The ArmarX Statechart Concept: Graphical Programing of Robot Behavior

ed through the Sensor–Actor unit concept. These Sensor–Actor units realize hardware or simulator access and hide the low-level communication from higher-level layers of the robot software. On the mid-level, robot capabilities, such as perception, planning, and motion generation, are implemented in a network transparent way. The high-level layer comprises a set of robot skills, realized as statecharts, which are used for assembling complex robot programs. The arrows depict middleware communication, which can be local or remote. The decision if a communication channel is local or incorporates remote calls is transparently taken on the fly by the middleware based on the current deployment. 2 Wächter et al. The ArmarX Statechart Concept Frontiers in Robotics and AI | www.frontiersin.org June 2016 | Volume 3 | Article 33 well as runtime introspection. It should also not be necessary to recompile programs upon structural or control flow changes. Furthermore, a graphical user interface is desirable in order to reduce the unavoidable complexity of describing robot behavior and to minimize development and comprehension efforts. This convenience feature should provide means for defining and parametrizing both control and data flow, online visualization of active states and transitions in running programs, and a convenient way to incorporate custom user code. Additionally, a code generator should be provided for enforcing type-safety and catching errors in user code as early as possible as well as allowing source code auto-completion in development environments of statechart-related data types and functions. We will discuss the statechart concept of the robot development environment ArmarX (Vahrenkamp et al., 2015) in detail and show how it provides both reusability of high-level robot skills realized as distributed, hierarchical statecharts, and the possibility to add user code with access to the external robot components. Figure 1 shows how statecharts are integrated in the basic structure of ArmarX. In Section 2, we elaborate on the state of the art and compare it to our approach. Our statechart concept is presented in detail in Section 3. This is extended in Section 4 in regard to usability and integration in the robot development framework ArmarX. In Section 5, we show some use cases for the presented approach to give a better understanding of how it can be utilized. The discussion in Section 6 reflects our experience with the ArmarX statecharts, and Section 7 concludes the paper.