Method and system for motion control of bottom loading and unloading swivel

Abstract

The application relates to the field of loading and unloading of a crane pipe, in particular to a movement control method and system for loading and unloading a crane pipe from the bottom, the method comprising the following steps: acquiring a ratio sequence, a deviation sequence and an inherent frequency of a servo motor on a target shaft in any historical alignment process; calculating a frequency domain coupling degree of a contrast shaft to the target shaft; calculating a time domain coupling degree of the contrast shaft to the target shaft; normalizing a sum of the frequency domain coupling degree and the time domain coupling degree to obtain a coupling coefficient of the contrast shaft to the target shaft; calculating a correction error of the target shaft; taking the correction error as an input of a discrete PID control; outputting a control signal of the target shaft at a control moment; and completing the control according to the control signal. Through the technical scheme, the precision of servo motor control in the loading and unloading process of the crane pipe can be improved.

Description

Technical Field

[0001] This invention relates to the field of loading arms, and more particularly to a motion control method and system for bottom-loading and unloading loading arms. Background Technology

[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 during operation to ensure safety and efficiency. In the design of bottom-loading loading arms, multi-axis servo motors are typically needed to achieve precise vertical and lateral control and positional movement of the loading arm during loading and unloading. These servo motors work in coordination through a drive system to achieve precise alignment of the loading arm during dock loading and unloading. However, because the alignment process requires high-precision displacement and rotation within a short time, the coupling problem between multi-axis servo motors becomes particularly prominent. Specifically, the movements of different motors can influence each other.

[0003] Due to the complex connection structure of the mechanical components of the bottom loading arm, there is strong coupling between different axes during servo motor control, and the torques between different axes will affect each other. Existing technology controls the servo motor of each axis by obtaining an independent error term for each axis. This reliance on individual control of each axis's servo motor ignores the motion coupling and torque effects between different axes, resulting in an underestimation of the PID error term. This leads to significant deviations in the actual movement position or rotation angle of the bottom loading arm on each axis, resulting in poor alignment path accuracy. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention provides solutions in the following aspects.

[0005] In the first aspect, the motion control method for the bottom loading arm includes: acquiring the ratio sequence, deviation sequence, and natural frequency of a servo motor on a target axis during any historical alignment process, wherein the target axis is any axis in an axis set, the axis set including linear axes and rotational axes, and the axes in the axis set other than the target axis are used as reference axes; obtaining the dominant frequency of each axis based on Fourier transform, and obtaining the energy value of the dominant frequency and the energy value of the natural frequency; calculating the frequency domain coupling degree of the reference axis to the target axis based on the dominant frequency, natural frequency, energy value of the dominant frequency, and energy value of the natural frequency; and calculating the first distance between the ratio sequence of the reference axis and the acceleration sequence of the target axis. The first distance is the second distance between the deviation sequence of the reference axis and the deviation sequence of the target axis. Based on the first and second distances, the time-domain coupling degree of the reference axis to the target axis is calculated. The frequency-domain coupling degree and the sum of the time-domain coupling degree are normalized to obtain the coupling coefficient of the reference axis to the target axis. 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.

[0006] Preferably, obtaining the ratio sequence includes: obtaining the acceleration sequence of the servo motor on any linear axis and the angular acceleration sequence of the servo motor on any rotational axis during any historical alignment process; removing dimensions from the acceleration sequence of any linear axis to obtain the ratio sequence; similarly, removing dimensions from the angular acceleration sequence of the rotational axis to obtain the ratio sequence; the removal of dimensions 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 rotational axis.

[0007] Preferably, obtaining the deviation sequence includes: obtaining the actual position sequence and ideal position sequence of the servo motor on any linear axis during any historical alignment process, and simultaneously obtaining the actual angle sequence and ideal angle sequence of the servo motor on the rotation axis; calculating the first difference between corresponding elements of the actual position sequence and the ideal position sequence, calculating the first ratio of the first difference to the theoretical maximum alignment distance, and constructing the deviation sequence of the linear axis from all the first ratios; calculating the second difference between corresponding elements of the actual angle sequence and the ideal angle sequence, calculating the second ratio of the second difference to the theoretical maximum rotation angle, and constructing the deviation sequence of the rotation axis from all the second ratios.

[0008] Preferably, obtaining the dominant frequency of each axis based on Fourier transform includes: obtaining the energy spectrum of any axis using Fourier transform, selecting the frequency with the largest energy value in the energy spectrum as the dominant frequency of any axis, and iterating through each axis to obtain the dominant frequency.

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

[0010] Preferably, calculating the temporal coupling degree includes: for any historical alignment process, taking the product of the first distance and the second distance as the second product, traversing to obtain the second product of each historical alignment process, and using the accumulated value of all the second products through negative correlation mapping as the temporal coupling degree of the reference axis to the target axis.

[0011] Preferably, the correction error satisfies the following relationship:

[0012] , 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.

[0013] Secondly, the motion control system for the bottom loading arm includes: a processor and a memory, wherein the memory stores computer program instructions, and when the computer program instructions are executed by the processor, the motion control method for the bottom loading arm described in any one of the claims is implemented.

[0014] The present invention has the following effects:

[0015] This invention optimizes the servo motor control strategy by precisely analyzing the dynamic characteristics and mutual influences of each axis during the loading and unloading of loading arms. Through quantification and comprehensive analysis of acceleration ratios, deviation sequences, and coupling degrees in the frequency and time domains, it can more accurately identify and correct motion errors of the target axis in actual operation. This method not only monitors the motion accuracy of each axis in real time and identifies potential resonance and coupling problems, but also dynamically adjusts the interaction between multiple axes by introducing coupling coefficients, ensuring coordinated movement of each axis. Ultimately, through optimized control to correct errors, the positioning accuracy and operational efficiency during loading and unloading of loading arms are significantly improved, avoiding motion errors caused by inter-axis coupling. This achieves higher precision loading and unloading operations, greatly enhancing the system's flexibility and stability, and ensuring precise positioning and efficient operation of loading arms in complex working environments. Attached Figure Description

[0016] Figure 1 This is a flowchart of the motion control method for the bottom loading and unloading arm in an embodiment of the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0018] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] Reference Figure 1 The motion control method for the bottom loading arm includes steps S1-S5, as detailed below:

[0020] S1: Obtain the ratio sequence, deviation sequence, and natural frequency of the servo motor on the target axis 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.

[0021] It should be noted that during the loading and unloading of loading arms, a four-axis and five-axis alternating iterative control method is typically employed to achieve efficient and precise alignment and operation. Specifically, although only four axes are used for control in certain stages (such as the x, y, and z axes for linear movement and the telescopic boom axis), a five-axis control system is actually used to ensure the loading arm can complete complex spatial adjustments and precise positioning during alignment. The five-axis control system, by simultaneously adjusting more degrees of freedom, especially by adding control to the rotation axis, allows the loading arm to make fine adjustments in multiple directions, thus providing greater flexibility and precision during loading and unloading. The alternating iterative approach allows the system to switch between four-axis and five-axis control as needed at different stages, optimizing operational efficiency at each stage and ensuring the precise completion of the alignment and loading / unloading process.

[0022] In one embodiment, during the alignment process controlled by the servo motor, the acceleration sequence of the servo motor on each linear axis (including the x-axis, y-axis, z-axis, and telescopic arm axis) is first acquired using an accelerometer, while the angular acceleration sequence on the rotation axis is acquired using the servo motor's encoder. Then, by performing dimensionless processing on the acceleration sequences, the ratio sequences for the linear and rotation axes are obtained separately to eliminate the influence of units and dimensions and unify the expression of acceleration.

[0023] Dimensionlessness includes: calculating the ratio of any element in the acceleration sequence to the theoretical maximum acceleration of the servo motor to construct a ratio sequence for linear axes; and calculating the ratio of any element in the angular acceleration sequence to the theoretical maximum angular acceleration of the servo motor to construct a ratio sequence for rotational axes.

[0024] For example, the acceleration sequence is The theoretical maximum acceleration is Then, the dimensionless sequence of ratios of the linear axes is: Similarly, the angular acceleration sequence is: The theoretical maximum angular acceleration is Then, the sequence of ratios of the rotation axes after dimensionless measurement is: Since both the acceleration sequences of the linear axis and the angular acceleration sequences of the rotational axis have undergone dimensionless processing, the dimensionless sequences are referred to as ratio sequences. The purpose of ratio processing is to eliminate dimensions; the theoretical maximum acceleration and theoretical maximum angular acceleration are set by those skilled in the art.

[0025] Obtain the actual position sequence and ideal position sequence, as well as the actual angle sequence and ideal angle sequence, for any historical alignment process. For any linear axis, calculate the first difference between corresponding elements of the actual position sequence and the ideal position sequence. This difference represents the deviation between the current position of the loading arm and the ideal position during the alignment process. Further, compare this difference with the theoretical maximum alignment distance; the calculated ratio constitutes the deviation sequence for that linear axis. Similarly, for a rotation axis, calculate the second difference between corresponding elements of the actual angle sequence and the ideal angle sequence, and the ratio of this difference to the theoretical maximum rotation angle constitutes the deviation sequence for the rotation axis.

[0026] For example, the actual position sequence on any linear axis is: The ideal position sequence is The theoretical maximum alignment distance is Therefore, the deviation sequence of the linear axis is: Similarly, the actual angle sequence of the rotation axis is: The ideal angle sequence is The theoretical maximum rotation angle is Therefore, the deviation sequence of the rotation axis is: The purpose of the ratio calculation is to eliminate dimensions. The theoretical maximum alignment distance and theoretical maximum rotation angle are set by those skilled in the art.

[0027] The above steps quantify the deviation of each linear and rotary axis during the alignment process, providing a quantitative basis for optimizing the servo motor control system. Comparing the actual and ideal deviation sequences helps determine whether the servo motor has accurately completed the alignment task, thereby evaluating and adjusting the servo motor's control performance and improving alignment accuracy.

[0028] Obtaining natural frequencies is a well-known technique among those skilled in the art and will not be elaborated upon here. It should be noted that when a structural system is subjected to external excitation and undergoes motion, it will naturally vibrate at a specific frequency; this specific frequency is called the structure's natural frequency. Natural frequencies are only related to the materials of the mechanical components.

[0029] S2: Obtain the dominant frequency of each axis based on Fourier transform, and obtain the energy value of the dominant frequency and the energy value of the natural frequency. Calculate the frequency domain coupling degree of the reference axis to the target axis based on the dominant frequency, natural frequency, energy value of the dominant frequency and energy value of the natural frequency.

[0030] In one embodiment, the energy spectrum of the acceleration signal in the frequency domain can be obtained by performing a Fourier transform on the acceleration signal on each axis. The Fourier transform converts the time-domain signal into a frequency-domain signal, making the energy distribution of each frequency component visible. After obtaining the energy spectrum, the frequency component with the highest energy value can be selected by analyzing the energy values ​​in the spectrum; this frequency corresponds to the dominant frequency of that axis. The dominant frequency represents the frequency component with the most concentrated energy during the axis's motion, typically reflecting the main characteristics or periodic changes of the axis's motion. By traversing the acceleration signals of all axes and extracting the dominant frequency of each axis, the dynamic characteristics of each axis during motion can be further analyzed, providing important frequency-domain information for system control optimization and fault diagnosis.

[0031] The frequency domain coupling degree of the reference axis to the target axis is calculated based on the dominant frequency, natural frequency, energy value of the dominant frequency, and energy value of the natural frequency. The calculation of the frequency domain coupling degree includes:

[0032] For any historical alignment process, calculate the first absolute difference between the principal frequency of any reference axis and 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 multiply the first absolute difference and the second absolute difference as the first product; iterate through each historical alignment process to obtain the first product, and use the cumulative value of all the first products through negative correlation mapping as the frequency domain coupling degree of the reference axis to the target axis.

[0033] The degree of frequency domain coupling satisfies the following relationship:

[0034] , Indicates the comparison axis The degree of frequency domain coupling to the target axis, Indicates the historical number During the alignment process, the reference axis The value of the main frequency, The value representing the natural frequency of the target axis. Indicates the first in history During the alignment process, the reference axis The energy value of the main frequency, The energy value representing the natural frequency of the target axis. Indicates the number of historical alignment processes. This represents an exponential function.

[0035] 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.

[0036] 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.

[0037] In one embodiment, the degree of temporal coupling satisfies the following relationship:

[0038] , 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.

[0039] The mechanical connection structure of the bottom loading arm is relatively complex, with multiple axes interacting through tight mechanical coupling. The motion pattern controlled by the servo motor is typically based on an S-curve; this smooth acceleration and deceleration pattern affects torque transmission between different axes. For example, the trolley's x-axis and y-axis are tightly coupled through a truss structure, with the x-axis acceleration directly transmitted to the y-axis, causing the motions of these two axes to influence each other. Due to this coupling, the acceleration sequences of the x-axis and y-axis exhibit high similarity in the time domain, meaning their acceleration trends and amplitude changes are synchronized. The more similar the acceleration sequences of the two axes, the stronger their time-domain coupling during motion. Furthermore, when the deviation sequences of these two axes also exhibit similar change patterns, it indicates a greater degree of mutual influence and stronger time-domain coupling between the two axes during motion.

[0040] Unlike similarity analysis that relies solely on deviation sequences, judging the temporal coupling between axes based solely on deviation similarity may have limitations. This is because the target axis may be coupled with multiple axes, and the deviations of these coupled axes on the target axis may be smoothed out by deviations caused by other axes, leading to an underestimation of the temporal coupling of the control axis. For example, during loading arm alignment, multiple axes may jointly influence the movement of the target axis, and these influences may cancel each other out or combine, making the temporal coupling obtained through deviation analysis inaccurate. This invention, by comparing the acceleration patterns of different axes, can more comprehensively consider the interactions within the mechanical structure and the temporal coupling between axes. Acceleration patterns reflect the motion characteristics of axes over different time periods, revealing the physical connections between axes in greater detail, thus accurately assessing their temporal coupling during motion.

[0041] S4: Normalize the sum of the frequency domain coupling degree and the time domain coupling degree to obtain the coupling coefficient of the reference axis to the target axis.

[0042] S5: Calculate the correction error of the target axis 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. Use the correction error as the input of discrete PID control and output the control signal of the target axis at the time to be controlled.

[0043] In one embodiment, to precisely control the movement of the loading arm and reduce errors, it is first necessary to calculate the deviation between the actual position and the final position of the loading arm on the target axis at the moment of control. This deviation reflects the actual error during the movement of the target axis. Furthermore, it is also necessary to calculate the deviation between the actual position and the ideal position of the loading arm on the target axis at the moment of control. This deviation represents the difference between the position the target axis should achieve under ideal control and the actual position.

[0044] 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 reflects the degree of influence of other axes on the target axis, thus correcting the target axis's correction error. By combining the coupling coefficient with the two deviations mentioned above (the deviation between the actual position and the final position, and the deviation between the actual position and the ideal position), the target axis's correction error can be calculated. The correction error satisfies the following relationship:

[0045] , 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.

[0046] The error correction not only considers the error of the target axis itself, but also the indirect effects caused by the coupling of other axes, thus more accurately reflecting the required adjustment amount of the target axis. Ultimately, by calculating the error correction, the control strategy can be optimized, the motion accuracy of the loading arm can be improved, and more precise motion control can be achieved.

[0047] By traversing steps S1-S5, the correction error for any axis can be obtained. The error of the linear axis is represented by distance error, and the error of the rotation axis is represented by angle error.

[0048] Since the control mode of the servo motor is a three-loop closed control mode consisting of position loop, speed loop and current loop, and its position loop has discrete position errors at different times, the correction error is used as the input of discrete PID control, and the output is the control signal of the target axis at the time to be controlled, and the control is completed according to the control signal.

[0049] The system includes a processor and a memory, the memory storing computer program instructions, which, when executed by the processor, implement the motion control method for the bottom loading arm according to the first aspect of the present invention.

[0050] The system also includes other components well known to those skilled in the art, such as communication buses and communication interfaces, the settings and functions of which are known in the art and will not be described in detail here.

[0051] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method of motion control of a bottom loading and unloading crane, characterized in that, The method comprises the following steps: Obtain the ratio sequence, the deviation sequence and the natural frequency of the servo motor in any alignment process in the past, the target axis is any axis in the axis set, the axis set comprises linear axes and rotary axes, and the axes in the axis set except the target axis are taken as the reference axes; Obtain the main frequency of each axis based on 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 reference axis 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; 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, and calculate the time domain coupling degree of the reference axis to the target axis based on the first distance and the second distance; Normalize the sum of the frequency domain coupling degree and the time domain coupling degree to obtain the coupling coefficient of the reference axis to the target axis; Calculate the correction error of the target axis according to the coupling coefficient, the deviation between the actual position of the crane pipe on the target axis at the time to be controlled and the final position, and the deviation between the actual position of the crane pipe on the target axis at the time to be controlled and the ideal position at the time to be controlled, take the correction error as the input of the discrete PID control, output the control signal of the target axis at the time to be controlled, and complete the control according to the control signal; The calculation of the frequency domain coupling degree comprises: For any alignment process in the past, calculate 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, calculate 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, and take the product of the first absolute difference value and the second absolute difference value as the first product; obtain the first product of each alignment process in the past, and map the cumulative value of all first products through negative correlation as the frequency domain coupling degree of the reference axis to the target axis; The calculation of the time domain coupling degree comprises: For any alignment process in the past, take the product of the first distance and the second distance as the second product, obtain the second product of each alignment process in the past, and map the cumulative value of all second products through negative correlation as the time domain coupling degree of the reference axis to the target axis; The correction error satisfies the relationship: , denotes the control time , denotes the reference axis , denotes the control time , denotes the control time , denotes the number of reference axes 2. The motion control method of a bottom loading and unloading hose according to claim 1, characterized by, The acquisition of the ratio sequence comprises: Obtain the acceleration sequence of the servo motor on any linear axis and the angular acceleration sequence of the servo motor on the rotary axis in any alignment process in the past, and obtain the ratio sequence by dimensionless processing of the acceleration sequence of any linear axis; and similarly, obtain the ratio sequence by dimensionless processing of the angular acceleration sequence of the rotary axis; The dimensionless processing comprises: calculating the ratio of any element in the acceleration sequence to the theoretical maximum acceleration of the servo motor, and constructing the ratio sequence of the linear axis; Similarly, calculating the ratio of any element in the angular acceleration sequence to the theoretical maximum angular acceleration of the servo motor, and constructing the ratio sequence of the rotary axis.

3. The motion control method of a bottom discharge loading arm according to claim 1, characterized in that, The acquisition of the deviation sequence comprises: Obtain the actual position sequence and the ideal position sequence of the servo motor on any linear axis in any alignment process in the past, and simultaneously obtain the actual angle sequence and the ideal angle sequence of the servo motor on the rotary axis; Calculate the first difference value of the corresponding elements of the actual position sequence and the ideal position sequence, calculate the first ratio value of the first difference value and the theoretical maximum alignment distance, and construct the deviation sequence of the linear axis by using all the first ratio values; The second difference value of the actual angle sequence and the corresponding element of the ideal angle sequence is calculated, the second ratio of the second difference value and the theoretical maximum rotation angle is calculated, and all the second ratios are constructed as a deviation sequence of the rotation axis.

4. The motion control method of a bottom discharge loading arm according to claim 1, characterized by The obtaining of the main frequency of each axis based on the Fourier transform comprises: An energy spectrum of any axis is obtained by using the Fourier transform, a frequency with the maximum energy value in the energy spectrum is selected as the main frequency of any axis, and the main frequency of each axis is obtained by traversal.

5. A motion control system for a bottom loading and unloading swivel, characterized in that The method comprises: A processor and a memory, wherein 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 any one of claims 1-4.

Images