CN1601282A - Micro-mechanical digital beat frequency accelerometer - Google Patents

Abstract

The invention relates to a micromechanical digital difference frequency accelerometer. It is characterized by that said invention utilizes semiconductor substrate, flexible rod, frame structure, detection mass, resonant tuning forks of upper and lower two sides of frame structure and induction electrode, etc. to form two-stage self-oscillation device. Said dipole resonant tuning forks can be used for driving the whole structure and outputting signal. Said invention also provides its working principle of utilizing dipole resonant tuning forks to apply acceleration and drive whole structure to make output frequency produce change. Said accelerometer has stronger anti-interference capability, high detection sensitivity and high accuracy. Its output digital signal can be directly connected with digital processor.

Description

The digital differential frequency accelerator of micromechanics

Technical field

The invention belongs to microelectronics technology, particularly the digital differential frequency accelerator of comb-tooth-type micromechanics.

Background technology

Accelerometer is a kind of sensor commonly used in the detection of machinery, physics and instrument and robotization control.Current, along with the fast development of microelectric technique and micromachining technology, micro-mechanical accelerometer formed product and application in 1993.Initial accelerometer is a force balance type.Employing is made in silicon chip surface micromachined technology, sensitive axes and substrate parallel, and detecting mass is " H " shape.Detecting quality can be freely along moving perpendicular to the direction of beam.Adopting comb structure, each broach is the float electrode or the fixed electorde of variable capacitance, and fixed electorde and float electrode are interconnected.Testing circuit is a bridge solution, applies the carrier signal that frequency is 1HZ on the fixed electorde that detects electric capacity, and the output voltage of accelerometer is directly proportional with the value that detects electric capacity.This output signal is amplified through buffering, and synchronous demodulation feeds back to the capacitor plate of torquer, produces electrostatic force, makes that detecting quality gets back to zero-bit.The entire circuit of accelerometer and microstructure are integrated on a slice silicon chip.With a 5V power supply power supply.The sensor output voltage analog quantity.

U.S. AD company had released the twin-axis accelerometer product line in 1998, and range is from ± 2g to ± 100g.As ADXL202 type accelerometer, range is from ± 2g, and bandwidth can be by outer electric capacity adjustment.Adopt pulsed modulation to account for and hold specific output, digital output signal directly can enter Computer Processing, or can the converting analogue amount by filtering.

The broach micro mechanical structure is a kind of typical structure of accelerometer now, discloses a kind of resonant acceleration meter with rods (spring) system as U.S. Pat 005969249A.It is a kind of point of fixity by a mass, the rods system (spring) that connect to support mass, two rods, and the accelerometer formed such as the resonance device of two comb structures.Top (the 1st) resonance device self-oscillation, the increase of rods system affacts the pulling force that makes progress that causes on the mass in acceleration force, bottom (the 2nd) resonance device self-oscillation, the increase of rods system affacts the downward pressure that causes on the mass in acceleration force.This accelerometer is made by micromachined with silicon chip.Resonance device in the accelerometer adopts comb structure, and each broach is the float electrode or the fixed electorde of variable capacitance, and fixed electorde and float electrode are interconnected and form a pair of drive electrode.Resonance device is converted into frequency signal to the acceleration that detects.Mass is under the effect of acceleration force, and the output frequency signal of two resonance devices multiplies each other after amplifying through amplifier up and down, again frequency signal of output behind the low pass filter filters out high-frequency interferencing signal.Be f=f1-f2.Output frequency is corresponding with the variation of acceleration.Output frequency signal can directly use a computer and carry out digital processing.Therefore, it is called the digital acceleration meter again.This arrangements of accelerometers is comparatively simple, and its main principle of work is: after accelerometer was subjected to downward acceleration, the frequency of this structure reduced; Otherwise after accelerometer was subjected to acceleration upwards, its output frequency rose.

Summary of the invention

The objective of the invention is to use and the complete different operating principle of above background technology, process is to comb structure, rods and detection mass, and interconnect isostructural research, provide that a kind of to have structure new and compact, intensity is good, serviceable life is longer, the digital differential frequency accelerator of the micromechanics that detection sensitivity and precision are high.

The digital differential frequency accelerator of micromechanics of the present invention comprises: a Semiconductor substrate; Its characteristics are:

One one one-level rods and one one secondary rods that end is connected with Semiconductor substrate that end is connected with Semiconductor substrate, this two-stage rods will support the one-level framed structure, the secondary framed structure is parallel is suspended on the Semiconductor substrate;

Two one-level framed structures that are connected with the rods other end respectively and secondary framed structure; Left and right sides symmetric offset spread has rods in the one-level framed structure; Left and right sides symmetric offset spread has rods in the secondary framed structure;

An one-level that links to each other with rods in the one-level framed structure detects quality, a secondary detection quality that is connected with rods in the secondary framed structure;

The secondary resonance tuning fork of both sides about the one-level of both sides resonance tuning fork and the secondary framed structure about the one-level framed structure, the said dipole resonant tuning fork is used for driving total and output signal; When not being subjected to the vertical direction acceleration, one-level, secondary framed structure can be done simple harmonic motion in the horizontal direction with different frequencies, and system will export their difference on the frequency this moment; After being subjected to the acceleration that vertical direction makes progress, the detection quality in the one-level framed structure is under pressure and moves downward, and causes whole framed structure barycenter to move down, and makes the vibration frequency of one-level framed structure increase; In like manner, secondary framed structure barycenter rising vibration frequency reduces; Therefore, the frequency by said dipole resonant tuning fork output terminal changes; Otherwise after being subjected to the downward acceleration of vertical direction, situation is opposite.

The digital differential frequency accelerator of micromechanics provided by the invention.Mainly comprised by the rods in Semiconductor substrate, rods, framed structure, the framed structure, detected quality, and the framed structure two-stage that constitutes of the resonance tuning fork etc. of both sides self-oscillating arrangement independently up and down.The oscillation frequency of supposing them has f1 and f2 respectively, does the time spent when they are subjected to an acceleration that makes progress, above the mass of oscillating body will move downward, the one-piece construction barycenter moves down, by $k=\frac{\mathrm{Eb}{\mathrm{\&omega;}}^3}{{\mathrm{<figure-callout\; id="3"\; label="L"\; filenames="A20041001257400111.png,A20041001257400142.png"\; state="\{\{state\}\}">L</figure-callout>}}^3}$ With $f=\sqrt{\frac{k}{m}}$ As can be known, the oscillation frequency f1 of vibration piece will increase above; In like manner, the oscillation frequency f2 of mass will reduce below.Corresponded in the variation of frequency with regard to the variation that makes acceleration like this.Output frequency Δ f=f1-f2 also can increase, and corresponds to the variation of frequency like this with regard to the variation that makes acceleration.

The digital differential frequency accelerator of micromechanics of the present invention is compared with background technology, though also be that its vibration frequency changes after utilizing accelerometer to be subjected to different acceleration,, basic functional principle is different fully.The digital differential frequency accelerator of micromechanics is after accelerometer is subjected to acceleration upwards, and the barycenter of total produces downward displacement, causes the output frequency of accelerometer to increase; Otherwise, after accelerometer is subjected to downward acceleration, to move on the barycenter of structure, this moment, the output frequency of accelerometer reduced.FM signal is only relevant with frequency, and is irrelevant with the amplitude of signal.Therefore, have stronger antijamming capability, this has great importance for the precision that improves acceleration.

The digital differential frequency accelerator of micromechanics of the present invention has outstanding advantage and marked improvement is:

Accelerometer has stronger antijamming capability, the high and precision height of detection sensitivity;

The framed structure of accelerometer, rods and detection mass reach compact conformations such as interconnected relationship, and intensity is good, and serviceable life is longer;

The output digital signal of accelerometer can directly be connected with digital processing unit, as computing machine etc.

Description of drawings

Fig. 1 is the digital differential frequency accelerator bb of a micromechanics cut-open view;

Fig. 2 is the digital differential frequency accelerator structural representation of micromechanics;

Fig. 3 is the digital differential frequency accelerator mechanical model of micromechanics;

Fig. 4 is that accelerometer king-rod beam is reduced to the spring equivalent schematic;

Fig. 5 is the ANSYS structure simulation figure of the digital differential frequency accelerator of micromechanics;

Fig. 6 is the digital differential frequency accelerator structural drawing of micromechanics of band external circuits;

Fig. 7 is the digital differential frequency accelerator of micromechanics frequency output waveform figure when being subjected to downward acceleration;

Fig. 8 is the digital differential frequency accelerator of micromechanics frequency output waveform figure when being subjected to normally (acceleration be zero);

Fig. 9 is the digital differential frequency accelerator of micromechanics frequency output waveform figure when being subjected to upwards acceleration;

Figure 10 is the digital differential frequency accelerator of micromechanics when being subjected to downward acceleration, the deformation map of the detection quality that ANSYS simulates;

Figure 11 is the ANSYS analogous diagram of the digital differential frequency accelerator of micromechanics when not being subjected to acceleration;

Figure 12 is the digital differential frequency accelerator of micromechanics when being subjected to upwards acceleration, the deformation map of the detection quality that ANSYS simulates.

Embodiment

Describe the specific embodiment of the present invention in detail below in conjunction with accompanying drawing.

Illustrated in figures 1 and 2, the digital differential frequency accelerator of micromechanics of the present invention comprises:

A Semiconductor substrate 4;

One one one-level rods 3 and one one secondary rods 5 that end is connected with Semiconductor substrate that end is connected with Semiconductor substrate, this two-stage rods will support one-level framed structure 6, secondary framed structure 7 parallel being suspended on the Semiconductor substrate;

Two one-level framed structures that are connected with the rods other end respectively and secondary framed structure; Left and right sides symmetric offset spread has three rods 8 and is parallel to each other in the one-level framed structure; Left and right sides symmetric offset spread has three rods 9 and is parallel to each other in the secondary framed structure;

An one-level that links to each other with rods in the one-level framed structure detects the secondary detection quality 11 that 10, one of quality are connected with rods in the secondary framed structure;

The secondary resonance tuning fork 13 of both sides about the one-level of both sides resonance tuning fork 12 and the secondary framed structure about the one-level framed structure, the said dipole resonant tuning fork is used for driving total and output signal; When not being subjected to the vertical direction acceleration, one-level, secondary framed structure can be done simple harmonic motion in the horizontal direction with different frequencies, and system will export their difference on the frequency this moment; After being subjected to the acceleration that vertical direction makes progress, the detection quality in the one-level framed structure is under pressure and moves downward, and causes whole framed structure barycenter to move down, and makes the vibration frequency of one-level framed structure increase; In like manner, secondary framed structure barycenter rising vibration frequency reduces; Therefore, said dipole resonant tuning fork driving total output frequency changes; Otherwise after being subjected to the downward acceleration of vertical direction, situation is opposite.

The above be actually by the rods in Semiconductor substrate, rods, framed structure, the framed structure, detect quality, and framed structure up and down the resonance tuning fork of both sides drive with induction electrode etc. and constitute independently self-oscillating arrangement 1,2 of two-stage.The resonance tuning fork is shaped as broach.Each broach is a float electrode of variable capacitance; Fixed electorde and float electrode are interconnected, form drive electrode (broach) and induction electrode (broach).

Shown in Figure 5, the digital differential frequency accelerator of micromechanics.For two-stage oscillation device 1,2 about fixedly Semiconductor substrate 4 is arranged up and down.On the digital differential frequency accelerator of above micromechanics shown in Figure 2 basis, characteristics are two one-level framed structures that are connected with the rods other end respectively and secondary framed structure; Left and right sides symmetric offset spread has two rods 8 and is parallel to each other in the one-level framed structure; Left and right sides symmetric offset spread has two rods 9 and is parallel to each other in the secondary framed structure.

Ultimate principle:

The digital differential frequency accelerator of micromechanics is different from the differential capacitive sensor that common sensitization capacitance polar plate spacing changes, and it is to utilize difference between the entire device change frequency to calculate the size of acceleration.This principle of sensing element can utilize traditional quality-spring-damper system to analyze, and Figure 3 shows that the digital differential frequency accelerator mechanical model of micromechanics; The framework of two symmetries by four long be L ₁Driving spring fix, constitute two self-oscillation structures, and have one in each framework by induction spring L ₂Fixing mass m, this structure is equivalent to a single pendulum.During beginning, upper and lower two self-oscillation structures under the driving action of driving comb respectively with frequency f ₁, f ₂Do the self-oscillation campaign, when being subjected to an acceleration a who makes progress, top mass is subjected to a downward power, at this moment spring L ₂Compression.Formula by the elastic coefficient:

$k=\frac{\mathrm{Eb}{w}^3}{L^3}---\left(1\right)$

(wherein E is the elastic modulus of spring, and L is the length of spring, and w is the width of spring, and b is the thickness of spring).Formula (1) is that utilization Microspring in micro mechanical structure can equivalent principle for girder construction propose.Shown in Figure 4, the isoboles of spring.

The spring vibration frequency formula:

$f=\sqrt{\frac{k}{m}}---\left(2\right)$

(k is the elasticity coefficient of spring, and m is spring-supported quality) as can be known: the formula of this structure the first half elasticity coefficient is:

$k=\frac{{\mathrm{Eb\&omega;}}^3}{L_2^3}---\left(3\right)$

Therefore, when the effect that is subjected to acceleration makes the barycenter of mass to move down, be equivalent to the length L of driving spring ₁Shorten, the elasticity coefficient k that can get driving spring thus increases, so cause the vibration frequency f of driving spring ₁Increase Δ f ₁In contrast, the elasticity coefficient k of following spring reduces, the vibration frequency f of driving spring below making ₂Reduce Δ f ₂Therefore, total system has just produced the difference DELTA f '=Δ f of frequency ₁+ Δ f ₂Show that thus the frequency variation of system is relevant with acceleration.So, just can judge by the size of measuring acceleration by the frequency variation of detection system.

The course of work:

Shown in Figure 6, the digital differential frequency accelerator of a kind of micromechanics of the present invention.Add ± V at first for the driving comb on left and right both sides _dBias voltage, to produce electrostatic force this moment between the differential capacitor of microstructure, the driving comb starting of oscillation produces micro displacement, and the driving comb of upper/lower terminal also begins left and right vibration, the tiny signal that produces during its vibration amplifies output by charge amplifier, the amplifying signal part of output is added on the driving comb on the right, and another part then is added on the driving comb in left side by phase inverter.Like this, the voltage that adds on the driving comb of left and right two ends increases, the amplitude of total system also increases thereupon, and output signal is grow also, and by that analogy, system's amplitude will more and more come greatly, and output signal is also more and more stronger; But because the damping action of external environment, the amplitude of system can undyingly not increase, and will tend towards stability to its vibration afterwards to a certain degree.

If the voltage on the driving comb of left and right two ends is respectively V _D1And V _D2, the output signal of upper/lower terminal charge amplifier is respectively A ₁Sin ω _N1T and A ₂Sin ω _N2T is so added voltage is V on the broach of the left and right two ends of the first half _D1+ A ₁Sin (ω _N1+ 180 °) t, V _D2+ A ₁Sin ω _N1T; Added voltage is V on the broach of the left and right two ends of the latter half _D1+ A ₂Sin (ω _N2+ 180 °) t, V _D2+ A ₂Sin ω _N2T; At output terminal the output signal of upper and lower two parts charge amplifier is multiplied each other:

$(V_{d2}+A_1\sin {\mathrm{\&omega;}}_{n1}t)*(V_{d2}+A_2\sin {\mathrm{\&omega;}}_{n2}t)$

$={V_{d2}}^2+A_1\sin {\mathrm{\&omega;}}_{n1}t{A}_2\sin {\mathrm{\&omega;}}_{n2}t+V_{d2}{A}_2\sin {\mathrm{\&omega;}}_{n2}t+V_{d2}{A}_1\sin {\mathrm{\&omega;}}_{n1}t$

$={V_{d2}}^2+\frac{1}{2}{A}_1{A}_2[\cos ({\mathrm{\&omega;}}_{n1}-{\mathrm{\&omega;}}_{n2})t-\cos ({\mathrm{\&omega;}}_{\mathrm{<figure-callout\; id="1"\; label="n"\; filenames="A20041001257400142.png"\; state="\{\{state\}\}">n</figure-callout>}1}+{\mathrm{\&omega;}}_{n2})t]$

$+V_{d2}{A}_2\sin {\mathrm{\&omega;}}_{n2}t+V_{d2}{A}_1\sin {\mathrm{\&omega;}}_{n1}t$

After bandpass filter, the high and low frequency signal is filtered out, and output signal is just only remaining $\frac{1}{2}{A}_1{A}_2\left[\cos ({\mathrm{\&omega;}}_{n1}-{\mathrm{\&omega;}}_{n2})t\right],$ So it is poor that its output signal frequency is exactly upper and lower induction broach output signal frequency.Therefore, just can obtain the size of difference frequency by the wave form varies of output signal.

Shown in Figure 7, frequency output waveform figure when the digital differential frequency accelerator of micromechanics is subjected to normally (acceleration is zero); Shown in Figure 8, frequency output waveform figure when the digital differential frequency accelerator of micromechanics is subjected to normally (acceleration is zero); Shown in Figure 9, frequency output waveform figure when the digital differential frequency accelerator of micromechanics is subjected to upwards acceleration; Further illustrating the digital differential frequency accelerator of micromechanics of the present invention by Computer Simulation is a kind of high Precision Detection sensor.

Shown in Figure 10, when the digital differential frequency accelerator of micromechanics is subjected to downward acceleration, the deformation map of the detection quality that ANSYS simulates; Shown in Figure 11, the ANSYS analogous diagram when the digital differential frequency accelerator of micromechanics is not subjected to acceleration; Shown in Figure 12, when the digital differential frequency accelerator of micromechanics is subjected to upwards acceleration, the deformation map of the detection quality that ANSYS simulates.Use a computer to the finite element analysis of the digital differential frequency accelerator of micromechanics more than the process, for concrete enforcement product design of the present invention provides reliable foundation.Be convenient to the further concrete enforcement of the present invention.

Claims (4)

1, the digital differential frequency accelerator of a kind of micromechanics comprises: a Semiconductor substrate (4); It is characterized in that:

One one one-level rods (3) and one one secondary rods (5) that end is connected with Semiconductor substrate that end is connected with Semiconductor substrate, this two-stage rods will support one-level, the secondary framed structure is parallel is suspended on the Semiconductor substrate;

Two one-level framed structures (6) that are connected with the rods other end respectively and secondary framed structure (7); Left and right sides symmetric offset spread has rods (8) in the one-level framed structure; Left and right sides symmetric offset spread has rods (9) in the secondary framed structure;

An one-level that links to each other with rods in the one-level framework detects quality (10), a secondary detection quality (11) that is connected with rods in the secondary framed structure;

The secondary resonance tuning fork (13) of both sides about the one-level of both sides resonance tuning fork (12) and the secondary framework about the one-level framework, the said dipole resonant tuning fork is used for driving total and output signal; When not being subjected to the vertical direction acceleration, one-level, secondary framed structure can be done simple harmonic motion in the horizontal direction with different frequencies, and system will export their difference on the frequency this moment; After being subjected to the acceleration that vertical direction makes progress, the detection quality in the one-level framed structure is under pressure and moves downward, and causes whole framed structure barycenter to move down, and makes the vibration frequency of one-level framed structure increase; In like manner, secondary framed structure barycenter rising vibration frequency reduces; Therefore, said dipole resonant tuning fork driving total output frequency changes; Otherwise after being subjected to the downward acceleration of vertical direction, situation is opposite.

2, according to the digital differential frequency accelerator of the described a kind of micromechanics of claim 1, described two one-level framed structures that are connected with the rods other end respectively and secondary framed structure; At least two rods (8) of left and right sides symmetric offset spread in the one-level framed structure, and these rods are parallel to each other; Left and right sides symmetric offset spread at least two rods (9) in the secondary framed structure, and these rods are parallel to each other;

3, be silicon according to Semiconductor substrate and framed structure in the digital differential frequency accelerator of the described a kind of micromechanics of claim 1.

4, be polysilicon according to the detection quality in the digital differential frequency accelerator of the described a kind of micromechanics of claim 1.

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