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PAKO experimental platform (2009 - 2015)

Investigation of gait specific leg function based on orthoprosthetics

PAKO Human gait was developed and optimized by evolutionary processes. A fascinating inter-joint coordination has been developed which uses the elastic behavior of the segmented leg in an laborate way. Up to now, this natural and efficient biomechanical leg function could be mimicked only to some extent in robotic and prosthetic systems.

In contrast to the general tendency in robotics to actuate the joints only by motors, the project uses an alternative approach.

Passive mechanisms for human gait shall be analyzed by experimental studies of human gait and gait transitions. Identified concepts shall be transferred to prosthetic prototypes.

By this procedure, locomotion concepts can be questioned and new designs ideas can be developed. The envisioned concepts could be also a draft for novel, energy efficient and autonomous walking robots with convenient system dynamics.

Prosthetics at TU Darmstadt

Elastic Actuators

Elastic elements in prosthetic devices can help to reduce peak power (PP) and energy requirements (ER) for the actuators. Calculations showed that it is impossible with current commercial motor technology to mimic human ankle behavior in detail for higher walking and running speeds with single motor solutions using a Serial Elastic Actuator (SEA). Concerning this result we checked the requirements of a parallel elastic actuator (PEA) and a combination of serial and parallel (SE+PEA) springs. We found that a PEA can reduce PP additionally in comparison to the SEA by pre-loading the spring in the flight phase. This reduces also peak torque. But this loading needs additional energy so that the ER increase in comparison to the SEA. The SE+PEA concept can further decrease PP. With that, the ER are less than the PEA but higher than for the SEA. The results show less benefit for the PEA and the SE+PEA when a constant stiffness and a fixed parallel spring slack length is used for both gaits and all speeds. All concepts show that mimicking human ankle joint behavior in running and walking at higher speeds is still challenging for single motor devices.

Involved People: Margrit Schaarschmidt, Martin Grimmer, Mahdy Eslamy, André Seyfarth

Previous People: Sebastian Riese, Andreas Merker, Frank Schütze, Stefan Gliech


Technische Orthopädie Gera Tetra Ilmenau GmbH


Passive biarticular actuation (2007 - 2008)

Human movement is influenced by the structure and alignment of bones, muscles and tendons. Gait is influenced by muscles crossing the hip, the knee and the ankle joint. Some of these muscles are crossing only one joint. They are called monoarticular. In contrast, biarticular muscles are coupling two joints. By this inter joint coupling it is possible to transfer energy from one to the other joint. In addition also the control of the leg could be simplified using a biarticular approach. These ideas were proofed at the Jena Walker II robot where only a hip motor drives the whole leg in running like motion. By the biarticular structures energy is transfered towards the ankle joint to do push off during the gait cycle. As such a concept worked in the robot this project aimed to transfer the idea to a prosthesis for lower limb amputees. The artificial biarticular gastrocnemius structure (passive spring) should transfer energy coming from the hip and the knee towards the ankle joint to improve push off motion.

Involved People: Martin Grimmer, André Seyfarth


Technische Orthopädie Gera


  • Grimmer, M. and Seyfarth, A. Biarticular structures to strengthen the push-off in lower leg prosthesis. Abstract and Poster. Dynamic Walking, Vancouver, 2009. abstract_dw2009.pdf
  • Grimmer, M. and Seyfarth, A. Gelenkkopplung zur Verstärkung des Fußabdrucks bei Unterschenkelprothesen. Poster. 6. Jahrestagung der Deutschen Gesellschaft für Biomechanik, Münster, 2009.    
  • Grimmer M. Biomechanik des Ganges bei Ober- und Unterschenkelamputation - Analyse und mechanische Intervention. Diploma thesis, Lauflabor, University of Jena, Germany, 2008.

Comparison of different prosthetic knee joints (2006 - 2007)

In 1997 a new generation of artifical knee joints, the C-Leg, was launched by the company Otto Bock. In comparison to the previous designs it has a microprocessor controlled damper for adaptations during the gait cycle. This study was comparing two passive knee joints (3R80, Otto Bock and Ultimate Knee, Ohio Willow Wood) with the new semi-active during level ground treadmill walking.

Involved People: Christine Gratz, Margrit Schaarschmidt, Martin Grimmer, Susanne Lipfert, André Seyfarth


Technische Orthopädie Gera


  • Seyfarth A, Gratz C. Comparison of prosthetic knees during walking, XXIth Congress of the International Society of Biomechanics, July 1-5 Taipei, Taiwan, 2007, In: Journal of Biomechanics 40 (Suppl. 2), S474, 2007.
  • Schaarschmidt, Margrit, et al. “Functional gait asymmetry of unilateral transfemoral amputees.” Human movement science 31.4 (2012): 907-917.
  • Schaarschmidt M. Biomechanik des Prothesenlaufs - Von der Analyse zur Intervention. Diploma thesis, Lauflabor, University of Jena, Germany, 2007.
  • Gratz C. Beinprothesen auf dem Prüfstand - Gang- und Stabilitätsanalyse. Diploma thesis Lauflabor, University of Jena, Germany, 2006.