Re: [CAD_CAM_EDM_DRO] Re: Position counter stop updating....Still there....

Babar,

The reason I asked about running stg2diag from dos is that
it is running under a different operating system. This then checks
the unlikely event that the operating system is causing a problem.

To answer you question about "star grounding".... this is simply
a description of grounding at one physical point only.Multiple
ground wires radiate from that point to other components similar
in appearance to the points of a star. It is an attempt to prevent
ground loops.

To Jon and Nassir:

I think you , I, and Nassir are on about the same wavelength as far as
the diagnostics. If the problem goes away when the servo amp inputs
are below 3 v surely amp noise is a major contributing factor. But it might
not
be the root cause.

I run the encoder wiring in an Igus flexible conduit right next to 3
unfiltered 22khz servo amp outputs at up to 90v and 20 amps each..
And a nasty triac controlled 120v 31/4 hp spindle power cable.
It is of course differential. No problems.

But.... I run twisted pair groups. I think Babar's 13 conductor cable
is not segregated into twisted pairs. If an offending electromagnetic
field has a lot of divergence a common mode signal will be induced
in even a differential pair if that pair is not close together.

The count rolling over at 65k (16 bit) is perplexing considering the stg
has 24 bit counters.

I am beginning to think filters... or a malfunctioning stg card.
Possibly filtering the encoders (Babar's bit rate seems to be pretty low)
Possibly easier than filtering amp outputs. RC = a microsecond or so
at the stg inputs?
What do you think?

Les

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.alltel.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.alltel.net/~leswatts/shop.html

----- Original Message -----
From: "Babar" <riet91@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>; <emc@...>
Sent: Saturday, September 14, 2002 8:05 AM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Position counter stop updating....Still
there....


>
> >Do you ever disable the 26LS31? (which is what I
> know the
> > SN75174 as in this part of the world)
> > Better not to here.
>
> John, We already have connected the Active High Enable
> signals of 75174
> (pins 4 & 12) to Vcc=+5V
> please tell us what do u mean by disabling the 26LS31?
>
> >Is the pair terminated (ie ~100 ohms across it) at
> the load end
> > well worth doing!
> > (the pair is the two wires connecting the the A and
> /A output pins
> > through to the far end)
>
> No we havent terminated the pair of each encoder
> outputs.
> And if we need to terminate it then the best place
> which i understand is at the inputs of receiver ic
> "26LS32" present on STG-II. meaning we
> will have to solder the resistors on STG-II??
>
> >Is the pair run as a twisted pair?
> > helps, but depends on your wiring.
>
> The cable that is coming from encoders is a 13 core
> sheileded cable. out of which 8 wires are being used.
> the Sheild is connected to system earth + ground. this
> sheild is connected to ground only at single side.
> Now this cable which has differential signals come to
> a board from where it goes to STG-II using simple
> ribbon cable (not shielded).
> This board also contains connections for DAC outputs
> of STG-II.
>
> >Do you use a 26LS32 or similar to receive the
> differential signal?
> > essential
>
> No we use 75174 ic at encoder side and since STG-II
> can accept differential signals therfore we didnt use
> any Receiver ic.
>
> >do you have any test equpiment (eg oscilloscope) to
> measure
> >noise levels?
>
>
> We have osciloscope. but We have rarely seen noise on
> osciloscope.
> although the stg2diag shows big errornous values
> following is the respone of stg2diag utility:
>
> [root@localhost bin]# stg2diag
> Servo To Go Board IO address = 0x200
> +1.000 +1.000 -2.000
> +1.000 +1.000 -65538.000
> +1.000 +1.000 -2.000
> +1.000 +1.000 -65538.000
> +1.000 +1.000 -2.000
> +65537.000 +65537.000 -65538.000
> +1.000 +1.000 -2.000
> +65537.000 +65537.000 -65538.000
> +1.000 +1.000 -2.000
> +65537.000 +65537.000 -258.000
> +1.000 +1.000 -2.000
> +1.000 +1.000 -65538.000
> +1.000 -3.000 -2.000
> +1.000 -3.000 -65538.000
> +1.000 -3.000 -2.000
> +1.000 -3.000 -65538.000
> +1.000 -3.000 -2.000
> +65537.000 -131075.000 -65538.000
> +1.000 -3.000 -2.000
> +65537.000 -131075.000 -65538.000
> +1.000 -3.000 -2.000
> +65537.000 -131075.000 -258.000
> +1.000 -3.000 -2.000
> +1.000 -3.000 -65538.000
>
>
> Looking at this response we see big errornous values
> after which
> the next value is same as before the erroronous value.
> Isnt this shows that this problem is perhaps something
> to do with the software?
> I meant if the actual problem is with errornous counts
> originating
> form encoder, then why these counter do not retain
> that errornous
> value?
>
> Les you wrote:
> >With computer ON, encoder supply ON, and servo amps
> OFF (at supply)
> >does the encoder count still smoothly change when the
> motors
> >are turned by hand with all axes?
>
> >If so when the servo amp is turned on does the
> problem appear
> >with all axes? (of course it should have 0 input when
> turning it on)
>
> >Does the problem disappear if the servo amps are on
> but not enabled?
>
> >Is the behavior noticed with BOTH EMC and stgdiag
> programs?
>
> We used external supply this time thinking that this
> might help us. isolating this encoder power suply from
> the machine. Our computer was
> ON servo amps and all the machine supplies were OFF.
> What we saw on STG2DIAG noise such as shwon in above
> response. We ran the EMC,
> run the motors with hands and didnt observed Counter
> stucking problem.
>
> Here please note that when the drives are powered, pc
> is ON and EMC running, When we run any axis drives
> using Testing dialog box then for
> upto 3 volts counters dont stuck (Although we see
> continous errornous big values in stg2diag)but for
> more than this 3 volts counters stop.
> To do this check we run stg2diag in parallel with EMC.
>
> When Stg2diag program is running it never stucks
> counters but gives
> errornous big values after some random period of time
> which is around
> 1 to 3 seconds.
>
> >Can you download the DOS version of stgdiag and run
> it from a >temporary
> >DOS boot floppy? If so what are the results?
>
> We'll try to do that but could you please explain,
> what is the
> difference in running stg2diag in linux and running
> that utility using
> MSDOS bootable floppy??
>
> >Is the 75174 IC enabled By +5 to pins 4 and 12 (if it
> is 16 pin dip
> >package)?
>
> YES, We already have connected the Active High Enable
> signals of 75174
> (pins 4 & 12) to Vcc=+5V
>
> >Now after the IC you should have 8 wires to each
> encoder. For me
> >there are 3 separate shielded twisted pairs for the
> encoder outputs
> >and +5 and a separate ground. The shields for the
> twisted pair are
> >hooked to star ground near the computer but LEFT
> UNHOOKED at
> >the encoder end 2 meters or so away.
>
> Yes We have 8 wires after 75174 but all the wires run
> in a single 13 core sheilded cable whose one end near
> pc side is connected to Earth+Ground.
> What is star ground?
>
> >Can you get a scope to measure the signals? Channels
> A+, B+, and I+
> > should be high and A-,B-, and I- low or vice versa
> relative to >ground.
>
> >I still use a 1 meter ribbon cable in the control box
> to go from a
> >breakout
> >board to the card. It is a special ribbon cable that
> uses twisted
> >pairs.
> >What do you use?
>
> Yes we measured the signals using osciloscope and have
> found that differential signals are always opposite to
> each other.
>
> We too have a ribbon cable which is one meter in
> length but is simple one (found mostly in computers to
> connect hard drives)
>
> >What model of encoder are you using? What is the
> count per revolution?
> >How many rpm do you want to turn it?
>
> >What is the base address of your stg card? Have you
> tried changing it?
>
> >How are your other card dip switches set?
>
> The X and Y axis Drives have 200 lines encoders. Index
> is working
> The Z axis has 250 lines encoders. (Z axis encoder was
> damage so we had fitted another encoder.) Index isnt
> working alignment is out. but we'll fix it.
>
> We dont know how many RPM should we run it at?
>
> Base address of our STG is 0x200 and we didnt try to
> change it.
> Can changing this address may affect counter stucking
> problem?
> the DIP switch have default configuration:
>
> Analog input range J2 = +/-10V
> DAC latch on interrupt J3 = latch on interrupt setting
> Watchdog J5 = Unlatched
> Watchdog timeout slection = 333 msec
> Source for CLK2 J7 = OSC/2
>
>
>
> Jon you wrote:
> >My servo amps have LC filters on the output, so that
> no more than 1
> >Volt of the
> >100 KHz chopping waveform is allowed to escape the
> servo amp. What
> >brand of
> >servo amp is used in this machine? I don't have to
> ask if the output
> >is filtered, it
> >almost certainly is not. Unfortunately, adding an
> output filter may
> >not be easy,
> >at least without retuning the servo amp. But, you
> would want to put
> >inductors of
> >probably several hundred microHenries in series with
> each motor output
> >lead
> >from the amplifier, and then a capacitor of perhaps
> .5 uF to the DC
> >power supply
> >ground from each motor wire. Without knowing the PWM
> chopping
> >frequency and
> >the motor current, it is hard for me to be more
> specific about this.
>
>
> We are using servoamps are from WestAmp.
> Peak current : +/-22Amp (for 500 msec)
> peak voltage : +/-100VDC
> Continous currnt +/-10 Amp
> Continous voltage +/-92VDC
> Switch frequency (constant) : 5Khz
> Frequncy responce : 500 Hz minmium
> Signal Input voltage : +/-10 V(typ) +/-50V Max
>
> And we are not sure about the presence of LC circuit
> in the drive.
>
>
> >One possibility is to change
> >the wiring location of the encoder signals. If the
> cable shield is
> >grounded at both ends, this
> >is incorrect practice. The encoder cable should be
> grounded only at
> >the STG card end.
> >Using an external power supply may be
> counterproductive, you may do
> >better with the
> >internal power source from the STG card.
>
> >Especially since the stg2diag ALSO shows the same
> problem when the
> >servo amps are
> >on, EMC is not to blame. And, in fact, nobody else's
> software will
> >run, either.
>
> >Jon
>
> No the encoder cable sheild isnt grounded at both
> ends.The encoder cable is grounded only at our
> breakout board and from there it goes to STG-II via
> ribbon cable.
>
> We were using STG-II supply to power encoders but
> since we used 75174
> we observed the Voltage droped to 4.3V. so we now are
> using external
> +5V PSU.
>
> Please comment
> best regards
>
> Babar
>
>
>
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