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Harib et al. Intell Robot 2022;2(1):37-71  https://dx.doi.org/10.20517/ir.2021.19       Page 55




































                                              Figure 7. Flexible-joint manipulator model.


                          [135]
               Chaoui et al.  suggested an ANN-based control technique in 2009, which used ANNs’ learning and
               approximation skills to estimate the system dynamics. The MRAC is made up of feedforward (ANN ) and
                                                                                                    FF
               feedback (ANN ) NN-based adaptive controllers. The reference model is built in the same manner as a
                             FBK
               sliding hyperplane in variable structure control, and its output, which may be regarded as a filtered error
               signal, is utilized as an error signal to adjust the ANN ’s weights. It comprises a first-order model that
                                                              FBK
               specifies the required dynamics of the error between the desired and real load locations, as well as between
               the motor and load velocity, in order to maintain internal stability. The ANN  offers an approximate
                                                                                    FF
               inverse model for the positioning system, while the ANN  corrects residual errors, assuring the
                                                                     FBK
               manipulator’s internal stability and rapid controller response.

               The feedback’s learning rate is dependent on the load inertia, which is a flaw in this construction. To
               improve the stability region of the NN-based controllers, a supervisor is proposed to modify the learning
               rate of the ANNs. The supervisor also increases the adaptation process’s convergence qualities.


               Nowadays, the subject of multiple-arms manipulation highlights some interesting progress in using
               intelligent control approaches. Hou et al.  used a dual NN to solve a multicriteria optimization problem
                                                  [136]
               for coordinated manipulation. Li et al. [137,138]  are representatives who operate on several mobile manipulators
               with communication delays. Some promising approaches, such as LMI and fuzzy-NN controls, were used in
               both articles [137,138] , to improve motion/force performances, which were crucial in multilateral teleoperation
               applications.
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