Research On Path Planning For Automated Pavement Crack Sealing

In recent years,road construction has been consummated in our country.However,the new built pavement has to be affected by vehicle load and environment,so that various diseases gradually appear on the pavement.Among these diseases,crack is difficult to avoid because of the influences of the inherent properties of road materials,temperature and construction factors.If crack is not treated,road surface water will enter the pavement through the crack,which can cause further damage to road materials and structure.Therefore,repairing crack is usually considered in road maintenance.The methods to repair crack mainly include sealing,sticking and digging.Sealing is most commonly used.Traditional sealing project requires workers to operate with hand-held machine.These heavy tasks will consume a lot of manpower,and the construction process will cause safety risks.With the continuous development of automated and intelligent technology,many machines emerged at the right moment in order to improve the efficiency of road maintenance,which can automatically seal crack.These machines can automatically collect road images,identify the shape and position of cracks,and then treat cracks one by one.For this purpose,the machine needs to plan a path of traversing all kinds of cracks.So,it is necessary to design the path planning algorithms with high computational efficiency and strong applicability.This paper focuses on the path planning problem for sealing many kinds of types of cracks based on automated pavement crack sealing machine.Firstly,necessary information for path planning was extracted according to the obtained and processed binary images of pavement and crack.And the process of walking along the crack was implemented in software.Secondly,the crack images were classified,the path planning problem models for all kinds of images were established respectively,and the corresponding algorithms were designed.The specific work is as follows:（1）The suitable types of cracks for sealing were analyzed according to the shape,damage degree,cause and the repairing process of crack in asphalt pavement.And the work tasks and functions of automated crack sealing machine were analyzed according to the artificial process.（2）The skeleton of crack was extract from binary images of pavement and crack based on the requirements of the location of crack for path planning.The location coordinates of endpoints and intersection points of crack were identified.The coordinates of all pixels of each crack were searched and the lengths of cracks were calculated.Besides,the dynamic process of traversing all the pixels of each crack was designed.（3）According to the characteristics of the images,the crack with single morphology and compound morphology are divided into three types: horizontal and vertical crack,connected crack as well as general unconnected crack.The first two types are single morphology,and the last one is compound morphology.The path planning problem of horizontal and vertical crack was simplified to Travelling Salesman Problem.The path planning problem of connected crack was simplified to Chinese Postman Problem.The path planning problem of general unconnected crack was simplified to Rural Postman Problem.（4）The problem of horizontal and vertical crack was solved by simplifying the edge distance to the point distance and using the circulation of ant colony algorithm to solve this problem.The problem of connected crack was solved by changing the images to the half Euler graph based on the idea of minimum weight perfect matching and using the Euler path as the final result.The problem of general unconnected crack was solved by regarding horizontal and vertical crack as well as connected crack as the smallest unit so that the final path was the integration of the path between the smallest units and within the smallest units.（5）The feasibility of the three algorithms was verified by examples,and the advantages and disadvantages of all the algorithms were analyzed respectively based on the calculation time and the total path length.Theoretically,it is proved that the simplified problem of horizontal and vertical crack as well as general unconnected crack belongs to the Non-deterministic Polynomial Problem,which cannot be solved accurately in polynomial time.However,the goal of traversing all cracks and obtaining the good feasible solutions was realized by the algorithms in this paper.And it is proved that the shortest path of traversing all of the connected crack can be obtained without considering the connection between the start and end points and cracks.