Leaf Spring Design 1

[dhanish.ab]

Hello,

I am working on design of flat spring, for unit wheel system
In this design, I need the feel to be on constant contact to the ground when mounted
unit has 3 predefined heights of 83mm, 113mm and 133mm

Need some advice on refine the spring design such that it fulfils the requirement above and have good contact to the ground (~5-20kgf?) for the 3 heights.

Looking forward of design ideas to achieve the same

 

[desertfox]

Hi

You need to design the spring for the smallest height (83mm) because this will give you the highest stress the spring will actually see. The deflections are quite large for such a small leaf spring indicated in the images, what are these springs actually doing?


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dhengr]

Dhanish.ab:
If your sketch is reasonably within proper proportions, the distance btwn. the two pivot pins is about 180-200mm. This is a bit of an iterative problem, in that, you have to play with the vert. travel of the wheel (83, 113 & 133mm), the length of the pivot arm (~200mm) and the distance of the top pivot pin from the top base pl. (~33mm), as changes in any of these relate to the forces which your flat spring will produce. Of course, the wheel force (flat spring force) will be greatest at 83mm and at its min. at 133mm. It’s a kinematics problem and the trick is to optimize the above variables, for a best solution. What exactly is a ‘unit wheel system’ and what does it actually do? On that kind of a cart and arrangement, I would expect some fairly high lateral forces on the wheels, at the floor, and you must design for those too. The two 200mm pivot arms might be two side arms/legs of a light braced frame, in the plane of the arms, such that these lateral loads are taken out in a cleaner fashion.

 

[rothers]

Looks like the ideal application for a constant force spring.

 

[Jboggs]

Or forget the spring and just use the weight of the wheels. You know it will always be constant. Can you just make the wheels heavy enough to satisfy the requirements?

 

[12345abc6ttyui67]

Agree with Jbogg. Simple hinge with weight of wheel adjusted to give pressure required.

 

[handleman]

As mentioned... Too much deflection for a leaf spring. Looks like you need a spring similar to those used to retain can lights:

 

[cowski]

One common name for those is "torsion spring" - in case you need a term for your favorite search engine.

 

[dhanish.ab]

@desertfox

Yes i have Designed for minimal height (83mm), The idea is to ensure contact between wheels and ground

 

[dhanish.ab]

dhengr

Thank you for the response,

Basically this acts as secondary wheel. This is a container unit which would be mounted onto module with 3 different heights (Mentioned), so idea is to have the set of secondary wheels (Common of 3 heights) with some kind of spring to ensure contact to ground with at least 5-20 KGf.

Maybe quick FEA analysis could help me figure out better, but unfortunately i do not have the required license for same.

Can u please elaborate on "The two 200mm pivot arms might be two side arms/legs of a light braced frame, in the plane of the arms, such that these lateral loads are taken out in a cleaner fashion"

Dhanish

 

[dhanish.ab]

@rothers

Will definitely look into this idea and its feasibility into this design

Thank you for your response

 

[dhanish.ab]

Jboggs

Was my Plan B, to ensure wheel carries enough weight. Just looking at constraint when the unit is mounted on to the module

 

[dhanish.ab]

@handleman, @cowski

Some reason my boss does not agree with torsion spring. Previously we used torsion unit. production unit had issues .


Thanks
Dhanish

 

[desertfox]

Hi
Don’t understand the secondary wheels concept, unless the four ordinary wheels are not in contact with the ground or some base

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dhanish.ab]

@desertfox

1. These comes with feed back unit to track from Station 1 to Station 2. Condition the unit has to be in contact with pallet below


2. The unit is lifted on to module using CAM mechanism. 4 wheels will not be in contact with ground when this happens (for brief amount of time)

Total weight will on CAM and secondary wheel.

Thanks
Dhanish

 

[dhengr]

Dhanish.ab:
You can’t have any lateral loading on the small wheels on the ground twisting on the connections (pivot pins) up near the container unit bottom. I scaled btwn. the three horiz. red lines, and used that approx. scale to determine the arm length btwn. the purple pivot pin about 33mm below the container unit bottom, and then down to the purple center pin on the wheel. That approx. 200mm long arm, which controls the wheel, is what I’m calling my 200mm pivot arm. It appears that the way you have the four corner casters arranged, I could just push the whole container unit sideways and likely rip these small wheels off (twist them off) the container unit at its upper purple pivot pin. Now, in your side view sketch of the wheel and its pivot arm, and in the plane of the two pivot arms; place two cross pieces btwn. the pivot arms, one down near the wheels and one up near the upper pivot points; then add some x-bracing in this same plane, btwn. the cross piece ends. Now, you have a braced frame which will tolerate and transmit lateral loads from the wheels, up to the container unit bottom, in a way that you can design for it. Any container unit movement, other than straight line movement along the long axis of the unit, will still cause lateral loads on your small wheels. Again, “what exactly is a ‘unit wheel system’ and what does it actually do,” how is it intended to work?

Edit: Jboggs’ 5 or 10lb. load could be supported by my cross piece down near the wheels, for an almost constant 5 or 10lb. wheel loading.

 

[desertfox]

Hi

Thanks for the explanation, how much do these bins weigh ? I don’t think leaf spring idea will work because the deflections are to large.
Have considered using spring loaded wheels, where the spring is loaded vertically downwards above the wheel, then when any is load is added the spring takes up the load.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[IFRs]

You coud try a single piece of 0.030" thick x 2" wide full hard spring tempered stainless steel. If that does not work, try two.

 

[GregLocock]

Why not use a torsion bar across the trolley?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?