Abstract
The accuracy of feedforward control model including system time-delay significantly affects the position tracking performance in a precision motion system. In this paper, an iterative tuning method for feedforward control with precise time-delay compensation is proposed. First, considering system time-delay from actuator, sensor, calculation, and communication in real platform, a feedforward control model with time-delay compensation is established, and a nonlinear objective function with time-delay is designed based on the measured data of a finite time task, to minimize the position tracking error. Second, in order to deal with both the nonlinear objective function and also unknown disturbances and noise in the real system, an optimization strategy combining the Gauss–Newton iterative (GNI) scheme and instrumental variable (IV) is proposed to realize the unbiased estimation of the feedforward parameters and precise delay time. Finally, with the identified feedforward control parameters, the precise system time-delay which is a nonintegral multiple of the sampling period is compensated accurately for the feedforward control with accurate path planning time-shift in the implementation. The effectiveness of the proposed feedforward parameter tuning and precise time-delay compensation scheme is verified by the simulation and also experimental result on a precision motion platform with obvious position tracking performance improvement.
Highlights
In real control systems, the sensors, actuators, data communication, and signal processing can all generate some time-delay [1, 2]
The feedforward control is introduced to compensate the time-delay by injecting the control signal in advance [5], which can significantly improve the tracking accuracy. is feedforward method is widely used in the high-speed and high-precision motion control systems such as photolithography equipment [6, 7], machine tool [8], and atomic force microscope system [9]
In terms of parameter estimation variance, an iterative refined instrumental variable is constructed to achieve optimal accuracy [13, 14], and the Kalman filtering (KF) approach is introduced into the IVIFT framework, which enables unbiased parameter estimation with zero asymptotic variance [15]. en, the iterative feedforward tuning (IFT) is extended to flexible motion systems
Summary
The sensors, actuators, data communication, and signal processing can all generate some time-delay [1, 2]. E main contributions of this paper are as follows: (1) fully considering the comprehensive system time-delay from actuator, sensor, calculation, and communication in real platform, a nonlinear objective function is proposed based on the measured data of a finite time task for iterative tuning of the feedforward parameters, to minimize the position tracking error; (2) in order to handle the proposed nonlinear objective function and tolerate unknown disturbances and noise in real system, a desired optimization strategy combining the Gauss–Newton iterative (GNI) scheme and instrumental variable (IV) is proposed in this paper to realize the unbiased estimation of the feedforward parameters and precise delay time, which is the key innovation of this paper; (3) the identified precise system time-delay which is a nonintegral multiple of the sampling period, is exactly compensated in the feedforward control with accurate path planning time-shift. E paper is organized as follows: in Section 2, the mathematical model of the feedforward controller with time-delay compensation is established, and a feedforward parameter tuning method considering the time-delay is elaborated; in Section 3, a discrete realization method of feedforward control with time-delay compensation is proposed; in Sections 4 and 5, the effectiveness of the proposed method is verified in the simulation example and experiment on an air floating precision motion platform
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