Tetsuya Morizono

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.

Highly soft viscoelastic robot skin with a contact object-location-sensing capability

This paper concerns the development of robot skin capable of accurately sensing the location of objects in area contact with the skin surface. There has been no report on tactile sensing which attained not only skin deformation detection but also contact object location sensing with high accuracy. In the category of optomechatronics technology, we apply optical fibers to transmit surface deformation information of soft skin for sensing the location of an object in contact with the soft skin accurately. In the paper, we illustrate the structure of the robot skin, and describe the principle of both detecting the position of the reflector chips and sensing the contact location of an object. The robot skin is characterized by the fact that the surface is low cost and easily replaceable, and the sensing performance is robust against any electromagnetic disturbance. We then show experimental results for verifying the principles using a wedge-shaped object. For evaluating the sensing accuracy, comparisons are made: 1) between the location of a real convex of the object and that of the corresponding estimated polygon and 2) for the position of two vertices of the object when independent fitting and Lagrangian fitting methods are applied.

Analysis and control of a force display system driven by parallel wire mechanism

In this paper, we develop a force display system using parallel wire mechanism for virtual sports training with high speed motion. We firstly point out a control issue of the force display system driven by parallel wire mechanism. Based on the analysis, control laws are proposed to improve performance of the force display system. It is experimentally demonstrated that the proposed control laws realize higher acceleration and lower reaction force than other force display systems. Using the experimental result, the performance of the system is evaluated quantitatively.

FTA-based issues on securing human safety in a human/robot coexistence system

On an FTA (fault tree analysis) basis, we deal in the paper with several issues on securing human safety in a human/robot coexistence system, where the system is developed for simulating and simplifying the environment of work/tool handling operations in production lines. The result of our FTA reveals three main factors which lead to hazardous situations, the factors being human errors, abnormal robot motions, and outsiders entrance. Based on the FTA, we develop fail-safe analog circuits (FSACs) which are effectively used in a parallel process of dual signal lines starting from two kinds of dual sensor signals (dual force sensor signals as well as dual joint sensor signals) and ending up with an FSAC which allows one of the dual analog control signals to pass through the gate only when they were checked the same with acceptable deviation, for the purpose of enhancing the diagnostic capability in 1 out of 2 logic. We equip the robot with mechanical safeguarding measures, a sphere-shaped joint, mechanical stoppers, and viscoelastic coverings to eliminate all hazardous parts around the robot links. Then, we claim that human intention becomes a very important factor when the robot is equipped with a tool/work which is hazardous, and propose to provide the robot with a function of inferring human-intended path patterns using a modified HMM. We also demonstrate that human/robot intention mismatch leads the robot to making an emergency stop.

Proposal of a SkilMate finger for EVA gloves

It has been pointed out that the hard structure of an EVA glove deteriorates efficiency of tasks in the space environment. We also found a claim that an EVA glove did not allow an astronaut to acquire contact information at the fingertips. In the study, we proposed a SkilMate Hand for space EVA gloves which has both a tactile media and a power assist devices. We locate SkilMate in a wider framework of wearable intelligent machines which assist in affording such working surroundings that they can exhibit their skills in spite of their necessity for wearing special suits typically in hazardous environments. The paper focuses on the development of a finger system of a SkilMate Hand, and begins with determination of the design guidelines through analyses from an interview with an astronaut. To improve the task efficiency, we manufacture a power assist device which compensates the bending moment exerted at a human finger joint utilizing an ultrasonic motor. We show the structure and the control strategy of the motor drives. To overcome the second problem of tactile insensibleness, we produce a tactile media device which is composed of a slip sensor element on the outer side and a vibrotactile display element on the inner side of a SkilMate Hand. Transduction characteristics of both pressure sensitive conductive rubber and piezo-rubber are experimentally examined in the low temperature region. Finally, piezo-rubber is chosen to be used as a slip sensing transducer.

Warning: to err is human [human-friendly robot dependability]

In this article we describe current and future technologies for ensuring the safety of the operators maneuvering a Skill-Assist working in an automobile final assembly process. It proposes a method that allows a Skill-Assist to detect operation slip from a sequence of an operators hand motion trajectory data represented using hidden Markov models (HMM). The method can also determine either safety- or productivity-oriented control policy throughout two-way interpretation of the belief structure. A workability improvement process that comprises a fault-warning (FW) safety-preservation (SP) space policy and teaching data renewal subprocesses allows for optimal reconstruction of the policy determinant observation space and HMMs. Some experimental results are shown to demonstrate the effectiveness of both the control policy determination and the workability improvement process.

Human error recovery for a human/robot parts conveyance system

The study concerns a human error recovery function for efficient human/robot collaborative parts conveyance tasks, which has not been discussed so far in construction of human/robot coexistence systems. We propose a human operational intention inference updater which allows a robot to judge whether the goal intended to reach by the operator is correct or not, from incomplete trajectory data sequence of the robot endtip maneuvered by the operator. Experimental results showed that a use of the proposed inference updater reduced the task execution time even when human error occurred in a task, which demonstrate the usefulness of the updater.

Proposal of a SkilMate Hand and its component technologies for extravehicular activity gloves

In this study, we propose a SkilMate Hand for space extravehicular activity gloves which is equipped with devices of both a power assist and a tactile media. The paper focuses on development of component technologies for constructing a SkilMate Hand, which is proposed for recovering deteriorated haptic sensation in human hands. First, we manufacture a power assist device which compensates the bending moment exerted at a human finger joint utilizing a standing-wave-type ultrasonic motor. We plot the examined characteristics, propose a control policy of the actuators and show some control perforce in Bode plots. Second, we produce a tactile media device which is composed of a vibrotactile sensor element on the outer side and a vibrotactile display element on the inner side at the fingertips of the SkilMate Hand. Piezo-rubber is chosen to be used as a vibrotactile sensing transducer whose sensing performance is examined in the extremely high/low-temperature regions. We locate SkilMate in a wider framework of wearable intelligent machines which assist in affording such working surroundings that they can exhibit their skills in spite of their necessity for wearing special suits typical in hazardous environments. A proposal of a wearable intelligent machine such as that of a SkilMate with its concept has not been made before.

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.

Adaptive Position Control for Fully Constrained Parallel Wire Driven Systems

A parallel wire driven mechanism uses flexible wires instead of heavy rigid links. In this paper, we propose an adaptive position control method for the fully constrained parallel wire-driven systems that use the minimum number of wires under zero-gravity conditions. Unfortunately, conventional methods of adaptive control cannot be used directly because of the nonlinearity of an internal force term. To overcome such an impossibility, we incorporate a new idea into the conventional method to separate the internal force term linearly. Not only does this adaptive control method ensure precise positioning using external sensors; it enhances the robustness for uncertainty of the Jacobian matrix, which results from the error of actuator installation. First, we explain the linearization of the internal force term. Next, the adaptive control method for the parallel wire driven system using the uncertain Jacobian matrix is proposed; then we prove the motion convergence to desired points and discuss its robustness based on Lyapunov stability analysis. Finally, the usefulness of the proposed control scheme is demonstrated through both experiments and simulation