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SciVerse ScienceDirect
Energy Procedía 14 (2012) 931 - 936
Energy
Procedía
Conference Title
Design and Realization of 3-DOF Welding Manipulator Control System Based on Motion Controller
LI Ru-xionga a*
Department of Mechanical and Electrical, Jingdezhen Ceramic Institute, Jingdezhen, 333403, China
Abstract
Using the hardware of motion controller, IPC , stepping motor system and so on , we develop a kind of plane curve welder. The welder adopt DLL of windows and multithreading software development technique, so it can meet the needs of plane curve weld bead, further more, software system of plane curve welder use modular design, some module are of generality. AutoCAD VBA software package use point-by-point comparison method, which guaranteed welding gun keeping superposition with normal of welding curve in welding process. Practice has proved, this system realize accuracy controlling of welding-torch position and gesture in the whole welding process.
© 2011 Published by Elsevier Ltd Selection and/or peer-review under responsibility of the organizing committee of2nd International Conference on Advances in Eneigy Engineering (ICAEE).
Keywords: welding process; manipulator; plane curve welder
1. Introduction
Along with fast development of automation techniques that pushes welding technique forward effectively. There are more and more variables involved in welding system, such as complex physical chemistry of process welding metallurgy changing, fram and realize the reasonable process flows, welding stability, practical flexibility, operational security, optimal design and economics etc. Using modern automatic control technology, such as open loop and closed loop control, it is conveniently to obtain high quality weld seam[It.
In auto parts, hardware processing industry, domestic appliance and decoration gift industry, plane curve weldment become more and more. For the production needs, such as traditional hand-operation, not only has low productivity effect, bur also can't meet the consistent needs of product quality; to single product, special welder can satisfy the demand of high productivity effect and better welding quality, but to multi-type and small batch production, it is obvious improper to design a special type of welder for each production. Although welding robot can measure the needs of multi-type, small batch, multiple-stage manufacture and welding quality consistency, to majority small and middle-sized enterprise, huge
* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . E-mail address: author@institute.xxx .
1876-6102 © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the organizing committee of 2nd International
Conference on Advances in Energy Engineering (ICAEE).
doi:10.1016/j.egypro.2011.12.887
one-time investment and expensive maintenance costs hinder popularization and application of welding robot. To commendably meet this kind of demand, this topic develops a three degree of freedom welding manipulator [2-5].
2. Structure design of welding manipulator
2.1. Precise X-Ymotion table
To finish plane curve welding, welder needs three degrees of freedom, among them, two are linear motion (X and Y direction), one is rotate motion (angle 6 ). This topic use precise X-Y motion table to realize X-Y plane position control, which realize automatic welding in the X-Y plane. Generally, precise X-Y motion table take linear rolling guide as guiding mechanism and ball screw as motion actuator. Mechanism hardware mainly includes worktable, torch grip mechanism, beam, guide, fixture, etc. Figure 1 is the mechanism schematic diagram of plane curve weld. When it works, motion controller will send signal to drive step motor X and Y, so guide X and Y were derived that realize the X-Y plane motion, and so on, according to the pulse signal from the software system, angle control step motor Z will rotate corresponding angle. The composite motion of those three step motors realize the accurate control of seam track and torch gesture.
Tn order to prevent splash from pollution the guide, design a suspended structure curved beam with " L- " shape (shown as fig.3), guide was arranged on the upper side of the mechanism, the clamp mechanism and torch were arranged underside, just shown as figure 2. For the sake of quick calculation, the tip torch was designed to coincide with the slide middle point of those two linear guides, the torch rotate angle is equal to the two linear angle, that makes the synthesis curve path of X-Y plane equal to the trajectory of tip torch , this design avoid the complicated matrix operation.
Hardware system include IPC-610 rack mount industrial computer, ISA bus, motion controller of GT-400-SG, connecting plate, driver and stepping motor. Fig.l is general block diagram of system.
Figure 1. Structure schematic diagram of plane curve welder
Figure 2. Layout schematic diagram of guide
2.2. Weld torch speed and posture control
The motion of welding torch are three dimensional, one is depend on X-Y motion table, another is the step motor Z which can control the rotation angle. In the process of operation, weld torch made uniform motion, in the rectangular coordinate system, velocity of welding seam X and Y coordinate direction were request to be same, and in regulating torch posture, the rate of torch lance point should be invariant. So in the mechanism designing, the author design a special kind of curved beam, which can avoid the complicated matrix operation in welding process and improve the efficiency of software processing. As fig.3 shows, the torch lance point was on the rotate axis, when regulate the torch posture, though the whole mechanism were moving(x, y axis has speed ), relative to X-Y motion table, lance point speed is equal to zero.
v = a~x r
In which, v is the speed of torch lance point, unit is cm / min ; a> is angular velocity of axis operation, unit is rad / s ; r is the distance from torch lance point to axis centerline, unit is cm .
¡it h 1 1
Figure 3. Structure schematic diagram of curve beam Figure 4. design schematic diagram of curved beam structure
If r = 0, then v = 0. Conversely, if the torch lance point wasn't on the rotate axis, namely r ^ 0, then v ^ 0, in the software system calculation process, this speed will be decomposed to x and y axis respectively, that will be superposed with the original speed, in anther word, the torch lance point speed will change. To ensure the torch weld the work piece at an even pace, complicated matrix operation will be induced.
In addition, this device designs the adjustable lateral lever and vertical angle adjustable lever. Adjustable lateral lever can adjust the distance from nip to rotation axis according to different torch; vertical angle adjustable lever can adjust torch gesture. Control principle of torch gesture just like figure 4 shows.
As figure 4 shows, line AO and OC are short line segments which generated by VBA software package, the torch run from point A and pass by point O to point C, DO L AO, OE //FB, FB L OC. The torch moving process can divided into three steps:
The first step: when the torch on the initial position (point A), the torch is perpendicular to AO trajectory, which ensure the torch gesture requirement in this trajectory operation.
The second step: the torch moved from X-Y table to point O, when it reach point position, it will trigger step motor Z and it will rotate several angle, the rotation angle is equal to ADOE, at the meanwhile, suppose FB . OC at point B position, the torch brined along by X-Y table will move toward point B .
The third step: After reaching point B, X-Y table keep on moving, but the step motor Z stop rotating. Thus it can ensure the torch gesture requirement of FB L OC.
Generally, because the high rotational speed of step motor Z and angle ADOE is smaller after interpolation, thus it can ignore the torch operating time form line DO to line FB, it is approximately considered that the torch is perpendicular to line OC in the moving process from point O to point C. Recycle three steps above; it can satisfy the torch always perpendicular to welding this gesture requirement in the whole process of operation.
3. Automatic welder control system design of plane curve
Plane curve automatic welder are composite by control system, actuator and auxiliary equipment. The control system include hardware and software system; actuator include X-Y motion table and weld torch; auxiliary equipment include frame, guide, fixture , torch clamping mechanism and so on.
3.1. hardware structure of control system
Hardware system includes IPC-610 rack mount industrial computer, ISA bus, GT-400-SG motion controller, connecting plate, driver and stepping motor. Figure 5 is the general block diagram of system. Industrial computer and motion controller transfer information mutually, motion controller sent out pulse signal and direction instruction to drive step motor, so that it can control the execution element to accomplish the motion real-time runs.
Figure 5. control system schematic diagram
Research uses three group of two phase step motor motion system which made by KINCO company, the first group and second group are step motor motion platform which contains guide, platform displacement are 230mm x 230mm , maximum operation speed is about 10mm/ s , load is 30N, matching driver are 2M4I2 type; the step motor of the third group is 2S56Q-02154, its maximum static torque is 0.98N ■ m, matching driver are 2M530 type.
In this system, the maximum acceptance pulse of step motor but not asynchronous is 12000plis\/ s ,step angle is 1.8°, maximum speed of single worktable in standard load is about 10mm / s , considering safety margin and manufacturer recommended parameters, the three step motor use 8 subdivision mode as standard working mode in this system.
3.2. software system design
This software system uses two kinds of language --VBA and Visual C++ to joint develop. VBA program is primary cognizance the graphic information. DLL that used in the research is belonging to GoogolTech Company; it use user interface function library for multi-axis motion controller.
According to different function, software can divided into nine module: communication module, machining module, parameter setting module, display module, fault diagnosis module, assistant module, trajectory simulation module, graphic information extracting and mathematical treatment module.
Figure 6. Program interface diagram Figure 1. Flow chart of graphic information extracting and
mathematical treatment module
Through program which shows in figure 6, it will read the AutoCAD VBA data file information, which will generate seam track and simulate the welding process; in the welding process, weld torch position and gesture can be real-time display on the main program interface.
3.3. Software system implementation
Graphic information extracting and mathematical treatment module is primary cognizance the graphic information extracting and generate seam track, seam track programming is one of the most important link.
Programming method is visual. Using AutoCAD VBA to treat graphic file. Contour curve, which jointed by line and arc and described by AutoCAD, can't be transport directly to motion controller, we should treat the extracted curve by using linear segments to approach. Mathematical approach module
using point-to-point comparison method to interpolate and error control the curve in allowable range. It can obtain curve which composed of short line segments , complicate mathematical operation will be complete quickly and accurately. The extracting data will be serialize treat to ensure welding continuous. Figure 7 is the flow chart of graphic information extracting and mathematical treatment module.
In general engineering, it is rarely use spline curve, for simply development process , it can approximately considered that weld contour is composed of line and arc.
Interpolation methods to curve are so many, for the particularity request of welding torch should perpendicular to weld seam timely, the method that using linear segments to approach curve is feasible, the finally obtained line coordinate points can be export as the data of motion torch.
In this research, using motion controller to complete the interpolate of curved weldment by point-to-point comparison method, the method can realize the line and arc interpolate in the plane, when feed mechanism move according to the requirement, it will constantly compare the relative position of current position and trajectory , according the compared result to determine the feed direction at the next step, which can decrease the feed error of feed mechanism, and it just feed on only one direction. Figure 8 is the work cycle diagram of point-to-point comparison method. Figure 9 is the interpolation calculation flowchart of point-to-point comparison method.
Figure 8. Work cycle diagram of point-to-point Figure 9. Interpolation calculation flowchart of
comparison method point-to-point comparison method.
4. Typical curved seam welding
Figure 10 (a) is a stainless tool holder, its seam curve is nearly one cycle, takes horizontal welding will be completed by one time. Work piece weld trajectory described by AutoCAD is shown as figure 10 (b), but this information can't be transmitted to motion controller directly, so it should accord with the flow chart shown as figure 8 to extract the graphic information of stainless tool holder, the extract information are lots of short line segments dates which have start point and endpoint, now the research should realign those coordinate points and form a complete, continuous coordinate point sequence. Meanwhile, based on the endpoint of anterior line segment is the start point of posterior line segment, so it is only need to consider Abs(point(k) - point(k+1)) < 0.0000001 true or not. If true, it shows the sequence is correct, it is no need for adjustment; if not, it should keep on searching the next coordinate. Suppose point 1 is start point, it will form the sequence as
^15. Through data serialization and anticlockwise select object, AutoCAD will automatically generate a coordinate sequence as figure 10 (c) shows. Figure 10 (d) is the contour curve of stainless tool holder; the curve is composed of line and arc. For the line composed entity, it is only need to obtain the line endpoint, it have not error that it shouldn't grant test, the input approximation error is 0.1.
Figure 10 (a) Stainless tool holder; (b) weld trajectory of Stainless tool holder described by AutoCAD; (c) diagram of data serialization result; (d) contour curve of stainless tool holder
5. Summary and Conclusions
This topic use hardware of motion controller > IPC > stepping motor system and so on , that develop a kind of plane curve welder. The welder adopt DLL of windows and multithreading software development technique, so it can meet the needs of plane curve weld bead, further more, software system of plane curve welder use modular design, some module are of generality.
(1) Based on GT-SG-400 motion controller, develop a Hnd of curved seam automatic welder which.
(2) Design a special kind of curved beam shape as " l— " in actuator, this special kind of structure simplify the computational complexity of main program, and the X-Y platform compound locus is weld lance point trajectory which avoid the complicated matrix operation in welding process and improve the efficiency of software processing; guide is arranged on the top of weld torch that splash pollutes the guide.
(3) In software designing, using Visual C++ and AutoCAD VBA to develop the welder software system, successfully apply point-by -point comparison interpolation technique in image extraction curve, this ensure the gesture requirement of he weld torch always coincide with curve normal in welding process.
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