Archive for October, 2010

Aerodynamic calibration rig

October 6th, 2010 by Ivan Lakhturov | 0 Category: Programming | Tags:

More than five years ago I worked for "DX-Complexes" and "Spectromed-UA". Here is a video about one of the projects I accomplished there. This is the aerodynamic calibration rig for metrological testing of spirographs. (What is a spirograph? See spirometry topic at Wikipedia).

There is no sound in this video, cause we wanted to make a promo-video out of this, and some voiceover was supposed to be done later. But the device was too specialized, so we decided not to. So, let it be an advertisement for myself.

The schematics is in the illustration:

I operate the control program, written in C#, which communicates by COM-port with the embedded program in C. Both are written by me. Then this embedded program drives the device you see on video. It consists of electronics, the engine, worm gear and a piston going forwards and backwards in a plexiglass cylinder. The air flow generated by the device is registered with a spyrograph, connected via USB-port to another PC, where a third-party spirometry program is installed (visible in the second part of video).

Naturally, to verify the accuracy of a spiro-device, the calibration rig has to be in sctrict accuracy limits itself. It wasn't so trivial to achieve those specs. I remember one of the problems with overjumps: when you turn off the power of an engine, the piston doesn't stop momentarily due to inertia and slips further. What's the solution? To apply maximal reverse force via the engine as soon as the piston is supposed to stop. A period of time when we apply that reverse force depends on a few hard-to-estimate factors, so it was easier to fit this empirically.

This device can be considered as a very simple 'robot' with just one degree of freedom. Despite simplicity, it took us (2 people, me for software and a colleague for electronics and mechanics) around half a year of occasional work to get it done. Nevertheless, my friends in Ukraine report this device is still in field, they use it up to now without any complaints rising.