Yongqiang Ye

Design and experiments of anticipatory learning control: frequency-domain approach

A frequency-domain design is presented for the anticipatory learning control. Convergence conditions are derived in terms of two design parameters, the lead-time and the learning gain. For minimum phase systems, the design of the anticipatory learning control in the frequency domain is decoupled into a two-step procedure. The design is robust against uncertainties in system modeling. The effectiveness of the anticipatory learning control is demonstrated by an example and experiments. Comparisons of the anticipatory learning control with the conventional P-type, D-type, and PD-type learning control highlight the differences between these close yet distinctive approaches.

Wavelet transform-based frequency tuning ILC

A discrete wavelet transform-based cutoff frequency tuning method is proposed and experimental investigation is reported. In the method, discrete wavelet packet algorithm, as a time-frequency analysis tool, is employed to decompose the tracking error into different frequency regions so that the maximal error component can be identified at any time step. At each time step, the passband of the filter is from zero to the upper limit of frequency region where the maximal error component resides. Hence, the filter is a function of time as well as index of cycle. The experimental results show that this method can suppress higher frequency error components at proper time steps. While at the time steps where the major tracking error falls into lower frequency range, the cutoff frequency of the filter is set lower to reduce the influence of noises and uncertainties. This way, learning transient and long-term stability can be improved.

Fractional zero-phase filtering based on the Riemann-Liouville integral

In this paper, two novel and computationally efficient, zero-phase filtering techniques are proposed based on the Riemann-Liouville integral. Thanks to the reverse phase characteristics of backward filtering, an overall zero-phase effect can be achieved by cascading a fractional forward filtering with a fractional backward filtering, and vice versa. The fractional zero-phase filtering can not only effectively suppress the phase distortion in the filtering process but also better enhance the compromise capability between signal denoising and signal information retention than the conventional filtering methods do. The proposed methods are evaluated on Electrocardiogram (ECG) signal, by adding disturbance, random, and white Gaussian noises to visually clean ECG record, and studying SNR and MSE of the filter outputs. The results of the study demonstrate superior performances compared with conventional signal denoising methods, such as Riemann-Liouville integral filtering, Grunwald-Letnikov integral filtering, zero-phase Butterworth filtering, and zero-phase average window filtering.

Parallel-type fractional zero-phase filtering for ECG signal denoising

Abstract In this paper, a parallel-type fractional zero-phase filtering technique based on the center Grunwald–Letnikov differintegrator is proposed. We first present a left and a right Grunwald–Letnikov differintegrators, which are generalized magnitude-and-phase modulations. By using them in parallel we obtain a center Grunwald–Letnikov differintegrator, essentially a parallel-type fractional zero-phase filter. And then a center symmetrical convolution mask is constructed to implement the proposed fractional zero-phase filter. The method presented eliminates the phase distortion while offering a better compromise between signal denoising and signal information retention than conventional filtering methods. To illustrate this, the differintegrator and conventional filters were applied to electrocardiogram signals. The results indicate that the method we propose has superior performance compared with conventional denoising methods.

Better robot tracking accuracy with phase lead compensated ILC

In this paper, a learning control scheme is proposed to improve robot tracking accuracy. Through the analysis in frequency domain, it is shown that phase lead compensation can broad the learnable frequency band of a learning control system. The phase lead compensation is realized by phase lead filtering the error of last repetition. In theory a filter whose phase difference to the system is within /spl plusmn/90/spl deg/ can be a candidate for the phase lead compensation process. Experimental results on an industrial robot system show that the proposed scheme is both effective and robust against dynamic modeling errors.

Time domain passivity control of teleoperation systems with random asymmetric time delays

In this paper, the power and energy behavior of bilateral communication with time delay is analyzed. Time delay may result in activeness and in turn generate energy. In a bilateral system, the energy generated by time delay communication can destabilize the whole system. Based on the power based time domain passivity control previously proposed by the authors, a time domain passivity control approach is derived for bilateral communication. After the compensation of time domain passivity control, the bilateral communication is kept passive at every time instant. Then the approach is applied to a bilateral teleoperation system with random asymmetric time delays. Simulation results verify the effectiveness of the approach.

Learning more frequency components using P-type ILC with negative learning gain

In this paper, through the analysis on error contraction conditions in the frequency domain, it is found that a negative learning gain can be used in iterative learning control (ILC). The proper use of negative learning gain can increase the learnable frequency range. The conventional P-type learning control with both positive and negative gains is used over multichannel learnable bands. The design procedure is demonstrated via an example of robot joint control. Two channels, one uses a positive learning gain and the other a negative learning gain, substantially increase the frequency components to be learned by the P-type controller. Experimental results verify the effectiveness of using a negative learning gain.

Cutoff-Frequency Phase-In Iterative Learning Control

In this brief, a cutoff frequency phase-in iterative learning control (ILC) method is proposed to deal with initial position offset and improve tracking accuracy. In the proposed method, the cutoff frequency of the filter for tracking error is time-varying and follows a predefined profile. The cutoff frequency at initial phase of each operation is high to allow learning system suppress the initial position offset and its influence to improve tracking performance. High initial cutoff frequency results in a quick error decay in the initial phase of operation and also prevents error accumulation in later phase of operation so that good learning transient can be expected at the same time. Profile design and parameter selections are discussed. Experimental results demonstrate the effectiveness of the proposed method.

Two-mode ILC with pseudo-downsampled learning in high frequency range

In this paper, an iterative learning control scheme that combines the designs in the frequency and time domains is proposed to improve the tracking accuracy. The scheme separates the error signals into low and high frequency band error components and employs different learning mechanisms to deal with these error components, respectively. On the low frequency band, a conventional iterative learning control is used. On the high frequency band, a downsampled learning is implemented to suppress more error components to generate a high tracking accuracy. We will address in detail the issues of signal separation, learning controller design, convergence analysis, and experimental verification of the proposed scheme.

Design of linear phase lead repetitive control for CVCF PWM DC-AC converters

A linear phase lead repetitive controller is introduced for the constant-voltage constant-frequency (CVCF) pulse-width modulated (PWM) DC-AC converters. The design of the repetitive control (RC) is discussed. Since phase lead can compensate the phase lag of feedback control system, more harmonics can he suppressed which leads to a low total harmonic distortion (THD) of the output voltage in the presence of nonlinear load disturbances and parameter uncertainties. Simulation results show that this method has a fast response and good tracking accuracy.