PLC Appalication for CNC Machines
In recent years, PLC is widely used in the field of industrial automation and control,it is in the control performance,machine cycle and hardware costs and other aspects showing the comprehensive advantages much better than other industrial products.With the development of PLC technology,it is widely used in the position control,process control,data processing and other aspects application.In the actual design and production process of the machine tool,in order to improve the precision of CNC machine tool processing,the choice of its positioning control device is particularly important.ECON series PLC NC positioning function more accurate than other PLC,and the program design and debugging is very convenient.This paper puts forward how to use the NC positioning control of ECON PLC to realize the control function of machine numerical control system to meet the control requirements.
Second,the composition of CNC machine tools and work process
This machine consists of input and output devices,numerical control devices,programmable controllers,servo systems,detection
feedback devices and machine tools and other components.The input device can transfer different processing information to the computer.In the early days of CNC machine tools,the input device is the perforated tape,now it becomes out;at present,the use of the keyboard, disk, etc.,greatly facilitate the information input work.Output refers to the output of the internal operating parameters(including the normal machine,the ideal working conditions of the original parameters,fault diagnosis parameters,etc.),generally,the machine starting work need to output these parameters for recording and preservation,after a period of time,then the output compare with the original Data,can help to determine whether the machine maintain normal work.CNC device is the core of CNC machine tools and leader,deal with and calculate all the processing data,and ultimately the NC machine tool functions of the command work.It contains microcomputer circuit,a variety of interface circuits,CRT monitors and other hardware and the corresponding software.Programmable controller control the spindle unit,deal with the program speed command to control the spindle speed;manage tool library,control automatic tool exchange,knife choosing mode,the cumulative number of tools used,the remaining life of the tool and the number of tool grinding;control the spindle CW&CCW,stopping,quasi-stop,cutting fluid switch,chuck clamping
release,robot handle knife and other actions;also control the machine external switch (limit switch, pressure switch, temperature control switch,etc.) ;control the output signal (magazine,manipulator,rotary table,etc.).The detection feedback device consists of the detection element and the corresponding circuit,mainly to detect the speed and displacement,and feedback information to the numerical control device to achieve closed-loop control to ensure the accuracy of CNC machine tools.
CNC machining preparation process is more complex,more content,including the structural understanding of the parts,process
analysis,process plan development,processing procedures,selection of tools and using methods.Machine adjustment mainly includes the tool naming,transferred to the magazine,workpiece installation,tool setting,measure tool position,machine parts status and other works.Program debugging is mainly to check and adjust the logic of the program itself and its design rationality.Test processing is dynamic inspection of components processing design,and the whole process are required to achieve the results of the previous step and after evaluation of the next step.After the success of the test,the parts can be processed and test the finished parts.Previously three steps are standby time,in order to improve work efficiency,the shorter standby time the better,more conducive for the rational use of machine tools.This indicator directly affects the evaluation of machine utilization (ie, machine speed).
Third,the machine numerical control system needs to solve several problems
Machine tool is composed of mechanical and electrical components,in the design of the overall program should be considered
from the electromechanical aspects of the implementation of various functions of the machine program,CNC machine tools and
CNC system functions are very complex,so good mechanical and electrical communication,will avoid weaknesses.The Machine
control system workpiece selection,assembly,programming and operation should be much reasonable,accuracy and stability must
meet the requirements.At the same time for the convenience of debugging and maintenance,each operation set manual function,
such as manual each axis speed movement,spindle high and low speed rotation,cutting fluid and lubrication switch.PLC in accordance with the logical conditions to do order action or in accordance with the timing action,in addition to the order,timing has nothing to do in accordance with the logical relationship between the interlock protection action control,PLC has become a replacement of relay line and main product of order control.It is very common in electrical control applications.
How to improve the positioning speed in the actual control and ensure positioning accuracy is a need to seriously consider and effectively solve the problem.Accuracy is a performance factor that the machine must guarantee.The position accuracy of the position servo control system determines the machining precision of CNC machine tools at a great extent.So the position accuracy is an extremely important indicator.
In order to ensure that there is sufficient accuracy of the location, on the one hand is correct to choose open-loop magnification size
of the system ,on the other hand is to require the accuracy of the location detection component.Because the error in the detection element itself is very difficult to distinguish from the deviation of the detected element in the closed-loop control system,the accuracy of the feedback detection element often plays a decisive role in the accuracy of the system.High-precision control system must have high-precision detection components as a guarantee.When the site conditions change,some control parameters of the system should make the appropriate changes,in order to meet continuos production,requiring changes to the control system variable parameters should be carried out online.
Although the use of programmer can quickly and easily change the original setting parameters,but the programmer generally can not give to site operators to use.Therefore,should consider the development of other simple and effective way to achieve PLC variable control parameters of the online changing.Also in order to prevent the voltage is too high to damage the PLC,power input side with a varistor.
In order to prevent overheating,PLC is not allowed to install to the directly avbove of the transformer and other heating
components,and PLC and servo drive maintain a certain distance to the inverter.Leaving an appropriate gap between the components
for heat dissipation and install the fan cooling on the distribution box.In addition,in order to ensure the safety and stability of the control system operation,also need to solve the control system security issues,such as the system travel protection,automatic detection of fault components and so on.
China is a widely machine tool production and application country ,but the level of application of CNC technology is not high,seriously restricting the improvement of China's manufacturing industry.Internationally related development plans presents a serious challenge for China's development of CNC technology,but also brought opportunity.Only select the appropriate PLC to achieve ideal positioning effect.
As a result of the PLC control,so that improve electrical part anti-interference ability,improve operation reliability of the machine,thus increasing the flexibility of the equipment,and improve the equipment using efficiency.