Chair capable of preventing waist from being suspended and rubbing back

Abstract

The invention discloses a chair capable of preventing waist suspension and back rubbing, comprising: a chassis assembly, the rear portion of which defines a first rotation axis extending transversely; the chair seat assembly is connected to the top of the chassis assembly; the positioning frame is connected to the chair seat assembly, and a second rotating axis which is located above the rear end of the chair seat assembly and transversely extends is limited on the positioning frame; the support frame is connected with the rear part of the chassis assembly and can rotate around a first rotating axis; the waist and back connecting assembly is used for supporting the waist and the back of the user, the bottom of the waist and back connecting assembly is rotationally connected to the positioning frame, and the rear side of the waist and back connecting assembly is longitudinally and slidably connected to the supporting frame, so that the waist supporting assembly is configured to synchronously rotate around a second rotating axis to tilt forwards or backwards and longitudinally slide relative to the supporting frame; and the first elastic reset piece is used for driving the waist and back connecting assembly to reset to the maximum forward leaning state by always applying elastic force. The invention has the beneficial effects of effectively preventing the waist from being suspended and rubbing the back when the user leans backwards, and improving the comfort level of the user.

Description

Technical Field

[0001] This invention relates to a chair, and more particularly to a chair that prevents the lower back from being unsupported and from rubbing against the back. Background Technology

[0002] In the field of chair technology, existing designs often suffer from support failure when the user leans back. Specifically, when a user leans back, due to structural design limitations, the lumbar support cannot adaptively follow the user's waist movement, easily detaching from the contact surface and becoming suspended, resulting in a loss of effective lumbar support. Simultaneously, relative sliding occurs between the chair back and the user's back, causing a rubbing sensation, which not only interferes with the stability of the relaxed posture but also leads to uneven distribution of support force. These defects significantly reduce comfort, potentially causing lumbar fatigue or discomfort, and impacting the user experience. Therefore, an innovative solution is urgently needed to optimize the chair's linkage mechanism to eliminate the suspension and rubbing phenomena, achieving a more fitting and stable lumbar support. Summary of the Invention

[0003] The purpose of this invention is to provide a chair that can effectively prevent the lower back from being unsupported and the back from rubbing when leaning back, thereby improving user comfort.

[0004] The present invention is achieved through the following technical solution.

[0005] A chair designed to prevent the lower back from being unsupported and to prevent back rubbing, comprising:

[0006] A chassis assembly, the rear of which is defined by a laterally extending first axis of rotation;

[0007] The seat assembly is attached to the top of the chassis assembly;

[0008] A positioning bracket is attached to the seat assembly and defines a second axis of rotation that is located above the rear end of the seat assembly and extends laterally.

[0009] A support frame, connected to the rear of the chassis assembly, and rotatable about a first axis of rotation;

[0010] The lumbar support assembly is used to support the user's waist and back. Its bottom is rotatably connected to the positioning frame, and its rear side is longitudinally slidably connected to the support frame, so that the lumbar support assembly is configured to be able to rotate synchronously about a second rotation axis to tilt forward or backward, and slide longitudinally relative to the support frame.

[0011] The first elastic reset component drives the lumbar and back connection assembly to return to the maximum forward tilt state by constantly applying elastic force.

[0012] As a further improvement of the present invention, the chassis assembly includes a lower support, a front support, an upper support, and a rear support that are rotatably connected end to end to form a four-bar linkage structure; the lower support is used to connect the support legs of the chair, the seat assembly is connected to the upper support; the support frame is connected to the rear support, and the first axis of rotation is defined by the rotatable connection between the rear support and the lower support.

[0013] As a further improvement of the present invention, the rear bracket is formed with an extension extending toward the rear of the chassis assembly, and the support frame and the extension are fixedly connected.

[0014] As a further improvement of the present invention, positioning brackets extending from the rear direction of the seat assembly are formed on both sides of the positioning frame, and the bottom sides of the backrest connection assembly are rotatably connected to the two positioning brackets respectively, and the middle part of the rear side of the backrest connection assembly is slidably connected to the support frame.

[0015] As a further improvement of the present invention, a first elastic reset member is disposed on the chassis assembly to maintain a state in which an elastic force is always applied to the support frame.

[0016] As a further improvement of the present invention, the support frame has a limiting structure, which abuts against the part of the lumbar and back connection assembly that is slidably connected to the support frame during the continuous backward tilting of the lumbar and back connection assembly, thereby limiting the maximum backward tilting angle of the lumbar and back connection assembly.

[0017] As a further improvement of the present invention, the lumbar support assembly includes:

[0018] A connecting frame, the bottom of which is rotatably connected to a positioning frame and can rotate about a second rotation axis;

[0019] A lumbar support is used to support the user's lower back and is mounted on a connecting frame;

[0020] A chair back frame for supporting the user's back, and the part where its bottom and the top of the connecting frame are rotatably connected and the two are rotatably connected to each other defines a third axis of rotation that extends laterally.

[0021] The chair back connecting part and the chair back sliding part are longitudinally slidably connected to the support frame and define a fourth rotation axis extending laterally. The chair back connecting part is formed on the rear side of the chair back frame, is rotatably connected to the chair back sliding part, and can rotate about the fourth rotation axis.

[0022] As a further improvement of the invention, a second elastic reset member is also included, which applies elastic force to the backrest connection and causes its top to rotate and reset in a direction that rotates forward about a fourth rotation axis.

[0023] As a further improvement of the present invention, the chassis assembly is provided with a locking mechanism for locking the chassis assembly when the backrest connection assembly is in the maximum forward tilt state, and preventing the support frame from rotating about the first rotation axis.

[0024] The beneficial effects of this invention are:

[0025] Through precise axis positioning and a linkage mechanism, the continuity and fit of the lumbar support are ensured, reducing the support lag or misalignment problems commonly found in traditional chairs, thereby improving user comfort and safety. Furthermore, the three-linkage mechanism makes the backward leaning motion smoother and more natural, conforming to ergonomic principles and helping to reduce fatigue in the user's lower back; long-term use can promote healthy posture. The reinforced support frame also enhances the overall structural durability, adapting to repeated use by users of different weights. Attached Figure Description

[0026] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings to aid in understanding the objectives and advantages of the present invention, wherein:

[0027] Figure 1 This is a side view of the chair;

[0028] Figure 2 A schematic diagram of a chair and its multiple axes of rotation;

[0029] Figure 3 A schematic diagram of a chair from one perspective;

[0030] Figure 4 A schematic diagram of a chair from another perspective;

[0031] Figure 5 This is a structural diagram of the lumbar support and connecting frame;

[0032] Figure 6 This is an exploded view of the support frame, the backrest connection, and the backrest sliding part. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0034] The directional terms such as up, down, left, right, front, back, front, back, top, and bottom mentioned or possibly used in this specification are defined relative to the construction shown in the accompanying drawings. The terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively. These are relative concepts and may therefore vary depending on their location and usage. Therefore, these or other directional terms should not be interpreted as restrictive.

[0035] This embodiment illustrates a chair that prevents the lower back from being unsupported and causes back rubbing, see reference. Figures 1-6 The system includes a chassis assembly 1, a seat assembly 2, a positioning frame 3, a support frame 4, a lumbar support assembly 5, and a first elastic reset member s1. The rear of the chassis assembly 1 defines a first laterally extending rotation axis r1. The seat assembly 2 is connected to the top of the chassis assembly 1. The positioning frame 3 is connected to the seat assembly 2 and extends rearward from the rear end of the seat assembly 2, then bends and extends upward. The positioning frame 3 defines a second laterally extending rotation axis r2 located above the rear end of the seat assembly 2, which approximately corresponds to the coccyx of the user's buttocks when the user is sitting in a normal sitting posture on the seat assembly 2. The support frame 4 is connected to the rear of the chassis assembly 1, extends rearward from the rear end of the chassis assembly 1, then bends and extends upward, and the support frame 4 is rotatable about the first rotation axis r1. The lumbar and back support assembly 5 is an integral component for supporting the user's waist and back. Its bottom is rotatably connected to the positioning frame 3, and its rear side is longitudinally slidably connected to the support frame 4. This allows the lumbar and back support assembly 5 to be configured to rotate synchronously about the second rotation axis r2, tilting forward or backward, and to slide longitudinally relative to the support frame 4. The first elastic reset member s1 drives the lumbar and back support assembly 5 to return to the maximum forward tilt state by constantly applying elastic force.

[0036] When the user is sitting upright on the seat assembly 2 in a normal sitting posture, and leans back supported by the lumbar and back connecting assembly 5, the lumbar and back connecting assembly 5 is activated, simultaneously achieving a three-linkage mechanism: the lumbar and back connecting assembly 5 rotates backward around the second rotation axis r2, the support frame 4 rotates backward around the first rotation axis r1, and the rear side of the lumbar and back connecting assembly 5 slides downward on the support frame 4. Since the second rotation axis r2 around which the lumbar and back connecting assembly 5 rotates corresponds to the user's buttocks and tailbone, the lumbar connecting assembly remains in contact with the user's waist and back during the backward leaning process, without sliding up and down relative to the user's waist and back, thus effectively avoiding the user's unsupported waist and back rubbing discomfort. When the user returns to a sitting posture, the lumbar and back connecting assembly 5 smoothly returns to its original position under the action of the first elastic reset member s1; the support frame 4 not only provides the track for the lumbar and back connecting assembly 5 to slide longitudinally to achieve the three-linkage mechanism, but also provides support for the lumbar and back connecting assembly 5, especially providing stable support when the lumbar and back connecting assembly 5 is in its maximum backward leaning state. The technical solution provided in this embodiment ensures the continuity and fit of lumbar support through precise axis positioning and a linkage mechanism, reducing the support lag or misalignment problems commonly found in traditional chairs, thereby improving user comfort and safety. Furthermore, the three-linkage mechanism makes the backward leaning motion smoother and more natural, conforming to ergonomic principles and helping to reduce fatigue in the user's lower back; long-term use can promote healthy posture. The reinforced support frame 4 also enhances the overall structural durability, adapting to repeated use by users of different weights.

[0037] In this embodiment, based on the structure of the chassis assembly 1, the chassis assembly 1 includes a lower support 11, a front support 12, an upper support 13, and a rear support 14 that are rotatably connected end to end to form a four-bar linkage. The lower support 11 is used to connect the support legs of the chair, thus remaining fixed during chair use; the seat assembly 2 is connected to the upper support 13; the support frame 4 is connected to the rear support 14, and the first rotation axis r1 is defined by the rotatable connection between the rear support 14 and the lower support 11. This four-bar linkage structure is a common chassis setting in chairs, but here it is combined with the movement of the lumbar support connection assembly 5 to produce a synergistic effect. When the user leans back, it will drive the lower support 11, the front support 12, the upper support 13, and the rear support 14 to rotate in a linked manner. During this process, the upper support 13 will slide backward relative to the lower support 11, that is, the seat assembly 2 will move backward. At the same time, combined with the lumbar support connection assembly 5 rotating backward around the second rotation axis r2, a compound movement of the entire seat leaning backward is formed. The rearward shift of seat assembly 2 compensates for the change in the user's center of gravity when leaning back, preventing the user from slipping off the seat and thus enhancing the stability of the leaning posture. The four-bar linkage makes the leaning motion more controllable and smooth, reducing sudden displacement or swaying and further improving comfort. In addition, this design allows the chair to achieve a large leaning angle within a limited space, optimizing the product's miniaturization and versatility, making it suitable for home or office environments.

[0038] In this embodiment, to further improve the structural strength of the support frame 4, the rear support 14 has an extension 141 extending rearward toward the chassis assembly 1, and the support frame 4 and the extension 141 are fixedly connected. The extension 141 can be configured as a plate, rod, or frame structure, extending rearward from the main body of the rear support 14, thereby increasing the connection area between the support frame 4 and the rear support 14. The support frame 4 typically bears most of the user's weight when leaning back, so a more robust fixation is achieved through the extension 141, for example, by using a bolted connection, to ensure that the support frame 4 does not loosen or deform under repeated loads. This configuration enhances the load-bearing capacity and fatigue resistance of the support frame 4, especially when the user leans back to the extreme position, the support frame 4 can provide reliable support, preventing structural failure or accidental damage. The extension 141 also disperses stress concentration, extends the service life of the chair, and improves safety, avoiding a decline in user experience due to insufficient support.

[0039] In this embodiment, considering the stability of the lumbar support assembly 5, positioning brackets 31 extending from the rear of the seat assembly 2 are formed on both sides of the positioning frame 3. The two sides of the bottom of the lumbar support assembly 5 are rotatably connected to the two positioning brackets 31, and the middle of the rear side of the lumbar support assembly 5 is slidably connected to the support frame 4. This arrangement forms a three-point support structure, with two rotatable connection points located on the bottom sides of the lumbar support assembly 5 and one slidable connection point located in the middle of the rear side. These three points form a triangular orientation. During movement, the triangular support of the lumbar support assembly 5 ensures even force distribution and reduces the possibility of lateral swaying or twisting. This three-point support setting improves the stability and balance of the lumbar support assembly 5 when leaning back, making the support action smoother and more controllable. During the leaning process, the lumbar support assembly 5 can always maintain a close fit with the user's body, avoiding swaying or misalignment caused by insufficient support points, thereby improving comfort and safety. The triangular orientation also enhances the rigidity of the structure, adapts to different user weights and sitting habits, and reduces wear and noise. This design allows the lumbar support component 5 to adapt to the curves of the user's lower back, providing dynamic support that meets individual ergonomic needs. Long-term use helps maintain correct posture and reduces lower back strain.

[0040] In this embodiment, to optimize the configuration of the first elastic reset element s1, the first elastic reset element s1 is disposed on the chassis assembly 1 to maintain a constant elastic force applied to the support frame 4. Specifically, the first elastic reset element s1 can be a torsion spring and is disposed at the rotatable connection between the rear bracket 14 and the lower bracket 11. Theoretically, the first elastic reset element s1 can also be disposed on the positioning frame 3, i.e., on the two positioning sub-support bodies 31. However, if disposed on the positioning sub-support bodies 31, the height and elastic force characteristics of the two first elastic reset elements s1 need to be highly uniform. Otherwise, any slight deviation may cause the rotation of the lumbar and back connection assembly 5 to be unsmooth or stuck. Distributing the first elastic reset element s1 on the chassis assembly 1 avoids this synchronization problem because the chassis assembly 1 provides a more stable installation base and more space, facilitating the installation of a single or centralized elastic system. This configuration ensures the uniformity and consistency of the elastic force application, making the reset action of the lumbar and back connection assembly 5 smoother and more reliable, reducing movement resistance, and improving the user experience. The spatial advantages of chassis component 1 also allow for the use of larger or more efficient elastic elements, enhancing the adjustability and durability of the reset force.

[0041] In this embodiment, to limit the backward tilt angle of the lumbar support assembly 5, the support frame 4 has a limiting structure 4a. During continuous backward tilting of the lumbar support assembly 5, the limiting structure 4a abuts against the portion of the lumbar support assembly 5 that is slidably connected to the support frame 4, thereby limiting the maximum backward tilt angle of the lumbar support assembly 5. When the sliding portion of the lumbar support assembly 5 moves to a specific position, it contacts the limiting structure 4a, preventing further backward tilting. This design provides safety protection, preventing excessive backward tilting that could lead to chair imbalance or structural damage, and also avoids the risk of injury to the user due to accidental excessive backward tilting. The limiting structure 4a ensures that the backward tilt angle is within an ergonomically reasonable range, optimizing comfort and support.

[0042] In this embodiment, based on considerations of balancing lumbar and back support forces, the lumbar and back connection assembly 5 includes a connecting frame 51, a lumbar support 52, a backrest frame 53, a backrest connection portion 54, and a backrest sliding portion 55. The bottom of the connecting frame 51 is rotatably connected to the positioning frame 3 and can rotate about a second rotation axis r2; the lumbar support 52 is used to support the user's waist and is mounted on the connecting frame 51; the backrest frame 53 is used to support the user's back, and its bottom and the top of the connecting frame 51 are rotatably connected, with the portion where they are rotatably connected to each other defining a laterally extending third rotation axis r3; the backrest sliding portion 55 is longitudinally slidably connected to the support frame 4 and defines a laterally extending fourth rotation axis r4; the backrest connection portion 54 is formed on the rear side of the backrest frame 53, is rotatably connected to the backrest sliding portion 55, and can rotate about the fourth rotation axis r4. During the user's reclining process, if the support force on the user's back is greater than that on the lumbar region, a multi-stage linkage mechanism is simultaneously triggered: the backrest connection 54 rotates backward around the fourth rotation axis r4, the backrest sliding part 55 slides downward on the support frame 4, the backrest frame 53 rotates backward around the third rotation axis r3, the connecting frame 51 rotates backward around the third rotation axis r3, the connecting frame 51 rotates forward around the second rotation axis r2, and the third rotation axis r3 moves forward. This series of actions causes the lumbar and back support assembly 5 to arch forward relative to the user's upper body at the connection point where it supports the lumbar and back, thereby reducing the support force of the backrest frame 53 on the user's back and increasing the support force of the lumbar support 52 on the user's lumbar region. This multi-stage linkage achieves a dynamic balance of support force for the user's lumbar and back, automatically adapting to different user body shapes and reclining habits, avoiding the discomfort caused by excessive lumbar or back support in traditional chairs. By adjusting the distribution of support force, overall comfort is improved, especially suitable for users who sit for long periods of time, helping to relieve lumbar and back pressure. This design also allows the chair to adapt to various sitting posture changes. For example, when the user makes a slight adjustment to their posture, the support system can respond in real time to ensure a consistent fit. This balancing mechanism promotes the natural curve of the spine, reduces muscle fatigue, and embodies an innovative ergonomic solution.

[0043] In this embodiment, to assist in the reset of the backrest connection 54, a second elastic reset member s2 is included. This member applies elastic force to the backrest connection 54 and causes its top to rotate forward about the fourth rotation axis r4. The second elastic reset member s2 can be configured as an elastic column, the number of which is determined according to the actual application. Specifically, it can be positioned between the backrest connection 54 and the backrest sliding part 55, supporting both. After the user's backward leaning motion ends, the second elastic reset member s2 provides a restoring force, causing the backrest connection 54 to quickly return to its initial position. This configuration ensures the complete reset of the multi-stage linkage action, allowing the lumbar support assembly 5 to quickly return to the forward-leaning state after the user stands up, preparing it for the next use.

[0044] In this embodiment, to provide additional extension functionality, the chassis assembly 1 is equipped with a locking mechanism (not shown in the figure) to lock the chassis assembly 1 when the backrest connection assembly 5 is in its maximum forward tilt state, and to prevent the support frame 4 from rotating around the first rotation axis r1. The locking mechanism is existing technology and can be a mechanical lock, manual lever, etc., integrated into the four-bar linkage structure of the chassis assembly 1. For example, by locking the connection point between the rear bracket 14 and the lower bracket 11, the movement of the entire chassis is fixed. After the user locks the chassis assembly 1, when leaning back, intentionally exerting force with the back and shoulders, the multi-stage linkage will be triggered simultaneously: the backrest connection 54 rotates backward around the fourth rotation axis r4, the backrest sliding part 55 slides downward on the support frame 4, the backrest frame 53 rotates backward around the third rotation axis r3, the connecting frame 51 rotates backward around the third rotation axis r3, the connecting frame 51 rotates forward around the second rotation axis r2, and the third rotation axis r3 moves forward. This movement causes the lumbar support component 5 to arch forward relative to the user's upper body at the connection point between the lumbar and back supports, guiding the user into a hunched-back extension posture. This forward arching posture is not forced but guided naturally by the mechanical structure. It simulates the posture of the human body actively arching and extending its back, effectively stretching the back muscles and fascia that have become tense and contracted due to prolonged sitting. More importantly, when the user is in this guided hunched-back posture, the support force of the backrest 53 on the user's back and the support force of the lumbar support 52 on the user's lower back reach a dynamic balance. This balance is not a simple static support but a force feedback balance formed during movement. It allows the user's spine, especially the junction of the lumbar and thoracic vertebrae, to receive a gentle and effective longitudinal stretch while the muscles are moderately relaxed. This greatly alleviates problems such as uneven intervertebral disc pressure, muscle stiffness, and poor blood circulation caused by maintaining the same sitting posture for a long time, achieving a deep relaxation and recovery effect. This hunched-back extension posture simulates professional stretching movements, helps improve posture, prevents back problems, and enhances the user experience.

[0045] More specifically, the lumbar support 52 includes two symmetrically arranged side lumbar supports 521. Correspondingly, on the left and right sides of the connecting frame 51, a fifth rotation axis r5 extending longitudinally is respectively provided. These two side lumbar supports 521 are rotatably connected to the left and right sides of the connecting frame 51 and can rotate independently around their respective fifth rotation axis r5. When a user sits in the chair, their lower back naturally contacts these two side lumbar supports 521. If the user twists or leans to the left or right, or if the lower back muscles contract when leaning back, the side lumbar supports 521 will be subjected to force and adaptively rotate around the fifth rotation axis r5. As a result of this rotation, the two side lumbar supports 521 dynamically conform to the user's lower back in a similar embracing posture. To ensure that this embracing posture is temporary and recoverable, each side lumbar support 521 is equipped with a third elastic reset member. The third elastic reset member applies elastic force to the side lumbar support 521, allowing it to automatically rotate and return to its initial position after the force is removed. The symmetrical and independently movable side lumbar support 521 can adapt to the width and narrowness of different users' waists, providing uniform lateral support, which helps stabilize the lumbar spine and reduce unilateral muscle tension in the lower back caused by incorrect posture.

[0046] The side lumbar support 521 has a support surface that smoothly curves from its inner side to its outer side. This curve allows it to better conform to the natural physiological curvature of the user's waist, increasing the contact area and distributing pressure. Near the inner side of the side lumbar support 521, a connecting arm 522 is located behind the support surface and extends outwards. The end of the connecting arm 522, away from the body of the side lumbar support 521, is rotatably connected to the connecting frame 51. By placing the rotatable connection point at the extension of the connecting arm 522, rather than directly on the back of the support surface of the side lumbar support 521, an effective lever arm is created. This structure makes the rotation of the side lumbar support 521 smoother and less strenuous when subjected to lateral pressure from the user's waist, reducing any feeling of jamming.

[0047] More specifically, the connecting frame 51 includes a laterally extending crossbeam 511 and side frames 512 located on both sides of the crossbeam 511. The main function of the crossbeam 511 is to movably connect the aforementioned lumbar support 52, providing a front mounting base for the lumbar support 52. The two side frames 512 are located at the left and right ends of the crossbeam 511, extending upward and downward respectively. The upper parts of the two side frames 512 are rotatably connected to the bottom sides of the chair back frame 53, forming the two end support points of the third rotation axis r3. The lower parts of the two side frames 512 are rotatably connected to the two positioning sub-support bodies 31 of the positioning frame 3, forming the two end support points of the second rotation axis r2.

[0048] More specifically, for the support frame 4, the front side of the support frame 4, i.e., the side facing the backrest connection part 54, is machined or constructed with an inwardly recessed groove 41 that extends longitudinally. The backrest sliding part 55 is longitudinally slidably embedded in this groove 41. This embedding relationship allows the sidewalls of the groove 41 to restrict the lateral swing and deflection of the backrest sliding part 55 from both sides, ensuring that its sliding trajectory is strictly a straight line along the longitudinal direction. This ensures that the spatial orientation of the fourth rotation axis r4 remains horizontal during the sliding process, making the rotation of the backrest connection part 54 around it precise and reliable, and preventing it from becoming inaccurate due to the shaking of the sliding parts. In addition, the bottom wall of the groove 41 forms the aforementioned limiting structure 4a.

[0049] In this embodiment, longitudinally extending and recessed slide rails 411 are formed on the two side walls of the groove 41. Correspondingly, raised slide strips 551 matching the shape of the slide rails 411 are designed on both sides of the backrest sliding part 55. These slide strips 551 are fitted into the corresponding slide rails 411 and can slide longitudinally along the slide rails 411. The cooperation between the slide rails 411 and the slide strips 551 transforms the sliding contact surface from a large area of ​​surface contact to a small area of ​​line contact or narrow surface contact. By selecting wear-resistant materials or adding lubricant, the sliding friction resistance can be significantly reduced, making the up-and-down sliding of the backrest sliding part 55 lighter and quieter. It also avoids play and abnormal noise between components, improving the quality and service life of the product.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chair that prevents the lower back from being unsupported and from rubbing the back, characterized in that, include: A chassis assembly, the rear of which is defined by a laterally extending first axis of rotation; A seat assembly is attached to the top of the chassis assembly; A positioning bracket is attached to the seat assembly and defines a second axis of rotation that is located above the rear end of the seat assembly and extends laterally. A support frame is connected to the rear of the chassis assembly and is rotatable about the first rotation axis; A lumbar support assembly for supporting the user's waist and back, with its bottom rotatably connected to the positioning frame and its rear side slidably connected to the support frame, such that the lumbar support assembly is configured to be able to rotate synchronously about the second rotation axis to tilt forward or backward and slide longitudinally relative to the support frame. The first elastic reset member drives the lumbar and back connection assembly to return to the maximum forward tilt state by constantly applying elastic force.

2. The chair according to claim 1, characterized in that, The chassis assembly includes a lower support, a front support, an upper support, and a rear support that are rotatably connected end to end to form a four-bar linkage structure; the lower support is used to connect the support legs of the chair, and the seat assembly is connected to the upper support; the support frame is connected to the rear support, and the first axis of rotation is defined by the rotatable connection between the rear support and the lower support.

3. The chair according to claim 2, characterized in that, The rear bracket has an extension extending toward the rear of the chassis assembly, and the support frame and the extension are fixedly connected.

4. The chair according to claim 1, characterized in that, The positioning frame has positioning sub-supports extending from the rear of the seat assembly on both sides. The bottom sides of the backrest connection assembly are rotatably connected to the two positioning sub-supports, and the middle of the rear side of the backrest connection assembly is slidably connected to the support frame.

5. The chair according to claim 4, characterized in that, The first elastic reset member is disposed on the chassis assembly to maintain a state in which an elastic force is always applied to the support frame.

6. The chair according to claim 1, characterized in that, The support frame has a limiting structure, which abuts against the part of the lumbar and back connection assembly that is slidably connected to the support frame during the continuous backward tilting of the lumbar and back connection assembly, thereby limiting the maximum backward tilting angle of the lumbar and back connection assembly.

7. The chair according to any one of claims 1-6, characterized in that, The back support assembly includes: A connecting frame, the bottom of which is rotatably connected to the positioning frame and can rotate about a second rotation axis; A lumbar support, used to support the user's lower back, is mounted on the connecting frame; A chair back frame for supporting the user's back, and the portion where its bottom and the top of the connecting frame are rotatably connected and rotatably connected to each other defines a third axis of rotation that extends laterally. The chair back connecting part and the chair back sliding part are provided. The chair back sliding part is slidably connected to the support frame in the longitudinal direction and defines a fourth rotation axis that extends laterally. The chair back connecting part is formed on the rear side of the chair back frame, is rotatably connected to the chair back sliding part, and can rotate about the fourth rotation axis.

8. The chair according to claim 7, characterized in that, It also includes a second elastic reset member for applying elastic force to the backrest connection and for resetting its top by rotating forward about a fourth rotation axis.

9. The chair according to claim 8, characterized in that, The chassis assembly is equipped with a locking mechanism for locking the chassis assembly when the backrest connection assembly is in the maximum forward tilt state, and for preventing the support frame from rotating around the first rotation axis.

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