Closing Control Loops

So, I've put the finishing touches on my book, and the publisher's marketing department is asking me questions. Some of them I don't have good answers to, because (a) I'm on the fringe of my target audience, and (b) everyone learns differently, and my way is through osmosis and thinking, which doesn't make it easy to cough up a bunch of specific information like conferences and magazines.

The book's title is "Applied Control Theory for Embedded Systems", the subject should be self explanatory. So if you feel that you're in the target audience, and if you're in a generous mood, here are some questions I have for you:

What do they call you at work (sorry -- what's your official job title?)

What magazines do you read? Websites you visit regularly?

Do you go to conferences? Which ones? (this is the one that motivated this posting, by the way -- I only go to the Embedded Systems Conference; I know there's a circuit-related one in Silicon Valley but I can't remember the name, nor do I know if there are any ones anywhere else.

Have you had to close a control loop recently? Did you do a web search? What keywords did you use?

Have you read any related books? Was it just a college text, or was it specifically directed at closed loop control for the practicing embedded systems designer? What did you think of it? What was it?

Thanks in advance.

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Tim Wescott
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Tim Wescott
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Isn't that what academicians call "negative feedback"? ;-)

Good Luck! Rich

Reply to
Rich Grise

Hi Tim

They call me Software Engineer (they call me other names too when they find bugs in the software, but I doubt you are interested in knowing), but my business card says Software Development Manager.

Nuts and Volt, Servo, Motorcyclist, Computer, IEEE Potentials, Dr. Dobbs

Google news, Orkut, CNN

Not so often, I wish I had the money/time to attend to more conferences. The last one was IC-AI (International Conference on Artificial Intelligence) which I published and presented a paper.

Yes. Yes. PID control; control theory; fuzzy control

Yes. A couple of books actually. Got some hints from Schaums for control theory, and two other books that I borrowed from the university's library. The problem with all of them is that they go deep on the math of control theory but are not practical (no relationship between CT and embedded devices)

Do I get a free book? ;)

Good luck with your publishing... A man has three missions on Earth: Have kids, plant a tree and write a book. I accomplish the first two... someday I'll write a book.

Cheers

Padu

Reply to
Padu

I hopr you have lest out Nyquist diagrasm and Root Locus. Never seen anybody using them on a real design other than academics.

Tam

Reply to
Dougal McDougal of that Elk

They need what they think they need for standard tick box list of checks.

Sounds like a sensible idea fo a book..

I used to have all sorts of job titles, as often every company has different meanings for job titles (let alone the made up ones that appear now).

Having spent over 12 years working for myself in a one man company I have various titles (some legal, some other meanings) depending on what I am doing at the time and the questioner. Job titles only really have relevance to questions.

Magazines IEE/IEEE periodicals (some), Circuit Cellar..

Websites are not something I spent a lot of regular time on specific ones as it depends what I am working on or doing, except in bursts for datasheets or specific issues, it would be Dilbert, Google, Ebay.

Never gone to a conference, occasionally seem some of the papers. From various sources it depends on the hosting country, speakers country, sometimes who is sponsoring their 'research' and what is deemed patentable under which jurisdiction as to whether you see enough detail anyway. I know of cases in many fields where published papers are very 'sanitised' for varying reasons to make you wonder if the paper is worthwhile.

Mainly revisiting various loop controls/tuning for PID, servo loops and nuances. Considering some of the project time spans, recent could be two years (due to many other things).

Most of them I found too abstract or too ideal mathematical models with lots of assumptions. some of the worst assumptions I have seen is we have a model for an actutator/motor that applies to all actuators/motors, where as in real life modeling of the subsystem is quite complex and cannot always be done theoretically but has to be done at first empirically as the full design is 'n' stages down the road. In one instance to get the model and even think of tuning it was complicated by differing response times of sensors to software

Quadrature encoders position indicators optical position from line scan processing

Further complicated by temperature, standing or moving before hand or worse still some of it was effected by different control loops controlling high voltage light sources and other parts of the system.

That was even before you looked at mechanical interactions, tolerances, determining fault conditions (mechanical, electrical, optical).

Too often the books forget about fault conditions, that can be directly determined or have to be determined from other sources.

A lot of theory books are a bit like the old sciences joke

A bookie wanted to know if there was a scientific way to determine the outcome of any horse race, so he asked the three scientists.

The chemist said "Too many unknowns and variables"

The biologist said "Too many factors to make it possible"

The Physicist said "Yes"

When the bookie asked how, the physicist said

"For spherical horses in a vacuum"

The worst demo of control software for computer (PC and larger) data acquistion systems I saw had classic limits and real world is somewhere else issues. Basically the demo consisted of a model of a simple oven that was heated and its temperature would rise, until the door was opened. The longer the door was closed or open the higher or lower the temperature would go.

Now those here would hopefully know that if the door was opened the lowest temperature that could be reached was ambient in real life, in a model should be absolute zero. This model had no limits so the temperature could go below absolute zero or higher than the sun! So did not show the software in best light of showing how good the software could be.

Hopefully your book will not be like that.

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Paul Carpenter          | paul@pcserviceselectronics.co.uk
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Reply to
Paul Carpenter

I knew it!

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The book is too small.

Reply to
Fred Bloggs

Engineer

EETimes, Sensors, Medical Devices, Machine Design IEEE Spectrum, .....for some reason they won't send me ESP I got ESP back in 1995, but they won't renew my free subscription :( CircuitCellar, Nuts and Volts, sometimes Servo.

No. Can't justify the cost. Way to expensive considering the lost time, conference fees and travel costs.

Sure, but what does that have to do with the websearch?

Quantum Programming. I thought it was great! A good summary of state machines and an alterative ways to use them.

On Time and Under Pressure by Ed Sullivan. An old book. . A great overview of what makes a great organization tick, particularly the Version Control and Automated Build processes,

Patent it Yourself, David Pressman. A great step by step process for submitting a patent.

The Scientist and Engineer's Guide to Digital Signal Processing Free PDF book. I've been reading chapters. Great stuff.

I don't generally read "controls" books anymore unless they are product manuals. For anything new, I'll read technical publications, or the web. For anything old I just refer to my bookshelf.

Reply to
AntiSPAM_g9u5dd43

You should look over my shoulder some time, then.

I use root locus when I'm brainstorming controllers, and I have my spreadsheet program display top & bottom Nyquist & Bode plots when I'm tuning from measured frequency responses -- I put a circle of diameter

1/sqrt(2) on the Nyquist plot to indicate the 3dB sensitivity point, and tune to that.

I _don't_ spend many pages showing how to construct root locus plots -- while you do learn something from it there's a gazillion math applications that will do it for you.

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Tim Wescott
Wescott Design Services
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Tim Wescott

-- snip --

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Yes, that's it. Done, thanks be.

That's three years worth of writing! Perhaps I've just managed to condense the wisdom down, eh?

I'm going to take the first complimentary copy they give me and tape a red pen to it on a string, to make marginal comments. I expect that if it lives to a 2nd edition it will grow.

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Tim Wescott
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Tim Wescott

-- snip --

I tried to keep it grounded in reality, to live up to the "Applied" in the title. Most of the examples are simplified, so that I can talk to the point that I'm trying to make, but I try to keep the other issues visible.

I think there's a place for simplistic models -- I've done motion controllers where the emphasis was on getting a mechanism from point A to point B without toasting any electronics or breaking/jamming the mechanism, and accuracy was taken care of by other parts of the system. In those cases a very simple model that ignored such complications like backlash and friction worked very well -- as long as I remembered what the limitations of the model were. I tried to keep up a continuing theme that you need to remember what assumptions you made about your model, and what those assumptions mean.

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Tim Wescott
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Tim Wescott

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I love "Readership: PRIMARY MARKET: ... SECONDARY MARKET: Engineering students at the *more practical* engineering and technical schools; ..." emphasis added ;/

Lets out my Alma Mater.

The advanced BS(Physics) students came to Phillips Hall to take our

*REQUIRED* course in quantum mechanics. In the 60's I would have gotten more hands on "engineering" experience as a BS(Physics) student than I had a chance of as a 5-yr BSEE candidate. I fault IEEE and other professional societies for creating that problem with ill thought out course "standards". But the basic problem predates the various societies. My father got an ME degree, rather than persuing an EE degree, because (in the 1920's) the ME candidates received a much broader background in what would now be considered EE. At that time and this institution, EE was power plant, power distribution, and AC/DC machines. Whereas, he had the opportunity to study in an "applicable [ *NOT APPLIED* ] math course" what we routinely use when working with op-amps.

I'll consider dismounting a major pet peeve hobby horse.

PS. If anyone reading this is member of appropriate IEEE committee on educational standards, my reply-to is valid and I would be more than happy to contribute to improving the situation.

Anyone get impression that this is a hot button issue for me ;/

Reply to
Richard Owlett

... snip ...

I was about to mention that no reply-to showed on your article, when I decided to look at the full headers and discovered it there. Yet it didn't show up for normal headers on NS 4.75, while my own reply-to does! Then I realized it was identical to your 'from' address, and concluded that NS had suppressed the non-useful additional header display.

I still keep finding ways in which NS 4.7x is superior to Thunderbird 1.5.

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Reply to
CBFalconer

d*****ad. oops, senior design engineer

IEEE trans: industry applications industrial electronics power electronics control systems (although almost entirely useless)

PCIM, HFPC, APEC

yep. nope. did it all from first principles, using a pen and paper. then fiddled with resultant parts to optimise both BOM and response.

a plethora of them. Computer Controller Systems, Astrom & Wittenmark are right at the top of the list. Slotine & Li, applied nonlinear control is damn good too, but not for the fainthearted. as is macejowskis multivariable control. I have a couple of dozen control books, some of the oldest ones are brilliant - far less use of brute-force techniques, much more emphasis on understanding. Automatic Control Systems Enigneering vol. 2, Langill, is fabulous.

Cheers Terry

Reply to
Terry Given

....

......

I realise that there has to be simplification, but a lot of theory does not USUALLY cover the applied like what to do when an external sensor or feedback in the loop says there is a fault and how to make sure the loop (and the system) return to the correct state (whatever that may be).

An example would be printing shop guillotines that usually require two spaced out buttons to be pressed at the same time for the whole of the cut process. On the basis that if both hands are on the buttons then the operator's hands are not in the machinery! Now dpending on how the system operates there are basically three safety stop states - stop, move back a little or return to start position.

I have seen some control systems really screwed by an 'abort' function that need complete restarts or worse after that, basically because the control loop hardware/software could not effectively reset correctly.

Quite often I have seen customers who do not understand the limitations and assumptions in their systems let alone any model they think they have created.

Some of the major control loop problems I have seen is applying open loop blocks to an overall system that is closed loop. Mainly because they did not understand the limits of the blocks they were using, most notably delays, determinicity and sampling restraints.

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Paul Carpenter          | paul@pcserviceselectronics.co.uk
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Paul Carpenter

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TW must be talking about WPI

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, pronounced Wuss-duh in those parts.

Wes

Reply to
Fred Bloggs

-snip-

If it was me it was supposed to be off the record.

My Thesis advisor once told me that the first time he visited WPI he spent about an hour on the interstate -- he was looking for Wu'sta. He passed by Wor-ches-ter several times before it sunk in...

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Tim Wescott
Wescott Design Services
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Tim Wescott

... snip ...

What happened when he needed fish from Gloss-tuh?

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Reply to
CBFalconer

The 'cester' bit in Worcester says that the original town had been a Roman camp (an obscure one, probably only there because the River Severn was navigable up to there from the sea). Your friend was lucky though, he could have been driving up and down, looking for the original Olde English name of Weogornaceaster.

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Tony Williams.
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Tony Williams
[snip]

Pronounced just like the sauce ;-)

And sort of like Gloucester.

Then there's Wooster, OH ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Does he slaver it with war-sester-shire saucr?

Jerry

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Jerry Avins

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