JPH07139966A - Magnetic encoder - Google Patents

Abstract

PURPOSE:To miniaturize a magnetic recording medium and a magnetoresistance effect (MR) sensor and to enhance the capacity of them by magnetically recording a magnetic pole position signal and a reference point position signal on the same track. CONSTITUTION:A reference point position signal 28 and a magnetic pole position signal 29 are written on the same track of a recording medium 23 but an incremental signal 27 is magnetized on a separate track. The reference point position signal 28 is previously magnetized and the magnetic pole position signal 29 is subsequently magnetized. Therefore, the magnetic pole position signal 29 is made preferential and the magnetizing directions of both signals 28, 29 are magnetized so as to mutually become right-angled. Since the anisotropy to the sensing of an MR sensor becomes a pattern longitudinal direction, the anisotropy of a reference point position detection part and a magnetic pole position detection part mutually become right-angled. As a result, two signals 28,29 can be sensed by respective detection parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic encoder to which a magnetoresistive effect sensor is applied, and more particularly to miniaturization of a magnetic encoder for generating an optimum magnetic pole position signal for a brushless motor or the like.

[0002]

2. Description of the Related Art Brushless motors are widely used as drive sources for robots, machine tools and the like. These brushless motors have excellent features such as maintenance-free, good control characteristics, and high-efficiency operation characteristics, but on the other hand, they have a negative point that magnetic pole position detection is required. For this reason, generally, Hall elements corresponding to the number of phases are arranged on the stator side to detect the magnetic pole position.
Japanese Patent Publication No. 3 discloses an encoder capable of simultaneously detecting incremental, reference point position and magnetic pole position at the same time. This encoder is a magnetoresistive sensor (hereinafter abbreviated as MR sensor) using a ferromagnetic material in the sensor section, so to speak, a magnetic encoder. FIG. 5 shows a schematic configuration of a brushless motor to which this encoder is applied. First,
A drum-shaped magnetic medium 3 is fixed to one end of a shaft 2 of the brushless motor 1. The base body of the magnetic medium 3 is made of a non-magnetic material such as aluminum, and a thin uniform hard magnetic film is formed on the side surface of the drum. In the figure, the magnetized states of the incremental signal 7, the reference point position signal 8 and the magnetic pole position signal 9 are schematically shown with arrows. The MR sensor 4 corresponding to the magnetic medium 3 is arranged as shown in the drawing through an appropriate gap. The magnetization signal of each track, which is the position information, is converted into an electric signal by the MR sensor 4, and is connected to the waveform shaping circuit board 6 through the FPC (flexible printed circuit board) 5. The waveform shaping circuit board 6 amplifies the output voltage of the MR sensor and converts it into a rectangular voltage signal. Further, the waveform shaping circuit board 6
The output of is fed back to a control operation circuit unit (not shown), and desired control is performed. The magnetic medium 3 and the MR sensor 4 are taken out and the positional relationship between each track and the detection portion is shown in FIG.
As can be seen from the figure, the incremental signal 7, the reference point position signal 8 and the magnetic pole position signal 9 magnetized and recorded on each track on the magnetic recording medium 3 are the incremental detection unit 10 and the reference point position detection unit 11 of the MR sensor 4, respectively. And the magnetic pole position detector 12. Now, FIG. 6 shows one rotation, and the magnetic pole position signal 9 shows the case of three-phase and four-pole of U, V and W phases having a phase difference of 120 ° in electrical angle. The solder terminal 2 under the MR sensor 4
Reference numeral 0 is a so-called sensor outlet to which the FPC is connected. The configuration and operation of the detection unit for each signal will be described with reference to FIGS. First, FIG. 7 shows a case of incremental signal detection. Incremental signals magnetized in the circumferential direction of the magnetic medium 3 at an equal pitch λ are represented by R _I1 ~
Detecting with the elongated sensor pattern element indicated by R _I4 , the sensor pattern elements are arranged at intervals of λ / 2,
The equivalent circuit is shown in FIG. Each of the sensor pattern elements R _{I1 to} R _I4 changes its resistance with a phase difference of 180 °,
Since the wires are connected as shown in (c), R _I1 and R _I4 ,
The midpoint potentials V _I and V _I ′ of R _I3 and R _I4 have an opposite phase relationship to each other and output a sinusoidal electric signal. This is shown in FIG.
Shown in. Next, FIG. 8 shows the case of detecting the reference position. Similar to the incremental case, it consists of four sensor pattern elements R _{Z1 to} R _Z4 , but the reference position signal is magnetized at only one location on the track, and as shown in FIG. It is magnetized with a length almost equal to the magnetizing pitch λ of the incremental signal. Therefore, from the connection relation of (c) in the figure, V _Z and V _Z ′ in (d) of the figure are almost V _CC / 2.
There is a phase relationship with the waveform as shown centering on the potential of. Finally, the case of magnetic pole position detection will be described with reference to FIG. The sensor configuration, magnetized state, equivalent circuit and output waveform are shown in the same figure. Unlike the case of the incremental and reference point positions described above, the sensor pattern and the magnetization direction are rotated by 90 °. If this is magnetized in the circumferential direction, the equivalent magnet length becomes large, resulting in a very elongated magnet.
As a result, the magnetic field concentrates only on the magnetized portions, and only a weak magnetic field exists between the poles, which makes it difficult to detect the magnetic pole position. From the relationship between the sensor pattern element arrangement and the magnetized track shown in FIGS. 7A and 7B, the sensor pattern elements R _U1 and R _U4 , and R _U2 and R _U3 are affected by the same signal magnetic field. , At the same time, resistance change occurs. Therefore, the midpoint potentials V _U and V _U ′ have an antiphase relationship with each other, and the magnetic pole position sensor pattern element length L _U
Is approximately the same as the magnetization pitch λ of the incremental signal, the output voltage waveform has a trapezoidal shape with a relatively steep rise, as shown in FIG. In FIG. 9, the operation principle has been described by taking the U phase as an example, but the V or W phase also performs the same operation, and only the phase difference of 120 ° is different.

[0003]

As described above,
In the conventional magnetic encoder, the incremental signal, the reference point signal, and the magnetic pole position signal can be simultaneously extracted at one time, but since there are three signal tracks, the magnetic medium and the MR sensor become long or large. This was a big problem in terms of manufacturing and securing characteristics. Also, the encoder was expensive and not easy to use.

[0004]

The present invention is a magnetic encoder using the magnetoresistive effect sensor as described above, which can be miniaturized even if the number of tracks is increased. For this reason, it is possible to select the sensing direction of the MR sensor by selecting a combination in which the magnetization directions of magnetization are 90 ° with each other, and even if different signals are written on the same track of the magnetic medium, the conventional method is used. An electric signal can be obtained without any problem in terms of characteristics as compared with. That is, the performance is the same as that of the conventional one, and the number of magnetized tracks can be reduced to achieve miniaturization. Specifically, the reference point position signal and the magnetic pole position signal are written in the same track, and the MR sensor is also provided with the corresponding anisotropic patterns that are substantially orthogonal to each other at the same position.

[0005]

In consideration of the fact that the magnetization directions of the reference point position signal and the magnetic pole position signal are perpendicular to each other, and that it is not necessary to write a uniform and constant signal over the entire circumference of the track, unlike the incremental signal, the same. Even if each signal is written on the track, there is little mutual interference. Correspondingly, the MR sensor side is also formed so that the direction of anisotropy, which is the sensing direction of the detection section, is at a right angle so that the magnetization signal on the same track can be selectively detected.

[0006]

EXAMPLES The present invention will be described below with reference to examples. FIG. 1 shows a magnetic medium of a magnetic encoder according to the present invention. An MR sensor corresponding to this is shown in FIG. In the recording medium 23 shown in FIG. 1, the reference point position signal 28 and the magnetic pole position signal 29 are written on the same track, but the incremental signal 27 is magnetized on another track. Further, an enlarged view of the overlapping portion of the reference point position signal and the magnetic pole position signal is as shown in FIG. That is, in the present invention, the reference point position signal is magnetized first, and then the magnetic pole position signal is magnetized. Therefore, as can be seen from the arrow indicating the magnetized state in the figure, the magnetic pole position signal is prioritized, and the magnetization directions of both signals are magnetized so as to be perpendicular to each other. On the other hand, the reference point position detector 31 and the magnetic pole position signal 32 of the MR sensor 24 in FIG.
It is as shown in FIG. The shape of each detection pattern element is basically the same as that of FIGS. 8 and 9, but is characterized in that the reference point position detection units 31 are arranged on both sides of the magnetic pole position detection unit 32. Further, since the anisotropy of the MR sensor for sensing is in the longitudinal direction of the pattern, the anisotropies of the reference point position detection unit 31 and the magnetic pole position detection unit 32 are perpendicular to each other as shown in the figure. Therefore, it can be seen that the two magnetized recording signals shown in FIG. 3 can be sensed by the respective detectors. In the present invention, the magnetic pole position signal 29 is written on the reference point position signal 28, but there is almost no problem in practical use when the reference point position signal is lowered or the waveform is distorted. This is because the ratio of overlapping portions is small and the sensor has anisotropy. As can be understood from the above description, it goes without saying that the present invention can be applied to a linear scale.

[0007]

According to the present invention, since the reference point position signal and the magnetic pole position signal can be magnetized and recorded on the same track, the magnetic recording medium and the MR sensor, which are conventionally too large and expensive, can be downsized. Further, the miniaturization of the magnetic recording medium and the MR sensor facilitates the assembly and adjustment, and improves the performance.

[Brief description of drawings]

FIG. 1 is a magnetic recording medium of a magnetic encoder according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an MR sensor according to an embodiment of the present invention.

FIG. 3 shows a case where a reference point position signal and a magnetic pole position signal are magnetized and recorded on the same track.

FIG. 4 is an enlarged view of a reference point position and magnetic pole position detection unit according to the present invention.

FIG. 5 is a brushless motor incorporating a magnetic encoder for explaining the related art.

FIG. 6 is an enlarged view of a magnetic medium and an MR sensor according to the related art.

FIG. 7 is an explanatory diagram of an operation principle of incremental detection.

FIG. 8 is an explanatory diagram of an operation principle of reference point detection.

FIG. 9 is an explanatory diagram of an operation principle of magnetic pole position detection.

[Explanation of symbols]

1 brushless motor, 2 shafts, 3 magnetic media,
23 magnetic medium, 4, 24 magnetoresistive effect sensor (MR
Abbreviated as a sensor), 5 FPC (flexible printed circuit board), 6 waveform shaping circuit board, 7 incremental, 27 incremental signal, 8 reference point position, 2 reference point position signal, 9 magnetic pole position signal, 29 magnetic pole position signal, 10 incremental, 30 detection unit, 10 incremental detection unit, 11 reference point position detection unit, 31 reference point position detection unit, 12 magnetic pole position detection unit, 3 magnetic pole position detection unit, 20 solder terminal, 40
Solder terminal

Claims (4)

[Claims] 1. A magnetic medium in which a magnetic pole position signal, a reference position signal and an incremental signal are magnetized and recorded on each track and a stripe-shaped ferromagnetic thin film are formed on a non-magnetic substrate, and a magnetic pole position detecting section is provided. A magnetic encoder comprising a reference position detector and a magnetoresistive effect sensor having an incremental detector, wherein the magnetic pole position detection signal and the reference position signal are magnetized and recorded on the same track. . 2. The magnetic recording medium according to claim 1, wherein the magnetic pole position signal and the reference position signal are magnetized and recorded in directions substantially orthogonal to each other, and the magnetic pole position is recorded after the reference point position signal. A magnetic encoder characterized in that a signal is magnetized and recorded. 3. The magnetic encoder according to claim 1, wherein the magnetic pole position detecting section and the reference point position detecting section of the magnetoresistive effect sensor have anisotropies substantially orthogonal to each other. 4. The magnetic encoder according to claim 1, wherein in the magnetoresistive effect sensor, the reference point position detector is arranged on both sides of the magnetic pole position detector.