KR102163661B1 - An Apparatus and A Method For Lidar Time Of Flight measurement - Google Patents

Abstract

A method for measuring a LIDAR flight time according to an embodiment of the present invention includes the steps of receiving a reflected wave signal reflected from an object to which a laser pulse signal transmitted from a laser diode is applied; Comparing the reflected wave signal with a threshold value and converting the reflected wave signal into a reflected wave pulse signal when the reflected wave signal is greater than or equal to a threshold value; Generating digital data corresponding to a rising edge and a falling edge of the reflected wave pulse signal; Measuring a peak time of the reflected wave signal based on digital data of a rising edge and a falling edge of the reflected wave pulse signal; And measuring a flight time based on the peak time of the reflected wave signal.

Description

An Apparatus and A Method For Lidar Time Of Flight measurement}

The present invention relates to an apparatus and method for measuring a time of flight of a lidar, and more particularly, to a device and method for measuring a time of flight of a lidar to increase the accuracy of measuring time of flight (ToF) of a lidar sensor.

LIDAR (Light Detection and Ranging) is a technology that measures distance using a laser, and it is developed in the form of constructing and visualizing terrain data for building 3D GIS (Geographic Information System) information. It has been applied to fields such as, and is attracting attention as a core technology as it is applied to autonomous vehicles and mobile robots in recent years.

In particular, a motor vehicle lidar is a device that enables warning or automatic vehicle control by measuring the distance between vehicles in real time so that a vehicle in front of the vehicle can avoid collision or minimize impact. It is used as the most essential part of the main parts of the vehicle distance sensor system for autonomous vehicles such as image sensors and communication 3D maps.

Lidar collects light emitted through a laser generator through a photo detector and measures the distance through the movement time of the light, and the photo detector is generally It consists of photodiodes (APD, SPAD, SiPM, etc.) that generate current when received.

However, in the case of the photodiode, as the temperature increases, the breakdown voltage that generates current increases, and as the temperature increases, the sensitivity of the signal decreases, which may cause an error in distance measurement.

In addition, LiDAR technology is a very precise technology that requires data collection and processing within tens to several ns. Even for a small time operation error in ns, it is expressed as a considerable distance error in actual distance measurement. For example, for an error of 1 ns. On the other hand, a distance error of about 15 cm may occur, and this distance error could seriously affect the safety of the vehicle and the driver.

The present invention has been devised to meet the above-described requirements, and is to provide a Lidar flight time measurement apparatus and method capable of improving the accuracy of the flight time (ToF) measurement of a Lidar sensor.

A method for measuring a LIDAR flight time according to an embodiment of the present invention includes the steps of receiving a reflected wave signal reflected from an object to which a laser pulse signal transmitted from a laser diode is applied; Comparing the reflected wave signal with a threshold value and converting the reflected wave signal into a reflected wave pulse signal when the reflected wave signal is greater than or equal to a threshold value; Generating digital data corresponding to a rising edge and a falling edge of the reflected wave pulse signal; Measuring a peak time of the reflected wave signal based on digital data of a rising edge and a falling edge of the reflected wave pulse signal; And measuring a flight time based on the peak time of the reflected wave signal.

In this case, in the measuring of the reflected wave signal peak time, the peak time of the reflected wave signal may be measured by calculating a half value of a value obtained by adding digital data of the rising edge and the falling edge of the reflected wave pulse signal.

In addition, the step of measuring the flight time may measure the flight time from the peak time of the laser pulse signal to the peak time of the reflected wave signal.

In addition, the peak time of the laser pulse signal can be obtained by calculating a half value of the amplitude of the laser pulse signal.

Meanwhile, in the LIDAR flight time measuring apparatus according to an embodiment of the present invention, in a control unit including a reflected wave signal processing unit for processing a reflected wave signal reflected from an object to which a laser pulse transmitted from a laser diode is applied, the reflected wave signal processing unit And a pulse signal conversion unit comparing the reflected wave signal with a threshold value and converting the reflected wave signal into a reflected wave pulse signal when the reflected wave signal is greater than or equal to a threshold value; A time-digital conversion unit receiving the reflected wave pulse signal and generating digital data corresponding to a rising edge and a falling edge of the reflected wave pulse signal; And a reflected wave signal peak measuring unit configured to measure a peak time of the reflected wave signal based on digital data of the rising edge and the falling edge of the reflected wave pulse signal, wherein the controller includes a flight time based on the peak time of the reflected wave signal. Can be measured.

In this case, the reflected wave signal peak measuring unit may be configured to measure a peak time of the reflected wave signal by calculating a half value of a value obtained by adding digital data of the rising edge and the falling edge of the reflected wave pulse signal.

In addition, the controller may calculate the flight time by measuring the flight time from the peak time of the laser pulse signal to the peak time of the reflected wave signal.

In addition, the controller may calculate a half value of the amplitude of the laser pulse signal to obtain a peak time of the laser pulse signal.

In addition, the time-digital conversion unit may include a plurality of buffers each having a time delay; And a plurality of registers connected to outputs of each of the plurality of buffers and outputting output values of each of the plurality of buffers.

In addition, the plurality of registers included in the time-to-digital conversion unit may include: a rising edge triggered D-flip-flop in which an output value changes at a rising edge of the reflected wave pulse signal; And a falling edge triggered D-flip-flop in which an output value changes at a falling edge of the reflected wave pulse signal.

The lidar flight time measurement apparatus according to an embodiment of the present invention made as described above measures the flight time (ToF) based on the peak time of the reflected wave signal input from the photodiode, so the temperature of the photodiode According to this, even if the sensitivity to the reflected wave signal is changed, the flight time can be measured without being affected by the change in the sensitivity of the reflected wave signal. Therefore, when measuring the flight time, it is possible to reduce a flight time measurement error due to a change in the sensitivity of the reflected wave signal, and thus, the accuracy of the flight time measurement may be improved. Of course, the scope of the present invention is not limited by these effects.

1 is a block diagram showing a lidar system according to an embodiment of the present invention.
2 is a flow chart for a method of measuring the flight time of Lida according to an embodiment of the present invention.
3 is a diagram showing a signal waveform for explaining a method of measuring a peak time of a reflected wave signal according to an embodiment of the present invention.
4 is a diagram showing a signal waveform for explaining a method of measuring a flight time (ToF) according to an embodiment of the present invention.
5 is a block diagram of a Time-to-Digital Converter (TDC) according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and the following embodiments make the disclosure of the present invention complete, and the scope of the invention to those of ordinary skill in the art. It is provided to fully inform you. In addition, in the drawings for convenience of description, the size of the components may be exaggerated or reduced. In addition, the following examples are provided so that the present invention may be sufficiently understood by those of ordinary skill in the art, and may be modified in various other forms, and the scope of the present invention is limited to the examples described below. It does not become.

1 is a block diagram showing a lidar system according to an embodiment of the present invention.

The lidar system 10 may include a lidar flight time measurement device 100, a laser diode 120, a photodiode 130, and an optical unit 140.

More specifically, the lidar flight time measurement device 100 may include a control unit 105.

At this time, the controller 105 can control the overall control of the lidar sensor system and measure the time of flight (ToF), and can output the laser diode driving current to drive the laser diode 120. have.

The laser diode 120 may transmit a laser pulse to the object 150 through the optical unit 140 under the control of the controller 105, and the photodiode 130 may transmit a laser pulse through the optical unit 140. A reflected wave signal reflected from the object 150 to which is applied may be input.

For example, the optical unit 140 is an optical lens 140 that considers optical characteristics such as a uniform laser emission distribution, a beam shaping ratio, and a condensing power of a beam at the time of receiving light in order to secure a laser pulse viewing angle transmitted from the laser diode 120 and to secure a precise angular resolution. , 145), and a prism (not shown).

Meanwhile, the control unit 105 may include a reflected wave signal processing unit 110 that processes a reflected wave signal received from the photodiode 130, and the reflected wave signal processing unit 110 is a pulse signal converter 113, a time-digital It may include a conversion unit (TDC, Time-to-Digital Converter, 115) and a reflected wave signal peak measurement unit 117.

The pulse signal converter 113 may receive a reflected wave signal from the photodiode 130, and compare the input reflected wave signal with a threshold value, and when the reflected wave signal is greater than the threshold value, the reflected wave signal is converted into a reflected wave pulse signal. Can be converted.

At this time, the reflected wave pulse signal generated by the pulse signal conversion unit 113 is input to the time-digital conversion unit (TDC, 115), and the time-digital conversion unit (TDC, 115) receives the reflected wave pulse signal and receives the reflected wave pulse. It is possible to generate digital data corresponding to the rising and falling edges of the signal.

Here, referring to FIG. 5, a time-to-digital conversion unit according to an embodiment of the present invention will be described in detail. The time-to-digital conversion unit (TDC, 115) includes a plurality of buffers B1 to Bn each having a time delay and a plurality of A plurality of registers 510 and 520 connected to the outputs of the buffers B1 to Bn and outputting output values of the plurality of buffers B1 to Bn may be included.

The plurality of buffers B1 to Bn may output a voltage applied as an input as an output. However, each of the plurality of buffers may include a delay time (τ1 to τn). Therefore, assuming that the delay time of each buffer is the same (τ1 = τ2 =… = τn-1 =τn), the voltage applied to the input unit moves to the kth buffer after kⅹτ1 second. k≤n)

Meanwhile, the plurality of registers 510 and 520 are a rising edge triggered D-flip-flop 510 in which the output value changes at the rising edge of the reflected wave pulse signal, and a falling edge in which the output value changes at the falling edge of the reflected wave pulse signal. It may include a falling edge triggered D-flip-flop 520.

In addition, the plurality of registers 510 and 520 of the time-to-digital conversion unit (TDC, 115) may receive a reflected wave pulse signal as an input of the clock unit 500, and the plurality of registers 510 and 520 are reflected wave pulses. The time of the rising edge and falling edge of the reflected wave signal can be detected by receiving a signal.

Referring to FIG. 1 again, the reflected wave signal peak measurement unit 117 may receive digital data of the rising edge and the falling edge of the reflected wave pulse signal from the time-digital converter (TDC, 115), and the rising edge of the reflected wave pulse signal The peak time of the reflected wave signal can be measured based on the digital data of the edge and the falling edge.

In this case, the reflected wave signal peak measurement unit 117 is an average of the half value of the sum of the digital data of the rising and falling edges of the reflected wave pulse signal, that is, the sum of the digital data of the rising and falling edges of the reflected wave pulse signal. By calculating, the peak time of the reflected wave signal can be measured. More specifically, a method of measuring the peak time of the reflected wave signal by the reflected wave peak measuring unit 117 will be described in detail later with reference to FIG. 3.

Meanwhile, the controller 105 may measure the flight time ToF based on the peak time of the reflected wave signal measured by the reflected wave signal peak measuring unit 117.

More specifically, the control unit 105 calculates a half value of the laser pulse signal amplitude, that is, a value obtained by dividing the laser pulse signal amplitude by 2 to obtain the peak time of the laser pulse signal, and calculates the peak time of the reflected wave signal from the peak time of the laser pulse signal. By measuring the flight time to time, you can calculate the flight time.

2 is a flow chart for a method of measuring the flight time of Lida according to an embodiment of the present invention.

Referring to FIG. 2, first, a reflected wave signal reflected from an object 150 to which a laser pulse signal transmitted from the laser diode 120 is applied may be received. (Step S200)

In more detail, a reflected wave signal may be input through the photodiode 130, and the reflected wave signal may be input to the pulse signal converter 113.

The pulse signal converter 113 may compare the reflected wave signal with a threshold value and convert the reflected wave signal into a reflected wave pulse signal when the reflected wave signal is greater than or equal to the threshold value. (Step S210)

In this case, if the reflected wave signal is not equal to or greater than the threshold value, the reflected wave signal may be received again.

Meanwhile, the reflected wave pulse signal is applied to the time-digital converter (TDC, 115), and the time-digital converter (TDC, 115) may generate digital data corresponding to the rising edge and the falling edge of the reflected wave pulse signal. . (Step S220)

At this time, the reflected wave signal peak measurement unit 117 receives digital data of the rising edge and the falling edge of the reflected wave pulse signal from the time-digital conversion unit 115, based on the digital data of the rising edge and the falling edge of the reflected wave pulse signal. Thus, the peak time of the reflected wave signal can be measured. (Step S230)

In more detail, the reflected wave signal peak measuring unit 117 may measure the peak time of the reflected wave signal by calculating a half value of the sum of the digital data of the rising edge and the falling edge of the reflected wave pulse signal, and measuring the peak time of the reflected wave signal. The half value of the sum of the digital data of the falling edge is a value obtained by dividing the sum of the digital data of the rising edge and the falling edge by 2.

Finally, the controller 105 may measure the flight time (ToF) based on the peak time of the reflected wave signal. (Step S240)

In this case, the control unit 105 can measure the flight time from the peak time of the laser pulse to the peak time of the reflected wave signal, and the peak time of the laser pulse calculates the laser pulse peak time by calculating the half value of the laser pulse amplitude. In this case, the half value of the laser pulse amplitude is the laser pulse amplitude divided by 2.

3 is a diagram showing a signal waveform for explaining a method of measuring a peak time of a reflected wave signal according to an embodiment of the present invention.

Referring to FIG. 3, in order to measure the peak time of the reflected wave signal, the pulse signal converter 113 first receives the reflected wave signal from the photodiode furnace 130, at this time, the laser diode 120 The laser pulse transmitted from is transmitted as a rectangular pulse, but since the signal is attenuated through the process of applying and reflecting the laser pulse to the object 150, when the reflected wave signal is input to the photodiode 130, the arch It can be changed to a shape signal or a Gaussian signal.

Accordingly, since the reflected wave signal input to the photodiode 130 is changed into an arcuate signal or a Gaussian signal in which the laser pulse is attenuated, the reflected wave signal has the highest point of the signal, that is, a peak time.

On the other hand, conventionally, when the reflected wave signal input from the photodiode 130 exceeds the threshold, it is determined as a valid signal, and the flight time from the transmission point of the laser pulse to the start point of the reflected wave signal (ToF: Time of Flight) Was measured. However, in the case of the photodiode 130, as the temperature increases, the breakdown voltage that generates current increases, so that the signal sensitivity of the received reflected wave decreases, which may cause an error in measuring the flight time.

For example, the sensitivity of the reflected wave signal when the temperature of the photodiode 130 is low is lower than that of the reflected wave signal when the temperature of the photodiode 130 is low, and thus the flight time (ToF) when the temperature of the photodiode 130 is low. ) It could be measured shorter than the flight time (ToF) when the temperature of the photodiode 130 is high. Meanwhile, since the Lidar sensor may have a distance error of about 15cm even with an error of 1ns, such an error could have a fatal effect on the driver's safety.

However, since the present invention measures the flight time based on the peak time of the reflected wave signal received from the photodiode 130, only the sensitivity of the signal is changed according to the temperature of the photodiode 130. However, since the peak time of the reflected wave signal is the same even with the change in temperature, it may not be affected by the change in the signal sensitivity according to the temperature change of the photodiode 130.

More specifically, in order to obtain the peak time of the reflected wave signal according to the embodiment of the present invention, first, the pulse signal converter 113 compares the reflected wave signal received from the photodiode 130 with a preset threshold 300 Thus, when the reflected wave signal exceeds the threshold value (300), it is converted into a reflected wave pulse signal.

At this time, the reflected wave pulse signal is input to the time-digital converter (TDC, 115), and the time-digital converter (TDC, 115) detects the rising edge time (t1) and the falling edge time (t2) of the reflected wave pulse signal. can do.

In more detail, the rising edge time (t1) and falling edge time (t2) generated by the time-to-digital conversion unit (TDC, 115) are input to the reflected wave signal peak measurement unit 117, and the reflected wave signal peak measurement unit 117 ) May measure a peak time (Peak Time, 320) of the reflected wave signal by calculating a value 310 obtained by dividing a value 310 obtained by dividing a value obtained by adding the rising edge time t1 and the falling edge time t2 of the reflected wave pulse signal.

In this case, since the half time 310 of the reflected wave pulse signal and the peak time 320 of the reflected wave signal are the same, the half value 310 of the reflected wave pulse signal, that is, the half time 310 of the reflected wave pulse signal If calculated, the peak time (Peak Time, 320) of the reflected wave signal can be obtained.

4 is a diagram showing a signal waveform for explaining a method of measuring a flight time (ToF) according to an embodiment of the present invention.

Referring to FIG. 4, the control unit 105 of the present invention may measure flight times 420 and 425 from peak times 405 of laser pulses to peak times 400 and 410 of reflected wave signals.

At this time, the control unit 105 can calculate the peak time 405 of the laser pulse signal by calculating the half value of the amplitude of the laser pulse signal. More specifically, the half value of the laser pulse signal amplitude is the laser pulse signal amplitude. It is divided by 2.

For example, in the present invention, since the flight time (420, 425) is calculated based on the peak time (400, 410) of the reflected wave signal, the starting point for measuring the flight time is set as the peak time 405 of the laser pulse signal, and the flight The flight time can be measured by setting the end point for measuring time as the peak times 400 and 410 of the reflected wave signal.

On the other hand, the signal sensitivity of the photodiode 130 changes depending on the temperature, and the sensitivity of the reflected wave signal at high temperature is smaller than that of the reflected wave signal at low temperature, so that the flight time from the start point of the laser pulse to the start point of the reflected wave signal is reduced. In the case of measurement, the flight time measurement could be measured differently depending on the temperature of the photodiode.

However, even if the signal sensitivity varies according to the temperature change of the photodiode 130, the peak time 400 of the reflected wave signal when the photodiode 130 is low temperature and the peak time 410 of the reflected wave signal when the photodiode is high temperature. ) Appears the same.

Therefore, if the flight time from the peak time 405 of the laser pulse, that is, the half time 405 with respect to the amplitude of the laser pulse to the peak time 400 and 410 of the reflected wave signal, is measured (420, 425), the photodiode 130 It is possible to accurately measure the flight times 420 and 425 without being affected by the change in signal sensitivity depending on the temperature of.

The lidar flight time measurement apparatus according to an embodiment of the present invention made as described above measures the flight time (ToF) based on the peak time of the reflected wave signal input from the photodiode, so the temperature of the photodiode According to this, even if the sensitivity to the reflected wave signal is changed, the flight time can be measured without being affected by the change in the sensitivity of the reflected wave signal. Therefore, when measuring the flight time, it is possible to reduce a flight time measurement error due to a change in the sensitivity of the reflected wave signal, and thus, the accuracy of the flight time measurement may be improved.

Although specific embodiments have been described in the detailed description and accompanying drawings of the present invention, the present invention is not limited to the disclosed embodiments and does not depart from the technical spirit of the present invention for those of ordinary skill in the technical field to which the present invention belongs. Various substitutions, modifications and changes are possible within the range. Accordingly, the scope of the present invention is limited to the described embodiments and should not be defined, and should be construed as including the claims and equivalents as well as the claims to be described later.

105: control unit
110: reflected wave signal processing unit
113: pulse signal conversion unit
115: Time-to-Digital Converter (TDC)
117: reflected wave signal peak measurement unit

Claims (10)

Receiving a reflected wave signal reflected from an object to which the laser pulse signal transmitted from the laser diode is applied;
Comparing the reflected wave signal with a threshold value and converting the reflected wave signal into a reflected wave pulse signal when the reflected wave signal is greater than or equal to a threshold value;
Generating digital data corresponding to a rising edge and a falling edge of the reflected wave pulse signal;
Measuring a peak time of the reflected wave signal based on digital data of a rising edge and a falling edge of the reflected wave pulse signal; And
Including; measuring a flight time based on the peak time of the reflected wave signal,
The step of generating the digital data,
A time-to-digital conversion unit including a plurality of buffers each having a time delay and a plurality of registers connected to the outputs of each of the plurality of buffers and configured to correspond to each of the plurality of buffers outputting output values of each of the plurality of buffers Create digital data,
The plurality of registers,
A rising edge triggered D-flip-flop whose output value is changed at a rising edge of the reflected wave pulse signal; And
Including; Falling edge triggered D-flip-flop in which the output value is changed at the falling edge of the reflected wave pulse signal,
The rising edge triggered D-flip-flop is formed in plural to correspond to the plurality of buffers, respectively,
The falling edge triggered D-flip-flop is formed in plural so as to correspond to the plural buffers, respectively,
In the rising edge triggered D-flip-flop and the falling edge triggered D-flip-flop, the reflected wave pulse signal is input as an input of a clock unit.
The method of claim 1,
Measuring the reflected wave signal peak time,
Calculating a half value of the sum of the digital data of the rising edge and the falling edge of the reflected wave pulse signal, and measuring a peak time of the reflected wave signal,
Lida flight time measurement method.
The method of claim 1,
The step of measuring the flight time
Measuring the flight time from the peak time of the laser pulse signal to the peak time of the reflected wave signal,
Lida flight time measurement method.
The method of claim 3,
The peak time of the laser pulse signal is obtained by calculating a half value of the amplitude of the laser pulse signal,
Lida flight time measurement method.
A control unit comprising a reflected wave signal processing unit for processing a reflected wave signal reflected from an object to which a laser pulse transmitted from a laser diode is applied,
The reflected wave signal processing unit,
A pulse signal converter configured to compare the reflected wave signal with a threshold value and convert the reflected wave signal into a reflected wave pulse signal when the reflected wave signal is greater than or equal to a threshold value;
A time-digital conversion unit receiving the reflected wave pulse signal and generating digital data corresponding to a rising edge and a falling edge of the reflected wave pulse signal; And
And a reflected wave signal peak measuring unit configured to measure a peak time of the reflected wave signal based on digital data of the rising edge and the falling edge of the reflected wave pulse signal, and
The time-digital conversion unit,
A plurality of buffers each having a time delay; And
A plurality of registers connected to outputs of each of the plurality of buffers and formed to correspond to each of the plurality of buffers for outputting output values of each of the plurality of buffers,
The plurality of registers,
A rising edge triggered D-flip-flop whose output value is changed at a rising edge of the reflected wave pulse signal; And
Including; Falling edge triggered D-flip-flop in which the output value is changed at the falling edge of the reflected wave pulse signal,
The rising edge triggered D-flip-flop is formed in plural to correspond to the plurality of buffers, respectively,
The falling edge triggered D-flip-flop is formed in plural so as to correspond to the plural buffers, respectively,
In the rising edge triggered D-flip-flop and the falling edge triggered D-flip-flop, the reflected wave pulse signal may be input as an input of a clock unit,
The control unit measures the flight time based on the peak time of the reflected wave signal,
Lida flight time measurement device.
The method of claim 5,
The reflected wave signal peak measurement unit,
By calculating a half value of the sum of the digital data of the rising edge and the falling edge of the reflected wave pulse signal, configured to measure the peak time of the reflected wave signal,
Lida flight time measuring device.
The method of claim 5,
The control unit calculates the flight time by measuring a flight time from the peak time of the laser pulse signal transmitted from the laser diode to the peak time of the reflected wave signal,
Lida flight time measuring device.
The method of claim 7,
The control unit calculates a half value of the amplitude of the laser pulse signal to obtain a peak time of the laser pulse signal,
Lida flight time measurement device.
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