Yvonne Blum | Royal Veterinary College (original) (raw)

Papers by Yvonne Blum

Research paper thumbnail of Does a crouched leg posture enhance running stability and robustness?

Journal of Theoretical …, Jan 1, 2011

Humans and birds both walk and run bipedally on compliant legs. However, differences in leg archi... more Humans and birds both walk and run bipedally on compliant legs. However, differences in leg architecture may result in species-specific leg control strategies as indicated by the observed gait patterns. In this work, control strategies for stable running are derived based on a conceptual model and compared with experimental data on running humans and pheasants (Phasianus colchicus). From a model perspective, running with compliant legs can be represented by the planar spring mass model and stabilized by applying swing leg control. Here, linear adaptations of the three leg parameters, leg angle, leg length and leg stiffness during late swing phase are assumed. Experimentally observed kinematic control parameters (leg rotation and leg length change) of human and avian running are compared, and interpreted within the context of this model, with specific focus on stability and robustness characteristics. The results suggest differences in stability characteristics and applied control strategies of human and avian running, which may relate to differences in leg posture (straight leg posture in humans, and crouched leg posture in birds). It has been suggested that crouched leg postures may improve stability. However, as the system of control strategies is overdetermined, our model findings suggest that a crouched leg posture does not necessarily enhance running stability. The model also predicts different leg stiffness adaptation rates for human and avian running, and suggests that a crouched avian leg posture, which is capable of both leg shortening and lengthening, allows for stable running without adjusting leg stiffness. In contrast, in straight-legged human running, the preparation of the ground contact seems to be more critical, requiring leg stiffness adjustment to remain stable. Finally, analysis of a simple robustness measure, the normalized maximum drop, suggests that the crouched leg posture may provide greater robustness to changes in terrain height.► We compared swing and landing behavior of avian and human running. ► Based on experimental data and spring mass simulations, predictions about stability, robustness and stiffness adaptation during swing phase were made. ► The model suggests that birds might be able to stabilize running by applying one constant stiffness adaptation rate. ► Humans may have to adjust their leg stiffness on a larger scale. ► Compared to humans, birds are more robust in terms of the maximum drop they can cope with.

Research paper thumbnail of Robust and efficient walking with spring-like legs

Bioinspiration & Biomimetics, Jan 1, 2010

The development of bipedal walking robots is inspired by human walking. A way of implementing wal... more The development of bipedal walking robots is inspired by human walking. A way of implementing walking could be performed by mimicking human leg dynamics. A fundamental model, representing human leg dynamics during walking and running, is the bipedal spring-mass model which is the basis for this paper. The aim of this study is the identification of leg parameters leading to a compromise between robustness and energy efficiency in walking. It is found that, compared to asymmetric walking, symmetric walking with flatter angles of attack reveals such a compromise. With increasing leg stiffness, energy efficiency increases continuously. However, robustness is the maximum at moderate leg stiffness and decreases slightly with increasing stiffness. Hence, an adjustable leg compliance would be preferred, which is adaptable to the environment. If the ground is even, a high leg stiffness leads to energy efficient walking. However, if external perturbations are expected, e.g. when the robot walks on uneven terrain, the leg should be softer and the angle of attack flatter. In the case of underactuated robots with constant physical springs, the leg stiffness should be larger than k = 14 in order to use the most robust gait. Soft legs, however, lack in both robustness and efficiency.

Research paper thumbnail of Swing Leg Control in Human Running

Research paper thumbnail of Stable and robust walking with compliant legs

… and Automation (ICRA), …

The implementation of bipedal gaits in legged robots is still a challenge in state-of-the-art eng... more The implementation of bipedal gaits in legged robots is still a challenge in state-of-the-art engineering. Human gaits could be realized by imitating human leg dynamics where a spring-like leg behavior is found as represented in the bipedal spring-mass model. In this study we explore the gap between walking and running by investigating periodic gait patterns. We found an almost continuous morphing of gait patterns between walking and running. The technical feasibility of this transition is, however, restricted by the duration of swing phase. In practice, this requires an abrupt gait transition between both gaits, while a change of speed is not necessary.

Research paper thumbnail of Effective leg stiffness in running

Journal of biomechanics, Jan 1, 2009

Leg stiffness is a common parameter used to characterize leg function during bouncing gaits, like... more Leg stiffness is a common parameter used to characterize leg function during bouncing gaits, like running and hopping. In the literature, different methods to approximate leg stiffness based on kinetic and kinematic parameters are described. A challenging point in estimating leg stiffness is the definition of leg compression during contact. In this paper four methods (methods A-D) based on ground reaction forces (GRF) and one method (method E) relying on temporal parameters are described. Leg stiffness calculated by these five methods is compared with running patterns, predicted by the spring mass model.

Research paper thumbnail of From Walking to Running

Autonome Mobile Systeme 2009, Jan 1, 2009

The implementation of bipedal gaits in legged robots is still a challenge in state-of-the-art eng... more The implementation of bipedal gaits in legged robots is still a challenge in state-of-the-art engineering. Human gaits could be realized by imitating human leg dynamics where a spring-like leg behavior is found as represented in the bipedal spring-mass model. In this study we explore the gap between walking and running by investigating periodic gait patterns. We found an almost continuous morphing of gait patterns between walking and running. The technical feasibility of this transition is, however, restricted by the duration of swing phase. In practice, this requires an abrupt gait transition between both gaits, while a change of speed is not necessary.

Research paper thumbnail of Advanced swing leg control for stable locomotion

Autonome Mobile Systeme 2007, Jan 1, 2007

Locomotion can be described as a subsequent series of stance and flight phases. In both phases th... more Locomotion can be described as a subsequent series of stance and flight phases. In both phases the leg properties can be adapted. Here we consider spring-mass running with a linear adaptation of two leg parameters, leg angle and leg stiffness, during swing phase. The region of stability is characterized by the basin of attraction with sufficient reduction of a given perturbation within one step. The proposed swing-leg control predicts a substantial region of alternative swing leg adjustment rates. The resulting control redundancy includes different foot placement strategies which could be used to manage landing impacts and running stability in one consistent approach.

Research paper thumbnail of Does a crouched leg posture enhance running stability and robustness?

Journal of Theoretical …, Jan 1, 2011

Humans and birds both walk and run bipedally on compliant legs. However, differences in leg archi... more Humans and birds both walk and run bipedally on compliant legs. However, differences in leg architecture may result in species-specific leg control strategies as indicated by the observed gait patterns. In this work, control strategies for stable running are derived based on a conceptual model and compared with experimental data on running humans and pheasants (Phasianus colchicus). From a model perspective, running with compliant legs can be represented by the planar spring mass model and stabilized by applying swing leg control. Here, linear adaptations of the three leg parameters, leg angle, leg length and leg stiffness during late swing phase are assumed. Experimentally observed kinematic control parameters (leg rotation and leg length change) of human and avian running are compared, and interpreted within the context of this model, with specific focus on stability and robustness characteristics. The results suggest differences in stability characteristics and applied control strategies of human and avian running, which may relate to differences in leg posture (straight leg posture in humans, and crouched leg posture in birds). It has been suggested that crouched leg postures may improve stability. However, as the system of control strategies is overdetermined, our model findings suggest that a crouched leg posture does not necessarily enhance running stability. The model also predicts different leg stiffness adaptation rates for human and avian running, and suggests that a crouched avian leg posture, which is capable of both leg shortening and lengthening, allows for stable running without adjusting leg stiffness. In contrast, in straight-legged human running, the preparation of the ground contact seems to be more critical, requiring leg stiffness adjustment to remain stable. Finally, analysis of a simple robustness measure, the normalized maximum drop, suggests that the crouched leg posture may provide greater robustness to changes in terrain height.► We compared swing and landing behavior of avian and human running. ► Based on experimental data and spring mass simulations, predictions about stability, robustness and stiffness adaptation during swing phase were made. ► The model suggests that birds might be able to stabilize running by applying one constant stiffness adaptation rate. ► Humans may have to adjust their leg stiffness on a larger scale. ► Compared to humans, birds are more robust in terms of the maximum drop they can cope with.

Research paper thumbnail of Robust and efficient walking with spring-like legs

Bioinspiration & Biomimetics, Jan 1, 2010

The development of bipedal walking robots is inspired by human walking. A way of implementing wal... more The development of bipedal walking robots is inspired by human walking. A way of implementing walking could be performed by mimicking human leg dynamics. A fundamental model, representing human leg dynamics during walking and running, is the bipedal spring-mass model which is the basis for this paper. The aim of this study is the identification of leg parameters leading to a compromise between robustness and energy efficiency in walking. It is found that, compared to asymmetric walking, symmetric walking with flatter angles of attack reveals such a compromise. With increasing leg stiffness, energy efficiency increases continuously. However, robustness is the maximum at moderate leg stiffness and decreases slightly with increasing stiffness. Hence, an adjustable leg compliance would be preferred, which is adaptable to the environment. If the ground is even, a high leg stiffness leads to energy efficient walking. However, if external perturbations are expected, e.g. when the robot walks on uneven terrain, the leg should be softer and the angle of attack flatter. In the case of underactuated robots with constant physical springs, the leg stiffness should be larger than k = 14 in order to use the most robust gait. Soft legs, however, lack in both robustness and efficiency.

Research paper thumbnail of Swing Leg Control in Human Running

Research paper thumbnail of Stable and robust walking with compliant legs

… and Automation (ICRA), …

The implementation of bipedal gaits in legged robots is still a challenge in state-of-the-art eng... more The implementation of bipedal gaits in legged robots is still a challenge in state-of-the-art engineering. Human gaits could be realized by imitating human leg dynamics where a spring-like leg behavior is found as represented in the bipedal spring-mass model. In this study we explore the gap between walking and running by investigating periodic gait patterns. We found an almost continuous morphing of gait patterns between walking and running. The technical feasibility of this transition is, however, restricted by the duration of swing phase. In practice, this requires an abrupt gait transition between both gaits, while a change of speed is not necessary.

Research paper thumbnail of Effective leg stiffness in running

Journal of biomechanics, Jan 1, 2009

Leg stiffness is a common parameter used to characterize leg function during bouncing gaits, like... more Leg stiffness is a common parameter used to characterize leg function during bouncing gaits, like running and hopping. In the literature, different methods to approximate leg stiffness based on kinetic and kinematic parameters are described. A challenging point in estimating leg stiffness is the definition of leg compression during contact. In this paper four methods (methods A-D) based on ground reaction forces (GRF) and one method (method E) relying on temporal parameters are described. Leg stiffness calculated by these five methods is compared with running patterns, predicted by the spring mass model.

Research paper thumbnail of From Walking to Running

Autonome Mobile Systeme 2009, Jan 1, 2009

The implementation of bipedal gaits in legged robots is still a challenge in state-of-the-art eng... more The implementation of bipedal gaits in legged robots is still a challenge in state-of-the-art engineering. Human gaits could be realized by imitating human leg dynamics where a spring-like leg behavior is found as represented in the bipedal spring-mass model. In this study we explore the gap between walking and running by investigating periodic gait patterns. We found an almost continuous morphing of gait patterns between walking and running. The technical feasibility of this transition is, however, restricted by the duration of swing phase. In practice, this requires an abrupt gait transition between both gaits, while a change of speed is not necessary.

Research paper thumbnail of Advanced swing leg control for stable locomotion

Autonome Mobile Systeme 2007, Jan 1, 2007

Locomotion can be described as a subsequent series of stance and flight phases. In both phases th... more Locomotion can be described as a subsequent series of stance and flight phases. In both phases the leg properties can be adapted. Here we consider spring-mass running with a linear adaptation of two leg parameters, leg angle and leg stiffness, during swing phase. The region of stability is characterized by the basin of attraction with sufficient reduction of a given perturbation within one step. The proposed swing-leg control predicts a substantial region of alternative swing leg adjustment rates. The resulting control redundancy includes different foot placement strategies which could be used to manage landing impacts and running stability in one consistent approach.