Access port length detection in surgical robotic systems

A method for controlling a surgical robotic instrument, the method comprising:

• performing a first calibration of an end effector of an instrument at a first position within a longitudinal tube of a surgical access port;
• advancing the end effector to a second position, distal of the first position, within the longitudinal tube;
• performing a second calibration of the end effector at the second position;
• monitoring contact between the end effector and the longitudinal tube;
• and
• determining a length of the longitudinal tube based on the contact.

A method for controlling a surgical robotic instrument, the method comprising:

• performing a first calibration of an end effector of an instrument at a first position within a longitudinal tube of a surgical access port, the instrument defining a longitudinal axis;
• advancing the end effector to a second position, distal of the first position, within the longitudinal tube;
• performing a second calibration of the end effector at the second position;
• measuring torque of at least one motor actuating the end effector;
• and
• determining a length of the longitudinal tube based on a location at which a change in torque was measured.