Test system and research object self-developed current diagnosis system 616 main drive system of the lathe This paper uses 61621 lathe as the research object, the current signal is picked up by the motor power input terminal, and enters the self-developed current diagnosis system. The main drive system of the lathe is as shown. The system is driven by a 4kW four-stage asynchronous motor with a rated speed of 1320r/min. It is transmitted to the main gearbox via the first-stage belt and then to the headstock via the second-stage belt for further deceleration. Since the size of the pulley is only an estimated value of manual measurement, in order to find a correctly matched transmission chain, through the preliminary processing of the test data, according to the proportional relationship of the four rotational speeds, the corresponding transmission chain is obtained, and the calculated structural characteristic frequency is as shown.
Signal processing and analysis Uniform cutting in uniform cutting state, tested 200r/min, 640r/min, 800r/min three-speed, is the current spectrum, the spectrum shows that the main characteristic frequency appears in the form of modulation on both sides of 50Hz . For the sake of specification, the marks used in the spectrum of this paper are defined as follows: spindle frequency: t; belt 1 characteristic frequency: o; belt 2 characteristic frequency: p; axis 2 rotation frequency: w; axis 3 rotation frequency.
It can be seen from the uniform cutting spectrum shown: (1) 50Hz energy increases with the increase of the rotational speed, which is in line with the law that the current is proportional to the load torque; (2) the frequency of the shaft 3 is under such normal conditions. It is the dominant characteristic frequency, which also increases with the rotational speed; (3) The characteristic frequency that appears mainly in addition to the above frequencies is the natural frequency of the belt 1 and the belt 2.
Uniform cutting conditions Current spectrum diagram 312 Comparative analysis of various operating conditions (200r/min) The conditions tested at 200r/min include uniform cutting, eccentricity, impact load and friction. It is the current spectrum of the latter three conditions.
The spectrum can be summarized in the case of different operating conditions at a speed of 200 r/min: in the case of the working condition, the dominant component is still the characteristic frequency of the belt 1. Since the belt 1 is relatively close to the motor, it is particularly noticeable at low speeds. In the eccentric operating condition of the spindle, there is a significant spindle frequency and its double frequency. Around 50 Hz during the impact load is the rotational frequency of the shaft 3.
The experimental results analyzed the signal analysis of the spindle eccentricity, impact load, friction disturbance and uniform cutting in the above experiments, and compared the different rotation speeds under the same cutting state and the comparison of different cutting states at the same rotation speed. Nearly 100 sets of data have been analyzed and processed repeatedly, and the following analysis results can be obtained: (1) The respective revolution frequencies of the gearbox and the headstock can be reflected in the motor current signal, reflecting the main characteristic frequency of the lathe operation, even if there is a belt The existence of this flexible connection form can still find the corresponding frequency; although the transmission ratio of the belt is not known exactly, the corresponding transmission chain is analyzed by the proportional relationship of the four speeds, and is confirmed in the spectrum analysis.
(2) In the case of this study, the rotational frequency of the motor drive shaft and the main shaft is generally not apparent. This is because the unloading device is installed at the input shaft of the transmission and at the main shaft, which attenuates the torque fluctuation of the corresponding shaft. The spindle frequency can only be seen in the case of spindle eccentricity, impact load, etc. It also shows that the electrical system and bearing of the motor body are in good condition, and the rotor of the motor is running smoothly.
(3) Under the same cutting conditions, the higher the rotational speed, the larger the 50 Hz component, that is, the larger the stator current. The main feature at low speed is the frequency of the belt 1; as the speed increases, the frequency of rotation of the shaft 3 and the characteristic frequency of the belt 2 become more and more pronounced. Although the difference between the eccentricity of the main shaft, the impact load and the frictional disturbance is not very large (because, in essence, these situations have similarities), careful analysis still has its own characteristics and is identifiable from the spectrum.
Conclusion This paper attempts to monitor the state of the transmission chain of the machine tool by using the current method and realize its fault diagnosis. It has achieved good experimental results and provides a simple and practical method for the analysis of the transmission chain of machine tools. It can be applied to the production and operation of machine tools. In order to improve manufacturing quality and safe operation level.
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