Path tracking control of autonomous agricultural mobile robots

In a tractor automatic navigation system, path planning plays a significant role in improving operation efficiency. This study aims to create a suboptimal reference course for headland turning of a robot tractor and design a path-tracking controller to guide the robot tractor along the reference course. A time-minimum suboptimal control method was used to generate the reference turning course based on the mechanical parameters of the test tractor. A path-tracking controller consisting of both feedforward and feedback component elements was also proposed. The feedforward component was directly determined by the desired steering angle of the current navigation point on the reference course, whereas the feedback component was derived from the designed optimal controller. Computer simulation and field tests were performed to validate the path-tracking performance. Field test results indicated that the robot tractor followed the reference courses precisely on flat meadow, with average and standard lateral devia- tions being 0.031 m and 0.086 m, respectively. However, the tracking error increased while operating on sloping meadow due to the employed vehicle kinematic model.

成熟型资源城市转型升级的路径依赖或路径创造——基于新企业进入视角

Firm entry plays an important role in the industrial transformation of mature resource-based cities.This study describes the industrial evolution of resource-based cities at the firm level and uses kernel density estimation and econometric models to study the spatiotemporal characteristics and determinants of new firm entry from 2011 to 2019 in four mature resource-based cities.The results are summarized as follows:(1)New resource-based firm entry tends to be natural resource-oriented and path-dependent.The new non-resource-based firms show a high concentration in central urban areas,and the industry types are mainly wholesale and retail of resource products,cultural tourism,and equipment manufacturing.(2)Heterogeneous incumbent firms affect firm entry differently.Affected by competition and agglomeration effects,resource-based and non-resource-based incumbent firms have negative and positive impacts on new resource-based firm entry,respectively.Resourcebased incumbent firm agglomeration positively influences new non-resource-based firm entry.(3)Besides incumbent firms,firm entry can also be affected by multidimensional factors,such as factor costs,economic environment,and institutional environment.Research on new firm entry can better reveal the path dependence and path creation process of the industrial development of resource-based cities from a micro-perspective.