CN114402225A - Distance measuring method, distance measuring device and movable platform - Google Patents

Distance measuring method, distance measuring device and movable platform Download PDF

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Publication number
CN114402225A
CN114402225A CN202080006252.9A CN202080006252A CN114402225A CN 114402225 A CN114402225 A CN 114402225A CN 202080006252 A CN202080006252 A CN 202080006252A CN 114402225 A CN114402225 A CN 114402225A
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Prior art keywords
time
time periods
preset threshold
measurement
count
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CN202080006252.9A
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Chinese (zh)
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梅雄泽
马亮亮
许友
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SZ DJI Technology Co Ltd
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SZ DJI Technology Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Electromagnetism (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

A method of ranging, a ranging apparatus and a movable platform, the method (300) comprising: repeatedly performing a plurality of measurement processes, the measurement processes comprising: transmitting a light pulse signal in a primary measurement window, receiving a return light pulse signal, converting the return light pulse signal into an electric signal, and recording the count of the electric signal triggering a preset threshold value in a plurality of time periods in the measurement window (S310); counting the counts recorded in the multiple measurement processes to obtain a total count of the electric signal triggering preset threshold values in the multiple measurement windows in each time period (S320); the receiving time of the return light pulse signal is determined according to the magnitude of the total count of the plurality of time periods, and the distance of the measured object is calculated according to the interval between the receiving time and the transmitting time of the light pulse signal (S330). The method and the device can realize longer measuring distance and higher measuring precision at lower cost.

Description

Distance measuring method, distance measuring device and movable platform
Description
Technical Field
The present invention generally relates to the field of laser ranging technology, and more particularly to a ranging method, a ranging device, and a movable platform.
Background
The laser ranging device is an instrument for measuring the distance of a target by using a certain parameter of modulated laser. Typical ranging methods of the laser ranging apparatus include both a pulse method and a phase method.
The pulse method includes emitting one or one sequence of short laser pulses to the object to be measured, receiving the laser pulses reflected by the object, and measuring the time interval from emitting to receiving of the laser beams so as to calculate the distance from the laser ranging device to the object. The high-frequency clock is usually used to drive a timer to time the time between sending and receiving pulses, the period of the clock directly determines the measurement accuracy, and the hardware cost required for measurement in millimeter level is very high.
Disclosure of Invention
In this summary, concepts in a simplified form are introduced that are further described in the detailed description. This summary of the invention is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
In view of the defects in the prior art, a first aspect of an embodiment of the present invention provides a ranging method, including:
repeatedly performing a plurality of measurement processes, the measurement processes comprising: transmitting a light pulse signal in a primary measurement window, receiving a return light pulse signal, converting the return light pulse signal into an electric signal, and recording the count of triggering a preset threshold value by the electric signal in a plurality of time periods in the measurement window;
counting the counts recorded in the multiple measurement processes to obtain a total count of triggering the preset threshold value by the electric signal in the multiple measurement windows in each time period;
and determining the receiving time of the return light pulse signal according to the total count of the time periods, and calculating the distance of the measured object according to the interval between the receiving time and the transmitting time of the light pulse signal.
A second aspect of the embodiments of the present invention provides a distance measuring device, including a transmitting module, a receiving module, a sampling module, an operation module, and a control module, where:
the control module is configured to control the transmitting module, the receiving module and the sampling module to perform a plurality of measurement processes, where the measurement processes include: in the window of one measurement,
the transmitting module is used for transmitting a light pulse signal;
the receiving module is used for receiving the return light pulse signal and converting the return light pulse signal into an electric signal;
the sampling module is used for recording the counting of the electric signal trigger preset threshold values in a plurality of time periods in the measurement window;
the operation module is used for counting the counts recorded in the measurement processes for multiple times so as to obtain the total count of triggering the preset threshold value by the electric signal in each time period; and determining the receiving time of the return light pulse signal according to the total count of the time periods, and calculating the distance of the measured object according to the difference between the transmitting time and the receiving time.
A third aspect of the embodiments of the present invention provides a movable platform, where a camera and the distance measuring device are mounted on the movable platform; and the camera carries out focusing according to the distance measured by the distance measuring device.
A fourth aspect of the embodiments of the present invention provides a movable platform, on which a camera and a distance measuring device are mounted, wherein:
the camera is used for determining a target according to a view field picture;
the distance measuring device is used for determining the direction of the target according to the position of the target in the view field picture, transmitting a plurality of times of light pulse signals to the direction of the target and determining the distance of the target according to the plurality of times of light pulse signals;
the camera is also used for focusing the target according to the distance determined by the distance measuring device.
The distance measuring method, the distance measuring device and the movable platform can realize longer measuring distance and higher measuring precision at lower cost.
Drawings
FIG. 1 is a block diagram of a ranging device according to an embodiment of the invention;
FIG. 2 is a schematic structural diagram of a distance measuring device according to an embodiment of the present invention;
FIG. 3 shows a schematic flow diagram of a ranging method of an embodiment of the present invention;
FIG. 4 shows a graph of noise magnitude versus statistics according to an embodiment of the invention;
FIG. 5 shows the signal magnitude over time for a single measurement and for statistical multiple measurements according to an embodiment of the invention;
FIG. 6 is a schematic block diagram of a movable platform according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. It is to be understood that the described embodiments are merely a subset of embodiments of the invention and not all embodiments of the invention, with the understanding that the invention is not limited to the example embodiments described herein. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the invention described herein without inventive step, shall fall within the scope of protection of the invention.
In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.
It is to be understood that the present invention 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 this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term "and/or" includes any and all combinations of the associated listed items.
In order to provide a thorough understanding of the present invention, a detailed structure will be set forth in the following description in order to explain the present invention. Alternative embodiments of the invention are described in detail below, however, the invention may be practiced in other embodiments that depart from these specific details.
The following describes the ranging method, ranging apparatus, and movable platform in detail with reference to the accompanying drawings. The features of the following examples and embodiments may be combined with each other without conflict.
First, referring to fig. 1 and 2, a detailed exemplary description will be made of a structure of a ranging apparatus in an embodiment of the present invention, the ranging apparatus including a laser radar is merely an example, and other suitable ranging apparatuses may be applied to the present application. The ranging apparatus may be used to perform the ranging method herein. The distance measuring device can be electronic equipment such as a laser radar, laser distance measuring equipment and the like. In one embodiment, the ranging device is used to sense external environmental information, such as distance information, orientation information, reflected intensity information, velocity information, etc. of environmental targets. In one implementation, the ranging device may detect the distance of the probe to the ranging device by measuring the Time of Flight (TOF), which is the Time-of-Flight Time, of light traveling between the ranging device and the probe.
For ease of understanding, the following describes an example of the ranging operation with reference to the ranging apparatus 100 shown in fig. 1.
As shown in fig. 1, the ranging apparatus 100 includes a transmitting module 110, a receiving module 120, a sampling module 130, an operation module 140, and a control module 150.
In particular, the transmit module 110 may emit a sequence of light pulses (e.g., a sequence of laser pulses). The receiving module 120 may receive the optical pulse sequence reflected by the detected object, that is, obtain the pulse waveform of the echo signal through the optical pulse sequence, perform photoelectric conversion on the optical pulse sequence to obtain an electrical signal, process the electrical signal, and output the electrical signal to the sampling module 130. The sampling module 130 may sample the electrical signal to obtain a sampling result. The operation module 140 may determine the distance, i.e., the depth, between the ranging apparatus 100 and the detected object based on the sampling result of the sampling module 130. The control module 150 may implement control of other circuits, for example, may control the operation time of each circuit and/or perform parameter setting on each circuit, and the like.
It should be understood that, although the distance measuring apparatus shown in fig. 1 includes a transmitting module, a receiving module, a sampling module, and an operation module, which are used for emitting one path of light beam for detection, the embodiment of the present application is not limited thereto, and the number of any one of the transmitting module, the receiving module, the sampling module, and the operation module may also be at least two, which are used for emitting at least two paths of light beams in the same direction or in different directions respectively; the at least two light paths may be emitted simultaneously or at different times. In one example, the light emitting chips in the at least two emission modules are packaged in the same module. For example, each of the emitting modules includes a laser emitting chip, and the die of the laser emitting chips of the at least two emitting modules are packaged together and accommodated in the same packaging space.
In some implementations, in addition to the circuit shown in fig. 1, the distance measuring apparatus 100 may further include a scanning module, configured to change a propagation direction of at least one light pulse sequence (e.g., a laser pulse sequence) emitted from the emitting module to emit the light pulse sequence, so as to scan the field of view. Illustratively, the scan area of the scan module within the field of view of the ranging device increases over time.
The module including the transmitting module 110, the receiving module 120, the sampling module 130 and the operation module 140, or the module including the transmitting module 110, the receiving module 120, the sampling module 130, the operation module 140 and the control circuit 150 may be referred to as a ranging module, which may be independent of other modules, for example, a scanning module.
The distance measuring device can adopt a coaxial light path, namely the light beam emitted by the distance measuring device and the reflected light beam share at least part of the light path in the distance measuring device. For example, at least one path of laser pulse sequence emitted by the emitting module changes the transmission direction through the scanning module and then is emitted, and the laser pulse sequence reflected by the detector enters the receiving module after passing through the scanning module. Alternatively, the distance measuring device may also adopt an off-axis optical path, that is, the light beam emitted by the distance measuring device and the reflected light beam are transmitted along different optical paths in the distance measuring device. FIG. 2 is a schematic diagram of one embodiment of the distance measuring device of the present invention using coaxial optical paths.
The ranging apparatus 200 comprises a ranging module 210, and the ranging module 210 comprises an emitter 203 (which may comprise the emitting module described above), a collimating element 204, a detector 205 (which may comprise the receiving module, the sampling module, and the computing module described above), and an optical path changing element 206. The distance measuring module 210 is configured to emit a light beam, receive return light, and convert the return light into an electrical signal. Wherein the emitter 203 may be configured to emit a sequence of light pulses. In one embodiment, the transmitter 203 may emit a sequence of laser pulses. Optionally, the laser beam emitted by the emitter 203 is a narrow bandwidth beam having a wavelength outside the visible range. The collimating element 204 is disposed on an emitting light path of the emitter, and is configured to collimate the light beam emitted from the emitter 203, and collimate the light beam emitted from the emitter 203 into parallel light to be emitted to the scanning module. The collimating element is also for converging at least a portion of the return light reflected by the detector. The collimating element 204 may be a collimating lens or other element capable of collimating a light beam.
In the embodiment shown in fig. 2, the transmit and receive optical paths within the distance measuring device are combined by the optical path altering element 206 before the collimating element 204, so that the transmit and receive optical paths may share the same collimating element, making the optical path more compact. In other implementations, the emitter 203 and the detector 205 may use respective collimating elements, and the optical path changing element 206 may be disposed on the optical path after the collimating elements.
In the embodiment shown in fig. 2, since the beam aperture of the light beam emitted from the emitter 203 is small and the beam aperture of the return light received by the distance measuring device is large, the optical path changing element can adopt a small-area mirror to combine the emission optical path and the reception optical path. In other implementations, the optical path changing element may also be a mirror with a through hole, wherein the through hole is used for transmitting the outgoing light from the emitter 203, and the mirror is used for reflecting the return light to the detector 205. Therefore, the shielding of the bracket of the small reflector to the return light can be reduced in the case of adopting the small reflector.
In the embodiment shown in fig. 2, the optical path altering element is offset from the optical axis of the collimating element 204. In other implementations, the optical path altering element may also be located on the optical axis of the collimating element 204.
The ranging device 200 also includes a scanning module 202. The scanning module 202 is disposed on the emitting light path of the distance measuring module 210, and the scanning module 202 is configured to change the transmission direction of the collimated light beam 219 emitted by the collimating element 204, project the collimated light beam to the external environment, and project the return light beam to the collimating element 204. The return light is converged by the collimating element 204 onto the detector 205.
In one embodiment, the scanning module 202 may include at least one optical element for changing the propagation path of the light beam, wherein the optical element may change the propagation path of the light beam by reflecting, refracting, diffracting, etc. the optical element includes at least one light refracting element having non-parallel exit and entrance faces, for example. For example, the scanning module 202 includes a lens, mirror, prism, galvanometer, grating, liquid crystal, Optical Phased Array (Optical Phased Array), or any combination thereof. In one example, at least a portion of the optical element is moved, for example, by a driving module, and the moved optical element can reflect, refract, or diffract the light beam to different directions at different times. In some embodiments, multiple optical elements of the scanning module 202 may rotate or oscillate about a common axis 209, with each rotating or oscillating optical element serving to constantly change the direction of propagation of an incident beam. In one embodiment, the multiple optical elements of the scanning module 202 may rotate at different rotational speeds or oscillate at different speeds. In another embodiment, at least some of the optical elements of the scanning module 202 may rotate at substantially the same rotational speed. In some embodiments, the multiple optical elements of the scanning module may also be rotated about different axes. In some embodiments, the multiple optical elements of the scanning module may also rotate in the same direction, or in different directions; or in the same direction, or in different directions, without limitation.
In one embodiment, the scanning module 202 includes a first optical element 214 and a driver 216 coupled to the first optical element 214, the driver 216 configured to drive the first optical element 214 to rotate about the rotation axis 209, such that the first optical element 214 redirects the collimated light beam 219. The first optical element 214 projects the collimated beam 219 into different directions. In one embodiment, the angle between the direction of the collimated beam 219 after it is altered by the first optical element and the axis of rotation 209 changes as the first optical element 214 is rotated. In one embodiment, the first optical element 214 includes a pair of opposing non-parallel surfaces through which the collimated light beam 219 passes. In one embodiment, the first optical element 214 includes a prism having a thickness that varies along at least one radial direction. In one embodiment, the first optical element 214 comprises a wedge angle prism that refracts the collimated beam 219.
In one embodiment, the scanning module 202 further comprises a second optical element 215, the second optical element 215 rotating around a rotation axis 209, the rotation speed of the second optical element 215 being different from the rotation speed of the first optical element 214. The second optical element 215 is used to change the direction of the light beam projected by the first optical element 214. In one embodiment, the second optical element 215 is coupled to another driver 217, and the driver 217 drives the second optical element 215 to rotate. The first optical element 214 and the second optical element 215 may be driven by the same or different drivers, such that the first optical element 214 and the second optical element 215 rotate at different speeds and/or turns, thereby projecting the collimated light beam 219 into different directions in the ambient space, which may scan a larger spatial range. In one embodiment, the controller 218 controls the drivers 216 and 217 to drive the first optical element 214 and the second optical element 215, respectively. The rotation speed of the first optical element 214 and the second optical element 215 can be determined according to the region and the pattern expected to be scanned in the actual application. The drives 216 and 217 may include motors or other drives.
In one embodiment, second optical element 215 includes a pair of opposing non-parallel surfaces through which the light beam passes. In one embodiment, second optical element 215 includes a prism having a thickness that varies along at least one radial direction. In one embodiment, second optical element 215 comprises a wedge angle prism.
In one embodiment, the scan module 202 further comprises a third optical element (not shown) and a driver for driving the third optical element to move. Optionally, the third optical element comprises a pair of opposed non-parallel surfaces through which the light beam passes. In one embodiment, the third optical element comprises a prism having a thickness that varies along at least one radial direction. In one embodiment, the third optical element comprises a wedge angle prism. At least two of the first, second and third optical elements rotate at different rotational speeds and/or rotational directions.
In one embodiment, the scanning module comprises 2 or 3 photorefractive elements arranged in sequence on an outgoing light path of the optical pulse sequence. Optionally, at least 2 of the photorefractive elements in the scanning module rotate during scanning to change the direction of the sequence of light pulses.
The scanning module has different scanning paths at least partially different times, and the rotation of each optical element in the scanning module 202 may project light in different directions, such as the direction of the projected light 211 and the direction 213, so as to scan the space around the distance measuring device 200. When the light 211 projected by the scanning module 202 hits the detection object 201, a part of the light is reflected by the detection object 201 to the distance measuring device 200 in the opposite direction to the projected light 211. The return light 212 reflected by the object 201 passes through the scanning module 202 and then enters the collimating element 204.
The detector 205 is placed on the same side of the collimating element 204 as the emitter 203, and the detector 205 is used to convert at least part of the return light passing through the collimating element 204 into an electrical signal.
In one embodiment, each optical element is coated with an antireflection coating. Optionally, the thickness of the antireflection film is equal to or close to the wavelength of the light beam emitted by the emitter 203, which can increase the intensity of the transmitted light beam.
In one embodiment, a filter layer is coated on a surface of a component in the distance measuring device, which is located on the light beam propagation path, or a filter is arranged on the light beam propagation path, and is used for transmitting at least a wave band in which the light beam emitted by the emitter is located and reflecting other wave bands, so as to reduce noise brought to the receiver by ambient light.
In some embodiments, the transmitter 203 may include a laser diode through which laser pulses in the order of nanoseconds are emitted. Further, the distance of the probe 201 to the ranging device 200 may be determined from the received laser pulses. The distance and orientation detected by ranging device 200 may be used for remote sensing, obstacle avoidance, mapping, modeling, navigation, and the like.
The distance measuring method adopted by the distance measuring device generally comprises a pulse method and a phase method. The pulse method laser distance measuring device emits one or a series of short laser pulses to a measured object when in work, a photoelectric element receives a laser beam reflected by a target, and a timer measures the time interval from the emission to the reception of the laser beam so as to calculate the distance from the distance measuring device to the measured object. The time between the receiving and sending of pulses is timed by a high-frequency clock driving timer, the period of the clock directly determines the measurement precision, the measurement precision of the current better distance measuring device can reach ten centimeters, and if the millimeter-level measurement is achieved, the hardware cost required by pulse type distance measurement is very high.
The phase method laser distance measuring device modulates the light intensity of emitted laser pulses, measures the phase difference generated when the emitted light and the reflected light are transmitted in the space to detect the distance, and the precision can reach millimeter and micron levels. For a range finder using a single modulation frequency, only phases within 2 pi can be resolved, and therefore distances exceeding one cycle cannot be measured. For example, when the frequency of the modulation signal is 1MHz, the corresponding range is 150m, and if the actual distance value exceeds 150m, the measurement result is still within 150 m. The modulation frequency can influence the maximum range of the phase type distance measuring device, and the smaller the modulation frequency is, the larger the range is; however, when the system phase measurement resolution is fixed, the smaller the modulation frequency (the larger the modulation signal period), the lower the measurement accuracy. Therefore, under the condition of a single modulation frequency, the large range and the high precision cannot be simultaneously satisfied.
The distance L measured by the phase method is c phi/2 pi T/2, wherein c is the speed of light, phi is the phase difference between the transmitted and received pulses, and T is the period of the modulation signal. When the power of the emitted laser beam is enough, the range can reach dozens of kilometers or even more, but the high-power laser has harm to human bodies and does not accord with relevant use specifications.
As described above, both the laser distance measuring device using the pulse method and the laser distance measuring device using the distance measuring method are limited by hardware conditions, and it is difficult to improve both the measurement distance and the measurement accuracy.
In view of the above problem, an embodiment of the present invention provides a ranging method, including: repeatedly performing a plurality of measurement processes, the measurement processes comprising: transmitting a light pulse signal in a primary measurement window, receiving a return light pulse signal, converting the return light pulse signal into an electric signal, and recording the count of triggering a preset threshold value by the electric signal in a plurality of time periods in the measurement window; counting the counts recorded in the multiple measurement processes to obtain a total count of triggering the preset threshold value by the electric signal in the multiple measurement windows in each time period; and determining the receiving time of the return light pulse signal according to the total count of the time periods, and calculating the distance of the measured object according to the interval between the receiving time and the transmitting time of the light pulse signal. The distance measuring method provided by the embodiment of the invention can realize a longer measuring distance and higher measuring precision within the safety regulation limit range with lower cost.
The ranging method of the present invention is described below with reference to fig. 3, where fig. 3 shows a schematic flow chart of a ranging method 300 in one embodiment of the present invention.
As shown in fig. 3, a ranging method 300 according to an embodiment of the present invention includes the following steps:
first, in step S310, a plurality of measurement processes are repeatedly performed, the measurement processes including: in a primary measurement window, emitting a light pulse signal, receiving a return light pulse signal, converting the return light pulse signal into an electric signal, and recording the count of the electric signal triggering a preset threshold value in a plurality of time periods in the measurement window.
Referring to the distance measuring device shown in fig. 1, in each measurement window, the transmitting module and the receiving module are simultaneously turned on, the transmitting module transmits an optical pulse signal, the receiving module receives a return optical pulse signal of the optical pulse signal reflected by a measured object and converts the return optical pulse signal into an electrical signal, and the sampling module records the number of times that the electrical signal triggers a preset threshold value in each time period in the measurement window. When the ranging device has a plurality of transmitting modules and a plurality of receiving modules, the corresponding transmitting modules and receiving modules are simultaneously turned on in each measurement window.
In each measurement process, the receiving module receives not only the return light pulse signal returned by the measured object but also a noise signal due to the influence of noise. The noise signal and the return light pulse signal are distributed in a plurality of time periods in the measurement window, when the distance is longer or the reflectivity of the measured object is lower, the return light pulse signal is weaker, and the return light pulse signal and the noise signal are difficult to distinguish through single measurement, so that the distance measurement method of the embodiment of the invention adopts a statistical mode to determine the time period of the return light pulse signal.
For example, in each measurement window, after the receiving module converts the received optical signal into an electrical signal, the electrical signal may be sent to a first-stage or second-stage amplifying circuit for amplification, and then the amplified electrical signal may be sent to a sampling circuit. The sampling circuit divides the measuring window into a plurality of time periods and compares the electric signal with a preset threshold value so as to count the times of triggering the preset threshold value by the electric signal in each time period. Illustratively, each measurement window is of equal length, each measurement window being divided into N time segments, where N > 1.
As one implementation, the sampling module includes a comparator (e.g., an analog Comparator (COMP) for converting the electrical signal into a digital pulse signal) and a time measurement circuit, the electrical signal amplified by the first-stage or second-stage amplifying circuit passes through the comparator and then enters the time measurement circuit, and the time measurement circuit performs time counting.
The Time measuring circuit may be a Time-to-Data Converter (TDC). The TDC may be an independent TDC chip, or a TDC Circuit that implements time measurement based on an internal delay chain of a Field-Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC) or a Complex Programmable Logic Device (CPLD), or a Circuit structure that implements time measurement by using a high-frequency clock or a counting method.
Illustratively, the first input terminal of the comparator is used for receiving an electric signal input from the amplifying circuit, and the electric signal can be a voltage signal or a current signal; the second input end of the comparator is used for receiving a preset threshold value, and the electric signal input into the comparator is compared with the preset threshold value for operation. The output signal of the comparator is connected to the TDC, which can measure the time information of the edge of the output signal of the comparator, and the measured time is the emission time of the optical pulse signal as a reference, that is, the time difference between the emission and the reception of the laser signal can be measured. In a single measurement, the TDC can count whether an electrical signal triggers a preset threshold value in each time period, wherein the count is 1 if the electrical signal triggers the preset threshold value, and the count is 0 if the electrical signal does not trigger the preset threshold value. When a 0 to 1 transition exists within a certain time period, it indicates that there is a rising edge trigger of the signal for that time period.
As another implementation, the sampling module may also include an Analog-to-Digital Converter (ADC). After analog signals input to the sampling module are subjected to analog-to-digital conversion of the ADC, digital signals can be output to the operation module.
In one embodiment, the emission direction of the optical pulse signal is kept unchanged during the multiple measurement processes, so that the return optical pulse of the same measured object is acquired during the multiple measurement processes.
As described above, the measurement method according to the embodiment of the present invention is mainly suitable for the case where the distance to be measured is long or the reflectance is low, that is, the signal-to-noise ratio is low. When the distance between the measured object and the measured object is long or the reflectivity is low, the returned return light pulse energy is low after the laser pulse emitted by the distance measuring device irradiates the measured object, the size of the electric signal generated after the conversion of the receiving circuit is equivalent to or even smaller than the noise, the signal-to-noise ratio is low, the measurement process is repeatedly executed for a plurality of times, and the signal-to-noise ratio is improved by adopting a statistical method for a plurality of times of measurements so as to obtain the distance between the measured object. In this case, one measurement result is obtained by a plurality of measurements, the refresh frequency of the measurement result is reduced, but the measurement accuracy is improved.
When the distance between the measured object and the object to be measured is short or the reflectivity is high, the returned laser energy is high after the laser irradiates the object, the pulse generated after the conversion of the photoelectric sensor is far larger than the noise, and the signal-to-noise ratio is high. At this time, the time information of the pulse can be directly measured through the TDC, and the arrival time of the return light pulse signal can be obtained. In this case, it is not necessary to repeatedly perform a plurality of measurement processes, and a correct result can be obtained by one measurement, thereby avoiding a decrease in the refresh frequency of the measurement result.
Therefore, in one embodiment, before performing step S310, it is first determined whether the measurement process needs to be repeatedly performed a plurality of times.
As an example, the method of determining whether the measurement process needs to be repeatedly performed a plurality of times includes: comparing the electrical signal with at least two preset thresholds, for example, the preset thresholds include at least a smaller first preset threshold and a larger second preset threshold, and if the electrical signal triggering the second preset threshold exists in the measurement window, it indicates that the return light pulse signal is stronger, and at this time, the multiple measurement processes do not need to be repeatedly performed, and the time when the electrical signal triggers the second preset threshold can be directly used as the receiving time for calculating the distance of the object to be measured.
If the electrical signal triggers the first preset threshold but does not trigger the second preset threshold, in other words, if the electrical signal triggering the first preset threshold exists in the measurement window but does not exist, it indicates that the return light pulse signal is weak, and at this time, the measurement process is repeatedly performed for many times to improve the measurement range. In this embodiment, the step of recording the count of the electrical signal triggering preset threshold value in the plurality of time periods in step S310 is the count of the electrical signal triggering the first preset threshold value.
In step S310, the number of times of performing the multiple measurement processes is fixed or may be variable, for example, the number of times may be adaptively adjusted according to the confidence of the measurement result, as described in detail below.
In step S320, counting the counts recorded in the multiple measurement processes to obtain a total count of the triggering of the preset threshold by the electrical signal in the multiple measurement windows for each of the time periods.
As described above, each measurement window is divided into N time segments, and in step S320, the counts recorded in the 1 st, 2 nd, 3 rd, … … th time segments of the plurality of measurement windows are added to obtain the total count of the electric signals triggering the preset threshold in the 1 st, 2 nd, 3 rd, … … th time segments of the plurality of measurement windows.
Due to the randomness of the noise, there is a possibility that a noise signal will randomly appear in each time segment during a single measurement. According to the statistical rule, the noise signal measured in a single time has certain randomness, and a larger noise signal may appear in a single time period, but the larger the number of times of statistics, the smaller the noise magnitude in each time period, and finally tends to be stable, see fig. 4. When the statistical times are large enough, the statistical result of the noise magnitude approaches a stable value, and the mathematical model of the noise magnitude and the statistical times can be represented as: noise0 (N0/N)1/2Where N0 and N are both statistical times, Noise0 is the Noise level at the statistical time N0. Therefore, when the counting times are large enough, the return light pulse signals with a certain size are superposed on the stable noise level, and a higher signal-to-noise ratio can be obtained, so that a correct result is obtained.
In order to facilitate implementation, the embodiment of the invention adopts a counting mode to count the measurement results. Referring to fig. 5, the signal magnitude curves 501, 502, 503 obtained from the first measurement, the second measurement, and the third measurement are shown along with the time, and the final statistical result. For the same measured object, the size of the return light pulse and the distributed time period are basically fixed, namely, an electric signal triggering a preset threshold exists in the corresponding time period of each measurement basically; while other time periods receive a noise signal, which is random. For example, referring to fig. 5, in the first measurement, there are electrical signals triggering the first preset threshold Th1 in the time periods T2, T5 and T8, so that the number of time periods is counted as 1, and the other time periods are counted as 0, wherein the time periods T2 and T5 are received as noise signals, and the time period T8 is received as a return light pulse signal; in the second measurement, since the receiving time of the noise signal is random and the receiving time of the return light pulse signal is fixed, the electric signal of the noise signal triggers the first preset threshold Th1 in the time period T1 and T4, and the electric signal of the return light pulse signal triggers the first preset threshold Th1 in the time period T8, so that the time periods T1, T4 and T8 are counted as 1, and the other time periods are counted as 0; in the third measurement, the electric signal of the noise signal in the T3 time period triggers the first preset threshold Th1, and the electric signal of the light pulse signal in the T8 time period triggers the first preset threshold Th1, so that the counts of the T3 and T8 time periods are 1, and the counts of the other time periods are 0; by analogy, substantially every measurement receives the return light pulse signal during the time period T8, while only the noise signal is randomly received during other time periods. Thus, as the number of statistics increases, see the graph of fig. 4, the magnitude of the noise signal gradually decreases and tends to stabilize in other time periods, and thus the statistical result of the signal magnitude in the time period T8 will be higher than in other time periods. When the count value is reflected, the count of the time period corresponding to the return light pulse signal is significantly higher than the count of the other time periods, so that even if the magnitude of the electrical signal of the return light pulse signal is not enough to trigger the second preset threshold Th2, the receiving time of the return light pulse signal can be statistically determined.
Therefore, in step S330, the receiving time of the return light pulse signal is determined according to the magnitude of the total count of the plurality of time periods, and the distance of the measured object is calculated according to the interval between the receiving time and the emitting time of the light pulse signal.
As one implementation, the total count for each time segment may be compared separately, and the time segment with the highest total count may be determined as the reception time. As described above, the time measured by the sampling circuit is referenced to the emission time of the optical pulse signal, and thus, after the time period in which the total count is the largest is determined, the interval between the reception time and the emission time can be obtained, and the distance L of the measured object from the distance measuring device to the distance measuring device can be calculated from the time interval between the emission and the reception of the laser signal, where c is the speed of light and T is the interval between the reception time and the emission time.
In addition, since the emergent light spot has a certain size and may irradiate more than one measured object, in another embodiment, a plurality of time periods with the largest total count may be determined as the receiving time, and the distance of the measured object is calculated by using each receiving time, so as to implement the function of measuring the distances of the plurality of measured objects. When determining a plurality of reception times, M time periods having the highest total count may be determined as the reception times, where M is a preset value. Alternatively, the number of time periods for determining the receiving time may also be determined according to the signal-to-noise ratio and the confidence, see the following.
Due to random jitter of sampling, in the process of multiple times of sampling, light return pulse signals at each time can be randomly distributed in a plurality of adjacent time periods, so that the correct time period count is reduced, which is equivalent to energy dispersion, and the signal-to-noise ratio is reduced. Thus, as an implementation, a "sliding window method" may be adopted, in which at least two adjacent time segments are used as a group of time segments, the sum of the total counts of each group of time segments is counted, the sum of the total counts of a plurality of groups of time segments is compared, and the receiving time is determined in the group or groups of time segments with the largest sum of the total counts. Of course, during actual calculation, the total count of each group of time periods in each measurement window may be counted first, and then the sum of the total counts of each group of time periods in a plurality of measurement windows may be counted.
Wherein, as an example, the 1 st, 2 nd and 3 rd time periods in each measurement window may be taken as a group, the 4 th, 5 th and 6 th time periods as a group, the 7 th, 8 th and 9 th time periods as a group, and so on, i.e. each group of time periods includes several different time periods. When divided in this manner, a set of time periods in which the total count is highest can be determined and taken as the reception time of the return light pulse signal.
Alternatively, the 1 st, 2 nd, and 3 rd time periods in each measurement window may be taken as a group, the 2 nd, 3 rd, and 4 th time periods may be taken as a group, and the 3 rd, 4 th, and 5 th time periods may be taken as a group, that is, there is a partial overlap between two adjacent groups of time periods. When the division is performed in this way, a curve of the total counts changing with time can be obtained by fitting the total counts of each group of time periods, and the time point corresponding to the peak value of the curve is used as the receiving time of the return light pulse signal.
It will be appreciated that in some cases, return light pulse signals from the object may not be received during the performance of multiple measurements. When the return light pulse signal does not exist, the probability of receiving the noise signal in each time period is basically the same, the total counting difference of each time period after multiple measurements is very small, and the signal-to-noise ratio is very low. And when only the return light pulse signal exists, the total count in the time period corresponding to the return light pulse signal after multiple measurements is obviously greater than the total count in other time periods. After determining one or more time segments, therefore, the signal-to-noise ratio of the time segment as the measurement result can be calculated, and the magnitude of the signal-to-noise ratio can be used as the confidence of the measurement result. The measurement is considered authentic when the confidence is above a threshold.
Specifically, the confidence of the reception time determined in step S330 may be calculated from the result of comparison of the total count in the one or more time periods in which the total count is the largest and the average value of the total count. Specifically, the confidence (i.e., signal-to-noise ratio) SNR is (C-CM)/CM, where C is the count value of the time period as the measurement result, and CM is the average value of the count values of all the time periods.
Similarly, when the above-described "sliding window method" is used for the statistics, the confidence of the reception time may be determined based on the comparison of the sum of the total counts in the one or more sets of time periods in which the total count is the highest and the average of the sum of the total counts of the sets of time periods in the measurement window.
In one embodiment, when the confidence is lower than a preset confidence threshold, it is considered that the statistical method using multiple measurements still cannot make the signal-to-noise ratio meet the requirement, and therefore, the distance of the measured object is calculated by using the receiving time, and at this time, it is considered that no object is measured.
In another embodiment, the count of the measurement process can be dynamically adjusted according to the confidence, and the confidence is improved by increasing the number of measurements, so that the reliability of the measurement result is ensured.
Specifically, assuming that the initial measurement result refresh rate is 1KHz, it may be determined whether the confidence of the measurement result is lower than a preset confidence threshold value at the refresh rate, and if the confidence is lower than the preset confidence threshold value, the count of performing the measurement process is increased, for example, the refresh rate is reduced to 500 Hz. After the number of times of measurement is increased, the confidence of the measurement result can be calculated again, if the confidence is higher than the confidence threshold, the distance of the measured object is calculated by adopting new receiving time, and if the confidence is still lower than the confidence threshold, the refresh rate can be continuously reduced until the confidence is higher than the threshold. Or, if the number of times of performing the measurement process reaches a preset maximum number of times, that is, the refresh rate of the measurement result reaches a preset lower limit, and the confidence is still lower than a preset confidence threshold, the distance of the measured object is calculated by using the receiving time, and at this time, it may be considered that no object is measured.
In some embodiments, when a plurality of time periods or a plurality of groups of time periods with the highest total count are taken as the receiving time, the confidence of each time period or each group of time periods can be respectively calculated, one or more time periods or one or more groups of time periods with the confidence higher than the confidence threshold value are reserved, and the time periods with the confidence lower than the confidence threshold value are abandoned to be used for calculating the distance of the measured object.
In summary, the distance measurement method 300 according to the embodiment of the present invention adopts a statistical manner for the multiple measurement results, so that the range can be greatly increased at a lower cost within the safety regulation limit range at the cost of appropriately reducing the result refresh frequency. In practical application, the impulse type distance measuring device with the measuring range of 20% reflectivity and 300 meters can measure an object with the reflectivity of 20% and the reflectivity of 1500 meters after the distance measuring method provided by the embodiment of the invention is adopted.
The ranging method according to the embodiment of the present invention is exemplarily described above. Referring back to fig. 1, a distance measuring apparatus 100 according to an embodiment of the present invention will be described. The ranging apparatus 100 according to an embodiment of the present invention is used to implement the ranging method 300 according to an embodiment of the present invention described above. For the sake of brevity, only the main structure and function of the distance measuring apparatus 100 will be described hereinafter, and some of the specific details that have been described above will be omitted.
As shown in fig. 1, the ranging apparatus 100 includes a transmitting module 110, a receiving module 120, a sampling module 130, an operation module 140, and a control module 150, wherein the control module 150 is configured to control the transmitting module 110, the receiving module 120, and the sampling module 130 to perform a plurality of measurement processes, and the measurement processes include: in a primary measurement window, the transmitting module 110 is configured to transmit an optical pulse signal; the receiving module 120 is configured to receive a return optical pulse signal and convert the return optical pulse signal into an electrical signal; the sampling module 130 is configured to record a count of the electric signal trigger preset thresholds in a plurality of time periods in the measurement window; the operation module 140 is configured to count the counts recorded in the multiple measurement processes to obtain a total count of the electrical signal triggering preset threshold in each time period, determine the receiving time of the return light pulse signal according to the total count of the multiple time periods, and calculate the distance between the measured object according to the difference between the transmitting time and the receiving time.
In one embodiment, determining the time of receipt of the return light pulse signal from said total count of time periods may be implemented as: comparing the total counts for a plurality of the time periods; determining one or more time periods for which the total count is the greatest as the reception time.
In one embodiment, determining the time of receipt of the return light pulse signal from said total count of time periods may be implemented as: taking at least two adjacent time periods as a group of time periods, and counting the sum of the total counts of each group of time periods; comparing the sum of the total counts for the plurality of sets of time periods, and determining the receive time for the one or more sets of time periods for which the sum of the total counts is the greatest.
In one embodiment, the operation module 140 is further configured to determine the confidence of the receiving time according to a comparison result of the total count in one or more time periods in which the total count is the largest and an average value of the total count.
In one embodiment, the operation module 140 is further configured to: determining a confidence level of the reception time based on a comparison of a sum of the total counts in one or more sets of time periods in which the total counts are the most and an average of the sum of the total counts. As an example, when the confidence is lower than a preset confidence threshold, the operation module 140 abandons the calculation of the distance of the measured object by using the receiving time.
In one embodiment, the control module 150 may also dynamically adjust the number of times the measurement process is performed based on the confidence level. Specifically, whether the confidence is lower than a preset confidence threshold is judged, and if the confidence is lower than the preset confidence threshold, the number of times of executing the measurement process is increased.
Further, if the confidence coefficient is still lower than the preset confidence coefficient threshold when the number of times of executing the measurement process reaches the preset maximum number of times, the operation module abandons the calculation of the distance of the measured object by using the receiving time.
In one embodiment, the preset threshold includes at least a first preset threshold and a second preset threshold, the first preset threshold is smaller than the second preset threshold, and if the electric signal triggers the first preset threshold but does not trigger the second preset threshold, the control module controls to execute the measurement process for multiple times; the recording of the count of the electrical signal triggering the preset threshold over the plurality of time periods comprises recording the count of the electrical signal triggering the first preset threshold over the plurality of time periods.
In one embodiment, if the electrical signal triggers the second preset threshold, the operation module uses the time when the electrical signal triggers the second preset threshold as the receiving time, that is, the measurement result is obtained through a single measurement without performing multiple measurements.
According to another aspect of the embodiment of the invention, a movable platform is further provided. A schematic block diagram of a mobile platform 600 provided by an embodiment of the present invention is described below in conjunction with fig. 6. In certain embodiments, the movable platform comprises at least one of an unmanned aerial vehicle, an automobile, a remote control car, a robot, a boat. As shown in fig. 6, a camera 610 and a distance measuring device 620 are mounted on the movable platform, and specific details of the distance measuring device 620 may refer to the distance measuring device 100 described above. The distance measuring device 620 may measure the distance of the measured object by using the distance measuring method 300 described above, and send the distance to the camera 610, and the camera 620 focuses according to the distance measured by the distance measuring device 620 to collect the image of the measured object. Because the distance measuring device 620 has higher precision and longer range, the camera 610 can focus more clearly on objects farther away.
The embodiment of the invention also provides a movable platform. As shown in fig. 6, a camera 610 and a distance measuring device 620 are mounted on the movable platform. Wherein, the camera 610 is used for determining the target according to the view field picture; the distance measuring device 620 is configured to determine a target direction according to the position of the target in the view field picture, transmit a plurality of light pulse signals to the target direction, and determine a distance of the target according to the plurality of light pulse signals; the camera 610 is also used to focus the target according to the distance determined by the ranging device. The specific details of the ranging device 620 determining the range of the target from the plurality of light pulse signals may be as described above with reference to the ranging method 300. Since the distance measuring device 620 determines the distance of the target according to the light pulse signals for a plurality of times, the measured distance of the target is more accurate, and the camera 610 can focus more clearly on a farther object based on the distance measured by the distance measuring device 620.
Based on the above description, the distance measuring method, the distance measuring device and the movable platform according to the embodiments of the present invention count the measurement results of multiple measurement processes to determine the distance of the measured object, without increasing the laser emission power, and achieve a longer measurement distance and higher measurement accuracy at a lower cost within the safety limit range.
Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the foregoing illustrative embodiments are merely exemplary and are not intended to limit the scope of the invention thereto. Various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the scope or spirit of the present invention. All such changes and modifications are intended to be included within the scope of the present invention as set forth in the appended claims.
Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
In the several embodiments provided in the present application, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the above-described device embodiments are merely illustrative, and for example, the division of the units is only one logical functional division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another device, or some features may be omitted, or not executed.
In the description provided herein, numerous specific details are set forth. It is understood, however, that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the invention and aiding in the understanding of one or more of the various inventive aspects. However, the method of the present invention should not be construed to reflect the intent: that is, the claimed invention requires more features than are expressly recited in a claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with the claims themselves being directed to separate embodiments of the present invention.
It will be understood by those skilled in the art that all of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where such features are mutually exclusive. The features disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.
Furthermore, those skilled in the art will appreciate that while some embodiments described herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments may be used in any combination.
The various component embodiments of the invention may be implemented in hardware, or in software modules running on one or more processors, or in a combination thereof. Those skilled in the art will appreciate that a microprocessor or Digital Signal Processor (DSP) may be used in practice to implement some or all of the functionality of some of the modules according to embodiments of the present invention. The present invention may also be embodied as apparatus programs (e.g., computer programs and computer program products) for performing a portion or all of the methods described herein. Such programs implementing the present invention may be stored on a computer-readable storage medium or may be in the form of one or more signals. Such a signal may be downloaded from an internet website or provided on a carrier signal or in any other form.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The usage of the words first, second and third, etcetera do not indicate any ordering. These words may be interpreted as names.
The above description is only for the specific embodiment of the present invention or the description thereof, and the protection scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and the changes or substitutions should be covered within the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (26)

  1. A method of ranging, the method comprising:
    repeatedly performing a plurality of measurement processes, the measurement processes comprising: transmitting a light pulse signal in a primary measurement window, receiving a return light pulse signal, converting the return light pulse signal into an electric signal, and recording the count of triggering a preset threshold value by the electric signal in a plurality of time periods in the measurement window;
    counting the counts recorded in the multiple measurement processes to obtain a total count of triggering the preset threshold value by the electric signal in the multiple measurement windows in each time period;
    and determining the receiving time of the return light pulse signal according to the total count of the time periods, and calculating the distance of the measured object according to the interval between the receiving time and the transmitting time of the light pulse signal.
  2. The method of claim 1, wherein said determining a time of receipt of a return optical pulse signal from said total count of a plurality of time segments comprises:
    comparing the total counts for a plurality of the time periods;
    determining one or more time periods for which the total count is the greatest as the reception time.
  3. The method of claim 1, wherein said determining a time of receipt of a return optical pulse signal from said total count of a plurality of time segments comprises:
    taking at least two adjacent time periods as a group of time periods, and counting the sum of the total counts of each group of time periods;
    comparing the sum of the total counts for the plurality of sets of time periods, and determining the receive time for the one or more sets of time periods for which the sum of the total counts is the greatest.
  4. The method of claim 2, wherein the method further comprises:
    determining a confidence level of the reception time based on a comparison of the total count with an average of total counts over one or more time periods in which the total count is the greatest.
  5. The method of claim 3, wherein the method further comprises:
    determining a confidence level of the reception time based on a comparison of a sum of the total counts in one or more sets of time periods in which the total counts are the most and an average of the sum of the total counts.
  6. The method according to claim 4 or 5, characterized in that, when the confidence is lower than a preset confidence threshold, the distance of the measured object is abandoned from being calculated by the receiving time.
  7. The method of claim 4 or 5, wherein the method further comprises: and dynamically adjusting the times of executing the measuring process according to the confidence coefficient.
  8. The method of claim 7, wherein said dynamically adjusting a number of times said measurement process is performed based on said confidence level comprises:
    and judging whether the confidence coefficient is lower than a preset confidence coefficient threshold value, and if the confidence coefficient is lower than the preset confidence coefficient threshold value, increasing the times of executing the measuring process.
  9. The method of claim 8, wherein the method further comprises:
    and if the confidence coefficient is still lower than the preset confidence coefficient threshold when the number of times of executing the measurement process reaches the preset maximum number of times, giving up to calculating the distance of the measured object by adopting the receiving time.
  10. The method of claim 1, wherein the preset threshold comprises at least a first preset threshold and a second preset threshold, the first preset threshold is smaller than the second preset threshold, and if the electric signal triggers the first preset threshold but does not trigger the second preset threshold, the measuring process is repeatedly performed for a plurality of times;
    the recording of the count of the electrical signal triggering the preset threshold over the plurality of time periods comprises recording the count of the electrical signal triggering the first preset threshold over the plurality of time periods.
  11. The method of claim 10, wherein the method further comprises:
    and if the electrical signal triggers the second preset threshold, taking the time when the electrical signal triggers the second preset threshold as the receiving time.
  12. The method of claim 1, wherein the emission direction of the optical pulse signal remains unchanged during the plurality of measurements.
  13. The utility model provides a distance measuring device, its characterized in that, distance measuring device includes transmitting module, receiving module, sampling module, operation module and control module, wherein:
    the control module is configured to control the transmitting module, the receiving module and the sampling module to perform a plurality of measurement processes, where the measurement processes include: in the window of one measurement,
    the transmitting module is used for transmitting a light pulse signal;
    the receiving module is used for receiving the return light pulse signal and converting the return light pulse signal into an electric signal;
    the sampling module is used for recording the counting of the electric signal trigger preset threshold values in a plurality of time periods in the measurement window;
    the operation module is used for counting the counts recorded in the measurement processes for multiple times so as to obtain the total count of triggering the preset threshold value by the electric signal in each time period; and determining the receiving time of the return light pulse signal according to the total count of the time periods, and calculating the distance of the measured object according to the difference between the transmitting time and the receiving time.
  14. The ranging apparatus of claim 13, wherein said determining a time of receipt of a return optical pulse signal based on said total count of a plurality of time segments comprises:
    comparing the total counts for a plurality of the time periods;
    determining one or more time periods for which the total count is the greatest as the reception time.
  15. The ranging apparatus of claim 13, wherein said determining a time of receipt of a return optical pulse signal based on said total count of a plurality of time segments comprises:
    taking at least two adjacent time periods as a group of time periods, and counting the sum of the total counts of each group of time periods;
    comparing the sum of the total counts for the plurality of sets of time periods, and determining the receive time for the one or more sets of time periods for which the sum of the total counts is the greatest.
  16. The range finder device of claim 14, wherein the arithmetic module is further configured to:
    determining a confidence level of the reception time based on a comparison of the total count in the one or more time periods in which the total count is the greatest and an average of the total counts.
  17. The range finder device of claim 15, wherein the arithmetic module is further configured to:
    determining a confidence level of the reception time based on a comparison of a sum of the total counts in one or more sets of time periods in which the total counts are the most and an average of the sum of the total counts.
  18. The range finder device according to claim 16 or 17, wherein the operation module abandons the calculation of the distance of the measured object using the receiving time when the confidence is lower than a preset confidence threshold.
  19. The ranging apparatus as claimed in claim 16 or 17, wherein the control module is further configured to: and dynamically adjusting the counting of the measurement process according to the confidence coefficient.
  20. The ranging apparatus of claim 19 wherein said dynamically adjusting the count of performing said measurement procedure according to said confidence level comprises:
    and judging whether the confidence coefficient is lower than a preset confidence coefficient threshold value, and if the confidence coefficient is lower than the preset confidence coefficient threshold value, increasing the count of executing the measuring process.
  21. The range finder device of claim 20, wherein if the confidence level is still lower than the preset confidence level threshold when the count of performing the measurement process reaches a preset maximum count, the computing module abandons the receiving time to calculate the distance of the measured object.
  22. The distance measuring device as claimed in claim 13, wherein the preset threshold comprises at least a first preset threshold and a second preset threshold, the first preset threshold is smaller than the second preset threshold, if the electric signal triggers the first preset threshold but does not trigger the second preset threshold, the control module controls to perform the measuring process for a plurality of times;
    the recording of the count of the electrical signal triggering the preset threshold over the plurality of time periods comprises recording the count of the electrical signal triggering the first preset threshold over the plurality of time periods.
  23. The range finder device of claim 22, wherein if the electrical signal triggers the second predetermined threshold, the operation module takes a time when the electrical signal triggers the second predetermined threshold as the receiving time.
  24. A ranging apparatus as claimed in claim 13, characterized in that the emission direction of the optical pulse signal is kept constant during the plurality of measurements.
  25. A movable platform, characterized in that a camera and a distance measuring device according to any one of claims 13-24 are mounted on the movable platform; and the camera carries out focusing according to the distance measured by the distance measuring device.
  26. A movable platform, characterized in that, the portable platform is loaded with camera and range unit, wherein:
    the camera is used for determining a target according to a view field picture;
    the distance measuring device is used for determining the direction of the target according to the position of the target in the view field picture, transmitting a plurality of times of light pulse signals to the direction of the target and determining the distance of the target according to the plurality of times of light pulse signals;
    the camera is also used for focusing the target according to the distance determined by the distance measuring device.
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