Tunable muscular damping to increase morphological computation in legged locomotion

• Applicants: Professor Dr. Daniel Häufle; Professor Dr. Tobias Siebert
• Subject Area: Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449912641

The animal’s (including human’s) neuromuscular control system seemingly effortless balances power generation, energy dissipation, and energy storage, for the complex task of robust and agile legged locomotion. For this, biological systems rely on the visco-elastic properties of muscle-tendon units to perform ‘morphological computation’, i.e., a contribution of the physical structures to the control. Especially in unknown ground conditions, where the systems kinetic energy differs at every impact, the visco-elastic properties of the muscle-tendon units generate the first response to unknown ground conditions. As a result, they achieve robust and agile locomotion despite neuronal delays which may be as large as 40% of the duration of a stance phase. In the first phase of this project, we simulated perturbed legged locomotion in a biomechanical computer model and reproduced the simulated muscle fibre boundary conditions in an in vitro muscle fibre setup. So far, we have examined and understood the muscle preflex reaction to perturbations in the case of constant muscle activity. We found that muscle fibers can adapt their force output based on the severity of the perturbation, showcasing a dynamic adjustment to mechanical demands. Furthermore, muscular preflex capability is essential in stabilizing hopping and cyclic locomotion. However, our project revealed two fundamental factors, which are crucial to deeper understand the muscular contribution to perturbation rejection: 1) The viscosity of a muscle fibre can be tuned by muscle activity, potentially allowing the nervous system to further enhance morphological computation by changing activity around impact. 2) The closed-loop coupling of muscle force and leg movement in the interaction with uneven ground is important. In this project phase, we will quantify the contribution of muscular visco-elastic force to the rejection of perturbations under realistic activation profiles and in (simulated) dynamic interaction with the biomechanics of the leg during cyclic locomotion. To this end, we will develop a new experimental setup which will allow us to control the activity of a skinned muscle fibre in real-time by regulating the calcium-ion concentration in the fibre bath. Furthermore, we will couple the muscle fibre length regulation in real-time to the biomechanical model. This fibre-in-the-loop approach will allow us, for the first time, to study the fibre force response to perturbations under realistic activity conditions. This study is important e.g. for the development of robust and stability-supporting applications in prosthetics and robotics, as well as for the development of future efficient control strategies in neuro-prosthetics or functional electric stimulation for e.g., paraplegic patients.

• DFG Programme: Research Grants
• International Connection: Belgium
• Co-Investigator: Professor Dr. Syn Schmitt
• Cooperation Partner: Professor Dr. Alexander Badri-Spröwitz