JP7634359B2 - Piezoelectric material measuring device and piezoelectric material measuring method - Google Patents

Description

Embodiments of the present invention relate to a piezoelectric material measurement device and a piezoelectric material measurement method.

Shear mode piezoelectric inkjet heads are known. In addition, in order to reduce the voltage and improve the performance of inkjet heads, it is desirable to use piezoelectric materials that can produce large distortions. The piezoelectric constant of a piezoelectric material varies depending on the operating conditions (electric field, frequency). Therefore, when adopting a piezoelectric material, it is desirable to measure the piezoelectric constant under the operating conditions of the inkjet head in order to determine the amount of distortion. However, there is a problem in that the measured values vary greatly under the operating conditions of the inkjet head, which are the large electric field (e.g., several hundred V/mm) and high frequency range (e.g., several hundred kHz).

Japanese Unexamined Patent Publication No. 4-152273

The problem that the present invention aims to solve is to provide a piezoelectric material measuring device and a piezoelectric material measuring method that can reduce the variability in the measured values.

The piezoelectric material measuring device according to one embodiment is a measuring device that measures a piezoelectric constant based on a shear strain amplitude obtained from a displacement speed of a measurement surface, which is an end face in the polarization direction, of a measurement object having two rectangular plate-shaped piezoelectric materials that shear deform in response to a voltage, the polarization directions of which are parallel and opposite to each other, and an electric field amplitude obtained from a voltage applied to the electrodes. The measuring device includes a driving source, a non-contact vibrometer, and a voltmeter. The driving source outputs an arbitrary voltage to the electrodes on both main surfaces of the measurement object, the voltage being set based on a driving condition of a device that uses the piezoelectric material of the measurement object . The non-contact vibrometer irradiates the measurement surface of the measurement object with a laser beam and senses the reflected light from the measurement surface to measure the displacement speed of the measurement surface . The voltmeter is connected to the driving source and measures the voltage output to the measurement object.

FIG. 1 is an explanatory diagram illustrating a schematic configuration of a measurement device according to an embodiment. FIG. 1 is a perspective view showing a schematic configuration of a measurement object to be measured by a measurement device according to an embodiment. FIG. 2 is an explanatory diagram illustrating a configuration of a holder of the measuring device according to the embodiment. FIG. 2 is a block diagram showing the configuration of a processing device of the measurement device according to the embodiment; FIG. 2 is an explanatory diagram showing an example of measurement of a measurement object using the measurement device according to the embodiment. 4 is a flowchart showing an example of a method for measuring a measurement object using the measurement device according to the embodiment. FIG. 11 is an explanatory diagram showing an example of the relationship between the piezoelectric constant and the frequency, which is a result of measuring a test piece by a conventional measuring method. FIG. 13 is an explanatory diagram showing the results of FEM analysis using a conventional measuring method. FIG. 4 is an explanatory diagram showing the result of an FEM analysis of the measurement method according to the embodiment, illustrating the relationship between the drive frequency and the shear strain amplitude. 4A to 4C are explanatory diagrams showing examples of measurement results of a soft-type PZT and a hard-type PZT measured using the measurement device and measurement method of the present embodiment. FIG. 11 is an explanatory diagram in which the deviation of each measurement point from an approximation line is plotted for the measurement values shown in FIG. 10 . 5A and 5B are explanatory diagrams showing the repeat measurement accuracy when measurements are repeatedly performed using the measurement device and measurement method of the present embodiment. FIG. 13 is an explanatory diagram illustrating a schematic configuration of a holder of a measuring device according to another embodiment.

Hereinafter, an example of a piezoelectric material measuring device 1 and a piezoelectric material measuring method according to an embodiment will be described with reference to the drawings.
Fig. 1 is an explanatory diagram showing a schematic configuration of a measuring device 1 according to an embodiment. Fig. 2 is a perspective view showing a schematic configuration of a measurement object 2 measured by the measuring device 1. Fig. 3 is an explanatory diagram showing a schematic configuration of a holder 11 of the measuring device 1. Fig. 4 is a block diagram showing a configuration of a processing device 16 of the measuring device 1. Fig. 5 is an explanatory diagram showing an example of measurement of the measurement object 2 using the measuring device 1, and Fig. 6 is a flow chart showing an example of a method of measuring the measurement object 2 using the measuring device 1.

First, a measurement object 2 to be measured by the measurement device 1 will be described.
As shown in FIG. 1, the measurement object 2 is an object to be measured by the measurement device 1. As shown in FIG. 2, the measurement object 2 includes, for example, two piezoelectric material pieces 4 (piezoelectric material) formed in a rectangular plate shape that shears in response to a voltage (electric field), and electrodes 5 provided on both main surfaces along the polarization direction of each piezoelectric material piece 4. The measurement object 2 is formed by joining two rectangular plate-shaped piezoelectric material pieces 4 with electrodes 5 provided on both main surfaces along the polarization direction so that they are anti-parallel polarized. In other words, the measurement object 2 is formed by joining two piezoelectric material pieces 4 with their polarization directions parallel and opposite to each other. In FIG. 2, the polarization direction of the piezoelectric material piece 4 is indicated by an arrow.

The two piezoelectric material pieces 4 used in the measurement object 2 are made of the same material. Furthermore, the two piezoelectric material pieces 4 are set to have the same dimensions of width W, length L, and thickness t. The electrodes 5 are made of, for example, gold. However, the electrodes 5 may be made of other materials such as silver or nickel. The electrodes 5 are formed on both main surfaces of the piezoelectric material piece 4 by a suitable method, for example, deposition, baking, plating, sputtering, or other methods.

For ease of explanation, in this embodiment, the direction along the polarization direction of the piezoelectric material piece 4 is defined as the longitudinal direction, and the stacking direction of the two piezoelectric material pieces 4 is defined as the thickness direction or the up-down direction. In addition, in this embodiment, the test piece including one of the piezoelectric material pieces 4 of the measurement object 2 and the electrodes 5 provided on both main surfaces of the piezoelectric material piece 4 is defined as the upper test piece 6, and the test piece including the other piezoelectric material piece 4 and the electrodes 5 provided on both main surfaces of the piezoelectric material piece 4 is defined as the lower test piece 7.

Next, the measuring device 1 for measuring the measuring object 2 will be described.
As shown in Fig. 1, the measuring device 1 includes a holder 11, a non-contact vibrometer 12, a transport device 13, a drive source 14, a voltmeter 15, and a processing device 16. The measuring device 1 drives the measuring object 2 held by the holder 11 with the drive source, and measures the displacement speed of one end face (measurement surface) in the longitudinal direction of the driven measuring object 2 at each position in the vertical direction. The measuring device 1 then obtains the tilt amplitude of each piezoelectric material piece 4 from the displacement amplitude obtained by integrating the measured displacement speed, and obtains the average value of the tilt amplitude as the strain amplitude of the piezoelectric material.

The holder 11 holds the object to be measured 2 in a position where one end face in the longitudinal direction of the object to be measured 2 faces the non-contact vibrometer 12. The holder 11 also provides electrical continuity between the electrodes 5 on both main surfaces of the object to be measured 2 and the driving source 14. As a specific example, the holder 11 abuts against the lower electrode 5 of the upper test piece 6 and the lower electrode 5 of the lower test piece 7 of the object to be measured 2.

For example, as shown in FIG. 3, the holder 11 has a pair of contact probe pins 111 that abut against the electrodes 5 on both main surfaces of the object to be measured 2 to hold the object to be measured 2. The contact probe pins 111 are formed of a highly conductive metal material. The pair of contact probe pins 111 are connected to the driving source 14.

The non-contact vibrometer 12 measures the displacement of the longitudinal end face, which is the measurement surface of the measurement object 2, and outputs the measured displacement value. For example, the non-contact vibrometer 12 measures the displacement speed of the measurement surface of each of the upper test piece 6 and the lower test piece 7 of the measurement object 2. The non-contact vibrometer 12 outputs the measured displacement speed as a signal. The non-contact vibrometer 12 is, for example, a laser Doppler vibrometer.

For example, as shown in FIG. 1, such a non-contact vibrometer 12 irradiates the measurement surface of the measurement object 2 with laser light L and measures the displacement velocity of the measurement surface by sensing the reflected light from the measurement surface. The non-contact vibrometer 12 outputs the measured displacement velocity (vibration velocity) as a vibration velocity signal of an analog voltage proportional to the vibration velocity.

For example, the non-contact vibrometer 12 is connected to a voltmeter 15 and a processing device 16. The non-contact vibrometer 12 outputs a vibration velocity signal to the voltmeter 15. The non-contact vibrometer 12 also measures the displacement velocity of the measurement surface of the measurement object 2 based on a command from the processing device 16.

The transport device 13 moves the measurement object 2 and the non-contact vibrometer 12 held by the holder 11 relatively in the vertical direction. For example, the transport device 13 can move at least the vertical distance of the end face of the measurement object 2. The transport device 13 is, for example, an electric stage having a motor and a stage that moves in the vertical direction by being driven by the motor. The transport device 13 is, for example, connected to a processing device 16, and moves the measurement object 2 held by the holder 11 in the vertical direction based on commands from the processing device 16.

The driving source 14 drives the measurement object 2 by applying a voltage (electric field) to the measurement object 2 via the holder 11. The driving source 14 is connected to, for example, a processing device 16, and applies a voltage to the measurement object 2 in response to a command from the processing device 16. The driving source 14 includes, for example, a waveform generator 141 and an amplifier 142.

The waveform generator 141 generates a voltage waveform (drive waveform) of an arbitrary drive voltage. The amplifier 142 is an amplifier. The amplifier 142 amplifies the voltage waveform generated by the waveform generator 141 to a voltage (electric field) or higher assumed for the drive conditions of the device that uses the piezoelectric material of the measurement object 2.

In this embodiment, the device using the piezoelectric material of the measurement object 2 is, for example, an actuator of an inkjet head. Note that the device using the piezoelectric material of the measurement object 2 is not limited to an actuator of an inkjet head, and can be set as appropriate.

In this embodiment, for example, two amplifiers 142 are used. The two amplifiers 142 apply voltage waveforms of opposite polarity to the upper test piece 6 and the lower test piece 7. In other words, by using two amplifiers 142, the driving source 14 can apply a potential difference to the measurement object 2 that is twice the voltage output specification of the amplifiers 142.

The voltmeter 15 monitors the drive voltage (voltage value) of the measurement object 2. For example, the voltmeter 15 receives a drive waveform signal as the drive voltage of the measurement object 2 and performs A/D conversion. The voltmeter 15 also monitors the vibration velocity signal output from the non-contact vibrometer 12. For example, the voltmeter 15 receives the vibration velocity signal output from the non-contact vibrometer 12 and performs A/D conversion. The voltmeter 15 also outputs data to the processing device 16 based on an instruction from the processing device 16. For example, the voltmeter 15 is connected to the processing device 16 and outputs the drive waveform signal and vibration velocity signal that have been A/D converted to the processing device 16.

Such a voltmeter 15 is, for example, a digital oscilloscope. The voltmeter 15 outputs data such as the monitored drive waveform signal and vibration velocity signal to the processing device 16. Note that the voltmeter 15 does not have to be a measuring instrument such as an oscilloscope, and may be a processing circuit provided in the processing device 16 that can monitor the drive voltage of the measurement object 2 and the output signal of the non-contact vibrometer 12.

The processing device 16 is a control device that controls each component of the measurement device 1. As shown in FIG. 4, the processing device 16 is, for example, a processing terminal such as a personal computer or a tablet terminal. The processing device 16 includes, for example, a communication unit 21, an input unit 22, an interface 23, a display unit 24, a memory 25, and a processor 26.

The communication unit 21 is an arbitrary communication interface that is controlled by the processor 26 and can communicate with an external terminal, which is another processing device, using wired or wireless communication technology. The communication unit 21 may be implemented, for example, as a communication module or a communication board. The communication unit 21 can connect to the communication unit of the external terminal using, for example, wireless communication technology such as the BLE standard (Bluetooth (registered trademark) Low Energy standard), Wi-Fi (registered trademark), or NFC, or wired communication technology such as USB.

The input unit 22 has a device for accepting user input, such as an operation panel including buttons, a touch panel, a keyboard, a mouse, etc. The interface 23 is a terminal or circuit that can be electrically connected to the non-contact vibrometer 12, the motor of the conveying device 13, the drive source 14, and the voltmeter 15.

The display unit 24 has a display device such as a liquid crystal display or an organic EL display. The display unit 24 functions as a display device that displays various information. The display unit 24 may also have a speaker, an LED (Light Emitting Diode) lighting unit, etc. instead of or in addition to the display device.

The memory 25 is a storage medium. Data can be read from and written to the memory 25. The memory 25 stores data used by the processor 26, various data and programs used for controlling the non-contact vibrometer 12, the conveying device 13, the driving source 14, the voltmeter 15, and measuring the measurement object 2. The memory 25 also stores other components of the processing device 16 and various data and programs used for controlling external devices, etc.

The memory 25 includes, for example, a non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read-Only Memory) (registered trademark), a ROM (Read only memory), or a NAND-type flash memory. The memory 25 also includes an SSD (Solid State Drive) equipped with a flash memory.

The processor 26 may be a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array), a DSP (Digital Signal Processor), a GPU (Graphics Processing Unit), a microcomputer, or any other general-purpose or dedicated processor. The processor 26 performs any process, such as communication control of the communication unit 21, display control of the display unit 24, and measurement control of the measurement object 2. In addition, the processor 26 is connected to the non-contact vibrometer 12, the transport device 13, the driving source 14, the voltmeter 15, an external terminal, etc., via the communication unit 21 and the interface 23.

The processor 26 includes, for example, a processing circuit and a memory. The processor 26 includes, for example, a storage area 261 such as a non-volatile EEPROM area or a volatile DRAM area as a memory. The processor 26 also includes a measurement control circuit 262 that controls the non-contact vibrometer 12, the conveying device 13, and the driving source 14 to measure the displacement speed of the measurement surface of the driven measurement object 2, and a calculation circuit 263 that calculates the piezoelectric constant d ₁₅ from the displacement speed measured by the non-contact vibrometer 12 and the electric field applied to the measurement object 2 measured by the voltmeter 15.

That is, the processor 26 performs the functions of the measurement control circuit 262 and the arithmetic circuit 263 by executing the programs stored in the memory 25 or the storage area 261. Note that the division of functions among the various parts of the processor 26 is for convenience and can be changed as appropriate.

The measurement control circuit 262 drives the object to be measured 2, measures the displacement speed of the object to be measured 2, and performs processing to acquire the measured displacement speed and the electric field applied to the object to be measured 2.

As a specific example, when a command to start measuring the object to be measured 2 is input to the input unit 22, the measurement control circuit 262 controls the drive source 14 to output the drive waveform of the object to be measured 2, which is the voltage waveform set by the input unit 22, to the object to be measured 2. The measurement control circuit 262 also controls the voltmeter 15 to output a drive waveform signal, which is data measuring the applied voltage (applied electric field) applied to the object to be measured 2. The measurement control circuit 262 also stores the drive waveform signal output from the voltmeter 15 in the memory 25 when it acquires it.

The drive waveform of the measurement object 2 is set arbitrarily based on the drive conditions of the device that uses the piezoelectric material. The measurement control circuit 262 controls the waveform generator 141 and amplifier 142 of the drive source 14 to output the drive waveform.

The measurement control circuit 262 also controls the transport device 13 to move the measurement object 2 and the non-contact vibrometer 12 relative to each other along the measurement direction. In this embodiment, the measurement control circuit 262 controls the transport device 13 to transport the holder 11 and move the measurement object 2 in the vertical direction (Z direction). The measurement range of the measurement object 2 is the vertical range of the measurement surface of the measurement object 2. In this embodiment, the measurement surface of the measurement object 2 is measured at multiple points in the vertical direction, so the movement amount of the measurement object 2 is set in advance and stored in the memory 25.

As a specific example, the measurement control circuit 262 controls the conveying device 13 to move the measurement object 2 in the vertical direction so that the non-contact vibrometer 12 measures the displacement velocity at each of the vertical measurement points on the measurement surface of the upper test piece 6 and the measurement surface of the lower test piece 7.

The position of the measurement object 2 moved vertically by the conveying device 13 can be detected by various methods. For example, the position of the measurement object 2 in the vertical direction may be detected by the laser light L irradiated by the non-contact vibrometer 12. For example, the vertical ends of the upper test piece 6 and the lower test piece 7 of the measurement object 2 may be estimated based on the position where the measurement object 2 cannot be detected by the non-contact vibrometer 12 or the position where the displacement speed of the measurement object 2 cannot be measured. For example, the position of the measurement object 2 may be detected by providing a sensor (not shown) for detecting the position of the measurement object 2 in the vertical direction, or by other methods.

The measurement control circuit 262 also controls the non-contact vibrometer 12 to measure the displacement of the measurement surface of the measurement object 2. As a specific example, the measurement control circuit 262 controls the non-contact vibrometer 12 to irradiate the measurement surface of the measurement object 2 with laser light L, and measures the displacement velocity with the non-contact vibrometer 12. The measurement control circuit 262 also controls the non-contact vibrometer 12 to output the measured displacement velocity as a vibration velocity signal. The measurement control circuit 262 also stores the vibration velocity signal output from the non-contact vibrometer 12 in the memory 25. The measurement control circuit 262 measures the displacement velocity at each measurement position between the measurement start position and measurement end position of the displacement velocity in the vertical direction of each of the upper test piece 6 and the lower test piece 7, and acquires the vibration velocity signal.

The calculation circuit 263 performs a process to calculate the piezoelectric constant of the piezoelectric material used in the measurement object 2 from the measured displacement speed and the electric field applied to the measurement object 2.

As shown by the two-dot chain line in FIG. 5, when a voltage (electric field) is applied to the measurement object 2, the end face in the polarization direction (longitudinal direction) is tilted by θ with respect to the end face before the electric field is applied. This tilt of the end face becomes the shear strain of each test piece 6, 7. For this reason, the calculation circuit 263 uses the non-contact vibrometer 12 to measure the displacement speed at multiple measurement positions in the vertical direction of the upper test piece 6 and the lower test piece 7 of the measurement object 2, and calculates the shear strain of the piezoelectric material used for the upper test piece 6 and the lower test piece 7 from these displacement speeds.

As a specific example, the arithmetic circuit 263 performs a tilt amplitude analysis by integrating the measured displacement velocity (vibration velocity signal) and determining the displacement amplitude at each position in the vertical direction of the upper test piece 6 and the lower test piece 7 of the measurement object 2. From the determined displacement amplitude, the arithmetic circuit 263 determines the tilt amplitude, which is the slope of the displacement amplitude of the upper test piece 6 and the lower test piece 7 relative to the vertical direction.

Then, the calculation circuit 263 calculates the average value of the tilt amplitude of the upper test piece 6 and the lower test piece 7 as the shear strain amplitude of the piezoelectric material used in the measurement object 2 (upper test piece 6 and lower test piece 7).

The arithmetic circuit 263 also analyzes the voltage amplitude (electric field amplitude). The arithmetic circuit 263 determines the electric field amplitude of the electric field applied to the upper test piece 6 from the drive waveform signal.

The calculation circuit 263 calculates the piezoelectric constant _d15 with respect to the frequency based on the obtained shear strain amplitude and electric field amplitude.

An example of a method for calculating the piezoelectric constant _d15 will now be described.
The equation for calculating the strain S that occurs when a stress T and an electric field E are applied to a piezoelectric material is given by equation (1) based on the fundamental piezoelectric equation.

S ^E : Elastic compliance (E = constant)
d: piezoelectric strain coefficient The equation for calculating the strain _S5 in the case of shear mode is given by equation (2).

In the measurement object 2 having antiparallel polarization, the movement in the shear direction is not hindered even if the upper electrode 5 of the upper test piece 6 and the lower electrode 5 of the lower test piece 7 are restrained, so that the shear stress _T5 is 0 and the shear strain _S5 is given by the formula (3).

The shear mode piezoelectric constant d ₁₅ is given by equation (4).

Therefore, by substituting the shear strain amplitude and the electric field amplitude into this equation (4), the piezoelectric constant _d15 can be calculated.

The method of calculating the piezoelectric constant _d15 is stored as a program in the memory 25. The processor 26 executes the program to thereby realize the function of the calculation circuit 263 for calculating the piezoelectric constant _d15 .

Next, as a method for measuring a piezoelectric material according to this embodiment, an example of a method for measuring a measurement object 2 using a measurement device 1 will be described with reference to the flow chart shown in FIG. 6. In the method for measuring a measurement object 2 according to this embodiment, an example is shown in which the measurement object 2 is measured in the order of the upper test piece 6 and the lower test piece 7.

As a method for measuring the object to be measured 2, first, the object to be measured 2 is prepared. For example, two test pieces (upper test piece 6 and lower test piece 7) made of the same piezoelectric material and having electrodes 5 formed on both main surfaces are joined so as to have anti-parallel polarization. The two test pieces are joined with thermoplastic wax so that at least partial contact is maintained between the electrodes of each of the test pieces 6 and 7. An example of the thermoplastic wax is Electron Wax (registered trademark) H7 from Furuuchi Chemical Co., Ltd., but the thermoplastic wax is not limited to this and can be set as appropriate.

As a specific example, a thin layer of thermoplastic wax is applied to a PET film heated to 90°C, and then the thermoplastic wax is transferred under heat to one side of the opposing electrode 5 of one of the test pieces 6 and 7 to be joined. The test piece with the thermoplastic wax transferred to it is then returned to room temperature, and the pair of test pieces are then overlapped, lightly pressed with a small vice, and the overlapped test pieces 6 and 7 are heated to about 90°C, and then cooled. Using these examples, a measurement object 2 is produced in which two test pieces 6 and 7 are joined together.

The dimensions of the measurement object 2, which is antiparallel polarized, are preferably those that have been shown to have a resonance suppression effect in FEM analysis. In particular, it is preferable that the thickness t of the measurement object 2 be 0.2 mm or less.

When measuring the displacement velocity using a laser Doppler vibrometer, the sensing of the reflected light from the measurement surface may be affected by the condition of the measurement surface of the measurement object 2, and the measurement accuracy may be affected by this. For example, if the measurement surface of the measurement object 2 is highly rough, poor sensing of the reflected light from the measurement surface may occur. Therefore, in preparing the measurement object 2, it is preferable to perform surface polishing of the measurement surface of the measurement object 2 so as to obtain sufficient reflection of the laser light L. For example, precision polishing using a wrapping film sheet is an example of surface polishing that can obtain sufficient reflection of the laser light L. As an example, when the final polishing of the measurement surface was performed using a wrapping film sheet (manufactured by 3M) with a grain size of 0.3 μm, suitable reflection of the laser light L was observed.

Next, the prepared measurement object 2 is held by the holder 11, and the electrodes 5 on both main surfaces of the measurement object 2 are connected to the driving source 14. Next, power is supplied to the non-contact vibrometer 12, the transport device 13, the driving source 14, the voltmeter 15, the processing device 16, etc., and they are put into a standby state.

When the processor 26 goes into standby mode, it determines whether or not a command to start measurement of the object to be measured 2 has been input to the input unit 22 (ACT 1), and monitors the input until a command to start measurement is received (NO in ACT 1). When the person measuring operates the input unit 22 and a command to start measurement of the object to be measured 2 is input to the input unit 22 (YES in ACT 1), the processor 26 starts measurement based on a signal from the input unit 22. First, the processor 26 controls the transport device 13 to move the object to be measured 2 to the measurement start position of the upper test piece 6 (ACT 2).

Next, the processor 26 controls the drive source 14 to output a preset drive waveform to the measurement object 2 (ACT 3). Next, the processor 26 controls the non-contact vibrometer 12 to measure the displacement velocity (ACT 4). At this time, the non-contact vibrometer 12 irradiates the laser light L onto the measurement position on the measurement surface of the upper test piece 6 of the measurement object 2, receives the reflected light, and detects the displacement velocity. The non-contact vibrometer 12 also outputs the detected displacement velocity to the voltmeter 15 as a vibration velocity signal.

The processor 26 commands the voltmeter 15 to output data such as the drive waveform signal and the vibration velocity signal. In response to the command from the processor 26, the voltmeter 15 outputs the drive waveform signal and the vibration velocity signal (ACT 5). Specifically, the voltmeter 15 receives the drive waveform signal output from the drive source 14 to the measurement object 2 and performs A/D conversion. The voltmeter 15 also receives the vibration velocity signal output from the non-contact vibrometer 12 and performs A/D conversion. The voltmeter 15 then outputs the A/D converted drive waveform signal and vibration velocity signal.

The processor 26 stores the drive waveform signal and vibration velocity signal output from the voltmeter 15 in the memory 25 (ACT 6). Next, the processor 26 controls the transport device 13 to change the measurement position of the measurement surface of the upper test piece 6 by the non-contact vibrometer 12, and moves the measurement object 2 a predetermined distance in the vertical direction toward the measurement end position (ACT 7). The movement amount of the measurement object 2 is, for example, set in advance. That is, since the measurement surface of the upper test piece 6 is measured at multiple positions in the vertical direction, the processor 26 controls the transport device 13 to move the measurement object 2 based on, for example, any measurement position, number of measurements, or movement amount of the measurement object 2 that is input in advance and stored in the memory 25, etc.

Next, the processor 26 determines whether the measurement position of the upper test piece 6 has moved to the end position (ACT 8). If the measurement position of the upper test piece 6 has not moved to the end position (ACT 8, NO), the processor 26 controls the non-contact vibrometer 12 at the measurement position after the movement to measure the displacement speed (ACT 4), and repeats the steps from ACT 4 onwards until the measurement position of the upper test piece 6 moves to the end position. Note that, for example, in ACT 4, if the drive source 14 stops outputting the drive waveform after measuring the displacement speed, and the measurement position of the upper test piece 6 has not moved to the end position (ACT 8, NO), the processor 26 returns to ACT 3 and repeats the steps thereafter.

If the measurement position of the upper test piece 6 has moved to the end position (YES in ACT 8), the processor 26 ends the measurement of the upper test piece 6 and starts the measurement of the lower test piece 7. The processor 26 controls the transport device 13 to move the measurement target 2 to the measurement start position of the lower test piece 7 (ACT 9).

Next, the processor 26 controls the drive source 14 to output a preset drive waveform to the measurement object 2 (ACT 10). Next, the processor 26 controls the non-contact vibrometer 12 to measure the displacement velocity (ACT 11). At this time, the non-contact vibrometer 12 irradiates the laser light L onto the measurement position on the measurement surface of the lower test piece 7 of the measurement object 2, receives the reflected light, and detects the displacement velocity. The non-contact vibrometer 12 also outputs the detected displacement velocity to the voltmeter 15 as a vibration velocity signal.

The processor 26 commands the voltmeter 15 to output data such as the drive waveform signal and the vibration velocity signal. In response to the command from the processor 26, the voltmeter 15 outputs the drive waveform signal and the vibration velocity signal (ACT12). Specifically, the voltmeter 15 receives the drive waveform signal output from the drive source 14 to the measurement object 2 and performs A/D conversion. The voltmeter 15 also receives the vibration velocity signal output from the non-contact vibrometer 12 and performs A/D conversion. The voltmeter 15 then outputs the A/D converted drive waveform signal and vibration velocity signal.

The processor 26 stores the drive waveform signal and the vibration velocity signal output from the voltmeter 15 in the memory 25 (ACT 13). Next, the processor 26 controls the transport device 13 to change the measurement position of the measurement surface of the lower test piece 7 by the non-contact vibrometer 12, and moves the measurement object 2 a predetermined distance in the vertical direction toward the measurement end position (ACT 14). The movement amount of the measurement object 2 is, for example, set in advance. That is, since the measurement surface of the lower test piece 7 is measured at multiple positions in the vertical direction, the processor 26 controls the transport device 13 to move the measurement object 2 based on, for example, any measurement position, number of measurements, or movement amount of the measurement object 2 that is input in advance and stored in the memory 25, etc. Here, the movement amount of the measurement object 2 in the measurement of the lower test piece 7 is set to be the same as the movement amount of the measurement object 2 in the measurement of the upper test piece 6.

Next, the processor 26 determines whether the measurement position of the lower test piece 7 has moved to the end position (ACT 15). If the measurement position of the lower test piece 7 has not moved to the end position (ACT 15, NO), the processor 26 controls the non-contact vibrometer 12 at the measurement position after the movement to measure the displacement speed (ACT 11), and repeats the steps from ACT 11 onwards until the measurement position of the lower test piece 7 moves to the end position. Note that, for example, in ACT 11, if the drive source 14 stops outputting the drive waveform after measuring the displacement speed, if the measurement position of the lower test piece 7 has not moved to the end position (ACT 15, NO), the processor 26 returns to ACT 3 and repeats the steps thereafter.

When the measurement position of the lower test piece 7 has moved to the end position (YES in ACT 15), the processor 26 ends the measurement of the lower test piece 7. The processor 26 performs a tilt amplitude analysis and a voltage amplitude (electric field amplitude) analysis from the drive waveform signal and the vibration velocity signal stored in the memory 25 in the measurement of the upper test piece 6 (ACT 16). Specifically, the processor 26 determines the tilt amplitude of the upper test piece 6 from the vibration velocity signal stored in the memory 25. The processor 26 also determines the electric field amplitude of the electric field applied to the upper test piece 6 from the drive waveform signal stored in the memory 25.

Similarly, the processor 26 performs a tilt amplitude analysis and a voltage amplitude (electric field amplitude) analysis from the drive waveform signal and the vibration velocity signal stored in the memory 25 in the measurement of the upper test piece 6 (ACT 17). Next, the processor 26 performs a shear strain amplitude analysis of the piezoelectric material used in the measurement object 2 (ACT 18). Specifically, the processor 26 determines the average value of the tilt amplitude of the upper test piece 6 and the tilt amplitude of the lower test piece 7 as the shear strain amplitude.

Next, the processor 26 calculates the piezoelectric constant d ₁₅ (ACT 19). Specifically, the processor 26 substitutes the obtained shear strain amplitude and electric field amplitude into the formula (4) to obtain the piezoelectric constant d _15. In this manner, the piezoelectric constant of the piezoelectric material used in the measurement target 2 is measured using the measurement device 1.

The measurement device 1 and measurement method configured in this manner determine the tilt amplitude of each test piece 6, 7 on the measurement surface of the measurement object 2, which is made of two test pieces made of piezoelectric materials joined together so that they are anti-parallel polarized, and determine the shear strain amplitude from this tilt amplitude. The piezoelectric constant of the piezoelectric material of the test pieces 6, 7 is then determined from the shear strain amplitude. Therefore, the measurement device 1 and measurement method can suppress variation in the measured piezoelectric constant.

To be more specific, for example, the operating conditions of a product that is assumed to use piezoelectric materials, such as a shear mode type piezoelectric inkjet head, are assumed to be a large electric field (several hundred V/mm) and a high frequency range (several hundred kHz). However, as is clear from the relationship between the piezoelectric constant and frequency in Figure 7, when measuring the piezoelectric constant of a conventional test piece with electrodes on both main surfaces of a single piece of piezoelectric material, a significant fluctuation (variation) in the value of the piezoelectric constant is observed in the frequency range of 100 kHz to 1 MHz. Note that Figure 7 shows an example of the measurement results when an electric field of 300 V/mm is applied to a test piece with electrodes on both main surfaces of a single piece of piezoelectric material with a width W = 1.43 mm, length L = 4.8 mm, and thickness t = 0.2 mm. Figure 8 shows the results of FEM analysis using conventional test pieces and conditions at frequencies of 10 kHz and 1 MHz. As shown in Figure 8, a conventional test piece with electrodes on both main surfaces of a single piece of piezoelectric material produces ideal shear deformation at 10 kHz, but at 1 MHz the test piece resonates and deforms in the thickness direction.

However, when the measurement object 2 in which two test pieces 6 and 7 are joined to have antiparallel polarization is used as in this embodiment, as shown in FIG. 9, the shear strain amplitude has flat characteristics up to a frequency range exceeding 100 kHz, and therefore the piezoelectric constant also has flat characteristics. FIG. 9 is a diagram showing the relationship between the drive frequency and the shear strain amplitude for each thickness of the test pieces 6 and 7 in the measurement object 2 with antiparallel polarization, as analyzed by FEM. The FEM analysis in FIG. 9 was performed under the conditions of an applied electric field of 5 V/mm, a test piece width W = 1.5 mm, a length L = 5 mm, and thicknesses t of the test pieces 6 and 7 used in the measurement object 2 with antiparallel polarization of 0.05 mm, 0.1 mm, and 0.2 mm.

As is clear from the results in Figure 9, by measuring the measurement object 2 in which two test pieces 6, 7 are joined so as to have antiparallel polarization, as in the measurement device 1 and measurement method of the embodiment, it is possible to suppress fluctuations in the value of the shear strain amplitude even in the high frequency range, and therefore the variability in the measured value of the piezoelectric constant can be suppressed. Therefore, the measurement device 1 and measurement method of the embodiment are effective for evaluating piezoelectric materials used in devices such as shear mode type piezoelectric inkjet heads, which operate under large electric fields and in the high frequency range.

In other words, by applying the measurement device 1 and measurement method of the embodiment, it is possible to select a piezoelectric material suitable for the actual operating conditions of the device while taking into account the electric field and frequency dependence of the shear strain of the piezoelectric material.

In addition, the measurement device 1 and the measurement method are configured to determine the shear strain amplitude as the average value of the slope amplitudes obtained from the two test pieces 6 and 7, which allows for improved measurement accuracy compared to obtaining the shear strain amplitude from a single test piece.

Furthermore, in the measurement device 1 and the measurement method, the thickness of the antiparallel polarized measurement object 2 is set to 0.2 mm or less, thereby suppressing the fluctuation of the shear strain amplitude. To be more specific, the cause of the increase in the shear strain amplitude is thought to be the resonance of the shear mode. Here, the frequency constant N can generally be used to obtain the resonance frequency, and the frequency constant N is defined as the product of the length in the direction corresponding to each vibration mode and the resonance frequency thereof. Therefore, the resonance frequency f _r of the shear mode is expressed by the formula (5) using the frequency constant N ₅ of the shear vibration and the thickness t of the test piece.

Therefore, it is effective to take measures to shift the resonance frequency to the higher frequency side by thinning the test piece. This is also evident from the fact that, as shown in Figure 9, the increase in shear strain amplitude at frequencies above 400 kHz gradually decreases, as can be seen from the FEM analysis results when the thickness t of the measurement object 2 is thinned to 0.2 mm, 0.1 mm, and 0.05 mm, and the resonance suppression effect can be confirmed. For this reason, by setting the thickness of the measurement object 2 with antiparallel polarization to 0.2 mm or less, it is possible to prevent fluctuations in the shear strain amplitude.

Next, the measurement results measured using the measuring device 1 and measuring method of this embodiment will be described below. First, measurement examples of soft-type PZT and hard-type PZT are shown in FIG. 10. Here, general piezoelectric ceramics can be roughly divided into soft-type materials and hard-type materials according to the mechanical quality factor Qm. Piezoelectric ceramics with a relatively small mechanical quality factor Qm of 100 or less can be divided into soft-type materials, and relatively large materials with a mechanical quality factor Qm of 1000 or more can be divided into hard-type materials. The piezoelectric constants d15 obtained from the soft-type PZT and hard-type PZT shown in FIG. ₁₅ are 720 and 582, respectively.

In both the results for soft-PZT and hard-PZT, no large fluctuations in the piezoelectric constant as shown in FIG. 10 were observed in the range of 10 kHz to 1 MHz, and non-resonant shear strain could be measured well. In particular, the piezoelectric constant d ₁₅ of soft-PZT showed a tendency to decrease linearly with respect to the logarithm of the frequency, as shown in FIG. 10 (soft-PZT). In addition, FIG. 11 shows a graph in which the measured values shown in FIG. 10 were approximated linearly on a graph of the logarithm of the frequency, and the deviation of each measurement point from the approximated line was plotted. As shown in FIG. 11, the deviation in the range of 10 kHz to 1 MHz was within about ±3%. From this, it became clear that the measurement of the piezoelectric constant d ₁₅ using the antiparallel polarized measurement object 2, as in the measurement device 1 and measurement method of this embodiment, has a resonance suppression effect.

The repeatability measurement accuracy when repeatability measurements were performed using the measurement device 1 and the measurement method of this embodiment was obtained by the following method. Soft-type PZT was used as the piezoelectric material, and the electric field was set to 300 V/mm, and the frequency was set to two conditions: 833 kHz and 1 MHz. The number of measurement samples of the measurement object 2 was set to three, and six measurements were performed for each sample, including the measurement procedure of removing and attaching the measurement object 2 from the holder 11. The repeatability measurement accuracy was determined by dividing the difference between the maximum and minimum values of the six measured values by the average value. Here, the lower the repeatability measurement accuracy, the less the measurement variation, and it can be determined that measurement with high accuracy is possible. As shown in FIG. 12, the evaluation results showed that the repeatability measurement accuracy of this measurement method was 3% or less for all samples and frequencies. This also clearly shows that the measurement device 1 and the measurement method of this embodiment have high measurement accuracy.

As described above, according to the piezoelectric material measuring device 1 and measuring method of this embodiment, the measurement object 2 having antiparallel polarization is measured, thereby suppressing the variation in the measurement value.

The measuring device 1 and measuring method according to the embodiment are not limited to the above-mentioned examples. For example, in the above-mentioned examples, an example of the holder 11 for holding the measurement object 2 using the contact probe pins 111 has been described, but the present invention is not limited to this. For example, as shown in FIG. 13, the holder 11 according to another embodiment may be configured to include a pair of metal blocks 112 and a pair of conductive rubbers 113 provided on the opposing surfaces of the pair of metal blocks 112. Such a holder 11 holds the measurement object 2 using the conductive rubbers 113 between the pair of metal blocks 112.

For example, the metal block 112 is made of an aluminum material of several hundred Ω, and has a gold-plated layer of several milliΩ on the surface. The pair of metal blocks 112 is connected to the driving source 14. The conductive rubber 113 is made of, for example, a TPSPCR series material. By using a holder 11 having such a pair of metal blocks 112 and a pair of conductive rubbers 113, it becomes easy to attach a small-sized measurement object. In addition, by gold plating the surfaces of the pair of metal blocks 112, it is inexpensive and can improve the accuracy of monitoring by the voltmeter 15.

At least one of the embodiments described above can provide a piezoelectric material measuring device and a piezoelectric material measuring method that can reduce the variation in the measured values.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.
The following provides a description equivalent to the invention described in the original claims of this application.
[1] A driving source that outputs an arbitrary voltage to a measurement object in which two rectangular plate-shaped piezoelectric materials that undergo shear deformation in response to a voltage are joined together with their polarization directions parallel and opposite to each other;
a non-contact vibrometer that measures the displacement of the measurement object;
A voltmeter that measures a voltage applied to the measurement object;
A measuring device comprising:
[2] A holder for holding the object to be measured;
a conveying device that conveys the holder to a position where the measurement object is measured by the non-contact vibrometer;
a storage medium for storing the displacement value measured by the non-contact vibrometer and the voltage value measured by the voltmeter;
a control device that transports one of the piezoelectric materials of the measurement object to a position where the non-contact vibrometer measures the piezoelectric material of the measurement object, outputs the voltage to the measurement object, and stores the measured displacement value and voltage value of the one piezoelectric material in the storage medium, and transports the other piezoelectric material of the measurement object to a position where the non-contact vibrometer measures the piezoelectric material of the measurement object, outputs the voltage to the measurement object, and stores the measured displacement value and voltage value of the other piezoelectric material in the storage medium;
The measuring device according to [1], comprising:
[3] The measuring device described in [1] or [2], wherein the displacement velocity of the object to be measured is measured at multiple locations in the stacking direction of the two piezoelectric materials using the non-contact vibrometer, the measured displacement velocity of the object to be measured is integrated, a displacement amplitude of the object to be measured at multiple locations in the stacking direction is determined, and an inclination amplitude with respect to the stacking direction is determined from the multiple displacement amplitudes.
[4] The measuring device described in [3], wherein the tilt amplitude of one of the piezoelectric materials of the measurement object and the tilt amplitude of the other of the measurement object are averaged to determine the shear strain amplitude of the measurement object.
[5] Two rectangular plate-shaped piezoelectric materials that undergo shear deformation in response to voltage are joined together with their polarization directions parallel and opposite to each other;
outputting a voltage to the measurement object formed by bonding the two sheets of piezoelectric material by a drive source that outputs a given voltage;
measuring a displacement of the object to be measured by a non-contact vibrometer while the voltage is being output to the object to be measured;
Measuring a voltage applied to the measurement object with a voltmeter;
A method for measuring a piezoelectric material comprising:

1...measuring device, 2...measurement object, 4...piezoelectric material piece, 5...electrode, 6...upper test piece, 7...lower test piece, 11...holding device, 12...non-contact vibrometer, 13...conveying device, 14...driving source, 15...voltmeter, 16...processing device (control device), 21...communication unit, 22...input unit, 23...interface, 24...display unit, 25...memory, 26...processor, 111...contact probe pin, 112...metal block, 113...conductive rubber, 141...waveform generator, 142...amplifier, 261...memory area, 262...measurement control circuit, 263...arithmetic circuit.

Claims (5)

A measuring device for measuring a piezoelectric constant based on a shear strain amplitude calculated from a displacement speed of a measurement surface, which is an end surface in the polarization direction, of a measurement object in which two rectangular plate-shaped piezoelectric materials that undergo shear deformation in response to a voltage are joined together with their polarization directions parallel and opposite to each other, and electrodes are formed on both main surfaces along the polarization direction, and the shear strain amplitude is calculated from a displacement speed of a measurement surface, which is an end surface in the polarization direction, and an electric field amplitude is calculated from a voltage applied to the electrodes,
a drive source that outputs an arbitrary voltage to the electrodes on both main surfaces of the object to be measured, the voltage being set based on a drive condition of a device that uses a piezoelectric material of the object to be measured;
a non-contact vibrometer that measures a displacement speed of the measurement surface by irradiating the measurement surface of the measurement object with a laser light and sensing the reflected light from the measurement surface;
a voltmeter connected to the driving source and configured to measure the voltage output to the measurement object;
A measuring device comprising: a holder that holds the object to be measured in such a manner that the electrodes on both main surfaces of the object to be measured are in contact with the object to be measured and the measurement surface of the object to be measured faces the non-contact vibrometer;
a conveying device that conveys the holder to a position where the measurement surface of the measurement object is measured by the non-contact vibrometer;
a storage medium for storing the displacement value measured by the non-contact vibrometer and the voltage value measured by the voltmeter;
a control device that transports one of the piezoelectric materials of the measurement object to a position where the non-contact vibrometer measures the piezoelectric material of the measurement object, outputs the voltage to the measurement object, and stores the measured displacement value and voltage value of the one piezoelectric material in the storage medium, and transports the other piezoelectric material of the measurement object to a position where the non-contact vibrometer measures the piezoelectric material of the measurement object, outputs the voltage to the measurement object, and stores the measured displacement value and voltage value of the other piezoelectric material in the storage medium;
The measurement device of claim 1 , comprising: The measurement device according to claim 1 or 2, which measures the displacement velocity of the measurement surface of the measurement object at multiple points in the stacking direction of each of the two piezoelectric materials with the non-contact vibrometer, integrates the measured displacement velocity of the measurement object, determines the displacement amplitude of the measurement object at multiple points in the stacking direction, and determines the tilt amplitude with respect to the stacking direction from the multiple displacement amplitudes. The measurement apparatus according to claim 3 , wherein the tilt amplitude of the piezoelectric material of one of the measurement objects and the tilt amplitude of the piezoelectric material of the other measurement object are averaged to determine the shear strain amplitude of the measurement object. A measurement object is formed by joining two rectangular plate-shaped piezoelectric materials that undergo shear deformation in response to a voltage with their polarization directions parallel and opposite to each other, and forming electrodes on both main surfaces along the polarization direction;
outputting a voltage to the electrodes on both main surfaces of the object to be measured by a drive source that outputs an arbitrary voltage set based on a drive condition of a device that uses the piezoelectric material of the object to be measured;
While the voltage is being output to the measurement object, a non-contact vibrometer is used to irradiate a laser beam onto a measurement surface, which is an end surface of the measurement object in the polarization direction, and to measure a displacement speed of the measurement surface by sensing reflected light from the measurement surface;
measuring the voltage output to the measurement object by a voltmeter connected to the driving source;
measuring a piezoelectric constant based on a shear strain amplitude calculated from a displacement speed of the measurement surface and an electric field amplitude calculated from a voltage applied to the electrodes;
A method for measuring a piezoelectric material comprising: