JP4786311B2 - Acceleration sensor - Google Patents

Description

  The present invention relates to an acceleration sensor that measures acceleration of a measurement object.

  For example, in Japanese Patent Publication No. 8-3420 (Patent Document 1), a magnet holding and holding a magnetic fluid is built in a flat-bottomed container so as to be movable by tilting, and the displacement of the magnet from the reference position is set in this container. A detection coil for detection and a drive coil for returning the magnet to the reference position are wound, and a drive circuit is provided. This drive circuit inputs the output from the detection coil as the magnet moves due to the inclination of the container. It is configured to output a control current for energizing the drive coil so that the displacement of the magnet is zero, and is configured to detect the inclination angle of the flat bottom container by measuring the magnitude and sign of this control current. An inclined angle detection sensor is disclosed. Although the tilt angle detection sensor of Patent Document 1 detects the tilt angle of a measurement object, the technique can be applied as an acceleration sensor that measures the acceleration of the measurement target.

Japanese Patent Publication No.8-3420

  In the tilt angle detection sensor disclosed in Patent Document 1, a detection coil is used as a magnetic sensor for detecting the movement of a permanent magnet. However, it is conceivable to use a magnetic sensor other than the coil.

For example, in Japanese Patent Publication No. 6-97236 (Patent Document 2), a magnetic fluid, a permanent magnet movably disposed in the magnetic fluid, a permanent magnet and a magnetic fluid are enclosed, and the magnetic capacity is increased depending on the inner volume shape. Hall element as detection means for detecting the position of a permanent magnet in an acceleration sensor comprising a non-magnetic case that governs the shape of the fluid, a detection means for detecting the position of the permanent magnet, and a processing circuit for processing the signal of the detection means Is disclosed.
Japanese Examined Patent Publication No. 6-97236

  The Hall element in the acceleration sensor disclosed in Patent Document 2 is a so-called horizontal type that detects a magnetic field in the vertical direction that penetrates the magnetic sensitive surface, and is in the direction in which both magnetic poles of the rod-shaped permanent magnet that is the acceleration measuring direction are aligned. The magnetic sensitive surface is arranged vertically, that is, it is arranged substantially perpendicular to the direction of the magnetic field with respect to the rod-shaped permanent magnet, and the magnetic field component in the vertical direction is the largest as the direction. It is the direction which can be applied.

  However, in the acceleration sensor, when the Hall element is arranged with the magnetic sensitive surface perpendicular to the arrangement direction of the two magnetic poles of the permanent magnet, which is the acceleration measurement direction, as in the acceleration sensor disclosed in Patent Document 2 above. Since the magnetic flux density applied to the Hall element increases, the Hall element output also increases. However, since the Hall element output is large, the change rate of the Hall element output with respect to the change in the position of the permanent magnet is reversed. For example, for a minute change in the position of the permanent magnet, that is, for a minute change in the magnetic flux density, the change in the output of the Hall element is too small. It may be difficult to grasp as.

  By the way, in recent years, accelerometers used in various electronic devices and the like are required to be able to measure with higher sensitivity and higher accuracy even with minute accelerations as the devices become smaller and more precise.

  Further, when increasing the measurement accuracy in the acceleration sensor, it is conceivable to suppress measurement errors caused by crosstalk other than in the acceleration measurement direction.

  Therefore, an object of the present invention is an acceleration sensor using a detection element such as a Hall element, which can measure acceleration, particularly minute acceleration, with high sensitivity and high accuracy, and crosstalk other than in the acceleration measurement direction. An object of the present invention is to obtain an acceleration sensor that can suppress measurement errors caused by.

To describe the present invention that achieves the above object, it includes a non-magnetic case, a magnetic fluid, a permanent magnet that adsorbs the magnetic fluid and moves in the non-magnetic case, and a detection element that detects the position of the permanent magnet. And a drive coil that is wound around the non-magnetic case and generates an electromagnetic force for holding the permanent magnet in the original position based on the output of the detection element, and a servo circuit that controls an applied current of the drive coil. An acceleration sensor comprising a detection unit, and further comprising an inner case that covers the detection unit and shields a magnetic field from the outside, wherein the detection element is a horizontal hole that detects a vertical magnetic field penetrating the magnetosensitive surface. An element, and the detection element is arranged in a direction parallel to the alignment direction of the two magnetic poles of the permanent magnet such that the magnetosensitive surface thereof is tangential to the direction of the magnetic field of the permanent magnet, Furthermore, the non-magnetic The case shall form a cylindrical shape, and its inner diameter is air in the non-magnetic casing also being able to suppress the movement in addition to its longitudinal direction said permanent magnet is acceleration measurement direction of the permanent magnet the permanent magnets so as not to hinder the movement in the longitudinal direction is an acceleration sensor, characterized in that it has a greater than the maximum outer diameter at the time of natural adsorbing magnetic fluid.

Further describing the present invention that achieves the above object, it includes a non-magnetic case, a magnetic fluid, a permanent magnet that adsorbs the magnetic fluid and moves within the non-magnetic case, and a detection that detects the position of the permanent magnet. An element, a drive coil that is wound around the non-magnetic case and generates an electromagnetic force for holding the permanent magnet in its original position based on the output of the detection element, and a servo circuit that controls an applied current of the drive coil a detection unit having, further, to cover the detection portion, a acceleration sensor having an internal casing for shielding the magnetic field from the outside, the detection element is horizontal to detect the vertical magnetic field penetrating the sensitive surface Hall element of the permanent magnet, which is arranged in a direction parallel to the arrangement direction of the two magnetic poles of the permanent magnet so that the magnetosensitive surface is tangential to the direction of the magnetic field of the permanent magnet, and the permanent magnet Of both poles And a first sensing element for detecting the position in the direction of the magnetic field, and a magnetic sensitive surface arranged in a direction perpendicular to the direction of arrangement of the two magnetic poles of the permanent magnet, An acceleration sensor comprising: a second detection element for crosstalk compensation for detecting a position in a vertical direction.

  In the acceleration sensor according to the present invention, for example, the inner case is a molded body made of a conductive rubber material, and at least the nonmagnetic case and the substrate on which the detection element is mounted are held inside. It can be fixed to.

  In the acceleration sensor according to the present invention, by arranging the detection element in such a direction that the magnetosensitive surface is parallel to the arrangement direction of the two magnetic poles of the permanent magnet, the magnetic flux density applied to the detection element is Although the electric potential difference generated at the output of the detection element can be increased, the magnetic potential density can be increased, although it is smaller than the case where it is arranged in the direction perpendicular to the arrangement direction of both magnetic poles of the permanent magnet. Even if it is a minute change, it is easy to capture the change as a quantity. That is, even a minute acceleration can be measured with high sensitivity and high accuracy. In addition, the non-magnetic case has a cylindrical shape, and its inner diameter is slightly larger than the maximum outer diameter when the permanent magnet naturally adsorbs the magnetic fluid. Can be suppressed from moving to, that is, the permanent magnets can be prevented from moving other than acceleration measurement direction, to suppress a measurement error caused by cross-talk than the acceleration measuring direction.

  In Patent Document 2, it is disclosed in FIG. 17 that the magnetic fluid case is slightly larger than the outer diameter of the permanent magnet. According to this, it is considered that the movement of the permanent magnet in the radial direction can be suppressed, that is, the occurrence of crosstalk other than the acceleration measurement direction can be suppressed. However, the acceleration sensor disclosed in Patent Document 2 fills the magnetic fluid case with the magnetic fluid. Therefore, when injecting the magnetic fluid into the magnetic fluid case, the magnetic fluid case is previously filled with air. Therefore, it takes a lot of man-hours and is not easy to assemble.

  In the acceleration sensor of the present invention, by making the inner diameter of the nonmagnetic case slightly larger than the maximum outer diameter of the magnetic fluid, a slight gap can be formed between the nonmagnetic case and the magnetic fluid, When the permanent magnet moves in the non-magnetic case, the air in the non-magnetic case can flow back and forth through the gap, so the air in the non-magnetic case is aligned in the direction in which the magnetic poles of the permanent magnet are aligned. It can be made so as not to interfere with the movement. That is, the acceleration sensor according to the present invention can suppress the movement of the permanent magnet in directions other than the acceleration measurement direction due to the shape of the nonmagnetic case. There is no need to do that.

  In the acceleration sensor according to the present invention, the detection element for detecting the position of the permanent magnet is disposed in a direction in which the magnetosensitive surface is parallel to the arrangement direction of the two magnetic poles of the permanent magnet. The first detection element for detecting the position in the arrangement direction of the magnet and the magnetic sensing surface is arranged in a direction perpendicular to the arrangement direction of the two magnetic poles of the permanent magnet, and with respect to the arrangement direction of the two magnetic poles of the permanent magnet By including a second detection element for crosstalk compensation that detects a position in the vertical direction, the ratio of the output of the first detection element to the output of the second detection element is obtained, whereby the permanent magnet It is possible to detect only the change in the direction in which the magnetic poles are arranged, that is, the change in the acceleration measurement direction, that is, it is possible to suppress measurement errors caused by crosstalk other than in the acceleration measurement direction.

  Embodiments of the present invention will be described with reference to the accompanying drawings.

[First embodiment]
A first embodiment of the present invention will be described with reference to FIGS. 1 is a cross-sectional view of the acceleration sensor of the present invention, FIG. 2 is a cross-sectional view taken along the line B-B in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line A-A in FIG. 4 is a schematic diagram of the internal structure of the detection unit, FIG. 5 is a block diagram showing the circuit configuration of the same, and FIG. 6 is an operation flow diagram of the same.

  1 to 4, in the acceleration sensor 1, a detection unit 4 that detects acceleration is housed in an internal case box 2 that is closed by an internal case lid 3. The detection unit 4 includes a circuit board 5 fixedly provided in the inner case box 2, a base 6 fixedly provided on the circuit board 5, and a cylindrical nonmagnetic case 7 supported by the base 6. A rod-shaped permanent magnet 9 sealed with the magnetic fluids 8a and 8b adsorbed in the nonmagnetic case 7, and a position of the permanent magnet 9 located outside the nonmagnetic case 7 and mounted on the circuit board 5 And a pair of drive coils 11a and 11b wound around the nonmagnetic case 7 so as to surround both magnetic pole ends of the permanent magnet 9 in the nonmagnetic case 7, respectively.

  The permanent magnet 9 accommodated in the nonmagnetic case 7 has magnetic pole ends at both ends in the length direction, and floats in the nonmagnetic case 7 by the magnetic fluids 8a and 8b adsorbed on both magnetic pole ends. In the direction A1 (that is, the length direction of the permanent magnet 9 in this embodiment).

  The Hall element 10 is a so-called horizontal type that detects a vertical magnetic field penetrating the magnetic sensitive surface, and the magnetic sensitive upper surface 10a thereof is parallel to the alignment direction A1 of both magnetic poles of the permanent magnet 9. The magnetic flux density from the permanent magnet 9 is applied, and a change in the magnetic flux density caused by the movement of both magnetic poles of the permanent magnet 9 in the alignment direction A1 can be detected. The drive coils 11a and 11b are The current applied based on the output from the hall element 10 is controlled to generate an electromagnetic force for holding the permanent magnet 9 in the original position (position in the no-load state). The unit 9 can detect the acceleration generated in the direction A1 in which both the magnetic poles of the permanent magnet 9 are arranged based on the current applied to the drive coils 11a and 11b.

  That is, the acceleration sensor 1 uses the direction A1 of the nine magnetic poles of the permanent magnet as the acceleration measurement direction.

  In the present embodiment, the permanent magnet 9 is a bar magnet having neodymium, samarium, cobalt, a cylindrical shape (Φ2 × 5 mm), and having an S / N pole at the middle in the length direction, The surface magnetic flux density is 250 mT, and the magnetic fluids 8a and 8b are made of iron oxide, the particle size is 100 mm (1 mm is 0.1 nm), the base oil is petroleum, and the viscosity is 1 mPa · s. The Hall element 10 is made of a compound semiconductor such as InSb or GaAs, the nonmagnetic case 7 is made of glass (or resin), and the shape is cylindrical. The inner case box 2 uses a molded body made of a conductive rubber material. An MR element or the like may be used instead of the Hall element.

  The circuit configuration of the detection unit 4 is, for example, as shown in FIG. 5, and a magnet position detection circuit C2, an amplification circuit C3, a servo circuit, that is, a drive coil circuit C4, and a signal output circuit C5 are connected to the power supply circuit C1. The output from the magnet position detection circuit C2, that is, the Hall element 10, is output to the drive coil circuit C4 through the amplification circuit C3, and the output from the drive coil circuit C4 is fed back to the magnet position detection circuit C2 and the acceleration signal is output. The output is to the signal output circuit C5 for output, and the operation flow in the circuit configuration is as shown in FIG. 6, that is, the presence or absence of acceleration is determined from the state where the magnet displacement A1 is 0 (P1). (P2) When the magnet is displaced (P3), the output of the Hall element 10 changes (P3), and the output signal is amplified by the amplifier circuit C3 (P4). In the drive coil circuit C4, an acceleration signal based on the applied current to the drive coil is output (P6) while controlling the applied current to the drive coil so as to apply a servo for setting the displacement of the magnet to 0 (P5). Become.

  As described above, the Hall element 10 is a so-called horizontal type, and is arranged so that the upper surface 10a of the magnetic sensitive surface thereof is parallel to the arrangement direction A1 of both magnetic poles of the permanent magnet 9. Accordingly, the Hall element 10 has the magnetic sensitive surface 10a tangential to the direction of the magnetic field of the permanent magnet 9, so that the applied magnetic flux density is in the direction A1 in which the magnetic sensitive surface 10a is aligned with the two magnetic poles of the permanent magnet 9. However, the potential difference generated in the Hall element 10 can be increased in contrast to the case of being arranged in a direction perpendicular to the vertical direction. Even in this case, it is possible to easily grasp the change as a quantity, that is, even a minute acceleration can be measured with high sensitivity and high accuracy. Further, since a large potential difference in the output of the Hall element 10, that is, a large change rate of the output, can be easily processed as a signal in peripheral circuits such as an amplifier circuit and a servo circuit, the circuit configuration in the detection unit 4 is simplified. It can be.

  In the present embodiment, as shown in detail in FIG. 4, the Hall element 10 is arranged on the side of the permanent magnet 9 so as to be separated from the permanent magnet 9 via a magnetic sensitive distance adjusting interval T2. The range of the separation distance between the permanent magnet 9 and the permanent magnet 9 is determined by the range of the vertical distance T1 in the assembly between the center axis X of both magnetic poles of the permanent magnet 9 and the bottom surface 10b of the magnetic sensing surface of the Hall element 10. In the case of the permanent magnet 9 having a surface magnetic flux density of 250 mT in this embodiment, the vertical distance T1 is preferably 2 to 6 mm from the shortest to the longest, and the range of the preferable vertical distance T1 is between the Hall element 10 and the permanent magnet 9. The separation distance is within a range in which the magnetic flux density detected by the Hall element 9 changes in direct proportion to the movement of the two magnetic poles of the permanent magnet 9 in the arrangement direction A1, and the Hall element 10 has the magnetic flux density. Ten changes In particular, a preferable range of a ratio between a change in the magnetic flux density applied to the Hall element 10 and a change in the vertical distance T1 is obtained. That is, it was obtained from the range of 125 mT / mm (shortest) to 41.7 mT / mm (longest).

  In addition, when the permanent magnet 9 moves from the original position to any one of the magnetic poles in the direction A1 of the two magnetic poles, the Hall element 10 is connected to the Hall element 10 with the middle between the two magnetic poles of the permanent magnet 9 as a boundary. By utilizing the fact that the direction of the magnetic vector in the applied magnetic flux density is reversed up and down, a positive potential is output for the movement of the permanent magnet 9 toward one magnetic pole, and the other magnetic pole of the permanent magnet is output. A negative potential is output for the movement to the side, and according to this, the output signal from the Hall element 10 can be easily processed in a peripheral circuit such as a drive coil circuit. The current applied to the drive coils 11a and 11b can be immediately controlled with respect to the output from the Hall element 10, that is, with respect to the movement in the arrangement direction A1 of both magnetic poles of the permanent magnet 9, that is, the permanent magnet 9 can be immediately controlled. To the original position To be able to servo control, it is possible to increase the responsiveness of the sensor.

  In this embodiment, the nonmagnetic case 7 has a cylindrical shape as described above, but the inner diameter D thereof is slightly larger than the maximum outer diameter R when the permanent magnet 9 naturally adsorbs the magnetic fluids 8a and 8b. It is supposed to be. Therefore, the shape of the nonmagnetic case 7 can suppress the permanent magnet 9 from moving in the radial direction A2 of the nonmagnetic case 7, that is, the permanent magnet 9 is in its length direction (alignment direction A1 of both magnetic poles). In other words, it is possible to suppress movement outside the acceleration measurement direction, and to suppress measurement errors caused by crosstalk other than the acceleration measurement direction, and between the nonmagnetic case 7 and the magnetic fluids 8a and 8b. Since a slight gap can be formed, when the permanent magnet 9 moves in the nonmagnetic case 7, the air in the nonmagnetic case 7 is passed through the gap in the length direction of the permanent magnet 9 (alignment of both magnetic poles). It is possible to flow back and forth along the direction A1) so that the air in the non-magnetic case 7 does not hinder the movement of the permanent magnet 9 in the length direction (alignment direction A1 of both magnetic poles). Can do. In other words, in the present embodiment, the acceleration sensor 1 can suppress the movement of the permanent magnet 9 in the direction other than the detection direction A1 due to the shape of the nonmagnetic case 7, but the inside of the nonmagnetic case 7 when the acceleration sensor 1 is assembled. It is possible to eliminate the need for air bleeding.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a diagram corresponding to FIG. 4 in the first embodiment.

  In the second embodiment, the structural difference from the first embodiment is that a Hall element 12 for crosstalk compensation is provided. That is, as shown in FIG. 7, in the acceleration sensor 1 according to the second embodiment, in addition to the Hall element 10, the magnetic sensitive surface upper surface 12 a is perpendicular to the arrangement direction A <b> 1 of both magnetic poles of the permanent magnet 9. A crosstalk compensating Hall element 12 is provided which is arranged in the direction and detects the position in the direction A2 perpendicular to the arrangement direction A1 of the two magnetic poles of the permanent magnet 9.

  The crosstalk compensating Hall element 12 is arranged such that the magnetic sensitive surface upper surface 12a is orthogonal to the magnetic sensitive surface 10a of the Hall element 10, and the movement in the direction A2 perpendicular to the arrangement direction A1 of both magnetic poles of the permanent magnet 9; That is, the crosstalk other than the acceleration measurement direction is detected. Although the description of the circuit configuration is omitted, the ratio of the output of the Hall element 10 to the output of the Hall element 12 for crosstalk compensation is obtained by providing the Hall element 12 for crosstalk compensation for detecting crosstalk other than the acceleration measurement direction. Thus, it is possible to detect only the change in the acceleration measurement direction. Therefore, according to the second embodiment, the acceleration sensor 1 of the present invention can suppress the measurement error due to crosstalk as much as possible. Further, the change in the acceleration measurement direction may be obtained from the difference between both output values.

It is sectional drawing of the acceleration sensor in 1st Embodiment of this invention. FIG. 1B is a cross-sectional view taken along line B-B. FIG. 1A is a cross-sectional view taken along line AA. It is a schematic diagram of the internal structure of a detection part same as the above. It is a block diagram which shows a circuit structure same as the above. It is an operation | movement flowchart same as the above. It is a schematic diagram of the internal structure of the detection part of the acceleration sensor in 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Acceleration sensor 2 Inner case box 3 Inner case lid 4 Detection part 5 Circuit board 6 Base 7 Nonmagnetic case 8a Magnetic fluid 8b Magnetic fluid 9 Permanent magnet 10 Hall element 10a Magnetosensitive surface upper surface 10b Magnetosensitive surface bottom surface 11a Drive coil 11b Drive coil 12 Hall element for crosstalk compensation 12a Upper surface of magnetosensitive surface T1 Vertical distance T2 Spacing for adjusting magnetosensitive distance

Claims (3)

A non-magnetic case, a magnetic fluid, a permanent magnet that adsorbs the magnetic fluid and moves in the non-magnetic case, a detection element that detects the position of the permanent magnet, and a wound around the non-magnetic case. A detection unit having a drive coil that generates an electromagnetic force for holding the permanent magnet in an original position based on an output, and a servo circuit that controls an applied current of the drive coil, and further covers the detection unit; An acceleration sensor having an inner case that shields a magnetic field from the outside,
The detection element is a horizontal Hall element that detects a vertical magnetic field penetrating the magnetosensitive surface,
Further, the detection element is arranged in a direction parallel to the arrangement direction of the two magnetic poles of the permanent magnet so that the magnetosensitive surface thereof is tangential to the direction of the magnetic field of the permanent magnet,
Furthermore, the non-magnetic case has a cylindrical shape, and the air in the non-magnetic case can be suppressed while the inner diameter of the non-magnetic case can be restrained from moving in directions other than the length direction that is the acceleration measuring direction. an acceleration sensor, characterized in that it has as the permanent magnets so as not to hinder the movement in the lengthwise direction of the permanent magnets is larger than the maximum outer diameter at the time of natural adsorbing magnetic fluid. A non-magnetic case, a magnetic fluid, a permanent magnet that adsorbs the magnetic fluid and moves in the non-magnetic case, a detection element that detects the position of the permanent magnet, and a wound around the non-magnetic case. A detection unit having a drive coil that generates an electromagnetic force for holding the permanent magnet in an original position based on an output, and a servo circuit that controls an applied current of the drive coil, and further covers the detection unit; An acceleration sensor having an inner case that shields a magnetic field from the outside,
The detection element is a horizontal Hall element that detects a vertical magnetic field penetrating the magnetosensitive surface, and both the permanent magnets are arranged such that the magnetosensitive surface is tangential to the direction of the magnetic field of the permanent magnet. A first detection element that is arranged in a direction parallel to the arrangement direction of the magnetic poles and detects a position in the arrangement direction of the two magnetic poles of the permanent magnet; and a magnetosensitive surface in the arrangement direction of the two magnetic poles of the permanent magnet An acceleration sensor including a second detection element for compensating for crosstalk that is disposed in a direction perpendicular to the magnetic poles of the permanent magnet and detects a position in a direction perpendicular to the direction in which the two magnetic poles of the permanent magnet are aligned. .   The inner case is a molded body made of a conductive rubber material, and at least the non-magnetic case and the substrate on which the detection element is mounted are fixed inside the casing. The acceleration sensor according to claim 1 or 2.

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