Articulatable structure with adjustable end-point compliance

A limb for use in an articulatable structure such as a robot, or the like, comprising

• a first limb section,
• an elongated second limb section which, during use, is resilient and flexible in one direction normal to its longitudinal axis and is substantially inflexible in a direction normal to both said one direction and said longitudinal axis,
• rotatable coupling means for rotatably coupling said first and second limb sections for relative rotation thereof about said longitudinal axis,
• motor means operatively connected between said first and second limb sections for rotating said second limb section relative to said first limb section about said longitudinal axis and controlling the passive stiffness matrix of the second limb section in two orthogonal directions normal to said longitudinal axis relative to a reference frame with origin at the first limb section,
• a third limb section in axial alignment with said first and second limb sections,
• rotatable coupling means for rotatably coupling said second and third limb sections for relative rotation thereof about said longitudinal axis, said rotatable coupling means for rotatably coupling said first and second limb sections and said rotatable coupling means for rotatably coupling said second and third limb section being kinematically redundant, and
• motor means operatively connected between said second and third limb sections for rotating said third limb section relative to said second limb section about said longitudinal axis,
• said motor means for rotating said second limb section relative to said first limb section and said motor means for rotating said third limb section relative to said second limb section being simultaneously operable such that the second limb section is simultaneously rotatable relative to both said first and third limb sections while said first and third limb sections are relatively rotatably stationary for controlling the passive stiffness matrix of the second limb section relative to a reference frame with origin at the first limb section.