Calculating your CMM’s overall equipment effectiveness (OEE)

Asset management software plays a crucial role in optimising overall equipment effectiveness (OEE). As its name suggests, OEE is a measure of how effective your machines are. It can be calculated either for a single coordinate measuring machine (CMM) or for a set of CMMs, over various periods of time. An understanding of a CMM’s OEE can help reduce spending on maintenance while achieving better overall machine performance and efficiency. But to effectively track OEE it’s important that your asset management system and metrology software can deliver the answers you need in an easy-to-use format.

How to calculate your CMM’s OEE

OEE is expressed as a percentage and is calculated using the formula: OEE = Availability x Performance x Quality.

Hexagon has designed its asset management software tool to simplify the task for operators and managers by drawing important data about the CMM’s availability, performance and quality from PC-DMIS. But there are still a number of factors operators need to consider when establishing an accurate OEE.

Getting availability right

It’s important to calculate availability on the basis of scheduled time and operating time. Scheduled time is when a machine’s use is anticipated during a shift and excludes planned holidays and scheduled shutdowns. Operating time is the amount of scheduled time that the equipment spends executing measurements and includes manual routine execution time, such as one-off measurements or the creation of “manual alignments,” as well as automated routine execution time. It does not include anything outside scheduled time, even if the machine is productive. These figures then feed into the standard equation:

Availability = Operating time / Scheduled time

Performance measurement

Performance measures the capacity, or speed, at which the equipment is operating during scheduled time and compares the actual output of a system to a theoretical “ideal”, which is the shortest time required to complete a measurement routine under ideal circumstances. The ideal execution time is a fixed value that should be set for each CMM separately as it may vary based on an individual CMM’s performance characteristics for separate routines. For this reason, we recommend creating separate routine documents within PC-DMIS for assets with different performance characteristics. The ideal execution time and the actual number of routines are used to calculate performance in the following equation:

Performance = (Routines Executed X Ideal Execution Time) / Operating Time

Quality

Quality measures the CMM’s success in completing measurement processes during the scheduled time and is calculated using the equation:

Quality = Routines Successfully Executed / Total Routines Executed

“Routines successfully executed” is the number of routine executions that completed all the intended measurements of the features belonging to the routine, whereas total routines executed includes both routines successfully completed and cancelled routines. Hexagon’s Manufacturing Intelligence division has designed its HxGN SFx | Asset Management  tool to deliver the data you need to easily and accurately determine the OEE of your metrology equipment by optimising it for use with PC-DMIS. And if you are using a metrology software version that supports quality, such as PC-DMIS 2019 R2 and higher, then Asset Management will automatically keep track of both routines successfully executed and total routines executed.

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