阅读说明：本技术 主动照明关联成像系统和主动照明关联成像方法 (Active illumination-associated imaging system and active illumination-associated imaging method ) 是由 不公告发明人 于 2020-06-09 设计创作，主要内容包括：本发明涉及一种主动照明关联成像系统,包括光源模块、分束模块、检测模块、空间光调制模块及接收模块；光源模块发射激光光束；分束模块将激光光束进行分束,形成第一光束及第二光束；检测模块设置于从分束模块出射的第一光束的光路上,检测模块根据第一光束检测激光光束的发射功率；第二光束照射至目标物体,并经目标物体反射形成反射光束；空间光调制模块接收反射光束,并对反射光束进行空间强度调制,形成调制光束；接收模块设置于空间光调制模块出射光线的光路上,接收调制光束并探测调制光束的强度,得到待测信号；接收模块还根据发射功率对待测信号进行校正,得到校正信号,接收模块还用于基于校正信号获得目标物体的图像。(The invention relates to an active illumination correlation imaging system, which comprises a light source module, a beam splitting module, a detection module, a spatial light modulation module and a receiving module, wherein the beam splitting module is used for splitting a beam; the light source module emits a laser beam; the beam splitting module splits the laser beam to form a first beam and a second beam; the detection module is arranged on a light path of a first light beam emitted from the beam splitting module and is used for detecting the emission power of the laser light beam according to the first light beam; the second light beam irradiates the target object and is reflected by the target object to form a reflected light beam; the spatial light modulation module receives the reflected light beam and performs spatial intensity modulation on the reflected light beam to form a modulated light beam; the receiving module is arranged on a light path of the emergent light of the spatial light modulation module, receives the modulated light beam and detects the intensity of the modulated light beam to obtain a signal to be detected; the receiving module is also used for correcting the signal to be detected according to the transmitting power to obtain a correction signal, and the receiving module is also used for obtaining an image of the target object based on the correction signal.)

1. An active illumination correlation imaging system, comprising:

the light source module is used for emitting laser beams;

the beam splitting module is used for splitting the laser beam to form a first beam and a second beam;

the detection module is arranged on a light path of a first light beam emitted from the beam splitting module and is used for detecting the emission power of the laser light beam according to the first light beam;

the second light beam irradiates a target object and is reflected by the target object to form a reflected light beam;

the spatial light modulation module is used for receiving the reflected light beam and carrying out spatial intensity modulation on the reflected light beam to form a modulated light beam;

the receiving module is arranged on a light path of the emergent light of the spatial light modulation module and used for receiving the modulated light beam and detecting the intensity of the modulated light beam to obtain a signal to be detected;

the receiving module is electrically connected with the detection module and is further used for correcting the signal to be detected according to the transmitting power to obtain a correction signal, and the receiving module is further used for obtaining the image of the target object based on the correction signal.

2. The active illumination correlation imaging system of claim 1, wherein the receiving module comprises a detector unit, a signal processing unit, and a control unit;

the detector unit is arranged on a light path of the emergent light of the spatial light modulation module and used for receiving the modulated light beam and detecting the intensity of the modulated light beam to obtain a signal to be detected;

the signal processing unit is respectively electrically connected with the detector unit, the control unit and the detection module and is used for controlling the control unit to send out a modulation signal;

the control unit is electrically connected with the spatial light modulation module and is used for controlling the spatial light modulation module according to the modulation signal;

the signal processing unit is further used for receiving the transmitting power and the signal to be detected, and correcting the signal to be detected according to the transmitting power to obtain a correction signal;

the signal processing unit is also used for obtaining the image of the target object based on the correction signal and the modulation signal.

3. The active illumination correlation imaging system of claim 1, wherein the light source module comprises:

a laser for emitting a laser beam; and

and the lens unit is arranged on the light path of the laser beam and is used for shaping and collimating the laser beam.

4. The active illumination correlation imaging system of claim 1, wherein the beam splitting module comprises a beam splitting prism or a beam splitting plate.

5. The active illumination correlation imaging system of claim 1 further comprising:

and the emission lens is arranged on the light path of the second light beam and is used for receiving the second light beam and projecting the second light beam to the target object.

6. The active illumination correlation imaging system of claim 5, wherein the emission lens comprises a first single lens disposed on the optical path of the second light beam for receiving the second light beam and projecting the second light beam to the target object; or

The emission lens comprises a first cemented lens, the first cemented lens is arranged on the light path of the second light beam and is used for receiving the second light beam and projecting the second light beam to the target object; or

The emission lens comprises a first lens group which comprises a plurality of lenses, and the first lens group is arranged on the light path of the second light beam and used for receiving the second light beam and projecting the second light beam to the target object.

7. The active illumination correlation imaging system of claim 1 further comprising:

and the receiving lens is used for receiving the reflected light beam and is also used for projecting the reflected light beam to the spatial light modulation module.

8. The active illumination correlation imaging system of claim 7, wherein the receiving lens comprises a second single lens for receiving the reflected light beam, the second single lens further for projecting the reflected light beam to the spatial light modulation module; or

The receiving lens comprises a second cemented lens for receiving the reflected light beam, the second cemented lens further for projecting the reflected light beam to the spatial light modulation module; or

The receiving lens includes a second lens group including a plurality of lenses, the second lens group being configured to receive the reflected light beam, the second lens group being further configured to project the reflected light beam to the spatial light modulation module.

9. The active illumination correlation imaging system of claim 1, wherein the spatial light modulation module comprises a digital micromirror array disposed on the light path of the light emitted from the receiving lens for receiving the reflected light beam and spatially intensity modulating the reflected light beam to form a modulated light beam; or

The spatial light modulation module comprises an absorption type modulator, the absorption type modulator is arranged on a light path of light rays emitted from the receiving lens and is used for receiving the reflected light beams and carrying out spatial intensity modulation on the reflected light beams to form modulated light beams, and the absorption type modulator comprises a superconducting material module.

10. An active illumination correlation imaging method, comprising:

emitting a laser beam;

splitting the laser beam to form a first beam and a second beam;

detecting the emission power of the laser beam according to the first beam;

irradiating the second light beam to a target object, and reflecting the second light beam by the target object to form a reflected light beam;

receiving the reflected light beam and performing spatial intensity modulation on the reflected light beam to form a modulated light beam;

receiving the modulated light beam and detecting the intensity of the modulated light beam to obtain a signal to be detected;

and correcting the signal to be detected according to the transmitting power to obtain a correction signal, and obtaining an image of the target object based on the correction signal.

Technical Field

The invention relates to the technical field of optical imaging, in particular to an active illumination associated imaging system and an active illumination associated imaging method.

Background

Ghost imaging is a novel imaging technology, and an image of an object is restored through a correlation algorithm or a compressed sensing method and the like. Compared with the traditional imaging mode, ghost imaging has strong anti-interference characteristic, high-sensitivity detection characteristic, wide-view imaging characteristic and the like, and has shown great application potential in the fields of astronomical observation, remote sensing imaging, military investigation, medical imaging and the like.

In the existing ghost imaging mode, the resolving of the object space information is realized by measuring the signal fluctuation of a detector. If the emitting power of the light source is unstable, the shaking of the light source can influence the accuracy of the calculation of the object space information, so that the imaging quality of the object is influenced.

Disclosure of Invention

Therefore, it is necessary to provide an active illumination-related imaging system and an active illumination-related imaging method for solving the problems that the emitting power of the light source is unstable and the jitter of the light source affects the accuracy of object spatial information calculation.

An active illumination correlation imaging system, comprising:

the light source module is used for emitting laser beams;

the beam splitting module is used for splitting the laser beam to form a first beam and a second beam;

the detection module is arranged on a light path of a first light beam emitted from the beam splitting module and is used for detecting the emission power of the laser light beam according to the first light beam;

the second light beam irradiates a target object and is reflected by the target object to form a reflected light beam;

the spatial light modulation module is used for receiving the reflected light beam and carrying out spatial intensity modulation on the reflected light beam to form a modulated light beam;

the receiving module is arranged on a light path of the emergent light of the spatial light modulation module and used for receiving the modulated light beam and detecting the intensity of the modulated light beam to obtain a signal to be detected;

the receiving module is electrically connected with the detection module and is further used for correcting the signal to be detected according to the transmitting power to obtain a correction signal, and the receiving module is further used for obtaining the image of the target object based on the correction signal.

According to the active illumination correlation imaging system, the emission power of the laser beam is detected in real time, the signal to be detected is corrected according to the emission power to obtain the correction signal, and the image of the target object is obtained based on the correction signal, so that the influence of unstable power of the laser beam on the imaging calculation of the target object can be reduced, the imaging calculation accuracy of the target object is improved, and the imaging quality of the target object is improved.

In one embodiment, the receiving module comprises a detector unit, a signal processing unit and a control unit;

the detector unit is arranged on a light path of the emergent light of the spatial light modulation module and used for receiving the modulated light beam and detecting the intensity of the modulated light beam to obtain a signal to be detected;

the signal processing unit is respectively electrically connected with the detector unit, the control unit and the detection module and is used for controlling the control unit to send out a modulation signal;

the control unit is electrically connected with the spatial light modulation module and is used for controlling the spatial light modulation module according to the modulation signal;

the signal processing unit is further used for receiving the transmitting power and the signal to be detected, and correcting the signal to be detected according to the transmitting power to obtain a correction signal;

the signal processing unit is also used for obtaining the image of the target object based on the correction signal and the modulation signal.

In one embodiment, the light source module includes:

a laser for emitting a laser beam; and

and the lens unit is arranged on the light path of the laser beam and is used for shaping and collimating the laser beam.

In one embodiment, the beam splitting module comprises a beam splitting prism or a beam splitting plate.

In one embodiment, the active illumination correlation imaging system further comprises:

and the emission lens is arranged on the light path of the second light beam and is used for receiving the second light beam and projecting the second light beam to the target object.

In one embodiment, the emission lens comprises a first single lens, which is arranged on the optical path of the second light beam and is used for receiving the second light beam and projecting the second light beam to the target object; or

The emission lens comprises a first cemented lens, the first cemented lens is arranged on the light path of the second light beam and is used for receiving the second light beam and projecting the second light beam to the target object; or a

The emission lens comprises a first lens group which comprises a plurality of lenses, and the first lens group is arranged on the light path of the second light beam and used for receiving the second light beam and projecting the second light beam to the target object.

In one embodiment, the active illumination correlation imaging system further comprises:

and the receiving lens is used for receiving the reflected light beam and is also used for projecting the reflected light beam to the spatial light modulation module.

In one embodiment, the receiving lens comprises a second single lens for receiving the reflected light beam, and the second single lens is further used for projecting the reflected light beam to the spatial light modulation module; or

The receiving lens comprises a second cemented lens for receiving the reflected light beam, the second cemented lens further for projecting the reflected light beam to the spatial light modulation module; or a

The receiving lens includes a second lens group including a plurality of lenses, the second lens group being configured to receive the reflected light beam, the second lens group being further configured to project the reflected light beam to the spatial light modulation module.

In one embodiment, the spatial light modulation module includes a digital micromirror array disposed on an optical path of the light emitted from the receiving lens, and configured to receive the reflected light beam and perform spatial intensity modulation on the reflected light beam to form a modulated light beam; or

The spatial light modulation module comprises an absorption type modulator, the absorption type modulator is arranged on a light path of light rays emitted from the receiving lens and is used for receiving the reflected light beams and carrying out spatial intensity modulation on the reflected light beams to form modulated light beams, and the absorption type modulator comprises a superconducting material module.

An active illumination correlation imaging method, comprising:

emitting a laser beam;

splitting the laser beam to form a first beam and a second beam;

detecting the emission power of the laser beam according to the first beam;

irradiating the second light beam to a target object, and reflecting the second light beam by the target object to form a reflected light beam;

receiving the reflected light beam and performing spatial intensity modulation on the reflected light beam to form a modulated light beam;

receiving the modulated light beam and detecting the intensity of the modulated light beam to obtain a signal to be detected;

and correcting the signal to be detected according to the transmitting power to obtain a correction signal, and obtaining an image of the target object based on the correction signal.

Drawings

FIG. 1 is a schematic diagram of an active illumination correlation imaging system in one embodiment provided herein;

FIG. 2 is a schematic diagram of an active illumination correlation imaging system in one embodiment provided herein;

FIG. 3 is a schematic diagram of an active illumination correlation imaging system in one embodiment provided herein;

fig. 4 is a schematic structural diagram of an active illumination correlation imaging system in an embodiment provided in the present application.

Detailed Description

To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present application are given in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

In active illumination ghost imaging, the resolution of object spatial information is achieved by measuring the signal fluctuations of the detector. In the solution of the object spatial information, the setting matrix of the spatial light modulator is I_i(x, y), the intensity value obtained by each measurement of the detector is S_iWhere i represents the number of samples and N is the total number of measurements. One of the second-order correlation algorithms for resolving the object space information can be given by the following equation:

therefore, when the emitting power of the light source is unstable, the light intensity irradiated on the object is influenced, and the intensity value measured by the detector is further influenced, so that the calculation of the object space information is influenced, namely the imaging image quality of the object is influenced.

Referring to fig. 1, an active illumination correlation imaging system according to an embodiment of the present disclosure includes a light source module 10, a beam splitting module 20, a detection module 30, a spatial light modulation module 40, and a receiving module 50. The light source module 10 is used to emit a laser beam. The beam splitting module 20 is configured to split the laser beam to form a first beam and a second beam. The detection module 30 is disposed on an optical path of the first light beam emitted from the beam splitting module 20, and the detection module 30 is configured to detect the emission power of the laser light beam according to the first light beam. The second light beam is irradiated to the target object 100 and reflected by the target object 100 to form a reflected light beam. The spatial light modulation module 40 is configured to receive the reflected light beam and perform spatial intensity modulation on the reflected light beam to form a modulated light beam. The receiving module 50 is disposed on a light path of the light emitted from the spatial light modulation module 40, and is configured to receive the modulated light beam and detect an intensity of the modulated light beam to obtain a signal to be detected. The receiving module 50 is electrically connected to the detecting module 30, and is further configured to correct the signal to be detected according to the transmission power to obtain a correction signal, and the receiving module 50 is further configured to obtain an image of the target object 100 based on the correction signal.

Referring to fig. 2, in one embodiment, the light source module 10 includes a laser 11 and a lens unit 12. The laser 11 is used to emit a laser beam. The lens unit 12 is disposed on the optical path of the laser beam, and is configured to shape and collimate the laser beam. The lens unit 12 may be a lens assembly, a single lens with a single aperture, a lens group, a plurality of cylindrical mirrors, or a plurality of spherical mirrors. Since the laser beam emitted by the laser 11 may be relatively divergent, the lens unit 12 performs spatial shaping, and thus, an efficient collimating and shaping effect can be achieved. Thus, the lens unit 12 projects the laser beam after the shaping and collimating processes to the beam splitting module 20.

In one embodiment, the beam splitting module 20 includes a beam splitting prism, a beam splitting plate, or a beam splitting device formed by any combination of the beam splitting prism, the beam splitting plate, and the beam splitting device, and is configured to split the laser beam to form a first beam and a second beam.

In one embodiment, the detection module 30 is a photodetector, which may be one of a single pixel detector, an avalanche photodiode, a charge coupled device, a complementary metal oxide semiconductor, and a multi-pixel photon counter.

Referring to FIG. 3, in one embodiment, the active illumination correlation imaging system further includes an emission lens 60. The emission lens 60 is disposed on an optical path of the second light beam, and the emission lens 60 is configured to receive the second light beam and project the second light beam to the target object 100.

In one embodiment, the emission lens 60 includes a first single lens disposed on the optical path of the second light beam for receiving and projecting the second light beam to the target object 100. Alternatively, the emission lens 60 includes a first cemented lens disposed on the optical path of the second light beam for receiving and projecting the second light beam to the target object 100. Alternatively, the emission lens 60 includes a first lens group including a plurality of lenses, and the first lens group is disposed on the optical path of the second light beam and is used for receiving the second light beam and projecting the second light beam to the target object 100.

In one embodiment, the active illumination correlation imaging system further includes a receiving lens 70. The receiving lens 70 is used for receiving the reflected light beam, and the receiving lens 70 is also used for projecting the reflected light beam to the spatial light modulation module 40.

In one embodiment, the receiving lens 70 includes a second single lens for receiving the reflected light beam and for projecting the reflected light beam to the spatial light modulation module 40. Alternatively, the receiving lens 70 includes a second cemented lens for receiving the reflected light beam, and the second cemented lens is also used for projecting the reflected light beam to the spatial light modulation module 40. Alternatively, the receiving lens 70 includes a second lens group including a plurality of lenses, the second lens group being configured to receive the reflected light beam, and the second lens group being further configured to project the reflected light beam to the spatial light modulation module 40.

The first single lens, the first cemented lens and/or the first lens group are made of metamaterial, and the second single lens, the second cemented lens and/or the second lens group are made of metamaterial. Any combination of the first single lens, the first cemented lens and the first lens group in the transmitting lens 60 and the second single lens, the second cemented lens and the second lens group in the receiving lens 70 can be performed, which is not limited in the drawings of the present application.

The spatial light modulation module 40 may modulate a certain parameter of the light field by the spatial light modulation unit under active control. In one embodiment, the spatial light modulation module 40 modulates the spatial intensity of the reflected light beam, so as to write the predetermined information into the light wave for the purpose of light wave modulation. The spatial light modulation module 40 may be configured to receive the reflected light beam and spatially intensity modulate the reflected light beam to form a modulated light beam. It is to be understood that the spatial light modulation device in the spatial light modulation module 40 is not particularly limited in the present application as long as it can emit a modulated light beam required for ghost imaging. Specifically, the Spatial Light modulation module 40 may be a digital micro-mirror array, an acousto-optic deflector, or a metamaterial (which may be a Light-manipulating metamaterial), and the Spatial Light modulation module 40 may further include a reflective Spatial Light Modulator (SLM) or an absorption Modulator.

In one embodiment, the spatial light modulation module 40 comprises a digital micromirror array disposed on the light path of the light emitted from the receiving lens 70 for receiving the reflected light beam and spatially intensity modulating the reflected light beam to form a modulated light beam. A digital micromirror array is a light modulation device consisting of an array of micron-sized aluminum mirrors, each micromirror having only two states, on and off (i.e., +12 and-12 degrees rotated about its diagonal), that can modulate the amplitude of light specifically. In the present embodiment, the reflected light beam emitted from the receiving lens 70 is spatially intensity modulated by the digital micromirror array to form a modulated light beam. In one embodiment, a preset number of micromirrors on the digital micromirror array may be flipped by +12 ° for each measurement, so that the modulated light is rotated by 24 ° and reflected to the receiving module 50. It can be understood that the digital micromirror array has the advantages of full digitalization and high image quality, and can realize accurate spatial intensity modulation of the reflected light beam, thereby ensuring the imaging quality of ghost imaging.

In one embodiment, spatial light modulation module 40 comprises an absorption modulator disposed in the optical path of the light exiting receiving lens 70 for receiving the reflected light beam and spatially intensity modulating the reflected light beam to form a modulated light beam, wherein the absorption modulator comprises a superconducting material module. In one embodiment, the spatial light modulation module 40 may further include one of any spatial light modulators, such as a low temperature LCOS spatial light modulator, a transmissive spatial light modulator, and the like, and may adaptively adjust the optical path structure according to the type of the spatial light modulator. It should be noted that the present application does not specifically limit the type of the spatial light modulator included in the spatial light modulation module 40, and it is within the scope of the present application as long as the spatial intensity modulation of the laser beam emitted by the light source module 10 to form a modulated beam can be achieved.

Referring to fig. 4, in one embodiment, the receiving module 50 includes a detector unit 51, a signal processing unit 52, and a control unit 53. The detector unit 51 is disposed on a light path of the light emitted from the spatial light modulation module 40, and is configured to receive the modulated light beam and detect an intensity of the modulated light beam to obtain a signal to be detected. The signal processing unit 52 is electrically connected to the detector unit 51, the control unit 53 and the detection module 30, respectively, and is configured to control the control unit 53 to send out a modulation signal. The control unit 53 is electrically connected to the spatial light modulation module 40, and is configured to control the spatial light modulation module 40 according to the modulation signal. The signal processing unit 52 is further configured to receive the transmission power and the signal to be detected, and correct the signal to be detected according to the transmission power to obtain a corrected signal. The signal processing unit 52 is also used to obtain an image of the target object 100 based on the correction signal and the modulation signal. Specifically, the signal processing unit 52 performs calculation (correlation operation, compressed sensing algorithm, or the like) on the correction signal and the modulation signal to obtain an image of the target object 100. The signal processing unit 52 may be a micro control unit 53 or a computer or the like. Compared with the traditional geometric imaging mode, the ghost imaging has the advantages of high sensitivity, low cost and the like, and can be applied to the fields of remote sensing, investigation, exploration and the like.

The signal to be detected can be corrected according to the emission power of the laser beam, so that the imaging quality of the object can be improved, and the detection error of the detector unit 51 caused by the unstable power of the laser beam emitted by the light source module 10 can be avoided.

If the transmission power detected by the detection module 30 is denoted by Ri and the signal to be detected by the detector unit 51 is denoted by Si, the correction signal is: si ═ Si/Ri, and the imaging calculation is performed with the corrected correction signal Si'.

In one embodiment, the detector unit 51 may be one of a single pixel detector, an avalanche photodiode, a charge coupled device, a complementary metal oxide semiconductor, and a multi-pixel photon counter. The single pixel detector may be adapted to indirect imaging without an array detector, which in combination with the spatial light modulation module 40 may replace the detector array in conventional imaging schemes. In this embodiment, the avalanche photodiode can also amplify a signal to be detected, so as to improve the sensitivity of detection. The charge coupled device, the avalanche photodiode and the complementary metal oxide semiconductor sensor have the function of converting optical signals into electric signals, so that the charge coupled device, the avalanche photodiode and the complementary metal oxide semiconductor sensor can be used as detectors to convert modulated light beams into signals to be measured. In addition, other devices having a function of converting an optical signal into an electrical signal may also be used as the detector unit 51, and the implementation of the detector unit 51 is not specifically limited in the present invention.

In one embodiment, the detector unit 51 may include a filter for performing a filtering process on the signal to be measured and transmitting the filtered signal to be measured to the signal processing unit 52. It can be understood that the signal to be measured output by the detector unit 51 includes a common-mode dc component and a noise signal, and therefore, the signal to be measured needs to be filtered by a filter to eliminate the common-mode dc component and the high-frequency signal in the signal to be measured, so as to improve the signal-to-noise ratio of the signal to be measured.

In one embodiment, the filter is a passive filter. It can be understood that the passive filter, also called as LC filter, is a filter circuit formed by using the combination design of inductor, capacitor and resistor, can filter out a certain or multiple harmonics, and has the advantages of simple structure, low cost, high operation reliability, low operation cost, etc., so the passive filter adopted in the embodiment is beneficial to simplifying the structural design of the laser radar system and reducing the production cost. It is to be understood that the filter may also be an active filter, and the present embodiment is not limited to the type of the filter.

The active illumination associated imaging system provided in the above embodiment detects the emission power of the laser beam in real time, corrects the signal to be detected according to the emission power to obtain the correction signal, and obtains the image of the target object 100 based on the correction signal, so that the influence of unstable power of the laser beam on the imaging calculation of the target object 100 can be reduced, the accuracy of the imaging calculation of the target object 100 is improved, and the imaging quality of the target object 100 is improved.

In one embodiment, the present application provides an active illumination correlation imaging method comprising:

emitting a laser beam;

splitting a laser beam to form a first beam and a second beam;

detecting the emission power of the laser beam according to the first beam;

irradiating the second light beam to the target object 100, and reflecting the second light beam by the target object 100 to form a reflected light beam;

receiving a reflected light beam, and performing spatial intensity modulation on the reflected light beam to form a modulated light beam;

receiving the modulated light beam and detecting the intensity of the modulated light beam to obtain a signal to be detected;

and correcting the signal to be detected according to the transmitting power to obtain a correction signal, and obtaining an image of the target object 100 based on the correction signal.

The active illumination associated imaging method provided in the above embodiment detects the emission power of the laser beam in real time, corrects the signal to be detected according to the emission power to obtain the correction signal, and obtains the image of the target object 100 based on the correction signal, so that the influence of unstable power of the laser beam on the imaging calculation of the target object 100 can be reduced, and the imaging quality of the target object 100 can be improved.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.