Isao Fujimoto

Development of artificial finger skin to detect incipient slip for realization of static friction sensation

The goal of our study is the realization of static friction sensation using a piece of artificial finger skin for robot hand manipulation. In order to realize the sensation, we recall the importance of incipient slip detection. First, artificial finger skin is designed which has characteristics similar to those of a human finger with respect to the shape and sensing functions which enable incipient slip detection: the finger skin has ridges on the surface in which a pair of artificial FAI receptors are embedded. The design process of artificial finger skin is also shown that includes three phases. Design phase 1 involves designing the characteristics of a FAI receptor, which has a transducer for which we chose 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 transducer is analyzed to find its best position. Design phase 3 involves manufacturing artificial finger skin. Experimental results show that incipient slip occurs at the surface of artificial finger skin and reveal that the differential output voltage signal from a pair of artificial FAI receptors embedded in a ridge captures not only low-frequency vibration to generate a predictive signal which warns of incipient slip of the ridge, but also a high frequency vibratory signal which indicates slip of the ridge. In order to judge automatically that incipient slip occurs, we use a multi-layered ANN (artificial neural network). Judging incipient slip using an ANN shows that the system is robust to noise and can detect incipient slip.

Mimicking and Evaluating Human Motion to Improve the Imitation Skill of Children with Autism Through a Robot

In this paper, we report techniques for mimicking and evaluating the human motion in real time by a therapeutic humanoid robot to improve the imitation skill of children with autism. For realizing the mimicking technique, we propose a method of selecting key frames using a Q-Learning approach to remove the significant noises. Then, in order to evaluate human motion in real time, we introduce a method of cluster-based framework of Mixture Gaussian and an Expectation-Maximization algorithm using parameters which are converted by Principal Component Analysis. Practical experiments have been performed to test the interaction of children with autism with the robot and evaluate the possibility of improving their imitation skills by training them to perform specific tasks through a robot.

Study on an assistive robot for improving imitation skill of children with autism

In this paper, we report the effectiveness of a therapeutic humanoid robot for children with autism to improve his/her imitation skill. In order to realize this system, a robot has to provide two functions: mimicking and evaluating the childs motion in real time. The former function is achieved by selecting key frames using the Q-Learning approach to remove noisy camera data. The latter is established via a cluster-based framework on Mixture Gaussian and Expectation-Maximization algorithm using parameters which are converted by Principal Component Analysis. Practical experiments are shown in which autistic children interact with a robot and are trained by executing specific tasks for improving imitation skill.

Experimental Study on Vibration Control of Flexible Structures Taking Power Assisted Conveyance Into Account

Abstract Power assist devices have been introduced to reduce physical burden of workers in conveying and mounting work in industries. Most of them handle controlled objects as rigid bodies. This paper discusses an effective vibration control method for conveying flexible structures with power assist. In this study, the power assist is realized by an impedance control method. The impedance characteristics of the power assisted object correspond to the dynamic characteristics of the disturbance for the vibration control. Our previous paper discussed a disturbance accommodating LQ optimal control (DAOC) method for the vibration control problem and the effectiveness was verified by state feedback control simulations only. In this paper, the DAOC method is applied to the same cart with a 1-DOF vibration system as in the previous paper but having more flexible structure. The natural frequency of the controlled object is set to 1.0 Hz. The effectiveness of DAOC in this case is demonstrated through actual experiments on the basis of output feedback control implementation.

Development of artificial skin surface ridges with vibrotactile sensing elements for incipient slip detection

Deals with the development of artificial skin surface ridges for incipient slip detection in pursuit of elucidating the mechanism of static friction sensing. We have two design phases of developing artificial skin with vibrotactile sensing elements incorporated in the skin surface ridges, before we can reach a solution to the optimized shape, size and functions. Phase #1 is to examine dynamic characteristics of the sensing elements following the results from circuit simulation analysis. Phase #2 is to design shapes and sizes of the artificial skin using FE analysis. In the study, we select PVDF film as the transducer of the sensing elements, and verify that the PVDF film transducer connected with an amplifier displayed unique characteristics of stress-rate and stress-jerk sensing functions. The characteristics are separated by a cut-off frequency of approximately 1.2 kHz in the frequency domain. We show by both analyses and experiments that the signal obtained from the transducer circuit with the above cut-off frequency characteristics convey useful information to predict a gross slip through detection of incipient slip.

Mode switching control from vibration reduction to positioning for power assisted moving flexible structures

This study discusses the problem that a worker conveys a flexible structure and positions it to the goal position with power assist. For the problem, this paper proposes the control method of the smooth switching from vibration reduction, when a worker conveys flexible structures, to their positioning taking power assist into account. The technical issues are: firstly, displacement of the goal position is unknown until the object conveys near the goal position. So, this displacement has to be determined before positioning the object. Secondly, one of sensors has a limit of its measurement range. So, there are unknown variables which have to be determined while conveying an object. Thirdly, we consider to minimize an overshoot. For clearing up the first and second issues, we discuss the method for determining the displacement of the goal position and unknown variables while conveying the object. Then we consider that two modes: in the first mode, we consider the control system which includes unknown variables. In the second one, we consider the system which all the variables are known. The two modes are connected smoothly by applying an adaptive nonstationary control method. For clearing up the third issue, the method for preventing collision occurrence is discussed. In order to verify the effectiveness of the proposed method, we conduct the experiments and their corresponding simulations. The results indicate that the proposed method is useful to position flexible structures to the goal position with minimum overshoot.