This paper presents a visual servoing methodology to realize a vision-based chip mounting, which makes it possible to mount micro chips to PCB with high precision. Because of continued down-sizing of electronic products, density of electronic parts to be packed into PCBs is ever getting higher and higher, thus requiring surface mounting technologies (SMT) to be more precise and productive. Down-sizing also tends toward miniaturization of components. The increased package density and component miniaturization require not only delicate handling of small chips but also delicate placement of them on PCBs. In order to place the small chips on the pattern of PCB, highly accurate mounting process is ultimately required. This is because it is difficult to place the chips a specified position with tiny small contact force due to uncertainty involved with the kinematic calibration error of the mounter and the deformation of PCB. In this paper, to avoid this difficulty we propose a visual servoing method for the chip mounting system. In such a way, the proposed visual servoing technique guarantees that chips are accurately placed at the desired positions. To achieve this, a CCD camera views the chip mounted with the mark on PCB simultaneously, and then the edge features and corner features are extracted from the acquired image. The proposed visual servoing algorithm generates the motion of the mounter to align the features of the chip with the ones of the mark on PCB on-line. The result obtained from real time experiment is discussed from the view points of practicality of the proposed method.
The visual information obtained from CCD camera is vulnerable to external illumination and the surface reflection properties of object images. Thus, the success of extracting aimed features from images depends mostly on the appropriate design of illumination. This paper presents a visual inspection system that is equipped with a flexible illumination and an auto-focusing unit. The proposed illumination system consists of a three-layered LED illumination device and the
controllable diffusers. Each layer is composed of LEDs arranged in a ring type, and a controllable diffuser unit is located in front of each layer. The diffuser plays a role of diffusing lights emitted from the LEDs so that the characteristics of illumination is made varied. This combined configuration of the LED light sources and the adjustable diffuser creates the various lighting conditions. In addition to this flexible illumination function, the vision system is equipped with an auto-focusing unit composed of a pattern projector and a working distance adjustable zoom camera. For the auto-focusing, hill climbing algorithm is used here based on a reliable focus measure that is defined as the variance of high frequency terms in an image. Through a series of experiments, the influence of the illumination system on image quality is analyzed for various objects that have different reflective properties and shapes. As an example study, the electrical parts inspection is investigated. In this study, several types of chips with different sizes and heights are segmented and focused automatically, and then analyzed for part inspection. The results obtained from a series of experiments confirm the usefulness of the proposed system and the effectiveness of the illumination and focusing method.