Using cheap DIY peristaltic pump for hydraulic extrusion drive
Recently we worked on the development of a cheap, yet accurate enough system for our bioprinter/paste extrusion printer. Our aim is to develop a modular extruder design where extrusion parameters can be easily controlled and adapted when changing the syringe content.
For this we wish to build a hydraulic system where the syringe piston will be moved according to the amount of water added into the hose. Ignoring the compressibility of the potential air trapped inside the hose and the flexibility of the walls of the hose, we can assume that the extrusion speed is proportional to the speed at which the water is pumped into the system. Moreover, a hydraulic system allows for easy variation of pressure by adapting the hose cross sectional area. This results in no need to modify the pump design to reach higher or lower pressure at the output but just replacing the hose instead.
We took an open source peristaltic pump design and developed it further to the stage of a working prototype. We made the following modifications:
1. Tube support regulation.
The tube support part was modified so that it can be moved towards and away from the bearings by adjusting two screws to squeeze the hose so that we can ensure that the pump is air tight during the circulation.
2. High torque generation.
Paste printing may require high extrusion pressure and therefore high torque generated by the motors. We used Nema17 bipolar stepper motors to drive the pump. The pump design was changed so that it is now driven via shaft and a coupler as the ABS plastic is not stiff enough to hold the torque and gets deformed.
3. Clamping the pump and motor.
The Nema17 and the peristaltic pump were clamped into the aluminium housing to achieve strong enough support for a given torque. We built the aluminium housing out of four parts using a CNC mill.
Overall functionality of the first pump prototype proved to be robust and strong enough. The regulation system of the tube compression inside the pump (so that it is air and water tight) also proved to do the job. The next big step is to test the peristaltic pump output profile at different rotational speeds. The main disadvantage of peristaltic pumps is that they have a pulsed output instead of an even one which would be desired in our case. However, we already found some solutions on how to reduce the pulsation, which we are currently testing and will be implementing them soon.
Check out our blog for further results in the next weeks!