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Tilli A., Montanari M.
"A low-noise estimator of angular speed and acceleration from shaft encoder measurements"
Type Conference
Author(s) Tilli A., Montanari M.
Title A low-noise estimator of angular speed and acceleration from shaft encoder measurements
Editor 9th Mediterranean Conference on Control and Automation (MED '01), Dubrovnik, June 27-29, 2001
Keywords real differentiators, nonlinear observers, encoder measurements, velocity estimation, acceleration estimation

This paper deals with the differentiation of discrete-time, quantized signals provided by encoder measurements. In particular, speed and acceleration estimation with large bandwidth is required for feedback control in automation and robotics applications. The main problem in the differentiation of the encoder measurements is to combine the demanded fast dynamics and the strong filtering of the quantization noise.

An innovative speed-acceleration estimator is presented. The proposed scheme relies on typical filtered differentiators nonlinearly combined with a state-variable filter. The former is a pure differentiator cascaded with a low-pass filter and produces a strongly filtered estimation, with large noise attenuation ("slow filter"); the latter is realized as a non-model-based position/speed observer characterized by a large bandwidth, in order to track fast signal transients ("fast filter"). The estimation produced by the "slow filter" is used as a feed-forward action in the "fast" one and a dead-zone element is inserted to inhibit the fast filter when the position estimation error is lower than a fixed level. In this way, the resulting estimator has a variable bandwidth depending on the harmonic content of the encoder signals. This solution is characterized by low noise and large bandwidth and guarantees very good performance in terms of signal to noise ratio. The proposed solution is suitable for applications where the mechanical characteristics of the plant are uncertain. In fact, no plant model is required. Two versions of the estimator are presented and compared. The first one gives only a speed estimation, while the second provides also an acceleration signal.

The performance of the proposed solutions have been tested by means of both simulative and experimental tests. An incremental 5k c/r encoder and a high resolution sine/cosine encoder have been considered.

Document d436.Document.pdf (383568 bytes)
Year 2001

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