How to connect while loops (in series, not parallel)

[anblan25]

Hello, I am new to LabVIEW programming; I am trying to figure out how to connect 2 while loops in series.

I'm trying to get the following :

1. all the code inside Loop A executes

2. end condition on Loop A is met

3. all the code inside Loop B executes

4. end condition on Loop B is met

I do not want any code in Loop B to start until Loop A finishes.

I've read multiple sections in my LabVIEW book, done research on NI forums as well as online in general, but I must be missing something pretty fundamental. This is a very easy thing to do I would think, but I can't figure it out.

I've tried the following thus far :

1. using the Connect Wire tool to connect the while loops

- if I connect wall of Loop A to wall of Loop B, I get an error saying I'm stringing an input to another input

- so I connect the "end condition block" of Loop A to Loop B, which works, but when I run the program, only Loop B executes (it skips Loop A); what's more, I don't necessarily want to "pass" any information from Loop A to Loop B - I just want Loop B to wait on executing until Loop A finishes

2. using the Flat Sequence Structure and placing Loop A in the left one, and Loop B in the right one

- no errors, but only Loop B executes

3. using the Stacked Sequence Structure, placing Loop A in Frame 0, and Loop B in Frame 1

- no errors, but only Loop B executes

Just to make it simpler, I even tried putting in basic code (without loops of any kind) into 2 frames of the Flat Sequence Structure. But, only the right frame of code executes; it ignores my code in the left frame (the frame that should execute first).

Thanks in advance for assistance.

[mikeporter]

Yes, you are missing something very basic. All three solutions you gave will woek. Show your code.

Mike...

[anblan25]

Here is my code.

The Flat Sequence Structure is inside of a larger container which executes when I press the START button on the Front Panel.

Loop A on the left; Loop B on the right.

Let me explain the code inside of these loops a little bit. This code controls a positioner device. The 6 orange inputs represent X, Y, Z, theta_X, theta_Y, and theta_Z (from top to bottom). So they represent the 6 degrees of freedom (translation & rotation) for the positioner device. Loop A is supposed to continuously move the positioner in the Z direction and then stop once it has moved 2 mm. Loop B is supposed to continuously move the positioner in the X direction and then stop once it has moved 2 mm. So the end result will be that the positioner first moves up 2 mm, then to the right by 2 mm.

Here is what I'm trying to get the code to do :

1. press START

2. Loop A executes

3. Loop A completes

4. Loop B executes

5. Loop B completes

6. sequence ends

As mentioned before, I do not want Loop B to start until Loop A finishes. That is, I do not want my positioner device moving to the right until it has finished moving up.

In the current setup (Flat Sequence Structure), only Loop B executes. That is, my positioner device only moves to the right by 2 mm, and does not move up. I can clearly see this when I run the program. If I place a Diagram Disable Structure over Loop B, leaving everything else the same, then only Loop A executes (confirming that the code does work). That is, I can see my positioner move up by 2 mm, but it does not translate to the right. So, it seems to me that it is "skipping" Loop A when both loops are placed inside this Flat Sequence Structure. I observe the same behavior with the Stacked Sequence Structure, as well as simply using the Connect Wire tool to connect the output of Loop A to the input of Loop B.

[crossrulz]

I think what is actually happening is you are moving your Z axis back to 0.  Therefore it just looks like only loop B ran.  Try setting the value for Z to be 2 in loop B.

[anblan25]

Okay, I just did that and it definitely changed. Good sign!

Although now, it moves to the position (0.002, 0, 0.002, 0, 0, 0) in 1 motion. That is, it translates along X and along Z simultaneously.

It appears like LabVIEW is still trying to run the 2 loops in parallel...

[crossrulz]

Looking at this code a little closer, I think you will be much better off using a single FOR loop.  What you do is make two arrays of what the positions should be for each iteration, 1 array for the X and another for the Z.  Then you just autoindex on those arrays and move as needed.  Code will become simpler, more scalable, and more reliable.

[crossrulz]

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@anblan25 wrote:

Okay, I just did that and it definitely changed. Good sign!

Although now, it moves to the position (0.002, 0, 0.002, 0, 0, 0) in 1 motion. That is, it translates along X and along Z simultaneously.

It appears like LabVIEW is still trying to run the 2 loops in parallel...

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It is more likely that your device just can't move fast enough for your commands.  It is hard to say since I have no clue what device you are using or what that subVI does.  Try running with highlight execution on and see what happens.  You might just need to add a delay to your loop(s).