Control of Flexible Manipulators. Theory and Practice

Novel robotic applications have demanded lighter robots that can be driven using small amounts of energy, for example robotic booms in the aerospace industry, where lightweight manipulators with high performance requirements (high speed operation, better accuracy, high payload/weight ratio) are required (Wang & Gao, 2003). Unfortunately, the flexibility of these robots leads to oscillatory behaviour at the tip of the link, making precise pointing or tip positioning a daunting task that requires complex closed-loop control. In order to address control objectives, such as tip position accuracy and suppression of residual vibration, many control techniques have been applied to flexible robots (see, for instance, the survey (Benosman & Vey, 2004)). There are two main problems that complicate the control design for flexible manipulators viz: (i) the high order of the system, (ii) the no minimum phase dynamics that exists between the tip position and the input (torque applied at the joint). In addition, recently, geometric nonlinearities have been considered in the flexible elements. This chapter gives an overview to the modelling and control of flexible manipulators and focuses in the implementation of the main control techniques for single link flexible manipulators, which is the most studied case in the literature.