Article Transactions of the Institute of Measurement and Control 1–9 Ó The Author(s) 2018 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0142331218774398 journals.sagepub.com/home/tim The evaluation of two methods for active vibration damping using RUS Hexapod platform Nael Nashawati, Chadi Albitar and Alaa Dib Abstract This paper presents a study on active vibration Isolation using RUS (revolute joint, universal joint, spherical joint) structure of Stewart platform, as it is less expensive and easier to build than PSS (prismatic joint, spherical joint, spherical joint) structure, which is used a lot in this field. Two control meth- ods are proposed; the fuzzy logic method and the adaptive feed forward control method with multiple error least mean square. Results are evaluated using the SimMechanics toolbox under Matlab 2014 with white noise signals to simulate vibrations. In addition, practical measured accelerations are applied and results are evaluated. Both strategies use a proportional–integral–derivative (PID) controller in parallel to control displacements of the Hexapod as vibrations at low frequencies generate high variations in displacements. The results prove that using a Hexapod with RUS structure can degrade vibrations and guarantee a good behavior for many applications, which is the main aim of this research. Keywords Vibration isolation, active damping, RUS Hexapod platform, Stewart platform, fuzzy logic control, feed forward control Introduction Transporting sensitive devices should be carefully performed because vibrations generated owing to speed and obstacles over roads can harmfully affect these devices. Practical experi- ences showed that the vibrations level increases as speed increases, meaning that transportation process should be done at low speed, which in turn means a waste of time and money. Vibrations Isolation has increasingly become a subject of many studies and the interest of many researchers as it con- cerns many fields in our modern life, including civil, industry and military fields. For example, Zhao et al. (2016) worked on adaptive control for degrading vibrations of an axially moving belt, which can achieve a great improvement in the industry field. Generally, isolation falls within two main categories; pas- sive and active isolation. Passive vibration isolation is inex- pensive and easy to implement; it has, however, some limits in the band of frequencies that it can reject and it needs a spe- cial study for each case, which makes it not suitable for gen- eral use. In addition, as many researches have stated, it is not suitable for low frequencies as a trade-off exists between the isolation performances in the low and high frequency regions. Therefore, to reduce the response at resonance, damping treatment is often applied at the expense of degradation of isolation at high frequencies (Bai and Liu, 2002). Preumont et al. (2007) made a comparison using a Sky-Hook damper that was used as a passive and active isolator, and they found that the active case is more suitable for the low band frequen- cies as it gives a suitable damping. Besides, it overcomes the resonance problem that was clear in the passive case. Moreover, passive vibration isolation can hardly deal with the uncertainties in the characteristics of the isolation system (Yang et al., 2009). As some practical tests found, passive iso- lators are sensitive to the place of mount which could vary according to the structure, dimensions and weight of the device. Finally, long use of passive isolators and the environ- mental effects may affect the characteristics of the passive iso- lator. As a result, active control is preferable for vibrations degradation especially at low frequencies. On the other hand, vibrations can be within one-axis or multi axes, but real vibrations are multi axes. Wayne Tustin mentioned (Tustin, 2008) failures on US Army land vehicles that could not be reproduced with one axis shakers at any fre- quency or any force level but was possible with simultaneous multi axes test. That is why Tustin insisted that any vibration test should be multi axes test in order to accommodate with real life. That leads to the fact that vibration isolation should deal with multi axes vibrations and the isolator must be able to move in all direction, which in turn leads to the use of Hexapod for active vibration isolation. Active vibration damping needs sensors, actuators and control system. The sensors measure the forces generated by vibrations, which are used as feedback to the control system. Higher Institute for Applied Sciences and Technology (HIAST), Damascus, Syria Corresponding author: Nael Nashawati, Mechatronics Department, Higher Institute for Applied Sciences and Technology (HIAST), Barzeh district, P.O. BOX: 31983, Damascus, Syria. Email: nael.nashawati@hiast.edu.sy