ew approach to measuring vibration parameters of the remote objects with the ZigBee technique Borowik Bohdan

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1 16 th IMEKO TC4 Sympoium Exploring New Frontier of Intrumentation and Method for Electrical and Electronic Meaurement Sept. -4, 8, Florence, Italy ew approach to meauring vibration parameter of the remote object with the ZigBee technique Borowi Bohdan Technical Univerity of Bielo-Biala, ul. Willowa, Bielo Biala, Poland, Abtract-The paper preent the monitoring and meaurement proce for the remote object vibration in the plain pace. Wirele, RF communication in Tx/Rx duplex mode provide tranfer of data with ZigBee tranceiver. Preented ZigBee technology operate in many variou mode on frequency,4 GHz allowing the coordinator node to elect certain path and data. Zig Bee technology can be alternative for other vibration reearch technique. The vibration diplacement i proceed further by DSP Digital Signal Proceing made with the microcontroller. Keyword Microcontroller, Acceleration, Duty Cycle, Accelerometer I. Introduction Contemporary indutrial world often create requirement for microcontroller application with the meaurement of vibration. Accelerometer application due to embedded control and I/O digital ignal proceor DSP play the crucial role in determining vibration and machine fatigue trength teting. It regiter, among other, the temporary indutrial parameter and monitor plant ytem parameter uch a vibration and/or preure. Our reearch, controlled by ZigBee technology can be alternative for other technique of vibration reearch. The paper preent diagnotic procedure and meaurement proce of the vibration in the plain pace. Role of the node play ZigBee tranceiver. The vibration monitoring ytem i gathering information from pace through tranceiver. The vibration diplacement i proceed further by DSP Digital Signal Proceing made with the microcontroller. The ZigBee technology are global tandard under the IEEE 8.15 woring group. IEEE thi i the tandard applicable to low-rate wirele Peronal Area Networ. ZigBee i the wirele networing tandard targeted at low power enor application. II. The acceleration enor We ue for meaurement the dual-axi acceleration meaurement ytem ADXLE, manufactured by Analog Device. It ha build in the polyilicon urface-micromachined enor. The polyilicon pring upend the tructure over the urface of the wafer and provide the reitance againt acceleration force. Deflection of the tructure i meaured uing the differential capacitor. The acceleration will deflect the beam and unbalance the differential capacitor, reulting in an output quare wave, whoe amplitude i proportional to acceleration. For determining the direction of the acceleration the Phae demodulation technique are ued. The ytem can meaure both dynamic acceleration lie vibration and tatic acceleration e.g., gravity. The output i digital ignal whoe pule i a Duty Cycle modulator. Thi pule equal: T1 P T (1) where: T1 - denote pule width, T - i a period. The acceleration i directly proportional to the ratio of P. Subequently the duty cycle can be directly meaured with a counter on board of the microcontroller dpic33fj56gp71. The architecture of the integrated circuit alo include the ignal conditioning circuitry to implement an open loop acceleration. For each axi an output circuit convert the analog ignal to a duty cycle modulated digital ignal DCM. Finally, the ignal DCM can be decoded by the tand alone microproceor. In our cae we applied the 16 bit microcontroller manufactured by Microchip, dpic33fj56gp71, operating a the digital ignal proceor DSP. It i preprogrammed with the firmware to fulfill it function a the digital ignal proceor for the

2 16 th IMEKO TC4 Sympoium Exploring New Frontier of Intrumentation and Method for Electrical and Electronic Meaurement Sept. -4, 8, Florence, Italy incoming DCM ignal from the enor. The functional bloc diagram of the accelerometer i preented on the figure1. V DD C DC X FILT X enor Demod R FILT X OUT Ocillator Y enor Demod R FILT Y OUT Y FILT Borowi 8 Fig.1. Functional bloc diagram of the accelerometer III. Interfacing the Accelerometer with the microcontroller dpic Acceleration i proportional to the ratio T 1 /T. The nominal output of the circuit i: g 5% Duty Cycle. Scale factor 1,5% Duty Cycle Change per g. The time period T doe not have to be meaured for every meaurement cycle. It need only to be updated to account for change due to ambient temperature. Since the T time period i hared by the X and Y channel, it i neceary only to meaure it on one channel. The decoding algorithm for the microcontroller dpic33f56gp71 wa burnt on firmware. Acceleration circuit i deigned epecially to wor with microcontroller. For the appropriate deign of the parameter meaured in the object which i endle bandaw, ome precondition hould be oberved in the ytem in term of: reolution bandwidth acquiition time on axi x and y. Thee requirement will help to determine the accelerometer bandwidth, the peed of the microcontroller cloc and the appropriate Duty Cycle. While the accelerometer i very accurate, it ha a wide tolerance for initial offet. The implet way to clear thi offet i with a calibration factor aved on the microcontroller, or by a uer calibration for zero g. When the offet i calibrated during manufacturing proce, the one time programmable microcontroller can be ued. IV. Setting the Bandwidth while adjuting the value of C x and C y capacitor Accelerometer ha proviion for band limiting the X FILT and Y FILT output. Capacitor mut be added to the output pin to implement Low-Pa filtering for antialiaing and noie reduction. The equation for the 3 db bandwidth i F 1 3 db 3Ω C x, () π y ( ( ) ( ) )

3 16 th IMEKO TC4 Sympoium Exploring New Frontier of Intrumentation and Method for Electrical and Electronic Meaurement Sept. -4, 8, Florence, Italy implifying: F 3dB 5µ F C ( X, Y ) (3) A minimum capacitance equal 1 pf for C (X, Y). The Filter capacitor election C x and C y are hown below Table 1 Selection Filter Capacitor Bandwidth [Hz] C x, C y [µf] rm noie [mg] Pea-to-Pea Noie [mg] 1,47,8,47 5,1 1,8,1 1,5,5,5,7 3,6,7 5,1 5,7,1 V. Seting the DCM Period with R et The analog ignal i converted for duty cycle modulated DCM output which i hown on fig.. Further more impule of DCM can be decoded by counter/timer included on microcontroller dpic33fj56gp71. T 1 U max U śr T Borowi 8 Fig.. Output of the Duty Cycle The period of the DCM output i et for both channel by a ingle reitor from R SET to ground. The equation for the period i: R SET ( Ω) T 15 MΩ (4) A( g ) T1,5 T 1,5% (5) where: g 5 % Duty Cycle A 15 Ω reitor will et the duty cycle repetition rate to approximately 1 Hz, or 1 m. The device i deigned to operate at duty cycle period between,5 m 1 m. VI. Selection the accelerometer OISE/BW In the accelerometer the filtering can be ued to lower the noie floor and improve the accelerometer reolution. Reolution i dependent on both the analog filter bandwidth at X FILT and Y FILT and the peed on the microcontroller counter, that can be attained. The analog output of the ADXLE ha a typical bandwidth of 5 Hz while the Duty Cycle modulator ha bandwidth of 5 Hz. In uch cae the aliaing error appear. Then the ignal mut be filtered. To minimize DCM error the analog bandwidth hould be le than 1/1 of the DCM frequency. Analog bandwidth may be increaed to up to 1/ the DCM frequency in mot application. In uch cae thi will reult in greater dynamic error generated at the DCM.

4 16 th IMEKO TC4 Sympoium Exploring New Frontier of Intrumentation and Method for Electrical and Electronic Meaurement Sept. -4, 8, Florence, Italy The analog bandwidth may be further decreaed to reduce noie and improve reolution. It i recommended to limit bandwidth to the lowet frequency needed by the application to maximize the reolution and dynamic range of the accelerometer. With the ingle pole roll-off characteritic the typical noie of the mentioned accelerometer i determined by the following equation: g ( ) ( BW 1,6 ) µ oie rm Hz then at 1 Hz the noie will be: g oie ( rm µ ) ( 1 ( 1,6 )), 53mg (7) Hz Very often the pea value of the noie i deired. Pea-to-pea noie can only be etimated by tatitical method. Table how etimating the probabilitie of exceeding variou pea-to-pea value for variou rm value. Table. Etimation of Pea-to-Pea noie Nominal Pea-to-Pea Value % of Time that Noie will Exceed Nominal Pea-to-Pea Value. x rm 3% 4. x rm 4.6% 6. x rm.7% 8. x rm.6% VII. Mounting the acceleration enor on the bandaw. During the normal operation of the bandaw there are arouing accompanying vibration of the chai, of it ub-aembly and of the bandaw itelf. Becaue of the teeth geometry thoe vibration have the pule waveform. In the urveillance a a x, y enor, the ADXL E accelerometer wa ued The accelerometer enor wa placed on the paive wheel of the bandaw (e figure 3). During the proce of cutting metal, the blade of the teeth receive the impule burden. It applie a well to the endle band aw. The everity of thi burden depend on everal factor, uch a the clamp between the aw and the toc, thicne of the material, to be cut, or the number of aw' teeth being in contact with the wor piece. Epecially the clamp of the wor piece to the aw ha the crucial meaning. It i difficult to protect the teeth of the aw againt overloading, when cutting the profiled material, tube, pipe or contour. (6) o Borowi Fig 3. Identification of Baic Cutting Bandaw Part during operation 1. Blade tightening crew. Stretching wheel 3. Aembling clamping bloc

5 16 th IMEKO TC4 Sympoium Exploring New Frontier of Intrumentation and Method for Electrical and Electronic Meaurement Sept. -4, 8, Florence, Italy 4. Stationery blade guard 5. Blade 6. Support of blade guard 7. Material to be cut 8. Hydraulic linear motor 9. Head frame pulley 1. Active wheel 11. Frame of cutting bandaw 1. Head of cutting bandaw 13. Accelerometer enor gathering the impule burden In the aumed bandaw vibration model the ocillation caued by the movement of the ma m. are decribed. The upper contrain of the exploitation peed equal: eo β 1 + (8) 1 r, l The critical peed for the parametric reonance equal: * r,1,1, while: * χ * χ eo l π χ (9) The equation of the vibration of ma m of the tretching wheel i equal: ( 1 β q ) x& x && + h x& + ω x (1) where:, m After applying the no-dimenional time: q c h, m τ ω t, π l T m, we obtain from (1) a follow: m ( a + χ coτ ) q + ( 1 β q )& x '' + (11) (1) & x ( 1 β q ) x& + h x& + (13) where:,, h h, π l m T The border cycle plot for the bandaw peed of: v,5 m/ and the tenion of the band S equal 4 N i hown on the figure 4. U 1 x m Fig. 4. The border cycle plot (,5 m/, 4 N) The untable phae portrait for the band aw peed of 4.7 m/ i preented on figure 5.

6 16 th IMEKO TC4 Sympoium Exploring New Frontier of Intrumentation and Method for Electrical and Electronic Meaurement Sept. -4, 8, Florence, Italy V X [m/] V X [m.] Fig. 5. The untable phae portrait for the band aw peed v 4.7 m/ VIII. Data acquiition and data tranfer by mean of the ZigBee olution Zigbee with inherent firmware provide a wirele peronal area networing PAN of data from the enor to microcontroller PIC18F4455. The bae of Zigbee hybrid module i IC ZDMAI18-B. It provide point-topoint communication. A erial port i ued to communicate with a hot device through an AT command interface, a hown bellow on chematic fig. 6. AT Communication Hot Device ZigBee Device ZigBee Device - axi Accelerometr Counter Cutting Bandaw wheel SPI Serial Pheriferial Interface SPI Dev In Circuit Serial Programing SPI Dev1 C C PIC18F13 1 PIC18F4455 Digital Controller & Expander SPI RS3 Borowi 8 Fig.6. The Zigbee module ued for data tranfer from the accelerometer enor IX. Concluion The aim of preent invetigation wa to coniderer the poibilitie of meaure the detachable part ocillation. The ADXL E accelerometer enor ha been choen becaue of it poibility of the dual axi operation. Thi way the data wa acquired during the normal wor of the cutting bandaw. The Aim wa achieved by employing the powerful microcontroller PIC18F4455. Reference 1. Wojnarowi: Ograniczenie Drgań Przecinare z Taśmowymi Piłami bez Końca, Monography of Sileian Politechni, Gliwice 7. (in Polih) B.Borowi: Miroontroler PIC dla pratyów, BTC, Warzawa 8 (accepted for publihing),