GB2049931A

GB2049931A - Gyroscopic direction apparatus

Info

Publication number: GB2049931A
Application number: GB8006812A
Authority: GB
Original assignee: Bodenseewerk Geratetechnik GmbH
Current assignee: Bodenseewerk Geratetechnik GmbH
Priority date: 1979-06-01
Filing date: 1980-02-28
Publication date: 1980-12-31
Also published as: FR2458052B1; DE2922412A1; FR2458052A1; DE2922412C2; GB2049931B

Abstract

Vehicle heading reference apparatus comprises a two-axis rate gyro (18) and an accelerometer (14), both mounted on an azimuth gimbal (12) which is rotatable about a vertical azimuth axis (z<C>) from a position in which the gyro spin axis (z<G>) is at a zero position to a position at 90 DEG thereto. One input axis (x<G>) of the gyro is parallel to the azimuth axis, and the other input axis (y<G>) is normal to the spin axis (z<G>) and to the first input axis (x<G>). The input axis (16) of the accelerometer (14) is parallel to the spin axis (z<G>). The apparatus operated in two modes, namely a "northing" mode and a "heading reference" mode. In the northing mode the azimuth gimbal (12) is rotated with a roll gimbal (10) about the longitudinal axis (x<F>) of the vehicle so that the azimuth axis is in a vertical plane through the longitudinal axis (x<F>), and a computer (52) computes an initial north deviation from gyro and accelerometer signals obtained at the two azimuth gimbal positions. In the second mode, the azimuth gimbal (12) is orientated with the roll gimbal (10) about the longitudinal axis (x<F>) of the vehicle so that the azimuth axis (z<C>) is parallel to the vertical axis (z<F>). In this mode, with the azimuth gimbal in the 90 DEG position, the computer computes the heading from the gyro angular speed signals. <IMAGE>

Description

SPECIFICATION Heading attitude reference unit This invention relates to a self-northing heading attitude reference unit.

In German Offenlegungsschrift 27 41 274 (to which British Application No. 14781/78 (Serial No. 1 579920) corresponds) there is described an instrument for the automatic determination of the north direction by means of a two-axis rate gyro, the spin axis of which is parallel to the vehicle vertical axis, and so is approximately vertical. The rate gyro with its two mutually perpendicular input axes responds to the components of the angular speed of the rotation of the earth. If the spin axis is exactly vertical, the ratio of these two components is equal to the tangent of the north diviation angle.

Accelerometers having input axes parallel to the longitudinal and pitch axes, respectively, of the vehicle provide indications of the attitude angles of the vehicle. The initial north deviation in an earth-fixed coordinate system is determined by means of a computer from the signals of the twoaxis rate gyro and the acceleration signals of the accelerometers. This is the procedure of "northing".

Subsequently, the same rate gyro is rotated through 900 so that its spin axis is substantially horizontal, parallel to the longitudinal axis of the vehicle. Then the two input axes of the rate gyro are parallel to the transverse and vertical axes of the vehicle, respectively, and respond to angular speeds about these axes. Transformation parameters for the transformation of a vector, for example of the speed vector for use in navigation by dead reckoning, from a vehicle-fixed coordinate system into an earth-fixed coordinate system can be derived from these angular speeds by integration, taking into account the initial values obtained during the northing. From these parameters the heading angle in an earth-fixed coordinate system can be derived.

Furthermore it is known, with such a selfnorthing heading attitude reference unit (German Patent Application P 29 03 282 or corresponding British Patent Application No. 7929977) (Serial No. 2040480) to measure the components of the angular speed of the rotation of the earth at two positions of the rate gyro, angularly offset by 1800 about the spin axis or a input axis. The initial north deviation or heading angle independent of certain gyro errors is derived from the sums or differences, respectively, of the signals thus obtained.

In another known self-northing heading attitude reference unit, the north direction is determined by means of a meridian gyro, while a separate heading gyro is provided as a heading attitude reference.

It is an object of the present invention to provide a self-northing heading attitude reference unit for the navigation of vehicles which is of simple and inexpensive construction and comprises only a single gyro.

According to the invention, a self-northing heading attitude reference apparatus for the navigation of a vehicle comprises a roll gimbal mounted for rotation about the longitudinal axis of the vehicle; an azimuth gimbal mounted for rotation about a substantially vertical azimuth axis normal to the longitudinal axis of the vehicle; a two-axis rate gyro and an accelerometer arranged on the azimuth gimbal, the spin axis of the rate gyro being radical with respect to the azimuth axis, a first input axis of the rate gyro being parallel to the azimuth axis, the second input axis being normal to the spin axis and to the first input axis, and the input axis of the accelerometer being parallel to the spin axis; means operative in a first mode of operation of "northing", to orientate the azimuth gimbal with the roll gimbal about the longitudinal axis of the vehicle such that the azimuth axis is located in a vertical plane passing through the longitudinal axis of the vehicle, and operative in a second mode of operation of "heading attitude reference", to orientate the azimuth gimbal with the roll gimbal about the longitudinal axis of the vehicle such that the azimuth axis is parallel to the vertical axis of the vehicle, the azimuth gimbal being rotatable about the azimuth axis into a 0 position, in which the spin axis is parallel to the longitudinal axis or into a position angularly spaced therefrom by 900; and computing means operable in a first mode of operation of "northing" to provide the initial deviation of a vertical plane, passing through the longitudinal axis of the vehicle, from the meridian plane (initial north deviation) from output signals of the rate gyro measured and stored in the two positions of the azimuth gimbal and representing the angular speeds about the second input axis, and from the acceleration signals of the accelerometer also measured and stored in these positions, and operable in a second mode of operation of "heading attitude reference", with the azimuth gimbal rotated into the 900 position, to provide a signal representing the true heading of the vehicle from the angular speed signals of the rate gyro.

One signal gyro only is provided in the instrument of the invention for the determination of the north direction and as the heading attitude reference. During the initial determination of the north direction, the gyro is aligned with respect to its roll attitude, while the pitch movement is detected by an accelerometer and is taken into account during the signal processing. This provides considerable simplification of the signal processing with favourable mechanical expenditure. The components of the angular speed of the rotation of the earth are determined by rotating the rate gyro, which is substantially horizontal with its spin axis, about the azimuth axis. For the mode of operation of "heading attitude reference", the azimuth axis is restrained to the vehicle vertical axis, whereby the rate gyro is aligned with a vehicle-fixed coordinate system.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic-perspective illustration of the structural arrangement of a self-northing heading attitude reference unit, and Fig. 2 is a schematic block diagram of associated signal processing apparatus.

Referring to the drawings, a vehicle-fixed coordinate system is determined by the longitudinal axis xF, the transverse axis yF and the vertical axis ZF of the vehicle. A roll gimbal 10 is mounted for rotation about the longitudinal axis xF and determines a coordinate system XH, yH, and ZH, of which the coordinate axis xH coincides with the longitudinal axis xF of the vehicle. An azimuth gimbal 12 is mounted in the roll gimbal 10 for rotation about an azimuth axis zc perpendicular to the longitudinal axis xF of the vehicle. The azimuth gimbal 12 determines a coordinate system having coordinate axes xc, yc and zc. The azimuth axis zc coincides with the coordinate axis zH of the roll gimbal-fixed coordinate system.

A first accelerometer 14 is arranged on the azimuth gimbal 12, the input axis 1 6 of the accelerometer being parallel to the coordinate axis xC. A two-axis rate gyro 1 8 is arranged on the azimuth gimbal 12. The spin axis zG of the rate gyro 18 is radial to the azimuth axis zc, i.e. is parallel to the coordinate axis Xc of the azimuth gimbal. The first input axis xG of the rate gyro 18 is parallel to the azimuth axis zc, and the second input axis yG of the rate gyro 18 8 is normal to the spin axis z5 and to the first input axis xG, i.e.

parallel to the coordinate axis yc of the azimuth gimbal-fixed coordinate system.

A second accelerometer 20 is provided on the roll gimbal 10. The input axis 22 of this accelerometer is normal to the longitudinal axis xF of the vehicle (or parallel to a normal to the longitudinal axis of the vehicle), i.e. parallel to the coordinate axis yH of the roll gimbal-fixed coordinate system.

The azimuth gimbal 12 is rotatable about the azimuth axis zc by means of an azimuth servomotor 24. The angle of rotation is designated by Oz This angle of rotation is monitored by an angle sensor 26. A servo loop 30 with the servomotor 24 and the angle sensor 26 can be changed-over by an angle selector switch 28, indicated purely schematically in Fig. 1 , such that the azimuth gimbal is optionally rotatable into a 00 position with Oz = O, a 900 position with Q = 900 and into a 1 800 position with Oz = 1 800.

In the 0 position, the coordinate axis xC of the azimuth gimbal-fixed coordinate system is parallel to the longitudinal axis zF of the vehicle. In Fig. 1, the azimuth gimbal 12 is shown in its 900 position.

The second accelerometer 20, an amplifier 32 and a roll servomotor 34 together form a righting loop 36, by which the roll gimbal and the azimuth gimbal are rotatable about the longitudinal axis xF of the vehicle until the acceleration signal of the accelerometer 20 becomes zero. In that condition, the input axis 22 of the accelerometer 20 is horizontal. The azimuth axis zc is then in a vertical plane containing the longitudinal axis xF of the vehicle.

A position sensor 36 provides a signal in accordance with an angle of rotation Ox of the roll gimbal 10 about the longitudinal axis xF of the vehicle. When Hx = 0, the coordinate axis yH of the roll gimbal-fixed coordinate system is parallel to the transverse axis yF, and the coordinate axis ZH coincides with the vertical axis ZF of the vehicle.

Hence, when Ox = 0, also the azimuth axis zc coincides with the vertical axis ZF of the vehicle.

The servomotor 34 can alternatively be connected through a switch 38, in a second switch position, to a position sensor 37 instead of to the righting loop 36. Hence, the azimuth axis zc is restrained to the vertical axis of the vehicle in this second position of the switch 38.

In order to determine the north direction prior to starting on a mission, the switch 38 is switched into the first switch position illustrated in Fig. 1, so that the azimuth axis zc is moved into the vertical plane containing the longitudinal axis xF of the vehicle. The azimuth gimbal 12 is rotated by the azimuth servomotor 24 consecutively in the 0 position, the 900 position and the 1800 position, as selected by seiector switch 28.In each position, acceleration signals at(00), at(900) and A,,x(1800,,), respectively, and angular speed signals To(00), Tax(900) and t( 1 800), respectively, measured about the second input axis yG (as restraining signals at a torquer acting about the axis xG) are stored in memories 40, 42; 44, 46; and 48, 50, respectively.

In a first mode of operation of "northing", a computor 52 provides an initial deviation 9,(0) of the vertical plane passing through the longitudinal axis x of the vehicle from the meridian plane, i.e.

the "initial north deviation" or the initial heading in the earth-fixed coordinate system, from the signals tx(O0), To(900) and Tx(1 800), of the rate gyro 18 representing the rotary speeds about the second input axisyG and measured and stored in the 0 position and the 900 position of the azimuth gimbal as well as, preferably, in the 1 800 position of the azimuth gimbal 12, and from the acceleration signals Ax(0 ), Ax(900 ) Ax( 1800) measured and stored also in these positions.

The computor 52 is illustrated in Fig. 2, as far as the precedure of "northing" is concerned.

The 0 angular speed signal Tax(00) is subtracted from the 1 800 angular speed signal to(1 800) at a first summing point 54. The difference signal thus obtained is divided by 2 Cos ep, as indicated by a block 56. Therein QE is the angular speed of the rotation of the earth, and P is geographic latitude. It can be shown that this results in a signal sinw(O), which represents the sine of the true initial north deviation w( ) The angle + ,(0) can be obtained by means of an inverse sine function generator, represented by a block 58. This angle information is, however, ambiguous because of the ambiguity of the inverse sine function. Therefore, quadrant logic 60 determines the quadrant I, II, Ill or IV in which the angle is located.

The signals supplied to the quadrant logic 60 are provided as follows: The 1 800 acceleration signal is subtracted from the 0 acceleration signal at second summing point 62. The difference signal obtained is divided by 29, as indicated by a block 64, g being the acceleration due to gravity. The signal obtained thereby reDresents the sine of the Ditch anale. i.e. sin V. This sin 2;signal is supplied to a

function generator 66 to provide a cos fl signal, v being the pitch angle of the vehicle.

The quotient of the sin v and cos v signals is formed by a divider 68 to provide a tan v signal.

The cos V signal is multiplied by QC = QE cos ?, as illustrated by a block 70. The signal thus obtained is supplied as a denominator quantity to a divider 72, to which the value "one" is supplied as numerator quantity, whereby the reciprocal value of the cos V signal is provided.

The reciprocal value 1/ n,cos V, together with the 900 rotary speed signal To(900), is supplied to a multiplier 74 to form a product signal. The tan v signal and the product signal with reversed sign are added at a third summing point 76, whereby a signal representing the cosine of the north deviation angle cos 9 is provided.

The 0 angular speed signal Tx(O) from the memory 46 is divided by -8 =QECOS qp, as indicated by a block 78. Thereby a signal representing the sine of the north deviaion angle sin Sb is provided.

The sin # signal and the cost glr signal are fed to the quadrant logic 60 to determine the quadrant of the north deviation angle from the signs of these signals. The criteria of the quadrant logic aregiven in the above-mentioned German Offenlegungsschrift 27 41 274.

The 0 acceleration signal At(00) and the 1 800 acceleration signal A'x(1 800) are added at a forth summing point 80. The sum signal thus obtained is halved, as indicated by a block 82. The 90 acceleration signal at(900) stored in the memory 42 is added at a fifth summing point 84. The signal provided at the fifth summing point is halved again, as indicated by a block 86. Thereby a signal representing a zero error bx of the accelerometer 14 is obtained.

Multiplying the sin v signal by -1, as represented by a block 88, yields the initial value of the element C3r(0) of the directional cosine matrix for the transformation from a vehicle-fixed coordinate system into an earth-fixed coordinate system.

The quantities bx and C3,(0) are required in signal processing, for example, according to the patent applications "Navigational instalment for Land Vehicles" (Addition to Patent Application P 28 18 202.7) and "Head-Attitude Reference Unit" filed concurrently herewith.

After the northing, the azimuth gimbal 12 is rotated into the 0 position, and the azimuth axis zc is restrained to the vertical axis of the vehicle by changing over of the switch 38.

The spin axis ZG of the rate gyro 1 8 is then parallel to the vehicle axis xF, and the two input axes xG and yG are parallel to the vertical axis zF of the vehicle and to the transverse axis yF of the vehicle, respectively. The heading and attitude angles can then be determined from the angular speed signals obtained, taking into account the initial values determined by the northing, as has been described in German Offenlegungsschrift 27 41 274 or the patent application "Heading Attitude Reference Unit" mentioned above and filed concurrently herewith.

Claims

1. Self-northing heading attitude reference apparatus for the navigation of a vehicle, comprising a roll gimbal mounted for rotation about the longitudinal axis of the vehicle: an azimuth gimbal mounted for rotation about a substantially vertical azimuth axis normal to the longitudinal axis of the vehicle; a two-axis rate gyro and an accelerometer arranged on the azimuth gimbal, the spin axis of the rate gyro being radial with respect to the azimuth axis, a first input axis of the rate gyro being parallel to the azimuth axis, the second input axis being normal to the spin axis and to the first input axis, and the input axis of the accelerometer being parallel to the spin axis; means operative in a first mode of operation of "northing" to orientate the azimuth gimbal with the roll gimbal about the longitudinal axis of the vehicle such that the azimuth axis is located in a vertical plane passing through the longitudinal axis of the vehicle, and operative in a second mode of operation of "heading attitude reference", to orientate the azimuth gimbal with the roll gimbal about the longitudinal axis of the vehicle such that the azimuth axis is parallel to the vertical axis of the vehicle, the azimuth gimbal being rotatably about the azimuth axis into a 0 position, in which the spin axis is parallel to the longitudinal axis, or into a position angularly spaced therefrom by 90 ;; and computing means operable in a first mode of operation of "northing" to provide the initial deviation of a vertical plane, passing through the longitudinal axis of the vehicle, from the meridian plane (initial north deviation) from output signals of the rate gyro measured and stored in the two positions of the azimuth gimbal and representing the angular speeds about the second input axis, and from the acceleration signals of the accelerometer also measured and stored in these positions, and operable in a second mode of operation of "heading attitude reference", with the azimuth gimbal rotated into the 900 position, to provide a signal representing the true heading of the vehicle from the angular speed signals of the rate gyro.

2. Apparatus as claimed in Claim 1, further comprising a second accelerometer on the roll gimbal, the input axis of the second accelerometer being normal to the longitudinal axis of the vehicle; a position sensor for sensing the angular position of the roll gimbal and of the azimuth gimbal about the longitudinal axis of the vehicle: a roll servomotor operable to rotate the roll gimbal and the azimuth gimbal about the longitudinal axis of the vehicle, the servomotor being controlled in the first mode of operation by the second accelerometer and in the second mode of operation by the position sensor such that the azimuth axis is restrained to the vertical axis of the vehicle.

3. Apparatus as claimed in Claim 1 or Claim 2, wherein in the first mode of operation, the azimuth gimbal is additionally rotatable into a 1 800 position; the computer comprises storage for acceleration signals obtained in the 00, 900 and 1 800 positions from the first accelerometer, and storage for angular speed signals obtained from the rate gyro for the second input axis in the 00, 900 and 1 800 positions; and the computer provides a signal representing the initial north deviation from the stored acceleration and angular speed signals.

4. Apparatus as claimed in Claim 3, wherein in the computer the 0 angular speed signal is subtracted from the 1 800 angular speed signal at a first summing point to produce a difference signal; and the difference signal is divided by 2 #Ecos P. wherein QE is the angular speed of the rotation of the earth and # is the geographic latitude; whereby a signal sin w( ) is obtained which represents the sine of the true initial north deviation.

5. Apparatus as claimed in Claim 4, wherein in the computer the 1 800 acceleration signal is subtracted from the 0 acceleration signal; the difference obtained thereby is divided by 29, g being the acceleration due to gravity, to represent thp sine no thin niter angle (sin @@)# cos @@ is obtained from

being the pitch angle of the vehicle; the quotient of the sin v and cos v values is used to provide tan v; cos v is multiplied by #c=#Ecos#; the reciprocal of the value thus obtained is formed; the product of the reciprocal value and the 900 rotary speed signal is formed; the tan v value and the product with reversed sign are added to provide the cosine of the north deviation angle cos #; the 0 anglular speed is divided by --, = ?, (p, to represent the sine of the north deviation angle sin #; sin 0 and cos # are supplied to a quadrant logic for determining the quadrant of the north deviation angle from the sign of these values.

6. Apparatus as claimed in any one of Claims 3 to 5, wherein in the computer the 0 acceleration signal and the 1800 acceleration signal and added; the sum signal thus obtained is halved; the stored 900 acceleration signal is added to the halved sum; the result is halved again to provide a representative of the zero error of the accelerometer.

7. Apparatus as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.