Variable stiffness methods of flexible robots for minimally invasive surgery: A review

With high flexibility and slim body, flexible robots have been widely used in minimally invasive surgery because they can safely reach the lesion deep inside the human body through small incisions or natural orifices. However, high stiffness of robot body is also required for transferring force and maintaining the motion accuracy. To meet these two contradictory requirements, various methods have been implemented to enable adjustable stiffness for flexible surgical robots. In this review, we first summarize the anatomic constraints of common natural tracts of human body to provide a guidance for the design of variable stiffness flexible robots. And then, the variable stiffness methods have been categorized based on their basic principles of varying the stiffness. In the end, two variable stiffness methods with great potential and the moving strategy of variable stiffness flexible robots are discussed.