Tendon-Sheath Mechanisms in Flexible Membrane Wing Mini-UAVs: Control and Performance

Flexible membrane wings (FMWs) are known for two inherent advantages, that is, adaptability to gusty airflow as the wings can flex according to the gust load to reduce the effective angle of attack and the ability to be folded for compact storage purposes. However, the maneuverability of UAV with FMWs is rather limited as it is impossible to install conventional ailerons. The maneuver relies only on the rudders. Some applications utilize torque rods to warp the wings, but this approach makes the FMW become unfoldable. In this research, we proposed the application of a tendon-sheath mechanism to manipulate the wing shape of UAV. Tendon-sheath mechanism is relatively flexible; thus, it can also be folded together with the wings. However, its severe nonlinearity in its dynamics makes the wing warping difficult to control. To compensate for the nonlinearity, a dedicated adaptive controller is designed and implemented. The proposed approach is validated experimentally in a wind tunnel facility with imitated gusty condition and subsequently tested in a real flight condition. The results demonstrate a stable and robust wing warping actuation, while the adaptive washout capability is also validated. Accurate wing warping is achieved and the UAV is easily controlled in a real flight test

Respons Getaran Non-Linier pada Sistem Poros-rotor Bagian I: Pengaruh Celah Bantalan

Sari. Dalam kegiatan anaiisis ini diiakukan permodelan sistem getaran dengan gaya eksitasi yang berasal dari ketidakseimbangan rotor dan ketaksesumbuan poros. Gaya eksitasi ini kemudian diteruskan ke bantalan dan selanjutnya melulaui bantalan diteruskan ke rumah bantalan. Ketaklinieran kekakuan sistem bantalan yang berasal dari celah (clearance) bantalan tersebut akan menghasilkan ciri sendiri sehinngga ciri ini dapat digunakan untuk mengidentifikasi keausan bantalan yang digunakan. Hasil analisis teoritik ini selanjutnya dibandingkan dengan data gertaran domain waktu (waveform) yang diperoleh dari kaji eksperimental pada sistem poros-tutor. Mechanical Signature Analysis of Synchronous and synchronous Excited Rotating Rotor Supported by Rolling Element BearingAbstract. An analytical model of a rotor shaft vibration system subjected to rotor unbalance and shaft misalignment excitation forces has been developed. Those excitation forces are transmitted to a bearing housing through a roller bearing housing where the vibration response is measured. The non-linearity of the bearing stiffness due to the bearing clearance reveals some specific vibration signatures, which can be utilized for bearing, wear identification. The theoretical results obtained in this study are compared with those obtained from experiment.

Integrated Condition Monitoring and Prognosis Method for Incipient Defect Detection and Remaining Life Prediction of Low Speed Slew Bearings

This paper presents an application of multivariate state estimation technique (MSET), sequential probability ratio test (SPRT) and kernel regression for low speed slew bearing condition monitoring and prognosis. The method is applied in two steps. Step (1) is the detection of the incipient slew bearing defect. In this step, combined MSET and SPRT is used with circular-domain kurtosis, time-domain kurtosis, wavelet decomposition (WD) kurtosis, empirical mode decomposition (EMD) kurtosis and the largest Lyapunov exponent (LLE) feature. Step (2) is the prediction of the selected features\u27 trends and the estimation of the remaining useful life (RUL) of the slew bearing. In this step, kernel regression is used with time-domain kurtosis, WD kurtosis and the LLE feature. The application of the method is demonstrated with laboratory slew bearing acceleration data

UAV Control in Close Proximities - Ceiling Effect on Battery Lifetime

With the recent developments in the unmanned aerial vehicles (UAV), it is expected them to interact and collaborate with their surrounding objects, other robots and people in order to wisely plan and execute particular tasks. Although these interaction operations are inherently challenging as compared to free-flight missions, they might bring diverse advantages. One of them is their basic aerodynamic interaction during the flight in close proximities which can result in a reduction of the controller effort. In this study, by collecting real-time data, we have observed that the current drawn by the battery can be decreased while flying very close to the surroundings with the help of the ceiling effect. For the first time, this phenomenon is analyzed in terms of battery lifetime degradation by using a simple full equivalent cycle counting method. Results show that cycling related effect on battery degradation can be reduced by a 15.77% if the UAV can utilize ceiling effect.Comment: ICoIAS 201

A non-contact measuring system for in-situ surface characterization based on laser confocal microscopy

The characterization of surface topographic features on a component is typically quantified using two-dimensional roughness descriptors which are captured by off-line desktop instruments. Ideally any measurement system should be integrated into the manufacturing process to provide in-situ measurement and real-time feedback. A non-contact in-situ surface topography measuring system is proposed in this paper. The proposed system utilizes a laser confocal sensor in both lateral and vertical scanning modes to measure the height of the target features. The roughness parameters are calculated in the developed data processing software according to ISO 4287. To reduce the inherent disadvantage of confocal microscopy, e.g. scattering noise at steep angles and background noise from specular reflection from the optical elements, the developed system has been calibrated and a linear correction factor has been applied in this study. A particular challenge identified for this work is the in-situ measurement of features generated by a robotized surface finishing system. The proposed system was integrated onto a robotic arm with the measuring distance and angle adjusted during measurement based on a CAD model of the component in question. Experimental data confirms the capability of this system to measure the surface roughness within the Ra range of 0.2 – 7 μm (bandwidth λc/λs of 300), with a relative accuracy of 5%

Characterization, Modelling and Control of Mechanical Systems Comprising Material and Geometrical Nonlinearities

status: publishe

In-process endpoint detection of weld seam removal in robotic abrasive belt grinding process

This paper proposes a novel approach for inprocess endpoint detection of weld seam removal during robotic abrasive belt grinding process using discrete wavelet transform (DWT) and support vector machine (SVM). A virtual sensing system is developed consisting of a force sensor, accelerometer sensor and machine learning algorithm. This work also presents the trend of the sensor signature at each stage of weld seam evolution during its removal process. The wavelet decomposition coefficient is used to represent all possible types of transients in vibration and force signals generated during grinding over weld seam. “Daubechies-4” wavelet function was used to extract features from the sensors. An experimental investigation using three different weld profile conditions resulting from the weld seam removal process using abrasive belt grinding was identified. The SVM-based classifier was employed to predict the weld state. The results demonstrate that the developed diagnostic methodology can reliably predict endpoint at which weld seam is removed in real time during compliant abrasive belt grinding.NRF (Natl Research Foundation, S’pore)Accepted versio