CN119001676A - Optical transceiver system for MEMS laser radar and radar - Google Patents
Optical transceiver system for MEMS laser radar and radar Download PDFInfo
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- CN119001676A CN119001676A CN202411137119.3A CN202411137119A CN119001676A CN 119001676 A CN119001676 A CN 119001676A CN 202411137119 A CN202411137119 A CN 202411137119A CN 119001676 A CN119001676 A CN 119001676A
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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
- 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
- G01S7/484—Transmitters
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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
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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
- 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
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4817—Constructional features, e.g. arrangements of optical elements relating to scanning
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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
- 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
- G01S7/4861—Circuits for detection, sampling, integration or read-out
- G01S7/4863—Detector arrays, e.g. charge-transfer gates
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- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Electromagnetism (AREA)
- Mechanical Optical Scanning Systems (AREA)
Abstract
本发明提供了一种用于MEMS激光雷达的光学收发系统及雷达，光学收发系统包括光学发射系统和接收系统；光学发射系统包括依次设置的边发射激光光源组件、菲涅耳型柱面准直透镜组、新型MEMS振镜扫描组件；光学接收系统包括弯月型接收透镜组、雪崩光电二极管组件。本发明采用了特殊的准直匀化方案和无串扰、双轴独立驱动的新型MEMS振镜，同时提高了测量距离、扫描精度和点云密度；并且采用了弯月透镜用于聚焦小光斑，增加了一块非球面透镜，在增大视场角的同时显著减小球面像差，提高成像质量，实现了±20°的光学视场角。本发明有效解决了大光斑和机械串扰导致扫描精度差的问题，同时设计了光学接收系统，可以在不降低成像质量的条件下显著增大接收视场角。
The present invention provides an optical transceiver system and radar for MEMS laser radar, wherein the optical transceiver system includes an optical transmitting system and a receiving system; the optical transmitting system includes an edge-emitting laser light source assembly, a Fresnel cylindrical collimating lens group, and a new MEMS galvanometer scanning assembly arranged in sequence; the optical receiving system includes a meniscus receiving lens group and an avalanche photodiode assembly. The present invention adopts a special collimation and homogenization scheme and a new MEMS galvanometer with no crosstalk and independent dual-axis drive, while improving the measurement distance, scanning accuracy and point cloud density; and adopts a meniscus lens for focusing a small light spot, and adds an aspherical lens, which significantly reduces spherical aberration while increasing the field of view, improves imaging quality, and achieves an optical field of view of ±20°. The present invention effectively solves the problem of poor scanning accuracy caused by large light spots and mechanical crosstalk, and designs an optical receiving system at the same time, which can significantly increase the receiving field of view without reducing imaging quality.
Description
Technical Field
The invention relates to the technical field of laser radars, in particular to an optical transceiver system for a micro-electromechanical system (MEMS) laser radar and a radar, and particularly relates to an optical transceiver system for the MEMS laser radar and a design method thereof.
Background
The laser radar is an abbreviation of a laser detection and ranging system, which performs object detection and ranging by externally transmitting laser pulses. MEMS laser radar adopts MEMS galvanometer as laser beam scanning original paper, has advantages such as small, macrostructure is simple, the reliability is high, the consumption is low, can realize miniaturization and the low cost of laser radar, and MEMS galvanometer passes through "vibration" adjustment laser reflection angle, realizes the scanning, and laser transmitter is motionless, can acquire information such as the distance of target, speed or realize target imaging with high accuracy, along with the range finding demand is from mechanical to miniaturized all-solid-state direction development, MEMS laser radar is widely used in unmanned car and robot field at present.
The scanning precision and the field of view (FOV) are two important parameters of the MEMS laser radar, the scanning precision is closely related to the radius of a laser spot of the MEMS laser radar and the mechanical crosstalk of a vibrating mirror, the smaller the spot is, the smaller the mechanical crosstalk is, the better the energy focusing property and the scanning linearity of laser are, the scanning precision is improved, and meanwhile, the detection distance and the point cloud density can be correspondingly improved. The field angle determines the field range that the lidar can see, and is divided into a horizontal field angle and a vertical field angle, and the larger the field angle is, the larger the representative field range is, and the more information amount of the acquired environmental distance is. In order to solve the problems of poor scanning precision and smaller receiving angle of view of the current mainstream MEMS laser radar, a multi-light source parallel receiving and transmitting principle is adopted to increase the angle of view, and laser power is increased to improve the return light receiving efficiency, so that the volume and the energy consumption of a radar system are increased, and the image reconstruction difficulty is improved; meanwhile, the laser divergence angle after collimation is still larger, so that the quality of a received light pulse signal is influenced, and the radar detection distance is limited.
Disclosure of Invention
In view of the defects in the prior art, the invention aims to provide an optical transceiver system for a MEMS laser radar and the radar.
The invention provides an optical transceiver system for MEMS laser radar, which comprises an optical transmitting system and a receiving system;
the optical emission system is used for emitting, collimating and homogenizing pulse laser and realizing two-dimensional scanning of the light beam;
The optical receiving system is used for focusing and receiving the diffuse reflected return light signals;
The optical emission system comprises an edge-emitting laser light source assembly, a Fresnel type cylindrical surface fast axis collimating lens, a Fresnel type cylindrical surface slow axis collimating lens, an aperture diaphragm and an MEMS galvanometer scanning assembly which are sequentially arranged;
The optical receiving system comprises an avalanche photodiode, an optical filter, an aspheric lens, a first meniscus lens, a second meniscus lens and a third meniscus lens which are sequentially arranged;
Light emitted by the edge-emitting laser light source component sequentially passes through the Fresnel type cylindrical fast axis collimating lens, the Fresnel type cylindrical slow axis collimating lens, the aperture diaphragm and the MEMS galvanometer scanning component, then is diffusely reflected by an external measured object, sequentially passes through the third meniscus lens, the second meniscus lens, the first meniscus lens, the aspheric lens and the optical filter, and finally is focused on the avalanche photodiode.
Preferably, the Fresnel type cylindrical surface fast axis collimating lens and the Fresnel type cylindrical surface slow axis collimating lens are both in a Fresnel surface type with saw teeth and groove structures on the surfaces; the Fresnel surface type lens can collimate and homogenize the power of divergent light at the focus of the lens; the base of the lens is rectangular;
The Fresnel type cylindrical fast axis collimating lens and the Fresnel type cylindrical slow axis collimating lens are mutually perpendicular.
Preferably, the fresnel cylindrical fast axis collimating lens is parallel to the fast axis direction of the laser beam through the generatrix, changes the meridional light emitted from the edge-emitting laser light source assembly into a quasi-parallel beam, and homogenizes the power in the fast axis direction.
Preferably, the Fresnel type cylindrical slow axis collimating lens is parallel to the slow axis direction of the laser beam through a generatrix, converts the sagittal light rays emitted by the edge-emitting laser light source assembly into quasi-parallel light beams, and homogenizes the power in the slow axis direction.
Preferably, the MEMS galvanometer scanning component comprises a supporting substrate, a fixed frame, a first electrode, a second electrode, a first slow-axis supporting beam, a second slow-axis supporting beam, a balance frame, an electromagnetic driving coil, a first fast-axis supporting beam, a second fast-axis supporting beam, a reflecting mirror surface and a driving permanent magnet;
the fixed frame, the first electrode and the second electrode are arranged on the supporting substrate; the first slow-axis supporting beam, the second slow-axis supporting beam and the balance frame are all arranged in the fixed frame; the electromagnetic driving coil, the first fast axis supporting beam and the second fast axis supporting beam are all positioned on the balance frame;
The reflecting mirror surface is positioned in the middle of the MEMS vibrating mirror; the two ends of the reflector surface are respectively and rotatably connected with the balance frame through a first fast-axis supporting beam and a second fast-axis supporting beam, and the two ends of the balance frame are respectively and rotatably connected with the fixed frame through a first slow-axis supporting beam and a second slow-axis supporting beam;
Two ends of the electromagnetic driving coil are respectively supported by a first slow-axis supporting beam and a second slow-axis supporting beam, and two ends of the electromagnetic driving coil are respectively and rotatably connected with the first electrode and the second electrode;
The driving permanent magnet is mounted on the supporting substrate and located below the reflecting mirror surface.
Preferably, the MEMS galvanometer scanning component further comprises
The magnetic field generator comprises a first permanent magnet, a second permanent magnet, a first magnetic yoke, a second magnetic yoke, an external driving coil, a fixed magnetic column and a non-magnetic tube shell;
The first magnetic yoke and the second magnetic yoke are inserted between the balance frame and the fast shaft support beam;
the first permanent magnet and the second permanent magnet are respectively arranged on the first magnetic yoke and the second magnetic yoke; the magnetization directions of the first permanent magnet and the second permanent magnet are perpendicular to the contact surface, and the magnetization directions of the first permanent magnet and the second permanent magnet are opposite;
the external driving coil is sleeved outside the fixed magnetic column;
The external driving coil is arranged right below the center of the reflecting mirror surface, and the distance between the external driving coil and the driving permanent magnet in the supporting substrate is 1.5-2 mm.
Preferably, the edge-emitting laser light source component, the Fresnel type cylindrical fast axis collimating lens, the Fresnel type cylindrical slow axis collimating lens, the aperture diaphragm and the MEMS galvanometer scanning component are connected by adopting a cage structure, so that the geometric centers of the mirrors are located on the same optical axis.
Preferably, the aspherical lens has negative optical power, the first meniscus lens has positive optical power, the second meniscus lens has positive optical power, and the third meniscus lens has negative optical power.
Preferably, the centers of the aspherical lens, the first meniscus lens, the second meniscus lens and the third meniscus lens are positioned on the same optical axis and fixed to a preset distance; the position and the connection among the aspheric lens, the first meniscus lens, the second meniscus lens and the third meniscus lens are adjusted by adopting a cage structure.
According to the radar provided by the invention, the optical transceiver system for the MEMS laser radar is adopted.
Compared with the prior art, the invention has the following beneficial effects:
1. The invention designs the Fresnel type cylindrical collimation lens group, performs collimation shaping and homogenization treatment on the pulse laser with large divergence angle, realizes 2.4mrad multiplied by 5.2mrad emergent laser, improves the collimation degree by two orders of magnitude, controls the diameter of a light spot at a 10m position to be 6cm, solves the technical problem of large divergence angle of the laser, and is beneficial to improving the scanning precision and the point cloud density. The invention adopts a Fresnel cylindrical collimating lens with compact structure and a single light source scheme instead of the scheme of multiple light sources in the prior art, so the invention has smaller overall volume and laser energy consumption.
2. The invention adopts the novel MEMS galvanometer scanning assembly design, realizes the double-shaft independent driving of the electromagnetic MEMS galvanometer based on two electromagnetic driving technologies of the movable coil and the movable magnet, eliminates the mechanical crosstalk between two shafts, eliminates the influence of the thermal deformation of the mirror surface by arranging the driving permanent magnet and the external driving coil below the reflecting mirror surface, improves the linearity of scanning point cloud, and more importantly, reduces the problem of poor scanning precision caused by the mechanical crosstalk for the whole optical receiving and transmitting system after the novel MEMS galvanometer scanning assembly is used.
3. The invention is improved based on the traditional Cooks three-separation objective lens scheme, uses the meniscus lens to replace the convex lens for focusing small light spots, and adds an aspheric lens, so that focusing can be performed according to the incident position and angle of light rays, the imaging quality is further improved, and finally, a large optical field angle of +/-20 degrees is realized.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a schematic diagram of an optical transceiver system for MEMS lidar according to the present invention;
FIG. 2 is a schematic diagram of an optical emission system according to the present invention;
FIG. 3 is a schematic view of a Fresnel type cylindrical collimating lens according to an embodiment of the present invention;
FIG. 4 is a graph showing the shape of the light spot at different distances and a comparison chart according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of an optical receiving system according to the present invention;
FIG. 6 is a schematic view of a spot shape of a light beam passing through an optical receiving system with different incident angles according to an embodiment of the present invention;
FIG. 7 is a graph showing curvature of field/distortion of a light beam passing through an optical receiving system at different incident angles according to an embodiment of the present invention;
FIG. 8 is a graph of Modulation Transfer Functions (MTFs) of light beams with different incident angles after passing through an optical receiving system according to an embodiment of the present invention;
FIG. 9 is a partial front perspective view of a MEMS galvanometer scanning assembly of the invention;
FIG. 10 is a partial rear perspective view of a MEMS galvanometer scanning assembly of the invention;
FIG. 11 is a schematic illustration of the driving mode of the moving coil of the MEMS galvanometer scanning assembly of the invention;
FIG. 12 is a schematic illustration of the driving mode of the moving magnet of the MEMS galvanometer scanning assembly of the invention;
FIG. 13 is a schematic representation of a three-dimensional exploded view of a MEMS galvanometer scanning assembly in accordance with the invention;
FIG. 14 is a schematic diagram of the layout of an electromagnetic MEMS galvanometer, a magnetic yoke, an external drive coil, and a permanent magnet of the MEMS galvanometer scanning assembly of the present invention;
FIG. 15 is a schematic view in section A-A' of FIG. 14;
FIG. 16 is a schematic diagram of a cloud of magnetic field intensity distribution for a slow axis drive mode of a MEMS galvanometer scanning assembly according to the invention;
FIG. 17 is a schematic diagram of a magnetic field intensity distribution cloud for a fast axis drive mode of a MEMS galvanometer scanning assembly according to the invention;
The figure shows:
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
The invention provides an optical transceiver system for MEMS laser radar, referring to FIGS. 1 and 2 in combination, comprising an optical transmitting system and a receiving system; the optical emission system is used for emitting, collimating, shaping and homogenizing 905nm pulse laser and realizing two-dimensional scanning of the laser;
The optical emission system comprises an edge-emitting laser light source component 1, a Fresnel type cylindrical fast axis collimating lens 2, a Fresnel type cylindrical slow axis collimating lens 3, an aperture diaphragm 4 and an MEMS galvanometer scanning component 5 which are sequentially arranged; the optical emission system adopts cage structure connection, namely, the side-emission laser light source component 1, the Fresnel type cylindrical fast axis collimating lens 2, the Fresnel type cylindrical slow axis collimating lens 3, the aperture diaphragm 4 and the MEMS galvanometer scanning component 5 are connected by adopting cage structure. The aperture diaphragm 4 is used for limiting light beams and filtering stray light existing in the optical emission system, so that the stray light is prevented from entering the MEMS galvanometer scanning assembly. In a preferred embodiment, the edge-emitting laser light source assembly 1 is an edge-emitting semiconductor laser diode (EEL).
The optical receiving system is used for focusing and receiving the return light signals diffusely reflected by the remote object; the optical receiving system is mounted on an external bracket or a mounting position in a sticking or mechanical fixing mode. The optical receiving system comprises an avalanche photodiode 7, an optical filter 8, an aspherical lens 9, a first meniscus lens 10, a second meniscus lens 11 and a third meniscus lens 12 which are sequentially arranged; in a preferred embodiment, the aspherical lens 9 is a concave lens. The Avalanche Photodiodes (APDs) and filters form photosensitive elements with high gain for 905nm photons for converting optical signals into current signals. In a preferred embodiment, the first meniscus lens 10, the second meniscus lens 11, and the third meniscus lens 12 may not be meniscus lenses, and may be spherical lenses.
Light emitted by the edge-emitting laser light source component 1 sequentially passes through the Fresnel type cylindrical fast axis collimating lens 2, the Fresnel type cylindrical slow axis collimating lens 3, the aperture diaphragm 4 and the MEMS galvanometer scanning component 5, is diffusely reflected by an external measured object 6, sequentially passes through the third meniscus lens 12, the second meniscus lens 11, the first meniscus lens 10, the aspheric lens 9 and the optical filter 8, and finally enters the avalanche photodiode 7.
The specific structure and working principle of the MEMS galvanometer scanning assembly 5 are as follows:
As shown in fig. 9, the MEMS galvanometer scanning assembly includes a supporting substrate 1011, a fixed frame 109, a first electrode 101, a second electrode 1010, a first slow-axis support beam 102, a second slow-axis support beam 108, a balance frame 104, an electromagnetic driving coil 103, a first fast-axis support beam 105, a second fast-axis support beam 107, a mirror surface 106, and a driving permanent magnet 120;
The fixed frame 109, the first electrode 101, and the second electrode 1010 are mounted on the support substrate 1011; the first slow-axis support beam 102, the second slow-axis support beam 108, and the balance frame 104 are all disposed in the fixed frame 109; the electromagnetic driving coil 103, the first fast axis supporting beam 105 and the second fast axis supporting beam 107 are all positioned on the balance frame 104;
In a preferred embodiment, the mirror 106 is located in the middle of the MEMS galvanometer scanning assembly; the two ends of the reflecting mirror surface 106 are rotatably connected with the balance frame 104 through a first fast-axis supporting beam 105 and a second fast-axis supporting beam 107 respectively, specifically, the first fast-axis supporting beam 105 and the second fast-axis supporting beam 107 are arranged in parallel and are connected to the centers of the two ends of the reflecting mirror surface 106 respectively, and more specifically, the first fast-axis supporting beam 105 and the second fast-axis supporting beam 107 are arranged in a collinear manner. Two ends of the balance frame 104 are rotatably connected with the fixed frame 109 through a first slow-axis supporting beam 102 and a second slow-axis supporting beam 108 respectively; specifically, the first slow-axis support beam 102 and the second slow-axis support beam 108 are disposed in parallel and are responsible for connecting the balance frame 104 and the fixed frame 109, and more specifically, the first slow-axis support beam 102 and the second slow-axis support beam 108 are disposed in a collinear manner.
Two ends of the electromagnetic driving coil 103 are respectively supported by a first slow-axis supporting beam 102 and a second slow-axis supporting beam 108, and two ends of the electromagnetic driving coil 103 are respectively rotatably connected with a first electrode 101 and a second electrode 1010; that is, the two ends of the electromagnetic driving coil 103 are respectively connected to the first electrode 101 and the second electrode 1010 through the first slow-axis support beam 102 and the second slow-axis support beam 108, and the electromagnetic driving coil 103 is energized through the two electrodes. The electromagnetic driving coil 103 can bear alternating current and direct current to drive the balance frame to rotate, the number of turns is usually 15-30, and the material is high conductivity materials such as copper, gold and the like, which are manufactured through an electroplating process. Specifically, the electromagnetic driving coil is manufactured by an electroplating process, and the slow axis is scanned under the action of lorentz force when alternating current is introduced into the electromagnetic driving coil in an external magnetic field.
The driving permanent magnet 120 is mounted on the supporting substrate 1011 and is located below the reflecting mirror surface 106. An antireflective metal layer is present on the upper surface of the mirror surface 106. The metal layer is made of high-reflectivity materials such as silver, aluminum, gold and the like, and the types of the materials depend on the wavelength of laser for operating the vibrating mirror.
The support substrate 1011 includes a first support substrate 1101 and a second support substrate 1102; the first support substrate 1101 is located below the fixing frame 109; a second support substrate 1102 is positioned below the mirror surface 106; as shown in fig. 10, the supporting substrate 1102 can increase the rigidity of the reflecting mirror 106, and the supporting substrate 1102 is provided with a groove in the center for carrying the driving permanent magnet 120 to reduce dynamic deformation during scanning. Specifically, the permanent magnet 120 is fixed in a central groove of the supporting substrate 1102, and the permanent magnet has any one of the following structures: a single permanent magnet; two square permanent magnets; two cylindrical permanent magnets, a first cylindrical permanent magnet 1201 and a second cylindrical permanent magnet 1202, respectively. That is, the driving permanent magnet below the reflecting mirror surface may be one permanent magnet or two permanent magnets. When the driving permanent magnet is a permanent magnet, the magnetization direction is perpendicular to the fast axis supporting beam. When the driving permanent magnets are two permanent magnets, the two permanent magnets are arranged in parallel, and the magnetization directions are opposite and are perpendicular to the mirror surface.
The structure of the MEMS galvanometer scanning assembly 5 described above can also be understood as: the supporting substrate is arranged below the fixed frame and the reflecting mirror surface, the driving permanent magnet is arranged in a groove of the supporting substrate below the reflecting mirror surface, two ends of the reflecting mirror surface are connected to the balance frame through one group of supporting beams (fast axis), the balance frame is connected to the fixed frame through the other group of supporting beams (slow axis), and the two groups of supporting beams are orthogonally distributed and respectively responsible for fast axis scanning and slow axis scanning.
Fig. 11 shows a schematic diagram of the slow axis coil driving method in this example. The first electrode 101 and the second electrode 1010 are supplied with a slow-axis driving current, and the electromagnetic driving coil 103 is subjected to lorentz force in an external magnetic field shown by a dotted line in the figure, so as to drive the balance frame 104 and the reflecting mirror 106 to perform rotational scanning. ω in fig. 3 represents the direction of rotation and I slow represents the slow axis current.
Fig. 12 shows a schematic diagram of the fast axis moving magnet driving method in this example. An alternating current with the resonant frequency consistent with the fast axis is fed into the external driving coil 160, and the driving permanent magnet 120 is acted by an electromagnetic force, so that the reflecting mirror 106 is driven to rotate around the fast axis. In fig. 12, F1 and F2 represent forces, and I fast represents a fast axis current.
As shown in fig. 13, the MEMS galvanometer scanning assembly structure further includes a first permanent magnet 130, a second permanent magnet 140, a first yoke 1501, a second yoke 1502, an external driving coil 160, a fixed magnet post 170, and a nonmagnetic shell 180 for carrying all the above components; specifically, the non-magnetic tube housing 180 is used to fix the above-mentioned set of magnetic yokes, two permanent magnets, external driving coils and electromagnetic MEMS galvanometer. The nonmagnetic shell 180 is made of nonmagnetic materials such as aluminum alloy or titanium alloy.
Referring to fig. 14 and 15, the first yoke 1501 and the second yoke 1502 are interposed between a balance frame and a fast axis support beam; the magnetic field on the electromagnetic driving coil can be maximized, so that the driving voltage is reduced, and the power consumption of the system is reduced; specifically, the first yoke 1501 and the second yoke 1502 are respectively inserted in the gap between the balance frame 104 and the first fast-axis support beam 105 and the gap between the balance frame 104 and the second fast-axis support beam 107 in a protruding manner. The first and second yokes 1501, 1502 are symmetrically distributed about an axis formed by the first and second slow-axis support beams 102, 108.
As shown in fig. 14 and 15, the first permanent magnet 130 and the second permanent magnet 140 are disposed on the first yoke 1501 and the second yoke 1502, respectively; the magnetization directions of the first permanent magnet 130 and the second permanent magnet 140 are perpendicular to the contact surface, and the magnetization directions of the first permanent magnet 130 and the second permanent magnet 140 are opposite; it is also understood that the magnetizing directions of the two permanent magnets are opposite and perpendicular to the lower surfaces of the set of yokes.
Referring to fig. 12 and 15, the external driving coil 160 is sleeved outside the fixed magnetic pole 170; the external driving coil 160 is disposed right below the center of the reflecting mirror 106, and has a distance of 1.5-2 mm from the driving permanent magnet 120 in the supporting substrate, so as to provide a movement space of the reflecting mirror. When alternating current is supplied to the external driving coil, an alternating magnetic field is generated around the external driving coil, so that electromagnetic force is generated on the driving permanent magnet above the external driving coil to drive the reflecting mirror to rotate. As shown in fig. 15, the fixed magnetic pole 170 is inserted in the center of the external driving coil 160, and a part of the length of the fixed magnetic pole 170 extends out of the external driving coil 160. The fixed magnetic column is arranged in the center of the external driving coil, is made of paramagnetic materials such as iron or nickel, and can fix a magnetic field generated by the external driving coil on the upper side and the lower side of the fixed magnetic column, so that electromagnetic force on the upper driving permanent magnet is increased, and system power consumption is reduced. The whole body composed of the external driving coil 160 and the fixed magnetic pole 170 is arranged under the driving permanent magnet 120 by 1-2 mm, and the centers of the external driving coil and the fixed magnetic pole are aligned.
When the first permanent magnet 130 and the second permanent magnet 140 are selected to have dimensions of 15mm×4mm×6mm and a brand of N52, a distribution cloud of magnetic field intensity at this time is shown in fig. 16. As can be seen from the figure, the average magnetic field strength of the electromagnetic driving coil 103 is about 0.4T, and under the action of the current, the two ends of the coil are respectively acted by lorentz forces with opposite directions, so as to drive the balance frame 104 and the reflecting mirror 106 to rotate.
When the first cylindrical permanent magnet 1201 and the second cylindrical permanent magnet 1202 are selected to have a size of 1mm×1mm and a brand of N52, the external driving coil 160 has a size of 2mm in inner diameter, 6mm in outer diameter, 6mm in height, and 100mA in driving current, and a magnetic field intensity distribution cloud chart is shown in fig. 17. As can be seen, the magnetic field of the external driving coil 160 is fixed in the fixed magnetic pole 170, and has the same and opposite directions as the first cylindrical permanent magnet 1201 and the second cylindrical permanent magnet 1202, respectively, so that the external driving coil is subjected to opposite electromagnetic forces, thereby driving the mirror 106 to rotate.
The MEMS galvanometer scanning component 5 in this embodiment has the technical advantages of biaxial independent driving and the technical effect of biaxial no crosstalk:
A sinusoidal ac voltage U 1 =0.1 sin (1440 pi t) with a bias voltage of 0V, an amplitude of 0.1V, a frequency of 720Hz, and an initial phase of 0 is applied to the external driving coil 160, where t represents time, and the mirror surface 106 is shown to perform fast axis resonance scanning in the horizontal direction.
As shown in fig. 17, a fast axis resonant horizontal scan of an electromagnetic MEMS galvanometer system is shown. At this point the scan field is 20 deg., and there is no cross-talk angle in the direction of the vertical scan curve. As can be seen from the fast axis resonance horizontal scanning result, the invention can realize biaxial independent driving without crosstalk.
Specifically, the mirror surface size diameter of the MEMS galvanometer scanning component is 7.2mm, the mechanical rotation angle in two directions is +/-10 degrees, and the MEMS galvanometer scanning component is used for deflecting emergent light and then shooting the emergent light to a field of view and carrying out two-dimensional scanning.
The MEMS galvanometer scanning assembly is based on two electromagnetic driving technologies of a moving coil and a moving magnet, realizes double-shaft independent driving of an electromagnetic MEMS galvanometer, and eliminates mechanical crosstalk between two shafts. The driving permanent magnet is stuck to the center of the lower surface of the reflecting mirror surface, and a driving coil is arranged at the lower part to realize fast axis scanning; and electroplating a slow axis driving coil on the balance frame, and interpolating between the reflecting mirror surface and the balance frame by utilizing the magnetic yoke to maximize the magnetic field on the slow axis driving coil, thereby realizing quasi-static scanning of the slow axis under lower voltage driving. Specifically, the invention drives the reflection mirror surface to scan by arranging the slow-axis driving electromagnetic driving coil on the balance frame; the magnetic yoke of the external magnetic field is inserted between the fast axis and the balance frame, so that the magnetic field intensity around the slow axis driving electromagnetic driving coil is amplified, and low-power consumption driving slow axis quasi-static scanning is realized; meanwhile, an electromagnetic driving mode of a moving magnet is adopted, a driving permanent magnet and an external driving coil are arranged below the reflecting mirror surface, the reflecting mirror surface is driven to scan under the action of electromagnetic force, the electromagnetic driving coil is prevented from being manufactured around the reflecting mirror surface, and the influence of thermal deformation of the mirror surface is eliminated; the driving between the fast axis and the slow axis are mutually independent, and the mechanical crosstalk between the two axes is avoided.
The specific parameters, structure and working principle of the optical emission system are as follows:
The large-divergence angle laser emitted by the side-emitting semiconductor laser diode is collimated and homogenized in the sagittal and horizontal directions respectively through the Fresnel type cylindrical fast axis collimating lens and the Fresnel type cylindrical slow axis collimating lens, the aperture diaphragm is used for filtering stray light, and the MEMS galvanometer is used for reflecting the collimated laser and performing two-dimensional scanning.
Specifically, the edge-emitting laser light source component emits pulse laser with the center wavelength of 905nm, the pulse width is 100ns, the repetition frequency is 1kHz, the duty ratio is 0.1%, the divergence angle in the direction of a sagittal (parallel to a junction plane) is 9 degrees, the divergence in the direction of a meridional (perpendicular to the junction plane) is 25 degrees, and the peak power of the whole light source component is 75W.
As shown in fig. 3, the fresnel type cylindrical fast axis collimating lens 2 and the fresnel type cylindrical slow axis collimating lens 3 are both of a fresnel type with saw teeth and grooves on the surface, and the fresnel type cylindrical fast axis collimating lens 2 and the fresnel type cylindrical slow axis collimating lens 3 are perpendicular to each other. Specifically, the fresnel surface is cylindrical and symmetrical in the direction of the fast axis or the slow axis, and each groove has a different angle with the adjacent groove, so that the divergent light at the focal point of the lens is collimated into two approximately parallel rays. The base of the lens is rectangular, and two mutually perpendicular Fresnel cylindrical lens groups are adopted to respectively collimate and homogenize the light beams in two directions according to the characteristic that the divergence angles of the semiconductor laser beams in two directions are different.
The fresnel cylindrical fast axis collimating lens 2 converts meridional rays emitted from the semiconductor laser (i.e., the edge-emitting laser light source assembly) into quasi-parallel rays through a generatrix parallel to the fast axis direction of the laser beam, and can be regarded as a plate glass for the divergence angle of the meridional rays emitted from the semiconductor laser. The Fresnel type cylindrical slow axis collimating lens 3 changes the sagittal light emitted by the semiconductor laser into quasi-parallel light beams in the direction parallel to the slow axis of the laser beam through the generatrix, and can be regarded as plate glass for the divergence angle of the meridional light emitted by the semiconductor laser. Specifically, the pulse laser diffused by the edge-emitting laser light source component 1 is collimated by the Fresnel type cylindrical fast axis collimating lens 2 and the Fresnel type cylindrical slow axis collimating lens 3, the Fresnel type cylindrical fast axis collimating lens is parallel to the direction of the laser beam fast axis by a generatrix, and after passing through the Fresnel type cylindrical fast axis collimating lens, meridian rays of the diffused pulse laser become quasi-parallel rays, and the divergence angle of sagittal rays is unchanged; the Fresnel type cylindrical slow axis collimating lens is parallel to the direction of the slow axis of the laser beam through a generatrix, and after pulse laser passes through the Fresnel type cylindrical slow axis collimating lens, the sagittal light of the pulse laser is changed into quasi-parallel light beams, and the divergence angle of the meridional light is unchanged.
More specifically, as shown in FIG. 3, assuming that the edge-emitting laser is an ideal point, the divergence angle of the pulse laser is α, and the aspherical curve expression of the Fresnel cylindrical mirror isWhere c is the curvature and m is a nonlinear minor term, m being equal to or less than 4, preferably m being equal to 4.R is the radius of curvature, k is the conic coefficient, a m is the pitch coefficient, x and y are the horizontal and vertical coordinates, respectively, assuming the incident spot coordinates on the cylindrical mirror are (x 0,y0), the normal slope of the incident spot isΘ is the horizontal angle of the normal, and the simultaneous incidence position relationship equation is: x 0+d＝y0 tan alpha, where d is the distance from the light source to the cylindrical mirror. The incident spot coordinates (x 0,y0) can be solved by the positional relationship equation. Assuming that the coordinates of the outgoing light spot on the cylindrical mirror are (x 1,y1), the outgoing position relationship equation is: x 1＝L,y1＝y0 +l·tan β, where L is the fresnel cylindrical lens thickness and β is the divergence angle through the first refraction. According to fresnel's law of refraction, the set of two refraction equations is: n·sinβ=sinγ, where n is the refractive index of the fresnel cylindrical mirror and γ is the divergence angle after the second refraction (i.e., the divergence angle after collimation). The divergence angles beta and gamma of the first and second refraction can be solved by the refraction equation set, and finally the coordinates of the emergent light spot can be solved as (x 1,y1). Therefore, in summary, the divergence angle of the outgoing beam collimated by the fresnel cylindrical mirror is γ, and the beam radius is y 1.
Parameters such as a curvature radius R, a conical coefficient k, a pitch coefficient a m, a thickness L, a distance d, a refractive index n and the like of a fast axis cylindrical mirror and a Fresnel type cylindrical slow axis collimating lens are set as optimization variables, a beam divergence angle gamma and a beam radius y 1 are set as optimization targets, and the divergence angle and the beam radius of emergent pulse laser can be optimized to the minimum through iterative calculation by utilizing a damping least square method.
As shown in FIG. 4, the optimized light spot profile condition can be observed by simulating the observation surfaces at positions 10cm, 1m and 10m away from the two-dimensional MEMS galvanometer. At 10cm, the radius of the RMS light spot is 1.51mm in X direction and 3.35mm in Y direction; at 1m, the RMS spot radius is 2.93mm in the X direction and 10.35mm in the Y direction; at 10m, the RMS spot radius was 25.66mm in the X direction and 54.3549mm in the Y direction. Through calculation, the emergent laser with the divergence angle of 2.4mrad (0.14 degrees, the sagittal direction) multiplied by 5.2mrad (0.3 degrees, the meridian direction) is realized, and the collimation degree is improved by two orders of magnitude compared with the original collimation degree. Meanwhile, the experimental result at the distance of 10m is compared with the simulation result, the diameter of the RMS light spot at the position of 10m is about 6cm, the diameter of the RMS light spot is consistent with the simulation result, the result is compared with the result of 13.6cm of the light spot diameter of the conventional commercial scheme, and the diameter of the RMS light spot is reduced by more than one time.
The collimated pulse laser passes through an aperture diaphragm 4 and a MEMS galvanometer scanning component 5 to limit light and scan. The aperture diaphragm is used for limiting light beams and filtering stray light, and noise is prevented from being introduced by the stray light reflected by the MEMS galvanometer. The mirror surface size diameter of the two-dimensional MEMS galvanometer is 7.2mm, the mechanical rotation angle in two directions is +/-10 degrees, the two-dimensional MEMS galvanometer is used for deflecting emergent light and then shooting the emergent light to a view field for two-dimensional scanning, and finally the two-dimensional scanning with the optical rotation angle of +/-20 degrees can be realized.
The specific parameters, structure and working principle of the optical receiving system are as follows:
The aspherical lens 9 has negative power, the first meniscus lens 10 has positive power, the second meniscus lens 11 has positive power, and the third meniscus lens 12 has negative power.
The centers of the aspheric lens 9, the first meniscus lens 10, the second meniscus lens 11 and the third meniscus lens 12 are positioned on the same optical axis and fixed to preset distances which are respectively 1.116mm,4.267mm,6.783mm and 18.283mm by taking the APD photosurface as a reference origin; the aspherical lens 9, the first meniscus lens 10, the second meniscus lens 11 and the third meniscus lens 12 are adjusted in position and coupled by using a cage structure.
The avalanche photodiode 7 (APD) and the optical filter 8 form a photosensor with high gain for 905nm photons, and are used for converting optical signals into current signals, the effective photosurface is a square area with the length of 3mm multiplied by 3mm, the side length of pixels is 10um, and the number of pixels is 89984.
Specifically, as shown in fig. 5, the optical receiving lens group is improved based on a kuk three-split objective lens, which is a commonly used optical element and is commonly used for imaging and focal length adjustment in an optical system. The invention improves the spherical lens in the Cooks three-split objective lens into a combination of the meniscus lens, and adds an aspherical lens, thereby greatly reducing spherical aberration and improving imaging quality. The effective focal length of the optical receiving lens group is 4mm, the total length of the system is 19.3mm, and the entrance pupil diameter is 5mm.
Specifically, the side length of the avalanche photodiode 7 is 3mm, the aspheric lens 9 has negative focal power, the first meniscus lens 10, the second meniscus lens 11 have positive focal power, and the third meniscus lens 12 has negative focal power. The aspheric lens, the first meniscus lens, the second meniscus lens and the third meniscus lens are centered on the same optical axis and fixed to a preset distance. The X-direction angles of the 6 view field rays are 0 degrees, and the Y-direction angles are 0 degrees, 4 degrees, 8 degrees, 12 degrees, 16 degrees and 20 degrees respectively. The 6 light rays form a light spot with the diameter of 2.8mm after passing through the receiving system, and the diameter of the light spot is smaller than the side length of the avalanche photodiode, so that all the light rays can be converted into electrical signals.
As shown in fig. 6, the light rays with different object angles pass through the receiving optical system, and the light spot form on the imaging surface presents diffuse spots due to the aberration and diffraction effect of the optical system, and smaller diffuse spots mean better imaging quality. In the optical receiving system, along with the increase of the field angle range of the light beam, the size of the diffuse spot is gradually increased, 0 degree, 4 degrees, 8 degrees, 12 degrees, 16 degrees and 20 degrees, the corresponding light spot RMS radius of the light beam is respectively 2.5um, 2.8um,4.0um, 5.8um, 8.3um and 7.1um, and the light spot RMS radius is smaller than the side length of a 10um pixel. According to sampling law, when the radius of the diffuse spot is smaller than the side length of a pixel, the highest resolution of the detector can be achieved, so that the optical lens group meets the working requirement of the MEMS laser radar.
As shown in fig. 7, after the light beam passes through the optical receiving system, a certain deviation is generated between the actual image height and the paraxial image height, the left image shows the image height deviation generated by meridian light and sagittal light in the positive direction of the Y axis, the right image shows the distortion value generated in the positive direction of the Y axis, and the optical system with the absolute value of distortion less than 4% is generally considered to be in the normal aberration range.
As shown in fig. 8, the Modulation Transfer Function (MTF) represents the response capability of the optical system to different spatial frequencies, i.e., contrast-resolution values, reflecting the transfer capability of the optical system to details. For the object light sources with different incidence angles, the meridian plane and the sagittal plane of the object light sources have slower attenuation of transfer functions (contrast ratios) under the space frequency (resolution ratio) within 200mm, which indicates that the imaging quality is good under the space frequency within 200mm, and the information quantity transmitted by the optical system is more.
The invention adopts an optimized Fresnel double-cylindrical lens scheme to perform collimation shaping and homogenization treatment on pulse laser emitted by a semiconductor edge-emitting laser, greatly compresses the divergence angle of the pulse laser in the meridian and sagittal directions, and adopts a novel MEMS vibrating mirror which is free from crosstalk and is driven independently by double shafts, thereby realizing the purpose of improving the measuring distance and the ranging precision. The invention is improved based on the traditional Cookie three-split objective lens scheme, on one hand, a meniscus lens is used for replacing a convex lens to focus small light spots, and the spherical aberration is obviously reduced while the angle of view is increased; on the other hand, an aspheric lens is added, focusing can be carried out according to the incident position and angle of light rays, and imaging quality is improved.
The invention provides an optical transceiver system for an MEMS laser radar with high precision, small volume and large view field, which is based on an optimized Fresnel type cylindrical lens scheme, performs collimation shaping and homogenization treatment on a pulse laser with a large divergence angle, realizes 2.4mrad multiplied by 5.2mrad emergent laser, improves the collimation degree by two orders of magnitude, solves the technical problem of the large divergence angle of a semiconductor laser, and is beneficial to improving the measurement distance, the scanning precision and the point cloud density by being matched with a novel MEMS galvanometer which is free of crosstalk and is driven by double shafts independently; the invention is improved based on the traditional Cooks three-separation objective lens scheme, uses the meniscus lens to replace the convex lens for focusing small light spots, obviously reduces spherical aberration while increasing the angle of view, and adds an aspheric lens, so that focusing can be performed according to the incident position and angle of light, the imaging quality is further improved, the optical angle of view of +/-20 degrees is finally realized, the imaging characteristics of low aberration, small distortion and high resolution are realized, and a solution is provided for the MEMS laser radar with a large mechanical scanning angle.
The invention can reduce the volume of the optical receiving and transmitting system, reduce the manufacturing cost of the optical lens through the optimal design, effectively solve the problems of poor laser collimation, low scanning precision and difficult return light focusing in the MEMS laser radar, reduce the optical aberration of the lens through the optimal design, improve the laser collimation degree, and realize a large field angle while limiting the optical receiving and transmitting caliber.
Aiming at the problems of large divergence angle of emitted laser and small view angle of recovered light beams in the existing receiving and transmitting system, the invention realizes the receiving and transmitting functions of the laser radar with the divergence angle of 2.4mrad (0.14 degrees, sagittal direction) multiplied by 5.2mrad (0.3 degrees, meridional direction) and the view angle of +/-20 degrees by optimizing the design.
The invention adopts a special collimation and homogenization scheme and a novel MEMS vibrating mirror which is free from crosstalk and independently driven by double shafts, and simultaneously improves the measurement distance, the scanning precision and the point cloud density; and a meniscus lens is adopted for focusing small light spots, an aspheric lens is added, the spherical aberration is obviously reduced while the field angle is increased, the imaging quality is improved, and the optical field angle of +/-20 degrees is realized. The invention is suitable for carrying out collimation shaping and homogenization treatment on the semiconductor pulse laser, effectively solves the problem of poor scanning precision caused by large light spots and mechanical crosstalk by matching with the novel MEMS galvanometer design, and simultaneously designs a unique optical receiving system, thereby being capable of obviously increasing the receiving field angle under the condition of not reducing the imaging quality.
In the description of the present application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application.
The foregoing describes specific embodiments of the present application. It is to be understood that the application is not limited to the particular embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without affecting the spirit of the application. The embodiments of the application and the features of the embodiments may be combined with each other arbitrarily without conflict.
Claims (10)
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