Electric endoscope anastomat jaw bending structure

Abstract

The application discloses a kind of electric endoscope anastomat jaw bending structure, it is related to medical instrument technical field, including shell structure and support structure, further including outer sleeve, cutting knife assembly, end effector, short sleeve and inner sleeve and center rod, the shell structure has bending knob upper housing and bending knob lower housing composition, the support structure is by upper support and lower support composition and and gun body rotatable connection;The electric endoscope anastomat jaw bending structure can realize that endoscope anastomat jaw is bent automatically, it is easy to operate, the small head end of safety pin moves from the proximal end of slot to the distal end, under the extrusion of the small head end of safety pin, brake proximal end is deformed to both sides, the ratchet on the brake is matched with the ratchet on steering pull rod one and steering pull rod two, prevent steering pull rod one and steering pull rod two axial movement, further reach the purpose of preventing end effector and cutting knife assembly bending when jaw closed state, and high safety.

Description

Technical Field

[0001] This invention relates to the field of medical device technology, specifically to a bending structure for the jaws of an electric laparoscopic stapler. Background Technology

[0002] Electric laparoscopic staplers are widely used in laparoscopic surgery. An electric laparoscopic stapler mainly consists of an end effector, a cutting blade assembly, a control button, a motor, and a transmission mechanism, used for cutting and anastomosing tissues within the human body. The control button drives the motor, which provides the driving power. The transmission mechanism then provides this power to the end effector and the cutting blade assembly. The end effector includes a pivotable jaw that can close and open to clamp and release tissue. The motor drives the cutting blade assembly forward and backward via the transmission mechanism. The forward movement of the cutting blade assembly cuts and anastomoses the tissue; after cutting and anastomosis are completed, the backward movement of the cutting blade assembly resets its original position.

[0003] However, existing electric staplers and the end actuators of current manual cutting staplers mostly rely on manual rotation for bending. During operation, clinicians need one hand to stabilize the stapler and the other to control the bending, increasing physician fatigue, distracting their attention, and causing significant inconvenience. Furthermore, existing electrically bendable laparoscopic staplers can still bend even when the tissue is clamped, if the bending control switch is triggered, which can cause tissue tearing and poses a significant clinical risk. Therefore, we propose a clamp bending structure for an electric laparoscopic stapler. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a bending structure for the jaws of an electric endoscopic stapler, which solves the problems mentioned in the background section.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a jaw bending structure for an electric laparoscopic stapler, comprising a housing structure and a support structure, and further comprising an outer sleeve, a cutting blade assembly, an end effector, a short sleeve, an inner sleeve, and a central rod.

[0006] The housing structure consists of an upper outer shell for the bendable knob and a lower outer shell for the bendable knob. The support structure consists of an upper support and a lower support and is rotatably connected to the gun body.

[0007] The inner cavity of the shell structure is provided with a transmission mechanism, which includes an output gear, a gear ring, a gear, a screw, a first steering control seat and a second steering control seat, a steering tie rod one, a steering tie rod two, a steering tie rod three, a steering tie rod four, a steering fixing seat, and a steering adjustment seat;

[0008] The inner cavity of the housing structure is equipped with a motor, which is fixedly mounted on the bracket structure. One end of the motor output shaft is fixedly connected to an output gear, which is located in the inner cavity of the gear ring and meshes with the gear ring. The gear ring is installed in the inner cavity of the upper outer shell of the bend knob and the lower outer shell of the bend knob.

[0009] The outer tube is equipped with an anti-bending safety structure, which includes a safety pin and a brake. The safety pin has a large end and a small end.

[0010] Preferably, the upper and lower supports are provided with grooves, and the first steering control seat, the second steering control seat, the screw, and the gear are all located within the groove cavities. The gear is fixedly connected to the middle position of the screw's axial direction. The first and second steering control seats can move axially back and forth within the upper and lower supports, while the screw is rotatable but not movable. The first and second steering control seats move synchronously in opposite directions.

[0011] Preferably, both ends of the screw are threaded with opposite thread directions. The first and second steering control seats are each provided with internal threads that mate with the threads at both ends of the screw, guide blocks, protrusions, and baffles. Both the upper and lower supports are provided with sliding grooves.

[0012] Preferably, when the first steering control seat and the second steering control seat move, the guide blocks on the first steering control seat and the second steering control seat move within the grooves on the upper bracket and the lower bracket.

[0013] Preferably, both the proximal and distal ends of the first and second steering tie rods are provided with positioning holes. The protrusions on the first and second steering control seats are respectively connected to the proximal positioning holes of the first and second steering tie rods. Both the proximal and distal ends of the third and fourth steering tie rods are provided with hooks in opposite directions. The proximal hooks of the third and fourth steering tie rods are pivotally connected to the distal positioning holes of the first and second steering tie rods.

[0014] Preferably, the steering fixing seat also has two positioning holes, and the two positioning holes are pivotally connected to the distal hooks of steering tie rod three and steering tie rod four, respectively. The steering fixing seat has a crescent-shaped groove, and the steering adjusting seat has a crescent-shaped protrusion. The crescent-shaped groove and the crescent-shaped protrusion cooperate with each other, and the steering fixing seat can drive the steering adjusting seat to bend. The back of the steering adjusting seat has a groove, and the steering adjusting seat accommodates the cutting blade assembly through the groove and provides guidance for the cutting blade assembly. The steering adjusting seat can drive the cutting blade assembly to bend.

[0015] Preferably, a PCB board is fixedly mounted on the upper and lower supports, and three photoelectric sensors are arranged axially on the PCB board. As the steering tie rod one and steering tie rod two move axially, the baffle passes through the three photoelectric sensors. When a photoelectric sensor is triggered, the motor stops rotating until the photoelectric sensor button is released, at which point the motor will start again when the photoelectric sensor is triggered again.

[0016] Preferably, the first and second steering tie rods are provided with ratchet teeth. The brake is an elastic body and has a groove structure, the width of which gradually narrows from the proximal end to the distal end. The brake is provided with another set of ratchet teeth. The small end of the safety pin has a clearance fit with the proximal end of the groove structure and an interference fit with the distal end of the groove structure. When the jaws are closed, the outer sleeve drives the safety pin to move distally. The small end of the safety pin moves from the proximal end of the groove to the distal end. Under the pressure of the small end of the safety pin, the proximal end of the brake deforms to both sides. The ratchet teeth on the brake engage with the ratchet teeth on the first and second steering tie rods to prevent the first and second steering tie rods from moving axially, thereby preventing the end effector and cutting blade assembly from bending when the jaws are closed.

[0017] Preferably, the outer sleeve is provided with a safety pin groove, the inner cavity of the outer sleeve is fitted with an inner sleeve, the inner sleeve is fitted to the surface of the center rod, the end of the center rod is provided with a boss, the end actuator is connected to the short sleeve, the end of the short sleeve is provided with a connecting piece, and the connecting piece is connected to one end of the outer sleeve.

[0018] Preferably, the lower outer shell and the upper outer shell of the bending knob are provided with positioning ribs, and the toothed ring is provided with positioning grooves around its periphery, with the positioning grooves and positioning ribs cooperating.

[0019] This invention provides a bending structure for the jaws of an electric laparoscopic stapler, which has the following advantages:

[0020] 1. The electric laparoscopic stapler jaw bending structure, through the coordinated use of an output gear, gear ring, gear, screw, first steering control seat and second steering control seat, steering tie rod one, steering tie rod two, steering tie rod three, steering tie rod four, steering fixing seat, steering adjustment seat and motor, can realize the automatic bending of the laparoscopic stapler jaw, which is convenient to operate. The small end of the safety pin moves from the proximal end of the groove to the distal end. Under the compression of the small end of the safety pin, the proximal end of the brake deforms to both sides. The ratchet on the brake engages with the ratchet on steering tie rod one and steering tie rod two to prevent the axial movement of steering tie rod one and steering tie rod two. Thus, when the jaw is closed, it can prevent the end actuator and cutting blade assembly from bending, which is highly safe.

[0021] 2. The electric endoscopic stapler jaw bending structure has a protruding baffle on the first and second steering control seats. The support structure is equipped with three photoelectric sensors. During bending, the baffle moves with the first and second steering control seats. The baffle moves to the positions of the three photoelectric sensors, which correspond to the left and right limits and the zero position, respectively. When the switch of any photoelectric sensor is triggered, the motor will stop rotating, thereby realizing the identification and control of the bending zero position and the left and right limits.

[0022] 3. The electric laparoscopic stapler jaw bending structure has positioning ribs inside the lower and upper housings of the bending knob, and positioning grooves around the toothed ring. The positioning grooves and positioning ribs cooperate to fix the lower and upper housings of the bending knob and the toothed ring. The motor is a small geared brushless DC motor. The toothed ring and the lower and upper housings of the bending knob increase the lever arm. Rotating the bending knob housing drives the toothed ring, which in turn drives the transmission mechanism to achieve the bending of the end effector and the cutting blade assembly. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention;

[0024] Figure 2 This is a partial structural schematic diagram of the present invention;

[0025] Figure 3 This is a schematic diagram of the front structure of the gear ring of the present invention;

[0026] Figure 4 This is a schematic diagram of the structure of the back of the gear ring of the present invention;

[0027] Figure 5 This is a front structural schematic diagram of the steering adjustment remote transmission of the present invention;

[0028] Figure 6 This is a schematic diagram of the reverse structure of the steering adjustment remote transmission of the present invention;

[0029] Figure 7 This is a schematic diagram of the structure of the third steering tie rod of the present invention.

[0030] Figure 8 This is a schematic diagram of the jaws of the present invention in the open state;

[0031] Figure 9 This is a schematic diagram of the structure of the steering fixing seat and the steering adjusting seat of the present invention;

[0032] Figure 10 This is a schematic diagram of the steering control seat of the present invention.

[0033] Figure 11 This is a schematic diagram of the shell structure of the present invention;

[0034] Figure 12 This is a structural schematic diagram of the appearance of the present invention.

[0035] In the diagram: 1. Steering tie rod one; 2. Steering tie rod two; 3. Steering tie rod three; 4. Steering tie rod four; 5. End actuator; 6. Short sleeve; 7. Connecting piece; 8. Safety pin; 9. Brake; 10. Inner sleeve; 11. Lower housing of the bend knob; 12. Upper housing of the bend knob; 13. Slide groove; 14. Upper bracket; 15. Center rod; 16. Safety pin slot; 17. Lower bracket; 18. Outer sleeve; 20. Boss; 1. Steering mounting base; 22. Cutting blade assembly; 23. PCB board; 24. Second steering control base; 25. Screw; 26. Gear; 27. First steering control base; 28. Motor; 29. ​​Gear ring; 30. Output gear; 31. Photoelectric sensor; 34. Steering adjustment base; 35. Racket; 36. Crescent-shaped groove; 37. Crescent-shaped protrusion; 38. Internal thread; 39. Protrusion; 40. Baffle; 41. Guide block. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0037] Please see Figures 1 to 12 The present invention provides a technical solution: a jaw bending structure for an electric laparoscopic stapler, comprising a shell structure and a support structure, and further comprising an outer sleeve 18, a cutting blade assembly 22, an end actuator 5, a short sleeve 6, an inner sleeve 10, and a central rod 15.

[0038] The housing structure consists of an upper outer shell 12 for the bendable knob and a lower outer shell 11 for the bendable knob. The support structure consists of an upper support 14 and a lower support 17 and is rotatably connected to the gun body.

[0039] The inner cavity of the shell structure is provided with a transmission mechanism, which includes an output gear 30, a gear ring 29, a gear 26, a screw 25, a first steering control seat 27 and a second steering control seat 24, a steering tie rod 1, a steering tie rod 2, a steering tie rod 3, a steering tie rod 4, a steering fixing seat 21, and a steering adjusting seat 34.

[0040] The inner cavity of the housing structure is equipped with a motor 28, which is fixedly mounted on the bracket structure. One end of the output shaft of the motor 28 is fixedly connected to an output gear 30. The output gear 30 is located in the inner cavity of the gear ring 29 and meshes with the gear ring 29. The gear ring 29 is installed in the inner cavity of the upper outer shell 12 and the lower outer shell 11 of the bend knob.

[0041] The outer tube 18 is equipped with an anti-bending safety structure, which includes a safety pin 8 and a brake 9. The safety pin 8 has a large end and a small end.

[0042] The upper bracket 14 and lower bracket 17 are provided with grooves, and the first steering control seat 27, the second steering control seat 24, the screw 25, and the gear 26 are all located in the inner cavity of the grooves. The gear 26 is fixedly connected to the middle position of the screw 25 in the axial direction. The first steering control seat 27 and the second steering control seat 24 can move axially back and forth within the upper bracket 14 and the lower bracket 17. The screw 25 can rotate but cannot move. The first steering control seat 27 and the second steering control seat 24 move synchronously in opposite directions.

[0043] The screw 25 has threads at both ends with opposite thread directions. The first steering control seat 27 and the second steering control seat 24 are each provided with internal threads 38 that mate with the threads at both ends of the screw 25, guide blocks 41, protrusions 39, and baffles 40. The upper bracket 14 and the lower bracket 17 are each provided with sliding grooves 13.

[0044] When the first steering control seat 27 and the second steering control seat 24 move, the guide blocks 41 on the first steering control seat 27 and the second steering control seat 24 move within the slide grooves 13 on the upper bracket 14 and the lower bracket 17.

[0045] The steering tie rod 1 and steering tie rod 2 are provided with positioning holes at their proximal and distal ends. The protrusions 39 on the first steering control seat 27 and the second steering control seat 24 are respectively connected to the positioning holes at the proximal ends of steering tie rod 1 and steering tie rod 2. The steering tie rod 3 and steering tie rod 4 are provided with hooks in opposite directions at their proximal and distal ends; the hooks at the proximal ends of steering tie rod 3 and steering tie rod 4 are pivotally connected to the positioning holes at the distal ends of steering tie rod 1 and steering tie rod 2.

[0046] The steering fixing seat 21 is also provided with two positioning holes, and the two positioning holes are pivotally connected to the distal hooks of the steering tie rod 3 and the steering tie rod 4, respectively. The steering fixing seat 21 is provided with a crescent-shaped groove 36, and the steering adjusting seat 34 is provided with a crescent-shaped protrusion 37. The crescent-shaped groove 36 and the crescent-shaped protrusion 37 cooperate with each other, and the steering fixing seat 21 can drive the steering adjusting seat 34 to bend. The back of the steering adjusting seat 34 is provided with a groove, and the steering adjusting seat 34 accommodates the cutting blade assembly 22 through the groove and provides guidance for the cutting blade assembly 22. The steering adjusting seat 34 can drive the cutting blade assembly 22 to bend.

[0047] A PCB board 23 is fixedly mounted on the upper bracket 14 and the lower bracket 17, and three photoelectric sensors 31 are arranged axially on the PCB board 23. As the steering tie rod 1 and the steering tie rod 2 move axially, the baffle 40 passes through the three photoelectric sensors 31. When a photoelectric sensor 31 is triggered, the motor 28 stops rotating. The motor 28 will only start again when the photoelectric sensor 31 button is released and triggered again.

[0048] The steering tie rod 1 and steering tie rod 2 are equipped with ratchet teeth 35. The brake 9 is an elastic body and has a groove structure, the width of which gradually narrows from the proximal end to the distal end. The brake 9 is also equipped with another set of ratchet teeth 35. The small end of the safety pin 8 has a clearance fit with the proximal end of the groove structure and an interference fit with the distal end of the groove structure. When the jaws are closed, the outer sleeve 18 moves the safety pin 8 to the distal end.

[0049] The small end of the safety pin 8 moves from the proximal end to the distal end of the groove. Under the pressure of the small end of the safety pin 8, the proximal end of the brake 9 deforms to both sides. The ratchet 35 on the brake 9 engages with the ratchet 35 on the steering tie rod 1 and the steering tie rod 2 to prevent the steering tie rod 1 and the steering tie rod 2 from moving axially. This prevents the end actuator 5 and the cutting blade assembly 22 from bending when the jaws are closed.

[0050] The outer sleeve 18 is provided with a safety pin groove 16, and the inner sleeve 10 is sleeved in the inner cavity of the outer sleeve 18. The inner sleeve 10 is sleeved to the surface of the center rod 15. The end of the center rod 15 is provided with a boss 20. The end actuator 5 is connected to the short sleeve 6. The end of the short sleeve 6 is provided with a connecting piece 7, and the connecting piece 7 is connected to one end of the outer sleeve 18.

[0051] The lower outer shell 11 and the upper outer shell 12 of the bending knob are provided with positioning ribs, and the toothed ring 29 is provided with positioning grooves around its periphery. The positioning grooves and positioning ribs cooperate with each other.

[0052] In summary, the electric laparoscopic stapler jaw bending structure, during use, has the motor 28 fixedly connected to the support structure, and the support structure and the gun body fixedly connected; the screw 25 rotates in place relative to the support structure without axial movement; the first steering control seat 27 and the second steering control seat 24 are fixedly connected to the first steering tie rod 1 and the second steering tie rod 2, respectively; the third steering tie rod 3 and the fourth steering tie rod 4 are pivotally connected to the first steering tie rod 1 and the second steering tie rod 2, and the third steering tie rod 3 and the fourth steering tie rod 4 are pivotally connected to the steering fixing seat 21; the steering fixing seat 21 is fixedly connected to the end effector 5; the output gear 30 of the motor 28 drives the gear ring 29 to rotate, and the gear... The ring 29 drives the gear 26 to rotate, and the gear 26 drives the screw 25 to rotate. The screw 25 has reverse threads on both sides. The first steering control seat 27 and the second steering control seat 24 are threaded to both sides of the screw 25. As the screw 25 rotates, the first steering control seat 27 and the second steering control seat 24 move forward or backward axially, respectively. This causes the steering tie rod 1 and the steering tie rod 2 to move forward or backward axially, respectively. This causes the steering tie rod 3 and the steering tie rod 4 to move forward or backward axially, respectively. This causes the steering fixed seat 21 to bend to the left or right, and then causes the end actuator 5 and the cutting blade assembly 22 to bend to the left or right.

[0053] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A bending structure for the jaws of an electric laparoscopic stapler, comprising a housing structure and a support structure, characterized in that: It also includes an outer sleeve (18), a cutting blade assembly (22), an end effector (5), a short sleeve (6), an inner sleeve (10), and a center rod (15). The housing structure consists of an upper outer shell (12) for the bend knob and a lower outer shell (11) for the bend knob, and the support structure consists of an upper support (14) and a lower support (17). The inner cavity of the housing structure is provided with a transmission mechanism, which includes an output gear (30), a gear ring (29), a gear (26), a screw (25), a first steering control seat (27) and a second steering control seat (24), a steering tie rod one (1), a steering tie rod two (2), a steering tie rod three (3), a steering tie rod four (4), a steering fixing seat (21), and a steering adjustment seat (34). The outer tube (18) is equipped with an anti-bending safety structure, which includes a safety pin (8) and a brake (9). The safety pin (8) has a large end and a small end. The first steering tie rod (1) and the second steering tie rod (2) are provided with ratchet teeth (35). The brake (9) is an elastic body and has a groove structure. The width of the groove structure gradually narrows from the proximal end to the distal end. The brake (9) is provided with another set of ratchet teeth (35). The small end of the safety pin (8) is clearance-fitted with the proximal end of the groove structure and interference-fitted with the distal end of the groove structure. The ratchet teeth (35) on the brake (9) are engaged with the ratchet teeth (35) on the first steering tie rod (1) and the second steering tie rod (2). When the jaws are closed, the outer sleeve (18) drives the safety pin (8) to move to the far end. The small end of the safety pin (8) moves from the proximal end of the safety pin slot (16) to the far end. Under the pressure of the small end of the safety pin (8), the proximal end of the brake (9) deforms to both sides. The ratchet (35) on the brake (9) engages with the ratchet (35) on the first steering tie rod (1) and the second steering tie rod (2) to prevent the first steering tie rod (1) and the second steering tie rod (2) from moving axially. Thus, when the jaws are closed, the purpose of preventing the end actuator (5) and the cutting blade assembly (22) from bending is achieved.

2. The electric laparoscopic stapler jaw bending structure according to claim 1, characterized in that: The inner cavity of the housing structure is equipped with a motor (28), which is fixedly mounted on the bracket structure. One end of the output shaft of the motor (28) is fixedly connected to an output gear (30). The output gear (30) is located in the inner cavity of the gear ring (29) and meshes with the gear ring (29). The gear ring (29) is installed in the inner cavity of the upper outer shell (12) of the bend knob and the lower outer shell (11) of the bend knob. The upper bracket (14) and lower bracket (17) are provided with grooves, and the first steering control seat (27), the second steering control seat (24), the screw (25), and the gear (26) are all located in the inner cavity of the groove. The gear (26) is fixedly connected to the middle position of the screw (25) in the axial direction. The first steering control seat (27) and the second steering control seat (24) can move axially back and forth in the upper bracket (14) and lower bracket (17). The screw (25) can rotate but cannot move. The first steering control seat (27) and the second steering control seat (24) move synchronously in opposite directions.

3. The jaw bending structure of the electric laparoscopic stapler according to claim 2, characterized in that: Both ends of the screw (25) are provided with threads and the threads rotate in opposite directions. The first steering control seat (27) and the second steering control seat (24) are provided with internal threads (38), guide blocks (41), protrusions (39) and baffles (40) that are in sync with the threads at both ends of the screw (25). The upper bracket (14) and the lower bracket (17) are provided with sliding grooves (13).

4. The jaw bending structure of the electric laparoscopic stapler according to claim 3, characterized in that: When the first steering control seat (27) and the second steering control seat (24) move, the guide blocks (41) on the first steering control seat (27) and the second steering control seat (24) move in the grooves (13) on the upper bracket (14) and the lower bracket (17).

5. The jaw bending structure of the electric laparoscopic stapler according to claim 4, characterized in that: The steering tie rod 1 (1) and steering tie rod 2 (2) are provided with positioning holes at their proximal and distal ends. The protrusions (39) on the first steering control seat (27) and the second steering control seat (24) are respectively connected to the positioning holes at the proximal ends of steering tie rod 1 (1) and steering tie rod 2 (2). The steering tie rod 3 (3) and steering tie rod 4 (4) are provided with hooks in opposite directions at their proximal and distal ends. The hooks at the proximal ends of steering tie rod 3 (3) and steering tie rod 4 (4) are respectively pivotally connected to the positioning holes at the distal ends of steering tie rod 1 (1) and steering tie rod 2 (2).

6. The jaw bending structure of an electric laparoscopic stapler according to claim 5, characterized in that: The steering fixing seat (21) is also provided with two positioning holes, and the two positioning holes are pivotally connected to the far-end hooks of the steering tie rod three (3) and the steering tie rod four (4), respectively. The steering fixing seat (21) is provided with a crescent-shaped groove (36), and the steering adjustment seat (34) is provided with a crescent-shaped protrusion (37). The crescent-shaped groove (36) and the crescent-shaped protrusion (37) cooperate with each other. The steering fixing seat (21) can drive the steering adjustment seat (34) to bend. The steering adjustment seat (34) is provided with a groove on the back. The steering adjustment seat (34) accommodates the cutting blade assembly (22) through the groove. The steering adjustment seat (34) can drive the cutting blade assembly (22) to bend.

7. The jaw bending structure of an electric laparoscopic stapler according to claim 6, characterized in that: A PCB board (23) is fixedly installed on the upper bracket (14) and the lower bracket (17), which drives three photoelectric sensors (31) to be arranged along the axial direction on the PCB board (23).

8. The jaw bending structure of an electric laparoscopic stapler according to claim 7, characterized in that: The outer tube (18) is provided with a safety pin groove (16), and the inner tube (10) is sleeved in the inner cavity of the outer tube (18). The inner tube (10) is sleeved to the surface of the center rod (15). The end of the center rod (15) is provided with a boss (20). The end actuator (5) is connected to the short sleeve (6). The end of the short sleeve (6) is provided with a connecting piece (7). The connecting piece (7) is connected to one end of the outer tube (18).

9. The jaw bending structure of an electric laparoscopic stapler according to claim 8, characterized in that: The lower outer shell (11) and upper outer shell (12) of the bend knob are provided with positioning ribs, and the toothed ring (29) is provided with positioning grooves around its periphery. The positioning grooves and positioning ribs cooperate with each other.

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