Online 3-D Modeling of Complex Workpieces for the Robotic Spray Painting With Low-Cost RGB-D Cameras

The 3-D model of workpieces plays a significant role in robotic spray painting, which needs the geometry and shape information for painting-path planning or pose estimation. However, the models are rarely provided beforehand, even if they are available, random pose changes during workpiece conveying on the spray-painting pipeline also necessitates the usage of real-time 3-D reconstruction. In this case, we propose an online modeling approach for automatic spray-painting applications. Specifically, with two consumer RGB-D cameras mounted on the two sides of the pipeline, the data streams of the moving workpiece are continuously collected. Then, incorporating the 3-D contour feature and approximate linear motion characteristics of the workpiece, a modified iterative closest point (ICP) algorithm is proposed for fast registration of multiple workpiece point clouds with varying positions. Finally, based on the spatial distribution and point cloud quality evaluation, a joint weighted algorithm for fusing point clouds from different perspectives is proposed, which is effective for the issues of self-occlusion and has superior noise resistance. To estimate the system performance, an experimental platform was established to simulate the spray-painting production line. According to our experiments, the proposed method can completely model the complex workpieces with irregular polyhedral structure within 1500 ms, and the modeled geometry accuracy can reach less than 8 mm, which has a significant improvement compared with the conventional methods.

I. Introduction

With the increasing demands for industrial automation, robotic spray-painting technology holds an important status in the modern industrial automatic paint system [1]. Such technology possesses many advantages, such as good uniformity of the coating thickness, high repetitive positioning accuracy, wide applicability, and high efficiency. Meanwhile, it frees workers from a toxic, flammable, and explosive working environment [2]. Owing to the above merits, robotic spray-painting has been ubiquitously used in various fields of the painting industry, such as ships, aircraft, automobiles, furniture, etc. [3]–[7]. During the robotic spray painting procedure, the digital 3-D model of the workpiece is an important prerequisite because it serves as a standard guide for painting trajectory planning [8] and pose estimation [9], [10]. However, for small and mid-size enterprises (SMEs) that specialize in small batch production of multiple varieties, 3-D models are seldom provided in advance. Even if they are available, real-time 3-D modeling is also needed because random pose changes often occur during workpieces conveying on the spray-painting pipeline, caused by a lack of frequently exchanging high-precision fixtures.