JPH04364467A - Differentiated acceleration sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a sensor for detecting the differential value of the acceleration of a moving body, that is, the jerk.

0002

[Prior Art] Physical quantities that describe the motion of an object usually include position, velocity (angular velocity), and acceleration (angular acceleration), and sensors have been devised to detect each physical quantity. It is a well-known fact that By the way, humans can only visually recognize position and velocity intellectually, and what they can sense and sense is acceleration and higher-order physical quantities. For example, when riding in a moving object such as a car, the user can experience changes in its state when it accelerates or decelerates.

[0003] Here, ``Development of acceleration sensor for automobiles (
According to documents such as "Nissan Technical Report No. 23, 1982-12)", it is known that humans react more sensitively to jerk, which is the differential value of acceleration, than to acceleration. This fact shows that jerk is deeply involved in the sensations of pleasure and displeasure felt by humans. Therefore, in order to make vehicles that involve movement, such as automobiles and elevators, more comfortable, it is necessary to detect information on not only this acceleration but also jerk.

0004

However, there are almost no systems that detect and control jerk. The reason for this is that comfort has only recently begun to play an important role in products, and ergonomic considerations have not progressed sufficiently.

[0005] On the other hand, acceleration sensors are increasingly being applied to products. For example, in active suspension systems for automobiles, multiple acceleration sensors are used to detect the driving behavior of the automobile, thereby improving ride comfort. This is aimed at achieving both maneuverability and stability. Changes in acceleration can also be obtained by passing the output of this acceleration sensor through a differential filter circuit, but there is a problem in that differential filters are generally susceptible to noise, making it difficult to detect with high accuracy.

[0006]

[Means for Solving the Problems] In order to solve the above problems, it is desirable to provide a sensor that directly detects jerk, that is, a physical quantity proportional to a change in acceleration. For this purpose, the sensor may be configured as follows. first,
A thin plate-like object (cantilever) is placed inside the sensor so that its wide plane is perpendicular to the detection direction. The vicinity of the tip of this cantilever faces the wall surface of the fixing part with a small gap in between. Further, the root portion to which the cantilever is fixed and the wall surface of the fixing portion are coupled via a permanent magnet. The cantilever and its fixed part (called a yoke) are made of a magnetic material with high magnetic permeability. Furthermore, a pickup coil made by winding a thin electric wire is arranged so as to surround a part of the cross section of the yoke. The entire detection section is housed in a casing made of diamagnetic material that does not allow magnetic flux to pass through. At this time, the system consisting of the cantilever, yoke, and permanent magnet forms a magnetic path through which the magnetic flux passes. The magnitude of this magnetic flux depends on the distance between the air gap between the cantilever and the yoke. If the distance of this air gap changes, the magnetic flux also changes, so an induced electromotive force proportional to the differential value of the magnetic flux is generated in the pickup coil according to the law of electromagnetic induction. This generated voltage is taken out to the outside as a sensor output.

[0007]

[Operation] According to the present invention, the cantilever inside the sensor is displaced by the action of acceleration, and the magnetic flux passing through the magnetic path including this cantilever is changed. As a result, an induced electromotive force is generated in the pickup coil arranged so as to surround the cross section of the magnetic path. This induced electromotive force is proportional to the differential value of magnetic flux,
The magnitude of the magnetic flux is proportional to the displacement of the cantilever, which in turn is proportional to the acceleration experienced by the sensor. That is,
By detecting the induced electromotive force at this time, change in acceleration - jerk can be detected.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to the drawings. FIG. 1 shows a cross-sectional view of a first embodiment of the invention. In the figure, a cantilever 1 and yokes 2 and 3 are made of a magnetic material that allows magnetic flux to pass through, and these, an air gap 4, and a permanent magnet 5 form a magnetic path. A pickup coil 6 is arranged so as to surround the cross section where the yoke is located. The entire structure is covered with a casing 7 made of a non-magnetic material.

Here, the casing 7 is fixed to a moving object, and has a length l and a width d as shown in FIG.
, a case where a cantilever 1 having a thickness th faces only its tip xg to the yoke 3 across a gap of δ. Now, at time t, acceleration α(t) is applied to the cantilever from the left direction.
acts on the entire cantilever, F(t)=
A force of m·α(t) (m: mass of the cantilever, f=F/l per unit length in the longitudinal direction) is applied. At this time,
Displacement size u at position x with respect to the tip of the cantilever
(x) is expressed by the following formula.

0010

[Math 1]

[0011] Here, E is the Young's modulus of the cantilever, I
is the second moment of area. And from x=0 to x=
The average displacement up to xg is obtained by integrating equation (1) and dividing by xg, as shown in the following equation.

0012

[Math 2]

When the initial setting value of the gap length δ is δ0, the average gap length δg is given by the following equation.

[0014]

[Math 3]

Next, in FIG. 1, if the magnetomotive force of the permanent magnet 5 is U, and the magnetic permeability of the cantilever 1 and yokes 2 and 3 is sufficiently larger than that of the air gap 4, then the amount of magnetic flux passing through this magnetic path is Φ is expressed by the following equation using Ampere's circuit theorem.

[0016]

[Math 4]

Here, Sg is the cross-sectional area of the air gap 4, and μ0 is the vacuum magnetic permeability. It can be seen from equation (4) that magnetic flux Φ is inversely proportional to δg, but if the design is made so that (C■/δg) f is sufficiently smaller than 1 for f within the measurement range using equation (3), the following can be obtained. It can be approximated as shown in Eq.

[0018]

[Math 5]

Next, due to the temporal change in the external force f(t), δ
Since g changes and the magnetic flux Φ also changes, an induced electromotive force e(t) expressed by the following equation is generated in the pickup coil 6.

[0020]

[Math 6]

[0021] Here, N is the number of turns of the pickup coil 6. Approximation using equation (5) and f(t)=(m/l)α(
Using the relationship t), it can be expressed as the following equation.

[0022]

[Math 7]

[0023] Therefore, a differential value of acceleration, that is, jerk is obtained.

[0024] As described above, a limiting condition was required that the approximation shown in equation (5) was established when the air gap length δ was used to change the magnetic flux Φ. Next, FIG. 3 shows a second embodiment of the present invention in which the cross-sectional area S of the void is varied. In FIG. 3, first, a weight 12 having a mass M is attached to the tip of the cantilever 11, and faces each other across a yoke 13 and a gap 14 having a gap length δ. The cantilever 11 is fixed to a yoke 15, and together with a permanent magnet 16, a magnetic path is formed. Here, the opposing surfaces of the weight 12 and the yoke 13 are surfaces with equal curvature with the radius of rotation at the base of the cantilever 11, and as shown in the figure, the weight 12 is on the left side and the yoke 13 is on the right side. , respectively. Now, assume that acceleration α(t) occurs and acts on the cantilever 11 and the weight 12 as shown in FIG. If the mass M of the weight 12 is sufficiently larger than the mass of the cantilever, the cantilever 11
The displacement of can be approximately considered as a force F(t)=Mα(t) acting on the tip, and the displacement v of the tip is expressed by the following equation.

[0025]

[Math. 8]

If the acceleration acts to the left, the cross-sectional area A■ forming the air gap 14 decreases, and if the acceleration acts to the right, the cross-sectional area A■
increases. The displacement u at the tip of the weight 12 can be approximated by the following equation.

[0027]

[Math. 9]

[0028] However, l is the length from the base of the cantilever to the tip of the weight. Therefore, equations (4), (6
), the induced voltage e(t) generated in the pickup coil 17 in FIG. 3 is expressed by the following equation.

[0029]

[Math. 10]

[0030] Letting the width of the void be d■, equations (8) and (9)
When rearranged using , the differential value of the cross-sectional area A is given by the following equation.

[0031]

[Math. 11]

Here, the relationship F=Mα was used. Formula (1
0), the induced voltage e(t) proportional to the jerk (dα/dt) can be obtained from equation (11).

[0033]

[Effect of the invention] According to the present invention, the jerk itself is
Since it can be detected directly, it is possible to perform highly accurate detection without worrying about being affected by noise, compared to the case where acceleration is detected and obtained using a differentiating circuit. Therefore, it can be used in a control system for improving the comfort of vehicles such as automobiles.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a first embodiment of the structure of a jerk sensor.

FIG. 2 is an explanatory diagram of the displacement of a cantilever under acceleration.

FIG. 3 is a sectional view of a second embodiment of the structure of a jerk sensor.

FIG. 4 is an explanatory diagram of changes in the cross-sectional area of the void when subjected to acceleration.

[Explanation of symbols]

1, 11... Cantilever, 2, 3, 13, 15... Yoke, 4, 14... Air gap, 5, 16... Permanent magnet, 6, 17... Pick-up coil, 12... Weight, 7... Casing.

Claims (1)

[Claims] Claims: 1. A flat member disposed on a moving body that undergoes acceleration motion and bends and deforms in accordance with the generated acceleration; a fixed part that holds one end of the plate member; another fixed part disposed to face one end of the flat member; a permanent magnet disposed between the two fixed parts; and at least one fixed part disposed so as to surround a cross section of the fixed part at an arbitrary position. Consisting of one pickup coil, the flat member and both fixed parts are made of a magnetic material with high magnetic permeability, and the magnetic material composed of the flat member, both fixed parts, the air gap, and the permanent magnet The circuit includes a circuit in which the length of the air gap changes due to bending deformation of the flat member, and an induced voltage induced in the pickup coil is detected due to a change in the amount of magnetic flux in the magnetic circuit caused by the change. , a jerk sensor that detects a physical quantity proportional to a change in acceleration applied to the flat member.