GB2254511A

GB2254511A - Attitude determination system

Info

Publication number: GB2254511A
Application number: GB9205289A
Authority: GB
Inventors: Kazuteru Sato; Kanshi Yamamoto; Mikio Morohoshi; Noriyuki Akaba; Atsushi Kawakami
Original assignee: Tokimec Inc
Current assignee: Tokyo Keiki Inc
Priority date: 1991-03-13
Filing date: 1992-03-11
Publication date: 1992-10-07
Anticipated expiration: 2012-03-11
Also published as: JPH04283615A; NO920960L; JP3044357B2; DE4208158A1; GB2254511B; NO920960D0; DE4208158C2; NO304046B1; GB9205289D0

Description

2 254511 1 1 GYRO APPARATUS The present invention relates to gyro

apparatus and, more particularly, but not exclusively, to gyro apparatus for detecting an azimuth angle, a position, a velocity and so on of vehicles, such as ships, automobiles or the like.

It is known to provide a ship or the like with a gyro compass and a magnetic compass as an apparatus for measuring its azimuth so that, under any conditions, she can sail safely while constantly measuring her own azimuth.

The gyro compass has the disadvantage that it has an actuation time as long as one hour or more. Also, the magnetic compass points to the north of terrestrial magnetism so that the ship's azimuth as indicated by the magnetic compass is deviated from the true north.

A global positioning system (GPS) navigation system has been proposed to obviate the aforesaid disadvantages and shortcomings of the prior art. This GPS system can constantly detect the position of a navigation vehicle such as a ship or the like. The GPS system can measure the position of the navigation vehicle in a three-dimensional fashion on the basis of data supplied thereto from three or more GPS satellites. It is expected that this GPS system will be able to be employed by using a commercially available code (i.e., a so-called C/A code) in the 1990s.

In GPS signal processing based on the above ordinary measuring process, only the position of the navigation vehicle can be measured. The azimuth of the vehicle cannot be measured using the ordinary GPS signal processing techniques. However, the azimuth angle of a navigation vehicle may be calculated using high accuracy simultaneous measurements from two spaced positions. Such systems measure the phase difference of received satellite radio waves at the two spaced positions and are called differential GPS systems.

The principle of operation of this measuring technique will be described below with reference to Figure 1 of the accompanying drawings.

In Figure 1, reference numerals 1 and 2 depict receiving antennas installed on a navigation vehicle (not shown) such as a ship, an automobile, an airplane or the like. A base line length (i.e., a 2 distance L between the two antennas 1 and 2) is known. Radio waves from the antennas 1 and 2 are supplied to a CPS azimuth computing unit 3 which calculates an azimuth angle 0 for the navigation vehicle on the basis of the following calculating processing.

As shown in Figure 1, radio waves from a single GPS satellite 5 are simultaneously received by the antennas 1 and 2. At that time, due to the position of the CPS satellite 5 and the distance L between the antennas 1 and 2, a path difference shown by reference letter D in Figure 1 is present between the radio waves received at the antenna 1 and the radio waves received at the antenna 2. If radio waves of a particular carrier frequency are detected, then this path difference D can be measured using the phase difference (time lag) of the radio waves. Accordingly, the path difference D can be obtained by multiplying the phase difference by the wavelength of the radio waves. If the path difference D is obtained, then, since the distance L is known, the azimuth angle 0 of the navigation vehicle relative to the CPS satellite 5 can be calculated as:

0 = COW' (D/L) In this measuring process, a reception code is not always decoded.

An azimuth angle 0 formed by a line connecting the GPS satellite 5 and the antennas 1, 2, and the true north (N) is calculated as described below.

After the radio waves from the GPS satellite 5 are received at the antenna 1. radio waves from at least two other GPS satellites (not shown) are received. Then, for each satellite, the C/A code of the received radio waves is decoded and a transmission time and a reception time of the radio wave from the GPS satellite are calculated to thereby obtain a propagation time of the radio waves from the GPS satellite to the antenna 1. Then, a distance from the antenna 1 to the GPS satellite (the distance from the GPS satellite to the navigation vehicle) is calculated by multiplying the calculated propagation time by the speed of the radio waves. Since equidistant positions from a GPS satellite exist on a spherical surface whose radius is equal to that distance, three spherical surfaces from the three GPS satellites are calculated and an intersection point of the three spherical surfaces is calculated to thereby uniquely identify the position of the reception antenna 1. If the position of the reception antenna 1 is obtained, then, since the position of the GPS satellite 5 is known, the azimuth angle 0 can be calculated by a directional cosine of a position vector between the antenna 1 to the GPS satellite 5.

The element for executing the position calculating process from the received radio waves in order to obtain the position of the antenna 1 is a GPS position computing unit 4 which receives the radio waves from the antenna 1. Further, the element for performing the aforementioned calculation of 0 and the calculation of (0 + 0) on the basis of the position data from the GPS position computing unit 4 and the data received from the antennas 1, 2 is the GPS azimuth computing unit 3.

As described above, the azimuth angle to the base line length L, and accordingly the azimuth angle of the navigation vehicle, calculated at the GPS azimuth computing unit 3 is presented as (0 + 0), which is then output as a digital signal therefrom.

In the conventional azimuth angle measuring apparatus which makes use of the GPS satellites, the measuring process of azimuth angle requires a long calculation time and consequently the azimuth angle cannot be measured continuously. As a consequence, when a ship, for example, turns, an error occurs in the azimuth angle measuring process because of a delay of time.

Further, there are positions and times in which use of the GPS radio waves is subject to an increased measuring error due to the particular GPS satellite locations. In addition, due to magnetic abnormalities caused by the activity of sun, the measuring process can sometimes become difficult.

The invention provides a gyro apparatus comprising:

a plurality of satellite reception antennas for installation on a navigation vehicle with predetermined distances therebetween; computing means for computing an azimuth angle of said navigation vehicle using satellite radio waves received at said antennas and a phase difference therebetween; an angular velocity sensor for securing to said navigation vehicle such that a yaw axis of said navigation vehicle is employed as 4 an input axis of said angular velocity sensor; an adder supplied with an output of said angular velocity sensor; integrating means for integrating an output of said adder; comparing means for comparing an output of said integrating means and an azimuth angle computed by said computing means; compensating means for scaling a difference detected said comparing means; and means for feeding an output of said compensating means to a negative input terminal of said adder.

As a way of obviating the aforesaid shortcomings, an azimuth angle measuring method is used in which an angular velocity sensor (e.g, rate gyro) and an azimuth angle measuring apparatus employing the aforementioned CPS are combined.

This combination displays a synergy in that the CPS system is not subject to cumulative errors in its readings, but can be adversely affected by external conditions, whereas the angular velocity sensing system may be subject to cumulative errors, but is largely immune to external conditions. The combination and interaction of the gyro apparatus of the invention allows the differing problems of each system to be overcome.

However, when an angular velocity detection axis (hereinafter referred to as an input axis) of the angular velocity sensor is inclined during ship turns, there is then the disadvantage that an error occurs in the azimuth angle detected by the angular velocity sensor. Preferred embodiments of the invention recognise and correct for this problem.

This gyro apparatus allows the azimuth angle to be continuously measured regardless of the output cycle value of the azimuth angle computing unit for the CPS satellite and also regardless of the attitude angle of the navigation vehicle. Therefore, the azimuth angle can be very accurately measured without a time delay in the measured azimuth value due to the movement of the navigation vehicle such as a ship or the like. The invention also provides a gyro apparatus comprising: 35 means for determining an azimuth angle from a phase difference between satellite radio waves received at satellite reception antennas spaced by a predetermined distance, a gyroscope for determining an azimuth angle by integrating sensed angular movements about a yaw axis; and means for correcting said azimuth angle determined by said gyroscope with said azimuth angle determined from satellite radio waves.

The invention will now be described, by way of example only, with reference to the accompanying drawings, throughout which like parts are referred to by like references. and in which:

Figure 1 is a schematic diagram used to explain a principle of measuring an azimuth angle of a navigation vehicle; Figure 2 is a schematic diagram used to explain a principle of measuring an azimuth angle, a roll angle and a pitch angle on the basis of a global positioning system (GPS) in the gyro apparatus; and Figure 3 is a block diagram showing one embodiment of a gyro apparatus according to the present invention.

Figure 2 is a schematic diagram used to explain the principle of measuring an azimuth angle, a roll angle and a pitch angle on the basis of the GPS system, and Figure 3 is a block diagram showing an embodiment of the present invention which employs a measured angle value provided by the GPS technique illustrated in Figure 2.

Figure 2 shows an arrangement in which angles other than the azimuth angle are measured by the GPS system shown in Figure 1, e.g., a roll angle and a pitch angle of a navigation vehicle can be measured. As shown in Figure 2, the reception antenna 1 is installed on a navigation vehicle (e.g., ship) in order to receive a radio wave from the GPS satellite (not shown). Then, with reference to the reception antenna 1 thus installed, the reception antenna 2 is installed at a point spaced from the reception antenna 1 by a certain base line length L, and a reception antenna 16 is installed at a point spaced from the reception antenna 1 by a certain base line length L2 on the same plane with a predetermined angle 0 therebetween.

The specific numerical values might be such that L = L '2 1 2 ' 1m and 0 = 90 degrees. In this case, the L, direction is assumed to a ship's heading direction. Outputs of the reception antennas 1, 2 and 16 thus installed are input to the GPS angle computing unit 6 which measures and then calculates an azimuth angle, a roll angle and a pitch angle of 6 a navigation vehicle in a three-dimensional manner by using the output of the GPS position computing unit 4 on the basis of the principle described in connection with Figure 1.

The system shown in Figure 3 uses the azimuth angle output, the roll angle output and the pitch angle output measured by the arrangement shown in Figure 2.

In Figure 3, reference numeral 10 designates an angular velocity sensor, such as a rate gyro, secured to a navigation vehicle's body (e.g.-a ship's body) in such a fashion that a yawing axis of the ship's body is its input axis. A vibration or vibratory gyro 10 is used as the rate gyro. A vibratory gyro 10 does not have a rotating member and operates on the basis of the principle of dynamics by which a Coriolis force acts in the direction perpendicular to both of a vibration vector and an angular velocity vector when the vibrating object is subject to an angular velocity in a direction perpendicular to the vibration vector. The vibratory gyro 10 detects the magnitude and direction of the angular velocity from Coriolis force and outputs an angular velocity measurement in the form of an analog voltage. The vibratory gyro 10 does not have a rotating member and is therefore long in life, short in actuation time, and low in power consumption.

As shown in Figure 3, an output angular velocity signal from the vibratory gyro 10 is supplied to an analog-to-digital (A/D) converter 11, in which it is converted into a digital signal. Then, this digital signal is corrected for any inclination of the gyro input axis by an inclination correcting unit 12, which will be described later. The digital signal thus corrected by the inclination correcting unit 12 is supplied through an adder E to an integrator 13. The integrator 13 functions to integrate the angular velocity and the output thereof represents an angle. The output angle from the integrator 13 is such that, since the input axis of the vibratory gyro 10 is the vertical axis, the output angle of the integrator 13 can be regarded as an azimuth angle of the navigation vehicle.

The azimuth angle output calculated by the OPS angle computing unit 6 in Figure 2 is compared with the azimuth angle which results from integrating the output of the vibratory gyro 10, by a comparator C, and any residual angle therebetween is input to a compensation computing unit 14. The compensation computing unit 14 is formed of a 7 proportional gain circuit and acts to multiply the residual angle by a scaling factor K. An output multiplied by K from the compensation computing unit 14 is fed back to a negative input of the adder E at the input stage of the integrator 13.

If the system is constructed as described above, then the azimuth angle, which results from integrating the output angular velocity of the vibratory gyro 10, follows the azimuth angle from the GPS angle computing unit 6. Accordingly, even if the output cycle of the GPS angle computing unit 6 is long, then the lack of azimuth angle from the GPS system is compensated for by the azimuth angle of the vibratory gyro 10 so that a continuous and accurate azimuth angle can be output.

The roll angle output and the pitch angle output from the GPS angle computing unit 6 are supplied to the inclination correcting unit 12 and are used to correct for errors in the output angular velocity of the vibratory gyro 10 due to change in the attitude angle of the navigation vehicle, thus making it possible to detect the motion of the navigation vehicle on the horizontal plane correctly.

Considering this function in the case when the navigation vehicle is at a roll angle a. A turning angular velocity Q detected by the gyro lies in a plane inclined by the angle a, whereby an angular velocity within the horizontal plane is represented as Qcos a. Since the azimuth angle which results from integrating the angular velocity should be the angle within the horizontal plane, when the output Q of a gyro secured to the ship's body is employed, an error of (1 - cos a) occurs between it and a true value.

This is also true in the case when the navigation vehicle turns during pitching and as a result an error occurs due to the pitching angle.

The inclination correcting unit 12 uses the signal from the GPS to correct for any errors due to the attitude angle of the navigation vehicle on the basis of the above-mentioned principle. Using this inclination correcting unit 12, it is possible to measure the azimuth angle with high accuracy.

An indicating unit 15 in Figure 3 is an element which indicates thereon the azimuth angle from the integrator 13 and the position output data from the GPS position computing unit 4.

In Figure 3, a phantom block 16 represents a control unit which 8 inhibits the output of the comparator C from being supplied to the compensation computing unit 14 when the output value of the comparator C exceeds a certain reference value (e.g.. 5). For example, the control unit 16 might be formed of a comparator which is supplied at one input terminal thereof with the above constant value and at the other input terminal thereof with the output of the comparator C. When the output of the unit 14 is larger than the above constant reference value, the control unit 16 does not supply the output of the comparator C to the compensation computing unit 14.

As set out above, according to at least preferred embodiments of the present invention, the following effects can be achieved; (1) The azimuth angle of navigation vehicle such as ship or the like can be continuously obtained with high accuracy; The azimuth angle can be measured without a delay of time; Even when an error of an azimuth angle obtained from the GPS satellite is increased, the azimuth angle can be continuously obtained with high accuracy; (4) When the vibratory gyro is employed, the gyro apparatus is long in life, low in power consumption and short in actuation time; and Not only the azimuth angle but also the position and the speed can be measured precisely.

(2) 15 (3) 9

Claims

1. A gyro apparatus comprising: a plurality of satellite reception antennas for installation on a navigation vehicle with predetermined distances therebetween; computing means for computing an azimuth angle of said navigation vehicle using satellite radio waves received at said antennas and a phase difference therebetween; an angular velocity sensor for securing to said navigation vehicle such that a yaw axis of said navigation vehicle is employed as an input axis of said angular velocity sensor; an adder supplied with an output of said angular velocity sensor; integrating means for integrating an output of said adder; comparing means for comparing an output of said integrating means and an azimuth angle computed by said computing means; compensating means for scaling a difference detected said comparing means; and means for feeding an output of said compensating means to a negative input terminal of said adder.

2. A gyro apparatus as claimed in claim 1, comprising three satellite reception antennas and wherein said computing means also computes a roll angle, a pitch angle and a position of said navigation vehicle using satellite radio waves received at said antennas and a phase difference therebetween.

3. A gyro apparatus as claimed in claim 2, comprising a navigation vehicle inclination correcting means inserted between an output of said angular velocity sensor and said adder for employing computed roll angle and pitch angle outputs to correct the angular velocity.

4. A gyro apparatus as claimed in any preceding claim, comprising control means provided between said comparing means and said compensating means, said control means being supplied at one input terminal thereof with a constant reference value and at another input terminal thereof with an output of said comparing means so that, when the output of said comparing means is larger than said constant reference value, said control means does not produce an output for input to said compensating means.

5. A gyro apparatus comprising: means for determining an azimuth angle from a phase difference between satellite radio waves received at satellite reception antennas spaced by a predetermined di-stance, a gyroscope for determining an azimuth angle by integrating sensed angular movements about a yaw axis; and means for correcting said azimuth angle determined by said gyroscope with said azimuth angle determined from satellite radio waves.

6. A gyro apparatus substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.