Total Assembly Time Research Articles

An approach for grouping circuit cards into families to minimize assembly time on a placement machine

This paper addresses a difficult problem that often arises in printed circuit card assembly systems: how should circuit cards be grouped into families to decrease total assembly time? Traditional approaches to this problem focus on setup time, without considering the possible impacts on processing time. A new approach for selecting card families to be processed on an assembly machine is developed to minimize total assembly time through the joint consideration of setup time and processing time. The overall approach for addressing the card grouping problem involves capturing the lower level machine configuration decisions through an empirical estimator function and incorporating this function with the higher level card grouping problem. The card grouping problem is solved using a branch-and-bound algorithm supplemented by techniques to improve the solution time. An industrial case study is conducted for a turret style placement machine, a Panasonic MV150 machine. The results demonstrate the positive impact of including the lower level decisions on the total assembly time and system throughput for certain types of assembly machines. In addition, this research provides insight on other process planning problems, such as line assignment and card sequencing, by demonstrating the importance of incorporating the related lower level decision problems.

A MODEL FOR ASSEMBLY SEQUENCE PLANNING IN A MULTIROBOT ENVIRONMENT

This paper presents a model for the selection of optimal assembly sequences for a product in multirobot systems. The objective of the plan is the minimization of the total assembly time (makespan). To meet this objective, the model takes into account, in addition to the assembly times and resources for each task, the times needed to change tools in the robots, and the delays due to the transportation of intermediate subassemblies between different machines. An A* algorithm that solves the problem is also presented, which starts from the And/Or graph for the product (compressed representation of all feasible assembly plans).

Extended dynamic point specification approach to sequencing robot moves for PCB assembly

In PCB assembly planning, most of the current works solved the assembly sequence and feeder assignment problem directly. They have not decomposed the problem into subproblems. Consequently, the problem remains very complex and, therefore, it is hard to solve. Few research works considered about the detail on how to determine the optimal picking points (or placement points), but results are still limited. The extension of these works is necessary. This paper extends the point specification problem based on the Dynamic Pick and Place (DPP) model, namely, the Extended Dynamic Pick and Place (EDPP0 model. The EDPP determined the picking/placement point coordinates from global consideration of point relationship in the system. The whole system is analysed to establish the new model. From this guideline the system is modelled in a systematic scheme based on the objectives of each object in the systems (robot arm, feeder rack, board table). These objectives should be satisfied together to reach the global objective of the system. Numerical experiment shows that the EDPP model is better than the DPP model in terms of total assembly time.

Modified method time measurements for ergonomic planning of production systems in the manufacturing industry

The paper reports on an evaluation of a method called ErgoSAM. This method is based on SAM, a higher-level method-time-measurement (MTM) system, and is for use by production planners, e.g. production engineers. In addition to the SAM information, the ErgoSAM method considers information on weight handled or forces applied and work zone. The method is designed to predict the physical demands of work postures, force and repetitivity, according to a scientific model, the Cube model. In co-operation with the Volvo Car Corporation, six work-stations of an assembly line were analysed by a production engineer using ErgoSAM. The total assembly time analysed was about 17 minutes. The results were compared to results from ergonomic analyses made by an ergonomist using the Volvo Car Corporation's standards. The results showed that ErgoSAM predicts work situations of high physical stress for the workers. However, the method does not consider stressful positions for the hand, wrist and neck or mental stress. The production engineer judged the ErgoSAM analyses to require about 5% more time than SAM analyses alone. It is concluded that the method shows considerable promise for predicting physically stressful work situations, but needs to be further evaluated and refined.

A Petri net model to determine optimal assembly sequences with assembly operation constraints

Abstract The assembly process in an automated assembly system is the execution of successive assembly operations in which each operation joins one component with another component to form a larger component. The selection of the assembly sequence of a product has a great effect on the efficiency of the assembly process. A systematic procedure is needed not only to generate all feasible assembly sequences but also to choose an optimal sequence. This paper describes a method for finding tight bounds on optimal sequences in an assembly system. A Petri net obtained from the AND/OR graph of a product can be formulated as a 0–1 integer linear program that minimizes the total assembly time or cost while satisfying three assembly operation constraints, namely, ease of component handling, ease of component joining, and tool changes. A Lagrangian dual formulation is then developed to obtain a lower bound. A dynamic programming algorithm provides a dual solution, and a subgradient optimization algorithm is used to maximize the lower bound obtained from the dual problem. The solution procedure is validated by determining the optimal assembly sequences of three products.

Multi-criteria assembly sequencing

This paper describes the elements of a multi-criteria optimization formulation of the assembly sequencing problem. The criteria considered are: total assembly time and number of reorientations. These two criteria are combined using multi-attribute utility theory to derive a single objective function. The combined objective function has been formulated subject to the precedence constraints of the assembly process. The model has been solved using simulated annealing. The elements of the developed algorithms and their performances are demonstrated in this paper.

Assembly scheduling for an integrated two-robot workcell

An assembly sequence planning scheme, giving the time optimal solution for a two-robot cell, is presented. The scheme is based on dynamic programming, and the time optimum assembly sequence is generated in two stages. In stage one, an initial candidate sequence is derived. The stage-one algorithm is computationally efficient, the complexity being O( log n k ) , where n is the number of elements in k groups. It also gives near-optimal results. Expression for the lower bounds for the total assembly time are derived in order to assess the departure from optimality of the stage-one sequence. In stage two, the initial candidate sequence is optimized using an iterative technique to yield the time optimal sequence. The scheme is extended to account for precedence constraints. It can also be extended for assembly cells with more than two robots. The scheme is tested using computer simulations, and some test results are presented. For the problems solved (typically involving 20 elements), the computational times were less than 5 sec in an Apollo 300 workstation.

SIMULTANEOUS COMPONENT SEQUENCING AND FEEDER ASSIGNMENT FOR HIGH SPEED CHIP SHOOTER MACHINES

This paper proposes a methodology for efficient process planning of concurrent machines in electronics assembly. The particular machine type under consideration is the High Speed Chip Shooter (HSCS) for surface mount assembly. Currently, most surface mount assembly operations are modeled in a cyclic manner. The model that is proposed herein is an asynchronous (acyclic) model that augments the benefits of the unique features of this assembly machine. A heuristic algorithm is developed, referred to as the Acyclic Assembly Time (AAT) algorithm, which is based on the asynchronous model. The algorithm is thoroughly tested with orthogonal arrays, compared against previously published problems, and applied to a real life example. The AAT algorithm produced excellent results throughout the test process. By increasing the utilization of the individual mechanisms, the efficiency of the overall system naturally improves and the ultimate goal of reducing the total assembly time is achieved.

Acquisition Time Reduction through New Design for Assembly Heuristics

SUMMARY SUMMARY Rearranging component positions and orientations inside products can reduce the acquisition times associated with handling distance and component orientation. Modeling the acquisition process with an information-based design for assembly methodology identifies and quantifies acquisition difficulty for manual and automatic processes. Heuristics based on evaluations of acquisition difficulty guide the relocation and reorientation of components inside the product to reduce assembly time. Since acquisition time averages one third of the total assembly time, significant improvements are shown to be feasible. A new information flow from downstream assembly issues to product design is demonstrated

Robotic assembly of printed circuit boards with component feeder location consideration

Abstract The use of industrial robots for the assembly of printed circuit boards (PCB) is fast gaining popularity. Minimization of the time required for board assembly while maintaining production quality is the process planner's main task. This task involves the specification of the insertion sequence of components in their respective locations and the assignment of component types to feeders or dispensing magazine slots. The time taken by a robot to fetch a component for insertion is dependent on the location of the feeder that holds the component type. Similarly, board assembly lime is dependent on the order of component insertion on the board and the fetch time of components between insertions. In this paper, models to minimize the total assembly time for a board are developed and studied. Factors considered in the analysis of the assembly time are the component assignment to magazine

FINDING PLACEMENT SEQUENCES AND BIN LOCATIONS FOR CARTESIAN ROBOTS

Abstract We model the repetitive placement by a Cartesian robot of n parts on a rectangular workpiece. There are n bins or feeders (one per part), to be placed around the boundary of the workpiece, which contain the parts. The robot picks a part from a bin, places it, picks another part, places it, etc.; any placement sequence is possible. The problem, to find bin locations and a placement sequence to minimize total assembly time, is formulated as a traveling salesman problem (on a graph with n nodes) with special structure. This structure allows the computation of a lower bound on the minimum total assembly time in order n effort. The lower bound improves as n increases, and leads to a simple solution algorithm which gives asymptotically optimal solutions in order n log n effort. For die case where parts are uniformly distributed on the workpiece, we give simple closed-form expressions for the expected value of the lower bound. These expressions should be helpful for design decisions; for example, holdin...

Application of Linear Assignment Model for Planning of Robotic Printed Circuit Board Assembly

A planning method is presented for achieving shorter working-in-process and thus better productivity of printed circuit board assembly. This method finds the optimal sequence of component placement (and insertion) and near-optimal arrangement of feeders. For placement of components on a printed circuit board with a set of given feeder locations, the sequencing problem is shown to be equivalent to, and therefore solvable as, a linear assignment problem, which involves assigning n components to m feeders with the objective to minimize the total assembly time. A heuristic approach based on a linear assignment model is employed for arrangement of feeders. An example is provided to illustrate the solution generated by the proposed method.

Concurrent Engineering—How Husqvarna Succeeded

SUMMARY Analysing the product structure with the aim to optimize the possibilities of forming variants in most cases results in large cost savings. If this analysis is connected to an improvement of the manufacturing process, the possibility to vary the working content of the staff is also affected and this, in its turn, may contribute to increased productivity. Husqvarna Sewing Machines AB has in this way in 2 years both reduced the total number of parts and the total assembly time by 30% for a new generation of sewing machines.

Two criteria for the selection of assembly plans: maximizing the flexibility of sequencing the assembly tasks and minimizing the assembly time through parallel execution of assembly tasks

The authors introduce two criteria for the evaluation and selection of assembly plans. The first criterion is to maximize the number of different sequences in which the assembly tasks can be executed. The second criterion is to minimize the total assembly time through simultaneous execution of assembly tasks. An algorithm that performs a heuristic search for the best assembly plan over the AND/OR graph representation of assembly plans is discussed. Admissible heuristics for each of the two criteria introduced are presented. Some implementation issues that affect the computational efficiency are addressed. >

Wood Bonding by Surface Reaction

Abstract Chemical bonding is a technique which attempts to involve chemically the surface of wood in the joint formation process. In this research, an attempt has been made to improve overall board properties while at the same time make the whole process more practical from a large-scale application point of view. Accordingly, a 50 weight% solution of nitric acid was applied to green Douglas fir flakes which were dried in a laboratory flake dryer after various time periods. The variables considered included contact time between acid and flakes before drying, time between drying and application of a gap-filling mixture, and total assembly time. Board properties determined were internal bond (IB), modulus of rupture (MOR), modulus of elasticity (MOE), and wet modulus of rupture (WMOR). Results showed a substantial improvement in board properties compared to boards made utilizing previously reported techniques. Boards which were dried after acid treatment showed a 55% improvement in IB, an 8% improvement in ...