Modeling of agricultural processes with hybrid petri nets

When management of agricultural activities are analyzed, it is noticeable that they are more complicated than the administration of general industrial processes. The reason for this is that uncertainty and risk factors in agricultural work may be so strong as to affect the overall activity. Weather conditions, environmental and biological factors can be cited as examples of this case. For these reasons, plannings to be conducted for agricultural activities must be considered from a broader perspective. In order to increase the productivity of agricultural activities, the structural improvement of agricultural vehicles has been taken into consideration. However, there is no opportunity to make much of a change in characteristics such as size and weight of the vehicle due to the conditions in agricultural activities and the aforementioned factors. Nevertheless, with advances in technology, transfer to the use of smart devices and autonomous systems in many areas has been started. Efficiency can be increased and environmental effects can be reduced with the use of these systems in agricultural activities. However, the effective use of those advances requires reconsideration of the agricultural machinery management processes. According to the ASABE standards, management of agricultural vehicles can be grouped under four headings: 1) Planning 2) Scheduling 3) Operating 4) Controlling It is seen that five management levels are described in general for agricultural production management processes in literature; 1) Strategic 2) Tactical 3) Operational 4) Execution 5) Evaluation Considering both ASABE standards and general management levels by Bochtis et. al (2014), 5 basic management tasks are stated for the management of agricultural vehicles: Capacity planning, task times planning, scheduling, route planning and performance evaluation. Capacity planning corresponds to strategic level, task times planning corresponds to tactical level, scheduling corresponds to operational level, route planning corresponds to execution phase and performance evaluation corresponds to the evaluation level. When considered with regard to ASABE Standards, capacity planning and task times planning can be evaluated in planning section, scheduling as in its own section, route planning in operating section and performance evaluation in controlling section. With these features, five basic management tasks contain most of the matters put forward by ASABE Standards. Petri nets enables to examine system analysis and functioning with a relatively simple approach due to being a modeling method with mathematical (state equations, algebraic equations, etc.) and graphical characteristics. It can be used in such systems as distributed, parallel, asynchronous, concurrent, non-causal and/or stochastic. Agricultural activities consist of discrete events such as whether machines are ready to operate or not, breakdowns, weather conditions, soil condition as well as continuous events such as plowing the fields, planting, watering, fertilizing. As in agricultural activities, both discrete and continuous processes can be modeled with hybrid petri nets. When the graphical characteristics are taken into consideration, modeling of agricultural activities with hybrid petri nets outclasses the modellings based on mathematical approach, and offers an efficient way to observe processes. When studies relating to the agricultural machinery management in the literature are analyzed, it is seen that petri nets and modellings are included for field workflow management within the scope of scheduling phase. However, no model has been found, which involves the other management tasks related to the agricultural machinery management and are implemented by petri nets. In this study, models related to agricultural management processes have been developed. Hybrid petri nets were also used to model discrete and continuous cases. These models can be used for five management tasks which are defined in accordance with the ASABE standardsand are capacity planning, task times planning, scheduling, route planning and performance evaluation. The models can be used not only for examples to be given but also for other agricultural activities. This study offers such models which cover fivetasks of the agricultural machinery management that may include potential uncertainties and risk factors, and allow to define new variables based on these factors related to the model types. In introduction, general history, characteristics and areas of use of petri nets are described. Applications in literature abouttheir use in agriculture, standards relating to agricultural management,management tasks and levels are outlined. In Section 2, basic information about petri nets are given. Mathematical definitions related to the petri nets, basic components, the structure, behavioral characteristics, firing rules and analysis methods of petri nets are mentioned. In Section 3, continuous petri nets are discussed.Why continuous petri nets are used are mentioned. Basic components, firing and admission features are listed. In Section 4, hybrid petri nets are described, which involve both discrete and continuous petri net structures. Advantages and main characteristics of hybrid nets are mentioned; mathematical definitions are made, and firing rules are examined. In addition, applications of them in agricultural areas and modeling approach are shown. In Section 5, models developed for the management of agricultural tasks presented in a way that will also include the issues to be considered at the design stage and several examples are given regarding the operation of the models. Also, for the last model, detailed analysis including liveness, reachable states and firing arrays is made. In the last section, evaluation of the study is mentioned and some recommendations have been made regarding the issues which might be examined for future studies.