While serial robots are known for their versatility in applications, larger workspace, simpler modeling and control, they have certain disadvantages like limited precision, lower stiffness and poor dynamic characteristics in general. A parallel robot can offer higher stiffness, speed, accuracy and payload capacity, at the downside of a reduced workspace and a more complex geometry that needs careful analysis and control. To bring the best of the two worlds, parallel submechanisms could be simply connected in series to achieve a robot with better dynamic characteristics and larger workspace. Such a design philosophy is being used in several robots at DFKI for example, Charlie, Recupera Exoskeleton, AILA2 etc.

Parallel robots bring their own set of challenges when it comes to their modeling and control and hence not well treated despite their certain clear advantages over serial robots. In the last 20 years, various techniques from mathematics like screw theory and algebraic geometry have started to find applications in robotics giving a whole new outlook to the traditional understanding of robot kinematics which is broadly based on analytical geometry. Providing generic closed form solutions to geometric and kinematic models in case of Parallel Kinematic Machines (PKMs) are still open problems for the research community. This talk will provide an overview of these methods and present the solution to geometric and kinematic problems related to Active Ankle - a newly invented PKM at DFKI RIC.

Traditional approaches in kinematic/dynamic modeling considers the robot as a set of different bodies and joints. Due to large number of moving parts in a submechanism with closed loops, such a modeling approach is inefficient and computationally expensive. Hence, a mathematical and software framework is envisioned around modular and distributed kinematic and dynamic modeling of complex hybrid robots which are built of various submechanisms catering to different motion groups. Essentially, it is about moving from the traditional body-joint based modeling methodology to a new body-joint composite or submechanism based modeling methodology. Efficient dynamic modeling of complex robotic systems can lead to more compliant behavior, better whole body control, walking and manipulating capabilities etc. which are highly desired in the present day and future robotic applications.