JPS6139592A - Magnetic encoder - Google Patents

Abstract

PURPOSE:To improve the resolution by specifying the relation between the magnetizing pitch lambdaP of permanent magnets and the arranging pitch lambdaMP of magnetic resistance elements. CONSTITUTION:When permanent magnets are provided on a permanent magnet rotating body 3 at a pitch of lambdaP, and magnetic resistance elements A1, A2, B1 and B2 forming an MR sensor 4 are arranged at a pitch of lambdaMP, the magnetizing pitch lambdaP and the arranging pitch lambdaMP are related such that lambdaP=(4/n).lambdaMP in which n is a natural number of three or more except for multiples of four. When n=3, for example, the output A of the MR sensor or the waveform B is an output one cycle of which corresponds to a half of the magnetizing pitch lambdaP of the permanent magnets, and therefore the number of cycles in the output waveform becomes twice as many as that of a prior art in which n=2. Further, the magnetizing pitch of the permanent magnets becomes 1/1.5, whereby the number of poles are increased. Thus, a magnetic encoder having a resolution 1.5X2=3 times as high as that of a prior art can be constructed with the use of the same MR sensor and permanent magnets having the same diameter as the prior art.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a magnetic encoder that magnetically detects the amount of movement of a moving body and outputs an electrical signal, and more specifically, a magnetic encoder that magnetically detects the amount of movement of a moving body and outputs an electrical signal. Four magnetoresistive elements, A1 and B2, which vary with each other, are arranged so that the pitch between A1 and A2 and between B1.82 is λHR, respectively, and B is at the center position between Ai and A2. , a constant voltage V is applied to a circuit in which the series connection circuit of Ai and A and the series connection circuit of 81 and 82 are connected in parallel.
c is applied, and the intermediate connection point A and B between A1 and A2 and B2
By arranging a magnetoresistive sensor whose voltage detection terminal is the intermediate connection point B of the permanent magnet, facing the permanent magnet whose N pole and S pole are alternately magnetized with a pitch of λP, through an air gap, A voltage signal corresponding to the amount of movement is sent to the voltage detection terminals A and B.
This relates to a magnetic encoder obtained from the
It is used in the control detection section of robots, VTRs (video tape recorders), etc.

[Background of the invention]

When a magnetic field is applied perpendicular to the current passing direction to a conductor made of a film made of magnetic materials such as iron or nickel and their alloys, the electrical resistance of the conductor decreases, as shown by the solid curve in Figure 4. This is known as the magnetoresistive effect, and is used in magnetic field measurement, position detection devices, etc.

Note that the broken line curve is a relationship curve when a bias magnet is placed side by side with a conductor.

A magnetic encoder that detects the position of a rotating body using this magnetoresistive effect is in practical use, and a conventional example is shown in Figure 5. In the example to be obtained, Fig. 5 (,) shows a side view of the magnetic encoder and its surrounding parts, and its XX cross-sectional view, where 1 is an electric motor, 2 is a rotor shaft, and 3 is a large number of North pole.

A permanent magnet rotating body equipped with a permanent magnet magnetized to the S pole and rotating integrally with the rotor shaft 2, and a magnetoresistive sensor (4) composed of a magnetoresistive effect element (hereinafter referred to as a magnetoresistive element).
(hereinafter referred to as an MR sensor), and 5 is a cover. The permanent magnets of the permanent magnet rotating body 3 and the MR sensor 4 are disposed opposite to each other with an air gap interposed therebetween, and the rotational position of the rotor shaft 2 is detected by the MR sensor 4.

The relationship between the MR sensor 4 and the permanent magnets of the permanent magnet rotating body 3 is as shown in FIG. The pitch between is λHR, the pitch between Bi and 82 is also λ■, and B
The element is arranged so that it is located in the center between A1 and A2, and each element forms an electric circuit as shown in FIG. 5(d). That is, a constant voltage Vc is applied to a circuit in which a series connection circuit of A and A2 and a series connection circuit of B1 and B2 are connected in parallel,
The intermediate connection point A between A□ and A2 and the intermediate connection point B between B1 and 82 are used as pressure detection terminals. Further, a bias magnet 6 is arranged on the surface of the MR sensor 4 that does not face the permanent magnet rotating body 3. The bias magnet 6 is fixed to the MR sensor 4 so that a magnetic field with constant magnetism (N pole in the illustrated example) is always applied to the MR sensor 4. Therefore, the MR sensor 4 is equipped with a permanent magnet. A composite magnetic field of the magnetic field of the rotating body 3 and the magnetic field of the bias magnet 6 acts,
Since the magnetic field generated by the permanent magnet of the permanent magnet rotating body 3 changes in magnitude and magnetism as the motor rotates, the position and rotation direction of the rotor shaft 2 of the motor can be determined from the detection terminals A and B of the MR sensor 4. Can be detected.

FIG. 5(c) shows the change in the voltage of the detection terminals A and B with respect to the ground potential when the rotating body moves through the magnetization pitch λP of the permanent magnet, and the magnitude of the magnetic field of the bias magnet 6. By adjusting the angle, it changes almost sinusoidally with respect to the moving angle of the rotating body, and the phase angle of the voltage signal appearing at detection terminals A and B is (1/4) λP, which is 1
It has a phase angle of 90 degrees and has the characteristics necessary for motor control.

However, the above-mentioned conventional technology has the following problems. That is, in order to improve the accuracy of motor control, it is necessary to increase the number of permanent magnets provided on the permanent magnet rotating body 3, but if the arrangement pitch λ■ of the elements of the MR sensor 4 is constant, the attachment of the permanent magnets will increase. Since the magnetic pitch λP is also determined, it is necessary to increase the diameter of the permanent magnet rotating body 3 in order to increase the number of permanent magnets, and a large diameter rotating body is required to increase control accuracy. There was a problem in that it became large.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems in the prior art, and to fix the arrangement pitch λHR of the magnetoresistive elements and the diameter of the permanent magnet rotating body to be constant, and to change the magnetization pitch λP of the permanent magnets by simply changing the An object of the present invention is to provide a magnetic encoder that can have a finer resolution without increasing the diameter of a permanent magnet rotating body.

[Summary of the invention]

The feature of the present invention is that the relationship between the magnetization pitch λP of the permanent magnets provided on the permanent magnet rotating body and the arrangement pitch λ The purpose is to adopt a configuration in which λp=(4/n)·λHR as a natural number.

[Embodiments of the invention]

When determining the magnetization pitch λP of the permanent magnet by setting n in the above-mentioned relational expression λp=(4/n)・λHR to various natural numbers, n=2 has already been adopted in the prior art,
When n=1, the magnetization pitch λP of the permanent magnet becomes larger than that of the conventional structure, which is contrary to the purpose of the present invention. Therefore, n=2 and n
The following describes the case where neither =1 is adopted and n is a natural number of 3 or more.

Figure 1(a) shows the arrangement relationship between the MR sensor 4 and the permanent magnet rotating body 3 in the case of n=3, the electric circuit diagram (c) shows the phase relationship of the voltage signals appearing at the detection terminals A and H. As shown in (b), the relational expression λP=(4/3)·λ■ holds between the arrangement pitch λHR of the elements of the MR sensor and the magnetization pitch λP of the permanent magnet, and Unlike the conventional configuration shown in FIG. 5(b), no bias magnet is provided.

The embodiment of FIG. 1 operates as follows. In the state shown in FIG. 1(a), element A1 has zero opposing magnetic flux and has the maximum resistance value, and element A receives the maximum magnetic flux of the S pole and has the lowest resistance value, so the level of output A is as follows. If Vc/2 is shown as a zero line, when the zero-order permanent magnet, which is at the position a in figure (b), rotates by (1/8)·λP in the direction of the arrow, element A
2 and A2 receive almost the same magnetic flux, so their resistance values are the same, and therefore the level of output A is Vc/2=O, which is at the position a2. When the permanent magnet further rotates by (1/8)·λP, the magnetic flux received by element A1 becomes maximum, and the resistance value becomes minimum.
A, (7) The received magnetic flux is zero, the resistance value is maximum, and the level of output A is at position a3. Below, the permanent magnet is (1/
8)...As it rotates by λP, the level of output A becomes a
The level changes by one cycle with respect to the change (1/2)·λP in the amount of rotational movement of the rotating body.

On the other hand, elements B1 and B2 are arranged with their positions shifted by 1/2)·λHR from elements A1 and A, so the waveform of output B is as shown in figure (b). The same waveforms b8 to b, . . . are output with a phase shift of 1/8)·λP with respect to the waveform of A.

In this way, in the embodiment of n=3 shown in FIG. 1, (1) no bias magnet is required;

(2) The waveform of the output A or B of the MR sensor is an output with one period having a pitch of 1/2 of the magnetization pitch λP of the permanent magnet, so the number of cycles of the output waveform is n = 2 of the conventional example.
On the other hand, if the magnetization pitch of the permanent magnet is 1
/1.5, and the number of poles increases, and with the same MR sensor and permanent magnet of the same diameter, 1.5X2=
A magnetic encoder with three times the resolution can be constructed.

Next, as another example, n=6. That is, λP=(476)・
The case of λHR=(2/3)·λ■ will be explained. M
The relationship between the R sensor 4 and the permanent magnet rotating body 3 is shown in Figure 2(a).
The waveform of the output voltage is shown in (b). The electric circuit of the MR sensor is the same as that in Fig. 1 (c), but in the embodiment shown in Fig. 2, it is necessary to provide a bias magnet 6. Become.

The embodiment shown in FIG. 2 operates as follows. At the zero position shown in the figure, both elements A1 and A2 receive zero magnetic flux from the permanent magnet.
Furthermore, since the N pole of the bias magnet receives the same magnetic flux, the resistance values are the same, and the output A level is Vc/2.
1. When the zero-order permanent magnet at position a in figure (b) rotates by (1/4)·λP in the direction of the arrow, element A
1 receives a large magnetic flux due to the combination of the maximum N pole of the permanent magnet and the N pole of the bias magnet, and the resistance value is the lowest, and element A1
, receives the magnetic flux of the difference between the maximum S pole of the permanent magnet and the N pole of the bias magnet, and the resistance value of is the maximum, so the output A is
The level is the highest, at position a2 in the figure (b).

When the rotation further advances in the direction of the arrow by (1/4)・λP,
Elements A□ and A2 both receive zero magnetic flux from the permanent magnet, and receive the same magnetic flux from the bias magnet, so their resistance values are equal, and the level of output A is Vc/2, so they are at position 83 in the diagram (b). becomes. Below, the permanent magnet is (1/4)・λP
Each time the permanent magnet rotates, the resistance values of elements A1 and A2 increase and decrease relative to each other, and when the permanent magnet rotates by λP, a waveform output A having one cycle of this rotation is obtained. On the other hand, elements B1 and B8 are element A
Since the positions are shifted by 1/2)・λHR relative to 1 and A2, the waveform of output B is the same waveform with a phase shift of 1/4)・λP compared to the waveform of output A. .

That is, the features of the case of n==6 shown in FIG. 2 are (1)
A bias magnet is required. (2) Since the magnetization pitch λP of the permanent magnet is λp = (2/3)・λ■, compared to the conventional example shown in Fig. 5, the permanent magnet of the same diameter However, by arranging three times as many magnetic poles, a magnetic encoder with three times the resolution can be obtained.

Furthermore, when considering the case of n=4, as shown in Figure 3(a), λp = (4/4)・λMk = λHR,
Even if a bias magnet is used, the resistance values of the paired elements A1 and A2 and B1 and B2 of the MR sensor change in the same direction at the same time, so they do not operate as a magnetic encoder.

Similarly, by substituting natural numbers for n = 5.8.1 (1, 12, ...), the operation is shown in Figure 3 (b) and (e).
.

(c), (d), ... were verified, and in conjunction with the above results, the relational expression λp = (4/n) between the element arrangement pitch λHR of the MR sensor 4 and the magnetization pitch λP of the permanent magnet was determined.・λ
It can be seen that the object of the present invention can be achieved by using "a natural number of 3 or more excluding multiples of 4" as n in HR.

The reason why multiples of 4 are excluded from n is that if n is a multiple of 4, the magnetism of the permanent magnets that act on each of the paired magnetoresistive elements will be the same, so even if a bias magnet is provided, This is because the change in resistance value remains the same, no output power is generated, and the device does not operate as a magnetic encoder.

On the other hand, if n is a natural number of 3 or more excluding multiples of 4, the direction of change in the magnetism or magnetic flux of the permanent magnet acting on each of the paired magnetoresistive elements will be in opposite directions. , the respective resistance values change in opposite directions, and an output voltage is obtained. Further, if n is an odd number, a bias magnet is not required, and if n is an even number, a bias magnet is required.

〔Effect of the invention〕

As explained above, according to the present invention, magnetic encoders with various resolutions can be constructed by simply setting the arrangement pitch λHR of the MR sensor elements constant and selecting the magnetization pitch λP of the permanent magnets provided facing each other. Therefore, a magnetic encoder with higher resolution can be obtained without increasing the diameter of the permanent magnet. In particular, the relational expression λp=(4/n)・
If n of λHR is set to an odd number of 3 or more, such as n = 3.5, etc., (1) a bias magnet is not required, and (2) the period of the output waveform of the MR sensor is equal to that of a permanent magnet. The magnetization pitch is 1/2 of λP, and the resolution is twice as high as that of the conventional configuration.Also, an even number excluding multiples of 4 such as n=6.10, etc. is used as n. (1) A bias magnet is required, but (2) the period of the output waveform of the MR sensor is the same as the magnetization pitch λP of the permanent magnet, and the output waveform is close to a sine wave. - It has the advantage that it can be used to detect minute angles that are further subdivided into wavelengths.

In the embodiment, a permanent magnet magnetized at a pitch of λP was described as a rotating body, but a linear motion magnetic encoder in which a linearly extending linear motion body is alternately magnetized with N poles and S poles in the moving direction. The present invention is also applicable to

[Brief explanation of drawings]

Fig. 1 is a diagram showing one embodiment of the present invention, (,) is a diagram of the arrangement relationship between the magnetoresistive sensor and the magnet rotating body, (b) is a diagram of the phase relationship of the output signals, and (C) is the electrical circuit of the magnetoresistive sensor. Figure 2 shows an example in which n = 6, (a) is a diagram of the arrangement relationship between the magnetoresistive sensor and the permanent magnet rotating body, (b) is an output signal waveform diagram, and Figure 3 is a diagram of various values for n. FIG. 4 is an explanatory diagram of characteristics of a magnetoresistive element; FIG. 5 is an explanatory diagram of a conventional example; (a) is a side view and its XX sectional view; (b) is a layout relationship diagram between a magnetoresistive sensor and a permanent magnet rotating body, (c) is an output signal waveform diagram, and (d) is an electric circuit diagram of the magnetoresistive sensor. Explanation of symbols 1...Electric motor 2...Rotor shaft 3...
Permanent magnet rotating body 4... Magnetoresistive sensor 5... Cover 6... Bias magnets A, B...
Voltage detection terminals A1, A2, B2...Magnetic resistance element t3 diagram (Q) n engineering 4 (NG) (d) n=+2 (NG) (e) n=s
(NG) Mouth==ko[22 ro221===koH...
・River −? A10 B, BZOA+[B+
'Picture 4

Claims (1)

[Claims] Four magnetoresistive elements A_1, A_2, B_1, and B_2 whose electrical resistance changes depending on the magnetic field strength are A_1 and A_2.
and the pitch between B_1 and B_2 is λ_H_R, respectively.
And B_1 is arranged at the center position of A_1 and A_2, and the series connection circuit of A_1 and A_2 and the series connection circuit of B_1 and B_2
A constant voltage Vc is applied to a circuit that is connected in parallel with a series-connected circuit of
By arranging a magnetoresistive sensor whose voltage detection terminal is the intermediate connection point B of _2, facing the permanent magnet whose N pole and S pole are alternately magnetized at a pitch of λ_P, with an air gap between the above permanent magnets. In the magnetic encoder which obtains a voltage signal from the voltage detection terminals A and B according to the amount of movement of the permanent magnet, the magnetization pitch λ_P of the permanent magnet and the arrangement pitch λ of the magnetic resistance element
A magnetic encoder characterized in that the relationship with _H_R is λ_P=(4/n)·λ_H_R, where n is a natural number of 3 or more excluding multiples of 4.