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  • Robots

    To investigate human and animal locomotion, a number of legged robots were developed in our group since 2004. Read about the bipedal robot BioBiped or the research in the Locomorph project focusing on morphology and morphosis strategies in locomotion.

  • Prostheses

    To investigate models of the muscle-tendon dynamics on humans we developed the research platform PAKO. Using our insights on gait biomechanics, walking and running could be realized with the robotic Walk-Run Ankle prosthesis.

  • Facilities

    Several indoor and outdoor facilities with state-of-the-art measurement equipment helps us to perform experiments on humans, animals and robots. Details can be found here: Facilities.

  • Experiments

    Experimental studies are performed in both research projects and in teaching courses at the Sports Science Institute at TU Darmstadt. Outcomes from student research and educational projects on biomechanics can be found in the awarded Teaching Wiki of our institute.

  • Models

    Models help us to study the fundamental principles of human and animal locomotion. The derived biomechanical concepts can be applied to bipedal robots, exoskeletons or prosthesis. In the European project Balance, we are working on an active orthosis.


News

  • LEARN&ACT DAY of the Movement Academy Motions and Emotions will be postponed due to the current situation

Latest Publications

Neuromechanical force-based control of a powered prosthetic foot

Previously Hartmut Geyer, a former member of the lab, developed a neuromechanical template model, which uses force, length and velocity feedback in combination with muscle modeling to enable walking in simulation and with a powered prosthetic foot (BiOM). Maziar Sharbafi had the idea of the FMCA based control (force modulated compliant ankle), which simplifies this concept and directly translates the feedback signals to an appropriate joint torque. Through efforts from Amirreza Naseri and Martin Grimmer, we were able to test FMCA with the Walk-Run-Ankle. Results were recently published in Wearable Technologies.

Abstract: This article presents a novel neuromechanical force-based control strategy called FMCA (force modulated compliant ankle), to control a powered prosthetic foot. FMCA modulates the torque, based on sensory feedback, similar to neuromuscular control approaches. Instead of using a muscle reflex-based approach, FMCA directly exploits the vertical ground reaction force as sensory feedback to modulate the ankle joint impedance. For evaluation, we first demonstrated how FMCA can predict human-like ankle torque for different walking speeds. Second, we implemented the FMCA in a neuromuscular transtibial amputee walking simulation model to validate if the approach can be used to achieve stable walking and to compare the performance to a neuromuscular reflex-based controller that is already used in a powered ankle. Compared to the neuromuscular model-based approach, the FMCA is a simple solution with a sufficient push-off that can provide stable walking. Third, to assess the ability of the FMCA to generate human-like ankle biomechanics during walking at the preferred speed, we implemented this strategy in a powered prosthetic foot and performed experiments with a non-amputee subject. The results confirm that, for this subject, FMCA can be used to mimic the non-amputee reference ankle torque and the reference ankle angle. The findings of this study support the applicability and advantages of a new bioinspired control approach for assisting amputees. Future experiments should investigate the applicability to other walking speeds and the applicability to the target population.

For further projects and publications of M. Grimmer and M. Sharbafi please check ResearchGate, Google Scholar, ORCID or LOOP and ResearchGate, Google Scholar, ORCID or LOOP.

Lower limb joint biomechanics-based identification of gait transitions in between level walking and stair ambulation

Gait transitions in between level walking and stair ambulation were investigated in one of our projects involving Martin Grimmer and the Department of Electrical Engineering and Information Technology of Ulrich Konigorski. A team of Postdocs, Phd candidates and students performed the one of the largest human gait studies ever, involving an instrumented staircase, in the Locomotion Laboratory. The work was recently published in the PLOS ONE.

Abstract: Lower limb exoskeletons and lower limb prostheses have the potential to reduce gait limitations during stair ambulation. To develop robotic assistance devices, the biomechanics of stair ambulation and the required transitions to level walking have to be understood. This study aimed to identify the timing of these transitions, to determine if transition phases exist and how long they last, and to investigate if there exists a joint-related order and timing for the start and end of the transitions. Therefore, this study analyzed the kinematics and kinetics of both transitions between level walking and stair ascent, and between level walking and stair descent (12 subjects, 25.4 yrs, 74.6 kg). We found that transitions primarily start within the stance phase and end within the swing phase. Transition phases exist for each limb, all joints (hip, knee, ankle), and types of transitions. They have a mean duration of half of one stride and they do not last longer than one stride. The duration of the transition phase for all joints of a single limb in aggregate is less than 35% of one stride in all but one case. The distal joints initialize stair ascent, while the proximal joints primarily initialize the stair descent transitions. In general, the distal joints complete the transitions first. We believe that energy- and balance-related processes are responsible for the joint-specific transition timing. Regarding the existence of a transition phase for all joints and transitions, we believe that lower limb exoskeleton or prosthetic control concepts should account for these transitions in order to improve the smoothness of the transition and to thus increase the user comfort, safety, and user experience. Our gait data and the identified transition timings can provide a reference for the design and the performance of stair ambulation- related control concepts.

For further projects and publications of M. Grimmer please check: ResearchGate, Google Scholar, ORCID or LOOP

Doppler Radar for the Extraction of Biomechanical Parameters in Gait Analysis

Doppler Radar for the extraction of biomechanical parameters during walking was investigated in one of our latest studies in cooperation with the Signal Processing Group of Prof. Zoubir. Ann-Kathrin Seifert and Martin Grimmer performed a series of experiments in the Locomotion Laboratory. The work was recently published in the IEEE Journal of Biomedical and Health Informatics.

Abstract: The applicability of Doppler radar for gait analysis is investigated by quantitatively comparing the measured biomechanical parameters to those obtained using motion capturing and ground reaction forces. Nineteen individuals walked on a treadmill at two different speeds, where a radar system was positioned in front of or behind the subject. The right knee angle was confined by an adjustable orthosis in five different degrees. Eleven gait parameters are extracted from radar micro-Doppler signatures. Here, new methods for obtaining the velocities of individual lower limb joints are proposed. Further, a new method to extract individual leg flight times from radar data is introduced. Based on radar data, five spatiotemporal parameters related to rhythm and pace could reliably be extracted. Further, for most of the considered conditions, three kinematic parameters could accurately be measured. The radar-based stance and flight time measurements rely on the correct detection of the time instant of maximal knee velocity during the gait cycle. This time instant is reliably detected when the radar has a back view, but is underestimated when the radar is positioned in front of the subject. The results validate the applicability of Doppler radar to accurately measure a variety of medically relevant gait parameters. Radar has the potential to unobtrusively diagnose changes in gait, e.g., to design training in prevention and rehabilitation. As contact-less and privacy-preserving sensor, radar presents aviable technology to supplement existing gait analysis tools for long-term in-home examinations.

For further projects and publications of M. Grimmer please check: ResearchGate, Google Scholar, ORCID or LOOP

A biarticular passive exosuit to support balance control can reduce metabolic cost of walking

In this research the advantages of a biarticular thigh exosuit in supporting human walking is demonstrated. Find the details in our recently published paper (open access) by Barazesh, H and Sharbafi, M. A. in Bioinspiration & Biomimetics.

Abstract:

Nowadays, the focus on the development of assistive devices just for people with mobility disorders has shifted towards enhancing physical abilities of able-bodied humans. As a result, the interest in the design of cheap and soft wearable exoskeletons (called exosuits) is distinctly growing. In this paper, a passive lower limb exosuit with two biarticular variable stiffness elements is introduced. These elements are in parallel to the hamstring muscles of the leg and controlled based on a new version of the FMCH (force modulated compliant hip) control framework in which the force feedback is replaced by the length feedback (called LMCH). The main insight to employ leg length feedback is to develop a passive exosuit. Fortunately, similar to FMCH, the LMCH method also predicts human-like balance control behaviours, such as the VPP (virtual pivot point) phenomenon, observed in human walking. Our simulation results, using a neuromuscular model of human walking, demonstrate that this method could reduce the metabolic cost of human walking by 10%. Furthermore, to validate the design and simulation results, a preliminary version of this exosuit comprised of springs with constant stiffness was built. An experiment with eight healthy subjects was performed. We made a comparison between the walking experiments while the exosuit is worn but the springs were slack and those when the appropriate springs were contributing. It shows that passive biarticular elasticity can result in a metabolic reduction of 14.7±4.27%. More importantly, compared to unassisted walking (when exosuit is not worn), such a passive device can reduce walking metabolic cost by 4.68±4.24%.

For further publications of the author please check: ResearchGate, ORCID or LOOP

Bio-inspired neuromuscular reflex based hopping controller for a segmented robotic leg

The bio-inspired neuromuscular reflex based controller can generate stable hopping motion in a real robot. Check out our recently published paper (open access) by Zhao et al. in Bioinspiration & Biomimetics for more details.

Abstract:

It has been shown that human-like hopping can be achieved by muscle reflex control in neuromechanical simulations. However, it is unclear if this concept is applicable and feasible for controlling a real robot. This paper presents a low-cost two-segmented robotic leg design and demonstrates the feasibility and the benefits of the bio-inspired neuromuscular reflex based control for hopping. Simulation models were developed to describe the dynamics of the real robot. Different neuromuscular reflex pathways were investigated with the simulation models. We found that stable hopping can be achieved with both positive muscle force and length feedback, and the hopping height can be controlled by modulating the muscle force feedback gains with the return maps. The force feedback neuromuscular reflex based controller is robust against body mass and ground impedance changes. Finally, we implemented the controller on the real robot to prove the feasibility of the proposed neuromuscular reflex based control idea. This paper demonstrates the neuromuscular reflex based control approach is feasible to implement and capable of achieving stable and robust hopping in a real robot. It provides a promising direction of controlling the legged robot to achieve robust dynamic motion in the future.

For further publications of the author please check: ResearchGate, ORCID or LOOP

Biarticular muscles in light of template models, experiments and robotics: a review

Read our recent review paper about biarticular muscles to learn about the scientific discoveries from simulation models, evidence from human experiments and beneficial design principles in robotic applications. Link to the published paper (open access): Link to Royal Society Interface.

[[https://doi.org/10.1098/rsif.2018.0413|Link to Royal Society Interface]]

Abstract: Leg morphology is an important outcome of evolution. A remarkable morphological leg feature is the existence of biarticular muscles that span adjacent joints. Diverse studies from different fields of research suggest a less coherent understanding of the muscles’ functionality in cyclic, sagittal plane locomotion. We structured this review of biarticular muscle function by reflecting biomechanical template models, human experiments and robotic system designs. Within these approaches, we surveyed the contribution of biarticular muscles to the locomotor subfunctions (stance, balance and swing). While mono- and biarticular muscles do not show physiological differences, the reviewed studies provide evidence for complementary and locomotor subfunction-specific contributions of mono- and biarticular muscles. In stance, biarticular muscles coordinate joint movements, improve economy (e.g. by transferring energy) and secure the zig-zag configuration of the leg against joint overextension. These commonly known functions are extended by an explicit role of biarticular muscles in controlling the angular momentum for balance and swing. Human-like leg arrangement and intrinsic (compliant) properties of biarticular structures improve the controllability and energy efficiency of legged robots and assistive devices. Future interdisciplinary research on biarticular muscles should address their role for sensing and control as well as non-cyclic and/or non-sagittal motions, and non-static moment arms.

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