M.Ing. / Parts feeding devices or feeders are used in automated assembly systems to deliver correctly oriented parts to the assembly station workhead. These devices play an important operational role since feeding is one of the major operations involved in an automated assembly process. However they account for much of the cost of an automated assembly system because most of the engineering time spent to develop such a system is used to devise a means of feeding the components in the correct orientation for the assembly process. This thesis describes the implementation of an integrated and computer controlled feeding and transfer system. The system consists of a vibratory bowl feeder for selecting, orienting and feeding parts and a flat conveyor belt for transferring parts to a prescribed location. The work focusses mainly on the design and analysis of the bowl feeder, on the mechanical and information interfacing aspects of the integration problem and on the control of the system. Sensing and electronic control circuits were also built to complete the system. The system implemented is to be integrated at a later stage with an industrial robot for handling purposes. Therefore, some issues related to the handling of parts from the conveyor belt by the robot are also discussed. Experimental results show that the recommendable operating frequency for the vibratory feeder is close to the value predicted by theoretical analysis. Several concurrent activities with critical time constraints and different periods were involved in the system, making the control more difficult due to the limited control capabilities of Visual basic, an easy to learn programming language used to implement the control program and the relatively slow speed of the computer used Nevertheless, it was observed that for feed rates close to 3 parts/min, the program developed performs well regarding the random control of the flow rate of parts on the conveyor, parts position and speed profiles obtained compare satisfactorily with the corresponding theoretical profiles. Recommendations for the integration of the robot to the system are made.

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This paper describes the development of an automated production system recently completed by the Martin Marietta Aerospace Division, Orlando, Florida, for the assembly, inspection and test of printed circuit boards. The project began in January 1981 with the purpose of increasing the then existing production capability and to create the building block for the total automation of the printed circuit board assembly area of the plant in Ocala, Florida. The system was implemented using a combination of off the shelf equipment modified and integrated to create a single production system. The system employs much of the new production philosophies tailored to meet the particular needs of Martin Marietta and to fulfill present production requirements as well as future production projections. During the development and implementation of this project, flexibility within the team was required to accommodate for the unforeseen problems which surfaced. The actual work required to perform this task far exceeded the expectations of the team and the company. This document covers all facets of this project, from inception to operation, and describes the problems encountered and lessons learned throughout the project.

A comparison of robotic positional control strategies was done using computer simulation on a three degree-of-freedom manipulator. The manipulator was subjected to different payloads, trajectories at different velocities, varying different controller sample rates and different motor saturation levels. The control schemes studied were the proportional plus integral plus derivative (PID) method, computed torque method, resolved motion rate control (RMRC) method and the model-referenced adaptive control (MRAC) method. These schemes were representative of three categories of robotic positional controllers - Joint Space control, Cartesian Space control and adaptive control. The criteria used for comparison were the maximum trajectory error, the maximum electrical controller. / M.S.

A new way of looking at scheduling and lot sizing is proposed by embedding material handling considerations in the determination of optimum delivery policies for a single stage, uniform demand assembly system in a finite horizon. Unit loads are used in place of lots; material handling and container costs are charged; and area and material handling constraints are imposed. A solution procedure based on a delivery period matrix is used to solve the minimization problem. Computational experience is provided. A special case of uniform delivery intervals is taken up and a discussion is given on variance penalty. / M.S.

A methodology for the solution of single-model, stochastic assembly line balancing problem is developed for the objective of minimizing the total labor cost (dictated by the number of stations on the line) and expected incompletion cost arising from tasks not completed within the prespecified cycle time. The proposed procedure is an approximation procedure that divides the problem into subproblems. For each subproblem, an approximate solution is obtained using the dynamic programming procedure developed for the problem. This procedure is incorporated with a special bounding strategy to overcome the rapidly increasing storage and computational requirements as the size of the problem increases. These approximate solutions are further improved by a branch-and-bound type of procedure called the improvement procedure. This procedure uses approximate costs, instead of lower bounds, to fathom the nodes of the enumeration tree constructed; thus, it is not, in the true sense of the word, the branch-and-bound technique. Consequently, the procedure is not guaranteed to result in the optimal solution; however, it is shown to generate solutions within (1 + ε) of the optimal solution. The improvement procedure either improves the approximate solutions obtained using the dynamic programming procedure or determines that they are quite close to the optimal ones. The improved solutions of the subproblems are then appended to each other to produce the solution of the original problem. Some dominance properties that contribute to the effectiveness of the improvement procedure and help in reducing the size of the enumeration tree are developed. Some sequencing and scheduling problems related to the node evaluation scheme of the improvement procedure are also investigated. A single-machine sequencing procedure is developed for the objective of minimizing the expected incompletion cost with tasks having a common due date and stochastic processing times. This procedure is extended to construct a schedule on M parallel machines. In these procedures, in-completion costs of the tasks are independent of their expected performance times; it can be interpreted as relaxing the precedence relations among the tasks. Solution procedures are also developed for the above sequencing and scheduling problems for the case in which the incompletion costs of the tasks are proportional to their expected performance times. Computational results and analyses made indicate that these procedures result in almost optimal solutions. / Ph. D.

An important issue in the design and operation of assembly systems is the coordination of part deliveries and processing operations. These decisions can have a significant impact on inventory cost and customer service. The problem is especially complex when actual delivery and processing times are stochastic in nature, as is the case in small lot manufacturing. In this research a new methodology is developed for determining optimal part delivery dates in stochastic small lot assembly systems. This methodology is based on the descriptive model that comprises of taking the maximum of several random variables. The part arrival and processing times are assumed to follow various known probability distributions. The model includes consideration of limited buffers between stations. The overall objective is to minimize the expected total of part and subassembly inventory cost, makespan cost and tardiness cost. An approach based on the optimization of individual stations in isolation is used to obtain the part delivery dates at each station. Comparison of the approach with the nonlinear programming based approach to the problem indicates that it generates almost as good solutions in a fraction of the computation time. This approach is then used to study system behavior under various operating conditions. Results indicate that the Iognormal and gamma distributions result in higher total costs than the normal distribution. However, the normal distribution can be used to determine part delivery dates even if the actual distribution is Iognormal or gamma, with relatively small errors compared to the solutions obtained using the correct distribution. Variability is the most important factor in the design of the system, and affects the determination of due dates, buffer capacity requirements, choice of distribution, and estimates of system performance. The role of buffer capacities, however, is not very critical in the design of small lot unbalanced lines. / Ph. D.

In this study we focus on two-sided mixed-model assembly line balancing type-I problem. There is a production target for a fixed time horizon and the objective is to produce this amount with the minimum level of workforce. A mathematical model is developed to solve this problem in an optimal manner. For large scale problems, the mathematical model fails to give the optimal solution within reasonable computational times. Thus, a heuristic approach based on threshold accepting algorithm is presented. Both the mathematical model and the heuristic approach are executed to solve several example problems from the literature and a case study problem which is derived from the refrigerator production. Computational experiments are carried out using both approaches. It is observed that the heuristic procedure finds good solutions within very reasonable computational times.