Prelim 1 – Module 2 Flashcards
Capacity
Output per unit time when fully busy, can refer to a single station, work area, or entire process
Throughput
Capacity for the entire process. This is the long-run average output per unit time.
Bottleneck
The resource that limits production. It determines the cycle time of the entire system.
Cycle Time (CT)
CT = 1/Capacity
Average time between completions of successive units for
- the entire system (think about a bell ringing upon each completion)
- an entire work area (i.e., group of workers doing same job), or
- a single work
- often convert units
Capacity Utilization
actual output rate/capacity
can refer to a single station, work area, or entire process
Rush Order Flow Time
The minimum (i.e., completion time minus entry time) to go through the system without any waiting.
Total Direct Labour Content
Sum of all the operation times
Direct Labour Utilization
What percent of the time are workers actually contributing value?
= total direct labour content/(process cycle time)(# of workers)
Throughput Time
How long does it take to complete a process from time of arrival to time of exit? (including wait time) aka “sojourn time”
Why do bottlenecks exist?
Inefficient process, too few resources, excess demand, unbalanced workload
What can we do about bottlenecks?
Change the process at the bottleneck, add resources, control demand, shift resources
Serial
Customer goes to one station and then the next
Capacity λ1 -> Capacity λ2
Has the same throughput as capacity min(λ1, λ2)
Parallel
Customer is “served” by both simultaneously, and needs both to be done before moving on; e.g., body screening and luggage screening in airport security line
Has the same throughput as Capacity min(λ1, λ2)
Diagram: Capacity λ1 over Capacity λ2
Multiple Servers
Customers can go to either
Has the same throughput as Capacity λ1+2λ
Diagram: Capacity 1λ over Capacity 2λ with a box around both
Strategy to solve
Convert everything to a rate = completions/unit of time
What does the process capacity calculation tell us?
Average completion rate with - a “fully loaded” system (i.e., infinite customers)
- note that the completion rate may vary over the short term
What does the process capacity not necessarily tell us?
- throughput time
- average number of customers in the system
Theory of Constraints
Core idea: every process has a single constraint that limits total process throughput.
Corollary: improving non-constraints will not provide significant benefits.
5 focusing steps and meaning
- Identify: determine the current constraint
- Exploit: make quick improvements to that constraint’s capacity
- Subordinate: review other activities and re-align to support the constraint
- Elevate: invest in more substantial improvements to the constraint
- Repeat: go back to step 1 once previous constraint is no longer a constraint
Fix the Mix to Improve Throughput
Some processes have customers of different “classes”.
If we don’t have the right mix of servers, throughput could suffer.
We need to know: customer mix, total resource budget ($, SF, # seats), and amount of resources needed for each type of server
