A relative displacement detection method, system and a stacker-reclaimer

Abstract

The application discloses a relative displacement detection method and system and a stacker-reclaimer, relates to the field of advanced manufacturing and automation, and acquires actual relative displacement data through a pull wire displacement detection module. The pull wire is connected with a reference element through a flexible buffer connecting element, effectively absorbs vibration impact, avoids stress fracture or measurement misalignment of the pull wire due to rigid connection, a dust scraping sealing structure arranged at a pull wire outlet can block impurities such as dust and water vapor from invading, and the detection reliability and module service life under harsh working conditions are significantly improved. Meanwhile, theoretical relative displacement data are determined based on running state data of a driving control unit, fusion verification of sensor data and driving data is realized, in a moving state, faults are diagnosed in real time through the difference between actual displacement and theoretical displacement, in a static state, abnormalities are detected through actual displacement change amounts at different moments, the deficiency of traditional single sensors in lacking effective fault diagnosis means is made up, and high-precision displacement detection and fault self-diagnosis are realized.

Description

Technical Field

[0001] This application relates to the fields of advanced manufacturing and automation technology, and in particular to a relative displacement detection method, system and stacker-reclaimer. Background Technology

[0002] In the operation of large industrial equipment, such as stacker-reclaimers and port machinery, it is often necessary to detect the precise displacement between two relatively moving parts.

[0003] However, such equipment typically operates under harsh conditions with high dust levels, strong vibrations, and large impact loads. Existing non-contact ranging methods, such as lidar and ultrasonic sensors, are highly susceptible to dust obstruction and environmental noise interference, leading to measurement failures. Traditional mechanical limit switches can only provide discrete position signals and cannot achieve continuous and accurate distance feedback to support smooth acceleration and deceleration control.

[0004] If conventional wire-type displacement sensors are used, although they have strong anti-interference capabilities, the wires are prone to fatigue fracture or jamming under frequent start-stop and large impact loads. Furthermore, existing control systems lack dedicated detection methods for this type of physical architecture failure mode. If a sensor malfunctions and is not identified in time, it may lead to equipment collisions or operational interruptions, posing a serious safety hazard.

[0005] In summary, existing technologies suffer from low reliability of relative displacement detection under harsh working conditions and a lack of effective fault diagnosis methods. Summary of the Invention

[0006] In view of the above problems, this application provides a relative displacement detection method, system, and stacker-reclaimer to achieve high-precision displacement measurement and dynamic / static fault identification in high-dust and high-impact environments. The specific solution is as follows:

[0007] The first aspect of this application provides a relative displacement detection method for detecting the relative displacement of a first moving member relative to a reference member, the method comprising:

[0008] The actual relative displacement data of the first moving part relative to the reference part is obtained by the wire displacement detection module; wherein, the wire of the wire displacement detection module is connected to the reference part through a flexible buffer connector, and the wire outlet of the wire displacement detection module is provided with a dust scraping and sealing structure.

[0009] The operating status data output by the drive control unit used to drive the first moving part is acquired, and the theoretical relative displacement data is determined based on the operating status data.

[0010] When the first moving part is in motion, motion state fault detection is performed based on the difference between the actual relative displacement data and the theoretical relative displacement data;

[0011] When the first moving part is stationary, a stationary fault detection is performed based on the change in the actual relative displacement data acquired at different times.

[0012] In one possible implementation, when the first moving component is in motion, motion state fault detection is performed based on the difference between the actual relative displacement data and the theoretical relative displacement data, including:

[0013] Within a preset detection time window, the theoretical relative displacement data is obtained by integral calculation based on the running speed output by the drive control unit.

[0014] Obtain the actual relative displacement data output by the wire displacement detection module within the preset detection time window;

[0015] Calculate the displacement difference between theoretical relative displacement data and actual relative displacement data;

[0016] If the displacement difference is greater than or equal to the preset difference threshold, and the duration reaches the preset time threshold, then a motion state fault is determined to have occurred.

[0017] In one possible implementation, the preset detection time window is an integer multiple of the controller's scan cycle;

[0018] The method also includes:

[0019] In response to receiving the operation command and operation feedback signal output by the drive control unit, or receiving the pulse feedback signal output by the encoder installed on the first moving part, it is determined that the first moving part is in motion.

[0020] In response to the absence of a running command, running feedback signal, and pulse feedback signal, it is determined that the first moving part is in a stationary state;

[0021] In response to the determination of a motion state fault, a stop operation command is generated to control the first moving part to decelerate and stop or to stop the brake.

[0022] In one possible implementation, when the first moving part is stationary, a stationary fault detection is performed based on the change in actual relative displacement data acquired at different times, including:

[0023] After the first moving part stops running and the preset delay time is reached, the current position value output by the wire displacement detection module is obtained according to the preset acquisition cycle;

[0024] Calculate the change in position between two consecutive current position values;

[0025] If the change in position exceeds the preset static error threshold, a static state fault is determined to have occurred.

[0026] In one possible implementation, the method further includes:

[0027] In response to the issuance of a start command for the first moving part, an anti-interference delay timer is initiated;

[0028] If the anti-interference delay time is not reached, the motion state fault detection will be suspended.

[0029] If the anti-interference delay time reaches the preset anti-interference delay time, resume motion state fault detection.

[0030] The preset anti-interference delay time is determined based on the buffer lag time of the flexible buffer connector under the starting impact.

[0031] In one possible implementation, the wire displacement detection module is mounted on the first moving part, and the wire displacement detection module also includes a housing, a threaded hub, a constant force spring device, and a rotation sensor.

[0032] The cable is wound around the threaded hub, and one end of the cable is led out of the cable outlet of the housing through the dust-scraping sealing structure and connected to the reference part through the flexible buffer connector.

[0033] The dust-scraping seal structure is configured to remove any adhering substances from the surface of the pull cord;

[0034] The flexible buffer connector is configured to absorb the impact load generated when the first moving part starts or stops suddenly.

[0035] In one possible implementation, the dust-scraping sealing structure includes a double-layer brush sealing ring and a dust-scraping ring, which are sequentially fitted onto the pull wire outlet.

[0036] The flexible buffer connector includes a spring buffer buckle, which includes a first connecting ring, a second connecting ring, and a helical spring disposed between the first connecting ring and the second connecting ring.

[0037] The free end of the pull wire is connected to the first connecting ring, and the second connecting ring is connected to the rigid structure of the reference component;

[0038] The threaded hub surface is machined with equidistant helical grooves, and the pull wire is wound in the equidistant helical grooves; a constant force spring device is built into the threaded hub and is configured to provide a constant retraction force to keep the pull wire taut; a rotation sensor is connected to the threaded hub and is configured to output an electrical signal proportional to the distance the pull wire moves.

[0039] A second aspect of this application provides a relative displacement detection system for detecting the relative displacement of a first moving member relative to a reference member. The system includes:

[0040] The wire displacement detection module is installed on the first moving part. The wire of the wire displacement detection module is connected to the reference part through a flexible buffer connector, and the wire outlet of the wire displacement detection module is provided with a dust scraping and sealing structure.

[0041] The drive control unit is configured to drive the first moving part to move and output operating status data;

[0042] The controller is communicatively connected to the wire displacement detection module and the drive control unit, and is configured to implement the relative displacement detection method of the first aspect or any implementation thereof.

[0043] In one possible implementation, the controller includes:

[0044] The signal filtering module is used to filter the electrical signal output by the wire displacement detection module using a first-order low-pass filter or a median average filter.

[0045] The wire breakage detection module is used to perform motion state fault detection and static state fault detection in the relative displacement detection method.

[0046] The human-computer interaction module is used to display fault prompts when a fault in motion or stationary state is detected.

[0047] A third aspect of this application provides a stacker-reclaimer, comprising:

[0048] The large cart serves as the primary moving component;

[0049] The tail section serves as a reference component;

[0050] The relative displacement detection system, as described in the second aspect or any implementation thereof, is installed between the main vehicle and the tail vehicle to detect the relative displacement of the main vehicle relative to the tail vehicle.

[0051] By employing the aforementioned technical solutions, the relative displacement detection method, system, and stacker-reclaimer provided in this application acquire actual relative displacement data through a wire displacement detection module. The wire is connected to the reference component using a flexible buffer connector, effectively absorbing vibration and shock, and preventing wire breakage or measurement inaccuracy due to rigid connection stress. The dust-scraping sealing structure at the wire outlet prevents the intrusion of dust, moisture, and other impurities, significantly improving detection reliability and module lifespan under harsh working conditions. Simultaneously, theoretical relative displacement data is determined based on the operating status data of the drive control unit, achieving fusion verification of sensor and drive data: in motion, the difference between actual and theoretical displacement is used to diagnose drive malfunctions, transmission jamming, and other faults in real time; in a stationary state, the actual displacement change at different times detects abnormalities such as wire loosening and micro-displacement, compensating for the lack of effective fault diagnosis methods in traditional single sensors, and achieving high-precision displacement detection and fault self-diagnosis under all working conditions. Attached Figure Description

[0052] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. Throughout the drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and the originals and elements are not necessarily drawn to scale.

[0053] Figure 1 A schematic flowchart of the relative displacement detection method provided in this application;

[0054] Figure 2 Example diagram of the system structure for implementing the relative displacement detection method provided in this application;

[0055] Figure 3 This is a schematic diagram of the structural composition of the relative displacement detection system provided in this application. Detailed Implementation

[0056] The embodiments of this application are described below with reference to the accompanying drawings. The terminology used in the implementation section of this application is for explaining specific embodiments only and is not intended to limit the scope of this application.

[0057] As will be known to those skilled in the art, with the development of technology and the emergence of new scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0058] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms are interchangeable where appropriate; this is merely a way of distinguishing objects with the same attributes in the embodiments of this application. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, so that a process, method, system, product, or apparatus that comprises a series of elements is not necessarily limited to those elements, but may include other elements not explicitly listed or inherent to those processes, methods, products, or apparatuses.

[0059] In large industrial equipment such as stacker-reclaimers and port machinery, there is frequent large-stroke relative motion between the main trolley and the movable tail trolley. In actual operating scenarios such as steel plants and port terminals, the equipment is subjected to harsh conditions of high dust concentration, strong mechanical vibration and large impact loads for a long time.

[0060] Specifically, if non-contact ranging methods such as laser or ultrasonic are used, high concentrations of dust and suspended particles in the air will severely scatter or absorb the detection signal, causing the measured value to jump or fail. If traditional mechanical limit switches are used, since they can only provide discrete switching signals indicating whether the device is in position or not, the control system cannot know the precise position of the trolley. As a result, it cannot perform smooth acceleration and deceleration control based on the distance to the target position, i.e., S-curve speed regulation, which leads to large shocks during equipment start-up and shutdown and affects the structural lifespan.

[0061] More importantly, attempting to introduce conventional wire-type displacement sensors to solve the continuous detection problem presents new challenges: under frequent equipment start-ups and shutdowns and strong impact loads, rigid wire connections are highly susceptible to fatigue fracture due to stress concentration; simultaneously, the wires are constantly exposed to dust, and without effective sealing, dust entering the winding mechanism can cause jamming, leading to inaccurate measurements. Furthermore, existing systems typically rely solely on sensor data; if the wire breaks or the sensor jams, the system cannot recognize the fault, potentially issuing incorrect position signals and causing safety accidents such as collisions between the main vehicle and the trailing vehicle.

[0062] To address the issues of low reliability and lack of effective fault diagnosis methods in relative displacement detection under the aforementioned harsh working conditions, this application provides a relative displacement detection method, system, and stacker-reclaimer.

[0063] See Figure 1 The present application provides a flowchart of a relative displacement detection method for detecting the relative displacement of a first moving member relative to a reference member.

[0064] like Figure 1 As shown, the method includes the following steps:

[0065] Step 101: Obtain the actual relative displacement data of the first moving part relative to the reference part through the wire displacement detection module; wherein, the wire of the wire displacement detection module is connected to the reference part through a flexible buffer connector, and the wire outlet of the wire displacement detection module is provided with a dust scraping and sealing structure.

[0066] It should be noted that there is a relative motion relationship between the first moving part and the reference part. For example, in the scenario of the tail car changing in a stacker-reclaimer, the first moving part is the main car and the reference part is the tail car. The main car moves along the track while the tail car remains stationary, thus generating relative displacement.

[0067] The wire displacement detection module is installed on the first moving part. The wire inside is not directly and rigidly fixed to the reference part after it is led out, but is connected through a flexible buffer connector.

[0068] This flexible connection method can absorb huge axial impact loads by using elastic deformation at the moment of acceleration or emergency braking of the first moving part, avoiding the impact force from being directly transmitted to the precision sensing components inside the wire displacement detection module, thereby preventing wire fatigue breakage or damage to the internal mechanism.

[0069] Meanwhile, considering that industrial sites are usually accompanied by high concentrations of dust, a dust-scraping and sealing structure is specially set at the wire outlet of the wire displacement detection module.

[0070] During the extension and retraction of the cable, the dust-scraping sealing structure can continuously remove particulate matter such as coal ash and mineral powder adhering to the surface of the cable, preventing external pollutants from entering the housing along with the cable and causing jamming or wear.

[0071] It is understood that although this embodiment describes the layout in which the wire displacement detection module is installed on the first moving part and the wire is connected to the reference part, in other embodiments, the detection module can also be installed on the reference part and the wire connected to the first moving part, as long as the relative displacement between the two can be measured.

[0072] This step, through a specific physical architecture design, ensures the long-term stability and environmental adaptability of the actual relative displacement data acquisition from the source.

[0073] For example, see Figure 2 The system structure example diagram for implementing the relative displacement detection method provided in this application is shown.

[0074] like Figure 2 As shown, the system structure includes a first moving part 100, a reference part 200, a wire displacement detection module 300 mounted on the first moving part 100, and a flexible buffer connector 400 for transitioning the wire led out from the displacement detection module 300 to the reference part 200.

[0075] Taking the tail car change scenario of a stacker-reclaimer as an example, the first moving part 100 is the main trolley, the reference part 200 is the tail car, and the flexible buffer connector 400 is a spring buffer buckle. The main trolley moves along the track while the tail car remains stationary, resulting in relative displacement. The pull wire displacement detection module 300 is installed on the main trolley to obtain the actual relative displacement data of the main trolley. The pull wire led out by the module is connected to the tail car using a spring buffer buckle.

[0076] Step 102: Obtain the operating status data output by the drive control unit used to drive the first moving part, and determine the theoretical relative displacement data based on the operating status data.

[0077] In this step, the theoretical relative displacement data does not come from an additional ranging sensor, but directly reuses the feedback information from the drive control unit itself.

[0078] The drive control unit is the power source controller for the first moving component, such as a frequency converter or servo drive. When controlling the motor's operation, it outputs real-time operating status data such as running speed, position commands, or torque. By processing this data, the theoretical distance that the first moving component should move under ideal conditions can be calculated.

[0079] The key to this dual-source data acquisition method lies in the fact that theoretical and actual values ​​originate from independent physical links: theoretical values ​​stem from the internal control model of the electric drive system, while actual values ​​originate from physical measurements at the end of the mechanical transmission chain. Under normal circumstances, the two should maintain a high degree of spatiotemporal correlation, while exhibiting significant decoupling characteristics when a fault occurs. This provides a solid data foundation for subsequent cross-validation.

[0080] Step 103: When the first moving part is in motion, perform motion state fault detection based on the difference between the actual relative displacement data and the theoretical relative displacement data.

[0081] When the system determines that the first moving part is in motion, dynamic comparison is activated.

[0082] Since the actual displacement curve output by the wire displacement detection module should keep in sync with the theoretical displacement curve fed back by the drive control unit when in motion, the health status of the system can be monitored by calculating the difference between the two in real time.

[0083] If the cable breaks or becomes severely jammed, or if the drive system experiences slippage or loss of control, the difference between the actual relative displacement data and the theoretical relative displacement data will rapidly increase and deviate from the normal allowable error range.

[0084] This step fully utilizes the dynamic characteristics of the equipment during operation, enabling rapid identification of latent faults that only manifest under stress or motion conditions, thus achieving online real-time diagnosis.

[0085] Step 104: When the first moving part is stationary, perform stationary state fault detection based on the change in actual relative displacement data acquired at different times.

[0086] When the first moving component stops running, the comparison logic in motion mode is no longer applicable, and the static stability monitoring mode is switched to the static stability monitoring mode.

[0087] Under ideal static conditions, unless subjected to external forces or mechanical creep, the position readings acquired by the wire displacement detection module should remain constant. By continuously sampling at preset intervals and calculating the position changes between adjacent moments, abnormal drift caused by accidental wire detachment, failure of internal sensor components, or accidental external contact can be effectively detected.

[0088] This step fills the blind spot in motion detection during off-peak hours, ensuring the system is in good working order before each restart and preventing safety incidents that could occur during the next operation due to sensors being damaged but not detected during downtime.

[0089] This embodiment forms a complete technical closed loop through the deep coupling of physical protection and dynamic-static dual-state soft detection algorithm, which significantly improves the reliability and safety of the relative displacement detection system under complex and harsh working conditions.

[0090] In summary, the relative displacement detection method provided in this application acquires actual relative displacement data through a wire displacement detection module. The wire is connected to the reference component using a flexible buffer connector, effectively absorbing vibration and shock, and preventing wire breakage or measurement inaccuracy due to rigid connection stress. The dust-scraping sealing structure at the wire outlet prevents the intrusion of dust, moisture, and other impurities, significantly improving detection reliability and module lifespan under harsh working conditions. Simultaneously, theoretical relative displacement data is determined based on the operating status data of the drive control unit, achieving fusion verification of sensor and drive data: in motion, the difference between actual and theoretical displacement is used to diagnose drive malfunctions, transmission jamming, and other faults in real time; in a stationary state, the actual displacement changes at different times detect abnormalities such as wire loosening and micro-displacement, compensating for the lack of effective fault diagnosis methods in traditional single sensors, and achieving high-precision displacement detection and fault self-diagnosis under all working conditions.

[0091] Based on the first embodiment described above, this embodiment further details the fault detection sub-process when the first moving part is in motion, as a second embodiment.

[0092] As one implementation method, before performing motion state fault detection, it is necessary to accurately identify the real-time motion state of the first moving part. This is a prerequisite for ensuring that the subsequent comparison algorithm is activated at the correct time.

[0093] Specifically, in response to receiving the operation command and operation feedback signal output by the drive control unit, or receiving the pulse feedback signal output by the encoder installed on the first moving part, it is determined that the first moving part is in motion.

[0094] This judgment logic employs a dual verification method involving both electrical control circuits and mechanical transmission circuits.

[0095] The combination of the running command and the running feedback signal confirms that the drive control unit has issued a power output command and is working normally, which is an electrical-level status confirmation; while the encoder pulse signal directly reflects the actual physical displacement of the first moving part, which is a mechanical-level status confirmation.

[0096] As long as any one condition is met, it is determined to be in motion, which can effectively avoid the detection blind spot caused by a single signal link failure, such as communication interruption but the motor is still gliding by inertia, or the driver malfunctions but the machine is dragged by external force.

[0097] Accordingly, in response to the absence of a running command, running feedback signal, and pulse feedback signal, it is determined that the first moving part is in a stationary state.

[0098] This negative decision logic based on the complete absence of signals ensures the integrity of the system state machine and prevents the incorrect maintenance of the motion detection mode when signals are abnormally lost.

[0099] After confirming that the first moving part is in motion, a high-precision theoretical displacement benchmark needs to be constructed for comparison.

[0100] As one implementation method, within a preset detection time window, the theoretical relative displacement data is obtained by integral calculation based on the running speed output by the drive control unit.

[0101] It is particularly important to emphasize here that the preset detection time window is configured as an integer multiple of the controller's scan cycle. This parameter limitation is not a simple numerical selection, but rather a means to achieve strict synchronization between data acquisition and the underlying control logic.

[0102] In industrial control systems, the speed update frequency of the drive control unit and the scan cycle of the controller are typically discrete and fixed. If the detection time window is not an integer multiple of the scan cycle, the integration operation will inevitably include data fragments from incomplete control cycles, resulting in periodic sawtooth-shaped fluctuation errors in the calculated theoretical displacement value.

[0103] The system error introduced by asynchronous sampling is easily misjudged as a sensor fault. By locking the window to an integer multiple of the scan period, for example, when the scan period is 50ms, setting the detection window to 500ms (10 cycles) can completely eliminate asynchronous sampling noise from the algorithm level, allowing the theoretical displacement curve to truly reflect the ideal output characteristics of the drive system, thereby significantly improving the signal-to-noise ratio of fault detection.

[0104] After obtaining the theoretical and actual displacements for synchronization and alignment, a fault determination under dual conditions is performed.

[0105] As one implementation method, the actual relative displacement data output by the wire displacement detection module within a preset detection time window is obtained, and the displacement difference between the theoretical relative displacement data and the actual relative displacement data is calculated; if the displacement difference is greater than or equal to a preset difference threshold and the duration reaches a preset time threshold, then a motion state fault is determined to have occurred.

[0106] This method employs a two-dimensional determination approach, combining amplitude and duration.

[0107] The preset difference threshold is used to define the severity of the fault. Its specific value can be obtained by taking multiple measurements and weighted averages under different operating speeds, loads and environmental conditions to cover the normal mechanical clearance and signal drift range.

[0108] The preset time threshold acts as a temporal filter to filter out transient data spikes caused by instantaneous electromagnetic interference, mechanical vibration, or sudden load changes.

[0109] For example, in a preferred embodiment, the preset detection time window can be set to 500ms, and the preset difference threshold can be calibrated according to the working conditions, with the preset time threshold set to 1s. This means that an alarm will only be triggered when the displacement deviation continuously exceeds the limit within multiple consecutive detection windows.

[0110] It is understood that the above 500ms and 1s are merely exemplary values, and in practical applications they can be flexibly adjusted according to the dynamic response characteristics of the first moving part 100 and process safety requirements. This application does not impose a unique limitation on this.

[0111] This dual-judgment method ensures a high fault detection rate while significantly reducing the false alarm rate, thus avoiding unplanned downtime caused by frequent false alarms.

[0112] Once a fault is confirmed, the system must immediately execute safety protection actions.

[0113] In one implementation, in response to the determination of a motion state fault, a stop operation command is generated to control the first moving part to decelerate and stop or to stop the brake.

[0114] This step reflects a tiered security response strategy.

[0115] For common cable breakage or minor jamming faults, the deceleration and stopping method should be used first to brake the first moving part smoothly and avoid secondary damage to the mechanical equipment caused by the huge inertial impact of sudden stop. For extreme faults that are detected as serious loss of control or endanger personal and equipment safety, the brake stopping mode can be switched to force the first moving part to lock in the shortest possible time.

[0116] The generated stop command can be directly sent to the drive control unit, or the power source can be cut off through an independent safety relay circuit, forming a dual safety redundancy in both software and hardware.

[0117] Through the complete logical chain from state recognition, synchronous integration, dual determination to hierarchical response, this embodiment anchors the abstract fault detection algorithm to specific industrial control timing and mechanical characteristics, proving that the scheme is a technical means deeply coupled with the underlying system, rather than a pure mathematical operation detached from reality.

[0118] Based on the dynamic and static dual-state detection framework mentioned in the first embodiment, this embodiment further describes in detail the fault detection logic when the first moving part is in a static state and the anti-interference method during the startup transition period, as the third embodiment.

[0119] As one implementation method, when the first moving part is stationary, a stationary state fault detection is performed based on the change in actual relative displacement data acquired at different times.

[0120] Unlike strategies that rely on comparing theoretical values ​​in motion, the core of detection in a stationary state lies in monitoring the absolute stability of the physical position.

[0121] Specifically, the detection does not start immediately upon the moment the first moving part stops moving. Instead, it acquires the current position value output by the wire displacement detection module according to a preset acquisition cycle only after a preset delay has elapsed since the first moving part stopped moving. The fundamental reason for setting this preset delay time is to eliminate transient aftershocks in the mechanical system.

[0122] In heavy equipment such as stacker-reclaimers, when the first moving component transitions from high-speed motion to a standstill, the entire system experiences a brief period of decay and oscillation due to immense inertia and the elasticity of the steel structure. If a high-precision position comparison is performed immediately during this period, the minute displacement fluctuations caused by mechanical vibration can easily be misinterpreted as sensor malfunctions. Therefore, by introducing a preset delay time, for example, no more than 5 seconds in a preferred example, to wait for the mechanical structure to fully stabilize before activating the monitoring logic, false alarms caused by environmental noise can be avoided at the source.

[0123] After the aforementioned stable waiting period, the system enters a normalized static health monitoring mode.

[0124] Specifically, the change in position between two consecutive acquired current position values ​​is calculated; if the change in position is greater than a preset static error threshold, a static state fault is determined to have occurred.

[0125] This process fills in the monitoring blind spots during equipment downtime. In actual operation, faults such as broken cables, damaged internal sensor components, or accidental external contact often occur during equipment downtime. Without static monitoring, these potential hazards will carry over to the next operating cycle, potentially causing the equipment to lose position feedback upon startup and leading to serious accidents.

[0126] By continuously verifying the stability of position data at fixed intervals during downtime, such as no more than 1 second and an integer multiple of the controller scan cycle, it is equivalent to performing an automated health check on the sensing system before each startup. Once position drift is detected to exceed the allowable static error range, the system can lock the fault in advance and issue an early warning, thereby ensuring that the equipment is always above a controllable safety baseline.

[0127] However, a new detection challenge arises the moment the device transitions from a static state to a dynamic state.

[0128] In one implementation, in response to issuing a start command for the first moving part, an anti-interference delay timer is started; if the anti-interference delay timer has not reached the preset anti-interference delay time, motion state fault detection is suspended; if the anti-interference delay timer reaches the preset anti-interference delay time, motion state fault detection is resumed.

[0129] This approach is not based on arbitrary software settings, but rather on the inherent characteristics of the physical architecture.

[0130] Specifically, the preset anti-interference delay time is determined based on the buffer hysteresis time of the flexible buffer connector under startup impact.

[0131] It should be noted that the flexible buffer connector contains a helical spring, whose core function is to absorb axial impact to protect the sensor. However, at the moment of startup acceleration, this elastic buffer structure inevitably produces a mechanical response lag: that is, the first moving part has begun to move, but the tension must first overcome the spring stiffness to deform it before it can be transmitted to the pull wire to extend. This results in the actual displacement value fed back by the pull wire displacement detection module being significantly behind the theoretical displacement value output by the drive control unit in the very short period of time at the beginning of startup. If this anti-interference delay is not set, the condition described in the second embodiment, where the displacement difference is ≥ the preset difference threshold, will inevitably be triggered every time a normal startup occurs, causing the system to misjudge the normal physical buffering effect as a wire breakage fault.

[0132] Therefore, this delay parameter is essentially a software compensation for the dynamic mechanical characteristics of the flexible buffer connector. Its specific value should be determined by measuring the response lag time of the buffer device under different working conditions on site to ensure that it can both shield the normal deviation of the start-up transient and avoid missing the real early faults due to excessive delay.

[0133] By combining the above-mentioned static state monitoring with the start-up anti-interference measures, this embodiment achieves full coverage protection for the non-steady-state transition period, ensuring a high degree of compatibility between the detection algorithm and the mechanical and physical characteristics.

[0134] This embodiment is independent of the aforementioned method flow and specifically describes in detail the physical architecture of the wire displacement detection module and its connection relationship with external components. It aims to provide solid structural support for the higher-level functional terms in the aforementioned embodiments and serves as the fourth embodiment.

[0135] In one implementation, the wire displacement detection module is mounted on the first moving part, and the wire displacement detection module also includes a housing, a threaded hub, a constant force spring device, and a rotation sensor.

[0136] In this physical architecture, the housing serves as a protective carrier, providing an IP65 or higher level of dust and water protection for the internal precision sensing components.

[0137] The threaded hub, as the core transmission component, is rotatably connected inside the housing, and its rotation angle directly maps to the extension and retraction length of the cable.

[0138] The constant force spring device is built into or coaxially mounted in the threaded hub and is configured to provide a constant return force to keep the cable tensioned. This constant tension method eliminates measurement nonlinearity errors caused by the cable's own weight sagging or slack, ensuring the linearity of displacement data across the entire range.

[0139] The rotation sensor is connected to the threaded hub and configured to output an electrical signal proportional to the distance the cable moves, such as a 4-20mA current signal or a digital pulse signal. This electrical signal is the original physical source for the controller to obtain the actual relative displacement data.

[0140] It is understood that although this embodiment uses a multi-turn absolute encoder as a preferred example of a rotation sensor, other types of angular displacement sensors such as potentiometers, magnetic encoders or photoelectric encoders can also be used in other embodiments, as long as a definite mapping relationship between the rotation angle and the linear displacement can be established.

[0141] To address environmental adaptability issues under harsh operating conditions, the cable is wound around a threaded hub, with one end leading out of the housing via a dust-scraping seal structure and connected to a reference component through a flexible buffer connector. The core design principle of this connection topology is to decouple the effects of environmental interference and mechanical shock on sensing accuracy.

[0142] Specifically, the dust-scraping sealing structure is configured to remove adhering substances from the surface of the pull wire. Its function is not only to prevent dust from entering the housing and contaminating the constant force spring device and rotary sensor, but more importantly, to prevent adhering substances from accumulating on the surface of the threaded hub, which could lead to rope misalignment or diameter changes, thus ensuring the long-term accuracy of displacement measurement from the source.

[0143] The flexible buffer connector is configured to absorb the impact load generated when the first moving part starts or stops suddenly. It creates an elastic mechanical isolation zone between the pull wire and the reference part, so that the transient high-frequency impact energy is dissipated by the elastic element, rather than being directly transmitted to the root of the pull wire or the threaded wheel hub bearing, which significantly reduces the risk of mechanical fatigue failure.

[0144] Furthermore, in order to achieve efficient cleaning and reliable buffering of the pull wire, this embodiment has carried out a specific structural design for key components.

[0145] In one embodiment, the dust-scraping sealing structure includes a double-layer brush sealing ring and a dust-scraping ring, which are sequentially fitted onto the pull wire outlet.

[0146] This multi-level serial layout forms a gradient protection system from the outside in.

[0147] Specifically, the outer dust scraper ring is usually made of wear-resistant hard material. Its inner hole fits the gap between the wire and the wire, and it is mainly responsible for scraping off large coal lumps, ore or crusts attached to the surface of the wire, playing a coarse filtration role. The inner double-layer brush sealing ring uses high-density bristles to make interference contact with the surface of the wire to further remove fine dust and block the intrusion of micro-dust carried by external airflow.

[0148] The two-stage structure works in tandem, avoiding the problem of rapid wear caused by large particles getting stuck in a single brush, and making up for the shortcomings of a single scraper ring in sealing micro-dust. It is particularly suitable for high-concentration dust scenarios such as near the hopper of a stacker-reclaimer.

[0149] It is understandable that although this embodiment describes the arrangement order of the dust scraper ring on the outside and the double-layer brush seal ring inside, in some low-dust but high-humidity environments, the order of the two can be adjusted or other sealing elements such as rubber lip seal rings can be added to adapt to different working conditions.

[0150] In terms of flexible connection, the flexible buffer connector includes a spring buffer buckle, which includes a first connecting ring, a second connecting ring, and a helical spring disposed between the first connecting ring and the second connecting ring.

[0151] This is a typical axial elastic damping structure. The free end of the draw wire is connected to the first connecting ring, and the second connecting ring is connected to the rigid structure of the reference component. When the first moving component suddenly accelerates or brakes, the huge inertial force first acts on the helical spring, causing it to undergo axial compression or tensile deformation, converting kinetic energy into elastic potential energy for storage and gradual release, thus smoothing the force curve transmitted to the draw wire.

[0152] Compared to rigid connections, the structural design can reduce peak impact force by several times or even tens of times, effectively preventing fatigue fracture of the guy wire at the root crimping point.

[0153] It should be noted that the spring buffer buckle is only one specific implementation of the flexible buffer connector. In other embodiments, the same buffer function can also be achieved by using components with elastic energy storage or energy dissipation characteristics, such as rubber shock-absorbing pads, hydraulic dampers, or disc spring assemblies. This application does not limit this to a single method.

[0154] In addition, to ensure the accuracy and stability of the displacement conversion mechanism, the surface of the threaded hub is machined with equidistant spiral grooves, and the wire is wound in the equidistant spiral grooves.

[0155] The equidistant spiral groove design mandates a fixed axial feed pitch during the winding and unwinding process, completely eliminating the overlapping and skipping of the rope caused by multi-layer disordered winding, and ensuring that the rotation angle corresponding to each turn of the rope remains constant. Combined with the constant return force provided by the built-in constant force spring device, the rope always remains tightly attached to the bottom surface of the spiral groove, preventing slippage or loosening caused by tension fluctuations.

[0156] This precise mechanical fit is the material basis for the actual relative displacement data in the aforementioned embodiments to truly reflect physical displacement, thereby supporting the accurate operation of the dynamic and static dual-state fault detection algorithm.

[0157] Without the synergistic effect of the equidistant spiral grooves and constant force springs, simple software algorithms cannot compensate for the nonlinear system errors introduced by mechanical rope tangles or uneven tension, and the reliability of the entire detection system will be greatly reduced.

[0158] Therefore, the physical architecture described in this embodiment is not an isolated stack of mechanical components, but an organic whole that is deeply coupled with and mutually supports the detection method.

[0159] This application also provides a relative displacement detection system for detecting the relative displacement of a first moving member relative to a reference member.

[0160] See Figure 3 The structural composition diagram of the relative displacement detection system provided in this application shows that the system constructs a physical architecture that deeply integrates hardware entities and software algorithms, mainly including a wire displacement detection module 300, a drive control unit 301, and a controller 302.

[0161] In one implementation, the wire displacement detection module 300 is mounted on the first moving part, the wire of the wire displacement detection module 300 is connected to the reference part through a flexible buffer connector, and the wire outlet of the wire displacement detection module 300 is provided with a dust scraping and sealing structure.

[0162] In the system-level physical topology, this connection constitutes the mechanical link for displacement sensing.

[0163] Specifically, the wire displacement detection module 300, as a sensing terminal, moves synchronously with the first moving component, and its internal wire is anchored to a stationary or relatively moving reference component via a flexible buffer connector.

[0164] The flexible buffer connector not only serves as a mechanical connection but also acts as the first line of defense against impact, absorbing axial loads during start-up and shutdown. The dust-scraping sealing structure acts as an environmental isolation barrier, ensuring the long-term effectiveness of the sensing link under high-dust conditions.

[0165] It is understood that although this embodiment uses the example of the wire displacement detection module 300 being installed on the first moving part, in other embodiments, the wire displacement detection module 300 can also be installed on the reference part and the wire can be connected to the first moving part, as long as a measurement path for the relative displacement between the two can be established.

[0166] In one implementation, the drive control unit 301 is configured to drive the first moving part to move and output operating status data.

[0167] The drive control unit 301 is the source of power execution and information feedback for the system, and it can be a frequency converter, servo drive or dedicated motor controller.

[0168] In terms of hardware connection, the drive control unit 301 is connected to the drive motor of the first moving part through a power cable, and communicates with the controller 302 through an industrial fieldbus, such as Profinet, EtherCAT, or hardwired IO, to upload operating status data such as running speed, position command, torque feedback and fault codes in real time.

[0169] These data form the reference input for subsequent theoretical displacement calculations, enabling the system to obtain high-precision motion reference values ​​without the need for additional speed sensors.

[0170] In one implementation, the controller 302 is communicatively connected to the wire displacement detection module 300 and the drive control unit 301, and is configured to execute the relative displacement detection method as described in the foregoing embodiments.

[0171] The controller 302 is the information processing center and safety decision-making core of the entire system.

[0172] In terms of hardware form, the controller 302 can be a programmable logic controller (PLC), an industrial personal computer (IPC), an embedded control board, or an application-specific integrated circuit (ASIC). Regardless of the hardware carrier used, its core function is to aggregate the actual displacement signal from the wire displacement detection module 300 and the operating status data from the drive control unit 301, and execute a dynamic and static dual-state fault detection algorithm through internally embedded program logic, ultimately outputting control commands or alarm information. This hardware-software decoupling design makes the system widely adaptable to different platforms, facilitating porting and upgrading on different types of industrial equipment.

[0173] Furthermore, in order to achieve efficient and reliable data processing and fault diagnosis, the controller 302 adopts a modular functional architecture.

[0174] In one implementation, the controller 302 includes a signal filtering module, a disconnection detection module, and a human-machine interaction module.

[0175] Specifically, the signal filtering module is configured to use a first-order low-pass filter or a median average filter to filter the electrical signal output by the draw wire displacement detection module 300.

[0176] Due to the complex electromagnetic environment and unavoidable mechanical vibrations in industrial settings, the raw analog or digital signals output by the wire displacement detection module 300 are often superimposed with high-frequency noise or random pulse interference. The signal filtering module, as the first stage of data preprocessing, smooths the signal trend through first-order low-pass filtering or removes occasional spikes through median averaging filtering, thereby extracting the effective components that truly reflect the physical displacement.

[0177] This step is crucial for improving the signal-to-noise ratio of subsequent disconnection detection algorithms, and can effectively prevent false triggering caused by signal glitches.

[0178] It is understood that first-order low-pass filtering and median average filtering are only preferred examples. In other implementations, moving average filtering, Kalman filtering or other digital filtering algorithms suitable for industrial signal processing can also be used, as long as they can achieve the purpose of suppressing noise and preserving effective features.

[0179] The disconnection detection module is configured to perform motion state fault detection and static state fault detection in the relative displacement detection method. This module is the core logic unit of the controller 302, and it encapsulates the complete detection algorithms detailed in the first to third embodiments described above.

[0180] In the data flow direction, the disconnection detection module receives clean displacement data processed by the signal filtering module and operating status data from the drive control unit 301. It automatically switches between motion comparison mode and static monitoring mode according to the preset state machine logic, and performs anti-interference delay shielding during the startup transition period.

[0181] By encapsulating complex timing logic and threshold determination into independent functional modules, not only is the calling complexity of the main program simplified, but it also facilitates subsequent parameter tuning or algorithm iteration for specific operating conditions without having to refactor the entire control system code.

[0182] The human-machine interface module is configured to display fault prompts when a fault in either the motion state or the stationary state is detected. Once the disconnection detection module confirms a fault, the human-machine interface module is responsible for converting the abstract internal state into information that maintenance personnel can intuitively perceive.

[0183] Specifically, the fault information may include the fault type, such as broken cable, stuck sensor, abnormal static drift, the time of occurrence, the displacement value at that time, and suggested handling measures.

[0184] In terms of hardware implementation, the human-machine interface module provides display, I / O and communication interfaces, which can connect to touch screens (Human Machine Interface, HMI devices), drive sound and light alarms, and interact with host computers running SCADA (Supervisory Control And Data Acquisition) and mobile terminals with operation and maintenance APP installed through standard communication interfaces such as RS485, Ethernet and Wi-Fi.

[0185] For example, in a preferred embodiment, the human-machine interaction module pushes fault messages to the cab touchscreen via the Modbus TCP protocol and displays them in a red pop-up window, while simultaneously recording fault logs for later traceability.

[0186] This multi-dimensional information feedback method significantly shortens troubleshooting time and improves equipment maintainability and operational safety.

[0187] Through the modular architecture described above, the relative displacement detection system provided in this embodiment achieves a closed-loop process from signal acquisition, preprocessing, intelligent diagnosis to human-machine interaction. The modules interact through standardized data interfaces, ensuring both the independence and professionalism of each function while maintaining the overall system's collaborative efficiency. In particular, by embedding the wire breakage detection algorithm into a dedicated module within the controller, this technical solution no longer relies on the built-in functions of external general-purpose sensors. Instead, it becomes a customized security component deeply integrated with the overall control strategy, thus providing stronger defensive capabilities in product infringement evidence collection and technical barrier construction.

[0188] This application also provides a stacker-reclaimer that uses the relative displacement detection system described in any of the foregoing embodiments.

[0189] As a specific application scenario, the stacker-reclaimer includes a trolley and a tail car, with the trolley serving as the first moving part and the tail car as the reference part. A relative displacement detection system is installed between the trolley and the tail car to detect the relative displacement of the trolley relative to the tail car in real time.

[0190] It is understood that although this embodiment uses a stacker-reclaimer with a movable tail car as an example for illustration, the technical solution provided in this application is also applicable to other industrial equipment such as port machinery and mining conveying equipment that have similar high dust and large impact and require precise relative displacement detection, as long as they have two relatively moving parts.

[0191] In the actual operation of a stacker-reclaimer, tail car change is a key step in switching between stacking and reclaiming modes.

[0192] Specifically, when it is necessary to switch from the stacking state to the picking state, the connecting hook between the tail car and the main car is raised, the tail car remains stationary, and the main car moves along the track to the predetermined position and stops; then the front end of the tail car boom is lowered to the lowest point, the main car then moves backward until it touches the backward stop limit, and finally the connecting hook is lowered to complete the change.

[0193] Conversely, when switching from the material picking state to the material stacking state, a similar process of the trolley moving forward and backward is also required. In this series of actions, the trolley generates continuous relative displacement with respect to the tail car, and the accurate measurement of this displacement is crucial for achieving smooth acceleration and deceleration control and precise positioning of the trolley.

[0194] In this application scenario, the cable displacement detection module 300 is typically installed at a suitable location near the connection point between the main trolley and the tail car, with its cable outlet aligned with the tail car and connected to the rigid structure of the tail car via a flexible buffer connector. Because this location is adjacent to the hopper, the working environment is filled with a high concentration of coal ash or mineral powder, making traditional lidar or ultrasonic sensors highly susceptible to failure due to light path obstruction or sound wave scattering.

[0195] This embodiment, by setting up a dust-scraping sealing structure, utilizes the multi-stage cleaning effect of the double-layer brush sealing ring and the dust-scraping ring to continuously remove dust particles attached to the surface of the cable during the reciprocating motion of the trolley driving the cable to extend and retract. This effectively prevents contaminants from entering the housing and causing the sensing element to jam or wear, thereby ensuring the long-term accuracy and stability of displacement data in high-dust environments.

[0196] Meanwhile, the stacker-reclaimer's trolley is a heavy-duty mobile device, which generates a huge axial inertial impact force during acceleration or emergency braking. If the cable and the tail car are rigidly connected, this impact force will be directly transmitted to the cable displacement detection module 300, which can easily cause fatigue fracture of the cable or damage to the precision transmission mechanism.

[0197] This embodiment introduces a flexible buffer connector, particularly a spring buffer buckle structure incorporating a helical spring, to create an elastic mechanical isolation zone between the cable and the tail anchor point. When the trolley starts and stops, generating impact loads, the helical spring absorbs and dissipates kinetic energy through elastic deformation, significantly reducing the peak stress transmitted to the cable root, thereby extending the sensor's service life and ensuring mechanical reliability under frequent start-stop conditions.

[0198] Furthermore, based on the continuous and accurate actual relative displacement data provided by the system, the stacker-reclaimer controller 302 can calculate the distance deviation between the current position of the trolley and the target position in real time, and then dynamically adjust the output frequency of the drive control unit 301 to achieve smooth acceleration and deceleration control of the trolley.

[0199] This not only solves the industry pain point that traditional limit switches can only provide discrete positioning signals and cannot support process speed regulation, but also avoids the safety hazard of large vehicles losing control and colliding due to limit switch failure. Especially in unattended automatic switching mode, the system, in conjunction with the dynamic and static fault detection in the aforementioned embodiments, can promptly identify and trigger a safe shutdown when abnormalities such as sensor disconnection or jamming occur, providing a solid technical guarantee for the intelligent and safe operation of the stacker-reclaimer.

[0200] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A relative displacement detection method for detecting the relative displacement of a first moving member relative to a reference member, characterized in that, The method includes: The actual relative displacement data of the first moving part relative to the reference part is obtained by the wire displacement detection module; wherein, the wire of the wire displacement detection module is connected to the reference part through a flexible buffer connector, and the wire outlet of the wire displacement detection module is provided with a dust scraping and sealing structure. The operating status data output by the drive control unit used to drive the first moving part is acquired, and the theoretical relative displacement data is determined based on the operating status data. When the first moving part is in motion, motion state fault detection is performed based on the difference between the actual relative displacement data and the theoretical relative displacement data; When the first moving part is stationary, a stationary state fault detection is performed based on the change in the actual relative displacement data acquired at different times.

2. The relative displacement detection method according to claim 1, characterized in that, When the first moving component is in motion, the motion state fault detection is performed based on the difference between the actual relative displacement data and the theoretical relative displacement data, including: Within a preset detection time window, the theoretical relative displacement data is obtained by integral calculation based on the running speed output by the drive control unit. Obtain the actual relative displacement data output by the wire displacement detection module within the preset detection time window; Calculate the displacement difference between the theoretical relative displacement data and the actual relative displacement data; If the displacement difference is greater than or equal to a preset difference threshold and the duration reaches a preset time threshold, then a motion state fault is determined to have occurred.

3. The relative displacement detection method according to claim 2, characterized in that, The preset detection time window is an integer multiple of the controller's scanning cycle; The method further includes: In response to receiving the running command and running feedback signal output by the drive control unit, or receiving the pulse feedback signal output by the encoder installed on the first moving part, it is determined that the first moving part is in the motion state; In response to the absence of the running instruction, the running feedback signal, and the pulse feedback signal, it is determined that the first moving part is in the stationary state; In response to the determination that the motion state fault has occurred, a stop operation command is generated to control the first moving part to decelerate and stop or to stop by braking.

4. The relative displacement detection method according to claim 1, characterized in that, The step of performing stationary state fault detection based on the change in the actual relative displacement data acquired at different times when the first moving part is stationary includes: After the first moving part stops running and a preset delay time is reached, the current position value output by the wire displacement detection module is obtained according to the preset acquisition cycle; Calculate the change in position between two consecutive current position values; If the change in position is greater than a preset static error threshold, a static state fault is determined to have occurred.

5. The relative displacement detection method according to claim 4, characterized in that, The method further includes: In response to issuing a start command for the first moving component, an anti-interference delay timer is initiated; If the anti-interference delay time is not reached, the motion state fault detection will be suspended. If the anti-interference delay timer reaches the preset anti-interference delay time, the motion state fault detection will resume. The preset anti-interference delay time is determined based on the buffer lag time of the flexible buffer connector under the starting impact.

6. The relative displacement detection method according to claim 1, characterized in that, The wire displacement detection module is installed on the first moving part, and the wire displacement detection module also includes a housing, a threaded hub, a constant force spring device, and a rotation sensor. The pull wire is wound around the threaded hub, and one end of the pull wire is led out of the pull wire outlet of the housing through the dust scraping sealing structure and connected to the reference piece through the flexible buffer connector. The dust-scraping sealing structure is configured to remove deposits from the surface of the pull wire; The flexible buffer connector is configured to absorb the impact load generated when the first moving part starts or stops suddenly.

7. The relative displacement detection method according to claim 6, characterized in that, The dust-scraping sealing structure includes a double-layer brush sealing ring and a dust-scraping ring, which are sequentially fitted onto the pull wire outlet. The flexible buffer connector includes a spring buffer buckle, which includes a first connecting ring, a second connecting ring, and a helical spring disposed between the first connecting ring and the second connecting ring. The free end of the pull wire is connected to the first connecting ring, and the second connecting ring is connected to the rigid structure of the reference member; The threaded hub surface is machined with equidistant helical grooves, and the pull wire is wound in the equidistant helical grooves; the constant force spring device is built into the threaded hub and is configured to provide a constant retraction force to keep the pull wire taut; the rotation sensor is connected to the threaded hub and is configured to output an electrical signal proportional to the distance the pull wire moves.

8. A relative displacement detection system for detecting the relative displacement of a first moving member relative to a reference member, characterized in that, The system includes: A wire displacement detection module is installed on the first moving part. The wire of the wire displacement detection module is connected to the reference part through a flexible buffer connector, and the wire outlet of the wire displacement detection module is provided with a dust scraping and sealing structure. The drive control unit is configured to drive the first moving part to move and output operating status data; The controller is communicatively connected to the wire displacement detection module and the drive control unit, and is configured to perform the relative displacement detection method as described in any one of claims 1 to 7.

9. The relative displacement detection system according to claim 8, characterized in that, The controller includes: The signal filtering module is used to filter the electrical signal output by the wire displacement detection module using a first-order low-pass filter or a median average filter. The wire breakage detection module is used to perform motion state fault detection and static state fault detection in the relative displacement detection method. The human-computer interaction module is used to display fault prompts when a fault in motion or stationary state is detected.

10. A stacker-reclaimer, characterized in that, include: The large cart serves as the primary moving component; The tail section serves as a reference component; The relative displacement detection system as described in claim 8 or 9 is installed between the main vehicle and the tail vehicle to detect the relative displacement of the main vehicle relative to the tail vehicle.

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