RU2163380C1 - Device measuring acceleration - Google Patents

Abstract

FIELD: instrumentation engineering. SUBSTANCE: device measuring acceleration can be used in stabilization systems, in navigation and stabilization systems, in navigation and guidance systems in the capacity of sensitive element. It has analog and digital channels. Digital channel incorporates synchronization circuit and first digitizer, adder, second digitizer, comparator, asynchronous D flip-flop, coincidence circuit, reversible counter and cumulative register connected in series. Analog channel has integrator, stabilization filter and voltage-to-current converter placed in series. Availability of digitizers leads to information storage in process of conversion which excludes aperture error related to change of input information which in its turn increases measurement precision of taken values. Device includes storage circuit of digital information which decreases measurement error related to distortion of input information on frequencies of input signal close to time of information conversion. Averaging of input information takes place in process of its storage. EFFECT: increased measurement precision. 2 dwg, 1 tbl

Description

 The invention is intended for use as an element in stabilization, guidance and navigation systems. The invention may find application in measuring instruments for mechanical quantities of a compensation type.

 A device for measuring acceleration is known (RF patent N 2098833, class 6 T 01 P 15/13, publ. 10.12.97) containing a sensor element including two fixed electrodes and a movable plate, three amplifiers, two resistors, the output of the first amplifier is connected to the first resistor, and the input of the second amplifier is connected to the second resistor and is the output of the device. To increase the noise immunity under the influence of electrical noise, a reference voltage source, an electric signal generator, two transistor pairs, three resistors, two capacitors are introduced into it, which make it possible to compensate for electrical noise due to the coverage of amplifiers with negative feedback.

 The disadvantage of this device is the low accuracy of the measurement, since the choice of gain in hard negative feedback is limited by the condition of stability of the system. In addition, the device contains an analog channel for processing information, which leads to low measurement accuracy, since information is not stored during its conversion and its averaging during accumulation.

 The closest in technical solution is the device (ed. St. N 742801, published in the bulletin of inventions N 23, 1980) containing a sensor, an angle sensor, an integrated feedback amplifier, a torque sensor, an additional integrated amplifier, an electronic key, a threshold element, and the first output of the angle sensor is connected through an integrating feedback amplifier to the moment sensor, and the second output of the angle sensor through a threshold element, an additional integrating amplifier is connected to the control input of the electronic key .

 The disadvantage of this device is the low accuracy of the measurement, due to the accuracy of the integrating analog amplifiers and a threshold element. In addition, the accuracy of the measurement depends on the parameters of the electronic key circuit that selects the information. The main error of the device is related to the finiteness of the charge time of the capacitor of the integrating amplifier. This error leads to an aperture error characteristic of a similar sampling and information processing scheme.

 The present invention solves the problem of increasing the accuracy of measuring acceleration.

 This is achieved by the fact that in the device for measuring acceleration containing an analog channel, including a series-connected sensor element, an angle sensor and an amplifier, a torque sensor, a digital channel is introduced containing a synchronization circuit and a first sampler, adder, second sampler connected in series with the information inputs, a comparator, an asynchronous D-flip-flop, a coincidence circuit, a reversible counter and a final register, and an integrator additionally introduced in series into the analog channel, a stabilizing filter and a voltage-current converter, and the voltage-current converter output connected to the input of the torque sensor, an amplifier output connected to an integrator input, the second output of which is an analog output connected to the first input of the first sampler, the second inputs of the first sampler, adder, second discretizer, comparator, final register, reverse counter, matching circuit are connected respectively to the first, second, third, fourth, fourth, fifth, sixth and seventh outputs of the sync circuit onization, the second output of the first sampler is connected to the first input of the synchronization circuit, the second output of the asynchronous D-trigger is connected to the second input of the synchronization circuit, and the output of the final register is the output of a digital code.

 Introduction to the negative feedback of the integrator with a stabilizing filter ensures the stability of the device for measuring accelerations. The accuracy is improved due to first-order astatism (an integrator in the reverse circuit), as well as due to the formation of analog and digital outputs in the device.

 In FIG. 1 shows a block diagram of a device; in FIG. 2 is a block diagram of a device.

 The proposed device contains a sensing element 1, made in the form of a pendulum, an angle sensor 2, the output of the angle sensor 2 is connected to the input of the amplifier 3, the output of which is connected to the input of the integrator 4, the first output of the integrator 4 is connected to the input of the stabilizing filter 5, the output of which is connected to the input the voltage-current converter 6, and the voltage-current converter output 6 is connected to the input of the torque sensor 7, the second output of the integrator 4 is connected to the first input of the first sampler 8, the first output of which is connected to the first input of the sum ator 9, the output of adder 9 is connected to the first input of the second sampler 10, the output of the second sampler 10 is connected to the first input of the comparator 11, the output of the comparator 11 is connected to the input of the asynchronous D-trigger 12, the second and third outputs of the D-trigger 12 are connected to the first and second the inputs of the matching circuit 13, the first and second outputs of the matching circuit 13 are connected respectively to the first and second inputs of the reverse counter 14, the output of the reverse counter 14 is the first input of the final register 15, the second input of which is connected to the fifth output with synchronization circuits 16, the second input of the first sampler 8 is connected to the first output of the synchronization circuit 16, the second output of the first sampler 8 is the first input of the synchronization circuit 16, the second input of the adder 9 is connected to the second output of the synchronization circuit 16, the second input of the second sampler 10 is connected to the third output synchronization circuit 16, the second input of the comparator 11 is connected to the fourth output of the synchronization circuit 16, the first output of the asynchronous D-trigger 12 is connected to the second input of the synchronization circuit 16, the third input of the circuit matches Nia 13 is connected to the seventh output of the synchronization circuit 16, the third input of down counter 14 is connected to a sixth output of the synchronization circuit 16, the second input of the final register 15 is connected to a fifth output of the synchronization circuit 16.

 The internal content of the blocks that implement the device for measuring acceleration are described in the book by Mayorov, S.A. Novikov G.I. Principles of organization of digital machines. L .: Engineering, 1974.432 s. The synchronization circuit is 64 s., The asynchronous D-trigger is 64-67 s., The registers are 113., the adders are 152 s., The comparators are 151 s. The functional circuit of the sampler is described in the book by V. G. Kartashev. Fundamentals of the theory of discrete signals and digital filters M: Higher school, 1982, p. 18-29. In addition, the blocks are described in the book of P. Horowitz. W. Hill: The Art of Circuit Engineering, M: Mir., Vols. 1-3, 1993

 A device for measuring acceleration works as follows.

 Under the action of the acceleration W on the sensing element 1, made in the form of a pendulum, the inertial moment equal to mlW acts (l, m is the length and mass of the pendulum). Under the influence of this moment, the sensing element 1 is deflected by an angle α. The value of this angle is fixed by the angle sensor 2, the signal from which is supplied in the form of voltage to the input of the amplifier 3, and then to the input of the integrator 4. The signal from the integrator 4, in the form of voltage, is fed to the input of the stabilizing filter 5, used not only to ensure the stability of the device for measuring acceleration (filter implementation schemes are given in the book by G. Lam. Analog and digital filters. Calculation and design. M: Mir, 1982, pp. 127-195), but also for expanding the bandwidth.

The signal from the output of the stabilizing filter 5 is fed to the input of the voltage-current 6 converter, the signal from the output of which is supplied to the input of the torque sensor 7 as a current sensor. The torque sensor 7 develops a torque that compensates for the inertial moment caused by the acceleration. The sensitive element 1 under the action of the moment developed by the moment sensor 7 returns to its original position (the signal at the output of the angle sensor U _DN2 = 0 The output signal from the integrator 4 serves as an estimate of the value of the effective acceleration W in the analogous form U _int = kW, where k is the proportionality coefficient The signal from the second output of the integrator 4 in the form of voltage is supplied to the first input of the first sampler 8, the second input of which receives a control signal in the form of pulses from the first output of the synchronization circuit 16. The first sampler 8 fix It takes the value of the analog signal from integrator 4 for the conversion time.

The voltage at the output of the first sampler 8 is fixed with the arrival of each pulse from the synchronization circuit 16. From the second output of the first sampler 8, the signal is fed to the first input of the synchronization circuit 16 and is used to form the sign of the incoming information, which biases the parametric compensation signal in the positive or negative region. The adder 9, the first input of which receives a signal in the form of a step voltage from the first output of the first sampler 8, and the second input of the adder 9 receives from the second output of the synchronization circuit 16 a parametric triangular signal U _τ , adds the signal from the outputs of the circuit of the first sampler 8 and a triangular saw , shifted depending on the sign, up or down. The signal from the first output of the adder 9 is fed to the first input of the second sampler 10, the second input of which receives a control signal from the third output of the synchronization circuit 16. The second sampler 10 stores information from the output of the adder 9 for the duration of the conversion. The signal from the first output of the second sampler 10 is fed to the first input of the comparator 11. In the comparator 11, the signal from the output of the second sampler 10 is compared in analog form with a triangular signal extracted from a square-wave signal with a stable frequency and amplitude from the fourth output of synchronization circuit 16.

 If the signal from the first output of the second sampler 10 is greater than the triangular voltage from the output of the synchronization circuit 16, then the output of the comparator 11 will have a high logic level, if less, then the output of the comparator 11 will have a low logic level. The signal from the output of the comparator 11 in the form of a level is fed to the input of the asynchronous D-trigger 12, the signals from the second and third outputs of which (direct and inverse) are supplied to the first and second inputs of the matching circuit 13. The first output of the asynchronous trigger 12 is sent to the second (direct) the input of the synchronization circuit 16, which is used to generate control signals for recording information in the final register 15 and set the reverse counter 14 to its initial state if the number of transitions of the output of the D-flip-flop 12 from low to high is equal to the specified quantity. Depending on the signal level from the asynchronous D-flip-flop 12, the signals are supplied either directly or to the inverse inputs of the matching circuit. The third input of the matching circuit 13 receives the count pulses from the seventh output of the synchronization circuit 16. The output signals of the matching circuit 13 are received respectively at the first and second inputs of the reversing counter 14. Depending on the signal level, the matching circuit 13 receives a signal either at the first summing input of the reversing counter 14, or subtracting from the second output of the matching circuit 13. The signal in the form of a digital code from the output of the reverse counter 14 is fed to the information inputs of the final register 15, the second input of which is the pulse of recording information from the fifth output of the synchronization circuit 16. drops. The pulse from the sixth output of the synchronization circuit 16 sets the counter 14 to its initial state. The output of the final register 15 is the output of the digital code of the device for measuring accelerations.

The technical efficiency of the proposed device can be estimated using the transfer functions according to the structural diagram depicted in FIG. 2. The following notation is used in the structural diagram:
T ₁ , T ₂ - time constants of the sensing element;
K _α is the transmission coefficient of the angle sensor;
K ₃ - gain of the amplifier;
T ₃ - time constant of the amplifier;
T _with - time constant of the smoothing filter;
T _and , T ' _g , T _f - time constants of the integrator (T' _g = T _g );
To _OS - feedback transfer coefficient;
p = d / dt - symbol of the Laplace transform,
τ, t _d , f _t - pulse duration, sampling time, clock frequency;
N, NS - digital code, accumulated digital code;
U _α , U _у , U _с , U, U _д - voltage from the output of the angle sensor, amplifier, smoothing filter, integrator, discreditor; (U _d = t _d K, where K = 0,1,2 ...);
ω _cf - cutoff frequency of the analog part of the proposed device;
δ is the relative error;
n is the bit capacity of a single converter (counter difference);
KS is the number of summations;
A is the amplitude of the saw;
INT (U _d , t _d KS f _t / A) is the integer part of the product of the sampling voltage during the sampling time by the summing number and the clock frequency divided by the amplitude of the saw;
B ₁ = Σ $\genfrac{}{}{0ex}{}{\text{kg-}}{\text{i = 0}}$ ¹ ΔU _c signU _d - the value of the parametric scan;
Δ U _s = A / (2 ⁿ KS)
C _i = U _d + B ₁
τ = C _i t _d / A - signal to duration conversion;
NS = Σ $\genfrac{}{}{0ex}{}{\text{ks}}{\text{i =}}$ ₀ N - accumulation of the whole digital code;
N = INT (τ t _T )
The relative acceleration W / g (g is the acceleration of gravity) is input to the device. The magnitude of this acceleration acts on the sensitive element, the dynamics of which is determined by two time constants T ₁ and T ₂ . The deviation of the sensor is detected by an angle sensor with a transmission coefficient K _α (the sensor has a limit on the deviation angle of ± 1/30 rad). The output signal U _α from the angle sensor is fed to the input of a strip amplifier U _у , which amplifies the signal at the carrier frequency and whose transfer function has the form:
K _at p / (T _at p ² + 2ζ _at T _at p + 1),
where K _y is the gain, T _y , ζ _y is the time constant of the amplifier, the relative damping coefficient.

If the amplifier amplifies the signal U _y along the envelope, then the transfer function of the amplifier is written as
K ₃ / (T ₃ p + 1),
where K _e = K _y / 2ζ _y , T _s = T _y / ζ _y .
The strip amplifier has output limits (± 10 V). After converting the carrier frequency into an envelope signal, a significant level of interference occurs; To isolate the constant component of the interference, two smoothing filters with a time constant T _{s are used} . The signal U _s from the filter is fed to the input of the integrator, and the parameters of the integrator are connected by the transfer function as
(T ' _r p + 1) (T _f p + 1) / T _and p,
where - T _and > T '_r; T _and > T _f .

The integrator parameters are selected in such a way as to ensure the equality of T ₂ = T ' ₂ .

The time constant T _f provides the necessary stability margins of the analog channel of the device for measuring accelerations. The signal from the output of the integrator U through the feedback coefficient enters the compensating feedback circuit.

At fixed times, the signal from the output of the integrator is stored in the sampler for the conversion time (U _d ).

The sampled signal U _{d is} added to the signal from the synchronization circuit, converted to a duration τ and, using the time interval count, converted to a digital code N, and then output, by accumulation, to a digital code NS.

В структурной схеме использованы следующие обозначения:
T²=Т_оТ_и/K_оК_ос, 2 ζ T=Т_и/K_оK_ос,
T₀ = T₁/(1+K_αK_зK_осT_ф/T_и),
K₀ = K_αK_з/(1+K_αK_зK_осT_ф/T_и).
Амплитуда частотной характеристики A(ω) аналоговой части определяется как:

Если выбрать параметры устройства так, чтобы выполнялось условие 2T²ω² = 4ζ²T²ω², то получим:

Потребуем, чтобы A(ω) аналоговой части устройства не отличалась от требуемой на величину относительной ошибки δ, которая определяется зависимостью:
δ =1/(2ⁿ-1)KS
С учетом значения относительной ошибки параметры эквивалентной структурной схемы определятся, как:

При параметрах n=12; KS=2⁷-1 получим
δ = 1.92·10^-6
T ω = 4.428·10^-2
На частоте полезного сигнала ω = 5c^-1 постоянная времени аналоговой части Т=8.856·10^-3с.To assess the accuracy of the proposed device, suppose that the input of the device receives relative acceleration, which varies according to a sinusoidal law, and the device operates in a steady state. Let also T _s ≪ 1 / ω _sr and T _s ≪ 1 / ω _sr . Given the accepted limitations, the structural diagram (Fig. 2) is converted to:

The following notation is used in the structural diagram:
T ² = T _about T _and / K _about K _OS , 2 ζ T = T _and / K _about K _OS ,
T ₀ = T ₁ / (1 + K _α K _s K _os T _f / T _u ),
K ₀ = K _α K _s / (1 + K _α K _s K _os T _f / T _u ).
The amplitude of the frequency response A (ω) of the analog part is defined as:

If we select the device parameters so that the condition 2T ² ω ² = 4ζ ² T ² ω ^{2 is} satisfied, then we obtain:

We require that A (ω) of the analog part of the device does not differ from the required relative error δ, which is determined by the dependence:
δ = 1 / (2 ⁿ -1) KS
Given the value of the relative error, the parameters of the equivalent structural scheme are determined as:

With parameters n = 12; KS = 2 ⁷ -1 we get
δ = 1.92 · 10 ^-6
T ω = 4.428 · 10 ^-2
At the frequency of the useful signal ω = 5c ^{-1 the} time constant of the analog part T = 8.856 · 10 ^-3 s.

We estimate the relative error of the analog (δа), digital channels (δц), the total relative error (δ _Σ ) of the proposed device
Error values are calculated in the following respects.

A=10
Относительная ошибка δа устройства для измерения ускорений равна
δa = (α-U_дK_ос)/0,1,
Относительная ошибка цифрового канала устройства δ_ц может быть определена, как
δ_ц= U/A=NS/(2¹²-1)KS
Суммарная относительная ошибка цифрового канала устройства δ_ц может быть оценена, как:

Результаты расчета ошибок устройства сведены в таблицу. Из таблицы следует, что δa и δц не принимают расчетного значения относительной ошибки
δ =1.92·10^-6
Суммарная ошибка δ_Σ превышает расчетное и поэтому параметры устройства Тω следует выбирать меньше в 1.11 раза.Take the values
α _max = W _max / g = 0,1 - the maximum possible angle of deviation of the sensing element;
α = 0,09sinwt - the law of change of the current angle of deviation of the sensing element;
K _OS = 0.01; U _d = 0.09Aωsinωt / K _wasps ;

A = 10
The relative error δa of the accelerometer is
δa = (α-U _d K _OS ) / 0.1,
The relative error of the digital channel of the device δ _c can be determined as
δ _c = U / A = NS / (2 ¹² -1) KS
The total relative error of the digital channel of the device δ _c can be estimated as:

The results of calculating device errors are summarized in a table. From the table it follows that δa and δc do not accept the calculated value of the relative error
δ = 1.92 · 10 ^-6
The total error δ _Σ exceeds the calculated one and, therefore, the device parameters Tω should be chosen 1.11 times less.

When the clock frequency f _t = 10 · 10 ⁶ Hz, the sampling time of the signal will be equal
t _d = KS (2 ⁿ -1) / t _T = (2 ⁷ -1) (2 ¹² -1) / 10 · 10 ⁶ = 5.2 · 10 ^-2 s
In this case, the period of the sinusoid (input information) α = 0.09 sinot is interrogated at a value of ω = 5 s ^-1 .
N _polling = (2π / ω) (1 / t _d ) = 24 times.
(6 polling values of 1/4 sine wave are given in the table). The conversion time by the second digitizer of the digital channel of the proposed device was
t _dw = t _d /KS=5.2·10 ^-2 /127=4.094488188·10 ^-4 s
and will be 127 times less than the time of the first sampling.

 The proposed device for measuring acceleration with a 12-bit conversion in accuracy will be equivalent to a device for measuring acceleration with a 19-bit converter.

 Thus, the introduction of a digital channel into the device containing the first sampler, adder, second sampler, comparator, synchronous D-flip-flop, coincidence circuit, reverse counter, final register, synchronization circuit, as well as the introduction of the analog channel containing the integrator, stabilizing filter, allowed improve measurement accuracy by scanning an analog signal into a digital code.

 The presence of discretizers leads to the storage of information for the conversion time, which eliminates the aperture error associated with a change in the input information, which in turn increases the accuracy of the measured quantity (acceleration). The device contains a digital information storage device, which reduces the measurement error associated with distortion of the input information at the input signal frequency close to the information conversion time. In the proposed device, the averaging of input information occurs during its accumulation, which also increases accuracy.

Claims (1)

 A device for measuring accelerations, comprising an analog channel, including a sensing element connected in series, an angle sensor and an amplifier, a torque sensor, characterized in that a digital channel is introduced into it, containing a synchronization circuit and a first sampler, adder, second sampler connected in series through the information inputs, a comparator, an asynchronous D-flip-flop, a matching circuit, a reverse counter and a final register, and an integrator is additionally introduced into the analog channel in series with a tabulating filter and a voltage-current converter, wherein the voltage-current converter output is connected to the input of the torque sensor, the amplifier output is connected to the integrator input, the second output of which, which is an analog output, is connected to the first input of the first sampler, the second inputs of the first sampler, adder, second discretizer, comparator, final register, reverse counter, matching circuit are connected respectively to the first, second, third, fourth, fourth, fifth, sixth and seventh outputs of the sync circuit onization, the second output of the first sampler is connected to the first input of the synchronization circuit, the second output of the asynchronous D-trigger is connected to the second input of the synchronization circuit, and the output of the final register is the output of a digital code.

Images