A crack detector for prefabricated tunnel segments

Abstract

The present invention discloses a crack detector for tunnel prefabricated pipe segments, including a base and a placement rack, wherein the base is provided with a lifting member and a visual detection member; the lifting member bracket, wherein a support plate is vertically slid in the base; the visual detection member includes a stand fixed on the base, wherein both sides of the stand are rotatably connected with a rotary arm, and a detection instrument is installed on the sliding sleeve; a telescopic mechanism is installed in the sliding shell, and a transmission component is installed on the sliding arm. In the present invention, firstly, by controlling the sliding arm to extend in and out relative to the sliding shell, the orientation of the detection instrument is synchronously switched, thereby realizing a comprehensive detection of the double-sided curved surface of the prefabricated pipe segment, facilitating the staff to collect crack data of the pipe segment and improving the detection efficiency; secondly, by switching the placing mode of the placement rack by the bracket and the support plate, corresponding space is provided for the movement of the rack rod and the rotation of the sliding arm, while satisfying the safe and stable placement of the pipe segment.

Description

Technical Field

[0001] The invention relates to the technical field of pipe segment detection equipment, and in particular to a crack detector for a tunnel prefabricated pipe segment. Background Art

[0002] Precast concrete lining segments are precast concrete components used in tunnel projects such as rail transit, highways, railways, water conservancy, electricity, municipal engineering, and urban underground integrated pipeline corridors. They are the main assembly components of shield construction and the outermost barrier of the tunnel. Their quality is directly related to the safety of the tunnel structure.

[0003] The bending resistance test of prefabricated pipe segments is one of the important tests to ensure the safety of the pipe segment structure. The purpose of the bending resistance test is to determine the crack load and failure load value of the pipe segment under load. After the sampled prefabricated pipe segments are subjected to pressure loading, the staff is required to record and analyze the cracks formed on the pipe segments, so as to obtain the bending resistance performance of the prefabricated pipe segments.

[0004] The existing technology usually uses a visual inspection instrument to replace manual observation to inspect and record the appearance of the pipe segment. The visual inspection instrument is based on optical principles and image processing technology. It collects images of cracks through a lens, and then uses an optical sensor to convert the image into a digital signal. The crack edge information is extracted through image processing technology to calculate the width of the crack. However, since the prefabricated pipe segment has an arc-shaped structure and a large size, it is usually inconvenient for users to use a handheld inspection instrument to comprehensively record and inspect the arc-shaped stress-bearing surface of the pipe segment.

[0005] In view of the above-mentioned defects, a crack detector for prefabricated tunnel segments is provided. Summary of the invention

[0006] The purpose of the present invention is to solve the above-mentioned problem and to propose a crack detector for prefabricated tunnel segments.

[0007] In order to achieve the above-mentioned object, the present invention adopts the following technical scheme: a crack detector for a tunnel prefabricated pipe segment, comprising a base and two placement racks arranged on the base for cooperating with the end racks of the pipe segment, wherein the base is provided with two groups of lifting components corresponding to the placement racks and a visual detection component for cooperating with the double-sided detection of the pipe segment;

[0008] The lifting member is a bracket that is horizontally slidably arranged on the base and lifts the two ends of the placement rack. A support plate that vertically slides in the base and cooperates with the middle part of the placement rack to lift the placement rack is provided. The base is provided with a driving component that drives the support plate and the bracket to alternately lift the placement rack.

[0009] The visual detection component comprises a frame fixed on a base, with swing arms rotatably connected on both sides of the frame, a bidirectional servo driving the swing arms on both sides to rotate synchronously is arranged in the frame, a sliding shell is slidably connected inside the swing arm, a sliding arm is slidably connected in the sliding shell, a frame rod is rotatably connected at one opposite end of the two sliding arms, a sliding sleeve is arranged on the outer sliding sleeve of the frame rod, a detection instrument is installed on the sliding sleeve, and a traveling component is arranged on the sliding sleeve;

[0010] A telescopic mechanism for controlling the relative sliding of the sliding arm is installed in the sliding shell, and a transmission component is installed on the sliding arm. When the sliding arm slides relative to the sliding shell, the frame rod rotates under the action of the transmission component to adjust the direction of the detection instrument.

[0011] Preferably, a bracket fixed to the bracket is slidably arranged in the base, and a square frame is fixedly arranged at the bottom of the support plate.

[0012] Preferably, the driving component includes a screw sleeve slidably set in the base, a guide assembly for acting on the square frame is arranged on the screw sleeve, a screw rod rotatably connected to the screw sleeve and the bracket is screwed in the base, and a driving motor for controlling the rotation of the screw rod is installed at the outer end of the base.

[0013] Preferably, the guide assembly includes a protrusion fixed on the outer end of the screw sleeve, and a strip groove for matching the sliding of the protrusion is formed in the square frame, and the strip groove consists of a transverse groove and an oblique groove.

[0014] Preferably, a guide rod is fixedly provided on the sliding shell, a sliding groove for the guide rod to slide through is formed in the rotary arm, an arc groove for the guide rod to slide is formed on the side of the platform, and the arc groove is cocentrically distributed with the pipe segment mounted on the placement rack.

[0015] Preferably, the moving component includes a rack fixed on the side end of the frame rod, a cavity is formed in the sliding sleeve for matching the rack and the frame rod to slide through, a gear meshing with the matching rack is rotatably connected in the cavity, and a servo motor for controlling the rotation of the gear is installed on the sliding sleeve.

[0016] Preferably, the transmission component includes a first wheel disc and a second wheel disc rotatably connected to the sliding arm, and a component for driving the second wheel disc to turn. The first wheel disc is coaxially fixed to the frame rod, and the outer engaging sleeves of the first wheel disc and the second wheel disc are provided with chains.

[0017] Preferably, the second wheel steering component includes a round block fixedly mounted on the outer end of the second wheel, and the round block is arranged offset from the center of the second wheel, and two baffles are fixedly mounted on the outer end of the sliding shell, and the opposite ends of the two baffles are formed with recessed grooves for the matching round block to be embedded.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0019] 1. In the present application, when the sliding arm slides inward relative to the sliding shell, the frame rod will drive the detection instrument to rotate outward relative to the frame; when the sliding arm slides outward relative to the sliding shell, the frame rod will drive the detection instrument to rotate inward relative to the frame. By controlling the sliding arm to extend in and out relative to the sliding shell, the direction of the detection instrument is switched synchronously to achieve a comprehensive inspection of the double-sided curved surfaces of the prefabricated pipe segment, which is convenient for the staff to collect crack data on the pipe segment and improves the inspection efficiency of prefabricated pipe segments with larger sizes.

[0020] 2. In the present application, by switching the supporting mode of the placement rack between the bracket and the support plate, corresponding space is provided for the movement of the rack rod and the rotation of the sliding arm, so as to meet the switching detection of the end face of the pipe segment by the detection instrument, and the switching mode in which the support plate first presses upward against the bottom of the placement rack and then the bracket slides away from the bottom of the placement rack, and the bracket first slides against the bottom of the placement rack and then the support plate moves downward away from the placement rack, so as to meet the safe and stable placement of the pipe segment by the placement rack at a certain height. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the three-dimensional structure of a base provided according to an embodiment of the present invention is shown;

[0022] Figure 2 A schematic diagram of a side cross-sectional structure of a base provided according to an embodiment of the present invention is shown;

[0023] Figure 3 A schematic diagram of the three-dimensional structure of a stand provided according to an embodiment of the present invention is shown;

[0024] Figure 4 An exploded schematic diagram of the outer structure of a platform provided in an embodiment of the present invention is shown;

[0025] Figure 5 A schematic diagram of the matching structure of a sliding sleeve and a rack rod provided according to an embodiment of the present invention is shown.

[0026] Legend:

[0027] 1. Base; 2. Placement rack; 3. Bracket; 4. Support; 5. Screw; 6. Drive motor; 7. Support plate; 8. Square frame; 9. Strip groove; 10. Screw sleeve; 11. Bump; 12. Stand; 1201. Arc groove; 13. Swing arm; 14. Slide groove; 15. Sliding shell; 16. Guide rod; 17. Telescopic mechanism; 18. Slide arm; 19. First wheel disc; 20. Second wheel disc; 21. Chain; 22. Round block; 23. Baffle; 24. Notch groove; 25. Rack; 26. Rack; 27. Slide sleeve; 28. Testing instrument; 29. ​​Cavity groove; 30. Gear; 31. Servo motor. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] See also Figure 1-5 The present invention provides a technical solution: a crack detector for a tunnel prefabricated pipe segment, comprising a base 1 and two placement racks 2 arranged on the base 1 for cooperating with the placement of the pipe segment ends, and the base 1 is provided with two groups of lifting components corresponding to the placement racks 2 and a visual detection component for cooperating with the double-sided detection of the pipe segment.

[0030] The lifting member is horizontally slidably arranged on the base 1, and the bracket 3 lifts the two ends of the placement rack 2. The base 1 has a vertically sliding support plate 7 that cooperates with the middle part of the placement rack 2 to lift the placement rack 2. The base 1 is provided with a driving component that drives the support plate 7 and the bracket 3 to alternately lift the placement rack 2.

[0031] A groove is formed at the bottom of the placement rack 2 for the horizontal sliding insertion of the bracket 3 and the vertical insertion of the support plate 7. When the support plate 7 moves upward under the action of the driving component, the two brackets 3 used to support the two sides of the bottom of the placement rack 2 will move in the opposite direction synchronously until the support plate 7 pushes upward into the groove and supports the bottom of the placement rack 2. The bracket 3 will slide away from the placement rack 2 in the opposite direction under the action of the driving component. The driving component drives the bracket 3 and the support plate 7 to alternately support the placement rack 2, thereby providing space for the switching of the visual inspection component relative to the pipe segment inspection surface, and in the process of alternating the bracket 3 and the support plate 7, the placement rack 2 is always kept at a certain height position to safely and stably place the pipe segment.

[0032] The visual detection component includes a platform 12 fixed on a base 1, with swing arms 13 rotatably connected on both sides of the platform 12, and a bidirectional servo driving the swing arms 13 on both sides to rotate synchronously is arranged in the platform 12, a sliding shell 15 is slidably connected inside the swing arm 13, and a sliding arm 18 is slidably connected in the sliding shell 15, and a frame rod 25 is rotatably connected at opposite ends of the two sliding arms 18, and a sliding sleeve 27 is provided on the outer sliding sleeve of the frame rod 25, a detection instrument 28 is installed on the sliding sleeve 27, and a moving component is arranged on the sliding sleeve 27.

[0033] The bidirectional servo is a prior art, which is a motor with a bidirectional output shaft. The rotation of the motor is controlled by a PWM signal, and the angle of the bidirectional output shaft is accurately adjusted through an internal feedback device and a control circuit, thereby achieving precise position control. The bidirectional servo is set to synchronously control the swing arms 13 distributed on both sides of the platform 12.

[0034] The detection instrument 28 is an existing visual detection mechanism. Based on optical principles and image processing technology, the visual detection machine uses an industrial camera (such as a CCD camera) to capture images of target objects under certain lighting conditions. These images are focused on the image sensor through the lens. The sensor converts the optical signal into an electrical signal to generate a digital image. The crack edge information is extracted through image processing technology, and the width of the crack in the pipe segment after the anti-bending test is calculated, thereby analyzing the anti-bending performance of the prefabricated pipe segment.

[0035] When the swing arm 13 rotates along the platform 12, the sliding shell 15 will slide along the swing arm 13, so that the sliding arm 18 installed in the sliding shell 15 drives the frame rod 25 to make circumferential movement relative to the arc-shaped end face of the pipe segment, thereby facilitating the detection instrument 28 installed on the sliding sleeve 27 to obtain crack information on the arc-shaped end face of the prefabricated pipe segment.

[0036] A telescopic mechanism 17 for controlling the relative sliding of a sliding arm 18 is installed in the sliding housing 15. A transmission component is installed on the sliding arm 18. When the sliding arm 18 slides relative to the sliding housing 15, the frame rod 25 rotates under the action of the transmission component to adjust the direction of the detection instrument 28.

[0037] The telescopic mechanism 17 is an existing hydraulic or pneumatic telescopic rod. To accommodate the telescopic mechanism 17, a chamber is formed in the sliding arm 18 to fit the telescopic mechanism 17. When the sliding arm 18 slides and extends relative to the sliding shell 15 under the action of the telescopic mechanism 17, the frame rod 25 will rotate under the action of the transmission member, so that the sliding sleeve 27 drives the detection instrument 28 to rotate outward relative to the frame 12 under the action of the frame rod 25, so that when the rotating arm 13 rotates, the detection instrument 28 can collect information on the arc end surface of the lower side of the pipe segment.

[0038] When the sliding arm 18 slides out relative to the sliding shell 15 under the action of the telescopic mechanism 17, the frame rod 25 will rotate under the action of the transmission member, so that the sliding sleeve 27 drives the detection instrument 28 to rotate inward relative to the frame 12 under the action of the frame rod 25, so that the detection instrument 28 can collect information on the arc end surface on the upper side of the pipe segment when the rotary arm 13 rotates.

[0039] When the rack rod 25 moves in the circumferential direction relative to the segment, the sliding sleeve 27 is driven to move laterally along the rack rod 25 by the traveling component installed on the sliding sleeve 27, which is beneficial for the detection instrument 28 to fully detect the prefabricated segment of larger size.

[0040] Specifically, Figure 1 and Figure 2 As shown, a bracket 4 fixed to a bracket 3 is slidably provided in the base 1, a square frame 8 is fixedly provided at the bottom of the support plate 7, a driving component comprises a screw sleeve 10 slidably provided in the base 1, a guide assembly acting on the square frame 8 is provided on the screw sleeve 10, a screw rod 5 screwedly connected to the screw sleeve 10 and the bracket 4 is rotatably connected in the base 1, and a driving motor 6 for controlling the rotation of the screw rod 5 is installed at the outer end of the base 1.

[0041] The drive motor 6 is started to control the rotation of the screw rod 5, so that the screw sleeve 10 and the bracket 4 that are screwed together with the screw rod 5 move synchronously. When the square frame 8 drives the support plate 7 to move upward under the action of the guide assembly, the two brackets 3 will also move synchronously in the opposite direction under the drive of the bracket 4 until the support plate 7 is upward against the bottom of the placement rack 2. As the screw rod 5 continues to rotate, the support plate 7 will remain stationary relative to the base 1. At this time, the two brackets 3 continue to move under the screw rod 5 The rotation of the bracket 4 until the slide is pulled away from the bottom of the placement rack 2, providing a lifting space for the sliding arm 18 that slides out relative to the sliding shell 15.

[0042] As the screw rod 5 rotates, when the two brackets 3 move synchronously towards each other under the drive of the bracket 4, the support plate 7 will first maintain the supporting state against the bottom of the rack 2, and as the bracket 3 slides and slides against the two sides of the bottom of the rack 2, at this time, as the screw sleeve 10 continues to move, the square frame 8 will drive the support plate 7 to move downward under the action of the guide member, and release the state of contact with the bottom of the rack 2, thereby providing space for the slide arm 18 to extend in and out relative to the sliding shell 15. The switching mode of the support plate 7 firstly contacts the bottom of the rack 2 upwards, and then the bracket 3 slides away from the bottom of the rack 2, and the bracket 3 first slides and contacts the bottom of the rack 2, and then the support plate 7 is separated from the rack 2 downwards, so that the rack 2 can safely and stably place the pipe segments at a certain height.

[0043] The guide assembly includes a protrusion 11 fixed on the outer end of the screw sleeve 10, and a strip groove 9 is formed in the square frame 8 to cooperate with the sliding of the protrusion 11. The strip groove 9 consists of a transverse groove and an oblique groove.

[0044] When the screw rod 5 rotates, the screw sleeve 10 screwed with the screw rod 5 will move in the horizontal direction. During this process, the protrusion 11 fixed on the screw sleeve 10 will slide along the strip groove 9. When the protrusion 11 slides along the oblique groove of the strip groove 9, the protrusion 11 presses the inner wall of the oblique groove to drive the support plate 7 fixed to the square frame 8 to move in the vertical direction. When the protrusion 11 slides along the transverse groove of the strip groove 9, the support plate 7 fixed to the square frame 8 will remain in a horizontal erection state.

[0045] Specifically, Figure 3 and Figure 4As shown, a guide rod 16 is fixedly provided on the sliding shell 15, a sliding groove 14 is formed in the swing arm 13 for the guide rod 16 to slide through, and an arc groove 1201 is formed on the side of the platform 12 for the guide rod 16 to slide. The arc groove 1201 is cocentrically distributed with the pipe segment mounted on the placement rack 2.

[0046] When the swing arm 13 rotates, the guide rod 16 fixed on the sliding shell 15 will slide along the arc groove 1201. The inner wall of the arc groove 1201 compresses the guide rod 16, driving the sliding shell 15 to slide relative to the swing arm 13 when rotating with the swing arm 13, thereby allowing the frame rod 25 to move circumferentially relative to the pipe segment along with the sliding arm 18.

[0047] Specifically, Figure 3 and Figure 5 As shown, the moving component includes a rack 26 fixed to the side end of the frame rod 25, a cavity 29 is formed in the sliding sleeve 27 for sliding through the matching rack 26 and the frame rod 25, a gear 30 is rotatably connected in the cavity 29 and meshes with the matching rack 26, and a servo motor 31 for controlling the rotation of the gear 30 is installed on the sliding sleeve 27.

[0048] The servo motor 31 is started to control the rotation of the gear 30, so that the gear 30 drives the sliding sleeve 27 to slide along the frame rod 25 under the meshing action of the rack 26. When the frame rod 25 moves circumferentially relative to the prefabricated pipe segment with the sliding arm 18, the sliding sleeve 27 moves back and forth along the frame rod 25, so that the detection instrument 28 can scan and detect the arc end face of the pipe segment.

[0049] Specifically, Figure 3 and Figure 4 As shown, the transmission component includes a first wheel 19 and a second wheel 20 rotatably connected to the sliding arm 18, and a component for driving the second wheel 20 to turn. The first wheel 19 is coaxially fixed to the frame rod 25, and the outer engaging sleeves of the first wheel 19 and the second wheel 20 are provided with a chain 21.

[0050] When the second wheel disc 20 rotates, the first wheel disc 19 will drive the frame rod 25 coaxially fixed therewith to rotate under the meshing action of the chain 21, thereby realizing the reversal of the detection instrument 28 installed on the sliding sleeve 27, thereby satisfying the comprehensive detection of the curved end faces on both sides of the pipe segment.

[0051] The component driving the second wheel disc 20 to turn includes a round block 22 fixedly mounted on the outer end of the second wheel disc 20, and the round block 22 is arranged away from the center of the second wheel disc 20. Two baffles 23 are fixedly mounted on the outer end of the sliding shell 15, and a notch 24 is formed at the opposite end of the two baffles 23 to fit the round block 22. The first wheel disc 19 and the second wheel disc 20 are both toothed discs that mesh with the chain 21.

[0052] When the sliding arm 18 moves relative to the sliding shell 15 under the action of the telescopic mechanism 17, as the round block 22 disengages from the notch 24, the rotation of the second wheel disc 20 will not be restricted. Due to the uneven weight distribution on the left and right sides of the sliding sleeve 27 relative to the frame rod 25, it deflects at a certain angle. The frame rod 25 will drive the first wheel disc 19 to rotate under the action of the sliding sleeve 27, so that the second wheel disc 20 drives the round block 22 to rotate relative to the notch 24 under the action of the chain 21. With the movement of the sliding arm 18, the round block 22 moves and contacts the baffle 23 on the other side. Since the second wheel disc 20 moves relative to the baffle 23 during the sliding process of the sliding arm 18, the round block 22 will drive the second wheel disc 20 to rotate under the push of the side wall of the baffle 23 until the round block 22 is embedded in the notch 24 in the corresponding baffle 23. At this time, the frame rod 25 rotates half a circle with the first wheel disc 19 to realize the reversing detection of the detection instrument 28 installed on the sliding sleeve 27.

[0053] The above description of the embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A crack detector for a tunnel prefabricated segment, comprising a base (1) and two placement racks (2) arranged on the base (1) for cooperating with the end racks of the segment, characterized in that: The base (1) is provided with two sets of lifting components corresponding to the placement rack (2) and visual inspection components for cooperating with double-sided inspection of the pipe segment; The lifting member is a bracket (3) which is horizontally slidably arranged on the base (1) and lifts the two ends of the placement rack (2); a support plate (7) which vertically slides in the base (1) and cooperates with the middle part of the placement rack (2) to lift the placement rack (2); and a driving component is arranged in the base (1) to drive the support plate (7) and the bracket (3) to alternately lift the placement rack (2); The visual detection component comprises a stand (12) fixed on a base (1), the two sides of the stand (12) being rotatably connected to swing arms (13), the stand (12) being provided with a bidirectional steering gear for driving the swing arms (13) on both sides to rotate synchronously, the inside of the swing arms (13) being slidably connected to a sliding shell (15), the sliding shell (15) being slidably connected to a sliding arm (18), the two opposite ends of the two sliding arms (18) being rotatably connected to a stand rod (25), the outer sliding sleeve of the stand rod (25) being provided with a sliding sleeve (27), the sliding sleeve (27) being provided with a detection instrument (28), and the sliding sleeve (27) being provided with a traveling component; The sliding housing (15) is provided with a telescopic mechanism (17) for controlling the relative sliding of the sliding arm (18), and a transmission component is installed on the sliding arm (18). When the sliding arm (18) slides relative to the sliding housing (15), the frame rod (25) rotates under the action of the transmission component to adjust the direction of the detection instrument (28); The transmission component includes a first wheel (19) and a second wheel (20) rotatably connected to the slide arm (18), and a component for driving the second wheel (20) to turn, the first wheel (19) is coaxially fixed to the frame rod (25), and the outer engaging sleeves of the first wheel (19) and the second wheel (20) are provided with a chain (21); The component for driving the second wheel disc (20) to turn comprises a round block (22) fixedly mounted on the outer end of the second wheel disc (20), and the round block (22) is arranged offset from the center of the second wheel disc (20), and two baffles (23) are fixedly mounted on the outer end of the sliding shell (15), and a notch groove (24) for fitting the round block (22) to be embedded is formed at opposite ends of the two baffles (23).

2. The crack detector for prefabricated tunnel segments according to claim 1, characterized in that: A bracket (4) fixed to the bracket (3) is slidably arranged in the base (1), and a square frame (8) is fixedly arranged at the bottom of the support plate (7).

3. The crack detector for prefabricated tunnel segments according to claim 2, characterized in that: The driving component comprises a screw sleeve (10) slidably arranged in a base (1), a guide assembly for acting on a square frame (8) being arranged on the screw sleeve (10), a screw rod (5) being rotatably connected in the base (1) and being screwed together with the screw sleeve (10) and a bracket (4), and a driving motor (6) for controlling the rotation of the screw rod (5) being installed at the outer end of the base (1).

4. The crack detector for prefabricated tunnel segments according to claim 3, characterized in that: The guide assembly comprises a protrusion (11) fixedly mounted on the outer end of the screw sleeve (10), and a strip groove (9) for slidingly cooperating with the protrusion (11) is formed in the square frame (8), wherein the strip groove (9) consists of a transverse groove and an oblique groove.

5. The crack detector for prefabricated tunnel segments according to claim 1, characterized in that: A guide rod (16) is fixedly provided on the sliding shell (15), a sliding groove (14) is formed in the swing arm (13) and is adapted for the guide rod (16) to slide through, and an arc groove (1201) is formed on the side of the stand (12) and is adapted for the guide rod (16) to slide, and the arc groove (1201) is coaxially distributed with a pipe segment mounted on the placement rack (2).

6. The crack detector for prefabricated tunnel segments according to claim 1, characterized in that: The moving component comprises a rack (26) fixed to the side end of the frame rod (25); a cavity (29) is formed in the sliding sleeve (27) and is slidably penetrated by the matching rack (26) and the frame rod (25); a gear (30) meshing with the matching rack (26) is rotatably connected in the cavity (29); and a servo motor (31) for controlling the rotation of the gear (30) is installed on the sliding sleeve (27).

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