The implementation of USB interface transformation

[2] Practical exploration on the transformation of USB interface for economical NC machine tools

in view of the defects of slow transmission speed of large amount of data of complex surfaces in NC machining, which leads to communication competition, this paper puts forward the idea of using a new interface between the upper computer in the NC system and the NC machine tool - USB interface to transform economical NC machine tools, and demonstrates the improvement of the corresponding software and hardware. This paper points out the method of realizing USB interface for CNC machine tools, and gives the USB driver under Windows system. Due to the significant acceleration of data transmission after the adoption of USB interface, and the improvement of the flexibility and diversity of the configuration between economic NC and PC, it expands the networking function for economic NC machine tools and solves the problem of data communication competition caused by slow transmission rate in Networking Manufacturing

I. raising problems

with the advent of the networking era, the machinery manufacturing industry is also facing the problem of how to adapt to networking manufacturing. Therefore, combining computer technology, network technology and traditional control technology, the CNC system with PC as the main controller is increasingly becoming a hot spot in the field of mechanical manufacturing. PC based numerical control can be divided into three types, which are introduced below by grabbing pages from the Internet

1. NC board insertion type

this NC system refers to the card of the core function board of NC and inserting it into the expansion slot of PC. PC is responsible for realizing user interface, document management, communication and other functions, while NC board is responsible for the motion control and switching value control of machine tool

2. Software CNC

software CNC can be understood as using the concept and means of PC to realize the functions of CNC. The main body of this CNC device is PC, which makes full use of PC's continuously improving computing speed, expanding storage capacity and continuously optimizing the performance of the operating system to realize the trajectory control and switching logic control in machine tool control. At present, there are still many problems to be solved in this scheme, which is still in the stage of laboratory research

3. Embedding PC board but endless service into CNC does not need to shift

this is a widely used CNC system at present. Connecting with PC through the front-end interface on CNC is a compromise scheme, but it can inherit the original mature CNC technology and obtain the flexibility and openness of PC at the same time

the USB interface technology discussed in this paper is based on this CNC system. This basic method of connecting numerical control equipment and upper control computer is called DNC technology, which is the most basic application technology of networked manufacturing. Most of the early economic CNC systems in China were refitted from single board computers, and a DNC interface board was needed to realize the basic DNC (download NC program) function, as shown in Figure 1

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Figure 1 Basic DNC communication interface of economic NC system

the communication mode between computer and NC processing equipment depends on the communication interface and communication protocol of NC system. The communication interface and communication protocol provided by NC system are as follows:

(1) recording interface, which is the communication interface of old-fashioned economic NC system made in Japan.

(2) Input interface of paper tape reader and output interface of paper tape puncher. CNC systems introduced in the early stage usually have this interface, such as FANUC 7m system. The newly developed CNC system has basically eliminated this interface, but there are still a certain number of CNC processing equipment including this interface in Chinese enterprises

(3) asynchronous serial communication interface, such as RS232, r5422, R485, etc. This is the most widely used communication interface. Almost all newly developed CNC systems contain this kind of interface. It adopts communication protocols such as xon/xoff, 3964R, simplified 3964, etc

(4) DNC interface, such as FANUC dnc2 interface, can realize long-distance communication, has the function of error feedback and real-time modification, and is convenient for remote management. However, due to its complex structure, difficult development of communication software and high price, it is rarely introduced in China

(5) network communication interfaces mainly include map interface, Ethernet interface and Fieldbus interface. These interfaces have high communication rate and high reliability. Most of the newly developed open CNC systems have Ethernet interface options, but few CNC systems imported from China are equipped with network communication interfaces

(6) map adopts map2.1 and map3 O manufacturing automation protocol is a widely used industry at present. It integrates broadband technology, bus technology and passive workstation, so as to ensure the error free transmission of information. However, when map is required to realize synchronous transmission of NC program with machining, it is difficult to meet the real-time requirements. This is because map adopts a complete seven layer protocol, which is not suitable for the connection of NC machining equipment because of its high network access cost, low transmission efficiency and poor real-time performance

from the above analysis, it can be seen that the asynchronous serial communication interface RS232 is the most commonly used communication interface of CNC system, and almost all CNC systems, such as bumper, reflector cover and tailgate, include this interface. Similarly, the DNC interface board in Figure 1 also adopts RS232 interface. With the rapid development of computer technology, RS232 interface is being replaced by a new USB interface in the field of computer application. From keyboard, mouse to printer and scanner, many USB based peripherals have replaced the devices that used to use RS232 interface in the past. Can such a new USB interface technology also be used in CNC system

dnc communication system, when multiple NC processing equipment process a complex part at the same time, due to the huge NC program, the memory of the NC system cannot store the entire NC program, and can only be processed by DNC transmission, which may lead to the phenomenon that the NC processing equipment stops processing due to the temporary lack of NC program, which is called "communication competition". Communication competition often has serious consequences in actual production. For example, the stoppage in the horizontal processing of automobile panel stamping die will cause local "Spotlight" phenomenon of the panel, which will directly affect the quality of stamping parts

the factors causing communication competition are roughly as follows:

(1) the number of NC processing equipment participating in the joint m. The more the number, the greater the possibility of causing communication competition

(2) fieldbus transmission rate, transmission efficiency C and node switching service time t. Transmission efficiency refers to the proportion of the number of transmission effective bytes in the total transmission bytes

(3) NC machining