Inertially Stabilized Platform Research Articles

The Static Unbalance Analysis and Its Measurement System For Gimbals Axes of an Inertial Stabilization Platform

Abstract To reduce the influence of the static unbalance on an infrared missile guidance system, a new static unbalance measure system for the gimbals axes has been developed. Considering the coupling effects caused by a mass eccentricity, the static balance condition and measure sequence for each gimbal axis are obtained. A novel static unbalance test approach is proposed after analyzing the dynamic model of the measured gimbal axis. This approach is to drive the measured gimbal axis to do sinusoidal reciprocating motion in a small angle and collect its drive currents in real time. Then the static unbalance of the measured gimbal axis can be obtained by the current multi-cycle integration. Also a measuring system using the proposed approach has been developed. A balanced simulator is used to verify the proposed approach by the load and repeatability tests. The results show the proposed approach enhances the efficiency of the static unbalance measurement, and the developed measuring system is able to achieve a high precision with a greater stability.

A compound control method based on the adaptive neural network and sliding mode control for inertial stable platform

To improve the control performance of the inertial stable platform (ISP), a compound control method based on the adaptive neural network and sliding mode control method is proposed to deal with the system model uncertainties and the disturbances. A sliding mode control is designed for the ISP system to achieve the initial stability. Moreover, an adaptive neural network is proposed to approximate the system uncertainties and unknown disturbances to argument the control performance. Based on the current state error information, the weight matrix of adaptive neural network can be updated on line. Therefore, the adaptive neural network can be constructed directly without priori training. The applicability of the proposed method is validated by a series of simulations and flight tests. The control method can improve the attitude stabilization accuracy of payloads effectively during the flight process.

Decoupling control for a three-axis inertially stabilized platform used for aerial remote sensing

A three-axis inertially stabilized platform (ISP) is an important component in an aerial remote sensing system, used for isolating the influences of various disturbances on imaging sensors. In order to deal with the coupling torques and improve the control precision of the ISP, a decoupling control method based on feedforward compensation is proposed in this paper. Firstly, the kinematic and dynamic model of three-axis ISP is developed by using a Lagrange equation. Then, the coupling effects among the three gimbals and base are analysed. Depending on the analysis of the model, the major coupling components are obtained and the dynamic model is simplified. Finally, a decoupling controller based on the feedforward compensation method is designed and applied to the ISP control system. Simulation and experimental results show that the stability and precision of the ISP are effectively improved.

Decoupling control for two-axis inertially stabilized platform based on an inverse system and internal model control

This paper describes a decoupling control scheme for a two-axis inertially stabilized platform (ISP) used in the airborne power line inspection system. The dynamic model of the ISP has been obtained by using the Newton–Euler equation first. The inverse system method combining with the internal model control has been proposed to deal with the nonlinearity and coupling of the ISP. The key idea is to design an inverse system with measured system states such as angular positions, rates and accelerations. Then a pseudo-linear system is constructed when the inverse system is connected with the original system in series. As a result, the coupled nonlinear MIMO (Multiple-Input Multiple-Output) system is converted to two linear decoupled SISO (Single-Input Single-Output) subsystems. Model uncertainties or unmeasurable disturbances existing objectively can be solved by introducing internal model control. Better decoupling effect and disturbance rejecting ability are demonstrated by numerical simulations and experiments carried out on a two-axis ISP system.

Dynamic lever arm compensation of SINS/GPS integrated system for aerial mapping

Strapdown inertial navigation system (SINS)/global positioning system (GPS) integrated system is an important way of accurate measurement of the mapping sensors for high resolution aerial mapping. However, for keeping the mapping sensor level and appointed direction, inertially stabilized platform (ISP) will be applied and rotate its three gimbals. The lever arm between inertial measurement unit (IMU) and GPS antenna will be time-varying. Therefore, the precise compensation of the effect of the dynamic lever arm will be significant for the measurement accuracy of SINS/GPS integrated system. An algorithm which tackles the problem is proposed, the dynamic lever arm is originally considered as the summation of two relative constant lever arms. Then, with the aid of the encoder data of ISP, the algorithm of dynamic lever arm compensation is derived in the paper. As the nonlinearity of the system, the demand of the on-line and off-line processing, unscented Kalman filter and smoother for nonlinear estimation are applied. Finally, the proposed algorithm of dynamic lever arm compensation is applied to a flight data of aerial mapping experiment. It is shown from the experiment results that the proposed algorithm can more effectively compensate the degradation of the measurement information than the traditional algorithm.

A friction identification approach based on dual-relay feedback configuration with application to an inertially stabilized platform

The low-velocity motion performance of servo system tends to be deteriorated greatly by friction due to its relay nonlinearity and Stribeck effect in low-velocity state. To achieve better low-velocity motion performance, an effective friction identification approach based on the dual-relay feedback configuration is presented for a typical low-velocity servo system, an inertially stabilized platform (ISP). An improved piecewise friction model derived from Tustin model is used to describe the frictional behaviors including static, Coulomb, viscous friction and especially Stribeck effect, so that the frictional behaviors can be appropriately formulated through describing functions. The dual-relay feedback configuration is designed to excite limit cycles in a velocity feedback loop, rather than in the position loop, so as to avoid noise arisen from the derivative of the position response signal. Properties of the limit cycle oscillations are analyzed for proper selections of dual-relay gains, based on which a systematic procedure for friction identification is proposed. Simulations and experiments on a servomechanism of ISP verify the effectiveness of the proposed approach.

Acceleration-based mass imbalance feedforward compensation for inertial stabilized platform

Focusing on the disturbance rejection for Inertial Stabilized Platform (ISP), an acceleration-based feedforward compensation method is proposed. The model of mass imbalance is established, through analyzing the relationships among the mass imbalance, the friction, the current of motor, and the attitude of gimbal. Then, the feedforward compensation controller is built for ISP using the data of accelerations acting on the ISP. It could estimate and compensate the mass imbalance torque of ISP in real time. The numerical simulations and vehicle experiments demonstrate the effectiveness of the designed controller. Compared to the traditional Proportion Integration Differentiation (PID) controller without feedforward compensation, the performance of ISP is significantly improved by the proposed compensation method in the presence of similar disturbances.

Application in prestiction friction compensation for angular velocity loop of inertially stabilized platforms

To overcome the influence of the nonlinear friction on the gimbaled servo-system of an inertial stabilized platforms (ISPs) with DC motor direct-drive, the methods of modeling and compensation of the nonlinear friction are proposed. Firstly, the inapplicability of LuGre model when trying to interpret the backward angular displacement in the prestiction regime is observed experimentally and the reason is deduced theoretically. Then, based on the dynamic model of direct-drive ISPs, a modified LuGre model is proposed to describe the characteristic of the friction in the prestiction regime. Furthermore, the state switch condition of the three friction regimes including presliding, gross sliding and prestiction is presented. Finally, a composite compensation controller including a nonlinear friction observer and a feedforward compensator based on the novel LuGre model is designed to restrain the nonlinear friction and to improve the control precision. Experimental results indicate that compared with those of the conventional proportion–integration–differentiation (PID) control method and the PID plus LuGre model-based friction compensation method, the dwell-time has decreased from 0.2s to almost 0s, the position error decreased to 86.7% and the peak-to-peak value of position error decreased to 80% after the novel compensation controller is added. It concludes that the composite compensation controller can greatly improve the control precision of the dynamic sealed ISPs.

Fuzzy-PID control for the position loop of aerial inertially stabilized platform

Due to multiple-source disturbances, frame dynamic characteristics of aerial inertially stabilized platform (ISP) changes, leading to nonlinear and time-varying position loop error. Therefore, conventional PID control with fixed parameters can't bring performance of high accuracy and fast response. In this paper, control strategy that sets Kd at a certain value, and adjusts Kp and Ki in real time is proposed. Meanwhile, a fuzzy-PID controller selecting position loop error and its changing rate as observed value is designed with online modification of proportion and integration parameters. The principle prototype of aerial ISP made by our research group helps to conduct static leveling and dynamic vehicle experiments. The results indicate that overall performance of the platform is improved much for the reason that compared with conventional PID control, the fuzzy-PID control brings faster leveling speed and better steady precision.

Dynamic Modeling and Nonlinear Decoupling Control of Inertial Stabilized Platform for Aerial Remote Sensing System

The mutual coupling between the motion of three frames exists when inertial stabilized platform (ISP) for aerial remote sensing system is working, due to the mechanical character of the stabilized platform. Based on Lagrange mechanics and starting from analytical mechanics, a kinetics model of inertial stabilized platform is developed for analyzing the complex coupling relation. On the basis of the model, a nonlinear decoupling control method using sliding mode control (SMC) is designed for rolling and pitching frames after coupling moment being taken for external disturbance. While, for azimuth frame, which can not directly adopt sliding mode control method, a novel method of introducing a judgment factor and combining SMC and PID is provided. Compared with PID method, the simulation results show that the overshoot of the system is reduced obviously and the decoupling effect is better. Results obtained will be a theoretical foundation for the further study of inertial stabilized platform, and guarantee high precision to stabilized platform system.

A RBFNN-Based Adaptive Disturbance Compensation Approach Applied to Magnetic Suspension Inertially Stabilized Platform

Compared with traditional mechanical inertially stabilized platform (ISP), magnetic suspension ISP (MSISP) can absorb high frequency vibrations via a magnetic suspension bearing system with five degrees of freedom between azimuth and pitch gimbals. However, force acting between rotor and stator will introduce coupling torque to roll and pitch gimbals. Since the disturbance of magnetic bearings has strong nonlinearity, classic state feedback control algorithm cannot bring higher precision control for MSISP. In order to enhance the control accuracy for MSISP, a disturbance compensator based on radial basis function neural network (RBFNN) is developed to compensate for the disturbance. Using the Lyapunov theorem, the weighting matrix of RBFNN can be updated online. Therefore, the RBFNN can be constructed without priori training. At last, simulations and experiment results validate that the compensation method proposed in this paper can improve ISP accuracy significantly.

Parameter identification of inertially stabilized platforms using current command design

Accurate parameter identification is essential when designing controllers for inertially stabilized platforms (ISPs). But traditional identification methods suffer from observation measurement noise and operating restrictions of ISPs. To address this issue, a novel identification method based on current command design and multilevel coordinate search (MCS) algorithm without any higher order measurement differentiations was proposed. The designed current commands were adopted to obtain parameter decoupled models with the platform operating under allowable conditions. MCS algorithm was employed to estimate the parameters based on parameter decoupled models. A comparison experiment between the proposed method and non-linear least square method was carried out and most of the relative errors of identified parameters obtained by the proposed method were below 10%. Simulation and experiment based on identified parameters were conducted. A velocity control structure was also developed with disturbance observer (DOB) for application in disturbance compensation control system of an ISP. Experimental results show that the control scheme based on the identified parameters with DOB has the best disturbance rejection performance. It reduces the peak to peak value (PPV) of velocity error integral to 0.8 mrad which is much smaller than the value (10 mrad) obtained by the single velocity controller without DOB. Compared with the control scheme based on sweep model with DOB compensation, the proposed control scheme improves the PPV of velocity error integral by 1.625 times.

Nonlinear Friction Modeling and Adaptive Compensation on an Inertially Stabilized Platform System for Aerial Remote Sensing Application

To decrease the influences of friction on control precision of a three-axis inertially stabilized platform(ISP) applied in the aerial remote sensing system,an adaptive backstepping control method based on the LuGre model is put forward.According to the characteristics of variable speed values over zero and flatheaded position,the LuGre model of a three-axis ISP is developed and parameters are identified through two-step and dynamic parameter optimization method.Then an adaptive backstepping controller is designed based on the theory of stability.The influences of friction on the precision of ISP’s control system are analyzed by Matlab and compared with those of feedforward controller,the validity and robust of the controller are evaluated.Finally,to validate the proposed model and compensation method,the experiments are carried out to the yaw-gimbal system of an ISP.The results show that the adaptive backstepping method can significantly reduce the influences of friction on control precision,by which the fluctuation range error and the root-mean-square error of the angular position are decreased by 78.7% and 91.5% respectively.

Target Tracking System Based on Inertial Stabilized Platform

A target tracking system based on inertial stabilized platform（ISP）is introduced, which can fulfill platform inertial navigation, platform stabilization and target tracking. An IMU is integrated with electro-optical sensors and a laser range finder on a gimbal, which performs attitude transformation by constructing navigation coordinates in a mathematic platform, and the platform inertial information is obtained by transformation matrix between platform and payload coordinates. The inertial platform comprising gyros, electro-optical sensors and servo mechanism is capable of stabilizing line of sight and can be used to track targets in the relevant field of view (FOV). The system can determine geography coordinates of the host platform and target only with inertial information and laser ranging data. The geo-tracking system always locked the target image at the center of FOV by calculating spatial geometry and adjusting LOS attitude. This tracking is different from TV tracking and geo-reference image tracking, which may be influenced by fog and obscurant. When the helicopter is flying over urban or mountain areas for rescue missions, it can avoid the loss of targets due to strong maneuver or LOS obscuration, and reduce the operation load of the aircrew and improve rescue efficiency.

Improved Angular Velocity Estimation Using MEMS Sensors with Applications in Miniature Inertially Stabilized Platforms

The performance of any inertially stabilized platform (ISP) is strongly related to the bandwidth and accuracy of the angular velocity signals. This paper discusses the development of an optimal state estimator for sensing inertial velocity using low-cost micro-electro-mechanical systems (MEMS) sensors. A low-bandwidth gyroscope is used alone with two low-performance accelerometers to obtain the estimation. The gyroscope has its own limited dynamics and mainly contributes to the low-frequency components of the estimation. The accelerometers have inherent biases and mainly contribute to the high-frequency components of the estimation. Extensive experimental results show that the state estimator can achieve high-performance signals over a wide range of velocities without drifts in both the t- and s-domains. Furthermore, with applications in miniature inertially stabilized platforms, the control characteristic presents a significantly improvement over the existing methods. The method can be also applied to robotics, attitude estimation, and friction compensation.

Structural Optimization of an Inertially Stabilized Platform for Aerial Remote Sensing Systems

The purpose of this paper is to study the methodology on structural optimization of inertially stabilized platform (ISP). It is difficult for the ISP structure design since lots of objects are required and many of them are conflicted each other, hence structural optimization should be carried out to seek a compromise between theses contradictions, such as high stiffness and light weight, high ratio of payload to mass and small size, etc. In this paper, first of all, an optimal configuration of 3-axis gimbals assembly is determined on the basis of analysis on the operating environment; and then, an approving structure is eventually obtained with the help of 3D CAD modeling and FEA. The structure is compact as well as lightweight. FEA results show that its strength and stiffness are both satisfied with the requirements.

Inertially stabilized platform technology Concepts and principles

We introduced some of the basic principles, techniques, and key design issues common to ISPs used in many diverse scientific, military, and commercial applications, and we touched on some of the less intuitive effects that must be dealt with. Many of these effects can influence the initial configuration of the system as well as design details later in the design process. The successful design of an ISP usually requires a multidisciplinary design team. The design of an ISP must often be closely coordinated with that of other major subsystems such as the primary sensor and the optics. The role of the systems engineer in the design process is perhaps the most critical because other members of the team may not be aware of the consequences of many of the effects discussed above. Inertially stabilized platforms (ISPs) are used to stabilize and point a broad array of sensors, cameras, telescopes, and weapon systems.

Inertially stabilized platforms for optical imaging systems

Optical imaging sensors, such as television or infrared cameras, collect information about targets or target regions. It is thus necessary to control the sensor's line-of-sight (LOS) to achieve accurate pointing. Maintaining sensor orientation toward a target is particularly challenging when the imaging sensor is carried on a mobile vehicle or when the target is highly dynamic. Controlling an optical sensor LOS with an inertially stabilized platform (ISP) can meet these challenges.A target tracker is a process, typically involving image processing techniques, for detecting targets in optical imagery. This article describes the use and design of ISPs and target trackers for imaging optical sensors.

First Tethered Satellite System: Satellite Gyro Drift On-Flight Identification

This paper. to be considerad as an application of existing stochastic estimator theories, presents the design of ihe algorithm used to identify on flight the initial bias of the TSS-1 Satellite gyro drift rates. This algorithm utilises the Space Shutlle Orbiter as an inertial stable platform and correlates its residual angular rates with the satellite gyro package measurements (when the satellite is still latched on the Shutlle cargo bay). The drift rates nave been computed by means of a stocastic Maximum Likelihood Estimator (MLE) that processes the two data streams synchronized by an opportune cross-correlation function. The algorithm description, as implemented on the Mission Control Center (MCC) of the NASA JSC in Houston, on flight results and their comparison with the design simulation analysis and gyro package manufacturar ground calibration data, before and after the TSS-1 flight mission, are provided in the paper