CNC equipment is a technology-intensive and knowledge-intensive machine and electricity integration product. Its advanced technology, complex structure, and high price, along with the continuous expansion of the scale of production enterprises and the continuous improvement of the degree of automation of equipment, CNC used in CNC workshops. Equipment types and quantities are also increasing. To make better use of CNC machine tools, you must have a full understanding of the structure, function and system of CNC machine tools. CNC machine tool motion control is usually implemented in two ways: one is controlled by digital information of the CNC system (dedicated computer), that is, "digital control", such as the front, rear, left, and right movement of the CNC machine tool table, The headstock moves up and down, and the amount of rotational movement around a linear axis, etc. These controls are achieved by controlling the servo feed motor using the difference obtained by comparing the calculated theoretical position with the actual feedback position. The core of this kind of control is to ensure that the contour of the machined part is realized. That is, in addition to point processing, the movement moment of each axis must maintain a strict proportional relationship; the other is in the CNC machine tool operation process, with the CNC system internal and The conditions of the switch signals, sensors, buttons, relays, etc. on the machine tool are the conditions, and according to a predetermined logic sequence, such as spindle start and stop, commutation, tool replacement, workpiece clamping, and loosening. Hydraulic, cooling, lubrication system operation control. The control of this type of action is mainly the sequential control of the binary signal, which is generally accomplished by the PLC.
1 Application of PLC Program on CNC Machine Tools
PLC is a programmable controller. The PLC used on CNC machine tools is also called PMC. It has the following advantages: Fast response. High control accuracy, good reliability, control program can be changed with different applications, and the interface with the computer and easy maintenance. In general, PLC programs used on CNC machine tools include system programs and user programs. The system program includes monitoring program, compiler program and diagnostic program, etc., provided by the PLC manufacturer, and solidified in the EPROM, the user can not directly access, and does not require user intervention. The Libya user program is an application program compiled by the PLC program language according to the needs of on-site control to achieve various control requirements. The commonly used PLC programming languages mainly include trapezoidal frames, statement tables, and function block diagrams.
Because many actuators of CNC machine tools are controlled by PLC control commands, PLC can be used to quickly detect and repair CNC machine tools, or modify and write PLC programs to add an executable action to CNC machine tools. Or function.
2 Safety Control Design of CNC Machine Tools
In the process of using CNC machine tools, the authors found that: some systems of machine tools in the improper operation or failure due to the machine itself, the alarm shutdown, need to eliminate the alarm and return to the HOME point to perform the program again, but some system of the machine after the elimination of the alarm You do not need to return to the HOME point to run the program again. Although the latter saves a little time, there are great security risks. A company has a CNC machining center has such a situation: a certain time the execution of the air run, generated a machine alarm to stop, the operator did not return to the HMOE point after eliminating the alarm to run the empty running program again, so that the spindle collided with the fixture As a result, the accuracy of the spindle and the balance of the dynamics are poor, and the process requirements of the equipment cannot be satisfied. Analysis of the reasons: When the machine tool stops running after the alarm, the position status of the machine fixture and the spindle has changed (it is no longer the initial state). If the alarm is immediately resumed after the elimination of the alarm, it will easily lead to the spindle of the machine tool. Malfunction caused the spindle to collide with the fixture or workpiece. In order to avoid unnecessary waste due to collisions. To further improve the equipment's ability to prevent mistakes, the author designed a safety control program for CNC machine tool movements for the FUNUC System Machining Center. The main purpose of this program is to ensure that a machine shutdown alarm occurs during the execution of a machining program or air running program. After the operator clears the alarm, it must execute the procedure of returning to the reference point. If the reference point program is not executed and the program, fixture, spindle, and tool of the device are restored to the initial position, the machine tool cannot execute the machining program or idle operation program. Effectively avoid the possibility of equipment collision.
2.1 Design Ideas
To increase the error prevention function of the machine tool to achieve the safety control of the machine tool movement is to modify the PMC program of the CNC machine tool and the condition of the automatic operation of the machine tool, increase the limitation of the machine start condition, and add the cycle start ready indicator on the operation panel (STEN- L), REUTLT indicator and return button. The specific plan is:
(1) Machine start conditions set: The 1x, y, and z axes must go back to the second reference point and the A axis is at 90. State (STA-ENI); 2 The tool on the spindle is the initial tool (T6) or the empty tool (T14) (STA-EN2); the 3A axis is in the clamped state (STA-EN3); 4 the fixture is released ( STA-EN4). The machine tool must satisfy these 4 conditions at the same time to be able to carry out the processing procedure to carry on automatic processing (STA-EN). The purpose of designing this restriction condition is to enable the machine tool to run the RETURN program after the alarm occurs. After the standby bed is restored to the normal operation state, the machine tool can be operated in the AUTO or MEM mode to prevent the program from starting from the intermediate state and cause the machine tool. collision.
(2) If the start condition is not satisfied and the cycle start ready indicator is off, press the [CYCLE START] button, and the machine will generate an alarm “61.0 CYCLE START NOT REDAY, PLEASERETURN!” to remind the operator that the machine tool is forbidden. The cause of automatic processing and the measures that should be taken.
(3) When a work piece needs to be repaired, it may only need to execute a specific program segment. At this time, you can take over the repair button. After the repair indicator is on, you can process the returned work piece. In the rework or single-segment processing mode, the equipment is not limited by the "Cycle Start Ready" condition and can be cycled.
2.2 Ladder Diagram Design
According to the previous design idea, the P110 subroutine is added to the PMC program of the CNC machine tool to generate R2.7 (STS-A); the cycle indicator is ready for the signal output point Y5.1, and the repair key signal input point is X4. 6, repair signal output point is Y4.6. The corresponding ladder diagram is shown in Figure 1.
3 Conclusion
CNC machine tool is a machine and electric integration product that integrates computer technology, PLC technology, and automation technology. As the core of the CNC machine tool, the control system is directly related to the normal operation of the equipment. The powerful function of the CNC machine tool PLC can make full use of the CNC machine tool. The role of the control system can also bring great convenience to the fault diagnosis and maintenance of CNC machine tools. The safety control function designed by the author to prevent the machine from colliding with the machining center effectively eliminates the hidden danger that the machine tool spindle collides with the fixtures and workpieces due to the operator's mistakes, ensures the safety of production, and has good economic benefits.
