JP2957130B2 - Rotational position detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotational position detecting device using a magnetic sensor having a magnetoresistive element.

2. Description of the Related Art Generally, factory automation,
Optical automation or magnetic encoders are used in office automation and other automated machinery in other fields to determine the exact position of a linear or rotary moving body. Among them, magnetic encoders are frequently used because they have a simple structure and are advantageous for environmental conditions such as water resistance and oil resistance. Taking this magnetic rotary encoder as an example, this encoder comprises a rotating drum magnetized at a predetermined pitch and a magnetic sensor arranged opposite thereto, for example, a magnetoresistive effect element provided on this magnetic sensor. By processing the output waveform from
By processing the relative or absolute position, the relative or absolute position of the rotation speed or rotation angle is obtained.

FIG. 7 is a perspective view showing a general configuration of a magnetic rotary encoder (rotational position detecting device). This encoder is mounted on a rotary shaft 2 whose rotational position is to be detected. It is mainly composed of a fixed rotating drum 4 and a magnetic sensor 6 arranged opposite to the outer peripheral surface of the drum at a predetermined interval (spacing) m.
On the outer peripheral surface of the rotating drum 4, at a predetermined pitch λ,
A multi-pole magnetic pattern 8 having N and S poles is provided. FIG. 8 shows a developed view of the multi-pole magnetic pattern. The magnetic sensor 6 is arranged at an interval of half the pitch λ, that is, at an interval of λ / 2, which is substantially 180 ° in electrical angle. It has two magnetoresistive elements R1 and R2, and can detect a change in a magnetic field accompanying rotation of the rotating drum 4.

Here, the distance between the elements R1 and R2 is
Substantially λ / 2 means that the distance between the two elements is precisely λ / 2
In some cases.
No. 4, the distance between the drum and the sensor, that is, a case where the distance between the elements R1 and R2 is set based on a temporary pitch determined when a circle contacting the sensor is assumed in consideration of the spacing m, or As will be described later, the word "substantially" is used, including the case where a radiation beam having a mechanical angle corresponding to the above-mentioned electrical angle is drawn from the center of rotation of the drum and an element may be arranged at the intersection of the radiation beam and the sensor. That is, the distance between the elements R1 and R2 is set to substantially λ / 2 (electrical angle of 180 °) although there is a slight difference. The magnetoresistive element, that is, the MR elements R1 and R2 are made of a material whose electric resistance changes depending on the strength of a magnetic field, for example, Ni.
A thin film of e, Ni, Co or the like is formed by a technique such as vapor deposition.

Next, the operation principle of the MR element will be described with reference to FIG. The resistance change of this type of MR element with respect to a magnetic field has characteristics as shown in FIG. 9A, the resistance changes in proportion to the magnitude of the magnetic field regardless of the direction of the magnetic field, and saturates at a certain value. I do. Here, it is assumed that the rotating drum 4 rotates and a magnetic field B whose magnitude changes in a sine wave shape as shown in FIG. 9B is applied to the MR elements R1 and R2. When such a magnetic field B is applied to the MR elements R1 and R2, the resistance values become similar to the half-wave rectified waveform of the pitch λ (FIG. 9C).
2 has a phase difference of λ / 2. Therefore,
If these MR elements R1 and R2 are connected in series as shown in FIG. 9D and a voltage V is applied from the detection DC power supply 10, an output ea can be obtained from the connection point.
The output waveform at this time can obtain a substantially sine wave output having a cycle of λ as shown in FIG.

The above description is based on the principle of detecting a change in the magnetic field. In practice, however, the amount of change in resistance of the MR element is as small as about 2%, and the relative rotation amount or rotation angle is obtained. In consideration of the incremental phase, two signals of the A phase and the B phase are required to recognize the forward / reverse rotation. Therefore, as shown in FIG.
A, RB, Ra, Rb, Ra ', Rb', RA ', R
B ′ are sequentially arranged at an interval of 1 / 4λ, that is, 90 ° in electrical angle, and are connected by wiring as shown in FIG. Note that λ here is a concept including the tentative pitch described above.

Here, the four MR elements R on the left side in FIG.
Since A, RB, Ra, and Rb are connected to the positive side of the detection DC power supply, they are configured as positive-side magnetoresistive elements. On the other hand, the four MR elements Ra ′, Rb ′,
Since RA 'and RB' are connected to the minus side (ground), they are configured as minus side magnetoresistive elements. Here, the MR elements RA, RA ', Ra, Ra' output signals on the A-phase side, and the MR elements RB, RB ', R'
b and Rb ′ output signals on the B-phase side. Each M
R element pairs, eg, RA and RA ', Ra and Ra', RB
And RB ', and Rb and Rb' have the relationship of the MR elements R1 and R2 described above, respectively. Therefore, there is a substantial (.lambda. / 2) .times.odd multiple between the two elements, that is, 180 electrical degrees.
Are spaced at odd multiples of °. And A
MR element RA for phase signals, RA ', Ra, Ra' is connected like a bridge (see Fig. 11 (A)), both connection point V _A, consisting of the V _a for example an operational amplifier, etc. A phase side amplifier 12 - has terminal and + both connection point V _a by inputting each terminal, the output of the V _a such that the differential amplifier. Thereby, the small amount of change in resistance of the MR element is compensated.

Similarly, an MR element RB for a B-phase signal,
RB ′, Rb, and Rb ′ are also connected in a bridge shape (see FIG. 11B). By inputting both connection points V _B and V _b to the − terminal and the + terminal of the B-phase side amplifier 14, respectively. , And differentially amplifies the outputs of the two connection points V _B and V _b . Also, the MR element for the A-phase signal and the B
By arranging the MR elements for phase signals at intervals of substantially 1 / 4λ, ideally the A-phase signal and the B-phase signal are shifted by 90 ° in electrical angle as shown in FIG. Since the phase is output in the state and the phase that advances according to the rotation direction of the forward / reverse rotation changes, it is recognized whether the rotation is the forward rotation or the reverse rotation.

The distance between each MR element of the conventional sensor is
Apart from using λ as a pitch or using a temporary pitch, they are all set to be constant values,
An element arrangement has also been proposed in which the distance between the MR elements is gradually increased gradually toward the sensor periphery to compensate for the difference in the distance between the sensor center and the periphery with respect to the rotating drum. . FIG. 13 is a diagram showing such an element arrangement. Here, the curvature of the drum 4 is greatly exaggerated for easy understanding. In FIG. 13, due to the curvature of the rotary drum 4, the distance between the element mounting surface of the magnetic sensor 6 and the drum 4 goes from the center to the periphery of the sensor, for example, m1, m2, and m3, respectively, but slightly larger. If the MR elements are arranged at equal intervals as described above due to the difference in the intervals, a certain amount of distortion is included in the output waveform. Therefore, in order to suppress this distortion, MR
In arranging the elements, it is assumed that a normal line Z passes through the rotation center O of the rotary drum 4 and is orthogonal to the sensor 6, and at the intersection, a substantially central MR element of the eight MR elements, for example, the MR element R
a 'is arranged. Here, the MR element Rb is arranged at this intersection for easy understanding, but in practice, the middle point between the two central MR elements Rb and Ra 'is often located at this intersection.

The other MR elements are provided on both sides of the MR element Ra 'by approximately .lambda. / 4, that is, 9 electrical degrees.
The MR elements are arranged at the intersections of the radiations H1, H2,... Extending in the direction rotated from the normal Z by a mechanical angle corresponding to this electrical angle and the sensor 6. . That is, since one pitch λ is between one NS of the drum 4 in the illustrated example,
Is 4α, the mechanical angle corresponding to λ / 4 is α, so the mechanical angle from the normal Z is α (corresponding to λ / 4), 2α (corresponding to 2λ / 4), etc. Are sequentially drawn from the rotation center O, and an MR element is arranged at each intersection of the radiations H1, H2, and the sensor 6. In this case, the distance between the MR elements gradually increases from the center of the sensor toward the periphery. As described above, when determining the arrangement position of the MR elements to be provided at an electrical angle of λ / 4, the radiations H1, H2,... Is set as the arrangement position, the distortion of the output waveform is suppressed as much as possible.

By the way, in a general relatively accurate rotational position detecting device, the value of the pitch λ is, for example, 1
It is relatively small at about 00 μm.
An output of about 000 pulses can be obtained.
If the number of pulses per rotation of the drum is large as described above, the sensor 6 must be brought very close to the drum 4 and a change in magnetic intensity must be detected effectively. Is very small, for example, about 80 μm.

However, there are some places where the rotational position detecting device is installed, where the use environment is extremely severe, such as in which the fluctuation of humidity and temperature is severe or the vibration is severe. For example, in a rotational position detecting device for obtaining a rotational angle of a steering wheel of an automobile, the use environment is extremely severe as described above. Therefore, in order to increase reliability against vibration and the like, the distance between the rotational drum 4 and the sensor 6 is increased. It is necessary to set m or m1 to a value larger than a certain value to avoid contact between the two which may occur due to vibration or the like. As described above, setting the distance m or m1 between them to be larger requires that the pitch λ of the multi-pole magnetic pattern 8 be set larger than in the past in order to effectively detect a change in magnetic intensity by the MR element. This means that the number of pulses per rotation of the drum is reduced, and that the entire length of the magnetic sensor 6 at which the MR element is mounted is inevitably increased.

When the pitch λ of the multi-pole magnetic pattern is very small as in the prior art, the length of the mounting portion of the sensor MR element can be made small. Therefore, when viewed microscopically as shown in FIG. Since the sensor surface and the drum surface are substantially parallel, the distance between each sensor and the drum can be considered to be substantially the same. However, as described above, in an apparatus used in a severe use environment, the magnetization pitch λ The sensor length also increases due to the expansion of
The difference between the distance between the element and the drum and the distance between the MR element and the drum in the peripheral portion becomes excessively large, and cannot be ignored in the output waveform even when the arrangement position determination method as shown in FIG. 13 is used. The distortion could not be avoided.

FIG. 15 shows the A-phase output and B-phase output of a large-pitch sensor formed by using the array position determining method shown in FIG.
The waveform of the phase output is shown. Both waveforms have a phase difference of 90 ° in a normal state. Here, a phase difference of 91.9 ° occurs, and the distortion factor is considerably large at 4.84%. .
Here, the distortion factor refers to a ratio of the difference between the maximum distance and the minimum distance from the center to the maximum distance when the A-phase output and the B-phase output are in a Lissajous waveform. The present invention has been devised in view of the above problems and effectively solving them. SUMMARY OF THE INVENTION An object of the present invention is to provide a rotational position detecting device capable of suppressing distortion of an output waveform by slightly adjusting a mounting position of an MR element.

[0014]

The inventor of the present invention has proposed that the distorted wave included in the output waveform is located at the arrangement position of the MR element between the output of the MR element at the center and the output of the MR element on the peripheral side. The present invention has been made based on the finding that a dependent phase difference exists. That is, it has been found that the output waveform distortion can be suppressed by shifting the mounting position of the MR element by a phase difference generated depending on the arrangement position of the MR element. The present invention relates to a rotating drum having a multipolar magnetic pattern in which N and S poles are magnetized at a predetermined pitch λ, and a normal line connected between a rotating center of a rotating drum provided opposite to the rotating drum. In a rotational position detecting device comprising a magnetic sensor having a plurality of magnetoresistive elements arranged at predetermined intervals obtained based on the electrical angle of, the formation position of each of the magnetoresistive elements, When the mechanical angle from the normal corresponding to the electrical angle is θ, and the number of magnetized poles of the multipolar magnetic pattern is P, the angle formed with the normal through the rotation center is defined by the following equation. The magnetic sensor is configured to be set at the respective intersections between radiation having an angle θ ′ and the magnetic sensor. θ ′ = θ (1-2 / P)

With this configuration, the phase difference generated between the outputs of the respective MR elements can be eliminated.
Distortion in the output waveform as a whole can be largely suppressed. In particular, this is effective when the length of the sensor, that is, the dimension becomes large, as in the case where the apparatus is designed to withstand a severe use environment by increasing the magnetization pitch λ.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the rotational position detecting device according to the present invention will be described below in detail with reference to the accompanying drawings. FIG.
FIG. 2 is a diagram showing an arrangement position of a magnetoresistive element of a magnetic sensor of the rotation position detecting device according to the present invention, and FIG. FIG. In FIG. 1, the rotational position detecting device 16 includes a rotating drum 4 and a plurality of, here, eight MR elements RA, RB, Ra, Rb, Ra ′, Rb ′, R
It is mainly composed of a magnetic sensor 6 using A ′ and RB ′.

The rotary drum 4 has a multipolar magnetic pattern 8 in which N and S poles are alternately arranged on the outer peripheral surface as described with reference to FIG. Here, the number of magnetized poles (number of pulses) P
Is set to about 60, and the conventional number of magnetized poles, for example, 10
It is much smaller than 00 so that it can withstand a severe use environment. The magnetic sensor 6, which is opposed to the side surface of the rotating drum 4 and is spaced apart therefrom by a predetermined distance (spacing), has the above-mentioned eight MR elements positioned by a method described later. Since the respective MR elements are connected in the same manner as described in FIG. 11, the description of the connection state is omitted here. Further, the interval M between the rotary drum 4 and the magnetic sensor 6 is set to be larger than that of the conventional device, and is set to, for example, about 1 mm here to improve the vibration resistance.

Now, as shown in FIG. 1, the features of the present invention are as follows.
The point is that the MR element is slightly shifted to the normal Z side from the mounting position designed by the method described with reference to FIG. Each shift amount is set to be larger as the distance from the normal Z increases. In FIG. 1, for ease of understanding, one MR element, for example, Ra 'is located on a normal line Z connecting the rotation center O of the rotating drum 4 and the sensor 6. Next, a method of determining each shift amount will be described. Now, when the mechanical angle θ 2 of the rotary drum 4 is considered in FIG. 2, the relationship between the mechanical angle θ ₂ and the electrical angle γ is as follows because the number of magnetized poles is P. Here, the magnetization pitch λ is shown large for convenience of explanation. γ = θ ₂ × P / 2 (1)

Here, M which is the intersection of the normal line Z and the sensor 6
The horizontal and vertical magnetic field components Hx and Hy in the R element Ra ′ are obtained, and the above equation is substituted. The magnetic field strength is h. Also note that the components that can be sensed by the sensor are only horizontal components in the figure. Hx = h · sin γ = h · sin (P / 2) θ ₂ (2) Hy = h · cos γ = h · cos (P / 2) θ ₂ (3)

Next, an MR element Rb indicated by a wavy line on the left side of the drawing from the MR element Ra 'will be examined. The MR element Rb indicated by the dashed line is the position determined by the method described with reference to FIG. 13, that is, rotated by a mechanical angle θ (α in FIG. 13) corresponding to the electrical angle λ / 4 from the normal Z. It is located at the intersection of the detected radiation H1 and the sensor 6. When the magnetic field component of the MR element Rb is divided into a rotation center direction Hy of the drum and a direction Hx orthogonal thereto, the respective magnitudes are Hy and H in the MR element Ra ′.
It is almost the same as x. However, since the MR element can sense only the horizontal component in the illustrated example, it is necessary to find the horizontal components Hxx and Hyx of the components Hx and Hy in the MR element Rb, respectively.
It is given by the following equation. Hxx = Hx · cos θ (4) Hyxx = −Hy · sin θ (5)

The horizontal component Hx 'sensed by the MR element Rb is the sum of the above Hxx and Hyx. Hx ′ = Hxx + Hyx = Hx · cos θ−Hy · sin θ (6) Here, the previously obtained Hx and Hy are substituted. Hx '= h · sin (P · θ 2/2) cosθ-h · cos (P · θ 2/2) sinθ = h · sin (P · θ 2/2-θ) = h · sin {(θ 2 −2 · θ / P) · P / 2} = h · sin {(θ ₂ −θ ₃ ) · P / 2} (7) where θ ₃ = 2 · θ / P.

Here, a comparison between the above-mentioned equations (7) and (2) reveals that the phase of Hx 'is delayed from the phase of Hx by θ ₃ . That is, the output waveform is distorted due to the phase delay. Therefore, in order to eliminate by compensating for the phase lag, a new radiation H was returned in the direction of the angle theta ₃ only normal Z than radiation H1 shown in FIG. 2
As shown by the solid line at the intersection of 1 ′ and the sensor 6, the MR element R
b is installed. That is, the MR element Rb is provided so as to be shifted from the position indicated by the dashed line to the position indicated by the solid line. As a result, the output of the MR element Rb at the position indicated by the solid line becomes the MR element Rb on the normal line Z.
It is possible to prevent the phase shift from occurring with the output of a 'and prevent the output waveform from being distorted.

At this time, the relationship between the mechanical angle θ ′ formed by the new radiation H1 ′ and the normal line Z and the mechanical angle θ is as follows. θ '= θ (1-2 / P ) ...... (8) back to FIG. 1, since the phase shift described above occurs similarly for the other MR element by an angle corresponding to the theta ₃ radiation H2, H3 and H4 are returned in the direction of the normal line Z to form new radiations H2 ', H3' and H4 ', and the respective intersections of these new radiations and the sensor 6 are defined as the mounting positions of the MR elements. I do. In this case, since the magnitude of θ ₃ is determined by the magnitude of the mechanical angle θ, the normal Z
, The greater the mechanical angle θ,
return amount θ ₃ of value even larger should be noted that the increases. Needless to say, the mechanical angle θ takes a discrete value obtained by increasing the mechanical angle α described in FIG. 13 by an integral multiple. Further, in FIG.
Of course, the two MR elements Rb ', RA', and RB 'are similarly shifted in the direction of the normal line Z.

As described above, since the output from each MR element is in phase with the MR element on the normal line Z, the phase difference set in advance is maintained, and the A-phase signal and B signal finally obtained are obtained.
It is possible to prevent the phase signal from containing a distortion component. In this embodiment, the case where the MR element Ra 'is positioned on the normal line Z has been described as an example. However, the present invention is not limited to this, and as shown in FIGS. The normal line Z may be set so as to pass through the center point C1 of the two elements Rb and Ra ′ of the section. According to this, the arrangement of each MR element is line-symmetric with respect to the normal Z. In this case as well, the mounting position of each MR element is set at each intersection of the sensors 6 with the radiations H1 'to H8' defined by the angles θ 'with respect to the normal Z. It should be noted that the MR element indicated by a broken line in FIG. 4 indicates an MR element provided at a position defined by the conventional positioning method described with reference to FIG.

FIG. 5 is a signal waveform showing the A-phase signal and the B-phase signal of the magnetic sensor configured as described above, and an output signal close to a substantially sine wave could be obtained. When the A-phase signal and the B-phase signal were applied to the X-axis and Y-axis of the oscilloscope to form a Lissajous waveform, as shown in FIG. 6, a waveform substantially close to a perfect circle could be obtained. When the distortion rate of this waveform was measured, the distortion rate was about 1.12%, which was a great improvement over the distortion rate of the conventional sensor of about 5%.

As described above, according to the rotational position detecting device of the present invention, the following excellent operational effects can be exhibited. Since the arrangement position of the magnetoresistive elements of the magnetic sensor is set slightly shifted so as to compensate for the phase shift of the output of each element caused by the curvature of the rotating drum, the A-phase signal And that the output waveform of the B-phase signal contains distortion.
Therefore, as a result of increasing the distance between the rotating drum and the sensor,
It is possible to provide a device that has high detection accuracy even when the magnetization pitch and the size of the sensor are large, and that can withstand use even in a severe environment such as vibration.

[Brief description of the drawings]

FIG. 1 is a diagram showing an arrangement position of magnetoresistive elements of a magnetic sensor of a rotation position detecting device of the present invention.

FIG. 2 is a diagram showing a shift amount of a mounting position of a magnetoresistive element of a magnetic sensor of a rotation position detecting device according to the present invention.

FIG. 3 is a view showing an arrangement position of magnetoresistive elements of a magnetic sensor of a rotational position detecting device according to another embodiment of the present invention.

4 is a diagram showing a shift amount of a mounting position of a magnetoresistive element of a magnetic sensor of the rotation position detecting device shown in FIG.

FIG. 5 is a waveform diagram showing an A-phase signal and a B-phase signal obtained by the device of the present invention.

6 is a Lissajous waveform diagram of the A-phase signal and the B-phase signal shown in FIG.

FIG. 7 is a perspective view showing a general rotational position detecting device including a magnetic sensor.

8 is a developed view showing a multi-pole magnetic pattern of the rotating drum shown in FIG.

FIG. 9 is an explanatory diagram for explaining the operation principle of the magnetic sensor.

FIG. 10 is a diagram showing a conventional arrangement pattern of magnetoresistive elements of a magnetic sensor.

11 is a circuit diagram showing a connection state of the magnetoresistance effect element shown in FIG.

FIG. 12 is a waveform diagram showing an A-phase signal and a B-phase signal obtained from an ideal magnetic sensor.

FIG. 13 is a diagram showing another conventional multipolar magnetic pattern of the magnetic sensor.

FIG. 14 is an enlarged view showing a relationship between a rotating drum and a sensor when a magnetization pitch is relatively small.

FIG. 15 shows an A-phase signal and B obtained from a conventional magnetic sensor.
FIG. 4 is a waveform diagram showing a phase signal.

[Explanation of symbols]

 Reference Signs List 2 rotation axis 4 rotation drum 6 magnetic sensor 8 multi-pole magnetic pattern 10 detection DC power supply 12 A-phase amplifier 14 B-phase amplifier 16 rotation position detector H1 'to H8' radiation O rotation center RA to Rb 'magnetoresistive element Z normal λ Magnetization pitch

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-261524 (JP, A) JP-A-6-82268 (JP, A) JP-A-6-18279 (JP, A) JP-A-2- 210218 (JP, A) JP-A-63-300909 (JP, A) JP-A-63-101707 (JP, A) JP-A-62-155312 (JP, U) (58) Fields investigated (Int. ⁶ , DB name) G01B 7/00-7/34 102 G01D 5/00-5/252 G01D 5/39-5/62

Claims (4)

(57) [Claims] 1. A normal line connected between a rotating drum having a multipolar magnetic pattern in which N and S poles are magnetized at a predetermined pitch λ, and a rotation center of a rotating drum provided to face the rotating drum. In a rotation position detection device including a magnetic sensor having a plurality of magnetoresistive elements arranged at a predetermined interval obtained based on the electrical angle from, in the rotational position detection device, the formation position of each of the magnetoresistive elements, When the mechanical angle from the normal corresponding to the electrical angle is θ, and the number of magnetized poles of the multi-pole magnetic pattern is P, the angle formed by the normal through the rotation center is defined by the following equation. The rotational position detecting device is configured to be set at respective intersections between the radiation having the angle θ ′ to be performed and the magnetic sensor. θ ′ = θ (1-2 / P) 2. The rotational position detecting device according to claim 1, wherein eight magnetoresistive elements are provided and connected to two bridge circuits in a differentially amplifying manner. 3. The rotational position detecting device according to claim 1, wherein the one of the magnetoresistive elements is provided at an intersection of the normal line and the magnetic sensor. 4. The intersection of the normal and the magnetic sensor is
The rotational position detecting device according to claim 1, wherein the rotational position detecting device is a center point between any two of the magnetoresistive elements.