The time delay control (TDC) is a promising technique for robot manipulators because it is model-free, efficient, and yet robust. Nevertheless, when a robot operates under significant payload changes, it is difficult to achieve satisfactory performance with a constant gain. To cope with this problem, several adaptive rules have already been proposed thus far, but they are less effective to significant payload changes, and parameter tuning procedures are too complicated. In this paper, we propose an adaptive gain dynamics that is more effective to payload changes and yet simpler to implement. Through simulations using a one-link arm and experiments using a whole arm manipulator with payload changes, the proposed dynamics was compared with the conventional TDC and two other existing methods. Simulation results show that the proposed algorithm can adapt to significant payload changes, achieving better accuracy than the conventional TDC. Experimental results show that the proposed method has consistently better adaptation capability than the other methods, achieving significantly better accuracy. In addition, the proposed method is the simpler to implement, having only one tuning parameter, whereas the existing methods require four or five such tuning parameters.

Significant payload variations often occur in many practical tasks for robotic applications. But its adequate control is a formidable challenge to control designers, and previous research works have exhibited either limited performance or noticeable difficulties in implementation. In this paper, we have proposed an adaptive PID control that is simple, model-free, and robust against payload variations. These advantages, already verified from the adaptive time-delay control (TDC), have been inherited to the proposed PID control through the equivalence relationship between the two controls. As a result, the proposed PID shares the simplicity, robustness, and the model free property, as well as the high levels of stability and performance with the adaptive TDC. In particular, the selection of its gains becomes especially simple and straightforward, while the adaptation becomes efficient under substantial payload variations. These positive attributes have been verified through simulations and experiments on robots under substantial payload variation. In particular, the proposed PID control was applied to the control of a WAM robot holding a baseball bat, with a result better than a standard PID control.

Objectives: To advance development of rehabilitation robots, the conditions to induce appropriate brain activation during rehabilitation performed by robots should be optimized, based on the concept of brain plasticity. In this study, we examined differences in cortical activation according to the speed of passive wrist movements performed by a rehabilitation robot. Methods: Twenty three normal subjects participated in this study. Passive movements of the right wrist were performed by the wrist rehabilitation robot at three different speeds: 0.25 Hz; slow, 0.5Hz; moderate and 0.75 Hz; fast. We used functional near-infrared spectroscopy to measure the brain activity accompanying the passive movements performed by a robot. The relative changes in oxy-hemoglobin (HbO) were measured in two regions of interest: the primary sensory-motor cortex (SM1) and premotor area (PMA). Results: In the left SM1 the HBO value was significantly higher at 0.5Hz, compared with movements performed at 0.25Hz and 0.75Hz (p0.05). In the group analysis, the left SM1 was activated during passive movements at three speeds (uncorrected p<0.05) and the greatest activation in the SM1 was observed at 0.5 Hz. Conclusions: In conclusion, the contralateral SM1 showed the greatest activation by a moderate speed (0.5 Hz) rather than slow (0.25 Hz) and fast (0.75 Hz) speed. Our results suggest an ideal speed for execution of the wrist rehabilitation robot. Therefore, our results might provide useful data for more effective and empirically-based robot rehabilitation therapy.

This paper proposes a performance index called telepresence index for bilateral teleoperation, which can be used both for the performance evaluation of bilateral control architectures and for design purposes. This index is intended to represent a comprehensive performance objective consisting of transparency and kinematic correspondence, which are two major performance objectives of bilateral teleoperation. In order to quantify the performance objective, telepresence index has employed the error vector magnitude, which enables a seamless combination of magnitude and phase errors and the accommodation of time delay. In comparison with existing performance indices, it was observed that telepresence index possesses the comprehensiveness of performance objectives, magnitude/phase integrity, and the capacity to include time delay, which the others lack in one way or another. The index was applied to evaluate the performances of two widely known control architectures: PD-type bilateral control and Ueda's ideal control. In all cases, telepresence index has been compared favorably with the other indices in terms of clarity, convenience, and accuracy, thereby demonstrating its superiority.

Objectives: Neuromuscular electrical stimulation (NMES) has been used in the field of rehabilitation for a long time. Previous studies on NMES have focused on the peripheral effect, in contrast, relatively little is known about the effect on the cerebral cortex. In the current study, we attempted to investigate the change of cortical activation pattern induced by NMES during execution of hand movements in normal subjects, using functional near infrared spectroscopy (fNIRS). Methods: Twelve healthy normal subjects were randomly assigned to the NMES group (six subjects) and the sham group (six subjects). We measured oxy-hemoglobin (HbO) in six regions of interest (ROI) during pre-NMES and post-NMES motor phase; the left dorsolateral and ventrolateral prefrontal cortex, premotor cortex, primary sensory-motor cortex (SM1), hand somatotopic area of SM1, and posterior parietal cortex. Between the pre-NMES and the post-NMES motor phases, real or sham NMES was applied on finger and wrist extensors of all subjects during a period of 5 minutes. Results: In all groups, during the pre-NMES motor phase, the HbO value in the hand somatotopic area of the left SM1 was higher than those of other ROIs. In the NMES group, during the post-NMES motor phase, HbO value variation in the hand somatotopic area of the left SM1 showed a significant decrease, compared with that of sham group (p < 0.05). However, in the sham group, similar aspect of results in HbO values of all ROIs was observed between pre-NMES and post-NMES motor phases (p > 0.05). Conclusions: Results of this study showed that NMES induced a decrease of cortical activation during execution of hand movements. This finding appears to indicate that application of NMES can increase the efficiency of the cerebral cortex during execution of motor tasks.