Triple-folding unfoldable light shield based on planar mechanism

Abstract

The invention provides a three-fold deployable light shield based on a planar mechanism, and aims to solve the technical problems that an existing deployable light shield is low in precision and low in rigidity after being unfolded and an existing rigid light shield can only be applied to a small-size space optical system. According to the three-folding unfoldable light shield based on the plane mechanism, the light shield lower portion and the bottom plate jointly form a plane three-connecting-rod mechanism through the two first elastic driving hinges, the light shield upper portion and the light shield lower portion jointly form a plane three-connecting-rod mechanism through the second elastic driving hinges, and the plane three-connecting-rod mechanism is matched with the first pressing base, the second pressing base and the locking device; the planar light shield can be folded in a triple-folding mode in the rocket launching process so that the small space size can be achieved, and meanwhile when the rocket reaches the expected on-orbit position, the planar light shield can be unfolded from the triple-folding folded state and locked through the cooperation of the two planar three-connecting-rod mechanisms and driving of the first elastic driving hinge and the second elastic driving hinge.

Description

Technical Field

[0001] The invention relates to a deployable sunshade, in particular to a three-fold deployable sunshade based on a planar mechanism. Background Art

[0002] With the increasing demand for space situational awareness, the aperture of space optical cameras has gradually increased, and the size of the components compatible with space optical cameras has also increased accordingly. Among them, the size of the sunshade, as the core component for realizing the functions of space optical cameras, has also increased significantly. At present, most of the large-sized sunshades used in space orbit are one-piece structures and do not have the function of being deployable. However, due to the limitation of rocket space, the large envelope volume of large-sized sunshades has obvious defects during rocket launch. Therefore, applying the idea of ​​foldability to large-sized sunshades is a new idea to solve this problem.

[0003] In recent years, many researchers have proposed some deployable sunshade solutions, mainly including sunshade solutions that combine rigid skeletons, elastic materials, inflatable composite materials and other new materials with flexible composite materials. However, the deployable sunshades based on the above solutions have low precision after deployment and have the limitation of low rigidity. Space optical cameras require rigid sunshades with higher rigidity. The existing solutions include a screw-driven cylindrical deployment method, but it can only be applied to smaller-sized space optical systems. Summary of the invention

[0004] The purpose of the present invention is to solve the limitations of low precision and low rigidity of existing deployable sunshades after deployment, and the technical problems that existing rigid sunshades can only be applied to smaller-sized space optical systems, and to provide a three-fold deployable sunshade based on a planar mechanism.

[0005] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0006] A three-foldable and deployable sunshade based on a planar mechanism, characterized in that:

[0007] It includes a plane sunshade, a bottom plate, two first elastic drive hinges and two second elastic drive hinges;

[0008] The plane sunshade comprises an upper sunshade portion and a lower sunshade portion;

[0009] The upper part of the light shield comprises an upper plane substrate and two upper fixed side plates vertically connected to both sides of the upper plane substrate; the lower part of the light shield comprises a lower plane substrate arranged at the lower end of the upper plane substrate and two lower fixed side plates vertically connected to both sides of the lower plane substrate; a plurality of light blocking strips are horizontally arranged on one side surface of the upper plane substrate and the lower plane substrate respectively;

[0010] The outer side walls of the two lower fixed side panels are connected to the upper surfaces of the two sides of the bottom plate through first elastic drive hinges respectively; the outer side walls of the two upper fixed side panels are connected to the outer side walls of the two lower fixed side panels through corresponding second elastic drive hinges respectively; the expansion angle of the first elastic drive hinge is 90 degrees, and the expansion angle of the second elastic drive hinge is 180 degrees;

[0011] An optical through hole is axially opened on the bottom plate, and the light shielding strip is located on the upper plane substrate and the lower plane substrate facing the bottom plate when unfolded;

[0012] A first clamping seat is respectively arranged on the outer side walls of the two lower fixed side plates, a second clamping seat is arranged at a corresponding position on the outer side walls of the two upper fixed side plates, and two locking devices are arranged at corresponding positions on the bottom plate, which are used to lock the planar light shield in the folded state through the cooperation of the first clamping seat, the second clamping seat and the corresponding locking device.

[0013] Further, the locking device includes a base and a locking rod arranged on the base;

[0014] The first pressing seat and the second pressing seat are respectively provided with locking holes adapted to the locking rod;

[0015] The base is provided with an pyrotechnic detonating device. After the remote-controlled pyrotechnic detonating device is detonated, the locking rod is separated from the base, thereby realizing the separation of the locking device from the first pressing seat and the second pressing seat.

[0016] Furthermore, the first elastically driven hinge and the second elastically driven hinge are both scroll spring locking hinges.

[0017] Further, the first elastic drive hinge is a sliding groove type vortex spring locking hinge, comprising a first fixing seat, a second fixing seat, a male hinge, a female hinge, a vortex spring, a clamping rod, a locking pin and a clamping torsion spring;

[0018] The first fixing seat is installed on the upper surface of the base, and the second fixing seat is installed on the outer side wall of the lower fixed side plate;

[0019] The female hinge is arranged on the first fixed seat and connected to the fixed end of the spiral spring, and the male hinge is arranged on the second fixed seat and connected to the movable end of the spiral spring, so as to make the male hinge rotate along the motion track of the movable end of the spiral spring;

[0020] A fixed shaft is installed on the female hinge, and a compression torsion spring is installed on the fixed shaft;

[0021] One end of the clamping rod is rotatably connected to the fixed shaft, and the other end is fixedly connected to the locking pin, and the locking pin is arranged corresponding to the male hinge;

[0022] A sliding groove is provided on the male hinge at a position corresponding to the locking pin, and a protrusion is provided on the male hinge at a position below the sliding groove. The working end of the compression torsion spring presses against the locking pin, so that the locking pin cooperates with the sliding groove or the protrusion respectively when the male hinge moves to different positions.

[0023] The second elastic drive hinge has the same structure as the first elastic drive hinge, the first fixed seat in the second elastic drive hinge is installed on the outer wall of the lower fixed side plate, and the second fixed seat is installed on the outer wall of the upper fixed side plate; the driving torque of the spiral spring in the second elastic drive hinge is twice the driving torque of the spiral spring in the first elastic drive hinge.

[0024] Further, the stiffness of the scroll spring in the first elastic drive hinge is greater than the stiffness of the scroll spring in the second elastic drive hinge.

[0025] Furthermore, the angle between the upper plane substrate and the upper surface of the corresponding light-blocking strip, and the angle between the lower plane substrate and the upper surface of the corresponding light-blocking strip are both obtuse angles, and the angles decrease from top to bottom;

[0026] The width of the upper fixed side plate and the width of the lower fixed side plate increase from top to bottom;

[0027] The inner side walls of the two upper fixed side plates and the inner side walls of the two lower fixed side plates are respectively abutted against two ends of the corresponding light shielding strips.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention provides a three-fold expandable sunshade based on a planar mechanism, wherein two first elastic drive hinges with an expansion angle of 90 degrees are used between the lower part of the sunshade and the bottom plate, and two second elastic drive hinges with an expansion angle of 180 degrees are used between the upper part 11 of the sunshade and the lower part 12 of the sunshade to form a planar three-link mechanism, and cooperate with a first clamping seat, a second clamping seat and a locking device, so that the planar sunshade can be folded in three parts to achieve a smaller space volume during rocket launch, and when the rocket reaches the expected position on orbit, two sets of planar three-link mechanisms are used to cooperate with the drive of the first elastic drive hinge and the second elastic drive hinge to make the planar sunshade unfolded from the three-folded state and locked, which provides a new idea for the on-orbit application of large-size sunshades and fills the gap of large-size high-rigidity sunshades.

[0030] 2. The present invention provides a three-fold expandable light shield based on a planar mechanism, wherein the first pressing seat, the second pressing seat and the locking device adopt a pyrotechnic unlocking device or a shape memory alloy unlocking device used in aerospace. When the light shield is in a fully folded state, the first pressing seat, the second pressing seat and the locking device fix the planar light shield to the base plate, thereby ensuring that the light shield can still meet the required rigidity in the fully locked state during the launch process.

[0031] 3. In the present invention, the stiffness of the scroll spring in the first elastic drive hinge is greater than the stiffness of the scroll spring in the second elastic drive hinge, so that the expansion speed of the first elastic drive hinge can be greater than the expansion speed of the second elastic drive hinge, ensuring that the second elastic drive hinge will not be subjected to excessive impact and damage during 180-degree expansion and locking. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of an embodiment of a three-foldable and deployable sunshade based on a planar mechanism of the present invention;

[0033] Figure 2 It is a schematic diagram of a planar three-link mechanism formed by the lower part of the light shield and the bottom plate through two first elastic drive hinges, and the upper part of the light shield and the lower part of the light shield through two second elastic drive hinges in an embodiment of the present invention;

[0034] Figure 3 This is a schematic structural diagram of a first elastically driven hinge in an embodiment of the present invention;

[0035] Figure 4 A schematic diagram of a locking process of a first elastically driven hinge in an embodiment of the present invention;

[0036] Figure 5 Schematic diagram of the unfolding process of the upper part and the lower part of the light shield in the embodiment of the present invention Figure 1 ;

[0037] Figure 6 Schematic diagram of the unfolding process of the upper part and the lower part of the light shield in the embodiment of the present invention Figure 2 .

[0038] The specific reference numerals are as follows:

[0039] 1. Plane sunshade; 11. Upper part of sunshade; 111. Upper plane substrate; 112. Upper fixed side plate; 12. Lower part of sunshade; 121. Lower plane substrate; 122. Lower fixed side plate; 13. Light shielding strip; 2. Bottom plate; 3. First elastic drive hinge; 31. First fixed seat; 32. Second fixed seat; 33. Male hinge; 34. Female hinge; 35. Volute spring; 36. Clamping rod; 37. Locking pin; 38. Clamping torsion spring; 4. Second elastic drive hinge; 5. First clamping seat; 6. Second clamping seat; 7. Locking device. DETAILED DESCRIPTION

[0040] In order to make the advantages and features of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] like Figure 1 As shown, a three-fold expandable sunshade based on a planar mechanism comprises a planar sunshade 1, a bottom plate 2, two first elastically driven hinges 3 and two second elastically driven hinges 4.

[0042] The planar sunshade 1 comprises a sunshade upper portion 11 and a sunshade lower portion 12. The sunshade upper portion 11 comprises an upper plane substrate 111 and two upper fixed side plates 112 vertically connected to both sides of the upper plane substrate 111; the sunshade lower portion 12 comprises a lower plane substrate 121 arranged at the lower end of the upper plane substrate 111 and two lower fixed side plates 122 vertically connected to both sides of the lower plane substrate 121; a plurality of light-blocking strips 13 are horizontally arranged on one side surface of the upper plane substrate 111 and the lower plane substrate 121, respectively, and the inner side walls of the two upper fixed side plates 112 and the inner side walls of the two lower fixed side plates 122 are respectively abutted against the two ends of the corresponding light-blocking strips 13. The angle between the upper plane substrate 111 and the upper surface of the corresponding light shielding strip 13, and the angle between the lower plane substrate 121 and the upper surface of the corresponding light shielding strip 13 are both obtuse angles, and each angle decreases from top to bottom. Correspondingly, the width of the upper fixed side plate 112 and the width of the lower fixed side plate 122 increase from top to bottom. The angle between the upper plane substrate 111 and the lower plane substrate 121 and the upper surface of the lower light shielding strip 13 is greater than the angle between them and the upper surface of the upper light shielding strip 13, which can better suppress stray light.

[0043] The outer side walls of the two lower fixed side panels 122 are connected to the upper surfaces of both sides of the bottom plate 2 through the first elastic drive hinge 3, and the lower end surface of the lower plane substrate 121 is gap-matched with the corresponding position of the upper surface of the bottom plate 2; the outer side walls of the two upper fixed side panels 112 are connected to the outer side walls of the two lower fixed side panels 122 through the corresponding second elastic drive hinge 4; preferably, the second elastic drive hinge 4 is arranged on the upper fixed side panels 112 and the lower fixed side panels 122 at a position away from the bottom plate 2, so as to enable the upper half of the plane sunshade 1 to be folded outward. The unfolding angle of the first elastic drive hinge 3 is 90 degrees, and the unfolding angle of the second elastic drive hinge 4 is 180 degrees, so as to enable the lower half of the plane sunshade 1 to be folded inward by 90 degrees, and the upper half of the plane sunshade 1 to be folded outward by 180 degrees.

[0044] An optical through hole is axially opened on the base plate 2, and multiple light-blocking strips 13 are located on the upper plane substrate 111 and the lower plane substrate 121 facing the side of the base plate 2 when unfolded, so as to block stray light in the space. At the same time, this arrangement can make the light-blocking strips 13 located inside the plane light-blocking cover 1 when the plane light-blocking cover 1 is in the folded state, effectively avoiding interference contact with the light-blocking strips 13.

[0045] The outer walls of the two lower fixed side panels 122 are respectively provided with first pressing seats 5, the outer walls of the two upper fixed side panels 112 are respectively provided with second pressing seats 6, and the corresponding positions of the bottom plate 2 are provided with two locking devices 7, which are used to make the plane light shield 1 in the folded state to be locked by the first pressing seat 5, the second pressing seat 6 and the corresponding locking device 7. Specifically, the locking device 7 includes a base and a locking rod arranged on the base, and a pyrotechnic detonating device is arranged in the base. The first pressing seat 5 and the second pressing seat 6 are respectively provided with locking holes adapted to the locking rod. When the light shield needs to be opened, the pyrotechnic detonating device is remotely controlled to detonate, so that the locking rod is separated from the base, thereby realizing the separation of the locking device 7 from the first pressing seat 5 and the second pressing seat 6. The locking device 7 can select the pyrotechnic unlocking device commonly used in aerospace, the memory alloy unlocking device, etc.

[0046] like Figure 2 As shown, a planar three-link mechanism is formed between the lower portion 12 of the sunshade and the base plate 2 via two first elastically driven hinges 3 with an unfolding angle of 90 degrees, and between the upper portion 11 of the sunshade and the lower portion 12 of the sunshade via two second elastically driven hinges 4 with an unfolding angle of 180 degrees. In conjunction with the first clamping seat 5, the second clamping seat 6 and the locking device 7, the planar sunshade 1 can be folded in three parts to achieve a smaller spatial volume during rocket launch. When reaching the expected position on orbit, the two sets of planar three-link mechanisms are driven by the first elastically driven hinges 3 and the second elastically driven hinges 4 to unfold and lock the planar sunshade 1 from the three-folded state, thereby providing a new idea for the on-orbit application of large-size sunshades.

[0047] In this embodiment, the first elastic drive hinge 3 and the second elastic drive hinge 4 are both sliding groove type vortex spring locking hinges. Figure 3 As shown, taking the first elastic drive hinge 3 as an example, it includes a first fixed seat 31, a second fixed seat 32, a male hinge 33, a female hinge 34, a spiral spring 35, a clamping rod 36, a locking pin 37 and a clamping torsion spring 38. The first fixed seat 31 is installed on the upper surface of the base 2, and the second fixed seat 32 is installed on the outer side wall of the lower fixed side plate 122; the female hinge 34 is arranged on the first fixed seat 31 and connected to the fixed end of the spiral spring 35, and the male hinge 33 is arranged on the second fixed seat 32 and connected to the movable end of the spiral spring 35, so as to make the male hinge 33 rotate along the motion track of the movable end of the spiral spring 35. A fixed shaft is installed on the female hinge 34, and the clamping torsion spring 38 is installed on the fixed shaft; one end of the clamping rod 36 is rotatably connected to the fixed shaft, and the other end is fixedly connected to the locking pin 37, and the locking pin 37 is arranged corresponding to the male hinge 33. When the male hinge 33 is locked, a sliding groove is provided on the male hinge 33 at a position corresponding to the locking pin 37, and a protrusion is provided on the male hinge 33 at a position below the sliding groove. The working end of the compression torsion spring 38 presses against the locking pin 37, so that when the male hinge 33 is in the initial state, under the action of the compression torsion spring 38, the locking pin 37 slides into the sliding groove for mechanical limit locking; when the male hinge 33 follows the spiral spring 35 to move away from the initial state, the locking pin 37 is pressed against the protrusion of the male hinge 33 under the action of the compression torsion spring 38. The second elastic drive hinge 4 has the same structure as the first elastic drive hinge 3, except that the first fixed seat in the second elastic drive hinge 4 is installed on the outer wall of the lower fixed side plate 122, and the second fixed seat is installed on the outer wall of the upper fixed side plate 112; accordingly, the driving torque of the spiral spring in the second elastic drive hinge 4 is twice the driving torque of the spiral spring 35 in the first elastic drive hinge 3. In addition, in this embodiment, it is preferred to make the stiffness of the spiral spring 35 in the first elastic drive hinge 3 greater than the stiffness of the spiral spring in the second elastic drive hinge 4, so as to make the expansion speed of the first elastic drive hinge greater than the expansion speed of the second elastic drive hinge, so as to ensure that the second elastic drive hinge 4 will not be subjected to excessive impact and damage during 180-degree expansion and locking.

[0048] The locking process of the vortex spring locking hinge is as follows Figure 4As shown, when the plane sunshade 1 is in the three-folded state, the vortex spring 35 continuously provides the vortex spring locking hinge with a driving torque in the unfolding direction, but at this time, due to the action of the locking device 7, the vortex spring locking hinge is in a non-expanded state. When the plane sunshade 1 arrives at the expected on-orbit working position with the rocket launch, the locking device 7 is unlocked, and the lower part 12 of the sunshade is driven to unfold under the action of the torque of the vortex spring 35, and the locking pin 37 is always pressed on the male hinge 33 under the action of the compression torsion spring 38. When the lower part 12 of the sunshade is unfolded to the predetermined working position, the locking pin 37 moves to the chute position of the male hinge 33, enters the chute under the action of the compression torsion spring 38, and is mechanically limited and locked; correspondingly, the upper part 11 of the sunshade is driven to unfold under the action of the vortex spring torque of the second elastic driving hinge 4, and when the upper part 11 of the sunshade is unfolded to the predetermined working position, the corresponding locking pin enters the chute under the action of the compression torsion spring and is mechanically limited and locked.

[0049] like Figure 5 , Figure 6 As shown, it is a schematic diagram of the unfolding process of the upper part 11 and the lower part 22 of the sunshade using two sets of symmetrically arranged planar three-link mechanisms. When the upper part 11 and the lower part 22 of the sunshade are in a fully retracted state, that is, the upper part 11 and the lower part 22 of the sunshade are fixedly connected with the base plate 2 through the clamping structure 7 and the first clamping seat 5 and the second clamping seat 6. When the planar sunshade 1 reaches the expected on-orbit working position with the rocket launch, the locking device 7 is unlocked to eliminate the fixed constraint. At this time, the volute spring in the first elastic drive hinge 3 and the second elastic drive hinge 4 provides the planar three-link mechanism with an unfolding driving torque, driving the planar three-link mechanism to unfold according to its own motion trajectory, that is, driving the upper part 11 and the lower part 22 of the sunshade to unfold respectively. After unfolding to the predetermined working position, the locking pins in the first elastic driven hinge 3 and the second elastic driven hinge 4 respectively move to the corresponding sliding groove positions of the male hinges, and enter the sliding grooves under the action of the compression torsion springs, thereby locking the first elastic driven hinge 3 and the second elastic driven hinge 4.

[0050] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. For ordinary professional and technical personnel in the field, the specific technical solution recorded in the above embodiment can be modified, or some of the technical features therein can be replaced by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution protected by the present invention.

Claims

1. A three-foldable and deployable sunshade based on a planar mechanism, characterized in that: It comprises a planar light shield (1), a bottom plate (2), two first elastic drive hinges (3) and two second elastic drive hinges (4); The planar light shield (1) comprises a light shield upper portion (11) and a light shield lower portion (12); The upper part (11) of the light shield comprises an upper plane substrate (111) and two upper fixed side plates (112) vertically connected to both sides of the upper plane substrate (111); the lower part (12) of the light shield comprises a lower plane substrate (121) arranged at the lower end of the upper plane substrate (111) and two lower fixed side plates (122) vertically connected to both sides of the lower plane substrate (121); a plurality of light blocking strips (13) are horizontally arranged on one side surface of the upper plane substrate (111) and the lower plane substrate (121); The outer side walls of the two lower fixed side panels (122) are respectively connected to the upper surfaces of the two sides of the bottom panel (2) through first elastic drive hinges (3); the outer side walls of the two upper fixed side panels (112) are respectively connected to the outer side walls of the two lower fixed side panels (122) through corresponding second elastic drive hinges (4); the unfolding angle of the first elastic drive hinge (3) is 90 degrees, and the unfolding angle of the second elastic drive hinge (4) is 180 degrees; An optical through hole is axially opened on the bottom plate (2), and the light blocking strip (13) is located on a side of the upper plane substrate (111) and the lower plane substrate (121) facing the bottom plate (2) when they are unfolded; First clamping seats (5) are respectively arranged on the outer side walls of the two lower fixed side plates (122), second clamping seats (6) are arranged at corresponding positions on the outer side walls of the two upper fixed side plates (112), and two locking devices (7) are arranged at corresponding positions on the bottom plate (2) for enabling the planar light shield (1) to be locked in a folded state through the cooperation of the first clamping seat (5), the second clamping seat (6) and the corresponding locking devices (7).

2. The three-foldable and deployable sunshade based on a planar mechanism according to claim 1, characterized in that: The locking device (7) comprises a base and a locking rod arranged on the base; A pyrotechnic detonating device is arranged in the base; The first pressing seat (5) and the second pressing seat (6) are respectively provided with locking holes adapted to the locking rod.

3. A three-foldable and deployable sunshade based on a planar mechanism according to claim 1 or 2, characterized in that: The first elastically driven hinge (3) and the second elastically driven hinge (4) are both scroll spring locking hinges.

4. The three-foldable and deployable sunshade based on a planar mechanism according to claim 3, characterized in that: The first elastic drive hinge (3) is a sliding groove type scroll spring locking hinge, comprising a first fixed seat (31), a second fixed seat (32), a male hinge (33), a female hinge (34), a scroll spring (35), a clamping rod (36), a locking pin (37) and a clamping torsion spring (38); The first fixing seat (31) is installed on the upper surface of the base (2), and the second fixing seat (32) is installed on the outer side wall of the lower fixing side plate (122); The female hinge (34) is arranged on the first fixed seat (31) and connected to the fixed end of the spiral spring (35); the male hinge (33) is arranged on the second fixed seat (32) and connected to the movable end of the spiral spring (35), so as to enable the male hinge (33) to rotate along the motion track of the movable end of the spiral spring (35); The female hinge (34) is provided with a fixed shaft, and the compression torsion spring (38) is provided on the fixed shaft; One end of the clamping rod (36) is rotatably connected to the fixed shaft, and the other end is fixedly connected to the locking pin (37), and the locking pin (37) is arranged corresponding to the male hinge (33); A sliding groove is provided on the male hinge (33) at a position corresponding to the locking pin (37); a protrusion is provided on the male hinge (33) at a position below the sliding groove; a working end of the compression torsion spring (38) is pressed against the locking pin (37) so as to enable the locking pin (37) to cooperate with the sliding groove or the protrusion respectively when the male hinge (33) moves to different positions; The second elastic drive hinge (4) has the same structure as the first elastic drive hinge (3); the first fixed seat in the second elastic drive hinge (4) is mounted on the outer wall of the lower fixed side plate (122), and the second fixed seat is mounted on the outer wall of the upper fixed side plate (112); the driving torque of the spiral spring in the second elastic drive hinge (4) is twice the driving torque of the spiral spring (35) in the first elastic drive hinge (3).

5. The three-foldable and deployable sunshade based on a planar mechanism according to claim 4, characterized in that: The stiffness of the spiral spring (35) in the first elastic drive hinge (3) is greater than the stiffness of the spiral spring in the second elastic drive hinge (4).

6. The three-foldable and deployable sunshade based on a planar mechanism according to claim 1, characterized in that: The angle between the upper plane substrate (111) and the upper surface of the corresponding light shielding strip (13), and the angle between the lower plane substrate (121) and the upper surface of the corresponding light shielding strip (13) are both obtuse angles, and the angles decrease from top to bottom. The width of the upper fixed side plate (112) and the width of the lower fixed side plate (122) increase sequentially from top to bottom; The inner side walls of the two upper fixed side plates (112) and the inner side walls of the two lower fixed side plates (122) are respectively abutted against two ends of the corresponding light shielding strips (13).

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