Automatic pose optimization for robotic processes

Abstract

In many robotic processes such as milling and drilling, there are multiple solutions for robot poses, as the rotation around the tool axis remains as a degree of freedom (DoF) in positioning. Yet until now, this DoF causes additional efforts in CAM programming as it requires manual intervention. Instead, this DoF can be used to optimize the robot pose according to different criteria of the robot such as stiffness or avoidance of backlash effects. This paper presents different criteria for optimization of the robot pose in machining and describes the optimization of robot stiffness based on a novel method for its identification, which is in detail described on this paper. Furthermore, the potential of the automatic resolution of the DoF is outlined enabling staff without robot knowledge to define reasonable robot paths

High accurate robotic drilling with external sensor and compliance model-based compensation

“…In our recent work [16], we proposed a compliance model ( f com (·)) for industrial robots. The model consists of nonlinear identifications for the backlash of each joint and linear identifications for the other areas of the identified compliance.…”

“…Deformations were calculated in the external industrial controller and compensated based on the compliance model defined in (5) given as inputs the robot pose, robot joint weights and center of masses, and exact known load of the endeffector 166 kg. The corner and center points of three symmetrical cuboids of the drilling work space with different dimensions (as in [16]) were measured. For each cuboid three different measurements were performed (1) without end-effector and compensating robot joint masses; (2) with end-effector and compensating just the robot joint masses; and (3) with end-effector and compensating the robot joint masses and the end-effector mass.…”

Automatic Motion Generation for Robotic Milling Optimizing Stiffness with Sample-Based Planning

“…The robot joint compliance model has been identified for the Kuka KR270 using the process described in one of our previous publications [9]. The model has been identified with one hundred measurements for each of three different measured robot poses.…”

“…The calculation of the Cartesian stiffness based on the polar stiffness and the use of the Jacobian matrix has also been proposed as a modeling alternative [18]. The robot stiffness used in this contribution is identified as linear descriptions on the ranges where no backlash is observed and nonlinear functions are addressed when gear deformation is noticed [9].…”

“…In one of our previous works, the automatic robot stiffness pose optimization for robotic processes has been presented, and the definition of different criteria, such as end-effector stiffness optimization in process direction, damping, collision and reachability, and the different interpretations for applications, such as drilling, deburring, cutting and milling, have been looked at [9]. Lehmann proposes a three-step approach, machining strategy generation, offline force compensation and online force compensation, as a strategy to compensate the force-induced accuracy influences.…”