Mechanical stretching device for liftable seat, and liftable seat

Abstract

Provided in the present invention is a mechanical stretching device for a liftable seat. The liftable seat comprises a seating portion, a backrest and a footrest. The mechanical stretching device comprises: a base, which is fixedly supported on the ground; a linkage mechanism, which is movably arranged above the base, wherein the linkage mechanism comprises a seat mounting plate, a backrest support and a leg assembly, the leg assembly comprising a footrest mounting plate and an outward turning assembly; and a lifting assembly, which is arranged between the base and the linkage mechanism, wherein the seat mounting plate can be switched between a sitting position and a lifting position by means of the lifting assembly.

Description

Mechanical extension device for liftable seat and liftable seat Technical Field

[0001] The present application relates to a mechanical extension device for a liftable seat and a liftable seat comprising the mechanical extension device. Background Art

[0002] With rising living standards and a growing demand for more sophisticated household items, movable chairs are becoming increasingly versatile. For example, senior citizen chairs, in addition to the standard sitting and reclining positions, also feature a so-called "lift position." In this lift position, the seat can be raised relative to the ground and tilted forward to assist the user in rising. However, this diversity of functions also brings structural complexity. This not only increases the number of required parts but also increases the overall size of the chair. Summary of the Invention

[0003] In view of this, the technical problem to be solved by this application is how to provide a seat that maintains a good user experience and comprehensive functionality while having a compact structure.

[0004] In order to solve the above technical problems, a mechanical extension device for a liftable seat is provided. The liftable seat includes a seat portion, a backrest and a footrest. The mechanical extension device includes:

[0005] -Fix the base supported on the ground;

[0006] - a linkage mechanism movably disposed above the base, the linkage mechanism comprising a seat mounting plate, a backrest bracket, and a leg assembly, wherein the leg assembly comprises a footrest mounting plate and an outward turning assembly; and

[0007] A lifting assembly is arranged between the base and the linkage mechanism, wherein the seat mounting plate can be moved between a sitting position and a raised position by means of the lifting assembly.

[0008] According to the present application, the linkage mechanism enables the mechanical extension device to be shifted between at least a sitting position and a reclining position. In the reclining position, the front end of the outward-facing assembly is located forward of the footrest mounting plate, and the backrest bracket is tilted rearward relative to the seat mounting plate. The front end of the outward-facing assembly is at least 490 mm above the ground. In some embodiments, in the reclining position, the front end of the outward-facing assembly is at least 550 mm above the ground.

[0009] In the sitting position, the backrest bracket and the backrest attached thereto are generally pointed upward, the leg assembly is folded, and the footrest attached to the leg assembly is folded under the seat portion. In the reclining position, the backrest bracket and the backrest attached thereto are significantly tilted rearward compared to the reclining position, the leg assembly is extended forward and upward, and the footrest attached to the leg assembly is raised forward and upward. During the transition from the sitting position to the reclining position, the leg assembly's folding assembly is unfolded, so that the front end of the folding assembly is located in front of the footrest mounting plate, thereby extending the support portion for the user's lower limbs, especially at least the feet and / or calves, providing a better user experience. At the same time, because the folding assembly itself is only unfolded during the transition from the sitting position to the reclining position and remains folded in the sitting position, a more compact structure is provided.

[0010] In one embodiment, the outward-turning assembly includes a first outward-turning link, a second outward-turning link, a third outward-turning link and an outward-turning drive rod, wherein a four-bar linkage is formed by the footrest mounting plate, the first outward-turning link, the second outward-turning link and the third outward-turning link, and wherein the four-bar linkage can be driven to deform by the outward-turning drive rod, so that the front end of the outward-turning assembly is located in front of the footrest mounting plate.

[0011] In one embodiment, the leg assembly further includes a first leg link, a second leg link, a third leg link and a fourth leg link, wherein the front ends of the third leg link and the fourth leg link are respectively hinged to the footrest mounting plate, wherein the front end of the outward-turning drive rod is hinged to the four-bar linkage, and the rear end of the outward-turning drive rod is hinged to the fourth leg link at a first hinge point.

[0012] In one embodiment, the first outward-turning link includes a second hinge point arranged on its first free end, a fourth hinge point arranged on its second free end, and a third hinge point located between the second hinge point and the fourth hinge point, wherein the first outward-turning link is hinged to the outward-turning drive rod at the second hinge point, is hinged to the footrest mounting plate at the third hinge point, and is hinged to the third outward-turning link at the fourth hinge point.

[0013] In one embodiment, during the deployment of the leg assembly, as the angle between the fourth leg link and the footrest mounting plate increases, the outward drive rod causes the second free end of the first outward link to pivot upward around the third hinge point.

[0014] In one embodiment, the first outward-turning connecting rod is configured as a bell crank, wherein a line connecting the second hinge point and the fourth hinge point is located in front of the third hinge point.

[0015] In one embodiment, two ends of the second outward-turned connecting rod are hinged to the front end of the footrest mounting plate and the third outward-turned connecting rod respectively.

[0016] In one embodiment, in the lying position, the angle of the front side of the backrest support to the horizontal plane is at most 22°. In some embodiments, in the lying position, the angle of the front side of the backrest support to the horizontal plane is at most 13°.

[0017] In one embodiment, in the sitting position, the leg assembly is retracted relative to the seat mounting plate.

[0018] In one embodiment, in the raised position, the seat mounting plate is raised and tilted forward relative to the base, and the leg assembly is folded relative to the seat mounting plate, wherein the lifting assembly can sequentially shift the mechanical extension device from a lying position, a sitting position to a raised position, and reversely shift the mechanical extension device sequentially from a raised position, a sitting position to a lying position.

[0019] To solve the above technical problems, the present application also provides a liftable chair. The liftable chair includes a mechanical extension device, a seat portion attached to the mechanical extension device, a backrest, and a footrest. The mechanical extension device includes:

[0020] -Fix the base supported on the ground;

[0021] - a linkage mechanism movably arranged above the base, the linkage mechanism comprising a seat mounting plate attached to the seat portion, a backrest bracket attached to the backrest, and a leg assembly attached to the footrest, wherein the leg assembly comprises a footrest mounting plate and an outward turning assembly; and

[0022] A lifting assembly is arranged between the base and the linkage mechanism, wherein the seat mounting plate can be moved between a sitting position and a raised position by means of the lifting assembly.

[0023] According to the present application, the linkage mechanism enables the mechanical extension device to be shifted between at least a sitting position and a reclining position. In the reclining position, the front end of the outward-facing assembly is located forward of the footrest mounting plate, and the backrest bracket is tilted rearward relative to the seat mounting plate. The front end of the outward-facing assembly is at least 490 mm above the ground. In some embodiments, in the reclining position, the front end of the outward-facing assembly is at least 550 mm above the ground.

[0024] In one embodiment, the outward-turning assembly includes a first outward-turning link, a second outward-turning link, a third outward-turning link and an outward-turning drive rod, wherein a four-bar linkage is formed by the footrest mounting plate, the first outward-turning link, the second outward-turning link and the third outward-turning link, and wherein the four-bar linkage can be driven to deform by the outward-turning drive rod, so that the front end of the outward-turning assembly is located in front of the footrest mounting plate.

[0025] In one embodiment, the leg assembly further includes a first leg link, a second leg link, a third leg link and a fourth leg link, wherein the front ends of the third leg link and the fourth leg link are respectively hinged to the footrest mounting plate, wherein the front end of the outward-turning drive rod is hinged to the four-bar linkage, and the rear end of the outward-turning drive rod is hinged to the fourth leg link at a first hinge point.

[0026] In one embodiment, the first outward-turning link includes a second hinge point arranged on its first free end, a fourth hinge point arranged on its second free end, and a third hinge point located between the second hinge point and the fourth hinge point, wherein the first outward-turning link is hinged to the outward-turning drive rod at the second hinge point and is hinged to the third outward-turning link at the fourth hinge point.

[0027] In one embodiment, during the deployment of the leg assembly, as the angle between the fourth leg link and the footrest mounting plate increases, the outward drive rod causes the second free end of the first outward link to pivot upward around the third hinge point.

[0028] In one embodiment, the first outward-turning connecting rod is configured as a bell crank, wherein a line connecting the second hinge point and the fourth hinge point is located in front of the third hinge point.

[0029] In one embodiment, two ends of the second outward-turned connecting rod are hinged to the front end of the footrest mounting plate and the third outward-turned connecting rod respectively.

[0030] In one embodiment, in the lying position, the front side of the backrest frame is at most 22° with the horizontal plane, and in the lying position, the front side of the backrest frame is at most 13° with the horizontal plane.

[0031] In one embodiment, in the sitting position, the footrest is tucked under the seat portion.

[0032] In one embodiment, in the raised position, the seat mounting plate is raised and tilted forward relative to the base, and the seat portion is folded under the seat portion, wherein the lifting assembly enables the mechanical extension device to be sequentially transformed from a lying position, a sitting position to a raised position, and the mechanical extension device to be reversely transformed from a raised position, a sitting position to a lying position.

[0033] It should be noted that the details and advantages described for the mechanical extension device also apply to a liftable seat comprising such a mechanical extension device.

[0034] In addition, it should be noted that the "fore-and-aft direction" or "longitudinal direction" in this application refers to the extension direction of the leg assembly of the height-adjustable seat or its mechanical extension device. Specifically, "forward" refers to the direction toward the leg assembly, and "rearward" refers to the direction toward the backrest assembly. The "left-right direction" or "lateral direction" refers to the horizontal direction of the height-adjustable seat or its mechanical extension device that is perpendicular to the "fore-and-aft direction" or "longitudinal direction." BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The embodiments of the present application are explained in detail below with reference to the accompanying drawings.

[0036] FIG1 schematically shows a perspective view of a mechanical extension device for a liftable seat according to one embodiment of the present application, which is in a lying position;

[0037] FIG2 schematically shows in perspective the mechanical extension device shown in FIG1 in a sitting position;

[0038] FIG3 schematically shows, in side view, the raised position of the mechanical stretching device shown in FIG1 ;

[0039] FIG4 schematically shows a side view of the mechanical extension device shown in FIG1 in a sitting position;

[0040] FIG5 schematically illustrates, in side view, the TV posture position of the mechanical stretching device shown in FIG1 ;

[0041] FIG6 schematically shows, in side view, the lying position of the mechanical stretching device shown in FIG1 ;

[0042] FIG7 schematically shows a partial enlarged view of the leg assembly of the mechanical extension device shown in FIG1 ;

[0043] FIG8 schematically shows a partial enlarged view of the leg assembly shown in FIG7 from another angle. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0045] References to "one embodiment" or "an embodiment" herein refer to specific features, structures, or characteristics that may be included in at least one implementation of the present application. Throughout the description of this application, it should be understood that the terms "upper," "lower," "left," "right," "top," "bottom," and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely for ease of description and simplification. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the present application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly specifying the number of the technical features referred to. Thus, a feature designated "first" or "second" may explicitly or implicitly include one or more of such features. Furthermore, the terms "first," "second," and the like are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential sequence. It should be understood that such terms are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0046] FIG1 schematically illustrates in perspective a mechanical extension device 1 for a height-adjustable chair according to an embodiment of the present application. Furthermore, the height-adjustable chair includes a seat portion, a backrest, and a footrest (not shown) attached to the mechanical extension device 1. FIG1 shows the mechanical extension device 1 in a reclining position, while FIG2 shows the mechanical extension device 1 in a sitting position.

[0047] The mechanical extension device 1 includes a base 10 , a linkage mechanism 11 , a lifting assembly 12 and an electric drive unit 13 .

[0048] The base 10 is fixedly supported on the ground. The liftable seat can be sequentially shifted from at least the reclining position shown in Figures 1 and 6 to the sitting position shown in Figures 2 and 4, and the raised position shown in Figure 3, through the linkage mechanism 11 and lift assembly 12. Furthermore, the liftable seat can be sequentially shifted from the raised position, the sitting position, and finally to the reclining position. The liftable seat can also be shifted to a TV position, intermediate between the reclining and sitting positions, as shown in Figure 5.

[0049] In the embodiment shown in Figures 1 and 2, the base 10 includes a rear base crossbeam 101 extending in the transverse direction of the liftable seat, a front base crossbeam 102, and two base longitudinal beams 103 extending in the longitudinal direction and spaced apart from each other on the left and right sides. The front base crossbeam 101, the rear base crossbeam 102, and the base longitudinal beams 103 form a rectangular base 10.

[0050] A linkage mechanism 11 is movably arranged above the base 10 . The linkage mechanism 11 is constructed as a multi-link mechanism and includes a supporting frame 110 , a seat assembly 111 , a backrest assembly 112 and a leg assembly 113 .

[0051] The supporting frame 110 is generally constructed as a rectangular frame and includes two supporting longitudinal beams 1100 extending longitudinally of the movable seat and spaced apart from each other on the left and right sides, and a front supporting cross beam 1106 and a rear supporting cross beam 1107 extending between and connecting the two supporting longitudinal beams 1100. At the front end of the supporting frame 110 near the leg assembly 113, particularly in the embodiment shown in FIG. 2 , the front supporting cross beam 1106 includes a front extension 1101. At the rear end of the supporting longitudinal beam 1100 near the backrest assembly 112, a rear extension 1102 is included.

[0052] It should be noted that the front extension 1101 can be either a part of the front load-bearing crossbeam 1106 or a component fixedly connected to the front load-bearing crossbeam 1106. The rear extension 1102 can be either a part of the load-bearing longitudinal beam 1100 or a component fixedly connected to the load-bearing longitudinal beam 1100.

[0053] The seat assembly 111 includes an L-shaped seat mounting member 1110, a front end mounting member 1111 constructed on the front end of the seat mounting member 1110, a seat front swing link 1112, a seat rear swing link 1113, a drive link 1114 and a laterally extending motor drive rod 1115.

[0054] The seat mounting member 1110 is used to attach the seat. The front mounting member 1111 is fixedly connected to the seat mounting member 1110 or is configured as a protrusion protruding upward from the front end of the seat mounting member 1110. A drive link 1114 is pivotally connected at one end to the front mounting member 111 and at its other end to drive rod protrusions 1115a protruding from both ends of the motor drive rod 1115. The front seat swing link 1112 is configured as a bell crank member. One free end is pivotally connected to the front end of the seat mounting member 1110 and the other free end is at least indirectly pivotally connected to the leg assembly 113 via the leg drive rod 1116. The rear seat swing link 1113 is pivotally connected at one end to the rear end of the seat mounting member 1110 and at least indirectly pivotally connected to the support frame 110, particularly the support longitudinal beam 1100, at its other end.

[0055] As shown in FIG4 , the seat assembly 111 is movably connected to the supporting frame 110 via a transmission mechanism. The transmission mechanism includes a first transmission rod 1103, a second transmission rod 1104, and a third transmission rod 1105. The middle portion of the front seat swing link 1112 is pivotally connected to the front end of the first transmission rod 1103, the rear end of the first transmission rod 1103 is pivotally connected to the front end of the second transmission rod 1104, and the middle portion of the first transmission rod 1103 is pivotally connected to the supporting longitudinal beam 1100, particularly the rear end extension 1102 of the supporting longitudinal beam. The rear end of the second transmission rod 1104 is pivotally connected to the lower end of the third transmission rod 1105, the upper end of the third transmission rod 1105 is pivotally connected to the lower end of the rear seat swing link 1113, and the middle portion of the third transmission rod 1105 is pivotally connected to the supporting longitudinal beam 1100, particularly the rear end extension 1102 of the supporting longitudinal beam.

[0056] The backrest assembly 112 includes a backrest bracket 1120 and a backrest link 1121. The backrest bracket 1120 is used to attach the backrest, and the front end of the backrest bracket 1120 is pivotally connected to the upper end of the seat mounting member 1110, the rear end of the backrest bracket 1120 is pivotally connected to the upper end of the backrest link 1121, and the lower end of the backrest link 1121 is pivotally connected to the load-bearing longitudinal beam 1100, in particular, the rear end extension 1102 of the load-bearing longitudinal beam.

[0057] The leg assembly 113 is constructed as a multi-link mechanism and includes a first leg link 1131 , a second leg link 1132 , a third leg link 1133 , a fourth leg link 1134 , a pedal mounting plate 1135 for attaching a pedal, and an outward rotation assembly pivotally connected to the pedal mounting plate 1135 .

[0058] As shown in Figures 5 and 6, the rear end of the first leg link 1131 is pivotally connected to the middle portion of the seat front swing link 1112, and the front end of the first leg link 1131 is pivotally connected to the rear end of the fourth leg link 1134. The rear end of the second leg link 1132 is pivotally connected to the front end of the seat mounting member 1110, and the front end of the second leg link 1132 is pivotally connected to the rear end of the third leg link 1133. The front ends of the third leg link 1133 and the fourth leg link 1134 are both pivotally connected to the footrest mounting plate 1135. The middle portion of the second leg link 1132 is also hingedly connected to the middle portion of the fourth leg link 1134.

[0059] As shown in Figures 7 and 8, the outward-turning assembly is pivotally connected to the front portion of the footrest mounting plate 1135. To this end, a footrest front-end extension portion 1135a is integrally formed on the front portion of the footrest mounting plate 1135. The outward-turning assembly includes a first outward-turning link 1136, a second outward-turning link 1137, a third outward-turning link 1138, and an outward-turning drive rod 1139. The footrest mounting plate 1135, the first outward-turning link 1136, the second outward-turning link 1137, and the third outward-turning link 1138 form a four-bar linkage.

[0060] The first outward-turning link 1136 is configured as a bell crank, wherein the first outward-turning link 1136 includes a second hinge point P2 at its first free end, a fourth hinge point P4 at its second free end, and a third hinge point P3 located between the second hinge point P2 and the fourth hinge point P4. The line connecting the second hinge point P2 and the fourth hinge point P4 is located forward of the third hinge point P3.

[0061] The outward-turning drive rod 1139 includes a front end and a rear end that are generally opposed to each other in the front-to-back direction. The rear end of the outward-turning drive rod 1139 is pivotally connected to the fourth leg link 1134 of the leg assembly 113 at a first hinge point P1, and the front end is hingedly connected to the first outward-turning link 1136 at a second hinge point P2. The first outward-turning link 1136 is hingedly connected to the front extension 1135a of the footrest at a third hinge point P3 and to the third outward-turning link 1138 at a fourth hinge point P4. One end of the second outward-turning link 1137 is hingedly connected to the front extension 1135a of the footrest, and the other end is hingedly connected to the third outward-turning link 1138. The second outward-turning link 1137 is hingedly connected to the front extension 1135a of the footrest more forward than the third hinge point P3.

[0062] During the deployment of the leg assembly 113, as the angle between the fourth leg link 1134 and the footrest mounting plate 1135 increases, the outward-turning drive rod 1139 causes the second free end of the first outward-turning link 1136 to pivot upward around the third hinge point P3, thereby causing the four-bar linkage composed of the footrest mounting plate 1135, the first outward-turning link 1136, the second outward-turning link 1137 and the third outward-turning link 1138 to deform through the outward-turning drive rod 1139, so that the front end of the outward-turning assembly is located in front of the footrest mounting plate 1135.

[0063] The lifting mechanism 12 includes a lifting base 120, a first lifting link 121, and a second lifting link 122. The lifting base 120 is fixedly mounted on the base longitudinal beam 101 of the base 10. The first lifting link 121 and the second lifting link 122 are each hinged at one end to the lifting base 120 and at the other end to the supporting frame 110, specifically, to a front extension 1101 fixedly connected to the front supporting crossbeam 1106. Thus, the lifting base 120, the first lifting link 121, the second lifting link 122, and the front extension 1101 form a four-bar linkage. This modification of the four-bar linkage enables the supporting frame 110 to be raised and lowered relative to the base 10, thereby driving the seat assembly 111, the backrest assembly 112, and the leg assembly 113 connected to the supporting frame 110 to be raised and lowered relative to the base 10. The second lifting link 122 is configured with a lifting stop plate 1220 on the side thereof facing the base 10. When the lifting mechanism 12 is not lifted, the lifting stop plate 1220 abuts against the upper surface of the base longitudinal beam 103 with its lower surface.

[0064] To facilitate the transition of the liftable seat between different postures, an electric drive unit 13 is also provided. In this embodiment, the electric drive unit 13 comprises a single electric motor. The electric motor can be configured as a push rod motor, comprising a motor head connected to the rear base crossbeam 101 and a motor push rod that is retractable relative to the motor head. The motor push rod is connected to the motor drive rod 1115.

[0065] The electric drive unit 13 can cause the liftable seat to be sequentially changed from a lying position to a sitting position and a raised position, or vice versa, from a raised position to a sitting position and a lying position.

[0066] Of course, in an embodiment not shown, the electric drive unit 13 may also include two motors, one of which causes the liftable seat to change between a sitting position and a lying position, and the other motor causes the liftable seat to change between a raised position and a sitting position and / or a lying position.

[0067] When the liftable chair is moved from the raised position shown in Figure 3 to the reclining position shown in Figure 6 , the motor push rod begins to retract relative to the motor head. This causes the lift mechanism 12 to retract, causing the support frame 110, and ultimately the entire linkage mechanism 11, to descend relative to the base 10. When the lift stop plate 1220 abuts the base longitudinal beam 103 , the lift mechanism 12 ceases retraction, the linkage mechanism 11 no longer descends, and the liftable chair reaches the sitting position shown in Figure 4 .

[0068] At this point, the motor push rod continues to retract relative to the motor head. This causes the motor drive rod 1115 to flip, which in turn causes the drive link 1114 to pivot, prompting the front mounting member 1111 to push the seat mounting member 1110 backward. Simultaneously, the backrest assembly 112 tilts backward, and under the action of the transmission mechanism, the seat front swing arm 1112 pivots, causing the leg drive rod 1116 to move forward, pushing the leg assembly 113 to unfold. This results in the TV posture shown in Figure 5, or even the reclining position shown in Figure 6.

[0069] As mentioned above, during the expansion process of the leg assembly 113, as the angle between the fourth leg link 1134 and the footrest mounting plate 1135 increases, the outward drive rod 1139 causes the second free end of the first outward link 1136 to pivot upward around the third hinge point P3, so that the front end of the outward assembly is located in front of the footrest mounting plate 1135.

[0070] In the lying position, the height H of the front end of the eversion assembly relative to the ground is at least 490 mm, and in some embodiments is 550 mm; the angle α of the front side of the backrest bracket 1120 with the horizontal plane is at most 22°, and in some embodiments is at most 13°.

[0071] List of Reference Numerals

Claims

1. A mechanical extension device for a height adjustable chair, the height adjustable chair comprising a seat portion, a backrest, and a footrest, the mechanical extension device comprising: -Fix the base supported on the ground; - a linkage mechanism movably disposed above the base, the linkage mechanism comprising a seat mounting plate, a backrest bracket, and a leg assembly, wherein the leg assembly comprises a footrest mounting plate and an outward turning assembly; and - a lifting assembly arranged between the base and the linkage mechanism, wherein the seat mounting plate can be moved between a sitting position and a raised position by means of the lifting assembly, The linkage mechanism enables the mechanical extension device to be transformed at least between a sitting position and a lying position, wherein in the lying position, the front end of the outward-turning component is located in front of the footrest mounting plate, and the backrest bracket is tilted backward relative to the seat mounting plate, wherein the height of the front end of the outward-turning component relative to the ground is at least 490 mm.

2. The mechanical stretching device according to claim 1, wherein: In the lying position, the height of the forwardmost end of the eversion assembly relative to the ground is at least 550 mm.

3. The mechanical stretching device according to claim 1, wherein: The outward-turning assembly includes a first outward-turning link, a second outward-turning link, a third outward-turning link and an outward-turning drive rod, wherein a four-bar linkage is formed by the footrest mounting plate, the first outward-turning link, the second outward-turning link and the third outward-turning link, and wherein the four-bar linkage can be driven to deform by the outward-turning drive rod, so that the front end of the outward-turning assembly is located in front of the footrest mounting plate.

4. The mechanical stretching device according to claim 3, wherein: The leg assembly also includes a first leg link, a second leg link, a third leg link and a fourth leg link, wherein the front ends of the third leg link and the fourth leg link are respectively hinged to the footrest mounting plate, wherein the front end of the outward-turning drive rod is hinged to the four-bar linkage, and the rear end of the outward-turning drive rod is hinged to the fourth leg link at a first hinge point.

5. The mechanical stretching device according to claim 4, wherein: The first outward-turning link includes a second hinge point arranged on its first free end, a fourth hinge point arranged on its second free end, and a third hinge point located between the second hinge point and the fourth hinge point, wherein the first outward-turning link is hinged to the outward-turning drive rod at the second hinge point, is hinged to the footrest mounting plate at the third hinge point, and is hinged to the third outward-turning link at the fourth hinge point.

6. The mechanical stretching device according to claim 5, wherein: During the unfolding of the leg assembly, as the included angle between the fourth leg link and the footrest mounting plate increases, the outward rotation driving rod causes the second free end portion of the first outward rotation link to pivot upward around the third hinge point.

7. The mechanical stretching device according to claim 5, wherein: The first outward-turning connecting rod is configured as a bell crank, wherein a line connecting the second hinge point and the fourth hinge point is located in front of the third hinge point.

8. The mechanical stretching device according to claim 5, wherein: Two ends of the second outward-turning connecting rod are hinged to the front end of the pedal mounting plate and the third outward-turning connecting rod respectively.

9. The mechanical stretching device according to claim 1, wherein: In the lying position, the front side of the backrest frame is at most 22° to the horizontal.

10. The mechanical stretching device according to claim 9, wherein: In the lying position, the front side of the backrest frame is at most 13° to the horizontal.

11. The mechanical stretching device according to claim 1, wherein: In the sitting position, the leg assembly is retracted relative to the seat-mounting plate.

12. The mechanical stretching device according to claim 11, wherein: In the raised position, the seat mounting plate is raised and tilted forward relative to the base, and the leg assembly is folded relative to the seat mounting plate, wherein the lifting assembly can sequentially shift the mechanical extension device from a lying position, a sitting position to a raised position, and reversely shift the mechanical extension device from a raised position, a sitting position to a lying position.

13. A liftable chair comprising a mechanical extension device, a seat portion attached to the mechanical extension device, a backrest, and a footrest, wherein: The mechanical stretching device comprises: -Fix the base supported on the ground; - a linkage mechanism movably arranged above the base, the linkage mechanism comprising a seat mounting plate attached to the seat portion, a backrest bracket attached to the backrest, and a leg assembly attached to the footrest, wherein the leg assembly comprises a footrest mounting plate and an outward turning assembly; and - a lifting assembly arranged between the base and the linkage mechanism, wherein the seat mounting plate can be moved between a sitting position and a raised position by means of the lifting assembly, The linkage mechanism enables the mechanical extension device to be transformed at least between a sitting position and a lying position, wherein in the lying position, the front end of the outward-turning component is located in front of the footrest mounting plate, and the backrest bracket is tilted backward relative to the seat mounting plate, wherein the height of the front end of the outward-turning component relative to the ground is at least 490 mm.

14. The liftable chair according to claim 13, wherein: In the lying position, the height of the forwardmost end of the eversion assembly relative to the ground is at least 550 mm.

15. The liftable chair according to claim 13, wherein: The outward-turning assembly includes a first outward-turning link, a second outward-turning link, a third outward-turning link and an outward-turning drive rod, wherein a four-bar linkage is formed by the footrest mounting plate, the first outward-turning link, the second outward-turning link and the third outward-turning link, and wherein the four-bar linkage can be driven to deform by the outward-turning drive rod, so that the front end of the outward-turning assembly is located in front of the footrest mounting plate.

16. The liftable chair according to claim 15, wherein: The leg assembly also includes a first leg link, a second leg link, a third leg link and a fourth leg link, wherein the front ends of the third leg link and the fourth leg link are respectively hinged to the footrest mounting plate, wherein the front end of the outward-turning drive rod is hinged to the four-bar linkage, and the rear end of the outward-turning drive rod is hinged to the fourth leg link at a first hinge point.

17. The liftable chair according to claim 16, wherein: The first outward-turning link includes a second hinge point arranged on its first free end, a fourth hinge point arranged on its second free end, and a third hinge point located between the second hinge point and the fourth hinge point, wherein the first outward-turning link is hinged to the outward-turning drive rod at the second hinge point and is hinged to the third outward-turning link at the fourth hinge point.

18. The liftable chair according to claim 17, wherein: During the unfolding of the leg assembly, as the included angle between the fourth leg link and the footrest mounting plate increases, the outward rotation driving rod causes the second free end portion of the first outward rotation link to pivot upward around the third hinge point.

19. The liftable chair according to claim 17, wherein: The first outward-turning connecting rod is configured as a bell crank, wherein a line connecting the second hinge point and the fourth hinge point is located in front of the third hinge point.

20. The liftable chair according to claim 17, wherein: Two ends of the second outward-turning connecting rod are hinged to the front end of the pedal mounting plate and the third outward-turning connecting rod respectively.

21. The liftable chair according to claim 13, wherein: In the lying position, the front side of the backrest frame is at most 22° to the horizontal.

22. The liftable chair according to claim 21, wherein: In the lying position, the front side of the backrest frame is at most 13° to the horizontal.

23. The liftable chair according to claim 13, wherein: In the sitting position, the footrest is tucked under the seat portion.

24. The liftable chair according to claim 23, wherein: In the raised position, the seat mounting plate is raised relative to the base and tilted forward, and the seat portion is folded under the seat portion, wherein the lifting assembly enables the mechanical extension device to be sequentially transformed from a lying position, a sitting position to a raised position, and the mechanical extension device to be reversely transformed from a raised position, a sitting position to a lying position.

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