A survey of the field of control for flexible multi-link robots is presented. This research area has drawn great attention during the last two decades, and seems to be somewhat less “attractive” now, due to the many satisfactory results already obtained, but also because of the complex nature of the remaining open problems. Thus it seems that the time has come to try to deliver a sort of “state of the art” on this subject, although an exhaustive one is out of scope here, because of the great amount of publications. Instead, we survey the most salient progresses – in our opinion – approximately during the last decade, that are representative of the essential different ideas in the field. We proceed along with the exposition of material coming from about 119 included references. We do not pretend to deeply present each of the methods quoted hereafter; however, our goal is to briefly introduce most of the existing methods and to refer the interested reader to more detailed presentations for each scheme. To begin with, a now well-established classification of the flexible arms control goals is given. It is followed by a presentation of different control strategies, indicating in each case whether the approach deals with the one-link case, which can be successfully treated via linear models, or with the multi-link case which necessitates nonlinear, more complex, models. Some possible issues for future research are given in conclusion.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263574703005642

Control of flexible manipulators: A survey

A review on two-link flexible manipulators

In recent decades, flexible manipulators have been studied by many researchers from robotics, solid mechanics, and control fields. Flexible manipulators have many advantages, including low weight b...

Review of modelling and control of flexible-link manipulators:

Adaptive extended Kalman filtering for visual motion estimation of 3D objects

This paper presents a robust control scheme for flexible link robotic manipulators, which is based on considering the flexible mechanical structure as a system with slow (rigid) and fast (flexible) modes that can be controlled separately. The rigid dynamics is controlled by means of a robust sliding-mode approach with well- established stability properties while an LQR optimal design is adopted for the flexible dynamics. Experimental results show that this composite approach achieves good closed loop tracking properties both for the rigid and the flexible dynamics. Flexible-link robotic manipulators have many advantages with respect to conventional rigid robots. These mechanisms are built using lighter, cheaper materials, which improve the payload to arm weight ratio, thus resulting in an increase of the speed with lower energy consumption. Moreover these lightweight arms are more safely operated due to the reduced inertia and compliant structure, which is very convenient for delicate assembly tasks and interaction with fragile objects, including human beings. However, the dynamic analysis and control of flexible- link manipulators is much more complex than the analysis and control of the equivalent rigid manipulators. From the modelling standpoint, the challenges are associated with the fact that the non-linear rigid body motions are now strongly coupled with the distributed effects of the flexibility along the mechanical structure. This coupling varies with the system configuration and the load inertia. Besides, the dynamic equations of flexible structures are infinite dimensional, although for control purposes approximated finite order models are usually considered. This truncation, along with the difficulties in modelling the coupling and nonlinearities of the system, can be the source of uncertainties in the

https://journals.sagepub.com/doi/pdf/10.5772/5798

Control of a Lightweight Flexible Robotic Arm Using Sliding Modes

An adaptive augmented state feedback control (AASFC) approach is presented for the two-link flexible manipulator, the Duisburg flexible manipulator 01 (DFM01). In order to describe the DFM01 accurately, two disturbance variables are introduced as augmented states. The controller design is based on the steady-state LQR technique in conjunction with an adaptive compensator, where all states are adaptively estimated by employing the strong tracking filter. This control strategy has been tested on DFM01 for both point-to-point and tracking control of the end-effector with different tip mass. Experimental results show that the controller is quite satisfactory, and has strong robustness against payload variations.

M. Bai

Papers

Adaptive augmented state feedback control for an experimental planar two-link flexible manipulator