Whenever a mobile robot has to deal with an environment that is totally or partially unknown or dynamically changing, local navigation strategies are very important for the robot to successfully achieve its goals. Unfortunately, local navigation algorithms that have been proposed in the literature offer poor performance (or even fail) whenever the geometry of the free space in which the robot is requested to operate increases its complexity. In this paper, we deal with a team composed of many robots, and we show how robots navigating within an unknown environment with local communication capabilities (only line-of-sight communication is allowed) can cooperate by helping each other to achieve their own goals.

In this paper, methods based on various spline techniques for planning and fast modifications of a trajectory for robot manipulators are investigated. Algebraic and trigonometric splines, their combined use, and the use of the B-spline technique are analyzed and compared in detail. In so doing, we focus on the performance of sudden changes in a predefined trajectory, e.g. obstacle avoidance in real-time applications. Some comparative examples illustrate our results.

Lie algebra is an area of mathematics that is largely used by electrical engineer students, mainly at post-graduation level in the control area. The purpose of this paper is to illustrate the use of Lie algebra to control nonlinear systems, essentially in the framework of mobile robot control. The study of path following control of a mobile robot using an input-output feedback linearization controller is performed. The effectiveness of the nonlinear controller is illustrated with simulation examples.

A new approach to the design of a polytopic gain scheduled H∞ controller with pole placement for n-joint rigid robotic manipulators is presented. With linearization around the equilibrium manifold, the robotic system is transformed into a continuous linear parameter-varying (LPV) system with respect to the equilibrium manifold. A filter is introduced to obtain an augmented system, which is apt to have the polytopic gain scheduled controller designed. This system is put into a polytopic expression by a convex decomposition. Based on the concepts of quadratic D-stability and quadratic H∞ performance, the polytopic features are used to simplify the controller design to be a vertices’ controller design for the polytope. A state feedback gain, which satisfies H∞ performance and dynamic characteristics for each vertex of the polytope, is designed with a Linear Matrix Inequality (LMI) approach. A global continuous gain scheduled controller is then obtained by a synthesis of the vertex gains. Experiments demonstrate the feasibility of the designed controller.

A novel hyper-redundant manipulator named RT1 is presented in this paper. The key feature of RT1 is that all degrees of freedom (DOF) are actuated with only one motor, via specially designed hinge bar universal joints. The mechanism of RT1 which includes a special hinge bar universal joint, bend structure and motion diversion structure is described. RT1 is a discrete manipulator; the discrete working space is described, and the parameter optimization for kinematical redundancy resolution is also studied. In selecting the unit increment of joints angles as an optimizing parameter, the criterion used is to alter the design parameter as little as possible during the manipulator’s motion from the initial to the expected position.

This paper proposes an algorithm for managing redundant measurements provided by a stereo multi-camera system to achieve accurate visual tracking of a moving object. Selfocclusion, different visual resolution zones and optimal selection of redundant measurements are some of the problems addressed. The algorithm uses the extended Kalman filter embedded in a computational efficient pose estimation procedure based on Binary Space Partitioning Tree geometric modelling of 3D objects. Experimental results are presented for the case of an object moving in the visual space of two fixed cameras.

A mobile manipulator is treated as a robotic system composed of a non-holonomic mobile platform and a holonomic manipulator mounted on the platform. The kinematics of the mobile manipulator can be represented as a driftless control system with outputs. By adopting the endogenous configuration space approach we propose two kinematic dexterity measures, called local and global dexterity. The local dexterity, modeled upon the manipulability of stationary manipulators, indicates how infinitesimal motions in the configuration space propagate to the taskspace of the mobile manipulator. The global dexterity corresponds to L2-norm of the local dexterity over a prescribed region of the configuration space. Advantages of the endogenous dexterity measures over traditional performance measures of mobile manipulators known from the literature are described. Both the dexterities are employed for determining optimal configurations and optimal geometries of an exemplary mobile manipulator.

Three joint space algorithms slow the Cartesian path motion when it appears that joint motion is approaching a joint, speed, or acceleration limit. All three algorithms use quadratic curve fitting to predict where the joint motion is heading, followed by a prediction as to how much time would elapse until a limit is reached.

If a joint motion limit is encountered in the time-to-stop the Cartesian motion, these algorithms reduce the Cartesian speed using pulsed speed settings so that the robot or machine tool will have the necessary time to come to a complete stop. The joint space velocity and acceleration control algorithms set the override Cartesian speed to either full or some reduced speed, several times a second. This allows the joints to reach, but not exceed, their maximum velocity and accelerations limit, while remaining within the physical joint limits.

In this paper, an analytical study of the kinematics and dynamics of Stewart platform-based machine tool structures is presented. The kinematic study includes the derivation of closed form expressions for the inverse Jacobian matrix of the mechanism and its time derivative. An evaluation of a numerical iterative scheme for an on-line solution of the forward kinematic problem is also presented. Effects of different configurations of the unpowered joints on the angular velocities and accelerations of the links are considered. The Newton-Euler formulation is used to derive the rigid body dynamic equations. Inclusion of models for actuator dynamics and joint friction is discussed.

The design of a parallel manipulator for a given workspace would be greatly facilitated, if the analytic expressions of the hypersurfaces bounding the workspace were available. In translational parallel manipulators (TPMs), the hypersurfaces bounding the workspace are actually threedimensional surfaces, which are the geometric locus of all the positions assumed by an end-effector point when the TPM reaches the workspace borders. These surfaces can be represented in a Cartesian reference system fixed to the frame. This paper studies the workspace of two TPMs, that have the same closure equations and workspace when a few geometric conditions are satisfied. The two TPMs are the translational 3-RUU and the DELTA robot. The kinematic analyses of these two TPMs are different from one another only when velocity and accelerations are considered. The result of this study is that the analytic expression of the surfaces bounding their workspace is a fourth degree polynomial equation, in the coordinates of a plattorm point, which contains all the manipulator geometric parameters. This analytic expression is given in an explicit form. The use of this expression is illustrated through a numerical example.

This paper proposes an effective top-down design approach for the mechanical design for assembly of a four degree-offreedom revolute jointed robotic arm. The design process begins by specifying top-level design criteria and passing down these criteria from the top level of the manipulator’s structure to all of the subsequent components. With this proposed approach, the sequential design intents are captured, organized and implemented based on the entire system’s objectives, as opposed to the conventional design process which aims at individual components’ optimization. By considering the mechanical arm’s performance objectives, the design starts with modeling the integration of all the individual links constituting the manipulator. During the design process, modifications are made based on the integrated information of kinematics, dynamics, and structural analyses of the desired robot configurations as a whole. An optimum assembly design is then achieved with workable subdesigns of the manipulator components. As a result, the proposed approach for manipulator design yields substantially less number of iterations, automatic propagation of design changes, and great saving of design efforts. Thus, it is suitable and can be used as a guideline for design automation purposes of complex systems such as robotic arms.

In this paper an algorithm for designing spatial parallel manipulator parameters for a given workspace has been presented. At the beginning, architecture has been chosen that describes a general parallel manipulator. The manipulator may possess any number of limbs, consisting of links connected by spherical, revolute or linear joints as well as actuators. The parameters, which will be determined, are the lengths of the links of kinematic chains, the coordinates of the fixing points of the chains to the platform and the base, and orientations of the revolute engines axes situated at the base. The workspace may be specified in the form of any shape in the space containing a set of points of known coordinates and the limits in which the geometrical parameters may vary. The algorithm does not determine the exact values of the parameters, but only their functions. It leads to the necessity for further research in order to optimise the solutions.

This paper presents a method for synthesising the joint profiles for a planar five-link biped walking on flat ground. Both single support and double support phases are considered. The joint profiles have been determined based on constraint equations cast in terms of step length, step period, maximum step height and so on. A special constraint equation is developed to eliminate the destabilising effect of the impact (heel strike) occurring in the system. Other advantages of our joint profiles include system stability during the double support phase and repeatability of gait. The method of formulating compatible trajectories of the hip and swing limb is employed. We demonstrate the advantages of this method over the one of direct formulation of the joint profiles in that it not only significantly simplifies the problem by de-coupling the biped into three subsystems (a trunk and two lower limbs), but also allows the incorporation of certain constraints without drastically increasing the complexity of the constraint equations. The effectiveness of the proposed method is demonstrated using computer simulations. We believe that this research can provide a valuable tool for generating motion patterns of bipedal gait.