Design Of Self-balancing Precise Electronic Analytical Balance Based On PSD And Optical Lever

Electronic analytical balance is a high-performance precision measuring instrument.It integrates sensor technology,analog and digital electronics technology,electromagnetism,materials science,precision machinery and manufacturing,intelligent information processing and other disciplines.It is widely used in national defense,quality control,medicine,laboratory and other fields.Its core component is the electromagnetic sensor,which consists of beam assembly,displacement sensor,magnetic cylinder structure.The displacement sensor detects the displacement generated by beam assembly.Its precision plays a decisive role for the accuracy of electronic analytical balance,and requires simple structure,good stability,strong anti-interference capability.Therefore,the key of improving the performance of the electronic analytical balance is to make the beam have a large displacement at a certain mass and to detect the displacement with high precision.Hereby,displacement sensor was designed by us,it was constituted by PSD(position sensitive detector),optical lever and beam group.Displacement sensor composes closed-loop system with electromagnetic sensor to further amplified displacement.The thesis briefly described the relevant background,research status of electronic analytical balance and research status of micro-displacement measurement methods,and expounded the key part of electronic analytical balance--position detection mechanism(i.e.,displacement sensor),and pointed out the research significance and key technology.Based on the research and analysis on the structure,type,principle and several common displacement sensor of electronic analytical balance,the overall design thought that self-balancing precision electronic analytical balance based on PSD and optical lever was proposed and the mathematical model of the system was derived.The thesis used optical levers to amplify the micro-displacement of the beam components in the electronic analytical balance,then used the high-resolution PSD to measure the amplified displacement.Firstly,the traditional optical lever structure was optimized,and the optical lever structure suitable for the system was proposed.Then,the bending deformation characteristics of the beam was analyzed,and the mathematical expression between the displacement of the beam and the gravity of theobject was derived.Finally,to ensure the measurement accuracy,the measurement principle of PSD,the influencing factors and the transformation characteristics of the lens were analyzed,and the overall design idea of the optical system was proposed.Based on the system scheme and theoretical analysis,the thesis constructed of the overall system,including the hardware circuit and system software construction of electronic analytical balance.According to the design scheme,PCB was drawn and welded of the hardware circuit,and analyzed the debugging results.Finally,according to the system scheme,a prototype with range from 0 to 210 g based on PSD and optical lever was built,and the performance of the prototype was tested.Including the mathematical model of the prototype system,stability,and background light impact test analysis.According to the experimental data,the static characteristics of the prototype were obtained: linearity was ±0.00176%,hysteresis was 0.00129%,and repeatability was ±0.0023%,the total precision of the prototype system was 0.0032%.