Abstract
In order to improve the performance in the practical engineering applications including so called low-speed video tracking and large-angle swing scanning imaging at the same time for a three-axis universal inertially stabilized platform (UISP), we propose an adaptive nonsingular fast terminal sliding mode control (ANFTSMC) strategy subjected to the uncertain disturbances and input saturation constraints. First of all, a second-order dynamic model is established with uncertain disturbances and input saturation constraints. Secondly, a nonsingular fast terminal sliding mode controller (NTSMC) is constructed to ensure the system error converges to zero fast in a finite time; meanwhile, a novel reaching law based on a modified normal distribution function is designed to adjust the control gain. Thirdly, an adaptive control law is designed to online estimate the parameters of the lumped uncertain disturbances. Additionally, the stability of the control system is proved by Lyapunov theory. Finally, extensive comparative simulations and experiments are carried out, the results comprehensively show the effectiveness and superiority of the proposed control method, which can accelerate convergence, weaken the chattering, and has the better control accuracy and robust performance both in the low-speed tracking and large-angle swing scanning applications. Moreover, the exact dynamic model and the prior knowledge of the upper bounds of the disturbances are not required during the procedure of the controller design, which make it have more extensive application value in practical engineering.
Highlights
Stabilized platform is widely used in the field of modern aerial remote sensing [1,2,3].Its main function is to isolate payloads from external disturbance and ensure the relative stability of the line of sight (LOS) in inertial space, so as to implement diverse missions such as battle reconnaissance, Sensors 2020, 20, 5785; doi:10.3390/s20205785 www.mdpi.com/journal/sensorsSensors 2020, 20, 5785 aerial photography, environmental disaster monitoring, etc
In this paper, aiming at the practical engineering applications, including so called low-speed video tracking and large-angle swing scanning imaging, we proposed an adaptive nonsingular fast terminal sliding mode control strategy for a cantilever three-axis inertially stabilized platform subjected to the uncertain disturbances and input saturation constraints, so as to obtain better control performances
A second-order dynamic model with friction and torques, unmodelled dynamics, external disturbances, and input saturation constraints was established, where the non-smooth input saturation dynamic was approximated by a smooth hyperbolic tangent function, which makes it more convenient in engineering implementation
Summary
Stabilized platform is widely used in the field of modern aerial remote sensing [1,2,3].Its main function is to isolate payloads from external disturbance and ensure the relative stability of the line of sight (LOS) in inertial space, so as to implement diverse missions such as battle reconnaissance, Sensors 2020, 20, 5785; doi:10.3390/s20205785 www.mdpi.com/journal/sensorsSensors 2020, 20, 5785 aerial photography, environmental disaster monitoring, etc. Most typical optical stabilized platforms have integrated multiple payloads to satisfy various surveillance and reconnaissance purposes [2,3]. The total number of payloads is limited by the structural space; on the other hand, the stacking of multiple payloads is redundant for different customers. In order to broaden the range of applications, a three-axis universal inertially stabilized platform studied in this work is designed as an azimuth axis cantilever structure, thanks to the rotation ranges of azimuth, roll and pitch angles are ±180◦ , ±80◦ , and ±45◦ , respectively, and different payloads can be conveniently installed and replaced by the standard interfaces, the UISP integrates the common characteristics of payloads including low-speed video tracking and large-angle swing scanning imaging, which makes it have advantages of lower cost, higher task efficiency, and wider customer groups. With the increasing requirements of information task, higher positioning and tracking performances are needed to adapt to some special applications
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