A neural network-based approach for an assembly cell control

• Published in: Applied soft computing 2008-09, Vol.8 (4), p.1335-1343
• Main Authors: Touati, Y., Amirat, Y., Saadia, N., Ali-Chérif, A.
• Format: Article
• Language: English
• Subjects: Adaptive control; Constrained motions; Hybrid force/position control; Identification and learning rules; Neural networks
• ISSN: 1568-4946; 1872-9681
• DOI: 10.1016/j.asoc.2007.10.001

In several robotics applications, the robot must interact with the workspace, and thus its motion is constrained by the task. In this case, pure position control will be ineffective since forces appearing during the contacts must also be controlled. However, simultaneous position and force control called hybrid control is then required. Moreover, the nonlinear plant dynamics, the complexity of the dynamic parameters determination and computation constraints makes more difficult the synthesis of control laws. In order to satisfy all these constraints, an effective hybrid force/position approach based on artificial neural networks for multi-inputs/multi-outputs systems is proposed. This approach realizes, simultaneously, an identification and control of systems, and it is implemented according to two phases: At first, a neural observer is trained off-line on the basis of the data acquired during contact motion, in order to realize a smooth transition from free to contact motion. Then, an online learning of the neural controller is implemented using neural observer parameters so that the closed-loop system maintains a good performance and compensates for uncertain/unknown dynamics of the robot and the environment. A typical example on which we shall focus is an assembly task. Experimental results on a C5 links parallel robot demonstrate that the robot's skill improves effectively and the force control performances are satisfactory, even if the dynamics of the robot and the environment change.