Cross Axis Research Articles

Performance of a Prototype Heliostat Having a Twisting Mechanism to Maintain Focus Throughout the Day

A prototype heliostat has been designed and built with a rectangular reflector whose shape is altered automatically through the day, to maximize concentration at the receiver. The shape changes needed to form solar disc images, which give the highest possible concentration, can be realized by twisting the reflector from its corners, provided that a target-oriented, dual-axis mount is used. Then a cam mechanism connected to the second (cross) axis drive, turning with the angle of incident sunlight, may be used to twist the reflector as needed. Our prototype reflector comprises a single glass mirror, 2.4 m x 3.3 m, attached to a steel frame. Four diagonal back struts extend from the central mechanism out to the rectangular frame corners. The glass mirror of the prototype is attached to the steel frame by 58 screw actuators. Before twisting the frame, the glass shape is adjusted to the biconic shape needed to form a 1 m diameter disc image on a 113 m distant target when sunlight is incident at 60°. To form disc images over the full range of angles of incidence from 0° (normal incidence) to 70°, the struts push the corners up and down by up to 17 mm. A reflectometry metrology system has been used to set the 58 adjustment screws for the initial shape to an accuracy of ≤ 0.6 mrad, and to measure the accuracy of the different twisted shapes. The prototype will be tested at NSTTF early next year.

Design and characterization of an accelerometer with low cross axis sensitivity

An out-of-plane capacitive accelerometer with low cross axis sensitivity at high accelerations based on a CMOS MEMS process is developed. A truss frame with a high ratio of in-plane stiffness to out-of-plane stiffness is designed to suspend the proof mass of the accelerometer. The configuration of the proof mass with four auxiliary masses surrounding a main mass boosts the sensitivity of the accelerometer in the out-of-plane direction. A sensing circuit with period modulated output signals is realized by applying a relaxation oscillator to the sensing capacitors. The relaxation oscillator converts the capacitance changes to frequency variations. Analytical models are developed to assist the design of the accelerometer. The nonlinearity and sensitivity of the accelerometer are 1.1% and 754 Hz/g, respectively, for the acceleration ranging from 0 to 9 g. Measured cross-axis sensitivity is 4% at an acceleration of 9 g. The power consumption is 1.7 mW under a 1.8 V supply.

Design and simulation of dual-axis MEMS accelerometer

Micro electro Mechanical systems (MEMS) are integrated electro-mechanical systems with microscale features. These devices are effective and low power consumers, making them one of the prospective technologies for use in a variety of industries and fields, including as the automotive, consumer, industrial, optical, robotic, biotechnology, medical engineering, and military sectors. MEMS accelerometer is one of the prominent inertial sensor allied in different applications.The proposed work is intended on design, modelling and simulation of a dual axis crab-legged suspension system. By using the SOI MUMPs fabrication process flow formulated by MEMSCAP Foundry a capacitive-based MEMS accelerometer is designed. Natural frequency, cross axis sensitivity, frequency response, and static capacitance analysis are the main design characteristics.Sensor is designed for a low frequency applicatons by assuming a natural frequency of 4KHz, he actual bandwidth vs sensitiviy is about 2KHz and 0.088um/g respectively. The measured stiffness along × and y are kx = 176.089 N/m ky = 176.089 N/m respectively.The proposed design of the capacities sensing comb drive structure is capable of producing linear change of the displacement for applied accelerations between 1 and 1000 g (1 g = 9.8 m/s2), over which the stress values exceed the tensile strength of the silicon material. By using stationary,frequency domain studies and electro-mechanics physics, the simulation is carried out in the COMSOL Multiphysics tool.

Design and fabrication of a micro-opto-mechanical-systems accelerometer based on intensity modulation of light fabricated by a modified deep-reactive-ion-etching process using silicon-on-insulator wafer

Accelerometers that work based on intensity modulation of light are more sensitive, economically feasible, and have a simpler fabrication process compared to wavelength modulation. A micro-opto-electro-mechanical-system accelerometer based on intensity modulation of light is designed and fabricated. A movable shutter that is attached to the proof mass is designed to change the intensity of light. Moreover, the mechanical part is designed to improve the overall sensitivity and linear behavior in the measurement range. The designed accelerometer is fabricated by a deep-reactive-ion-etching (DRIE) process. The DRIE process used in this report is based on a Bosch-like process, which uses SF6 and a mixture of H2, O2, and SF6 gases in etching and passivation subsequences, respectively. This method has a lower plasma density and a higher base pressure and causes higher verticality, which results in lower optical efficiency loss in comparison with the Bosch process. Furthermore, the functional characteristics of the accelerometer are derived with analytical and numerical methods, and the results are compared. The functional characteristics of the accelerometer are as follows: a resonant frequency of 0.56 kHz, a mechanical sensitivity of 0.6μm/g, an optical sensitivity of 16%/nm, an overall sensitivity of 9.6%/g, a footprint of 2000×2000μm2, a measurement range of 3g, a mechanical cross axis sensitivity of 0.058μm/g, and an overall cross axis sensitivity of 0.00029%/g. These functional characteristics make the design appropriate for a large range of applications.

Recent technology and challenges of wind energy generation: A review

Energy is an integral part of economic growth and social development. Renewable energy sources are naturally occurring, which can help in reducing the dependency on non-renewable resources. The increasing effects of climate change have led to the utilization of renewable energy resources for power generation, among which wind is one of the significant sources of power generation. It provides a reliable, sustainable, and environmentally friendly alternative contributing to national energy security in the current age of decreasing global reserves of non-renewable resources across the globe. This paper reviews the wind energy technologies used, mainly focusing on the types of turbines used and their future scope. Further, the paper briefly discusses certain future wind generation technologies, namely airborne, offshore, smart rotors, multi-rotors, and other small wind turbine technologies. It also briefly discusses ways to improve the efficiency of different turbine generation technologies, majorly non-conventional ideas of wind turbine technologies based on cross axis wind turbine (CAWT), vertical axis wind turbine (VAWT), magnetic-based wind turbine. Overall, the summarization of wind energy here consists of four aspects: (1) wind turbine structure, (2) wind power generation technologies, (3) wind energy assessment methodologies, (4) limitation of developed technologies and future scope of wind energy development.

English

The aim of this study was to compare heart rate variability (HRV) indices before and after a table tennis match, depending in match result. HRV indices were measured before (PRE) and after (POST) match periods to 21 table tennis players (21.86 ± 8.34 yr) in 30 matches. No significant differences were found neither in PRE nor in POST measures comparing winners and losers. A significantly lower value (p < 0.05) was found in mean of RR intervals (mean RR), standard deviation of RR intervals (SDNN), the natural logarithm transform of the root mean square of successive differences between normal heartbeats (LnRMSSD), relative number of successive RR interval pairs that differ more than 50 ms (pNN50), cross (SD1) and longitudinal (SD2) axis of Poincaré plot comparing POST values with PRE values. Nevertheless, low frequency index expressed in absolute power (LF Power) and high frequency indices expressed in absolute power (HF power) and normalised power (HF Power) showed different trends depending on the results (p < 0.05). The obtained results show a HRV decrease after table tennis match regardless the match result, in both time domain and non-linear indices. However, frequency domain indices show a different trend depending on the match outcome.

Location of the Ankle Osteochondral Lesion of the Talus (OLT) Corresponding to the Anatomical Axis of the Tibia (Loading Axis) Crosses the Ankle Joint

Category:Ankle; SportsIntroduction/Purpose:studies demonstrated that mechanical axis alignment affects the clinical outcome of the chondral repair surgery in the knee. Reduction in stress concentration around chondral defects with HTO has been found to favor cartilage repair in knee surgery. this study aimed to determine the relationship between the tibia mechanical axis alignment and OLT size and location.Methods:57 patients that underwent OLT repair between 2016-2020 were included. X-rays and MRIs of the ankle were used to collect data on OLT in the study group. X-ray measurements included (a)-measured as distance from where vertical line through center of tibia crosses to center the talar joint in AP view (medial, lateral), (b)- measured as distance from where vertical line through center of tibia crosses to the center talar body in lateral view (ant, post). The coverage angle, TLS, TAS, MA, TI, TTI angles were measured. MRI measurements included distance of the edge of the OLT lesion from the center of the talar surface, in three plans, and for location of the OLT lesion based on the 9-zone grid system.Results:37.3% of these patients had the mechanical axis of the joint cross posterolaterally, 15.6% anteromedially, 5.9% anterolaterally, and 3.9% posteromedially. 33.3% had the mechanical axis cross posteriorly along the midline of the lateral axis. Using the 9-zone grid to localize lesion location, lesions were most often seen in location 6 (37.3%), location 7 (21.6%), location 9 (21.6%), and location 4 (19.6%). Of note, 36.8% of patients with a posterolateral axis had lesions at location 6 and 26.3% at location 9. For patients with poster joint axis along the midline of the lateral axis, 47.1% had lesions at location 6 and 23.5% at location 7. There is a correlation between Lesion Surface Area and axis location in the AP view (Correlation coefficient: 0.301, P Value: 0.023). we found a significant difference for coverage angle (P<0.001), TLS (P<0.001), and TTI (P<0.001) for different groups.Conclusion:The significant correlation shows that the farther medial the location of the axis crosses the joint, the larger the surface area of the lesion. there is no significant difference between lesion length or area and location.

A Steady Flow of The Viscous Compressible Liquid in Vertical Pipe

In the study of the flow of gas-liquid mixture over circular vertical pipe rising from the deep zone to ground level, it is observed that, the velocity on surface of tube is much more than in the center of flow. Such a picture is seen also in the water filtration process in sands ordering from high permeability zone to lower. Same phenomena occur in transportation of the water carbon nana-tubes. In order to predict behavior of those processes in this paper, we have studied the compressible liquid flow over the circular vertical pipe ordered from the deep zone to the ground surface for some concrete inlet and outlet regimes of the pipe. The Navier-Stokes equations system as a model of study. For certain inlet and outlet regimes of the flow splitting the equation into the cross section and axes variables, the pressure and velocity distribution are found. The Lane-Emden equation arises for determining the pipe cross section velocity distribution, which is also justified by our calculations on the used model.

Monolithic Fully Decoupled Tri-Axis Gyroscope With Lateral-Comb and Low Cross-Coupling

Multi-axis integration is important for micro-electromechanical system(MEMS) gyroscopes in the future. In this paper, a monolithic integrated tri-axis gyroscope and interface circuit are designed and implemented. The presented tri-axis gyroscope with single drive and multi sense axes is fully decoupled in structure among the drive and sense modes. Quadrature coupling can also be further reduced by the in-plane and out-of-plane correction electrodes. The pitch(roll) structure is designed as a unilateral unequal height comb, which reduces the damping and improves the Q value of pitch and roll modes and simplifies the fabrication process. In addition, the interface circuit adopts a closed-loop drive and open-loop sense circuit, an additional decoupling module that effectively reduces the cross axis sensitivity. Finally, a gyroscope prototype was tested to evaluate its performance. The designed tri-axis gyroscope has low bias instability(1.2821°/h) and good noise performance(0.1635°/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd \text{h}$ </tex-math></inline-formula> ). The coupling coefficient is even below 1% after adding decoupling modules. Meanwhile, the bandwidth can meet the needs of the gyroscope working in a low-frequency environment.

Biomechanical matrix-multibody coupled human body model for seat to head transmissibility

Health hazards of human body to whole body vibrations (WBV) have been linked with the incidence of spinal ailments within the drivers of vibrating moving equipment. The investigations on the biodynamic responsiveness of body segments; thus, it is relevant for a profound understanding of prospective impairment anticipations and design refinements. Current research work concentrates on seated body biodynamic direct and cross axis responses to seat induced vertical vibration, and establishment of an analytical model for the prediction of human anatomy comfort parameters. In the course of WBV vibrations of the human anatomy in a seated position (driver or passenger), the movement of the head is affected by the backrest forces transmitting to the lumbar section of the spinal column. Accordingly, it is crucial to reflect backrest assistance while building the human body model to captivate direct and cross axis seat to head transmissibility. Thus, the model results should accurately represent the internal forces, power absorbed, body acceleration accurately. The human anatomy is viewed as a biodynamic system of interconnected masses. A two-dimensional nine degree of freedom (DoF) matrix-multibody coupled backrest supported seated human anatomy model is established and validated to depict vertical and fore-aft head motion. Multi-objective genetic algorithm-based optimization has been used for model parameter identification by minimizing the error difference separating the experimental and model-derived seat to head transmissibility.

Cross-Coupling Coefficient Estimation of a Nano-gAccelerometer by Continuous Rotation Modulation on a Tilted Rate Table

Nano- $g$ accelerometers are widely used in space exploration and measurement of the earth’s gravitational field. It is essential to precisely evaluate error effects at high orders such as cross-coupling for applications in a dynamic environment. Nevertheless, it remains challenging to meet the precision requirements using conventional calibration measures. In this article, we propose a method to separate the cross-coupling coefficients of a linear single-axis accelerometer by mounting it on a steadily rotating rate table that is tilted at a fixed deviation angle with respect to the horizontal plane. The gravity component is periodically modulated along the input axis per revolution. Simultaneously, a series of centripetal acceleration is applied along the cross axis in sequence while adjusting the rotation frequency of the rate table by steps. Thus, the cross-coupling coefficient can be separated by its dependence both on the modulated gravity acceleration and the centripetal acceleration. In comparison to the static multipoint angular rotation test on a tilted dividing head, the proposed dynamic modulation method demonstrates improved robustness against corruption from bias drift, with an improved uncertainty. This method to separate the cross-coupling coefficient is suitable for testing high-resolution accelerometers, without requiring high bias stability or sensitive response sustaining at ultralow frequency.

Simulation of three-phase short circuit electromagnetic transient process of synchronous generator

This paper studies the transient process of synchronous generator after three-phase short circuit, deduces the expression of stator current in the transient process of synchronous generator, and verifies the theoretical conclusion through simulation. After the short circuit occurs, the electromagnetic transient process is complex. In the electromagnetic transient process, the stator current and rotor current of synchronous generator appear attenuation oscillation due to direct-axis reactance, cross-axis reactance, transient reactance and sub-transient reactance. Based on the basic principle of synchronous generator, this paper analyzes the analytical expressions of stator straight axis current, stator cross axis current and total current. After that, the simulation model is built in Matlab/Simulink, and the simulation results are consistent with the theoretical analysis results. This simulation method provides convenience for analyzing the transient process of synchronous generator and has good engineering application value.

Simulation design and optimization of production line of a cross axis machining based on Plant Simulation

In order to study the operation process and results of an actual intelligent production line, Plant Simulation was used to simulate the production line of a cross shaft. First of all, the basic layout is modeled, 3D model is used, and the actual machine model is imported or designed to make the effect more realistic. This study analyzed the production process, created orders according to customer requirements, used Simtalk language to complete the simulation logic of the model, and displayed the simulation data in the form of charts after the operation, so as to make the results more intuitive. Finally, the results are analyzed and optimized.

A review on development of offshore wind energy conversion system

Wind energy conversion system, aiming to convert mechanical energy of air flow into electrical energy has been widely concerned in recent decades. According to the installation sites, the wind energy conversion system can be divided into land-based wind conversion system and offshore wind energy conversion (OWEC) system. Compared to land-based wind energy technology, although OWEC started later, it has attracted more attentions due to its significant advantages in sufficient wind energy, low wind shear, high power output and low land occupancy rate. In this paper, the principle of wind energy conversion and the development status of offshore wind power in the world are briefly introduced at first. And then, the advantages and disadvantages of several offshore wind energy device (OWED), such as horizontal axis OWED, vertical axis OWED and cross axis OWED are compared. Subsequently, several major constraints, such as complex marine environment, deep-sea power transmission and expensive cost of equipment installation faced by offshore wind conversion technology are presented and comprehensively analysed. Finally, based on the summary and analysis of some emerging technologies and the current situation of offshore wind energy utilization, the development trend of offshore wind power is envisioned. In the future, it is expected to witness multi-energy complementary, key component optimization and intelligent control strategy for smooth energy generation of offshore wind power systems.

Design and Evaluation of Compliant Modular XY Positioning Stage

ABSTRACT In precision engineering applications, compliant micropositioning stages with properties of long travel range, high accuracy and compact size are desirable. The majority of the existing research efforts are focused on monolithic compliant positioning stages with above merits. However, the monolithic stages possess a major drawback that failed components cannot be replaced and it requires time-costly machining process, i.e. wire electric discharge machining. To overcome these drawbacks, the stage using the concept of modular design with parallelogram flexure module is proposed. In the modular design, failed components can be easily replaced. The stage is driven by large range voice coil actuators (VCA). The static and dynamic analytical models based on stiffness matrix method are adopted for evaluating the performances of the stage. The accuracy of analytical models is validated by FEA results. Finally, experimental test is carried out to evaluate the performance. The stage provides translational motion of ± 5 mm along working direction and limited cross axes coupling of 10m in other direction for nonlinear behaviour. The proposed stage has resonant frequency of 15 Hz. The results obtained validate similar static and dynamic performances and trajectory tracking capabilities of the modular micro-positioning stage as that of monolithic stage.

A novel single axis capacitive MEMS accelerometer with double-sided suspension beams fabricated using μWEDM

Design and fabrication of the first micromachined accelerometer made from steel and the first MEMS accelerometer fabricated using micro-wire electrical discharge machining (μWEDM) process is presented in this paper. By utilizing this fabrication method, it is possible to achieve a huge proof mass that has a prominent effect on reducing noise. The proof mass in this design has a mass of 7.85 mg which leads to the Brownian noise of 0.8 μg/Hz that is comparable to low noise MEMS accelerometers. Another advantage is the higher density of the steel relative to the silicon, so a heavier proof mass can be achieved in a smaller size, providing a better control over the damping. The finite element analysis of the accelerometer shows that this sensor is able to measure high-amplitude accelerations up to 131 g without the risk of failure and fatigue because of the high yield stress and fracture toughness of the steel. Consequently, due to its low noise, resulting from its heavy mass, and also the ability to measure high amplitude acceleration, resulting from the high yield stress, the fabricated accelerometer has a dynamic range of more than 100 dB. Experimental tests showed that the accelerometer has the sensitivity, nonlinearity and range of 18 mV/g, 3% and 100 g respectively. This sensor provides the ability to operate in the air, which makes the packaging process easier. Also, the accelerometer shows the cross axis sensitivity of 0.44% accruing from the symmetrical arrangement of suspension beams used to suspend the proof mass.

Numerical Modeling of Instability and Breakup of Elliptical Liquid Jets

Numerical simulations are performed to provide an in-depth insight into the effect of instabilities on liquid jets discharging from elliptical orifices. The axis-switching phenomenon and breakup are simulated and characterized under the effect of disturbances imposed at the nozzle exit. The simulations are based on the volume of fluid approach and an adaptive meshing. A range of orifice aspect ratios from 1 to 4 at the Rayleigh breakup regime is considered. The evolution of the jet cross section and axis switching under the influence of disturbances is compared with that of nonperturbed elliptical jets. It is found that the axis-switching repetition and breakup length exponentially decrease with the initial amplitude of disturbances. For a fixed amplitude, the optimum wavenumber responsible for minimum breakup length is observed to be dependent on ellipticity of the orifice. Moreover, it is found that the form of final breakup leads to elimination of the satellite droplets at the optimum wavenumbers, while the droplet size decreases and becomes more uniform.

Comparison of single-input single-output and multi-input multi-output control strategies for performing sequential single-axis random vibration control test

This study investigates the use of single-input single-output and multi-input multi-output control strategies for performing single-axis vibration control tests. In particular, the work addresses the problem of high-level cross-axis responses during those tests. To compare the two control strategies, the study presents a test campaign carried out on an automotive component by exploiting two different test facilities: a single-axis shaker and a three-degree-of-freedom shaker table. The analysis points out the limitations of the single-input single-output control strategy. The coupling between the excitation system and the test specimen causes cross-axis excitations that compromise the test validity. In some cases, the cross-axis vibration level even exceeds the acceptable threshold of 14 dB. The multi-input multi-output control strategy instead, besides the feedback control of the main axis, allows the simultaneous vibration control along the two cross axes, thus, improving the quality of the single-axis test. Moreover, the work provides a detailed study followed by practical examples on how to better exploit the evident potential of the multi-input multi-output control strategy for definitely avoiding cross-axis vibration control problems.

Superior performance area changing capacitive MEMS accelerometer employing additional lateral springs for low frequency applications

This paper introduces an effective and efficient microstructure of a differential area changing capacitive accelerometer to ensure low cross-axis sensitivity, high linearity and low noise figure for low frequency applications like Structural Health Monitoring and seismic sensing. The major design concern in an area dependent capacitance structure is that even small magnitude of cross axis displacement can drastically affect the sensitivity and linearity. The authors first focused their effort to obtain the guidelines for the best performance in the conventional structure of area changing capacitive sensors. The results clearly demonstrated that the existing structures used conventionally cannot meet the stringent requirements for low frequency applications. Subsequently, the various studies on the new structure proposed in this work were presented and the results are compared with latest reports for benchmarking. It has been estimated that the new structure can give cross-axis displacement as low as 0.5%, linearity of 2.53% and noise figure of 4.89 ng/ $$\sqrt {\text{Hz}}$$ , the best achieved in so for. These studies clearly demonstrate that the ill effects of parasitic capacitance on voltage sensitivity and linearity can be suppressed by the new design. These results further show that the area changing capacitive structure employing additional lateral springs is a promising candidate for low frequency applications like seismography. The other major advantage of this structure is that the fabrication process flow need not be changed in the production line.

Programming the trajectories of machine-tractor units

The control of trajectories of self-propelled agricultural vehicles and machine and tractor units (MTU) is carried out according to certain programs stored in memory of the tractor driver or in the system of autonomous driving. In the tractor driver’s memory, the programs are laid down at the stage of studying and mastering the specialty, and are specified when receiving a task to perform a specific job. A common opinion about programming a trajectory following a previous MTU passage is erroneous as the trace is the coordinate line used to bind the desired trajectory to the terrain. The quality of trajectory driving depends on the tractor’s driver, his experience and qualification but not the system of coordinates. Similarly, for autonomous driving of MTU the possible driving programs must be put into the autonomous system at the design stage, and be specified with settings before work start. The quality of autonomous driving is defined by technological level of a system of autonomous driving, which integral part is the coordinate system. There are various ways to define system of coordinates. The most promising of them is to stationary reference points in the form of underground current-carrying wires. Such systems have the high definition, universality, autonomous waymarks, noise stability and long-term stability. To realize all the advantages of coordinates systems set by underground current-carrying wires it is necessary to determine the location of MTU by point-to-point differential and amplitude method by a projection of magneto-field vector to a cross axis of the tractor or a single-point two-level amplitude and phase method. High programming accuracy is achieved by means of current-carrying wires made by commutable ones, power supply of adjacent wires by counter currents and creation of navigation magnetic field by currents of three adjacent wires, where the middle wire is a contact line. The high definition of the guidelines and the noise immunity of the algorithms allow determining both the path mismatch and the direction of the longitudinal axis of the tractor and the direction of the velocity vector as well. Introduction of these parameters into the control law of steering mechanism allows increasing the stability of systems of autonoumus driving and accuracy of trajectories control of working bodies of technological machine tools.