Fault diagnosis of gears by monitoring the stator current of the motor

Gears are the most common transmission components in mechanical equipment and are also consumable parts. Studying gear failures will make a lot of sense in reducing maintenance costs of mechanical equipment and improving product quality. The most direct dynamic behavior of gear defects or failures (such as tooth surface damage, cracks, excessive wear, or broken teeth) is reflected in the torsional vibration of its drive shaft. In this paper, the indirect measurement of the torsional vibration of the drive shaft and the measurement of the vibration signal, as well as the processing of these signals, the extraction of fault features, etc., are carried out. However, due to the difficulty in direct measurement of the torsional vibration of the gear and the high cost, the author proposes to monitor the stator. Current to achieve a new method of indirect measurement of the torsional vibration of the gear, through the extraction of the signal characteristics of the stator current to achieve gear fault diagnosis. The main idea is that the torsional vibration of the gear causes the air-gap torque of the motor to fluctuate through the rotary axis, and the change of the air-gap torque causes the change of the stator current through the stator flux. Therefore, by analyzing the frequency component of the stator current, the gear can be realized. The identification of the fault frequency.

1 Characteristics of vibration signal of damaged gear Under normal circumstances, that is, when the gear is well meshed, the vibration of the gear transmission is mainly the gear meshing excitation vibration. The main component is the meshing frequency and its harmonic components. The response can be expressed as: x ( t) Measured vibration signal X is the third harmonic frequency of the meshing frequency. The amplitude is the phase of the meshing frequency of the harmonic component. The phase f is the meshing frequency of the gear, and f is the frequency of the shaft where the gear is located.

When the gear has eccentricity, pitting, and broken teeth, the amplitude of the vibration signal is modulated. The amplitude modulation is caused by the influence of the fluctuation of the tooth surface load on the vibration amplitude. Due to motor speed fluctuations, gear machining errors, profile deformation, and gear tooth bending, cyclical changes in the overall gear stiffness result in frequency modulation of gear vibrations. In fact, the gear failure caused by the same frequency of 25Hz. After unpacking inspection, it was found that gear 1 had severe pitting wear, which was caused by theoretical inference.

In summary, the torsional vibration information of the gear is very sensitive to the failure of the gear. Therefore, by analyzing the torsional vibration of the motor stator current monitoring gear, the fault characteristics of the gear can be extracted. Through a large number of experiments, the variation law of the stator current signal can be found from the normal to the slightest damage to the final failure of the gear. When the characteristics of the stator current in the various stages of the damage of the gear signal are known, the fault characteristics in the early stages of the gear damage can be identified. To take measures as soon as possible to eliminate the malfunction.

In addition, when the load changes, its frequency of change can also be measured by the stator current of the transmission system. In general, the frequency of the load change is different from the gear's fault frequency. In this way, after grasping the characteristic law of the stator current in the faults of each gear, the characteristics of the load change in the stator current can be improved, and the basis for measuring the change law of the load can be provided.

4 Conclusion This article has proved both in theory and practice that the indirect monitoring of the torsional vibration of gears through monitoring and determination of the current gear to achieve the effectiveness of the fault diagnosis and practicality. A typical gear fault diagnosis method is to measure a gear vibration signal through an acceleration sensor mounted on a bearing seat, extract a signal feature, and diagnose a gear fault. However, this method is limited by the site, and it is inconvenient to install the sensor. In addition, the path of the vibration signal transmitted from the gear to the sensor is complicated, and the mathematical model of the transfer function and the gear box is not easy to obtain. Therefore, currently used methods are mostly qualitative researches. . The above problems can be solved by using the theory proposed in this paper. At the same time, remote diagnosis can also be realized, which has a high value of use.