Rockwell Automation Arena Packaging Users Guide - Manual (Page 91)

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Equipment Reliability and Loss
This appendix provides detailed descriptions on the Arena Packaging template’s features
for equipment reliability and loss.
Defining reliability
A key characteristic of a piece of equipment is its ability to perform without failing (i.e.,
its reliability). Equipment failures result in lost production time and product and can
dramatically impact system design and performance.
Arena Packaging provides three approaches for defining random downtimes of machines,
conveyors, or palletizers. To implement one of the approaches, simply check Reliability in
the Other Options section of the module’s main dialog box. Then click on the Reliability
dialog box.
Each of the three options is described below.
Using expected uptime
„
“I expect the filler to be failed about 1% of the time.”
„
“The conveyor is running about 97% of the time.”
When selecting this option, specify the percentage of available operational time that you
expect the equipment to be up (i.e., Expected Uptime) and the mean time to repair a
failure when one occurs (i.e., Time to Repair). The word mean is emphasized because
Time to Repair must be specified here as a real value and not a random distribution.
This simple way of describing equipment reliability is useful when you do not require or
have the data for more detailed analysis. An uptime percentage is sometimes referred to as
the “Availability” of the equipment.
When the simulation begins, Arena Packaging creates a single random failure stream for
the piece of equipment. The times between failure arrivals are sampled from the stochastic
distribution Exponential (MTBF), where MTBF (i.e., the mean time between failures) is
calculated using the equation
MTBF = Time to Repair * (Expected Uptime % / (100 – Expected Uptime %)).
It is important to emphasize that this MTBF is not calendar time. For machines and pallet-
izers, the MTBF is interpreted as the mean processing time between failures (i.e., time that
the machine or palletizer is running and not starved). For conveyors, the MTBF is inter-
preted as the mean running time between failures (i.e., time that the conveyor’s belt is
actually moving).