In this paper, the optimum design of parallel kinematic toolheads is implemented using genetic algorithms with the consideration of the global stiffness and workspace volume of the toolheads. First, a complete kinetostatic model is developed which includes three types of compliance, namely, actuator compliance, leg bending compliance and leg axial compliance. Second, based on this model, two kinetostatic performance indices are introduced to provide a new means of measuring compliance over the workspace. These two kinetostatic performance indices are the mean value and the standard deviation of the trace of the generalized compliance matrix. The mean value represents the average compliance of the Parallel Kinematic Machines over the workspace, while the standard deviation indicates the compliance fluctuation relative to the mean value. Third, design optimization is implemented for global stiffness and working volume based on kinetostatic performance indices. Additionally, some compliance comparisons between Tripod toolhead and other two principal Tripod-based Parallel Kinematic Machines are conducted.

In this paper, an optimal fuzzy sliding mode controller has been designed for controlling the end-effector position in the task space. In the proposed control, feedback linearization method, sliding mode control, first-order fuzzy TSK system and optimization algorithm are utilized. In the proposed controller, a novel heuristic algorithm namely self-adaptive modified bat algorithm (SAMBA) is employed. To achieve an optimal performance, the parameters of the proposed controller as well as the input membership functions are optimized by SAMBA simultaneously. In this method, the bounds of structural and non-structural uncertainties are reduced by using feedback linearization method, and to overcome the remaining uncertainties, sliding mode control is employed. Mathematical proof demonstrates that the closed loop system with the proposed control has global asymptotic stability. The presence of sliding mode control gives rise to the adverse phenomenon of chattering in the end-effector position tracking in the task space. Subsequently, to prevent the occurrence of chattering in control input, a first-order TSK fuzzy approximator is utilized. Finally, to determine the fuzzy sliding mode controller coefficients, the optimization algorithm of Self-Adaptive Modified Bat is employed. To investigate the performance of the proposed control, a two-degree-of-freedom manipulator is used as a case study. The simulation results indicate the favorable performance of the proposed method.

The WiRo-6.3 is a six-degrees of freedom (six-DOF) robotic parallel structure actuated by nine wires, whose characteristics have been thoroughly analyzed in previous papers in reference. It is thought to be a master device for teleoperation; thus, it is moved by an operator through a handle and can convey a force reflection on the operator's hand. A completely new method for studying the workspace of this device, and of virtually any nine-wire parallel structure actuated by wire is presented and discussed, and its results are given in a graphical form.

In this paper, we will present a new 6-DOF parallel robot using a set oftwo Delta structures. An effective method is proposed to establish explicitrelationships between the end effector co-ordinates and the active and passivejoint variables. A simulation of the 2-Delta robot on a C.A.D. Robotics systemwill also be presented. This simulation will allow us to validate the cohesionof our calculations, and to show the workspace depending on the mechanicallimits on passive joints variables. Finally, an approach is proposed to studythe influence of small clearances of the passive joint on the precision of theposition and rotation of the effector. This approach is based on a conceptsimilar to that of Yoshikawa's manipulability.

This paper presents a novel kinematic approach for controlling the end-effector of a continuum robot for in-situ repair/inspection in restricted and hazardous environments. Forward and inverse kinematic (IK) models have been developed to control the last segment of the continuum robot for performing multi-axis processing tasks using the last six Degrees of Freedom (DoF). The forward kinematics (FK) is proposed using a combination of Euler angle representation and homogeneous matrices. Due to the redundancy of the system, different constraints are proposed to solve the IK for different cases; therefore, the IK model is solved for bending and direction angles between (−π/2 to +π/2) radians. In addition, a novel method to calculate the Jacobian matrix is proposed for this type of hyper-redundant kinematics. The error between the results calculated using the proposed Jacobian algorithm and using the partial derivative equations of the FK map (with respect to linear and angular velocity) is evaluated. The error between the two models is found to be insignificant, thus, the Jacobian is validated as a method of calculating the IK for six DoF.

This paper reports the design, analysis, and control of a miniature vibration-driven planar locomotion robot called Shell. A vibration-driven system is able to achieve locomotion based on internal oscillations and anisotropic friction forces. In this robot design, two parallel oscillators are employed to provide propelling forces, and a blade-like support is designed to generate anisotropic frictional contact with the ground. If the two parallel oscillators are of different frequencies and amplitudes, two-dimensional locomotion of the robot can be achieved. To predict the robot's planar locomotion, a dynamic model is developed. Controlling the robot's locomotion and especially, the locomotion modes can be achieved by adjusting the vibration frequencies of the two internal oscillators. Experimental results show that Shell can be controlled to move rectilinearly and along circles with certain curvatures. In addition, by combining these basic trajectories, Shell can move freely on a horizontal plane.

Inverse kinematics (IK) is a nonlinear problem that may have multiple solutions. A modified genetic algorithm (GA) for solving the IK of a serial robotic manipulator is presented. The algorithm is capable of finding multiple solutions of the IK through niching methods. Despite the fact that the number and position of solutions in the search space depends on the position and orientation of the end-effector as well as the kinematic configuration (KC) of the robot, the number of GA parameters that must be set by a user are limited to a minimum through the use of an adaptive niching method. The only requirement of the algorithm is the forward kinematics (FK) equations which can be easily obtained from the Denavit–Hartenberg link parameters and joint variables of the robot. For identifying and processing the outputs of the proposed GA, a modified filtering and clustering phase is also added to the algorithm. For the postprocessing stage, a numerical IK solver is used to achieve convergence to the desired accuracy. The algorithm is validated on three KCs of a modular and reconfigurable robot (MRR).

A wheeled mobile manipulator system is modeled using Kane's dynamic equations. Kane's equations are constructed with minimum effort, are control oriented and provide both physical insight and fast simulations. The powerful tools of Kane's approach for incorporating nonholonomic motion constraints and bringing noncontributing forces into evidence are exploited. Both nonholonomic constraints associated with slipping and skidding as well as conditions for avoiding tipping over are included. The resulting equations, along with the set of constraint equations provide a safe and complete framework for developing control strategies for mobile manipulator systems.

This paper describes and evaluates the use of a head-mounted display (HMD) for the teleoperation of a field robot. The HMD presents a pair of video streams to the operator (one to each eye) originating from a pair of stereo cameras located on the front of the robot, thus providing him/her with a sense of depth (stereopsis). A tracker on the HMD captures 3-DOF head orientation data which is then used for adjusting the camera orientation by moving the robot and/or the camera position accordingly, and rotating the displayed images to compensate for the operator's head rotation. This approach was implemented in a search and rescue robot (RAPOSA), and it was empirically validated in a series of short user studies. This evaluation involved four experiments covering two-dimensional perception, depth perception, scene perception, and performing a search and rescue task in a controlled scenario. The stereoscopic display and head tracking are shown to afford a number of performance benefits. However, one experiment also revealed that controlling robot orientation with yaw input from the head tracker negatively influenced task completion time. A possible explanation is a mismatch between the abilities of the robot and the human operator. This aside, the studies indicated that the use of an HMD to create a stereoscopic visualization of the camera feeds from a mobile robot enhanced the perception of cues in a static three-dimensional environment and also that such benefits transferred to simulated field scenarios in the form of enhanced task completion times.

One of the main challenges in robotics is navigating autonomously through large, unknown, and unstructured environments. Simultaneous localization and mapping (SLAM) is currently regarded as a viable solution for this problem. As the traditional metric approach to SLAM is experiencing computational difficulties when exploring large areas, increasing attention is being paid to topological SLAM, which is bound to provide sufficiently accurate location estimates, while being significantly less computationally demanding. This paper intends to provide an introductory overview of the most prominent techniques that have been applied to topological SLAM in terms of feature detection, map matching, and map fusion.

An assistive device for upper limb support was developed and evaluated in terms of usability, user satisfaction and motor performance on six end-users affected by neuro-motor disorders (three spinal cord injury; one multiple sclerosis; two Friedreich's ataxia). The system consisted of a lightweight 3-degrees-of-freedom robotic exoskeleton arm for weight relief, equipped with electromagnetic brakes. Users could autonomously control the brakes using a USB-button or residual electromyogram activations. The system functionally supported all of the potential users in performing reaching and drinking tasks. For three of them, time, smoothness, straightness and repeatability were also comparable to healthy subjects. An overall high level of usability (system usability score, median value of 90/100) and user satisfaction (Tele-healthcare Satisfaction Questionnaire - Wearable Technology, median value of 104/120) were obtained for all subjects.

We describe a robot capable of performing all procedures necessary to carry out a complete stereotactic neurosurgical operation under the control and supervision of a surgeon. The operation consists of the introduction of a small probe with diameter 2–3 mm through a hole without trepanation. The robot has been built and is now being tested and evaluated. The accompanying control software as well as various medical probes are either in development or partially tested. The installation will be able to carry out a complete intervention under the surveillance of a computed tomography scanner. In this article we emphasize the design choices required to eliminate gearing backlash in a crucial degree of freedom.

A novel ostraciiform swimming, vision-based autonomous robotic fish is developed in this paper. Its feasibility and capability are shown by implementing a dynamic target following task in a swimming pool. Inspired by boxfish that is highly stable and fairly maneuverable, the robotic fish is designed and constructed by locating multiple propulsors peripherally around a rigid body. Swimming locomotion of the robotic fish is achieved through harmonic oscillations of the tail and pectoral fins. The forces and moments acting on the fins and body are analyzed and the governing motion equations are derived. Through coordinating the movements of the propulsors, several typical swimming patters are empirical designed and realized. A digital camera is integrated in the robotic fish, and the visual information is processed with the embedded microcontroller. To treat the degradation of underwater image, a continuously adaptive mean shift (Camshift) algorithm is modified to keep visual lock on the moving target. A fuzzy logic controller is designed for motion regulation of a hybrid swimming pattern, which employs synchronized pectoral fins for thrust generation and tail fin for steering. A simple target following task is designed via an autonomous robotic fish swimming after a manually controlled robotic fish with fixed distance. The swimming performance of the robotic fish is tested and the effectiveness of the proposed target following method is verified experimentally.

In this paper, a closed-form dynamic model of flexible manipulators is developed, based on the Newton–Euler formulation of motion equations of flexible links and on the adoption of the spatial vector notation. The proposed model accounts for two main innovations with respect to the state of the art: it is obtained in closed form with respect to the joints and modal coordinates (including the quadratic velocity terms) and motion equations of the whole manipulator can be computed for any arbitrary shape of the links and any possible link cardinality starting from the output of several commercial (finite element analysis) FEA codes. The Newton–Euler formulation of motion equations in terms of the joint and elastic variables greatly improves the simulation performances and makes the model suitable for real-time control and active vibration damping. The model has been compared with literature benchmarks obtained by the classical multibody approach and further validated by comparison with experiments collected on an experimental manipulator.

Many research works on the control of nonholonomic wheeled mobile robots (WMRs) do not consider the actuator saturation problem and the absence of velocity sensors in practice. The actuator saturation deteriorates the tracking performance of the controller, and the use of velocity sensors increases the cost and weight of WMR systems. This paper simultaneously addresses these problems by designing a saturated output feedback controller for uncertain nonholonomic WMRs. First, a second-order input–output model of nonholonomic WMRs is developed by defining a suitable set of output equations. Then a saturated adaptive robust tracking controller is proposed without velocity measurements. For this purpose, a nonlinear saturated observer is used to estimate robot velocities. The risk of actuator saturation is effectively reduced by utilizing saturation functions in the design of the observer–controller scheme. Semi-global uniform ultimate boundedness of error signals is guarantied by the Lyapunov stability analyses. Finally, simulation results are provided to show the effectiveness of the proposed controller. Compared with one recent work of the author, a comparative study is also presented to illustrate that the proposed saturated controller is more effective when WMR actuators are subjected to saturation.

Safe and cost-efficient inspection of large concrete buildings is a great challenge for mobile robots. This paper presents the locomotion system of the climbing robot, Cromsci, which uses three steerable standard wheels and negative pressure adhesion. We will introduce criteria to avoid robot slip and tilt, and methods to enhance stability. One elementary part is the close-loop-controlled adhesion system with seven individual negative pressure chambers to balance out tilt or dynamic effects caused by leaky pressure chambers. The second part is the locomotion control using a special traction control mechanism to enhance robot navigation, which will also be presented here.

In this paper, an efficient motion planning method is proposed for a six-legged robot walking on irregular terrain. The method provides the robot with fast-generated free-gait motions to traverse the terrain with medium irregularities. We first of all introduce our six-legged robot with legs in parallel mechanism. After that, we decompose the motion planning problem into two main steps: first is the foothold selection based on a local footstep cost map, in which both terrain features and the robot mobility are considered; second is a whole-body configuration planner which casts the problem into a general convex optimization problem. Such decomposition reduces the complexity of the motion planning problem. Along with the two-step planner, discussions are also given in terms of the robot-environmental relationship, convexity of constraints and robot rotation integration. Both simulations and experiments are carried out on typical irregular terrains. The results demonstrate effectiveness of the planning method.

The aim of this work has been the implementation and testing in real conditions of a new algorithm based on the cell-mapping techniques and reinforcement learning methods to obtain the optimal motion planning of a vehicle considering kinematics, dynamics and obstacle constraints. The algorithm is an extension of the control adjoining cell mapping technique for learning the dynamics of the vehicle instead of using its analytical state equations. It uses a transformation of cell-to-cell mapping in order to reduce the time spent during the learning stage. Real experimental results are reported to show the satisfactory performance of the algorithm.

A cable manipulator controls its end-effector by a number of cables. If the cables can balance any external and inertia wrenches at a certain pose of the end-effector, the cable manipulator is said to have a force-closure at this pose. Since a cable can work only in tension, the force-closure at a specific pose may not exist. Thus, how to check the existence of force-closure at a given pose is an important issue for design and control of cable manipulators. This paper describes a systematic method of verifying the existence of force-closure at a specific pose of a general 6-DOF cable manipulator with seven or more cables. By examining the Jacobian matrix of the manipulator, the method can determine whether a force-closure exists at the pose corresponding to the Jacobian matrix. The necessity and sufficiency of the proposed method are mathematically proven. Moreover, a convex-analysis-based simplification of the method for manipulators with more than seven cables is also discussed.

Robotic-assisted surgery is a continuously developing field because robots have demonstrated clear benefits in operating rooms. Until now, vast majority of robots used in surgery had serial structures. This paper presents the kinematic modelling of a 5-degree of freedom hybrid parallel architecture in two slightly different variants. The kinematics of this structure is determined, and following the analysis of singularities, the best variant is chosen. The robot workspace is computed and finally the experimental model and some simulation results are presented.