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

[Babar <riet91-at-yahoo.com>]

>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-at-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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