A simulation test device for the stability of goaf pillars

Abstract

The present invention discloses a device for simulating the stability of goaf pillars. The present invention relates to the field of simulation test technology and includes a test box, wherein the top inner wall of the test box is fixedly connected to a connecting spring, one end of the connecting spring is fixedly connected to a first U-plate, the inner wall of the first U-plate is rotatably connected to a first round rod, and the side wall of the first U-plate is fixedly connected to a first motor. When a simulation test is required for the stability of goaf pillars, the present invention can adjust the inclination angles of the bottom plate and the pressure plate according to the specific angles of the upper and lower inclined surfaces of the pillars, so that the outer walls of the bottom plate and the pressure plate can fit with the upper and lower ends of the pillar mold. The simulation test shows the stability of the pillars when the contact surfaces between the pillars and the rock formations are inclined at different angles, thereby accurately predicting the deformation trend of the pillars, and greatly improving the reliability and accuracy of the device in testing the stability of the pillars.

Description

Technical Field

[0001] The invention belongs to the technical field of simulation tests, and in particular relates to a simulation test device for the stability of goaf pillars. Background Art

[0002] Goaf pillars refer to the pillars retained during underground mining to support the pressure of the overlying rock strata and maintain the stability of the goaf. After the ore deposit is mined, these pillars form a supporting structure above the goaf, which plays an important role in maintaining the safety and stability of the mine.

[0003] When conducting simulation tests on the stability of the pillars in the goaf, a stability simulation test device is used to test the stability of the pillars in the goaf. However, the underground rock formations themselves may have a certain natural inclination angle, which will cause the contact part of the pillars and the rock formations to naturally form an inclined surface. In addition, geological structures such as faults and folds will also cause the rock formations to tilt, thereby forming an inclined surface in the contact part of the pillars and the rock formations. When the contact surface between the pillars and the rock formations is positive, the pillars are prone to local deformation due to excessive local stress, resulting in instability of the overall structure of the pillars. When the contact surface is an inclined surface, the deformation of the pillars is relatively uniform, and the overall structure will be more stable. However, when conducting simulation tests on the stability of the pillars, the existing technology can only simulate the stability when the contact surface between the pillars and the rock formations is positive, and cannot simulate the stability of the pillars when the contact surface between the pillars and the rock formations is an inclined surface, resulting in the inability to accurately predict the deformation trend of the pillars, which may lead to unreasonable support design, increase the risk of mine collapse, and reduce the reliability and accuracy of the pillar stability test.

[0004] Therefore, we propose a goaf pillar stability simulation test device to solve the above problems. Summary of the Invention

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A goaf pillar stability simulation test device comprises a test box, the top inner wall of the test box is fixedly connected to a connecting spring, one end of the connecting spring is fixedly connected to a first U-plate, the inner wall of the first U-plate is rotatably connected to a first round rod, the side wall of the first U-plate is fixedly connected to a first motor, the output end of the first motor passes through the side wall of the first U-plate and is fixedly connected to one end of the first round rod, the rod wall of the first round rod is fixedly connected to a connecting column, one end of the connecting column is fixedly connected to a test assembly, the bottom side wall of the test box is rotatably connected to a rotating plate, the top side wall of the rotating plate is fixedly connected to a bottom mounting assembly, the bottom side wall of the test box is fixedly connected to a second motor, and the output end of the second motor passes through the side wall of the test box and is fixedly connected to the bottom side wall of the rotating plate.

[0007] Preferably, the test assembly includes a pressure plate fixedly connected to one end of the connecting column, a first groove is opened on the bottom side wall of the pressure plate, an ultrasonic receiving transducer is fixedly connected to the inner wall of the first groove, two second U-plates are symmetrically fixedly connected to the bottom side wall of the pressure plate, the inner walls of the two second U-plates are rotatably connected to a second round rod, and one end side wall of the second U-plate is fixedly connected to a third motor.

[0008] Preferably, the output end of the third motor passes through the side wall of the second U-plate and is fixedly connected to one end of the second round rod, the rod wall of the second round rod is fixedly connected to the first electric telescopic rod, the telescopic end of the first electric telescopic rod is fixedly connected to the support plate, the side wall of one end of the support plate is fixedly connected to the second electric telescopic rod, and the telescopic end of the second electric telescopic rod is fixedly connected to the first fixed plate.

[0009] Preferably, two second grooves are symmetrically opened on the top inner wall of the test box, the inner walls of the second grooves are fixedly connected with electric slide rails, the bottom side walls of the electric slide rails are slidably connected with slides, the bottom side walls of the slides are fixedly connected with third electric telescopic rods, the telescopic ends of the two third electric telescopic rods are fixedly connected with a third U-plate, and the inner wall of the third U-plate is rotatably connected with a third round rod.

[0010] Preferably, a fourth motor is fixedly connected to the side wall of one end of the third U-plate, the output end of the fourth motor passes through the side wall of the third U-plate and is fixedly connected to one end of the third round rod, the rod wall of the third round rod is fixedly connected to the first side rod, one end of the first side rod is fixedly connected to the test plate, the bottom side walls of the test plate are each provided with a third groove, and the inner walls of the third grooves are each fixedly connected to a pressure sensor.

[0011] Preferably, the bottom mounting assembly includes a fourth U-plate fixedly connected to the top side wall of the rotating plate, the inner wall of the fourth U-plate is rotatably connected to a fourth round rod, one end side wall of the fourth U-plate is fixedly connected to a fifth motor, the output end of the fifth motor passes through the side wall of the fourth U-plate and is fixedly connected to one end of the fourth round rod, the rod wall of the fourth round rod is fixedly connected to the second side rod, and one end of the second side rod is fixedly connected to the bottom plate.

[0012] Preferably, a fourth groove is provided on the top side wall of the base plate, an ultrasonic emitting transducer is fixedly connected to the inner wall of the fourth groove, two fifth U-plates are symmetrically fixedly connected to the top side wall of the base plate, a fifth round rod is rotatably connected to the inner wall of the fifth U-plate, a sixth motor is fixedly connected to the side wall of the fifth U-plate, and the output end of the sixth motor passes through the side wall of the fifth U-plate and is fixedly connected to one end of the fifth round rod.

[0013] Preferably, the rod wall of the fifth round rod is fixedly connected to the fourth electric telescopic rod, the telescopic end of the fourth electric telescopic rod is fixedly connected to the side plate, one end side wall of the side plate is fixedly connected to the fifth electric telescopic rod, and the telescopic end of the fifth electric telescopic rod is fixedly connected to the second fixed plate.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The test assembly and the bottom mounting assembly that are set up can adjust the inclination angle of the bottom plate and the pressure plate according to the specific angles of the upper and lower inclined surfaces of the pillar when a simulation test is needed for the stability of the goaf pillar. This allows the outer walls of the bottom plate and the pressure plate to fit with the upper and lower ends of the pillar mold. The simulation test shows that the stability of the pillar is tested when the contact surface between the pillar and the rock formation is an inclined surface at different angles, thereby accurately predicting the deformation trend of the pillar. At the same time, after the pillar mold is placed on the bottom plate, it can be ensured that the pillar mold can be vertically upward, which is convenient for using the pressure plate to simulate the stability of the pillar. The angles of the first fixed plate and the second fixed plate can also be adjusted according to the inclination angle of the bottom plate and the pressure plate, which is convenient for using the first fixed plate and the second fixed plate to fix the pillar mold, thereby greatly improving the reliability and accuracy of the device in testing the stability of the pillar. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0017] Figure 2 This is a schematic diagram of other angle structures of the present invention Figure 1 ;

[0018] Figure 3 This is a schematic diagram of other angle structures of the present invention Figure 2 ;

[0019] Figure 4 For the present invention Figure 3 A magnified view of part A;

[0020] Figure 5 For the present invention Figure 3 A magnified view of part B;

[0021] Figure 6 Schematic diagram of part of the structure of the present invention Figure 1 ;

[0022] Figure 7 Schematic diagram of part of the structure of the present invention Figure 2 .

[0023] In the figure: 1. test box; 2. connecting spring; 3. first U-plate; 4. first round rod; 5. first motor; 6. connecting column; 7. test assembly; 71. pressure plate; 72. first groove; 73. ultrasonic receiving transducer; 74. second U-plate; 75. second round rod; 76. third motor; 77. first electric telescopic rod; 78. support plate; 79. second electric telescopic rod; 710. first fixed plate; 711. second groove; 712. electric slide rail; 713. slide plate; 714. third electric telescopic rod; 715. third U-plate; 716. third round rod ;717, fourth motor;718, first side rod;719, test board;720, third groove;721, pressure sensor;8, rotating plate;9, bottom mounting assembly;91, fourth U plate;92, fourth round rod;93, fifth motor;94, second side rod;95, bottom plate;96, fourth groove;97, ultrasonic transmitting transducer;98, fifth U plate;99, fifth round rod;910, sixth motor;911, fourth electric telescopic rod;912, side plate;913, fifth electric telescopic rod;914, second fixed plate;10, second motor. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] The following electrical components are all electrically connected to the peripheral PLC controller.

[0026] Reference Figure 1 - Figure 7 A goaf pillar stability simulation test device includes a test box 1, the top inner wall of the test box 1 is fixedly connected to a connecting spring 2, one end of the connecting spring 2 is fixedly connected to a first U-plate 3, the inner wall of the first U-plate 3 is rotatably connected to a first round rod 4, the side wall of the first U-plate 3 is fixedly connected to a first motor 5, the output end of the first motor 5 passes through the side wall of the first U-plate 3 and is fixedly connected to one end of the first round rod 4, the rod wall of the first round rod 4 is fixedly connected to a connecting column 6, one end of the connecting column 6 is fixedly connected to a test assembly 7, the bottom side wall of the test box 1 is rotatably connected to a rotating plate 8, the top side wall of the rotating plate 8 is fixedly connected to a bottom mounting assembly 9, the bottom side wall of the test box 1 is fixedly connected to a second motor 10, and the output end of the second motor 10 passes through the side wall of the test box 1 and is fixedly connected to the bottom side wall of the rotating plate 8.

[0027] In the embodiment, the test assembly 7 includes a pressure plate 71 fixedly connected to one end of the connecting column 6, a first groove 72 is formed on the bottom side wall of the pressure plate 71, an ultrasonic receiving transducer 73 is fixedly connected to the inner wall of the first groove 72, two second U-plates 74 are symmetrically fixedly connected to the bottom side wall of the pressure plate 71, the inner walls of the two second U-plates 74 are rotatably connected to the second round rod 75, and one end side wall of the second U-plate 74 is fixedly connected to the third motor 76;

[0028] The output end of the third motor 76 passes through the side wall of the second U-plate 74 and is fixedly connected to one end of the second round rod 75. The rod wall of the second round rod 75 is fixedly connected to the first electric telescopic rod 77. The telescopic end of the first electric telescopic rod 77 is fixedly connected to the support plate 78. The side wall of one end of the support plate 78 is fixedly connected to the second electric telescopic rod 79. The telescopic end of the second electric telescopic rod 79 is fixedly connected to the first fixed plate 710.

[0029] Two second grooves 711 are symmetrically formed on the inner wall of the top of the test box 1. The inner walls of the second grooves 711 are fixedly connected to electric slide rails 712. The bottom side walls of the electric slide rails 712 are slidably connected to slide plates 713. The bottom side walls of the slide plates 713 are fixedly connected to third electric telescopic rods 714. The telescopic ends of the two third electric telescopic rods 714 are fixedly connected to third U-plates 715. The inner wall of the third U-plate 715 is rotatably connected to a third round rod 716.

[0030] A fourth motor 717 is fixedly connected to a side wall of one end of the third U-plate 715. The output end of the fourth motor 717 passes through the side wall of the third U-plate 715 and is fixedly connected to one end of a third round rod 716. A first side rod 718 is fixedly connected to the rod wall of the third round rod 716. One end of the first side rod 718 is fixedly connected to a test plate 719. The bottom side walls of the test plate 719 are each provided with a third groove 720. The inner wall of each third groove 720 is fixedly connected to a pressure sensor 721.

[0031] The bottom mounting assembly 9 includes a fourth U-plate 91 fixedly connected to the top side wall of the rotating plate 8, a fourth round rod 92 being rotatably connected to the inner wall of the fourth U-plate 91, a fifth motor 93 being fixedly connected to one end of the side wall of the fourth U-plate 91, an output end of the fifth motor 93 passing through the side wall of the fourth U-plate 91 and fixedly connected to one end of the fourth round rod 92, a second side rod 94 being fixedly connected to the rod wall of the fourth round rod 92, and one end of the second side rod 94 being fixedly connected to the bottom plate 95;

[0032] A fourth groove 96 is formed on the top side wall of the bottom plate 95. An ultrasonic emitting transducer 97 is fixedly connected to the inner wall of the fourth groove 96. Two fifth U-plates 98 are symmetrically fixedly connected to the top side wall of the bottom plate 95. A fifth round rod 99 is rotatably connected to the inner wall of the fifth U-plate 98. A sixth motor 910 is fixedly connected to the side wall of the fifth U-plate 98. The output end of the sixth motor 910 passes through the side wall of the fifth U-plate 98 and is fixedly connected to one end of the fifth round rod 99.

[0033] The rod wall of the fifth round rod 99 is fixedly connected to the fourth electric telescopic rod 911, the telescopic end of the fourth electric telescopic rod 911 is fixedly connected to the side plate 912, one end side wall of the side plate 912 is fixedly connected to the fifth electric telescopic rod 913, and the telescopic end of the fifth electric telescopic rod 913 is fixedly connected to the second fixed plate 914.

[0034] Specifically, when it is necessary to conduct a simulation test on the stability of the goaf pillar, the inclination angle of the bottom plate 95 and the pressure plate 71 can be adjusted according to the specific angles of the inclined surfaces at the upper and lower ends of the pillar, so that the outer walls of the bottom plate 95 and the pressure plate 71 can fit with the upper and lower ends of the pillar mold. The simulation test shows the stability of the pillar when the contact surface between the pillar and the rock formation is an inclined surface at different angles, thereby accurately predicting the deformation trend of the pillar. At the same time, after the pillar mold is placed on the bottom plate 95, it can be ensured that the pillar mold can be vertically upward, which is convenient for using the pressure plate 71 to simulate the stability of the pillar. The angle of the first fixed plate 710 and the second fixed plate 914 can also be adjusted according to the inclination angle of the bottom plate 95 and the pressure plate 71, so that the pillar mold can be fixed with the first fixed plate 710 and the second fixed plate 914, which greatly improves the reliability and accuracy of the device when testing the stability of the pillar.

[0035] The operating principle of the present invention is now described as follows:

[0036] In the present invention, when it is necessary to conduct a simulation test on the stability of the goaf pillar, the pillar mold with flat upper and lower ends is placed in the middle position of the upper surface of the bottom plate 95, and then the fifth electric telescopic rod 913 is controlled to start, and the second fixed plate 914 is used to fix the bottom of the pillar mold, and then the third electric telescopic rod 714 is controlled to start, driving the test plate 719 to move downward, so that the test plate 719 drives the pressure plate 71 to overcome the elastic force of the connecting spring 2 and move downward, so that the pressure plate 71 is in contact with the upper end of the pillar mold, and then the second electric telescopic rod 79 is controlled to start, driving the first fixed plate 710 to move, and the first fixed plate 710 is used to fix the top of the pillar mold, and then the third electric telescopic rod 714 is controlled to start, driving the two test plates 719 to move upward. The pressure sensor 721 can detect the pressure of the pressing plate 71 on the pillar mold in real time. In this process, the ultrasonic receiving transducer 73 and the ultrasonic transmitting transducer 97 are controlled to start to detect whether there are defects inside the pillar mold, and to judge the changes caused by the pressure brought by the pressing plate 71. The stability of the pillar mold is tested when the pillar mold is in front contact with the pressing plate 71 and the bottom plate 95. Then, the second electric telescopic rod 79, the third electric telescopic rod 714 and the fifth electric telescopic rod 913 are controlled to return to their original positions, and the pillar mold with flat upper and lower ends is taken out. Then, the fifth motor 93 is controlled to start. The fourth round rod 92 is driven to rotate, and the second side rod 94 is used to drive the bottom plate 95 to rotate, so that the inclination angle of the bottom plate 95 matches the inclination angle of the inclined surface of the lower end of the pillar mold, so that after the pillar mold is placed on the bottom plate 95, the pillar mold can be vertically upward. At the same time, the sixth motor 910 is controlled to start, driving the fifth round rod 99 to rotate, so that the fifth electric telescopic rod 913 and one end of the second fixed plate 914 can be perpendicular to the outer wall of the pillar mold. Then, by controlling the fourth electric telescopic rod 911 to start, the two second fixed plates 914 can be in the same plane after contacting the outer wall of the pillar mold. Then, the fifth electric telescopic rod 913 is controlled to start, and the bottom of the pillar mold is fixed by the second fixed plate 914. Then, the second motor 10 is controlled to start. The first motor 5 is then controlled to start, driving the first round rod 4 to rotate, and the connecting column 6 is used to drive the pressing plate 71 to rotate, so that the inclination angle of the pressing plate 71 is the same as the inclination angle of the upper end of the pillar mold. Then, the fourth motor 717 is controlled to start, driving the third round rod 716 to rotate, so that the first side rod 718 drives the test plate 719 to rotate, so that the inclination angle of the test plate 719 is the same as the inclination angle of the pressing plate 71, so that when the subsequent test plate 719 squeezes the pressing plate 71, the side wall of the test plate 719 can fit with the side wall of the pressing plate 71. Then, the electric slide rail 712 is controlled to start, driving the corresponding slide plate 713 to move.The test plate 719 is moved to the middle position on both sides above the pressure plate 71, and then the third electric telescopic rod 714 is controlled to start, driving the test plate 719 to move downward, so that the pressure plate 71 contacts the inclined surface at the upper end of the pillar mold, and then the third motor 76 is controlled to start, driving the second round rod 75 to rotate, so that the second electric telescopic rod 79 and one end of the first fixed plate 710 can be perpendicular to the outer wall of the pillar mold, and then the first electric telescopic rod 77 is controlled to start, so that the two first fixed plates 710 are in the same plane when fixing the pillar mold, and then the second electric telescopic rod 79 is controlled to start, driving the first fixed plate 710 to move, and using the first fixed plate 710 to fix the top of the pillar mold, and then the stability of the pillar with inclined surfaces at the upper and lower ends is tested according to the above steps, which can be used to test the pillar in the goaf when it is necessary to do so. When conducting a stability simulation test, the inclination angles of the bottom plate 95 and the pressing plate 71 are adjusted according to the specific angles of the inclined surfaces at the upper and lower ends of the pillar, so that the outer walls of the bottom plate 95 and the pressing plate 71 can fit the upper and lower ends of the pillar mold. The simulation test shows the stability of the pillar when the contact surface between the pillar and the rock formation is an inclined surface at different angles, thereby accurately predicting the deformation trend of the pillar. At the same time, after the pillar mold is placed on the bottom plate 95, it can be ensured that the pillar mold can be vertically upward, which facilitates the simulation test of the pillar stability using the pressing plate 71. The angles of the first fixing plate 710 and the second fixing plate 914 can also be adjusted according to the inclination angles of the bottom plate 95 and the pressing plate 71, which facilitates the use of the first fixing plate 710 and the second fixing plate 914 to fix the pillar mold. This greatly improves the reliability and accuracy of the device when testing the pillar stability.

[0037] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A goaf pillar stability simulation test device, comprising a test box (1), characterized in that: The top inner wall of the test box (1) is fixedly connected to a connecting spring (2), one end of the connecting spring (2) is fixedly connected to a first U-plate (3), the inner wall of the first U-plate (3) is rotatably connected to a first round rod (4), the side wall of the first U-plate (3) is fixedly connected to a first motor (5), the output end of the first motor (5) passes through the side wall of the first U-plate (3) and is fixedly connected to one end of the first round rod (4), the rod wall of the first round rod (4) is fixedly connected to a connecting column (6), one end of the connecting column (6) is fixedly connected to a test assembly (7), the bottom side wall of the test box (1) is rotatably connected to a rotating plate (8), the top side wall of the rotating plate (8) is fixedly connected to a bottom mounting assembly (9), the bottom side wall of the test box (1) is fixedly connected to a second motor (10), the output end of the second motor (10) passes through the side wall of the test box (1) and is fixedly connected to the bottom side wall of the rotating plate (8); Two second grooves (711) are symmetrically provided on the inner wall of the top of the test box (1), the inner walls of the second grooves (711) are fixedly connected to electric slide rails (712), the bottom side walls of the electric slide rails (712) are slidably connected to slide plates (713), the bottom side walls of the slide plates (713) are fixedly connected to third electric telescopic rods (714), the telescopic ends of the two third electric telescopic rods (714) are fixedly connected to third U-plates (715), and the inner walls of the third U-plates (715) are rotatably connected to third round rods (716); A fourth motor (717) is fixedly connected to a side wall at one end of the third U-plate (715); an output end of the fourth motor (717) passes through the side wall of the third U-plate (715) and is fixedly connected to one end of a third round rod (716); a first side rod (718) is fixedly connected to the rod wall of the third round rod (716); a test plate (719) is fixedly connected to one end of the first side rod (718); a third groove (720) is provided on the side wall at the bottom end of the test plate (719); and a pressure sensor (721) is fixedly connected to the inner wall of the third groove (720).

2. The device for simulating the stability of goaf pillars according to claim 1, characterized in that: The test assembly (7) includes a pressure plate (71) fixedly connected to one end of the connecting column (6), a first groove (72) is provided on the bottom side wall of the pressure plate (71), an ultrasonic receiving transducer (73) is fixedly connected to the inner wall of the first groove (72), two second U-plates (74) are symmetrically fixedly connected to the bottom side wall of the pressure plate (71), the inner walls of the two second U-plates (74) are both rotatably connected to a second round rod (75), and one end side wall of the second U-plate (74) is fixedly connected to a third motor (76).

3. The device for simulating the stability of goaf pillars according to claim 2, characterized in that: The output end of the third motor (76) passes through the side wall of the second U-plate (74) and is fixedly connected to one end of the second round rod (75); the rod wall of the second round rod (75) is fixedly connected to the first electric telescopic rod (77); the telescopic end of the first electric telescopic rod (77) is fixedly connected to the support plate (78); the side wall of one end of the support plate (78) is fixedly connected to the second electric telescopic rod (79); and the telescopic end of the second electric telescopic rod (79) is fixedly connected to the first fixed plate (710).

4. The device for simulating the stability of goaf pillars according to claim 1, characterized in that: The bottom mounting assembly (9) comprises a fourth U-plate (91) fixedly connected to the top side wall of the rotating plate (8); the inner wall of the fourth U-plate (91) is rotatably connected to a fourth round rod (92); one end side wall of the fourth U-plate (91) is fixedly connected to a fifth motor (93); the output end of the fifth motor (93) passes through the side wall of the fourth U-plate (91) and is fixedly connected to one end of the fourth round rod (92); the rod wall of the fourth round rod (92) is fixedly connected to a second side rod (94); and one end of the second side rod (94) is fixedly connected to the bottom plate (95).

5. The device for simulating the stability of goaf pillars according to claim 4, characterized in that: A fourth groove (96) is provided on the top side wall of the bottom plate (95), and an ultrasonic emitting transducer (97) is fixedly connected to the inner wall of the fourth groove (96). Two fifth U-plates (98) are symmetrically fixedly connected to the top side wall of the bottom plate (95), and a fifth round rod (99) is rotatably connected to the inner wall of the fifth U-plate (98). A sixth motor (910) is fixedly connected to the side wall of the fifth U-plate (98), and an output end of the sixth motor (910) passes through the side wall of the fifth U-plate (98) and is fixedly connected to one end of the fifth round rod (99).

6. The device for simulating the stability of goaf pillars according to claim 5, characterized in that: The rod wall of the fifth round rod (99) is fixedly connected to a fourth electric telescopic rod (911), the telescopic end of the fourth electric telescopic rod (911) is fixedly connected to a side plate (912), one end side wall of the side plate (912) is fixedly connected to a fifth electric telescopic rod (913), and the telescopic end of the fifth electric telescopic rod (913) is fixedly connected to a second fixed plate (914).

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