Study On Data Exchange Of Open Architecture CNC System

Since our country was affiliated to WTO in due form in 2001, the economic development is speedier. With the development of automobile industry, aeronautics and astronautics industry and some new high-tech industries, the larger is the proportion of NC machining parts with free-form surface in all, the higher and higher requirements are made for quality and efficiency of machining on free-form surfaces. However, these subsequent processes of precision machining still depend mainly on the handwork of skilled mechanists presently. Productivity effect of handwork is very low and its quality is unstable. As to the machining of free-form surfaces, low cost and short period and high quality were its main aim. As a result of that, the research of a kind of increasingly automated polishing equipment is imperative.JiLin University has designed alone the JDYP51 model five-coordinate virtual axis polishing machine tool. t is a"3+2"model virtual axis machine tool .Three parallel axis carry out there movements in Xcoordinates,Ycoordinates and Z coordinates. Parallel mechanism drives move platform to move flatly. In series mechanism which have two degree of freedoms is fixed in move platform. principal axis mechanism is fixed with In series mechanism. The machine tool can be used to polish free-form surfaces of mold. This paper regards the JDYP51 machine tool. The work is study on open architecture CNC system, especially on data communication.Hardware structure of open architecture CNC system based on PC and Motion controller is built, in which PC acts as master computer and Motion controller acts as slave one(Fig.1). The communication between master computer and slave one is achieved by PCI bus and DPROM. The core of Motion controller is TI company's DSP (TMS320F2812) and the interface is PCI9054 chip. PCI bus is a kind of advanced partial lines of high performance. Because its high performance , PCI bus eliminate ISA bus to become major bus standard nowadays. This motion controller is just designed based on the PCI bus interface, which selects function excellent PCI9054 as the interface bridge conjunction chip of DSP and PCI in realizing. The paper designed the bus interface of the chip PCI9054 of the motion controller, which communications with DSP by DPROM. The signals of use of the port of partial bus are mainly as follows: data signal lines, address signal lines and control signal lines, and the DPROM which is used for the conjunction to read and write. 16 data bus used for LAD [15:0 ]to join DPROM, LA[ 14:2 ] is used to choose address; bidriection to transmit the data WR# , RD# that connect with R/W# signal line respectively. CS0# input, choose the signal for the DPROM slice; LHOLD is partial buses that cut off the input signals.Disposing register is information exchange area of PCI equipment , initialized software of PCI equipment and the mistake processing software, for the purpose of software carrying on recognizing and controlling to the equipments of PCI and the equipments of PCI reflecting the appearance and requests toward software. Local disposing register give the Characteristics of local bus, base address and scope of local space . Some as follows: LAS0RR,FFFF2000H;LAS0BA,00000001H;CS0BASE,00001001H。In the paper the motion controller take TMS320F2812 as a microprocessor, uses in each kind of order which carries out PC to send out or interpolation computation, and completes the axise position control. After position instruction colding, PC places the data in DPRAM through the PCI bus ,carries on the data communication with DSP; DSP reads out these data to carry on interpolation computation, obtains the theory position.Based on the master-slave hardware structure, software system is divided into two parts: CNC management system and motion control system, which communicate by the communicational module. CNC system functional module is divided as follow:CNC management system functional module Fig.2, motion control system functional module Fig.3.The paper studies the function realizing of communication module, motion controller communication module can visit the DPROM directly; PC Creates a dynamic link library PYTX , packaging the card driver procedures and other related procedures with communication, which can be called by user program as DLL like the Window API.The paper defines the data structure of data communication. A lot of data transmite as block, The CNC management system can monitor and control the process. Based on the Interrupted logic function of DPROM, data communication mechanism realizes by DPROM space partition and different modes of operation in mail box. That system works with the interrupted information is the biggest feature of data communication.Data checkout is an indispensable link in data communication, the paper choose CRC.The system has two checkout mechanism: CRC-32 and CRC-CCITT, which choosed by processing speed of data. If data has mistakes through the transmission, ARQ will request PC to transmit the old data again. It is a part of Interrupted acts. NUBS curve interpolation can provide smoothly stable is high speed, the precision work, is one kind new interpolation way, is becoming the NC manufacture technology. algorithm for controlling chord error this paper studied, through to in the interpolation process makes the chord error and enters for the speed real-time monitoring, enables the curve speed along with the curve curvature change auto-adapted adjustment, reduces chord error. The paper puts forward a kind of method between CRC-32 and CRC-CCITT.