Robot-assisted subretinal injection system

Abstract

Disclosed in the present invention is a robot-assisted subretinal injection system, comprising a base, wherein a controller is mounted on the base; one side of the base is connected to a robotic arm by means of a rotating assembly to make the robotic arm rotate horizontally; an angle adjustment seat is rotationally connected to an end of the robotic arm; an injection platform is movably connected to the angle adjustment seat; a clamp capable of sliding along the injection platform is provided on the front side of the injection platform; a driving assembly is provided in the clamp, and is configured to push a syringe out of the front end of the clamp or retract same into the clamp; a thrust linear motor is further provided on the front side of the injection platform; a pressing plate configured to be connected to the tail end of a plunger on the syringe is mounted on a spindle of the thrust linear motor; and an injection micropump is provided on the base, and is connected to the syringe by means of tubing. The present invention can solve the problem of potential safety hazards caused by a needle tip of the syringe being exposed to the outside during the movement of existing ocular subretinal injection devices.

Description

A robot-assisted subretinal injection system Technical Field

[0001] This invention relates to the field of medical device technology, specifically to a robot-assisted subretinal injection system. Background Technology

[0002] Subretinal injection is a precise injection procedure that delivers drugs to retinal vessels or the subretinal space, i.e., between the retinal neuron epithelium and the retinal pigment epithelium. It is commonly used for gene therapy of hereditary retinal diseases, cell therapy for age-related macular degeneration, injection of tissue plasminogen activator (t-PA) for retinal vascular occlusion, and anti-VEGF therapy for retinal neovascularization.

[0003] Due to the limited space beneath the retina, injections in this area require extremely high precision to avoid adverse consequences such as retinal rupture and immune responses caused by drug reflux. Currently, there is still debate both domestically and internationally regarding the general procedure for subretinal injections. It is generally believed that subretinal injections should be performed in two steps: first, after vitrectomy, a balanced salt solution (BSS) is injected to create a pre-constructed blister, followed by the injection of the drug into the blister. This procedure aims to improve the tolerance for errors caused by the low precision of manual injection and hand tremors. While the two-step method is suitable for low-precision subretinal artificial injections, it has some drawbacks, such as the need for vitrectomy before injection, which causes significant intraocular damage, and the difficulty of repeated drug administration.

[0004] The prior art 202110063385.6 discloses a remote fixed-point control method for a robot for subretinal injection in the human eye. By setting a syringe at the end of the robotic arm, the syringe is controlled to move along a motion path and the needle tip of the syringe is inserted into the designated target position. However, when the syringe moves with the robotic arm along the motion trajectory, there is a certain safety hazard because the needle tip of the syringe is exposed on the outside. Summary of the Invention

[0005] This invention provides a robot-assisted subretinal injection system that can solve the safety hazard caused by the needle tip of the syringe being exposed on the outside during the movement of existing subretinal injection devices.

[0006] To achieve the above objectives, the present invention provides a robot-assisted subretinal injection system, comprising a machine base, on which a controller is mounted. One side of the machine base is connected to a robotic arm via a rotating assembly to enable the robotic arm to rotate horizontally. The robotic arm includes a vertical lifting assembly and a horizontal moving assembly mounted on the vertical lifting assembly. A horizontally movable slider is provided on the horizontal moving assembly. An angle adjustment seat is rotatably connected to the end of the horizontal moving assembly. The upper end of the angle adjustment seat is connected to the slider via an angle adjustment linkage. An injection platform is movably connected to the angle adjustment seat. A clamp that can slide along the injection platform is provided on the front side of the injection platform. A drive assembly is provided inside the clamp. The injection platform is used to push the syringe out of the front end of the clamp or retract it into the clamp. A thrust linear motor is also provided on the front side of the injection platform. A pressure plate for connecting to the tail end of the plunger on the syringe is installed on the main shaft of the thrust linear motor. An injection micropump is provided on the machine base. The injection micropump is connected to the syringe through a pipeline. The robotic arm, drive assembly, thrust linear motor and injection micropump are all electrically connected to the controller. Through the multi-angle movement of the robotic arm, the injection platform can be moved to a designated position quickly and accurately, and the angle of the syringe can be adjusted. During the movement of the robotic arm, the needle tip of the syringe enters the clamp, which can improve the safety of use and avoid safety hazards during the movement of the syringe driven by the robotic arm.

[0007] Preferably, a first adjusting screw is provided on the inner side of the angle adjusting seat along its length direction. A fine-tuning nut is provided on the first adjusting screw. The fine-tuning nut is movably connected to the injection platform through at least one connecting rod. The position of the fine-tuning nut can be adjusted by rotating the first adjusting screw, thereby adjusting the front and rear position of the injection platform. At the same time, the swinging of the connecting rod can also adjust the position of the injection platform, making the adjustment of the injection platform position more flexible.

[0008] Preferably, the rotating assembly includes a rotating connecting seat connected to the robotic arm and an electric rotating seat mounted on the machine base. The rotating connecting seat is sleeved on the electric rotating seat, which can drive the robotic arm to rotate horizontally.

[0009] Preferably, the injection platform is provided with a second adjusting screw, and an adjusting nut is provided on the second adjusting screw. The clamp is installed on the adjusting nut, and the position of the clamp on the injection platform can be adjusted by rotating the second adjusting screw.

[0010] Preferably, the clamp has a mounting hole, and the drive assembly is installed in the mounting hole. The drive assembly includes a fixed sleeve and a first electromagnet installed at the tail end of the fixed sleeve. The syringe passes axially through the fixed sleeve, and a second electromagnet is fixed to the outside of the syringe. An elastic element is provided between the second electromagnet and the front end of the fixed sleeve. The magnetic fields generated by the first and second electromagnets when energized are opposite in magnetism. When the first and second electromagnets are energized, they generate a magnetic field that moves the first electromagnet and the syringe together toward the front end, compressing the elastic element. The front end of the syringe can then extend from the front end of the clamp, allowing injection to be performed. When the first and second electromagnets are de-energized, the magnetic field disappears, and the elastic element can push the second electromagnet and the syringe back into the clamp.

[0011] Preferably, the tail end of the fixing sleeve is equipped with a detachable first fixing ring, and the first electromagnet is connected and fixed to the first fixing ring. After the first fixing ring is removed, the syringe can be easily removed, making it very convenient to replace the syringe.

[0012] Preferably, a second fixing ring is installed at the front end of the fixing sleeve, and one end of the elastic element abuts against the second fixing ring. The second fixing ring can limit the elastic element and guide the axial movement of the syringe, thereby improving the stability of the syringe movement.

[0013] Preferably, the injection micropump is connected to a switch control foot pedal, which can be used to control the operation of the injection micropump. When the pressure plate is stepped on, the pressure plate will press down on the sensor, and the sensor will transmit a signal to the controller. Then the controller controls the micropump to pump a specified amount of medicine into the syringe. Each time the switch control foot pedal is stepped on, the injection micropump can be controlled to inject a specified amount of medicine into the syringe once, which is convenient to operate.

[0014] Preferably, the controller is a PLC controller or an intelligent computer, and the control program can be adjusted according to actual needs.

[0015] Preferably, the horizontal moving component includes a connecting block connected to the lifting block on the vertical lifting component and an extension seat extending horizontally forward from one side of the connecting block. The slider slides along the groove on the extension seat, and the lower end of the angle adjusting seat is rotatably connected to the front end of the extension seat. The horizontal moving component has a compact structure and can cooperate with the vertical lifting component to lift and lower while simultaneously adjusting the angle of the angle adjusting seat.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] By configuring the drive assembly, the syringe needle tip can enter the gripper during the movement of the robotic arm, improving safety and avoiding potential safety hazards during the robotic arm's movement of the syringe. The push linear motor can drive the puncture syringe barrel for retinal puncture, and retract into the syringe's larger needle after injection, minimizing damage and protecting the smaller needle.

[0018] The multi-angle movement of the robotic arm allows the injection platform to move quickly and accurately to the designated position, eliminating physiological tremors that occur during manual puncture and injection by doctors. This significantly enhances the stability of the puncture process and avoids problems such as repeated punctures and damage to retinal tissues caused by tremors. By introducing a precision infusion pump specifically designed for retinal injections, the volume of injected medication is kept stable and controllable, preventing injection movements from affecting puncture stability. Attached Figure Description

[0019] Figure 1 is a front view structural diagram of the present invention;

[0020] Figure 2 is a three-dimensional structural diagram of the clamp of the present invention;

[0021] Figure 3 is an exploded structural diagram of the clamp and drive assembly of the present invention;

[0022] Figure 4 is a first schematic diagram of the working state of the drive component of the present invention;

[0023] Figure 5 is a second schematic diagram of the working state of the driving component of the present invention.

[0024] Figure label:

[0025] 1. Robotic arm; 2. Syringe; 3. Injection platform; 4. Clamp; 5. Drive assembly; 6. Controller; 7. Injection micropump; 8. Fixing sleeve; 9. Elastic element; 10. Second electromagnet; 11. First electromagnet; 12. Mounting hole; 13. Second retaining ring; 14. First retaining ring; 15. Screw; 16. Thrust linear motor; 17. Pressure plate; 18. Switch control foot pedal; 100. Machine base; 101. Fine-tuning nut; 102. Angle adjustment linkage; 103. Horizontal movement assembly; 104. Up and down lifting assembly; 105. Rotation assembly; 106. Extension seat; 107. Slider; 108. Angle adjustment seat; 109. Linkage rod; 110. First adjusting screw. Detailed Implementation

[0026] 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.

[0027] As shown in Figures 1-5, to address the current lack of experimental devices and methods that can realistically simulate the pre-braking collision process of a car with active braking function, this invention provides the following technical solution: A robot-assisted subretinal injection system, comprising a machine platform 100, on which a controller 6 is installed. One side of the machine platform 100 is connected to a robotic arm 1 via a rotating assembly 105 to allow the robotic arm 1 to rotate horizontally. The robotic arm 1 includes a vertical lifting assembly 104 and a horizontal moving assembly 103 disposed on the vertical lifting assembly 104. A horizontally movable slider 107 is disposed on the horizontal moving assembly 103. An angle adjustment seat 108 is rotatably connected to the end of the horizontal moving assembly 103. The upper end of the angle adjustment seat 108 is connected to the slider 107 via an angle adjustment link 102. An injection platform 3 is movably connected to the angle adjustment seat 108. The front side of the injection platform 3 is provided with a movable... The injection platform 3 is slidably supported by a clamp 4. A drive assembly 5 is installed within the clamp 4 to push the syringe 2 out of the front end of the clamp 4 or retract it into the clamp 4. A linear thrust motor 16 is also installed on the front side of the injection platform 3. A pressure plate 17 is mounted on the main shaft of the linear thrust motor 16 to connect to the tail end of the push rod on the syringe 2. An injection micropump 7 is installed on the machine base 100 and is connected to the syringe 2 via a pipeline. The robotic arm 1, drive assembly 5, linear thrust motor 16, and injection micropump 7 are all electrically connected to a controller 6. Through the multi-angle movement of the robotic arm 1, the injection platform 3 can be moved quickly and accurately to a designated position, and the angle of the syringe 2 can be adjusted. During the movement of the robotic arm 1, the needle tip of the syringe 2 enters the clamp 4, improving safety and preventing potential safety hazards during the movement of the syringe 2 driven by the robotic arm 1.

[0028] Specifically, the machine 100 generally adopts a floor-standing structure and is placed next to the treatment bed during treatment. The controller 6 has a display screen on which various parameters can be set. The position between the machine 100 and the treatment bed can be relatively fixed, and the patient's position on the treatment bed is also relatively fixed. This allows the robotic arm 1 to move quickly to a relatively accurate position. The horizontal movement component 103 and the vertical lifting component 104 on the robotic arm 1 can be electrically controlled, such as by using a linear motor or a lead screw drive. The vertical lifting component 104 drives the horizontal movement component 103 to move up and down, and the horizontal movement component 103 drives the slider 107 to move horizontally. The angle of the angle adjustment seat 108 is adjusted by driving the slider 107. The relative position of the clamp 4 on the injection platform 3 is also adjusted by an electric cylinder or a linear motor, all controlled by the controller 6. These are all existing technologies and can be selected and set as needed.

[0029] When the robotic arm 1 moves the syringe 2 to the designated position, such as directly above the retina, there is a relatively long distance between the syringe 2 and the retina. Then, the drive component 5 drives the syringe 2, causing the needle tip of the syringe 2 to extend out of the clamp 4. Then, the robotic arm 1 drives the syringe 2 to make fine adjustments to its position, so that the needle tip of the syringe 2 reaches the needle insertion position on the ocular surface and adjusts the injection angle. Subsequently, the injection platform 3 drives the syringe 2 downward to pierce into the eyeball, completing the puncture action from the ocular surface to in front of the retina, and stops in front of the retina. Then, the push linear motor 16 drives the pressure plate 17 to move downward, driving the small puncture syringe inside the syringe 2. The small puncture needle tip passes through the large needle tip of the syringe 2, completing the retinal puncture action.

[0030] The controller 6 is a PLC controller or intelligent computer, which can adjust the control program according to actual needs to control the movement trajectory of the robotic arm 1 and the movement distance of the injection platform 3 and the thrust linear motor 16, facilitating the control of surgical precision. The injection micropump 7 is an existing structure used to inject a specified amount of medication into the syringe 2. The volume and speed of the injected medication can be directly set via the controller 6. A switch control foot pedal 18 can be connected to the injection micropump 7. The operation of the injection micropump 7 can be controlled by the switch control foot pedal 18. When the pressure plate is stepped on, the pressure plate presses down on the sensor, which transmits a signal to the controller 6. The controller 6 then controls the micropump 7 to pump the specified amount of medication into the syringe 2. Each time the switch control foot pedal 18 is stepped on, the injection micropump 7 injects the specified amount of medication into the syringe 2, making operation convenient.

[0031] After the medication is injected, the linear motor 16 drives the pressure plate 17 to move backward, causing the puncture needle to retract into the coarse needle of the syringe 2. Next, the injection platform 3 drives the clamp 4 and syringe 2 to move backward, causing the needle to retract away from the eyeball. Subsequently, the drive assembly 5 further drives the coarse needle of the syringe 2 to retract into the clamp 4 as well, to avoid potential safety hazards. The injection platform 3 has a second adjusting screw with an adjusting nut. The clamp 4 is mounted on the adjusting nut. Rotating the second adjusting screw adjusts the position of the clamp 4 on the injection platform 3. A drive motor can be installed at one end of the second adjusting screw, controlled by the controller 6, allowing for precise adjustment of the positions of the clamp 4 and syringe 2, ensuring accurate retinal puncture.

[0032] In this embodiment, as shown in Figure 1, a first adjusting screw 110 is provided on the inner side of the angle adjusting seat 108 along its length. A fine-tuning nut 101 is provided on the first adjusting screw 110. The fine-tuning nut 101 is movably connected to the injection platform 3 through at least one connecting rod 109. The position of the fine-tuning nut 101 can be adjusted by rotating the first adjusting screw 110, thereby adjusting the front and rear position of the injection platform 3. At the same time, the swinging of the connecting rod 109 can also adjust the position of the injection platform 3, making the adjustment of the position of the injection platform 3 more flexible. A drive motor can be installed at one end of the first adjusting screw 110, which is driven by the controller 6. The position of the connecting rod 109 is adjusted manually.

[0033] In this embodiment, in order to improve the accuracy of automation and positioning of syringe 2, the rotating assembly 105 includes a rotating connecting seat connected to the robotic arm 1 and an electric rotating seat disposed on the machine base 100. The rotating connecting seat is sleeved on the electric rotating seat, and the robotic arm 1 can be driven to rotate horizontally through the electric rotating seat.

[0034] In this embodiment, as shown in Figures 2-5, the clamp 4 has a mounting hole 12, and the drive assembly 5 is installed in the mounting hole 12. The drive assembly 5 includes a fixing sleeve 8 and a first electromagnet 11 installed at the tail end of the fixing sleeve 8. The syringe 2 passes axially through the fixing sleeve 8, and a second electromagnet 10 is fixed to the outside of the syringe 2. An elastic element 9 is provided between the second electromagnet 10 and the front end of the fixing sleeve 8. The magnetic fields generated by the first electromagnet 11 and the second electromagnet 10 after being energized are opposite in magnetism. When the first electromagnet 11 and the second electromagnet 10 are energized, they generate a magnetic field that moves the first electromagnet 11 and the syringe 2 together toward the front end, compressing the elastic element 9. The front end of the syringe 2 can extend from the front end of the clamp 4, thus allowing injection. When the first electromagnet 11 and the second electromagnet 10 are de-energized, the magnetic field disappears, and the elastic element 9 can push the second electromagnet 10 and the syringe 2 back into the clamp 4. The entire drive assembly 5 has a simple structure and does not require traditional drive components such as motors, electric cylinders, or air cylinders. It only requires the first electromagnet 11, the second electromagnet 10, and the elastic element 9 to complete the extension and retraction of the syringe 2. The first electromagnet 11 and the second electromagnet 10 are both ring-shaped and connected to an external power supply. The power supply is controlled by the controller 6. The elastic element 9 can be a spring and is sleeved on the outside of the syringe 2.

[0035] The fixed sleeve 8 is equipped with a detachable first fixing ring 14 at its tail end. The first electromagnet 11 is connected and fixed to the first fixing ring 14. After removing the first fixing ring 14, the syringe 2 can be easily removed, making it very convenient to replace the syringe 2. The first fixing ring 14 can be connected to the end face of the tail end of the fixed sleeve 8 by multiple screws 15, or by other methods such as threads, snap-fit, etc.

[0036] Meanwhile, a second fixing ring 13 is installed at the front end of the fixing sleeve 8, and one end of the elastic member 9 abuts against the second fixing ring 13. The second fixing ring 13 can limit the elastic member 9 and guide the axial movement of the syringe 2, thereby improving the stability of the movement of the syringe 2.

[0037] In this embodiment, the horizontal moving component 103 includes a connecting block connected to the lifting block on the vertical lifting component 104 and an extension seat 106 extending horizontally forward from one side of the connecting block. The slider 107 slides along the groove on the extension seat 106. The lower end of the angle adjusting seat 108 is rotatably connected to the front end of the extension seat 106. The horizontal moving component 103 has a compact structure and can cooperate with the vertical lifting component 104 to lift and lower while simultaneously adjusting the angle of the angle adjusting seat 108. The slider 107 is driven by the extension seat 106 using existing technologies, such as linear motors, lead screw drives, etc., which will not be elaborated here.

[0038] In summary, during use, the eye image can be observed through an external ophthalmic surgical microscope system to select the needle insertion position. The movement path of the robotic arm 1 is set via the controller 6. When the robotic arm 1 moves the syringe 2 above the eye, it pauses briefly to allow the needle tip to extend from the fixing sleeve 8. The controller 6 can control the start or stop of the robotic arm 1. After the needle tip extends from the fixing sleeve 8, the syringe 2 remains fixed within the fixing sleeve 8 under the action of the first electromagnet 10 and the second electromagnet 11, preventing any shaking. At this point, the robotic arm 1 fine-tunes the syringe 2, ensuring the needle tip reaches the previously selected insertion position on the ocular surface. Then, the injection platform 3 is controlled to guide the needle tip into the eye at a predetermined position and angle, stopping in front of the retina. This position can be adjusted based on the fundus image from the surgical microscope. Subsequently, the pressure plate 17 pushes the small injection syringe inside the syringe 2, allowing the puncture needle to extend below the retina for injection.

[0039] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0040] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly and specifically defined.

[0041] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A robot-assisted subretinal injection system comprising a machine table (100) having a controller (6) mounted thereon, characterized in that, The side of the machine table (100) is connected with the mechanical arm (1) through the rotating assembly (105) to make the mechanical arm (1) horizontally rotate, the mechanical arm (1) comprises the up-down lifting assembly (104) and the horizontal moving assembly (103) arranged on the up-down lifting assembly (104), the horizontal moving assembly (103) is provided with the horizontally movable sliding block (107), the end of the horizontal moving assembly (103) is rotatably connected with the angle adjusting seat (108), the upper end of the angle adjusting seat (108) is connected with the sliding block (107) through the angle adjusting connecting rod (102), the angle adjusting seat (108) is movably connected with the injection platform (3), the front side of the injection platform (3) is provided with the clamp (4) which can slide along the injection platform (3), the clamp (4) is provided with the driving assembly (5) inside, the driving assembly (5) is used for pushing the syringe (2) out of the front end of the clamp (4) or retracting into the clamp (4), the front side of the injection platform (3) is further provided with the thrust linear motor (16), the spindle of the thrust linear motor (16) is provided with the pressing plate (17) which is used for being connected with the tail end of the push rod on the syringe (2), the machine table (100) is provided with the injection micropump (7), the injection micropump (7) is connected with the syringe (2) through the pipeline, the mechanical arm (1), the driving assembly (5), the thrust linear motor (16) and the injection micropump (7) are electrically connected with the controller (6).

2. The robotic-assisted subretinal injection system of claim 1, wherein: The first adjusting screw rod (110) is arranged on the inside of the angle adjusting seat (108) along the length direction, the first adjusting screw rod (110) is provided with the fine adjustment nut (101), the fine adjustment nut (101) is movably connected with the injection platform (3) through at least one connecting rod (109).

3. The robotic-assisted subretinal injection system of claim 1, wherein: The rotating assembly (105) comprises the rotating connecting seat connected with the mechanical arm (1) and the electric rotating seat arranged on the machine table (100), the rotating connecting seat is sleeved on the electric rotating seat.

4. The robotic-assisted subretinal injection system of claim 1, wherein: The second adjusting screw rod is arranged in the injection platform (3), the second adjusting screw rod is provided with the adjusting nut, and the clamp (4) is mounted on the adjusting nut.

5. The robotic-assisted subretinal injection system of claim 1, wherein: The mounting hole (12) is formed in the clamp (4), the driving assembly (5) is mounted in the mounting hole (12), the driving assembly (5) comprises the fixed sleeve (8) and the first electromagnet (11) mounted at the tail end of the fixed sleeve (8), the syringe (2) passes through the fixed sleeve (8) in the axial direction, the second electromagnet (10) is fixed to the outside of the syringe (2), the elastic element (9) is arranged between the front end of the fixed sleeve (8) and the second electromagnet (10), and the magnetic fields generated by the first electromagnet (11) and the second electromagnet (10) are opposite in magnetism.

6. The robotic-assisted subretinal injection system of claim 5, wherein: The detachable first fixing ring (14) is mounted at the tail end of the fixed sleeve (8), and the first electromagnet (11) is connected and fixed with the first fixing ring (14).

7. The robotic-assisted subretinal injection system of claim 5, wherein: The front end of the fixing sleeve (8) is provided with a second fixing ring (13), and one end of the elastic member (9) is in abutment with the second fixing ring (13).

8. The robotic-assisted subretinal injection system of claim 1, wherein: The injection micropump (7) is connected with a switch control pedal (18).

9. The robotic-assisted subretinal injection system of claim 1, wherein: The controller (6) is a PLC controller or an intelligent computer.

10. The robotic-assisted subretinal injection system of claim 1, wherein: The horizontal moving assembly (103) comprises a connecting block connected with the lifting block on the up-and-down lifting assembly (104) and an extension seat (106) horizontally extended to the front side from one side of the connecting block, the sliding block (107) slides along the sliding groove on the extension seat (106), and the lower end of the angle adjusting seat (108) is rotationally connected with the front end of the extension seat (106).

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