Position Accuracy of a 6-DOF Passive Robotic Arm for Ultrasonography Training

Abstract

Image processing was applied for the real-time evaluation of ultrasound imaging quality. Simultaneous observation of the ultrasound probe's contacting force, tilting orientation, and operational trajectory in spatial coordinates can provide useful feedback for supporting ultrasonography training. This paper presents a 6-DOF passive robotic arm enabling the complete tracking of the probe position and orientation. The custom designed handle located at the end effector is assembled from the inner and outer shells, which allows installation of a tiny three-axis force sensor for measuring the probe contact force. The forward kinematics of the robot arm is derived for mapping the joint variables to the position and orientation of the tip. The real-time measurement of the joint angles is achieved from the non-contact magnetic encoders for the first to fourth revolute joints and the rotary potentiometers for the 2-DOF ball joint. The three-dimensional testbed consisting of the radial arrays of hexagonal slots is used for evaluating the position and orientation accuracy of the passive arm. The results of this study can be used as a guideline for further development of passive robotic arms to achieve a higher level of accuracy on tracking the probe trajectory.