How to model operators' efficiency?

For production lines, there are machines and operators. Machines are relatively steady, which have steady cycle times and predictable maintenance and breakdown. But Manpower is much more complicated, which may involve fatigue, irregular short break and other emergencies. Thus industrial engineers often define operator efficiencies, e.g., 85%, which means operators are available for processing in 85% time of the whole working shift and in the other 15% of the working hour, the workers are absent and not available for work.
In Flexsim, how to represent this Operator Efficiency parameter? I am thinking of using MTBF and MTTR. Does anyone has a good approach for this? Thanks.

Since the operator's resting is a random event that is not influenced by anything else in the model, you could make a user event named MakeOperatorRest with code similar to this:

double avgRestTime=10;
double operatorEfficiency=0.85;//0 is never working, 1 is always working
double avgTimeBetweenRests=operatorEfficiency*avgRestTime/(1-operatorEfficiency);
//This is just a simple preempting tasksequence that makes him stop whatever he is doing
//and rest for a random time with average avgRestTime.  You could make a more complicated
//task sequence that makes him finish what he's doing, and even go to a break room then take 
//a break.
treenode ts=createemptytasksequence( node("/Operator4",model()) ,0,PREEMPT_ONLY);
inserttask(ts,TASKTYPE_DELAY,NULL,NULL,exponential(0,avgRestTime),STATE_IDLE);
dispatchtasksequence(ts);
//This sets the time for his next break in avgTimeBetweenRests time units.
seteventtime("MakeOperatorRest",exponential(0,avgTimeBetweenRests),1,0);

I made the First Event Time 0.00 and I checked Repeat event. The Repeat Event Time doesn't matter because we change it with the last line of code.

You would also need to know (or estimate) the average rest time. It looks quite strange to have an operator rest for .15 seconds every second on average, because he stops suddenly to rest but accelerates to continue.

Anyway, I attached a simple model of this in action.

Liu Bin,

We use the MTBF/MTTR for that as well, That works quite nicelly. If you give him a preempting tasksequence (just as Alex describes) instead of using stopobject, you can even sent him to a toilet or a cantine where he waits until his break is over.

Steven

Thanks！Guys

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