Which Compact RIO Chassis and Controller for 3 axis control

[paubine]

yes, it was exactly my question!

The spline engine is only available with the NI Softmotion Developement Module?

tks

Patrick

[Jochen]

Yes, the spline engine and the trajectory generator are major features of the NI SoftMotion Development Module.

[paubine]

Hi Jochen,

I will definetly need Softmotion for the Spline Engine... any other solution to save money?

I read that the spline engine need four setpoints ? Destination point (I guess) and what are the others?

Thanks again,

Patrick

[Jochen]

Patrick,

as long as you don't want to write your own trajectory generator and a cubic spline algorithm with fixed point arithmetic, which will be very time consuming, SoftMotion seems to be the only reasonable option to me. Compared to the work time that you would have to invest to implement this math by your own, I think the SoftMotion Development Module is priced adequately. Still you should contact your local NI fieldsales engineer who might have an open ear for negotations.

The trajectory generator generates at runtime the coefficients for the spline engine, so you don't need to care too much about the mathematical details. In fact these are not available to the public and I'm also not familiar with them. Just feed the trajectory generator with your move constraints and you are done. I'm sorry, that I'm a bit fuzzy with this topic.

Jochen 

[paubine]

Hi again and sorry for the delay.

As I said, I have to control slave mouvement of two axis by a master encoder.

I can't use the trajectory generator from Softmotion with move constraints.... I have to write my own code and give the new setpoint of the slave in the control loop reading the master encoder.... I will have to understand how the spline engine work or write the code directly on the fpga (which I don't want)...

correct my if I'm wrong, but I will need to know how the spline engine work. I'm not in function of time but in function a the master encoder.

Thanks again.

Patrick

[Rodj]

Patrick,

If you are gearing from one axis to two others (sorry I am only reading the last response and not the complete thread) in the FPGA, do you really need the spline?  What is the loop rate you are running on the FPGA?  Would it be good enough to just directly take the master encoder data at this rate and apply it to the slave?  For most systems I would think the answer is yes, but I don't know the specifics of what you are trying to do.

Thanks,

Rodger

[paubine]

Jochen,

Yes I'm gearing but I have to stop this gearing and use straight line move also... (with the same axis, when the operation is complete), it's not permanently doing the gearing.

I was thinking the best way is to use the fpga spline engine from the RT to reduce the amount of coding on the fpga...activate straight line TG when needed and use my own code for the gearing, then come back to straight line... so the only thing I have on the fpga is the control pid loop.

thanks again

Patrick

[paubine]

Oops, I just realize it's not Jochen, sorry about that...

The only thing I see how spline engine work is :

p0 = pt before (to know how to start segment p1 to p2) 

p1= actual point

p2= next point

p3= next next point (to know how to end segment p1 to p2)

Pat

[Jochen]

Pat,

in this case I think you should differ between two modes:

1.  Master/Slave mode: Implement this mode directly on the FPGA. You can feed the master feedback signal directly into the position setpoint of the PID controller. Maybe some scaling is required. This shouldn't be too hard to implement.
   
2. Straight line moves: Usethe SoftMotion trajectory generator and the spline engine for this mode.

Does this work for you? Rodger, do you see a better approach?

Jochen

[paubine]

Hi Jochen,

you're right, directly on the fpga will be more precise and direct....I will go this way...

I'll give you news soon!

thanks!

Pat