On Friday, March 1, 2013 11:45:38 AM UTC-8, John Griessen wrote:
On 03/01/2013 06:24 AM, Patrik D'haeseleer wrote:
> I think modifying an actual CD drive for polar printing onto a standard Petri dish would be very difficult.
He was pointing out that it is easy. The linear drive from the CDROM is one axis -- you locate it
from center to radius MaxR, then install a stepper motor with stout shaft under point called center,
then attache a petri dish holder to the stout shaft. Voila -- petri dish coordinates.
I'm not saying it's impossible, but it would definitely be harder than the way we did it. For one, you'd have to take the whole thing out of the CD drive chassis anyway, because there's no way you'd be able to fit this entire contraption "in situ", as it were. Then you'd have to engineer a turntable from scratch, because you should probabaly use a stepper motor instead of the spindle motor in the drive. You'll also need some way to keep the Petri dish in place as it's spinning, because I don't think you'd want to use the same clamping mechanism used to hold a CD.
In the end, it comes down to one linear actuator + a Petri dish turn table built from scratch, versus two linear actuators. Disassembling and controlling two linear actuators is no harder than one (which you'd need for polar coordinates anyway), so the second solution is definitely easier to build. Not to mention the issues you may have with variable resolution in polar coordinates, having to do coordinate transformations for everything, the ready availability of cartesian-based stepper controllers and software from the 3D printing field, etc.
I really would love to see someone build a bioprinter that uses polar coordinates. But so far I haven't heard any arguments to make me think that approach would be any easier or better than what we did.
If someone feels inspired - go for it though!
Patrik
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