JPH01239413A - Magnetic absolute encoder device - Google Patents

Abstract

PURPOSE:To improve detection accuracy by making both sides of the border of the 1st and 2nd magnetism areas of a magnetic track opposite in polarity from each other. CONSTITUTION:The pattern of a Gray code consisting of the 1st magnetism area 13a and 2nd magnetism area 13b is formed on the magnetic track 13 of a magnetic drum 2 fitted on a motor shaft. When this pattern is formed, the 2nd magnetism area 13b is magnetized to the overall periphery and the 1st magnetism area 13a is magnetized thereupon. In this case, the 1st magnetism area 13a has an odd number of magnetic poles, and the border part contacting the 2nd magnetism area 13b is opposite in polarity from the area 13b. Both sides of the border part between the areas 13a and 13b are opposite in polarity, a spread of magnetic flux is small, and a detection signal with sharp leading and trailing edges is obtained, so that the detection accuracy is improved greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a single position detection device, and more particularly to an absolute encoder device suitable for absolute position detection using a magnetic sensor.

2. Description of the Related Art Recently, automatic assembly devices such as robots and NO machines have become widespread, and as a result, demand for rotary encoder devices used for rotation control, position detection for stopping at fixed positions, etc. is rapidly increasing. Currently, most rotary encoders are optical, but magnetic rotary encoders are increasingly being used to improve reliability against dust and condensation, improve response speed, resolution, and lower prices.

Particularly when the object to be detected is stationary, the absolute position of the object to be detected can be directly detected as an address of all multiple bits. As a so-called absolute type encoder device, a rotary encoder device as shown in FIG. 5 has been proposed.

In FIG. 6, a magnetic drum 2 made of a magnetic material is directly connected to the shaft of a motor 1 whose rotation is controlled. A plurality of magnetic tracks 3 provided on the magnetic drum 2 form a predetermined gray code pattern by magnetized areas and non-magnetized areas, and these notches are detected by a magnetic sensor 4 arranged along the magnetic drum 2. The rotation information of the motor 1 is detected based on the electrical signal obtained thereby.

Figure 6 shows an example of a 4-bit gray code to be recorded on the magnetic drum 2 in Figure 5. When this gray code is recorded on the magnetic drum 2, the developed view of the surface of the magnetic drum 2 is as shown in Figure 6. It will look like B.

The shaded area in FIG. 6B is an area in which a pattern of magnetization that is repeatedly reversed at a certain frequency is recorded, and the white area is an area in an unmagnetized state.

On the other hand, the magnetoresistive element 6 (hereinafter referred to as MR element) provided on the substrate of the magnetic sensor 4 is constructed by folding the magnetoresistive pattern back to the width of the MR element 6 at a folding pitch a as shown in FIG. .

MR elements 5 as shown in FIG. 7 are arranged on the magnetic tracks 3 of FIG. 6 with an air gap of about 0.1 mW in between.

The MR element 6 in FIG. 7 is an alloy having a magnetoresistive effect made of ferromagnetic materials such as Fe-Ni and N1-Go.
It is deposited on a substrate such as glass to a thickness of S .mu.m to 0.1 .mu.m by a thin film forming method such as vacuum evaporation, and then etched.

The length l in the longitudinal direction of this pattern is generally [0.5 mm ~
By making the width approximately 3 mm and the width 2 μm to 30 μm, the magnetic domains will be oriented in the longitudinal direction.

-2% to magnetic field perpendicular to the current direction and parallel to the membrane
There is a resistance change of -4%, and it has uniaxial anisotropy with no resistance change against a magnetic field parallel to the current direction.

The magnetic sensor configured as described above allows the magnetic drum 2 to
When the magnetic field of each track is detected, a detected waveform as shown in FIG. 8 is obtained. In FIG. 8, reference numerals 91 to 94 represent waveforms output by each strip of the MR element 6 shown in FIG. 7, and their combined output becomes a reference numeral 96 in the magnetization region.

By shaping this output signal through a waveform processing circuit using a comparator or the like, it is possible to obtain an ON output in any part of the magnetized region of track 3 and an OFF output in the non-magnetized region. The combination of ON and OFF of the detection signal makes it possible to detect the absolute address corresponding to the gray code.The magnetization pitch in the magnetization region, the film thickness and width of the MR element, and the number of patterns depend on the rotation speed of the motor 1. The optimum value can be determined based on the required resolution, the distance between the magnetized drum and the MR sensor, etc.

Problems to be Solved by the Invention However, in the conventional example described above, a magnetized region θ and an unmagnetized region 7 are provided as shown in FIG. Therefore, at the boundary 8 between these regions, the magnetic flux distribution at the end of the magnetized region is wider than the magnetic flux distribution 9 at the continuously magnetized portion, as indicated by reference numeral 1o. Therefore the 9th
When the human track diagram is scanned from left to right, the detected waveform becomes as shown in FIG. 9B. When this waveform is shaped by comparing its Mv with a predetermined threshold value using a comparator or the like, a detection output as shown in FIG. 9C is obtained. In other words, as shown in FIG. 9, the detection signal is
A detection error of T has occurred. This error similarly occurs even if the direction of rotation of the magnetic drum 2 is reversed. Therefore, it is difficult to obtain good detection accuracy with the conventional configuration.

The present invention aims to solve such problems and improve detection accuracy.

Means for Solving the Problems Technical means of the present invention for solving the above problems is that if the conventional magnetization region of the magnetic track is a first magnetization region, this first magnetization region has an odd number of magnetic poles. In the conventional non-magnetized area, a second magnetized area is provided which is magnetized to a magnetic pole opposite to the magnetic pole at the end of the first magnetized area.

On the other hand, a bias magnetic field from K, such as a permanent magnet, is applied to the 1MR element in order to provide linearity to changes in the magnetic field (particularly to changes in the magnetic pole).

At the boundary between the first magnetized region and the second magnetized region, the magnetic poles are opposite to each other, so there is no spread of magnetic flux at the boundary, and a detection signal with a sharp rise (fall) can be obtained. Accuracy can be significantly improved.

Example An embodiment of the present invention will be described below with reference to the accompanying drawings.

The encoder device according to the present invention has a configuration as shown in FIG. 2. In FIG. 2, 1 is a motor whose rotation is controlled, and a magnetic drum 2 whose circumferential surface is made of a magnetic material is attached to the motor shaft. Directly connected. The plurality of magnetic tracks 13 provided on the magnetic drum 2 include a first magnetized region 131L,
The second magnetized region 13t) forms a predetermined gray code pattern, and this pattern is detected by the MR element 11 of the magnetic sensor 14 arranged along the magnetic drum 2, and the electrical signal obtained thereby is used to detect the pattern. The rotational state of the motor 1 is detected.

The magnetic track 13 is first magnetized over the entire circumference of the surface by magnetizing the second magnetized region 1-3b, and then the first magnetized region 1-3b is magnetized from above.
The magnetized region 132L is magnetized. At this time.

The first magnetized region 13a has a diagonal number of magnetic poles, and the boundary portion in contact with the second magnetized region 13b is the second magnetized region 13b.
and the opposite magnetic pole. In this case, the first magnetized region 132
Although the pitches of the magnetic poles of the integer number of L are the same in FIG. 1, the pitches of the magnetic poles do not have to be the same. As shown in FIGS. 1 and 2, magnetized regions corresponding to predetermined gray codes are formed.

1st. As shown in FIG. 3, the MR element 11 facing the second magnetized regions 13a and 13b has a pattern such that the magnetic field and current of the first magnetized region 13a are orthogonal to each other in the tenth MR element 11a. The second MR element 11b has the first M
A pattern is formed so as to be orthogonal to the R element 11a. M
R element 11a.

11b are connected in series, and the connection point is the output terminal Y.
Current supply terminals E and G are formed from the other end side of the MR elements 11a and 11b. A bias magnetic field I (B) is applied by a permanent magnet or the like in the same direction as the current direction of the MR element 11a.

FIG. 4 shows the resistance change of the MR element with respect to the magnetic field. Midfielder
The t-element changes in a hanging mirror shape around the 0 magnetic field, and changes in the same way at both N and 3 poles. When a bias magnetic field 1 (B) is added to this, the resistance suddenly changes to the + side on the north pole side and to one side on the south pole side around the bias point Bi.

In FIG. 1, when the magnet moves in the direction of the arrow, the magnetic field in the MR element 111L is in the film thickness direction at the location (a), so there is no resistance change in the MR element 11a.

At location (B), the magnetic field changes in the direction of the film surface and is an S pole, so the resistance change of the MR element 111L changes negatively.

At the location ←→, since it is the N pole, the resistance of the MR element 112L changes significantly in the positive direction. Since the MR element 11a has an S pole, the resistance change is negative in the central part of the MR element 111L.
Since the a width is wide, it also covers the N pole.

Overall, this is a positive change. At location (e), since it is the north pole, the resistance of the MR element 111L changes significantly in the positive direction.

At the location (to), since it is the S pole, the resistance change of the MRg element 11a changes negatively. At location (G), the magnetic field is in the film thickness direction, so there is no resistance change in the 1MR element 111L. Furthermore, M
Since the magnetic field and current direction of the R element 11b match, the resistance does not change and is used as a temperature compensation resistor. When the resistance change is viewed as a voltage at the output terminal F, it becomes as shown in FIG. 1B. The output obtained by shaping this waveform using a comparator or the like has a rising edge that accurately corresponds to the position of the boundary, as shown in FIG. 1C. Therefore, detection errors do not occur as in the conventional case.

Further, the MR elements 111L and 11b are connected to the MR elements 11a and 11b in order to prevent the output voltage from drifting with respect to temperature.
It is preferable to form similar patterns on the same substrate at the same time.

Effects of the Invention As is clear from the above explanation, according to the present invention, by making the polarities different from each other on both sides of the boundary between the first magnetization region and the second magnetization region, the spread of magnetic flux is eliminated, and the magnetic field is The boundaries of the distribution become clear. Furthermore, by applying a bias magnetic field to the MR element, the resistance changes rapidly at the point where the polarity changes, thereby making the output voltage at the boundary steeper, which improves detection accuracy compared to conventional methods. can be significantly improved.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the relationship between a magnetic track and an MR element to explain a magnetic absolute encoder device according to an embodiment of the present invention, and Figures 1B and C are output waveforms and waveform shaping of the MR element of the present invention. FIG. 2 is a perspective view of an encoder device according to an embodiment of the present invention, FIG. 3 is an explanatory diagram of a pattern of the MR element used in the present invention, and FIG. 4 is an explanatory diagram showing the MR element used in the present invention. 5 is a perspective view of a conventional encoder device, and FIG. 6 is an explanatory diagram of a gray code recorded on a magnetic drum and a corresponding magnetic recording pattern, respectively. , FIG. 7 is a pattern explanatory diagram of a conventional MR element, FIG. 8 is a waveform diagram showing the output of a conventional MFt element, and FIG. 9 is a diagram showing the output of a conventional MFt element.
C is an explanatory diagram showing the spread of magnetic flux, the output of the MR element, and the detected output after waveform shaping in a conventional device. 11.111L, 1 l b-・---MR element,
13----Magnetic track, 131L...
First magnetized region, 13b... Second magnetized region,
14...Magnetic sensor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure <A) εFG (Japanese) (CJ Figure 2 1a Figure 4 Figure 5 Figure 6 φ) Figure 7 Figure 9 <A> (B) (CJ

Claims (3)

[Claims] (1) It has a magnetic recording medium supported by the position detection object,
Moreover, after the magnetic track of this magnetic recording medium is magnetized with one pole around the entire circumference, a repeating magnetic signal is applied to the magnetic track in a constant number so as to generate a magnetic field in a direction parallel to the moving direction of the magnetic recording medium. A magnetic absolute encoder device that records a predetermined length. (2) The magnetic absolute encoder device according to claim 1, wherein a ferromagnetic magnetoresistive element to which a bias magnetic field is applied is used as the magnetoelectric transducer disposed close to and facing the magnetic track. (3) The magnetic absolute encoder device according to claim 1, wherein the width of the magnetic recording portion having the same polarity as both ends of the first magnetized region having an odd number of repetitions is widened.