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Free-flying space manipulator systems, in which robotic manipulators are mounted on a free-flying spacecraft, are envisioned for assembling, maintenance, repair, and contingency operations in space. Nevertheless, even for fixed-base systems, control of mechanical manipulators is a challenging task. This is due to strong nonlinearities in the equations of motion, and consequently different algorithms have been suggested to control end-effector motion or force, since the early research in robotic systems. In this paper, first a brief review of basic concepts of various algorithms in controlling robotic manipulators is introduced. Then, specific problems related to application of such systems in space and a microgravity environment is highlighted. Basic issues of kinematics and dynamics modeling of such systems, trajectory planning and control strategies, cooperation of multiple arm space free-flying robots, and finally, experimental studies and technological aspects of such systems with their specific limitations are discussed.

In this paper, a design optimization approach for assistive devices based on the simulation of the robot and human model is proposed. The proposed human model in the loop (HMIL) approach exploits an augmented human-robot model for interaction analysis, and to evaluate and modify the assistive device effectiveness. In this regard, a lower-limb assistive device (RoboWalk) for elderly and a human skeletal system are modeled and augmented to use the human-robot interaction forces in the proposed HMIL strategy. Due to the particular design of RoboWalk, a complete set of constraints are specified to ensure the solution feasibility and compatibility of the device in different poses. This constrained optimization problem is solved by weighted sum particle swarm optimization (WSPSO) and multi-objective PSO (MOPSO) algorithm. As a result of this optimization, several appropriate sets of design parameters are found to minimize the load on human joints, actuator torque and mass. Among the obtained optimal points, the point minimizing an introduced index is selected as the final design.

Wheeled mobile robots are a special class of nonholonomic mechanical systems. The mobility of such highly nonlinear systems is restricted due to the presence of nonholonomic constraints of wheels, also the system severe underactuated nature. These conditions generate major difficulties in system stabilization, i.e. to park or reach a given configuration for the overall system. This leads to a challenging control problem for research that is the focus of this paper. In this paper a new method based on time-varying feedbacks has been developed for a Tractor-trailer wheeled robot (TTWR). First kinematic model of the TTWR is obtained. Next, a novel method using timevarying feedbacks is investigated in order to stabilize the TTWR around the origin. The proposed kinematic control algorithm is developed based on switching between two finite-time controllers. Appropriate control algorithms have been designed for each step based on the stability of the closed loop system. Obtained simulation and experimental results show the effectiveness of the proposed control law.

Nowadays, aerial robots or Unmanned Aerial Vehicles (UAV) have many applications in civilian and military fields. For example, of these applications is aerial monitoring, picking loads and moving them by different grippers. In this research, a quadrotor with a cable-suspended load with eight degrees of freedom is considered. The purpose is to control the position and attitude of the quadrotor on a desired trajectory in order to move the considered load with constant length of cable. So, the purpose of this research is proposing and designing an antiswing control algorithm for the suspended load. To this end, control and stabilization of the quadrotor are necessary for designing the antiswing controller. Furthermore, this paper is divided into two parts. In the first part, dynamics model is developed using Newton-Euler formulation, and obtained equations are verified in comparison with Lagrange approach. Consequently, a nonlinear control strategy based on dynamic model is used in order to control the position and attitude of the quadrotor. The performance of this proposed controller is evaluated by nonlinear simulations and, finally, the results demonstrate the effectiveness of the control strategy for the quadrotor with suspended load in various maneuvers.

Tractor-trailer wheeled robot (TTWR) is a modular robotic system that consists of a tractor module towing a trailer. Control of these systems started from motion aid facilities in human-driven vehicles, to fully autonomous mobile robots in recent years. The mobility of such highly nonlinear systems is restricted due to the presence of nonholonomic constraints of wheels, also the system severe underactuated nature. Trajectory tracking is one of the challenging problems focused in the context of Wheeled mobile robots (WMRs) that has been discussed in this paper. First, kinematic equations of TTWR are obtained. Then, reference trajectories for tracking problem are produced. Subsequently, a non-model-based controller based on Modified transpose jacobian (MTJ) method is designed to steer the TTWR asymptotically follow reference trajectories. Obtained simulation and experimental comparison results show the effectiveness of the proposed controller.

This article presents vision-based formation flight control for aerial robots with a special focus on failure conditions in visual communication. Then, by proposing and combining two strategies, a new solution is presented for formation control. In vision-based formation flight, the state variables of the leader are estimated using image processing and unscented Kalman filter. The follower adjusts its position with respect to the leader based on the results of the estimation. In the case of visual communication failure an error will occur in the estimation of variables, which would increase with the decreased image quality. In the first proposed strategy, during the failure emergence, the position of the follower aerial robot is obtained by combining the unscented Kalman filter's estimated velocity vector and the velocity vector before failure. The weighting coefficient of each velocity vector is obtained by fuzzy logic and based on image quality. In the second strategy, to reduce the possibility of collision between the members, the geometry of the formation pattern is expanded as a function of image quality and the distance between the members. The expansion coefficient is also extracted by a fuzzy inference method, and the desired distance between the members is increased as a function of expansion coefficient. These two strategies are combined to be used during failure periods. Finally, simulation studies are presented which are conducted based on the system nonlinear equations, a model with 6 degrees of freedom for each member, and the proposed visual noise model. Obtained results reveal the proper capability of the proposed hybrid strategy in terms of controlling the formation flight during failure conditions.

Precise model-based control of parallel robots necessitates an analytically accurate and consolidated model of the robotic platform. Lack of accuracy in modeling causes lots of dynamic uncertainties. This fact can result in higher control gains and efforts. Furthermore, imposing modification for optimization purposes is implausible without the derivation of an exact model. Hence, in this paper an elaborative kinematical and dynamical model of redundant cable-driven parallel robots is studied. In fact, a general procedure for modeling of cable-actuated parallel robots is presented to tackle down the difficulties for model-based control. The presented dynamic modeling approach rigorously enumerates the kinematics of robot winches and pulleys. The intrinsic behavior of cables is represented with a linear spring and damper having variable mass and constant density in the workspace. To this end, sagging in cables is neglected as a computationally intractable effect with insignificant impact on robot’s dynamics. Next, model validation is carried out within an experimental study of a redundant cable-driven parallel robot, the RoboCab which is designed and manufactured in Advanced Robotics and Automated Systems (ARAS) Lab. Experimental results reveal the merits and capabilities of proposed model to capture the explicit dynamics of robot. Results also demonstrate the high rate of flexibility and applicability of model for dealing with diverse control applications.

Impedance Control imposes a desired behavior on a single manipulator interacting with its environment. The Multiple Impedance Control (MIC) enforces a designated impedance on both a manipulated object, and all cooperating manipulators. Similar to the standard impedance control, one of the benefits of this algorithm is the ability to perform both free motions and contact tasks without switching control modes. At the same time, the potentially large object inertia and other forces are taken into account. In this paper, the general formulation for the MIC algorithm is developed for distinct cooperating manipulators, and important issues are detailed. Using a benchmark system, the response of the MIC algorithm is compared to that of the Object Impedance Control (OIC). It is shown that in the presence of flexibility, the MIC algorithm results in an improved performance. Next, a system of two cooperating two-link manipulators is simulated, in which a Remote Centre Compliance is attached to the second end-effector. As simulation results show, the response of the MIC algorithm is smooth, even in the presence of an impact due to collision with an obstacle. It is revealed by both error analysis and simulation that under the MIC law, all participating manipulators, and the manipulated object exhibit the same designated impedance behavior. This guarantees good tracking of manipulators and the object based on the chosen impedance laws which describe desired error dynamics, in performing a manipulation task.

Grasping objects by continuum arms or fingers is a new field of interest in robotics. Continuum manipulators have the advantages of high adaptation and compatibility with respect to the object shape. However, due to their extremely nonlinear behavior and infinite degrees of freedom, continuum arms cannot be easily modeled. In fact, dynamics modeling of continuum robotic manipulators is state-of-the-art. Using the exact modeling approaches, such as theory of Cosserat rod, the resulting models are either too much time-taking for computation or numerically unstable. Thus, such models are not suitable for applications such as real-time control. However, based on realistic assumptions and using some approximations, these systems can be modeled with reasonable computational efforts. In this paper, a planar continuum robotic arm is modeled, considering its backbone as two circular arcs. In order to simulate finger grasping, the continuum arm experiences a point-force along its body. Finally, the results are validated using obtained experimental data.

This paper presents a novel hand, consisting of both rigid link and continuum mechanisms, and the application of a newly proposed Multi-Aspect Grasp (MAG) index in Form Closure Grasp (FCG) constraint for holding objects, by the presented robotic hand. The KNTU hand, exploits the characteristics of both, rigid-link fingers and continuum fingers, in order to achieve a better grasp. This hand can hold any symmetrical or unsymmetrical object with FCG constraint. First, as a case study, the application of MAG index to Staubli TX40 manipulator is presented. Then, to grasp objects with KNTU hand based on the MAG index, two sets of candidate points with the form closure property are evaluated and the better set is determined. Using MAG index, the grasp by this novel robotic hand is analyzed and the obtained results of such system are introduced.