413 Received 22 March 2013, revised 5 June 2013 online published 19 July 2013 Defence Science Journal, Vol. 63, No. 4, July 2013, pp. 413-417  2013, DESIDOC 1. INTRODUCTION The very irst analysis of any measured data from a vibrating system is to convert it from time domain into frequency domain so as to ind the frequency content of measured data. In a normal engineering system investigation process, a complex physical system or real system is studied as a physical model. It is then mathematically modelled so that further analysis can be carried out on the model instead of the system. This helps in attaining a clear understanding of the system behaviour and is also cost effective. Finally, the physical system is put to the same tests as is its model. The simulated and experimental results from the model are then compared. If they do not match, the assumption made to build the model is re-deined and the entire process is repeated till a satisfactory solution is obtained. The development in piezoelectric materials have motivated many researchers to work in the ield of smart structures 9-15 . A smart structure can be deined as the structure that can sense external disturbance and respond to it actively as per the designed control algorithm so as to maintain its dynamics within the desired levels. They comprise of distributed active devices like sensors and actuators that may either be embedded or attached to the structure with integrated processor networks. Smart structures are widely used in place of the traditional structures on account of their ability to adapt according to the prevailing disturbances. Mechanical vibrations of these structures tend to affect their operational eficiency to a great extent and so the need to damp out these vibrations is felt. The simplest control algorithm that can be implemented to suppress the occurring vibrations in the system is direct feedback of the output parameter back into the sytem 1,2,4,15 . Measurable parameters like strain, displacement, velocity, accelaration, etc are the commonly fed signals. This type of control is simple to implement and yet yeilds satisfactory results. In this work, a simple cantilever beam was used as the system whose dynamics was studied and active vibration control technique was applied. The system parameters were analysed through the free vibration test. The setup consisted of one Lead-Zirconate-Titanate (PZT) patch producing the primary disturbance (the exciter), another PZT patch sensing the occurring disturbance (the sensor), and inally the third PZT patch that suppressed the vibration (the actuator). The setup with the embedded PZT patches is as shown in Fig.1a. As reported by Lim 5 , et al., presence of the patches shifts the natural frequencies of the passive structure to higher frequencies. Waghulde and Kumar 6 used piezoelectric material on a cantilever beam thereby making it smart. The placement of the piezo sensors and actuators on the beam were determined through modal analysis as reported by Tripathi and Gangadharan 1 . Active control of hybrid smart structures under forced vibrations was investigated by Choi 7 , et al. 2. DESIGN SIMULATION FOR FREE VIBRATION USING LABVIEW The entire work was executed on LABVIEW 2010 on a windows platform. The graphical programming nature of LAB VIEW made the design of the algorithm simple and also it was user friendly with respect to debugging. Good reliability, near linear response to the applied voltage and exhibition of excellent response to the applied electric ield over very large range of frequencies coupled with low cost of PZT makes it a very popular choice as a sensor and actuator that enables the Active Vibration Control of a Smart Cantilever Beam on General Purpose Operating System A.P. Parameswaran * , A.B. Pai, P.K. Tripathi, and K.V. Gangadharan National Institute of Technology, Surathkal-575 025, India * E-mail: arunmnl@gmail.com ABSTRACT All mechanical systems suffer from undesirable vibrations during their operations. Their occurrence is uncontrollable as it depends on various factors. However, for eficient operation of the system, these vibrations have to be controlled within the speciied limits. Light weight, rapid and multi-mode control of the vibrating structure is possible by the use of piezoelectric sensors and actuators and feedback control algorithms. In this paper, direct output feedback based active vibration control has been implemented on a cantilever beam using Lead Zirconate-Titanate (PZT) sensors and actuators. Three PZT patches were used, one as the sensor, one as the exciter providing the forced vibrations and the third acting as the actuator that provides an equal but opposite phase vibration/force signal to that of sensed so as to damp out the vibrations. The designed algorithm is implemented on Lab VIEW 2010 on Windows 7 Platform. Keywords: Smart cantilever beam, active vibration control, direct output feedback, Lead Zirconate-Titanate