The Data Acquisition and Processing Based on MEMS. Accelerometer

Transcription

1 Iteratioal Joural of Research i Egieerig ad Sciece (IJRES) ISSN (Olie): , ISSN (Prit): Volume 3 Issue 5 ǁ May 2015 ǁ PP The Data Acquisitio ad Processig Based o MEMS Accelerometer We Huag,Li Qia (College of Mechaical Egieerig, Shaghai Uiversity of Egieerig Sciece, Shaghai,Chia) ABSTRACT:A data acquisitio module is desiged based o the ADXL345 of MEMS accelerometer.the Corte-M3 commuicates with the ADXL345 via the iteral IIC bus to acquire the output data of accelerometer. Have a curve fittig because of the output sigal of MEMS accelerometer with a large oise. ADXL345, as a iput compoet, takes advatage of aalyzig the relatioship betwee the attitude of iput compoet ad gravitatioal acceleratio to elimiate the ifluece of gravity o the trajectory. As a result, acceleratio of the movemet of the iput compoet is collected,ad displacemet is got through the secodary itegral of the acceleratio,so the trajectory ca be simulated by MATLAB. Calculatig the deflectio agle of the iput compoet i the space,ad data processig i the MATLAB. Keywords-MEMS,Data Processig,IIC,Simulate,Curve fittig I. INTRODUCTION For a log time, usig the body's movemets to iteract with a computer has bee oe of the targets the huma-computer iteractio techology i pursuit of perfectio. At the preset,there are two mai kids of huma-computer iteractio techologies: actio recogitio techology i the video ad actio recogitio techology of iertial devices [1]. With the developmet of Micro-Electro-Mechaical Systems(MEMS) ad the developmet of micro processig techology, MEMS acceleratio,mems gyroscope, magetometer sesor, micro sesor iput cotrol uit, ca meet the higher requiremets of the iput termial. Usig MEMS acceleratio sesor to measure speed ad get the displacemet ca be applied to hard disk pedometer, fall protectio, rotatio agle measuremet, rotatio detectio, shakig detectio, ad click, double-click detectio as well as other itelliget detectio fuctio ad the cotrol compoet of the game [2-4]. The ADXL345 is a small, thi, ultra-low power, 3-ais accelerometer with high resolutio (13-bit) measuremet at up to ±16 g. Digital output data is formatted as 16-bit twos complemet ad is accessible through either a SPI (3- or 4-wire) or I2C digital iterface. The ADXL345 is well suited for mobile device applicatios. It ca measures the static acceleratio of gravity i tilt-sesig applicatios, as well as dyamic acceleratio resultig from motio or shock. Its high resolutio (3.9 mg/lsb) eables the measuremet of icliatio chages less tha 1.0. [4] This article desigs the ADXL345 of MEMS accelerometer as a iput cotrol compoet, ad discusses the data acquisitio, data processig ad simulatio, ad puts forward the prospect of the applicatio of ADXL345.Data processig ad simulatio is the most importat part of this article which maily icludes:curvig fittig of the output sigal, aalyzig the relatioship betwee the attitude of iput compoet ad gravitatioal acceleratio to elimiate the ifluece of gravity o the trajectory, acquirig the acceleratio of the output of X ais ad Y ais, simulatig the trajectory through the secodary itegral of the acceleratio i 25 Page

2 the MATLAB eviromet. Aalyzig the acceleratio of X ais, Y ais ad Z ais ad calculatig the deflectio agle of the iput compoet i the space. II. THE DESIGN OF THE DATA ACQUISITION SYSTEM 2.1 Hardware Desig The data acquisitio uit of the hardware circuit is composed of a microprocessor module ad a acceleratio sesor module. The STM32F103ZE chip which is based o Corte-M3 kerel is used as the microprocessor. Acceleratio measuremet module applies ADXL345 of MEMS accelerometer. The ADXL345 chip has a IIC iterface, commuicates with the IIC serial bus of microprocessor. The sesor data ca be acquired through the IIC serial bus iterface 5-6]. The hardware circuit is show i Figure-1; STM32F103ZE chip is used as the data-processig systems ad ADXL345 is used as iput compoet. The SDA ad SCL iterface lik STM32F103ZE with ADXL345 through the IIC serial bus. Figure-1:Schematic Diagram of Hardware Circuit STM32F103ZE microprocessor commuicates with persoal computer through serial port USART. STM32F103ZE read the data of ADXL345 registers DATAX, DATAY, DATAZ (register address:0x32-0x37) ad commuicate with the persoal computer through USART to save the X-ais, Y-ais, Z-ais acceleratio data. 2.2 Software Desig The whole developmet system ca be programmed i two software tool; The programmig software of STM32F103ZE chip is MDK Keil4 ad the data receivig software is Serial Debuggig Assistat. Programmig i the MDK eviromet ad geerated.hex file. Dowloadig the.hex file to the STM32F103ZE chip through J-Lik. Whe receivig the acceleratio,the eviromet could be set as baud rate, serial umber COM, 8 data bits,o parity, ad 1 stop bit. After the Assistat prit out the DATAX, DATAY, DATAZ register data of ADXL345,serial commuicatio succeeds. As show i the Figure-2, the software realizatio process. 26 Page

3 Figure-2:The Software Realizatio Process I the iitializatio process of ADXL345: Readig the ADXL345 device address, settig the ID 0E5 because the DEVID register holds a fied device ID code of 0E5 (345 octal), Not self-check, low level output termial, 13 for full resolutio to rage 16g. The data output rate of 100Hz ad lik eable, measuremet mode iterrupt eable. X, Y ais offset calibratio is 000. The Z ais offset calibratio is 0F9 accordig to the measured data. The DATA_FORMAT register (Address 031) cotrols the format of the data. It is recommeded that a multiple-byte read of all registers be performed to prevet a chage i data betwee reads of sequetial registers. Recostruct the data after acquirig the acceleratio it from the data register. DATAX0 is the low byte register of the X-ais acceleratio ad DATAX1 is the high byte register. DATAY0 is the low byte register of the Y-ais acceleratio, high byte register is DATAY1. DATAZ0 is the low byte register of the Z-ais acceleratio, high byte register is DATAZ1. ADXL345 uses biary data format ad uder the 13 bit mode, 1LSB is o behalf of 3.9mg. So the X-ais acceleratio ca be calculated as: a = XTemp= DATAX 3.9mg ; (1) I the formula, a is the measuremet acceleratio;the calculatio of a, a are similar to the process of y z calculatig the a. III. THE DATA PROCESSING The iput compoet slowly rotated aroud the X ais a circle ad the rotated aroud the Y ais i three-dimesioal space. The data output shows as Figure-3; 27 Page

4 3.1 Curve Fittig data( Figure-3:The Acquirig Origial Data The basic idea of curve fittig costructs the polyomial fuctio ad approachig the measuremet i, y i )(i=1,2,3 ). [7] Costructig a polyomial fuctio: f ( ) a a +a a (2) For measurig a set of metrical data y, obtai a epressio f( ) which reflects the relatioship with the measuremet value y, the reach the miimum value E. 2 i 2 i i i i i1 i0 (3) E mi y f ( ) = ( y a ) E equals to the smallest valve of the square of the measuremet value mius the polyomial fuctio of curve fittig. The above fuctio fittig problem ca be regarded as the etreme valve problem of multivariate fuctio, therefore, solves the Equatio: de da 0;( N 0,1,2 ) (4) It could get +1 liear equatios cosisted of equatio. m j ai yi i i0 j0 i0 (5) It is Kow that acquirig the output data of X-acceleratio, Y-acceleratio, Z-acceleratio is discrete poits. Obtaiig a aalytic fuctio y=f () accordig to the collected data. f( ) ca keep the X out, Y out, Z out get close to the curve fittig of F, Fy, Fz as far as possible. Least square method is the most commoly used method of Curve fittig ad the fittig results ca make mii the square deviatio. It is to fid the optimum F: 28 Page

5 mi F Xout i=1 2 (6) Similarly, Fy, Fz abide by the same priciple. Obtai the Curve fittig of X-ais, Y-ais, Z-ais output from the above priciple solutio.get each of them is show i Table 1. Table 1.The Polyomial of Degree of F, F, y F z F F y F z Polyomial of Degree (the valve of ) Accordig to this method, gettig the optimal curve fittig ad simulatig i the MATLAB. curve fittig is Show as Figure-5. The Figure-4:The Simulatio of the Curve Fittig 3.2 Space Agle Coversio I the three-dimesioal space,measurig the acceleratio of each ais which cotais acceleratio of compoet gravity ad motio acceleratio, therefore, it caot be directly calculated the displacemet by the measured acceleratio valve. The MEMS accelerometer measuremet value is relative to the carrier coordiates, whe the iput compoet is ot i the horizotal coordiates, it creates a acceleratio of compoet gravity i the X-ais, Y-ais, Z-ais. Three ais i the space coordiates system project o the horizotal plae ad get the horizotal value of acceleratio. I horizotal plae, remove the gravitatioal acceleratio (Z ais) to get the horizotal acceleratio of motio for calculatig displacemet.the relatioship betwee horizotal coordiate system ad space is showed as Figure Page

6 Figure-5:The Relatioship Betwee Horizotal Coordiate System ad Space Accordig to the measured MEMS values of accelerometers, calculate the attitude of iput cotrol termial. The calculated agle (Igorig the effect of acceleratio):(the agel show i Figure-5) XTemp = (7) 2 2 YTemp + ZTemp YTemp = (8) 2 2 XTemp + ZTemp ZTemp = (9) 2 2 XTemp + YTemp MEMS accelerometer coordiate trasform betwee vector coordiates ad horizotal coordiates: C b cos si si cos si 0 cos si si cos si cos cos (10) It ca calculate the acceleratio accordig to the projectio trasformatio matri i the horizotal coordiate system.so as to elimiate the ifluece of acceleratio of gravity acceleratio i horizotal coordiate, the calculatio formula is as follows: a a cos a si si a si cos (11) y z a a cos a si (12) y y z a a si a si cos a cos cos (13) z y z I the formula: a, a, y a is the accelerated speed of X-ais,Y-ais,Z-ais. z 3.3 Motio Trajectory 30 Page

7 Based o the priciple of mathematical physics, motio displacemet ca be calculated by the double itegral of accelerated speed. Regardig a output compoet as gravity acceleratio, have the accelerated speed double itegral to track ad accumulate space trajectory.calculate the displacemet by double itegratig the processig data of acceleratio. Firstly,itegratig the valve could get the move speed,the formula is: N V ( t) a ( t) dt a ( t) t (14) m m mi i1 Secodly,double itegratig the valve could get the trajectory,the formula is: N S ( t) V ( t) dt V ( t) t m m mi i1 I the formula, Vm () t is the move speed. am () t, ami () t is the acquisitio of the processed data. Sm () t is the distace of the iput compoet moved. Usig the X-acceleratio valve ad Y-acceleratio valve, double itegratig,the simulate the trajectory i MATLAB. It gives us the Figure-6.The trajectory i the picture is similar with the path of iput compoet. (15) Figure-6:The Motio Trajectory of the Iput Compoet IV. CONCLUSION The STM32F103ZE chip which is based o Corte-M3 core ca acquire the ADXL345 data of MEMS accelerometer. This article simulate the output data of ADXL345 to get the trajectory of the iput compoet i MATLAB. It also aalyzes the relatioship betwee the output data ad the acceleratio of gravity,which ca get cotrol devices attitude.the iput cotrol termial ca be used to optimize the curret iput cotrol techology i 3-D game; It ca be used i ati-huma fall detectio device, ca obtai the real-time attitude of people. V. Ackowledgemets Ackowledgemet: This project is sposored by Shaghai Uiversity of Egieerig Sciece Iovatio Fud for Graduate Studets(14KY0123). Refereces [1] Wag Chog, Shi Yuia,Lu Xiog. Huma Motio Measurig Equipmet Based o Acceleratio Sesor[J]. Microcotrollers ad Embedded Systems,2011,11(8): [2] HAN Yig-dag, LI Zheg. Data Acquisitio ad Pre-processig Based o MEMS Accelerometer[J]. Istrumet Techique ad Sesor,2015(2): [3] Li Bou, Nig Wei. The Desig of Three Ais Accelerometer Based o Three-Dimesioal Mouse[J].computer CD Software ad Applicatios, 2013(9): Page

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