The biggest issue is that copper is very effective reflecting many frequencies of lasers, though one thing that I have seen as an effective solution a while back was where they painted the dual layer board with black spray paint. They then used a very cheap laser that was pulled from a blueray player to etch the paint. Once this was done, it was placed in a dip tank and etched.
One might be able to take this a step further and after you have etched the board, then remove the original paint mask. Then apply solder mask over the entire board, and etch the doler mask to expose the pads. This could be a rather interesting thing. I am not sure that it would work, but would be interesting to see.
The challenge that our machine would have is that we currently get to cheat in the sense that the path is not important, we just need to get from point A to point B. Doing laser etching, we would have to do a specific path. This would get trickier, but I am sure not impossible.
I have gotten to the point that for all the boards that are under a few square inches that it is just too easy to get the from OSHPark.
@adam - I wonder if you could get a light (ie not heavy) laser that would make holes in PCB? itf so it would be lighter than a motorised drill. But I don't know anything about the capabilities of laser diodes. And you might have problems from carbonising the edges of the PCB, hence making a semi-plated-thru hole.... Do you or anyone else know more about lasers? I had an idea to use an x-y plotter mechanism with a UV laser to print-expose pre-coated PCB without going to the hassle of having a positive transparency, I'm not sure if that's what the Bread-Box PCB maker guys are doing....
Though I do have to admit that it is inline with some of the goals that have been set out for this device. Having interchangable heads has always been one of the concepts. It allows for you to have a solder dispensing head and a vacuum head, and then to be able to mount a camera if needed. So adding one more head, that is not a huge deal, and because this is something that could most assuridly be done with a high speed brushless motor from the hobby side of things, then it is not all that difficult. Designing the spindle so that it is accurate will be the greatest trick.
If once everything else is done, and it works without modification, then we will go for it. That is after we have gotten all the other base model things working.
I see that you are mentioning the C5030 and C5055 but have you taken a look at the C5047 device? The only reason that I mention it is that it has not only a serial digital out, but it also has a standard quaderature interface. In other words, it acts as a drop in encoder replacement. This could simplify any roll our own efforts as we may be able to completely leaverage a dev kit from one of these motor control solutions with little modifications to their code. This could make the transition to a BLDC servo solution very palitable.
As an announcement to all those that are reading, Bob (aka salbayeng) has been invited to participate in an official capacity with this project. I think that all of us have been able to learn from his very detailed posts.
He sent me his detailed calcs in the spreadsheet that he pulled these numbers from, and it is top notch work. We should look forward to seeing more from him as he has indicated that he is willing to do some guest posts for us.
Hi Adam -- did you see this Desktop PCB Printer project? Actually, it's more of a desktop PCB etcher.
But the point is, there's a lot of talk about the problem of drillig holes in PCBs. If your pick-and-place machine were modular, would it be possible tow swap the "place" head for a "drill" head and actually drill through-hold PCBs?
Hi Adam, looked at the numbers in your last post, call this AC1, put them in a spreadsheet , errors looked good, but very high motor speed and low torque utilisation. So toned it down a bit , AC2 used a coarse leadscrew of 0.5", and only 2g accel, and trapezoidal speed profile. So now have manageable motor speeds but larger errors, would need a second 1024count encoder somewhere?. (I've randomly called the error budget 0.1mm)
Overview: All cases are 0.5lb payload, with 10" travel. Error budget = 0.1mm total Case AC1: 10g triangular profile with 20tpi leadscrew = 0.050" lead (1.27mm) Use an outrunner motor , say 5% error due to angle estimation, (=18% of budget) An AS50xx mag encoder requires 4.9% of budget. And 0.001" of backlash is 25% of budget. Maximum speed=16fps (5m/s) and ~100msec travel time. Big problem is motor RPM = 236,000rpm And torque is a miniscule 4.5mNm (about 1% of motor's spec) Basically we are doing 200mph in first gear.
Alternate case AC2: has 10x longer lead (0.5") , and trapezoidal velocity profile with 2g max. Has some error problems, e.g. 152% of budget if we want to hold using 12step mode. Magnetic encoder 49% of budget. Total travel time = 240ms Max motor=7500rpm Torque=.01Nm (2% of motor spec) OK now we are doing 60MPH in 2nd gear
I guess what all this says is we need to match the motor and gearing to the payload and error requirements. Most commercial PnP machines have very coarse gearing (consider a typical 1"diameter toothed belt pulley has a 3.142" lead)
Yes, the BeagleBone black is high on the list of parts that we anticipate using. We were able to speak to Jason Kridner at EELive and he said that he would be willing to help get us pointed in the right direction.
As to the encoders, I really think that it will depend on the overall stiffness of the system. If you are mounting to the opposite end of a 3/8" leadscrew that is only 10 inches long, then at the maximum capacity of a plastic leadnut (which we would not be running at) the deflection due to torque would be .8°. This would be a 350 lb load. If we were to say that the gantry head weighed .5 lbs and we were to be running at a max accel of 10g's, then the deflection would be .01°. For an encoder to be able to register this, it would need to be over 30,000 counts per revolution.
As for going with the Geko drives, that is probably out of the range of what we are able to handle. Most likely we will have to leverage some other solutions that are already out there.
We did just get some information from Trinamic on a new dev kit that they have. This is something that we may want to look at. I know that the TI solution is a full closed loop control for BLDC motors, essentially creating a servo motor. I have a feeling that we are going to have a lot to learn in this area.
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