Posture analysis of the cross-country autonomous land vehicle

Abstract

In this paper, a posture analysis method for the Crass-Country Autonomous Land Vehicle (CCALV) is proposed.To simplify the discussion, assume that(1) the terrain is hard and with random height.(2) the local terrain map is known through sensory system and described by a set of height data (2, 1 of the discrete ground pints I (x, ,y, ) 1 which are divided equally along x and y axes.(3) the C%ALV is replaced with a regular rectangular plane ABCD.At a special moment during steering of the FCALV, assume that its center (xo,y,) and steering direction, i.e the yaw angle p are given, we shall determine the contact plane between the plane ABCD and the ground. This plane is defined as the posture plane of the ccL4V with respect to (xo,yol 9) and the corresponding posture angle pair ( 0 ,~) is defined as the posture of the CCALV with respect to (xo,yo,p), where the 8 , y are the pitching angle and the r o l l angle of the CCALV respectively.The basic idea of the nunerica1 algorithm for solving the posture of the CCALV can be expressed as follows. For given (x ,yo,@), consider the admissible range of 0 , y E ( -5 , :). Divide it into small parts so that ( 0 ,~) is fixed relatively in each one. For each specially fixed p i r ( e l , y I J ) , find the projection region of the plane ABCD on XOY plane Q l , and based on it solve the contact posture of the plane with the ground ( 0 , y ) . Verify weather the postrue of the plane is coincident with the given (el , y I ) . The whole procedure may On n be described by the following step-by-step search algorithm.Main Algorithm step 1 Translate the origin of the ground coordinate system to (xoryOrO) and rotate @ around the new 2 axis; step 2 Determine the search series (y,(i=l,---,k), 0 (i=l,----,k; j=l,--.-,ml ) ) according to the projection region of ABCD on XOY plane which can be calculated through the hmrogeneous transformation between the plane and the ground coordinate systems;1.i step 3 For each projection region Q I J determined by ( y , , 0 ) , find the covering plane which contains the three heightest points P, (xk , y,, zk), k=1,2,3 on Q I J while the center line of ABCD passes throuh AP1pzP3. It is the possible contact plane of CCALV with the ground and can be easily obtained accoding to the heiht data (2,) on Q step 4 Solve the corresponding (@,I) according to the above covering plane.