A stable one-section two-step ladder

Abstract

The application discloses a stable one-section two-step telescopic ladder and belongs to the technical field of ladders. The one-section two-step telescopic ladder comprises a plurality of pairs of ladder pipes connected in a step-by-step sleeving mode, a plurality of connecting sleeves, a plurality of steps, a locking structure and a hand supporting rod. The outer side of the ladder pipe is provided with a supporting hook hole. The connecting sleeve in sliding connection with the ladder pipe is provided with a supporting hook matched with the supporting hook hole. When the ladder pipe and the connecting sleeve slide, the supporting hook is clamped into the supporting hook hole, the ladder pipe can support the connecting sleeve, the ladder pipe connecting sleeve is smoothly locked, the stable locking of the second-step step is realized, the hand supporting rod is sleeved at the head of the lowermost ladder pipe and is in sliding connection with the ladder pipe, the ladder pipe can be quickly unlocked and contracted when the hand supporting rod is supported, and the efficiency of the one-section two-step telescopic ladder when being folded is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ladders, and more particularly to a stable one-section two-step telescopic ladder. BACKGROUND

[0002] The one-section two-step telescopic ladder known in the art is lighter in weight and simpler in process than the one-section one-step telescopic ladder, and can save production cost, and has good verticality after being extended. To realize stable operation of the one-section two-step telescopic ladder, gradual extension is a basic requirement. However, the second step of the one-section two-step telescopic ladder sometimes cannot be extended in time, resulting in that the second step is extended simultaneously with the lower step, and a fault of missing a step is caused. Meanwhile, the closed height of the one-section two-step telescopic ladder is slightly higher than that of the one-section one-step telescopic ladder, which causes inconvenience in carrying. Moreover, when the ladder is fully unfolded, two unlocking switches must be operated simultaneously with both hands when the one-section two-step telescopic ladder is lowered, which is very inconvenient in operation. SUMMARY

[0003] The present application aims to provide a stable one-section two-step telescopic ladder, which can realize stable telescopic operation and convenient contraction.

[0004] The stable one-section two-step telescopic ladder comprises a plurality of pairs of ladder pipes connected in a step-by-step sleeved manner, a plurality of connecting sleeves, a plurality of steps and a locking structure. The connecting sleeves are provided with square interface ends and round hole ends. The two ends of the steps are fixedly connected with the square interface ends of a pair of connecting sleeves. The round hole ends of the pair of connecting sleeves are sleeved on a pair of ladder pipes. One pair of ladder pipes is fixedly connected with one pair of connecting sleeves and slidably connected with another pair of connecting sleeves. The locking structure is arranged in the connecting sleeve and can be inserted into the ladder pipe to lock the adjacent ladder pipes.

[0005] The ladder pipe of the one-section two-step telescopic ladder is provided with a hook hole on the outside of the second step. The connecting sleeve slidably connected with the ladder pipe is provided with a hook matched with the hook hole. When the ladder pipe and the connecting sleeve slide, the hook is clamped into the hook hole to lock the ladder pipe and the connecting sleeve. The ladder pipe lifts the connecting sleeve, so that the locking structure synchronously operates and is smoothly locked with the hole between the adjacent ladder pipes.

[0006] As a further improvement of the present application, the locking structure comprises a spring sleeve, a spring, a lock catch and a lock pin, the upper end of the round hole end of the connecting sleeve is provided with a lock slot, the inner side is provided with a circular through hole, the spring sleeve is fixedly connected in the spring sleeve, the spring sleeve is provided with a spring slot on one side, the spring is arranged in the spring slot, the end of the spring in contact with the spring slot bottom of the spring sleeve is fixedly connected with the spring sleeve, one end of the lock pin passes through the circular through hole of the connecting sleeve, the other end of the lock pin is compressed in the spring slot of the spring sleeve, the lock pin is slidingly connected with the connecting sleeve, the middle end of the lock pin is provided with a clamping part, the lower end of the lock catch is inserted into the two sides of the lock pin and abuts against one side of the clamping part of the lock pin close to the circular through hole of the connecting sleeve, the connecting sleeve is provided with a groove matched with the lock catch, the middle part of the lock catch is rotationally connected with the connecting sleeve at the groove and forms a lever structure with the connecting sleeve, the lock catch is provided with a lock tongue at the rotation end, and the lock tongue is clamped with the lock slot.

[0007] As a further improvement of the present application, the ladder pipe is provided with an upper fixed hole and a lower fixed hole on one side close to the locking structure, when the lower fixed holes of any two adjacent ladder pipes run to the hole positions of the lock pins of each other, the lock pins are popped out and the adjacent two ladder pipes are locked, the ladder pipe can drive the next ladder pipe to run and stretch out.

[0008] As a further improvement of the present application, it further comprises a hand holding rod, the hand holding rod is sleeved on the head of the lowermost ladder pipe, the hand holding rod and the ladder pipe are slidingly connected, the hand holding rod comprises a top rod and a pair of unlocking sleeves, the two ends of the top rod are respectively fixedly connected with the unlocking sleeves, the unlocking sleeves are slidingly connected with the ladder pipe, the unlocking sleeves are provided with a hook matched with the hook hole, and the inner lower end of the unlocking sleeve is provided with a limiting groove on the ladder pipe, the head of the lowermost ladder pipe is provided with a limiting convex rib, the limiting convex rib and the limiting groove are slidingly connected, the outer side of the unlocking sleeve is provided with a hook, and the hook is clamped with the hook hole of the ladder pipe; when the lowermost ladder pipe runs upward, the limiting convex rib at the lower end of the ladder pipe runs to the hook hole, and the limiting convex rib pushes out the hook in the sliding process of the ladder pipe, so that the clamping of the hook and the hook hole is disconnected, at this time, the hand holding rod drives the two unlocking sleeves to move downward to the limiting groove under the elastic force of the lock tongue, at this time, the lock shaft can be inserted into the fixed hole in the corresponding aluminum pipe, and the purpose of the step lock catch is achieved; when the hand holding rod is lifted, the two ends of the lock tongue are pushed open, at this time, the unlocking is successful, and the lowermost ladder pipe can run downward; when the limiting convex rib pushes out the hook in the sliding process of the ladder pipe, at this time, the hand is not loosened, so that the process of pushing out the hook by the limiting convex rib in the sliding process of the ladder pipe is invalid, and the unlocking sleeves at the two ends of the hand holding rod remain unchanged.

[0009] As a further improvement of the present application, the lowermost ladder pipe is provided with only an upper fixing hole on the side close to the locking structure, so that the connection of the lowermost ladder pipe and its adjacent ladder pipe is one step, and the closing height of the product can be reduced after the one-step two-step telescopic ladder is closed, and when the closing height has special requirements, all the ladder pipes can be changed into the one-step structure, so that the product is more convenient to carry; the adjacent ladder pipe of the lowermost ladder pipe is provided with a restoring protruding rib, which can push out the supporting hook during the sliding process of the ladder pipe, so as to disconnect the clamping connection of the supporting hook and the supporting hook hole.

[0010] As a further improvement of the present application, the driving structure is further included, the driving structure includes a motor, a screw rod and a switch, the motor is fixedly connected to the bottom of the ladder pipe, the switch is electrically connected with the motor, the motor is a driving motor with a reducer, the screw rod includes a light shaft part and a threaded part, one end of the light shaft part of the screw rod is directly connected with the motor, the ladder pipe further includes a plurality of nuts, the nuts are fixedly installed at the lower end of the ladder pipe, the threaded part of the screw rod is threadedly connected with the nuts, and the nuts can be threadedly driven on the threaded part of the screw rod, so as to drive the ladder pipe to be telescopic.

[0011] A one-step two-step electric telescopic double ladder includes a main ladder, a sub-ladder and a hinge, the main ladder is a stable one-step two-step telescopic ladder as described in the first embodiment, the sub-ladder is a stable one-step two-step hand-pulled telescopic ladder without a driving structure, and the hinge is fixedly connected to the inner side of the top of the main ladder and the sub-ladder at both ends.

[0012] As a further improvement of the present application, the auxiliary connector is further included, the auxiliary connector includes an auxiliary shaft and an auxiliary shaft sleeve, the auxiliary shaft and the auxiliary shaft sleeve are fixedly connected to the lower end of the main ladder and the sub-ladder at both ends, and the auxiliary shaft is detachably sleeved with the auxiliary shaft sleeve, so that the main ladder can drive the sub-ladder to synchronously operate during the operation of the one-step two-step electric telescopic double ladder, and the auxiliary connector can ensure the synchronization of the operation of the main ladder and the sub-ladder, thereby improving the reliability of the telescopic operation of the double ladder.

[0013] Compared with the prior art, the present application has the beneficial effects that the connecting sleeve is provided with a supporting hook, so that the second step telescopic operation of the one-step two-step ladder is normal and smooth; the transmission mode of the lowermost ladder pipe and the adjacent ladder pipe is one step, thereby reducing the closing height of the product and making the product convenient to carry; the hand supporting top rod is unlocked by one supporting upward, thereby facilitating the operation process; the auxiliary connector is arranged between the main ladder and the sub-ladder, thereby improving the synchronization rate and the reliability of the one-step two-step electric telescopic double ladder during the telescopic operation. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a perspective view of the structure of the present application;

[0015] Figure 2 It is a schematic view of the structure of the present application in the closed state;

[0016] Figure 3 It is a front view of the structure of the present application in the expanded state;

[0017] Figure 4 For the invention Figure 3 Area zoomed in view;

[0018] Figure 5 For the invention Figure 4 Area zoomed in view;

[0019] Figure 6 For the invention Figure 5 Area zoomed in view of the unlocking sleeve connection changes;

[0020] Figure 7 For the invention

[0021] Figure 8 For the invention

[0022] Figure 9 For the invention

[0023] Figure 10 For the invention

[0024] Figure legend:

[0025] Ladder pipe 1; upper fixed hole 1-1; lower fixed hole 1-2; limiting convex rib 1-3; hook hole 1-4; reduction convex rib 1-5; nut 1-6; connecting sleeve 2; lock slot 2-1; hook 2-2; pedal 3; drive structure 4; motor 4-1; screw rod 4-2; switch 4-3; locking structure 5; spring sleeve 5-1; spring 5-2; lock catch 5-3; lock tongue 5-3-1; lock pin 5-4; hand lever 6; top rod 6-1; unlocking sleeve 6-2; limiting groove 6-2-1; auxiliary connector 7; auxiliary shaft 7-1; auxiliary shaft sleeve 7-2; main ladder a; vice ladder b; hinge c. DETAILED DESCRIPTION

[0026] Specific embodiment one: please refer to Figures 1-8 The invention relates to a stable one-section two-step telescopic ladder, which comprises a ladder pipe 1, a connecting sleeve 2, a pedal 3, a drive structure 4 and a locking structure 5. A plurality of connecting sleeves 2 are provided with square interface ends and round hole ends. The pedal 3 is fixedly connected with the square interface ends of a pair of connecting sleeves 2 at both ends respectively. The round hole ends of the pair of connecting sleeves 2 are sleeved on a pair of ladder pipes 1 respectively. One pair of ladder pipes 1 is fixedly connected with one pair of connecting sleeves 2 and is slidingly connected with the other pair of connecting sleeves 2. The locking structure 5 is arranged in the connecting sleeve 2. The locking structure 5 can be inserted into the ladder pipe 1 to lock the adjacent ladder pipes 1 with each other.

[0027] The ladder pipe 1 is provided with a hook hole 1-4 on the side away from the locking structure 5 in the second step, and the connecting sleeve 2 connected with the ladder pipe 1 is provided with a hook 2-2 matched with the hook hole 1-4. When the ladder pipe 1 slides with the connecting sleeve 2, the hook 2-2 is clamped into the hook hole 1-4, thereby locking the ladder pipe 1 and the connecting sleeve 2. The ladder pipe 1 lifts the connecting sleeve 2, so that the locking structure 5 synchronously runs smoothly with the upper fixing hole 1-1 between the adjacent ladder pipes 1.

[0028] Further, as shown in the embodiment, Figure 8 The locking structure 5 includes a spring sleeve 5-1, a spring 5-2, a lock catch 5-3 and a lock pin 5-4. The connecting sleeve 2 is provided with a lock groove 2-1 on the upper end of the round hole end, and is provided with a circular through hole on the inner side. The spring sleeve 5-1 is fixedly connected with the connecting sleeve 2. The spring sleeve 5-1 is provided with a spring groove on one side. The spring 5-2 is arranged in the spring groove. One end of the spring 5-2 in contact with the bottom of the spring groove of the spring sleeve 5-1 is fixedly connected with the spring sleeve 5-1. One end of the lock pin 5-4 penetrates through the circular through hole of the connecting sleeve 2, and the other end compresses the spring 5-2 in the spring groove of the spring sleeve 5-1. The lock pin 5-4 is slidably connected with the connecting sleeve 2. The middle end of the lock pin 5-4 is provided with a clamping part. The lower end of the lock catch 5-3 is inserted into the two sides of the lock pin 5-4 and abuts against one side of the clamping part of the lock pin 5-4 close to the circular through hole of the connecting sleeve 2. The connecting sleeve 2 is provided with a groove matched with the lock catch 5-3. The middle part of the lock catch 5-3 is rotatably connected with the connecting sleeve 2 at the groove and forms a lever structure with the connecting sleeve 2. The rotating end of the lock catch 5-3 is provided with a lock tongue 5-3-1. The lock tongue 5-3-1 is clamped with the lock groove 2-1.

[0029] Further, as shown in the embodiment, Figure 4 The ladder pipe 1 is provided with an upper fixing hole 1-1 and a lower fixing hole 1-2 on the side close to the locking structure. When the lower fixing holes 1-2 of any two adjacent ladder pipes 1 run to the hole positions of the lock pins 5-4 of each other, the lock pins 5-4 are popped out and lock the two adjacent ladder pipes 1. The ladder pipe 1 can drive the next ladder pipe 1 to run. The upper fixing hole 1-1 at the upper end of the ladder pipe 1 and the lower fixing hole 1-2 at the lower end are different in size or shape and are matched with the lock pin 5-4 of the same specification. The difference in size or shape of the upper fixing hole 1-1 and the lower fixing hole 1-2 satisfies that the lock pin 5-4 should be inserted into the lower fixing hole 1-2 when the ladder pipe 1 runs out, but cannot be inserted into the upper fixing hole 1-1 in advance, thereby ensuring that the ladder pipe 1 runs in a one-step-two-step manner.

[0030] Further, as shown in the embodiment, Figures 4-6As shown, the bottommost ladder tube 1 has only an upper fixing hole 1-1 on the side near the locking structure, so that the connection between the bottommost ladder tube 1 and its adjacent ladder tube 1 is one step, thereby reducing the closed height of the product and making the product easy to carry; the ladder tube 1 adjacent to the bottommost ladder tube 1 is provided with a restoration rib 1-5, which can push out the hook 2-2 during the sliding process of the ladder tube 1, thereby breaking the engagement between the hook 2-2 and the hook hole 1-4.

[0031] In a further embodiment, such as Figure 4 As shown, the drive structure 4 includes a motor 4-1, a lead screw 4-2, and a switch 4-3. The motor 4-1 is fixedly connected to the bottom of the ladder tube frame 1 of the electric telescopic single-sided ladder a. The switch 4-3 is electrically connected to the motor 4-1. The motor 4-1 is a drive motor with a built-in reducer. The lead screw 4-2 includes a shaft part and a threaded part. The motor 4-1 is directly connected to one end of the shaft part of the lead screw 4-2, which optimizes the transmission structure. The ladder tube 1 also includes several nuts 1-6. The nuts 1-6 are fixedly installed at the lower end of the ladder tube 1. The threaded part of the lead screw 4-2 is threadedly connected to the nuts 1-6. The nuts 1-6 can drive the ladder tube 1 to extend and retract through the threaded part of the lead screw 4-2.

[0032] In a further embodiment, such as Figures 4-6As shown, it also includes a hand support rod 6, which is fitted onto the head of the lowest ladder tube 1. The hand support rod 6 and the ladder tube 1 are slidably connected. The hand support rod 6 includes a top rod 6-1 and a pair of unlocking sleeves 6-2. The two ends of the top rod 6-1 are fixedly connected to the unlocking sleeves 6-2 respectively. The unlocking sleeves 6-2 and the ladder tube 1 are slidably connected. The unlocking sleeves 6-2 are provided with hooks 2-2 that match the hook holes 1-4. The lower end of the unlocking sleeves 6-2 is provided with a limiting groove 6-2-1 on the ladder tube 1. The head of the lowest ladder tube 1 is provided with a limiting rib 1-3. The outer side of the unlocking sleeves 6-2 is provided with hooks 2-2, which are engaged with the hook holes 1-4 on the outer side of the ladder tube 1. When the lowest ladder tube 1 moves upward, the limiting rib 1-3 at its lower end moves to the hook hole 2-2. During the sliding process of the ladder tube 1, the limiting rib 1-3 pushes the hook 2-2 out, thereby disconnecting the hook 2-2 from the hook hole 1-4. -4 is engaged. At this time, under the action of the spring force of the locking tongue 5-3-1, the top rod 6-1 moves the unlocking sleeves 6-2 at both ends down to the limiting groove 6-2-1. At this time, the locking pin 5-4 can be inserted into the upper fixing hole 1-1 in the corresponding ladder tube 1. When the hand support rod 6 is lifted, it can push open the locking tongues 5-3-1 at both ends. At this time, the unlocking is successful, and the bottom ladder tube 1 can move down. When the limiting rib 1-3 slides with the ladder tube 1 and tries to push out the hook 2-2, the hand support rod 6 is not released at this time. Therefore, the process of the limiting rib 1-3 pushing out the hook 2-2 during the sliding of the ladder tube 1 is invalid. The unlocking sleeves 6-2 at both ends of the hand support rod 6 remain in the unlocked state. The limiting rib 1-3 and the limiting groove 6-2-1 are slidably connected. The unlocking sleeve 6-2 is provided with a hook 2-2 on the outside. The hook 2-2 is engaged with the hook hole 2-2 on the outside of the ladder tube 1.

[0033] When the telescopic ladder retracts, when the hand support rod 6 is lifted by hand, the hook 2-2 of the unlocking sleeve 6-2 engages with the hook hole 1-4 of the lowest ladder tube 1, the top rod 6-1 presses against the locking tongue 5-3-1, and at the same time the lock 5-3 rotates through the lever principle to drive the locking pin 5-4, breaking the self-locking between the ladder tubes 1, and the ladder tube 1 begins to retract. When the ladder tube 1 with the restoring rib 1-5 slides past the hook 2-2, the restoring rib 1-5 presses against the hook 2-2, breaking the engagement between the hook 2-2 and the hook hole 1-4, and the hand support rod 6 slides downward. When the limiting rib 1-4 slides to the upper edge of the limiting groove 6-2-1, the hand support rod 6 stops sliding.

[0034] Specific Implementation Example 2: As shown in the example Figures 9-10 As shown, a one-section two-step electric telescopic ladder includes a main ladder a, an auxiliary ladder b, and a hinge c. The main ladder a is a stable one-section two-step electric telescopic ladder as described in Embodiment 1, and the auxiliary ladder b is a stable one-section two-step manual telescopic ladder without the drive structure 4 installed. The two ends of the hinge c are fixedly connected to the inner top of the main ladder a and the auxiliary ladder b, respectively.

[0035] In a further embodiment, such as Figure 10As shown, the auxiliary connector 7 includes an auxiliary shaft 7-1 and an auxiliary shaft sleeve 7-2, the auxiliary shaft 7-1 is sleeved in the auxiliary shaft sleeve 7-2, and the two ends of the auxiliary shaft 7-1 and the auxiliary shaft sleeve 7-2 are fixedly connected to the lower ends of the main ladder a and the auxiliary ladder b respectively. When the main ladder a and the auxiliary ladder b are combined, the auxiliary shaft 7-1 and the auxiliary shaft sleeve 7-2 are sleeved, the lower parts of the main ladder a and the auxiliary ladder b are connected successfully, so that the double ladders can normally run in and out. When the one-section two-step electric extension double ladder runs, the auxiliary ladder b is driven to run synchronously by the main ladder a. The auxiliary connector 7 can ensure the synchronization of the main ladder a driving the auxiliary ladder b to run, so as to improve the reliability of the one-section two-step electric extension double ladder when running in and out.

Claims

1. A stable one-section, two-step telescopic ladder, characterized in that: The system includes several pairs of ladder tubes (1) that are connected in a step-by-step manner, several connecting sleeves (2), several treads (3), and a locking structure (5). The ladder tubes (1) and several connecting sleeves (2) are slidably connected. Each end of a tread (3) is fixedly connected to a pair of connecting sleeves (2). The end of a connecting sleeve (2) that is not connected to a tread (3) is fitted onto the ladder tube (1). One pair of ladder tubes (1) is fixedly connected to one pair of connecting sleeves (2) and slidably connected to the other pair of connecting sleeves (2). The locking structure (5) is fixedly installed inside the connecting sleeve (2). The locking structure (5) can be inserted into the ladder tube (1) to lock it with the adjacent ladder tube (1). The outer side of the ladder tube (1) away from the locking structure (5) is provided with a hook hole (1-4). The connecting sleeve (2) that is slidably connected to the ladder tube (1) is provided with a hook (2-2) that matches the hook hole (1-4). When the ladder tube (1) and the connecting sleeve (2) slide together, the locking structure (5) locks the connecting sleeve (2) into place. The hook (2-2) on the connecting sleeve (2) is inserted into the hook hole (1-4) to lock the ladder tube (1) and the connecting sleeve (2). The ladder tube (1) lifts the connecting sleeve (2), so that the locking structure (5) can smoothly lock the adjacent ladder tubes (1). It also includes a hand support rod (6), which is sleeved on the head of the lowest ladder tube (1). The hand support rod (6) and the ladder tube (1) are slidably connected. The hand support rod (6) includes a top rod ( 6-1) and a pair of unlocking sleeves (6-2), the two ends of the top rod (6-1) are fixedly connected to the unlocking sleeves (6-2) respectively. The unlocking sleeves (6-2) are fitted on the ladder tube (1) and slidably connected to the ladder tube (1). The unlocking sleeves (6-2) are provided with hooks (2-2) that match the hook holes (1-4) on the bottom ladder tube (1). The hooks (2-2) on the unlocking sleeves (6-2) are engaged with the hook holes (1-4) and can be disengaged.

2. The stable one-section two-step telescopic ladder according to claim 1, characterized in that: The lower end of the unlocking sleeve (6-2) is provided with a limiting groove (6-2-1), and the head of the lowest ladder tube (1) is provided with a limiting rib (1-3). The limiting rib (1-3) and the limiting groove (6-2-1) are slidably connected.

3. A stable one-section two-step telescopic ladder according to claim 2, characterized in that: The bottom ladder tube (1) has only an upper fixing hole (1-1) on the side near the locking structure (5), so that the connection between the bottom ladder tube (1) and its adjacent ladder tube (1) is one step. The ladder tube (1) adjacent to the bottom ladder tube (1) is provided with a restoration rib (1-5). The restoration rib (1-5) can push out the hook (2-2) on the unlocking sleeve (6-2) during the sliding process of the ladder tube (1), thereby disconnecting the bottom ladder tube (1) from the hand support rod (6).

4. A stable one-section two-step telescopic ladder according to claim 1, characterized in that: It also includes a drive structure (4), which includes a motor (4-1), a lead screw (4-2), and a switch (4-3). The motor (4-1) is fixedly connected to the bottom of the ladder tube (1), and the switch (4-3) is electrically connected to the motor (4-1). The motor (4-1) is a drive motor with its own reducer. The lead screw (4-2) includes a shaft part and a threaded part. The motor (4-1) is directly connected to one end of the shaft part of the lead screw (4-2). The ladder tube (1) also includes several nuts (1-6). The nuts (1-6) are fixedly installed at the lower end of the ladder tube (1). The threaded part of the lead screw (4-2) is threadedly connected to the nuts (1-6). The nuts (1-6) can drive the ladder tube (1) to extend and retract through the threaded part of the lead screw (4-2).

5. A single-section, two-step electrically extendable double ladder, characterized in that: The system includes a main ladder (a), a secondary ladder (b), a hinge (c), and an auxiliary connector (7). The main ladder (a) and the secondary ladder (b) are both stable one-section two-step telescopic ladders as described in claim 1. The two ends of the hinge (c) are fixedly connected to the inner top of the main ladder (a) and the secondary ladder (b), respectively. The auxiliary connector (7) includes an auxiliary shaft (7-1) and an auxiliary bushing (7-2). The two ends of the auxiliary shaft (7-1) and the auxiliary bushing (7-2) are fixedly connected to the lower ends of the main ladder (a) and the secondary ladder (b), respectively. The auxiliary shaft (7-1) and the auxiliary bushing (7-2) are detachably sleeved together.

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