A mechanism_comprising_at least two links (400-410; 410-420;420-430) -connected by a joint (100:100:300), wherein said joint (100;100; 300) is of electro- or magneto- rheological fluid type and comprises: - a first body and a second body, slidably coupled to each other, - wherein the first body comprises a piston having a head and a stem, - wherein the second body comprises a chamber in which the piston slidingly engages,the chamber arranged as a closed circuit filled with an electro- or magneto- rheological fluid, wherein said circuit has a first branch of said chamber in which said piston tightly slides, and a second branch of said chamber in which at least one couple of electrodes is provided that are facing each other, defining between said electrodes a channel where said fluid is present; - a supply unit arranged to supply said electrodes of said second body to make an electric or magnetic field that passes through said channel; - said piston of said first body configured for pushing said fluid in said channel and to pass between said electrodes when a relative movement between said first body and second body occurs; - and said supply unit configured for modulating said electric or magnetic field of the electrodes of said second body in order to adjust the resistance against the movement of said fluid in said channel when said relative movement between said first and second body occurs; - wherein said first body and second body are pivotally coupled to each other about a center of rotation, wherein said piston has said stem of curvilinear shape concentric to said center of rotation (210, and wherein said first branch of said chamber and said second branch of said chamber have curvilinear shape and are concentric to said center of rotation. - a first body and a second body, slidably coupled to each other, - wherein the first body comprises a piston having a head and a stem, - wherein the second body comprises a chamber in which the piston slidingly engages,the chamber arranged as a closed circuit filled with an electro- or magneto- rheological fluid, wherein said circuit has a first branch of said chamber in which said piston tightly slides, and a second branch of said chamber in which at least one couple of electrodes is provided that are facing each other, defining between said electrodes a channel where said fluid is present; - a supply unit arranged to supply said electrodes of said second body to make an electric or magnetic field that passes through said channel; - said piston of said first body configured for pushing said fluid in said channel and to pass between said electrodes when a relative movement between said first body and second body occurs; - and said supply unit configured for modulating said electric or magnetic field of the electrodes of said second body in order to adjust the resistance against the movement of said fluid in said channel when said relative movement between said first and second body occurs; - wherein said first body and second body are pivotally coupled to each other about a center of rotation, wherein said piston has said stem of curvilinear shape concentric to said center of rotation (210, and wherein said first branch of said chamber and said second branch of said chamber have curvilinear shape and are concentric to said center of rotation.