Mounting frame

Abstract

The utility model discloses a mounting rack, which comprises a stand column and a first connecting piece fixed on the stand column, the first connecting piece is provided with a hook used for hooking a chassis of unmanned aerial vehicle supervision equipment, the top end of the stand column is provided with a first slot extending along the axial direction of the stand column, and the first slot is used for inserting and mounting a matched antenna of the unmanned aerial vehicle supervision equipment. The inner wall of the first slot is provided with a first threaded hole, and the first threaded hole is connected with a first hand screw used for abutting against the antenna. The mounting rack provided by the utility model not only can meet the erection requirement of a chassis of the unmanned aerial vehicle supervision equipment, but also can meet the erection requirement of a matched antenna of the unmanned aerial vehicle supervision equipment, thereby being beneficial to quickly and efficiently erecting the unmanned aerial vehicle supervision equipment and the matched antenna thereof.

Description

Technical Field

[0001] The utility model relates to the technical field of equipment erection and installation, in particular to a mounting frame. Background Art

[0002] In recent years, with the increasing application of drones, the supervision and control of drones has become increasingly important. Drone monitoring equipment usually involves comprehensive means such as signal acquisition, interference, deception, and attack to complete the supervision of drones. This requires that drone monitoring equipment be equipped with many antennas. However, there is currently a lack of mounting frames that can quickly and efficiently set up drone monitoring equipment and its supporting antennas. Utility Model Content

[0003] In view of this, the purpose of the utility model is to provide a mounting frame so as to quickly and efficiently set up drone monitoring equipment and its supporting antenna.

[0004] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0005] A mounting frame, comprising:

[0006] A column, wherein a first slot extending along the axial direction of the column is provided at the top of the column, the first slot is used to insert and install a matching antenna of a drone monitoring device, and a first threaded hole is provided on the inner wall of the first slot, and a first hand-tightened screw for tightening the antenna is connected to the first threaded hole;

[0007] The first connecting member is fixed to the column, and the first connecting member is provided with a hook for hanging the chassis of the drone monitoring device.

[0008] Optionally, in the above-mentioned mounting frame, the column includes a column body and a column head detachably mounted on the top end of the column body, and the first slot is provided at an end of the column head away from the column body.

[0009] Optionally, in the above-mentioned mounting frame, a second slot extending along the axial direction of the column is provided at the top end of the column body, a second threaded hole is provided on the inner wall of the second slot, and a stop screw is connected to the second threaded hole;

[0010] The column head is provided with an inserting portion for inserting and cooperating with the second slot, and the surface of the inserting portion is provided with a first groove for accommodating the front end of the stop screw.

[0011] Optionally, in the above-mentioned mounting frame, a through hole is formed on the inner wall of the second slot, a bolt for connecting the column body and the first connecting member is passed through the through hole, and a notch for avoiding the bolt is provided at one end of the plug-in portion away from the first slot.

[0012] Optionally, in the above-mentioned mounting frame, the first connecting member includes a column embracing body surrounding the column body, and the column embracing body is provided with a first mounting hole that cooperates with the bolt.

[0013] Optionally, in the above-mentioned mounting bracket, the first connecting member is located at a position of the column near the top end, and the mounting bracket includes a second connecting member fixed to a position of the column near the bottom end, and the second connecting member is provided with a third threaded hole, and the third threaded hole is connected to a second hand-tightened screw for engaging with a snap-fit ​​structure on the back of the chassis to limit the tilting of the chassis.

[0014] Optionally, in the above-mentioned mounting frame, a second mounting hole for connecting to the column is provided in the middle of the second connecting member, and pairs of third threaded holes are symmetrically provided at both ends of the second connecting member, and the connecting line of the two pairs of third threaded holes is perpendicular to the axial direction of the column.

[0015] Optionally, in the above-mentioned mounting frame, the second connecting member is provided with a plurality of groups of paired third threaded holes distributed along the first direction, and a connecting line between two third threaded holes in the same group is perpendicular to the first direction.

[0016] Optionally, the above-mentioned mounting frame includes:

[0017] A tripod having a mounting base and three legs rotatably connected to the mounting base, wherein the legs are telescopically adjustable;

[0018] The base is detachably connected to the mounting base, and the top of the base is provided with a third slot for inserting and installing the bottom end of the column, the inner wall of the third slot is provided with a fourth threaded hole, and the fourth threaded hole is connected with a third hand screw for fixing the column.

[0019] Optionally, in the above-mentioned mounting frame, a second groove for accommodating the front end of the third hand screw is provided near the bottom end of the column.

[0020] The mounting bracket provided by the utility model has the following beneficial effects:

[0021] The mounting frame includes a column and a first connecting piece fixed to the column, the first connecting piece is provided with a hook for hanging the chassis of the drone monitoring device, and the top of the column is provided with a first slot extending along the axial direction of the column, the first slot is used to plug and install the supporting antenna of the drone monitoring device. Therefore, the mounting frame of the utility model can meet the installation requirements of the chassis of the drone monitoring device, and can also meet the installation requirements of the supporting antenna of the drone monitoring device, which is conducive to the quick and efficient installation of the drone monitoring device and its supporting antenna. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0023] Figure 1 It is a schematic diagram of the use state of the mounting bracket provided by the embodiment of the utility model;

[0024] Figure 2 yes Figure 1 An exploded schematic diagram of the structure shown;

[0025] Figure 3 It is a schematic diagram of a column assembly of a mounting frame provided by an embodiment of the utility model;

[0026] Figure 4 yes Figure 3 An exploded schematic diagram of the structure shown;

[0027] Figure 5 yes Figure 3 A schematic diagram of the structure shown in another viewing angle;

[0028] Figure 6 yes Figure 4 Schematic diagram of the stigma in;

[0029] Figure 7 yes Figure 4 A schematic diagram of a first connecting member in FIG.

[0030] Figure 8 yes Figure 4 A schematic diagram of the second connecting member in FIG.

[0031] Fig. 9 yes Figure 1 A partial and partial enlarged schematic diagram of;

[0032] Fig.10 yes Figure 2 A schematic diagram of a base assembly in FIG.

[0033] Fig.11 yes Fig.10 An exploded schematic diagram of the structure shown;

[0034] Fig.12 yes Fig.11 Schematic diagram of the base in .

[0035] The markings in the figure are:

[0036] 100, antenna; 200, chassis; 300, column assembly; 400, base assembly; 500, tripod;

[0037] 310, column body; 311, first alignment mark; 312, second groove;

[0038] 320, column head; 321, first slot; 322, first groove; 323, notch; 324, first threaded hole;

[0039] 330, first hand tighten the screw;

[0040] 340, first connecting member; 341, hook; 342, third mounting hole; 343, column body; 344, first mounting hole;

[0041] 350, second hand tightens the screw;

[0042] 360, second connecting member; 361, second mounting hole; 362, third threaded hole;

[0043] 410, base; 420, third hand screw; 430, pressure plate; 440, fastener;

[0044] 411, pin; 412, disc body; 413, reinforcing rib; 414, cylinder body; 415, fourth threaded hole; 416, second alignment mark;

[0045] 601, bolt; 602, first fastening screw; 603, second fastening screw; 604, stop screw; 605, nut. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0047] See also Figure 1 to Figure 12The embodiment of the utility model provides a mounting frame, including a column assembly 300, the column assembly 300 includes a column and a first connecting member 340 fixed to the column, wherein the first connecting member 340 is provided with a hook 341 for hanging the chassis 200 of the drone monitoring device, the top of the column is provided with a first slot 321 extending along the axial direction of the column, the first slot 321 is used to plug and install the matching antenna of the drone monitoring device, the inner wall of the first slot 321 is provided with a first threaded hole 324, and the first threaded hole 324 is connected with a first hand screw 330 for tightening the antenna 100. When using the mounting frame, the chassis 200 of the drone monitoring device is hung on the hook 341 of the first connecting member 340 to achieve installation, and the antenna 100 matched with the drone monitoring device is plugged into the first slot 321 at the top of the column, and the antenna 100 is tightened and fixed with the first hand screw 330 to achieve installation. It can be seen that the mounting frame of the utility model can meet the requirements for the installation of the chassis of the drone monitoring device, and can also meet the requirements for the installation of the supporting antenna of the drone monitoring device, which is conducive to the quick and efficient installation of the drone monitoring device and its supporting antenna. It should be noted that the antenna 100 plugged into the top of the column is an antenna independent of the chassis 200 that is additionally configured to realize the multiple functions of the drone monitoring device. In some embodiments, the chassis 200 of the drone monitoring device can have some antennas, and these antennas are installed together with the chassis 200, that is, the installation requirements of these antennas do not need to be considered separately, and only the installation requirements of the chassis 200 need to be considered. In other words, the antennas provided by the chassis 200 do not use the first slot 321 at the top of the column to complete the installation.

[0048] It should be understood that a hand screw is a screw with a hand-tightening operating part, which can be turned by hand without the need for tools. The hand-tightening operating part of a hand screw can be set in a variety of structural forms, such as butterfly shape, S shape, etc. The present invention does not limit the structural form of the hand screw, as long as it can meet the requirements of tool-free installation.

[0049] The hook 341 of the first connecting member 340 is used to hang the chassis 200. The position of the first connecting member 340 on the column can be set as needed, as long as the chassis 200 does not affect the antenna 100 being installed on the top of the column after being hung on the first connecting member 340. Since the chassis 200 is hung on the hook 341 of the first connecting member 340, the chassis 200 itself has a structure that cooperates with the hook 341, and the structure bears the upward force applied by the hook 341, so that the chassis 200 is supported by the hook 341. It is easy to understand that in order to make the chassis 200 hung on the hook 341 more stable, the size of the hook 341 in the horizontal direction should be as large as possible, so as to form a greater support for the chassis 200 to prevent the chassis 200 from swinging. For example, two hooks 341 can be set and distributed in the horizontal direction.

[0050] like Figure 3~Figure 6 As shown, in some embodiments, the column may include a column body 310 and a column head 320 detachably mounted on the top of the column body 310, and a first slot 321 is provided at one end of the column head 320 away from the column body 310. In this structure, the column head 320 can be removed from the column body 310, so by configuring a plurality of column heads 320 that can be connected to the column body 310, and providing first slots 321 of different sizes on different column heads 320, the adaptability of the mounting frame to antennas 100 of different specifications can be improved. For example, for antennas 100 of different thicknesses, the antenna 100 can be conveniently installed by replacing the column head 320 with a suitable first slot 321. In addition, the split design of the column also facilitates the column body 310 and the column head 320 to be made of different materials, so that different parts of the column can be appropriately selected according to different requirements, thereby achieving better comprehensive benefits. For example, the main part of the column is usually required to have a higher structural strength, and generally a thicker tube body is required. The inner diameter of the thicker tube body may be much larger than the diameter of the lower end of the antenna 100. Directly plugging the antenna 100 into the top of the tube body will not be very stable. Therefore, the column body 310 can be set as a thicker tube body, and the column head 320 can be set as a thinner tube body. The inner diameter of the thinner tube body matches the diameter of the lower end of the antenna 100. In this way, the requirements of the main part of the column having a higher strength are met, and the requirements of stably setting up the antenna 100 are also met. Of course, in other embodiments, the column can also adopt an integrated design, that is, the column body 310 and the column head 320 are set as an integrated structure.

[0051] In some embodiments, in order to realize the detachable connection between the column head 320 and the column body 310, the top of the column body 310 may be provided with a second slot extending along the axial direction of the column, the inner wall of the second slot is provided with a second threaded hole, and the second threaded hole is connected with a stop screw 604; the column head 320 may be provided with a plug-in portion for plugging and matching with the second slot, and the surface of the plug-in portion is provided with a first groove 322 for accommodating the front end of the stop screw 604. The column head 320 and the column body 310 are assembled, the column head 320 is inserted into the second slot, and then the stop screw 604 is tightened. Since the front end of the stop screw 604 is accommodated in the first groove 322 on the surface of the column head 320, the column head 320 can be prevented from falling out of the second slot. In order to complete the assembly more easily, the first groove 322 can be set as an annular groove extending along the circumference of the column head 320, so that the front end of the stop screw 604 can be accommodated in the first groove 322 without deliberately rotating the column head 320. Of course, in other embodiments, the connection structure between the column head 320 and the column body 310 can also be set to other forms, as long as the column head 320 can be detachably installed on the top of the column body 310. For example, the column head 320 and the column body 310 are connected by threads, that is, the lower end of the column head 320 and the top end of the column body 310 are provided with threads that can be screwed together.

[0052] like Figure 3~Figure 6 As shown, in some embodiments, a through hole is formed on the inner wall of the second slot, and a bolt 601 for connecting the column body 310 and the first connecting member 340 is passed through the through hole, and a notch 323 for avoiding the bolt 601 is formed at one end of the plug-in portion of the column head 320 away from the first slot 321. In this structure, when the column head 320 is inserted into the second slot at the top of the column body 310, the notch 323 at the lower end of the column head 320 is clamped on the bolt 601 connecting the column body 310 and the first connecting member 340, and the bolt 601 can limit the rotation of the column head 320 relative to the column body 310, so that the column head 320 is more firmly installed on the column body 310.

[0053] like Figure 4 , Figure 5 and Figure 7 As shown, in some embodiments, the first connecting member 340 may include a column body 343 surrounding the column body 310, and the column body 343 is provided with a first mounting hole 344 that cooperates with the bolt 601. When installing the first connecting member 340, the column body 343 is inserted from the top end of the column body 310 to the column body 310, and the position of the first connecting member 340 is adjusted so that the first mounting hole 344 is aligned with the through hole of the column body 310, and then the bolt 601 is inserted and tightened with the nut 605, so as to fix the first connecting member 340 to the column body 310. Figure 7As shown, the first connecting member 340 can be a sheet metal part, the hook 341 is formed by bending a part of the sheet metal part upward, and the column body 343 is formed by bending two parts of the sheet metal part horizontally toward each other. The column body 343 is located above the hook 341, that is, in the axial direction of the column, the column body 343 is located above the hook 341. Figure 4 and Figure 7 As shown, in order to further improve the stability of the connection between the first connecting member 340 and the column, the first connecting member 340 can be provided with a third mounting hole 342 below the holding body, and the first fastening screw 602 passes through the third mounting hole 342 to connect the first connecting member 340 to the column. The third mounting hole 342 can be set as a conical countersunk hole, so that the head of the first fastening screw 602 can be prevented from protruding from the side where the hook 341 of the first connecting member 340 is located, so as not to scratch the chassis 200 hung on the hook 341. The third mounting hole 342 and the first mounting hole 344 are staggered in the circumferential direction of the column, so that the connection between the first connecting member 340 and the column can be more stable. The third mounting hole 342 and the first mounting hole 344 can be respectively provided with a plurality of holes along the axial direction of the column, for example, the first mounting hole 344 is provided with three holes arranged vertically, and the third mounting hole 342 is provided with four holes arranged vertically.

[0054] like Figure 3~Figure 9 As shown, in some embodiments, the mounting bracket may include a second connecting member 360 fixed to a position near the bottom of the column, the second connecting member 360 is provided with a third threaded hole 362, and the third threaded hole 362 is connected with a second hand screw 350 for locking with the clamping structure at the back of the chassis 200 to limit the tilting of the chassis 200. In this structure, the first connecting member 340 is located near the top of the column, and after the chassis 200 is hooked to the hook 341 of the first connecting member 340, the clamping structure at the back of the chassis 200 is against the position where the second connecting member 360 is located, and the second hand screw 350 is screwed to move it toward the chassis 200 until it is locked with the clamping structure at the back of the chassis 200, as shown in FIG. Fig. 9 As shown, after the second hand screw 350 is screwed forward to the right position, the chassis 200 can be restricted from tilting. Tilt means that the chassis 200 tilts to the left or right. That is, the second hand screw 350 forms a locking fit with the clamping structure at the back of the chassis 200, which can prevent the chassis 200 from tilting. Fig. 9 The chassis 200 in the machine body rotates counterclockwise or clockwise, so that when the front cover of the chassis 200 is opened, although the overall center of gravity of the chassis 200 is offset, the chassis 200 does not rotate, so the staff does not need to hold the chassis 200 with their hands.

[0055] In some embodiments, a second mounting hole 361 for connecting to a column may be provided in the middle of the second connecting member 360, and a pair of third threaded holes 362 may be symmetrically provided at both ends of the second connecting member 360, and the connecting line of the two pairs of third threaded holes 362 is perpendicular to the axial direction of the column. The second fastening screw 603 passes through the second mounting hole 361 to connect the second connecting member 360 to the column, and the second mounting hole 361 may be provided as a circular countersunk hole, so that the head of the second fastening screw 603 is prevented from protruding on the side of the second connecting member 360 facing the chassis 200, thereby preventing it from hitting the back of the chassis 200. The third threaded holes 362 are provided in pairs at both ends of the second connecting member 360 in the horizontal direction, which can better prevent the chassis 200 from rotating. Fig. 9 As shown, the snap-in structure on the back of the chassis 200 can be a long hole extending horizontally. Figure 8 As shown, in some embodiments, the second connecting member 360 may be provided with a plurality of groups of paired third threaded holes 362 distributed along the first direction, and the line connecting the two third threaded holes 362 in the same group is perpendicular to the first direction. As mentioned above, the line connecting the two paired third threaded holes 362 is perpendicular to the axial direction of the column, so the first direction is parallel to the axial direction of the column, that is, a plurality of groups of third threaded holes 362 are provided along the axial direction of the column. When chassis 200 of different sizes are hung on the mounting frame, the position height of the clamping structure on the back of the chassis 200 may be different. By providing a plurality of groups of third threaded holes 362 along the axial direction of the column, the third threaded holes 362 at appropriate positions can be selected as needed to screw in the second hand screws 350.

[0056] like Figure 1 , Figure 2 , Figure 10~Figure 12As shown, in some embodiments, the mounting frame may include a tripod 500 and a base assembly 400, wherein the tripod 500 has a mounting seat and three legs rotatably connected to the mounting seat, and the legs are telescopically adjustable, and the base assembly 400 includes a base 410 detachably connected to the mounting seat, and the top of the base 410 is provided with a third slot for inserting the bottom end of the mounting column, and the inner wall of the third slot is provided with a fourth threaded hole 415, and the fourth threaded hole 415 is connected with a third hand screw 420 for fixing the column. The mounting frame can be flexibly and firmly placed in a desired location, such as a rooftop of a building, through the tripod 500. The top of the tripod 500 is a mounting seat, and the base 410 can be installed on it, and the base 410 is used to connect the column. During assembly, the lower end, i.e., the bottom end of the column is inserted into the third slot of the base 410, and then the third hand screw 420 is tightened to fix the column. In order to improve the stability of the column on the base 410, a second groove 312 for accommodating the front end of the third hand screw 420 may be provided near the bottom of the column. The second groove 312 may be set as a round hole matching the front end of the third hand screw 420, so that when the front end of the third hand screw 420 is accommodated in the second groove 312, the column can be restricted from horizontal rotation and vertical sliding relative to the base 410. In this structure, the column needs to be rotated to a suitable position to align the second groove 312 with the third hand screw 420. In order to improve the convenience of assembly, a first alignment mark 311 may be provided on the outer surface of the column, and a second alignment mark 416 cooperating with the first alignment mark 311 may be provided near the top of the outer surface of the base 410. When the first alignment mark 311 is aligned with the second alignment mark 416, the second groove 312 is aligned with the fourth threaded hole 415. The first alignment mark 311 and the second alignment mark 416 may be engraved lines or arrow patterns.

[0057] like Figure 10~Figure 12 As shown, in some embodiments, the base 410 may include a cylinder 414 and a disk 412 connected to the lower end of the cylinder 414. The disk 412 is provided with three pins 411 on a side away from the cylinder 414. The pins 411 are used to be plugged into the mounting base of the tripod 500, that is, the mounting base of the tripod 500 is provided with three sockets corresponding to the pins 411. The cross-sectional shape of the pin 411 is adapted to the shape of the socket of the mounting base, for example, Fig.12 In the embodiment shown, the cross section of the pin 411 is a curved oblong hole. In order to improve the overall strength of the base 410, the base 410 may include a reinforcing rib 413 connecting the side wall of the cylinder 414 and the surface of the disk 412, such as Fig.12 As shown, the reinforcing ribs 413 are provided in plurality and are evenly distributed along the circumference of the cylinder 414. Fig.10 and Fig.11As shown, a center column with a threaded hole can be provided at the center position of the side of the disk body 412 away from the cylinder body 414. When the base 410 is inserted into the mounting base of the tripod 500, the center column is inserted into the center hole of the mounting base. The fastener 440 (such as a bolt or a screw) is screwed into the threaded hole of the center column to fix the pressure plate 430. The pressure plate 430 is pressed against the side of the mounting base of the tripod 500 away from the column, that is, pressed against the lower surface of the mounting base, thereby limiting the upward movement of the base 410 relative to the tripod 500.

[0058] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0059] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A mounting frame, characterized in that: include: A column, wherein a first slot extending along the axial direction of the column is provided at the top of the column, the first slot is used to insert and install a matching antenna of a drone monitoring device, and a first threaded hole is provided on the inner wall of the first slot, and a first hand-tightened screw for tightening the antenna is connected to the first threaded hole; The first connecting member is fixed to the column, and the first connecting member is provided with a hook for hanging the chassis of the drone monitoring device.

2. The mounting bracket according to claim 1, characterized in that: The column comprises a column body and a column head detachably mounted on the top end of the column body, and the first slot is arranged at one end of the column head away from the column body.

3. The mounting bracket according to claim 2, characterized in that: A second slot extending along the axial direction of the column is disposed at the top end of the column body, a second threaded hole is formed on the inner wall of the second slot, and a stop screw is connected to the second threaded hole; The column head is provided with an inserting portion for inserting and cooperating with the second slot, and the surface of the inserting portion is provided with a first groove for accommodating the front end of the stop screw.

4. The mounting bracket according to claim 3, characterized in that: A through hole is formed on the inner wall of the second slot, through which a bolt for connecting the column body and the first connecting member passes, and a notch for avoiding the bolt is formed at one end of the plug-in portion away from the first slot.

5. The mounting bracket according to claim 4, characterized in that: The first connecting member includes a column-embracing body that embraces the column body, and the column-embracing body is provided with a first mounting hole that cooperates with the bolt.

6. The mounting bracket according to claim 1, characterized in that: The first connecting member is located near the top of the column, and the mounting frame includes a second connecting member fixed to the bottom of the column. The second connecting member is provided with a third threaded hole, and the third threaded hole is connected with a second hand-tightened screw for engaging with the snap-fit ​​structure on the back of the chassis to limit the tilting of the chassis.

7. The mounting bracket according to claim 6, characterized in that: A second mounting hole for connecting the column is arranged in the middle of the second connecting member, and a pair of third threaded holes are symmetrically arranged at both ends of the second connecting member, and a connecting line of the two pairs of third threaded holes is perpendicular to the axial direction of the column.

8. The mounting bracket according to claim 7, characterized in that: The second connecting member is provided with a plurality of groups of paired third threaded holes distributed along the first direction, and a connecting line between two third threaded holes in the same group is perpendicular to the first direction.

9. The mounting bracket according to any one of claims 1 to 8, characterized in that: include: A tripod having a mounting base and three legs rotatably connected to the mounting base, wherein the legs are telescopically adjustable; The base is detachably connected to the mounting base, and the top of the base is provided with a third slot for inserting and installing the bottom end of the column, the inner wall of the third slot is provided with a fourth threaded hole, and the fourth threaded hole is connected with a third hand screw for fixing the column.

10. The mounting bracket according to claim 9, characterized in that: A second groove for accommodating the front end of the third hand screw is provided near the bottom end of the column.

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