Coordinated Motion Control of Multiple Robotic Devices for Welding and Redundancy Coordination through Constrained Optimization in Cartesian Space

In this paper we consider the problem of coordinating multiple motion devices for welding. We focus on the problem of coordinating a positioning table and a seven axis manipulator, given the parametric definition of a trajectory on a weld piece. The problem is complex as there are more than nine axis involved and a number of permutations are possible which achieve the same motions of the weld torch. The system is redundant and the robot has singular configurations. As a result, manual programming of the robot system is rather complex. Our approach to the coordination problem is based on subdivision of constraints. The welding table is coordinated to ensure down-handed welding convention, while the seven axis robot (a six axis Cybotech WV15 robot and track) are coordinated to track the weld point. The coordination is achieved by keeping the robot in good maneuverability position, so as to avoid the robots singularity conditions and motion limits of the track. We were able to express the singularity conditions in terms of cartesian coordinates [I]. As a result, we could obtain analytic solution to our optimization of the maneuversability and therefore avoid using known pseudoinverse techniques which are known to exhibit inaccuracies [2]. The output of our optimization process is the positions of the track and the robot end-effector, these positions are used to generate the joint angles of the arm by inverse kinematics

Simplified Motion Control of a Vehicle manipulator for the Coordinated Mobile Manipulation

This paper considers a resolved kinematic motion control approach for controlling a spatial serial manipulator arm that is mounted on a vehicle base. The end-effector’s motion of the manipulator is controlled by a novel kinematic control scheme, and the performance is compared with the well-known operational-space control scheme. The proposed control scheme aims to track the given operational-space (end-effector) motion trajectory with the help of resolved configuration-space motion without using the Jacobian matrix inverse or pseudo inverse. The experimental testing results show that the suggested control scheme is as close to the conventional operational-space kinematic control scheme

Programming of Path Specific Robot Operations with Optimal Part Placement

In this paper we describe a task level programming system for path specific robot operations. We define path specific tasks as those robot tasks in which the path the manipulator end effector has to follow is fixed and is given, such operations may include welding or sealant application. The initial path selection is made through a graphical interface using a pointing device (such as a mouse) to outline the desired path on a CAD model of the workpiece. The final result of the system is the part location, which enables the chosen manipulator to optimally perform the desired task. Optimality is based on maximizing the manipulability of the manipulator performing the task using a function of the jacobian. User defined constraints, joint limit constraints, and collision avoidance constraints are used to guide the optimal location selection. The workable task is then executed using calls to a C language based motion control library outlined in [Guptill88] [Guptill & Stahura 87]. The usefulness of the system described in this paper is indicated by an example of two robotic devices performing a down-hand welding operation

Time Scaling of Cooperative Multi-Robot Trajectories

In this paper we develop an algorithm to modify the trajectories of multiple robots in cooperative manipulation. If a given trajectory results in joint torques which exceed the admissible torque range for one or more joints, the algorithm slows down or speeds up the trajectory so as to maintain all the torques within the admissible boundary. Our trajectory modification algorithm uses the concept of time scaling developed by Hollerbach[10] for single robots. A multiple robot system in cooperative manipulation has significantly different dynamics compared to single robot dynamics. As a result, time scaling algorithm for single robots is not usable with multi-robot system. The trajectory scaling schemes described in this paper requires the use of linear programming techniques and is designed to accommodate the internal force constraints and payload distribution strategies. As the multi-robot system is usually redundantly actuated, the actuator torques may be found from the quadratic minimization which has the effect of lowering energy consumption for the trajectory. A scheme for generating a robust multi-robot trajectories when the carried load mass and inertia matrix are unknown but vary within a certain range is also described in this paper. Several examples are given to show the effectiveness of our multi-robot trajectory sealing scheme