JP2000234934A - Conversion device for gyro scope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conversion device for a gyro scope wherein more accurate angular output is detected by effectively removing a disturbance noise contained in the angular speed output of a gyro, especially that in synchronous with the sampling cycle of an A/D converter. SOLUTION: A time constant T1 of a first low-pass filter 10 is set to a sampling cycle Ts of an A/D conversion means 7 or below while a cutoff frequency f2 of a second low-pass filter 20 is set to a sampling frequency fs or above. With this, since the first low-pass filter 10 is operated as a primary low-pass filter, or an integrator, at the sampling frequency fs, a disturbance noise is integrally interpolated as a simple manner for cancel. Further, it functions as a secondary low-pass filter to the disturbance noise at a frequency above that, an angular output where a disturbance noise is more effectively removed is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibratory gyroscope, and more particularly to a converter for obtaining an output corresponding to a change in angle from an output corresponding to a change in angular velocity.
The present invention relates to a gyroscope conversion device capable of effectively removing disturbance noise synchronized with a sampling period of a converter.

[0002]

2. Description of the Related Art A vibration type gyroscope is generally constituted mainly of a piezoelectric vibrator. If the piezoelectric vibrator is placed in a certain rotating system while applying bending vibration to the piezoelectric vibrator, an output proportional to the Coriolis force is obtained from the piezoelectric vibrator. This output is an output that follows (changes in proportion to) the angular velocity of the rotary system. The output is subjected to A / D conversion and further time-integrated to obtain an output that follows (changes in proportion to) the angle given to the piezoelectric vibrator in the rotating system. In the following, the output that follows the angular velocity change obtained from the piezoelectric vibrator is referred to as “angular velocity output”, and the output that follows the angular change after time integration is referred to as “angle output”.

FIG. 7 shows the angular velocity output of the piezoelectric vibrator and the angular output after time integration. A and B show the case of normal operation without disturbance noise, and C and D show the case of including disturbance noise. For example, when an angular velocity output as shown in FIG. 7A is obtained from the piezoelectric vibrator, the angular velocity output is A / D converted,
Fig. 7 shows the results of numerical integration over time with a digital integrator.
An angle output as shown in B can be obtained.

On the other hand, the angular velocity output of the piezoelectric vibrator includes:
In many cases, disturbance noise components other than angular velocity are included due to electric pulse noise, ripple voltage of a detection circuit, or shock of external vibration. For example, as shown in FIG. 7C, when disturbance noise is generated in the angular velocity output that coincides with the sampling cycle of the A / D converter, the angular output after numerical integration includes a large error as shown in FIG. 7D. Become. Therefore, means for removing such unnecessary disturbance noise from the angular velocity output is required.

Conventionally, in order to remove unnecessary disturbance noise as described above, firstly, the response of the piezoelectric vibrator itself is slowed down so that the piezoelectric vibrator does not pick up disturbance noise. The means for increasing the sampling rate of the / D converter or resetting the analog integrator in accordance with the frequency, and the third means for providing a low-pass filter to remove disturbance noise eliminate the need for the angular velocity output of the piezoelectric vibrator. It is conceivable to remove unnecessary disturbance noise.

[0006]

However, in the first means, the structure of the piezoelectric vibrator is restricted, and the gyro itself may not be reduced in size. Further, in the second means, there is a situation that only the sampling frequency of the A / D conversion means cannot be set high because of the host device side which acquires the angular velocity output after numerical integration as data. In addition, there is another problem that means for resetting the digital integrator and the analog integrator is separately required, and the configuration and control thereof are complicated.

The removal of such disturbance noise is performed by A
It is common to use a low-pass filter, which is the third means, to remove the signal before performing the / D conversion. However, with a conventional low-pass filter removing means, it is unclear what low-pass filter is optimal. there were.

Generally, A / D of a navigation system
Although the sampling frequency fs of the converter is about 40 Hz (sampling period = 25 msec), in order to remove disturbance noise synchronized with the sampling frequency fs, the cutoff frequency of the low-pass filter must be set to a lower frequency. .

However, when a simple low-pass filter of the primary system is used, since the attenuation slope of the gain is uniquely determined to be -6 db / oct, it is possible to remove noise near the cutoff frequency fs. Even if there is, it becomes difficult to remove disturbance noise of a higher frequency component without affecting the angular velocity output.

In particular, if an attempt is made to remove disturbance noise near the sampling frequency fs by directly using a low-pass filter of a secondary system or higher, the angular velocity output itself that is not originally planned is also removed, and an accurate angle is detected. It may not be possible.

The present invention has been made to solve the above-mentioned conventional problems, and effectively eliminates disturbance noise included in an angular velocity output of a gyro, particularly disturbance noise synchronized with a sampling cycle of an A / D converter. It is an object of the present invention to provide a converter for a gyroscope capable of detecting a more accurate angle output.

[0012]

SUMMARY OF THE INVENTION The present invention provides a piezoelectric vibrator, drive means for supplying a predetermined AC drive power to the piezoelectric vibrator to vibrate, and an output corresponding to a change in angular velocity from the piezoelectric vibrator. Noise removing means for removing unnecessary frequency components, A / D converting means for A / D converting the output from which noise has been removed at a predetermined sampling period, and numerically integrating the output after A / D conversion And an integrator that obtains a value corresponding to the angle change by the gyroscope, wherein the noise removing unit includes a first low-pass filter and a second low-pass filter; The time constant of the filter is set to be equal to or less than the sampling period of the A / D conversion means, and the second
Is set to a frequency higher than the frequency corresponding to the sampling period.

In the converter for angular velocity-angle conversion for a gyroscope according to the present invention, the time constant of the first low-pass filter is set to the same frequency as the sampling period of the A / D converter or to a slightly lower frequency. By doing so, in a frequency band equal to or higher than the sampling frequency,
The first low pass filter can be operated as a perfect integrator. Therefore, it is possible to reduce disturbance noise composed of frequency components synchronized with the sampling cycle without lowering the gain of the angular velocity output which is a lower frequency.

By setting the cut-off frequency of the first low-pass filter to a frequency higher than the cut-off frequency of the second low-pass filter, more preferably at least five times higher, The influence on the integration operation of the low-pass filter can be eliminated.

In the above, it is preferable that the first low-pass filter comprises a first-order low-pass filter and the second low-pass filter comprises a first-order or higher-order low-pass filter.

In the above configuration, it is possible to operate as an integrator having an attenuation gradient of −6 db / oct from the cutoff frequency of the first low-pass filter to the cutoff frequency of the second low-pass filter, and At frequencies higher than the cut-off frequency of the low-pass filter, -12
It can function as a low-pass filter with db / oct as the attenuation gradient.

Therefore, with respect to disturbance noise having a component between the cut-off frequency of the first low-pass filter and the cut-off frequency of the second low-pass filter as a component, the first-order system low-pass filter, that is, the integral It functions as a detector, and can easily cancel disturbance noise by performing integral interpolation. Also, disturbance noise composed of higher frequency components functions as a secondary low-pass filter and can be reduced. Therefore,
Disturbance noise can be effectively removed from the angular velocity output, and an accurate angle can be obtained.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a converter for a gyroscope. As shown in FIG. 1, the detection of the angular velocity of the gyroscope is performed by a vibrator 1 composed of a piezoelectric tuning fork or the like. A drive / detection circuit A for driving and detecting the vibrator 1 is provided.

The drive / detection circuit A is provided with an oscillating means 4 and a driving means 2 for receiving the oscillation of the oscillating means 4 and applying a predetermined AC driving power to the vibrator 1 for driving. Further, there is provided a phase difference detecting means 3 for detecting a phase difference from an output from the vibrator 1 and obtaining an angular velocity output (an output following a change in the angular velocity or an output proportional to the angular velocity) Vω. A part of the output of the phase difference detecting means 3 is amplified by the amplifying means 5 and fed back to the driving means 2. The oscillation unit 4 includes an oscillation control unit (not shown), and is feedback-controlled so that the oscillation unit 4 performs normal oscillation based on the output of the phase difference detection unit 3.

A noise removing means (low-pass filter) 6 for removing unnecessary frequency components other than the angular velocity output from the angular velocity output Vω is provided downstream of the amplifying means 5. Then, the angular velocity output Vω after the noise has been removed
A / D conversion means 7 for performing A / D conversion at a predetermined sampling cycle is provided. Further, the angular velocity output converted into a digital value is numerically integrated to obtain an angle output (an output that follows an angle change or an output that is proportional to the angle). ) Is provided.

FIG. 2 is a perspective view showing a tripod tuning fork type piezoelectric vibrator as an example of the angular velocity detecting means. The vibrator 1 is formed by laminating a piezoelectric material on both front and back surfaces of a flat plate made of a constant elastic material such as an elinvar, or is formed entirely by a plate material of a piezoelectric material. There are three vibrating legs 1a, 1b and 1c.
Each of the vibrating legs 1a, 1b and 1c is provided with a drive electrode. When AC drive power is applied to the drive electrodes from the drive means 2, the vibrating legs 1a, 1b and 1c are driven to vibrate in the X direction, which is the direction in which the vibrating legs are arranged, by the piezoelectric effect.

Each vibrating leg generates bending deformation vibration in the X direction in the first mode. The vibrating legs 1a and 1b on both sides are driven in the same phase, and the central vibrating leg 1c is driven so that the phases are 180 degrees different from the phases of the vibrating legs 1a and 1b on both sides. When the direction of the amplitude of the vibrating legs 1a and 1b on both sides at a certain point is the + X direction, the amplitude direction of the central vibrating leg 1c is -X.
Direction.

When placed in a rotating system about the Z-axis while being driven as described above, Coriolis force acts on each of the vibrating legs in a direction orthogonal to the vibration driving direction, and each of the vibrating legs becomes Y-shaped.
Vibrates in the direction. The vibration components due to the Coriolis force also have opposite phases between the vibrating legs 1a and 1b on both sides and the center vibrating leg 1c. When the vibrating legs 1a and 1b on both sides have an amplitude component in the + Y direction due to Coriolis force at a certain point in time, the center vibrating leg 1c has an amplitude component in the -Y direction. In FIG. 2, detection electrodes 1A and 1B are provided on a center vibrating leg 1c, and signals having different phase differences from the detection electrodes 1A and 1B are detected by the piezoelectric effect of a vibration component in the Y direction due to Coriolis force. .

The phase difference detecting means 3 obtains a phase difference from the signals detected from the detection electrodes 1A and 1B and outputs this as an angular velocity output Vω. After the angular velocity output Vω is amplified to an appropriate signal level by the amplification means 5, unnecessary disturbance noise is removed by the noise removal means (low-pass filter) 6.

The angular velocity output Vω from which disturbance noise has been removed by the noise removing means 6 is converted from an angular velocity output Vω from the noise removing means 6 into a digital signal by an A / D converter 7 at a predetermined sampling period Ts. Then, the digital signal is numerically integrated by an integrator 8 provided at the subsequent stage of the A / D conversion means 7 to obtain an angle output. This angle output is output to a host device 9 such as a navigation system, and the host device 9 performs various controls based on the angle output.

The noise removing means (low-pass filter) 6 in the gyroscope converter will be described below. FIG. 3A is a circuit diagram of the noise removing means (low-pass filter) according to the present invention, and FIG. 3B is a circuit diagram around the power supply. The noise removing means 6 shown in FIG.
Low-pass filter 10 and second low-pass filter 20
It is composed of

The first low-pass filter 10 is a Butterworth-type primary active low-pass filter mainly composed of an operational amplifier 11. That is, the operational amplifier 1
One power supply terminal 11a is connected to the power supply Vcc, and the ground terminal 11b is connected to the ground G of the power supply Vcc. The power supply voltage V is applied to the non-inverting input terminal 11c of the operational amplifier 11.
A voltage Vcc / 2 which is half (1/2) of cc is supplied. A resistor R2 and a capacitor C1 are connected in parallel between the inverting input terminal 11d and the output terminal 11e.
The input resistance R1 is connected to the inverting input terminal 11d, and the angular velocity output Vω of the amplifying means 5 is input to the input resistance R1.

The second low-pass filter 20 shown in FIG. 3A is a Butterworth-type primary active low-pass filter similar to the first low-pass filter. The order of the second low-pass filter 20 may be a secondary system, a tertiary system,... Or a passive filter as long as it is a primary system or higher.

In the second low-pass filter 20, the power supply terminal 21a of the operational amplifier 21 is connected to the power supply Vcc, and the ground terminal 21b is connected to the ground G at 0 potential.
The power supply voltage V is applied to the non-inverting input terminal 21c of the operational amplifier 21.
A voltage Vcc / 2 which is half (1/2) of cc is supplied. A resistor R4 and a capacitor C2 are connected in parallel between the inverting input terminal 21d and the output terminal 21e.
An input resistor R3 is connected to the inverting input terminal 21d, and the input resistor R3 is connected to the output terminal 11e of the first low-pass filter 20.

In the circuit diagram of FIG. 3A, the operational amplifiers 11 and 21 are driven by a single power supply Vcc as shown in FIG. 3B. For this reason, the angular velocity output V of the amplification means 5
ω is a voltage Vcc / 2 corresponding to の of the power supply voltage Vcc.
Are biased, so that the operational amplifiers 11 and 21
Is Vcc / 2.

FIG. 4 is a gain frequency characteristic diagram of a first-order filter as a first low-pass filter, FIG. 5 is a gain frequency characteristic diagram of a first-order filter as an example of a second low-pass filter, and FIG. It is a gain frequency characteristic diagram of the whole means.

The navigation system serving as the host device is generally used for a vehicle, but the frequency of the angular velocity generated there is low no matter how rapidly the steering wheel of the car is changed. Therefore, the sampling cycle Ts of the A / D converter 7 in the navigation system is usually about 25 msec (sampling frequency fs = 40 Hz).

As shown in the gain frequency characteristic diagram of FIG.
In order for the first low-pass filter to function as an integrator near the sampling frequency fs (40 Hz) of the A / D conversion means 7, the cutoff frequency f1 (-3d
b point) is about 7 Hz.

Here, the time constant T1 of the first low-pass filter shown in FIG. 3A is T1 = 1 / (2π · f1) = 1 /
(2π · 7 [Hz]) ≒ 23 (msec). Therefore, the time constant T1 of the first low-pass filter 10
To the sampling period Ts (25 m
In the vicinity of the sampling frequency fs (40 Hz), the first low-pass filter 10 functions as a first-order filter having an attenuation gradient of -6 db / oct, that is, as an integrator. be able to. The gain attenuation near the sampling frequency fs (40 Hz) is about -15 db.

On the other hand, as shown in the gain frequency characteristic diagram of FIG. 5, the cut-off frequency f2 (−3 db point) of the second low-pass filter 20 is set to about 120 Hz. Is about 17 times the cut-off frequency f1. The gain attenuation near the sampling frequency fs = 40 Hz is 0 db. The time constant T2 in this case is T2 = 1 / (2π
・ F2) = 1 / (2π · 120 [Hz]) ≒ 1.3 (mse
c) degree.

FIG. 6 shows a gain frequency characteristic diagram of the entire noise removing means (low-pass filter) 6 in which the first low-pass filter 10 and the second low-pass filter 20 are cascade-connected in two stages. As shown in FIG. 6, the gain attenuation of the noise removing means (low-pass filter 6) around the sampling frequency fs (40 Hz) is about −15 db, which is the same as that of the first low-pass filter 10. This means that the noise removing means (low-pass filter) 6
Indicates that at the sampling frequency fs, the first filter 10 operates as a filter of the same primary system as the first filter 10, that is, as an integrator. At this frequency, the first filter 10 It turns out that it is not affected.

A high frequency equal to or higher than the sampling frequency fs (40 Hz) of the A / D conversion means 7, especially the cutoff frequency f2 (120H) of the second low-pass filter 20 is used.
At frequencies above z), it can be confirmed that attenuation is at an attenuation gradient of -12 db / oct.

Therefore, it can be seen that the noise removing means (low-pass filter) 6 operates as a secondary low-pass filter at a high frequency equal to or higher than the sampling frequency fs (40 Hz) of the A / D converting means 7.

As described above, the time constant T1 of the first low-pass filter is set to the sampling period Ts of the A / D converter 7.
By setting the cut-off frequency f2 of the second low-pass filter 20 to be higher than the frequency fs corresponding to the sampling period Ts, the cut-off frequency f1 of the first low-pass filter 10 is preferably set to By setting the frequency equal to or more than five times the frequency corresponding to the sampling period, the noise elimination unit 6 performs the first filter 1 with the sampling frequency fs of the A / D conversion unit 7.
It can be operated as a primary filter similar to 0, that is, as an integrator. Further, at the sampling frequency fs, the second low-pass filter 20 can have no influence on the first low-pass filter 10 at all. Further, at high frequencies equal to or higher than the sampling frequency fs, the noise removing means 6 can be operated as a secondary low-pass filter.

Thus, any disturbance noise synchronized with the sampling period T1 of the A / D converter 7 can be particularly effectively removed, and the gain of the angular velocity output Vω itself can be prevented from attenuating. Therefore, an accurate angle can be obtained when numerical integration is performed after A / D conversion.

In the above embodiment, the second low-pass filter 20 has been described as a primary filter.
As long as the second low-pass filter 20 does not affect the first low-pass filter 10, the order of the second low-pass filter 20 may be a first-order system or higher.

Also, the first low-pass filter 10 has been described as a primary system and the second low-pass filter 20 has been described as a filter of a primary system or higher.
Is a first-order or higher-order filter, and the second low-pass filter 2
0 may be a primary filter. Further, the second low-pass filter may be an active filter or a passive filter.

[0043]

According to the present invention described above, a first-order low-pass filter, that is, a frequency region operating as an integrator and a second-order low-pass filter can be obtained. By setting the time constant of the first-order low-pass filter so that the sampling frequency corresponding to the sampling period of the converter falls within the frequency region operating as an integrator, in particular, effectively canceling disturbance noise synchronized with the sampling period. Will be able to

[Brief description of the drawings]

FIG. 1 is a block diagram showing a converter for a gyroscope;

FIG. 2 is a perspective view showing a tripod tuning fork type piezoelectric vibrator as an example of an angular velocity detecting unit;

3A is a circuit configuration diagram showing a noise removing means (low-pass filter) in the gyroscope converter according to the present invention, FIG. 3B is a circuit diagram around the power supply, FIG.

FIG. 4 is a gain frequency characteristic diagram using a primary filter as a first low-pass filter;

FIG. 5 is a diagram showing a gain frequency characteristic of a primary filter as an example of a second low-pass filter;

FIG. 6 is a gain frequency characteristic diagram of the entire noise removing unit;

FIG. 7 shows the angular velocity output of the piezoelectric vibrator and the angular output obtained by time-integrating the angular velocity output, where A and B have no disturbance noise, C and D have disturbance noise,

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillator (piezoelectric oscillator) 2 Drive means 3 Phase difference detection means 5 Amplification means 6 Noise removal means (low-pass filter) 7 A / D conversion means 8 Integrator 10 First low-pass filter 20 Second low-pass filter f1 First No. 1 cut-off frequency of low-pass filter f2 Cut-off frequency of second low-pass filter fs Sampling frequency of A / D converter T1 Time constant of first low-pass filter T2 Time constant of second low-pass filter Ts A / D conversion Means sampling period Angular velocity output Vω

Claims (2)

[Claims] 1. A piezoelectric vibrator, drive means for supplying a predetermined AC drive power to the piezoelectric vibrator and vibrating the piezoelectric vibrator, and generating an unnecessary frequency component from an output corresponding to a change in angular velocity from the piezoelectric vibrator. A noise removing means for removing the noise and the noise-removed output at a predetermined sampling period,
A converter for a gyroscope, comprising: an A / D conversion unit for performing D conversion; and an integrator for numerically integrating an output after the A / D conversion to obtain a value corresponding to an angle change. The first low-pass filter and the second
Wherein the time constant of the first low-pass filter is set to be equal to or less than the sampling period of the A / D conversion means, and the cut-off frequency of the second low-pass filter corresponds to the sampling period. A converter for a gyroscope, wherein the converter is set to a frequency higher than the frequency. 2. The conversion device for a gyroscope according to claim 1, wherein the first low-pass filter comprises a first-order low-pass filter, and the second low-pass filter comprises a first-order or higher-order low-pass filter.