Accuracy of position tracking and fabrication of thin diameter sensor

Abstract

Abstract The shape reconstruction of medical surgical instruments in robotic laryngeal surgery, positioning a needle to puncture a breast tumour, shape display during intestinal endoscopy, and positioning a cardiac vascular catheter, is affected by not only the end position and the shape reconstruction accuracy but also the diameter and curvature of the sensor owing to the limited application space. A sensor with a substrate is manufactured by pasting a fibre Bragg grating (FBG) on the surface of nitinol wire. The measuring range of the substrate is improved by applying a certain preload before glue injection. The sensor has the advantages of being less prone to breakage and greater durability but has a limited bending curvature and diameter. In minimally invasive surgery, the curvature of the body cavity is complex, and the space is narrow, and thus the FBG sensor must have a smaller diameter and good bending curvature. The present paper proposes a method of filling and encapsulating a small-diameter substrate sensor. A substrate-less sensor with a diameter of 1.5 mm and sensing length of 200 mm is encapsulated by improving the packaging positioning piece, current glue injection method, and packaging process. Four FBGs with two grating points for each fibre are distributed at 90° to each other, and four measuring points are obtained by wavelength division multiplexing and space division multiplexing. A calibration and shape reconstruction experiment is carried out for the shape sensor, while a packaging error compensation calibration method is introduced to improve the precision of shape reconstruction. Results of a two-dimensional experiment show that the shape reconstruction accuracy of the sensor on the plane bending is 2.71%. In a three-dimensional spiral experiment, the measurement accuracy of FBG shape sensor out-of-plane bending is 3.42%.