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In this study, a novel robust impedance control for a lower-limb rehabilitation robotic system using voltage control strategy is used. Most existing control approaches are based on control torque strategy, which require the knowledge of robot dynamics as well as dynamics of patients. This requires the controller to overcome complex problems such as uncertainty and nonlinearity involved in the dynamics of the system, robot and patients. Conversely, the voltage-based control approaches is free from the system dynamics. In addition, it considers the actuator dynamics. The performance of voltage-based approaches is demonstrated by experimental result in robotic applications. Compared with a torque control scheme, it is simpler, less computational and more efficient. Nevertheless, uncertainty of actuator dynamics results in challenges for the voltage control strategy applications. The present paper, presents a novel robust impedance control based on the voltage control strategy. To overcome uncertainties, the adaptive fuzzy estimator is designed based on the voltage-based strategy. The proposed control is verified by a stability analysis. To illustrate the effectiveness of the control approach, a 1-DOF lower-limb rehabilitation robot is designed. Both torque-based impedance control and the voltage-based impedance control are compared through a therapeutic exercise. It is shown that the voltage-based impedance control perform better than the traditional torque-based impedance control. Simulation and experimental results both shows that the proposed voltage-based robust impedance control is superior to voltage-based impedance control in presence of uncertainties.

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In this paper, online manual guidance of industrial robots using impedance control with singularity avoidance is studied. In this method, operator enters the robot workspace, physically holds the end-effector equipped with force sensor and manually guides the robot. In doing so, the operator generates the desired trajectory for applications like welding or painting. Robot singular configuration is possible during the process which makes it unsafe due to unexpected high velocity robot joints and the physical human-robot interaction. Therefore, real-time identification of singularity position and orientation must be evaluated during trajectory generation. The use of manipulability ellipsoid is suggested as a simple method for the singularity identification. By combining the manipulability ellipsoid and impedance control, a simple and new approach is proposed to warn operator before reaching singularity. Based on the proposed approach, effect of opposite force is exerted on the human hand in the predefined distance to singularity. Real-time implementation is the main advantage of the proposed approach because it keeps robot away from reaching singularity. Real-time experiments are performed using a SCARA robot. In the first experiment, the operator stops the trajectory generation process when an opposite force is produced. In the second experiment, the operator insists on entering the singular points. Experimental results show the effectiveness of the proposed approach in dealing with singularity problem during the trajectory generation by an operator for industrial robots.

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This paper studies path generation using manual guidance procedure for industrial robots by considering real-time singularity avoidance. Main feature of the proposed approach is singularity avoidance by variating impedance control parameters in preset distance from singularity in order to warn operator. Robot end-effector is equipped with a force sensor which operator grasps it and produces desired path. The desired end-effector path is generated by operator’s manual guidance for applications such as welding and spray painting and is recorded by robot controller. Robot singular configuration is possible during the manual guidance. So real-time detection of singularity position and orientation have to be considered during path generation because it can lead to unexpected high robot joints velocity. This problem is not safe due to physical human-robot interaction. Manipulability ellipsoid method is utilized so as to singularity identification. The method can be utilized in on-line due to its simple and low calculation process. On the other hand, the end-effector velocity is saturated in a specific value in the approach considering safety issues. Two main advantages of the proposed approach are real-time application and high safety because of the singularity avoidance. Experiments are applied on a SCARA robot to study the effectiveness of the proposed approach. Experimental results show the ability of proposed approach in dealing with singularity problem during the manual guidance.

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This paper investigates mapping of stiffness, damping and mass matrices for joint and Cartesian space in robot impedance control. The stiffness mapping is studied more than others for serial and parallel robots by lots of researchers. But all the mapping methods are considered for small displacement or static problems. In fact there is no formulation for large displacement or dynamic problems. So in the presented paper, impedance mapping is studied by considering old methods against new one. The new proposed method is called Large Displacement Mapping Method. Two main methods are presented in researchers’ works and are studied beside the new proposed one in this paper. A test is designed and simulated by Simulink/MATLAB in order to analyze different methods clearly. Then the proposed test is applied on a SCARA robot practically. According to simulation and experimental results, only the proposed method can map the stiffness, damping and mass matrices in large displacement case. The results show, as robot is getting away from the initial position, more deviation is happened. Considering impedance control mapping results, two main differences are seen in stiffness and damping matrices while mass matrix mapping result is the same in all three methods.

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Precise Prismatic actuators are one of the most important actuators used in robotic industry and the main base of parallel robots as 6PUS Stewart-Gough robot. Because of bearing large axial forces by this actuators, elastic deformations are inevitable in the main parts of them. This results in elongation and compression of the piston and ball screw, which deteriorates the dynamic linear positioning accuracy of these actuators. The existence of accurate dynamic equations can seriously help to control these errors. Most of the dynamic models which have been used for these actuators based on lumped parameter approach have one DOF for rigid and two or three DOF for flexible state and the stiffness of parts are considered as constant. In this study, the direct dynamic equations of a rotating prismatic actuator which has three DOF in axial direction and ball screw drive system, are proposed using the Lagrange method. In addition to the flexibility of the moving piston, the ball screw is considered with variable stiffness. The important point of this study is the variability of ball screw stiffness. As the nut moves along the shaft, the active length and stiffness of the shaft change; which is very similar to the reality. In addition to the analytical method, the actuator is modeled in the finite element software, ABAQUS and the results of the analytical method and the finite element method are compared.

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Todays, parallel robots with six degrees of freedom are widely used in motion simulation industry. Spreading application of motion simulation for different means of transportation has led to advance training in a safe way with less time and equipment cost. Mostly, the 6-UPS structure Stewart parallel manipulator is used as motion simulators due to their large workspace, rigidity and load capacity. Since the massive moving actuated prismatic joint is located between fixed and moving platforms, the dynamic performance of the mechanism is not efficient. The robot with PUS structure can be a good alternative for UPS type as its actuators are fixed to the ground. This results in lowering of the overall robot cost in addition to stiffness increase. In this paper the inverse kinematic and dynamic of a general 6-PUS robot is presented using Newton-Euler method. The theoretical dynamic model results are verified using motion analysis software. A simplified dynamic model is prepared eliminating links’ inertial terms from dynamic equation. The accuracy of the model is evaluated for different link to payload mass properties ratio. The simplified dynamic model used to improve the computational efficiency of the inverse dynamics.