This paper discusses the behavior of a sphere object sandwiched by a parallel gripper, while catching. Through the analysis, we found an interesting behaviors of the sphere, where the object never stops under υTω ≠ 0 and the object with υTω ≠ 0 first results in υTω = 0 before starting a rolling motion at one side of contact point. These behaviors are supported by three theorems. We also show some simulation for confirming the analytical results.
When a plate enters the water, cavity forms around the plate. J.W. Glasheen and T.A. McMahon (Phys. Fluid, 8 (8), 1996; Journal of Experimental Biology, 199, 1996) suggested equations for duration of a cavity around a circular plate and for hydrodynamic force acting on the circular plate. We confirmed the reliability of these equations by two kinds of experiments. Furthermore the analysis by using these equations showed the robot having four legs can support its weight on the water surface when the diameter of the legs and the stroke and frequency of the legs' motion are several times as large as their present values.
The planning-from-observation paradigm is widely noticed as a novel robot-programming technique. It consists of two parts: (1) recognition of a human demonstration from observation as symbolic representation, i.e., a sequence of movement primitives and (2) execution of the same task. Symbolic representation enables a robot to achieve the same task even in a different environment. We already proposed a method to build a symbolic representation for an assembly task. However, for a robot to execute the task, it is necessary to adjust parameters of each movement primitive to generate appropriate trajectories of objects, especially a path which maintains one of any contact states. Many researchers have proposed methods to calculate such a path using a non-linear optimization method, for example, the potential field method, the probabilistic method, and so on. Although these methods are very powerful as calculation tools on a computer, their solutions are not optimal. We propose a novel method to calculate such an optimal path using a linear solution.
The remaining aspect of robot simulation is calculating external force from environment. Two major subproblems of this are detecting collisions and computing collision forces. Although studied in isolation, these problems are closely related in simulation. This paper presents a method for fitting the pieces together on the rigid bodies which are formed convex polyhedron and covered with rubber-like material. We consider that the collision force between such objects is the function of the intersection of those, therefore calculating the collision force comes to finding the shape of the convex polyhedron because the intersection of two convex polyhedra is also a convex polyhedron. In order to find the shape of the convex polytope, we propose an approach based on the revised simplex method, which computational cost is approximately linear in the total number of faces.
We introduce a method to generate whole body motion of a humanoid robot such that the resulted total linear/angular momenta become specified values. First, we derive a linear equation which gives the total momentum of a robot from its physical parameters, the base link speed and the joint speeds. Constraints between the legs and the environment are also considered. The whole body motion is calculated from a given momentum reference by using a pseudoinverse of the inertia matrix. As examples, we generated kicking and walking motions and tested on an actual humanoid robot HRP-2. This method, the Resolved Momentum Control, gives us a unified framework to generate various maneuver of humanoid robots.
This paper presents a visual servoing of robot manipulator based on intersample disturbance rejection with switching scheme and dead-time compensation. First, multirate intersample disturbance rejection algorithm is reviewed, which was proposed by authors for general digital control system with restricted sampling frequency. Second, the novel feedforward scheme is proposed with open-loop estimation and switching function, which enables the disturbance rejection without any sacrifice of the closed-loop characteristics. Third, new precise formulation of delay problems in visual servoing is established as the image processing latency, the difference between sampling period of camera signal and control period of joint servo system, and delay of inner-loop joint servo system. By introducing the workspace controller and nonlinear perspective transformation, the proposed intersample disturbance rejection controller becomes applicable to the visual servoing problem of 2 DOF manipulator with moving object points. Finally, the advantages of the proposed control system are verified through simulations and experiments.
This paper presents a randomized manipulation planner for a multi-fingered hand by switching contact modes. Manipulation planning for such a system should consider changing kinematics and dynamics of the system according to the contact modes. We derive the conditions that give the restrictions of feasible contact modes and the number of contact points, based on the properties of a manipulation system. Inspired by randomized motion planning techniques, we propose a new algorithm for manipulation planning in order to explore object configuration space, rapidly and uniformly. The basis for this approach is for the construction of exploring random trees. Simulation examples for 3-D manipulation by switching contact modes are presented to verify the planner's effectiveness.
Metal spinning is a plastic forming process that forms a metal sheet or tube by forcing the metal onto a rotating mandrel using a roller tool. This is a study on metal spinning applying robot control techniques such as force feedback control with the aim to develop flexible and intelligent forming processes, and to expand a new application area for robot control. An experimental setup was developed for gathering basic data on the forming process. Some results of preliminary experiments are presented. The influence of the clearance between the roller and mandrel is also discussed. The author proposes applying hybrid position/force control for shear spinning, which is free from fine adjustment of the clearance. The effectiveness of the proposed method was experimentally verified.
The goal of our study is development of a sensor which has static friction sensation using paired pieces of PVDF film strips. In order to develop the sensor, we recall that the sensing function is supposed to be attained through incipient slip detection. First is designed the artificial finger whose characteristics are associated with those of a human finger with respect to the shape and a part of the sensing functions enabling the incipient slip detection: The finger skin has ridges on the surface in each of which a pair of artificial FAI receptors are embedded. The design process of two phases is also shown to secure useful information without any plastic deformation of the film strips. Design phase #1 is to design the characteristics of a FAI receptor. As the transducer for the FAI receptors, we choose PVDF film sheets which have a dynamic stress rate characteristic. Design phase #2 involves determination of the shape and size of the artificial finger skin, and the location of the transducers in a ridge. Signals from the transducers are analyzed concerning where the best position for each of the transducers is to utilize the information acquired from the transducers in the future process. We analyze the stress in the finger skin when incipient slip occurs at the surface. The experimental results reveal that the differential output voltage signal from a pair of artificial FAI receptors embedded in a ridge captures low-frequency vibration to generate a predictive signal which warns incipient slip of the ridge. The results also show, that high-frequency vibratory signal itself cannot be detected using the artificial FAI receptors and suggests a need of artificial FAII receptors in static friction sensory information processing.