A motion planning method for robot groups is presented in this paper. The method aims at considering the tasks of the robots while determining motion of the group. The concept of “cohesion”is proposed to express characteristics of tasks of groups. A motion planning method including“cohesion”is presented. The method is implemented in Virtual Impedance Method, which was proposed by authors. Each robot has two kinds of impedance mode between another robot : one is connecting model, in which the two robots keep near distance each other. The other is independent model, in which each robot moves individually and independently. Each robot decide the mode with the robots of the same group by comparing “cohesion” given to the group and index of danger calculated by environmental situation. Effectiveness of the method is verified by simulation results.
A multifingered hand can manipulate an object skillfully with fingertip contacts. It can also grasp an object stably with finger link contacts. Such grasp is called power grasp. When Coulomb friction is assumed at contact points and the number of contacts is greater than the number of joint torques, the contact forces balancing the joint torques are not necessarily determined uniquely. This paper investigates how indeterminate grasp forces of power grasps are distributed assuming that both the finger links and grasped object are rigid bodies. We show that the sliding motion between a grasped object and finger links is restricted when the grasp forces are indeterminate. In general, a frictional force can occur only in the reverse direction of sliding. Thus the indeterminate grasp forces of power grasps are also restricted. This analysis leads to the condition that they are uniquely determined. This paper also discusses form closure of power grasps which can generate unique grasp forces against any disturbances.
This paper describes a method for sub-minimal-time trajectory planning of a dual manipulator system required to move a rigid task object from one spatial point to another. In this method, in order to transform the time optimal control problem into a non-linearly constrained optimisation problem, a piece-wise constant function is used to approximate the third derivatives of the generalised coordinates of the active joints of the dual manipulator system. However, the system is underspecified due to the redundancy, which is inherent to the system. A technique to overcome the problem, in which an excessive torque is used as optimisation variables, is proposed accordingly. A numerical example involving two SCARA type manipulators handling a long beam was used to illustrate the proposed scheme and results showed the effectiveness of the proposed technique.
This paper concerns a new tactile sensor with both 3-axis force sensing and slip vibration sensing functions. The first three axis force sensing is achieved with tactile heads, each of which transmits the 3-axis contact force and is supported by three pressure transducers. The pressure transducer measures a change in the contact resistance between a specially treated polyimide film and a resistive substrate. The slip sensing function is achieved through the use of a stress-rate sensor that responds to smallscale variations in a surface profile with roughness. Detecting circuits for each of the transduction method were shown with their input stress (rate) -output voltage formulae. Static analysis of the 3-axis force sensing was made and compared with the experimental results. We show an index which gives the curvature of slip direction and enables the sensor for distinguishing rotational slip of an object on the sensor from translational slip. Further experiments were conducted to show the applicability of the index.
Understanding human intention is an essential function for a robot which can offer adequate support to human beings. It requires smooth communication between the human and the robot. Human behavior is an expressive media of communication. This paper proposes a new function of“active understanding of human intentions”by a robot through monitoring of human behavior. The unique feature of the proposed function lies in the fact that it utilizes multi-communication channels in parallel, i.e., human intentions are understood not only through conscious behavior but also through unconscious behavior. The paper also proposes a robot architecture to realize the function. Following points are the key features of the architecture: 1) A robot possesses multi-sensors which surround the human. 2) Information processing is carried out by dual loops — a loop for information exchange between the human and the robot and a loop for human intention understanding. As an example of a robot with the human intention understanding functions, the authors constructed a micro-teleoperation robot. It can automatically understand an operator's intention through such unconscious behavior of touching a desk with an operator's hand which holds a pen-shaped master. The understood result is utilized to change the control mode of a master-slave manipulation system from fine motion to rough motion and vice versa. The experimental results prove that the proposed function is effective in making the operation of the system easier. Consequently the system is friendly to the operator.
In this paper, the authors devise a method that a biped walking robot realizes a learning process of walking stabilization with the cooperation of a human, by imitating the learning process of a baby. We have developed a biped walking robot which has a trunk, and equipped the robot with a ZMP (Zero Moment Point) measurement system, which is composed of two universal force-moment sensors, and with a mechanical interface for the cooperation. We performed walking experiments with the biped walking robot, in which a human directly taught the robot the desired ZMP, and the robot learned to stabilize its walking with the cooperation of the human. As a result, the robot acquired the taught desired ZMP by modifying its trunk motion and it achieved stable walking by itself through the process of several walking trials.
This paper presents a symbolic analysis method of the minimum set of dynamic parameters for general closed-link manipulator by means of the computer algebra software. This method allows us to obtain all the minimum dynamic parameters (MDP) explicitly and systematically in most cases. A key step is to determine fundamental functions that are necessary and sufficient to express the coefficient matrix of dynamic parameters. The linear independence of column vectors of the coefficient matrix is tested by using fundamental functions and the dynamic parameters are regrouped based on the linear independency. The paper also discusses a sufficient condition in which the dynamics of the closed-link mechanism can be considered to be equivalent to that of the serial-link mechanism. To illustrate the merits of the new method, the authors also examined the MDP of some closed-link mechanisms, using the computer algebra software called“Maple V.”
This paper studies on range image segmentation using curvature signs. The signs of mean curvature and Gaussian curvature can determine local surface shapes and they have been used for the range image segmentations. Range images are usually distorted by noise which is caused in range data acquisition, quantization and so on. The noise contamination affects curvature computation. This paper first evaluates the accuracy and the noise robustness of several curvature computation methods. The experimental results show that the robustness depends on the number of neighborhood points from which the curvatures are computed and that the method which uses first and second derivatives computed from quadric fitting is more robust than others. This paper then studies the characteristics of surface types and thresholds, which determine the curvature signs. The study shows that the noise robustness of plane, cylinder and sphere shape are different and that the smaller thresholds segment curved regions correctly.
We have developed a master-slave manipulator with a 7 DOF slave arm and the redundancy control of the slave arm has been investigated. In the redundancy control, the redundancy is used not to avoid singular attitude but to compensate the loss of freedom at singular attitude. The developed redundancy control enables the movement at singular attitude and avoids each joint limit as much as possible so that the slave arm can move widely. The desired position and direction of the slave arm are transformed to the desired joint angles by the pseudo-inverse Jacobian. The redundant item is set to maximize the value of a performance index. The wrist joint of the slave arm consists of R -P-R, so a coincidence of 2 roll axes is the singular configuration. The performance index is set as the difference between the desired hand orientation and the current forearm orientation when the attitude of the slave arm is near the singular configuration so that the desired direction can be achieved by the wrist direction even at the singular configuration. Finally, the validity of the developed control method has been confirmed by experiments.
For the purpose of coinciding the virtual environment displayed by See-Through Head-Mounted Display (STHMD) with the actual environment, a new calibration method is proposed. The method is for the calibration of the difference between supposed position and actual position of the user's viewpoint, which is mainly caused by the individual difference of inter-pupil distance. This method is efficient to minimize the error concerning distance. The efficiency is evaluated by sensitivity analysis of visual parameters. It is also confirmed by experiment in which visual parameters of STHMD are calibrated individually, and the calibrated virtual environment matched the actual environment.