Design & development of modular compact series elastic actuator for lower limb extremity assistant exoskeleton

This paper presents a comprehensive process of designing series elastic actuators to be used in active joints of assistive exoskeleton robots. In this process, the stiffness parameter of torsional spring is selected based on two main criteria to satisfy all the requirements of human motions. The first criterion is an appropriate frequency response for the actuator, according to human motion needs. The second criterion is to provide a sufficient protection of actuator hardware against collision and impact. By determining the desired value for the stiffness parameter, spring architecture is designed to have sufficient mechanical strength and provide the desired stiffness in practice while occupying a minimum space. Along with motor and gearbox, the designed spring is assembled in a module to be used in active joints of exoskeleton robots. The module is designed in a way that the spring can be detached easily and the motor and gearbox can be used as a stiff actuator as well. The considerations in the optimization of the spring and in the design of the module has led to a very compact series elastic actuator which can be used in different human motions such as stair ascend and descend, sit to stand and walking.