Influence Of Sheet Micro-topography On The Performances In Piezoelectric Force Sensors

Piezoelectric force sensors have been widely used in precision machining and assembling fields of the high-performance components,which are significant force measurement devices.The technical parameters of the sensors,such as crystal materials,sheet size,shell structure and number of electrodes have been mainly researched now.Influence of sheet surface micro-topographic on performance of piezoeletrcict force sensors has been not presented.Neglecting this influence factor will lead to several problems:sensor stiffness lowers,sensitivity of sensors reduces and sensor hygroscope enhances,which affect the use of sensors seriously.Therefore,surface micro-topographic of sheets is studied in this dissertation.Preparation of sheets,characterization of surface micro-topographic,influence mechanisms and rules on sensor performances are researched.(1)Sheets with different surface micro-topographic are prepared.Piezoelectric crystals are cut using the Ping-Pong Diamond Wire Saws.A method through controlling the tangential force to improve planeness of sheet surfaces is proposed.Orientation of sheets are operated using the X-ran Orientation.Influence of orientation error on sensor performances is analyzed.Machining and characteristic of sheet side surfaces are stated.Finally,different surface micro-topographic sheets are machined by grinding for the following experiments.(2)Influence of sheet up/down surface micro-topographic on sensor stiffness is researched.The fractal theory is used to characterize the surface micro-topographic of sheets.Based on the structure function method,fractal parameters of sheet surfaces are calculated.Influence models of sheet surface micro-topographic on sensor stiffness is built.Influence of sheet surface micro-topographic,reload,electrode materials,piezoelectric materials on sensor stiffness are studied.Experiments with two kinds of crystal materials(quartz and langasite)and four electrode materials(titanium alloy,stainless steel,copper and aluminium alloy)are conducted.The results show that the stiffness first improves then decrease,as the fractal dimension increases.The stiffness is inversely proportional to the fractal scale coefficients.Choosing crystals or electrode materials with smaller E,increasing reload are conducive to improve joint stiffness of sheets and electrodes,sensor stiffness,and inherent frequency of the sensors.The dynamic property of sensors will be improved,then.(3)Influence of sheet up/down surface micro-topographic on sensor sensitivity is researched.The surface micro-topographic first affects crystal group sensitivity through sheet equivalent capacitance effect,then affects sensor sensitivity through load-sharing effect.Sensitivity models included sheet size,surface micro-topographic,piezoelectric coefficient of crystals,structure parameter of sensors,charge-amplifier parameters is presented.In the sheet equivalent capacitance effect,the statistics theory is used to characterize sheet surface micro-topographic.The sheet equivalent capacitance effect model is proposed based on charge-amplifiers.Experiments are carried out.As sheet roughness increases,microscopic contact distance of sheets and electrodes increases and crystal group sensitivity improves.In the load-sharing effect,effect models are built and experiments are carried out.The experiment results show that in low contact stiffness,as contact stiffness increases,sensitivity of sensors improves.The range of sensitivity rising weakens as contact stiffness increasing.In high contact stiffness,there is a decreasing tendency of sensitivity,as contact stiffness increases.The two influence mechanisms are series.The load-sharing effect is more significant than the sheet equivalent capacitance effect.Finally,single direction sensors and three directions force sensors are machined by different roughness sheets.Comparison experiments of sensitivity are carried out.The results show that optimization roughness makes the sensitivity of piezoelectric force sensors higher.The recommended values of sheet roughness are given towards different measuring ranges for high performance piezoelectric force sensors.(4)Influence of sheet side surface micro-topographic on sensor hygroscopicity is researched.The theory of induced charges neutralization is proposed:induced charges are neutralized through side surface of sheets.The relationship among sheet roughness,relative humidity and bulk resistor is researched by experiments.In high humidity environment,as the roughness of sheet side surfaces increases,sheet hygroscopicity reduces and sheet waterproofness enhances.In low humidity environment,waterproofness of smooth surface sheets is better.A fluorination technology is proposed to shield water vapor.Self-assembly formation mechanism of fluorination film is analyzed.Experiments of shielding the water vapor are carried out.The experiments verify that fluorination films make the fluorination films work in high humidity(90%RH),successfully.Influence of temperature and damage of the fluorination films are researched.Fluorination films are effective in the temperature range of 0-80?.The waterproofness of fluorination films still exists,as a damage happens on upper and lower surfaces of sheets and circumferential direction along side surface of sheets.But there is no waterproofness when a damage happens through up and down surfaces.The results show that the induced charge neutralization theory is reasonable.