Using LabView and Modbus to Communicat​e with AKD Servo Drive

Question

I’m working on a project to control a Kollmorgen AKD servo application using Modbus directly from LabVIEW.  I’m new to both LabVIEW and servo drives so forgive me if this seems simple.  I have established communications to the drive through Modbus and have been successful at some rudimentary control of the servo.  I know the drive only supports "Write Multiple Registers” and “Read Holding Registers” functions and there are scaling factors that need to be applied.  What I need is some help with taking the Modbus information supplied by Kollmorgen for each command and formatting it for communication to the servo and vice versa.  I need to understand how to take the supplied 8, 16, 32, and 64 bit information for commands, scale it, and format it into the two or four registers required for the drive to read the parameters.  In turn, I also need to understand how to take the same information and read it and scale it from the drive.  I’ve attached a spreadsheet with the particular commands I’m interested in and a sample VI that seems to work for speed control but to be honest, I'm not sure how/why.
Attachments:
KM Modbus Cross Reference.xlsx ‏57 KB
VEL.CMDU.vi ‏10 KB

Answer 1

OK, I've got the ability to read values from the AKD drive pretty well sorted out.  I'm now having trouble with the ability to write.  I want to use Labview to program Motion Tasks in the AKD drive.  To do this I need to perform three commands: MT.NUM (specify the motion number), MT.P (specify the angular position), and MT.SET to set the parameters for the task.  MT.P requires sending a 64 bit signed float or a 32 bit signed float (requiring four or two registers respectively).  I used ModPoll to see what values the drive held in the MT.P registers after entering the desired angular position using the AKD Workbench software.  For example: using Workbench I entered 234.567 for the angular position and read 208 and -32506 from registers 2060 & 2061 (the 32 bit registers for MT.P).  After scouring the forum I put together the attached VI to try to write to the same registers but I can not seem to get the translation of the input (angular position) to the register values correct (entering 234.567 does not produce 208 and -32506 in registers 2060 & 2061).  Anyone have any ideas?
Attachments:
Motion Task Definition Rev H.vi ‏21 KB