Wheeled mobile robots are representative of nonholonomic systems. It is already known that there does not exist a continuous state feedback law to stabilize a nonholonomic system to a single equilibrium point. However, it may be possible to stabilize a nonholonomic system to a manifold, instead of a single equilibrium point, by using continuous state feedback. In this paper, we show that by suitably choosing a cartesian coordinate the position (corresponding to a manifold in the configuration space) of mobile robots can be controlled very easily.
This paper deals with a kinematics analysis of cooperation necessary for two mobile robots to carry a long bar along a sinusoidal wavy road. The robots are assumed to be driven by crawler mechanism and to have a single link arm which moves only prismatically. For the task to carry a long bar with keeping its height constant and its attitude horizontal, we analyse the kinematic conditions necessary for the two mobile robots to perform the given task and find that there exist two kinds of cooperation mode ; one is to change the direction of proceeding and the other is to change the robot role from “master” to “servant” and vis-vasa. The kinematic condition for these two cooperation mode are derived and confirmed by simulation study.
In this paper, we discuss the modeling of flexible manipulators. In the modeling of flexible manipulators, there are two approaches: one is based on the distributed-parameter modeling and the other on the lumped-parameter modeling. The distributed-parameter model is effective for simple flexible manipulators such as a one-link planar manipulator. For flexible manipulators with multi-link and multi-DOF (degree-of-freedom), however, the distributed-parameter model will be too complicated to use in control. In this paper, we propose a new model for the flexible manipulators based on the lumped-parameter model. Our model is simple enough to construct and implement in control schemes. This model can also be easily applied to manipulators which have flexibility at their joints. Based on our model, dynamic equations of motion are derived by the Lagrange's method. The effectiveness of our model is shown by comparing simulation results with the experimental results.
This paper presents a navigation scheme for a mobile robot which works even in an environment with multiple moving obstacles. An “iterated forecast and planning” approach is proposed by the authors. It is assumed that each obstacle moves at a constant velocity in the approach. The most feasible path for a robot is planned in (x, y, t) space. The planning and motion according to the plan are iterated frequently to cope with changes of motion of the moving obstacles. The behavior of proposed navigation algorithm is also presented by means of computer simulations.
In this papar, the path planning of two manipulators of a space robot is considered. The equations of the motion of a free-flying space robot that has two manipulators are derived. On the basis of the dynamic model, an optimal trajectory, which accomplishes the desired end-position of the manipulator hands and minimizes the deviation of the attitude of the body of the space robot from the initial configuration, are calculated by using a numerical algorithm. Simulation results for a planar space robot with two 2. D. O. F. manipulators are shown.
Recently, not only repeatability but also absolute accuracy began to be required with regard to the positioning accuracy of a robot arm. That is mainly because the absolute positioning accuracy of a robot arm is becoming necessary in applying such technologies practically as robot sensors which measure the three dimensional position and posture of an object or the offline programming system etc. In this paper, an automatic calibration method which uses a simple sensor comprising three laser displacement sensors and a unique argorithm to compensate for the measured data is described. This method will promote to make automatic calibration of a robot arm practical because it proved to bring high accuracy irrespective of low cost of the sensor.
The manipulability for wire suspension mechanisms is discussed. For kinematics of a wire driving mechanism, we need not only the geometrical constraints of wire lengths but also the force constraints that each wire tension should be always greater than or equal to zero. First, the sufficient and necessary mechanical conditions corresponding to the force conditions are shown. Using these conditions, we can obtain the manipulability of a wire driving mechanism almost same as that of popular multi-link manipulators. Second, a more practical evaluation index including wire tensions that are driving forces for the object is proposed as“manipulating force set”and the way of calculation is shown. We also derive both manipulability indexes of wire suspension mechanisms in gravity field by modeling the gravitational force as a wire with the tension of the gravity. Numerical examples are given to explain the proposed methods and to show their validity. The method is expected to be effective in designing and task planning of wire driving systems including wire suspension mechanisms.
Human beings have various manipulation skills and execute tasks using them intelligently. Intelligent manipulation is a series of manipulation skills combined to execute a task. However robot manipulation skills in practical use are limited to pick-and-place operations, i.e. to move an object grasping fixedly. There have been previously some researches on intelligent manipulations by pick-and-place operations. But the problem is that, when using only pick-and-place operations in some environments, it may happen that the goal cannot be achieved or the motions become uneffective. This paper describes a motion planning system using not only pick-and-place operations but also sliding operations with a parallel two-fingered gripper. This system can plan manipulator motions which we have failed to plan before or which are more efficient using sliding operations in addition to pick-and-place operations. The motions are ones to escape an object from situations where the gripper cannot grasp some parts of it. In the following, first we describe the situations and actions to escape from there. Then we propose a new method to plan the manipulator motions using sliding and pick-and-place operations based on geometrical information. Lastly we show the results of our method and its validity.
This paper discusses foot force control of a quadruped walking vehicle on rough terrain. The proposed control algorithm has two parts. One is a feed-forward control to produce a smooth touch-down and lift-up motion of the leg. The other part is a feedback control to maintain the body's posture under the conditions of some disturbances. A command force of the feed forward control is calculated beforehand from the data of the body's position, its acceleration and leg positions. The force increases smoothly from zero after touch-down on the ground, and it decreases smoothly to zero before lift-up. On the other hand, a command force of the feedback control is calculated from the data of the body's posture measured by gyroscopes. The effect of the feedback control is as if the body is suspended to an absolute frame by springs and dampers. Therefore, it is called“Sky-Hook Suspension”. By this control algorithm, the experimental vehicle TITAN VI is able to walk smoothly on a rough terrain.
The present paper proposes a new feedback control strategy of mobile robots with nonholonomic constraints. This method includes a function generator called a Time Base Generator (TBG) as a time varying feedback gain, and synchronizing linear and angular velocities of the mobile robot with a scalar variable generated by the TBG, the mobile robot can be positioned to the origin in the state space for any initial condition. The time behavior of the generated trajectory such as the velocity profile and the movement time from the initial position to the goal can be controlled through adjusting the parameters of the TBG without any change of the control law itself. In this paper, mechanism and stability of the proposed method are described using a particular type of the TBG with a bell shaped velocity profile and it is shown that the method can naturally generate straight and circular trajectories for certain initial conditions and provide a robust position control of the mobile robot for external disturbances.