Automatic arching machine

Abstract

The invention discloses an automatic arch pulling machine, and belongs to the technical field of agricultural machinery. Comprising an arch pulling frame, a driving mechanism, a transmission mechanism, an arch pulling wheel, a front transmission shaft, a pressing claw and a tensioning mechanism, the front transmission shaft is rotationally connected to the arch pulling frame, the arch pulling wheel is sleeved on the front transmission shaft, the driving mechanism is arranged on the arch pulling frame and is in transmission connection with the front transmission shaft through the transmission mechanism, and the pressing claw is rotationally connected to the arch pulling wheel. The tensioning mechanism is connected with the arch pulling frame and used for driving the pressing claws to tightly press the arch frame. The pressing claw on the arch pulling wheel acts on the arch frame, the tensioning mechanism is used for enabling the pressing claw to press the arch frame, the driving mechanism drives the arch pulling wheel to rotate to drive the pressing claw to move so as to drive the arch frame to move to pull out the arch frame, the arch frame is pulled out in a mechanical mode, and the working efficiency can be improved. And accidental injury caused by springback of the arch center during manual pulling-out can be prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural machinery, in particular to an automatic arch pulling machine. Background Art

[0002] In agricultural production, arches (usually arched supports made of bamboo or metal) are used to support mulch film to maintain the temperature and humidity required for seedling growth. When the seedlings grow, the arches must be manually removed and the mulch film recovered. This traditional method relies entirely on manual labor, which is inefficient, time-consuming, and labor-intensive. Especially for large-scale plantings, the manual removal of arches is labor-intensive and cannot meet the requirements of efficient modern agricultural production.

[0003] The scissors are typically somewhat elastic, making their rebound force prone to injury during manual removal. For example, metal scissors have a strong rebound force, potentially injuring arms or faces during removal. Bamboo scissors can break, creating sharp edges that could scratch the operator. These issues increase labor risks and compromise agricultural safety.

[0004] Traditional manual extraction methods can easily damage the arches, rendering them unreusable. For example, uneven force during extraction can cause the arches to deform or break, increasing agricultural production costs. Furthermore, manual extraction makes it difficult to ensure the neat recovery of the arches, and subsequent sorting and storage are cumbersome.

[0005] With the advancement of agricultural modernization, the demand for mechanization and automation in agricultural production is increasing. Traditional manual methods of removing sedges are no longer sufficient for large-scale, high-efficiency agricultural production. Designing a device that can automatically remove sedges would not only improve efficiency but also reduce labor intensity and production costs.

[0006] While some automated agricultural machinery already exists (e.g., automatic film mulching machines and automatic rice transplanters), specialized equipment for removing rice stalks remains a niche. Existing technologies fail to address the rebound force during stalk removal, nor do they enable efficient stalk recovery. Therefore, there is an urgent need to design an automatic stalk removal machine to address these challenges. Summary of the Invention

[0007] The purpose of the present invention is to provide an automatic arch pulling machine, which solves the problem of rebound force during the arch pulling process and realizes efficient recovery of the arch.

[0008] To achieve the above-mentioned objectives, the present invention provides an automatic arch pulling machine, comprising an arch pulling frame, a driving mechanism, a transmission mechanism, an arch pulling wheel, a front transmission shaft, a pressure claw and a tensioning mechanism. The front transmission shaft is rotatably connected to the arch pulling frame, the arch pulling wheel is sleeved on the front transmission shaft, the driving mechanism is arranged on the arch pulling frame, the driving mechanism is connected to the front transmission shaft through the transmission mechanism, the pressure claw is rotatably connected to the arch pulling wheel, and the tensioning mechanism is connected to the arch pulling frame and is used to drive the pressure claw to press the arch frame.

[0009] Preferably, the tensioning mechanism includes a tensioning support, the tensioning support is connected to the arch pulling frame, the tensioning support is arranged as a fan-shaped structure, the tensioning support is coaxially arranged with the arch pulling wheel, the front side and / or the rear side of the arch pulling wheel is provided with a mounting groove, the tensioning support is located in the mounting groove, and a mounting opening is provided on the side wall of the arch pulling wheel. The middle part of the pressure claw is rotatably connected to the arch pulling wheel, the tail of the pressure claw is located in the mounting groove, and is used to abut against the arc-shaped side wall of the tensioning support, the head of the pressure claw is located on the outside of the mounting groove, and is used to press the arch frame.

[0010] Preferably, the automatic arch pulling machine further comprises a roller, which is rotatably connected to the tail of the pressure claw, and is used to abut against the arc-shaped side wall of the tensioning support.

[0011] Preferably, the automatic arch pulling machine also includes a spring and a rotating shaft, the rotating shaft is connected to the arch pulling wheel, the middle part of the pressure claw is rotatably connected to the rotating shaft, the spring is sleeved on the rotating shaft, one end of the spring is connected to the arch pulling wheel, and the other end of the spring is connected to the pressure claw.

[0012] Preferably, the driving mechanism is configured as an arch pulling motor, and the transmission mechanism includes a main transmission shaft, a first transmission gear, a second transmission gear, a third transmission gear, a fourth transmission gear, a first chain and a second chain. The front transmission shaft and the main transmission shaft are arranged on the arch pulling frame from front to back, the first transmission gear is sleeved on the front transmission shaft, the second transmission gear and the third transmission gear are both sleeved on the main transmission shaft, the fourth transmission gear is sleeved on the output shaft of the arch pulling motor, the first chain is sleeved on the first transmission gear and the second transmission gear, and the second chain is sleeved on the third transmission gear and the fourth transmission gear.

[0013] Preferably, the automatic arch pulling machine also includes two positioning supports, which are located on the front and rear sides of the tensioning support and are both connected to the front transmission shaft. The two positioning supports are used to position the two ends of the arch frame.

[0014] Preferably, the automatic arch pulling machine further comprises a collecting rack, which is connected to the arch pulling frame, and the arch pulling wheel is used to transfer the arch frame to the collecting rack.

[0015] Preferably, the automatic arch pulling machine further comprises an external protective frame, which is connected to the arch pulling frame, and has two ends extending to two positioning supports respectively.

[0016] Preferably, the automatic arch pulling machine also includes an upper conveyor belt, a lower conveyor belt and a transmission gear set. The transmission gear set is connected to the main transmission shaft, and the lower conveyor belt is connected to the transmission gear set. The upper conveyor belt is located above the lower conveyor belt and rubs against each other. The upper conveyor belt and the lower conveyor belt are used to transfer the arch frame to the collection rack.

[0017] Therefore, the present invention adopts an automatic arch pulling machine with the above structure, which has the following beneficial effects: (1) The present invention acts on the arch frame through the pressure claws on the arch pulling wheel, and uses a tensioning mechanism to press the arch frame with the pressure claws. The driving mechanism drives the arch pulling wheel to rotate and drives the pressure claws to move, thereby driving the arch frame to move and pull out the arch frame. The mechanized method of pulling out the arch frame is conducive to improving work efficiency and preventing accidental injuries caused by the rebound of the arch frame during manual pulling out.

[0018] (2) The present invention can be used on either metal or bamboo arches.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a structural schematic diagram of an automatic arch pulling machine of the present invention; Reference numerals 1. Arch pulling frame; 2. Arch pulling motor; 31. Main transmission shaft; 32. First transmission gear; 33. Second transmission gear; 34. Third transmission gear; 35. Fourth transmission gear; 36. First chain; 37. Second chain; 4. Arch pulling wheel; 41. Mounting slot; 42. Mounting port; 5. Front transmission shaft; 6. Pressure claw; 61. Roller; 62. Spring; 63. Rotating shaft; 7. Tensioning support; 81. Positioning support; 811. Pillar; 82. External protective frame; 91. Collection frame; 92. Upper conveyor belt; 93. Lower conveyor belt; 94. Adjusting bolt; 95. Transmission gear set. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0022] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0023] Example like Figure 1 As shown, the present invention provides an automatic arch pulling machine, including an arch pulling frame 1, a driving mechanism, a transmission mechanism, an arch pulling wheel 4, a front transmission shaft 5, a pressure claw 6 and a tensioning mechanism. The front transmission shaft 5 is rotatably connected to the arch pulling frame 1, and the arch pulling wheel 4 is sleeved on the front transmission shaft 5. The driving mechanism is arranged on the arch pulling frame 1, and the driving mechanism is connected to the front transmission shaft 5 through the transmission mechanism. The pressure claw 6 is rotatably connected to the arch pulling wheel 4. The tensioning mechanism is connected to the arch pulling frame 1 and is used to drive the pressure claw 6 to press the arch frame.

[0024] The automatic arch pulling machine also includes an oil cylinder connected to the arch pulling frame 1, which is used to control the arch pulling frame 1 to rise and fall to a suitable height. Secondly, the automatic arch pulling machine also includes a telescopic axle, which is used to control the arch pulling frame 1 to adjust to a suitable width.

[0025] In this embodiment, the driving mechanism drives the transmission mechanism to operate, and the transmission mechanism is connected to the front transmission shaft 5 by transmission, thereby driving the front transmission shaft 5 to rotate. The arch pulling wheel 4 is connected to the front transmission shaft 5, and the arch pulling wheel 4 is driven to rotate during the rotation of the front transmission shaft 5. The pressing claw 6 is connected to the arch pulling wheel 4, and the pressing claw 6 is driven to rotate during the rotation of the arch pulling wheel 4. The pressing claw 6 can act on the arch frame during the rotation process and remove the arch frame by moving from bottom to top. Secondly, the tensioning mechanism is used to drive the pressing claw 6 to rotate relative to the arch pulling wheel 4, so that the arch frame is pressed during the rotation of the pressing claw 6, preventing the arch frame from separating from the pressing claw 6, and facilitating the arch frame to be pulled out by rotating the arch pulling wheel 4.

[0026] Thus, the arch frame is acted on by the pressure claw 6 on the arch pulling wheel 4, and the tensioning mechanism is used to press the arch frame with the pressure claw 6. The arch pulling wheel 4 is driven by the driving mechanism to rotate and drive the pressure claw 6 to move, thereby driving the arch frame to move and pull out the arch frame. The mechanized extraction of the arch frame is conducive to improving work efficiency and can also prevent accidental injuries caused by the rebound of the arch frame caused by manual extraction.

[0027] Alternatively, as Figure 1 As shown, the tensioning mechanism includes a tensioning support 7, which is connected to the arch pulling frame 1, and the tensioning support 7 is arranged as a fan-shaped structure. The tensioning support 7 is coaxially arranged with the arch pulling wheel 4, and a mounting groove 41 is provided on the front and / or rear side of the arch pulling wheel 4. The tensioning support 7 is located in the mounting groove 41, and a mounting opening 42 is provided on the side wall of the arch pulling wheel 4. The middle part of the pressure claw 6 is rotatably connected to the arch pulling wheel 4, and the tail part of the pressure claw 6 is located in the mounting groove 41 and is used to abut against the arc-shaped side wall of the tensioning support 7. The head of the pressure claw 6 is located on the outside of the mounting groove 41 and is used to press the arch frame.

[0028] Specifically, mounting grooves 41 are provided on both the front and rear sides of the arch puller 4, and tensioning supports 7 are provided in both mounting grooves 41. Secondly, multiple mounting openings 42 are opened around the mounting grooves 41, and the mounting openings 42 are connected to the mounting grooves 41, and a pressure claw 6 is provided at each mounting opening 42.

[0029] In this embodiment, the pressing claw 6 can be driven to rotate synchronously with the arch pulling wheel 4 by the driving mechanism. When the pressing claw 6 moves closer to the tensioning support 7, the tail of the pressing claw 6 acts on the arc-shaped side wall of the fan-shaped structure of the tensioning support 7. Because the middle part of the pressing claw 6 is rotatably connected to the arch pulling wheel 4, under the restraining effect of the tensioning support 7 on the tail of the pressing claw 6, the pressing claw 6 can rotate around the middle part of the pressing claw 6 and drive the head of the pressing claw 6 to rotate, so that the head of the pressing claw 6 presses the arch frame tightly.

[0030] Thus, the tail of the pressing claw 6 moves to the tensioning support 7, and the curved side wall of the tensioning support 7 is used to limit the tail of the pressing claw 6 to drive the pressing claw 6 to rotate, so that the arch frame is compressed by the head of the pressing claw 6, thereby ensuring the effect of the tensioning mechanism. Secondly, the tensioning mechanism is set as the tensioning support 7, and a purely mechanical structure is used to drive the pressing claw 6 to compress the arch frame. There is no need to add an electric or pneumatic mechanism to drive the pressing claw 6, which is conducive to simplifying the overall structure of the automatic arch pulling machine and saving energy.

[0031] Alternatively, as Figure 1 As shown, the automatic arch pulling machine further includes a roller 61 , which is rotatably connected to the tail of the pressure claw 6 , and is used to abut against the arc-shaped side wall of the tensioning support 7 .

[0032] In this embodiment, when the pressure claw 6 moves to the tensioning support 7, when the tail of the pressure claw 6 directly acts on the curved side wall of the tensioning support 7, there is sliding friction between the pressure claw 6 and the tensioning support 7, and the friction force is relatively large, and the tensioning support 7 may jam the pressure claw 6. By providing a roller 61 at the tail of the pressure claw 6, the roller 61 is used to act on the curved side wall of the tensioning support 7, and the roller 61 is rotatably connected to the pressure claw 6, there is rolling friction between the roller 61 and the tensioning support 7, and the friction force is relatively small, the friction force between the pressure claw 6 and the curved side wall inside the tensioning support can be reduced, thereby preventing the pressure claw 6 from being jammed by the tensioning support 7.

[0033] Secondly, the distance between the tensioning support 7 and the arch pulling wheel 4 can be adjusted to apply different forces to the roller 61 at the tail of the pressing claw 6 to adjust the tension of the pressing claw 6, so that the pressing claw 6 can act on arches of different diameters.

[0034] Alternatively, as Figure 1 As shown, the automatic arch pulling machine also includes a spring 62 and a rotating shaft 63. The rotating shaft 63 is connected to the arch pulling wheel 4. The middle part of the pressure claw 6 is rotatably connected to the rotating shaft 63. The spring 62 is sleeved on the rotating shaft 63. One end of the spring 62 is connected to the arch pulling wheel 4, and the other end of the spring 62 is connected to the pressure claw 6.

[0035] In this embodiment, the tail of the pressure jaw 6 acts on the curved sidewall of the tensioning support 7, restricting the tail of the pressure jaw 6. The pressure jaw 6 rotates about the rotating shaft 63 relative to the arch puller 4, thereby compressing the spring 62. When the pressure jaw 6 moves away from the tensioning support 7, the tail of the pressure jaw 6 is no longer restricted, and the spring 62 releases its elastic force, causing the rotating shaft 63 to rotate in the opposite direction, thereby resetting the pressure jaw 6. Thus, by providing the spring 62, the pressure jaw 6 can be reset by the spring 62, eliminating the need for manual reset and facilitating automated control.

[0036] Alternatively, as Figure 1 As shown, the driving mechanism is set as the arch pulling motor 2, and the transmission mechanism includes a main transmission shaft 31, a first transmission gear 32, a second transmission gear 33, a third transmission gear 34, a fourth transmission gear 35, a first chain 36 and a second chain 37. The front transmission shaft 5 and the main transmission shaft 31 are arranged on the arch pulling frame 1 from front to back. The first transmission gear 32 is sleeved on the front transmission shaft 5, the second transmission gear 33 and the third transmission gear 34 are both sleeved on the main transmission shaft 31, and the fourth transmission gear 35 is sleeved on the output shaft of the arch pulling motor 2. The first chain 36 is sleeved on the first transmission gear 32 and the second transmission gear 33, and the second chain 37 is sleeved on the third transmission gear 34 and the fourth transmission gear 35.

[0037] Specifically, the first transmission gear 32, the second transmission gear 33 and the first chain 36 are provided on both the front and rear sides of the arch pulley 4. The third transmission gear 34 is sleeved on the middle part of the main transmission shaft 31.

[0038] In this embodiment, the arch pulling motor 2 drives the fourth transmission gear 35 to rotate. The main transmission shaft 31, third transmission gear 34, fourth transmission gear 35, and second chain 37 are connected to each other, driving the main transmission shaft 31 to rotate. The main transmission shaft 31 and the front transmission shaft 5 are connected via the first transmission gear 32, second transmission gear 33, and first chain 36, driving the front transmission shaft 5 to rotate. The front transmission shaft 5 is connected to the arch pulling wheel 4, driving the rotation of the arch pulling wheel 4.

[0039] Alternatively, as Figure 1 As shown, the automatic arch pulling machine also includes a positioning support 81. Two positioning supports 81 are provided. The two positioning supports 81 are located on the front and rear sides of the tensioning support 7 and are both connected to the front transmission shaft 5. The two positioning supports 81 are used to position the two ends of the arch frame.

[0040] Specifically, a plurality of pillars 811 are provided on the positioning support 81, which can ensure uniform force on the arch frame when rotating synchronously with the arch pulling wheel 4 to pull out the arch frame.

[0041] In this embodiment, by setting positioning supports 81 at the front and rear ends of the front drive shaft 5, the two positioning supports 81 can be used to limit the two ends of the arch frame, which can prevent the arch frame from being damaged due to excessive force and reduce the vibration of the arch frame when lifting the frame.

[0042] Alternatively, as Figure 1 As shown, the automatic arch pulling machine further includes a collecting rack 91 , which is connected to the arch pulling frame 1 , and the arch pulling wheel 4 is used to transfer the arch to the collecting rack 91 .

[0043] In this embodiment, a collection rack 91 is provided, and the arch frame is driven to the top of the collection rack 91 by the arch pulling wheel 4 , and the pressing claw 6 is released, so that the arch frame can fall onto the collection rack 91 .

[0044] Alternatively, as Figure 1 As shown, the automatic arch pulling machine further includes an external protective frame 82 , which is connected to the arch pulling frame 1 , and has two ends extending to two positioning supports 81 .

[0045] In this embodiment, the external protective frame 82 is supported by a retractable square tube mounted on top, a semicircular bracket at the front, and inverted S-shaped guardrails at each end. This prevents the arch from bouncing around when it is raised, potentially preventing it from entering the conveyor belt and minimizing the risk of injury.

[0046] Alternatively, as Figure 1As shown, the automatic arch pulling machine also includes an upper conveyor belt 92, a lower conveyor belt 93 and a transmission gear set 95. The transmission gear set 95 is connected to the main transmission shaft 31, and the lower conveyor belt 93 is connected to the transmission gear set 95. The upper conveyor belt 92 is located above the lower conveyor belt 93 and rubs against each other. The upper conveyor belt 92 and the lower conveyor belt 93 are used to transfer the arch frame to the collection rack 91.

[0047] Specifically, if Figure 1 As shown, the upper conveyor belt 92 and the lower conveyor belt 93 are both configured as telescopic structures. Secondly, the upper conveyor belt 92 and the lower conveyor belt 93 are both provided with adjusting bolts 94 for adjusting the lengths of the upper conveyor belt 92 and the lower conveyor belt 93.

[0048] In this embodiment, the transmission gear set 95 includes a transmission shaft gear and a gear on the transmission belt shaft. The transmission shaft gear is connected to the main transmission shaft 31. The transmission shaft gear and the gear on the transmission belt shaft mesh with each other to rotate the lower transmission belt 93, so that the upper transmission belt 92 and the lower transmission belt 93 frictionally move relative to each other. Secondly, the upper transmission belt 92 extends above the middle position between the arch pulling wheel and the positioning support, so that after the arch frame is pulled out, it can pass through the guardrail and positioning support 81 to reduce vibration and accurately fall under the upper transmission belt 92. When the arch pulling wheel 4 drives the arch frame to the friction point between the upper transmission belt 92 and the lower transmission belt 93, the pressure claw 6 is released, and the upper transmission belt 92 and the lower transmission belt 93 transmit the arch frame to the collection rack 91 at the rear.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An automatic arch pulling machine, characterized in that: It includes an arch pulling frame, a driving mechanism, a transmission mechanism, an arch pulling wheel, a front transmission shaft, a pressure claw and a tensioning mechanism. The front transmission shaft is rotatably installed above one side of the arch pulling frame. The arch pulling wheel is sleeved on the front transmission shaft. The driving mechanism is arranged on the arch pulling frame. The driving mechanism is connected to the front transmission shaft through the transmission mechanism. The pressure claw is rotatably connected to the arch pulling wheel. The tensioning mechanism is connected to the arch pulling frame and is used to drive the pressure claw to press the arch frame.

2. The automatic arch drawing machine according to claim 1, characterized in that: The tensioning mechanism includes a tensioning support, which is connected to the arch pulling frame. The tensioning support is arranged in a fan-shaped structure. The tensioning support is coaxially arranged with the arch pulling wheel. A mounting groove is provided on the front and / or rear side of the arch pulling wheel. The tensioning support is located in the mounting groove. A mounting opening is provided on the side wall of the arch pulling wheel. The middle part of the pressure claw is rotatably connected to the arch pulling wheel. The tail of the pressure claw is located in the mounting groove and is used to abut against the arc-shaped side wall of the tensioning support. The head of the pressure claw is located on the outside of the mounting groove and is used to press the arch frame.

3. The automatic arch pulling machine according to claim 2, characterized in that: It also includes a roller, which is rotatably connected to the tail of the pressure claw and is used to abut against the arc-shaped side wall of the tensioning support.

4. The automatic arch drawing machine according to claim 3, characterized in that: It also includes a spring and a rotating shaft, the rotating shaft is connected to the arch pulling wheel, the middle part of the pressure claw is rotatably connected to the rotating shaft, the spring is sleeved on the rotating shaft, one end of the spring is connected to the arch pulling wheel, and the other end of the spring is connected to the pressure claw.

5. The automatic arch drawing machine according to claim 1, characterized in that: The driving mechanism is set as an arch pulling motor, and the transmission mechanism includes a main transmission shaft, a first transmission gear, a second transmission gear, a third transmission gear, a fourth transmission gear, a first chain and a second chain. The front transmission shaft and the main transmission shaft are arranged on the arch pulling frame from front to back. The first transmission gear is sleeved on the front transmission shaft, the second transmission gear and the third transmission gear are both sleeved on the main transmission shaft, the fourth transmission gear is sleeved on the output shaft of the arch pulling motor, the first chain is sleeved on the first transmission gear and the second transmission gear, and the second chain is sleeved on the third transmission gear and the fourth transmission gear.

6. The automatic arch drawing machine according to claim 2, characterized in that: It also includes two positioning supports, which are located on the front and rear sides of the tensioning support and are both connected to the front drive shaft. The two positioning supports are used to position the two ends of the arch frame.

7. The automatic arch drawing machine according to claim 6, characterized in that: It also includes a collecting rack, which is connected to the arch pulling frame, and the arch pulling wheel is used for transferring the arch frame to the collecting rack.

8. The automatic arch pulling machine according to claim 7, characterized in that: It also includes an external protective frame, which is connected to the arch frame, and has two ends extending to two positioning supports respectively.

9. The automatic arch drawing machine according to claim 8, characterized in that: It also includes an upper conveyor belt, a lower conveyor belt and a transmission gear set. The transmission gear set is connected to the main transmission shaft, and the lower conveyor belt is connected to the transmission gear set. The upper conveyor belt is located above the lower conveyor belt and rubs against each other. The upper conveyor belt and the lower conveyor belt are used to transfer the arch frame to the collection rack.

10. The automatic arch drawing machine according to claim 1, characterized in that: The pressure claws are arranged in two rows on the arch pulling wheel, and there are at least 6 pairs.

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