Design and modelling of an anisotropic continuum robot end-effector for single-port access surgery suturing

Abstract

Single port access surgery has brought many advantages and new challenges to the field of minimally invasive surgery. In principle, many of these challenges can be addressed through robotics. Continuum robots in particular have seen a surge in interest in recent years for their miniaturisation potential. However, many applications with these robots have been developed for contactless or low-force tasks. This paper tackles several barriers to high-force tasks with continuum robots such as suturing for Open Spina Bifida repair. A novel continuum robot end-effector is proposed. The end-effector is composed of a distal bending segment and hybrid gripper. First, the novel hybrid gripper specifically designed for continuum robots is introduced. The hybrid gripper can function both as a general surgical gripper and as a needle driver while overall keeping the required input force limited. Second, an optimisation of the continuum structure of the distal bending segment is conducted. The objective of this optimisation is to sustain high tip forces – required by the said high-force contact tasks – while keeping deformations acceptable. Third, a quasi-static model that predicts the coupled effect of bending and gripping is derived. This model predicts the deformation of the continuum structure that is induced by the gripping action itself. It could hence be used to compensate for such deformation and establish a stable grip with the otherwise flexible instruments. Finally, experiments are conducted to validate the new designs and the model. The hybrid gripper has a diameter of 3 . 4 mm, a length of 15 . 5 mm and can hold securely a needle with a 4 N input force, outputting a 12 N gripping force. The optimised bending segment is validated for Open Spina Bifida suture: it can bend freely up to 90° and it can support a 1 N tip load up to a 35° bending angle. The bending and gripper model error varies between 1% and 14.55%, yielding useful results to predict the shape of the bending segment and potentially compensate for the disturbance created by actuating the gripper.