Motion control method and system for bottom loading and unloading crane pipe

Abstract

The invention relates to the field of crane tubes, in particular to a bottom loading and unloading crane tube motion control method and system, and the method comprises the steps: obtaining a ratio sequence, a deviation sequence and an inherent frequency of a servo motor on a target axis in any historical alignment process; calculating the frequency domain coupling degree of the contrast axis to the target axis; calculating the time domain coupling degree of the contrast axis to the target axis; normalizing the sum of the frequency domain coupling degree and the time domain coupling degree to obtain a coupling coefficient of the contrast axis to the target axis; and calculating a correction error of the target axis, taking the correction error as input of discrete PID control, outputting a control signal of the target axis at the moment to be controlled, and completing control according to the control signal. According to the technical scheme, the control precision of the servo motor in the loading and unloading process of the loading arm can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of loading arms. In particular, it relates to a method and system for controlling the movement of a bottom loading arm. BACKGROUND

[0002] The working principle of a loading arm is to transport liquid from one side to the other through a pipeline. Precise control of the liquid flow and the movement of the loading arm is required to ensure the safety and efficiency of the operation. In the design of a bottom loading arm, multi-axis servo motors are usually used to achieve precise control and position movement of the loading arm in the loading and unloading process. These servo motors work in coordination through a drive system to achieve precise alignment of the loading arm during the loading and unloading process at the dock. However, due to the need for high-precision displacement and rotation in a short time during the alignment of the loading arm, the coupling problem between multi-axis servo motors becomes particularly prominent. Specifically, the movements of different motors affect each other.

[0003] Due to the complex connection structure of the mechanical components of the bottom loading arm, there is strong coupling between the different axes when the servo motors control the movement, and the torque between different axes will affect each other. The existing technology controls the servo motor of each axis by obtaining the independent error term of each axis, relies on the independent control of the servo motor of each axis, and ignores the motion coupling and torque influence between different axes. The PID error term obtained is small, resulting in a large deviation in the actual movement position or rotation angle of the bottom loading arm on each axis, which causes poor alignment path accuracy. SUMMARY

[0004] To solve the above technical problems, the present application provides solutions in the following aspects.

[0005] In a first aspect, a method for controlling movement of a bottom loading and unloading swivel includes: obtaining a ratio sequence, a deviation sequence and a natural frequency of a servo motor in a target axis in any historical alignment process, the target axis being any one axis in an axis set, the axis set including linear axes and rotary axes, and the axes in the axis set except the target axis being reference axes; obtaining a main frequency of each axis based on Fourier transform, and obtaining an energy value of the main frequency and an energy value of the natural frequency; calculating a frequency domain coupling degree of the reference axes to the target axis according to the main frequency, the natural frequency, the energy value of the main frequency and the energy value of the natural frequency; calculating a first distance between the ratio sequence of the reference axes and an acceleration sequence of the target axis, and a second distance between the deviation sequence of the reference axes and the deviation sequence of the target axis, and calculating a time domain coupling degree of the reference axes to the target axis based on the first distance and the second distance; normalizing a sum of the frequency domain coupling degree and the time domain coupling degree to obtain a coupling coefficient of the reference axes to the target axis; calculating a correction error of the target axis according to the coupling coefficient, a deviation between an actual position of the swivel at a time to be controlled in the target axis and a final position, and a deviation between the actual position of the swivel at the time to be controlled in the target axis and an ideal position at the time to be controlled; taking the correction error as an input of a discrete PID control to output a control signal of the target axis at the time to be controlled; and completing the control according to the control signal.

[0006] Preferably, obtaining the ratio sequence includes: obtaining an acceleration sequence of the servo motor on any linear axis and an angular acceleration sequence of the servo motor on a rotary axis in any historical alignment process; and de-dimensioning the acceleration sequence of any linear axis to obtain the ratio sequence, and de-dimensioning the angular acceleration sequence of the rotary axis to obtain the ratio sequence.

[0007] Preferably, obtaining the deviation sequence includes: obtaining an actual position sequence and an ideal position sequence of the servo motor on any linear axis, and simultaneously obtaining an actual angle sequence and an ideal angle sequence of the servo motor on a rotary axis in any historical alignment process; calculating a first difference value of corresponding elements of the actual position sequence and the ideal position sequence, and calculating a first ratio value of the first difference value and a theoretical maximum alignment distance; constructing all the first ratio values as a deviation sequence of the linear axis; calculating a second difference value of corresponding elements of the actual angle sequence and the ideal angle sequence, and calculating a second ratio value of the second difference value and a theoretical maximum rotation angle; and constructing all the second ratio values as a deviation sequence of the rotary axis.

[0008] Preferably, the method further includes: obtaining an energy spectrum of any axis by using Fourier transform, and selecting a frequency with the largest energy value in the energy spectrum as a main frequency of the axis, and iteratively obtaining the main frequency of each axis.

[0009] Preferably, the calculating the frequency domain coupling degree comprises: for each historical alignment process, calculating a first absolute difference between a value of the any reference axis principal frequency and a value of the target axis natural frequency, calculating a second absolute difference between an energy value of the any reference axis principal frequency and an energy value of the target axis natural frequency, taking a product of the first absolute difference and the second absolute difference as a first product; traversing the first product of each historical alignment process, mapping an accumulated value of all the first products through a negative correlation as the frequency domain coupling degree of the reference axis to the target axis.

[0010] Preferably, the calculating the time domain coupling degree comprises: for each historical alignment process, taking a product of the first distance and the second distance as a second product, traversing the second product of each historical alignment process, mapping an accumulated value of all the second products through a negative correlation as the time domain coupling degree of the reference axis to the target axis.

[0011] Preferably, the correction error satisfies a relationship: , denotes a control time a correction error of the target axis, denotes a reference axis a coupling coefficient of the target axis, denotes a deviation between an actual position of the crane boom at the control time and a final position, denotes a deviation between an actual position of the crane boom at the control time and an ideal position at the control time, denotes a number of the reference axes.

[0012] In a second aspect, a motion control system of a bottom loading and unloading crane boom comprises: a processor and a memory, the memory storing computer program instructions, when the computer program instructions are executed by the processor, realizing any of the motion control methods of the bottom loading and unloading crane boom.

[0013] The present application has the following effects: The application optimizes the control strategy of the servo motor by accurately analyzing the dynamic characteristics and mutual influence of each shaft in the loading and unloading process of the crane pipe. Through quantitative and comprehensive analysis of the acceleration ratio, deviation sequence, and coupling degree in the frequency domain and time domain, the motion error of the target shaft can be more accurately identified and corrected in actual operation. This method not only can monitor the motion accuracy of each shaft in real time, identify potential resonance and coupling problems, but also can dynamically adjust the interaction between multiple shafts by introducing the coupling coefficient, to ensure the coordination of each shaft during the movement process. Finally, through the optimization control of the correction error, the positioning accuracy and operation efficiency in the loading and unloading process of the crane pipe are significantly improved, the motion error caused by the coupling between shafts is avoided, and higher-precision loading and unloading operation is realized, greatly improving the flexibility and stability of the system, and ensuring the accurate positioning and efficient operation of the crane pipe in complex working environment. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a flowchart of the motion control method of the bottom loading and unloading crane pipe according to the embodiment of the application. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments of the application.

[0016] The specific embodiments of the application will be described in detail below with reference to the drawings.

[0017] Referring to Figure 1 The motion control method of the bottom loading and unloading crane pipe includes steps S1-S5, which are as follows: S1: obtaining the ratio sequence, deviation sequence, and natural frequency of the servo motor in the target shaft in any alignment process, the target shaft being any one of the shaft set, the shaft set including linear shafts and rotary shafts, and the shafts in the shaft set except the target shaft being the control shaft.

[0018] It should be noted that during the loading and unloading process of the crane pipe, in order to realize efficient and accurate alignment and operation, a four-axis and five-axis alternating iterative control mode is usually adopted. Specifically, although only four axes are used for control at some stages (such as the linear movement of x, y, z axes and the telescopic arm axis), in order to ensure that the crane pipe can complete complex spatial adjustment and accurate positioning during the alignment process, the system actually adopts a five-axis control system. The five-axis control system adjusts more degrees of freedom at the same time, especially by increasing the control of the rotation axis, so that the crane pipe can be finely adjusted in multiple directions, thereby providing higher flexibility and accuracy during the loading and unloading process. The alternating iterative mode allows the system to switch between four-axis and five-axis control according to the needs at different stages, optimizing the operation efficiency of each stage and ensuring accurate completion of the alignment and unloading process.

[0019] In an embodiment, during the alignment process controlled by the servo motor, the acceleration sequence of the servo motor on each linear axis (including x-axis, y-axis, z-axis and telescopic arm axis) is first collected by the accelerometer, and the angular acceleration sequence on the rotation axis is collected by the encoder of the servo motor. Then, by dimensionless processing of the acceleration sequence, the ratio sequence of the linear axis and the rotation axis is obtained respectively, so as to eliminate the influence of units and dimensions and unify the expression of acceleration.

[0020] The dimensionless processing includes: calculating the ratio of any element in the acceleration sequence to the theoretical maximum acceleration of the servo motor to construct the ratio sequence of the linear axis; calculating the ratio of any element in the angular acceleration sequence to the theoretical maximum angular acceleration of the servo motor to construct the ratio sequence of the rotation axis.

[0021] For example, the acceleration sequence is , the theoretical maximum acceleration is , and the ratio sequence of the linear axis after dimensionless processing is ; similarly, the angular acceleration sequence is , the theoretical maximum angular acceleration is , and the ratio sequence of the rotation axis after dimensionless processing is . Since the acceleration sequence of the linear axis and the angular acceleration sequence of the rotation axis have been dimensionless processed, the sequences after dimensionless processing are called ratio sequences. The purpose of ratio processing is to eliminate the dimension, and the theoretical maximum acceleration and the theoretical maximum angular acceleration are set by those skilled in the art.

[0022] The actual position sequence and the ideal position sequence in any alignment process are obtained, as well as the actual angle sequence and the ideal angle sequence. For any linear axis, the first difference value between the actual position sequence and the ideal position sequence is calculated, which represents the deviation between the current position and the ideal position of the gooseneck in the alignment process. Further, the difference value is compared with the theoretical maximum alignment distance, and the ratio obtained will constitute the deviation sequence of the linear axis. Similarly, for the rotating axis, the second difference value between the actual angle sequence and the ideal angle sequence is calculated, and the ratio with the theoretical maximum rotation angle constitutes the deviation sequence of the rotating axis.

[0023] For example, the actual position sequence on any linear axis is , the ideal position sequence is , and the theoretical maximum alignment distance is , then the deviation sequence of the linear axis is ; similarly, the actual angle sequence of the rotating axis is , the ideal angle sequence is , and the theoretical maximum rotation angle is , then the deviation sequence of the rotating axis is . The purpose of the ratio processing is to eliminate the dimension, and the theoretical maximum alignment distance and the theoretical maximum rotation angle are set by those skilled in the art.

[0024] Through the above steps, the deviation of each linear axis and rotating axis in the alignment process can be quantified, which provides a quantitative basis for optimizing the servo motor control system. Comparing the actual and ideal deviation sequences can help determine whether the servo motor has accurately completed the alignment task, and further evaluate and adjust the control performance of the servo motor to improve the alignment accuracy.

[0025] The acquisition of the natural frequency is known to those skilled in the art, and will not be described here. It should be noted that when a structure system is excited by external excitation, it will naturally vibrate at a certain frequency, which is called the natural frequency of the structure. The natural frequency is only related to the material of the mechanical parts.

[0026] S2: Obtain the main frequency of each axis based on the Fourier transform, and obtain the energy value of the main frequency and the energy value of the natural frequency, and calculate the frequency domain coupling degree of the target axis to the reference axis according to the main frequency, the natural frequency, the energy value of the main frequency and the energy value of the natural frequency.

[0027] In one embodiment, by Fourier transforming the acceleration signal on each axis, the energy spectrum of the signal in the frequency domain can be obtained. Fourier transform converts time domain signal into frequency domain signal, so that the energy distribution of each frequency component becomes visualized. After obtaining the energy spectrum, by analyzing the energy values in the spectrum, the frequency component with the largest energy value can be selected, and this frequency corresponds to the main frequency of the axis. The main frequency represents the most concentrated frequency component of the axis during the movement, which usually reflects the main characteristics or periodic changes of the axis movement. By traversing the acceleration signals of all axes, the main frequency of each axis is extracted respectively, which can further analyze the dynamic characteristics of each axis during the movement, and provide important frequency domain information for system control optimization and fault diagnosis.

[0028] The frequency domain coupling degree of the target axis to the reference axis is calculated according to the main frequency, the natural frequency, the energy value of the main frequency and the energy value of the natural frequency, and the calculation of the frequency domain coupling degree comprises: For any alignment process in history, the first absolute difference value between the value of the main frequency of any reference axis and the value of the natural frequency of the target axis is calculated, the second absolute difference value between the energy value of the main frequency of any reference axis and the energy value of the natural frequency of the target axis is calculated, and the product of the first absolute difference value and the second absolute difference value is taken as the first product; the first product of each alignment process in history is obtained by traversal, and the cumulative value of all first products is mapped by negative correlation as the frequency domain coupling degree of the target axis to the reference axis.

[0029] The frequency domain coupling degree satisfies the relationship: , represents the frequency domain coupling degree of the target axis to the reference axis, represents the value of the main frequency of the reference axis in the historical alignment process, represents the value of the natural frequency of the target axis, represents the energy value of the main frequency of the reference axis in the historical alignment process, represents the energy value of the natural frequency of the target axis, represents the number of historical alignment processes, represents the exponential function.

[0030] ​​​Bottom loading arms are complex systems composed of multiple mechanical components, each typically driven by a servo motor. Servo motors achieve independent movement of each axis by providing different torques, but due to the interaction between axes, resonance may occur during movement. Resonance occurs when the frequency of one axis's motion approaches the natural frequency of another axis, causing a sharp increase in the system's vibration amplitude and a decrease in motion accuracy. Specifically, the closer the dominant frequency of one axis's acceleration sequence is to the natural frequency of another axis, and the smaller the energy difference between them, the higher the likelihood of resonance between the two axes, leading to increased error deviation on the target axis. Resonance causes significant deviations during movement, reducing the accuracy of loading and unloading operations. At this point, the frequency coupling between the two axes becomes more pronounced, as the movement of one axis affects the trajectory and accuracy of the other. Therefore, monitoring the proximity of the dominant frequencies and energy differences between axes helps determine the presence of resonance, provides a basis for optimizing system design and control, reduces errors, and improves motion accuracy.

[0031] S3: Calculate the first distance between the ratio sequence of the reference axis and the acceleration sequence of the target axis, and the second distance between the deviation sequence of the reference axis and the deviation sequence of the target axis. Calculate the temporal coupling degree of the reference axis to the target axis based on the first and second distances.

[0032] In one embodiment, the degree of temporal coupling satisfies the following relationship: , Indicates the comparison axis The degree of temporal coupling with respect to the target axis, Indicates the first in history During the alignment process, the reference axis The first distance from the target axis Indicates the first in history During the alignment process, the reference axis The second distance from the target axis Indicates the number of historical alignment processes. This represents an exponential function.

[0033] The mechanical connection structure of the bottom loading and unloading crane pipe is relatively complex, and multiple shafts interact through close mechanical coupling. The motion mode controlled by the servo motor is usually based on an S-shaped curve, and this smooth acceleration and deceleration mode will affect the torque transmission between different shafts. For example, the trolley of the x-axis and the y-axis is tightly coupled through the truss structure, and the acceleration of the x-axis is directly transmitted to the y-axis, causing the motion of the two shafts to affect each other. Due to this coupling, the acceleration sequences of the x-axis and the y-axis will show high similarity in the time domain, that is, their acceleration change trends and amplitude changes will be synchronized. The more similar the acceleration sequences of the two shafts are, the stronger the time domain coupling between them during the motion. Further, when the deviation sequences of the two shafts also show similar change patterns, it indicates that the two shafts have a greater mutual influence and a stronger time domain coupling during the motion.

[0034] Unlike the similarity analysis that only relies on the deviation sequence, judging the time domain coupling degree between shafts by the deviation similarity alone may have limitations. The reason is that the target shaft may be coupled with multiple shafts, and the influence of these coupled shafts on the target shaft's deviation may be smoothed by the deviation caused by other shafts, resulting in an underestimated time domain coupling degree of the reference shaft. For example, during the crane pipe alignment process, multiple shafts may jointly affect the motion of the target shaft, and these influences may cancel each other out or be integrated, so that the time domain coupling degree obtained through deviation analysis is not completely accurate. The present application can more comprehensively consider the interaction in the mechanical structure and the time domain coupling degree between shafts by comparing the acceleration patterns of different shafts. The acceleration pattern can reflect the motion characteristics of the shafts at different time periods, which more accurately reveals the physical connection relationship between the shafts and accurately evaluates their time domain coupling degree during the motion.

[0035] S4: Normalize the sum of the frequency domain coupling degree and the time domain coupling degree to obtain the coupling coefficient of the reference shaft to the target shaft.

[0036] S5: Calculate the correction error of the target shaft according to the coupling coefficient, the deviation between the actual position of the crane pipe on the target shaft at the control time and the final position, and the deviation between the actual position of the crane pipe on the target shaft at the control time and the ideal position at the control time, and use the correction error as the input of the discrete PID control to output the control signal of the target shaft at the control time.

[0037] In one embodiment, in order to accurately control the motion of the crane pipe and reduce errors, it is necessary to first calculate the deviation between the actual position of the crane pipe on the target shaft at the control time and the final position, which reflects the actual error of the target shaft during the motion. In addition, it is also necessary to calculate the deviation between the actual position of the crane pipe on the target shaft at the control time and the ideal position, which represents the difference between the position that the target shaft should reach under ideal control and the actual position.

[0038] In order to comprehensively consider these errors and the coupling effects between axes, a coupling coefficient is introduced to quantify the mutual influence between different axes. The coupling coefficient can reflect the influence degree of other axes on the target axis, and then correct the correction error of the target axis. By combining the coupling coefficient with the above two deviations (the deviation between the actual position and the final position, the deviation between the actual position and the ideal position), the correction error of the target axis can be calculated. The correction error satisfies the relationship: , denotes the control time of the target axis, denotes the reference axis of the target axis, denotes the deviation between the actual position and the final position of the crane pipe at the control time of the target axis, denotes the deviation between the actual position and the ideal position at the control time of the crane pipe at the control time of the target axis, denotes the number of reference axes.

[0039] The correction error not only considers the error of the target axis itself, but also considers the indirect influence due to the coupling of other axes, so as to more accurately reflect the adjustment amount required by the target axis. Finally, through the calculation of the correction error, the control strategy can be optimized, the motion accuracy of the crane pipe can be improved, and more precise motion control can be realized.

[0040] By traversing steps S1-S5, the correction error of any one axis can be obtained. The error of the linear axis is expressed as a distance error, and the error of the rotary axis is expressed as an angle error.

[0041] Since the control mode of the servo motor is a three-loop closed control mode of position loop, speed loop and current loop, the position loop is a discrete position error between different times. Therefore, the correction error is taken as the input of the discrete PID control, and the control signal of the target axis at the control time is output, and the control is completed according to the control signal.

[0042] The system includes a processor and a memory, and the memory stores computer program instructions which, when executed by the processor, implement the motion control method of the bottom loading and unloading crane pipe according to the first aspect of the application.

[0043] The system also includes a communication bus and a communication interface and other components familiar to those skilled in the art, the settings and functions of which are known in the art, and therefore will not be described here.

[0044] It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and all these belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A motion control method for bottom loading and unloading arms, characterized in that, include: The ratio sequence, deviation sequence, and natural frequency of the servo motor on the target axis are obtained during any historical alignment process. The target axis is any axis in the axis set, which includes linear axes and rotary axes. The axes in the axis set other than the target axis are used as reference axes. The dominant frequency of each axis is obtained based on Fourier transform, and the energy values ​​of the dominant frequency and the natural frequency are obtained. The frequency domain coupling degree of the reference axis to the target axis is calculated based on the dominant frequency, the natural frequency, the energy value of the dominant frequency, and the energy value of the natural frequency. Calculate the first distance between the ratio sequence of the reference axis and the acceleration sequence of the target axis, and the second distance between the deviation sequence of the reference axis and the deviation sequence of the target axis. Calculate the temporal coupling degree of the reference axis to the target axis based on the first and second distances. The coupling coefficient of the reference axis to the target axis is obtained by normalizing the sum of the frequency domain coupling degree and the time domain coupling degree. The correction error of the target axis is calculated based on the coupling coefficient, the deviation between the actual position and the final position of the loading arm on the target axis at the time to be controlled, and the deviation between the actual position and the ideal position of the loading arm on the target axis at the time to be controlled. The correction error is used as the input of discrete PID control, and the control signal of the target axis at the time to be controlled is output. The control is completed according to the control signal.

2. The motion control method for the bottom loading arm according to claim 1, characterized in that, Obtaining the ratio sequence includes: Obtain the acceleration sequence of the servo motor on any linear axis and the angular acceleration sequence of the servo motor on any rotation axis during any alignment process in history. Dimensionally remove the acceleration sequence on any linear axis to obtain the ratio sequence. Similarly, dimensionlessly remove the angular acceleration sequence on the rotation axis to obtain the ratio sequence. Dimensionlessness includes: calculating the ratio of any element in the acceleration sequence to the theoretical maximum acceleration of the servo motor, and constructing a ratio sequence for the linear axis; Calculate the ratio of any element in the angular acceleration sequence to the theoretical maximum angular acceleration of the servo motor, and construct a ratio sequence for the rotation axis.

3. The motion control method for the bottom loading arm according to claim 1, characterized in that, Obtaining the deviation sequence includes: Obtain the actual position sequence and ideal position sequence of the servo motor on any linear axis during any alignment process in history, and at the same time obtain the actual angle sequence and ideal angle sequence of the servo motor on the rotation axis; Calculate the first difference between the corresponding elements of the actual position sequence and the ideal position sequence, calculate the first ratio of the first difference to the theoretical maximum alignment distance, and construct a deviation sequence of all the first ratios for the linear axis; Calculate the second difference between the corresponding elements of the actual angle sequence and the ideal angle sequence, calculate the second ratio of the second difference to the theoretical maximum rotation angle, and construct a deviation sequence of the rotation axis from all the second ratios.

4. The motion control method for the bottom loading arm according to claim 1, characterized in that, The method of obtaining the dominant frequency of each axis based on Fourier transform includes: The energy spectrum of any axis is obtained by using Fourier transform. The frequency with the largest energy value in the energy spectrum is selected as the dominant frequency of any axis. The dominant frequency of each axis is obtained by iterating through the spectrum.

5. The motion control method for the bottom loading arm according to claim 1, characterized in that, Calculating the frequency domain coupling degree includes: For any historical alignment process, calculate the first absolute difference between the value of the principal frequency of any reference axis and the value of the natural frequency of the target axis, calculate the second absolute difference between the energy value of the principal frequency of any reference axis and the energy value of the natural frequency of the target axis, and use the product of the first absolute difference and the second absolute difference as the first product; The first product of each alignment process in history is obtained by iterating through the process. The accumulated value of all the first products is mapped by negative correlation and used as the frequency domain coupling degree of the reference axis to the target axis.

6. The motion control method for the bottom loading arm according to claim 1, characterized in that, Calculating the degree of temporal coupling includes: For any historical alignment process, the product of the first distance and the second distance is taken as the second product. The second product of each historical alignment process is obtained by iterating through the process. The accumulated value of all the second products is mapped by negative correlation and used as the temporal coupling degree of the reference axis to the target axis.

7. The motion control method for the bottom loading arm according to claim 1, characterized in that, The correction error satisfies the following relationship: , Indicates the time to be controlled Correction error of the target axis, Indicates the comparison axis The coupling coefficient with respect to the target axis. Indicates the moment when the loading arm is to be controlled on the target axis. The deviation between the actual position and the final position, Indicates the moment when the loading arm is to be controlled on the target axis. The deviation between the actual position and the ideal position at the moment to be controlled. Indicates the number of reference axes.

8. A motion control system for bottom loading and unloading arms, characterized in that, include: A processor and a memory, the memory storing computer program instructions that, when executed by the processor, implement the motion control method for bottom loading and unloading arms according to any one of claims 1-7.

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