Performance Index And Calibration Method Research On The Heavy-payload Forging Manipulator

Forging manipulator is a special industrial robot with large size, big inertialparameters and high endurance. It is used in the forging workshop, in order toaccomplish the task of forging different sizes of workpiece with the forging pressmachine. There are a lot of challenges for the forging manipulator due to its owncharacteristics and its applications, including how to choose the simplest kind ofactuator mechanism to complete the demands of the movement, how to determine thedirect position of the grasping mechanism of the forging manipulator with extra degreeof freedom, how to improve the efficiency of the conventional method for thekinematic calibration of the complex mechanism, how to perform the identification ofthe dynamic parameters of the mechanism over-constrained and over-actuated. Thispaper presents the definition of Kinematic Coupling Complexity to measure thekinematic coupling degree of a manipulator based on the input/output velocity matrix,analyze the direct kinematics of the heavy-payload forging manipulator equivalent to a3-DOF underactuated mechanism in the grasping stage, perform the identification of the kinematic and dynamic parameters based on its KCC index. The main contributionis as following.1) The direct position kinematics of the3-DOF underactuated mechanism isanalyzed as follows: firstly, we add a virtual constraint on the mechanism, convert it toa2-DOF fully actuated mechanism and calculate the direct kinematics of theconstrained mechanism. Then, the constraint is applied to many different positions andthe mechanism with lower gravitational potential energy than any other constrainedmechanism is chosen, and its direct position is what we need for the3-DOFunderactuated mechanism.2) The definition of Kinematic Coupling Complexity is presented to measure thekinematic coupling degree of a manipulator based on the input/output velocity matrix.In order to distinguish the differences among many matrixes, three factors will beconsidered includingKCC sthe proportion of nonzero elements in matrix J,KCCe thedifference of nonzero elements’ numbers in every row among many matrixes andKCC dthe difference of nonzero elements’ positions among many matrixes.3) A new method for the kinematic calibration is proposed based on KCC of theforging manipulator. This method can be used if KCC of the mechanism is very small,or even the movement of the output platform is decoupled. When the kinematiccalibration of several different movements is separated, the according equation will besimpler than the conventional calibration method. Therefore, the kinematic calibrationof the overall mechanism will be easier because of its iteration times and computationconsumption.4) The method of dynamic parameter identification is proposed for the forgingmanipulator. Firstly, the pitching mechanism is analyzed, and the result is used as apayload for the lifting mechanism. Secondly, the dynamic parameter identification forthe lifting mechanism is proposed with over-constrained mechanism in consideration. The modified Newton Euler method is used during the whole process, and the dynamicparameters can be calculated by the least squares method. Lastly, the dynamicparameters of the workpiece are identified, when the workpiece is grasped by theforging manipulator.