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 Piezo electrics
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By: setlahs (offline) on Tuesday, May 29 2007 @ 03:58 AM PDT (Read 8356 times)  

I must truely be crazy, because I just spend the previous 6 hours surfing the web, scouring the web for information on piezo electrics. Or more specifically, Piezo electric actuators, pumps, and motors. Why? Well, who wouldn't want to control 50 picoliters of fluid, thats why!
I started off by looking at Piezo printheads. ya know, like the kind Epson uses in their printers, and many top end manufacturers use in their flatbed or large format printers. Problem, The stuff that we could use easily, the commercial stuff, is expensive! Gee golly Crickets is it expensive! like 600$ for a printhead. And of course I'm not all too satisfied in buying a lowend epson C88+ from a store, just to tear it apart. well, at least not to just rip out the printhead and leave the rest for another project. Naw, I would have better uses like a direct to PCB printer.
So I continue on one of my searches, and finally run into a little project by the good ol' folks at berkley! I knew I wanted to go to that school for a reason. Anyways, the project was headed by Hyuck Choo and Prof. Richard S. Muller, It was a design of MEMS-Integratable Polymer Microlenses. Ok so the title may not be all that interesting to some, but the matter in how they made these lenses was astounding. Using a Microjet dispenser made by Microfab Tech, inc. They extruded a UV reactive epoxy onto a hydrophillic substance surrounded by a hydrophobic susbstance, they were able to create a lense array with no single lense greater than 200um. Pretty cool, eh?

Ok but that pointed me to what i was looking for, Microfab. They have a range of piezo electric microjets, at an undisclosed cost. In my experience, when they don't tell you the cost, then it's usually too high for you to pay it.
Ok so I just continued. Now I know things like this exist, maybe other companies made some? eek, not likely. thats why i've been searching for 6 hours. A number of companies make piezo electric actuators, but only one i've found so far makes a specialized jet (or extruder),

Soo, doing a couple hundred searches, I found a few companies that sell basically raw piezo electric ceramic materials, which may be adapted into a piezo micropump, which in turn I could use to make my own jet, and from there, it's up to your imagination. Mine tells me to put it on a CNC 3-axis coordinate table, and start making... stuff... Smile

there are more readily avialable piezo electric materials. say, that buzzer in your wrist watch, or speaker in your PC, etc... Looking up a few designs, and a piezo electric pump seems of moderate difficulty with these common items, though I haven't seen anyone do it, or at least write an article on it.
Piezo electric material is pretty cool when you think about it. it can resonate, and act as a clock. It can flex when current is applied. And It generates current when pressure is applied. While i may not make it sound interesting, the uses seem to be growing every day. With all my free time I have right now, I might start digging through my electronics depository to see what I can do.

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By: Windell (offline) on Tuesday, May 29 2007 @ 03:12 PM PDT  

Piezo materials are great, but they can be a little expensive and difficult to control. Oh, and toxic, and they break easily, and can be killed by overvoltage. Oh, and they're a little bit dangerous too with the high voltage and all, but other than that, they're great! Big Grin Chunks of PZT (lead zirconate titanate) piezo ceramics are common enough to not be *that* expensive, but typically you need up to 1 kV DC to control them, and the total stroke that you can get with any piece is measured in the tens of microns. Longer (mm-scale) travel is typically possible with large stacks of thin piezo elements that run on lower voltages. However, the capacitance tends to be very high, so high currents are needed to drive them. 3D motion control systems based on piezo elements are quite common, but most of them are designed for true micropositioning, e.g., of atomic force microscope samples. On the topic of inkjets, I was recently told about a $100 inkjet dev kit from Parallax that uses an HP cartridge. I am also interested in microfluidics, but principally for food applications, so I wouldn't want to start with one of their icky ink-filled cartridges. Food-grade inkjets *do* exist, and are used all over the place, for egg and pill marking, and for custom cake decoration. (I'm putting one on my christmas list, right after the chaos machine!) You may also want to consider looking at micro-sized fuel-injector type devices and at building your own from scratch. Looking at the options, I would certainly go the thermal route rather than the piezo route; see the wikipedia inkjet article for a comparison.

Windell H. Oskay

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By: setlahs (offline) on Wednesday, May 30 2007 @ 01:11 AM PDT  

Lol, thats actually one of the applications I would be interested in too. Smile
Of course printing on various materials would be nice too. Some piezo electrics use voltages as low as 200-400v, which I think is managable with a decent charge pump.
The thermal route doesn't seem so appeasing to me because it acts directly on the fluid by applying heat. in some cases this may not be desirable.
I looked into printheads for a while, but I favor a single jet with replacible nozzles. That way you could choose a nozzle to fit the application and type of fluid. a single nozzle may be a multitude times slower requiring multiple passes, but you would gain a benefit of control.
I've thuroughly examined the inkjet article on wikipedia, in addition there are a few manufacturers who have great explainations of how theirs work.
Microfuel injectors seem like a good option too, though cost is always a concern. even 100$ seems too much for me.
I recieved an email from microlab today, their lowest price nozzles start at 600$. yikes!
I think it may be cool or a project in itself to design and creat my own microjet. maybe try a variety of different methose to achieve it.
I was thinking of a way to make a nozzle that would be small enough... Electroplating came to mind. Imagine drilling a hole in a piece of brass or aluminum with a .5mm drill bit (or larger, depending on how well the process works)
Then use some simple electroplating techniques to add material to the nozzle, until a proper gap size is reached. Think it'll work? i could try this at home with some very simple materials.

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By: setlahs (offline) on Wednesday, May 30 2007 @ 02:40 AM PDT  

A cool link about printheads

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By: Anonymous: Dave () on Thursday, June 14 2007 @ 12:47 PM PDT  
Anonymous: Dave

Piezoelectrics are definitely interesting, but they can be hard to work with. One of the earliestly exploited piezoelectric materials was Quartz. One of the early applications for it was for use as an underwater transducer for sonar, and, later, as the frequency determining elements for radios. Quartz is hard, reasonably robust, chemically non-reactive, non-water soluable (at normally encountered pressures and temperatures), and reasonably temperature stable. On the down side, though, because of these characteristics, it's difficult to machine. Additionally, even when hit with a high voltage, it doesn't move much. Modern Quartz is man-made via high pressure/high temperature synthesis (as opposed to using the naturally mined material).

Another early material is Rochelle Salt. This is quite a bit more responsive than Quartz, but has the annoying habit of absorbing moisture from the air (unless it's hermetically sealed) and dissolving. It, too, can be man made (by reacting and crystallizing Baking Soda and Cream of Tartar!).

Some of the more modern Piezoelectric materials exhibit even larger responses, and don't tend to dissolve. However, most of these are crystalline materials which are rather expensive. Additionally, some of these are quite brittle. Examples of some of these materials are PZT (Lead Zirconate Titanate).

One additional material which may deserve some consideration is PVDF (Polyvinylidene Fluoride), which is a plastic piezoelectric material. It's not exactly cheap, but, since it's a plastic, it can often be machined or formed much easier than a crystalline solid.



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