A Review on Energy-Saving Optimization Methods for Robotic and Automatic Systems <s> Natural Motion <s> It is traditional to make the interface between an actuator and its load as stiff as possible. Despite this tradition, reducing interface stiffness offers a number of advantages, including greater shock tolerance, lower reflected inertia, more accurate and stable force control, less inadvertent damage to the environment, and the capacity for energy storage. As a trade-off, reducing interface stiffness also lowers zero motion force bandwidth. In this paper, the authors propose that for natural tasks, zero motion force bandwidth isn't everything, and incorporating series elasticity as a purposeful element within the actuator is a good idea. The authors use the term elasticity instead of compliance to indicate the presence of a passive mechanical spring in the actuator. After a discussion of the trade-offs inherent in series elastic actuators, the authors present a control system for their use under general force or impedance control. The authors conclude with test results from a revolute series-elastic actuator meant for the arms of the MIT humanoid robot Cog and for a small planetary rover. <s> BIB001 </s> A Review on Energy-Saving Optimization Methods for Robotic and Automatic Systems <s> Natural Motion <s> This paper proposes an energy saving control method of periodic motions composed of multi-frequency components based on adaptive stiffness optimization for mechanical systems. In the case of sinusoidal motions, the concept of resonance can be easily applied to determine an optimal stiffness. This paper tries to extend resonance to deal with periodic motions composed of multi-frequency components. For this purpose, we define a cost function, which represents an amount of actuator torque. Next, an optimal stiffness is defined as the stiffness that minimizes the cost function. The relationship between the optimal stiffness and the desired motions is analytically derived. Based on the preparations, we propose two types of controller. These controllers generate the desired motions using the least amount of actuator torque as possible by optimizing the stiffness adaptively. The controllers work well without using parameters of the objective systems. Stability and effectiveness of the stiffness optimization are proved mathematically. Simulation results demonstrate the effectiveness of the proposed method. <s> BIB002 </s> A Review on Energy-Saving Optimization Methods for Robotic and Automatic Systems <s> Natural Motion <s> This paper proposes an energy efficient method for pick and place tasks of SCARA robots. In the proposed method, an adaptive elastic device at each joint of a robot is effectively utilized to reduce the total energy of pick and place tasks. For practical pick and place tasks, start/end points must be changed depending on the required task. In the previous works related to adaptive elastic device for energy saving, it is not clear how to change the start/end points. In this paper, a method to change positions of start/end points of pick and place tasks is proposed. The energy efficient performance of the method is demonstrated by the experiments, in which a SCARA robot with an air cylinder and a vacuum pad is used for the pick and place task of chocolate plates. <s> BIB003 </s> A Review on Energy-Saving Optimization Methods for Robotic and Automatic Systems <s> Natural Motion <s> In pick and place operations a mechanism moves an object from an initial to a final pose and repeats, with frequencies of operation that can achieve 150 picks per minute. The paper presents the concept of natural motion for this kind of operations, where the basic idea is to add elastic elements to the mechanism and try to match the desired motion with the natural motion of the system. This concept was implemented in a multibody simulation of a five-bar linkage by using numerical optimization to find the required spring constants as well as the trajectory that minimize the torque on the motors. The required energy of the system using the concept of natural motion was compared with that of a typical trajectory, finding that the use of springs and natural motion reduces the energy consumption by 68 % per cycle. <s> BIB004 </s> A Review on Energy-Saving Optimization Methods for Robotic and Automatic Systems <s> Natural Motion <s> In this paper, we propose a concept for the design and control of an energy saving robot utilizing springs and reaction wheels. Firstly, we examine the simultaneous optimization problem of spring parameters and trajectories with respect to the energy consumption based on optimal control theory. We analyze the relationship between the consumed energy and the robot cycle time, derive a condition for an optimal energy efficient cycle, and propose a corresponding design method for springs. After that, we consider the practical design problem to realize the proposed energy saving manipulator concept. In order to verify the proposed method, a prototype 2DOF manipulator is developed by using linear springs and reaction wheels. The experimental results show the effectiveness of the proposed energy saving manipulator concept. <s> BIB005
This method involves the modification of the physical system by means of the insertion of elastic elements into the mechanism, with proper motion planning BIB001 BIB004 BIB003 BIB005  BIB002 , with the aim of exploiting the free vibration mode of a mechanical system performing a cyclic task. In this way, most of the required energy needed for carrying out the task could be supplied by the elastic elements instead of the actuators (i.e., elastic elements store energy during part of the cycle as potential elastic energy, and then they release it to the rigid bodies, increasing their kinetic energy). Then, the actuators have to counteract the effect of dissipative forces and guide the mechanism through the desired trajectory. A possible drawback of this approach is when the end-effector has to be maintained in a fixed position (e.g., during a picking or a placing operation). This could be overcome by releasing the mechanical brake during the stop BIB004 . Two different approaches are presented in  : • Natural dynamics modification (NDM), in which the mechatronic system body or parts of it are designed to perform a given periodic task efficiently; that is, the system's natural frequency is adapted to the task. • Natural dynamics exploitation (NDE), in which the mechatronic system motion is altered in order to exploit the system's natural frequency; that is, the task is adapted to the system's characteristics. Almost all works deal with planar mechanisms. Barreto et al. BIB004 consider a multibody optimization of a two-degrees-of-freedom, five-bar linkage in order to find the proper joints' spring constants as well as the trajectory that minimizes the torque requested to the motor, exploiting the natural motion. The formulation for both the NDM and NDE approaches are derived; that is, the best elastic constant and the optimal cycle frequency are computed, respectively. In  , a two-degrees-of-freedom manipulator with prismatic joints in which elastic elements are inserted is considered. Here, an off-line analytical method for energy consumption minimization that exploits both the NDM and NDE methods is presented. In BIB005 , a NDM approach in which a new design concept of an energy-saving planar serial robot composed by springs and reaction wheels, as actuators are considered. An enhancement can be found in BIB003 , where adaptive elastic devices are adopted at each joint of a SCARA (Selective Compliance Assembly Robot Arm) robot to reduce the total energy in pick-and-place tasks. This solution allows for choosing the cycle time and to change the start and stop points' position, as a result of a proper tuning of the adaptive elastic devices (i.e., NDM approach). A similar approach is considered in the work of Uemura and Kawamura BIB002 . Here, a generic energy-saving control based on system resonance for various robotic systems (i.e., multiple degrees of freedom) performing a pick-and-place task (i.e., non-linear dynamics) is proposed. Indeed, the control method adapts the joints' stiffness in order to minimize the necessary actuators' torque, considering a periodic motion that is not necessarily harmonic (i.e., strictly sinusoidal).