Akihiro Kawamura

Dynamic grasping for an arbitrary polyhedral object by a multi-fingered hand-arm system

This paper proposes a novel control method for stable grasping using a multi-fingered hand-arm system with soft hemispherical finger tips. The proposed method is simple but easily achieves stable grasping of an arbitrary polyhedral object using an arbitrary number of fingers. Firstly, we formulate nonholonomic constraints between a multi-fingered hand-arm system and an object constrained by rolling contact with finger tips, and derive a condition for stable grasping by stability analysis. A new index for evaluating the possibility of stable grasping is proposed and efficient initial relative positions between finger tips and the object for realizing stable grasping are analyzed. The stability of the proposed system and the validity of the index are verified through numerical simulations.

Externally sensorless dynamic regrasping and manipulation by a triple-fingered robotic hand with torsional fingertip joints

This paper presents an improvement of our previously proposed dynamic object grasping and manipulation method. This method, which utilizes a dual-fingered hand of which each soft and hemispheric fingertip owns a torsional joint, has performed novel 3-dimensional dynamic object grasping and manipulation stably without the use of any external sensing device. However, several limitation and weakness have still remained in terms of dexterity and robustness. In order to improve it, firstly a triple-fingered hand is newly introduced instead of the dual-fingered hand to perform regrasping. Next, the previously proposed stable object grasping controller is adequately modified to perform dynamic regrasping during manipulation. Additionally, the virtual object attitude controller is also modified to improve its performance. Finally, several experiments are conducted by using a prototype, and the usefulness of proposed controller is demonstrated through these results.

Improvement of position accuracy for inflatable robotic arm using visual feedback control method

Inflatable robotic arms have been studied as a lightweight and flexible robotic structure for applications to new fields. In general the motion control of inflatable robotic arms is difficult, because they have complicated nonlinear characteristics. This paper proposes a new control method suitable for inflatable robotic arms that realizes precise position control on the basis of a visual feedback system. The effectiveness of the control method is verified by the results of an experiment, in which an inflatable robotic arm with two degrees of freedom and a web camera are used.

Encoderless robot motion control using vision sensor and back electromotive force

This paper focuses on a possibility of application of a method to simplification of robotic arm systems by removal joint encoders. The method which has been proposed achieves precise control of robotic arms using visual feedback with camera calibration errors. In this paper, the method is improved for an encoderless robotic arm system to ease several difficulties to use encoders. Encoders are fundamental components of most robotic arm systems to control joint angles precisely. However, encoders sometimes make some difficulties of wiring, structure and maintenance. The enhanced method for encoderless robotic arm systems is able to overcome these difficulties. Moreover, this method is also useful for robotic systems which have encoders since the method is able to be activated as a fail-safe system of robots with encoders just in case encoders are broken down. This new approach acquires information on joint angles from not encoders but estimation using back electromotive force. The information on joint angles includes some errors. The method, however, realizes precise manipulation. It is finally shown that this method allows errors caused by not only from camera calibrations but also joint angles.

Dynamic object manipulation using a multi-fingered hand-arm system: Enhancement of a grasping capability using relative attitude constraints of fingers

In this paper, an enhancement of a dynamic object grasping and manipulation method, which has been proposed by us previously, is presented. This enhancement makes it possible to grasp more various shaped objects which could not have been grasped by our previous method. In our previous method, a force/torque equilibrium condition to satisfy stable object grasping has been realized by only using grasping forces normal to an object surfaces. It is because each fingertip is soft and hemispheric and then rolling constraints arise during movement, and these phenomena cannot be stopped while existing the rolling constraint forces. Therefore, satisfying the dynamic force/torque equilibrium condition depends not only on a configuration of the multi-fingered hand system, but also on the shape of the grasped object. In this paper, a class of satisfying the force/torque equilibrium condition is expanded by generating counter tangential forces to suspend the rolling motion of each fingertip. In order to generate the counter tangential force, a relative attitude constraint between each finger is introduced. Firstly, a rolling constraint between each fingertip and object surface is given. Then, a relative attitude constraint control signal to generate constantly-produced tangential forces is designed. Finally, it is demonstrated through numerical simulations that the proposed control method accomplishes to grasp arbitrary shaped polyhedral objects and regulate its position and attitude, simultaneously.

Development of an inflatable robotic arm system controlled by a joystick

This paper presents an inflatable robotic arm controlled by a joystick to be used for healthcare applications. The arm is constructed almost entirely of plastic elements: inflatable links, air bag actuators, and acrylonitrile butadiene styrene (ABS) joints. Therefore, it is softer and lighter than typical robotic arms that are made of metal and heavy elements. Because the softness and lightness of the inflatable robotic arm is intrinsically safer, it is suitable for healthcare applications. In this paper, a new control method is proposed which allows the inflatable system to be controlled with a joystick. To verify the usefulness of the proposed method, we used an inflatable robotic arm with four degrees of freedom (4 DOF) to obtain experimental results for the control performance of the inflatable robotic arm. Moreover, we conducted preliminary tests which simulated patients controlling the robotic arm with a joystick in order to assist with eating their meals.

Automatic planning of laser measurements for a large-scale environment using CPS-SLAM system

In recent years, several low-cost 3D laser scanners are being brought to the market and 3D laser scanning is becoming widely used in many fields. For example, 3D modeling of architectural structures or digital preservation of cultural heritages are typical applications for 3D laser scanning. Despite of the development of light-weight and high-speed laser scanners, however, the complicated measurement procedure and long measurement time are still a heavy burden for the widespread use of laser scanning. We have proposed a robotic 3D scanning system using multiple robots named CPS-SLAM, which consists of parent robots with a 3D laser scanner and child robots with target markers. In this system, a large-scale 3D model can be acquired by an on-board 3D laser scanner on a parent robot from several positions determined precisely by the localization technique using multiple robots named Cooperative Positioning System, CPS. Therefore, this system enables to build a 3D model without complicated post-processing procedures such as ICP. In addition, this system is an open-loop SLAM system and a quite precise 3D model can be obtained without closed loops. This paper proposes an automatic planning technique of a laser measurement for CPS-SLAM. By planning a proper scanning strategy depending on a target structure, it is possible to perform laser scanning efficiently and accurately even for a large-scale and complex environment. Proposed technique plans an efficient scanning strategy automatically by taking account of several criteria, such as visibility between robots, error accumulation, and efficient traveling. We conducted computer simulations and outdoor experiments to verify the performance of the proposed technique.

Adaptive motion control of a robotic arm with movable counterweights

This paper proposes a new robotic arm which has active movable counterweights as an actuator in addition to motor drives. The active counterweights reduce gravity effect of cantilever structure adaptively by movement of counterweights. Additionally, the counterweight has offset angle between links and movement axis of the counterweight. This structure makes it possible to regulate joint angles not using joint motors but only using gravity of the counterweights. Using the two features, gear reduction ratio of motors decreases and base unit becomes light and small. Consequently, the robotic arm has flexibility and is suitable for narrow and high altitude environment such as on vehicles. It is however difficult to control the robot precisely due to the effects of physical parameter errors and friction. Therefore, an adaptive control method of this new robotic arm is proposed. The usefulness of the method is demonstrated by experiments using a prototype.

Robust visual servoing for object manipulation with large time-delays of visual information

This paper proposes a new visual servoing method for object manipulation robust to considerable time-delays of visual information. There still remain several problems in visual servoing methods although they are quite useful and effective for dexterous object manipulation. For instance, time-delays to obtain necessary information for object manipulation from visual images induce unstable behavior. The time-delays are mainly caused by low sampling rate of visual sensing system, computational cost for image processing, and latency of data transmission from visual sensor to processor. The method makes it possible to avoid such unstable behavior of the systems due to considerable time-delays using virtual object frame defined by only each joint angle. Firstly, a new control scheme for object manipulation using the virtual object frame is designed. Next, numerical simulations are conducted to verify the effectiveness of the control scheme. Finally, experimental results are shown to demonstrate the practical usefulness of proposed method.

Robust manipulation for temporary lack of sensory information by a multi-fingered hand-arm system

This paper proposes a novel vision-based grasping and manipulation scheme of a multi-fingered hand-arm system robust for a temporary lack of sensory information. Visual information is one of the fundamental components for reliable grasping and manipulation by a multi-fingered hand-arm system. However, in case that visual information such as position and attitude of an object comes to be unavailable due to the occlusion or if the object goes out-of-sight temporarily, unstable and unfavorable behavior is often induced. The proposed method, which utilizes the stable grasping control and the concept of virtual frame, enables to grasp and manipulate an object stably even if the visual information becomes suddenly and temporarily unavailable during manipulation. Firstly, a dynamical model of object grasping using a multi-fingered hand-arm system is formulated. Next, a new control scheme for robust object grasping and manipulation using the virtual frame is proposed. Finally, numerical simulations are performed to verify the usefulness of the proposed method.