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This paper gives a detailed analysis of direct torque control (DTC) strategy in a five-level drive and proposes a 24-sector switching table. The overvoltage problem due to high dv/dt is reduced compared to the 12-sector DTC. Using all vectors leads to better flexibility and reduces speed oscillations. Simulation and experimental results for a 3kVA prototype confirm the proposed solutions. A TMS320F2812 is used to implement the above strategy.

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The Direct Torque Control (DTC) of Interior Permanent Magnet Synchronous Motor (IPMSM) offers simple structure and fast torque response. The conventional Switching Table-based DTC (ST-DTC) presents some disadvantages like high torque and flux ripple and also variable switching frequency. This paper investigates the improved ST-DTC strategies to reduce both torque and flux ripple in DTC of IPMSM with emphasis on structure simplicity and fast dynamics. New switching table with only two active vectors for each sector is introduced and the torque control hysteresis band is replaced by duty cycle calculation unit. For flux ripple reduction, conventional hysteresis-based controller is replaced by simple dithering technique. The duty cycle calculation unit is implemented to operate on each selected vector with the aim of torque ripple RMS minimization. The increase of switching frequency in ST-DTC because of delay in torque and flux estimation process, actually, is not possible; even when hysteresis bands are sufficiently diminished. This paper incorporates the combination of duty cycle modulated DTC and dithering technique to enlarge switching frequency. It therefore provides smoother waveform concurrently for the motor torque and the flux.  In the proposed method waveform comparison structure for duty cycle calculation is used; hence, the merits of classical ST-DTC, such as fast dynamic and simple structure, are mostly preserved

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In this paper, a multivariate statistical method called Principal Components Analysis, PCA, is utilized for detection faults in a 3-PSP parallel manipulator. This statistical method transfers original correlated variables into a new set of uncorrelated variables. PCA method can be used to determine the thresholds of statistics and calculate square prediction errors of new observations for checking the system when a fault occurs in the robot. To investigate on the ability of the PCA method for faults detection of the robot, a nonlinear model-based controller called Computed Torque Control, CTC, is designed. In this control scheme, rigid-body inverse dynamics model of the robot is utilized to linearize and to cancel the nonlinearity in the controlled system. Also, instead of using the robot prototype model, direct dynamics of the robot is used in the robot-control system. In this paper, two faults are artificially applied to the robot-control system. These two faults consist of faults in servo drive or servo motors and faults in joints clearances or position sensors. Finally, these faults are applied on the robot throughout a desired end-effector trajectory and the resultant outputs are obtained for both with and without faults in the manipulator. Consequently, the desired and faulty outputs are compared and faults detection using PCA method for the robot is performed.

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In electromagnetic motors, increase in output torque leads to increase in rotor inertia. Various robotics applications, especially haptic interfaces, oblige convenient dynamic performances of electromagnetic motors which are strongly in turn influenced by the rotor’s inertia. In the present paper, a robust control method for a viscous hybrid actuator is developed which supplies a desired varying torque while maintaining a constant low inertia. This hybrid actuator includes two dc motors with the shafts coupled through a rotational damper using a viscous non-contact coupler. This coupling method is based on Eddy current to provide the required performances. The large far motor eliminates or reduces the inertial forces and external dynamics effects on the actuator. The small near motor provides the desired output torque. Since the system is essentially linear, the applied robust control method is based on Hꝏ and parametric uncertainties and physical constraints including motors’ voltages saturation, rotary damper’s speed saturation, fastest user’s speed and acceleration applied to the actuator and force sensor noise are considered in its design. Also the robust method of µ-synthesis for the system in presence of parameteric uncertainties and other physical constraints are studied. The implementation of the controller on a 1 dof haptic interface model validate the achievement of the desired performances.

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Nowadays the exoskeleton, known as a useful device in robotic rehabilitation and elderly assistance, has been attracted the attention of many researches. One of the most important feathers of the exoskeleton robots are the compliant interaction with patient. The Series Elastic Actuators (SEA) not only interact with human compliantly but also provide several advantaged such as torque measurement and torque control. The pervious researches have used an inner position loop and an outer force loop. In this paper, the motor and power transmission model is also integrated in the controller design. In this paper, the parameters of the SEA, motor and links are identified firstly. Then, two model-based torque control is designed and introduced based on the velocity and current commands. In contrast to previous researched, the controller is proposed for the locked and free condition and the Lyapunov stability analysis is presented. Finally, the experimental validation test on the Sharif lower limb exoskeleton is presented for these controller. The experimental results of the controller show that the accuracy of torque control based on the current and velocity is 1.2 and 0.2 N.m, respectively.

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Energy saving, low robot mass to carried mass ratio, more ability to work in various environments, easier delivery of parts and lower production costs in flexible robots make these robots more attractive than rigid robots to many researchers and industries. But due to nonlinearities in flexible robot system and high vibration in operation points and also more sensitivity against external disturbances, control of these robots is more difficult and complex. In this paper a controller for a flexible link manipulator based on fractional calculus is practically implemented. At first the dynamic model of a single flexible-link robot is introduced. Then various controllers such as fuzzy control, PID control, and fractional order PID torque control are practically implemented on a single flexible-link robot made in laboratory, and then the performance of each controllers in decreasing of arm vibration in final desired point and tracking error reduction are investigated. Further, to compare the robustness of the designed controllers, a same constant disturbance is applied to all controllers and their performance are compared. Finally, the simulation results and experimental results show that the fractional order PID torque controller has the best results among the implemented controllers.

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This paper discussed nonlinear adaptive control of a 6 DOF biped robot. The studied robot was divided to three part, fix leg, moving leg and a torso and all the joints were considered rotational. Generally, for calculations, robots are considered as a whole which makes the related calculations complex. For balance calculations, the zero moment point (ZMP) was either considered as a fix point on the ground or a moving point on the foot plate. In the presented robot in this study with priority of movements, first, the calculations were carried out on the moving foot, then the effect of the motion on the foot was inspected and a pendulum was used to balance the robot. To check the balance, ZMP in the simulation in MATLAB software was considered as a fix point While in Adams software simulation, ZMP was considered moving along the bottom of the sole. All the charts active with both software met each other. In the presented study the inverse kinematics was calculated by trigonometric method and inverse dynamics of each leg was investigated by Newton-Euler iterative method. All calculations were carried out in MATLAB software and were verified by ADAMS software. By writing the equilibrium equations, the angle of torso at each time was achieved. In the next step, because of uncertainties in manufacturing and some parameters like mass, length, etc. adaptive computed torque control was used on each leg to achieve the maximum torque that each joint needs for stable walking.