Vertical Axis PID Tuning questions

I prefer a battery box, a switched output of a 9 volt run through a trim pot to change the voltage.

By the way, what do you have for feedback. The DeVliegs normally have Farrand inductosyn scales.

scotth wrote:

By the way, what do you have for feedback. The DeVliegs normally have Farrand inductosyn scales.

This has Heidenhain Glass scales with EXE boxes. 1 micron resolution. This is on XYZ. I have Heidenhain rotary encoders on the W (quill) and B (rotary) axis and on the spindle.

I had a few hours today to work on this machine. I decided to hook my scope onto the X axis drive and tune that using the AB 1388 docs. I got it tuned so that there is less than .001 following error when running the table at 200 inches/min (max speed) with a spike at the beginning and small overshoot at the end (viewed on halscope) I had my physical o-scope hooked to the tacho and velocity command pins and they track very closely.

Then I moved onto the Y axis. This one is more tricky..I adjusted the offset potentiometer on the drive itself so that at idle, the voltage output of the mesa 7i77 is very close to zero, about 1-4 mV. Following error going UP is about .005" and stable with no spikes or overshoots. Going down, the commanded velocity is the same, but voltage spikes and sends the drive rocketing downward, followed immediately by a following error. I'm going to try the AA battery tomorrow which should be a 30 in/min jog on this system, and see how it behaves.

If you need to look at the tach feedback, I have used a 12 volt car battery to drive the axis motor. Then you can watch the tach output with your scope. Jumper cables are best so you can disconnect quickly.

Well, I believe I've narrowed down what is wrong with this axis. It's the encoder. I found that if I jog the axis up and down, I get a continuously higher and higher reading... If I jog up .01, it moves about .023. If I jog down .01 it travels about .1

This is a heidenhain 603 glass scale with EXE 602 box. I've swapped boxes with another axis and it made no difference, so I'm guessing it's the scale.

That said, has anyone had any experience with using the glass scales off of ebay that are for DROs? Most are 1um scales like this heidenhain and supposedly TTL output without a translator box..