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In classical robotic applications, robotic systems consist of servo motors, high-ratio reduction and rigid links; mechanical designers prefer to design robotic applications as stiff as possible to make robots manipulate with remarkable speed and precise position movements. However, these robotic applications can hardly interact with people and environments under safety constraints. It poses the very fundamental problem of ensuring safety to humans and protecting the robot. This paper presents an Active Variable Stiffness Elastic Actuator (AVSEA) that is designed and application for safe physical human robot interaction. The AVSEA consists of two DC-motors: one is used to control the position of the joint and the other is used to adjust the stiffness of the system. The stiffness is generated by a leaf spring. By changing the effective length of the leaf spring, AVSEA has the ability to minimize large impact forces due to shocks, to safely interact with the user and/or to become as stiff as possible to make precise position movements or trajectory tracking control easier. Experiment results are presented to show that AVSEA is capable of providing precise position movements while offering safe human-robot interaction.

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A vertically intersected dual-axis modularized actuator system (DAMA) is developed and applied to a six-axis humanoid robot arm in this article. The DAMA consists of a two independent joint system, and the system structure is further refined using finite element analysis. It will be shown that the novel DAMA modular system can be used to easily construct a mechanism with any degrees of freedom. In other words, a modular or reconfigurable system can be achieved using the DAMA module. Based on simulations with ADAMS and MATLAB software packages, the system dynamic properties can be observed. In addition, the hardware and software systems of the DAMA are developed. The hardware architecture is composed of a microprocessor, an RS-232 to CAN bus module, and two independent-joint controller modules. The software control system is written in Visual Cþþ. The system employs a simple but effective PID scheme to independently control the DAMA's two joints. The experimental results show that for an S-curve and circle trajectory input position command, the DAMA and the six-axis humanoid robot arm, which is formed by the DAMA module, can track the command well. Hence, the DAMA can be used as a generic module for multiple-degree-of-freedom systems.