Scheduling and sequencing, del 2 Flashcards
Describe FCFS
FCFS = First come, first served
- Focuses only on the time of arrival for the customer or job – no priority rule
- Fair
- Urgent orders may wait for less urgent orders
- Orders with short short processing time may wait for order with longer processing time to be completed.
Sequencing rules when prioritizing jobs that arrive intermittently (med jämna mellanrum) –> one process:
FCFS
FNO
Describe FNO
FNO = Fewest number of operations remaining
- Does not consider the length of time for each operation
Sequencing rules when prioritizing jobs in the short term - one process:
SPT
EDD
LWR
DEscribe SPT
SPT = Shortest processing time
- Tends to minimize average flow time and WIP inventory and miximize resource utilization
- Risk of tardiness of orders with long processing time if new sequences of orders are made continuously
- Flow time = Que time + Processing time
Describe EDD
EDD = Earliest due date
- Minimizes the maximum of jobs past the due date
- Does not perform well on average flow time, WIP inventory or resource utilization
Describe LWR
LWR = Least work remaining
- Sum of all processing times for operations not yet performed
Vad är one process samt two process problems?
One process = en enda maskin eller arbetsstation
Two process = två maskiner / arbetsstationer
Vad används vid two processes?
Johnsons rule
Beskriv de 4 stegen i Johnsons rule
Step 1 - List the jobs and their processing times on Resources #1 and #2
Step 2 - Find the job with the shortest sequencing time
Step 3 - If this time corresponds to Resource #1, sequence the job first; if it corresponds to resource #2, sequence the job last
Step 4 - Repeat steps 2 and 3 using the next-shortest processing time
- Work inward from both ends of the sequence until all jobs have been schedule
Vad är vehicle routing problem?
Ett optimeringsproblem där målet är att hitta “best routes”, dvs med kortaste distans eller lägst kostnad, för a fleet of vehicles
How to find best option in vehicle problem?
Through enumeration. Enumeration is carried out for all possible route to find the best route plan and shortest total delivery time. It helps reduce operating costs and greenhouse gas emissions
Vad är Clark-Wright Heurestic Method?
En metod som utgår från att varje kund is serviced individually from the depot.
Metoden går sedan ut på att kombinera kunder i längre routes för att minska total travel time and remain withthin capacity requirements
