Design & Sim. of Mfg. Systems/Mfg Syst Design & Simulation-SP18-001

Basic Arena Blocks - 1

To better understanding the Arena simulation software blocks, students should associate these blocks with the system components (Notes 1).

Create

Create entities.

The starting point for entities in a simulation model.

Entities are created using a schedule or based on a time between arrivals. Entities then leave the

module to begin processing through the system. The entity type is specified in this module.

· The start of a part’s production in a manufacturing line

· A document’s arrival (e.g., order, check, application) into a business process

· A customer’s arrival at a service process (e.g., retail store, restaurant, information desk)

Assign

Assign block is used for assigning new values to variables, entity attributes, entity types, entity pictures, or other system variables. Multiple assignments can be made with a single Assign block. Most of time, there should be an Assign block after the entities are created.

TYPICAL USES

· Collect the number of jobs completed each hour

· Count how many orders have been late being fulfilled

· Record the time spent by priority customers in the main check-out line

· …

Process

Options for seizing and releasing resource constraints are available. The process time is allocated to the entity and may be considered to be value added, non-value added, transfer, wait, or other. The associated cost will be added to the appropriate category.

· Machining a part

· Reviewing a document for completeness

· Fulfilling orders

· Serving a customer

Resources

This is a data block (not actually in the process mapping model). This block defines the resources in the simulation system, including costing information and resource availability. Resources may have a fixed capacity that does not vary over the simulation run or may operate based on a schedule. Resource failures and states can also be specified in this module.

TYPICAL USES

· Equipment (machinery, cash register, phone line)

· People (clerical, order processing, sales clerks, operators)

Queue

This is a data block. Queue block may be utilized to change the ranking rule for a specified queue. The

default ranking rule for all queues is First In, First Out unless otherwise specified in this module. There is an additional field that allows the queue to be defined as shared.

TYPICAL USES

· Stack of work waiting for a resource at a Process module

· Holding area for documents waiting to be collated at a Batch module

Variables and Attribute

Variables and Attributes are created/defined in the “Assign” block. Some of their characteristics can be changed in the assign windows.

Some of the System Status Parameters (Variables) are preprogramed in the Arena software. Engineers can also define variables based on their study interests.

System Performance Parameters (statistics)

Arena simulation outputs contains a set of system performance parameter statistics. Engineers can also ask the software to collect the statistics defined by the themselves (in order to do so, the “Collect Statistics” option needs to be checked.

Define statistics is the art work in simulation modeling. Most of time there are multiple ways to collect statistics.

Other Useful Blocks – Decide

The Decide block allows for decision-making processes in the system. It includes options to make decisions based on one or more conditions (e.g., if entity type is Gold Card) or based on one or more probabilities (e.g., 75%, true; 25%, false). Conditions can be based on attribute values (e.g., Priority), variable values (e.g., Number Denied), the entity type, or an expression (e.g., NQ(ProcessA.Queue)).

There are two exit points out of the Decide module when its specified type is either 2-way by Chance or 2-way by Condition. There is one exit point for “true” entities and one for “false” entities. When the N-way by Chance or by Condition type is specified, multiple exit points are shown for each condition or probability and a single “else” exit. The number of entities that exit from each type (true/false) is displayed for 2-way by Chance or by Condition modules only.

Equal Sign – “==”

AND – “&&” - “Shift+7”

OR – “||” – “Shift+Slash”

Other Useful Blocks – Dispose

Dispose block is intended as the ending point for entities in a simulation model. Entity statistics may be recorded before the entity is disposed.

“Record Entity Statistics” option needs to be checked.

Connect Line

Connect line is used to link blocks, these links define the actual work flow in the system.

During simulation modeling, click the “connect” icon, then link multiple blocks based on the actual work flow sequences.

Clock

Clock shows the system time in the simulation model.

Run Setup

Define the actual simulation model running parameters such as base time unit, number of replications, system operations hours…

Let’s have some fun with Arena!

Set

This is a data block defines various types of sets, including resource, counter, tally, entity type, and entity picture. Resource sets can be used in the Process modules (and Seize, Release, Enter, and Leave of the Advanced Process and Advanced Transfer panels). Counter and Tally sets can be used in the Record module. Queue sets can be used with the Seize, Hold, Access, Request, Leave, and Allocate modules of the Advanced Process and Advanced Transfer panels.

TYPICAL USES

· Machines that can perform the same operations in a manufacturing facility

· Supervisors, check-out clerks in a store

· Shipping clerks, receptionists in an office

· Set of pictures corresponding to a set of entity types

System Variables

1. NQ(ProcessA.Queue) – Return the number of entities waiting in the “ProcessA.Queue” at the current simulation clock time.

2. TNOW – Return the current system clock time.

Statistical Distributions

Arena contains a set of built-in functions for generating random numbers from the commonly used probability distributions. These distributions appear on pull-down menus in many Arena modules where they’re likely to be used. They also match the distributions in the Arena Input Analyzer. Each of the distributions in Arena has one or more parameter values associated with it. Engineer must specify these parameter values to define the distribution fully. The number, meaning, and order of the parameter values depend on the distribution. A summary of the distributions (in alphabetical order) and parameter values is given in the table below.

Batch

Batch module is intended as the grouping mechanism within the simulation model. Batches can be permanently or temporarily grouped. Temporary batches must later be split using the Separate module. Batches may be made with any specified number of entering entities or may be matched together based on an attribute. Entities arriving at the Batch module are placed in a queue until the required number of entities has accumulated. Once accumulated, a new representative entity is created.

TYPICAL USES

· Collect a number of parts before starting processing

· Reassemble previously separated copies of a form

· Bring together a patient and his record before commencing an appointment

Separate

Separate module can be used to either copy an incoming entity into multiple entities or to split a previously batched entity. Rules for allocating costs and times to the duplicate are also specified. Rules for attribute assignment to member entities are specified as well. When splitting existing batches, the temporary representative entity that was formed is disposed and the original entities that formed the group are recovered. The entities proceed sequentially from the module in the same order in which they originally were added to the batch. When duplicating entities, the specified number of copies is made and sent from the module. The original incoming entity also leaves the module.

TYPICAL USES

· Send individual entities to represent boxes removed from a container

· Send an order both to fulfillment and billing for parallel processing

· Separate a previously batched set of documents

Schedule

Schedule is a data module. It may be used in conjunction with the Resource module to define an operating schedule for a resource or with the Create module to define an arrival schedule. Additionally, a schedule may be used and referenced to factor time delays based on the simulation time. Duration-formatted schedules are defined within this module.

TYPICAL USES

· Work schedule for staff, including breaks

· Breakdown patterns for equipment

· Volume of customers arriving at a store

· Learning-curve factors for new workers

Match

The Match module brings together a specified number of entities waiting in different queues. The match may be accomplished when there is at least one entity in each of the desired queues.

Additionally, an attribute may be specified such that the entities waiting in the queues must have the same attribute values before the match is initiated. When an entity arrives at the Match module, it is placed in one of up to five associated queues, based on the entry point to which it is connected. Entities will remain in their respective queues until a match exists.

Once a match exists, one entity from each queue is released to be matched. The matched entities are then synchronized to depart from the module.

TYPICAL USES

· Assembling a part

· Gathering various products for a customer order

· Synchronizing a customer exit with a filled order

Hold

The Hold module will hold an entity in a queue to wait for a signal, wait for a specified condition to become true (scan), or be held infinitely (to be removed later with the Remove module).

If the entity is holding for a signal, the Signal module is used elsewhere in the model to allow the entity to move on to the next module. If the entity is holding for a given condition to be true, the entity will remain at the module (either in a defined or internal queue) until the condition(s) becomes true. When the entity is in an infinite hold, the Remove module is used elsewhere in the model to allow the entity to continue processing.

TYPICAL USES

· Waiting for a traffic light to turn green

· Holding a part for authorization

Signal

The Signal module sends a signal value to each Hold module in the model set to Wait for Signal and releases the maximum specified number of entities.

When an entity arrives at a Signal module, the signal is evaluated and the signal code is sent. At this time, entities at Hold modules that are waiting for the same signal are removed from their queues. The entity sending the signal continues processing until it encounters a delay, enters a queue, or is disposed.

TYPICAL USES

· Analyzing traffic patterns at an intersection (signal when the light turns green)

· Signaling an operator to complete an order that was waiting for a component part

Seize / Delay / Release

Special Process activites.

Arena Input Analyzer

Determine the distribution:

1. Save data (in single column) with the “.csv” format

2. Start Arena

3. “Tools” – “Input Analyzer” – “New”

4. “Use Existing Data File” – Open the “*.*” format file.

5. “Fit” – “Fit All”

6. Pick the distribution for simulation.

7. In general, 10,000 observations are required to determine the accurate distribution.

Hypothesis Testing for Process Improvement with Arena Simulation Output

Please note the following steps are used for analyze the output of Arena Model only.

After modeling the process, the process evaluation team should be able to find out the “bottlenecks” of the process.

The next step of simulation study is to propose process improvement ideas to have a more “balanced” system or increase the “throughput” of the system. The simulation model can be modified and perform the what-if analysis (for example, adding more resources, changing staff work schedule, reducing the cycle time for a station (think about the capstone projects) and improve the process quality…).

To evaluate if the proposed approach actual achieves the goal, statistical analysis of the outcome of the new simulation vs. the current process model needs to be done.

1. Data collection

Individual replication data need to be collected for both models.

2. Perform hypothesis testing – “t-test” (with Minitab or MS Excel Data Analysis Tool Pack)

1) State the null hypothesis and Alternate Hypothesis

H0: Opposite to what you suspect

H1: “What you hope for”

The test will always be a one-tailed test (why?)

2) Key in data to MS Excel or Minitab.

3) Establish alpha level – (alpha = 0.05 for our class)

Alpha - The chance of Reject (correct statement) – Type I risk/Error

4) Test for equal variance

H0: Equal Variance / H1: Unequal Variance

P value < alpha, Reject H0.

P value > alpha, fail to reject H0.

5) Use the correct t-test to see if the process improved or not (statistically)

6) Decide what is the next move.

3. It is possible that there are multiple goals the organization wants to achieve. If this is the case, multiple tests will be needed to determine if the proposed change works or not.

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