A new System

Good morning Class.

Todays topic of discusstion shall be the forming of a totally new control system. The system will have the following:

1) 13 control stations filling parts into boxes
2) Centralized control of all Stations
3) Data collection for all stations
4) RFID read/write heads at all stations
5) Alarm Handeler
6) Bar Code printers/readers at one station
7) Automation to be spread out over three rooms

Sounds like fun right! Well it will be (eventually) Oh, before I forget, the control stations are mobile and interchangeable. If I move one or take it offline, I cannot loose the rest of the network. Ethernet IP - TCP/IP looks good but not all the equipment has that capability.

Oh I know what you were thinking Remote I/0, Profibus, Devicenet and the likes. All of which are unsuitable comm protocols for this venture. If you loose one drop, the network will fault.

I'm in contact with AB, Moeller and GE. I'm (sort of) getting the "deer-in-the-headlights" look from them with "I'll have to make some phone calls and get back with you."

Any Ideas?

Tim R

Oh I know what you were thinking Remote I/0, Profibus, Devicenet and the likes. All of which are unsuitable comm protocols for this venture. If you loose one drop, the network will fault.

Click to expand...

It might not be the most elegant way, but depending on how far apart your stations are, you can solve the problem of faulting the network when you remove a station by using an optical fibre backbone (as a Siemens user, I would automatically use Profibus) and then use an OBT to drop the connection via RS485 to each station. That way you only disconnect the individual Stations from the OBT and the Backbone stays intact and the network stays up.

Tim R.
You write "centralised control" and "control stations are mobile and interchangeable".
It looks like a case for either ProfiNet or Ethernet/IP over WLAN.
I have seen WLAN modules for ProfiNet. They look good but are expensive.
I know that for ProfiNet and ET200S you can get small CP cards that accept serial protocols like Modbus and ASCII. That may be the way to connect your RFID readers. (What does a RFID writer do ? Arent the RFID codes fixed ?).
Something similar may be possible with Ethernet/IP.

(What does a RFID writer do ? Arent the RFID codes fixed ?).

Click to expand...

I was involved in the development of 1st generation RFID systems in the early '90s (actually, they weren't RF, the communication was optical, but the principle was the same). The actual project was to automate the commissioning lines in the stores of a major Swedish wholesaler in Malmö supplying local drugstores. Basically the local drugstore would send in his order either directly online, or per Fax and a secretary keyed the data into the system. This data was then programmed into the RFID chip (as it would be nowadays) along with the stations where the items were stored. These chips were mounted on the hanger assembly of basket carriers on an overhead conveyor system, which were loaded with an empty basket and sent on their way. At each junction the chip would be read and the basket shunted in the appropriate direction until it had visited each (necessary) Station to get loaded with the appropriate goods by the station operators. The required goods were read out of the chip and displayed on a screen for the operators. If for some reason certain items were not available, the operator noted that on the screen and that was written back to the chip.

When the basket eventually arrived at the loading bay, the chip was now read out and an invoice created which reflected only those items which were actually supplied (can't remember now how the other items were handled). After unloading the the baskets continued back round to the starting stations, where the chip would be erased in preparation for the next order.

By the way, the overhead conveyor system was supplied by a Danish company. Can't remember the name now, but it's academic anway, because three months before the end of the project, they went bust!

Tim R said:

Oh, before I forget, the control stations are mobile and interchangeable.

Click to expand...

Ooooh! I like this part!
Two things occur to me: wireless and multitaps.

Can you use wireless data radios in this area/application?


If radio is out, how would this work? There are devices available which will allow you to tee-off from an RS232/485 or other serial data network (Westermo makes one of these: the LD-01, I think). If the PLC on the tee fails, the device switches to a pass-through mode.

If your equipment is going to be in roughly the same area when you're done moving it: put the "tee boxes" on the wall nearby. Use twisted-pair "hoses" with Amphenol/Cannon connecters on the end to attach to the machines. VIOLA!

AK

Ok guys, you both have vaild ideas. Both of which I have considered.

To say Profinet is expensive it a touch of an understatement. Their quote was well over 100K. And I'm pretty sure they missed some stuff.

The stations are going to be about 10 feet apart from one another. However, I can't run anything overhead as there will be an overhead craine in the way. So the actual cable runs will probably be closer to 50 feet each. Not to mention the other two rooms which are probably about 100-150ft away. Both distances are within specs for such a system, but there are too many "if's" in writing that type of code.

The two options I'm taking a solid look at are Contrologix and Moellers XL200 series. The two platforms have their pros and cons. Contrologix wiould put everything on the same network (TCP-IP) which will try to send a hell of a lot of data over one network. Which makes me nervous.

Moeller has the RFID on a separate network with the control stations having their own processors. Data collection would be accomplished with CanOpen. That in itself make me nervous as I don't consider CanOpen to be that stable.

Any other ideas?

Tim R

akreel said:

Ooooh! I like this part!
Two things occur to me: wireless and multitaps.

Can you use wireless data radios in this area/application?


If radio is out, how would this work? There are devices available which will allow you to tee-off from an RS232/485 or other serial data network (Westermo makes one of these: the LD-01, I think). If the PLC on the tee fails, the device switches to a pass-through mode.

If your equipment is going to be in roughly the same area when you're done moving it: put the "tee boxes" on the wall nearby. Use twisted-pair "hoses" with Amphenol/Cannon connecters on the end to attach to the machines. VIOLA!

AK

Click to expand...

Wireless is out of the question. That was the first thing I thought of. The problem is that the RFID will not operate that way. At least not yet. Your RS-232 idea is not a bad one. (On a totally irrelevet line of thought, does anyone know what the RS stands for? I know, I'm just curious to see who else knows.) As I was saying, I think the ditances will be too far to keep the comm stable.

Tim R

Contrologix wiould put everything on the same network (TCP-IP) which will try to send a hell of a lot of data over one network. Which makes me nervous.

Click to expand...

Yes and no. The key element of all TCP/IP networks is the specification and configuration of the switches. Without going into a whole tutorial on the subject, which I am not qualified to attempt, what I do know is that you will need a "Layer 2" switch that supports ICMP Snooping. Because control networks over Ethernet typically use UDP broadcasting, these packets can easily flood a network UNLESS your switch knows how to constrain the traffic to the correct ports.

There really is no need to be nervous about large and busy Ehternets; it is the switches that do all the work.

PhilipW said:

Yes and no. The key element of all TCP/IP networks is the specification and configuration of the switches. Without going into a whole tutorial on the subject, which I am not qualified to attempt, what I do know is that you will need a "Layer 2" switch that supports ICMP Snooping. Because control networks over Ethernet typically use UDP broadcasting, these packets can easily flood a network UNLESS your switch knows how to constrain the traffic to the correct ports.

There really is no need to be nervous about large and busy Ehternets; it is the switches that do all the work.

Click to expand...

An interesting point. I forgot about that. Something to consider.

Tim R

I think Ethernet would be the choice. As mentioned traffic can be controlled, high speed, and shutting down or moving a station wont crash the system.

Recommended Standard, I probably have 20 or more posts on that.

On a totally irrelevet line of thought, does anyone know what the RS stands for? I know, I'm just curious to see who else knows

Click to expand...

I was going to guess "Receive/Send" but looked it up.

I'll just say, "Receive/Send" is NOT the right answer.

It wouldn't bother me at all to put such a system onto a DeviceNet network. DNet doesn't "fail the network" when you unplug one node unless you daisy-chain the wiring and undo the trunk. In fact, hot plug-in is an absolute requirement for ODVA certification.

DeviceNet makes RS232 ASCII interfaces almost trivial, and I have done several RFID/DeviceNet direct interface projects.

You can get around the DeviceNet droplength restriction with copper or fiber repeaters.

The last-inch interface requirements of your RFID and barcode equipment are going to dictate the I/O or network requirements. If the RFID equipment has EtherNet/IP or DeviceNet or Profibus or CANOpen, then that's where you start looking.

You said "the RFID doesn't work that way" with regard to wireless Ethernet, so you must already have one or two vendors and models in mind.

does anyone know what the RS stands for

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Recommended Standard Number 232 was the original title.

I think the formal name now is: Interface Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange.

For short you can call it EIA/TAI RS-232-E.

When I was a kid, I thought that the "RS" in "RS-232" stood for "Radio Shack".

Ken Roach said:

It wouldn't bother me at all to put such a system onto a DeviceNet network. DNet doesn't "fail the network" when you unplug one node unless you daisy-chain the wiring and undo the trunk. In fact, hot plug-in is an absolute requirement for ODVA certification.

DeviceNet makes RS232 ASCII interfaces almost trivial, and I have done several RFID/DeviceNet direct interface projects.

You can get around the DeviceNet droplength restriction with copper or fiber repeaters.

The last-inch interface requirements of your RFID and barcode equipment are going to dictate the I/O or network requirements. If the RFID equipment has EtherNet/IP or DeviceNet or Profibus or CANOpen, then that's where you start looking.

You said "the RFID doesn't work that way" with regard to wireless Ethernet, so you must already have one or two vendors and models in mind.

Click to expand...

DeviceNet was another consideration but running that cable in a clean room enviornment would be a pain. Not to mention I've had to fight my way around all kinds of devicenet problems in the past. Also keep in mind that these stations are to be interchangeable. That would require the operator to change the DeviceNet address. Seeing as I had to explain what a PLC was when I talked with them, I don't think that will be such a good idea. It does have profibus but as previously stated, it is VERY expensive. I have the specs for the RFID but I'm pretty sure it will change before it is all over.

Wireless ethernet is something I've considered. Problem is that it is in a very noisy (electrical) area. All kinds of interference to deal with. I have seen others try to use wireless in this type of application and had all kinds of problems.

The RFID I'm looking at is the Balluff system. According to my salesman, they've had pretty good success with it on a DH-485 setup. He wasn't specific in regards to who he sold it to or how many heads it needed or how far apart it was. And I'm pretty sure it wasn't mobile.

Pretty good ideas so far people, keep it up.

TJR