Fault Self-diagnosis of CNC Machine Tool

1. POST
The so-called power-on self-diagnosis refers to the diagnosis automatically executed by the internal diagnostic program of the system when the CNC system is powered on, which is similar to the power-on diagnosis of a computer.
Power-on self-diagnosis can check the key hardware in the system, such as: CPU, memory, I/O unit, CRT/MDI unit, paper tape reader, floppy drive and other devices are automatically checked; determine the specified equipment Installation, connection status and performance: Some systems can also support some important chips, such as: PAM, ROM, dedicated LSI, etc. for diagnosis.
The self-diagnosis of the numerical control system is carried out when starting up, and it can only enter the normal operation state when all items are confirmed to be correct. The time of diagnosis depends on ten numerical control systems generally only need a few seconds, but some need several minutes. Power-on self-diagnosis is generally carried out according to the prescribed steps, with FANUC II of Take the system as an example during the execution of the diagnostic program, the seven-segment display on the system board presses 9→8→7→ 6→5→4→3→2→1, the corresponding The inspection content is:
9―reset CPU and start to execute diagnostic commands:
8―do a ROM test, indicating ROM When checking error, the display becomes b;
7―Clear RAM, the system will set RAM to clear the content in preparation for normal operation;
6A pair of BAC (bus random control) chips are initialized . At this time, if the display changes to A, it means that the mainboard is compatible with CRT There is an error in the transmission; change to C, indicating a connection error: change to F, indicating I/O board or connecting cable is bad: change to H , Indicates that the connection unit identification number used is wrong; display lowercase lettersc indicates an error in optical cable transmission; J is displayed, indicating plc Or the interface conversion circuit is bad and so on.
5 – Check for MDI elements
4 – initialize the CRT cell
3―display the initial screen of CRT, such as: software version number, serial number, etc. At this time, if the display changes to L, it indicates the control of PLC There is a problem with the software: change to O, it means that the system failed to initialize, and there is a problem with the control software:
2—indicates that the initialization of the system has been completed;
1―means that the system is ready to operate normally, if the display changes to E indicates the main board of the system or ROM board, or CNCControl software is faulty.
Under normal circumstances #p#page title#e# CRT After the initialization is completed, if there is a failure in other parts, CRT can display the alarm information.
2. online monitoring
Online monitoring can be divided into CNC internal program monitoring and external device monitoring
CNCInternal program monitoring is a method to automatically diagnose, check and monitor the status of each part through the internal program of the system. The scope of online monitoring includes CNC itself and the servo connected to CNC unit, servo motor, spindle servo unit, spindle motor, external equipment, etc. Online monitoring is always effective during system work.
The internal program monitoring of the CNC system includes interface signal display, internal status display and faultShow three sides.
⑴ Interface signal display It can display CNC and PLC, CNC and the machine tool. Refers to the on-off clearing of digital input/output signals to help analyze faults.
You must understand CNC and PLC, CNC and the significance of each signal between the machine tool and the various conditions that should be met for the generation and cancellation of the signal can be checked accordingly. The “Function Manual” and “Connection Manual” provided by the CNC system manufacturer and the “Machine Electrical Schematic Diagram” provided by the machine tool manufacturer are the technical guidelines for the above status inspection.
⑵ Internal state display Generally speaking, the internal state is not displayed function, which can display the following aspects:
1) The external reason that causes the cycle command (processing program) not to be executed. For example: CNC Whether the system is in the “in-position check”: whether it is in the state of “machine lock”: whether it is in the state of “waiting for speed arrival” signal to be turned on : Whether to wait for the measurement signal of the “position encoder” when programming the feedrate per revolution of the spindle; whether to wait for the “spindle Iturn signal” Whether the feedrate override is set to 0 %, etc.
2) Reset state display, indicating whether the system is in the “emergency stop” state or the “external reset” signal is on.
3) TH alarm state display. It can show the location of the paper tape error hole when the alarm occurs.
4) Display of memory content and abnormal status of magnetic bubble memory.
5) Display of position following error.
#p#page title#e#6) The control information display of the servo part
7) Input pulse display of position measuring components such as encoders and gratings, etc.
⑶ The fault information is displayed in the CNC system, and the fault information is generally displayed on the CRT in the form of “alarm display”. The contents of the alarm display are different according to the different numerical control systems. Most of these information appear in the form of “alarm number” plus text, and the specific content and troubleshooting methods can be consulted in the “maintenance manual” provided by the CNC system manufacturer.
Monitoring through external equipment refers to a method of automatically diagnosing, checking and monitoring the status of each part of the CNC machine tool using computers, PLC programmers and other equipment. For example, the PLC program is dynamically detected in the form of ladder diagram and function diagram through the computer and PLC programmer. It can read the dynamic waveform display of the PLC program when the machine tool manufacturer does not provide the PLC program. Usually, it also needs the help of The necessary online monitoring equipment is carried out.
With the development of computer network technology, as a kind of online monitoring of external equipment, remote diagnosis technology through network connection is being further popularized and improved. Through the network, CNC system manufacturers can directly detect and monitor the working conditions of their products on site, solve problems in the system in time, and provide guidance and help for site maintenance personnel.
3. offline test
Offline test is also called “offline diagnosis”. It is a test and inspection of the CNC system itself after the CNC system is separated from the machine tool. The faults of the system can be further located through the off-line test, trying to minimize the range of faults. Such as: through the off-line test of the printed circuit board, the fault range can be located to a certain part of the printed circuit board or even a certain chip or device, which is very necessary for the repair of the printed circuit board. The off-line test of the CNC system requires special diagnostic software or a special test device, so it can only be carried out by the manufacturer of the CNC system or a special maintenance department.
With the development of computer technology, the offline diagnosis software of modern CNC is gradually integrating with CNC control software. Some systems have introduced “expert system” into fault diagnosis. With such software, the operator only needs to do some simple operations on the CRT/MDI.With a single session operation, you can diagnose the fault of the CNC system or machine tool.