This paper studies the impact of nonlinear distortions on linear system identification. It collects a number of previously published methods in a fully integrated approach to measure and model these systems from experimental data. First a theoretical framework is proposed that extends the linear system description to include the impact of nonlinear distortions: the nonlinear system is replaced by a linear model plus a 'nonlinear noise source'. The class of nonlinear systems covered by this approach is described and the properties of the extended linear representation are studied. These results are used to design the experiments; to detect the level of the nonlinear distortions; to measure efficiently the 'best' linear approximation; to reveal the even or odd nature of the nonlinearity; to identify a parametric linear model; and to improve the model selection procedures in the presence of nonlinear distortions.

Identification of Linear Systems with Nonlinear Distortions

A two-wheeled inverted pendulum robot with friction compensation

This paper presents a compound control strategy for high-precision disturbance compensation in order to improve control accuracy of a three-axis gyro-stabilized camera mount. The influences of unknown disturbances are first analyzed, and the structural properties of the disturbances are given. For these disturbances that can be described by an exosystem, the internal model principle-based controllers are designed to eliminate the influences. For others, a general polynomial function is used to approximate them and a kind of proportional multiple-integral observer-based control method is adopted to estimate and compensate them. Finally, to verify the effectiveness and superiority of the compound control strategy, comparative experiments between the traditional methods and the proposed one have been carried out. Experiments with the proposed method demonstrate stronger disturbance rejection capability and better steady accuracy.

High-Precision Disturbance Compensation for a Three-Axis Gyro-stabilized Camera Mount

Gyro-stabilized camera mounts are used to maintain and stabilize airborne remote sensing sensors, such as aerial cameras, light detection and ranging, and imaging spectrometers, for the purpose of isolating the line-of-sight of optical sensors from disturbing aircraft movements. However, it is difficult to achieve accurate line-of-sight pointing and even the system stability cannot be guaranteed due to the influences of unknown disturbance, such as mass imbalance, gimbal friction, aircraft attitude turbulence and model uncertainty. In order to realize high-precision disturbance rejection and robustness stability, a kind of compound control system is configured and designed in the framework of active fault-tolerant control. The basic idea of this paper is to handle the disturbance as a fault for disturbance compensation by applying online fault estimation and accommodation. Based on H∞ norm sub-optimization, a robust disturbance observer is designed to estimate the fault and then a fault compensator is emp...

Jan Salášek

Papers

HOSIDF-based feedforward friction compensation in low-velocity motion control systems