In recent years, space has attracted special interest as a new application field of robotics. A robotic teleoperator system installed with space manipulators will play an important role in future space projects, such as constructing space structures or servicing satellites. However, in space environment, the lack of a fixed base arises many problems in controlling space robotic systems. In general, any motion of the manipulator arm will induce reaction forces and moments which disturb position and attitude of the supporting base satellite. To establish a control method for space manipulators taking dynamical interaction between the manipulator arm and the base satellite into account, the authors investigate the kinematics of free-flying multi-jointed link systems by introducing the momentum conservation law into the formulation and derive a new Jacobian matrix in generalized form for space robotic arms. By means of the new matrix, they develop a control method for space manipulators based on the resolved motion rate control concept. The proposed method is widely applicable for not only free-flying manipulation problems but also attitude control problems. The validity of the method is demonstrated by computer simulations with a realistic model of robot satellite.
In this report, the numerical simulation of the horizontal articulated robot consisting of two horizontal rotating links and a vertical linear link is presented. In the numeriacal simulation, the pendulum vibrations of the vertical linear link, in the plane perpendicular to the second horizontal rotating link, are considered. Then, in the derivation of the state equation of the robot, the equation of motion of the mechanical system is derived in considerration of the flexibility and viscosity of the coupling mechanism between the second horizontal rotating link and the vertical linear link as well as the nonlinear flexibility of the harmonic drives, and the nonlinear state equation of the robot is obtained by coupling the equation of motion with the electric current equation of the servo position control system. based on the proportional plus integral plus derivative control. Furthermore, the numerical simulation results are demonstrated, and the effects of the pendulum vibrations of the vertical linear link on the dynamic characteristics of the robot and the control accuracy are investigated.
This paper presents a general and efficient method using a configuration space for planning a collision-free path among known stationary obstacles for a manipulator. The basic approach taken in this method is to restrict the free space concerning path planning and to avoid executing unnecessary collision detections, based on the idea that a collision-free path can be planned using only partial information of the configuration space. The configuration space is equally quantized into cells in a six dimensional array, and the cells cencerning path planning are enumerated by simultaneously executing multiple search strategies. The coefficients for heuristic functions are randomly generated, and search strategies of different characteristics are defined for enumerating free space cells. The efficiency of each search strategy is evaluated during free space enumeration, and a more promising one is automatically selected and is preferentially executed. The total number of necessary collision detections for free space enumeration mainly depends on the most efficient search strategy among these ones. Therefore, the free space cells are efficiently enumerated for all kinds of manipulators of different kinematic characteristics in all kinds of working environments. This method has been actually implemented and has been applied to several examples which have different characteristics.