Reseting an SQO?

Hi everybody!
Is there a way to reset a sequencer at any time of the cycle.
Lets say the SQO has 7 positions and right now it is at position 3, then I want to reset the SQO to start over to position 1. Is there a way to do that?
So far I see when I stop or turn off a SQO then turn it back on, the same outputs that where energized still on.
Thanks.

Think of the SQO as a MVM (masked move) with indirect addressing and a built in counter that increments the POS on a false to true transition.

You can write to the POS word, then the next time the SQO rung goes true, it will increment and update the destination word. So MOVe a zero in there on a branch just above the SQO, and it may do what you want. Put your reset condition on the branch ahead of the MOVe.

If you want to manipulate the POSition, you may be better off with an unconditionally true SQO rung, or do what I did, and use an indirectly addressed MVM instead and take full control of the "pointer" with external logic. If you use the same address for the pointer in both your source and mask words, it will be very similar to SQO but it won't increment all by itself. Of course you must limit the pointer's range to legal values within your source and mask files.

Hope this helps,
Paul

When resetting a SQO with a RES instruction you need to use a MVM in parallel to move the appropriate bit pattern for step 0 into the output word, or use CLR to clear the word if all bits are clear. Also, when I directly change a sequencer step, say from step 7 backwards to step 3 by writing to the .POS word I also use an MVM to update the output word. If I need a sequencer where I have lots of non-monotonic steps in it then I usually ditch the SQO in favor of a MVM and an integer that designates a step number and is alos the indirect addresss for the MVM source word.

FWIW, I never bother pairing an SQI with the SQO, I condition the SQO runs leadin logic instead for each step.

Thanks Okiepc and Alaric for the information.

Let me tell you what I'm trying to do.
I have at work a vinyl window frame corner welder that is inactive because the backup battery of the plc discharged and the program lost.
Now I'm trying to do the program to make it work. I thought that the best option is to use a sequencer.
These are the steps of the cycle:
step 1- press button to bring in lacating plate.
step 2- press button close head.
step 3- press button to bring back clamp down.
step 4- press button to bring front clamp down.
step 5- press button to start cycle.
Once the button is pressed the head(in step two) should open to let the locating plate go out, then a heat plate comes in, then the head(in step two) closes again. After 15 seconds of melting the head(in step two) goes out again to let the heat plate go out, once the heat plate is out the head(in step two) comes in again to join the melted parts. After another 15 seconds, everything releases and its ready to stert a new cycle.
As you can see steps 1 through 4 are manually and controlled by the same pushbutton. Ance the button is pressed for step 5, it runs automatically.
Is ther a way to use timers with an SQO or you think there is a different way to make it work?
By the way, the PLC that lost the program is an LG and now I'm trying to program a micrologix 1000.
Any help will be appreciated.
Thanks.

Sure, you can use a sequencer, but this is a pretty simple sequence that would be easier to follow with a simpler construct.

If you use a sequencer, your step done conditions can be conditioned by the appropriate timers for each step that requires them or you can get fancy and parallel another SQO word to write the preset for the step time into a single timer.

My sequencer was forty steps and was configurable for hundreds of different products, some required different outputs, and certain steps skipped, it was pretty complicated but made very short and sweet with a sequencer. We had four words of sequenced inputs and 6 words of outputs, so the sequencer was definitely the way to go.

Being only seven steps, I would approach it like this:

http://www.plctalk.net/qanda/showthread.php?t=29918&highlight=simple+sequence

I don't have RSLogix at home, or I could customize this for your specific application, but it is food for thought...

josesaucedo said:

Hi everybody!
Is there a way to reset a sequencer at any time of the cycle.
Lets say the SQO has 7 positions and right now it is at position 3, then I want to reset the SQO to start over to position 1. Is there a way to do that?
So far I see when I stop or turn off a SQO then turn it back on, the same outputs that where energized still on.
Thanks.

Click to expand...

I am assuming you are referring to AB SLC/PLC5 or Clgx. I do this all the the time by using a one shot to set the value of the sequencer's control register R6:1.POS or Clgx_Seq.POS

Thanks guys!

Okiepc please read

Okiepc, I'd like to tell you the steps of the cycle for this machine.

step 1. Press push button once, locating plate comes in, then after two sec. the head closes.
step 2. Press push button once, then back clamp comes down.
step 3. Press push button once, then front clamp comes down.
step 4. Press push button once to start cycle.
Cycle: Once the push button has been pressed and released, the cycle starts.
First, the head opens.
Second, the locating plate goes out.
third, heat plate comes in.
fourth, the head closes.
Fifth, after 15 sec. the head opens.
sixth, heat plate goes out.
seventh, the head closes.
eighth, after 15 seconds clamps(back and front) go up.
nineth, head opens and the cycle is complete.

It has an emergency stop to stop the cycle at any moment and start all over again.
My problem is to combine the sequencer with timers.
Thanks for your help.

Here is an example based on your list of steps.

I made many assumptions about your I/O and devices just to give you a start. You must make necessary corrections to match your I/O and device types, and you must carefully consider what will happen during e-stop conditions, etc, and add any other mode controls that are on your machine.

Of course, you will have to edit the I/O to match your stuff too.

Good luck, and I hope this helps.
Paul

I usually use the brute force approach, by setting the sequencer position to 1 less than the position you're going to, then energizing the rung with the SQO instruction for one scan.

ie. to reset to the first position, MOV 0 R6:0.POS

This works to go to any position in the sequence. To step back one step, you move to the current position minus 2, then step forward on the next scan.

I've used this many times on the PLC-5 and CLX, so it should also work on the SLCs.

Paul, I have not been able to open the attached file. Could that be because I'm using WinZip Evaluation version?
Is there a way you can send the file to my e-mail box?
Thanks.

josesaucedo,
Its not really a zip file, just change the extension to .RSS and double-click it. It will open with RSLogix500.

Mickey said:

josesaucedo,
Its not really a zip file, just change the extension to .RSS and double-click it. It will open with RSLogix500.

Click to expand...

Sorry, I forgot to include that little tidbit of info...

As Mickey said, just save it, change the extension to RSS, and voila...