Sensor device

Abstract

To provide a sensor device capable of improving dynamic range. [Solution] The sensor device includes a sensor element 11, a switch 12 connected to the sensor element 11, an amplifier 14 connected to the switch 12, a load resistor 13 connected between the input of the amplifier 14 and the ground terminal, and a control unit 7 that switches the switch 11. The control unit 7 sets an off period for turning off the switch 11 based on the output voltage of the amplifier 14.

Description

Technical Field

[0004] , , , , , , , , , ,

[0005]

[0001] The present invention relates to a sensor device.

Background Art

[0002] When a piezoelectric film is strained (elongated or contracted) by deformation, polarization proportional to the strain on the surface of the piezoelectric film occurs, generating electric charges. Piezoelectric sensors that detect various pressures by utilizing this piezoelectric effect are used. For example, when a piezoelectric sensor is fixed to a detection site, the piezoelectric sensor is deformed by pressure (e.g., movement of human muscles, pulse) or vibration, and electric charges are generated in each sensor element included in the piezoelectric sensor. This electric charge is converted into a voltage, and the pressure is detected based on this voltage. Since the detected pressure is easy to analyze, visualize, and record, it is expected to be effectively utilized in various fields such as medical, sports, and justice UI (user interface).

[0003] By taking advantage of the flexibility of the piezoelectric film, it is possible to attach the piezoelectric sensor to the human body or mount the piezoelectric sensor in a form that follows a curved surface. Depending on the degree of deformation of the mounting site, the pressure and the amount of film deformation vary, and the output voltage of the piezoelectric sensor may change over a wide range. Therefore, improvements are required in the material of the piezoelectric sensor, as well as the detection circuit and detection method, so that pressures from minute to large can be detected.

[0004] Also, when designing the circuit of the piezoelectric sensor according to a large pressure, the output voltage due to a minute pressure becomes at the same level as noise (e.g., power supply noise), making it difficult to detect the pressure. Conversely, when designing the circuit of the piezoelectric sensor according to a minute pressure, the output voltage exceeds the voltage range that is always handled, and the overall picture of the pressure change cannot be determined.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] The present invention provides a sensor device capable of improving the dynamic range. [Means for solving the problem]

[0007] According to a first aspect of the present invention, a sensor device is provided comprising a sensor element, a switch connected to the sensor element, an amplifier connected to the switch, a load resistor connected between the input of the amplifier and a ground terminal, and a control unit that causes the switch to switch, wherein the control unit sets an off period for turning off the switch based on the output voltage of the amplifier.

[0008] According to a second aspect of the present invention, a sensor device according to the first aspect is provided, wherein the control unit relatively shortens the off period when the output voltage of the amplifier is above a threshold, and relatively lengthens the off period when the output voltage of the amplifier is below the threshold.

[0009] According to a third aspect of the present invention, a sensor device according to the first aspect is provided, wherein the control unit sets the off period based on an external switching signal.

[0010] According to a fourth aspect of the present invention, a sensor device according to the first aspect is provided, further comprising an A / D converter connected to the output of the amplifier.

[0011] According to a fifth aspect of the present invention, a sensor device according to the fourth aspect is provided, wherein the control unit controls the operation of the A / D converter so that the switching period of the switch and the sampling period of the A / D converter are the same.

[0012] According to a sixth aspect of the present invention, a sensor device according to the first aspect is provided, wherein the sensor element is a piezoelectric element.

[0013] A sensor device is provided, comprising a plurality of sensor elements, a multiplexer connected to the plurality of sensor elements, an amplifier connected to the multiplexer, a load resistor connected between the input of the amplifier and a ground terminal, and a control unit that controls the operation of the multiplexer, wherein the multiplexer operates to select one of the plurality of sensor elements, and the control unit determines the charge accumulation period based on the output voltage of the amplifier and operates the multiplexer for each charge accumulation period.

[0014] According to an eighth aspect of the present invention, a sensor device according to the seventh aspect is provided, wherein the control unit relatively shortens the charge storage period when the output voltage of the amplifier is above a threshold, and relatively lengthens the charge storage period when the output voltage of the amplifier is below the threshold.

[0015] According to a ninth aspect of the present invention, a sensor device according to the seventh aspect is provided, wherein the control unit sets the charge storage period based on an external switching signal.

[0016] According to a tenth aspect of the present invention, a sensor device according to the seventh aspect is provided, wherein each of the plurality of sensor elements is a piezoelectric element. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a sensor device that can improve the dynamic range. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1 is a block diagram of a sensor device according to the first embodiment of the present invention. [Figure 2] Figure 2 is a block diagram of the sensor unit, switch unit, amplifier unit, and A / D converter unit shown in Figure 1. [Figure 3] Figure 3 is a circuit diagram showing an example of an amplifier. [Figure 4] Figure 4 is a flowchart for explaining the operation of the sensor device. [Figure 5] Figure 14 is a block diagram of the main part of a sensor device according to the second embodiment of the present invention. [Figure 6] Figure 17 is a block diagram of the main part of a sensor device according to the fourth embodiment of the present invention. [Figure 7] Figure 7 is a diagram for explaining an example of a detection signal in the embodiment. [Figure 8] Figure 8 is a diagram for explaining the measurement method according to the first embodiment. [Figure 9] Figure 9 is a diagram for explaining the measurement conditions of the first embodiment. [Figure 10] Figure 10 is a diagram for explaining the measurement results of the first embodiment. [Figure 11] Figure 11 is a diagram for explaining the measurement results of the first embodiment. [Figure 12] Figure 12 is a diagram for explaining an example of a detection signal according to the second embodiment. [Figure 13] Figure 13 is a diagram for explaining an example of a detection signal according to the second embodiment. [Figure 14] Figure 14 is a flowchart for explaining the operation of a sensor device according to the second embodiment of the present invention. [Figure 15] Figure 15 is a block diagram of the main part of a sensor device according to the third embodiment of the present invention. [Figure 16] Figure 16 is a flowchart for explaining the operation of the sensor device. [Figure 17] Figure 17 is a block diagram of the main part of a sensor device according to the fourth embodiment of the present invention. [Modes for carrying out the invention]

[0019] The embodiments will be described below with reference to the drawings. However, the drawings are schematic or conceptual, and the dimensions and proportions in each drawing are not necessarily the same as those in reality. Furthermore, even when the same part is represented between drawings, the relationship between dimensions and proportions may be represented differently. In particular, the embodiments shown below are illustrative examples of devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not determined by the shape, structure, arrangement, etc. of the components. In the following description, elements having the same function and configuration are denoted by the same reference numerals, and redundant descriptions are omitted.

[0020] In the following embodiment, a piezoelectric sensor (also called a pressure sensor) will be used as an example of the sensor device 1.

[0021] [1] First Embodiment [1-1] Configuration of Sensor Device 1 Figure 1 is a block diagram of a sensor device 1 according to a first embodiment of the present invention. The sensor device 1 comprises a sensor unit 2, a signal processing unit 6, a control unit 7, a storage unit 8, an external interface 9, and a voltage generation circuit 10.

[0022] Sensor unit 2 detects the applied pressure. Sensor unit 2 can detect pressure in multiple sub-regions, which are obtained by dividing the detection area (the area in which sensor unit 2 is located). Sensor unit 2 outputs multiple detection signals corresponding to each of the multiple sub-regions. The detection signals output by sensor unit 2 consist of electric charge.

[0023] The signal processing unit 6 receives multiple detection signals from the sensor unit 2 and performs signal processing on these multiple detection signals. The signal processing unit 6 includes a switch unit 3, an amplification unit 4, and an A / D converter unit 5.

[0024] The switch unit 3 is connected to the sensor unit 2. Based on the control of the control unit 7, the switch unit 3 switches the contacts (also called current paths) on and off. The switch unit 3 switches the contacts for each of the multiple detection signals. The switch unit 3 is composed of, for example, an analog switch.

[0025] The amplification unit 4 is connected to the switch unit 3. The amplification unit 4 receives multiple detection signals from the switch unit 3. The amplification unit 4 amplifies the electrical signals input to itself.

[0026] The A / D converter unit 5 is connected to the amplifier unit 4. The A / D converter unit 5 converts the analog signal output from the amplifier unit 4 into a digital signal. The detection signal (digital signal) output from the A / D converter unit 5 is transmitted to the control unit 7.

[0027] The control unit 7 comprehensively controls the operation of the sensor device 1. The control unit 7 is configured to include one or more processors, such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The control unit 7 implements various functions by executing programs stored in the memory unit 8.

[0028] The control unit 7 receives multiple detection signals from the A / D converter unit 5. Based on the multiple detection signals, the control unit 7 controls the operation of the switch unit 3. The control unit 7 also switches each of the multiple switches 12, which will be described later, based on the multiple detection signals.

[0029] The storage unit 8 stores various data necessary for the operation of the sensor device 1 and also functions as a workspace for the control unit 7. The storage unit 8 includes volatile memory and non-volatile memory. The volatile memory includes RAM (Random Access Memory) and registers, etc. The non-volatile memory includes ROM (Read Only Memory), HDD (Hard Disk Drive), and SSD (Solid State Drive), etc.

[0030] The external interface 9 is connected to an external device by wire and / or wireless means and has the function of communicating with the external device. The external interface 9 performs interface processing with the external device based on a predetermined standard.

[0031] The voltage generation circuit 10 generates multiple voltages necessary for the operation of the sensor device 1. The voltage generation circuit 10 supplies voltage to the corresponding circuit.

[0032] Next, the detailed configuration of the sensor unit 2 and the signal processing unit 6 will be described. Figure 2 is a block diagram of the sensor unit 2, switch unit 3, amplifier unit 4, and A / D converter unit 5 shown in Figure 1.

[0033] The sensor unit 2 comprises a plurality of sensor elements 11. Each of the plurality of sensor elements 11 is composed of, for example, a piezoelectric element. A piezoelectric element is a sensor element that utilizes the piezoelectric effect and is capable of outputting an electrical signal in response to the pressure applied to the piezoelectric body. The plurality of sensor elements 11 are configured, for example, on the same substrate. The piezoelectric element is configured to include a lower electrode, an upper electrode, and a piezoelectric layer sandwiched between them.

[0034] The switch unit 3 comprises a plurality of switches 12. Each of the plurality of switches 12 is connected to a plurality of sensor elements 11. The switches 12 are composed of SPST (Single-Pole Single-Throw) switches that can switch between one pole and one contact. The on and off states of the switches 12 are controlled based on control signals supplied from the control unit 7.

[0035] The amplification unit 4 comprises a plurality of load resistors 13 and a plurality of amplifiers 14. The amplifiers 14 amplify the input signal and output it. The amplifiers 14 are composed of, for example, operational amplifiers. The inputs of each of the plurality of amplifiers 14 are connected to a plurality of switches 12. The plurality of load resistors 13 are each connected to the inputs of the plurality of amplifiers 14. The other end of each load resistor 13 is connected to the ground terminal GND (ground voltage is supplied). The load resistors 13 have the function of converting the charge output from the sensor element 11 into a voltage.

[0036] Figure 3 is a circuit diagram showing an example of amplifier 14. Amplifier 14 is composed of, for example, a non-inverting amplifier. Figure 3 is an example of a voltage follower configuration.

[0037] The input terminal IN is connected to switch 12, and the output terminal OUT is connected to the A / D converter described later. A positive power supply V+ (e.g., 5V) is supplied to the positive power supply terminal of amplifier 14. A negative power supply V- (e.g., -5V) is supplied to the negative power supply terminal of amplifier 14.

[0038] The non-inverting input terminal (+) of amplifier 14 is connected to the input terminal IN. One end of the load resistor 13 is connected to the non-inverting input terminal of amplifier 14, and the other end is connected to the ground terminal GND. 0V is supplied to the ground terminal GND.

[0039] The inverting input terminal (-) of amplifier 14 is connected to the output of amplifier 14. The output of amplifier 14 is connected to the output terminal OUT. Amplifier 14 amplifies the input voltage and outputs it. In the example in Figure 3, the amplification factor of amplifier 14 is 1.

[0040] The A / D converter section 5 comprises multiple A / D converters 15 (ADCs). Each of the multiple A / D converters 15 is connected to one of the multiple amplifiers 14. The A / D converters 15 convert analog signals into digital signals. The A / D converters 15 sample the input voltage at predetermined sampling periods and output the sampled voltage as a digital signal.

[0041] [1-2] Operation The operation of the sensor device 1 configured as described above will now be explained. Figure 4 is a flowchart illustrating the operation of the sensor device 1. Below, the operation of one sensor element 11 will be described, but the same operation is performed for each of the multiple sensor elements 11.

[0042] Initially, for example, the control unit 7 turns on the switch 12. Alternatively, the control unit 7 switches the switch 12 at an initially set switching cycle.

[0043] The sensor element 11 detects the pressure applied to it and outputs an electric charge as a result of the detection. The electric charge output from the sensor element 11 is supplied to the load resistor 13. The load resistor 13 converts the electric charge output from the sensor element 11 into a voltage.

[0044] Amplifier 14 amplifies the voltage across load resistor 13 and outputs it. A / D converter 15 converts the output voltage of amplifier 14 into a digital signal. The output signal of A / D converter 15 is called the detection signal.

[0045] The control unit 7 receives a detection signal from the A / D converter 15 (step S100). Next, the control unit 7 determines the voltage level of the detection signal (step S101). Note that the voltage level of the output signal of the amplifier 14 and the voltage level of the output signal of the A / D converter 15 are the same, except for the difference between an analog signal and a digital signal.

[0046] Next, the control unit 7 determines the off period of the switch 12 based on the voltage level of the detection signal (step S102). Specifically, the control unit 7 compares the voltage level of the detection signal with a predetermined threshold, and sets the off period to be relatively shorter if the voltage level of the detection signal is greater than or equal to the predetermined threshold, and sets the off period to be relatively longer if the voltage level of the detection signal is less than the predetermined threshold.

[0047] Next, the control unit 7 switches the switch 12 based on the off period set in step S102 (step S103). Specifically, the control unit 7 supplies a switching signal to the switch 12, causing the switch 12 to switch. During the switching operation, the switch 12 repeatedly switches on and off, and the off period is set to the off period set in step S102. The off period of the switch 12 includes 0 (ms). An off period of 0 (ms) for the switch 12 is equivalent to keeping the switch 12 constantly on.

[0048] The specific operation of sensor device 1 is described below.

[0049] Figure 5 is a block diagram of the sensor element 11 and its peripheral circuitry according to the comparative example. The comparative example does not have a switch 12 to switch the connection state between the sensor element 11 and the amplifier 14. That is, the sensor element 11 is always connected to the load resistor 13.

[0050] Figure 6 illustrates an example of a detection signal in a comparative example. The detection signal in Figure 6 corresponds to the output of amplifier 14. In Figure 6, the horizontal axis represents time, and the vertical axis represents voltage (in arbitrary units).

[0051] The detection signal changes according to the pressure applied to the sensor element 11. The multiple points appended to the waveform in Figure 6 represent the sampling period (also called ADC sampling) of the A / D converter 15. In the comparative example, it becomes difficult to detect pressure when the voltage level of the detection signal is low.

[0052] Figure 7 illustrates an example of a detection signal in the embodiment. Figure 7 shows the waveform of the detection signal and the switching signal from the control unit 7. The solid line waveform in the detection signal in Figure 7 corresponds to the output of the amplifier 14. The dashed line waveform in the detection signal in Figure 7 corresponds to a hypothetical voltage waveform illustrating the dynamic range. The dashed-dotted line waveform in the detection signal in Figure 7 corresponds to the voltage waveform of the comparative example described above.

[0053] The control unit 7 supplies a switching signal to the switch 12. The switch 12 performs a switching operation based on the switching signal. When the switching signal is high level (H), the switch 12 turns on, and when the switching signal is low level (L), the switch 12 turns off. The switching signal consists of multiple pulse signals with the same pulse width.

[0054] The period during which switch 12 is off (referred to as the off period) corresponds to the period during which the sensor element 11 accumulates charge (referred to as the charge accumulation period). The off period (charge accumulation period) is the interval between two consecutive pulses of the switching signal. The control unit 7 sets the off period based on the voltage level of the detection signal.

[0055] When switch 12 is turned on, the sensor element 11 releases its charge all at once. The charge in the sensor element 11 is converted into a voltage by the load resistor 13. The amplifier 14 amplifies the voltage across the load resistor 13 and outputs it. If the pressure is changing, the voltage level of the detection signal increases when switch 12 is turned on. After the charge accumulated during the on period of switch 12 is released, the detection signal becomes a voltage corresponding to the current pressure change. When switch 12 is turned off, the detection signal becomes 0V.

[0056] The multiple points appended to the waveform in Figure 7 represent the sampling period (ADC sampling) of the A / D converter 15. The control unit 7 controls the A / D converter 15 so that the switching period of the switch 12 and the sampling period of the A / D converter 15 are the same. Based on the control signal from the control unit 7, the A / D converter 15 samples the voltage and converts it into a digital signal, and outputs this digital signal. As a result, the A / D converter 15 can output a voltage value corresponding to the spike in the detection signal.

[0057] As can be seen from Figure 7, in this embodiment, the voltage value of the detection signal from amplifier 14 can be increased compared to the comparative example. Therefore, the dynamic range of sensor device 1 can be improved.

[0058] Increasing the off period of switch 12 lengthens the charge accumulation period of sensor element 11, increasing the voltage value of the detection signal from amplifier 14. Conversely, shortening the off period of switch 12 shortens the charge accumulation period of sensor element 11, decreasing the voltage value of the detection signal from amplifier 14. The control unit 7 sets a threshold value and the off period of switch 12 to obtain the desired voltage value.

[0059] The control unit 7 sets the off period of switch 12 to be relatively shorter when a large pressure is applied to the sensor unit 2, and sets the off period of switch 12 to be relatively longer when a small pressure is applied to the sensor unit 2. When the pressure applied to the sensor unit 2 is sufficiently large, the control unit 7 sets the off period of switch 12 to 0 (ms).

[0060] The control unit 7 has information about multiple off periods and may continuously change the off periods so that they become progressively longer until the desired voltage value (threshold) is obtained. The information about the multiple off periods is stored in the storage unit 8.

[0061] If the leakage current of switch 12 (leakage current when off) is large, the charge of sensor element 11 will leak. Therefore, it is desirable for the leakage current of switch 12 to be as small as possible. It is desirable for the leakage current of switch 12 to be 100 pA or less.

[0062] [1-3] Examples Next, the first embodiment will be described. Figure 8 is a diagram illustrating the measurement method according to the first embodiment. The sensor unit 2 is placed on the base 20.

[0063] A digital force gauge 22 is fixed above the sensor unit 2, and is secured to a measuring stand 21. The digital force gauge 22 is a device for measuring load. The digital force gauge 22 includes a rod-shaped metal part 22A and a rubber part 22B attached to the tip of the metal part 22A. Pressure is applied to the sensor unit 2 by the rubber part 22B of the digital force gauge 22, and the pressure at that time is measured by the digital force gauge 22.

[0064] Figure 9 illustrates the measurement conditions of the first embodiment. In the first embodiment, measurements were performed under two conditions. Condition 1 involved placing the sensor unit 2 on a metal plate and performing the measurement. Under condition 1, the maximum pressure was 2.5 (N), the travel distance of the digital force gauge 22 was 10.8 (mm), the travel speed of the digital force gauge 22 was 350 (mm / min), and the force change δF was 1.4 (N / s).

[0065] Condition 2 involved placing the sensor unit 2 on an elastomer and performing the measurement. Elastomer is a type of elastic material. In Condition 2, the maximum pressure was 0.2 (N), the travel distance of the digital force gauge 22 was 9.2 (mm), the travel speed of the digital force gauge 22 was 350 (mm / min), and the force change δF was 0.1 (N / s).

[0066] Figures 10 and 11 illustrate the measurement results of the first embodiment. The off periods are 0 (ms), 4 (ms), 8 (ms), 12 (ms), and 16 (ms). An off period of 0 (ms) means that the switch 12 is always on, and the sensor element 11 does not accumulate charge (no charge accumulation). In the first embodiment, when pressure is applied to the sensor unit 2, the voltage value becomes negative, and when the pressure on the sensor unit 2 is removed, the voltage value becomes positive.

[0067] Compared to the case without charge accumulation, it can be seen that the voltage amplitude is 2 to 4 times larger. Minute pressures that are undetectable without charge accumulation become detectable with charge accumulation. The control unit 7 sets the optimal threshold and sets the off period of switch 12 so that the desired voltage is obtained.

[0068] Next, a second embodiment will be described. Figures 12 and 13 illustrate an example of a detection signal according to the second embodiment. Figures 12 and 13 show the waveforms of the detection signal and pressure. In Figures 12 and 13, the left vertical axis is voltage (V), the right vertical axis is force (N), and the horizontal axis is time. Figure 12 shows the voltage waveform without charge accumulation, and Figure 13 shows the voltage waveform with charge accumulation. The charge accumulation period in Figure 13 is 16 ms. In Figures 12 and 13, the results after averaging over 200 points are shown because the pressure is very small.

[0069] When the pressure changes from 0(N) to 2.5(N), the voltage decreases, and when it changes from 2.5(N) to 0(N), the voltage increases. Without charge accumulation, the generated voltage is minute and equivalent to the noise level, making detection difficult. In contrast, with charge accumulation, the voltage is about three times greater than the noise, making detection possible.

[0070] While the sensor element 11 is accumulating charge, positive and negative charges may be generated due to pressure changes, and these charges may cancel each other out. Therefore, it is desirable to set the switching period of the switch 12 to 50% or less of the period during which pressure changes between positive and negative voltages occur.

[0071] [1-4] Effects of the first embodiment According to the first embodiment, when pressure is applied to the sensor element 11, the switch 12 can be turned off to accumulate charge in the sensor element 11. Then, by turning the switch 12 on, the charge accumulated in the sensor element 11 can be released to the load resistor 13. As a result, even a minute pressure applied to the sensor element 11 can be detected as a large voltage. Therefore, the voltage amplitude and dynamic range of the detection signal can be increased. Consequently, a sensor device 1 capable of improving the dynamic range can be realized.

[0072] Furthermore, the voltage of the detection signal can be adjusted by adjusting the off period of switch 12. This makes it possible to output a desired voltage value as the detection signal.

[0073] Furthermore, if a large pressure is applied to the sensor element 11, the off period can be set to 0 (ms). This makes it possible to detect even large pressures.

[0074] Furthermore, the control unit 7 can adjust the off period of the switch 12 (the charge accumulation period of the sensor element 11) by comparing the voltage level of the detection signal with a threshold. Therefore, there is no need to switch circuit components that adjust the amplification factor of the amplifier 14, nor is there a need to prepare multiple load resistors. This makes it possible to simplify the circuit and miniaturize the circuit board. It also reduces the effort required for selecting and replacing components.

[0075] [2] Second embodiment The second embodiment switches the off period of switch 12 based on a signal from an external device.

[0076] Figure 14 is a flowchart illustrating the operation of the sensor device 1 according to the second embodiment of the present invention. The control unit 7 has information regarding multiple off periods. Information regarding multiple off periods is stored in the storage unit 8.

[0077] The control unit 7 monitors whether or not it has received a switching signal from an external device (step S200). The switching signal includes information that identifies the off period. The switching signal is received by the external interface 9 and then transmitted to the control unit 7.

[0078] Next, the control unit 7 determines the off period of the switch 12 based on the switching signal (step S201). Subsequently, the control unit 7 switches the switch 12 based on the off period determined in step S201 (step S202). Specifically, the control unit 7 supplies a switching signal to the switch 12 and switches the switch 12. During the switching operation, the switch 12 repeatedly switches on and off, and the off period is set to the off period determined in step S201. The off period of the switch 12 includes 0 (ms). For example, in the example in Figure 11, the off period can be selectively set to 0 (ms), 4 (ms), 8 (ms), 12 (ms), or 16 (ms).

[0079] According to the second embodiment, the switch 12 can be operated in a switching operation based on an external signal. Other effects are the same as in the first embodiment.

[0080] [3] Third embodiment The third embodiment is configured to selectively connect multiple sensor elements 11 to a single amplifier 14.

[0081] Figure 15 is a block diagram of the main components of a sensor device 1 according to a third embodiment of the present invention. The sensor device 1 comprises a sensor unit 2, a signal processing unit 6, a control unit 7, a storage unit 8, an external interface 9, and a voltage generation circuit 10. Although not shown in the figure, the block configuration of the control unit 7, storage unit 8, external interface 9, and voltage generation circuit 10 is the same as in the first embodiment.

[0082] The sensor unit 2 comprises multiple sensor elements 11. The signal processing unit 6 comprises a multiplexer (MUX) 30, a load resistor 13, an amplifier 14, and an A / D converter 15.

[0083] The multiplexer 30 is a circuit that selects one input from multiple inputs and outputs it. Multiple sensor elements 11 are connected to each of the multiple inputs of the multiplexer 30. Based on a control signal from the control unit 7, the multiplexer 30 selects one of the multiple sensor elements 11 and outputs the signal of the selected sensor element 11.

[0084] The output of the multiplexer 30 is connected to one end of the load resistor 13 and to the input of the amplifier 14. The output of the amplifier 14 is connected to the A / D converter 15. The output of the A / D converter 15 is supplied to the control unit 7.

[0085] Figure 16 is a flowchart illustrating the operation of the sensor device 1. The control unit 7 receives a detection signal from the A / D converter 15 (step S300). Subsequently, the control unit 7 determines the voltage level of the detection signal (step S301).

[0086] Next, the control unit 7 determines the charge storage period based on the voltage level of the detection signal (step S302). Specifically, the control unit 7 compares the voltage level of the detection signal with a predetermined threshold, and sets the charge storage period to be relatively shorter if the voltage level of the detection signal is greater than or equal to the predetermined threshold, and sets the charge storage period to be relatively longer if the voltage level of the detection signal is less than the predetermined threshold. The control unit 7 has information on multiple charge storage periods and can set the charge storage period so that the voltage level of the detection signal reaches the target level.

[0087] Next, the control unit 7 transmits a selection signal to the multiplexer 30 so that each of the multiple sensor elements 11 has a charge accumulation period determined in step S302 (step S303). Based on the selection signal, the multiplexer 30 connects one of the sensor elements 11 to the amplifier 14.

[0088] In the third embodiment, the sensor elements 11 that have not been selected among the plurality of sensor elements 11 can accumulate charge. For example, by sequentially selecting the plurality of sensor elements 11 at predetermined charge accumulation intervals, it becomes possible to switch each sensor element 11. As a result, each of the plurality of sensor elements 11 can accumulate charge to output a detection signal at a more optimal voltage level.

[0089] Furthermore, the second embodiment may be applied to the third embodiment. That is, the control unit 7 may receive a switching signal from an external source and determine the charge accumulation period based on this switching signal.

[0090] [4] Fourth Embodiment The fourth embodiment is a modification of the third embodiment, wherein the sensor device 1 is equipped with a plurality of multiplexers 30.

[0091] Figure 17 is a block diagram of the main part of the sensor device 1 according to the fourth embodiment of the present invention. The overall block diagram of sensor device 1 is the same as in Figure 1.

[0092] The switch unit 3 includes multiple multiplexers 30. Multiple sensor elements 11 are connected to the input of one multiplexer 30.

[0093] The amplification unit 4 comprises multiple load resistors 13 and multiple amplifiers 14. The load resistors 13 and amplifiers 14 are connected to the output of the multiplexer 30.

[0094] The A / D converter section 5 includes multiple A / D converters 15. The output of the amplifier 14 is connected to the A / D converters 15.

[0095] The operation of each multiplexer 30 is the same as in the third embodiment. According to the fourth embodiment, a sensor device 1 with more sensor elements 11 can be realized. Other effects are the same as in the third embodiment.

[0096] Although the above embodiments were described using the case where the sensor device 1 is a piezoelectric sensor as an example, they can also be applied to other types of sensors. For example, the above embodiments can also be applied to pyroelectric sensors and the like.

[0097] The present invention is not limited to the embodiments described above, and can be modified in various ways during implementation without departing from its essence. Furthermore, each embodiment may be combined as appropriate, and in that case, the combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be extracted by selecting combinations from the multiple constituent elements disclosed. For example, if the problem can be solved and effects obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, then the configuration with these deleted constituent elements can be extracted as an invention. [Explanation of symbols]

[0098] 1...Sensor device, 2...Sensor unit, 3...Switch unit, 4...Amplifier unit, 5...A / D converter unit, 6...Signal processing unit, 7...Control unit, 8...Memory unit, 9...External interface, 10...Voltage generation circuit, 11...Sensor element, 12...Switch, 13...Load resistor, 14...Amplifier, 15...A / D converter, 20...Unit, 21...Measurement stand, 22...Digital force gauge, 22A...Metal parts, 22B...Rubber parts, 30...Multiplexer.

Claims

1. Sensor element and A switch connected to the aforementioned sensor element, The amplifier connected to the aforementioned switch, A load resistor connected between the input of the amplifier and the ground terminal, A control unit that performs the switching operation of the aforementioned switch, It is equipped with, The control unit sets an off period for turning off the switch based on the output voltage of the amplifier. Sensor device.

2. The control unit shortens the off period relatively when the output voltage of the amplifier is above a threshold, and lengthens the off period relatively when the output voltage of the amplifier is below the threshold. The sensor device according to claim 1.

3. The control unit sets the off period based on an external switching signal. The sensor device according to claim 1.

4. The system further comprises an A / D converter connected to the output of the aforementioned amplifier. The sensor device according to claim 1.

5. The control unit controls the operation of the A / D converter so that the switching period of the switch and the sampling period of the A / D converter are the same. The sensor device according to claim 4.

6. The aforementioned sensor element is a piezoelectric element. The sensor device according to claim 1.

7. Multiple sensor elements, A multiplexer connected to the aforementioned plurality of sensor elements, The amplifier connected to the multiplexer, A load resistor connected between the input of the amplifier and the ground terminal, A control unit that controls the operation of the multiplexer, It is equipped with, The multiplexer operates to select one of the plurality of sensor elements, The control unit determines the charge accumulation period based on the output voltage of the amplifier and operates the multiplexer for each charge accumulation period. Sensor device.

8. The control unit shortens the charge storage period relatively when the output voltage of the amplifier is above a threshold, and lengthens the charge storage period relatively when the output voltage of the amplifier is below the threshold. The sensor device according to claim 7.

9. The control unit sets the charge storage period based on an external switching signal. The sensor device according to claim 7.

10. Each of the aforementioned plurality of sensor elements is a piezoelectric element. The sensor device according to claim 7.

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