| As a high sophisticated precision measurement instrument,electronic analytical balance is the integration of sensors,electromagnetism,analog and digital electronic technology,intelligent information process,materials,structural mechanics,precision machinery and manufacturing.And the electronic analytical balance is widely used in national defense,medicine,quality control,laboratory,and so on.The electromagnetic force balance sensor is the core of electronic analytical balance.The design of domestic sensors is imitating,and lack of basic research,so it is difficult to guarantee the sensitivity,stability and consistency of the sensor output.As the restriction on the material basis level and precision manufacturing technology,the dispersion of reed materials and permanent magnet materials in the electromagnetic force balance sensor is large,that makes the electronic analytical balance have large drift,poor stability,long response time and large error of indications.Thus,lots of researches are studied by the domestic scholars to ensure the measurement performance of electronic analytical balance,such as drift compensation,nonlinear compensation and information preprocessing.However,these researches are lack of basic design and research for the electromagnetic force balance sensor,including the mechanical weighing institutions and the permanent magnetic circuit structure,lack of comprehensive analysis for drift mechanism and nonlinear effect,and lack of the effective intelligent detection and information processing methods.These researches can't compensate the effect on the measurement performance of electronic analytical balance caused by the defects of material basis level and precision manufacturing technology.In this paper,based on the material basis level and precision manufacturing technology,some researches are performed to improve the existing electronic analytical balance:(1)Aiming at the lack of basic research in the electromagnetic force balance sensor,the force model of mechanical weighing institution is established.According to the law of energy conservation,the equivalent stiffness of mechanical weighing institution is solved,the dimension of bearing reed,fulcrum reed and strap reed are optimized,so the sensitivity and stability of sensor are effectively guaranteed.A position detect institution is designed to ensure the minimum amount of displacement generating by the minimum scale in the mechanical weighing institution can be distinguished.The optimal parameters of coil structure and the optimal dimension of permanent magnetic circuit structure are designed,the engineering model of permanent magnetic circuit based on ANSYS soft is built to verify the reasonableness of the optimized permanent magnetic circuit design,and ensure the performance of the single coil permanent magnetic circuit institution maximizing,so the coil current magnetic effect and thermal effect are effectively reduced,the consistency of the sensor output is improved.(2)Aiming at the current compensation methods for the temperature drift and time drift of electronic analytical balance are backward and the drift of indications is large,the temperature drift and time drift mechanism of electronic analytical balance are thoroughly analyzed.A differential photoelectric detection circuit with feedback and a constant current source circuit with low temperature drift are designed to overcome the temperature effect on the electromechanical balance position,lots of measures are taken to reduce the time drift effect on the electronic analytical balance,such as magnetic stabilization techniques of permanent magnet,intelligent calibration,electronic components optimization,and so on.For the temperature-sensitive components,the permanent magnet and the coil,which caused large temperature drift and whose temperature can't be directly detected,a finite element temperature field thermal analysis model of electromagnetic force balance sensor based on ANSYS soft is built,the temperature rise characteristic of the permanent magnet and the coil by coil heating and thermal convection are researched in detail,the temperature soft measurement mathematical model of the permanent magnet and the coil based on the detection of multi-point temperature are established.Combined the research of temperature drift test,the mathematical model based on binary linear regression model between the temperature drift of electronic analytical balance and the temperature rise of the permanent magnet and the coil is built,thus the automatic temperature drift compensation method of electronic analytical balance is proposed,which based on the multi-point temperature soft measurement,three temperature point calibration and binary linear regression.Combined the research of time drift test,the automatic time drift compensation method based on zero tracking technology is proposed.By all of that,the dispersion effect of permanent magnet materials is effectively solved,and the automatic temperature and time drift compensation of electronic analytical balance are achieved.(3)Aiming at the defects for the current nonlinear compensation methods of electronic analytical balance are complex,and the error of indications are large,the nonlinear of electronic analytical balance affected by the coil current magnetic effect and thermal effect are in-depth analyzed,three coil magnetic effect analysis models such as single-coil permanent magnetic circuit,single-coil core magnetic circuit and double coil permanent magnetic circuit based on ANSYS soft are established to research the additional magnetic induction density generated by the coil current magnetic effect and the nonlinear effect of electronic analytical balance.Combining with the theoretical analysis and simulation experiment,the nonlinear mathematical model of electronic analytical balance affected by the coil current magnetic effect and thermal effect is obtained.The electromechanical balance parameter optimization and the sampling resistor optimization are taken to effectively ensure the consistency,the dynamic range and the resolution of electronic analytical balance.Combined with lots of experimental researches and the use characteristics of electronic analytical balance,a nonlinear correction method based on the Newton interpolation is proposed,a full scale correction model is established to ensure that the electronic analytical balance can have good linearity in all of the scale,and which is also easy to auto-production and debugging.(4)Aiming at the current problem of electronic analytical balance with long response time and poor stability,a weighing information filtering method based on Kalman filter and a weighing discrimination method based on multi-level threshold constraint are established to ensure both of the stability and sensitivity of electronic analytical balance,improve the response time and reduce the settling time.(5)On the basis of the above researches,a precision electronic analytical balance with 220g/0.1mg is manufactured,which has the temperature and time drift automatic compensation,nonlinear automatic compensation and intelligent calibration technology,with fast response,good stability and high accuracy.Reference to Chinese National Standard "GB/T 26497-2011 electronic balance",the measurement performance of precision electronic analytical balance is verified,including the error of eccentricity,the error of indications,repeatability and discrimination.And the test error of precision electronic analytical balance is analyzed,and the uncertainty model of precision electronic analytical balance is established to estimate the uncertainty of weighing results in the normal use.The test results of precision electronic analytical balance show that the error of eccentricity are less than 0.0002g,the error of indications in all of the scale are less than 0.0002g,and the repeatability is 0.0003g,all of those can meet the design requirements,and better than the maximum permissible error for the 1st class balance specified by Chinese National Standard "GB/T 26497-2011 electronic balance". |
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