Need some direction

I have a very customized PC based control system that is currently using pci data acquisition. There were very specific reasons for choosing a PC based system when this project was first developed.
I have become pretty familiar with the micrologix plcs and now am interested in two things. First is system expansion to include control of few dozen or so ball screw type axis which is basic encoder input and fwd rev output. PLC is perfect for this and much simplier than adding additional pc type cards. Second interest is to try to port some of the existing pc software/hardware over to a plc. There are many if's in that part mostly due to speed issues. Our code is all written in visual c++ and we'd greatly like to keep that end in tact.
So, I've read over this site a bunch and it seems what I am looking for is probably a PC for the HMI that can pass data to and from the plc. Additionally, I can see the need to use multiple plcs so as to take advantage of the multiple cpu's. This means either multiple serial comm ports on the pc or a networking of the plcs. For simplicity, I will state the need to have 3 micrologix 1200 plcs.
Now the confusion starts on my end. I'm certain that we don't want to develop our own comm driver. I'm very weary of using a dedicated HMI thats limited in graphics and programming capabilities (thus the desire to maintain a pc for the hmi). Also concerned about licensing fees per unit produced. We are a small Oem that will put out hundreds of these systems.
So my question is what specific products do some of you guys recommend to make this happen. I think what I am after is a practical (ie $) way to pass data to and from multiple plcs from a generic windows based pc. Looking for specific answers on bare bones configuration for this with some input on licensing structure for suggested configuration. I can add that I'm open to other plc brands as well.

Contact your local GEIP rep./distributor and ask about PAC Motion and RX3i. It can have "C" blocks within the ladder where you may be able to port some of your existing logic. Get on the GEIP OEM program for very competitive licensing. Just not practical to try explaining all the options available here.

Thanks Russ. Was looking for something a little more specific but I do appreciate the input. I don't need to convert any existing c language to ladder logic, just need a practical method of communicating with the plc with a pc.
Surely someone has some input here.
Mike

just need a practical method of communicating with the plc with a pc.

Click to expand...

Is this what you are looking for?

http://www.plctalk.net/qanda/showthread.php?t=42656

The standard method for PC -> PLC communication is to use a driver that handles the low-level protocol and connects to your PC program using OPC. There are many dozens of OPC Server software products on the market with various licensing costs and mechanisms. The first three I would look at are Kepware, Matrikon, and Software Toolbox.

There are a handful of open-source projects that implement serial protocols and Ethernet protocols for common PLCs. The most popular open-source protocol is Modbus RTU, and the Allen-Bradley DF1 command set is a distant second. You'll find most of these on Sourceforge.

Many small controllers, including MicroLogix, implement Modbus RTU protocol on their serial ports in addition to a vendor-specific protocol.

A veteran member of this Forum leads a free HMI project that includes A-B drivers:

http://advancedhmi.com/default.html

Thanks guys. This is the info I was seeking. Installing Archie's project now for a test ride. His efforts seem incredible. Will also look at the other things you suggested Ken.

VaMike said:

Thanks Russ. Was looking for something a little more specific but I do appreciate the input. I don't need to convert any existing c language to ladder logic, just need a practical method of communicating with the plc with a pc.
Surely someone has some input here.
Mike

Click to expand...

You misunderstood, the PAC can run a "C" program as a 'Block'(Subroutine) not convert from "C" to Ladder.

Russ, I did misunderstand a bit. The code that would be moved to the plc would not be a block of logic for say but actually contains a ton of driver specific calls of the pci card currently used. So porting that over is not possible or atleast not likely. The ladder logic would just be written from scratch for the new plc. The issue of keeping the pc and c++ pertains mainly to some of the complex operations we perform on the data being collected and the full control of the user interface.