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In repetitive control (RC), the enhanced servo performance at the fundamental frequency and its higher order harmonics is usually followed by undesired error amplifications at other frequencies. In this paper, we discuss a new structural configuration of the internal model in RC, wherein designers have more flexibility in the repetitive loop-shaping design, and the amplification of nonrepetitive errors can be largely reduced. Compared to conventional RC, the proposed scheme is especially advantageous when the repetitive task is subject to large amounts of nonperiodic disturbances. An additional benefit is that the transient response of this plug-in RC can be easily controlled, leading to an accelerated transient with reduced overshoots. Verification of the algorithm is provided by simulation of a benchmark regulation problem in hard disk drives, and by tracking-control experiments on a laboratory testbed of an industrial wafer scanner.
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... where a new parameter µ ∈ {0, 1} is introduced for switching between estimation use with µ = 0 and compensation use Conventional periodic-disturbance observer [20] No control (c) Results of the conventional methods [15] and [20]. ...
... The frequency response with the QDOB from the external torque v to the angle y was validated and compared with those of the conventional repetitive control [15] and periodicdisturbance observer [20]. Two direct-drive motors connected by a coupling were used, as shown in Fig. 7(a), where the left motor is controlled by the QDOB, and the right motor generated external torque v = a v sin(ω v t). ...
... The proposed QDOB was compared with the conventional methods in Fig. 7(c). The conventional repetitive control [15] showed aperiodic disturbance amplification caused by the trade-off between the wideband suppression and the amplification. The conventional periodic-disturbance observer [20] showed wider suppression around the harmonics and nonamplification of the aperiodic disturbances from 1 to 35 rad/s; however, the harmonic suppression performance was less than that of the repetitive control, the amplification appeared from 35 rad/s, and the high-order harmonic suppression frequencies deviated slightly. ...
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Periodic disturbances composed of harmonics usually appear during periodic operation, impairing performance in mechanical and electrical systems. To improve the performance, control for periodic-disturbance suppression has been studied, such as repetitive control and periodic-disturbance observer. For robustness against perturbations in each cycle, slight changes over cycles, slight variations in the period, and/or aperiodic disturbances, although wideband harmonic suppression is expected, the conventional methods have trade-offs among the wideband harmonic suppression, non-amplification of aperiodic disturbances, and deviation of harmonic suppression frequencies. This article proposes a quasi-periodic disturbance observer to estimate and compensate for a quasi-periodic disturbance. The quasi-periodic disturbance is defined to consist of harmonics and surrounding signals, based on which the quasi-periodic disturbance observer is designed using a periodic-pass filter of a first-order periodic/aperiodic separation filter, time delay integrated with a zero-phase low-pass filter, and an inverse plant model with a first-order low-pass filter. For the implementation of the proposed observer, its Q-filter is discretized by the exact mapping of the s-plane to the z-plane, and the inverse plant model is discretized by the backward Euler method. The experiments validated the frequency response and position-control precision of the quasi-periodic disturbance observer in comparison with conventional methods.
... In order to address these problems, a modified RC scheme has been developed by incorporating a disturbance-observerbased spectrum-selection filtering scheme into the feedforward channel of the feedback control system [262][263][264]. To improve the robustness of CRC against the signal frequency fluctuation, high-order RC schemes are proposed by introducing the actual tracking information of several previous reference periods [265][266][267]. ...
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In repetitive control, the enhanced servo performance at multiple repetitive frequencies is usually followed by undesired error amplifications at other frequencies. This paper presents a new structural configuration of the internal model principle in repetitive control, wherein designers have more flexibility in the repetitive loop-shaping design, and amplification of non-repetitive errors can be greatly reduced. The proposed algorithm is particularly advantageous when repetitive control is required in environments where large amounts of non-repetitive disturbances exist. Verification of the algorithm is provided in a benchmark regulation problem of hard disk drives.
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