Is it possible to condition a load cell signal with a 1520 SCXI and then use it as the primary analog feedback for a 735X motion control board?

[Patrick_Aubin]

My system

PXI 1052 chassis

PXI 8196 RT controller

Flexmotion 7356 motion controller

Flexmotion 7354 motion controller

6259 M series DAQ

1520 SCXI

1520 SCXI

1314 SCXI frount mounting terminal block

DSM strain gage load cells

Exlar SR Brushless PM motors

Kollmorgen servo star CD series 5 drives

My objective:

I want to measure the force on the load cells with the 1520 SCXI (i.e. excite the load cell then amplify and condition its output) then I want to use this analog (force) signal as the primary feedback for my motion control system (7356 and 7354 motion controller connected to my drives and motors).

The problem:

The motion controller boards (7356 and 7354) can be configured for force feedback control via analog feedback from a load cell.  However the boards implicitly expect the load cell signal to be amplified and conditioned with and external signal conditioner rather then using an NI SCXI module.  Currently I’m am reading the SCXI signals via the 6259 M seriers DAQ and consequentially have no way to route the signal into the 735X boards for force feedback control.  I can use softmotion to control the motors but then I loose the fast PID update rates possible with the 735X boards.

The question:

Is it possible to condition a load cell signal with a 1520 SCXI and then use it as the primary analog feedback for a 735X motion control board? 

Thanks

Patrick Aubin

Ph.D Candidate

University of Washington &

VA Medical Center of Excellence for

Limb Loss Prevention and Prosthetic Engineering  

[GiGe]

Hi Patrick,

If I understand correctly you would like to route your signal that is being read in on your DAQ card (from the SCXI module) to your motion controller.  Unfortunately there isn’t any way to route that analog signal to a different board.  One thing that you could do is to use a UMI with your motion controller and then wire your signal from your SCXI to the UMI. 

Another thing you could do is to create your own external circuitry to amplify the signal.  This is a more common way of approaching this problem.  I hope this helps.  Let me know if you have any other questions.

Regards,

GG

[Patrick_Aubin]

Hi GG,

Thank you for your feedback.

 

>create your own external circuitry to amplify the signal.>

True a few op-amps could amplify and filter the signal externally but the performance of such an amateur built system will never match the accuracy and functionality of the 1520 SCXI.  That’s why we spent the $2500 for the professional version.

>One thing that you could do is to use a UMI with your motion controller and then wire your signal from your SCXI to the UMI.>

As I understand it the UMI is basically a break out connectivity interface for third party drives.  After conditioning and amplifying the analog force signal with the SCXI module the analog signal isn’t available to wire into a UMI.  To my knowledge the conditioned signal of the SCXI resides only in the PXI backplane (i.e. there is no physical access to the conditioned analog signal).  Can you explain how the UMI could be help here.

Again thanks for your input GG.

Patrick

[Terry Thompson]

Hi,

You didn't say what input your boards needed, if you are looking for a 0-10 V input, there are a number of signal conditioners available. We are now manufacturing GSX 40 actuators with internal strain gage and piezo load cells and are experimenting with a force feedback motion controller. The GSX model is similar to our SR model. These load cell actuators are preloaded for tension/compression with a load shunt ratio approachin 98%. I can recommened signal conditioners to amplify your output to high grade voltage.

Terry Thompson,

Sr. Engineer, Exlar Corp

Tthompson@exlar.com

[Patrick_Aubin]

Hi Terry Thompson,

Yes, the 735X flexmotion boards can take 0-10V as an analog feedback. 

Thank you for mentioning the GSX 40 actuators with force feedback as a solution.  We currently own and are familiar with both SR21 and GSX Exlar actuators.  I’m aware that we can purchase third party signal conditioning units that can integrate into our system and meet our performance needs.  However, we have already purchased two 1520 SCXI modules with the expectation that they can be seamlessly integrate into our PXI system to provide a force feedback solution for us.  

Our primary object then is to simply determine how we can route the output of the 1520 SCXI into the input of the 735X flexmotion boards.  Does anyone know how to do this?

Thank you for your feedback and suggestions.

Patrick

[jslouie]

Hi Patrick,

With the PXI-1052 Chassis, we are unable to directly route the analog signal between the SCXI and PXI portions of the system.  This thread discusses it further detail:

http://forums.ni.com/ni/board/message?board.id=320&message.id=776&requireLogin=False

With the PXI-1010 SCXI/PXI combo chassis, we have access to the SCXI's backplane and use the feedthrough module, SCXI-1180, to break out the analog channel.  This would not be a direct route, but then the analog signal could be wired up to the input of the motion boards.


Justin Louie