1 Basic method of CNC machine tool maintenance
1.1 "Collective consultation" method
It is presided over by the competent personnel to convene personnel in the process, equipment, operation, etc. to conduct consultations. Each person proposes individual plans and checks them one by one to solve them. This method is often used in foreign companies.
1.2 plc input and output point recording method (PLC I/O LED photo record)
In the past maintenance, we found that many equipment failures occurred when the machine was turned on. In fact, there is no hardware failure in the device, which is often caused by improper operation or other reasons. Although the fault is not big, it is troublesome to find. To this end, we used a digital camera to take pictures of the I/O indicators on the PLC at normal times and print them out next to the PLC. In this way, once a similar problem occurs, the maintenance worker can quickly find the problem by comparing the photos, and sometimes the operator can find the problem accordingly. The advantage of using a digital camera is that it can be saved in a microcomputer for easy classification management and long-term storage. This kind of photo recording comparison method, we also use on some adjustable valves, limit switches and mechanical positioning devices, which play a very good role in guiding operation and maintenance.
1.3 Hard disk backup method (hard disk backup)
Many existing devices use an industrial microcomputer as a host computer control device or a human-machine interface. More than 80% of microcomputer failures are software failures. In the past, software failures often required professional computer technicians to come to the repair. It was generally a re-installation of the system, which was very time consuming. The hard disk backup method we use now is to pre-purchase a new hard disk that is the same as or similar to the original one. Use Ghost or similar software to copy all the hard disk data of the original machine, including the system, to the new hard disk as a backup. In the event of a software failure, simply replace the backup drive with a short change in repair time. It also prevents real hard drive damage. This kind of work can be done by a general maintenance worker.
1.4 spare parts rapid replacement method (spare parts rapid replacement)
Due to the rapid development of electronic components, some electrical spare parts have been updated quickly. High-tech products such as inverters have been updated for almost two or three years. Therefore, it is difficult to purchase the same type of spare parts when purchasing spare parts, and sometimes it is possible to purchase products of different companies. For the replacement of these spare parts, the general maintenance workers have certain difficulties, especially like the inverter. If you change the products of different manufacturers, not only the hardware wiring is different, but also the parameter settings are different. In order to ensure that the repairman can accurately and quickly replace, we will send a direct replacement operation flow chart and parameter setting table to each maintenance worker according to the technical parameters of the existing inverter and spare parts library. Next to the field inverter. Similar methods are used for other complex spare parts, which effectively shortens the replacement time of spare parts.
1.5 key point checking and main taining
How to use the limited number of maintenance personnel to ensure the maximum operation of the equipment is the subject of research by our equipment management personnel. Many large-scale equipment and production lines may have many faults, and it is very difficult for maintenance workers to want to cover everything during inspections. On the contrary, many maintenance workers are often left unattended and spend a lot of energy on some minor issues. In response to this situation, we have implemented a working method called “checking and repairing†to guide the daily inspection and maintenance of maintenance workers. This method is to list several of the most critical parts according to the different conditions of each equipment, and send them to the relevant maintenance workers in the form of graphs. It is required to carry out key inspections on these places every day, and find abnormal and timely maintenance. Good result. When setting up the checklist, you must pay attention to the following two points.
1) The key points must be properly and accurately determined. We have integrated the technical manual of the equipment, the opinions of experienced service technicians, and the failure of the previous equipment.
2) The key point should be “fineâ€. Generally, there are no more than 10 key points in a large equipment or 500 m2 production line, otherwise it is likely to flow in form.
1.6 defect retrofitted
In the long-term maintenance work, we found that some devices often have some repeated faults, and the randomness is very strong. After further analysis, we found and confirmed that the equipment is defective in the design and manufacturing process. It cannot be eradicated only by maintenance, and must be modified to eradicate hidden dangers. To give a typical example, a factory has a vacuum thermoforming machine for refrigerators imported from Italy. The heating control part uses a single-chip system to exchange data with a host computer. The fault that often occurs is that the communication between the single-chip microcomputer and the microcomputer is not smooth, but the power-on or the replacement of a single-chip motherboard may return to normal, and one of the faults will burn out the COM1 port of the microcomputer. Later, after looking up the information, we found that the communication method used in the design was unreasonable. The single-chip microcomputer and the microcomputer adopt the RS232C mode direct connection, there is no isolation, and the cable length exceeds 30 m. We know that the RS232C communication method has poor anti-interference and the communication distance is generally less than 15 m. To this end, we have modified the communication cable, and installed ADAM's 7520-RS485/RS232 optical-to-space converter on both ends, so that RS485 is used to transmit data in most distances, and no fault has ever occurred.
1.7 Real time monitoring
CNC machine tools often have some soft faults, which makes it difficult to diagnose. At this time, the key point signal can be collected and recorded in real time by using a data acquisition card, etc., so that comprehensive analysis can be performed at the time of diagnosis. The advent of "virtual instruments" offers the possibility of real-time monitoring. It should be noted that the monitoring system and the CNC are independent of each other, and the monitoring system is self-made by the end user.
2 Several options for CNC transformation
2.1 Using PLC to realize CNC transformation
In some occasions where the printing and packaging requirements are not too high, and some production line control occasions, the NC transformation task can be completed by PLC. At this time, a general-purpose PLC is used instead of a numerical control-specific type such as FANUCPMC.
At present, the general-purpose PLC function is very powerful, including positioning module, A/D, D/A, I/O mode, which can realize many industrial control functions.
2.2 Commercial CNC (PLC), servo system transformation
This method is currently a popular transformation mode. CNC system manufacturers provide increasingly convenient debugging methods and tool software to facilitate machine tool builders and rebuilders.
The debugging software mainly includes servo system adaptation, ladder diagram and machine parameters. CNC manufacturers usually provide CD and commissioning manuals. For example, when Siemens sells its economical CNC 802D, it will provide a debugging CD and a simple debugging guide for SINUMERIK 802D. When AB Corporation sells 9 series CNC, it will let users purchase ODS (offline development system) floppy disk and manual. The ODS can be used for ladder diagram development, machine parameter setting, part program editing, etc. on a personal computer, and communicates with the CNC through the 232 port.
2.3 Select industrial computer for CNC transformation
It is not only the numerical control transformation of metal cutting machine tools, but also the industrial control occasions such as process control and sequence control. It can utilize the reliability of the industrial computer, select the appropriate tool software or develop the software by itself.
In the early 1990s, we used STD industrial computer and 4 sets of DC servo system to develop software to transform the domestic 5040 CNC milling machine .
The industrial control computer consists of three 8088 CPU STD computers. Connected by the communication interface. Each STD computer consists of several templates. As a hardware support for distributed computer numerical control.
2.4 Select PC-based CNC
PC-based CNC is the current implementation of open CNC. But there is still a long way to go from the open CNC in the true sense. At present, there is still no consistent definition of "open structure". Some users believe that the open representation can accept the communication protocol used locally; while others believe that openness means that all controllers operate exactly the same. For machine tool application engineers, openness means standard input/output interfaces for tool holder movement, sensors and logic control. For research engineers at large companies and universities, openness means that all of the above comes from the blocks that are used immediately. The development of open architecture is moving forward and will continue due to pressure from users and integrators. A positive result today is the PC based PC, PC-based CNC. The current specific implementation, its hardware composition is a personal computer plus motion control card. The software consists mainly of computer software platforms (such as WIN, DOS) plus CNC system software. The development of the PMAC multi-axis motion control card of Delta Tau of the United States has gone faster in this respect. The PMAC card of PC bus, VME bus and STD bus has been developed. The entire motion control is done independently by PMAC. The software running on the host is only a development environment, responsible for display, debugging, part programming, communication, etc. The PMAC runtime is responsible for the coordinate axis motion control and the background is responsible for the PLC. Using the US MOTOROLA 56001 DSP as the CPU, it can be connected to DC, AC, and stepper motors. The feedback element can be an incremental/absolute encoder, a resolver, a scale, or the like.
Another workaround is to refer to the personal computer architecture in hardware and software, but has changed. For example, Siemens 840D, according to the current MMC, CNC, PLC trinity CNC control machine mode, is a standard IPC industrial computer on the MMC, but the operating system uses Flex OS. The CNC and PLC are concentrated in the NCU. The peripheral interfaces include the spindle, the feed module, and the I/O port. The connection between the 840D and the driver 611D is performed via the bus (the fieldbus profibus is used in the 802D), which is closer to the information transmission mode of the computer. In addition, due to the operating system Flex OS, its operating interface is very similar to a normal personal computer.
The above-mentioned PMAC motion control card and Siemens 840D, etc., they have done a lot of work on the PC-based CNC, but there are still many ways to go from the real open.
The ideal mode should be the mode of industrial computer + real-time operating system + development environment + CNC function library. The CNC control software should be ready for assembly. The object of the assembly is the library function in the CNC function library. The development environment provides users with development tools to incorporate library functions into the real-time operating system. In this way, just as the development of PLC programs has shifted from CNC manufacturers to machine tool manufacturers and CNC integrators, the formation of CNC systems can also be transferred from CNC manufacturers to machine tool manufacturers, integrators, and even end users. This is the open CNC in the final sense.
3. Process of CNC transformation
The CNC transformation process is as follows:
1) When ordering, purchase is mainly based on indicators such as spindle power, feed torque, installation, and I/O points. If the original machine tool has information, it can be better. If it is not, you can only go to the site for actual measurement.
2) The hardware connection should mainly refer to the hardware manufacturer's hardware connection manual.
3) Ladder diagram development mainly refers to the manufacturer plc programming manual.
4) The debugging is mainly based on the parameter manual and the debugging guide.
In summary, the hardware connection manual, PLC programming, commissioning manual, and parameter manual provided by the CNC manufacturer must be digested. Especially before the first renovation.
As CNC systems become more and more "personal computers", software is often used for CNC debugging. For example, Siemens 840D, the PG programming machine and the PG port of the 840D should be connected with the MPI cable (multi-terminal communication interface) before debugging. There are two debugging contents, one is the PLC basic program application - activate MCP (machine control panel) and axis enable, and the second is machine data MD (ie machine parameter) adjustment.
4, the relationship between CNC maintenance and transformation
The engineering and technical personnel engaged in CNC transformation in China are all engaged in CNC maintenance or CNC system. However, those who have done maintenance and renovation find that there are still many differences between the two.
Some people say that CNC transformation is a high-level form of maintenance. Some people say that people who are engaged in transformation may not be able to do maintenance well, and most people who have done maintenance have not made any modifications.
It should be said that both of these are the contents of CNC technology services, but after all, it is two different things.
According to China's national conditions, CNC maintenance is more difficult than retrofitting. Mainly because the maintenance market is not mature and the spare parts are difficult to solve. In addition, the maintenance discipline is involved in a wide range of uncertainties, diagnostic techniques and equipment are backward, and the cost is low. While the numerical control transformation requires a higher level of overall knowledge, there are fewer uncertainties and a higher relative hit rate.
At present, the tendency of heavy-duty transformation and light maintenance in domestic CNC service enterprises is becoming more and more serious. However, the most demanding and large-scale CNC repairs that the end user needs most can not be satisfactorily resolved.
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