JP2007114085A - Piezoelectric shock sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shock sensor capable of detecting shocks in any directions, while having monolithic in structure. <P>SOLUTION: In the piezoelectric shock sensor that uses a ring-shaped piezoelectric ceramic trunk body with outer and inner shapes of square cross section: the sensor is equipped with independent signal detecting electrodes on each of four external surfaces of the trunk body and is also equipped with a common electrode on an internal surface of the trunk body; the piezoelectric ceramic trunk is polarized in the thickness direction; two sets of signal detecting circuit are composed from two facing signal detecting electrodes pair; and then displacement in the two directions generated by shock is detected from the two sets of signal detection circuit. Moreover, similar constitution is also possible, even when use of cylindrical ring-shaped piezoelectric ceramic trunk is used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a small-sized shock sensor used for impact detection or the like, and more particularly to a structure of a cylindrical piezoelectric element capable of detecting an impact in three axial directions.

  Shock sensors (acceleration sensors) are widely used for external impact detection, vibration countermeasures, pickup control, general acceleration detection, and the like in writing disk devices such as HDDs and DVDs. In particular, HDDs have penetrated DVD recorders and mobile phones, and demand for small shock sensors is expected to increase. As a detection method of the shock sensor, there are methods such as a piezoelectric type, a piezoresistive type, a MEMS capacitance type, and a magnetic type. Piezoelectric types are widely used because they are excellent in cost reduction and miniaturization. Conventionally, various types of shock sensors using a piezoelectric ceramic, such as a compression mode, a shear mode, and a bending mode, have been proposed, but those equipped with a sensitive bending type detection element are generally used.

FIG. 6 shows a small-sized shock sensor composed of a single layer ceramic that can achieve both low cost and high detection sensitivity. Two pairs of electrodes 2a, 2b and 3a, 3b divided by two gaps 6 are formed on the front and back surfaces of the rectangular plate-shaped piezoelectric ceramic 1, and the two portions of the piezoelectric ceramics with the electrode dividing gap 6 as a boundary are each It is polarized along the direction opposite to the other side in the thickness direction. In the case of fixing at one end perpendicular to the electrode split gap, the detection element 1 is deformed by the action of inertial force when the acceleration G is applied, and the front and back electrodes opposed in the thickness direction are deformed as the detection element 1 is deformed. Electric charges are generated, and electric charges with opposite signs are generated on two divided electrodes on the same surface. That is, when negative charges are generated on the electrodes 2a and 2b, positive charges are generated on the electrodes 3a and 3b. Therefore, if the electrodes 2a and 2b are connected, the electrodes 3a and 3b are connected, and the signal extraction electrodes 2 and 3 are respectively connected, the application state of the acceleration G can be detected from the signal extraction electrodes 2 and 3. it can.
JP 2000-121661 A JP 2000-162233 A

  However, a plate bending shock sensor detects shocks in one direction, and in order to detect in multiple directions, it is necessary to place the detection element at an angle with the substrate plane or to use several sensors. It takes either man-hours and costs. The present invention provides a shock sensor that can detect an impact in any direction while having a single structure.

  The present invention solves the above problems by using a cylindrical piezoelectric ceramic. That is, in a piezoelectric shock sensor using a ring-shaped piezoelectric ceramic cylindrical body having a square outer shape and inner shape, each of the four outer surfaces of the cylindrical body has independent signal detection electrodes, and the inner surface of the cylindrical body. The piezoelectric ceramic cylindrical body is polarized in the thickness direction, and two sets of signal detection circuits are constituted by two opposing signal detection electrodes, and two sets of signal detection are made for displacement in two directions caused by an impact. It is characterized by detection by a circuit.

  In addition, the piezoelectric shock sensor using the cylindrical ring-shaped piezoelectric ceramic cylindrical body includes a signal detection electrode that is independently formed by being divided into four on the outer surface of the cylindrical body, and a common electrode on the inner surface of the cylindrical body. The piezoelectric ceramic cylindrical body is polarized in the thickness direction, and two sets of signal detection circuits are formed by two opposing signal detection electrodes, and two-direction displacement caused by impact is detected by the two sets of signal detection circuits. It has the characteristics.

  According to the present invention, by adopting a cylindrical structure piezoelectric body, it is possible to realize a small and low-cost multi-directional shock sensor that can detect an impact in any direction while having a single structure.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A shows the structure of a cylindrical piezoelectric shock sensor according to the present invention. FIG. 2 is a side view thereof. In the cylindrical piezoelectric body 5 having a square ring-shaped cross section, the signal detection electrodes 1, 2, 31 and 32 are provided on the four main surfaces, the electrode 4 is provided on the inner wall of the cylindrical body, and the piezoelectric body is the thickness of the cylindrical body. An example of a piezoelectric shock sensor that detects an impact as a channel from each of a first pair of external electrodes 1 and 31 and a second pair of external electrodes 2 and 32 that are polarized in the direction is shown.

  The cylindrical piezoelectric element may be regarded as a three-dimensional bimorph. When the detecting element 5 bends in the Z direction due to the inertial force action when the acceleration G is applied, charges with opposite signs are generated on the upper and lower surfaces, so that the acceleration is detected by the potential difference generated between the electrode 1 and the electrode 31. Can do. In this case, since the potentials of the horizontal electrodes 2 and 23 are equal, no signal is generated. Similarly, when bending in the Y direction, charges having opposite signs are generated in the horizontal electrodes 2 and 23, so that the acceleration can be detected by the potential difference generated between the electrodes 2 and 32. In this case, no signal is generated because the potentials of the upper and lower electrodes 1 and 13 are equal. FIG. 1B shows a structure in which one end of the piezoelectric body is fixed to the substrate by a U-shaped ceramic support 6. Here, for the convenience of signal processing, the electrodes 31 and 32 are short-circuited to be the common electrode 3 of CH1 and CH2. The signal detection electrodes 1, 2 and 3 are connected to the respective extraction electrodes formed on the ceramic support 6 (omitted in the drawing).

  Table 1 shows the analysis results of the voltage sensitivity of CH1 and CH2 when receiving an impact in each direction. Here, the length of the element is 6 mm, the inner and outer side lengths of the cross section are 1.2 and 0.8 mm, the thickness is 0.2 mm, and the length of the support 6 is 1.5 mm. In this case, since the electrodes 31 and 32 are forced to be equipotential, even if they are bent only in the Z direction, a potential difference is generated between the electrodes 2 and 3, so that a signal is also output to the horizontal CH2. On the other hand, when receiving an impact in the Y direction (lateral direction), since the restraining force of the support portion 6 with respect to the upper and lower surfaces of the element is asymmetric, it is not a simple flexural vibration in the horizontal direction. The output is large. Conventional plate bending shock sensors are difficult to detect shocks in the X direction (length direction), but in the case of a cylindrical element fixed at one end, there is a moment of force with respect to the substrate support at the center of gravity of the element. When an impact in the (length direction) is received, flexural vibration in the Z direction is generated.

  The output signals of CH1 and CH2 are output as voltage sensitivity by the circuit processing and the maximum value of CH1 and CH2 is output. From the results in Table 1, there is no significant difference in voltage sensitivity in each direction. Therefore, the piezoelectric shock sensor according to the present invention is capable of detecting impacts in all directions while having a single structure. However, since the cylindrical piezoelectric element is less likely to bend than the conventional plate-like shock sensor, the sensitivity is as low as about 1/2 to 1/3 as compared with the plate-like conventional type.

  Here, a PZT piezoelectric material having a Qm of about 2000 and a dielectric constant of about 1600 was used, and a cylindrical piezoelectric shock sensor was prototyped by an extrusion molding method. The shock sensor is fixed to the substrate at one end. 3 and 4 show examples of responses when an impact is applied to the substrate in the Z and Y directions, respectively. In the case of impact in the Z direction, the sensitivity of CH1 is greater, but in the case of impact in the Y direction, CH2 is greater. It almost agrees with the simulation result shown in Table 1.

  The piezoelectric shock sensor described above has a square ring cross section, but the piezoelectric body may be cylindrical. FIG. 5 shows a cross-sectional view of the structure. On the surface of the cylindrical piezoelectric body 5, the signal detection electrodes 1, 2, 31 and 32 that are equally divided into the outer circumferential direction are provided, the polarization common electrode 4 is provided on the inner wall of the cylindrical body, and the cylindrical body is polarized in the thickness direction, A piezoelectric shock sensor characterized in that an impact is detected by two channels if the first pair of external electrodes 1 and 31 and the second pair of external electrodes 2 and 32 are opposed to each other. Here, the electrodes 31 and 32 may be short-circuited to form a common electrode for CH1 and CH2.

  The present invention can be widely used as a shock sensor (acceleration sensor) for external impact detection, vibration countermeasures, pickup control, general acceleration detection, and the like in writing disk devices such as HDDs and DVDs.

The perspective view which shows the Example of this invention Side sectional view Illustration of response characteristics Illustration of response characteristics The perspective view which shows the Example of this invention A perspective view showing a conventional piezoelectric shock sensor

Explanation of symbols

1, 2, 31, 32: Detection electrode 4: Electrode CH1, CH2: Detection circuit (channel)

Claims (3)

In the piezoelectric shock sensor using the ring-shaped piezoelectric ceramic cylindrical body whose outer shape and inner shape of the cross section are square,
In addition to providing an independent signal detection electrode on each of the four outer surfaces of the cylindrical body, including a common electrode on the inner surface of the cylindrical body,
Piezoelectric ceramic cylinder is polarized in its thickness direction,
Two signal detection circuits are composed of two signal detection electrodes facing each other,
A piezoelectric shock sensor, wherein two sets of signal detection circuits detect displacement in two directions caused by an impact. In the piezoelectric shock sensor using the cylindrical ring-shaped piezoelectric ceramic cylindrical body,
A signal detection electrode formed independently on the outer surface of the cylindrical body and divided into four; and a common electrode on the inner surface of the cylindrical body;
Piezoelectric ceramic cylinder is polarized in its thickness direction,
Two signal detection circuits are composed of two signal detection electrodes facing each other,
A piezoelectric shock sensor, wherein two sets of signal detection circuits detect displacement in two directions caused by an impact.   The piezoelectric shock sensor according to claim 1 or 2, wherein one end of the cylindrical body in the length direction is fixed.

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