Servohydraulic control with load cell feedback

[pallengb]

Hello,
 
We are planning to build a tie rod fatigue test system with Labview and NI PCI-7344 4-Axis Motion Control Board. We have two linear servohydraulic actuators for applying linear force to tie rod and a servo motor for steering wheel movement. Tie rod must be vibrated by linear servo hydraulic actuators with constant force (+/- 50N , compression and tension direction) as 20 Hz while the steering turns (this is for road simulation) .

 
I think we can generate the 20 hz triangle waveform with 7344 motion control board for controlling servo hydraulic. But the main problem is to apply stable force with servo hydraulic actuators while steering wheel is turned by servo motor with constant frequency. There are two load cell as load link in the system so can we solve this problem with connect load cell to 7344 as feedback ?

Could you please share your opinions about hardware and software selection and application? What do you think about onboarb programming for this system?

I have attached two images regarding this systems which was build by some companies.

Best Regards

Steward

[Jochen]

Steward,

I think you should be able to use the analog feedback feature of the 7344 to accomplish your task. Please refer to this link where you can find an attachment that explains the details of using analog feedback.
I don't think that you will need any onboard programming for the control task but depending on your security needs you might want to use it for emergency stop actions (e. g. when something goes wrong and the speed or the force become too high).

Please note that the 7344 does provide 12 bit ADCs for analog feedback. If the accurracy of these ADCs is not enough for you you should consider to use a 7356 instead which provides 16 bit ADCs.

Please read the document linked above. If you find that for some reason analog feedback is not the solution for your task we can talk about other options.

Best regards,

Jochen Klier
National Instruments Germany

[pallengb]

Jochen,

Thank you for your answer. I think 16 bit is better for our application. we will consider this situation.

Do you know any Labview example about generation frequency controlled sine or tringle analog waveform with motion control board ?

We will use Parker Servohydraulic which is controlled +/- 10 VDC.

I think the weakest link will be load cell. Load Cell should have fatique rated, high response and accurate.

Best Regadrs

Steward

[Jochen]

Steward,

To generate the motion profiles you could use several approaches.
E. g. to generate a sine velocity profile you could run two axes in circular interpolation mode. In this scenario you would only use one of the two axes to control the servo which would result in a sinusoidal move. The other axis should be configured as open loop stepper so you wouldn't have to connect a motor to it.
For triangles you could use blended 1D moves.

On the other hand I think the more flexible approach is to use contouring as this allows you to generate any motion profile you want. Please refer to the shippping contouring examples.

Jochen