Device for determining the north direction

• US 4,807,138 A
• Filed: 11/04/1986
• Issued: 02/21/1989
• Est. Priority Date: 11/22/1985
• Status: Expired due to Fees

• Current Assignee: Bodenseewerk Gerätetechnik Gmbh
• Original Assignee: Bodenseewerk Gerätetechnik Gmbh
• Inventors: Krogmann, Uwe
• Primary Examiner(s): Chin, Gary
• Assistant Examiner(s): Black, Thomas G.
• Application Number:
  US06/926,976
• Time in Patent Office: 840 Days
• Field of Search: 364/571, 364/565, 364/566, 364/443, 364/453, 364/454, 33/316, 33/320, 33/324, 33/326, 33/328, 73/504, 73/178 R
• US Class Current: 701/220
• CPC Class Codes: G01C 19/38 with north-seeking action by other than magnetic means, e.g. gyrocompasses using earth's rotation

Abstract

The north direction shall be determined by a carrier fixed two-axis rate gyro having a substantially vertical spin axis from the two components of the horizontal component of the rotary speed of the earth. Deviations of the position of the rate gyro from an exact vertical alignment of the spin axis are detected by two accelerometers which provide acceleration signals. The ratio of acceleration signals and acceleration due to gravity provide values of the angles of inclination. Correction signals are formed out of the accelerometer signals and are subtracted from the signals obtained by the rate gyro. One of the correction signals compensates for the component of the vertical component of the rotary speed of the earth falling into the direction of the input axes of the rate gyro. Another signal compensates the rotary speed of the carrier relative to the earth and thus rotatory interferences. The tangent of the true azimuth angle is obtained by forming quotients of the rate gyro signals corrected in this way.

Claims

1. A device for determining the north direction comprising:

(a) two-axis rotary speed sensor means, which are arranged carrier-fixed and have a first input axis and a second input axis, said second input axis being perpendicular to said first input axis, said two input axes defining a plane which in operation is at least approximately horizontal, said rotary speed sensor means providing first and second output signals indicative of rotary speed about said first and second input axes, respectively,

(b) first accelerometer means which respond to acceleration parallel to said first input axis and provide a first acceleration signal indicative of the acceleration sensed by said first accelerometer means along said first input axis,

(c) second accelerometer means which respond to acceleration parallel to said second input axis an provide a second acceleration signal indicative of the acceleration sensed by said second accelerometer means along said second input axis,

(d) means for forming from said first acceleration signal a first correction signal indicative of the component, effective about said first input axis due to the inclination of said first input axis, of the vertical component of the rotary speed of the earth,

(e) means for forming from said second acceleration signal a second correction signal indicative of the component, effective about said second input axis due to the inclination of said second input axis, of the vertical component of the rotary speed of the earth,

(f) means for forming from said first acceleration signal a third correction signal indicative of the angular motion of said carrier relative to earth about said first input axis,

(g) means for forming from said second acceleration signal a fourth correction signal indicative of the angular motion of said carrier relative to earth about said second input axis,

(h) means for subtracting said first and third correction signal from said first output signal of said rotary speed sensor means to provide a first corrected output signal,

(i) means for subtracting said second and fourth correction signals from said second output signal of said rotary speed sensor means to provide a second corrected output signal, and

(j) means for forming the quotient of said first and second corrected output signals to provide a signal indicative of the deviation of said first input axis from North.

2. A device as set forth in claim 1 wherein the rotary speed signals are additionally superposed by one correction signal each which takes into account the known drifts (d_x^k, d_y^k) of the rotary speed sensor means (10).

3. A device for determining the north direction, comprising

(a) two-axis rotary speed sensor means (10) which are arranged carrier-fixed (strapdown) having a first input axis an a second input axis (X^k, Y^k) perpendicular to the first on in a plane which is at least approximately horizontal,

(b) first accelerometric means (16) which respond to acceleration (A_y^k) in the direction of the first input axis (X^k),

(c) second accelerometric means (18) which respond to acceleration (A_y^k) in the direction of the second input axis (Y^k),

(d) signal processing means to which the signals of the rotary speed sensor means (10) and of the accelerometric means (16, 18) are supplied for generating an output signal indicative of the angle between a reference direction and north (X^R),

wherein

(e) the signals (W_y^k, W_y^k) obtained from the rotary speed sensor means (10) by the signal processing means, which signals would be proportional to the components of the horizontal component (Ω

_c) of the rotary speed of the earth falling into the directions of the input axes (X^k, Y^k) if the plane of the input axes were exactly horizontally aligned, are superposed by correction signals derived from the associated accelerometric means (16,

     18) when said plane is not aligned horizontally, said correction signals compensating

(e1) components of the vertical component of the rotary speed of the earth falling into the direction of the input axes (Y^k, Y^k) and

(e2) the rotary speed of the carrier relative to the earth, and

(f) wherein the signal processing means comprises quotient forming means (62,

     100) to form the quotient of the corrected rotary speed signals to provide a signal indicative of the deviation of said first input axis from North,

wherein the signal processing means for each input axis (X^k, Y^k) comprises

(g) means (24,

     26) for integrating with respect to time and signal (W_x^k, W_y^k) from the rotary speed sensor means (10) to generate said signal obtained from the rotary speed sensor means (10),

(h) means (28,

     30) for integrating with respect to time the acceleration signal (A_x, A_y) associated with the respective input axes (X^k, Y^k) from the accelerometric means (16,

     18),

(i) means (32,

     34) for multiplying the integrated acceleration signal by the ratio of the vertical component (Ω

_s) of the rotary speed of the earth and the acceleration due to gravity (g),

(j) means (40) for dividing acceleration signal associated with the respective input axis (X^k, Y^k) by the acceleration due to gravity (g), and

(k) means (52, 56 and 54, 58, respectively) for subtracting said multiplied and integrated acceleration signal and said acceleration signal multiplied by the acceleration due to gravity as correction signals from the integrated signal of the rotary speed sensor means (10) to generate the corrected rotary speed signal.

4. A device as set forth in claim 3 further comprising

(a) means (44, 46) for memorizing the gyro drift (d_x^k, d_y^k) of the rotary speed sensor means,

(b) means (48, 50) for multiplying the memorized drifts by the time (T), and

(c) means (52, 56) for subtracting the product obtained in such way as a further correction signal from the integrated signal of the rotary speed sensor means (10).

5. A device as set forth in claim 3 wherein the signal processing means comprise for each input axis (X^k, Y^k)

(a) means (68) for sampling the signals from the rotary speed sensor means (10) at a given clock frequency to generate said signals obtained from the rotary speed sensor means, as well as

(b) means (66) for sampling the signals from the accelerometers (16, 18) at the given clock frequency,

(c) means (70, 72) for multiplying the sampled acceleration signals with the quotient of the vertical component of the rotary speed of the earth and acceleration due to gravity,

(d) means (78, 80) for dividing the scanned acceleration signals by the acceleration due to gravity (g),

(e) means (82, 84) for delaying the sampled and divided acceleration signals by one clock interval (T),

(f) means (86, 88) for subtracting the undelayed and the delayed divided acceleration signals,

(g) means (90, 92) for dividing the differences obtained in such way by the clock time (T), and

(h) means (74, 76) for subtracting said multiplied acceleration signals and said divided differences as correction signal from the scanned signals of the rotary speed sensor means (10) to generate said corrected rotary speed signals.

6. A device as set forth in claim 5, wherein the drift signals (d_x^k, d_y^k) as further correction signals are subtracted from the sample signals of the rotary speed sensor means.