Browsing by Subject "Robotic cell"

Now showing 1 - 10 of 10

Open Access
Bicriteria robotic cell scheduling
(Springer, 2008) Gultekin, H.; Akturk, M. S.; Karasan, O. E.
This paper considers the scheduling problems arising in two- and three-machine manufacturing cells configured in a flowshop which repeatedly produces one type of product and where transportation of the parts between the machines is performed by a robot. The cycle time of the cell is affected by the robot move sequence as well as the processing times of the parts on the machines. For highly flexible CNC machines, the processing times can be changed by altering the machining conditions at the expense of increasing the manufacturing cost. As a result, we try to find the robot move sequence as well as the processing times of the parts on each machine that not only minimize the cycle time but, for the first time in robotic cell scheduling literature, also minimize the manufacturing cost. For each 1-unit cycle in two- and three-machine cells, we determine the efficient set of processing time vectors such that no other processing time vector gives both a smaller cycle time and a smaller cost value. We also compare these cycles with each other to determine the sufficient conditions under which each of the cycles dominates the rest. Finally, we show how different assumptions on cost structures affect the results.
Open Access
Bicriteria robotic cell scheduling with controllable processing times
(Taylor & Francis, 2011) Yildiz, S.; Akturk, M. S.; Karasan, O. E.
The current study deals with a bicriteria scheduling problem arising in an m-machine robotic cell consisting of CNC machines producing identical parts. Such machines by nature possess the process flexibility of altering processing times by modifying the machining conditions at differing manufacturing costs. Furthermore, they possess the operational flexibility of being capable of processing all the operations of these identical parts. This latter flexibility in turn introduced a new class of robot move cycles, called pure cycles, to the literature. Within the restricted class of pure cycles, our task is to find the processing times on machines so as to minimise the cycle time and the manufacturing cost simultaneously. We characterise the set of all non-dominated solutions for two specific pure cycles that have emerged as prominent ones in the literature. We prove that either of these pure cycles is non-dominated for the majority of attainable cycle time values. For the remaining regions, we provide the worst case performance of one of these two cycles.
Open Access
Bicriteria robotic operation allocation in a flexible manufacturing cell
(Elsevier, 2010) Gultekin, H.; Akturk, M. S.; Karasan, O. E.
Consider a manufacturing cell of two identical CNC machines and a material handling robot. Identical parts requesting the completion of a number of operations are to be produced in a cyclic scheduling environment through a flow shop type setting. The existing studies in the literature overlook the flexibility of the CNC machines by assuming that both the allocation of the operations to the machines as well as their respective processing times are fixed. Consequently, the provided results may be either suboptimal or valid under unnecessarily limiting assumptions for a flexible manufacturing cell. The allocations of the operations to the two machines and the processing time of an operation on a machine can be changed by altering the machining conditions of that machine such as the speed and the feed rate in a CNC turning machine. Such flexibilities constitute the point of origin of the current study. The allocation of the operations to the machines and the machining conditions of the machines affect the processing times which, in turn, affect the cycle time. On the other hand, the machining conditions also affect the manufacturing cost. This study is the first to consider a bicriteria model which determines the allocation of the operations to the machines, the processing times of the operations on the machines, and the robot move sequence that jointly minimize the cycle time and the total manufacturing cost. We provide algorithms for the two 1-unit cycles and test their efficiency in terms of the solution quality and the computation time by a wide range of experiments on varying design parameters.
Open Access
Cyclic scheduling of a 2-machine robotic cell with tooling constraints
(Elsevier, 2006) Gultekin, H.; Akturk, M. S.; Karasan, O. E.
In this study, we deal with the robotic cell scheduling problem with two machines and identical parts. In an ideal FMS, CNC machines are capable of performing all the required operations as long as the required tools are stored in their tool magazines. However, this assumption may be unrealistic at times since the tool magazines have limited capacity and in many practical instances the required number of tools exceeds this capacity. In this respect, our study assumes that some operations can only be processed on the first machine while some others can only be processed on the second machine due to tooling constraints. Remaining operations can be processed on either machine. The problem is to find the allocation of the remaining operations to the machines and the optimal robot move cycle that jointly minimize the cycle time. We prove that the optimal solution is either a 1-unit or a 2-unit robot move cycle and we present the regions of optimality. Finally, a sensitivity analysis on the results is conducted.
Open Access
Multiple part-type scheduling in flexible robotic cells
(2009) Batur, Gül Didem
This thesis considers the scheduling problem arising in two-machine manufacturing cells which repeatedly produce a set of multiple part-types, and where transportation of the parts between the machines is performed by a robot. The cycle time of the cell depends on the robot move sequence as well as the processing times of the parts on the machines. For highly flexible CNC machines, the processing times can be adjusted. As a result, this study tries to find the robot move sequence as well as the processing times of the parts on each machine that minimize the cycle time. The problem of determining the best cycle in a 2- machine cell is first modeled as a travelling salesman problem. Then, an efficient 2-stage heuristic algorithm is constructed and compared with the most common heuristic approach of Longest Processing Time.
Open Access
Robotic assembly line design with tool changes
(2009) Tula, Adnan
This thesis is focused on assembly line design problems in robotic cells. The mixed-model assembly line design problem that we study has several subproblems such as allocating operations to the stations in the robotic cell and satisfying the demand and cycle time within a desired interval for each model to be produced. We also ensure that assignability, precedence and tool life constraints are met. The existing studies in the literature overlook the limited lives of tools that are used for production in the assembly lines. Furthermore, the studies in the literature do not consider the unavailability periods of the assembly lines and assume that assembly lines work 24 hours a day continuously. In this study, we consider limited lives for the tools and hence we handle tool change decisions. In order to reflect a more realistic production environment, we deal with designing a mixed-model assembly line that works 24 hours a day in three 8-hour shifts and we consider lunch and tea breaks that are present in each shift. This study is the first one to propose using such breaks as tool change periods and hence eliminate tool change related line stoppages. In this setting, we determine the number of stations, operation allocations and tool change decisions jointly. We provide a heuristic algorithm for our problem and test the performances of our heuristic algorithm and DICOPT and CPLEX solvers included in GAMS software on different instances with varying problem parameters.
Open Access
Robotic cell scheduling with operational flexibility
(Elsevier, 2005) Akturk, M. S.; Gultekin, H.; Karasan, O. E.
In this paper, we study the problem of two-machine, identical parts robotic cell scheduling with operational flexibility. We assume that every part to be processed has a number of operations to be completed in these two machines and both machines are capable of performing all of the operations. The decision to be made includes finding the optimal robot move cycle and the corresponding optimal allocation of operations to these two machines that jointly minimize the cycle time. We prove that with this definition of the problem 1-unit robot move cycles are no longer necessarily optimal and that according to the given parameters either one of the 1-unit robot move cycles or a 2-unit robot move cycle is optimal. The regions of optimality are presented.
Open Access
Robotic cell scheduling with operational flexibility
(2002) Gültekin, Hakan
In this thesis, we study the problem of two-machine, identical parts robotic cell scheduling with operational flexibility. We assume that every part to be processed has a number of tasks to be completed in these two machines and both machines are capable of performing all of the tasks. The decision to be made includes finding the optimal robot move cycle and the optimal allocation of tasks to these two machines corresponding to this robot move cycle that jointly minimize the cycle time. We proved that 1-unit robot move cycles are not necessarily optimal with this definition of the problem any more and that according to given parameters either one of the 1-unit robot move cycles or a 2-unit robot move cycle is optimal. We proposed a new robot move cycle, which is a result of the assumption of operational flexibility. This cycle is not only simple and practical but also dominates all of the common cycles reported in the literature. Finally, we considered the change of layout and showed that the cycle time of the proposed cycle can be further reduced by a change in the layout while the cycle times of all other cycles remain the same. Keywords: Robotic cell, cyclic scheduling, automated manufacturing.
Open Access
Scheduling in a three-machine robotic flexible manufacturing cell
(Elsevier, 2007) Gultekin, H.; Akturk, M. S.; Karasan, O. E.
In this study, we consider a flexible manufacturing cell (FMC) processing identical parts on which the loading and unloading of machines are made by a robot. The machines used in FMCs are predominantly CNC machines and these machines are flexible enough for performing several operations provided that the required tools are stored in their tool magazines. Traditional research in this area considers a flowshop type system. The current study relaxes this flowshop assumption which unnecessarily limits the number of alternatives. In traditional robotic cell scheduling literature, the processing time of each part on each machine is a known parameter. However, in this study the processing times of the parts on the machines are decision variables. Therefore, we investigated the productivity gain attained by the additional flexibility introduced by the FMCs. We propose new lower bounds for the 1-unit and 2-unit robot move cycles (for which we present a completely new procedure to derive the activity sequences of 2-unit cycles in a three-machine robotic cell) under the new problem domain for the flowshop type robot move cycles. We also propose a new robot move cycle which is a direct consequence of process and operational flexibility of CNC machines. We prove that this proposed cycle dominates all 2-unit robot move cycles and present the regions where the proposed cycle dominates all 1-unit cycles. We also present a worst case performance bound of using this proposed cycle.
Open Access
Scheduling in robotic cells: process flexibility and cell layout
(Taylor & Francis, 2008) Gultekin, H.; Akturk, M. S.; Karasan, O. E.
The focus of this study is the identical parts robotic cell scheduling problem with m machines under the assumption of process and operational flexibility. A direct consequence of this assumption is a new robot move cycle that has been overlooked in the existing literature. We prove that this new cycle dominates all classical robot move cycles considered in the literature for m = 2. We also prove that changing the layout from an in-line robotic cell to a robot-centered cell reduces the cycle time of the proposed cycle even further, whereas the cycle times of all other cycles remain the same. For the m-machine case, we find the regions where the proposed cycle dominates the classical robot move cycles, and for the remaining regions present its worst case performance with respect to classical robot move cycles. Considering the number of machines as a decision variable, we also find the optimal number of machines that minimizes the cycle time of the proposed cycle.