Abstarct: In recent years, for better of rehabilitation exercises, robot are used to help physiotherapists. Due to variety of interaction between robot and human, safety of work with to robot is one of the most important issues of rehabilitation robots. Therefore, variable stiffness actuator are designed to increase safety of interaction between robot and human. In this research a VSA named AwAS is improving. In the first step , it is needed to change the mechanism such that the necessary force to move springs, is perpendicular to the displacement of the springs in any case, thus, due to this change, the new mechanism helps to minimize the energy required to change the stiffness and increase of changing stiffness. In the second step a Magnetorheological fluid damper is used to decrease vibration. Simulation results show that rate of changing stiffness of modified mechanism have been increased. As well as the vibration of system is decreased. Moreover mechanical lock that it is used to decrease the energy consumption are deleted with no energy consumption.