JP3190978B2 - Accelerometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device (acceleration sensor) for detecting acceleration, vibration, etc. of a moving body such as an automobile.

[0002]

Conventionally, as the acceleration sensor using a magnetic sensor and magnet, by using a magnet or a magnetically permeable material to detect the mass displacement of the detection mass which is fixed to the spring as shown in Figure 5, the magnetic sensor A method of using as a change in output, or a method of forming a spring system similar to that of FIG. 5 by a magnet itself using repulsive force of a magnet as shown in FIG. 6 , or a magnet and a magnet or a magnetically permeable material as shown in FIG. And the like, which detects the detected mass that is displaced by overcoming the attractive force by an acceleration equal to or higher than a predetermined threshold value using an electric contact or the like using the attractive force. However, in the first method, the relationship between the output of the magnetic sensor and the amount of displacement corresponding to the acceleration becomes complicated, and the device itself is complicated because a magnetic sensor array must be used for accurate measurement. And it is difficult to respond only to acceleration exceeding a certain threshold value.It is also difficult to check the operation and calibrate the sensitivity. There were problems. Further, in the second method, by using the repulsive force of the magnet to form a spring system similar to the first method, the problem of the reliability of the spring can be cleared, but the remaining problem of the first method remains. Could not be solved. Further, in the third method, the apparatus reacts only to an acceleration equal to or higher than a certain threshold value. However, it is difficult to set the threshold value accurately with the strength of the magnet.
Lack of real-time quantification of acceleration itself
There was a problem that some operation for returning to the initial position is required to operate again after the operation.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems, to enable real-time quantification of acceleration, and to easily set a threshold value of a responsive acceleration. To provide an acceleration sensor that is simple and reliable.

[0004]

According to the present invention, there are provided two magnets which are masses for detecting an acceleration, a housing having a passage through which the magnets can be freely displaced on one axis, and a method for measuring the displacement of the detected mass by the magnetic flux density. The Hall element can be detected as a change, and the detection mass composed of the two magnets is disposed on the side walls of both ends of the housing by repulsion by opposing the same poles, and the Hall element is provided in the housing.
To detect the magnetic flux density in the magnet movement direction at the center of the magnet.
An acceleration sensor, wherein the acceleration sensor is disposed at a position corresponding to the acceleration sensor.

Hereinafter, an acceleration sensor according to the present invention will be described with reference to FIG. In the figure, 1
Ho is the magnet which is detected by mass of the acceleration, 2 can detect the displacement of the magnet is detected by mass as a change in magnetic flux density
Reference numeral 3 denotes a passage through which a magnet serving as a detection mass can be freely displaced on one axis. Reference numeral 4 denotes a housing. Reference numeral 5 denotes side walls of both ends of the housing. Reference numeral 6 denotes a lead for taking out input and output of the Hall element . . The two magnets 1 that are the detected masses of acceleration are pressed against the side walls 5 at both ends of the housing by mutual repulsion by facing the same poles, and are not fixed to the side walls 5 at both ends of the housing. Thus, it is possible to freely move in the passage 3 as shown in FIG. 2 in accordance with the acceleration exceeding the force pressed against the side walls 5 at both ends of the housing. The relationship between this acceleration and the displacement of the detected mass in the state of FIG. 2 where the repulsive forces of the two magnets are balanced can be approximately described by the following equation of motion.

Ma = 3M ² / 2πμ ₀ L ⁴ (Equation 1) where m is the mass of the magnet, a is the acceleration received by the sensor, M is the strength of the magnetic pole, μ ₀ is the magnetic permeability in vacuum, and L is The distance between the centers of the two magnets. The acceleration can be measured by extracting the displacement of the detected mass in a state where the acceleration and the repulsive force of the two magnets are balanced as an output of the magnetic sensor corresponding to the change in the magnetic flux density. In the state where the acceleration as shown in FIG. 2 and the repulsion of the two magnets are balanced,
The strength of the magnetic field at the position of the Hall element arranged at the center of the passage is approximately represented by the following equation. _{H = 2M / 4πμ 0 × {} (1 / (L-L 0/2) 3 -
(1 / (L _0/2 ) ³ )｝ (Equation 2) Here, L ₀ is the distance between the centers of the two magnets at the time of stationary or constant-speed linear motion.

Accordingly, since B = μ ₀ H (Equation 3), the magnetic flux density is determined by the output V of the magnetic sensor.
_By taking _out as out, the acceleration can be measured in real time according to the relationship shown in FIG. 3 determined by Expressions 1, 2, and 3. In the acceleration sensor of the present invention, as can be seen from Equations 1 and 2, not only the mass m of the two magnets, which is the detected mass, or the strength M of the magnetic pole, but also the distance L ₀ between the two magnets is changed. This has the characteristic that the threshold value of the responsive acceleration can be freely changed.
That is, by changing the length of the housing, it is possible to freely change the threshold value of the acceleration that reacts.

In the acceleration sensor according to the present invention, in which the threshold value of the responsive acceleration can be freely changed , the displacement of the magnet, which is the detected mass, is determined by the change of the magnetic flux density.
Hall element that detects and detects acceleration in real time
The output voltage V _out is the magnetic flux
Those that are proportional to the density B are particularly preferred. Also, Hall element
Integrated with integrated circuit with control drive function
Or into a single package by making it monolithic
It is also preferable to use a Hall IC that has been used. or,
The displacement of the magnet, which is the detection mass used in the present invention, is
Hall element detected as a change in degree is ± two directions on one axis
The resulting symmetrical ± bidirectional output voltage V _o is relative acceleration
The magnetic flux density in the direction of magnet movement in the housing
The magnetic flux density in the direction of magnet movement is
It is arranged to detect the degree.

The housing used in the acceleration sensor according to the present invention comprises a cylindrical or square pipe made of a non-magnetic metal material or a resin material, and lids at both ends. The inner wall of the passage in which the magnet moves is required to be sufficiently smooth to minimize the frictional resistance during the movement of the magnet. For this reason, in the case of a metal material, a material whose inner wall is mirror-polished by electrolytic polishing or another method, or a material coated with a Teflon resin or the like is preferably used. In the case of a resin material, a Teflon resin or the like is preferably used. Also, for the purpose of minimizing the contact area between the magnet and the housing, a hole is provided at the center of the magnet axis, and the hole of the magnet is passed through the housing,
Providing a supporting column for sliding is also a preferable method. Further, in the housing used for the acceleration sensor of the present invention, in order to eliminate air resistance in the passage, it is also preferable to provide a hole portion for releasing air when the magnet is moved in the pipe portion and the lid portion of the housing,
It is also preferable to previously form a groove in the inner wall of the pipe portion in the axial direction for the same purpose.

[0010] Also, the magnet is detected by mass of the acceleration used in the acceleration sensor of the present invention is strong in small, remanence B _r, the coercive force H _c, the maximum energy product BH _max
Anything can be used as long as it is large, but ferrite magnets,
Samarium cobalt magnets, neodymium iron boron magnets and the like are preferably used, and plastic magnets using the above materials are particularly preferably used because of their smooth surface state. Further, regarding the shape of the magnet used in the present invention, for the purpose of minimizing the contact area between the magnet and the housing described above and minimizing frictional resistance and eliminating air resistance in the passage, a hole or a hole is formed in the axial direction. A member having a groove may be used.

Further, the acceleration sensor according to the present invention is characterized in that two magnets as detection masses are arranged on the side walls of both ends of the housing by repulsion by opposing the same poles to each other. In order to increase the mass m of the magnet, one of the means for freely changing the threshold value and sensitivity of the acceleration to be reacted may be used in combination with a magnet and a weight as one detection mass. It is within the scope of the present invention.

Further, in the acceleration sensor of the present invention,
Depending on the sensitivity of the sensor and the degree of frequency required to react, the magnet that is the detected mass is filled with a viscous fluid having a function like a lubricant in the passage where the magnet is displaced according to the magnitude of the acceleration. It is also preferable to provide a function of a damper in the system. The damper function can be adjusted by changing the viscosity of the viscous fluid, and it is also preferable to use a lubricant mainly for the purpose of filling the fluid with a low viscosity.

In the acceleration sensor according to the present invention,
As shown in FIG. 4 , a so-called servo type that performs high-precision measurement by using a coil for generating a magnetic field for canceling the displacement of a magnet, which is a detected mass corresponding to the acceleration, and detecting the amount of current flowing through this coil. It is also preferably used as a sensor. In this case, when the acceleration sensor receives the acceleration, the Hall element generates an output corresponding to the displacement amount by the movement of the magnet as the detected mass, and the Hall element cancels the output according to the output of the Hall element. , A current is passed through the coil. By detecting this amount of current, highly accurate measurement of acceleration can be performed.
In this case, it goes without saying that a viscous fluid may be filled in a passage in which the magnet, which is the detection mass of the acceleration, is freely displaceable.

In the acceleration sensor according to the present invention,
For the purpose of eliminating the influence of the external magnetic field, the sensor itself may be provided with a means such as a magnetic shield, and for the purpose of suppressing the demagnetization of the magnet, it is also preferable to form an appropriate magnetic circuit or the like around the housing. .

[0015]

【Example】

[0016]

Example 1 Inner diameter of inner wall smoothed by electrolytic polishing
A 1 mm, 18 mm long Al pipe was made with a hole large enough to receive the Hall element, and the Hall element was inserted from the lateral direction and solidified using resin. It was set so that the magnetic flux density in the direction could be measured. Next, using a plastic magnet LJ-120 made of samarium cobalt manufactured by Tohoku Metal Co., Ltd., two magnets having a weight of 0.2 g and a surface magnetic flux density of 2.2 kG were formed into a column having a diameter of 3.0 mm and a height of 4 mm. After setting in the pipe so that the same poles face each other,
By making Al lids on both ends of the housing, an acceleration sensor having a structure as shown in FIG. 1 was produced in which two magnets as detection masses were pressed against the side walls of both ends of the housing by repulsive force.

In order to eliminate air resistance in the passage, holes are formed in the pipe portion and the lid portion of the housing of the acceleration sensor to allow air to escape when the magnet is moved.
Then, by inserting a rod through the hole formed in the lid, the magnet is forcibly moved as shown in FIG. 2, thereby examining the relationship between the displacement of the magnet and the output of the Hall element. Calibration was performed.

Further, FIG. 3 shows the results of actual measurement of the relationship between acceleration and output voltage using the manufactured acceleration sensor. This shows that the acceleration could be measured as the magnitude of the magnetic flux density at the position of the magnetic sensor, almost as calculated. Thus, in the acceleration sensor of the present invention, real-time quantification of acceleration is possible,
Further, it can be understood that the setting of the threshold value of the reaction acceleration can be easily performed by changing not only the mass m of the magnet and the strength M of the magnetic pole but also the length of the housing. In addition, in the acceleration sensor of the present invention, it is possible to easily perform the virtual operation check and the sensitivity calibration, which are difficult with the conventional acceleration sensor, as described in the present embodiment.

Further, in the acceleration sensor according to the present invention,
As an application, as shown in Fig. 4, a simple modification to add a coil to generate a magnetic field that cancels out the displacement of the magnet, which is the detected mass corresponding to the acceleration, enables high-precision detection by detecting the amount of current flowing through this coil. The measurement can be performed as described above.

[0020]

EXAMPLE 2 A hole having a size for receiving a Hall element was formed in the center of an Al pipe having an inner diameter of 3.1 mm and a length of 18 mm, the inner wall of which was smoothed by electrolytic polishing in the same manner as in Example 1.
The Hall element was inserted from the lateral direction, and was set using a resin. The Hall element was set so that the magnetic flux density in the axial direction of the pipe could be measured. Next, a plastic magnet L made of samarium cobalt made of Tohoku Metal
J-120 was used to form a column having a diameter of 3.0 mmφ and a height of 4 mm, weighing 0.2 g, and a surface magnetic flux density of 2.2 kG.
By setting the two magnets in the pipe so that the same poles face each other, filling the pipe with lubricating oil, and covering both ends of the housing with Al-made lids, the repelling force is used to detect the mass. An acceleration sensor having a structure as shown in FIG. 1 in which two magnets are pressed against the side walls of both ends of the housing was manufactured. A groove serving as an escape route for lubricating oil was previously formed in the inner wall of the pipe in order to reduce the resistance during the movement of the magnet. Further, when the relationship between the acceleration and the output voltage was actually measured using the manufactured acceleration sensor, the value of the output voltage with respect to the constant acceleration was smaller than that of the first embodiment due to the damper function due to the filling of the lubricating oil. However, the tendency of the output voltage responding to the acceleration was almost the same as in the first embodiment.

[0021]

According to the acceleration sensor of the present invention, two magnets which are masses for detecting acceleration have the same poles facing each other.
By adopting a structure in which the housing is pressed against the side walls of both ends of the housing by repulsion, the acceleration sensor with a simple and innovative structure has been realized, thereby greatly improving the reliability and mass productivity of the acceleration sensor. It was made. That is, the spring system of the conventional acceleration sensor having one detected mass as shown in FIGS. 5 and 6 is disassembled, and the two detected masses are allowed to perform the measurement of the acceleration in both directions. Mass m of the two magnets, which is the mass
Not only the strength M of the or poles, the distance between the two magnets L ₀
By changing the threshold value, it is possible to change the threshold value of the acceleration that easily reacts. In particular,
In the acceleration sensor of the present invention, the threshold value of the acceleration to be reacted can be freely changed by changing the length of the housing.

Further, with such a structure, it becomes possible to arrange the Hall element so as to measure the magnetic flux density in the axial direction in which the magnet, which is the detected mass, is displaced. The displacement can be easily and accurately measured as the intensity of the magnetic flux density, and real-time quantification of the acceleration is realized. Furthermore, in the acceleration sensor according to the present invention, the virtual operation check and the sensitivity calibration, which were difficult with the conventional acceleration sensor, can be easily performed, so that the product check at the time of mass production is easy. The merit is great, and it has made it possible to mass-produce low-cost and highly reliable acceleration sensors.

As described above, the acceleration sensor of the present invention realizes high reliability and high mass productivity while realizing high-accuracy measurement of acceleration by its innovative and simple structure. From the feature that the threshold value of the responsive acceleration can be freely changed, it can be used in a wide range of applications including applications such as automobiles and other airbags, so that the industrial merit of the present invention cannot be largely measured. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of an acceleration sensor of the present invention. (The figure which shows the state at the time of stationary or linear motion at constant velocity.)

FIG. 2 is a diagram showing a state of the acceleration sensor according to the present invention during an acceleration motion.

FIG. 3 is a diagram showing a relationship between acceleration and output voltage of the acceleration sensor of the present invention.

FIG. 4 is a diagram showing a structure of a servo type acceleration sensor of the present invention.

FIG. 5 is a diagram showing a conventional acceleration sensor using a Hall element and a magnet.

FIG. 6 is a diagram showing a conventional acceleration sensor using a Hall element and a magnet.

FIG. 7 is a diagram showing a conventional acceleration sensor using a Hall element and a magnet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet (detection mass) 2 Hall element 3 Passage 4 Housing (pipe part) 5 Housing (both side wall parts) 6 Lead wire 7 Coil 8 Spring 9 Fixed magnet 10 Conductive material 11 Electrical contact

Claims (2)

(57) [Claims] 1. Two magnets that are masses for detecting acceleration,
The magnet comprises a housing having a passage through which the magnet can be freely displaced on one axis, and a Hall element capable of detecting the displacement of the detected mass as a change in magnetic flux density. The detected mass composed of the two magnets has the same polarity. the by repulsive force by causing opposing, it is arranged on the side wall of the housing end portions, front
The Hall element moves the magnet in the center of the housing.
An acceleration sensor, wherein the acceleration sensor is arranged to detect a magnetic flux density in a direction . 2. The servo type acceleration sensor according to claim 1, further comprising a coil for generating a magnetic field for canceling a displacement of a magnet which is a mass for detecting the acceleration.