Dynamic Simulation - Finding Unknown Force

[Ted_Zillich-Henshaw]

Good day all, this one is beyond me... I am alright with FEA analysis but Dyn Sim is eluding me at this time.  Please assist.

I have a scissor lift we are designing that uses a servo ball screw to lift the mechanism....

I have it constrained to move correctly in a normal assembly...  When i go into dynamic sim....  I get very confused.

I would like to use unknown force to determine how much force the ball screw has to exert to lift the mechanism with 300lbs and 500 lbs hanging from the lower frame.

I have attached my assy if someone wouldn't mind assisting.

[WHolzwarth · Accepted solution]

Hi Ted,

my comments:

- Create as much sub-assys as possible

- Don't use fictive constraints, without real parts behind. I've added rollers and conical shapes for working around that problem.

Attached are only the changed or added parts in your assembly. Copy the existing ones into a separate folder, and add my changes. DS should be moving after that.

Walter

[Ted_Zillich-Henshaw · Accepted solution]

Thank you for the assist,  Still cannot get Unknown Force of the cylinder to push the scissor.  Maybe i am unsure of how to apply the unknow force correctly.

When i select the "piston" of the cylinder, it gives me degrees, as in rotational.

As the cylinder extends, the scissor should collapse upwards.  I am trying to find this force the cylinder needs to exert on the frame to make it lift.

this is en example of what i am trying to accomplish.

[JDMather · Accepted solution]

For your Unkown force you will want to select Jack relative to a Prismatic Joint for the motion of the Piston.  

I have not looked at Walter's solution yet, but I have been revising to remove the redundant joints.

It may take some time to clean up.

[Ted_Zillich-Henshaw]

Thank you for taking the time to help me out.

[Ted_Zillich-Henshaw]

I believe after some pointers that i have figured this out....  Mainly it was constraining correctly (axis to centerpoint constraints) and aligning my objects with centerplane constraints.

Once i did this and removed some of the redundant automatic joints, i was able to show the force required to move the structure was 500+ Lbs and ramps up to 4000+ Lbs once fully retracted

Thank you again

[gsadiq]

Is it possible to apply two unknown forces if you have a 2 jack mechanism? Also the machine is not symmetric so I cannot assume that my load will be applied equally to both jacks.

[JDMather]

It would be best to start a new discussion thread and Attach the assembly in question.

I assume the problem will need to be split up into sub assemblies for analysis if not symmetrical.