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技術レポート 振動とそのセンサーについて 4

3. Principles and Features of Vibration Sensors

3.5 Torsional Vibration Meter

Torsional vibrations occur with rotation. Even when referring to torsional vibrations, in a directly connected rotating system, they arise from fluctuations in the rotation of the rotating parts. In multi-axis systems that combine gears, belts, chains, etc., they are caused not only by rotational fluctuations but also by transmission errors due to processing precision and deformation. In actual devices, it is common for these rotational fluctuations, torsional vibrations, and transmission errors to be intricately intertwined.

In systems where rotational fluctuations, torsional vibrations, and transmission errors occur, various negative effects manifest.

  1. Increase in vibration and noise.

  2. Deterioration of positioning accuracy

  3. Deterioration of sending accuracy

  4. fatigue failure

Therefore, in a system that includes rotating and transmission components, it is important to measure the three factors of rotational fluctuations, torsional vibrations, and transmission errors, and to analyze their causal relationships.

3.5.1 Rotational Fluctuation

It is the increase or decrease (fluctuation) of the rotational angular velocity with respect to the average angular velocity at a point on the rotation axis. The measurement uses a high-resolution rotary encoder, and the obtained output is processed through high-speed F/V conversion for each pulse to determine the rotational fluctuations per revolution.

3.5.2 Torsional Vibration

It is the fluctuation of relative angular displacement between two points on the rotation axis. Generally, a pair of electromagnetic rotary sensors is used for measurement, detecting the twist of the drive side and load side axes as a phase difference, which is then converted into frequency through high-speed F/V conversion.

3.5.3 Transmission Error

In a multi-axis rotating machine, there is a delay or advance in the rotation angle before and after the transmission device. The measurement is fundamentally similar to detecting torsional vibrations, where the phase difference before and after the transmission device is detected, and the transmission error per pitch is determined by calculating the frequency.

Finally, I will present the formulas for the mutual conversion of acceleration, velocity, and displacement.

From the above equation, if one of the quantities frequency f, displacement D, velocity V, or acceleration G is measured, the other two physical quantities can be calculated.