18-09-2014, 04:00 PM
The concept of the vibration absorber using variable stiffness beam has two important requirements. 1.The two absorber beams should deform as a single beam in bending as a cantilever. Thus, the two beams should act as a top and bottom fiber of a cantilever and no movement should take place with respect to each other of these two fibers. 2.The opening/closing movement between the rods should be independent of the attached mass. Also, there should not be any relative motion between the beam and mass, when the machine is running.
The concept of the vibration absorber using variable stiffness beam has two important requirements. 1.The two absorber beams should deform as a single beam in bending as a cantilever. Thus, the two beams should act as a top and bottom fiber of a cantilever and no movement should take place with respect to each other of these two fibers. 2.The opening/closing movement between the rods should be independent of the attached mass. Also, there should not be any relative motion between the beam and mass, when the machine is running. The weight of the absorber should be as low as possible. The resonant device used is a parallel beam combination with one common lumped mass at each end. A mechanical system has been used to change the distance between the parallel beams and hence the moment of area about the neutral axis and thus the natural frequencies. Figure 1 shows the mechanism used in the proposed device. The rotary device from the stepper motor is converted into opening and closing liner motion of the absorber rods. This has been achieved by a gear device arrangement. A gear mounted on the stepper motor devices another gear mounted at the center of the shaft. This shaft has right hand and left hand threads on the top and bottom portions. Accordingly two internally threaded (right and left hand) blocks have been mounted on the shaft’s top and bottom portions. Further, the sub assembly of the vibration absorber has been mounted on these two blocks. For one complete rotation of the gears, the total liner distance covered is twice the pitch of the thread.