A method for multi-robot conflict-free path planning based on dynamic interference area constraint

Abstract

The present invention proposes a method for multi-robot conflict-free path planning based on dynamic interference area constraint. Based on the pre-planned trajectories of the robots, the overlapping areas of each joint of the robots in space are determined to realize the extraction of the minimum interference area of the robots. On the basis of determining the dynamic priorities of multiple robots, through the segmentation of the envelope space of the motion trajectories of the high-priority robots, the obstacle treatment of the space trajectories of the robots is realized. At the same time, the RRT algorithm is used to realize the path replanning of the robots with low priorities. For the scenario where the replanning fails, the present invention further determines the waiting time of the robots with low priorities to stop outside the interference area based on the strategy of stopping and waiting, and finally eliminates the conflicts between the robots. The present invention combines the coordination strategy of robot dynamic replanning and waiting outside the interference area to realize the coordinated planning of multi-robot trajectories in a high-dimensional complex space, thereby solving the "deadlock" phenomenon between multiple robots, improving the efficiency of coordinated planning, and reducing the motion time of the robots.

Description

Technical Field

[0001] The present invention relates to the field of motion planning of process robots, and particularly to a method for conflict-free path planning of multiple robots based on dynamic interference area constraints. Background Art

[0002] In a flexible manufacturing workshop, multi-robot path planning is the key to ensuring the completion of system tasks and improving operating efficiency. Based on the workshop environment, planning a conflict-free path for multiple robots can effectively reduce the time for robots to execute tasks and improve the overall operating efficiency of the robot system. Currently, Erdmann et al. proposed to first search for a collision-free path for the first robot in the entire configuration space. Then, when the second robot searches for a path, it will regard the position of the first robot in the time space as an obstacle for searching. In this way, the collision-free paths of the robots are determined in turn. However, at present, most studies often assume that the robot priorities are fixed in the process of solving the multi-robot conflict problem, which may cause low-priority robots to wait for a long time, resulting in space congestion. To address the above problems, this paper proposes a multi-robot coordination planning method based on interference area constraints to reduce the robot downtime waiting time and lower the search complexity and search time. Summary of the Invention

[0003] The purpose of the present invention is to propose a multi-robot coordination planning method based on interference area constraints. This method is applicable to various industrial sites. At the same time, in view of the deficiencies of the prior art, the trajectory planning is improved from two directions: time control and space resources. The improved method reduces the solution complexity and planning time.

[0004] To achieve the above object, the present invention proposes a method for conflict-free path planning of multiple robots based on dynamic interference area constraints, including the following steps:

[0005] S101: Optimize the order of the given task set for each robot based on the solution idea of the traveling salesman problem;

[0006] S102: Based on the RRT algorithm, achieve conflict-free path planning for each robot and determine the robot motion time on the premise of ignoring the conflicts between robots;

[0007] S103: Determine the motion envelope of the robots according to the robot trajectories planned in S101 and S102, further determine the overlapping area between the robots and set it as the interference area;

[0008] S104: Set dynamic priorities for the robots in conflict in the interference area based on time constraints, and perform envelope processing on the robot trajectories based on the equal-interval minimum bounding box radius method;

[0009] S105: For the newly generated robot environment, plan for the robots with high priority based on the RRT algorithm. If a feasible trajectory cannot be planned, go to S106;

[0010] S106: In order to eliminate the phenomenon that the replanning strategy in S105 cannot eliminate the conflicts between robots, determine the waiting time for the robots with low priority to stop outside the interference area based on the strategy of halting and waiting. Repeat S104 - S106 until all conflicts between robots are eliminated.

[0011] Further, S103 determines the coordinate values of each joint of the robot according to the robot paths planned in S101 and S102, calculates the overlapping area of the two robots in space, that is, the interference area of the two robots; the minimum values of robot R1 on each axis are (X r1 , Y r1 , Z r1 ), and the maximum values of robot R2 on each axis are (X r2 , Y r2 , Z r2 ). If X r2 < X r1 , Y r2 < Y r1 , Z r2 < Z r1 ; then the interference area of robots R1 and R2 is expressed as

[0012] Further, in S104, the robot trajectory is made into an obstacle using a moving bounding box. Based on the interference area divided in S103, determine the motion trajectory of the robots located in the interference space at this time; at the same time, based on the dynamic priority strategy, sort the priorities of the robots in the interference area using the rule that the longer the robot moves, the higher its priority; envelope the trajectory of the robot with high priority; in order to form a complete obstacle area, perform envelope processing on the robot trajectory based on an equidistant method; envelope the robot motion trajectory based on the minimum bounding box radius to ensure the completeness of the obstacle.

[0013] Further, based on the single - robot trajectory planning result in S105, determine whether there is a section of the trajectory result in the interference area. If adjacent robots are both in the conflict space, use dynamic collision detection to determine whether the adjacent robots conflict; if there is a conflict, based on the dynamic priority, make one of the robot trajectories into an obstacle and re - plan the local trajectory of the other robot.

[0014] Further, in the case of a conflict, the trajectory planning steps for multiple robots are as follows:

[0015] 1) Determine whether a conflict occurs between robots based on a dynamic collision detection algorithm. If a conflict occurs, execute step 2); otherwise, output the allocated space for each robot.

[0016] 2) Determine the characteristics of adjacent robots in the intersection space and the working time of the robots.

[0017] 3) Compare the working times of adjacent robots, and obstacle the space occupied by the robot with the longer working time. On the premise of meeting the process specifications of the short-time robot, re-plan the trajectory of the other robot in the intersection space based on the RRT algorithm.

[0018] 4) Re-determine the space occupied by multiple robots and execute step 1).

[0019] Furthermore, for the phenomenon that the conflict between robots cannot be eliminated by the result of the re-planning in S105, determine the time t0 when the robot with a higher dynamic priority enters the interference area, and at the same time determine the time t1 when the robot with a higher dynamic priority passes through the interference area. Finally, determine the waiting time Δt = t1 - t0 for the robot with a lower priority to stop outside the interference area; repeat steps S104 - S106, and combine the above-mentioned obstacle-based robot trajectory re-planning strategy and dynamic waiting outside the interference area to eliminate conflicts between all robots.

[0020] Compared with the prior art, the advantages of the present invention are as follows: Based on the interference area constraint, integrating the two major strategies of space segmentation and dynamic priority, the multi-robot is coordinately planned. Specifically, it includes steps such as the determination of the interference area, the segmentation of the robot working space, the determination of the robot dynamic priority, and the coordination strategy between robots, realizing the multi-robot trajectory coordination planning in a high-dimensional complex space, improving the coordination efficiency, and reducing the robot movement time. The present invention determines the interference area between robots by using the extreme value of the single-robot motion joint in space; realizes the obstacle of the robot trajectory by using the minimum bounding box radius, and uses the RRT to realize the local path planning of the robot. For the conflict between robots where the re-planning fails, use the interference area to determine the waiting time for the robot with a lower dynamic priority to stop, so as to eliminate the conflict between robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flowchart of multi-robot coordinated planning based on interference area constraint in an embodiment of the present invention;

[0022] Figure 2 It is a schematic diagram of the interference space in an embodiment of the present invention;

[0023] Figure 3 It is a schematic diagram of the obstacle of the motion trajectory of a certain joint of the robot in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0025] As Figure 1 shown, the present invention provides a method for multi-robot conflict-free path planning based on dynamic interference region constraint, including the following steps:

[0026] S101: Optimize the order of the given task set for each robot based on the solution idea of the traveling salesman problem;

[0027] S102: On the premise of ignoring the conflicts between robots, implement conflict-free path planning for each robot based on the RRT algorithm and determine the robot movement time;

[0028] S103: Determine the coordinate values of each joint of the robot according to the robot trajectories planned in S101 and S102, and then calculate the overlapping area of the two robots in space, that is, the interference region of the two robots. For example, the minimum values of the R1 robot on each axis are (X r1 , Y r1 , Z r1 ), and the maximum values of the R2 robot on each axis are (X r2 , Y r2 , Z r2 ). If X r2 < X r1 , Y r2 < Y r1 , Z r2 < Z r1 . Then the interference region of the R1 and R2 robots can be expressed as

[0029] S104: As Figure 2 shown, based on the interference region divided in S103, determine the movement trajectory of the robot located in the interference space at this time. At the same time, based on the dynamic priority strategy, use the rule that the longer the robot movement time, the higher the robot priority to sort the priorities of the robots in the interference region. At the same time, envelope the trajectory of the robot with a higher priority. In order to form a complete obstacle region, the present invention performs envelope processing on the robot movement trajectory based on the minimum bounding box radius to ensure the completeness of the obstacle region; further, based on equidistant (bounding box radius) screening, delete the overlapping obstacle regions to improve the robot planning efficiency.

[0030] S105: For the newly generated robot environment, plan the robots with lower priority based on the RRT algorithm. Based on the results of trajectory planning, determine whether there is a section of the trajectory result in the interference area. If adjacent robots are both in the conflict space, further use dynamic collision detection to determine whether the adjacent robots conflict. If a conflict occurs, based on the dynamic priority, obstacle the trajectory of one of the robots and re-plan the local trajectory of the other robot. As Figure 3 shown, the steps are as follows:

[0031] (1) Determine whether there is a conflict between robots based on the dynamic collision detection algorithm. If a conflict occurs, execute step (2); otherwise, output the allocated space of each robot.

[0032] (2) Determine the characteristics of adjacent robots in the intersection space and the working time of the robots.

[0033] (3) Compare the working times of adjacent robots, and obstacle the space occupied by the robot with the longer working time. On the premise of meeting the process specifications of the robot with the shorter working time, re-plan the trajectory of the other robot in the intersection space based on the RRT algorithm.

[0034] (4) Re-determine the space occupied by multiple robots and execute step (1); if a feasible trajectory cannot be planned, execute S106.

[0035] S106: In order to eliminate the phenomenon that the replanning strategy in S105 cannot eliminate the conflict between robots, the present invention further determines the waiting time outside the interference area for the robots with lower priority based on the strategy of stopping and waiting. First, determine the time t0 when the robot with higher dynamic priority enters the interference area; secondly, determine the time t1 when the robot with higher dynamic priority passes through the interference area. Finally, determine the waiting time Δt outside the interference area for the robot with lower priority as Δt = t1 - t0; repeat the steps of S104 - S106, combine the obstacle of the robot trajectory, the robot trajectory replanning strategy and the dynamic waiting to eliminate the conflict between robots.

[0036] Aiming at the problem of multi-robot coordinated planning, the present invention proposes a multi-robot coordinated planning method that integrates robot replanning and waiting outside the interference area. Based on the robot trajectories, the present invention determines the overlapping areas of each joint of the robot in space, realizing the rapid and effective determination of the minimum interference area of the robot; envelopes the motion trajectories of the robots with higher priorities based on the radius of the minimum bounding box, realizing the rapid obstacle conversion of the robot trajectories, and realizes the path replanning of the robots with lower priorities through the RRT algorithm. Finally, for the scenario where replanning fails, the waiting time of the robots with lower priorities waiting outside the interference area is further determined based on the strategy of stopping and waiting, thus realizing the coordinated planning of multi-robot trajectories in a high-dimensional complex space, solving the "deadlock" phenomenon among multi-robots, improving the efficiency of coordinated planning, and reducing the robot motion time.

[0037] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed by the present invention, which are all within the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A method for multi-robot conflict-free path planning based on dynamic interference area constraint, characterized in that It includes the following steps: S101: Optimize the order of the task sets given to each robot based on the solution idea of the Traveling Salesman Problem; S102: On the premise of ignoring the conflicts between robots, implement conflict-free path planning for each robot based on the RRT algorithm and determine the robot movement time; S103: Determine the motion envelope of the robots according to the robot trajectories planned in S101 and S102, further determine the overlapping area between the robots and set it as the interference area; S104: Set dynamic priorities for the robots in conflict in the interference area based on time constraints, and perform envelope processing on the robot trajectories based on the method of equal-interval minimum bounding box radius; S105: For the newly generated robot environment, plan for the robots with high priorities based on the RRT algorithm. If a feasible trajectory cannot be planned, go to S106; S106: In order to eliminate the phenomenon that the replanning strategy in S105 cannot eliminate the conflicts between robots, determine the waiting time outside the interference area for the robots with low priorities based on the strategy of halting and waiting, and repeat S104 - S106 until all conflicts between robots are eliminated.

2. The method for multi-robot conflict-free path planning based on dynamic interference area constraint according to claim 1, wherein S103 determines the coordinate values of each joint of the robot according to the robot path planned in S101 and S102, and calculates the overlapping area of the two robots in space, that is, the interference area of the two robots; the minimum value of the R1 robot on each axis is , and the maximum value of the R2 robot on each axis is ; if , , ; then the interference area of the R1 and R2 robots is expressed as .

3. The method for multi-robot conflict-free path planning based on dynamic interference region constraint according to claim 2, wherein In S104, use a moving bounding box to make the robot trajectories into obstacles. Based on the interference area divided in S103, determine the motion trajectories of the robots located in the interference space at this time; meanwhile, based on the dynamic priority strategy, sort the priorities of the robots in the interference area according to the rule that the longer the robot movement time, the higher the robot priority; envelope the trajectories of the robots with high priorities; in order to form a complete obstacle area, perform envelope processing on the robot trajectories based on an equal-interval method; envelope the robot motion trajectories based on the minimum bounding box radius to ensure the completeness of the obstacles.

4. The method for multi-robot conflict-free path planning based on dynamic interference area constraint according to claim 3, wherein Based on the single-robot trajectory planning results in S105, judge whether there is a certain trajectory result in the interference area. If adjacent robots are both in the conflict space, use dynamic collision detection to determine whether the adjacent robots conflict; If a conflict occurs, make one of the robot trajectories into an obstacle based on the dynamic priority and re-plan the local trajectory of the other robot.

5. The method for multi-robot conflict-free path planning based on dynamic interference area constraint according to claim 4, wherein In the case of a conflict, the multi-robot trajectory planning steps are as follows: 1) Determine whether there is a conflict between the robots based on the dynamic collision detection algorithm. If a conflict occurs, execute step 2), otherwise output the allocated space of each robot; 2) Determine the characteristics of the adjacent robots in the intersection space and the working time of the robots; 3) Compare the working times of the adjacent robots, make the space occupied by the robot with the longer working time into an obstacle, and re-plan the trajectory of the other robot in the intersection space based on the RRT algorithm on the premise of meeting the process specifications of the short-time robot; 4) Re-determine the space occupied by the multi-robots and execute step 1).

6. The method for multi-robot conflict-free path planning based on dynamic interference region constraint according to claim 4, wherein, For the phenomenon that the replanning result in S105 cannot eliminate the conflicts between robots, determine the time t0 when the robot with a high dynamic priority enters the interference area. At the same time, determine the time t1 when the robot with a high dynamic priority passes through the interference area. Finally, determine the waiting time Δt = t1 - t0 for the robot with a low priority to stop outside the interference area. Repeat steps S104 - S106 to eliminate all conflicts between robots based on the above obstacle-based robot trajectory replanning strategy combined with dynamic waiting outside the interference area.

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