Toward Multiple-Point Stiffness Changing Surgical Needle for Eye Surgery Robotic System

Nowadays, minimally invasive surgeries require thin and slender instruments, such as needles and catheters, which can reach the surgical sites inside the human body. Especially, eye surgery requires high precision and steady manipulation of the inside of the the human eyeball. Through this manipulation, diseases such as epiretinal membrane, retinal detachment, diabetic retinopathy, and macular holes can be treated, and drugs can be delivered to the target sites for effective treatment [1]. There are two classifications of stiffness change robots that can be used for ophthalmic surgery. One is to use two or more pre-curved elastic material tubes and control it by the insertion/retraction and axial rotation motions. Another one is to use the tendon-pulley mechanism [2],[3]. Ravigopal et al. proposed the mechanism using one tendon and notched tube [4] and Jeong et al. utilized one tendon and two notched tubes [5], which are for cardiovascular diseases. Kim et al. presented interaction forces of one inner tube and one outer tube with a specific pattern to change the stiffness of wires with diameters of 8~10mm[6] and 1~2mm[7]. In this paper, we propose a mechanism that can change change the stiffness of the needle at two different points independantly.