Research On Expansion Joint Pitch Detecting Device And Measuring System

Expansion joint,which is mainly composed of bellows and other parts,is arranged on container shell or pipes to compensate for the additional stress caused by temperature difference and mechanical vibration.Expansion joint obtains the role of telescopic compensation mainly based on bellows.In this paper,to solve the problem that is no measurement reference for expansion joint waveform,a testing device and a data-processing software for detecting the change of the bellows wave distance before and after tests are developed applying the technology of the non-contact laser measurement.It has important significance to improve the mechanization and automation level of the expansion performance test equipment,especially for the special environment,special requirements of the bellow expansion joint inspection.The design requirements of the expansion joint wave distance detection device were analyzed.Overall structure of the detection device was designed,including the axial motion structure,the radial motion structure and the rotary motion structure.The hardware of the control system of the detection device was designed with the Siemens S7-226 CPU and Omron incremental encoder as the hardware core.STEP 7 MiacroWin software of Siemens was used as the control program design platform to design the motion control program of the detection device.LMI laser scanners were used as the core hardware for non-contact detection.The expansion joint wave measurement software,was based on measurement principle of laser triangulation method and failure condition of expansion joint wave distance detection,It was developed using software development kit of LMI laser scanner on the Visual Studio software development platform.Many functions were integrated in the software,such as user login,accessing to the database,expansion of the waveform data acquisition and waveform wave distance display,monitoring the status of test equipment.PC monitoring interface was also developed.Data was collected into the database by ADO technology.Host computer communicated with the lower computer by OPC technology.The scanners were driven by Industrial Ethernet and waveform data of the expansion joint was obtained.The collected data was diagnosed and fitted by the diagnosis algorithm of estimated data point curvature.Peak-finding algorithms,such as direct peak method,the second order differential search method,Zero-convolution peak-finding algorithm,etc.were compared and applied to search the wave crest of the bellows,calculated the wave distance of the expansion joint and qualify the product.In this paper,for the expansion joints produced by a factory,the wave distance of expansion joint was measured by manual vernier caliper and laser scanning system before and after fatigue tests.The expansion joint product was qualified through analyzing the measured waveform distance data.The error of the two detection methods was also compared and analyzed.