Re: Low cost Servo Controller

----- Original Message -----
From: Mike Gann <mikegann@...>
To: <CAD_CAM_EDM_DRO@onelist.com>
Sent: Saturday, September 18, 1999 9:47 AM
Subject: Re: [CAD_CAM_EDM_DRO]Low cost Servo Controller


> From: Mike Gann <mikegann@...>
>
> I could be way off base here, as I haven't reviewed the LM629
> in quite a while. But if I recall, don't you set up the parameters
> in the LM629 telling it where to go and it handles the rest?
>
> If thats the case, again its been awhile since I looked at this chip,
> the problem would be keeping the axis' in sync.
>
> Mike
>
> CG wrote:
> >
> > From: "CG" <cnk@...>
> >
> > Bertho-
> >
> > Take a look at the LM629 Motion Controller chip from National
Instruments.
> > It's an all-in-one motion controller that handles the encoders, current
> > sensing, programmable PID loop, and either 8/12 bit DAC output or 8 bit
> > sign-magnitude PWM output to the servo amplifier. They show a simple
> > circuit with the LM629 using PWM to talk to their own LMD18201 3A 55V
> > H-bridge. You need to talk to the LM629 with a micro of course, but the
> > language is very straightforward. It seems like a good starting point
for
> > figuring out the basic functions and architecture for an all-digital
> > low-cost system we're talking about. These chips are expensive, as far
as
> > chips go ($25 ea.), but they do just about everything. I don't have
much
> > time now, but I've got the data book in front of me if you need more
info.
> > (National Power ICs Databook).
> >
> > Carlos Guillermo
> >
> > > -----Original Message-----
> > > From: Bertho Boman [mailto:boman@...]
> > > Sent: Friday, September 17, 1999 7:43 AM
> > > To: CAD_CAM_EDM_DRO@onelist.com
> > > Subject: Re: [CAD_CAM_EDM_DRO]Low cost Servo Controller
> > >
> > >
> > > From: Bertho Boman <boman@...>
> > >
> > > I am very interested in the design of an all digital servo amp.
> > > I have mentioned the pieces in several previous post but here
> > > is a summary:
> > >
> > > I like to stay away form the analog circuitry if possible and
> > > have a well defined simple digital unit. I know how to design
> > > analog circuits, that is not the issue. Simply we will have a
> > > more repeatable and easier to buil system if it is all digital.
> > > Also, do not be scared of the "DSP". It is basically a
> > > microprocessor that has been optimized for certain math calculations
but
> > > a regular microprocessor can also be used.
> > >
> > > The interface to the PC would be all digital and the PC would
> > > send a two-byte speed command to the servo amp. As it is now, the
> > > software sends the 2-bytes to a D-A (Digital to Analog) on an
> > > internal I-O board so there would not be any significant software
> > > changes. The actual interface could be through a digital I-O
> > > card, the printer port, USB or even high speed serial I-O.
> > >
> > > A "real" servo amp needs a tach input but we would use the
> > > encoder signals to calculate the speed and avoid the analog issues
> > > and extra mounting headaches of a tach.
> > >
> > > The last input needed is the motor current. We would sense the
> > > current and feed it to an A-D converter. Some
> > > microprocessors/DSP even have built in A-D.
> > >
> > > The central component of course would be a microprocessor or DSP
> > > chip, programmed to do the servo loop calculations and the gain
> > > & filtering would be software adjustable.
> > >
> > > If this approach is followed we basically would end up with the
> > > controller chip with all the smarts and it would do all the
> > > calculations and produce the PWM output drive to the high power
> > > output switching sections.
> > >
> > > Envision the best case: One DSP chip with inputs from the PC, the
> > > encoder and the motor current and it produces a PWM that is
> > > feed to the power output switching stage.
> > >
> > > Questions?
> > >
> > > What digital I-O is used today for servo amps that would be
> > > similar to what I am proposing. I am sure I am reinventing the
> > > wheel and do not claim any originality. It is simply the obvious
> > > answer to a problem. Is there any type of standard? What
> > > digital output options do high end commercial software have?
> > >
> > > Bertho Boman
> > >
> > >
> > >
> > > Dean Franks wrote:
> > >
> > > > From: "Dean Franks" <dean@...>
> > > >
> > > > ----- Original Message -----
> > > > From: Tom Kulaga <tkulaga@...>
> > > > To: <CAD_CAM_EDM_DRO@onelist.com>
> > > > Sent: Thursday, September 16, 1999 5:00 PM
> > > > Subject: [CAD_CAM_EDM_DRO] Re: Low cost Servo Controller
> > > >
> > > > <snip>
> > > >
> > > > > When it comes to the amps, I'm not much of a help, but can anyone
say
> > > > > whether it is possible to convert an analog signal to a PWM
> > > signal? It
> > > > > would be impossible for EMC to handle a software generated PWM
signal,
> > > > > and the only way I know how to do it is by using a dedicated
motion
> > > > > controller chip which is set up to output PWM. It's gotta be
possible
> > > > > to convert one signal to the other, right? Especially given that
we
> > > > > can decide here and now what level the signals will be (industry
> > > > > standards of +/-10VDC for analog, and 0-5VDC for PWM).
> > > > >
> > > >
> > > > Yes, use a linear ramp oscillator and a comparator. Configure
> > > the circuit
> > > > so the oscillator runs at the desired PWM frequency, the oscillator
and
> > > > input ref signal are connected to the comparator. Set things up so
the
> > > > comparator generates a "true" output when the input ref signal
> > > > linear ramp
> > > > signal. If you want to prevent 100% duty cycle, put a divider
> > > (and maybe a
> > > > zener) on the input ref signal to scale/clip it to the desired max
duty
> > > > cycle value.
> > > >
> > > > You can generate a close linear ramp using analog methods, or
> > > you can use a
> > > > counter connected to a D/A converter. Assuming that you use an 8
bit
> > > > counter and D/A, run the counter at 256x the pwm frequency.
> > > You could also
> > > > use a cheap PIC with a software counter driving a single D/A source,
> > > > although using the same ramp for all PWM channels will generate
> > > a bucket of
> > > > EMI. If you do this in software, you might take the
> > > opportunity to stagger
> > > > the master PWM clock, or use spread spectrum PWM generation to
> > > reduce noise
> > > > [drop me a note if you want details on this].
> > > >
> > > > Hope this is useful.
> > > >
> > > > Dean
> > > >
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> > > Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for
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> >
> > > > Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the
discussion of shop built systems in the above catagories.
> > To Unsubscribe, read archives, change to or from digest.
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> > bill,
> > List Manager
>
> > Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the
discussion of shop built systems in the above catagories.
> To Unsubscribe, read archives, change to or from digest.
> Go to: http://www.onelist.com/isregistered.cgi
> Log on, and you will go to Member Center, and you can make changes there.
> For the FAQ, go to http://www.ktmarketing.com/faq.html
> bill,
> List Manager
>