Planning - Bridgeport Interact 1 linuxCNC Retrofit

cncnoob1979 wrote: Im at work at the moment, however last night I managed to get somewhat stable. I think something is wrong however since I tried tuning the PID, but the P value only ran away with positive P values.

You need things set up so that the encoder counts positive in the positive direction and positive velocity commands move the axis in the positive direction.

The first can be achieved by changing the sign of the encoder scale.
The second might be simplest by swapping the motor wires. (for DC servos).
I can't remember if you still have tachometers?

Basically, everything needs to agree which direction is positive. This is probably table-towards-operator and table-to-left as G-code works on the movement of the tool relative to the work.

Thanks for such a quick response Andy,

I have the belt disconnected for testing purposes, I'm pretty sure I had it set up with positive directions and jog inputs in the positive direction. I will check again to be sure.

I do have tach's on each axis, not sure how to look at the inputs from the tachs yet.

cncnoob1979 wrote: I do have tach's on each axis, not sure how to look at the inputs from the tachs yet.

Use a multimeter, they output DC voltage.

Ok, I will check that.

How do I increase jog speed?

I verified the DAC output voltage and made a very small change so it was spot on to the commanded voltage. When in open loop test the servos move quite well. But under PID, I have my jog speed set to 60in/m and move so very slowly - a crawl just trying to move 1/2 inch. I'm curious if I have something set wrong or what. Also the machine max is set to 60in/m.

I've tried to find where the max limit is set. Do you have a suggestion where I could read up on the subject? Would the most relevant information be in the Linuxcnc doc's? From what I have seen mostly its outdated information, or I'm looking in the wrong spot.

Having recently done this I can save you a little time. I found that the encoder direction was wrong and needed to be reversed. The easiest way to fix this is to use a negative encoder scale. With 25 fold interpolation the correct scale for you should be -127000. The servos should have the correct polarity.

Here are my final numbers from my tuning for the X axis:

MAX_ACCELERATION = 3.6
P = 170
I = 0.35
D = 0
FF0 = 0
FF1 = 2.62
FF2 = 0.01
BIAS = 0.0034
DEADBAND = 0.000059
MAX_OUTPUT = 10
ENCODER_SCALE = -25400
OUTPUT_SCALE = 10
OUTPUT_MIN_LIMIT = -10
OUTPUT_MAX_LIMIT = 10

Because your encoder scaling is very different you probably need to scale these but the ratios should be similar. You might want to start with P, I, FF1 and FF2 at 25% of what I have as a starting point. Easier to deal with a sluggish servo than one that oscillates. Also you should set the BIAS to 0 since each servo will have a different offset. I set the MAX_VELOCITY quite low since there is some delay in the servos that causes a fairly big following error at the start and end of movement. It's trading speed for accuracy. It takes a little time to see how each of the parameters affect the results. Take your time and carefully note what happens. I ended up making 3 passes on each axis. Each time I was able to get a slightly better result.

I found that doing a G01 move of about 0.8" + immediately followed by a move - was a good test case. Having both + and - movement makes it much easier to set FF1.

Good Luck!

csbrady,

Thanks for taking the time to help me out! Did you get yours sorted out? The issues you were having?
Also, did you set your index pulse to 90deg or 270deg? I noticed that it was a selection with the documentation you received for your settings.

My 702b were set for 270deg, but I couldn't see them until I set them for 90deg [default settings from the manual].