Vibration evaluation

Use the RMS vibration velocity (mm/s rms) to evaluate machine vibration

Vibration is expressed as displacement (µm, mm), velocity (mm/s), or acceleration (m/s²). Velocity is used to judge the severity of machine vibration; displacement is used when the amplitude itself matters, such as for machining accuracy or the risk of contact; acceleration is used when you want to look at high frequencies. Because ISO's evaluation of machine vibration uses RMS velocity, expressing it as RMS has become normal in Japan too.^[1][2]

RMS value, peak value, and crest factor

For a sine wave: peak value = RMS value × √2  /  crest factor CF = peak value ÷ RMS value

The RMS value is the square root of the mean of the squared instantaneous values over a fixed time, and corresponds to the energy contained in the waveform. The crest factor is a clue when comparing bearing deterioration relatively (IMV).^[2][1]

Machine groups in ISO 10816-3:2009

These are further divided by whether the foundation (installation) is "rigid" or "flexible". This evaluation is for rotating machinery such as pumps, fans, and electric motors, not for machine tool spindles themselves.^[3](1 source, for reference)

Zone boundaries in ISO 10816-3:2009 (RMS vibration velocity, mm/s)

Boundary values read from IMV's figure ("Examples of good/poor judgment by machine group"). The zones are A: good, B: acceptable, C: warning, D: danger (IMV's labels). The standard itself is paid, and conditions such as the zone definition text and the measurement frequency range were not checked.^[3](1 source, for reference)

Three methods of simple diagnosis

^[3](1 source, for reference)

Rotation speed and vibration frequency

f (Hz) = n (min⁻¹) ÷ 60

Example: for a fan bearing running at 1,860 min⁻¹, the rotation frequency is 31 Hz. In an FFT, a large component at the rotation frequency with few harmonics suggests imbalance, and a prominent 2nd order (twice the frequency) suggests misalignment (Rion's example).^[1](1 source, for reference)

When looking for bearing abnormalities

To detect bearing and abnormal sounds, envelope processing (IMV's H function) that applies a 2–15 kHz filter to the acceleration waveform is effective. Estimating the cause from the components corresponding to the rotation frequency is precision diagnosis (FFT analysis).^[3][2](1 source, for reference)

How to choose measurement points

Choose a point that meets these 5 conditions: easy to reach, little affected by anything other than the abnormality, sensitive to changes in the abnormality, little signal attenuation, and measurable the same way every time. Measuring on the bearing housing is the basic rule.^[2](1 source, for reference)

Vibration of a machine tool spindle

Haas's preventive maintenance measures spindle vibration, compares it with the reference, and uses the records as the baseline for future comparison (progress of wear). Whether ISO 10816 zone values can be applied to a machine tool spindle could not be confirmed in public documents.^[4](1 source, for reference)