PLC Based Project

[elecrobot]

Hi All I am going to start my postgraduation in control systems and I am planning to do my university project in PLCs. I have good working knowledge about microcontrollers but have no idea how plc works. I have few questions below. I would be very grateful if someone can answer them. Thanks 1)What would be an ideal postgraduate level project? I want to do something in which there is some practical building in involved. I was thinking of making an automatic carpark system e.g. the driver leaves the car on the gate and then from there, PLC takes control of the car and parks it on an empty space. But for that purpose, I will need some motors, sensors and stuff like that. do u think its practical to make? I mean for instance i can use toy cars and can build a frame like structure made of wood but can i find other parts which are compatible with plcs? And will it be too costly to build? 2)how much difference there is among plcs manufactured by different companies? i mean in terms of programming them, are they all the same? 3)which model of plcs will be good to use in a university project? if there is not much difference between plcs, then i will prefer to use siemens because i only heard of siemens. what would be your suggestion? I really appreciate for your time. Thanks again. Kind Regards, Tariq

[paulengr]

If cost is not an issue, then go with either AB or Siemens depending on your geographic location. If cost is an issue, you may want to look elsewhere. Low end AB & Siemens processors are not badly priced but the higher end process and machine control PLC's are very expensive ($10,000+ US is typical for a complete installation including software, PLC, racks, IO modules, etc.) If you manage to land a research contract, then hopefully the sponsor will give you some of their spare hardware. From personal experience, the best way to actually do any real research is to do it in an operating plant on real equipment. You will get far more personal satisfaction and knowledge that way, and probably produce product which ultimately has real value instead of theoretical garbage that mostly produces a couple of uninspired technical papers in peer reviewed journals.

[JRoss]

A company in York, PA, USA that I know of has made an automated valet system for a parking garage. I'm pretty sure the install was in Europe. The drivers would park their cars on a platform that would then take the car to a parking spot. If I'm recalling correctly, the system could even adjust for different car sizes for more efficient use of space.

[Mickey]

See Link below http://www.gizmag.com/go/6848/

[BobLfoot]

Maybe Mikey can find the link, but I remember seeing an automated garage that was proportedly in Germany or France. It was a round multi level unit and the lift was in the center. Very similiar to this but no width just 6 or 8 spots one ach level of the 'silo". To answer the original posters question, here is a project which sound simple but is very tricky to do correctly and has a lot of practical application. 1. Start with an Oval Conveyor for moving boxes. {assume orientation East and West} 2. Now on the north side add four stub conveyors holding product to be added to the loop. 3. Now on the south add eight stub conveyors to receive product coming off the loop. 4. Place a bar code reader or other product identifying unit {RFID, Reflectors, etc} 5. Write your code to emrge in from the four lanes and track boxes to their destination. Assume different entry rates at each stub and different pack off rates. What happens if a pack off is full and the box recirculates? What happens if a supply lane fills to max and youa re pilling from another. Boxes must never collide! Delivery must be right 100 % of the time Good luck if you try this one.

[paulengr]

Just thought of another idea which should be fairly low cost. The only "open source" PLC out there is pretty lousy. It would be interesting to see how far you could develop an open source version. And if you do a decent job at it, you might end up being like some of the other major open source projects down the road and turn it into a full time paying career. Aside from the potential cost advantages and many more interfacing possibilities, you could implement a lot of very wild and different interfaces and/or control schemes with this platform. For instance, consider the gumstix (www.gumstix.com) controllers loaded with PLC software that you can program and read from a web browser with an implementation of Modbus and Modbus TCP on board for IO. Although there are some dinky PLC's out there in terms of cost and size, none come operating on Linux with full web server support for access and programming. Another direction would be in the editors. Although some of the newer PLC's are beginning to approach it with function block programming, the ancient Bailey DCS programming interface was just plain much easier to work with than current PLC programming interfaces. Note that I said programming interface...the hardware was an entirely different story, the primary reason that Bailey's are going the way of the dinosaur. Another direction is in the languages themselves. It shouldn't be too hard to create a PLC language front end that can interface to the backend of a modern compiler such as the GNU C compiler or even the Java compiler. This would provide for some very interesting performance comparisons, even if you simply generated the "text" formatted program out of a modern PLC and ran it through a front end and didn't actually develop a new GUI at all. Edited August 21, 2008 by paulengr

[Mickey]

More links http://gizmodo.com/gadgets/gadgets/vws-aut...rage-173049.php http://automatedparkinggarage.net/ http://www.sciencedaily.com/videos/2007/10...ree_parking.htm

[ssommers]

BobLFoot's project is very practical. I worked on the PLC programming for an automated warehouse where I had basically the same configuration of in/out and then a whole cube of warehouse space to park my loads between times. A database sent a code to the initial PLC to pick the pallet from the warehouse. Once the pallet got to the elevator, the code was passed to the PLC that controlled the incoming/outgoing functions. Writing the logic to merge lanes was challenging, but not too bad. Recirculating pallets that missed their drop off point just adds to the fun - especially if they're supposed to be on a particular truck that's scheduled to leave before the pallet would make it back around the loop! The more challenging part of this project is writing the external database software to input & track the packages (pallets, cars, etc). If you do it right, you should be able to emulate the system & check out your PLC program before hooking up sensors. Good luck & feel free to ask lots of questions! Susan

[elecrobot]

thanks to all of you people for this kind support. ssommers.......seems like you have worked on a very similar project. The situation is my university doesn't have any hardware with them and they are not willing to buy any PLC related stuff for me. But I am interested in working on it on my own. From your prospective, do you think its very expensive to build? I am happy to spend upto 200 pounds on it. Do you think that would be enough? thanks Edited August 21, 2008 by elecrobot

[ssommers]

Hi Tariq - I had the luxury (?) of working on the warehouse project at an automation design company called Retrotech and there was a real customer paying for everything. The system was so complex that there were 5 people on software development - 2 on PLC & 3 on Database/HMI - and we were using Allen-Bradley ControlLogix & DriveLogix PLCs. We even had full size, 3 level working warehouse with pallet lifts, slides & conveyors in the back of the shop. The final project was 20x that! Our testing model was expensive to say the least, but we couldn't afford to fail when everything was installed on-site. If it were my college project, I'd be looking to find a local automation company willing to let you work for them as a co-op student and borrow their equipment after hours for your own project. Then you could possibly do this for almost no investment until you're ready to make your working model. You might even get them to "donate" some used equipment for the model if you're lucky and a permanent job when you graduate. Good luck and keep us updated on the project... Susan

[BobLfoot]

Glad to help when we can. 200 Pounds , {chuckle} now that makes things interesting. If the rates haven't changed thats $400 U.S., Just enough to get you a shoebox no-name plc and a few led lights. You could lake them light up in some paattern and have them represent real world objects, but no where enar what you are hoping for. Sue's idea of an internship is the best for your situation. You might even be able to claim the work projects as your school project if your write it up correctly.

[DanW]

I'm aware of sensing difficulties for rotary kilns/driers, but what are some of the difficulties, for instance in gold extraction? ( I thought current technique was leaching gold from its ore using some toxic chemical )

[Moggie]

If you decide to go with Siemens PLC's have a look at the following http://support.automation.siemens.com/WW/view/en/22764848 Here you can download a "lite" version of the S7 software for the S7 300/400 PLC's. Fully functional and free.

[paulengr]

Cyanide is perfectly safe as long as you keep the pH high! That's the standard modern technique, and the most simple. Any time you are dealing with a kinetics problem (flotation of ores, or almost any metallurgical reaction), it often becomes difficult to measure precisely what's going on, or to get the information in a timely manner to apply standard PID controls, or it is log/exponential scale, or some combination of all these. With most preg robbing gold ores for instance, they often have to use an autoclave. The reaction is exothermic (generates it's own heat and pressure) and can easily go into runaway conditions. This is bad obviously because the natural tendency of the autoclave is either to burn itself up or to blow apart. Another example is flotation. This is a notoriously touchy chemical process with all kinds of ways it can go bad. With simple heap leaching, controlling pH and cyanide concentration is not so simple to do. With "simple" kiln operations, the kiln is typically radiative heating in nature and thermal mass is a huge player (and hard to predict). Simple PID often struggles. Sliding mode controllers do better but are not a 100% answer. Another example of a gold problem is monitoring water levels and dealing with them. There are lots of ponds scattered all over the place typically and water management becomes quite a headache.