Trajectory planning along continuous paths subject to process constraints
Creators: name: Li, Dan
Publisher: name: University of British Columbia
Year: 2009

description: This thesis presents a new trajectory planning algorithm for planning safe and smooth tra jectories of a robot tool moving along a specified curve subject to application constraints. The application constraints include geometric constraints (allowable orientation and po sition of the tool) and motion constraints (joint limits, robot configuration inversions and collision avoidance). The algorithm, which is based on a configuration space approach for robot motion planning, addresses the problem of motion planning along a curve rather than point-to-point motion associated with pick and place operation. Configuration spaces are searched to assess the locations of the obstacles in the vicinity of the curve and the curvature of the curve in the work space. The trajectory is planned by searching between path segments connecting successive curve points, generating the path along a curve linking the path segments, and selecting the optimal configurations along the path to construct the final trajectory. If more than one paths exist, an A* search is em ployed to optimize the path. The selected path specifies a sequence of tool configuration ranges, and each configuration produces several inverse kinematic solutions. A second A* search is used to select inverse kinematic solutions, which avoid major changes of robot configuration (i.e. joint inversion). Since the algorithm searches the allowable tool orientation range, the optimal trajectory which maximizes process quality is obtained. The trajectory allows the tool to translate and rotate simultaneously without collision, and the tool remains within the allowable orientation range and tracks the desired curve within a given tolerance. Since the step size between curve points is varied dynamically as the search proceeds, the path is planned based on a minimum number of curve points, resulting in fast path planning. A smaller step size is used if the curvature of the curve or the likelihood of collision is high. The primary advantage of the algorithm is not only in finding a collision free path but in planning a trajectory which satisfies application constraints. It is felt that this algorithm provides a high quality process which is difficult to achieve with manual robot programming. An off-line simulation program, TRAJPLAN, has been developed based on this al gorithm. After the user inputs the application specifications, selects the curves to be processed and the environment objects of interest, TRAJPLAN automatically plans the trajectory of robot tool and generates the required set of sequential robot joint angles. TRAJPLAN plans the motion with different precision depending on the requirements of the application. This algorithm has been demonstrated for robotic fish butchering and welding, and the issues related to these applications are discussed in this thesis. As an example of a typical problem, the system automatically plans the trajectory of a robot tool moving along a 3-D curve with 31 points and surrounded by 5 obstacles in 1’20”. The algorithm is suitable for a variety of robot applications which require the robot tool to move along a curve, keep a certain orientation and position relative to the curve, and avoid collision with the environment.