A Variable Length, Variable Stiffness Flexible Instrument for Transoral Robotic Surgery

Transoral robotic surgery (TORS) in upper aerodigestive tract remains challenging due to the rigidity and insufficient workspace of existing instruments, and inappropriate balance between compliance and stiffness in flexible instruments. In this letter, a flexible surgical robotic instrument, featuring a shape memory alloy (SMA)-based continuously variable length bending joint (CVLBJ), was developed for TORS. The integration of the CVLBJ allows bending length adjustment, leading to enhanced distal workspace compared to traditional fixed length flexible instruments. The instrument also exhibits variable stiffness capability via the length variation of the CVLBJ and the SMA temperature variation. The quasi-static, kinematics, and stiffness model were developed to evaluate quantitatively the instrument workspace and stiffness range. The instrument was experimentally characterized and shown to provide a range of bending configurations suitable for the easily accessible oropharynx and the less accessible larynx, and stiffness range between 0.21 N/m and 1.83 N/m that is sufficiently large for tissue manipulation tasks. The instrument was also demonstrated to be capable of accurate motion tracking, given significant payload and 3D trajectory references. The proposed CVLBJ-integrated flexible instrument offers the variable length and variable stiffness properties missing in existing instruments that could potentially improve the clinical outcomes of TORS.