Measuring velocity by differentiation of analog encoder signals

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In this report a new method for measuring velocities has been introduced. During the research in literature an overview has been made of the existing methods of measuring velocities. From this research, it can be concluded that a lot of existing approaches only work in specific settings. Besides this, it can be concluded that the proposed new method does not exist yet. The proposed method has been explained in theory and it has been theorized that this new method is not influenced by at least one dominant error source, namely the phase errors in the encoder. In addition, a calibration method has been introduced that makes it possible to use the proposed method accurately. This method works independent of measurement errors near the peaks of the encoder signals, like for example errors caused by saturation of the light sensors inside an encoder. In addition it has been shown that the proposed methods can be easily adapted to work with sawtooth signals instead of sinusoidal signals. This eliminates the errors caused by waveform distortion that used to be present when encoders are used that output sawtooth signals. And finally it has been theorized that misalignments of the encoder slits no longer influence the velocity measurement. Simulation and experiments using the proposed methods confirm that measuring the velocity by differentiation of the separate encoder channels is possible. It has also been shown that the sampling frequency limits the maximum velocity, because the differentiation of an encoder channel becomes inaccurate when insufficient samples are available per increment. In addition it has been shown that quick changes in the velocity do not influence the accuracy of the measurement. It has also been shown that for sawtooth signals, it is now possible to measure velocity without being disturbed by this waveform distortion. This made it possible to measure the velocity with a 100 slits analog encoder with about the same accuracy as with a high resolution TTL encoder (which measures 80000 counts per rotation).
Original languageEnglish
Place of PublicationEindhoven
PublisherEindhoven University of Technology
Number of pages47
Publication statusPublished - 2013

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