Oscillator

Abstract

To provide an oscillator which can stably oscillate an oscillating body under environment with disturbance.SOLUTION: An oscillator 3 comprises: an A / D converter 31 to which an oscillation signal is input to convert the oscillation signal into a digital signal to be output; a band pass filter 32 to which the digital signal is input to attenuate frequency components except a specific frequency band component in the digital signal; a phase generator 40 which generates a phase of a feedback signal on the basis of the specific frequency band component having passed through the band pass filter 32; and a signal generator 36 which generates the feedback signal on the basis of the phase generated by the phase generator 40.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an oscillator. [Background technology]

[0002] A sensor that detects a physical quantity (acceleration, viscosity, flow rate, etc.) based on the vibration frequency of a vibrating body includes a receiving section (e.g., a piezoelectric element) that detects vibration and outputs a vibration signal, an exciting section (e.g., a piezoelectric element) that vibrates based on a feedback signal, and an oscillator that vibrates the exciting section. In general, in order to vibrate the exciting section, a sensor acquires a vibration signal from the receiving section and positively feeds back the feedback signal to the exciting section. A vibrating body has natural modes in addition to the fundamental mode used to detect the physical quantity. The natural modes can be excited by external disturbances. For this reason, the oscillator must selectively oscillate only in the fundamental mode.

[0003] Patent Document 1 discloses a driving circuit (oscillator) for a piezoelectric actuator that has an amplifier circuit that applies a driving voltage to a piezoelectric actuator that vibrates a vibrating body and inputs a detection signal generated according to the driving voltage to the piezoelectric actuator, and the driving circuit has a bandpass filter that passes the fundamental resonance frequency of a piezoelectric device formed by attaching a piezoelectric actuator to a vibrating body in a positive feedback circuit that provides positive feedback to the amplifier circuit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-83767 A Summary of the Invention [Problem to be solved by the invention]

[0005] In oscillators, generally, band-pass filters such as those described above are used to selectively oscillate only the fundamental mode. However, since the oscillator must satisfy the oscillation conditions, there are restrictions on the phase delay characteristics. Specifically, the phase delay characteristics of the oscillator must be designed according to the characteristics of the vibrating body. If the band-pass filter is given high selectivity, an excessive phase delay will occur, causing a mismatch in the phase relationship between the oscillator and the vibrating body, and the oscillation conditions will not be satisfied. Therefore, there are restrictions on the phase delay characteristics in the design of the band-pass filter, and it is difficult to give the band-pass filter high selectivity. Therefore, there is room for improvement in terms of the vibration of the vibrating body in an environment with external disturbances.

[0006] An object of one aspect of the present invention is to provide an oscillator that can stably vibrate a vibrating body even in an environment with external disturbances. [Means for solving the problem]

[0007] An oscillator according to one aspect of the present invention is an oscillator that acquires a vibration signal, which is an analog signal output from a receiving part of a vibrating body, generates a feedback signal, which is an analog signal, from the vibration signal, and outputs the feedback signal to a vibration part of the vibrating body.The oscillator includes an A / D converter that inputs the vibration signal and converts the vibration signal into a digital signal and outputs it, a band-pass filter that inputs the digital signal and attenuates frequency components in the digital signal other than a specific frequency band component, a phase generator that generates the phase of the feedback signal based on the specific frequency band component that has passed through the band-pass filter, and a signal generator that generates the feedback signal based on the phase generated by the phase generator.

[0008] In an oscillator according to one aspect of the present invention, the phase delay depends only on the vibration frequency. Therefore, in the oscillator, the phase generator generates the phase of the feedback signal based on the specific frequency band component that has passed through the band-pass filter, and the signal generator generates the feedback signal based on the phase. This allows the oscillator to be configured not to depend on the phase delay characteristics of the band-pass filter. Therefore, the oscillator can have a high selectivity in the band-pass filter. As a result, the oscillator can stably vibrate the vibrating body even in an environment with external disturbances.

[0009] In one embodiment, the phase generator may have a phase detector that detects an instantaneous phase of a frequency band component that has passed through the band pass filter, a frequency detector that detects the frequency of the frequency band component, and a phase shift calculator that calculates a phase shift based on the frequency detected by the frequency detector, and may generate the phase of the feedback signal based on the instantaneous phase detected by the phase detector and the phase shift calculated by the phase shift calculator. In this configuration, the phase of the feedback signal can be generated.

[0010] In one embodiment, the phase shift calculator may calculate a phase shift amount for correcting at least a phase delay caused by the band pass filter and the phase detector. In this configuration, the phase delay caused by the band pass filter and the phase detector can be canceled. Effect of the Invention

[0011] According to one aspect of the present invention, it is possible to stably vibrate a vibrating body in an environment with external disturbances. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic perspective view of a tuning fork sensor including an oscillator according to one embodiment. [Diagram 2] FIG. 2 is a diagram showing a configuration of an oscillator. [Diagram 3] FIG. 3 is a diagram showing a configuration of an oscillator according to another embodiment. [Figure 4] FIG. 4 is a diagram for explaining how to obtain the instantaneous phase. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0014] 1 is a schematic perspective view of a tuning fork sensor including an oscillator according to one embodiment. The tuning fork sensor 100 includes a tuning fork vibrator (vibrator) 1 configured to change its natural frequency (vibration frequency) according to the magnitude of a load F applied to a load receiving portion 16, an oscillator 3 that drives the tuning fork vibrator 1, and a load measuring portion 5 (see FIG. 2) that measures the magnitude of the load F based on the vibration frequency of the tuning fork vibrator 1.

[0015] The tuning fork vibrator 1 is composed of two rectangular plate-shaped vibrating bars 1a and 1b arranged parallel to each other, U-shaped connecting portions 2a and 2b that connect both ends of the vibrating bars 1a and 1b in the longitudinal direction LD, and thin plate-shaped support pieces 3a and 3b that support the vibrating part composed of the vibrating bars 1a and 1b and the connecting portions 2a and 2b on both sides in the longitudinal direction LD.

[0016] Piezoelectric elements 4a, 4b are attached to both side surfaces of one of the coupling parts (coupling part 2b in this case) of the tuning fork vibrator 1 by, for example, adhesive bonding or vapor deposition. The piezoelectric elements 4a, 4b are respectively connected to the output and input parts of an oscillator 3 installed externally. This allows the piezoelectric element 4a to operate as an excitation part for vibrating the tuning fork vibrator 1 at a constant frequency. In other words, the piezoelectric element 4a functions as a vibration part that vibrates the tuning fork vibrator 1 at a constant frequency. The piezoelectric element 4b operates as a pickup for detecting the vibration of the tuning fork vibrator 1. In other words, the piezoelectric element 4b functions as a vibration receiving part that detects the vibration waveform of the tuning fork vibrator 1.

[0017] The tuning fork sensor 100 has a lever portion 10 and a base portion 11 as a transmission mechanism for transmitting the load F of the load receiving portion 16 to the tuning fork vibrator 1. One end of the tuning fork vibrator 1 in the longitudinal direction LD is connected to one end of the lever portion 10 via a support piece 3a. The one end of the lever portion 10 constitutes a force point 12 in the lever portion 10. The other end of the tuning fork vibrator 1 in the longitudinal direction LD is attached to the base portion 11 via a support piece 3b. The lever portion 10 is supported by a thin-walled fulcrum 13 connected to the base portion 11. The other end of the lever portion 10 on the opposite side of the fulcrum 13 from the force point 12 constitutes a weight point 14. The load receiving portion 16 is suspended from the weight point 14 via a thin-plate tensile piece 15. With this configuration, the load F applied to the load receiving portion 16 pulls the tuning fork vibrator 1 via the lever portion 10. The magnitude of the force that the load F exerts on the tuning fork vibrator 1 is adjusted by the ratio of the distance from the fulcrum 13 to the point of force 12 and the distance from the fulcrum 13 to the point of force 14, and the like.

[0018] Next, a description will be given of the oscillator 3. The oscillator 3 vibrates the vibrating elements 1a and 1b at a constant frequency.

[0019] 2, the oscillator 3 includes a first amplifier 30, an A / D converter 31, a band-pass filter 32, a Hilbert transformer (phase detector) 33, a frequency detector 34, a phase shift calculator 35, a signal generator 36, a D / A converter 37, and a second amplifier 38. The Hilbert transformer 33, the frequency detector 34, and the phase shift calculator 35 constitute a phase generator 40. Each of the first amplifier 30 and the second amplifier 38 may be configured with an operational amplifier. Each of the A / D converter 31 and the D / A converter 37 may be configured with a dedicated IC or a peripheral function of a CPU or the like. Each of the band-pass filter 32, the signal generator 36, and the phase generator 40 may be configured with a microprocessor such as a CPU, a DSP, or an FPGA.

[0020] The first amplifier 30 receives a voltage waveform (vibration signal) that is an analog signal acquired via the piezoelectric element 4b, and amplifies the voltage waveform at a predetermined amplification factor. The first amplifier 30 outputs the voltage waveform to the A / D converter 31. The first amplifier 30 constitutes an input section of the oscillator 3.

[0021] The A / D converter 31 converts the voltage waveform (vibration waveform detected by the piezoelectric element 4b) output from the first amplifier 30 into a digital signal at a predetermined constant sampling frequency. For example, the A / D converter 31 may be configured as an electronic circuit that performs a known A / D conversion process on the input analog signal and outputs the converted digital signal. The A / D converter 31 outputs the digital signal to the band-pass filter 32.

[0022] The band-pass filter 32 is a digital circuit that inputs the digital signal converted by the A / D converter 31 and attenuates frequency components outside a predetermined band of the digital signal. That is, the band-pass filter 32 passes only a predetermined specific frequency band component in the digital signal. Here, a band set based on the natural frequency of a vibration mode (here, the first mode) that is predetermined as a vibration mode used for load measurement and a change in frequency according to a predetermined measurable load can be set as the above-mentioned "predetermined band". That is, in this embodiment, the frequency band required for the load measurement described above can be set as the above-mentioned "predetermined band". The digital signal (digital signal of a specific frequency component) that has passed through the band-pass filter 32 is output to a Hilbert transformer 33 and a frequency detector 34.

[0023] The Hilbert transformer 33 detects the instantaneous phase of the digital signal. The Hilbert transformer 33 executes the following first and second processes for detecting the instantaneous phase.

[0024] (First Processing) The Hilbert transformer 33 receives the digital signal D that has passed through the band-pass filter 32. The digital signal D is expressed, for example, by the following equation (1). D = A cos(θ-φ1(f)) … (1) Here, A represents the amplitude, θ represents the phase of the digital signal, and φ1(f) represents the phase delay of the band-pass filter 32.

[0025] The Hilbert transformer 33 generates a complex digital signal C=D1+jD2 (j is an imaginary unit) from the digital signal D. The Hilbert transformer 33 obtains a first digital signal D1, which is the real part of the complex digital signal C, and obtains a second digital signal D2, which is the imaginary part of the complex digital signal C, by performing a Hilbert transform on the digital signal D. The circuit for executing the first processing is composed of a known digital circuit including, for example, an FIR filter, a delay circuit, and the like. The digital circuit has a phase delay characteristic, and generates a phase delay in the first digital signal D1 and the second digital signal D2. The digital signal D, the first digital signal D1, and the second digital signal D2 are expressed, for example, as in the following formulas (2) and (3). D1=A·cos(θ-φ1(f)-φ2(f)) …(2) D2=A sin(θ-φ1(f)-φ2(f)) …(3) Here, A represents the amplitude, θ represents the phase of the digital signal, φ1(f) represents the phase delay of the band-pass filter 32, and φ2(f) represents the phase delay of the digital circuit that executes the first processing.

[0026] (Second Processing) Next, the Hilbert transformer 33 calculates the phase angle θ-φ1(f)-φ2(f) based on the ratio (D2 / D1) between the first digital signal D1 and the second digital signal D2 obtained by the first processing. Specifically, the Hilbert transformer 33 calculates the arctangent (tan -1 ) is calculated to calculate the phase angle θ-φ1(f)-φ2(f). The phase angle θ-φ1(f)-φ2(f) is the instantaneous phase of the digital signal.

[0027] The frequency detector 34 is a digital circuit that receives the digital signal that has passed through the band-pass filter 32 and detects the frequency of the digital signal. The frequency detector 34 can be configured as a digital circuit that performs a known frequency detection process on the received digital signal and detects the frequency. The frequency detector 34 obtains, for example, one period of the digital signal and detects the frequency from the period. The frequency detector 34 outputs a signal related to the frequency to the phase shift calculator 35.

[0028] The phase shift calculator 35 is a digital circuit that receives the signal related to the frequency output from the frequency detector 34 and calculates the phase shift based on the frequency. In this embodiment, the phase shift calculator 35 calculates the phase shift to correct the phase delay caused by the band pass filter 32 and the Hilbert transformer 33. The phase shift calculator 35 calculates the phase shift to cancel the phase delay (-φ1(f)-φ2(f)) caused by the band pass filter 32 and the Hilbert transformer 33. Both φ1(f) and φ2(f) are known functions with the frequency determined at the time of design as a parameter, so the phase shift calculator 35 can calculate φ1(f) and φ2(f) by substituting the input frequency. The phase shift calculator 35 calculates the phase shift based on the input frequency and the known functions φ1(f) and φ2(f).

[0029] The phase generator 40 generates a phase based on the instantaneous phase detected by the Hilbert transformer 33 and the phase shift amount calculated by the phase shift amount calculator 35. The phase generator 40 outputs a signal related to the phase to the signal generator 36.

[0030] The signal generator 36 receives the signal related to the phase generated by the phase generator 40 and generates a feedback signal based on the phase. The signal generator 36 is realized by calculating an arbitrary periodic function. If the output of the phase generator 40 is ψ(t), the signal generator 36 generates a feedback signal of, for example, N·sin(ψ(t)), where N represents the amplitude. The signal generator 36 outputs the feedback signal to the D / A converter 37.

[0031] The D / A converter 37 converts the feedback signal into an analog signal at a predetermined constant sampling frequency. The D / A converter 37 may be configured as an electronic circuit that performs a known D / A conversion process on the digital signal generated by the signal generator 36 and outputs the converted analog signal. The D / A converter 37 outputs the feedback signal, which is an analog signal, to the second amplifier 38.

[0032] The second amplifier 38 receives the feedback signal output from the D / A converter 37 and amplifies the feedback signal at a predetermined amplification factor. The second amplifier 38 outputs the feedback signal to the piezoelectric element 4a. The second amplifier 38 constitutes an output section of the oscillator 3.

[0033] Next, the load measuring unit 5 will be described. The load measuring unit 5 converts an analog signal output from the D / A converter 37 of the oscillator 3 into a digital signal, and specifies the magnitude of the load F based on the digital signal. Specifically, the load measuring unit 5 specifies a vibration frequency of the tuning fork vibrator 1 according to the magnitude of the load F (for example, a natural frequency corresponding to a first mode of vibration) based on the digital signal, and specifies the magnitude of the load F based on the specified vibration frequency. The load measuring unit 5 can be configured by a computer including a processor such as a CPU, a memory, and the like.

[0034] As described above, in the tuning fork sensor 100 according to this embodiment, in the oscillator 3, the phase delay depends only on the vibration frequency. Therefore, in the oscillator 3, the phase generator 40 generates the phase of the feedback signal based on the specific frequency band component that has passed through the band pass filter 32, and the signal generator 36 generates the feedback signal based on this phase. This allows the oscillator 3 to be configured not to depend on the phase delay characteristics of the band pass filter 32. Therefore, in the oscillator 3, the band pass filter 32 can have high selection performance. As a result, in the oscillator 3, the tuning fork vibrator 1 can be stably vibrated even in an environment with external disturbances.

[0035] Although the embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0036] In the above embodiment, an example has been described in which the frequency detector 34 receives a digital signal that has passed through the band-pass filter 32 and detects the frequency of the digital signal. As shown in Fig. 3, the frequency detector 34 may detect the frequency based on the output of a Hilbert transformer 33. The frequency detector 34 may calculate an angular frequency by differentiating the instantaneous phase output from the Hilbert transformer 33, and calculate the frequency from the angular frequency.

[0037] In the above embodiment, the phase detector is described as a Hilbert transformer 33 as an example. However, the configuration of the phase detector (method of detecting the instantaneous phase) is not limited to this. For example, the instantaneous phase can be obtained by the following method. As shown in FIG. 4, first, the period T between the most recent rising zero crossing "1" and the most recent rising zero crossing "2" is calculated. Next, the elapsed time Δt from the current sample to the most recent zero crossing "2" is calculated. Then, the instantaneous phase is calculated by substituting the obtained period T and elapsed time Δt into the following equation.

number

[0038] In addition to the above embodiment, the oscillator 3 may further include an analog filter between the first amplifier 30 and the A / D converter 31. In this case, the phase shift amount calculator 35 calculates the phase shift amount including the phase delay of the analog filter.

[0039] In addition to the above embodiment, the oscillator 3 may further include a band-pass filter between the signal generator 36 and the D / A converter 37. The oscillator 3 may further include an analog filter between the D / A converter 37 and the second amplifier 38 or on the output side of the second amplifier 38.

[0040] In the above embodiment, the vibration receiving unit and the vibration applying unit are each a piezoelectric element. However, the vibration receiving unit and the vibration applying unit may each be, for example, an element that uses electromagnetic force (a coil and a magnet).

[0041] In the above embodiment, the load measuring unit 5 converts the analog signal output from the D / A converter 37 of the oscillator 3 into a digital signal, and identifies the magnitude of the load F based on the digital signal. However, the load measuring unit 5 may identify the magnitude of the load F based on the digital signal output from the signal generator 36. [Explanation of symbols]

[0042] 3...oscillator, 31...A / D converter, 32...bandpass filter, 33...Hilbert transformer, 34...frequency detector, 35...phase shift calculator, 36...signal generator.

Claims

1. An oscillator that acquires a vibration signal, which is an analog signal, output from a receiving portion of a vibrating body, generates a feedback signal, which is an analog signal, from the vibration signal, and outputs the feedback signal to a vibration applying portion of the vibrating body, an A / D converter that receives the vibration signal, converts the vibration signal into a digital signal, and outputs the digital signal; a band pass filter that receives the digital signal and attenuates frequency components other than a specific frequency band component in the digital signal; a phase generator that generates a phase of the feedback signal based on the specific frequency band component that has passed through the band pass filter; a signal generator that generates the feedback signal based on the phase generated by the phase generator.

2. The phase generator includes: a phase detector for detecting an instantaneous phase of the specific frequency band component that has passed through the band pass filter; a frequency detector for detecting a frequency of the specific frequency band component; a phase shift amount calculator that calculates a phase shift amount based on the frequency detected by the frequency detector, 2. The oscillator according to claim 1, further comprising: a phase detector that detects an instantaneous phase of the feedback signal and a phase shift calculator that calculates the phase shift.

3. 3. The oscillator according to claim 2, wherein said phase shift amount calculator calculates said phase shift amount for compensating for at least a phase delay caused by said band pass filter and said phase detector.

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