Computational scheme for MEMS inertial navigation system

• US 7,957,898 B2
• Filed: 12/28/2007
• Issued: 06/07/2011
• Est. Priority Date: 12/28/2007
• Status: Active Grant

• Current Assignee: Alpine Electronics Incorporated (Alps Alpine Co., Ltd.)
• Original Assignee: Alpine Electronics Incorporated (Alps Alpine Co., Ltd.)
• Inventors: Tashiro, Eric, Hoshizaki, Takayuki
• Primary Examiner(s): ARTHUR JEANGLAUD, GERTRUDE
• Application Number:
  US12/005,969
• Publication Number:
  US 20090171585A1
• Time in Patent Office: 1,257 Days
• Field of Search: 701/201, 701/207, 701/213, 701/214, 701/220, 701/225, 701/222, 342/357.01, 342/357.06, 342/357.14, 342/357.12, 342/357.15, 342/357.32
• US Class Current: 701/214
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled

Abstract

A computational scheme for an INS which utilizes micro-electro mechanical systems (MEMS) sensors resolves issues of unnecessarily large computational burden and numerical instability which happen in using conventional methods using high-end inertial sensors. The first aspect is to omit computing Earth radii of curvatures that were used in a high-frequency application. The second aspect is to ignore the Earth rotation and the rotation of the local tangent plane with respect to Earth which are much smaller than noise and bias in the MEMS sensor output. The last aspect is to assume that the absolute amount of the platform pitch and roll angles is less than 90 degrees. According to the aspects noted above, the computational load will be one-fourth of the conventional method without degradation of accuracy.

Claims

1. A method of updating three dimensional tracking of a platform by a micro-electro mechanical systems (MEMS) based INS, comprising the following steps of:

numerically integrating Northerly, Easterly, and downward velocities to track Northerly, Easterly, and vertical displacement from a reference point along a local tangent plane about the reference point;

converting latitude and longitude into Northerly and Easterly displacement from the reference point using the Earth North-South and East-West curvatures computed for the reference point;

ignoring the Earth rotation and the rotation of the local tangent plane with respect to Earth since they are much smaller than MEMS gyro noise and bias; and

assuming the platform orientation conditions of;

−

90 (deg)<

pitch<

90 (deg)

−

90 (deg)<

roll<

90 (deg)

to reduce the number of parameters rectuired to track in a direction cosine matrix.

2. A method of updating three dimensional tracking of a platform by a MEMS based INS as defined in claim 1, further comprising a step of recovering a direction cosine matrix from its four elements assuming the platform orientation conditions of:

−

90 (deg)<

pitch<

90 (deg)

−

90 (deg)<

roll<

90 (deg).

3. A method of updating three dimensional tracking of a platform by a MEMS based INS as defined in claim 1, further comprising a step of normalizing a direction cosine matrix periodically which is updated only from its four parameters assuming the platform orientation conditions of:

−

90 (deg)<

pitch<

90 (deg)

−

90 (deg)<

roll<

90 (deg).

4. An integrated INS/GPS navigation system implementing micro-electro mechanical systems (MEMS) sensors for tracking a vehicle, comprising:

an inertial navigation system (INS) having an inertial measurement unit (IMU) which incorporates MEMS sensors;

a GPS (global positioning system) receiver which receives GPS satellite signals from a plurality of GPS satellites to produce GPS measurement output indicating an absolute position and velocity of the vehicle;

a Kalman filter which combines outputs of the INS and the GPS receiver and performs a Kalman filter processing; and

a processor which controls an overall operation of the navigation system including a simplified computation for position tracking;

wherein said simplified computation is conducted by assuming that Earth is flat so as not to incorporate a radius of curvature of the Earth in the computation for tracking three-dimensional positions of the vehicle.

5. The integrated INS/GPS navigation system as defined in claim 4, wherein said simplified computation is conducted by ignoring rotation of the Earth and rotation of a local tangent plane with respect to the Earth in the computation for tracking three-dimensional velocities of the vehicle.

6. The integrated INS/GPS navigation system as defined in claim 4, wherein said simplified computation is conducted by limiting a range of vehicle “

pitch”

within −

90 degrees and +90 degrees, and limiting a range of vehicle “

roll”

within −

90 degrees and +90 degrees in the computation for tracking the three-dimensional orientations of the vehicle.

7. The integrated INS/GPS navigation system as defined in claim 4, wherein said simplified computation is conducted by the steps of ignoring rotation of the Earth and rotation of a local tangent plane with respect to the Earth in the computation for tracking three-dimensional velocities of the vehicle, and limiting a range of vehicle “

pitch”

within −

90 degrees and +90 degrees, and limiting a range of vehicle “

roll”

within −

90 degrees and +90 degrees in the computation for tracking the three-dimensional orientations of the vehicle.