Signal processing method, signal processing device, physical quantity measurement device, and sensor module

A signal processing method includes a processing target signal generation step of generating a processing target signal which is a time-series signal based on a source signal which is a time-series signal output from an object, and a vibration rectification error calculation step of calculating a plurality of vibration rectification errors by performing product-sum operation processing of a first signal based on the processing target signal and a second signal based on a phase-shifted signal of the processing target signal a plurality of times by changing a shift amount.

BACKGROUND

The present application is based on, and claims priority from JP Application Serial Number 2020-219506, filed Dec. 28, 2020, the disclosure of which is hereby incorporated by reference herein in its entirety.

1. Technical Field

The present disclosure relates to a signal processing method, a signal processing device, a physical quantity measurement device, and a sensor module.

2. Related Art

Synchronous addition is known as a method for reducing components that are asynchronous with a target stationary repetitive waveform. However, this method has a problem that waveform components that are correlated with the repetitive waveform but are not synchronized with a synchronous addition timing are also reduced. As a method of dealing with this problem, in Pete Sopcik and Dara O'Sullivan, “How Sensor Performance Enables Condition-Based Monitoring Solutions”, Analog Dialogue 53-06, June 2019, a method has been proposed in which envelope processing is performed on a target stationary repetitive time-series waveform and spectral analysis is performed on the obtained waveform.

However, in the envelope processing, it is necessary to perform the smoothing processing after rectifying the time-series waveform, and it is necessary to appropriately select the cutoff frequency of a smoothing filter so that a desired signal component is appropriately extracted, and therefore, the method described in Pete Sopcik and Dara O'Sullivan, “How Sensor Performance Enables Condition-Based Monitoring Solutions”, Analog Dialogue 53-06, June 2019 complicates the calculation.

SUMMARY

A signal processing method according to an aspect of the present disclosure includes a processing target signal generation step of generating a processing target signal which is a time-series signal based on a source signal which is a time-series signal output from an object, and a vibration rectification error calculation step of calculating a plurality of vibration rectification errors by performing product-sum operation processing of a first signal based on the processing target signal and a second signal based on a phase-shifted signal of the processing target signal a plurality of times by changing a shift amount.

A signal processing device according to another aspect of the present disclosure includes a processing target signal generation circuit of generating a processing target signal which is a time-series signal based on a source signal which is a time-series signal output from an object, and a vibration rectification error calculation circuit of generating a plurality of vibration rectification errors by performing product-sum operation processing of a first signal based on the processing target signal and a second signal based on a phase-shifted signal of the processing target signal a plurality of times by changing a shift amount.

A physical quantity measurement device according to still another aspect of the present disclosure includes a reference signal generation circuit that outputs a reference signal, a frequency delta-sigma modulation circuit that performs frequency delta-sigma modulation on the reference signal by using a measured signal to generate a frequency delta-sigma modulated signal, a first filter that operates in synchronization with the measured signal and has a variable group delay amount, and a second filter that operates in synchronization with the reference signal, in which the first filter is provided on a signal path from an output of the frequency delta-sigma modulation circuit to an input of the second filter, and the device has a first operation mode for measuring a frequency ratio of the measured signal and the reference signal, and a second operation mode in which a cutoff frequency of the second filter is lower than that in the first operation mode.

A sensor module according to still another aspect of the present disclosure includes the physical quantity measurement device according to still another aspect, and a physical quantity sensor, in which the measured signal is a signal based on an output signal of the physical quantity sensor.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to drawings. The embodiments described below do not unduly limit the contents of the present disclosure described in the aspects. In addition, not all of the configurations described below are essential constituent requirements of the present disclosure.

Hereinafter, the signal processing method according to the present disclosure will be described assuming that an object for signal processing is a sensor module. The type of the object is not particularly limited as long as the object generates a signal having periodicity, and may be, for example, various devices such as a motor, a structure such as a bridge or a building, or an electric circuit, in addition to the sensor module.

1. First Embodiment

1-1. Structure of Sensor Module

First, an example of the structure of a sensor module, which is an example of the object to which a signal processing method of the present embodiment is applied, will be described.

FIG.1is a perspective view of a sensor module1when viewed from a mounting target surface side to which the sensor module1is fixed. In the following description, a direction along a long side of the sensor module1that forms a rectangle in a plan view will be described as an X-axis direction, a direction orthogonal to the X-axis direction in a plan view will be described as a Y-axis direction, and a thickness direction of the sensor module1will be described as a Z-axis direction.

The sensor module1is a rectangular parallelepiped having a rectangular planar shape, and has a long side along the X-axis direction and a short side along the Y-axis direction orthogonal to the X-axis direction. Screw holes103are formed at two locations near each end portion of one long side and at one location in a central portion of the other long side. Each of the screw holes103at three locations is used in a state of being fixed to a mounting target surface of a mounting target body of a structure such as a building, a bulletin board, or various devices via a fixing screw.

As illustrated inFIG.1, an opening portion121is provided at a front surface of the sensor module1viewed from the mounting target surface side. A plug-type connector116is disposed inside the opening portion121. The connector116has a plurality of pins arranged in two rows, and in each row, the plurality of pins are arranged in the Y-axis direction. A socket-type connector (not illustrated) is coupled to the connector116from the mounting target body, and an electric signal such as a drive voltage of the sensor module1and detection data is transmitted and received.

FIG.2is an exploded perspective view of the sensor module1. As illustrated inFIG.2, the sensor module1includes a container101, a lid102, a sealing member141, a circuit substrate115, and the like. More specifically, in the sensor module1, the circuit substrate115is attached to the inside of the container101with a fixing member130interposed, and an opening of the container101is covered with the lid102via the sealing member141having buffering properties.

For example, the container101is an accommodation container for the circuit substrate115made of aluminum and formed into a box shape having an internal space. Similar to an overall shape of the sensor module1described above, an outer shape of the container101is a rectangular parallelepiped having a substantially rectangular planar shape, and fixed protrusions104are provided at two locations near both end portions of one long side and at one location in a central portion of the other long side. The screw hole103is formed in each of the fixed protrusions104.

The container101is a box shape whose outer shape is a rectangular parallelepiped and opened on one side. The inside of the container101is an internal space surrounded by a bottom wall112and a side wall111. In other words, the container101has a box shape in which one surface facing the bottom wall112is an opening surface123. The container101is disposed so that an outer edge of the circuit substrate115is disposed along an inner surface122of the side wall111, and the lid102is fixed thereto so as to cover the opening. On the opening surface123, the fixed protrusions104are erected at two locations near both end portions of one long side of the container101and at one location in the central portion of the other long side. An upper surface of the fixed protrusion104, that is, a surface exposed in the −Z direction protrudes from the upper surface of the container101.

In addition, the internal space of the container101is provided with a protrusion129that protrudes from the side wall111toward the internal space from the bottom wall112to the opening surface123at the central portion of one long side facing the fixed protrusion104provided in the central portion of the other long side. A female screw174is provided on an upper surface of the protrusion129. The lid102is fixed to the container101via the sealing member141with a screw172and the female screw174inserted through a through-hole176. The protrusion129and the fixed protrusion104are provided at positions facing constricted portions133and134of the circuit substrate115described later.

In the internal space of the container101, a first pedestal127and a second pedestal125are provided that protrude from the bottom wall112toward the opening surface123in a stepped manner. The first pedestal127is provided at a position facing a disposition region of the plug-type connector116attached to the circuit substrate115. The first pedestal127is provided with the opening portion121illustrated inFIG.1, and a plug-type connector116is inserted into the opening portion121. The first pedestal127functions as a pedestal for fixing the circuit substrate115to the container101.

The second pedestal125is located on a side opposite to the first pedestal127with respect to the fixed protrusion104and the protrusion129located in the central portion of the long side, and is provided in the vicinity of the fixed protrusion104and the protrusion129. The second pedestal125functions as a pedestal for fixing the circuit substrate115to the container101on the side opposite to the first pedestal127with respect to the fixed protrusion104and the protrusion129.

The outer shape of the container101is described as a box-shaped rectangular parallelepiped having the substantially rectangular planar shape with no lid, and is not limited thereto. The planar shape of the outer shape of the container101may be a square, a hexagon, an octagon, or the like. In addition, in the planar shape of the outer shape of the container101, the corners of the polygonal apex portion may be chamfered, and furthermore, any one of the sides may be a planar shape made of a curve. In addition, the planar shape inside the container101is not limited to the shape described above, and may be another shape. Furthermore, the planar shape of the outer shape and the inside of the container101may be similar or may not be similar to each other.

The circuit substrate115is a multilayer substrate in which a plurality of through-holes and the like are formed. For example, a glass epoxy substrate, a composite substrate, a ceramic substrate, or the like is used.

The circuit substrate115includes a second surface115ron the bottom wall112side, and a first surface115fthat has a front-rear relationship with the second surface115r. On the first surface115fof the circuit substrate115, the physical quantity measurement device2, three physical quantity sensors200, and other electronic components (not illustrated) are mounted. In addition, the connector116is mounted on the second surface115rof the circuit substrate115. Although illustration and description thereof are omitted, the circuit substrate115may be provided with other wirings, terminal electrodes, and the like.

The circuit substrate115is provided with the constricted portions133and134in which the outer edge of the circuit substrate115is constricted in the central portion in the X-axis direction along the long side of the container101in a plan view. The constricted portions133and134are provided on both sides in the Y-axis direction of the circuit substrate115in a plan view, and are constricted from the outer edge of the circuit substrate115toward the center. In addition, the constricted portions133and134are provided to face the protrusion129and the fixed protrusion104of the container101.

The circuit substrate115is inserted into the internal space of the container101with the second surface115rfacing the first pedestal127and the second pedestal125. The circuit substrate115is supported by the container101by the first pedestal127and the second pedestal125.

Each of the three physical quantity sensors200is a frequency change type sensor in which the frequency of the output signal changes according to an applied physical quantity. Of the three physical quantity sensors200, a physical quantity sensor200X detects a physical quantity in the X-axis direction, a physical quantity sensor200Y detects a physical quantity in the Y-axis direction, and a physical quantity sensor200Z detects a physical quantity in the Z-axis direction. Specifically, the physical quantity sensor200X is erected so that the front and rear surfaces of a package face in the X-axis direction and the side surface faces the first surface115fof the circuit substrate115. The physical quantity sensor200X outputs a signal corresponding to the detected physical quantity in the X-axis direction. The physical quantity sensor200Y is erected so that the front and rear surfaces of a package face the Y-axis direction and the side surface faces the first surface115fof the circuit substrate115. The physical quantity sensor200Y outputs a signal corresponding to the detected physical quantity in the Y-axis direction. The physical quantity sensor200Z is provided so that the front and rear surfaces of a package face the Z-axis direction, that is, the front and rear surfaces of the package face the first surface115fof the circuit substrate115. The physical quantity sensor200Z outputs a signal corresponding to the detected physical quantity in the Z-axis direction.

The physical quantity measurement device2is electrically coupled to the physical quantity sensors200X,200Y, and200Z via wiring and electronic components (not illustrated). Further, the physical quantity measurement device2generates physical quantity data in which a vibration rectification error is reduced based on the output signals of the physical quantity sensor200X,200Y, and200Z.

1-2. Structure of Physical Quantity Sensor

Next, an example of a structure of the physical quantity sensor200will be described by taking the case where the physical quantity sensor200is an acceleration sensor as an example. The three physical quantity sensors200illustrated inFIG.2, that is, the physical quantity sensors200X,200Y, and200Z may have the same structure to one another.

FIG.3is a perspective view of the physical quantity sensor200,FIG.4is a plan view of the physical quantity sensor200, andFIG.5is a cross-sectional view taken along line P1-P1ofFIG.4.FIGS.3to5illustrate only the inside of the package of the physical quantity sensor200. In the subsequent drawings, for convenience of description, the x axis, the y axis, and the z axis are illustrated as three axes orthogonal to each other. In addition, in the following description, for convenience of description, a plan view when viewed from the z-axis direction as a thickness direction of extension portions38aand38bis simply referred to as “plan view”.

As illustrated inFIGS.3to5, the physical quantity sensor200includes a substrate portion5and four weights50,52,54, and56.

The substrate portion5is provided with a plate-like base portion10having principal surfaces10aand10bextending in the x-axis direction and facing opposite to each other, a joining portion12extending from the base portion10in the y-axis direction, a movable portion13extending in a rectangular shape from the joining portion12in a direction opposite to the base portion10, two support portions30aand30bextending along an outer edge of the movable portion13from both ends of the base portion10in the x-axis direction, and a physical quantity detection element40spanned from the base portion10to the movable portion13and joined to the base portion10and the movable portion13.

In the two support portions30aand30b, the support portion30ais provided with a bonding portion36aextending along the y axis with the movable portion13and a gap32atherebetween and fixing the support portion30a, and the extension portion38aextending along the x axis with the movable portion13and a gap32ctherebetween. In other words, the support portion30ais provided with the extension portion38aextending along the y axis with the movable portion13and the gap32atherebetween and extending along the x axis with the movable portion13and the gap32ctherebetween, and the bonding portion36ais provided from the support portion30ato the extension portion38a. In addition, the support portion30bis provided with a bonding portion36bextending along the y axis with the movable portion13and a gap32btherebetween and fixing the support portion30b, and the extension portion38bextending along the x axis with the movable portion13and the gap32ctherebetween. In other words, the support portion30bis provided with the extension portion38bextending along the y axis with the movable portion13and the gap32btherebetween and extending along the x axis with the movable portion13and the gap32ctherebetween, and the bonding portion36bis provided from the support portion30bto the extension portion38b.

The bonding portions36aand36bprovided on the support portions30aand30bare for mounting the substrate portion5of the physical quantity sensor200on an external member such as a package. In addition, the base portion10, the joining portion12, the movable portion13, the support portions30aand30b, and the extension portions38aand38bmay be formed integrally.

The movable portion13is surrounded by the support portions30aand30band the base portion10, and is coupled to the base portion10via the joining portion12and is cantilevered. The movable portion13includes the principal surfaces13aand13bfacing opposite to each other, a side surface13calong the support portion30a, and a side surface13dalong the support portion30b. The principal surface13ais a surface facing the same side as the principal surface10aof the base portion10, and the principal surface13bis a surface facing the same side as the principal surface10bof the base portion10.

The joining portion12is provided between the base portion10and the movable portion13and couples the base portion10to the movable portion13. The joining portion12is formed to have a smaller thickness than those of the base portion10and the movable portion13. The joining portion12has grooves12aand12b. The grooves12aand12bare formed along the X axis. In the joining portion12, when the movable portion13is displaced with respect to the base portion10, the grooves12aand12bfunction as fulcrums, that is, intermediate hinges. Such a joining portion12and the movable portion13function as cantilever.

In addition, the physical quantity detection element40is fixed to a surface from the principal surface10aof the base portion10to the principal surface13aof the movable portion13by a bonding agent60. The fixed positions of the physical quantity detection element40are two locations of the central positions in the x-axis direction of the principal surface10aand the principal surface13a, respectively.

The physical quantity detection element40includes a base portion42afixed to the principal surface10aof the base portion10with a bonding agent60, a base portion42bfixed to the principal surface13aof the movable portion13with a bonding agent60, and vibration beams41aand41bfor detecting a physical quantity between the base portion42aand the base portion42b. In this case, the shapes of the vibration beams41aand41bare prismatic shapes, and when an AC voltage drive signal is applied to excitation electrodes (not illustrated) provided on the vibration beams41aand41b, flexural vibration is caused to be separated from or close to each other along the x axis. That is, the physical quantity detection element40is a tuning fork type vibrator element.

On the base portion42aof the physical quantity detection element40, lead electrodes44aand44bare provided. These lead electrodes44aand44bare electrically coupled to excitation electrodes (not illustrated) provided on the vibration beams41aand41b. The lead electrodes44aand44bare electrically coupled to connection terminals46aand46bprovided on the principal surface10aof the base portion10by metal wires48. The connection terminals46aand46bare electrically coupled to external connection terminals49aand49bby wiring (not illustrated). The external connection terminals49aand49bare provided on the principal surface10bside of the base portion10that is a surface side on which the physical quantity sensor200is mounted on a package or the like so as to overlap a package bonding portion34in a plan view. The package bonding portion34is for mounting the substrate portion5of the physical quantity sensor200on an external member such as a package, and is provided at two locations on end portions at both end sides of the base portion10in the x-axis direction.

The physical quantity detection element40is formed by patterning a quartz crystal substrate cut out at a predetermined angle from a quartz crystal ore or the like by a photolithography technique and an etching technique. In this case, the physical quantity detection element40is preferably made of the same material as the base portion10and the movable portion13in consideration of reducing a difference between the linear expansion coefficient between the base portion10and the movable portion13.

The weights50,52,54, and56are rectangular in a plan view, and are provided on the movable portion13. The weights50and52are fixed to the principal surface13aof the movable portion13by a bonding member62, and the weights54and56are fixed to the principal surface13bof the movable portion13by the bonding member62. Here, in the weight50fixed to the principal surface13a, the directions of one side as a rectangular edge side and the side surface13cof the movable portion13are aligned, and the directions of the other side and the side surface31dof the extension portion38aare aligned in a plan view. By aligning the directions in this manner, the weight50is disposed on the side surface13cside of the movable portion13, and the weight50and the extension portion38aare disposed so as to overlap each other in a plan view. Similarly, in the weight52fixed to the principal surface13a, the directions of one side as a rectangular edge side and the side surface13dside of the movable portion13are aligned, and the directions of the other side and the side surface31eof the extension portion38bare aligned in a plan view. As a result, the weight52is disposed on the side surface13dof the movable portion13, and the weight52and the extension portion38bare disposed so as to overlap each other in a plan view. In the weight54fixed to the principal surface13b, the directions of one side of a rectangle and the side surface13cside of the movable portion13are aligned, and the directions of the other side and the side surface31dof the extension portion38aare aligned in a plan view. As a result, the weight54is disposed on the side surface13cof the movable portion13, and the weight54and the extension portion38aare disposed so as to overlap each other in a plan view. Similarly, in the weight56fixed to the principal surface13b, the directions of one side of a rectangle and the side surface13dside of the movable portion13are aligned, and the directions of the other side and the side surface31eof the extension portion38bare aligned in a plan view. As a result, the weight56is disposed on the side surface13dof the movable portion13, and the weight56and the extension portion38bare disposed so as to overlap each other in a plan view.

In the weights50,52,54, and56disposed in this manner, the weights50and52are disposed symmetrically with respect to the physical quantity detection element40, and the weights54and56are disposed so as to overlap the weights50and52, respectively, in a plan view. These weights50,52,54, and56are fixed to the movable portion13by bonding members62provided at the positions of the center of gravity of the weights50,52,54, and56, respectively. In addition, the weights50and54and the extension portion38aand the weights52and56and the extension portion38boverlap each other respectively, in a plan view. Therefore, when an excessive physical quantity is applied, the weights50,52,54, and56abut on the extension portions38aand38b, and the displacement amounts of the weights50,52,54, and56can be suppressed.

The bonding member62is made of a silicone resin thermosetting adhesive or the like. The bonding member62is applied to the principal surface13aand the principal surface13bof the movable portion13at two locations, respectively, and the weights50,52,54, and56are placed thereon. Thereafter, the weights50,52,54, and56are fixed to the movable portion13by being cured by heating. Bonding surfaces of the weights50,52,54, and56facing the principal surface13aand the principal surface13bof the movable portion13are rough surfaces. As a result, when the weights50,52,54, and56are fixed to the movable portion13, a bonding area on the bonding surface is increased, and the bonding strength can be improved.

As illustrated inFIG.6, when the acceleration in the +Z direction represented by the arrow α1is applied to the physical quantity sensor200configured as described above, a force acts on the movable portion13in the −Z direction, and the movable portion13is displaced in the −Z direction with the joining portion12as a fulcrum. As a result, a force in a direction where the base portion42aand the base portion42bare separated from each other along the Y axis is applied to the physical quantity detection element40, and tensile stress is generated in the vibration beams41aand41b. Therefore, the frequency at which the vibration beams41aand41bvibrate increases.

On the other hand, as illustrated inFIG.7, when acceleration in the −Z direction represented by the arrow α2is applied to the physical quantity sensor200, a force acts on the movable portion13in the +Z direction, and the movable portion13is displaced in the +Z direction with the joining portion12as a fulcrum. As a result, a force in a direction where the base portion42aand the base portion42bapproach each other along the Y axis is applied to the physical quantity detection element40, and compressive stress is generated in the vibration beams41aand41b. Therefore, the frequency at which the vibration beams41aand41bvibrate decreases.

When the frequency at which the vibration beams41aand41bvibrate changes according to the acceleration, the frequency of signals output from the external connection terminals49aand49bof the physical quantity sensor200changes. The sensor module1can calculate the value of the acceleration applied to the physical quantity sensor200based on the change in the frequency of the output signal of the physical quantity sensor200.

In order to increase the detection accuracy of acceleration which is a physical quantity, the joining portion12that connects the base portion10as a fixed portion and the movable portion13is preferably a quartz crystal that is a member having a high Q value. For example, the base portion10, the support portions30aand30b, and the movable portion13may be formed of a quartz crystal plate, and the grooves12aand12bof the joining portion12may be formed by half etching from both surfaces of the quartz crystal plate.

1-3. Functional Configuration of Sensor Module

FIG.8is a functional block diagram of the sensor module1. As described above, the sensor module1includes physical quantity sensor200X,200Y, and200Z and a physical quantity measurement device2.

The physical quantity measurement device2includes an oscillation circuit201X,201Y, and201Z, a frequency ratio measurement circuit202X,202Y, and202Z, a micro-control unit210, a storage unit220, and an interface circuit230.

The oscillation circuit201X amplifies the output signal of the physical quantity sensor200X to generate a drive signal, and applies the drive signal to the physical quantity sensor200X. Due to the drive signal, the vibration beams41aand41bof the physical quantity sensor200X vibrate at a frequency corresponding to the acceleration in the X-axis direction, and a signal of the frequency is output from the physical quantity sensor200X. Further, the oscillation circuit201X outputs a measured signal SIN_X, which is a rectangular wave signal obtained by amplifying the output signal of the physical quantity sensor200X, to the frequency ratio measurement circuit202X. The measured signal SIN_X is a signal based on the output signal of the physical quantity sensor200X.

Similarly, the oscillation circuit201Y amplifies the output signal of the physical quantity sensor200Y to generate a drive signal, and applies the drive signal to the physical quantity sensor200Y. Due to the drive signal, the vibration beams41aand41bof the physical quantity sensor200Y vibrate at a frequency corresponding to the acceleration in the Y-axis direction, and a signal of the frequency is output from the physical quantity sensor200Y. Further, the oscillation circuit201Y outputs a measured signal SIN_Y, which is a rectangular wave signal obtained by amplifying the output signal of the physical quantity sensor200Y, to the frequency ratio measurement circuit202Y. The measured signal SIN_Y is a signal based on the output signal of the physical quantity sensor200Y.

Similarly, the oscillation circuit201Z amplifies the output signal of the physical quantity sensor200Z to generate a drive signal, and applies the drive signal to the physical quantity sensor200Z. Due to the drive signal, the vibration beams41aand41bof the physical quantity sensor200Z vibrate at a frequency corresponding to the acceleration in the Z-axis direction, and a signal of the frequency is output from the physical quantity sensor200Z. Further, the oscillation circuit201Z outputs a measured signal SIN_Z, which is a rectangular wave signal obtained by amplifying the output signal of the physical quantity sensor200Z, to the frequency ratio measurement circuit202Z. The measured signal SIN_Z is a signal based on the output signal of the physical quantity sensor200Z.

The reference signal generation circuit203generates and outputs a reference signal CLK having a constant frequency. In the present embodiment, the frequency of the reference signal CLK is higher than the frequencies of the measured signals SIN_X, SIN_Y, and SIN_Z. The reference signal CLK preferably has high frequency accuracy, and the reference signal generation circuit203may be, for example, a temperature compensated crystal oscillator.

The frequency ratio measurement circuit202X counts the number of pulses of the reference signal CLK included in a predetermined period of the measured signal SIN_X, which is a signal based on the signal output from the oscillation circuit201X, and outputs a count value CNT_X. The count value CNT_X is a reciprocal count value corresponding to the frequency ratio of the measured signal SIN_X and the reference signal CLK.

The frequency ratio measurement circuit202Y counts the number of pulses of the reference signal CLK included in a predetermined period of the measured signal SIN_Y output from the oscillation circuit201Y, and outputs a count value CNT_Y. The count value CNT_Y is a reciprocal count value corresponding to the frequency ratio of the measured signal SIN_Y and the reference signal CLK.

The frequency ratio measurement circuit202Z counts the number of pulses of the reference signal CLK included in a predetermined period of the measured signal SIN_Z output from the oscillation circuit201Z, and outputs a count value CNT_Z. The count value CNT_Z is a reciprocal count value corresponding to the frequency ratio of the measured signal SIN_Z and the reference signal CLK.

The storage unit220stores programs and data, and may include a volatile memory such as SRAM or DRAM. SRAM is an abbreviation for static random access memory, and DRAM is an abbreviation for dynamic random access memory.

In addition, the storage unit220may include a non-volatile memory such as a semiconductor memory such as EEPROM or flash memory, a magnetic storage device such as a hard disk device, or an optical storage device such as an optical disk device. EEPROM is an abbreviation for electrically erasable programmable read only memory.

The micro-control unit210operates in synchronization with the reference signal CLK, and performs predetermined arithmetic processing and control processing by executing a program (not illustrated) stored in the storage unit220. For example, the micro-control unit210measures the physical quantities detected by the physical quantity sensors200X,200Y, and200Z, respectively based on the count value CNT_X output from the frequency ratio measurement circuit202X, the count value CNT_Y output from the frequency ratio measurement circuit202Y, and the count value CNT_Z output from the frequency ratio measurement circuit202Z. Specifically, the micro-control unit210converts the count value CNT_X, the count value CNT_Y, and the count value CNT_Z into a measurement value of the physical quantity in the X-axis direction, a measurement value of the physical quantity in the Y-axis direction, and a measurement value of the physical quantity in the Z-axis direction, respectively. For example, the storage unit220stores table information that defines the correspondence relationship between the count value and the measurement value of the physical quantity, or information on the relational expression between the count value and the measurement value of the physical quantity, and the micro-control unit210may convert each count value into a measurement value of a physical quantity with reference to the information.

The micro-control unit210may transmit the measurement value of the physical quantity in the X-axis direction, the measurement value of the physical quantity in the Y-axis direction, and the measurement value of the physical quantity in the Z-axis direction to the signal processing device400via the interface circuit230. Alternatively, the micro-control unit210may write the measurement value of the physical quantity in the X-axis direction, the measurement value of the physical quantity in the Y-axis direction, and the measurement value of the physical quantity in the Z-axis direction to the storage unit220, respectively, and the signal processing device400may read out each measurement value via the interface circuit230.

Since the configuration and operation of the frequency ratio measurement circuits202X,202Y, and202Z are the same, any one of the frequency ratio measurement circuits202X,202Y, and202Z will be referred to as a frequency ratio measurement circuit202hereafter. Further, any one of the measured signals SIN_X, SIN_Y, and SIN_Z input to the frequency ratio measurement circuit202is referred to as a measured signal SIN, and any one of the count values CNT_X, CNT_Y, and CNT_Z output from the frequency ratio measurement circuit202is referred to as a count value CNT.

A vibration rectification error corresponds to the DC offset generated during rectification due to the non-linearity of the response of the sensor module1to vibration, and is observed as an abnormal shift of the output offset of the sensor module1. The vibration rectification error causes a serious measurement error in an application such as an inclinometer using the sensor module1in which the DC output of the sensor module1is a measurement target as it is. There are three main mechanisms that cause a vibration rectification error: 1. due to asymmetric rails, 2. due to non-linearity of scale factors, and 3. due to structural resonance of the physical quantity sensor200.

1. Vibration Rectification Error Due to Asymmetric Rails

When the sensitivity axis of the physical quantity sensor200is in the direction of gravitational acceleration, the measurement value of the sensor module1has an offset corresponding to the gravitational acceleration of 1 g=9.8 m/s2. For example, if the dynamic range of the physical quantity sensor200is 2 g, vibration can be measured up to 1 g without clipping. If vibration exceeding 1 g is applied in this state, clipping occurs asymmetrically, and therefore the measurement value includes a vibration rectification error.

When the dynamic range is as wide as 15 g, for example, clipping is rarely a problem in a normal usage environment. On the other hand, the physical quantity sensor200has a built-in physical protection mechanism for the purpose of preventing damage to the physical quantity detection element40, and when the vibration level exceeds a certain threshold value, the protection mechanism works, and therefore clipping occurs. In order to prevent clipping, it is necessary to devise an attachment for installing the sensor module1and take measures such as damping the vibration of a resonance frequency band.

2. Vibration Rectification Error Due to Non-Linearity of Scale Factors

FIG.9is a diagram illustrating in principle that a vibration rectification error occurs due to output waveform distortion. InFIG.9, the solid line indicates a sinusoidal vibration waveform and a smoothed waveform of the vibration waveform, and the broken line indicates an asymmetrical vibration waveform above and below the center of vibration and a smoothed waveform of the vibration waveform. The smoothed waveform indicated by the solid line is 0, while the smoothed waveform indicated by the broken line has a negative value, and an offset occurs during smoothing.

The physical quantity sensor200is a frequency change type sensor, and the count value CNT corresponding to the frequency ratio of the measured signal SIN and the reference signal CLK is a reciprocal count value. The relationship between the acceleration applied to the physical quantity sensor200and the reciprocal count value has non-linearity. The broken line inFIG.10indicates the non-linearity between the applied acceleration and the reciprocal count value. The broken line inFIG.11indicates the non-linearity between the applied acceleration and the oscillation frequency of the physical quantity sensor200. The broken line inFIG.12indicates the non-linearity between the oscillation frequency of the physical quantity sensor200and the reciprocal count value. The broken line inFIG.10is obtained by combining the broken line inFIG.11and the broken line inFIG.12.

Here, by correcting the relationship between the oscillation frequency and the reciprocal count value as indicated by the solid line inFIG.12, the relationship between the acceleration and the reciprocal count value can be made linear as indicated by the solid line inFIG.10. Specifically, the above-mentioned micro-control unit210can correct the count value CNT by using the correction function represented by Equation (1).
Y={c−d}2(1)

In Equation (1), c is the count value before correction corresponding to the broken line inFIG.10, Y is the count value after correction corresponding to the solid line inFIG.10, and d is a coefficient that determines the degree of correction illustrated inFIG.12. For example, the coefficient d is stored in the storage unit220or set by the signal processing device400.

3. Vibration Rectification Error Caused by Cantilever Resonance

As a principle of detecting acceleration, the physical quantity sensor200changes the tension acting on the physical quantity detection element40by transmitting the deflection of the cantilever with a weight due to the acceleration to the physical quantity detection element40which is a twin tuning fork resonator, thereby changing the oscillation frequency. Therefore, the physical quantity detection element40has a resonance frequency due to the structure of the cantilever, and when the cantilever resonance is excited, an inherent vibration rectification error occurs. The cantilever resonance has a frequency higher than the frequency bandwidth corresponding to the range of detectable acceleration, and the vibration component thereof is removed by the low-pass filter inside the physical quantity measurement device2, but a vibration rectification error occurs as a bias offset that reflects the asymmetry of vibration. As the amplitude of the cantilever resonance increases, the asymmetry of the output waveform of the physical quantity sensor200increases, and therefore the vibration rectification error also increases. Therefore, it is an important issue to reduce the vibration rectification error caused by the cantilever resonance.

In the present embodiment, since the frequency ratio measurement circuit202is a reciprocal counting system that counts the number of pulses of the reference signal CLK included in a predetermined period of the measured signal SIN, the timing of acquiring this count value is synchronized with the measured signal SIN. On the other hand, the count value CNT output from the frequency ratio measurement circuit202needs to be synchronized with the frequency division signal of the reference signal CLK, and resampling is required because the timing of acquiring the count value of the number of pulses of the reference signal CLK and the frequency division signal of the reference signal CLK are not synchronized. By devising the configuration required for resampling in the frequency ratio measurement circuit202, it is possible to generate the count value CNT_in which the vibration rectification error caused by the cantilever resonance is corrected.

1-5. Configuration of Frequency Ratio Measurement Circuit

The frequency ratio measurement circuit202measures the frequency ratio of the measured signal SIN and the reference signal CLK by the reciprocal counting system.FIG.13is a diagram illustrating a configuration example of the frequency ratio measurement circuit202. As illustrated inFIG.13, the frequency ratio measurement circuit202includes a frequency delta-sigma modulation circuit300, a first low-pass filter310, a latch circuit320, and a second low-pass filter330.

The frequency delta-sigma modulation circuit300performs frequency delta-sigma modulation on the reference signal CLK by using the measured signal SIN to generate a frequency delta-sigma modulated signal. The frequency delta-sigma modulation circuit300includes a counter301, a latch circuit302, a latch circuit303, and a subtractor304. The counter301counts the rising edge of the reference signal CLK and outputs a count value CT0. The latch circuit302latches and holds the count value CT0in synchronization with the rising edge of the measured signal SIN. The latch circuit303latches and holds the count value held by the latch circuit302in synchronization with the rising edge of the measured signal SIN. The subtractor304subtracts the count value held by the latch circuit303from the count value held by the latch circuit302to generate and output a count value CT1. This count value CT1is a frequency delta-sigma modulated signal generated by the frequency delta-sigma modulation circuit300.

This frequency delta-sigma modulation circuit300is also called a primary frequency delta-sigma modulator, and latches the count value of the number of pulses of the reference signal CLK twice by the measured signal SIN, and sequentially holds the count value of the number of pulses of the reference signal CLK, triggered by the rising edge of the measured signal SIN. Here, the frequency delta-sigma modulation circuit300has been described as performing the latch operation at the rising edge of the measured signal SIN, but the latch operation may be performed at the falling edge or both the rising edge and the falling edge. Further, the subtractor304calculates the difference between the two count values held in the latch circuits302and303to output an increment of the count value of the number of pulses of the reference signal CLK observed during one period of the measured signal SIN_with the passage of time without a dead period. When the frequency of the measured signal SIN is fx and the frequency of the reference signal CLK is fc, the frequency ratio is fc/fx. The frequency delta-sigma modulation circuit300outputs a frequency delta-sigma modulated signal indicating the frequency ratio as a digital signal sequence.

The first low-pass filter310operates in synchronization with the measured signal SIN, and outputs a count value CT2from which the noise component included in the count value CT1which is the frequency delta-sigma modulated signal output from the frequency delta-sigma modulation circuit300is removed or reduced. InFIG.13, the first low-pass filter310is provided immediately after the frequency delta-sigma modulation circuit300, but may be provided on the signal path from the output of the frequency delta-sigma modulation circuit300to the input of the second low-pass filter330.

The latch circuit320latches the count value CT2output from the first low-pass filter310in synchronization with the rising edge of the reference signal CLK, and holds the latched value as a count value CT3.

The second low-pass filter330operates in synchronization with the reference signal CLK, and outputs a count value obtained by removing or reducing a noise component included in the count value CT3held by the latch circuit320. The count value output from the second low-pass filter330is output to the micro-control unit210as the count value CNT.

FIG.14is a diagram illustrating a configuration example of the first low-pass filter310. In the example ofFIG.14, the first low-pass filter310includes a delay element311, an integrator312, an integrator313, a decimator314, a delay element315, a differentiator316, a delay element317, and a differentiator318. Each part of the first low-pass filter310operates in synchronization with the measured signal SIN.

The delay element311outputs a count value obtained by delaying the count value CT1in synchronization with the measured signal SIN. The number of taps of the delay element311is na. For example, the delay element311is realized by a shift register in which na registers are serially coupled.

The integrator312outputs a count value obtained by integrating the count values output from the delay element311in synchronization with the measured signal SIN.

The integrator313outputs a count value obtained by integrating the count values output from the integrator312in synchronization with the measured signal SIN.

The decimator314outputs a count value obtained by decimating the count value output from the integrator313to a rate of 1/R in synchronization with the measured signal SIN.

The delay element315outputs a count value obtained by delaying the count value output from the decimator314in synchronization with the measured signal SIN. The number of taps of the delay element315is n1. For example, the delay element315is realized by a shift register in which n1registers are serially coupled.

The differentiator316outputs a count value obtained by subtracting the count value output from the delay element315from the count value output from the decimator314.

The delay element317outputs a count value obtained by delaying the count value output from the differentiator316in synchronization with the measured signal SIN. The number of taps of the delay element317is n2. For example, the delay element317is realized by a shift register in which n2registers are serially coupled.

The differentiator318outputs the count value CT2obtained by subtracting the count value output from the delay element317from the count value output from the differentiator316.

The number of taps n1and n2and a decimation ratio R are fixed, and the number of taps na is variable. For example, the number of taps na is stored in the storage unit220or set by the signal processing device400.

The first low-pass filter310configured in this way functions as a CIC filter in which the group delay amount is variable depending on the number of taps na. CIC is an abbreviation for cascaded integrator comb.

FIG.15is a diagram illustrating a configuration example of the second low-pass filter330. In the example ofFIG.15, the second low-pass filter330includes an integrator331, a delay element332, a differentiator333, and a decimator334. Each part of the second low-pass filter330operates in synchronization with the reference signal CLK.

The integrator331outputs a count value obtained by integrating the count values CT3in synchronization with the reference signal CLK.

The delay element332outputs a count value obtained by delaying the count value output from the integrator331in synchronization with the reference signal CLK. The number of taps of the delay element332is n3. For example, the delay element332is realized by a shift register in which n3registers are serially coupled.

The differentiator333outputs a count value obtained by subtracting the count value output from the delay element332from the count value output from the integrator331.

The decimator334outputs the count value CNT obtained by decimating the count value output from the differentiator333to a rate of 1/n3in synchronization with the reference signal CLK.

The number of taps and the decimation ratio n3are fixed.

Since the second low-pass filter330configured in this way integrates the count values CT3while resampling the count values CT3with the reference signal CLK, the second low-pass filter330functions as a weighted moving average filter for weighting the count values CT3by the duration thereof.

Since the first low-pass filter310operates in synchronization with the measured signal SIN, and the second low-pass filter330performs resampling synchronized with the reference signal CLK n this way, non-linearity occurs in the input and the output of the frequency ratio measurement circuit202. Therefore, the count value CNT output from the frequency ratio measurement circuit202includes a vibration rectification error due to this non-linearity. This vibration rectification error can be adjusted by adjusting the number of taps na of the delay element311included in the first low-pass filter310.

FIGS.16A to16Dare diagrams illustrating that the vibration rectification error due to the non-linearity of the input and the output of the frequency ratio measurement circuit202can be adjusted.FIGS.16A to16Dillustrate examples of the case where the period of the measured signal SIN is longer than the period of the reference signal CLK and the update period of the count value CNT is longer than the period of the measured signal SIN, and the horizontal-axis direction corresponds to the passage of time. InFIGS.16A to16D, regarding the reference signal CLK, the timing of the rising edge is indicated by the short vertical line. Further, regarding the count values CT1and CT2, the timing at which the values change is indicated by the short vertical line. InFIGS.16A to16D, for the purpose of describing the adjustment mechanism of the vibration rectification error, simplified numerical values are used for easy understanding. Further, it is described that the count value CT2is fixed before the count value CT1is fixed although the count value CT2is not fixed until after the count value CT1is fixed. But the actual calculation of the count value CT2is executed after the count value CT1is fixed.

InFIGS.16A to16D,FIG.16Ais an example of the case where the period of the measured signal SIN is constant, andFIGS.16B,16C, and16Dare examples of the case where the measured signal SIN is frequency-modulated. InFIGS.16B,16C, and16D, the group delay amounts of the first low-pass filters310are different from each other. For the sake of simplicity, the period of the reference signal CLK and the period of the measured signal SIN are set to a simple integer ratio, and the count value CT1input to the first low-pass filter310is output as it is with a constant group delay. The second low-pass filter330integrates the count values CT3in which the count value CT2output from the first low-pass filter310is latched in synchronization with the reference signal CLK, and outputs the accumulated value for16times as the count value CNT.

In the example ofFIG.16A, the count value CT2is always 4, and the count value CNT is 4×16=64. In the example ofFIG.16B, since the measured signal SIN is frequency-modulated and the group delay of the first low-pass filter310is set to 0, the count value CT2repeats 5, 5, 3, and 3. Since weighting is performed by time at the time of integration, the count value CNT is 5×10+3×6=68, which is larger than the count value CNT ofFIG.16A. In the example ofFIG.16C, the count value CT2repeats 5, 5, 3, and 3, as in the example ofFIG.16B, but the case where a group delay occurs in the first low-pass filter310is illustrated. As a result of weighting by time at the time of integration, the count value CNT is 5×8+3×8=64, which is the same value as the count value CNT inFIG.16A. In the example ofFIG.16D, the count value CT2repeats 5, 5, 3, and 3, as in the examples ofFIGS.16B and16C, but the case where the group delay occurring in the first low-pass filter310is larger than that of the example ofFIG.16Cis illustrated. In the example ofFIG.16D, the count value CNT is 5×6+3×10=60, which is smaller than the count value CNT ofFIG.16A.

From the consideration usingFIGS.16A to16D, it can be qualitatively understood that the vibration rectification error due to the non-linearity of the input and the output of the frequency ratio measurement circuit202changes depending on the group delay amount of the first low-pass filter310. By adjusting the group delay amount of the first low-pass filter310so that the vibration rectification error due to the non-linearity of the input and the output of the frequency ratio measurement circuit202has the opposite phase to the vibration rectification error caused by the cantilever resonance, it is possible to cancel each other's vibration rectification errors. The group delay amount of the first low-pass filter310can be adjusted by setting the number of taps na of the delay element311.

FIG.17is a diagram illustrating the dependence of the vibration rectification error included in the measurement value by the physical quantity measurement device2on the number of taps na. InFIG.17, the horizontal axis is the number of taps na, and the vertical axis is the vibration rectification error. VRE on the vertical axis is an abbreviation for vibration rectification error. FromFIG.17, if the number of taps na is set appropriately, it is possible to correct the vibration rectification error and bring the error closer to 0.

1-6. Configuration of Signal Processing Device

In the present embodiment, the signal processing device400performs processing of detecting a signal component having periodicity included in the signal output from the sensor module1.FIG.18is a diagram illustrating a configuration example of the signal processing device400. As illustrated inFIG.18, the signal processing device400includes a processing circuit410, a storage circuit420, an operation unit430, a display unit440, a sound output unit450, and a communication unit460. The signal processing device400may have a configuration in which some of the components ofFIG.18are omitted or changed, or other components are added.

The processing circuit410acquires a source signal, which is a digital time-series signal output from the sensor module1, and performs signal processing on the source signal. Specifically, the processing circuit410executes a signal processing program421stored in the storage circuit420, and performs various calculation processing on the source signal. In addition, the processing circuit410performs various processing according to the operation signals from the operation unit430, processing of transmitting display signals for displaying various information to the display unit440, processing of transmitting sound signals for causing the sound output unit450to generate various sounds, processing of controlling the communication unit460to perform data communication with other devices, and the like. The processing circuit410is realized by, for example, a CPU or a DSP. CPU is an abbreviation for central processing unit, and DSP is an abbreviation for digital signal processor.

By executing the signal processing program421, the processing circuit410functions as a source signal acquisition circuit411, a processing target signal generation circuit412, and a vibration rectification error calculation circuit413. That is, the signal processing device400includes the source signal acquisition circuit411, the processing target signal generation circuit412, and the vibration rectification error calculation circuit413.

The source signal acquisition circuit411acquires a source signal which is a time-series signal output from the sensor module1. The source signal is a signal containing a signal component having periodicity. For example, the source signal may be a signal including a signal component of the structural resonance frequency of the sensor module1, specifically, the cantilever resonance frequency of the physical quantity sensor200. For example, the source signal acquisition circuit411may acquire time-series data of the count value CT1which is a delta-sigma modulated signal input to the first low-pass filter310in the physical quantity measurement device2as the source signal.

The processing target signal generation circuit412generates a processing target signal which is a time-series signal, based on the source signal acquired by the source signal acquisition circuit411. For example, the processing target signal generation circuit412may cut out a part of the time-series signal included in the source signal to generate the processing target signal. Alternatively, the processing target signal may be the source signal itself. The processing target signal generated by the processing target signal generation circuit412is stored in the storage circuit420as processing target signal422.

The vibration rectification error calculation circuit413performs the product-sum operation processing of the first signal based on the processing target signal and the second signal based on the phase-shifted signal of the processing target signal a plurality of times by changing the shift amount to calculate a plurality of vibration rectification errors. The plurality of vibration rectification errors calculated by the vibration rectification error calculation circuit413are stored in the storage circuit420as vibration rectification error information423.

The first signal may be the processing target signal itself. Further, the first signal may be a signal obtained by filtering the processing target signal. For example, a filtering process may be a smoothing filtering process. Further, the first signal may be a signal obtained by removing or reducing the DC component of the processing target signal. Further, the first signal may be a signal obtained by removing or reducing the DC component of the processing target signal and filtering the signal.

The second signal may be the phase-shifted signal itself of the processing target signal. Further, the second signal may be a signal obtained by filtering a phase-shifted signal of the processing target signal. For example, a filtering process may be a smoothing filtering process. Further, the second signal may be a signal obtained by removing or reducing the DC component of the phase-shifted signal of the processing target signal. Further, the second signal may be a signal obtained by removing or reducing the DC component of the phase-shifted signal of the processing target signal and filtering the signal.

Assuming that an i-th sample value of the processing target signal having N samples is S(i), the i-th sample value of the phase-shifted signal of the processing target signal is S(i+k). N is an integer of 2 or more, and i is each integer of 1 or more and N or less. For example, when the first signal is the processing target signal itself and the second signal is the phase-shifted signal itself of the processing target signal, a k-th vibration rectification error VRE(k) of the M vibration rectification errors is calculated by Equation (2). M is an integer of 2 or more, and k is each integer of 1 or more and M or less. In Equation (2), S(i) is the i-th sample value of the first signal, and S(i+k) is the i-th sample value of the second signal.
VRE(k)=(1/N)Σi=0N−1s(i)·s(i+k)  (2)

Further, for example, when the first signal is a signal obtained by removing or reducing the DC component of the processing target signal and the second signal is the phase-shifted signal itself of the processing target signal, a k-th vibration rectification error VRE(k) is calculated by Equation (3). In Equation (3), fHPF(S(i)) is the i-th sample value of the first signal, and S(i+k) is the i-th sample value of the second signal.
VRE(k)=(1/N)Σi=0N−1fHPF(s(i))·s(i+k)  (3)

Further, for example, when the first signal is a signal obtained by removing or reducing the DC component of the processing target signal, and smoothing and filtering the signal and the second signal is the phase-shifted signal itself of the processing target signal, the k-th vibration rectification error VRE(k) is calculated by Equation (4). In Equation (4), fLPF(fHPF(S(i))) is the i-th sample value of the first signal, and S(i+k) is the i-th sample value of the second signal.
VRE(k)=(1/N)Σi=0N−1fHPF(fHPF(s(i))·s(i+k)  (4)

Further, for example, when the first signal is a signal obtained by removing or reducing the DC component of the processing target signal and smoothing and filtering the signal and the second signal is a signal obtained by smoothing and filtering the phase-shifted signal of the processing target signal, the k-th vibration rectification error VRE(k) is calculated by Equation (5). In Equation (5), fLPF(fHPF(S(i))) is the i-th sample value of the first signal, and fLPF(S(i+k)) is the i-th sample value of the second signal.
VRE(k)=(1/N)Σi=0N−1fLPF(fHPF(s(i))·fLPF(s(i+k)  (5)

In Equations (2), (3), (4), and (5), division by N may be omitted.

Ergodic signal components such as noise are attenuated by such product-sum operation processing, and a signal having periodicity included in the processing target signal appears as a vibration rectification error according to the phase difference between the first signal and the second signal. Specifically, assuming that the period of the signal having periodicity included in the processing target signal is T, when the first signal and the second signal have a phase difference corresponding to an even multiple of T/2, the vibration rectification error obtained by the product-sum operation processing is maximized. Further, when the first signal and the second signal have a phase difference corresponding to an odd multiple of T/4, the vibration rectification error obtained by the product-sum operation processing becomes 0. Further, when the first signal and the second signal have a phase difference corresponding to an odd multiple of T/2, the vibration rectification error obtained by the product-sum operation processing is minimized. Therefore, if a plurality of vibration rectification errors calculated while changing the phase difference between the first signal and the second signal are plotted, since the value of the vibration rectification error changes with a period T, it is possible to detect a signal component having periodicity included in the processing target signal.

When it is desired to detect the signal component of the structural resonance of the sensor module1, specifically, the signal component of the cantilever resonance as a signal having periodicity, in the vibration rectification error calculation circuit413, it is preferable that the number of additions N in the product-sum operation processing is larger than the value obtained by dividing the sampling frequency of the source signal by the resonance frequency. The sampling frequency of the source signal is, for example, the frequency of the measured signal SIN, which is the sampling signal of the count value CT1input to the first low-pass filter310. In this way, the signal component of the resonance frequency is integrated for one period or more in the product-sum operation processing, and the signal component of the resonance frequency is effectively detected. Further, the cantilever resonance is excited even in a general environment, but since the vibration rectification error calculated when the excitation level of the cantilever resonance changes also changes, it is preferable that the signal processing device400performs the product-sum operation processing by using the source signal acquired in a stable environment.

The storage circuit420includes a ROM and a RAM (not illustrated). ROM is an abbreviation for read only memory, and RAM is an abbreviation for random access memory. The ROM stores various programs such as the signal processing program421and predetermined data, and the RAM stores the signal generated by the processing circuit410such as the processing target signal422and the vibration rectification error information423, and the calculated information. The RAM is also used as a work area of the processing circuit410, and stores programs and data read from the ROM, data input from the operation unit430, and signals and data temporarily generated by the processing circuit410.

The operation unit430is an input device composed of operation keys, button switches, and the like, and outputs an operation signal corresponding to the operation by a user to the processing circuit410.

The display unit440is a display device composed of an LCD or the like, and displays various information based on a display signal output from the processing circuit410. LCD is an abbreviation for liquid crystal display. The display unit440may be provided with a touch panel that functions as the operation unit430. For example, the display unit440may display an image in which the vibration rectification error information423is plotted based on the display signal output from the processing circuit410.

The sound output unit450is composed of a speaker or the like, and generates various sounds based on the sound signal output from the processing circuit410. For example, the sound output unit450may generate a sound indicating the start or end of signal processing based on the sound signal output from the processing circuit410.

The communication unit460performs various controls for establishing data communication between the processing circuit410and another device. For example, the communication unit460may transmit the vibration rectification error information423to another device.

At least a part of the source signal acquisition circuit411, the processing target signal generation circuit412, and the vibration rectification error calculation circuit413may be realized by dedicated hardware. Further, the signal processing device400may be a single device or may be composed of a plurality of devices. Further, for example, the processing circuit410and the storage circuit420are realized by a device such as a cloud server, the device calculates the vibration rectification error information423, and the calculated vibration rectification error information423may be transmitted to a terminal including the operation unit430, the display unit440, the sound output unit450, and the communication unit460via a communication line.

1-7. Signal Processing Method

FIG.19is a flowchart illustrating a procedure of a signal processing method of the first embodiment. As illustrated inFIG.19, the signal processing method of the first embodiment includes a source signal acquisition step S1, a processing target signal generation step S2, and a vibration rectification error calculation step S3. The signal processing method of the present embodiment is performed by, for example, the signal processing device400.

First, in the source signal acquisition step S1, the signal processing device400acquires a source signal which is a time-series signal output from the sensor module1which is an object.

Next, in the processing target signal generation step S2, the signal processing device400generates a processing target signal which is a time-series signal based on the source signal acquired in step S1.

Finally, in the vibration rectification error calculation step S3, the signal processing device400performs the product-sum operation processing of the first signal based on the processing target signal generated in step S2and the second signal based on the phase-shifted signal of the processing target signal a plurality of times by changing a shift amount, and calculates a plurality of vibration rectification errors.

FIG.20is a flowchart illustrating an example of the procedure of the vibration rectification error calculation step S3ofFIG.19.

As illustrated inFIG.20, first, in step S31, the signal processing device400generates a first signal based on the processing target signal generated in step S2.

Next, in step S32, the signal processing device400generates a second signal based on the phase-shifted signal of the processing target signal generated in step S2.

Next, in step S33, the signal processing device400performs product-sum operation processing of the first signal generated in step S31and the second signal generated in step S32, and calculates the vibration rectification error.

Next, in step S33, the signal processing device400determines whether or not the calculation of the required number of vibration rectification errors has been completed.

When the calculation of the required number of vibration rectification errors has not been completed, the signal processing device400changes the phase shift amount in step S34, and repeats the processing after step S32until the calculation of the required number of vibration rectification errors is completed.

1-8. Specific Example of Calculated Vibration Rectification Error Information

Below, a specific example in which the signal processing device400acquires the count value CT1input to the first low-pass filter310in the physical quantity measurement device2of the sensor module1as a source signal to plot a plurality of calculated vibration errors will be given.

FIGS.21to24are diagrams illustrating frequency spectrum obtained by performing FFT on the source signal acquired under four measurement condition. The cantilever resonance frequency of the physical quantity sensor200is 850 Hz, and as illustrated inFIG.21, the signal component due to the cantilever resonance included in the source signal acquired under the first measurement condition has a high intensity. Further, as illustrated inFIG.22, the signal component due to the cantilever resonance included in the source signal acquired under the second measurement condition has a slightly lower intensity than the signal component due to the cantilever resonance included in the source signal acquired under the first measurement condition. Further, as illustrated inFIG.23, the signal component due to the cantilever resonance included in the source signal acquired under the third measurement condition is even smaller than the signal component due to the cantilever resonance included in the source signal acquired under the second measurement condition. Further, as illustrated inFIG.24, the signal component due to the cantilever resonance included in the source signal acquired under the fourth measurement condition is even smaller than the signal component due to the cantilever resonance included in the source signal acquired under the third measurement condition.

FIGS.25to27are diagrams plotting the vibration rectification error VRE(k) obtained by the product-sum operation with k=1 to 2048 and N=2048 by using the source signal acquired under each of the four measurement conditions. InFIGS.25to27, the horizontal axis is k, the vertical axis is VRE(k), and VRE(k) is standardized so that the difference between the maximum value and the minimum value is a constant value. InFIGS.25to27, the equation of the product-sum operation used to calculate the vibration rectification error VRE(k) is different.

FIG.25is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (3). InFIG.25, A1is a vibration rectification error VRE(k) obtained by using the source signal acquired under the first measurement condition. A2is a vibration rectification error VRE(k) obtained by using the source signal acquired under the second measurement condition. A3is a vibration rectification error VRE(k) obtained by using the source signal acquired under the third measurement condition. A4is a vibration rectification error VRE(k) obtained by using the source signal acquired under the fourth measurement condition. In any of A1to A4, the periodicity of the vibration rectification error VRE(k) cannot be clearly confirmed.

FIG.26is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (4). InFIG.26, B1is a vibration rectification error VRE(k) obtained by using the source signal acquired under the first measurement condition. B2is a vibration rectification error VRE(k) obtained by using the source signal acquired under the second measurement condition. B3is a vibration rectification error VRE(k) obtained by using the source signal acquired under the third measurement condition. B4is a vibration rectification error VRE(k) obtained by using the source signal acquired under the fourth measurement condition. The noise component included in the first signal is reduced by performing the smoothing filtering process on the processing target signal, and the periodicity of the vibration rectification error VRE(k) can be confirmed in B1to B3. The distance between two adjacent maximum values of the vibration rectification error VRE (k) corresponds to the period of cantilever resonance. In B4, the periodicity of the vibration rectification error VRE (k) is unclear. Further, it can be seen from B1to B4that the larger the signal component due to the cantilever resonance included in the source signal, the clearer the periodicity of the vibration rectification error VRE(k). InFIGS.21and22, the source signal includes a signal component having a frequency of ½ of the cantilever resonance frequency, and due to the influence of this signal component, the maximum value of the vibration rectification error VRE(k) increases or decreases in B1and B2.

FIG.27is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (5). InFIG.27, C1is a vibration rectification error VRE (k) obtained by using the source signal acquired under the first measurement condition. C2is a vibration rectification error VRE (k) obtained by using the source signal acquired under the second measurement condition. C3is a vibration rectification error VRE (k) obtained by using the source signal acquired under the third measurement condition. C4is a vibration rectification error VRE (k) obtained by using the source signal acquired under the fourth measurement condition. The noise component included in the first signal is reduced by performing the smoothing filtering process on the processing target signal, the noise component included in the second signal is reduced by performing the smoothing filtering process on the phase-shifted signal of the processing target signal, and in any of C1to C4, the periodicity of the vibration rectification error VRE (k) can be confirmed. Further, as compared with B1to B4ofFIG.26, the periodicity of the vibration rectification error VRE(k) is clearer in C1to C4. Further, it can be seen from C1to C4that the larger the signal component due to the cantilever resonance included in the source signal, the clearer the periodicity of the vibration rectification error VRE(k).

In any ofFIGS.25to27, the periodicity of the vibration rectification error VRE(k) is clear in the order of the first measurement condition, the second measurement condition, the third measurement condition, and the fourth measurement condition, and it can be seen that the larger the signal component due to cantilever resonance, the higher the detection accuracy of the signal component.

FIGS.28to30are diagrams plotting the vibration rectification error VRE(k) obtained by the product-sum operation in 4 cases of N=2048, 512, 128, and 32 with k=1 to 2048 by using the source signal acquired under the second measurement condition. InFIGS.28to30, the horizontal axis is k, the vertical axis is VRE(k), and VRE(k) is standardized so that the difference between the maximum value and the minimum value is a constant value. InFIGS.28to30, the equation of the product-sum operation used to calculate the vibration rectification error VRE(k) is different.

FIG.28is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (3). InFIG.28, D1is the vibration rectification error VRE(k) obtained with N=2048. D2is the vibration rectification error VRE(k) obtained with N=512. D3is the vibration rectification error VRE(k) obtained with N=128. D4is the vibration rectification error VRE(k) obtained with N=32. In any of D1to D4, the periodicity of the vibration rectification error VRE(k) cannot be clearly confirmed.

FIG.29is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (4). InFIG.29, E1is the vibration rectification error VRE(k) obtained with N=2048. E2is the vibration rectification error VRE(k) obtained with N=512. E3is the vibration rectification error VRE(k) obtained with N=128. E4is the vibration rectification error VRE(k) obtained with N=32. The noise component included in the first signal is reduced by performing the smoothing filtering process on the processing target signal, and the periodicity of the vibration rectification error VRE(k) can be confirmed in E1. In E2to E4, the number of additions N of the product-sum operation is insufficient, and the periodicity of the vibration rectification error VRE(k) is unclear.

FIG.30is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (5). InFIG.30, F1is the vibration rectification error VRE(k) obtained with N=2048. F2is the vibration rectification error VRE(k) obtained with N=512. F3is the vibration rectification error VRE(k) obtained with N=128. F4is the vibration rectification error VRE(k) obtained with N=32. The noise component included in the first signal is reduced by performing the smoothing filtering process on the processing target signal, the noise component included in the second signal is reduced by performing the smoothing filtering process on the phase-shifted signal of the processing target signal, and in F1, the periodicity of the vibration rectification error VRE(k) can be clearly confirmed compared with E1inFIG.29. In F2to F4, the number of additions N of the product-sum operation is insufficient, and the periodicity of the vibration rectification error VRE(k) is unclear.

FIGS.31to33are diagrams plotting the vibration rectification error VRE(k) obtained by the product-sum operation in 4 cases of N=2048, 512, 128, and 32 with k=1 to 2048 by using the source signal acquired under the first measurement condition. InFIGS.31to33, the horizontal axis is k, the vertical axis is VRE(k), and VRE(k) is standardized so that the difference between the maximum value and the minimum value is a constant value. InFIGS.31to33, the equation of the product-sum operation used to calculate the vibration rectification error VRE(k) is different.

FIG.31is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (3). InFIG.31, G1is the vibration rectification error VRE(k) obtained with N=2048. G2is the vibration rectification error VRE(k) obtained with N=512. G3is a vibration rectification error VRE(k) obtained with N=128. G4is the vibration rectification error VRE(k) obtained with N=32. In any of G1to G4, the periodicity of the vibration rectification error VRE(k) cannot be clearly confirmed.

FIG.32is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (4). InFIG.32, H1is the vibration rectification error VRE(k) obtained with N=2048. H2is the vibration rectification error VRE(k) obtained with N=512. H3is the vibration rectification error VRE(k) obtained with N=128. H4is the vibration rectification error VRE(k) obtained with N=32. The noise component included in the first signal is reduced by performing the smoothing filtering process on the processing target signal, and the periodicity of the vibration rectification error VRE(k) can be confirmed in H1to H3. In H4, the number of additions N of the product-sum operation is insufficient, and the periodicity of the vibration rectification error VRE(k) is unclear. Further, since the signal component due to the cantilever resonance included in the source signal is larger than that in the case ofFIG.29, it can be seen that the periodicity of the vibration rectification error VRE (k) is clearer in H1to H3as compared with E1to E3inFIG.29.

FIG.33is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (5). InFIG.33, I1is the vibration rectification error VRE(k) obtained with N=2048. I2is the vibration rectification error VRE(k) obtained with N=512. I3is the vibration rectification error VRE(k) obtained with N=128. I4is the vibration rectification error VRE(k) obtained with N=32. The noise component included in the first signal is reduced by performing the smoothing filtering process on the processing target signal, the noise component included in the second signal is reduced by performing the smoothing filtering process on the phase-shifted signal of the processing target signal, and in any of I1to I4, the periodicity of the vibration rectification error VRE(k) can be confirmed. Further, as compared with H1to H4inFIG.32, in I1to I4, the periodicity of the vibration rectification error VRE(k) can be clearly confirmed. Further, since the signal component due to the cantilever resonance included in the source signal is larger than that in the case ofFIG.30, it can be seen that the periodicity of the vibration rectification error VRE(k) is clearer in I1to I4as compared with E1to E4inFIG.30.

In any ofFIGS.28to33, the periodicity of the vibration rectification error VRE(k) is clear in the order of N=2048, 512, 128, and 32, and it can be seen that the larger the number of additions N in the product-sum operation processing, the higher the detection accuracy of the signal component due to the cantilever resonance.

1-9. Operational Effects

As described above, the first signal based on the processing target signal generated based on the source signal output from the sensor module1and the second signal based on the phase-shifted signal of the processing target signal include a signal component having periodicity generated by the sensor module1, specifically, a signal component due to cantilever resonance, in common. Therefore, ergodic signal components such as noise are attenuated by the product-sum operation processing of the first signal and the second signal, while the signal components due to cantilever resonance strengthen or weaken each other according to the phase difference between the first signal and the second signal. As a result, the plurality of vibration rectification errors obtained by performing the product-sum operation processing a plurality of times by changing the shift amount have different magnitudes depending on the phase difference between the first signal and the second signal and the period of the signal component due to the cantilever resonance. Therefore, according to the first embodiment, the signal processing device400can detect the signal component due to the cantilever resonance included in the signal output from the sensor module1without performing the envelope processing. The signal processing device400may reduce the measurement error when detecting the periodicity by performing the product-sum operation processing a plurality of times with the same shift amount for a part of the signal processing device400.

Further, according to the first embodiment, since the signal processing device400needs to acquire the source signal for a predetermined time only once in order to calculate a plurality of vibration rectification errors, high-speed arithmetic processing is possible, and environmental changes such as temperature changes in a short time when the source signal is acquired are extremely small, calculation errors caused by environmental changes are reduced.

Further, according to the first embodiment, if the first signal is a signal obtained by smoothing and filtering the processing target signal, the high-frequency noise components included in the first signal are reduced, and if the second signal is a signal obtained by smoothing and filtering the phase-shifted signal of the processing target signal, the high-frequency noise components included in the second signal are reduced, and therefore the detection accuracy of the signal components due to cantilever resonance is improved.

Further, according to the first embodiment, if the first signal is a signal obtained by removing or reducing the DC component of the processing target signal, each sample value of the first signal becomes smaller, and if the second signal is a signal obtained by removing or reducing the DC component of the phase-shifted signal of the processing target signal, each sample value of the second signal becomes smaller, and therefore the load of the product-sum operation of the first signal and the second signal is reduced, and the calculation accuracy is improved.

Further, according to the first embodiment, by making the number of additions N in the product-sum operation processing larger than the value obtained by dividing the sampling frequency of the source signal by the cantilever resonance frequency, the signal components due to the cantilever resonance included in the first signal and the second signal are integrated for one period or more, and therefore the signal components are effectively detected.

2. Second Embodiment

Hereinafter, regarding a second embodiment, the same components as those in the first embodiment are designated by the same reference numerals, the description overlapping with the first embodiment will be omitted or simplified, and the contents different from those in the first embodiment will be mainly described.

In the first embodiment, the smoothing filtering process is used as a filtering process for a processing target signal or a phase-shifted signal of the processing signal. When the source signal includes a signal component having a frequency of ½ of the cantilever resonance frequency, the smoothing filtering process does not reduce the signal component, and therefore, the maximum value of the vibration rectification error VRE(k) such as C1inFIG.27increases or decreases and is not constant. Therefore, in the second embodiment, as the filtering process for the processing target signal and the phase-shifted signal of the processing signal, by using the band-limiting filtering process in which only the vicinity of the cantilever resonance frequency is set as a passing region, the influence of the signal component having the frequency of ½ of the cantilever resonance frequency on the calculated vibration rectification error VRE(k) is reduced.

For example, when the first signal is a signal obtained by the band-limiting filtering process of the processing target signal and the second signal is the phase-shifted signal itself of the processing target signal, the k-th vibration rectification error VRE(k) is calculated by Equation (6). In Equation (6), fBPF(S(i)) is the i-th sample value of the first signal, and S(i+k) is the i-th sample value of the second signal.
VRE(k)=(1/N)Σi=0N−1fBPF(s(i))·s(i+k)  (6)

Further, for example, when the first signal is a signal obtained by the band-limiting filtering process of the processing target signal and the second signal is a signal obtained by the smoothing filtering process of the phase-shifted signal of the processing target signal, the k-th vibration rectification error VRE(k) is calculated by Equation (7). In Equation (7), fBPF(S(i)) is the i-th sample value of the first signal, and fLPF(S(i+k)) is the i-th sample value of the second signal.
VRE(k)=(1/N)Σi=0N−1fBPF(s(i))·fLPF(s(i+k))  (7)

In Equations (6) and (7), division by N may be omitted. Further, in Equations (6) and (7), the first signal obtained by the band-limiting filtering process of the processing target signal is used, but the second signal obtained by the band-limiting filtering process of the phase-shifted signal of the processing target signal may be used.

Since the procedure of the signal processing method of the second embodiment is the same as that ofFIG.19, the illustration and description thereof will be omitted. Further, since the configuration of the signal processing device400of the second embodiment is the same as that ofFIG.18, the illustration and description thereof will be omitted.

FIGS.34and35are diagrams plotting the vibration rectification error VRE(k) obtained by the product-sum operation with k=1 to 2048 and N=2048 by using the source signal acquired under each of the four measurement conditions. InFIGS.34and35, the horizontal axis is k, the vertical axis is VRE(k), and VRE(k) is standardized so that the difference between the maximum value and the minimum value is a constant value. InFIGS.34and35, the equation of the product-sum operation used to calculate the vibration rectification error VRE (k) is different.

FIG.34is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of Equation (6). InFIG.34, J1is the vibration rectification error VRE(k) obtained by using the source signal acquired under the first measurement condition described above. J2is the vibration rectification error VRE(k) obtained by using the source signal acquired under the second measurement condition described above. J3is a vibration rectification error VRE(k) obtained by using the source signal acquired under the third measurement condition described above. J4is a vibration rectification error VRE(k) obtained by using the source signal acquired under the fourth measurement condition described above. The noise components included in the first signal are reduced by performing the band-limiting filtering process of the processing target signal, and the periodicity of the vibration rectification error VRE(k) can be confirmed in J1to J3. The distance between two adjacent maximum values of the vibration rectification error VRE(k) corresponds to the period of cantilever resonance. In J4, the periodicity of the vibration rectification error VRE(k) is unclear. Further, it can be seen from J1to J4that the larger the signal component due to the cantilever resonance included in the source signal, the clearer the periodicity of the vibration rectification error VRE(k). Further, since the band-limiting filtering process is performed on the processing target signal, the signal components having a frequency of ½ of the cantilever resonance frequency are reduced, in J1and J2, the increase and decrease range of the maximum value of the vibration rectification error VRE(k) is smaller compared with B1and B2inFIG.26.

FIG.35is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of Equation (7). InFIG.35, K1is a vibration rectification error VRE(k) obtained by using the source signal acquired under the first measurement condition. K2is a vibration rectification error VRE(k) obtained by using the source signal acquired under the second measurement condition. K3is a vibration rectification error VRE(k) obtained by using the source signal acquired under the third measurement condition. K4is a vibration rectification error VRE(k) obtained by using the source signal acquired under the fourth measurement condition. The noise components included in the first signal are reduced by performing the band-limiting filtering process on the processing target signal, the noise component included in the second signal is reduced by performing the smoothing filtering process on the phase-shifted signal of the processing target signal, and in any of K1to K4, the periodicity of the vibration rectification error VRE(k) can be confirmed. Further, it can be seen from K1to K4that the larger the signal component due to the cantilever resonance included in the source signal, the clearer the periodicity of the vibration rectification error VRE(k). Further, since the band-limiting filtering process is performed on the processing target signal, the signal components having a frequency of ½ of the cantilever resonance frequency are reduced, in K1and K2, the increase and decrease range of the maximum value of the vibration rectification error VRE(k) is smaller compared with C1and C2inFIG.27.

FIGS.36and37are diagrams plotting the vibration rectification error VRE(k) obtained by the product-sum operation in 4 cases of N=2048, 512, 128, and 32 with k=1 to 2048 by using the source signal acquired under the second measurement condition. InFIGS.36and37, the horizontal axis is k, the vertical axis is VRE(k), and VRE(k) is standardized so that the difference between the maximum value and the minimum value is a constant value. InFIGS.36and37, the equation of the product-sum operation used to calculate the vibration rectification error VRE (k) is different.

FIG.36is a plot of the vibration rectification error VRE(k) obtained by the product-sum operation of Equation (6). InFIG.36, L1is the vibration rectification error VRE(k) obtained with N=2048. L2is the vibration rectification error VRE(k) obtained with N=512. L3is the vibration rectification error VRE(k) obtained with N=128. L4is the vibration rectification error VRE(k) obtained with N=32. The noise components included in the first signal are reduced by performing the band-limiting filtering process of the processing target signal, and the periodicity of the vibration rectification error VRE(k) can be confirmed in L1and L2. In L3and L4, the number of additions N of the product-sum operation is insufficient, and the periodicity of the vibration rectification error VRE(k) is unclear. Further, since the band-limiting filtering process is performed on the processing target signal, the signal components having a frequency of ½ of the cantilever resonance frequency are reduced, in L1, the increase and decrease range of the maximum value of the vibration rectification error VRE(k) is smaller compared with E1inFIG.29.

FIG.37is a plot of the vibration rectification error VRE(k) obtained by the product-sum operation of Equation (7). InFIG.37, M1is the vibration rectification error VRE(k) obtained with N=2048. M2is the vibration rectification error VRE(k) obtained with N=512. M3is the vibration rectification error VRE(k) obtained with N=128. M4is the vibration rectification error VRE(k) obtained with N=32. The noise component included in the first signal is reduced by performing the band-limiting filtering process on the processing target signal, the noise component included in the second signal is reduced by performing the smoothing filtering process on the phase-shifted signal of the processing target signal, and in M1to M3, the periodicity of the vibration rectification error VRE(k) can be confirmed. Further, as compared with L1and L2inFIG.36, in M1and M2, the periodicity of the vibration rectification error VRE(k) can be clearly confirmed. In M4, the number of additions N of the product-sum operation is insufficient, and the periodicity of the vibration rectification error VRE(k) is unclear. Further, since the band-limiting filtering process is performed on the processing target signal, the signal components having a frequency of ½ of the cantilever resonance frequency are reduced, in M1, the increase and decrease range of the maximum value of the vibration rectification error VRE(k) is smaller compared with F1inFIG.30.

FIGS.38and39are diagrams plotting the vibration rectification error VRE(k) obtained by the product-sum operation in 4 cases of N=2048, 512, 128, and 32 with k=1 to 2048 by using the source signal acquired under the first measurement condition. InFIGS.38and39, the horizontal axis is k, the vertical axis is VRE(k), and VRE(k) is standardized so that the difference between the maximum value and the minimum value is a constant value. InFIGS.38and39, the equation of the product-sum operation used to calculate the vibration rectification error VRE (k) is different.

FIG.38is a plot of the vibration rectification error VRE(k) obtained by the product-sum operation of Equation (6). InFIG.38, N1is the vibration rectification error VRE(k) obtained with N=2048. N2is the vibration rectification error VRE(k) obtained with N=512. N3is the vibration rectification error VRE(k) obtained with N=128. N4is the vibration rectification error VRE(k) obtained with N=32. The noise components included in the first signal are reduced by performing the band-limiting filtering process of the processing target signal, and the periodicity of the vibration rectification error VRE(k) can be confirmed in N1to N3. In N4, the number of additions N of the product-sum operation is insufficient, and the periodicity of the vibration rectification error VRE(k) is unclear. Further, since the signal component due to the cantilever resonance included in the source signal is larger than that in the case ofFIG.36, it can be seen that the periodicity of the vibration rectification error VRE(k) is clearer in N1to N3as compared with L1to L3inFIG.36. Further, since the band-limiting filtering process is performed on the processing target signal, the signal components having a frequency of ½ of the cantilever resonance frequency are reduced, in N1to N3, the increase and decrease range of the maximum value of the vibration rectification error VRE(k) is smaller compared with H1to H3inFIG.32.

FIG.39is a plot of the vibration rectification error VRE(k) obtained by the product-sum operation of Equation (7). InFIG.39, O1is the vibration rectification error VRE(k) obtained with N=2048. O2is the vibration rectification error VRE(k) obtained with N=512. O3is the vibration rectification error VRE(k) obtained with N=128. O4is the vibration rectification error VRE(k) obtained with N=32. The noise component included in the first signal is reduced by performing the band-limiting filtering process on the processing target signal, the noise component included in the second signal is reduced by performing the smoothing filtering process on the phase-shifted signal of the processing target signal, and in any of O1to O4, the periodicity of the vibration rectification error VRE(k) can be confirmed. Further, as compared with N1to N4inFIG.38, in O1to O4, the periodicity of the vibration rectification error VRE(k) can be clearly confirmed. Further, since the signal component due to the cantilever resonance included in the source signal is larger than that in the case ofFIG.37, it can be seen that the periodicity of the vibration rectification error VRE(k) is clearer in O1to O4as compared with M1to M4inFIG.37. Further, since the band-limiting filtering process is performed on the processing target signal, the signal components having a frequency of ½ of the cantilever resonance frequency are reduced, in M1to M4, the increase and decrease range of the maximum value of the vibration rectification error VRE(k) is smaller compared with I1to14inFIG.33.

According to the second embodiment described above, the same effect as that of the first embodiment is obtained. Further, according to the second embodiment, if the first signal is a signal obtained by the band-limiting filtering process of the processing target signal, many signal components other than the signal component of the resonance frequency included in the first signal are reduced, and if the second signal is a signal obtained by the band-limiting filtering process of the phase-shifted signal of the processing target signal, many signal components other than the signal component of the resonance frequency included in the second signal are reduced, and therefore the detection accuracy of the signal component of the resonance frequency is improved.

Hereinafter, regarding a third embodiment, the same components as those of the first embodiment or the second embodiment are designated by the same reference numerals, the description overlapping with the first embodiment or the second embodiment is omitted or simplified, and the contents different from the first embodiment and the second embodiment will be mainly described.

In the first embodiment and the second embodiment, when a part of the time-series signal included in the source signal is cut out to generate the processing target signal, in the first signal based on the processing target signal and the second signal based on the phase-shifted signal of the processing target signal, the first sample value and the last sample value become discontinuous, and due to the noise caused by this discontinuity, the accuracy of the vibration rectification error obtained by the product-sum operation may decrease. Therefore, in the third embodiment, in order to alleviate the discontinuity of the sample values, it is assumed that the first signal is a signal obtained by applying a window function to the processing target signal, or the second signal is a signal obtained by applying a window function to the phase-shifted signal of the processing target signal. The type of the window function is not particularly limited, and examples of the window function include a Hanning window function, a rectangular window function, a Gaussian window function, a Hamming window function, a Blackman window function, and a Kaiser window function.

The first signal may be a signal obtained by filtering the processing target signal and applying a window function. For example, the filtering process may be a smoothing filtering process or a band-limiting filtering process. Further, the first signal may be a signal obtained by removing or reducing the DC component of the processing target signal and applying a window function. Further, the first signal may be a signal obtained by removing or reducing the DC component of the processing target signal, filtering the signal, and applying a window function.

The second signal may be a signal obtained by filtering the phase-shifted signal of the processing target signal and applying a window function to the signal. For example, the filtering process may be a smoothing filtering process or a band-limiting filtering process. Further, the second signal may be a signal obtained by removing or reducing the DC component from the phase-shifted signal of the processing target signal and applying a window function to the signal. Further, the second signal may be a signal obtained by removing or reducing the DC component of the phase-shifted signal of the processing target signal, filtering the signal, and applying a window function.

Further, for example, when the first signal is a signal obtained by removing or reducing the DC component of the processing target signal filtering the signal, and applying a window function to the signal, and the second signal is a signal obtained by the smoothing filtering process of the phase-shifted signal of the processing target signal, the k-th vibration rectification error VRE(k) is calculated by Equation (8). In Equation (8), Fwindowis a window function. Further, Fwindow(i)·fLPF(S(i))) is the i-th sample value of the first signal, and fLPF(S(i+k)) is the i-th sample value of the second signal.
VRE(k)=(1/N)Σi=0N−1Fwindow(i)·fLPF(fHPF(s(i)))·fLPF(s(i+k))  (8)

In Equation (8), division by N may be omitted. Further, in Equation (8), the first signal obtained by applying a window function to the processing target signal is used, but the second signal obtained by applying a window function to the phase-shifted signal of the processing target signal may be used.

Since the procedure of the signal processing method of the third embodiment is the same as that ofFIG.19, the illustration and description thereof will be omitted. Further, since the configuration of the signal processing device400of the third embodiment is the same as that ofFIG.18, the illustration and description thereof will be omitted.

FIG.40is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation with k=1 to 2048 and N=256 by using the source signal acquired under the second measurement condition. InFIG.40, the horizontal axis is k, the vertical axis is VRE(k), and VRE(k) is standardized so that the difference between the maximum value and the minimum value is a constant value. InFIG.40, the equation of the product-sum operation used to calculate the vibration rectification error VRE(k) is different.

InFIG.40, P1is a vibration rectification error VRE(k) obtained by Equation (8) with the window function Fwindowas the Hanning window function. P2is the vibration rectification error VRE(k) obtained by the above Equation (5). Since the discontinuity of the sample value is alleviated by applying a window function to the processing target signal, the periodicity of the vibration rectification error VRE(k) of P1is clearer than that of P2.

According to the third embodiment described above, the same effect as that of the first embodiment or the second embodiment is obtained. Further, according to the third embodiment, if the first signal is a signal obtained by applying a window function to the processing target signal, the discontinuity between the first sample value and the last sample value of the first signal is alleviated, and if the second signal is a signal obtained by applying a window function to the phase-shifted signal of the processing target signal, the discontinuity between the first sample value and the last sample value of the second signal is alleviated, and therefore the detection accuracy of signal component having periodicity is improved.

Hereinafter, regarding a fourth embodiment, the same components as any of the first to third embodiments are designated by the same reference numerals, the description overlapping with any of the first to third embodiments is omitted or simplified, and the contents different from those of the first to third embodiments will be mainly described.

FIG.41is a diagram illustrating a configuration example of the signal processing device400of the fourth embodiment. As illustrated inFIG.41, the signal processing device400includes the processing circuit410, a storage circuit420, the operation unit430, the display unit440, the sound output unit450, and the communication unit460. The signal processing device400may have a configuration in which some of the components ofFIG.41are omitted or changed, or other components are added.

Since the configurations and functions of the storage circuit420, the operation unit430, the display unit440, the sound output unit450, and the communication unit460are the same as those of any one of the first to third embodiments, the description thereof will be omitted.

By executing the signal processing program421, the processing circuit410functions as a source signal acquisition circuit411, a processing target signal generation circuit412, a vibration rectification error calculation circuit413, a resonance frequency calculation circuit414, and a determination circuit415. That is, the signal processing device400includes a source signal acquisition circuit411, a processing target signal generation circuit412, a vibration rectification error calculation circuit413, a resonance frequency calculation circuit414, and a determination circuit415.

Since the functions of the source signal acquisition circuit411, the processing target signal generation circuit412, and the vibration rectification error calculation circuit413are the same as those of any one of the first to third embodiments, the description thereof will be omitted.

The resonance frequency calculation circuit414calculates the resonance frequency of the sensor module1which is an object, based on a plurality of vibration rectification errors calculated by the vibration rectification error calculation circuit413. The resonance frequency of the sensor module1calculated by the resonance frequency calculation circuit414is stored in the storage circuit420as a resonance frequency424. For example, the resonance frequency of the sensor module1is the cantilever resonance frequency. Specifically, the resonance frequency calculation circuit414reads out the vibration rectification error information423stored in the storage circuit420to acquire two k values k1and k2in which the vibration rectification error VRE(k) becomes two continuous maximum values or two continuous minimum values. Assuming that the frequency of the measured signal SIN is fx, the resonance frequency calculation circuit414can calculate a cantilever resonance frequency fCL, by Equation (9).

The resonance frequency calculation circuit414may acquire three or more k values that are three or more continuous maximum values or three or more continuous minimum values to calculate a plurality of cantilever resonance frequencies by Equation (9) and calculate the average value thereof as the cantilever resonance frequency fCL.

The determination circuit415determines whether the resonance frequency calculated by the resonance frequency calculation circuit414is correct or not based on the difference between the maximum value and the minimum value of the plurality of vibration rectification errors calculated by the vibration rectification error calculation circuit413. The determination result by the determination circuit415is stored in the storage circuit420as a determination result425. Specifically, the resonance frequency calculation circuit414reads out the vibration rectification error information423stored in the storage circuit420to acquire the maximum value and the minimum value of the vibration rectification error VRE(k) and calculate the difference therebetween. The determination circuit415compares the difference between the maximum value and the minimum value with a predetermined threshold value, and when the difference is larger than the threshold value, determines that the calculated resonance frequency is correct, and when the difference is smaller than the threshold value, determines that the calculated resonance frequency is incorrect. That is, the determination circuit415determines that the resonance frequency is correct because the resonance frequency calculated in an environment in which the cantilever resonance is sufficiently excited is highly reliable.

Further, since the sensitivity of the physical quantity sensor200strongly correlates with the cantilever resonance frequency, the determination circuit415can also check the abnormal sensitivity of the physical quantity sensor200based on the resonance frequency calculated by the resonance frequency calculation circuit414. For example, if the weight fixed to the cantilever is missing for some reason, the mass of the cantilever decreases and the cantilever resonance frequency is shifted to a high frequency. At the same time, the sensitivity of the physical quantity sensor200decreases, and the sensitivity of the physical quantity sensor200becomes abnormal. Further, when the cantilever is damaged by a strong impact or the like, the sensitivity of the physical quantity sensor200becomes abnormal and the cantilever resonance frequency is also shifted. Therefore, identifying the cantilever resonance frequency is one method for determining whether or not the sensitivity of the physical quantity sensor200is within the specifications. Accordingly, the determination circuit415can determine whether or not the sensitivity of the physical quantity sensor200is within the specifications depending on whether or not the resonance frequency calculated by the resonance frequency calculation circuit414is within a predetermined frequency range.

The RAM of the storage circuit420stores signals generated by the processing circuit410such as the processing target signal422, the vibration rectification error information423, the resonance frequency424, and the determination result425, and calculated information.

The display unit440may display information including an image obtained by plotting the vibration rectification error information423, the resonance frequency424, and the determination result425based on the display signal output from the processing circuit410.

At least a part of the source signal acquisition circuit411, the processing target signal generation circuit412, the vibration rectification error calculation circuit413, the resonance frequency calculation circuit414, and the determination circuit415may be realized by dedicated hardware. Further, the signal processing device400may be a single device or may be composed of a plurality of devices. Further, for example, the processing circuit410and the storage circuit420are realized by a device such as a cloud server, and the device may calculate the vibration rectification error information423, the resonance frequency424, and the determination result425to transmit the calculated vibration rectification error information423, resonance frequency424, and determination result425to a terminal including an operation unit430, the display unit440, the sound output unit450, and the communication unit460via a communication line.

FIG.42is a flowchart illustrating a procedure of a signal processing method of the fourth embodiment.

As illustrated inFIG.42, the signal processing method of the fourth embodiment includes a source signal acquisition step S1, a processing target signal generation step S2, a vibration rectification error calculation step S3, and a resonance frequency calculation step S4, a determination step S5. The signal processing method of the present embodiment is performed by, for example, the signal processing device400.

First, the signal processing device400performs the source signal acquisition step S1, the processing target signal generation step S2, and the vibration rectification error calculation step S3in the same manner as in any of the first to third embodiments.

Next, in the resonance frequency calculation step S4, the signal processing device400calculates the resonance frequency of the sensor module1which is an object, based on the plurality of vibration rectification errors calculated in step S3.

Finally, in the determination step S5, the signal processing device400determines whether the resonance frequency calculated in step S4is correct or not based on the difference between the maximum value and the minimum value of the plurality of vibration rectification errors calculated in step S3. Further, in the determination step S5, the signal processing device400may determine whether or not the sensitivity of the physical quantity sensor200is within the specifications based on the resonance frequency calculated in step S4.

In the determination step S5, the signal processing device400may calculate the difference between the maximum value and the minimum value of the plurality of vibration rectification errors calculated in step S3to output the value of the difference as an index for determining whether the resonance frequency is correct or not, instead of determining whether the resonance frequency is correct or not. In this case, the signal processing device400may determine whether the resonance frequency is correct or not based on the determination index.

FIGS.43and44are diagrams plotting the vibration rectification error VRE(k) obtained by the product-sum operation with k=1 to 2048 and N=2048 by using the source signal acquired under each of the four measurement conditions. InFIGS.43and44, the horizontal axis is k, and the vertical axis is VRE(k). InFIGS.43and44, the equation of the product-sum operation used to calculate the vibration rectification error VRE (k) is different.

FIG.43is diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (4). InFIG.43, Q1is a vibration rectification error VRE(k) obtained by using the source signal acquired under the first measurement condition. Q2is a vibration rectification error VRE(k) obtained by using the source signal acquired under the second measurement condition. Q3is a vibration rectification error VRE(k) obtained by using the source signal acquired under the third measurement condition. Q4is a vibration rectification error VRE(k) obtained by using the source signal acquired under the fourth measurement condition.

FIG.44is a diagram plotting the vibration rectification error VRE(k) obtained by the product-sum operation of the above Equation (5). InFIG.44, R1is a vibration rectification error VRE(k) obtained by using the source signal acquired under the first measurement condition. R2is a vibration rectification error VRE(k) obtained by using the source signal acquired under the second measurement condition. R3is a vibration rectification error VRE(k) obtained by using the source signal acquired under the third measurement condition. R4is a vibration rectification error VRE(k) obtained by using the source signal acquired under the fourth measurement condition.

For example, in the signal processing device400, in Q1, Q2, R1, and R2, the difference between the maximum value and the minimum value of VRE(k) is larger than the threshold value, and therefore it is determined that the resonance frequency calculated by using VRE(k) of Q1, Q2, R1, and R2is correct, and it is determined whether or not the sensitivity of the physical quantity sensor200is within the specifications based on the calculated resonance frequency. On the other hand, in Q3, Q4, R3and R4, the difference between the maximum value and the minimum value of VRE(k) is smaller than the threshold value, and the signal processing device400uses VRE(k) of Q3, Q4, R3and R4to determine that the calculated resonance frequency is not correct.

According to the fourth embodiment described above, the same effects as those of the first to third embodiments are obtained. Further, according to the fourth embodiment, since the signal processing device400calculates the cantilever resonance frequency, the user or the signal processing device400can perform various analyses based on the cantilever resonance frequency.

Further, according to the fourth embodiment, the larger the cantilever resonance is excited, the larger the difference between the maximum value and the minimum value of the calculated plurality of vibration rectification errors becomes, and therefore the signal processing device400can determine whether the calculated cantilever resonance frequency is correct or not based on the difference. For example, only when it is determined that the calculated cantilever resonance frequency is correct, the user or the signal processing device400can perform various analyses based on the cantilever resonance frequency, for example, determine whether or not the sensitivity of the physical quantity sensor200is within the specifications.

Hereinafter, regarding a fifth embodiment, the same components as any of the first to fourth embodiments are designated by the same reference numerals, the description overlapping with any of the first to fourth embodiments is omitted or simplified, and the contents different from those of the first to fourth embodiments will be mainly described.

As described with reference toFIGS.16A to16D, in the frequency ratio measurement circuit202included in the physical quantity measurement device2of the sensor module1, the vibration rectification error changes at regular periods with respect to the change in the group delay amount of the first low-pass filter310. This period is determined by the cantilever resonance frequency and the frequency of the physical quantity detection element40, and when the cantilever resonance frequency or the frequency of the physical quantity detection element40changes, the fluctuation period of the vibration rectification error also changes. Therefore, by measuring the period of the change in the vibration rectification error with respect to the change in the group delay amount of the first low-pass filter310, it is possible to obtain a determination index as to whether or not the sensitivity of the physical quantity sensor200is within the specifications. Therefore, in the fifth embodiment, a plurality of vibration rectification errors are generated by changing the group delay amount of the first low-pass filter310.

In the fifth embodiment, since the structure and functional configuration of the sensor module1are the same as those inFIGS.1to8, the description thereof will be omitted.

In the fifth embodiment, the physical quantity measurement device2of the sensor module1has a normal operation mode for measuring the frequency ratio between the measured signal SIN and the reference signal CLK described above, and an inspection mode for checking the sensitivity of the physical quantity sensor200. When the micro-control unit210receives a predetermined command from the signal processing device400via the interface circuit230, the physical quantity measurement device2is set to the normal operation mode or the inspection mode. For example, in the manufacturing step of the sensor module1, the signal processing device400may set the physical quantity measurement device2to the inspection mode, and the physical quantity measurement device2may check the sensitivity of the physical quantity sensor200. The signal processing device400may select non-defective products of the sensor module1based on the result of the sensitivity check. Alternatively, after the sensor module1is installed and before operation, the signal processing device400may set the physical quantity measurement device2to the inspection mode, and the physical quantity measurement device2may check the sensitivity of the physical quantity sensor200. If there is no abnormality in the sensitivity of the physical quantity sensor200based on the result of the sensitivity check, the signal processing device400sets the physical quantity measurement device2to the normal operation mode and operates the sensor module1. In the normal operation mode, the measurement value with the vibration rectification error corrected can be obtained. Further, the signal processing device400may periodically set the physical quantity measurement device2to the inspection mode, and the physical quantity measurement device2may check the sensitivity of the physical quantity sensor200. The normal operation mode is an example of a “first operation mode”, and the inspection mode is an example of a “second operation mode”.

In the inspection mode, the physical quantity sensor200is operated in a stable vibration environment, and the micro-control unit210of the physical quantity measurement device2functions as a control circuit to acquire the group delay amount dependence of the vibration rectification error based on the output signal of the physical quantity sensor200while changing the group delay amount of the first low-pass filter310. Therefore, first, the micro-control unit210sets the cutoff frequency of the second low-pass filter330to be lower than that in the normal operation mode. Specifically, the micro-control unit210sets the cutoff frequency of the second low-pass filter330to, for example, several Hz so that the vibration rectification error included in the output value of the second low-pass filter330is emphasized. For example, the micro-control unit210may set the cutoff frequency to be lower than that in the normal operation mode by increasing the number of taps of the second low-pass filter330.

Further, the micro-control unit210acquires the vibration rectification error of the measurement value while sequentially changing the number of taps na with respect to the first low-pass filter310having the configuration illustrated inFIG.14, and stores the number of taps and the vibration rectification error in the storage unit220in association with each other.

The signal processing device400reads out the correspondence information between the number of taps and the vibration rectification error from the storage unit220via the interface circuit230to calculate the period in which the vibration rectification error changes from a graph plotting the relationship between the number of taps and the vibration rectification error as illustrated inFIG.17. Since this period is determined by the cantilever resonance frequency and the frequency of the physical quantity detection element40, the signal processing device400can back-calculate the cantilever resonance frequency. The signal processing device400can determine whether or not the sensitivity of the physical quantity sensor200is within the specifications based on the calculated cantilever resonance frequency.

Alternatively, the micro-control unit210may read out the correspondence information between the number of taps and the vibration rectification error from the storage unit220to calculate the cantilever resonance frequency based on the graph plotting the relationship between the number of taps and the vibration rectification error and determine whether or not the sensitivity of the physical quantity sensor200is within the specifications.

The first low-pass filter310is an example of the “first filter”. The second low-pass filter330is an example of the “second filter”.

FIG.45is a flowchart illustrating an example of a procedure of a signal processing method of the fifth embodiment.

As illustrated inFIG.45, first, when the normal operation mode is set in step S110, the physical quantity measurement device2measures the frequency ratio of the measured signal SIN and the reference signal CLK in step S120.

In step S130, the physical quantity measurement device2repeats step S120until the measurement is completed.

When the normal operation mode is not set in step S110and the inspection mode is set in step S140, in step S150, the physical quantity measurement device2sets the cutoff frequency of the second low-pass filter330to be lower than that in the normal operation mode.

Next, in step S160, the physical quantity measurement device2sets the group delay amount of the first low-pass filter310to a predetermined value. Specifically, the physical quantity measurement device2sets the number of taps na to a predetermined value.

Next, in step S170, the physical quantity measurement device2acquires the output value of the second low-pass filter330.

Next, in step S180, the physical quantity measurement device2determines whether or not all the output values of the second low-pass filter330necessary for the sensitivity determination have been acquired.

When the acquisition of the required output value is not completed, the physical quantity measurement device2changes the group delay amount of the first low-pass filter310in step S190. Specifically, the physical quantity measurement device2changes the number of taps na.

When the acquisition of the required output value is completed, in step S200, the signal processing device400or the physical quantity measurement device2calculates the period of change in the vibration rectification error by using the output values of the plurality of second low-pass filters330acquired in the step S170.

Next, in step S210, the signal processing device400or the physical quantity measurement device2calculates the cantilever resonance frequency from the period of change in the vibration rectification error.

Next, in step S220, the signal processing device400or the physical quantity measurement device2determines whether or not the sensitivity of the physical quantity sensor200is within the specifications based on the cantilever resonance frequency.

In step S230, the inspection mode of the physical quantity measurement device2is terminated, and steps S110and subsequent steps are repeated.

In the fifth embodiment described above, in the normal operation mode of the physical quantity measurement device2, as described in the first embodiment, the first low-pass filter310operates in synchronization with the measured signal SIN, and the second low-pass filter330operates in synchronization with the reference signal CLK different from the measured signal SIN, and therefore non-linearity occurs in the relationship between the frequency delta-sigma modulated signal input to the first low-pass filter310and the output signal of the second low-pass filter330. The vibration rectification error caused by this non-linearity changes according to the group delay amount of the first low-pass filter310. Therefore, according to the fifth embodiment, in the normal operation mode of the physical quantity measurement device2, by setting the group delay amount of the first low-pass filter310to an appropriate value, the vibration rectification error caused by this non-linearity and the vibration rectification error caused by the asymmetry of the measured signal SIN cancel each other out, and the vibration rectification error included in the output signal of the second low-pass filter330is reduced.

On the other hand, in the inspection mode of the physical quantity measurement device2, by setting the cutoff frequency of the second low-pass filter330to be lower than that in the normal operation mode, the vibration rectification error included in the signal output from the second low-pass filter330is emphasized. Therefore, by acquiring the output signal of the second low-pass filter330while changing the group delay amount of the first low-pass filter310, information indicating the relationship between the group delay amount and the vibration rectification error can be obtained. The period of change in the vibration rectification error included in this information correlates with the period of the signal component due to the cantilever resonance included in the measured signal SIN. Therefore, according to the fifth embodiment, in the inspection mode of the physical quantity measurement device2, it is possible to detect the signal component having periodicity included in the measured signal SIN without performing the envelope processing. Further, for example, the physical quantity measurement device or the signal processing device400can calculate the cantilever resonance frequency of the physical quantity sensor200by using the information indicating the relationship between the group delay amount and the vibration rectification error to determine whether or not the sensitivity of the physical quantity sensor200is within the specifications based on the cantilever resonance frequency.

6. Modification Example

The present disclosure is not limited to the present embodiment, and various modifications can be made within the scope of the gist of the present disclosure.

For example, in each of the above embodiments, the sensor module1includes three physical quantity sensors200, but the number of the physical quantity sensors200included in the sensor module1may be one, two, or four or more.

In addition, in each of the above embodiments, as the physical quantity sensor200, the sensor module1provided with an acceleration sensor is described as an example, but the sensor module1may include sensors such as an angular velocity sensor, a pressure sensor, and an optical sensor as the physical quantity sensor200. In addition, the sensor module1may be provided with two or more types of physical quantity sensors among various physical quantity sensors such as an acceleration sensor, an angular velocity sensor, a pressure sensor, and an optical sensor.

In addition, in each of the above embodiments, an element configured by using quartz crystal as the physical quantity detection element40included in the physical quantity sensor200is given as an example, but the physical quantity detection element40may be configured by using a piezoelectric element other than quartz crystal, or may be a capacitance type MEMS element. MEMS is an abbreviation for micro electro mechanical systems.

The present disclosure is not limited to the present embodiment, and various modifications can be made within the scope of the gist of the present disclosure.

The above embodiments and modification examples are merely examples, and the present disclosure is not limited thereto. For example, it is possible to appropriately combine each embodiment and each modification example.

The present disclosure includes substantially the same configuration as the configuration described in the embodiments (for example, a configuration having the same function, method, and result, or a configuration having the same object and effect). In addition, the present disclosure includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present disclosure includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the present disclosure includes a configuration in which a known technique is added to the configuration described in the embodiment.

The following contents are derived from the above-described embodiments and modification examples.

The signal processing method according to one aspect includes a processing target signal generation step of generating a processing target signal which is a time-series signal based on a source signal which is a time-series signal output from an object, and a vibration rectification error calculation step of performing product-sum operation processing of a first signal based on the processing target signal and a second signal based on a phase-shifted signal of the processing target signal a plurality of times by changing a shift amount to calculate a plurality of vibration rectification errors.

In this signal processing method, the first signal based on the processing target signal generated based on the source signal and the second signal based on the phase-shifted signal of the processing target signal include the signal component having periodicity generated by the object in common. Therefore, ergodic signal components such as noise are attenuated by the product-sum operation processing of the first signal and the second signal, while the signal components having periodicity strengthen or weaken each other according to the phase difference between the first signal and the second signal. As a result, the plurality of vibration rectification errors obtained by performing the product-sum operation processing a plurality of times by changing the shift amount have different magnitudes depending on the phase difference between the first signal and the second signal and the period of the signal components having periodicity. Therefore, according to this signal processing method, it is possible to detect a signal component having periodicity included in a signal output from an object without performing envelope processing.

Further, according to this signal processing method, since it is necessary to acquire the source signal for a predetermined time only once in order to calculate a plurality of vibration rectification errors, high-speed arithmetic processing is possible, and environmental changes such as temperature changes in a short time when the source signal is acquired are extremely small, calculation errors caused by environmental changes are reduced.

In the signal processing method according to one aspect, the first signal may be a signal obtained by filtering the processing target signal.

According to this signal processing method, the noise components included in the first signal are reduced by the filtering process, and therefore the detection accuracy of the signal component having periodicity is improved.

In the signal processing method according to one aspect, the second signal may be a signal obtained by filtering a phase-shifted signal of the processing target signal.

According to this signal processing method, the noise components included in the second signal are reduced by the filtering process, and therefore the detection accuracy of the signal component having periodicity is improved.

In the signal processing method according to one aspect, the filtering process may be a smoothing filtering process.

According to this signal processing method, the smoothing filtering process reduces the high-frequency noise components included in the first signal or the second signal, and therefore the detection accuracy of the signal component having periodicity is improved.

In the signal processing method according to one aspect, the filtering process may be a band-limiting filtering process.

According to this signal processing method, the band-limiting filtering process reduces many signal components other than the signal components having periodicity included in the first signal and the second signal, and therefore the detection accuracy of signal components having periodicity is improved.

In the signal processing method according to one aspect, the first signal may be a signal obtained by removing or reducing the DC component of the processing target signal.

According to this signal processing method, each sample value of the first signal becomes smaller, and therefore the load of the product-sum operation of the first signal and the second signal is reduced, and the calculation accuracy is improved.

In the signal processing method according to one aspect, the second signal may be a signal obtained by removing or reducing the DC component of the phase-shifted signal of the processing target signal.

According to this signal processing method, each sample value of the second signal becomes smaller, and therefore the load of the product-sum operation of the first signal and the second signal is reduced, and the calculation accuracy is improved.

In the signal processing method according to one aspect, the first signal may be a signal obtained by applying a window function to the processing target signal.

According to this signal processing method, because the discontinuity between the first sample value and the last sample value of the first signal is alleviated, the detection accuracy of the signal component having periodicity is improved.

In the signal processing method according to one aspect, the second signal may be a signal obtained by applying a window function to a phase-shifted signal of the processing target signal.

According to this signal processing method, because the discontinuity between the first sample value and the last sample value of the second signal is alleviated, the detection accuracy of the signal component having periodicity is improved.

In the signal processing method according to one aspect, the number of additions in the product-sum operation processing may be larger than a value obtained by dividing a sampling frequency of the source signal by a resonance frequency of the object.

According to this signal processing method, in the product-sum operation processing, the signal components of the resonance frequency of the object included in the first signal and the second signal are integrated for one period or more, and therefore the signal component of the resonance frequency is effectively detected.

The signal processing method according to one aspect may further include a resonance frequency calculation step of calculating a resonance frequency of the object based on the plurality of vibration rectification errors.

According to this signal processing method, the resonance frequency of the object is calculated, and therefore the user can perform various analyses based on the resonance frequency.

The signal processing method according to one aspect may further include a determination step of determining whether the calculated resonance frequency is correct or not based on the difference between a maximum value and a minimum value of the plurality of vibration rectification errors.

In this signal processing method, the larger the resonance is excited in the object, the larger the difference between the maximum value and the minimum value of the calculated plurality of vibration rectification errors becomes, and therefore it is possible to determine whether the calculated resonance frequency is correct or not based on the difference. According to this signal processing method, for example, the user can perform various analyses based on the resonance frequency only when it is determined that the calculated resonance frequency is correct.

The signal processing device according to one aspect includes a processing target signal generation circuit that generates a processing target signal which is a time-series signal based on a source signal which is a time-series signal output from an object, and a vibration rectification error calculation circuit that performs product-sum operation processing of a first signal based on the processing target signal and a second signal based on the phase-shifted signal of the processing target signal a plurality of times by changing a shift amount to generate a plurality of vibration rectification errors.

In this signal processing device, the first signal based on the processing target signal generated based on the source signal and the second signal based on the phase-shifted signal of the processing target signal include a signal component having periodicity output from the object in common. Therefore, ergodic signal components such as noise are attenuated by the product-sum operation processing of the first signal and the second signal, while the signal components having periodicity strengthen or weaken each other according to the phase difference between the first signal and the second signal. As a result, the plurality of vibration rectification errors obtained by performing the product-sum operation processing a plurality of times by changing the shift amount have different magnitudes depending on the phase difference between the first signal and the second signal and the period of the signal components having periodicity. Therefore, according to this signal processing device, it is possible to detect a signal component having periodicity included in a signal output from an object without performing envelope processing.

Further, according to this signal processing device, since it is necessary to acquire the source signal for a predetermined time only once in order to calculate a plurality of vibration rectification errors, high-speed arithmetic processing is possible, and environmental changes such as temperature changes in a short time when the source signal is acquired are extremely small, calculation errors caused by environmental changes are reduced.

The physical quantity measurement device according to one aspect includes a reference signal generation circuit that outputs a reference signal, a frequency delta-sigma modulation circuit that performs frequency delta-sigma modulation on the reference signal by using a measured signal to generate a frequency delta-sigma modulated signal, a first filter that operates in synchronization with the measured signal and has a variable group delay amount, and a second filter that operates in synchronization with the reference signal, in which the first filter is provided on a signal path from an output of the frequency delta-sigma modulation circuit to an input of the second filter, and the physical quantity measurement device has a first operation mode for measuring a frequency ratio of the measured signal and the reference signal, and a second operation mode in which a cutoff frequency of the second filter is lower than that in the first operation mode.

In this physical quantity measurement device, in the first operation mode, the first filter operates in synchronization with the measured signal, and the second filter operates in synchronization with a reference signal different from the measured signal, and therefore non-linearity occurs in the relationship between the frequency delta-sigma modulated signal and the output signal of the second filter. The vibration rectification error caused by this non-linearity changes according to the group delay amount of the first filter. Therefore, according to this physical quantity measurement device, in the first operation mode, by setting the group delay amount of the first filter to an appropriate value, the vibration rectification error caused by this non-linearity and the vibration rectification error caused by the asymmetry of the measured signal cancel each other out, and the vibration rectification error included in the output signal of the second filter is reduced.

Further, in this physical quantity measurement device, in the second operation mode, by setting the cutoff frequency of the second filter to be lower than that in the first operation mode, the vibration rectification error included in the signal output from the second filter is emphasized. Therefore, by acquiring the output signal of the second filter while changing the group delay amount of the first filter, information indicating the relationship between the group delay amount and the vibration rectification error can be obtained. The period of change in the vibration rectification error included in this information correlates with the period of the signal component having periodicity included in the measured signal. Therefore, according to this physical quantity measurement device, in the second operation mode, it is possible to detect the signal component having periodicity included in the measured signal without performing the envelope processing.

The sensor module according to one aspect includes the physical quantity measurement device according to still another aspect, and a physical quantity sensor, in which the measured signal is a signal based on an output signal of the physical quantity sensor.

According to this sensor module, by providing the physical quantity measurement device, in the first operation mode, a highly accurate measurement value of the physical quantity with reduced vibration rectification error can be obtained, and in the second operation mode, the signal component of the resonance frequency generated by the structural resonance of the physical quantity sensor can be detected.