[nickcornilsen]

I just got the wiring and most of the programming done on my Tree 325 retrofit. (Kflop/Kanalog) After battling with an air pressure interlock (forgot I tied that in...) I got the E-stop loop enabled, which activates the servo cards.
As soon as they go enabled, all three axis's began creeping slowly (may 5 IPM) in a particular direction. (When I say enabled, the relay supplying voltage to it gets turned on. Has nothing to do with the KFLOP)

The DAC's appear to read 0V.

Is this what people refer to as run-away? It seems that if the gains were backward, it would go to full rapid speed... not slowly, steadily roll one way.
I hesitate to reverse the gain, lest I create a REAL run away and crash something.

Is there something I should check?

[TomKerekes]

Hi Nick,

This is a common issue with analog drives. It is almost impossible to command exactly zero speed with an analog signal with no offset or noise. This won't matter when the servo is enabled because the servo will command whatever voltage is necessary to hold position. It is only a problem when the servo feedback loop is disabled. The only sure way to avoid creep is to disable the amplifier. If you allow KFLOP to enable/disable the amplifiers you can avoid this. You will need to add a watchdog loop that watches the axis enables and if any are disabled then disable the amplifiers.

There is also an Axis Channel OutputOffset parameter that can be used to reduce the creep.

HTH
Regards
TK

[nickcornilsen]

Tom,
I've done a bit of digging.

As it stands now, the amps can't activate unless the SWENABLE relay driver on the Kanalog is activated.

So that means I might have an encoder feedback problem? I did notice on the axis screen that when I manual moved the axis, some of them would advance one way, but not the other. Z didn't seem to change at all. Y worked fine both ways, but was still creeping.


I have my servo tachs on the same ground pin as the servo amps... would that cause this issue if they were referencing different grounds?

[TomKerekes]

Hi Nick,

Using the SWE (Switch enable output) doesn't fully solve the problem because it comes on as soon as KFLOP boots up and initializes all the IO but before the servo is initialized and enabled. You really need an additional enable output that you can turn on at the same time as you enable the servo.

Working or not encoders will have no effect on this drift when the axis is disabled (but the amplifiers are enabled). But it doesn't sound like they are working properly. If you rotate them by hand the position should track and return to the same position when the encoder goes back to the same position.

A common problem is to wire single ended encoders to the Kanalog differential inputs leaving half of the inputs floating. This will not work.

Regards

[nickcornilsen]

Thanks!

I'm still a bit confused though. The way my system is setup is that the servo amps are activated is by the relay Estop replay 1CRE (pg3, upper right hand corner)

In order for this to pull in, I have to hit a physical "reset" button on the user console. (makes wire 214 +24V via a momentary on button.)
So, the amps can't really come on 'till I hit that button, and even if I wait a few seconds and hit reset the problem persists.

I suppose I could move the output anyway, but it still seems like I'd have this problem. Could there be a problem with my drive initialization code that's causing the drives never to enable?

[TomKerekes]

Hi Nick,

Aren't we all

I don't really understand your point or the sequence of operations.

But yes, if you wait however long and then just enable the amplifiers then they will always start drifting.

The key is to enable the amplifiers and the servo at the same time. So the amplifier enables need to be interfaced to KFLOP so your init program can do both.

But before you worry about slow drift when disabled you should get your encoders and servos working.

Regards

[Al_The_Man]

Well evidentally the LBL come in 3 flavours, but RS420 differential not one of them.
5v,12v & 15v, with Open collector, Open collector complementary, and TTL Line driver.
So at 5v, yours could be TTL?
Unless they mean the TTL Line driver is RS420?
You could pop the cover off to see what driver IC is used?
Al.

[TomKerekes]

I'm guessing these are open collector complementary.

I think adding 1K pull ups to both + and - signals should work.

Kanalog uses a AM26LS32ACD differential receiver which only needs to see +0.2 and -0.2V to switch.

Repeat the test you described after adding pullups on both sides and you should then observe (measuring across the 480ohm resistor) the voltage toggle between +1.4V and -1.4V.

Regards

[nickcornilsen]

I'm guessing these are open collector complementary.

I think adding 1K pull ups to both + and - signals should work.

Kanalog uses a AM26LS32ACD differential receiver which only needs to see +0.2 and -0.2V to switch.

Repeat the test you described after adding pullups on both sides and you should then observe (measuring across the 480ohm resistor) the voltage toggle between +1.4V and -1.4V.

Regards

I'll give that a try!

[nickcornilsen]

Ok, so I put a 1K pull up to the A_ and B_ channel wires. Now when I move the axis, it toggles between -1.47 and +1.47.

I'm thinking this is what I want to see right?

[TomKerekes]

Yes!

[Al_The_Man]

Like I mentioned in post 22, when I am in doubt with an unknown encoder, popping the cover off and noting the transmission IC can usually fill in the blanks.
Al.