Normally closed mechanical expansion shaft

Abstract

The invention discloses a normally-closed mechanical expansion shaft structure and an expansion shaft thereof, and aims to overcome the defect that an existing normally-open mechanical expansion shaft is poor in stability. The device comprises a fixing structure and a piston structure, the fixing structure comprises an air pipe, a shaft pipe and a plurality of positioning covers, the air pipe is inserted into the shaft pipe, the positioning covers are installed between the air pipe and the shaft pipe, a piston cavity is formed between every two adjacent positioning covers, the piston structure comprises a piston and a key strip, and the piston is elastically connected with the positioning cover on one side of the piston cavity. The other side of the piston cavity is communicated with the air pipe, the piston is matched with the key strip in a wedge angle mode, the shaft pipe is provided with a through hole matched with the key strip, and when thrust generated by air pressure on the piston is smaller than elastic force of the elastic piece, the piston axially moves to push the key strip to extend outwards in the radial direction. And compared with a normally-open structure, better stability is achieved, and the stability of a production line is facilitated.

Description

Technical Field

[0001] The present invention relates to a coiling device, and more particularly to a normally closed mechanical expansion shaft. Background Art

[0002] The reeling and unwinding device is suitable for food machinery, packaging machinery, rubber machinery, and equipment for producing films. It can reel and unwind by rotating, and can store and release flexible sheets or wire bundles of equal cross-sectional size. The material is generally wound onto a hollow roller, and then transferred by a forklift or a transporter.

[0003] The rewinding and unwinding device generally includes a chuck and an expansion shaft. The expansion shaft is inserted into the center of the roller and fixed to the roller by changing the diameter. The two ends of the expansion shaft are detachably connected to the chuck, and the chuck is retracted and unwound by rotating.

[0004] Chinese patent announcement number CN207497838U, named "An automatic centering inflatable shaft for a coating machine", discloses an automatic centering inflatable shaft for a coating machine, including an inflatable shaft body, the outer side of the inflatable shaft body is provided with telescopic bosses uniformly distributed at equal angles and distances, two ends of the inflatable shaft body are connected to one end of two groups of symmetrically distributed main shafts, the middle position of one end of the inflatable shaft body close to the main shaft is provided with more than four groups of connecting ribs symmetrically distributed at equal angles, a fixing plate is provided between the connecting ribs, a control switch is provided on one side of the fixing plate, an air inlet pipe is provided on one side of the main shaft, and an air outlet pipe is provided on the side of the main shaft close to the air inlet pipe, an arc-shaped support plate connected to one side of the telescopic boss through a first electric telescopic rod can prevent the center position of the external cylinder from being offset, a positioning boss provided on one side of the positioning baffle can well position and fix the cylinder, and a friction strip provided on one side of the friction pad can prevent the relative rotation of the inflatable shaft and the external cylinder.

[0005] The disadvantage of this device is that the telescopic boss used to carry the external roller positioning function can only be protruded outward to realize the positioning function through the air supply pipe. If the air pressure fluctuates greatly, or the air is cut off in the middle, the air shaft will jump greatly during work, or it will affect production after the air is cut off and retracted, causing trouble to production safety and material safety. Once there is an air leak in the middle of production, the coil production is generally stopped, which will cause very large losses, firstly, the waste of material coils, and secondly, the need to readjust the machine.

[0006] The present application aims to provide a normally closed mechanical expansion shaft to address the deficiencies of the existing normally open expansion shaft. Summary of the invention

[0007] The invention overcomes the disadvantage of poor stability of the existing normally open mechanical expansion shaft and provides a normally closed mechanical expansion shaft, which has better stability. The expansion key retracts under air supply, has low requirements on the stability of the air source, and has better stability.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions: A normally closed mechanical shaft expansion structure comprises a fixed structure and a piston structure. The fixed structure comprises an air pipe, a shaft pipe and a plurality of positioning covers. The air pipe is inserted into the shaft pipe. A plurality of positioning covers are installed between the air pipe and the shaft pipe. A piston cavity is formed between adjacent positioning covers. The piston structure comprises a piston and a key strip. The piston is elastically connected to the positioning cover on one side of the piston cavity. The other side of the piston cavity is connected to the air pipe. The piston and the key strip are matched at a wedge angle. A through hole accommodating the key strip is provided on the shaft pipe. When the thrust generated by the air pressure on the piston is less than the elastic force of the elastic member, the piston moves axially to push the key strip to extend radially outward.

[0009] Since the expansion shaft structure in the present application is in rotation when in working state, the present application places the gas path structure in the axis and sets the gas pipe at the axis of the expansion shaft. The present application sets multiple positioning covers to form several independent piston structures. Even if a single piston fails, the whole device can still work and has high stability.

[0010] In order to realize the normally closed structure to be achieved in the above text, the wedge angles of the piston and the key strip, as well as the left-right positional relationship between the corresponding elastic member and the cavity that produces the air pressure change are set. Under normal pressure, the elastic force of the elastic member is greater than the pressure generated by the air pressure, and the piston moves toward the side away from the elastic member. As the piston moves, it is affected by the wedge surface and extends outward in the radial direction, abutting against the roller outward to achieve the positioning of the roller. When the air pipe is ventilated, the air pressure on one side of the piston increases, overcoming the elastic force of the elastic member to cause the piston to move in the opposite direction. The key strip loses the support of the piston wedge surface and no longer provides pressure against the roller, thereby losing the corresponding friction force. Based on the above structure and the movement principle of the expansion shaft structure, it can be seen that air supply is only required when loading and unloading the expansion shaft, and the time to maintain the air pressure is shorter than that of the normally open expansion shaft structure, which can reduce the requirements for the stability of the air source.

[0011] The expansion shaft is divided into several sections by the positioning cover, and each piston cavity has a piston structure. This feature has two main functions. The first is to increase the distribution density of the key strips and generate sufficient friction to position the roller. The second is to reduce the requirements for the elastic member. In the present application, a piston has only a single key strip in the length direction. Under the condition of providing the same expansion force, the elastic force requirement for the elastic member is lower. Preferably, the piston includes a piston body and a cone, the cross-section of the piston is annular, the inner edge of the piston body fits the outer wall of the trachea and the outer edge fits the inner wall of the shaft tube, the cone has a conical surface and cooperates with the wedge angle of the key bar through the conical surface, a positioning hole is provided at the bottom of the cone, the aperture of the positioning hole is larger than the outer diameter of the trachea, the elastic part is installed in the positioning hole and abuts against the bottom wall of the positioning hole.

[0012] The piston body is fitted with the air pipe and the shaft pipe and is sealed, and the conical surface of the cone produces a corresponding wedge angle. The positioning hole is used to position the elastic member.

[0013] Preferably, the outer edge of the piston is fitted with a plurality of key strips, adjacent key strips are arranged at equal intervals, the key strips in the same piston cavity form a key strip group, a key strip group has j key strips arranged at equal intervals, the mechanical expansion shaft has i groups of piston cavities, the projections of the key strip groups in the same group of piston cavities about the axis coincide, and the angle of deflection of the key strip group of the nth piston cavity about the axis is This structure enables the key strip to contact the roller alternately, reducing stress, expanding the coil more evenly and achieving higher roundness.

[0014] Preferably, the shaft tube is provided with pressing plates at both ends of the through hole in the length direction, and the projections of the pressing plates and the key strip partially overlap on a plane perpendicular to the normal line of the top surface of the key strip. This structure is used to prevent the key strip from coming off the shaft tube.

[0015] Preferably, the key bar is provided with mounting holes at both ends in the length direction, and a reset elastic member is installed in the mounting hole, and the other end of the reset elastic member abuts against the bottom surface of the pressing plate. This structure is used for rapid reset of the key bar.

[0016] Preferably, the key bar is provided with an abutment block extending in the axial direction on one side close to the elastic member, the mounting hole is located in the abutment block, and the bottom of the piston is provided with a step for reaching the position, and the key bar reaches the travel limit on one side when the step wall of the step reaches the abutment block. In addition to providing installation for the reset elastic member, the abutment block also provides a limit for the piston, and bears the pressure brought by the air pressure together with the positioning cover, thereby reducing the load on the positioning cover.

[0017] Preferably, the top surface of the key bar is provided with anti-skid grooves. This structure improves the friction between the key bar and the roller, and better transmits torque.

[0018] Preferably, a roller key is provided on the surface of the shaft tube, and the roller key includes a roller key body and a roller connected to the roller key body by a rotating shaft, and the top of the roller is higher than the surface of the shaft tube. This structure can improve the smoothness of introducing the coil. The travel limit of the key bar extending outward is higher than the height of the roller.

[0019] Preferably, the roller keys are arranged in an array along the axial and circumferential directions of the side wall of the shaft tube.

[0020] A normally closed mechanical expansion shaft also includes a shaft head, a support wheel and a connecting flange. Both ends of the shaft tube are fixedly connected to the shaft head. The support wheel is mounted on the shaft head. The support wheel and the shaft head are rotatably connected through a bearing. The connecting flange is coaxially connected to the shaft head through a coupling. The end of the connecting flange is fixedly mounted with a spline. The shaft head and the connecting flange are both provided with an air passage connected to the air pipe, and an air nozzle is provided at the end of the air passage. The structure is used to connect the expansion shaft structure to connect with the corresponding active chuck and passive chuck. The support wheel plays a supporting role and bears the gravity of the expansion shaft and the coil. The expansion shaft structure is connected to an external power through the shaft head and the connecting flange. One end of the expansion shaft is connected to the external power, and the air nozzle at the other end is connected to the air source. The expansion shaft is connected to the external power through a spline, and the connection and disconnection with the external power are achieved through this structure.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The expansion shaft structure is a normally closed structure, which has low requirements on the stability of the air source. Compared with the normally open structure, it has better stability and is conducive to the stability of the production line; (2) The alternately arranged key strips make the material roll more uniform and round. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is an axonometric view of the present invention; Figure 2 is an axonometric view of the present invention with the shaft tube removed; Figure 3 is a front view of the present invention; Figure 4 yes Figure 3 Sectional view at AA in the middle; Figure 5 It is a schematic diagram of the piston chamber formed by the air tube and the shaft tube; Figure 6 It is the principle diagram of wedge angle fit; In the figure: Air pipe 1, shaft tube 2, positioning cover 3, piston chamber 4, sealing ring 5, piston 6, key strip 7, compression spring 8, wedge surface 9, through hole 10, piston body 11, cone 12, positioning hole 13, neck 14, pressure plate 15, mounting hole 16, reset elastic member 17, anti-slip groove 18, roller key 19, roller 20, shaft head 21, support wheel 22, connecting flange 23, coupling 24, spline 25, air nozzle 26, air duct 27, air inlet 28. DETAILED DESCRIPTION

[0023] The present disclosure is further described below in conjunction with the accompanying drawings and embodiments.

[0024] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] In the present disclosure, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various structural parts or elements of the present disclosure, and do not specifically refer to any structural part or element in the present disclosure and should not be understood as limitations on the present disclosure.

[0027] In the present disclosure, terms such as "fixed connection", "connected", "connection", etc. should be understood in a broad sense, indicating that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. For relevant scientific research or technical personnel in this field, the specific meanings of the above terms in the present disclosure can be determined according to specific circumstances, and they cannot be understood as limitations on the present disclosure.

[0028] Example: A normally closed mechanical expansion shaft structure, reference Figures 1 to 3 As shown, it includes a fixing structure and a piston structure.

[0029] Ginseng Figure 5 The fixed structure includes an air pipe 1, an axle tube 2 and a plurality of positioning covers 3. The air pipe 1 is inserted into the axle tube 2. A plurality of positioning covers 3 are installed between the air pipe 1 and the axle tube 2. A piston 6 cavity 4 is formed between adjacent positioning covers 3. The air pipe 1 is a hollow rigid tube body. The axle tube 2 is sleeved on the periphery of the air pipe 1, and the air pipe 1 and the axle tube 2 are coaxially arranged. The cross section of the positioning cover 3 is annular. The inner and outer walls of the positioning cover 3 are provided with mounting grooves. A sealing ring 5 is installed through the mounting groove. The positioning cover 3 is sealed to connect the air pipe 1 and the axle tube 2 to avoid air leakage.

[0030] The positioning cover 3 is fixed to the shaft tube 2 , and a plurality of fasteners are threadedly connected to the outer wall of the positioning cover 3 , and the fasteners pass through the shaft tube 2 to position the positioning cover 3 .

[0031] Ginseng Figure 2 ,4 The piston structure includes a piston 6 and a key strip 7, and the piston 6 is elastically connected to the positioning cover 3 on one side of the piston 6 chamber 4. In some embodiments, the elastic connection is connected by a compression spring 8, but it is not limited to this. The other side of the piston 6 chamber 4 is connected to the air pipe 1. Specifically, on the other side of the piston 6 chamber 4, the air pipe 1 is provided with an air inlet hole 28. The piston 6 and the key strip 7 both have wedge surfaces 9, and the wedge angles of the two wedge surfaces 9 match. The shaft tube 2 is provided with a through hole 10 that accommodates the key strip 7. The key strip 7 extends out of the shaft tube 2 through the through hole 10. The shaft tube 2 uses the side wall of the through hole 10 as a guide to limit the freedom of the key strip 7 in other directions. When the thrust generated by the air pressure on the piston 6 is less than the elastic force of the elastic member, the piston 6 moves axially to push the key strip 7 to extend radially outward, that is, under normal pressure, the piston 6 is pushed by the compression spring 8 to extend the key strip 7 outward.

[0032] Ginseng Figure 2 The piston 6 includes a piston body 11 and a cone 12. The cross section of the piston 6 is annular. The inner edge of the piston body 11 fits the outer wall of the air pipe 1 and the outer edge fits the inner wall of the shaft tube 2. The cone 12 has a conical surface and is wedge-angled with the key bar 7 through the conical surface. A positioning hole 13 is provided at the bottom of the cone 12. The aperture of the positioning hole 13 is larger than the outer diameter of the air pipe 1. The elastic member is installed in the positioning hole 13 and abuts against the bottom wall of the positioning hole 13. The inner and outer edges of the piston body 11 are similar to the positioning cover 3. The sealing ring 5 is also installed through the mounting groove to improve the air tightness. The conical surface of the cone 12 produces a corresponding wedge angle. The positioning hole 13 is used to position the elastic member.

[0033] In some embodiments, a neck 14 is further provided between the piston body 11 and the cone 12. The outer diameter of the neck 14 is the same everywhere and is the same as the thinnest part of the cone 12. This structure can reduce the difficulty of producing the piston 6 and prevent the piston body 11 from hitting the key bar 7 and causing damage to the piston body 11.

[0034] Ginseng Figure 1 , 2 As shown, the outer edge of the piston 6 is fitted with a plurality of key strips 7, and each of the key strips 7 has a row in the axial direction. In the circumferential direction around the axis, adjacent key strips 7 are arranged at equal intervals, and the key strips 7 in the same piston 6 cavity 4 form a key strip 7 group, and a key strip 7 group has j key strips 7 arranged at equal intervals. The mechanical expansion shaft has i groups of piston 6 cavities 4, and the projections of the key strips 7 groups in the same group of piston 6 cavities 4 about the axis coincide, and the angle of deflection of the key strip 7 group of the nth piston 6 cavity 4 about the axis is . This structure enables the key strips 7 to contact the roller alternately, reducing stress, expanding the coil more evenly and with higher roundness. In this embodiment, one piston 6 is fitted with 4 key strips 7, and the angle between adjacent key strips 7 is 90°. The piston 6 cavity 4 has 2 groups, and the two groups of piston 6 cavities 4 are arranged alternately. The angle between the projections of the key strips 7 of adjacent piston 6 cavities 4 on the axis is 45°. It is worth noting that the value of "the mechanical expansion shaft has i groups of piston 6 cavities 4" described in this application is not the specific number of piston 6 cavities 4, but the number of groups, and the angle of deflection of the key strip 7 group corresponding to each group of piston 6 cavities 4 about the axis is the same.

[0035] The shaft tube 2 is provided with a pressure plate 15 at both ends of the through hole 10 in the length direction, and is installed on the shaft tube 2 through fasteners. On the plane perpendicular to the normal of the top surface of the key bar 7, the projections of the pressure plate 15 and the key bar 7 partially overlap. This structure is used to limit the key bar 7 from coming off the shaft tube 2. The key bar 7 is provided with mounting holes 16 at both ends of the length direction, and the mounting holes 16 are installed with a reset elastic member 17, and the other end of the reset elastic member 17 abuts the bottom surface of the pressure plate 15. This structure is used for quickly resetting the key bar 7. The key bar 7 is provided with an abutment block extending in the axial direction on the side close to the elastic member, and the mounting hole 16 is located in the abutment block. The bottom of the piston 6 is provided with a step for reaching the position, and the step wall of the step reaches the stroke limit of one side when the key bar 7 reaches the abutment block. In addition to providing the installation of the reset elastic member 17, the abutment block also provides the limit of the piston 6, and jointly bears the pressure brought by the air pressure with the positioning cover 3, reducing the load on the positioning cover 3.

[0036] The top surface of the key bar 7 is provided with anti-skid lines 18. This structure improves the friction force of the key bar 7 to the roller and better transmits torque.

[0037] The surface of the shaft tube 2 is provided with a roller key 19, and the roller keys 19 are arranged in an array along the axial and circumferential directions of the side wall of the shaft tube 2. The roller key 19 includes a roller key 19 body and a roller 20 rotatably connected to the roller key 19 body through a rotating shaft, and the top of the roller 20 is higher than the surface of the shaft tube 2. This structure can improve the smoothness of introducing the coil. The limit of the outward extension of the key bar 7 is higher than the height of the roller 20. In some embodiments, the density of the roller keys 19 on the side walls at both ends of the shaft tube 2 is higher than the density in the middle of the shaft tube 2.

[0038] Ginseng Figure 6 In addition to converting the direction of the force, the wedge surface 9 also plays a role in amplifying the force. The wedge angle of the wedge surface 9 is , the elastic force is , is the circumferential pressure provided to the key bar 7, then Wedge Angle The angle is 5° in this embodiment, and the circumferential pressure A considerable magnification can be obtained. Where K is the sum of the circumferential pressures of each key bar 7, specifically the force generated on the key bar 7 It should also be divided by the number of corresponding key strips 7. In this embodiment, Since the expansion shaft structure in the present application is in a rotating state when in working state, the present application places the gas path structure at the axis and sets the gas pipe 1 at the axis of the expansion shaft. The present application sets multiple positioning covers 3 to form several independent piston structures. Even if a single piston 6 fails, the entire device can still work and has high stability.

[0039] In order to realize the normally closed structure to be achieved in the above text, the wedge angles of the piston 6 and the key strip 7 and the left-right positional relationship between the corresponding elastic member and the cavity that produces the air pressure change are set. Under normal pressure, the elastic force of the elastic member is greater than the pressure generated by the air pressure, and the piston 6 moves toward the side away from the elastic member. As the piston 6 moves, it is affected by the wedge surface 9 and extends outward in the radial direction, abutting against the roller outward to achieve the positioning of the roller. When the air pipe 1 is ventilated, the air pressure on one side of the piston 6 increases, and the piston 6 moves in the opposite direction to overcome the elastic force of the elastic member. The key strip 7 loses the support of the wedge surface 9 of the piston 6 and no longer provides pressure on the roller, thereby losing the corresponding friction force. Based on the above structure and the movement principle of the expansion shaft structure, it can be seen that air supply is only required when loading and unloading the expansion shaft, and the time to maintain the air pressure is shorter than that of the normally open expansion shaft structure, which can reduce the requirements for the stability of the air source.

[0040] The expansion shaft is divided into several sections by the positioning cover 3, and each section of the piston 6 cavity 4 has a piston structure. This feature has two main functions. The first is to increase the distribution density of the key strip 7 and generate sufficient friction to position the roller. The second is to reduce the requirements for the elastic member. In the present application, a piston 6 has only a single key strip 7 in the length direction. Under the condition of providing the same expansion force, the elastic force requirement of the elastic member is lower.

[0041] A normally closed mechanical expansion shaft, based on the above-mentioned expansion shaft structure, also includes a shaft head 21, a support wheel 22 and a connecting flange 23, both ends of the shaft tube 2 are fixedly connected to the shaft head 21, the shaft head 21 is equipped with a support wheel 22, the support wheel 22 and the shaft head 21 are rotatably connected through a bearing, the connecting flange 23 is coaxially connected to the shaft head 21 through a coupling 24, the end of the connecting flange 23 is fixedly equipped with a spline 25, the shaft head 21 and the connecting flange 23 are both provided with an air channel 27 connected to the air pipe 1, and the end of the air channel 27 is provided with an air nozzle 26. The structure is used to connect the expansion shaft structure to connect with the corresponding active chuck and passive chuck. The support wheel 22 plays a supporting role and bears the gravity of the expansion shaft and the coil. The expansion shaft structure is connected to the external power through the shaft head 21 and the connecting flange 23. One end of the expansion shaft is connected to the external power, and the air nozzle 26 at the other end is connected to the air source. The expansion shaft is connected to the external power through the spline 25, and the connection and disconnection with the external power are achieved through this structure.

[0042] The embodiments described above are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A normally closed mechanical expansion shaft structure, characterized in that: It includes a fixed structure and a piston structure. The fixed structure includes an air pipe, a shaft pipe and several positioning covers. The air pipe is inserted in the shaft pipe. Several positioning covers are installed between the air pipe and the shaft pipe. A piston cavity is formed between adjacent positioning covers. The piston structure includes a piston and a key strip. The piston is elastically connected to the positioning cover on one side of the piston cavity. The other side of the piston cavity is connected to the air pipe. The piston and the key strip are matched at a wedge angle. A through hole that adapts to the key strip is provided on the shaft pipe. When the thrust generated by the air pressure on the piston is less than the elastic force of the elastic member, the piston moves axially to push the key strip to extend radially outward.

2. A normally closed mechanical expansion shaft structure according to claim 1, characterized in that: The piston includes a piston body and a cone. The cross-section of the piston is annular. The inner edge of the piston body fits the outer wall of the trachea and the outer edge fits the inner wall of the shaft tube. The cone has a conical surface and cooperates with the key bar wedge angle through the conical surface. A positioning hole is provided at the bottom of the cone. The aperture of the positioning hole is larger than the outer diameter of the trachea. The elastic part is installed in the positioning hole and abuts against the bottom wall of the positioning hole.

3. The normally closed mechanical expansion shaft structure according to claim 1 is characterized in that: The outer edge of the piston is fitted with a plurality of key strips, and adjacent key strips are arranged at equal intervals. The key strips in the same piston cavity form a key strip group, and a key strip group has j key strips arranged at equal intervals. The mechanical expansion shaft has i groups of piston cavities, and the projections of the key strip groups in the same group of piston cavities about the axis coincide. The angle of deflection of the key strip group of the nth piston cavity about the axis is .

4. The normally closed mechanical expansion shaft structure according to claim 1 is characterized in that: The shaft tube is provided with pressing plates at both ends of the through hole in the length direction. On a plane perpendicular to the normal line of the top surface of the key bar, the projections of the pressing plates and the key bar are partially overlapped.

5. A normally closed mechanical expansion shaft structure according to claim 4, characterized in that: The key strip is provided with mounting holes at both ends in the length direction, and a reset elastic member is installed in the mounting hole, and the other end of the reset elastic member abuts against the bottom surface of the pressing plate.

6. A normally closed mechanical expansion shaft structure according to claim 4, characterized in that: The key bar is provided with an abutment block extending in the axial direction on one side close to the elastic member, the mounting hole is located in the abutment block, and the bottom of the piston is provided with a step for reaching the position. When the step wall of the step reaches the abutment block, the key bar reaches the travel limit on one side.

7. The normally closed mechanical expansion shaft structure according to claim 1 is characterized in that: The top surface of the key bar is provided with anti-slip grooves.

8. The normally closed mechanical expansion shaft structure according to claim 1 is characterized in that: A roller key is arranged on the surface of the shaft tube. The roller key comprises a roller key body and a roller rotatably connected to the roller key body through a rotating shaft. The top of the roller is higher than the surface of the shaft tube.

9. A normally closed mechanical expansion shaft structure according to claim 8, characterized in that: The roller keys are arranged in an array along the axial and circumferential directions of the side wall of the shaft tube.

10. A normally closed mechanical expansion shaft, characterized in that: It includes the normally closed mechanical expansion shaft structure as described in any one of claims 1 to 9, and also includes a shaft head, a support wheel and a connecting flange, both ends of the shaft tube are fixedly connected to the shaft head, a support wheel is mounted on the shaft head, the support wheel and the shaft head are rotatably connected through a bearing, the connecting flange is coaxially connected to the shaft head through a coupling, the end of the connecting flange is fixedly mounted with a spline, the shaft head and the connecting flange are both provided with an air duct connected to the air pipe, and an air nozzle is provided at the end of the air duct.

Images