JP5343101B2 - Detection signal correction method of angle sensor - Google Patents

Description

  The present invention relates to a detection signal correction method of an angle sensor suitable for measuring a minute angle using a Hall element.

In a general Hall element, as shown in FIG. 6, the magnetic flux density of a magnetic field orthogonal to the chip surface T which is a magnetic flux density detection surface of the Hall element 1 which is a thin metal piece is B, and the Hall element 1 When a constant current I is passed through the Hall element 1, the Hall element 1 receives an Lorentz force by the magnetic flux density B and generates an electromotive force. The output V, which is the electromotive force of the Hall element 1, is expressed by the following equation (1), where K is the Hall coefficient and d is the thickness of the Hall element.
V = (K / d) B · I (1)

  In order to use the Hall element 1 as an angle sensor, the angle at which the chip surface T intersects the magnetic flux direction is detected as the output of the Hall element 1. For example, Patent Document 1 discloses a method of increasing the sensitivity of the Hall element 1 by making the chip surface T of the Hall element 1 parallel to the direction of the magnetic flux by the magnet when the angle to be detected is small.

  When detecting a small angular displacement θ, the Hall element 1 is arranged in a magnetic field having a magnetic flux density B as shown in FIG. 7, and when θ = 0, the chip surface T of the Hall element 1 is parallel to the direction of the magnetic flux. That is, it arrange | positions so that the direction of the magnetic flux with respect to the chip surface T may become 0 degree.

Thus, when the chip surface T of the Hall element 1 is arranged in parallel with the magnetic flux, high sensitivity to the angular displacement θ can be obtained. As shown in FIG. 8, the output V of the Hall element 1 generated when the arranged Hall element 1 is tilted with respect to the magnetic flux as shown in FIG. 8 is measured. For example, an angular displacement θ having a resolution of about 1/1000 of 1 ° is obtained. It can be detected by the following equation (2).
V = (K / d) · B · I · sin θ (2)

If the angular displacement θ is a minute angle near 0 °, sin θ≈θ, and equation (2) becomes equation (2) ′.
V = (K / d) · B · I · θ (2) ′

On the other hand, in order to correct the magnetic flux density B, as shown in FIG. 8, the chip surface T of the reference Hall element 2 of the same type as the Hall element 1 is obtained so that the same magnetic field or a component proportional to the magnetic flux density can be obtained. Is arranged so as to be orthogonal to the direction of the magnetic flux. When a constant current I is applied to the reference Hall element 2, the output Vs of the reference Hall element 2 is given by Equation (3) where Ks is the Hall coefficient and the thickness is ds.
Vs = (Ks / ds) · B · I (3)

For these outputs V and Vs, when the output V of the Hall element 1 is divided by the output Vs of the reference Hall element 2, equation (4) is obtained.
V / Vs = (K / d) · θ / (Ks / ds) (4)

  Here, since K, d, Ks, and ds are constants, it is possible to detect a stable minute angular displacement θ that is not affected by the change with time of the magnetic flux density B from the equation (4).

  However, since the Hall coefficients K and Ks of the Hall elements 1 and 2 are easily affected by temperature and have temperature dependence, a pair of Hall elements having uniform temperature characteristics are selected from a large number of Hall elements, and the Hall element 1 is selected. 2 corresponds to fluctuations in ambient temperature.

Japanese Patent Laid-Open No. 2002-22485

  It is known that even when the Hall elements are selected in this way, an offset voltage independent of the angle is generated by supplying the current I to the Hall elements. However, when the output voltage is obtained by arranging as shown in FIG. 6, since the electromotive force due to the Lorentz force is large and the offset voltage value is extremely small, the offset voltage value is generally ignored.

  However, in the measurement of a minute angle in which the direction of the magnetic flux is parallel to the chip surface T, a first offset voltage value that cannot be ignored is generated due to the internal resistance of the Hall element. This first offset voltage value varies depending on the ambient temperature and is superimposed on the outputs V and Vs to give an error in angle measurement. In particular, when the ambient temperature varies over a wide range, it is necessary to take a countermeasure.

  Further, when the direction of the magnetic flux and the chip surface T of the Hall element 1 are made parallel, an electromotive force based on the Lorentz force is generated on the cut surface C orthogonal to the chip surface T and facing the magnetic flux, and according to the temperature change It was found that an error was given to the angle measurement by superimposing it on the output V of the Hall element 1 as well.

An object of the present invention comprises a first offset voltage value by the current based on the internal resistance with the Hall element will vary in response to ambient temperature, a second offset voltage due to the Lorentz force due to the cut surface of the Hall element An object of the present invention is to provide a detection signal correction method of an angle sensor that corrects an error of a signal value of a minute angle by removing the value by calculation.

  In addition, the detection signal correction method of the angle sensor according to the present invention is attached to a shaft that is rotatable relative to a magnetic field generation mechanism that uniformly generates magnetic flux, and detects a relative angle of the magnetic field generation mechanism with respect to the magnetic field direction. And a chip surface, which is a magnetic flux density detection surface of the angle detection sensor, at a zero angle where the measurement angle is 0 °, is arranged in parallel with the direction of the magnetic flux from the magnetic field generating mechanism. In the detection signal correction method of the angle detection sensor, the angle detection sensor is fixed to the zero angle so that the magnetic field direction and the chip surface of the angle detection sensor are parallel to each other, and a predetermined magnetic flux is generated offline. In the generated magnetic field state, a constant current is supplied to the angle detection sensor, and a first offset caused by internal resistance due to a plurality of ambient temperatures of the angle detection sensor. A first step of measuring a second offset voltage value obtained by adding an electromotive force caused by the Lorentz force by the cut surface of the angle detection sensor to obtain a temperature characteristic of the second offset voltage value; During the on-line angle measurement, the ambient temperature is measured by the temperature detection sensor, and the second offset voltage value corresponding to the temperature characteristic is corrected from the output of the angle detection sensor. These steps are included.

In addition, according to the detection signal correction method of the angle sensor according to the present invention, the second offset voltage value including the first offset voltage value generated in the Hall element and generated by the magnetic flux with respect to the cut surface of the Hall element is set to the ambient temperature. To improve the measurement accuracy of minute angles.

It is a longitudinal cross-sectional view of an Example. It is a cross-sectional view of an example. It is explanatory drawing of the state which the axis | shaft rotated. 3 is a graph showing an error with respect to temperature in Example 1. FIG. 6 is a graph showing an error with respect to temperature in Example 2. FIG. It is a principle explanatory view of a general Hall element. It is explanatory drawing at the time of arrange | positioning the magnetic flux density detection surface of a Hall element in parallel with magnetic flux. It is explanatory drawing at the time of tilting a Hall element.

  The present invention will be described in detail based on the embodiment shown in FIGS.

  In FIG. 1, a through hole 12 is provided in a housing 11 made of a magnetically permeable material, and a shaft 13 made of a magnetically permeable material is also rotatably held in the through hole 12 via a bearing 14. An angle detection sensor 15 made of a Hall element is attached to the shaft 13 at a notch or the like. For example, a float of a liquid level gauge is connected to the shaft 13, and the liquid level of the float rotates by a minute angle of the shaft 13. It has been converted to.

  As shown in FIG. 2, a pair of magnets 16 and 16 ′, which are magnetic field generation mechanisms, are fixed on both sides of the through hole 12 so as to sandwich the shaft 13, and in the through hole 12 from the N pole toward the S pole. A magnetic flux having a magnetic flux density B is uniformly generated. A reference sensor 17 composed of a Hall element of the same type as the angle detection sensor 15 is fixed in a magnetic field by magnets 16 and 16 ′ outside or inside the housing 11, and the chip surface T corresponds to the magnetic flux direction of the magnets 16 and 16 ′. It arrange | positions so that it may orthogonally cross. The reference sensor 17 corresponds to the reference Hall element 2 described in the background art.

  In the housing 11, a temperature detection sensor 18 made of a resistance temperature detector for detecting the ambient temperature is disposed. The angle detection sensor 15, the reference sensor 17, and the temperature detection sensor 18 are connected to the signal processing unit 19 through lead wires.

  In the embodiment, the housing 11 is fixed and the shaft 13 is rotated. However, the housing 11 may be rotated and the shaft 13 may be fixed, and the relative angle with respect to the magnetic field direction may be measured.

  As shown in FIG. 3, the angle detection sensor 15 has a zero angle where θ = 0 when the chip surface T, which is the magnetic flux density detection surface of the Hall element, is parallel to the magnetic flux direction of the magnets 16 and 16 ′. Has been placed. The temperature detection sensor 18 detects the ambient temperature of the angle detection sensor 15 and the reference sensor 17. The signal processing unit 19 supplies a constant current I to the angle detection sensor 15 and the reference sensor 17 and detects the output V of the angle detection sensor 15, the output Vs of the reference sensor 17, and the temperature signal of the temperature detection sensor 18. Then, as will be described later, a small angular displacement θ is calculated through arithmetic processing.

  When the shaft 13 rotates, the signal processor 19 calculates the angular displacement θ based on the outputs V and Vs of the two sensors 15 and 17 according to the equation (4) described above.

However, the angle detection sensor 15 supplies the constant current I, so that the first offset voltage value O1 caused by the internal resistance, that is, the minute angular displacement is independent of the angular displacement θ as in the following equation (5). In the measurement of θ, a voltage that is difficult to ignore is generated and superimposed on the output V, so correction is necessary.
V = (K / d) · B · I · θ + O1 (5)

  In the equation (5), in order to obtain an output V that is not affected by the first offset voltage value O1, a process of subtracting the first offset voltage value O1 from the output V must be performed.

The first offset voltage value O1 is generated in proportion to the constant current I, and the internal resistance R that generates the first offset voltage value O1 has a temperature coefficient α. O1 is an approximated expression (6) as a linear expression depending on the temperature Δt that is a temperature change width with respect to the reference temperature of 25 ° C.
O1 = I · R · (1 + α · Δt) (6)

  In order to obtain the first offset voltage value O1, the temperature Δt is changed while the constant current I is supplied to the angle detection sensor 15 in a constant temperature bath or the like in a non-magnetic state, that is, B = 0, and output. V is obtained. From the obtained temperature characteristic data, the internal resistance R and the temperature coefficient α that generate the first offset voltage value O1 are calculated. Alternatively, a table of the first offset voltage value O1 with respect to the temperature Δt may be created. When obtaining this data, since the first term of the equation (5) is not relevant in the absence of a magnetic field, the magnitude of the angular displacement θ may be any.

Similarly, in the reference sensor 17, the first first offset voltage value O1s is superimposed on the output Vs as shown in the following equation (7).
Vs = (Ks / ds) · B · I + O1s (7)

When the internal resistance of the reference sensor 17 by the chip surface T is Rr and the temperature coefficient is αs, the first offset voltage value O1s can be expressed as the following equation (8).
O1s = I · Rr · (1 + αs · Δt) (8)

  The first offset voltage value O1s of the reference sensor 17 is also obtained by changing the temperature Δt with respect to the reference sensor 17 in the absence of a magnetic field, and the internal resistance Rr and temperature coefficient αs in equation (8) are calculated. Or a table of the first offset voltage value O1s with respect to the temperature Δt may be created.

  During online angle measurement, the ambient temperature is measured by the temperature detection sensor 18, and the first offset voltage values O 1 and O 1 s are calculated or obtained from the stored table. ) And (7), the outputs V and Vs from which the first offset voltage values O1 and O1s have been removed are obtained.

After such correction, if the outputs V and Vs are calculated by the same equation (9) as the equation (4), the signal processing unit 19 can obtain a stable minute angular displacement θ that is not affected by the temperature fluctuation. It is done.
V / Vs = (K / d) · θ / (Ks / ds) (9)

  FIG. 4 is a graph of the characteristic E1 of the error (%: full scale 1 °) with respect to the actually measured full scale in the range of ± 50 ° C. of the temperature Δt from which the first offset voltage values O1 and O1s of Example 1 are removed. The characteristic E0 indicates an actually measured error of the conventional example, and the characteristic E1 is corrected for errors due to the first offset voltage values O1 and O1s as compared with the characteristic E0.

  For the reference sensor 17, the value of the first term in the equation (7) due to the Lorentz force is sufficiently larger than the first offset voltage value O1s, and the minute first offset voltage value O1s is ignored. Therefore, the first offset voltage value O1s does not have to be obtained and may not be used in the calculation.

  When the minute angular displacement θ is measured by the angle detection sensor 15 so that the chip surface T is substantially parallel to the magnetic flux as shown in FIG. 3, the magnetic flux density is also applied to the cut surface C orthogonal to the chip surface T. Under the influence of B, a slight electromotive force is generated and superimposed on the output V. In the present specification, the electromotive force is added to the first offset voltage value O1 to define the second offset voltage value O2.

  The Lorentz force in the strict sense on the cut surface C is considered not to occur because the current I and the direction of the magnetic flux are parallel to each other, but the constant current flows three-dimensionally in the Hall element and is perpendicular to the magnetic flux. Also, it is estimated that a part of the current flows, and a minute electromotive force is generated due to the Lorentz force, and this electromotive force has a temperature dependency unique to the Hall element.

  Although the influence of the angular displacement θ on the cut surface C is expressed as cos θ, it can be regarded that cos θ = 1 in a range where the angular displacement θ is extremely small.

In FIG. 4, the error remaining as the characteristic E1 is mainly due to the electromotive force caused by the cut surface C, and this electromotive force is also linear with respect to the temperature Δt from FIG. Therefore, this electromotive force can be approximated to β · Δt + D, which is a linear expression with respect to the temperature Δt, where β is a temperature coefficient and D is a constant value in a constant magnetic flux density B, and the output of the angle detection sensor 15 V can be the following equation (10) obtained by adding this electromotive force β · Δt + D to equation (5).
V = (K / d) · B · I · θ + O1 + β · Δt + D (10)

The second offset voltage value O2 is represented by the following linear expression (11) where γ is a temperature coefficient and F is a constant value.
O2 = O1 + β · Δt + D = I · R · (1 + α · Δt) + β · Δt + D
= Γ · Δt + F (11)

  In the first embodiment, the first offset voltage values O1 and O1s are obtained in an off-line and no magnetic field state. However, in the second embodiment, since the second offset voltage value O2 varies depending on the magnetic flux, data is obtained in a magnetic field state. Further, in order to remove the first term of the equation (10), it is necessary to set θ = 0, and the second offset voltage value O2 is obtained in this state.

  That is, a constant current I is supplied to the angle detection sensor 15 offline in the thermostatic chamber in a magnetic field state of θ = 0 and magnetic flux density B in the thermostat, and the temperature Δt is changed to change the data of the second offset voltage value O2. Ask for. From this data, linear constants γ and F of the second offset voltage value O2 with respect to the temperature Δt are calculated, or a table of the second offset voltage value O2 with respect to the temperature Δt is created.

  Since the output Vs of the reference sensor 17 does not generate an electromotive force due to the cut surface C, and the first offset voltage value O1s is small as described in the first embodiment, it can be obtained as in the first embodiment. However, it may be ignored in the second embodiment.

  When measuring the angle online, the ambient temperature Δt is measured by the temperature detection sensor 18, and the second offset voltage value O 2 is obtained based on the ambient temperature Δt using the stored primary equation or table to detect the angle. The signal processing unit 19 performs correction to remove the second offset voltage value O2 that is an error factor superimposed on the output V of the sensor 15 for use, so that an accurate angular displacement θ can be obtained based on the equation (9). can get.

  FIG. 5 is a graph of the characteristic E2 of the actually measured error (%: full scale 1 °) of the angular displacement θ with respect to the temperature Δt of Example 2. This characteristic E2 is corrected better than the characteristic E1 obtained in the first embodiment.

DESCRIPTION OF SYMBOLS 11 Housing 12 Through-hole 13 Axis 14 Bearing 15 Angle detection sensor 16, 16 'magnet 17 Reference | standard sensor 18 Temperature detection sensor 19 Signal processing part

Claims (4)

Mounted on a shaft that is rotatable relative to a magnetic field generating mechanism that uniformly generates magnetic flux, and includes an angle detection sensor that includes a Hall element that detects a relative angle of the magnetic field generating mechanism with respect to the magnetic field direction. In the detection signal correction method of the angle detection sensor, the chip surface which is the magnetic flux density detection surface of the angle detection sensor at a zero angle of 0 ° is arranged in parallel with the direction of the magnetic flux from the magnetic field generation mechanism.
In the offline state, the angle detection sensor is fixed at the zero angle so that the magnetic field direction and the chip surface of the angle detection sensor are parallel to each other, and a constant current is applied in a magnetic field state in which a predetermined magnetic flux is generated. Supply to the angle detection sensor and add an electromotive force due to the Lorentz force due to the cut surface of the angle detection sensor to the first offset voltage value due to the internal resistance due to a plurality of ambient temperatures of the angle detection sensor Measuring a second offset voltage value and determining a temperature characteristic of the second offset voltage value;
During the online angle measurement, the ambient temperature is measured by the temperature detection sensor, and the second offset voltage value corresponding to the temperature characteristic is corrected from the output of the angle detection sensor. And a detection signal correction method for an angle sensor.   The relative angle is obtained by dividing the corrected output of the angle detection sensor by the output of a reference sensor in which the chip surface, which is a fixed magnetic flux generation detection surface of the magnetic field generation mechanism, is arranged so as to be orthogonal to the direction of the magnetic flux. The detection signal correction method of the angle sensor according to claim 1, wherein the detection signal correction method calculates the detection signal. In the offline state, a constant current is supplied to the reference sensor in the absence of a magnetic field, and the reference sensor offset voltage values caused by internal resistance due to a plurality of ambient temperatures of the reference sensor are respectively measured. The temperature characteristics of the offset voltage value of
During online angle measurement, the ambient temperature is measured by the temperature detection sensor, and correction is performed to remove the offset voltage value of the reference sensor corresponding to the temperature characteristic from the output of the reference sensor. 3. The detection signal correction method for an angle sensor according to claim 1, wherein the detection signal is corrected. The angle sensor detection signal correction method according to any one of claims 1 to 3 , wherein the shaft is connected to a float of a liquid level gauge.

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