Liaison (mécanique)

Résumé

thumb|Les contacts piston/bielle et piston/chemise peuvent être modélisés par des liaisons pivots. Un mécanisme, ou transmetteur, est l'association de plusieurs pièces liées entre elles par des contacts physiques qui les rendent totalement ou partiellement solidaires, selon qu'ils autorisent ou non des mouvements relatifs des pièces. La liaison mécanique est le modèle de comportement cinématique utilisé pour décrire cette relation, dont la considération est primordiale dans l'étude des mécanismes. Elle peuvent être exprimées sous l'aspect cinématique ou sous l'aspect des actions mécaniques. Modèle cinématique L’étude des mécanismes s’appuie sur le parcours de chaînes de solides, sur lesquelles on compose les mouvements. Le graphe de structure et le schéma cinématique sont utilisés en phase d’analyse de l'ingénieur. Un modèle cinématique est constitué :

de Classes d’Équivalence Cinématique (CEC) d’ensembles indéformables (une pièce ou un ensemble de pièces encastrées) ;

Source officielle

https://fr.wikipedia.org/wiki/Liaison_(m%C3%A9canique)

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The study provides derivation and application of novel formula for the calculation of general imposed constraints for kinematic chains (including mechanisms and zero-degrees-of-freedom Assur groups) depending on the types of kinematic pairs and numbers of movable links. The presented formula is adopted for all mechanisms families and may be used for kinematic chains with various DoF. The study proves existence of kinematic chains which include parts from different families having diverse numbers of imposed constraints. Provided formula allows not only to calculate number of constraints, but it can be also used for the task of structural synthesis of kinematic chains, for identification of mobility of a whole system, numbers of movable links and kinematic pairs as well as their types depending on the technological requirements.

Elsevier2017

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This article presents a new modular robotic platform for enabling reconfigurable, actively controlled, high-degree-of-freedom (high-DoF) systems with compact form factor. The robotic modules exploit the advantages of origami-inspired construction methods and materials, and soft pneumatic actuators (SPAs) to achieve an actuator embedded, parallel kinematic mechanism with three independently controlled ‘‘waterbomb’’ base legs. The multi-material, layer-fabricated body of the modules features selectively compliant flexure hinge elements between rigid panels that define the module as a kinematic 6R spherical joint. The precision layer-fabrication technique is also used to form embedded distribution channels within the module base to connect actuators to onboard control hardware. A decentralized control architecture is applied by integrating each module with small-scale solenoid valves, communication electronics, and sensors. This design approach enables a single pneumatic supply line to be shared between modules, while still allowing independent control of each leg joint, driven by soft, inflatable pouch actuators. A passive pneumatic relay is also designed and incorporated in each module to leverage the coupled, inverted inflation, and exhaust states between antagonistic actuator pairs allowing both to be controlled by a single solenoid valve. A prototype module is presented as the first demonstration of integrated modular origami and SPA design, or pneumagami, which allows predefined kinematic structural mechanisms to locally prescribe specific motions by active effect, not just through passive compliance, to dictate task space and motion. The design strategy facilitates the composition of lightweight, high-strength robotic structures with many DoFs that will benefit various fields such as wearable robotics

2020

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The revelation of mechanism bifurcation is essential in the design and analysis of reconfigurable mechanisms. The first- and second-order based methods have successfully revealed the bifurcation of mechanisms. However, they fail in the novel Schatz-inspired metamorphic mechanisms presented in this paper. Here, we present the third- and fourth-order based method for their bifurcation revelation using screw theory. Based on the constraint equations derived from the first- and second-order kinematics, only one linearly independent relationship between joint angular velocities at the singular configuration of the new mechanism can be generated, which means the bifurcation cannot be revealed in this way. Therefore, we calculate constraint equations from the third- and fourth-order kinematics, and attain two linearly independent relationships between joint angular accelerations at the same singular configuration that correspond to different curvatures of the kinematic curves of two motion branches in the configuration space. Moreover, motion branches in Schatz-inspired metamorphic mechanisms are demonstrated. (C) 2020 Elsevier Ltd. All rights reserved.

PERGAMON-ELSEVIER SCIENCE LTD2020

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