張一鳴，宋曉梅

沈陽大學機械工程學院，沈陽 110044

1．Introduction

Nowadays the competitions between nations are very drastic，and one of the most important indexes to measure modern mechanical manufacturing level in one country is NCrate．The developed countries have already surpassed 20%in 1980s［1-2］，and by an astounding 47% in old capitalist countries such as German and USA，according to census date there is only 16．5%in China 2010，so there brooks no further delay to reforming universal lathe，meanwhile it’s one of the major methods to raise the rate of NC．There has been 20 years for NC reform in China，not only it has got plenty of experience，but also leaves a lot of detours［3］．The reason why it fails mainly is that the process is not perfect in CNCreform，and the method is excessively simple［4］．For example，there has not replaced in aging components or destroyed in stability of universal lathe，and the critical parts on lathe probably get unreasonable reform or selection，unreasonable design of interface circuit and so on．Nowadays NCreform on universal lathe is mainly limited to medium and small size lathe and milling machine，It gives little attention to a lot of CA6140 universal lathe in market［5］．Based on the background mentioned above，the solution of NC reform such as CA6140 has been deeply explored in this paper，and the selected reform solution has been also implemented．

2．Implementation scheme of CA6140 NC reform

The process flow of CA6140 universal lathe in NC reform is shown in Fig．1，and the general planning of NC reform on CA6140 universal lathe is shown in Fig．2．

NC reform is divided into two parts．The first is used for repairing，replacing，fixing the mechanical components，and adjusting the basic parts so as to recover and improve the accuracy and performance．For example，it mainly improves the geometrical accuracy of the lathe and rotary accuracy of the spindle etc．The second is used for installing the NCsystem，and turning the universal lathe into the CNC lathe．

Fig．1 Process flow of NC reform

Fig．2 General planning structure

3．The NC reform for CA6140

3．1．Transformation and design on longitudinal，transverse feeding system

The structure of longitudinal and transverse feeding system is shown in Fig．3．The feeding system receives orders from NC system，to drive the tools which locates accurately on the rest or moves relatively according to the prescribed trajectory，so the accuracy must meet the need of the feeding system．To select longitudinal，transverse ball screw via the calculation including strength，efficiency，rigidity etc，the cost is under consideration as well，and then select ball screw made in Hanjiang guide screw factory，to select longitudinal，transverse servo motor via the calculation including rotational inertia，the maximum static torque，frequency etc，to select plum coupling via the calculation once again，so it not only ensures the high accuracy and low cost，but also avoids the lost of torque efficiently，and meantime it can meet the high demand of lathe automation．

Fig．3 Structure of longitudinal and transverse device

3．2．Reform and design on machine guide

Firstly，the long-time used slide-way on lathe，it has not only the obvious wear and scratch track，but even more lumpy surface on the lathe，and it is easy to creep and distortion on feed movement．In this case，in order to recover the accuracy of slide-way on lathe，to reduce the friction and to increase the wear resistance，to improve the stability of lathe，to prevent the creeping and the ability of absorbing the shock on lathe，it takes the cost of factor under consideration，and uses the PTFE based soft belt to reform the universal lathe so as to recover the design size of the slide-way．Secondly，for the short-time used lathe，the wear is not serious or the error related to small design size，it is general to give a coating treatment，and the conventional methods are plastic coating and metallic coating．

3．3．Reform and design on main drive system

The cost and overall structure is under consideration，and the main drive system is nearly unchanged which retains the spindle motor and manual transmission，and it separates the main movement and feeding movement after the NC reform is finished．The main feed system is still adopted the original motor，and it must install an encoder for threading，so there must have a rotary encoder，information transfer system to realize the work piece turning a bout via NC system—actuator—servo motor—encoder—spindle， and the kinematic relationship of tools feeds a helical pitch．Based on helical pitch of longitudinal，transverse ball screw and the maximum speed，it chooses F5815C-1024BM-L5003MN132M-4 rotary photoelectric encoder made in Wuxi Ge-en technology co． Ltd．Based on the specific transmission structure of headstock，it is convenient to assemble and retain the original structure，the encoder adopts the way of different spindle coupling，it can make not only the encoder spindle and main spindle drive under the rate of 1:1，but also retain the original structure of the lathe，and the spindle hole can still be used．

3．4．Reform and design on the components of automatic circular cutter holder

According to the needs，it must remove the original manual tool rest，and install four station tetragonal tool rests controlled by NCsystem of high and reliable performance．According to the height of spindle and the model of lathe，to select SWD120 four station tetragonal tool rests，it takes advantage of system inset stationary PLC so as to control the roll of motor，and consequently control the movement of tool rests．

3．5．Selection of NC control mode

Based on the drive mode of servo drive，the selection of NC reform can be divided into three types，namely the open-loop control，half-closed loop control and closed loop control．According to the design task and general design scheme，half-closed loop control should be used．It is not only economic and easy to reform，but also it can meet the precision requirement．

3．6．Selection of NC system

The most important part of NC reform is to select the type of NC Device．After the NC reform is finished，the performance and reliability of lathe can only be relied on it．This paper bases on the sequence of selecting NC system，that is to select the grade first，the manufactures second，and finally select models． After all aspects considered， it selects GSK980TA2 universal lathe economic NC system made in GSK Co．，Ltd．This system not only adopts 32-bit embedded CPU and large scale device FPGA in PLC，but also it is compatible with Japanese FANUC system．It has vast majority functions，and it is almost the same as the universal NC system，such as hand wheel，figure tracking and simulation，analog output of spindle，servo spindle etc．

4．Interface definition of NC system

The NC system GSk980TA2 has 24 ways switch input via photoelectric isolation，3 ways relay normally open contact output，12 ways relay power drive output，4 ways differential output，single way hand wheel input，single way encoder input，single way analog quantity(8 bit)output，and a RS232 string mouth．General wiring diagram is shown in Fig．4，and the definitions are as follows．

Fig．4 General wiring diagram

IS30:X-axis，15 cores D-type-hole socket，couple to X-axis drive

IS31:Z-axis，15 cores D-type-hole socket，couple to Z-axis drive

IS32:encoder，15 cores D-type-hole socket，couple to encoder on spindle

IS36:communication，9 cores D-type-hole socket，couple to PC RS232 interface

IS37:frequency transformer，9 cores D-typehole socket

IS38:hand wheel，9 cores D-type-hole socket，couple to hand wheel

IS39:output1，25 cores D-type-hole socket，interface which is CNC signals output to lathe．

IS40:input1，25 cores D-type-hole socket，CNC interface which receives signals from lathe

IS41:input2，25 cores D-type-hole socket，expansion interface which is input signals

IS42:output2，25 cores D-type-hole socket，expansion interface which is output signals．

5．Conclusions

The above explored the method of the implementation scheme and procedures of NC reform on CA6140 universal lathe．Based on the results of the NC reform，the stability and accuracy of lathe has been increased dramatically，so it can be said the NC reform is successful．

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