Surgical tool

A medical instrument for robotic surgery, the medical instrument comprising:

• a frame;
• a shaft having a proximal end attached to the frame and a distal end;
• a jointed device attached to the distal end of the shaft, the jointed device comprising:
• a first link connected to the frame through the shaft;
• a second link connected via a first rotational joint to the first link;
• a third link connected via a second rotational joint to the second link;
• a first pair of tendons connected to the third link to pull on the third link and thus move the third link with respect to the second link;
• and
• at least a second pair of tendons,
• wherein each link comprises a main, one-piece structural body having one or more convex contact surfaces,
• wherein each of the convex contact surfaces is a convex ruled surface formed by multiple straight line portions that are parallel to each other and parallel to a joint movement axis of the first and second rotational joints,
• wherein each tendon of the first and second pairs of tendons comprises:
• a first tendon endpoint, associable to the frame;
• a second tendon endpoint, secured to the second link or to the third link;
• and
• a tendon main portion, extending between the first tendon endpoint and the second endpoint,
• wherein the tendon main portion of each tendon of the first and second pairs of tendons contacts the jointed device only onto the convex contact surfaces, so that only the convex contact surfaces of the links are in contact with the tendon main portion, and
• wherein the main tendon portion of at least two tendons of the first and second pairs of tendons slides onto a same convex contact surface.