Dougal McDougal of that Elk wrote:> "Tim Wescott" <tim@seemywebsite.com> wrote in message > news:EqmdnWnD9PR-z2LenZ2dnUVZ_s2dnZ2d@web-ster.com... > >>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. > > > I hopr you have lest out Nyquist diagrasm and Root Locus. Never seen anybody > using them on a real design other than academics. > > > Tam > >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. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/
Closing Control Loops
Started by ●February 24, 2006
Reply by ●February 25, 20062006-02-25
Reply by ●February 25, 20062006-02-25
Fred Bloggs wrote:> >-- snip --> > I knew it! > http://books.elsevier.com/us//elsevier/us/subindex.asp?maintarget=&isbn=0750678399&country=United+States&srccode=&ref=&subcode=&head=&pdf=&basiccode=&txtSearch=&SearchField=&operator=&order=&community=elsevierYes, that's it. Done, thanks be.> > The book is too small. >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. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/
Reply by ●February 25, 20062006-02-25
Paul Carpenter wrote:> On Friday, in article > <EqmdnWnD9PR-z2LenZ2dnUVZ_s2dnZ2d@web-ster.com> > tim@seemywebsite.com "Tim Wescott" wrote: >-- snip -->>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? > > > 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. >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. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/
Reply by ●February 25, 20062006-02-25
Fred Bloggs wrote:> > > Tim Wescott wrote: > >> 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. >> > > I knew it! > http://books.elsevier.com/us//elsevier/us/subindex.asp?maintarget=&isbn=0750678399&country=United+States&srccode=&ref=&subcode=&head=&pdf=&basiccode=&txtSearch=&SearchField=&operator=&order=&community=elsevier > > The book is too small. >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 by ●February 25, 20062006-02-25
Richard Owlett wrote:>... snip ...> > 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.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. -- Some informative links: news:news.announce.newusers http://www.geocities.com/nnqweb/ http://www.catb.org/~esr/faqs/smart-questions.html http://www.caliburn.nl/topposting.html http://www.netmeister.org/news/learn2quote.html
Reply by ●February 25, 20062006-02-25
"Richard Owlett" <rowlett@atlascomm.net> wrote in message news:12017sgl188k635@corp.supernews.com...> > 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 ;/ > >It am easy try rowremovethisbitherelett@atandthisbittoolascomm.reverseten See and I have not even have to be member of committeeee to give you appropriate information to solve your problem plus you am not have pay me monee for find wrong answer........ Plus I went back and peer reviewed myselv so iz correct. DNA
Reply by ●February 25, 20062006-02-25
Hi Tim, Tim Wescott wrote:> 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?) >dickhead. oops, senior design engineer> What magazines do you read? Websites you visit regularly? >IEEE trans: industry applications industrial electronics power electronics control systems (although almost entirely useless)> 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. >PCIM, HFPC, APEC> Have you had to close a control loop recently? Did you do a web search? > What keywords did you use?yep. nope. did it all from first principles, using a pen and paper. then fiddled with resultant parts to optimise both BOM and response.> > 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? >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.> Thanks in advance. >Cheers Terry
Reply by ●February 25, 20062006-02-25
On Saturday, in article
<lZ6dnS0pVYzZA53ZnZ2dnUVZ_v-dnZ2d@web-ster.com>
tim@seemywebsite.com "Tim Wescott" wrote:
>Paul Carpenter wrote:
>> On Friday, in article
>> <EqmdnWnD9PR-z2LenZ2dnUVZ_s2dnZ2d@web-ster.com>
>> tim@seemywebsite.com "Tim Wescott" wrote:
>>
>-- snip --
>
>>>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?
>>
>> 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
....
>> 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.
......
>> Hopefully your book will not be like that.
>>
>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 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.
>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.
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.
--
Paul Carpenter | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.gnuh8.org.uk/> GNU H8 & mailing list info
<http://www.badweb.org.uk/> For those web sites you hate
Reply by ●February 25, 20062006-02-25
Richard Owlett wrote:> Fred Bloggs wrote: > >> >> >> Tim Wescott wrote: >> >>> 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. >>> >> >> I knew it! >> http://books.elsevier.com/us//elsevier/us/subindex.asp?maintarget=&isbn=0750678399&country=United+States&srccode=&ref=&subcode=&head=&pdf=&basiccode=&txtSearch=&SearchField=&operator=&order=&community=elsevier >> >> The book is too small. >> > > I love > "Readership: PRIMARY MARKET: ... > SECONDARY MARKET: Engineering students at the *more practical* > engineering and technical schools; ..." emphasis added ;/ > > Lets out my Alma Mater.TW must be talking about WPI http://www.wpi.edu/ , pronounced Wuss-duh in those parts.> > 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 ;/ > >Wes
Reply by ●February 26, 20062006-02-26
Fred Bloggs wrote: -snip->> I love >> "Readership: PRIMARY MARKET: ... >> SECONDARY MARKET: Engineering students at the *more practical* >> engineering and technical schools; ..." emphasis added ;/ >> >> Lets out my Alma Mater. > > > TW must be talking about WPI http://www.wpi.edu/ , pronounced Wuss-duh > in those parts. >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... -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Posting from Google? See http://cfaj.freeshell.org/google/
