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
Texas A&M Computer Aided
Manufacturing Lab
Pratt & Whitney
(MP1)
Leadwell
Adept (MP2)
(MH1)
Port
(P1)
Sabre 500
(MP3)
GE-A4
Robot (MH3)
Manual Wksstn 1
(OP1)
Manual Wksstn 2
(OP1)
Puma
Robot (MH2)
Port
(P2)
Port
(P3)
Kardex
(ASI)
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.
• pi is the time per period (time per unit ?units per
period) required by part type i on the key bottleneck
resource.
• si is the savings per period (savings per unit ? units
per period) if part type i is added to the FMS.
• xi is the binary decision variable indicating whether
or not product i is produced in the FMS.
Part Type Selection Formulation
• Knapsack problem
Formulation
N
max
s x
i 1
i
i
s.t
N
px
i 1
i
i
P
xi  0,1
– IP with a single
‘capacity’ constraint
– LP relaxation can be
solved by inspection.
– Solution method :
• Heuristic
• Dynamic
Programming
• Branch and Bound
Greedy Heuristic for Part Type
Selection
1. Order the part types [1] to [N] such that:
S 1
P1

S 2 
P2 
 ...
S N 
P N 
2. For i = 1 to N, select part type [i] if si > 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
si
1
50
1
100
5000
100
50
2
100
1
50
5000
50
100
3
70
.3
75
5250
22.5
233.3
4
30
.5
300
9000
150
60
5
25
.2
25
625
5
125
Sequence: 3-5-2-41
Assignment:
Part Hrs.
3
22.5
5
5
2
50
4
150
pi si/pi
Cumlative
22.5
27.5
77.5
227.5
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.
s1   p1
If s  0
f1    
0
For 2 i  N
otherwise
max si xi  f i 1   pi xi ,   pi
f i     x i 0,1
 f i 1  
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 pi’s are independent of
the parts selected.
• The si’s can be very difficult to assess