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CHAPTER II PROBLEM DESCRIPTION
Problem Overview
This thesis focuses on two of the areas of process optimization: determining the component placement sequence and the feeder assignment for a Chip Shooter type placement machine. These two tasks are performed after the allocation of components to the different machines that may exist in an SMT line has been performed. The allocation of components to different machines determines which machine in the SMT line will place each of the component types required for a single PCB type or a group of PCB types. The purpose of allocating components is to balance the workload across the machines and also to reduce setup time. An optimization model that addresses this problem is presented in [4]. Once the components have been allocated to the different placement machines of the SMT line, a lower level set of decisions needs to be performed to address two important questions:
• In which sequence should the components be placed on the PCB by each of the placement machines, and
• How should the feeders containing the components be arranged in the feeder carriages of the placement machines?
The order in which the components are placed on the PCB as well as the arrangement of the feeders in the feeder carriages affect the assembly cycle time. The purpose of determining a placement sequence and a feeder assignment is to reduce the assembly cycle time at the Chip Shooter placement machines.
Problem Statement
The placement sequence and feeder assignment problems addressed in this research are described in this section. Of the different types of placement machines, the Chip Shooter machine is one of the most commonly used surface mount machines for placing small components at very high speeds. This research will focus on developing a new algorithm to determine a component placement sequence and feeder assignment to minimize assembly time for a Chip Shooter machine. The component placement sequence and feeder assignment problem statement is shown in Figure 2.1.
Research Strategy for Addressing the Problem
The research strategy for addressing the feeder assignment and placement sequencing problem involves the following activities:
• Review related literature,
• Develop a component placement time estimator function empirically,
• Develop a solution approach, for generating a feeder assignment and placement sequence,
• Conduct a case study to compare research results with commercial software results, and
• Summarize findings and make recommendations for further research.
A brief overview of these activities is summarized in this section.
A literature review is conducted to review existing solution approaches, evaluate the assumptions employed by these approaches, and review existing case studies results. This literature review provides background on some of the algorithms incorporated in this research. A placement time estimator function is developed to use as a performance measure to evaluate the proposed solution approaches. The estimator function accounts for the functional characteristics of the Chip Shooter machine as well as the characteristics of the components that are mounted. An experiment using a Fuji CP4-3 Chip Shooter machine is conducted to determine the relevant machine parameters. A solution approach is developed that incorporates the theoretical developments in the literature with the relevant characteristics of an actual production floor. Both the component placement sequence and feeder assignment problem are considered Non-Polynomial (NP) Complete problems [30]. NP-Complete problems are often difficult to solve to optimality in a reasonable time, thus a heuristic solution approach is developed in this research. The heuristic solution approach constructs an initial solution for the problem and then improves the initial solution using an iterative improvement algorithm. Through a case study with the industrial partner, actual PCB and component specifications are used to evaluate the solution approaches developed. The Chip Shooter machine used in the case study is the Fuji CP4-3 Chip Shooter machine. The results obtained with the proposed solution approaches are compared with the results obtained using commercial software. The results and conclusions from the case study and research are then presented.
ABSTRACT
ACKNOWLEDGEMENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF NOTATION
CHAPTER
I. INTRODUCTION
1.1 Overview of Electronic Assembly
1.2 Motivation of Research
1.3 Assembly Process and Machine Description
1.4 Organization of Thesis
II. PROBLEM DESCRIPTION
2.1 Problem Overview
2.2 Statement of the Problem
2.3 Research Strategy for Addressing Problem
III. LITERATURE SURVEY
3.1 Placement Sequencing
3.2 Feeder Assignment
3.3 Placement Sequencing and Feeder Assignment
3.4 Summary of Literature Review
IV. ESTIMATOR FUNCTION FOR COMPONENT
PLACEMENT TIME
4.1 Detailed Chip Shooter Machine Description
4.2 Development of Placement Time Estimator Function
4.3 Calculation of Experimental Placement Velocity Functions
4.3.1 Calculation of Minimum Turret Rotation Time and
Fixed Pick and Place Time
4.3.2 Calculation of PCB Table Average Velocity
Functions
4.3.3 Calculation of Feeder Carriage Average Velocity
Function
4.4 Overall Placement Time Estimator Function
4.5 Validation of the CP4-3 Placement Time Estimator Function
V. SOLUTION APPROACH AND OPTIMIZATION
CONSTRAINTS
5.1 General Optimization Solution Approach
5.2 Fixed Setup Optimization Solution Approach
5.3 Calculation of Lower Bound
VI. CASE STUDY
6.1 Free Setup Case Study Results
6.2 Fixed Setup Case Study Results
6.3 Partial Fixed Setup Case Study Results
6.4 Summary of Case Study Results
VII. RESULTS AND CONCLUSION
7.1 Conclusions
7.2 Areas of Further Research
REFERENCES
APPENDIX A – GENERAL OPTIMIZATION SOLUTION
APPROACH EXAMPLE
APPENDIX B – FIXED SETUP OPTIMIZATION SOLUTION
APPROACH EXAMPLE
APPENDIX C – CASE STUDY DATA AND RESULTS
VITA
