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Linear Positioning Systems for Programmed Hoists

October 5, 2021

Q. We currently run an anodizing line and use lasers for hoist positioning. In the cold months we have difficulty capturing the steam off our hot tanks and it ends up causing laser faults. We have been approached by a company to change over to non-contact linear encoder system. Just wanted to see if anyone has any experience with this type system. Pros/Cons. We asked for a few customer contacts and the sales rep could not supply them.

Any feedback is greatly appreciated.

TIA

Bryant Tokarz
- Clanton, Alabama
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October 2021

A. Hi Bryant. I think you're wise to want actual feedback from users because things don't always work as robustly as the technology and sales literature implies :-)

I spent most of my career designing and installing programmed hoist systems for the plating & anodizing industry, but my last installation was probably 25 years ago, and I still used a small tab of metal at the center of each station and hall effect non-contact proximity sensors on the hoists to count stations/tabs. I put 3 sensors on each hoist, with the center one being the stopping point, and the 'slowdown' ones fore and aft as secondary counters to execute a shutdown if the counts of where the hoists were didn't agree (patience please, I'm not here to describe an antique, but am about to make a point).

In years of operation on about a dozen such installations, there never was a single miscount except when one of the proximity switches had become defective and had to be replaced. I'm not saying that station counting systems are better than absolute positioning systems -- they're not. Rather, my point is that robustness, freedom from error, and complete elimination of shutdowns for trivial control system errors was very possible even decades ago -- so you should certainly settle for nothing less today!

So, if the laser system and the steam situation cannot be fixed such that it *never* causes these self-induced errors, it should be replaced. I don't know how the absolute positioning system you are contemplating works, maybe you're talking radar instead of lasers, I don't know. But if you are talking some sort of encoding wheels, I understand that the encoding wheels don't touch what is sensing their position, but if we are speaking of wheels, is there mechanical contact somewhere turning them?

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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October 11, 2021

Q. Ted,

Thank you for your reply and most importantly the basis of what you are stating is that we shouldn't accept a solution that does not fully meet our needs. I understand every solution or system requires maintenance but a robust solution should only require maintenance not just partially solve problems. Below is a link to the system being proposed. I could be positioned off to the side of the line furthest away from the steam accumulation. However, I can't say it would never fail because I have no experience with the system.

We are trying to avoid wheels encoder systems due to the environment we operate in and to keep maintenance to a minimum.

www.pepperl-fuchs.com/usa/en/classid_822.htm

You have answered some of my questions before and I definitely appreciate your knowledge and real world experience.

Bryant Tokarz [returning]
- Tennessee
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  ^- Privately respond to this RFQ -^

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Ed. note: As always, gentle readers, technical replies in public and commercial replies in private please ( huh? why?)


October 2021

A. Hi again, Bryant. It sounds like a very reasonable technical approach. I have no experience with the brand but we can't post public testimonials or slams anyway. If anyone has a comment on brands/sources they can reply to you in private. Good luck!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^

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