Summary for linear positioning systems Discussion
linear positioning systems for programmed hoists are discussed in the context of an anodizing line where lasers are being disrupted by steam from hot tanks in cold weather. Bryant Tokarz asks whether a non-contact linear encoder system is a good replacement and notes the supplier would not provide customer references. Ted Mooney, P.E. replies that Bryant is wise to seek real user feedback, since sales literature can overstate reliability. He says his own past hoist systems used station-counting with metal tabs and hall-effect proximity sensors, and in years of operation across about a dozen installations there were no miscounts except when a sensor failed and was replaced. Ted does not claim station counting is superior to absolute positioning, but uses the example to stress that modern systems should be robust enough to avoid nuisance shutdowns. His practical advice is that if the laser system cannot be made immune to steam-caused faults, it should be replaced; he also asks whether the proposed encoder system has any mechanical contact points that could create wear.
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
October 5, 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,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
October 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
October 11, 2021
Ed. note: This RFQ is outdated, but technical replies are welcome, and readers are encouraged to post their own RFQs. But no public commercial suggestions please ( huh? why?).
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,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
October 2021