A Compact FBG-Based Triaxial Force Sensor With Parallel Helical Beams for Robotic-Assisted Surgery

Force sensing is important for surgical robotics in order to realize surgical palpation and ensure surgical safety. In this article, we design a compact triaxial force sensor based on fiber Bragg gratings (FBGs). The force sensor is composed of an elastic structure, two supporting disks, and four fibers. To achieve a good balance between the axial resolution and radial resolution, the elastic structure has parallel helical beams and the structure parameters of the sensor are optimized. The mechanical model of the sensor is proposed and the influence of temperature is also considered. The force sensor has the advantages of compact structure, easy assembly, and good scalability. An experimental setup is used to calibrate and evaluate the force sensor. The performance of the force sensor under dynamic force with different frequencies is also evaluated. The resolutions for the axial force and radial force are, respectively, 0.01 and 0.012 N with a range of 0–5 N. In addition, the sensor is fixed on a robot arm to further evaluate its palpation ability. The experimental results show that the sensor can recognize different materials with different stiffnesses and the position of the rigid body in a silica model can also be determined.

I. Introduction

Robotic-assisted technology has greatly improved the performance of surgeons in minimally invasive surgeries by providing superior visualization, enhanced dexterity, and greater precision [1], [2]. Many surgical robots employ the master–slave control mode and the surgeons control the motion of instruments by operating a master device [3]–[5]. For laparoscopic surgery, the master–slave control enhances the position and orientation accuracy of the surgical operation but breaks the physical relation between the surgeon’s hand and instruments. The surgeon loses the direct force sense, unlike the traditional minimally invasive procedures. However, the force-sensing capability is important for robotic-assisted surgery to ensure the safety of surgeries. In surgeries, the end-effector of the surgical robot frequently interacts with tissue, organs, and lesions. The lacking force-sensing capability will cause serious tissue trauma and bleeding. In addition, some surgical operations, such as palpation, also need force information to locate tumors.