Variable performance system for auditorium and stage area
By designing a variable auditorium and stage area system, using flipped seats and lifting power systems, the problem of low space utilization caused by fixed settings in the prior art is solved, and flexible and variable performance space and efficient space utilization are achieved.
Patent Information
- Application Number
- CN202422028301.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-21
- Publication Date
- 2025-06-27
- Estimated Expiration
- 2034-08-21
AI Technical Summary
The existing fixed settings of stages and chairs cannot be changed, resulting in low utilization of the space in the venue and unable to adapt to the diversified market demand.
A variable performance system for the auditorium and stage area is designed, using a flip seat system and a lifting power system, and the seat is flipped and lifted through the flip drive mechanism and the flip transmission mechanism, allowing the transformation of the auditorium and stage area.
It realizes a flexible and changeable performance space, improves space utilization, meets the needs of different time periods and performance forms, saves costs, and simplifies the mechanical structure.
Smart Images

Figure CN223034638U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of stage performing arts equipment, and particularly relates to a variable performing arts system for auditoriums and stage areas. Background Art
[0002] With the continuous improvement of living standards, the requirements of audiences for the effects of literary and artistic performances are also getting higher and higher, and various art performance forms are emerging continuously. Venues for performances generally include an auditorium area with bench seats and a stage area for performances.
[0003] Existing stages and bench seats are generally fixedly arranged, and the size, direction and position of the stage cannot be changed. Moreover, the fixed bench seat facilities are troublesome to disassemble when not in use. Whether they are left in place without disassembly or stored after disassembly, they take up a lot of space, resulting in low space utilization rate of the venue and inability to meet the diversified needs of the market. Summary of the Utility Model
[0004] The purpose of the utility model is to solve the above-mentioned deficiencies of the prior art, and provide a variable performing arts system for auditoriums and stage areas, which can realize the transformation between the auditorium and the stage area, use a flipping drive mechanism to realize the flipping of the whole row, simplify the automatic control system, save costs, simplify the mechanical structure, set and change the space as needed, form a flexible and variable performance space, and improve the space utilization rate.
[0005] To achieve the above purpose, the technical solution adopted by the utility model is as follows:
[0006] A variable performing arts system for auditoriums and stage areas includes a first movable stage area, a second stage area in front of the first movable stage area, and a third stage area behind the first movable stage area. The first movable stage area includes a certain number of flipping seat systems arranged side by side and a lifting power system below them.
[0007] The flip seat system includes a certain number of seats arranged in a row, a load-bearing frame located above the foundation, a flip drive mechanism, and a flip transmission mechanism. A fixed frame is provided at the bottom of the seat. The fixed frame includes a front cross bar and a rear cross bar arranged in parallel along the seat arrangement direction. A certain number of web members are connected between the front cross bar and the rear cross bar, and the seat is fixed to the web members. The flip drive mechanism includes a flip drive motor and a flip shaft. The flip drive motor is fixed in the middle area of the load-bearing frame, and a first sprocket is provided on its output shaft. Both ends of the flip shaft are fixed to the load-bearing frame through pillow block bearings, and a second sprocket is provided thereon. The first sprocket and the second sprocket are connected by a chain drive. The flip transmission mechanism includes a certain number of active flip linkages. The active flip linkages are located in the area where the flip shaft is located and include a C-shaped connection block and an L-shaped connection block. The upper end of the C-shaped connection block is connected to the rear cross bar, the upper end of the vertical part of the L-shaped connection block is connected to the lower end of the C-shaped connection block, and the outer end of the horizontal part is connected to the flip shaft. The seat is not installed on the load-bearing frame but on the fixed frame, and the flip transmission mechanism is connected through the fixed frame. The flip transmission mechanism is then connected to the flip drive mechanism installed on the load-bearing frame. When the flip drive motor operates, the first sprocket rotates, drives the second sprocket and the flip shaft to rotate through the chain, thereby driving the active flip linkages to flip around the central axis of the flip shaft. The fixed frame and the seats thereon flip accordingly. When flipped upward, the seats are located above the load-bearing frame for people to use. When flipped downward, the seats are hidden below the load-bearing frame, and the space above the load-bearing frame can be used for other purposes.
[0008] The lifting power system includes a lifting drive motor fixed at the middle position of the foundation below the load-bearing frame. Transmission shafts are symmetrically arranged on both sides of the lifting drive motor. The outer ends of the transmission shafts are connected to flexible chain boxes. Flexible chains are provided inside the flexible chain boxes, and the outer ends of the flexible chains are connected to the load-bearing frame. At least two groups of guide wheels distributed vertically are provided on both lower sides of the front side of the load-bearing frame. Corresponding first guide columns are provided on both sides of the rear side of the load-bearing frame except for the last row. Corresponding second guide columns are provided below the second stage area. At least two groups of guide wheels distributed vertically are provided on both lower sides of the rear side of the last row of the load-bearing frame. Corresponding third guide columns are provided below the third stage area. The lifting power system can control the flip seat system to lift and is independently controlled. Specifically, when the lifting drive motor operates, the transmission shafts rotate, and the flexible chains inside the flexible chain boxes extend to have a rigid support function, thereby lifting the flip seat system. Conversely, when the flexible chains retract into the flexible chain boxes, the flip seat system descends. When the heights of adjacent flip seat systems are staggered, the seats can be flipped without interfering with each other. When the seats are in use, the same height of all seats can be controlled, or they can be arranged with the front lower and the rear higher, or the front higher and the rear lower to meet different stage performance requirements. When the seats are not in use, the first activity stage area, the second stage area, and the third stage area form a large stage area.
[0009] Preferably, the flexible chain boxes and flexible chains of different lifting power systems are staggered from each other, and the lengths of the corresponding transmission shafts change accordingly. The lengths can be staggered, or gradually increase from short to long and then gradually decrease, or gradually decrease from long to short and then gradually increase, which can reduce the overall width and prevent interference with each other.
[0010] Preferably, the flipping transmission mechanism further includes a certain number of driven flipping connecting rods. The driven flipping connecting rods are located in the area outside the flipping shaft and include C-shaped connecting blocks and vertical connecting blocks. The upper ends of the C-shaped connecting blocks are connected to the rear crossbar, and the upper ends of the vertical connecting blocks are connected to the lower ends of the C-shaped connecting blocks. Synchronous rods are connected between the vertical parts of the L-shaped connecting blocks, between the vertical parts of adjacent L-shaped connecting blocks and the lower ends of the vertical connecting blocks, and between the lower ends of the vertical connecting blocks to ensure more uniform force on the fixing frame during flipping and synchronous flipping of the whole row of seats.
[0011] Preferably, a first stage layer is provided on the load-bearing frame. The edge of the first stage layer protrudes from the load-bearing frame and can be inserted into the opening of the C-shaped connecting block. Second stage layers and third stage layers are respectively provided on the tops of the second stage area and the third stage area. The thickness of the C-shaped connecting block is not greater than the gaps between adjacent first stage layers and between the first stage layer and the third stage layer. After the seats are hidden, the first stage layer is controlled to be at the same height as the second stage layer and the third stage layer to form a large stage area, which can be used for stage performances and other purposes.
[0012] Preferably, a certain number of first bolt assemblies arranged in a row are provided on the front crossbar. A height adjustment block matching the bolt is provided at the bottom of the first bolt assembly, which can make all seats fit the first stage layer surface and keep the seats stable.
[0013] Preferably, the cross-section of the web member is an inverted L shape and is formed by sheet metal bending. A number of reinforcing ribs are provided on the web member. The two ends of the web member are respectively connected to the front crossbar and the rear crossbar by welding.
[0014] Preferably, the vertical and horizontal parts of the L-shaped connecting block are respectively square tubes, the vertical connecting block is a square tube, and the cross-section of the C-shaped connecting block is C-shaped and is formed by sheet metal bending. The C-shaped connecting block is respectively connected to the L-shaped connecting block and the vertical connecting block by welding.
[0015] Preferably, the vertical part of the L-shaped connecting block is a two-piece structure, and rectangular connecting plates are respectively provided at the ports. The two rectangular connecting plates are connected by a number of second bolt assemblies. The C-shaped connecting block and the rear crossbar are connected by second bolt assemblies. The two-piece structure is convenient for installation and disassembly.
[0016] Preferably, the connecting through holes on the C-shaped connecting block and the rectangular connecting plate are waist-shaped holes.
[0017] Preferably, the front cross bar and the rear cross bar are channel steels.
[0018] Preferably, the tilting drive motor is provided with a symmetric double output shaft, and correspondingly, two symmetric groups of the first sprocket, the tilting shaft, the second sprocket and the chain are provided. The driving force of the double output shaft is more balanced, making the tilting movement of the seat smoother.
[0019] The advantages of the present utility model are as follows: 1. The performing arts system can realize the transformation between the auditorium and the stage area. With the change of the seat position and the different lifting heights of the stage, the space can be set and changed as needed, forming a flexible and variable performance space, meeting the requirements of different time periods and different performance forms, improving the space utilization rate, and changing the deficiency of the single use of the space.
[0020] 2. The row chair can be tilted in a whole row by one tilting drive mechanism, making the automatic control system simple and saving costs;
[0021] 3. The structural reliability of the tilting drive mechanism and the tilting transmission mechanism is high, and the mechanical structure is simplified;
[0022] 4. The seat, the fixing frame and the tilting transmission mechanism are detachably connected through a bolt structure, which is convenient for adjustment and ensures the installation accuracy.
[0023] 5. The tilting row chair can be hidden when not in use, does not occupy space, improves the space utilization rate of the venue, can be used for other purposes, and meets the diversified needs of the market. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 is a top view structure diagram of the present utility model;
[0025] Figure 2 is a side view cross-section Figure 1 ;
[0026] Figure 3 is a side view cross-section Figure 2 ;
[0027] Figure 4 is a front view cross-section diagram of the present utility model;
[0028] Figure 5 is a front view of the tilting seat system of the present utility model;
[0029] Figure 6 is Figure 5 the cross-section view taken along the line A-A in
[0030] Figure 7 is Figure 6 the structural schematic diagram after the seat tilts downward in
[0031] Figure 8 is Figure 5 an enlarged schematic view of position B in
[0032] Figure 9 a structural schematic diagram of the fixing frame and the active flipping link in the present utility model;
[0033] Figure 10 a bottom view structural diagram of the upper half of the active flipping link in the present utility model;
[0034] Figure 11 a top view structural diagram of the lower half of the active flipping link in the present utility model;
[0035] Figure 12 a structural schematic diagram of the fixing frame and the driven flipping link in the present utility model;
[0036] Figure 13 a bottom view structural diagram of the driven flipping link in the present utility model.
[0037] Description of the main component symbols in the figure:
[0038] 100, the first movable stage area; 101, the flipping seat system; 102, the lifting power system;
[0039] 11, seat; 12, load-bearing frame; 13, the first stage layer; 14, guide wheel; 15, the first guide post;
[0040] 20, fixing frame; 21, front cross bar; 22, rear cross bar; 23, web member; 24, the first bolt assembly; 25, height adjustment block; 26, reinforcing rib;
[0041] Flipping drive mechanism: 31, flipping drive motor; 32, flipping shaft; 33, the first sprocket; 34, pedestal bearing; 35, the second sprocket; 36, chain;
[0042] Flipping transmission mechanism: 41, active flipping link; 42, driven flipping link; 43, C-shaped connecting block; 44, L-shaped connecting block; 45, vertical connecting block; 46, synchronizing rod; 47, rectangular connecting plate.
[0043] 50, the second bolt assembly;
[0044] 61, lifting drive motor; 62, transmission shaft; 63, flexible chain box; 64, flexible chain;
[0045] 200, the second stage area; 201, the second guide post; 202, the second stage layer;
[0046] 300, the third stage area; 301, the third guide post; 302, the third stage layer. Detailed implementation manners
[0047] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with the accompanying drawings.
[0048] Embodiment 1: Figures 1-4 As shown, a variable performance system of auditorium and stage area includes a first movable stage area 100, a second stage area 200 in front of the first movable stage area 100, and a third stage area 300 behind the first movable stage area 100. The first movable stage area 100 includes a certain number of flip seat systems 101 arranged side by side and a lifting power system 102 thereunder.
[0049] like Figures 5-7 As shown, the flip seat system 101 includes a certain number of seats 11 arranged in a row, a load-bearing frame 12 located above the foundation, a flip driving mechanism and a flip transmission mechanism.
[0050] Combination Figure 9 and Figure 12 As shown, a fixing frame 20 is arranged at the bottom of the seat 11, and the fixing frame 20 includes a front cross bar 21 and a rear cross bar 22 arranged in parallel along the arrangement direction of the seats 11, and a certain number of abdominal bars 23 are connected between the front cross bar 21 and the rear cross bar 22, and the seat 11 is fixed on the abdominal bars 23.
[0051] Among them, the flipping drive mechanism includes a flipping drive motor 31 and a flipping shaft 32. The flipping drive motor 31 is fixed in the middle area of the load-bearing frame 12, and a first sprocket 33 is arranged on its output shaft. Both ends of the flipping shaft 32 are fixed to the load-bearing frame 12 through seat bearings 34, and a second sprocket 35 is arranged on it. The first sprocket 33 and the second sprocket 35 are connected by a chain 36.
[0052] Combination Figures 9-11 As shown, the flip transmission mechanism includes a certain number of active flip connecting rods 41, which are located in the area where the flip axis 32 is located, and include a C-shaped connecting block 43 and an L-shaped connecting block 44. The upper end of the C-shaped connecting block 43 is connected to the rear cross bar 22, the upper end of the vertical part of the L-shaped connecting block 44 is connected to the lower end of the C-shaped connecting block 43, and the outer end of the horizontal part is connected to the flip axis 32.
[0053] Combination Figures 2-4As shown in the figure, the lifting power system 102 includes a lifting drive motor 61 fixed at the middle position of the foundation under the load-bearing frame 12. Drive shafts 62 are symmetrically arranged on both sides of the lifting drive motor 61. The outer ends of the drive shafts 62 are connected to a flexible chain box 63. A flexible chain 64 is arranged inside the flexible chain box 63. The outer end of the flexible chain 64 is connected to the load-bearing frame 12. At least two groups of guide wheels 14 distributed up and down are arranged on both sides of the lower part of the front side of the load-bearing frame 12. Corresponding first guide columns 15 are arranged on both sides of the rear side of the load-bearing frame 12 except for the last row. Corresponding second guide columns 201 are arranged below the second stage area 200. At least two groups of guide wheels 14 distributed up and down are arranged on both sides of the lower part of the rear side of the last row of the load-bearing frame 12. Corresponding third guide columns 301 are arranged below the third stage area 300. The guide wheels 14 of the first row of the load-bearing frame 12 abut against the second guide columns 201 below the second stage area 200. The guide wheels 14 of the other rows of the load-bearing frame 12 abut against the first guide columns 15 on the adjacent front load-bearing frame 12. The guide wheels 14 on the rear side of the last row of the load-bearing frame 12 abut against the third guide columns 301 below the third stage area 300.
[0054] Embodiment 2: As Figure 1 and Figure 4 shown, on the basis of Embodiment 1, the flexible chain boxes 63 and flexible chains 64 of different lifting power systems 102 are arranged in a staggered manner. The lengths of the corresponding drive shafts 62 change accordingly. The lengths can be staggered, or can gradually increase from short to long and then gradually decrease, or gradually decrease from long to short and then gradually increase, which can reduce the overall width and will not interfere with each other.
[0055] Embodiment 3: As Figure 5 、 Figure 8 and Figures 12-13 shown, on the basis of Embodiment 1, the flipping transmission mechanism further includes a certain number of driven flipping connecting rods 42. The driven flipping connecting rods 42 are located in the area outside the flipping shaft 32 and include a C-shaped connecting block 43 and a vertical connecting block 45. The upper end of the C-shaped connecting block 43 is connected to the rear cross bar 22. The upper end of the vertical connecting block 45 is connected to the lower end of the C-shaped connecting block 43. Synchronous rods 46 are connected between the vertical parts of the L-shaped connecting blocks 44, between the vertical part of the adjacent L-shaped connecting block 44 and the lower end of the vertical connecting block 45, and between the lower ends of the vertical connecting blocks 45.
[0056] Embodiment 4: As Figures 6-7 、 Figure 9 and Figure 12 shown, on the basis of Embodiment 3, a first stage layer 13 is arranged on the load-bearing frame 12. The edge of the first stage layer 13 protrudes from the load-bearing frame 12 and can be embedded into the opening of the C-shaped connecting block 43. Combining Figures 1-3As shown, a second stage layer 202 and a third stage layer 302 are respectively provided at the tops of the second stage area 200 and the third stage area 300. The thickness of the C-shaped connection block 43 is not greater than the gaps between adjacent first stage layers 13 and between the first stage layer 13 and the third stage layer 302.
[0057] Wherein, a certain number of first bolt assemblies 24 arranged in a column are provided on the front cross bar 21, and a height adjustment block 25 matching the bolt is provided at the bottom of the first bolt assembly 24.
[0058] Wherein, the cross section of the web member 23 is in an inverted L shape and is formed by sheet metal bending. A number of reinforcing ribs 26 are provided on the web member 23, and both ends of the web member 23 are respectively connected to the front cross bar 21 and the rear cross bar 22 by welding.
[0059] Embodiment Five: As Figures 9-13 shown, on the basis of Embodiment One, Embodiment Two, Embodiment Three or Embodiment Four, the vertical part and the horizontal part of the L-shaped connection block 44 are respectively square tubes, the vertical connection block 45 is a square tube, the cross section of the C-shaped connection block 43 is in a C shape and is formed by sheet metal bending. The C-shaped connection block 43 is respectively connected to the L-shaped connection block 44 and the vertical connection block 45 by welding.
[0060] The vertical part of the L-shaped connection block 44 is a two-stage structure, and rectangular connecting plates 47 are respectively provided at the ports. The two rectangular connecting plates 47 are connected by a number of second bolt assemblies 50, and the C-shaped connection block 43 is connected to the rear cross bar 22 by the second bolt assemblies 50.
[0061] Wherein, the connection through holes on the C-shaped connection block 43 and the rectangular connecting plates 47 are waist-shaped holes, and the front cross bar 21 and the rear cross bar 22 are channel steels.
[0062] Embodiment Six: As Figure 5 shown, on the basis of the above embodiments, the flipping drive motor 31 is provided with symmetric double output shafts, and correspondingly, two symmetric groups of the first sprocket 33, the flipping shaft 32, the second sprocket 35 and the chain 36 are provided.
[0063] The above are only specific embodiments of the present invention, but the structural features of the present invention are not limited thereto. The present invention can be used for similar products, and any changes or modifications made by any person skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.
Claims
1. A performance system with variable auditorium and stage area, characterized by: It comprises a first movable stage area (100), a second stage area (200) in front of the first movable stage area (100), and a third stage area (300) in the rear of the first movable stage area (100); The first movable stage area (100) comprises a certain number of flip seat systems (101) arranged side by side and a lifting power system (102) thereunder; The flip seat system (101) comprises a certain number of seats (11) arranged in a row, a load-bearing frame (12) located above a foundation, a flip driving mechanism and a flip transmission mechanism; A fixing frame (20) is provided at the bottom of the seat (11), the fixing frame (20) comprising a front crossbar (21) and a rear crossbar (22) arranged in parallel along the arrangement direction of the seats (11), a certain number of abdominal bars (23) are connected between the front crossbar (21) and the rear crossbar (22), and the seat (11) is fixed on the abdominal bars (23); The flipping drive mechanism comprises a flipping drive motor (31) and a flipping shaft (32); the flipping drive motor (31) is fixed to the middle area of the load-bearing frame (12); a first sprocket (33) is arranged on the output shaft of the flipping drive motor (31); both ends of the flipping shaft (32) are fixed to the load-bearing frame (12) via seat bearings (34); a second sprocket (35) is arranged on the flipping shaft; the first sprocket (33) and the second sprocket (35) are connected by a chain (36); The flip transmission mechanism comprises a certain number of active flip connecting rods (41), the active flip connecting rods (41) are located in the area where the flip shaft (32) is located, and include a C-shaped connecting block (43) and an L-shaped connecting block (44), the upper end of the C-shaped connecting block (43) is connected to the rear cross bar (22), the upper end of the vertical part of the L-shaped connecting block (44) is connected to the lower end of the C-shaped connecting block (43), and the outer end of the horizontal part is connected to the flip shaft (32); The lifting power system (102) comprises a lifting drive motor (61) fixed at a middle position of a foundation below the load-bearing frame (12), transmission shafts (62) are symmetrically arranged on both sides of the lifting drive motor (61), the outer ends of the transmission shafts (62) are connected to flexible chain boxes (63), a flexible chain (64) is arranged in the flexible chain box (63), and the outer ends of the flexible chains (64) are connected to the load-bearing frame (12); At least two groups of guide wheels (14) distributed vertically are arranged on both sides of the lower part of the front side of the load-bearing frame (12); corresponding first guide columns (15) are arranged on both sides of the rear side of the load-bearing frame (12) except the last row; corresponding second guide columns (201) are arranged below the second stage area (200); at least two groups of guide wheels (14) distributed vertically are arranged on both sides of the lower part of the rear side of the load-bearing frame (12) in the last row; and corresponding third guide columns (301) are arranged below the third stage area (300).
2. The performance system with variable auditorium and stage area according to claim 1, characterized in that: The flexible chain boxes (63) and flexible chains (64) of the different lifting power systems (102) are distributed in a staggered manner.
3. The performance system with variable auditorium and stage area according to claim 1, characterized in that: The flip transmission mechanism further comprises a certain number of driven flip connecting rods (42), the driven flip connecting rods (42) being located in an area outside the flip shaft (32), and comprising a C-shaped connecting block (43) and a vertical connecting block (45), the upper end of the C-shaped connecting block (43) being connected to the rear cross bar (22), the upper end of the vertical connecting block (45) being connected to the lower end of the C-shaped connecting block (43), the vertical parts of the L-shaped connecting blocks (44), the vertical parts of adjacent L-shaped connecting blocks (44) and the lower ends of the vertical connecting blocks (45), and the lower ends of the vertical connecting blocks (45) being connected via a synchronization rod (46).
4. The performance system with variable auditorium and stage area according to claim 3, characterized in that: A first stage layer (13) is arranged on the load-bearing frame (12); the edge of the first stage layer (13) protrudes from the load-bearing frame (12) and can be embedded in the opening of the C-shaped connecting block (43); a second stage layer (202) and a third stage layer (302) are arranged on the top of the second stage area (200) and the third stage area (300), respectively; and the thickness of the C-shaped connecting block (43) is not greater than the gap between adjacent first stage layers (13) and between the first stage layer (13) and the third stage layer (302).
5. The performance system with variable auditorium and stage area according to claim 4, characterized in that: A certain number of first bolt assemblies (24) arranged in a row are arranged on the front crossbar (21), and a height adjustment block (25) matching the bolts is arranged at the bottom of the first bolt assemblies (24).
6. The performance system with variable auditorium and stage area according to claim 3, characterized in that: The cross section of the web member (23) is in an inverted L-shape and is formed by bending a sheet metal. A plurality of reinforcing ribs (26) are provided on the web member (23). The two ends of the web member (23) are respectively connected to the front cross bar (21) and the rear cross bar (22) by welding. The vertical portion and the horizontal portion of the L-shaped connection block (44) are respectively square tubes, the vertical connection block (45) is a square tube, the C-shaped connection block (43) has a C-shaped cross section and is formed by bending a sheet metal, and the C-shaped connection block (43) is connected to the L-shaped connection block (44) and the vertical connection block (45) by welding.
7. The performance system with variable auditorium and stage area according to claim 6, characterized in that: The vertical portion of the L-shaped connection block (44) is a two-section structure, and rectangular connection plates (47) are respectively provided at the ends. The two rectangular connection plates (47) are connected via a plurality of second bolt assemblies (50), and the C-shaped connection block (43) is connected to the rear cross bar (22) via the second bolt assembly (50).
8. The performance system with variable auditorium and stage area according to claim 7, characterized in that: The connecting through holes on the C-shaped connecting block (43) and the rectangular connecting plate (47) are waist-shaped holes.
9. The performance system with variable auditorium and stage area according to claim 1, characterized in that: The front cross bar (21) and the rear cross bar (22) are channel steels.
10. A performance system with variable auditorium and stage area according to any one of claims 1 to 9, characterized in that: The flip drive motor (31) is provided with symmetrical dual output shafts, and the corresponding first sprocket (33), the flip shaft (32), the second sprocket (35) and the chain (36) are provided in two symmetrical groups.