System Network Structure The structure of the experimental system is shown in Figure 1. It consists of three parts: design subnets, servers, and device subnets. The LAN of the design department (CAD/CAM lab) is called the design subnet. The equipment subnet consists of the bottom processing equipment connected by the Ethernet network. The bottom layer equipment is a representative numerical control equipment (or manufacturing system), which are: flexible production line (its monitoring software is based on Kingview 5.1 design), machining center (using PC numerical control system), CNC milling machine and CNC lathe (all adopt Siemens 802D CNC system). The underlying device can be expanded. Subnets and device subnets are designed to use a server as a gateway to form a networked manufacturing experiment system. The networked manufacturing process is as follows: After the management function department receives the order, it assigns tasks to the design department through the network. The design department carries out engineering design and process design for the product, and then feeds back to the management functional department through the network. After review by the management department, the design proposal was considered feasible, and the task was assigned to the equipment subnet through the web server. The server distributes tasks to various processing devices via the network according to the actual production conditions of the workshop. The server in the networked manufacturing experiment system completes task scheduling (job scheduling), job management, device monitoring, device management, and network communication services. Among them, task scheduling and device monitoring are the core.
Figure 1 System network structure
The information exchange model of the designer, dispatcher (server), and device (executor) in the information interaction model system is shown in Figure 2. After the designer of the designer (student) completes the product design and generates the NC program, it also determines the status of the task (partial emergency, common), the task processing time (that is, the time when the NC program processes the workpiece), and the task completion time (ie, the part (Delivery time), the processing equipment required to complete this task (CNC milling machine, CNC lathe, machining center, flexible production line). Start the designer's task sending software and send the task attributes (status, processing time, completion time, processing equipment) and the corresponding NC program to the dispatcher. The scheduler software running on the server on the dispatcher accepts the processing tasks sent by each design client and determines all attributes of the task. The dispatcher creates a task queue for each processing device according to the scheduling strategy. The task scheduling strategy is: according to the status of the task, the emergency before the row, the ordinary after the row; according to the time received, the first come before the row; according to the processing time, the shortest row before; according to the completion time, the most urgent row ahead. After the completion of a task, the equipment side (executive side) equipment side applies for the next task to the dispatcher. After the task is delivered, the equipment side software will prompt â€œa new task is deliveredâ€ and give the storage path of the NC program. Other relevant information returns a confirmation message to the dispatcher.
Figure 2 System Information Interaction Model
Figure 3 designer software process
Figure 4 Communication software flow between dispatcher and designer
2 The key technology development task scheduling and equipment monitoring of the networked manufacturing experiment system are the key technologies for the networked manufacturing experiment system. Its function software is implemented with VB6.0. The development of the task scheduling module is known from the system information interaction model. The information flows from the designer to the device and involves three phases of task sending, task queuing, and task acceptance. Therefore, the task scheduling involves the designer, dispatcher, and equipment. The following describes the task scheduling software development in three aspects. The designer's software development and design software, also known as the "task transmitter," sends the encapsulated job to the dispatcher. Encapsulated job content includes: task status, task processing time, task completion time, task processing equipment, storage path of NC program. The software flow of the designer is shown in Figure 3. The dispatcher software development dispatcher software is the core of the task scheduling module, including: communication between the dispatcher and the designer, communication between the dispatcher and the device, job scheduling (job sorting, queue insertion, queue sorting), and saving job queues, etc. . The following describes the software design work process using the dispatcher and designer communication module as an example: First, listen on the communication port and wait for the connection of the designer client; after the design client connects to the dispatcher, it starts to send files, and the dispatcher Accept the files sent by the client of the design client and store the files in the specified directory; then encapsulate the job information and store it in a dynamic array, wait for scheduling; and finally send a confirmation message to the design client to confirm that Accept the assignment. The implementation of other modules is no longer introduced due to limited space. The communication software flow of dispatcher and designer is shown in Figure 4, and the software interface of dispatcher is shown in Figure 5. Equipment-side software development Equipment-side software mainly completes the application and acceptance of tasks, also known as the â€œtask application deviceâ€, and the software flow of the equipment side is shown in Figure 6.
Figure 5 dispatcher software interface
Development monitoring of the equipment monitoring module means that the server monitors the remote processing equipment and adopts the client/server model. Remote monitoring is implemented through screen capture and coordinate conversion. The client continuously sends the screen image to the server and receives the mouse operation command from the server. The server displays the client's screen image. When the user clicks on the image, the mouse coordinates are obtained and converted to the client. The TCP connection between the server and the remote device (client) is programmed using the Winsock control in VB6.0. The server-side program runs first and listens on the specified port. When the client requests a connection, it establishes a connection between the two. When the server issues a "start monitoring" command, the client calls an API function to intercept the entire screen, save it as a BMP bitmap file, and send its file size (bytes) to the server. Because the resolution and color value of the screen are fixed, the size of the saved bitmap file is also fixed, so it is only necessary to send the file size once. After receiving the server, the server sends a confirmation signal to the client, and the client starts sending the contents of the bitmap file. Because the bitmap file is large, the Winsock control can automatically split it into multiple packets. After receiving the complete bitmap file, the server sends the client a confirmation signal. The client then starts the sending of the next screen image so that repeated transmission of the screen image is repeated. After the server receives the bitmap file, it is displayed in a picture box, and the user can simulate clicking on the client's screen in this picture box. To respond to a mouse click on the server, the client must call an API function to generate a simulated mouse event at the corresponding click position. There are two API functions involved, one is SetCursorPos. This function is used to set the X and Y positions of the mouse pointer in the screen pixel coordinate system. The other is mouse-event. This function is used to generate simulated mouse events. 3 Conclusion Networked manufacturing involves a wide range. The networked manufacturing experiment system developed in this paper integrates two major aspects of design and manufacturing, but it does not involve enterprise management and market networking. This is a system that needs further study and improvement. The system has been applied in the CNC practice center of the hospital and is operating normally to meet the design requirements.
Figure 6 Equipment-side software flow