CN114881284A

CN114881284A - Anti-blocking scheduling strategy for OHT (open high-head) carrying system based on variable track

Info

Publication number: CN114881284A
Application number: CN202210328947.XA
Authority: CN
Inventors: 钱晓明; 楼佩煌; 郭大宏; 翟晶晶
Original assignee: Nanjing University of Aeronautics and Astronautics; Miracle Automation Engineering Co Ltd
Current assignee: Nanjing University of Aeronautics and Astronautics; Miracle Automation Engineering Co Ltd
Priority date: 2022-03-30
Filing date: 2022-03-30
Publication date: 2022-08-09
Also published as: WO2023184770A1

Abstract

The invention relates to an anti-blocking scheduling strategy of an OHT (open hybrid railway) carrying system based on a variable track, which is characterized in that a scheme is allocated to an OHT vehicle according to a task scheduling method, and a shortest path and a track changing point in the path are determined according to a path planning method; according to the travel time prediction method, predicting the time of the trolley passing through each orbital transfer point, and sequencing; the trolley executes tasks according to the planned path, the variable track is changed into tracks in advance according to the passing sequence and the trolley state, and the trolley waits for passing; when the trolley reaches the target work site, the station track moves to a working state, the limiting block works, the trolley starts to be loaded or unloaded, and when the trolley finishes loading or unloading and the preparation track of the station track has no trolley, the limiting block is loosened, and the station track moves to an idle state. And finally, updating the system state when the trolley completes the task. The method adopts the variable track and the station track, and solves the problems of low resource utilization rate and station blockage based on the fixed track in the prior art.

Description

Anti-blocking scheduling strategy for OHT (open high-head) carrying system based on variable track

Technical Field

The invention relates to the field of intelligent control, in particular to an anti-blocking scheduling strategy for an OHT (open high-altitude transportation) system based on a variable track.

Background

With the rapid development of semiconductor manufacturing technology, the size of wafers is increasing, the weight is increasing, and under the condition that the manual transportation can not meet the transportation requirements of a manufacturing system, Overhead Hook Transport (OHT) does not occupy the ground space due to the arrangement of tracks in the air, and the speed of a trolley is high, so that the transportation efficiency can be improved, the waste of resources is avoided, and the Overhead hook Transport is widely applied to an automatic material transportation system of a wafer manufacturing factory with the diameter of 300 mm. Therefore, reasonable OHT trolley scheduling is carried out, collision-free and congestion-free transportation is realized, and the method has important significance for improving the overall efficiency of the semiconductor manufacturing system under the integrated layout.

In order to ensure the punctuality of the material and improve the efficiency of the system, the problem of traffic management of the OHT trolley against blockage needs to be considered. However, referring to the existing documents related to the scheduling of the intelligent transport system, the research subject mainly uses an Automated Guided Vehicle (AGV), and the research on the scheduling problem of the OHT transport system is relatively small, and mainly focuses on the design and scheduling problem of the OHT transport system under the fixed track, such as the chinese patent publication No. CN112650211A, while there are relatively few research documents in the aspect of the scheduling problem of the OHT transport system based on the variable track.

Disclosure of Invention

In order to solve the technical defects in the prior art, the invention provides an anti-blocking scheduling strategy for an OHT (open hybrid railway) carrying system based on a variable track.

The invention is realized by the following technical scheme:

the anti-blocking scheduling strategy of the OHT carrying system based on the variable track comprises the following steps:

step 1: when the OHT carrying system meets the task allocation triggering condition, acquiring system information;

step 2: determining an OHT vehicle task allocation scheme according to a task scheduling method;

and step 3: determining the shortest path and a track transfer point in the path according to a path planning method;

and 4, step 4: predicting the time of the OHT vehicle passing each orbital transfer point according to a travel time prediction method;

and 5: sequencing the passing sequence of the OHT vehicles of each orbital transfer point according to a passing sequence optimization method;

step 6: the OHT car executes tasks according to the planned path, the variable track is changed in advance according to the passing sequence and the car state, and the OHT car waits for passing;

and 7: judging whether the OHT trolley reaches the target work site, if so, entering a step 8, and if not, entering a step 6;

and 8: the station track moves to a working state, the limiting block works, and the OHT trolley starts to load or unload;

and step 9: judging whether the OHT trolley finishes loading or unloading, if so, entering a step 10, otherwise, waiting for T seconds, and entering a step 9;

step 10: judging whether a preparation track of the station track has no OHT trolley or not, if so, loosening the limiting block, and moving the station track to an idle state; if not, waiting for t seconds, and entering the step 10;

step 11: judging whether the OHT vehicle completes the task, if so, entering step 13, and if not, entering step 6;

step 12: and updating the system state and entering the step 1.

Further, the task allocation trigger conditions include periodic triggers and event triggers.

Further, the system information includes task information, OHT vehicle information, and path information.

Further, the task scheduling method comprises a task scheduling method based on heuristic rules and a task scheduling method based on an intelligent optimization algorithm.

Further, the path planning method comprises the following steps:

step 3.1: according to Dijkstra algorithm, completing path planning of the task on the system path, and recording a path sequence of the task shortest path in a task shortest path table, namely a path number sequence of the shortest path;

step 3.2: and sequentially judging whether a path in the path sequence of the task shortest path has a track change point or not according to the path sequence of the task shortest path, if so, marking the path in the task shortest path table, and recording the position of the track change point in the path, otherwise, not marking the path in the task shortest path table.

Further, the task shortest path table includes information of a start point of the task, an end point of the task, a name of the OHT vehicle to be transported, a path sequence of a shortest path of the task, a path flag of the path including the orbital transfer point, a position of the orbital transfer point in the path, and a time when the OHT vehicle passes each orbital transfer point.

Further, the track changing point is a central point of the variable track.

Further, the variable track is a track capable of forming a passage with other different tracks by switching directions through a turntable in the system.

Further, the travel time prediction method comprises the following steps:

step 4.1: predicting the travel time of the OHT vehicle to each orbital transfer point under the condition of no traffic jam according to the shortest path of the task and the position of the orbital transfer point;

step 4.2: predicting the traffic flow of each path in the path sequence of the task shortest path, and defining the traffic congestion level of the path;

step 4.3: predicting the traffic jam time of the OHT vehicle passing through each path according to the traffic jam level of each path;

step 4.4: and (3) integrating the predicted travel time of the OHT vehicle reaching each orbital transfer point under the condition of no traffic jam and the traffic jam time passing through each path, and predicting the time of the OHT vehicle passing through each orbital transfer point.

Further, the traffic congestion levels comprise four levels of 'smooth', 'light congestion', 'medium congestion' and 'heavy congestion', the larger the traffic flow value of the path is, the more serious the traffic congestion condition is, the higher the traffic congestion level of the path is, and the longer the traffic congestion time is.

Further, the passing sequence optimization method is used for sequencing the passing sequence of the OHT vehicles at each orbital transfer point by adopting a first-come-first-pass rule according to the predicted time for the OHT vehicles to pass each orbital transfer point.

Further, the orbital transfer selects a proper orbit for the variable orbit to connect according to the task shortest path planned by the OHT trolley, namely selecting a proper inlet and a proper outlet.

Furthermore, the station track is a movable track arranged beside the station and comprises a working track, a preparation track and a limiting block, and the station track can be switched into an idle state and a working state by sliding on a slide way.

Further, orbital idle state of station for orbital work track of station directly links to each other with other tracks of system and forms the passageway, the stopper loosens, prepares the track and is in idle state.

Furthermore, the working state of the station track is that the working track of the station track moves to the station, the three points of the working point of the working track, the central point of the station and the central point of the OHT trolley coincide, the limiting block works, the preparation track is connected with other tracks of the system to form a passage, and the OHT trolley is guaranteed not to be blocked when the OHT trolley is loaded or unloaded.

Compared with the prior art, the invention has at least the following beneficial effects or advantages:

the invention provides an anti-blocking scheduling strategy for an OHT (open high-altitude transport) system based on a variable track, which solves the problems of low resource utilization rate and work site blockage based on a fixed track in the prior art by adopting the variable track and a station track and considering the problem of scheduling of the OHT system based on the variable track in the system.

Drawings

The invention will be described in further detail below with reference to the accompanying drawings:

FIG. 1 is a flow chart of the jam-resistant dispatch strategy for a variable-track based OHT handling system of the present invention;

FIG. 2 is a schematic view of a variable track of the present invention;

fig. 3(a) and (b) are schematic diagrams of the idle state and the working state of the station track of the invention respectively.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Since the OHT scheduling system is complex, the following assumptions are made for the transport system:

1. the running speed of the OHT trolley is a constant, and the influence of acceleration and deceleration is ignored;

2. once the OHT starts to carry and convey, the path cannot be automatically replaced, and the task unloading sequence cannot be adjusted;

3. each OHT trolley can only carry out loading, unloading or waiting operation at a station point, no parking is allowed at non-station points, and if a plurality of OHT trolleys need to be parked at the same station point, queuing and waiting are needed. (ii) a

4. In order to avoid collision or congestion, each node only allows one OHT vehicle to pass or stop at the same time

5. The system path network is a one-way single lane and does not support overtaking or parallel;

6. the unloading time of the AGV with the large loading capacity is fixed, and if a plurality of AGVs are at the same loading and unloading point, queuing is needed.

7. And a path re-planning method is not adopted in the traffic control process to avoid the motion conflict of the OHT system.

Fig. 1 is a flowchart of an anti-jamming scheduling policy for an OHT handling system based on a variable track according to the present invention, wherein the anti-jamming scheduling policy for the OHT handling system based on the variable track specifically includes the following steps:

step 1: and when the OHT carrying system meets the task allocation triggering condition, acquiring system information.

When the OHT carrying system calls the anti-blocking dispatching strategy based on the OHT carrying system with the track changing, whether the task allocation triggering condition is met or not is firstly checked. And when the task allocation triggering condition is met, acquiring task information in the system, wherein the task information comprises task information, OHT vehicle information and path information. The task information includes a conveyance start point, a conveyance end point, a task generation time, a task end time, and the like of the task, the OHT vehicle information includes vehicle states, speeds, and the like, and the route information includes information such as the number, position, and traffic flow of the tracks.

In the embodiment of the invention, the task allocation triggering condition comprises periodic triggering and event triggering, wherein the periodic triggering is periodic triggering at a fixed time interval, the event triggering is task allocation triggering when a set event occurs, and the set event comprises that the number of tasks in a task set to be allocated reaches a certain numerical value.

It should be noted that the task allocation triggering condition may also be only a periodic trigger or an event trigger, and the setting event in the event trigger may not be the setting event in the embodiment of the present invention, for example, the setting event may also be a new task generated in the task set to be allocated.

Step 2: and determining an OHT vehicle task allocation scheme according to the task scheduling method.

And when the OHT carrying system meets the task allocation triggering condition, judging an idle trolley set and a task set to be allocated in the OHT carrying system. The idle trolley set is an idle OHT trolley which completes the last task in the system and is not allocated with a new task; the task set to be allocated is a set of all generated tasks in the system and not allocated to the OHT vehicle for carrying. If the idle trolley set and the task set to be allocated are not empty, allocating the tasks in the allocable task set to the idle trolley according to a task scheduling method, and determining an OHT trolley task allocation scheme; if the idle trolley set or the task set to be distributed is empty, no idle trolley carries out carrying tasks or does not need to distribute the tasks to be carried of the trolley, and therefore task scheduling is not needed, and the system waits for the next time to meet the task distribution triggering condition.

In the embodiment of the invention, the task scheduling method comprises a task scheduling method based on a heuristic rule and a task scheduling method based on an intelligent optimization algorithm. The heuristic rules include but are not limited to task priority, shortest distance and minimum time, and the intelligent optimization algorithm includes but is not limited to genetic algorithm, ant colony algorithm and particle swarm algorithm.

And step 3: and determining the shortest path and the track transfer point in the path according to the path planning method.

When the task allocation is completed, an optimal path from the start point to the end point of the transportation needs to be found. Because the track in the system contains a variable track, the shortest path and the track change point in the path need to be determined according to a path planning method.

As shown in fig. 2, in the embodiment of the present invention, the variable track is a track that can realize a path with other different tracks by switching the direction of the turntable in the system. The central point of the variable track is a track changing point.

The path planning method comprises the following steps:

after a certain task is allocated with a trolley, completing path planning of the task on a system path according to a Dijkstra algorithm, and recording a path sequence of the shortest task path, namely a path number sequence of the shortest path, in a task shortest path table;

in the embodiment of the invention, the task shortest path table comprises information of a starting point of a task, an end point of the task, a name of a transported OHT (overhead hoist transport) vehicle, a path sequence of a task shortest path, a path mark of a path containing a track transfer point, a position of the track transfer point in the path and time of the OHT vehicle passing each track transfer point.

Because the planned path sequence of the shortest task path contains the variable track, in order to conveniently predict the time when the OHT vehicle reaches the orbital transfer point of the variable track, the orbital transfer point information in the path sequence of the shortest task path needs to be recorded. That is, whether a path in the path sequence of the shortest task path has a track change point is sequentially determined according to the path sequence of the shortest task path, if the track change point exists, the path is marked in the shortest task path table, and the position of the track change point in the path is recorded, otherwise, the path is not marked in the shortest task path table.

And 4, step 4: the time for the OHT vehicle to pass each of the orbital transfer points is predicted according to the travel time prediction method.

After the system determines the shortest path and the orbital transfer points in the path according to a path planning method, the time of the OHT vehicle passing through each orbital transfer point is predicted according to a travel time prediction method.

The travel time prediction method comprises the following steps:

according to the shortest path of the task and the position of the orbital transfer point, the distance from the task starting point to the position of the orbital transfer point can be obtained, and according to the speed of the OHT trolley, the travel time of the OHT trolley reaching each orbital transfer point under the condition of no traffic jam can be predicted.

since the OHT vehicle may encounter traffic congestion during the task, so that the travel time of the OHT vehicle to each of the transition points is increased, it is necessary to predict the traffic flow of each path in the sequence of paths of the shortest path of the task, define the traffic congestion level of the path, and calculate the traffic congestion time.

In the embodiment of the invention, the traffic congestion levels comprise four levels of 'smooth', 'light congestion', 'medium congestion' and 'severe congestion', the larger the traffic flow value of the path is, the more severe the traffic congestion condition is, the higher the traffic congestion level of the path is, and the longer the traffic congestion time is.

Step 4.3: and predicting the traffic jam time of the OHT vehicle passing through each path according to the traffic jam level of each path.

And predicting the traffic jam time of the OHT vehicle passing through each path according to the traffic jam level of each path in the shortest path of the task. When the traffic jam level is smooth, no traffic jam exists, namely the traffic jam time is 0; when the traffic congestion level is 'light congestion', slight traffic congestion exists, and the traffic congestion time is less, and when the traffic congestion level is 'moderate congestion' and 'severe congestion', the traffic congestion is more serious, and the traffic congestion time is more. The specific value of the traffic congestion time is related to the length of each route and the number of OHT vehicles on the route.

And (3) integrating the predicted travel time of the OHT vehicle reaching each orbital transfer point under the condition of no traffic jam and the traffic jam time passing through each path, and predicting the time of the OHT vehicle passing through each orbital transfer point. That is, the predicted travel time of the OHT vehicle to each of the orbital transfer points without traffic congestion and the traffic congestion time through each of the routes are added to obtain the time at which the OHT vehicle passes each of the orbital transfer points.

And 5: the order of passage of the OHT vehicles for each orbital transfer point is sorted according to a passage order optimization method.

For a variable track in the system, a plurality of OHT vehicles may pass through each time slot, so the passing sequence of the OHT vehicles at each track transfer point needs to be sequenced according to a passing sequence optimization method, and the variable track can be transferred in advance according to the passing sequence while collision is avoided, so that the system efficiency is improved.

In the embodiment of the invention, the passing sequence of the OHT vehicles at each orbital transfer point is sequenced by a sequence optimization method by adopting a first-come-first-pass rule according to the predicted time for the OHT vehicles to pass each orbital transfer point.

It should be noted that the order of OHT vehicle passage can be optimized according to the emergency situation of the mission, including but not limited to the first-come first-pass rule.

Step 6: the OHT car executes task according to the planned path, the variable track changes track in advance according to the passing sequence and car state, and waits for the OHT car to pass.

And the trolley starts to execute the task according to a task allocation scheme and a task shortest path scheme obtained by the task scheduling method and the path planning method. The variable track in the system is changed in advance according to the passing sequence and the state of the trolley, and the OHT trolley is waited to pass; the vehicle state refers to whether the vehicle normally executes the tasks according to the sequence of the shortest task paths, and if the OHT vehicle fails in executing the tasks or cannot pass through the track change point according to the originally predicted time point due to other reasons, the variable track needs to reorder the passing sequence of the OHT vehicle.

In the embodiment of the invention, the orbital transfer is realized by selecting a proper track for connection according to the shortest task path planned by the OHT (OHT) trolley, namely selecting a proper inlet and a proper outlet.

and judging whether the OHT trolley reaches the target work site, if so, starting loading or unloading, entering a step 8, otherwise, continuing to execute the task according to the shortest path scheme, and entering a step 6.

And 8: the trolley waits for loading on a target work station, the work station track moves to a working state at the moment, the limiting block works, and the OHT trolley starts to load or unload;

when the OHT trolley reaches the target work site, the station track moves to a working state, the limiting block works, and the OHT trolley starts to load or unload.

As shown in fig. 3, in the embodiment of the present invention, the rail where the work site is located is a working rail, the station rail is a movable rail disposed on one side of the working rail, and includes a working rail, a preparation rail and a limiting block, wherein the limiting block is used for fixing the station rail to prevent the station rail from sliding during working, the preparation rail is parallel to the working rail and connected to the working rail through the station rail, and the station rail is disposed on the slide way. The station rail is switched between the idle state and the working state through the sliding of the station rail on the slide way. The idle state of the station track is that the working track of the station track is directly connected with other tracks of the system to form a passage, at the moment, the limiting block is loosened, and the preparation track is not communicated with other tracks and is in the idle state. The working state of the station track is that the working track of the station track moves to the station, at the moment, the three points of the work station point of the working track, the central point of the station and the central point of the OHT trolley coincide, the limiting block works to fix the position of the working track, the preparation track is connected with other tracks of the system to form a passage, and the OHT trolley is guaranteed not to block other OHT trolleys when being loaded or unloaded.

And step 9: and judging whether the OHT trolley finishes loading or unloading, if so, entering a step 10, otherwise, waiting for T seconds, and entering a step 9.

And if the OHT vehicle finishes loading or unloading, the step 10 is carried out, otherwise, the OHT vehicle waits for T seconds, and the OHT vehicle finishes loading or unloading again.

Step 10: and judging whether the prepared track of the station track has no OHT trolley, if so, entering a step 11, otherwise, waiting for t seconds, and entering a step 10.

When the OHT vehicle finishes loading or unloading, the station track can not slide immediately and is converted into an idle state from a working state, because although the OHT vehicle finishes loading or unloading, the situation that no OHT vehicle passes through the preparation track of the station track cannot be guaranteed, if the station track slides immediately at the moment, the working state is converted into the idle state, the OHT vehicle on the preparation track can be remained on the preparation track until the OHT vehicle on the preparation track can leave until the next time the station track is converted into the working state from the idle state, and the task on the OHT vehicle is delayed. Therefore, whether the prepared track of the station track has no OHT vehicle needs to be judged, if yes, the step 11 is carried out, if not, the t second time is waited, and whether the prepared track of the station track has no OHT vehicle is carried out again.

Step 11: the limiting blocks are loosened, and the station rail moves to an idle state.

When the preparation track of the station track is free of the OHT trolley, the limiting block of the station track is loosened, the station track starts to slide, and the working state is converted into the idle state.

Step 12: judging whether the OHT vehicle completes the task, if so, entering step 13, and if not, entering step 6;

and judging whether the OHT vehicle completes the distributed task, if so, entering step 13, otherwise, continuing to execute the task, and entering step 6.

Step 13: and updating the system state and entering the step 1.

And when the OHT vehicle finishes the distributed tasks, updating the states of the system tasks, the track and the vehicle, entering the step 1 and waiting for the next task scheduling.

The foregoing is only a preferred embodiment of this invention and it should be noted that modifications can be made by those skilled in the art without departing from the principle of the invention and these modifications should also be considered as the protection scope of the invention.

Claims

1. An anti-blocking scheduling strategy of an OHT carrying system based on a variable track is characterized by comprising the following steps:

step 2: determining an OHT vehicle task allocation scheme by combining task information in system information according to a task scheduling method;

and step 3: determining a shortest path from a carrying starting point to a target work site point and a track transfer point in the path according to a path planning method;

and 4, step 4: predicting the time of the OHT vehicle passing through each orbital transfer point by combining the shortest path and the orbital transfer point according to a travel time prediction method;

and 5: for each orbital transfer point, sequencing the passing sequence of the OHT vehicles according to a passing sequence optimization method based on the predicted time of the OHT vehicles passing the orbital transfer point;

step 6: the OHT trolley executes the tasks according to the shortest path planned in the step 3, and the OHT system continuously monitors the trolley state, namely whether the trolley executes the tasks according to the shortest path of the tasks, if faults or other interruption reasons occur in the execution, the step 4 is returned, the time of the OHT trolley passing each orbital transfer point is predicted again, otherwise, the variable track is enabled to be orbital transferred in advance according to the trolley state and the passing sequence of each orbital transfer point obtained in the step 5, and the OHT trolley waits for the OHT trolley to pass;

and 7: the OHT system judges whether the OHT vehicle reaches the target work site, if yes, the step 8 is carried out, otherwise, the step 6 is carried out;

and 8: the track where the target work site is located is a working track, a preparation track parallel to the working track is arranged on one side of the working track, the working track moves to a work station when the trolley reaches the target work site, the corresponding preparation track is connected into the original track, and at the moment, the OHT trolley starts to load or unload;

and step 9: judging whether the OHT trolley finishes loading or unloading, if so, entering a step 10, and otherwise, waiting for T seconds to judge again;

step 10: judging whether the preparation track has no OHT vehicle, if so, moving the working track to the original track, and otherwise, waiting for t seconds for re-judgment;

step 11: and (4) judging whether the OHT vehicle completes the task, if so, updating the system state, returning to the step 1, and otherwise, returning to the step 6.

2. The variable-track-based OHT handling system anti-jam scheduling strategy of claim 1, wherein the task scheduling methods comprise heuristic rule based task scheduling methods and intelligent optimization algorithm based task scheduling methods.

3. An OHT handling system jam-prevention scheduling strategy according to any of claims 1-2 where the point of change is the centre point of a variable track, the variable track is located in a turntable, the turntable is placed at the junction of different tracks in the system, and the variable track is connected to other different tracks by turning the turntable to form a pathway.

4. A variable-trajectory OHT handling system jam-resistant scheduling strategy according to claim 3 wherein said path planning method comprises the steps of:

step 3.1: according to Dijkstra algorithm, completing path planning of the task on the system path, and recording a path sequence of the shortest path on a task shortest path table;

step 3.2: and sequentially judging whether a path in the path sequence of the shortest task path has a track change point or not according to the path sequence of the shortest task path, marking the path on the shortest task path table when the track change point exists, and recording the position of the track change point in the path.

5. The path planning method according to claim 4, wherein the task shortest path table includes information of start point of task, end point of task, name of OHT vehicle to be transported, path sequence of task shortest path, path flag of path containing orbital transfer point, position of orbital transfer point in the path, and time of OHT vehicle passing each orbital transfer point.

6. A variable-track based OHT handling system jam-resistant scheduling strategy according to claim 1 or 5, wherein said time-of-flight prediction method comprises the steps of:

7. The travel time prediction method according to claim 6, wherein the traffic congestion levels include four levels of "clear", "light congestion", "medium congestion" and "heavy congestion", and the larger the value of the path traffic flow is, the more serious the traffic congestion condition is, the higher the level of the path traffic congestion is, and the longer the traffic congestion time is.

8. The variable-trajectory-based OHT handling system anti-jam scheduling strategy of claim 7, wherein the passing sequence optimization method sequences the order of passage of the OHT vehicles at each orbital transfer point using a first-come-first-pass rule based on the predicted time for the OHT vehicle to pass each orbital transfer point.

9. An OHT handling system jam-prevention scheduling strategy based on track change as claimed in claim 1 or 8 wherein the track where the work station is located is a working track, and a movable work station track and a corresponding preparation track are provided on one side of the working track, wherein the preparation track is parallel to the working track and connected with the working track through the work station track, and the work station track is provided on a slide way;

the preparation track has a working state and an idle state, the working state is that the station track slides on the slideway to coincide with the working site of the working track, the central point of the station and the central point of the OHT trolley, the working track is not communicated with other tracks, at the moment, the OHT trolley carries out loading and unloading work, the preparation track is connected with other tracks of the system to form a passage, so that the OHT trolley does not block other OHT trolleys when carrying out loading and unloading work;

the idle state is that the working track is directly connected with other tracks of the system to form a passage, and the corresponding preparation track is not communicated with other tracks and is in the idle state.

10. The work station track as claimed in claim 9, wherein the OHT vehicle in step 8 is loaded or unloaded while the preparation track is in operation; in step 10, moving the working track to the original track is that the preparation track is in an idle state.