VIRTUAL GEOMETRIC MODEL WITH DYNAMIC PARAMETERS FOR 6 DOF ARTICULATED ARM ROBOT

Abstract

To calculate joints angles of an articulated arm robot, when the coordinates of the point to be reached are known, different calculation methods or iterative algorithms for inverse kinematics (IK) can be used. IK requires that the dimensions of the robot segments and the initial positions of the joints to be known, described, and implemented mathematically, so it is based on the geometric model of the robot. In practice, the geometric modeling of the robots is done considering that all their structural elements are rigid, and their dimensions and positions are considered constant (while in reality the robots suffer certain deformations that can have different causes). This article considers the thermal deformations that a robot suffers during operation which are leading to positioning errors. The deformations are variable during the warm-up period of the robot and become constant after reaching the thermal stabilization level. From this point of view, if it is desired to consider and possibly compensate these thermal induced errors, the elaboration of the geometric model of the robot in the classical way is no longer possible and the geometric parameters must be somehow described as variables. Thermal deformations produce displacements and torsions of the robot elements. Linear and angular deviations may occur from the initial (theoretical) position in all 3 directions of the cartesian axis systems used in robot modeling. This paper presents a technique for creating a virtual model of the ABB IRB140 robot in CoppeliaSim, programming and modeling environment, with the positioning of the axis systems attached to the joints identical to the real position (unlike simplified versions of Denavit-Hartenberg geometric models) and the logic of a custom written software algorithm for automatic deformation of the model.