A super-tonnage frame type multi-cylinder synchronous hydraulic machine rack device

Abstract

The application discloses a rack device of a super-large tonnage frame type multi-cylinder synchronous hydraulic machine, which adopts double-row four-point universal spherical surface support, screw top end pre-tightening suspension, and the front and rear sides of an upper beam are expanded and fastened with inclined wedge block groups and the inner sides of columns, the outer sides are fastened and connected with the inner sides of the columns through fixed bases and positioning, the left and right end faces are connected with the columns and the upper beam through flange plates, the columns and a lower beam are supported by universal support bases, the front and rear sides of the lower beam are expanded and fastened with inclined wedge block groups and the inner sides of the columns, the lower fixed bases are positioned and fastened with the inner sides of the columns, and the left and right sides are connected with the columns through lower end face flange plates; the frame type composite connection structure is adopted for the connection of the columns and the lower beam. The device has the advantages that the instability of the rack caused by the stress and deformation changes at the contact position is solved, the stability of the machine tool is improved, the mechanism is optimized, the weight and cost are reduced, and the device is convenient for machining, transportation and installation.

Description

TECHNICAL FIELD

[0001] The present application relates to the super tonnage hydraulic machine body structure, specifically to the fixed connection structure of the column and the top beam and the bottom beam of the super tonnage hydraulic machine, and belongs to the field of forging and pressing mechanical equipment, in particular to a super tonnage frame type multi-cylinder synchronous hydraulic machine rack device. BACKGROUND

[0002] With the rapid development of sheet metal forming industry and the wide application of high-strength materials, the processing demand of large thickness and high-strength plate bending forming process in various industries increases sharply, and the conventional small tonnage forming equipment cannot meet the production needs.

[0003] Therefore, the market demand for super tonnage hydraulic machine increases sharply, and the super tonnage hydraulic machine not only meets the requirements of long and thick workpiece bending, but also has good reliability and stability. The machine body structure after design is complex and large in size. When the hydraulic machine works, the rack is subjected to alternating stress and deformation, and there are problems of uneven stress and stress concentration caused by working force bias load and processing and manufacturing errors, which seriously affect the stability and reliability of the machine body. In order to solve the above problems, a frame type multi-cylinder synchronous hydraulic machine composite connection rack is needed to solve the above problems. SUMMARY

[0004] The purpose of the present application is to provide a super tonnage frame type multi-cylinder synchronous hydraulic machine rack device, which adopts an integral temple type welding structure, and the upper beam and the lower beam are integral box type welding structures. The stress and deformation of each part under full load are designed by using three-dimensional finite element analysis and optimization design, so that the material distribution of the box type structure is more reasonable, and the utilization rate of the material is the highest.

[0005] In order to achieve the above purpose, the super tonnage frame type multi-cylinder synchronous hydraulic machine rack device provided by the present application comprises a rack, and the rack comprises a first column, a second column, an upper beam and a lower beam. The first column and the second column are two side support columns of the rack, and the first column and the second column are connected by the upper beam and the lower beam. The first column and the second column are rectangular frames.

[0006] The upper beam penetrates the rectangular frames of the first column and the second column, and the lower beam penetrates the rectangular frames of the first column and the second column.

[0007] One end side of the upper beam is fixedly connected with the top end of the first column through a first upper end plate, and the other end side of the upper beam is fixedly connected with the top end of the second column through a second upper end plate.

[0008] A first double-row universal spherical surface support is arranged between one end of the upper beam and the top of the frame of the first column, and a first top inclined wedge block group is arranged between the first double-row universal spherical surface support and the inner side surface of the frame of the first column.

[0009] A second double-row universal spherical surface support is arranged between the other end of the upper beam and the inner top of the second rectangular frame of the stand column, and a second top inclined wedge block group is arranged between the second double-row universal spherical surface support and the inner side of the second rectangular frame of the stand column;

[0010] One end of the lower beam is fixedly connected to the bottom end of the first stand column through a first lower end plate, and the other end of the lower beam is fixedly connected to the bottom end of the second stand column through a second lower end plate;

[0011] A first bottom universal support group is arranged between one end of the lower beam and the inner bottom of the first rectangular frame of the stand column, and a first bottom inclined wedge block group is arranged between the first bottom universal support group and the inner side of the first rectangular frame of the stand column;

[0012] A second bottom universal support group is arranged between the other end of the lower beam and the inner bottom of the second rectangular frame of the stand column, and a second bottom inclined wedge block group is arranged between the second bottom universal support group and the inner side of the second rectangular frame of the stand column.

[0013] The first top inclined wedge block group is provided with two groups of inclined wedge blocks, and the two groups of inclined wedge blocks are arranged on opposite sides of the upper beam, and each group of inclined wedge blocks is provided with two;

[0014] The second top inclined wedge block group is provided with two groups of inclined wedge blocks, and the two groups of inclined wedge blocks are arranged on opposite sides of the upper beam, and each group of inclined wedge blocks is provided with two.

[0015] The first bottom inclined wedge block group is provided with two groups of inclined wedge blocks, and the two groups of inclined wedge blocks are arranged on opposite sides of the lower beam, and each group of inclined wedge blocks is provided with two;

[0016] The second bottom inclined wedge block group is provided with two groups of inclined wedge blocks, and the two groups of inclined wedge blocks are arranged on opposite sides of the lower beam, and each group of inclined wedge blocks is provided with two.

[0017] The first stand column top end is provided with a first pre-tightening screw, and the first pre-tightening screw is installed at the first stand column top end through a first upper end pre-tightening nut, and a pre-tightening pad is arranged between the first upper end pre-tightening nut and the first stand column; the first pre-tightening screw penetrates one end of the upper beam; a first lower pre-tightening nut is installed on the first pre-tightening screw extending out of one end of the upper beam, and a pre-tightening pad is arranged between the first lower pre-tightening nut and the upper beam;

[0018] The second stand column top end is provided with a second pre-tightening screw, and the second pre-tightening screw is installed at the second stand column top end through a second upper end pre-tightening nut, and a pre-tightening pad is arranged between the second upper end pre-tightening nut and the second stand column; the second pre-tightening screw penetrates the other end of the upper beam; a second lower pre-tightening nut is installed on the second pre-tightening screw extending out of one end of the upper beam, and a pre-tightening pad is arranged between the second lower pre-tightening nut and the upper beam.

[0019] The first upright column is connected with the upper beam through a first upper outer fixing base, and the second upright column is connected with the upper beam through a second upper outer fixing base; the first upright column is connected with the lower beam through a first lower outer fixing base, and the second upright column is connected with the lower beam through a second lower outer fixing base.

[0020] The first upper outer fixing base, the second upper outer fixing base, the first lower outer fixing base and the second lower outer fixing base are right-angle fixing supports.

[0021] The first upper outer fixing base is provided with two, and is fixedly connected with two sides of the first upright column and the upper beam correspondingly; one right-angle fixing edge of the right-angle fixing support of the first upper outer fixing base is connected with the upper beam, and the other right-angle fixing edge is connected with the first upright column.

[0022] The second upper outer fixing base is provided with two, and is fixedly connected with two sides of the second upright column and the upper beam correspondingly; one right-angle fixing edge of the right-angle fixing support of the second upper outer fixing base is connected with the upper beam, and the other right-angle fixing edge is connected with the second upright column.

[0023] The first lower outer fixing base is provided with two, and is fixedly connected with two sides of the first upright column and the lower beam correspondingly; one right-angle fixing edge of the right-angle fixing support of the first lower outer fixing base is connected with the lower beam, and the other right-angle fixing edge is connected with the first upright column.

[0024] The second lower outer fixing base is provided with two, and is fixedly connected with two sides of the second upright column and the lower beam correspondingly; one right-angle fixing edge of the right-angle fixing support of the second lower outer fixing base is connected with the lower beam, and the other right-angle fixing edge is connected with the second upright column.

[0025] The inner side of the rectangular frame of the first upright column is a trapezoid with a long top end and a short lower end; and the inner side of the rectangular frame of the second upright column is a trapezoid with a long top end and a short lower end.

[0026] The frame device of the super-large-tonnage frame type multi-cylinder synchronous hydraulic machine has the following advantages: 1. The upper beam and the upright column are supported by double-row four-point universal spherical surfaces, and the screw top end is pre-tightened and suspended; the front and rear sides of the upper beam are tightened by the inner side of the upright column through the inclined wedge block group, and the outer side is positioned and tightly connected with the inner side of the upright column through the fixing base; the left and right end faces are connected with the upright column and the upper beam through the flange plate; the upright column and the lower beam are supported by the universal support seat; the front and rear sides of the lower beam are tightened by the inner side of the upright column through the inclined wedge block group; the lower fixing base is positioned and tightly connected with the inner side of the upright column; and the left and right sides are connected with the upright column through the lower end flange plate.

[0027] 2. The upper beam and lower beam are connected with the column by spherical surface support connection. The contact stress caused by the alternating stress and deformation and the processing error of the upper and lower beams will not change during work, thereby solving the instability of the rack caused by the change of stress and deformation at the contact;

[0028] 3. The upper beam is suspended and pre-tightened at the top of the column. The inside of the column in the front and rear directions is connected by a combination of inclined expansion wedge blocks and an external fixed seat, and the left and right end flange plates are combined and positioned to constrain, which greatly improves the stability of the machine tool;

[0029] 4. The device adopts a box structure, optimizes the mechanism, greatly reduces the weight and cost, and is convenient for processing, transportation and installation. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a front view of the device;

[0031] Figure 2 is a side view of Figure 1 ;

[0032] Figure 3 is a top view of Figure 1 ;

[0033] Figure 4 is a perspective view;

[0034] In the figure: 1 - first column; 2 - upper beam; 3 - second column 3; 4 - first upper end plate; 4-1 - second upper end plate; 5 - first upper outer fixed seat; 5-1 - second upper outer fixed seat; 5-2 - first lower outer fixed seat; 5-3 - second lower outer fixed seat; 6 - first lower end plate; 6-1 second lower end plate; 7 - lower beam; 8 - first upper end pre-tightening nut; 8-1 - second upper end pre-tightening nut; 9 - pre-tightening pad; 10 - first pre-tightening screw; 10-1 - second pre-tightening screw; 11 - first double-row universal spherical surface support; 11-1 - second double-row universal spherical surface support; 12 - first top inclined expansion wedge block group; 12-1 - second top inclined expansion wedge block group; 13 - first lower pre-tightening nut; 13-1 - second lower pre-tightening nut; 14 - first bottom inclined expansion wedge block group; 14-1 - second bottom inclined expansion wedge block group; 15 - first bottom universal support group; 15-1 - second bottom universal support group; 16 - fixed seat screw; 17 - tensioning bolt; 18 - end plate screw. DETAILED DESCRIPTION

[0035] Example 1

[0036] As Figures 1-4As shown, the rack device of the super-large tonnage frame type multi-cylinder synchronous hydraulic machine of the application comprises a rack, the rack comprises a first column 1, a second column 3, an upper beam 2 and a lower beam 7, the first column 1 and the second column 3 are two side support columns of the rack, the first column 1 and the second column 3 are connected through the upper beam 2 and the lower beam 7, and the first column 1 and the second column 3 are rectangular frames;

[0037] The upper beam 2 penetrates the rectangular frame of the first column 1 and the second column 3, and the lower beam 7 penetrates the rectangular frame of the first column 1 and the second column 3;

[0038] One end side of the upper beam 2 is fixedly connected with the top end of the first column 1 through a first upper end plate 4, and the other end side of the upper beam 2 is fixedly connected with the top end of the second column 3 through a second upper end plate 4-1;

[0039] A first double-column universal spherical surface support 11 is arranged between one end of the upper beam 2 and the top part inside the rectangular frame of the first column 1, and a first top inclined expansion wedge block group 12 is arranged between the inner side surface of the rectangular frame of the first column 1;

[0040] A second double-column universal spherical surface support 11-1 is arranged between the other end of the upper beam 2 and the top part inside the rectangular frame of the second column 3, and a second top inclined expansion wedge block group 12-1 is arranged between the inner side surface of the rectangular frame of the second column 3;

[0041] One end side of the lower beam 7 is fixedly connected with the bottom end of the first column 1 through a first lower end plate 6, and the other end side of the lower beam 7 is fixedly connected with the bottom end of the second column 3 through a second lower end plate 6-1;

[0042] A first bottom universal support group 15 is arranged between one end of the lower beam 7 and the bottom part inside the rectangular frame of the first column 1, and a first bottom inclined expansion wedge block group 14 is arranged between the inner side surface of the rectangular frame of the first column 1;

[0043] A second bottom universal support group 15-1 is arranged between the other end of the lower beam 7 and the bottom part inside the rectangular frame of the second column 3, and a second bottom inclined expansion wedge block group 14-1 is arranged between the inner side surface of the rectangular frame of the second column 3.

[0044] The first top inclined expansion wedge block group 12 is provided with two groups of inclined expansion wedge blocks, and the two groups of inclined expansion wedge blocks are arranged on opposite sides of the upper beam 2, and each group of inclined expansion wedge blocks is provided with two;

[0045] The second top inclined expansion wedge block group 12-1 is provided with two groups of inclined expansion wedge blocks, and the two groups of inclined expansion wedge blocks are arranged on opposite sides of the upper beam 2, and each group of inclined expansion wedge blocks is provided with two.

[0046] The first bottom inclined surface tension wedge group 14 is provided with two groups of inclined surface tension wedges, and each group of inclined surface tension wedges is arranged on the opposite side of the lower beam 7, and each group of inclined surface tension wedges is provided with two.

[0047] The second bottom inclined surface tension wedge group 14-1 is provided with two groups of inclined surface tension wedges, and each group of inclined surface tension wedges is arranged on the opposite side of the lower beam 7, and each group of inclined surface tension wedges is provided with two.

[0048] The first pre-tightening screw 10 is installed at the top end of the first column 1, and the first pre-tightening screw 10 is installed at the top end of the first column 1 through the first upper end pre-tightening nut 8, and the first upper end pre-tightening nut 8 is provided with a pre-tightening pad 9 between the first column 1; one end of the first pre-tightening screw 10 penetrates the upper beam 2; the first lower pre-tightening nut 13 is installed on the first pre-tightening screw 10 extending out of one end of the upper beam 2, and the first lower pre-tightening nut 13 is provided with a pre-tightening pad 9 between the upper beam 2.

[0049] The second pre-tightening screw 10-1 is installed at the top end of the second column 3, and the second pre-tightening screw 10-1 is installed at the top end of the second column 3 through the second upper end pre-tightening nut 8-1, and the second upper end pre-tightening nut 8-1 is provided with a pre-tightening pad 9 between the second column 3; the second pre-tightening screw 10-1 penetrates the other end of the upper beam 2; the second lower pre-tightening nut 13-1 is installed on the second pre-tightening screw 10-1 extending out of one end of the upper beam 2, and the second lower pre-tightening nut 13-1 is provided with a pre-tightening pad 9 between the upper beam 2.

[0050] The first column 1 and the upper beam 2 are connected through the first upper outer fixed seat 5, and the second column 3 and the upper beam 2 are connected through the second upper outer fixed seat 5-1; the first column 1 and the lower beam 7 are connected through the first lower outer fixed seat 5-2, and the second column 3 and the lower beam 7 are connected through the second lower outer fixed seat 5-3.

[0051] The first upper outer fixed seat 5, the second upper outer fixed seat 5-1, the first lower outer fixed seat 5-2 and the second lower outer fixed seat 5-3 are right angle fixed supports.

[0052] The first upper outer fixed seat 5 is provided with two, which are respectively fixedly connected to the corresponding two sides of the first column 1 and the upper beam 2, and one of the right angle fixed edges of the right angle fixed support of the first upper outer fixed seat 5 is connected to the upper beam 2, and the other right angle fixed edge is connected to the first column 1.

[0053] The second upper outer fixed seat 5-1 is provided with two, which are respectively fixedly connected to the corresponding two sides of the second column 3 and the upper beam 2, and one of the right angle fixed edges of the right angle fixed support of the second upper outer fixed seat 5-1 is connected to the upper beam 2, and the other right angle fixed edge is connected to the second column 3.

[0054] The first lower outer fixing seat 5-2 is provided with two, which are fixedly connected with the two sides of the first column 1 and the lower beam 7 respectively, one right angle fixed edge of the right angle fixed support of the first lower outer fixing seat 5-2 is connected with the lower beam 7, and the other right angle fixed edge is connected with the first column 1.

[0055] The second lower outer fixing seat 5-3 is provided with two, which are fixedly connected with the two sides of the second column 3 and the lower beam 7 respectively, one right angle fixed edge of the right angle fixed support of the second lower outer fixing seat 5-3 is connected with the lower beam 7, and the other right angle fixed edge is connected with the second column 3.

[0056] The inner side of the rectangular frame of the first column 1 is a trapezoid with long top end and short lower end, and the inner side of the rectangular frame of the second column 3 is a trapezoid with long top end and short lower end.

[0057] The right angle fixed supports are connected with the first column 1, the second column 3, the upper beam 2 and the lower beam 7 through the fixing seat screw 16;

[0058] The right angle fixed supports are connected with the first column 1 and the second column 3 through the tensioning bolt 17;

[0059] The first upper end plate 4, the second upper end plate 4-1, the first lower end plate 6 and the second lower end plate 6-1 are connected with the first column 1 and the second column 3 through the end plate screw 18.

[0060] The first upper end plate 4, the second upper end plate 4-1, the first lower end plate 6 and the second lower end plate 6-1 are end face flange plates.

[0061] In use, the upper beam 2 and the lower beam 7 are connected with the first column 1 and the second column 3 at the connection positions, spherical surface support connection is adopted, the contact stress caused by the alternating stress and deformation and the machining error of the upper beam 2 and the lower beam 7 does not change during work, and the stability is improved;

[0062] The upper beam 2 is suspended and pre-tightened with the first column 1 and the second column 3 at the top, the first column 1 and the second column 3 adopt the connection mode of inclined surface tensioning wedge block group and external fixing seat, the left and right ends of the upper beam 2 and the lower beam 7 are positioned and constrained through the end face flange plate, and the stability of the machine tool is improved.

Claims

1. An ultra-tonnage frame-type multi-cylinder synchronous hydraulic press frame device comprising a frame, characterized in that: The rack comprises a first column (1), a second column (3), an upper beam (2), and a lower beam (7). The first column (1) and the second column (3) are two side support columns of the rack. The first column (1) and the second column (3) are connected by the upper beam (2) and the lower beam (7). The first column (1) and the second column (3) are rectangular frames. The upper beam (2) penetrates the rectangular frame of the first column (1) and the second column (3), and the lower beam (7) penetrates the rectangular frame of the first column (1) and the second column (3). One end of the upper beam (2) is fixedly connected to the top end of the first column (1) through a first upper end plate (4), and the other end of the upper beam (2) is fixedly connected to the top end of the second column (3) through a second upper end plate (4-1). One end of the upper beam (2) and the top inside of the rectangular frame of the first column (1) are provided with a first double-row universal spherical surface support (11), and the inside of the rectangular frame of the first column (1) is provided with a first top inclined wedge block group (12). The other end of the upper beam (2) and the top inside of the rectangular frame of the second column (3) are provided with a second double-row universal spherical surface support (11-1), and the inside of the rectangular frame of the second column (3) is provided with a second top inclined wedge block group (12-1). One end of the lower beam (7) is fixedly connected to the bottom end of the first column (1) through a first lower end plate (6), and the other end of the lower beam (7) is fixedly connected to the bottom end of the second column (3) through a second lower end plate (6-1). One end of the lower beam (7) and the bottom inside of the rectangular frame of the first column (1) are provided with a first bottom universal support group (15), and the inside of the rectangular frame of the first column (1) is provided with a first bottom inclined wedge block group (14). The other end of the lower beam (7) and the bottom inside of the rectangular frame of the second column (3) are provided with a second bottom universal support group (15-1), and the inside of the rectangular frame of the second column (3) is provided with a second bottom inclined wedge block group (14-1).

2. The frame type multi-cylinder synchronous hydraulic press rack apparatus of super large tonnage according to claim 1, characterized in that: The first top inclined wedge block group (12) is provided with two groups of inclined wedge blocks, and the two groups of inclined wedge blocks are respectively arranged on opposite sides of the upper beam (2), and each group of inclined wedge blocks is provided with two. The second top inclined wedge block group (12-1) is provided with two groups of inclined wedge blocks, and the two groups of inclined wedge blocks are respectively arranged on opposite sides of the upper beam (2), and each group of inclined wedge blocks is provided with two.

3. The frame type multi-cylinder synchronous hydraulic press machine frame apparatus of super large tonnage according to claim 2, characterized in that: The first bottom inclined wedge block group (14) is provided with two groups of inclined wedge blocks, and the two groups of inclined wedge blocks are respectively arranged on opposite sides of the lower beam (7), and each group of inclined wedge blocks is provided with two. The second bottom inclined wedge block group (14-1) is provided with two groups of inclined wedge blocks, and the two groups of inclined wedge blocks are respectively arranged on opposite sides of the lower beam (7), and each group of inclined wedge blocks is provided with two.

4. The frame type multi-cylinder synchronous hydraulic press machine frame apparatus of super large tonnage according to claim 3, characterized in that: The first upright column (1) is provided with a first pre-tightening screw rod (10) at the top end, the first pre-tightening screw rod (10) is installed at the top end of the first upright column (1) through a first upper end pre-tightening nut (8), and a pre-tightening pad (9) is arranged between the first upper end pre-tightening nut (8) and the first upright column (1); the first pre-tightening screw rod (10) penetrates one end of the upper beam (2); the first pre-tightening screw rod (10) extending out of one end of the upper beam (2) is provided with a first lower pre-tightening nut (13), and a pre-tightening pad (9) is arranged between the first lower pre-tightening nut (13) and the upper beam (2). The second upright column (3) is provided with a second pre-tightening screw rod (10-1) at the top end, the second pre-tightening screw rod (10-1) is installed at the top end of the second upright column (3) through a second upper end pre-tightening nut (8-1), and a pre-tightening pad (9) is arranged between the second upper end pre-tightening nut (8-1) and the second upright column (3); the second pre-tightening screw rod (10-1) penetrates the other end of the upper beam (2); the second pre-tightening screw rod (10-1) extending out of one end of the upper beam (2) is provided with a second lower pre-tightening nut (13-1), and a pre-tightening pad (9) is arranged between the second lower pre-tightening nut (13-1) and the upper beam (2).

5. The frame type multi-cylinder synchronous hydraulic press machine frame apparatus of super large tonnage according to claim 4, characterized in that: The first upright column (1) and the upper beam (2) are connected through a first upper outer fixing seat (5), and the second upright column (3) and the upper beam (2) are connected through a second upper outer fixing seat (5-1); the first upright column (1) and the lower beam (7) are connected through a first lower outer fixing seat (5-2), and the second upright column (3) and the lower beam (7) are connected through a second lower outer fixing seat (5-3).

6. A frame type multi-cylinder synchronous hydraulic press machine frame apparatus of super tonnage according to claim 5, wherein: The first upper outer fixing seat (5), the second upper outer fixing seat (5-1), the first lower outer fixing seat (5-2) and the second lower outer fixing seat (5-3) are right-angle fixing supports.

7. A frame type multi-cylinder synchronous hydraulic press machine frame apparatus of super tonnage according to claim 6, wherein: The first upper outer fixing seat (5) is provided with two, which are respectively fixedly connected to the two sides of the first upright column (1) and the upper beam (2) corresponding to each other, one right-angle fixing edge of the right-angle fixing support of the first upper outer fixing seat (5) is connected to the upper beam (2), and the other right-angle fixing edge is connected to the first upright column (1); The second upper outer fixing seat (5-1) is provided with two, which are respectively fixedly connected to the two sides of the second upright column (3) and the upper beam (2) corresponding to each other, one right-angle fixing edge of the right-angle fixing support of the second upper outer fixing seat (5-1) is connected to the upper beam (2), and the other right-angle fixing edge is connected to the second upright column (3).

8. A frame type multi-cylinder synchronous hydraulic press machine frame apparatus of super tonnage according to claim 6, wherein: The first lower outer fixing seat (5-2) is provided with two, which are respectively fixedly connected to the two sides of the first upright column (1) and the lower beam (7) corresponding to each other, one right-angle fixing edge of the right-angle fixing support of the first lower outer fixing seat (5-2) is connected to the lower beam (7), and the other right-angle fixing edge is connected to the first upright column (1); The second lower outer fixing seat (5-3) is provided with two, which are respectively fixedly connected to the two sides of the second upright column (3) and the lower beam (7) corresponding to each other, one right-angle fixing edge of the right-angle fixing support of the second lower outer fixing seat (5-3) is connected to the lower beam (7), and the other right-angle fixing edge is connected to the second upright column (3).

9. A frame type multi-cylinder synchronous hydraulic press machine frame apparatus of super tonnage capacity as claimed in claim 1 wherein: The inner side of the rectangular frame of the first upright column (1) is a trapezoid with long top end and short lower end; the inner side of the rectangular frame of the second upright column (3) is a trapezoid with long top end and short lower end.

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