Xin Huo

Angular Rate Sensing with GyroWheel Using Genetic Algorithm Optimized Neural Networks

GyroWheel is an integrated device that can provide three-axis control torques and two-axis angular rate sensing for small spacecrafts. Large tilt angle of its rotor and de-tuned spin rate lead to a complex and non-linear dynamics as well as difficulties in measuring angular rates. In this paper, the problem of angular rate sensing with the GyroWheel is investigated. Firstly, a simplified rate sensing equation is introduced, and the error characteristics of the method are analyzed. According to the analysis results, a rate sensing principle based on torque balance theory is developed, and a practical way to estimate the angular rates within the whole operating range of GyroWheel is provided by using explicit genetic algorithm optimized neural networks. The angular rates can be determined by the measurable values of the GyroWheel (including tilt angles, spin rate and torque coil currents), the weights and the biases of the neural networks. Finally, the simulation results are presented to illustrate the effectiveness of the proposed angular rate sensing method with GyroWheel.

Vibration analysis of flex-gimbal system with high spinning velocity

GyroWheel is an innovative device that combines the actuating capabilities of the control moment gyro with the rate sensing capabilities of the tuned rotor gyro by using a spinning flex-gimbal system. For a 3-DOF GyroWheel rotor with high spinning velocity, the uneven mass distribution, called unbalance, is inevitable which leads to unexpected vibration and uncertain dynamics, which needs to be corrected to a certain level. In this paper, the vibrations of the GyroWheel rotor are analyzed by experiment designs and classifications, and some properties introduced by uneven mass distribution are disclosed which can be utilized to develop reasonable unbalance identification algorithm for these kinds of flex-gimbal Systems.

Aerodynamic Drag Analysis of 3-DOF Flex-Gimbal GyroWheel System in the Sense of Ground Test

GyroWheel is an innovative device that combines the actuating capabilities of a control moment gyro with the rate sensing capabilities of a tuned rotor gyro by using a spinning flex-gimbal system. However, in the process of the ground test, the existence of aerodynamic disturbance is inevitable, which hinders the improvement of the specification performance and control accuracy. A vacuum tank test is a possible candidate but is sometimes unrealistic due to the substantial increase in costs and complexity involved. In this paper, the aerodynamic drag problem with respect to the 3-DOF flex-gimbal GyroWheel system is investigated by simulation analysis and experimental verification. Concretely, the angular momentum envelope property of the spinning rotor system is studied and its integral dynamical model is deduced based on the physical configuration of the GyroWheel system with an appropriately defined coordinate system. In the sequel, the fluid numerical model is established and the model geometries are checked with FLUENT software. According to the diversity and time-varying properties of the rotor motions in three-dimensions, the airflow field around the GyroWheel rotor is analyzed by simulation with respect to its varying angular velocity and tilt angle. The IPC-based experimental platform is introduced, and the properties of aerodynamic drag in the ground test condition are obtained through comparing the simulation with experimental results.

Control design with Lipschitz switching surfaces based on new contingent cone criteria

In this paper, a control design method for a class of non-linear uncertain systems is proposed based on the new contingent cone criteria, which are used to estimate the relation between the phase trajectories and an arbitrary Lipschitz continuous surface. A series of Lipschitz domains are constructed recursively, each of which contains two Lipschitz switching surfaces that may be non-smooth. Filippovs differential inclusion is adopted to describe the dynamics of the closed-loop system. Based on the constructed Lipschitz domains, a feedback controller is designed to drive the trajectories of the closed-loop system to the origin asymptotically. Finally, the validity of the method is illuminated by some numerical examples.

On-off Control Design of a Class of Linear Systems via Lipschitz Switching Surfaces

Abstract In order to achieve more flexibility for state feedback control design, a new design method based on Lipschitz switching surfaces is proposed for a class of n -th order linear systems subject to on-off control input in this paper. The Lipschitz switching surface is piecewise smooth and developed by the combination of several available smooth subsurfaces due to the partitioned domains of interest. Due to the discontinuity of the on-off input, Filippovs differential inclusion is adopted to describe the dynamics of trajectories of the closed-loop system. The globally asymptotic stability of the on-off control system with Lipschitz switching surfaces is illustrated by means of nonsmooth analysis and LaSalles invariant principle for nonsmooth systems.

Nonsmooth control design of mechanical systems with friction in the sense of Filippov

Utilizing the notion of Filippov solution, a sliding mode control law is derived for generic second order nonlinear mechanical system with friction. The control law is designed with some tunable parameters and optional functions. The asymptotically stability of the closed-loop system is proved by the concept of the solution, nonsmooth analysis and nonsmooth Lyapunov stability theory. By some numerical examples, the correctness of the control law is illuminated. Finally, the validity of the controller design is verified by a simulation example for a flight simulation table system with Stricbeck friction model.

Dyna-Q Algorithm for Path Planning of Quadrotor UAVs

In this paper, the problem of path planning of quadrotor unmanned aerial vehicles (UAVs) is investigated in the framework of reinforcement learning methodology. With the abstraction of the environment in the form of grid world in 2D, the design procedure is presented by utilizing the Dyna-Q algorithm, which is one of the reinforcement method combining both model-based and non-model framework. In this process, an optimal or suboptimal safe flight trajectory will be obtained by learning constantly and planning by simulated experience, thus calculative reward can be maximized efficiently. Matlab software is used for maze establishing and computation, and the effectiveness of the proposed method is illustrated by two typical examples.

Modeling and analysis of unbalance for GyroWheel system

For rotating machineries, unbalance of the rotor is widely existed which plays a bad role resulting in unexpected vibrations, uncertain dynamics and even unstable motions. The GyroWheel system, a typical rotating machine, is an innovative attitude determination and control device, which provides a varying amplitude and direction of the angular moment vector by using a spinning flex-gimbal suspension. In this paper, the uneven mass distribution of the GyroWheel rotor, called unbalance, is modeled and investigated by simulations and comparisons. The results can be utilized to reveal the operating properties, and to develop reasonable unbalance identification algorithm for the GyroWheel system.

Error Analysis and Error Allocation for Turntable Systems Used in GyroWheel Calibration Tests

Calibration tests are of great importance to ensure rate-sensing accuracy of GyroWheel, an innovative attitude determination and control device. In the process of calibration tests, turntable errors are inevitable, which hinder the calibration accuracy and rate-sensing capability. Hence, error analysis for GyroWheel calibration tests is conducted, and the relationship between the calibration accuracy and the orientation error is established based on analytical derivation and numerical simulations. Subsequently, an error model of the turntable system is derived using rigid body kinematics, by which the relationship between the orientation error and turntable errors is described. According to sensitivity analysis and manufacturing capability, an error allocation method is proposed to determine the accuracy requirement of the test turntable, and the effectiveness of the proposed method is verified by repeated simulation tests. Based on the presented analysis and proposed method in this paper, the effects of various turntable errors on the calibration accuracy can be obtained quantitatively, and a theoretical basis for the determination of the turntable accuracy is provided, which are of great significance to guide the calibration tests and improve the calibration accuracy of GyroWheel.

A modified synchronous control method for 2-DOF arm-typed precision centrifuge

Precision centrifuge is an important electromechanical equipment which is used to test and calibrate model parameters of accelerometers. For a 2-DOF(Degree of Freedom) precision centrifuge, which offers a high overload environment and two rotating degree of freedom at the same time, a continuously rotary countershaft is configured reasonably to counteract the rotation motion of the mainshaft system in order to maintain the directivity of the unit under test in the inertial space. Therefore, the pointing accuracy is a significant index, which is influenced mostly by the angular velocity tracking error between the mainshaft and the countershaft. In this paper, the mathematical models of the mainshaft and the countershaft are established by experimental data and frequency spectrum analysis tools, respectively. Also, several synchronous control methods are presented and compared for the 2-DOF arm-typed precision centrifuge by simulation experiments.