Inertia Force of Moving Body

[JonReynolds]

Hi all,

I have a very simple assembly, that simulates a mass reciprocating to and fro along an axis, very much like a piston in an engine.

I want to be able to measure the inertia force this mass exerts on the system as a whole.

On paper, (for a reciprocating crank mechanism) the force would be:

mrw^2.cos(theta) + (r/l)mrw^2.(cos2*theta)

where r = crank throw, l = rod length, w = angular velocity, m = reciprocating mass, theta = crank angle.

So I can work it out on paper easy enough but not in Pro/E.

I have tried using connection reaction measures but they do not compute.

If it was a simple single rotating object (like a flywheel) then the connection reaction measure works, but since I have an arm (crank throw) connected to a rod, then to the mass...it does not work.

Any ideas greatly appreciate.

Regards,

Jon

 

[SRINIVASANIYER1]

Your analysis falls under "Dynamic Analysis" which requires
MDX or Mechanism Design Extension. What comes with
Foundation is only the Motion analysis.
With Dynamic analysis, you can define the direction of
gravity and thus weight.
The consolation is you can get a graph of acceleration for
a 360 deg rotation of your crank at the specified speed of
motor; from which you can calculate the inertia of your
mass. The graph should be for a point at the center of the
sphere.
Edited by: SRINIVASANIYER1

 

[JonReynolds]

Hi Srini,

Thanks for the input.

I have moved on to using Dynamics instead and to make it work I have had to create 'dummy' rod and crank parts (as you cannot have parts with no mass) and just made them a very low mass to become negligible.

This seems to be doing the trick!

 

[SRINIVASANIYER1]

please have a look at my edited answer. You were rather
quick...

 

[JonReynolds]

Indeed that it what I have done.

Although, using a radial force in X on the crank axis, gives me a force (which is simply the accel. * the mass of the sphere anyway).

I am now trying this on a system with seperate bodies, i.e. the crank mechanism with balance shafts sitting to the side. To get the overall effect of the system I am just creating a 'user defined' measure to sum up the reaction force at each rotation axis.

Cheers

Jon