Variable geometry and steady volume inflatable tube, robotic arm and robot

A variable geometry and constant-volume inflatable tube, comprising an inflatable envelope made of impermeable flexible material and having a central axis, the inflatable tube further comprising means for bearing longitudinal tensile stress applied to the envelope by the internal pressure within the latter, wherein the stress-bearing means comprise pairs of a first and a second inextensible linking means extending inside the envelope, said pairs being distributed in N longitudinal half-planes of the envelope, each extending between the central axis of the envelope and a respective generatrix of the surface of the envelope, N being an integer divisor of 360 and greater than or equal to 2, and in that, in each longitudinal half-plane, the at least one first inextensible linking means of said longitudinal half-plane is oriented along a first longitudinal direction which is inclined with respect to the central axis of the envelope and the at least one second inextensible linking means is oriented along a second longitudinal direction which is also inclined with respect to the central axis of the envelope, at a same angle of inclination as the first longitudinal direction, and the at least one first and the at least one second inextensible linking means are attached, at a first end, to said respective generatrix of the surface of the envelope and have a point of intersection with the central axis of the envelope, whereby the inflatable tube is bendable around N first pivot axes, each first pivot axis both being located in a respective longitudinal half-plane and being perpendicular to the central axis of the envelope, and around N second pivot axes, each second pivot axis being both perpendicular to the central axis and perpendicular to a respective one of the N first pivot axes, the longitudinal tensile stresses applied to the envelope by the internal pressure within the latter being concentrated on the central axis by the at least one first and the at least one second inextensible linking means, whether or not the inflatable tube is bent.