Augmented Reality for Collaborative Assembly Design in Manufacturing Sector

Introduction

For a typical machine, one may look inside and find that it consists of accessories, modules and parts which have to be combined and integrated to fulfill its function. As the last step of mechanical manufacture to satisfy the technical requirements, assembly also includes the relative works such as regulation of assembly accuracy, inspection of tolerance, test of integration, painting and package other than the pure combination of components. During the process, correctly guaranteeing the assembly precision of machine and components is one of the critical criteria determines the product quality. Before shaping the finished product, the traditional assembly of mechanical components is mainly on the basis of parameters deriving from assembly drawings or some business software such as CAD/CAM. Although being guaranteed a realization of strict assembly sequence and considerable assembly precision, such methods guided by assembly drawings or software also manifest their defects. Because of the lack of combination with the real environment, they can’t provide a better understanding of different constrains and complicated plant environments in the real assembly circumstances while the after evaluation of assembly workload such as assembly cost, time consuming and hardship could not be easily commanded either. Moreover, concerning a large amount of components to be assembled, an obstacle to understand the assembly drawing between the designers and the assemblers has been introduced. Again, the repetitive assembly operation would also create a incorrect assembly because of the physical tiredness and the mental negligence. Accordingly, such a serious occlusion of information exchange greatly limits the development of the assembly level. To solve this problem, a concept of collaborative assembly design by using AR technology has been arisen, aiming at completing the interconnection of every character in the before-product period. This technology will allow designers, manufacturers and assemblers to collaborate in a distributed way.

This paper mainly focuses on a novel technology to evaluate mechanical assembly sequences, say, the Augmented Reality technology. Defined as the combination of the real and virtual scene, such a technology has been widely used in areas such as product maintenance (Feiner & MacIntyre & Seligmann, 1993), manufacturing (Curtis & Mizell & Gruenbaum & Janin, 1998; Sims, 1994), training (Back, 2001), battlefield (Urban, 1995; Metzger, 1993), medicine (Mellor, 1995; Uenohara & Kanade, 1995), and so on (Pope, 1994). Comparing with Virtual Reality (VR) which aims at totally mimicking the real world into the synthetic virtual perception according to the help of computer and separates the real and virtual environment, AR maintains a sense of presence in the real world and balances the perception of real and virtual world. With the help of a see-through head-mounted device, a data glove and a tracking system, the virtual components can be placed in the real one which can be seen from the head-mounted device. Wearing eyeglasses which are also called the HMD, an operator manipulates the virtual components directly and superimposes them on the real ones with the whole process can be seen from the HMD. Besides, during the operation process of integrating the virtual objects, the operator will detect the real interferences coming from the real objects and the ambient environment that would delay the assembly schedule or need to be further modified. What is more, because of the feedback of other “non-situated” elements like recorded voice, animation, replayed video, short tips, arrows, it could simultaneously guide the operators through the whole assembly operation, release their tension and even notify an error assembly (Raghavan & Molineros & Sharma, 1999). This way, the reality being perceived is augmented. In AR, two noticeable key techniques have to be mentioned. They are the generation of assembly sequence and the superimposition of virtual objects.