An automatic Kjeldahl nitrogen analyzer

Abstract

The present invention discloses a novel automatic Kjeldahl nitrogen analyzer, and relates to the technical field of Kjeldahl nitrogen analyzers, including a fully automatic Kjeldahl nitrogen analyzer body, wherein the Kjeldahl nitrogen analyzer body is provided with a test tube placement area for placing test tubes, a lifting plate movable in a vertical direction is arranged at the bottom of the test tube placement area, a test tube holder is rotatably connected to the upper surface of the lifting plate, a plurality of outer tube grooves for placing test tubes are provided in the circumference of the test tube holder, and a positioning mechanism for limiting the circumference of the bottom of the test tube is arranged in each outer tube groove. The present invention can load different kinds of test substances into test tubes at one time through a turntable test tube holder, and then move them to the middle middle tube barrel in turn for titration detection, thereby eliminating the step of placing the test tubes one by one under the test tube placement area for titration, greatly improving the detection efficiency, and having a significant use effect.

Description

Technical Field

[0001] The invention relates to the technical field of Kjeldahl nitrogen analyzers, in particular to an automatic Kjeldahl nitrogen analyzer. Background Art

[0002] The Kjeldahl nitrogen analyzer is an instrument that calculates the protein content by measuring the nitrogen content in the sample based on the principle that the nitrogen content in protein is constant. Because its method of measuring and calculating protein content is called the Kjeldahl method, it is called the Kjeldahl nitrogen analyzer, also known as nitrogen analyzer, protein analyzer, crude protein analyzer. The Kjeldahl nitrogen analyzer uses the Kjeldahl method to detect ammonia, protein nitrogen content, phenol, volatile fatty acids, cyanide, sulfur dioxide, ethanol and other contents in grains, food, feed, water, soil, silt, sediment and chemicals. It has a very good cost-effectiveness. Only the titration process requires manual operation. It is very suitable for routine testing in laboratories and inspection agencies, and is widely used in nitrogen or protein content analysis of food, crops, seeds, soil, fertilizer and other samples.

[0003] The substances to be tested are usually placed in test tubes for titration. The test tubes in most existing Kjeldahl nitrogen analyzers can only be used one by one and titrated in turn, which undoubtedly requires repeated loading of the substances to be tested into the test tubes, and the test tubes need to be placed one by one under the test tube placement area for titration. Especially when a large amount of substances to be tested need to be measured, the detection efficiency is low. Summary of the invention

[0004] The object of the present invention is to provide an automatic Kjeldahl nitrogen analyzer to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An automatic Kjeldahl nitrogen analyzer comprises a fully automatic Kjeldahl nitrogen analyzer body, the Kjeldahl nitrogen analyzer body is provided with a test tube placement area for placing test tubes, a lifting plate movable in a vertical direction is arranged at the bottom of the test tube placement area, a test tube seat is rotatably connected to the upper surface of the lifting plate, a plurality of outer tube grooves for placing the test tubes are opened in the circumference of the test tube seat, and a positioning mechanism for limiting the bottom circumference of the test tube is arranged in each outer tube groove, and each outer tube groove is semicircular and annular, and a guide groove channel for sliding the test tube is opened on one side facing the center of the test tube seat, and the guide groove channel is connected to the groove opened on the circumference of the limiting cylinder, and a middle tube tube is fixedly connected at the center of the inner bottom of the limiting cylinder, the middle tube tube is located directly below the liquid outlet tube in the test tube placement area, and a gravity-triggered clamping mechanism for automatically clamping the test tube after the test tube is placed in the middle tube tube is also provided.

[0007] As a further solution of the present invention: the gravity-triggered clamping mechanism includes a plurality of evenly distributed spring sheets fixedly connected to the bottom surface of the middle tube, a support sheet for supporting the test tube is fixedly arranged on the top of the plurality of spring sheets, and the bottom surfaces of the test tube seats on both sides of the middle tube are fixedly connected with a vertical vertical sliding shaft, one end of a horizontal lifting shaft is slidably connected to the vertical sliding shaft, and a sliding block is slidably connected to the upper side, the front side surface of the sliding block is rotatably connected to one end of the second connecting rod through a rotating shaft, the other end of the second connecting rod is rotatably connected to the outer end of the mounting rod fixedly connected to the upper wall of the middle tube, and the rear side surface of the sliding block is rotatably connected to one end of the first connecting rod through a rotating shaft, the other end of the first connecting rod is rotatably connected to one end of the connecting rod through the rotating shaft, the connecting rod is slidably connected to a through hole opened in the side wall of the middle tube, and the end of the connecting rod in the middle tube is fixedly connected with a stop block, the stop block is integrally formed into an arc surface structure matching the outer periphery of the test tube, and the inner bottom of the middle tube is also provided with a trigger assembly for lifting the lifting shaft when the test tube is under weight.

[0008] As a further solution of the present invention: the trigger assembly includes a second gear rod fixedly connected to the two side surfaces of the support plate, the second gear rod is meshedly connected to one side of a gear, the gear is rotatably connected to the inner bottom surface of the middle tube through a bracket, and the other side of the gear is meshedly connected to the first gear rod, and the top end of the first gear rod is fixedly connected to the end of the lifting shaft away from the vertical sliding shaft.

[0009] As a further solution of the present invention: the top of the limiting cylinder is open and the bottom is a blocking structure, and the slot on the limiting cylinder extends vertically downward from the top opening.

[0010] As a further solution of the present invention: the positioning mechanism includes a receiving groove opened in the test tube holder corresponding to the periphery of the outer tube groove, a positioning column is fixedly connected to the bottom surface of the receiving groove, one end of a compression spring is wrapped around the positioning column, and the other end of the compression spring is wrapped around another positioning column fixedly connected to the corresponding side of the splint, the splint is in the receiving groove, and the splint is integrally formed into a curved surface structure matching the outer periphery of the test tube.

[0011] As a further solution of the present invention: a side of the clamping plate facing away from the corresponding compression spring is compositely connected with a rubber pad.

[0012] As a further solution of the present invention: the front and rear sides of one end of the lifting plate are provided with through holes for the sliding rod to slide through, and the two sliding rods are symmetrically arranged in parallel, the top and bottom ends of the sliding rod are respectively fixedly connected to the bottom surface and the bottom surface of the test tube placing area, and the other end of the lifting plate is provided with a threaded through hole for the screw shaft to pass through and be threadedly connected, the bottom end of the screw shaft is rotatably connected to the bottom surface of the test tube placing area through a bearing, and the top end of the screw shaft is vertically upward and connected to the output shaft of the reduction motor through a coupling, and the reduction motor is fixedly installed at the corresponding position on the upper part of the test tube placing area.

[0013] As a further solution of the present invention: an annular guide rail is fixedly connected to the circumference of the upper surface of the lifting plate, and balls are rollingly connected to the annular guide rail. The balls are rollingly connected to the rolling grooves provided on the lower surface of the positioning block, and the positioning block is fixedly connected to the circumference of the lower surface of the test tube holder. The test tube holder is also provided with a limiting mechanism for temporarily positioning the test tube holder with the lifting plate after the test tube holder is rotated to the desired position.

[0014] As a further solution of the present invention: the limiting mechanism includes a plurality of vertical through holes opened around the test tube holder for the compression screw to pass through, and a threaded tube is fixedly connected to the top of the through hole corresponding to the upper surface of the test tube holder, and the compression screw is threadedly connected to the threaded tube.

[0015] As a further solution of the present invention: the top end of the clamping screw is fixedly connected with a knob, and the bottom end of the clamping screw is fixedly connected with an anti-slip pad.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention can load different kinds of test substances into test tubes at one time through the turntable test tube holder, and then move them to the middle tube in turn for titration detection, or titration detection of test substances of the same substance with different concentrations at one time, thereby eliminating the step of placing the test tubes one by one under the test tube placement area for titration, greatly improving the detection efficiency, and having a significant use effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention;

[0019] Figure 2 A top view of the test tube holder of the present invention;

[0020] Figure 3 for Figure 2 A magnified view of the structure at B in FIG.

[0021] Figure 4 It is a schematic diagram of the structure of the limiting cylinder in the present invention;

[0022] Figure 5 for Figure 1 A magnified view of the structure at A;

[0023] Figure 6 It is a structural schematic diagram of the limiting mechanism in the present invention.

[0024] In the figure: 1. Kjeldahl nitrogen analyzer body; 2. test tube placement area; 3. test tube; 4. screw shaft; 5. reduction motor; 6. slide rod; 7. lifting plate; 8. test tube holder; 9. outer tube groove; 10. stop block; 11. support plate; 12. spring; 13. middle tube; 14. guide channel; 15. slot; 16. limit tube; 17. knob; 18. splint; 19. receiving groove; 20. positioning column; 21. compression spring; 22. anti-skid pad; 23. ball; 24. threaded tube; 25. vertical sliding shaft; 26. slider; 27. first gear rod; 28. gear; 29. ​​second gear rod; 30. first connecting rod; 31. connecting rod; 32. clamping screw; 33. second connecting rod; 34. mounting rod; 35. lifting shaft. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] See also Figures 1 to 6In an embodiment of the present invention, an automatic Kjeldahl nitrogen analyzer includes a fully automatic Kjeldahl nitrogen analyzer body 1, the Kjeldahl nitrogen analyzer body 1 has a test tube placement area 2 for placing a test tube 3, a lifting plate 7 movable in a vertical direction is arranged at the bottom of the test tube placement area 2, and a test tube seat 8 is rotatably connected to the upper surface of the lifting plate 7, and a plurality of outer tube grooves 9 for placing the test tube 3 are opened in the circumference of the test tube seat 8, and each outer tube groove 9 is provided with a positioning mechanism for limiting the bottom circumference of the test tube 3, and each outer tube groove 9 is semicircular and annular, and a guide groove channel 14 for sliding the test tube 3 is opened on one side facing the center of the test tube seat 8, and the guide groove channel 14 is connected to the groove opened on the circumference of the limiting cylinder 16 15, and the middle tube 13 is fixedly connected to the center of the inner bottom of the limiting tube 16, the middle tube 13 is located just below the liquid outlet tube in the test tube placement area 2, and the middle tube 13 is also provided with a gravity-triggered clamping mechanism for automatically clamping the test tube 3 after the test tube 3 is placed therein, the purpose of which is that different kinds of test substances can be loaded into the test tubes 3 at one time through the turntable test tube holder 8, and then moved to the middle middle tube 13 in turn for titration detection, or the test substances of the same substance with different concentrations can be titrated and detected at one time, thereby eliminating the step of placing the test tubes 3 one by one under the test tube placement area 2 for titration, greatly improving the detection efficiency, and having a significant use effect.

[0028] Further, the gravity-triggered clamping mechanism includes a plurality of evenly distributed spring pieces 12 fixedly connected to the bottom surface of the middle tube 13, a support sheet 11 for supporting the test tube 3 is fixedly placed on the top of the plurality of spring pieces 12, and the bottom surfaces of the test tube holders 8 on both sides of the middle tube 13 are fixedly connected with vertical vertical sliding shafts 25, one end of the horizontal lifting shaft 35 is slidably connected to the vertical sliding shaft 25, and a slider 26 is slidably connected to the upper side, and the front side of the slider 26 is rotatably connected to one end of the second connecting rod 33 through a rotating shaft, and the other end of the second connecting rod 33 is rotatably connected to the upper surface of the middle tube 13 The outer end of the mounting rod 34 is fixedly connected to the wall, and the rear side surface of the slider 26 is rotatably connected to one end of the first connecting rod 30 through a rotating shaft, and the other end of the first connecting rod 30 is rotatably connected to one end of the connecting rod 31 through the rotating shaft, and the connecting rod 31 is slidably connected to the through hole opened in the side wall of the middle tube 13, and the end of the connecting rod 31 in the middle tube 13 is fixedly connected with a stop block 10, and the stop block 10 is integrally formed into a curved structure matching the outer periphery of the test tube 3, and the inner bottom of the middle tube 13 is also provided with a trigger component for lifting the lifting shaft 35 when the test tube 3 is under weight.

[0029] Furthermore, the trigger assembly includes a second gear rod 29 fixedly connected to the two side surfaces of the support plate 11, and one side of the second gear rod 29 is meshedly connected to the gear 28, and the gear 28 is rotatably connected to the inner bottom surface of the middle tube 13 through the bracket, and the other side of the gear 28 is meshedly connected to the first gear rod 27, and the top end of the first gear rod 27 is fixedly connected to the end of the lifting shaft 35 away from the vertical sliding shaft 25. When the support plate 11 is pressed down by the weight of the test tube 3, the spring piece 12 is in a compressed state. At this time, the second gear rod 29 descends and drives the first gear rod 27 to rise through the gear 28, and then the lifting shaft 35 is lifted, and the second connecting rod 33 pushes the slider 26 to move in the direction of the middle tube 13, and then drives the block 10 to be pressed against the test tube 3 through the first connecting rod 30, so as to achieve an automatic positioning effect, and fully ensure the stability of the test tube 3 where the substance to be tested is located.

[0030] Furthermore, the top of the limiting cylinder 16 is open and the bottom is a blocking structure, and the slot 15 on the limiting cylinder 16 extends vertically downward from the top opening. First, the test tube 3 is pushed from the outer tube groove 9 to the corresponding guide groove channel 14 by applying force, and then the test tube 3 continues to slide into the middle tube 13 in the guide groove channel 14, and first the titration test of the substance to be detected is performed.

[0031] Furthermore, the positioning mechanism includes a receiving groove 19 opened in the test tube holder 8 corresponding to the periphery of the outer tube groove 9, and a positioning column 20 is fixedly connected to the bottom surface of the receiving groove 19, and one end of a compression spring 21 is wound around the positioning column 20, and the other end of the compression spring 21 is wound around another positioning column 20 fixedly connected to the corresponding side of the clamp 18, the clamp 18 is in the receiving groove 19, and the clamp 18 is integrally formed into an arc-shaped structure matching the periphery of the test tube 3, so that when the test tube 3 is placed in the outer tube groove 9, the periphery of the test tube 3 contacts the clamp 18 and the compression spring 21 is compressed to a certain extent. At this time, the compression spring 21 provides a certain elastic force, so that the clamp 18 can be tightly attached to the test tube 3, so as to maintain the vertical state of the test tube 3, thereby ensuring smooth connection of the test tube 3 with the liquid.

[0032] Furthermore, a side of the clamping plate 18 facing away from the corresponding compression spring 21 is compositely connected with a rubber pad, so as to increase the friction coefficient between the clamping plate 18 and the surface wall of the test tube 3 and improve the tightening effect.

[0033] Furthermore, the front and rear sides of one end of the lifting plate 7 are provided with through holes for the sliding rod 6 to slide through, and the two sliding rods 6 are symmetrically arranged in parallel, the top and bottom ends of the sliding rod 6 are respectively fixedly connected to the bottom surface and bottom surface of the test tube placement area 2, and the other end of the lifting plate 7 is provided with a threaded through hole for the screw shaft 4 to pass through and be threadedly connected, the bottom end of the screw shaft 4 is rotatably connected to the bottom surface of the test tube placement area 2 through a bearing, and the top end of the screw shaft 4 is vertically upward and connected to the output shaft of the reduction motor 5 through a coupling, and the reduction motor 5 is fixedly installed at the corresponding position on the upper part of the test tube placement area 2, so that by starting the reduction motor 5 to drive the screw shaft 4 to rotate, the lifting and lowering movement of the lifting plate 7 is realized, thereby changing the height of the test tube 3 in the test tube holder 8, so that the depth of the liquid outlet tube in the test tube 3 can be adjusted to prevent liquid splashing due to the shallow position of the liquid outlet tube in the test tube 3.

[0034] Furthermore, an annular guide rail is fixedly connected to the circumference of the upper surface of the lifting plate 7, and a ball 23 is rollingly connected to the annular guide rail. The ball 23 is rollingly connected to the rolling groove provided on the lower surface of the positioning block, and the positioning block is fixedly connected to the circumference of the lower surface of the test tube holder 8, so that the test tube holder 8 can be rotated relative to the lifting plate 7 under manual operation, so that the test tubes 3 can be placed in the outer tube grooves 9 on the test tube holder 8 in sequence, thereby improving the convenience of operation. The test tube holder 8 is also provided with a limiting mechanism for temporarily positioning it with the lifting plate 7 after it is rotated to the desired position.

[0035] Furthermore, the limiting mechanism includes a plurality of vertical through holes around the test tube holder 8 for the clamping screw 32 to pass through, and a threaded tube 24 is fixedly connected to the top of the through hole corresponding to the upper surface of the test tube holder 8, and a clamping screw 32 is threadedly connected in the threaded tube 24. The clamping screw 32 is rotated and guided downward in the threaded tube 24, so that the lower end of the clamping screw 32 can contact and tighten to the upper surface of the lifting plate 7 to achieve positioning.

[0036] Furthermore, the top end of the clamping screw 32 is fixedly connected to a knob 17, and the bottom end of the clamping screw 32 is fixedly connected to an anti-skid pad 22. The purpose is that the knob 17 can facilitate hand-tightening of the clamping screw 32, and the anti-skid pad 22 can replace the bottom end surface of the clamping screw 32 to contact the lifting plate 7, thereby increasing the friction force after tightening, so that the test tube 3 on the test tube holder 8 remains stable when receiving liquid.

[0037] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0038] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An automatic Kjeldahl nitrogen analyzer, comprising a fully automatic Kjeldahl nitrogen analyzer body (1), wherein the Kjeldahl nitrogen analyzer body (1) has a test tube placement area (2) for placing a test tube (3), characterized in that: A lifting plate (7) movable in the vertical direction is arranged at the bottom of the test tube placement area (2); a test tube seat (8) is rotatably connected to the upper surface of the lifting plate (7); a plurality of outer tube grooves (9) for placing the test tubes (3) are provided in the circumference of the test tube seat (8); and a positioning mechanism for limiting the bottom circumference of the test tube (3) is arranged in each outer tube groove (9); and each outer tube groove (9) is in the shape of a semicircular groove and faces the center of the test tube seat (8). A guide channel (14) for the test tube (3) to slide is provided on one side, and the guide channel (14) is connected to a slot (15) provided on the periphery of the limiting tube (16), and a middle tube (13) is fixedly connected to the center of the inner bottom of the limiting tube (16), the middle tube (13) is located directly below the liquid outlet tube in the test tube placement area (2), and a gravity-triggered clamping mechanism is provided in the middle tube (13) for automatically clamping the test tube (3) after the test tube (3) is placed therein; The gravity-triggered clamping mechanism comprises a plurality of evenly distributed spring sheets (12) fixedly connected to the bottom surface of the middle tube (13); a support sheet (11) for supporting the test tube (3) is fixedly arranged on the top of the plurality of spring sheets (12); the bottom surfaces of the test tube holders (8) on both sides of the middle tube (13) are fixedly connected to vertical vertical sliding shafts (25); one end of a horizontal lifting shaft (35) is slidably connected to the vertical sliding shaft (25); a slider (26) is slidably connected to the upper side of the slider (26); the front side of the slider (26) is rotatably connected to one end of a second connecting rod (33) via a rotating shaft; the other end of the second connecting rod (33) is rotatably connected to a fixed plate on the upper wall of the middle tube (13); The outer end of the mounting rod (34) is fixedly connected, and the rear side surface of the slider (26) is rotatably connected to one end of the first connecting rod (30) through a rotating shaft, and the other end of the first connecting rod (30) is rotatably connected to one end of the linkage rod (31) through the rotating shaft, and the linkage rod (31) is slidably connected to a through hole provided in the side wall of the middle tube (13), and one end of the linkage rod (31) in the middle tube (13) is fixedly connected to a stop block (10), and the stop block (10) is integrally formed into a curved surface structure matching the outer periphery of the test tube (3), and the inner bottom of the middle tube (13) is also provided with a trigger assembly for lifting the lifting shaft (35) when the test tube (3) is subjected to weight; The trigger assembly comprises a second gear rod (29) fixedly connected to two side surfaces of the support plate (11), one side of the second gear rod (29) is meshedly connected to a gear (28), the gear (28) is rotatably connected to the inner bottom surface of the middle tube (13) through a bracket, and the other side of the gear (28) is meshedly connected to a first gear rod (27), and the top end of the first gear rod (27) is fixedly connected to an end of the lifting shaft (35) away from the vertical sliding shaft (25); The positioning mechanism comprises a receiving groove (19) provided in the test tube holder (8) at the periphery of the outer tube groove (9), a positioning column (20) being fixedly connected to the bottom surface of the receiving groove (19), one end of a compression spring (21) being wound around the positioning column (20), and the other end of the compression spring (21) being wound around another positioning column (20) fixedly connected to the corresponding side surface of the clamping plate (18), the clamping plate (18) being located in the receiving groove (19), and the clamping plate (18) being integrally formed into a curved surface structure matching the periphery of the test tube (3).

2. An automatic Kjeldahl nitrogen analyzer according to claim 1, characterized in that: The limiting cylinder (16) is open at the top and has a blocking structure at the bottom, and the slot (15) on the limiting cylinder (16) extends vertically downward from the top opening.

3. An automatic Kjeldahl nitrogen analyzer according to claim 1, characterized in that: A side surface of the clamping plate (18) facing away from the corresponding compression spring (21) is compositely connected with a rubber pad.

4. An automatic Kjeldahl nitrogen analyzer according to claim 1, characterized in that: The front and rear sides of one end of the lifting plate (7) are provided with through holes for the sliding rod (6) to slide through, and the two sliding rods (6) are symmetrically arranged in parallel. The top and bottom ends of the sliding rod (6) are respectively fixedly connected to the bottom surface and the bottom surface of the test tube placement area (2), and the other end of the lifting plate (7) is provided with a threaded through hole for the screw shaft (4) to penetrate and be threadedly connected. The bottom end of the screw shaft (4) is rotatably connected to the bottom surface of the test tube placement area (2) through a bearing, and the top end of the screw shaft (4) is vertically upward and is connected to the output shaft of the reduction motor (5) through a coupling. The reduction motor (5) is fixedly installed at a corresponding position on the upper part of the test tube placement area (2).

5. An automatic Kjeldahl nitrogen analyzer according to claim 1, characterized in that: The upper surface periphery of the lifting plate (7) is fixedly connected to an annular guide rail, on which a ball (23) is rollingly connected, and the ball (23) is rollingly connected to a rolling groove provided on the lower surface of a positioning block, and the positioning block is fixedly connected to the lower surface periphery of a test tube holder (8), and a limiting mechanism is also provided on the test tube holder (8) for temporarily positioning the test tube holder (8) with the lifting plate (7) after the test tube holder (8) is rotated to a desired position.

6. An automatic Kjeldahl nitrogen analyzer according to claim 5, characterized in that: The limiting mechanism comprises a plurality of vertical through holes provided around the periphery of the test tube holder (8) for the compression screw (32) to pass through, and a threaded tube (24) fixedly connected to the top of the through hole corresponding to the upper surface of the test tube holder (8), and the compression screw (32) is threadedly connected in the threaded tube (24).

7. An automatic Kjeldahl nitrogen analyzer according to claim 6, characterized in that: The top end of the pressing screw (32) is fixedly connected to a knob (17), while the bottom end of the pressing screw (32) is fixedly connected to an anti-slip pad (22).

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