RESONANT FREQUENCY
If the running speed is close to one of the natural frequencies, the small amount of unbalance causes unacceptable vibration. Balancing the machine would not eliminate the vibration (because unbalance will return). The solution in this case is not to remove the forcing fre- quency, but to change the vibration characteristics of the machine.
This can be done by any of the following:
1. Increase the stiffness of the machine to raise the natural frequency.
2. Add mass to lower the natural frequency.
3. Add damping such as shock absorbers to reduce the machine’s response to the forcing frequency.
Here is a general rule: If the forcing frequency is below resonance, damping is the most effective way to reduce the response. If the forcing frequency is higher than resonance, the mass should be increased.