GCON unable to solve function that include model parameters as a variable. Suggestions to run two coupled shafts with variable speed ratio?

Hi, In my model(attached) I am trying to drive a pump shaft(slave) with respect to the motor shaft(master) based on a variable efficiencies. I have coupled the two shafts using GCON.

The efficiency is calculated using the output torque and the input speed. The coupler(GCON) seems to be not working when the model parameters are used to calculate the ratio at which the pump shaft should spin. It works fine with some arbitrary generated variable that dose not involve model parameters.

Any suggestions to run two coupled shafts with variable speed ratio?

Attached Files (1)

coupler_test.cmd.zip

0 Jesper Slattengren over 1 year ago

From the documentation on GCON:

The FUNCTION expression exp can reference variables defined in the .adm file through the VARVAL construct. It should be stressed again that correct handling of the GCON requires that the expression defining the VARIABLE only depends on time, and position and velocity measures; in other words, the Pfaffian character of the GCON is not undermined by the presence of the VARVAL.

Your VARVAL is dependent on a reaction force.
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0 ashok over 1 year ago

Hi there,

Thank you for clearing the GCON functionality.

Do you have any suggestions to run two coupled shafts with variable speed ratio where the speed ratio are dependent on reaction force?

Thanks,

Ashok
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0 Jesper Slattengren over 1 year ago

I assume that what you are trying to model is some sort of belt drive? Or CVT?

Anyway, there could be a possibility to use a good control element to do this. Is reaction forces on the driving axle important to you? Or will that be motion driven?

The problem is that forces tends to be a bit noisy, so good solver tuning will be important. I will see if I can get something together.

But I think there are a couple of logical mistakes in your setup.

First, you have the GCON defined as

AZ(master.MAR_3, ground.MAR_1)+AZ(slave.MAR_3, MAR_2_reaction)*VARVAL(Calc_Vol_eff)

which means that the output shaft will rotate in opposite direction and faster than the input shaft as the Calc_Vol_eff < 1.

You see this clearly when rewriting the rewriting the equation as

WZ(slave) = -WZ(master)/Calc_Vol_eff

The other mistake is to drive the input with a torque and have a torsion spring on the output. The output spring SILL wind-up until the shaft stops, no matter what, and the reaction torque on the driving shaft WILL stop that as well. It becomes a very hard system to control.
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0 Jesper Slattengren over 1 year ago

Motion driven on the input shaft, I can get a pretty good following. I can't say how this controller would work in a larger, more dynamic system. This system only have one degree of freedom, the output shaft rotation. This makes it very easy to tune a controller
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0 Jesper Slattengren over 1 year ago

Even driving it with a ramping up torque, it behaves pretty much the same. Now it has two DOF. But still easily controlled.
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0 Jesper Slattengren over 1 year ago

Here is an example of a simple controller. Almost a P-controller but with some stabilizing elements.

Attached Files (1)

coupler_test_jslat.cmd.zip
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0 ashok over 1 year ago

Hey Mate,

Your model works like a charm. It performs as per the requirements I had for the model. i,e Change in shaft speeds without altering the torque.

Since I am new to Adams, I have hard time understanding the energy loss in the coupling. Its kind of frustrating that I cant understand the solution and it works beautifully.

In regards to what I am trying to achieve, I would like to model a pump with volumetric inefficiencies.

Thanks for your help.

Cheers,

Ashok
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0 ashok over 1 year ago

Hello again,

I ran a few more simulations of the same last week. The solvers crashing when I couple the slave shaft to a load and drive it backwards. I need the model to regenerate .

Please advice,

Cheers,

Ashok
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