Key result
The constant sample-time digital tachometer (CSDT) method demonstrated limited error across its entire speed range compared to pulse count and elapsed time methods.
The constant sample-time digital tachometer (CSDT) method provides limited error across all speed ranges compared to pulse count and elapsed time methods for optical-encoder-based speed estimation.
CSDT may enhance encoder-based speed estimation in devices; leaves open clinical validation for cardiovascular applications.
Three speed estimation methodologies: pulse count, elapsed time, and constant sample‐time digital tachometer (CSDT) methods, used with optical incremental encoders, are implemented and compared in a closed‐loop system setup using a specialised Analog Devices CM403f DSP. Dedicated hardware for quadrature encoders on the DSP facilitates the implementation of advanced speed estimation methods, such as the CSDT, by minimising the delay resulting from software intervention. The error of each methodology is evaluated theoretically and experimentally. The CSDT has limited error over all its speed range. The error of the elapsed time method increases as the speed increases. On the contrary, the relative error of the pulse count method (which is often substantial) decreases with increased speed. Several filtering techniques can be used to reduce the error of the elapsed time method; here an oversampling technique is implemented with that aim.
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Vazquez‐Gutierrez et al. (2019) studied this question. Constant sample-time digital tachometer (CSDT) vs. Pulse count and elapsed time methods was evaluated on Speed estimation error. The constant sample-time digital tachometer (CSDT) method demonstrated limited error across its entire speed range compared to pulse count and elapsed time methods.
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