Designing a Poka-Yoke for Flat Marks on Rocker Arm Bearing

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Discussion Overview

The discussion revolves around the design of a poka-yoke system to detect flat marks on the outer diameter (OD) of rocker arm bearings, which are used as cam followers in automotive applications. Participants explore various methods for detection and quality control, including the use of air gauges and machine vision systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires whether an air gauge can be used to measure flat marks on the OD of rocker arm bearings and if a simple poka-yoke can be designed for this purpose.
  • Another participant suggests using machine vision to inspect finished parts for defects, noting the challenges of handling large production volumes and the high cost of vision systems.
  • Some participants express uncertainty about the definition of "poka-yoke" and its application in this context, with requests for clarification and examples.
  • A suggestion is made to use a displacement sensor to monitor the surface edge of the bearing during grinding, with various types of sensors discussed, including mechanical, optical, and electronic options.
  • Concerns are raised about potential root causes of the flat marks, including improper assembly lubrication leading to the bearings not rolling correctly.
  • Participants discuss the possibility of customers observing the behavior of the rocker arm and camshaft in operation to provide feedback on the issue.
  • Questions arise regarding the capability of optical sensors to detect displacements in microns, with some participants affirming that sub-millimeter detection is possible depending on budget and equipment.

Areas of Agreement / Disagreement

Participants express a range of ideas and suggestions, but no consensus is reached on the best approach to detect the flat marks or the effectiveness of the proposed solutions. Multiple competing views remain regarding the methods and technologies that could be employed.

Contextual Notes

Limitations include the need for further characterization of the flat marks, such as their dimensions and visibility, which may affect detection strategies. The discussion also highlights the dependence on specific definitions and applications of the technologies mentioned.

billy_boy
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I am a quality control engineer in an automotive parts manufacturing company. One of our products is a rocker arm bearing which is essentially a cam follower. The OD and ID of the bearing is ground using CBN grinding wheels. The ID contains cylindrical rolling needles. Recently we have received a lot of customer complaints for flat marks on OD of the bearing. Can an air gauge be used to measure or detect these flat marks and also can a simple poka yoke be designed using the same.
 
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billy_boy said:
can a simple poka yoke be designed
Interesting, I hadn't seen that term before. Learn something new here at the PF every day...

https://en.wikipedia.org/wiki/Poka-yoke

Have you considered using machine vision to look at the finished parts to catch these problems?
 
What is a poka yoke? How is a bearing to function as a cam follower? is it acting as a roller follower? A picture might help explain your situation.
 
Dr.D said:
What is a poka yoke?
(See the Wikipedia link that I posted...) :smile:
 
upload_2017-8-4_22-3-7.png
 
that cam roller is basically a needle roller bearing
 
berkeman said:
Interesting, I hadn't seen that term before. Learn something new here at the PF every day...

https://en.wikipedia.org/wiki/Poka-yoke

Have you considered using machine vision to look at the finished parts to catch these problems?
we manufacture 1.2 mil. of these in a month. we use a vision system for checking missing needles. it is difficult handling such large volumes. also vision systems cost a lot of money
 
Another vision system is also my guess for detecting the flats.

But you are the engineer in there. Characterise the symptom.
How wide? How deep? Can you see it by eye? Can you see it by camera? Is it one part randomly? Is it a bunch of parts in a row?

You can't ask yourself, let alone us, how to detect it until you know exactly what it is you want to detect
 
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Hmm, first time I've heard the word/phrase/expression "poka-yoke" as well, either way...
So if I understand correctly, you need to ensure that the bearings are circular without any flat spots? It is difficult to get into any specifics without understanding the application in detail, however a displacement sensor monitoring the surface edge of the bearing while it is being ground may suit your needs.
 
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  • #10
Tolklein said:
however a displacement sensor monitoring the surface edge of the bearing while it is being ground may suit your needs.
I would vote for that approach. The sensor could be mechanical (potential problem due to speed & wear), optical (LASER displacement sensor or similar as supplied by industrial Manufacturers ( two that come to mind are Banner and Keyence)), electronic (capacitance distance sensor). Of the three, probably Optical is the best bet.

As for Root Cause, sounds like a bad bearing in one of your grinders.

Let us know what you find.
 
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  • #11
So the bearing is not rolling?

If this is say...a crower rocker arm, maybe the customers are using improper assembly lube which may cause the roller to not roll during that important first few minutes of operation.

Since oil is super slippery, it doesn't take much resistance to rolling to stop the rolling action without causing any damage to the needles...so the outside of the bearing glides on the oil film.

Once there is even a slight flat spot on the outside of the roller where it contacts the cam, it may stop rolling and now acts as a "pad type cam follower" instead of a bearing because oil is such a good lubricant that it allows the cam to turn against a stopped roller causing a flat spot to get worn eventually instead of causing damage that snowballs into galling and or catastrophic heating.

If a hydraulic "lifter" is employed, the bearing could stop turning every time there is oil pressure to keep it against the cam with any amount of pressure while a mechanical follower may allow turning when it's not under pressure of opening the valve.

In stock factory usage, you have less chance of the wrong lubricant being used but in the aftermarket horsepower world, every guy has his own recipe and many are just wrong.

If a customer can send back the rocker arm and the camshaft, you could install it in an engine and just watch the roller to see if it's stopping and you should easily hear the "thumping" if it is.

Maybe a customer can make the observation himself and let you know what he's seeing.
 
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  • #12
Can you post a picture of the product you make and the defects you encounter?
 
  • #13
Tom.G said:
optical (LASER displacement sensor or similar as supplied by industrial Manufacturers ( two that come to mind are Banner and Keyence))
can these detect displacements in microns??
 
  • #14
salmansl said:
Can you post a picture of the product you make and the defects you encounter?
upload_2017-8-9_23-2-21.png
 

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