Force estimation for a minimally invasive robotic surgery system

A minimally invasive medical system comprising:

• a six-degrees-of-freedom manipulator having a flange;
• a sensorless detachable minimally invasive instrument having a first end and a second end;
• an effector unit connected to the flange, the effector unit configured to hold the first end of the detachable minimally invasive instrument;
• a sensorless trocar configured to be mounted on a patient, wherein the second end of the instrument is configured to be positioned inside the patient through the trocar and beyond a fulcrum, the trocar configured to define said fulcrum which kinematically constraints the instrument;
• a six-degrees-of-freedom force-torque sensor disposed between said effector unit and said manipulator, and between said first end of the instrument and said manipulator, and configured to sense forces and torques exerted onto said effector unit by the first end of the instrument;
• and
• a programmable computing device configured to:
• determine an initial reference position of said instrument relative to said fulcrum;
• determine the position of said instrument relative to said fulcrum based on said determined initial reference position and on continuous updating of the position using manipulator motion information;
• processes measurements made with said six-degrees-of-freedom force;
• apply the principle of superposition to calculate an estimate of a force exerted onto the second end of said instrument by a tissue or organ and a force exerted at said fulcrum based on said determined position, said measured force and said measured torque;
• and
• provide haptic feedback signals to the manipulator based on the estimate.