Miniaturized Inertial Measurement Unit and Associated Methods

• US 20090326851A1
• Filed: 04/28/2009
• Published: 12/31/2009
• Est. Priority Date: 04/13/2006
• Status: Active Grant

• Current Assignee: Tanenhaus and Associates, Inc.
• Original Assignee: Jaymart Sensors, LLC
• Inventors: Tanenhaus, Martin E.
• Granted Patent: US 8,239,162 B2
• Time in Patent Office: Days
• US Class Current: 702/96
• CPC Class Codes: G01C 21/1654 with electromagnetic compass
• CPC Class Codes: G01C 21/166 Mechanical, construction or arrangement details of inertial navigation systems
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01P 15/00 Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
• CPC Class Codes: G01P 3/00 Measuring linear or angular speed; Measuring differences of linear or angular speeds G01P5/00 - G01P11/00 take precedence; direction and speed indication G01P13/045; counting mechanisms G06M

Abstract

An inertial measurement unit includes a base having a plurality of physically distinct sectors, upon which are positioned thereon three groups of orthogonally oriented angle rate sensors, each group positioned on a different sector of the base. Three high-G orthogonally oriented accelerometers are also positioned on the base, as well as three low-G orthogonally oriented accelerometers. A processor is positioned on the base having software resident thereon for receiving signals from the three groups of angle rate sensors and the three high-G and three low-G accelerometers. Software is also resident on the processor for calculating from the received signals one or more of the following: a change in attitude, a change in position, a change in angular rate, a change in velocity, and a change in acceleration of the unit over a plurality of finite time increments. Preferably, each gyro is subjected to oversampling, temperature and bias compensation, and bias offset compensation.

Claims

1. An inertial measurement unit comprising:

a base comprising a plurality of physically distinct sectors;

three groups of orthogonally oriented angle rate sensors, each group positioned on a different sector of the base;

three high-G orthogonally oriented accelerometers positioned on the base;

three low-G orthogonally oriented accelerometers positioned on the base;

a processor positioned on the base; and

means resident on the processor for receiving signals from the three groups of angle rate sensors and the three high-G and three low-G accelerometers and for calculating therefrom at least one of a change in attitude, a change in position, a change in angular rate, a change in velocity, and a change in acceleration of the unit over a plurality of finite time increments.

2. The unit recited in claim 1, wherein the calculating means comprises means for combining output from each group of angle rate sensors to form a composite angle rate signal for each group of angle rate sensors, for denoising the composite angle rate signals and the six accelerometer signals, and for calculating from the denoised composite angle rate signals and the three accelerometer signals the at least one of a change in attitude, a change in position, a change in angular rate, a change in velocity, and a change in acceleration of the unit.

3. The unit recited in claim 2, wherein the denoising means comprises a wavelet denoising algorithm adapted to produce a denoised signal.

4. The unit recited in claim 3, wherein the calculating means further comprises a Kalman filter adapted to receive the denoised signal from the wavelet denoising algorithm, the Kalman filter for reducing sensor errors.

5. The unit recited in claim 3, wherein the calculating means further comprises means for performing a bias drift compensation on the denoised signal.

6. The unit recited in claim 1, wherein the angle rate sensors each comprise an oversampled, temperature-, bias-, and bias-offset-compensated gyro.

7. The unit recited in claim 1, wherein the three sets of orthogonally oriented angle rate sensors comprise:

three sets of angle rate sensors oriented triaxially in a first direction, each set oriented normal to the other two; and

three sets of angle rate sensors oriented triaxially in a second direction opposite the first direction, each set oriented normal to the other two.

8. The unit recited in claim 7, wherein each of the sets of angle rate sensors comprise four gyros oriented at 90-degree increments.

9. The unit recited in claim 1, wherein the angle rate sensors comprise micro-electro-mechanical system (MEMS) gyros and the low-G and the high-G accelerometers each comprise a MEMS accelerometer.

10. The unit recited in claim 1, wherein the base comprises a unitary, substantially planar base, the sectors oriented relative to each other to form a three-dimensional structure having at least three faces, each face comprising at least one sector.

11. A method of making an inertial measurement unit comprising:

positioning three groups of orthogonally oriented angle rate sensors on a base, each group positioned on a different sector of the base;

positioning three high-G orthogonally oriented accelerometers on the base;

positioning three low-G orthogonally oriented accelerometers on the base;

positioning a processor on the base;

receiving signals from the three groups of angle rate sensors and the three high-G and three low-G accelerometers into the processor; and

calculating from the received signals at least one of a change in attitude, a change in position, a change in angular rate, a change in velocity, and a change in acceleration of the unit over a plurality of finite time increments.

12. The method recited in claim 11, wherein the calculating comprises combining output from each group of angle rate sensors to form a composite angle rate signal for each group of angle rate sensors, denoising the composite angle rate signals and the six accelerometer signals, and calculating from the denoised composite angle rate signals and the three accelerometer signals the at least one of a change in attitude, a change in position, a change in angular rate, a change in velocity, and a change in acceleration of the unit.

13. The method recited in claim 12, wherein the denoising step comprises using a wavelet denoising algorithm adapted to produce a denoised signal.

14. The method recited in claim 13, wherein the calculating step further comprises using a Kalman filter adapted to receive the denoised signal from the wavelet denoising algorithm, the Kalman filter for reducing sensor errors.

15. The method recited in claim 13, wherein the calculating step further comprises performing a bias drift compensation on the denoised signal.

16. The method recited in claim 11, wherein the angle rate sensors each comprise an oversampled, temperature-, bias-, and bias-offset-compensated gyro.

17. A method of calculating from inertial measurement unit data at least one of a change in attitude, a change in position, a change in angular rate, a change in velocity, and a change in acceleration of the unit over a plurality of finite time increments comprising:

receiving angle rate data from three groups of orthogonally oriented angle rate sensors oriented;

receiving accelerometer data from three high-G orthogonally oriented accelerometers and from three low-G orthogonally oriented accelerometers, the accelerometer on the inertial measurement unit; and

calculating from the received angle rate data and the received accelerometer data at least one of a change in attitude, a change in position, a change in angular rate, a change in velocity, and a change in acceleration of the unit over a plurality of finite time increments.

18. The method recited in claim 17, wherein the calculating step comprises combining output from each group of angle rate sensors to form a composite angle rate signal for each group of angle rate sensors, denoising the composite angle rate signals and the six accelerometer signals, and calculating from the denoised composite angle rate signals and the three accelerometer signals the at least one of a change in attitude, a change in position, a change in angular rate, a change in velocity, and a change in acceleration of the unit.

19. The method recited in claim 18, further comprising performing bias drift compensation on the denoised composite angle rate signals.

20. The method recited in claim 18, wherein the denoising step comprises applying a wavelet denoising algorithm to produce a denoised signal.

21. The method recited in claim 20, further comprising applying a Kalman filter to the denoised signal for reducing sensor errors.

22. The method recited in claim 17, wherein each of the angle rate sensors comprises a gyro having embedded therein a temperature sensor, and further comprising, prior to the angle rate data receiving step:

using data received from each of the temperature sensors, performing a temperature and null change compensation for each gyro; and

measuring each gyro temperature sensor at a predetermined frequency; and

correcting each gyro using the respective measured gyro temperature, for maximizing accuracy of each gyro.

23. The method recited in claim 22, further comprising performing a DC offset removal following the gyro correcting step.

24. The method recited in claim 23, further comprising averaging data from the gyros at an oversampled rate.