A THEORETICAL STUDY AND 3D MODELING OF NONLINEAR PASSIVE VIBRATION ISOLATOR

The study of sound and vibration are closely related. Sound or "pressure waves" are generated by vibrating structures (e.g. vocal cords); these pressure waves can also induce the vibration of structures (e.g. ear drum). Hence, when trying to reduce noise it is often a problem in trying to reduce vibration. The high speed engines and machines when mounted on foundations and supports cause vibrations of excessive amplitude because of unbalance forces setup during their working. These are the disturbing forces which damage the foundation on which the machines are mounted. So the vibration transmitted to the foundation should be eliminated or reduced considerably by using some devices such as springs, dampers etc. between the foundation and machine. "Passive vibration isolation" refers to vibration isolation or mitigation of vibrations by passive techniques such as rubber pads or mechanical springs, as opposed to "active vibration isolation" or "electronic force cancellation" employing electric power, sensors, actuators, and control systems. Passive vibration isolation is a vast subject, since there are many types of passive vibration isolators used for many different applications. [1-6]. The proposed isolator is divided into three portions. The upper portion is a table on which the isolated objects are placed. The upper portion consists of one horizontal top plate and two vertical hexagonal plates. The middle portion consists of two shafts connected by elements to provide a nonlinear restoring force. Constant force springs, coil springs and wires are examples of such elements. Here constant force springs are composed of rolled spring steel and have constant restoring force regardless of their stretch. At both ends of each shaft, inner and outer roller bearings are installed. In the lower portion one screw connected by two beams. The beams are connected to the cranks using pin connections. Half of the length of the screw jack is threaded by the opposite direction to that of the outer half. With such a composition the horizontal restoring force provides by the middle portion can be converted into the vertical restoring force. In conversion, the vertical resisting force can be adjusted simply by changing the angle of the inclined bars of the cranks which is the key ingredient of the present vibration isolator. All the 3 different portions are designed using CATIA V5 and assembled together [1]