PRODUCTION ACTIVITY CONTROL
(PAC)
Shop floor control
PLANNING AND CONTROL ACTIVITIES IN
MANUFACTURING ENTERPRISE
Demand
Resources
Strategic plan
Sales &Operation Plan
(aggregated)
Resource
Planning
Master Production
Schedule (MPS)
Rough-cut
Capacity Plan
Material Requirements Plan
Detailed
Capacity Req. P.
Forcasts
Customers
Orders
Plan
Execution
Purchasing
Control
Production
Control (PAC)
Input /Output
Control
Production Activity Control – PAC
Shop Floor Control
PAC – the lowest level of production management
system in a company
PAC - regulates the work flow through the production
system
– Master scheduling (MPS/MRP) is a Planning activity
– Production Activity Control is an Execution Control activity
Production Activity Control
Master Production Scheduling
Material Reguirements Planning
Capacity Reguirements Planning
Planned Orders
Data
Production Activity Control
Scheduling, Dispaching, Monitoring
Instructions
Data
Manufacturing processes
Production Activity Control transfers the data from higher levels of production
planning (MPS, MRP, CRP) into manufacturing processes instructions.
It also tranforms data from shop floor level into information for higher planning
levels.
Production Activity Control
Production Activity Control scope, complexity, principles,
methods depend on production continuity
Production continuity could be:
• flow shop type (continuous flow)
• job shop type (intermittent flow, irregular flow)
Production control systems:
•
Flow control - for continuous production flow
•
Order control - for intermittent production flow
(irregular flow, not continuous production flow)
Intermittent production flow
Intermittent production flow:
•
•
•
•
•
The products are produced based on customer's orders, on a small scale.
The flow of production is intermittent (irregular)
The large varieties of products are produced
The products are different sizes. No continuous flow of the same size.
The production system is very flexible
The types of intermittent production flows:
1. Project production flows
2. Jobbing production flows
3. Batch production flows
Examples:
• Tailor
• Goldsmith
• Furniture to order industry, car to order, ship to order
• Product to order industry
Continuous production flow
Continuous production flow:
1.The flow of production is continuous.
2.The products are standardized.
3.The products are produced in anticipation of demand, based on
demand forecast.
4.Standardized routing sheets and schedules are prepared.
The types of a continuous production flows:
1.Mass production flows
2.apparatus (prosess) production flows.
Examples:
• Food industry
• Fuel industry
• Cosmetics industry
• Washing and hygiene industry (soaps, tooth pastes, etc)
Production Activity Control
The main elements of PAC
1. Scheduling – to develop detailed schedule based on timely
knowledge and data which will ensure that all the production
requirements are fulfilled .
2. Dispatching – to implement the schedule taking into account
the current status of the production system (orders releasing)
3. Monitoring – to monitor the status of vital components in the
system, either with the naked eye or by using technology based
methods.
Order Control
The objective of Order Control is to optimize the particular order
flow through the facility so that production aims are met
The goals of Order Control:
1.
2.
3.
4.
5.
High percentage of orders completed on time
High utilisation of workers and facilities
Low work-in-process (WIP) inventory
Minimize customer wait time
Minimize costs
Job shop scheduling
The main Order Control activity is job shop scheduling
Scheduling involves assigning due dates to specific jobs (when to
start the job, when to finish the job)
Job shop scheduling involves:
1. Allocating jobs to specific work centers (loading)
2. Prioritizing all jobs at each work center (sequencing)
3. Release jobs to workcenters (dispaching)
4. Revising priorities as changes occur
5. Monitoring the progress of jobs
Job shop scheduling is used to all operations in a factory, hospital,
university or office. For service operations, „job” is replaced by
patient, customer or whatever flows through the facility. The work
center may be a desk, office, room, or skill speciality.
Production Activity Control
Job shop control process
Start
Allocate jobs to work centers
(Loading)
Prioritize all jobs at work centers
(Sequencing)
Release jobs to workcenters
(Dispaching)
Review jobs progress
Completed jobs
Uncompleted jobs
Scheduling techniques
There are two scheduling techniques to assigning due dates to
specific jobs:
• Forward scheduling
• Backward scheduling
Forward scheduling – an approach to scheduling that starts from
the present time and schedules each job to start at the earliest
possible moment. Advantages: time buffers, Disadvantages: increase
work in process inventory
Backward scheduling - an approach to scheduling that starts from
desired due date and works backward. Advantages: decrease the
work in process inventory; Disadvantages: no time buffers.
Forward Scheduling
B
Today
Backward Scheduling
B
E
Due Date
Today
E
Due Date
Shop Loading
The allocation of jobs to work centers is called shop loading
Loading methods :
1. Infinite loading - It does not take into consideration the limited capacity of
the facility. Scheduling with unlimited capacity
2. Finite loading – assigns jobs to work centers without regard to
capacity limitations. Scheduling with limited capacity
INFINITE LOADING (without regard for capacity)
Capacity
over
under
1
2
3
4
5
6
Time period
Shop loading
Finite loading - scheduling with limited capacity –
It takes into considaration the limited capacity of each work center.
FINITE LOADING (never to exceed capacity)
Capacity
1
2
3
4
5
6
Time perid
Infinite loading
Planned orders to relise emitted by MRP system: 1,2,3,4,5.
Completion due date.: Orders1 and 4 – end of period 4.
Orders 2,3,5 – end of period 5
Start due date: Order.1 & 2 – beginning of period 1., Order.3 & 4 – b. period 2. Order 5 – b.
period 3.
Order
1
2
3
4
5
Work station load
(normal hours)
Load calculation:
Setup time + (n x tj)
E.g. order 1:
Setup = 1 h
Volume = 100 unites
Unit time = 0,4 h
Load = 1 + 100 x 0,4 = 41 h
80
40
1
2
3
4
5
Period
Finite loading
3 Orders planned to execution in week X (one week = 40 hours)
Order
Turning [h]
Milling [h]
Driling [h]
1
8
12
2
2
4
2
2
3
2
8
2
Machine
1 Day
8h
Lathe
1
2 Day
16h
3
3 Day
24h
Move time: 2 h.
Orders execution sequense (1,3,2)
determined with help of critical ratio
4 Day
32h
5 Day
40h
2
Mill
1
3
Drill
2
1
Load
of Lathe [h]
3
2
Capacity
8
6
0
1
2
3
4
5
Day
Sequencing
Gantt Chart - at the same time assign the operations to machines and define the sequence
Gantt Chart - based on forward scheduling principles
Example:
Order
Operation 1
[h]
Operation 2
[h]
Operation3
[h]
Order
Completion due date
A
B
C
D
24
16
24
16
A
Lathe
3
Drill
2
B
Mill
4
Drill
3
C
Lathe
2
Mill
3
D
Drill
5
Lathe
4
Mill
4
Drill
4
Delay and move time between machines 6 h.
Machine
1
Lathe
OrderA
Oper1
1
Mill
2
3
4
5
2
6
7
3
4
5
3
4
Order D Oper 1
8
9
Order D Oper 2
interval
sequencing
6
7
8
9
interval
5
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
interval
Order
C
Oper1
Order B Oper 1
1
Drill
2
6
7
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Order C
Oper 2
8
interval
9
interval
Order A Oper 3 interval
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Order Order B
A
Oper 2
Oper2
interval
Order C Oper
3
sequencin
g
Sequencing Jobs In Work Centers
Priority Rules for Dispatching Jobs
Scheduling - provides a basis for assigning jobs to work centers
Loading - is a capacity-control technique that highlights overloads and underloads
Sequencing - specifies the order in which jobs should be done at each work center.
Priority rules - determine the sequence of jobs in process-oriented facilities
1. First Come, First Served - FCFS. Job that enters the work center first has first pririty
2. Shortest processing time (SPT). Job with the shortest processing time is first executed
3. Longest processing time (LPT). Job with the longest processing time is first executed
4. Earliest due date (EDD). Job which is due first should be started first
5. Total slack (S). Job with the least total slack (buffor time) is done first
6. Random selection (RS). Random selected job is first executed .
7. Critical Ratio (CR). Job with the lowest critical ratio is done first
Critical Ratio
The critical – ratio (CR) is the rule that considers both due date and processing
time .
Due date – Today’s date
CR =
Total processing time remaining
The job with the lowest CR is scheduled next.
CR = 1 – the order job has time to be completed on time
CR < 1 – the order job is delayed (it is already past due)
CR > 1 – the order job has time buffer
The CR rule is dynamic. The job’s critical ratio will change over time. The critical ratio
must be constantly updated
Input-Output Control
Many firms have difficulty in scheduling because they overload the
production processes. This often occurs because they do not know
actual performance in the work centers. Effective scheduling depends
on matching the schedule to performance in the work centers. Lack of
knowledge about capacity and performance causes increasing in lead
times.
Input-Output Control is a technique that allows operations personnel
to manage facility work flows.
• If the work is arriving faster than it is being processed, we are
overloading the facility and a backlog develops. Overloading causes
crowding in the facility, leading to inefficiencies and quality
problems.
• If the work is arriving at a slower rate than jobs are being performed,
we are underloading the facility and the work center may run out of
work. Underloading the facility results in idle capacity and wasted
resources
Input-Output Control
Example: (work
Past
Period
Future
1
2
3
4
5
6
48
50
50
52
52
52
156
154
152
Planned Input
[h]
50
56
48
Actual Input
[h]
54
56
52
Planned output
[h]
52
52
52
Actual output
[h]
56
52
48
Planned load
[h]
152
156
152
Actual load
[h]
152
156
160
PRODUCTION ACTIVITY CONTROL SYSTEM
Production Activity Control system modules:
1.SCHEDULING - to develop a plan (schedule) based on current knowledge and data which
will ensure all the production requirements are fulfilled
2.DISPACHING - to implement the schedule taking into account the current status of the
production system
3.MONITORING – to monitor the status of vital components in the production system during
the dispatching activity
MASTER PRODUCTION SCHEDULING
MATERIAL PRODUCTION SCHEDULING
CAPACITY PLANNING
Planned orders
SCHEDULING
Schedules
MONITORING
DISPACHING
Instructions
Data collection
Devices, machines, production process
PAC system
A Production Activity Control System
Should
• Schedule incoming orders without violating capacity
constraints of individual work centers
• Check availability of tools and materials before releasing
an order to a department
• Establish due dates for each job and check progress
against need dates and order lead times
• Check work in progress as jobs move through the shop
• Provide feedback on plant and production activities
• Provide work efficiency statistics and monitor operator
times for payroll and labor distribution analyses
Order Release Begins Shop Loading
1
2
3
Gross Requirements
Scheduled Receipts
Available
Release
Order
Yes
100
Priority &
Capacity OK?
Net Requirements
Planned Order Rec.
Planned Order Rel. 100
No
Hold
Release
Johnson’s Rule – Johnson’s Algorithms
• Used to sequence n jobs through 2 machines in the
same order
Jobs (n = 3)
Job A
Job B
Job C
Saw
Drill
Sequencing Jobs on Two Machines
Job I
Sequence I, II
Job II
Machine 1
Machine 2
Cumulated Lead Time 15 hours
Sequence II, I
Machine 1
Machine 2
Cumuleted Lead Time 12 hours
The sequance of jobs has impact on total processing time (lead time) of the
jobs
Johnson’s rule for sequencing n jobs (orders) on two
machines
Johnson’s rule can be used to minimize the total processing time by sequencing a
group of jobs on two machines . All jobs must followed the same sequence through the
two machines
Start
List all job times for m1 and m2
Select the shortest job time in m1 or m2
No
Yes
Is it in m1?
Assign it as late as possible to m1
Assign it as early as possible to m1
Delete the job assigned from the list
Are all jobs assigned
Stop
Johnson’s rule for sequencing n jobs on
two machines
Work processing time for five jobs (in hours)
Job
Machine 1
(drill)
Machine 2
(lathe)
1
5
22
2
3
3
8
6
44
4
10
7
5
77
12
Initial jobs sequence:
1,2,3,4,5
Optimal jobs sequence: 2,5, 4, 3, 1
Lead time = 45h
Lead time = 35h