Quickly-assembled backrest frame and backrest

Abstract

The utility model relates to a fast-assembly type backrest frame and a backrest, and relates to the technical field of furniture, the fast-assembly type backrest frame comprises a frame body, connecting pieces installed on the frame body and elastic pieces connected to the connecting pieces, the number of the connecting pieces is at least two, and the elastic pieces are connected between any two connecting pieces; the connecting piece is provided with the connecting part used for being connected with the elastic piece, the connecting part is arranged on the connecting piece and can be directly connected with the elastic piece, installation pieces such as buckling strips and hooks are reduced, the installation steps of the elastic piece are simplified, and the installation efficiency is improved.

Description

Technical Field

[0001] The present application relates to the field of furniture, and in particular to a quick-install backrest frame and a backrest. Background Art

[0002] With the development of the furniture industry, prefabricated furniture is becoming more and more popular among users, which is convenient for users to install and pack for transportation. As a common structure in furniture, the backrest is widely used and is commonly found in sofas, beds, chairs and other furniture to provide back support for users. Generally, flexible parts such as covers, soft bags or elastic parts are set on the backrest to improve the comfort and user experience of the back support for users.

[0003] With respect to the above-mentioned related technologies, the inventors found that: the installation steps of the elastic member on the backrest are complicated, the number of installation parts (such as buckle strips, hooks, etc.) installed in conjunction with the elastic member is large, and the installation efficiency is low. Utility Model Content

[0004] In order to solve the above technical problems, the present application provides a quick-install backrest frame and backrest.

[0005] The quick-install backrest frame provided in this application adopts the following technical solution:

[0006] A quick-install backrest frame comprises a frame body, a connecting piece installed on the frame body and an elastic piece connected to the connecting piece, wherein at least two connecting pieces are provided and the elastic piece is connected between any two connecting pieces, wherein: the connecting piece has a connecting portion for connecting the elastic piece.

[0007] By adopting the above technical solution, the connecting member is provided with a connecting portion for connecting the elastic member, which reduces the installation of components such as buckle strips and hooks installed in conjunction with the elastic member, simplifies the installation steps of the elastic member, and improves the installation efficiency of the elastic member and the backrest.

[0008] Optionally, the connecting portion and the connecting piece are integrally formed.

[0009] By adopting the above technical solution, the connecting part and the connecting piece are integrally formed, which is convenient for production and manufacturing, and can also ensure the structural strength between the connecting part and the connecting piece.

[0010] Optionally, the connecting portion and the connecting piece are detachably fixedly connected.

[0011] By adopting the above technical solution, the connection between the connecting part and the connecting piece is detachably fixed, which is convenient for replacement and maintenance of the connecting part and the connecting piece. Since the connecting part and the connecting piece are detachable, they can be separately packaged before and after installation for easy transportation.

[0012] Optionally, the connecting portion and the connecting piece are fixedly connected in a non-detachable manner.

[0013] By adopting the above technical solution, the connecting part and the connecting piece can be packaged separately in front of the connecting piece for easy transportation, and the structural strength between the connecting part and the connecting piece can also be guaranteed after being connected in a non-detachable manner.

[0014] Optionally, the connecting portion has a displacement margin for the elastic member to move.

[0015] By adopting the above technical solution, the connection part has a displacement margin for the elastic member to move, so that the elastic member can stretch to both sides when being squeezed by the user's backrest to adapt to the deformation of the elastic member, giving the user a better experience.

[0016] Optionally, the frame body includes two mounting members, and the connecting member is fixedly mounted between the two mounting members and abuts against the two mounting members to limit movement of the connecting member relative to the mounting members along the first direction.

[0017] By adopting the above technical solution, the connecting member is fixedly installed between the two mounting members and abuts against the mounting members to limit the movement of the connecting member along the first direction, wherein the connecting member abuts against the mounting member, and the first direction is the vertical direction of the abutting surface of the connecting member and the mounting member, thereby increasing the restriction on the degree of freedom of the connecting member, thereby improving the stability and reliability of the connection, and reducing the shaking of the connecting member during use.

[0018] Optionally, the mounting member has a connector and the connecting member has a socket for plugging the connector, or the connecting member has a connector and the mounting member has a socket for plugging the connector; wherein: the mounting member and the connecting member are plugged into each other to limit the movement of the connecting member relative to the mounting member along a first direction perpendicular to the mounting member, and to limit the rotation of the connecting member relative to the mounting member around a first direction.

[0019] By adopting the above technical solution, the mounting member and the connecting member are connected by the plug-in fit between the connector and the socket, and the plug-in fit limits the movement of the connecting member relative to the mounting member along a first direction perpendicular to the first direction and the rotation around the first direction, thereby further improving the restriction on the degree of freedom of the connecting member and enhancing the connection stability and reliability.

[0020] Optionally, the mounting member and the connecting member are fixedly connected by a fastener, wherein: the connection direction of the fastener is consistent with the first direction, so as to limit the movement of the connecting member relative to the mounting member along a direction perpendicular to the first direction, and to limit the rotation of the connecting member relative to the mounting member around the first direction.

[0021] By adopting the above technical solution, the mounting member and the connecting member are connected by a fastener, and the connection direction of the fastener is consistent with the first direction, so that the fastener can limit the movement of the connecting member relative to the mounting member along the first direction perpendicular to the first direction and the rotation around the first direction, thereby further improving the restriction on the degree of freedom of the connecting member and improving the connection stability and reliability.

[0022] Optionally, the mounting member further has an abutment portion abutting against the connecting member to limit the movement of the connecting member relative to the mounting member along a first direction perpendicular to the mounting member, and to limit the rotation of the connecting member relative to the mounting member around the first direction.

[0023] By adopting the above technical solution, an abutment portion is provided to limit the movement of the connecting member in a first direction perpendicular to the first direction and the rotation around the first direction through an abutment action, thereby further improving the restriction on the degree of freedom of the connecting member and improving the connection stability and reliability.

[0024] The present application also discloses a backrest adopting the following technical solution:

[0025] A backrest comprises the quick-install backrest frame as described above.

[0026] By adopting the above technical solution, the above quick-install backrest frame is applied to the backrest, and the elastic member can be connected without installing buckle strips, hooks and other mounting parts on the connecting parts, which makes the installation convenient and quick.

[0027] In summary, the present application includes at least one of the following beneficial technical effects:

[0028] 1. In the present application, the connecting member has a connecting portion that can be directly connected to the elastic member, thereby reducing installation parts such as buckle strips and hooks, simplifying the installation steps of the elastic member, and improving the installation efficiency;

[0029] 2. In the further configuration of the present application, the connecting member and the connecting portion may be integrally formed, or may be connected in a detachable fixed installation or a non-detachable fixed installation manner, and the installation manner is diversified to meet different installation requirements;

[0030] 3. In a further configuration of the present application, the connector is connected to the mounting member, and the degree of freedom of the connector is restricted by plugging, fastener connection, abutment, etc., thereby improving the connection stability and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a three-dimensional structural diagram of a quick-install frame;

[0032] Figure 2 yes Figure 1 Explosion diagram of

[0033] Figure 3 yes Figure 1 A schematic diagram of the three-dimensional structure after the third connecting member and the back plate are installed;

[0034] Figure 4 yes Figure 1 Schematic diagram of the three-dimensional structure of the backrest after the soft bag and the surface cover are installed;

[0035] Figure 5It is a side view structural schematic diagram and a partial enlarged schematic diagram of the mounting member after the connecting member and the elastic member are connected to the mounting member;

[0036] Figure 6 It is a side view structural diagram of the mounting part and a partial enlarged diagram;

[0037] Figure 7 It is a schematic diagram of the three-dimensional structure of the connecting piece and the connecting part being integrally formed, and a schematic diagram of the structure after punching;

[0038] Figure 8 yes Figure 7 A schematic side view of the connecting member and the connecting portion after the middle punching, wherein the connecting portion has a through hole;

[0039] Fig. 9 It is an exploded schematic diagram of the connector and the connecting part as independent parts before installation;

[0040] Fig.10 It is a schematic diagram of a side view structure with a through groove on the connecting part.

[0041] Explanation of the accompanying drawings: 1. Frame body; 11. Mounting part; 111. Abutment part; 21. Connecting part; 211. First connecting part; 212. Second connecting part; 213. Connecting part; 2131. Through hole; 2132. Through groove; 2133. Anti-slip part; 215. Third connecting part; 22. Back plate; 3. Face cover; 4. Soft bag; 5. Connector; 6. Socket; 7. Fastener; 8. Connecting hole; 9. Elastic part; 10. Countersunk hole. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various configurations. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0043] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0044] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0045] In the description of the present application, it should be understood that the terms "up", "down", "left", "right", 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 application 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 should not be understood as a limitation on the present application.

[0046] The following is combined with Figure 1-10 This application is described in further detail.

[0047] The present application embodiment discloses a quick-install backrest frame, as shown in the attached Figure 1 , Attachment Figure 2 As shown, it includes a frame body 1, a connecting member 21 and an elastic member 9. At least two connecting members 21 are provided and installed on the frame body 1. The elastic member 9 is connected between any two connecting members 21. The connecting member 21 has a connecting portion 213 for connecting the elastic member 9.

[0048] In this embodiment, two connecting members 21 are provided and are distributed along the height direction of the frame body 1. For the convenience of explanation, the two connecting members 21 are respectively referred to as the first connecting member 211 and the second connecting member 212. Specifically, the first connecting member 211 is installed on the top of the frame body 1, and the second connecting member 212 is installed on the bottom of the frame body 1, so that after the elastic member 9 is connected between the two connecting members 21, it can provide complete support for the user's back along the height direction of the frame body 1. In this embodiment, the elastic member 9 adopts a serpentine spring.

[0049] In other embodiments, the number of connectors 21 and the positions where the connectors 21 are installed on the frame body 1 can be customized according to user needs, and the elastic members 9 between the connectors 21 can be arranged for specific positions on the back of the user. Specifically, more than three connectors 21 are arranged along the height direction of the frame body 1, and the elastic member 9 can be connected between any two connectors 21 according to user needs.

[0050] Regarding the connection relationship between the connecting member 21 and the connecting portion 213, Figure 3 To Attachment Figure 6 , the present application provides the following embodiments:

[0051] Embodiment 1

[0052] The connecting portion 213 and the connecting piece 21 are integrally formed. Common integral forming methods include extrusion molding and blow molding, but are not limited to the above two processes. The connecting portion 213 and the connecting piece 21 are generally but not limited to profiles or plastic materials.

[0053] In addition, the connecting member 21 is overall in the shape of an elongated strip, and multiple connecting portions 213 may be provided along the length direction of the connecting member 21 so as to connect multiple elastic members 9. In this embodiment, after the connecting member 21 and the connecting portion 213 are integrally formed and produced, a plurality of connecting portions 213 may be punched out through a punching process, and the number of the connecting portions 213 and the intervals between the connecting portions 213 may be customized according to the actual installation requirements of the elastic member 9.

[0054] In this embodiment, the punching of the connection part 213 can be performed at the assembly site, and the position and quantity of the connection part 213 can be adjusted flexibly and variedly, and has strong applicability.

[0055] Embodiment 2

[0056] The connection portion 213 is detachably fixedly connected to the connection member 21, that is, the connection portion 213 and the connection member 21 are two separate parts that can be packaged and transported independently before and after disassembly. Specifically, the detachable connection between the connection portion 213 and the connection member 21 can be, but is not limited to, mortise and tenon, scarf, embedded or bolted.

[0057] The detachable connection method generally requires pre-setting mortise and tenon, embedded holes or embedded grooves (not shown) for connection on the connecting piece 21, which can be prefabricated during the factory production process, reducing on-site processing and making installation simpler and more convenient.

[0058] Embodiment 3

[0059] The connection portion 213 and the connection member 21 are fixedly connected in a non-detachable manner, that is, the connection portion 213 and the connection member 21 are two independent parts before installation, and after installation, the connection portion 213 and the connection member 21 cannot be separated or can only be separated from the connection member 21 by destroying the connection structure. Specifically, common non-detachable connection methods include welding, bonding, etc. It should be noted that the bonding connection is to glue the connection portion 213 and the connection member 21 together using solid glue, etc. If the glued connection portion 213 and the connection member 21 are to be separated, the solid glue needs to be destroyed, so the bonding method is also defined as a non-detachable connection method.

[0060] The non-detachable connection mode can not only be customized on site, with high installation flexibility, but also has good connection strength, and will not cause excessive waste of materials of the connecting piece 21 and the connecting portion 213.

[0061] Different connecting members 21 and the connecting portions 213 thereon may be connected in different ways. Generally, for the convenience of production and processing, all connecting members 21 and the connecting portions 213 may be connected in one of the three embodiments described above.

[0062] As for the connection part 213, in a further configuration, the connection part 213 has a displacement margin for the elastic member 9 to move. In this embodiment, a through hole 2131 for the end of the elastic member 9 to connect is provided on the connection part 213, and the through hole 2131 is in a strip shape. When the elastic member 9 is squeezed by the back of the user, the end of the elastic member 9 moves along the through hole 2131 to stretch the elastic member 9, so as to better fit the back of the user, and avoid the elastic member 9 being sunken at the part where the user's back is squeezed, which affects the user experience. In addition, the connection part 213 can also be hollowed out to make it lighter.

[0063] In another embodiment, a through slot 2132 is provided on the connecting portion 213, so that the end of the elastic member 9 can be directly hooked to the connecting portion 213 from the notch of the through slot 2132, which makes installation more convenient and quick. An anti-slip portion 2133 is provided at the notch to reduce the possibility of the elastic member 9 being detached from the notch, thereby improving reliability. It should be noted that the connecting portion 213 itself needs to have a certain elasticity, and when the elastic member 9 is hooked into the through slot 2132, the anti-slip portion 2133 needs to be squeezed and pushed open to elastically deform it until the elastic member 9 is hooked into the through slot 2132; if the elastic member 9 is to be detached from the through slot 2132, the force generated by the elastic deformation of the anti-slip portion 2133 also needs to be overcome.

[0064] For the frame body 1, combined with the attached Figure 7 , Attachment Figure 8 , comprising two mounting members 11, a connecting member 21 fixedly mounted between the two mounting members 11 to form a backrest frame, and the connecting member 21 abuts against the mounting members 11 to limit the movement of the connecting member 21 relative to the mounting members 11 along a first direction. In this embodiment, the left and right ends of the connecting member 21 are respectively fixedly connected to the two connecting members 21, and the left and right ends of the connecting member 21 abut against the connecting member 21 to limit the movement of the connecting member 21 in the left and right directions.

[0065] Further explanation: the left and right direction of the backrest frame is the X direction, the up and down direction is the Z direction, and the front and back direction is the Y direction, wherein the X direction is the first direction, and the abutment between the connecting member 21 and the mounting member 11 can limit the freedom of movement of the connecting member 21 along the X direction and the freedom of rotation around the Y direction and the Z direction, so as to ensure the stability and reliability of the connection between the connecting member 21 and the mounting member 11.

[0066] In addition, the following three implementation modes are specifically provided for further setting of the movement freedom of the connecting member 21 along the Y direction and the Z direction and the rotation freedom around the X direction, which can further improve the stability and reliability of the connecting structure.

[0067] Implementation method 1:

[0068] The mounting member 11 has a plug-in member 5 and the connecting member 21 has a socket 6 for plugging in the plug-in member 5, or the connecting member 21 has a plug-in member 5 and the mounting member 11 has a socket 6 for plugging in the plug-in member 5, wherein: the plug-in fit between the mounting member 11 and the connecting member 21 is used to limit the movement of the connecting member 21 relative to the mounting member 11 along a first direction perpendicular to the mounting member 11, and to limit the rotation of the connecting member 21 relative to the mounting member 11 around a first direction, that is, through the plug-in fit to limit the movement of the connecting member 21 relative to the mounting member 11 along the Y direction and the Z direction, and at the same time limit the rotation of the connecting member 21 around the X direction, thereby cooperating with the abutment between the connecting member 21 and the mounting member 11 to limit the six degrees of freedom of the connecting member 21.

[0069] It should be noted that the plug-in component 5 and the plug-in hole 6 are generally not cylindrical, so as to prevent the connecting component 21 from easily rotating relative to the mounting component 11 after plugging.

[0070] Implementation method 2:

[0071] The mounting member 11 and the connecting member 21 are fixedly connected by a fastener 7, wherein the connection direction of the fastener 7 is consistent with the first direction, so as to limit the movement of the connecting member 21 relative to the mounting member 11 along the first direction perpendicular to the first direction, and limit the rotation of the connecting member 21 relative to the mounting member 11 around the first direction, and also cooperate with the abutment effect of the connecting member 21 and the mounting member 11 to limit the six degrees of freedom of the connecting member 21.

[0072] It should be noted that: the latch, as a kind of fastener 7, adopts an interference fit to fasten the connecting member 21 and the mounting member 11. In the implementation method, the latch is generally not cylindrical to avoid the connecting member 21 from rotating relative to the mounting member 11 after the latch is inserted and fastened.

[0073] Implementation method three:

[0074] The mounting member 11 further has an abutting portion 111 abutting against the connecting member 21 , thereby limiting the movement of the connecting member 21 relative to the mounting member 11 along a first direction perpendicular to the connecting member 21 and limiting the rotation of the connecting member 21 relative to the mounting member 11 around the first direction.

[0075] It should be noted that the abutment portion 111 needs to abut and restrict the connector 21 in four directions, namely, the positive and negative directions in the Y direction and the positive and negative directions in the Z direction, and cooperate with the abutment between the connector 21 and the mounting member 11 to restrict the six degrees of freedom of the connector 21.

[0076] In other embodiments, any two or three of the above three embodiments may be combined for application. When more than two embodiments are combined for application, the connector 5 and the socket 6 may adopt cylindrical plug-in according to actual conditions, and the fastener 7 may also adopt cylindrical pin. The combination of two or more of the three embodiments may over-restrict the degree of freedom of the connector 21, thereby ensuring the stability of the connector 21 and the connection reliability.

[0077] In this embodiment, the first connecting member 211 and the second connecting member 212 both adopt a combination of the above three implementation methods to limit the degree of freedom. Specifically, the left and right ends of the connecting member 21 are respectively abutted against the two mounting members 11, a plug hole 6 is provided on the connecting member 21, and a plug connector 5 plugged into the plug hole 6 is provided on the mounting member 11. The plug connector 5 is in contact with the positive and negative side walls of the plug hole 6 along the Y direction and the positive and negative side walls along the Z direction, so as to achieve the purpose of limiting the movement of the connecting member 21 in the Y direction and the Z direction and the rotation around the X direction; the fastener 7 adopts a bolt, a connecting hole 8 is provided on the connecting member 21, and a plug connector 5 is provided on the mounting member 11 to connect the plug connector 5 to the plug hole 6. A countersunk hole 10 is formed on the top, and the connecting hole 8 is opposite to the countersunk hole 10 along the X direction. The bolt is installed into the connecting hole 8 from the X direction to fasten the connecting member 21 and the mounting member 11. The countersunk hole 10 is convenient for hiding the bolt and restricting the movement of the connecting member 21 along the Y direction and the Z direction. The abutting portion 111 is adapted to the outer contour of the connecting member 21 and can abut the positive and negative sides of the connecting member 21 along the Y direction and the reverse side of the Z direction, thereby further restricting the degree of freedom of the connecting member 21.

[0078] In addition, the connector 21 is produced by an extrusion molding process, and its socket 6 can be formed by the extrusion process. In this embodiment, the socket 6 passes through the connector 21 along the X direction; the mounting member 11 is produced by a blow molding process, and its plug-in member 5 imitates the inner wall contour of the socket 6 in the connector 21, and the abutment portion 111 imitates the outer contour of the connector 21 to improve the degree of plug-in adaptation and abutment adaptation between the mounting member 11 and the connector 21. It should be noted that: the plug-in member 5 imitating the inner wall contour of the socket 6 does not mean that the plug-in member 5 needs to completely abut against the inner wall of the socket 6 when it is inserted into the socket 6, but it only needs to satisfy the limitation of the movement of the connector 21 along the Y direction and the Z direction.

[0079] The present application also discloses a backrest, as shown in the attached Fig. 9 , Attachment Fig.10 Specifically, a third connecting member 215 is installed on the frame body 1, and the third connecting member 215 is installed in the middle of the height direction of the frame body 1, and is connected to the mounting member 11 by combining the second embodiment and the third embodiment.

[0080] In addition, the face cover 3 is connected between the second connecting member 212 and the third connecting member 215, and the frame body 1 is covered by the face cover 3. A soft bag 4 is arranged on the front side of the face cover 3 to provide the user with a better usage experience, and the elastic member 9 is supported on the inner side of the front side of the face cover 3; the back plate 22 is connected between the first connecting member 211 and the third connecting member 215 to support the inner side of the back side of the face cover 3, thereby reducing wrinkles and depressions of the face cover 3 and improving the aesthetics.

[0081] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A quick-install backrest frame, characterized in that: The invention comprises a frame body (1), a connecting piece (21) mounted on the frame body (1), and an elastic piece (9) connected to the connecting piece (21), wherein at least two connecting pieces (21) are provided and the elastic piece (9) is connected between any two connecting pieces (21), wherein the connecting piece (21) has a connecting portion (213) for connecting to the elastic piece (9).

2. The quick-install backrest frame according to claim 1, characterized in that: The connecting portion (213) and the connecting piece (21) are integrally formed.

3. The quick-install backrest frame according to claim 1, characterized in that: The connecting portion (213) and the connecting member (21) are detachably fixedly connected.

4. The quick-install backrest frame according to claim 1, characterized in that: The connecting portion (213) and the connecting member (21) are fixedly connected in a non-detachable manner.

5. The quick-install backrest frame according to claim 1, characterized in that: The connecting portion (213) has a displacement margin for the elastic member (9) to move.

6. The quick-install backrest frame according to claim 1, characterized in that: The frame body (1) comprises two mounting members (11), and the connecting member (21) is fixedly mounted between the two mounting members (11) and abuts against the two mounting members (11) to limit movement of the connecting member (21) relative to the mounting members (11) along a first direction.

7. The quick-install backrest frame according to claim 6, characterized in that: The mounting member (11) has a plug-in member (5) and the connecting member (21) has a socket (6) for plugging the plug-in member (5), or the connecting member (21) has a plug-in member (5) and the mounting member (11) has a socket (6) for plugging the plug-in member (5); wherein: the plug-in fit between the mounting member (11) and the connecting member (21) is used to restrict the movement of the connecting member (21) relative to the mounting member (11) in a first direction perpendicular to the mounting member (11), and to restrict the rotation of the connecting member (21) relative to the mounting member (11) around a first direction.

8. The quick-install backrest frame according to claim 6, characterized in that: The mounting member (11) and the connecting member (21) are fixedly connected via a fastener (7), wherein the connection direction of the fastener (7) is consistent with a first direction, so as to limit the movement of the connecting member (21) relative to the mounting member (11) in a direction perpendicular to the first direction, and to limit the rotation of the connecting member (21) relative to the mounting member (11) around the first direction.

9. The quick-install backrest frame according to claim 6, characterized in that: The mounting member (11) also has an abutment portion (111) abutting against the connecting member (21) so as to limit the movement of the connecting member (21) relative to the mounting member (11) along a first direction perpendicular to the connecting member (21), and to limit the rotation of the connecting member (21) relative to the mounting member (11) around the first direction.

10. A backrest, characterized in that: It comprises a quick-install backrest frame as claimed in any one of claims 1 to 9.

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