Need ideas for building a panel length measuring system

Hey fellas,

I'm looking for ideas. I've been asked to look into creating a system that will measure the length of panels cut by our flying cut saws. I'm most likely on a tight budget (no I don't know how much yet).

Here's some details...
- continuous MDF press followed by flying cut saws. Panels accelerate away after cut. Panles to be measured immedaitely after being cut as they pull a gap.
- panel lengths vary from 16' to 24'.
- panel speed where we intend to measure: The leading edge can vary anywhere from 20 fpm to 120 fpm (press speed) while the trailing edge (after cut) will accelerate to approx 220 fpm.
- accuracy of +/- 1/8" would be lots.
- overall process is controlled by an AB PLC5/40. Processor rack is 200' away in mcc room. There is RIO near where measurement will be done.
- We tried this with a SLC, a HSC module, an encoder mounted to a homemade wheel and a laser as an edge trigger. It worked pretty well, but (according to the guys who where working the project) it takes too long for the HSC module to report the mumber so we couldn't get an accurate length.
- I need to get the measured length to the PLC5 somehow

Ideas I'm tossing around:
- Low end CLX, HSC, encoder, DC input trigger, DHRIO (like the SLC setup but with CLX hardware this time) Overkill?
- 1771-VHSC in an old 1771 rack (but it's update rate is 100 ms, that's slower that the slc HSC we tried)
- what about Compact, Flex or MicroLogix? I have no experience with these? Can they talk RIO? How about serial to the PLC5 CH0?
- are there any solutions "in a box" out there?

Any ideas you fellas can toss into the ring would be very much appreciated. Thanks.

Why measure after the cut?? Think I would concentrate on getting my cut length to operate correctly. Then confirm with random check using a tape measure.

Dan Bentler

I would just use the encoder you have already developed without the RIO connection...just run a long cable back to the main rack...provided you have a spare slot for the HSC card.

The key thing is going to be that the counting begins and ends immediately with the "part presence" sensor.

Why measure after the cut?? Think I would concentrate on getting my cut length to operate correctly. Then confirm with random check using a tape measure.

Click to expand...

Thats funny thats the same thing I was thinking.

I think that would be the first thing to look at. Not just fixing the saw but the saw has to measure as well. Who knows you may come up with something that will work for both.

I agree with OkiePC,

If your using remote I/O to report to the main panel, comm lag might be a problem. With proper sheilding you should be able to run your encoder cable hundreds of feet.

I've done ad-hoc measuring just with MicroLogix controllers.

A 24-foot board with 1/8" precision requires only 12 bits of counter capacity, and 220 feet per minute on, say, a 12" circumference measuring wheel with a 200 ppr encoder is only 733 Hz. These are well within the capacity of even the cheapest $90 MicroLogix 1000 controller.

You could set up a 10-point MicroLogix with its little onboard 6.6 kHz counter to count the length of the board in encoder pulses.

Getting that data into the PLC-5 becomes the challenge. Obviously the MicroLogix does not have a RIO adapter.

You could run a serial cable to the PLC-5 Channel 0 port and have the MicroLogix squirt it a DF1 message each time a board is measured. If the PLC-5 is an Ethernet model you could maybe (there are some protocol wrinkles) use a MicroLogix 1100 and send that data over Ethernet.

Ditto

leitmotif said:

Why measure after the cut?? Think I would concentrate on getting my cut length to operate correctly. Then confirm with random check using a tape measure.

Dan Bentler

Click to expand...

After you get the motion controller to cut accurately then get the length from the motion controller. The motion controller should know what the following error was when the cut was made. It should know the length of the pieces.

My opinion is the same, do not see the reason to measure after the cut, but anyway i´m gonna put my two cents.
The system I describe is used to measure steel pipe length before been printed as is required by the american petroleum institute.
Use a fast plc like control logix or compact logix, pipe is running on a conveyor up to 250 fpm, depending on pipe length, you install several photocells they have to be very fast like the ones from banner engineering or better, the distance between photocells is known when you set up the system, also an encoder is needed I use a 1200 ppr with a polyurethane roll with one feet of circumference, so minimum distance detected by the encoder is (12/(4*1200)) inches, when the head of the pipe is detected by the first photocell the encoder is already been rotated by the pipe because the encoder is located before the first photocell, so when the first photocell is covered by the head of the pipe you have to use a event task to reset encoder counter and at the same time count number of photocell been covered by the pipe, but you know what is the lenght of the pipe that cover some photocells, at this time the encoder starts counting and when the last photocell that was covered by the pipe is now not being covered by the then you set another event task and get the count from the counter and add that value to the original value you got when the head covered the first photocell and that is the length of the pipe. Then later that value is printed on the pipe. The encoder has a pneumatic mechanism to raise it or lower it depending whether or not a pipe is being measured.

Peter Nachtwey said:

After you get the motion controller to cut accurately then get the length from the motion controller. The motion controller should know what the following error was when the cut was made. It should know the length of the pieces.

Click to expand...

Used to work in plastic extrusions (window frame shapes). Pieces were generally cut about 20 foot long with flying cutoff saw. Methods of controlling (actuating ??) the saw parameters varied (air cylinders, clutched chain drive etc) and different controllers PLC etc. What was common to all control methods was that the cut length was displayed on the controller. We still verified accurate cut length with random checks using tape measure.

Also thought of another question
so you get cut length from the saw controller or by independent measurement method.
Now that you have this piece of data
what are you going to do with it??

Dan Bentler

Thanks for all the feeback fellas. Much apprecaited. To add some info...this issue only comes up once every few months, so it's not like the saws are all over the place all the time. Most of the time the cut's just fine.

leitmotif said:

Why measure after the cut?? Think I would concentrate on getting my cut length to operate correctly. Then confirm with random check using a tape measure.

Click to expand...

Yes, I agree as well. Our existing set up has some quirks that can affect cut length. We plan to eventually replace the entire saw system but that's not in the budget right now. Those quirks can be easily dealt with if we know about them, thus the interim desire to double check length.

As for delay in getting the number to the 5, it's not a big deal. I've got a couple seconds after the cut before having to decide what to do. The delay that's most important to minimize is the time between sensing of the trailing edge and saving the value of the encoder count. In the SLC setup the delay in getting the number from the HSC card into the SLC processor would result in a measured length that was 1/2" or more greater than actual.

leitmotif said:

...so you get cut length from the saw controller or by independent measurement method.
Now that you have this piece of data
what are you going to do with it??

Click to expand...

We can either alert operators/maintenance via HMI of an impending issue or, if the variation is great enough, we can divert the panel to a hogger and instruct operator to shut down and have maintenance fix the problem.

Like I said, this is not my preferred path, but tight budgets are calling for some alternative thinking.

When tiy are ready for an upgrade let me know

We can control flying shears or flying cutoff saw or rotary shears with accuracies down to 0.01 inches. This is much better than you need but then you wouldn't need to be paranoid about measuring. I have videos and skeleton programs with the math already done. All that is needed is the motion controller and the HMI. The cutlength is entered at the HMI and the motion controller does the rest.

Those quirks can be easily dealt with if we know about them, thus the interim desire to double check length.

Click to expand...

What if you can graph the motion profile real time? Then you will find your quirks very quickly! The data can be gathered at half millisecond intervals. My customers find out about their machine quirks very quickly.

The crtical part to these systmes is the refernce encoder because the whole system is geared to it. The reference encoder must have a high resolution so the motion controller can calculate more accurate velocities and accelerations. This makes the gearing more accurate. The tricky part is making sure the reference encoder is not affected by the cut. Another common mistake is not getting enough resolution for the shear ir saw fedbacj,
After one gets reliable counts from the encoders the rest is easy.

Thanks Peter.

The two issues we hjav with our saw system are:

1 - build up on the main encoder wheel. This is usually taken care of by regular cleaning but is sometimes missed. If missed enough times we cut long panels.

2 - [this one takes some set up] Our saw systen is made up of 2 independant AB 1394 systems each controlling it's own saw. Normally we cut with one saw only and use the other when taking a sample cut [a short piece for lab inspection]. The system was designed this way for redundancy. If one fails, we can run on the other. The single line encoder is wired to both controllers [resolution works out to about 664 counts per inch of board]. During a test (before commissioning) during which we turned the encoder (with a small motor) we found that, after a while, the controllers didn't agree with each other on encoder position. A Rockwell motion control tech recommended installing a laser as a registration input to synch the two controllers after every cut (leading edge of panel redefines encoder value at a known position). It's this laser that occassionly get's knocked out of position during an upset [very rare occurance - this was the latest issue that brought up the checking system again]. Once that happens the cut is off. Operators are supposed to occassionaly check length with measuring tape.

Yes, I've asked till I was blue in the face to have this thing guarded, but whenever this happens they keep coming back to me with checking the length again. Hmph!

FYI - this saw control system was an in-house project designed, built and programmed by myself and two other techs years ago, without any outside help other than some commissioning help from Rockwell. It replaced a "black box" OEM system. As I said, it works well most of the time. It's these occassional hick ups that catch us off guard.

Peter, when the budget's there to replace this system, I'll definately be putting you on our short list.

Ken Roach said:

...You could run a serial cable to the PLC-5 Channel 0 port and have the MicroLogix squirt it a DF1 message each time a board is measured. If the PLC-5 is an Ethernet model you could maybe (there are some protocol wrinkles) use a MicroLogix 1100 and send that data over Ethernet.

Click to expand...

Sorry. I'm a complete Newbie when it comes to the ML line of controllers. So sending from ML1000 to PLC5 over serial is possible? I ask because I started monkeying with RSL500 and found that the ML1000 does not have a PLC5 write selection in the MSG instruction, whereas the higher end MLs do. Is there a more elaborate way of sending a # over serial from ML1000 to a 5?

No the 5 is not ethernet capable.

Another question about the ML line of controllers. Just curious. None other than the 1000 specify a high speed counter. Those with IO modules can use a HSC card. Would these IO modules be as fast (getting the number to the processor) as the 1000's internal HSC?

ML1100 has a built in high speed counter as well.

Thanks for the quick reply. I just checked and see that the 1100's MSG instruction supports a PLC5 write.

Thanks again.