The DLR Robots library - Using replaceable packages to simulate various serial robots

Abstract

In order to simulate different kinds of serial robots, the implementation of functionalities such as the calculation of their direct and inverse kinematics, visualization, collision behavior, etc. is necessary. However, providing these functionalities in robot specific models leads to additional modeling overhead in cases where one would like to switch between several different robot models. The DLR Robots library demonstrates an implementation of all robot specific components as replaceable Modelica packages, allowing for an user-friendly way to exchange robot models without modifying the general structure of the overlying model. The simulation of robotic systems is a great example for the multi-domain versatility of Modelica, combining multi-body mechanics with controllers, electric drives and algorithms, e.g. path-planning. A multitude of scientific works use Modelica to simulate a specific robot, providing models for the mechanics and all other components exclusively for the simulated robot. Other approaches use parameter sets to simulate more than one robot model within a given structure. However, both approaches lack flexibility regarding switching between different robot types in a Modelica model, e.g. if the number of axes is changing. In this case, instead of changing a parameter value, the complete model structure has to be altered and adapted for the new robot model. In this paper, a new approach to model robots in Modelica is presented. By separating the robot functionalities (e.g. visualization, dynamics, path-planning, etc.) from the model-based description of the robot itself, and wrapping the latter in a replaceable package, it becomes possible to switch between entirely different robot models without the need for changing the structure of the main model. This approach is inspired by the Modelica Media library, where different media provide their own functions and models, also wrapped in a replaceable package, enabling the user to switch easily between different media in a model. Utilizing the scripting language LUA, it becomes possible to control the simulated robots with a virtual robot controller. This enables the user to design complex robot programs and execute them in a Modelica simulation. Several applications of the library are shown, from feasibility studies of robotic systems to real-time path-planning algorithms for real robot arms.