DEVICE AND METHOD FOR OPERATING AN ULTRASOUND SENSOR

Abstract

Device for operating an ultrasonic sensor, comprising: a driver unit for providing a transmit pulse to the ultrasonic sensor, which emits an ultrasonic wave and receives an ultrasonic echo of the ultrasonic wave; an amplifier for amplifying an electrical signal for the ultrasonic echo; an analog-to-digital converter for converting the amplified electrical signal into an original digital signal; a signal processing unit for performing envelope extraction processing on the original digital signal and for generating a signal processed by envelope extraction; and a control unit for outputting a distance between the ultrasonic sensor and an external object based on the original digital signal and the signal processed by envelope extraction.wherein the control unit monitors a frequency or phase change of the oscillation of a transducer of the ultrasonic sensor based on the original digital signal at least during a second period and analyzes the signal processed by envelope extraction at least during a third period, provided that there is a first period in which the transducer oscillates according to the transmitted pulse, there is a second period in which the transducer oscillates after the transmission of the pulse has ceased, and there is a third period in which the transducer ceases to oscillate, and wherein the control unit outputs the distance between the ultrasonic sensor and the external object, which is determined on the basis of a transit time between an initial detection time and a transmission time of the ultrasonic wave, wherein the initial detection time is determined,if the frequency or phase change of the transducer of the ultrasonic sensor is first detected during the second period and ultrasonic echoes are received at least twice through repeated mutual reflections between the ultrasonic sensor and the external object within a predetermined time.

Description

BACKGROUND ART OF THE INVENTION1. Field of the InventionThe present invention relates to an ultrasonic sensor, and more particularly to an apparatus and method for operating an ultrasonic sensor.2. Prior ArtRecently, vehicle manufacturers have developed vehicle safety techniques extensively and introduced vehicle products on the market using advanced safety techniques. Representative examples of the advanced safety techniques are modern driver assistance systems (engl. Advanced Driver Assistance Systems, ADAS), which are mainly used in parking a vehicle. In particular, parking assistants (Engl. Parking Assistance Systems (PAS) and Automatic Parking Assistants (PAS). Automatic Parking Assistance Systems - APAS) among the ADAS are widely used to indicate the distance between the vehicle and external objects. In these systems, an essential technique is to accurately measure positions or distances of external objects using ultrasonic sensors mounted on the vehicle.The ultrasonic sensor may detect ultrasonic echoes reflected from the external objects after transmitting ultrasonic waves at a frequency of 20 KHz or more, which is in a non-audible range. The ultrasonic sensor can also measure distances to the external objects on the basis of the detected ultrasonic echoes. In this case, the vehicle driver can be informed based on the measured distances in a variety of ways, such as a warning sound, a display on the vehicle display, or the like. Accordingly, the safety of the driver and the vehicle can be greatly improved by the ultrasonic sensor technique.However, the conventional distance measurement technique using the ultrasonic sensor has had many limitations on the detection ranges or the detection accuracy. In particular, conventional ultrasonic sensors can receive the actual ultrasonic echoes reflected from the external objects only after the physical vibration of the transducers of the ultrasonic sensors has been completely stopped, since the transducer is still vibrated for a period of time even if the ultrasonic sensor has finished driving the transducer. Accordingly, it has been very difficult to measure the distance of the external objects located at very close positions to the ultrasonic sensor.However, the need for various applications requiring very precise distance sensing with a wider sensing range than existing ultrasonic sensors has increased more and more. As a result, the improvement of the existing distance measurement systems has become very urgent. For example, in a narrow parking space, for more effective parking, it is necessary to measure the distance shorter than the currently measurable distance.Prior art: Korean Unexamined Patent Publication No. 10-2005-0006750 (Appearance Date: Jan. 17, 2005).DE 10 2010 062 983 A1 discloses a method and a device for acoustically scanning an area, in which an object is detected in the area on the basis of a deviation of an actual phase profile from a setpoint phase profile.DE 10 2009 049 069 A1 discloses a method for measuring the transit time, in which time differences with respect to transmitted and received ultrasonic pulses are determined by comparing the respective envelopes, in order to thus extrapolate a reference time of the received ultrasonic pulse.EP 2 881 181 A1 discloses a method for determining electrical parameters of a tuning unit for an ultrasonic transducer.SUMMARY OF THE INVENTIONIt is an object of the present invention to substantially avoid various problems and disadvantages of the prior art caused by limitations. The object of the present invention is in particular to provide an apparatus and a method for operating an ultrasonic sensor for a more precise measurement of a position of the distance to very nearby external objects.In order to achieve the above object, an apparatus for operating an ultrasonic sensor according to an embodiment of the present invention may include, as set forth in claim 1, a driving unit for providing a transmission pulse to the ultrasonic sensor to transmit an ultrasonic wave and receiving an ultrasonic echo for the ultrasonic wave; an amplifier for amplifying an electric signal for the ultrasonic echo; an analog-to-digital converter for converting the amplified electric signal into a digital original signal; a signal processing unit for performing envelope extraction processing on the digital original signal and generating an envelope extraction processed signal; and a control unit for outputting a distance between the ultrasonic sensor and an external object on the basis of the digital original signal and the envelope extraction processed signal, wherein the control unit monitors a frequency or phase change of vibration of a transducer of the ultrasonic sensor based on the digital original signal at least during a second period and analyzes the signal processed by envelope extraction at least during a third period, as long as there is a first period in which the transducer vibrates according to the transmission pulse, there is the second period in which the transducer vibrates after the transmission pulse has stopped providing, and there is the third period in which the transducer stops vibrating, and wherein the control unit outputs the distance between the ultrasonic sensor and the external object determined based on a delay time between an initial detection time and a transmission time of the ultrasonic wave, the initial detection time being determined, when the frequency or phase change of the transducer of the ultrasonic sensor is first detected during the second period and the ultrasonic echo is received within a predetermined time.In this case, a frequency of the transmit pulse may be in the middle of a resonant frequency and an antiresonant frequency of the transducer.Moreover, a ringing frequency of the transducer during the second period may correspond to a resonant frequency of the transducer.The control unit may further include a memory for storing the propagation time between the initial detection time and the transmission time of the ultrasonic wave.The control unit may also comprise a phase or frequency change detection unit which detects the phase or frequency change of the converter.Meanwhile, a method of operating an ultrasonic sensor according to an embodiment of the present invention may include: providing a transmission pulse to the ultrasonic sensor to transmit an ultrasonic wave and receiving an ultrasonic echo for the ultrasonic wave; amplifying an electric signal for the ultrasonic echo; converting the amplified electric signal into a digital original signal; performing envelope extraction processing on the digital original signal and generating an envelope extraction processed signal; outputting a distance between the ultrasonic sensor and an external object based on the digital original signal and the signal processed by envelope extraction, wherein outputting the distance comprises: monitoring an oscillation frequency of a transducer of the ultrasonic sensor based on the digital original signal at least during a second period; and analyzing the signal processed by envelope extraction at least during the third period, if there is a first period in which the transducer oscillates corresponding to the transmission pulse, there is the second period in which the transducer oscillates after it has stopped providing the transmission pulse, and there is the third period in which the transducer stops oscillating; outputting the distance between the ultrasonic sensor and the external object determined based on a time of flight between an initial detection time and a transmission time of the ultrasonic wave, wherein the initial detection time is determined when a change in the vibration frequency of the transducer is first detected during the second period and the ultrasonic echo is received within a predetermined duration.In this case, a frequency of the transmission pulses may be in the middle of a resonant frequency and an antiresonant frequency of the transducer.Moreover, the oscillation frequency of the transducer during the second period corresponds to a resonant frequency of the transducer.Outputting the distance may further include saving the propagation time between the initial detection time and the transmission time of the ultrasonic wave.The change in the oscillation frequency is also detected based on a phase or frequency change of the transducer.According to the present invention, a position of the distance to nearby external objects can be measured more accurately. The distance to the external objects is outputted based on the transit time between the transmission of the ultrasonic waves and the detection of a first ultrasonic echo of the ultrasonic waves, when the first ultrasonic echo of the ultrasonic waves is detected by the detection of the frequency or phase change of the transducer of the ultrasonic sensor during a reverberation period in which the transducer of the ultrasonic sensor continues to resonate after the ultrasonic sensor has stopped transmitting ultrasonic waves and a second ultrasonic echo of the ultrasonic waves is received within a predetermined time from the reception of the first ultrasonic echo. Conventionally, it has not been possible to measure the distances of external objects during the reverberation period, and then the possible distance range of the detected external objects has been limited to more than 30 cm. However, according to the present invention, the ultrasonic sensor can measure a distance of a nearby external object of about 5 cm.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 illustrates a block diagram of an ultrasonic sensor driving apparatus according to an embodiment of the present invention. FIG. 2 illustrates a graph of an original digital signal received in a reverberation period according to an embodiment of the present invention. FIG. 3 illustrates an example in which the ultrasonic waves are reflected at least twice according to an embodiment of the present invention. FIG. 4 illustrates a diagram in which the ultrasonic echoes are received at least twice according to an embodiment of the present invention. FIG. 5 illustrates an example of a transmitted ultrasonic wave and at least two multiple received ultrasonic echoes according to an embodiment of the present invention. FIG. 6 illustrates a flowchart of a method for driving an ultrasonic sensor according to an embodiment of the present invention.<BESCHREIBUNG OF REFERENCE NUMERAL>100 Ultrasonic sensor 200 Ultrasonic sensor driving device 220 Amplifier 230 Analog-to-digital converter 240 Signal processing unit 250 Control unitDETAILED DESCRIPTION OF THE INVENTIONHereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be understood, however, that the invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete. For the purpose of explanation, the size of the components may also be greatly increased or decreased in the drawings.The following embodiments are to be considered as illustrative and not restrictive, and the scope of the present invention is not limited solely by the following embodiments.FIG. 1 shows a configuration of an apparatus for operating an ultrasonic sensor according to an embodiment of the present invention.Referring to FIG. 1, an ultrasonic sensor driving system according to an embodiment of the present invention includes an ultrasonic sensor 100 and an ultrasonic sensor driving device 200.The ultrasonic sensor 100 includes a transducer. The ultrasonic sensor 100 vibrates the transducer according to the transmission pulse received from the ultrasonic sensor driving device 200 to transmit ultrasonic waves. Then, when the echoes of the ultrasonic waves reflected from an object re-oscillate the transducer, the transducer converts the oscillation into an electric signal and outputs the electric signal. In general, the transmission and reception of the ultrasonic waves are temporally divided into a transmission period and a reception period, and the transmission and reception are sequentially and repeatedly performed.The ultrasonic sensor driving device 200 includes a driving unit 210, an amplifier 220, an analog-to-digital converter (ADC) 230, a signal processing unit 240, and a control unit 250. The ultrasonic sensor driving device 200 analyzes the ultrasonic echoes received via the transducer of the ultrasonic sensor 100 for the ultrasonic waves to calculate the distance to an external object.The driving unit 210 transmits ultrasonic waves by vibrating the transducer by providing transmission pulses to the transducer. The ultrasonic sensor 100 converts received ultrasonic echoes for the transmitted ultrasonic waves into electrical signals. The amplifier 220 amplifies the electrical signals for the received ultrasonic echoes 414 and 418. The driving unit 210 outputs transmission pulses so that the transducer can be vibrated at a frequency having a value between the resonance frequency and the antiresonance frequency of the transducer of the ultrasonic sensor 100 in consideration of the reception sensitivity of the transmitted ultrasonic waves and the received ultrasonic echoes.The analog-to-digital converter 230 converts the amplified signals into digital signals in the amplifier 220 and transmits the digital signals to the signal processing unit 240. In addition, according to the present invention, the digital signals converted by the analog-to-digital converter 230 are input to the control unit 250 as original digital signals 232.The signal processing unit 240 is a module for converting and processing the ultrasonic waves into analytic signals, which can be analyzed in the control unit 250 so as to eliminate the noise of the electric signals for the ultrasonic echoes and extract the envelope from the electric signals. The signal processing unit 240 may include, for example, a band pass filter that filters a certain frequency range around a transmission frequency by various digital filters, an envelope extractor that extracts envelope signals from signals passed through the band pass filter, and / or a low pass filter for filtering the noise of the extracted envelope signals.The control unit 250 comprises a phase and / or frequency change detection unit 252 and a memory 254 and analyzes the digital signals processed by envelope extraction for outputting a distance to an external object.Next, the principle of the present invention will be described with reference to FIGS. 2, 3, 4 to 5, and then the operation of the control unit 250 will be described in detail. Hereinafter, with reference to FIGS. 2, 3, 4 to 5, a method for distance measurement using the ultrasonic sensor of the present invention will be described in detail. FIG. 2 shows a graph of digital original signals 232 of the second period, which is the reverberation period. FIG. 3 is a diagram for explaining reflections of ultrasonic signals between the ultrasonic sensor 100 and the external object adjacent to the ultrasonic sensor 100. Fig. 4 shows a graph of the signals for the signals processed by envelope extraction. FIG. 5 further shows a diagram for the transmission and reception cycles of the ultrasonic sensor 100 according to the present invention.First, with reference to FIG. 5, a transmission period and a reception period of the ultrasonic waves will be described.The ultrasonic sensor 100 is driven in the transmission period and the reception period as shown in FIG. 5.Referring to FIG. 5, the transmission and reception periods include a first period (t0-t1) in which the transducer of the ultrasonic sensor 100 is vibrated by transmission pulses of the driving unit 210, a second period (t1-t2) in which the transducer of the ultrasonic sensor 100 continues to vibrate (ringing) after the driving unit 210 stops providing the transmission pulse, a third period (t2-until the next transmission pulses are provided by the driving unit 210) in which the transducer stops vibrating. In the following description, the control of the ultrasonic sensor 100 by the control unit 250 in the above-described transmission and reception period will be described in detail.As described above, in the first period, the driving unit 210 provides transmission pulses to oscillate the transducer of the ultrasonic sensor 100, and then interrupts the provision of the transmission pulses upon entering the second period. The transducer then oscillates at the resonant frequency and the intensity of the ringing is attenuated. The ringing and attenuation stop at the end of the second period. Such attenuation and ringing are referred to as reverberation. After completion of reverberation, the transducer stops oscillating unless the echoes of the transmitted ultrasonic waves are received until the next transmission pulses are provided (third period).A conventional ultrasonic sensor driving apparatus cannot process received signals during a reverberation period (ringing period) because it is difficult to extract precise ultrasonic echoes due to the influence of reverberation in the second period (reverberation period). It was thus impossible to measure a distance to an external object during the reverberation period, and there was a limitation in measuring a position of an external object very close to the conventional ultrasonic sensor. In the case of the conventional ultrasonic sensor mounted on the vehicle, measurement was not possible within the range of 30 cm from the ultrasonic sensor.Referring to FIG. 2, the control unit 250 monitors the digital original signals 232 received from the analog-to-digital converter 230 during the second period. Even if the transducer of the ultrasonic sensor 100 is not driven by the transmission pulses at the resonance frequency in the first period, the ringing frequency of the transducer changes rapidly to the physical resonance frequency of the transducer in the second period. However, when the ultrasonic echoes of the ultrasonic waves reflected from the external object are received in the second period, the ringing frequency of the transducer changes to a composite frequency of the resonance frequency and the frequency of the ultrasonic echoes of the reflected ultrasonic waves.A phase and / or frequency shift detection unit 252 detects an output time (Tfc) at which the transducer begins to resonate at the composite frequency, which output time may be stored as a potential time of flight (TOF1) in a memory 254.Referring to FIG. 3, when the transducer is vibrated such that ultrasonic waves are emitted when the transducer and the object are in close proximity to each other, the ultrasonic echoes reflected from the object are again reflected by the transducer a second time. The ultrasonic waves reflected by the transducer are reflected a second time from the object. The transmitted ultrasonic waves are continuously attenuated as they move in space, these secondary reflections being repeated until they disappear completely. When the object is in a very close position, the ultrasonic echoes are thus received at least twice by repeating mutual reflections, even in the case of a single transmission of the ultrasonic waves. In the present invention, this principle is used to extend the measurable distance in the near range.According to the present invention, during the second period, the control unit 250 first detects the ultrasonic echoes 414 with the phase and / or frequency change detector 252. In this case, the distance to the external object is output based on the potential travel time, which is the output timing detected by the phase and / or frequency change detector 252, and is stored in the memory 254 when the control unit 250 receives the ultrasonic waves 414 within a predetermined time 416 (see FIGS. 4 and 5 ).As shown in FIG. 5, if the ultrasonic echoes 414 extend for the second and third time periods due to the reflection of the external object, they could be received within the predetermined time 416. Thus, the distance to the external object can be outputted based on the time point (Tfc) at which the frequency and / or phase change of the natural vibration is detected. Accordingly, in the embodiment of FIG. 5, the distance to the object in the reverberation period may be calculated without considering the echo 418 for the secondary reflected waves.Conventionally, it has been attempted to measure the flight distance with respect to the reverberation period. In the conventional embodiment, however, most signals are filtered out during the reverberation period due to the self-oscillation of the transducer. For example, there has been a conventional configuration for measuring a distance during the reverberation period in which the difference between timings of detecting the first reflected signal and the secondary reflected signal is output as the distance when the difference is less than a predetermined time. However, since the secondary reflected signal has a very weak intensity, it was difficult to measure the distance during the reverberation period.However, in the present invention, the reflected waves from the object in the reverberation period can be accurately detected by monitoring the phase and / or frequency change of the digital original signals 232 in the reverberation period. Moreover, by using secondary reflections from nearby objects, the accuracy of detection of nearby objects is greatly improved. However, as shown in FIG. 5, even if no secondary reflections of the object are taken into account, it is possible to accurately detect the transit time of nearby objects by recognizing them as a nearby object when the envelope of the external object is detected within the predetermined time.Next, the method of driving an ultrasonic sensor according to an embodiment of the present invention will be described with reference to FIG. 6.FIG. 6 illustrates a flowchart of an ultrasonic sensor driving method according to an embodiment of the present invention.Ultrasonic waves are transmitted from the ultrasonic sensor 100 according to transmission pulses 408, and the ultrasonic echoes 414 of the ultrasonic waves are received (step S502).The amplifier 220 amplifies the electric signal of the received ultrasonic echoes 414 (step S 504).The analog-to-digital converter 230 converts the amplified electric signal into a digital signal (step S 506), and supplies the digital signal as an original digital signal 232 to the control unit 250 and the signal processing unit 240.The signal processing unit 240 performs envelope extraction processing on the digital original signal, and the control unit 250 monitors the digital original signal 232 to detect whether there is a frequency change in the second period (reverberation period) (step S 508).The control unit 250 analyzes the digital original signal to determine whether a frequency and / or phase change was detected during the second period and an external object was detected within a predetermined duration based on the extracted envelope. The control unit 250 recognizes the distance calculated based on the frequency and / or phase change as an effective distance, and outputs the effective distance to the external object (step S 510).Assuming that there is a first period (t0-t1) in which the transducer of the ultrasonic sensor 100 is vibrated according to the transmission pulses provided from the driving unit 210, there is a second period (t1-t2) in which the transducer of the ultrasonic sensor 100 continues to be vibrated (ringing) after the driving unit 210 has stopped providing the transmission pulse, and there is a third period (t2-until the next transmission pulses are provided by the driving unit 210) in which the transducer stops vibrating, the step S510 of outputting the effective distance to the external object includes the step in which the digital original signals are analyzed during the second period and the step in which the digital signals processed by envelope extraction are analyzed during the third period.When there is a frequency and / or phase change during the second period and the ultrasonic echoes 414 are detected within the predetermined time, the control unit 250 recognizes the distance calculated based on the frequency and / or phase change as an effective distance and outputs the effective distance to the external object.According to the present invention, in the case where the phase and / or frequency change of the transducer during a reverberation period is first detected during a reverberation period in which the transducer of the ultrasonic sensor 100 continues to be oscillated (ringing) after the driving unit 210 stops providing the transmission pulse and the ultrasonic echoes are received within the predetermined time, it is possible to more accurately measure the position of the adjacent external object by outputting the distance to external objects on the basis of the travel time calculated on the basis of the initial detection time and the transmission time of the ultrasonic waves. Since it was not possible to measure the distance of the object in the reverberation period, only objects having a distance of more than 30 cm from the ultrasonic sensor could be detected in the past. However, according to the present invention, it is possible to detect external objects at a distance of about 5 cm.While the present invention has been described in terms of what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, it is to be understood that the invention is not limited to the disclosed embodiments and is intended to include various modifications and similar elements. Accordingly, the scope of the present invention should not be construed as limited to the described embodiments.

Claims

An apparatus for driving an ultrasonic sensor, comprising: a driving unit for providing a transmission pulse to the ultrasonic sensor, which transmits an ultrasonic wave and receives an ultrasonic echo of the ultrasonic wave; an amplifier for amplifying an electric signal for the ultrasonic echo; an analog-to-digital converter for converting the amplified electric signal into a digital original signal; a signal processing unit for performing envelope extraction processing on the digital original signal and generating an envelope extraction processed signal; and a control unit for outputting a distance between the ultrasonic sensor and an external object on the basis of the digital original signal and the envelope extraction processed signal, wherein the control unit monitors a frequency or phase change of vibration of a transducer of the ultrasonic sensor based on the digital original signal at least during a second period and analyzes the signal processed by envelope extraction at least during a third period, as long as there is a first period in which the transducer vibrates according to the transmission pulse, there is the second period in which the transducer vibrates after the transmission pulse has stopped providing, and there is the third period in which the transducer stops vibrating, and wherein the control unit outputs the distance between the ultrasonic sensor and the external object determined based on a delay time between an initial detection time and a transmission time of the ultrasonic wave, the initial detection time being determined, when the frequency or phase change of the transducer of the ultrasonic sensor is first detected during the second period and ultrasonic echoes are received at least twice by repeating mutual reflections between the ultrasonic sensor and the external object within a predetermined time.The apparatus of claim 1, wherein a frequency of the transmit pulses is at the center of a resonant frequency and an anti-resonant frequency of the transducer.The apparatus of claim 1, wherein a decay frequency of the transducer during the second period corresponds to a resonant frequency of the transducer.The apparatus according to claim 1, wherein the control unit comprises a memory for storing the transit time between the initial detection time and the transmission time of the ultrasonic wave.The apparatus according to claim 1, wherein the control unit comprises a phase or frequency change detection unit that detects the phase or frequency change of the converter.A method of operating an ultrasonic sensor, comprising: providing a transmission pulse to the ultrasonic sensor to transmit an ultrasonic wave and receive an ultrasonic echo of the ultrasonic wave; amplifying an electric signal for the ultrasonic echo; converting the amplified electric signal into a digital original signal; performing envelope extraction processing on the digital original signal and generating a signal processed by envelope extraction; outputting a distance between the ultrasonic sensor and an external object based on the digital original signal and the signal processed by envelope extraction, wherein outputting the distance comprises: monitoring an oscillation frequency of a transducer of the ultrasonic sensor based on the digital original signal at least during a second period; and analyzing the signal processed by envelope extraction at least during the third period, if there is a first period in which the transducer oscillates corresponding to the transmission pulse, there is the second period in which the transducer oscillates after it has stopped providing the transmission pulse, and there is the third period in which the transducer stops oscillating; outputting the distance between the ultrasonic sensor and the external object determined based on a time of flight between an initial detection time and a transmission time of the ultrasonic wave, wherein the initial detection time is determined when a change in the vibration frequency of the transducer is first detected during the second period and ultrasonic echoes are received at least twice by repeating mutual reflections between the ultrasonic sensor and the external object within a predetermined time.The method of claim 6, wherein a frequency of the transmit pulses is at the center of a resonant frequency and an anti-resonant frequency of the transducer.The method of claim 6, wherein the oscillation frequency of the transducer during the second period corresponds to a resonant frequency of the transducer.The method according to claim 6, wherein the control unit comprises a memory for storing the propagation time between the initial detection time and the transmission time of the ultrasonic wave.The method of claim 6, wherein the change in the oscillation frequency is detected based on a phase or frequency change of the transducer.

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