Embedded Multi-point Bridge Deflection Monitoring System Research And Implementation

Bridge deflection monitoring is an important part of bridge health monitoring,through continuous exploration in practice, lots of bridge deflection measurementmethods were studied. Among them, the laser image method has the characteristics ofhigh measuring accuracy, long measurement distance, low power consumption, smallsize, low price, convenient installation and debugging so that it has been widely used.However, the system still exists the inaccurate measurement and poor stability,specifically four aspects reasons caused:(1) Laser transmitter system response time isso long, and laser diffraction phenomenon is obvious;(2) Differential spot centerlocation algorithm is flawed to cause the spot center calculation error;(3) USB camerapixels is too low to meet the high precision demand,(4) As the wireless communicationprotocol is not perfect, it often appear to send and receive data interrupt, data transceiverprogram crash and other abnormal situations. Therefore, the main work of this thesis isto design a specific technical scheme to solve these shortcomings.For the laser emitter return slowly and diffraction obvious shortcomings, this paperdesign a kind of self leveling deflection laser launching system. The system uses gravitypendulum for keeping laser device balance, through analysing the gravity pendulum’sforce and trajectory, resistance coefficient is obtained based on the correspondingcritical damping principle, then matched by adjusting the magnetic damper magneticinduction intensity and resistance coefficient, it can let pendulum stop quickly; In orderto maintain laser still has a good energy concentration when it has long distancebetween the laser and the screen, paper design the laser lens which is composed of theGalileo beam expander and the focusing lens, experiments confirm that the laser lenscan ensure the laser distance projection is focusing enough.When the case of strong light or the laser power is insufficient, the differenceoperation of the spot often lead to the edge is incomplete, so that the differential spotlocalization algorithm appears to a large deviation. So an improved circle fitting centerlocation algorithm was proposed. The algorithm firstly binarized the spot image that obtained by preprocessing, and then the coordinates of the spot edge pixels wasextracted to calculated the distance between two adjacent points, through the distance,the edge of the abnormal data were excluded according to the Pauta criterion. Finally,the center was located with the circle fitting algorithm. Experimental resultsdemonstrated that the method’s accuracy is higher than ordinary circle fitting in the spotedge crippled case.For the issue of low image pixels, a high-definition camera access module isdesigned to improve the image quality, through the ARM processor control modulefrom the HD video camera to obtain the PAL format video signal, after the treatment ofthe module, the analog signal will be converted to YCrCb format digital signal. Whenthe collection to the YCrCb format digital signal, through color space change into RGBcolor space, shield the G, B color is extracted by R Gezer, finally, it will be used tocalculate the spot center.For the issue of the data transceiver system instability, so as to realize the data linklayer of the data reliable transmission,the stop and wait protocol was implement inMAC layer, and established the acknowledgment repetition and numbering mechanism,and the data frame anti-interference ability is analyzed in theory and experiment.A combination of the above four schemes, this paper discusses the design of a highstability of embedded multi point bridge deflection monitoring system, including a laseremitting system, data process system, data collection system,wireless communicationsystem. In the successful preliminary design system, carried out the followingexperiments: time and precision of the laser, the experimental fitting round spot centerlocation algorithm, system stability test. The experimental results show that shorteningthe pendulum return time, improve accuracy, reduce the return beam diffraction, the HDvideo camera image acquisition system and the improved circle-fit method can improvethe positioning accuracy and stability.