JPH0692981B2 - Piezoelectric acceleration sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor that detects vibration of an object, and more particularly to a piezoelectric acceleration sensor that applies a piezo effect.

2. Description of the Related Art A device for detecting an inertial acceleration of an object-an acceleration sensor is widely used for detecting a shock acting on an object, measuring a vibration, and the like.

As the acceleration sensor, various types such as an electrodynamic type, a piezoelectric type, a photoelectric type, and a servo type have been proposed and put into practical use depending on the operation principle and the form. Among them, the piezoelectric acceleration sensor is one of the most widely used because of its simple structure, small size, light weight, and robustness. Piezoelectric accelerometers utilize the properties of ferroelectric ceramics, such as barium titanate and zirconate, or quartz, which generate electrical signals when subjected to mechanical deformation-the piezoelectric effect. The inertial force applied to the weight is applied to the piezo element, the resulting electrical output is detected, and the inertial acceleration is obtained.

At this time, there are a method of taking out an open circuit voltage and a method of taking out a short-circuit charge as a method of taking out an electric signal from the piezo element, and one of the methods is used in a conventional piezoelectric acceleration sensor.

Problems to be Solved by the Invention The sensitivity of the piezoelectric acceleration sensor configured as described above is proportional to the open circuit voltage generated per unit working force or the short circuit charge. Sex matters. This is mainly due to the temperature dependence of the material constant of the piezo element, but this problem will be described below.

The following relationship is established between the force acting on the piezo element and the generated electric output, paying attention to an appropriate directional component.

Q = A · V + B · F F: Working force Q: Generated electric charge V: Generated voltage Here, A and B are proportional coefficients determined by the shape of the piezo element, material constant, and the like.

In the above formula, the ratio of V (that is, open-circuit voltage) and F when Q = 0: K _V , and the ratio of Q (that is, short-circuit charge) and F when V = 0: K _O is the sensitivity of each sensor. It will be proportional. When K _V and K _O are represented by A and B, K _V = −B / AK _O = B Therefore, when A and B change with temperature, the sensor sensitivity also changes. At this time, of the determinants of the proportional constants A and B, those relating to the shape can be ignored, but the temperature dependence of the material constant poses a problem.

Generally, the dominant material constants for the proportional constants A and B are the dielectric constant: E ₃₃ and the piezoelectric constant: D ₃₁ , which are approximately connected by the following proportional relationship.

A E ₃₃ B D ₃₁ Therefore, K _V −D ₃₁ / E ₃₃ = −G ₃₁ K _O D ₃₁ A typical example of the temperature dependence of the piezoelectric constants G ₃₁ and D ₃₁ is often used in a piezoelectric acceleration sensor. The piezoelectric ceramic is shown in FIG.

Therefore, when an acceleration sensor is constructed using this piezoelectric material, its sensitivity is as shown in FIG. 2 (a) when a method for extracting an open circuit voltage is used, and a method for extracting a short circuit charge is used. When it is used, it has temperature dependence as shown in FIG.

And such temperature dependence, that is, D ₃₁ and G ₃₁ have temperature dependence, respectively, and the inclinations thereof are opposite to each other, is not peculiar to the example given here. There are some differences in piezoelectric materials in general.

It is an object of the present invention to provide a highly accurate acceleration sensor with such sensitivity having little temperature dependency.

Means for Solving the Problems In order to solve the above problems, the present invention uses a pair of piezo elements whose sensitivity directions are matched with each other, takes out an electric signal proportional to its open circuit voltage from one piezo element, and The above-mentioned object is achieved by taking out an electronic signal proportional to the short-circuit charge from the piezo element and adding it.

Operation According to the above means, it is possible to cancel the temperature dependence of the material constant and realize a highly accurate acceleration sensor with a small change in sensitivity with respect to a temperature change.

Embodiment An embodiment of the piezoelectric acceleration sensor of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the piezoelectric acceleration sensor of the present invention.

In FIG. 1, 1a and 1b are matched piezo elements which are arranged close to each other so that the sensitivity directions are matched, 2 is a voltage amplifier which generates an output proportional to the open voltage of the piezo element of 1a, and 3 is 1b. Is a charge amplifier that generates an output proportional to the short-circuit charge of the piezo element.

The outputs of the voltage amplifier 2 and the charge amplifier 3 are added by the adder 4 with weights Ka and Kb, respectively.

In the above structure, when acceleration acts, the pair of piezo elements generate electric signals matching them, but their sensitivities are piezoelectric constants when they are extracted as an open circuit voltage and when they are extracted as a short circuit charge. G ₃₁ ,
It has a temperature dependence associated with the temperature characteristic of D ₃₁ .

Since this temperature dependence is as shown in FIG. 2, by setting the ratio of the gain of the voltage amplifier, the gain of the charge amplifier, and the weighting of the adder so as to cancel out the changes, the change in temperature is suppressed. The change in sensitivity
It can be much smaller than if the voltage or charge amplifier were used alone.

For example, when using the piezoelectric ceramics given as an example in the description of the conventional technique, the absolute value of the slope of D ₃₁ is about 1.5 times larger near room temperature, so there are two types of voltage-amplified ones and charge-amplified ones near room temperature. If the sensitivity ratio is set to 1.5: 1, the temperature dependence of the combined sensitivity is improved as shown in Fig. 3 and becomes almost flat near room temperature.

EFFECTS OF THE INVENTION As will be apparent from the detailed description above, the piezoelectric acceleration sensor of the present invention uses a pair of piezo elements whose sensitivity directions are matched with each other, and an electric signal proportional to the open circuit voltage is output from one of the piezo elements. Since the electric signal proportional to the short circuit charge is taken out from the other piezo element and is added, the temperature change of the material characteristic peculiar to the piezo element is canceled out, and the temperature of the sensitivity is It is possible to realize highly accurate characteristics with little dependence.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a graph showing a typical example of temperature dependence of a material constant of piezoelectric ceramics, and FIG. It is a graph which shows the temperature dependence of the sensitivity in an Example. 1a, 1b ... Piezo element, 2 ... Voltage amplifier, 3 ... Charge amplifier, 4 ... Adder.

Claims (1)

[Claims] 1. A pair of piezo elements which are arranged so that their sensitivity directions coincide with each other, a voltage amplifier which produces an output proportional to an open circuit voltage of one piezo element, and a short circuit charge of the other piezo element. A piezoelectric acceleration sensor, comprising: a charge amplifier that generates a proportional output; and an adding unit that adds the output of the voltage amplifier and the output of the charge amplifier.