| It is important for logistic industry to automatically trace and handle the material and according information efficiently and synchronously.The logistic equipments should be developed with providing the properties of multifunction,multi operation mode and flexibility.Unit equipment should possess the capability of working with other equipments cooperatively to handle the material continuously,and the capability of communicating with the information system and dispatching system.The modern control and supervisory control system for logistic equipment is a kind of large-scale,complex,distributed and integrated automation system,which involves motion control,discrete logic control and discrete process control,real-time multi-task control,Fieldbus,electromechanical transmission,software technology.It is common that the manufacturers rarely report their advanced equipments technology.And,the academic research did not focus on the dominating industrial practices of development of logistic equipments.All these factors have hindered the advance of the manufacture technology of logistic equipments inside China.The development of logistic equipment will lead to late delivery,over budget or even failure for can not satisfy the functional requirements or non-functional requirements unless the developer choosing right methods and innovating the key technologies.The control and supervisory control system for logistic equipment is layered in bottom-up order as control system for unit equipment,control system for equipments group and supervisory control system.Several key technologies for developing the system have been studied,and illustrated as follows.Firstly,the technology of system integration of the hardware of the control and supervisory control system for logistic equipments is presented,which is led by the fact that the control and supervisory control system is a layered and distributed system.The hardware consists of controllers,actors,sensors,and many information devices such as bar-code scanners,RFID readers,kinds of displays,broadcast systems,touch panels,et al,which makes the network structure of the system differ from that of the Supervisory Control and Data Acquisition systems which are widely used in process control systems.The popular architecture used in industry distributed control systems is Ethernet-based networks integrated with different Fieldbus.However,the selection of the protocol for the networks for each layer is still an important issue to consider.Within the unit equipment control system layer,serial Fieldbus which support exchanging data cyclically and automatically is selected to link the controllers,actors and sensors,for the control system in this layer involving motion control,which require to exchange a small amount of data with high reliability and within the time-delay of milliseconds.Ethernet with client-server based protocol is chosen to integrate the control system and the supervisory control system for they exchange data irregularly.Combining the advantages of Ethernet and Fieldbus,the network architecture fit to be applied in automated storage and retrieval system is proposed,which takes the switched Ethernet as its upper layer net,and takes Fieldbus as its bottom layer net.The time delay of the networks for each layer of an industrial project as an example is calculated and verified.The second key technology involves methodology of system development of control software for unit logistic equipments.A kind of structured and system analysis and design method which is based on functions and control process of the control system has been expanded.Following the formal method,the sub-functions of the system can not be detached completely.And the system model developed consequently figures a tight coupling structure.With the function based method of system analysis and design been reserved,task-oriented system analysis and design method is proposed.Task-oriented system analysis and design method emphasizes task-centric system analyzing and developing process.By their property,control tasks are classified into four types,which are private-sequential task,global-real-time task asynchronous-concurrent task,and periodic task.The classification prompts developers to find tasks and analyze a system to subroutines.And hierarchical modeling method is presented.Inter-task communication and multitask scheduling method is given.By encapsulating the tasks into subroutines,and by means of setting or resetting the enable input bit of the subroutines to enable or disable the subroutines to be active or inactive to dispatch the tasks,a structured and time-efficient control program is developed,which can be reused as a framework of Programmable Logic Controller software for mechanical system control.The third key technology involves methodology of development of control software for distributed logistic equipments group.Technology of Object-Oriented system analysis and modeling and software architecture are introduced in development of the control software,which is running in resource-constrained and operating system absence environment.Considered with the peculiarity of control system and Object-Oriented philosophy,concept of abstract object,which has not been straightforward,is explained.It is advised that the controller and controlled object should be treated and designed as two objects.The limitation of the Object-Oriented technology in development of control software based on Programmable Logic Controller is discussed.A systematic programmable logic controller program development methodology is proposed,which adopts software architecture in system level,and object oriented technology in unit equipment level,and task-oriented technology in level of inside unit equipment.The methodology is demonstrated by the control software for a material handling system,which consists of several logistic equipments.The control software employed pipe and filter model as its architecture,which has been modified at its sub-layer.The controller objects are activated dynamically by the supervisory object.And it employs message queue for inter-objects communication.The last key technology involves methodology of supervisory control of logistic equipments.The common used technology such as supervisory control and data acquisition system,monitoring and control system,supervisory computer control system can not meet the demand of supervisory control of logistic equipments.The applicability of supervisory control theory for discrete event dynamic system in supervisory control of logistic equipments is discussed.Agent-based architecture for supervisory control of logistic equipments is proposed.For application protocol of the supervisory computer and the field controller is the hinge for implementing the agent-based architecture,communication protocol for the supervisor system of automated storage and retrieval system base on Ethernet is constructed.And the communication software for supervisory control system based on Common Industrial Protocol is designed,which has been applied in the control system for a path-configurable transporting and handling line for large cargo.Focused on the difficulties in developing control and supervisory control system for logistic processing equipments,the technical for system integration,methods for control software development,and typical architectures for the systems are given.The system analysis and modeling method for development of real-time control software for the unit equipments is proposed.Object oriented and architecture based method are introduced in the control software for groups of logistic equipments.Agent-based architecture for supervisory control of logistic equipments is proposed.The proposed methods and technologies have been applied in several industrial projects,and proved to be capable of managing the complexity and alleviating the difficulties in developing control and supervisory control system for logistic equipments,and can help the developers to improve the work efficiency and reduce the cost of the hardware. |
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