How to carry out Gage R&R for automatic machines? Automated Equipment

Stijloor

Staff member
Super Moderator
#11
Re: How to carry out Gage R&R for automatic machines?

If we load the same part differently each time, we would get different readings thus a R & R that could be substantial. We would be establishing different datums.
What if the datum reference frame is established after loading the part? For example: probing like a CMM?
 
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David DeLong

#12
Re: How to carry out Gage R&R for automatic machines?

What if the datum reference frame is established after loading the part? For example: probing like a CMM?
Yes you are correct here. The "clocking" of the part could be different and the CMM probe would pick up different points and thus have different readings.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#13
Re: How to carry out Gage R&R for automatic machines?

actually that's not what I meant.
any time the parts under test are placed into an automatic tester the placement can vary. technically speaking these humans are not appraisers but operators. I have have too often seen the act of placing the unit under test into the tester be the largest source of measurement. not all unit "holding" schemes are stable or repeatable. cables can be placed incorrectly, parts can be misaligned, parts can be mishandled, etc. I've seen this most often with CMMs but also with clam shells and other devices used to hold and contact the unit. This is operator to operator variation. it may be small; it may be large but until you assess it in your MSA you don't know.

We must remember that it's called measurement system analysis not gage analysis.
 
S

syeedabu

#14
Re: How to carry out Gage R&R for automatic machines?

Thanks for reply,

But our case is,Its a automatic measuring line system.there is no operator to place the part which we are measure.parts (we measure camshaft,crank shaft etc) comes through a conveyor system and it stops on the measuring station a lifter is lift the part for measuring.the meadsuring system measure the diameter, height ..........,we use digital sensors and mini probe some times air gauge then the parts goes to the next measuring station like that the process going.

For this system how can i study GAGE R&R.
 

Miner

Forum Moderator
Staff member
Admin
#15
Re: How to carry out Gage R&R for automatic machines?

I would still recommend the approach described in my initial response. This will allow you to assess Repeatability by itself.

Based on your latest information, all of BevD's comments regarding fixturing would apply. Each part will lie on the conveyor slightly different. The lifter will present the part to the gage slightly different each time. This will all add toward the Repeatability variation.
 

Caster

An Early Cover
Trusted Information Resource
#16
Re: How to carry out Gage R&R for automatic machines?

But our case is,Its a automatic measuring line system.there is no operator to place the part which we are measure.parts (we measure camshaft,crank shaft etc) comes through a conveyor system and it stops on the measuring station a lifter is lift the part for measuring.the meadsuring system measure the diameter, height ..........,we use digital sensors and mini probe some times air gauge then the parts goes to the next measuring station like that the process going.

For this system how can i study GAGE R&R.


Can you find the original MSA from when the system was bought and commissioned, there should be one somewhere? It should give you lots of clues how to proceed.

You likely already have hundreds or thousands of measurements. Why not just plug them into software and see what you get.

If you get a really bad R&R read more here. 10 parts in a row from your process likely have very little part to part variation (in fact I am certain they would given they are crankshafts). This creates a poor R&R result.

If that happens , select 10 parts that show normal expected process variation (multiple lines, different set ups, different shifts, different weeks, different grinding wheels, etc.). Or you may have to make special parts for the study.

If you need to get good R&R numbers just to satisfy a customer, get 10 parts ranging from under spec thru over spec. It should pass. Very few customers know the problem with this method. Or even better use 2 each of 5 different parts. A tiny crank all the way to a monster if you have them. You will get a great R&R. A totally bogus study but again most customers know only to look for less than 10% R&R.

If you are doing a study to understand and improve, please ignore the above, and good for you (and are you hiring?)

But, hey, why not just grab the data and get started.

The people on this forum are genuine experts, I am just a user. They will help.
 
A

artichoke

#17
Re: How to carry out Gage R&R for automatic machines?

I want to know that how we do Gage R&R study for Automatic machine.
for automatic machine no appraiser in needed.So how we calculate the reproducibility in this case.
You might be interested in reading this paper by Dr Wheeler, where he concludes that "Gauge R&R guidlines ... have no basis in fact, no basis in practice ..." . " ... merely a superstitious tradition"

http://www.spcpress.com/pdf/good_data_ bad_data.pdf
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#18
Re: How to carry out Gage R&R for automatic machines?

Thanks for reply,

But our case is,Its a automatic measuring line system.there is no operator to place the part which we are measure.parts (we measure camshaft,crank shaft etc) comes through a conveyor system and it stops on the measuring station a lifter is lift the part for measuring.the meadsuring system measure the diameter, height ..........,we use digital sensors and mini probe some times air gauge then the parts goes to the next measuring station like that the process going.

For this system how can i study GAGE R&R.
If you can't assess reproducibility because their are truly no operators and you don't have more than one measurement system then you can only calculate repeatability. since you can't calculate reproducibility don't. and dont' worry about it. R&R is simply a generic name. when you don't a reproducibility component you are actually performing a gage R, but we still call it an R&R...whatever. it is not a law that you must have a system that has reproducibility components, only that you assess the capability of your system.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#19
Re: How to carry out Gage R&R for automatic machines?

You might be interested in reading this paper by Dr Wheeler, where he concludes that "Gauge R&R guidlines ... have no basis in fact, no basis in practice ..." . " ... merely a superstitious tradition"

http://www.spcpress.com/pdf/good_data_ bad_data.pdf
Artichoke - it is always helpful to add context. I am also opposed to the traditional R&R studies as mandated by AIAG and other major Customers. Thsi method is based on an article by Rober Traver entitled "The Rubber Ruler" and published in the early sixties. Many things about the traditional study are not very useful: n= 10 parts is too small to adequately assess the measurement error (standard deviation); replicate measurements of 3 instead of 2 is excessive and adds no more statistical insight than replicates of 2; the % of tolerance calculation is a violation of mathematical rules involving standard deviations; and the arbitrary selection of 10%, 20% and 30% are not very value add as they are arbitrary and those categories have little insight into the affect on control charts or acceptance testing.

However, good well planned R&R studies are value add. Wheeler does have soem of the best material on how to perform effective studies. unfortunately too many companies are given the AIAG standard and they think it's gospel. They won't talk to their customers to get acceptance to use a better method. (in these cases they might not even really be concerned with understanding their measurement systems; only checking the box on a customer requirement. That statement oughta generate a spirited debate!)
 

Jim Wynne

Staff member
Admin
#20
Re: How to carry out Gage R&R for automatic machines?

Artichoke - it is always helpful to add context. I am also opposed to the traditional R&R studies as mandated by AIAG and other major Customers. Thsi method is based on an article by Rober Traver entitled "The Rubber Ruler" and published in the early sixties. Many things about the traditional study are not very useful: n= 10 parts is too small to adequately assess the measurement error (standard deviation); replicate measurements of 3 instead of 2 is excessive and adds no more statistical insight than replicates of 2; the % of tolerance calculation is a violation of mathematical rules involving standard deviations; and the arbitrary selection of 10%, 20% and 30% are not very value add as they are arbitrary and those categories have little insight into the affect on control charts or acceptance testing.

However, good well planned R&R studies are value add. Wheeler does have soem of the best material on how to perform effective studies. unfortunately too many companies are given the AIAG standard and they think it's gospel. They won't talk to their customers to get acceptance to use a better method. (in these cases they might not even really be concerned with understanding their measurement systems; only checking the box on a customer requirement. That statement oughta generate a spirited debate!)
I think you raise some interesting and valid points, as does the Wheeler paper that Artichoke posted. The problem is that the vast majority of people who use GR&R, and MSA in general, have no understanding of what the numbers really mean, or how they come to be. It's a customer requirement, so it gets done in the best tradition of automotive industry self-fulfilling prophecy. If the "ideal" number is < 10%, then that's what it will be, one way or another.

I've seen many instances where in a relatively simple application that's worked well for many years, a GR&R study is done and the results are >10%, or even 30%. Failing to understand the concepts involved, the customer won't listen to reason and the supplier just manipulates the numbers in order to get on with his life. The customer looks only at the bottom line, and if it appears satisfactory, he gets on with his life and begins another line of ignorant nitpicking with another supplier. The result is that MSA is rarely used for improvement purposes, unless blindly satisfying the customer requirement is considered improvement.
 
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