Acceleration sensor module, acceleration sensor, and control method of acceleration sensor

Abstract

To provide a technique capable of appropriately diagnosing a piezoelectric element while reducing an influence to detection of acceleration because of resonance of the piezoelectric element by a damping effect.SOLUTION: An acceleration sensor module 1 includes: a signal processing section 12 for processing a signal outputted from a piezoelectric element; a voltage application section 13 for applying a diagnosis signal for diagnosing a piezoelectric element to the piezoelectric element; a damping resistance section 14 connected to a piezoelectric element; and a control section 20 for controlling the signal application section and the damping resistance section. The control section reduces a resistance value of the damping resistance section in a diagnosis mode for diagnosing a piezoelectric element much mo re than in an acceleration detection mode for detecting acceleration and applies a diagnosis signal to the piezoelectric element.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an acceleration sensor module that detects acceleration using a piezoelectric element, an acceleration sensor, and a control method for the acceleration sensor.

Background Art

[0002] Conventionally, an acceleration sensor that detects acceleration using a piezoelectric element is known. Such an acceleration sensor is configured to diagnose the piezoelectric element by applying a diagnostic signal to the piezoelectric element. For example, International Publication No. 2006 / 109501 (Patent Document 1) and Japanese Patent Application Laid-Open No. 8-5654 (Patent Document 2) disclose a technique for determining whether a piezoelectric element is abnormal based on a signal output from the piezoelectric element when a diagnostic signal is applied to the piezoelectric element. Further, Japanese Patent Application Laid-Open No. 8-5654 (Patent Document 2) discloses connecting a filter resistor (damping resistor) to the piezoelectric element.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The acceleration sensor disclosed in Patent Document 2 can reduce the influence of resonance of the piezoelectric element on acceleration detection by the damping effect of the damping resistor connected to the piezoelectric element. However, due to the damping effect, it becomes difficult for the change in the impedance of the piezoelectric element when a diagnostic signal is applied to appear, so there is a possibility that the piezoelectric element cannot be diagnosed appropriately.

[0005] The present disclosure has been made to solve such problems, and an object thereof is to provide a technique capable of reducing the influence on acceleration detection due to resonance of a piezoelectric element caused by a damping effect while appropriately diagnosing the piezoelectric element.

Means for Solving the Problems

[0006] An acceleration sensor module according to an aspect of the present disclosure includes a signal processing unit that processes a signal output from a piezoelectric element, a signal application unit that applies a diagnostic signal for diagnosing the piezoelectric element to the piezoelectric element, a damping resistor unit connected to the piezoelectric element, and a control unit that controls the signal application unit and the damping resistor unit. The control unit reduces the resistance value of the damping resistor unit in a diagnostic mode for diagnosing the piezoelectric element as compared with an acceleration detection mode for detecting acceleration, and applies a diagnostic signal to the piezoelectric element.

[0007] An acceleration sensor according to another aspect of the present disclosure includes a signal processing unit that processes a signal output from a piezoelectric element, a signal application unit that applies a diagnostic signal for diagnosing the piezoelectric element to the piezoelectric element, and a damping resistor unit connected to the piezoelectric element. The damping resistor unit has a smaller resistance value in a diagnostic mode for diagnosing the piezoelectric element than in an acceleration detection mode for detecting acceleration. The signal application unit applies a diagnostic signal to the piezoelectric element in the diagnostic mode.

[0008] A control method according to another aspect of the present disclosure includes, as processing executed by a computer, a step of reducing the resistance value of a damping resistor unit connected to a piezoelectric element in a diagnostic mode for diagnosing the piezoelectric element as compared with an acceleration detection mode for detecting acceleration, and a step of applying a diagnostic signal for diagnosing the piezoelectric element to the piezoelectric element.

Advantages of the Invention

[0009] According to the present disclosure, while reducing the influence on acceleration detection due to the resonance of the piezoelectric element by the damping resistance portion connected to the piezoelectric element, in the diagnostic mode, by making the resistance value of the damping resistance portion smaller than in the acceleration detection mode, it is possible to appropriately diagnose the piezoelectric element by avoiding the difficulty in detecting a change in the impedance of the piezoelectric element during the diagnostic mode.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their descriptions will not be repeated.

[0012] <Embodiment 1> The acceleration sensor module 1 according to Embodiment 1 will be described with reference to FIGS. 1 to 11.

[0013] [Configuration of Acceleration Sensor Module] The configuration of the acceleration sensor module 1 according to Embodiment 1 will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing the configuration of the acceleration sensor module 1 according to Embodiment 1. The acceleration sensor module 1 is mounted on an object such as an automobile, a mobile terminal such as a smartphone, or mechanical equipment, and detects the acceleration applied to the object.

[0014] As shown in FIG. 1, the acceleration sensor module 1 includes an acceleration sensor 10 and a control unit 20. The acceleration sensor module 1 may be configured such that the acceleration sensor 10 and the control unit 20 are integrally formed as one processing circuitry, or the acceleration sensor 10 and the control unit 20 may be configured as different processing circuitries.

[0015] The acceleration sensor 10 includes a piezoelectric element 11, a signal processing unit 12, a signal application unit 13, a damping resistance unit 14, reference terminals 15, 16, and an output terminal 17.

[0016] The reference terminals 15 and 16 are, for example, ground. The damping resistor section 14, the piezoelectric element 11, and the signal processing section 12 are connected in series between the reference terminal 15 and the output terminal 17. The signal application section 13 is provided between the reference terminal 16 and the signal processing section 12 and is connected to the reference terminal 16 and the signal processing section 12.

[0017] The piezoelectric element 11 is configured such that an upper electrode and a lower electrode sandwich a piezoelectric body. The piezoelectric body is formed of, for example, ceramics and exhibits a piezoelectric effect in which a voltage (charge signal) is generated when pressure is applied, and an inverse piezoelectric effect in which it deforms when a voltage is applied. The upper electrode is connected to the output terminal 17 via the signal processing section 12. The lower electrode is connected to the reference terminal 15 via the damping resistor section 14.

[0018] The signal processing section 12 includes a charge amplifier 121, a filter section 123, and an amplifier section 124. The charge amplifier 121 converts the charge signal generated from the piezoelectric element 11 into a voltage signal, amplifies it, and outputs it to the filter section 123. The filter section 123 is, for example, a band-pass filter, and allows only the voltage signal in a specific frequency band among the voltage signals output from the charge amplifier 121 to pass through and outputs it to the amplifier section 124. The amplifier section 124 amplifies the voltage signal output from the filter section 123 and outputs it to the output terminal 17. By having the configuration as described above, the signal processing section 12 processes the charge signal output from the piezoelectric element 11 and outputs it to the output terminal 17.

[0019] The signal application section 13 includes a power supply 131 and a diagnostic switch 132. The power supply 131 is connected to the reference terminal 16 and the diagnostic switch 132. The diagnostic switch 132 is provided on a line 133 that connects the power supply 131 and the signal processing section 12 (in this example, the charge amplifier 121) and is connected to the power supply 131 and the signal processing section 12. The line 133 is an example of the "third line".

[0020] The power supply 131 is an AC power supply that outputs a diagnostic signal for diagnosing the piezoelectric element according to the control of the control unit 20. The diagnostic signal is a signal having an AC voltage waveform of a single frequency.

[0021] The diagnostic switch 132 short-circuits or opens the line 133 according to the control of the control unit 20. For example, when the diagnostic switch 132 is controlled to be in the ON state by the control unit 20, the line 133 is short-circuited. When the line 133 is short-circuited, the diagnostic signal output from the power supply 131 is applied to the piezoelectric element 11 via the charge amplifier 121. When the diagnostic switch 132 is controlled to be in the OFF state by the control unit 20, the line 133 is opened. When the line 133 is opened, the diagnostic signal from the power supply 131 is not applied to the piezoelectric element 11.

[0022] The damping resistance unit 14 includes a damping resistance 141 and a damping switch 142. The damping resistance 141 is provided on the line 143 connecting the reference terminal 15 and the piezoelectric element 11, and is connected to the reference terminal 15 and the piezoelectric element 11. The line 143 is an example of the "first line". The damping switch 142 is provided on the line 144 connecting the reference terminal 15 and the piezoelectric element 11 in parallel with the line 143, and is connected to the reference terminal 15 and the piezoelectric element 11. The line 144 is an example of the "second line".

[0023] The damping switch 142 short-circuits or opens the line 143 according to the control of the control unit 20. For example, when the damping switch 142 is controlled to be in the ON state by the control unit 20, the line 143 is short-circuited. When the damping switch 142 is controlled to be in the OFF state by the control unit 20, the line 143 is opened.

[0024] The control unit 20 includes an arithmetic unit 21 that executes a predetermined process, and a storage unit 22 that stores a program, data, etc. used by the arithmetic unit 21 to execute the predetermined process.

[0025] The arithmetic unit 21 is an arithmetic entity (computer) that executes predetermined processing. The arithmetic unit 21 is composed of, for example, a processor such as a CPU (Central Processing Unit), an MPU (Micro-Processing Unit), a TPU (Tensor Processing Unit), or a GPU (Graphics Processing Unit). Note that a processor, which is an example of the arithmetic unit 21, has a function of executing predetermined processing by executing a predetermined program, but some or all of these functions may be implemented using a dedicated hardware circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). The "processor" is not limited to a narrow-sense processor that executes processing in a stored-program manner such as a CPU, an MPU, a TPU, or a GPU, and may include a hardwired circuit such as an ASIC or an FPGA. Also, the arithmetic unit 21 is not limited to a Neumann-type computer such as a CPU or a GPU, and may be composed of a non-Neumann-type computer such as a quantum computer or an optical computer. The arithmetic unit 21 as described above can also be read as a processing circuit that executes predetermined processing. Note that the arithmetic unit 21 may be composed of one chip or a plurality of chips. Furthermore, the processor and related processing circuits may be composed of a plurality of computers interconnected by wire or wirelessly via a local area network or a wireless network. The processor and related processing circuits may be composed of a cloud computer that remotely performs arithmetic operations based on input data and outputs the arithmetic operation results to another device located at a remote location.

[0026] The memory unit 22 includes a storage area (e.g., a working area) for storing program codes or working memories when the arithmetic unit 21 executes various programs. The memory unit 22 includes volatile memories such as DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory), non-volatile memories such as ROM (Read Only Memory) and flash memory, and storage devices such as HDD (Hard Disk Drive) and SSD (Solid State Drive). The memory unit 22 may be one or more non-transitory computer readable media, or may be one or more computer readable storage media.

[0027] The memory unit 22 stores the processing program 23 executed by the arithmetic unit 21. The arithmetic unit 21 controls the signal enabling unit 13 and the damping resistance unit 14 by executing the processing program 23.

[0028] The acceleration sensor module 1 configured as described above is controlled to operate in either an acceleration detection mode for detecting acceleration using the piezoelectric element 11 or a diagnosis mode for diagnosing the piezoelectric element 11.

[0029] As shown in FIG. 1, in the acceleration detection mode, the control unit 20 controls the damping switch 142 to the OFF state to open the line 144. Further, in the acceleration detection mode, the control unit 20 controls the diagnosis switch 132 to the OFF state to open the line 133.

[0030] In the acceleration detection mode, when the object equipped with the acceleration sensor 10 vibrates and acceleration is applied, pressure is applied to the piezoelectric element 11, and the piezoelectric element 11 generates a voltage (charge signal) corresponding to the pressure. The charge signal output from the piezoelectric element 11 is processed by the signal processing unit 12 to be converted into a voltage signal and amplified, and only the voltage signal in a specific frequency band is output from the output terminal 17. The control unit 20 detects the acceleration applied to the object equipped with the acceleration sensor 10 based on the voltage signal output from the output terminal 17.

[0031] In the acceleration detection mode, since the line 133 is open, the diagnostic signal output from the power supply 131 is not applied to the piezoelectric element 11. Further, since the line 144 is open, the damping effect of the damping resistor 141 provided on the line 143 reduces the influence on acceleration detection due to the resonance of the piezoelectric element 11.

[0032] FIG. 2 is a diagram showing the connection state of the acceleration sensor module 1 in the diagnostic mode. As shown in FIG. 2, in the diagnostic mode, the control unit 20 controls the diagnostic switch 132 to be in the ON state to short-circuit the line 133.

[0033] In the diagnostic mode, the diagnostic signal output from the power supply 131 is applied to the piezoelectric element 11 via the charge amplifier 121. The piezoelectric element 11 deforms when the diagnostic signal is applied, and the piezoelectric element 11 generates a voltage (charge signal) as it deforms. The charge signal output from the piezoelectric element 11 is processed by the signal processing unit 12 to be converted into a voltage signal and amplified, and only the voltage signal in a specific frequency band is output from the output terminal 17. The control unit 20 determines whether an abnormality has occurred in the acceleration sensor 10, such as a crack generated in the piezoelectric element 11, based on the voltage signal output from the output terminal 17.

[0034] Here, in the acceleration detection mode, the control unit 20 is configured to reduce the influence on acceleration detection caused by the resonance of the piezoelectric element 11 due to the damping effect of the damping resistor 141 provided on the line 143 by opening the line 144. However, in the diagnosis mode, when the damping effect of the damping resistor 141 occurs, it becomes difficult for the change in the impedance of the piezoelectric element 11 when a diagnostic signal from the power supply 131 is applied to the piezoelectric element 11 to appear. As a result, there is a possibility that the control unit 20 cannot appropriately diagnose the piezoelectric element 11.

[0035] Therefore, as shown in FIG. 2, the control unit 20 is configured to control the damping switch 142 to the ON state to short-circuit the line 144 in the diagnosis mode. Thereby, in the diagnosis mode, the resistance value of the damping resistor unit 14 becomes smaller than that in the acceleration detection mode. That is, ideally, since the potential difference between the reference terminal 15 and the piezoelectric element 11 becomes 0 V, no current flows through the damping resistor 141, and the damping effect of the damping resistor 141 does not occur. Thereby, the control unit 20 can avoid the change in the impedance of the piezoelectric element 11 becoming difficult to appear during the diagnosis mode and can appropriately diagnose the piezoelectric element 11.

[0036] [Configuration of Piezoelectric Element] With reference to FIGS. 3 and 4, the configuration of the piezoelectric element 11 will be described. FIG. 3 is a diagram showing an equivalent circuit of the piezoelectric element 11. As shown in FIG. 3, the piezoelectric element 11 includes a resistor Rs, a capacitor Cs, a capacitor Co, and an inductor Ls. The capacitor Cs is the free capacitance of the piezoelectric element 11. The capacitor Co is the braking capacitance of the piezoelectric element 11. The resistor Rs, the capacitor Cs, and the inductor Ls are connected in series between the terminals 111 and 112. The capacitor Co is connected in parallel with the resistor Rs, the capacitor Cs, and the inductor Ls between the terminals 111 and 112.

[0037] The impedance Z(ω) of the equivalent circuit of the piezoelectric element 11 is represented by the following equation (1). [Equation]

[0038] Here, when the frequency ω is sufficiently smaller than the series resonance frequency ωs (ω << ωs), the following equation (2) holds.

Equation

[0039] In the above case, the reactance X(ω) is represented by the following equation (3).

Equation

[0040] That is, when the frequency ω is sufficiently smaller than the series resonance frequency ωs (ω << ωs), the equivalent capacitance Cp of the piezoelectric element 11 is represented by the following equation (4).

Equation

[0041] Also, when the frequency ω is sufficiently larger than the series resonance frequency ωs (ω >> ωs), the following equation (5) holds.

Equation

[0042] In the above case, the reactance X(ω) is represented by the following equation (6).

Equation

[0043] That is, when the frequency ω is sufficiently larger than the series resonance frequency ωs (ω >> ωs), the equivalent capacitance Cp of the piezoelectric element 11 is represented by the following equation (7).

Equation

[0044] FIG. 4 is a graph showing the frequency characteristics of the impedance of the piezoelectric element 11. In FIG. 4, in the graph with the frequency on the horizontal axis and the impedance on the vertical axis, the change in the impedance of the piezoelectric element 11 for each frequency is shown.

[0045] As shown in FIG. 4, the equivalent capacitance Cp of the piezoelectric element 11 varies with the series resonance frequency ωs as the boundary. Specifically, when the frequency ω is smaller than the series resonance frequency ωs, the equivalent capacitance Cp of the piezoelectric element 11 is affected by the capacitor Cs and the capacitor Co. On the other hand, when the frequency ω is larger than the series resonance frequency ωs, only the capacitor Co affects the equivalent capacitance Cp of the piezoelectric element 11.

[0046] [Damping effect] With reference to FIGS. 5 to 8, the damping effect of the damping resistor 141 will be described. FIG. 5 is a graph showing the frequency characteristics of the gain of the acceleration sensor 10 when there is a damping effect and when there is no damping effect. In FIG. 5, in the graph with the frequency on the horizontal axis and the gain of the acceleration sensor 10 on the vertical axis, the change in the gain of the acceleration sensor 10 for each frequency is shown. Note that the gain is a value indicating the ratio of the input voltage to the output voltage.

[0047] As shown in FIG. 5, when there is no damping effect, resonance and anti-resonance appear in the gain of the acceleration sensor 10 due to the influence of the equivalent capacitance Cp. On the other hand, when there is a damping effect, since it is difficult to be affected by the equivalent capacitance Cp, resonance does not appear in the gain of the acceleration sensor 10, and only anti-resonance appears.

[0048] FIG. 6 is a graph showing the frequency characteristics of the sensitivity of the acceleration sensor 10 when there is a damping effect and when there is no damping effect. In FIG. 4, in the graph with the frequency on the horizontal axis and the sensitivity on the vertical axis, the change in the sensitivity of the acceleration sensor 10 for each frequency is shown.

[0049] As shown in FIG. 6, when there is a damping effect, the peak sensitivity of the acceleration sensor 10 at resonance is lower than when there is no damping effect.

[0050] FIG. 7 is a graph showing the peak sensitivity of the acceleration sensor 10 with respect to the resistance value when there is a damping effect and when there is no damping effect. In FIG. 7, in the graph with the resistance value on the horizontal axis and the peak sensitivity on the vertical axis, the change in the peak sensitivity of the acceleration sensor 10 for each impedance is shown.

[0051] As shown in FIG. 7, when the resistance value of the damping resistor 141 is within a predetermined range (in this example, 1000 Ω to 1,000,000 Ω), when there is a damping effect, the peak sensitivity of the acceleration sensor 10 is lower than when there is no damping effect.

[0052] FIG. 8 is a graph showing the peak sensitivity ratio of the acceleration sensor 10 with respect to the resistance value when there is a damping effect and when there is no damping effect. In FIG. 8, in the graph with the resistance value on the horizontal axis and the peak sensitivity ratio on the vertical axis, with the peak sensitivity of the acceleration sensor 10 when there is no damping effect set to 1, the change in the ratio of the peak sensitivity of the acceleration sensor 10 when there is a damping effect to the peak sensitivity of the acceleration sensor 10 when there is no damping effect is shown.

[0053] As shown in FIG. 8, when the resistance value of the damping resistor 141 is a predetermined value (in this example, 10,000 Ω), when there is a damping effect, the peak sensitivity of the acceleration sensor 10 is lower than when there is no damping effect.

[0054] Thus, when the resistance value of the damping resistor 141 is within a predetermined range (in this example, 1000 Ω to 1,000,000 Ω), the acceleration sensor module 1 can reduce the influence on acceleration detection due to the resonance of the piezoelectric element 11 by the damping effect of the damping resistor 141.

[0055] [Diagnosis of cracks generated in the piezoelectric element] Referring to FIGS. 9 and 10, the diagnosis of cracks generated in the piezoelectric element 11 will be described. FIG. 9 is a graph showing the frequency characteristics of the gain of the acceleration sensor 10 for each degree of crack generated in the piezoelectric element 11 when there is no damping effect. FIG. 10 is a graph showing the frequency characteristics of the gain of the acceleration sensor for each degree of crack generated in the piezoelectric element when there is a damping effect. In FIGS. 9 and 10, in the graph with the frequency on the horizontal axis and the gain of the acceleration sensor 10 on the vertical axis, the change in the gain of the acceleration sensor 10 for each frequency is shown.

[0056] As shown in FIG. 9, when a crack occurs in the piezoelectric element 11, the frequencies at which resonance and anti-resonance appear in the gain of the acceleration sensor 10 are lower than when no crack occurs in the piezoelectric element 11. Also, the larger the crack generated in the piezoelectric element 11, the lower the frequencies at which resonance and anti-resonance appear in the gain of the acceleration sensor 10.

[0057] Therefore, in the acceleration sensor module 1, in the diagnosis mode, the control unit 20 applies a diagnosis signal having a single-frequency AC voltage waveform output from the power supply 131 to the piezoelectric element 11, and based on the signal output from the piezoelectric element 11 when the diagnosis signal is applied and a threshold value previously stored in the storage unit 22, determines whether an abnormality (in this example, a crack) has occurred in the piezoelectric element 11.

[0058] Specifically, in the diagnosis mode, the control unit 20 determines whether a crack has occurred in the piezoelectric element 11 by comparing the gain of the acceleration sensor 10 when a single-frequency diagnosis signal is applied to the piezoelectric element 11 with the threshold value.

[0059] For example, in the diagnostic mode, the control unit 20 controls the power supply 131 to apply a diagnostic signal of a single first frequency (around 23000 Hz in this example) to the piezoelectric element 11. The control unit 20 compares the gain of the acceleration sensor 10 when the diagnostic signal of the first frequency is applied to the piezoelectric element 11 with a first threshold value (around 0.2 times in this example). When the gain of the acceleration sensor 10 is equal to or greater than the first threshold value, the control unit 20 tentatively determines that no crack has occurred in the piezoelectric element 11. When the gain of the acceleration sensor 10 is less than the first threshold value, the control unit 20 determines that a crack has occurred in the piezoelectric element 11.

[0060] Here, in the case of diagnosis using the diagnostic signal of the first frequency and the first threshold value, the control unit 20 can detect an abnormality in which the crack has progressed relatively significantly and become large, but it is difficult to detect an abnormality in which the crack has not progressed much.

[0061] Therefore, when determining that no abnormality has occurred in the piezoelectric element in the determination when the diagnostic signal of the first frequency is applied to the piezoelectric element 11, the control unit 20 applies a diagnostic signal of a single second frequency different from the first frequency to the piezoelectric element 11. For example, the control unit 20 applies a diagnostic signal of a second frequency (around 29000 Hz in this example) higher than the first frequency to the piezoelectric element 11. The control unit 20 compares the gain of the acceleration sensor 10 when the diagnostic signal of the second frequency is applied to the piezoelectric element 11 with a second threshold value (around 0.06 times in this example). When the gain of the acceleration sensor 10 is equal to or greater than the second threshold value, the control unit 20 determines that no crack has occurred in the piezoelectric element 11. When the gain of the acceleration sensor 10 is less than the second threshold value, the control unit 20 determines that a crack has occurred in the piezoelectric element 11. The crack detected at this time is smaller than the crack detected by the diagnosis using the diagnostic signal of the first frequency and the first threshold value.

[0062] Here, as shown in FIG. 10, when there is a damping effect, resonance does not appear in the gain of the acceleration sensor 10, and only anti-resonance appears. Therefore, it is difficult for the control unit 20 to detect a crack generated in the piezoelectric element 11 by diagnosis using the diagnostic signal and threshold value as shown in FIG. 9. In this regard, as described above, in the diagnostic mode, the control unit 20 controls the damping switch 142 to the ON state to short-circuit the line 144, so as not to cause the damping effect of the damping resistor 141. Thereby, the control unit 20 avoids the change in the impedance of the piezoelectric element 11 being difficult to appear during the diagnostic mode, and can appropriately diagnose the piezoelectric element 11 by the diagnostic method described with reference to FIG. 9.

[0063] Also, in the diagnosis of the piezoelectric element 11, if the frequency characteristics of the gain of the acceleration sensor 10 can be obtained over a wide range of frequencies over a long period of time, even in a state with a damping effect as shown in FIG. 10, the presence or absence of cracks and the degree of crack progress can be detected. However, in the acceleration sensor module 1 according to the first embodiment, the control unit 20 deliberately eliminates the damping effect during diagnosis, applies a diagnostic signal of a single frequency to the piezoelectric element 11, and only compares the gain of the acceleration sensor 10 with the threshold value, thereby being able to detect the presence or absence of cracks and the degree of crack progress. Thereby, the acceleration sensor module 1 can detect the presence or absence of cracks and the degree of crack progress in a shorter time than obtaining the frequency characteristics of the gain of the acceleration sensor 10 over a wide range of frequencies.

[0064] Incidentally, the creator of the acceleration sensor module 1 may set the frequency and threshold of the diagnostic signal by using defective products with cracks that occurred during the design of the acceleration sensor 10. Further, the creator of the acceleration sensor module 1 may create a plurality of defective products with different degrees of crack progression, and use the plurality of defective products to set the frequencies (e.g., the first frequency, the second frequency) of a plurality of diagnostic signals and the thresholds (e.g., the first threshold, the second threshold) for each of the plurality of defective products. In the example shown in FIG. 9, the control unit 20 used the frequencies and thresholds of two types of diagnostic signals. However, for example, in order to detect the degree of crack progression in more detail, frequencies and thresholds of three or more types of diagnostic signals may be used.

[0065] Also, in the example shown in FIG. 9, the control unit 20 compared the gain and threshold of the acceleration sensor 10 when the diagnostic signal was applied to the piezoelectric element 11. However, the control unit 20 may compare the output voltage of the signal output from the output terminal 17 of the acceleration sensor 10 with the threshold when the diagnostic signal is applied to the piezoelectric element 11. That is, the control unit 20 may detect the crack generated in the piezoelectric element 11 by comparing the output voltage with the threshold instead of comparing the ratio (gain) of the input voltage and the output voltage.

[0066] [An example of the processing of the control unit] An example of the processing executed by the control unit 20 in the diagnostic mode will be described with reference to FIG. 11. The arithmetic unit 21 of the control unit 20 executes the processing of the flowchart shown in FIG. 11 by executing the processing program 23. In the figure of FIG. 11, "S" is used as an abbreviation for "STEP".

[0067] FIG. 11 is a flowchart relating to the processing executed by the control unit 20 in the diagnostic mode. As shown in FIG. 11, the control unit 20 reduces the resistance value of the damping resistance unit 14 (S1). Specifically, the control unit 20 controls the damping switch 142 to the ON state to short-circuit the line 144. The control unit 20 controls the diagnostic switch 132 to the ON state to short-circuit the line 133, controls the power supply 131, and applies the first diagnostic signal to the piezoelectric element 11 (S2).

[0068] The control unit 20 determines whether or not the gain of the acceleration sensor 10 when a first diagnostic signal of a first frequency is applied to the piezoelectric element 11 is equal to or greater than a first threshold value (S3). When the gain of the acceleration sensor 10 is less than the first threshold value (NO in S3), the control unit 20 determines that a crack has occurred in the piezoelectric element 11 (S4). The crack detected at this time is, for example, a relatively advanced and large crack. Then, the control unit 20 ends this process.

[0069] On the other hand, when the gain of the acceleration sensor 10 is equal to or greater than the first threshold value (YES in S3), the control unit 20 controls the power supply 131 to apply a second diagnostic signal of a second frequency greater than the first frequency to the piezoelectric element 11 (S5).

[0070] The control unit 20 determines whether or not the gain of the acceleration sensor 10 when a second diagnostic signal of a second frequency is applied to the piezoelectric element 11 is equal to or greater than a second threshold value (S6). When the gain of the acceleration sensor 10 is less than the second threshold value (NO in S6), the control unit 20 determines that a crack has occurred in the piezoelectric element 11 (S7). The crack detected at this time is a crack smaller than the crack detected in S4. Then, the control unit 20 ends this process.

[0071] On the other hand, when the gain of the acceleration sensor 10 is equal to or greater than the second threshold value (YES in S6), the control unit 20 determines that no crack has occurred in the piezoelectric element 11 (S8). Then, the control unit 20 ends this process.

[0072] As described above, the acceleration sensor module 1 according to the first embodiment reduces the influence on acceleration detection due to the resonance of the piezoelectric element 11 by the damping resistance unit 14 connected to the piezoelectric element 11. On the other hand, in the diagnostic mode, by making the resistance value of the damping resistance unit 14 smaller than in the acceleration detection mode, it is possible to appropriately diagnose the piezoelectric element 11 by avoiding the difficulty of the change in the impedance of the piezoelectric element 11 from appearing during the diagnostic mode.

[0073] <Embodiment 2> The acceleration sensor module 1A according to Embodiment 2 will be described with reference to FIG. 12. In the acceleration sensor module 1A according to Embodiment 2, only the parts different from the acceleration sensor module 1 according to Embodiment 1 will be described.

[0074] FIG. 12 is a diagram showing the configuration of the acceleration sensor module 1A according to Embodiment 2. As shown in FIG. 12, in the acceleration sensor module 1A according to Embodiment 2, the acceleration sensor 10A includes a damping resistance part 14A instead of the damping resistance part 14. The damping resistance part 14A includes a variable resistor 146 connected to the reference terminal 15 and the piezoelectric element 11.

[0075] In the diagnosis mode, the control unit 20 makes the resistance value of the variable resistor 146 smaller than that in the acceleration detection mode. Thereby, similar to the acceleration sensor module 1 according to Embodiment 1, the acceleration sensor module 1A according to Embodiment 2 reduces the damping effect of the variable resistor 146 in the diagnosis mode, avoids the change in the impedance of the piezoelectric element 11 from being difficult to appear, and can appropriately diagnose the piezoelectric element 11.

[0076] <Aspect> (Item 1) An acceleration sensor module (1, 1A) according to one aspect includes a signal processing unit (12) that processes a signal output from a piezoelectric element (11), a signal application unit (13) that applies a diagnosis signal for diagnosing the piezoelectric element to the piezoelectric element, a damping resistance part (14, 14A) connected to the piezoelectric element, and a control unit (20) that controls the signal application unit and the damping resistance part. In the diagnosis mode of diagnosing the piezoelectric element, the control unit makes the resistance value of the damping resistance part smaller than that in the acceleration detection mode of detecting acceleration, and applies the diagnosis signal to the piezoelectric element.

[0077] (2) In the acceleration sensor module according to claim 1, the damping resistance section (14) includes a damping resistor (141) provided on a first line connecting the reference terminal and the piezoelectric element, and a damping switch (142) provided on a second line connecting the reference terminal and the piezoelectric element in parallel with the first line. The control unit controls the damping switch to open the second line in the acceleration detection mode, and controls the damping switch to short-circuit the second line in the diagnosis mode.

[0078] (3) In the acceleration sensor module according to claim 1 or 2, the damping resistance section (14A) includes a variable resistor (146) connected to the reference terminal and the piezoelectric element. The control unit reduces the resistance value of the variable resistor in the diagnosis mode compared to that in the acceleration detection mode.

[0079] (4) In the acceleration sensor module according to any one of claims 1 to 3, the signal enabling section includes a power supply (131) that outputs a diagnosis signal, and a diagnosis switch (132) provided on a third line connecting the power supply and the signal processing section. The control unit controls the diagnosis switch to open the third line in the acceleration detection mode, and controls the diagnosis switch to short-circuit the third line in the diagnosis mode.

[0080] (5) In the acceleration sensor module according to any one of claims 1 to 4, the control unit applies, in the diagnosis mode, a signal having an alternating voltage waveform of a single frequency as a diagnosis signal to the piezoelectric element, and determines whether an abnormality has occurred in the piezoelectric element based on the signal output from the piezoelectric element when the diagnosis signal is applied and a threshold value.

[0081] (Item 6) In the acceleration sensor module according to any one of Items 1 to 5, in the diagnostic mode, the control unit applies, as a diagnostic signal, a first diagnostic signal having an AC voltage waveform of a first frequency to the piezoelectric element, and based on the signal output from the piezoelectric element when the first diagnostic signal is applied and a first threshold value, determines whether an abnormality has occurred in the piezoelectric element. When no abnormality has occurred in the piezoelectric element, as a diagnostic signal, a second diagnostic signal having an AC voltage waveform of a second frequency different from the first frequency is applied to the piezoelectric element, and based on the signal output from the piezoelectric element when the second diagnostic signal is applied and a second threshold value, determines whether an abnormality has occurred in the piezoelectric element.

[0082] (Item 7) In the acceleration sensor module according to any one of Items 1 to 6, the second frequency is greater than the first frequency.

[0083] (Item 8) The acceleration sensors (10, 10A) according to one aspect include a signal processing unit (12) that processes a signal output from a piezoelectric element (11), a signal application unit (13) that applies a diagnostic signal for diagnosing the piezoelectric element to the piezoelectric element, and a damping resistance unit (14, 14A) connected to the piezoelectric element. The damping resistance unit has a smaller resistance value in the diagnostic mode for diagnosing the piezoelectric element than in the acceleration detection mode for detecting acceleration. The signal application unit applies a diagnostic signal to the piezoelectric element in the diagnostic mode.

[0084] (Item 9) A control method according to one aspect includes, as processes executed by a computer (21), a step (S1) of making the resistance value of a damping resistance unit connected to a piezoelectric element smaller in a diagnostic mode for diagnosing the piezoelectric element than in an acceleration detection mode for detecting acceleration, and a step (S2) of applying a diagnostic signal for diagnosing the piezoelectric element to the piezoelectric element.

[0085] As described above, a plurality of embodiments have been described, and the features in each of these plurality of embodiments can be appropriately combined as long as no contradiction occurs.

[0086] The embodiments disclosed herein should be considered illustrative in all respects and not restrictive. The scope of the present disclosure is indicated by the scope of the claims rather than the description of the above embodiments, and it is intended that all modifications within the meaning and scope equivalent to the scope of the claims be included.

Description of Reference Numerals

[0087] 1, 1A Acceleration sensor module, 10, 10A Acceleration sensor, 11 Piezoelectric element, 12 Signal processing unit, 13 Signal enabling unit, 14, 14A Damping resistance unit, 15, 16 Reference terminal, 17 Output terminal, 20 Control unit, 21 Arithmetic unit, 22 Storage unit, 23 Processing program, 111, 112 Terminal, 121 Charge amplifier, 123 Filter unit, 124 Amplification unit, 131 Power supply, 132 Diagnostic switch, 133, 143, 144 Circuit, 141 Damping resistance, 142 Damping switch, 146 Variable resistor.

Claims

1. An acceleration sensor module that detects acceleration using a piezoelectric element, comprising: a signal processing unit that processes a signal output from the piezoelectric element; a signal application unit that applies a diagnostic signal for diagnosing the piezoelectric element to the piezoelectric element; a damping resistor unit connected to the piezoelectric element; a control unit that controls the signal application unit and the damping resistor unit, wherein, in a diagnostic mode for diagnosing the piezoelectric element, the control unit reduces the resistance value of the damping resistor unit to be smaller than that in an acceleration detection mode for detecting the acceleration, and applies the diagnostic signal to the piezoelectric element.

2. The damping resistor unit includes a damping resistor provided on a first line connecting a reference terminal and the piezoelectric element, and a damping switch provided on a second line connecting the reference terminal and the piezoelectric element in parallel with the first line, and the control unit controls the damping switch to open the second line in the acceleration detection mode, and controls the damping switch to short-circuit the second line in the diagnostic mode. The acceleration sensor module according to claim 1.

3. The damping resistor unit includes a variable resistor connected to a reference terminal and the piezoelectric element, and the control unit reduces the resistance value of the variable resistor to be smaller than that in the acceleration detection mode in the diagnostic mode. The acceleration sensor module according to claim 1.

4. The signal application unit includes a power source that outputs the diagnostic signal, and a diagnostic switch provided on a third line connecting the power source and the signal processing unit, and the control unit controls the diagnostic switch to open the third line in the acceleration detection mode, and controls the diagnostic switch to short-circuit the third line in the diagnostic mode. The acceleration sensor module according to any one of claims 1 to 3.

5. The control unit applies, in the diagnostic mode, a signal having an AC voltage waveform of a single frequency as the diagnostic signal to the piezoelectric element, and determines whether an abnormality has occurred in the piezoelectric element based on a signal output from the piezoelectric element when the diagnostic signal is applied and a threshold value. The acceleration sensor module according to any one of claims 1 to 3.

6. The control unit In the diagnosis mode, as the diagnostic signal, a first diagnostic signal having an AC voltage waveform of a first frequency is applied to the piezoelectric element, Based on the signal output from the piezoelectric element when the first diagnostic signal is applied and a first threshold value, it is determined whether an abnormality has occurred in the piezoelectric element, When no abnormality has occurred in the piezoelectric element, as the diagnostic signal, a second diagnostic signal having an AC voltage waveform of a second frequency different from the first frequency is applied to the piezoelectric element, Based on the signal output from the piezoelectric element when the second diagnostic signal is applied and a second threshold value, it is determined whether an abnormality has occurred in the piezoelectric element. The acceleration sensor module according to any one of claims 1 to 3.

7. The acceleration sensor module according to claim 6, wherein the second frequency is higher than the first frequency.

8. An acceleration sensor that detects acceleration using a piezoelectric element, A signal processing unit that processes a signal output from the piezoelectric element, A signal application unit that applies a diagnostic signal for diagnosing the piezoelectric element to the piezoelectric element, And a damping resistance unit connected to the piezoelectric element, In the diagnosis mode for diagnosing the piezoelectric element, the damping resistance unit has a smaller resistance value than in the acceleration detection mode for detecting the acceleration, The signal application unit applies the diagnostic signal to the piezoelectric element in the diagnosis mode. An acceleration sensor.

9. A control method for controlling, by a computer, an acceleration sensor that detects acceleration using a piezoelectric element, As a process executed by the computer, In the diagnosis mode for diagnosing the piezoelectric element, a step of reducing the resistance value of the damping resistance unit connected to the piezoelectric element to be smaller than in the acceleration detection mode for detecting the acceleration, And a step of applying a diagnostic signal for diagnosing the piezoelectric element to the piezoelectric element. A control method.

Images