JPH0843432A - Acceleration sensor and its manufacture - Google Patents

Abstract

PURPOSE:To detect vibration and impact in both X and Y axes with a single element by using a piezoelectric ceramics body formed by cutting in polarization direction a intersectingly. CONSTITUTION:On the tap surface of piezoelectric ceramics 1, placed on a printed board, an additive mass 2 is added, and electrodes 3 and 4 are soldered on side surfaces, thus, an acceleration sensor is constituted. The piezoelectric ceramics 1 is polarization-processed in 45 degree direction. That is, the plate-like piezoelectric ceramics 1 is provided with end face electrodes 3 and 4, and polarization is done between end faces, while across in polarization direction, the piezoelectric ceramics 1 thus cut-formed. Thus, polarization is made in diagonal direction shown with arrow 7. So, with a single element, vibration in both X and Y axes is detected. With this, a acceleration sensor is miniaturized, and in a to-be-mounted device such as a hard disk, the acceleration near the one inherent to the device is detected, so that, a acceleration sensor which slightly depends on the weight of sensor itself is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly to an improvement of a small acceleration sensor which can be directly soldered to a printed circuit board and a manufacturing method thereof.

[0002]

2. Description of the Related Art Many computers such as personal computers use magneto-optical disk devices, disk devices called hard disk devices, etc., which have a higher recording density and a larger storage capacity than floppy disks, but are vulnerable to shocks. There are drawbacks such as. For this reason,
In order to read and write, when there is a shock, it is essential to stop reading and writing. An acceleration sensor mounted on the apparatus itself is used as an impact sensor that detects this impact and particularly issues a write stop command.

For example, there is JP-A-64-41865. According to this, as shown in FIG. 7, the piezoelectric element 1 and the weight 2 (additional mass) are mounted inside the housing 40.
The housing 40 is mounted on a printed circuit board 41, and the output from the piezoelectric element 1 is taken out from one electrode through a lead wire 45 and the same substrate circuit 41, and the other electrode is grounded to the housing.

As another attempt, for example, the actual opening 63
-228. According to this, as shown in FIG. 1 of the publication, a weight (additional mass) is attached to the tip of the plate-shaped bimorph piezoelectric element, and the base of the other element is fixed to the vibrating body via an elastic material. There is a vibration pickup that takes the method. This piezoelectric element is 30 to 6 with respect to the mounting surface of the vibrating body.
It is attached with being tilted in the range of 0 degree.

[0005]

The above-mentioned conventional acceleration sensor has a drawback that it is too large to be used for a vibrating body such as a hard disk as an object to be mounted. As a result, the shock of the vibrating body itself is not detected, and the vibration sensor is used as a shock sensor including an acceleration sensor.
Therefore, there are many problems to be solved such as meeting the purpose of downsizing, the number of parts is small, the labor of wiring work is reduced, and the manufacturing cost is greatly reduced.

In the former known example, since the housing, the piezoelectric element, and the additional mass are integrally assembled, the overall size becomes large, and the weight ratio to the vibrated body itself is high, which is unsuitable for uniform acceleration detection. Met. Also,
Even in the latter known example, there was a circumstance that it could not be actually used for the same reason. Further, in the former case, the single acceleration sensor in the Z-axis direction alone cannot detect the X-axis. In the latter, since the plate-shaped bimorph and the type in which the additional mass is placed on the end portion of the plate-shaped bimorph, the resonance frequency cannot be made high and only limited applications can be used.

The present invention has been made in view of the conventional problems described above, and is different from the conventional handmade manufacturing method, and comprises an acceleration sensor mounted on a miniaturized direct printed circuit board that can be mass-produced. The present invention relates to the provision of a novel acceleration sensor that can detect vibrations and shocks in both the Z-axis and the Z-axis with a single element and that ensures the reliability of the shock resistance of products such as hard disks.

[0008]

According to the acceleration sensor of the present invention, an electrode is provided on an end surface of a plate-shaped piezoelectric ceramic, and the piezoelectric ceramic cut out from the plate-shaped piezoelectric ceramic polarized between the end surfaces has a direction of polarization. The piezoelectric ceramic body includes electrodes provided on the front and back sides of the piezoelectric ceramic body formed by crossing and cutting, end face electrode terminals electrically connected to the electrodes, and an additional mass bonded to the piezoelectric ceramic.

Further, it is effective when the piezoelectric ceramic is formed by intersecting and cutting in the polarization direction within an angle of at least 15 to 75 degrees when the piezoelectric ceramic is intersected and cut in the polarization direction. It is more effectively provided in the range of 30 to 60 degrees. As a method of manufacturing the same, an end face electrode is provided on a plate-shaped piezoelectric ceramic to polarize between the end faces, the piezoelectric ceramic is cut and formed by intersecting in the polarization direction, and electrodes are provided on the front and back sides to electrically connect with the electrode. Is provided by forming an end surface electrode terminal connected to the piezoelectric ceramic and adhering an additional mass to the piezoelectric ceramic.

Further, the angle at which the above-mentioned polarization direction is crossed and cut and formed is effectively in the range of at least 15 to 75 degrees by crossing and cutting in the polarization direction. Offered more effectively in the range.

[0011]

The piezoelectric output depending on the polarization direction of the piezoelectric element and the additional mass is detected from the vibration of the piezoelectric element and the additional mass, and this is changed to the acceleration output by the control circuit or the like on the printed circuit board to perform the necessary control operation. Regarding the polarization direction of the element, since an end face electrode is provided on the plate-shaped piezoelectric ceramic to polarize between the end faces, and the piezoelectric ceramic is cut and formed by intersecting with the polarization direction, so to speak, as indicated by arrow 7 in FIG. It is polarized diagonally. Therefore, the vibration of both the X and Z axes can be detected with a single element. By reducing the size of the acceleration sensor, a hard disk or the like as a mounted device can detect an acceleration close to that peculiar to the device, and operates as an acceleration sensor having very small weight dependence of the sensor itself.

[0012]

EXAMPLES Examples will be described with reference to the drawings.
FIG. 1 is a perspective view showing an embodiment of an acceleration sensor obtained by the present invention. In FIG. 1, the additional mass 2 is bonded to the upper surface of the piezoelectric ceramic 1 and the lower surface is a printed circuit board (not shown).
It is used as an acceleration sensor after being mounted on the substrate and soldered by the electrodes 3 and 4 on the side surface. The piezoelectric ceramic 1 is polarized in the lower right direction of 45 degrees in the figure. The upper and lower electrodes 5, 6 are brushed with a silver electrode paint and baked in a fixed pattern. Similarly, the electrodes 3 and 4 provided on both sides of the piezoelectric ceramic 1 are also baked with silver electrodes.

The electrodes 4 and 6 are electrically connected between the lower side and the side surface of the piezoelectric ceramic 1, and similarly, the electrodes 3 and 5 are electrically connected between the lower side, the side and the upper surface of the piezoelectric ceramic 1.
Reference numeral 8 is a space for ensuring insulation between the electrodes 4 and 6 by masking. For the additional mass 2, a metal plate or an insulator such as alumina can be used. In the case of metal, it is possible to secure insulation between the electrodes 4 and 5 by interposing an insulating film between the piezoelectric ceramic 1 and the additional mass 2. This acceleration sensor is attached to a part of a circuit board of a vibrating body such as a hard disk or to the vibrating body to operate as a sensor through an interface or the like, and outputs an operation command or the like to the vibrated body.

FIG. 2 is a perspective view of a plate-shaped piezoelectric ceramic 14 before cutting out a large number of piezoelectric ceramics 1. Silver electrodes 15 and 16 were burned on both end faces of the plate-shaped piezoelectric ceramic 14, and were polarized with a DC voltage of 1 kv / mm. From this, a large number of piezoelectric ceramics 1 are cut into a rectangular parallelepiped as shown in the central portion of the figure. In addition, although it is described as a rectangular parallelepiped, it is also possible to use a trapezoidal section, a rhombic section, a plate shape, etc., and the shape to be cut out can be arbitrarily set depending on the application.

The angle of polarization of the cut-out piezoelectric ceramic 1 with respect to the horizontal plane can be arbitrarily set depending on the cut-out angles 9 and 10 from the plate-shaped piezoelectric ceramic 14, for example, 1
The effect was recognized in actual use in the range of 5 to 75 degrees. Further, in the range of 30 to 60 degrees, advantages such as output balance surface of both X and Z axes and ease of calculation were observed.

In the case of FIG. 2, it is set to 45 degrees for convenience of explanation, but it is not limited to this. Lead zirconate titanate is suitable as the plate-shaped piezoelectric ceramic material used, and the cut out piezoelectric ceramic 1 is approximately 6.8 mm in length and width.
The size was 7.5 mm square and the thickness was about 0.6 mm. Although it depends on the measurement application and the degree of impact, it has recently been demanded to cut out to an extremely thin piezoelectric ceramic 1 due to the progress of circuit technology, and a thickness of 0.2 to 0.5 mm, which is compatible with them, was also possible. Further, the size of the piezoelectric ceramic 1 to be cut out can also be cut out to the size-reduced piezoelectric ceramic 1 and, for example, the size of 3 to 5 mm square can be dealt with.

The cut-out piezoelectric ceramic 1 corresponds to the silver electrode 6 of FIG. 1 on the outer surface 12, the silver electrode 3 to the outer surface 13 and the same 11 to the outer surface 11, and the arrow 1 indicates the polarization direction.
7 corresponds to 7 in FIG. 18 to 21 showing a cut surface
Determines the polarization direction of the piezoelectric ceramic, and the angles 9 and 10 from the horizontal plane of the plate-shaped piezoelectric ceramic 14 are selected to be 45 degrees.

FIG. 3 is a diagram for explaining the relationship between the vibration output and the polarization direction of the obtained piezoelectric ceramic 1. Here, when the angle between the horizontal plane of the piezoelectric ceramic and the polarization direction P is Θ, and the combined output Q in the X and Z axis directions is the force F in any given direction, and the angle between the horizontal direction is α, ,

[Equation 1] Is shown to operate as an acceleration sensor.

FIG. 4 is a graph showing the sensitivity of the entire circumference of the acceleration sensor obtained in the embodiment. The output characteristics in the X and Z axis directions can be confirmed. The vertical direction of the acceleration sensor is 0 ° and 180 ° in the Z-axis direction, and the vertical direction is 90 ° and 270 ° in the X-axis direction. The maximum sensitivity from now on is about 20 ° and about 270 °.
It can be seen that there are biaxial directions in the vicinity. From these, the so-called main axis sensitivity of the Z-axis direction component,
The horizontal axis sensitivity of the X-axis direction component is required. Therefore, in the conventional acceleration sensor, only the so-called main axis sensitivity of the Z-axis direction component was obtained, but in the present invention, vibration in both the X and Z axis directions is controlled by a single acceleration sensor by controlling the polarization direction. Can be detected.

FIG. 5 shows X of the acceleration sensor obtained in the embodiment.
It is an output frequency characteristic in the axial direction. Horizontal axis is frequency 50Hz
~ 50kHz, vertical axis is sensor output 10db / scale,
The sensitivity is 0.77 mV / G acceleration. Similarly, FIG. 6 shows ringing characteristics with respect to the impact force of the acceleration sensor. The horizontal axis is the time, and the vertical axis is the output of the sensor. As seen from the waveform, no ringing was observed. From these, it is possible to obtain a sensor that is flat up to about 10 kHz and is small and lightweight, so that it can be mounted on a printed circuit board. As a result, the vibration system is not disturbed and it can be expected to be used in a wide range of fields of use. For example, it is possible to detect not only the X-axis direction vibration of a hard disk used in a notebook computer, but also the Z-axis direction simultaneously.
It was confirmed to be suitable as an impact sensor.

It can be seen from FIG. 6 that the relative sensitivity of the acceleration output significantly improved the influence of ringing because the resonance frequency increased, and there was an effect that no ringing countermeasures such as the use of a filter were required. In general, when a shock is applied to the acceleration sensor, it is excited at the resonance frequency and is added to the original waveform of the output as ringing, which causes an error.The magnitude of the ringing amplitude is reduced by increasing the resonance frequency or filtering. Is improved by using. Further, as can be seen from the frequency characteristic shown in FIG. 5, the resonance frequency is increased, so that it can be expected to be used in a wider field of use.

Further, this acceleration sensor can be used with an impact force of 0.1 G or more, which is considerably small, and is suitable for use with a hard disk or the like. Further, since the weight ratio of the acceleration sensor to the vibrating body such as the mounted device can be made extremely low, the resonance frequency also becomes high, and the acceleration sensor capable of measuring the acceleration of the mounted device without being conscious of sensor mounting was obtained. Therefore, it was clear that an acceleration close to the peculiar to the device can be detected, and that the sensor operates as an acceleration sensor having very small weight dependence of the sensor itself.

[0023]

As described above, according to the present invention, the polarization from the end face electrode in the state of the plate-shaped piezoelectric ceramic and the piezoelectric ceramic is cut and formed so as to intersect with the polarization direction. Is polarized obliquely from the horizontal plane. Therefore, vibration of both X and Z axes can be detected by a single element, and it can be expected to be used in a wider field of use.

Further, it is possible to provide an acceleration sensor suitable for use in a hard disk or the like, which is unprecedented in size reduction, the number of parts can be reduced, and the manufacturing cost can be drastically reduced. Furthermore, since the weight ratio of the acceleration sensor to the vibration body such as the mounted device is extremely low, the resonance frequency can be increased and the acceleration measurement closer to that of the vibration body itself can be achieved. In addition, sensor mounting is simple, shock resistance and reliability are high. The effect was recognized as a high acceleration sensor.

[0025]

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an acceleration sensor obtained according to the present invention.

FIG. 2 is a perspective view of a plate-shaped piezoelectric ceramic before the piezoelectric ceramic is cut out.

FIG. 3 is a diagram illustrating a relationship between a vibration output and a polarization direction.

FIG. 4 is an all-around sensitivity graph showing the output characteristics of the acceleration sensor in the X and Z axis directions.

FIG. 5: Frequency characteristic of acceleration sensor output

FIG. 6 is a ringing characteristic of the acceleration sensor with respect to impact force.

FIG. 7 is a sectional view of a conventional acceleration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramic 2 Additional mass 3 Electrode 7 Polarization direction 9 Cutting angle with horizontal plane 10 Cutting angle with horizontal plane 14 Plate-shaped piezoelectric ceramic

Claims (6)

[Claims] 1. A piezoelectric ceramic body provided with electrodes on the end faces of a plate-shaped piezoelectric ceramic and cut out from the plate-shaped piezoelectric ceramic polarized between the end faces, the piezoelectric ceramic body being cut and formed so as to intersect in the polarization direction. An acceleration sensor comprising a piezoelectric ceramic having electrodes provided on the front and back, end face electrode terminals electrically connected to the electrode, and an additional mass bonded to the piezoelectric ceramic. 2. The acceleration sensor according to claim 1, wherein the acceleration sensor is made of a piezoelectric ceramic which is cut and formed so as to intersect with the polarization direction within a range of at least 15 to 75 degrees. 3. The acceleration sensor according to claim 1, which is made of a piezoelectric ceramic which is cut and formed so as to intersect with the polarization direction within a range of at least 30 to 60 degrees. 4. An acceleration sensor made of a piezoelectric ceramic cut out from a plate-shaped piezoelectric ceramic, wherein the plate-shaped piezoelectric ceramic is provided with end face electrodes to polarize between the end faces, and the piezoelectric ceramic is cut by intersecting in the polarization direction. A method for manufacturing an acceleration sensor, comprising forming electrodes and forming electrodes on the front and back surfaces thereof, forming end face electrode terminals electrically connected to the electrodes, and adhering an additional mass to the piezoelectric ceramic. 5. A piezoelectric ceramic is cut and formed by intersecting with the polarization direction within a range of at least 15 to 75 degrees.
A method for manufacturing the acceleration sensor according to claim 1. 6. The piezoelectric ceramic is cut and formed by intersecting in the polarization direction within a range of at least 30 to 60 degrees.
A method for manufacturing the acceleration sensor according to claim 1.