Portal crane damage detection method based on amplitude-variable trolley acceleration response

Abstract

A portal crane damage detection method based on amplitude-variable trolley acceleration response comprises the following steps that 1, an amplitude-variable trolley-simply supported beam portal crane system is built, and an amplitude-variable trolley is arranged on a cargo boom of a portal crane; 2, an acceleration sensor is arranged on the variable-amplitude trolley, the variable-amplitude trolley moves on the cargo boom of the portal crane at the moving speed v, and the acceleration sensor collects acceleration response data of the variable-amplitude trolley in real time and transmits the acceleration response data to an FFT conversion module; 3, the FFT conversion module converts the acceleration response data of the variable amplitude trolley to obtain an acceleration spectrogram; 4, according to the acceleration spectrogram, modal parameters of the portal crane are obtained through recognition; and 5, detecting and identifying the damage condition of the portal crane according to the modal parameters or the acceleration response data. The method has the effect that the damage result of the simply supported beam portal crane can be accurately detected.

Description

Technical Field

[0001] The invention relates to the technical field of gantry crane damage detection, and in particular to a gantry crane damage detection method based on the acceleration response of a variable-length trolley. Background Art

[0002] At present, we usually use destructive and non-destructive testing methods including visual inspection, X-ray inspection, ultrasonic inspection, stress testing, magnetic particle inspection, acoustic emission inspection, etc. to monitor the health and safety of gantry cranes. The first step of most of the methods listed above is to detect the damage location or damage degree of the gantry crane by identifying the modal parameters of the gantry crane. It can be seen that the modal parameters of the structure are very important in the health and safety monitoring of gantry cranes.

[0003] In reality, the modal parameters of all objects are different, just like human fingerprints, and are composed of countless unique data. The modal parameters of each structure itself usually do not change, such as natural frequency, modal vibration shape, and structural damping, but when the structure itself is damaged, its modal parameters will also change. In theory, this is why damage can be identified by analyzing the modal parameters. The main content of modal analysis is actually to perform coordinate transformation on the data. It converts the response value originally in the physical coordinate to the description under the defined modal coordinate. Each basis vector under the modal coordinate is the characteristic vector of the vibration response under the original physical coordinate, that is, the correlation between the basis vectors under this coordinate can simply describe the relationship between the response vectors.

[0004] However, the computational modal analysis method cannot take into account the coupling relationship between each response vector. Therefore, the experimental modal analysis method is often used in combination with it to identify structural damage. The experimental modal analysis method, as the name implies, is to obtain the response value through field tests or model tests and then identify the actual modal parameters of the structure through numerical processing. In recent years, people usually give external excitation to the structure to pick up the vibration response value of the structure, and then obtain the modal parameters of the structure through fast Fourier transform FFT. However, this method has strict requirements on the environment, and when using this method to measure large machinery, more test instruments such as sensors are required, the amount of data collected by the measuring points is large, and data processing is more cumbersome. Summary of the invention

[0005] The present invention provides a gantry crane damage detection method based on the acceleration response of the variable-length trolley, which can realize accurate detection of damage results of a simply supported beam gantry crane.

[0006] To achieve the above object, the present invention provides a gantry crane damage detection method based on the acceleration response of the variable-luffing trolley, the key of which is to include the following steps:

[0007] Step 1: Build a luffing trolley-simple-beam gantry crane system. The luffing trolley is set on the boom of the gantry crane. The boom length is set to L. The unit length mass of the gantry crane is The material elastic modulus of the gantry crane is E, the section inertia moment of the gantry crane is I, and the mass of the luffing trolley is m v ;

[0008] Step 2: An acceleration sensor is arranged on the luffing trolley, and the luffing trolley moves on the boom of the gantry crane at a moving speed v. The acceleration sensor collects acceleration response data of the luffing trolley in real time and transmits it to a fast Fourier transform (FFT) conversion module;

[0009] The expression of the acceleration response data of the luffing trolley is as follows:

[0010]

[0011] in, represents the acceleration response of the luffing trolley, represents the nth-order acceleration response coefficient, i represents a mathematical imaginary number, ω Tn represents the nth-order frequency of the simply supported beam system structure, t represents time, n represents the response order, 1≤n≤M, M represents the order range; v represents the speed of the variable-luffing trolley, and L represents the length of the gantry crane;

[0012] Step 3: The fast Fourier transform (FFT) conversion module transforms the acceleration response data of the variable amplitude vehicle to obtain an acceleration spectrum diagram;

[0013] Step 4: According to the acceleration spectrum diagram, the modal parameters of the gantry crane are identified;

[0014] According to the peak distribution of the acceleration frequency spectrum, the modal parameters of the gantry crane are obtained, wherein the modal parameters include the natural frequency and vibration mode of the gantry crane, and the natural frequency includes the left frequency and the right frequency of the gantry crane;

[0015] Step 5: Detect and identify the damage of the gantry crane according to the modal parameters or acceleration response data;

[0016] The method used to detect and identify damage to the gantry crane is either:

[0017] a. Damage identification method based on natural frequency change;

[0018] b. Damage identification method based on vibration mode change;

[0019] c. Damage identification method based on flexibility change;

[0020] d. Damage identification method based on wavelet transform.

[0021] Through the above design, the acceleration response of the luffing trolley is calculated. According to the proposed expression of the acceleration response data of the luffing trolley, the acceleration response of different positions of the cross arm of the gantry crane can be reconstructed. The reconstructed acceleration response is then converted to obtain the acceleration frequency spectrum of the luffing trolley. Through the acceleration frequency spectrum, the modal parameters such as frequency and vibration mode of the gantry crane can be accurately obtained, and then the damage results of the gantry crane can be detected and identified. The damage results of the gantry crane include whether the gantry crane is damaged, the damage location and the degree of damage.

[0022] As a preference: in step 2, the nth order frequency ω of the gantry crane Tn The expression is as follows:

[0023]

[0024] The nth order acceleration response coefficient of the variable-luffing trolley The expression is as follows:

[0025]

[0026] Among them, A 1,n , A 2,n , A 3,n is the nth-order response coefficient of the luffing trolley, and its expression is as follows:

[0027]

[0028] Among them, Δ st,n is the deformation of the gantry crane, S n is the speed variable of the luffing trolley, and its expression is as follows:

[0029]

[0030] Where g represents the acceleration due to gravity, g = 9.8 m / s 2 .

[0031] As a preference: in step 4, the left frequency ω of the gantry crane Tn1 The expression is as follows:

[0032]

[0033] The right frequency ω of the gantry crane Tn2 The expression is as follows:

[0034]

[0035] Preferably, in step 2, the movement speed v of the boom-changing trolley is controlled within a range of 25%-80% of the maximum boom-changing speed of the gantry crane.

[0036] Preferably, in step 1, a hook is connected to the luffing trolley, a hanging object is hung on the hook, and the weight of the hanging object is controlled to be 25% to 60% of the maximum lifting weight of the gantry crane.

[0037] Since the luffing structure and lifting structure are used more frequently in the operation of gantry cranes, the two parameters of the luffing trolley's running speed and the weight of the hoisted object will affect the recognition of the gantry crane frequency by the luffing trolley's acceleration response. When the luffing trolley's speed is slow, it will affect the gantry crane's frequency recognition rate, but when the speed is fast, the recognition result will also be greatly distorted. When the speed is 25% to 80% of the gantry crane's maximum luffing speed, the recognition result is most accurate; when the lifting weight is controlled at 25% to 60% of the gantry crane's maximum lifting weight, the luffing trolley can recognize high-order frequencies without causing the gantry crane to produce additional vibrations that affect the accuracy of the luffing trolley's recognition frequency.

[0038] Preferably, in step 5, the damage identification method based on natural frequency change is as follows:

[0039] A luffing trolley-simply supported beam gantry crane is built. Before the gantry crane is damaged, the luffing trolley moves on the gantry crane to obtain acceleration response data of the luffing trolley before damage, and a fast Fourier transform is performed to obtain an acceleration spectrum before damage, and the natural frequency of the gantry crane before damage is identified through the acceleration spectrum before damage;

[0040] After the gantry crane is damaged, the acceleration response data of the luffing trolley after the damage is obtained by moving the luffing trolley on the gantry crane, and a fast Fourier transform is performed to obtain an acceleration spectrum after the damage, and the natural frequency of the gantry crane after the damage is identified by the acceleration spectrum after the damage;

[0041] The natural frequency of the gantry crane before the damage and the natural frequency of the gantry crane after the damage are compared to obtain the damage result of the gantry crane.

[0042] The natural frequency is the easiest parameter to obtain among the modal parameters and has high identification accuracy. There are many methods for damage identification based on the change of natural frequency. Their characteristics are: when the structure is damaged, only the stiffness of the structure is reduced, while the change of the structural mass is ignored, and a modified theoretical model is established before the early damage of the structure. Theoretically, the ratio of any second-order frequency change after the damage is only a function of the damage position and has nothing to do with the size of the damage.

[0043] Preferably, in step 5, the damage identification method based on vibration mode change is as follows:

[0044] (1) Building a luffing trolley-simple-beam gantry crane, and obtaining acceleration response data of the luffing trolley by moving the luffing trolley on the gantry crane.

[0045] (2) performing a fast Fourier transform on the acceleration response data of the variable-length trolley to obtain an acceleration spectrum diagram, and identifying the frequency of the gantry crane;

[0046] (3) extracting response data related to the gantry crane frequency from the acceleration response data by using a bandpass filter method (BPS);

[0047] (4) obtaining the instantaneous amplitude of the response data by using Hilbert transform;

[0048] (5) obtaining the vibration mode of the gantry crane from the instantaneous amplitude;

[0049] (6) performing regularization processing on the vibration mode of the gantry crane;

[0050] (7) Identify the damage of the gantry crane by using the vibration mode curvature method or the vibration mode change graph method.

[0051] The vibration mode is a basic modal parameter. Although its test accuracy is relatively low, it contains a lot of information, so there are many damage identification and diagnosis technologies based on vibration mode changes. (1) Vibration mode curvature method: If the structure is damaged, the stiffness of the damaged part will decrease and the curvature will increase. The change in vibration mode curvature increases with the increase in curvature. Therefore, the location of the damage can be determined based on the change in vibration mode curvature. (2) Vibration mode change graph method: The relative change in vibration mode is used as the positioning parameter, that is, the ratio of the difference in vibration mode before and after damage to the vibration mode before damage. When damage occurs, the relative change in vibration mode on the affected degree of freedom will appear relatively large in the damaged area. Therefore, the location of the damage can be identified using the vibration mode relative change graph.

[0052] The damage identification method based on flexibility change is as follows:

[0053] Under the condition that the mode satisfies normalization, the flexibility matrix is ​​a function of the inverse of the frequency and the vibration mode. As the frequency increases, the inverse of the high frequency in the flexibility matrix can be ignored. In this way, a matrix with good accuracy can be obtained by measuring the first few low-order modal parameters and frequencies. The maximum element in each column of the difference matrix is ​​obtained based on the difference matrix of the two flexibility matrices before and after the damage. The location of the damage can be found by checking the maximum element in each column.

[0054] The damage identification method based on wavelet transform is as follows:

[0055] The acceleration response signal of the variable amplitude trolley is filtered and integrated twice to obtain the displacement time history signal of the sampling point. Wavelet analysis is performed on the acceleration time history signal and the displacement time history signal respectively, thereby realizing the detection of structural damage.

[0056] Beneficial effects of the present invention: In previous studies, there is no method to use the luffing trolley response to measure the gantry crane response. The present invention builds a luffing trolley-simply supported beam gantry crane system and measures the acceleration response of the luffing trolley to accurately reflect the modal parameters of the gantry crane, and then detects and identifies the damage results of the gantry crane, providing a theoretical basis and method guidance for the subsequent realization of intelligent damage detection of structural movement similar to that of a simply supported beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a schematic diagram of the process of the present invention;

[0058] Figure 2 It is a structural schematic diagram of a luffing trolley-simple-beam gantry crane in an embodiment;

[0059] Figure 3 It is a comparison chart of the frequency results of the scaled model identified by finite element, theory and experiment in the embodiment;

[0060] Figure 4 It is a frequency diagram of the gantry crane identified by the trolley response under five variable amplitude working conditions in the embodiment;

[0061] Figure 5 It is a frequency diagram of the gantry crane identified by the trolley response under five lifting weight conditions in the embodiment. DETAILED DESCRIPTION

[0062] The present invention is further described in detail below in conjunction with the accompanying drawings and specific examples. The following examples or drawings are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0063] like Figure 1 As shown: A gantry crane damage detection method based on the acceleration response of the variable-length trolley includes the following steps:

[0064] Step 1: Build a luffing trolley-simple-beam gantry crane system. The luffing trolley is set on the boom of the gantry crane. The boom length is set to L. The unit length mass of the gantry crane is The material elastic modulus of the gantry crane is E, the section inertia moment of the gantry crane is I, and the mass of the luffing trolley is m v ;

[0065] Step 2: An acceleration sensor is arranged on the luffing trolley, and the luffing trolley moves on the boom of the gantry crane at a moving speed v. The acceleration sensor collects acceleration response data of the luffing trolley in real time and transmits it to a fast Fourier transform (FFT) conversion module;

[0066] The expression of the acceleration response data of the luffing trolley is as follows:

[0067]

[0068] in, represents the acceleration response of the luffing trolley, represents the nth-order acceleration response coefficient, i represents a mathematical imaginary number, ω Tn represents the nth-order frequency of the simply supported beam system structure, t represents time, n represents the response order, 1≤n≤M, M represents the order range; v represents the speed of the variable-luffing trolley, and L represents the length of the gantry crane;

[0069] Step 3: The fast Fourier transform (FFT) conversion module transforms the acceleration response data of the variable amplitude vehicle to obtain an acceleration spectrum diagram;

[0070] Step 4: According to the acceleration spectrum diagram, the modal parameters of the gantry crane are identified;

[0071] According to the peak distribution of the acceleration frequency spectrum, the modal parameters of the gantry crane are obtained, wherein the modal parameters include the natural frequency and vibration mode of the gantry crane, and the natural frequency includes the left frequency and the right frequency of the gantry crane;

[0072] Step 5: Detect and identify the damage of the gantry crane according to the modal parameters or acceleration response data;

[0073] The method used to detect and identify damage to the gantry crane is either:

[0074] a. Damage identification method based on natural frequency change;

[0075] b. Damage identification method based on vibration mode change;

[0076] c. Damage identification method based on flexibility change;

[0077] d. Damage identification method based on wavelet transform.

[0078] like Figure 2 As shown: the length of the gantry crane 1 is L, and the mass of the luffing trolley 2 is m v , the luffing trolley 2 moves on the gantry crane 1 at a uniform speed v, and the mass per unit length of the gantry crane 1 is The distance that the variable-length trolley 2 moves over time is xv , the vertical displacement of the luffing trolley 2 is u c .

[0079] For a luffing trolley-simple-beam gantry crane, the motion equation of the gantry crane system is:

[0080]

[0081] Among them, u j represents the vertical displacement of the gantry crane, E is the material elastic modulus of the gantry crane, I represents the section inertia moment of the gantry crane, and f c (t) represents the load effect of the luffing trolley 2 on the gantry crane over time; δ represents the delta function, which means that when x=vt, the delta function value is 1, and the value is 0 at other times; represents the derivative of the vertical displacement of the gantry crane with respect to time t, u j ″″ represents the fourth differential of the vertical displacement of the gantry crane with respect to the position x, x represents the position of the luffing trolley 2 along the axis of the gantry crane from the left end point, and v is the running speed of the luffing trolley 2.

[0082] For the theoretical derivation of this embodiment, according to Figure 2 The simplified calculation model of the gantry crane shown in the figure uses the modal superposition method to represent the vertical displacement of the gantry crane. In layman's terms, the solution of equation (1) is the gantry crane displacement u j It can be expressed as many vibration modes φ(x) and modal coordinates q Tn For the gantry crane structure, the modal form that meets the boundary conditions of the simplified model is sinusoidal, and the dynamic response of the gantry crane can be expressed as the following formula:

[0083]

[0084] Among them, q Tn It represents the modal coordinates of a gantry crane of a certain order, and n is expressed as the order of the gantry crane vibration mode, ranging from 1 to M.

[0085] The relationship between the luffing trolley 2 and the gantry crane 1 is reflected by the contact force between the luffing trolley and the gantry crane. The contact force between the luffing trolley and the gantry crane can be regarded as the sum of the elastic force of the luffing trolley system on the gantry crane system and the gravity of the luffing trolley. Since the tires of the luffing trolley system are rigid tires, the elastic force is 0, f c (t) is expressed as:

[0086] f c (t) = -m v g (3)

[0087] Where g is the gravitational acceleration of the object, which is g = 9.8 m / s 2 .

[0088] The basic motion equations of the gantry crane system and the luffing trolley system have been listed above. Next, we will start to solve the response expressions of the above two systems. v and the frequency of the gantry crane ω Tn They are:

[0089]

[0090] Among them, k v Indicates the stiffness of the luffing trolley 2.

[0091] It should be noted here that since the luffing trolley is rigidly connected to the boom and there is no tire elastic force, the stiffness is not considered when simplifying the model, so the frequency of the luffing trolley will not be considered here.

[0092] From (5), we can get:

[0093]

[0094] Substituting formulas (2)-(5) into formula (1), combined with the zero boundary condition, the following is obtained:

[0095] u j (x,t)| x＝0,t＝0 =0 (7)

[0096]

[0097] u j (x,t)| x＝L,t＝0 =0 (9)

[0098]

[0099] The modal coordinates of the gantry crane system considering the contact force of the mobile luffing trolley can be obtained as follows:

[0100]

[0101] Substituting equation (11) into equation (2), the dynamic response of the gantry crane can be obtained as follows:

[0102]

[0103] It is easy to see from formula (12) that the response of each order of the gantry crane system is:

[0104]

[0105] Observing formula (13), we can get the following results. The various order responses of the simplified mathematical model of the gantry crane are affected by the combined influence of the two parameters of the boom position and the luffing trolley time. A simple trigonometric function analysis is performed on this. When the contact observation point on the selected boom meets the following conditions:

[0106]

[0107] In this case, sin(nπx / L)=0, that is, u n (x, t) = 0, so the modal response value received by the sensor at the corresponding moment of the observation point here is zero. For example, at the mid-span position of the gantry crane, x = L / 2, substituting into formula (14), we can get n = 2N, that is, the response of the 2nd, 4th, 6th and other even-order modes of the gantry crane system is zero at this position. In other words, in reality, the most common distributed accelerometer is used to measure the modal response value when an external load is applied. At the above position, since the even-order modal response of the gantry crane system is zero, theoretically no relevant data can be measured. In this way, when selecting the layout location of the sensor, the direct measurement method needs to consider in advance the data loss caused by these factors, which reduces the measurement efficiency to a certain extent, which also increases the workload and difficulty of the direct measurement method.

[0108] Another interesting phenomenon is that according to the response formula obtained above, it can be found that when the luffing trolley moves to any position on the gantry crane boom, the specific response value of the entire boom at that moment can be obtained. That is, the response value of the gantry crane can be derived from the response value of the luffing trolley, and the frequency of the gantry crane can be derived. Because during the movement of the luffing trolley, the moving position has the following time, speed and position relationship:

[0109] x c =vt,u c =u j (x,t)| x＝vt (15)

[0110] u c =u j (x,t)| x＝vt (16)

[0111] Among them, u c Expressed as the vertical displacement value of the luffing trolley.

[0112] Substituting formula (15) and formula (16) into formula (12), the response of the gantry crane system luffing trolley can be obtained as follows:

[0113]

[0114] Expanding the above formula, we can get the response of the variable-luffing trolley as follows:

[0115]

[0116] It can be expressed as:

[0117]

[0118] Each coefficient is expressed as:

[0119]

[0120] In the above formula, Δ st,n It is roughly equal to the deformation of the gantry crane when the luffing trolley is stationary on the boom. This is because the luffing trolley is light in weight, and the deformation of the gantry crane boom when it is stationary is small. The deformation at different positions cannot be reasonably expressed. n is a speed variable, they are:

[0121]

[0122] By taking the derivative of (19) twice, we can get the acceleration response formula of the variable-luffing trolley:

[0123]

[0124] It can be expressed as:

[0125]

[0126] It means that each coefficient is derived twice with respect to t, and each coefficient is expressed as:

[0127]

[0128] From formula (26), it can be clearly judged that the response of the luffing trolley is composed of two parts. One part is the driving frequency caused by the change of its own motion state. The frequency of this part is related to the speed and time of the trolley as nπvt / L. Secondly, when the luffing trolley moves on the boom of the gantry crane, the vibration of the gantry crane also changes with the mode of the luffing trolley, and the mode is nπx / L. When the luffing trolley is operating, it causes the boom to vibrate vertically, and its vibration wave is transmitted along the x-axis direction of the boom to form an excess frequency component, which is called the driving frequency here. It can be found that the reason for the generation of this frequency component is that the luffing trolley acts on the boom, and the boom transmits the action back to the luffing trolley, and the two interact with each other. Therefore, if the luffing trolley does not perform the luffing mechanism operation, then this frequency component will not be formed on the boom. The other part is the offset frequency of the gantry crane itself. The left frequency of the gantry crane is And gantry crane right frequency Obviously, the frequency of the gantry crane is related to its own properties and only to the speed of the luffing trolley. Under the simplified mathematical calculation model of this embodiment, the frequency component of the luffing trolley response is the same as the frequency component of the gantry crane. However, if other simplified calculation models that take into account the trolley stiffness are used, the luffing trolley response will also include the trolley's own natural frequency. The specific expressions of the driving frequency and the gantry crane frequency in this embodiment are as follows:

[0129]

[0130] It can be seen from formulas (30)-(32) that the left and right frequencies of the gantry crane are within the natural frequency ω of the gantry crane. Tn The frequency of the square of the amplitude nπv / L is increased or decreased based on the square of the amplitude nπv / L. The reason for this phenomenon is that the spatial position relationship between the luffing trolley and the crane arm changes over time, generating vibration waves. There is also a relative motion between the wave source and the receiver. When the wavelength is compressed, the frequency will increase, which is the right frequency of the gantry crane. When the wavelength is elongated, the frequency will decrease, which is the left frequency of the gantry crane. This phenomenon is called the Doppler phenomenon. In the simplified mathematical calculation model of the gantry crane assumed in this paper, the frequency composition contained in the response of the variable-length trolley is almost the same as that contained in the response of the gantry crane itself, which provides a theoretical basis and method guidance for the subsequent realization of intelligent detection of gantry crane movement.

[0131] In previous studies, there is no method to use the response of the luffing trolley to measure the response of the gantry crane. The present invention builds a luffing trolley-simply supported beam gantry crane and measures the acceleration response of the luffing trolley to accurately reflect the frequency of the gantry crane, and then detects and identifies the damage results of the gantry crane, providing a theoretical basis and method guidance for the subsequent intelligent damage detection of structural movement similar to that of a simply supported beam.

[0132] Next, we analyze the influence of the two parameters, the luffing speed and the weight of the hanging object, on the frequency recognition of the gantry crane based on the luffing trolley signal. The luffing speed parameter research is carried out by model test, and the hanging object weight parameter research is carried out by finite element simulation. If the model test is used to carry out the hanging object weight, the difference in the selected values ​​of the test scheme is not large, and it cannot obviously reflect the influence of the parameters on the method. This embodiment will study the influence of five luffing trolley speed conditions and five hanging object weight conditions on the method. The specific conditions are shown in Table 1:

[0133] Table 1 Parameter analysis working condition table

[0134]

[0135] The selection of the above working conditions depends on the investigation of the maximum luffing speed and the maximum lifting weight that can be achieved under the normal working state of the actual gantry crane. The luffing speed is based on the movement speed of the luffing trolley of the actual gantry crane converted into the motor rotation speed, and the lifting weight is determined by reducing it by about 20% according to the maximum lifting weight.

[0136] Before conducting this parameter research test, it is necessary to compare and analyze the accuracy of theoretical principles, finite element simulation and field tests. By using finite element simulation, theoretical derivation and field tests to identify the gantry crane frequency based on the variable-length trolley response on the same scale model, the smoothed frequency comparison results are Figure 3 As shown. Figure 3 It can be clearly seen that the finite element numerical simulation results are basically consistent with the test results, while the results obtained by theoretical derivation are slightly different. The reason for the different energy generated at the same frequency may be that the motion equation does not take the coupling effect between the vehicle and the tower into account, so the energy generated is smaller than the energy values ​​obtained by the other two methods. At the same time, since the theoretical derivation uses a simplified mathematical model of a simply supported beam, the effect of identifying the frequency is not as good as that of the finite element and model test.

[0137] After completing the mutual verification of the accuracy of the three methods of theory, finite element and model test, this paper first carried out the study of the variable-length trolley speed. Figure 4 The results of the frequency identification of the gantry crane by the luffing trolley response under different luffing speed conditions are shown. -3m / s (Case 1), it is a very low uniform motion state. The body response can identify the first-order frequency of the gantry crane, but the second-order frequency is difficult to identify. -3 m / s (Case 3), the body response can well identify the first and second order frequencies of the door crane. However, when the amplitude change speed exceeds the upper limit control, for example 2.1×10 -2 m / s (Case 5), the identified frequency will be seriously distorted. This may be because when the boom trolley moves faster, the acceleration sensor installed on the boom trolley will receive a larger deviation value in the same period of time, thus affecting the accuracy of data reception. In addition, when the boom speed is faster, the acceleration sensor will recognize the signal distortion, which will cause more serious spectrum leakage during FFT transformation, resulting in incorrect numerical analysis and affecting the accuracy of spectrum recognition. Based on the above analysis, it is believed that within the range of boom trolley speeds that the gantry crane can accept, when identifying the gantry crane frequency based on it, 25% to 80% of the maximum boom speed that can be achieved under the normal working state of the actual gantry crane should be used for modal recognition of the gantry crane, otherwise the measured results will be highly inaccurate.

[0138] In order to analyze the influence of the hoisting weight on the identification frequency of the gantry crane during the luffing movement of the trolley, the study was carried out at the actual luffing trolley working speed of 0.6m / s. The influence of the hoisting weight on the identification frequency of the gantry crane during the luffing movement was analyzed through MATLAB simulation. The results are as follows: Figure 5 As shown. Figure 5 It can be clearly seen that when the weight hung on the luffing trolley is greater, the response value of the luffing trolley can better identify the frequency of the portal crane. Figure 5When the medium-length variable-length trolley moves from static to starting to move, it is obvious that the greater the lifting weight, the greater the energy generated by the variable-length trolley when it is working. This is because the trolley does not generate any additional vibration when it is static. When the trolley starts to move at a uniform speed, the vertical deformation of the trolley changes, and then vertical vibration is generated. When the hanging weight is heavier, the deformation of the trolley is greater, the additional vibration response is greater, and the energy value of the identification frequency is greater. Carefully observing the first-order frequency in the figure, it can be found that under the working conditions of 160kg (Case1), 480kg (Case2) and 800kg (Case3), the left and right frequencies of the gantry crane at this order cannot be seen. The specific reasons have been analyzed above. According to the spacing formula of the left and right frequencies, it can be known that the left and right frequency spacing decreases with the decrease of the order. This reflects the second reason. When the lifting weight is heavy, the weight moves left and right with the trolley, which will cause the weight to swing, causing additional vibration of the gantry crane, resulting in obvious left and right frequency changes. Therefore, the lifting weight must be controlled within 25% to 60% of the maximum lifting weight that can be achieved under normal working conditions of the actual gantry crane, so that the luffing trolley can identify high-order frequencies without causing additional vibrations to the gantry crane that affect the accuracy of the recognition frequency of the luffing trolley. It should also be noted that when the mass is too large, the luffing trolley will cause geometric nonlinearity at the free end of the cantilever, and the degree of geometric nonlinearity is related to the mass size. The greater the weight, the greater the influence of the degree of geometric nonlinearity on the recognition frequency. Since geometric nonlinearity is different from the linear assumption of the recognition method in this article, it will affect the overall effect of point recognition. Therefore, this embodiment does not consider geometric nonlinearity, which is also a part of the recognition method that needs to be improved later.

[0139] In summary, since the luffing trolley is rigidly connected to the gantry crane, the body frequency of the luffing trolley is a high-order frequency and will not affect the identification of the gantry crane frequency. The frequency of the gantry crane can be well identified from the body response of the mobile luffing trolley. The frequency of the gantry crane is identified by theoretical derivation, finite element simulation and field test of the same gantry crane scale model. The identification results are consistent with each other, indicating that the feasibility of identifying the gantry crane frequency based on the response of the luffing trolley is excellent. The influence of different parameters, luffing speed and hoisting weight on the frequency identification method is analyzed. It is found that when the luffing trolley speed is slow, it is difficult to identify the gantry crane frequency, but when the speed is fast, the identification result will also be greatly distorted. When the speed is 25% to 80% of the maximum luffing speed of the actual gantry crane, the identification result is most accurate; when the lifting weight is controlled at 25% to 60% of the maximum lifting weight of the actual gantry crane, the luffing trolley can identify the high-order frequency without causing additional vibration of the gantry crane to affect the accuracy of the luffing trolley identification frequency.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A gantry crane damage detection method based on the acceleration response of the variable-luffing trolley, characterized in that: The following steps are involved: Step 1: Build a luffing trolley-simple-beam gantry crane system. The luffing trolley is set on the boom of the gantry crane. The boom length is set to L. The unit length mass of the gantry crane is The material elastic modulus of the gantry crane is E, the section inertia moment of the gantry crane is I, and the mass of the luffing trolley is m v ; Step 2: An acceleration sensor is arranged on the luffing trolley, and the luffing trolley moves on the boom of the gantry crane at a moving speed v. The acceleration sensor collects acceleration response data of the luffing trolley in real time and transmits it to a fast Fourier transform (FFT) conversion module; The expression of the acceleration response data of the luffing trolley is as follows: in, represents the acceleration response of the luffing trolley, represents the nth-order acceleration response coefficient, i represents a mathematical imaginary number, ω Tn represents the nth-order frequency of the simply supported beam system structure, t represents time, n represents the response order, 1≤n≤M, M represents the order range; v represents the speed of the variable-luffing trolley, and L represents the length of the gantry crane; Step 3: The fast Fourier transform (FFT) conversion module transforms the acceleration response data of the variable amplitude vehicle to obtain an acceleration spectrum diagram; Step 4: According to the acceleration spectrum diagram, the modal parameters of the gantry crane are identified; According to the peak distribution of the acceleration frequency spectrum, the modal parameters of the gantry crane are obtained, wherein the modal parameters include the natural frequency and vibration mode of the gantry crane, and the natural frequency includes the left frequency and the right frequency of the gantry crane; Step 5: Detect and identify the damage of the gantry crane according to the modal parameters or acceleration response data; The method used to detect and identify damage to the gantry crane is either: a. Damage identification method based on natural frequency change; b. Damage identification method based on vibration mode change; c. Damage identification method based on flexibility change; d. Damage identification method based on wavelet transform.

2. The gantry crane damage detection method based on the acceleration response of the luffing trolley according to claim 1 is characterized in that: In step 2, the nth order frequency ω of the gantry crane Tn The expression is as follows: The nth order acceleration response coefficient of the variable-luffing trolley The expression is as follows: Among them, A 1,n , A 2,n , A 3,n is the nth-order response coefficient of the luffing trolley, and its expression is as follows: Among them, Δ st,n is the deformation of the gantry crane, S n is the speed variable of the luffing trolley, and its expression is as follows: Where g represents the acceleration due to gravity, g = 9.8 m / s 2 .

3. The gantry crane damage detection method based on the acceleration response of the luffing trolley according to claim 1 is characterized in that: In step 4, the left frequency ω of the gantry crane Tn1 The expression is as follows: The right frequency ω of the gantry crane Tn2 The expression is as follows:

4. The gantry crane damage detection method based on the acceleration response of the luffing trolley according to claim 1 is characterized in that: In step 2, the movement speed v of the luffing trolley is controlled at 25%-80% of the maximum luffing speed of the gantry crane.

5. The gantry crane damage detection method based on the acceleration response of the luffing trolley according to claim 1 is characterized in that: In step 1, a hook is connected to the luffing trolley, and a hanging object is hung on the hook. The weight of the hanging object is controlled to be 25% to 60% of the maximum lifting weight of the gantry crane.

6. The gantry crane damage detection method based on the acceleration response of the luffing trolley according to claim 1 is characterized in that: In step 5, the damage identification method based on natural frequency change is as follows: A luffing trolley-simply supported beam gantry crane is built. Before the gantry crane is damaged, the luffing trolley moves on the gantry crane to obtain acceleration response data of the luffing trolley before damage, and a fast Fourier transform is performed to obtain an acceleration spectrum before damage, and the natural frequency of the gantry crane before damage is identified through the acceleration spectrum before damage; After the gantry crane is damaged, the acceleration response data of the luffing trolley after the damage is obtained by moving the luffing trolley on the gantry crane, and a fast Fourier transform is performed to obtain an acceleration spectrum after the damage, and the natural frequency of the gantry crane after the damage is identified by the acceleration spectrum after the damage; The natural frequency of the gantry crane before the damage and the natural frequency of the gantry crane after the damage are compared to obtain the damage result of the gantry crane.

7. The gantry crane damage detection method based on the acceleration response of the luffing trolley according to claim 1 is characterized in that: In step 5, the damage identification method based on vibration mode change is as follows: (1) Building a luffing trolley-simple-beam gantry crane, and obtaining acceleration response data of the luffing trolley by moving the luffing trolley on the gantry crane. (2) performing a fast Fourier transform on the acceleration response data of the variable-length trolley to obtain an acceleration spectrum diagram, and identifying the frequency of the gantry crane; (3) extracting response data related to the gantry crane frequency from the acceleration response data by using a bandpass filter method (BPS); (4) obtaining the instantaneous amplitude of the response data by using Hilbert transform; (5) obtaining the vibration mode of the gantry crane from the instantaneous amplitude; (6) performing regularization processing on the vibration mode of the gantry crane; (7) Identify the damage of the gantry crane by using the vibration mode curvature method or the vibration mode change graph method.

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