Erik's deli serves hot and cold food items. Customers choose between hot or cold queues upon entering. They are assigned patience levels and may leave if wait times exceed theirs. Servers and cashiers have varying service times. Erik plans to add dining to encourage more purchases. A wafer tool has two process modules A and B. Wafers are assigned modules and queue accordingly. They are given attributes like process time. Modules and robots have varying cycle times. The robot is a bottleneck. There are plans to improve throughput by optimizing the tool architecture and components. [DOCUMENT]: What’s with Scheduling? (Queues, Delays & Throughput) G. Mustafa

1. What’s with Scheduling?
(Queues, Delays & Throughput)
G. Mustafa ©
11|21|2016

2. PART I : Erik’s Deli – Customer Flow

3. Erik’s Deli – The Lunch Scene
Erik’s Lunch Scene
Erik’s lunch menu consists of cold cuts
and hot food. Customers, upon entrance
choose between cold or hot food, and
form queues, one for the cold, the other
for hot. In addition, each customer is
attributed with patience (low to high).
Those with low patience will leave the
queue, after a pre-assigned time and is
lost business. Customers wait in
respective queues to be served by
servers, attributed by service time –
some are slower. After customers are
served, they proceed to form a queue at
the cash register. The cashiers charge
them – these are also characterized by
their service time. Customers leave
Erik’s Deli with their food.
Erik plans to include a dinning area to
entice customers to stay longer and
hopefully order more food.
ColdFood
HotFood
Menu
Cashier
Customers
Enter
Customers
Exit
Customers
Leaving
G. Mustafa©| 2016

4. Erik’s Deli Open for Lunch
Customers come in
(exponentially distributed
mean arrival time 1)
They randomly choose
between cold and hot food
(with 50% probability)
Customers are assigned
serve time (exp. 5 mean)
They are
handed menus
(Assigned attributes)
Hostess routes them to
cold or hot counters
Hot food queue
Cold cut queue
Hot Food servers
Cold Food servers
G. Mustafa©| 2016

5. Erik’s Deli  Customer Flow Diagram
Customers Enter
Assigned Number
Handed Menu
Cold or HotCold Queue Hot Queue
Cold Counter Hot Counter
Cold Cus.
Served
Hot Cus.
Served
Checkout
Queue
Checkout
Cashier
G. Mustafa©| 2016

6. Erik’s Deli  Customer Flow Model
Customers come in
(exponentially distributed
mean arrival time 1)
They randomly choose
between cold and hot food
(with 50% probability)
Customers are assigned
serve time (exp. 5 mean)
They are
handed menus
(Assigned attributes)
Hostess routes them to
cold or hot counters
Cold food queue
Hot food queue
Cold food queue length
Hot food queue
length
Cold food serve counter
Hot Food counter
Cold food served
Cold food average wait
Hot Food served
Hot Food average wait
Served
Customers
G. Mustafa©| 2016

7. Erik’s Deli  Customer Flow Simulation
Cold Food Queue Hot Food Queue
Hot Food WaitCold Food Wait
G. Mustafa©| 2016

8. Traffic on N85 @ Almedan Expressway (6-9am)
1
1
2
2
3
3
4
4
5
5
6
7
8
7
6
8
Average wait @ Almedan
Queue @ Almedan
G. Mustafa©| 2016

9. PART II : Cluster Tool Scheduling
G. Mustafa©| 2016

10. Input
Output
Process
Module A
Process
Module B
Wafer
Handling
Robot
Tool Architecture
A wafer processing tool comprises
of two process modules. A single
wafer handling robot serves process
modules. Incoming wafers are
sorted and put in FOUPS of given
capacity. Once inside FOUPS, wafers
are transferred to process models A
or B. After the wafers are
processed, they are moved by the
Tool Architecture & Wafer Sequence
FOUP
A
FOUP
B
G. Mustafa©| 2016

11. Tool Architecture & Wafer Sequence
Wafer Process Sequence
A wafer processing tool consists of two
process modules. Wafers, as they arrive,
are assigned a process A or B, and form
two queues, one for A, the other for B.
In addition, each wafer is attributed
with pre-process qualification metric
(process time etc). The wafers wait in
their respective queues (FOUPS) to be
served by process modules, that are
endowed with some process time with some
variability. After the wafers have been
processed, they proceed to form a queue
at the tool output. Wafers depart the
tool.
It has been determined that wafer handing
presents a major bottleneck. There are
plans to improve robot designs and motion
profiles. Tool architecture also needs
improvement (multiple process modules,
process time reduction, etc.) The
baseline architecture, as described,
needs to be evaluated for throughput to
prioritize design options.
Incoming wafers
FOUP A
Robot
Process
A
Process
B
Outgoing wafers
Inspection
Queue
FOUP B
G. Mustafa©| 2016

12. Create discrete wafers
can be timed, random
or event based
Assign attributes to wafers
They can be characteristics
Process time type, quality
Rout wafers
Based on attributes
Provide Process Modules
Define process characteristics
(constraints, timeouts, queue length)
System Model
process, wafer handling
Retire wafers
System Output
Bottlenecks
Efficiency
Utilization
Uptime
Downtime
Failure Rate
Statistics
Statistics Statistics
Statistics Statistics
System Optimization
Cluster Tool Discrete Event Model
G. Mustafa©| 2016

13. Cluster Tool Model
Incoming wafers
FOUP
A
FOUP
B
Process
A
Process
B
Robot
Wafers come in at regular
Intervals, based on an
event Or randomly
Wafers are sorted based
on Attributes,
characteristics, process
Wafers are moved based
on motion profile or
robot characteristics
Wafers are processed
according to attributes.
Modules are assigned
process times, process
steps, etc.
G. Mustafa©| 2016

14. Cluster Tool Performance
Incoming wafers
Wafers in
FOUP B
Robot
Process B
Process AWafers in
FOUP A
Utilization
Handling
Time
Utilization
Utilization
Process
Time
Process
Time
G. Mustafa©| 2016

15. Wafer Sorter (2 POD)
A1 A2
B1 B2R
A1 A2
B1
B2
R
Fast Robotics Slow Robotics
Wafer Sorting
Two type of wafers are to be sorted (A, B) and transported from input FOUPS
(A1, B2) to output FOUPS (A2, B2). Wafer handling is carried out by a wafer
handling robot that can move one wafer at a time from input to output. Sorting
is done according to FIFO.
G. Mustafa©| 2016

16. PART II : Tool Design Optimization
G. Mustafa©| 2016

17. Throughput Improvement
Wafer Process Sequence
A wafer processing tool consists of two
process modules. Wafers, as they arrive,
are assigned a process A or B, and form
two queues, one for A, the other for B.
In addition, each wafer is attributed
with pre-process qualification metric (low
to high). Those with low will leave the
queue. This amounts to productivity loss.
The wafers wait in their respective queues
to be served by process modules, that are
with some process time with some
variability – some are slower. After the
wafers have been processed, they proceed
to form a queue at the tool output for
inspection – these are also characterized
by their inspection time. Wafers depart
the tool.
There are plans to include a storage area
to improve wafer flow bottleneck; wafer
handling robots and process modules. The
baseline architecture, as described, needs
to be evaluated for throughput to
prioritize design options.
G. Mustafa©| 2016

18. PART III : Tool Architectures
G. Mustafa©| 2016

19. Sorters, Buffers and Clusters
G. Mustafa©| 2016

20. Cluster Tool Architectures
Robotics
G. Mustafa©| 2016

21. Cluster Tool Architectures
G. Mustafa©| 2016