Inverse Kinematics Analysis of Humanoid Robot Arm by Fusing Denavit–Hartenberg and Screw Theory to Imitate Human Motion With Kinect

The closed-form solution of each rotation joint angle is the most direct and convenient method for humanoid robot arms to imitate the real-time motion of the human arm. Occasionally, the human structure differs from that of a robot, and sensor information is inadequate. Therefore, it is difficult to obtain a closed-form solution for the inverse kinematics (IK) of a robot when using the Denavit–Hartenberg (D–H) method or screw theory alone. This study proposes combining the screw theory and the D–H method to solve the closed-form solution of the IK of a robotic arm with two unique structures: the elbow joint offset and the non-vertical state at the shoulder joint of the robotic arm. The proposed combination method first solves the elbow joint angle using screw theory. Then, the other rotation joint angles are solved using the D–H method. With the proposed method, human arm motion is successfully mapped to the corresponding joint of the robotic arm, and the closed-form solution allows the robotic arm to imitate human arm motion in real–time. Simulation results show that IK can be used to obtain high–precision angles and positions. Experiments show that the robotic arm has an accurate imitation performance, the accuracy of the
$z$
-axis of the manipulator is significantly improved by 73.6%, and that of the
$x$
-axis and
$y$
-axis is also improved by 37.36% and 21.89%, respectively.