阅读说明：本技术 一种激光测距与主动照明复合探测系统及探测方法 (Laser ranging and active lighting composite detection system and detection method ) 是由 潘浩 胡黎明 武春风 李强 宋磊 张贵清 彭小康 熊准 李梦庆 于 2020-11-26 设计创作，主要内容包括：本发明涉及一种激光测距与主动照明复合探测系统及探测方法,其包括：激光发射装置,其用于产生第一激光束,且所述激光发射装置内设有第一分光装置,所述第一分光装置用于将所述第一激光束分为射向探测目标的照明光和第一测距光；测控子系统,其用于根据照明光的反射光和第一测距光计算快门开启时间和快门持续时间；成像子系统,其用于接收照明光的反射光并根据所述快门开启时间和快门持续时间对探测目标成像。本发明可以解决相关技术中目标照明系统和激光测距系统独立布局引起的光轴不共线问题,保证系统的实时性,提高目标成像的精确度。(The invention relates to a laser ranging and active lighting composite detection system and a detection method, wherein the detection method comprises the following steps: the laser detection device comprises a laser emitting device, a first light splitting device and a second light splitting device, wherein the laser emitting device is used for generating a first laser beam, the first light splitting device is arranged in the laser emitting device and is used for splitting the first laser beam into illumination light and first distance measuring light which are emitted to a detection target; the measurement and control subsystem is used for calculating the shutter opening time and the shutter duration time according to the reflected light of the illuminating light and the first ranging light; and the imaging subsystem is used for receiving the reflected light of the illumination light and imaging the detection target according to the shutter opening time and the shutter duration. The invention can solve the problem that optical axes are not collinear caused by independent layout of the target illumination system and the laser ranging system in the related technology, ensure the real-time performance of the system and improve the accuracy of target imaging.)

1. A laser ranging and active illumination composite detection system, comprising:

the laser detection device comprises a laser emitting device, a first light splitting device and a second light splitting device, wherein the laser emitting device is used for generating a first laser beam, the first light splitting device is arranged in the laser emitting device and is used for splitting the first laser beam into illumination light and first distance measuring light which are emitted to a detection target;

the measurement and control subsystem is used for calculating the shutter opening time and the shutter duration time according to the reflected light of the illuminating light and the first ranging light;

and the imaging subsystem is used for receiving the reflected light of the illumination light and imaging the detection target according to the shutter opening time and the shutter duration.

2. The laser ranging and active illumination composite detection system of claim 1, further comprising:

an optical receiving device for receiving reflected light of the illumination light;

a second light splitting means for splitting the illumination light from the optical receiving means into imaging light and second ranging light directed to an imaging subsystem;

the measurement and control subsystem is used for receiving the first distance measuring light and the second distance measuring light and calculating the shutter opening time and the shutter duration time according to the first distance measuring light and the second distance measuring light;

the imaging subsystem is used for receiving the imaging light and imaging a detection target according to the shutter opening time and the shutter duration.

3. The laser ranging and active illumination composite detection system of claim 1, wherein:

the measurement and control subsystem and the imaging subsystem respectively comprise an optical receiving device for receiving reflected light of illumination light;

the optical receiving device of the measurement and control subsystem is used for converting the received reflected light of the illuminating light into second ranging light, and the optical receiving device of the imaging subsystem is used for converting the received reflected light of the illuminating light into imaging light;

the measurement and control subsystem is used for calculating the shutter opening time and the shutter duration time according to the first distance measuring light and the second distance measuring light;

the imaging subsystem is used for receiving the imaging light and imaging a detection target according to the shutter opening time and the shutter duration.

4. The laser ranging and active illumination composite detection system of claim 1, wherein the measurement and control subsystem comprises a photoelectric conversion unit and a signal processing unit;

the photoelectric conversion unit is used for converting the first ranging light into an initial electric signal and converting the received reflected light of the illumination light into a termination electric signal;

the signal processing unit is used for calculating the shutter opening time according to the starting electric signal and the stopping electric signal.

5. The laser ranging and active illumination composite detection system of claim 4 wherein said signal processing unit comprises an amplifying and shaping circuit;

the amplifying and shaping circuit is connected with the photoelectric conversion unit and is used for converting the starting electric signal into a starting pulse voltage signal and converting the stopping electric signal into a stopping pulse voltage signal.

6. The laser ranging and active illumination composite detection system of claim 5, wherein the signal processing unit comprises:

the comparison module is used for determining a trigger pulse according to the starting pulse voltage signal and the ending pulse voltage signal;

a calculating module for calculating the shutter opening time and shutter duration from the trigger pulse.

7. The laser ranging and active illumination composite detection system of claim 6,

the first laser beam is pulse laser;

the comparison module comprises a comparator and a counter;

the comparator is used for comparing t₀And n/f_repMaking a comparison and at t₀<n/f_repDetermining the nth pulse as a trigger pulse;

the counter is used for counting when t₀≥n/f_repThe count of n is increased by 1 until t₀<n/f_repUntil the end;

said t is₀The total time of a laser pulse passing through the measurement and control subsystem;

f is_repIs the repetition frequency of the pulsed laser.

8. The laser ranging and active illumination composite detection system of claim 7, wherein the calculation module comprises:

a minimum depth of field value calculation unit for calculating a minimum depth of field value of the detection target corresponding to the imaging device set in the imaging subsystem;

a shutter duration calculation unit for calculating the shutter duration τ according to a first formula₀；

The first formula is: tau is₀＝2×(2·Z_min+L+v·t₀)/c，

Wherein Z is_minThe minimum depth of field value is obtained, L is the radial length of the detection target, v is the running speed of the detection target, and c is the light speed;

a shutter open time calculating unit for calculating a shutter open time t according to a second formula_op；

The second formula is:

wherein, t_nRepresenting the time difference, t, between the terminating and the initiating electrical signals of the nth pulse_n-endTime of triggering of the terminating electrical signal for the nth pulse, t_n-startThe trigger time of the starting electrical signal of the nth pulse.

9. The laser ranging and active illumination composite detection system of claim 1,

the laser emitting device comprises a pulse laser and a laser beam emitting end;

the laser beam emitting end is used for emitting the illumination light to a detection target.

10. A laser detection method using a laser ranging and active illumination combined detection system according to any one of claims 1 to 9, comprising:

the laser emitting device generates a first laser beam and emits the first laser beam to the first optical splitter;

the first optical splitter splits the first laser beam into illumination light and first ranging light which are emitted to a detection target;

the measurement and control subsystem calculates the shutter opening time and the shutter duration time according to the reflected light of the illumination light received by the measurement and control subsystem and the first ranging light;

and the imaging subsystem images the detection target according to the shutter opening time and the shutter duration.

Technical Field

The invention relates to the field of laser detection, in particular to a laser ranging and active illumination composite detection system and a detection method.

Background

In military countermeasure, imaging detection of targets under natural conditions such as long distance, low illuminance, poor atmospheric transmission and the like is often required. Due to the influence of various background radiation noises, the energy of the echo signal of the target is very weak, the useful signal is submerged by interference light and background light, and the target is difficult to detect. At present, a high repetition frequency pulse laser is generally used as an irradiation light source to irradiate a target area, and a light wave reflected by the target area is received by an optical system and used for imaging. In order to suppress atmospheric backscattering to obtain a sharp image of the target region, the time delay for the laser emission pulse and the imaging reception device to trigger the shutter needs to be strictly controlled.

In the related art, ranging information is provided through a laser ranging machine, and due to the independent layout of the laser ranging machine and the photoelectric detection device, the optical axes of the ranging machine and the photoelectric device are not collinear, so that target measurement is inaccurate, and the detection performance of a target is reduced. The independent layout mode can increase the volume and the weight of the system, and is not beneficial to the miniaturization development of the photoelectric detection system. There are also some related arts that employ a lens displacement mechanism to achieve switching between auxiliary illumination and laser ranging. However, researches show that the lens displacement mechanism of the scheme not only affects the real-time performance of the optoelectronic system, but also the switching back and forth easily causes firmware damage and reduces the service life of the system.

Therefore, aiming at the detection of a long-distance weak target, an effective integrated detection device is not available, which can strictly control the time delay of laser emission pulse and the time delay of the trigger shutter of the imaging receiving equipment so as to obtain a high-resolution target image, solve the problem that the optical axes are not collinear caused by the independent layout of a target illumination system and a laser ranging system, ensure the real-time performance of the system and improve the accuracy of target imaging.

Disclosure of Invention

The embodiment of the invention provides a laser ranging and active illumination composite detection system and a detection method, which are used for solving the problem that optical axes are not collinear due to independent layout of a target illumination system and a laser ranging system in the related technology, ensuring the real-time performance of the system and improving the accuracy of target imaging.

In a first aspect, a laser ranging and active illumination composite detection system is provided, which includes: the laser detection device comprises a laser emitting device, a first light splitting device and a second light splitting device, wherein the laser emitting device is used for generating a first laser beam, the first light splitting device is arranged in the laser emitting device and is used for splitting the first laser beam into illumination light and first distance measuring light which are emitted to a detection target; the measurement and control subsystem is used for calculating the shutter opening time and the shutter duration time according to the reflected light of the illuminating light and the first ranging light; and the imaging subsystem is used for receiving the reflected light of the illumination light and imaging the detection target according to the shutter opening time and the shutter duration.

In some embodiments, the laser ranging and active illumination composite detection system further comprises: an optical receiving device for receiving reflected light of the illumination light; a second light splitting means for splitting the illumination light from the optical receiving means into imaging light and second ranging light directed to an imaging subsystem; the measurement and control subsystem is used for receiving the first distance measuring light and the second distance measuring light and calculating the shutter opening time and the shutter duration time according to the first distance measuring light and the second distance measuring light; the imaging subsystem is used for receiving the imaging light and imaging a detection target according to the shutter opening time and the shutter duration.

In some embodiments, the measurement and control subsystem and the imaging subsystem each include an optical receiving device for receiving reflected light of the illumination light; the optical receiving device of the measurement and control subsystem is used for converting the received reflected light of the illuminating light into second ranging light, and the optical receiving device of the imaging subsystem is used for converting the received reflected light of the illuminating light into imaging light; the measurement and control subsystem is used for calculating the shutter opening time and the shutter duration time according to the first distance measuring light and the second distance measuring light; the imaging subsystem is used for receiving the imaging light and imaging a detection target according to the shutter opening time and the shutter duration.

In some embodiments, the measurement and control subsystem comprises a photoelectric conversion unit and a signal processing unit; the photoelectric conversion unit is used for converting the first ranging light into an initial electric signal and converting the received reflected light of the illumination light into a termination electric signal; the signal processing unit is used for calculating the shutter opening time according to the starting electric signal and the stopping electric signal.

In some embodiments, the signal processing unit comprises an amplification shaping circuit; the amplifying and shaping circuit is connected with the photoelectric conversion unit and is used for converting the starting electric signal into a starting pulse voltage signal and converting the stopping electric signal into a stopping pulse voltage signal.

In some embodiments, the signal processing unit includes: the comparison module is used for determining a trigger pulse according to the starting pulse voltage signal and the ending pulse voltage signal; a calculating module for calculating the shutter opening time and shutter duration from the trigger pulse.

In some embodiments, the first laser beam is a pulsed laser; the comparison module comprises a comparator and a counter; the comparator is used for comparing t₀And n/f_repMaking a comparison and at t₀<n/f_repDetermining the nth pulse as a trigger pulse; the counter is used for counting when t₀≥n/f_repThe count of n is increased by 1 until t₀<n/f_repUntil the end; said t is₀The total time of a laser pulse passing through the measurement and control subsystem; f is_repFor the repetition frequency of the pulsed laser。

In some embodiments, the calculation module comprises: a minimum depth of field value calculation unit for calculating a minimum depth of field value of the detection target corresponding to the imaging device set in the imaging subsystem; a shutter duration calculation unit for calculating the shutter duration τ according to a first formula₀(ii) a The first formula is: tau is₀＝2×(2·Z_min+L+v·t₀) C, wherein Z_minThe minimum depth of field value is obtained, L is the radial length of the detection target, v is the running speed of the detection target, and c is the light speed; a shutter open time calculating unit for calculating a shutter open time t according to a second formula_op；

The second formula is:

wherein, t_nRepresenting the time difference, t, between the terminating and the initiating electrical signals of the nth pulse_n-endTime of triggering of the terminating electrical signal for the nth pulse, t_n-startThe trigger time of the starting electrical signal of the nth pulse.

In some embodiments, the laser emitting device comprises a pulsed laser and a laser beam emitting end; the laser beam emitting end is used for emitting the illumination light to a detection target.

In a second aspect, there is provided a laser detection method, comprising: the laser emitting device generates a first laser beam and emits the first laser beam to the first optical splitter; the first optical splitter splits the first laser beam into illumination light and first ranging light which are emitted to a detection target; the measurement and control subsystem calculates the shutter opening time and the shutter duration time according to the reflected light of the illumination light received by the measurement and control subsystem and the first ranging light; and the imaging subsystem images the detection target according to the shutter opening time and the shutter duration.

The technical scheme provided by the invention has the beneficial effects that:

the embodiment of the invention provides a laser ranging and active illumination composite detection system, wherein a first light splitting device is arranged in a laser emitting device, a first laser beam emitted by the laser emitting device can be split into illumination light and first ranging light which are emitted to a detection target, a measurement and control subsystem can calculate the shutter opening time and the shutter duration time according to the reflection light of the illumination light and the first ranging light, and an imaging subsystem can receive the reflection light of the illumination light and image the detection target according to the shutter opening time and the shutter duration time. Through the transmission of the lighting light and the first distance measuring light on the same optical axis, the target lighting system and the laser distance measuring system work on the same optical axis, and therefore the radial distance information of the target and the high-resolution image information of the target are obtained quickly. Meanwhile, atmospheric backscattering can be inhibited by controlling the time delay of the laser emission pulse and the shutter triggered by the imaging subsystem, a clear image of a target area is obtained under the condition of not influencing the real-time performance of the system, and the target imaging accuracy is effectively improved. The invention has simple and compact structure, can overcome the mutual crosstalk problem of ranging and illumination echo signals, can solve the problem that optical axes are not collinear caused by the independent integration of an active illumination detection and ranging system, and improves the integration level of the detection system.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic diagram of a laser ranging and active illumination combined detection system according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a laser ranging and active illumination combined detection system according to a second embodiment of the present invention;

FIG. 3 is a schematic diagram of a measurement and control subsystem provided in an embodiment of the present invention;

FIG. 4 is a diagram of a signal processing unit according to an embodiment of the present invention;

fig. 5 is a schematic diagram of a photoelectric conversion unit according to an embodiment of the present invention;

fig. 6 is a schematic flowchart of a laser detection method according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

As shown in fig. 1, a laser ranging and active illumination combined detection system according to a first embodiment of the present invention includes: the system comprises a laser emitting device, a measurement and control subsystem and an imaging subsystem; the laser emitting device is used for generating a first laser beam, a first light splitting device is arranged in the laser emitting device, and the first light splitting device is used for splitting the first laser beam into illumination light and first distance measuring light which are emitted to a detection target. The measurement and control subsystem is used for calculating the shutter opening time and the shutter duration time according to the reflected light of the illumination light and the first ranging light; the imaging subsystem is used for receiving the reflected light of the illumination light and imaging the detection target according to the shutter opening time and the shutter duration.

The embodiment realizes that the target illumination system and the laser ranging system work on the same optical axis through the transmission of the illumination light and the first ranging light on the same optical axis, so that the radial distance information of the target and the high-resolution image information of the target are rapidly acquired. Meanwhile, atmospheric backscattering can be inhibited by controlling the time delay of the laser emission pulse and the shutter triggered by the imaging subsystem, a clear image of a target area is obtained under the condition of not influencing the real-time performance of the system, and the target imaging accuracy is effectively improved. The invention has simple and compact structure, can overcome the mutual crosstalk problem of ranging and illumination echo signals, can solve the problem that optical axes are not collinear caused by the independent integration of an active illumination detection and ranging system, and improves the integration level of the detection system.

In some embodiments, the first light splitting device is a high-pass filtering low-reflectivity light splitter, and preferably, the light splitter is coated with an optical film layer with high transmittance (> 99%) and low reflectivity (< 1%), when the first laser beam passes through the light splitter, the transmitted laser beam is illumination light emitted to the detection target, and the reflected laser beam is first ranging light, which can meet the requirement of irradiation of the remote detection target and can avoid damage to the measurement and control subsystem by the laser.

In some embodiments, the imaging subsystem is a high-speed gated camera operable to control shutter opening time and shutter duration based on range delay and depth of field of the detected object.

In some embodiments, the laser ranging and active illumination composite detection system provided by the invention further comprises an optical attenuator, which can be arranged in the measurement and control subsystem, and is used for attenuating the power of the optical signal.

In some embodiments, a laser emitting device includes a pulsed laser and a laser beam emitting end; the pulse laser is a high repetition frequency pulse laser and is used for generating high repetition frequency laser pulses; the laser beam emitting end is used for emitting the illumination light to a detection target. Preferably, the laser beam emitting end is a high-transmittance beam expanding and collimating optical system, and the beam divergence angle of the system in different action distances can be changed in a defocusing mode so as to meet the requirements of illumination ranges at different action distances.

As shown in fig. 2, a second embodiment of the present invention provides a laser ranging and active illumination composite detection system, further including: an optical receiving device and a second light splitting device; wherein the optical receiving device is used for receiving the reflected light of the illumination light; the second light splitting device is used for splitting the illuminating light from the optical receiving device into imaging light and second ranging light which are emitted to the imaging subsystem; the measurement and control subsystem is used for receiving the first distance measuring light and the second distance measuring light and calculating the shutter opening time and the shutter duration time according to the first distance measuring light and the second distance measuring light; the imaging subsystem is used for receiving the imaging light and imaging the detection object according to the shutter opening time and the shutter duration time. Preferably, the optical receiving device may be in a reflective cassegrain telescope configuration.

In some embodiments, the measurement and control subsystem and the imaging subsystem each include an optical receiving device for receiving reflected light of the illumination light; the illumination light received by the optical receiving device of the measurement and control subsystem is second ranging light, and the illumination light received by the optical receiving device of the imaging subsystem is imaging light; the measurement and control subsystem is used for calculating the shutter opening time and the shutter duration time according to the first distance measuring light and the second distance measuring light; the imaging subsystem is used for receiving the imaging light and imaging the detection object according to the shutter opening time and the shutter duration time.

As shown in fig. 3, in some embodiments, the measurement and control subsystem includes a photoelectric conversion unit and a signal processing unit; the photoelectric conversion unit is used for converting the first ranging light into an initial electric signal and converting the reflected light of the received illumination light into a termination electric signal; the signal processing unit is used for calculating the shutter opening time according to the starting electric signal and the ending electric signal.

In some embodiments, the photoelectric conversion unit includes a photodiode and an avalanche photodiode. Specifically, as shown in fig. 5, the photodiode is used for performing photoelectric conversion on a first laser beam emitted by the laser emitting device, and converting the first laser beam into a starting electrical signal; the avalanche photodiode is used to photoelectrically convert the reflected light of the illumination light, which is converted into a termination electric signal. Here, the reflected light of the illumination light received by the avalanche photodiode may be the second distance measurement light split after passing through the second beam splitter. Preferably, the avalanche photodiode is further connected with a semiconductor refrigeration sheet, and the semiconductor refrigeration sheet is used for refrigerating the avalanche photodiode by using the Peltier effect, so that the dark current of the avalanche photodiode is reduced, and the detection sensitivity is improved.

As shown in fig. 4, in some embodiments, the signal processing unit includes an amplification shaping circuit; the amplifying and shaping circuit is connected with the photoelectric conversion unit and used for converting the starting electric signal into a starting pulse voltage signal and converting the stopping electric signal into a stopping pulse voltage signal.

In some embodiments, the amplifying and shaping circuit is composed of a transimpedance amplification circuit, a voltage-controlled amplification circuit, a pulse shaping circuit and a noise feedback circuit, and can shape, amplify and perform noise feedback on the starting pulse voltage signal and the ending pulse voltage signal so as to output a pulse voltage signal capable of meeting a trigger threshold.

As shown in fig. 4, in some embodiments, the signal processing unit includes: a comparison module and a calculation module; the comparison module is used for determining a trigger pulse according to the starting pulse voltage signal and the ending pulse voltage signal; the calculating module is used for calculating the shutter opening time and the shutter duration time according to the trigger pulse. The comparison module also comprises a high-speed comparator and an auxiliary control circuit, so that the comparison module acquires a trigger pulse according to the received initial pulse voltage signal and the received termination pulse voltage signal;

in some embodiments, the signal processing unit is provided with a micro control unit, which is used for controlling the comparison module and the calculation module to work cooperatively, and simultaneously converting the shutter opening time and the shutter duration calculated by the calculation module into control signals to be sent to the imaging subsystem, so as to control the imaging subsystem to image the detection target according to the shutter opening time and the shutter duration.

In some embodiments, the comparison module comprises a comparator and a counter; the first laser beam is pulse laser; a comparator for comparing t₀And n/f_repMaking a comparison and at t₀<n/f_repDetermining the nth pulse as a trigger pulse; the counter is used when t₀≥n/f_repThe count of n is increased by 1 until t₀<n/f_repUntil the end; wherein, t₀Is the total time, f, of a laser pulse passing through the measurement and control subsystem_repThe repetition frequency of the pulsed laser.

In some embodiments, the calculation module includes a minimum depth of field value calculation unit, a shutter duration calculation unit, and a shutter open time calculation unit;

the minimum depth of field value calculation unit is used for calculating a minimum depth of field value of the detection target corresponding to the imaging equipment; specifically, the following formula can be used for calculation:

wherein the minimum depth of field value of the imaging device is recorded as Z_minWherein, R is the distance from the target to be measured to the optical receiving device, f is the focal length from the imaging device to the optical receiving device, l' is the focal position of the imaging device, D is the optical aperture of the imaging device, and D is the pixel size of the imaging device. It should be noted that the imaging device mentioned in the embodiments refers to an imaging camera, typically a gating camera, provided in the imaging subsystem.

The shutter duration calculation unit is used for calculating the shutter duration tau of the imaging device according to a first formula₀Wherein the first formula is: tau is₀＝2×(2·Z_min+L+v·t₀) L is the radial length of the detection target, v is the running speed of the detection target, t₀C is the total time of a laser pulse passing through the measurement and control subsystem, and c is the speed of light;

the shutter opening time calculation unit is used for calculating the shutter opening time t according to a second formula_op，

The second formula is:

wherein, t_nRepresenting the time difference, t, between the terminating and the initiating electrical signals of the nth pulse_n-endTime of triggering of the terminating electrical signal for the nth pulse, t_n-startThe trigger time of the starting electrical signal of the nth pulse.

In a second aspect, as shown in fig. 6, a fourth embodiment of the present invention provides a laser ranging method, including:

s1, generating a first laser beam by a laser emitting device and emitting the first laser beam to a first light splitter;

s2, the first beam splitter splits the first laser beam into illumination light and first ranging light which are emitted to a detection target;

s3, the measurement and control subsystem calculates the shutter opening time and the shutter duration time according to the reflected light of the illumination light received by the measurement and control subsystem and the first ranging light;

and S4, the imaging subsystem images the detected object according to the shutter opening time and the shutter duration.

In some embodiments, to effectively suppress atmospheric backscattering, the shutter may be opened according to the selected firing frequency of the pulsed laser emitter after the imaging subsystem has performed a first exposure and imaging according to the shutter opening time and shutter duration. Specifically, it may be preferable to 1/f every time_repOpening the gate once, wherein f_repThe repetition frequency of the pulsed laser.

In the description of the present invention, it should be noted that the terms "upper", "lower", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and operate, and thus, should not be construed as limiting the present invention. Unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are intended to be inclusive and mean, for example, that they may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

It is to be noted that, in the present invention, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.