Automobile ultrasonic sensor optimization method, sensor and distance measurement method

Abstract

The invention belongs to the technical field of intelligent automobiles, and provides an automobile ultrasonic sensor optimization method, a sensor and a distance measuring method.The automobile ultrasonic sensor optimization method comprises the steps that the standard uncertainty of the measurement distance under the influence of the air temperature and the air humidity is calculated; the air humidity serves as a random variable, standard uncertainty contribution is determined within the preset air humidity range and the preset air temperature, and whether a humidity sensor is added or not is determined according to the determined standard uncertainty contribution; according to the approximate equation between the propagation speed of the sound in the air and the air temperature and the preset air temperature, the sound velocity change range is determined; determining whether to add a temperature sensor by determining a sound velocity change range; on the basis of meeting the requirements of distance detection precision and automobile control, the cost is reduced by limiting the application of the temperature sensor and the humidity sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent automobiles, and in particular relates to an automobile ultrasonic sensor optimization method, a sensor and a distance measurement method. Background Art

[0002] As smart cars evolve, sensors that can measure in the centimeter to meter range are needed. Parking assistance devices, as well as smart suspension and headlight leveling, all require distance measurement using non-contact sensors.

[0003] In actual distance measurement, in order to improve the accuracy of the measured distance, the uncertainty of air temperature, air humidity and vehicle speed will be considered to correct or modify the measured output value, so that the more accurate the detection value is, the more accurate the control of the car will be. However, when considering the above uncertainties, it is necessary to set auxiliary components such as temperature sensors and humidity sensors on the sensor, which leads to an increase in the structural cost and calculation cost of the sensor; and, in order to solve the problem of sound attenuation, the high-cost transducer used or the digital processing required to be used also increases the cost of the sensor, resulting in a high cost of automotive ultrasonic sensors for ranging; in summary, the current automotive ultrasonic sensors for ranging have a contradiction between cost and meeting automotive needs. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes an automobile ultrasonic sensor optimization method, a sensor and a distance measurement method. The present invention takes air humidity as a random variable, determines the standard uncertainty contribution within a preset air humidity range and a preset air temperature, and determines whether to add a humidity sensor according to the determined standard uncertainty contribution; and determines the sound speed variation range according to an approximate equation between the sound propagation speed in the air and the air temperature, as well as the preset air temperature; determines whether to add a temperature sensor by determining the sound speed variation range; and reduces costs by limiting the application of temperature sensors and humidity sensors on the basis of meeting the distance detection accuracy and automobile control requirements.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for optimizing an automotive ultrasonic sensor, comprising:

[0007] An automotive ultrasonic sensor optimization method, comprising:

[0008] Calculate the standard uncertainty of distance measurement under the influence of air temperature and air humidity;

[0009] Taking air humidity as a random variable, determining the standard uncertainty contribution within a preset air humidity range and a preset air temperature, and deciding whether to add a humidity sensor based on the determined standard uncertainty contribution;

[0010] The sound speed variation range is determined based on the approximate equation between the speed of sound propagation in the air and the air temperature, as well as the preset air temperature. The determination of the sound speed variation range is used to determine whether to add a temperature sensor.

[0011] Furthermore, under the influence of air temperature and air humidity, the standard uncertainty μ(D) of the measured distance is:

[0012]

[0013] Where k is a constant; T f is the emission time of the ultrasonic pulse; μ(θ) is the standard uncertainty of air temperature, θ is the air temperature; μ(θ) is the standard uncertainty of air humidity, h is the air humidity; μ(T d ) is the standard uncertainty of the flight time, V s is the speed of sound.

[0014] Furthermore, the speed of sound in air V s The approximate equation between ρ and air temperature is:

[0015]

[0016] Where T is the absolute temperature.

[0017] In a second aspect, the present invention further provides an automotive ultrasonic sensor distance measurement system, comprising:

[0018] A sensor is obtained by the automotive ultrasonic sensor optimization method as described in the first aspect.

[0019] Furthermore, it includes a signal generator and a zero-crossing detector; the signal generator includes an erasable programmable read-only memory, and the erasable programmable read-only memory is provided with a digital-to-analog converter for generating a signal; the zero-crossing detector includes two threshold detectors, a first detector and a second detector; the threshold of the first detector is a part of the peak value of the received signal, and the second detector compares the received signal with a preset reference.

[0020] Furthermore, the driving signal X of the erasable programmable read-only memory opt (f) is:

[0021]

[0022] Where H(f) is the frequency response of the transmit channel; λ1 and λ 2 is the Lagrange multiplier.

[0023] Furthermore, the invention also includes a noise measurement system, wherein the noise measurement system estimates actual noise by monitoring the input signal in an echo-free interval.

[0024] In a third aspect, the present invention further provides a distance measurement method, comprising:

[0025] A distance measurement method, using the sensor as described in the second aspect, includes: the distance from a preset point on the vehicle body to the ground is equal to the product of the wave emission time of the ultrasonic pulse, a preset constant and the speed of sound; wherein the uncertainty contribution of the constant is eliminated by sensor calibration after installing the measuring head.

[0026] Furthermore, a voltage proportional to the flight time is generated using the latch counter output and a preset multiplication algorithm; a voltage proportional to the distance is determined based on the voltage proportional to the flight time and a preset operational amplifier.

[0027] Furthermore, the latch counter outputs N l The multiplication fed into this is:

[0028]

[0029] V ref =V refo +A 1 ·k T ·T;

[0030] Among them, V out is a voltage proportional to the flight time; V ref is the reference voltage; V refo A is a fixed reference; 1 is the adjustment coefficient; T is the absolute temperature; k T is a constant.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. In this embodiment, air humidity is taken as a random variable, and within a preset air humidity range and a preset air temperature, the standard uncertainty contribution is determined. Whether to add a humidity sensor is determined by the determined standard uncertainty contribution; and the sound velocity variation range is determined according to the approximate equation between the propagation speed of sound in the air and the air temperature, as well as the preset air temperature; whether to add a temperature sensor is determined by determining the sound velocity variation range; on the basis of meeting the distance detection accuracy and automobile control requirements, the cost is reduced by limiting the application of temperature sensors and humidity sensors;

[0033] 2. The present invention uses a latch counter output and a preset multiplication algorithm to generate a voltage proportional to the flight time; based on the voltage proportional to the flight time and a preset operational amplifier, a voltage proportional to the distance is determined; this is a low-cost algorithm that avoids the problems of high-cost transducers or high-cost digital processing algorithms. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings in the specification that constitute a part of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments of this embodiment and their descriptions are used to explain this embodiment and do not constitute improper limitations on this embodiment.

[0035] Figure 1 The temperature compensation circuit of embodiment 1 of the present invention;

[0036] Figure 2 1 is an example of a trace during the test of Example 1 of the present invention (the thick line is the ultrasonic sensor output, and the thin line is the calculation output). DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0038] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0039] Embodiment 1:

[0040] This embodiment provides a method for optimizing an automobile ultrasonic sensor, which can perform non-contact measurement of the height of a vehicle body from the ground.

[0041] Specifically, first, the standard uncertainty of the measured distance under the influence of air temperature and air humidity is calculated; then, the air humidity is taken as a random variable, and the standard uncertainty contribution is determined within a preset air humidity range and a preset air temperature, and whether to add a humidity sensor is determined based on the determined standard uncertainty contribution; and the sound speed variation range is determined based on an approximate equation between the speed of sound propagation in the air and the air temperature, as well as the preset air temperature; whether to add a temperature sensor is determined by determining the sound speed variation range; on the basis of meeting the distance detection accuracy and automobile control requirements, the cost is reduced by limiting the application of temperature sensors and humidity sensors; this embodiment is designed based on the measurement requirements of the automobile within a temperature range of 0°C to 40°C, a measurement distance within a range of 0.1m-0.3m, and a standard uncertainty of 1mm.

[0042] The distance D from a certain point on the vehicle body to the ground is calculated as:

[0043] D=k·T f ·V s (1)

[0044] Among them, T f represents the emission time of the ultrasonic pulse, that is, the time it takes for the pulse to travel the distance D; k represents a constant, optional, close to or equal to 0.5, depending on the geometry of the sensor; V s Indicates the speed of sound.

[0045] Optionally, the ultrasonic pulse is generated by a piezoelectric transducer and the echo reflected from the ground is received by another piezoelectric transducer. These two transducers are mounted close to each other and form the measuring head. The uncertainty contribution of the constant k can be neglected by calibrating the sensor after installing the measuring head.

[0046] Since the measured wave time and sound speed can be considered unrelated, the standard uncertainty μ(D) of the measured distance is:

[0047]

[0048] Where, μ(V s ) and μ(T f ) represent the standard uncertainties of the speed of sound and the flight time, respectively.

[0049] The speed of sound in air is V s Depends on the air temperature and, to a lesser extent, the air humidity, namely:

[0050] V s =f(θ,h) (3)

[0051] Therefore, the standard uncertainty of the measured distance μ(D) becomes:

[0052]

[0053] Where μ(θ) is the standard uncertainty of air temperature, θ is the air temperature; μ(θ) is the standard uncertainty of air humidity, h is the air humidity.

[0054] If the air humidity is treated as a random variable, uniformly distributed in the range of 10% RH to 90% RH, the effect of humidity on the speed of sound is about 0.15% at 20°C. This results in a standard uncertainty contribution of about 0.3mm over a distance of 0.3m, so a humidity sensor is not required.

[0055] Ultrasonic sensor arrangement and two examples of stimulus signals and expected echoes. i (f) (peak amplitude V) Stimulate the transmitter with signal r() to obtain a narrower and weaker echo y suitable for low noise conditionso (f)(peak amplitude 0.4-V o vo) is the stimulus signal r 0 (t)e obtained.

[0056] Optionally, the speed of sound in air V s The approximate equation depends on the temperature:

[0057]

[0058] Where T is the absolute temperature in Kelvin.

[0059] Therefore, within a temperature range of 0-40°C, the speed of sound varies from 330m / s to 360m / s. This effect must be taken into account when determining the distance, so a temperature sensor is required.

[0060] Another phenomenon that influences the uncertainty of the measured distance is the vehicle speed, which has the same effect as the wind component perpendicular to the ultrasonic pulse path. This effect includes an increase in the pulse path and, therefore, also an increase in the measured distance. Since the maximum vehicle speed is about 10% of the speed of sound, the vehicle speed V for a certain period of time ω The distance error caused can be approximately estimated as:

[0061]

[0062] Among them, the distance D between a certain point of the vehicle body and the ground; the speed of sound propagation in the air V s ; ΔD represents the distance traveled by the car within a certain period of time.

[0063] For a car with a speed of 33 m / s (about 120 km / h), the distance error speed. At 0°C (Va≈330 m / s), the distance error is about 0.5%. It should be noted that this error can be easily corrected by the car speed.

[0064] The measurement of flight time is within the range of 0.5ms-2ms. The required distance standard uncertainty is 1mm, which can be achieved by measuring the flight time under the standard. The accuracy is 2.5us, the standard uncertainty of temperature is 1℃, and the use of humidity sensors is avoided.

[0065] Ultrasonic signals with frequencies in the range of 30kHz to 5MHz can be used to generate pulses. Higher frequency pulses may be preferable because they imply lower wavelengths and therefore potentially better resolution, but the attenuation of sound in air increases dramatically with increasing frequency. In addition, higher frequencies require expensive transducers and fast electronics, so low-cost ranges are not available. Lower frequencies have the advantage of low scattering problems and can be obtained with low-cost transducers, but the wavelength in air is several millimeters, so considerations must be given to obtaining measurement uncertainties below the wavelength.

[0066] In current technology, obtaining sub-wavelength uncertainty has achieved quite good results, but the proposed solutions usually require the use of some form of digital processing of the obtained data, thereby increasing the cost of the sensor. Based on this, this embodiment proposes a sensor that avoids the cost issues brought by digital processing to keep the cost low. The sensor implementation includes:

[0067] Time of flight measurement: The sensor uses a 40 kHz piezoelectric resonant transducer to generate ultrasonic pulses. This transducer is commonly used in anti-theft systems, is installed in a waterproof container, and is cheap. The signal period generated is 25us, which corresponds to a wavelength of about 9mm at 20°C. Therefore, in order to obtain the uncertainty of the alternative sub-wavelength detection is required.

[0068] The required ultrasonic pulse emission time T f The standard uncertainty of 2.5us is achieved through a low-cost transmitter module, which includes a signal generator and a zero-crossing detector.

[0069] like Figure 1 As shown, the signal generator includes a 16kbyte erasable programmable read-only memory (EPROM), which includes an 8-bit digital-to-analog converter (DAC) corresponding to the signal sampling for generating the signal and a 16-bit counter for scanning the feed of the transmitting piezoelectric transducer.

[0070] The zero crossing detector includes two threshold detectors, a first detector and a second detector. The threshold of the first detector is a fraction of the peak value of the received signal, which enables the second detector to compare the received signal with respect to a reference. This allows detection in the signal region of maximum slope, thereby minimizing the effects of noise.

[0071] The stimulus signal stored in the EPROM is designed to obtain a sufficiently narrow echo to prevent the first detector from triggering on different periods of the echo. This signal is designed by a constrained optimization procedure, in this embodiment, based on minimization of the echo energy while constraining the echo peak to a fixed value. The narrowest echo Y with a fixed amplitude is allowed to be received p (f) The optimal driving signal X opt (f) can be obtained by solving the following equation:

[0072]

[0073] Where H(f) is the frequency response of the transmission channel consisting of the transmitter, propagation medium and receiver; 1 and λ 2 is the Lagrange multiplier, by numerically solving the nonlinear system of equations:

[0074]

[0075] Where W is the maximum allowable energy of the stimulus signal.

[0076] The lower the required amplitude, the narrower the echo, and therefore the lower the probability of miss for a given relative noise amplitude. Figure 1 Two examples of stimulus signals x(t) and the corresponding desired echoes y(t) are given. Therefore, the best signal to use under any conditions depends on the actual noise.

[0077] The sensor in this embodiment also includes a simple noise measurement system that estimates the actual noise by monitoring the input signal during the anechoic interval. The output of the noise measurement system is used to switch between three optimal signals designed to achieve good results in low, medium and high noise conditions.

[0078] Furthermore, the amplitude of the echo depends strongly on the reflectivity of the ground and its distance. This effect is minimized by employing an automatic gain control amplifier in the receiving circuit, which keeps the echo amplitude at a fixed value. This allows the first detector to have a fixed threshold and the output of the zero-crossing detector is used to drive a latch which freezes the counter output at the value reached at the echo arrival time. If no new echo is detected, the latch output is not updated, thus avoiding meaningless measurements. The value actually latched is the count corresponding to the flight time and the known fixed value N o The sum of , a fixed value that depends on how the stimulus signal is stored in the EPROM and on the threshold level of the first detector.

[0079] The system's time base operates at 8 MHz, so the time resolution is 125 ns, and the maximum measurable flight time is about 8 ms, corresponding to a distance greater than 1 m. A 50 Hz multivibrator restarts the counter, providing a reading every 20 ms.

[0080] The air temperature is measured by using the sensitivity k t The error is less than 1°C without calibration.

[0081] Distance from Figure 1 The simple analog circuit shown is used to calculate the output N of the latch counter. l It is fed into a low-cost multiplying 14-bit DAC to generate a voltage V proportional to the flight time. out :

[0082]

[0083] The 14 DAC digital inputs are connected to the most significant bits of the counter, so the least significant bits correspond to a time interval of 0.5 μs. The effect of DAC nonlinearity on the overall measurement uncertainty is negligible.

[0084] By setting the fixed reference V refo The DAC voltage reference V is obtained by adding a calibrated fraction of the voltage generated by the temperature sensor to produce a voltage proportional to temperature according to the formula ref :

[0085] V ref =V refo +A 1 ·k T ·T (11)

[0086] k T is a preset constant.

[0087] By adjusting the coefficient A 1 The value of DAC voltage reference V can be obtained by changing the temperature ref , which partially compensates for the speed of sound changes. This compensation is incomplete because the speed of sound varies with the square root of the temperature and the reference voltage varies linearly with temperature. By comparing the effect of the speed of sound in air with the temperature-related effects, the residual temperature effect is analyzed and estimated. The expected temperature effect of the reference voltage on the output voltage V is less than ±0.03% in the range of 0℃ to 40℃ (about ±0.1mm at a measurement distance of 0.3m). If a temperature range of -20℃ to 70℃ is considered (which is a reasonable temperature range for automotive sensors), the same effect becomes about

[0088] ±0.1% (±0.3mm when D=0.3m).

[0089] The analog circuit consists of an operational amplifier A 2 and A 3 completed, they are subtracted from the output with the fixed code N o The corresponding voltage, thus producing a voltage that is only proportional to the distance.

[0090] The latched digital output is available for further digital processing, along with an optional digital temperature value provided by an 8-bit analog-to-digital converter. Sensor calibration can be obtained by operating the gain and zero trimmers while moving the sensor head between two known distances.

[0091] The sensor in this embodiment was subjected to laboratory tests and field tests, and the experimental results were as follows:

[0092] Laboratory testing: The sensor was calibrated and tested in the laboratory over a distance range of 0.1m-0.6m and a temperature range of 0-40°C. The experimental standard deviation of linearity versus distance was found to be 0.3mm, while the standard deviation due to temperature effects was less than 0.2mm.

[0093] The air turbulence effect was studied by moving the air with a variable speed fan at speeds up to 10 m / s; the noise measurement system and the signal automatic variation facility were tested by artificially generating ultrasonic noise with an additional piezoelectric transducer. The overall standard uncertainty, when the distance is measured from a flat surface, is less than 1 mm under noise-free conditions for temperatures between 0 and 40 °C and distances between 0.1 and 0.6 m.

[0094] Field test: The measuring head was mounted on the rear of the car, which was equipped with four potentiometer sensors to measure the spring height during the movement of the car. A portable digital recorder was used to record the ultrasonic sensor and potentiometer outputs. Tests were carried out at different speeds on asphalt and rough ground.

[0095] The four potentiometer outputs have been used to calculate distance reference values ​​to compare with the ultrasonically measured distances. The end spring height, estimated by adding the tire deformation to the spring height measured by the potentiometers, has been used to identify the plane of the vehicle body. By substituting the measuring head coordinates into the plane equation, the distance reference value corresponding to the distance that the ultrasonic sensor should produce has been determined.

[0096] The results of one of the tests were as follows Figure 2 As shown, the thicker line represents the ultrasonic sensor output and the thinner line is the calculated output. The two traces are in good agreement except for a few time intervals where the road is irregular and the effect of this irregularity is that the distances sensed by the ultrasonic sensor mounted at the center of the vehicle body and the potentiometer sensors distributed on both sides of the vehicle are different.

[0097] The tests were conducted under real driving conditions and showed the normal behavior of the sensor under all typical driving maneuvers at speeds up to 33 m / s (120 km / h). The sensor in this embodiment features simple and cost-free analog processing of the signals without the use of a microprocessor.

[0098] The sensor in this embodiment, based on its simplicity and low cost, allows to obtain a resolution better than 1 mm in quiet conditions. The sensor output is updated every 20 milliseconds, and the additional digital output can be easily smoothed by the car's computing system to obtain a sufficiently accurate measurement.

[0099] Embodiment 2:

[0100] This embodiment provides a sensor obtained by the automotive ultrasonic sensor optimization method described in Embodiment 1.

[0101] Optionally, the sensor includes a signal generator, a zero-crossing detector, a noise measurement system, etc.; the signal generator includes an erasable programmable read-only memory, and the erasable programmable read-only memory is provided with a digital-to-analog converter for generating a signal; the zero-crossing detector includes two threshold detectors, a first detector and a second detector; the threshold of the first detector is a part of the peak value of the received signal, and the second detector compares the received signal with a preset reference.

[0102] Driving signal X of EEPROM opt (f) is:

[0103]

[0104] Where H(f) is the frequency response of the transmit channel; λ 1 and λ 2 is the Lagrange multiplier.

[0105] The noise measurement system estimates the actual noise by monitoring the input signal during the anechoic interval.

[0106] Embodiment 3:

[0107] This embodiment provides a distance measurement method, using the sensor as described in Example 2, including: the distance from a preset point on the vehicle body to the ground is equal to the product of the wave emission time of the ultrasonic pulse, a preset constant and the speed of sound; wherein the uncertainty contribution of the constant is eliminated by calibrating the sensor after installing the measuring head.

[0108] Optionally, a latch counter output and a preset multiplication algorithm are used to generate a voltage proportional to the flight time; a voltage proportional to the distance is determined based on the voltage proportional to the flight time and a preset operational amplifier.

[0109] Optionally, use a latched counter output N l The multiplication fed into this is:

[0110]

[0111] V ref =V refo +A 1 ·k T ·T (14)

[0112] Among them, V out is a voltage proportional to the flight time; V ref is the reference voltage; V refo A is a fixed reference; 1 is the adjustment coefficient; T is the absolute temperature; k T is a constant.

[0113] The above description is only a preferred embodiment of the present embodiment and is not intended to limit the present embodiment. For those skilled in the art, the present embodiment may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present embodiment shall be included in the protection scope of the present embodiment.

Claims

1. An automotive ultrasonic sensor optimization method, characterized in that: include: Calculate the standard uncertainty of distance measurement under the influence of air temperature and air humidity; Taking air humidity as a random variable, determining the standard uncertainty contribution within a preset air humidity range and a preset air temperature, and deciding whether to add a humidity sensor based on the determined standard uncertainty contribution; The sound speed variation range is determined based on the approximate equation between the speed of sound propagation in the air and the air temperature, as well as the preset air temperature. The determination of the sound speed variation range is used to determine whether to add a temperature sensor.

2. The automotive ultrasonic sensor optimization method according to claim 1, characterized in that: Under the influence of air temperature and air humidity, the standard uncertainty μ(D) of the measured distance is: Where k is a constant; T f is the emission time of the ultrasonic pulse; μ(θ) is the standard uncertainty of air temperature, θ is the air temperature; μ(θ) is the standard uncertainty of air humidity, h is the air humidity; μ(T d ) is the standard uncertainty of the flight time, V s is the speed of sound.

3. The automotive ultrasonic sensor optimization method according to claim 1, characterized in that: The speed of sound in air is V s The approximate equation between and air temperature is: Where T is the absolute temperature.

4. A sensor, characterized in that The method is obtained by the automotive ultrasonic sensor optimization method as described in any one of claims 1 to 3.

5. The sensor according to claim 4, characterized in that It includes a signal generator and a zero-crossing detector; the signal generator includes an erasable programmable read-only memory, and the erasable programmable read-only memory is provided with a digital-to-analog converter for generating a signal; the zero-crossing detector includes two threshold detectors, a first detector and a second detector; the threshold of the first detector is a part of the peak value of the received signal, and the second detector compares the received signal with a preset reference.

6. The sensor according to claim 5, characterized in that Driving signal X of EEPROM opt (f) is: Where H(f) is the frequency response of the transmit channel; λ1 and λ2 are Lagrange multipliers.

7. The sensor according to claim 4, characterized in that Also included is a noise measurement system that estimates actual noise by monitoring the input signal during anechoic intervals.

8. A distance measurement method, characterized in that: A sensor as described in any one of claim 7 is used, including: a distance from a preset point on the vehicle body to the ground, which is equal to the product of the emission time of the ultrasonic pulse, a preset constant and the speed of sound; wherein the uncertainty contribution of the constant is eliminated by calibrating the sensor after installing the measuring head.

9. The distance measurement method according to claim 8, characterized in that: A voltage proportional to the flight time is generated by using the latch counter output and a preset multiplication algorithm; a voltage proportional to the distance is determined based on the voltage proportional to the flight time and a preset operational amplifier.

10. The distance measurement method according to claim 9, characterized in that: Use latch counter to output N l The multiplication fed into this is: V ref =V refo +A1·k T ·T; Among them, V out is a voltage proportional to the flight time; V ref is the reference voltage; V refo is a fixed reference; A1 is an adjustment coefficient; T is an absolute temperature; k T is a constant.

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