Abstract
A labyrinth piston compressor is one of the important reciprocating machines because it can supply a large amount of oil-free gas. It is important to improve its stability and to reduce its resonance amplitude if we plan to increase its rotating speed in order to improve its efficiency. Bending stiffness of its piston rod fluctuates as its crank rotates. Thus, this compressor can be modeled as a parametric excitation system when its bending vibration mode is considered. Unstable regions near the rotating speed corresponding to twice natural frequency divided by arbitrary positive integer value becomes larger as a fluctuation ratio of stiffness becomes increases. These regions become small as corresponding rotating speed decreases or damping ratio increases. Not only typical resonance but also subharmonic and superharmonic resonances occur when the fluctuation ratio of stiffness increases and damping ratio decreases. In unstable and resonance vibration, the component of the natural frequency harmonic vibration is dominant. Thus, its vibration can be reduced by using a dynamic vibration absorber whose stiffness and damping are determined under conditions that the fluctuation ratio of stiffness and the damping ratio of the compressor are zero.
