The kinematics of a general double-tripod manipulator is presented. Th
e double tripod manipulator is based on a spatial three-degrees-of-fre
edom (3-DOF) parallel mechanism. The device possesses a moving platfor
m, a fixed platform, and three legs. Each leg comprises kinematically
similar rotary, spherical, and rotary joints. The kinematic model of t
he mechanism used here consists of a generalized, non-reflective mecha
nism. The mobility of the mechanism is examined, and solutions to the
forward and inverse kinematics problems are presented. It is also show
n that special geometries of the mechanism result in closed-form solut
ions for both the forward and inverse kinematics, Numerical results ar
e presented for the general case and also for the simplified case, and
algorithm speed is examined. (C) 1998 Elsevier Science Ltd. All right
s-reserved.