Welding device for handheld packing machine having handle

Abstract

A welding device for a handheld packing machine having a handle. A motor of the welding device drives, by means of a downward pressing and lifting motion assembly, a movable welding workpiece to move downward; the welding device is provided with a connecting component which can move back and forth synchronously with the lifting / lowering motion of the movable welding workpiece; the connecting component is arranged on a rotating member; a reset driving member is connected to the handle; the handheld packing machine is provided with a sensor; and after the welding is finished, the motor starts to rotate reversely according to a signal of the sensor until transmission teeth on the rotating member and a gear connected to the motor are switched from a disengaged state to an engaged state. According to the present invention, the movable welding workpiece can be reset by operating the handle of the strapping tensioning device, and through signal control, the handheld packing machine operated by the handle can also achieve a smooth switching from a disengaged state to an engaged state, eliminating the need for a separate reset connection mechanism with a one-way bearing and a rotating gear controlled by a program for start-stop time.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a welding device, in particle to a welding device of packing strap for a handheld packing machine having a handle.BACKGROUND OF THE INVENTION

[0002] In handheld electric packing machines, PET or PP strapping is used to strap products or packages. The two parts of the strap to be bonded are thermally fused and bonded through frictional heating. For a handheld packing machine with a handle, the strapping tensioning device is switched between the strap loading / unloading working state and the strap tensioning working state by lifting and lowering the handle. When the handle is lifted, the movable welding workpiece is lifted together. For a welding device adopting a single-motor drive form, that is, the vibration drive and the downward pressing drive of the movable welding workpiece are driven by the same motor, a connection transition from disengagement to engagement is required between the downward pressing and lifting motion assembly and the motor-driven gear when the movable welding work piece resets and lifts. Conventionally, a handheld packing machine having a handle whose welding devices adopt single-motor drive have solved this problem by using elastic teeth or shifting teeth, but the effect is unsatisfactory, and an uncomfortable jerking sensation easily occurs during the connection transition.SUMMARY OF THE INVENTION

[0003] An object of the present invention is to provide a welding device for a handheld packing machine having a handle, which enables the movable welding workpiece in the welding device to rise and reset by driving with the handle when the movable welding workpiece resets, and ensures smoother handle operation and a simpler structure. To achieve this object, the present invention adopts the following technical solutions: A welding device for a handheld packing machine having a handle, the handheld packing machine being provided with a handle for a tensioning mechanism, the welding device comprising a movable welding workpiece, a motor, and a downward pressing and lifting motion assembly for the movable welding workpiece, the downward pressing and lifting motion assembly being provided with a rotating member; the rotating member matching with a gear connected to the motor through transmission teeth; wherein the motor drives, by means of the downward pressing and lifting motion assembly, the movable welding workpiece to move downward, the welding device is provided with a connecting component which can move back and forth synchronously with the lifting / lowering motion of the movable welding workpiece, the welding device is provided with a reset driving member, the reset driving member is connected to the handle, the connecting component is located at a position corresponding to the driving member, and when the movable welding workpiece is in the welding working position, the connecting component is located on the motion path of the reset driving member when the handle is lifted, and when the handle is lifted, the connecting component can be driven by the reset driving member to move in a first direction, thereby driving the movable welding workpiece through the downward pressing and lifting motion assembly to the initial position; the handheld packing machine is provided with a sensor, after the welding is finished, the motor starts to rotate reversely according to a signal of the sensor until transmission teeth on the rotating member and a gear connected to the motor are switched from a disengaged state to an engaged state.

[0004] On the basis of adopting the above technical solution, the present invention may further adopt the following further technical solutions, or use these further technical solutions in combination: The downward pressing and lifting motion assembly is provided with a lifting assembly and a connecting rod mechanism, a lower end of the connecting rod mechanism is rotatably connected to the rotating member at a position deviating from the rotation center of the rotating member, and an upper end of the connecting rod mechanism is movably connected to the lifting assembly, the movable welding workpiece is mounted on a lower end of the lifting assembly.

[0005] The rotating member is provided with a position-limiting fitting for limiting the rotational stroke of the rotating member in a second direction, the second direction is opposite to the first direction and is the direction of rotation for lowering the movable welding workpiece; the position-limiting fitting is matched with a fixed position-limiting structure to limit the maximum rotation angle of the rotating member in the second direction.

[0006] The handle is connected to the reset driving member through a rotating connection structure, and the rotation axis of the reset driving member is perpendicular to a rotation axis of the handle and parallel to a rotation axis of the rotating member.

[0007] The rotating connection structure comprises a first rocker and a second rocker, the reset driving member and the second rocker are fixed together, the first rocker is rotationally connected to the handle and located below the handle, a first end of the second rocker is rotationally connected to the first rocker through a liftable first shaft, the first shaft is perpendicular to the rotation axis of the handle, a second end of the second rocker is rotationally connected to a base through a second shaft.

[0008] The welding device is further provided with a second sensor, the position of the second sensor corresponds to the position where the position-limiting fitting piece just leaves the position-limiting structure when moving from the position matching with the position-limiting structure in the first direction, and the second sensor forms a control combination for the motor together with the first sensor that senses the operation of the handle.

[0009] The connecting component is connected to the rotating member.

[0010] The power of a vibration assembly of the welding device is derived from the motor through the connection of a transmission mechanism, and the welding device is not provided with a separate driving motor for the vibration assembly; the second sensor senses the motion that the corresponding position-limiting fitting piece just leaves when moving from the position matching with the position-limiting structure in the first direction.

[0011] Control steps of the packing machine comprise: after a round of packing work is completed and a strap is taken out, the handle is lowered, the tensioning mechanism is in the tensioning working position, the movable welding workpiece is in the initial position, and the reset driving member is in a position away from the connecting component; when a new round of packing work starts, the handle is raised to release the strap, at this time, the handle is raised and the connecting component is just at the end of the movement path of the reset driving member; after the strap is put in, the handle is lowered, the tensioning mechanism enters the tensioning working position, the tensioning mechanism motor is started to tighten the strap, and at this time, the reset driving member is away from the connecting component again; after the strap is tightened, the motor of the welding device is started to drive the rotating member to rotate in the second direction, the movable welding workpiece descends to a welding working position, the transmission teeth on the rotating member and the gear connected to the motor are switched from an engaged state to a disengaged state, the connecting component moves with the rotating member to just in front of the reset driving member, and when the handle is raised again, the rotating member will be driven by the reset driving member to move in the first direction, and the motor of the welding device continues to operate for welding; after the welding work is completed, the handle is raised, and the motor rotates reversely according to a signal of the sensor and stops until transmission teeth on the rotating member and a gear connected to the motor are in an engaged state, the rotating member is driven by the driving member to rotate, and the lifting assembly is linked to rise, and the movable welding workpiece rises to the initial position; meanwhile the tensioning mechanism is lifted, and the packing strap is removed; after releasing the handle, the handle rotates and falls, and drives the reset driving member to rotate away from the connecting component, and automatically enter the next strapping cycle.

[0012] The control combination uses the second sensor to obtain a second signal that the position-limiting fitting piece leaves the position-limiting structure, which represents that the rotating member has normally started reset rotation, and the control combination uses the first sensor to obtain a signal that the handle starts to be lifted, so as to obtain a first signal that the strap needs to be taken out after the welding is completed; when the first signal is obtained, the motor is caused to rotate reversely by a small angle, and when the second signal is obtained, the motor is caused to stop rotating.

[0013] Due to the adoption of the technical solutions of the present invention, the movable welding workpiece can be reset by operating the handle of the strapping tensioning device, and through signal control, the handheld packing machine operated by the handle can also achieve a smooth switching from a disengaged state to an engaged state, eliminating the need for a separate reset connection mechanism with a one-way bearing and a rotating gear controlled by a program for start-stop time.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIGS. 1a and 1b illustrate the switching from engagement to disengagement in different working states of the present invention. S1 shows the initial state of the entire machine, where the handle 100 is put down, the tensioning mechanism is in the tensioning working position, the movable welding workpiece 21 is at the initial position, and reset driving member 6 is located away from connecting component 5; S2 shows the state when the handle is lifted to release the strap, where the handle 100 is lifted, but connecting component 5 is just at the end of the movement path of the reset driving member 6, and the welding device is not affected nor interferes with the lifting of the tensioning mechanism; S3 shows the component positions in the tensioning working state, where the handle is put down, and tensioning mechanism motor 300 is started for strap tensioning, at which time the reset driving member 6 is again away from connecting component 5; S4 shows the component positions in the welding working state, after tensioning is completed, the welding motor 1 is started to drive the rotating member 71 to rotate in the second direction, the movable welding workpiece 21 descends to the welding working position, the transmission teeth 711 and the gear 11 are just disengaged, the connecting component 5 moves with the rotating member 71 just in front of the reset driving member 6 (when the handle 100 is lifted again, it will be driven by the reset driving member 6 to move in the first direction), and the welding motor 1 continues to operate for welding; S5 shows the strap removal and welding device reset state after the welding work is completed, the handle 100 is lifted, the rotating member is driven by the driving member to rotate, so that the connecting rod mechanism moves in a linked manner, the lifting assembly rises, and the movable welding workpiece 21 rises to the initial position; at the same time, the tensioning mechanism is lifted to take the packing strap; S6 shows that after S5, the handle is released, the handle rotates and falls, driving the driving member to turn away from the connecting component, thus automatically entering the next packing cycle. FIG. 2 is an exploded structural schematic diagram of an embodiment of the present invention. FIGS. 3 and 4 are structural schematic diagrams of an embodiment of the present invention observed from different angles, respectively. FIGS. 5 and 6 are structural cross-sectional views of an embodiment of the present invention when the welding working mechanism is in the welding working state and returns to the initial position, respectively. DETIALED DESCRIPTION

[0015] Referring to the accompanying drawings, the present invention provides a welding device for a handheld packing machine having a handle, wherein the handheld packing machine is provided with a handle 100 of a tensioning mechanism, and handle 100 is rotatably mounted on base 200 of the handheld packing machine. Since the tensioning mechanism is not the object of concern of the present invention, the tensioning mechanism is omitted in the drawings. The tensioning mechanism is connected to the handle 100. During operation, the tensioning mechanism is lifted by lifting the handle 100, allowing strap loading and unloading. After loading or unloading is completed, the handle 100 is released, and the tensioning mechanism and the handle 100 rotate downward by gravity, with the tensioning mechanism rotating to the tensioning working position.

[0016] The welding device includes movable welding workpiece 21, a motor 1, and a downward pressing and lifting motion assembly for the movable welding workpiece 21. The movable welding workpiece 21 is mounted at the lower end of the lifting assembly 3 in the downward pressing and lifting motion assembly.

[0017] The welding device is provided with a lower fixed welding plate 22 below movable welding workpiece 21. When the movable welding workpiece 21 descends to engage the lower fixed welding plate 22 to press the packing strap joint, the vibration assembly 4 of the welding device acts on the lifting assembly 3 to generate vibration, which is then transmitted to the movable welding workpiece 21, causing vibration of the movable welding workpiece 21 to rub the packing strap for thermal fusion bonding. The structures of the downward pressing and lifting motion assembly, the vibration assembly 4, the movable welding workpiece 21, and the lower fixed welding plate 22 can all adopt existing technologies.

[0018] The downward pressing and lifting motion assembly is provided with a rotating member 71, which is provided with transmission teeth 711. The transmission teeth 711 are engaged with a gear 11 of the motor 1, transitioning from an engaged state to a disengaged state when the movable welding workpiece 21 is pressed downward, and from a disengaged state to an engaged state when the movable welding workpiece 21 is reset. The motor 1 drives, by means of a downward pressing and lifting motion assembly, a lifting assembly 3 to move downward, while the upward movement of the lifting assembly 3 is driven by lifting the handle 100, which is the same action as lifting the tensioning mechanism, not only making operation very convenient but also forming an interlocking effect to ensure no mispacking occurs.

[0019] The welding device is provided with a connecting component 5 that can move back and forth synchronously with the lifting / lowering motion of the movable welding workpiece 21. The connecting component 5 is arranged on a rotating member 71. The welding device is provided with a reset driving member 6, and the reset driving member 6 is connected to the handle 100. The position of connecting component 5 corresponds to that of the driving member 6. When the movable welding workpiece 21 is in the welding working position, the connecting component 5 is located in the motion path of the reset driving member 6 when the handle 100 is lifted. When the handle is lifted, the connecting component 5 can be driven by the reset driving member 6 to move in the first direction. In this embodiment, the rotating member 71 rotates clockwise at this time, and the movable welding workpiece 21 is driven by the downward pressing and lifting motion assembly to return to the initial position (see FIG. 6).

[0020] The downward pressing and lifting motion assembly is further provided with a connecting rod mechanism, a lower end of the connecting rod mechanism is rotatably connected to the rotating member 71 at a position deviating from the rotation center of rotating member 71, and an upper end of the connecting rod mechanism is movably connected to the upper end of the lifting assembly 3.

[0021] A connecting rod mechanism of the downward pressing and lifting motion assembly includes a first connecting rod 31 and a second connecting rod. The first connecting rod is rotatably connected to the top of a base 200 via an axle pin 33. A first end of the first connecting rod 31 is rotatably connected to a top end of the lifting assembly 3, a second end of the first connecting rod 31 is rotatably connected to an upper end of the second connecting rod, and a lower end of the second connecting rod is rotatably connected to a rotating member 71 at a position deviating from the rotation center of the rotating member 71 via a rotating connecting shaft 74. The second connecting rod is preferably an elastic rod. The second connecting rod includes an upper connecting rod 321 and a lower connecting rod 322. The lower connecting rod 322 is connected to a core rod 323, enabling sliding connection between the upper connecting rod 321 and the lower connecting rod 322 via the core rod 323. A compression spring 324 is arranged between the upper connecting rod 321 and the lower connecting rod 322, with the compression spring 324 sleeved on the core rod 323. The upper connecting rod 321 is rotatably connected to the first connecting rod 31, and the lower connecting rod 322 is rotatably connected to the rotating member 71. In this embodiment, the lifting assembly 3 employs a lifting column, the lower portion of which is provided with a hole for placing the vibration assembly 4 and receiving the vibration of vibration assembly 4; the upper portion is provided with a compression spring to press the vibration assembly downward, cushioning to eliminate part clearances, and the outer side is provided with a guide cylinder for the lifting of the lifting column.

[0022] During implementation, preferably, the rotating connecting shaft 74 of the rotating member 71 and the second connecting rod (lower connecting rod 322) can be lengthened, and the connecting component 5 directly utilizes the end of rotating connecting shaft 74.

[0023] The rotating member 71 is provided with a position-limiting fitting piece 73 for the rotation stroke of the rotating member in a second direction. The second direction is opposite to the first direction and is the direction of rotation for lowering the movable welding workpiece. In this embodiment, for the second direction, the rotating member 71 rotates counterclockwise. The position-limiting fitting piece 73 is matched with a fixed position-limiting structure 201 to limit the rotation stroke in the second direction. Depending on the position, the matching between the position-limiting structure 201 and the position-limiting fitting piece 73 at another position can form a position-limiting matching for rotating member 71 in the first direction. The fixed position-limiting structure 201 can be fixed on the base or be a configuration on the base 200. This position-limiting matching ensures smooth operation, so that during welding, the connecting component 5 stops at a reasonable position, and after welding is completed, the driving member 6 can smoothly drive the connecting component 5 to drive the rotating member 71 to rotate smoothly in the first direction.

[0024] The handle 100 is connected to the reset driving member 6 via a rotating connection structure, such that the rotation axis of reset driving member 6 is perpendicular to the rotation axis of handle 100, parallel to the rotation axis of rotating member 71, located below the handle, and matched with the height of the rotating member 71. When the reset driving member 6 rotates and lifts, it does not interfere with the handle 100 when it rotates and falls, thus improving the overall space utilization of the machine. Meanwhile, the handle 100 and the connecting rod structure are orthogonal, located below the first connecting rod 31, making the structure more compact.

[0025] In this embodiment, the rotating connection structure includes a first rocker 61 and a second rocker 62. The reset driving member 6 and the second rocker 62 are fixed together. The upper end of the first rocker 61 is rotatably connected to the handle 100 via a shaft 63 and is located below the handle. The shaft 63 is parallel to the rotation axis 101 of the handle. The first end of the second rocker is rotatably connected to the lower end of the first rocker via a liftable first shaft 64, and the first shaft 64 is perpendicular to the rotation axis of handle 100. The second end of the second rocker 62 is rotatably connected to the base 200 via a second shaft. In this embodiment, the second shaft and the shaft 712 of the rotating member 71 are coaxial, and the rotating member 71 is rotatably connected to the shaft 712, while the second rocker 62 is movably sleeved on the shaft 712.

[0026] A slot 102 can be formed in the handle to accommodate the upper end of the first rocker 61 and set the shaft 63.

[0027] The welding device is further provided with a second sensor 8. The position of the second sensor 8 corresponds to the position where the position-limiting fitting piece 73 has just left the position-limiting structure 201 after moving in the first direction from the position engaging with the position-limiting structure 201. This second sensor 8 also forms a control combination with the first sensor 103, which senses when the handle 100 is lowered into position (controlling the tensioning mechanism motor 300, which begins operating when the start button is pressed). Specifically, this combination enables the sensor (the second sensor 8) to obtain a second signal indicating that the position-limiting fitting piece 73 has left the position-limiting structure 201, indicating that the rotating member 71 has properly begun its reset rotation. The first sensor 103 also detects the start of the lift of the handle 100, thereby obtaining a first signal indicating that the strap needs to be removed after welding. Thus, when the first signal is received, motor 1 can be rotated slightly in the opposite direction. When the second signal is received, the motor 1 stops rotating, ensuring perfect gear engagement and smooth movement of handle 100 in raising and lowering the welding workpiece 21, while requiring almost no additional power from the motor 1.

[0028] The second sensor 8 can be directly matched with the position-limiting fitting piece 73 to sense its position, and can also be matched with other moving parts associated with the movement of the position-limiting fitting piece 73. The first sensor 103 can be directly matched with the handle 100 to sense its position, and can also be directly matched with other moving parts associated with the movement of the handle 100.

[0029] In this embodiment, the vibration assembly 4 is powered by the motor 1. The power input shaft 41 is drivingly connected to the output shaft of the motor 1 via a strap drive mechanism 40. The driving wheel of the strap drive mechanism 40 is larger than the driven wheel, which increases the vibration frequency of the vibration assembly. The vibration assembly 4 employs an eccentric shaft arrangement.

[0030] Unless otherwise specified, in the description of the present invention, the orientation or position relationship indicated by terms such as "upper", "lower", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", etc. is based on the orientation or positional relationship shown in the figures, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated device or element must have the particular orientation, construction and operation in the particular orientation, therefore, the terms describing the orientation or position relationship in the present invention are only used for illustrative purposes and cannot be understood as limitations on the present invention. A person of ordinary skill in the art can understand the specific meaning of the above terms in combination with the accompanying drawings according to specific circumstances.

[0031] Unless otherwise clearly specified and limited, in the present invention, the terms "provided / arranged", "clamped" and "connected" should be construed in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be internal communication between two elements. A person of ordinary skill in the art can understand the specific meaning of the above terms according to specific circumstances.

[0032] The foregoing description merely describes the specific embodiments of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art in the field of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A welding device for a handheld packing machine having a handle, the handheld packing machine being provided with a handle for a tensioning mechanism, the welding device comprising a movable welding workpiece, a motor, and a downward pressing and lifting motion assembly for the movable welding workpiece, the downward pressing and lifting motion assembly being provided with a rotating member; the rotating member matching with a gear connected to the motor through transmission teeth; wherein the motor drives, by means of the downward pressing and lifting motion assembly, the movable welding workpiece to move downward, the welding device is provided with a connecting component which can move back and forth synchronously with the lifting / lowering motion of the movable welding workpiece, the welding device is provided with a reset driving member, the reset driving member is connected to the handle, the connecting component is located at a position corresponding to the driving member, and when the movable welding workpiece is in the welding working position, the connecting component is located on the motion path of the reset driving member when the handle is lifted, and when the handle is lifted, the connecting component can be driven by the reset driving member to move in a first direction, thereby driving the movable welding workpiece through the downward pressing and lifting motion assembly to the initial position; the handheld packing machine is provided with a sensor, after the welding is finished, the motor starts to rotate reversely according to a signal of the sensor until transmission teeth on the rotating member and a gear connected to the motor are switched from a disengaged state to an engaged state.

2. The welding device for a handheld packing machine with a handle according to claim 1, wherein the downward pressing and lifting motion assembly is provided with a lifting assembly and a connecting rod mechanism, a lower end of the connecting rod mechanism is rotatably connected to the rotating member at a position deviating from the rotation center of the rotating member, and an upper end of the connecting rod mechanism is movably connected to the lifting assembly, the movable welding workpiece is mounted on a lower end of the lifting assembly.

3. The welding device for a handheld packing machine with a handle according to claim 1, wherein the rotating member is provided with a position-limiting fitting for limiting the rotational stroke of the rotating member in a second direction, the second direction is opposite to the first direction and is the direction of rotation for lowering the movable welding workpiece; the position-limiting fitting is matched with a fixed position-limiting structure to limit the maximum rotation angle of the rotating member in the second direction.

4. The welding device for a handheld packing machine with a handle according to claim 1, wherein the handle is connected to the reset driving member through a rotating connection structure, and the rotation axis of the reset driving member is perpendicular to a rotation axis of the handle and parallel to a rotation axis of the rotating member.

5. The welding device for a handheld packing machine with a handle according to claim 4, wherein the rotating connection structure comprises a first rocker and a second rocker, the reset driving member and the second rocker are fixed together, the first rocker is rotationally connected to the handle and located below the handle, a first end of the second rocker is rotationally connected to the first rocker through a liftable first shaft, the first shaft is perpendicular to the rotation axis of the handle, a second end of the second rocker is rotationally connected to a base through a second shaft.

6. The welding device for a handheld packing machine with a handle according to claim 3, wherein the welding device is further provided with a second sensor, the position of the second sensor corresponds to the position where the position-limiting fitting piece just leaves the position-limiting structure when moving from the position matching with the position-limiting structure in the first direction, and the second sensor forms a control combination for the motor together with the first sensor that senses the operation of the handle.

7. The welding device for a handheld packing machine with a handle according to claim 3, wherein the connecting component is connected to the rotating member.

8. The welding device for a handheld packing machine having a handle according to claim 6, wherein the power of a vibration assembly of the welding device is derived from the motor through the connection of a transmission mechanism, and the welding device is not provided with a separate driving motor for the vibration assembly; the second sensor senses the motion that the corresponding position-limiting fitting piece just leaves when moving from the position matching with the position-limiting structure in the first direction.

9. The welding device for a handheld packing machine having a handle according to claim 3, wherein control steps of the packing machine comprise: after a round of packing work is completed and a strap is taken out, the handle is lowered, the tensioning mechanism is in the tensioning working position, the movable welding workpiece is in the initial position, and the reset driving member is in a position away from the connecting component; when a new round of packing work starts, the handle is raised to release the strap, at this time, the handle is raised and the connecting component is just at the end of the movement path of the reset driving member; after the strap is put in, the handle is lowered, the tensioning mechanism enters the tensioning working position, the tensioning mechanism motor is started to tighten the strap, and at this time, the reset driving member is away from the connecting component again; after the strap is tightened, the motor of the welding device is started to drive the rotating member to rotate in the second direction, the movable welding workpiece descends to a welding working position, the transmission teeth on the rotating member and the gear connected to the motor are switched from an engaged state to a disengaged state, the connecting component moves with the rotating member to just in front of the reset driving member, and when the handle is raised again, the rotating member will be driven by the reset driving member to move in the first direction, and the motor of the welding device continues to operate for welding; after the welding work is completed, the handle is raised, and the motor rotates reversely according to a signal of the sensor and stops until transmission teeth on the rotating member and a gear connected to the motor are in an engaged state, the rotating member is driven by the driving member to rotate, and the lifting assembly is linked to rise, and the movable welding workpiece rises to the initial position; meanwhile the tensioning mechanism is lifted, and the packing strap is removed; after releasing the handle, the handle rotates and falls, and drives the reset driving member to rotate away from the connecting component, and automatically enter the next strapping cycle.

10. The welding device for a handheld packing machine having a handle according to claim 9, wherein the welding device is further provided with a second sensor, the position of the second sensor corresponds to the position where the position-limiting fitting piece just leaves the position-limiting structure when moving from the position matching with the position-limiting structure in the first direction, and the second sensor forms a control combination for the motor together with the first sensor that senses the operation of the handle; the control combination uses the second sensor to obtain a second signal that the position-limiting fitting piece leaves the position-limiting structure, which represents that the rotating member has normally started reset rotation, and the control combination uses the first sensor to obtain a signal that the handle starts to be lifted, so as to obtain a first signal that the strap needs to be taken out after the welding is completed; when the first signal is obtained, the motor is caused to rotate reversely by a small angle, and when the second signal is obtained, the motor is caused to stop rotating.

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