RE: Microkinetics style

> ----Original Message-----
> From: PTENGIN@... [SMTP:PTENGIN@...]
> Sent: Tuesday, November 30, 1999 4:21 PM
> To: dharrison@...
> Subject: Testing Step Motors ala Microkinetics style
>
>
> I scoped it too. I found closer to ten volts on the lines. I found that
> the
> signal ground is not tied to the chassis. I tried scoping the signal
> ground
> to chassis ground. No DC component but there was a lot of noise. I figured
> if
> there is no DC, what the hey? I put a ground strap between them and
> reduced
> the noise by about 75%. Almost usable. The popcorn noise is almost gone.
>
> Are you referring to the lack of connection between the negative on the 5V
> supply and the input side of the drivers? I noticed this too, but assumed
> that they intended to let the input float (not tied to ground). Problem -
> where then does the return path come from? Through the chassis? I'll try
> your ground method tonight. The other thing I want to try is putting small
> capacitors across the 5V terminals at the drivers. I still think the
> drivers are feeding noise back into the 5V circuit, not the other way
> around. Again, this coincides with my belief that optoisolation is of
> little use if the supply is not isolated.
>
> The computer I/O connector to the drive rack could be removed from the
> back of the case to the front, I wonder about the efficacy of that move.
> It
> would move the signal lines away from the output lines. I'm positive the
> noise is coming from there.
>
> If I have to go through this I might as well build a new case. The
> existing cabinet is banged up anyway, courtesy five trips on UPS.
>
> I killed the the computer, the fan, the +5 from
> the logic power out on the on board PS and fed the signal lines with an
> external +5 PS. (I scoped the PS and found it to be clean.) Sure enough,
> if
> there is a motor hung on the output of the driver, the thing showers the
> whole assembly with noise. I tried powering the amp up with no motor. No
> noise. The stock motor connector has no shield from the card output to the
>
> connector. This seems to be the problem area.
>
> Consider that the noise is probably also a function of driver load. No
> motor - no load.
>
> I'll try to shield it some
> more. I tried shielded cables for the motors. When the shield is
> connected
> to the chassis ground, it makes the situation worse. Seems the noise is
> sent
> right into the chassis. I checked ground between the chassis and building
> power. Again, no DC component, just the ringing. I wanted to run shielded
> cable since it causes the radio and TV to go static'ky on me.
>
> Help. Are you attuned to EMF/RF radiation attenuation? It goes through
> every thing.
>
> I don't think any of the limit switch or motor cables are shielded on our
> BOSS-5 bridgeport. I will double check this though. My best suggestion
> is as you say, isolate input and signal lines from HV and output lines.
> This is standard practice (though apparently not at Microkinetics). You
> might also look at the proximity of the LED indicator wires to the power
> supplies. I do not recall ever seeing power supplies in close proximity
> to signal lines in commercial CNC equipment.
>
> Next chance I get, I'm gonna look at a commercial axis drive box and
> see
> how they work around these problems. I no longer have microkinetics
> drivers.
> I figure any problem now is the way the cables are routed and or shielded
> /unshielded. Military Specification stuff has the cast aluminum box and
> the
> MS AMP connectors. You kinda gotta admit that it may be required. I'm
> trying
> to determine if I should build my own aluminum "sealed for RF" boxes for
> each
> axis. Much like the cage on a PC power supply. Then I would have a large
> chassis box for the individual power supplies. I figure key is to keep the
>
> signal and power "out" far apart and shielded/grounded. I'm not an
> electronics designer. I'm willing to bet there are components that can be
> used to reduce the ringing/noise on the circuits. Ferrite beads? ferrite
> cores? inductors? capacitors? transorbs? I don't know the components well
> enough to make a call. Applied Motion Products has optional perforated
> metal
> cages for the drives I have. I suppose the factory offers them cause there
> is
> a real problem to address.
>
> Another thing I found was that the limit switch cables acted as antenna
>
> and manage to pull more noise in from the surroundings. I need to run a
> shield on it too?
>
> Does everybody else have these problems?
>
> Regards
> Peter