In a manipulation system that executes assembly tasks, contact-state recognition or contact-state-transition detection are important functions. These functions should be modularized as a motion monitoring and evaluation (MME) module. This paper mainly presents a real-time detection method of contact-state-transition with high reliability, and the implementation of the method into the MME module. In the detection algorithm, features which fluctuate abruptly when the contact-state-transition occur are selected according to the motion pattern. In the detection algorithm, the differential of the feature locus is monitored and the transition region is distinguished from the stable region. Then, to confirm whether state-transition really occur in the region, the duration of the region and the feature deviation are counted. Using this method, contact-state-transition is detected with only 40 [msec] delay. An experimental manipulation system, in which motion control and MME modules are independently executed, is developed using transputers and the 6 D.O.F direct drive manipulator ETA 3. In the experiment, six patterns of motion, in which different types of transition occur, are selected. The experimental results show that contact-state-transition is accurately detected and motion commands can be quickly switched using detected transition information.
In this paper, we describe a map acquiring system MARSHA for multi-robot environments. MARSHA addresses an important problem in multi-robot environments; how to share distributed/local knowledge. MARSHA tackles this problem in terms of relational expressions, which represent differences between every two robots. These relational expressions are computed by applying Matching Procedure to local maps which are generated by each robot individu-ally. By using these relational expressions, MARSHA makes it possible for all of the robots to utilize a global terrain map as their own map even if they do not travel around all the region. The effectiveness of the algorithm is shown through experiments with the implemented system on autonomous mobile robots.
This paper proposes a new identification method of self-positioning of an autonomous mobile robot. A CCD camera reads a code of pixels on the mark pattern drawn on a ceiling. The proposed method dose not require complicated calculation compared with other methods such as conventional triangular surveying ones. The most benefit point is that it can do identification of selfpositioning on real time by only reading the pattern. This real time is necessary requirement for mobile robots. Validity of the method is confirmed by experiments of self-positioning on real time by reading the pattern.
Since the working environment in ocean is very severe for human being, the development of underwater robot has been demanded. The influence of fluid surrounding a robot and its unconstrained state are characteristic of the underwater robot. As a first step of the study for the underwater robot, this paper investigates the workspace and the dynamic manipulability measure, which are used for the standards to evaluate the manipulator performance, for the manipulator mounted on a unconstrained robot in water and furthermore compares them to those of the space robot manipulator. The workspace of underwater robot which is called the straightpass workspace is smaller than the space robot in the condition of the model used in this paper. However its workspace depends on the shape of robot and manipulator. The tendency of dynamic manipulability at the position of the hand is almost the same as that of the space robot, but the dynamic manipulability measure is smaller because of the influence of the added mass and added inertia.
A learning control based on repetitive operations of robotic manipulators is one of the most promising methods to realize high speed and high precision control for robotic manipulators. The learning algorithm being implemented by using many memories, the stability of learning control system should be analized in discrete-time domain. The joint servo system usually has an unstable zero. In our previous paper, we have clarified that this fact leads to unstable learning, when a sampling period is small. In this paper, we propose a new learning algorithm based on so-called 2-Delay input method. By using the 2-Delay input method, we can stabilize the unstable zero and realize the stable learning even if the sampling period is small. Also, we show some simulation results to verify the effectiveness of our proposed method.
In this paper, a real-time trajectory planning method which is effective for a robot to track a moving object is derived. This method generates the optimal trajectory based on the minimum acceleration criterion whose position and velocity are coincident with those of a moving object at predefined time. Therefore, this method is effective for reliable capture of a moving object. First, the optimal trajectory for a moving object with constant velocity is derived. The problem is formulated as an inhomogeneous regulator problem, and the optimal trajectory to minimize a cost function is solved analytically. Next, the way to generate the trajectory when the maximum speed or acceleration is limited is discussed. Optimal trajectory planning for a moving object with acceleration or rotation is developed also. Finally, results of experiments to capture moving objects are presented. The experimental system consists of a 3-DOF manipulator, a dummy object, a CCD hand-eye camera and a vision processing system. The manipulator and dummy object are floating on a plate base using air bearings. The vision system can detect the position/direction of the dummy object every 17 [msec] .
For the robot cooperation in a large system with many mobile robots, the locality and concurrence of communication must be taken into account. The time-delay in communication becomes important for task planning in such a robot environment. We introduced a simple model of local communication among mobile robots and derived from a mathematical analysis that the information diffusion is described by a logistic function. The effectiveness of the analytical results is verified by a computer simulation which implements many mobile robots. Utilizing this simple logistic function, the time-delay required so that the task information is transmitted to necessary number of robots is computed, and unnecessary diffusion of the information can also be avoided. As an application of the analytical results to task planning, another simulation of cooperative task execution is undertaken, in which a method is shown to control the degree of diffusion by specifying the diffusion time according to task requirements.
In order to execute various contacting tasks, a robot must be controlled contacting force or contacting resistance. In the former case, a force-control is available, and in the latter case, an impedance-control and a compliance-control are useful. In this paper, we propose a Hybrid Compliance/Force Control (H. C. C.) which is a combination of a Hybrid Position/Force Control and a compliance-control. In this method, a position control, a force-control, and a compliance-control can be switched for any direction of a given task. Moreover we compose typical 2 types of H. C. C. (torque-based and position-based), and both methods are installed in a 6-D. 0. F. industrial robot. This study shows compositions of 2 types of H. C. C. and their experimental results.
This paper is concerned with some control experiments of a flexible manipulator mounted on a free-flying space robot by using a hardware experimental system. By means of a concept called virtual rigid manipulator, the manipulation variable feedback controls can be realized, which satisfy the collocation condition of sensors and actuators. To control the position and orientaion of the hand to a specified target, three control schemes for the flexible manipulators are examined, i. e., extended local PD-control, pseudo resolved motion rate control, and pseudo resolved acceleration control. The effectiveness of the proposed control schemes is successfully demonstrated through hardware experiments, where each joint of manipulator has a torque servo actuator for a fine torque control.
In the near future, mobile robots will play an important roll in various tasks in factory automations or indoor services. Such various tasks involve specifications like urgency or safety. As a result, planners must take those factors into account to generate motions for mobile robots. This paper proposes a trajectory planning method addressing this problem : Environment, moving obstacles, robot motion dynamics, and user's specifiaations are described with cost functions, and an optimization technique is applied. Our method can be applied to some time-varying environments that the time-space technique cannot treate, can consider the motion dynamics, and need not prepare particular algorithms for each user's specifiaction.
It is expected that See-Through Head-Mounted Display (STHMD), which superimposes the virtual environment generated by computer graphics (CG) on the real world, can vividly execute various simulations and designs by using both of the real and virtual environment around us. In STHMDs, information given as a virtual environment has to exactly match with the real environment, because both environments are visible. This is one of the problems to be solved for practical use. Particularly for matching of locations and size between real and virtual objects, disaccordance is likely to occur between the world coordinate of the real environment where the user of STHMD actually exists and that of the virtual environment described as parameters of CG, which directly causes displacement of locations where virtual objects are superimposed. This must be calibrated so that the virtual environment is superimposed properly. Among causes of such errors, we focused both on systematic errors of visual parameters caused in manufacturing process and differences between actual and supposed location of user's eye on STHMD when in use. The former is required to be calibrated only once after the fabrication of STHMDs, whereas the latter has to be calibrated every time users start using STHMDs. We have proposed calibration methods which are suitable to properties of these causes of errors. In the method, the direct fitting of the virtual cursor drawn in the virtual environment onto targets in the real environment is performed. Then, based on the result of fitting, the least square method identifies values of the visual parameters which minimize differences between locations of virtual cursor in the virutal environment and targets in the real environment. Application of the method to the STHMD which we have made is also repored. The differences between the virtal cursor and targets in the real environment due to systematic errors caused in the manufacturing process were reduced to about 1 [mm] per target, which was less than one-thirtieth of that before the calibration. The differences between the virtual cursor and targets in the real environment due to the location of user's eyes were also reduced about 2 [mm] per target, which was a half of that before the calibration. This result was well enough to prove the effectiveness of the calibration methods.