OPERATIONS
MANAGEMENT
& CONTROL
Quirine Rodenberg
,Week 1 - Reader Deterministic Performance
Estimation
2. Flow Diagram
- Flow diagrams
o Illustrate the movement of materials, information or people through
all processes required to transform resources into products or
services
Blocks production or service process
Arrows direction of flow
o Used to analyse and record activities in an objective and structured
way
- Incorporating data
o Interarrival time
Time between two subsequent arrivals of products and their
entrance in the process
o Arrival rate = lambda
The number of products that arrive per time unit
- Other tools
o Time-function mapping
Flow diagram in which the time is added on a horizontal axis
o Process charts
Analysing the movement of people or material by using
symbols, time and distance
o Service blueprinting
Used to focus on the customer and the interaction with the
customer
3. Throughput times
- Throughput time
o The time that passes between the moment at which the
product/customer enters the system ad the moment at which the
product/customer is ready
o Deterministic process adding the expected processing times of
different processes
Using the average value and neglecting stochastic effects
such as probability distributions
Lowe than or equal to actual throughput time
- Throughput times with multiple paths
o Estimate the throughput time for one of the possible paths in the
production process
o Multiple the resulting TH time with the probability that this path will
be followed
o Repeat this till all paths have been handles
o Estimate TH time by adding up the results for all paths
, - TH time estimates for different types of products in one system
o Calculating for separate paths
- Difference between actual and estimated TH times
o Difference might be big due to exclusion of waiting lines (buffers) on
the TH time
The case with deterministic estimation
Only useful for mutual comparisons and easily
obtainable information
o In practice simulation is used to include the effect of waiting lines
4. Design and effective capacity
- Capacity
o The upper limit a process can handle
o Matching supply and demand
Might be a gap between achieved and desired capacity
Overcapacity non-working machines and employees
higher operational costs
- Design capacity
o The theoretical maximum output of the process in a given period of
time
o Ideal situation without waiting times and with deterministic
processing times
o Number of units that can be produced
o Calculation
Determine the deterministic processing time of the process
Translate into production rate
Number of units produced per time unit
o Multiply this when there are multiple
operators/machines working in parallel
- Sufficiency of design capacity
o Compare the number of arriving products with the design capacity
o Determination
Calculate the design capacity
Calculate the expected number of products arriving at the
process
When there are different paths, take the related
percentage into account
Compare
- Effective capacity
o Capacity that can be expected given the current constraints
Differences might be because the process was designed for a
different products or has a known machine failure
o Design capacity – productivity loss
, 5. Bottleneck
- Bottleneck
o Limits the output of the production/server system
Slowest process in the system, has less design capacity
If none of the processes in the system is the bottleneck, then
the arrival process is the bottleneck
o Determination single path
Calculate the design capacity of each process
Calculate the expected number of products arriving at the
system
If the design capacity of all processes is sufficient
arrival process is bottleneck
If one or more processes have insufficient design
capacity select process with smallest design capacity
this process is the bottleneck
o Determination multiple paths
Calculate the design capacity of each process
Calculate for each process the expected number of products
arriving at the process
If the design capacity of all processes is sufficient
arrival process is bottleneck
Check for each path if one or multiple processes on the
path have insufficient design capacity
o Select the process with the smallest design
capacity bottleneck
6. Departure rate
- Departure rate = throughput = TH = mu
o Indicates the number of products/customers that leave the system
per time unit
o Determined by the output of the bottleneck
o Only equals the value of the arrival rate when the arrival process is
the bottleneck in the system
7. Utilisation and efficiency
- Utilisation
o The fraction of total time in which a machine/service-unit is used for
production/service
o Total time in operation / total time
o Actual output / design capacity
- Efficiency
o Some constraints limit the utilisation
Breaks, machine failures
o Efficiency is a measure for the achieved output compared to the
effective capacity constraints not taken into account
If there are no additional constraints efficiency = utilisation
- Utilisation rate for n identical parallel machines
o Several machines/operators working in parallel at the same process
MANAGEMENT
& CONTROL
Quirine Rodenberg
,Week 1 - Reader Deterministic Performance
Estimation
2. Flow Diagram
- Flow diagrams
o Illustrate the movement of materials, information or people through
all processes required to transform resources into products or
services
Blocks production or service process
Arrows direction of flow
o Used to analyse and record activities in an objective and structured
way
- Incorporating data
o Interarrival time
Time between two subsequent arrivals of products and their
entrance in the process
o Arrival rate = lambda
The number of products that arrive per time unit
- Other tools
o Time-function mapping
Flow diagram in which the time is added on a horizontal axis
o Process charts
Analysing the movement of people or material by using
symbols, time and distance
o Service blueprinting
Used to focus on the customer and the interaction with the
customer
3. Throughput times
- Throughput time
o The time that passes between the moment at which the
product/customer enters the system ad the moment at which the
product/customer is ready
o Deterministic process adding the expected processing times of
different processes
Using the average value and neglecting stochastic effects
such as probability distributions
Lowe than or equal to actual throughput time
- Throughput times with multiple paths
o Estimate the throughput time for one of the possible paths in the
production process
o Multiple the resulting TH time with the probability that this path will
be followed
o Repeat this till all paths have been handles
o Estimate TH time by adding up the results for all paths
, - TH time estimates for different types of products in one system
o Calculating for separate paths
- Difference between actual and estimated TH times
o Difference might be big due to exclusion of waiting lines (buffers) on
the TH time
The case with deterministic estimation
Only useful for mutual comparisons and easily
obtainable information
o In practice simulation is used to include the effect of waiting lines
4. Design and effective capacity
- Capacity
o The upper limit a process can handle
o Matching supply and demand
Might be a gap between achieved and desired capacity
Overcapacity non-working machines and employees
higher operational costs
- Design capacity
o The theoretical maximum output of the process in a given period of
time
o Ideal situation without waiting times and with deterministic
processing times
o Number of units that can be produced
o Calculation
Determine the deterministic processing time of the process
Translate into production rate
Number of units produced per time unit
o Multiply this when there are multiple
operators/machines working in parallel
- Sufficiency of design capacity
o Compare the number of arriving products with the design capacity
o Determination
Calculate the design capacity
Calculate the expected number of products arriving at the
process
When there are different paths, take the related
percentage into account
Compare
- Effective capacity
o Capacity that can be expected given the current constraints
Differences might be because the process was designed for a
different products or has a known machine failure
o Design capacity – productivity loss
, 5. Bottleneck
- Bottleneck
o Limits the output of the production/server system
Slowest process in the system, has less design capacity
If none of the processes in the system is the bottleneck, then
the arrival process is the bottleneck
o Determination single path
Calculate the design capacity of each process
Calculate the expected number of products arriving at the
system
If the design capacity of all processes is sufficient
arrival process is bottleneck
If one or more processes have insufficient design
capacity select process with smallest design capacity
this process is the bottleneck
o Determination multiple paths
Calculate the design capacity of each process
Calculate for each process the expected number of products
arriving at the process
If the design capacity of all processes is sufficient
arrival process is bottleneck
Check for each path if one or multiple processes on the
path have insufficient design capacity
o Select the process with the smallest design
capacity bottleneck
6. Departure rate
- Departure rate = throughput = TH = mu
o Indicates the number of products/customers that leave the system
per time unit
o Determined by the output of the bottleneck
o Only equals the value of the arrival rate when the arrival process is
the bottleneck in the system
7. Utilisation and efficiency
- Utilisation
o The fraction of total time in which a machine/service-unit is used for
production/service
o Total time in operation / total time
o Actual output / design capacity
- Efficiency
o Some constraints limit the utilisation
Breaks, machine failures
o Efficiency is a measure for the achieved output compared to the
effective capacity constraints not taken into account
If there are no additional constraints efficiency = utilisation
- Utilisation rate for n identical parallel machines
o Several machines/operators working in parallel at the same process
