AN2350 datasheet(27/41 Pages) STMICROELECTRONICS

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Control algorithm

AN2350

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Control algorithm

4.1

Motion and path planning

Path planning problems generally involve computing a continuous sequence (a path) of

configurations (generalized coordinates) between an initial configuration (start) and a final

configuration (goal) respecting certain constraints.

The term motion planning is usually distinguished from path planning in that the computed

path is parameterized by time (i.e. a trajectory). The consideration of time is often important

for problems requiring time-parameterized solution trajectories.

The aim of the motion planning is to generate the inputs of the motion control system in

order to ensure the correct execution of the planned trajectory by the manipulator.

The path planning can be realized in the joint space or in the workspace. The latter has

been used in this work according to the scheme of the following figure.

Figure 20.

General scheme for the path planning

As can be seen, all the reference points necessary to the control of the desired trajectory

are calculated off-line. The trajectory planning algorithm generates a temporal sequence of

variables that specify the position and orientation of the end-effector in the workspace.

Because the control of the manipulator is realized as control of the joints, from this

sequence of variables it is necessary to perform the kinematics inversion to build a

sequence of variables in the joint space. These joint variables must be opportunely

converted in incremental encoder pulses, because the position closed loop control is

performed on the feedback of the incremental encoders of the two joints.

The path planning method used in this work is the straight-line motion. In this method the

end-effector of the robot travels in a straight line between the start and stop points, using a

trapezoidal velocity profile, in which the motion controller must command the motor driver to

AN2350 Datasheet(PDF) 27 Page - STMicroelectronics