RU2450278C2 - Microsystem accelerometre - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method is realised by using a proportional-integral differential controller and increasing the optimum setup relationship between the proportional, integral and differential components of the controller.

EFFECT: high accuracy of sensor with power compensation.

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Description

The invention relates to measuring equipment and can be used in integrated accelerometers and microgyroscopes with power compensation.

Known microsystem accelerometer [1], containing a magnetic system located on a fixed base, returning a winding located on a movable node, and a system of temperature compensators with specially selected temperature coefficients embedded between the magnetic system and the housing. The claimed accuracy is achieved without taking into account the load resistor, i.e. at current output.

A disadvantage of the known device is the low accuracy of the measurements when output voltage, since the load resistor makes a significant part of the error in the output signal.

Known microsystem accelerometer [2], containing a magnetic system located on a fixed base, returning a winding located on a movable node. Known microsystem compensation accelerometer has the following disadvantages:

1 - the device is prone to loss of stability due to the use of the integrator and requires gas-dynamic damping;

2 - the device has a large error of the zero signal (up to 0.1% of the measurement limit with dry nitrogen) caused by relaxation in the damping gas.

Closest to the claimed invention is a compensation accelerometer [3], containing an acceleration-sensitive pendulum made in a silicon wafer and connected to it by elastic suspensions, a capacitive displacement sensor, an integrator in a direct circuit and a magnetoelectric system for practicing the effects of accelerations.

Known microsystem compensation accelerometer has the following disadvantages:

1 - the static coefficient of accelerometer transmission includes the value of the stiffness of the elastic suspensions, which depends on the ambient temperature;

2 - the device is prone to loss of stability due to the use of the integrator and requires gas-dynamic damping;

3 - the device has a large error of the zero signal (up to 0.1% of the measurement limit with dry nitrogen) caused by relaxation in the damping gas.

The problem to which the invention is directed, is to increase the accuracy of sensors with power compensation by performing the optimal ratio between the differential, proportional and integrating components of the control signal for testing and evacuating the sensing element.

This technical result is achieved by the fact that in the microsystem compensation accelerometer containing a sensitive mass made in a silicon wafer and connected with elastic suspensions, a capacitive displacement sensor and a magnetic system with a return winding, in accordance with the invention, a correction device is introduced into its direct control circuit in the form of a proportional-integral-differential controller with the following transfer function

, α₂=1, α₄ - период релаксации шумов дифференциатора, J - момент инерции чувствительной массы относительно оси качания, G_у - жесткость упругих подвесов чувствительной массы, s - оператор Лапласа.where α ₁ is the transfer coefficient of the controller in the differential component, α ₂ is the transmission coefficient of the controller in the proportional component, α ₃ is the transfer coefficient of the controller in the integrating component, α ₄ is the time constant of the filter for smoothing the noise of the differentiator, and

, α ₂ = 1, α ₄ is the relaxation period of the differentiator noise, J is the moment of inertia of the sensitive mass relative to the swing axis, G _у is the stiffness of the elastic suspensions of the sensitive mass, s is the Laplace operator.

A significant difference of the invention lies in the fact that it provides optimal damping in the electrical circuit and increase static accuracy through the use of a proportional-integral-differential controller and its settings in accordance with the application.

The inventive device is illustrated by the drawings shown in figures 1, 2 and 3, where figure 1 shows a side view of the proposed device in section. In silicon wafer 1, sensitive mass (pendulum) is made in the form of two plates 3 and 5, rigidly connected along the rocking line (y axis), by anisotropic etching along contour 2. The sensitive mass by means of elastic suspensions 4 is connected to the silicon wafer 1. On the lower surface of the sensitive mass, a layer 7 of the magnetic circuit is etched with etched two rectangular windows 8 into which the permanent magnets are inserted 6. Thus, gaps in which the conductors are placed between the permanent magnets and the magnetic circuit return winding. To align the magnetic induction in the gap along the height of the permanent magnets 6 and the magnetic circuit 7, pole pieces are formed. On the other hand, a silicon wafer is welded to it a fixed plate with electrodes of a capacitive displacement sensor (not shown in the figure).

Figure 2 shows the device when viewed from above. On the wafer 1 is made a load resistor 2 in the form of a meander track. The ends of the load resistor are connected to the contact pads 4. Nearby are the conductors of two identical windings 3 and 5. One of the windings 3 is power for testing feedback, the second winding 5 is designed to test the microsystem accelerometer.

- передаточная функция подвижного узла (маятника); K_чэ=ml - коэффициент передачи чувствительного элемента; m - чувствительная масса; l - рычаг маятника; K_пп=U_опl/h - коэффициент передачи датчика перемещений; h - зазор между поверхностью чувствительной массы и неподвижной обкладкой; U_оп - опорное напряжение; W_кор(s) - передаточная функция корректирующего устройства (функция определена формулой 1); K_ус - коэффициент передачи масштабного усилителя;

- коэффициент передачи силового звена обратной связи; R_н - сопротивление нагрузки; B - магнитная индукция в зазоре; n - число витков в возвращающей обмотке (в заявляемом устройстве один виток); L - длина одного витка.Figure 3 shows the structural diagram of the inventive device. The following notation is used in the diagram:

- transfer function of the moving unit (pendulum); K _ce = ml - transmission coefficient of the sensitive element; m is the sensitive mass; l is the lever of the pendulum; K _PP = U _op l / h - transfer coefficient of the displacement sensor; h is the gap between the surface of the sensitive mass and the stationary lining; U _op - reference voltage; W _cor (s) is the transfer function of the correction device (the function is defined by formula 1); K _us - the gain of the scale amplifier;

- transmission coefficient of the power feedback link; R _n - load resistance; B - magnetic induction in the gap; n is the number of turns in the return winding (in the inventive device, one turn); L is the length of one turn.

Figure 4 shows a schematic diagram of the implementation of the corrective device in accordance with the claims. On OS1, the first term of formula (1) is implemented — the differentiator, where R ₁ C ₁ = α ₁ and the aperiodic filter R ₁ C ₂ = α ₄ . An integrator is implemented on OS2, where R ₂ C ₃ = α ₃ . The proportional component of the regulator transmission coefficient is realized by the ratio of resistors R ₆ / R ₅ = α ₂ . The summation of the proportional, integral and differential components is carried out using OS3. The correcting device with its input in accordance with the structural diagram is connected to the output of a large-scale amplifier, and the output to the input of the power feedback link.

The operation of the claimed device is as follows. In the neutral position, without the action of accelerations, the sensitive mass is stationary, and at the output of the device there is a zero voltage signal. Under the action of linear acceleration of one or another sign, the sensitive mass carries out angular motion, the capacitive bridge is unbalanced, and the voltage amplified by the electronic amplifier is supplied to the input of the proportional-integral-differential controller. First of all, a differentiating chain comes into play, accelerating the passage of the signal and thereby damping the movement of the sensitive mass in the electrical circuit. After that, a proportional control chain comes into effect, tracking the position of the sensitive mass. The voltage of the signal entering the return winding creates a magnetoelectric force that counteracts the inertial one. In this case, the sensitive mass is forced to its original state. By the end of the movement, the signal in the integrating chain has a maximum value, keeping the sensitive mass in a close to neutral position. With sharp jumps in the sensitive mass, all three components of regulation come into effect almost simultaneously, thereby effectively damping the movement.

From the analysis of the control loop of the microsystem accelerometer, the transmission coefficient in static is determined as:

The load resistor is made of the same material as the return winding, and its temperature changes are evaluated mainly by changing the length of the conductor. On the substrate, the load resistor is located next to the return winding, so their ratio is stable and introduces a slight error in the sensitivity coefficient. As for the magnitude of the magnetic induction B, modern industry can provide a zero temperature coefficient for permanent magnets using additives from rare-earth metals, for example, from a cobalt-samarium-gadalinium alloy. Thus, the accuracy of the claimed device does not depend on temperature changes.

The advantages of the claimed device in comparison with the known are: 1 - achieved static accuracy, determined only by the accuracy of the technological manufacture of the elements of the device; 2 - optimal damping obtained by applying and adjusting the proportional-integral-differential controller in accordance with the invention.

Information sources

1. Vavilov V.D., Pozdyaev V.I. Design of integrated sensors. - M: publishing house MAI, 1993, - 68 p.

2. Vavilov V.D. Integrated Sensors. Nizhny Novgorod: NSTU Publishing House, 2003, p. 500.

3. Patent of Russia No. 2231795, M.cl. G01B 15/08, December 10, 2002

Claims (1)

A microsystem accelerometer containing a sensitive mass made in a silicon wafer and connected to it by elastic suspensions, a fixed dielectric plate attached to it with electrodes of a capacitive displacement sensor, a control loop containing a direct circuit with a scaling amplifier and a feedback circuit, characterized in that it is direct the control loop circuit includes a correction device in the form of a proportional-integral-differential controller containing a differentiator with which a noise filter and an integrator are placed, with the next transfer function

,
where α ₁ is the transfer coefficient of the controller in the differential component, α ₂ is the transmission coefficient of the controller in the proportional component, α ₃ is the transfer coefficient of the controller in the integrating component, α ₄ is the time constant of the filter for smoothing the noise of the differentiator, and

, α ₂ = 1, α ₄ = τ is the relaxation period of the differentiator noise.

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