Motor torque requirements

Question

Hello,

I am trying to estimate the torqie required to drive a lead screw. To do this, so far I 've been using a motion instead of the torque and then viewing the required torque to produce said motino throught the ppt. This doesn't seem to be the correct way though as the results I am getting seem completely off.

Is there a more standard way to do this?

Thanks,

Josef K.

Jesper Slattengren · Accepted Answer

No, why would you need to do that?

A PID controller is a very simple element combined by a variable and two differential equations.

In Adams/View, look under Elements -> Controls Toolkit and there is a PID element.

Or you can create it yourself.

It's a little tricky with rotations due to flip at +/-180 deg. It might be better to control rotational velocity instead of angle.

Create a variable with the function of the velocity profile you want, for example spinning up from 0 to 30 deg/s over one second. q=step(time,0,0,1,30d)

Create another variable that measures the angular velocity of the screw: x=WZ(Mi,Mj,Mj)

Error is now: e=VARVAL(x)-VARVAL(q)

Now you can create a P-controller: P*VARVAL(e)

Create a diff-equation to integrate to angle: x1_dot = dx1/dt = VARVAL(e)

Now you have a PI-controller: P*VARVAL(e)+I*DIF(x1_dot)

That is probably enough to get you going and should be able to produce a smooth curve. Tune P and I to have sufficient small error in angular velocity.

For the D-part, you can do an approximation and just use WDTZ(Mi,Mj,Mj), but that is really only valid for steady state target.

To create a real differential part, create an implicit differential equation:

0 = VARVAL(e) - DIF(x2)

This is a weird construct, it basically says that the integrated value of the differential equation x2 is equal to the error. From this follows that the derivative of x2 must be equal to the derivative of x.

Now you have the final PID controller:

F = P*VARVAL(e) + I*DIF(x1_dot) + D*DIF1(x2)

So no co-simulation is necessary.