Space Grant Consortium - University of Wisconsin - Green Bay

The system began movement at approximately 0.66 seconds. The target velocity of 50 i nches
per minute was overshot by over 100%. It also overshot zero after beginning its down ramp at
1.85 seconds, eventually stopping after 2.5 seconds.
The velocity plot of a move in the x direction shows that the robotics system is under damped
when ramping up to the target velocity and when ramping down to zero while stopping.
Exploration of t he pr ogramming m anual r evealed a lternative c ommands f or c ontrolling t he
movements. D ifferent combinations of ne w c ommands pr oduced uni que d ynamic responses.
The overshoot of a normal move command can be eliminated using existing G-code commands
that modify settings in the robotic control system. F igure 3 s hows velocity versus time of the
same axis after new commands have been added to the programming.
Figure 3 - Ramp from 0 to 50 IPM and back to 0, X Axis, one inch move, alternative commands
Figure 3 shows that the percent overshoot has been reduced to under 10% from over 100%. The
movement be gins a t 0.7 5 s econds and r eached target s peed i n unde r a qua rter of a s econd.
However, this motion was much more controlled than the motion from the previous method.
Testing t he y an d z ax es yielded similar r esults, an unde r damped motion that overshot target
velocity. The less massive z axis had less overshoot because less mass is easier to control by the
robot, while the more massive y axis (which consists of a table weighing nearly one thousand
pounds) displayed a more erratic overshoot. Repeating the new programming method for the y
and z axis yielded similar results, dampening the movement and reducing overshoot.
4