Improvement of control system for CNC machine tool lubrication system
The design, commissioning and maintenance of the machine tool lubrication system play an important role in improving the machining accuracy of the machine tool and prolonging the service life of the machine tool. However, in the electrical control of the lubrication system, the following problems still exist: First, the monitoring of the working state of the lubrication system. In the CNC machine tool control system, only the oil level monitoring of the fuel tank is generally provided to prevent the shortage of oil supply, and the oil leakage and oil circuit blockage which are easy to occur in the lubrication system cannot respond in time. Second, the set lubrication cycle and the oil supply time are single, which is easy to cause waste. The amount of lubricant required for a CNC machine tool is different under different working conditions. For example, during the machine pause phase, the amount of lubricant required is less than that required during the machining phase. In view of the above situation, in the electric control system of CNC machine tool, the lubrication control part has been improved and the working condition of the lubrication system is monitored at all times to ensure that the mechanical parts of the machine tool are well lubricated, and can also be automatically adjusted according to the working state of the machine tool. Oil, cycle time to save oil.
Monitoring of the working state of the lubrication system
In the lubrication system, in addition to the oil consumption, the fuel tank oil is too small, so that the lubrication system is insufficiently supplied with oil. Common failures include oil pump failure, oil supply line blockage, shunt operation abnormality, and serious oil leakage. Therefore, the following detection device is provided in the lubrication system for monitoring the working state of the lubrication pump to prevent the machine tool from working in an oil-deficient state, which affects the performance and service life of the machine tool.
Overload detection uses an overload protection component in the lubrication circuit of the lubrication pump and uses its thermal overload contact as an input signal to the PMC system. Once the lubrication pump is overloaded, the PMC system can detect and process it, causing the machine to stop running immediately.
The oil level detection lubricant is a consumable item. Therefore, after the machine is working for a period of time, the lubricating oil in the lubrication pump tank will gradually decrease. If the operator does not add it in time, when the oil in the tank reaches the minimum oil level, the oil level detection switch will act and send this signal to the PMC system for processing.
The pressure sensing machine uses a progressive centralized lubrication system that ensures a predetermined lubricant for each lubrication point as long as the system is working properly. Once the lubrication pump itself is not working properly, fails, or there is a situation in the oil supply circuit where the oil supply line is blocked or leaking, the pressure in the system will be abnormal. According to this feature, the pressure detection switch is installed at the outlet of the lubrication pump during design, and the switch signal is input into the PMC system. After each lubrication pump operation, the pressure in the system is checked. Once an abnormality is found, the machine tool is stopped immediately and generated. Alarm.
Control of lubrication time and lubrication times
In order to reduce the wear of the machine tool pair, it is necessary to maintain a proper clean lubricating oil film on the surface of the moving pair, that is, to maintain a constant supply of oil between the friction surfaces to form an oil film. However, when the amount of lubricating oil required for the CNC machine tool pair is not too much, it is neither economic nor reasonable to use the continuous oil supply method. Because excessive oil supply and fuel supply are equally harmful, additional heat, pollution and waste are generated. Therefore, the lubrication system uses a regular, quantitative cycle of work.
The centralized lubrication system itself can be configured with a microprocessor that is specifically designed to set the time at which the lubrication pump is stopped and the time of each fuel supply to control the lubrication pump gap. Designers often use this to simplify their PMC procedures.
However, when the machine tool is in different working conditions, such as the initial working phase of power-on, the machining operation, and the machine is suspended due to adjustment and inspection of the workpiece, the demand for lubricating oil varies from machine tool to machine. In the machine tool with FANUC control system, the amount of lubricant supplied is usually adjusted by controlling the working time of the lubrication pump. However, it is customary to consider the oil supply mode of the lubrication system under the processing state of the machine tool, without considering other working conditions. In this way, when the machine is in other working conditions, the amount of lubricant supplied by the lubrication system is either insufficient or too much.
The amount of lubricant required for the machine guide can be approximated by the following formula: (length + travel stroke) × width × K. It can be seen from the formula that the amount of lubricant required for the machine guide rail is related to the distance of movement of the shaft on the guide rail. The numerical control systems produced in Europe and the United States are mostly based on the stroke volume to control the lubrication pump work, the clearance oil supply, and provide corresponding parameters in the system, which is convenient for the machine tool manufacturer to electrically control the lubrication pump through the PMC program. In the FANUC 0i system, there is no similar control method. In order to control the lubrication pump by using the approximate oil supply method on the CNC machine equipped with FANUC 0i, we have improved the electrical design of the lubrication control part so that the control system can be based on the machine tool. The specific working conditions automatically adjust the working frequency of the lubrication pump and the working time of each time, and appropriately reduce the oil supply amount when the machine is suspended, and the machine tool is appropriately increased during the initial work.
The working state of the lubrication pump is now divided into three categories, and the working time and frequency of the lubrication pump are set separately.
At the initial stage of starting the machine, the machine starts to work, and the lubrication pump starts working immediately. The oil supply is continuously supplied for a period of time. At this time, the working time T1 of the lubrication pump is longer than that under normal conditions, so as to provide sufficient lubricating oil in a short time to form a rapid guide on the machine tool rail. A layer of oil film. Lubrication pump run time is set by the TMRB command in the PMC program. Unlike the TMR command, the time set by the TMRB cannot be modified by the user.
After the machine is turned on during the machining operation phase, after the preloading of the no-load operation, it enters a stable working state. Thereafter, the control system controls the lubrication pump to work intermittently to ensure that the machine guide rails are regularly and quantitatively lubricated. The time each time the lubrication pump is operated and the time it is stopped are set by the TMR command in the PMC program. The time parameters set by TMR can be adjusted as needed by the user in the PMC data window.
When the workpiece is to be processed or processed in the pause phase, the machine tool is often in a suspended state, and the demand for lubricating oil is correspondingly reduced. Therefore, it is necessary to adjust the control mode in time to appropriately extend the time when the lubrication pump stops working to reduce its working frequency and thus reduce Oil consumption. The key to implementation is how the system knows when the machine is in a paused state. The FANUC 0i CNC system provides signals MVX (F102.0), MVY (F102.1), and MVZ (F102.3) to reflect the movement status of each axis of the machine. If the signal status is "0", it indicates that the corresponding machine axis is stationary. If all the moving axes are stationary, the machine is in the pause state. Therefore, as long as all the above signal states are "0", the PMC program automatically changes the lubrication pump operation and stop time by design. At this time, the time T2 of the lubrication pump operation and the time T3 of the stop are both set using the TMRB command. Similarly, the user cannot arbitrarily modify the two time parameters.
Lubrication alarm signal processing
Pressure Abnormality The lubrication system in CNC machine tools is an intermittent oil supply mode. Therefore, the pressure in the lubrication system is checked periodically, that is, after each operation of the lubrication pump. If there is a fault, such as oil leakage, oil pump failure, oil circuit blockage, the pressure in the lubrication system will suddenly drop or rise. At this time, the machine should be forced to stop running and check to avoid the situation.
The oil surface is too low. The customary treatment method is to classify the “oil level too low†signal and the “pressure abnormality†alarm signal as an emergency stop signal. Once the PMC system receives the above signals, the machine immediately enters an emergency stop state and the servo system is powered off. However, unlike the case where the lubrication system is "pressure abnormal" due to oil blockage or oil leakage, if the oil in the lubrication pump tank is not enough, the performance of the machine tool will not be affected for a short time, and the machine tool does not need to be stopped immediately. However, after this phenomenon occurs, the control system should display the corresponding information in time to remind the operator to add lubricant in time. If the operator does not replenish within the specified time, the system will control the machine to immediately enter the pause state. Only when the lubricating oil is replenished in time, the operator is allowed to run the machine and continue the interrupted work. For “low oil level†signals, this treatment can avoid unnecessary downtime and reduce auxiliary machining time, especially when machining large molds. At the time of design, we classify the “oil level too low†signal as the “feed pause†signal of the electric control system, and adopt the alarm handling method of “reminder——warning-pause, prohibit automatic operationâ€. Once there is too little oil in the fuel tank, not only the red indicator light is displayed on the operation panel, but also a warning message is displayed on the screen to remind the operator. If the signal does not disappear within the specified time, let the machine quickly enter the feed hold state, then suspend the machine for any automatic operation. After the operator adds enough lubricating oil to the fuel tank, he only needs to press the “Cycle Start†button to release the state and let the machine continue to suspend the machining operation.
Conclusion
In the process of designing the electrical control of CNC machine tools, if the treatment of the lubrication system is neglected, it is very important for the user of the machine tool whether the various parts of the machine tool can be quantitatively lubricated regularly. The design of the product should be continuously improved and improved, the number of failures of the machine tool should be reduced, and the reliability of the product should be improved.
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