To improve work efficiency and enable robots to complete specific tasks in the shortest possible time, reasonable motion planning is essential. Offline motion planning is divided into path planning and trajectory planning.
The goal of path planning is to maximize the distance between the path and obstacles while minimizing the path length; the goal of trajectory planning is primarily to minimize the robot's running time or energy consumption during joint space movement. Trajectory planning incorporates time-series information into path planning, planning the robot's speed and acceleration during task execution to meet requirements such as smoothness and speed controllability.
Teach-and-playback is one method for path planning. It involves teaching the robot in the operating space and recording the results, which are then reproduced during the work process. On-site teaching directly corresponds to the actions the robot needs to perform, making the path intuitive and clear. The disadvantages are that it requires experienced operators, consumes a significant amount of time, and the path may not be optimal. To address these issues, a virtual robot model can be created, allowing for virtual, visual operation to complete the path planning for the task.
Path planning can be performed in joint space. A quintic B-spline can be used as the interpolation function for the joint trajectories, and the integral of the square of the jerk relative to the motion time can be used as the objective function for optimization to ensure sufficiently smooth joint motion. Alternatively, the robot's joint trajectories can be interpolated using quintic B-splines, and the velocity and acceleration endpoint values of each joint can be arbitrarily configured according to smoothness requirements. Furthermore, trajectory planning in joint space avoids the singularity problem in the operational space. Another team has designed a joint trajectory optimization algorithm in joint space to avoid singularities. This algorithm utilizes the functional redundancy of a certain joint in a 6-DOF arc welding robot during the task, using robot singularities and joint constraints as constraints, and employs the TWA method for optimization calculations.
Compared with operation space path planning, joint space path planning has the following advantages:
1. It avoids the singularity problem of robots in the operating space;
2. Because the robot's movement is achieved by controlling the movement of joint motors, a large amount of forward and inverse kinematics calculations are avoided in joint space;
3. Optimization of joint trajectories in joint space to facilitate control.
