Design and implementation of motion control system for plate cutting machine based on PLC

Li-xin TIAN

(Ⅰntelligence andⅠnformation Engineering College，Tangshan University，Tangshan 063020，China)

1 Introduction

In modern society，it often needs to cut plates into various shapes in engineering to meet different production requirements，so it needs all kinds of cutting equipments［1］．Plate cutting equipments are divided into two main categories:the metal cutting machine and the nonmetallic cutting machine．The metal cutting machine can be used in ship building，automobile，engineering machinery，boiler and other metal processing manufacturing occasions，while the nonmetallic cutting machine is mainly used in packaging design，clothing proofing，shoe sample making and so on．The core of the cutting equipment is the automatic control system and．At present，some of the cutting machine control systems mainly make the single chip microcomputer，ARM or DSP as the core of control［2-6］．The open CNC cutting machine system based on PC and motion controller has become one of the mainstreams in the automation industry．It integrates the information processing ability of the PC and the trajectory control ability of the motion controller［7-9］．But at present in our country the development of motion controllers is relatively backward．Some of the controllers have relatively weaker openness and extensibility．

PLCs as a kind of industrial control computer with high reliability，strong anti-interference ability and short development cycle are widely used in industrial control field．So in modern industry some cutting machines make PLC as the core of the automatic control system．The trajectory control system can be constructed by matured control components，such as programmable terminal，PLC，motion control unit and servo drive system［10］．Using this system the quality of workpiece，degree of automation of the machine and the operational performance can be greatly improved［10］．This type of control system has advantages of obvious economy and good practicability with broad market prospects［11］．

In this design，it makes the PLCas the control core of the plate cutting machine．It inputs all kinds of operation commands to the lower computer PLC by the touch screen which also displays the various operational parameters and data．PLC sends signal commands to the servo motors to drive the movements of each axis．The strokes of the two axes are limited by the position detecting sensors．The lifting position of the cutting torch is controlled by the position detection switches and the pressure relay．The control system can realize the automatic control mode and the manual control mode，meanwhile，the user can choose two kinds of cutting forms-flame cutting and plasma cutting．

2 Control system structure and function

The system consists of five major components:Mitsubishi FX2N series programmable controller PLC FX2N-32MR，F(xiàn)X2N-20GM positioning unit，GT1050-QBBD-Ctouch screen，ACservo motor and servo driver．As man-machine interface the touch screen realizes the upper computer control，parameters inputting and status displaying．The FX2N-32MR PLC is the core controller and the FX2N-20GM is used for controlling the two axes moving in coordination to realize the linear interpolation and the circular interpolation．The Servo motor is used to drive the two axes motion in the horizontal plane to complete arbitrary planar graph cutting．The hardware structure diagram of the cutting machine control system is shown in Fig．1．

Fig．1 Control System Hardware Structure Diagram

The control system requires a total of 10 inputs and 14 outputs．The I/O address allocation is shown in Table 1．

Table 1 I/OAddress Allocation

3 Software design of the control system

As the core of control system，PLC is mainly used for realizing the manual control and the automatic control．Automatic control involves programming for all kinds of cutting path to complete the corresponding cutting function．

3．1 Manual control program design

Manual control is mainly for system debugging of the installation of the production line in order to test whether all of the equipments can operate normally．When choose the manual cutting mode，pressing the manual button on the control panel will have the corresponding action．For example，when pressing the“torch up”button the rising electromagnetic valve of the torch is powered on and pressing the“work pressing”button then the work pressing electromagnetic valve is powered on and so on．The manual operation panel is shown in Fig．2．

Fig．2 Manual Operation Panel

3．2 Automatic control mode

After the system is powered on，in the automatic mode，the working starting point is defined artificially．The cutting gun is ignited at the defined origin point，and then it will work according to the select plasma or flame cutting mode and the graph cutting form．Fig．3 gives the programming flow chart of the automatic control mode．After the cutting form is chose，it will call the 20GM procedures，namely the VPSprogram，and then input the corresponding cutting parameters．PLC controls the cutting of the required trajectory according to the setting．After the cutting of the graphics trajectory，the cutting gun goes back to the original position．The control process of the triangle cutting is shown in Fig．4．

Fig．3 Flow Chart of the Automatic Control Mode

Fig．4 Flow chart of triangular cutting control process

The cutting patterns involve the triangular，quadrilateral，circular trajectory cutting and so on．Different locus needs different cutting parameters．The triangular cutting needs to set the side lengthL1，side lengthL2 and the angleβbetween the two sides，while the circular cutting requires inputting the parameter of radiusR．

4 Examples of application

In this paper，it make triangular cutting as the example to introduce the control process．The user can input the parameters by the touch screen which is shown in Fig．5，and the PLC calls the triangle data calculation procedures to calculate the required triangular trajectory parameters．

Fig．5 Triangular parameter inputting screen

The triangle data calculation program segment is shown in Fig．6．The input angleβand lengthL1 are converted into floating point numbers，and the angleβis changed to radian，then through the corresponding operation algorithm to obtain the height of the trianglehand the foot pointd．Converthanddinto the corresponding real numbers to form the vertex coordinates of the triangle which are given to VPS program of the positioning module 20 GM．The equations ofhanddare as follow．

h=L1*sinβ

d=L1*cosβ

Fig．6 Triangle data calculation procedures

After the choice of the cutting modes it calls the triangle VPSprocedures．The triangular data parameters including the second edgeL2 and the height of the trianglehwith the foot pointdare written into the corresponding storage units of the VPS．The corresponding program segment is shown in Fig．7．

Fig．7 Procedures of writing parameters and calling VPSfor a triangle

The Triangular VPSprogram is shown in Fig．8．The DRV command is used to realize the high-speed positioning．The setting value of the target coordinate location relative to theXaxis is specified by the(DD200)，in which DD200 is stored with the triangle side lengthL2．The operation speed ofXaxis is specified by the“fx”．LINE is the“l(fā)inear interpolation positioning”，which can make the two axesXandYmove to the target coordinate(x，y)along with a linear path．The“f”is the vector velocity．The coordinates of the two vertices of the cutting triangle are respectively(DD202，DD204)and(DD206，DD208)．Under the control function of PLC and the positioning module，the cutting machine can complete the cutting of the triangle of any shape according to the predetermined parameters．

5 Conclusions

The motion control system for cutting machine has adopted the control mode of PLC with the motion controller which has strong ability of resisting disturbance and high working stability．With the application of the servo control system it reduced the system motion error．In the system the locus of the cutting graphic was completed by the motion control unit and with this way it saved the algorithm programming of linear and circular interpolation for PLC．The system has the advantages of friendly interface and strong interactivity by using the touch screen as human-machine interface to realize the selection of arbitrary shapes，the inputting of various parameters and the displaying of the field operation data．The application of this control system for plate cutting machine can greatly improve the level of automation，the cutting precision and the work stability．

Acknowledgement

This paper is supported by Key Laboratory Project of Tangshan College(No．140080312)．

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