beginner needs to know if it will work

I have 5 PLC projects under my belt. All are with AD click units with pretty basic functions. I am still in the learning curve. Thanks to all that helped out on those.

Without doing my homework for me, I want to struggle through it, is it possible to have rotary encoder running and if the encoder changes speed the PLC will open an output? Which PLC unit is the best to do something like this?

Some of the projects this will be used for will need multiple encoders being tracked. This will be watching the feed rate of material being used. If the rate changes that means the machine missed a step.

Thanks

Jason

That should be fairly simple to implement, however i believe you are going to need a high speed counter (HSC) input on the PLC to be able to capture the counts of the encoder.

Depending on the speed of the encoder pulses you may be able to use the interrupt capability of the Click to increment a number then make a periodic decision on the values in these numbers and clear them for the next accumulation period.

As has been mentioned the best approach is going to be dependant on what is the fastest encoder you'll need to track. This will then govern whether you can use a normal PLC input or a high speed counter input. And then the scan time of the software will denote whether you need to put the encoder count into an interrupt or not.

So... how fast will you need to be going?

;-)

uptown47 said:

As has been mentioned the best approach is going to be dependant on what is the fastest encoder you'll need to track. This will then govern whether you can use a normal PLC input or a high speed counter input. And then the scan time of the software will denote whether you need to put the encoder count into an interrupt or not.

So... how fast will you need to be going?

;-)

Click to expand...

I have a scope and can track it, but a rough guess would say it is a 1" disk is rotating well under 1500 rpm. However once I have the system designed there are going to be many different applications for it. If cost is not so different I would rather go with the components that will cover me for every situation. Some applications may go as high as 2000-2500 RPM.

The one thing that has me worried is the change in speed is only for a brief moment, say a .25 seconds or less. I am using this to see if a sewing machine skips a stitch.

Thanks

Jason

Jason,

While RPM must be considered, encoders come in different "speeds." Most are classified by the number of pulses generated in each revolution denoted as Pulses Per Revolution or PPR. Some are rated at 10 PPR, some at 100 PPR some at 1000 PPR and a multitude of others. This is something you need to take into account.

Jason_H said:

I have a scope and can track it, but a rough guess would say it is a 1" disk is rotating well under 1500 rpm. However once I have the system designed there are going to be many different applications for it. If cost is not so different I would rather go with the components that will cover me for every situation. Some applications may go as high as 2000-2500 RPM.

The one thing that has me worried is the change in speed is only for a brief moment, say a .25 seconds or less. I am using this to see if a sewing machine skips a stitch.

Thanks

Jason

Click to expand...

Jason,

If your trying to sense the speed up and slow down of the sewing machine shaft during the brief interval when it skips a stitch. Then I believe you will be exceeding the capability of the CLICK PLC.

milldrone said:

Jason,

If your trying to sense the speed up and slow down of the sewing machine shaft during the brief interval when it skips a stitch. Then I believe you will be exceeding the capability of the CLICK PLC.

Click to expand...

What I am looking at is a thread control which I got the idea from this video:

http://www.youtube.com/watch?v=jV07wLxQKMc

At 1:30 in the video you see two disks spinning triggering some prox sensors. ( not the large gears on the left ) I want to put those disks on encoders and if a machine is running improperly and the stitch is not forming right, then those disks will change speed. If I drop the prox sensors from the disks and just use the encoders to sense if the thread is broken or sewing right, those disks do not need to be that big and the speed can be reduced.

Thanks

Jason

Jason_H said:

http://www.youtube.com/watch?v=jV07wLxQKMc

At 1:30 in the video you see two disks spinning triggering some prox sensors. ( not the large gears on the left )

Click to expand...

For some reason this concept or project sounds familiar.

Jason_H said:

If I drop the prox sensors from the disks and just use the encoders to sense if the thread is broken or sewing right, those disks do not need to be that big and the speed can be reduced.

Click to expand...

Can you explain how the speed would be reduced? Also what each disk is monitoring and how the controller acts on the sensor information?

Jason,

(Speaking here as a former Levi Strauss automated sewing-machine mechanic, and also as a 40-year mechanic for my wife's home sewing machine!)

A missed stitch (bobbin thread does not encircle the sewing thread) is one of the less-common sewing-machine problems. I think you could detect that problem, and many other stitch defects, with a photo detector mounted downstream of the sewing head to examine the length of the stitch. A missed stich will be detected as an extra-long stitch.

The most common problem with sewing machines is the bobbin thread tension and the sewing thread tension. Almost any change (ambient temperature, humidity, sewing speed, thread diameter, or thickness of the cloth) can cause either of the thread tensions to become too loose or too tight. Too-tight on the sewing thread tension results in the stitch being pulled to the surface of the top layer of cloth, while too-loose allows the bobbin thread to pull the stitch toward the bottom layer of cloth.

Lancie1 said:

Jason,

(Speaking here as a former Levi Strauss automated sewing-machine mechanic, and also as a 40-year mechanic for my wife's home sewing machine!)

A missed stitch (bobbin thread does not encircle the sewing thread) is one of the less-common sewing-machine problems. I think you could detect that problem, and many other stitch defects, with a photo detector mounted downstream of the sewing head to examine the length of the stitch. A missed stich will be detected as an extra-long stitch.

The most common problem with sewing machines is the bobbin thread tension and the sewing thread tension. Almost any change (ambient temperature, humidity, sewing speed, thread diameter, or thickness of the cloth) can cause either of the thread tensions to become too loose or too tight. Too-tight on the sewing thread tension results in the stitch being pulled to the surface of the top layer of cloth, while too-loose allows the bobbin thread to pull the stitch toward the bottom layer of cloth.

Click to expand...

Hi Lancie,

Thanks for the response, These are actually lock chain machines, like the Union Special 54 class / Singer 300W. They have been modified to do specialty pleating operations and some work with elastic and such. They are doing automatic runs in long yardage. The video shows prox sensors as thread break detectors and the group here did a great job in the past helping me get that to work. The looper thread will travel half the distance if the stitch does not form. I didn't know if that was enough, about 1/16 of an inch of thread distance, on a 1 inch wheel, for an encoder to pick up on. Rotational speed as previously discussed.

What type of photo detection would you recommend? I have been looking at the keyence product for a while. Never plunked down on anything yet.


It would be cool to talk shop with you one day if you are around.

Jason

milldrone said:

For some reason this concept or project sounds familiar.

You had helped me get this going like shown in the video.

Can you explain how the speed would be reduced? Also what each disk is monitoring and how the controller acts on the sensor information?

Click to expand...

I can slow the machine down if needed there by reducing thread consumption. I just set this up as a prox that is resetting a timer. If the timer trips becuase the thread is no longer moving the disk, then the machine shuts off. Is there a better way?

Thanks

Jason

The looper thread will travel half the distance if the stitch does not form. I didn't know if that was enough, about 1/16 of an inch of thread distance, on a 1 inch wheel, for an encoder to pick up on.

Click to expand...

Yes, if you get a high-resolution encoder coupled to the 1" wheel, it should change to the next number when the wheel moves 1/16" inch.

If the timer trips becuase the thread is no longer moving the disk, then the machine shuts off. Is there a better way?

Click to expand...

I assume that the thread going around the disk before going to the needle? That sounds like a good way to detect a thread break. I am not familiar with that particular machine, but I doubt if there is any better way to detect thread breaks. As for missed stitches, I know there are photosensors that approach "vision" capability and can detect very small changes. I think though that the seam would have to always cross under the photodetector at exactly the same place, so that might be difficult on some machines. It sounds like that this particular machine is running long straight seams, so a photodetector could possibly work to "see" missed stitches. I suspect the speed will be a big factor. At slow speeds there are most likely photodetectors that can do the job, but as the speed increases, the detection rate may fall off so that the device is not practical.

Unlike some of the garment materials which have different shades and textures I am using fabric and thread that is all dyed to match each other. Having not used the vision systems I don't know if this will be a problem.

What are some of the encoders that would work well for this setup? How does the encoder tie into the PLC? The end result is I want to measure a change in rotation speed, is there a better way to solve this?

Thanks

Jason

Jason_H; said:

Unlike some of the garment materials which have different shade sand textures I am using fabric and thread that is all dyed to match each other. Having not used the vision systems I don't know if this will be a problem.

Click to expand...

Yes, that would be a problem but to know for sure, a vision expert might need to see it live and in person. In almost all cases, a vision system is going to be highly (totally?) dependent on the lighting, so usually, there is a required added expense of providing that consistent lighting on the product. I can remember having to change two 8' flourescent tubes that looked perfectly fine to me to fix a measurement system problem. Those lamps were a couple of hundred dollars each, and we replaced them ~6mo. intervals.

If that can be done, there are a lot of other things you can do with a vision system that you cannot do with a prox switch. Look for wrinkles, defects, measure holes, widths, lengths, and more. Vision is very cool, but can be a PITA if not done very well up front.

Jason_H; said:

What are some of the encoders that would work well for this setup? How does the encoder tie into the PLC?

Click to expand...

It sounds like you are going to be measuring with more than one encoder. Many PLCs offer high speed local inputs that can be wired directly to an encoder. There is quite a difference in performance among the models. Some of them allow two or more high speed counters.

I have a couple of hours with a mid-level Click (thanks to bce123), and it does have high speed input capability in the software settings for the local I/O but I have not tried to utilize those features yet.

It sounds like we are starting to get a clear definition of the problem:

Jason_H; said:

The looper thread will travel half the distance if the stitch does not form. I didn't know if that was enough, about 1/16 of an inch of thread distance, on a 1 inch wheel, for an encoder to pick up on.

Click to expand...

If you have two thread letoff bobbins, or one bobbin and a fabrice speed, and if there should be a constant relationship in their movements, you should be able to set up a comparison to detect when one of the encoders doesn't keep up at the expected rate. For example, you find that for every 300 pulses from the master, the stitch bobbin should spit out 42 pulses (+/- a few), then the math to detect this isn't bad at all.

Gearing those encoders to your thread? That is going to take someone with hands on experience with your equipment to help advise.

If you can get your gearing such that you get 100 pulses per inch or more, I think you can get the job done. Then you can figure out the frequency of those pulses to help select the right PLC/input type/filter settings.
The looper thread will travel half the distance if the stitch does not form. I didn't know if that was enough, about 1/16 of an inch of thread distance, on a 1 inch wheel, for an encoder to pick up on.