Fighting with computers

Computers are not always friendly.

Tuesday, March 11, 2014

Of pumps and stepper motors

I have been quite busy lately due to several factors. One of them things not working out as expected. Of course every failure is a learning opportunity and this case, my chance to get familiar with the world of hydraulics and fluid dynamics. As a Computer Scientist, you do not get any training on that matter (other than maybe learning about fans for cooling down electronic parts).

I have been working for more than a year on a project where the least I was expecting was to have trouble with what it is eating a lot of my time lately: pushing a viscous fluid in a precise, controlled-way, from a container to the printing area of a 3D-printer we have designed and successfully built as part of our research project.

If you are familiar with 3D printing, you can think of us trying to create a reliable paste extruder. There are many open paste extruder designs out there, but many are designed for not so viscous pastes or liquids. Others can handle viscous fluids but only a very small amount of it (ie. syringe-based ones). And one effect I have learned is the more viscous the fluid the less likely is to move through a narrow tube. And every inch of tube will increase the need of output pressure in your pump.

Another thing I have learned is that pressurized tubes and 3D printed parts are not a good match, so it is difficult to create your own pump. Or more exactly, it is difficult to achieve a good performance level (ie pressure) with your 3D printed parts.

So I kind of gave up and looked around for pump manufacturers, but those that have small pumps could not work with the viscosity levels I needed. After getting some help from an hydraulics professor, the nice people from Food Technology department came to the rescue and lend us a mono pump that worked great with our material. The only problem being that the pump was powered by a 1CV AC motor driven by a variable frequency drive (VFD) to allow the user select different speeds.

But what we needed was a pump that can start and stop on a dime and that we can precisely control the material flow. That is was not possible with the setup of our pump. So our next step is to replace that motor with an stepper motor we can control.

In the previous blog entry I was visiting a company in Rome helping them out to put to work their home-built CNC machine. They have used powerful nema34 motors.

I thought I could use similar steppers, reaching up to 12.5 Nm of torque, to move a mono pump. The only current problem is that we run out of funds. So I am now in the process of piecing together the paperwork for a funding round to see if we can put the thing together and finally finish our research project successfully.

Till then, most of what I can show does not look pretty:


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