Integrated GPS/IMU method and microsystem thereof

• US 6,480,152 B2
• Filed: 07/20/2001
• Issued: 11/12/2002
• Est. Priority Date: 07/20/2000
• Status: Expired due to Term

• Current Assignee: American GNC Corporation
• Original Assignee: American GNC Corporation
• Inventors: An, Dong, Lin, Ching-Fang
• Primary Examiner(s): Phan, Dao
• Application Number:
  US09/912,158
• Publication Number:
  US 20020021245A1
• Time in Patent Office: 480 Days
• Field of Search: 342/357.01, 342/357.06, 342/357.14, 701/213, 701/214, 701/220
• US Class Current: 342/357.32
• CPC Class Codes: G01C 21/1654 with electromagnetic compass
• CPC Class Codes: G01S 19/35 Constructional details or hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/41 Differential correction, e.g. DGPS [differential GPS]
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial
• CPC Class Codes: G01S 19/52 Determining velocity
• CPC Class Codes: G01S 19/53 Determining attitude

Abstract

An integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) method and MicroSystem is disclosed, wherein data from an IMU, a MEMS IMU preferred, a GPS chipset, and an earth magnetic field detector are mixed in a mixed GPS/IMU/Magnetic Data microprocessor to achieve a low cost, micro size, and low power consumption mixed GPS/IMU/magnetic position, velocity, and attitude solution. Furthermore, to deal with sensitivity of the MEMS inertial sensors to environment temperature, a temperature based scheduler, error estimator, and a current acting error estimator are co-operated to minimize the mismatching between the filter system modules and the actual ones due to change of environment temperature, so that the system of the present invention can provide high performance and stable navigation solution over a wide range of environment temperature.

Claims

1. An integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem for a carrier, comprising:

an IMU, for producing orthogonal three-axis (X axis, Y axis and Z axis) angular rate signals and orthogonal three-axis (X-axis, Y axis and Z axis) acceleration signals to a mixed GPS/IMU/Magnetic Data Microprocessor through an IMU processing interface;

an Earth'"'"'s magnetic field detector, for producing said Earth'"'"'s magnetic field vector measurement signals, including X, Y, Z axes signals of said Earth'"'"'s magnetic field vector measurement in said body frame of said carrier, to said mixed GPS/IMU/Magnetic Data Microprocessor through a magnetic processing interface;

a GPS chipset, for receiving GPS RF (Radio Frequency) signals and providing GPS measurements, including GPS position and velocity data or GPS raw pseudorange, range rate, and carrier phase measurements and ephemeris and navigation message from is GPS satellites to said mixed GPS/IMU/Magnetic Data Microprocessor through an GPS interface;

wherein said mixed GPS/IMU/Magnetic Data Microprocessor, for computing a mixed GPS/IMU/magnetic position, velocity, attitude and heading solution, by means of combining said three-axis angular rate and three-axis acceleration, said GPS measurements, and said Earth magnetic field vector measurement, in order to provide a rich and accurate motion measurement of said carrier to meet diverse needs;

an user Interface, for exchanging said mixed GPS/IMU/magnetic position, velocity, attitude and heading data with an external user; and

a power supply and clock module, for providing all voltage and timing signals for other devices of said system of said present invention.

2. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 1, wherein said output of said Earth'"'"'s magnetic field detector is analog voltage signal, Said Earth'"'"'s magnetic field detector interface, is used to condition said output signal of said Earth'"'"'s magnetic field detector, and digitize said output signal of said Earth'"'"'s magnetic field detector, and output said digital Earth'"'"'s magnetic field vector to said mixed GPS/IMU/Magnetic Data Microprocessor.

3. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 2, wherein said mixed GPS/IMU/Magnetic Data Microprocessor comprises:

a controlled position, velocity and attitude module, for processing said digital angular rate and acceleration from said IMU processing interface to compute inertial position, velocity, and attitude data; and

performing error correction to control and remove said drift of said inertial position, velocity, and attitude data, using optimal estimates of inertial position, velocity, and attitude errors from an error estimator module to obtain highly accurate mixed GPS/IMU/magnetic position, velocity, and attitude data;

an error estimator module, for processing said position, velocity, and attitude solution from said position, velocity and attitude module, said GPS measurements from said GPS chipset magnetic heading data from a magnetic heading computation to produce optimal estimates of inertial position, velocity, and attitude errors, which are fed back to said position, velocity and attitude module;

a magnetic heading computation, receiving said three-axis digital Earth'"'"'s magnetic field vector data from said magnetic field processing interface and said pitch and roll angle data from said controlled position, velocity, and attitude module and computing magnetic heading data to error estimator module, and

a user communication data frame producer, for managing input and output data for said external user.

4. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 3, wherein said magnetic field processing interface, connected between said Earth'"'"'s magnetic field detector and said mixed GPS/IMU/Magnetic Data Microprocessor:

receiving said electronic analog magnetic field signals, which are proportional to said Earth'"'"'s magnetic field, from said Earth'"'"'s magnetic field detector;

amplifying said analog magnetic field signals to suppress noise in said electronic analog signal, which is not proportional to said Earth'"'"'s magnetic field;

converting said amplified signals to form three-axis digital Earth'"'"'s magnetic field data, which are input to said mixed GPS/IMU/Magnetic Data Micro processor; and

providing data/address/control bus connection and producing an address decode function, so that said mixed GPS/IMU/Magnetic Data Microprocessor accesses said magnetic field processing interface and pickups said three-axis digital Earth'"'"'s magnetic field data.

5. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 4, wherein said GPS chipset board comprises:

a GPS RF (Radio Frequency) IC (Integrated Circuit), for receiving said GPS RF signals from a GPS antenna and downconverting, and sampling said incoming RF GPS signal, and providing Sign and Magnitude digital output to a Correlation IC;

a correlation IC, for correlating said Sign and Magnitude digital stream with said appropriate local carrier an d code to de-spread said GPS signals to output I and Q (in-phase and quadraphase) samples to a GPS microprocessor; and

a GPS microprocessor, for processing said I and Q samples to close said GPS signal tracking loops and to derive said GPS raw measurements and navigation solution.

6. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 4, wherein said GPS chipset board comprises:

a GPS RF (Radio Frequency) IC (Integrated Circuit), for receiving said GPS RF signals from a antenna and downconverting, and sampling said incoming RF GPS signal, and providing Sign and Magnitude digital output to a Correlation IC;

a correlation IC, for correlating said Sign and Magnitude digital stream with said appropriate carrier and code to de-spread said GPS signals to output I and Q (in-phase and quadraphase) samples to a GPS microprocessor;

a data link IC, for receiving said data link RF signal from a differential GPS site and downconverting it to Data link IF (Intermediate Frequency IF) signal to a Data link demodulation module;

a data demodulation module, for demodulating said data link IF signal to output GPS differential correction data to a GPS microprocessor; and

a GPS microprocessor, for processing said I and Q samples and said GPS differential data to close said GPS signal tracking loops and to derive said GPS navigation solution.

7. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 4, wherein said controlled Position, velocity, and attitude Module comprises:

a coning correction module, for receiving said three angular rate data to form three digital angular increments by integrating said three angular rate during a predetermined short interval;

accepting said digital three-axis angular increment and coarse angular rate bias obtained from an IMU calibration procedure at a high data rate (short interval) and for computing coning effect errors using said input digital three-axis angular increment values and coarse angular rate bias, and outputting three-axis coning effect data and three-axis angular increment data at a reduced data rate (long interval), which are called three-axis long-interval angular increment values and output into said angular rate compensation module;

an angular rate compensation module, for receiving said coning effect errors and three-axis long-interval angular increment values from said coning correction module and angular rate device misalignment parameters and fine angular rate bias from said angular rate producer and acceleration producer calibration procedure and for compensating definite errors in said three-axis long-interval angular increment values using said coning effect errors, angular rate device misalignment parameters, fine angular rate bias, and coning correction scale factor in said three-axis long-interval angular increments and outputting said real three-axis angular increments to an alignment rotation vector computation module;

an alignment rotation vector computation module, for receiving said compensated three-axis angular increments from said angular rate compensation module and said rotation rate vector of said local navigation frame (n frame) of said carrier relative to said inertial frame (i frame) from an earth and carrier rate computation module and updating a quaternion, which is a vector representing rotation angle of said carrier and outputting said updated quaternion is connected to a direction cosine matrix computation module;

a direction cosine matrix computation module, for computing said direction cosine matrix by using said updated quaternion and receiving said optimal estimates of said attitude errors from error estimator to correct said direction cosine matrix;

an acceleration compensation module, for receiving said three acceleration data to form three digital velocity increments by integrating said three acceleration during a predetermined interval;

compensating said definite errors in three-axis velocity increments using said acceleration device misalignment, accelerometer bias, wherein said compensated three-axis velocity increments are connected to said level acceleration computation module;

a level acceleration computation module, for receiving said compensated three-axis velocity increments and computing level velocity increments using said compensated three-axis velocity increments from said acceleration compensation module and said direction cosine matrix from said direction cosine matrix computation module;

an attitude and heading angle extract module, for extracting. GPS/IMU mixed attitude and heading angle using said corrected direction cosine matrix;

a position and velocity update module which accepts said level velocity increments from said level acceleration computation module and computes position and velocity solution and receiving said optimal estimates of said position and velocity errors from error estimator to compensate said errors in said position and velocity solution to form mixed GPS/IMU/magnetic position and velocity data; and

an earth and carrier rate computation module which accepts said position and velocity solution from said position and velocity update module and computes said rotation rate vector of said local navigation frame (n frame) of said carrier relative to said inertial frame (i frame), which is connected to said alignment rotation vector computation module.

8. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 7, wherein said error estimator, which is further embodied as a robust Kalman filter, comprises:

a GPS error compensation module which gathers said GPS measurements from said GPS microprocessor, and perform GPS measurement compensation using said optimal estimates of GPS error variables from an updating state vector module to perform GPS error compensation, wherein said corrected GPS measurements are sent to said preprocessing module; and

a preprocessing module which receives said GPS satellite ephemeris from said GPS microprocessor, said corrected GPS measurements from said GPS error compensation module, and INS solutions from said controlled position, velocity and attitude module, wherein said preprocessing module performs said calculation of said state transition matrix and sends with said previous state vector to a state vector prediction module, wherein said calculated state transit matrix is also sent to a covariance propagation module and said preprocessing module calculates said measurement matrix and said current measurement vector according to said computed measurement matrix and said measurement model, wherein said measurement matrix and said computed current measurement vector are passed to a computing measurement residue module;

wherein said state vector prediction module receives said state transition matrix and said previous state vector from said preprocessing module to perform state prediction of said current epoch, wherein said predicted current state vector is passed to said computing measurement residue module;

wherein said computing measurement residue module receives said predicted current state vector from said state vector prediction module and said measurement matrix and said current measurement vector from said preprocessing module, wherein said computing measurement residue module calculates said measurement residues by subtracting said multiplication of said measurement matrix and said predicted current state vector from said current measurement vector, wherein said measurement residues are sent to a residue monitor module as well as said updating state vector module,

wherein said residue monitor module performs a discrimination on said measurement residues received from said computing measurement residue module, wherein said discrimination law is whether said square of said measurement residues divided by said residual variance is larger than a given threshold, wherein when said square of said measurement residues divided by said residual variance is larger than said given threshold said current measurement leads to said divergence of said Kalman filter, and then said residue monitor module selectively calculates a new covariance of said system process or rejects said current measurement, wherein when said square of said measurement residues divided by said residual variance is less than this given threshold said current measurement is used by said Kalman filter without changing said current covariance of system process to obtain said current navigation solution, wherein said covariance of said system process is sent to said covariance propagation module;

wherein said covariance propagation module gathers said covariance of said system process from said residue monitor module, said state transition matrix from said preprocessing module, and said previous covariance of estimated error to calculate said current covariance of said estimated error. Said computed current covariance of said estimated error is sent to a computing optimal gain module;

wherein said computing optimal gain module receives said current covariance of said estimated error from said covariance propagation module to compute said optimal gain, wherein said optimal gain is passed to a covariance updating module as well as said updating state vector module, and said covariance updating module updates said covariance of said estimated error and sends it to said covariance propagation module;

wherein said updating state vector module receives said optimal gain from said computing optimal gain module and said measurement residues from said computing measurement residue module, wherein said updating state vector module calculates said current estimate of state vector including position, velocity and attitude errors and GPS errors, and sends them to said GPS error compensation module and said controlled position velocity and attitude module.

9. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 7, wherein said magnetic heading computation module:

(a) loads said calibration parameters of said Earth'"'"'s magnetic field detector from said non-volatile memory of said mixed GPS/IMU/magnetic data microprocessor to form a magnetic calibration vector;

(b) receives said three-axis digital Earth'"'"'s magnetic field signals from said magnetic field processing interface, which is expressed in said body frame, to form a magnetic measurement vector;

(c) receives said pitch and roll angle data from said controlled INS position, velocity, and attitude module to form a transformation matrix from said body frame to level frame;

(d) compensates said magnetic measurement vector with said magnetic calibration vector;

(e) transforms said compensated magnetic measurement vector from said body frame to said level frame to form a transformed magnetic measurement vector, which is expressed in said level frame; and

(f) computes magnetic heading data using said transformed magnetic measurement vector expressed in said level frame, which is output to error estimator.

10. The integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) microsystem, as recited in claim 3, wherein a thermal sensor is installed inside or outside said MEMS IMU to measure said operational temperature of said MEMS IMU, wherein said temperature processing interface is used to condition said output of said a thermal sensor to provide digital temperature data to said temperature based scheduler of said mixed GPS/IMU/Magnetic data microprocessor, wherein said error estimator comprises:

a temperature based scheduler, for receiving said current operation temperature of said MEMS IMU from said thermal sensor through said temperature processing interface and forming a query parameter of an optimal Kalman filter to an error estimator base, based on a predetermined logic relationship between temperature and Kalman filter member; and

an error estimator base, for receiving said query parameter of an optimal Kalman filter and finding said parameters of said optimal Kalman filter and constructing said optimal Kalman filter and updating said current acting error Kalman filter;

wherein said current acting Kalman error estimator receives said current INS Poisson, velocity and attitude data from said controlled INS position, velocity, and attitude module, GPS measurements from said GPS microprocessor, and magnetic heading from said magnetic heading computation module to produce optimal estimates of errors of said current INS position, velocity and attitude data, which is sent to said controlled INS position, velocity, and attitude module to achieve said mixed GPS/IMU/magnetic position, velocity and attitude data.

11. An integrated GPS/IMU method, comprising the steps of:

(a) producing orthogonal three-axis (X axis, Y. axis and Z axis) angular rate signals and orthogonal three-axis (X-axis, Y axis and Z axis) acceleration signals to a mixed GPS/IMU/Magnetic Data Microprocessor through an IMU processing interface by an IMU;

(b) producing said Earth'"'"'s magnetic field vector measurement signals, including X, Y, Z axes signals of said Earth'"'"'s magnetic field vector measurement in said body frame of said carrier, to said mixed GPS/IMU/Magnetic Data Microprocessor through a magnetic processing interface, by an Earth'"'"'s magnetic field detector;

(c) receiving GPS RF (Radio Frequency) signals and providing GPS measurements, including GPS position and velocity data or GPS raw pseudorange, range rate, and carrier phase measurements and ephemeris and navigation message from GPS satellites to said mixed GPS/IMU/Magnetic Data Microprocessor through an GPS interface by a GPS chipset;

(d) computing a mixed GPS/IMU/magnetic position, velocity, attitude and heading solution, by means of combining said three-axis angular rate and three-axis acceleration, said GPS measurements, and said Earth magnetic field vector measurement, in order to provide a rich and accurate motion measurement of said carrier to meet diverse needs, by said mixed GPS/IMU/Magnetic Data Microprocessor;

(e) exchanging said mixed GPS/IMU/magnetic position, velocity, attitude and heading data with an external user, by an user Interface; and

(f) providing all voltage and timing signals for other devices of said system of said present invention, by a power supply and clock module.

12. The integrated GPS/IMU method, as recited in claim 11, wherein said step (d) further comprises:

d.1. processing said digital angular rate and acceleration from said IMU processing interface to compute inertial position, velocity, and attitude data by a controlled position, velocity and attitude module, for; and

performing error correction to control and remove said drift of said inertial position, velocity, and attitude data, using optimal estimates of inertial position, velocity, and attitude errors from an error estimator module to obtain highly accurate mixed GPS/IMU/magnetic position, velocity, and attitude data;

d.2 processing said position, velocity, and attitude solution from said position, velocity and attitude module, said GPS measurements from said GPS chipset, magnetic heading data from a magnetic heading computation to produce optimal estimates of inertial position, velocity, and attitude errors, which are fed back to said position, velocity and attitude module, by a error estimator module;

d.3 receiving said three-axis digital Earth'"'"'s magnetic field vector data from said magnetic field processing interface and said pitch and roll angle data from said controlled position, velocity, and attitude module and computing magnetic heading data to error estimator module, by a magnetic heading computation; and

d.4 managing input and output data for said external user, by an user communication data frame producer.

13. The integrated GPS/IMU method as recited in claim 12, wherein between said step (c) and (d) further comprises additional step (dA):

(dA.1) measuring said operational temperature of said IMU, by a thermal sensor installed inside or outside said IMU; and

(dA.2) conditioning said operational temperature of said a thermal sensor to provide digital temperature data operational temperature by a temperature processing interface;

and, step (d.2) further comprising;

(d.2.1) receiving said current operation temperature of said MEMS IMU from said thermal sensor through said temperature processing interface and forming a query parameter of an optimal Kalman filter to an error estimator base, based on a predetermined logic relationship between temperature and Kalman filter member, by a temperature based scheduler;

(d.2.2) receiving said query parameter of an optimal Kalman filter and finding said parameters of said optimal Kalman filter and constructing said optimal Kalman filter as a current acting error Kalman filter, by an error estimator base; and

(d.2.3) receiving said current INS Poisson, velocity and attitude data from said controlled INS position, velocity, and attitude module, GPS measurements from said GPS microprocessor, and magnetic heading from said magnetic heading computation module to producing optimal estimates of errors of said current INS position, velocity and attitude data, which is sent to said controlled INS position, velocity, and attitude module to achieve said mixed GPS/IMU/magnetic position, velocity and attitude data, by said updated current acting Kalman error estimator.

14. The integrated GPS/IMU method, as recited in claim 13, wherein said step (d.3) further comprises:

(d.3.1) loading said calibration parameters of said Earth'"'"'s magnetic field detector from said non-volatile memory of said mixed GPS/IMU/magnetic data microprocessor to form a magnetic calibration vector;

(d.3.2) receiving said three-axis digital Earth'"'"'s magnetic field signals from said magnetic field processing interface, which is expressed in said body frame, to form a magnetic measurement vector;

(d.3.3) receiving said pitch and roll angle data from said controlled INS position, velocity, and attitude module to form a transformation matrix from said body frame to level frame;

(d.3.4) compensating said magnetic measurement vector with said magnetic calibration vector;

(d.3.5) transforming said compensated magnetic measurement vector from said body frame to said level frame to form a transformed magnetic measurement vector, which is expressed in said level frame; and

(d.3.6) computing magnetic heading data using said transformed magnetic measurement vector expressed in said level frame, which is output to error estimator.