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Message ID: 682     Entry time: Thu Jul 25 22:51:39 2013
Author: Giorgos 
Type: DailyProgress 
Category: SUS 
Subject: Computer Feedback (Integrator & Damping), Motors' Speed and ADC bits/voltage conversion 

Computer Feedback Filter

I installed Linux on my office computer today, because Windows was sometimes crashing. Then, using secure shell (SSH) I remotely accessed the supercomputer that receives the input signal from the HE sensors. With the Foton software, I created a preliminary feedback filter with an integrator and a damping factor. Assuming a normal response function R(s)=1/[m(s2+ωn2-γs)] for our plate, the transfer function is very large near the resonance frequency (where s2 and ωn2 cancel) and at small frequencies (where only the resonance frequency term, presumably small, remains). Therefore, we need our feedback filter to add to the response function of the plate; the integrator --proportional to s--adds a large term near small frequencies, and the damping factor--proportional to s--adds another factor near the resonance frequency. I designed the filter so that the cut-off frequencies occur at roughly 2, 5, 20, and 200Hz. Below are the results. WIth the correct gain factor, we have a unity gain from 2Hz to 5Hz.

Final_TF_of_Integral_and_damping.png

 

DC Motors

We tried to test the motors, but they did not move as fast. Apparently, we had include a 3.6kΩ resistor in series with them, using a 15V source; no wonder they did not work. We replaced the 3.6kΩ resistors with 1kΩ ones and achieved a better movement.

HE sensors output

We compared the bits of the input signal digitally diagnosed with the output signal of the HE signal measured manually with a voltage meter to check whether the correspondence made any sense. I plotted the pair of data ( {millivolts, bits}, ..) and found the best fit for the data; the slope was 1.64 (1mV corresponds to 1.64bits). For our ADC converters, 20V correspond to 216 or (65536) bits, so 1mV corresponds roughly to 3.3bits. However, the bits correspond to the voltage difference, so the actual readings for the bits should be half (1mV=215/20=1.638bits). Our conversion works. 

Simulink

I started using Simulink and looked at Rana's examples. I will keep building our setup with Simulink to ultimately simulate the behavior of our plate.

Attachment 1: Integral_and_Damping_Digital_Filtering_together.png  747 kB  | Show | Hide all | Show all
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