Contact-Dependent Balance Stability of Biped Robots

Mummolo, Carlotta; Peng, William Z.; González, Carmelo Javier León; Kim, Joo Hyun

doi:10.1115/1.4038978

Cited by 24 publications

(18 citation statements)

References 33 publications

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“…For the dynamic balance of a biped robot, several models have been introduced as indicators of whether the current state is balanced or falling. The prevalent approaches are based on the virtual foot‐rotation point on the ground (Goswami, 1999), the ability of a biped system to come to a stop after taking maximum N steps (Koolen, De Boer, Rebula, Goswami, & Pratt, 2012), or a contact‐specific partition of the COM state space (position and velocity) (Mummolo, Peng, Gonzalez, & Kim, 2018). Moreover, we may be able to apply dynamic mechanical models and evaluation indices such as virtual time‐to‐contact approaches, which quantify the temporal proximity to the stability boundary (Dutt‐Mazumder, Challis, & Newell, 2016; Kilby et al, 2014).…”

Section: Discussionmentioning

confidence: 99%

Investigation of the functional stability limits while squatting

Sugama

Tonoike

Seo

2020

Hum Ftrs & Erg Mfg Svc

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This study investigates the functional stability limits (FSLs) in the squatting positions.Eleven male participants leaned and moved their pelvis horizontally in the clockwise and counter-clockwise directions while squatting at 11 depth levels. The depth was controlled by changing the hip height from 100% to 0% of the upright position. The FSLs and the center of pressure excursion lengths were calculated from the force-plate data, and the musculoskeletal loads on the lower limbs were estimated from the joint torques and surface electromyograms. As the hip height reduced, the area of the FSLs narrowed by up to 20% of the base of support (BOS) area at the deepest squatting position. The narrowing was affected by the decreasing FSLs in the forward direction, which also decreased by up to 20% of BOS. These quantitative data accurately evaluate the postural stability, suggesting a considerable fall risk during tasks requiring the squatting position. K E Y W O R D S center of pressure, functional stability limits, musculoskeletal loads, postural stability, squatting posture

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Section: Discussionmentioning

confidence: 99%

Investigation of the functional stability limits while squatting

Sugama

Tonoike

Seo

2020

Hum Ftrs & Erg Mfg Svc

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“…In this study, the unknowns of the optimization problems for the construction of the BSB in double contact are joint trajectories and contact wrenches at both feet, while joint torques are again determined from inverse dynamics. This formulation in double contact is based on the conjunction of joint- and COM-space dynamics of the given biped system [full details available in Mummolo et al ( 2018 )].…”

Section: Contact-dependent Balance Stability Analysismentioning

confidence: 99%

“…In this study, the capability of the combined human-exoskeleton system to maintain balance solely through the support of the legs (i.e., without crutches) is quantified in the sagittal plane, thus isolating the role of crutches in assisting stability in the fore-aft (+ X and – X ) directions. A state-based stability criterion for legged systems that was recently introduced (Mummolo et al, 2018 ) is used to evaluate the balancing capabilities of Mina v2 in its two main foot-ground (single and double) contact configurations. In the proposed criterion, the equivalent DH model's COM state as its global Cartesian position

and velocity

at a given time t 0 is used to determine whether the system is in a balanced state with respect to a specified contact configuration, according to the definitions in the authors' previous study (Mummolo et al, 2018 ).…”

Section: Contact-dependent Balance Stability Analysismentioning

confidence: 99%

“…A state-based stability criterion for legged systems that was recently introduced (Mummolo et al, 2018 ) is used to evaluate the balancing capabilities of Mina v2 in its two main foot-ground (single and double) contact configurations. In the proposed criterion, the equivalent DH model's COM state as its global Cartesian position

and velocity

without ever altering its contact configuration, that state is balanced with respect to that contact configuration.…”

Section: Contact-dependent Balance Stability Analysismentioning

confidence: 99%

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Stability of Mina v2 for Robot-Assisted Balance and Locomotion

et al. 2018

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The assessment of the risk of falling during robot-assisted locomotion is critical for gait control and operator safety, but has not yet been addressed through a systematic and quantitative approach. In this study, the balance stability of Mina v2, a recently developed powered lower-limb robotic exoskeleton, is evaluated using an algorithmic framework based on center of mass (COM)- and joint-space dynamics. The equivalent mechanical model of the combined human-exoskeleton system in the sagittal plane is established and used for balance stability analysis. The properties of the Linear Linkage Actuator, which is custom-designed for Mina v2, are analyzed to obtain mathematical models of torque-velocity limits, and are implemented as constraint functions in the optimization formulation. For given feet configurations of the robotic exoskeleton during flat ground walking, the algorithm evaluates the maximum allowable COM velocity perturbations along the fore-aft directions at each COM position of the system. The resulting velocity extrema form the contact-specific balance stability boundaries (BSBs) of the combined system in the COM state space, which represent the thresholds between balanced and unbalanced states for given contact configurations. The BSBs are obtained for the operation of Mina v2 without crutches, thus quantifying Mina v2's capability of maintaining balance through the support of the leg(s). Stability boundaries in single and double leg supports are used to analyze the robot's stability performance during flat ground walking experiments, and provide design and control implications for future development of crutch-less robotic exoskeletons.

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“…Characterizing the full balance capabilities in the form of a region of dynamic balance for general biped systems and foot models is therefore an open research question, relevant to the stability analysis of human gait and posture, as well as to the quantification of balance performance in biped robots and exoskeletons (Mummolo et al, 2018a;Mummolo et al, 2018b;Torricelli et al, 2020;Pinto-Fernandez et al, 2020). A novel general framework for benchmarking the balance capabilities of biped systems is proposed in this study, by characterizing a system's balanced region in the COM state space.…”

Section: Introductionmentioning

confidence: 99%

State-Space Characterization of Balance Capabilities in Biped Systems with Segmented Feet

2021

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The human ability of keeping balance during various locomotion tasks is attributed to our capability of withstanding complex interactions with the environment and coordinating whole-body movements. Despite this, several stability analysis methods are limited by the use of overly simplified biped and foot structures and corresponding contact models. As a result, existing stability criteria tend to be overly restrictive and do not represent the full balance capabilities of complex biped systems. The proposed methodology allows for the characterization of the balance capabilities of general biped models (ranging from reduced-order to whole-body) with segmented feet. Limits of dynamic balance are evaluated by the Boundary of Balance (BoB) and the associated novel balance indicators, both formulated in the Center of Mass (COM) state space. Intermittent heel, flat, and toe contacts are enabled by a contact model that maps discrete contact modes into corresponding center of pressure constraints. For demonstration purposes, the BoB and balance indicators are evaluated for a whole-body biped model with segmented feet representative of the human-like standing posture in the sagittal plane. The BoB is numerically constructed as the set of maximum allowable COM perturbations that the biped can sustain along a prescribed direction. For each point of the BoB, a constrained trajectory optimization algorithm generates the biped’s whole-body trajectory as it recovers from extreme COM velocity perturbations in the anterior–posterior direction. Balance capabilities for the cases of flat and segmented feet are compared, demonstrating the functional role the foot model plays in the limits of postural balance. The state-space evaluation of the BoB and balance indicators allows for a direct comparison between the proposed balance benchmark and existing stability criteria based on reduced-order models [e.g., Linear Inverted Pendulum (LIP)] and their associated stability metrics [e.g., Margin of Stability (MOS)]. The proposed characterization of balance capabilities provides an important benchmarking framework for the stability of general biped/foot systems.

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Contact-Dependent Balance Stability of Biped Robots

Cited by 24 publications

References 33 publications

Investigation of the functional stability limits while squatting

Investigation of the functional stability limits while squatting

Stability of Mina v2 for Robot-Assisted Balance and Locomotion

State-Space Characterization of Balance Capabilities in Biped Systems with Segmented Feet

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