Long Reach Articulated Carrier: Geometric and Elastic Error Calibration of the Flexible Model Followed by Nonlinear Generalized Error Calibration With Ordinary Polynomials

The Interactive Robotics Unit of CEA LIST has developed a very challenging robotic carrier (called P.A.C.) which is able to perform high range intervention tasks inside blind hot cells. This long reach multi-link carrier has 11 degrees of freedom (DOF), an operational range over 6 meters of full extension and weighs less than 30 kg. The gravity effect in the manipulator is largely compensated by a special mechanical structure (the parallelogram) that helps to reduce the size of the actuators used to operate the robot. Due to its size and weight, this large robot manipulator holds lots of elastic and geometric deformations. Hence, it presents very low position accuracy. A flexible model is developed to take into account most of the structure deformations. A calibration method of the robot flexible parameters is used to reduce the positioning error of the end effector and the intermediate joints. Then, a second calibration method of the robot using generalized error matrices is applied to further reduce the residual positioning error of the system. These matrices are a polynomial function of the system geometry and joint variables. This method is first tested by simulation to ensure its viability on large manipulators. After encouraging simulation results, an experimental field is made for the calibration of the PAC manipulator. Results show that the adopted flexible model, with the new calibrated parameters, followed by the polynomial model is a good combination to correct and reduce the system errors.