Any of you who is using EPOS from MAXON motor and LabVIEW Real-Time might face the same problem with me. The RS232 -IMHO- is not fast enough to achieve real-time communication between the EPOS and RT controller, also I am using the LV-RT for the main program, thus it will be difficult to synchronize between two LVs program from two different computers which mainly caused by the communication overhead. The problem got worse when I knew that we could not download the EPOS dll file onto the RT. After getting my answer from NI forum, I decided to use the CAN Protocol which can reach up to 1Mbps.

For the first trial, we have the IXXAT CAN-USB device. The question is, how to interface USB device to the RT? Because if I use this device, then it will be RT <-> USB <-> CAN, which means that I need a driver for IXXAT CAN-USB for the RT! I emailed the IXXAT company, the engineer replied that they do not support the LV-RT. Anyway I successfully send command through CANOpen with this device on Windows platform, but it took 1 day for me to realize that I need to terminate the final CAN-bus with 120 Ohm. Fiuhh.. alhamdulillah it was working though

Then we bought the NI-CAN PXI 2 Port from NI with the OPENCan library. I successfully controlled the speed of the BLDC motor with the CANOPen using SDO only, but then I realized that there was a big delay between two SDO commands, which resulted almost 100% error (current speed – desired speed), currently I am going to write a new program by using both SDO and PDO.

I -insyaAllah- will continue this writing and explain briefly about SDO & PDO especially in the case of Maxon EPOS.

Monday, 4/feb/2007 @ 20:52 KST

The definition of CAN and CANOpen can be found by yourself in google . I will explain briefly what I have learned, the CANOpen method to control the Maxon Motor using EPOS, for more detail you can read the EPOS Application Note: CANOpen Basic Information (pdf).

In EPOS there is an important dictionary (the source of everything), called Object Dictionary Access. It contains the System parameter (e.g. PID tuning value, velocity, etc), the DataRecorder(Encoder counter, etc), and so on. To control the motor, these parameters need to be changed. We can change the value by 3 methods:

1. Directly click the field (of the column) and enter the desired value
2. Using the Serial communication RS232 protocol
3. CANOpen protocol

In the case of 1, you must be joking, but if you want to do it manually, no one can blame on you =P. The 2nd method, I have explained above, that it is not possible if we want to utilize the LabView RT, because there is a dll file which does not support the RT so it can not be downloaded onto the RT, unless you know how to reverse engineer this file and re-write your own code .

Now the 3rd method, with CANOpen there are 2 ways of writing the object dictionary access:

#1 is SDO (Service Data Object). It is a confirmed service, means that after you send the command, in between the timeout value you specified, there will be a confirmation packet which contains the value whether you successfully write the object or not.

#2 is PDO (Process Data Object). Opposite to the SDO, it is unconfirmed, thus it is very fast. But as a trade off, there are a “little” work to do, which is the PDO mapping.

At first time, I am using the SDO only, the problem is that, there is a big gap between sending the packet and receiving the confirmation packet, thus it become less real-time and worse, the data is not valid (I am writing a quite time critical program) .

Here’s some picture with SDO only:

If you take a look at the picture above the error looks very big, I guess it is caused by the delay of the SDO packets.

And in the above picture the error is very small with PDO packets.

And here is the video, if you need the code just write me a comment or send an email

This is an example program to initialize the Maxon EPOS through CANOpen. To be noted that the maxon UI Interface is always on when the lv program is running. Download here (rename the file to become .zip)!