I'm not sure what you mean by "contact dispensing" but the peristaltic pump approach can eject droplets into the air at a pretty good velocity, centimeters away from a well. i.e. either droplets or a stream of liquid can fly many centimeters beyond the end of the tube. Probably depends on the tip shape but I doubt it's rocket science either. Peristaltic pumps with the right tubing can generate good amount of pressure. The design of the 'wheel' of the pump and the gearing/type of the motor determines the steadiness of the stream (i.e. does the pressure of the stream oscillate or is it steady pressure). Stepper motor for example creates more variation in pressure since the motor "locks" to the magnet at each step. When I asked the lead designers at a couple different pump companies why they didn't use DC motors for smooth dispensing they said: "Well our engineers didn't want to bother with PID controllers and it doesn't really matter anyway [i.e. doesn't affect results]". Naturally using a dc motor with PID algorithm would be part-wise $$ cheaper (and electrically less power) than a stepper. ..that's a whole other tangent..
If I remember right, inkjet heads have good velocity & accuracy many centimeters away too. I think there was a graffiti artist who was using an inkjet head to spray ink a foot away from the platform surface without any slop.
If the goal is to make a 3D bio-printer then the next question is whether the printer should move the print head vertically or move the platform vertically. I think repraps faced the same conundrum...
## Jonathan Cline
## jcline@ieee.org
## Mobile: +1-805-617-0223
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On Friday, March 1, 2013 11:39:20 AM UTC-8, John Griessen wrote:
On 03/01/2013 02:58 AM, Jonathan Cline wrote:
> The liquid dispensing could be done by very small diameter tubing run through a peristaltic pump from a large well/beaker source
> which dispenses drops as needed from above
Like Nathan said. Are you proposing contact dispensing to transfer liquid that otherwise would be trapped by surface tension?
The jet part of ink jet overcomes surface tension and gives you contactless dispensing.
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