Abstract
Artificial muscles define a large category of actuators we propose to analyze in a systemic framework by considering any artificial muscle as an open-loop stable system for any output which represents an artificial muscle dimension resulting from its “contraction”, understood in a broad meaning. This approach makes it possible to distinguish the artificial muscle from other actuators and to specify an original model for a linear artificial muscle, according to the theory of linear systems. Such a linear artificial muscle concept exhibits a constant stiffness independent on its control value. It is shown that a biomimetic actuator, made of two antagonist artificial muscles, requires that artificial muscle static characteristic, even in its most simplified form, is non-linear in the meaning of systems theory, to make possible the control of both actuator position and stiffness. However, we also attempt to show that a linear viscous damping can be a practical way for the dynamic behavior of the artificial muscle to be in relatively good accordance with the so-called Hill curve, interpreted as the dynamic characteristic linking the maximum contraction velocity of the artificial muscle to varying loads lifted against gravity.
Highlights
Artificial muscle is a kind of actuator generally defined by analogy with the skeletal muscle
While contraction in skeletal muscle is essentially understood as a straight contraction, the term contraction applied to artificial muscle is used in a broader meaning: this can be Actuators 2015, 4 the straight contraction of a more or less complex structure in the case of fluidic artificial muscles with a sheath, or the straight contraction of thin string in the case of shape memory materials, like filaments of Nitinol, and the bending of strings, like in the case of some ionic electronic active polymers or, even, the extension of thin plates, as in the case of dielectric elastomers
In order to better understand the link to be made between the proposed concept of artificial muscle and the real skeletal muscle which will be here considered as our biological reference, we propose to introduce an original concept of linear artificial muscle
Summary
Artificial muscle is a kind of actuator generally defined by analogy with the skeletal muscle. In a general way any material, or device, whose shape can change in response to a stimulus can potentially be a candidate to the label “artificial muscle”. This very large, broad definition of the artificial muscle notion can explain the difficulty to synthetic reviews of all kinds of artificial muscles [1,2,3,4,5].
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