Automatic transmission method of aircraft parts in narrow space

Abstract

The present application relates to the technical field of aircraft assembly, and specifically provides a narrow space aircraft part automatic transmission method. Specifically, a position calibration method is used to realize accurate automatic position calibration of part mounting holes and aircraft mounting holes, so as to realize automatic transportation in cooperation with a two-degree-of-freedom synchronous mechanical gripper. The position calibration method is specifically as follows: laser emission and reception technology is used, and laser emission and reception devices are placed in part assembly holes and aircraft mounting support assembly holes. In the part transportation process, a total of 8, i.e. 4 pairs of laser emission and reception devices, perform real-time position calibration. The two-degree-of-freedom synchronous mechanical gripper moves according to the calibration results, and position alignment is performed in X-axis, Y-axis and Z-axis three dimensions. After the four pairs of mounting holes are completely fitted, the work is stopped. The present application provides a new idea and design, and can effectively solve the difficult problem of unmanned aerial vehicle narrow space part assembly.

Description

Technical Field

[0001] This invention relates to the field of aircraft assembly technology, specifically to the research and application of an automatic transfer technology for aircraft components in confined spaces. Background Technology

[0002] During aircraft assembly, components need to be transported to the aircraft compartment for installation. For open areas or lightweight components, manual handling is feasible. However, for heavier components located in confined spaces, manual handling is inefficient, requires a high level of operator skill and physical strength, and carries the risk of damage to components or the aircraft due to instability caused by manual handling. With the continuous upgrading and iteration of military and civilian aircraft, and the pursuit of lightweight design and improved space utilization, aircraft assembly space is becoming increasingly limited. Therefore, the automated transportation of components within confined aircraft spaces urgently needs to be addressed.

[0003] With the development of science and technology, the application of automated equipment in various mechanical industries is becoming increasingly widespread, and the degree of automation of mechanical equipment is also getting higher and higher. However, robotic arms are commonly used in the automotive industry and are not suitable for aircraft assembly processes. This is because in the automotive manufacturing field, robots or other manipulators must be equipped with gripper mechanisms or gripper tools to perform certain operations or manufacturing tasks. These grippers are similar to the fingers of a human hand. When the grippers work, the corresponding clamping process is equivalent to clamping the object to be clamped between at least two grippers. The grippers can move relative to each other. In order to perform this clamping process, a pushing or pulling force is usually required to bring the grippers closer or further apart. In current automotive manufacturing technology, because robotic arms are used for the assembly of large components such as car doors and roofs, the synchronization of the grippers is not a high requirement for grasping functions. However, aircraft system components are small in size, have high requirements for installation position accuracy, and are located in confined spaces. Therefore, the robotic arms commonly available on the market cannot meet the requirements for aircraft use. Specifically, the synchronization of the two grippers is poor, the grasping effect of the object is poor, and the grippers are prone to not extending properly or the grasped parts are misaligned.

[0004] Meanwhile, after aircraft components are transported to their installation locations in the cabin area, since they are typically fixed to the fuselage at four mounting points using a hole-shaft fit, the mounting holes on the component must be aligned with the mounting holes on the fuselage before the shaft can be used for installation. Currently, the only way to align the mounting holes is to manually move the component visually and manually after it has been manually transported to its approximate location using tools such as a flashlight. However, this method is extremely inefficient, unable to quickly align the four pairs of holes (eight in total), and manually moving the component causes friction between the component and the fuselage, damaging both surfaces and affecting product quality. Therefore, technological innovation is needed. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a research and application of an automatic transfer technology for aircraft components in confined spaces, combining a two-degree-of-freedom synchronous mechanical gripper with a synchronous gripper assembly featuring two grippers that exhibit good linkage with each gripper, and a position calibration method.

[0006] The technical solution of this invention:

[0007] The method for automatic transfer of aircraft parts in confined spaces specifically employs a position calibration method to achieve precise and automated position calibration between the mounting holes of the parts and the mounting holes of the fuselage, thereby enabling automatic transport in conjunction with a two-degree-of-freedom synchronous mechanical gripper.

[0008] The specific position calibration method is as follows: using laser emission and reception technology, laser emission and reception devices are placed in the assembly holes of the component itself and the assembly holes of the mounting bracket of the machine body. During the transportation of the component, a total of 8 laser emission and reception devices, or 4 pairs, are used to perform position calibration in real time. The two-degree-of-freedom synchronous mechanical gripper moves according to the calibration results and performs position alignment in the three dimensions of X-axis, Y-axis and Z-axis until the 4 pairs of mounting holes are completely aligned, and then the work stops.

[0009] Furthermore, the two-degree-of-freedom synchronous mechanical gripper serves as the execution structure for the position calibration method, enabling precise and automated alignment of the component mounting holes with the machine body mounting holes, thereby achieving automatic transportation. The two-degree-of-freedom synchronous mechanical gripper includes a base 1, an X-axis moving module 2, a Y-axis moving module 3, and a gripper module 4. The X-axis moving module 2 is fixedly mounted on the upper end of the base 1, the Y-axis moving module 3 is movably mounted on the X-axis moving module 2 in a mutually perpendicular manner, and the gripper module 4 is mounted on the Y-axis moving module 3. Under the drive of the X-axis moving module 2 and the Y-axis moving module 3, a two-degree-of-freedom gripping motion is achieved.

[0010] Furthermore, the establishment and analysis process of the fixed-point position calibration algorithm model in the aforementioned position calibration method is as follows:

[0011] 1) Set the fixed point position model as

[0012] S G ={(x,y,z)}

[0013] Where x is the horizontal coordinate; y is the vertical coordinate; z = h(x,y) represents the height.

[0014] 2) The model of the fixed point position of the body support in the first pair of fixed points is as follows:

[0015] S G1 ={(x1,y1,z1)}

[0016] Where x1 is the horizontal coordinate; y1 is the vertical coordinate; z1 = h(x1, y1), representing the height.

[0017] 3) The model of the fixed point position of the component in the first pair of fixed points is as follows:

[0018] S′ G1 ={(x′1,y′1,z′1)}

[0019] Where x′1 is the horizontal coordinate; y′1 is the vertical coordinate; z′1 = h(x′1, y′1), which represents the height.

[0020] 4) The formula for calculating the positional deviation of the first pair of fixed points is:

[0021] F G1 =S′ G1 -S G1

[0022] To ensure precise alignment, the position deviation should be set to 0.

[0023] 5) The formula for calculating the overall positional deviation of all fixed points is as follows:

[0024] F G =F G1 +F G2 +F G3 +F G4

[0025] =|S′ G1 -S G1 |+|S′ G2 -S G2 |+|S′ G3 -S G3 |+|S′ G4 -S G4 |

[0026] To ensure accurate alignment, the position deviation is set to 0. Before the position deviation reaches 0, the system performs a loop judgment until the value is 0, at which point the comparison calculation stops.

[0027] Furthermore, the two-degree-of-freedom synchronous mechanical gripper is specifically as follows:

[0028] The base 1 includes a base plate, a vertical plate, and side plates. The vertical plate is vertically mounted on the base plate, and the side plates are connected to the base plate and the vertical plate respectively to improve the stability of the base 1.

[0029] The X-axis moving module 2 includes an X-axis base plate 5, an X-axis drive motor 6, two X-axis pulleys 7, an X-axis transmission belt 8, an X-axis slide rail 9, and an X-axis slider 10. The X-axis base plate 5 is arranged along the X-axis direction and its back center is fixedly connected to a vertical plate. The X-axis drive motor 6 is installed at the middle position of the left end of the back of the X-axis base plate 5. The output shaft of the X-axis drive motor 6 passes through the X-axis base plate 5 and is connected to one X-axis pulley 7. Another X-axis pulley 7 is rotatably installed at the symmetrical position of the right end of the X-axis base plate 5. The two X-axis pulleys 7 are equipped with X-axis transmission belts 8. The upper and lower ends of the X-axis base plate 5 are equipped with X-axis slide rails 9 of the same specifications along the X-axis direction. The length of the X-axis slide rail 9 is the same as the length of the X-axis base plate 5. Each X-axis slide rail 9 is equipped with two X-axis sliders 10. The X-axis sliders 10 are fixedly installed with the X-axis transmission belt 8 and can slide along the X-axis slide rail 9 under the drive of the X-axis transmission belt 8.

[0030] The Y-axis moving module 3 includes a Y-axis drive motor 11, a Y-axis base plate 12, a limit block 13, a Y-axis slide rail 14, a Y-axis slider 15, a bearing seat 16, a lead screw 17, and a connecting plate 18. The Y-axis base plate 12 is set along the Y-axis direction and fixedly installed on the X-axis slider 10. The Y-axis drive motor 11 and the limit block 13 are installed on the upper end of the Y-axis base plate 12. Two Y-axis slide rails 14 of the same specification are set on the left and right ends along the Y-axis direction. The Y-axis slider 15 is slidably connected to the Y-axis slide rail 14. The lead screw 17 is set between the two Y-axis slide rails 14. One end of the lead screw 17 is rotatably connected to the bearing seat 16, and the other end drives the other bearing seat 16 and is fixedly connected to the output end of the Y-axis drive motor 11 through a coupling. The middle part of the Y-axis slider 15 is threadedly connected to the lead screw 17 and can slide along the Y-axis slide rail 14 under the drive of the lead screw 17. One end of the connecting plate 18 is fixedly installed on the Y-axis slider 15, and the other end is connected to the gripper module 4.

[0031] The gripper module 4 includes a gripper drive motor 19, a base plate 20, a drive pulley A21, a drive pulley 22, a drive belt 23, a tension pulley 24, a reversing synchronous pulley 25, a drive gear 26, a tension pulley adjusting nut 27, a left gripper 28, a left gripper spring 29, a right gripper 30, and a right gripper spring 31. The base plate 20 is fixedly mounted on the lower end of the connecting plate 18. The gripper drive motor 19 is mounted on the back of the upper end of the base plate 20. The output shaft of the gripper drive motor 19 passes through the front side of the base plate 20 and is mounted on the drive pulley A21. The drive pulley 22 is rotatably mounted on the left front end of the base plate 20. The reversing synchronous pulley 25 and the drive gear 26 are rotatably mounted on the right front end of the base plate 20. The reversing synchronous pulley 25 consists of the drive pulley and the reversing gear. The system consists of a drive pulley fixedly mounted on the front side of the reversing gear. The drive gear 26 meshes with the reversing gear of the reversing synchronous pulley 25. The drive pulleys A21, 22, and 25 are connected by a drive belt 23. A mounting hole is provided in the middle of the base plate 20. The tension wheel 24 passes through the mounting hole and is connected to the tension wheel adjusting nut 27. A left gripper 28 is mounted on the left rear side of the base plate 20. The upper end of the left gripper 28 is fixedly connected to the shaft of the drive pulley 22. A right gripper 30 is mounted on the right rear side of the base plate 20. The upper end of the right gripper 30 is fixedly connected to the shaft of the drive gear 26. A left gripper spring 29 and a right gripper spring 31 are respectively mounted on the gripping side surfaces of the left gripper 28 and the right gripper 30.

[0032] The beneficial effects of this invention are:

[0033] (1) This invention provides a new idea and design. Based on laser emission and reception technology, it designs a position alignment method and a two-degree-of-freedom synchronous mechanical gripper to cooperate in a narrow space automatic assembly technology, which can effectively solve the difficult problems in the assembly of UAV components in narrow space.

[0034] (2) The position calibration method provided by the present invention performs synchronous position calibration with 4 pairs of mounting holes according to the actual installation situation of the component, so as to avoid the inability to install due to misalignment of a single mounting position;

[0035] (3) During the use of this invention, the position calibration method can be used in conjunction with the mechanical gripper to adjust the position of the component in real time throughout the entire process of gripping the component, moving the component, and aligning the component with the mounting bracket, and the position determination is accurate.

[0036] (4) The present invention can realize the gripping and handling of components. It uses the X-axis moving module and the Y-axis moving module as carriers to realize the two-degree-of-freedom motion of the gripper module. It has the advantages of simple structure, small footprint, low cost and flexible application scenarios.

[0037] (5) The gripper module adopts a drive method that combines belt drive and gear drive, and the two grippers move with high synchronization, which solves the shortcomings of poor synchronization of traditional manipulators; driven by a single motor, the structure is simple and compact, the control operation is convenient, and it is safe and reliable. Attached Figure Description

[0038] Figure 1 This is a schematic diagram showing the placement of the laser transmitter and receiver on the mounting bracket on the aircraft. Similarly, the laser transmitter and receiver are placed at the four fixed points on the component using the same method.

[0039] Figure 2 This is a schematic diagram of a two-degree-of-freedom synchronous mechanical gripper.

[0040] Figure 3 This is a schematic diagram of the X-axis movement module of a two-degree-of-freedom synchronous mechanical gripper.

[0041] Figure 4 This is a schematic diagram of the Y-axis movement module of a two-degree-of-freedom synchronous mechanical gripper.

[0042] Figure 5 This is a schematic diagram of the gripper module of a two-degree-of-freedom synchronous mechanical gripper.

[0043] Figure 6 This is the front view of a two-degree-of-freedom synchronous mechanical gripper.

[0044] In the diagram: 1. Base, 2. X-axis moving module, 3. Y-axis moving module, 4. Gripper module, 5. X-axis base plate, 6. X-axis drive motor, 7. X-axis pulley, 8. X-axis transmission belt, 9. X-axis slide rail, 10. X-axis slider, 11. Y-axis drive motor, 12. Y-axis base plate, 13. Limit block, 14. Y-axis slide rail, 15. Y-axis slider, 16. Bearing seat, 17. Lead screw, 18. Connecting plate, 19. Gripper drive motor, 20. Base plate, 21. Drive pulley A, 22. Drive pulley, 23. Drive belt, 24. Tensioner, 25. Reversing synchronous pulley, 26. Drive gear, 27. Tensioner adjusting nut, 28. Left gripper, 29. Left gripper spring, 30. Right gripper, 31. Right gripper spring. Detailed Implementation

[0045] The specific implementation methods and steps of this invention are as follows:

[0046] (1) Installation of laser transmitting and receiving device

[0047] When in use, place the laser emission and receiving devices into the bolt holes at the fixed points, ensuring that the devices are flush with the contact surfaces of the bracket and the finished product, and prepare for automatic transportation.

[0048] (2) Laser alignment determines the position of the grasped component.

[0049] When using a two-degree-of-freedom synchronous mechanical gripper (hereinafter referred to as mechanical gripper) with a good linkage effect between two grippers, the base 1 is fixedly installed around the installation area. The position of the part to be gripped is determined by the laser emission and reception of the laser emission and reception device using the position calibration method.

[0050] (3) Autonomous movement of the mechanical gripper along the X-axis

[0051] After the position is determined, the mechanical gripper automatically controls the X-axis drive motor 6 to rotate, which drives the X-axis pulley 7 to rotate. The rotation of the X-axis pulley 7 drives the X-axis transmission belt 8 to move. The movement of the X-axis transmission belt 8 drives the X-axis slider 10, which is fixedly connected to the X-axis transmission belt 8, to move along the X-axis slide rail 9, which in turn drives the Y-axis moving module 3 to move, thereby driving the gripper module 4 to move along the X-axis direction.

[0052] (4) Autonomous movement of the mechanical gripper along the Y-axis

[0053] The mechanical gripper automatically controls the rotation of the Y-axis drive motor 11, which drives the lead screw 17 to rotate. Since the middle part of the Y-axis slider 15 is threadedly connected to the lead screw 17, the rotation of the lead screw 17 will drive the Y-axis slider 15 to move along the Y-axis slide rail 14, thereby driving the gripper module 4 to move along the Y-axis direction.

[0054] (5) Autonomous movement of the gripper

[0055] After the above steps, the gripper module 4 is driven by the X-axis moving module 2 and the Y-axis moving module 3 to achieve two degrees of freedom of movement. The gripper drive motor 19 is controlled to drive the drive pulley A21 to rotate clockwise. Under the transmission of the drive belt 23, the drive pulley 22 and the reversing synchronous pulley 25 are driven to rotate clockwise, thereby driving the drive gear 26, which meshes with the reversing gear of the reversing synchronous pulley 25, to rotate counterclockwise, thereby realizing the opening of the left gripper 28 and the right gripper 30.

[0056] (6) Automatic gripping component

[0057] When the mechanical gripper automatically reaches the position of the part to be gripped, the gripper drive motor 19 automatically controls the drive pulley A21 to rotate counterclockwise. Under the transmission of the drive belt 23, the drive pulley 22 and the reversing synchronous pulley 25 rotate counterclockwise. Through the reversing action of the reversing gear of the reversing synchronous pulley 25, the drive gear 26 meshing with the reversing gear of the reversing synchronous pulley 25 rotates counterclockwise, thereby driving the left gripper 28 and the right gripper 30 to close, thus realizing the gripping of the part.

[0058] (7) Grab synchronization guarantee

[0059] The left gripper 28 and right gripper 30 are respectively equipped with left gripper spring 29 and right gripper spring 31 on their gripping side surfaces. The gripper springs are made of elastic material, and their shape can be set according to the shape of the part to be gripped, which can improve the stability and safety of gripping. The tension wheel 24 is in contact with the drive belt 23 and can move up and down in the mounting hole. The tension wheel 24 is adjusted to a suitable position and locked with the tension wheel adjusting nut 27 to ensure that the drive belt 23 is in the optimal state, thereby ensuring the synchronous movement of multiple pulleys.

[0060] (8) Position calibration

[0061] During the movement of the robotic gripper, eight laser emission and receiving devices (four pairs) are positioned in real time for position calibration using laser emission and receiving technology. The robotic gripper moves synchronously based on the calibration results, aligning itself in the X, Y, and Z axes. (Press F...) G =F G1 +F G2 +F G3 +F G4 The calculation is performed, and to ensure accurate alignment, the position deviation is set to 0. Before the position deviation reaches 0, the system performs a loop judgment until the value is 0 and then stops the comparison calculation. At this point, the mechanical gripper stops working after the 4 pairs of mounting holes are completely aligned.

Claims

1. A method for automatic transfer of aircraft parts in a confined space, characterized in that, Specifically, a position calibration method is used to achieve precise and automated position calibration between the component mounting holes and the machine body mounting holes, thereby enabling automatic transportation in conjunction with a two-degree-of-freedom synchronous mechanical gripper. The specific position calibration method is as follows: using laser emission and reception technology, laser emission and reception devices are placed in the assembly holes of the component itself and the assembly holes of the mounting bracket of the machine body. During the transportation of the component, a total of 8 laser emission and reception devices, or 4 pairs, are used to perform position calibration in real time. The two-degree-of-freedom synchronous mechanical gripper moves according to the calibration results and performs position alignment in the three dimensions of X-axis, Y-axis and Z-axis until the 4 pairs of mounting holes are completely aligned, and then the work stops. The establishment and analysis process of the fixed-point position calibration algorithm model in the described position calibration method is as follows: 1) Set the fixed point location model as Where x is the horizontal coordinate; y is the vertical coordinate; z = h(x,y) represents the height; 2) The model of the fixed point position of the body support in the first pair of fixed points is as follows: in, The horizontal axis; The vertical axis; =h( , ), indicating altitude; 3) The model of the fixed point position of the component in the first pair of fixed points is as follows: in, The horizontal axis; The vertical axis; =h( , ), indicating altitude; 4) The formula for calculating the positional deviation of the first pair of fixed points is: To ensure precise alignment, the position deviation should be set to 0. 5) The formula for calculating the overall positional deviation of all fixed points is as follows: To ensure accurate alignment, the position deviation is set to 0. Before the position deviation reaches 0, a loop is performed to determine the position until the value is 0, at which point the comparison calculation stops.

2. The automatic transfer method for aircraft parts in confined spaces according to claim 1, characterized in that, The two-degree-of-freedom synchronous mechanical gripper serves as the execution structure for the position calibration method, enabling precise and automated alignment of the component mounting hole with the machine body mounting hole, thereby achieving automatic transportation. The two-degree-of-freedom synchronous mechanical gripper includes a base (1), an X-axis moving module (2), a Y-axis moving module (3), and a gripper module (4). The X-axis moving module (2) is fixedly mounted on the upper end of the base (1), and the Y-axis moving module (3) is movably mounted on the X-axis moving module (2) in a mutually perpendicular manner. The gripper module (4) is mounted on the Y-axis moving module (3), and the two-degree-of-freedom gripping motion is achieved under the drive of the X-axis moving module (2) and the Y-axis moving module (3).

3. The automatic transfer method for aircraft parts in confined spaces according to claim 2, characterized in that, The base (1) includes a base plate, a vertical plate and a side plate. The vertical plate is installed vertically on the base plate, and the side plate is connected to the base plate and the vertical plate respectively to improve the stability of the base (1).

4. The automatic transfer method for aircraft parts in confined spaces according to claim 2, characterized in that, The X-axis moving module (2) includes an X-axis base plate (5), an X-axis drive motor (6), two X-axis pulleys (7), an X-axis transmission belt (8), an X-axis slide rail (9), and an X-axis slider (10). The X-axis base plate (5) is set along the X-axis direction and its back is fixedly connected to the vertical plate in the middle. The X-axis drive motor (6) is installed at the middle position of the left end of the back of the X-axis base plate (5). The output shaft of the X-axis drive motor (6) passes through the X-axis base plate (5) and is connected to an X-axis pulley (7). On the right side of the X-axis base plate (5) Another X-axis pulley (7) is rotatably mounted at the symmetrical position at the end. An X-axis drive belt (8) is provided on the two X-axis pulleys (7). X-axis slide rails (9) of the same specifications are provided at the upper and lower ends of the X-axis base plate (5) along the X-axis direction. The length of the X-axis slide rail (9) is the same as the length of the X-axis base plate (5). Two X-axis sliders (10) are provided on each X-axis slide rail (9). The X-axis sliders (10) are fixedly installed with the X-axis drive belt (8) and can slide along the X-axis slide rail (9) under the drive of the X-axis drive belt (8).

5. The automatic transfer method for aircraft parts in confined spaces according to claim 4, characterized in that, The Y-axis moving module (3) includes a Y-axis drive motor (11), a Y-axis base plate (12), a limit block (13), a Y-axis slide rail (14), a Y-axis slider (15), a bearing seat (16), a lead screw (17), and a connecting plate (18). The Y-axis base plate (12) is set along the Y-axis direction and fixedly installed on the X-axis slider (10). The Y-axis drive motor (11) and the limit block (13) are installed on the upper end of the Y-axis base plate (12). Two Y-axis slide rails (14) of the same specification are set on the left and right ends along the Y-axis direction. The upper sliding connection has a Y-axis slider (15), and the lead screw (17) is set between two Y-axis slide rails (14). One end of the lead screw (17) is rotatably connected to the bearing seat (16), and the other end drives the other bearing seat (16) and the output end of the Y-axis drive motor (11) through a coupling. The middle part of the Y-axis slider (15) is threadedly connected to the lead screw (17), and can slide along the Y-axis slide rail (14) under the drive of the lead screw (17). One end of the connecting plate (18) is fixedly installed on the Y-axis slider (15), and the other end is connected to the gripper module (4).

6. The automatic transfer method for aircraft parts in confined spaces according to claim 5, characterized in that, The gripper module (4) includes a gripper drive motor (19), a base plate (20), a drive pulley A (21), a drive pulley (22), a drive belt (23), a tension pulley (24), a reversing synchronous pulley (25), a drive gear (26), a tension pulley adjusting nut (27), a left gripper (28), a left gripper spring (29), a right gripper (30), and a right gripper spring (31). The base plate (20) is fixedly installed on the lower end of the connecting plate (18). The gripper drive motor (19) is installed on the back of the upper end of the base plate (20). The output shaft of the gripper drive motor (19) passes through the front side of the base plate (20) and is installed with the drive pulley A (21). The drive pulley (22) is rotatably installed on the left front end of the base plate (20). The reversing synchronous pulley (25) and the drive gear (26) are rotatably installed on the right front end of the base plate (20). The reversing synchronous pulley (25) is driven by the drive pulley. The system consists of a pulley and a reversing gear. The drive pulley is fixedly installed on the front side of the reversing gear. The drive gear (26) meshes with the reversing gear of the reversing synchronous pulley (25). The drive pulley A (21), drive pulley (22), and drive pulley of the reversing synchronous pulley (25) are connected by a drive belt (23). The middle part of the base plate (20) has a mounting hole. The tension wheel (24) passes through the mounting hole and is connected to the tension wheel adjusting nut (27). A left gripper (28) is installed on the left rear side of the base plate (20). The upper end of the left gripper (28) is fixedly connected to the shaft of the drive pulley (22). A right gripper (30) is installed on the right rear side of the base plate (20). The upper end of the right gripper (30) is fixedly connected to the shaft of the drive gear (26). The gripping side surfaces of the left gripper (28) and the right gripper (30) are respectively equipped with a left gripper spring (29) and a right gripper spring (31).

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