Colloquia

Summary

Safety is the most important when considering the use of a robotic manipulator. When a robotic

manipulator is intended to perform its tasks in a space also inhabited by humans, great care must be

taken to prevent any injury. Preventing collisions between the manipulator and its enviroment is the best

way to achieve this goal. Since prevention is not always possible, collission detection is also a valuable

tool. Detection can be done using dedicated sensors of the manipulator but it can also be done by

prediction driving forces and comparing the prediction with measured forces. A difference in these forces

might indicate a collision and the control system can then take apropriate actions. For this method to

work the reaction forces must be predicted in realtime. When a manipulator can be assumed to behave

as a rigid body this prediction is realifly straightforward. For manipulators where, due to lower stiffness,

the internal flexibilty contributes significantly to the reaction forces a more complex model is required.

The flexibilty of the manipulator is typically determined using a Finite Element Model. These models

are large and slow to solve. By reducing the number of degrees of freedom in the model an attempt can

be made to implement the flexibilty in realtime. In this research a benchmark problem, a 3D slider crank

mechanism, was modeled in Abaqus. A number of reduced models where derived using the substructure

functionality of Abaqus. Dynamic simulations where performed of the full order model and the reduced

order models. The reduced models where simulated using Abaqus and Amesim. Amesim is a system

modeling tool that can also support realtime applications. Comparing the results of all these simulations

it can be concluded that Abaqus has issues running a dynamic simulation with a small number of nodes

(3 or less). This can be attributed to the choice of computational frame by Abaqus. Amesim requires

less degrees of freedom for an accurate simulation. The process of modeling a flexible body simulation

in Amesim has still some chalenges but the delevopment is still ongoing.