This work presents a study of the frictional effect on the stability of a three-rigid link object manipulated by two cooperative robot arms in a plane. It is supposed that the three-rigid link object interacts with the two robot arms at multi contact points to perform the nonprehensile manipulation of the object. The object is figured out in a way such that one of the arms is in contact with two links of the object, while the other arm is free to slide along the third link. The effect of changing frictional forces at the contact points as well as their directions on the stability of the manipulated object is to be explored by defining the system constraints. A definition of what is called the “Stability Margin” is obtained. For the same orientation of the object links, the Stability Margin is a region of equilibrium contact points between the sliding arm and the corresponding object link where the robot arm could be placed in without dropping the object. Later, an experimental system consisting of a three-rigid link object and a two planar robot arms manipulation system is equipped to verify the concept.

Recently, the double generating function method for finite time linear quadratic optimal control problems was proposed. This paper applies it to the on-demand optimal gaits generation of a compass biped robot walking on the level ground. The double generating function method is employed to generate reference optimal gaits and inputs considering the energy consumption by linearizing the compass biped robot. The simulation result shows that the modeling error caused by the linearization is small when the robot walks with a reasonable step length and a appropriate time period. This implies that the optimal states and inputs for the linearized system can be treated as the optimal ones for the original nonlinear system. The biggest advantage of the double generating function method is that it can generate a parametrization of optimal gaits for different boundary conditions and different time periods. Therefore, it is very useful to generate the optimal states and inputs on demand and in real time for the real biped robots.

In aging societies, there is a strong demand for robotics to tackle problems resulting from the aging population. Patient transfer, such as lifting and moving a bedridden patient from a bed to a wheelchair and back, is one of the most physically challenging tasks in nursing care. We have developed a prototype nursing-care assistant robot, RIBA, that can conduct patient transfer using human-type arms. The basic robot motion trajectories are created by interpolating several postures designated in advance. To accomplish more flexible and suitable motion, adjustment using sensor information is necessary, because the patient's posture and positions in contact with the robot may differ slightly in each trial. In this paper, we propose a motion adjustment method in patient lifting using tactile sensors mounted on the robot arms. The results of experiments using a lifesize dummy are also presented.

In aging societies, there is a strong demand for robotics to tackle problems resulting from the aging population. We have developed a prototype nursing-care assistant robot, RIBA, which was designed to come in direct contact with patients and conduct physically challenging tasks. RIBA interacts with its object, typically a human, through multiple and distributed contact regions on its arms and body. To obtain information on such whole-body contact, RIBA has tactile sensors on a wide area of its arms. The regions where hard contact with the manipulated person may occur have almost flat surfaces, leading to surface contact involving a finite area, in order to reduce contact pressure and not to cause the person's pain. When controlling the position and orientation of the person, the relative positions and orientations of the distributed contacting surfaces should be preserved as far as possible to maintain stable contact and not to graze the person's skin. Preserving the force and the pressure pattern of each contact region using tactile feedback is also important to provide stable and comfortable human-robot physical interaction. In this paper, we propose a whole-body contact manipulation method using tactile information to meet these requirements.

Ionic polymer-metal composite (IPMC) actuators are expected as artificial muscles for bio-mimetic soft robots. The IPMC gel first bends quickly and then bends back slowly when a constant voltage is applied to the sample. The latter phenomenon, referred to as the stress relaxation, can be modeled by electrostress diffusion coupling theory. The theory can predict the behavior of the actuator for the different species of counterions. In order to describe the actuator dynamics as a system with inputs and outputs, this paper proposes a linear state space model based on the electrostress diffusion coupling theory. The model consists of the three systems, the electrical, the electro-mechanical, and the mechanical systems. The results of the simulation and the experiment demonstrate the validity of the model.

This paper proposes a method to achieve paddle juggling of a ball by a racket attached to a robot manipulator with two visual camera sensors. The proposed method is composed of juggling preservation problem and ball regulation problem. The juggling maintenance problem means going on hitting the ball iteratively. The ball regulation problem means regulating the position and orientation of the hit ball. The juggling preservation problem is achieved by the tracking control of the racket position for a symmetry trajectory of the ball with respect to a horizontal plane. The ball regulation problem is achieved by controlling the racket orientation, which is determined based on a discrete transition equation of the ball motion. The effectiveness of the proposed method is shown by an experimental result

Ionic polymer-metal composite (IPMC), which is one of the electro-active polymer actuators, is expected as artificial muscles for robots. An interesting property of IPMC is that it requires water to work, therefore it is suitable for underwater robots. In this paper, we developed an underwater robot which mimics rajiform swimming, that is the swimming form of a ray fish. Fins are designed using sixteen IPMCs. For autonomous operation, miniaturization of the electrical devices such as a micro controllers and small amplifiers are performed. A simple traveling wave control input is employed to generate moment on the fin. In the experiment, propulsion speed is measured under various control parameters. Furthermore, incremental wave of the fin is observed although the amplitude of the control input is spatially uniform. We also discuss this phenomenon from the point of view of interaction between elasticity of the actuator and fluid dynamics

Many control strategies have been proposed to compensate for uncertainties of robotic system, where the uncertain parameters are assumed to be constant. However, this assumption may not be satisfied in practice. In this paper, we consider the tracking problem for robot manipulator with unknown and time-varying physical parameters and disturbances. Our proposed state feedback adaptive robust controller consists of a nonlinear compensation based on nominal physical parameters, a linear and a nonlinear state feedback, and an adaptation algorithm for adjustment of the gravitational parameters. The effects of time-varying parameters and disturbances on the tracking performance can be attenuated within a prescribed level. Exact asymptotic tracking can be achieved for set point control with vanishing disturbances and constant parameters. By adding feedback input to penalty variable, high gain feedback can be strategically avoided. The effectiveness of the proposed method is verified by simulation and experiments.

We consider the tracking problem for robot manipulators with unknown and time-varying physical parameters and disturbances which belong to L/sub 2/. Proposed state feedback adaptive robust controller consists of a nonlinear compensation based on nominal physical parameters, a linear and a nonlinear state feedback, and an adaptation algorithm for adjustment of the gravitational parameters. The effects of time-varying parameters and disturbances on the tracking performance can be attenuated within a prescribed level. Exact asymptotic tracking can be achieved for vanishing disturbances, constant parameters, and set point problem. By adding feedback input to penalty variable, high gain feedback can be strategically avoided.