| CPC B25J 13/085 (2013.01) [A61B 34/30 (2016.02); A61B 34/35 (2016.02); A61B 34/70 (2016.02); A61B 34/76 (2016.02); B25J 9/04 (2013.01); A61B 34/10 (2016.02); A61B 2090/062 (2016.02); A61B 2090/064 (2016.02)] | 9 Claims |

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1. A method of operating a minimally invasive medical system having a manipulator and a surgical instrument to determine coordinates of an external fulcrum that limits said surgical instrument in motion, said method comprising:
positioning a tip of a surgical instrument through an incision into a body cavity, said surgical instrument having an instrument shaft with a longitudinal instrument axis Z;
mounting the surgical instrument to an effector unit of said-manipulator, the effector unit of said manipulator including a 6 DOF force-torque sensor being mounted in force transmission between a connection interface of the instrument on the effector unit and an extreme member of the manipulator that supports the effector unit;
moving said minimally invasive instrument along a first axis X and a second axis Y, each of said first and second axes perpendicular to the instrument axis Z, until a reaction force along each axis is below a given threshold, and defining X and Y axis coordinates of the external fulcrum at a location where the reaction forces along said both axes are below the given threshold; and
determining a Z axis coordinate position of the external fulcrum along said instrument axis by pivoting the instrument with respect to the instrument tip until a sufficient contact force is reached, and determining the Z axis coordinate position using the lever principle.
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