Apparatus for rotating chair back and back chair having the apparatus

Abstract

A chair backrest rotation device capable of adjusting tension strength and a chair backrest having the same are disclosed. The chair backrest rotation device comprises a spring body having a cylindrical shape that rotates at least once, a first spring leg connected to one end of the spring body, and a second spring leg connected to the other end of the spring body, wherein the angle between the first spring leg and the second spring leg (hereinafter referred to as the 'spring angle') has an initial angle; a first rotational body connected to one side of either a chair frame supporting a seat or a backrest, and a first rotational body portion including a first spring fixing part formed on one surface of the first rotational body facing the tension spring and fixing the first spring leg; a second rotational body connected to the other side of the chair frame and the backrest and rotatably coupled to the first rotational body, and a second rotational body portion including a second spring fixing part formed on one surface of the second rotational body facing the tension spring and fixing the second spring leg; and a second rotational body portion coupled to the second rotational body and adjusting the spring angle by changing the position of the second spring leg. It includes a tension adjustment unit capable of adjusting the tension strength of the tension spring. Thus, the user can adjust the tension of the backrest by adjusting it through the tension adjustment unit.

Description

Technology Field

[0001] The present invention relates to a chair backrest rotation device and a chair backrest having the same, and more specifically, to a chair backrest rotation device that enables the chair backrest to rotate and a chair backrest having the same. Background Technology

[0002] A chair is a device used for a person to sit on. A typical chair consists of a seat on which a person sits, a chair frame that supports the seat, and a backrest connected to the chair frame to support the person's back. Here, the backrest may be fixed to the chair frame so as not to rotate, but it may also be connected to the chair frame so that the backrest can rotate at a certain angle.

[0003] In order for the backrest to rotate at a certain angle, a chair backrest rotation device must be provided. The chair backrest rotation device is positioned between the backrest and the chair frame and is equipped with a spring inside to provide tension of a certain strength to the backrest. That is, when a person pushes the backrest with their back after sitting on the chair, the backrest can rotate clockwise, and when the force pushing with the back is reduced or removed, the tension provided by the spring acts to rotate the backrest counterclockwise.

[0004] Meanwhile, the chair backrest rotation device is equipped with a single spring and operates with a single tension strength. That is, the chair backrest equipped with the chair backrest rotation device provides a single tension strength to the backrest regardless of who sits on it. However, the tension strength felt may vary depending on the person's physique, and the tension strength preferred by each person may differ. Therefore, the spring tension of the chair backrest rotation device needs to be adjusted. The problem to be solved

[0005] Therefore, the present invention is intended to solve these problems, and the objective of the present invention is to provide a chair backrest rotation device capable of adjusting tension strength.

[0006] In addition, the problem to be solved by the present invention is to provide a chair with a backrest equipped with the above-mentioned chair backrest rotation device. means of solving the problem

[0007] A chair backrest rotation device according to one embodiment of the present invention includes a tension spring, a first rotational body part, a second rotational body part, and a tension adjustment part. The tension spring includes a spring body having a cylindrical shape by rotating at least once, a first spring leg connected to one end of the spring body, and a second spring leg connected to the other end of the spring body, and the angle between the first spring leg and the second spring leg (hereinafter referred to as the 'spring angle') has an initial angle. The first rotational body part includes a first rotational body connected to one side of either a chair frame supporting a seat plate or a backrest, and a first spring fixing part formed on one surface of the first rotational body facing the tension spring and fixing the first spring leg. The second rotating body part includes a second rotating body connected to one side of the other of the chair frame and the backrest and rotatably coupled to the first rotating body, and a second spring fixing part formed on one surface of the second rotating body facing the tension spring and fixing the second spring leg. The tension adjustment part is coupled to the second rotating body and can adjust the tension strength of the tension spring by changing the position of the second spring leg to adjust the spring angle.

[0008] The second spring fixing part may include a spring leg receiving groove formed on one surface of the second rotating body to accommodate at least a portion of the second spring leg, and the width of the spring leg receiving groove may be formed to a size that allows the position of the second spring leg to be changed. At this time, at least a portion of the tension adjusting part is placed in the spring leg receiving groove, and the position of the second spring leg can be changed by pushing the second spring leg.

[0009] A tension adjustment groove connected to the spring leg receiving groove may be formed in the second rotating body. The tension adjustment part may include a tension adjustment screw that penetrates the tension adjustment groove and contacts the second spring leg, and when rotated in one direction, moves inward into the tension adjustment groove to push the second spring leg and change the position of the second spring leg.

[0010] The above tension spring may include a torsion spring.

[0011] A first spring body groove that accommodates a part of the spring body may be formed on one surface of the first rotating body, and a second spring body groove that accommodates another part of the spring body may be formed on one surface of the second rotating body.

[0012] A first rotational shaft portion accommodated within the spring body may be formed in the first spring body groove, and a second rotational shaft portion accommodated within the spring body may be formed in the second spring body groove at a position corresponding to the first rotational shaft portion.

[0013] The above chair backrest rotation device may further include a rotation shaft coupling screw that penetrates either of the first rotation shaft portion and the second rotation shaft portion in a rotatable state and is screw-coupled to either of the first rotation shaft portion and the second rotation shaft portion.

[0014] The first rotating body may further include a first rotation limiting part formed on one surface of the first rotating body facing the second rotating body. Additionally, the second rotating body may further include a second rotation limiting part formed on one surface of the second rotating body facing the first rotating body and coupled with the first rotation limiting part to restrict the first rotating body to rotate only at a reference angle relative to the second rotating body.

[0015] Either of the first rotation limiting part and the second rotation limiting part may include a rotation receiving groove, and the other of the first rotation limiting part and the second rotation limiting part may include a rotation projection that is at least partially inserted into the rotation receiving groove and can move within the rotation receiving groove so that the first rotation body rotates relative to the second rotation body.

[0016] Either one of the first rotating body and the second rotating body may be coupled to the other of the first rotating body and the second rotating body so that at least a part of it is inserted to enable rotation.

[0017] Furthermore, a backrest chair according to one embodiment of the present invention comprises a seat plate on which any person can sit, a chair frame supporting the seat plate, a backrest capable of supporting the back of the person when the person is sitting on the seat plate, and a chair backrest rotation device connecting one side of the chair frame and one side of the backrest. The chair backrest rotation device comprises a tension spring, a first rotational body part, a second rotational body part, and a tension adjustment part. The tension spring comprises a spring body having a cylindrical shape by rotating at least once, a first spring leg connected to one end of the spring body, and a second spring leg connected to the other end of the spring body, wherein the angle between the first spring leg and the second spring leg (hereinafter referred to as the 'spring angle') has an initial angle. The first rotational body part comprises a first rotational body connected to one side of either the chair frame or the backrest, and a first spring fixing part formed on one surface of the first rotational body facing the tension spring and fixing the first spring leg. The second rotating body part includes a second rotating body connected to one side of the other of the chair frame and the backrest and rotatably coupled to the first rotating body, and a second spring fixing part formed on one surface of the second rotating body facing the tension spring and fixing the second spring leg. The tension adjustment part is coupled to the second rotating body and can adjust the tension strength of the tension spring by changing the position of the second spring leg to adjust the spring angle. Effects of the invention

[0018] As such, according to the chair backrest rotation device and the backrest chair having the same according to the present invention, the chair backrest rotation device is provided with a tension adjustment unit capable of adjusting the tension strength of the tension spring by changing the position of the spring leg of the tension spring, so that a person using the backrest chair can adjust the tension strength of the tension spring to a tension strength of their choice by operating the tension adjustment unit. Brief explanation of the drawing

[0019] FIG. 1 is a perspective view illustrating a backrest chair according to one embodiment of the present invention. FIG. 2 is an exploded perspective view showing an enlarged view of the chair backrest rotation device of FIG. 1. FIG. 3 is an exploded perspective view showing only the chair backrest rotation device of FIG. 2 in enlarged view. Figure 4 is an exploded perspective view showing the chair backrest rotation device of Figure 3 at a different angle. Figure 5 is a side view illustrating the state in which the backrest is rotated in the backrest chair of Figure 1. Figure 6 is a conceptual diagram illustrating the change in the tension spring in the backrest chair of Figure 5. FIG. 7 is a partially cutaway perspective view illustrating the lowest tension strength of the chair backrest rotation device when the backrest of FIG. 5 is in the initial rotation position. FIG. 8 is a partially cutaway perspective view showing the maximum tension strength of the chair backrest rotation device when the backrest of FIG. 5 is in the initial rotation position. FIG. 9 is a conceptual diagram showing only the tension spring according to FIG. 7 and FIG. 8 in the chair backrest rotation device of FIG. 5. FIG. 10 is an exploded perspective view to explain that the chair backrest rotation device of FIG. 1 has a different connection relationship than FIG. 2. Specific details for implementing the invention

[0020] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated in the drawings and described in detail in the text.

[0021] However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. Such terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the invention, the first component may be named the second component, and similarly, the second component may be named the first component.

[0022] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0023] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings.

[0024] FIG. 1 is a perspective view illustrating a backrest chair according to one embodiment of the present invention.

[0025] Referring to FIG. 1, the backrest chair according to the present embodiment includes a seat plate (10) on which any person can sit, a chair frame (20) that supports the seat plate (10), a backrest (30) that supports the back of the person when the person is sitting on the seat plate (10), and at least one chair backrest rotation device (100) that connects the chair frame (20) and the backrest (30). Here, the chair frame (20) may include a left frame support (22) positioned on the left side of the seat plate (10) and a right frame support (24) positioned on the right side of the seat plate (10), and may further include a central support frame (not shown) that supports the seat plate (10) by connecting the left frame support (22) and the right frame support (24). The above backrest (30) may include a back plate (32) that supports the back of the person, a left back plate support (34) positioned on the left side of the back plate (32), and a right back plate support (36) positioned on the right side of the back plate (32).

[0026] The chair backrest rotation device (100) can connect one side of the chair frame (20) and one side of the backrest (30). At this time, the chair backrest rotation device (100) may be a left backrest rotation device connecting the left frame support (22) and the left backrest support (34), or a right backrest rotation device connecting the right frame support (24) and the right backrest support (36).

[0027] FIG. 2 is an exploded perspective view showing an enlarged view of the chair backrest rotation device of FIG. 1, FIG. 3 is an exploded perspective view showing only the chair backrest rotation device of FIG. 2 in enlarged view, and FIG. 4 is an exploded perspective view showing the chair backrest rotation device of FIG. 3 at a different angle.

[0028] Referring to FIGS. 2 to 4, the chair backrest rotation device (100) may include a tension spring (110), a first rotation body part (120), a second rotation body part (130), a tension adjustment part (140), and a rotation shaft coupling screw (150).

[0029] The tension spring (110) may include a spring body (112) having a cylindrical shape after rotating at least once, a first spring leg (114) connected to one end of the spring body (112), and a second spring leg (116) connected to the other end of the spring body (112). At this time, the tension spring (110) may have an initial angle (hereinafter referred to as the 'spring angle') between the first spring leg (114) and the second spring leg (116). For example, the tension spring (110) may include a torsion spring.

[0030] The first rotating body part (120) may include a first rotating body (120a) and a first spring fixing part (122).

[0031] The first rotating body (120a) may be connected to one side of either the chair frame (20) or the backrest (30). For example, the first rotating body (120a) may be connected to the left backrest support (34) of the backrest (30). Here, the first rotating body (120a) may be connected to be integrated with the left backrest support (34), or it may be connected by being combined with the left backrest support (34).

[0032] The first spring fixing part (122) is formed on one surface of the first rotating body (120a) facing the tension spring (110) and can fix the first spring leg (114). For example, the first spring fixing part (122) may include a spring fixing groove capable of receiving and fixing at least a portion of the first spring leg (114).

[0033] The second rotating body part (130) may include a second rotating body (130a) and a second spring fixing part (132).

[0034] The second rotating body (130a) may be connected to one side of the other of the chair frame (20) and the backrest (30). For example, the second rotating body (130a) may be connected to the left frame support (22) of the chair frame (20). Here, the second rotating body (130a) may be connected to be integrated with the left frame support (22), or may be connected by being combined with the left frame support (22).

[0035] Additionally, the second rotating body (130a) may be rotatably coupled to the first rotating body (120a). In this embodiment, either the first rotating body (120a) or the second rotating body (130a) may be rotatably coupled by having at least a portion of it inserted into the other of the first rotating body (120a) and the second rotating body (130a). In the drawing, the first rotating body (120a) may be inserted into the second rotating body (130a) and rotatably coupled. Specifically, the first rotating body (120a) may have a cylindrical shape, and the second rotating body (130a) may have a shape capable of accommodating the first rotating body (120a).

[0036] The second spring fixing part (134) is formed on one surface of the second rotating body (130a) facing the tension spring (110) and can fix the second spring leg (116). For example, the second spring fixing part (134) may include a spring leg receiving groove that can receive and fix at least a portion of the second spring leg (116). At this time, the width of the spring leg receiving groove may be formed to a size that allows the position of the second spring leg (116) to be changed.

[0037] The tension adjustment unit (140) is coupled to the second rotating body (130a) and can adjust the tension strength of the tension spring (110) by changing the position of the second spring leg (116) to adjust the spring angle. At this time, at least a portion of the tension adjustment unit (140) is placed in the spring leg receiving groove and can change the position of the second spring leg (116) by pushing the second spring leg (116). For example, at least a portion of the tension adjustment unit (140) is placed in the spring leg receiving groove and contacts the second spring leg (116), and can change the position of the second spring leg (116) by pushing the second spring leg (116) through user operation.

[0038] A tension adjustment groove (142) connected to the spring leg receiving groove may be formed in the second rotating body (130a). The tension adjustment part (140) may include a tension adjustment screw that penetrates the tension adjustment groove (142) and contacts the second spring leg (116), and when rotated in one direction, moves inward into the tension adjustment groove (142) to push the second spring leg (116) and change the position of the second spring leg (116). Accordingly, when the user of the above-mentioned backrest chair rotates the tension adjustment screw in the above-mentioned direction, the tension adjustment screw moves inward into the tension adjustment groove (142) to push the second spring leg (116) and change the position of the second spring leg (116), and when the user rotates the tension adjustment screw in the opposite direction to the above-mentioned direction, the tension adjustment screw moves outward into the tension adjustment groove (142) and changes the second spring leg (116) back to its original position.

[0039] Meanwhile, although the drawing illustrates the tension adjustment unit (140) in direct contact with the second spring leg (116) and directly pushes the second spring leg (116), at least one push means (not shown) may be disposed between the tension adjustment unit (140) and the second spring leg (116). That is, when a user operates the tension adjustment unit (140) to push the push means, the push means can push the second spring leg (116) again. The push means can perform the role of pushing the second spring leg (116) more easily. For example, the push means can perform the role of making the direction of movement of the tension adjustment unit (140) and the direction of movement of the second spring leg (116) different from each other. As an example, the push means may have a wedge shape. When the above-mentioned push means has the wedge shape, if the tension adjustment part (140) pushes the lower end of the wedge shape, the side of the wedge shape that gradually becomes thicker as it moves can push and move the second spring leg (116).

[0040] A first spring body groove (124) that accommodates a part of the spring body (112) may be formed on one side of the first rotating body (120a), and a second spring body groove (134) that accommodates another part of the spring body (112) may be formed on one side of the second rotating body (130a).

[0041] A first rotational shaft portion (126) that is received within the spring body (112) may be formed in the first spring body groove (124), and a second rotational shaft portion (136) that is received within the spring body (112) may be formed in the second spring body groove (134) at a position corresponding to the first rotational shaft portion (126).

[0042] The above-mentioned rotational shaft connecting screw (150) may rotatably penetrate either the first rotational shaft portion (126) or the second rotational shaft portion (136) and may be screw-coupled to either the first rotational shaft portion (126) or the second rotational shaft portion (136). For example, the above-mentioned rotational shaft connecting screw (150) may rotatably penetrate the second rotational shaft portion (136) and be screw-coupled to the first rotational shaft portion (126) to be fixed.

[0043] The first rotating body part (120) may further include a first rotation limiting part (128) formed on one surface of the first rotating body (120a) facing the second rotating body (130a), and the second rotating body part (130) may further include a second rotation limiting part (138) formed on one surface of the second rotating body (130a) facing the first rotating body (120a). At this time, the second rotation limiting part (138) may be combined with the first rotation limiting part (128) to limit the first rotating body (120a) to rotate only at a reference angle relative to the second rotating body (130a).

[0044] For example, either of the first rotation limiting part (128) and the second rotation limiting part (138) may include a rotation receiving groove. The other of the first rotation limiting part (128) and the second rotation limiting part (138) may include a rotation projection that can move within the rotation receiving groove, at least a portion of which is inserted into the rotation receiving groove, so that the first rotation body (120a) rotates relative to the second rotation body (130a). In the drawing, as an example, the first rotation limiting part (128) may include the rotation receiving groove, and the second rotation limiting part (138) may include a rotation projection that can move within the rotation receiving groove.

[0045] FIG. 5 is a side view illustrating the state in which the backrest is rotated in the backrest chair of FIG. 1, and FIG. 6 is a conceptual diagram illustrating the change of the tension spring in the backrest chair of FIG. 5.

[0046] Referring to FIGS. 5 and 6, the backrest chair has the backrest (30) in an initial rotational position, and when a user sits on the chair (10) and pushes the backrest (30) backward with their back, the backrest (30) can rotate to a maximum rotational position. Afterward, when the user removes the force pushing the backrest (30) backward, the backrest (30) can return to the initial rotational position. At this time, the user can feel a reference tension strength in the backrest (30).

[0047] FIG. 7 is a partially cutaway perspective view showing the lowest tension strength of the chair backrest rotation device when the backrest of the chair backrest of FIG. 5 is in the initial rotational position, FIG. 8 is a partially cutaway perspective view showing the maximum tension strength of the chair backrest rotation device when the backrest of the chair backrest of FIG. 5 is in the initial rotational position, and FIG. 9 is a conceptual diagram showing only the tension spring according to FIG. 7 and FIG. 8 in the chair backrest rotation device of FIG. 5.

[0048] Referring to FIGS. 7 through 9, the tension spring (110) may have a minimum tension strength in the state before the tension adjustment screw is inserted into the tension adjustment groove (142) and tightened inward. When a user rotates the tension adjustment screw in the one direction, the tension adjustment screw is tightened inward within the tension adjustment groove (142), and the position of the second spring leg (116) can be changed by slowly pushing it. Accordingly, the tension strength of the tension spring (110) may gradually increase from the minimum tension strength. Subsequently, when the user tightens the tension adjustment screw to the maximum, the tension strength of the tension spring (110) may increase to the maximum tension strength. When the user rotates the tension adjustment screw in the opposite direction of the above one direction, the tension strength of the tension spring (110) can be gradually reduced from the maximum tension strength.

[0049] FIG. 10 is an exploded perspective view to explain that the chair backrest rotation device of FIG. 1 has a different connection relationship than FIG. 2.

[0050] Referring to FIG. 10, the first rotating body (120a) may be connected to the left frame support (22) of the chair frame (20) differently from FIG. 2. Here, the first rotating body (120a) may be connected to be integrated with the left frame support (22), or may be connected by being combined with the left frame support (22).

[0051] On the other hand, the second rotating body (130a) may be connected to the left backrest support (34) of the backrest (30) differently from FIG. 2. Here, the second rotating body (130a) may be connected to be integrated with the left backrest support (34), or it may be connected by being combined with the left backrest support (34).

[0052] As such, according to the present embodiment, the chair backrest rotation device (100) is equipped with a tension adjustment unit (140) capable of adjusting the tension strength of the tension spring (110) by changing the position of the spring leg of the tension spring (110), so that a person using the backrest chair can adjust the tension strength of the tension spring (110) to a tension strength of their choice by operating the tension adjustment unit (140).

[0053] Although the detailed description of the present invention described above has been explained with reference to preferred embodiments of the invention, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the invention without departing from the spirit and technical scope of the invention as described in the claims set forth below. Explanation of the symbols

[0054] 10 : Seat 20 : Chair frame 22: Left frame support 24: Right frame support 30 : Backrest 32 : Backrest 34: Left back support 36: Right back support 100: Chair backrest swivel mechanism 110: Tension spring 112: Spring body 114: First spring leg 116: Second spring leg 120: First rotating body part 120a: First rotating body 122: First spring fixing part 124: First spring body groove 126: First rotating shaft part 128: First rotation limiting part 130: Second rotation body part 130a: Second rotating body 132: Second spring fixing part 134: Second spring body groove 136: Second rotating shaft part 138: Second rotation limiting part 140: Tension adjustment part 142 : Tension adjustment groove 150 : Connecting screw

Claims

Claim 1 A tension spring comprising a spring body having a cylindrical shape by rotating at least once, a first spring leg connected to one end of the spring body, and a second spring leg connected to the other end of the spring body, wherein the angle between the first spring leg and the second spring leg (hereinafter referred to as the 'spring angle') has an initial angle; a first rotating body part comprising a first rotating body connected to one side of either a chair frame supporting a seat or a backrest, and a first spring fixing part formed on one surface of the first rotating body facing the tension spring and fixing the first spring leg; and a second rotating body part comprising a second rotating body connected to the other side of the chair frame and the backrest and rotatably coupled to the first rotating body, and a second spring fixing part formed on one surface of the second rotating body facing the tension spring and fixing the second spring leg.and includes a tension adjustment unit coupled to the second rotating body and capable of adjusting the tension strength of the tension spring by changing the position of the second spring leg to adjust the spring angle, wherein the second spring fixing unit includes a spring leg receiving groove formed on one surface of the second rotating body and capable of receiving at least a portion of the second spring leg, wherein at least a portion of the tension adjustment unit is disposed in the spring leg receiving groove and can change the position of the second spring leg by pushing at least a portion of the second spring leg in a position change direction, wherein the spring leg receiving groove is formed with a width such that the portion of the second spring leg received in the spring leg receiving groove is movable in the position change direction, wherein when the portion of the second spring leg received in the spring leg receiving groove contacts the first inner wall of the spring leg receiving groove, the tension spring has a minimum tension strength, and the tension adjustment unit pushes at least a portion of the second spring leg in the position change direction so that the portion of the second spring leg received in the spring leg receiving groove is the first A chair backrest rotation device characterized in that the tension spring has a maximum tension strength when in contact with the second inner wall of the spring leg receiving groove facing the inner wall. Claim 2 delete Claim 3 A chair backrest rotation device according to claim 1, wherein the second rotating body has a tension adjustment groove formed therein connected to the spring leg receiving groove, and the tension adjustment part includes a tension adjustment screw that penetrates the tension adjustment groove and contacts the second spring leg, and when rotated in one direction, moves inward into the tension adjustment groove to push the second spring leg and change the position of the second spring leg. Claim 4 A chair backrest rotation device according to paragraph 3, characterized in that the tension spring includes a torsion spring. Claim 5 A chair backrest rotation device according to claim 4, characterized in that a first spring body groove is formed on one side of the first rotating body to accommodate a part of the spring body, and a second spring body groove is formed on one side of the second rotating body to accommodate another part of the spring body. Claim 6 A chair backrest rotation device according to claim 5, characterized in that a first rotation shaft portion received within the spring body is formed in the first spring body groove, and a second rotation shaft portion received within the spring body is formed in the second spring body groove at a position corresponding to the first rotation shaft portion. Claim 7 A chair backrest rotation device according to claim 6, further comprising a rotation shaft coupling screw that penetrates either of the first rotation shaft portion and the second rotation shaft portion in a rotatable state and is screw-coupled to either of the first rotation shaft portion and the second rotation shaft portion. Claim 8 A chair backrest rotation device according to claim 3, wherein the first rotational body part further includes a first rotation limiting part formed on one surface of the first rotational body facing the second rotational body, and the second rotational body part further includes a second rotation limiting part formed on one surface of the second rotational body facing the first rotational body and coupled with the first rotation limiting part to limit the first rotational body to rotate only at a reference angle with respect to the second rotational body. Claim 9 A chair backrest rotation device according to claim 8, wherein either of the first rotation limiting part and the second rotation limiting part comprises a rotation receiving groove, and the other of the first rotation limiting part and the second rotation limiting part comprises a rotation projection that is at least partially inserted into the rotation receiving groove and is movable within the rotation receiving groove so as to allow the first rotation body to rotate relative to the second rotation body. Claim 10 A chair backrest rotation device according to claim 3, characterized in that either of the first rotational body and the second rotational body is coupled to the other of the first rotational body and the second rotational body so as to be rotatable by having at least a part of it inserted therein. Claim 11 A seat on which any person can sit; a chair frame supporting the seat; a backrest capable of supporting the back of the person when the person is sitting on the seat; The chair backrest rotation device includes a connection between one side of the chair frame and one side of the backrest, wherein the chair backrest rotation device includes a spring body having a cylindrical shape that rotates at least once, a first spring leg connected to one end of the spring body, and a second spring leg connected to the other end of the spring body, and a tension spring having an initial angle between the first spring leg and the second spring leg (hereinafter referred to as 'spring angle'); a first rotation body part including a first rotation body connected to one side of either the chair frame or the backrest, and a first spring fixing part formed on one surface of the first rotation body facing the tension spring and fixing the first spring leg; and a second rotation body part including a second rotation body connected to the other side of the chair frame or the backrest and rotatably coupled to the first rotation body, and a second spring fixing part formed on one surface of the second rotation body facing the tension spring and fixing the second spring leg.and includes a tension adjustment unit coupled to the second rotating body and capable of adjusting the tension strength of the tension spring by changing the position of the second spring leg to adjust the spring angle, wherein the second spring fixing unit includes a spring leg receiving groove formed on one surface of the second rotating body and capable of receiving at least a portion of the second spring leg, wherein at least a portion of the tension adjustment unit is disposed in the spring leg receiving groove and can change the position of the second spring leg by pushing at least a portion of the second spring leg in a position change direction, wherein the spring leg receiving groove is formed with a width such that the portion of the second spring leg received in the spring leg receiving groove is movable in the position change direction, wherein when the portion of the second spring leg received in the spring leg receiving groove contacts the first inner wall of the spring leg receiving groove, the tension spring has a minimum tension strength, and the tension adjustment unit pushes at least a portion of the second spring leg in the position change direction so that the portion of the second spring leg received in the spring leg receiving groove is the first A backrest chair characterized in that the tension spring has a maximum tension strength when in contact with the second inner wall of the spring leg receiving groove facing the inner wall.

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