Leaf spring

[tinkerer]

I am designing a mechanism that has two parallel leaf springs connecting two components, effectively forming a parallelogram when undisturbed.


I need (eventually) to animate this mechanism. I need some help on:


1. how to model the leaf springs so that they are springs


2. how to assemble (constrain) them into the assembly as springs


3. how to animate them


I'd be very grateful for suggestions

 

[shivdeep]

The fisrt biggest leafspring is tied to truck chasis with one end having pin allowing it to rotate on its axis and other with shakle and pin allowing it to rotate and translate then size down goes down and making a parallelogram. all these leaf springs are tied with centrebolt at centre which ties to axle and U bolts on either sides. depending upon size and quantity of leaf springs used.

 

[Mloew]

The problem is that a leaf spring is a flexible body. There are closed form solutions to calculate the position of a point of interest on the spring (it was a 6th order polynomial, if I recall correctly). The problem is more complicated if you wish to consider more than the kinematics of this problem.

Suggestion is to simply assume that the fixed end of the leaf and the point of interest prescribe an acr and develop the mechanism accordingly.

Post the geometry and I'll take a deeper look.

Good luck.

 

[Israr]

What you want to do is simply not possible in the current releases of Pro/Engineer (WF 3.0 M080 the latest). Its unfortunate but a truth. The leaf spring you want is available on the site www.simpack.com


The software that can do what you want are: MSC ADAMS, SIMPACK, and LMS VirtualLab, to name a few big ones.


We look forward to ptc if they can put the capability in WF 4.0


Israr

 

[Mloew]

Israr,

Not impossible, just very difficult. It can be done.

 

[Ray Ellender]

There is a very comprehensiveSAE Manual on leaf springs, SAE HS J788 I believe, (although my copy is very old, so it may have been superceded) which amongst a lot of information includes a drawing board procedure for sn equivalent kinematic mechanism, which you could replicate in Pro/E. We have also successfully analysed leaf springs using Mechanica Motion in the past, and if you have Mechanica Structure you may get what you want from that, probably using large displacement analysis.

 

[Kaz Z06]

Tinkerer,


This problem is not even difficult and can be easily solved. Use standard theory to describe the spring rate for your geometry and split the leaf spring Pro/E partitself into two halves. Connect each half with a pin joint and apply the proper torsional spring rate at this joint to create the correct, relativevertical displacement (end-to-pint location) underits associated load - this is where you need to convert between torsional and linear spring rates to get it to work out numerically correct and animate well. Obviously, the animation won't be perfect since we're simplifying a smoothly bending beam with two rigid halves. but it will look pretty good and, more importantly, it will be accurate. I imagine you would connect the spring to one of the bodies at the same location you split the spring (like at an axel point).


For extra credit, you can associate the geometry of your leaf spring with beam-theory's spring rate equations and create a joint "force motor" that uses parameters from your model to drive your spring rate on the Mechanism side. This way you can conduct sensitivity and optimization studies "hands-free". You'll need to use the "User Defined" loading option for the force motor in order to access parameters on the Pro/E side.


Good Luck,


Kaz Z06
Edited by: Kaz Z06

 

[Mloew]

The trick is getting the right properties from the geometry into the closed form equations. The other issue is getting the spring to animate correctly without using flexible bodies (this will require splitting the beam into more than two pieces to be be accurate). Again, solvable, bot not easy.

Israr is certainly right about how this is typically solved in industrial practice. I am currently working on several projects that integrates Adams with Pro/E and FEA for flexible bodies.

 

[Israr]

What I meant was that MDO does not have the ability to cope with the flexible bodies. ADAMS and SIMAPCK does.


We are waiting for the comet soltions. That would a great breakthrough in this field.


Israr

 

[proe_33]

If you wish to define the motion of the spring analyticallythis can be done by th centre- link extension layoutmethod which is defined in the SAE Spring Manual SAE HS J788, which Roy mentioned.As far as making it work in the CAD domainKAZ's solution sounds like a good bet to me if not see if you can get a trial version of the MSC software to complete this project (if it is a one off). MitCALC also provide arelatively cheap add- in for excel that can aid you with the calculations for the spring, which to the best of my knowledge is in- keeping with the design methods specified in the SAE manual.





Cheers

 

[yangtse]

There is a very comprehensiveSAE Manual on leaf springs, SAE HS J788 I believe, (although my copy is very old, so it may have been superceded) which amongst a lot of information includes a drawing board procedure for sn equivalent kinematic mechanism, which you could replicate in Pro/E. We have also successfully analysed leaf springs using Mechanica Motion in the past, and if you have Mechanica Structure you may get what you want from that, probably using large displacement analysis.

Hello, Ray,Could you please send me a copy of the SAEHS J788 which isabout leaf springs? Thank you very much!

 

[Ray Ellender]

No. Buy it from the SAE like everybody else.

 

[CaptnPea]

Right on Ray....

Really getting sick of the "give me this for free" attitude on this site, it is just getting out of hand. People who have done the work deserved to get paid for it.