  Flexible tendon sheath mechanism is commonly used in NOTES systems because it
offers high flexibility, light weight, and easy transmission. Due to the size
constraints and sterilization problems, traditional sensors like force/torque
sensor are extremely difficult to place at the tool tips of surgical arms. In
addition, nonlinear dynamic friction and backlash cause challenges to provide
haptic feedback to the surgeons when the robotic arms are inside the patient's
body. Hence, it is extremely difficult to provide the force information to
haptic devices and subsequently to the surgeons. To deal with these problems,
in this paper we propose a new approach of friction model in the tendon-sheath
mechanism to provide the force at distal end of endoscopic system. In
comparison with current approaches in the literature, the proposed model is
able to provide force information at zero velocity and it is smooth. In
addition, the model is independent configuration and able to capture friction
force with any complex sheath shapes. A suitable experimental setup is
established to validate the proposed approach using the two degrees of freedom
Master-Slave system. The validity of the proposed approach is confirmed with a
good agreement between the estimated model and real experimental data. Finally,
a force feedback structure is also given for use in flexible endoscopic
systems.
