In laparoscopic surgeries, robotic systems commonly use trocar fixation to achieve remote center motion (RCM). However, this fixation occupies the surgeon's operational space and limits surgical flexibility. It is essential to ensure adequate workspace while maintaining RCM to enhance procedural efficiency and safety. This paper introduces a novel approach to preserve RCM without relying on trocar fixation. The proposed method integrates a six-degree-of-freedom robotic arm with a dual end-effector system, employing tool coordinate storage and remote center point definition to achieve precise four- degree-of-freedom RCM motion control. To validate this method, an experimental setup with an optical tracking system was utilized to measure and calibrate the remote center position. The results indicate that the robot maintained RCM with mean positional errors of 0.672, 0.318, and 0.704 mm along the x, y, and z axes, respectively, yielding a three-dimensional mean error of 1.136 mm. These findings demonstrate the effectiveness of the method in maintaining RCM while maximizing surgical workspace and operational flexibility.

In CAD/CAM, NURBS (Non-Uniform Rational B-Spline) is used to represent a wide variety of free-form curves. NURBS interpolation is advantageous in the processing of smooth curves and is capable of high-speed and high-precision CNC machining. In this paper, a real-time 5-axis NURBS curve interpolator is proposed. The proposed interpolator is based on tool center point control and can produce smooth tool orientations as well as accurate tool paths, thereby realizing high precision and efficient 5-axis machining. Using newly defined G codes, tool orientations are described by vectors and the proposed interpolator can be applied to any 5-axis machines regardless of their rotary axis configurations. In addition, the proposed interpolator calculates both tool positions and orientations simultaneously using a shared interpolation routine and we can reduce the computation load. The proposed NURBS interpolator is implemented on a PC-based 5-axis CNC testbed. The performance of the proposed interpolator is compared with the conventional linear interpolator in terms of smoothness of feedrate, contour errors, and tool orientation errors.