CN116604604A - Multi-degree-of-freedom transmission mechanism - Google Patents

Abstract

The invention provides a multi-degree-of-freedom transmission mechanism, which comprises a transmission structure and an assembly structure; the transmission structure comprises a lifting module and an adjusting module, wherein a guide rail is arranged on the lifting module, one end of the adjusting module is in sliding connection with the guide rail, and a driving device is arranged on the other end of the adjusting module; the assembly structure comprises a driving gear set, a transmission assembly and a mounting seat connected with the adjusting module, wherein the output end of the driving device is in transmission connection with one end of the driving gear set, the other end of the driving gear set is inserted and connected with the mounting seat in a penetrating manner and in transmission connection with the transmission assembly, the transmission assembly is connected with the assembly, and the mechanical arm is detachably mounted on the assembly. The invention solves the problem of high assembly difficulty of the traditional robot transmission mechanism, and has the advantages of simple structure, low production cost and high assembly efficiency.

Description

Multi-degree-of-freedom transmission mechanism

Technical Field

The invention relates to the technical field of robots, in particular to a multi-degree-of-freedom transmission mechanism.

Background

The robot joint is an essential core component for realizing movement of the robot, in the structure of the industrial robot, a joint driving device is an important link for ensuring the manual performance of the industrial robot, a gear transmission device is used as a very important part, the robot joint is widely applied to the industrial robot joint, the manufacturing cost can be reduced by using less structure transmission and the movement as complex structure, the mechanism capable of realizing the less structure transmission multi-degree-of-freedom movement is designed to have great pushing effect on the development of the industrial robot, and the traditional industrial robot transmission mechanism is complex and has high assembly difficulty and high manufacturing cost for realizing multi-degree-of-freedom movement.

Disclosure of Invention

Based on the above, in order to solve the problem of high assembly difficulty of the traditional robot transmission mechanism, the invention provides a multi-degree-of-freedom transmission mechanism, which has the following specific technical scheme:

a multi-degree-of-freedom transmission mechanism comprises a transmission structure and an assembly structure; the transmission structure comprises a lifting module and an adjusting module, wherein a guide rail is arranged on the lifting module, one end of the adjusting module is in sliding connection with the guide rail, and a driving device is arranged on the other end of the adjusting module; the assembly structure comprises a driving gear set, a transmission assembly and a mounting seat connected with the adjusting module, wherein the output end of the driving device is in transmission connection with one end of the driving gear set, the other end of the driving gear set is inserted and connected with the mounting seat in a penetrating manner and in transmission connection with the transmission assembly, the transmission assembly is connected with the assembly, and the mechanical arm is detachably mounted on the assembly.

According to the multi-degree-of-freedom transmission mechanism, the guide rail is arranged, the adjusting module can slide on the guide rail to enable the adjusting module to finish lifting movement, the adjustment of the height position of the manipulator is realized, and grabbing operation can be finished better; the rotation of the transmission assembly can be controlled by arranging the driving gear set, so that the rotation of the assembly is controlled, and the grabbing angle of the manipulator can be adjusted; through being provided with transmission structure and assembly structure, above-mentioned structure is the setting of modularization, and all detachable dismantles and installs, and the setting of modularization can make production efficiency higher, and the cost is lower, and the installation of structure is more convenient, has solved the high problem of traditional robot transmission mechanism assembly degree of difficulty.

Further, the lifting module comprises a fixing seat, a threaded rod and a first driving piece, the guide rail is installed on the fixing seat, the threaded rod is rotationally assembled on the fixing seat, a mounting groove is formed in the fixing seat, the first driving piece is inserted into the mounting groove, the output end of the first driving piece is in transmission connection with the threaded rod, and a thread seat in threaded connection with the threaded rod is arranged on the adjusting module.

Further, the adjusting module comprises a first adjusting arm, a second adjusting arm and a third adjusting arm, a thread seat in threaded connection with the threaded rod is arranged at one end of the first adjusting arm, one end of the first adjusting arm is in sliding connection with the guide rail, the other end of the first adjusting arm is in rotary connection with the second adjusting arm, the second adjusting arm is rotationally assembled between the first adjusting arm and the third adjusting arm, the driving device is installed on the third adjusting arm, and the third adjusting arm is fixedly connected with the installation seat.

Further, the first adjusting arm and the second adjusting arm and the third adjusting arm are in rotary connection through a rotary rod; the adjusting module further comprises a second driving piece and a third driving piece, the second driving piece is arranged at the bottom of the first adjusting arm in an erected mode, a first driving belt is wound on the output end of the second driving piece, and the first driving belt is wound on a rotating rod at the joint of the first adjusting arm and the second adjusting arm; the third driving part is arranged at the bottom of the second adjusting arm, a second driving belt is wound on the output end of the third driving part, and the second driving belt is wound on a rotating rod at the joint of the second adjusting arm and the third adjusting arm.

Further, the driving gear set comprises a driving shaft, the driving shaft is provided with a limit post, the outer circumferential surface of the limit post is sleeved with a collar which is in threaded engagement with the mounting seat, the outer circumferential surface of the collar is provided with a plurality of external threads, the driving shaft sleeve is provided with a gear, the outer circumferential surface of the gear is provided with a tooth slot, the driving shaft is sleeved with a locking ring, and the locking ring is in butt joint with the driving shaft through threads; the end part of the driving shaft is provided with a driving end in transmission connection with the driving device.

Further, a plurality of positioning grooves for sleeving the gears are formed in the driving shaft at intervals; the driving shaft is provided with a connecting end, the other end far away from the driving end is provided with a connecting end, the connecting end is inserted into the connecting seat, the connecting seat is provided with a through hole, one end of the transmission assembly is installed on the installation seat, and the other end of the transmission assembly is inserted into and penetrates through the through hole and is fixedly connected with the assembly.

Further, the transmission assembly comprises a fixed cylinder, an inner layer transmission shaft and an outer layer transmission shaft which is movably sleeved outside the inner layer transmission shaft, the fixed cylinder is inserted into the through hole, the outer layer transmission shaft is movably assembled in the fixed cylinder, the inner layer transmission shaft and the outer layer transmission shaft can relatively rotate, inner layer transmission teeth are sleeved on the surface of the inner layer transmission shaft, outer layer transmission teeth are sleeved on the surface of the outer layer transmission shaft, the inner layer transmission teeth are located above the outer layer transmission teeth, inner layer driving teeth are sleeved on the bottom end of the inner layer transmission shaft, outer layer driving teeth are sleeved on the bottom end of the outer layer transmission shaft, and the outer layer driving teeth are located above the inner layer driving teeth.

Further, the assembly component comprises a swinging piece and a connecting piece sleeved on the outer surface of the fixed cylinder, the swinging piece is rotatably assembled on the connecting piece, and the swinging piece is rotatably provided with an assembly part detachably connected with the manipulator.

Further, the assembly component further comprises a swinging tooth, a connecting tooth and a rotating tooth sleeved on the assembly component, the swinging tooth is sleeved on the swinging piece and meshed with the outer driving tooth, one end of the connecting tooth is sleeved on the connecting piece and meshed with the inner driving tooth, and the other end of the connecting tooth is meshed with the rotating tooth.

Further, the manipulator includes setting element, fourth driving piece and is used for the cooperation centre gripping object first holder and second holder, the setting element with the assembly part is connected, first holder with the second holder rotate respectively install in on the setting element, the fourth driving piece is fixed in on the setting element be used for controlling first holder with the cooperation clamping state between the second holder.

Drawings

The invention will be further understood from the following description taken in conjunction with the accompanying drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments. Like reference numerals designate corresponding parts throughout the different views.

FIG. 1 is a schematic diagram of a multiple degree of freedom transmission mechanism according to an embodiment of the present invention;

FIG. 2 is a second schematic diagram of a multiple degree of freedom transmission mechanism according to an embodiment of the invention;

FIG. 3 is a schematic view of a portion of a multiple degree of freedom transmission mechanism according to an embodiment of the invention;

FIG. 4 is a schematic structural view of an assembly structure of a multiple degree of freedom transmission mechanism according to an embodiment of the present invention;

FIG. 5 is a second schematic structural view of an assembling structure of a multiple degree of freedom transmission mechanism according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a manipulator of a multiple degree of freedom transmission mechanism according to an embodiment of the invention;

fig. 7 is a schematic diagram of a driving gear set of a multiple degree of freedom transmission mechanism according to an embodiment of the invention.

Reference numerals illustrate:

1. a lifting module; 11. a guide rail; 12. a fixing seat; 13. a threaded rod; 2. an adjustment module; 21. a driving device; 22. a screw seat; 23. a first adjustment arm; 24. a second adjustment arm; 25. a third adjustment arm; 26. a second driving member; 27. a third driving member; 28. a first belt; 29. a second belt; 3. a drive gear set; 31. a drive shaft; 32. a limit column; 33. a collar; 34. a gear; 35. tooth slots; 36. a locking ring; 37. a positioning groove; 4. a transmission assembly; 41. a fixed cylinder; 42. inner layer transmission teeth; 43. outer layer transmission teeth; 44. inner layer driving teeth; 45. outer layer driving teeth; 5. a mounting base; 6. assembling the assembly; 61. a swinging member; 62. a connecting piece; 63. a fitting; 64. oscillating teeth; 65. a connecting tooth; 66. rotating the teeth; 7. a manipulator; 71. a positioning piece; 72. a fourth driving member; 73. a first clamping member; 74. a second clamping member; 8. and a connecting seat.

Detailed Description

The present invention will be described in further detail with reference to the following examples thereof in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the invention.

It will be understood that when an element is referred to as being "fixed to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like are used herein for illustrative purposes only and are not meant to be the only embodiment.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

The terms "first" and "second" in this specification do not denote a particular quantity or order, but rather are used for distinguishing between similar or identical items.

1-5, a multiple degree of freedom transmission mechanism in one embodiment of the invention includes a transmission structure and an assembly structure; the transmission structure comprises a lifting module 1 and an adjusting module 2, wherein a guide rail 11 is arranged on the lifting module 1, one end of the adjusting module 2 is in sliding connection with the guide rail 11, and a driving device 21 is arranged on the other end of the adjusting module 2; the assembly structure comprises a driving gear set 3, a transmission assembly 4 and a mounting seat 5 connected with the adjusting module 2, wherein the output end of a driving device 21 is in transmission connection with one end of the driving gear set 3, the other end of the driving gear set 3 is inserted and connected with the mounting seat 5 in a penetrating manner and in transmission connection with the transmission assembly 4, the transmission assembly 4 is connected with an assembly 6, and a manipulator 7 is detachably arranged on the assembly 6.

According to the multi-degree-of-freedom transmission mechanism, the guide rail 11 is arranged, the lifting movement of the adjusting module 2 can be completed by sliding the adjusting module on the guide rail 11, the adjustment of the height position of the manipulator 7 is realized, and the grabbing operation can be completed better; by the driving gear set 3, the rotation of the transmission assembly 4 can be controlled, so that the rotation of the assembly 6 is controlled, and the grabbing angle of the manipulator 7 can be adjusted; through being provided with transmission structure and assembly structure, above-mentioned structure is the setting of modularization, and all detachable dismantles and installs, and the setting of modularization can make production efficiency higher, and the cost is lower, and the installation of structure is more convenient, has solved the high problem of traditional robot transmission mechanism assembly degree of difficulty.

Specifically, the guide rail 11 is disposed in a vertical direction.

As shown in fig. 1-3, in one embodiment, the lifting module 1 includes a fixed seat 12, a threaded rod 13 and a first driving member, the guide rail 11 is installed on the fixed seat 12, the threaded rod 13 is rotatably assembled on the fixed seat 12, a mounting groove is provided in the fixed seat 12, the first driving member is inserted in the mounting groove, an output end of the first driving member is in transmission connection with the threaded rod 13, and a thread seat 22 in threaded connection with the threaded rod 13 is provided on the adjusting module 2. Thus, by being provided with the first driving member, the first driving member drives the threaded rod 13 to rotate, thereby utilizing the threaded connection between the threaded seat 22 and the threaded rod 13, the lifting movement of the adjusting module 2 along the guide rail 11 is controlled.

As shown in fig. 1-3, in one embodiment, the adjusting module 2 includes a first adjusting arm 23, a second adjusting arm 24 and a third adjusting arm 25, a threaded seat 22 screwed with the threaded rod 13 is provided on one end of the first adjusting arm 23, one end of the first adjusting arm 23 is slidably connected with the guide rail 11, the other end of the first adjusting arm 23 is rotatably connected with the second adjusting arm 24, the second adjusting arm 24 is rotatably assembled between the first adjusting arm 23 and the third adjusting arm 25, the driving device 21 is mounted on the third adjusting arm 25, and the third adjusting arm 25 is fixedly connected with the mounting seat 5.

As shown in fig. 3, in one of the embodiments, the first adjusting arm 23 and the second adjusting arm 24 and the third adjusting arm 25 are both rotatably connected by a rotating rod; the adjusting module 2 further comprises a second driving piece 26 and a third driving piece 27, the second driving piece 26 is erected at the bottom of the first adjusting arm 23, a first driving belt 28 is wound on the output end of the second driving piece 26, and the first driving belt 28 is wound on a rotating rod at the joint of the first adjusting arm 23 and the second adjusting arm 24; the third driving part 27 is arranged at the bottom of the second adjusting arm 24, and a second driving belt 29 is wound on the output end of the third driving part 27, and the second driving belt 29 is wound on a rotating rod at the joint of the second adjusting arm 24 and the third adjusting arm 25. In this way, the second driving piece 26 and the third driving piece 27 are arranged to drive the transmission of the first transmission belt 28 and the transmission of the second transmission belt 29 respectively, so that the rotation of the second adjusting arm 24 and the third adjusting arm 25 is adjusted, and the degree of freedom of the manipulator 7 is adjusted, so that the horizontal movement can be realized in multiple directions.

As shown in fig. 7, in one embodiment, the driving gear set 3 includes a driving shaft 31, the driving shaft 31 is provided with a limit post 32, the outer circumferential surface of the limit post 32 is sleeved with a collar 33 screwed in the mounting seat 5, the outer circumferential surface of the collar 33 is provided with a plurality of external threads, the driving shaft 31 is sleeved with a gear 34, the outer circumferential surface of the gear 34 is provided with a tooth slot 35, the driving shaft 31 is sleeved with a locking ring 36, and the locking ring 36 is in butt joint with the driving shaft 31 through threads; the end of the drive shaft 31 is provided with a drive end in driving connection with the drive means 21.

As shown in fig. 4, 5 and 7, in one embodiment, a plurality of positioning slots 37 for sleeving the gears 34 are arranged on the driving shaft 31 at intervals; the other end of the driving shaft 31 far away from the driving end is a connecting end, the connecting end is inserted into the connecting seat 8, a through hole is formed in the connecting seat 8, one end of the transmission assembly 4 is installed on the installation seat 5, and the other end of the transmission assembly 4 is inserted into the through hole and fixedly connected with the assembly 6. Thus, the driving end can connect the driving shaft 31 with the driving device 21, and the driving device 21 can control the driving shaft 31 to rotate, so that the gear 34 can rotate, and the driving of the gear 34 is facilitated; by providing the positioning grooves 37, the position height of each positioning groove 37 is different, and the gear 34 can adjust the driving height of the gear 34 by adjusting the mounting position between the respective positioning grooves 37.

As shown in fig. 4 and 5, in one embodiment, the transmission assembly 4 includes a fixed cylinder 41, an inner transmission shaft, and an outer transmission shaft movably sleeved outside the inner transmission shaft, the fixed cylinder 41 is inserted into the through hole, the outer transmission shaft is movably assembled in the fixed cylinder 41, the inner transmission shaft and the outer transmission shaft can rotate relatively, an inner transmission tooth 42 is sleeved on the surface of the inner transmission shaft, an outer transmission tooth 43 is sleeved on the surface of the outer transmission shaft, the inner transmission tooth 42 is located above the outer transmission tooth 43, an inner driving tooth 44 is sleeved on the bottom end of the inner transmission shaft, an outer driving tooth 45 is sleeved on the bottom end of the outer transmission shaft, and the outer driving tooth 45 is located above the inner driving tooth 44. So, through being provided with inlayer transmission shaft and outer transmission shaft, same drive gear group 3 can realize simultaneously to inlayer drive tooth 44 and the rotary drive of outer drive tooth 45 or different drive gear groups 3 can be respectively to inlayer drive tooth 44 and the rotary drive of outer drive tooth 45 through same transmission structure, has saved installation space, has improved the stability of structure.

As shown in fig. 4 and 5, in one embodiment, the assembly component 6 includes a swinging member 61 and a connecting member 62 sleeved on the outer surface of the fixed cylinder 41, the swinging member 61 is rotatably assembled on the connecting member 62, and an assembly member 63 detachably connected to the manipulator 7 is rotatably provided on the swinging member 61.

As shown in fig. 4 and 5, in one embodiment, the assembly 6 further includes a swinging tooth 64, a connecting tooth 65, and a rotating tooth 66 sleeved on the assembly 63, the swinging tooth 64 is sleeved on the swinging member 61 and engaged with the outer driving tooth 45, one end of the connecting tooth 65 is sleeved on the connecting member 62 and engaged with the inner driving tooth 44, and the other end of the connecting tooth 65 is engaged with the rotating tooth 66. Thus, by arranging the swinging teeth 64, the outer layer transmission shaft controls the rotation of the outer layer driving teeth 45, thereby controlling the rotation of the swinging teeth 64, controlling the swinging of the swinging piece 61 on the connecting piece 62, and realizing the adjustment of the grabbing angle of the manipulator 7; the inner layer transmission shaft controls the rotation of the inner layer driving teeth 44 by being provided with the connecting teeth 65 and the rotating teeth 66, so that the connecting teeth 65 are used for controlling the rotation of the rotating teeth 66, and the rotation of the assembly 63 on the swinging member 61 is controlled, so that the grabbing position of the manipulator 7 is adjusted.

As shown in fig. 6, in one of the embodiments, the manipulator 7 includes a positioning member 71, a fourth driving member 72, and a first clamping member 73 and a second clamping member 74 for cooperatively clamping an object, the positioning member 71 is connected to the fitting member 63, the first clamping member 73 and the second clamping member 74 are rotatably mounted on the positioning member 71, respectively, and the fourth driving member 72 is fixed on the positioning member 71 and is used for controlling the clamping state of the cooperation between the first clamping member 73 and the second clamping member 74. In this way, by providing the fourth driving member 72, control of the gripping state between the first gripping member 73 and the second gripping member 74 is achieved, facilitating completion of the object gripping operation.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (10)

1. A multiple degree of freedom transmission mechanism, comprising:

the transmission structure comprises a lifting module and an adjusting module, wherein a guide rail is arranged on the lifting module, one end of the adjusting module is in sliding connection with the guide rail, and a driving device is arranged on the other end of the adjusting module;

the assembly structure comprises a driving gear set, a transmission assembly and a mounting seat connected with the adjusting module, wherein the output end of the driving device is in transmission connection with one end of the driving gear set, the other end of the driving gear set is inserted and connected with the mounting seat in a penetrating manner and in transmission connection with the transmission assembly, the transmission assembly is connected with the assembly, and the mechanical arm is detachably mounted on the assembly.

2. The multi-degree-of-freedom transmission mechanism of claim 1, wherein the lifting module comprises a fixed seat, a threaded rod and a first driving member, the guide rail is mounted on the fixed seat, the threaded rod is rotatably assembled on the fixed seat, a mounting groove is formed in the fixed seat, the first driving member is inserted into the mounting groove, the output end of the first driving member is in transmission connection with the threaded rod, and a threaded seat in threaded connection with the threaded rod is arranged on the adjusting module.

3. The multiple degree of freedom transmission mechanism of claim 2 wherein the adjustment module includes a first adjustment arm, a second adjustment arm and a third adjustment arm, wherein one end of the first adjustment arm is provided with a threaded seat in threaded connection with the threaded rod, one end of the first adjustment arm is slidably connected with the guide rail, the other end of the first adjustment arm is rotatably connected with the second adjustment arm, the second adjustment arm is rotatably assembled between the first adjustment arm and the third adjustment arm, the driving device is mounted on the third adjustment arm, and the third adjustment arm is fixedly connected with the mounting seat.

4. A multiple degree of freedom transmission mechanism according to claim 3, wherein the first and second adjustment arms and the second and third adjustment arms are rotatably connected by a rotary rod; the adjusting module further comprises a second driving piece and a third driving piece, the second driving piece is arranged at the bottom of the first adjusting arm in an erected mode, a first driving belt is wound on the output end of the second driving piece, and the first driving belt is wound on a rotating rod at the joint of the first adjusting arm and the second adjusting arm; the third driving part is arranged at the bottom of the second adjusting arm, a second driving belt is wound on the output end of the third driving part, and the second driving belt is wound on a rotating rod at the joint of the second adjusting arm and the third adjusting arm.

5. The multi-degree-of-freedom transmission mechanism of claim 1, wherein the driving gear set comprises a driving shaft, the driving shaft is provided with a limit post, the outer circumferential surface of the limit post is sleeved with a collar which is in threaded engagement with the mounting seat, the outer circumferential surface of the collar is provided with a plurality of external threads, the driving shaft sleeve is provided with a gear, the outer circumferential surface of the gear is provided with a tooth socket, the driving shaft is sleeved with a locking ring, and the locking ring is in butt joint with the driving shaft through threads; the end part of the driving shaft is provided with a driving end in transmission connection with the driving device.

6. The multiple degree of freedom transmission mechanism of claim 5 wherein the drive shaft is provided with a plurality of positioning slots for the gear to socket; the driving shaft is provided with a connecting end, the other end far away from the driving end is provided with a connecting end, the connecting end is inserted into the connecting seat, the connecting seat is provided with a through hole, one end of the transmission assembly is installed on the installation seat, and the other end of the transmission assembly is inserted into and penetrates through the through hole and is fixedly connected with the assembly.

7. The multiple degree of freedom drive mechanism of claim 6, wherein the drive assembly includes a fixed cylinder, an inner drive shaft and an outer drive shaft movably sleeved outside the inner drive shaft, the fixed cylinder is inserted into the through hole, the outer drive shaft is movably assembled in the fixed cylinder, the inner drive shaft and the outer drive shaft can rotate relatively, an inner drive tooth is sleeved on the surface of the inner drive shaft, an outer drive tooth is sleeved on the surface of the outer drive shaft, the inner drive tooth is located above the outer drive tooth, an inner drive tooth is sleeved on the bottom end of the inner drive shaft, an outer drive tooth is sleeved on the bottom end of the outer drive shaft, and the outer drive tooth is located above the inner drive tooth.

8. The multiple degree of freedom transmission mechanism of claim 7 wherein the assembly includes a swinging member rotatably mounted to the connecting member and a connecting member sleeved on the outer surface of the fixed barrel, the swinging member rotatably provided with an assembly member detachably connected to the manipulator.

9. The multiple degree of freedom transmission mechanism of claim 8 wherein the assembly further includes a rocking tooth, a connecting tooth and a rotating tooth sleeved on the assembly, the rocking tooth being sleeved on the rocking member and engaged with the outer driving tooth, one end of the connecting tooth being sleeved on the connecting member and engaged with the inner driving tooth, the other end of the connecting tooth being engaged with the rotating tooth.

10. The multiple degree of freedom transmission mechanism of claim 9 wherein the manipulator includes a positioning member, a fourth driving member, and first and second clamping members for engaging and clamping an object, the positioning member being coupled to the assembly member, the first and second clamping members being rotatably mounted to the positioning member, respectively, the fourth driving member being secured to the positioning member and adapted to control the engaged state between the first and second clamping members.