Did LV 8.0 can do same accumulation like this?

[guangli]

Hi, Guys,

I try to accumulate all the past position error to feedback the motion loop. I can use this formula node in LV8.5 and 9.0. I cannot use it in LV8,0 or 8.2? In my lab pc, it's LV 8.0 or8.2. I cannot wire back the output sum to input sum. How can I resolve the problem in LV 8.0? The input variable is acquired by Machine vision Loop in real time.

Thank you!

[BruceAmmons]

Feedback nodes are probably not in LV 8.0 or 8.2.  Instead, do it the old fashioned way with a single iteration while loop and a shift register.

Bruce

[guangli]

Hi, Bruce,

Thank you. I do see the feedback node in LV8.2. It doesn't work in the same way as LV8.5, anyway.

Could you tell me a little bit about single iteration while loop. Doesn't while loop a true fault condition structure?

I need to add all the past value for PI controller in real time. I use the acquired postion to actuate the caculation. Can I still use it?

THKS!

Guangli  

[BruceAmmons]

It is just a while loop with a True wired to the stop condition.

This should work fine for the I term of a PI controller.  I would probably make it a little more complex to limit the range of the I term and have the option to zero it when necessary.

Bruce

[guangli]

Bruce,

I still don't understand what you said. Is this like the follwing figure? It cannot stop.

[BruceAmmons]

That is it, mostly.  Change the Stop control to a TRUE constant.  This way, the loop will run once and exit.  This will give you the exact same functionality as your feedback node.

Bruce

[guangli]

Hi, Bruce,

You mean control variable change to constant control, right? This one doesn't work for my program.

it may work if control variable inside while loop. But, I still get some error in this case.

If the control variable(acquired position ) is outside while loop, I'm pretty sure it doesn't work because while loop won't stop until true button is pressed.

The following figure is the part of my program. The accumulation is in black circle. And the most outside of the program is while loop, too.

[BruceAmmons]

The constant wired to the stop terminal has to be TRUE!!!!

Also, don't wire anything to the initialization of the shift register (the zero on the left of the while loop should be removed).

Bruce