Inertially Stabilized Platform Research Articles

Robust predictive visual servoing control for an inertially stabilized platform with uncertain kinematics

In this paper, a disturbance observer (DOB) based predictive control approach is developed for the image-based visual servoing of an inertially stabilized platform (ISP). As the limitation in degrees of freedom of a two-axes ISP, it is hard to estimate the variable feature depth of the target at each control cycle when using an uncalibrated camera, which brings the challenge in the design of the visual servoing controller. To this end, a depth-independent kinematic matrix that only involves nominal parameters is obtained by employing the partitioned scheme in the system modeling. The uncertain kinematics arising from the unknown feature depth, angular velocity tracking errors, and uncalibrated intrinsic parameters is considered as the lumped uncertainty. A discrete-time DOB is then constructed to estimate the lumped uncertainty in real time. Instead of taking an integral action to eliminate tracking errors induced by the uncertain kinematics, the disturbance estimation is actively incorporated into the receding optimization process of the predictive controller. The stability of the closed-loop system is fully analyzed. Experiments on tracking a moving target are performed to validate promising qualities of the proposed approach.

Active Vibration Isolation of a Maglev Inertially Stabilized Platform Based on an Improved Linear Extended State Observer

An inertially stabilized platform is subject to the vibration force and moment from its support base, and low-frequency vibrations cannot be eliminated by mechanical vibration isolation. Combining gimbals with magnetic bearings instead of mechanical bearings, a maglev inertially stabilized platform (MISP) is characterized by no friction or an active vibration control capability. In this paper, an improved linear extended state observer (LESO) replacing displacement error with next-order error is proposed to estimate the low-frequency vibration and improve the estimation accuracy. An active vibration isolation control method is then designed to realize cancellation compensation on the MISP. Finally, a simulation example is presented to validate that the proposed measures can effectively eliminate the low-frequency vibration force transmitted from the base and ensure the stability of the MISP.

High Performance Both in Low-Speed Tracking and Large-Angle Swing Scanning Based on Adaptive Nonsingular Fast Terminal Sliding Mode Control for a Three-Axis Universal Inertially Stabilized Platform.

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.

A Robust Double Active Control System Design for Disturbance Suppression of a Two-Axis Gimbal System

This paper presents a robust controller design with disturbance decoupling and rejection of a two-degree-of-freedom (2-DOF) Inertially Stabilized Platform (ISP). The objective of these mechanisms is to stabilize the line of sight (LOS) of imaging sensors pointing towards a specific target. There is currently tremendous interest in ISP applications in marine systems. Such a harsh environment subjects the imaging sensors to multiple disturbances, which requires the design of robust control strategies to enhance the performances of ISP systems. The controller designed in this study is a double active controller composed of an inner compensator, and a feedback controller designed based on the H∞ framework. The main advantage of the proposed controller is that it can be implemented in real time, with lower computational complexity and good performance. In this paper, a comparative experimental study was conducted between the designed controller and an integral sliding-mode controller (ISMC). The comparison was achieved through two major tasks of ISP systems: motion tracking and target tracking.

Adaptive Kalman Filter Enhanced With Spectrum Analysis for Wide-Bandwidth Angular Velocity Estimation Fusion

The optoelectronic inertial stabilization platform is widely used in the fields of astronomical observation, monitoring and search, quantum communication and other fields, which all need strong vibration suppression and tracking capability. To realize high-precision angular measurement throughout the wide bandwidth for inertial stabilization platform, the fusion algorithm is studied to fuse the signals of magnetohydrodynamic (MHD) and microelectromechanical (MEMS) gyroscope. The basic adaptive Kalman filter experiences signal-to-noise ratio and fusion-frequency jitter problems because of the measurement transfer matrix deviation, making it unsuitable for quick dynamic systems. This paper proposes an adaptive Kalman filter enhanced with spectrum analysis by connecting the measurement covariance with the signal frequencies. This method divides the trace of the modified measurement covariance into three parts according to frequency domain characteristics. Based on the frequency analysis, the filter output mainly depended on the MEMS gyroscope at low frequencies, fusion results of the two gyroscopes in the intermediate frequency-domain, and the MHD gyroscope at high frequencies. This theory is verified in the swept frequency experiment and comparative experiments, including multi-harmonic sinusoidal and step response tests compared with combing filter and closed-loop filter. The tests results show that the fusion signal is identical with the actual signal throughout the measurement bandwidth, and the fusion signal-to-noise ratio is improved. The frequency characteristics and noise level of the fusion algorithm satisfy the requirements of optoelectronic inertial stabilization vibration measurement.

Design of Composite Feedback and Feedforward Control Law for Aircraft Inertially Stabilized Platforms

The design of the control systems of the inertially stabilized platforms (ISPs) as part of airborne equipment for the majority of aircraft has its peculiarity. The presence of rate gyros in the inertial measurement unit gives the possibility to measure the rotation rate of the ISP base, which is the main disturbance interfering with the ISP accuracy. Inclusion of the feedforward disturbance gain in the control law with the simplest PI feedback significantly improves the accuracy of stabilization by the invariance theory. A combination of feedback and feedforward controllers produces a synergetic effect, thus, improving ISP accuracy. This article deals with the design of the airborne ISP control systems consisting of two stages: the parametric optimization of the PI feedback control based on composite “performance-robustness” criterion and the augmentation of the obtained system with feedforward gain. To prove the efficiency of the proposed control laws, the simulation of the ISP was undertaken. We have used a simulation of the heading-hold system of the commuter aircraft Beaver and the yaw rate output of this closed-loop system we have used as a source of the disturbance. The results of modeling proved the efficiency of the proposed design method.

Coupling Analysis and Cross-Feedback Control of Three-Axis Inertially Stabilized Platform with an Active Magnetic Bearing System

An active magnetic bearing (AMB) system is used to suspend the yaw gimbal of three-axis inertially stabilized platform (ISP) to minimize the friction. The dynamic functions of three gimbals in ISP are developed. The base coupling at dynamic base plate is stronger than that at static base plate, and the gimbal coupling among three gimbals increases with the number of unlocked gimbals. Therefore, a cross-feedback control scheme is designed to minimize the base coupling and the gimbal coupling, and then the multi-input multioutput system of three-axis ISP with coupling terms is simplified into three decoupled single-input single-output systems. Experimental results verify that the yaw gimbal suspended by AMB system has better vibration isolation ability than the roll gimbal supported by mechanical bearing, and the gimbal coupling and the base coupling are effectively suppressed by the cross-feedback control scheme.

High Precision Low-Speed Control for Permanent Magnet Synchronous Motor.

Due to the process defects and imperfection of drivers, permanent magnet synchronous motors (PMSM) are problematic to control. There is still a lack of effective high-performance control methods for inertial stabilized platforms based on PMSM currently. At present, the most frequently used method is sliding mode control (SMC), but traditional sliding mode control cannot overcome the contradiction between high performance and system chattering. In order to solve this problem and improve the system reliability and pointing accuracy, a new approach law for the sliding mode controller is proposed in this paper. In view of the large periodic torque ripple in PMSM, an iterative learning controller (ILC) is introduced to compensate for the disturbance. Based on these, aimed at suppressing all kinds of real-time disturbances in the working environment of the system, the extended state observer (ESO) is brought into the servo system to observe the lumped disturbance of the system, and the total disturbance observed is compensated into the sliding mode controller, so as to better suppress the system chattering and enhance the system’s ability of resisting external disturbance. Experiments are carried out on an inertial stabilization platform based on DSP + CPLD. The final experiments verify that the SMC with the new approach, combined with ILC and ESO, is of outstanding performance when compared with the traditional proportional integral (PI) + disturbance observer (DOB) control scheme.

A High Precision Compound Control Scheme Based on Non-singular Terminal Sliding Mode and Extended State Observer for an Aerial Inertially Stabilized Platform

This paper presents a high precision compound control scheme based on non-singular terminal sliding mode and extended state observer (ESO) for an aerial inertially stabilized platform (ISP) to suppress the effects of multi-source disturbances on the control performance of the ISP. Firstly, a non-singular terminal sliding mode controller is proposed to achieve high disturbance rejection ability, by which the multi-source disturbances are integrally suppressed as an aggregate disturbance. And then, to restrain the chattering effect of the sliding mode control, a disturbance compensation scheme based on the extended state observer is proposed. By the ESO, the disturbances are observed and compensated in real time and hence the chattering effect is significantly alleviated. Meanwhile, a parameter configuration method is proposed to simplify the ESO design. To verify the method, simulations and experiments are conducted. The results show that the proposed compound control scheme has excellent ability in both disturbance rejection and chattering reduction, by which the stabilization precision of the ISP is improved significantly.

Modified ADRC for Inertial Stabilized Platform With Corrected Disturbance Compensation and Improved Speed Observer

In this article, a modified scheme of nonlinear active disturbance rejection control (ADRC) is proposed by correcting the disturbance compensation and improving the speed observer. The stability, disturbance rejection and tracking performance of the modified ADRC scheme are analyzed and compared with that of the typical ADRC scheme utilizing the describing function method and numerical method, which shows that the dynamic stiffness and tracking performance are significantly improved while the stability almost remains invariant. Both the simulations and experiments are conducted in inertial stabilized platform (ISP) control system. It turns out that the simulation and experimental results further support the analysis.

Robust PID Control of Single-axis Gimbal Actuator via Stability Boundary Locus

The gimbal or inertial stabilization platform (ISP) is used to stabilize the payload’s line of sight (LOS) towards a stationary or moving target. It can be achieved if there is isolation between the payload and the base of the gimbal. This paper presents a single-axis gimbal loop in which the LOS rate is stabilized using a robust proportional-integral-derivative (PID) controller. The PID controller parameters are obtained by using a graphical technique known as stability boundary locus (SBL) approach such that the overall gimbal stabilization loop will have some minimum specific gain margin and phase margin. The PID controller is further designed in the presence of time delay. The proposed controller is compared with PI control scheme available in literature for rise time, settling time, percentage overshoot, ISE, ITSE, IAE, and ITAE. The simulations are carried out in MATLAB which exhibit better results in comparison with PI control based approach.

Research on inertial stabilization platform on mobile carrier in complex environment

The inertial stabilization platform on the mobile carrier has been widely used in military and civilian fields, such as modern satellite TV receiving and broadcasting, mobile satellite communication for vehicles and ships, as well as cash transport vehicles, public security, fire protection, disaster relief, environmental monitoring and many other industries. The platform needs the ability to isolate the effects of carrier motion, and to ensure the interception, identification and tracking of the target signal under various meteorological conditions. We choose the platform of photodetector component. It uses the electromechanical to control detector according to the instructions, automatically identifing and capturing the target. In the working process, the servo system is the key guarantee of the high performance of the platform. According to the high precision, fast response, wide frequency band and strong robust performance requirements of the system, we propose a single neuron adaptive PI+DOB (Proportional Integral+Disturbance Observer) control strategy, a method for continuous nonsingular terminal sliding mode control and a improved statistical model adaptive filtering algorithm. Through theoretical research and experimental analysis, our method improves the performance parameters based on the original system, and provides theoretical support for future researchers to develop high-precision inertial stabilization platform.

Modeling and Robust Continuous TSM Control for an Inertially Stabilized Platform With Couplings

Inertially stabilized platforms (ISPs), typically involving two or three axis gimbal, are extensively utilized to achieve accurate tracking of optical axis regardless of vehicle motion or vibration. Due to the complex nonlinearities induced by cross-couplings, parameter uncertainties, and external disturbances, high-performance control for ISPs is always a challenging task for practical applications, especially when the dynamic mass imbalance exists. In this brief, the situation that the mass distribution of an ISP is nonsymmetrical with respect to the mass center is emphatically analyzed, where the couplings are modeled and resolved into the known and unknown parts. To cope with the unmeasured states as well as the uncertainties composed of unknown couplings and remaining dynamics that are unmodeled, a higher order sliding mode observer (HOSMO) is developed for both the states and the lumped uncertainties estimation. By incorporating the estimated information, a robust continuous terminal sliding mode (TSM) control law is synthesized to admit the desired inertial angular rates tracking in finite time without offset. The validity of the presented control approach is demonstrated by experimental studies.

Analysis and Design of the Stewart Platform-Based Parallel Support Bumper for Inertially Stabilized Platforms

Stewart platform-based parallel support bumpers are widely used to prevent external shocks from damaging inertial navigation systems. Aiming at a severe problem that the inertially stabilized platform becomes out of control as soon as a specified shock is posed on the base of the bumper in shock tests, analysis, and design of the 18-leg Stewart platform-based parallel support bumper are conducted in this paper. With the help of generalized coordinate definition, a kinetic model of the parallel support bumper is established, of which inertia, stiffness, and damping matrices are derived based on kinetic energy, elastic potential energy, and damping dissipation function, respectively. The stiffness matrix is subsequently calculated in detail; intensive parameter design of the 18-leg bumpers is carried out according to the principle of stiffness equality and coupled motion reduction, and the corresponding kinetics is analyzed with Laplacian transformation. Theoretical and simulation results show that a half-sinusoidal shock with a magnitude of 25 g along a horizontal axis of the bumper base can cause rotational motion along the perpendicular horizontal axis with maximum acceleration of 2.762 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> °/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , velocity of 42.3 °/s, and displacement of 3.16°, which would cause the aforementioned losing control problem if the inertially stabilized platform were not reasonably designed.

Robust Output Feedback Tracking Control for Inertially Stabilized Platforms With Matched and Unmatched Uncertainties

The use of an inertially stabilized platform (ISP) as a key component in electro-optical tracking instruments to control the sensor’s line of sight (LOS) has been investigated for over decades. Its aim is to achieve an accurate tracking for a target and isolate the LOS from the carrier vibrations. A typical assumption in such a system is that the mass distribution of the ISP is symmetrical with respect to the frame axes under consideration. This assumption is rarely satisfied in practice. This paper explores the development of an output feedback controller for an ISP while considering dynamic mass unbalance , where the controller derivation is based on the assumption that all parameters used in the system modeling are unknown , but bounded in size. This assumption implies that the ISP is affected by both matched and unmatched uncertainties. The research, in this paper, illustrates how an indirect robust control can be incorporated with a modified extended state observer-based feedforward term to achieve a high performance on the tracking in the presence of uncertainties, mass imbalance, kinematic coupling, carrier vibrations, and external disturbances. Simulation results are presented to confirm the effectiveness of the proposed scheme.

Anti-Disturbance Neural-Sliding Mode Control for Inertially Stabilized Platform With Actuator Saturation

To consider the environment during ground vehicle driving, the inertially stabilized platform (ISP) can be used for electro-optical tracking instruments to isolate the senor's line of sight (LOS) from the carrier's vibrations with high precision and stability. This paper proposes the combination of a backstepping sliding mode controller with the adaptive neural networks approach (BSMC-NN) for ISP that achieves output torque saturation and considers parametric uncertainties, friction, and gimbal mass imbalance. An adaptive radial basis function neural network is adopted to approximate uncertain disturbances in this dynamic system. In contrast to the existing saturated control structures, an auxiliary function is designed to compensate for any error between the designed and the actual control torque. The closed-loop stability and asymptotic convergence performance are guaranteed based on the Lyapunov stability theory. Finally, the simulation and experimental results demonstrate that this proposed controller can effectively regulate the gimbal rotation angle under different external disturbances. This offers superior control performance despite the existence of the nonlinear dynamics and control input constraints.

Stabilization Control Mothed for Two-Axis Inertially Stabilized Platform Based on Active Disturbance Rejection Control With Noise Reduction Disturbance Observer

To improve the stability accuracy of two-axis inertially stabilized platform (ISP) for airborne star tracker application, a stable control method based on active disturbance rejection control (ADRC) is presented to handle the system nonlinearities, parameter uncertainties, and disturbances. A noise reduction method based on a modified disturbance observer (DOB) structure is proposed to suppress sensor noise and improve anti-disturbance capability and rapidity. Moreover, the robust stability of the proposed method is discussed. To illustrate the effectiveness of the proposed method, simulations and laboratory experiments are implemented. Finally, the vehicle tracking star experiments are performed. In addition, the contrast results show that for the two-axis ISP the presented controller has superior performance in anti-jamming ability, rapidity, and isolation.

Discrete-Time Direct Model Reference Adaptive Control Application in a High-Precision Inertially Stabilized Platform

This paper studies the practical use of discrete-time direct adaptive control in a high-precision inertially stabilized platform's turbulence isolation system for the purpose of enhancing isolation performance. Under low-frequency and low-velocity environments, the velocity-stabilized loop of the platform shows severe nonlinear characteristic; therefore, its isolation performance is limited. In previous research, we constructed a nonlinear model of the velocity-stabilized loop by using an improved Stribeck friction model, and also designed a feed-forward compensation strategy. Both have obtained outstanding performance during practical experiments. However, errors still exist as disturbance of the unmodeled part and environmental change causes the system's parameter to vary. To solve this, a novel discrete-time direct model reference adaptive control based on nonlinear friction compensation is introduced to the original proportional-integral control system. An improved projection algorithm and a recursive least-square algorithm with fading memory are respectively used to design the adaptive law. By using a turbulence observer to provide a reference signal, both types of controls are applied to the carrier turbulence isolation system. Results of the practical experiments prove that model reference adaptive control can further enhance the system's isolation ability.

Automatic Estimation of Dynamic Lever Arms for a Position and Orientation System

An inertially stabilized platform (ISP) is generally equipped with a position and orientation system (POS) to isolate attitude disturbances and to focus surveying sensors on interesting targets. However, rotation of the ISP will result in a time-varying lever arm between the measuring center of the inertial measurement unit (IMU) and the phase center of the Global Positioning System (GPS) antenna, making it difficult to measure and provide compensation. To avoid the complexity of manual measurement and improve surveying efficiency, we propose an automatic estimation method for the dynamic lever arm. With the aid of the ISP encoder data, we decompose the variable lever arm into two constant lever arms to be estimated on line. With a complete 21-dimensional state Kalman filter, we accurately and simultaneously accomplish navigation and dynamic lever arm calibration. Our observability analysis provides a valuable insight into the conditions under which the lever arms can be estimated, and we use the error distribution method to reveal which error sources are the most influential. The simulation results demonstrate that the dynamic lever arm can be estimated to within [0.0104; 0.0110; 0.0178] m, an accuracy that is equivalent to the positioning accuracy of Carrier-phase Differential GPS (CDGPS).

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.