Modbus/ModTCP/OPC communications
Willie from South Africa  [1 posts]
10 years
Hi, I have started playing with RR (Amazing software, and free to boot!) to use it for  counting  objects on a conveyor. I see you have got a serial comms module. My question is whether you have plans to make the open Modbus protocol availble for it. That would enable RR users to use a vast selection of I/O devices and PLC's with RR. Modbus over TCP/IP would be even better!
There are Modbus ActiveX modules freely available . (Modbus Master/Slave implementations). Will it be possible to implement them in RR?

I need to trigger RR from an external device to aquire an image at the right time , process it (easily done with RR!) and send the calculated result back. The device is a Modbus master. alternatively I will have to resort to using parralel port /USB IO but the communications route is a more elegant solution.

Any suggestions or thoughts on this issue?

Thanks for a great program!
Anonymous 10 years

That seems like a great addition to RoboRealm and we are already looking into adding that capability. I assume you need a Modbus Slave? Also we intend to just implement the TCP/IP version. Would this work for you?

As we can only simulate the interaction between devices (we don't have a PLC master hardware device) we would need to rely on you to actually test it with a hardware device. Is this something you'd be willing to do?

Also, I assume you just need to send back a couple bits of information from the image processing as apposed to the entire image? As modbus does not support blob information sending back the entire image will be a problem. Sending back COG and orientation information etc. using registers should not so we will assume that this is the intended use.

Willie  [3 posts] 10 years

Thanks a lot for replying. Yes, a Modbus TCP/IP slave will be perfect. I would certainly be willing to test this  for you.

Your assumption is correct that I only need to read some variables in RR from the Modbus master and not the entire image.  I also need to trigger the RR pipeline to execute  at the correct time, so I would also need to write a variable from the MB master to RR. The Modbus standard protocol is not that complicated and very well documented (Modbus.org/tech.php) so you should find it a breeze to implement compared to RR!

I actually have been playing with RR and some open source Modbus modules written in Python. I incorporated the RR Python API example code into the Modbus Python programs and managed to transfer data from RR to a Modbus slave device. (The Python Modbus program acted as master in this case) However, I think that this solution is a bit slow and might be a little complicated to get to work smoothly in practice. For you to implement a Modbus slave in RR will be the perfect solution.  

If you are interested, the open source Modbus modules are available at http://sourceforge.net/news/?group_id=228414 . It is called MBLogic. As is the case with RR, it is quite amazing that people will make available their own hard work for everybody to use. I certainly am very grateful.

I look forward to assist in the process.



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