Force obtained with "Unknown Force" tool to get 1 deg angle

[otrosrecursos]

Hi,

Why the force obtained using "Unknown Force" tool (in Dynamic Simulation) to get 1 deg angle, produces different angles when same magnitude is applied using "External Force" with input grapher or constant value?

The assembly used is very simple: 2 flat rectangular parts (VerticalSupport.ipt and SegmentL.ipt perpendicular to each other) connected by a revolution joint used as a torsion spring (in Dynamic Simulation) with "Enable joint torque" selected.

The "revolution joint" has "Spring Elastic Stiffness" = 10 N mm/deg.

The length of SegmentL.ipt is 100 mm (lever arm)

Force will be applied (at the tip of the lever arm) to obtain equilibrium

The required force was found using "Unknown Force" tool, to get a deflection of 1.0 deg.

settings: "Initial position" = 0.0 deg, "Final position" = 1.0 deg. The result = 0.10002 N.

"External Force" was applied (0.10002 N found above), using "Input Grapher", X1 = 0 N , Y1 = 0 seg, X2 = 0.10002 N , Y2 = 1 seg. Result angle = 0.87 deg.

"External Force" was applied (0.10002 N found above), using "Constant Value" = 0.10002 N. Result angle = 0.72 deg.

 Am I missing something?  Both angles were supposed to be equal to 1 deg, but they are not.

Attached a zip file containing the assembly file and the files of the 2 parts.

I am using Inventor 2011.

Thanks in advance for your help

[otrosrecursos]

I think I found the problem.

The revolution joint had "elastic stiffness" but no "damping", therefore the horizontal flat part was oscillating above and below the expected deflection of 1 deg ; the oscillation can be seen extending the time of the simulation to 3 seg, and opening "output grapher" to check the "revolution joint" position.

To avoid the oscillation certain amount "damping" is required. According to "Up and Running with Inventor Simulation 2011": "As a rule of thumb, apply damping in the ratio 1 : 10 to value of stiffness".

I set "damping" to 1 N mm s/deg and the equilibrium was found at expected 1 deg.

It worked for both "constant value" force and for "input grapher" force.