Highlights • A bond graph model of the extensor mechanism of a human finger has been developed and simulated. • Tendon topology of the Winslow’s rhombus is considered as a hook-string subsystem. • The model emulates grazing action of soft tendons along surfaces of rigid phalanges as they move. • Normal contact force as well as friction between tendon and curved bone profile is modeled. • Nonlinear behavior of tendons (4-element Hill's muscle model) and presence of cartilage in synovial joints is accounted for. Abstract Biomechanical modeling of a finger is a challenging task especially due to excursion and gliding of tendons along bone geometry, the presence of articular cartilage between mating phalanges, nonlinear viscoelastic properties, load specific change in properties of tendons and complexity of deformable tendinous network (Winslow's rhombus) of the extensor mechanism. In this work, a bond graph model of the extensor mechanism of a finger is developed. Tendons are considered as deformable strings and assumed to pass through hooks fixed at predetermined points on rigid phalanges. This enables them to remain clinging to the phalanx surface while sliding on it, and retain network topology during the movement of phalanges. Word bond graph objects (WBGOs) are developed for dynamics of phalanges, hook–string interaction, normal reaction and frictional forces, and coupling of phalanges in rotation as well as translation, etc. Friction losses and extension of tendons due to applied load are accounted for. Study of motion and tension in tendons, joint variables, location of hooks and characteristics of individual tendons can be conveniently carried out based on the bond graph model. This has been effectively demonstrated through computer simulations.

In prosthetic systems, the mechanism, sensing and actuation systems, and controls are some of the important areas which require modeling and analysis. Causal representation based on power transactions provides better understanding of interactions between these subsystems. A unified approach is therefore required to deal with the dynamics of such systems. Bond graph offers such a unified approach to the dynamics of such biomechanical systems. The concept of Word Bond Graph Objects (WBGOs) provides several advantages in modeling such large systems, including: compact representation; facilitation of understanding of energetic and causal interactions between component subsystems; algorithmic, quick and easy object oriented programming for numerical simulations. The approach had been applied earlier to develop models for a class of hand prosthesis. This work is an elaborate extension to a redundant under-actuated three-joint string-tube based finger prosthesis for a partially impaired hand. It systematically explains the dynamics of behavior of the mechanism, interactions at translational and revolute couplings between rigid phalanges, and, string-tube based joint actuation principles involved in this class of prosthesis through simulations of the bond graph models. (C) 2017 Elsevier Ltd. All rights reserved.

A system dynamics approach, based oil bond graphs, is presented for the analysis of prosthetic devices for a partially impaired hand. The partial impairment implies that the hand has lost one or more fingers but retains the ability of its remaining natural fingers. It is shown that the existing natural joints can be used for the actuation of prosthetic finger joints and enable performance of tasks that would not have been possible otherwise. This is a challenging task as motion has to be transmitted from the remaining natural joints to the prosthetic joints. The joint axes move with respect to each other during performance of tasks and do not have any fixed relative orientation. In this work, basic concepts for the actuation of the prosthesis required,for such tasks are developed systematically. Based on these concepts, Bowden cable based joint actuation mechanisms for transmission of motion from natural Joints to corresponding prosthetic joints are presented and analyzed. The analysis of dynamics of the resulting under-actuated prosthesis with joint actuation mechanism is based oil bond graph models that are systematically developed. Using these models, system equations are derived and numerical simulations performed for the analysis. One- and two-joint actuated prototypes of the prosthesis have been presented and effectively demonstrate the proposed concepts.