Angle adjusting apparatus of backrest

Abstract

The present invention comprises a rotating part connected to a fixed part by a hinge joint and rotatable within a certain angle range; an index head having a plurality of first stop holes arranged at regular intervals along a circumference at a predetermined angle from the rotation center of the rotating part, and a plurality of second stop holes arranged at regular intervals along a circumference having the same center as the circumference where the first stop holes are arranged but a different radius; a first pin hole penetrating and aligning with at least one of the first stop holes of the index head; a second pin hole formed horizontally at a position having a radius different from the first pin hole of the rotating part and penetrating and aligning with at least one of the second stop holes of the index head; a first lock pin that maintains the angle of the rotating part relative to the fixed part by being fitted and caught between the first pin hole and the first stop hole by the elastic force of a first spring embedded in the first pin hole when the first pin hole and at least one of the first stop holes of the index head coincide; and the first lock pin located on the opposite side of the index head. A backrest angle adjustment device is disclosed, comprising a release lever that is joined at the end portion and rotates relative to the rotating portion upon pressing operation, thereby releasing the state in which the first lock pin is inserted into the first pin hole and the first stop hole by the elastic force of the first spring.

Description

Technology Field

[0001] The present invention relates to a backrest angle adjustment device for a chair, wheelchair, stroller, etc., which allows the user to adjust the backrest to a desired angle. More specifically, it relates to a backrest angle adjustment device for preventing the angle of the backrest from changing abruptly as the tilting lock state is released due to the user's mistake, carelessness, or malfunction. Background Technology

[0002] Generally, the backrest that supports the user's back in chairs, wheelchairs, strollers, etc. is equipped to be tilted at a certain angle relative to the seat that supports the user's buttocks or to be bent elastically in order to provide convenience and comfort.

[0003] For example, the user can freely adjust the backrest to the desired angle using the backrest angle adjustment device.

[0004] These backrest angle adjustment devices are broadly divided into electric and manual types; electric types use a motor to easily adjust the angle by tilting the backrest backward or upright, while manual types allow the user to adjust the desired angle by turning a handle or operating a lever by hand.

[0005] In relation to this, prior art disclosed in Patent Document 1 is an ‘automatic rotating device for a wheelchair handle.’

[0006] As shown in FIG. 1, the pivot pin (17) connected to the operating part (23) of the operating handle (13) can be fixed in an extended state by passing through the fixing holes (18)(18') by the elastic action of the spring (24) inserted into the fixing hole (18) of the pivot bracket (25). Additionally, the middle part of the operating handle (13) is attached to the fixing bracket (14) by a hinge joint, so when the operating handle (13) is pulled outward as needed, the pivot pin (17) can be easily detached from the fixing holes (18)(18') by the lever principle, allowing the handle support rod (21) to be folded.

[0007] However, in such conventional technology, there is a problem with significantly reduced safety of use, such as the possibility of serious injury if the angle of the handle support rod (21) changes abruptly due to a user's mistake or carelessness in operating the operating handle (13) incorrectly, causing the pivot pin (17) to come out of the fixing hole (18)(18') and the locking state to be released.

[0008] The background technology or prior art described herein is information possessed by the inventor or acquired during the process of deriving and completing the present invention, and is specified merely to aid in understanding the technical significance of the present invention and to be useful for prior art search and examination; it is not to be understood as technology generally known and widely used in the technical field to which the invention belongs prior to the filing of the present invention, and furthermore, drawing symbols in the prior art are mutually unrelated to drawing symbols in the present invention. Prior art literature

[0009] (Patent Document 0001) KR 20-0343455 Y1(2004. 02. 19.)(Patent Document 0002) KR 10-2014-0053228 A(2024. 04. 24.)(Patent Document 0003) KR 10-1093254 B1(2011. 12. 06.) The problem to be solved

[0010] Accordingly, the inventors of the present invention, while comprehensively considering the aforementioned matters and seeking a solution to the technical limitations and problems of existing backrest angle adjustment devices, derived a structural improvement method to prevent the tilting lock state from being released due to user error, carelessness, or malfunction.

[0011] In other words, while making strenuous efforts to continuously research and develop a new type and structure of backrest angle adjustment device that can prevent accidents in which a passenger loses balance and falls backward due to a sudden change in backrest angle caused by the tilting lock state being unintentionally released by external force while the user is adjusting the backrest angle, the present invention was conceived as a result.

[0012] Therefore, the technical problem and objective of the present invention is to provide a backrest angle adjustment device that can prevent malfunctions in which the tilting lock state is unintentionally released.

[0013] Another technical problem and objective of the present invention is to provide a backrest angle adjustment device that can prevent abrupt changes in angle.

[0014] The technical problems and objectives that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems and objectives will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0015] A specific means according to an embodiment of the present invention for effectively achieving a specific technical purpose while embodying a new concept for solving the technical problem of the present invention as described above comprises: a fixed part; a rotating part connected to the upper part of the fixed part by a hinged joint and rotatable within a certain angular range around a pintle of the hinge; an index head integrally formed on one upper part of the fixed part, having a plurality of first stop holes arranged at regular intervals along a circumference at a predetermined angle from the rotation center of the rotating part, and a plurality of second stop holes arranged at regular intervals along a circumference having the same center as the circumference where the first stop holes are arranged but a different radius; a first pin hole formed horizontally on the rotating part and penetrating and aligning with at least one of the first stop holes of the index head according to rotation around the pintle; and a position formed horizontally at a location having a radius different from the first pin hole of the rotating part, and among the second stop holes of the index head according to rotation around the pintle A second pin hole penetrating in alignment with at least one of the first pin hole and the first stop hole of the index head, a first lock pin that maintains the angle of the rotating part relative to the fixed part by being inserted and caught in the first pin hole and the first stop hole by the elastic force of a first spring embedded in the first pin hole when the first pin hole and at least one of the first stop holes of the index head coincide, a second lock pin that suppresses the rotation of the rotating part to stop at a certain angle in stages by being inserted and caught in the second pin hole and the second stop hole by the elastic force of a second spring embedded in the second pin hole when the second pin hole and at least one of the second stop holes of the index head coincide, and the end portion of the first lock pin located opposite the index head is coupled.A backrest angle adjustment device is provided, characterized by comprising a release lever that, upon pressing operation, rotates around the rotating part and releases the first lock pin from being engaged between the first pin hole and the first stop hole by the elastic force of the first spring, and upon pulling operation, rotates around the rotating part and releases the second lock pin from being engaged between the second pin hole and the second stop hole by the elastic force of the second spring.

[0016] Thus, the present invention can prevent the tilting lock state from being unintentionally released by external force due to user error, carelessness, or while the user is adjusting the backrest angle.

[0017] Therefore, the angle of the backrest changes abruptly, preventing the occupant from losing balance and falling backward.

[0018] In addition, as a preferred embodiment of the present invention, the first stop holes and the second stop holes may be arranged to have different angles from the center of the hinge.

[0019] Thus, the present invention can prevent the backrest angle from changing abruptly by maintaining a locked state in stages even when operating with excessive force applied to the release lever.

[0020] In addition, a preferred embodiment of the present invention may further comprise a support member formed on one side of the index head and supporting the state in which the rotating part is extended vertically relative to the fixed part.

[0021] Thus, the present invention can prevent the rotating part from bending forward or folding.

[0022] In addition, a preferred embodiment of the present invention may further comprise a first support member formed on one side of the support member and supporting to amplify the force acting during the pressing operation of the release lever, a second support member formed on one side of the rotating member and supporting to amplify the force acting during the pressing and pulling operation of the release lever, and a pivot member formed protruding from both sides of the release lever and guiding the release lever to move smoothly along the guide surfaces of the first and second support members.

[0023] Thus, the present invention utilizes the principle of a lever so that the user can pull the first lock pin with little force, allowing the backrest angle to be adjusted simply and easily.

[0024] In addition, as a preferred embodiment of the present invention, a clearance hole is formed on the inside of the release lever to allow the end of the first lock pin to pass through and be coupled, and the clearance hole may be formed as an elongated oval shape.

[0025] Thus, the present invention allows for smoother and more convenient operation during the pressing and pulling of the release lever.

[0026] In addition, as a preferred embodiment of the present invention, a first stopper is formed protruding from the front of the first pin hole to prevent the first lock pin from moving beyond a certain range or coming loose, and a first stopper is formed around the rear portion of the first lock pin to which one end of the first spring is in close contact, and a second stopper is formed protruding from the rear of the second pin hole to prevent the second lock pin from moving beyond a certain range or coming loose, and a second stopper is formed around the rear portion of the second lock pin to which one end of the second spring is in close contact and which can be caught on the second stopper.

[0027] Thus, the first and second lock pins can move smoothly and stably according to the pressing and pulling operations of the release lever in accordance with the present invention. Effects of the invention

[0028] According to an embodiment that implements the technical concept on which a unique solution means is based to solve the technical problem of the present invention, even if the locking state of the first lock pin is released due to a user's mistake or carelessness or while the user is adjusting the angle, the second lock pin temporarily maintains the locked state, so the tilting locking state can be prevented from being completely released by an external force.

[0029] Therefore, it can prevent accidents where the backrest angle changes abruptly and unintentionally, causing the occupant to lose balance and fall backward.

[0030] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims. Brief explanation of the drawing

[0031] Figure 1 is a schematic diagram showing a conventional angle adjustment device. FIG. 2 is a perspective view showing the backrest angle adjustment device according to an embodiment of the present invention as viewed from the rear. FIG. 3 is an exploded perspective view of a backrest angle adjustment device according to an embodiment of the present invention. FIG. 4 is a perspective view showing a backrest angle adjustment device according to an embodiment of the present invention as viewed from the front. FIG. 5 is a side view showing the usage state of a backrest angle adjustment device according to an embodiment of the present invention. FIG. 6 is a rear view showing a backrest angle adjustment device according to an embodiment of the present invention. Figure 7 is a longitudinal section view showing an enlarged cross-sectional view from A to A' in Figure 6. FIG. 8 is a longitudinal section view showing an enlarged cross-sectional view from B to B' in FIG. 6. FIGS. 9 and FIGS. 10 are rear views to help understand the operating state of a backrest angle adjustment device according to an embodiment of the present invention. Specific details for implementing the invention

[0032] Hereinafter, embodiments according to the present invention will be described in more detail with reference to the attached drawings.

[0033] Prior to this, it is specified that the terms described below are defined in consideration of their functions in the present invention, and should be interpreted in accordance with the concept consistent with the technical spirit of the present invention and the meaning commonly accepted or recognized in the relevant technical field.

[0034] In addition, if it is determined that a detailed description of known functions or configurations related to the present invention could obscure the essence of the present invention, such detailed description is omitted.

[0035] It is stated that the attached drawings may be partially exaggerated or simplified to facilitate an understanding of the configuration of the technology and to provide a clear and efficient explanation of its operation and principles, and that each component depicted in the drawings does not exactly correspond to its actual size and shape.

[0036] Furthermore, terms such as "and / or" as used in this specification mean a combination of multiple related described items or any of the multiple related described items; and when a part is described as including a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0037] In other words, terms such as "include" and "have" as set forth in this specification mean that there is a feature, number, step, process, operation, component, part, or combination thereof, and should be understood as not excluding the existence or addition of one or more other features, numbers, steps, processes, operations, components, parts, or combinations thereof.

[0038] Meanwhile, the terms "part" and "unit" used in the present invention refer to a unit or module form that performs a role in processing at least one intended function or a certain operation in a device or system, and this can be implemented mechanically or electronically, such as through means including hardware, software, or a combination of hardware and software, or a device or assembly capable of performing independent operations.

[0039] Furthermore, terms such as top, bottom, upper surface, lower surface, or upper, lower, upper side, lower side, front / rear, left / right, etc. used in the present invention are used for convenience to distinguish relative positions or explain directions of movement for each component. For example, the upper part of a drawing may be named or referred to as the upper part and the lower part as the lower part, and the length direction may be named or referred to as the front / rear direction and the width direction as the left / right direction.

[0040] In addition, terms such as "first," "second," etc. used in the present invention may be used to describe various components. That is, terms such as "first," "second," etc. may be used solely for the purpose of distinguishing one component from another.

[0041] [Best mode for carrying out the invention]

[0042] As illustrated in FIGS. 2 to 8, the main elements constituting the backrest angle adjustment device according to an embodiment of the present invention include a fixed part (10), a rotating part (20), an index head (30), a first lock pin (40), a second lock pin (50), and a release lever (60).

[0043] Fixed part (10) It can be fixed to the top of the first frame (1).

[0044] And the upper part of the fixed part (10) is connected to the lower part of the rotating part (20) by a hinge joint.

[0045] That is, a first knuckle (12) is formed at the top of the fixed part (10) to attach the second knuckle (24) of the rotating part (20) by a hinge joint, and the first knuckle (12) and the second knuckle (24) are connected to each other by inserting a pintle (11).

[0046] In addition, a first through hole (13) is horizontally drilled at the bottom of the fixed part (10) to insert the first frame (1) and to insert a separate fixing pin for fixing.

[0047] Rotating part (20) It is connected to the upper side of the fixed part (10) by a hinged joint.

[0048] That is, the rotating part (20) can rotate within a certain angle range around the pintle (11).

[0049] And in the rotating part (20), a first pin hole (21) is horizontally formed that passes through, corresponding to at least one of the first stop holes (31) of the index head (30) according to rotation around the pintle (11).

[0050] Additionally, a second pin hole (22) is horizontally formed in the rotating part (20) and passes through it in alignment with at least one of the second stop holes (32) of the index head (30) according to rotation around the pintle (11).

[0051] That is, the second pin hole (22) is drilled at a position having a different radius from the first pin hole (21) of the rotating part (20).

[0052] And on one side of the rotating part (20), a second support part (23) is formed to support the force acting during the pressing and pulling operation of the release lever (60) so as to amplify it.

[0053] In addition, a second knuckle (24) is formed at the bottom of the rotating part (20) to attach the first knuckle (12) of the fixed part (10) by a hinge joint.

[0054] And at the top of the rotating part (20), a second through hole (25) is horizontally drilled to insert the second frame (2) and secure it by inserting a separate fixing pin.

[0055] That is, the rotating part (20) can be fixed to the bottom of the second frame (2).

[0056] In addition, a first stopper (26) is formed protruding from the front of the first pin hole (21) to prevent the first lock pin (40) from moving beyond a certain range or coming loose.

[0057] And at the back of the second pin hole (22), a second stopper (27) is formed protruding to prevent the second lock pin (50) from moving beyond a certain range or coming loose.

[0058] Index head (30) It is integrally formed on one upper side of the fixed part (10).

[0059] And inside the index head (30), a plurality of first stop holes (31) are arranged at regular intervals along the circumference at a predetermined angle from the rotation center of the rotating part (20).

[0060] Additionally, on the inside of the index head (30), a plurality of second stop holes (32) are arranged at regular intervals along a circumference that has the same center as and a different radius as the circumference where the first stop holes (31) are arranged from the rotation center of the rotating part (20).

[0061] That is, the first stop holes (31) and the second stop holes (32) are formed at regular intervals so as to have different angles from the center of the pintle (11).

[0062] For example, the center of the second stop hole (32) may be located between the center of one first stop hole (31) and the center of another first stop hole (31) adjacent to it, along a circumference having a radius smaller than the radius of the circumference in which the first stop holes (31) are arranged from the center of rotation of the pintle (11).

[0063] And on one side of the index head (30), a support part (33) is integrally formed to support the state in which the rotating part (20) is vertically extended relative to the fixed part (10).

[0064] That is, the support member (33) is formed to protrude from the upper side opposite to the pintle (11) on the upper side of the fixed member (10).

[0065] Additionally, a first support member (34) is formed at one end of the support member (33) to support the force acting when the release lever (60) is pressed, thereby amplifying the force.

[0066] First lock pin (40) It is embedded in the first pin hole (21) to maintain the angle of the rotating part (20) rotating around the pintle (11) relative to the fixed part (10).

[0067] That is, when at least one of the first pin hole (21) of the rotating part (20) and the first stop hole (31) of the index head (30) coincides, the first lock pin (40) is inserted into the first pin hole (21) and the first stop hole (31) by the elastic force of the first spring (41) embedded in the first pin hole (21), thereby maintaining the locked state of the fixed part (10) and the rotating part (20).

[0068] And the front end of the first lock pin (40) is formed in a semicircular shape so that it can be smoothly fitted into the first stop hole (31).

[0069] Additionally, a first stop (43) is formed around the rear portion of the first lock pin (40) to which one end of the first spring (41) is in close contact.

[0070] And the first spring (41) is mounted between the first stopper (43) and the first stopper (26) so that when the pulling action of the release lever (60) is released, the first lock pin (40) returns to its original position and shape.

[0071] That is, the first spring (41) is compressed as the first lock pin (40) moves, and an elastic force is applied so that the rear end of the first lock pin (40) is inserted and caught in the first pin hole (21) and the first stop hole (31). A steel wire with a circular cross section is wound spirally so that one end in the longitudinal direction is supported by the first stopper (26) of the rotating part (20), and the opposite end is in close contact with the first stop (43).

[0072] Accordingly, the first spring (41) pushes the first lock pin (40) by a compression force, and when the compressive force that occurs when the first lock pin (40) moves becomes greater than the compression force, compressive deformation naturally occurs, accumulating elastic energy, and an elastic restoring force is generated to return the first lock pin (40) to its original position in opposition to the compression force.

[0073] Here, it is preferable to use a compression coil spring for the first spring (41) that accumulates elastic energy when compression deformation occurs due to the applied load, i.e., the force pressing the second lock pin (40), and generates a force (restoring force) that attempts to return to its original state by repelling the compression force. However, it is not limited to this, and any material that resists the force attempting to compress and has the same effect as a coil spring through elastic restoring force, such as elastic rubber, may be used.

[0074] 2nd lock pin (50) It is embedded in the second pin hole (22) to suppress the rotation of the rotating part (20), which rotates around the pintle (11) relative to the fixed part (10), so that it stops at a certain angle in stages.

[0075] That is, when at least one of the second pin hole (22) of the rotating part (20) and the second stop hole (32) of the index head (30) coincides, the second lock pin (50) is inserted into the second pin hole (22) and the second stop hole (32) by the elastic force of the second spring (51) embedded in the second pin hole (22), thereby maintaining the locked state of the fixed part (10) and the rotating part (20).

[0076] And the front end of the second lock pin (50) is formed in a semicircular shape so that it can be smoothly fitted into the second stop hole (32).

[0077] Additionally, one end of the second spring (51) is in close contact with the rear circumference of the second lock pin (50), and a second stopper (52) is formed that can be caught on the second stopper (27).

[0078] And the second spring (51) is mounted between the second stop (52) and the operating part (63) of the release lever (60) so that when the pushing action of the release lever (60) is released, the second lock pin (50) returns to its original position and shape.

[0079] That is, the second spring (51) is compressed as the second lock pin (50) moves, and an elastic force is applied so that the rear end of the second lock pin (50) is inserted and caught in the second pin hole (22) and the second stop hole (32). A steel wire with a circular cross section is wound spirally so that one end in the longitudinal direction is supported by the operating part (63) of the release lever (60), and the opposite end is in close contact with the second stop (52).

[0080] Here, the second spring (51) is preferably a compression coil spring that accumulates elastic energy when compression deformation occurs due to the applied load, i.e., the force pressing the second lock pin (50), and generates a force (restoring force) that attempts to return to its original state by repelling the compression force. However, it is not limited to this, and any material that resists the force attempting to compress, such as elastic rubber, which has the same effect as a coil spring through elastic restoring force, may be used.

[0081] Release lever (60) It serves to selectively maintain or release the locked state of the fixed part (10) and the rotating part (20) by means of the first lock pin (40) and the second lock pin (50).

[0082] The upper part of the release lever (60) is formed so that the user can operate it comfortably and securely with their hand, and the lower part is connected to the end of the first lock pin (40) located opposite the index head (30).

[0083] That is, when the release lever (60) is pressed, it moves relative to the rotating part (20) and releases the first lock pin (40) from being stuck in the first pin hole (21) and the first stop hole (31) by the elastic force of the first spring (41).

[0084] Additionally, when the release lever (60) is pulled, it moves relative to the rotating part (20) and releases the state in which the second lock pin (50) is inserted into the second pin hole (22) and the second stop hole (32) by the elastic force of the second spring (51).

[0085] And on both sides of the release lever (60), pivot parts (61) are formed protruding toward the first and second support parts (34)(23) to guide the lever to move smoothly along the guide surfaces of the first and second support parts (34)(23).

[0086] Additionally, a clearance hole (62) is formed on the inside of the release lever (60) to allow the end of the first lock pin (40) to pass through and be connected.

[0087] Here, the clearance hole (62) is formed as an elongated vertical oval shape that is larger and wider than the diameter of the first lock pin (40) to allow for smooth movement of the release lever (60) relative to the rotating part (20).

[0088] And at the lower part of the release lever (60), an action part (63) is formed in which force is applied to the first and second lock pins (40)(50) when moving relative to the pivot part (61).

[0089] [Operating Principles and Functions of Major Components]

[0090] The main operations, operating principles, and functions of each element constituting the backrest angle adjustment device according to the embodiment of the present invention configured as described above are as follows.

[0091] First, as shown in FIG. 7, when the first lock pin (40) is inserted into one of the first stop holes (31) that match the first pin hole (21) by the elastic force of the first spring (41) embedded in the first pin hole (21), the angle of the rotating part (20) relative to the fixed part (10) can be maintained.

[0092] At this time, the second lock pin (50) is positioned between the index head (30) and the second spring (51), and the second spring (51) is maintained in a compressed state between the second stop (52) and the operating part (63) of the release lever (60).

[0093] In this state, as illustrated in FIG. 9, when the user presses the release lever (60) to adjust the backrest angle, the first lock pin (40) is pulled forward by the principle of a lever while moving relative to the first support part (34) and the second support part (23), and accordingly, it naturally comes out of the first stop hole (31) of the index head (30), thereby temporarily releasing the lock.

[0094] Next, the tilting angle can be adjusted step by step by rotating the rotating part (20) around the pintle (11) at a constant angle.

[0095] In this process, as illustrated in FIG. 8, when at least one of the second pin hole (22) and the second stop hole (32) coincides, the second lock pin (50) is inserted into the second pin hole (22) and the second stop hole (32) by the elastic force of the second spring (51) and is caught, thereby restraining the rotating part (20) to stop at a certain angle.

[0096] In this state, when the release lever (60) is pulled, the gap between the operating part (63) and the rotating part (20) widens, and the compressed second spring (51) moves forward due to elastic action, and accordingly, the second lock pin (50) is inserted into the second stop hole (32) and released from the restrained state.

[0097] Afterwards, as illustrated in FIG. 10, when the user rotates the rotating part (20) to a certain angle to adjust the backrest angle, the first lock pin (40) is inserted into one of the first stop holes (31) that match the first pin hole (21) by the elastic force of the first spring (41), thereby maintaining the angle of the rotating part (20) relative to the fixed part (10).

[0098] In this way, even if the locking state of the first lock pin (40) is released due to user error, carelessness, or the user adjusting the angle, the second lock pin (50) temporarily maintains the locked state, so the tilting locking state can be prevented from being completely released by external force.

[0099] Therefore, it can prevent accidents where the backrest angle changes abruptly and unintentionally, causing the occupant to lose balance and fall backward.

[0100] Meanwhile, it is obvious to those skilled in the art that the present invention is not limited by the embodiments described above and the attached drawings, and that it can be modified and applied in various ways not exemplified within the scope of the technical concept of the present invention, as well as widely applied by substituting each component and changing to equivalent alternative embodiments.

[0101] Therefore, content related to modifying and applying the technical features of the present invention should be interpreted as being included within the technical concept and scope of the present invention. Explanation of the symbols

[0102] 10: Fixed part 11: Pintle 12: 1st knuckle 13: 1st penetration hole 20: Rotating part 21: First pin hole 22: Second pin hole 23: Second support part 24: Second knuckle 25: Second penetration hole 26: 1st stopper 27: 2nd stopper 30: Index head 31: First stop hole 32: Second stop hole 33: Support part 34: First support part 40: First lockpin 41: First spring 42: Nut 43: 1st stop 50: 2nd lock pin 51: 2nd spring 52: 2nd stop 60: Release lever 61: Pivot part 62: Clearance hole

Claims

Claim 1 A fixed part; a rotating part connected to the upper part of the fixed part by a hinged joint and rotatable within a certain angular range around a pintle of the hinge; an index head integrally formed on one upper part of the fixed part, having a plurality of first stop holes arranged at regular intervals along a circumference at a predetermined angle from the rotation center of the rotating part, and a plurality of second stop holes arranged at regular intervals along a circumference having the same center as the circumference where the first stop holes are arranged but a different radius; a first pin hole formed horizontally on the rotating part and penetrating by aligning with at least one of the first stop holes of the index head according to rotation around the pintle; a second pin hole formed horizontally at a position having a radius different from the first pin hole of the rotating part and penetrating by aligning with at least one of the second stop holes of the index head according to rotation around the pintle; when the first pin hole and at least one of the first stop holes of the index head coincide, the first pin hole A first lock pin that maintains the angle of the rotating part relative to the fixed part by being inserted and caught in the first pin hole and the first stop hole by the elastic force of a first spring embedded therein; and a second lock pin that, when the second pin hole and at least one of the second stop holes of the index head coincide, is inserted and caught in the second pin hole and the second stop hole by the elastic force of a second spring embedded in the second pin hole, thereby suppressing the rotation of the rotating part to stop at a certain angle in stages.A backrest angle adjustment device comprising: a release lever in which the end portion of the first lock pin located opposite the index head is coupled, and which, upon pressing operation, moves relative to the rotating part to release the first lock pin from being engaged between the first pin hole and the first stop hole by the elastic force of the first spring, and upon pulling operation, moves relative to the rotating part to release the second lock pin from being engaged between the second pin hole and the second stop hole by the elastic force of the second spring; Claim 2 A backrest angle adjustment device according to claim 1, wherein the first stop holes and the second stop holes are arranged to have different angles from the rotation center of the hinge. Claim 3 A backrest angle adjustment device according to claim 1, further comprising: a support member formed on one side of the index head and supporting the state in which the rotating part is vertically extended relative to the fixed part. Claim 4 A backrest angle adjustment device according to claim 3, further comprising: a first support member formed on one side of the support member and supporting to amplify the force acting during the pressing operation of the release lever; a second support member formed on one side of the rotating member and supporting to amplify the force acting during the pressing and pulling operations of the release lever; and a pivot member formed protruding from both sides of the release lever and guiding the release lever to move smoothly along the guide surfaces of the first and second support members. Claim 5 A backrest angle adjustment device according to claim 1, wherein a clearance hole is formed on the inside of the release lever to allow the end of the first lock pin to pass through and be connected, and the clearance hole is formed as an elongated oval shape. Claim 6 A backrest angle adjustment device according to claim 1, wherein a first stopper is formed protrudingly on the front of the first pin hole to prevent the first lock pin from moving beyond a certain range or coming loose, a first stopper is formed on the rear circumference of the first lock pin to which one end of the first spring is in close contact, a second stopper is formed protrudingly on the rear of the second pin hole to prevent the second lock pin from moving beyond a certain range or coming loose, and a second stopper is formed on the rear circumference of the second lock pin to which one end of the second spring is in close contact and which can be caught on the second stopper.

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