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The Stewart platform with six degree of freedom (three translational and three rotational motions) consists of two rigid bodies, lower plate (base) and upper one (mobile). These two bodies are connected together by six extensible legs between three pairs of joints on each of the bodies. This platform can be used to isolate the top plate of the platform and its payload from the applied motions to the base. Since the passive isolation methods are not effective in elimination of the high amplitude (and usually) low frequency motions, this paper practically investigates the possibility of using the 6DOF Stewart platform as an active vibration isolator. In this study, a Stewart platform was designed and constructed based on electric actuators (servo-motors). And then it was practically utilized to isolate its top plate from the applied pitch and roll rotations to the base plate. MEMS sensors including two accelerometers and one rate gyro along with Kalman filter and kinematic relations were utilized for measuring the pitch and roll motions. A PI controller was implemented to keep the top plate at level position using the MEMS sensors installed on the bottom plate. The experimental results indicated that the platform can effectively isolate the pitch and roll motions while the frequency of these motions is in the working speed range of the electric actuators.

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This paper presents a nonlinear predictive approach, for Stewart platform (6 degrees of freedom). The optimal control is computed directly from the minimization of receding horizon cost function with offline optimization. The main purpose of this research is designing the predictive controller for Stewart platform. In this study, the kinematics and dynamics of Stewart robot is introduced, considering the dynamics of actuators. Following the introduction of nonlinear model predictive control will be discussed and according to robot dynamics, controller will be design. In addition, given the various uncertainties, robot dynamic equation could be rewritten. The controller is designed according to these uncertainties and then stability control is confirmed using Lyapunov theory. Due to the limited engine power and the output torque electric drive in practice, the proposed controller manages Stewart platform in such a way that it could track the desired trajectory well. To review the proposed method at the end of the study, Stewart platform is simulated and the control method proposed in this paper was compared with computed torque control (CTC) method, sliding mode control and Proportional-Integrator-Differentiation (PID) controller.

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Rotary forging is an incremental bulk forming process, possessing salient advantages compared with the conventional forging, including reduced force, smoothness of operation, lower investment, apt for near net shaping and producing workpieces with intricate profiles. However, the conventional rotary forging machines suffer serious limitation in their kinematics, which originates from their simple eccentric mechanism of the actuating device. The parallel-kinematics hexapod mechanism with six degrees of freedom can circumvent this limitation. The theory and practice of this concept has been successfully implemented in the present study. The inverse kinematics of hexapod has been adapted to the kinematics of the rotary forging processes. This could yield a proper method to generate the orbitally rocking motion prevailing in the process. In order to investigate the material flow in the lower die, physical modeling was carried out by the use of plasticine and several experiments were conducted in a hexapod machine. The final shapes of the workpieces, the degrees of die filling, and the forging forces were compared with the conventional forging, indicating improved results. It was observed that the motion pattern in the rotary forging influences the time and the force required for forming. The maximum forces required for rotary forging using the circular and planetary motion patterns were 32 N and 38 N respectively. In comparison, conventional forging required a significantly higher force, approximately 200 N. The time required to form a bevel gear using planetary motion was almost half of the time needed for circular motion