Professor Miomir Vukobratović passed away on March 11, 2012 at the age of 81. However, his achievements in robotics will remain with us always.

Miomir Vukobratović was born in 1931. He graduated in 1957 from the Faculty of Mechanical Engineering, University of Belgrade, where he also obtained his first PhD in 1964. In January 1958 he joined the Aeronautical Institute in Belgrade. At the beginning of 1965 he moved to the Mihajlo Pupin Institute in Belgrade, where he became director of the Robotics Laboratory. In 1980, he became professor at the Production Engineering Department of the Faculty of Mechanical Engineering, University of Belgrade.

The paper introduces a novel general feedback control framework, which allows applying the motion controllers originally dedicated for the unicycle model to the motion task realization for the car-like kinematics. The concept is formulated for two practically meaningful motorizations: with a front-wheel driven and with a rear-wheel driven. All the three possible steering angle domains for car-like robots—limited and unlimited ones—are treated. Description of the method is complemented by the formal stability analysis of the closed-loop error dynamics. The effectiveness of the method and its limitations have been illustrated by numerous simulations conducted for the three main control tasks, namely, for trajectory tracking, path following, and set-point regulation.

When employing autonomous helicopters, it is desirable to use navigation approaches, which firmly ensure safety. In this paper, we propose and compare two approaches to navigation through environments containing obstacles. The first uses sliding mode boundary following to maintain a prespecified distance to obstacles, and the second uses a model predictive control approach to plan short horizon trajectories around detected objects, while ensuring that the helicopter is brought to a halt within the sensor visibility radius. The navigation approaches are subjected to analysis for robustness, and simulations are carried out with a realistic helicopter model for verification. Additional real-world experiments were performed with a wheeled robot to demonstrate potential for real-time application.

There exist several kinds of definitions for complexity in different areas. In mechanical engineering area, some formulations capable of measuring the complexity of robotic architectures have been proposed at the conceptual-design stage. This paper presents the definition of Kinematic Coupling Complexity to measure the kinematic coupling degree of a manipulator based on the input/output velocity matrix. In order to distinguish the differences among many matrixes, three factors will be considered including the proportion of nonzero elements in matrix J, the difference of nonzero elements' numbers in every row among many matrixes, and the difference of nonzero elements' positions among many matrixes. To illustrate the methods introduced in this paper, four types of heavy-payload forging manipulators are analyzed and the type of forging manipulator with the smallest Kinematic Coupling Complexity is chosen as our prototype.

A computational derivation of valid kinematic limbs for spatial 3-DOF parallel mechanisms (PMs) without redundant constraint is studied based on contracted graphs, topological graphs, and basic joints. First, some contracted graphs without any binary links are constructed, some curves with only binary links are distributed over contracted graphs and many valid topological graphs are derived. Second, a software is developed in Visual Basic for deriving the kinematic limb, and some basic chain structures are constructed by connecting various basic joints in series. Third, all valid kinematic limbs of the 3-DOF PMs without redundant constraint are derived computationally from the basic chain structures and some novel 3-DOF PMs are synthesized using this approach. Finally, the number of the different 3-DOF PMs without redundant constraint are determined based on the topological graphs and valid chain structures of the limb.

Robot navigation is a large area of research, where many different approaches have already been tried, including navigation based on visual memories. The Sparse Distributed Memory (SDM) is a kind of associative memory based on the properties of high-dimensional binary spaces. It exhibits characteristics, such as tolerance to noise and incomplete data, ability to work with sequences and the possibility of one-shot learning. Those characteristics make it appealing to use for robot navigation. The approach followed here was to navigate a robot using sequences of visual memories stored into a SDM. The robot makes intelligent decisions, such as selecting only relevant images to store, adjusting memory parameters to the level of noise and inferring new paths from the learnt trajectories. The method of encoding the information may influence the tolerance of the SDM to noise and saturation. This paper reports novel results of the limits of the model under different typical navigation problems. The SDM showed to be very robust to illumination and scenario changes, occlusion and saturation. An algorithm to build a topological map of the environment based on the visual memories is also described.

This work is dedicated to the analysis of the application of active impedance control for the realisation of three objectives simultaneously: velocity regulation in free motion, impact attenuation and finally force tracking. At first, a brief analysis of active impedance control is made, deducing the value of each parameter in order to achieve the three objectives. It is demonstrated that the system may be made overdamped with the adequate selection of the parameters if the characteristics of the environment are known, avoiding high overshoots of force during the impact. The second and most important contribution of this work is an additional measure for impact control in the case when the characteristics of the environment are unknown. It consists in switching among different values of the parameters of the impedance in order to dissipate faster the energy of the system, limiting the peaks of force and avoiding losses of contact. The optimal switching criteria are deduced for every parameter in order to dissipate the energy of the system as fast as possible. The results are verified in simulation.

This paper introduces the mathematical logical proposition into kinematics and presents a novel method for topological design and representation of mechanisms. The six-value non-classical logical matrix in three orders is proposed to represent spatial basic motions, relations, and selection of moving reference frame. The combinatorial logical sets of mechanisms are built and axiomatized to analyze serial–parallel hybrid mechanisms. In accordance to the logical relations, the mapping between topological arrangement and topological geometry is developed, and algorithm of decomposition synthesis is presented. Furthermore, the higher dimensional topological arrangement of multi-loop hybrid mechanism can be obtained by mapping of higher dimensional geometry. At last, four typical examples are developed to illustrate application of method of logical proposition in topological design of mechanisms. The method is helpful for topological design and analysis of multi-loop hybrid mechanisms.

This paper presents a new method to analyze frictionless grasp immobility based on defined surface-to-surface signed distance function. Distance function's differential properties are analyzed and its second-order Taylor expansion with respect to differential motion is deduced. Based on the non-negative condition of the signed distance function, the first- and second-order free motions are defined and the corresponding conditions for immobility of frictionless grasp are derived. As one benefit of the proposed method, the second-order immobility check can be formulated as a nonlinear programming problem. Numerical examples are used to verify the proposed method.

The gallop is the preferred gait by mammals for agile traversal through terrain. This motion is intrinsically complex as the feet are used individually and asymmetrically. Simple models provide a conceptual framework for understanding this gait. In this light, this paper considers the footfall projections as suggested by an impulse model for galloping as a measurement simplifying strategy. Instead of concentrating on forces and inverse dynamics, this view focuses observations on leg motion (footfalls and stance periods) for subsequent gallop analysis and parameter estimation. In practice, this eases experiments (particularly for IR-based motion capture) by extending the experimental workspace, removing the need for single-leg contact force-plate measurements, and reducing the marker set. This provides shorter setup times, and it reduces postprocessing as data are less likely to suffer from occlusion, errant correspondence, and tissue flexion. This approach is tested using with three canine subjects (ranging from 8 to 24 kg) performing primarily rotary gallops down a 15 m runway. Normalized results are in keeping with insights from previous animal and legged robot studies and are consistent with motions suggested by said impulse model.

Self-reconfiguration of robotic manipulators under joint failure can be achieved via fault-tolerance strategies. Fault-tolerant manipulators are required to continue their end-effector motion with a minimum velocity jump, when failures occur to their joints. Optimal fault tolerance of the manipulators requires a framework that can map the velocity jump of the end-effector to the compensating joint velocity commands. The main objective of the present paper is to propose a general framework for the fault tolerance of the manipulators, which can minimize the end-effector velocity jump. In the present paper, locked joint failures of the manipulators are modeled using matrix perturbation methodology. Then, the optimal mapping for the faults with a minimum end-effector velocity jump is presented. On the basis of this mapping, the minimum end-effector velocity jump is calculated. A generalized framework is derived from the extension of optimal mapping toward multiple locked joint failures. Two novel expressions are derived representing the generalized optimal mapping framework and the generalized minimum velocity jump. These expressions are suitable for the optimal fault tolerance of the serial link redundant manipulators. The required conditions for a zero end-effector velocity jump of the manipulators are analyzed. The generalized framework in this paper is then evaluated for different failure scenarios for a 5-DOF planar manipulator and a 5-DOF spatial manipulator. The validation includes three case studies. While the first two are instantaneous studies, the third one is for the whole trajectory of the manipulators. From the results of these case studies, it is shown that, when locked joint faults occur, the faulty manipulator is able to optimally maintain its velocity with a zero end-effector velocity jump if the conditions of a zero velocity jump are hold.

This paper presents a new methodology for the joint stiffness identification of industrial serial robots and as consequence for the evaluation of both translational and rotational displacements of the robot's end-effector subject to an external wrench (force and torque). In this paper, the robot's links are supposed to be quite stiffer than the actuated joints as it is usually the case with industrial serial robots. The robustness of the identification method and the sensitivity of the results to measurement errors, and the number of experimental tests are also analyzed. The Kuka KR240-2 robot is used as an illustrative example throughout the paper.

We study a problem of K-barrier coverage by employing a network of self-deployed, autonomous mobile robotic sensors. A decentralized coordination algorithm is proposed for the robotic sensors to address the coverage problem. The algorithm is developed based on some simple rules that only rely on local information. By applying the algorithm to the robotic sensors, K layers of sensor barriers are formed to cover the region between two given points. To illustrate the proposed algorithm, numerical simulations are carried out for a number of scenarios.

This paper presents the results of a study on the dynamical modeling, analysis, and control of a spherical rolling robot. The rolling mechanism consists of a 2-DOF pendulum located inside a spherical shell with freedom to rotate about the transverse and longitudinal axis. The kinematics of the model has been investigated through the classical methods with rotation matrices. Dynamic modeling of the system is based on the Euler–Lagrange formalism. Nonholonomic and highly nonlinear equations of motion have then been decomposed into two simpler subsystems through the decoupled dynamics approach. A feedback linearization loop with fuzzy controllers has been designed for the control of the decoupled dynamics. Rolling of the controlled mechanism over linear and curvilinear trajectories has been simulated by using the proposed decoupled dynamical model and feedback controllers. Analysis of radius of curvature over curvilinear trajectories has also been investigated.

This paper proposes a dynamic localization algorithm for a variable speed mobile robot. In order to localize a mobile robot with active beacon sensors, a relatively long time is needed, since the distance to the beacon is measured using the time-of-flight of the ultrasonic signal. The measurement time does not cause a high error rate when the mobile robot moves slowly. However, with an increase of the mobile robot's speed, the localization error becomes too high to use for accurate mobile robot navigation. Therefore, in this research into high-speed mobile robot operations, instead of using two active beacons for localization, an active beacon and the predicted path are utilized to localize the mobile robot. This new approach resolves the high-localization error caused by the speed of mobile robot. The performance of this method was verified by comparing it to the conventional method through real-world experiments.