JP4775705B2 - Magnetic absolute encoder - Google Patents

Description

The present invention relates to a magnetic absolute encoder using a magnetoresistive effect type magnetic sensor.

The present invention relates to a magnetic absolute encoder that detects the absolute rotation position of a rotating body such as a servo motor used in an industrial machine or the like and the absolute position of a linear moving body.

A magnetoresistive effect type magnetic sensor (hereinafter, referred to as a magnetoresistive effect type magnetic sensor) is opposed to a magnetic medium magnetized according to an m-sequence pattern or the like in each pitch region of 2 ⁿ pitch regions (n = positive integer) formed at an equal pitch. Called a magnetic sensor). The magnetic medium and the magnetic sensor move relatively.
In a magnetic medium magnetized with an m-sequence pattern or the like, a magnetized pitch area and a non-magnetized pitch area are mixedly arranged. By detecting the leakage magnetic field in the magnetized pitch region and performing the encoding process with the magnetic sensor, the arrangement of the magnetized pitch region and the non-magnetized pitch region can be made to correspond to the encoded signals “1” and “0”. it can. When a plurality of magnetic sensor elements are arranged at a pitch corresponding to the magnetization pitch region and the non-magnetization pitch region, each magnetic sensor element simultaneously detects a leakage magnetic field in the magnetization pitch region and performs an encoding process. The signals “1” and “0” are detected. By determining the signal arrangement, the absolute position on the magnetic medium can be detected.

However, at present, an optical absolute encoder as shown in Patent Document 1 is mainly used as an encoder for absolute position detection. The reason why it is mainly used is that the optical encoder can easily produce a pattern such as an m series. Since the part of the light-shielding medium with holes is the translucent part, it is easy to produce a scale with holes in the m series pattern, and the output difference between the light-receiving part and the light-transmitting part is large. This is because high signal accuracy can be easily obtained. However, since the arrangement of the light receivers is limited, the pitch of the optical encoder that is mainly used is several hundred μm or more.

JP-A-4-40321

It has been pointed out that optical absolute encoders are vulnerable to dirt and oil mist and other contaminants, and that the detection accuracy is less stable against changes in the operating environment temperature. In order to prevent contamination, casings with high sealing performance and high airtightness are used for optical absolute encoders. However, when the airtightness is increased, it becomes difficult to follow changes in the environmental temperature, and it becomes difficult to realize a small size and a low price. There is a growing demand for magnetic absolute encoders that are relatively resistant to adhering dirt such as dust and oil mist and that are highly stable against changes in the operating environment temperature. The pitch of the magnetic absolute encoder can be easily obtained at 100 μm or less, but the problem is that the detection accuracy is low.

In order to increase the detection accuracy of a magnetic absolute encoder, a magnetic medium magnetization method has been studied. Patent Document 2 discloses that the medium surface is magnetized so as to have a single pole in the pitch region. Since the number of pitches where the N pole or S pole continues varies depending on the location, the leakage magnetic field strength varies depending on each pitch region. Further, since the magnetic field is magnetized in the entire pitch region, the magnetic field distribution is distorted due to interference with the adjacent non-magnetized pitch region, and a significant improvement in detection accuracy cannot be expected. Patent Document 3 discloses a measure for reducing the interference between the magnetization pitch region and the non-magnetization pitch region. A signal magnetized area is provided only in a part of the central part of the magnetized pitch area, and the other part of the magnetized pitch area is not magnetized to reduce interference with the adjacent magnetized pitch area. . However, in order to prevent the leakage magnetic field from the signal magnetization region provided in a part of the magnetization pitch region from interfering with the adjacent non-magnetization pitch region, it is necessary to reduce the magnetic field strength of the signal magnetization region. is there. In order to reduce the magnetic field strength, it is necessary to reduce the signal magnetization region in the magnetization pitch region or lower the magnetization strength. If the leakage magnetic field strength is lowered, the output of the magnetic sensor is lowered, and a significant improvement in detection accuracy cannot be expected. In order to increase the output of the magnetic sensor, it is conceivable that the gap between the magnetic sensor and the magnetic medium is close, but if the gap is made small, there is a high risk of damaging the magnetic medium or the magnetic sensor by enclosing fine dust. Become.

JP, 2000-352523, A FIG. 2, FIG. Japanese Patent Laid-Open No. 02-201118 FIG.

When the width of the signal magnetization area of the magnetization pitch area is reduced with reference to Patent Document 3 in FIG.
The magnetization pattern is shown. In this method, the signal magnetization regions of all the magnetization pitch regions are magnetized in the same magnetic field direction. In this magnetization method, a signal output from the magnetic sensor can be obtained in each magnetization pitch region. However, as shown in FIG. 7c), the magnetic sensor output in the portion where the magnetization pitch region continues is small, and the non-magnetization pitch region. The magnetic sensor output in the adjacent magnetized pitch region becomes larger. Further, in the non-magnetized pitch region that continues for one or more, an unnecessary magnetic field is generated due to the influence of the magnetized pitch regions on both sides. When the magnetic sensor detects an unnecessary magnetic field, there is a problem that the read encoding pattern in FIG. 7d) differs from the write encoding pattern in FIG. 7a). These are considered because the continuous magnetization pitch region apparently works as one magnet (magnetization pattern).

As a measure for eliminating the unnecessary magnetic field generated in the continuous non-magnetized region as shown in FIG. 7c), there is a method of reversing the magnetic field direction in the discontinuous portion of the magnetized pitch region as shown in FIG. 8b). . Although an unnecessary magnetic field generated in the non-magnetized pitch region is reduced, when a large number of the magnetized pitch regions continue, it acts as one magnet, and thus a reversed magnetic field is generated in the adjacent non-magnetized pitch region. The reversal magnetic field is detected by the magnetic sensor, and the readout coding pattern of FIG.
There may be a problem that the writing code pattern of a) is different.

As a measure for solving the problem described with reference to FIGS. 7 and 8, a method of magnetizing the magnetic field directions of the signal magnetization regions in all adjacent magnetization pattern regions as shown in FIG. 9 is reversed. Devised. The magnetic field in the signal magnetization region of each magnetization pitch region forms a closed magnetic field in the signal magnetization region. Therefore, since the continuous magnetization pitch region does not become one large magnet as shown in FIGS. 7 and 8, the unnecessary magnetic field and the reversal magnetic field appearing in the non-magnetization pitch region can be greatly reduced. FIG. 9d) The read code pattern of FIG. 9 and the write code pattern of FIG. 9a) are the same, and high signal accuracy was obtained.

However, even with a method of magnetizing the magnetic field directions of the signal magnetization regions in all adjacent magnetization pattern regions to be reversed, high signal accuracy may not be obtained depending on the code pattern of writing. In particular, a decrease in signal accuracy was observed when a large number of magnetized pattern areas continued. As an example, FIG. 10 shows a state in which six magnetization pitch regions are continuous. FIG. 10a) shows the write code pattern, FIG. 10b) shows the magnetized pattern, FIG. 10c) shows the magnetic sensor output, FIG. 10d) shows the encoded signal waveform, and FIG. 10e) shows the read code pattern. As shown in FIG. 10c), the leakage magnetic field from the signal magnetization region in the magnetization pitch region adjacent to the non-magnetization pitch region becomes distorted. When the leakage magnetic field becomes distorted, the pulse width of the signal waveform after the encoding process is widened as shown in FIG. 10D), and there is a risk of erroneous detection in the next clock region. Depending on the degree of distortion of the magnetic sensor output waveform, the clock pulse width, etc., as shown in FIG. 10e), unlike the original code pattern of 01111110, an incorrect code pattern of 11111111 is a very low occurrence frequency. Had occurred. In FIG.
Although an example of six continuous magnetization pitch regions has been shown, the same problem occurs in one or more consecutive magnetization pitch regions depending on the ratio between the length of the magnetization pitch region and the length of the signal magnetization region. It is possible to do.

The present invention has been made in order to solve the above-described problems, and it is possible to individually extract a signal magnetization region in a continuous magnetization pitch region as a signal, and to magnetize adjacent to the non-magnetization pitch region. An object of the present invention is to provide a magnetic absolute encoder capable of preventing the magnetic field distribution in the pitch region from becoming distorted and obtaining high signal accuracy.

A magnetic absolute encoder according to the present invention is a magnetic absolute encoder having a magnetic medium having a randomly magnetized absolute pattern and a magnetoresistive effect type magnetic sensor that moves relative to each other in the moving direction. The arranged absolute pattern is composed of at least one non-magnetized pitch area that is continuous with at least one continuous magnetized pitch area and the same pitch area width. The magnetized pitch area is pinned to the signal magnetized area. There is a magnetized area, the pinned magnetized areas are arranged on both sides adjacent to the signal magnetized area, and the magnetization directions of the adjacent signal magnetized areas are opposite to each other. It is preferable that the magnetization direction of the pinned magnetization region adjacent to the signal magnetization region is opposite to the magnetization direction.

By performing pinning magnetization in the opposite direction to the magnetization direction of the signal magnetization region on both sides of the signal magnetization region, both sides of the signal magnetization region are compared to the non-magnetized state. The magnetic field distribution in the signal magnetization region can be made steep. In particular, it is possible to prevent the bottom of the magnetic field distribution from spreading. When the magnetized pitch area and the non-magnetized pitch area are adjacent to each other, the magnetic field distribution in the signal magnetized area is affected by the non-magnetized pitch area, and the bottom of the magnetic field distribution is pulled toward the non-magnetized pitch area. The distribution is uneven. This distorted magnetic field distribution can be converted into an electric signal by a magnetoresistive effect type magnetic sensor. When the analog output of the magnetic sensor is digitally encoded, the pulse width is widened by the irregular portion and the next clock region is applied, giving an erroneous detection result. By performing pinning magnetization, it is possible to prevent the magnetic field distribution in the signal magnetization region from becoming distorted.

Since pinning magnetization is to prevent the magnetic field distribution in the signal magnetization region from becoming distorted, no signal should be generated in the pinning magnetization region. When the magnetic sensor detects the magnetic field in the pinned magnetization region, the detected signal becomes noise relative to the signal obtained from the signal magnetization region. For this reason, the magnetic field intensity in the pinned magnetized region needs to be small enough not to be detected by the magnetic sensor and so large that the magnetic field distribution in the signal magnetized region is not distorted.

The magnetization direction of the pinned magnetization region needs to be opposite to the magnetization direction of the adjacent signal magnetization region. When magnetization is performed in the same direction, it is not only possible to prevent the magnetic field distribution in the signal magnetization region from becoming distorted, but also the base of the magnetic field distribution in the signal magnetization region is further expanded. Of course, the pinned magnetization regions are also adjacent to each other, but in this case, it is important that the magnetization directions are different. For example, when a pattern of a non-magnetized pitch region, three magnetized pitch regions, and a non-magnetized pitch region is used and the magnetization direction is indicated by an arrow, the magnetized portion and the magnetization direction are as follows. Non-magnetized area, pinned magnetized area →, signal magnetized area ←, pinned magnetized area →, pinned magnetized area ←, signal magnetized area →, pinned magnetized area ←, pinned and magnetized Magnetic region → Signal magnetization region ←, Pinned magnetization region → Non-magnetization region. As can be seen from this, adjacent signal magnetization regions are magnetized in the opposite direction of → ← →, and adjacent pinned magnetization regions and signal magnetization regions,
The pinned magnetized regions are also magnetized in the opposite directions. By magnetizing in this way, it is possible to individually extract signal magnetization regions in a continuous magnetization pitch region as signals. Further, it is possible to prevent the magnetic field distribution in the signal magnetization region adjacent to the non-magnetization pitch region from becoming distorted.

It is preferable that the signal magnetization region and the pinning magnetization region in the magnetization pitch region have the following relationship. The center of the magnetization pitch area width (corresponding to the length of the magnetization pitch area in the moving direction) and the center of the signal magnetization area width (corresponding to the length of the signal magnetizing area in the movement direction) coincide with each other, and the magnetization pitch The two pinned magnetization widths adjacent to the region (corresponding to the length of the pinned magnetization region in the moving direction) are preferably the same. By making the two pinning magnetization widths the same, it becomes easy to obtain the left-right symmetry of the magnetic field distribution in the signal magnetization region. It is possible to shift the center of the signal magnetization pitch width in the left or right direction with respect to the center of the magnetization pitch area width, but the left and right pinned magnetization widths are different, so the magnetic field distribution in the signal magnetization area There is a possibility that the left-right symmetry of will deteriorate.

The clock signal is obtained by performing the increment pattern magnetization in parallel with the absolute pattern arranged in the moving direction, and converting the leakage magnetic field from the magnetization pattern into the clock signal by the increment magnetic sensor. Since the absolute pattern and the increment pattern are integrally drawn on the magnetic medium and are detected by the integrated absolute and increment magnetic sensors, there is no time error between the absolute signal and the increment signal. Therefore, it can be used even in a situation where the relative movement speed of the magnetic medium and the magnetic sensor changes. However, in order to obtain the increment signal, it is necessary to enlarge the magnetic medium and the magnetic sensor. Although there is a restriction that it can be adopted only when the relative moving speed of the magnetic medium and the magnetic sensor is constant, the clock signal can also be generated by an electric circuit. By using an electric circuit, there is an advantage that the size of the magnetic medium and the magnetic sensor can be reduced.

Magnetic media include, for example, a magnetic drum in which a hard magnetic material is added to a non-magnetic substrate and a hard ferrite powder is applied to an aluminum drum, and a magnetic scale in which hard ferrite powder is applied to a resin tape or a non-magnetic metal. Alternatively, it is possible to use a permanent magnet itself that does not use a non-magnetic substrate, or a material obtained by kneading and molding a magnetic powder in plastic or rubber.

A magnetic absolute encoder of the present invention is a magnetic absolute encoder having a magnetoresistive effect type magnetic sensor that moves relative to a magnetic medium having a randomly magnetized absolute pattern and moves in a moving direction. The arranged absolute pattern is composed of at least one non-magnetized pitch area that is continuous with at least one continuous magnetized pitch area and the same pitch area width. The magnetized pitch area is pinned to the signal magnetized area. It has a magnetized region, the pinned magnetized region is arranged on both sides adjacent to the signal magnetized region, the magnetization directions of the adjacent signal magnetized regions are opposite to each other, and the non-magnetized pitch region The pinned magnetization area on at least the non-magnetized pitch area side of the adjacent magnetization pitch area is magnetized, and the magnetization direction of the signal magnetization area and the signal It is preferred magnetization direction of the pinned magnetization region adjacent to the magnetized zone are opposite.

The pinned magnetization region can be on both sides of the signal magnetization region in the magnetization pitch region adjacent to the non-magnetization pitch region, or only on the non-magnetization pitch region side. At least the non-magnetized pitch area side of the non-magnetized pitch area adjacent to the non-magnetized pitch area is pinned and the magnetic field distribution in the signal magnetized area becomes distorted. Can be prevented. In addition to the non-magnetized pitch region side of the signal magnetized region of the magnetized pitch region adjacent to the non-magnetized pitch region, it is possible to freely determine the number of pinned magnetizations.

Magnetization is preferably carried out by continuously moving the magnetic head facing the demagnetized magnetic medium and changing the strength and direction of the current flowing through the coil of the magnetic head to continuously perform signal magnetization and pinning magnetization. . When changing the current value, it may take time until the current reaches a predetermined value due to a transient phenomenon. Therefore, signal magnetization with a large current value required for magnetization and pinning magnetization with a small current value should be performed separately, for example, pinning magnetization is performed after signal magnetization is performed. You can also. A magnetizing method can be appropriately selected by those skilled in the art in consideration of a magnetizing device, a magnetizing pattern, and the like.

In the magnetic absolute encoder of the present invention, the ratio b / a of the moving direction length a of the magnetization region for signals in the magnetization pitch region to the moving direction length b of the pinned magnetization region is 1/100 or more and 2/3.
The following is preferable.

As described above, the magnetic field strength of the pinned magnetization region needs to be small enough not to be detected by the magnetic sensor and so large that the magnetic field distribution in the signal magnetization region is not distorted. One method of reducing the magnetic field strength of the pinned magnetization region is to reduce the pinned magnetization region width (corresponding to the length of the pinned magnetization region in the moving direction).
When the movement direction length b of the pinned magnetization region is 2/3 or more of the movement direction length a of the signal magnetization region, the magnetic sensor detects a leakage magnetic field in the pinned magnetization region, and an erroneous detection result May give.
In addition, the effect obtained by pinning magnetization is that the distribution of the leakage magnetic field from the signal magnetization region of the magnetization pitch region adjacent to the non-magnetization pitch region is such that the leakage magnetic field distribution is not pulled toward the non-magnetization pitch region. If the length b of the pinned magnetized region is too small, a sufficient effect cannot be obtained. Therefore, the length b of the pinned magnetized region is preferably 1/100 or more of the length a of the signal magnetized region. When the length b of the pinned magnetization region is increased, the magnetic field strength leaked from the signal magnetization region is reduced. Therefore, the length b of the pinned magnetization region is b / a. It is preferable to set = 2/3 as the upper limit.

A magnetic absolute encoder according to the present invention is a magnetic absolute encoder having a magnetic medium having a randomly magnetized absolute pattern and a magnetoresistive effect type magnetic sensor that moves relative to each other in the moving direction. The arranged absolute pattern is composed of at least one non-magnetized pitch area that is continuous with at least one continuous magnetized pitch area and the same pitch area width. The magnetized pitch area is pinned to the signal magnetized area. It has a magnetized region and a non-magnetized region, and the pinned magnetized region is arranged on both sides adjacent to the signal magnetized region, and has a non-magnetized region adjacent to the pinned magnetized region. The magnetization directions of the matching signal magnetization areas are opposite to each other, and the magnetization directions of the signal magnetization areas and the pinned magnetization areas adjacent to the signal magnetization areas are opposite to each other. It is preferable that.

It is preferable that the signal magnetized region, the pinned magnetized region, and the non-magnetized region in the magnetized pitch region have the following relationship. The center of the magnetization pitch area width and the center of the signal magnetization area width are the same, and the two pinned magnetization widths adjacent to the magnetization pitch area and the non-magnetization area width adjacent to the pinned magnetization area are The same is preferred. By making the two pinning magnetization widths and the non-magnetization area widths the same, it becomes easy to obtain left-right symmetry of the magnetic field distribution in the signal magnetization area. The pinned magnetization width and the non-magnetized area width need not be the same width.

A magnetic absolute encoder according to the present invention is a magnetic absolute encoder having a magnetic medium having a randomly magnetized absolute pattern and a magnetoresistive effect type magnetic sensor that moves relative to each other in the moving direction. The arranged absolute pattern is composed of at least one non-magnetized pitch area that is continuous with at least one continuous magnetized pitch area and the same pitch area width. The magnetized pitch area is pinned to the signal magnetized area. It has a magnetized region and a non-magnetized region, the pinned magnetized region is arranged on both sides adjacent to the signal magnetized region, has a non-magnetized region adjacent to the pinned magnetized region, The magnetization directions of adjacent signal magnetization areas are opposite to each other, and pinning is performed at least on the non-magnetization pitch area side of the magnetization pitch area adjacent to the non-magnetization pitch area. Magnetized area is magnetized, it is preferable magnetization direction of the pinned magnetization region adjacent to the magnetized areas for magnetizing direction and signal of the signal magnetic areas are opposite.

In the magnetic absolute encoder of the present invention, the movement direction length a of the signal magnetization region in the magnetization pitch region, the movement direction length b of the pinned magnetization region, and the movement direction length c of the non-magnetization region are: (
It is preferable that b + c) / a is 1/100 or more and 2/3 or less, and b / c is 1 or more and 5 or less.

The effect obtained by pinning magnetization is a distorted distribution in which the leakage magnetic field distribution from the signal magnetization region of the magnetization pitch region adjacent to the non-magnetization pitch region is pulled to the non-magnetization pitch region side. If the length b of the pinned magnetized region and the length c of the non-magnetized region are too small, a sufficient effect cannot be obtained. Therefore, the total length of the length b of the pinned magnetized region and the length c of the non-magnetized region is preferably 1/100 or more of the length a of the signal magnetized region. When the total length of the length b of the pinned magnetization region and the length c of the non-magnetized region is increased, the strength of the magnetic field leaking from the signal magnetized region is reduced. The total length c of the magnetized regions is preferably set to (b + c) / a = 1, which is the same as the length a of the signal magnetized region.

The ratio of the moving direction length b of the pinned magnetized region to the moving direction length c of the non-magnetized region is b / c =
It is preferable that it is 1 or more and 5 or less. This is because if b / c is less than 1, the length b of the pinned magnetized region becomes too small and the pinning effect is reduced. Movement direction length c of non-magnetized region
Is zero, the previously described magnetization pitch region is composed of a signal magnetization region and a pinned magnetization region. The non-magnetized region can be reduced to such an extent that the non-magnetized region is not apparently magnetized by the magnetic field of the pinned magnetized region. From the experimental results, if b / c is 5 or less, a non-magnetized region can be secured.

When the magnetic absolute encoder of the present invention is mounted, the magnetic field strength from the magnetic medium applied to the magnetic sensing portion of the magnetoresistive effect type magnetic sensor when the magnetic absolute encoder is mounted is the same as the magnetic field strength f in the signal magnetization region and the pinned attachment. It is the magnetic field strength g in the magnetic region, and the magnetic field strength ratio g / f is preferably ½ or less.

In addition to the method of changing the magnetic field intensity by changing the width of the pinned magnetization region, a method of changing the magnetization current value can also be adopted. By changing the magnetization current value, it is possible to increase the width of the pinning region. When the pinned magnetized region is magnetized with a small magnetizing current, the generated magnetic field also becomes weak and cannot be detected by the magnetism sensitive part of the magnetic sensor, so there is no noise.

If the magnetic field strength g in the pinned magnetization region is ½ or less of the magnetic field strength f in the signal magnetization region, the output waveform generated by the magnetic sensor in the pinned magnetization region is the signal magnetization. It is sufficiently smaller than the output waveform generated in the region. If digital encoding processing is performed in comparison with an encoded comparison voltage that is larger than the output waveform in the pinned magnetization region and smaller than the output waveform in the signal magnetization region, a desired encoded signal can be obtained. it can. If the magnetic field strength g in the pinned magnetization region is too large, not only is it difficult to set the encoding comparison voltage, but the risk of erroneous detection increases.

The magnetization directions of adjacent signal magnetization regions are opposite to each other, and the pinned magnetization region is magnetized in the opposite direction adjacent to the magnetization direction of the signal magnetization region and the signal magnetization region. Is provided. By providing a pinned magnetized region, the signal magnetized regions in the continuous magnetized pitch region can be taken out individually as signals, and the magnetic field distribution in the magnetized pitch region adjacent to the non-magnetized pitch region is distorted. Thus, a magnetic absolute encoder capable of obtaining high signal accuracy was obtained.

Hereinafter, the present invention will be described in detail based on examples with reference to the drawings. In order to make the explanation easy to understand, the same reference numerals are used for the same parts and parts.

FIG. 1 shows a magnetized pitch region and a non-magnetized pitch region magnetized on a magnetic medium.
Magnetization is 512 pulses (total number of magnetized pitch area and non-magnetized pitch area) in the outer circumferential direction of a magnetic drum having a diameter of 65.2 mm. The length was 400 μm. Magnetization is performed by bringing a ring-type magnetic head into contact with a magnetic drum and passing a current in a predetermined direction according to the relative movement distance to the coil of the ring-type magnetic head so that the signal magnetized region and the pinned magnetized region are continuously magnetized. Magnetized. FIG. 1 shows a part of a magnetic medium, and a magnetization pitch region 1 is symmetrical to a signal magnetization region 3 and a pinned magnetization region with a center line of the moving direction length of the magnetization pitch region 1 in between. 4 was magnetized. The length of the signal magnetized region 3 was 200 μm, and the length of the pinned magnetized region 4 was 100 μm. The ratio b / a = 0.5 of the length b of the pinned magnetization region 4 and the length a of the signal magnetization region 3 is 0.5. Reference numeral 5 denotes a non-magnetized region.

FIG. 2 shows output voltages and encoded signal waveforms in six consecutive magnetization pitch regions.
Before the detailed description of FIG. 2, the magnetic medium and the magnetic sensor will be described with reference to FIG.
A magnetic sensor 20 is arranged facing the rotating magnetic medium 10 (in this embodiment, a magnetic drum) with a predetermined interval. In this embodiment, the distance between the magnetic medium 10 and the magnetoresistive sensor element 22 of the magnetic sensor is 250 μm. The magnetic medium 10 has a signal region 11 in which a magnetization pitch region and a non-magnetization pitch region are mixed in the circumferential direction, and a comparison region 12 in the circumferential direction. The magnetic sensor 20 includes a plurality of magnetic sensor elements 21, and the magnetic sensor element 21 includes a magnetoresistive element 22 whose resistance is changed by a magnetic field, and a resistance when no magnetic field is applied to the magnetoresistive element 22. Comparative resistance element 2 having a resistance value equivalent to the value
3 are connected in series. The other end of the comparison resistance element 23 is connected to the ground, and the other end of the magnetoresistive element 22 is connected to the power supply voltage Vcc. A midpoint potential is taken from the connection point 24 between the magnetoresistive effect element 22 and the comparative resistance element 23, and this voltage becomes the output voltage of the magnetic sensor 20. The magnetoresistive effect element 22 faces the signal region 11 of the magnetic medium, and the comparative resistance element 23 faces the comparison region 12. The magnetoresistive effect element 22 and the comparative resistance element 23 are permalloy (Ni-F) having the same composition.
e alloy). Since no magnetic field is applied to the comparison resistance element 23, the resistance is constant, and it acts as a comparison resistance for the magnetoresistance effect element 22. When the magnetoresistive element 22 detects a leakage magnetic field from the signal area 11 of the magnetic medium 10, the resistance changes and the intermediate potential changes. This change in intermediate potential is detected as a relative position signal between the magnetic medium and the magnetic sensor.

The output voltage and encoded signal waveform of the magnetic sensor when the pinned magnetized region 4 is formed will be described with reference to FIG. For comparison, the result of a magnetic medium in which a non-magnetized region is not used without pinning is also shown.
As shown in FIG. 2a), in the magnetic sensor output voltage waveform without pinning magnetization, the output voltage waveform in the magnetization pitch region adjacent to the non-magnetization pitch region is spread toward the non-magnetization pitch region. The output voltage waveform of the magnetic sensor with pinned magnetization does not spread to the non-magnetized pitch area side, but is output in all the magnetized pitch areas. The width of the magnetic sensor output voltage waveform is almost the same. FIG. 2b) shows a waveform obtained by converting an output voltage waveform without pinning magnetization into an encoded signal. The signal width of the magnetized pitch region in contact with the non-magnetized region is increased. FIG. 2c) shows an encoded signal waveform with pinned magnetization.
All signal widths were substantially the same, and no signal was applied to the non-magnetized region. By providing a pinned magnetized area, a reliable absolute signal was obtained.

A second embodiment of the present invention will be described with reference to FIG.
The second embodiment is the same as the first embodiment in the length of the signal magnetized region 3 and the pinned magnetized region 4, but the pinned magnetized region has a non-magnetized pitch region. The difference is that it is limited to the adjacent magnetized pitch region. Although the output voltage waveform of the magnetic sensor and the encoded signal waveform are not shown, the same result as in the first embodiment can be obtained even if the pinned magnetization region is provided only in the magnetization pitch region in contact with the non-magnetization pitch region. It was. The same result was obtained even when the pinned magnetization region of the magnetization pitch region in contact with the non-magnetization pitch region was only the non-magnetization pitch region side. A region where no pinning magnetization is performed is a non-magnetized region 6 which is not magnetized.

A third embodiment of the present invention will be described with reference to FIG.
The signal magnetization region 3, the pinned magnetization region 4, and the non-magnetization region 7 are formed symmetrically across the center line of the moving direction length of the magnetization pitch region 1. The length of the signal magnetized region 3 is 40 μm, the length of the pinned magnetized region 4 is 6 μm, and the length of the non-magnetized region 7 is 4 μm. The sum of the length b of the pinned magnetized region 4 and the length c of the non-magnetized region 7 (b + c) = 10 μm. Length a of the signal magnetization region 3
(B + c) / a = 1/4. The ratio of the length b of the pinned magnetized region 4 to the length c of the non-magnetized region 7 is b / c = 1.5. The magnetic medium of Example 3 used a magnetic scale instead of a magnetic drum.

Even if the non-magnetized region 7 is provided at both ends of the magnetized pitch region 1, the pinned magnetized region 4 is provided at both ends of the signal magnetized region 3, so that the output voltage waveform and the encoded signal waveform of the magnetic sensor are provided. Although an illustration of is omitted, a reliable absolute signal was obtained.

A fourth embodiment of the present invention will be described with reference to FIG. The fourth embodiment is the same as the third embodiment in that the signal magnetized region 3 and the pinned magnetized region 4 have the same length as the non-magnetized region 7, but the pinned magnetized region 4 has the same length. And the non-magnetized region 7 is limited to the magnetized pitch region 1 adjacent to the non-magnetized pitch region 2. Although illustration of the output voltage waveform and the encoded signal waveform of the magnetic sensor is omitted, even if the pinned magnetization region and the non-magnetization region are provided only in the magnetization pitch region in contact with the non-magnetization pitch region, The same result was obtained. The same result was obtained even when the pinned magnetization region of the magnetization pitch region in contact with the non-magnetization pitch region was only the non-magnetization pitch region side.

In the magnetization pitch region of Example 1, magnetization is performed by changing the ratio b / a of the length a of the signal magnetization region 3 and the length b of the pinned magnetization region 4 to obtain an accurate absolute signal. The ratio of b / a obtained was examined. b / a was changed from 1/200 to 1, and it was determined whether or not an error occurred in the absolute signal. For 10,000 revolutions of the magnetic drum, that is, 512 pulses × 10,000 times = 512
It was assumed that 10,000 pulses with errors even in one pulse could not be used. Considering the variation in magnetization, 20 magnetic drums were tested at a ratio of 1 b / a. Details are omitted, but b / a
It was confirmed that no error occurred when the ratio of 1/120 or more and 0.75 or less. If the ratio of b / a is less than 1/120, the pinned magnetization region is too small, and the pinning effect cannot be obtained. Also, if b / a exceeds 0.75, the signal magnetization region becomes too small, and the magnetic field leaking from the signal magnetization region becomes small, resulting in an output voltage comparable to the encoded comparison voltage. It is done. If the encoding comparison voltage is lowered, errors that occur because the output voltage is low are reduced. However, since the baseline noise is picked up and an error occurs, it is not preferable to change the encoding comparison voltage. With a margin, b / a can be determined to be 1/100 or more and 2/3 or less.

In the magnetization pitch region of Example 3, magnetization is performed by changing the length a of the signal magnetization region 3, the length b of the pinned magnetization region 4, and the length c of the non-magnetization region 7. A simple absolute signal (
The ratio of b + c) / a and b / c was examined. The evaluation method is the same as in Example 5. (B + c
) / A was changed from 1/250 to 2. Also, the ratio of b / c was changed from 0.2 to 8. The length of the non-magnetized region c was constant at 4 μm. Although details are omitted, it was confirmed that no error occurred when the ratio of (b + c) / a was 1/130 or more and 5/6 or less and b / c was 0.8 or more and 5.7 or less. Looking at the margin, (b + c) / a is 1/100 or more and 1 or less,
b / c can be determined to be 1 or more and 5 or less.

In Examples 5 and 6, the optimum ranges of the length a of the signal magnetized region 3, the length b of the pinned magnetized region 4, and the length c of the non-magnetized region 7 were obtained. The magnetic field strength leaking from the magnetic medium magnetized in these optimum ranges was measured at a position separated by a predetermined amount. When the magnetization pitch region of Example 5 was 600 μm, measurement was performed at a position 250 μm away, and when the magnetization pitch region of Example 6 was 60 μm, measurement was performed at a position 25 μm apart. When the magnetic field strength f in the signal magnetization region and the magnetic field strength g in the pinned magnetization region of the magnetization pattern set in the optimum range in Examples 5 and 6 were measured, the magnetic field strength ratio g / f was ½. The following values were found.

It is a figure explaining the magnetization pattern of the 1st Example of this invention. It is a figure explaining the output voltage and encoding signal waveform of a magnetic sensor at the time of the presence or absence of the pinning magnetization area | region of this invention. It is a figure explaining the magnetization pattern of the 2nd Example of this invention. It is a figure explaining the magnetization pattern of the 3rd Example of this invention. It is a figure explaining the magnetization pattern of the 4th Example of this invention. It is a figure explaining the magnetic medium and magnetic sensor of the magnetic-type absolute encoder of this invention. It is a figure explaining the magnetization pattern which made the signal magnetization area | region width | variety of the conventional magnetization pitch area | region small. It is a figure explaining the magnetization pattern which reverses a magnetic field direction in the discontinuous part of the conventional magnetization pitch area | region. It is a figure explaining the magnetization pattern from which the magnetic field direction of the signal magnetization area | region of all the adjacent magnetization pattern area | regions of the past is reverse. It is a figure explaining a magnetic sensor output and an encoding signal waveform when the conventional magnetization pitch area | regions continue six.

Explanation of symbols

1 magnetized pitch area, 2 non-magnetized pitch area,
3 Signal magnetization area, 4 Pinned magnetization area,
5, 6, 7 non-magnetized region, 10 magnetic medium,
11 signal area, 12 comparison area,
20 magnetic sensor, 21 magnetic sensor element,
22 magnetoresistive effect type elements, 23 comparative resistance elements,
24 connection point.

Claims (7)

A magnetic absolute encoder having a magnetic medium having an absolute pattern magnetized at random and a magnetoresistive effect type magnetic sensor that moves relative to each other.
The absolute pattern arranged in the moving direction is composed of at least one or more continuous non-magnetized pitch regions with the same pitch region width as the one or more continuous magnetized pitch regions,
The magnetization pitch area has a signal magnetization area and a pinned magnetization area,
The pinned magnetization area is located on both sides adjacent to the signal magnetization area,
The magnetization directions of adjacent signal magnetization regions are opposite to each other,
The magnetization direction of the signal magnetization region is opposite to the magnetization direction of the pinned magnetization region adjacent to the signal magnetization region ,
Magnetic absolute encoder characterized in that the magnetization direction is a direction along the moving direction . A magnetic absolute encoder having a magnetic medium having an absolute pattern magnetized at random and a magnetoresistive effect type magnetic sensor that moves relative to each other.
The absolute pattern arranged in the moving direction is composed of at least one or more continuous non-magnetized pitch regions with the same pitch region width as the one or more continuous magnetized pitch regions,
The magnetization pitch area has a signal magnetization area and a pinned magnetization area,
The pinned magnetization area is located on both sides adjacent to the signal magnetization area,
The magnetization directions of adjacent signal magnetization regions are opposite to each other,
The pinned magnetized region on at least the non-magnetized pitch region side of the magnetized pitch region adjacent to the non-magnetized pitch region is magnetized,
The magnetization direction of the signal magnetization region is opposite to the magnetization direction of the pinned magnetization region adjacent to the signal magnetization region ,
Magnetic absolute encoder characterized in that the magnetization direction is a direction along the moving direction . A magnetic absolute encoder having a magnetic medium having an absolute pattern magnetized at random and a magnetoresistive effect type magnetic sensor that moves relative to each other.
The absolute pattern arranged in the moving direction is composed of at least one or more continuous non-magnetized pitch regions with the same pitch region width as the one or more continuous magnetized pitch regions,
The magnetization pitch area has a signal magnetization area, a pinned magnetization area, and a non-magnetization area.
The pinned magnetization region is arranged on both sides adjacent to the signal magnetization region, and has a non-magnetized region adjacent to the pinned magnetization region,
The magnetization directions of adjacent signal magnetization regions are opposite to each other,
A magnetic absolute encoder characterized in that the magnetization direction of the signal magnetization region and the magnetization direction of the pinned magnetization region adjacent to the signal magnetization region are opposite to each other. A magnetic absolute encoder having a magnetic medium having an absolute pattern magnetized at random and a magnetoresistive effect type magnetic sensor that moves relative to each other.
The absolute pattern arranged in the moving direction is composed of at least one or more continuous non-magnetized pitch regions with the same pitch region width as the one or more continuous magnetized pitch regions,
The magnetization pitch area has a signal magnetization area, a pinned magnetization area, and a non-magnetization area.
The pinned magnetized region is arranged on both sides adjacent to the signal magnetized region, has a non-magnetized region adjacent to the pinned magnetized region,
The magnetization directions of adjacent signal magnetization regions are opposite to each other,
The pinned magnetized region on at least the non-magnetized pitch region side of the magnetized pitch region adjacent to the non-magnetized pitch region is magnetized,
A magnetic absolute encoder characterized in that the magnetization direction of the signal magnetization region and the magnetization direction of the pinned magnetization region adjacent to the signal magnetization region are opposite to each other.   The ratio b / a between the movement direction length a of the signal magnetization region in the magnetization pitch region and the movement direction length b of the pinned magnetization region is 1/100 or more and 2/3 or less. The magnetic absolute encoder according to claim 1.   The movement direction length a of the signal magnetization area in the magnetization pitch area, the movement direction length b of the pinned magnetization area, and the movement direction length c of the non-magnetization area are (b + c) / a being 1/100. 5. The magnetic absolute encoder according to claim 3, wherein the magnetic absolute encoder is 2/3 or less and b / c is 1 or more and 5 or less. When the magnetic absolute encoder is mounted, the magnetic field strength from the magnetic medium applied to the magnetic sensing part of the magnetoresistive effect type magnetic sensor is the magnetic field strength f in the signal magnetization region and the magnetic field strength g in the pinned magnetization region. 5. The magnetic absolute encoder according to claim 1, wherein the magnetic field intensity ratio g / f is 1/2 or less.

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