Tae-Hyoung Park

A hierarchical method to improve the productivity of a multi-head surface mounting machine

This paper considers the problem of minimizing the assembly time of multi-head surface mounting machines. The problem is decomposed into a hierarchy of related subproblems. Since all subproblems in the hierarchy are known to be of a combinatorial nature and computationally intractable, we develop heuristics which are based on dynamic programming and the nearest neighbour travelling salesman problem technique. We implement the method as a computer program and perform computer simulations. The results are compared to a heuristic that is currently in use.

A dynamic programming approach to a reel assignment problem of a surface mounting machine in printed circuit board assembly

We consider the problem of assigning reels of components to slots on feeder racks of a surface mounting machine which is used to populate printed circuit boards with surface mount technology. This reel assignment problem (RAP) is one of a series of optimization problems that should be addressed to improve the production rate. We preprocess RAP to facilitate the application of dynamic programming and then formulate it as an integer programming problem. We solve the problem by using a heuristic algorithm based on dynamic programming. We implement the algorithm as a computer program and perform computer simulations. The simulation results are compared to those of the Effective Algorithm previously proposed.

An approach to robot motion analysis and planning for conveyor tracking

Robot motion is analyzed and planned for conveyor tracking considering the speed of the conveyor belt and the locations of the part and the robot. The joint torque limit, joint velocity, acceleration, and jerk limits of the robot are taken into account in the motion analysis and planning. To include the robot arm dynamics, the problem is formulated as second order state equations using a parametric function. The conveyor tracking problem is then converted to an optimal tracking problem. The solution that minimizes the specified performance index is obtained using the dynamic programming approach. Numerical examples are presented to demonstrate the significance of the proposed method for conveyor tracking of the robot in a workcell.<<ETX>>

Path planning of automatic optical inspection machines for PCB assembly systems

We propose a path planning method to improve the productivity of AOI (automatic optical inspection) machines in PCB (printed circuit board) assembly lines. To minimize the overall working time, the inspection clusters and visiting sequence of camera should be determined optimally considering the FOV (field-of-view) size of camera. A unified method is newly proposed to determine the inspection clusters and visiting sequence simultaneously. We apply a hybrid genetic algorithm to solve the highly complicated optimization problem. Comparative simulation results are presented to verify the usefulness of proposed method.

Vision inspection system for holograms with mixed patterns

We propose an vision inspection system for hologram with mixed patterns. The system hardware consists of LED illuminator, CCD camera, and vision processor. The LEDs of illuminator emit alternatively and change the incident angle to acquire each image of pattern. The system software consists of the stages of pattern generation and pattern matching. The acquired images of hologram are compared with their reference images by matching algorithm. Since the several patterns are mixed in one hologram, the reference image should be changed if the hologram is rotated. To compensate for the positioning error of hologram, reference images are generated in on-line. We apply a frequency-transformation based CGH (computer-generated hologram) method to generate reference images. For the fast pattern matching, we also apply the matching method in the frequency domain. Experimental results using holograms attached at Korean currency are then presented to verify the usefulness of the proposed system.

Automatic Extraction of Component Inspection Regions from Printed Circuit Board by Image Clustering

The inspection machine in PCB (printed circuit board) assembly line checks assembly errors by inspecting the images inside of the component inspection region. The component inspection region consists of region of component package and region of soldering. It is necessary to extract the regions automatically for auto-teaching system of the inspection machine. We propose an image segmentation method to extract the component inspection regions automatically from images of PCB. The acquired image is transformed to HSI color model, and then segmented by several regions by clustering method. We develop a modified K-means algorithm to increase the accuracy of extraction. The heuristics generating the initial clusters and merging the final clusters are newly proposed. The vertical and horizontal projection is also developed to distinguish the region of component package and region of soldering. The experimental results are presented to verify the usefulness of the proposed method.

A localization system of mobile robots using artificial landmarks

This paper proposes a localization system for indoor mobile robots. The localization system includes a camera and artificial landmarks for global positioning, and encoders and gyro sensors for local positioning. The Kalman filter is applied to take into account the stochastic errors of all sensors. Also, we develop a dead reckoning system to estimate the global position when the robot moves into blind spots, where it cannot see artificial landmarks. Learning engines using modular networks are designed to improve the performance of the dead reckoning system. The experimental results are then presented to verify the usefulness of the proposed localization system.

An automatic inspection system for hologram with multiple patterns

We propose an automatic inspection system for hologram with multiple patterns. The system hardware consists of illuminations, camera, and vision processor. Multiple illuminations using LED are arranged in different directions to acquire each image of patterns. The system software consists of pre-processing, pattern generation, and pattern matching. The acquired images of input hologram are compared with theirs reference patterns by developed matching algorithm. To compensate for the positioning error of input hologram, reference patterns of hologram for different position should be generated in on-line. We apply a frequency transformation based CGH (computer-generated hologram) method to generate reference images. For the fast pattern matching, we also apply the matching method in the frequency domain. Experimental results for hologram of Korean currency are then presented to verify the usefulness of proposed system.

A Hierarchical Method to Improve the Productivity of Multi–Head Surface Mounting Machines

Abstract This paper considers the problem of improving the productivity of multi-head surface mounting machines which are used to populate printed circuit boards with surface mount technology. The complexity of this problem is highly dependent on the specific number of heads which are used to pick and place components. This paper proposes a method for surface mounting machines with any number of heads. That is, our method can be applied regardless of the number of heads. The PCB assembly time depends on two decision variables: (1) assignment of reels to slots on feeder racks; and (2) sequencing of pick-an-place movements. These two problems are decomposed into a hierarchy of related subproblems. Since all subproblems in the hierarchy are known to be of a combinatorial nature and computationally intractable, we develop heuristics which are based on dynamic programming and the nearest neighbor traveling salesman problem technique. We implement the method as a computer program and perform computer simulation...

Automatic Extraction of Component Window for Auto-Teaching of PCB Assembly Inspection Machines

We propose an image segmentation method for auto-teaching system of PCB (Printed Circuit Board) assembly inspection machines. The inspection machine acquires images of all components in PCB, and then compares each image with its standard image to find the assembly errors such as misalignment, inverse polarity, and tombstone. The component window that is the area of component to be acquired by camera, is one of the teaching data for operating the inspection machines. To reduce the teaching time of the machine, we newly develop the image processing method to extract the component window automatically from the image of PCB. The proposed method segments the component window by excluding the soldering parts as well as board background. We binarize the input image by use of HSI color model because it is difficult to discriminate the RGB colors between components and backgrounds. The linear combination of the binarized images then enhances the component window from the background. By use of the horizontal and vertical projection of histogram, we finally obtain the component widow. The experimental results are presented to verify the usefulness of the proposed method.We propose an image segmentation method for auto-teaching system of PCB (Printed Circuit Board) assembly inspection machines. The inspection machine acquires images of all components in PCB, and then compares each image with its standard image to find the assembly errors such as misalignment, inverse polarity, and tombstone. The component window that is the area of component to be acquired by camera, is one of the teaching data for operating the inspection machines. To reduce the teaching time of the machine, we newly develop the image processing method to extract the component window automatically from the image of PCB. The proposed method segments the component window by excluding the soldering parts as well as board background. We binarize the input image by use of HSI color model because it is difficult to discriminate the RGB colors between components and backgrounds. The linear combination of the binarized images then enhances the component window from the background. By use of the horizontal and vertical projection of histogram, we finally obtain the component widow. The experimental results are presented to verify the usefulness of the proposed method.