Pemilihan Tipe Komponen D0394 Perancangan Sistem Manufaktur Kuliah Ke XIX - XX

Flexible Manufacturing Systems (FMS) An FMS is a “reprogrammable” manufacturing system capable of producing a variety of products automatically. Conventional manufacturing systems have been marked by one of two distinct features: –The capability of producing a variety of different product types, but at a high cost (e.g., job shops). –The capability of producing large volumes of a product at a lower cost, but very inflexible in terms of the product types which can be produced (e.g., transfer lines). An FMS is designed to provide both of these features.

FMS Component Numerical Control (NC) machine tools Automated material handling system (AMHS) –Automated guided vehicles (AGV) –Conveyors –Automated storage and retrieval systems (AS/RS) Industrial Robots Control Software

GE-A4 Robot (MH3) Kardex (ASI) Port (P3) Sabre 500 (MP3) Leadwell (MP2) Puma Robot (MH2) Port (P2) Port (P1) Manual Wksstn 1 (OP1) Manual Wksstn 2 (OP1) Adept (MH1) Pratt & Whitney (MP1) Texas A&M Computer Aided Manufacturing Lab

Classification of FMS-related Problems Strategic analysis and economic justification, which provides long-range, strategic business plans. Facility design, in which strategic business plans are coalesced into a specific facility design to accomplish long-term managerial objectives. Intermediate-range planning, which encompasses decisions related to master production scheduling and deals with a planning horizon from several days to several months in duration. Dynamic operations planning, which is concerned with the dynamic, minute-to-minute operations of FMS.

FMS Problems Part type selection (Askin) - selecting parts that will be produced in the FMS over some relatively long planning horizon. Part selection (Stecke) - from the set of parts that have current production requirements and have been selected for processing in the FMS, select a subset for immediate and simultaneous processing. Machine grouping (Stecke) – partition machines into groups where each machine in a group can perform the same set of operations. Loading (Stecke) - allocate the operations and required tools of the selected part types among the machine groups. Control - provide instructions for, and monitor the equipment in the FMS so that the production goals identified by the above problems are met.

FMS Part Type Selection Problem The part type selection problem is involves determining which parts should be produced in an FMS. –In theory, there should by some savings achieved by producing some parts in the FMS rather than producing them on manual equipment or purchasing them from outside. –The objective is to load the FMS to maximize the savings achieved by producing parts in the FMS subject to FMS capacity constraints. Typically, the part type selection problem is solved infrequently For example, the decision to outsource a part rather than producing it in-house requires time for the subcontractors to do the required design and tooling.

Part Type Selection Formulation Parameters/Variables: P is the production time per period available on the key,bottleneck resource. p i is the time per period (time per unit  units per period) required by part type i on the key bottleneck resource. s i is the savings per period (savings per unit  units per period) if part type i is added to the FMS. x i is the binary decision variable indicating whether or not product i is produced in the FMS.

Part Type Selection Formulation Knapsack problem –IP with a single ‘capacity’ constraint –LP relaxation can be solved by inspection. –Solution method : Heuristic Dynamic Programming Branch and Bound Formulation

Greedy Heuristic for Part Type Selection 1.Order the part types [1] to [N] such that: 2.For i = 1 to N, select part type [i] if s i > 0 and inclusion is feasible. 3.Example: Given the following parts, and assuming that there are 250 hours available on the FMS, use the above heuristic to perform the part type selection:

Example ( cont’d ) Parts Unit Savings Unit Proc. Time Demand sisi pipi s i /p i Assignment: Part Hrs. Cumlative Sequence:

Optimal Solutions Dynamic programming –Principle of Optimality - For any initial stage, state, and decision, subsequent decisions must be optimal for the remainder of the problem that results from the initial decision. In other words, given a stage and state, the optimal decision from that point on is independent of how you got to that state. –The decision of whether or not to include each part type in the FMS is a stage. The state is the remaining processing time on the FMS.

Dynamic Programming Let fi(  ) be the cost savings for the optimal decision regarding part types 1 to i if they occupy  time units per period on the FMS. If s  0 For 2  i  N

Comment on the Part Type Selection Problem Assumes that either all or none of a product is produced in the FMS. Assumes that there is a single key, bottleneck resource and that the other resources have sufficient capacity to handle any configuration of parts Assumes that the p i ’s are independent of the parts selected. The s i ’s can be very difficult to assess