Apparatus and method for sensing force on a robotically controlled medical instrument

A medical instrument system, comprising:

• an elongated probe body having a bendable section, a distal tip section, and an axially variable-length section disposed between the bendable and distal tip sections, the probe body having a lumen axially extending therethrough;
• a push-pull member slidably disposed in the lumen of the probe body, the push-pull member having a distal end affixed to the distal tip section of the probe body and a proximal end portion extending out a proximal end of the probe body;
• a dithering mechanism configured to mechanically couple to the proximal end portion of the push-pull member, the dithering mechanism further configured for cyclically displacing the push-pull member axially back and forth within the lumen of the probe body, such that the distal tip section is axially displaced relative to bendable section via the axially variable-length section;
• at least one force sensor positioned adjacent to the proximal end portion of the push-pull member, the at least one force sensor being configured for measuring a load applied to the push-pull member;
• and
• a processor operatively coupled to the at least one force sensor and configured for determining an external force axially applied to the distal tip section of the probe body based on signals received from the at least one force sensor.