Encoder, Stepper, Exact position in one direction

[Berggy]

OK ... I have a cog belt, 2500 pulse encoder, stepper, H2-CRTIO etc.

It is 5,000 encoder pulses from start to start of each piece of work.
I can set the stepper drive to 800, 2000, 4000 or 20000 steps/piece of work (2 revolutions of the shaft).
I have a prox sensor on the gearing to zero/home the encoder and stop the motor at each piece and I don't really care if it overshoots a bit as the pushers will pick up the work anyway.

What I do care is: If my belt stopped at encoder value 16 (Decimal) and I need to move my next piece of work to 3200 (encoder decimal), which profile setup on the H2-CTRIO is best suited to move my belts 3184 decimal encoder points?

I have had zero luck getting "22-Run to position" to work or even move the motor. "20-Velocity Mode" works rather well ... but I'm at a loss to get it to precision place my work.

Thoughts?

 

[Greg]

Berggy, the problem with using 22-Run-to-position and 20-Velocity-Mode is they just start outputting pulses at the frequency you've selected (i.e. no acceleration or deceleration) and the 22-Run-to-position does not use any encoder feedback. Instead it merely keeps up with the number of pulses it sent to the CTRIO Output.

You might try configuring a Pulse Profile called Dynamic Positioning; this one has acceleration and deceleration.

• Configure Pulse Profile (Dynamic Positioning)
• To run: Do a Load File of the above Pulse Profile for the CTRIO Pulse Output.
• SET the Enable Output bit.
• Enter (in decimal) the Position into Parameter 3.
• TOGGLE the Goto Position bit. At this point the stepper should accel to max freq and then decel to the position you desired.
• To go to another position, just write another absolute position to Parameter 3, and TOGGLE the Goto Position bit again.

Of course, the problem with this, again, is there is really no encoder feedback for the operation. The CTRIO is simply keeping up with the number of pulses it outputs. So, you'd have to calculate the position-to-encoder ratio manually and determine position in that manner. A pain, yes.

We currently have designed an H2-CTRIO2 that is much faster than the current one. It is being tested as we speak and will soon be released in 2011. One of the enhancements of the CTRIO2 is it has Dynamic Positioning (as described above) with encoder feedback. You can also scale both the output and encoder feedback to match, for example, your 2500 ppr encoder with whatever resolution you pick for your stepper.