JP2001083176A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acceleration sensor that has the advantages of a capacitance-type acceleration sensor for detecting DC-like acceleration, can detect the change in capacitance due to the deformation of an elastic body when acceleration is applied from a single element without using two electrodes, namely fixed and movable electrodes. SOLUTION: A ferroelectric thick-film layer 12 whose thickness is nearly uniform and whose permittivity changes due to distortion is formed on the surface of an insulation rectangular plate 11. A cross finger electrode 13 that is vertical or parallel to a distortion direction where the direction of a linear finger electrode 14 is generated by acceleration to be detected is formed at a part where distortion is generated by acceleration to be detected on the film layer 12 as a first capacitance element. Then, at least one end part of the longitudinal direction of a rectangular plate is supported and fixed, thus detecting acceleration being applied according to the change in the capacitance of the first capacitance element caused by the deformation of the rectangular plate being generated by the applied acceleration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for detecting vibrations of automobiles and acceleration during collisions, vibrations and accelerations of portable electronic equipment, and abnormal vibrations of motors and various machines. It relates to an acceleration sensor.

[0002]

2. Description of the Related Art Conventionally, many types of acceleration sensors have been used to detect vibration and impact of machinery. As the acceleration sensor, a sensor suitable for the application is used depending on the magnitude and frequency range of the acceleration to be detected. For example, for detecting vibration due to knocking of an automobile engine or vibration of a machine, as shown in FIG. Sheets of piezoelectric rings 51 and 52
Are stacked in such a manner that their polarization directions are reversed, and an acceleration sensor 50 having a structure in which a metal hollow cylinder 53 serving as a weight is fixed together with screws 54 is used.
It is used to detect acceleration. The case 55 of the acceleration sensor 50 is generally connected to the ground, and is connected to the ground of the terminal via the mounting screw 57 together with the ground of the terminal 56.

[0003] In the acceleration sensor of FIG. 5, when acceleration alpha ₅ from the outside is applied to the piezoelectric ring 51 and 52,
The Power of F ₅ = _{M 5} α ₅ is applied. Here, M ₅ is the mass of the weight. Piezoelectric ring 51 and 52, when applied pressure as shaped a device for generating a voltage, generates a voltage given by V = kgF _5. Here, k is a constant determined by the shape and dimensions of the acceleration sensor, and g is a constant determined by the piezoelectric material. That is, the operating principle of the piezoelectric acceleration sensor represented by the acceleration sensor shown in FIG. 5 is that the applied acceleration acts on the weight 53 to generate a force, and the piezoelectric rings 51 and 52 are deformed by the force. It generates a voltage.

Further, recently, a so-called micromachine type capacitance type acceleration sensor formed by making full use of semiconductor fine processing technology has been developed. This requires not only the detection of DC acceleration, but also the resonance frequency of the mechanical vibration system and the mechanical strength of each part in a wide range from a small acceleration of 1 G or less to a large acceleration of several tens G at the time of an automobile collision. It can be handled by designing together.

FIG. 6 is a perspective view schematically showing the structure of one example of a capacitance type acceleration sensor utilizing micromachine technology. This capacitance-type acceleration sensor is configured such that a movable electrode X63 integrally formed on a Si single crystal plate 60 and a movable plate 62 serving as a weight supported by an anchor 61 is opposed to the movable electrode by a surface micromachine technology. And two fixed electrodes Y64 and Z65 that form a capacitance. FIG. 7 is an operation explanatory diagram of the capacitance type acceleration sensor shown in FIG.

The principle of acceleration detection will be described below with reference to FIGS. 6 and 7. In FIG. 6, each electrode X (63),
Since Y (64) and Z (65) are commonly connected to each other, as shown in FIG.
It can be considered as a circuit in which another capacitor X (63) is inserted between (65) and two capacitors are connected in series. In FIG. 6, the directions of the detected acceleration are X, Y, Z
Since the direction is perpendicular to the length direction of each electrode, when the acceleration α ₆ is applied, a force of F ₆ = M ₆ α ₆ is generated as in the case of the piezoelectric acceleration sensor. Mass M ₆ in this case is the mass of the movable plate 62 including the movable electrode X (63). When the force F ₆ is generated, the movable electrode X (63) is displaced to a position where the movable electrode X (63) is balanced with the spring of the support 66 fixed to the anchor 62. That is, in FIG.
(63) are fixed electrodes Y (64), Z (6) from the center position.
5) It will shift in either direction. In FIG. 6, the phases of the electrodes Y (64) and Ζ (65) are 18
By applying voltages 67 and 68 which differ by 0 ° and have the same amplitude,
As shown in FIG. 7, the movable electrode X (63) is fixed
When located at the center of (64) and Z (65), the voltage 79 of the movable electrode X (63) cancels each other and is zero, but the acceleration is applied and the movable electrode X (63) is applied.
Is shifted from the center between the fixed electrodes Y (64) and Z (65), a voltage 79 is generated at the movable electrode X (63), and the magnitude of the voltage is determined by the displacement of the movable electrode X (63), that is, the applied voltage. Is proportional to the magnitude of the applied acceleration. Therefore, the movable electrode X
The applied acceleration can be detected from the voltage of (63).

[0007]

The piezoelectric acceleration sensor shown in FIG. 5 has the advantage that the structure is simple and no power source is required in principle. When the force is applied to the piezoelectric element, the charge generated by the deformation flows out through the surface or inside of the electronic circuit for detection or the piezoelectric material, so that the voltage decreases and the applied acceleration is reduced. There is a disadvantage that it cannot be detected correctly.

Further, in the capacitance type acceleration sensor shown in FIGS. 6 and 7, a fixed electrode and a movable electrode are required in order to form a capacitance. This is converted into a change in the distance between the fixed electrode and the movable electrode, and as a result is converted into a change in capacitance. Therefore, in order to produce the fixed electrode and the movable electrode with high accuracy, expensive equipment capable of providing high processing accuracy was required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an advantage of a capacitance type acceleration sensor capable of detecting a DC acceleration, and to use an acceleration sensor without using two electrodes, a fixed electrode and a movable electrode. It is an object of the present invention to provide an acceleration sensor capable of detecting, from a single element, a change in capacitance due to deformation of an elastic body when is applied.

[0010]

According to the present invention, there is provided a plate-like or rod-like elastic body having a flat or curved surface and having an insulating property, the thickness of which is substantially uniform and whose dielectric constant changes due to distortion. A film or a thin film layer is formed, and the direction of the linear finger electrode is perpendicular or parallel to the direction of the strain caused by the detected acceleration at a portion where the strain occurs due to the detected acceleration on the thick film layer or the thin film layer. Forming at least one interdigital electrode as a first capacitance element, and supporting and fixing at least one end or peripheral portion in the longitudinal direction of the plate-like or rod-like elastic body; An acceleration sensor is provided which detects an applied acceleration based on a change in capacitance of the first capacitance element accompanying a deformation of the plate-like or rod-like elastic body caused by the applied acceleration.

[0011] A mass may be added near or at the center of the plate-shaped or rod-shaped elastic body, which is not supported and fixed.

An interdigital electrode having substantially the same size and shape as the interdigital electrode constituting the first capacitance element is formed in a region where no distortion is generated by the applied acceleration of the plate-like or rod-like elastic body. Alternatively, the second capacitance element may be used to obtain a capacitance serving as a reference for acceleration detection.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of an element whose capacitance changes due to applied strain, which is a basic principle of an acceleration sensor according to the present invention. In FIG. 1, a ferroelectric thick film 12 whose permittivity changes due to strain is formed on one surface of a rectangular plate 11 made of an insulating material, and interdigital electrodes 13 are formed on the surface thereof. As shown in FIG. 1, the interdigital electrode is an electrode formed by connecting every other linear finger electrodes 14 and 15 to a common electrode. It has a pair of terminals 16 and 17 so as to have a capacitance. When the substrate 11 on which the interdigital electrodes shown in FIG. 1 are formed is bent in a direction perpendicular to the length direction of the linear finger electrodes 14 and 15, the distance between the linear electrodes adjacent to each other changes. On the other hand, in the case of a deformation in which the electrode surface is convex, extension strain occurs in the dielectric layer 12, and in the case of the deformation in which the electrode surface is concave, compression strain occurs in the dielectric layer 12.

FIG. 2 shows a zirconia porcelain plate having relatively excellent flexibility as an insulating rectangular plate 21 having a lead-based high dielectric constant dielectric thick film used for a ceramic capacitor on its surface. A state in which a longitudinal direction both ends of a rectangular zirconia porcelain plate is supported on a capacitor element in which a layer 22 is formed and a finger direction is formed on the layer 22 and a cross finger electrode in which a finger direction is parallel to a short side of the zirconia porcelain plate. The figure shows a measurement example of the relationship between the pressing force and the capacitance when the central part of a rectangular zirconia porcelain plate is pressed in parallel with its short side by a knife-edge-shaped pressing plate.

In FIG. 2, the line of the seal is a case where the back side of the interdigital electrode surface is pressurized, and the line of the Δ mark is a measured value when the interdigital electrode surface is pressurized. As can be seen from FIG. 2, in the case of the seal, the capacitance value increases as the pressing force increases, even though the deformation is such that the electrode interval is increased. In the case of, despite the deformation that the electrode spacing becomes smaller,
As the applied pressure increases, the value of the capacitance decreases, and the dielectric layer 22 has a so-called “positive strain-dielectric constant characteristic” in which the dielectric constant in that direction increases when strain is applied. It indicates that you are doing.

FIG. 3 is a perspective view showing an acceleration sensor according to an embodiment of the present invention. A ferroelectric thick film whose thickness is substantially uniform and whose dielectric constant changes due to strain is formed on the surface of a zirconia substrate 31. A layer 32 is formed, and an interdigital finger electrode 33 in which the direction of the linear finger electrodes 34 and 35 is perpendicular or parallel to the direction of the distortion generated by the detected acceleration is formed substantially at the center of the thick film layer 32. Then, the terminals 36 and 37 of the first capacitance element are drawn from the common electrode. One end of the zirconia substrate 31 is fixed by a block 38 for supporting and fixing, and a weight 39 is added to the other end. In the acceleration sensor shown in FIG.
When acceleration alpha ₃ is applied to the first plane perpendicular to the direction, force F _{3 =} M _{3 α 3} acts on the weight 39, the zirconia substrate 31 is deformed so as to bend by the force F _3. As a result, the value of the capacitance of the terminals 36 and 37 changes. Since the change in capacitance changes in proportion to the applied force, that is, the applied acceleration, as shown in FIG. 2, the applied acceleration can be detected from the change in capacitance.

FIG. 4 is a perspective view showing an acceleration sensor according to another embodiment of the present invention. A ferroelectric material whose thickness is substantially uniform and whose dielectric constant changes due to strain is formed on the surface of a zirconia substrate 41. A thick film layer 42 is formed, and at approximately the center of the thick film layer 42, the direction of the linear finger electrodes 44, 45 is perpendicular to or parallel to the direction of the distortion generated by the previously detected acceleration. Are formed, and the terminals 46 and 47 of the first capacitive element are drawn out from the common electrode. One end of the zirconia substrate 41 is provided with a support and fixing block 48.
, And a weight 49 is added to the other end. Further, at the portion where the zirconia substrate 41 is joined to the block 48 for supporting and fixing, there are formed cross finger electrodes 43 'having linear finger electrodes 44' and 45 'having the same shape and dimensions as the cross finger electrodes 43. From the common electrode of each linear finger electrode to the terminals 46 ', 4 of the second capacitance element.
7 'is pulled out. In the acceleration sensor of FIG. 4, similarly to the case of FIG. 3, when the acceleration α ₄ is applied in a direction perpendicular to the plane of the zirconia substrate 41, F ₄ is applied to the weight 49.
= M ₄ α ₄ acts, and the zirconia substrate 41 is deformed to be bent by the force F ₄ . As a result, terminal 4
The capacitance values of 6, 47 change. Meanwhile, the portion interdigital 43 'is formed, since the zirconia substrate 41 is joined to the block 48 for supporting and fixing, there is little to be deformed by the force F ₄ to occur through cowpea to applied acceleration . Therefore, the capacitance values of the terminals 46 'and 47' hardly change due to the applied acceleration.

In the acceleration sensor shown in FIG. 4, the interdigital electrodes 43 and 43 'are formed on the ferroelectric thick film of the same material and are very close to each other with almost the same shape and size. The capacitance is similarly affected by environmental conditions other than acceleration such as changes in ambient temperature and electromagnetic noise, and by using a differential amplifier circuit, which is a conventional means in such a case, These disturbances can be canceled. That is, the capacitance obtained by the second capacitance element can be used as a reference for detecting acceleration.

In the above description, the structure of the acceleration sensor has been described in the case where a weight is added to the tip end in a so-called cantilever structure in which one end is fixed, but both ends of the rectangular plate are fixed. The same effect can be obtained with a structure in which a weight is added to the center. Further, when a substrate on a circular plate or a square plate is used, the same effect can be obtained by fixing the peripheral portion and adding a weight to the central portion. In particular, when the shape of the substrate is circular or square, the strain generated when an acceleration in the direction perpendicular to the plate surface is applied is substantially concentric, so the shape of the interdigital electrode is also adjusted to the strain distribution. It is more effective to make them concentric.

In the embodiment, a zirconia substrate is used as the insulating substrate, and the ferroelectric layer is formed as a thick film.
_A ferroelectric thin film layer may be formed by sputtering or the like on the surface of the substrate on which the _two films are formed.

In the description of the embodiment, the case where a weight is added has been described. However, depending on the conditions of the detection sensitivity and the resonance frequency, the weight of the substrate itself may be used without adding a special weight.

[0022]

As described above, according to the present invention,
The disadvantage of the conventional piezoelectric acceleration sensor that it cannot detect DC acceleration in principle, and the conventional capacitive acceleration sensor requires fixed electrodes and movable electrodes, and requires high processing accuracy. It is possible to provide a sensor capable of detecting the applied acceleration from a change in capacitance due to its own deformation with a simple structure by eliminating the above-mentioned drawback.

[Brief description of the drawings]

FIGS. 1A and 1B are explanatory diagrams of an element whose capacitance changes due to applied strain, which is a basic principle of an acceleration sensor of the present invention, wherein FIG. 1A is a plan view and FIG. 1B is a front view.

FIG. 2 shows a measurement example of a relationship between a pressing force and a capacitance when a force is applied to a central portion of the substrate having the structure of FIG.

FIG. 3 is a perspective view showing an acceleration sensor according to the embodiment of the present invention.

FIG. 4 is a perspective view showing an acceleration sensor according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a structure of a conventional piezoelectric acceleration sensor.

FIG. 6 is a perspective view schematically showing the structure of a capacitance type acceleration sensor using micromachine technology.

FIG. 7 is an operation explanatory diagram of the capacitance type acceleration sensor shown in FIG. 6;

[Explanation of symbols]

11 Insulating rectangular plate 12, 32, 42 Ferroelectric thick film layer 13, 33, 43, 43 'Cross finger electrode 14, 15, 34, 35, 44, 45, 44', 45 '
Linear finger electrodes 16, 17, 36, 37, 46, 47, 46 ', 47'
Capacitor terminals 31, 41 Zirconia substrate 38, 48 Supporting and fixing block 39, 49, 53 Weight 50 Acceleration sensor 51, 52 Piezoelectric ring 54 Screw 55 Acceleration sensor case 56 Terminal 57 Mounting screw 61 Anchor 62 Movable plate 63 serving as a weight 63 movable electrode X 64 fixed electrode Y 65 fixed electrode Z 66 support 77, 78 applied voltage 79 voltage of movable electrode X

Claims (3)

[Claims] 1. A thick film or thin film layer having a substantially uniform thickness and a dielectric constant that changes due to strain is formed on the surface of an insulating plate-like or rod-like elastic body having a flat surface or a curved surface. At least one cross finger electrode in which the direction of the linear finger electrode is perpendicular or parallel to the direction of the strain caused by the detected acceleration is formed at the portion of the film layer or the thin film layer where the strain occurs due to the detected acceleration. And at least one end or peripheral portion of the plate-shaped or rod-shaped elastic body in the longitudinal direction is fixed, and the plate-shaped or rod-shaped elastic body is generated by an applied acceleration. An acceleration sensor for detecting an applied acceleration from a change in capacitance of the first capacitance element accompanying the deformation of the elastic body. 2. The acceleration sensor according to claim 1, wherein a mass is added near or at the center of the plate-shaped or rod-shaped elastic body that is not supported and fixed. 3. An inter-finger electrode having substantially the same size and shape as the inter-finger electrode constituting the first capacitance element, in a region where no distortion occurs due to the applied acceleration of the plate-shaped or rod-shaped elastic body. 3. The acceleration sensor according to claim 1, wherein the acceleration sensor is formed as a second capacitance element, and the second capacitance element obtains a capacitance serving as a reference for acceleration detection. 4.