Calibration Using Generalized Error Matrices of a Long Reach Articulated Carrier

This work concerns the development of advanced robotic systems for nuclear application. The manipulator will be used for light intervention in spent fuel management facilities. The robot must meet severe specifications: small diameter, long reach within a minimum range of 6 m, high dexterity to move in constrained environment and lots of degrees of freedom (DOF) for obstacle avoidance. In order to meet these requirements, The interactive robotics unit of CEA LIST has developed a very challenging robotic carrier (called P.A.C.) which is able to perform light intervention tasks inside high range of blind hot cells using existing engineering penetrations. This long reach multi-link carrier has 11 DOF and weighs less than 30 kg. The gravity effect in the manipulator is largely compensated by a special mechanical structure (the parallelogram) that helps reducing the size of the rotation actuators used to operate the robot. Also, a glass fiber epoxy equilibrium spring is used to compensate the gravity effect over the elevation actuators. A field test is made to measure the robot´s repeatability and accuracy by using a laser tracker to measure the end effector´s position. Due to its size and weight, this large robot manipulator holds lots of elastic and geometric deformations. Thus it possesses a very low accuracy. A calibration method of the robot using generalized error matrices is applied to reduce the positioning error of the system. These matrices are a polynomial function of the system geometry and joint variables. The method is first tested by simulation to examine its viability on large manipulators. After an encouraging simulation results, an experimental field is made for the calibration of the PAC manipulator. Results show that the adopted polynomial model, with the new identified parameters, is capable of correcting and reducing the system errors of long reach manipulators.