Design and control of a fast steering mirror based on flexible supports and piezoelectric ceramic actuators.

The use of the fast steering mirror in an optical path requires strict volume control, and traditional structures have low space-utilization efficiency, resulting in traditional actuators having limited output in narrow spaces. The design in this paper adopts a combination of flexible universal supports and piezoelectric ceramic actuators, greatly reducing the layout space of the rotating-shaft system. We accurately model the design structure and develop closed-loop control methods to further improve the closed-loop control accuracy of the system. The experimental results indicate that the developed control method effectively improves the response speed and bandwidth and thus has good potential for use in engineering applications.

Liquid crystal spatial light modulator based non-mechanical beam steering system fractional-order model.

The liquid crystal spatial light modulator (LCSLM) is an optical device that can realise non-mechanical beam scanning. However, the traditional integer-order model cannot adequately characterise the dynamic performance of LCSLM beam steering because of the viscoelasticity of liquid crystals. This paper uses the memory characteristics of fractional calculus to construct a fractional constitutive equation for liquid crystals. Combining this equation with the LCSLM beam steering principle, a fractional-order model of the beam steering system is established, and the Legendre wavelet integration operational matrix method is used to estimate the model parameters. In addition, we established a test platform for the dynamic characteristics of LCSLM beam steering system and verified the effectiveness of the established model through experiments. The fitting effects of the integer-order and fractional-order models are compared, and the influence of different model orders on the dynamic performance of beam steering is analysed. Experimental results show that the fractional-order model can accurately describe the dynamic process of beam steering, and this model can be applied to the study of LCSLM-based two-dimensional non-mechanical beam steering control strategies to achieve fast, accurate, and stable beam scanning.

Diffraction characteristics of a non-mechanical beam steering system with liquid crystal polarization gratings.

The non-mechanical beam steering system is composed of multiple liquid crystal polarization gratings (LCPGs) cascaded by binary or ternary technologies. However, cascading multiple LCPGs cause the beam from one LCPG to obliquely enter the subsequent LCPGs, changing their diffraction efficiency and working voltage at different steering angles. This paper uses the elastic continuum theory of liquid crystals to simulate the tilt angle of liquid crystal molecules under different voltages. The transmission process of the beam in the system at oblique incidence is described with an extended Jones matrix, and the highest diffraction efficiency and working voltage of each LCPG at different steering angles are calculated using vector diffraction theory. It is convenient to calibrate the LCPGs' working voltage and analyze the system's diffraction characteristics. In addition, we used an improved binary cascade technology to design a LCPG non-mechanical beam steering system with a steering angle of ±10° and an angular resolution of 0.67°. Compared with binary cascade, this technology can effectively reduce the number of cascaded devices and increase the system throughput under the same maximum beam steering angle and angular resolution.

Additional fractional gradient descent identification algorithm based on multi-innovation principle for autoregressive exogenous models.

This paper proposed the additional fractional gradient descent identification algorithm based on the multi-innovation principle for autoregressive exogenous models. This algorithm incorporates an additional fractional order gradient to the integer order gradient. The two gradients are synchronously used to identify model parameters, thereby accelerating the convergence of the algorithm. Furthermore, to address the limitation of conventional gradient descent algorithms, which only use the information of the current moment to estimate the parameters of the next moment, resulting in low information utilisation, the multi-innovation principle is applied. Specifically, the integer-order gradient and additional fractional-order gradient are expanded into multi-innovation forms, and the parameters of the next moment are simultaneously estimated using multi-innovation matrices, thereby further enhancing the parameter estimation speed and identification accuracy. The convergence of the algorithm is demonstrated, and its effectiveness is verified through simulations and experiments involving the identification of a 3-DOF gyroscope system.