Can PLC system do this?

[MrWeigel]

I'm new here, and besides that I know very little about electrical systems. I have a project in mind, and it's going to be a learning experience to be sure. My main background is in toolmaking, fixture building, and general machining. I found this sight hoping you guys could steer me in the right direction with this project.

Here is what I had in mind...

I am trying to build a custom liquid dispenser. The basics of it is that there will be containers sitting on a shelf, and the liquid will run through a tube down to a nozzle. A glass will be underneath the nozzle. I would like to control the volume of the liquid dispensed via a valve with a timer, and possibly add a "power assist" to the liquid by shooting a bit of compressed air through the line a few seconds after the other valve shuts.

After a little research I found out about PLCs, and was wondering if this is something a PLC could do? Open a valve for a set amount of time, then closing it, and then opening another valve?

I was also thinking along the lines of using a PC for the interface, and having a menu where you can select a liquid or a combination of liquids. And with the PC having some sort of database that you can add combinations to or subtract them from. I would have 10+ containers with 2 valves for each container, one controlling the disppensing, and one controling the air assist.

Is this something I could do with PLCs?

Is there an interface out there that can do what I want or would I need to program one from scratch?

What are some good guides/research material for setting this type of system up?

As I said, this is a learning experience for me...I'm not looking for someone to do it for me, though any help would be appreciated.

 

[nbucska]

PLC is used in industrial environment, for your application
some kind of microcontroller seems to be cheaper and simpler. PLC is much more expensive.

You can use PC but if you need more than one, a microcontroller is cheaper.

Most likely you have to program it from scratch but it
should be simple.



<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[gcaudill]

This is something a PLC could do with ease.

You would have to program it from scratch, but it would be easy.

Look at cheap and easy PLC types such as: Koyo (automationdirect.com), Allen Bradley CompactLogix (

http://www.ab.com),

Super PLC (

http://www.tri-plc.com/t100md.htm).

You are interested in digital inputs and outputs from your description. Any measurement of liquid flow would most likely require an analog input.

 

[MrWeigel]

I'm not so much measuring the actual flow of liquid, as much as using a timer to control the opening and closing of the valve, or is that what you are talking about?

 

[gcaudill]

If you are not measuring flow, no analog I/O will be required. Digital I/O is all that you need.

To build your standard PLC you need:
Rack
Power Supply
Processor
1 8-point digital input (I assume you need to start/stop the process, i.e. a switch of some type needs to interface with the PLC, thus the digital inputs)
2 16-point relay outputs -OR- 1 16-point plus 1 8-point

Digital inputs and relay outputs come in all flavors. They can be AC, DC, and many different voltages.

Based on your application, I would recommend trying the Super PLC as it is cheap and simple. In the case of the Super PLC you would need to also purchase the I/O expander card, but this is still probably the cheapest application.

By the way, you could probably also accomplish your mission with timers and relays, no PLC.

 

[MrWeigel]

Thanks gcaudill. If I went to a timer/relay setup could I hook it up to a PC? The end result I would like would be to be able to input into the computer which mixture and which measurements, via a touchscreen or some such, and have the PLC (or other control) pour the liquids in the correct proportions.

I have read some of the materials in the FAQ section on PLCs and I'm not sure that PLCs can do what I'm asking, or maybe I need to switch to something more PC based.

 

[gcaudill]

The PLC has timer functions, among many others. I'm certain it can handle this application. Via the I/O, you could interface nearly any external control system with the PLC. PLC manufactuers do offer touchscreen displays, but that starts to add considerable expense.

 

[dpc]

If this a one-of-a-kind you might be able to find a cheap PLC on eBay. We have purchased Koyo PLCs on eBay in the past.

A PLC can certainly do what you want to do.

 

[Guest0527211403]

Something (instinct) tells me that you are building a machine to dispense liquor from bottles. Tell me if I'm warm...

My former roommates and I did this for one of our design projects in college. We ended up using a (huge!) OMRON CS1 PLC with a Touch Screen HMI just like you've described.

If it is liquor you are dispensing, you may have a bit of trouble in terms of valve timing. Different types of booze have different viscosities, and when we experimented with this, we found that a fixed "valve open" time would not yield the same amount of liquid for different types of alcohol.

I still have the thing in the basement actually. I'd like to get it going again (boy did we have some great parties with it..), but I need a new PLC. I like the TriLogi's for their form factor and the fact that I can connect an additional module to it and connect it to a LAN (to replace the touch screen HMI).

I also got to tinker with a Zen Micro from OMRON and I believe that it would have done the job as well.

 

[MrWeigel]

You nailed it justkeepgiviner, if you have any help I would really appreciate it.

 

[Guest0527211403]

I will dig up my old report and see what I can give you.

The best advice I can offer now is TEST WITH WATER. We had many a late night "development session" that ended up with us sleeping through class the next day, if we even made it there. That's all I can remember, for obvious reasons.

 

[Guest0527211403]

Me again.

This isn't us, but this is right along the lines of what you are looking to do. Ours operates on a different principle (gravity assists our machine in serving.. way less tubing that way).

It even includes a drink database and some VB source files.

http://www.barmonkey.net/

Still trying to get a copy of the old report....

 

[MrWeigel]

Thanks, I found that site too...good stuff there.

 

[pdupreez]

I would suggest you look at a Zelio programmable controller coupled with a GSE 350 weight controller (alternative to time based control, although the Zelio can do).

We have used these in industrial applications, and they are cheap and easy to configure. You will have Digital IO and analog output from GSE350. See the following sites:

http://www.schneiderelectric.com.tr/html/en/products/aut/zelio_logic/zelio_logic.htm

http://www.gse-inc.com/indicators/model350.aspx

 

[ChainDawg]

If you are looking for more accurate dispensing, try using the method used for dispensing IV drugs. A motor driven milking action would dispense the same volume no matter what the viscosity. Just a suggestion.

 

[Guest0527211403]

To keep ours simple, we used prepurchased 'upside-down' valves from a bar supply store. At the time these things were extremely difficult for us to find. Now, stands with 6 of these are available at a few major retailers. You can see how broke we were, because there are only four (of 6) bottles on the machine. We were able to afford another 2 brackets after this picture was taken. aah, college days..

Here's a picture of it (The PLC is hiding behind the touch screen):

http://www.gbrownc.on.ca/techcity/TechnologyintheCity2004/images/PICT0016.jpg

The machine was actually called "The Giver", and we got a clothing 'sponsorship' from a local clothing brand of the same name (really, they just gave us some stickers and t-shirts, but sponsorship sounded better)

 

[entertronplcs]

We actually have a customer that has designed a 12 bottle dispensing unit made up of 7 liquors and 5 mixes. He has a touch screen as the front end that holds all the drink dispensing information.

Works quite well.

So in answer to your question...a PLC will work quite well.

Going the microcontroller route means so much more design. You can work with something that is off the shelf, interface with standard devices through the protocols that are offered, such as a touch screen.



Stephen Luft
Entertron Industries -

http://www.entertron.com

Providing solutions to OEMs Since 1978 (end users also welcome)

 

[nornrich]

MrWeigel & Justkeepgiviner,

If you are looking for a "homebrew" drink dispensing machine, there were a group of students at Michigan State that developed a machine and won the Gadget Freak contest in DesignNews Magazine. You can find details at

http://www.designnews.com/index.asp?layout=siteInfoWebzine&view=Detail&doc_id=129558

It even gives a preliminary BOM.

Regards,

Rich....

Richard Nornhold, PE

 

[Guest0527211403]

Glad to see that one I saw a project this past year where a couple of students made a machine which opened a beer bottle and poured it into a tipped glass with "just the right amount" of head (so they said)...

One big difference that ours had was the number of outputs our system needed. We only needed to use two relay outputs to simple (surplus) DC gearmotors.

One motor rotated the bottles (as opposed to the glass). Position sensing was achieved using three cams and three very cheap mechanical limit switches. The cams were identical (180 on, 180 off) and offset 120 degrees to each other. As the shaft rotated, the three switches output a gray code logic which we used in our PLC program to trigger the motor to stop turning. We had a problem with the motor overshooting, so we put a wire (we replaced it with a resistor after some tweaking) to short out the motor when the relay coil wasn't energized to ensure that it would stop good and fast.

The other motor turned a crank which was attached to a bearing that moved inside a slot to create a Scotch Yoke mechanism. This moved a plate with a hole in it up and down so as to trigger the Upside-Down Valve (normally you would use a glass to trigger the valve). Again, a couple of mechanical limit switches were put in place as input for when the plate was in its upper- and lower- most positions.

Most of these solutions were out of the fact that we had no real experience with electronics in the group at that time. Actually it took us about 2 months to figure out how to make the PLC work, and another 2 months to produce a program which did what we needed it to do... It was good times, though. We took over a storage closet in the school to work on it and stayed there until the early hours of the morning on a regular basis, or until security caught us