JP2011047809A - Physical quantity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a physical quantity sensor capable of detecting a predetermined physical quantity with higher detection accuracy, while having a relatively simple configuration. <P>SOLUTION: The physical quantity sensor 1 includes first and second frequency signal generators 10, 20 for generating first and second frequency signals 12, 22 of frequencies corresponding to respective resonance frequencies of first and second resonators 11, 21, respectively; first and second counter portions 30, 40 for counting the respective frequencies of the first and second frequency signals, respectively; a digital calculator 50 for calculating a digital value 52, indicating the difference between frequencies of the first and second frequency signals based on the respective counted values 32, 42 of the first and second counter portions; and a detection signal generator 60 for generating a detection signal 62 of a digital value, corresponding to a physical quantity, based on a digital value 52. The resonance frequency of the second resonator 21 changes with the change in the acceleration, and the frequencies of the first and second frequency signals in a state in which no acceleration is applied do not agree with each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a physical quantity sensor.

  In order to detect physical quantities such as the speed and moving distance of an object, various sensors are used depending on the application. For example, a frequency difference caused by the Doppler effect is generated by emitting a pulse-modulated transmission signal from the transmitter toward the signal reflection surface and receiving the transmission signal scattered by the signal reflection surface at each receiver. For example, a speed sensor that detects the traveling speed of a moving body is known.

  In contrast to this speed sensor, the speed sensor of Patent Document 1 does not require a transmission signal, and detects the speed with a simpler configuration based on signals from two frequency signal generation sources, at least one of which is an acceleration detection piece. Has the advantage of being able to.

JP 2008-76166 A

  However, since the speed sensor of Patent Document 1 performs analog processing on the detection signal with a low-pass filter, noise generated in the analog circuit is superimposed on the final speed value output. Therefore, it may be difficult to use the speed sensor of Patent Document 1 as it is for applications that require high detection accuracy.

  Moreover, since the speed sensor of Patent Document 1 may output an erroneous detection result when the phase difference between two frequency signals exceeds the range of 0 ° to 180 °, the detection sensitivity of the acceleration detection element is high. In some cases it is difficult to apply.

  The present invention has been made in view of the above-described problems. According to some aspects of the present invention, a predetermined physical quantity (speed, A physical quantity sensor capable of detecting a movement distance, acceleration, force, and the like) can be provided.

  (1) The present invention is a physical quantity sensor that detects a predetermined physical quantity, includes a first resonator, and outputs a first frequency signal having a frequency associated with a resonance frequency of the first resonator. A first frequency signal generating unit that generates, and a second resonator that changes a resonance frequency in accordance with a change in acceleration, and a second frequency corresponding to the resonance frequency of the second resonator. A second frequency signal generator for generating a frequency signal; a first count unit for counting the number of periods of the first frequency signal; and a second count unit for counting the number of periods of the second frequency signal And a digital value representing a difference between the number of cycles of the first frequency signal and the number of cycles of the second frequency signal based on the count value of the first count unit and the count value of the second count unit A digital operation unit for calculating And a detection signal generation unit that generates a detection signal of a digital value corresponding to the physical quantity based on the digital value calculated by the control unit, and the frequency of the first frequency signal in a state where no acceleration is applied And the frequency of the second frequency signal match.

  In the state where acceleration is applied to the physical quantity sensor of the present invention, the frequency of the second frequency signal changes according to the applied acceleration, so the count speed of the second count unit also changes according to the added acceleration. Therefore, the difference between the count value of the first count unit and the count value of the first count unit changes while acceleration is applied. On the other hand, in a state where acceleration is not applied to the physical quantity sensor of the present invention (at rest or at a constant speed), the frequency of the first frequency signal and the frequency of the second frequency signal coincide with each other. The count speed of the second count unit also matches. Therefore, if acceleration is not applied, the difference between the count value of the first count unit and the count value of the first count unit does not change. Therefore, according to the physical quantity sensor of the present invention, it is possible to detect physical quantities such as speed, moving distance, and acceleration based on the difference between the count value of the first count unit and the count value of the first count unit.

  The physical quantity sensor of the present invention digitally calculates the difference between the number of periods of the first frequency signal and the number of periods of the second frequency signal based on the count value of the first count unit and the count value of the second count unit. Although it is a relatively simple configuration that is obtained by calculation, the physical quantity can be detected with higher accuracy compared to the case where the physical quantity is detected by analog processing based on the phase difference between the two frequency signals.

  In addition, according to the physical quantity sensor of the present invention, the physical quantity is detected based on the difference between the count value of the first count unit and the count value of the second count unit. Therefore, the first frequency signal and the second frequency signal are detected. Even if the phase difference exceeds 0 ° to 180 °, no erroneous detection result is output. Therefore, an acceleration sensor with high detection sensitivity can be used as the second resonator.

  (2) In this physical quantity sensor, the first resonator may change a resonance frequency in accordance with a change in acceleration.

  (3) In this physical quantity sensor, the first resonator and the second resonator may be arranged such that acceleration detection directions are opposite to each other.

  In the physical quantity sensor of the present invention, the first resonator and the second resonator are both acceleration sensors, and when acceleration is applied, the directions of changes in the resonance frequency are reversed. Therefore, according to the physical quantity sensor of the present invention, the difference between the count value of the first count unit and the count value of the second count unit is larger than when only the second resonator is an acceleration sensor. Therefore, the physical quantity detection sensitivity can be further increased.

  (4) The physical quantity sensor synchronizes the first frequency signal with the clock signal based on a clock signal having a frequency higher than both the frequency of the first frequency signal and the frequency of the second frequency signal. A first synchronization circuit for generating a first synchronized frequency signal, and a second synchronization frequency signal for synchronizing the second frequency signal with the clock signal based on the clock signal And a second synchronization circuit that generates a first synchronization signal based on the first synchronization frequency signal, and counting the number of periods of the first frequency signal. The counting unit may count the number of periods of the second frequency signal based on the second synchronization frequency signal.

  Since the first frequency signal and the second frequency signal are asynchronous, the change point of the count value of the first count unit and the change point of the count value of the second count unit are also asynchronous. In the physical quantity sensor according to the present invention, since the first frequency signal and the second frequency signal are synchronized by the same clock signal having a higher frequency, the number of periods is counted. The change point and the change point of the count value of the second count unit are synchronized. Therefore, according to the physical quantity sensor of the present invention, since the digital calculation can be performed while avoiding the change point of the count value of the first count unit and the change value of the count value of the second count unit, an erroneous detection result Can be reduced.

  (5) In this physical quantity sensor, the detection signal generation unit may multiply the digital value calculated by the digital calculation unit by a predetermined coefficient to generate the detection signal having a digital value corresponding to the speed. Good.

  According to the physical quantity sensor of the present invention, it is possible to detect the speed with higher accuracy compared to the case where the speed is detected by analog processing based on the phase difference between the two frequency signals, although the configuration is relatively simple. it can.

  (6) In this physical quantity sensor, the detection signal generation unit may integrate the velocity signal and generate the detection signal having a digital value corresponding to a moving distance.

  According to the physical quantity sensor of the present invention, the moving distance is detected with higher accuracy than the case of detecting the moving distance by analog processing based on the phase difference between the two frequency signals, although the configuration is relatively simple. be able to.

  (7) In this physical quantity sensor, the detection signal generation unit may differentiate the velocity signal and generate the detection signal having a digital value corresponding to acceleration.

  According to the physical quantity sensor of the present invention, the acceleration can be detected with higher accuracy compared to the case where the acceleration is detected by analog processing based on the phase difference between the two frequency signals, although the configuration is relatively simple. it can.

An example of the block diagram of the physical quantity sensor which concerns on this embodiment. The figure which shows the structure of the speed sensor of 1st Embodiment. The figure which shows the structural example of a crystal oscillator. The figure which shows the structural example of a crystal oscillator. The figure for demonstrating an example of the crystal oscillator in the speed sensor of 1st Embodiment. The timing chart for demonstrating an example of operation | movement of the speed sensor of 1st Embodiment. The timing chart for demonstrating another example of operation | movement of the speed sensor of 1st Embodiment. The figure which shows the structure of the speed sensor of 2nd Embodiment. The figure for demonstrating an example of the crystal oscillator in the speed sensor of 2nd Embodiment. The timing chart figure for demonstrating an example of operation | movement of the speed sensor of 2nd Embodiment. The timing chart for demonstrating another example of operation | movement of the speed sensor of 2nd Embodiment. The figure which shows the structure of the speed sensor of 3rd Embodiment. The figure which shows the structure of the distance sensor of this embodiment. The figure which shows the structure of the acceleration sensor of this embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. Also, not all of the configurations described below are essential constituent requirements of the present invention.

1. Physical Quantity Sensor FIG. 1 is an example of a block diagram of a physical quantity sensor according to this embodiment.

  The physical quantity sensor 1 includes a first frequency signal generator 10. The first frequency signal generation unit 10 includes a first resonator 11 and generates a first frequency signal 12 having a frequency associated with the resonance frequency of the first resonator 11. The first resonator 11 may be a resonator having a constant resonance frequency regardless of whether acceleration is applied, or may be an acceleration sensor in which the resonance frequency changes in accordance with a change in acceleration. .

  The physical quantity sensor 1 includes a second frequency signal generator 20. The second frequency signal generation unit 20 includes a second resonator 21 and generates a second frequency signal 22 having a frequency associated with the resonance frequency of the second resonator 21. The second resonator 21 is an acceleration sensor whose resonance frequency changes according to a change in acceleration, and the frequency of the first frequency signal 12 and the frequency of the second frequency signal 22 in a state where no acceleration is applied are the same. To do. Here, the state where acceleration is not applied may be either a state where the physical quantity sensor 1 is stationary or a state where it is moving at a constant speed.

  Each frequency of the first frequency signal 12 and the second frequency signal 22 only needs to be associated with each resonance frequency of the first resonator 11 and the second resonator 21, respectively. The resonance frequencies of the resonator 11 and the second resonator 21 do not have to coincide with each other. For example, each frequency of the first frequency signal 12 and the second frequency signal 22 is P / Q times the resonance frequencies of the first resonator 11 and the second resonator 21 (P and Q are determined in advance). The frequency may be a predetermined integer).

  The first resonator and the second resonator may be configured by using a vibrator, for example, a single crystal material such as a crystal vibrator, a ceramic vibrator, a lithium niobate vibrator, or a lithium tantalate vibrator. Any of a vibrator using a piezoelectric thin film such as a zinc oxide piezoelectric thin film vibrator or an aluminum oxide piezoelectric thin film vibrator may be used.

  The physical quantity sensor 1 includes a first count unit 30. The first count unit 30 counts the number of periods of the first frequency signal 12.

  The physical quantity sensor 1 includes a second count unit 40. The second count unit 40 counts the number of periods of the second frequency signal 22.

  The physical quantity sensor 1 includes a digital calculation unit 50. Based on the count value 32 of the first count unit 30 and the count value 42 of the second count unit 40, the digital arithmetic unit 50 calculates the number of cycles of the first frequency signal 12 and the number of cycles of the second frequency signal 22. A digital value 52 representing the difference is calculated.

  The physical quantity sensor 1 includes a detection signal generation unit 60. The detection signal generation unit 60 generates a detection signal 62 having a digital value corresponding to a predetermined physical quantity based on the digital value 52 calculated by the digital calculation unit 50. Here, the predetermined physical quantity is, for example, the speed, acceleration, moving distance, force or the like of the physical quantity sensor 1.

  Hereinafter, a speed sensor, a distance sensor, and an acceleration sensor will be taken as an example of the physical quantity sensor, and specific embodiments will be described in order.

2. Speed sensor (first embodiment)
FIG. 2 is a diagram illustrating a configuration of the speed sensor according to the first embodiment.

  The speed sensor 1 </ b> A of the first embodiment includes a crystal oscillator 14. The crystal oscillator 14 includes a crystal resonator 100 and an oscillation circuit 110. In the present embodiment, the crystal unit 100 is configured as a crystal resonator having a constant resonance frequency. FIG. 3 shows a more specific configuration example of the crystal oscillator 14. As shown in FIG. 3, an oscillation loop for oscillating the crystal unit 100 is formed by capacitors 111 and 112, resistors 113 and 114, and an inverter 115 included in the oscillation circuit 110, and the crystal unit 100 has a frequency equal to the resonance frequency. Oscillates. Then, the drive signal of the crystal unit 100, that is, the output signal of the inverter 115 is output as the clock signal 120.

  The crystal oscillator 14 corresponds to the first resonator 11 in FIG. 1, and the clock signal 120 corresponds to the first frequency signal 12 in FIG.

  The speed sensor 1 </ b> A according to the first embodiment includes a crystal oscillator 24. The crystal oscillator 24 includes a crystal resonator 200 and an oscillation circuit 210. In the present embodiment, the crystal unit 200 is configured as a crystal oscillator whose resonance frequency changes according to a change in acceleration. FIG. 4 shows a more specific configuration example of the crystal oscillator 24. As shown in FIG. 4, capacitors 211 and 212, resistors 213 and 214, and an inverter 215 included in the oscillation circuit 210 form an oscillation loop that oscillates the crystal resonator 200. The crystal resonator 200 has a resonance frequency (accelerated acceleration). Oscillates at a frequency equal to Then, the drive signal of the crystal unit 200, that is, the output signal of the inverter 215 is output as the clock signal 220. That is, the crystal oscillator 24 functions as an acceleration sensor in which the frequency of the output signal (clock signal 220) changes according to the acceleration.

  The crystal oscillator 24 corresponds to the second resonator 21 in FIG. 1, and the clock signal 220 corresponds to the second frequency signal 22 in FIG.

  The speed sensor 1 </ b> A according to the first embodiment includes synchronous counters 300 and 400. The synchronous counter 300 is configured as an N-bit counter that counts the number of clocks (cycle number) of the clock signal 120 and outputs an N-bit count value 302. Similarly, the synchronous counter 400 is configured as an N-bit counter that counts the number of clocks (the number of cycles) of the clock signal 220, and outputs an N-bit count value 402.

  The synchronous counters 300 and 400 correspond to the first count unit 30 and the second count unit 40 in FIG. 1, respectively, and the count value 302 and the count value 402 respectively correspond to the count value 32 and the count value 32 in FIG. This corresponds to the count value 42.

  The speed sensor 1A according to the first embodiment includes a subtraction processing unit 500 and a register 510. The subtraction processing unit 500 performs a process of subtracting the other from one of the N-bit count value 302 and the N-bit count value 402 by digital processing, and outputs an N-bit subtraction value 502. The subtraction processing unit 500 may be realized as a dedicated digital circuit, or may be realized by a CPU (Central Processing Unit) executing a subtraction program. The N-bit subtraction value 502 is stored in the register 510 at a predetermined timing, for example, at the falling edge of the clock signal 120.

  The circuit constituted by the subtraction processing unit 500 and the register 510 corresponds to the digital operation unit 50 in FIG. 1, and the subtraction value 512 stored in the register 510 corresponds to the digital value 52 in FIG.

The speed sensor 1 </ b> A according to the first embodiment includes a multiplication processing unit 600. The multiplication processing unit 600 multiplies the N-bit subtraction value 512 and the M-bit predetermined coefficient k by digital processing, and outputs the multiplication result as a speed detection signal 602. A rounding process may be performed as necessary in the calculation of the least significant bit of the multiplication result (speed detection signal 602). The multiplication processing unit 600 may be realized as a dedicated digital circuit, or may be realized by a CPU executing a multiplication program. For example, if α = 2 ⁿ (n is a positive integer), the multiplication processing unit 600 can be realized with a simple configuration as an n-bit shift circuit.

  Note that the multiplication processing unit 600 corresponds to the detection signal generation unit 60 in FIG. 1, and the speed detection signal 602 corresponds to the detection signal 62 in FIG.

  FIG. 5A to FIG. 5C are diagrams for explaining an example of the crystal resonator 200 in the present embodiment. The crystal resonator 200 is configured as a double tuning fork resonator in which the double tuning fork vibrating piece 201 and the cantilever 206 shown in FIGS. 5A to 5C are hermetically sealed inside a package (not shown). . By using a double tuning fork resonator having excellent stability and quick response as the quartz resonator 200, accurate acceleration detection can be performed.

  FIG. 5A is a front view of the double tuning fork vibrating piece 201 and shows a schematic structure of the double tuning fork vibrating piece 201. In FIG. 5A, 202 and 203 are bases, and two vibrating arms 204 and 205 connect them.

  FIG. 5B is a side view showing the double tuning fork vibrating piece 201 fixed to the cantilever 206. In FIG. 5B, the cantilever 206 has a fixed end portion 207 and a free end portion 208, and a connecting portion 209 connects them. The fixed end 207 is fixed to the speed sensor 1A directly or indirectly by a package (not shown). The base 203 of the double tuning fork vibrating piece 201 is fixed to the fixed end 207 of the cantilever 206, and the base 202 of the double tuning fork vibrating piece 201 is fixed to the free end 208 of the cantilever 206.

FIG. 5C shows a change in the shape of the double tuning fork vibrating piece 201 when the speed sensor 1A is accelerated. When the speed sensor 1A accelerates in a direction perpendicular to the axis formed by the fixed end 207, the connecting portion 209, and the free end 208 of the cantilever 206 and in the direction from the cantilever 206 to the double tuning fork vibrating piece 201, Since the inertia force F _i acts on the free end 208 of the cantilever 206 in the direction opposite to the acceleration, the connecting portion 209 of the cantilever 206 bends in the direction opposite to the acceleration.

Double-ended tuning fork resonator element 201 because it is secured to the cantilever 206, compressive force F _s is applied. Resonant frequency of the double-ended tuning fork vibrating reed 201 is reduced by the action of the compressive force F _s. For example, if the resonance frequency of the double tuning fork vibrating piece 201 when the speed sensor 1A is not accelerating is 4000 kHz, the resonance frequency of the double tuning fork vibrating piece 201 in FIG. 5C changes to, for example, 39.99 kHz. To do. The double tuning fork vibrating piece 201 is connected to the oscillation circuit 210 via a connection electrode (not shown), and the oscillation frequency of the crystal oscillator 24 is lowered.

On the contrary, when the speed sensor 1A accelerates in the direction opposite to that in the case of FIG. 5C, the inertial force _Fi also acts in the opposite direction to that in FIG. The pulling force that acts. For example, if the resonance frequency of the double tuning fork vibrating piece 201 when the speed sensor 1A is not accelerating is 4000 kHz, the double tuning fork vibrating piece when the speed sensor 1A is accelerated in the opposite direction to that in FIG. The resonance frequency of 201 changes to 40.01 kHz, for example. Therefore, the oscillation frequency of the crystal oscillator 24 is increased.

  FIG. 6 is a timing chart for explaining an example of the operation of the speed sensor 1A of the present embodiment.

6, the speed sensor 1A is time t ₁ earlier is stationary, accelerated to a time t ₁ ~t ₅ at an acceleration alpha _1, it is after time t ₅ in the timing chart of the case to be moved at a constant speed is there.

6, the time t ₁ before the speed sensor 1A is stationary, the oscillation frequency of the oscillation frequency and a crystal oscillator 24 of the crystal oscillator 14 are equal. Therefore, the frequency of the clock signal 120 and the frequency of the clock signal 220 are also equal.

  The count value 302 is counted up by the synchronous counter 300 performing a count-up operation at the rising edge of the clock signal 120. Similarly, the count value 402 is counted up when the synchronous counter 400 performs a count-up operation at the rising edge of the clock signal 220.

Prior to time t ₁ , the frequency of the clock signal 120 is equal to the frequency of the clock signal 220, so the count-up speed of the count value 302 and the count-up speed of the count value 402 are the same.

  Here, if the subtraction processing unit 500 subtracts the count value 402 from the count value 302 and outputs the subtraction value 502, and the register 510 takes in the subtraction value 502 at the falling edge of the clock signal 120, the subtraction value 512 (register 510 output) remains 0.

When the speed sensor 1A to time _t 1 ~t ₅ acceleration alpha ₁ is applied, since a state where the crystal oscillator 200 shown in FIG. 5 (C), the oscillation frequency of the crystal oscillator 24 is lowered. Therefore, the frequency of the clock signal 220 is lower than the frequency of the clock signal 120. Therefore, at time t _{1 to} t ₅ , the count value 402 is counted up later than the count value 302 is counted up. As a result, the subtraction value 512 increases to 1, 2, and 3 at each timing of times t ₂ , t ₃ , and t ₄ .

At time t _5, the acceleration becomes zero, the speed sensor 1A is to move at a constant speed, the oscillation frequency of the oscillation frequency and a crystal oscillator 24 of the crystal oscillator 14 is equal. Therefore, the frequency of the clock signal 120 and the frequency of the clock signal 220 are also equal. Therefore, after time t _5, the count up of count-up and count value 402 of the count value 302 becomes the same speed. As a result, the subtraction value 512 remains 3 and remains unchanged.

As described above, in the case of FIG. 6, the subtraction value 512 increases to 0, 1, 2, and 3, so that the digital value of the speed detection signal 602 increases stepwise to 0, k, 2k, and 3k. Here, if the coefficient k is set to the speed v ₀ when the subtraction value 512 is 1, the digital value of the speed detection signal 602 is 0 according to the acceleration α _{1 applied} from the time t _{1 to} t _5. The trajectory of the speed rising in three steps from 3 to ₀ is shown.

  FIG. 7 is a timing chart for explaining another example of the operation of the speed sensor 1A of the present embodiment.

7, the speed sensor 1A is time _{t 6} before is constant speed state of after time _{t 5} in FIG. 6, the acceleration-.alpha. ₁ to time _t 6 _{~t 10} (case and opposite and the same size in FIG. 6 decelerates the acceleration), the time t ₁₀ after is a timing chart of the case to be stationary.

7, the time t ₆ before the acceleration is not applied to the velocity sensor 1A, the oscillation frequency of the oscillation frequency and a crystal oscillator 24 of the crystal oscillator 14 are equal. Therefore, the frequency of the clock signal 120 and the frequency of the clock signal 220 are also equal, and the count-up speed of the count value 302 and the count-up speed of the count value 402 are also the same. Accordingly, the subtraction value 512, remains unchanged at 3 is a constant value of after time t ₅ in FIG.

When to time _t 6 _{~t 10} to the speed sensor 1A acceleration-.alpha. ₁ is applied, since the quartz oscillator 200 is in a state bent in FIG. 5 (C) opposite to, the oscillation frequency of the crystal oscillator 24 becomes high. Therefore, the frequency of the clock signal 220 is higher than the frequency of the clock signal 120. Therefore, from time t _{5 to} t ₁₀ , the count value 402 counts up faster than the count value 302 counts up. As a result, the subtraction value 512 decreases to 2, 1, 0 at each timing of times t ₇ , t ₈ , and t ₉ .

At time t _10, the acceleration becomes 0, the speed sensor 1A is stationary, the oscillation frequency of the oscillation frequency and a crystal oscillator 24 of the crystal oscillator 14 is equal. Therefore, the frequency of the clock signal 120 and the frequency of the clock signal 220 are also equal. Therefore, the time _{t 10} after the count up of count-up and count value 402 of the count value 302 becomes the same speed. As a result, the subtraction value 512 remains 0.

As described above, in the case of FIG. 7, the subtraction value 512 decreases to 3, 2, 1, 0, and thus the digital value of the speed detection signal 602 decreases stepwise to 3k, 2k, k, 0. Here, if the coefficient k is set to the aforementioned speed v ₀ , the digital value of the speed detection signal 602 is divided into 3 steps from 3v ₀ to 0 according to the acceleration −α _{1 applied} from time t _{5 to} t _10. Indicates the trajectory of the descending speed.

  As described above, in the state where acceleration is applied to the speed sensor 1A of the first embodiment, the frequency of the clock signal 220 changes according to the applied acceleration, so that the count speed of the synchronous counter 400 is also added. The frequency of the clock signal 120 does not change, but the count speed of the synchronous counter 300 does not change. Therefore, the difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400 changes while acceleration is applied. On the other hand, in the state where acceleration is not applied to the speed sensor 1A of the first embodiment (at rest or at constant speed), the frequency of the clock signal 120 and the frequency of the clock signal 220 coincide with each other. The count speed of the counter 400 also matches. Therefore, if acceleration is not applied, the difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400 does not change. Therefore, according to the speed sensor 1A of the first embodiment, the speed can be detected based on the difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400.

  The speed sensor 1A according to the first embodiment has a relatively simple configuration in which a difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400 is obtained by digital calculation. Compared to the case where the speed is detected by analog processing based on the phase difference, the speed can be detected with higher accuracy.

  Further, according to the speed sensor 1A of the first embodiment, the speed is detected based on the difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400, so that the clock signal 120 and the clock signal 220 are Even if the phase difference exceeds the range of 0 ° to 180 °, an erroneous detection result is not output. Therefore, an acceleration sensor with high detection sensitivity can be used.

(Second Embodiment)
FIG. 8 is a diagram illustrating a configuration of the speed sensor according to the second embodiment.

  The configuration of the speed sensor 1B of the second embodiment is the same as the configuration of the speed sensor 1A of the first embodiment shown in FIGS. However, in the second embodiment, not only the crystal oscillator 24 but also the crystal oscillator 14 is configured as an acceleration sensor. Further, the multiplication processing unit 600 performs a multiplication process with a coefficient (k / 2) that is 1/2 of the coefficient k at the time of multiplication in the speed sensor 1A of the first embodiment.

  FIG. 9A and FIG. 9B are diagrams for explaining an example of the crystal unit 100 and the crystal unit 200 in the present embodiment.

  In the present embodiment, as shown in FIG. 9A, the crystal resonator 100 and the crystal resonator 200 are arranged such that the detection directions are opposite to each other. Here, the crystal resonator 200 in the present embodiment has the same structure as that shown in FIGS. 5A and 5B, and therefore, in FIG. 5 (A) and FIG. 5 (B) are given the same numbers, and the description thereof is omitted. The structure of the crystal unit 100 is the same as that of the crystal unit 200, and the elements 101 to 109 of the crystal unit 100 correspond to the elements 201 to 209 of the crystal unit 200, respectively.

  FIG. 9B shows a change in the shape of the double tuning fork vibrating pieces 101 and 201 when the speed sensor 1B is accelerated. When the speed sensor 1B accelerates in a direction perpendicular to the axis formed by the fixed end 207, the connecting portion 209, and the free end 208 of the cantilever 206 and in the direction from the cantilever 206 to the double tuning fork vibrating piece 201, The change of the double tuning fork vibrating piece 201 is the same as in FIG. 5C, and the resonance frequency of the double tuning fork vibrating piece 201 is lowered. Therefore, the oscillation frequency of the crystal oscillator 24 is lowered.

On the other hand, since the inertia force F _i acts on the free end portion 108 of the cantilever 106 in the opposite direction to the acceleration, the free end portion 108 of the cantilever 106 also bends in the opposite direction to the acceleration. Double-ended tuning fork resonator element 101 because it is secured to the cantilever 106, the tensile force F _s is applied. Resonant frequency of the double-ended tuning fork resonator element 101 is increased by the action of the tensile force F _s. For example, if the resonance frequency of the double tuning fork vibrating piece 101 when the speed sensor 1B is not accelerating is 4000 kHz, the resonance frequency of the double tuning fork vibrating piece 101 in FIG. 9B changes to, for example, 40.01 kHz. To do. The double tuning fork resonator element 101 is connected to the oscillation circuit 110 via a connection electrode (not shown), and the oscillation frequency of the crystal oscillator 14 is increased.

Conversely, when the speed sensor 1A accelerates in the direction opposite to that in FIG. 9B, the inertial force _Fi also acts in the opposite direction to that in FIG. 9B, so that the double tuning fork vibrating piece 201 is extended. A tensile force that acts to compress the double tuning fork vibrating piece 101 acts. By the action of the tensile force and the compressive force, the resonance frequency of the double tuning fork vibrating piece 201 is increased and the resonance frequency of the double tuning fork vibrating piece 101 is lowered. For example, if the resonance frequency of the double tuning fork vibrating pieces 101 and 201 when the speed sensor 1A is not accelerating is 4000 kHz, the double tuning fork when the speed sensor 1A is accelerated in the opposite direction to that in FIG. 9B. The resonance frequency of the vibrating piece 201 changes to, for example, 40.01 kHz, and the resonance frequency of the double tuning fork vibrating piece 101 changes, for example, to 39.99 kHz. Therefore, the oscillation frequency of the crystal oscillator 24 is increased, and the oscillation frequency of the crystal oscillator 14 is decreased.

  As described above, when the crystal resonator 100 and the crystal resonator 200 are arranged so that the detection directions are opposite to each other, the crystal oscillator 14 and the crystal oscillator 24 are oppositely changed in the direction of oscillation frequency. Therefore, in the speed sensor 1B of the second embodiment, the change amount of the subtraction value 502 is twice that of the speed sensor 1A of the first embodiment, so that the speed detection sensitivity can be increased.

  It is preferable that the crystal unit 100 and the crystal unit 200 have the same characteristics. In this way, for example, an error in the frequency difference between the clock signal 120 and the clock signal 220 due to temperature drift can be suppressed, so that stable speed detection can be performed even with respect to temperature changes.

  FIG. 10 is a timing chart for explaining an example of the operation of the speed sensor 1B of the present embodiment.

10, like the case of FIG. 6, the speed sensor 1B are time _{t 1} earlier is stationary, accelerated at time _t 1 ~t ₈ toward acceleration alpha _1, after the time _{t 8} at a constant speed It is a timing chart figure of the case which moves. The size and direction of the acceleration alpha ₁ is the same as the case of FIG. 6, it is assumed the time that the acceleration alpha ₁ is applied is the same as the case of FIG.

10, the time t ₁ before the speed sensor 1B is stationary, the oscillation frequency of the oscillation frequency and a crystal oscillator 24 of the crystal oscillator 14 are equal. Therefore, the frequency of the clock signal 120 and the frequency of the clock signal 220 are also equal, and the count-up speed of the count value 302 and the count-up speed of the count value 402 are also the same. Accordingly, the subtraction value 512 remains 0.

When the time _t 1 ~t acceleration alpha ₁ of the speed sensor 1B toward ₈ is applied, since the quartz oscillator 100 and a crystal oscillator 200 is in a state shown in FIG. 9 (B), the higher the oscillation frequency of the crystal oscillator 14 At the same time, the oscillation frequency of the crystal oscillator 24 is lowered. Therefore, since the frequency of the clock signal 120 increases and the frequency of the clock signal 220 decreases, the count-up speed of the count value 302 increases and the count-up speed of the count value 402 decreases. As a result, the subtraction value 512 increases to 1, ₂ , ₃ , ₄ , ₅ , ₆ at each timing of times t ₂ , t ₃ , t ₄ , t ₅ , t ₆ , and t ₇ .

At time t _8, the acceleration becomes zero, the speed sensor 1B is to move at a constant speed, the oscillation frequency of the oscillation frequency and a crystal oscillator 24 of the crystal oscillator 14 is equal. Therefore, the frequency of the clock signal 120 and the frequency of the clock signal 220 are also equal. Therefore, after time t _8, the count up of count-up and count value 402 of the count value 302 becomes the same speed. As a result, the subtraction value 512 remains 6 and remains unchanged.

Thus, in the case of FIG. 10, the subtraction value 512 increases to 0, 1, 2, 3, 4, 5, 6, and therefore the digital value of the speed detection signal 602 is 0, 0.5 k, k,. It increases in steps of 5k, 2k, 2.5k, 3k. Here, if the coefficient k is set to the aforementioned speed v ₀ (speed when the subtraction value 512 is 1), the digital value of the speed detection signal 602 is the acceleration α applied from time t _{1 to} time t _8. A trajectory of a speed that rises in 6 steps from 0 to 3v ₀ according to ₁ is shown.

  FIG. 11 is a timing chart for explaining another example of the operation of the speed sensor 1B of the present embodiment.

11, similarly to the case of FIG. 7, the speed sensor 1B are time _{t 9} earlier is constant-speed state at time _{t 8} and later 10, the acceleration-.alpha. ₁ (FIG. 10 to time _t 9 _{~t 16} and deceleration in case the opposite direction and the acceleration of the same size), after time t ₁₆ is a timing chart of the case to be stationary. The size and direction of the acceleration-.alpha. ₁ is the same as the case of FIG. 7, it is assumed the time that the acceleration-.alpha. ₁ is applied is the same as the case of FIG.

11, the time t ₉ earlier, the acceleration is not applied to the velocity sensor 1B, the oscillation frequency of the oscillation frequency and a crystal oscillator 24 of the crystal oscillator 14 are equal. Therefore, the frequency of the clock signal 120 and the frequency of the clock signal 220 are also equal, and the count-up speed of the count value 302 and the count-up speed of the count value 402 are also the same. Accordingly, the subtraction value 512, remains unchanged at 6 is a constant value of time t ₈ after the FIG.

When the speed sensor 1B to time _t 9 _{~t 16} acceleration-.alpha. ₁ is applied, since a state crystal oscillator 100 and the quartz oscillator 200 is bent, respectively 9 and (B) in the reverse direction, the crystal oscillator 14 As the oscillation frequency decreases, the oscillation frequency of the crystal oscillator 24 increases. Therefore, since the frequency of the clock signal 120 decreases and the frequency of the clock signal 220 increases, the count-up speed of the count value 302 decreases and the count-up speed of the count value 402 increases. As a result, the subtraction value 512 decreases to 5, 4, 3, 2, 1, 0 at each timing of times t ₁₀ , t ₁₁ , t ₁₂ , t ₁₃ , t ₁₄ , and t ₁₅ .

At time t _16, the acceleration becomes zero, the speed sensor 1B is stationary, the oscillation frequency of the oscillation frequency and a crystal oscillator 24 of the crystal oscillator 14 is equal. Therefore, the frequency of the clock signal 120 and the frequency of the clock signal 220 are also equal. Therefore, after time _{t 16,} the count up of count-up and count value 402 of the count value 302 becomes the same speed. As a result, the subtraction value 512 remains 0.

Thus, in the case of FIG. 11, since the subtraction value 512 decreases to 6, 5, 4, 3, 2, 1, 0, the digital value of the speed detection signal 602 is 3k, 2.5k, 2k,. It decreases in steps of 5k, k, 0.5k, 0. Here, if the coefficient k is set to the above-mentioned speed v ₀ , the digital value of the speed detection signal 602 has 6 levels from 3v ₀ to 0 depending on the acceleration −α _{1 applied} from time t _{9 to} t _16. Indicates the trajectory of the descending speed.

  As described above, in the speed sensor 1B of the second embodiment, both the crystal oscillator 14 and the crystal oscillator 24 are acceleration sensors, and the positive directions of the detection axes are opposite to each other. As compared with the speed sensor 1A of the first embodiment in which is an acceleration sensor, the subtraction value 512 is doubled. Therefore, in the speed sensor 1B of the second embodiment, the resolution of the speed detection signal 602 is doubled as compared with the speed sensor 1A of the first embodiment. That is, according to the speed sensor 1B of the second embodiment, the speed detection sensitivity can be further increased.

  In addition, according to the speed sensor 1B of the second embodiment, by using the crystal resonator 100 and the crystal resonator 200 having the same characteristics, for example, an oscillation frequency error due to a temperature drift can be canceled. A stable detection result can be output regardless of the temperature of time.

(Third embodiment)
In the first embodiment and the second embodiment, since the clock signal 120 and the clock signal 220 are asynchronous, the timing at which the count value 302 and the count value 402 change is also asynchronous. For this reason, the subtraction value 502 is taken into the register 510 at the change point, and as a result, the speed value indicated by the speed detection signal 602 may become an indefinite value. Therefore, in the speed sensor of the third embodiment, the count value 302 and the count value 402 are generated after the clock signal 120 and the clock signal 220 are synchronized.

  FIG. 12 is a diagram showing the configuration of the speed sensor of the third embodiment. 12, the same components as those in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  As shown in FIG. 12, the speed sensor 1C of the third embodiment includes two synchronization circuits 70 (corresponding to the first synchronization circuit in the present invention) and a synchronization circuit 80 (second synchronization in the present invention). Corresponding to the circuit). The synchronization circuit 70 generates a clock signal 72 (corresponding to the first synchronization frequency signal in the present invention) obtained by synchronizing the clock signal 120 with the clock signal 90. Similarly, the synchronization circuit 80 generates a clock signal 82 (corresponding to the second synchronization frequency signal in the present invention) obtained by synchronizing the clock signal 220 with the clock signal 90. Here, the clock signal 90 is a clock signal having a higher frequency than both the frequency of the clock signal 120 and the frequency of the clock signal 220.

  The synchronization circuit 70 and the synchronization circuit 80 can be configured as a known synchronization circuit in which, for example, two or more flip-flops are connected in series, and the clock signal 90 is input to the clock terminal of each flip-flop. .

  The synchronous counter 300 and the synchronous counter 400 count the clock number (cycle number) of the clock signal 72 and the clock signal 82, respectively, and the subtraction value 502 of the count value 302 and the count value 402 is synchronized with the clock signal 90. The data is taken into the register 510 at the predetermined timing. Here, as the predetermined timing, any timing that is not the changing point of the subtraction value 502 can be selected. For example, the rising or falling timing of any one of the clock signal 90, the clock signal 72, and the clock signal 82 may be used.

  As described above, according to the speed sensor 1C of the third embodiment, the subtraction value 502 is taken into the register 510 except for the change point, and as a result, the speed value indicated by the speed detection signal 602 becomes an indefinite value. Can be prevented.

  In order to increase detection accuracy, it is desirable that the frequency of the clock signal 90 be sufficiently higher than the frequency of the clock signal 120 and the frequency of the clock signal 220.

3. Distance Sensor FIG. 13 is a diagram showing a configuration of the distance sensor of the present embodiment.

  When the speed is integrated, the distance from the integration start time can be obtained. Therefore, as shown in FIG. 13, in the distance sensor 1D of the present embodiment, an integration processing unit 610 is added to the output of the speed sensor 1B of the second embodiment shown in FIG. 13, the same components as those in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  The integration processing unit 610 performs integration calculation in discrete time of the speed detection signal 602 by digital processing, and outputs an integration result as a distance detection signal 612. In the calculation of the least significant bit of the integration result (distance detection signal 612), rounding may be performed as necessary. The integration processing unit 610 may be realized as a dedicated digital circuit, or may be realized by a CPU executing an integration calculation program.

  Note that the circuit configured by the multiplication processing unit 600 and the integration processing unit 610 corresponds to the detection signal generation unit 60 in FIG. 1, and the distance detection signal 612 corresponds to the detection signal 62 in FIG.

  According to the distance sensor 1D of the present embodiment, the moving distance can be detected based on the difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400.

  The distance sensor 1D of the present embodiment moves with higher accuracy while having a relatively simple configuration in which the difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400 is obtained by digital calculation. The distance can be detected.

4). Acceleration sensor FIG. 14 is a diagram showing a configuration of the acceleration sensor of the present embodiment.

  Acceleration can be obtained by differentiating the speed. Therefore, as shown in FIG. 14, in the acceleration sensor 1E of this embodiment, a differential processing unit 620 is added to the output of the speed sensor 1B of the second embodiment shown in FIG. 14, the same components as those in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  The differential processing unit 620 performs a differential calculation in discrete time of the speed detection signal 602 by digital processing, and outputs a differential result as an acceleration detection signal 622. In the calculation of the least significant bit of the differentiation result (acceleration detection signal 622), rounding may be performed as necessary. The differential processing unit 620 may be realized as a dedicated digital circuit, or may be realized by the CPU executing a differential calculation program.

  Note that the circuit constituted by the multiplication processing unit 600 and the differentiation processing unit 620 corresponds to the detection signal generation unit 60 in FIG. 1, and the acceleration detection signal 622 corresponds to the detection signal 62 in FIG.

  According to the acceleration sensor 1E of the present embodiment, acceleration can be detected based on the difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400.

  The acceleration sensor 1E according to the present embodiment has a relatively simple configuration in which the difference between the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400 is obtained by digital calculation, but the acceleration sensor 1E has a higher accuracy. Can be detected.

  In addition, this invention is not limited to this embodiment, A various deformation | transformation implementation is possible within the range of the summary of this invention.

  For example, in the speed sensor 1A of the first embodiment shown in FIG. 2, the crystal oscillator 14 and the crystal oscillator 24 may be replaced.

  Further, for example, in the speed sensors 1A to 1C of the first to third embodiments, the synchronous counter 300 and the synchronous counter 400 are both configured as an up counter, but the synchronous counter 300 and the synchronous counter 400 are both configured. Both can be configured as a down counter. Further, one of the synchronous counter 300 and the synchronous counter 400 is configured as an up counter and the other is configured as a down counter, and the subtraction processing unit 500 adds the count value 302 of the synchronous counter 300 and the count value 402 of the synchronous counter 400. Alternatively, an addition processing unit that performs the processing may be replaced.

Further, for example, in FIGS. 6 and 10, the clock signal 120 and the clock signal 220 at time t ₁ prior quiescent has become in phase, and the count value 302 and the count value 402 becomes the same value . However, if the oscillation stabilization time of the crystal oscillator 14 and the oscillation stabilization time of the crystal oscillator 24 change due to factors such as the temperature at startup, the phase difference between the clock signal 120 and the clock signal 220 and the difference between the count value 302 and the count value 402 May differ from FIGS. 6 and 10. For this reason, the subtraction value 512 in the stationary state may not become 0. For example, the subtraction value 512 after the oscillation of the crystal oscillator 14 and the oscillation of the crystal oscillator 24 are stabilized at the time of startup is stored as a reference value. The speed value may be calculated based on a value obtained by subtracting the reference value from the subsequent subtraction value 512.

  As an example of the speed sensor 1C of the third embodiment, FIG. 12 shows a configuration in which the synchronization circuit 70 and the synchronization circuit 80 are added to the speed sensor 1B of the second embodiment shown in FIG. For example, a configuration in which a synchronization circuit 70 and a synchronization circuit 80 are similarly added to the speed sensor 1A of the first embodiment shown in FIG. Furthermore, the distance sensor 1D shown in FIG. 13 and the acceleration sensor 1E shown in FIG. 14 can also be configured by adding a synchronization circuit 70 and a synchronization circuit 80 similarly.

  For example, in the distance sensor 1D shown in FIG. 13 or the acceleration sensor 1E shown in FIG. 14, one of the crystal oscillator 14 and the crystal oscillator 24 may not be an acceleration sensor.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention 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. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 Physical quantity sensor, 1A-1C Speed sensor, 10 1st frequency signal generation part, 11 1st resonator, 12 1st frequency signal, 14 Crystal oscillator, 20 2nd frequency signal generation part, 21 2nd Resonator, 22 Second frequency signal, 24 Crystal oscillator, 30 First count unit, 32 Count value, 40 Second count unit, 42 Count value, 50 Digital operation unit, 52 Digital value, 60 Detection signal generation unit 62, detection signal, 70 synchronization circuit, 72 clock signal, 80 synchronization circuit, 82 clock signal, 90 clock signal, 100 crystal resonator, 101 double tuning fork vibrating piece, 102-103 base, 104-105 vibrating arm, 106 Cantilever, 107 fixed end, 108 free end, 109 connecting part, 110 oscillation circuit, 111-112 carrier Sitter, 113 to 114 resistance, 115 inverter, 120 clock signal, 200 crystal resonator, 201 double tuning fork vibrating piece, 202 to 203 base, 204 to 205 vibrating arm, 206 cantilever, 207 fixed end, 208 free end, 209 Connection unit, 210 oscillator circuit, 211-212 capacitor, 213-214 resistance, 215 inverter, 220 clock signal, 300 synchronous counter, 302 count value, 400 synchronous counter, 402 count value, 500 subtraction processing unit, 502 subtraction value , 510 register, 512 subtraction value, 600 multiplication processing unit, 602 speed detection signal, 610 integration processing unit, 612 distance detection signal, 620 differentiation processing unit, 622 acceleration detection signal

Claims (7)

A physical quantity sensor for detecting a predetermined physical quantity,
A first frequency signal generator that has a first resonator and generates a first frequency signal having a frequency associated with a resonance frequency of the first resonator;
A second frequency signal generator that has a second resonator whose resonance frequency changes in response to a change in acceleration, and generates a second frequency signal having a frequency associated with the resonance frequency of the second resonator. And
A first count unit that counts the number of periods of the first frequency signal;
A second count unit that counts the number of periods of the second frequency signal;
A digital value representing a difference between the number of periods of the first frequency signal and the number of periods of the second frequency signal is calculated based on the count value of the first count unit and the count value of the second count unit. A digital computing unit to
A detection signal generation unit that generates a detection signal of a digital value corresponding to the physical quantity based on the digital value calculated by the digital operation unit,
A physical quantity sensor in which a frequency of the first frequency signal matches a frequency of the second frequency signal in a state where acceleration is not applied. In claim 1,
The first resonator is a physical quantity sensor whose resonance frequency changes according to a change in acceleration. In claim 2,
The physical quantity sensor, wherein the first resonator and the second resonator are arranged such that acceleration detection directions are opposite to each other. In any one of Claims 1 thru | or 3,
A first synchronization in which the first frequency signal is synchronized with the clock signal based on a clock signal having a frequency higher than both the frequency of the first frequency signal and the frequency of the second frequency signal. A first synchronization circuit for generating a frequency signal;
A second synchronization circuit that generates a second synchronized frequency signal obtained by synchronizing the second frequency signal with the clock signal based on the clock signal;
The first counting unit includes:
Based on the first synchronized frequency signal, count the number of periods of the first frequency signal,
The second count unit includes:
A physical quantity sensor that counts the number of periods of the second frequency signal based on the second synchronization frequency signal. In any one of Claims 1 thru | or 4,
The detection signal generator is
A physical quantity sensor that multiplies the digital value calculated by the digital arithmetic unit by a predetermined coefficient to generate the detection signal having a digital value corresponding to speed. In claim 5,
The detection signal generator is
A physical quantity sensor that integrates the velocity signal and generates the detection signal having a digital value corresponding to a moving distance. In claim 5,
The detection signal generator is
A physical quantity sensor that differentiates the speed signal and generates the detection signal having a digital value corresponding to acceleration.

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