JP2546233B2 - Origin detection unit of magnetic head for magnetic encoder - Google Patents

Description

The present invention relates to an origin detection unit of a magnetic head for an incremental type magnetic encoder.

(Prior Art) A magnetic encoder is composed of a scale and a magnetic head. The scale is a plate-shaped, disk-shaped, or cylindrical magnetic recording medium with magnetic scales (N pole, S pole) magnetized, and is an incremental type. There is an absolute type. In the incremental type, the N and S poles as scales are alternately and repeatedly magnetized at equal intervals λ as shown in 1b of FIG.

The magnetic head reads the scale magnetized on the scale, and basically includes a magnetoresistive effect element (hereinafter referred to as MR element) and an electric circuit. As the MR element approaches the scale, the electrical resistance of the MR element decreases as shown in Fig. 3. When the magnetic head is moved in contact with or close to the scale, the MR When the resistance of the element changes according to the scale and the current flowing therethrough is made constant, the voltage V across the MR element changes according to the change of the resistance R from V = IR, as shown in FIG. Such a sine wave or a voltage signal similar to this (hereinafter referred to as an original signal) is obtained. However, in practice, the constant current driving method uses a constant voltage driving method because the response speed of the constant current power source is slow. In the latter case, for example, the MR element and the fixed resistor are connected in series. In any case, the number of waves of the original signal is N pole and S
Since it corresponds to the sum of the poles, if the number of waves is counted, the relative movement amount of the magnetic head and the scale or the physical amount related to this, for example, the rotation angle, can be known.

By the way, whether it is a linear encoder or a rotary encoder, the scale 1 needs the origin position detection pattern shown in (1a) in Fig. 2 for the confirmation of the absolute position when the power is turned on, in addition to the magnetic scale (1b). Then, it consists of N pole or S pole magnetized in another track with a predetermined width w. Generally, the origin position detection pattern (1a) is N of width w.
It is performed by single pole magnetization of the pole or the S pole.

Then, the magnetic head needs an origin detection unit for reading the origin position detection pattern (1a) and detecting the origin position in addition to the sensor unit for reading the magnetic scale (1b).

Conventionally, origin detection unit is arranged two MA elements M _1, M ₂ in parallel, the fifth ground terminal as shown in FIG. (GND) -M ₁ -M ₂ - power supply voltage terminal and connected to M ₁ - It is known that the output is taken from the connection part of M ₂ . When the origin position detection pattern (1a) approaches and moves away from this detector, the output changes as shown in FIG. 6 (1). From this output, the final origin signal as shown in FIG. 6 (2) is obtained by the rectangular wave conversion circuit.

Normally, in this rectangular wave conversion circuit, two threshold voltages V _SH , V
Square wave conversion is performed using _SL . Origin signal is V _SH
When it becomes higher, the square wave is set to the high level, and when the original signal becomes lower than V _{SL, the} square wave is set to the low level. V
The reason to have a difference in _SH and V _SL is, V _SH is the original the V _SL after the origin original signal is higher than V _SH and the same potential still V
_Although it is higher than _SH , it becomes lower than V _SL due to noise mixing and then becomes higher than V _SH again, so multiple origin signals are generated, so only one origin signal is obtained with a difference between V _SH and V _SL. To do so.

Since the conventional origin signal is asymmetrical as shown in FIG. 6 (1), when the origin position detection pattern shown in FIG. 5 approaches from the left side (assuming normal rotation), As shown in Fig. 6 (2) and (3), the widths P1 and P2 of the final origin signal are different from each other and the position of the origin signal becomes unclear. Waveforms near the original signal V _SH and V _SL must be symmetrical.

(Problems to be Solved by the Invention) The first problem to be solved by the present invention is that the pulse width P of the origin signal differs depending on the moving direction. Secondly, the height of the first peak (P _K1 ) of the original signal is low. If the height of the first peak (P _K1 ) is low, the amplification factor must be increased when amplifying with the amplification circuit, which lowers the maximum limit frequency at which the amplification circuit functions, and as a result, the relative scale and magnetic head If the amount of movement changes at high speed, measurement becomes impossible. This is said to have poor high-speed response.

(Means for Solving Problems) The present invention relates to an origin detection unit of a magnetic head for a magnetic encoder for reading an origin position detection pattern consisting of “N-pole or S-pole single-pole magnetization” of a magnetic scale. One block consists of n (n is a positive integer) magnetoresistive element blocks B ₁ , B ₂ , B ₃ , B ₄ in total of 4 blocks B ₁ , B ₂ ,
B ₃ and B ₄ are geometrically parallel in this order, and the block B ₁ and
The distance from B ₂ is x ₁ , the distance between B ₂ and B ₃ is x ₂ , the distance between B ₃ and B ₄ is x ₃ (when the width of the origin position detection pattern is w, When the resistance change rate of each block is represented by the same symbol as the block name, the above equation is connected so that the output is obtained as follows: B ₂ + B ₃ − (B ₁ + B ₄ ) = output The present invention provides an origin detection unit characterized by including a bridge circuit and providing a differential circuit. Hereinafter, the present invention will be specifically described with reference to examples.

(Embodiment) The origin detecting portion of this embodiment is an example of n = 1. As shown in FIG. 1, one MR element having a line width of 10 to 20 μm constitutes one block, and four blocks B ₁ to B ₄ from left B ₁ , B ₂ , B ₃ , B ₄
Geometrically arranged in this order. Space between each block x ₁ ~
x ₃ is the width of the scale origin position detection pattern (1a) w
(For example, w = 50 to 200 μm), all were set to 2 w. Incidentally, w is made equal to the interval λ of the scale (1b).

Each block is as shown in Fig. 1. As shown in the figure, aluminum (Al) is connected in series to form an annular circuit, and the first output (-) is output from the first connection (L ₁ ) of B ₁ -B ₂ .
Take out the ground terminal (GND) from the second connection part (L ₂ ) of B ₂ -B ₄ and the second output (+) from the third connection part (L ₃ ) of B ₄ -B ₃ . the fourth connection portion of the B ₃ -B ₁ from (L ₄₎ taking out the power supply voltage terminal.

To make this origin detection part, aluminum (Al) or other conductive material having a film thickness of 0.2 to 5 μm is vapor-deposited on one surface of a non-magnetic substrate, and then patterned by photolithography into the pattern shown in FIG. To form a connection pattern, and then deposit an MR element material, for example, a Ni Fe alloy or a Ni Co alloy on the entire surface to a thickness of 0.01 to 1 μm, and then pattern the pattern shown in FIG. 1 by photolithography. 4 MR elements (4 blocks B ₁ ~
B ₂ ) is formed. This completes the origin detector.

Then, the rectangular wave conversion circuit 3 is attached to the output terminal of the origin detection section through the differential amplifier circuit 2. FIG. 7 is this circuit diagram.

The origin position detection pattern (1a) is the first
When approaching from the left side of the figure and moving away from the right side, blocks
It is magnetized in the order of B ₁ → B ₂ → B ₃ → B ₄ . At this time, the resistance value of the block B ₁ is as shown in FIG. 8 (1), that of the block B ₂ is that of the block (2), that of the block B ₃ is that of the block (3), and that of the block B _{4 is} the same. It changes as shown in Fig. (4). In both cases, the change curve has two peaks, and the interval between the peaks is twice the width w2 of the origin position detection pattern (1a).

The blocks B ₁ and B ₂ are connected in series, and both ends thereof are connected to the power supply voltage terminal and the ground terminal (GND). Therefore, the block from the first connection part (L ₁ ) of B ₁ -B ₂ is connected. The potential of one output signal is output as a potential equal to the difference between the resistance change rates of B ₁ and B ₂ , and is as shown in FIG. 8 (5). Similarly, B ₃ −
Regarding B _4, the potential of the output signal from the third connection portion (L ₃ ) is as shown in FIG. 8 (6).

The voltage difference between the above-mentioned two output signals is taken and amplified by the differential amplifier circuit 2, and the output of this circuit 2 shows a change as shown in FIG. 8 (7). The first peak (P _K1 ) of this output signal has good symmetry. Therefore, when this output signal is processed by the rectangular wave conversion circuit 3, a rectangular wave origin signal as shown in FIG. 8 (8) appears at the output terminal 4 in FIG. P1 does not change even when reversing.

In addition, the height of the first peak (P _K1 ) of the original signal is doubled compared to the conventional one, so the amplification factor of the differential amplifier circuit 2 is only half that of the conventional one, so high-speed response Will get better.

In order to further reduce the second peak (P _K2 ) in the present embodiment, the width w of the origin position detection pattern (1a) is modified so that the distance between the two peaks in (1) of FIG. It should be close to 4w.

(Effect of the invention) As described above, according to the present invention, the first peak (P
_Since the symmetry of _K1 ) is good, the pulse width P does not change even if the relative movement direction of the scale and the magnetic head changes from the forward direction to the reverse direction. In addition, the height of the first peak (P _K1 ) can be doubled as compared with the conventional one, so that the amplification rate is only 1/2, and a magnetic head with good high-speed response is possible. Further, the distance between the blocks B ₁ and B ₂ is x ₁ , B ₂
When the distance between B ₃ and B ₃ is x ₂ , the distance between B ₃ and B ₄ is x _3, and the width of the origin position detection pattern of the magnetic scale is w, By arranging each block so that, the S / S of the first peak (P _K1 ) and the second peak (P _K2 )
A large N ratio can be obtained, and a magnetic head that is not easily affected by noise can be obtained.

[Brief description of drawings]

FIG. 1 is a composite view of a schematic plane pattern of an origin detection unit according to an embodiment of the present invention and an origin position detection pattern (1a) of a magnetic scale. FIG. 2 is a conceptual diagram of a magnetic scale. FIG. 3 is a graph showing the rate of change of electric resistance of the magnetoresistive effect element with respect to the magnetic field. FIG. 4 is a voltage waveform diagram. FIG. 5 is a composite view of a schematic plane pattern of a conventional origin detection unit and an origin position detection pattern (1a) of a magnetic scale. FIG. 6 is a waveform diagram (1) of an output signal from a conventional origin detector and waveform diagrams (2) and (3) of an origin signal obtained by converting the output signal into a rectangular wave. FIG. 7 is a circuit diagram according to the embodiment of the present invention. FIG. 8 is various signal waveform diagrams for explaining the origin signal obtained in the embodiment of the present invention. [Explanation of symbols of main part] 1a …… Origin position detection pattern 1b …… Magnetic scale 1 …… Magnetic scale 2 …… Differential amplifier circuit 3 …… Square wave amplifier circuit 4 …… Origin signal output terminal L ₁ …… 1st connection part, L ₂ ...... 2nd connection part L ₃ ...... 3rd connection part, L ₄ ...... 4th connection part V _SH ...... High level voltage V _SL ...... Low level voltage B ₁ ~ B ₄ …… Magnetoresistive element block

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Ushizu 1-6-3 Nishioi, Shinagawa-ku, Tokyo Nihon Kogaku Kogyo Co., Ltd. (56) Reference JP-A-60-244813 (JP, A) JP-A-59-166812 (JP, A) JP-A-62-180216 (JP, A) JP-A-60-218025 (JP, A)

Claims (1)

(57) [Claims] 1. An origin detection unit of a magnetic head for a magnetic encoder for reading an origin position detection pattern consisting of "N-pole or S-pole single-pole magnetization" of a magnetic scale, wherein one block has n lines. A total of four blocks B ₁ , B ₂ , B ₃ and B ₄ (n is a positive integer) composed of magnetoresistive elements are B ₁ ,
Geometrically parallel in the order of B ₂ , B ₃ , B ₄ , and the block
The distance between B ₁ and B ₂ is x ₁ , the distance between B ₂ and B ₃ is x ₂ , the distance between B ₃ and B ₄ is x ₃ (when the width of the origin position detection pattern is w) , When the resistance change rate of each block is represented by the same symbol as the block name, the above equation is connected so that the following output can be obtained: B ₂ + B ₃ − (B ₁ + B ₄ ) = output The origin detection section is characterized by including a bridge circuit and a differential circuit.