JP6561546B2 - Laser distance measuring device and laser distance measuring method - Google Patents

Description

  The present invention relates to a laser distance measuring device and a laser distance measuring method, and more particularly to adjustment when pointing changes from an initial value.

  In an asteroid exploration mission using a spacecraft, a laser range finder may be used to reliably reach the target asteroid and to scientifically observe the asteroid. In addition, since the spacecraft has a weight limit, there are restrictions on the functions to be installed. Laser ranging devices require highly accurate and reliable measurement results, but in space, structural changes may occur due to external factors such as the environment. A slight change will affect the distance measurement performance.

  In order to realize higher performance and higher accuracy measurement, a function capable of correcting the optical axis on the orbit after launch is required. From the viewpoint of scientific observation, it is expected to observe the reflectance distribution of laser light with high resolution in order to identify the material on the target asteroid surface. It is desirable to realize these problems while considering weight restrictions.

  Patent Document 1 relates to a laser range finder, and a transmission pulse laser beam obtained by mixing a fundamental pulse laser beam and a second harmonic pulse laser beam by a wavelength conversion element whose wavelength conversion efficiency changes with temperature. It has been proposed that Thereby, even when the measurement distance of the laser distance measuring device changes significantly, the distance measurement accuracy is ensured.

JP 2014-173966 A

  The laser light transmitted from the laser distance measuring device is attenuated in light quantity in inverse proportion to the square of the distance. For example, in a laser distance measuring device that measures a distance from an asteroid to a distance of 50 km to 50 m, the received light quantity changes by 6 to 7 digits depending on the distance measured. In order to establish distance measurement with such a small amount of received light, it is desirable that the pointing of the transmission laser light does not change from the initial value. However, there is a problem that pointing changes from the initial value due to vibration and temperature environment. When the pointing changes from the initial value, it is necessary to adjust the focus of the light receiving system based on the direction of the reflected beam.

  In addition, the reflectance distribution of asteroids is scientifically important, and its means has been a challenge.

  An object of the present invention is to provide a laser distance measuring apparatus and a laser distance measuring method that can be adjusted so that the focus of a light receiving system is matched based on the direction of a reflected beam even when pointing changes from an initial value. is there.

In order to achieve the above object, a laser distance measuring device according to the present invention includes:
A transmission optical means for receiving the laser light from the light source means and outputting it as a transmission laser light to the object;
A transmission optical axis correction unit that is inserted in a path between the light source unit and the transmission optical unit and corrects the transmission optical axis of the laser beam in accordance with an input control signal;
Receiving optical means for inputting the receiving laser light reflected by the object, the transmitting laser light;
Monitoring means for receiving and monitoring part of the transmission laser light and part of the reception laser light;
Count means for generating counter information indicating the distance from the timing information of the transmission laser light of the transmission optical means and the reception laser light of the reception optical means to the object;
Control means for calculating a distance to the object based on the counter information of the counting means and outputting the control signal to the transmission optical axis correction means based on a monitoring result of the monitoring means.

In the laser distance measuring method according to the present invention, the laser beam is received from the light source unit, and the transmission optical unit outputs the transmission laser beam to the object.
The transmission laser beam is input as a reception laser beam reflected by the object,
Receive and monitor a part of the transmission laser light and a part of the reception laser light,
A counter information indicating a distance to the object is generated from timing information of the transmission laser light and the reception laser light, a distance to the object is calculated based on the counter information, and a part of the transmission laser light The transmission optical axis of the laser beam outputted from the light source unit to the transmission optical unit is corrected based on the monitoring result of a part of the received laser beam.

  According to the present invention, a part of the transmission laser beam and a part of the reception laser beam are monitored, and based on this, the transmission optical axis of the laser beam is corrected. Therefore, even if the pointing changes from the initial value, the reflection is reflected. The light receiving system can be adjusted to be in focus based on the beam direction.

It is a block diagram for demonstrating the structure of the laser range finder of the highest concept of this invention. It is a block diagram for demonstrating the structure of the laser ranging apparatus by 1st Embodiment of this invention. It is a block diagram for demonstrating the more specific structural example of the laser ranging apparatus of FIG.

  Preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram for explaining the configuration of the laser range finder according to the highest concept of the present invention.

  1 includes a light source means 21, a transmission optical axis correction means 22, a transmission optical means 23, a reception optical means 24, a monitor means 25, a counting means 26, and a control means 27. Have.

  The light source means 21 outputs laser light for laser ranging. The transmission optical unit 23 irradiates the target with the laser beam from the light source unit 21 and transmits the laser beam from the light source unit 21 to the monitor unit 25. The transmission optical unit 23 gives start timing information indicating the start of counting to the counting unit 26. The receiving optical means 24 receives the laser beam reflected by the object as a receiving laser beam. The receiving optical means 24 branches the received laser light and supplies it to the monitoring means 25. The receiving optical means 24 gives stop timing information indicating the count stop to the counting means 26.

  The monitor unit 25 monitors a part of the transmission laser beam from the transmission optical unit 23 and a part of the reception laser beam from the reception optical unit 24 and supplies the result to the control unit 27 as a monitoring result.

  The count unit 26 gives the control unit 27 counter information corresponding to the distance to the object based on the start timing information from the transmission optical unit 23 and the stop timing information from the reception optical unit 24.

  The control unit 27 calculates the distance to the object based on the counter information from the counting unit 26. Further, a control signal is output to the transmission optical axis correction unit 22 based on the monitoring result of the monitoring unit 25. The monitoring result of the monitor means 25 is, for example, a change from the reference position of a part of the center of gravity of the transmission laser light and a part of the center of gravity of the reception laser light.

  Then, the transmission optical axis correction unit 22 corrects the optical axis of the laser beam output from the light source unit 21 to the transmission optical unit 23 based on the control signal from the control unit 27.

  According to the laser distance measuring device of FIG. 1, the distance to the object can be calculated by irradiating the object with laser light and receiving the reflected laser light. Further, based on the monitoring result of the monitor unit 25, the optical axis of the laser beam output from the light source unit 21 to the transmission optical unit 23 is corrected. As a result of the optical axis correction of the laser light, even when the pointing is changed from the initial value, it is possible to adjust the focus of the light receiving system based on the direction of the reflected beam. Hereinafter, the present invention will be described with respect to more specific embodiments.

[First Embodiment]
A laser range finder according to a first embodiment of the present invention will be described. FIG. 2 is a block diagram for explaining the configuration of the laser distance measuring apparatus according to the first embodiment of the present invention.

(Description of the configuration of the present embodiment)
The laser distance measuring device of FIG. 2 is a laser distance measuring device having a function of monitoring the transmission optical axis and the reception optical axis to correct the transmission laser optical axis and a function of observing the intensity distribution of the reflectance of the asteroid. . This laser range finder is mounted on, for example, an asteroid explorer, and is used for navigation support for calculating the distance from the laser range finder to the asteroid by measuring the round trip time of the pulse laser and guiding the probe to the asteroid.

  Simultaneously with normal distance measurement as a laser distance measuring device, the transmission optical axis and the reception light that fluctuate due to external factors such as vibration and heat are monitored by the function of monitoring the transmission optical axis and the reception optical axis and correcting the transmission laser optical axis Compensate for axis changes. By comparing the intensity distribution of the transmitted laser beam and the received laser beam, the intensity distribution of the reflectance of the asteroid is observed, and the function of identifying the reflectance distribution of the asteroid with high spatial resolution is realized. In FIG. 2, a solid line indicates a path of an optical signal such as a transmission laser beam or a reception laser beam, and a dotted arrow indicates a path of an electric signal.

  2 includes a laser oscillator 1, a transmission optical axis correction unit 2, a transmission optical system 3, a light transmission detection unit 4, a separation / coupling optical system 5, a reception optical system 6, and a monitor unit. 7, a light reception detection unit 8, a distance measurement counter unit 9, a control unit 10, and a power supply unit 11.

  The laser oscillator 1 outputs a pulse laser.

  The transmission optical axis correction unit 2 has a mechanism for adjusting the optical axis of the transmission laser light output from the laser oscillator 1. The transmission optical axis correction unit 2 adjusts the optical axis of the transmission laser light in accordance with a control signal given from the control unit 10.

  The transmission optical system 3 has an optical component that shapes the transmission laser light, outputs a laser beam to the outside, branches a part of the transmission laser light, guides the part to the transmission detection unit, and partially guides it to the separation / coupling optical system. And has a function of controlling the polarization of the transmitted light. The light transmission detector 4 detects the transmission laser light and converts it into an electrical signal, amplifies the transmission signal converted into the electrical signal, provides a threshold value, and converts it into a timing signal. The light transmission detection unit 4 detects the transmission laser light and converts it into an electrical signal, amplifies the transmission signal converted into the electrical signal, provides a threshold value, and converts it into a timing signal. The light transmission detection unit 4 outputs transmission timing information indicating the start of counting to the distance measurement counter unit 9.

  The separation / coupling optical system 5 includes optical components that guide the transmission laser light branched from the transmission optical system 3 and the reception laser light from the reception optical system 6 inside the laser distance measuring device. The receiving optical system 6 condenses the received laser beam and branches a part thereof to the monitor unit 7 and a part thereof to the separation / coupling optical system 5. The reception optical system 6 further includes an optical component that propagates the transmission laser light to the monitor unit 7. The light reception detector 8 detects the received laser light and converts it into an electrical signal, amplifies the received signal converted into the electrical signal, provides a threshold value, and converts it into a timing signal. The light reception detection unit 8 outputs reception timing information indicating the count stop to the distance measurement counter unit 9.

  The monitor unit 7 has a level detection function by the array sensor, and can observe the transmission laser light branched from the transmission optical system 3 and the reception laser light branched from the reception optical system 6. The intensity distribution of the transmission laser beam branched from the transmission optical system 3 is compared with the intensity distribution of the reception laser beam branched from the reception optical system 6, and the reflectance of the object is observed as two-dimensional distribution information in the footprint. To do. The monitor unit 7 having this level detection function is installed at a position where a part of the received laser beam and the transmitted laser beam branched by the receiving optical system 6 can be monitored simultaneously.

  The distance measurement counter unit 9 transmits the detection of the transmission laser beam to the control unit 10 as a counter value for starting the distance measurement, and transmits the detection of the reception laser beam to the control unit 10 as a counter value for stopping the distance measurement.

  The control unit 10 calculates the intensity centroid and intensity distribution of the branched transmission laser light and the branched reception laser light based on the intensity distribution information obtained by the monitor unit 7. The control unit 10 calculates the transmission optical axis correction amount and controls the transmission optical axis correction unit 2. Further, the control unit 10 has a function of controlling the polarization of the transmission laser based on the intensity information, controlling the emission timing of the laser oscillator 1, and outputting a distance measurement counter value and other statuses to an external device.

  The power supply unit 11 supplies power to each unit constituting the laser distance measuring device.

  FIG. 3 is a block diagram for explaining a more specific configuration example of the laser distance measuring device of FIG. The transmission optical system 3 includes a half-wave plate (HWP) 31, a first polarizer (POL1) 32, a beam splitter (BS) 33, a Pockels cell 34, and a beam expander 35.

  The receiving optical system 6 includes a third polarizer (POL 3) 61, a quarter wavelength plate (QWP) 62, a folding mirror 63, a primary mirror 64, and a secondary mirror 65.

  The separation / coupling optical system 5 includes a relay lens 51, a band pass filter (BPF) 52, a second polarizer (POL 2) 53, a relay lens 54, and a pinhole 55.

(Description of operation of this embodiment)
The detailed operation of the laser distance measuring device of this embodiment and the laser distance measuring method will be described with reference to FIG. The laser distance measuring device of the present embodiment receives a distance measurement execution command from a probe as an example of an external device, and drives the laser oscillator 1 to output a pulse laser.

  A transmission laser beam is branched by a beam splitter (BS) 33 in the transmission optical system 3, detected by a light transmission detection unit 4, and transmitted to a distance measurement counter unit 9 as a distance measurement start timing signal.

  The transmission laser beam propagates to the transmission optical system 3 by changing the optical axis according to the initial value or the correction value calculated by the transmission optical axis correction unit 2. The transmission laser light is linearly polarized light, and the polarization direction is adjusted by a half-wave plate (HWP) 31 in the transmission optical system 3.

  In order to monitor the pointing change of the transmission laser beam, the transmission laser beam is branched before the beam expander 35 of the transmission optical system 3, and the branched transmission laser beam is guided inside the laser distance measuring device. That is, a part is propagated to the separation / coupling optical system 5 by the first polarizer (POL 1) 32 of the transmission optical system 3.

  Further, it passes through a beam expander 35 via a beam splitter (BS) 33 at the rear stage in the transmission optical system 3 and a Pockels cell 34 for controlling polarization, and is output to the outside. The beam expander 35 can expand the beam diameter and adjust the transmission beam divergence angle. The Pockels cell 34 of the transmission optical system 3 can adjust the polarization of the transmission laser to circularly polarized light or elliptically polarized light according to the control signal of the control unit 10, and the transmitted light of the third polarizer (POL 3) 61 in the reception optical system 6. And the ratio of the reflected light can be adjusted. This adjustment of the ratio is a ratio of the amount of light branched to the light reception detection unit 8 and the monitor unit 7. The received laser light maintains the polarization of the transmitted laser light. When circularly polarized light is received, the transmission and reflection of the third polarizer (POL3) 61 are substantially equal. A part of the received laser light is transmitted through the third polarizer (POL 3) 61 through the main mirror 64 and the sub mirror 65 of the receiving optical system 6, and forms an image at the pinhole 55 in the separation / coupling optical system 5.

  Further, the light reflected by the third polarizer (POL3) 61 becomes circularly polarized light by the quarter wavelength plate (QWP) 62, and is transmitted through the quarter wavelength plate (QWP) 62 again by the folding mirror 63, thereby being 90 °. Return to rotated linearly polarized light. Then, the light passes through the third polarizer (POL 3) 61 with little loss and propagates to the monitor unit 7.

  Here, the monitor unit 7 has an imaging lens, and the focal plane coincides with the surface of the pinhole 55 and the folding mirror 63 by the imaging lens. The pinhole 55 is installed at a focal position determined by the primary mirror 64 and the secondary mirror 65, so that the monitor unit 7 monitors the far-field image observed by the primary mirror 64 and the secondary mirror 65. .

  The received laser beam that has passed through the pinhole 55 is image-transferred to the detection surface of the light receiving detector 8 by the relay lens 51 of the separation / coupling optical system 5. At this time, the light passes through a bandpass filter (BPF) 52 that cuts other than the wavelength of the received laser light and a second polarizer (POL2) 53 that guides part of the transmitted light to the monitor unit 7.

  The transmission laser beam branched by the first polarizer (POL1) 32 is adjusted to be coaxial with the reception laser beam by light guide. Then, the branched transmission laser light is adjusted to have the same angle as the transmission laser light that is externally output on the same axis as the reception laser light, and the branched transmission laser light and the reception laser light are coaxially formed by one monitor unit 7. Be monitored.

  That is, there is almost no transmission loss by making the transmission (P polarization) directions of the third polarizer (POL3) 61 and the second polarizer (POL2) 53 coincide. A part of the transmission laser beam reflected by the first polarizer (POL1) 32 is coaxial with the reception optical axis by the second polarizer (POL2) 53, and is condensed by one of the relay lenses (relay lens 54). , And is reflected by the third polarizer (POL 3) 61 and propagates to the monitor unit 7.

  Simultaneously with the normal distance measurement as the laser distance measuring device, changes from the initial values of the branched transmission laser light and reception laser light detected by the monitor unit 7 are calculated and used as a reference for the angle correction value.

  The intensity distribution of the transmission laser light is condensed at the position of the pinhole 55 by the relay lens 54. The intensity distribution of the focused spot at the position of the pinhole 55 represents the intensity distribution of the far-field image of the transmission laser light. Here, since the monitor unit 7 monitors the image plane at the position of the pinhole 55, the intensity distribution of the far-field image of the transmission laser beam is monitored. As a result, the monitor unit 7 can simultaneously monitor the intensity distribution of the far-field images of the transmission laser beam and the reception laser beam.

  A mechanism (transmission optical axis correction unit 2) for adjusting the optical axis of the transmission laser light is provided in front of the branch of the transmission laser light (first polarizer 32 of the transmission optical system 3) as angle correction. Based on the angle correction value obtained as described above, the pointing of the transmission laser beam is corrected by a mechanism for adjusting the optical axis of the transmission laser beam.

  If the optical axis of the transmission laser beam incident on the monitor unit 7 and the optical axis of the reception laser beam are completely coincided with each other, the images overlap each other. Therefore, the folding mirror 63 in the reception optical system 6 is slightly angled. Two images can be separated on the array sensor surface of the monitor unit 7.

  By simultaneously monitoring the far-field images for transmission and reception, the control unit 10 can calculate the deviation of the transmission and reception optical axes based on the center of gravity from the intensity distribution, and can control the transmission optical axis correction unit 2 to correct it to the optimum optical axis. . Moreover, the two-dimensional distribution of the reflectance of the target asteroid surface can be calculated by comparing the intensity distribution of transmission and reception.

  A part of the received laser beam is detected by the light receiving detector 8. The light receiving detector 8 detects the received laser beam, converts it into an electrical signal, amplifies the received signal converted into the electrical signal, provides a threshold value, and transmits it to the distance measuring counter 9 as a distance measuring timing signal.

  The distance measurement counter unit 9 transmits the detection of the transmission laser beam to the control unit 10 as a counter value for starting the distance measurement, and transmits the detection of the reception laser beam to the control unit 10 as a counter value for stopping the distance measurement. The counter information is converted into distance calculation information by the control unit 10 and transmitted to a probe as an example of an external device.

  By performing this series of operations for each distance measurement, it is possible to always perform correction to the optimum optical axis. At the same time, the reflectance distribution on the target surface can be observed with high spatial resolution.

(Description of the effect of this embodiment)
The first is that the pointing can be corrected by correcting the optical axis of the transmission laser beam. A part of the transmitted laser beam and a part of the received laser beam reflected from the asteroid are observed on the same sensor surface by the monitor unit 7 installed at the end of the beam transmitted through the separation / coupling optical system 5 and the receiving optical system 6. To do. In this observation, the control unit 10 monitors the variation of the partial centroid of the transmission laser beam and the partial centroid of the reception laser beam from the reference position, and the transmission optical axis correction unit 2 performs the change according to the change amount of the optical axis. The transmission laser optical axis can be corrected.

  Second, it is possible to observe the intensity distribution of asteroid reflectance with high spatial resolution. The monitor unit 7 having a level detection function is installed at a position where a part of the received laser beam and the transmitted laser beam branched by the receiving optical system 6 can be monitored simultaneously. Compared with a method of calculating reflectance by repeatedly acquiring data multiple times with a single light receiving element by observing each far-field image of transmitted / received light in two dimensions with the monitor unit 7 having a level detection function. The reflectance can be observed with higher spatial resolution.

  Third, the set of monitoring units 7 can realize correction of the transmission optical axis and the reception optical axis to the optimum optical axis and observation of the intensity distribution of the asteroid.

[Other Embodiments]
The laser distance measuring device of the present invention is not limited to the configuration of the above-described embodiment. For example, an application in which the functions of the light transmission detection unit 4 and the light reception detection unit 8 in FIGS. 2 and 3 are provided in the monitor unit 7 is also possible. The apparatus to which the laser distance measuring device of the present invention is applied is not limited to an asteroid explorer, and can be applied to a laser distance measuring device mounted on a satellite or an aircraft.

  As mentioned above, although preferable embodiment and the Example of this invention were described, this invention is not limited to this. It goes without saying that various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention.

  As an application example of the present invention, the present invention can be used for a ranging device for supporting navigation in an asteroid explorer, an observation mission for reflectance of a target planet, and earth observation on an artificial satellite or a space station.

DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Transmission optical axis correction | amendment part 3 Transmission optical system 4 Light transmission detection part 5 Separation | coupling optical system 6 Reception optical system 7 Monitor part 8 Light reception detection part 9 Ranging counter part 10 Control part 11 Power supply part 21 Light source means 22 Transmission Optical axis correction means 23 Transmission optical means 24 Reception optical means 25 Monitor means 26 Count means 27 Control means

Claims (8)

A transmission optical means for receiving the laser light from the light source means and outputting it as a transmission laser light to the object;
A transmission optical axis correction unit that is inserted in a path between the light source unit and the transmission optical unit and corrects the transmission optical axis of the laser beam according to an input control signal;
Receiving optical means for inputting the receiving laser light reflected from the object by the transmitting laser light;
A separation / coupling optical system including an optical component for guiding a part of the transmission laser light branched from the transmission optical means and the reception laser light from the reception optical means, and branched from the transmission optical means A separation and coupling optical system for outputting a part of the transmission laser light to the reception optical means from a direction opposite to the input direction of the reception laser light to the reception optical means;
Monitoring means for receiving and monitoring a part of the transmission laser light and a part of the reception laser light;
Counting means for generating counter information indicating a distance from the timing information of the transmission laser light of the transmission optical means and the reception laser light of the reception optical means to the object;
To calculate a distance to the object based on the counter information of the counting means, based on the monitoring result of the monitor means, have a, and a control means for outputting the control signal to the transmission optical axis correcting means ,
The receiving optical means splits a part of the transmission laser light from the separation / coupling optical system to the monitoring means and an optical to split a part of the receiving laser light from the receiving optical means to the monitoring means. Laser ranging device including parts .   The monitoring means receives a part of the transmission laser light and a part of the reception laser light reflected by the object, and reflects a part of the center of gravity of the transmission laser light and the object. The laser distance measuring device according to claim 1, wherein fluctuations of a part of the center of gravity of received laser light from a reference position are monitored.   The laser range finder according to claim 2, wherein the monitoring unit observes a part of the transmission laser beam and a part of the reception laser beam reflected by the object on the same sensor surface.   The control means includes the light source based on a monitoring result of fluctuations from a reference position of a part of the center of gravity of the transmitted laser light and a part of the center of gravity of the received laser light reflected by the object by the monitor unit. 4. The laser distance measuring device according to claim 2, wherein a control signal for correcting the optical axis of the laser beam from the means is output to the transmission optical axis correcting means. The transmission optical means receives laser light from the light source means and outputs it as a transmission laser light to the object,
The reception laser beam reflected by the object is input to the reception optical means, the transmission laser beam,
Monitor means receives a part of the transmission laser light and a part of the reception laser light,
Generating counter information indicating the distance from the timing information of the transmission laser beam and the reception laser beam to the object;
Calculate the distance to the object based on the counter information,
Based on the monitoring results of a part of the transmission laser light and a part of the reception laser light, the transmission optical axis of the laser light output from the light source means to the transmission optical means is corrected ,
An optical component for guiding a part of the transmission laser light branched from the transmission optical means and the reception laser light, and a part of the transmission laser light branched from the transmission optical means Output to the receiving optical means from a direction opposite to the input direction to the receiving optical means,
An optical component having said receiving optical means, Ru is branched and a portion of the received laser beam a portion of the transmission laser beam causes the branches to the monitoring means from the receiving optical means to said monitoring means, measuring laser Distance method.   The monitor receives a part of the transmission laser light and a part of the reception laser light reflected by the object, and reflects a part of the center of gravity of the transmission laser light and the object. The laser distance measuring method according to claim 5, wherein a fluctuation of a part of the center of gravity of the received laser beam from a reference position is monitored.   The laser ranging method according to claim 6, wherein the monitor observes a part of the transmission laser light and a part of the reception laser light reflected by the object on the same sensor surface.   Based on a monitoring result of fluctuations from a reference position of a part of the center of gravity of the transmitted laser beam by the monitor and a part of the center of gravity of the received laser beam reflected by the object, the light source unit to the transmission optical unit The laser distance measuring method according to claim 6 or 7, wherein a transmission optical axis of the laser light outputted to the light is corrected.

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