I was thinking about building a variable resistor using coiled copper wire and a float to determine the water level, and by offsetting multiple coils could give you better resolution.
any suggestions would be greatly welcome
Printable View
I was thinking about building a variable resistor using coiled copper wire and a float to determine the water level, and by offsetting multiple coils could give you better resolution.
any suggestions would be greatly welcome
Sounds like you're aiming for real time feedback rather than a calibration aide. For your idea I think static friction between the float and coil is going to be an issue, you might find you get jumps rather than a continuous change. For real time sensing then solid state wins it for me, I'm thinking guage pressure or capacitive ATM.
The idea of a calibration aide might be good though. For drip calibration you set a rate and let it count for a given rise in liqiud, then you can put in a drips per mm number. This may take some time and the more level you measure the better the result will be as you minimize errors. You could make a circuit board with a more accurate smaller gap which would take calibration time right down but hopefully maintain accuracy, this is as simple as a few transisistors and a cheap circuit board with some LEDs.
Having a think about this............. how about a finely graduated scale on the side of the tank (printed and laminated) and an optical mouse chip on a float. The chip returns changes in Y as it floats up the scale. This is a robust solution, which could have amazing accuracy. Plus, dirt cheap.
They have a resolution from 300 dpi up to at least 800 dpi. So about 3 thou up to just over 1 thou.......... that shud be plenty.
An alternate and simpler auto calibrator would be a pair of wires with gaps that both go into the microphone like so:
Tone generator (speaker)_____ ____Mic in
Drip Sensor__________________ _|
Such that the spacing between the lower and upper gap is exactly a centimeter (or whatever unit the Peachy uses for calibration). Then run just saline through the dripper without any resin. The software won't start counting drips until the level reaches the first wire and have the software automatically stop the count when it hears the tone coming through the second wire. Suddenly, you know exactly how many drips are between the first and second gap!
It would probably be good to run multiple calibration measurements with it at different heights on the tank wall to be sure, so that you get a good average fill rate per drip.
@Atztecphoenix - there shouldn't be a problem with the scale. Even an old Laserjet 4000 can print at 600 DPI. The mouse chip can resolve movement at 800 dpi on any surface (apart from very reflective) using very clever digital signal processing, so the scale is almost immaterial. You could just chose a surface with a fine texture and use that. All that for a £1 or so (English money). But just gutting an optical mouse, and putting it in an IP65 box would work. http://pickandplace.wordpress.com/20...optical-mouse/
or what about Ultrasonic Proximity Sensors?
Is the precision good for that?
It can interface with the standard peachy using a picaxe chip, which reads the y output and pulses the mic input of the Peachy as if it was a drip. But an absolutely accurate drip.
as mike said... you only need to generate a drip pulse. Not too hard to do (in fact, just touching the 2 cables).
Mount the peachy printer on a float and the mouse chip. A reasonably tight fit in the tank.
yeah...... u can create your own chips using visual basic and picaxe chips. I am a big fan. You then programme them using a laptop and a serial link cable. They can do anything you tell them to. Very very easy to use. You would soon get into it. The dev/programming software is also free:-
http://www.picaxe.com/Software/PICAX...amming-Editor/
We can go completely closed loop Z control, by having the same picaxe chip turn a pump like the one Pete suggested ON and OFF. So the Picaxe could turn the pump ON and quickly allow 2 thou of fluid into the tank, send the drip pulse to the mic input, then turn OFF and harden that layer, then ON again and so forth. All using the basic Peachy.
I'm working on something like that. Except, I wont be using a pump but a solenoid valve. Just waiting to see if the noise is acceptable (on/off each drip). Else, would take a variable valve, but they are not cheap.
you might find it more acurate to use both, since water drop vary in sizeplacing a solonoid valve right at the end of your input tube to stop all water flowthe instand the desired level is reached would giv you far more accuracy, but in all I like where this train of thought is going, I'm looking into getting a PICAXE setup when I can get enough money together (currently laid off)
I'm working on a solution for a pump with a standard peachy (I'm gonna upgrade my'n to USB so I'll have whatever control and feedback I want!). For the moment it will consist of circuitry so that you can feedback into audio and use the stock software. This does mean that the drips become mega size so the 'drips' will probably need be quite slow but because they're larger it shouldn't compromise the printing speed. For extra control, USB is the way forward (I'm convinced of it) once I get up and running with the standard, USB and the pump will be my first major hacks so I'll be sure to post the results.
When I get a moment I'll splash down a circuit diagram and a partslist so you could get started building if you like. I'm hoping that everything will be achievable with moderate soldering skill, all through hole components and some stripboard.
Pete, in other word, you're builing the "Pro" Peachy" :P
this got me thinking, if we can get real time feedback for the Z axis, what if we used a laser rangefinder type system to identify how far the print head is from the base of your build area and then by adding small photosensors, one at each corner and one in the middle of your build area, in theory wouldn't we be able to make the Peachy "self calibrating"?
so, the laser would shine and the range finder would count how long the light takes to reach it, then the laser would scan to find the center photosensor establishing that as zero, it would then move to each corner measuring it's travel distance on the X and Y, after locating the corner it would return to center and repeat for the other three corners, it could then take those measurements to determine the X and Y build area and by having the real time Z axis feedback calculating the entire build volume would no longer be required and the machine would be able to calibrate itself prior to each build.
the main reason I am looking into this is I plan to use different sized build resivoirs for different prints ( no need to use a three cubic foot resivoir for a print that only takes up five cubic inches)
unfortunatley the speed of light vs speed of electricity in wires is light is several times faster, partly due to the resistance of the wire, so using the laser to calibrate the distance would not be effective or reliable
Well sure it's possible to use a laser rangefinder. The code's in python, open and easy to learn and change. Problem is that I don't think you can get either method of detection and still get a printer out for under $100.
Refining the optical mouse idea, it is much simpler to use a strip of textured plastic about 1/2 inches wide, 1/10 inch thick and an appropriate length. Attach this to a small polystyrene float. Mount the mouse circuitry in a static position at the top of the tank, so that the float strip moves paste the mouse window (feed the strip thru a slot by the mouse read window), as the depth in the tank increases. This would definitely work and give excellent Z resolution at a very cheap price.
not necessarily..... u cud have the upper tank offset by 1 inch or so and have a scale slot on the side of that too !!!!
on further reflection, a separate tank off to the side of the whole machine attached with an umbilical to the build tank, that way the water would displace both at an equal rate, it just might work.
this setup could also be used as an overflow cut off switch, the gauge has a contact on top and an adjustable slide with the second contact, this way as the gauge floats up when the top reaches the slide it can activate a solenoid valve to stop the drip flow.
This thread is super awesome. I hope someone tries this and reports back!
I apologize if these questions are redundant, but how many "dots per inch" is required for proper z-axis resolution of a general purpose 3-D printer? And assuming our z-axis measuring equipment was capable of measuring in increments that were infinitely small, at what point does the argument become moot because the laser's field of view in our Peachys (or perhaps the behavior of the MakerJuice in relation to the laser that we're using) can't keep up with the performance level? In other words, I guess, what's the lowest resolution that everyone would be okay with?
The resolution of the Peachy is a tricky thing, because it's analog rather than digital. It has a measurable precision, but that can change drastically based on the software (which is still changing quite a bit) and the clarity of the sound card used. Possibly even the quality and shielding of the cable, being able to actually see sound quality as a physical object can really turn someone into an audiophile. :p
Also, the laser currently has to be calibrated by eye, meaning the overall scale would be hard to get better than +-.5mm, but details smaller than that would still show up if you have the sound quality for it.
As an example, the Form1 3D printer can resolve Z to .001 inches. There is no reason why Peachy can not match that as the two use very similar technology. I think the Peachy hardware seems excellent. The only question mark for me relates to the Z axis calibration in terms of drip control and the software corrections for each Z layer. The beta prints so far all appear to have Z dimension problems, hence this thread to identify a way of doing closed loop Z with a basic Peachy.
I meant to add that the chip used in digital vernier calipers looks very interesting. http://www.ebay.co.uk/itm/6-Digital-...item2ec3149f37
in a sense, the argumant is moot,
as get better with our calibrations and others develop ways of fine tuning the laser and mirrors we would be able to get finer and finer resolutions possibly even the the point of nano. the whole purpose of this thread is to try and make the Peachy the most reliable 3D printer on the market even if everything we are talking about is to be done after market. to be able for the printer to accurately know what its current Z height is simply means you get that much more precise of a final product with less fussing around.
3D printing technology is constantly advancing, and there is no law that states that it has to advance in a certain order, if we can measure more accurately than our printer can print it just gives us an excuse to make the printer more accurate to match.
An interesting article on reading data from digital calipers http://www.instructables.com/id/Read...n-Arduino-USB/
Could we get a float to turn the caliper mechanicals?
Just had a fiddle about with my digital calipers and I am really warming to the idea. I can open them fully and zero them (do this at the start of the print). As you close them, the reading increases as expected but with a negative sign (so just get picaxe/arduino to ignore the sign). The caliper is a bit stiff and would need loosening up, but not sure whether this would affect the capacitance. The Z value is easy to read with a PIC chip and you can simply look at the display to get current Z height (ignoring the sign). The resolution required could be set using dip switches (say 8), which would give 256 combinations of vertical res. The PIC just reads the dip switch pattern to get the required Z res. The PIC simply then turns on a solenoid or pump until required Z reached then pulses the mic and turns pump/solenoid OFF. Then delay to allow hardening then pump on again.
I've just splashed out on these calipers..... will report back to see if I can loosen them enough to be float operated. These can resolve to 10 thou. They operate off capacitance ............. will report back when I've had a go. http://www.ebay.co.uk/itm/4006804750...84.m1439.l2649
love the idea... wonder if they are good, I would buy some for personnal use! :P
sebastian.... they are very useful for general purpose use...... will let you know how my experiments progress.
I don't know if this has already been discussed, but what about using a Kalman filter (which is just something to be implemented in software) to make use of the information from the drip and whatever is used to accurately measure the present liquid level (such as the caliper)? This way the caliper (or whatever equivalent used) would give it good accuracy, and the individual drips would give it amazing resolution.
For example say each drip adds 0.001 mm. Then even if the caliper had poor resolution the Kalman filter would just "trust" the drip in the short run giving .001 mm resolution, and then use the caliper data to prevent it from drifting after several drops. So with this system you would still have to do a test calibration of the drip system to understand roughly how many drips it takes to go up a given height, but then after that it would have great accuracy and awesome resolution. The accuracy would be as good as the caliper and the resolution as good as the drips.