Horizontal four-axis synchronous positioning method for vertical rail shuttle vehicle
By using dynamic origin calibration and multi-axis synchronous positioning methods, combined with hole positioning and absolute encoders, efficient and reliable positioning of the vertical track shuttle is achieved, solving the problems of low efficiency and susceptibility to accuracy in existing technologies, and improving the system's response speed and positioning accuracy.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-04-03
AI Technical Summary
The existing positioning control schemes for vertical rail shuttles are inefficient, require a long time to return to zero after a power outage, and are susceptible to cumulative errors in terms of positioning accuracy. Furthermore, they rely on a single mechanical origin, which is prone to failure.
The system employs a dynamic origin calibration process combined with hole positioning and absolute encoders. Absolute coordinate values are mapped through a cargo location coordinate table to achieve multi-axis synchronization and external position loop control. Real-time calibration is performed using laser rangefinders, tilt sensors, and hole positioning sensors.
It improves positioning accuracy and reliability, ensures the shuttle does not lose its position after a power outage, has a fast system response speed, eliminates accumulated errors, and is easy and efficient to maintain.
Smart Images
Figure CN121778342A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of logistics and warehousing, and specifically proposes a method for horizontal four-axis synchronous positioning of a vertical track shuttle car for storage and retrieval of material bins in a high-density automated warehouse. Background Technology
[0002] In the logistics and warehousing sector, with the continuous rise in industrial and commercial land and labor costs, intensive automated storage and retrieval systems (AS / RS) are widely used due to their ability to fully utilize space and correspondingly reduce the need for human labor. Currently, in industries such as e-commerce, food, pharmaceuticals, new energy, and logistics, bin-type automated warehouses commonly employ vertical rail shuttles to achieve automated storage, retrieval, and management of boxed goods.
[0003] As attached Figure 1 As shown, the existing automated warehouse has narrow aisle widths. The tracks are horizontally integrated into the vertical side of the rack 1. The vertical track shuttle 3 has a frame-type integral structure that can move horizontally along the horizontal track. Powered by the sliding contact line assembly 4, the upper and lower sets of drive wheels of the vertical track shuttle 3 are suspended and run on the first horizontal track 2-1 and the second horizontal track 2-2, respectively. The storage and retrieval trolley 5 moves vertically along the frame, thereby completing the fast and accurate storage and retrieval of the boxes on the left and right racks 1.
[0004] The positioning control of vertical track shuttles directly determines the operational efficiency, reliability, and application cost of the entire automated storage and retrieval system (AS / RS). Existing known positioning control schemes mainly include the following two types: one is a positioning method based on "incremental encoder + zero-return sensor." This system uses a PLC or dedicated controller, with servo or variable frequency motors as the actuators, including incremental encoders and mechanical or photoelectric zero-return sensors. After each power outage and power-on, the control system cannot obtain the absolute position of the shuttle. A lengthy zero-return process must be initiated, controlling the shuttle to move in a preset direction until the zero-return sensor is triggered. Once triggered, the motor usually continues to move slowly, searching for the encoder's zero-point signal and using this point as the mechanical origin of the entire system. After zero-return, the controller calculates the relative displacement from the zero point to the target storage location by recording the number of pulses emitted by the incremental encoder. The disadvantages of this method include low efficiency; the need to perform a zero-return operation after each power outage and restart is time-consuming, severely impacting the equipment's restart efficiency and continuous operation capability. There is a significant cumulative error. Occasional loss or interference of pulses during long-distance, high-frequency operation may lead to imperceptible cumulative errors. After long-term operation, the positioning accuracy decreases and requires regular manual calibration.
[0005] Another method is absolute positioning based on absolute encoders, using multi-turn absolute encoders instead of incremental encoders. The position is known immediately upon power-up. The multi-turn absolute encoder can immediately feed back a unique absolute value representing the position of the motor's multiple rotations via communication or analog signals after power-up. Therefore, the current absolute position can be known without returning to zero after power-down. Furthermore, the controller can directly send the target absolute position command to the driver. The main drawbacks of this method are: first, the positioning logic of the absolute encoder is essentially relative rather than absolute; the system's "zero position" still depends on a fixed mechanical origin switch; the encoder's feedback value is still relative to this mechanical origin. If this origin switch drifts or is damaged, the entire positioning system will fail. Second, the positioning accuracy is lower. Because it cannot automatically compensate for long-term changes in the mechanical system (such as lead screw wear, belt tension, and track thermal expansion and contraction), manual intervention is still required when positioning deviations occur, involving tedious steps to re-teach the positions of all locations.
[0006] In view of the above, this application is hereby submitted. Summary of the Invention
[0007] The horizontal four-axis synchronous positioning method for the vertical rail shuttle described in this application aims to solve the problems existing in the prior art by proposing a method based on a dynamic origin calibration process that combines hole positioning and absolute encoders to establish the origin of system operation calculation. By establishing a data structure that maps physical cargo locations to absolute coordinate values through a cargo location coordinate table, the method dynamically implements multi-axis synchronization and external position loop control to achieve the design goal of significantly improving positioning accuracy and reliability.
[0008] To achieve the above objectives, the vertical rail shuttle horizontal four-axis synchronous positioning method is equipped with a positioning control system including a PLC. The actuator of the system includes a laser rangefinder, tilt sensor and hole positioning sensor installed on the frame near the upper or lower drive wheels, a laser detection plate for reflecting signals installed on one side of the shelf, an absolute encoder built into the servo motor of each drive wheel, and positioning holes installed on the transverse rail corresponding to each storage position in that row. The execution steps include the following: Step (1), Calibration; Step (2): System initialization and absolute position calculation; After the positioning control system is powered on, it performs initialization and safety attitude calibration to ensure that the shuttle enters the ready state before executing the order task in a safe operating posture. Step (3): Four-axis synchronous closed-loop motion control; Before the shuttle car executes the order task, it sets the running direction and speed of the output shafts of the four servo motors by calculating the difference between the current position and the target coordinate position; By setting a virtual axis that forms a position mapping relationship with the output axes of four servo motors, the PLC controls the running posture. The output axes of the four servo motors follow the virtual axis. During operation, the position is calculated and calibrated based on the real-time data collected by the laser rangefinder, tilt sensor and hole positioning sensor.
[0009] Further, step (1) includes: Step (1.1), Cargo location coordinate mapping; Establish a coordinate table for all storage locations along the horizontal track. This involves pre-setting the positioning hole corresponding to each storage location based on its location number, and pre-setting an absolute target coordinate value, expressed as follows: MarkPosition: ARRAY [0..n] OF REAL:= [0,500,…,21100]; When the positioning control system receives the target location instruction, the PLC directly queries and obtains the absolute coordinates of the corresponding positioning hole in the location coordinate table; Step (1.2): Calculate the current position; The moving shuttle uses a laser rangefinder to measure distance and perform preliminary calculations of its current coordinates. First, determine the distance measurement value D(t) between the laser rangefinder and the laser detection board; Then, select the two sets of cargo location coordinates adjacent to the distance measurement value D(t) from the cargo location coordinate table. That is, when MarkPosition[n] < D(t) < MarkPosition[n+1], it means that the shuttle car is located between the nth column and the (n+1)th column. Finally, compare and determine which row of cargo positions the shuttle is closer to; L1=ABS(D(t)- MarkPosition[n]), where L1 is the horizontal distance between the laser range sensor and the nth column of the warehouse position, and ABS is the absolute value operation; L2 = ABS(D(t) - MarkPosition[n+1]), where L2 is the horizontal distance between the laser range sensor and the (n+1)th column of the cargo position; If L1 < L2, then the shuttle is currently positioned in the nth column of the cargo location.
[0010] Furthermore, step (2) includes: Step (2.1), posture perception and state judgment; The PLC reads the tilt angle θ between the upper and lower axes detected by the tilt sensor, where the tilt angle θ ∈ [0°, 90°]. The formula for determining whether the shuttle's offset is within the safe operating range is as follows: Where H is the preset vertical spacing between the upper and lower axes of the shuttle; l is the offset in the horizontal direction calculated based on the tilt angle θ; Determine whether the calculated offset l exceeds the preset threshold; if not, the shuttle is in a safe posture and proceeds directly to step (2.3); if so, proceed to step (2.2). Step (2.2), Active attitude closed-loop correction; The PLC activates the PID controller, with the tilt angle θ=0° as the target set value and the current tilt angle as the process value, to calculate the running direction and correction speed value of the servo motor output shaft that drives the upper axis, until the offset l detected and calculated again does not exceed the preset threshold. Step (2.3): Obtain the reference position; After confirming that the shuttle is in a safe posture, the PLC reads the current distance measurement value between the laser range sensor and the laser detection board, and defines this current value as the current absolute reference position of the overall positioning control system. The PLC writes the above current value into the motor driver of the output shaft of the servo motor where the four absolute encoders are located; Step (2.4), precise positioning; Control the shuttle to move at a low speed in the positive direction of the X-axis of the coordinate system; During operation, the system locates the nearest positioning hole. Once the hole positioning sensor is triggered, the PLC immediately records the reading of the laser rangefinder sensor, denoted as D1. Simultaneously, the PLC sends a command to the motor driver to stop operation. When the shuttle car comes to a complete stop, the current reading D1 of the laser rangefinder sensor is compared with the coordinate value MarkPosition[n] of the triggered positioning hole in the cargo location coordinate table. If the difference between the two is less than the preset threshold, the shuttle car is considered to be in the nth column of the shelf, and the current coordinate position of the shuttle car is MarkPosition[n]. This completes the initialization and position mapping. If the difference between the two is not less than the preset threshold, the PLC sends the instruction to the motor driver again, and the shuttle runs in reverse until the reading of the laser sensor is the same as the coordinate value MarkPosition[n] of the triggered positioning hole in the cargo location coordinate table. At this point, the initialization and position mapping are completed.
[0011] Furthermore, step (3) includes: Step (3.1): Set the virtual axis; A virtual axis is simulated by the PLC based on a mathematical motion model. This virtual axis has no actual physical motor or mechanical load, but serves as the main axis controlled by the PLC to generate a virtual motion trajectory. The output axes of four servo motors simultaneously refer to the virtual axis to generate their own actual motion trajectories. The PLC sets the target coordinate position determined by the order task as the motion endpoint of the virtual axis, and binds the output shafts of the four servo motors to the virtual axis to follow the movement. Step (3.2), position correction during movement; Whenever the hole positioning sensor detects and reads the signal of the positioning hole, the laser range sensor records the current distance value D(t) between itself and the laser detection board. The PLC calculates and compares the difference between the current positioning hole's corresponding cargo position coordinate value MarkPosition[n] and the distance measurement value D(t); if the difference exceeds a preset threshold, an alarm signal is output and the equipment operation is terminated; if the difference does not exceed the preset threshold, the difference is added as position compensation data to the virtual axis's running position parameters. When the shuttle reaches the preset remaining distance Lend from the target cargo location, the shuttle performs a preset low-speed operation. During the low-speed operation, the output shafts of the four servo motors simultaneously follow the virtual axis to search for the hole. When the difference between the reading D(t1) of the laser rangefinder and the coordinate value MarkPosition[n] of the positioning hole at the trigger position in the cargo location coordinate table is less than the preset threshold, the two servo motors located above the frame stop running. When the hole positioning sensor triggers the signal of the positioning hole, the two sets of servo motors located below the frame stop running, and the closed-loop motion control process of the shuttle for this order task ends.
[0012] In summary, this application has the following advantages and beneficial effects compared with the prior art: 1. This application enables the shuttle car to maintain its position even when the power is off. By using a multi-turn absolute encoder, the shuttle car does not need to return to the origin after the system is powered off. The current position of the shuttle car can be known as soon as the power is restored, which greatly improves the response speed and work efficiency after the equipment is restarted.
[0013] 2. This application has high precision and reliability. The closed-loop position control process can eliminate cumulative errors, and the calibration of the dynamic origin effectively reduces the dependence on a single physical origin.
[0014] 3. This application features high efficiency and easy integration. It can store all key system parameters (such as origin offset and coordinates of each cargo location) as variable data, which can be modified and calibrated later through software such as HMI without modifying the program or adjusting the hardware. The system is easy and efficient to maintain. Attached Figure Description
[0015] The present invention will now be further described with reference to the following figures.
[0016] Figure 1 This is a diagram showing the current usage status of the existing vertical rail shuttle. Figure 2 This is a flowchart of the horizontal four-axis synchronous positioning method for the vertical track shuttle described in this application; Figure 3 This is a schematic diagram of the actuator layout of the positioning control system; Figure 4 This is a diagram illustrating the current location calculation; Figure 5 This is a schematic diagram of tilt angle calculation for attitude determination; Figure 6 This is a schematic diagram of hole positioning after the safe posture has been determined; Figure 7 This is a schematic diagram of position correction during movement; Detailed Implementation
[0017] Example 1, such as Figure 3 As shown, the shuttle 3 has a frame 6, which runs horizontally along the first horizontal track 2-1 and the second horizontal track 2-2 located on the vertical side of the shelf 1 via four sets of upper and lower drive wheels. The horizontal four-axis synchronous positioning method for the vertical rail shuttle car proposed in this application is equipped with a positioning control system including a PLC. The actuator of the system includes a laser range sensor 11, an inclination sensor 12 and a hole positioning sensor 13 mounted on the frame 6 and located near the upper or lower drive wheels. A laser detection plate 15 for reflecting signals is set on one side of the shelf 1, and the laser range sensor 11 is located vertically above the inclination sensor 12 and the hole positioning sensor 13. Each drive wheel's servo motor incorporates an absolute encoder, specifically including a first absolute encoder 3-1, a second absolute encoder 3-2, a third absolute encoder 3-3, and a fourth absolute encoder 3-4. In the figure, the first absolute encoder 3-1 and the second absolute encoder 3-2 correspond to the two sets of servo motor output shafts on the upper part of the frame 6, and are therefore defined as the upper shafts. Based on the same principle, the third absolute encoder 3-3 and the fourth absolute encoder 3-4 are defined as the lower shafts. And, positioning holes 14 provided on the first transverse track 2-1 and / or the second transverse track 2-2, corresponding to each cargo position in that row.
[0018] Based on the application of the above positioning control system, the horizontal four-axis synchronous positioning method for the vertical rail shuttle includes the following execution steps: Step (1), Calibration; Step (1.1), Cargo location coordinate mapping; Along the first transverse track 2-1 or the second transverse track 2-2, establish a "cargo location coordinate table" for all cargo locations in the row. This involves pre-setting a positioning hole 14 corresponding to each cargo location based on its location number, and pre-setting an absolute target coordinate value. The expression is as follows: MarkPosition: ARRAY [0..n] OF REAL:= [0,500,…,21100]; When the positioning control system receives the target cargo location instruction from the host system or HMI, the PLC does not calculate the relative displacement of the shuttle 3 along the horizontal direction, but directly queries and obtains the absolute coordinates of the corresponding positioning hole 14 in the "Cargo Location Coordinate Table". For example: if the host system issues a control command requiring shuttle 3 to go to the cargo position in the second column, then by querying the "cargo position coordinate table", the position coordinates of MarkPosition[2] will be output as the target position of the servo motor output shaft; Step (1.2): Calculate the current position; The moving shuttle 3 uses the laser rangefinder 11 to measure distance and perform preliminary calculations of its current coordinate position; To more intuitively and accurately determine the initial coordinates of the task execution, such as Figure 4 As shown, the coordinates of the cargo location closest to the laser rangefinder 11 are taken as the initial coordinates of the shuttle 3 when it executes the order task. Specifically, first, the ranging value D(t) between the laser ranging sensor 11 and the laser detection plate 15 is determined; Then, select the two sets of cargo position coordinates adjacent to the distance measurement value D(t) from the "cargo position coordinate table". That is, when MarkPosition[n] < D(t) < MarkPosition[n+1], it means that shuttle car 3 is between the nth column and the n+1th column. Finally, compare and determine which row of cargo positions shuttle car 3 is closer to; L1=ABS(D(t)- MarkPosition[n]), where L1 is the horizontal distance between the laser range sensor 11 and the nth column of the cargo position, and ABS is the absolute value operation; L2 = ABS(D(t) - MarkPosition[n+1]), where L2 is the horizontal distance between the laser range sensor 11 and the (n+1)th column of the cargo position; If L1 < L2, then the shuttle car 3 is currently positioned in the nth column of the cargo location. Step (2): System initialization and absolute position calculation; After the positioning control system is powered on, it performs initialization and safety attitude calibration to ensure that shuttle 3 enters the ready state before executing the order task in a safe operating posture. The purpose of this step is to eliminate the risk of jamming, collision, or overturning that may be caused by abnormal initial posture of the equipment (such as tilting caused by power failure, emergency stop, or mechanical disturbance). Specifically, Step (2.1), posture perception and state judgment; The PLC reads the tilt angle θ between the upper shaft (first absolute encoder 3-1 or second absolute encoder 3-2) and the lower shaft (third absolute encoder 3-3 or fourth absolute encoder 3-4) detected by the tilt sensor 12. The tilt angle θ∈[0°,90°]. When θ=0°, it means that the shuttle 3 is in an absolutely safe vertical state. The formula for determining whether the offset of shuttle 3 is within the safe operating range is as follows: Where H is the preset vertical distance between the upper and lower axes of shuttle 3; l is the offset in the horizontal direction calculated based on the tilt angle θ; Determine whether the calculated offset l exceeds the preset threshold, such as l>5mm; if not, the shuttle 3 is in a safe posture and directly proceeds to step (2.3); if so, proceed to step (2.2). Step (2.2), Active attitude closed-loop correction; The PLC activates the PID controller, with the tilt angle θ=0° as the target set value and the current tilt angle as the process value, to calculate the running direction and correction speed value of the servo motor output shaft that drives the upper axis, until the offset l detected and calculated again does not exceed the preset threshold. Step (2.3): Obtain the reference position; After confirming that the shuttle 3 is in a safe posture, the PLC reads the current distance measurement value between the laser range sensor 11 and the laser detection board 15, and defines this current value as the current absolute reference position of the overall positioning control system. The PLC writes the above current value into the motor driver of the output shaft of the servo motor where the first absolute encoder 3-1, the second absolute encoder 3-2, the third absolute encoder 3-3, and the fourth absolute encoder 3-4 are located; Step (2.4), precise positioning; The tilt sensor 12 may be subject to problems such as interference from external signals. After obtaining the reference position (coarse positioning), the following hole positioning process (fine positioning) is performed to locate the adjacent positioning hole. Control shuttle 3 to move at a low speed in the positive direction of the X-axis of the coordinate system; During operation, instead of searching for a fixed mechanical origin, it searches for the nearest positioning hole 14. Once the hole positioning sensor 13 is triggered, the PLC immediately records the reading of the laser rangefinder sensor 11 at this time, which is recorded as D1. At the same time, the PLC sends a command to the motor driver to stop running. After shuttle 3 comes to a complete stop The reading D1 of the current laser rangefinder sensor 11 is compared with the coordinate value MarkPosition[n] of the triggered positioning hole 14 in the "cargo location coordinate table"; If the difference between the two is less than the preset threshold, such as when ABS(D1- MarkPosition[n])<2mm, it is considered that the shuttle car 3 is in the nth column of the shelf, and the current coordinate position of the shuttle car 3 is MarkPosition[n]. The initialization and position mapping are completed at this point. If the difference between the two is not less than the preset threshold, the PLC sends the instruction to the motor driver again, and the shuttle runs in reverse until the reading of the laser sensor 11 is the same as the coordinate value MarkPosition[n] of the triggered positioning hole 14 in the "cargo location coordinate table". At this point, the initialization and position mapping are completed. Step (3): Four-axis synchronous closed-loop motion control; Before executing the order task, the shuttle 3 has been precisely positioned, that is, the current specific coordinate position (which storage location it is in) is known, the target coordinate position (which storage location to run to for storing goods) is obtained from the order, and the running direction and speed of the four sets of servo motor output shafts are set by calculating the difference between the current and target coordinate positions. By setting a virtual axis that forms a position mapping relationship with the output axes of the four servo motors, the PLC controls the running posture. The output axes of the four servo motors follow the virtual axis. During the operation, the position is calculated and calibrated based on the data collected in real time by the laser rangefinder 11, tilt sensor 12 and hole positioning sensor 13. Step (3.1): Set the virtual axis; A virtual axis is simulated by the PLC based on a mathematical motion model. This virtual axis has no actual physical motor and mechanical load, but serves as the main axis controlled by the PLC to generate a virtual motion trajectory. The output axes of four servo motors simultaneously refer to the virtual axis to generate their own actual motion trajectories. That is, the virtual axis serves as the main axis, and the output axes of the four servo motors serve as the slave axes. The PLC sets the target coordinate position determined by the order task as the motion endpoint of the virtual axis, and binds the output shafts of the four servo motors to the virtual axis to follow the movement. Step (3.2), position correction during movement; like Figure 7 As shown, in order to avoid slippage caused by uneven load on the four sets of drive wheels of shuttle 3 or different track friction coefficients, the real-time position of shuttle 3 needs to be corrected during the execution of the order task. Specifically, whenever the hole positioning sensor 13 detects and reads the signal of the positioning hole 14, the laser ranging sensor 11 records the current ranging value D(t) between itself and the laser detection plate 15. The PLC calculates and compares the difference between the current positioning hole 14 corresponding to the cargo position coordinate value MarkPosition[n] and the distance measurement value D(t); If the difference between the two exceeds the preset threshold, such as ABS(D(t)- MarkPosition[n])>10mm, an alarm signal will be output and the operation of the equipment will be terminated. If the difference between the two does not exceed the preset threshold, that is, the difference is within a reasonable range, the difference between the two is added as position compensation data to the running position parameters of the virtual axis, so that position compensation is performed once every time the axis passes through a set of positioning holes 14. When shuttle 3 reaches the preset remaining distance Lend from the target storage location, shuttle 3 will operate at a preset low speed. During low-speed operation, the output shafts of the four servo motors simultaneously follow the virtual axis to search for the hole; when the difference between the reading D(t1) of the laser rangefinder 11 and the coordinate value MarkPosition[n] of the positioning hole 14 at the trigger position in the "cargo coordinate table" is less than the preset threshold, for example, when ABS(D(t1)- MarkPosition[n])<2mm, the two servo motors located above the frame stop running; When the hole positioning sensor 13 triggers the signal of the positioning hole 14, the two sets of servo motors located below the frame stop running, and the closed-loop motion control process of the shuttle 3 for this order task ends.
[0019] As described above, the embodiments given in conjunction with the accompanying drawings are merely preferred solutions for achieving the objectives of this invention. Those skilled in the art can draw inspiration from this and directly derive other alternative structures that conform to the design concept of this invention. Other structural features derived therefrom should also fall within the scope of the solutions described in this invention.
Claims
1. A method for horizontal four-axis synchronous positioning of a vertical track shuttle, characterized in that: The system is equipped with a positioning control system including a PLC. The actuators of the system include laser rangefinders, tilt sensors and hole positioning sensors mounted on the frame and adjacent to the upper or lower drive wheels. A laser detection board for reflecting signals is set on one side of the shelf. An absolute encoder is built into the servo motor of each drive wheel. Positioning holes are set on the transverse track corresponding to each storage position in that row. The execution steps include the following: Step (1), Calibration; Step (2): System initialization and absolute position calculation; After the positioning control system is powered on, it performs initialization and safety attitude calibration to ensure that the shuttle enters the ready state before executing the order task in a safe operating posture. Step (3): Four-axis synchronous closed-loop motion control; Before the shuttle car executes the order task, it sets the running direction and speed of the output shafts of the four servo motors by calculating the difference between the current position and the target coordinate position; By setting a virtual axis that forms a position mapping relationship with the output axes of four servo motors, the PLC controls the running posture. The output axes of the four servo motors follow the virtual axis. During operation, the position is calculated and calibrated based on the real-time data collected by the laser rangefinder, tilt sensor and hole positioning sensor.
2. The horizontal four-axis synchronous positioning method for a vertical track shuttle car according to claim 1, characterized in that: Step (1) includes, Step (1.1), Cargo location coordinate mapping; Establish a coordinate table for all storage locations along the horizontal track. This involves pre-setting the positioning hole corresponding to each storage location based on its location number, and pre-setting an absolute target coordinate value, expressed as follows: MarkPosition: ARRAY [0..n] OF REAL:= [0,500,…,21100]; When the positioning control system receives the target location instruction, the PLC directly queries and obtains the absolute coordinates of the corresponding positioning hole in the location coordinate table; Step (1.2): Calculate the current position; The moving shuttle uses a laser rangefinder to measure distance and perform preliminary calculations of its current coordinates. First, determine the distance measurement value D(t) between the laser rangefinder and the laser detection board; Then, select the two sets of cargo location coordinates adjacent to the distance measurement value D(t) from the cargo location coordinate table. That is, when MarkPosition[n] < D(t) < MarkPosition[n+1], it means that the shuttle car is located between the nth column and the (n+1)th column. Finally, compare and determine which row of cargo positions the shuttle is closer to; L1=ABS(D(t)- MarkPosition[n]), where L1 is the horizontal distance between the laser range sensor and the nth column of the warehouse position, and ABS is the absolute value operation; L2 = ABS(D(t) - MarkPosition[n+1]), where L2 is the horizontal distance between the laser range sensor and the (n+1)th column of the cargo position; If L1 < L2, then the shuttle is currently positioned in the nth column of the cargo location.
3. The horizontal four-axis synchronous positioning method for a vertical track shuttle according to claim 2, characterized in that: Step (2) includes, Step (2.1), posture perception and state judgment; The PLC reads the tilt angle θ between the upper and lower axes detected by the tilt sensor, where the tilt angle θ ∈ [0°, 90°]. The formula for determining whether the shuttle's offset is within the safe operating range is as follows: Where H is the preset vertical spacing between the upper and lower axes of the shuttle; l is the offset in the horizontal direction calculated based on the tilt angle θ; Determine whether the calculated offset l exceeds the preset threshold; if not, the shuttle is in a safe posture and proceeds directly to step (2.3); if so, proceed to step (2.2). Step (2.2), Active attitude closed-loop correction; The PLC activates the PID controller, with the tilt angle θ=0° as the target set value and the current tilt angle as the process value, to calculate the running direction and correction speed value of the servo motor output shaft that drives the upper axis, until the offset l detected and calculated again does not exceed the preset threshold. Step (2.3): Obtain the reference position; After confirming that the shuttle is in a safe posture, the PLC reads the current distance measurement value between the laser range sensor and the laser detection board, and defines this current value as the current absolute reference position of the overall positioning control system. The PLC writes the above current value into the motor driver of the output shaft of the servo motor where the four absolute encoders are located; Step (2.4), precise positioning; Control the shuttle to move at a low speed in the positive direction of the X-axis of the coordinate system; During operation, the system locates the nearest positioning hole. Once the hole positioning sensor is triggered, the PLC immediately records the reading of the laser rangefinder sensor, denoted as D1. Simultaneously, the PLC sends a command to the motor driver to stop operation. When the shuttle car comes to a complete stop, the current reading D1 of the laser rangefinder sensor is compared with the coordinate value MarkPosition[n] of the triggered positioning hole in the cargo location coordinate table. If the difference between the two is less than the preset threshold, the shuttle car is considered to be in the nth column of the shelf, and the current coordinate position of the shuttle car is MarkPosition[n]. This completes the initialization and position mapping. If the difference between the two is not less than the preset threshold, the PLC sends the instruction to the motor driver again, and the shuttle runs in reverse until the reading of the laser sensor is the same as the coordinate value MarkPosition[n] of the triggered positioning hole in the cargo location coordinate table. At this point, the initialization and position mapping are completed.
4. The horizontal four-axis synchronous positioning method for a vertical track shuttle car according to claim 1, characterized in that: Step (3) includes, Step (3.1): Set the virtual axis; A virtual axis is simulated by the PLC based on a mathematical motion model. This virtual axis has no actual physical motor or mechanical load, but serves as the main axis controlled by the PLC to generate a virtual motion trajectory. The output axes of four servo motors simultaneously refer to the virtual axis to generate their own actual motion trajectories. The PLC sets the target coordinate position determined by the order task as the motion endpoint of the virtual axis, and binds the output shafts of the four servo motors to the virtual axis to follow the movement. Step (3.2), position correction during movement; Whenever the hole positioning sensor detects and reads the signal of the positioning hole, the laser range sensor records the current distance value D(t) between itself and the laser detection board. The PLC calculates and compares the difference between the current positioning hole's corresponding cargo position coordinate value MarkPosition[n] and the distance measurement value D(t); if the difference exceeds a preset threshold, an alarm signal is output and the equipment operation is terminated; if the difference does not exceed the preset threshold, the difference is added as position compensation data to the virtual axis's running position parameters. When the shuttle reaches the preset remaining distance Lend from the target storage location, the shuttle will operate at a preset low speed. During low-speed operation, the output shafts of the four servo motors simultaneously follow the virtual axis to search for the hole; when the difference between the reading D(t1) of the laser rangefinder and the coordinate value MarkPosition[n] of the positioning hole at the trigger position in the cargo location coordinate table is less than the preset threshold, the two servo motors located above the frame stop running. When the hole positioning sensor triggers the signal of the positioning hole, the two sets of servo motors located below the frame stop running, and the closed-loop motion control process of the shuttle for this order task ends.