Paste jetter – inkjet lessons

I ordered my Piezo actuator today. My Piezo actuators came from  http://www.piezodrive.com/    I got a -30>>150V actuator type SA050520.  Have been learning about making small features, including  EDM

The block that houses the delivery chamber will be temperature controlled I’ve done alot of reading, including this short gem http://doc.utwente.nl/58366/1/thesis_Wijshoff.pdf

drawing below from the above thesis :

ink

Other required reading..
http://web.tuke.sk/scyr/data/upload/1268901041.pdf

Particularly figures 6,7 and 8 showing  the Thixotropy

 

Posted in Pick and place

random thoughts toward a successful paste dispenser.

These are RANDOM thoughts out loud, right now….there are a few things that need to be done to make the paste dispenser work, I have studied the various syringe/ auger constructions, their claims over others etc etc extensively.

rough drawing……

Visio-dispenser

Visio-dispenser_2

simpler Visio-dispenser

MK1 will be direct syringe pressure type.
the syringe types need a bit of work- a combination of the below :
0) needs temperature stability/control
1) no air piston- direct piston driven by lead screw/stepper. no air anywhere .
2) pressure in the chamber needs to be monitored . have to figure this one out. something on the wall that provides pretty reasonable consistency. I am thinking resistive or similar sensor on the walls of the pressure chamber.
3) pressure into the chamber by a piston is easy to increase by pushing the piston down, but on the withdrawal which is important has to be done without introducing air.

A withdrawal is required as part of the cycle. Many system have problems with voids created. A vac created may not pull back the fluid reliably and as desired, so that needs to be worked on. there may need to be the vac created by the retreating piston PLUS another means to pull the fluid back up the needle. Perhaps an opposing (with hole in the middle) piston at the bottom of the chamber to push the fluid back up. Surface tension will permit the fluid in the nozzle also to assist pulling the fluid back up (and avoid any voids- that’s the idea- no voids are to be created.
There are other means to push/pull the fluid.   Constricting a channel of sorts (squeeze) or expand- the fluid needs to be pulled up the nozzle.
It’s hydraulics, also.  Hydraulic systems are using push , pull…..Must remember. if only the piston moves back, we are relying on the vac and the surface tension to pull everything up. the question is for example, if the pressure chamber was full, that’s alot of fluid to pullback on vac and surface tension. So I think there needs to be assistance of sorts. maybe there are ribs or something on the walls that move, I dunno, but I will start thinking.  if there is pullup (by vac due to piston pullback) AND pressure from the bottom of the chamber UP (by another piston) then we can avoid voids in the main chamber and only the small quantity in the nozzle needs to be pulled back up the nozzle, not a large volume up the chamber.
Perhaps…. deforming the walls , changing the shape of the entire chamber with a crush, or a expansion would provide useful methods, also,

IE use a piston for movement  of fluid to ensure the chamber stays pressurized, but also use deformation of the chamber for dispensing. Epiphany : If  a large surface area of the chamber deforms  this is acting on a much larger  surface area than the end of a piston.
such a deformative wall though is a difficult thing to build . The pushing piston is required to keep the deformation chamber  full, as the deformation chamber has finite breathing ability.  so the deformative chamber for dispensing is a  hard but interesting option.

Either the chamber (stock) or the applicator (needle ) could be deformed..There is a good supply of piezoelectric actuators around, time to learn about them…
Air or fluid could be used to deform a container, also, like a bladder or sealed container inside a container to squeeze or open the contents.

now we have good pressure and release control and pressure sensors, when the dot is deposited, best performance is a precise delay before the precise pullup.
Distance to Z=0 is going to have to be known to at least half the dot size- at least 0.1mm , so there will need to be a very precise distance sensor and height control of the head.

The 32 gauge auger system that is designed for 01005s and it is successful, uses a 0.1mm nozzle internal diameter.  I will start with that size.
There will need to be multiple devices to be able to deposit with reasonable speed on a mixed PCB- IE different nozzle sizes. Watching on my air dispenser dispensing through a 0.1mm nozzle, there is at least a 1/2 of a second for the dot to be let go- IE takes a while for the small amount of surface tension, presumably because the area is very small, takes time to let go. Pull up too fast and the blob is not reliable, the head pullup needs to be slow. So the smaller dots end up being quite time consuming to put down.

I read that the surface tension and behaviour  changes quite a bit with temperature so the chamber paste AND the PCB surface will need to be temperature controlled.  No use dropping carefully controlled paste onto an icy PCB.

To summarize :
VERY accurate control of Z height  with better than 10um movement resolution .
Piston compression from one end of the chamber
Piston compression from the other end of the chamber..
Deformation of the chamber or applicator (needle)

another idea is that once the paste is moved into the applicator (needle) this area could be sealed off from the stock chamber.(rotating / sliding ) , constriction of the applicator etc) and the applicator could then be deformed by a fast pulse (IE a piezo actuator or solenoid) . This way the only way for the paste to go is out the needle.

ideas…ideas.. a solenoid smacking into a deformable wall would work…
if there was a sub chamber from the main stock chamber like a hollow block that had the applicator on it and it was sealed from the stock chamber, an deformation actuator could be one or more of the walls of this stock chamber. I think for success, the pushing force needs to be applied over a very large area  to volume ratio. Not just over a small area of the volume.
Additionally, if there is a separate deformation chamber to the stock chamber, a pull-back motion in the stock chamber may not be required.

In fact, ipso facto, if the paste is pumped in, there might really be no need of a piston/ construction bladder for the stock chamber.

Constriction of the duct  between the stock  and delivery chamber can be simplified. A duck valve. (thanks Robert)

OR just constrict the stock chamber (for delivery and pullback)  and have no separate delivery chamber.This solves the problem if refilling the delivery chamber without ooze.
The thing is, the small chamber removes a whole lot of fluid the pulse has to be transferred through.. so perhaps another valve is required on the delivery needle.

My guess if the bigger the volume getting squeeze, the more  low-pass the delivery behaviour. and the harder to control over temperature and paste variation…

Might use ultrasonics to measure density, voids, pressure.
Like three transducers in a 120 deg  arond… 1MHz transducers…

 

No need to go crazy with piezo though, voice coils, solenoids they all work.
golly there are all sorts of piezo things

http://kineticceramics.com/piezomotor_act.html?gclid=CKWTweL12swCFQwnvQodQ0MN4Q

https://www.americanpiezo.com/piezo-theory/actuators.html
http://www.physikinstrumente.com/products/integrated-piezo-actuators.html
http://www.cedrat-technologies.com/en/mechatronic-products/actuators.html

 

Posted in Pick and place

Guides arrived…

guides

From “Jiean Robot” in Zhejiang, China. “Zhejiang Sikete Technology co ltd”
Very easy to deal with Chinese company, good customer service, understood my needs, able to customize, and 7 day delivery once TT received. Well priced also, about USD400 each approx .

Photo is before the mounting plates go on to interface the rails and the extrusion.

Well I think I went a bit  too big !   NSS95 for the dual X rails and a smaller NSS75 for the Y gantry. The idea is X gantry has to support (and accelerate )  the Y guide and the gear.
Motion specs for the 75 and 95 are the same, just the loading. In hindsight, NSS75 all round would have been fine.  I went with the ’95 because they were only about 15% more .

75 guide is 7.5 kg, and ’95 is 12.5 kg. Lots of extra Aluminium plate…The 75 guide (Y) is 600 travel. The X is 800 travel,
The guides come with photo-interrupter limit and home switches and cables that can be put on either side of the guide.

There is 780 between the supports so the head on the Y can be quite wide (in Y) and still run full travel.

They are silky smooth… I have run them up with a motor and they scared me….

Posted in Pick and place

PnP : On stereo imaging and more focus

I had in my plans for two cameras in a stereo scopic setup for down vision so I could figure out depth and distance to things on the table .

However. doh! , I was playing with my fancy PointGrey camera last night and realised I don’t need two cameras, I just need to take a image, and move the camera and take another image ! and I can move the camera with sub pixel accuracy in the FOV.

And then, another obvious penny dropped.  Image de blurring and refocussing  (enhancing depth of field) can be done with a series of images takes when a camera moves in a plane tangential to the object. I read that many  years ago .

And of course I can move my down (and up) camera and take multiple shots.

So a bit of searching and googling later reveals google have done it for Android

http://googleresearch.blogspot.com.au/2014/04/lens-blur-in-new-google-camera-app.html

 

 

 

 

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OpenPNp multithreaded directions..

added here  from my post in the forum..

I had a chat to Jason about this a week ago.. essentially…
after component pickup, Open PNP motion thread tells motion-controller (external)  to go to the target location (PCB place)
motion thread blocks on image processing thread.
image processing thread is also blocked at this time.
motion controller takes care of getting the UP camera in the right place and takes the exposure.
motion controller then sends signal to PC (say a char on a serial  port) and this unblocks the image thread
image thread now unblocked processes image, and comes up with a new offset for the placement and rotation.
Image thread posts this new info to the motion thread and blocks-
motion thread unblocks and updates the new target positon to the motion controller , and also updates rotation.
motion thread blocks waiting for ‘on station’ signal to come from the motion controller, and the placement ensues.
of course there various things that might happen different if we are placing a big component  where we most likely need to STOP over the camera and have afew goes at rotation, putting the part down, picking it up again, rotating etc to get that right- but that’s not often (for hard parts) .
and also if people  have a camera that requires everything to be stationary, slightly different but similar events occur.
However my idea is basically to decouple the motion and image processing so that the machine can be on its way while the images are being worked on..
of course if the image was bad, or the uncertainly level by the image processor was low, then it is going to have to tell the motion thread to send the head back to where the camera is (or sent the camera to it or something)
Of course this having to have another look at the component and moving the head back  to the camera etc is a great advantage of flipping a mirror in the way and looking at the component that way.. I just have not yet found a good way of doing that for multiple nozzles. More thought required.

Posted in Pick and place

L6470 ST stepper driver

Wow, this baby is complex.
Read this first…L6470 presentation

I bought two eval kits from digikey/mouser $25 each. (mouser: 511-EVAL6470H-DISC )
It  has a USB interface, JTAG interface and some buttons. The eval software for the board is  comprehensive. There is alot to this chip- it is NOT for the non engineering types.

It is not just a fancy bridge driver, it is a stepper /motion control ‘co-processor’ you tell it where you want to go and it goes and manages it… SPI interface…

In a nutshell- on my steppers this chip is smooth. I mean REALLY smooth on microsteps.
it uses Voltage Mode drive (rather than current mode drive) with BEMF compensation, and from my non stepper standpoint, voltage drive is much preferable for driving this sort of device.

I have steppers clamped to my steel bench for eval, so any vibration gets amplified through the bench…. I tested steppers with inertial load, and without.

The results are chalk-and-cheese against my other stepper drivers 8825, 6620 etc.This chip does not want to do anything BUT microsteps. I found compared to the other drivers, the microsteps were pretty much within the 5% of a full step tolerance.

and, as expected, the microstep performance was vastly improved by having some sort of load on the shaft. This is why i think the component rotation application is going poorly for some users  – no load and undamped resonances and vibrations. IE needs a chunk of steel on the shaft.
(And even worse with the abrupt current mode chopper drivers I am used to_

Its a good eval kit (Discovery kit), but before you start, you MUST read at least the eval datasheet, the eval software manual, upgrade the software on the board etc.

Then you MUST READ (because results will be disappointing otherwise)  AN4144. I say again. MUST READ.

Then be sure to read AN4241, UM1691, AN3991, then, optionally, AN4290, DT0055, DT0056.

 

 

 

 

 

 

 

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Nozzle pitch

The main reason I went to NEMA14 for the  Z axis was the need to pack the nozzles in tighter. NEMA14 body is 35mm versus ’17 which is ~43.

Ideally my nozzles will be the same pitch as the tape feeders, or the same pitch as the strip feeder tape component pitch- IE 4mm or 8mm multiples. This way multiple nozzles can do a simultaneous plunge and pick  without moving the gantry .

I will likely use NEMA8 rather than NEMA11  for the rotation, so weight will drop 60 grams.

Also I have assumed a accel=decel curve for maximums.. but -if decel is to be faster, the stepper is going to have to be bigger, which helps for it to have more authority. This means going to the next NEMA14 up  , the 0.22Nm.
There IS a 0.4Nm one, also.  You are well and truly into ’17 territory there. A ’17  can do bigger work with a shorter body , but the nozzle pitch suffers. 0.4Nm is approx midrange ’17 territory.
On the DOWN plunge is easy for the Z, because the UP is lifting against gravity.  Of course on decel, the opposite applies- lots of work required to slow the payload as the nozzle approaches the Z=0 at mach2.

Posted in Pick and place