feedback application for a maxon brushed motor controlled with a EPOS2

[MatteoNI]

Hi,

I want to implement a VI that controls a linear stage moving vertically. On the platform that is mounted on the linear stage i sitting a load cell. The platform has to move up and down in a sinusoidal kind of way, maintaining a constant load on the load cell (one can imagine a piston and cam system, where the piston is applying the load).

The load cell is connected through a PCI 6014 and is working fine. 

The computer can communicate with the motor through the "EPOS studio" provided by maxon, but it cannot perform such an advanced task and therefore I decide to use labview.

I'm trying to modify the VI that is provided by maxon by implementing a feedback with the voltage from the load cell. I want the motor to move in such a way to maintain the voltage from the load cell constant. 

I'm not very proficient with labview and I would like to know if this is possible and if so can anyone give some directions?

Thank you very much,

Matteo 

[Andy_C.]

Hello Matteo,

Do you currently have any of the control design toolkits or just LabVIEW?

Here's a tutorial of Motor Position PID Control using Control Design and Simulation Module

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000x4ToCAI&l=en-US

In order to maintain the voltage level, you would need some sort of control algorithms to monitor the system output and our Control Design and Simulation Module and other toolkits such as PID, System Identification, etc would be able to accomplish such task. Please let me know if you have further questions.

[MatteoNI]

Thank you. 

I'm doing the controller's tutorials now, I'll ask more questions when I'm done. I'm particularly concerned about interfacing the controller with the EPOS VIs.

Regards,

Matteo 

[Jochen]

Matteo,

could you please provide some more information about your taskß

1. Which type of EPOS drive are you using? Could you please provide a link to a datasheet? 
2. Are you using a CANopen interface to the EPOS drive and is there also an option to use an analog signal as torque command?
3. Are you using LabVIEW for Windows?
4. What's the voltage level of your load cell signal?
5. Do you have any idea about the required control loop timing?

My first guess is that you probably need a realtime operating system for your application or at least a motion control device that provides realtime capabilities, so I don't believe your current approach will be successful, but I'll have to wait for your answers to be sure.

Kind regards,

Jochen Klier

National Instruments

[MatteoNI]

Dear Jochen,

Thank you for your answer.

1. Which type of EPOS drive are you using? Could you please provide a link to a datasheet? 

I am using a EPOS2 50/5, see attached pdf.

2. Are you using a CANopen interface to the EPOS drive and is there also an option to use an analog signal as torque command?

No, I'm not using the CANopen interface, but the labview VI provided by maxon (see attached).

No, the controller has no input analog signal capability. 

3. Are you using LabVIEW for Windows?

Yes. 

4. What's the voltage level of your load cell signal?

+10V to - 10V 

5. Do you have any idea about the required control loop timing?

I'm not even sure I understand what you mean, so no, I don't.

I just want to add that my application won't require a high speed. The vertical motion will be around 2 cm/s at most 3 cm/s and I was considering that quasi-static.

Thanks a lot,

Matteo 

[Jochen]

Matteo,

I know many customers who work with the EPOS2 50/5 and it does provide +/10 V analog inputs that can be used as command inputs. I'm pretty sure that the communication speed to your controller will be too slow to run your force control over that link. Instead you better should use a plugin controller like the PCI-7350 and use the 50/5 as a power drive only (configure it for analog command inputs and torque/current control).

A PCI-7350 provides analog feedback inputs, so you can connect your load cell directly to this board to run the force control on the onboard DSP. Here you can find some more information about using analog feedback signals with NI-Motion controllers.

Jochen

[MatteoNI]

Jochen, 

My intention is to use NI cards to drive the motor, using the EPOS2 only as a power drive. I have doubts about the interface with the subVIs (which use the digital usb line) and the speed of the feedback that you also  mentioned in your previous message.

I have a PCI 6034 and a PCI 6014. Would it be ok to use on of these cards? 

Thanks,

Matteo 

[Jochen]

Matteo,

the boards that you have suggested are data acquisition boards that could be used for motion control tasks if you are running your PC under a real-time operating system. Even in such an environment this would mean a significant amount of programming. The motion control board that I have mentioned doesn't require a real-time OS, so you can run it under Windows, as it does all low-level control tasks onboard. With an NI-Motion board you should use your drive's analog input lines and connect them to the board's analog command outputs. This approach will significantly reduce your development time while providing a solution with superior performance.

Jochen