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Balance and stability issues in lower extremity exoskeletons: A systematic review

Hamza Mukhtar Fatihu, Ghazilla Raja Ariffin Raja, Muhammad Bashir Bala, Yap Hwa Jen

Biocybernetics and Biomedical Engineering

2020

Vol. 40, no. 4

1666--1679

The lower extremity exoskeletons (LEE) are used as an assistive device for disabled people, rehabilitation for paraplegic, and power augmentation for military or industrial workers. In all the applications of LEE, the dynamic and static balance, prevention of falling, ensuring controller stability and smooth human-exoskeleton interaction are of critical importance for the safety of LEE users. Although numerous studies have been conducted on the balance and stability issues in LEEs, there is yet to be a systematic review that provides a holistic viewpoint and highlights the current research challenges. This paper reviews the advances in the inclusion of falling recognition, balance recovery and stability assurance strategies in the design and application of LEEs. The current status of research on LEEs is presented. It has been found that Zero Moment Point (ZMP), Centre of Mass (CoM) and Extrapolated Center of mass (XCoM) ideas are mostly used for balancing and prevention of falling. In addition, Lyapunov stability criteria are the dominant methods for controller stability confirmation and smooth human-exoskeleton interaction. The challenges and future trend of this domain of research are discussed. Researchers can use this review as a basis to further develop methods for ensuring the safety of LEE's users.

Study of postural adjustments for humanoidal helpmates

Villalobos J., Zielińska T.

Journal of Automation Mobile Robotics and Intelligent Systems

2017

Vol. 11, No. 4

15--25

Humanoid robots and humans look alike, and therefore are expected to adjust their posture in a similar way. We analysed a set of human static postures that should be considered for humanoids acting as caretakers. A dynamic situation was studied to learn how humanoids can react in a dynamical way. Human data were obtained with a professional motion capture system and anthropometric tables. The static postures were studied using a segmented human body model, but for motion analysis the single and double pendulums with moving masses were also employed. For robot motion synthesis we need to know the relation between the posture and the postural stability. We have shown that the positions of mass centres of the pendulum segments (which match the human body point masses) are crucial for postural stabilization. The Zero-Moment Point criterion was applied for the dynamic case. The static analysis demonstrates that there are some common features of the postures. The dynamic analysis indicated that both pendulums are good models of human body motion, and are useful for humanoid motion synthesis. In humanoids, it is easier to apply results represented by inverted pendulums than postural models represented by stick diagrams. This is because humanoids and humans do not obviously share the same mass distribution and sizes (proportions) of all body segments. Moreover our descriptions indicate where to locate the supporting leg/legs in single and double support, which in general, is missing in inverted pendulum models discussed in the literature. The paper’s aim is to deepen the knowledge about the adjustment of human postures for the purpose of robotics.