtained from the sensor element unit is input;
A comparator to which the output of the differential circuit is input;
An arithmetic circuit to which the output from the comparator is input,
The arithmetic circuit has a pulse input terminal that captures a pulse waveform output from the comparator as a digital value, and the magnetic field direction that is equivalent to the rotation angle of the rotating shaft based on the value captured at the pulse input terminal. A rotation angle measuring device characterized by calculating and outputting. In the rotation angle measuring device according to claim 6,
It has four outputs from the sensor element section,
The differential angle circuit and the comparator are each composed of two pieces. In the rotation angle measuring device according to any one of claims 1 to 7,
The sensor element is an element using a spin valve type giant magnetoresistive effect comprising at least a fixed magnetic layer whose magnetization direction is not changed by an external magnetic field, a nonmagnetic conductive layer, and a free magnetic layer whose magnetization direction is changed by an external magnetic field. The rotation angle measuring device characterized by being.

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