Parallel Dual CPU Open CNC System Based on PMAC
AxesController) The multi-axis motion controller is a dual CPU numerical control system with a CNC module and an industrial control machine as the system support unit. It achieves two levels of openness: human-machine interface and customization and parameterization of non-real-time control components; real-time control components Parameterization.
1 The hardware structure of the numerical control system 1.1 PMAC multi-axis motion controller PMAC multi-axis motion controller is a product of DeltaTau, USA, and is a controller with high-performance servo motion. With the help of Motorola’s DSP56001/56002 digital signal processor, it can control 18 axes at the same time. It can execute the program stored in it alone, can also execute the motion program and PLC program, and can update the servo loop and communicate with the host computer in two ways: serial port and bus. PMAC can also automatically distinguish the task priority, so as to perform real-time multitasking. This function makes it greatly reduce the burden on the host and programmer in terms of processing time and task switching, and improves the running speed and control accuracy of the entire control system.
1.2 The hardware structure and working principle of the numerical control system The control center of the numerical control system adopts the PMAC multi-axis motion controller and dual-port memory (DPRAM) on the basis of the industrial control computer (IPC) platform. The CPU on the industrial computer and the CPU (DSP56001) of the PMAC form a master-slave dual microprocessor structure. PMAC mainly completes the three-axis movement of the machine tool and the control of the switch value of the control panel, while the industrial computer mainly realizes the management function of the system. In order to realize the function of PMAC multi-axis motion control, it is necessary to expand the corresponding I/O board, servo drive unit, servo motor, encoder, etc. on the PMAC board, and finally form a complete CNC system. Its structure principle is as shown.
(l) The communication between the PMAC motion controller and the host adopts two methods. One is bus communication; the other is to use DPRAM for data communication. The host computer and the PMAC motion controller communicate mainly through the PC bus, and the control card and the motor status, motor position, speed, following error and other data exchange information through DPRAM. The bus communication mode means that the host searches for the PMAC motion controller at the specified address, and the specified address is determined by the jumper of the PMAC. Dual-port RAM is mainly used for fast data communication and command communication with PMAC. On the one hand, when dual-port RAM writes data to PMAC, it can quickly and repeatedly download position data or program information in real time; on the other hand, dual-port RAM can quickly and repeatedly obtain data when reading data from PMAC System status information. For example, the status, position, speed, following error and other data of the AC servo motor can be updated continuously, and can be automatically written into DPRAM by PLC or PMAC. Because the data access of DPRAM does not need to send commands and wait through the communication port Response, so the response speed and processing accuracy of the system are improved, and it also facilitates the rapid communication between the modules in the control system and the setting of the address table, and reduces the programming difficulty.
Serial parallel port keyboard floppy drive hard disk video I. Main CPU board and main I video card I ISA bus board 2 I servo signal transfer board A/D board 1 TZ axis servo unit and frequency conversion 1 profiling instrument motor control panel machine tool electrical power cabinet I /O signal numerical control system structure schematic diagram port input and output realization. In the control system, the input signals sent to the PLC mainly include: the operation panel and the control buttons and selection switches on the machine tool; signals such as the travel switch and mechanical zero switch of each axis; the machine tool electrical action, limit, alarm and other signals ; Signals such as the contact of contactors and pneumatic switches in the strong electric cabinet; signals of the working status of each servo module, etc. These signals are then sent to the intelligent I/O interface through photoelectric isolation. Photoelectric isolation effectively isolates the computer digital channel from the external process analog channel, greatly reduces the interference of external factors, and improves the reliability and stability of the entire system. The signals output by PLC mainly include: indicator light signal; control relay, contactor, solenoid valve and other action signals; servo module drive enable and speed enable signals, etc. These signals are sent to the corresponding relays via the I/O interface to control the corresponding electrical appliances.
2 The software design of the numerical control system The numerical control system software is divided into two parts: PMAC real-time control software and system management software. The design of real-time control software fully considers the openness of the software, and users can add software functional modules according to some specific requirements. Real-time control software mainly includes interpolation module, servo drive module, PLC monitoring module, processing program interpretation module, data acquisition and digital processing module, etc. Its function module diagram is shown as below.
PMAC real-time control software module diagram Interpolation module includes linear interpolation, circular interpolation and spline interpolation. PMAC also provides a PVT (Position-Speed-Time) motion mode, which can directly and compactly control the trajectory graph. Users can choose and combine the above modes.
The servo drive module can select PID position loop servo filter, notch filter or extended filter, and set its control parameters. Users can also customize their own servo algorithm to achieve personalized servo control.
The PLC monitoring module mainly includes watchdog PLC, power-on PLC, main PLC, indicator light management PLC and power-off PLC. The watchdog PLC is started immediately after the PMAC is powered on, and it continuously reads the count of an address unit in the DPRAM Value to determine whether the host enters the CNC system. When the difference between two consecutive readings is greater than a certain number, it starts powering on the PLC and powers on the entire CNC system; when the difference between it readings is less than a certain number, it starts powering off the PLC and shuts down the entire CNC system. The main PLC is used to complete the task of monitoring the input and output of the control panel and the machine tool. It mainly includes the realization of manual and automatic functions, and the control of the spindle movement.
PLC programming first needs to mirror the I/O port and the DPRAM address, and then operate the I/O port by operating some units of the DPRAM. Such as: Secondly, define the DPRAM address associated with the host DLL, so that IPC and PMAC share this storage space to exchange information. For example: DDFO //The command word VSFEEDOVERRIDEMM50 of the rotary switch on the control panel defines the unused address in the DPRAM, thus realizing the user-defined communication function. Such as: the system’s automatic manual mode, spindle forward and reverse and other commands, status information; feedrate override, spindle speed and other numerical information.
The processing program interpretation module is composed of G code interpreter, M code de-sequence and T code interpreter. These interpreters are edited and debugged under the PEWIN execution program, downloaded to the fixed memory of PMAC, and automatically called by PMAC during actual processing. In addition, parameters such as servo interruption time and motor phase are set by the PEWIN execution program, thus realizing the parameterization of real-time control components.
The digital module adopts a special control algorithm according to the feedback information of the three-dimensional profiling instrument to realize the tracking and scanning of the workpiece, and complete the data collection of the surface of the workpiece.
The system management software mainly realizes the functions of initialization, parameter input and processing program editing, system management and dual CPU communication. Its function module diagram is shown as below.
Initialization of system management software I丨Initial input and i-work procedures丨Fault diagnosis丨System kaifcpul system management software module diagram In the system management software, the development workload of dual CPU communication programs is large and very skillful. The communication programs of the upper computer and the lower computer of this numerical control system are compiled using the Pcomm32 dynamic link library and the PTALKDT control provided by Delta Tau. Pcmm32 includes all the ways of communicating with PMAC, and classifies and encapsulates its main functions, and finally forms the ActiveX control PTALKDT. The communication program compiled to realize the download of processing programs, PLC programs and motion programs, and the host computer to PMAC Communication functions such as command transmission and PMAC’s status feedback to the host computer.
The man-machine interface for system configuration, CNC program editing, processing control, fault diagnosis, and parameter input is compiled in Vlsual Basic language, using the rich GUI functions of Windows and 32-bit processing capabilities. Development of CK6130 small CNC lathe Zhang Lixin Wang Weibing Wu Jie (Xinjiang Shihezi University) The main body of the control lathe is transformed with an old ordinary lathe and equipped with a 4-station electric tool post for receiving letters, so as to realize the multifunctional and low-cost automation of the lathe.
At present, economical cnc machine tools are still the CNC machine tools with the largest market demand and the highest sales volume in my country. Utilizing the existing idle old machine tools and transforming them into a new high-efficiency, multi-functional economical CNC machine tool through numerical control is an effective method to revitalize the existing funds, and it is also one of the ways to realize automation at low cost. The CK6130 small CNC lathe developed by us is the exploration and practice of this idea.
1 Working principle The CK6130 small CNC lathe is composed of two parts: a microcomputer numerical control system and a machine tool body. When processing the workpiece, first compile the numerical control program of the workpiece, and then input the feasible numerical control program into the numerical control device, and then the numerical control device calculates the feed pulse sequence according to the program instructions, and then the multi-function NC board performs pulse distribution, and then the power amplifier or After the power is amplified by the driving power supply, the control signal of the driving device is formed to control the rotation speed, start and stop of the machine tool spindle, the movement direction, speed and displacement of the feed system, as well as the selection of tools, the start and stop of cooling and lubrication, etc. Cutters, workpieces and other auxiliary devices work strictly in accordance with the sequence, stroke and parameters specified by the CNC program, so as to process the shape, size, and accuracy to achieve a friendly human-machine interface.
3 Conclusion The CNC system is based on a general industrial control machine, and uses a powerful motion controller PMAC to undertake real-time tasks such as interpolation calculation, position control, and speed control. It has achieved two levels of openness, making the CNC system more specific The system has better human-computer interaction capabilities and upper-level application system integration capabilities, which is convenient for manufacturers and users to customize system functions and parameter adjustments, so that the system has better adaptability. This numerical control system has been applied to the development of SKB2320A wall Milling Machine, and has achieved good results.
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