In this paper we consider the problem of planning paths for articulated bodies operating in workplaces containing obstacles and regions with preferences expressed as degrees of desirability. Degrees of desirability could specify danger zones and desire zones. A planned path should not collide with the obstacles and should maximize the degrees of desirability. Region desirability can also convey search-control strategies guiding the exploration of the search space. To handle desirability specifications, we introduce the notion of flexible probabilistic roadmap (flexible PRM) as an extension of the traditional PRM. Each edge in a flexible PRM is assigned a desirability degree. We show that flexible PRM planning can be achieved very efficiently with a simple sampling strategy of the configuration space defined as a trade-off between a traditional sampling oriented toward coverage of the configuration space and a heuristic optimization of the path desirability degree. For path planning problems in dynamic environments, where obstacles and region desirability can change in real time, we use dynamic and anytime search exploration strategies. The dynamic strategy allows the planner to replan efficiently by exploiting results from previous planning phases. The anytime strategy starts with a quickly computed path with a potentially low desirability degree which is then incrementally improved depending on the available planning time.

This work presents the experimental validation and updating of a flexible multibody model ideated for taking into account installation conditions of industrial serial planar manipulators without resorting to cumbersome modeling. The flexibility of the frame, the manipulator is fixed, is modeled over the flexibility of joints, which is introduced as lumped stiffness. In particular, the flexible frame is included in the model by using the Component Mode Synthesis methodology, in which only the natural modes of vibration and the static constrain modes are accounted. The flexible multibody model has been developed because these commercial machines are mainly used to perform low-speed tasks, and they are designed by taking into account their flexibility at most in the joints. Unfortunately, there are particular installation conditions in which even low-speed tasks can generate low-frequency vibrations that highly interfere with the task. This aspect is considered here, and how to manage this problem is explained by using the developed multibody model. The model is validated through experimental measurements. The experimental tests consist of several modal analyses, together with acceleration and laser Doppler measurements in operational conditions. This methodology takes into account the installation conditions through the model of flexible frame, and gives a tool for studying ad hoc solutions which prevent the occurrence of unwanted low-frequency vibrations.

This paper presents a modified passive dynamic walking model with hip friction. We add Coulomb friction to the hip joint of a two-dimensional straight-legged passive dynamic walker. The walking map is divided into two parts – the swing phase and the impact phase. Coulomb friction and impact make the model's dynamic equations nonlinear and non-smooth, and a numerical algorithm is given to deal with this model. We study the effects of hip friction on gait and obtain basins of attraction of different coefficients of friction.

Fast and robust tracking against unknown disturbances is required in many modern complex robotic structures and applications, for which knowledge of the full exact nonlinear system is unreasonable to assume. This paper proposes a regressor-free nonlinear controller of low complexity which ensures prescribed performance position error tracking subject to unknown endogenous and exogenous bounded dynamics assuming that joint position and velocity measurements are available. It is theoretically shown and demonstrated by a simulation study that the proposed controller can guarantee tracking of the desired joint position trajectory with a priori determined accuracy, overshoot and speed of response. Preliminary experimental results to a simplified system are promising for validating the controller to more complex structures.

This paper presents a multi-agent behavior to cooperatively rescue a faulty robot using a sound signal. In a robot team, the faulty robot should be immediately recalled since it may seriously obstruct other robots, or collected matters in the faulty robot may be lost. For the rescue mission, we first developed a sound localization method, which estimates the sound source from a faulty robot by using multiple microphone sensors. Next, since a single robot cannot recall the faulty robot, the robots organized a heterogeneous rescue team by themselves with pusher, puller, and supervisor. This self-organized team succeeded in moving the faulty robot to a safe zone without help from any global positioning systems. Finally, our results demonstrate that a faulty robot among multi-agent robots can be immediately rescued with the cooperation of its neighboring robots and interactive communication between the faulty robot and the rescue robots. Experiments are presented to test the validity and practicality of the proposed approach.

The teaching of how to exert fingertip forces and how to move the fingers is essential for transferring skill using the fingers to perform fine motor tasks. In this paper we accomplish the transfer of fingertip forces and positions in three-dimensional space by combining a multi-fingered haptic interface robot, which can measure and present the three-dimensional forces and positions at five fingertips, and an image display system that records a trainer's hand image and displays it to a trainee. Several experimental results show a high fingertip force and position transferability and the great potential of our proposed transfer system.

A novel path planner is presented for the local path planning of a single robot (represented with R) in a complicated dynamic environment. Here a series of attractive points are computed based on attractive segments for guiding R to move along a shorter path. Each attractive segment is obtained by using the full environmental knowledge and will be used for several sampling times in general. A motion controller, which is designed based on artificial moments and a robot model that has a principal motion direction line(PMDline), makes R move closely to attractive points while away from obstacles. Attractive and repulsive moments are designed, which only make R's PMDline face toward attractive points and opposite to obstacles in general, as in most cases, R will move along its PMDline with its full speed. Because of the guidance of attractive points and R's full-speed motion, the global convergence is guaranteed. Simulations indicate that the proposed path planner meets the requirements of real-time property while can optimize R's traveling path.

The design of control laws for flexible manipulators is known to be a challenging problem, when using a conventional actuator, i.e., a motor with gear. This is due to the friction of the nonlinear actuator, which causes torque dead zone and stick-slip behavior, thereby hampering the good performance of the control system. The torque needed to attenuate the vibrations, although calculated by the control law, is consumed by the friction inside the actuator, rendering it ineffective to the flexible structure control. Nonlinear friction varies with different operational conditions of the actuator and a friction compensation mechanism based on these models cannot always keep a good performance. This study proposes a new control strategy using wavelet network to friction compensation. Experimental results obtained with a flexible manipulator attest to the good performance of the proposed control law.

This paper presents a motion planning method for a simple wheeled robot in two cases: (i) where translational and rotational speeds are arbitrary, and (ii) where the robot is constrained to move forwards at unit speed. The motions are generated by formulating a constrained optimal control problem on the Special Euclidean group SE(2). An application of Pontryagin's maximum principle for arbitrary speeds yields an optimal Hamiltonian which is completely integrable in terms of Jacobi elliptic functions. In the unit speed case, the rotational velocity is described in terms of elliptic integrals, and the expression for the position is reduced to quadratures. Reachable sets are defined in the arbitrary speed case, and a numerical plot of the time-limited reachable sets is presented for the unit speed case. The resulting analytical functions for the position and orientation of the robot can be parametrically optimised to match prescribed target states within the reachable sets. The method is shown to be easily adapted to obstacle avoidance for static obstacles in a known environment.

In this paper the tip-over stability of mobile robots during manipulation with redundant arms is investigated in real-time. A new fast-converging algorithm, called the Circles Of INitialization (COIN), is proposed to calculate globally optimal postures of redundant serial manipulators. The algorithm is capable of trajectory following, redundancy resolution, and tip-over prevention for mobile robots during eccentric manipulation tasks. The proposed algorithm employs a priori training data generated from an exhaustive resolution of the arm's redundancy along a single direction in the manipulator's workspace. This data is shown to provide educated initial guess that enables COIN to swiftly converge to the global optimum for any other task in the workspace. Simulations demonstrate the capabilities of COIN, and further highlight its convergence speed relative to existing global search algorithms.

Series elastic actuators have beneficial properties for some robot applications. Several recent implementations contain alternative placements of the compliant element to improve instrumentation design. We use a class 1 versus class 2 lever model and energy-port methods to demonstrate in this paper that these alternative placements should still be classified as series elastic actuators. We also note that the compliance of proximal series elastic actuators is reflected by an augmented gear ratio dependent on the nominal gear ratio, which is significant for small gear ratios and approaches unity for large gear ratios. This reflected compliance is shown to differ depending on the sign of the gear ratio. We demonstrate that although the reflected compliance is only marginally influenced by the magnitude of the gear ratio, there are several notable differences, particularly for small gear ratios.

In this paper the design and operation for a 2-Degree-of-Freedom, leg–wheel hybrid mobile robot are presented. A prototype of a low-cost and easy-to-use system, which is capable of straight walking and steering with two actuators only, has been designed and built. Simulation and experimental tests have been carried out to verify the engineering feasibility and operation of the proposed solution. The designed robot can be used for applications such as surveillance and inspection of disaster sites.

We introduce a novel probabilistic algorithm (CPRM) for real-time motion planning in the configuration space ${\EuScript C}$. Our algorithm differs from a probabilistic road map (PRM) algorithm in the motion between a pair of anchoring points (local planner) which takes place on the boundary of the obstacle subspace ${\EuScript O}$. We define a varying potential field f on ∂${\EuScript O}$ as a Morse function and follow $\vec{\nabla} f$. We then exemplify our algorithm on a redundant worm climbing robot with n degrees of freedom and compare our algorithm running results with those of the PRM.

We developed a novel small rat-like robot called Waseda Rat No. 4 (WR-4) to interact with real rats. WR-4 can perform both rearing (rising up on its hind limbs) and rotating (body bending during movement) actions faster than live mature rats. After robot–rat interaction involving rearing and body grooming (body cuddling and head curling) actions of WR-4, real rats showed more activity and greater interest in the robot. Similar results evident from rat–rat interaction suggest that a rat-like robot is able to interact with rats in the same way as real rats. Furthermore, lower variances between the rat subjects in robot–rat interaction reveals that a rat-like robot can more effectively impact rat's behavior in a controllable, predictable way.

The present paper presents a new approach to a leader–follower-based dynamic trajectory planning for multirobot formation. A near-optimal trajectory is generated for each robot in a decentralized manner. The main contributions of the current paper are the proposal of a new objective function that considers both collision avoidance and formation requirement for the trajectory generation, and an analytical solution of trajectory parameters in the trajectory optimization. Simulations and experiments on multirobots are performed to demonstrate the effectiveness of the proposed approach to the multirobot formation in a dynamic environment.

This paper addresses the orientation-singularity analysis and the orientationability evaluation of a special class of the Stewart–Gough parallel manipulators in which the moving and base platforms are two similar semi-symmetrical hexagons. Based on the half-angle transformation, an analytical polynomial of degree 13 that represents the orientation-singularity locus of this special class of parallel manipulators at a given position is derived. Graphical representations of the orientation-singularity locus of this class of manipulators are illustrated with examples to demonstrate the results. Based on the description of the orientation-singularity and nonsingular orientation region of this class of parallel manipulators, a performance index, referred to as orientationability, which describes the orientation capability of this class of manipulators at a given position, is introduced. A discretization algorithm is proposed for computing the orientationability of the special class of parallel manipulators at a given position in the workspace. Moreover, the effects of the design parameters and position parameters on the orientationability are also investigated in detail. Based on the orientationability performance index, another performance index, referred to as practical orientationability, representing the practical orientation capability of the manipulators at a given position, is introduced. In this performance index, singularities, the limitations of active and passive joints and link interferences are all taken into consideration. Furthermore, the practical orientationability of the special class of parallel manipulators studied here is also analyzed over several plane sections of the position-workspace in detail.