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Beer is promised to whoever can come up with a good and plausible solution to my problem!

I am studying second year Industrial Design at university. The project I am working on is designing a set of kitchen scales that a) would be sold in a low volume boutique store, and b) utilises two main materials, and uses these materials in a particularly innovative way. The materials I have chosen are billet alumiminum and acrylic, and I will be using the light conducting properties of the acrylic in a kind of funky way. In a nutshel I will use the billet aluminium to create a mechanism (that works in theory). This mechanism will angle a mirror according to the weight, which then changes the angle of reflection of a laser beam - the laser dot on an opposing surface will then show the weight. All very sexy if it works in practise, but thats another problem for another day!

My problem today is this. The table that holds the weight is mounted to a swingarm. As a force is applied, the swingarm pivots. Only problem is that the weight table is firmly fixed to the swingarm, meaning whatever you place on the table will fall off as the swingarm pivots. The simple solution would be to put some kind of wall so it doesnt fall of, but that doesnt work very well for liquids contained in a vessel, then it gets messy! So obviously my table will need to be located in more than one position (or weighted somehow), and may even need sliders and runners to ensure it stays vertical. But how do I actually do this? Does anyone have any other ideas as a way of keeping the table horizontal? And dont hold back on those zany ideas, sometimes they can be turned into something that works! Perpetual motion is too far, but you get the point!

The swingarm will have an extension spring attatched for resistance, and I actually have to build one prototype of this! And please excuse my dodgy MS Paint "renderings", I thought this was the best way to quickly visualise my idea. The actual swingarm looks a bit different to get the centres of gravity right and all that jazz, but the concept is there. And no, I dont actually look like that...

 

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I am an engineer (though I rarely engineer anything)

Add a second pivot, as seen in this crude drawing.

PM me for the beer delivery address.
 

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Add a strain gauge

When I worked for Bell+Howell, Phillipsburg Division, they used a hunk of billet aluminum machined thin with a hole in the middle. They added a strain gauge to an area around the hole.

When a weight was laid on top, the strain gauge would react in a reliable and uniform way sending the information to a low cost computer for resolution.

The hunk of aluminum had a conveyor belt on top that passed letters over it and down to another section of the machine. This device weighed the envelope as it flew over top on the belt.

Very ingenious!
 

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Here is how it looks...

Here is a quick PC Paint sketch on how it works.

There is a gap at the top of the hole in the billet aluminum. The strain gauge measures the gap.

As weight presses down, the gap lengthens a bit.

The strain gauge can sense the spread and sends that in real time to the CPU. Software decides what that data represents and sets its weight.

We had to adjust the sensitivity of the gauge using an ohmmeter as I recall. The manual said we should NEVER press down on it in any way other than laying envelopes down on it because it would be pressed beyond its limits and be rendered useless.
 

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My explanation voids your thoughts based on the following:
 

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I stand corrected!

;)

Of course this is more of what I should have said:

Achtung

Alles Lookenpeepers!

Dies Machine is nicht fur gefingerpoken und mittengraben. Is easy schnappen der springenwerk, blowenfusen und poppencorken mit spitzensparken. Is nicht fur gewerken by das dummkopfen. Das rubbernecken sightseeren keepen Cotten-pickenen hands in das pockets - relaxen und Watch Das Blinken Lights.

:D
 

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Wow, I haven't seen that spizensparken thing in twenty five years. A mechanic I used to know had it up in his shop.

Random, if you want to keep it simple with as few parts as possible, and not necessarily postal rate accurate, just handy for the kitchen, maybe try changing design so the Table is on a very very short pivot arm, that is, as close to the pivot as possible, reducing the swing, and the travel of the table to perhaps 3/16 of an inch. At rest the table can be a bit slanted one way, and at full travel just a bit slanted the other way, but still easily usable.
 

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Confused

How can you be studying "Industrial Design at university" and not understand very basic engineering concepts. Surely you have had to do some engineering?

This concerns me because it's like an Architect that also does not understand how a building is actually built ... the end result is that Architect is very costly to use because things are not practical. Very quickly that Architect gets this reputation and has a harder job getting work.

Thus I seriously suggest if you want to be a really good industrial designer that you do some basic engineering courses, or at the very least pull you car apart and have a look at how real things work.

I used to be a design draughtsman and when I started a new job I used to walk around the workshop to see what was made to immerse myself in "real" work. I'd speak to the guys and learn what their concerns were with the current designs, etc. I also used to build a lot of things myself (at home) like club race cars and my Alfa restoration (and many times I borrowed the machines at work to make something ... myself) and I seriously believe that made me a better designer.

Good luck, and I hope I've made sense and you will take my comments on board. Basically there are good designers and not so good designers ... good designers see the object from ALL angles, that includes the engineering side.
Pete
 

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Okay, lets try the KISS principal (and see if I can keep the explaination simple too!).

First, design the weight table to work it's way up and down in a vertical motion - sliders on each corner would work well.
Then, try fitting a spring to the underside of the table. With a known weight, the table should drop a set amount (e.g. put 500 grams on it, and the spring compresses 1 cm), so you could simply add a back/side panel alongside the edge of the weight table, and graduate it for the known weight.

Now, if you want you could adding a lever, so when the table goes down, it pushes onto an indicator and makes it move (much like a see-saw).

I hope that this is enough to get you started - failing this, simply pull apart some scales to pinch some more ideas (like oil dampening of the mechanism, etc.)

Dino
 

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If you hinge your table to the arm that it is acting on. If you place your tables surface below the hinge then the surface of the table will always stay flat.
quick and easy
 
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