Development of a 6 degrees- of-freedom hybrid interface intended for teleoperated robotic cervical spine surgery

This paper deals with the development of a 6-degrees-of-freedom (DoF) hybrid interface for a teleoperated robotic platform intended to assist surgeons in cervical spine surgery. The targeted task is the drilling of cervical vertebrae for the attachment of spinal implants. Given the complex anatomy of the cervical region, with the proximity of the spinal cord and vertebral arteries, high accuracy in the drilling procedure is required to avoid complications for the patient. In this context, the proposed hybrid interface has been designed to meet the requirements of the drilling task, in terms of degrees of freedom, workspace and force feedback, which have been identified through a literature review. It consists of an association of two parallel mechanisms and a centrally located serial mechanism. Direct and inverse kinematic modelling of each mechanism as well as the one of the complete interface were carried out. A study of the dexterity distribution of the parallel mechanisms was carried out in order to select the suitable interface working mode that would keep the singularities away from the prescribed workspace. In addition, the force feedback was implemented in static mode, neglecting in a first time the weight of the system. The interface design parameters were then optimized to avoid singularities within the prescribed workspace, to minimize motor torques, and to reduce the size of the interface. These development stages led to the design of a motorized prototype of the hybrid interface.