Gimbal Axis Research Articles

Model predictive control of rigid spacecraft with two variable speed control moment gyroscopes

In this paper, an attitude maneuver control problem is investigated for a rigid spacecraft using an array of two variable speed control moment gyroscopes (VSCMGs) with gimbal axes skewed to each other. A mathematical model is constructed by taking the spacecraft and the gyroscopes together as an integrated system, with the coupling interaction between them considered. To overcome the singular issues of the VSCMGs due to the conventional torque-based method, the first-order derivative of gimbal rates and the second-order derivative of the rotor spinning velocity, instead of the gyroscope torques, are taken as input variables. Moreover, taking external disturbances into account, a feedback control law is designed for the system based on a method of nonlinear model predictive control (NMPC). The attitude maneuver can be realized fast and smoothly by using the proposed controller in this paper.

Gimbal Influence on the Stability of Exterior Orientation Parameters of UAV Acquired Images.

In this paper, results from the analysis of the gimbal impact on the determination of the camera exterior orientation parameters of an Unmanned Aerial Vehicle (UAV) are presented and interpreted. Additionally, a new approach and methodology for testing the influence of gimbals on the exterior orientation parameters of UAV acquired images is presented. The main motive of this study is to examine the possibility of obtaining better geometry and favorable spatial bundles of rays of images in UAV photogrammetric surveying. The subject is a 3-axis brushless gimbal based on a controller board (Storm32). Only two gimbal axes are taken into consideration: roll and pitch axes. Testing was done in a flight simulation, and in indoor and outdoor flight mode, to analyze the Inertial Measurement Unit (IMU) and photogrammetric data. Within these tests the change of the exterior orientation parameters without the use of a gimbal is determined, as well as the potential accuracy of the stabilization with the use of a gimbal. The results show that using a gimbal has huge potential. Significantly, smaller discrepancies between data are noticed when a gimbal is used in flight simulation mode, even four times smaller than in other test modes. In this test the potential accuracy of a low budget gimbal for application in real conditions is determined.

Study on the friction torque test and identification algorithm for gimbal axis of an inertial stabilized platform

To reduce the influence of nonlinear friction on the dynamic and static performance of gimbal axis for inertial stabilized platform, a novel method based on steady-state error response to identify LuGre friction parameters is proposed in this paper, and a kinetic friction torque testing system using the proposed method is developed. On account of the introduction of structure and electromechanical model for inertial stabilized platform, the relation among the input signals, interfering signals and steady-state error are analyzed. And then the torque ripple compensation function is identified and introduced into the control loop to eliminate the effects of torque ripple on parameter identification of friction model. Based on the friction torque testing system designed, the parameters of LuGre friction model for gimbal axis are got by the method of Two-step identification and dynamic parameter optimization. According to the identified friction model, the tracking process of the framework is compensated. The tracking performance is verified through both simulation and experimental results.

Effects of Flight Dynamics on Performance of One Axis Gimbal System, Considering Disturbance Torques

The gimbal stabilization mechanism system is used to provide the stability to an object mounted on the gimbal by isolating it from the base angular motion and vibration. In this paper the model of one axis gimbal system with dynamics flying object is introduced. The gimbal torque relationships are obtained using Newton’s second law equation on the assumption that gimbal is rigid body. The system is modelled using Simulink MATLAB. In fact, the purpose of this research was to analyse effects of flight dynamics on performance of one axis gimbal system. The simulation results are discussed and compared to show the validity of the gimbal system proposed at the flight path. Also, the results show that the gimbal system stabilizes the line of sight even when the disturbance torques effect on the system performance.

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.

Global attraction of steady motions of a gimbal-mounted asynchronous gyroscope

The subject of consideration is a gyroscope mounted in the gimbal (Cardan) suspension and placed on the immovable foundation in the field of gravity. Dissipative and control torques on the axes of gimbals are supposed to be absent, but the fast rotating rotor is under the action of the frictional torque, and so the device is supplied with the asynchronous electric motor that forms a driving torque acting about the axis of rotation of the rotor in the inner gimbal. The inner gimbal serves as the stator of the motor. This device has a family of steady motions, which are steady precessions of the rotor about the outer gimbal axis and steady rotations of the rotor about its axis of rotation in the inner gimbal. In the paper, the global attraction property is proved for the set of steady motions. This means that every motion of the device tends to one of its steady motions as time tends to infinity. Outcomes of numerical simulation are presented to give a demonstration of this property.

High-Efficiency Thrust Vector Control Allocation

A generalized approach to the allocation of redundant thrust vector slew commands for multi-actuated launch vehicles is presented, where deflection constraints are expressed as omniaxial or elliptical deflection limits in gimbal axes. More importantly than in the aircraft control allocation problem, linear allocators (pseudoinverses) are preferred for large booster applications to facilitate accurate prediction of the control-structure interaction resulting from thrust vectoring effects. However, strictly linear transformations for the allocation of redundant controls cannot, in general, access all of the attainable moments for which there is a set of control effector positions that satisfies the constraints. In this paper, the control allocation efficiency of a certain class of linear allocators subject to multiple quadratic constraints is analyzed, and a novel single-pass control allocation scheme is proposed that augments the pseudoinverse near the boundary of the attainable set. The controls are determined over a substantial volume of the attainable set using only a linear transformation; as such, the algorithm maintains compatibility with frequency-domain approaches to the analysis of the vehicle closed-loop elastic stability. Numerical results using a model of a winged reusable booster system illustrate the proposed technique’s ability to access a larger fraction of the attainable set than a pseudoinverse alone.

Modeling, Control and Simulation of Cascade Control Servo System for One Axis Gimbal Mechanism

The gimbal stabilization mechanism is used to provide the stability to an object mounted on the gimbal by isolating it from the base angular motion and vibration. The purpose of this paper is to present a model of control servo system for one axis gimbal mechanism using a cascade PID controller. The gimbal torque relationships are derived by taking into consideration the base angular motion. The conventional PID controller and three cascade controller structures are investigated. The servo control loop is built and modelled in MATLAB/Simulink using these controllers. The simulation results are compared and the servo system performance is analysed for each controller in terms of performance criteria. The comparison results prove that a further improved system performance is achieved using I-PD controller as compared to the system performance obtained when the other controllers are utilized. The paper’s value lies in designing the servo control system using a modified controller constitutes of tow parallel I-PD controllers related with a switch depends on the base angular rate as a threshold. The results show that the modified system realizes the desired servo system requirements.

Fuzzy Stabilization Loop of One Axis Gimbal System

The application of inertial stabilization system is to stabilize the sensor’s line of sight toward a target by isolating the sensor from the disturbances induced by the operating environment. The purpose of this paper is to present a model of control servo system for one axis gimbal mechanism using fuzzy PID type controller. The gimbals torque relationships are derived using Newton’s law considering the base angular motion and dynamic unbalance. Then, the stabilization loop is constructed and the proposed fuzzy controller is designed. The overall control system is simulated using MATLAB/Simulink, then the system performance is investigated in different cases for both conventional PI and fuzzy PID controller. A comparison study is made based on some performance criteria. The results obtained in different conditions confirms that a further improved system performance can be achieved using the proposed fuzzy controller as compared to the conventional PI controller. The simulation results proves the efficiency of the proposed fuzzy controller which offers a better response than PI one, and improves further the transient and the steady-state performance. General Terms Inertial stabilization systems, fuzzy control, servo systems

A novel single thruster control strategy for spacecraft attitude stabilization

Feasibility of achieving three axis attitude stabilization using a single thruster is explored in this paper. Torques are generated using a thruster orientation mechanism with which the thrust vector can be tilted on a two axis gimbal. A robust nonlinear control scheme is developed based on the nonlinear kinematic and dynamic equations of motion of a rigid body spacecraft in the presence of gravity gradient torque and external disturbances. The spacecraft, controlled using the proposed concept, constitutes an underactuated system (a system with fewer independent control inputs than degrees of freedom) with nonlinear dynamics. Moreover, using thruster gimbal angles as control inputs make the system non-affine (control terms appear nonlinearly in the state equation). This necessitates the control algorithms to be developed based on nonlinear control theory since linear control methods are not directly applicable. The stability conditions for the spacecraft attitude motion for robustness against uncertainties and disturbances are derived to establish the regions of asymptotic 3-axis attitude stabilization. Several numerical simulations are presented to demonstrate the efficacy of the proposed controller and validate the theoretical results. The control algorithm is shown to compensate for time-varying external disturbances including solar radiation pressure, aerodynamic forces, and magnetic disturbances; and uncertainties in the spacecraft inertia parameters. The numerical results also establish the robustness of the proposed control scheme to negate disturbances caused by orbit eccentricity.

On steady motions of a rigid body bearing a two-degree-of-freedom control momentum gyroscope with precession axis arbitrarily oriented in the carrying body

Steady motions of a rigid body with a control momentum gyroscope are studied versus the gimbal axis direction relative to the body and the magnitude of the system angular momentum. The study is based on a formula that gives a parametric representation of the set of the system steady motions in terms of the rotation angle of the gimbal. It is shown that, depending on the values of the parameters, the system has 8, 12, or 16 steady motions and the number of stable motions is 2 or 4.

Spacecraft Attitude Control Using a Double-Gimbal Control Moment Gyro

This paper presents a novel attitude control scheme for a spacecraft. It involves the use of a double-gimbal control moment gyro (CMG), wherein the rotational speed of the momentum wheel is kept constant. Tilting the spin axis of the momentum wheel around either an inner or an outer gimbal axis can generate attitude control torques in one rotational direction. In order to compensate for the absence of control torque in the other rotational direction, a combination of rotations of the inner and outer axes is designed to generate a cyclic motion about the spin axis of the momentum wheel resulting in three-axis attitude control. Analytical and numerical algorithms are developed to compute the control inputs, i.e., the tilt angles of the inner and outer gimbal axes, which are responsible for the desired change in attitude. The effectiveness of the proposed control scheme is verified by numerical simulations.

Underactuated spacecraft angular velocity stabilization and three-axis attitude stabilization using two single gimbal control moment gyros

Angular velocity stabilization control and attitude stabilization control for an underactuated spacecraft using only two single gimbal control moment gyros (SGCMGs) as actuators is investigated. First of all, the dynamic model of the underactuated spacecraft is established and the singularity of different configurations with the two SGCMGs is analyzed. Under the assumption that the gimbal axes of the two SGCMGs are installed in any direction, and that the total system angular momentum is not zero, a state feedback control law via Lyapunov method is designed to globally asymptotically stabilize the angular velocity of spacecraft. Under the assumption that the gimbal axes of the two SGCMGs are coaxially installed along anyone of the three principal axes of spacecraft inertia, and that the total system angular momentum is zero, a discontinuous state feedback control law is designed to stabilize three-axis attitude of spacecraft with respect to the inertial frame. Furthermore, the singularity escape of SGCMGs for the above two control problems is also studied. Simulation results demonstrate the validity of the control laws.

Fast Model Predictive Control of the Nadir Singularity in Electro-Optic Systems

RECISION pointing and stabilization of the sightline are vital capabilities in all airborne electro-optic (EO) equipment. In traditional control theoryterminology,the pointingtask isatracking requirement,eitherofadynamictargetorsomeotherspecialpointof interest, and stabilization refers to the disturbance rejection capability of the sightline controller; typical disturbances are a combinationofownshipmotionandbearingfriction. Therelativeimportance between the pointing and stabilization tasks is a function of the intendedoperationoftheEOsystem;forexample,long-rangetargetingrequiresprecisestabilization,butanagilesightlineisessentialfor directed infrared countermeasures (DIRCM) systems [1], although both pointing and stabilization loops should be optimized for all systems. A DIRCM engagement occurs when the host platform is attacked by a surface-to-air missile, usually a shoulder-launched Man-Portable Air Defence missile, which is defeated when the DIRCM system positions a jamming signal onto the missile seeker. Obviously, accurate target tracking is essential over a full hyperhemispherical field of regard (FOR), as any tracking deficiencies are sure to be exploited by future missile guidance systems and tactics. Given the particular threat of global terrorism to the airline industry, future DIRCM systems should be small, lightweight, and costeffective for inclusion on commercial aircraft, which invariably limits the number of available axes for sightline control. A minimum of two axes are necessary to attain full hyperhemispherical FOR. The outer gimbal (OG) axis is usually constrained to rotate with respect to the platform z axis (through azimuth angle � ) and the inner gimbal (IG) with respect to the OG y axis (through elevation angle ). This is shown in Fig. 1. When the outerandinneraxesareorthogonal,thesightlinecanbepositionedto any orientation in space, as the IG and OG axes form an ideal orthogonal basis. However,whenthe innergimbal angleapproaches the nadir (defined as �� 90 deg) (i.e., the sightline becomes aligned with the axis of rotation of the outer gimbal), the pointing system experiences the loss of a degree of freedom known as gimbal

On steady rotations of a rigid body bearing a single-axis powered gyroscope whose precession axis is parallel to a principal plane of inertia

The set of steady motions of the system named in the title is represented parametrically via the gyro gimbal rotation angle for an arbitrary position of the gimbal axis.

Spacecraft Pointing Control Using a Variable-Speed Control Moment Gyro

The objective of this study is to align a certain axis of a spacecraft in an arbitrary direction by using a variable-speed single-gimbal CMG. Because the total angular momentum of the spacecraft is conserved in inertial space, the final attitude of the spacecraft is restricted, and it is possible to achieve pointing control of the axis that is orthogonal to the gimbal axis. Using new parameters to express pointing errors, we have proposed a simple pointing control law that can be used to align the pointing axis in an arbitrary direction in inertial space. The validity of the proposed control law is verified by numerical simulations.

On limit motions of a system of control moment gyros with intrinsic dissipation in a homogeneous gravitational field

We study the limit motions of a free rigid body bearing n two-degree-of-freedom control moment gyros with dissipation in the gyro gimbal suspension axes. We show that, in the absence of dynamic symmetry, the limit motions of the system are only steady rotations at a constant angular velocity. In the case of dynamic symmetry, the gyros can be arranged so that, in addition to steady rotations, the system exhibits limit motions that are regular precessions.

Stability analysis of steady rotations of a rigid body bearing two-degree-of-freedom control moment gyros with dissipation in gimbal suspension axes

To study the stability of steady rotations of a control moment gyro system with internal dissipation, we use the Barbashin-Krasovskii theorem and the relation, established in [1], between the Lyapunov function and steady motions. Taking into account the special properties of the original problem, we reduce it to a lower-dimensional problem.

4113 コントロール・モーメント・ジャイロの内部擾乱補償制御(S75-2 宇宙システムの誘導・制御(2),S75 宇宙システムの誘導・制御)

Future generation mission of satellites is to understanding global environment extensively and disaster monitoring in an acute situation and so on. Therefore, satellites need to observe given observation points in given times. Requirements of satellites attitude control are high speed attitude changes and high stability, and requirements of attitude control actuator are high torque and high resolution torque. Currently, Attitude control actuator which is able to generate high torque is only Control Moment Gyro. However, CMG generates disturbance torque because of complicated structure and dynamics interference. In this study, modeling disturbance torque in gimbal axis and analyzing control torque error make understanding effect of control torque error against satellites attitude control. In addition, Use of disturbance estimation observer and disturbance elimination filter has control over control torque error.

Two-axis MEMS Scanning Catheter for Ultrahigh Resolution Three-dimensional and En Face Imaging

Ultrahigh resolution two and three-dimensional optical coherence tomography (OCT) imaging was performed using a miniaturized, two-axis scanning catheter based upon microelectromechanical systems (MEMS) mirror technology. The catheter incorporated a custom-designed and fabricated, 1-mm diameter MEMS mirror driven by angular vertical comb (AVC) actuators on both an inner mirror axis and an outer, orthogonal gimbal axis. Using a differential drive scheme, a linearized position response over +/- 6 degrees mechanical angle was achieved. The flexible, fiber-optic catheter device measured < 5 mm in outer diameter with a rigid length of ~ 2.5 cm at the distal end. In vivo and ex vivo images are presented with < 4 microm axial and ~ 12 microm transverse resolution in tissue.