Inertially Stabilized Platform Research Articles

Design and implementation of continuous finite-time sliding mode control for 2-DOF inertially stabilized platform subject to multiple disturbances

Control performances of inertially stabilized platforms (ISPs) are always affected by various disturbed phenomena such as cross-couplings, mass unbalance, parameter variations, and external disturbances in real applications. To improve the dynamic response and the disturbance rejection ability of the ISP, a continuous finite-time sliding mode control (SMC) approach with cascaded control structure is proposed. By constructing a finite-time disturbance observer, the multiple disturbances are precisely estimated in real time without the complex modeling and calibration work. Under the field oriented control framework, for the stabilized loop subsystem, an improved super-twisting controller incorporating the disturbance estimates is developed whereas for the current loop subsystem, the super-twisting control method is directly employed. Finite-time convergence of the inertial angular rates is guaranteed with the continuous control action such that chattering is alleviated remarkably. Moreover, by utilizing the manner of disturbance compensation, the feedback control gains can be tuning down without sacrificing the disturbance rejection ability. Comparative experiments are performed to verify the effectiveness of the proposed control approach.

A least mean square based active disturbance rejection control for an inertially stabilized platform

Inertially stabilized platform (ISP) is widely used in aerial remote sensing for stabilizing imaging sensors to improve imagery quality. Due to the nonlinearity, time variation, and disturbances of the ISP system, conventional feedback control algorithms cannot achieve precise attitude control. To realize the control performance with fast dynamic response and high stabilization precision, a least mean square based active disturbance rejection control (LMS-ADRC) system is designed to reject multiple disturbances. In particular, the servo system model of the ISP is firstly established. Then, based on the model, the LMS-ADRC controller is designed, in which a least mean square based approach is proposed to estimate the control loop gain. The applicability of the proposed method is validated by a series of simulations and vehicle experiments, and significant improvements are observed in the presence of model uncertainties and external disturbances comparing to the traditional ADRC and PID controllers.

A GA-based parameters tuning method for an ADRC controller of ISP for aerial remote sensing applications

This paper presents a parameters tuning method based on the genetic algorithm (GA) for an active disturbance rejection control (ADRC) of a three-axis inertially stabilized platform (ISP) with imaging sensors. To improve the stabilization accuracy and robustness of an aerial ISP under multi-source disturbances environment, an ADRC control scheme is first proposed. Then, to accurately identify and tune the parameters in the ADRC controller, a GA-based parameters tuning method is proposed. In this way, the performance of the ADRC is superior to the empirical method. To validate the proposed method, the simulations and experiments are carried out. The results show that the proposed ADRC with GA-based parameters tuning method has significant disturbance rejection ability which can improve the stabilization accuracy obviously. Compared with the ADRC with empirically tuning method, the stabilization error (RMS) under movable base is decreased up to 50.09%.

An Improved Fuzzy Neural Network Compound Control Scheme for Inertially Stabilized Platform for Aerial Remote Sensing Applications

An improved fuzzy neural network (FNN)/proportion integration differentiation (PID) compound control scheme based on variable universe and back-propagation (BP) algorithms is proposed to improve the ability of disturbance rejection of a three-axis inertially stabilized platform (ISP) for aerial remote sensing applications. In the design of improved FNN/PID compound controller, the variable universe method is firstly used for the design of the fuzzy/PID compound controller; then, the BP algorithm is utilized to finely tune the controller parameters online. In this way, the desired performances with good ability of disturbance rejection and high stabilization accuracy are obtained for the aerial ISP. The simulations and experiments are, respectively, carried out to validate the improved FNN/PID compound control method. The results show that the improved FNN/PID compound control scheme has the excellent capability in disturbance rejection, by which the ISP’s stabilization accuracy under dynamic disturbance is improved significantly.

A High-Precision Control Scheme Based on Active Disturbance Rejection Control for a Three-Axis Inertially Stabilized Platform for Aerial Remote Sensing Applications

This paper presents a high-precision control scheme based on active disturbance rejection control (ADRC) to improve the stabilization accuracy of an inertially stabilized platform (ISP) for aerial remote sensing applications. The ADRC controller is designed to suppress the effects of the disturbance on the stabilization accuracy that consists of a tracking differentiator, a nonlinear state error feedback, and an extended state observer. By the ADRC controller, the effects of both the internal uncertain dynamics and the external multisource disturbances on the system output are compensated as a total disturbance in real time. The disturbance rejection ability of the ADRC is analyzed by simulations. To verify the method, the experiments are conducted. The results show that compared with the conventional PID controller, the ADRC has excellent capability in disturbance rejection, by which the effect of main friction disturbance on the control system can be weakened seriously and the stabilization accuracy of the ISP is improved significantly.

An improved cerebellar model articulation controller based on the compound algorithms of credit assignment and optimized smoothness for a three-axis inertially stabilized platform

An improved cerebellar model articulation controller (CMAC) based on the compound algorithms of credit assignment (CA) and optimized smoothness (OS) is proposed to improve the control performances of a three-axis inertially stabilized platform (ISP). On the basis of both advantages of CA and OS algorithms, the improved CMAC neural network controller can deal with the disadvantages of conventional CMAC in learning interference and output fluctuation. As a result, the main dynamic performances of the ISP control system are systematically promoted. To verify the method, the simulations and experiments are carried out respectively, in which the LuGre friction model is introduced to represent the main disturbances. The results show that the CA&OS-CMAC controller can efficiently restrain the nonlinear disturbances and obviously improve the ISP's pointing precision and output smoothness. Compared with the conventional CMAC controller, the root-mean-square (RMS) errors of tracking the angular position under the static base swinging and dynamic base leveling conditions are reduced by 17.17% and 30.55%, respectively.

Heterogeneous Nonlinear Systems Synchronization Based on Adaptive Super Twisting

In this work, the synchronization of a group of heterogeneous uncertain nonlinear systems is addressed. A strategy based on adaptive super twisting algorithm is proposed, in order to synchronize the outputs of the heterogeneous systems. With the aim of implementing the proposed control strategy, unmeasurable states are estimated by means of high-order sliding modes differentiators. This control scheme increases robustness against unknown dynamics and disturbances, whose bounds are not required to be known. Finally, experimental results for synchronizing a heterogeneous system platform, constituted by an inertial stabilization platform (ISP) and a helicopter of two degrees-of-freedom (DOF), are used to illustrate the performance of the proposed control scheme.

A Novel Separated Position and Orientation System Integrated with Inertially Stabilized Platform

Considering the application requirements of independent imaging payloads design, a novel scheme of separated position and orientation system (POS) is proposed, in which the high-precision inertial sensors of traditional centralized POS fixed on the imaging payloads are mounted on three gimbals of the inertially stabilized platform (ISP), respectively, and make them integrated. Then, the kinematics model of the ISP system is built to transmit the inertial information measured by separated inertial sensors mounted on ISP gimbals and flight body to the imaging payloads, calculating the position and attitude of the imaging payloads to achieve the function of separated POS. Based on the model, a series of simulations indicate that the precision difference between separated system and centralized system is ignorable under the condition of angular motion and variable velocity motion. Besides the effective function equal to traditional centralized system, the separated POS enhances the integration with the ISP. Moreover, it improves the design independence of the imaging payloads significantly.

An Adaptive B-Spline Neural Network and Its Application in Terminal Sliding Mode Control for a Mobile Satcom Antenna Inertially Stabilized Platform.

The mobile satcom antenna (MSA) enables a moving vehicle to communicate with a geostationary Earth orbit satellite. To realize continuous communication, the MSA should be aligned with the satellite in both sight and polarization all the time. Because of coupling effects, unknown disturbances, sensor noises and unmodeled dynamics existing in the system, the control system should have a strong adaptability. The significant features of terminal sliding mode control method are robustness and finite time convergence, but the robustness is related to the large switching control gain which is determined by uncertain issues and can lead to chattering phenomena. Neural networks can reduce the chattering and approximate nonlinear issues. In this work, a novel B-spline curve-based B-spline neural network (BSNN) is developed. The improved BSNN has the capability of shape changing and self-adaption. In addition, the output of the proposed BSNN is applied to approximate the nonlinear function in the system. The results of simulations and experiments are also compared with those of PID method, non-singularity fast terminal sliding mode (NFTSM) control and radial basis function (RBF) neural network-based NFTSM. It is shown that the proposed method has the best performance, with reliable control precision.

A compound scheme on parameters identification and adaptive compensation of nonlinear friction disturbance for the aerial inertially stabilized platform

A compound scheme is proposed to compensate the effect of nonlinear friction disturbance on the control precision of a three-axis inertially stabilized platform (ISP) for aerial remote sensing applications. The scheme consists of friction parameters identification and adaptive compensation. A LuGre model-based ISP friction model is first developed. Then, a comprehensive experimental scheme is proposed to obtain the static friction parameters. Further, the dynamic parameters are identified by experiments and dynamic optimization. On the basis of identified parameters and Lyapunov stability theory, a backstepping integral adaptive compensator is designed to compensate the nonlinear friction disturbance. Simulations and experiments are carried out to validate the scheme. The results show that the compound scheme can accurately obtain the friction parameters and improve the control precision and stability of ISP.

A Dynamic Model and Control Method for a Two-Axis Inertially Stabilized Platform

To realize high-performance control for a two-axis inertially stabilized platform (ISP), a nonlinear dynamic model based on the geographic coordinate and a compound control method based on the back-stepping sliding mode control and adaptive radial basis function neural network (RBFNN) are proposed. Compared with the traditional dynamic model based on the inertial coordinate, the nonlinear dynamic model based on the geographic coordinate constructs the direct relationship among the control inputs and criteria of the ISP. Moreover, the back-stepping sliding mode control method is proposed to handle the system nonlinearity, parameter variations, and disturbances. Furthermore, the adaptive RBFNN is constructed and optimized to estimate the upper bound of the residual error on line to reduce the chatting phenomenon. The asymptotic stability of the proposed control method has been proven by the Lyapunov stability theory. The effectiveness of the proposed method is validated by a series of simulations and flight tests.

四反射镜结构极坐标红外惯性稳像平台像旋研究

四反射镜结构极坐标红外惯性稳像平台像旋研究

Application of Acceleration Feedback Techniques on Inertial Stabilization Platform

The performance of the inertial stabilized platform will be affected heavily by inner or outer factors, which will change the transfer characteristic of the inertial stabilized platform and result in the degradation of the precision of the system. Therefore, the high-gain acceleration feedback will be inserted in the velocity feedback loop to compensate the change of these factors. And the acceleration feedback loop can stabilize the platform because that the accelerometers are inertial sensors, the active disturbance suppression of the platform is the product of the error attenuation of the acceleration loop and the velocity loop. Extensive experimental results show that the acceleration feedback can enhance the active disturbance suppression of the platform.

Designing and Experimental Verification of the Axial Hybrid Magnetic Bearing to Stabilization of a Magnetically Suspended Inertially Stabilized Platform

To decrease the mass and power loss of axial hybrid magnetic bearings (HMBs) in the application of inertially stabilized platform (ISP) with a large axial diameter, this paper investigates the effects of the layout of axial HMBs and the degree of asymmetry (DOA). An asymmetry axial HMB is proposed for ISP based on DOA. Each single axial HMB is modeled and analyzed using the reluctance network method. And the relationship between current and force, as well as the displacement and force, are studied. Additionally, the optimization design method of the axial HMB is presented based on DOA. According to the principle of the design, the layout of the complete asymmetry axial HMB is designed with eight single axial HMBs in the upper end and four single axial HMBs in the lower end of ISP. Furthermore, the relationship among displacement, current, and displacement stiffness and the relationship among displacement, current, and current stiffness are analyzed as the DOA varies. A prototype is manufactured based on the above design and analysis, and experiments are carried out. Experimental results illustrate that the mass and power loss will be decreased dramatically compared with the symmetry layout of axial HMBs.

Control System Design for a Three-Axis Inertially Stabilized Platform in Aerial Remote Sensing

This paper describes a control system of a three-axis aerial inertially stabilized platform (ISP). A control scheme based on PID is proposed, whose parameters are determined with the help of simulation analysis. The hardware and software systems are then designed. The experiments are carried out to validate the system. The results show that the system is effective and with satisfied precision.

Robust control of magnetically suspended gimbals in inertial stabilized platform with wide load range

Comparing with the normal mechanical inertial stabilized platform (ISP), the novel ISP with magnetic bearing to suspend the yaw gimbal owns the ability of isolating the vibration and disturbance of external gimbal. However, on the one hand, complex structure of the magnetically suspended gimbal introduces parametric uncertainties into modeling of magnetic suspension force, and the disturbance of magnetic fields brings the unmodeled force into dynamics of magnetically suspended gimbal. On the other hand, external disturbances such as wind drag affect the stability of magnetically suspended gimbal. Therefore, H∞robust controllers for translation and tilting of gimbal are designed to dampen the negative influence on stability and improve the robustness of system. The experimental results indicate that the robust controller of magnetically suspended gimbal owns the excellent robustness when the load of magnetically suspended gimbal changes.

Experimental Validation of a Compound Control Scheme for a Two-Axis Inertially Stabilized Platform with Multi-Sensors in an Unmanned Helicopter-Based Airborne Power Line Inspection System.

A compound control scheme is proposed to achieve high control performance for a two-axis inertially stabilized platform (ISP) with multi-sensors applied to an unmanned helicopter (UH)-based airborne power line inspection (APLI) system. Compared with the traditional two closed-loop control scheme that is composed of a high-bandwidth rate loop and a lower bandwidth position loop, a new current loop inside rate loop is particularly designed to suppress the influences of voltage fluctuation from power supply and motor back electromotive force (BEMF) on control precision. In this way, the stabilization accuracy of the ISP is greatly improved. The rate loop, which is the middle one, is used to improve sensor’s stability precision through compensating for various disturbances. To ensure the pointing accuracy of the line of sight (LOS) of multi-sensors, the position loop is designed to be the outer one and acts as the main feedback path, by which the accurate pointing angular position is achieved. To validate the scheme, a series of experiments were carried out. The results show that the proposed compound control scheme can achieve reliable control precision and satisfy the requirements of real APLI tasks.

Robust Control of Magnetic Bearing in the Inertially Stabilized Platform for Aerial Remote Sensing

Comparing with the normal mechanical inertial stabilized platform (ISP), the novel ISP with magnetic bearing to suspend the yaw gimballing owns the ability of isolating the vibration and disturbance of external gimballing. However, on the one hand, complex structure of the magnetically suspended gimballing introduces the parametric uncertainties into modelling of magnetic suspension force, and the disturbance between the magnetic fields brings the un-modeled force into dynamics of magnetically suspended gimballing. On the other hand, the external disturbances such as wind drag affect the stability of magnetically suspended gimballing. Therefore, to weaken the negative influence on stability and improve the robustness of system, the H ∞ robust controllers for translation and tilting of gimballing are designed. The experimental results indicate that the robust controller of magnetically suspended gimballing owns the excellent robustness when the load of magnetically suspended gimballing changes.

A Model Reference Adaptive Control/PID Compound Scheme on Disturbance Rejection for an Aerial Inertially Stabilized Platform

This paper describes a method to suppress the effect of nonlinear and time-varying mass unbalance torque disturbance on the dynamic performances of an aerial inertially stabilized platform (ISP). To improve the tracking accuracy and robustness of the ISP, a compound control scheme based on both of model reference adaptive control (MRAC) and PID control methods is proposed. The dynamic model is first developed which reveals the unbalance torque disturbance with the characteristic of being nonlinear and time-varying. Then, the MRAC/PID compound controller is designed, in which the PID parameters are adaptively adjusted based on the output errors between the reference model and the actual system. In this way, the position errors derived from the prominent unbalance torque disturbance are corrected in real time so that the tracking accuracy is improved. To verify the method, the simulations and experiments are, respectively, carried out. The results show that the compound scheme has good ability in mass unbalance disturbance rejection, by which the system obtains higher stability accuracy compared with the PID method.

The Effects of Matched Filter on Stable Performance of Semistrapdown Inertially Stabilized Platform

To enhance the optimization performance of matched filter and further improve line of sight (LOS) stability of platform in inertial space, the proposed matched filter algorithm is conducted by adjusting matched filter coefficients of first-order low pass filter utilizing the regional search method based on invariance principle. The coefficients of the fraction molecule and denominator of proposed regional search algorithm are altered instead of denominator coefficients only being modified. Simulations are performed to verify the validity of inside factors performed with stabilization control model and quartz rate sensor (QRS) mathematical model. The stable angular error is sharply alleviated, so the decoupling accuracy of airborne semistrapdown inertially stabilized platform is largely promoted. The optimization matched filter can effectively increase stability of LOS in inertial space.