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Locomotion Laboratory
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home [2014/05/18 15:36]
Filip Cengic [Locomotion Laboratory]
home [2019/02/18 11:48]
Maziar Sharbafi [Pick of the month - Workshop in BioRob 2018: Novel bioinspired actuator designs for robotics (BioAct).]
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 ===== NEWS ===== ===== NEWS =====
  
-==== Pick of the month - Compliant ankle function results in landing-take off asymmetry in legged locomotion====+==== Pick of the month - Concerted control concept in locomotion published in IEEE Transactions on Medical Robotics and Bionics ==== 
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 + {{ :fig_2.png?nolink&200|}} {{ :fig_1a.png?nolink&200|}} 
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 +A new concept termed concerted control is introduced in our recently published paper in the //IEEE Transactions on Medical Robotics and Bionics// journal titled [[https://doi.org/10.1109/TMRB.2019.2895891|Concerted control of stance and balance locomotor subfunctions -Leg force as a conductor]].  
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 +**Abstract:**  
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 +In human locomotion, the complex structure of the human body is controlled such that conceptual models (e.g., the spring-loaded-inverted-pendulum model) can describe the significant features. This suggests that the interplay of the complex control and musculoskeletal systems projects into a low-dimensional space to perform different movements. Such simplification can involve splitting the task into different modular control subproblems (locomotor subfunctions) that can be solved individually. Here, we asked how two locomotor subfunctions, namely stance, and balance, could be coordinated to generate repeatable and robust motor commands. We developed a simple neuromechanical hopping model, based on decoupling axial and perpendicular leg forces. For this, bouncing behaviors and trunk posture control can be addressed by a knee extensor muscle and biarticular thigh muscles, respectively. We suggest utilizing the leg force feedback as interplay among environment, body mechanics, and sensory control to synchronize the decoupled subfunctions. We evaluated this approach in push recovery, attenuating ground drop perturbations and by investigating its sensitivity to the reflex gain as the control parameter. Leg force feedback can improve the robustness of hopping by generating rhythmic hopping patterns. Such a parsimony model-based control concept could simplify controlling assistive devices, such as exoskeletons and prostheses.  
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 +**Keywords:** Locomotor subfunction, positive force feedback, reflex control, sensor-motor map. 
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-[{{ :potm_fslip.png?400|Fig1: FSLIP. Stance phase (A) in FSLIP and (B) in human running. Black lines show the leg spring axis and the foot segment (FSLIP model) respectively the line from hip to heel and heel to metatarsal marker (human running), grey lines indicate the alignment of the GRF.}}] 
  
-The spring loaded inverted pendulum (SLIP) model is widely used to explain basic characteristics of human walking and running. Its periodic running solutions can be mirrored at the instant of the vertical orientation of the leg and thus are symmetric between landing and take-off. In contrast, human running shows asymmetries between touchdown and take-off (e.g. shorter brake than push duration, greater mean ground reaction force during braking phase). Yet it is not fully understood whether these asymmetries are caused by asymmetric muscle properties (e.g. velocity-dependent force generation) or the asymmetric lever arm system in the human leg. We extend the SLIP model by a foot segment and a compliant ankle joint (called FSLIP). This represents the extended foot contact and the displacement of the center of pressure during contact. 
  
-The FSLIP model shows the same asymmetries as found in human running without considering asymmetric muscle properties. Together with the reversed asymmetry observed in human backward running, this indicates that the asymmetric lever arms created by the foot can cause the observed landing-take-off asymmetry in human running. 
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 [[publications:publications_podcasts_pick_of_the_month|Read previous news...]] [[publications:publications_podcasts_pick_of_the_month|Read previous news...]]
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