WANG Bing-qiang LI Jin-wei

(1.Mechanical&Electrical College,Qingdao University,Qingdao Shandong 266071,China

0 Introduction

The CNC cutting machine is through digital program to drive the machine movement,and carrying flame cutting system.It’s using CNC system to control the switch of the flame cutting system,and cutting steel and other metal materials.This mechanical cutting equipment is named CNC flame cutting machine[1].The X-axis cantilever of traditional CNC cutting machine is fixed with the cutting head,and then the cutting head must be driven by the moving of the cantilever when people use the machine,this method increasing the space occupied by the X-axis direction.This design want to separate cutting head and the cantilever,when people need the X-axis to machine,only need to move the cutting head on it,saving space needed for the actual production,improve production efficiency.

1 Select Transmission Component

Commonly used in mechanical transmission components include rack and pinion drive,belt drive,high-speed belt drive and various nonlinear transmission components.Since the mechanical transmission components can significantly affect the servo characteristic of servo drive system,particularly transmission style,transmission mode,transmission flexibility and stability have a significant impact on system accuracy,stability and reaction efficiency[2].Therefore,we should choose the moving parts which have few transmission space,small size,high accuracy,low mass and movement stability.According to the requirements of this design,we compared for performance between the gear,pulley,lever mechanism,a link mechanism,cam mechanism,worm,chain,and screw nut.Eventually we decided to adopt screw nut.Screw nut mechanism can be divided into sliding and rolling friction.Since the ball screw nut mechanism,although the structure is complicated,the manufacturing cost is relatively large,but because the advantages of the movement it has been widely applied.

In summary,this design eventually chose rolling screw nut as mechanical transmission components.Compared with other screw nut,Ball has the following advantages：high transmission efficiency,precise positioning,fast response,long life,and easy to operate.

2 Servo system selection

Servo system is an automatic control system which controls the position and speed of CNC machine moving parts(such as tables,spindle or tool,etc.),is the executive body of numerical control system[3].Servo system accepts motion commands which are exported by computer,and converts it to mechanical movement of moving parts.

According to the control mode,the servo system can be divided into the open-loop system,semi-closed loop system,and the closed-loop system.Open-loop system,only have the forward path without a feedback loop,the CNC device directly controls the rotation of the motor,the most typical is the stepper motor servo system.Closed-loop systems typically control DC servo motor or AC servo motor as objects.The results of the closed-loop system can affect the value of the input variables,the actual value constant close to expectations by constantly comparing.Semiclosed loop interposed between the open-loop system and the closedloop system.

Through comparing the principle of the three servo systems we can find that accuracy of open-loop system is too low and cost of closed-loop system is too high.So we choose semi-closed loop system which let AC servo motor as the drive and pulse encoder as feedback device with considering the price of the equipment,the principle as shown in Figure 1.

3 Design guide

The function of the machine guide is guide and support,which is to ensure the moving part can have a certain direction under the action of an external force (the weight of the moving part itself,the weight of the part,the cutting force and traction,etc.)[4].In the guide rail,it called movable rail when the rail is fixed with the moving part into one part,and the other side which is fixed with the support member into one called the support rail.The movable rail just has one DOF with respect to the support rail.The guide should meet the basic requirements which main including guiding precision,stiffness,wear resistance,low-speed stability,reasonable structure and so on.Through considering the purpose of the design and rail requirements,we have finished the design to the rails of the three axes.

X-axis chose dovetail guide,the structure as shown in Figure 2.

4 Conclusions

The completion of a machine’s overall design is a complex project；we need to consider many factors.Our design have solved some problems of traditional CNC cutting machine,but because we have the ability to limit,the CNC machine still have some shortcomings which need to further improvements and enhancements.

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