Realizing a Humanoid Neck with Serial Chain Four-bar Mechanism

In this article, we present design, fabrication, and characterization of a two-degree freedom humanoid neck based on serial chain four-bar mechanism. The nodding mechanism is designed in such a way that an eccentric center of gravity of the robotic head is counterbalanced by pre-tensioned springs which makes the modular neck prototype statically in equilibrium. In addition, due to installation of drive motor away from the rotation axis of nodding system, the torque requirement is significantly reduced allowing the use of low-cost RC servo motor to drive the head assembly. We describe in detail modeling and characterization of the neck rotational movement focusing on nodding mechanism. Extensive mathematical model for interaction of two dynamical systems, head-neck and servomechanism, is developed. Humanoid neck design based on RC servo motor having potentiometer feedback experiences inherent overshooting. In order to overcome the overshoot associated with servo dynamics, an external PD controller is implemented and the motion similar to that of human neck is demonstrated by numerical simulation.