Summary Operations Management and Control

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