NI-9514 with external absolute encoder

[Jabba]

Hi All,

I'd like to use a NI-9514 (Servo Module) through the FPGA interface, but I don't want to connect my encoder directly to the module : My encoder is an absolute encoder decoded through a dedicated cRIO module.

My idea was to implement my own position control loop on FPGA (based on my absolute position) and send the computed torque setpoint (0-10V) to the 9514, but it seems that the 9514 embeddeds its own Position Loop (based on the encoder connected to the connector). As I won't have any encoder connected to the 9514, my idea is not possible....

My 2 questions are the following:

- Is my conclusion right?

- Is there any way to disable the PID loop on the 9514 module, and use the 9514 as a simple open loop torque générator (0-10V génération) ?

Thanks for your answer.

[PaulRB]

Hi Raphael,

Fortunately for you, your conclusion is not correct. When you run the 9514 in FPGA mode, you have direct control of the +/-10V torque setpoint (which is Drive Command Output in the Write method). That means that you have to implement your own control loops to generate the drive command. It is perfectly okay to ignore the encoder feedback from the module and get it from another source (for example, analog feedback or absolute feedback). I would look at the Servo Drive (9514).lvproj shipping example as a place to get started. This example gets its feedback from the 9514, but you can replace that with feedback from any source.

Thanks,

[Jabba]

Hi Paul,

Thanks for your precious answer. But after some reflexion,  I still don't understand how we can  disable the "Position Loop" embedded in the 9514 module.

The 9514 specifications document mentions that the module embeddeds 2 loop (Position and Torque Loops).... Do I miss something?

Thanks

[PaulRB]

Hi Raphael,

When you use the 9514 in FPGA mode, the position loop on the module is automatically disabled. 

I agree that the documentation terms aren't the best. Position loop mode is when the position loop is running on the 9514. You send the 9514 position setpoints and it generates a torque output. This mode is not accessible from FPGA.

Torque loop mode is when no position loop is running on the 9514. You can run in this mode by using the 9514 in FPGA mode or by using it in scan mode and unchecking the "Run Position Loop on Hardware" button in the axis configuration settings. Note that torque loop mode does not imply that the torque loop is running on the 9514; the torque loop is always running on the drive.

Thanks,

[fjy]

Hi Paul,
After reading the context which you've replyed to Raphael, I have to say that I really confused with the the relationship between position loop & torque loop running on NI9514.

Firstly, when I run  NI9514 in the torque mode,  how can I set the position loop?
In the other word, what kind of hardware can be made up  the position loop? 

Secondly, if running NI9514 in torque mode, of  what NI9514 play role in the entire loop(entire loop include position loop, velocity loop, current loop)?
(your reply: Note that torque loop mode does not imply that the torque loop is running on the 9514; the torque loop is always running on the drive.)

Finally, I have noticed that NI9514 can be run in the position mode while one can configure the driver(such as AKD) in the velocity mode(your reply on :
NI 9514 and AKD P00306 Position and Torque mode does not work). But in the NI9415 manual & NI help, the analog output of NI9514 represent torque other than velocity.

I looking forward for your reply.

Thanks

[fjy]

Hi Paul,
After reading the context which you've replyed to Raphael, I have to say that I really confused with the the relationship between position loop & torque loop running on NI9514.

Firstly, when I run  NI9514 in the torque mode,  how can I set the position loop?
In the other word, what kind of hardware can be made up  the position loop? 

Secondly, if running NI9514 in torque mode, of  what NI9514 play role in the entire loop(entire loop include position loop, velocity loop, current loop)?
(your reply: Note that torque loop mode does not imply that the torque loop is running on the 9514; the torque loop is always running on the drive.)

Finally, I have noticed that NI9514 can be run in the position mode while one can configure the driver(such as AKD) in the velocity mode(your reply on :
NI 9514 and AKD P00306 Position and Torque mode does not work). But in the NI9415 manual & NI help, the analog output of NI9514 represent torque other than velocity.

Looking forward for your reply.

Thanks