Rockwell Automation Arena Packaging Users Guide - Manual (Page 102)

A RENA P ACKAGING T EMPLATE U SER ’ S G UIDE
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The chart above shows the output rate and good output rate of the conveyor over time
given the 10% production loss and the units lost after each failure. Let’s first examine the
operating period before the failure at time t
1
. Machine 1 is placing units onto the conveyor
at a rate of 115 units per minute. Machine 2 is taking good units off the conveyor at a rate
of 100 units per minute.
Because a 10% production loss occurs at the end of the conveyor, the total output rate of
the conveyor is calculated as follows:
Output Rate = Good Output Rate + (Lost Production % * Output Rate)
Output Rate = 100 + (.10 * Output Rate)
Output Rate = 100/.90
Output Rate » 111 units/min
Thus, we see that the total output rate from the conveyor consists of 100 good units per
minute to Machine 2 and approximately 11 units per minute of loss. Because the output
rate of Machine 1 is 115 units per minute, units accumulate on the conveyor.
Let’s now examine what occurs after the conveyor fails from time t
1
to t
2
. At time t
2
, the
conveyor immediately transfers off the Lost Units After Failures at 100% of its output
rate. Note that this output rate is 120 units per minute. Why 120? The reason is that a
significant number of units had accumulated on the conveyor by the time the failure
occurred. Therefore, at time t
2
, the conveyor transfers the loss from those accumulated
units at its run speed of 120 units per minute.
When the quantity of Lost Units After Failures is transferred, the conveyor’s output rate
returns to 111 units per minute. The good output rate increases to 100 to resume feeding
Machine 2.
Questions and answers about loss
Q: What statistics are available for loss?
A: For each equipment module, Arena Packaging automatically tracks statistics on the
number of units lost and the yield (i.e., the percentage of good units processed or
transferred out of the total units processed or transferred). You can also apply and
report costs for loss in the Costs dialog box.
Q: Suppose event-based loss is defined for the scheduled stops or failures on a conveyor.
When the stop or failure occurs, there is an amount of WIP on the conveyor (i.e., the
number of units accumulated plus the number of units traveling). Can the loss associ-
ated with the event be more than this WIP?
A: No. Regardless of what is sampled from the Lost Units After Failures or Lost Units
After Stops parameters, the maximum amount of loss that can be taken off the
conveyor for an event is the current WIP.