Atsushi Konno

Configuration-dependent vibration controllability of flexible-link manipulators

In this article, the structural vibration controllability of flexible- link manipulators is discussed. For some spatial flexible- link manipulators, the structural vibration controllability is configuration-dependent. Therefore, the flexible-link manipulator may have some vibration-uncontrollable configurations. To un derstand the physical interpretation of vibration-uncontrollable configurations, we propose the modal accessibility concept, which indicates how well the actuators can affect the structural vibration modes. The configuration in which all of the actua tors cannot affect at least one of the manipulators vibration modes is vibration uncontrollable. Main contributions of this article are the following two points: first, interesting structural vibration-uncontrollable configurations are found within the two-link, three-joint-type manipulators workspace, and are verified experimentally; second, the modal accessibility index is introduced to indicate how well the corresponding vibration mode is controllable. Experimental results show that even in the controllable configurations, it becomes difficult to suppress vibration if the modal accessibility is small.

Development of a humanoid robot Saika

This article addresses the development of a light-weight, human-size and low-cost developing humanoid robot named Saika. Saika has a 2-DOF neck, two 5-DOF upper arms, a torso and a head. Several types of hands and forearms are developed. They are chosen depending upon the tasks to perform. The features of Saika are: (a) Saika as modularized to reduce the developing cost and to make maintenance easy, (b) the total weight of the head, the neck, the two upper arms and the torso is only eight kilograms and (c) most of the motors are installed inside the arms and the torso.

Acquisition of visually guided swing motion based on genetic algorithms and neural networks in two-armed bipedal robot

We describe the method in which a visually guided swing motion for a 16 DOF two-armed bipedal robot is acquired by applying a GA (genetic algorithm) to a NN (neural network) controller. The evolutionary approach to the acquisition of various motions for robots has been successfully used by many researchers, but most studies have been carried out only through computer simulations. In this research, we adopt a real robot with a complicated body used in a noisy environment. The evolutionary processes are examined in. A virtual world constructed on a CRS-CS6400 parallel computer which simulates such factors as swing dynamics, visual processes noise reduction processes, and time lags in a control system. It took about and hours for an artificial evolution to create a successfully individual after 50 generations from an initial population of 200 unsuccessful genes. Using the NN decoded from the most successful individual of the last generation, a real two-armed bipedal robot that could swing successfully was obtained.

Design and development of a legged robot research platform JROB-1

A legged robot JROB-1 is developed for a robotics research platform as a result of inter-university research program on intelligent robotics supported by the Ministry of Education Grant-in-Aid for Scientific Research on Priority Areas in Japan. The JROB-1 features: 1) self-contained, 2) RT-Linux running on PG/AT processes vision and sensor processing, motion planning and control, 3) connected to a network via radio Ethernet as to utilize networked resources, 4) Fujitsu color tracking vision board and Hitachi general purpose vision processing board, 5) all parts are commercially available, and 6) it is extensible with respect to sensor, sensor processing hardware and software. JROB-1 is expected to be a common testbed for experiment and intelligent robotics research by integrating perception and motion.

Vibration suppression control of 3D flexible robots using velocity inputs

Research on vibration suppression control of flexible robots has concentrated mainly on the one-link and two-link planar manipulators. Most of the techniques that have been presented cannot be easily extended to the case of a general 3D flexible robot. In this article we present a general control scheme based on hardware velocity servo cards. The velocity commands to move the robot are calculated by adding a vibration suppression term to the joint position feedback employed in “rigid” robots. Two different methods are proposed to calculate this term, one based on optimum quadratic control and the other based on pseudo-inverse nonlinear decoupling. These techniques are studied numerically in the case of a real two-link three-joint flexible robot, by computing the values of the closed-loop poles at different configurations. Experiments on position stabilization of the robot prove the validity of our methods.© 1997 John Wiley & Sons, Inc.

Modeling of a flexible manipulator dynamics based upon Holzer's model

An approach to modeling flexible manipulators consisting of rotary joints and flexible kinks is proposed. In the proposed approach, flexible manipulators are modeled by lumped-masses and massless springs on the basis of Holzers model, which is known as an approximate model for vibration analysis of flexible systems. Due to its simplicity, the constructed model is advantageous to the study of kinematics, dynamics and control strategy of complicated systems such as 3D multi-link multi-DOF flexible manipulators. Based on the model, dynamic equations of motion are derived using Lagrangean equation. Kinematics and the relationship between the dynamics of rigid manipulators and flexible manipulators are also discussed. The effectiveness of the model is evaluated by comparing the results of simulation with those of the experiment.

Modeling, Controllability and Vibration Suppression of 3D Flexible Robots

A robot with flexible structure called a flexible robot is necessitated. Among various flexible robots 3D (three dimensional) flexible robots are important in practice because most tasks done by robots are in three dimensional space. Modeling, controllability and vibration suppression control of the 3D flexible robot are exclusively discussed in this paper. A lumped-parameter technique using a so-called Holzer’s method is presented and how simply the technique can make a practical model for the flexible robot is shown. Using the technique controllability of the flexible robot is analyzed and interesting uncontrollable configurations for an example are found. A model-based, and thus variable-gain, depending on robot configurations, vibration suppression control scheme is derived using the model. In the scheme feedback gains for the control are varied depending on the robot configuration. The results in this paper are all verified experimentally.

A vision-based legged robot as a research platform

View changing because of vibration while walking is one of the most fundamental problem for a vision based legged robot. To overcome this difficulty, three key issues are denoted: a) integration of color segmentation, optical flow and stereo, which is able to apply to vibrating view using correlation hardware, b) software servo loop implemented as a kernel module for the purpose of soft actuation, and c) smooth walking pattern generation using solid model and dynamics simulator. Furthermore, a quadruped legged robot JROB-1 is developed as a platform for the research on perception-action coupling in intelligent behavior of robots.

Drum Beating and a Martial Art Bojutsu Performed by a Humanoid Robot

Over the past few decades a considerable number of studies have been made on impact dynamics. Zheng and Hemami discussed a mathematical model of a robot that collides with an environment (Zheng & Hemami, 1985). When a robot arm fixed on the ground collides with a hard environment, the transition from the free space to constrained space may bring instability in the control system. Therefore, the impact between robots and environments has been the subject of controversy. Asada and Ogawa analyzed the dynamics of a robot arm interacting with an environment using the inverse inertia matrices (Asada & Ogawa, 1987). In the early 90’s, the optimum approach velocity for force-controlled contact has been enthusiastically studied (Nagata et al., 1990, Kitagaki & Uchiyama, 1992). Volpe and Khosla proposed an impact control scheme for stable hard-on-hard contact of a robot arm with an environment (Volpe & Khosla, 1993). Mills and Lokhorst proposed a discontinuous control approach for the tasks that require robot arms to make a transition from non-contact motion to contact motion, and from contact motion to non-contact motion (Mills & Lokhorst, 1993). Walker proposed measures named the dynamic impact measure and the generalized impact measure to evaluate the effects of impact on robot arms (Walker, 1994). Mandal and Payandeh discussed a unified control strategy capable of achieving a stable contact against both hard and soft environment (Mandal & Payandeh, 1995). Tarn et al. proposed a sensor-referenced control method using positive acceleration feedback and switching control strategy for robot impact control (Tarn et al., 1996). Space robots does not have fixed bases, therefore, an impact with other free-floating objects may bring the space robots a catastrophe. In order to minimize the impulsive reaction force or attitude disturbance at the base of a space robot, strategies for colliding using reaction null-space have been proposed (Yoshida & Nenchev, 1995, Nenchev & Yoshida, 1998). Most of the researches have been made to overcome the problems introduced by impacts between robots and environments. Some researchers have tried to use the advantages of impacts. When a robot applies a force statically on an environment, the magnitude of force is limited by the maximum torque of the actuators. In order to exert a large force on the environment beyond the limitation, applying impulsive force has been studied by a few researchers. Uchiyama performed a nail task by a 3-DOF robotic manipulator (Uchiyama, 1975). Takase et al. developed a two-arm robotic manipulator named Robot Carpenter, and performed sawing a wooden plate and nailing (Takase, 1990). Izumi and Hitaka proposed to use a flexible link manipulator for nailing task, because the flexible link has an advantage in absorbing an impact (Izumi & Kitaka, 1993).

Development of a 3-fingered hand and grasping unknown objects by groping

This paper addresses the development of a 3-fingered hand and discusses a strategy for grasping unknown objects by groping. First, the design of the developed robot hand is presented. The robot hand has thumb, index finger and middle finger with a total of eight degrees-of-freedom. The location of thumb is designed considering opposability of human hand. Eighty-seven touch sensors are distributed over the surface of palm and fingers of the robot hand. Next, a strategy for grasping unknown objects by groping using the developed hand is discussed. Groping is a kind of active sensing. When the system does not have any model of object to grasp, active sensing becomes inevitable. The aim of the groping is to find a grasping configuration for unknown objects. A can, ball, cone, plate, and cube are chosen for the unknown objects in the experiments. Experimental results demonstrate the capability of the strategy for grasping unknown objects. This strategy needs neither models of objects nor complicated computation, and therefore, is useful especially for assembly tasks in the real world.