Escalator main driving chain elongation detection method and system

Abstract

The invention discloses a method and system for detecting elongation of a main driving chain of an escalator, and the method comprises the steps: judging whether the escalator is in a stable stop state or not by analyzing an image sequence, collected by a camera, of a main driving chain region; when the stable stop state is confirmed, collecting a static digital image of the main driving chain; processing the static digital image, and extracting and fitting a droop curve of the main driving chain; and calculating the sag of the main driving chain based on the sag curve, and calculating the elongation of the main driving chain through a geometric model according to the sag. The method is easy to operate and low in maintenance cost, the accuracy of main driving chain elongation detection is improved, and a non-contact and transformation-free online detection scheme capable of directly converting the absolute elongation is provided for detecting the elongation of the escalator driving chain.

Description

Technical Field

[0001] This invention belongs to the field of special equipment testing technology, and relates to a method and system for detecting the elongation of the main drive chain of an escalator. Background Technology

[0002] The main drive chain of an escalator is the core load-bearing component for transmitting power. During long-term operation, wear on chain links and loosening of pins can lead to cumulative elongation of the pitch. When the elongation exceeds the safety threshold (usually 1%-2% of the original length), it can easily cause chain slippage and tooth skipping, and in severe cases, chain breakage, resulting in sudden escalator stoppage or injury to passengers. Existing research mainly focuses on chain drive systems in automobiles and scraper conveyors, with limited research on chain drives in escalators and moving walkways. Current methods for detecting chain elongation include manual inspection and the addition of sensors and auxiliary devices to the sprockets and chain discs. Both methods are affected by numerous factors. The former requires stopping the machine and manual measurement, resulting in low efficiency and significant subjective errors; the latter uses sensors with low accuracy, leading to large errors in the detection results, high maintenance costs, and potential disruption to normal equipment operation.

[0003] The technical solution described in Chinese patent application "CN115754328A A Real-time Detection Method for Chain Elongation of Escalators and Moving Walkways" involves real-time detection without stopping the machine. However, during long-term operation of escalators, the pads are susceptible to damage from friction (such as contact between the chain and the guide rail), vibration, and oil contamination, leading to issues such as detachment, wear, or decreased reflectivity. Once the pads fail, the laser signal cannot be reflected normally, causing detection interruption or data distortion, requiring machine shutdown for inspection and replacement, thus affecting normal equipment use. Furthermore, the installation location of the detection terminal and the synchronization of multiple terminals directly affect detection accuracy, but the solution does not mention effective calibration methods. Accurate elongation detection requires corresponding calibration measures, and the long-term operation of this technical solution relies on continuous maintenance, which demands high technical skills from maintenance personnel.

[0004] Chinese patent application CN114440812A, "Method and Device for Detecting Chain Elongation," transforms "chain elongation, which is difficult to measure directly," into "the easily detectable arc length of the driving / driven wheel rotation," thus avoiding the drawbacks of manual measurement. However, the arc length detection method provided by this technical solution still relies on adding sensors or rotary encoders to calculate the arc length. The detection device depends on multiple precision components (such as rotary encoders and linear velocity sensors). These components are easily contaminated in dusty and oily environments such as escalators. For example, dust accumulation on the shaft sleeve of a rotary encoder can lead to coaxiality deviation, and oil covering the probe of a linear velocity sensor can reduce detection sensitivity. These factors can cause detection interruptions or data errors, increasing detection errors and raising equipment maintenance costs and safety risks. Summary of the Invention

[0005] To address the aforementioned technical problems, the purpose of this invention is to provide a system for detecting and controlling the elongation of the main drive chain of an escalator.

[0006] This invention provides a method for detecting the elongation of the main drive chain of an escalator, comprising:

[0007] Step 1: By analyzing the image sequence of the main drive chain area captured by the camera, determine whether the escalator is in a stable stopped state;

[0008] Step 2: When the stable stopping state is confirmed, acquire a static digital image of the main drive chain;

[0009] Step 3: Process the static digital image to extract and fit the droop curve of the main driving chain;

[0010] Step 4: Based on the droop curve, calculate the sag of the main drive chain, and calculate the elongation of the main drive chain using a geometric model based on the sag.

[0011] The present invention also provides a system for detecting the elongation of the main drive chain of an escalator, comprising:

[0012] The image acquisition unit is used to acquire images of the main drive chain area of ​​the escalator.

[0013] An illumination unit is used to provide illumination for the image acquisition unit;

[0014] A control and processing unit, connected to the image acquisition unit and the illumination unit, is used to control image acquisition, process image data, and calculate elongation.

[0015] The data storage and communication unit is connected to the control and processing unit and is used for storing data and external communication.

[0016] The present invention provides a system for detecting and controlling the elongation of the main drive chain of an escalator, which has the following advantages:

[0017] (1) The present invention realizes full automation from state perception, image acquisition to result calculation, completely freeing up manpower and greatly improving detection efficiency;

[0018] (2) The present invention uses machine vision technology, which eliminates the safety hazard by eliminating the need for personnel to approach the operating parts;

[0019] (3) This invention suppresses reflections through an optimized imaging system, and avoids human error by combining precise image processing algorithms and physical models. The results are objective, reliable and have good repeatability.

[0020] (4) The system of the present invention can automatically detect and record data periodically. By analyzing the historical trend of elongation, it can issue an early warning in time before the chain reaches the scrap standard, changing passive maintenance to active prevention and avoiding sudden failures.

[0021] (5) This invention integrates visual perception, intelligent processing and communication early warning into one, and uses general industrial vision components. It can be installed once and used for a long time, reducing the maintenance cost throughout the entire life cycle. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for detecting the elongation of the main drive chain of an escalator according to the present invention;

[0023] Figure 2 This is a schematic diagram of the geometric relationship between the sag of the main drive chain and the chain length. Detailed Implementation

[0024] like Figure 1 As shown, the present invention provides a method for detecting the elongation of the main drive chain of an escalator, comprising:

[0025] Step 1: By analyzing the image sequence of the main drive chain area captured by the camera, determine whether the escalator is in a stable stopped state. Specifically:

[0026] Step 1.1: Analyze the image sequence of the continuously acquired main drive chain region using optical flow method, and calculate the motion vector of feature points in the image.

[0027] Step 1.2: If the average value of the motion vectors in multiple consecutive frames is lower than a preset threshold, the escalator is determined to be in a stable stopped state.

[0028] Step 2: When the stable stopping state is confirmed, acquire a static digital image of the main drive chain;

[0029] In practice, the static digital images are acquired under low-angle linear illumination or backlighting conditions, and polarized light is used to suppress reflections on the chain surface.

[0030] The low-angle linear lighting condition refers to: installing a strip light source parallel to the drive chain and illuminating it from the side of the chain at an angle of <15°.

[0031] The backlighting conditions refer to installing a strip light source behind the chain so that the chain forms a clear silhouette in the camera's field of view.

[0032] Step 3: Process the static digital image to extract and fit the droop curve of the main driving chain, specifically as follows:

[0033] Step 3.1: Convert the acquired static digital image to grayscale, and then use a Gaussian filter or median filter to smooth and denoise it, preserving edges while suppressing noise.

[0034] Step 3.2: Define the main drive chain in the image as the region of interest, which precisely covers the entire drooping section from the upper sprocket to the lower chain, excluding interference from other irrelevant structures.

[0035] Step 3.3: Perform edge detection within the region of interest to obtain edge pixels.

[0036] Step 3.4: Based on the length, area, position and geometric features of the contour, intelligently filter out the contours that represent the lower edge of the main driving chain from all edge pixels.

[0037] Step 3.5: The selected contour of the lower edge of the main driving chain, which is composed of discrete pixels, is fitted with a quadratic curve or spline curve using the least squares method to obtain a smooth and continuous digital curve, namely the drooping curve.

[0038] Step 4: Based on the sag curve, calculate the sag of the main drive chain, and calculate the elongation of the main drive chain using a geometric model based on the sag. Figure 2 This is a schematic diagram of the geometric relationship between the sag and length of the main drive chain. The calculation process for the elongation of the main drive chain is as follows:

[0039] Step 4.1: Determine the tangent points A and B at the bottom of the sprockets at the left and right ends of the drive chain in the image, and connect the two points to obtain the reference chord.

[0040] Step 4.2: Calculate the pixel value L of the reference chord length. P Using the known actual length L of the reference chord R Perform calibration and calculate the pixel equivalent K;

[0041]

[0042] Step 4.3: Traverse all points on the fitted sag curve, calculate the vertical distance from each point to the reference chord, find the maximum vertical distance, and record it as the pixel value D of the maximum sag.

[0043] Step 4.4: Using the pre-calibrated pixel equivalent K, convert the pixel value D of the sag into the actual physical sag value S;

[0044]

[0045] Step 4.5: Combine the actual physical sag value S with the known actual length L of the reference chord. R Substituting the values, we can calculate the current length L of the main drive chain:

[0046]

[0047] Step 4.6: Based on the original length L of the main drive chain O Calculate the elongation ΔL of the main drive chain based on the current length L.

[0048] The present invention also provides an escalator main drive chain elongation detection system for implementing the above detection method, comprising: an image acquisition unit, an illumination unit, a control and processing unit, and a data storage and communication unit.

[0049] The image acquisition unit is used to acquire images of the main drive chain area of ​​the escalator. The image acquisition unit includes: a camera module, a mounting bracket, and a polarizing filter.

[0050] The camera module uses an industrial-grade digital camera with a resolution of at least 2 megapixels and employs a global shutter sensor. The mounting bracket is used to rigidly fix the camera module to the side of the escalator's main drive chain. It must be decoupled from the escalator's vibration to avoid image blurring caused by escalator vibration; the optical axis should be perpendicular to the plane of the drive chain. A polarizing filter is placed in front of the camera module's lens. By rotating the polarizing filter and coordinating it with the polarized light from the illumination unit, highlights and diffuse reflections on the drive chain's metal surface can be minimized, resulting in a high-contrast image of the chain edges.

[0051] The illumination unit is used to provide illumination for the image acquisition unit. The illumination unit includes an LED strip light source and a polarizer disposed in front of the LED strip light source. The illumination unit is configured to provide low-angle linear illumination or backlight illumination for the main drive chain.

[0052] The low-angle linear lighting refers to installing a strip light source parallel to the drive chain and illuminating the chain from the side at an angle of less than 15°. This "grazing light" can project clear shadows onto the edges and uneven surfaces of the chain plates, greatly enhancing the contrast of edge features.

[0053] The backlighting refers to installing a strip light source behind the chain, creating a clear silhouette of the chain in the camera's field of view. This method perfectly extracts the overall outline of the chain, and is particularly suitable for extracting drooping curves.

[0054] A polarizer is installed in front of the LED strip light source to emit polarized light in a specific direction. Working in conjunction with a polarizing filter in front of the lens, it forms a cross-polarization system, which can effectively suppress specular reflection, penetrate surface reflections, and capture the true details of the object's surface.

[0055] The control and processing unit, connected to the image acquisition unit and the illumination unit, is used to control image acquisition, process image data, and calculate elongation. The control and processing unit includes: a status recognition module, an image processing module, a sag calculation module, and an elongation calculation module.

[0056] The status recognition module is used to analyze the image sequence of the main drive chain area captured by the camera to determine whether the escalator is in a stable stopped state, and after confirming that the escalator is in a stable stopped state, it issues an image acquisition trigger command.

[0057] In practice, the state recognition module runs the optical flow algorithm to analyze the continuously acquired image sequence. When the average motion vector of multiple consecutive frames is lower than a preset threshold, it is determined to be in a stable stopping state.

[0058] The image processing module is used to perform smoothing and denoising processing on the acquired static digital images, define regions of interest, perform edge detection, extract the contour of the lower edge of the main driving chain, and perform curve fitting to obtain the droop curve of the main driving chain. In specific implementations, the image processing module includes:

[0059] Preprocessing submodule: Converts the acquired static digital image to grayscale, and then uses a Gaussian filter or median filter to smooth and denoise it, preserving edges while suppressing noise.

[0060] ROI Definition Submodule: Defines the main drive chain in the image as the region of interest, which precisely covers the entire drooping segment from the upper sprocket to the lower chain, excluding interference from other irrelevant structures.

[0061] Edge detection and contour extraction submodule: Within the ROI, algorithms such as the Canny edge detector are used to extract all edge pixels in the image. Subsequently, based on the contour's length, area, position, and geometric features (such as the contour's approximate polygonal shape), the longest contour most likely representing the lower edge of the driving chain is intelligently selected from all edges.

[0062] The curve fitting submodule takes the selected contour, composed of discrete pixels, and performs quadratic curve fitting or spline curve fitting using the least squares method to obtain a smooth, continuous digital curve, i.e., a drooping curve. This curve is the basis for subsequent accurate calculations.

[0063] The sag calculation module is used to calculate the maximum sag value of the main drive chain based on the sag curve, the preset reference chord, the pixel value of the reference chord length, and the actual length of the reference chord.

[0064] In practice, the reference chord is obtained by connecting the bottommost tangent points A and B of the sprockets at the left and right ends of the drive chain in the image.

[0065] The elongation calculation module is used to calculate the current length and elongation of the main drive chain based on the maximum sag value using a geometric model.

[0066] The formula for calculating the current length L of the main drive chain is:

[0067]

[0068]

[0069]

[0070] Where L is the current length of the main driving chain, L R The reference chord's actual length is given by L, where S is the actual physical sag value. P is the pixel value of the reference chord length; D is the maximum vertical distance from all points on the sag curve to the reference chord, recorded as the pixel value of the maximum sag.

[0071] The data storage and communication unit, connected to the control and processing unit, is used for data storage and external communication. The data storage and communication unit includes:

[0072] The data storage module is used to store system parameters, historical detection data, and early warning thresholds;

[0073] The communication interface module provides wired or wireless communication interfaces for sending detection results and early warning information to the remote monitoring center.

[0074] This invention proposes a method for detecting the elongation of the main drive chain of an escalator based on machine vision (optical flow method), which realizes the full automation of the detection process, ensures that images are acquired only at the optimal time (in a static state), and guarantees the validity of the data.

[0075] This invention designs an imaging scheme that incorporates low-angle backlight LED illumination and polarized light technology, effectively suppressing reflections and glare on the chain surface. This provides a high-contrast, sharp-edge original image for subsequent image processing, which is a prerequisite for achieving high-precision measurement.

[0076] This invention employs an image processing flow that involves edge detection, contour filtering, and spline curve fitting. This process can robustly and accurately extract the drooping contour of a chain from a complex background and quantify it into a continuous mathematical curve, thus overcoming measurement errors caused by pixel discreteness.

[0077] This invention creatively applies the physical geometric model of "sag-chain length" to indirectly calculate the total chain length and elongation, which are difficult to measure directly, by measuring the easily observable sag value, thus realizing a non-contact quantitative wear assessment.

[0078] This invention integrates status monitoring, image acquisition, image processing, physical modeling, and result output into a complete automated solution that can replace manual inspection, improving inspection efficiency, safety, and objectivity.

[0079] This invention can record the sag and elongation data for each test and generate historical curves. When the elongation or single change exceeds a preset threshold, the system can automatically issue an early warning, prompting maintenance or replacement, thus achieving predictive maintenance.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the ideas of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting the elongation of the main drive chain of an escalator, characterized in that, include: Step 1: By analyzing the image sequence of the main drive chain area captured by the camera, determine whether the escalator is in a stable stopped state; Step 2: When the stable stopping state is confirmed, acquire a static digital image of the main drive chain; Step 3: Process the static digital image to extract and fit the droop curve of the main driving chain; Step 4: Based on the droop curve, calculate the sag of the main drive chain, and calculate the elongation of the main drive chain using a geometric model based on the sag.

2. The method for detecting the elongation of the main drive chain of an escalator according to claim 1, characterized in that, Step 1 specifically involves: Step 1.1: Analyze the image sequence of the continuously acquired main drive chain region using optical flow method, and calculate the motion vectors of feature points in the image; Step 1.2: If the average value of the motion vectors in multiple consecutive frames is lower than a preset threshold, the escalator is determined to be in a stable stopped state.

3. The method for detecting the elongation of the main drive chain of an escalator according to claim 1, characterized in that, The static digital images are acquired under low-angle linear illumination or backlight illumination conditions, and polarized light is used to suppress reflections on the chain surface. The low-angle linear lighting condition refers to: installing a strip light source parallel to the drive chain and illuminating it from the side of the chain at an angle of <15°. The backlighting conditions refer to installing a strip light source behind the chain so that the chain forms a clear silhouette in the camera's field of view.

4. The method for detecting the elongation of the main drive chain of an escalator according to claim 1, characterized in that, Step 3 specifically involves: Step 3.1: Convert the acquired static digital image to grayscale, and then use a Gaussian filter or median filter to smooth and denoise it, preserving edges while suppressing noise; Step 3.2: Define the main drive chain in the image as the region of interest, which precisely covers the entire drooping section from the upper sprocket to the lower chain, excluding interference from other irrelevant structures; Step 3.3: Perform edge detection within the region of interest to obtain edge pixels; Step 3.4: Based on the length, area, position, and geometric features of the contour, intelligently filter out the contour representing the lower edge of the main driving chain from all edge pixels; Step 3.5: The selected contour of the lower edge of the main driving chain, which is composed of discrete pixels, is fitted with a quadratic curve or spline curve using the least squares method to obtain a smooth and continuous digital curve, namely the drooping curve.

5. The method for detecting the elongation of the main drive chain of an escalator according to claim 1, characterized in that, Step 4 specifically involves: Step 4.1: Determine the tangent points A and B at the bottom of the sprockets at the left and right ends of the drive chain in the image, and connect the two points to obtain the reference chord; Step 4.2: Calculate the pixel value L of the reference chord length. P Using the known actual length L of the reference chord R Perform calibration and calculate the pixel equivalent K; Step 4.3: Traverse all points on the fitted sag curve, calculate the vertical distance from each point to the reference chord, find the maximum vertical distance, and record it as the pixel value D of the maximum sag. Step 4.4: Using the pre-calibrated pixel equivalent K, convert the pixel value D of the sag into the actual physical sag value S; Step 4.5: Combine the actual physical sag value S with the known actual length L of the reference chord. R Substitute the values ​​and calculate the current length L of the main driving chain; Step 4.6: Based on the original length L of the main drive chain O Calculate the elongation ΔL of the main drive chain based on the current length L.

6. A system for detecting the elongation of the main drive chain of an escalator, characterized in that, include: The image acquisition unit is used to acquire images of the main drive chain area of ​​the escalator. An illumination unit is used to provide illumination for the image acquisition unit; A control and processing unit, connected to the image acquisition unit and the illumination unit, is used to control image acquisition, process image data, and calculate elongation. The data storage and communication unit is connected to the control and processing unit and is used for storing data and external communication.

7. The escalator main drive chain elongation detection system according to claim 6, characterized in that, The image acquisition unit includes: The camera module uses an industrial-grade digital camera with a resolution of no less than 2 megapixels and a global shutter sensor. The mounting bracket is used to rigidly fix the camera module to the side of the main drive chain of the escalator. It must be decoupled from the vibration of the escalator body to avoid image blurring due to escalator operation vibration. The optical axis should be perpendicular to the plane where the drive chain is located. A polarizing filter is placed in front of the lens of the camera module.

8. The escalator main drive chain elongation detection system according to claim 7, characterized in that, The lighting unit includes: an LED strip light source and a polarizer disposed in front of the LED strip light source; The lighting unit is configured to provide low-angle linear illumination or backlight illumination to the main drive chain. The low-angle linear lighting refers to: installing a strip light source parallel to the drive chain and illuminating the chain from the side at an angle of <15°. The backlighting refers to installing a strip light source behind the chain so that the chain forms a clear silhouette in the camera's field of view.

9. The escalator main drive chain elongation detection system according to claim 7, characterized in that, The control and processing unit includes: The status recognition module is used to analyze the image sequence of the main drive chain area captured by the camera to determine whether the escalator is in a stable stop state, and after confirming that the escalator is in a stable stop state, it issues an image acquisition trigger command. The image processing module is used to perform smoothing and denoising on the acquired static digital images, define regions of interest, perform edge detection, extract the contour of the lower edge of the main driving chain, and fit curves to obtain the droop curve of the main driving chain. The sag calculation module is used to calculate the maximum sag value of the main drive chain based on the sag curve, the preset reference chord, the pixel value of the reference chord length, and the actual length of the reference chord. The elongation calculation module is used to calculate the current length and elongation of the main drive chain based on the maximum sag value using a geometric model.

10. The escalator main drive chain elongation detection system according to claim 9, characterized in that, The formula for calculating the current length L of the main drive chain is: Where L is the current length of the main driving chain, L R The reference chord's actual length is given by L, where S is the actual physical sag value. P is the pixel value of the reference chord length; D is the maximum vertical distance from all points on the sag curve to the reference chord, recorded as the pixel value of the maximum sag. The reference chord is obtained by connecting the bottommost tangent points A and B of the sprockets at the left and right ends of the drive chain in the image.

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