High precision ultrasonic ranging system platform based on peak-detected self-interference technique

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  • 1. IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 60, NO. 12, DECEMBER 2011 3775 High-Precision Ultrasonic Ranging System Platform Based on Peak-Detected Self-Interference TechniqueJi-De Huang, Chih-Kung Lee, Chau-Shioung Yeh, Wen-Jong Wu, Member, IEEE, and Chih-Ting Lin, Member, IEEE Abstract—A high-precision ultrasonic ranging system platform problem, it is necessary to develop a hardware solution tois presented and evaluated in this work. By queuing peaks of the promote detection precision without statistical manipulations.self-destructive interference, the proposed hardware platform can In brief, the TOF method is achieved by two ultrasonicenhance the accuracy without complex algorithms. At the emit-ter, the developed technique generates two amplitude-modulated transducers. One of them is a transmitter, and the other is apulses with 180◦ phase shift. At the receiver, on the other hand, the receiver. The transmitter sends out modulated ultrasonic waves.two pulses create a self-destructive interference. This interference The waves induce the resonant vibration of the transducer inwaveform can be used to directly determine the time of flight. the receiver. The time difference between transmission and re-By implementing the developed technique on a low-cost micro- ceiving can be used to estimate the distance between two trans-controller platform, the experimental result shows the accuracywith 0.06 mm over a range of 50–1000 mm. Moreover, the system ducers as follows: distance = speed of velocity × TOF. As aaccuracy remains 0.15 mm within the range of 2000 mm. The consequence, it is critical to identify the TOF. With the helpdeveloped system establishes an effective method for low-cost and of hardware setup, previously, varying works utilize amplitude/high-performance ranging systems. phase modulation to identify the TOF [4], [11], [12]. To ob- Index Terms—Distance measurement, self-interference, ultra- tain better time resolution of wave detections in the receiver,sonic system. the self-interference method is introduced [13]. This method transmits two pulse trains to generate an interfering response I. I NTRODUCTION at the receiver. As the second pulse train hits the receiver, the destructive interference occurs because of the integrated re-T HE ultrasonic ranging system has been applied in various applications, i.e., robotic control, vehicle navigation, andfactory automation [1]–[3]. Because of the low cost and ease sponse of the two pulse trains. The receiver output signal decays sharply because of the destructive interference. Because of this interference, the receiver response has a zero response in ampli-in implementation, most ultrasonic ranging systems utilize the tude with a phase inversion at designed time. With this phase-time-of-flight (TOF) method to obtain distance information. inversion detection, the TOF can be identified by counting theSince ultrasonic signal decays rapidly in air, however, this time zero-crossing time. Although this method can be achieved bymeasurement suffers from factors of temperature, humidity, and a hardware setup, the major deficiencies are the ignorance ofreflective interference [4]. Because of the interference, the am- temperature and environmental-reflective interference.plitude and phase information received in ultrasonic receivers In general, the temperature can be compensated by a built-typically have low signal-to-noise ratio. As a consequence, in temperature sensor. However, the environmental-reflectiveresearchers have proposed and implemented various techniques interference should be addressed in detection algorithms. Theto improve the performance of the ultrasonic ranging system interference is caused by the reflective wave from other unde-[5]–[10]. In previous works, most of these techniques were sired obstacles. Because of the divergence angle θ in ultrasonicachieved by signal processes and statistical analyses. However, transmitters, obstacles within θ will reflect the ultrasonic wavecomplicated and unpredicted environmental obstacles result and become one of the reflective-interfering sources. Thesein errors of expected receiving ultrasonic information. This reflective interferences degrade the detection precision. More-leads to the limitations of using signal processes and statistical over, these also decrease the allowable distance-detection limitalgorithms to solve the distance information. To overcome this of ultrasonic ranging systems. Therefore, many researchers proposed various methods to overcome this problem [4], [12], [13]. However, the complicated hardware setup and compu- Manuscript received February 11, 2011; revised April 10, 2011; accepted tation algorithms limit the implementation of high-precisionApril 11, 2011. Date of publication June 9, 2011; date of current versionNovember 9, 2011. This work was supported in part by the National Science ultrasonic ranging systems. To address this issue, we proposeCouncil, Taiwan, under Grant NSC 98-2218-E-002-042, Grant 99-2218-E-002- a method utilizing self-destructive interference to implement a009, Grant 99-2218-E-002-007, and Grant 99-2218-E-002-017. The Associate high-performance and low-cost ultrasonic ranging system.Editor coordinating the review process for this paper was Dr. Shant Kenderian. J.-D. Huang, C.-K. Lee, and C.-S. Yeh are with the Institute of AppliedMechanics, National Taiwan University, Taipei 10617, Taiwan. W.-J. Wu is with the Department of Engineering Science and Ocean II. R EFLECTIVE -I NTERFERENCE R EJECTION M ETHODEngineering, National Taiwan University, Taipei 10617, Taiwan (e-mail:wjwu@ntu.edu.tw). The environmental-reflective interference problem can be C.-T. Lin is with the Graduate Institute of Electronics Engineering, NationalTaiwan University, Taipei 10617, Taiwan (e-mail: timlin@ntu.edu.tw). clearly illustrated as Fig. 1. Two ultrasonic transducers, i.e., Digital Object Identifier 10.1109/TIM.2011.2149391 a transmitter and a receiver, are separately placed with 0018-9456/$26.00 © 2011 IEEE
  • 2. 3776 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 60, NO. 12, DECEMBER 2011Fig. 1. Schematic of the environmental-reflective interference of an ultrasonicranging system.distance D, and both of them have height H above the obstacle.The transmitter has a divergence angle θ. As shown in Fig. 1,the environmental-reflective interference can be ignored withinthe light shadow region. However, it affects the receiving wave-form if the receiver is placed within the dark shadow region, i.e., Fig. 2. Schematic of the ultrasonic signal detection method.D > 2H/ tan θ. At the dark shadow region, the environmental-reflective wave lags behind the directly transmission wave for of the second ultrasonic pulse to be transmitted. This timera time period Tenvi . Assume that the algorithm needs Tdelay in is synchronized with timer A at the receiver. After the twoaddition to the actual TOF to identify the impact of ultrasonic ultrasonic pulses are transmitted, a peak detector is used towave at the receiver, i.e., Tdelay caused by the inertia delay record the peak voltage of the ultrasonic receiver output signal.[7]. As the consequence, an ultrasonic system can ignore the As the recorded peak voltage is smaller than the previousenvironmental-reflective interference as long as Tdelay < Tenvi . stored value, a microcontroller starts to save the zero-crossingConsidering the distance H between transmitter/receiver to the timing to FIFO at the receiver. This timing is obtained fromobstacle, the condition can be rewritten as the synchronized high-speed timer, i.e., timer A. It also starts Tdelay < Tenvi = ( D2 + 4H 2 − D)/Vs (1) another timer, i.e., timer B, to trigger a timeout event for the identification of self-destructive interferences. As timer B goeswhere Vs represents the speed of sound. Furthermore, (1) can to 45 µs without restarting, the timeout event arises and triggersbe used to obtain the maximum detection range without being the microcontroller to read the value from FIFO as the receivinginterfered by the environmental-reflective wave as time, i.e., the TOF of the second ultrasonic pulse at this case. It should be noted that the depth of FIFO is dependent on the D < 2H 2 /(Vs × Tdelay ) − (Vs × Tdelay )/2. (2) pulse design of the systems. The proper depth value can avoid the effect of unstable signals. In our implemented system, theTo obtain good ultrasonic range detection, according to (2), it is depth of FIFO is 1.clear that Tdelay should be kept as small as possible, i.e., finishthe ultrasonic detection step before the reflective interferencewaves arrived. To minimize Tdelay , instead of phase detection or III. E XPERIMENTAL S ECTIONwaveform identification, the peak-detection method is used inthis work. Compared with other methods, the major advantage In the proposed method, the low-cost microcontroller-basedof this peak-detection method is replacing the computation time platform is developed. The experimental setup of the developedrequired by traditional methods by hardware-memory accessing system is described as follows:time. This reduces Tdelay and improves the performance ofultrasonic ranging systems. A. System Implementation To obtain the self-destructive interference signal, we developthe event-time queuing method, as shown in Fig. 2. The ultra- The system diagram of the developed platform can be shownsonic transmitter emits two successive pulses with 25-µs time in Fig. 3. The developed platform is composed of the emitterseparation. The second pulse is sent with larger amplitude than module and the receiver module. MSP430F1611 (Texas Instru-the first pulse. Both of the pulses have 12.5-µs pulsewidth. ment, TI) is used as the microcontroller in both the emitter andTherefore, the two pulses have 180◦ phase difference by using receiver modules. In the emitter module, it creates a 40-kHz40-kHz ultrasonic transducers. As the second pulse hits the signal to the ultrasonic driver and sends the transmission timingreceiver, destructive interference occurs because of the inte- to the receiver module. TS5A3159 (TI) is implemented for thegrated response of the two pulses. Utilizing the peak detection selection of ultrasonic driving voltages. This selection is de-circuit, the incoming zero crossing of the receiver output signal signed to drive the transmitted pulse with different voltages. Incan be recorded and stored in first-in–first-out (FIFO) memory. the ultrasonic driving circuit, TLV2371 (TI) is used to amplifySince peak detection can be used to identify the occurrence the selected voltage for the ultrasonic driver, i.e., UCC37324of self-destructive interference, the receiving time can be ex- (TI). To provide a stable driving power to UCC37324, intracted directly from FIFO. The receiving time of our method addition, the amplifier circuit includes push–pull transistors asis obtained by hardware operation without any mathematical the output stage. Then, the pulse signal is sent to the ultra-manipulation. As a result, it not only reduces Tdelay but can sonic transmitter 400ST12 (Kobitone). Considering the effectalso be implemented by low-cost microcontroller platforms. of temperature and humidity [14], moreover, we also integrate In brief, the hardware operation can be described as follows: the humidity/temperature sensor SHT1X (Sensirion) into theAt the transmitter, a high-speed timer begins at the rising edge developed platform.
  • 3. HUANG et al.: ULTRASONIC RANGING SYSTEM PLATFORM BASED ON PEAK-DETECTED SELF-INTERFERENCE 3777Fig. 3. Schematic of the developed ultrasonic ranging system. Fig. 4. Consideration of distance in an experimental system setup. The critical time can be determined by the nearest distance between an emitter and In the receiver module, the ultrasonic receiver 400SR12 obstacles.(Kobitone) is connected to the instrument amplifier (INA141,TI) for the first-stage amplification. Followed by the 60-Hznotch filter, the second-stage amplifier (VGA810, TI) boosts thereceived signal to both the peak detector and the comparator.The comparator (LM311, National Semiconductor), which isdenoted as Trigger B, is used to compare the received signaland 0 V. This triggers the complex programmable logic device(EPM1270, Altera) for the timing of zero-crossing events. Onthe other hand, the other LM311, i.e., trigger A, compares thereceived signal and the output from the peak detector. Thisis used to trigger the recording of the destructive interferencetiming, i.e., TOF. To obtain this precise timing, synthesizer Fig. 5. Real-time experimental signal obtained from a receiver module.CDCE913 (TI) is implemented to offer a stable 100-MHz clock IV. R ESULT AND D ISCUSSIONfor the complex programmable logic device to measure TOF inreal-time manner. After retrieving the TOF, the information is To demonstrate the capability of the developed system, wetransferred to MSP430F1611. Then, it can be passed to any dig- focus on the precision performance of our system.ital process platform, such as a personal computer, by universalasynchronous receiver/transmitter communication. It should be A. Real-Time Receiver Responsenoted that the system has 10-ns time resolution because ofthe 100-MHz clock. As the consequence, theoretically, it has The real-time signal obtained from the receiver of the devel-a 3.46-µm ranging resolution at room temperature. oped system can be shown as Fig. 5. Curve A represents the amplified receiver response; curve B shows the output of the peak detector; curve C is the signal obtained from the Trigger-AB. Experimental Setup comparator; and curve D is the signal recorded from the Because of the interference from environmental reflections, Trigger-B comparator. According to the system design, curve Ca critical transmitter–receiver distance to avoid this interference is the digital output of the comparison between curve A andcan be obtained by assuming an obstacle position. To achieve curve B. As the time between two positive edges of curve C isself-destructive mechanism, in other words, the second trans- larger than 45 µs, based on our settings, it can be identified asmitted ultrasonic pulse should be received before the arrival the occurrence of self-destructive interferences. Then, curve Dof other environmental-reflective waves. According to (2), with triggers the recording of each zero-crossing time by its negativeH = 150 mm, the theoretical distance to obtain a good self- edges. As previously mentioned, the time is stored in the FIFOdestructive response can be obtained as Fig. 4. In Fig. 4, the of the receiver module. Utilizing the digital output of curve Cvertical axis represents the minimal path difference between and curve D, therefore, the TOF can be precisely obtained fromthe direct ultrasonic wave and the reflective ultrasonic wave. the FIFO with the error being less than one ultrasonic period.This quantity indicates the critical distance to avoid reflectiveinterference noise. As X increases, the minimal path difference B. Distance Measurementdecreases, and the required Tdelay , which is represented inperiod cycles of ultrasonic waves, also decreases. To evaluate To examine the capability of the distance measurement of thethe developed ultrasonic ranging system, therefore, the emitter developed system, the result of the actual distance, comparedand receiver are placed on fixtures with 150-mm height, as with the measured distance, can be shown in Fig. 6. Based onshown in Fig. 4. the optical table (Newport), the actual distance was calibrated
  • 4. 3778 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 60, NO. 12, DECEMBER 2011Fig. 6. (a) Experimental result of the actual distance versus the measured distance. (b) Measurement error of the distance measurement. (c) Onboard temperaturemeasurement at different distances. (d) Onboard humidity measurement at difference distances.by an optical laser scale. This measurement started from 100 to frequency noise. The high-frequency noise resulted from the1200 mm. The temperature and humidity of this measurement electronics. It can be suppressed by the method of movingwere also obtained by the onboard SHT1X sensor. The online average, as shown in Fig. 7(b). In addition, the low-frequencytemperature/humidity data of the distance measurement can drifting is because of the drifting of temperature, humidity, andbe demonstrated in Fig. 6(c) and (d). This information was air flow. After using the high-pass filter to remove the low-used to compensate the distance measurement with a real- frequency drifting, the resulting signal has the error withintime manner. As illustrated in Fig. 6(b), the measured distance 0.5 ms with good stability, as shown in Fig. 7(c). The histogramerror was within 1 mm, and the deviation of measured dis- of the processed signal shows a normal distribution behavior,tance was within 0.2 mm. Checking with the specifications of as shown in Fig. 7(d). Based on this analysis, the standardthe temperature/humidity sensor, it was clear that the relative deviation of the developed system is 0.1287 ms. In other words,large measurement error and deviation resulted from the uncer- this ultrasonic ranging system has the standard deviation oftainty in accuracy of the SHT1X (Sensirion) sensor. To further 0.045 mm under 25 ◦ C.strengthen this statement, the stability of TOF measurement The same analysis method is used to measure the distancewas carried. from 50 to 2000 mm. The standard deviation of each measured distance can be shown in Fig. 8. It shows that the measured precision decreases as the distance increases. This resultedC. Stability of TOF Measurement from the decay of ultrasonic intensity and the interference Utilizing the developed system, the continuous 20 000 sam- of reflective waves. Since our fixture has 150 mm in height,ples of TOF measurement at the distance of 1000 mm can with our experimental setup, we have previously identifiedbe shown as Fig. 7. This experiment was carried under the that the reflective interference can be minimized within thecontrolled environment with 30 ◦ C and relative humidity of range of 1000 mm. As a consequence, the standard deviation42%. The overall time data fluctuation was within ±2 µs. error is significantly affected by intensity decay, and it has aThis showed the capability of the developed system. However, linear behavior before 1000 mm. From 1000 to 2000 mm, thethe obtained signal still contained high-frequency and low- error increases in a parabolic manner because of additional
  • 5. HUANG et al.: ULTRASONIC RANGING SYSTEM PLATFORM BASED ON PEAK-DETECTED SELF-INTERFERENCE 3779 Fig. 8. Precision of the developed system at the range of 50–2000 mm. Fig. 9. Comparison of the developed method to the traditional level-trigger method.Fig. 7. Experimental TOF results at a distance of 1000 mm. (a) Original datapoints. (b) Data removing the electronic noise by method of moving average.(c) Data removing the environmental noise by high-pass filter. (d) Histogram ofthe analyzed results (N = 20000).reflection-interference effects. Based on Fig. 8, the standarddeviation of measurements is only 0.03 mm at a distance of50 mm. It still has a standard deviation of 0.15 mm at a distanceof 2000 mm. This demonstrates the superiority of the developedsystem.D. Comparison of Other Methods The major advantage of the developed system is minimizingthe effect of reflective interference. To demonstrate this advan-tage, the experimental comparison of the developed method and Fig. 10. Experimental comparison of the deviation for different methods.the traditional level-trigger method can be shown in Fig. 9. “ref” represents the amplitude/phase modulation method, and “new” representsSpecifically, this level-trigger method used the voltage level the proposed self-interference method with peak detection.of the receiver signal to identify the TOF. This experimentalresult showed the histogram of two methods at a distance of Considering advanced methods, moreover, the amplitude/1000 mm (N = 20 000). The traditional level-trigger method phase modulation method was implemented and compared withhad the missed TOF identification with 25 µs. This resulted this self-interference method. The comparison result of thefrom the failure to capture the first receiving pulse. In addition, measurement deviation is demonstrated in Fig. 10. For thethe precision of the traditional level-trigger method is also amplitude/phase modulation method, we obtained the mea-larger than that of the developed method. surement deviation within 0.2 mm before 750 mm, which is
  • 6. 3780 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 60, NO. 12, DECEMBER 2011similar as a previous report [7]. At the same time, the proposed [12] G. Mauris, E. Benoit, and L. Foulloy, “Local measurement validation forself-interference method had the measurement deviation within an intelligent chirped-FM ultrasonic range sensor,” IEEE Trans. Instrum. Meas., vol. 49, no. 4, pp. 835–839, Aug. 2000.0.1 mm from 100 to 1200 mm. It should be noted that the mea- [13] C. Cai and P. P. L. Regtien, “Accurate digital time-of-flight measurementsurement of the amplitude/phase modulation method became using self-interference,” IEEE Trans. Instrum. Meas., vol. 42, no. 6,unstable after 750 mm. We suspected that this was a result of pp. 990–994, Dec. 1993. [14] W. Y. Tsai, H. C. Chen, and T. L. Liao, “An ultrasonic air temperaturethe decay of ultrasonic amplitude and environmental-reflective measurement system with self-correction function for humidity,” Meas.interference because it used pulse train, instead of a single Sci. Technol., vol. 16, no. 2, pp. 548–555, Feb. 2005.pulse. As a result, the pulse train might interfere with each otherat the receiver and reduce its stability at a larger distance than750 mm. Ji.-De Huang received the M.S. degree from National Taiwan University, Taipei, Taiwan. He is currently working toward the Ph.D. degree in the Institute of Applied Mechanics, National Taiwan V. C ONCLUSION University. His current research interests include wireless In this work, we have developed a low-cost and high- sensor networks and embedded systems.precision ultrasonic ranging system. The system utilizes theself-destructive interference method with peak detection toovercome the reflective interference effects. In addition, themethod has been experimentally implemented and examined bythe low-cost microcontroller platform. Based on the developed Chih-Kung Lee received the M.S. and Ph.D. degreesmethod, a precision of 0.15 mm within 2000 mm can be in theoretical and applied mechanics from Cornellachieved. Moreover, the environmental-reflective interference University, Ithaca, NY.has been discussed and verified experimentally. Therefore, this In 1994, he joined the faculty of the Institute of Applied Mechanics, National Taiwan Univer-ultrasonic ranging system establishes an effective platform for sity, Taipei, Taiwan. He currently holds an Adjunctlow-cost and high-performance ranging systems. Moreover, it appointment as Executive Vice-President of theoffers a better hardware platform for add-on analysis algorithms Industrial Technology Research Institute. His re- search interests include microelectromechanical,to be implemented into applications. nanosystems, piezoelectric systems, automation, optoelectronic system design and fabrication, preci- sion metrology, and biochip systems. R EFERENCES [1] H. Choset, K. Nagatani, and N. A. Lazar, “The arc-transversal median algorithm: A geometric approach to increasing ultrasonic sensor azimuth Chau-Shioung Yeh received the M.S. degree from accuracy,” IEEE Trans. Robot. Autom., vol. 19, no. 3, pp. 513–521, National Taiwan University, Taipei, Taiwan, and the Jun. 2003. Ph.D. degree in theoretical and applied mechanics [2] G. Oriolo, G. Ulivi, and M. Vendittelli, “Fuzzy maps: A new tool for from Cornell University, Ithaca, NY. mobile robot perception and planning,” J. Robot. Syst., vol. 14, no. 3, In 1975, he joined the faculty of the Institute pp. 179–197, Mar. 1997. of Applied Mechanics, National Taiwan Univer- [3] F. Tong, S. K. Tso, and T. Z. Xu, “A high precision ultrasonic docking sity. His research interests include elastic wave in system used for automatic guided vehicle,” Sens. Actuators A, Phys., solids, magneto-elasticity, earthquake engineering, vol. 118, no. 2, pp. 183–189, Feb. 2005. and structural mechanics. [4] H. Hua, Y. T. Wang, and D. Y. Yan, “A low-cost dynamic range-finding device based on amplitude-modulated continuous ultrasonic wave,” IEEE Trans. Instrum. Meas., vol. 51, no. 2, pp. 362–367, Apr. 2002. [5] C.-C. Tong, J. F. Figueroa, and E. Barbieri, “A method for short or long range time-of-flight measurements using phase-detection with an analog Wen-Jong Wu (M’06) received the M.S. and Ph.D. circuit,” IEEE Trans. Instrum. Meas., vol. 50, no. 5, pp. 1324–1328, degrees from National Taiwan University, Taipei, Oct. 2001. Taiwan, in 1998 and 2003, respectively. [6] L. Angrisani, A. Baccigalupi, and R. S. L. Moriello, “A measure- Since 2003, he has been an Assistant Professor ment method based on kalman filtering for ultrasonic time-of-flight with the Department of Engineering Science and estimation,” IEEE Trans. Instrum. Meas., vol. 55, no. 2, pp. 442–448, Ocean Engineering, National Taiwan University. His Apr. 2006. research interests include systems design, integration [7] Y. P. Huang, J. S. Wang, K. N. Huang, C. T. Ho, J. D. Huang, and of precision metrology, smart sensor networks, and M. S. Young, “Envelope pulsed ultrasonic distance measurement system piezoelectric power devices. based upon amplitude modulation and phase modulation,” Rev. Sci. Instrum., vol. 78, no. 6, p. 065103, Jun. 2007. [8] A. Baccigalupi and A. Liccardo, “Field programmable analog arrays for conditioning ultrasonic sensors,” IEEE Sensors J., vol. 7, no. 8, pp. 1176–1182, Aug. 2007. [9] J. Majchrzak, M. Michalski, and G. Wiczynski, “Distance estimation with Chih-Ting Lin (M’07) received the Ph.D. degree a long-range ultrasonic sensor system,” IEEE Sensors J., vol. 9, no. 7, from the University of Michigan, Ann Arbor. pp. 767–773, Jul. 2009. He is currently an Assistant Professor with[10] F. Alonge, M. Branciforte, and F. Motta, “A novel method of distance the Graduate Institute of Electronics Engineering, measurement based on pulse position modulation and synchronization National Taiwan University, Taipei, Taiwan. His of chaotic signals using ultrasonic radar systems,” IEEE Trans. Instrum. current research interests include biosensors and Meas., vol. 58, no. 2, pp. 318–329, Feb. 2009. microdevices.[11] C. F. Huang, M. S. Young, and Y. C. Li, “Multiple-frequency continuous wave ultrasonic system for accurate distance measurement,” Rev. Sci. Instrum., vol. 70, no. 2, pp. 1452–1458, Feb. 1999.