An airport luggage carousel belt speed measurement method based on a laser displacement sensor

Abstract

The application provides an airport luggage carousel conveying belt speed measurement method based on a laser displacement sensor, comprising the following steps: vertically fixing the sensor on a rack, and vertically irradiating the conveying belt with laser; configuring a hardware timing unit for synchronous triggering; pre-calibrating the physical pitch of adjacent wave crests; collecting distance data at a fixed frequency and synchronously capturing time stamps; judging luggage shielding, and freezing the speed output if the distance is continuously greater than the range threshold and exceeds the maximum time length of a single cycle, and resuming after the shielding is removed; if there is no shielding, after sliding average filtering, extreme value preliminary judgment, amplitude verification and cycle legality verification, calculating the instantaneous linear speed according to the time interval of adjacent effective wave crests combined with the physical pitch, and outputting the measured linear speed after sliding average; and performing slip detection and alarm according to the deviation between the measured linear speed and the theoretical speed of the motor encoder. The application can improve the safety and reliability of the operation of the airport luggage carousel.

Description

Technical Field

[0001] This invention relates to the field of sensing and detection technology for airport baggage handling systems, and more specifically, to a method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor. Background Technology

[0002] Airport baggage carousels are key equipment for efficient baggage transport and sorting within terminals. Their conveyor belts typically employ an inclined, overlapping structure, consisting of multiple belt plates connected sequentially at a specific angle and overlap length to form a circular operating system. Accurate monitoring of the conveyor belt speed directly impacts baggage transport efficiency, equipment operational safety, and passenger service experience. Currently, conveyor belt speed detection primarily relies on motor encoder feedback or contact speed measuring devices. Motor encoders indirectly calculate the theoretical conveyor belt speed by measuring the drive motor's rotational speed; however, this method cannot reflect slippage caused by wear, insufficient tension, or load variations between the conveyor belt and drive wheels, posing a risk of speed detection lag and distortion. Contact speed measuring devices, such as encoder wheels or speed rollers, require direct contact with the conveyor belt surface. Over long-term operation, they are prone to failure due to mechanical wear, vibration, and baggage collisions. Furthermore, they have poor adaptability to the periodic wave structure of inclined, overlapping conveyor belt surfaces, making measurement accuracy susceptible to interference.

[0003] Laser displacement sensors, as a non-contact measurement method, have been gradually applied to distance, displacement, and contour detection in industrial settings. By emitting a laser beam and receiving the reflected light signal, they can accurately acquire distance information from the surface of the measured object, offering advantages such as fast response, high resolution, and no need for contact with the object. However, directly applying laser displacement sensors to speed measurement scenarios on airport baggage carousels faces multiple technical challenges, including feature extraction of the periodic peak structure on the surface of the inclined overlapping conveyor belt, data interruption caused by baggage obstruction, and interference from environmental vibration and noise. Existing technologies lack mature algorithms for identifying the peak features on the surface of inclined overlapping conveyor belts, making it difficult to stably extract effective peaks and accurately calculate peak intervals under complex operating conditions. Furthermore, the lack of effective baggage obstruction detection and speed freezing mechanisms leads to erroneous speed outputs during obstruction periods. In addition, instantaneous speed calculation results fluctuate significantly, and smoothing and outlier removal strategies are insufficient, failing to meet the stringent requirements for speed measurement stability and reliability at airport baggage carousels. More importantly, the existing speed measurement scheme fails to effectively compare the measured linear speed with the theoretical speed of the motor encoder, making it impossible to achieve real-time online monitoring and early warning of conveyor belt slippage faults. Summary of the Invention

[0004] This invention provides a method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor, comprising: The laser displacement sensor is vertically fixed to the baggage carousel frame so that the laser beam shines vertically downwards onto the upper surface of the inclined overlapping conveyor belt. Configure the hardware timing unit to be triggered synchronously with the sampling of the laser displacement sensor; The physical pitch of adjacent wave crests along the direction of motion of the inclined overlapping conveyor belt is pre-calibrated; The laser displacement sensor continuously collects distance data at a fixed sampling frequency, and the hardware timing unit synchronously captures the absolute timestamp when the sampling point is completed, forming a discrete distance sequence with a time tag. Based on the distance data, it is determined whether there is luggage obstruction. If the distance data is continuously greater than the range threshold and exceeds the maximum duration of a single cycle, it is determined that the laser spot is obstructed by luggage, the speed output is frozen, and detection is automatically resumed after the obstruction is removed. If there is no luggage obstruction, the discrete distance sequence is subjected to sliding mean filtering to obtain a smooth distance sequence. Perform initial extreme value judgment on the smoothed distance sequence and mark candidate peak points; The amplitude of the candidate peaks is verified to eliminate spurious extrema caused by noise. Perform periodic validity checks on the time interval between adjacent valid peaks and eliminate false detection points that do not meet physical constraints; The time interval is calculated based on the timestamps of adjacent valid peaks, and the instantaneous linear velocity is calculated in combination with the physical pitch. The measured linear velocity is then output after a moving average is applied to the continuous valid instantaneous velocities. Based on the deviation between the measured linear velocity and the theoretical velocity calculated by the motor encoder, slippage fault detection is performed, and an alarm signal is output.

[0005] Furthermore, the pre-calibration of the physical pitch of adjacent wave crests of the inclined overlapping conveyor belt along the direction of motion includes: In the stationary state of the inclined overlapping conveyor belt, the plate length parameter, inclination angle parameter, overlap length parameter and plate thickness parameter of the inclined overlapping conveyor belt are obtained; Based on the plate length parameter, the tilt angle parameter, the overlap length parameter, and the plate thickness parameter, the theoretical spacing between adjacent wave crests along the direction of motion is calculated as a reference value for the physical pitch; After the actual installation is completed, based on the reference value, multiple adjacent peaks are selected on the surface of the inclined overlapping conveyor belt for spacing measurement, and the arithmetic mean of each measurement result is taken as the final calibrated physical pitch.

[0006] Furthermore, after calculating the time interval based on the timestamps of adjacent valid peaks and calculating the instantaneous linear velocity in combination with the physical pitch, if the instantaneous linear velocity exceeds the normal operating speed range of the inclined overlapping conveyor belt, the currently calculated instantaneous linear velocity is determined to be an abnormal value, the abnormal value is discarded, the measured linear velocity is not updated, and the effective speed of the previous frame is kept as the currently output measured linear velocity.

[0007] Furthermore, in the step of performing moving mean filtering on the discrete distance sequence, the length of the moving window is an odd number; The time span corresponding to the length of the sliding window is less than the duration of a single cycle; The length of the sliding window is not less than 3; Furthermore, the length of the sliding window does not exceed one-tenth of the number of sampling points in a single cycle.

[0008] Further, the initial extreme value determination of the smoothed distance sequence includes: Perform a first-order difference on the smoothed distance sequence; When the first-order difference changes from negative to positive, the point is marked as a candidate point for the peak.

[0009] Furthermore, amplitude verification of the candidate peak points includes: Set a fixed height difference threshold; If the distance difference between the candidate peak and the adjacent trough is greater than the fixed height difference threshold, it is determined to be a valid peak. The fixed height difference threshold is 50% to 70% of the height difference between the inherent crest and trough of the inclined overlapping conveyor belt.

[0010] Furthermore, the periodic validity check of the time interval between adjacent valid peaks includes: Based on the physical pitch and the design speed range of the inclined overlapping conveyor belt, calculate the minimum and maximum allowable time intervals between adjacent effective peaks; The minimum allowable value is the maximum value of the physical pitch divided by the design speed range; The maximum allowable value is the minimum value of the physical pitch divided by the design speed range; If the time interval between adjacent valid peaks falls between the minimum allowable value and the maximum allowable value, it is determined to be a valid period.

[0011] Furthermore, after performing initial extreme value judgment and marking candidate peak points on the smoothed distance sequence, and before performing amplitude verification on the candidate peak points, a subsampling-level peak time correction is also included: The interpolation interval is formed by the candidate peak point and one adjacent sampling point before and after it; The precise time corresponding to the extreme point is calculated using quadratic polynomial interpolation. If the precise time falls within the interpolation interval and the coefficient of the quadratic term of the quadratic polynomial is greater than zero, then the precise time is used as the timestamp of the candidate peak point.

[0012] Furthermore, the step of calculating the time interval based on the timestamps of adjacent valid peaks, calculating the instantaneous linear velocity in conjunction with the physical pitch, and then outputting the measured linear velocity after performing a moving average of the continuous valid instantaneous velocities includes: Obtain the timestamps of adjacent valid peaks within the m-th valid period, and calculate the time interval between the adjacent valid peaks; Divide the physical pitch by the time interval between adjacent effective peaks to obtain the instantaneous linear velocity of the m-th effective period; Set the sliding window length to N, and store N consecutive valid instantaneous velocities into the velocity sliding window; Calculate the arithmetic mean of all valid instantaneous velocities within the velocity sliding window, and output it as the measured linear velocity.

[0013] Furthermore, the step of detecting slippage faults based on the deviation between the measured linear velocity and the theoretical speed converted from the motor encoder, and outputting an alarm signal, includes: Obtain the theoretical speed of the inclined overlapping conveyor belt calculated by the motor encoder; Calculate the velocity deviation between the measured linear velocity and the theoretical velocity; If the speed deviation continues to exceed the slippage threshold and reaches a set number of cycles, the inclined overlapping conveyor belt is determined to be slipping. Output a slippage alarm signal to the turntable control system.

[0014] The embodiments of the present invention have at least the following beneficial effects: 1. By vertically fixing the laser displacement sensor to the baggage carousel frame and illuminating the upper surface of the conveyor belt with the laser beam vertically downward, and synchronously capturing the absolute timestamp with the hardware timing unit, non-contact high-precision acquisition of the periodic peak characteristics of the inclined overlapping conveyor belt surface is achieved. This effectively overcomes the failure problems of contact speed measuring devices caused by mechanical wear, vibration and baggage collision, and avoids the defect of indirect speed measurement by motor encoder that cannot reflect the actual belt speed. This significantly improves the long-term operational reliability and measurement accuracy of the speed measuring system.

[0015] 2. By establishing a baggage obstruction detection mechanism, the speed output is automatically frozen when the distance data continuously exceeds the range threshold and exceeds the maximum duration of a single cycle, and detection resumes after the obstruction is removed. Combined with multiple data processing strategies such as sliding average filtering, amplitude verification, cycle validity verification, and outlier removal, the problem of data interruption and noise interference caused by baggage obstruction under complex working conditions is effectively solved, ensuring the continuity and stability of speed measurement output and meeting the actual operational needs of high-frequency start-stop and load changes of airport baggage carousels.

[0016] 3. By comparing the measured linear velocity of the laser displacement sensor with the theoretical velocity converted by the motor encoder in real time, the system determines that the conveyor belt is slipping and outputs an alarm signal when the speed deviation continuously exceeds the slippage threshold and reaches the set number of cycles. This enables online monitoring and early warning of conveyor belt slippage faults, making up for the shortcomings of existing technologies that rely solely on a single speed source and cannot identify transmission failures. This provides key technical support for the proactive maintenance and safe operation of airport baggage carousel control systems. Attached Figure Description

[0017] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated in the drawings by way of example and not limitation, wherein: Figure 1 This is a schematic diagram of the speed measurement method for airport baggage carousel conveyor belt based on laser displacement sensor in an embodiment of this application. Figure 2 This is a simplified schematic diagram of the delivery line of the laser displacement sensor in the embodiments of this application; Figure 3 This is a schematic diagram of an inclined overlapping scale conveyor belt in an embodiment of this application. Detailed Implementation

[0018] The principles and spirit of the invention will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are provided merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided to make the invention more thorough and complete, and to fully convey the scope of the invention to those skilled in the art.

[0019] like Figure 1 As shown, a method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor includes: S1, the laser displacement sensor is vertically fixed to the baggage carousel frame so that the laser beam shines vertically downwards onto the upper surface of the inclined overlapping conveyor belt.

[0020] like Figure 2As shown, an unobstructed installation location is selected on the straight conveyor section of the baggage carousel. The laser triangulation displacement sensor is mounted on the steel frame of the carousel using a fixed bracket. The sensor's orientation is adjusted so that the laser beam shines vertically downwards onto the upper surface of the inclined overlapping conveyor belt. Vertical installation means that the laser beam's emission direction is parallel to the normal direction of the conveyor belt's movement plane, ensuring that the measurement distance is the normal height of the conveyor belt surface and avoiding geometric measurement errors introduced by inclined illumination. After installation, a level is used to calibrate the sensor housing's levelness, controlling the perpendicularity deviation between the laser beam and the conveyor belt surface within ±1°. The fixed bracket uses a rigid connection to prevent sensor loosening or beam shift caused by carousel vibration.

[0021] The laser displacement sensor employs laser triangulation, and its working principle is as follows: a laser beam is emitted from a laser source and irradiates the surface of the object being measured. After reflection from the object's surface, the beam is received by an internal charge-coupled device (CCD) image sensor. Based on the change in the imaging position of the reflected light point on the CCD image sensor, the distance from the sensor to the surface of the object is calculated using triangulation geometry. In this embodiment, the laser displacement sensor has a sampling frequency of 200Hz, is installed 200mm above the conveyor belt, and is in high-gain mode to adapt to the black, low-reflection surface.

[0022] The range threshold is the boundary value of the effective measurement range of the laser displacement sensor. In this embodiment, the sensor is installed 200mm above the conveyor belt. When the luggage blocks the laser spot, the measurement distance increases sharply to more than 250mm. Therefore, the range threshold is set to 250mm.

[0023] S2, Configure the hardware timing unit to be synchronously triggered with the sampling of the laser displacement sensor.

[0024] The hardware timing unit is a hardware timer inside the embedded microcontroller. In this embodiment, the timer input capture function of the STM32 series microcontroller is used, with a clock frequency of 80MHz, which can achieve a time resolution of 12.5ns. The hardware timing unit is connected to the laser displacement sensor through a hardware trigger signal line. When the laser displacement sensor completes the distance data acquisition of a sampling point, it synchronously outputs a pulse trigger signal to the hardware timing unit. The hardware timing unit responds to the pulse signal by immediately capturing the current count value and converting it into an absolute timestamp.

[0025] The sampling trigger output pin of the laser displacement sensor is connected to the timer input capture channel pin of the STM32 microcontroller via a signal line. The timer in the STM32 microcontroller is configured to operate in input capture mode, and the internal sampling clock of the laser displacement sensor is configured to 200Hz, meaning a distance measurement is completed every 5ms and a trigger pulse is output. When the laser displacement sensor completes a sampling, its trigger output pin generates a rising edge pulse. Upon detecting this rising edge, the timer input capture channel immediately latches the current count value into the capture compare register and simultaneously triggers an interrupt service routine. The interrupt service routine reads the count value from the capture compare register and calculates the absolute timestamp of the sampling point by combining it with the timer reference time. The timestamp resolution is better than 1 microsecond. The absolute timestamp is set to zero at the microcontroller's power-on time, and the timestamps of all subsequent sampling points continuously increase relative to this zero time.

[0026] S3, pre-calibrate the physical pitch of adjacent wave crests of the inclined overlapping conveyor belt along the direction of movement.

[0027] S31, in the stationary state of the inclined overlapping conveyor belt, obtain the plate length parameter, inclination angle parameter, overlap length parameter and plate thickness parameter of the inclined overlapping conveyor belt.

[0028] like Figure 3 As shown, the inclined overlapping conveyor belt refers to the scale-type conveyor belt widely used in airport baggage claim carousels. Multiple load-bearing plates are equidistantly inclined and overlap along the direction of movement, forming a tile-like overlap at both ends. The front end of each load-bearing plate is higher than the rear end, forming a wedge-shaped overlap structure. The overlapping area of ​​adjacent load-bearing plates is lower than the non-overlapping area, creating a periodic undulation on the upper surface of the conveyor belt consistent with the plate pitch. The highest point is the non-overlapping area of ​​a single plate, i.e., the crest, and the lowest point is the overlapping area, i.e., the trough. The normal operating speed range of baggage carousel conveyor belts is typically 0.2 m / s to 0.6 m / s.

[0029] After the conveyor belt has completely stopped running, the geometric parameters of the conveyor belt support plates are measured manually using vernier calipers and an angle measuring instrument. The plate length parameter is the length of a single support plate along the direction of movement. The tilt angle parameter is the angle between the tilted surface of the support plate and the horizontal plane. The overlap length parameter is the length of the overlapping portion of two adjacent support plates in the direction of movement. The plate thickness parameter is the thickness of the support plate. These parameters can also be obtained directly from the product specifications provided by the conveyor belt manufacturer.

[0030] S32, based on the plate length parameter, the tilt angle parameter, the overlap length parameter and the plate thickness parameter, calculate the theoretical distance between adjacent wave crests along the direction of motion, as a reference value for the physical pitch.

[0031] The theoretical spacing between adjacent crests is calculated based on the geometric relationship of the inclined overlapping structure. A crest is the highest point of a single load-bearing plate, and the physical spacing between adjacent crests is equal to the plate length parameter minus the overlap length parameter, projected horizontally. Since the load-bearing plates are placed at an incline, the plate length needs to be calculated by horizontal projection along the direction of movement.

[0032] S33. After the actual installation is completed, based on the reference value, select multiple adjacent peaks on the surface of the inclined overlapping conveyor belt for spacing measurement, and take the arithmetic mean of each measurement result as the final calibrated physical pitch.

[0033] After the conveyor belt is installed on the baggage carousel and tensioning is completed, at least three sets of adjacent wave crest positions are selected on the conveyor belt surface. A laser rangefinder or steel ruler is used to measure the actual distance between each adjacent wave crest along the direction of movement. During measurement, ensure that the measurement direction is parallel to the direction of conveyor belt movement. The arithmetic mean of each set of measurements is taken as the final calibrated physical pitch P. In this embodiment, after calibration, the physical pitch P of the black PVC inclined overlapping scale conveyor belt on an airport baggage carousel is 0.4057m.

[0034] S4, the laser displacement sensor continuously collects distance data at a fixed sampling frequency, and the hardware timing unit synchronously captures the absolute timestamp when the sampling point is completed, forming a discrete distance sequence with a time tag.

[0035] The laser displacement sensor is activated in continuous sampling mode, with a sampling frequency of 200Hz, i.e., a sampling period. The laser displacement sensor continuously outputs distance data for 5ms. At the instant distance data acquisition is completed at each sampling point, the laser displacement sensor outputs a trigger pulse to the hardware timing unit, which simultaneously captures an absolute timestamp. The laser displacement sensor transmits the distance data to the signal processing unit via a serial peripheral interface or a universal asynchronous transceiver interface. The hardware timing unit transmits the corresponding timestamp to the signal processing unit via its internal bus. The signal processing unit combines the distance data and timestamps according to the sampling time, forming a time-stamped discrete distance sequence. ,in For the first Distance value of each sampling point, For the first The absolute timestamps corresponding to each sampling point. In this embodiment, the laser displacement sensor is in high-gain mode to enhance the intensity of the reflected light signal from the black, low-reflection surface, ensuring effective acquisition of distance data.

[0036] S5. Based on the distance data, determine whether there is luggage obstruction. If the distance data is continuously greater than the range threshold and exceeds the maximum duration of a single cycle, it is determined that the laser spot is obstructed by luggage, the speed output is frozen, and detection is automatically resumed after the obstruction is removed. If there is no luggage obstruction, the discrete distance sequence is subjected to sliding mean filtering to obtain a smooth distance sequence.

[0037] The signal processing unit receives each distance data Afterwards, With the preset range threshold The range threshold is compared. The measurement distance is set based on the sensor installation height. When the laser spot is unobstructed, the laser beam illuminates the conveyor belt surface, and the measurement distance is approximately 200mm above the sensor installation height, with a fluctuation range within ±1mm. When luggage passes directly below the laser spot, the laser beam is reflected by the luggage surface, and the measurement distance drops sharply to the distance corresponding to the height of the luggage surface, which is much less than 200mm. When luggage obstructs the light, causing the laser reflection to be completely lost, the measurement distance output value jumps to near the upper limit of the sensor's range, exceeding the range threshold of 250mm. The maximum duration of a single cycle is specified. The maximum allowable time interval between adjacent peaks is specified in this embodiment.

[0038] If the signal processing unit continuously detects > And the duration exceeds If the distance data does not exceed the range threshold, indicating that luggage is obstructing the laser beam, the signal processing unit freezes the velocity output, using the most recent valid measured linear velocity as the current output value, and does not perform subsequent peak identification and velocity calculation. If the distance data does not continuously exceed the range threshold, i.e., there is no luggage obstruction, the signal processing unit performs a moving average filter on the discrete distance sequence to obtain a smooth distance sequence.

[0039] Furthermore, a moving average filter is applied to the discrete distance sequence, with an odd-numbered sliding window. The time span corresponding to the sliding window length is less than the duration of a single period. The sliding window length is not less than 3, and the sliding window length does not exceed one-tenth of the number of sampling points in a single period.

[0040] The signal processing unit processes the distance data in the discrete distance sequence. A moving average filtering operation is performed using a centrally symmetric sliding window. The length W of the sliding window is an odd number to ensure that the filtered data is perfectly aligned with the original data on the time axis, without introducing phase shift. In this embodiment, a sliding window length W=5 is selected, meaning that five points, centered at the current sampling point, are taken from the two adjacent sampling points before and after it, for a total of five points, to participate in the averaging calculation.

[0041] The continuous sampling time span corresponding to the sliding window length W is W× This time span must be less than the time length corresponding to a single peak period to ensure that the filtering window does not span multiple peak waveform periods, avoiding the averaging of signals from different peaks and thus protecting the peak characteristics from distortion. In this embodiment, W=5, and the sampling period is... =5ms, the window time span is 25ms, which is much smaller than the single cycle time of the conveyor belt at the maximum speed of 0.6m / s, approximately 0.676s, thus satisfying the condition.

[0042] To ensure that the moving average filter has sufficient suppression effect on high-frequency shot noise, the sliding window length W is at least 3. When the window length W=3, it can cover at least one complete high-frequency noise pulse width, achieving positive and negative noise cancellation. If the window length is too small, such as W=1, it is equivalent to no filtering and cannot suppress noise; W=2 is an even number, which cannot achieve central symmetry and is not conducive to noise statistical cancellation. In this embodiment, W=5 satisfies this condition.

[0043] Number of sampling points per cycle This refers to the number of sampling points corresponding to one physical pitch P of the conveyor belt. = ,in Sampling frequency, The current conveyor belt speed. To ensure that the filtering does not distort the peak shape, the sliding window length W must be much smaller than... This scheme limits W to W ≤ / 10. In this embodiment, the maximum conveyor belt speed is 0.6 m / s. ≈135, W=5≤13.5 satisfies the condition; at the minimum speed of 0.2m / s ≈406, W=5≤40.6 satisfies the condition. W=5 accounts for only 1.2% to 3.7% of the number of sampling points in a single cycle across the entire speed range, which is far below the 10% fidelity threshold.

[0044] After moving average filtering, the th... The values ​​of each point are shown in the following formula:

[0045] in For the first The smoothed distance value for each point, where W is the length of the sliding window. This represents the distance value of the k-th sampling point in the original discrete distance sequence. In this embodiment, W=5, and after smoothing, high-frequency noise is suppressed from ±0.3mm to within ±0.1mm, while retaining clear periodic fluctuation characteristics.

[0046] S6, perform initial extreme value judgment on the smooth distance sequence and mark the candidate peak points.

[0047] S61, perform a first-order difference on the smoothed distance sequence.

[0048] For smooth distance sequences Calculate the first-order difference, which represents the change in distance between two adjacent sampling points. The calculation method is to subtract the smoothed distance value of the current point from the smoothed distance value of the next point, as shown in the following formula:

[0049] in For the first First-order difference values ​​at each sampling point For the first The smoothed distance value of each sampling point For the first The smoothed distance value of each sampling point.

[0050] S62, when the first-order difference changes from negative to positive, mark the point as the candidate point of the wave peak.

[0051] The signal processing unit sequentially judges the sign change of the first-order difference sequence. When the distance signal on the conveyor belt surface changes from a trough to a crest, the distance value gradually decreases, and the first-order difference becomes negative; at the crest, the distance value is minimum, and the first-order difference approaches zero; from a crest to a trough, the distance value gradually increases, and the first-order difference becomes positive. Therefore, when the signal is detected... and When the first-order difference changes from a negative value to a positive value, it indicates that the signal has reached a positive value at the sampling point. and The interval between +1 and 1 reached a minimum point, at which point the th value was marked. Each sampling point is a candidate peak point.

[0052] In some embodiments, after performing initial extreme value judgment and marking peak candidate points on the smooth distance sequence, and before performing amplitude verification on the peak candidate points, a subsampling-level peak time correction is further included, including: Step a: The interpolation interval is formed by the candidate peak point and one adjacent sampling point before and after it.

[0053] Using the marked candidate peak point as the center, select the time index of the candidate point. Take the previous sampling point ( -1) and the next sampling point ( +1), a total of three consecutive sampling points constitute the interpolation interval. The data corresponding to these three sampling points are ,in For the first The absolute timestamp of each sampling point For the first The smoothed distance value of each sampling point. The candidate peak points satisfy the local minimum characteristic, that is... and .

[0054] Step b involves using quadratic polynomial interpolation to calculate the precise time corresponding to the extreme point.

[0055] The signal processing unit fits a continuous curve of the distance signal changing with time using a quadratic polynomial within the interpolation interval. The general form of the quadratic polynomial is: ,in Let be a function of distance values ​​changing with time, where t is the time variable and a, b, and c are undetermined coefficients. Substituting the data from the three sampling points in S81 and their corresponding timestamps into the quadratic polynomial, we obtain the following system of three linear equations:

[0056] Because the sampling points are at equal time intervals, The coefficients can be simplified by using second-order differences. After solving for the coefficients a and b, the time corresponding to the extreme point is located where the derivative of the quadratic function is zero. Differentiating gives Setting the derivative to zero, the extreme point time is obtained as shown in the following equation:

[0057] Step c: If the precise time falls within the interpolation interval and the coefficient of the quadratic term of the quadratic polynomial is greater than zero, then the precise time is used as the timestamp of the candidate peak point.

[0058] The signal processing unit calculates the... Perform a validity determination. If... Falling within the interpolation interval If the quadratic term coefficient a > 0, then the quadratic polynomial is determined to open upwards and has a unique minimum point. This is the precise moment of the minimum point. At this point, with... Sampling time of replacing the original candidate points This serves as the final timestamp of the candidate peak point, achieving sub-sampling level time positioning accuracy. If... If the value exceeds the interpolation range or a ≤ 0, it is determined to be an abnormal interpolation caused by noise interference. The correction result is discarded, and the original sampling time is retained. The timestamps of the candidate peak points are used as the basis for wave peak location. After correction by quadratic polynomial interpolation, the wave peak location error is reduced from ±2.5ms at the sampling period level to within ±0.1ms at the sub-sampling level.

[0059] S7. Perform amplitude verification on the candidate peak points, eliminate false extreme values ​​caused by noise, and obtain valid peaks.

[0060] S71, set a fixed height difference threshold.

[0061] The signal processing unit internally stores a preset fixed height difference threshold. The fixed height difference threshold is used to distinguish between true peaks and false extremes caused by noise. The fixed height difference threshold is set based on the actual height difference between the inherent peaks and troughs of the inclined overlapping conveyor belt. In this embodiment, the height difference between the peaks and troughs of the inclined overlapping conveyor belt is approximately 0.8 mm, and the peak-to-peak noise value after five-point sliding average filtering is approximately 0.2 mm. =0.5mm is used as the fixed height difference threshold.

[0062] S72, if the distance difference between the candidate peak and the adjacent valley is greater than the fixed height difference threshold, it is determined to be a valid peak.

[0063] For each corrected candidate peak, the signal processing unit calculates the difference between the smoothed distance value of that candidate peak and the smoothed distance value of its adjacent trough. The adjacent trough positions are determined by detecting points where the first-order difference changes from positive to negative, i.e., the inflection point where the distance value changes from increasing to decreasing. If this difference is greater than the fixed height difference threshold... If the difference is less than or equal to the actual peak on the conveyor belt surface, then the candidate peak is determined to be a true peak on the conveyor belt surface and marked as a valid peak; if the difference is less than or equal to the actual peak, then the candidate peak is determined to be a true peak on the conveyor belt surface and marked as a valid peak. If the candidate peak is determined to be a spurious extremum caused by noise, it will be discarded. In this embodiment... =0.5mm, any candidate point with an amplitude less than 0.5mm is considered noise and is rejected.

[0064] Fixed height difference threshold The value range is the actual height difference between the inherent crests and troughs of the inclined overlapping conveyor belt. The value range is 50% to 70%. The principle for setting this range is: a lower limit of 50% ensures that the fixed height difference threshold is higher than the peak value of the smoothed noise, avoiding misjudging noise as a peak; an upper limit of 70% ensures that the fixed height difference threshold is lower than the actual peak depth, avoiding missing inherent characteristics of the conveyor belt. In this embodiment... =0.8mm, =0.5mm, accounting for The proportion was 62.5%, falling within the range of 50% to 70%.

[0065] S8 performs periodic validity checks on the time interval between adjacent valid peaks, eliminates false detection points that do not meet physical constraints, and obtains the final valid peaks.

[0066] Based on the physical pitch and the design speed range of the inclined overlapping conveyor belt, calculate the minimum and maximum allowable time intervals between adjacent effective peaks.

[0067] After completing effective peak identification, the pre-calibrated physical pitch P and the design speed range of the inclined overlapping conveyor belt are obtained. The design speed range refers to the permissible speed interval during normal operation of the baggage carousel, determined by the design parameters of the airport baggage handling system. In this embodiment, P = 0.4057m. =0.2m / s, =0.6m / s.

[0068] The boundary values ​​for the time interval between adjacent wave crests are derived from the velocity formula. At the maximum operating speed... Below, the time interval between adjacent wave peaks passing under the sensor is the smallest, and this minimum allowable value is... As shown in the following formula:

[0069] In this embodiment =0.4057 / 0.6≈0.676s. If the detected time interval is less than This indicates that the speed corresponding to the interval exceeds the maximum design speed of the conveyor belt, and the wave crest pair corresponding to the time interval is invalid.

[0070] At minimum operating speed Below, the time interval between adjacent wave peaks passing under the sensor is the largest, and this maximum allowable value is... As shown in the following formula:

[0071] In this embodiment =0.4057 / 0.2≈2.029s. If the detected time interval is greater than... This indicates that the speed corresponding to this interval is lower than the minimum design speed of the conveyor belt, possibly due to missed peak detection or signal abnormality. The peak pair corresponding to this time interval is invalid.

[0072] If the time interval between adjacent valid peaks falls between the minimum and maximum allowable values, it is considered a valid period. (The time interval between adjacent valid peaks is defined as follows.) Make a judgment, if ≤ ≤ If the adjacent valid peak pairs constitute a valid period, then the period is determined to be valid. Used for subsequent velocity calculations. If < or > If a peak pair is detected incorrectly, it is considered a false alarm and the pair is discarded and not included in the instantaneous velocity calculation. In this embodiment, the legal period range is 0.676s to 2.029s. If the time interval exceeds the limit for 3 to 5 consecutive periods, the signal processing unit determines that the conveyor belt is stuck, running at overspeed, or the sensor is faulty, and triggers an equipment abnormality alarm signal to be pushed to the turntable control system.

[0073] S9: Calculate the time interval based on the timestamps of adjacent valid peaks, calculate the instantaneous linear velocity in combination with the physical pitch, and output the measured linear velocity after performing a moving average on the continuous valid instantaneous velocities.

[0074] S91, obtain the timestamps of adjacent valid peaks within the m-th valid period, and calculate the time interval between the adjacent final valid peaks.

[0075] For the m-th effective period, obtain the timestamp of its starting point and the final effective peak. and the timestamp of the final valid peak at the endpoint The time interval of the effective period is obtained by calculating the difference between the two. As shown in the following formula:

[0076] in Let m be the time interval of the m-th effective period. This is the timestamp of the m-th peak. This is the timestamp of the (m-1)th peak.

[0077] S92, divide the physical pitch by the time interval between adjacent final effective peaks to obtain the instantaneous linear velocity of the m-th effective period.

[0078] According to the velocity formula, the pre-calibrated physical pitch P is divided by the time interval. Obtain the instantaneous linear velocity of the m-th effective period. As shown in the following formula:

[0079] in Let P be the instantaneous linear velocity during the m-th effective period, and let P be the physical pitch. is the time interval of the m-th effective period.

[0080] S93, set the sliding window length to N, and store N consecutive valid instantaneous velocities into the velocity sliding window.

[0081] The signal processing unit allocates a first-in-first-out velocity sliding window buffer in memory, with a preset window length of N. The sliding window length N is a positive integer; in this embodiment, N=5. Whenever a new effective instantaneous velocity is calculated... The signal processing unit will The data is stored at the tail of the velocity sliding window, while the oldest data at the head of the window is removed, ensuring that the window always stores the N most recent valid instantaneous velocity values. In the initial stage of velocity calculation, when the window is not full, the average is calculated based on the number of valid instantaneous velocities already collected.

[0082] S94, calculate the arithmetic mean of all effective instantaneous velocities within the velocity sliding window, and output it as the measured linear velocity.

[0083] The arithmetic mean of all valid instantaneous velocities currently stored within the velocity sliding window is calculated, and the average value is taken as the measured linear velocity. As shown in the following formula:

[0084] in The output is the measured linear velocity, where N is the sliding window length and k is the index of the latest valid instantaneous velocity. This refers to the j-th effective instantaneous velocity within the velocity sliding window. In this embodiment, N=5. It is the arithmetic mean of the most recent 5 valid instantaneous velocities, which effectively suppresses single-cycle velocity fluctuations and outputs a smooth and stable measured linear velocity.

[0085] Furthermore, after calculating the instantaneous linear velocity Then, before storing in the speed sliding window, first... Perform amplitude limiting judgment. Normal operating speed range. The values ​​are set based on the actual operating conditions of the baggage carousel, and are within the design speed range. , The speed should be consistent with or slightly larger than this range to include instantaneous fluctuations. In this embodiment, the normal operating speed range is 0.1 m / s to 0.8 m / s. If... <0.1m / s or If the speed is >0.8 m / s, then it is determined that... If the value is an outlier, the signal processing unit discards it, does not store it in the velocity sliding window, and does not update the current measured linear velocity. The measured linear velocity from the previous frame is retained as the current output. If the speed falls within the normal operating speed range, a speed update will be performed.

[0086] S95 detects slippage faults based on the deviation between the measured linear velocity and the theoretical speed converted from the motor encoder, and outputs an alarm signal.

[0087] The motor encoder is a rotary encoder mounted on the shaft of the conveyor belt drive motor. It calculates the linear displacement of the drive wheel by measuring the angular displacement of the motor rotation, thereby obtaining the theoretical linear speed of the drive wheel. However, due to slippage, transmission chain gaps, or local jamming that may occur during long-term operation of the conveyor belt, this theoretical speed cannot accurately reflect the actual operating speed of the conveyor belt surface.

[0088] S951, obtain the theoretical speed of the inclined overlapping conveyor belt calculated by the motor encoder.

[0089] The signal processing unit reads the motor encoder's rotational speed data in real time from the baggage carousel's motor drive controller via an industrial Ethernet or RS-485 communication interface. The motor encoder is an incremental encoder, mounted on the output shaft of the drive motor. Its output pulse signal is converted into the actual motor speed by a high-speed counter in the drive controller. The drive controller then converts the motor speed into the linear velocity of the drive wheel based on the gear ratio of the reducer; this linear velocity is the theoretical speed. The signal processing unit uses the measured linear velocity... Acquire at the same update frequency .

[0090] S952, calculate the velocity deviation between the measured linear velocity and the theoretical velocity.

[0091] The signal processing unit acquires the measured linear velocity of the current period at the same time reference. and the theoretical speed Calculate the absolute velocity difference between the two. As shown in the following formula:

[0092] in For speed deviation, The measured linear velocity is... The theoretical speed is given.

[0093] S953, if the speed deviation continues to exceed the slippage threshold and reaches the set number of cycles, then the inclined overlapping conveyor belt is determined to be slipping.

[0094] The signal processing unit contains a slippage counter, initially set to zero. For each speed calculation cycle, the calculated speed deviation is... With the preset slippage threshold A comparison is made. The slippage threshold is set based on the maximum permissible deviation between the measured speed and the theoretical speed during normal conveyor belt operation. In this embodiment... =0.08m / s. If > If the slippage counter is incremented by 1; if ≤ If the slippage counter reaches the set number of cycles, meaning the speed deviation exceeds the slippage threshold for multiple consecutive cycles, then the inclined overlapping conveyor belt is determined to have slipped. In this embodiment, the set number of cycles is 5 cycles, meaning that slippage is detected 5 times consecutively. Slippage detection is triggered when the speed is >0.08m / s.

[0095] S954 outputs a slippage alarm signal to the turntable control system.

[0096] When slippage is detected on the inclined overlapping conveyor belt, the signal processing unit sends a slippage alarm signal to the motor drive controller of the baggage carousel via a digital output interface or communication bus. The slippage alarm signal includes an alarm type identifier and the current measured linear speed value and theoretical speed value. Upon receiving the slippage alarm signal, the motor drive controller executes corresponding protective actions, such as reducing speed, stopping for inspection, or prompting maintenance personnel to inspect the transmission mechanism.

[0097] Furthermore, the storage medium in the embodiments of this application stores program instructions capable of implementing all the above methods. These program instructions can be stored in the storage medium in the form of a software product, including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks, or terminal devices such as computers, servers, mobile phones, and tablets.

[0098] The above description is merely an explanation of some preferred embodiments of the present invention and the technical principles employed. Those skilled in the art should understand that the scope of the invention as described in the embodiments of the present invention is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of the present invention.

Claims

1. A method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor, characterized in that, include: The laser displacement sensor is vertically fixed to the baggage carousel frame so that the laser beam shines vertically downwards onto the upper surface of the inclined overlapping conveyor belt. Configure the hardware timing unit to be triggered synchronously with the sampling of the laser displacement sensor; The physical pitch of adjacent peaks of the inclined overlapping conveyor belt along the direction of movement is pre-calibrated, wherein the physical pitch is the actual physical distance between adjacent peaks of the inclined overlapping conveyor belt along the direction of movement. The laser displacement sensor continuously collects distance data at a fixed sampling frequency, and the hardware timing unit synchronously captures the absolute timestamp when the sampling point is completed, forming a discrete distance sequence with a time tag. Based on the distance data, determine whether there is luggage obstruction. If luggage obstruction exists, freeze the output speed; if there is no luggage obstruction, apply a moving average filter to the discrete distance sequence to obtain a smooth distance sequence. Perform initial extreme value judgment on the smoothed distance sequence and mark candidate peak points; The amplitude of the candidate peaks is verified to eliminate false extreme values ​​caused by noise and obtain valid peaks. The time interval between adjacent valid peaks is periodically validated, and false detection points that do not meet the physical constraints are eliminated to obtain the final valid peaks. The time interval is calculated based on the timestamps of adjacent final effective peaks, and the instantaneous linear velocity is calculated in combination with the physical pitch. The measured linear velocity is then output after a moving average of the continuous effective instantaneous velocities. Based on the deviation between the measured linear velocity and the theoretical velocity calculated by the motor encoder, slippage fault detection is performed, and an alarm signal is output.

2. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, The pre-calibrated physical pitch of adjacent wave crests of the inclined overlapping conveyor belt along the direction of motion includes: In the stationary state of the inclined overlapping conveyor belt, the plate length parameter, inclination angle parameter, overlap length parameter and plate thickness parameter of the inclined overlapping conveyor belt are obtained; Based on the plate length parameter, the tilt angle parameter, the overlap length parameter, and the plate thickness parameter, the theoretical spacing between adjacent wave crests along the direction of motion is calculated as a reference value for the physical pitch; After the actual installation is completed, based on the reference value, multiple adjacent peaks are selected on the surface of the inclined overlapping conveyor belt for spacing measurement, and the arithmetic mean of each measurement result is taken as the final calibrated physical pitch.

3. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, After calculating the instantaneous linear velocity in conjunction with the physical pitch, if the instantaneous linear velocity exceeds the normal operating speed range of the inclined overlapping conveyor belt, the currently calculated instantaneous linear velocity is determined to be an abnormal value. The abnormal value is discarded, the measured linear velocity is not updated, and the effective speed of the previous frame is kept as the currently output measured linear velocity.

4. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, In the step of performing moving mean filtering on the discrete distance sequence, the length of the moving window is an odd number; The time span corresponding to the length of the sliding window is less than the duration of a single cycle; The length of the sliding window is not less than 3; Furthermore, the length of the sliding window does not exceed one-tenth of the number of sampling points in a single cycle.

5. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, Preliminary extreme value determination of the smoothed distance sequence includes: Perform a first-order difference on the smoothed distance sequence; When the first-order difference changes from negative to positive, the point is marked as a candidate point for the peak.

6. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, The amplitude verification of the candidate peak points includes: Set a fixed height difference threshold; If the distance difference between the candidate peak and the adjacent trough is greater than the fixed height difference threshold, it is determined to be a valid peak. The fixed height difference threshold is 50% to 70% of the height difference between the inherent crest and trough of the inclined overlapping conveyor belt.

7. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, Periodic validity checks on the time interval between adjacent valid peaks include: Based on the physical pitch and the design speed range of the inclined overlapping conveyor belt, calculate the minimum and maximum allowable time intervals between adjacent effective peaks; The minimum allowable value is the maximum value of the physical pitch divided by the design speed range; The maximum allowable value is the minimum value of the physical pitch divided by the design speed range; If the time interval between adjacent valid peaks falls between the minimum allowable value and the maximum allowable value, it is determined to be a valid period.

8. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, Before performing amplitude verification on the candidate peak points, the method further includes: The interpolation interval is formed by the candidate peak point and one adjacent sampling point before and after it; The precise time corresponding to the extreme point is calculated using quadratic polynomial interpolation. If the precise time falls within the interpolation interval and the coefficient of the quadratic term of the quadratic polynomial is greater than zero, then the precise time is used as the timestamp of the candidate peak point.

9. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, The measured linear velocity is output after performing a moving average of the continuous effective instantaneous velocities, including: Obtain the timestamps of adjacent valid peaks within the m-th valid period, and calculate the time interval between the adjacent final valid peaks; Based on the physical pitch and the time interval between adjacent final effective peaks, the instantaneous linear velocity of the m-th effective period is obtained. Set the sliding window length to N, and store N consecutive valid instantaneous velocities into the velocity sliding window; Calculate the arithmetic mean of all valid instantaneous velocities within the velocity sliding window, and output it as the measured linear velocity.

10. The method for measuring the speed of an airport baggage carousel conveyor belt based on a laser displacement sensor according to claim 1, characterized in that, The method for detecting slippage faults based on the deviation between the measured linear velocity and the theoretical velocity converted from the motor encoder, and outputting alarm signals, includes: Obtain the theoretical speed of the inclined overlapping conveyor belt calculated by the motor encoder; Calculate the velocity deviation between the measured linear velocity and the theoretical velocity; If the speed deviation continues to exceed the slippage threshold and reaches a set number of cycles, the inclined overlapping conveyor belt is determined to be slipping. Output a slippage alarm signal to the turntable control system.

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