very rough prototype pick place head type thingy

While waiting for the parts for an actual reprap, I decided to play with some parts I had around and some shapelock and try to make a picker placer head type thing. The idea is using a vaccum, it can arbitrarily place objects in 3 dimensions. The thing is real rough, but I was wondering if anyone had any comments on the basic design. I am mainly a programmer and have very little experience building mechanical things in the real world (which shows greatly in this prototype), but was wondering what people thought.

[notanumber.net]

That is again some great work. I think that if you added an axis which allowed for the whole tilt head to swivel you would have a robust design that could essentially place objects anywhere. Great work, and could you post that arduino interface code for the Wii nunchuck? I am thinking of getting one and playing around with it.

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Jay

John,
That's a clever mechanism. I made a vacuum pump for a similar application from an aquarium pump. It normally blows but I sealed the case with glue and attached a pipe to its air inlet hole. I also made a three way valve to turn the vacuum on and off sharply with a solenoid. Some pictures and details here: [hydraraptor.blogspot.com]

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[www.hydraraptor.blogspot.com]

Cool!

That's pretty swank. I may have to get me one of those wii nunchucks.

The pick and place system looks like it could be very functional given a bit more work. nice work

Demented

Good stuff. I am very impressed. Can't wait for when little gadgets like this can be effortlessly replicated!

Thanks for the feedback. I think I am gonna start work on beta 2 pretty soon, with any luck, beta 3 will be made with nice repraped parts The only non-reprapable parts in there are the servos and I gather that repraping parts for a servo is something that will be actively worked on by others.

Yeah, the Wii accesories are great, there are 4 wires coming off of them, connect them to +5, GND, and analog ports 4 and 5 on the arduino and they are just simple I2C (TWI) devices. the arduino has built in hardware to speak I2C so it is really straightforward. There is also the classic controller with 2 joysticks, a d-pad and a whole compliment of pressure sensitive buttons. I imagine these will be extremely useful in the prototyping phase for various projects. To build the actual plug adaptor, I cut a pcb to the right size to fit in the plug and used 4 strips of copper tape along each corner to make contact and soldered wires directly to the copper tape. The nunchuck responds to device id 0x52 via I2C. I have not tried the classic controller yet.

I am thinking about the following changes

1. the bottom servo is upside down. doh! I intended the shaft to be at the bottom so I could dremel off the servo mount on that side so when the picker is bent to 90 degrees it can be brought down flush with the table to set an object on its side.

2. I think I will add 90 degree stops in each direction, as that will allow arbitrary placement in 3-d by repositioning and grabbing objects again. and I can physically adjust the stops for very precise positioning at the extrema, which are likely to be the most important places.

3. the linkage has a bit too much give, probably due to my joints made of bent leads cut from resistors. any ideas for making more robust joints?

4. actually calculate the length of the linkage elements to give the most resolution over the full 90 degrees.

A longer term goal of this is to attempt pick-n-place circuit creation. namely, I have this copper foil I can cut into tiny strips, the idea is the machine picks up pieces of foil and places them on the pcb to form a pattern. the syringe head (being worked on by others) then dobs a bit of solder paste to each copper-copper joint as well as smd mount spots, the smd chips are laid and the whole thing goes in the reflow oven bonding everything together nicely. I am not sure how well it will work... but it helps to have some vauge idea in mind when designing something even if it turns out to be useful for something else entirely My next best idea is using the pick-n-place head to build mini replicas of stonehenge out of grains of rice. (okay.. maybe I have some intermediate ideas )

if the solder paste doesn't work too well, perhaps a simple ironing will be enough to bond the copper to the pcb, I am assuming some heat activated adhesive (perhaps just a very thin layer of CAPA or some other thermoplastic?) can be applied to the pcb beforehand to hold the coper down after heat has been applied.


Any ideas other than a vaccum pump to put on the end of it as a manipulator? some I have thought of are a small electromagnet for ferrous stuff and a small piece of foil that can be brought to a high voltage to use electrostatic attraction to pick up (small) non conductive things. little grippers are also plausable but I can't think of a way to make them very precise.

nophead, could you explain your 3 way valve design a little? I think I have an old aquarium pump and solenoids somewhere, I was controlling the fan with a darlington array and a free arduino output pin and I can easily switch that to control a solenoid.

Edited 1 time(s). Last edit at 05/06/2008 04:47AM by John Meacham.

Great work on the pick and place thingy!

Your pick & place circuit creation idea is gnarly. All I can add to it is that you might want combine pick-n-place copper connectors with a sparse stripboard.

You could have a stripboard with zones with short copper tracks on every line and zones with short tracks on every second line., then you could place the components on the tracks and use your copper foil busbars to connect the tracks to other tracks. You would need a custom stripboard and copper busbars insulated in the middle, but that's the only two custom components you would need and a group buy could be made for those.

For manipulator ideas, the electrostatic attractor can and indeed should be insulated, in which case it is safer and it can be used to attract anything, even conductors. Two interleaved conducting combs with an insulator on top when polarized will attract anything. They're sometimes used on plotters to keep the paper from moving and you can touch them without getting a shock.

Ah, excellent ideas. A nice thing about copper tape I was thinking is that the same process can be used for a variety of metals as copper becomes more expensive, and a roller-press could perhaps just be fed recycled copper wire to get nice flat copper tape. I have no idea if that is feasable on a small scale though, but on a large scale, I imagine metal foil isn't hard to come by and a simple chopper type thingy can cut it into known sized pieces. (perhaps of a few different lengths, to speed up production when laying long traces)

I am really interested in what you said about electrostatic attractors, is there a diagram you can point me to? What do you mean by 'interleaved conducting combs'? interleaved in what fashion? I was thinking you would need a single polarity for some reason, could you elaborate some? I am eager to test out ideas there as when the scale gets very small a vaccum seems less practical to me somehow. I imagine that a simple high voltage w/ almost no current supply would be fine like perhaps a van de graf?

I surfed for explanations of electrostatic induction attractors but didn't find any, so I posted a diagram of a polarized interleaved comb at:
[members.axion.net]

Make the comb pattern on a printed circuit board, slap on an insulating film and when you polarize the combs, everything will be attracted to it. The fringing force is small and decreases rapidly with distance, so it can only lift light, thin stuff like paper.

The downside of electrostatics is that you need a high voltage to get even a small force. The upside is that you can make em large with little money, they will work in vacuum and insulated electrostatic induction attractors will attract anything; dielectrics or conductors.

With a comb spacing of a few millimeters, you would need on the order of a kilovolt. Since you only have to supply the leakage current, you'd want a very low power circuit. Something like the 130$ 5AV1000:
[www.picoelectronics.com]

would work, but you should be able to make a cheap, inefficient, really low power high voltage circuit. Indeed, for safety reasons, you would want the circuit to be unable to deliver much power and have the tiniest capacitors possible.

In general, thanks to your experiment, we know that off the shelf vacuums work well enough at atmospheric pressure to lift electronic components. So although electrostatic attractors are really neat, you'll only really need em if you're working in vacuum.

You can make 1000V much cheaper than that. You just need a few diodes and compactitors wired in a Cockcroft multiplier, often used to generate high voltages for CRT final anodes and ionizers: [www.freewebs.com]

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[www.hydraraptor.blogspot.com]

... you can salvage old and/or outweared copiers or laser-printers; they have one or more small high-volt-modules.

I have some from 2kV until 8kV, in DC or AC - but my best (and sure deadliest) salvaged device for 'sparks-n-fun' is a sealed module capable of 1mA @ 14kV ...

Viktor

Edited 1 time(s). Last edit at 05/08/2008 05:00AM by Viktor.

You know I think the simplest manipulator for SMD components might be a vacuum pump. You could use a coil driven magnet attached to a plastic membrane covered chamber connected to some membrane valves. This is pretty much what Plus, your not as likely to kill the more static sensitive components with a vacuum pump.

I have access to a high voltage source(gutted ionizer), so I'll have to try this out though.

... i too wouldn't recommend using hv for SMD-handling.

In one of my old XY-writers i have a 2kv-static-sheet for adhesing the paper, on another it's a vacuum-plate and on the plotters i use magnetic stripes.

This kind of fixing is only intended for elastic sheets or big plates ...

Viktor

Wow, I'd love to be able to print that as my second toolhead! This is really awsome work. And the fact that the main part is a (ubiquitous and cheap) straw makes it really 'reprap' compatible. If you start making parts, be sure to post them on the wiki. I'll definitly print it and give you my results and perhaps help you with it. Servo accessiories would also be nice.

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Regards,

Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]

Two thoughts. I tried to make an electrostatic generator a long time ago and I remember that mylar was an excellent insulating film. I dimly remember depositing hot melt from a glue gun on the conductive surface and then binding the mylar by putting a cloth on it and ironing it carefully. My main concern with electrostatics is that they're fun, but can be dangerous so use very low power circuitry, ideally running off a low voltage with all the high voltage stuff insulated so that you don't get electrocuted by mains voltage either.

For the toolhead, I'm glad the straw worked. However since stuff happens, like the toolhead bashing against a component, maybe silicon rubber tubing or some other flexible material could be used so that it could survive accidents.

If it's easily replaced I don't mind an occasional replacement straw. If you can detect the flow rate (as negative pressure, perhaps by measuring the straw width) you can detect if a component sticks (and whether it is dropped, then you can pause and call for help).

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Regards,

Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]

Erik,

Good point about the straw. I didn't think about the fact that you can get many straws for less than the cost of one silicone tube and you can get em at the corner store rather than mail order.

Silicone tubing has a minimum price of about 20$ for ten feet:
www.smallparts.com/products/descriptions/2100%2Ecfm

so it would only be worth getting as a group buy from the reprap store.

For electrostatics I forgot to mention, I dimly also remember using epoxy for gluing the mylar. Also I think there was some kind of spray, maybe a spray epoxy, that I used to insulate the circuit board, especially the high voltage parts.

Enrique

... best for glueing and shielding electrostatic stripes is Polyimide - it's commonly used in flexible PCB's, but you can by it as fluid too which will harden when cured at 175

sensing whether you have picked up a part or not should be a case of measuring pressure differential.

Flow rate is kind of tricky.

But given a constant known flow rate (easy) for a given length of tube etc there will be a depression (reduction in pressure). Measure it and remember the value

Once you put something over the end of the tube like a component it will cause an increase in the depression. Subtract the baseline Depression to get the difference caused by the component. Apply a threshold and say anything above X difference means we have something on the end of the pickup.

Car engine management systems use a similar technique to guess at what the flow rate of air into the engine is. And the sensor is a MAP sensor (Manifold Air Pressure) aka differential pressure sensor (Atmospheric to Manifold Difference) to measure how much vacuum your engine is drawing in the manifold.

aka47

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Necessity hopefully becomes the absentee parent of successfully invented children.