WO2024183407A1

WO2024183407A1 - Liftable seat tilting mechanism

Info

Publication number: WO2024183407A1
Application number: PCT/CN2023/140119
Authority: WO
Inventors: 任秉文; 孙祝兵; 曹生炜
Original assignee: 浙江联宜电机有限公司
Priority date: 2023-03-06
Filing date: 2023-12-20
Publication date: 2024-09-12
Also published as: CN116831404A

Abstract

A liftable seat tilting mechanism, comprising an upper support. A cushion frame connected to a seat is arranged above the upper support, the cushion frame comprises a cushion plate located above the upper support and cushion side plates that are arranged on two sides of the cushion plate and are movably connected to two sides of the upper support, and the cushion side plates are slidably connected to the two sides of the upper support. A middle inner side of each cushion side plate is provided with a support arm that is rotatable and rotatably connected to a side end part of the upper support. A first electrical push rod used for driving two sides of a cushion side plate to slide horizontally is disposed on the upper support. A lower support is arranged below the upper support, and the upper support can move up and down relative to the lower support. Multiple instances of trial sitting are not needed, a user can conveniently adjust the angle of inclination and lifting height of a seat at any time, the steps required for adjusting the seat are reduced, and operation is simpler and more convenient.

Description

Liftable seat reclining mechanism

Technical Field

The invention belongs to a reclining mechanism, and in particular relates to a liftable seat reclining mechanism.

Background Art

Type your background paragraph here.

Technical issues

A seat is a kind of seating furniture with a backrest and sometimes also with armrests. Currently commonly used seats can only adjust the reclining angle of the backrest, but cannot adjust the reclining angle of the entire seat, resulting in poor adjustment freedom and poor comfort.

A seat reclining adjustment mechanism is disclosed in a Chinese patent application with publication number CN207257436U, including a seat body, characterized in that an upper support frame is connected to the bottom surface of the seat body, a lower support frame is arranged below the upper support frame, a front lifting mechanism close to the front side of the seat body and a rear lifting mechanism close to the rear side of the seat body are arranged between the upper support frame and the lower support frame, and the front lifting mechanism and the rear lifting mechanism are hinged to the upper support frame and the lower support frame.

When this mechanism is actually used, it is necessary to manually operate the mechanical structure to adjust the seat reclining angle. Different reclining angles are locked by moving the locking plate. There are many operating steps. It is necessary to try sitting several times before adjusting to a reclining angle that is comfortable for oneself. The reclining angle is pre-limited, which has limitations. It is inconvenient for some users with limited mobility to operate. At the same time, the seat cannot be adjusted in height according to the height and body shape of the user, and the scope of use is small.

Technical Solutions

The above-mentioned technical purpose of the present invention is mainly solved by the following technical solutions: a liftable seat reclining mechanism, comprising an upper bracket, a seat cushion frame connected to the seat is provided above the upper bracket, the seat cushion frame comprises a seat cushion plate located above the upper bracket and seat cushion side plates arranged on both sides of the seat cushion plate and movably connected to both sides of the upper bracket, the seat cushion side plates are slidably connected to both sides of the upper bracket, the middle inner side of the seat cushion side plates is provided with a support arm which is rotatable and rotatably connected to the side end portions of the upper bracket, the upper bracket is provided with a first electric push rod for driving both sides of the seat cushion side plates to slide horizontally, a lower bracket is provided below the upper bracket, and the upper bracket can move up and down relative to the lower bracket; the seat cushion plate is driven by the first electric push rod and supported by the support arm on the upper limb frame to achieve tilting movement, thereby realizing automatic tilting movement of the seat, without the need for users to try sitting and adjusting multiple times, the user operation is simpler, and a larger seat reclining angle can be achieved, and at the same time, the seat can achieve lifting movement by the upper bracket relative to the lower bracket Up and down movement, so that the lifting and lowering adjustment can be performed while the seat is reclining, effectively increasing the scope of application and convenient operation.

Preferably, slide grooves are provided on both sides of the upper bracket, convex plates are provided on both side ends of the seat cushion side panels, and pulleys that can move along the slide grooves are provided on the inner sides of the convex plates; with the arrangement of the above-mentioned slide grooves and pulleys, one side of the seat cushion panel can slide along the slide groove in the slide groove through the pulley on the inner side of the convex plate, thereby realizing the adjustment of the inclination angle of the seat cushion panel, and the seat cushion panel can be kept in a horizontal state by the movement of the pulley, thereby reducing the thickness between the seat cushion panel and the upper bracket when the seat cushion panel is in a horizontal state.

Preferably, the fixed end of the first electric push rod is rotatably connected to the upper bracket, and the output end of the first electric push rod is rotatably connected to a side of the seat cushion plate close to the pulley; both ends of the above-mentioned first electric push rod can be rotated, so that the first electric push rod can push the pulley of the seat cushion plate to slide along the slide groove, and adapt to the tilting movement of the seat cushion plate through the rotation of the two ends of the first electric push rod, thereby ensuring the stability of the structure.

Preferably, a first scissors-fork structure and a second scissors-fork structure which are symmetrically arranged with each other are provided between the upper bracket and the lower bracket, and the first scissors-fork structure and the second scissors-fork structure are respectively provided at the two side edges of the upper bracket and the lower bracket, and the lower bracket is provided with a second electric push rod for driving the first scissors-fork structure and the second scissors-fork structure to move; the arrangement of the above-mentioned first scissors-fork structure and the second scissors-fork structure can support the upper bracket, and through the cooperation of the first scissors-fork structure and the second scissors-fork structure and the driving of the second electric push rod, the seat cushion plate and the upper bracket can be moved up and down, thereby achieving the effect of lifting and lowering.

Preferably, the first scissor structure includes a first scissor arm whose upper end is rotatably connected to the left rear side of the upper bracket and whose lower end is slidably connected to the left side of the lower bracket, and a second scissor arm whose upper end is slidably connected to the left side of the upper bracket and whose lower end is rotatably connected to the left rear side of the lower bracket, the first scissor arm is hinged at the midpoint of the first scissor arm and the midpoint of the second scissor arm, the second scissor structure includes a third scissor arm whose upper end is rotatably connected to the right rear side of the upper bracket and whose lower end is slidably connected to the right side of the lower bracket, and a third scissor arm whose upper end is slidably connected to the right side of the upper bracket and whose lower end is rotatably connected to the right rear side of the lower bracket The fourth scissor arm is connected, and the midpoint of the third scissor arm and the midpoint of the fourth scissor arm are hinged; the first scissor arm and the second scissor arm can rotate around the midpoint, the third scissor arm and the fourth scissor arm can rotate around the midpoint, the second electric push rod can drive the second scissor arm and the fourth scissor arm to flip, and the first scissor arm and the third scissor arm rotate around the hinge point synchronously, thereby realizing automatic lifting of the seat, making the lifting and adjustment of the seat simpler, and the height can be adjusted while sitting on the seat, without multiple trial sitting and adjustment, making the lifting and adjustment more convenient.

Preferably, a fixed plate is provided on the top surface of the upper bracket, and a rotatable first slider and a second slider are respectively provided on the inner sides of the upper ends of the second scissors arm and the fourth scissors arm, a first slide rail is provided on the bottom surface of the fixed plate near the left side of the upper bracket, and a second slide rail is provided on the bottom surface of the fixed plate near the right side of the upper bracket, and the first slider and the second slider can slide on the first slide rail and the second slide rail respectively; the above-mentioned first slider can slide on the first slide rail, and the second slider can slide on the second slide rail, thereby realizing the movement of the lower end of the second scissors arm and the lower end of the fourth scissors arm, and playing a guiding role, so that the movement of the lower end of the second scissors arm and the lower end of the fourth scissors arm is more stable and smooth.

Preferably, a bottom plate is provided on the bottom surface of the lower bracket, and a third slider and a fourth slider are respectively provided on the inner sides of the lower ends of the first scissors arm and the third scissors arm, a third slide rail is provided on the top surface of the bottom plate near the left side of the lower bracket, and a fourth slide rail is provided on the top surface of the bottom plate near the right side of the lower bracket, and the third slider and the fourth slider can slide on the third slide rail and the fourth slide rail respectively; the third slider can slide on the third slide rail, and the fourth slider can slide on the fourth slide rail, thereby realizing the movement of the lower ends of the first scissors arm and the third scissors arm, and playing a guiding role, making the movement of the lower ends of the first scissors arm and the third scissors arm more stable and smooth, and at the same time cooperating with the third slider and the fourth slider, the first scissors arm, the second scissors arm, the third scissors arm and the fourth scissors arm can move synchronously, thereby ensuring the stable lifting and lowering movement of the upper bracket.

Preferably, a rotating shaft is provided in the width direction of the lower bracket, and the rotating shaft can drive the second scissors arm and the fourth scissors arm to flip synchronously. The fixed end of the second electric push rod can rotate up and down on the lower bracket, and the output end of the second electric push rod can control the rotation of the rotating shaft; the above-mentioned rotating shaft can drive the second scissors arm and the fourth scissors arm to flip synchronously through the drive of the second electric push rod, thereby driving the first scissors arm and the third scissors arm to move synchronously to realize lifting movement.

Preferably, the driving direction of the second electric push rod is perpendicular to the axial direction of the rotating shaft, and the first connecting rod and the second connecting rod connected to the rotating shaft are respectively provided on both sides of the output end of the second electric push rod, the lower ends of the first connecting rod and the second connecting rod are rigidly connected to the rotating shaft, and a pin shaft passing through the output end of the second electric push rod is provided between the upper ends of the first connecting rod and the second connecting rod; the output section of the above-mentioned second electric push rod can push the first connecting rod and the second connecting rod through the pin shaft, and drive the rotating shaft to rotate through the transmission of the first connecting rod and the second connecting rod, thereby converting the linear motion into rotational motion, so that the second electric push rod can control the lifting and lowering motion of the upper bracket through the rotating shaft, and at the same time, the setting of the first connecting rod and the second connecting rod can limit the travelable range of the second electric push rod, thereby controlling the rotatable angle of the rotating shaft, so that the driving range of the second electric push rod is within the normal controllable range.

Preferably, a first connecting arm and a second connecting arm are respectively provided on the side walls at both ends of the rotating shaft, one end of the first connecting arm is rigidly connected to the rotating shaft, the other end of the first connecting arm is provided with a third connecting arm that can rotate up and down, the end of the third connecting arm is rotationally connected to the lower half of the second scissors arm, one end of the second connecting arm is rigidly connected to the rotating shaft, the other end of the second connecting arm is provided with a fourth connecting arm that can rotate up and down, the end of the fourth connecting arm is rotationally connected to the fourth scissors arm; the above-mentioned first connecting arm and the third connecting arm are connected to the rotating shaft and the second scissors arm for transmission, and the second connecting arm and the fourth connecting arm are connected to the rotating shaft and the fourth scissors arm for transmission, so that the second electric push rod can transmit the flipping of the second scissors arm through the first connecting arm and the third connecting arm, and transmit the flipping of the fourth scissors arm through the second connecting arm and the fourth connecting arm. The above-mentioned structure increases the torque and shortens the travel required for the output rod of the second electric push rod to travel, so that the second electric push rod can drive the second scissors arm to perform sufficient movement in a smaller space, saving space and ensuring sufficient torque drive.

Beneficial Effects

Therefore, the present invention has the characteristics of not requiring multiple trial sittings, facilitating users to adjust the seat reclining angle and lifting height at any time, reducing the steps required for adjusting the seat, and making the operation easier.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a three-dimensional structural diagram of the present invention;

FIG2 is a schematic diagram of the structure of FIG1 from another perspective;

FIG. 3 is a diagram showing the structure of FIG. 1 when it is fully folded.

Best Mode for Carrying Out the Invention

The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

As shown in Fig. 1-3, a liftable seat reclining mechanism comprises an upper bracket 1, a cushion frame 2 connected to the seat is arranged above the upper bracket 1, the cushion frame 2 comprises a cushion plate 21 located above the upper bracket 1 and cushion side plates 22 arranged on both sides of the cushion plate 21 and movably connected to both sides of the upper bracket 1, the cushion side plates 22 are slidably connected to both sides of the upper bracket 1, a support arm 23 is rotatably arranged on the inner side of the middle part of the cushion side plate 22 and rotatably connected to the side end of the upper bracket 1, and a support arm 23 for driving the cushion is arranged on the upper bracket 1. A first electric push rod 11 slides horizontally on both sides of the side plate 22, a lower bracket 3 is provided below the upper bracket 1, the upper bracket 1 can move up and down relative to the lower bracket 3, and slide grooves 12 are provided on both sides of the upper bracket 1. Both side ends of the cushion side plate 22 are provided with convex plates 221, and the inner side of the convex plate 221 is provided with a pulley 222 that can move along the slide groove 12. The fixed end of the first electric push rod 11 is rotatably connected to the upper bracket 1, and the output end of the first electric push rod 11 is rotatably connected to a side of the cushion plate 21 close to the pulley 222.

When the first electric push rod is started, the first electric push rod will push or pull the bottom edge of the seat cushion plate, so that the convex plates at the two side ends of the seat cushion plate slide in the slide groove through the pulleys, and the middle part of the seat cushion plate is supported by the support arms. As the two side ends of the seat cushion plate move, the inclination angle thereof changes, and the seat cushion plate can be completely horizontally located on the upper bracket, and the two sides of the seat cushion plate can be surrounded by the two sides of the upper bracket, that is, the seat cushion plate is buckled on the upper bracket, and the upper bracket can be close to and abutted against the lower bracket to achieve overall folding, thereby minimizing the space occupied by the seat, facilitating transportation and storage, and can be automatically extended by the drive of the first and second electric push rods, for user convenience.

As shown in Figure 1, a first scissors structure and a second scissors structure are symmetrically arranged between the upper bracket 1 and the lower bracket 3. The first scissors structure and the second scissors structure are respectively arranged at the two side edges of the upper bracket 1 and the lower bracket 3. A second electric push rod 31 is provided on the lower bracket 3 for driving the first scissors structure and the second scissors structure to move. The first scissors structure includes a first scissors arm 32 whose upper end is rotatably connected to the left rear side of the upper bracket 1 and whose lower end is slidably connected to the left side of the lower bracket 3, and a second scissors arm 33 whose upper end is slidably connected to the left side of the upper bracket 1 and whose lower end is rotatably connected to the left rear side of the lower bracket 3. The first scissors arm 32 is hinged at the midpoint of the first scissors arm 32 and at the midpoint of the second scissors arm 33. The second scissors structure includes a third scissors arm 34 whose upper end is rotatably connected to the right rear side of the upper bracket 1 and whose lower end is slidably connected to the right side of the lower bracket 3, and a fourth scissors arm 35 whose upper end is slidably connected to the right side of the upper bracket 1 and whose lower end is rotatably connected to the right rear side of the lower bracket 3. The midpoint of the third scissors arm 34 and the midpoint of the fourth scissors arm 35 are hinged at the midpoint of the third scissors arm 34 and the midpoint of the fourth scissors arm 35.

The cushion plate on the top of the above-mentioned upper bracket fixes the seat seat of the chair, and the first scissors structure and the second scissors structure are respectively located at the two side edges of the upper bracket and the lower bracket, and the second electric push rod is arranged between the first scissors structure and the second scissors structure. The second electric push rod first drives the second scissors arm and the fourth scissors arm to flip, and the second scissors arm and the fourth scissors arm drive the first scissors arm and the third scissors arm to tilt synchronously through the hinge structure, thereby realizing the lifting movement of the upper bracket. The lifting adjustment of the seat can be controlled by controlling the start and stop of the second electric push rod.

As shown in Figures 1-2, a fixed plate 13 is provided on the top surface of the upper bracket 1, and a rotatable first slider 331 and a second slider 351 are respectively provided on the inner sides of the upper ends of the second scissor arm 33 and the inner sides of the upper ends of the fourth scissor arm 35. A first slide rail 131 is provided on the bottom surface of the fixed plate 13 near the left side of the upper bracket 1, and a second slide rail 132 is provided on the bottom surface of the fixed plate 13 near the right side of the upper bracket 1. The first slider 331 and the second slider 351 can be respectively on the first slide rail 131 and the second slide rail 132, a bottom plate 36 is provided on the bottom surface of the lower bracket 3, a third slider 321 and a fourth slider 341 are respectively provided on the inner sides of the lower ends of the first scissor arm 32 and the inner sides of the lower ends of the third scissor arm 34, a third slide rail 141 is provided on the top surface of the bottom plate 14 near the left side of the lower bracket 3, and a fourth slide rail 142 is provided on the top surface of the bottom plate 14 near the right side of the lower bracket 3, and the third slider 321 and the fourth slider 341 can slide on the third slide rail 141 and the fourth slide rail 142 respectively.

When the second electric push rod drives the first scissors structure and the second scissors structure to move, the second scissors arm and the fourth scissors arm are pushed and rotate around the lower ends of the second scissors arm and the fourth scissors arm as the axis, and the first scissors arm and the third scissors arm are controlled by the hinge point and rotate around the upper ends of the first scissors arm and the third scissors arm as the axis. At this time, the first slider and the second slider move synchronously on the first slide rail and the second slide rail, and the third guide wheel and the fourth slider move synchronously on the third slide rail and the fourth slide rail, thereby bringing about a change in the height of the upper bracket.

As shown in FIG1 , a rotating shaft 37 is provided in the width direction of the lower bracket 3, and the rotating shaft 37 can drive the second scissor arm 33 and the fourth scissor arm 35 to flip synchronously. The fixed end of the second electric push rod 31 can rotate up and down on the lower bracket 3, and the output end of the second electric push rod 31 can control the rotation of the rotating shaft 37. The driving direction of the second electric push rod 31 is perpendicular to the axial direction of the rotating shaft 37. The first connecting rod 371 and the second connecting rod 372 connected to the rotating shaft 37 are respectively provided on both sides of the output end of the second electric push rod 31. The lower ends of the first connecting rod 371 and the second connecting rod 372 are rigidly connected to the rotating shaft 37. The first connecting rod 371 and the second connecting rod 372 are A pin shaft 373 passing through the output end of the second electric push rod 31 is provided between the upper ends, and a first connecting arm 374 and a second connecting arm 375 are respectively provided on the side walls at both ends of the rotating shaft 37. One end of the first connecting arm 374 is rigidly connected to the rotating shaft 37, and the other end of the first connecting arm 374 is provided with a third connecting arm 376 that can rotate up and down. The end of the third connecting arm 376 is rotationally connected to the lower half of the second scissors arm 33, one end of the second connecting arm 375 is rigidly connected to the rotating shaft 37, and the other end of the second connecting arm 375 is provided with a fourth connecting arm 377 that can rotate up and down, and the end of the fourth connecting arm 377 is rotationally connected to the fourth scissors arm 35.

When the second electric push rod is started, the output rod of the second electric push rod pushes the pin shaft, and the pin shaft drives the first connecting rod and the second connecting rod to flip around the rotating shaft, and the fixed end of the electric push rod rotates slightly with the rotation of the rotating shaft, and the rotation of the rotating shaft drives the first connecting arm and the second connecting arm to flip, and the first connecting arm and the second connecting arm drive the second scissors arm and the fourth scissors arm to flip through the third connecting arm and the fourth connecting arm respectively, thereby realizing the lifting and lowering control of the upper bracket, thereby realizing the lifting and lowering adjustment of the cushion frame and the seat.

Claims

A liftable seat reclining mechanism, characterized in that it comprises an upper bracket (1), a seat cushion frame (2) connected to the seat is provided above the upper bracket (1), the seat cushion frame (2) comprises a seat cushion plate (21) located above the upper bracket (1) and seat cushion side plates (22) provided on both sides of the seat cushion plate (21) and movably connected to both sides of the upper bracket (1), the seat cushion side plates (22) being slidably connected to both sides of the upper bracket (1), a support arm (23) rotatably provided on the inner side of the middle part of the seat cushion side plates (22) and rotatably connected to the side ends of the upper bracket (1), a first electric push rod (11) for driving both sides of the seat cushion side plates (22) to slide horizontally is provided on the upper bracket (1), a lower bracket (3) is provided below the upper bracket (1), and the upper bracket (1) can move up and down relative to the lower bracket (3).
The liftable seat reclining mechanism according to claim 1 is characterized in that: both sides of the upper bracket (1) are provided with slide grooves (12), both side ends of the seat cushion side panels (22) are provided with convex plates (221), and the inner side of the convex plates (221) is provided with pulleys (222) that can move along the slide grooves (12).
The liftable seat reclining mechanism according to claim 2 is characterized in that: the fixed end of the first electric push rod (11) is rotatably connected to the upper bracket (1), and the output end of the first electric push rod (11) is rotatably connected to a side of the seat cushion plate (21) close to the pulley (222).
The liftable seat reclining mechanism according to claim 1 is characterized in that: a first scissors-type structure and a second scissors-type structure are symmetrically arranged between the upper bracket (1) and the lower bracket (3), the first scissors-type structure and the second scissors-type structure are respectively arranged at the two side edges of the upper bracket (1) and the lower bracket (3), and a second electric push rod (31) is provided on the lower bracket (3) for driving the first scissors-type structure and the second scissors-type structure to move.
The liftable seat reclining mechanism according to claim 4 is characterized in that: the first scissors structure includes a first scissors arm (32) whose upper end is rotatably connected to the left rear side of the upper bracket (1) and whose lower end is slidably connected to the left side of the lower bracket (3); and a second scissors arm (33) whose upper end is slidably connected to the left side of the upper bracket (1) and whose lower end is rotatably connected to the left rear side of the lower bracket (3); the first scissors arm (32) is hinged at the midpoint and the second scissors arm (33) at the midpoint; the second scissors structure includes a third scissors arm (34) whose upper end is rotatably connected to the right rear side of the upper bracket (1) and whose lower end is slidably connected to the right side of the lower bracket (3); and a fourth scissors arm (35) whose upper end is slidably connected to the right side of the upper bracket (1) and whose lower end is rotatably connected to the right rear side of the lower bracket (3); the third scissors arm (34) is hinged at the midpoint and the fourth scissors arm (35) at the midpoint.
The liftable seat reclining mechanism according to claim 5 is characterized in that: a fixing plate (13) is provided on the top surface of the upper bracket (1), a rotatable first slider (331) and a second slider (351) are respectively provided on the inner sides of the upper ends of the second scissor arm (33) and the fourth scissor arm (35), a first slide rail (131) is provided on the bottom surface of the fixing plate (13) near the left side of the upper bracket (1), and a second slide rail (132) is provided on the bottom surface of the fixing plate (13) near the right side of the upper bracket (1), and the first slider (331) and the second slider (351) can be respectively on the first slide rail (131) and the second slide rail (132).
The liftable seat reclining mechanism according to claim 5 is characterized in that: a bottom plate (36) is provided on the bottom surface of the lower bracket (3), a third slider (321) and a fourth slider (341) are provided on the inner sides of the lower ends of the first scissor arm (32) and the third scissor arm (34), respectively; a third slide rail (141) is provided on the top surface of the bottom plate (14) near the left side of the lower bracket (3); a fourth slide rail (142) is provided on the top surface of the bottom plate (14) near the right side of the lower bracket (3); the third slider (321) and the fourth slider (341) can slide on the third slide rail (141) and the fourth slide rail (142), respectively.
The liftable seat reclining mechanism according to claim 5 is characterized in that: a rotating shaft (37) is provided in the width direction of the lower bracket (3), and the rotating shaft (37) can drive the second scissors arm (33) and the fourth scissors arm (35) to flip synchronously, and the fixed end of the second electric push rod (31) can rotate up and down on the lower bracket (3), and the output end of the second electric push rod (31) can control the rotation of the rotating shaft (37).
The liftable seat reclining mechanism according to claim 8 is characterized in that: the driving direction of the second electric push rod (31) is perpendicular to the axial direction of the rotating shaft (37), and the first connecting rod (371) and the second connecting rod (372) connected to the rotating shaft (37) are respectively provided on both sides of the output end of the second electric push rod (31), the lower ends of the first connecting rod (371) and the second connecting rod (372) are rigidly connected to the rotating shaft (37), and a pin shaft (373) passing through the output end of the second electric push rod (31) is provided between the upper ends of the first connecting rod (371) and the second connecting rod (372).
The liftable seat reclining mechanism according to claim 8 is characterized in that: a first connecting arm (374) and a second connecting arm (375) are respectively provided on the side walls at both ends of the rotating shaft (37), one end of the first connecting arm (374) is rigidly connected to the rotating shaft (37), and the other end of the first connecting arm (374) is provided with a third connecting arm (376) which can rotate up and down, and the end of the third connecting arm (376) is rotationally connected to the lower half of the second scissors arm (33), one end of the second connecting arm (375) is rigidly connected to the rotating shaft (37), and the other end of the second connecting arm (375) is provided with a fourth connecting arm (377) which can rotate up and down, and the end of the fourth connecting arm (377) is rotationally connected to the fourth scissors arm (35).