A case study on off-line programming of the hottes

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Case study on off-line programming of robot welding system

1 introduction

with the rapid development of domestic aerospace industry and the increasingly fierce competition in the international satellite launch market, higher requirements are put forward for the production cycle and manufacturing cost of the engine. In order to adapt to this situation, trying to improve the quality of welded joints and the stability of welded joint quality, and ensuring the production cycle has become a top priority. The flexibility advantage of robot welding system is a good solution to this contradiction

2 problems of robot welding

in order to meet the requirements of welding quality, it is necessary to select one of the welds for robot programming for each section. The current programming method is teaching programming. The operator uses the teaching box to control the robot movement, make the welding gun reach the pose required to complete the welding operation, and record the pose data of each teaching point. Then the robot can complete the welding of this weld in the "reproduction" state

according to the previous tests, there are two problems at present:

(1) the teaching accuracy is unstable, which affects the welding quality

in the teaching process, the programming effect is greatly affected by the level and state of the operator. When teaching, try to ensure that the teaching point is on the weld track, ensure the appropriate height of the welding gun, and ensure the continuous change of the welding gun attitude, which requires a high level of operators. In addition, the operators are in a state of high concentration for a long time, so it is difficult to ensure the accuracy of each teaching point. Thus, the final programming accuracy becomes unstable, and sometimes problems such as the collision between the welding gun and the workpiece will occur

(2) long programming time and low welding efficiency

in order to ensure the accuracy of the trajectory, 50 points need to be taught on the 100mm weld to ensure the smooth operation of the welding robot and the consistent position of the arc termination point. In the teaching and programming of each section, it takes 2 hours, that is, the whole product needs 200 hours in teaching and programming. In total, it takes 25 working days, which increases the total welding time of the nozzle extension section

therefore, how to improve the efficiency and accuracy of programming, shorten the total welding time of products, and improve the welding quality has become an urgent problem to be solved

3 robot welding off-line programming technology

at present, robot programming can be divided into teaching programming and off-line programming. In the case that the task to be completed by the robot is not very complex and the programming time is relatively short compared with the working time, teaching programming is effective and feasible, but it is not satisfactory in many complex job applications

3. 1 Characteristics of robot off-line programming

robot welding off-line programming and simulation technology is to use the achievements of computer graphics to establish the model of robot and its working environment in the computer, through the control and operation of graphics, program without using the actual robot, and then generate the robot program. Compared with traditional teaching programming, offline programming has the following advantages:

A. reduce the time when the robot does not work

b. keep programmers away from dangerous working environment

c. easy to modify the robot program

d. various artificial intelligence and other technologies can be combined to improve programming efficiency

e. it is convenient to combine with cadicam system to achieve the integration of cad/cam/robotics

therefore, robot welding off-line programming and simulation is a key technology to improve the flexibility of robot welding system, and it is also an important development trend of modern robot welding manufacturing industry

3. 2 status of robot offline programming technology

at present, there are commercial robot offline programming software based on ordinary PC in the international market. According to the industry and functional characteristics, tensile testing machines can be divided into: workspace, robcad, igrip, etc

workspace is the first commercialized computer-based robot simulation and offline programming software developed by robot simulations. The latest version of the software adopts ACIS as the core of modeling, and achieves good data exchange with some microcomputer based CAD systems such as AutoCAD

Robcad is a robot CAD and simulation system launched by tecnomatix in 1986. In just a few years, robcad has been widely used in practical industrial systems. Many automotive companies such as Ford, Volkswagen, Fiat and Lockheed space agency all use robcad to design, simulate and program robot production lines offline

another famous robot offline programming and simulation software package in the United States is igrip, which is an interactive robot graphic programming and simulation software package launched by American Deneb robotics company. It is mainly used for robot work unit layout, simulation and offline programming. Igrip can run on SGI, HP, sun and other workstations. Igrip software is divided into three parts: IMS, gsl GLI。 In addition, it also provides users with some more advanced functions through a shared library. In China, Harbin University of technology, Beijing University of technology, Nanjing University of technology and other units have carried out research work on robot welding off-line programming. Among them, Harbin Dingye university has carried out research work more than ten years ago, and the research level is in the leading position in China. It has successively developed rawcad and other machine maintenance offline programming systems for human arc welding for about 7 days, and has been applied to some products

4 robot off-line programming and simulation solution

develop an off-line programming and simulation system for arc welding robot based on SolidWorks platform to realize off-line programming in the welding process of nozzle extension

4. 1 workflow

a. establish the CAD model and robot model of the nozzle extension mold and pipe

b. segment and number the welds, and use the offline programming system for automatic programming for each section of welds, including the planning of welding torch trajectory and welding torch posture

c. simulate the programming results, and correct the planned pose according to the simulation results

d. calibrate the robot coordinate system to make it consistent with the coordinate system in the offline programming system

e. convert the program obtained by offline programming into Motoman robot program and import it into the robot controller through communication interface or CF card

f. the robot completes the welding of the workpiece by using the off-line program

4. 2 three point calibration method

three point calibration method uses the spatial coordinates of the three feature points of the actual workpiece and the three feature points of the virtual workpiece respectively. Where, the label point (x) is a point on the x-axis of the calibration coordinate system, the label point (y) is a point on the Y-axis of the calibration coordinate system, and the label point (o) is the origin position of the calibration coordinate system

4.3 example

4.3.1 calibrate

to teach the actual robot, teach the robot welding gun to the three feature points of the workpiece, record the size of the robot joint angle at the three feature points, and save it to the file. Then rewrite the joint angle file of the LAN group robot into a robot program file, and then upload it to the offline programming system by using the program upload function of the "programmer", control the robot's single step motion in the "programmer", and record the position of the end of the robot into the corresponding point every time it moves to a point, as shown in Figure 1

Figure 1 workpiece calibration coordinate system

here is the calibration function of saddle weld workpiece. Six label points are required in the calibration process, three in the upper circle and three in the lower circle. The recording method of each point is the same as the previous three-point calibration. Note that the recording sequence of each point on the circle should be the same, generally counterclockwise. See Figure 2

Figure 2 simulation results of saddle weld workpiece

4.3.2 create welding joint feature object

generate welding joint feature object: a check the name; b. Perform pose calculation. The current pose calculation only supports fillet weld. The calculation principle is: the section of fillet weld is approximately inverted triangle, and the whole is approximately triangular. The welding path point is generated on the bottom edge of the weld where the two welding plates intersect, and the spatial position information is extracted from the edge. The tangent direction of the edge at this point is the x-axis direction of the weld point, the included angle direction of the normal direction of the two sides of the weld is the z-axis direction of the weld point, and the y-axis is obtained by X, Z cross multiplication. See Figure 3

Figure 3 weld joint characteristics

without generating Weld Geometry, the calculation principle of generating weld path and the principle of generating weld points from weld geometry are shown in Figure 4

Fig. 4 simulation results of welding path

4.3.3 robot welding simulation of nozzle extension

simulation results of robot welding system of nozzle extension are shown in Fig. 5

5 conclusion

due to offline programming, the normal production of welding robot will not be affected during programming. Moreover, the off-line programming system can automatically program, the selection of welding gun position points and the transition of welding gun posture will be very smooth, and the programming accuracy will be improved. Through the simulation system, programmers can fully check the programming results and manually correct them

adopting such a mechanism programming system for off-line professional production can improve the programming efficiency, reduce the labor intensity of programmers, and improve the productivity and welding quality of products. (end)

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