JP2546281B2 - Origin detection part 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 disposed the two MR 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 obtained 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). This output is used by the rectangular wave conversion circuit to obtain the final origin signal as shown in FIG. 6 (2).

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), the origin position detection pattern shown in FIG. 5 approaches from the left side (assuming forward rotation) and the right side. When approaching from one side (during reverse rotation), the widths P1 and P2 of the final origin signal are different from each other, as shown in FIGS. 6 (2) and (3), and the position of the origin signal becomes unclear. Waveforms near the origin 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) In the present invention, one block is composed of n (n is a positive integer) magnetoresistive element blocks B ₁ , B ₂ , B ₃ , B ₄ in total. Are arranged geometrically in parallel in the order of B ₁ , B ₂ , B ₃ , and B ₄ , and one end of the block B ₁ and one end of B ₃ are connected to each other to form a first connection portion. The other end of ₃ and one end of B ₂ are connected to form a second connection part, the other end of block B ₂ and one end of B ₄ are connected to form a third connection part, and a second connection part of block B ₄ is formed. The other end and the other end of B ₁ are connected to form a fourth connection part, a power supply voltage is applied between the second connection part and the fourth connection part, and a first output signal is output from the first connection part. And a circuit for taking the second output signal from the third wire connection portion and for taking the sum of the first output signal and the second output signal, the origin detecting portion of the magnetic head for a magnetic encoder. provide.

That is, in the present invention, the block is Connection to form a cyclic circuit in series as, B ₁ first wire connecting portion connecting portion of -B _3, B ₃ second wire connecting portions to connecting portions of -B _2, B ₂ -B ₄
When the connection part of B is called the third connection part and the connection part of B ₄ -B ₁ is called the fourth connection part, the first output signal is taken from the first connection part
A power supply voltage terminal is taken from one of the wire connection portion and the fourth wire connection portion, a ground terminal is taken from the other wire connection portion, and a second output signal is taken from the third wire connection portion.

The distance between the blocks B ₁ and B ₂ is x ₁ , and the distance between B ₂ and B ₃ is
When the distance between x ₂ and B ₃ and B ₄ is x ₃ and the width of the origin position detection pattern of the magnetic scale is w, x ₁ is x ₂ is x ₃ is It is preferred that

 Hereinafter, the present invention will be specifically described with reference to examples.

(Example) The origin detecting section of this example 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 are provided. _{1 to} B ₄ from the left B ₁ , B ₂ , B ₃ , B
They were arranged in geometrical parallel in the order of ₄ . Space between each block x ₁
˜x ₃ are all set to 2w when the width of the scale origin position detection pattern (1a) is w (for example, w = 50 to 200 μm). 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, the first output is taken from the first connection part (L ₁ ) of B ₁ -B ₃ , and the second connection part of B ₃ -B ₂ ( Take the power supply voltage terminal from L ₂ ), take out the 2nd output from the 3rd connection part (L ₃ ) of B ₂ -B ₄ and take the ground terminal (GND) from the 4th connection part (L ₄ ) of B ₄ -B ₁ . )I take the.

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 MR element material such as Ni Fe alloy or Ni Co alloy is vapor-deposited on the entire surface to a thickness of 0.01 to 1 μm, and then patterned into a 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 two output terminals of the origin detection unit through the 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 w of the origin position detection pattern (1a).

The blocks B ₃ and B ₁ 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 ₃ can be connected. The potential of one output signal is output as a potential equal to the difference between the resistance change rates of B ₃ and B ₁ , and is as shown in FIG. 8 (5). Similarly, B ₂ −
The potential of the output signal from the third connection portion (L ₃ ) of B ₄ is as shown in FIG. 8 (6).

The above two output signals are added together, and the sum is amplified by the 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.

Further, compared to the conventional one, the height of the first peak (P _K1 ) of the original signal is doubled, so that the amplification factor of the amplifier circuit 2 is half that of the conventional one, resulting in good high-speed response. Become.

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.

[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 …… Amplifier circuit 3 …… Square wave amplifier circuit 4 …… Origin signal output terminals B _{1 to} B ₄ … … Block of magnetoresistive element 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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (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 (2)

(57) [Claims] 1. An origin detecting portion of a magnetic head for a magnetic encoder for reading an origin position detecting pattern having N or S magnetic poles provided on a magnetic scale, wherein one block has n blocks (n: A total of four blocks B ₁ , B ₂ , B ₃ , B ₄ consisting of magnetoresistive elements of positive integer) are geometrically arranged on a non-magnetic substrate in the order of B ₁ , B ₂ , B ₃ , B _4. Are arranged in parallel with each other, and one end of the block B ₁ is connected to one end of B ₃ to connect the first
Forming a connection portion, connecting the other end of the block B ₃ and one end of B ₂ to form a second connection portion, connecting the other end of the block B ₂ and one end of B ₄ to a third connection portion To form the other end of block B ₄
The other end of B ₁ is connected to form a fourth connection part, a power supply voltage is applied between the second connection part and the fourth connection part, and a first output signal is taken from the first connection part, An origin detector of a magnetic head for a magnetic encoder, comprising a circuit for taking a second output signal from a third connection portion and taking a sum of the first output signal and the second output signal. _2. The interval between the blocks B ₁ and B ₂ is x ₁ , B ₂ and B ₃
The distance between the distance between x _2, B ₃ and B ₄ and x _3, the width of the origin position detection pattern of the magnetic scale when the w, x ₁ is x ₂ is x ₃ is The origin detection unit according to claim 1, wherein