Mitsunori Uemura

Power assist system for sinusoidal motion by passive element and impedance control

In this paper, we propose a power assist system that amplifies sinusoidal humans torque and attains minimization of control input requirement using an impedance control and resonance. This impedance control is designed to realize the following features: 1) sinusoidal torque amplification. 2) Minimization of control input requirement by adjusting stiffness. 3) No requirement for the knowledge of amplitude, frequency and phase of humans torque. 4) No requirement for myoelectric signals. 5) Satisfaction of causality. Convergence of the proposed controller is proven theoretically. Simulation results verify the validity of the control scheme including some conditions not discussed in the theory. Experimental results show the validity of the control system including real humans complex dynamics and feedback loops

A New Control Method Utilizing Stiffness Adjustment of Mechanical Elastic Elements for Serial Link Systems

This paper proposes a tracking control method of sinusoidal motions utilizing stiffness adjustment of mechanical elastic elements for serial link systems. Although dynamics of the controlled objects is nonlinear, the stiffness adjustment realize a condition similar to a resonance of linear systems. We present a controller that adjusts stiffness of the elastic elements to reduce torque requirement of actuators while generating desired motions. The proposed controller works without using dynamics models nor parameters of the controlled objects. Stability of the controller is proved, and tracking errors are guaranteed to converge to a certain region. Simulation results demonstrate the validity of the proposed method. We also present an application of the proposed method to power assist systems.

Power Assist Systems based on Resonance of Passive Elements

This paper proposes power assist controllers that realize control input minimization using resonance of passive elements. To satisfy the objective, two types of systems are considered and controllers are proposed for each system. These controllers require no biosignals and satisfy causal manner. Convergence of the controllers is discussed theoretically. Simulation results show the validity of the proposed controllers. Experimental results show effectiveness of the proposed controller when the systems are used by a human operator

A new mechanical structure for adjustable stiffness devices with lightweight and small size

In this paper, we propose a new mechanical structure for adjustable stiffness devices with lightweight and small size. The proposed structure utilize a ball screw mechanism to adjust a relationship between infinitesimal displacements of joint rotation and a linear spring. Then, stiffness around the joint is adjusted. Unlike many of other adjustable stiffness structures, available elastic energy of the elastic element is maximum when the stiffness of the proposed structure is maximum. Therefore, the elastic element of this structure can be smaller and more lightweight than the other structures. Another advantage of the proposed structure is to require fewer and smaller mechanical parts, because the proposed mechanism mostly requires the ball screw mechanism and the linear spring. We developed an actual hardware to test the proposed structure.

Realization of high-energy efficient pick-and-place tasks of SCARA robots by resonance

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.

Virtual Power Limiter System which Guarantees Stability of Control Systems

In this paper, a Virtual Power Limiter System is proposed. This requires no modeling and makes it possible to guarantee the stability of control systems which include unknown characteristics: flexibility in flexible manipulators, compressibility in pneumatic servo systems, human dynamics in man-machine systems, hardware nonlinearity in mechatronic systems, and so on. The details of the proposed virtual power limiter system and experimental verification with a man-machine system are presented.

Passivity-based controllers for periodic motions of multi-joint robots with impact phenomena

This paper proposes passivity-based controllers for periodic motions of multi-joint robots with impact phenomena. Even the robot motions with impact phenomena have complex dynamics, we try to analyze stability of the controlled systems by adopting some assumptions and using Lyapunov-like functions. At first, we present a passivity-based feedback controller. Secondly, we present a repetitive controller based on passivity-based iterative learning control. These controllers generate desired periodic motions, which are specified by users of the controllers. Advantages of the proposed controllers are to works well without using exact parameter values of the controlled systems nor huge numerical calculations.

Resonance-based task space controller for multi-joint robot with adjustable equilibrium angle of elastic element

This paper proposes a task space trajectory tracking controller based on resonance for multi-joint robots. This controller generates desired motions, which are specified in the task space, while adjusting stiffness of mechanical elastic elements installed in each joint of the robots. This controller also adjusts equilibrium angles of the elastic elements. These parameter adjustments minimize actuator torque. Advantages of the proposed controller are to work without using exact parameter values of the controlled systems nor huge numerical calculations. We mathematically discuss stability of the controlled systems. Simulation results demonstrate the effectiveness of the proposed controller.