In this paper, a reflective force generation method of a force feedback joystick is suggested for a nonautonomous mobile robot maneuvered by a teleoperator. Three types of the reflective forces are defined such as obstacle detection, obstacle avoidance and robot posture recognition forces. To generate the reflective force for obstacle detection and avoidance, range data from ultrasonic sensors of the robot are used. Using these data, wall and center following of the robot are implemented by a fuzzy logic controller for obstacle avoidance. Next, the reflective force for robot posture recognition is generated using a gyro sensor of the robot. Thus the operator can not only maneuver the robot without collisions but also recognize the existence of obstacles and the posture of the robot by the reflective forces while driving the robot. Then, to determine the type of the reflective forces according to robot and obstacle states a state transition diagram is suggested. Finally, the experimental and simulation results with the mobile robot, ROBHAZ-DT developed by KIST show the effectiveness of the suggested method.

In this paper, a real-time obstacle avoidance method is discussed for a remote mobile robot controlled by a teleoperator. The method enables the remote user to drive the mobile robot without collisions. It consists of a real-time environment modeling algorithm using ultrasonic sensors, and a mobile robot control algorithm for obstacle avoidance. The former solves the limitations of the ultrasonic sensors such as noise sensitivity, poor directionality, and specular reflection for obtaining more accurate sensor data. Then the latter conducts wall or center following implemented by a fuzzy controller for obstacle avoidance using the environment model obtained by the previous algorithm. The command for obstacle avoidance is actually applied as a reflective force using a haptic device such as a force feedback joystick. The remote mobile robot, ROBHAZ-DT(RoBot in HAZardous environment-Double Track) developed by KIST(Korea Institute of Science and Technology), is employed as the mobile robot model. The normal and the maximum speed of the ROBHAZ-DT are 3.1 km/h and 7.2 km/h, respectively. The weight of the robot is 50 kg. Simulations with the ROBHAZ-DT model are carried out to verify the performance of the proposed method.

Current database trigger systems have extremely limited scalability. This paper proposes a way to develop a truly scalable trigger system. Scalability to large numbers of triggers is achieved with a trigger cache to use the main memory effectively, and a memory-conserving selection predicate index based on the use of unique expression formats called expression signatures. A key observation is that if a very large number of triggers are created, many will have the same structure, except for the appearance of different constant values. When a trigger is created, tuples are added to special relations created for expression signatures to hold the trigger's constants. These tables can be augmented with a database index or main-memory index structure to serve as a predicate index. The design presented also uses a number of types of concurrency to achieve scalability, including token (tuple)-level, condition-level, rule action-level and data-level concurrency.