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J DESIGN OF AUTOMATIC PIPE PROFILE CUTTING MACHINE BY CNC CONTROL
THIET KE MAY CAT BifiN DANG 6 N G T U D O N G DIEU KHIEN CNC
Msc. Phan Huy Le, AssocProf.PhD. Bui Van Hanh
Department of Welding Engineering and Metal's Technology- School of Mechanical Engineering Hanoi University of Science and Technology
ABSTRACT
The manufacture of auto-lifred oilrig and the oil pipeline system in the petroleum refinery are important projects, occupying a large volume in Vietnam's industry. In such works, the process of making structural system from steel tube is mostly works. The tube cutting especially at the intersection of multiple tubes, is required to have accurate edges. It is important to have precision gap welding in progress of assembly welding after that. Manual cutting has the disadvantages such as low productivity, wide, inexactly gap welding, wasting welding metal, leading to increase stress, strain in the intersections of the tubes. The solution automatically CNC controlled cutting causes the increasing performance, beautiful cutting edge, steady gap welding. This report introduces the result of research, design automotive cutting system. It includes four sections; design calculation mechanical system, building equation of machine's orbital, design controller and control algorithms.
Keywords: CNC, Automatic pipe profile cutting, oilpipe, nut.
TOM TAT
Viec che tao chdn gidn khoan ddu khi vd cdc he thdng dudng ong ddn ddu, khi cda cdc nhd mdy Igc ddu dang la cdc cong trinh quan trgng, chiem khdi lugng ldn trong cong nghiep Viet Nam.
Trong cdc cong trinh do, viec che tao ket cdu he dng ddn td phoi thep dng chiem chu yeu. Viec cat cdc ong dd yeu cdu diit do chinh xdc cao nhdm ddm bdo khe hd hdp ly cho qud trinh hdn lap ghep he thong ong ve sau, ddc biet Id tai cdc nut giao nhau cda nhieu dng. PhUdng phdp cat thu cdng cd nhuac diem la cho ndng sudt thdp vd ddc biet Id khe hd hdn ldn ldm tang lUdng kim loai dip din den ldm tdng dng sudt vd bien dang tcii nut giao nhau cua cdc ong. Gidi phdp cat tU dgng dieu khien CNC cho ndng sudt cao vd mep cat dep, khe hd hdn dong deu. Bieu dd cho phep nhdn dudc mdi hdn cd chdt lUdng cao, it cong venh, hien dang Bdi bdo gidi thieu cdc ket qud nghien cdu tinh todn thiet kl mdy cat hien dang ong tU dgng dieu khien CNC ldm viec tqi hiin trudng Ndi dung bao gom cdc phdn; Tinh todn thiet kehe thong ddn dgng vd truyen dgng xdy diing phudng trinh quy diio cat cho mdy, thiet kehe thong dieu khien vd xdy dung thudt todn dieu khien.
Tii khoa: CNC, cat dng tU dgng ong ddn ddu, nut.
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1. INTRODUCTION
In fact, to cut pipes follow the intersection of two pipes before welding, there are many different ways classified two main types: cut manually or by machine. Commerciahzed pipe cutting machines are many different types such as large pipe cutter CNC controls, small cutter on the surface of the pipe follow fixed rails, equipment or tube beveling cutting ma- chining.... On the large mower, the cutter head has 3-axis motion and tubes rotate. However, the actual production requites to cut the tube to achieve high accuracy right on the site. To solve this demand, it is forced to use CNC cutting machines. Nevertheless, in Vietnam, the available CNC cutting machines are large, operate on the principle of rotating pipe dur- ing cutting and cutting machines are fixed in the workshop. The inconvenience of this kind of cutter is hard to induct and dismount tubes on the site. On the other hand, rotating the tubes, which have large site and volume (12 m length, diameter from 400 mm to 1000 mm, av- erage thickness 40 mm) requires a lot of energy.
From above analysis, the authors have proposed design solutions orbital cutter CNC pipe work at the site according to the principle of spinning tube cutter, tube fixes in the cutting process.
2. BUILDING SOLUTIONS
Through analyzing the existing design of the cutter, the authors have chosen the fol- lowing solutions:
• This machine is portable cutting machine, using plasma or acetylene-oxygen flame to be able to cut various metals, including nonferrous metals.
size, small volume (<20 kg), can be easily in- stalled on different diameter tubes, are fixed by the cable system.
• The machine is controlled automati- cally follow the orbital from intersection of two cylinders. Its model has two degrees of freedom: the first degree is spinning around the tube axis (the whole machine), the second - degree transfer along the straight-line parallels to axis of the tube (the cutting head). Head tilt angle is adjusted by hand before cutting.
This cutting machine has compact
Figure 1: System of cutting machine 2.1. Calculate and design mechanical transmission and body of machine
Mechanical structure of this machine include some main parts: (fig 2)
1- Main body;
2- Clusters of driver wheels;
3- Cable system;
4- Servo motor 1;
5- Cutting head;
6- Ball screw assemblies;
7- Servo motor 2.
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Figure 2: Mechanical structure of cutter Cluster of drive wheels performs the task of creating rotational motion around the tube. This cluster includes tooth belt driven, wave gear reducer and proactive textured wheel. The rotation around the tube axis is created by roll motion of proactive wheel on surface of tube.
Cable assembly is kept on the main body by the ringbolt. This cluster is responsible for keeping the machine on the surface of tube, creating pressure and friction force between wheel and tube.
Ball screw assembly performs linear motion along the axis of tube. This cluster includes the second servomotor, screw and cutting clamping. The cutting clamping is re- sponsible for fix cutting head on machine and adjusts the distance between the head and surface of tube.
2.2. Building equation of intersection of two cylinder
Figure 3: Coordinate system
General problem of two intersection cylinders is:
Considering two cylinders with axis is two overlap lines;
The angle between 2 center fine is (p;
The distance between 2 center line is 1^;
The first cylinder radius is R 1;
The second cylinder radius is R,;
In the decade coordinate Oxyz, cylinder equation is:
x^ + y-=R^
To facilitate the calculations, we switch to the cylindrical coordinate system. By trans- forming the coordinate system, it can be cho- sen equations of Tl cylinder in simple form;
The cylindrical coordinate system of T^
is Oxyz, so equation of T, in Oxyz is:
{
x = a y-R,.sin(^,) z = R|.cos(^i)The cylindrical coordinate system of T is OX|y|Z|, so equation of T^ in Ox^y^Zj is:
i
x = Rj.cos(^,) y-R..sin(6'.) z = ^Equation of T^ in Oxyz coordinate system can be obtained from equation of T^ in Ox y|Z| by moving coordinate system:
- Translating Ox^y^z^ along Oy: 1^^.
- Rotatmg OxjjZj an angle (p around Oy axis.
Meanwhile, the transfer matrix is' '^
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NGHIEN cufu - TRAO DOI
c o s ^ 0 s i n ^ 0 0 1 0 0 - s i n ^ 0 c o s ^ 0
0 0 0 1 1 0 0 0
0 1 0 /„
0 0 1 0 0 0 0 1 costp 0 s'mtp 0
0 1 0 7, - s i n ^ 0 cos^ 0
0 0 0 1 cos^ 0 sin ip 0
0 1 0 / , - s i n ^ 0 costp 0
0 0 0 1 ''R,cos(.e,f
^OxI^lzl
c o s ^ 0 sin Cf) 0 0 1 0 ;„
- s i n ^ 0 c o s ^ 0 0 0 0 1
R^sin{e,)
Equation of T, in Oxyz is
X = R, .cos (6j). Cos (<p)+ p. Sin ((p).
y=R,.'Sin (6,) +10
z=-R^ .sin (cp).cos (e2)+p.cos (9)
Intersection of two cylinders is root of equations;
R2 .cos(e,). cos((p)-if. sm((p)=a R,sm(e2) + lj=Ri.sm(ei)
-R. .sm((p).cos(9j>t^.cos(cp)=R,.cos(ei)
Root of above equations is:
1 |R:.co<ej I
a>i(ip) I =^/R'-R,=.air(9,>2J<,.ai<9JJ„4.V3il(ip) J 1 ;R-aa:(i)).co<6,) -j ccs:?) I = . / R ; - R ; - . S ! I I = ( 9 J - 2 J ? . . ai<9,)Vlo" J
|'R..sm(e.)H^ ]
^ ' R . ' I
^.arosi ;
~l ViVjR;'m'(6,>2J!.. aa;e,)tc4j' i ' R Conditions for root exist: R, + 1 < R,.
' V =R .siii(6,)=
• cotg(e,) [z =R,.oos(6,)= -R,.siii(i(i),cos(6,)+p.oos(i(i)
Transfer above equations to Decade co- ordinate system:
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1 rRjxxKce,) \
"^9) [±7R-,--R,=jiin-(ej>.2Jl,.sin(e.)J,-l„'ai)(ip) J y=Rj.siii(e,)tl,
z = ±^R,'-Rj^sin^(0, >.2Jlj.sin(ej).l,-lj=
With 6^ is a variable parameter in range 0 < 0^ <27t
Suppose the tube need be cut is T j, 9^ could be control parameter for the first servo motor:
So moving equation of the first degree of freedom:
e^=^-^Mag 'R,.sin(e,H
R;
^'-R,'A'(e,>2R.sm(9.).l„"V
With u is transmission ratio from first servomotor to proactive wheel.
So moving equation of the second degree of freedom:
1 j^Rj .006(6,) -j co6(9)[±^R,--R,-.s!n-(e;>2A,.siii(e,)J„4j-.sil(<p) J
Design control system Requirements:
The control system has function that drives movement of cutting machine during cutting process through servomotor Movement of machine includes two following motions:
- First motion: Motion of the whole machine around tube.
- Second motion: Motion of cutting head along axis of tube.
Both two motions are created and combined together to make relative motion between
cutting head and tube follow orbit was calculated. ' '
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paiameta
CoaaptAet 4 molioiis (kive]
card
pand
Control process as following algorithm diagram:
ConHmnncatioii droiit l-Sovomotor
z
Odver — nitatia]
[notion
Z-Savonwtor
H
Driv^ — t^m^tionmotioi
X
2- SovomotDi Tooth bdt
dnv'ea, wave gear
Rotabon of machine
TraosUtion of cutting head
Figure 4: Control system
The control system must perform two modes: automatic and manual. In automatic mode, cutting machine is automatically controlled by software on computer. The mo- tion parameter: rotation angle of machine and distance of cutting head, are calculated from input geometry parameters of two tubes. Input parameters include diameters D l , D2 of two tubes, angle and distance between two axes.
Through motion driver card, control signal pulse will be send to two ser\'omotors to control the cutting head sticking exactly orbit. This cutting process is done simultaneously in real and computer interface.
(^ Start ^
/
Infvt pararoetet^
Sohiog oibital equation
X
Choose staxtmg point of oibit to cut mm on cuttina pon-er Display oibit on the screen, export conool sipuJ, starting
Figure 5: Control algorithm diagram
In manual control mode, cutting machine will rotate and cutting head will translate along axis of tube when pressing and holding the moving button by hand. This mode is used when installing and adjusting the cutting head into right position. In this mode, each motion is independently controlled via buttons on software interface or manual control box.
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H 9, ^
Figure 6: Control interface
3.CONCLUSIONS:
The main content of this paper presents in the following contents:
- Provide design solution of potable tube cutting machine, bases on the theoretical basis about cutting profile of tube has been smdied: two cylinders with respective radius is R^, R^, overlap in space with angle (p and axis distance 1. Since then, calculate to find the intersection between the tubes. Equation will be build orbital motion of cutting head.
- Selection of structural mechanics and conduct body design, driver system ensures most compact structure. Total mass of this machine is less than 20 Kg. it uses precision actuators, compact as: ball screw system, wave gear reducer to ensure accuracy edge.
- Choose the design solution and control system based on the center console is com puter, driver system using servomotors and motion driver card. This is optimal design solution for high accuracy motions.
- Develop algorithms and control software written in C language and combine with OpenGL library. •
Ngay nhan bai: 16/7/2014 Ngay phan bien: 17/8/2014 References:
[1]. Pham Cong Ngo (2005), Automatic control theory Science and Technology Publishing House [2]. Trinh Chat, Le Van Uyen (2001), Mechanical transmission design guidlines. Science and Technology Publishing House.
[3].http://www.hiwin.com/html/!inear%20stages/index.htmLRetrievedfromhttp://www.hiwin.com.
[4]. http://www.koike.com/MachLnes/Machine.aspx?MachineID-44I(2010), Retrieved from http://www, koike.com/.
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