it works, but now i am trying to figure out why

ok, so machine movement trying to keep track of position on x and y.
getting the actual frequency applied to the motor back via the 4 to 20 from the atv312. 8 bit resoultion scared me, but at 2 to the 8 power (256) 20ma = twice ncr out on drive, aka 16 divided by 256, that is 0.06 amps per tick.

I know the inches per second, as I ran a known distance per time. I divided that by the hz so I could get a rate multiplier. there is chains, pullies, gear boxes et al. was not trying to do that kind of math.

every inch of travel I accum. the distance traveled.

I feel like my 3 second acccel is actually helping me.

I've been drinking. gonna stop now before someone calls me stupid again.

ex nay on the 3 second accel.
I understand the formulas for calculating accel and decel ramps, but I find that if I keep them under a second I don't have to worry about that.

If you want to keep track of position, use position feedback.

Highland Controls said:

If you want to keep track of position, use position feedback.

Click to expand...

I'm interested in position feedback.

Are my only options encoder and a high speed counter card?

Fortunately, 100% accuracy wasn't necessary on this job.

I set the drive up to give the plc the actual motor freq. to the plc analog input.

Every 0.1 inch of travel I recorded in the plc.

It works great.

The friction brush gives the current back to the plc via 4 to 20.

This way, I'm able to tell how much brush penetration I have on the car and can adjust via position as necessary.

Works great, just wish I could speed up the process.

Have to move the trolley and gantry slow during this penetration measurement process.

Distance measuring devices by sick or Ifm are very nice. No need to keep track with high speed counters like with an encoder. The device gives you 4-20ma according to its min max distance setup in it.

chud said:

Distance measuring devices by sick or Ifm are very nice. No need to keep track with high speed counters like with an encoder. The device gives you 4-20ma according to its min max distance setup in it.

Click to expand...

Yep....for gantry movement never rely on anything from the motor, even encoder. Just because the motor spins X amount, doesn't mean the gantry moves that much unless you have a zero backlash gearing system, which doesn't sound like you (OP) do. Over time, unless you're rehoming this system often it's going to accumulate error somewhere.

Use a Sick Laser eye mounted to the gantry and pointing to a fixed reference (wall) to measure position. I've used them on the last two gantry projects and they worked well.