Angle adjustment mechanism and adjustable backrest

Abstract

The embodiment of the present invention discloses an angle adjustment mechanism and an adjustable backrest thereof, comprising: an adjustment tooth plug, the adjustment tooth plug comprising a tooth cap and a tooth column, the tooth cap having first saw teeth evenly distributed in a ring shape on the upper edge, and the tooth column having second saw teeth evenly distributed in a ring shape on the upper edge; an adjustment tooth seat, the adjustment tooth seat having a first tooth groove; a first connecting member, the first connecting member having a second tooth groove; wherein the adjustment tooth seat has a first through hole, the adjustment tooth plug is arranged to pass through the first through hole, so that the first saw tooth and the second saw tooth are respectively arranged in the first tooth groove and the second tooth groove. After the first saw tooth and the second saw tooth of the present invention are respectively rotated in the same direction by a distance of one slot, the relative rotation angle between the first connecting member and the adjustment tooth seat is the difference between and, and the rotation angle is small, thereby realizing the fine adjustment operation of the angle between the first connecting member and the adjustment tooth seat, and the adjustment operation is simple and convenient with high adjustment accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of backrest wheelchair products, and in particular to an angle adjustment mechanism and an adjustable backrest thereof. Background Art

[0002] A recumbent wheelchair is a wheelchair with a backrest mounted on a frame and equipped with wheels to help replace walking. It is also a common medical device. Recumbent wheelchairs can not only meet the needs of people with physical disabilities and mobility impairments, but also facilitate family members to move and take care of patients, so that patients can exercise and participate in social activities with the help of recumbent wheelchairs. Therefore, they have entered many ordinary families and are widely used.

[0003] However, the recumbent wheelchairs in the prior art have the following technical defects and shortcomings: the backrest angles of most traditional recumbent wheelchairs cannot be adjusted or are difficult to adjust; in addition, even if the backrest angles of some recumbent wheelchairs can be adjusted, the backrest angle adjustment of such recumbent wheelchairs is relatively large (that is, only a large angle can be adjusted), and the backrest angle adjustment is not precise, which is not suitable for most usage scenarios, thereby seriously affecting the customer's usage experience.

[0004] Therefore, there is an urgent need in the prior art to invent a backrest mechanism that is easy to adjust and has a precise angle adjustment. Summary of the invention

[0005] In order to overcome at least one of the defects of the prior art described above, the present invention provides an angle adjustment mechanism and an adjustable backrest thereof, which have the characteristics of simple and reasonable structural design, convenient adjustment operation and precise angle adjustment.

[0006] The technical solution adopted by the present invention to solve the problem is:

[0007] An angle adjustment mechanism, comprising:

[0008] An adjusting tooth plug, the adjusting tooth plug comprising a tooth cap and a tooth column, the tooth cap is provided with first saw teeth evenly distributed in a ring shape, and the tooth column is provided with second saw teeth evenly distributed in a ring shape;

[0009] An adjusting tooth seat, wherein the adjusting tooth seat is provided with first tooth grooves, the number of the first tooth grooves and the number of the first saw teeth are equal, and the two are arranged correspondingly;

[0010] A first connecting member, wherein the first connecting member is provided with second tooth grooves, the number of the second tooth grooves and the number of the second saw teeth are equal, and the two are arranged correspondingly;

[0011] The adjusting tooth seat is provided with a first through hole, and the adjusting tooth plug is arranged through the first through hole, so that the first saw tooth and the second saw tooth are arranged in the first tooth groove and the second tooth groove respectively.

[0012] Furthermore, the number of the first saw teeth and the number of the second saw teeth are A and B respectively, and after the first saw teeth are rotated in two adjacent first tooth grooves, and the second saw teeth are rotated in two adjacent second tooth grooves in the same direction, the rotation angle of the first connecting member relative to the adjusting tooth seat is for and The difference.

[0013] Furthermore, the number A of the first saw teeth is greater than the number B of the second saw teeth, and the rotation angle of the first connecting member relative to the adjusting tooth seat is for:

[0014] Furthermore, the number A of the first saw teeth is smaller than the number B of the second saw teeth, and the rotation angle of the first connecting member relative to the adjusting tooth seat is for:

[0015] Furthermore, the number A of the first saw teeth is: A=20, the number B of the second saw teeth is: B=18, then the rotation angle of the first connecting member relative to the adjusting tooth seat is for:

[0016] Furthermore, it also includes a fastener, the first connecting member is provided with a second through hole, the adjusting tooth plug is provided with an assembly hole, and the fastener passes through the second through hole and the assembly hole in sequence to fix and assemble the adjusting tooth plug, the adjusting tooth seat and the first connecting member together.

[0017] Furthermore, the fastener is any one of a screw, a bolt or a screw.

[0018] Further, the cross section of the first sawtooth gradually decreases from an end close to the tooth cap to an end far away from the tooth cap;

[0019] The cross section of the second sawtooth gradually decreases from an end close to the tooth column to an end far away from the tooth column.

[0020] Based on the same design concept, the present invention also provides an adjustable backrest, which includes the angle adjustment mechanism described above.

[0021] Furthermore, it also includes a second connecting member, and the second connecting member is assembled and connected to the adjusting gear seat;

[0022] Wherein, the first connecting member is a backrest frame base, and the second connecting member is the backrest frame connecting head.

[0023] In summary, compared with the prior art, the angle adjustment mechanism and the adjustable backrest provided by the present invention have at least the following technical effects:

[0024] 1) The angle adjustment mechanism and the adjustable backrest provided by the present invention, wherein the first connecting member and the adjusting tooth seat are fixedly assembled together by the adjusting tooth plug, when the angle between the first connecting member and the adjusting tooth seat needs to be adjusted, the adjusting tooth plug is completely or partially removed from the first through hole, and then the relative angle between the two is rotated, and the angle adjustment operation is simple and convenient;

[0025] 2) The angle adjustment mechanism and the adjustable backrest provided by the present invention, wherein after the first sawtooth and the second sawtooth rotate by a slot distance respectively, the relative rotation angle between the first connecting member and the adjusting tooth seat is and The difference between the first connecting member and the adjusting gear seat is small, so that the angle between the first connecting member and the adjusting gear seat can be fine-tuned, and the adjustment accuracy is high;

[0026] 3) The angle adjustment mechanism and adjustable backrest provided by the present invention, wherein the adjusting tooth plug, the adjusting tooth seat and the first connecting member are fixedly assembled together by fasteners. When it is necessary to adjust the angle between the first connecting member and the adjusting tooth seat, the fastener is first unscrewed, and then the adjusting tooth plug is fully or partially pulled out of the first through hole, and finally the relative angle between the two is rotated. The angle adjustment operation is simple and convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the angle adjustment mechanism of the present invention;

[0028] Figure 2 An exploded view of the angle adjustment mechanism of the present invention;

[0029] Figure 3 It is a structural schematic diagram of the adjusting tooth plug of the present invention;

[0030] Figure 4 It is a schematic structural diagram of the adjusting gear seat and the second connecting member of the present invention;

[0031] Figure 5 is a schematic structural diagram of a first connecting member of the present invention;

[0032] The meanings of the reference numerals are as follows:

[0033] 1. Adjusting tooth plug; 11. Assembly hole; 2. Tooth cap; 21. First sawtooth; 3. Tooth column; 31. Second sawtooth; 4. Adjusting tooth seat; 41. First tooth groove; 42. First through hole; 5. First connecting piece; 51. Second tooth groove; 52. Second through hole; 6. Fastener; 7. Second connecting piece. DETAILED DESCRIPTION

[0034] For better understanding and implementation, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0037] See also Figure 1-Figure 5 As shown, according to an embodiment of the present invention, the angle adjustment mechanism includes:

[0038] The adjusting tooth plug 1 comprises a tooth cap 2 and a tooth column 3, wherein the tooth cap 2 is provided with first saw teeth 21 evenly distributed along a ring, and the tooth column 3 is provided with second saw teeth 31 evenly distributed along a ring. The first saw teeth 21 are evenly distributed along a ring at the end of the tooth cap 2, and the second saw teeth 31 are evenly distributed along a ring at the end of the tooth column 3, and the first saw teeth 21 and the second saw teeth 31 are arranged in the same direction.

[0039] The adjusting tooth seat 4 is provided with a first tooth groove 41, the number of the first tooth groove 41 and the first saw teeth 21 are equal, and the first tooth groove 41 and the first saw teeth 21 are arranged correspondingly. The number of the first tooth groove 41 and the first saw teeth 21 are equal, the size is similar, and the structure distribution form is consistent, so as to ensure that when the adjusting tooth plug 1 is inserted through the first through hole 42, the first saw teeth 21 can be matched with the corresponding first tooth groove 41.

[0040] The first connecting member 5 is provided with second tooth grooves 51, the number of the second tooth grooves 51 and the second saw teeth 31 are equal, and the second tooth grooves 51 and the second saw teeth 31 are arranged correspondingly. The number of the second tooth grooves 51 and the second saw teeth 31 are equal, the size is similar, and the structure distribution form is consistent, so as to ensure that when the adjusting tooth plug 1 is inserted through the first through hole 42, the second saw teeth 31 can be loosely matched with the corresponding second tooth grooves 51.

[0041] In the technical solution of this embodiment, the adjusting tooth seat 4 is provided with a first through hole 42, and the adjusting tooth plug 1 is arranged to pass through the first through hole 42, so that the first sawtooth 21 and the second sawtooth 31 are respectively arranged in the first tooth groove 41 and the second tooth groove 51. Specifically, the first connecting member 5 and the adjusting tooth seat 4 are fixedly assembled together through the adjusting tooth plug 1, and after the adjusting tooth plug 1 is inserted into the first through hole 42 on the adjusting tooth seat 4, the first sawtooth 21 and the corresponding first tooth groove 41 are clearance-matched, and the second sawtooth 31 and the corresponding second tooth groove 51 are clearance-matched, so that the first connecting member 5 and the adjusting tooth seat 4 cannot rotate relative to each other. More specifically, when it is necessary to adjust the angle between the first connecting member 5 and the adjusting tooth seat 4, the adjusting tooth plug 1 is completely or partially removed from the first through hole 42, at which time the first serration 21 is pulled out from the corresponding first tooth groove 41, and the second serration 31 is pulled out from the corresponding second tooth groove 51, and then the angle between the first connecting member 5 and the adjusting tooth seat 4 is adjusted. After the adjustment is completed, the adjusting tooth plug 1 can be reinserted into the first through hole 42. This structural design is simple and reasonable, the angle adjustment operation is easy, and can significantly improve the user experience.

[0042] In one embodiment of the present invention, the number of the first saw teeth 21 and the number of the second saw teeth 31 are A and B respectively. After the first saw teeth 21 are rotated in two adjacent first tooth grooves 41, and the second saw teeth 31 are rotated in two adjacent second tooth grooves 51 in the same direction, the rotation angle of the first connecting member 5 relative to the adjusting tooth seat 4 is for and In the technical solution of this embodiment, when the angle between the first connecting member 5 and the adjusting tooth seat 4 needs to be adjusted, if the adjusting tooth seat 4 is rotated one slot relative to the adjusting tooth plug 1 (that is, the first sawtooth 21 on the tooth cap 2 rotates between two adjacent first tooth grooves 41), the angle at which the adjusting tooth seat 4 rotates relative to the adjusting tooth plug 1 is When the first connecting member 5 is rotated one slot in the same direction relative to the adjusting tooth plug 1 (that is, the second saw teeth 31 on the tooth column 3 rotate in the same direction in two adjacent second tooth grooves 51), the rotation angle of the first connecting member 5 relative to the adjusting tooth plug 1 is That is to say, the relative rotation angle between the first connecting member 5 and the adjusting gear seat 4 is for and The difference between the first connecting member 5 and the adjusting gear seat 4 is small, thereby achieving fine-tuning of the angle between the first connecting member 5 and the adjusting gear seat 4, and the adjustment accuracy is significantly improved.

[0043] In combination with the above embodiment, by analogy, when a larger angle adjustment operation is required between the first connecting member 5 and the adjusting tooth seat 4, the adjusting tooth seat 4 can be rotated N slots relative to the adjusting tooth plug 1 (that is, the first sawtooth 21 rotates in the N first tooth grooves 41), and the first connecting member 5 is rotated N slots relative to the adjusting tooth plug 1 in the same direction (that is, the second sawtooth 31 rotates in the N second tooth grooves 51). The relative rotation angle between the first connecting member 5 and the adjusting tooth seat 4 is and The difference is N times, thus approaching the effect of stepless adjustment of the rotation angle.

[0044] In an optional technical solution of this embodiment, the number A of the first saw teeth 21 is greater than the number B of the second saw teeth 31, and the rotation angle of the first connecting member 5 relative to the adjusting tooth seat 4 is for: In this optional technical solution, the number A of the first serrations 21 on the tooth cap 2 is greater than the number B of the second serrations 31 on the tooth column 3. At this time, the first serrations 21 on the tooth cap 2 are densely distributed, and the second serrations 31 on the tooth column 3 are sparsely distributed. By rotating the first connecting member 5 and adjusting the angle of the tooth seat 4 relative to the adjusting tooth plug 1, respectively, the angle between the two can be fine-tuned, which can significantly improve the adjustment accuracy of the backrest.

[0045] In another optional technical solution of this embodiment, the number A of the first saw teeth 21 is less than the number B of the second saw teeth 31, and the rotation angle of the first connecting member 5 relative to the adjusting tooth seat 4 is for: In this optional technical solution, the number A of the first serrations 21 on the tooth cap 2 is smaller than the number B of the second serrations 31 on the tooth column 3. At this time, the first serrations 21 on the tooth cap 2 are sparsely distributed, and the second serrations 31 on the tooth column 3 are densely distributed. By rotating the first connecting member 5 and adjusting the angle of the tooth seat 4 relative to the adjusting tooth plug 1, respectively, the angle between the two can be fine-tuned, which can significantly improve the adjustment accuracy of the backrest.

[0046] Furthermore, the number A of the first saw teeth 21 is: A=20, and the number B of the second saw teeth 31 is: B=18, then the rotation angle of the first connecting member 5 relative to the adjusting tooth seat 4 is for: Specifically, the number A of the first saw teeth 21 is 20, so the angle between two adjacent first saw teeth 21 (that is, two adjacent first tooth grooves 41) is 360°÷20=18°; the number B of the second saw teeth 31 is 18, so the angle between two adjacent second saw teeth 31 (that is, two adjacent second tooth grooves 51) is 360°÷18=20°. Therefore, after the adjustment tooth seat 4 is rotated one slot relative to the adjustment tooth plug 1 (that is, the first saw tooth 21 rotates in the two adjacent first tooth grooves 41), and the first connecting member 5 is rotated one slot relative to the adjustment tooth plug 1 in the same direction (that is, the second saw tooth 31 rotates in the same direction in the two adjacent second tooth grooves 51), the rotation angle of the first connecting member 5 relative to the adjustment tooth seat 4 is for: Finally, the rotation angle is small, thereby achieving a fine adjustment operation of the angle between the first connecting member 5 and the adjustment gear seat 4, which can significantly improve the adjustment accuracy of the backrest.

[0047] By analogy, when a larger angle adjustment operation is required between the first connecting member 5 and the adjusting tooth seat 4, the adjusting tooth seat 4 can be rotated N slots relative to the adjusting tooth plug 1 (that is, the first saw tooth 21 rotates in N first tooth grooves 41), and after the first connecting member 5 is rotated N slots relative to the adjusting tooth plug 1 in the same direction (that is, the second saw tooth 31 rotates in N second tooth grooves 51), the relative rotation angle between the first connecting member 5 and the adjusting tooth seat 4 is 2N°, thereby nearly achieving the effect of stepless adjustment of the rotation angle.

[0048] See also Figure 2 , Figure 3 and Figure 5 As shown, in another embodiment of the present invention, the angle adjustment mechanism further includes a fastener 6, the first connecting member 5 is provided with a second through hole 52, the adjusting tooth plug 1 is provided with an assembly hole 11, and the fastener 6 passes through the second through hole 52 and the assembly hole 11 in sequence to fix and assemble the adjusting tooth plug 1, the adjusting tooth seat 4 and the first connecting member 5 together. Specifically, the fastener 6 is provided with an external thread, and the inner wall of the assembly hole 11 is provided with an internal thread. After the fastener 6 is screwed into the second through hole 52 and the assembly hole 11, the fastener 6 is connected to the adjusting tooth plug 1 by threaded engagement to fix and assemble the adjusting tooth plug 1, the adjusting tooth seat 4 and the first connecting member 5 together; similarly, when it is necessary to adjust the angle between the adjusting tooth seat 4 and the first connecting member 5, the fastener 6 is screwed out from the second through hole 52 and the assembly hole 11, and then the adjusting tooth plug 1 is taken out from the first through hole 42, which is simple and convenient to operate.

[0049] In the preferred technical solution of this embodiment, the fastener 6 is any one of a screw, a bolt or a screw. By screwing any one of the connecting components, such as the screw, the bolt or the screw, into the second through hole 52 and the assembly hole 11 in sequence, the adjusting tooth plug 1, the adjusting tooth seat 4 and the first connecting member 5 can be fixedly assembled together by threaded connection.

[0050] More specifically, the screw, bolt or screw may be a countersunk screw, a countersunk bolt or a countersunk screw, respectively.

[0051] See also Figure 3 As shown, in another embodiment of the present invention, the cross section of the first sawtooth 21 gradually decreases from one end close to the tooth cap 2 to the end away from the tooth cap 2. Specifically, the first sawtooth 21 is a sharp-shaped structure with a large tooth root and a small tooth end, and its side wall is inclined. Similarly, since the first tooth groove 41 and the first sawtooth 21 are arranged correspondingly, the size of the groove of the first tooth groove 41 also gradually decreases from shallow to deep, and the side wall is inclined. Through the structural design of the first sawtooth 21 and the inclined side wall of the first tooth groove 41, the convenience of the user to install the adjustment tooth plug 1 can be improved during assembly, specifically: after aligning the first sawtooth 21 on the tooth cap with the first tooth groove 41 on the corresponding adjustment tooth seat 4, it can be directly inserted along the inclined side wall of the first tooth groove 41. Compared with the structural design of square teeth and square grooves, this structural design can significantly improve the convenience of users aligning and inserting multiple first sawtooths 21 into multiple first tooth grooves 41.

[0052] In another parallel technical solution of this embodiment, the cross-section of the second serration 31 gradually decreases from one end close to the tooth column 3 to one end away from the tooth column 3. Specifically, the second serration 31 is a sharp-shaped structure with a large tooth root and a small tooth end, and its side wall is inclined. Similarly, since the second tooth groove 51 and the second serration 31 are arranged correspondingly, the size of the groove of the second tooth groove 51 also gradually decreases from shallow to deep, and the side wall is inclined. Through the structural design of the inclined side walls of the second serration 31 and the second tooth groove 51, the convenience of the user to install and adjust the tooth plug 1 can be improved during assembly, specifically: after aligning the second serration 31 on the tooth cap with the corresponding second tooth groove 51 on the first connecting member 5, it can be directly inserted along the inclined side wall of the second tooth groove 51. Compared with the structural design of square teeth and square grooves, this structural design can significantly improve the convenience of users to align and insert multiple second serrations 31 into multiple second tooth grooves 51.

[0053] Based on the same design concept, the present invention also provides an embodiment of an adjustable backrest, which includes the angle adjustment mechanism described in the above embodiments.

[0054] See also Figure 1 and Figure 4 As shown, in the preferred technical solution of this embodiment, the adjustable backrest also includes a second connecting member 7, and the second connecting member 7 is assembled and connected with the adjustment gear seat 4. Among them, the first connecting member 5 is the backrest frame base, and the second connecting member 7 is the backrest frame connector. In this preferred solution, the first connecting member 5 (also known as the backrest frame base) is an elliptical tube structure, and the second connecting member 7 (also known as the backrest frame connector) is a circular tubular structure.

[0055] In summary, the angle adjustment mechanism and the adjustable backrest provided by the present invention, wherein the first connecting member and the adjusting tooth seat are fixedly assembled together by the adjusting tooth plug, when the angle between the first connecting member and the adjusting tooth seat needs to be adjusted, the adjusting tooth plug is fully or partially pulled out of the first through hole, and then the relative angle between the two is rotated, and the angle adjustment operation is simple and convenient. The angle adjustment mechanism and the adjustable backrest provided by the present invention, wherein the relative rotation angle between the first connecting member and the adjusting tooth seat is and The difference between the first connecting member and the adjusting tooth seat is small, so that the angle between the first connecting member and the adjusting tooth seat can be fine-tuned, and the adjustment accuracy is high. The angle adjustment mechanism and the adjustable backrest provided by the present invention, wherein the adjusting tooth plug, the adjusting tooth seat and the first connecting member are fixedly assembled together by fasteners, when the angle between the first connecting member and the adjusting tooth seat needs to be adjusted, the fastener is first unscrewed, and then the adjusting tooth plug is fully or partially pulled out of the first through hole, and finally the relative angle between the two is rotated, and the angle adjustment operation is simple and convenient.

[0056] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes composed of any combination of the above-mentioned technical features. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims

1. An angle adjustment mechanism, characterized in that: include: An adjusting tooth plug, the adjusting tooth plug comprising a tooth cap and a tooth column, the tooth cap is provided with first saw teeth evenly distributed in a ring shape, and the tooth column is provided with second saw teeth evenly distributed in a ring shape; An adjusting tooth seat, wherein the adjusting tooth seat is provided with first tooth grooves, the number of the first tooth grooves and the number of the first saw teeth are equal, and the two are arranged correspondingly; A first connecting member, wherein the first connecting member is provided with second tooth grooves, the number of the second tooth grooves and the number of the second saw teeth are equal, and the two are arranged correspondingly; Wherein, a first through hole is provided on the adjusting tooth seat, and the adjusting tooth plug is arranged through the first through hole, so that the first sawtooth and the second sawtooth are arranged in the first tooth groove and the second tooth groove respectively; The number of the first saw teeth is unequal to the number of the second saw teeth.

2. The angle adjustment mechanism according to claim 1, characterized in that: The number of the first saw teeth and the number of the second saw teeth are A and B respectively. After the first saw teeth are rotated in two adjacent first tooth grooves, and the second saw teeth are rotated in two adjacent second tooth grooves in the same direction, the rotation angle of the first connecting member relative to the adjusting tooth seat is for and The difference.

3. The angle adjustment mechanism according to claim 2, characterized in that: The number A of the first saw teeth is greater than the number B of the second saw teeth, and the rotation angle of the first connecting member relative to the adjusting tooth seat is for:

4. The angle adjustment mechanism according to claim 2, characterized in that: The number A of the first saw teeth is smaller than the number B of the second saw teeth, and the rotation angle of the first connecting member relative to the adjusting tooth seat is for:

5. The angle adjustment mechanism according to claim 3, characterized in that: The number A of the first saw teeth is: A=20, the number B of the second saw teeth is: B=18, then the rotation angle of the first connecting member relative to the adjusting tooth seat is for:

6. The angle adjustment mechanism according to claim 1, characterized in that: It also includes a fastener, the first connecting member is provided with a second through hole, the adjusting tooth plug is provided with an assembly hole, and the fastener passes through the second through hole and the assembly hole in sequence to fix and assemble the adjusting tooth plug, the adjusting tooth seat and the first connecting member together.

7. The angle adjustment mechanism according to claim 6, characterized in that: The fastener is any one of a screw, a bolt or a screw.

8. The angle adjustment mechanism according to claim 1, characterized in that: The cross section of the first sawtooth gradually decreases from an end close to the tooth cap to an end far away from the tooth cap; The cross section of the second sawtooth gradually decreases from an end close to the tooth column to an end far away from the tooth column.

9. An adjustable backrest, characterized in that: It comprises the angle adjustment mechanism described in any one of claims 1-8.

10. The adjustable backrest according to claim 9, characterized in that It also includes a second connecting member, which is assembled and connected to the adjusting gear seat; Wherein, the first connecting member is a backrest frame base, and the second connecting member is the backrest frame connecting head.

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