JPH0626852Y2 - Accelerometer - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to an acceleration sensor which is mounted on various types of machinery, transportation, etc. to detect the presence or absence of an abnormal operation state.

[Conventional technology]

Conventionally, sensors for this type of application are classified as vibration sensors, and basically, a vibration system fixed to the measurement target, generally a seismo system and the reaction of external vibration (inertial force, pressure change, mass movement, etc.) are electrically It is composed of a transducer that converts into a signal, and there are various configurations depending on the application.

The response of the seismo system varies greatly depending on the magnitude relationship between the natural frequency of the seisei system and the frequency of the measurement target and some conditions, and when the frequency of the seismo system is sufficiently smaller than the frequency of the measurement target, The particle moves in the direction opposite to the displacement of external vibration and acts as a displacement meter.
When the two frequencies are equal, mechanical resonance occurs, but at this time, the movement of the mass point of the seismo system, whose damping coefficient of the system is sufficiently larger than 1, acts as a speedometer in proportion to the speed.

When the resonance frequency of the seismo system is sufficiently higher than the frequency of the measurement target, the motion of the mass point is proportional to the acceleration of external vibration.

For example, referring to the drawings, first, the natural frequency and response of the seismo system will be described.

FIG. 5 is a diagram showing a dynamic model of the Seismo system. In the figure, where x is the displacement of the weight with respect to the basic frame and y is the displacement with respect to the spatial fixed point of the basic frame, the system equation of motion is given by equation (1) when vibration is applied to the basic frame from the outside. . .

Or here fn: natural frequency in the absence of damping h: coefficient representing the degree of damping of the system (damping ratio) Now, assuming that the basic frame vibration is a sine wave and y = Ysinωt, the equation of motion is In the steady state after a sufficient time has passed from the transient state, the solution of equation (2) is However If u >> 1 Then, the equation (3) becomes x = −Ysinωt (4). That is, the displacement of the weight with respect to the base frame becomes equal to the displacement of the base frame, and it functions as a displacement meter. Next, transform equation (3) If u << 1 And equation (5) is Becomes In this case, the displacement of the weight with respect to the foundation frame is equal to the acceleration of the foundation frame and functions as an accelerometer.

Similarly, equation (3) becomes If h >> 1 And equation (7) becomes The displacement of the weight with respect to the foundation frame acts as a velocity system proportional to the velocity of the foundation frame.

As described above, the response of the Seismo system is summarized in Table 1 from the conditions of its natural frequency and damping ratio.

A general acceleration sensor is constructed based on this principle. Piezoelectric ceramics are mainly used as a transducer of an acceleration sensor, and a vertical effect type or a lateral effect type is devised depending on a target frequency range and a degree of vibration intensity. The lateral effect type is suitable for weak vibrations.

[Problems to be Solved by the Invention] As a method for sensitively detecting the acceleration of weak vibration, a lateral effect type acceleration sensor using a cantilever is suitable as described above. However, the natural frequency of the structure using a cantilever is generally small, and it is necessary to set the target frequency to a fraction (30% or less) of the natural frequency in order to act as an accelerometer as described later. The frequency range that can be used as is an extremely low value.

Therefore, the technical problem of the present invention is to eliminate this drawback.
In a system that uses the lateral effect of piezoelectric ceramics using a cantilever beam, the cantilever beam is used in two stages to form a dual-sized seismo system, each of which acts as a velocity sensor to function as an acceleration sensor and weak vibration. The purpose is to expand the frequency range in which the acceleration of can be detected with high sensitivity.

[Means for Solving the Problems]

According to the present invention, two first cantilever beams, whose fixed ends are fixed to the object to be measured and which are made of elastic plates of equal length, are arranged in parallel so that the elastic plates face each other. A first vibration system having a first natural frequency and a first damping coefficient, in which a coupling member is coupled to the free ends of the cantilever beam;
A second vibration system having a second natural frequency and a second damping coefficient, in which a weight is provided between the free ends of the piezoelectric vibrating reeds arranged in parallel with the elastic plate with the connecting member as a fixed end. And selecting the first natural frequency and the second natural frequency to be substantially equal and selecting the first damping coefficient and the second damping coefficient to values sufficiently larger than one. An acceleration sensor characterized in that the acceleration of the vibration displacement of the measuring object is detected as the position displacement of the weight, and the detected displacement is taken out as an electric signal generated in the piezoelectric vibrating piece.

[Action]

 The operation of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a schematic diagram of the configuration of the present invention. In this figure, in a structure in which two cantilevers 2 and 2 are connected by a connecting member composed of hinges 3 and 3 and a rigid body 4, when the swing width is small, the rigid body 4 is in a direction perpendicular to the axis of the cantilever. Can be kept. Fixed part 1 of cantilever 2 and 2 connected here
The movement of the weight 6 attached to the rigid body and the tip of the second cantilever 5 having the rigid body as the fixed end will be described as an example. However, the natural frequencies of the two cantilevers 2 and 2 are the same, ω _n , and the damping coefficient is h,
It is assumed that h'is sufficiently larger than 1 and satisfies the condition given by the above equation (8). The motion of the measured object is y = Ysi
When nωt, the motion x of the rigid body is calculated from Eq. (8). Next, this rigid body is used as the fixed end. The movement x'of the weight at the tip of the second cantilever beam 5 is That is, since the motion of the weight at the tip of the second cantilever beam 5 is proportional to the acceleration of the motion of the object to be measured, when the second cantilever beam is composed of the piezoelectric bimorph or the unimolyph, the electric terminal is used to An electric signal proportional to the acceleration of the motion of the object to be measured can be taken out. Also, in this case, the frequency range that can be used as an accelerometer is around ω _n , and ω is the same as in the conventional cantilever configuration.
Only the region sufficiently smaller than _n is not targeted, and the frequency range can be expanded.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

Example 1 An acceleration sensor according to Example 1 of the present invention will be described.

FIG. 2 is a perspective view showing a specific configuration of the acceleration sensor according to the first embodiment.

As shown in the figure, two cantilever beams 2 and 2 made of elastic plates having the same length ₁ and width w ₁ are arranged in parallel with a distance d, and a fixed end 1 is provided at one end and the other end is provided. The free ends of are rigidly connected via hinges 3 respectively. Further, the rigid body 4 has a weight 6 at one end on the side opposite to the fixed end 1 side, and has terminals 8 and 8 on each surface. Length ₂ , width w ₂
The other end of the piezoelectric bimorph 5 was fixed and contacted to the cantilever 7. In addition, the damping adjusting plate 7,
7'is adhered. Here, the dimensions and materials of each part are as shown in Table 2.

The acceleration sensor created in this way is f = 1.00k
Acceleration was measured by vibrating at an amplitude of 0 to 170 µ at Hz. The results are shown in FIG. As indicated by the circles in this figure, the logarithm of the reading of the acceleration sensor according to the first embodiment and the logarithm of acceleration of the vibration exciter showed a linear relationship. The resonance frequency and the reduction coefficient are as shown in Table 3, and the resonance frequency of the beam of length ₁ (vibration system 1) is 1.198 kHz, the damping coefficient (h) is 12.3, and the beam of length ₂ ( The resonance frequency (ω _n / 2π) of the vibration system 2) was 1.068 kHz, and the damping coefficient (h) was 10.5.

Second Embodiment An acceleration sensor according to a second embodiment of the present invention will be described.

FIG. 3 is a perspective view showing a specific configuration of the acceleration sensor according to the second embodiment. As shown in this figure, length ₁ and width w
The cantilever beam 2 and 2 'made of a ₁ equal elastic plate with a distance d, two parallel positioned, the fixed end provided corresponding end, each through a hinge 3 and 3 a free end of the other end Rigid body 4
Connected with.

The assembly up to this point is the same as in the first embodiment. Next, on the fixed end 1 side of the rigid body 4, the other end of the piezoelectric bimorph 5 having a length ₂ and a width w ₂ having a weight at one end and terminals 8 and 8 on each surface is fixed. I contacted Hold 7.
Attenuation adjusting plates 7 and 7'are adhered to the surfaces of the cantilevers 2 and 5. Here, ₁ = 40, w ₁ = 10, d
= 10, ₂ = 10, the size and material of each part are the same as those in the first embodiment.
The same as shown in Table 2 was used.

The acceleration sensor manufactured in this way is f = 1.00k
The acceleration was measured by vibrating at a frequency of Hz and an amplitude of 0 to 170 μ. The results are shown in FIG. As indicated by the triangle in this figure,
The logarithm of the reading of the accelerometer and the logarithm of the acceleration showed a linear relationship. The resonance frequency and reduction coefficient are shown in Table 3.
The resonance frequency (ω _n / 2π) of the beam of length ₁ (oscillation system 1) is 1.058 kHz and the damping coefficient (h)
Is 13.0, and the resonance frequency (ω _n / 2π) of the beam of length ₂ (oscillation system 2) is 1.052 kHz damping coefficient (h)
Was 10.3.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an acceleration sensor that can detect acceleration with respect to weak vibrations and has a relatively high target frequency range, and its industrial effect is extremely large. .

[Brief description of drawings]

FIG. 1 is a side view schematically showing the construction of the present invention, FIG. 2 is a perspective view showing a concrete construction of an acceleration sensor according to an embodiment of the present invention, and FIG. 4 is a perspective view showing a specific configuration of the acceleration sensor according to the embodiment of the present invention, FIG. 4 is a view showing an example of acceleration measurement of the acceleration sensor according to the embodiment of the present invention, and FIG. 5 is a dynamic model of the seismo system. FIG. In the figure, 1 is a fixed end, 2 is an elastic plate that constitutes a first vibrating system, 3 is a hinge, 4 is a rigid body, 5 is a piezoelectric bimorph that constitutes a second vibrating system, 6 is a weight, 7 and 7. ′ Is a hard rubber plate for adjusting the damping coefficient, 8 and 8 ′ are lead terminals, 51 is a basic frame, 52 is a weight, 53 is a spring, and 54 is a dashpot.

Claims (1)

[Scope of utility model registration request] 1. A first cantilevered beam having elastic plates whose fixed ends are fixed to an object to be measured and which are made of elastic plates having the same length. A first vibrating system having a first natural frequency and a first damping coefficient formed by connecting a connecting member to free ends of a cantilever, and the connecting member serving as a fixed end and parallel to the elastic plate. A second vibration system having a second natural frequency and a second damping coefficient, in which a weight is provided on the free end side of the arranged piezoelectric vibrating piece,
The first natural frequency and the second natural frequency are selected to be substantially equal to each other, and the first damping coefficient and the second damping coefficient are selected to be sufficiently larger than 1, and the object to be measured is selected. The acceleration sensor is characterized in that the acceleration of the vibration displacement is detected as the position displacement of the weight, and the detected displacement is taken out as an electric signal generated in the piezoelectric vibrating piece.