Attitude sensing apparatus for determining the attitude of a mobile unit

Abstract

The invention provides an attitude sensing apparatus for determining the attitude of a mobile unit that can reliably estimate an alignment angle between a GPS antenna coordinate system and an IMU coordinate system with good accuracy regardless of the magnitude of the alignment angle. Based on observation of the difference between a GPS angular velocity and an IMU angular velocity, an alignment angle estimating section estimates an alignment angle and sensor errors. An alignment angle adder and a sensor error adder cumulatively add and update the estimated alignment angle and sensor errors, respectively. The estimated alignment angle is fed back to an inertia data converter while the estimated sensor errors are fed back to an inertia data correcting section. The apparatus repeatedly performs estimation until the estimated alignment angle gradually approaches a true alignment angle by successively feeding back estimated values to a flow of alignment angle estimation process.

What is claimed is:  
     
         1 . An attitude sensing apparatus for determining the attitude of a mobile unit by successively performing a process of estimating an alignment angle between an antenna coordinate system of a GPS attitude sensing system which determines the attitude of the mobile unit in the antenna coordinate system and an IMU coordinate system of an IMU attitude sensing system which determines the attitude of the mobile unit in the IMU coordinate system and thereby integrating the attitudes of the mobile unit determined in the individual coordinate systems, said attitude sensing apparatus comprising: 
 an alignment angle estimator for successively estimating an alignment angle to be used in a succeeding calculation process based on the difference between inertia data calculated from observations by said GPS attitude sensing system and inertia data observed by said IMU attitude sensing system; and    an alignment angle adder for generating an updated alignment angle by cumulatively adding the successively estimated alignment angle and thereby updating the estimated alignment angle in sequence and for outputting the updated alignment angle to said alignment angle estimator;    wherein the estimated alignment angle is successively fed back for use in the alignment angle estimation process.    
     
     
         2 . The attitude sensing apparatus according to  claim 1 , wherein individual components θ x , θ y , θ z  of the alignment angle satisfy the following conditions:  
       −85°≦θ x ≦85°, −85°≦θ y ≦85°, −85°≦θ z ≦90° 
       and the estimated alignment angle is successively fed back together with the updated alignment angle for use in the alignment angle estimation process.  
     
     
         3 . The attitude sensing apparatus according to  claim 1  or  2 , wherein said alignment angle estimator successively estimates a sensor error caused by an inertia sensor of said IMU attitude sensing system from the estimated alignment angle, said attitude sensing apparatus further comprising: 
 a sensor error adder for generating an updated sensor error by cumulatively adding the successively estimated sensor error and thereby updating the estimated sensor error in sequence and for outputting the updated sensor error to said alignment angle estimator;  
 wherein the updated sensor error is successively fed back for use in the alignment angle estimation process.  
 
     
     
         4 . The attitude sensing apparatus according to one of  claims 1  to  3  further comprising: 
 a setter for setting a provisional alignment angle upon installation of a GPS antenna of said GPS attitude sensing system and an inertia sensor of said IMU attitude sensing system;  
 wherein initial conditions for said alignment angle estimator are set by using the provisional alignment angle.  
 
     
     
         5 . The attitude sensing apparatus according to one of  claims 1  to  4 , wherein the alignment angle estimation process is performed until the alignment angle is finally determined.