A large dynamic range laser distance measurement method and laser distance meter

Abstract

The invention discloses a large dynamic range laser distance measurement method and a laser distance meter, belonging to the field of laser distance measurement, the laser distance meter comprises a transmitting module, a receiving module and a control module; the transmitting module comprises a driving board, a pump laser, a total reflector, an output mirror, a gain medium, a switchable initial transmittance Q-switched crystal component, a photodiode, and a laser beam expansion lens; the receiving module comprises a receiving objective lens, a switchable transmissive liquid crystal panel, a narrow-band filter, an avalanche photodiode, and a preamplifier circuit; the control module enables the laser distance measurement to work in five distance measurement modes, namely, an extremely close distance mode (<50 meters), a close distance distance measurement mode (50-1000 meters), a medium distance distance measurement mode (1k-10km), a long distance distance measurement mode (>10km), and a high temperature environment distance measurement mode. By controlling the laser output state and the laser echo power, the laser distance meter can measure the extremely close distance mode (<50 meters).

Description

Technical Field

[0001] The invention belongs to the technical field of laser ranging, and more specifically, relates to a large dynamic range laser ranging method and a laser rangefinder. Background Art

[0002] At present, the single pulse energy of the laser emitted in the long-distance pulse laser rangefinder is relatively high. When measuring close-range targets, it will cause the avalanche photodiode to be deeply saturated and unable to extract the target distance signal. In severe cases, the avalanche photodiode will be broken down. In order to protect the avalanche photodiode, the laser rangefinder is generally limited to measuring the distance of targets less than 100 meters.

[0003] Although there are methods such as reducing the bias voltage of the avalanche photodiode and controlling the amplification factor of the preamplifier, these methods are only effective for lasers with relatively low single pulse energy. When the single pulse reaches tens to hundreds of millijoules, it is difficult to achieve close-range ranging functions. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention proposes a laser ranging method and a laser rangefinder with a large dynamic range, which are used to solve the problem of using a high single pulse energy laser to measure close-range targets, while improving the ranging accuracy of medium targets.

[0005] To achieve the above object, according to one aspect of the present invention, a laser rangefinder with a large dynamic range is provided, comprising: a transmitting module, a receiving module and a control module;

[0006] The transmitting module comprises a driving board, a pump laser, a total reflection mirror, an output mirror, a gain medium, a switchable initial transmittance Q-switched crystal component, a photodiode and a laser beam expander lens; the current signal output by the driving board enters the pump laser, and the laser signal output by the pump laser passes through the total reflection mirror, the gain medium, the switchable initial transmittance Q-switched crystal component, the output mirror and the laser beam expander lens in sequence; the total reflection mirror, the output mirror, the gain medium and the switchable initial transmittance Q-switched crystal component constitute a resonant cavity, and the photodiode is used to collect stray light signals in the resonant cavity;

[0007] The receiving module comprises a receiving objective lens, a switchable transmissive liquid crystal panel, a narrow-band filter, an avalanche photodiode and a preamplifier circuit which are arranged in sequence;

[0008] The control module is responsible for controlling the driving board and the switchable initial transmittance Q-switched crystal component, the switchable transmissive liquid crystal panel and the preamplifier circuit to control the laser ranging to work in the extremely close distance mode, the close distance ranging mode, the medium distance ranging mode, the long distance ranging mode and the high temperature environment ranging mode.

[0009] In some optional embodiments, the driver board included in the transmitting module is controlled by the control module. In the extremely close distance mode, the control module controls the driver board to output a continuous current to the pump laser and the current intensity changes periodically over time. In the close distance ranging mode and the medium distance ranging mode, the control module controls the driver board to output a low repetition frequency pulse current below the laser threshold to the pump laser, and the duty cycle is controlled by the control module. In the long distance ranging mode, the control module controls the driver board to output a high repetition frequency pulse current above the laser threshold to the pump laser, and the duty cycle is controlled by the control module.

[0010] In some optional embodiments, the switchable initial transmittance Q-switched crystal assembly included in the transmitting module is controlled by the control module, the Q-switched crystal is a passive Q-switched crystal, fixed on the turntable and divided into a low initial transmittance gear, a high initial transmittance gear and a non-Q-switched crystal gear. The turntable as a whole has two angle states relative to the light-emitting surface of the gain medium, namely, a state parallel to the light-emitting surface of the gain medium and a Brewster angle with the light-emitting surface of the gain medium. It is switched according to the requirements of each ranging mode. The extremely close distance mode is the non-Q-switched crystal gear, the low initial transmittance gear is inserted at the Brewster angle in the close distance ranging mode and the medium distance ranging mode, and the high initial transmittance gear is inserted at an angle parallel to the light-emitting surface of the gain medium in the long distance ranging mode and the high temperature environment ranging mode.

[0011] In some optional embodiments, the switchable transmissive liquid crystal panel in the receiving module is controlled by the control module, and has the function of inserting and moving between the receiving objective lens and the narrow-band filter. In the extreme close distance mode and the close distance ranging mode, the panel is inserted between the receiving objective lens and the narrow-band filter in the receiving module, and in the medium distance ranging mode and the long distance ranging mode, the panel is moved out between the receiving objective lens and the narrow-band filter. The high temperature environment ranging mode is related to different distance modes.

[0012] According to another aspect of the present invention, there is provided a laser ranging method with a large dynamic range based on any one of the laser rangefinders described above, comprising:

[0013] In the extremely close distance mode, the switchable initial transmittance Q-switched crystal component is switched to the non-Q-switched crystal gear through the control module, the driver board outputs a continuous current higher than the laser threshold, and the current intensity changes periodically with time. At the same time, the avalanche photodiode bias and the preamplification magnification of the receiving module are reduced, and the control module adjusts the switchable transmissive liquid crystal panel state to the low transmittance gear;

[0014] In the short-distance ranging mode, the switchable initial transmittance Q-switched crystal component is switched to the low initial transmittance position through the control module and inserted into the resonant cavity at the Brewster angle. The driver board outputs a low-frequency pulse current higher than the laser threshold. The avalanche photodiode bias and preamplifier circuit magnification in the receiving module are at the highest bias and high magnification at which the preamplifier circuit output signal does not oscillate. The control module adjusts the switchable transmissive liquid crystal panel state to the high transmittance position. The transmittance needs to be determined based on the echo signal. The determination principle is that the echo signal pulse width does not change significantly when the echo signal is in the short-distance ranging mode (50 to 1000 meters).

[0015] In the medium-distance ranging mode, the switchable initial transmittance Q-switched crystal component is switched to the low initial transmittance gear through the control module and inserted into the resonant cavity at the Brewster angle, the driver board outputs a low-frequency pulse current higher than the laser threshold, the avalanche photodiode in the receiving module is in a high bias state and the preamplifier circuit is at the highest magnification, and the control module moves the switchable transmissive liquid crystal panel out from between the receiving objective lens and the narrow-band filter;

[0016] In the long-distance ranging mode, the switchable initial transmittance Q-switched crystal component is switched to a high initial transmittance position through the control module and inserted into the resonant cavity at a light output angle parallel to the gain medium, the driver board outputs a high-frequency pulse current higher than the laser threshold, the avalanche photodiode in the receiving module is in a high bias state and the preamplifier circuit is at the highest magnification, and the control module moves the switchable transmissive liquid crystal panel out from between the receiving objective lens and the narrow-band filter;

[0017] In the ranging mode in a high temperature environment, the switchable initial transmittance Q-switched crystal component is switched through the control module to insert the Q-switched crystal at an angle parallel to the light-emitting surface of the gain medium. The initial transmittance of the inserted passive Q-switched crystal and the output logic of the driver board are related to the extreme close distance mode, short distance ranging mode, medium distance ranging mode, and long distance ranging mode under normal circumstances.

[0018] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0019] (1) The laser rangefinder includes a transmitting module, a receiving module and a control module; the transmitting module includes a driving board, a pump laser, a total reflector, an output mirror, a gain medium, a switchable initial transmittance Q-switched crystal component, a photodiode, and a laser beam expander lens; the receiving module includes a receiving objective lens, a switchable transmissive liquid crystal panel, a narrow-band filter, an avalanche photodiode, and a preamplifier circuit; the control module enables the laser rangefinder to work in five ranging modes, namely, an extremely close distance mode (<50 meters), a short-distance ranging mode (50 to 1000 meters), a medium-distance ranging mode (1k to 10km), a long-distance ranging mode (>10km), and a high-temperature environment ranging mode. By controlling the laser output state and the laser echo power, the laser rangefinder can measure the extremely close distance mode (<50 meters).

[0020] (2) In the present invention, in the extremely close distance mode, the high single pulse energy pulse laser is switched to the continuous output mode by removing the Q-switched crystal, changing the pump mode to the continuous mode, and inserting a switchable transmissive liquid crystal panel between the receiving objective lens and the narrowband filter in the receiving module to reduce the laser echo intensity on the avalanche photodiode, so as to realize the phase ranging function in the extremely close distance mode. In the close distance ranging mode and the medium distance ranging mode, the laser outputs polarized light by inserting a low initial transmittance passive Q-switched crystal at the Brewster angle, and the ranging accuracy can be improved by combining the transmittance control of the transmissive liquid crystal panel. In the long-distance ranging mode, the passive Q-switching angle is changed to make the passive Q-switched crystal parallel to the light-emitting surface of the gain medium to reduce the laser threshold, and the high initial transmittance passive Q-switched crystal is switched to make the high single pulse energy pulse laser switch to the high repetition frequency low single pulse energy mode, and the switchable transmissive liquid crystal panel is removed from the optical system of the receiving module to improve the transmittance of the optical system of the receiving module. At this time, the rangefinder works in the pulse correlation ranging mode, which greatly improves the ranging capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the basic structure of a large dynamic range laser ranging system provided by an embodiment of the present invention;

[0022] Figure 2 This is a basic structure of an extremely close distance mode provided by an embodiment of the present invention;

[0023] Figure 3 It is a basic structure of a close distance mode provided by an embodiment of the present invention;

[0024] Figure 4 It is a basic structure of a medium-distance mode provided by an embodiment of the present invention;

[0025] Figure 5 It is a basic structure of a long-distance mode provided by an embodiment of the present invention;

[0026] Figure 6 It is a basic structure of a high temperature mode provided by an embodiment of the present invention;

[0027] Figure 7 This is a basic structure of a switchable initial transmittance Q-switched crystal component provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] like Figure 1 The figure is a schematic diagram of the structure of a laser rangefinder involved in a large dynamic range laser ranging method provided by an embodiment of the present invention, which includes three parts: a transmitting module 1, a receiving module 2 and a control module 3;

[0030] The transmitting module 1 is responsible for emitting laser light, and includes a laser driver board 101, a pump laser 102, a total reflector 103, an output mirror 104, a gain medium 105, a switchable initial transmittance Q-switched crystal assembly 106, a photodiode 107, and a laser beam expansion lens 108;

[0031] The receiving module 2 is responsible for receiving the laser light emitted by the transmitting module and then scattered after being irradiated to the object to be measured, and includes a receiving objective lens 201, a switchable transmissive liquid crystal panel 202, a narrow-band filter 203, an avalanche photodiode 204, and a preamplifier circuit 205;

[0032] The control module 3 is responsible for controlling the working mode of the transmitting module 1 and controlling the transmittance and the insertion and cutting-out state of the switchable transmissive liquid crystal panel 202 according to the characteristics of the echo signal scattered by the measured object.

[0033] The control module 3 controls the laser rangefinder to work in five ranging modes, namely, very close distance mode (<50m), short distance ranging mode (50m-1000m), medium distance ranging mode (1km-10km), long distance ranging mode (>10km) and high temperature environment ranging mode.

[0034] like Figure 7 The figure shows the basic structure of a switchable initial transmittance Q-switched crystal assembly provided by an embodiment of the present invention, which is fixed on a turntable and is divided into three gears, namely a low initial transmittance gear 10601, a high initial transmittance gear 10602 and a non-Q-switched crystal gear 10603.

[0035] Extreme close range mode Figure 2 As shown, the switchable initial transmittance Q-switched crystal component 106 is switched to the non-Q-switched crystal gear 10603 through the control module, the driver board 101 outputs a continuous current higher than the laser threshold to the pump laser 102, and the original high single pulse energy pulse laser is switched to a continuous output mode. The output current intensity of the driver board 101 changes with the sine wave periodicity over time, and the avalanche photodiode bias voltage in the receiving module is reduced to 5V and the preamplification circuit magnification is 0. The switchable transmissive liquid crystal panel 202 is inserted between the receiving objective lens 201 and the narrowband filter 203 in the receiving module 2, and the purpose of not saturating the echo signal is achieved by adjusting the output current intensity of the driver board 101 and the transmittance of the switchable transmissive liquid crystal panel 202. At this time, the laser rangefinder works in the phase ranging mode.

[0036] In other modes, the laser rangefinder works in the pulse ranging mode, the driving board 101 outputs a pulse current to the pump laser, and the output pulse current width is determined according to the signal collected by the photodiode 107. When the laser in the resonant cavity oscillates, the photodiode 107 will collect the stray light in the resonant cavity and output a pulse signal to the control module 3. After receiving the pulse signal from the photodiode 107, the control module 3 stops the current output of the driving board.

[0037] Close range measurement mode Figure 3 As shown, the low initial transmittance passive Q-switched crystal 10601 placed on the switchable initial transmittance Q-switched crystal assembly 106 is inserted into the laser resonant cavity at the Brewster angle to achieve high single-pulse energy laser output. After the laser irradiates the object to be measured, the echo signal received by the receiving module will still have a low ranging accuracy due to the excessive signal. At this time, the control module controls the transmittance of the transmissive liquid crystal panel and attenuates the echo signal intensity to improve the ranging accuracy.

[0038] Medium distance ranging mode Figure 4 As shown, during medium-distance ranging, the echo signal naturally attenuates as the distance increases. At this time, in order to ensure the ranging capability, the switchable transmissive liquid crystal panel is moved out of the image relay system based on the short-distance ranging mode to improve the transmittance of the receiving module to the echo signal.

[0039] In long distance ranging mode Figure 5As shown, the echo signal intensity is weak and the signal-to-noise ratio is poor during long-distance ranging. By utilizing the randomness of the noise signal and the fixedness of the target signal, the target signal can be extracted using a pulse-related algorithm. The pulse-related algorithm requires multiple superpositions to achieve the effect of improving the signal-to-noise ratio. At this time, the switchable initial transmittance Q-switched crystal component 106 is switched to a high initial transmittance passive Q-switched crystal 10602, and the laser is switched from a low repetition frequency high single pulse energy mode to a high repetition frequency low single pulse energy mode. The pulse laser is emitted at a higher frequency, and the control module 3 performs echo signal acquisition and superposition. The signal-to-noise ratio of the echo signal can be improved through long-term superposition, and the measured target signal can be extracted, which greatly improves the laser ranging capability.

[0040] High temperature environment ranging mode, such as Figure 6 As shown, due to the influence of structural deformation, thermal lens effect, etc., the laser threshold becomes higher, and the insertion loss of the switchable initial transmittance Q-switched crystal component 106 inserted into the resonant cavity parallel to the light-emitting surface of the gain medium will be lower than that of the Brewster angle inserted into the resonant cavity. The transmittance of the Q-switched crystal inserted into the resonant cavity and the output logic of the driver board are consistent with the very close distance mode, the close distance ranging mode, the medium distance ranging mode, and the long distance ranging mode.

[0041] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0042] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A laser rangefinder with a large dynamic range, characterized in that: include: Transmitting module, receiving module and control module; The transmitting module comprises a driving board, a pump laser, a total reflection mirror, an output mirror, a gain medium, a switchable initial transmittance Q-switched crystal component, a photodiode and a laser beam expander lens; the current signal output by the driving board enters the pump laser, and the laser signal output by the pump laser passes through the total reflection mirror, the gain medium, the switchable initial transmittance Q-switched crystal component, the output mirror and the laser beam expander lens in sequence; the total reflection mirror, the output mirror, the gain medium and the switchable initial transmittance Q-switched crystal component constitute a resonant cavity, and the photodiode is used to collect stray light signals in the resonant cavity; The receiving module comprises a receiving objective lens, a switchable transmissive liquid crystal panel, a narrow-band filter, an avalanche photodiode and a preamplifier circuit which are arranged in sequence; The control module is responsible for controlling the driving board and the switchable initial transmittance Q-switched crystal component, the switchable transmissive liquid crystal panel and the preamplifier circuit to control the laser ranging to work in the extremely close distance mode, the close distance ranging mode, the medium distance ranging mode, the long distance ranging mode and the high temperature environment ranging mode.

2. The laser rangefinder according to claim 1, characterized in that: The driver board included in the transmitting module is controlled by the control module. In the extremely close distance mode, the control module controls the driver board to output a continuous current to the pump laser and the current intensity changes periodically over time. In the close distance ranging mode and the medium distance ranging mode, the control module controls the driver board to output a low repetition frequency pulse current higher than the laser threshold to the pump laser, and the duty cycle is controlled by the control module. In the long distance ranging mode, the control module controls the driver board to output a high repetition frequency pulse current higher than the laser threshold to the pump laser, and the duty cycle is controlled by the control module.

3. The laser rangefinder according to claim 2, characterized in that: The switchable initial transmittance Q-switched crystal assembly included in the transmitting module is controlled by the control module. The Q-switched crystal is a passive Q-switched crystal, fixed on the turntable and divided into a low initial transmittance gear, a high initial transmittance gear and a non-Q-switched crystal gear. The turntable as a whole has two angle states relative to the gain medium light-emitting surface, namely, a state parallel to the gain medium light-emitting surface and a Brewster angle with the gain medium light-emitting surface. It is switched according to the requirements of each ranging mode. The extremely close distance mode is the non-Q-switched crystal gear. In the close distance ranging mode and the medium distance ranging mode, the low initial transmittance gear is inserted at the Brewster angle. In the long distance ranging mode and the high temperature environment ranging mode, the high initial transmittance gear is inserted at an angle parallel to the gain medium light-emitting surface.

4. The laser rangefinder according to claim 3, characterized in that: The switchable transmissive liquid crystal panel in the receiving module is controlled by the control module and has the function of being inserted and removed between the receiving objective lens and the narrow-band filter. In the extremely close distance mode and the close distance ranging mode, it is inserted between the receiving objective lens and the narrow-band filter in the receiving module, and in the medium distance ranging mode and the long distance ranging mode, it is removed between the receiving objective lens and the narrow-band filter. The high temperature environment ranging mode is related to different distance modes.

5. A laser ranging method with a large dynamic range based on the laser rangefinder according to any one of claims 1 to 4, characterized in that: include: In the extremely close distance mode, the switchable initial transmittance Q-switched crystal component is switched to the non-Q-switched crystal gear through the control module, the driver board outputs a continuous current higher than the laser threshold, and the current intensity changes periodically with time. At the same time, the avalanche photodiode bias and the preamplification magnification of the receiving module are reduced, and the control module adjusts the switchable transmissive liquid crystal panel state to the low transmittance gear; In the short-distance ranging mode, the switchable initial transmittance Q-switched crystal component is switched to the low initial transmittance gear through the control module and inserted into the resonant cavity at the Brewster angle, the driver board outputs a low-frequency pulse current higher than the laser threshold, the avalanche photodiode bias and the preamplifier circuit magnification in the receiving module are at the highest bias and high magnification at which the preamplifier circuit output signal does not oscillate, and the control module adjusts the switchable transmissive liquid crystal panel state to the high transmittance gear; In the medium-distance ranging mode, the switchable initial transmittance Q-switched crystal component is switched to the low initial transmittance gear through the control module and inserted into the resonant cavity at the Brewster angle, the driver board outputs a low-frequency pulse current higher than the laser threshold, the avalanche photodiode in the receiving module is in a high bias state and the preamplifier circuit is at the highest magnification, and the control module moves the switchable transmissive liquid crystal panel out from between the receiving objective lens and the narrow-band filter; In the long-distance ranging mode, the switchable initial transmittance Q-switched crystal component is switched to a high initial transmittance position through the control module and inserted into the resonant cavity at a light output angle parallel to the gain medium, the driver board outputs a high-frequency pulse current higher than the laser threshold, the avalanche photodiode in the receiving module is in a high bias state and the preamplifier circuit is at the highest magnification, and the control module moves the switchable transmissive liquid crystal panel out from between the receiving objective lens and the narrow-band filter; In the ranging mode in a high temperature environment, the switchable initial transmittance Q-switched crystal component is switched through the control module to insert the Q-switched crystal at an angle parallel to the light-emitting surface of the gain medium. The initial transmittance of the inserted passive Q-switched crystal and the output logic of the driver board are related to the very close distance mode, short distance ranging mode, medium distance ranging mode, and long distance ranging mode.

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