Review article Proc IMechE Part I: J Systems and Control Engineering 1–13 Ó IMechE 2016 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0959651816642099 pii.sagepub.com Review of modelling and control of flexible-link manipulators Mostafa Sayahkarajy 1,2 , Z Mohamed 1 and Ahmad Athif Mohd Faudzi 1 Abstract In recent decades, flexible manipulators have been studied by many researchers from robotics, solid mechanics, and con- trol fields. Flexible manipulators have many advantages, including low weight because of the slenderness of the links of the robot. Although the original objective was to take advantages of the slenderness or flexibility in real robots, the chal- lenging dynamics of the systems intrigued interests to employ an experimental flexible manipulator as a test bed to evalu- ate different modelling or control methods. With such a vast and various literatures, a review is indispensable for researchers who want to adapt their interests with the area. Some valuable review articles have been published, referen- cing numerous articles on single-link or multi-link flexible arms. This article pays an inclusive focus on trends of the research on modelling and control of multi-link flexible-link manipulators. The scope of this review article is particularly on two-link flexible manipulators, relevant models presented for closed-loop applications, and model-based control. Recent and historical contributions in the modelling and control of flexible-link manipulators are presented and dis- cussed. As regular industrial manipulators normally have multiple links with two long links, that is, upper arm and fore- arm, this review can introduce advances in considering elasticity effects to robotic researchers. Keywords Multi-link flexible manipulators, modelling and control, elastic-link serial manipulators, review Date received: 4 December 2014; accepted: 6 March 2016 Introduction The everlasting demand for decreasing the weight or increasing operation speed of robotic arms is associated with increasing flexibility and its consequences, that is, excessive vibrations and elastic deflections. The term ‘flexible-link manipulator’ (FLM) can refer to a robot whose link flexibility (mainly bending and torsion) affects the tip position or joint parameters, consider- ably. The first studies on FLMs emerged in the publica- tions in 1970s and 1980s. 1–9 These studies were concurrent with the need for lightweight space manipu- lators in National Aeronautics and Space Administration’s (NASA) space shuttle programme in order to reduce a launching cost. This fact was reflected in the design of the remote manipulator system, Canadarm. 10–12 The size of space robotic devices tends to be very large for handling satellites and other equip- ment or for being compatible with the human scale. The remote manipulator system, Canadarm 1, is 15.3m long and weighs 408 kg. Its diameter is 38 cm and has a payload capability of 29,500 kg. The main challenge and contribution of the early studies were, first, to include the elastic behaviour in the dynamic equations of two-link manipulators and, second, to apply a model-based control for concurrent manoeuvring and vibration suppression of the system. In fact, the major modelling methods for flexible multi- link manipulators were presented in that period. Later on, because of the complexities in the nature of the FLM, researchers were attracted to more advanced control schemes. As the time passed, the FLM became a test bed for evaluations of different control strategies. Figure 1 shows a two-link flexible manipulator (TLFM) system used as a test bed for verifications of modelling and control algorithms at the Faculty of Electrical Engineering, Universiti Teknologi Malaysia. Some researchers show more interest in FLMs moving in a three-dimensional (3D) space, under gravity, for 1 Faculty of Electrical Engineering, Universiti Teknologi Malaysia, Johor Bahru, Malaysia 2 UTM-IJN Cardiovascular Engineering Centre, Universiti Teknologi Malaysia, Johor Bahru, Malaysia Corresponding author: Z Mohamed, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia. Email: zahar@fke.utm.my at TULANE UNIV on April 20, 2016 pii.sagepub.com Downloaded from