Syringe Driver w/ Acoustic Levitator (bad audio warning!):
Syringe Driver Demo:
About the gears and drive mechanism:
A large gear is attached to the output of the DC motor. This large gear interfaces with a smaller gear which is fitted to a helical corkscrew drive. As the corkscrew spins, it pushes the plunger of the syringe along with it, dispensing liquid. Top and bottom cover plates are fitted around the corkscrew to prevent the corkscrew from bending and to prevent the syringe plunger from slipping over the top of the corkscrew. This design was only tested on low viscosity fluids and there may be an issue if high viscosity fluids were used. I specifically wanted a small footprint for this device. The design of the gears should be substantially improved. One of the photos shows the iterative design process I went through from testing a clip-on syringe piece to a basic syringe holder body to the fully integrated syringe holder and motor mount. (You can also see where my red spool ran out and I switched to black.) The gears in the corner of the image also show change. I didn't take the time to learn how to design gears, and just drew was looked like a gear in CAD. The small, sharp teeth of the first gears didn't work well, so I switched to the larger, rounded gears. While not ideal gears, they work. As I will describe, I did not need a precise gear ratio at the time.
About the application:
I was working on acoustic levitation and a colleague of mine wanted to perform an experiment on levitated drops of a specific chemical in-situ at an x-ray beamline at Argonne National Lab. Due to safety constraints, no human can be in the room while x-rays are present, and the safety process to turn-on x-rays takes over 60 seconds from when you leave the room. We could levitate drops and close the door, but by time we had x-rays, we had missed the interesting bit of science. My colleague had a commercial syringe driver which we were able to use, but it was challenging to work with. Since we were aiming to inject single droplets of liquid, not dispense the whole syringe, we had to find a way to start and stop the syringe driver. While the device didn't have any digital inputs, there was a power-failure mode; if the device lost power while dispensing, it could continue to dispense upon regaining power. All we had to do to remote control the commercial syringe driver was run a power cord out of the room and plug it in to start it dispensing and unplug it to stop. Next was the problem of orientation and mounting. The syringe mounts into the large, heavy syringe driver which usually sits on a table. If we attached a long tube to the syringe with a needle at the end of the tube, as might be typical for injecting drugs into a human patient, we found fine control to be a challenge when turning the device on and off. The moving fluid in the tube wouldn't instantly start and stop, but there would be a lag and recoil as the pressure waves moved through the long, flexible tubing. Eventually we drilled holes in the base of the unit and attached brackets to the whole syringe driver. This let us mount it up in the air, at the angle we wanted, and eliminate the flexible tubing. While this worked, it was very frustrating to achieve fine adjustment of the position of the needle tip. Further, there was no way would be able to fit more than one of these in the space if we wanted to mix drops from two different syringes. Since we didn't need the precise volume control nor the (hopefully) medically certified status of the commercial unit, I reasoned I could build my own syringe driver from scrap parts around the lab, resulting in the project you see here today.
I have a potential application that would require a redesign, but I will save that for another day.