Huang Shanglian

Maximal Modal Force Rule for Optimal Placement of Point Piezoelectric Actuators for Plates

Optimal placement of actuators on intelligent structures is an important part of intelligent structure designs. The optimal collocation of actuators includes placement collocation and number collocation. It decides stability, controllability and control efficiency of structural control systems. With the development of control technology, the optimal collocation of actuators in structures is more and more important. Although optimal collocation of actuators can be determined by experience in some cases, experience is useless for complicated structures. So optimal collocation of actuators must be realized by optimal theory. Based on modal control theory, the Maximal Modal Force Rule is put forward for intelligent flexible plates bonded point piezoelectric actuators on their surface in this paper. The rule points out that point piezoelectric actuators should be bonded on the places of maximal modal strains of every order mode to produce maximal modal control forces. The formulae for independent modal space control and coupling modal space control are derived. The results of computer emulating of a plate show that the rule is right and effective.

Two-dimensional grating light modulator for projection display

A novel two-dimensional (2D) phase grating light modulator for projection display is proposed. It consists of an upper moveable grating, a bottom mirror, and four supporting posts between them. After the driving voltage is applied to the modulator, the upper grating will move down, which induces a phase difference and, therefore, leads to a controlled variation of its diffraction pattern. Optical characteristics of the modulator and the modulator array are analyzed with Fourier optics theory. The analysis shows the incident light will be switched from its zero order diffraction fringe to the first order diffraction fringe when the phase difference between the moveable grating and the bottom mirror changes from 2 pi to pi. The diffraction pattern of the light modulator array is the coherent superposition of all single modulators. A 16 x 16 modulator array is fabricated by surface micromachining technology. The test result shows that the device works well when it is actuated by a voltage with a 1 kHz frequency and 10V amplitude. Both theoretical analysis and experiment results indicate that the 2D phase grating light modulator has potential application in a projection display system.

A new kind of gear measurement technique

A new method of gear measurement is introduced in this paper. It is based on the traditional gear single-flank measurement, but it uses a special master gear with three kinds of measuring tooth and a tranmission tooth. The first kind of measurement tooth has a projective involute which is used as a reference. When it is engaged in mesh with the tooth of the workpiece, the deviation of transmission reflects the involute profile error of the workpiece. When a projective helix on the second kind of measurement tooth is meshed with the tooth of the workpiece the lead error can be obtained. Because the third kind of measurement tooth is the same as that used by a traditional single-flank tester, the tangential composite error can be easily obtained. The transmission tooth - whose thickness is reduced - is used to make the contact ratio less than one. When the new master gear is meshed with the workpiece for several turns the pitch error of the latter can be measured. Experimental results using equipment based on the new technique have shown that the method is feasible and efficient.

Remote Real-time Health Monitoring and Evaluation System for Long Bridge Structure

In this paper, a fast evaluation system for remote real-time health monitoring and evaluation of long bridge structure is proposed. The main idea of this system is to apply the reliability design theory for static structure into the dynamic remote health monitoring and reliability evaluation of bridges. The real-time safety evaluation of bridges includes the following components: (1) dynamic acquisition of optimal statistical parameters through distribution testing of fitting performance; (2) real-time analysis of section dynamic reliability of bridge structure; and (3) evaluation of bridge structure reliability by using PNET method in comparison to the standard reliability index commonly used in highway engineering. This research first realizes the real-time dynamic bridge reliability analysis based on the monitoring data analysis and then evaluates in real time the objective health conditions of bridge. The performance of remote monitoring and evaluation over long bridges demonstrates that the proposed evaluation system can deal with real-time information monitoring, evaluate reliably the bridge safety and promote intelligent development of bridge structures.

A Fiber Optic Sensor for Measuring Distributed Forces

A fiber optic sensor system for measuring distrib uted forces is presented in this paper. A high-birefringent fiber is chosen as a sensing element. Based on the coupling effects of polarization modes in high-birefringence fibers, the distribution of the force points along the sensing fiber can be measured by detect ing mode couplings in the fiber which are caused by external force disturbance. The location and magnitude of the measured forcesA fiber optic sensor system for measuring distrib uted forces is presented in this paper. A high-birefringent fiber is chosen as a sensing element. Based on the coupling effects of polarization modes in high-birefringence fibers, the distribution of the force points along the sensing fiber can be measured by detect ing mode couplings in the fiber which are caused by external force disturbance. The location and magnitude of the measured forces

Application of Modern Sensor- and Info-Technology in Long-Term Safety Monitoring of Long Span Rigid-Frame Bridge

The issue of safety has been concerned throughout the world. This paper, taking a long span continuous rigid-frame bridge as an example, introduces the application of the modern sensor- and info-technology in the said bridge by presenting the components of the monitoring system, the acquisition and transmission of the monitored data, and the bridge safety evaluation system. The experiment has proved that the application of the sensor- and info-technology into civil engineering projects can bring about good social, economical and scientific effects

Fiber Optic Whole-Circum Sensor To Improve The Accuracy Of Radial Grating Measurement Systems

In an angle calibration instrument and a generating machine of radial grating, the opto-electronic signal is generated by a novel fiber optic whole-circum sensor. The construction of the sensor is introduced, the principle to i prove the accuracy under partially coherent illumination is derived, and the experimental results are presented. Because of its excellent characteristic, the residual phase error (peak to peak) of moire signal is less than 0.03 sec. of arc., the accuracy of machine is increased about 30 times.

Optical Fiber Humidity Sensor

The optical fiber humidity sensor is based on the principle of the absorption spectrum of unclad optical fiber coated with colorimetric reagent film. The absorption spectrum changes with relative humidity. The output characteristic and sensitivity of the sensor are discussed. Theoretical results show that the sensitivity of the sensor is related to the diameter and the length of the unclad optical fiber, the thickness and the absorption coefficient of the colorimetric reagent film. A new scheme of the optical fiber humidity sensing is put forward. Tests on experimental models have shown performance coinciding with theory, the measurement upper limit of relative humidity to 96%RH, the sensitivity of 0.0196dB/RH to 0.0342dB/RH and the response time of 2.5 sec.. The sensor is more compact and cheaper.

The Influences Of Several Parameters Of Grating Sensor On The Modulation Depth Of Moire Signal Under Incoherent Illumination

In this paper, the theoretical expressions of modulation depth of moire signal under the incoherent illumination are derived. It follows as a concequence that, the modulation depth of moire signal is in relation to the following factors: the geometric share and size of light source, the diffraction effect of grating,which relates to the line numbers of grating, the line and space ratio, the gap of grating pairs, the geometric shape and size of receiving window, etc. In addition, the influences of grating fair on the period and inclination of moire fringes under the noncollimated illumination are discussed, and the comparisons of the changes of modulation depth of moire signals and the noncollimated illumination with that under the collimated illumination are made. Finally, some exoeriment results are given to verify the theoretical expressions. This parer is useful to the actual design of grating sensors.

Effects Of Spatial Coherence Of Light Sources And Grating Gaps On The Quality Of Moire Signal Of Linear Grating Sensors

In this paper, first, the insufficient of the metheds used to determinate light sources size and grating gaps in linear grating sensors is refered. Then, according to the general model of grating measurement systems, the complete expressions of moire intensity distribution are derived by means of partially coherent light theory. The effects of spatial coherence of light sources and grating gaps are particalarly discussed, too. In this paper, not only the simple and correct formulas and rule of determinating the modulation depth of moire signal and grating gaps are derived, but also it is proved that coherent light illumination is only one special case of this paper. In the end, an experiment whose results are fundamental in agreement with the theoretical analysis is presented. The conclusions of this paper are very important to design linear grating sensors and its formulas are very practical.