Basic Research on Visual Servo System which Dynamically Combines the Position/Force Control and Environment Recognition

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Previous visual feedback control schemes assumed ideal tracking performance of the joint servo mechanisms.The robot dynamics wereneglected when designing the visual servo systems. Thus they were notsuitable for high speed motions. The investigators developed a newvisual servoing scheme which considers the visual servo system as a dynamical system and which computes the inverse dynamics of the visual servo system in the task level.However, the task level inverse dynamic scheme does not have the model of the object motion. Thus it only guarantees the convergence for the step motion of the object, in other words it is the type 1 servo system. Therefore errors are inevitable if the object moves continuously. The investigators formulated the conditions required to track the continuous object motions and proposed a tracking controller which adaptively estimates the object motions.The proposed control scheme is composed of two modules, one is a nonlinear observer which estimates the object motion and the other is the task level inverse dynamics based on the estimated object velocity. The investigators proved the asymptotic stability of the proposed method. The effectiveness of the proposed method is validated by the real time experiments on the 2 link direct drive robot. Moreover, a position/force controller was implemented on the 2 link DD robot and ball-on-ball control was performed. The ball-on ball controlis similar to the inverted pendulum. A small ball is controlled tokeep the top of the other larger ball which is attached to the end ofthe 2 link robot. The camera is used to obtain the small ball position which compensate the noisy output of the force sensor. The visual information is proven to be effective to stabilize the ball. At present the combination of the force control and the environment recognition is not satisfactory, but the nonlinear observer developed in this research project will play a important role in the future study.