JP2510275B2 - Acceleration sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an acceleration sensor using a permanent magnet for detecting acceleration in a two-dimensional plane and a magnetic fluid, for example, front and rear, left and right directions of a vehicle. Sensor that detects the acceleration of
Alternatively, it is effectively used as a sensor for detecting angular acceleration when the vehicle turns.

[Conventional technology]

As a conventional acceleration sensor, a magnetic fluid is enclosed in a case so as to be movable in an accelerating direction, and a fixed permanent magnet that gives a certain magnetism to the magnetic fluid and a coil that detects the position of the magnetic fluid are provided. There is known one in which the electromotive force generated in the coils constituting the differential transformer is measured by the displacement of (1) and the acceleration is detected from the magnitude thereof (see, for example, JP-A-60-133370).

[Problems to be Solved by the Invention]

However, in the acceleration sensor according to the above-mentioned conventional technique, since the magnetic fluid moves in another medium such as air, bubbles,
There are problems that liquid bubbles and the like are likely to occur and that a complicated structure is required to facilitate the movement of the magnetic fluid.
In addition, since the principle is to detect the shape change of the magnetic fluid, there is a problem that it is greatly affected by the viscosity change, volume expansion, etc. due to the temperature change.

Therefore, the applicant has previously proposed Japanese Patent Application No. 63-30068 (Japanese Patent Laid-Open No. 138875) as a prior application. This is because by filling the space with magnetic fluid, changing the inner volume shape of the space, and limiting the magnetic path of the magnetic flux generated by the permanent magnet placed in the magnetic fluid in the space, the position and identification of the permanent magnet can be determined. It adjusts the ease of movement in the direction. Further, by utilizing this concept, Japanese Patent Application No. 63-243136 (Japanese Patent Laid-Open No. 90061)
Has also been proposed earlier.

However, in each of the above-mentioned prior applications, an acceleration sensor that prevents the permanent magnet from rotating by providing a concave convex portion in the circumferential direction of the permanent magnet and allows only linear movement in the horizontal plane in the horizontal direction in the concave direction. However, since there are concave convex portions in the circumferential direction, when the permanent magnet moves in the multiple axis direction when viewed from the center of the permanent magnet, a difference occurs in the magnetic elasticity of the magnetic fluid that the permanent magnet receives, and It was difficult to measure linear acceleration in the same direction with the same gain. Further, since it is impossible to prevent the permanent magnet from linearly moving in the horizontal direction and to permit only the rotation of the permanent magnet, it cannot be configured as an angular acceleration sensor.

Therefore, according to the present invention, it is possible to measure the acceleration acting on the plane in the multi-axis direction from the center of the permanent magnet with the same gain, and by setting the dimensions and changing the number and position of the magnetic detection elements, An object of the present invention is to obtain an acceleration sensor that uses a magnetic fluid that can also serve as an acceleration sensor.

[Means for solving the problem]

Therefore, the present invention provides a main housing made of a non-magnetic material having a substantially cylindrical space with one end face open, and a non-magnetic main housing fixed to the main housing to close the one end face of the main housing. A sub-housing made of magnetic material; a bottom projection radially formed on the bottom surface of the space of the main housing; a top projection radially formed on the space side surface of the sub housing facing the bottom projection; A magnetic fluid filled and sealed in the space, a disk-shaped permanent magnet that is sealed in the space together with the magnetic fluid, is magnetized in the radial direction in the circumferential surface, and has a flat surface portion facing the bottom surface projection and the top surface projection. A magnetic detection element that is provided between a pair of projections formed by each of the bottom surface projections and each of the top surface projections and that detects the position of the permanent magnet to generate a detection output. It has a child.

[Action]

According to the above configuration, since the magnetic fluid is filled in the space, no bubbles are generated, and the permanent magnet floats in the magnetic fluid due to its own magnetic force.

Further, the bottom surface projection and the top surface projection are provided so that the flat surface portions of the permanent magnets face each other, and the bottom surface projection and the top surface projection cause a blocking force in the rotation direction of the permanent magnet or an elastic restoring force against the movement in the rotation direction. Can be freely set by designing the dimensions and shape. Moreover, since the bottom surface projection and the top surface projection do not need to face the peripheral surface of the permanent magnet,
It is possible to prevent linear movement of the permanent magnet in any direction around the permanent magnet, and elastic restoration for uniform linear movement over the entire circumference that is not related to the direction of this linear movement. Since the force can be set, the sensor detects the displacement of the permanent magnet to detect the linear acceleration acting on the two-dimensional plane in the multi-axis direction, and also detects the angular acceleration centered on the permanent magnet. It can also be configured as a sensor.

〔The invention's effect〕

According to the present invention, it is possible to configure a highly accurate sensor without generating bubbles due to rocking of the magnetic fluid. Further, as a sensor for detecting a straight acceleration on a two-dimensional plane, it is possible to detect acceleration at any angle.

As a result, not only the front-back direction of the object but also any lateral acceleration can be detected, so that the behavior of the object can be detected more accurately. It can also be configured to detect angular acceleration when the object is turning, and by applying magnetic fluid and a permanent magnet, it is possible to detect angular acceleration directly and with high accuracy in a non-contact manner. It can be used as a guide device for detecting the traveling position of the vehicle.

〔Example〕

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the first embodiment, linear acceleration is detected without rotating the permanent magnet. FIG. 1 (a) is a transverse sectional view taken along the line II of FIG. 2, and FIG. 2 is a longitudinal sectional view of the first embodiment.

Reference numeral 1 denotes a main housing made of aluminum, which is a non-magnetic body, and has a substantially cylindrical space 2 whose one end face is open inside. An aluminum sub-housing 3 is fixed to the main housing 1 by screws 11a and 11b and unillustrated screws 11c and 11d to close one end surface of the space 2. screw
11a, 11b, 11c and 11d are made of non-magnetic material.

FIG. 3 shows a perspective sectional view of the main housing 1, and FIG. 4 shows a perspective view of the sub housing 3. Reference numerals 50a to 50b are bottom projections radially formed on the bottom surface of the cylindrical space 2 of the main housing 1 at the same depth, and 51a to 51d are radial surfaces on the closed surface of the cylindrical space 2 of the sub-housing 3, that is, the upper surface on the space side. The upper surface protrusions are formed to have the same depth. The bottom surface protrusions 50a to 50d face the top surface protrusions 51a to 51d, respectively, and form four pairs of protrusions in the cylindrical space 2.

A small hole 7 is formed in the sub-housing 3 so as to communicate the cylindrical space 2 with the external space, concentric with the cylindrical axis of the cylindrical space 2. Reference numeral 4 in FIG. 1A is a magnetic fluid, for example, ultrafine particles of manganese zinc ferrite or the like dispersed in isoparaffin, which is enclosed in the cylindrical space 2 together with the permanent magnet 5.

Reference numeral 5 denotes a disk-shaped permanent magnet that is magnetized in the radial direction on the peripheral surface, and the number of magnetic poles is the same as that of the pair of protrusions (50a
And 51a, 50b and 51b, 50c and 51c, and 50d and 51d), and the thickness of the permanent magnet 5 is from the depth of the space 2 to the depth of the pair of protrusions (the depth of the bottom protrusion 50a and the top protrusion). Slightly less than the sum of the depths of 51a). Further, the permanent magnet 5 is enclosed together with the magnetic fluid 4 in the space 2, and the plane portion of the permanent magnet 5 faces the bottom surface projections 50a, 50b, 50c, 50d and the top surface projections 51a, 51b, 51c, 51d. A substantially circular ring-shaped space filled with the magnetic fluid 4 exists between the inner wall of the space 2 and the peripheral surface of the permanent magnet 5, and the bottom surface of the main housing 1 and one flat surface of the permanent magnet 5 are present. Between the sub housing 3 and the other flat surface of the permanent magnet 5, there are thin plate-shaped spaces filled with the magnetic fluid, which are opposed to each other.

The ring-shaped space (inner wall) of the space 2 has a size of wide eyes that allows a large number of linear movements of the permanent magnet 5 in the plane direction, and functions as a restoring force generating portion. That is, since the apparent density of the magnetic fluid 4 is large near the magnetic poles of the permanent magnet 5, a magnetic stickiness or elastic force (hereinafter, magnetic force) is generated between the inner wall that is the restoring force generating portion and each magnetic pole of the permanent magnet. Elasticity) works. The permanent magnet 5 moves in the multiple axis direction of each magnetic pole and stands still until the magnetic elastic force and the acceleration received by the permanent magnet 5 are balanced. In addition, the thin plate-like spaces on the top surface and the bottom surface of the space 2 face each other in the normal direction of the intermediate portion of each magnetic pole (N, S) of the permanent magnet 5, and the restoring force generating portion and the permanent magnet 5 are opposed to each other. Anti-rotation member (the projection pair) provided at a distance smaller than the distance from the magnetic pole of
There is. This serves to substantially prevent the rotational movement of the permanent magnet 5, as will be described later. The magnetic fluid 4 is injected from the small hole 7 of the sub-housing 3, sealed with a rubber plug 8, and then sealed and fixed with a camp 9.
An O-ring 10 is provided between the main housing 1 and the sub-housing 3. Reference numerals 12a to 12d denote Hall elements that are magnetic detection elements, and are arranged so as to face the inner wall of the cylindrical space 2 with a predetermined space at an intermediate angular position with respect to each pair of protrusions of the main housing 1. It is adhered and fixed to the outside of 1.

Reference numeral 14 is a glass epoxy printed plate, which is fixed to the main housing 1 by a non-magnetic screw 15, and each terminal of the Hall elements 12a to 12d is soldered. Reference numeral 16 denotes a processing circuit unit, which is formed on the print plate 14.

Reference numeral 17 denotes an iron shield cover, which is fixed to the main housing 1 by a screw (not shown). A shield plate 18 is fixed to the shield cover 17 with screws 19a to 19c. The shield cover 17 and the shield plate 18 form the outer shape of the present sensor.

Reference numeral 20 denotes a rubber grommet, which is fixed in a hole 23 provided on the side surface of the shield cover 17, and the lead wire bundle 21 from the processing circuit 16 is led out through the grommet 20.

 FIG. 5 shows a block diagram of the circuit system.

The lead wire bundle 21 shown in FIG. 2 taken out of the processing circuit 16 is connected to the terminals 37, 38, 39, 40 of the processing circuit 16. 39 is connected to the power supply and 40 is connected to the ground. The Hall elements 12a to 12d are connected to a power source 39 and a ground 40, respectively.

 31 to 36 are differential amplifiers.

Two output terminals for extracting the detection output of the hall element 12a are connected to the input terminal of the differential amplifier 31. Hall element
The two output terminals of 12c are connected to the input terminals of the differential amplifier 32. The output terminals of the differential amplifiers 31 and 32 are connected to the input terminal of the amplifier 35, and the output terminal of the amplifier 35 is the processing circuit 16
Connected to the output terminal 37 of the.

Similarly, the two output terminals of the Hall element 12b are connected to the input terminals of the differential amplifier 33, and the two output terminals of the Hall element 12d are connected to the input terminal of the differential amplifier 34, and The output terminal is connected to the input terminal of the differential amplifier 36, and the output terminal of the differential amplifier 36 is connected to the terminal 38 of the processing circuit 16.

Reference numeral 100 denotes an external arithmetic circuit, which is a mean square circuit 103 and a division circuit 10.
Composed of 4 and. The external operation circuit 100 is known, and for example, the vector function and division function of a multifunctional converter (model 4302) manufactured by Burr Brown Co. may be used. The input terminals 101 and 102 of the external arithmetic circuit 100 are connected to the output terminals 37 and 38 of the processing circuit 16 via the lead wire bundle 21 (FIG. 2). The input terminals 101 and 102 are connected together to a root mean square circuit 103 and a division circuit 104. The output terminal of the root mean square circuit 103 is connected to the output terminal 105 of the external arithmetic circuit 100 and the division circuit 104
The output terminal of is connected to the output terminal 106 of the external arithmetic circuit 100.

 Next, the operation will be described based on the above configuration.

In this device, the permanent magnet 5 placed in the magnetic fluid 4 attracts the magnetic fluid 4 and the magnetic elastic force resulting from the apparent density of the magnetic fluid 4 being proportional to the magnetic field gradient causes the permanent magnet 5 and the magnetic fluid 4 to move. By utilizing the position adjustment phenomenon that works between the housings 1 and 3 that house 4
By realizing the displacement and detecting the displacement, stable two-dimensional acceleration detection is performed.

The permanent magnet 5 magnetized in the radial direction with multiple poles levitates in the magnetic fluid 4. This is because the apparent density of the magnetic fluid 4 increases as the magnetic field gradient increases, that is, the closer to the magnetic pole. At this time, when the acceleration a is applied in the plane direction of the disk-shaped permanent magnet 5, an inertial force acts on the permanent magnet 5 as shown in FIG. As the permanent magnet 5 moves, the apparent density of the magnetic fluid 4 in the vicinity of the inner peripheral wall of the cylindrical space 2 of the main housing 1 becomes large at a position close to the magnetic pole of the permanent magnet 5 and becomes small at a position far away from the permanent magnet 5. Force due to dynamic elastic force works. The permanent magnet 5 stands still at the equilibrium point between the restoring force and the inertial force. Therefore, the cylindrical space 2 of the permanent magnet 5
If the position inside is detected, a signal corresponding to the acceleration a can be obtained. Hall elements 12a to 12d are used to detect the position of the magnet 5.
To use.

However, when the magnet 5 rotates, it is affected by it and cannot be separated from the acceleration signal. In order to prevent the permanent magnet 5 from rotating, a pair of protrusions 50a to 5a are provided on the upper bottom surface of the cylindrical space 2.
0d and 51a to 51d are provided. This is because the magnetic elastic force is used also in the rotation direction. FIG. 6 shows a perspective view of the permanent magnet 5 attracted to the magnetic fluid 4, and FIG. 7 shows a longitudinal sectional view of FIG. With respect to the permanent magnet 5, the magnetic fluid 4 has a substantially spherical distribution in which the magnetic fluid 4 is connected around each magnetic pole. Therefore, a pair of radial projections (50a and 51a, 50b and 51b, 50c and 51c and 50d between the magnetic poles are formed on the upper bottom surface of the cylindrical space 2.
And 51d), the magnetic elastic force acting between the high apparent density portion of the magnetic fluid 4 near the magnetic pole and the side surface portion of the protrusion when the magnet 5 tries to rotate is applied to the permanent magnet 5. It works as the return torque of the. Therefore, the permanent magnet 5 is prevented from rotating in the space 2 and is allowed to move only linearly in the direction of the inner peripheral surface of the space 2 in the horizontal plane.

Further, the permanent magnet 5 is made hard to move in the axial direction of the cylinder in the space 2. This is to give sensitivity only to the acceleration in the horizontal direction. To achieve this, the distance between the bottom surface of the permanent magnet 5 and the bottom surface of the space 2 is set sufficiently smaller than the distance between the outer peripheral surface of the permanent magnet 5 and the inner surface of the space 2. Done. This utilizes the fact that the magnetic field distribution near the magnetic poles is spatially distributed not only to the side surfaces of the permanent magnet but also to the bottom surface as described above. In other words, the distance between the bottom surface of the permanent magnet 5 and the projection pair provided on both bottom surfaces of the space 2 is made sufficiently small, and the bottom area of the projection pair is set appropriately, so that the magnetic fluid 4 near the magnetic pole is high. The apparent density portion fills the axial gap between the permanent magnet 5 and the housings 1 and 3 to suppress the movement of the permanent magnet 5 with respect to the acceleration in the axial direction of the cylinder.

As described above, in the configuration of the permanent magnet 5 and the magnetic fluid 4 sealed in the space 2, the same number of protrusion pairs as the magnet magnetic poles are radially provided on both bottom surfaces of the space 2 so as to face the middle of the magnetic poles, and By setting the axial cylindrical length of the permanent magnet 5 to be slightly longer than the length of the permanent magnet 5, the following three effects can be obtained.

(1) The permanent magnet 5 floats stably in the magnetic fluid 4 in the space 2.

(2) The permanent magnet 5 receives a large return torque due to the magnetic elastic force.

(3) The permanent magnet 5 is movable in the horizontal plane and does not translate in the axial direction.

Therefore, the position of the permanent magnet, that is, the position of each magnetic pole is uniquely determined with respect to the acceleration in the horizontal plane. Therefore, the applied acceleration can be known by detecting the magnetic pole position using a magnetic field detecting element such as a Hall element.

A specific example will be described with reference to FIGS. 1 and 5. In FIG. 1 (b), the x-axis is the Hall element 12a-12c direction and the y-axis is the Hall element 12b-12d direction. The magnetic poles of the permanent magnet 5 in the x-axis direction are both S poles, and the Y-axis direction is an N pole 4
The case of a polar magnet is shown. This device is shown in Fig. 1 (b).
When the acceleration A is applied as described above, the acceleration a is applied to the permanent magnet 5 relative to the main housing 1. The acceleration a is a vector having the same magnitude as the acceleration A and traveling in the opposite direction. When the weight of the permanent magnet 5 is m, the inertial force F ₁ acting on the permanent magnet 5 can be expressed as F ₁ = k ₁ · m · a. Note that F ₁ and a are vector values. Here, k ₁ is a constant determined by various conditions.

Further, the magnetic elastic force F ₂ (vector value) has the same magnitude as the inertial force F ₁ in the opposite direction.

Here, in the horizontal cross section of the cylindrical space 2, with its center as the origin, the central position of the permanent magnet 5 when the magnetic elastic force F ₂ and the inertial force F ₁ are balanced is P (x, y) Then, when the movement amount of the permanent magnet 5 is small, The relationship is established. Here, k ₂ is a constant. Therefore, by setting | F ₁ | = | F ₂ | Becomes

In other words, (x, y) ＝ (k ・ | a | ・ cos θ, k ・ | a | ・ sin
θ), and knowing the position (x, y) of the permanent magnet, the applied acceleration can be known.

Therefore, as shown in FIG. 1 (a), Hall elements 12a-12d
Are arranged so as to face the magnetic poles. The Hall elements 12a and 12c face the south pole of the magnet 5 and are arranged so that the positive output increases when the north pole approaches. Hall element 12
b and 12d face the north pole of the magnet 5 and are arranged so that the positive output becomes large when the north pole approaches. Therefore, for example, when the permanent magnet 5 moves horizontally in the x direction in FIGS. 1A and 1B, the Hall element 12a and the magnetic pole N approach each other, and the output of the Hall element 12a becomes large. At the same time, the output of the Hall element 12c becomes small. Hall element output voltage is
The output is approximately inversely proportional to the square of the distance between the magnetic poles.

Therefore, if the differential output between the Hall elements 12a and 12c is taken,
When the amount of movement of the permanent magnet is small, an output voltage approximately proportional to the x-direction component of the magnet position can be obtained. Similarly, if the differential outputs of the Hall elements 12b and 12d are obtained, it is possible to obtain an output voltage substantially proportional to the y-direction component of the magnet position. The differential output voltage Vx of the Hall elements 12a, 12c and the differential output Vy of the Hall elements 12b, 12d obtained in this way are values corresponding to the central position (x, y) of the permanent magnet 5, respectively. .
Further, by taking a differential output, high gain, good linearity and temperature compensation can be performed.

Therefore, as shown in FIG. 5, by the external processing circuit 100, based on the differential voltages Vx and Vy, And Vy / Vx, the former is the magnitude of acceleration a | a |
The latter represents the direction tan θ of the acceleration a.

The processing circuit 16 of FIG. 5 will be briefly described. The Hall elements 12a-12d are coupled to the regulated power supply via terminal 39. The output of the Hall element 12a is the differential amplifier 3
1 and similarly the outputs of the Hall elements 12b-12d are obtained via the differential amplifiers 32-34. Then, a differential output of the outputs of the differential amplifiers 31 and 32 is obtained via the differential amplifier 35 and connected to the terminal 37. Further, the differential output of the outputs of the differential amplifiers 33 and 34 is obtained through the difference amplifier 36 and connected to the terminal 38. Therefore, the output voltage Vx from the terminal 37
The output voltage Vy is obtained from 38.

The amount of magnetic fluid 4 enclosed in the space 2, that is, the space 2
The remaining volume obtained by subtracting the volume of the permanent magnet 5 from the volume of 1 is preferably equal to the total amount of magnetic fluid that the permanent magnet 5 can hold in the free state. Here, in the free state, the permanent magnet 5
The total amount of magnetic fluid that can be held by the permanent magnet 5 when the permanent magnet 5 is inserted into the magnetic fluid 4 at normal temperature and pressure and pulled up.
It means the total amount of magnetic fluid attached to the. This state is the sixth
It is shown in the figure. If the remaining volume is determined so as to be larger than this amount, a dead zone occurs in the amount of movement of the permanent magnet with respect to acceleration. On the other hand, if it is set small, the amount of movement with respect to acceleration is reduced, and the sensitivity is reduced.

FIG. 8 shows the differential output Vx [V] of the Hall elements 12a, 12c with respect to the magnitude | a | of the applied acceleration a, and FIG. 9 shows the differential output Vy of the Hall elements 12b, 12 similarly. The parameter θ is the angle of acceleration shown in FIG. Vx is acceleration a
On the other hand, | a | ・ cos θ, Vy shows almost the same value as | a | ・ sin θ.

In the above embodiment, the number of magnetic poles of the permanent magnet 5 and the number of protrusions of the cylindrical space are shown as 4 (two sets facing each other).
The former may be two pairs, and the latter may be any pair as long as it is one or more.

Also, the Hall element has been taken as an example of the magnetic detection element,
Other components such as a magnetoresistive element or a pickup coil may be used.

Next, a second embodiment of the present invention will be described with reference to the drawings. In this second embodiment, the permanent magnet is rotated to detect the angular acceleration. FIG. 10 (a) is a transverse sectional view of the second embodiment, and is a sectional view taken along the line S10-S10 in FIG. 11, and FIG. 11 is a longitudinal sectional view of the second embodiment.

Reference numeral 1 denotes a main housing, which forms a space 2 inside. 3 is a sub-housing, which is screwed into the main housing 1 to close the open end surface of the space 2.
It is fixed by 11a, 11b and screws 11c, 11d (not shown). The screws 11a, 11b, 11c, 11d are made of non-magnetic material.

FIG. 12 shows a perspective sectional view of the main housing 1, and FIG. 13 shows a perspective view of the sub housing 3. Reference numerals 50a to 50d are bottom projections, and 51a to 51d are top projections. The bottom protrusion 50
The a to 50d face the upper surface protrusions 51a to 51d, respectively, and form four pairs of protrusions in the cylindrical space 2.

The number of magnetic poles of the disk-shaped permanent magnet 5 is equal to the number of pairs of protrusions (50a and 51a, 50b and 51b) in the space 2, and the thickness thereof is from the depth of the space 2 to the depth of the pair of protrusions (bottom protrusion 50a). And the sum of the depth of the upper surface projection 51a)). Further, the diameter of the permanent magnet 5 is slightly shorter than the inner diameter of the space 2, and the difference is about the same as the difference in the depth direction.

The ring-shaped space on the inner wall of the space 2 is narrowly dimensioned so as to function as a translational motion preventing portion. That is, since the apparent density of the magnetic fluid 4 is large near the magnetic poles of the permanent magnet 5, a strong magnetic viscoelastic force acts between the inner wall, which is the translational motion preventing portion, and each magnetic pole of the permanent magnet 5, and the permanent magnet 5 has a strong magnetic viscoelastic force. The translational movement is suppressed. In addition, the thin plate-shaped spaces on the top surface and the bottom surface of the space 2 are formed to have a size of wide eyes, and each magnetic pole (N, N,
S) There is a return torque generating portion (the pair of protrusions) facing each other in the normal direction of the intermediate portion and provided with a distance substantially equal to the distance between the translational movement preventing portion and the magnetic pole of the permanent magnet. As will be described later, this acts to generate a return torque with respect to the rotational movement of the permanent magnet 5. The magnetic fluid 4 is injected through the small hole 7 of the sub-housing 3, sealed with a rubber plug 8 and then sealed and fixed with a cap 9. An O-ring 10 is provided between the main housing 1 and the sub-housing 3. Reference numerals 12a and 12b denote Hall elements which are magnetic detection elements, and are arranged outside the main housing 1 so as to face the inner wall of the space 2 at a middle angle position between the pair of protrusions of the main housing 1 with a constant space. Adhesive fixed.

 FIG. 14 shows a block diagram of the circuit system.

The lead wire bundle 21 taken out from the processing circuit 16 is
It is connected to the terminals 234 and 235 of the processing circuit 16. 235 is connected to the power source and 236 is connected to the ground. Hall element 12a, 12b
Are connected to the power supply terminal 235 and the ground, respectively.

 Reference numerals 31 to 33 are differential amplifiers.

The two output terminals of the Hall element 12a are connected to the input terminals of the differential amplifier 31. The two output terminals of the Hall element 12b are connected to the input terminals of the differential amplifier 32. The output terminals of the differential amplifiers 31, 32 are connected to the input terminal of the amplifier 33, and the output terminal of the amplifier 33 is connected to the terminal 234 of the processing circuit 16. The rest of the configuration is the same as in the first embodiment.

 Next, the operation will be described based on the above configuration.

When the angular acceleration a is applied to the disk-shaped permanent magnet 5, an inertia torque acts on the permanent magnet 5 to try to rotate in the main housing 1. The apparent density of the magnetic fluid 4 in the vicinity of the protrusions 50a to 50d, 51a to 51d, which are return torque generating portions formed on both bottom surfaces of the cylindrical space 2 of the main housing 1 as the permanent magnet 5 rotates, It becomes large at a position close to the magnetic pole and becomes small at a position far from it, and a magnetoelastic restoring torque acts on the permanent magnet 5. The permanent magnet 5 stands still at the equilibrium angular position between the restoring torque and the inertia torque.

Therefore, if the angular position of the permanent magnet 5 in the space 2 is detected, a signal corresponding to the angular acceleration a can be obtained. Hall elements 12a and 12b are used to detect the position of the magnet 5.

However, if the permanent magnet 5 moves (translates) in parallel with its own plane, it will be affected by it and cannot be separated from the angular acceleration signal. In order to prevent the translational movement of the permanent magnet 5, the space between the inner surface of the space 2 and the outer peripheral surface of the permanent magnet 5 is made small.

In addition, when the permanent magnet 5 is about to rotate by providing a pair of radial projections between the magnetic poles on the upper bottom surface of the space 2, between the high apparent density portion of the magnetic fluid 4 near the magnetic poles and the side surface portion of the projection. The magnetic viscoelastic force that acts as a return torque to the permanent magnet 5 works to function as a return torque generating means. Here, in order to have this function also in the translational direction, the inner wall of the space 2 is used as the translational movement preventing portion,
It is arranged in the high density portion of the magnetic fluid 4 in the vicinity. Therefore, the permanent magnet 5 is prevented from translational movement within the space 2, and only rotational movement within the same space within the space 2 is permitted.

Further, the permanent magnet 5 is similarly made hard to move in the axial direction of the cylinder in the space 2. This is for suppressing not only the horizontal translational movement but also the vertical translational movement. To achieve this, the distance between the bottom surfaces of the permanent magnet 5 and the bottom surfaces of the space 2 is set to be substantially equal to the distance between the outer peripheral surface of the permanent magnet 5 and the inner side surface of the space 2, and sufficiently small. Done. This utilizes the fact that the magnetic field distribution near the magnetic pole is spatially distributed not only on the side surface of the magnet but also in the bottom surface direction as described above. That is, the distance between the bottom surface of the permanent magnet 5 and the pair of protrusions provided on the bottom surface of the cylindrical space 2 is made sufficiently small, and the bottom area of the pair of protrusions is set appropriately, whereby the magnetic fluid 4 near the magnetic poles is The high apparent density area fills the axial gap between the magnet and the housing,
The movement of the permanent magnet 5 with respect to the axial acceleration is suppressed.

As described above, in the configuration including the permanent magnet 5 and the magnetic fluid 4 enclosed in the space 2, the same number of pairs of protrusions as the magnet magnetic poles are radially provided on both bottom surfaces of the space 2 so as to face the middle of the magnetic poles, and By setting the diameter of the permanent magnet 5 to be slightly smaller than the inner diameter of the space 2 and simultaneously setting the length of the space 2 in the axial direction of the permanent magnet 5 to be slightly longer than the length of the permanent magnet 5, the following three The effect is obtained.

(1) The permanent magnet 5 floats stably in the magnetic fluid 4 in the space 2.

(2) The permanent magnet 5 receives a return torque due to magnetic viscoelasticity.

(3) The permanent magnet 5 does not translate.

Therefore, the angular position of the permanent magnet 5 with respect to the angular acceleration, that is, the position of each magnetic pole is uniquely determined. Therefore, the applied angular acceleration can be found by detecting the magnetic pole position using a magnetic detection element such as a Hall element.

A specific example will be described with reference to FIG. 10 (b) and FIG. In FIG. 10 (b), the x-axis is the Hall elements 12a-12b.
Direction, the y axis is taken in the direction orthogonal to the x axis. The case of a 4-pole permanent magnet is shown, and the S pole-S pole axis of the permanent magnet 5 forms a 45 degree angle with the X axis, and the N pole-N pole axis stabilizes at a position that forms a 45 degree angle with the Y axis. There is. When the angular acceleration A is applied to the apparatus as shown in FIG. 10 (b), the angular acceleration a is applied to the permanent magnet 5 relative to the main housing 1. The angular acceleration a is a vector having the same magnitude as the angular acceleration A and heading in the opposite direction. If the weight of the magnet 5 is m, the inertia torque T ₁ acting on the magnet 5 can be expressed as T ₁ = k ₁ · m · a. here,
k ₁ is a constant determined by various conditions.

Further, the magnetoelastic torque T ₂ has the same magnitude as the inertia torque T ₁ in the opposite direction.

Here, in the horizontal cross section of the space 2, the center of rotation is taken as the center of rotation, and the angular position at which the line connecting the S poles of the permanent magnets 5 coincides with the line connecting the Hall elements 12a and 12b is taken as the origin of rotation. Letting P (R, θ) be the magnetic pole position of the permanent magnet 5 when the magnetoelastic torque T ₂ and the inertia torque T ₁ are in equilibrium, the relationship | T ₂ | = k ₂ · sin (4θ) To establish.
Here, k ₂ is a constant.

Therefore, by setting | T ₁ | = | T ₂ |, in the region where θ is small, approximation can be performed as in the following equation.

here, In other words, (R, θ) = (R, | a | / k), and the applied angular acceleration can be known by knowing the magnetic pole position (R, θ).

Therefore, as shown in FIG. 10 (a), Hall elements 12a, 12b
Are arranged so as to face the magnetic pole intermediate position. Hall element 12a,
12b is arranged so that the positive output increases when the N pole of the permanent magnet 5 approaches. Therefore, for example, when the permanent magnet 5 rotates in the θ direction in FIGS. 10A and 10B, the Hall element 12a and the magnetic pole N approach each other, and the output of the Hall element 12a becomes large. At the same time, the output of the Hall element 12b also becomes large.
The Hall element output voltage is an output that is substantially proportional to the square of the distance between the Hall element and the magnetic pole.

Therefore, if the sum output of the Hall elements 12a and 12b is taken, an output voltage substantially proportional to the magnetic pole position can be obtained when the magnet rotation amount is small. Also, by taking the sum output, a high gain can be obtained. In addition, if the permanent magnet 5
Even if the robot makes a translational movement, the output of the hall element 12a increases and the output of the hall element 12b decreases, so that the change in the sum is small. Therefore, the output voltage according to the angular acceleration can be obtained from the output terminal 34 of the processing circuit 16.

It should be noted that the processing circuit 16 of FIG. 14 will be briefly described. The Hall elements 12a, 12b are coupled to the regulated power supply via the terminal 235. The output of the Hall element 12a is obtained via the differential amplifier 31, and similarly, the output of the Hall element 12b is obtained via the differential amplifier 32. And with the differential amplifier 31
The sum output of the outputs of 32 is obtained via the operational amplifier 33,
Connected to 234.

The amount of the magnetic fluid 4 enclosed in the space 2, that is, the space 2
The volume obtained by subtracting the volume of the permanent magnet 5 from the volume of is preferably equal to the total amount of the magnetic fluid 4 that the permanent magnet 5 can hold in the free state. Here, in the free state, the permanent magnet 5
The total amount of the magnetic fluid 4 that can be held by means the total amount of the magnetic fluid 4 attached to the permanent magnet 5 when the permanent magnet 5 is inserted into the magnetic fluid 4 at normal temperature and pressure and pulled up. This state is the same as in FIG. If the volume is determined to be larger than this amount, the translational movement of the permanent magnet 5 with respect to the acceleration occurs. This is because if it is set small, the amount of rotation with respect to the angular acceleration is reduced and the sensitivity is reduced.

FIG. 15 shows the output Vo of the terminal 234 with respect to the magnitude of the applied angular acceleration. The parameter θ is an angle formed by the S-pole-S-pole axis and the X-axis.

In the above-described second embodiment, the number of magnetic poles of the permanent magnet 5 and the pair of protrusions in the space 2 are shown as two sets facing each other, but any number of sets may be used as long as the former is two and the latter is one or more.

Further, although two Hall elements are used as magnetic detection elements and are arranged in the middle of the magnetic pole, it is needless to say that the number of Hall elements may be one or more, and the position thereof can be arbitrarily set.

Although a disk-shaped magnet is shown as the permanent magnet,
A ring-shaped permanent magnet as shown may be used. In this case, the magnetic detection element 12 can be arranged inside the ring.

[Brief description of drawings]

FIG. 1 (a) shows I- of FIG. 2 showing the first embodiment of the present invention.
A transverse sectional view taken along the line I, FIG. 1 (b) is a vector diagram for explaining the direction in which acceleration acts, FIG. 2 is a longitudinal sectional view of the first embodiment, and FIG. 3 is used in the first embodiment. FIG. 4 is a perspective sectional view of the main housing, FIG. 4 is a perspective view of the sub-housing used in the first embodiment, FIG. 5 is a circuit diagram showing an electric circuit of the first embodiment, and FIG. FIG. 7 is a perspective view showing a state in which magnetic fluid is attached to the permanent magnets used in Examples.
FIG. 8 is a vertical sectional view of FIG. 6, and FIGS. 8 and 9 are characteristic diagrams showing the characteristics of the output voltage of the acceleration sensor of the first embodiment. FIG. 10 (a) shows an eleventh embodiment of the present invention.
A transverse sectional view taken along the line S10-S10 in the figure, FIG. 10 (b) is a vector diagram for explaining the direction in which the angular acceleration acts, and FIG.
FIG. 12 is a perspective sectional view of a main housing of the second embodiment, FIG. 13 is a perspective view of a sub-housing of the second embodiment, and FIG. 14 is an electric circuit of the second embodiment. The circuit diagram shown in FIG. 15 is a characteristic diagram showing the output characteristic of the angular acceleration sensor,
FIG. 16 is a partial configuration diagram showing a positional relationship between a ring-shaped permanent magnet and a magnetic detection element as a modified example of the second embodiment. 1 ... Main housing, 2 ... Space, 3 ... Sub housing, 4
... Magnetic fluid, 5 ... Permanent magnets, 12a-12d ... Magnetic sensing element, 50
a to 50d, 51a to 51d ... Protrusion pair.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihisa Ishihara 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Japan Auto Parts Research Institute, Inc. (72) Inventor Tatsuo Sugitani 1 Toyota-cho, Aichi Prefecture Toyota Motor Corporation Stock In-house (72) Inventor Hideo Inoue 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (56) Reference JP-A-2-138875 (JP, A) JP-A-2-90061 (JP, A) JP 61-62870 (JP, A)

Claims (4)

(57) [Claims] 1. A main housing made of a non-magnetic material having a substantially cylindrical space whose one end surface is open, and a non-magnetic material fixed to the main housing so as to close the one end surface of the main housing. Made of a sub-housing, bottom projections radially formed on the bottom surface of the space of the main housing, top projections radially formed on the space side surface of the sub-housing facing the bottom projections, in the space A magnetic fluid that is filled and sealed; a disk-shaped permanent magnet that is sealed together with the magnetic fluid in the space and is magnetized in the radial direction on the circumferential surface, and a flat surface portion faces the bottom surface projection and the top surface projection; A magnetic detection element is provided between the pair of projections formed by each of the bottom surface projections and each of the top surface projections, and detects a position of the permanent magnet to generate a detection output. Acceleration sensor. 2. A substantially perfect circular ring-shaped space filled with the magnetic fluid exists between the inner wall of the cylindrical space of the main housing and the peripheral surface of the permanent magnet, and the bottom surface of the main housing. Thin plate-like spaces filled with the magnetic fluid are present to face each other between the flat surface of the permanent magnet and the flat surface of the sub housing and the other flat surface of the permanent magnet. The acceleration sensor according to claim 1. 3. The ring-shaped space is set to have a size of wide eyes that allow a large number of linear movements of the permanent magnet along the plane direction, and the thin plate-shaped space is configured to rotate the permanent magnet. Is set to have a narrower size so as to substantially prevent the magnetic field, and the magnetic detection element has at least four locations at predetermined intervals around the permanent magnet so as to generate a detection output according to the linear movement of the permanent magnet. The acceleration sensor according to claim 2, wherein the acceleration sensors are dispersed in the same. 4. The ring-shaped space is narrowly dimensioned so as to substantially prevent linear movement of the permanent magnet along the planar direction, while the thin plate-shaped space is rotational movement of the permanent magnet. The size of a wide eye is set so as to allow the magnetic field, and at least one magnetic detection element is provided opposite to the permanent magnet so as to generate a detection output according to the rotational movement of the permanent magnet. The acceleration sensor according to claim 2, wherein: