Method for controlling the wire rope torque balance of the hoisting and opening / closing mechanism of a grab bucket ship unloader

Abstract

This invention relates to the field of opening and closing mechanism control technology, specifically disclosing a wire rope torque balance control method for the hoisting and opening / closing mechanisms of a grab unloader. This invention addresses the problems of existing speed synchronization control methods, which are prone to rope length differences due to the accumulation of small speed differences, leading to wire rope tension imbalance. It also addresses the limitations of torque limiting methods in actively correcting deviations, and the susceptibility of external tension sensors to environmental interference and high maintenance costs. The invention collects the angular velocities of the hoisting and opening / closing drums, calculates the linear velocity difference, integrates it to obtain the rope length difference as the closed-loop deviation, and outputs a compensation coefficient through the controller to correct only the torque of the opening / closing motor, while keeping the hoisting motor torque unchanged. Simultaneously, it incorporates multi-level amplitude limiting and smooth reset logic for non-operating conditions. This invention requires no additional hardware, has low computational overhead, and can suppress rope length differences and tension imbalances at their source, effectively preventing grab tilting and material spillage. It offers stable operation and strong anti-interference capabilities, is suitable for complex port operating environments, and is easy to promote and apply throughout the industry.

Description

Technical Field

[0001] This invention relates to the field of opening and closing mechanism control technology, and in particular to a method for controlling the wire rope torque balance of the lifting and opening / closing mechanisms of a grab bucket ship unloader. Background Technology

[0002] The four-rope grab unloader is the core equipment for bulk cargo loading and unloading operations in ports. During the material lifting operation phase after the grab closes, the hoisting mechanism and the opening and closing mechanism support the grab and the material together through two sets of wire ropes. The two sets of drums need to work together to ensure that the wire ropes are of consistent length and have balanced tension in order to maintain the horizontal posture of the grab and ensure the normal operation.

[0003] Currently, the mainstream approach in the industry is speed synchronization control, which uses the hoisting mechanism's operating speed as a benchmark to control the opening and closing mechanism to follow suit. However, during actual operation, mechanical transmission components have machining and assembly errors, brakes have gaps, and the wire ropes possess elastic deformation characteristics. Furthermore, frequent acceleration and deceleration during operation mean that even with closed-loop speed regulation, a small instantaneous speed difference will continuously exist between the hoisting drum and the opening / closing drum. While this speed difference has limited impact per cycle, it accumulates over time, gradually transforming into a length difference between the two sets of wire ropes. Inconsistent wire rope lengths directly cause tension imbalance, leading to problems such as bucket tilting and material leakage. Simultaneously, wire ropes under prolonged uneven tension will experience accelerated fatigue and aging, significantly shortening the equipment's lifespan. To alleviate tension overload issues, some equipment employs direct torque limiting control, achieving passive overload protection by setting a maximum motor torque threshold. This method can only avoid the risk of motor overload operation, but cannot actively eliminate the existing wire rope length difference and tension deviation. It is a post-event protection measure and cannot solve the core problem of grab bucket tilting and material spillage from the root. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling the wire rope torque balance of the lifting and opening / closing mechanism of a grab unloader, comprising the following steps: Obtain the angular velocity data of the hoisting drum and the opening and closing drum; Based on the angular velocity data of the hoisting drum and the angular velocity data of the opening and closing drum, the linear velocity difference between the two drums is calculated, and the linear velocity difference is integrated over time to obtain the rope length difference, which characterizes the length deviation of the two wire ropes. The rope length difference is input as a deviation to the proportional-integral controller, which then outputs a dimensionless compensation coefficient. The reference torque setpoint of the opening and closing motor is obtained from the speed loop, and the reference torque setpoint of the opening and closing motor is corrected according to the compensation coefficient to generate the corrected torque setpoint of the opening and closing motor, while keeping the torque setpoint of the hoisting motor unchanged. The corrected torque setpoint of the switching motor is output to the switching frequency converter, and the rope length difference is cleared to zero when the preset reset condition is detected.

[0005] Furthermore, the present invention also discloses a wire rope torque balance control system for the lifting and opening / closing mechanism of a grab unloader, comprising: The acquisition module is used to acquire the angular velocity data of the hoisting drum and the opening and closing drum; The calculation module is used to calculate the difference in linear velocity between the two drums based on the angular velocity data of the hoisting drum and the angular velocity data of the opening and closing drum, and to perform time integration on the difference in linear velocity to obtain the rope length difference characterizing the deviation in length between the two wire ropes. The output module is used to input the rope length difference as a deviation to the proportional-integral controller, and output a dimensionless compensation coefficient through the proportional-integral controller. The generation module is used to obtain the reference torque setpoint of the opening and closing motor from the speed loop, correct the reference torque setpoint of the opening and closing motor according to the compensation coefficient, generate the corrected torque setpoint of the opening and closing motor, while keeping the torque setpoint of the hoisting motor unchanged. The control module is used to output the corrected torque setpoint of the switching motor to the switching frequency converter, and to clear the rope length difference to zero when the preset reset condition is detected.

[0006] Furthermore, the output module includes: A determining unit is used to determine the proportional coefficient and integral coefficient of the proportional-integral controller through on-site self-tuning. The calculation unit is used to calculate the proportional output value based on the rope length difference of the current cycle and the proportional coefficient in each control cycle, and to recursively calculate the integral output value based on the rope length difference, the integral coefficient and the control cycle. The limiting unit is used to add the proportional output value and the integral output value to obtain the original compensation coefficient, and to limit the overall amplitude of the original compensation coefficient so that its variation range is limited to a preset safe range. The output unit is used to perform rate-of-change limiting processing on the compensation coefficient after the limit is applied, limiting its change amplitude in each control cycle to not exceed the preset maximum change step size, and outputting the final compensation coefficient after processing.

[0007] The beneficial effects of this application are as follows: Firstly, this invention utilizes the existing standard hardware of the grab unloader, such as encoders and frequency converters, to build the control loop, eliminating the need for additional detection devices. This completely avoids the problems of easy failure and signal interference of external sensors in the harsh port environment, and achieves zero incremental hardware cost, reducing investment in equipment modification and subsequent maintenance. It is suitable for various on-site application scenarios of existing and newly built grab unloaders. Breaking away from the traditional approach of using instantaneous speed and torque as closed-loop feedback quantities, this invention uses the wire rope length difference obtained by integrating the drum speed difference over time as the core deviation quantity for closed-loop adjustment. This directly addresses the technical root cause of tension imbalance caused by the continuous accumulation of small speed differences, actively converging the rope length difference to a reasonable range. This effectively improves the operational problems of grab bucket tilting and material spillage, while reducing abnormal fatigue wear of the wire rope and extending the service life of accessories.

[0008] Secondly, this invention adopts an asymmetric control strategy that only adjusts the torque of the opening and closing motors while keeping the operating state of the hoisting motor unchanged. This differs from the traditional dual-motor synchronous adjustment mode, effectively weakening the control coupling between the two drive mechanisms and avoiding system oscillation and instability. At the same time, the solution is equipped with multiple constraint mechanisms, such as integral limiting, compensation coefficient change rate limiting, torque safety limiting, and exponential decay reset of compensation coefficient under non-operational conditions. This ensures that the control parameters and torque output change smoothly and continuously, eliminating grab shaking and mechanical shock caused by sudden torque changes, and further improving the smoothness and safety of equipment operation. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of a method flow proposed in an embodiment of this application.

[0010] Figure 2 This is a schematic diagram of the system structure proposed in an embodiment of the present invention.

[0011] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0012] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0013] like Figure 1 As shown, this application provides a method for controlling the wire rope torque balance of the lifting and opening / closing mechanism of a grab unloader, including the following steps: S1: Real-time acquisition of the angular velocity of the hoisting drum and the angular velocity of the opening and closing drum; S2: Calculate the difference in linear velocity between the two drums based on the angular velocity of the hoisting drum and the angular velocity of the opening and closing drum. The difference in linear velocity is equal to the drum radius multiplied by the difference in angular velocity between the hoisting drum and the opening and closing drum. Integrate the difference in linear velocity over time to obtain the difference in rope length. S3: The rope length difference is used as the deviation and input to the proportional-integral controller. The controller outputs a dimensionless compensation coefficient, which is equal to the proportional coefficient multiplied by the rope length difference plus the integral coefficient multiplied by the integral value of the rope length difference. S4: Obtain the reference torque setpoint of the opening and closing motor from the original speed loop, and correct the torque setpoint of the opening and closing motor using the compensation coefficient. The correction method is to multiply the reference torque setpoint by 1 and add the sum of the compensation coefficients, while keeping the torque setpoint of the hoisting motor unchanged. S5: Output the corrected torque setpoint of the opening and closing motor to the opening and closing frequency converter, and reset the rope length difference to zero when the grab bucket is opened, the unloader stops, or the hoisting drum reaches the top limit signal.

[0014] The above technical solution can be applied to the closed bucket lifting operation scenario of a bridge-type grab unloader in a port. During long-term operation, the lifting drum and the opening and closing drum are affected by objective factors such as differences in mechanical transmission components, brake clearance, and elastic deformation of the wire rope. The instantaneous operating speed of the two sets of drums cannot be completely synchronized, and a small linear speed difference will always exist. The traditional industry generally adopts the speed synchronization control method. This method only follows and adjusts the instantaneous speed and cannot deal with the problem of small speed differences accumulating over time. The long-term accumulation of speed difference will form a significant wire rope length difference, which will cause uneven tension distribution of the wire ropes on both sides, leading to problems such as grab bucket tilting and material spillage during operation. Some equipment uses direct torque limiting, which is only a passive overload protection and cannot actively correct the existing wire rope length difference. Some equipment is equipped with a dedicated wire rope tension sensor for feedback control. However, the port site has the characteristics of high dust, high humidity, and strong vibration. The failure rate of external tension sensors is high, and it will also significantly increase the hardware cost and daily maintenance workload of the equipment. None of the aforementioned existing technical solutions can fundamentally solve the problem of wire rope tension imbalance caused by the accumulation of speed difference without adding new hardware. Therefore, it is necessary to design a completely new control logic to carry out closed-loop adjustment on the rope length difference formed by the integral of speed difference and actively eliminate the wire rope length deviation.

[0015] The above technical solution is the basic and complete process of the wire rope torque balance control method for the lifting and opening / closing mechanism of the grab unloader. It can sequentially complete the entire process of drum angular velocity acquisition, linear velocity difference calculation and integral solution of rope length difference, proportional-integral controller calculation to generate compensation coefficient, torque setpoint correction of opening / closing motor, torque command output, and zeroing of rope length difference under non-operational conditions. The entire process relies on the existing encoder and frequency converter of the grab unloader to build a closed-loop control system, and adopts an asymmetric torque adjustment strategy. The whole system is used to achieve the core control objective of torque balance and tension matching of the lifting wire rope and opening / closing wire rope during the lifting and closing operation of the grab unloader in the port bridge grab unloader.

[0016] To address the shortcomings of existing technologies, this solution abandons the traditional control approach that uses instantaneous speed and real-time torque as direct feedback quantities. Instead, it uses the rope length difference obtained by integrating the speed difference between the two drums over time as the core deviation quantity for closed-loop control, constructing a dedicated outer-loop closed-loop control circuit. At the same time, it adopts an asymmetric control architecture that only adjusts the torque of the opening and closing motors while keeping the torque of the hoisting motor constant. Combined with the integral zeroing logic under non-operating conditions to avoid the accumulation of invalid data, it relies on the original hardware of the equipment to actively correct the wire rope length difference, thus solving the tension imbalance problem at its root.

[0017] This invention relies on the existing incremental encoders of the grab unloader to collect the real-time angular velocities of the hoisting drum and the opening / closing drum. After signal filtering to remove on-site interference, the instantaneous linear velocity difference between the two sets of drums is calculated. Then, through a fixed control cycle, time integration is performed on the instantaneous linear velocity difference to convert the continuously existing minute velocity difference into a quantifiable wire rope length deviation, i.e., rope length difference. The rope length difference is used as the core feedback deviation quantity of the closed-loop control and is connected to the proportional-integral controller. The controller dynamically outputs a dimensionless compensation coefficient according to the magnitude of the rope length difference. This compensation coefficient is used to correct the reference torque output of the original speed loop of the opening / closing motor, so that the hoisting motor torque always remains in its original state. The system maintains constant torque and adjusts the force and release rate of the opening and closing wire ropes by dynamically changing the torque of the opening and closing motors, continuously adjusting the rope length difference to zero. This eliminates the tension imbalance caused by the wire rope length deviation. The system also incorporates multiple auxiliary mechanisms, including integral limiting, compensation coefficient limiting, torque safety limiting, signal filtering, and compensation coefficient smoothing, to suppress problems such as integral drift, signal distortion, and torque mutation. Simultaneously, it identifies non-operating conditions such as grab bucket opening, equipment shutdown, and lifting upper limit, promptly clearing the rope length difference and resetting the control logic. Without adding any hardware, the entire system achieves dynamic balance of torque and tension of the two wire ropes during the lifting and lowering of the grab bucket unloader.

[0018] This invention innovatively uses the rope length difference, obtained by integrating the speed difference, as the feedback quantity, instead of the traditional design approach that relies on instantaneous speed and torque. It addresses the root cause of long-term speed difference accumulation by proactively eliminating wire rope length deviations, effectively resolving long-standing industry problems such as uneven wire rope tension, grab bucket tilting, and material spillage caused by rope length differences. Secondly, it utilizes existing standard hardware such as encoders and frequency converters to implement all control logic, eliminating the need for additional detection equipment like tension sensors, achieving zero incremental hardware costs and reducing equipment failure probability and daily maintenance workload in the complex port environment. Finally, it employs an asymmetric control strategy that only adjusts the opening and closing motors, significantly weakening the control coupling between the two drive mechanisms. Combined with multi-level limiting, condition reset, and signal filtering protection logic, the stability and anti-interference capabilities of the control system are significantly improved, allowing for long-term stable operation in high-vibration and high-dust port environments.

[0019] In one embodiment, the real-time acquisition of the angular velocity of the hoisting drum and the angular velocity of the opening and closing drum in step S1 specifically includes: S11: Install incremental rotary encoders on the lifting drum shaft end and the opening and closing drum shaft end respectively. The encoder resolution is not less than 1024 pulses per revolution. Connect the encoder signal to the high-speed counter module of the programmable logic controller. In step S11, the incremental rotary encoder and the high-speed counter are both conventional hardware in the field of industrial speed acquisition. By directly mounting the encoder on the end of the drum shaft, the rotation pulses of the drum can be directly picked up. The resolution of 1024 pulses per revolution can increase the number of sampling points in a single rotation process and reduce the speed calculation error caused by the hardware. The pulse signal acquired by this set of hardware is also the basic data for all subsequent angular velocity conversion work.

[0020] S12: A separate interrupt task is set up in the programmable logic controller (PLC). The control cycle of this interrupt task is between 200 and 500 milliseconds. Each control cycle triggers a speed acquisition. The original speed loop of the grab unloader has a control cycle of 10 to 50 milliseconds. By setting a separate interrupt task and using a 200-millisecond control cycle, the timing conflict between the speed acquisition process and the original speed loop can be completely avoided. Simultaneously, the fixed 200-millisecond control cycle serves as the standard time reference for subsequent linear velocity difference time integration calculations. The integration calculation is used to accumulate the linear velocity difference to obtain the rope length difference. A unified time reference avoids timing errors during integration, ensuring that the final rope length difference accurately reflects the cumulative deviation in the lengths of the two wire ropes.

[0021] S13: The system completes the physical quantity conversion from pulse signal to angular velocity. Within a 200-millisecond control cycle, the system reads the pulse increment generated by the hoisting encoder and the opening / closing encoder in the current cycle through a high-speed counter. The pulse increment is divided by the encoder resolution of 1024 pulses per revolution to obtain the number of revolutions of the drum in a single cycle. This number of revolutions is then multiplied by twice pi to convert it into the number of radians of drum rotation. Finally, the number of radians is divided by the 200-millisecond control cycle to obtain the angular velocities of the hoisting drum and the opening / closing drum, in radians per second. This conversion process follows the basic physical calculation rules of circular motion. The angular velocities obtained after conversion have a unified dimension and can be directly substituted into subsequent calculations. Furthermore, the linear velocity difference between the two drums can be calculated, achieving continuous data flow from pulse signal to angular velocity and then to the linear velocity difference.

[0022] S14: Perform first-order low-pass filtering on the collected hoisting drum angular velocity and opening / closing drum angular velocity. The filtering time constant is set to 0.5 seconds to 1.0 seconds to eliminate the influence of mechanical vibration and encoder quantization noise on the angle signal. The filtered angular velocity value is used for subsequent calculations.

[0023] In step S14, the mechanical vibration at the port site and the quantization noise generated by the encoder operation cause frequent fluctuations in the instantaneous angular velocity value. The first-order low-pass filter with a time constant of 0.5 seconds can smooth the fluctuating signal and effectively eliminate signal distortion. After filtering and optimization, the fluctuation amplitude of the angular velocity value is significantly reduced, and the linear velocity difference calculated accordingly will not have abnormal jumps. This can prevent instantaneous changes in the rope length difference, thereby ensuring a smooth change in the compensation coefficient output by the proportional-integral controller. It also avoids sudden changes in the torque of the opening and closing motor that could cause the grab bucket to shake, continuously supporting the core functions of the present invention: wire rope torque balance and tension imbalance suppression.

[0024] As described in steps S11-S14 above, by standardizing hardware selection, configuring independent interrupt tasks, designing standardized numerical conversion logic, and adding signal filtering processing, the entire process of acquiring the hoisting drum angular velocity and the opening and closing drum angular velocity is completed. The obtained angular velocity data will be directly used for subsequent linear velocity difference calculation, linear velocity difference time integration, rope length difference solution, and proportional-integral controller calculation. This provides a stable and accurate raw input for the wire rope torque balance control method of the grab unloader hoisting and opening and closing mechanism, supporting the equipment to achieve the core control objective of wire rope tension balance.

[0025] Most existing grab unloaders use the general-purpose input / output ports of programmable logic controllers (PLCs) to poll encoder signals, without setting up a separate interrupt task for speed acquisition. The acquisition cycle is often mixed with the existing speed loop's control cycle of 10 to 50 milliseconds, easily leading to timing conflicts. Furthermore, existing equipment generally does not specify a minimum encoder resolution; low-resolution encoders amplify speed calculation errors, and most solutions lack dedicated signal processing for field vibrations and encoder quantization noise, resulting in insufficient anti-interference performance of the speed signal.

[0026] This technical solution is applied to the closed-bucket lifting operation scenario of a bridge-type grab unloader in a port. During operation, the equipment continuously generates mechanical vibrations, and the incremental rotary encoder produces inherent quantization noise. Both types of interference cause irregular fluctuations in the speed acquisition signal. The core control logic calculates the linear velocity difference between the two drums' angular velocities, then integrates this difference over time to obtain the rope length difference, which is used as the core deviation for closed-loop control. The accuracy of the angular velocity acquisition directly determines the accuracy of the rope length difference. If the angular velocity signal is distorted due to interference, the calculated rope length difference will deviate from the actual length deviation of the two wire ropes. This leads to abnormal compensation coefficients in the proportional-integral controller output, and the torque correction of the opening and closing motors exceeds a reasonable range. This prevents the active elimination of the wire rope length difference, ultimately causing problems such as wire rope tension imbalance, grab bucket tilting, and material spillage. Therefore, it is necessary to build an angular velocity acquisition system with strong anti-interference capabilities, standardized timing, and controllable accuracy.

[0027] In one embodiment, the step S2 of calculating the linear velocity difference and integrating it to obtain the rope length difference specifically includes: S21: Used to calculate the instantaneous linear velocity difference. The angular velocities of the hoisting drum and the opening / closing drum used in the calculation are effective data after first-order low-pass filtering with a 0.5-second time constant. The actual drum radius of the equipment is selected as 0.75 meters. The instantaneous linear velocity difference between the two wire ropes is obtained by multiplying the drum radius by the difference between the hoisting drum angular velocity and the opening / closing drum angular velocity. The linear velocity difference has a clear positive / negative determination rule: a positive result indicates that the opening / closing rope is continuously stretched relative to the hoisting rope, while a negative result indicates that the opening / closing rope is continuously shortened relative to the hoisting rope. This calculation method is based on the fundamental physical relationship of drum transmission. The unified calculation rules and positive / negative definitions clearly define the trend of wire rope length change corresponding to the linear velocity difference, giving clear physical meaning to subsequent integration calculations and avoiding data interpretation errors caused by inconsistent calculation logic.

[0028] S22: Define a variable to store the rope length difference, with an initial value of 0. In each control cycle, the control cycle value is between 200 milliseconds and 500 milliseconds. Update the rope length difference in an incremental manner, that is, add the rope length difference of the previous cycle to the linear velocity difference of the current cycle and multiply by the control cycle. This incremental operation is essentially a numerical integration of the linear velocity difference, reflecting the historical cumulative amount of the length deviation between the two wire ropes. Step S22 performs time integration of the linear velocity difference. The system predefines a variable with an initial value of zero to store the rope length difference. The integration operation follows the previously set 200-millisecond control cycle. Within each control cycle, the rope length difference value stored in the previous cycle is added to the product of the instantaneous linear velocity difference obtained in the current cycle and the 200-millisecond control cycle. This numerical integration is completed by accumulating the values ​​cycle by cycle. This accumulation process is equivalent to performing time integration on the linear velocity difference. The accumulated result directly reflects the historical change in the length deviation of the two wire ropes, i.e., the rope length difference. The specific formula for calculating the rope length difference is as follows: t; Among them, the Indicates the first The rope length difference per control cycle Indicates the first Historical rope length difference for each control cycle Indicates the instantaneous linear velocity difference. t represents the system's unified control cycle.

[0029] By relying on a fixed control cycle of 200 milliseconds to perform integral calculations, the unified time reference mentioned above can be maintained, ensuring the consistency of the timing of integral calculations. This allows the rope length difference to be continuously and stably recorded in terms of the accumulation process of the wire rope length deviation, providing continuous and effective deviation data for closed-loop control.

[0030] S23: Set upper and lower limits for the rope length difference, with an upper limit of +0.1 meters and a lower limit of -0.1 meters. When the rope length difference exceeds the upper limit, it is forcibly assigned a value of +0.1 meters; when it falls below the lower limit, it is forcibly assigned a value of -0.1 meters. This prevents integral drift from causing controller saturation. Upper and lower limits are set for the rope length difference generated by integration, with a uniform upper limit of +0.1 meters and a lower limit of -0.1 meters. When the calculated rope length difference exceeds +0.1 meters, the system forcibly assigns a value of +0.1 meters; when the calculated rope length difference falls below -0.1 meters, the system forcibly assigns a value of -0.1 meters. During long-term continuous operation of the equipment, small linear velocity differences will accumulate through integration, leading to integral drift and ultimately controller saturation. The fixed amplitude limit range of ±0.1 meters can limit the maximum fluctuation range of the rope length difference, block the development path of integral drift from the calculation level, prevent the rope length difference value from increasing indefinitely, avoid the subsequent proportional integral controller from malfunctioning due to excessive input, and ensure the continuous and stable operation of the entire closed-loop control system.

[0031] S24: When the grab bucket is not in the closed bucket lifting and lowering state, including when the grab bucket is fully open, the main power supply of the unloader is disconnected, or the hoisting drum reaches the upper limit of the mechanical position, the rope length difference shall be immediately forced to 0 to eliminate the accumulation of false rope length difference caused by mechanical displacement during non-operation periods.

[0032] Existing control schemes of the same type only complete the linear velocity difference calculation and basic integral operation, without setting an upper and lower limit mechanism for integral, and do not distinguish between working conditions and non-working conditions to clear the integral variable. Therefore, the problems of integral drift and accumulation of false rope length difference cannot be effectively curbed.

[0033] The aforementioned step, which connects to the angular velocity acquisition step, is primarily used in the normal operating conditions of the grab unloader's closed bucket lifting and lowering. During operation, the equipment also switches to non-operating conditions such as the grab bucket fully open, the entire machine stopped, and the lifting drum reaching its upper limit. This invention uses the time integral result of the linear velocity difference—that is, the rope length difference—as the core deviation quantity for closed-loop control. The accuracy of the rope length difference directly determines the effectiveness of subsequent control logic. When the linear velocity difference persists, the integral calculation accumulates over time, easily leading to integral drift. Furthermore, when the equipment is in a non-operating state, passive mechanical displacement generates velocity signals without practical operational significance, resulting in false accumulation of the rope length difference. If the rope length difference drifts or accumulates falsely, the deviation will not correspond to the actual length difference between the two wire ropes. The proportional-integral controller will output an abnormal compensation coefficient based on the erroneous data, causing the torque correction of the opening and closing motor to deviate from the reasonable range and fail to offset the wire rope length difference. Ultimately, this leads to continuous problems such as wire rope tension imbalance, grab bucket tilting, and material spillage. Therefore, it is essential to constrain and control the entire process of linear velocity difference calculation, integration, and integral values.

[0034] The rope length difference is forcibly zeroed based on the equipment's operating conditions. Zeroing trigger conditions include the grab bucket being fully open, the unloader's main power being disconnected, and the hoisting drum reaching its mechanical upper limit. None of these scenarios constitute valid operating conditions for grab bucket lifting and lowering. When the equipment is not in an operating condition, the rotation of the drum is not driven by normal lifting operations, and the corresponding linear velocity difference does not represent the actual change in wire rope length during operation. Continuous integration will result in a false accumulation of rope length difference. By immediately forcibly zeroing the rope length difference upon detecting the corresponding operating condition signal, invalid integral data generated during non-operating phases can be cleared. This ensures that when the equipment re-enters closed-bucket lifting operations, the rope length difference accumulates from zero, ensuring that the rope length difference only represents the length deviation between the two wire ropes under valid operating conditions. This further improves the accuracy of the core deviation and helps the control system accurately complete the wire rope torque balance adjustment.

[0035] Based on the previously collected and first-order low-pass filtered angular velocities of the hoisting and opening / closing drums, the system sequentially performs operations such as instantaneous linear velocity difference calculation, cycle-by-cycle integration to generate rope length difference, integral value limiting, and forced zeroing under non-operational conditions. Finally, it outputs reliable rope length difference data. This rope length difference, as the core deviation of the entire closed-loop control system, is directly input into the proportional-integral controller for calculation. It provides the core basis for dynamic torque correction of the opening / closing motor and achieving wire rope torque balance, ensuring the achievement of the core objective of balanced wire rope tension during the hoisting and closing operation of the grab unloader.

[0036] In one embodiment, step S3, in which the rope length difference is input as a deviation into the proportional-integral controller and a compensation coefficient is output, specifically includes: S31: Set the initial values ​​of the proportional coefficient and the integral coefficient, where the value of the proportional coefficient ranges from 0.5 to 2.0 and the value of the integral coefficient ranges from 0.1 to 0.4. Use the field self-tuning method to determine the final parameters: first set the integral coefficient to 0, then gradually increase the proportional coefficient until the rope length difference exhibits a small constant amplitude oscillation with an oscillation period of about 2 to 3 seconds. Record the critical proportional coefficient at this point. Take the critical proportional coefficient as 0.45 times the critical proportional coefficient. Then take the integral coefficient as the initial value of the proportional coefficient divided by 5. Finally, fine-tune the integral coefficient according to the steady-state error. For example, during on-site commissioning, the integral coefficient is set to zero, and the proportional coefficient is gradually increased. The rope length difference data is observed until a small, constant-amplitude oscillation with a period of 2.5 seconds appears. This is used to obtain the critical proportional coefficient and complete the parameter conversion. This standardized self-tuning process replaces the traditional experience-based parameter setting method, enabling the dynamic response characteristics of the proportional-integral controller to accurately match the operating conditions of the equipment. This ensures both the adjustment response speed and avoids system oscillations. At the same time, combined with fine-tuning of the integral coefficient, it can effectively eliminate the steady-state deviation corresponding to the rope length difference, improving the adjustment accuracy of the closed-loop control.

[0037] S32: Within each control cycle, the control cycle value is between 200 milliseconds and 500 milliseconds. The proportional output is calculated according to the proportional term formula, that is, the proportional coefficient is multiplied by the current rope length difference to obtain the proportional output value. The integral output is calculated according to the integral term recursively, that is, the integral output of the previous cycle is added to the integral coefficient, multiplied by the current rope length difference, and then multiplied by the control cycle to obtain the integral output of the current cycle. The integral output is limited to the upper and lower limits, with the limit value being ±0.2, to prevent integral saturation. Step S32 continues the 200-millisecond control cycle from the previous step to perform proportional and integral term calculations. The proportional output value is calculated based on the rope length difference of the current cycle and the already tuned proportional coefficient. Then, the integral output value is calculated recursively, by adding the integral output of the previous cycle to the integral coefficient, the current rope length difference, and the product of the 200-millisecond control cycle. Simultaneously, an upper and lower limit of ±0.2 is set for the integral output. If the integral output exceeds the limit, it is forcibly assigned the corresponding boundary value. The integral term uses a cycle-by-cycle recursive accumulation method, which can continuously accumulate rope length difference deviations to achieve zero steady-state error adjustment. The ±0.2 limit rule effectively suppresses integral saturation, preventing the integral output from increasing without limit and causing controller failure, thus ensuring that the proportional-integral controller's operational logic remains normal during long-term continuous operation.

[0038] S33: The proportional output and integral output are added together to obtain the original compensation coefficient, and the original compensation coefficient is limited as a whole to keep its value range between -0.2 and +0.2, that is, the compensation coefficient does not exceed ±20%, to ensure that the torque correction range of the switching motor is within a safe range. Step S33, based on the integral output limit, applies a secondary constraint to the overall amplitude of the final compensation coefficient. Combined with the maximum deviation range of ±0.1 meters for the rope length difference mentioned earlier, it matches the adjustment capability of the equipment to avoid excessive compensation coefficient causing excessive torque correction of the opening and closing motor, preventing motor overload, or abnormal grab bucket closure state caused by sudden torque change, and further strengthening the safety boundary of torque adjustment.

[0039] S34: Perform rate-of-change limiting processing on the compensation coefficient after limiting: Calculate the difference between the current cycle compensation coefficient and the previous cycle compensation coefficient. If the absolute value of the difference is greater than 0.02, then forcibly set the difference to its sign multiplied by 0.02, then update the current cycle compensation coefficient to the previous cycle compensation coefficient plus the difference, and finally assign the current cycle compensation coefficient to the previous cycle compensation coefficient for the next cycle. This rate-of-change limiting ensures that the change amplitude of the compensation coefficient in each control cycle does not exceed 2%, avoiding sudden torque changes that cause grab bucket shaking. Step S34 performs rate-of-change limiting processing on the compensation coefficient after overall limiting. The system calculates the difference between the current cycle compensation coefficient and the previous cycle compensation coefficient. When the absolute value of the difference is greater than 0.02, the difference is forcibly set to ±0.02. Then, the current cycle value is updated in conjunction with the previous cycle compensation coefficient, and cycle data backup is completed simultaneously. This rule limits the change of the compensation coefficient within each 200-millisecond control cycle to no more than 2%, which can effectively slow down the dynamic change rate of the compensation coefficient, prevent sudden torque changes in the opening and closing motors caused by instantaneous jumps in the compensation coefficient, reduce the impact of torque shock on the grab bucket and wire rope, make the entire adjustment process smoother, avoid grab bucket shaking, and ensure the stability of equipment operation.

[0040] S35: Output the final compensation coefficient, which is dimensionless and used in step S4 to correct the torque setpoint of the switching motor.

[0041] Step S35 outputs the final compensation coefficient after multi-level amplitude limiting and rate of change constraints. This dimensionless coefficient is directly transmitted to step S4 to participate in the correction calculation of the torque setpoint of the switching motor. This step completes the data termination of this stage and the data transfer between stages, connecting the rope length difference deviation input, proportional-integral calculation and torque correction stages, ensuring the continuous and complete data flow of the entire control logic, and providing compliant and effective core parameters for subsequent torque balance adjustment.

[0042] This section applies to the closed-bucket lifting operation scenario of a port bridge-type grab unloader. The rope length difference is the only deviation input of the proportional-integral (PI) controller. The controller's parameter matching, operational stability, and output variation characteristics directly affect the torque correction effect. In actual operation, relying on experience to set the PI parameters can lead to system response mismatch. Either the adjustment speed is too slow to eliminate the steady-state deviation caused by the rope length difference, or the adjustment speed is too fast, causing continuous system oscillation. Long-term accumulation of integral operations can easily lead to integral saturation, causing the controller to lose its adjustment capability. Unconstrained compensation coefficient amplitude can cause excessive torque correction amplitude for the opening and closing motors, exceeding the safe operating range of the equipment. Sudden single-cycle changes in the compensation coefficient can directly cause sudden torque changes, resulting in grab bucket vibration and impact loads on the wire rope. All of these problems undermine the effectiveness of torque regulation, fail to eliminate wire rope length deviations, and further exacerbate tension imbalance, grab bucket tilting, and material spillage. Therefore, it is necessary to impose comprehensive constraints on the PI controller's parameter tuning, operational process, output amplitude, and rate of change.

[0043] Furthermore, most existing proportional-integral control schemes rely on manual experience to set controller parameters, lacking a standardized self-tuning process adapted to this system. The parameters have a low degree of matching with the equipment's operating characteristics. At the same time, most schemes only limit the integral term without setting constraints on the overall amplitude and single-cycle change rate of the compensation coefficient. Problems such as integral saturation, excessive torque correction, and sudden output changes cannot be effectively controlled.

[0044] The above steps, taking the output rope length difference data, sequentially complete the self-tuning of the proportional-integral controller parameters, step-by-step calculation of the proportional and integral terms, multi-level numerical limiting, and rate of change constraint, ultimately outputting a stable and compliant dimensionless compensation coefficient. This compensation coefficient, as the core parameter for torque correction of the opening and closing motor, is directly input into the subsequent torque calculation stage. Through precise and stable torque adjustment, it ensures the torque balance of the wire rope during the closing bucket lifting operation of the grab unloader, achieving the overall control objective of suppressing tension imbalance.

[0045] In one embodiment, step S4, which involves correcting the torque setpoint of the switching motor while keeping the hoisting motor unchanged, specifically includes: S41: Read the reference torque setpoint of the opening and closing motor from the original speed loop control module in the programmable logic controller. The unit of the reference torque setpoint is Newton-meter or rated torque percentage, which is calculated by the speed regulator based on the deviation between the actual angular velocity of the opening and closing drum and the target angular velocity. Step S41 is used to read the reference torque setpoint of the switching motor. The system reads the reference torque setpoint from the existing speed loop control module inside the programmable logic controller. The unit of this value is Newton-meters or a percentage of the rated torque. It is calculated and generated by the speed regulator based on the deviation between the actual angular velocity of the drum and the target angular velocity. The actual angular velocity of the drum is the effective angular velocity data obtained after first-order low-pass filtering. By clearly defining the data source and generation logic of the reference torque, it is possible to ensure that the basic instructions for torque adjustment are consistent with the original speed control system of the equipment, avoid introducing additional calculation errors, and allow torque correction to be based on stable and reliable basic control instructions.

[0046] S42: Add the compensation coefficient output in step S3 to constant 1 to obtain the correction factor, and then multiply it by the reference torque setpoint to calculate the corrected torque setpoint of the opening and closing motor, which is equal to the reference torque setpoint multiplied by the correction factor. At the same time, the torque setpoint of the hoisting motor remains unchanged at the original speed loop output value without any correction. Step S42 performs torque correction calculation and implements the asymmetric control strategy. The compensation coefficient is added to a constant 1 to obtain a correction factor. This correction factor is then multiplied by the reference torque setpoint to calculate the corrected torque setpoint for the opening and closing motor. Simultaneously, the torque setpoint for the hoisting motor uses the original speed loop output without any modification. Continuing with the previous parameter example, when the compensation coefficient is 0.1, the correction factor is 1.1, increasing the opening and closing motor torque by 10% from the reference value. When the compensation coefficient is -0.1, the correction factor is 0.9, decreasing the opening and closing motor torque by 10% from the reference value. This calculation logic is simple and matches the range of the compensation coefficient mentioned earlier. Adjusting only the opening and closing motor completely decouples the control of the two drive mechanisms, avoiding system oscillations caused by mutual interference between the two motors. This allows torque adjustment to precisely act on the opening and closing mechanism, specifically offsetting the tension deviation caused by the difference in wire rope length.

[0047] S43: Set a safety limit on the corrected torque setpoint of the opening and closing motor. Set the upper limit to 1.3 times the rated torque of the motor and the lower limit to 0.5 times the rated torque of the motor. If the corrected torque setpoint exceeds the upper limit, it will be forcibly assigned to the upper limit. If it is lower than the lower limit, it will be forcibly assigned to the lower limit to prevent the opening and closing motor from being overloaded or the grab bucket from opening unexpectedly due to low torque.

[0048] Step S43 applies a safety limit to the corrected torque setpoint of the opening and closing motor, setting the upper limit to 1.3 times the rated torque of the motor and the lower limit to 0.5 times the rated torque. When the corrected torque exceeds the upper limit, the system forcibly assigns a value of 1.3 times the rated torque; when the corrected torque is below the lower limit, the system forcibly assigns a value of 0.5 times the rated torque. Combined with the previously mentioned adjustment range of ±0.2 for the compensation coefficient, this limiting mechanism, beyond the constraint of the compensation coefficient amplitude, further defines the safe operating range of the motor torque. The upper limit prevents the opening and closing motor from operating under overload for extended periods, protecting the motor body and its associated mechanical transmission structure. The lower limit ensures that the opening and closing motor outputs sufficient torque to maintain the closed state of the grab bucket, preventing accidental opening of the grab bucket during operation. This safety limiting rule serves as the final layer of protection for torque output, ensuring that torque adjustment is always carried out within the allowable operating range of the equipment, guaranteeing the safe and continuous operation of the entire torque balance control system.

[0049] As described in steps S41-S43 above, the compensation coefficients obtained through the preceding multi-stage processing are only dimensionless adjustment parameters. They must be converted in conjunction with the original torque reference of the motor before the motor can be driven to perform adjustment actions. Using asymmetric control logic that only adjusts the opening and closing motor and locks the hoisting motor, if the source and calculation logic of the reference torque are not clearly defined in the torque correction stage, it will cause distortion of the basic control commands. If the torque output of both the hoisting motor and the opening and closing motor are modified simultaneously, the two drive systems will become coupled and dynamically compete, causing system oscillations. If no limit is set for the corrected torque, the superposition of compensation coefficients can easily cause the opening and closing motor torque to be too large, leading to equipment overload, or the torque to be too small, failing to maintain the closed state of the grab bucket, resulting in unexpected opening of the grab bucket and a large amount of material spillage. All of these problems will directly undermine the torque adjustment effect and fail to offset the tension imbalance caused by the wire rope length deviation. Therefore, it is necessary to comprehensively constrain the reference torque reading, torque correction calculation, and torque safety range.

[0050] Most existing torque regulation schemes lack a clear source for obtaining the reference torque. Some schemes employ a dual-motor synchronous regulation method, which is highly susceptible to system coupling oscillations. Furthermore, most schemes rely solely on the controller's internal logic to limit the adjustment range, failing to incorporate hard limits based on the motor's rated operating parameters, resulting in significant safety hazards during equipment operation. This new solution, based on the final compensation coefficient, sequentially completes operations such as reading the reference torque setpoint of the opening and closing motors, calculating the torque value correction, and setting a safe torque limit after correction, maintaining the hoisting motor torque setpoint unchanged throughout the entire process. These steps constitute the instruction conversion stage of the entire closed-loop control system, converting the compensation coefficient obtained from rope length difference calculations into motor torque control commands recognizable by the frequency converter. Through precise and safe torque regulation, an asymmetric control strategy is implemented, ultimately achieving the core control objective of balancing the wire rope torque of the grab unloader's hoisting and opening / closing mechanisms.

[0051] In one embodiment, step S5, which involves outputting the corrected torque setpoint and resetting the integrator, specifically includes: S51: Write the torque setpoint value of the switching motor calculated in step S4 into the additional torque setpoint channel or torque limiting channel of the switching frequency converter through the industrial Ethernet bus, so that the switching frequency converter drives the switching motor to run according to the corrected torque value. Step S51 is responsible for issuing and executing the corrected torque setpoint. The final calculated torque setpoint of the switching motor is written to the additional torque setpoint channel or torque limiting channel of the switching inverter via the industrial Ethernet bus, enabling the inverter to drive the switching motor according to the received torque parameters. Both the industrial Ethernet bus and the inverter's designated channel are standard techniques in industrial frequency conversion control. This step establishes a data transmission link between the controller and the actuator, ensuring that all algorithm results, including angular velocity acquisition, rope length difference calculation, proportional-integral adjustment, and torque correction, are effectively transmitted to the drive unit. This allows the torque balance adjustment command to be truly implemented, ensuring the entire closed-loop control logic forms a complete closed loop.

[0052] S52: Real-time monitoring of the opening and closing status signals of the grab bucket, the operating status signals of the unloader, and the upper limit switch signal of the hoisting drum. The opening and closing status signals come from the grab bucket closing limit sensor, the operating status signals come from the emergency stop button on the control panel and the main power contactor, and the upper limit switch signal is installed at the mechanical limit of the hoisting drum. Step S52 enables real-time monitoring of all-dimensional operating condition signals. The system continuously collects three types of equipment status signals: the grab bucket opening / closing status signal is taken from the grab bucket closing limit sensor; the equipment operating status signal is taken from the emergency stop button on the control panel and the main power contactor; and the lifting position signal is taken from the upper limit switch installed at the mechanical limit of the lifting drum. These three types of signals correspond to the grab bucket opening / closing status, the overall machine start / stop status, and the lifting mechanism's limit position status, respectively. The signal acquisition points and sources are clearly defined, enabling comprehensive identification of three non-operating conditions: the grab bucket fully open, the unloader stopped, and the lifting drum reaching its upper limit. This accurately provides the triggering basis for subsequent integrator reset actions, effectively avoiding problems such as false or untimely reset logic triggering.

[0053] S53: When it is detected that the grab bucket is fully open, the unloader is in a stopped state (i.e., the emergency stop button is pressed or the main power is disconnected), or the hoisting drum triggers the upper limit switch, immediately execute the integrator reset operation: force the rope length difference variable to 0, force the integral output in the proportional-integral controller to 0, and gradually return the compensation coefficient to 0 in an exponential decay manner. That is, in each control cycle (the value of this control cycle is 200 milliseconds to 500 milliseconds), make the compensation coefficient equal to the compensation coefficient of the previous cycle multiplied by 0.9, until the absolute value of the compensation coefficient is less than 0.001 and is completely set to 0; Upon detecting the reset trigger signal, the integral variable is cleared and the compensation coefficient is smoothly reset. The process follows the unified 200ms control cycle of the entire system. First, the rope length difference variable and the integral output of the proportional-integral controller are forcibly reset to zero, clearing invalid accumulated data generated during non-operational conditions. Then, the compensation coefficient is gradually reduced to zero using an exponential decay method. Specifically, within each 200ms control cycle, the current compensation coefficient is multiplied by 0.9 until the absolute value of the compensation coefficient is less than 0.001, at which point it is completely reset to zero. Continuing with the previous parameter example, if the current compensation coefficient is 0.1, this value will slowly decrease according to the rule of multiplying by 0.9 each cycle, without instantaneous jumps. Combined with the previous limitation that the maximum range of the compensation coefficient is -0.2 to +0.2, the exponential decay method can significantly reduce the rate of change of the compensation coefficient, avoiding sudden changes in the torque of the opening and closing motor that could generate impact loads and prevent the grab bucket from shaking. Simultaneously, forcibly clearing the rope length difference and integral output can completely eliminate the accumulation of false deviations formed during non-operational phases, ensuring a thorough reset of the control system.

[0054] S54: During the integrator reset, the torque setpoint of the switching motor is restored to the original reference torque setpoint output by the speed loop, that is, the torque setpoint of the switching motor is forced to be equal to the reference torque setpoint. At the same time, the operator is prompted through the human-machine interface that "torque balance control has been paused". After the above reset conditions are eliminated, the torque balance control in steps S1 to S4 is automatically restarted.

[0055] Step S54 completes the torque switching, HMI status prompts, and automatic restart after the working condition is restored during the reset process. Throughout the reset phase of the integrator and compensation coefficient, the system forcibly restores the torque setpoint of the opening and closing motor to the original reference torque setpoint output by the speed loop, avoiding safety hazards caused by torque correction in non-operating conditions. Simultaneously, a prompt message indicating that torque balance control is paused is output on the HMI, allowing operators to monitor the equipment control status in real time. When all reset trigger conditions, such as grab opening, equipment shutdown, and lifting upper limit, are eliminated, and the equipment re-enters the effective working condition of closed-bucket lifting, the system automatically reactivates the aforementioned torque balance control process. Switching the torque back to the original reference value matches the basic operating requirements of the equipment in non-operating conditions, ensuring equipment safety. The HMI prompt function enhances on-site operation and maintenance interaction capabilities, while the automatic restart logic eliminates manual intervention steps, improving the level of automated operation. It also allows the wire rope torque balance control function to quickly resume operation after the working condition is restored, continuously suppressing problems such as wire rope tension imbalance and grab tilting.

[0056] As described in steps S51-S54 above, this technical solution is applied to the closed-bucket lifting operation of a port bridge-type grab unloader, and covers various working condition switching scenarios such as the grab bucket fully open, equipment shutdown, and the lifting drum touching the upper limit. The entire control logic ultimately relies on the frequency converter to drive the motor to complete torque regulation. If the torque command transmission channel is unclear, all the algorithm calculation results mentioned above will fail to be implemented, and the torque balance adjustment function will directly fail. In non-operating conditions, if only the rope length difference and integral term are simply cleared without transition processing of the compensation coefficient, the compensation coefficient will instantly return to zero, directly causing a sharp change in the torque of the opening and closing motor, generating impact loads and causing the grab bucket to shake. At the same time, continuously using the corrected torque setpoint in non-operating conditions will also bring additional operational risks to the equipment. In addition, there is a lack of status prompts when switching working conditions, and operators cannot keep track of the start and stop status of the control function in a timely manner. Furthermore, the control logic cannot be automatically restarted after the working condition is restored, requiring manual intervention and reducing the continuity of equipment operation. The aforementioned issues will affect the safety and efficiency of equipment operation and will also make it impossible to continuously maintain the control target of wire rope tension balance. Therefore, it is necessary to standardize the method of issuing torque commands, clarify the source of working condition monitoring signals, design a smooth reset mechanism, and provide supporting torque cut-off, status prompts and automatic restart logic.

[0057] Existing control schemes of this kind typically only use conventional communication methods to issue torque commands, without distinguishing the usage scenarios of different functional channels of the frequency converter. At the same time, most of them only set a single stop reset condition, resulting in insufficient coverage of operating condition identification. When resetting the integrator, they generally use the method of directly clearing the compensation coefficient, which can easily cause sudden torque changes. Most schemes do not restore the torque setpoint to the original speed loop output state after reset, lack human-machine interaction prompts, and cannot automatically restore torque balance control after the operating condition is removed, relying on manual operation to restart, resulting in a low degree of automation.

[0058] Based on the calculated corrected torque setpoint of the switching motor, the system sequentially performs operations such as torque command bus transmission, real-time monitoring of multiple operating condition signals, smooth reset of integral variables and compensation coefficients, torque reference revert, human-machine status prompts, and automatic restart control after operating condition recovery. This enables the execution of control commands and cross-operating condition logic switching. These steps serve as the execution terminal and operating condition switching guarantee unit for the entire control method. On one hand, they convert the torque parameters calculated above into actual drive commands for the frequency converter. On the other hand, they complete the orderly reset of the control system when the equipment switches to a non-operating condition and automatically restart torque balance control after operating condition recovery. This comprehensively ensures the stable, safe, and smooth operation of the wire rope torque balance control function of the grab unloader under different operating conditions.

[0059] like Figure 2 As shown, the present invention also discloses a wire rope torque balance control system for the lifting and opening / closing mechanism of a grab unloader, comprising: The acquisition module is used to acquire the angular velocity data of the hoisting drum and the opening and closing drum; The calculation module is used to calculate the difference in linear velocity between the two drums based on the angular velocity data of the hoisting drum and the angular velocity data of the opening and closing drum, and to perform time integration on the difference in linear velocity to obtain the rope length difference characterizing the deviation in length between the two wire ropes. The output module is used to input the rope length difference as a deviation to the proportional-integral controller, and output a dimensionless compensation coefficient through the proportional-integral controller. The generation module is used to obtain the reference torque setpoint of the opening and closing motor from the speed loop, correct the reference torque setpoint of the opening and closing motor according to the compensation coefficient, generate the corrected torque setpoint of the opening and closing motor, while keeping the torque setpoint of the hoisting motor unchanged. The control module is used to output the corrected torque setpoint of the switching motor to the switching frequency converter, and to clear the rope length difference to zero when the preset reset condition is detected.

[0060] In one embodiment, the output module includes: A determining unit is used to determine the proportional coefficient and integral coefficient of the proportional-integral controller through on-site self-tuning. The calculation unit is used to calculate the proportional output value based on the rope length difference of the current cycle and the proportional coefficient in each control cycle, and to recursively calculate the integral output value based on the rope length difference, the integral coefficient and the control cycle. The limiting unit is used to add the proportional output value and the integral output value to obtain the original compensation coefficient, and to limit the overall amplitude of the original compensation coefficient so that its variation range is limited to a preset safe range. The output unit is used to perform rate-of-change limiting processing on the compensation coefficient after the limit is applied, limiting its change amplitude in each control cycle to not exceed the preset maximum change step size, and outputting the final compensation coefficient after processing.

[0061] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0062] The above description is merely a preferred embodiment of the present invention and does not limit the scope of this application. Any equivalent results or equivalent process transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of protection of this application.

Claims

1. A method for controlling the wire rope torque balance of the lifting and opening / closing mechanism of a grab bucket ship unloader, characterized in that, Includes the following steps: Obtain the angular velocity data of the hoisting drum and the opening and closing drum; Based on the angular velocity data of the hoisting drum and the angular velocity data of the opening and closing drum, the linear velocity difference between the two drums is calculated, and the linear velocity difference is integrated over time to obtain the rope length difference, which characterizes the length deviation of the two wire ropes. The rope length difference is input as a deviation to the proportional-integral controller, which then outputs a dimensionless compensation coefficient. The reference torque setpoint of the opening and closing motor is obtained from the speed loop, and the reference torque setpoint of the opening and closing motor is corrected according to the compensation coefficient to generate the corrected torque setpoint of the opening and closing motor, while keeping the torque setpoint of the hoisting motor unchanged. The corrected torque setpoint of the switching motor is output to the switching frequency converter, and the rope length difference is cleared to zero when the preset reset condition is detected.

2. The wire rope torque balance control method for the lifting and opening / closing mechanism of the grab unloader according to claim 1, characterized in that, The steps of obtaining the angular velocity data of the hoisting drum and the opening and closing drum specifically include: Angular velocity pulse signals are acquired by encoders installed on the ends of the hoisting drum shaft and the opening / closing drum shaft, respectively. Set up an interrupt task independent of the speed loop control cycle, and read the pulse increment of the encoder within the control cycle of each interrupt task; Based on the pulse increment, encoder resolution, and control cycle, the angular velocity of the hoisting drum and the angular velocity of the opening and closing drum are calculated. The calculated angular velocity is subjected to low-pass filtering, and the filtered angular velocity data is used in subsequent steps.

3. The wire rope torque balance control method for the lifting and opening / closing mechanism of the grab unloader according to claim 1, characterized in that, The step of integrating the linear velocity difference over time to obtain the rope length difference characterizing the length deviation of the two wire ropes specifically includes: The instantaneous linear velocity difference is calculated based on the difference between the drum radius and the angular velocities of the hoisting drum and the opening / closing drum. Within each control cycle, the product of the rope length difference of the previous cycle and the instantaneous linear velocity difference of the current cycle and the control cycle is accumulated, and the rope length difference of the current cycle is updated by numerical integration. The updated rope length difference is subject to upper and lower limit processing to prevent integral drift; When the equipment is detected to be in a non-operational state, the rope length difference is forcibly set to zero.

4. The wire rope torque balance control method for the lifting and opening / closing mechanism of the grab unloader according to claim 1, characterized in that, The step of inputting the rope length difference as a deviation to the proportional-integral controller, and then outputting a dimensionless compensation coefficient through the proportional-integral controller, specifically includes: The proportional coefficient and integral coefficient of the proportional-integral controller are determined by on-site self-tuning. Within each control cycle, the proportional output value is calculated based on the rope length difference of the current cycle and the proportional coefficient, and the integral output value is recursively calculated based on the rope length difference, the integral coefficient, and the control cycle. The proportional output value and the integral output value are added together to obtain the original compensation coefficient, and the original compensation coefficient is subjected to overall amplitude limiting so that its variation range is limited to a preset safety range. The rate of change of the compensation coefficient after the limit is applied to limit its change in each control cycle to no more than the preset maximum change step size, and the final compensation coefficient after processing is output.

5. The wire rope torque balance control method for the lifting and opening / closing mechanism of the grab unloader according to claim 1, characterized in that, The step of correcting the reference torque setpoint of the switching motor according to the compensation coefficient and generating the corrected torque setpoint of the switching motor specifically includes: The reference torque setpoint of the switching motor, calculated by the speed regulator, is read from the existing speed loop control module. The correction factor is obtained by adding the compensation coefficient to the constant 1, and the correction factor is multiplied by the reference torque setpoint to calculate the corrected torque setpoint of the switching motor. The corrected torque setpoint of the switching motor is subject to a safety limit to ensure that it does not exceed the preset upper and lower limits of the motor's rated torque, and then output.

6. The wire rope torque balance control method for the lifting and opening / closing mechanism of the grab unloader according to claim 1, characterized in that, The step of outputting the corrected on / off motor torque setpoint to the on / off frequency converter and clearing the rope length difference to zero when a preset reset condition is detected includes: Real-time monitoring of the opening and closing status signals of the grab bucket, the operating status signals of the ship unloader, and the upper limit switch signal of the hoisting drum; When it is detected that the grab bucket is fully open, the unloader is in a stopped state, or the hoisting drum triggers the upper limit switch, it is determined that the reset condition is met. Immediately reset the rope length difference and the integral output of the proportional-integral controller to zero, and gradually return the compensation coefficient to zero in an exponential decay manner. During the reset, the torque setpoint of the motor is forcibly restored to the reference torque setpoint, and the torque balance control is automatically restarted after the reset condition is eliminated.

7. The method for controlling the wire rope torque balance of the lifting and opening / closing mechanism of the grab bucket ship unloader according to claim 1, characterized in that, The compensation coefficient output by the proportional-integral controller is used to correct the torque setpoint of the opening and closing motor, and the torque correction range of the opening and closing motor is positively correlated with the value of the rope length difference.

8. The wire rope torque balance control method for the lifting and opening / closing mechanism of the grab unloader according to claim 3, characterized in that, The non-operational conditions include the grab bucket being fully open, the main power supply of the unloader being disconnected, and the hoisting drum reaching the upper mechanical limit position. The limit values ​​for the upper and lower limit processing of the rope length difference are pre-calibrated according to the mechanical characteristics and safe operation requirements of the grab bucket unloader.

9. A wire rope torque balance control system for the hoisting and opening / closing mechanism of a grab bucket ship unloader, characterized in that, include: The acquisition module is used to acquire the angular velocity data of the hoisting drum and the opening and closing drum; The calculation module is used to calculate the difference in linear velocity between the two drums based on the angular velocity data of the hoisting drum and the angular velocity data of the opening and closing drum, and to perform time integration on the difference in linear velocity to obtain the rope length difference characterizing the deviation in length between the two wire ropes. The output module is used to input the rope length difference as a deviation to the proportional-integral controller, and output a dimensionless compensation coefficient through the proportional-integral controller. The generation module is used to obtain the reference torque setpoint of the opening and closing motor from the speed loop, correct the reference torque setpoint of the opening and closing motor according to the compensation coefficient, generate the corrected torque setpoint of the opening and closing motor, while keeping the torque setpoint of the hoisting motor unchanged. The control module is used to output the corrected torque setpoint of the switching motor to the switching frequency converter, and to clear the rope length difference to zero when the preset reset condition is detected.

10. The wire rope torque balance control system for the lifting and opening / closing mechanism of the grab unloader according to claim 9, characterized in that, The output module includes: A determining unit is used to determine the proportional coefficient and integral coefficient of the proportional-integral controller through on-site self-tuning. The calculation unit is used to calculate the proportional output value based on the rope length difference of the current cycle and the proportional coefficient in each control cycle, and to recursively calculate the integral output value based on the rope length difference, the integral coefficient and the control cycle. The limiting unit is used to add the proportional output value and the integral output value to obtain the original compensation coefficient, and to limit the overall amplitude of the original compensation coefficient so that its variation range is limited to a preset safe range. The output unit is used to perform rate-of-change limiting processing on the compensation coefficient after the limit is applied, limiting its change amplitude in each control cycle to not exceed the preset maximum change step size, and outputting the final compensation coefficient after processing.

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