Base Angular Motion Research Articles

The effect of time-periodic base angular motions upon dynamic response of asymmetric rotor systems

The effect of time-periodic base angular motions upon dynamic response of asymmetric rotor systems is investigated in this article. Both the disk and rotating shaft with asymmetric cross sections a...

Nonlinear dynamic modeling of a simple flexible rotor system subjected to time-variable base motions

Rotor systems carried in transportation system or under seismic excitations are considered to have a moving base. To study the dynamic behavior of flexible rotor systems subjected to time-variable base motions, a general model is developed based on finite element method and Lagrange’s equation. Two groups of Euler angles are defined to describe the rotation of the rotor with respect to the base and that of the base with respect to the ground. It is found that the base rotations would cause nonlinearities in the model. To verify the proposed model, a novel test rig which could simulate the base angular-movement is designed. Dynamic experiments on a flexible rotor-bearing system with base angular motions are carried out. Based upon these, numerical simulations are conducted to further study the dynamic response of the flexible rotor under harmonic angular base motions. The effects of base angular amplitude, rotating speed and base frequency on response behaviors are discussed by means of FFT, waterfall, frequency response curve and orbits of the rotor. The FFT and waterfall plots of the disk horizontal and vertical vibrations are marked with multiplications of the base frequency and sum and difference tones of the rotating frequency and the base frequency. Their amplitudes will increase remarkably when they meet the whirling frequencies of the rotor system.

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.

Parametric instability of flexible rotor-bearing system under time-periodic base angular motions

Parametric instability of flexible rotor-bearing system under time-periodic base angular motions is analyzed in this paper. The accurate finite element model for the flexible rotor-bearing system under time-varying base angular motions is derived based upon the energy theorem and Lagrange’s principle. Three base angular motions, including the rolling, pitching and yawing motions, are assumed to be sinusoidal perturbations superimposed upon constant terms. Considering the time-varying base movements, the second order differential equations of the system will have time-periodic gyroscopic and stiffness coefficients. The discrete state transition matrix (DSTM) method is introduced for numerically acquiring the instability regions. Based upon these, instability computations for a rotor-bearing system with one base motion alone and two base motions together are conducted, respectively. The effects of rotating speed, amplitudes of base motion and phases between two base motions on both the primary and combination instability regions are discussed in detail.

Stabilizing a Gimbal Platform using Self-Tuning Fuzzy PID Controller

The aim of the inertial stabilization system is to stabilize the sensor’s line of sight (LOS) toward a target while is isolating the sensor against the disturbances which are caused by the operating environment. The purpose which this paper is following is a model of control servo system for an inertially stabilized gimbal mechanism to improve the performance of system which is using only PID controller by finding a way to tune the PID gains online, for this purpose a self-tuning Fuzzy PID type controller is used. First the relationships that governs gimbals torque will be derived from Newton’s law under consideration of the dynamic mass unbalance and base angular motion. The next step is construction of stabilization loop through designing the proposed self-tuning Fuzzy-PID controller. For simulation and investigate the system performance in different cases of controller, the Matlab/Simulink is used and Based on different performance criteria a comparison study is made. Based on the results in different conditions on proposed controller the system performance is improved. The simulation result shows improvement on transient and the steady-state performance.

Dynamic behaviors of a geared rotor system under time-periodic base angular motions

The dynamic behaviors of a geared rotor system under time-periodic base motions are studied in this paper. The equations of motion for a spur gear pair system are derived based on the energy theorem and Lagrange's principle. Three base angular motions, including the rolling, pitching and yawing motions, are assumed to be sinusoidal perturbations superimposed upon constant terms. Considering the time-varying base movements and gear meshing, the second order differential equations of the system will not only have time-periodic gyroscopic and stiffness coefficients, but also the multi-frequency external excitations. Numerical method is utilized to obtain the lateral and torsional responses of the geared system under transmission error and unbalanced mass excitations. The effects of various base angular motions on both frequency response and response spectra are discussed in detail. Compared with the other two types of periodic base motions, the rolling base motion has the greatest impact on the dynamic behaviors of the geared system. The transient response of the geared rotor system is always greatly enhanced no matter which type of base angular motion is in operation.

Stabilization loop of a two axes gimbal system using self-tuning PID type fuzzy controller

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 aim of this paper is to present two axes gimbal system. The gimbals torque relationships are derived using Lagrange equation considering the base angular motion and dynamic mass unbalance. The stabilization loops are constructed with cross coupling unit utilizing proposed fuzzy PID type controller. The overall control system is simulated and validated using MATLAB. Then, the performance of proposed controller is evaluated comparing with conventional PI controller in terms of transient response analysis and quantitative study of error analysis. The simulation results obtained in different conditions prove the efficiency of the proposed fuzzy controller which offers a better response than the classical one, and improves further the transient and steady-state performance.

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

Dynamic response of cracked rotor-bearing system under time-dependent base movements

Dynamic response of cracked rotor-bearing system under time-dependent base movements is studied in this paper. Three base angular motions, including the rolling, pitching and yawing motions, are assumed to be sinusoidal perturbations superimposed upon constant terms. Both the open and breathing transverse cracks are considered in the analysis. The finite element model is established for the base excited rotor-bearing system with open or breathing cracks. Considering the time-varying base movements and transverse cracks, the second-order differential equations of the system will not only have time-periodic gyroscopic and stiffness coefficients, but also the multi-frequency external excitations. An improved harmonic balance method is introduced to obtain the steady-state response of the system under both base and unbalance excitations. The response spectra, orbits of shaft center and frequency response characteristics, are analyzed accordingly. The effects of various base angular motions, frequency and amplitude of base excitations, and crack depths on the system dynamic behaviors are considered in the discussions.

3D DYNAMIC ANALYSIS OF A FLEXIBLE DEPLOYING ARM SUBJECTED TO BASE ANGULAR MOTIONS

Problems related to the three-dimensional (3D) dynamics of the deploying flexible arms subjected to base angular motions are studied with simulated tip payloads and actual deployment trajectories. To facilitate the solution, an equivalent dynamical system is developed by introducing the inertial reaction forces on the arm, while the equations of motion are derived in the non-Newtonian reference frame attached to the arm. The dynamic behavior of the arm is investigated both by the finite element and assumed Modes methods for the purpose of verification. This study reveals that base angular motions lead to considerable couplings between the two lateral displacements and axial motions. Meanwhile, the induced loadings on the flexible arm due to the base angular motions are obtained, which are useful for the design of more efficient arms. Furthermore, one may use the resulting arm–tip position envelop to predict the antenna positioning accuracy, which paves the way for possible control systems to limit undesirable motions.

Impact analysis and post-impact motion control issues of a free-floating Space robot subject to a force impulse

This article presents impact dynamic analysis of a free-floating space robot, subject to a force impulse at the hand. We study the joint and the base reactions in terms of finite velocity changes and clarify their role for the post-impact motion behavior of the robot. The analysis makes use of a joint-space orthogonal decomposition procedure involving the so called reaction null space. The article focuses on the specific case of a nonredundant arm and a reaction null space in terms of base angular motion. We further show that with proper post-impact control it is possible to transfer the whole angular momentum from the base toward the manipulator, and in the same time to reduce the joint velocity.