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:


Comments

Post a Comment

Popular posts from this blog

VFD control with Arduino using RS485 link

-
Image
Variable Frequency Drives ( VFD ) allow the control of spindles so speed can accurately be controlled and a detailed acceleration profile for the spindle and reverse rotation can all be handled. In essence a VFD is an three phase inverter for three-phase AC motor. I am using a popular (I mean cheap) Chinese VFD and though the reference manual is not great, I could see there is a built-in RS-485 port. I usually control the start, stop and speed selection using the keyboard on the unit but I thought it will be more useful if I could control everything from the same Arduino is doing our CNC table control. Some cheap RS-485 off eBay and some lines of code later, I can start, stop and change the speed from an Arduino. What a cool thing to have! Some configuration of your VFD are needed before you can use it like that.  You need to set PD163=1 (I am using address 1 in the code). PD=164=1 (for setting serial to 9600bps) and PD165=0 (for using ASCII and 8N1 character format)
Read more

How to get sinusoidal s-curve for a stepper motor

-
Image
After some experimentation, and delving a bit into the math of motion, I realized there can be a significant difference on the motion of a machine by just making small changes. A common and popular approach to smooth one axis of motion is to use a trapezoidal speed pattern, where acceleration and deceleration are uniformly accelerated movements (aka constant acceleration motion) separated by a portion happening at cruising speed. The problem comes with the fact that, while that approach is simple to understand and to code, it does contain sudden changes in the acceleration, that show as spikes on the acceleration derivative, called jerk. These sudden changes in the acceleration translate into undesired vibration in our machines. Most of that can be eliminated by selecting a motion pattern that does not contain sudden changes of acceleration. If we chose a mathematical function for our speed whose second derivative is continuous, then we reduce system vibration quite a lot. One ma
Read more

Importing OpenSCAD designs into Onshape

-
Image
After using Onshape CAD software for a while I am really fond of it. So one natural thing to do, specially once they have released the Instructor's kit is to start using it in the classroom too. But one thing I was not so sure how to do was to use old designs I made using OpenSCAD. It does not mean I am completely quitting using OpenSCAD but suddenly I can see I can do assemblies in Onshape that will look quite nice for showing and documentation purposes if only I could easily import from OpenSCAD. I am glad to report that the route OpenSCAD --> FreeCAD --> Onshape worked brilliantly. Even more when a few tricks were applied. While some people suggest to import CSG files from OpenSCAD to FreeCAD, I have had more success by directly importing SCAD files into FreeCAD. One trick that worked well for me was to get rid of $fn references, so now circles become real circles (or cylinders) in FreeCAD. If a part keeps some $fn references then your cylinders or circles wi
Read more