Robotics
　　The aim of robotics research at MEL is to develop advanced robotics technology using knowledge obtained by analyzing the way in which tasks are performed by living beings. Current work includes the engineering implementation of skills found in humans and animals such as dynamic walking and manipulation, and behaviour development by learning, virtual reality, tele-robotics, and human friendly machines. A selection of robotics topics is introduced in more detail below.
　
Mobile robots with dynamic behaviour
　　We have proposed a new method for achieving autonomy in mobile robots. We define robustness to the changing environment and various dynamic skills in terms of "Dynamic behaviour modules", and aim to achieve autonomy on mobile robots by a non-hierarchical combination of these modules. A wheeled inverted pendulum type robot known as the "Variable structure 4-wheeled robot" has been developed and used in experiments in which a step of unknown height was negotiated in as little as 3 seconds. We have also developed a "Biped leg-wheeled robot" which has succeeded in climbing stairs using dynamic trajectories with nominal reference to static gait. [201]
　
　　Work using a biped walking robot "MELTRAN �U" (a two-dimensional biped robot which can walk on a flat floor and go up and down stairs) lead to theoretical studies of a three-dimensional biped. First results indicate that even fewer actuators are necessary to attain three-dimensional walking capability that were used in previous research.
　
　　Legged mechanisms have high adaptability which helps when negotiating rough terrain, whereas wheeled mechanisms enable fast efficient movement over a flat surface. A leg-wheel hybrid mobile robot which combines the advantages of these two types of robot has been developed. The robot has two front legs with three joints and a passive wheel, and has two active wheels mounted on links with one degree of freedom at the rear.
　
Fig.1 Going up stairs by 'Biped type leg-wheeled robot'
　
　
　　A quadruped robot with coordinated leg operation, known as "MELHORSE" has been developed. The fore and rear legs of the robot perform different functions in that the forelegs mainly support the body against gravity while the rear legs thrust the body forward. Experiments testing the thrust were done using an apparatus with a fuselage and rear legs, and fundamental experiments on redundant leg behaviour were also made with this apparatus. [186,209]
　
Dynamic control of robot systems
　　Nonholonomic robot systems have nonlinear constraints formulated as non-integrable differential equations involving velocity or acceleration. By applying these dynamics, robotic tasks involving more degrees of freedom than the number of control inputs can be realised. We are investigating control of a 3-axis horizontal underactuated manipulator which has a nonholonomic constraint at the passive joint. Motion planning and feedback stabilisation of the manipulator have been successfully achieved.[178,187]
　
　　Casting manipulators are a new type of manipulator which include flexible elements, for example flexible cord. These manipulators have a large working space for their size and complexity. Current research interest centres around utilisation of the dynamics of the system to achieve suitable manipulation capability. A casting manipulator incorporating a rigid link, a cord, and a gripper has been proposed and methods for control of this manipulator (in particular swing control) are currently under investigation. [196]
　
Fig.2 Position control of underactuated manipulator
　
　
　　A general framework for supporting skill discovery during the execution of robotic tasks has been developed. We define skill as a time varying function which generates control information from sensory information so that skills cover dynamics as well as kinematics and statics. Skill functions were approximated with polynomial expressions and skill discovery was reduced to a combinatorial optimisation of the polynomial coefficients. The technique was demonstrated using the visual servo problem of a robot baseball player catching a flying ball.
　
　　A vibration control system using wave control theory has been developed for a robot crane. Load transference and vibration control are realised by lateral motion of the load-supporting point, controlled by a travel input and a vibration control input. Experiments on this system have shown the effectiveness of vibration control.
　
　　A synchronous motor with three-dimensional motion has been developed for application to shoulder joints, and tests done to determine the its control characteristics.
　
　
Human modelling and the human interface
　　A mathematical model of the learning processes going on in human hand-eye coordination is under investigation. The coordinate transformation gain of the visual feedback controller is set by a novel learning model which uses the change in the square of the hand position error norm. A parallel link manipulator system is under development in order to analyse human hand control and evaluate the learning model using virtual reality technologies.
　
　　Virtual reality has attracted considerable attention as a new human interface technology. A new head mounted display is under development in which a small high resolution image is displayed in the center of the operator's field of vision, on top of a wide-angle low-resolution image which fills the periphery. A wide angle image capture and display system has been developed and evaluation experiments carried out. [180]
　
　　A cooperative multiple robot system is under development. In this work, a human operator gives a single instruction to the system. Each robot in the system refers to this and generates an evaluation function to realise overall cooperation which is achieved by learning appropriate behaviour. [172,202] In research on emotional robot behaviour for human-machine interaction, the robot generates its motivation depending on its internal state and stimulation. To a human interacting with it, the robot then appears to display emotion. [184,213]
　
Integration of locomotion and manipulation
　　Integration of locomotion and manipulation requires that both locomotion and manipulation tasks are considered together so that the design, mechanics, and control of legs and arms are integrated together in the final robot. The "Integrated Limb Mechanism" is a mechanism that may be used either as a leg or an arm. It usually performs as a leg with a large force output for supporting the body of the machine, but sometimes transforms to an arm with faster motion than a leg in upper motion space. [188] Experiments were done using "MELMANTIS-1" to demonstrate the enhanced mobility achievable with active intervention to move obstacles in the path of the robot.
　
Fig.3 Obstacle removing mobility by MELMANTIS-1
　
　
Tele-robotics
　　Tele-robotic research has been in progress since 1993. The objective is to develop methods for generating commands for control of a slave robot, by manipulating simulations of the slave environment which are displayed to the operator. In these systems, discrepancies between the simulated environment and the real environment can lead to un-expected awkward states during task execution. To solve this problem, a new method for automatic command generation based on a sub-goal concept is under investigation.
　
　　The remarkable advances currently seen in communication network capabilities have stimulated research into networked tele-robotics and have opened new potential for tele-robotic systems in other projects. Tele-robotic experiments have been carried out with LRP/CNRS in France and Toshiba in Japan where multiple robots and joysticks, all at different locations, were connected through ISDN. [206]
　
Fig.4 Virtual environment display with force-reflection
　
　
Technology to assist humans
　　 "Human Friendly Machines" are machines which are physiologically and psychologically "friendly" to human beings.
　
　　An new type of stair lift for wheelchair users has been developed with the aim of providing a system which is both inexpensive and practical. A "crawl type" mechanism has been developed for this purpose, in which rotational motion of a disk is converted to linear motion of the hoist carrier plate. The hoist carrier plate is equipped with a disk driven by an electric motor. Several rollers are attached to the rim of the disk and the hoist carrier plate can move up and down by engaging the rollers with drive guides. A prototype model was fabricated to demonstrate the characteristics of this mechanism which can go up and down the inner side of a stair with a 180゜ turn. [212]
　
　　Arm disabilities prevent full participation in everyday activities, and an upper limb motion assistance system has been proposed which uses flexible cords to provide assisted movement. The arm is suspended on a parallel arrangement of cords, and is moved by changing the length of the cords. An experimental prototype has been built and is under evaluation.
　
　　A new, efficient, assist power control system has been proposed which uses two different assist power ratios: one for static loads and one for dynamic loads. This technique has proved to very effective in avoiding actuator saturation and achieving stable power control. A new mobile power assist system is planned for working over a wide area. [204]
　
Fig.5 Crawl-type stair lift for half-turn staircase
　
　
Human friendly robotics
　　One of the results of a two-year feasibility study entitled "Friendly Network Robotics", carried out under the auspices of the Industrial Science and Technology Program, was a MEL proposal for a five year research project to develop technologies for making robots that provide services to humans in the home, factories, and disaster areas. The debut of the Honda humanoid robot at the end of 1996 made this proposal more realistic, and now one of the targets in the first two years of the project is to develop a humanoid robot as a common research -platform. The research agenda　includes: Mechanisms for human-friendly robotics, human-robot collaborative control methods, and distributed intelligence technologies.

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produced by General Research Counselor