I. Introduction
Modular robotic systems (MRSs) use robotic modules as building blocks to create a variety of kinematic configurations, see Fig. 1. Each module is an independent mechatronic subsystem with a single function. Modules can be of different types. A new kinematic configuration can be specifically selected for a given task and built with modules of different types. This system design principle brings great versatility and flexibility. Throughout this paper, the phrase “kinematic configuration” refers to the robot morphology, whereas “configuration” indicates the robot state.