TABLE OF CONTENTS A robotic motion task is specified by defining a path along which the robot must move. A path may be defined by a geometric curve or a sequence of points defined either in operational coordinates (end-effector coordinates) or in joint coordinates. The issue of trajectory generation is to calculate, for the control system, the desired reference joint or end-effector variables as a function of time, such that the robot tracks the desired path. Thus, a trajectory refers to a path and a time history along this path.
The trajectories of a robot can be classified as follows:
trajectory between two points with free path between them;
trajectory between two points via a sequence of desired intermediate points, also called via points, with free paths between these via points;
trajectory between two points with constrained path between them (straight line segment for instance);
trajectory between two points via intermediate points with constrained paths between these via points.
For the first two classes, the trajectory is generally created in the joint space. For the last two classes, it is usually better to generate the trajectory in the operational space.
Trajectory generation in the joint space presents several advantages:
it requires fewer online calculations, since there is no need to calculate the inverse geometric or kinematic models;
the trajectory is not affected by crossing singular configurations;
maximum velocities and torques are determined from actuator data sheets.
The drawback of joint-space trajectory generation is...
