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摘要
Cable robots are a type of parallel robots where the rigid links are replaced by flexible cables. This flexibility produces internal dynamic which challenges the rigid model based controller. In this paper, the dynamic equations of cable robots with viscoelastic cables are obtained. The Feedback Linearization (FL) method is used to provide a linearized dynamic error for the closed loop model of the system with rigid cables. Using the Lyapunov criterion, the stability analysis of the flexible system with the rigid FL control input is performed. It is shown that considering a minimum damping coefficient and employing the rigid FL controller, the system stability can be guaranteed. In order to achieve a trade-off between the control input and the tracking error, the FL gains are obtained using LQR method. In practice, measurement noise usually exists. On the other hand, the end-effector vibration caused by the cables elasticity can be considered as a process noise. Therefore, the LQG approach is used to estimate the states in presence of the process and measurement noise. Using simulation, it is shown that in presence of measurement noise, the LQG method effectively controls the system while the LQR and also the SMC approach, employed in Korayem et al. (Robotica 33(3), 578-598, 2015), lead to the system instability. Another simulation demonstrates that the system with damping less than the specified minimum value can be stable with the LQG approach, in contrary to the LQR controller. Moreover, in order to investigate the vibrational effect of the cable stiffness and damping coefficient, a frequency analysis is performed. Finally, experimental result obtained by implementation on a manufactured cable robot is presented and verified the approach.
- 出版日期2017-10
