A novel approach for fiber optics shape sensing, applicable to mini-invasive bio-medical devices, is presented. A kinematic model based on rotation vector is established and used to predict the trajectory. The movement of the flexible needle caused by two control inputs (the straight forward and the bevel orientation velocity) is described as the circular motion around the equivalent axis and the rotation of the needle axis. The model is simple, precise and efficient, and has an acceptable reconstruction effect on complex spatial curves. With the characteristics of compact structure (less than $100~ \mu \text{m}$ ), high strain sensitivity, low temperature sensitivity and ultra-low cost, Fabry-Perot interferometer (FPI) is used for curvature sensing. Calibration experiments show that FPI has higher (more than three times) curvature sensitivity and lower curvature-temperature cross sensitivity than fiber Bragg grating. The three dimensional shape sensing is obtained by converting the measured bending curvature and shape deformation using the proposed kinematic model.

(1) Objectives: This article presents a dual linear-motor differential drive micro-feed servo system, mainly through the optimization design of the transmission mechanism. Owing to the differential synthesis of the micro feed from the upper and under linear motors, the impact of friction nonlinearity during the ultra-low velocity micro feed is avoided, endowing the system with a lower stable feed speed to achieve precise micro-feed control. (2) Methods: Transmission components of the dual linear-motor differential-drive system are analyzed using the lumped parameter method, and a dynamic model of electromechanical coupling is created, which takes into account nonlinear friction. The motion relationship of the dual linear-motor differential-drive servo feed system is characterized using a transfer function block diagram. (3) Discussions: Through simulation, the differences in response between the linear-motor single-drive system and the dual linear-motor differential-drive system are examined under fixed or variable feeding velocities as well as the impact of varying velocity combinations of dual linear motors on the output speed of the differential drive system. (4) Results: Nonlinear friction factors exert an impact on the feed velocity of both linear-motor single-drive and dual linear-motor differential-drive systems during low-velocity micro feed. However, regardless of the constant or variable speed conditions, the dual linear-motor differential-drive servo system significantly outperforms the linear-motor single-drive system regarding low-velocity micro feed. Our simulation results are basically consistent with engineering practice, thus validating the rationality of the created system models, which paves the ground for the micro-feed control algorithms.

To address the need for improving the flexibility of flexible needles, a technique that achieves needle steering by altering the needle’s stiffness is proposed. Needle tip forces were simplified, and a deflection model was then developed based on the Timoshenko beam theory. By combining theory and simulation, the influences of the stylet diameter, extension length, and tip direction on needle bending were analyzed. The deflection of the flexible needle is proportional to the cube of the stylet extension length. The needle with a 0.4 mm stylet diameter and an 8 mm extension length produces 8.841 mm more deflection than conventional flexible needles. The extension length can effectively regulate the bending curvature of the flexible needle, thus improving the flexibility of the puncture to some extent.