Implementation of AR based automobile assembly system.

Park, Hong Seok ; Choi, Hung Won ; Park, Jin Woo 等

1. INTRODUCTION

To survive in the turbulent and competitive market, automobile manufacturers must design and implement the manufacturing systems which respond rapidly to the market demands. Currently, the implementation of a manufacturing system for assembling new automobile body is done based on the prototype manufactured after the design of a new body model by changing a conventional system or newly designing. For this purpose, a system planner stops a current system and evaluates the manufacturability of a new model in that system as well as executes the work for changing it by putting a new model instead of the conventional automobile body to the current system. This traditional method leads to the critical problems such as reduction of system productivity and delay of the introduction of new product into market.

For these reasons, VR(Virtual Reality) based digital manufacturing technologies are used to analyze the static and dynamic behavior of system at all stages for configuration of manufacturing system(Gunter et al., 2005; Park et al., 2006). However, most of methods and softwares for digital manufacturing require the perfect 3D models of the whole system in virtual environment to represent the target system and surrounding environment. That means this modeling work requires a lot of expenses and effort.

To solve these problems, the AR technology is applied in this paper. The AR technology can remarkably reduce modeling work because it uses the real manufacturing environment to design and plan manufacturing systems. It is also possible to obtain the information in real time from manufacturing field by superimposition of virtual objects to real scene(Wolfgang, 2004). Consequently, the application of AR technology is expected as an epochal method for implementing manufacturing systems in an efficient and user friendly manner.

For the development of an AR based assembly system, the architecture of AR browser is firstly introduced. Then, the optimal values of environment parameter for robust superimposition between virtual objects and real scene are proposed through lots of experiments. Through an initial test, the problems are derived for the application of AR system. For an implement of AR system through solving them, the methods for appropriate allocation of camera, avoidance of collision between virtual objects and marker structural configuration for recognizing in multi directions in consideration of robot behaviors are proposed. With these results and experiments, an operation program for cockpit assembly system is generated.

2. AUGMENTED REALITY SYSTEM

2.1 Architecture of Augmented reality browser

AR browser as the core component for the interaction and visualization in an augmented environment consists of 4 modules for digital image processing and interfaces for communicating between devices(Fig. 1). The modules of AR browser are classified to tracking module to track positions of target markers, rendering module for generation and handling of virtual objects and measurement module to calculate the distance between objects. Then, all cameras used in research are calibrated to compensate for radial and decentering distortion using calibration module.

[FIGURE 1 OMITTED]

2.2 Environment variables for robust superimposition

While AR system internally executes the image processes for positioning virtual objects using a square marker, the chattering of virtual objects occures according to the environmental conditions of camera. In order to apply AR system to practice, it is important to find and maintain the condition to remove this chatter. To determine the appropriate conditions, a lot of tests were carried out with the environmental variables as below(Park et al., 2008);

* The angle between the marker and camera

* The distance between camera and marker

* The angle among the marker, camera and light

* The intensity of light

* The size of marker

Using the results of tests, the AR system is configured under appropriate conditions for robust superimposition between virtual objects and real scene.

3. PROBLEMS AND SOLUTIONS FOR IMPLEMENTATION OF AR BASED ASSEMBLY SYSTEM

To apply AR system to practice, there are some problems to be solved besides the environmental conditions for robust superimposition. For grasping them, a test bed of the H company's assembly station was realized with twelve times reduction model. Through lots of experiments with it, the problems occurring at implementing a AR based assembly system were examined(Fig. 2). To solve these problems, lots of methods are proposed as shown Fig. 3.

[FIGURE 2 OMITTED]

* Solutions f for problem 1 & 2

--Because the image acquired from one camera deliver only 2D information, it is necessary to get more than two image information obtained from different places.

--In case of the cockpit module assembly, two cameras are required because this process should be done in two different directions such as assembly and insert direction.

* Solution for problem 3

--For viewing an assembly area, the virtual object was partitioned into several parts. Through that, the divided parts can be shown or hidden for supporting the execution of the assembly process.

--To increase the adjusting degree of two objects, the alignment line was modeled to guide the correct approach of one object to its counter part.

* Solution for problem 4

--The clipping plane was generated to express the only information of the sectional surface for showing the possibility of collision.

* Solutions for problem 5 & 6

--The marker system mounted on the robot gripper was manufactured in the structure of a box type, because the system should be seen in every direction due to free movement of robot.

--The light intensity should be adjusted to an environmental condition. In case of entering a robot gripper into the inside of automobile body, the light condition is so dark that a camera cannot catch the marker system. This problem was solved by setting up a light inside of the box type marker system.

With these methods, the system planner can generate operation program of assembly, i.e. a robot program.

[FIGURE 3 OMITTED]

4. GENERATION OF OPERATION PROGRAMS FOR ASSEMBLY SYSTEM OF NEW MODEL

For generating an operation program for assembling a new model of automobile in a conventional assembly station by using AR technology, the implemented test bed is presented. Base on the test bed, the camera and the marker systems were optimally allocated according to the results of the previous studies for applying AR technology to practical. With this test bed, the operation of the assembly station for a new model was planned and programmed by AR technology. The completeness of the generated operation program was proven by applying it to the conventional assembly station. Fig. 4 shows the pratical test for generating operation program for automobile chassis assembly. The boundary conditions such as the position tolerance range within 10 mm were fulfilled.

[FIGURE 4 OMITTED]

5. CONCLUSION

AR in manufacturing system applications faces several technical challenges. This paper outlined some of the major working areas and highlighted new approaches and developed solutions. These systematical solving approaches overcome the problems against the implement of an AR-based assembly system. With the experimental results of the developed system through the test bed, it is clear that AR system can help the system planer to analyze the actual assembly process in the early stages of the manufacturing process planning and save valuable costs and time for testing the real process with the prototype.

6. ACKNOWLEDGEMENT

This research was supported by the MKE(Ministry of Knowledge Economy), Korea, under the ITRC(Information Technology Research Center) support program supervised by the IITA (Institute of Information Technology Assessment).

7. REFERENCES

Gunter, W. & Emmerich, S. (2005). Digital planning validation in automobile industry. Computers in Industry, Vol. 56, pp. 393-405.

Park, H. S. & Lee, G. B. (2007). Development of digital laser welding system for automobile side panels. Int. Jr. of Automotive Technology, Vol. 8, No. 1, 83-91.

Park, H. S.; Choi, H. W. & Park, J. W. (2008). Implementation of automobile cockpit module assembly system using augmented reality technology. Transactions of NAMRI/SME, Vol. 36, No. 1, 493-500.

Wolfgang, F. (2004). ARVIKA: Augmented Reality fur Entwicklung, Produktion und Service, Publicis Corporate Publishing.