Weishan Chen

The Terminal Guidance System Performance Analysis: a Finite-time Gain Measurement Approach

In this paper, we consider the performance analysis problem of a terminal guidance system. The aim of the problem is to compare the miss distance between a flight vehicle and a target in the presence of noise, disturbance and other influencing factors. We establish a linear time-varying system model in a finite time horizon to study the performance analysis problem, and we also provide several augmentation form models of the terminal guidance system. A finite time gain measurement index is proposed to be the metric of the zero effort miss distance(ZEM), which is the estimation of the minimal miss distance between the flight vehicle and the target. A sufficient and necessary condition is proved for the finite-time gain measurement index. The statistical significance of the finite time gain measurement is also treated. Some simulation results are given to illustrate the effectiveness of the proposed performance analysis method.

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.

Unbalance identification for mainshaft system of 2-DOF precision centrifuge: A displacement sensor-based approach

Precision centrifuge is an important electromechanical equipment which is used to test and calibrate inertial components, and dynamic unbalance is the most egregious factor which influences its performance and causes vibration. In this paper, the problem of dynamic unbalance identification for main shaft system of a 2-DOF precision centrifuge is investigated. The causes which result in dynamic unbalance with respect to the introduced main shaft system are discussed, and a dynamical analytical model is established in the framework of ADAMS to facilitate the analysis. By using two axis-layout displacement sensors, a new algorithm is proposed by considering both of the centrifugal force and the gravity of the unbalance mass, and further an integrated identification approach is developed. The effectiveness of the approach is analyzed by numerical simulations in ADAMS environment, and some experimental studies are also demonstrated to illustrate the validity of our work.

Output Tracking Control of Switched Hybrid Systems: A Fliess Functional Expansion Approach

The output tracking problem is investigated for a nonlinear affine system with multiple modes of continuous control inputs. We convert the family of nonlinear affine systems under consideration into a switched hybrid system by introducing a multiple-valued logic variable. The Fliess functional expansion is adopted to express the input and output relationship of the switched hybrid system. The optimal switching control is determined for a multiple-step output tracking performance index. The proposed approach is applied to a multitarget tracking problem for a flight vehicle aiming for one real target with several decoys flying around it in the terminal guidance course. These decoys appear as apparent targets and have to be distinguished with the approaching of the flight vehicle. The guidance problem of one flight vehicle versus multiple apparent targets should be considered if no large miss distance might be caused due to the limitation of the flight vehicle maneuverability. The target orientation at each time interval is determined. Simulation results show the effectiveness of the proposed method.

A finite-time generalized H2 gain measure and its performance criterion

In this paper, the performance measure problem is considered for a linear time-varying system with non-zero initials and bounded external disturbance in a finite-time horizon. A finite-time generalized H2 gain is proposed which is defined as a ratio of the maximal penalty output and the sum of the energy of the exogenous input and nonzero initial conditions in a finite time interval. The finite-time generalized H2 gain proposed can be used as a performance metric of such a class of systems in the worst-case which are not required to be stable and with zero initials. We proved several properties of the proposed finite-time generalized H2 gain and its performance criterion is also proved. The computation of the finite-time generalized H2 gain is then treated. We also provide an application and simulation results of the proposed finite-time generalized H2 gain measure.

Extended optimum frequency tracking scheme for ultrasonic motor

HighlightsThe application scope of the optimum frequency tracking scheme is greatly extended.The orthogonal applied voltages are constructed.Ultrasonic motor has an optimal working frequency even under orthogonal voltages. ABSTRACT This work presents a general optimum frequency tracking scheme for an ultrasonic motor, which no longer requires the amplitudes of the applied voltages to keep identical. The proposed scheme here greatly extends the application of the optimum frequency in comparison to the existing studies. The mechanical quality factor of an ultrasonic motor is initially derived to describe the loss, which further is also in proportion to the temperature rise. The optimum frequency from the loss reduction viewpoint is then obtained, at which frequency the ultrasonic motor maintains the minimum loss and subsequently the minimum temperature rise. The optimum‐frequency tracking scheme is subsequently constructed. Experiments are carried out to verify the existence of the optimum frequency and the reduction of the temperature‐rise under the applied voltages in the general form, whose amplitudes and phase difference are all adjustable. The results have inferred that the optimum frequency still exists even though the applied voltages are in the general form, at which frequency the temperature‐rise is obviously reduced in the absence of any external cooling equipment. The optimum frequency of the ultrasonic motor now gets closer to the industrial applications, especially when the applications require the velocity adjustment in a wide range.