A Miniature Manipulator with Variable Stiffness towards Minimally Invasive Transluminal Endoscopic Surgery

This letter presents a miniature manipulator with variable stiffness towards minimally invasive transluminal endoscopic surgery, such as the endoscopic submucosal dissection (ESD). The manipulator comprises hollow modules with holes in the sidewall, compact with a 4 mm diameter, and dexterous with six degrees of freedom (DOFs). Basic operations of grasping and stripping can be achieved via the terminal surgical tools. The flexible tubes and torque coils are adopted to avoid the motion coupling of the joints. The worm gears with an anti-backdrive property are used to transfer power from the motor to the reels. The variable stiffness is achieved by using the spring-sliding block-based driver system, delivering both high payload/accuracy and flexibility. The system is described in detail. The kinematics, workspace and variable stiffness are analyzed. Tests in terms of the grasping force and variable stiffness are conducted. Results show that the grasping force is larger than 3 N, and the manipulator's stiffness can be tuned with high rates of change. The manipulator's performances, such as the dexterity and the coordination of operation under the master-slave configuration, were preliminarily demonstrated through the basic mock-up operations.