TIMEOUTR.MOD
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- See also: How to read .MOD pages
Contents |
Description
Time-constrained processing is where two processes must be performed within a certain interval. Examples of time-constrained processes are common in semiconductor manufacturing, metal foundries, food processing, etc. where priming, pre-heating, or cleaning is required before performing a major processing step.
TIMEOUTR.MOD models a heat and press sequence; parts arrive every t_a minutes and must be heated in a furnace (taking t_h minutes) before they can be pressed by a mold press machine (taking t_p minutes). The interarrival times and both processing steps are somewhat random. The sequence is time-constrained because there is a maximum cooling time limit of TC after a part is heated during which the pressing step must start. If a part waits longer than TC minutes after being heated before pressing starts, it must be returned to the furnace for reheating.
TIMEOUT.MOD models the same system using transient entities instead of event cancellation. TIMEOUTR.MOD is a faster model than TIMEOUT.MOD; however, it is valid only if TC is a fixed constant.
State Variables
| Variable Name | Abbreviation | Variable Description | Size | Type |
|---|---|---|---|---|
| QUEUEF | QF | Queue length of parts waiting for the furnace | 1,1 | Integer |
| QUEUEP | QP | Queue length of parts waiting for the mold press | 1,1 | Integer |
| FURNACE | F | Status of the furnace (busy=0, idle=1) | 1,1 | Integer |
| PRESS | P | Status of the mold press (busy=0, idle=1) | 1,1 | Integer |
| TC | TC | Maximum cooling time limit | 1,1 | Real |
| FPT | FPT | Mean furnace processing time | 1,1 | Real |
| MPT | MPT | Mean mold machine process time | 1,1 | Real |
Vertices
| Vertex Name | Vertex Description | State Changes |
|---|---|---|
| RUN | Initialization of the servers and input of TC | F=1, P=1 |
| ENTER | Part entering the queue for the furnace | QF=QF+1 |
| HEAT | The start of heating a part | F=0, QF=QF-1 |
| READY | Completion of part heating, ready for the press | F=1, QP=QP+1 |
| REDO | Re-routing of a part back to the furnace | QP=QP-1, QF=QF+1 |
| PRESS | Start of the mold press operation | P=0, QP=QP-1 |
| DONE | The completion of a finished part | P=1 |
Initialization Conditions
| Variable | Description |
|---|---|
| TC | Maximum cooling time limit |
| FPT | Mean furnace processing time |
| MPT | Mean mold machine process time |
Event Relationship Graph
English Translation
An English translation is a verbal description of a model, automatically generated by SIGMA.
The SIGMA Model, TIMEOUTR.MOD, is a discrete event simulation. It models TIME-CONSTRAINED PROCESSING (RESIDENT ENTITIES).
I. STATE VARIABLE DEFINITIONS.
For this simulation, the following state variables are defined:
F: STATUS OF THE FURNACE (BUSY=0, IDLE=1) (integer valued) P: STATUS OF THE MOLD PRESS (BUSY=0, IDLE=1) (integer valued) QF: QUEUE LENGTH OF PARTS WAITING FOR THE FURNACE (integer valued) QP: QUEUE OF PARTS WAITING FOR THE MOLD PRESS (integer valued) TC: MAXIMUM COOLING TIME LIMIT (real valued) FPT: MEAN FURNACE PROCESSING TIME (real valued) MPT: MEAN MOLD MACHINE PROCESS TIME (real valued)
II. EVENT DEFINITIONS.
Simulation state changes are represented by event vertices (nodes or balls) in a SIGMA graph. Event vertex parameters, if any, are given in parentheses. Logical and dynamic relationships between pairs of events are represented in a SIGMA graph by edges (arrows) between event vertices. Unless otherwise stated, vertex execution priorities, to break time ties, are equal to 5.
1. The RUN(TC,FPT,MPT) event occurs when INITIALIZATION OF THE SERVERS AND INPUT OF TC. Initial values for, TC,FPT,MPT, are needed for each run. This event causes the following state change(s): F=1 P=1 After every occurrence of the RUN event: Unconditionally, THE FIRST CUSTOMER CAN ENTER; that is, schedule the ENTER() event to occur without delay.
2. The ENTER() event occurs when PART ENTERING THE QUEUE FOR THE FURNACE.
This event causes the following state change(s):
QF=QF+1
After every occurrence of the ENTER event:
Unconditionally, AFTER A TIME DELAY THE NEXT CUSTOMER CAN ENTER;
that is, schedule the ENTER() event to occur in 1*ERL{1} time units.
If F>0, then THE FURNACE IS IDLE AND HEATING CAN START;
that is, schedule the HEAT() event to occur without delay.
3. The HEAT() event occurs when THE START OF HEATING A PART.
This event causes the following state change(s):
F=0
QF=QF-1
After every occurrence of the HEAT event:
Unconditionally, AFTER A TIME DELAY THE HEATED PART IS READY;
that is, schedule the READY() event to occur in FPT*ERL{1} time units.
4. The READY() event occurs when COMPLETION OF PART HEATING, READY FOR THE PRESS. This event causes the following state change(s): F=1 QP=QP+1 After every occurrence of the READY event: If QF>0, then THERE IS WORK IN QUEUE, START HEATING NEXT PART; that is, schedule the HEAT() event to occur without delay. (Time ties are broken by an execution priority of 4.) If P>0, then THE PRESS IS IDLE, START PROCESSING; that is, schedule the PRESS() event to occur without delay. Unconditionally, AFTER THE WAITING TIME LIMIT THE PART IS COLD; that is, schedule the REDO() event to occur in TC time units.
5. The PRESS() event occurs when START OF THE MOLD PRESS OPERATION.
This event causes the following state change(s):
P=0
QP=QP-1
After every occurrence of the PRESS event:
Unconditionally, AFTER A TIME DELAY THE PRESSED PART WILL BE DONE;
that is, schedule the DONE() event to occur in MPT*ERL{1} time units.
Unconditionally, THE PART HAS NOT COOLED AND NEED NOT BE REDONE;
that is, immediately cancel the next scheduled occurrence of the REDO event.
6. The DONE() event occurs when THE COMPLETION OF A FINISHED PART. This event causes the following state change(s): P=1 After every occurrence of the DONE event: If QP>0, then THERE IS WORK IN QUEUE, START PRESSING NEXT PART; that is, schedule the PRESS() event to occur without delay. (Time ties are broken by an execution priority of 4.)
7. The REDO() event occurs when RE-ROUTING OF A PART BACK TO THE FURNACE. This event causes the following state change(s): QP=QP-1 QF=QF+1 After every occurrence of the REDO event: If F>0, then THE FURNACE IS IDLE SO START HEATING; that is, schedule the HEAT() event to occur without delay.
