Surgery assistance system for guiding a surgical instrument

A surgery assistance system for guiding a surgical instrument, comprising an endoscope, the surgery assistance system comprises an arm system comprising an instrument mount and a control apparatus provided for controlling said arm system, control apparatus is connected to a computer system (CS) connected to a control element (BE), the computer system is for guiding the surgical instrument based on manual actuation of at least one function key (T1-T6), whereby at least the tip (S) of the surgical instrument can be moved in a controlled manner by means of the arm system in a Cartesian patient coordinate system (PKS) and at least one of the three spatial axes (x, y, z) of the Cartesian patient coordinate system (PKS) extends through a surgical opening or a trocar point (T) receiving the surgical instrument, wherein

• a control and analysis routine (SAR) is provided, which is for determining an angle of inclination (w) of the surgical instrument in relation to the spatial axis (z) of the Cartesian patient coordinate system (PKS) extending through the trocar point (T) and for comparing the angle of inclination (w) so determined with a predetermined set angle of inclination (wS), whereby if the determined angle of inclination (w) exceeds the set angle of inclination (wS) the tip (S) of the surgical instrument is guided on a semi-spherical surface (TK) receiving the tip (S) and when the determined angle of inclination (w) is below the set angle of inclination (wS) the tip (S) of the surgical instrument is guided along a tangent (TG) extending through the tip (S) of the surgical instrument on the semi-spherical surface (TK).