A novel trajectory planning technique for anthropomorphic robots with non-spherical wrist

In this paper, an innovative trajectory planning algorithm, aimed at limiting the accelerations of joints in robots with non-spherical wrist, is presented. Due to the presence of a non-spherical wrist, there is no closed-form solution of the inverse kinematics of the robot. Thus, in order to limit the accelerations of the joints, as well as to obtain a suitable ve-locity profile, numerical algorithms have to be used. The trajectory planning technique proposed in this paper is based on a B-spline parametrization of the end-effector path. A set of points on the path is defined: the end-effector velocity at any of such points is computed on the basis of the ve-locity at the previous point and of the maximum admissible acceleration of the joints. The proposed methodology has been applied to painting robots in order to reduce the accelerations, as well as the motor torques, at the joints. Also, this technique allowed to keep constant the velocity of the end-effector even for complex painting paths. A model of the robot was implemented in the Matlab™ environment and the trajectory obtained from the simulations was then tested on a GR680 painting robot, manufactured by CMA Robotics. The results of the experi-mental tests showed a reduction of the motor torques at the joints, as well as a smoother velocity profile.