Supporting structures used in machines/production lines

[olii245]

TL;DR Summary

I am a mechanical engineering hobbyist. By now I'm designing some small production line in which I'm gonna include a robotic station. In general, heavy robotic arm is gonna be suspended on a beam that moves in one direction along the rails.

I'd like to calculate the whole structure including welded beams and then calculate rails and the beam used for suspend a robotic arm. The problem is I've no idea how could I start.

I was trying to find some training materials (mainly books) on this topic (design of supporting structures for machines) but I only found books for Civil Engineers.

So I have a few questions for you:
Do you know some books/articles/YT materials/etc.. where I'll find information about
- how to design and calculate supporting structures for machine applyings
- FEA analysis of such supporting structures
- type of sections and their applyings (when to use I-beam, channel section, rectengular section, etc..)

If you have some more tips for me I'll be very grateful.
Thank you in advance for every reply!

 

[Baluncore]

- how to design and calculate supporting structures for machine applyings

There are many ways of solving the problem. The wisdom is something learned by experience in the industry.

There are fashions of machine support that come and go, like motor vehicle styles.

For a single small unit, it is better to build something quickly and get it working. The cost of the extra materials, needed to be sure, will be less than the extra design time. If something is wobbly, improve the design and fix it.

Perfection is the enemy of progress.

 

[olii245]

There are many ways of solving the problem. The wisdom is something learned by experience in the industry.

There are fashions of machine support that come and go, like motor vehicle styles.

For a single small unit, it is better to build something quickly and get it working. The cost of the extra materials, needed to be sure, will be less than the extra design time. If something is wobbly, improve the design and fix it.

Perfection is the enemy of progress.

Thank you for your answer, Baluncore!

That's a shame because I came up with this project specifically to learn about calculations and analysis of supporting structures :/ Maybe I should try with something more difficult but still related to mechanical concept like crane trusses? But still I don't know where could I learn about FEA and basic calculations

 

[Baluncore]

Maybe I should try with something more difficult but still related to mechanical concept like crane trusses? But still I don't know where could I learn about FEA and basic calculations

In the real world, you cannot calculate a design from 0% to 100%. You must start with a conceptual design, then apply successive refinements.

When a part fails in some way, refine that component by calculating the structure needed to satisfy the requirements at the lowest cost and complexity. Refine your specifications as necessary.

If a part is too heavy and never fails, reduce the weight in the next incarnation, until it almost fails. That is a safe way to reduce the cost of materials and shipping.

With time, your initial concept and the specifications will evolve together into a reliable structure that can be manufactured and sold competitively. By then, you will understand the constraints, and have numerical models of all the major components.

You must design and build the third best now, to get it working. Second best will be the next model, with some refinements to the design. First best is perfect, impossible, and can never be.

 

[Frabjous]

Try looking at machine element references. If they are too advanced you will need to look at mechanics texts (statics, dynamics, materials). For FEA, it is probably better to look into training on the code you have access to. You will need the mechanics for this also.

 

[olii245]

Try looking at machine element references. If they are too advanced you will need to look at mechanics texts (statics, dynamics, materials). For FEA, it is probably better to look into training on the code you have access to. You will need the mechanics for this also.

Thank you, Frabjous, for your answer!

Yeah, I know this stuff (statics, kinematics, dynamics, materials) a bit. I mean I can calculate simple cases like bending beam or beam in tension, compression or shear. The problem is sometimes I dunno how to apply this knowledge to realistic projects. Let's say I'd like to calculate one of my rail which is a C-profile like on the following figure

the beam can move along the C-profile, F=1500N. So I guess for C-profile I should calculate:
- bending stresses for bottom wall of the C-profile (the torsion/bending moment around the Y axis), and this is simple because this is gonna be const regardless of actual location of the beam
- weld strength (C-profile is fixed by welding on its ends) - and this also seems to be quite simple but specific result will depend on actual beam location, so I don't know which location choose to calculate max stresses (maybe center location?)
- bending stresses for entire C-profile (the torsion/bending moment around the X axis), but again, specific result will depend on actual beam location .

All of the calculations in this project I make to determine max stresses and based on that choose the correct C-profile type (in this project I assume that I don't have any C-profile to use and need to choose and buy the correct one)
So Is it right for this case?

 

[Baluncore]

The problem is sometimes I dunno how to apply this knowledge to realistic projects. Let's say I'd like to calculate one of my rail which is a C-profile like on the following figure

A floppy structure, with minimum cost and weight, can be rigid in the dimensions that are critical. For the rail, consider:
1. A closed section rail (torque tube) to prevent axial twist;
2. Having the bridge beam run on the rail at the centre of rail twist, so any twist of the rail does not result in a change in the x or z of the bridge beam end, and vice versa, reduces twist;
3. Having the bridge beam ends, constrain the rail rotation by running on two edges or corners, not on one flat;
4. More than one of the above, but keep one degree of freedom flexible, so accuracy of construction is not over-constrained.

 

[jrmichler]

Be very aware of real world constraints. There was the time, very early in my engineering career, when I proudly designed a frame to support a machine that weighed about a ton. The support frame was about four feet high. I carefully calculated the support columns, even doing Euler buckling calculations. Then a millwright rather bluntly pointed out that this frame was next to an aisle, and that we could expect a forklift truck to bump into one of the support columns. The real design constraint was to survive a collision with a 10,000 lb truck, not merely supporting 2,000 lbs of machine.

But still I don't know where could I learn about FEA and basic calculations

It's best to stay away from FEA until you fully understand the basic calculations. You need to understand the basic calculations in order to check the FEA results. Machine frames are normally simple enough that FEA is not needed.

I suggest getting copy of the AISC Steel Construction Manual. You do not need the latest edition for your needs, a used copy of an older edition is plenty good enough.

 

[russ_watters]

If "hobbyist" means you have no formal engineering training, I'd start with an Engineering Statics textbook.

 

[gmax137]

Be very aware of real world constraints. There was the time, very early in my engineering career, when I proudly designed a frame to support a machine that weighed about a ton. The support frame was about four feet high. I carefully calculated the support columns, even doing Euler buckling calculations. Then a millwright rather bluntly pointed out that this frame was next to an aisle, and that we could expect a forklift truck to bump into one of the support columns. The real design constraint was to survive a collision with a 10,000 lb truck, not merely supporting 2,000 lbs of machine.

This is sound advice. I remember a similar epiphany, when I discovered bent instrument tubing (3/8 stainless tube) out in the plant. Bubba the 260 pound maintenance guy had been using the tubing runs as a ladder to reach a valve in the overhead.

 

[Juanda]

Be very aware of real world constraints. There was the time, very early in my engineering career, when I proudly designed a frame to support a machine that weighed about a ton. The support frame was about four feet high. I carefully calculated the support columns, even doing Euler buckling calculations. Then a millwright rather bluntly pointed out that this frame was next to an aisle, and that we could expect a forklift truck to bump into one of the support columns. The real design constraint was to survive a collision with a 10,000 lb truck, not merely supporting 2,000 lbs of machine.

This is sound advice. I remember a similar epiphany, when I discovered bent instrument tubing (3/8 stainless tube) out in the plant. Bubba the 260 pound maintenance guy had been using the tubing runs as a ladder to reach a valve in the overhead.

These couple of messages reminded me of this video with a fun and illustrative anecdote talking about a similar concept.
I consider the whole video to be interesting although the anecdote itself is from 13:00 to 14:00 more or less.

 

[gmax137]

These couple of messages reminded me of this video with a fun and illustrative anecdote talking about a similar concept.
I consider the whole video to be interesting although the anecdote itself is from 13:00 to 14:00 more or less.

Thanks for the link, I haven't seen his videos before. I watched a couple just now, pretty good stuff for engineers / designers / makers.

And I liked his anecdote, a good approach to keep in mind!

 

[Lnewqban]

...If you have some more tips for me I'll be very grateful.

Welcome!

Study practical solutions that have been optimized after years of experimentation.
Every element of such structures has a reason to be.

https://www.midasstructure.com/blog/en/blog/crane-girder

Draw your particular situation as close to scale as possible.
That will give you a perspective of where supports, reinforcements, gussets and joints are needed.