position, orientation, and location of a
rigid body
the study of the kinematics of robot manipulators, we are constantly dealing with the location of
several bodies in space, the bodies of interest include the links of a manipulator, the tools, the
workpieces, and so on
of a body with respect to a reference coordinate system is known if the position of the body are
known. if the body of interest is rigid, six independent parameters would be sufficient to describe its
location in three dimensional space
as shown in
descriiption of position
of any point eith respect to reference frame
can be described by a 3*1 position vector
description of an
orientation
angle representations
the direction cosine representation of an orientation contains nine parameters, and
the screw representation requires four
the rotation matrix
the resulting rotation matrix is obtained by
premultiplying three basic rotation matrices
the equivalent roll-pitch-yaw angeles as follows
successive rotations about the moving coordinate axes
hence the overall rotation matrix
we can expand
euler angles as follows
the resulting rotation matrix is obtained by a
postmultiplication of three basic rotation matrices as
follows
axis representation
we seek a description of de orientation of a rigid body in terms of a rotation about a sceww axis
were the elements of the ratation matrix are given by
it appears that there are two solutions of the serew axis
direction cosine representation
one convenient way of describing the orientation of a rigid body is by means
of the direction cosines of the coordinate axes of the moving frame with
respect to the fixed frame, three unit vectors pointing along the coordinate
axes of the moving frame B, respectively, as shown in fig.
the position vector os a point P, and the rotated frame B
equating x,y,z componets of aP, to the coresponding componets
matrix from we obtain
the determinant of the coefficients must
vanish
description of a location
as a pointed out earlier, the location of the rigid body can be described
by the position of the origin Q and the orientation of the moving frame
with respect in the dixed frame