Method for detecting internal leakage of hydraulic cylinder and application thereof in TBM support shoe hydraulic cylinder

Abstract

This invention discloses a method for detecting internal leakage in hydraulic cylinders and its application in TBM support shoe hydraulic cylinders, comprising the following steps: S1, acquiring stroke data of the hydraulic cylinder within a predetermined time t1; S2, cleaning and segmenting the acquired hydraulic cylinder stroke data; S3, acquiring and filtering pressure data of the hydraulic cylinder in each specified time period; S4, performing wavelet decomposition and reconstruction on each group of filtered pressure data; S5, calculating the proportion of the energy of each order of high-frequency reconstructed signal in the total energy of the original pressure signal to determine whether internal leakage has occurred in the hydraulic cylinder. This invention completes the detection of internal leakage in TBM support shoe hydraulic cylinders using only pressure and stroke data, without the need to establish a complex physical model based on the geometric parameters of the TBM support shoe hydraulic cylinder, thus improving calculation speed and detection efficiency.

Description

Technical Field

[0001] This invention relates to the field of tunnel boring machine and hydraulic cylinder internal leakage detection technology, and more specifically to a method for detecting internal leakage in hydraulic cylinders and its application in the hydraulic cylinder of TBM support shoe. Background Technology

[0002] The hydraulic cylinder for the support shoe is a crucial component of the support system of a full-face tunnel boring machine (TBM). During TBM excavation, it not only provides sufficient support force but also adjusts the TBM's position and posture. Because the hydraulic cylinder for the support shoe frequently operates under strong vibration and high pressure, over time, components such as seals, piston rods, and cylinder bodies are highly susceptible to damage. This can lead to malfunctions such as leakage, insufficient support force, and poor stability, severely impacting the normal excavation of the TBM and causing incalculable economic losses and safety hazards. Therefore, it is essential to conduct timely internal leakage detection on the TBM hydraulic cylinder for the support shoe.

[0003] While existing technologies offer methods for detecting internal leaks in hydraulic cylinders, most are only applicable to cylinders operating under experimental conditions. These cylinders typically reciprocate under constant loads and work cycles, and are equipped with various sensors for flow, vibration, and strain. Some methods also require further analysis using the cylinder's geometric parameters and operating conditions to establish an accurate physical model of the internal leak. However, due to the limitations of on-site construction, the hydraulic cylinders of TBM support shoes lack a defined work cycle and are difficult to install with additional sensors. The collected data is easily affected by noise and tunneling conditions. Therefore, using current diagnostic methods for internal leak detection often results in significant errors.

[0004] Therefore, how to provide an internal leakage detection method that is applicable to TBM support shoe hydraulic cylinders and can be widely applied to other hydraulic cylinders is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method for detecting internal leakage in a hydraulic cylinder and its application in the hydraulic cylinder of a TBM support shoe, aiming to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for detecting internal leakage in a hydraulic cylinder includes the following steps:

[0008] S1. Obtain the stroke data of the hydraulic cylinder within a predetermined time t1;

[0009] S2. Clean and segment the acquired hydraulic cylinder stroke data;

[0010] S3. Obtain and filter the pressure data of the hydraulic cylinder for each specified time period;

[0011] S4. Perform wavelet decomposition and reconstruction on each of the selected pressure data groups;

[0012] S5. Calculate the proportion of the energy of each order of high-frequency reconstructed signal in the total energy of the original pressure signal to determine whether the hydraulic cylinder has internal leakage.

[0013] Preferably, in the above-mentioned method for detecting leakage in a hydraulic cylinder, in step S1, the predetermined time t1 is set to ensure that the hydraulic cylinder can undergo at least one process of returning from near the maximum stroke point to near the starting position.

[0014] Preferably, in the above-mentioned method for detecting leakage inside a hydraulic cylinder, step S2 specifically includes the following steps:

[0015] S2.1 Detect whether there is a travel maximum point in the data segment. If there is no travel maximum point in the data segment, the travel data obtained in step S1 is determined to be invalid data. Then return to step S1 and adjust the predetermined time t1 in step S1.

[0016] S2.2, sequentially determine whether each maximum stroke point in step S2.1 is the initial timing point for hydraulic cylinder retraction;

[0017] S2.3 Find the minimum point of travel corresponding to each maximum point of travel obtained in step S2.2. If a minimum point of travel corresponding to a certain maximum point of travel cannot be found, the maximum point of travel is determined to be invalid and needs to be removed.

[0018] S2.4 If no set of travel maximum and minimum points satisfying the conditions can be obtained after steps S2.2 and S2.3, the travel data obtained in step S1 is determined to be invalid data. Then, return to step S1 and adjust the predetermined time t1 in step S1.

[0019] Preferably, in the above-mentioned method for detecting internal leakage in a hydraulic cylinder, the judgment criteria in step S2.2 must simultaneously meet the following conditions:

[0020] a. The stroke value s1 at the peak point of the stroke is not less than the maximum stroke s of the hydraulic cylinder. max 95% of: s1 ≥ 0.95s max ;

[0021] b. Starting from the timing point corresponding to the maximum stroke value, the stroke value of the hydraulic cylinder continuously decreases within a predetermined time t2, where the predetermined time t2 is between the average time t required for the hydraulic cylinder to return from the maximum stroke point to the starting position. sBetween 70% and 90% of: 0.7t s ≤t2≤0.9t s ;

[0022] c. Starting from the timing point corresponding to the maximum stroke value, the range Δs in which the stroke value of the hydraulic cylinder decreases within a predetermined time t2 is not less than the maximum stroke s of the hydraulic cylinder. max 70% of: Δs ≥ 0.7s max Where t2 is the same as the predetermined time t2 in step b, s max With respect to the maximum stroke s of the hydraulic cylinder in step a max Consistent.

[0023] Preferably, in the above-mentioned method for detecting leakage inside a hydraulic cylinder, the method for finding the minimum stroke point in step S2.3 must simultaneously meet the following conditions:

[0024] a. The travel value at this point is lower than the travel value of the previous adjacent sampling point and not higher than the travel value of the next adjacent sampling point;

[0025] b. The stroke value s2 at this point is not greater than the maximum stroke s of the hydraulic cylinder. max 5% of: s² ≤ 0.05s max ;

[0026] c. The sampling time corresponding to this point is after the sampling time corresponding to the maximum travel point.

[0027] Preferably, in the above-mentioned method for detecting internal leakage in a hydraulic cylinder, the screening criteria in step S3 must simultaneously meet the following conditions:

[0028] a. The maximum value p of the selected pressure data max Between threshold p1 and threshold p2: p1≤p max ≤p2;

[0029] b. The range of change Δp of the selected pressure data in the first n1 seconds should not be less than the maximum value p of the selected pressure data. max 90% of: Δp ≥ 0.9p max ;

[0030] c. The value of the last data point of the selected pressure data should not exceed the threshold p3.

[0031] Preferably, in the above-mentioned method for detecting leakage in a hydraulic cylinder, the basis function selected for wavelet decomposition and reconstruction in step S4 is the db8 wavelet.

[0032] Preferably, in the above-mentioned method for detecting leakage in a hydraulic cylinder, the pressure signal is decomposed into wavelets four times.

[0033] Preferably, in the above-mentioned method for detecting leakage inside a hydraulic cylinder, in step S5, the formula for calculating the energy contained in a discrete signal is:

[0034]

[0035] In the formula, E is the energy of the signal segment, N is the number of sampling points of the signal segment, and x(i) is the value of the i-th sampling point of the signal segment;

[0036] After performing four wavelet decompositions and reconstructions on the original pressure signal, the energy proportion q of each order of high-frequency reconstructed signal in the original pressure signal is calculated. k The formula is:

[0037]

[0038] In the formula, E k E0 represents the energy of the k-th order high-frequency reconstructed signal, and E0 represents the energy of the original pressure signal.

[0039] In summary, the final formula for calculating the energy percentage is as follows:

[0040]

[0041] In the formula, n represents the number of groups of the original pressure signal, N represents the number of sampling points for each group of pressure signal, p0(i,j) represents the value of the j-th group of the original pressure signal at the ith sampling point, p k (i,j) represents the value of the j-th group of k-th order high-frequency reconstructed signal at the i-th sampling point;

[0042] When determining whether a hydraulic cylinder has internal leakage, the energy ratio of the fourth-order high-frequency reconstructed signal to the original pressure signal is selected as the main indicator parameter. When the energy ratio of the fourth-order high-frequency reconstructed signal is less than the threshold r, the hydraulic cylinder is considered to have internal leakage.

[0043] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a method for detecting internal leakage in a hydraulic cylinder and its application in the hydraulic cylinder of a TBM support shoe, which has the following beneficial effects:

[0044] 1. This invention utilizes the pressure sensor and displacement sensor commonly found in the hydraulic cylinder of the TBM support shoe to collect relevant signals, eliminating the need to add extra sensors and making it highly feasible.

[0045] 2. This invention can detect internal leakage of the TBM support shoe hydraulic cylinder using only the pressure and stroke data of the TBM support shoe hydraulic cylinder, without the need to build a complex physical model based on the geometric parameters of the TBM support shoe hydraulic cylinder, thus improving the calculation speed and detection efficiency.

[0046] 3. This invention can perform online testing of the TBM support shoe hydraulic cylinder when the TBM is in normal tunneling mode. It does not require disassembly of the TBM support shoe hydraulic cylinder, nor does it require specifying the specific working state of the TBM support shoe hydraulic cylinder, and has good application prospects in actual engineering. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0048] Figure 1 The attached figure is a flowchart illustrating the framework of the hydraulic cylinder internal leakage detection method provided by the present invention.

[0049] Figure 2 The attached figure is a graph showing the stroke data of the TBM support shoe hydraulic cylinder obtained by the present invention within a time period set in the embodiment;

[0050] Figure 3 The attached figure shows the rod chamber pressure data of the TBM support shoe hydraulic cylinder provided by the present invention within a specified time period (284 seconds to 338 seconds);

[0051] Figure 4 The attached figure shows the rod chamber pressure data of the TBM support shoe hydraulic cylinder provided by the present invention during a specified time period (3045 seconds to 3079 seconds). Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] See appendix Figure 1 This invention discloses a method for detecting internal leakage in the hydraulic cylinder of a TBM support shoe, specifically including the following steps:

[0054] Step 1: Obtain the stroke data of the TBM support shoe hydraulic cylinder within a predetermined time t1.

[0055] The predetermined time t1 can be set according to the specific working conditions of the TBM. It should be ensured that the TBM completes at least one step change within the set time, that is, the TBM support shoe hydraulic cylinder undergoes at least one process of returning from near the maximum stroke point to near the starting position.

[0056] Step 2: Clean and segment the acquired TBM support shoe hydraulic cylinder stroke data, specifically including:

[0057] Step 2.1: Detect whether there is a travel maximum point in the data segment, that is, the travel value of the point is not lower than the travel value of the previous adjacent sampling point and higher than the travel value of the next adjacent sampling point. If there is no travel maximum point in the data segment, the travel data obtained in Step 1 is determined to be invalid data, and it is necessary to return to Step 1 and adjust the predetermined time t1 in Step 1. Specifically, the predetermined time t1 can be appropriately increased or the starting timing point can be changed.

[0058] Step 2.2: Sequentially determine whether each maximum stroke point in Step 2.1 is the initial timing point for the retraction of the TBM support shoe hydraulic cylinder. The specific criterion is as follows:

[0059] (1) The stroke value s1 at the peak of the stroke is not less than the maximum stroke s of the TBM support shoe hydraulic cylinder. max 95%, that is, s1 ≥ 0.95s max , where s max The value can be set according to the geometric parameters of the TBM support shoe hydraulic cylinder.

[0060] (2) Starting from the timing point corresponding to the maximum stroke value, the stroke value of the TBM support shoe hydraulic cylinder continuously decreases within a predetermined time t2, meaning that the stroke value at any sampling point within the predetermined time t2 is higher than the stroke values ​​at all subsequent sampling points. The predetermined time t2 can be set according to the specific working conditions of the TBM, and is typically between the average time t required for the TBM support shoe hydraulic cylinder to return from its maximum stroke point to its starting position. s Between 70% and 90%, that is, 0.7t s ≤t2≤0.9t s .

[0061] (3) Starting from the timing point corresponding to the maximum stroke value, the range Δs of the TBM support shoe hydraulic cylinder's stroke value decreasing within a predetermined time t2 should not be less than the maximum stroke s of the TBM support shoe hydraulic cylinder. max 70%, that is, Δs ≥ 0.7s max , where t2 is consistent with the predetermined time t2 in (2), s max With the maximum stroke s of the TBM support shoe hydraulic cylinder in (1) max Consistent.

[0062] If any of the above three criteria are not met, the maximum value point of the stroke is determined to be not the initial timing point for the retraction of the TBM support shoe hydraulic cylinder, and it needs to be discarded.

[0063] Step 2.3: Find the minimum stroke point corresponding to each maximum stroke point obtained in Step 2.2, i.e., the termination timing point when the TBM support shoe hydraulic cylinder retracts to the starting position. This minimum stroke point must satisfy the following:

[0064] (1) The travel value of this point is lower than the travel value of the previous adjacent sampling point and not higher than the travel value of the next adjacent sampling point.

[0065] (2) The stroke value s2 at this point is not greater than the maximum stroke s of the TBM support shoe hydraulic cylinder. max 5%, that is, s² ≤ 0.05s max .

[0066] (3) The sampling time corresponding to this point is after the sampling time corresponding to the maximum travel point.

[0067] If a minimum point corresponding to a maximum point of travel cannot be found based on the above three conditions, then the maximum point of travel is deemed invalid and must be removed.

[0068] If no set of travel maximum and minimum points that meet the conditions can be obtained after steps 2.2 and 2.3, the data obtained in step 1 is determined to be invalid data. It is necessary to return to step 1 and adjust the predetermined time t1 in step 1. Specifically, the predetermined time can be increased or the starting timing point can be changed.

[0069] Step 3: Obtain and filter the pressure data of the TBM support shoe hydraulic cylinder for each specified time period.

[0070] The specified time period is determined by the sampling time corresponding to the maximum and minimum stroke points obtained in step 2. However, since the change in hydraulic cylinder stroke data is controlled by the hydraulic cylinder pressure signal and lags behind the change in pressure signal, in order to grasp a more complete change in the TBM support shoe hydraulic cylinder pressure signal, the sampling time corresponding to the maximum stroke point can be moved forward or the sampling time corresponding to the minimum stroke point can be moved backward according to the actual situation, so as to extend the specified time for acquiring pressure data.

[0071] The pressure data specifically refers to the rod chamber pressure data of the TBM support shoe hydraulic cylinder.

[0072] The purpose of the screening is to ensure that the acquired pressure data varies within a certain range and covers the three common stages of hydraulic cylinder operation: pressure increase, pressure holding, and pressure release. The screening criteria are as follows:

[0073] (1) The maximum value p of the selected pressure data max It must be between the threshold p1 and the threshold p2, that is, p1≤p max≤p2, where the sizes of p1 and p2 can be set according to the actual working conditions of the TBM.

[0074] (2) The range of change of the selected pressure data in the first n1 seconds, Δp, should not be less than the maximum value p of the selected pressure data. max 90%, that is, Δp ≥ 0.9p max The size of n1 can be set according to the actual working conditions of the TBM.

[0075] (3) The value of the last data point of the selected pressure data should not be greater than the threshold p3, where the size of p3 can be set according to the actual working conditions of the TBM.

[0076] If no set of pressure data that meets the conditions can be obtained after the above screening process, the travel data obtained in step 1 is determined to be invalid data. It is necessary to return to step 1 and adjust the predetermined time t1 in step 1. Specifically, the predetermined time can be increased or the starting timing point can be changed.

[0077] Step 4: Perform wavelet decomposition and reconstruction on each selected group of pressure data.

[0078] The basis functions chosen for wavelet decomposition and reconstruction are db8 wavelets. Here, db represents the Daubechies wavelet series, and 8 indicates the wavelet order is 8. The Daubechies wavelet series is a wavelet function constructed by the renowned physicist and mathematician Ingrid Daubechies. Its support region in the wavelet and scaling functions is 2N-1, and the vanishing moment of the wavelet function is N (N represents the wavelet order). Except for the db1 wavelet, the other db wavelets lack symmetry and explicit functional expressions, but the square modulus of the transformation function h for all db wavelets is definite. For an Nth-order db wavelet, let... in Let h be the binomial coefficients, then the square modulus of the transformation function h can be expressed as: In the formula, h k This represents the k-th order transformation function. Studies have shown that the db8 wavelet can accurately detect abrupt changes and discontinuities in signals, demonstrating excellent performance in processing non-stationary signals. Using it to decompose pressure data allows for further analysis of the signal distribution across different frequency bands in the original signal, providing a valuable basis for diagnosing leaks within hydraulic cylinders.

[0079] The pressure signal was decomposed into wavelet coefficients four times. After four wavelet decompositions, the original pressure signal was decomposed into five groups of wavelet coefficients of different lengths: one group of low-frequency approximation coefficients—the fourth-order low-frequency coefficient (cA4) and four groups of high-frequency detail coefficients—the first-order high-frequency coefficient (cD1), the second-order high-frequency coefficient (cD2), the third-order high-frequency coefficient (cD3), and the fourth-order high-frequency coefficient (cD4).

[0080] Wavelet reconstruction is essentially the inverse operation of wavelet decomposition, restoring the wavelet coefficients obtained from wavelet decomposition to a reconstructed signal with the same length as the original signal. After reconstructing the five sets of wavelet coefficients (cA4, cD1, cD2, cD3, and cD4), the original pressure signal was completely divided into five sub-signals of different frequency bands: a low-frequency approximation signal (sA), a first-order high-frequency detail signal (sD1), a second-order high-frequency detail signal (sD2), a third-order high-frequency detail signal (sD3), and a fourth-order high-frequency detail signal (sD4). Let the sampling frequency of the original pressure signal be f. The frequency range corresponding to the obtained low-frequency approximation signal is 0–0.0625f, and the frequency ranges corresponding to the high-frequency detail signals are, respectively: 0.5f–f (sD1), 0.25f–0.5f (sD2), 0.125f–0.25f (sD3), and 0.0625f–0.125f (sD4).

[0081] Step 5: Calculate the proportion of the energy of each order of high-frequency reconstructed signal in the total energy of the original pressure signal to determine whether the TBM support shoe hydraulic cylinder has internal leakage.

[0082] The formula for calculating the energy contained in a discrete signal is as follows:

[0083]

[0084] In the formula, E is the energy of the signal segment, N is the number of sampling points of the signal segment, and x(i) is the value of the i-th sampling point of the signal segment;

[0085] After performing four wavelet decompositions and reconstructions on the original pressure signal, the energy proportion q of each order of high-frequency reconstructed signal in the original pressure signal is calculated. k The formula is:

[0086]

[0087] In the formula, E k E0 represents the energy of the k-th order high-frequency reconstructed signal, and E0 represents the energy of the original pressure signal.

[0088] Because the pressure data obtained in steps 1-3 may include multiple sets of data from different time periods, the wavelet decomposition and reconstruction in step 4 may also yield multiple sets of reconstructed signals in the same frequency band. In order to analyze multiple sets of data in a centralized manner, it is necessary to first accumulate the energy of multiple sets of high-frequency reconstructed signals of the same order and the energy of multiple sets of original pressure signals, and then calculate the energy ratio of each order of high-frequency reconstructed signals.

[0089] In summary, the final formula for calculating the energy percentage is as follows:

[0090]

[0091] In the formula, n represents the number of groups of the original pressure signal, N represents the number of sampling points for each group of pressure signal, p0(i,j) represents the value of the j-th group of the original pressure signal at the ith sampling point, p k (i,j) represents the value of the j-th group of k-th order high-frequency reconstructed signal at the i-th sampling point;

[0092] When determining whether internal leakage has occurred in the hydraulic cylinder of the TBM support shoe, the energy ratio of the 4th-order high-frequency reconstructed signal to the original pressure signal is selected as the main indicator parameter. When the energy ratio of the 4th-order high-frequency reconstructed signal is less than the threshold r, the TBM support shoe hydraulic cylinder is considered to have internal leakage. The threshold r can be set based on experimental analysis and the actual working conditions of the TBM.

[0093] Example:

[0094] 1. Set the predetermined time t1 in step S1 to 1 hour (3600 seconds), and obtain the stroke data of the TBM support shoe hydraulic cylinder during this time period, as follows: Figure 2 As shown in the figure, the stroke information of the TBM support shoe hydraulic cylinder can be used to determine that the TBM completed two step-changing processes within the predetermined time t1.

[0095] 2. Based on the criteria in step S2.1, 941 maximum travel points were detected in this data segment; further, the maximum travel s in step S2.2 was set. max Given a travel length of 450 mm and a predetermined time t2 of 30 seconds, the 941 travel maximum points in step S2.1 are sequentially evaluated. Two travel maximum points that meet the conditions are obtained: the travel value at the 284th second (448.277 mm) and the travel value at the 3045th second (446.771 mm). By appropriately shifting the sampling time corresponding to these two travel maximum points, the corresponding travel minimum points can be found by the criteria in step S2.3: the travel value at the 338th second (2.218 mm) and the travel value at the 3079th second (17.098 mm).

[0096] 3. In step S3, set p1 to 80 bar, p2 to 120 bar, p3 to 10 bar, and n1 to 10 seconds. Analyze the rod-side pressure data of the TBM support shoe hydraulic cylinder during the two specified time periods (284 seconds–338 seconds and 3045 seconds–3079 seconds). Since the pressure increase and decrease processes of the TBM support shoe hydraulic cylinder are relatively slow during these two time periods, this embodiment has adjusted the specified time for acquiring pressure data based on actual conditions. The final two pressure data segments are as follows: Figure 3 and Figure 4 As shown. The maximum value p of the two pressure data segments. max The pressure readings were 102.0833 bar and 85.15625 bar, respectively; the range of change (Δp) of the two pressure data points within the first 10 seconds was 93.837 bar and 77.879 bar, respectively; and the values ​​of the two pressure data points at the last data point were 9.664351463 bar and 7.552083492 bar, respectively. Calculations show that both extracted pressure data points are valid and can be used as the basis for constructing the leakage index of the TBM support shoe hydraulic cylinder.

[0097] 4. Perform four wavelet decompositions and reconstructions on the two pressure data segments above using the db8 wavelet, decomposing each original signal into one low-frequency approximate signal and four high-frequency detail signals of different frequencies.

[0098] 5. Calculate the energy proportion of each order of high-frequency reconstructed signal in the original signal. Select the energy proportion of the 4th order high-frequency reconstructed signal as the main indicator parameter for judging whether internal leakage has occurred in the TBM support shoe hydraulic cylinder, and set the threshold r to 0.015. The total energy of the two 4th order high-frequency reconstructed signals is calculated to be 8087.540, and its energy proportion in the original pressure signal is 0.0093, which does not exceed the threshold r. Therefore, it can be concluded that no internal leakage has occurred in the TBM support shoe hydraulic cylinder during the operation within the predetermined time t1.

[0099] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0100] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting internal leakage in a hydraulic cylinder, characterized in that, Includes the following steps: S1. Obtain the hydraulic cylinder at the predetermined time. t Trip data within 1; S2. Clean and segment the acquired hydraulic cylinder stroke data; S3. Obtain and filter the pressure data of the hydraulic cylinder for each specified time period; S4. Perform wavelet decomposition and reconstruction on each of the selected pressure data groups; S5. Calculate the proportion of the energy of each order of high-frequency reconstructed signal in the total energy of the original pressure signal to determine whether the hydraulic cylinder has internal leakage. Step S2 specifically includes the following steps: S2.1 Detect whether there is a travel maximum point in the data segment. If there is no travel maximum point in the data segment, the travel data obtained in step S1 is determined to be invalid data. Then return to step S1 and adjust the predetermined time in step S1. t 1. Make adjustments; S2.2, sequentially determine whether each maximum stroke point in step S2.1 is the initial timing point for hydraulic cylinder retraction; S2.3 Find the minimum point of travel corresponding to each maximum point of travel obtained in step S2.

2. If a minimum point of travel corresponding to a certain maximum point of travel cannot be found, the maximum point of travel is determined to be invalid and needs to be removed. S2.4 If, after steps S2.2 and S2.3, no set of travel maximum and minimum points satisfying the conditions can be obtained, then the travel data obtained in step S1 is determined to be invalid data. Therefore, the process returns to step S1 and the predetermined time in step S1 is adjusted. t 1. Make adjustments; The judgment criteria for step S2.2 must simultaneously meet the following conditions: a. The travel value at the peak point of the trip s 1. Not less than the maximum stroke of the hydraulic cylinder s max 95% of: s 1≥0.95 s max ; b. Starting from the timing point corresponding to the maximum stroke value, the stroke value of the hydraulic cylinder continuously decreases within a predetermined time t2. t 2. Given the average time required for the hydraulic cylinder to retract from its maximum stroke point to its starting position. t s Between 70% and 90%: 0.7 t s ≤ t 2≤0.9 t s ; c. Starting from the timing point corresponding to the maximum stroke value, the stroke value of the hydraulic cylinder is within a predetermined time. t The range of descent Δs within 2 hours shall not be less than the maximum stroke of the hydraulic cylinder. s max 70% of: Δs≥0.7 s max ,in t 2. The scheduled time in step b t 2. Consistent s max With the maximum stroke of the hydraulic cylinder in step a s max Consistent.

2. The method for detecting internal leakage in a hydraulic cylinder according to claim 1, characterized in that, In step S1, the predetermined time t The setting of 1 ensures that the hydraulic cylinder can undergo at least one process of returning from near the maximum stroke point to near the starting position.

3. The method for detecting internal leakage in a hydraulic cylinder according to claim 1, characterized in that, The method for finding the minimum point of the journey in step S2.3 must simultaneously meet the following conditions: a. The travel value at this point is lower than the travel value of the previous adjacent sampling point and not higher than the travel value of the next adjacent sampling point; b. Travel distance at this point s 2. Not greater than the maximum stroke of the hydraulic cylinder s max 5% of: s 2≤0.05 s max ; c. The sampling time corresponding to this point is after the sampling time corresponding to the maximum travel point.

4. The method for detecting internal leakage in a hydraulic cylinder according to claim 1, characterized in that, The selection criteria in step S3 must simultaneously meet the following conditions: a. Maximum value of the selected pressure data p max Between the threshold p 1 and threshold p Between 2: p 1≤ p max ≤ p 2; b. Selected pressure data is listed first. n The range of numerical change Δ in 1 second p It should not be less than the maximum value of the selected pressure data. p max 90% of: Δ p ≥0.9 p max ; c. The value of the last data point in the selected pressure data should not exceed the threshold. p 3.

5. The method for detecting internal leakage in a hydraulic cylinder according to claim 1, characterized in that, The basis function selected for wavelet decomposition and reconstruction in step S4 is the db8 wavelet.

6. A method for detecting internal leakage in a hydraulic cylinder according to any one of claims 1-5, characterized in that, The pressure signal was decomposed into wavelets four times.

7. The method for detecting internal leakage in a hydraulic cylinder according to claim 6, characterized in that, In step S5, the formula for calculating the energy contained in a discrete signal is as follows: ； In the formula, E The energy of this signal segment. N This represents the number of sampling points for this signal segment. x ( i ) is the first segment of the signal. i The values ​​of each sampling point; After performing four wavelet decompositions and reconstructions on the original pressure signal, the energy proportion of each order of high-frequency reconstructed signal in the original pressure signal was calculated. q k The formula is: ； In the formula, E k Indicates the first k The energy of the high-frequency reconstructed signal, E 0 represents the energy of the original pressure signal; In summary, the final formula for calculating the energy percentage is as follows: ； In the formula, n The number of groups representing the original pressure signal. N This represents the number of sampling points for each pressure signal. p 0( i , j ) represents the j-th group of original pressure signals in the first position. i The value of each sampling point p k ( i , j ) represents the first j Group k The first-order high-frequency reconstructed signal is in the first order. i The values ​​of each sampling point; When determining whether internal leakage has occurred in a hydraulic cylinder, the energy ratio of the 4th-order high-frequency reconstructed signal to the original pressure signal is selected as the main indicator parameter. When the energy ratio of the 4th-order high-frequency reconstructed signal is less than a threshold... r At that time, it was determined that the hydraulic cylinder had an internal leak.

8. The application of the hydraulic cylinder internal leakage detection method according to any one of claims 1-7 in the hydraulic cylinder of a TBM support shoe.

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