RS Logix 5000-Looking for any examples of speed cascading methods change Conv Speed

Good Evening ,

I have a Conveyor system that requires Speed Cascading from one conveyor to another. Meaning that if one conveyor speed is changed , by a HMI pushbutton , that all the others behind it are changed by .1 FPM also.

Attached is an example that I have . It is working , but the operator said when she selected the Cascade HMI Pushbutton to put it in cascade mode , that the FPM jumped from 5.2 FPM to 3.2 FPM. I can't imagine the ONS malfuntioned .

What type of speed cascading systems and programs have you done that are simple and consistant ?

Also , just one more question. I would like to use a Ramp instead of a HMI Pushbutton . When you use a Ramp , and keep your finger on it , the output is still pulses , correct ? If so , these pulses are not too fast for ONS's , correct ?

Thanks so much for your advice ,

Surely there should be only one speed reference for the whole line, and you send that value to all the sections ?

Anyway, I would do all the logic for "bumping" that speed reference in the PLC, driven off a momentary pushbutton from the HMI. You will almost certainly get issues with HMI update times if you try to do it in the HMI.

Short press, bump the speed by 1 increment, long press use a timer to bump the speed continuously every 0.5 or 1 second intervals. You should not look at the button input again after a "dwell" timer has elapsed, which gives the HMI chance to turn it off again for the short press, but if it is still on after the dwell timer, the operator is holding it down, so bump the speed reference again.

Baker in Virginia said:

Good Evening ,

Also , just one more question. I would like to use a Ramp instead of a HMI Pushbutton . When you use a Ramp , and keep your finger on it , the output is still pulses , correct ? If so , these pulses are not too fast for ONS's , correct ?

Thanks so much for your advice ,

Click to expand...

Yes, If you look at the Timing tab of the ramp buttons you can set the number of repeats and the time delay in between pulses.

Dabe,


in conveyor process lines with multiple sections each section is slightly faster than the previous section. Otherwise product could could get pushed into each other or, if it is sheets of product, they could overlap and cause untreated areas.


What I use for a HMI ramp button is a normal pushbutton that controls a timer. When the PB is pressed a OneShot changes the setpoint, then when the timer resets and starts timing again ]T4:x/TT for RSLogix 5 & 500] I increment again. I also have a second timer on the PB that when it's accumulator reaches 2 seconds I write a shorter time to the first timer or change the value of the ADD or SUB integer, say from 1 to 5 at 2 seconds, then to 10 at 4 seconds, then to 20 at 8 seconds for larger changes. When the PB is released set the value back to 1 for the next time.


Another thing about the screenshot - it would be faster and use a little less memory (if that becomes an issue) and look cleaner if instead of cascading branches you extended the current branch down. Here is the TXT of what I mean:



XIC ? BST XIC ? NXB BST XIC ? NXB BST XIC ? NXB XIC ? BND BND BND



XIC ? BST XIC ? NXB XIC ? NXB XIC ? NXB XIC ? BND

Aabeck said:

Dabe,


in conveyor process lines with multiple sections each section is slightly faster than the previous section. Otherwise product could could get pushed into each other or, if it is sheets of product, they could overlap and cause untreated areas.

Click to expand...

That small offset for each section could be added before sending the speed reference to each drive. I also think a single "master reference" could be ramped easier than multiple references for each drive. And I also think this should be done in the PLC, so it would be easier to modify the repeat delays etc. if needed, rather than having to go to the HMI button configuration.

I do like your idea of "accelerating" the ramp increment, this is often done for a single pushbutton value setting interface.

If it would always work that would be OK. But too many times one of the following sections needs to be set to a higher speed than the offset from the previous.


A good example is in a develop/etch line for circuit boards. The develop speed to treat the photo resist stays pretty consistent unless a special resist material is used. However, the following etch speed can vary greatly depending on the thickness of the copper on the panel. It just has to be set faster than the develop.



I always do all this in the PLC. What I do is if one conveyor is ramped up I then check if the following conveyor(s) are set fast enough, if not I increase them as needed.


The HMI would have to show a setpoint and process speed for each section individually, each with it's own alarms and warnings.

Thanks all of you for your advice ,

So Aabeck , you are saying that "Cascading" the branches , will make it slower and use more memory ? For educational purposes , what would cause this ? It looks the same , what would the processor be seeing different ?

Also , from my original "Screenshot" , do you guys see any obvious problems with my program that would cause any issues , such as consistant pulses going thru the ONS and the ADD and SUB ( Not shown in my screenshot ) ?

If you look at the 2 text lines, the way your example has it after each NXB to the next branch there is another BST [branch start]. Then at the end there is a BND [branch end] for every branch started.



In your screenshot there are 3 more BST's and 3 more BND's than stacking them. This is 6 extra commands the PLC has to do every scan of this line, and if there are more lines like this it could affect the scan time. Another limitation is RSLogix 500 & 5 (never tested this in RSL/Studio5K) you can only have 6 (I think, maybe 8) cascaded branches, where an extended branch can go down until you max out the instructions per rung limit.



After you create the first branch right click on the lower left corner and select Extend Branch Down, Or you can Extend Branch Up if there is an instruction on the branch and you want to put something before it.


For the existing line you can click on the start of the branch, where the BST graphically is, and drag it to the small red square marked in my screenshot here. Be careful because if you go to a different red square you can lose the branch or get other unusual results. I would create a new project and make some branches around instructions, then see what happens when you move things differently. The large red rectangle (the BST) can be dragged to any of the red squares shown.

Ok . I understand what you mean by BST [branch start]. But what does
NXB mean ? Yea , I plan on setting up the same application in the office tomorrow.

Thanks for your advice.

After an instruction, or all the instructions, on the first line are checked and they are not TRUE the PLC uses the NXB as "Go To Next Branch" to go down one branch and see if it is true. If not and there is another NXB it will go down again. After the last branch it comes to a BND and then it continues on with the remainder of the rung.


Just remember, each instruction uses a word of memory and a (some more than one) click of the CPU scan to execute. Getting into programming this way could add hundreds of extra instructions in a large program. That on smaller PLC's could become a memory problem, and on all PLC's could make a noticeable impact on scan times.

On a side note this looks like a rademaker pizza sheeting line...am i correct? I've dealt with lines like this before.