CN109269745B

CN109269745B - Large bucket wheel machine cantilever low-frequency vibration testing method based on carrier roller excitation method

Info

Publication number: CN109269745B
Application number: CN201811275564.0A
Authority: CN
Inventors: 姜永正; 王广斌; 蒋玲莉; 肖冬明; 沈意平; 冯和英
Original assignee: Hunan University of Science and Technology
Current assignee: Hunan University of Science and Technology
Priority date: 2018-10-30
Filing date: 2018-10-30
Publication date: 2021-01-19
Anticipated expiration: 2038-10-30
Also published as: CN109269745A

Abstract

The invention discloses a cantilever low-frequency vibration testing method of a large bucket wheel machine based on a carrier roller vibration excitation method.

Description

Large bucket wheel machine cantilever low-frequency vibration testing method based on carrier roller excitation method

Technical Field

The invention relates to the field of bucket wheel machine cantilever detection, in particular to a large bucket wheel machine cantilever low-frequency vibration testing method based on a carrier roller vibration excitation method.

Background

The arm type bucket-wheel stacker reclaimer is a kind of high-efficient bulk material conveying equipment which is extensively used in port and wharf, cement and mine raw material storage and transportation fields. The cantilever beam is a key part for taking materials, and is tens of meters long and hundreds of tons in weight. The cantilever beam has a very prominent vibration problem due to the severe working conditions of the bucket wheel machine, a plurality of excitation sources and complex characteristics. Therefore, the vibration characteristics of the cantilever of the large-scale bucket-wheel stacker-reclaimer are researched, the violent vibration of the cantilever is avoided, and the method has important significance for prolonging the fatigue life of the structure.

For the vibration reduction design of the structure, the natural frequency of the structure is the most basic key problem, and because the cantilever of the stacker-reclaimer belongs to an ultra-large complex structure, and the numerical simulation model is difficult to accurately establish, the natural frequency obtained by a test means is the most rapid and effective mode. In the aspect of vibration testing of a bucket-wheel stacker reclaimer, a hammer excitation method is generally adopted in China to measure vibration signals, and the excitation method has the defects that the whole vibration of a large-scale structure cannot be excited, the measured signals are local high-frequency vibration, and the low-frequency vibration signals of the large-scale structure cannot be accurately obtained. To solve the problem, Rusinski et al abroad propose to generate impact excitation by an initial displacement release method, suspend a heavy object at the far end of a cantilever to generate initial elastic deformation, then drop the heavy object by blasting, rebound the cantilever to generate vibration excitation, and then measure the free vibration response of the large cantilever to obtain the natural frequency of the bucket wheel machine. This method has proven to be effective, but has the disadvantage of being too difficult and expensive to test.

Disclosure of Invention

In order to solve the problems, the invention provides a large bucket wheel machine cantilever low-frequency vibration testing method based on a carrier roller excitation method, which is simple, economical and effective without introducing external equipment.

In order to achieve the purpose, the invention adopts the technical scheme that:

the method for testing the cantilever low-frequency vibration of the large bucket wheel machine based on the carrier roller vibration excitation method comprises the steps of exciting vibration by utilizing carrier roller rotation on a cantilever, releasing initial displacement in a mode of suddenly stopping a belt conveyor and a bucket wheel motor, and continuously testing cantilever vibration free attenuation signals after the motor runs and suddenly stops through an accelerometer so as to obtain the natural frequency of the cantilever; the method specifically comprises the following steps:

s1, mounting five accelerometers on a cantilever with a carrier roller, wherein two accelerometers are mounted at the far end of the cantilever and used for collecting acceleration signals in the y direction, the other two accelerometers are mounted at the near end of the cantilever and used for collecting acceleration signals in the y and Z directions, and the last sensor is vertically mounted on an oblique rod and used for measuring vertical vibration signals;

s2, during measurement, turning on a bucket wheel motor, enabling a bucket wheel to rotate at the speed of 5.8rpm, after a few seconds, driving a conveyor belt to rotate at the speed of 400 rpm by a belt conveyor, after 15 seconds, stopping the belt conveyor and the bucket wheel motor after the conveyor belt stably runs, enabling cantilever vibration to be freely attenuated until the cantilever is completely stopped, repeating the operation for three times, and continuously testing a cantilever running time signal and a free attenuation time signal after the motor runs and is suddenly stopped by an accelerometer in the whole testing process;

and S3, converting the stable operation time signal and the free decay time signal into a frequency domain through Fast Fourier Transform (FFT), thereby obtaining the natural frequency of the cantilever.

The invention has the following beneficial effects:

the natural frequency of the cantilever can be obtained without introducing external equipment, and the method is simple and economical.

Drawings

FIG. 1 shows the test results of five accelerometers in an embodiment of the present invention.

In the figure: (a) an acceleration time domain graph; (b) a partial enlarged view of the free decay signal; (c) stabilizing the FFT transformation result of the operation stage; (d) and FFT transforming the free attenuation section.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.

Examples

A bucket wheel excavator DQLZ 1200 manufactured by China Taifu heavy industry manufacturing Co., Ltd is used as a test object. The DQLZ 1200 bucket wheel machine is 43 meters high, the total weight is 1260 tons, and the theoretical reclaiming efficiency is 7200 cubic meters per hour. The cantilever is a complex welding structure consisting of a plurality of plates and beams, the weight can reach 80 tons, the length is 60 meters, and the vibration of the cantilever is the main low-frequency vibration in the working process. For low frequency vibration testing of such large structures, it is difficult to provide suitable external excitation. It would be advantageous if the appropriate stimulus could be obtained from within the machine rather than from the outside. Wherein the idler above the cantilever acts as a low frequency vibration exciter, since there are many idlers arranged across the long arm, it is sufficient to excite the whole structure to vibrate. Furthermore, the idler speed is about 6.67Hz, closest to the natural frequency of the cantilever.

A cantilever with a carrier roller is used as an exciter for low-frequency vibration tests, and a total of five accelerometers are mounted on the cantilever, wherein two accelerometers are mounted at the far end of the cantilever and used for collecting acceleration signals in the y direction, and the other two accelerometers are mounted at the near end of the cantilever and used for collecting acceleration signals in the y direction and the Z direction. The last sensor is vertically mounted on the diagonal for measuring vertical vibration signals.

In a single measurement, when the bucket wheel motor is turned on, the bucket wheel begins to rotate at 5.8 rpm. At this time, only slight vibration is felt. After a few seconds, the conveyor belt starts to rotate at a speed of 400 rpm (6.67Hz), so that during this period significant vibrations occur. Then, the belt conveyor and the bucket wheel motor are suddenly powered off, so that the vibration of the cantilever is freely attenuated until the cantilever is completely stopped. The test procedure was repeated three times and the signals measured from the five sensors are shown in figure 1. FIG. 1(a) shows the timely signal of the acceleration measured by accelerometer No. 1. It clearly shows that the signal covers three phases of bucket wheel start, idler start and free decay after sudden power failure. Fig. 1(b) shows a partial amplification of the free decay period after the first power down. Obviously, the attenuated signal does not drop completely to zero, and the free attenuated signal exhibits multi-frequency vibration characteristics. For frequency identification, the stable run-time signal and the free decay-time signal are converted into the frequency domain by Fast Fourier Transform (FFT), and the transformation results are shown in fig. 1(c) and 1 (d). The comparison of the two graphs shows that the stable operation frequency is very rich, not only reflects the natural frequency of the arm support, but also reflects the rotation frequency (24.7Hz) and the electrical noise frequency of the motor

(49.8Hz,) while the free decay period includes only four frequencies of 0.1,1.76,2.02, and 2.56 Hz. The true natural frequencies of the boom are 1.76,2.02 and 2.56Hz due to the inertial rotation from the bucket wheel at 0.1 Hz.

The signals captured by the other four accelerometers are similar to accelerometer 1. Finally, a total of five natural frequencies are clearly identified from the five accelerometers. They were 0.51,0.74,1.78,2.02 and 2.56Hz, respectively, as shown in table 1.

TABLE 1 test of the resulting natural frequencies

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims

1. A large bucket wheel machine cantilever low-frequency vibration testing method based on a carrier roller excitation method is characterized in that: the method comprises the following steps of (1) carrying out induced vibration by utilizing the rotation of a carrier roller on a cantilever, releasing initial displacement in a mode of suddenly stopping a belt conveyor and a bucket wheel motor, and continuously testing cantilever vibration free attenuation signals after the bucket wheel motor runs and suddenly stops by an accelerometer so as to obtain the natural frequency of the cantilever; the method comprises the following steps:

s1, mounting five accelerometers on a cantilever with a carrier roller, wherein two accelerometers are mounted at the far end of the cantilever and used for collecting acceleration signals in the Y direction, the other two accelerometers are mounted at the near end of the cantilever and used for collecting acceleration signals in the Y and Z directions, and the fifth accelerometer is vertically mounted on an oblique rod and used for measuring vertical vibration signals;

s2, during measurement, turning on a bucket wheel motor, enabling the bucket wheel to start rotating at the speed of 5.8 revolutions per minute, then driving a conveyor belt to start rotating at the speed of 400 revolutions per minute by a belt conveyor, after 15 seconds, after the bucket wheel and the conveyor belt stably run, suddenly cutting off the power of the belt conveyor and the bucket wheel motor, enabling the cantilever to vibrate and freely attenuate until the cantilever completely stops, then repeating the operation for three times, and continuously testing the cantilever running time signal and the free attenuation time signal after the bucket wheel motor runs and suddenly stops through an accelerometer in the whole testing process;

and S3, converting the cantilever operation time signal and the free decay time signal into a frequency domain through fast Fourier transform, thereby obtaining the natural frequency of the cantilever.