71 research outputs found
Towards efficient and robust control of bipedal walking: basic models of posture and rhythmic movement
Get PDFWalking is a very important function of the human movement apparatus. The question how walking is controlled by the central nervous system is yet to be answered. A number of reasons lead us to believe that neural oscillators in the spinal cord, termed Central Pattern Generators (CPGs), have a major contribution to human gait control. Firstly, CPGs play a key role in locomotion of many animals by providing the basic rhythm for muscular activity and by interacting with the reflex system. Secondly, normal walking does not require attention: it goes automatically. Finally, a growing number of observations indicate the presence of CPGs in the human spine. A convincing example of the latter is the fact that anencephalic babies – having a brain stem but no cerebellum or cerebrum – are able to ‘walk’ on a treadmill and display coordinated stepping movements when their feet touch the ground. At present, no bipedal gait model combines efficiency and robustness up to the level of human walking. The main motivation for the research in this thesis is to obtain fundamental knowledge of the principles that account for this reconciliation of efficiency and robustness in human walking. Other motivations come from the fields of rehabilitation and bipedal gait robots. The goal of the conducted research is to find the basic principles of neural control that make human walking both efficient and robust. To achieve this goal, a bottom-up approach was chosen that started with analyzing the behavior and stability of posture under reflexive control and concluded with an efficient and robust spinal control of bipedal gait
Design of an experimental environment to investigate balance during cycling and for validation purpose
Get PDFDesign of a dynamic and adaptive head support
Get PDFFor people with severe muscle weakness or paresis in the trunk and neck muscles, adequate head support is required. Although several assistive devices exist that can support a person’s head position, there is an absence of devices that are capable to support head movements in a natural and safe way. The large individual variation between users requires an individual match between user and assistive device. Existing solutions to stabilize the head are mainly static, meaning that the head can only be stabilized in one position. Some systems offer freedom of movement but do not provide support to the head. Additionally, some systems can be configured to allow a certain level of adaptability to the user. However, if head support systems are adjustable, mostly they are systems which enable the caregiver to manually change the head support to another position. There is no opportunity for adjustment by the user. It can be concluded that there is a need for assistive devices that provide dynamic adjustability by combining changes in position of the trunk and head with continuous stabilization. The main objectives of this project are to characterize this need for support, and to develop a first proof‐of‐concept of a dynamic and adaptive head support. This report explores the use of new control methods, implementing position control on an actuated head support system. The presented system can steer the head support position in 3D (including orientation) in a more efficient and natural way. Additionally, the system can autonomously adapt the head support position according to the back seat angle of the electric wheelchair. Thus, it is a first step in the development of a new generation of dynamic and adaptive head supports that are intelligent enough to autonomously personalize their behavior to the user. This PDEng project is done in collaboration with the company Focal Meditech B.V. and is part of the TTW research project Symbionics
Towards effficient and robust control of bipedal walking. Basic models of posture and rhythmic movement
No full textBicycling stability: simulations & experiments to improve cycling safety for older cyclists
Get PDFIn this thesis, it was shown that computer simulation models are a useful tool to guide bicycle design, as can be seen from the aforementioned design guidelines. Furthermore, it was shown that it is not always necessary to have the most complex models in order to improve cycling safety. Simulations with an open-loop bicycle - cyclist model were used to improve stability at low speeds. More complex models could be necessary, however, when testing more complex cycling situations
Dynamic sitting
Get PDFMany wheelchair-users with reduced postural stability adopt a static body posture and have problems with the performance of functional movement tasks. Prolonged static sitting with a flexed spinal posture and posterior tilted pelvis unconditionally leads to all kinds of physical discomfort including the development of pressure ulcers and low back injury. Most of these problems occur from sustained mechanical tissue loading. Dynamic seating interventions are therefore needed to alleviate the load bearing tissue periodically. We developed an experimental simulator chair en evaluated several seating interventions that are designed to enhance functional movement and to prevent physical discomfort due to prolonged static sitting. Theoretical and experimental evaluations were performed in ablebodied subjects and in subjects with a spinal cord injury (SCI). The following research questions have been answered. How can sitting be controlled? Based on a parallelogram design that aligns the chair pivots with the anatomical axes for body segments rotation, we developed a technique that adjusts all three body segments (trunk, pelvis, thighs) separately. Together with simultaneous measurement of body segments orientation, so-called body segments decoupling seemed applicable to control sitting posture when individuals lack the strength to do this themselves. What interventions are effective to regulate body load associated with physical discomfort (i.e. pressure ulcers and low back pain)? A combination of seat inclination, saggital decoupled pelvis rotation and a dynamic tuberal support appeared beneficial to regulate the load bearing tissue of the ischial buttock region and lower back simultaneously. What interventions benefit the performance of functional movement in impaired sitting? It has been suggested in literature that seating interventions which adjust pelvis angle in sagittal direction might influence spinal posture and the performance of functional movement. We investigated this in ten male SCI-individuals and found that decoupled pelvis alignment affects balance control in impaired sitting and that anterior tilted pelvis postures potentially benefit the functional performance in daily wheelchair-use
Twente Spine Model: Development, validation, and application of a complete and coherent musculoskeletal model of the human spine
Get PDFA comprehensive assessment of the spinal loads throughout the spine can advance our understanding of its functioning but is largely unavailable. Musculoskeletal modeling offers a non-invasive means to estimate in vivo spinal loads and can thus provide clinical insights into the spine’s functioning. The primary objective of this dissertation was to develop a validated, complete and coherent musculoskeletal model of the entire human spine for investigating the spinal loads. Firstly, an anatomical dataset (the Twente Spine Dataset) including necessary musculoskeletal parameters for creating this model was measured. For each muscle-tendon element, locations of the attachment sites at the origin, insertion, and via points were digitized, and morphological parameters consisting of the fiber length, tendon length, sarcomere length, optimal fiber length, pennation angle, mass, and physiological cross-sectional area were measured. Next, a complete and coherent musculoskeletal model of the entire human spine (the Twente Spine Model) was developed based on the previously acquired anatomical dataset. In this model, cervical, thoracic, and lumbar vertebrae, a flexible ribcage, and comprehensive muscular anatomy were incorporated. An inverse dynamics based static optimization routine minimizing muscle fatigue was used for calculating muscle and joint forces during basic neck and trunk movements. For validation of the predicted internal loads, quasi-static trunk tasks as measured in previous in vivo studies were simulated, and calculated intradiscal pressures at thoracic and lumbar discs and normalized resultant loads were compared. Subsequently, the sensitivity of muscle and intervertebral disc force computations against potential errors in modeling muscle attachment sites (muscle origin, insertion, and via points) were investigated. For this, every muscle attachment location was perturbed in the Twente Spine Model during upright standing, flexion, lateral bending, and axial rotation of the trunk. The changes in the T6/T7, T12/L1, and L4/L5 disc forces were analyzed, and an overall sensitivity index value was calculated for every perturbed muscle. Furthermore, electromyographic activities and trunk movements during isometric and dynamic trunk activities were simultaneously measured. Finally, musculoskeletal and patient-specific finite element models were used in combination to investigate if modeling more physiological load regimes can significantly affect the vertebral fracture risk prediction
Building gyms for cells - development of combinatorial screening platforms for mechanical stimulation
Get PDFThis thesis describes the development and validation of medium throughput combinatorial screening platforms for mechanical stimulation of cells. The developed platforms allow for the simultaneous application of substrate strains and flow-induced shear stresses to cells and can test for 100 conditions per device. Two devices were developed - one allows for the screening of all combinations of five equibiaxial strains and five shear stresses, each with four replicates. The other device can screen for the effects of four anisotropic biaxial strains, each aligned at five separate angles to flow-induced shear stress and five equibiaxial strains, and all of these conditions with four replicates. The devices were designed with the help of computational modeling, fabricated, characterized empirically and validated with cell studies. Screenings for relevant biological applications such as in pre-vascularized tissue engineering and in osteogenic-adipoenic differentiation balance have also been explored
Dynamics of human movement
Get PDFThe part of (bio)mechanics that studies the interaction of forces on the human skeletal system and its effect on the resulting movement is called rigid body dynamics. Some basic concepts are presented: A mathematical formulation to describe human movement and how this relates on the mechanical loads acting on the skeletal system. These equations of motion depend on the mechanical properties of the skeletal system, such as dimensions and mass distribution. It is applied to describe and analyze human gait
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