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Adaptive control of time-varying mechanical systems is considered in this paper. A new adaptive controller for time-varying mechanical systems is proposed based on two assumptions. First, the dynamics of time-varying mechanical systems is derived under the assumption that the generalized constraints on the system do not depend on time but the system parameters such as masses and payloads are time-varying. Second, the time-varying parameters are given by a group of known bounded time functions and unknown constants. It is shown that the proposed adaptive controller results in a stable closed-loop system. Further, if the desired trajectory of the system is periodic, a time-scaling technique of mapping one cycle period of the desired trajectory into a unit interval is proposed to provide robustness to the parameter adaptation algorithm. An experimental platform consisting of a two-link robot with a time-varying payload is developed to test the proposed adaptive controller. The experimental platform mimics robotic pouring and filling operations in industry. Comparative experimental results demonstrate the effectiveness of the proposed design.

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Control of robotic surface finishing processes such as deburring, grinding, chamfering, and polishing is considered in this paper. A complete dynamic model that describes the dynamic behavior of the robot for surface finishing tasks is developed. A complete surface finishing task is divided into three phases (free motion phase, transition phase, and constrained motion phase) depending on the location of the robot end-effector with respect to the constraint surface. Stable control algorithms are developed for each phase. Emphasis is given to the transition phase and constrained motion phase, where surface finishing takes place. An experimental platform for performing robotic surface finishing operations is developed. The robotic surface finishing system consists of a planar robot with a force sensor and a deburring tool on its end-effector, and a fixture to hold the constraint surface. Extensive experiments based on the proposed control design were conducted for both surface following and surface finishing. Results of surface following and surface finishing experiments are shown and discussed.

Cognitive control has been extensively studied from Event-Related Potential (ERP) point of view in visual modality using Stroop paradigms. Little work has been done in auditory Stroop paradigms, and inconsistent conclusions have been reported, especially on the conflict detection stage of cognitive control. This study investigated the early ERP components in an auditory Stroop paradigm, during which participants were asked to identify the volume of spoken words and ignore the word meanings. A series of significant ERP components were revealed that distinguished incongruent and congruent trials: two declined negative polarity waves (the N1 and the N2) and three declined positive polarity wave (the P1, the P2 and the P3) over the fronto-central area for the incongruent trials. These early ERP components imply that both a perceptual stage and an identification stage exist in the auditory Stroop effect. A 3-stage cognitive control model was thus proposed for a more detailed description of the human cognitive control mechanism in the auditory Stroop tasks.