Trajectory generation describes the position velocity and acceleration of each link. This
includes how the front user interfaces to describe the desired behavior of the manipulator.
This could be a very complicated problem depending on the desired accuracy of the system.
In some applications we might need to specify only the goal position, whereas in some
application, we might need to specify the velocity with which the end effector should move.
Since trajectory generation occurs at run time on a digital computer, the trajectory points are
calculated at a certain rate, called the path update rate. One disadvantage of using a PID controller
is a high update rate is required to achieve reasonable accurcy.
Our package role here is to calculate trajectory points which generate a smooth motion for the manipulator. The smoothness of
motion is a very important issue due to physical considerations such as the required torques
that causes this motion, the friction at the joints, and the frequency of update required to
minimize the sampling error.
Figure 5: Trajectory Genrator integrated in the control loop
Figure 5 shows how trajectory generator can integrated in the control loop. It also shows two update rates, one is the inner update rate which update the system control with the actual joint position and velocity. Other updates the system control with the required joint values. The sampling of the two update rates can be different.