Device for automatically assembling piston rod and piston of hydraulic oil cylinder

Abstract

The utility model discloses a device for automatically assembling a piston rod and a piston of a hydraulic oil cylinder, and belongs to the technical field of hydraulic oil cylinder piston assembling. The device mainly comprises a clamping device used for clamping a piston, the clamping device is installed at the movable end of a first mechanical arm, and a gluing device is installed on the side wall of the clamping device; the positioning tool is fixedly provided with a piston rod, the tightening device comprises a tightening tool, a second driving device and a mounting assembly, an output shaft of the second driving device and the tightening tool are fixedly mounted, and the second driving device and the movable end of the second mechanical arm are fixedly mounted through the mounting assembly. The rapid assembly of the piston rod and the piston is achieved, the production efficiency is greatly improved, the assembly quality is improved, the high-precision visual system and the control system are applied, it is ensured that the assembly position is accurate, thread glue coating is even, torque control is accurate, the assembly quality is remarkably improved, and the labor cost is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of hydraulic cylinder piston assembly, and in particular to a device for automatically assembling a piston rod and piston of a hydraulic cylinder. Background Art

[0002] The piston rod and piston assembly method of the hydraulic cylinder. The piston rod end of the hydraulic cylinder is usually equipped with a piston, which is used to install the hydraulic sealing system to seal the hydraulic medium and transmit hydraulic kinetic energy. Figure 1 As shown, the piston rod 7 and the piston 8 are sometimes connected by threads, and manual thread glue is required to be applied and the piston 8 is installed.

[0003] This manual assembly method has problems such as low efficiency and unstable assembly quality, which affects the delivery and reliability of the hydraulic cylinder. Therefore, there is an urgent need for a device for automating the assembly of piston rods and pistons to improve assembly efficiency and quality.

[0004] After searching, the announcement number is CN214980739U, which discloses an assembly tool for a piston and a piston rod, including a support frame, a fixed bracket and an auxiliary bracket arranged on the support frame, and the fixed bracket and the auxiliary bracket are both fixedly provided with two V-shaped blocks; it is characterized in that the two blocks of the fixed bracket are both provided with clamping cylinders, and the piston rods of the two clamping cylinders are arranged opposite to each other; two guide rails and a telescopic cylinder are also fixedly provided on the support frame, and a workbench is arranged on the two guide rails through a slide seat, and the workbench is connected to the piston rod of the telescopic cylinder, and a hydraulic motor is fixedly provided on the workbench, and a sleeve is fixedly connected to the output shaft of the hydraulic motor, and one end of the sleeve is provided with two opposite notches, and a booster rod is placed in the two notches. This technical solution has the advantages of easy operation and smooth rotation of the piston, can improve the assembly quality and efficiency, and ensure the smooth progress of the assembly.

[0005] However, although the existing technical solution can realize the assembly of the piston rod and the piston instead of the manual assembly process, the following problems still exist when the piston rod and the piston are pre-assembled:

[0006] 1. The fixed position of each piston rod cannot be guaranteed, which causes the position of the piston rod to shift. As a result, when the piston thread is installed on the piston rod, it cannot be rotated enough to make the piston rod loose, or it rotates too much to cause the thread of the piston rod to be stripped and damaged.

[0007] 2. When assembling the piston rod and the piston, it is often necessary to apply glue to ensure the sealing. The existing assembly tooling lacks a glue application device.

[0008] Therefore, it is necessary to provide a device for automatically assembling the piston rod and piston of a hydraulic cylinder to solve the above problems.

[0009] It should be noted that the above information disclosed in this background technology section is only for understanding the background technology of the present application concept, and therefore, it may contain information that does not constitute the prior art. Utility Model Content

[0010] Based on the above problems existing in the prior art, the problem to be solved by the present application is: to provide a device for automatically assembling a piston rod and a piston of a hydraulic cylinder, so as to solve the problems of inaccurate assembly position of the piston rod and the piston and inconvenient gluing.

[0011] The technical solution adopted by this application to solve its technical problem is:

[0012] A device for automatically assembling a piston rod and a piston of a hydraulic cylinder, comprising a clamping device for clamping the piston, the clamping device being mounted on the movable end of a first manipulator, and a gluing device being mounted on the side wall of the clamping device;

[0013] A positioning tool, wherein the positioning tool is fixedly mounted with a piston rod, the clamping device clamps the piston and places it on the top of the piston rod through the movement of the first manipulator, and the gluing end of the gluing device is located at the thread of the end of the piston rod;

[0014] A tightening device, the tightening device comprising a tightening tool, a second drive device and a mounting assembly, the output shaft of the second drive device is fixedly mounted on the tightening tool, and the second drive device is fixedly mounted on the movable end of the second manipulator through the mounting assembly;

[0015] The tightening device performs a rotational tightening movement on the piston installed on the piston rod through the movement of the second manipulator.

[0016] Preferably, the gluing device includes a first mounting plate, a mounting clamp and a glue injection head, the first mounting plate is fixedly mounted on the side wall of the clamping device, the side wall of the first mounting plate is fixedly mounted with a mounting clamp, and the glue injection head is clamped and mounted inside the mounting clamp.

[0017] Preferably, the positioning fixture comprises a first driving device, a V-shaped block, a guide rail assembly and a fixed plate, the fixed plate is fixedly mounted on the table top of the processing table, the guide rail assembly and the first driving device are both mounted on the side wall of the fixed plate, the V-shaped block is provided in two groups, one of the V-shaped blocks of the two groups is fixedly mounted on the side wall of the fixed plate, and the other V-shaped block is fixedly mounted on the side wall of the slide table of the guide rail assembly, and the side wall of the V-shaped block mounted on the guide rail assembly is fixedly mounted on the output shaft of the first driving device;

[0018] Wherein, the first driving device drives the V-block to slide on the guide rail assembly to change the distance between the V-block and another V-block, so as to clamp and fix the side wall of the piston rod.

[0019] Preferably, the mounting assembly includes a second mounting plate, a third mounting plate and a quick-change assembly, the second mounting plate is fixedly mounted on the movable end of the second manipulator, the top surface of the third mounting plate is fixedly mounted on the second driving device, and the second mounting plate is fixedly mounted on the first mounting plate through the quick-change assembly.

[0020] Preferably, a high-precision vision system is installed on one side of the second mounting plate.

[0021] Preferably, a support frame is fixedly installed on the table top of the processing table and located on one side of the positioning tooling, and a high-precision visual system is installed on the top of the support frame.

[0022] Preferably, the tightening tool comprises a tightening pin and a spring, a cavity for accommodating the spring is provided inside the tightening tool, a sliding hole is also provided inside the tightening tool, the tightening pin is slidably connected in the sliding hole, the tightening pin is fixedly connected to a limiting block on the side wall of the cavity, the top surface of the limiting block contacts the spring, and the spring is sleeved on the side wall of the tightening pin.

[0023] The beneficial effects of this application are:

[0024] 1. Assembling the piston with the piston rod through the first manipulator, the second manipulator, the clamping device and the tightening device can improve production efficiency: the manipulator and the automatic control system can realize the rapid assembly of the piston rod and the piston, which greatly improves production efficiency and assembly quality: the application of high-precision visual system and control system ensures accurate assembly position, uniform coating of thread glue, accurate torque control, significantly improves assembly quality, and reduces labor costs: fully realizes unmanned assembly, reduces dependence on highly skilled operators, and reduces labor costs.

[0025] 2. A gluing device is installed on the side wall of the clamping device, so that when the piston rod is assembled, the thread of the piston rod can be glued, replacing the manual gluing method, so as to further improve the assembly efficiency.

[0026] In addition to the above-described purposes, features and advantages, the present application also has other purposes, features and advantages. The present application will be further described in detail with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0028] In the attached picture:

[0029] Figure 1A schematic diagram of a traditional manual piston assembly in the background art of this application;

[0030] Figure 2 This is a schematic diagram of the structure of a device for automatically assembling a piston rod and a piston of a hydraulic cylinder in Example 1;

[0031] Figure 3 for Figure 2 Schematic diagram of the assembly structure of the first manipulator, the clamping device and the gluing device;

[0032] Figure 4 for Figure 2 Schematic diagram of the center positioning tooling structure;

[0033] Figure 5 for Figure 2 Schematic diagram of the installation position of the tightening device and the high-precision vision system;

[0034] Figure 6 This is the schematic diagram of the automation control system in this application;

[0035] Figure 7 This is the workflow diagram for the automatic assembly of piston rod and piston in the application;

[0036] Figure 8 This is a schematic diagram of the installation position structure of the high-precision visual system in Example 2;

[0037] Fig. 9 This is a schematic diagram of the structure of the device for automatically assembling the piston rod and piston of the hydraulic cylinder in Example 3;

[0038] Fig.10 for Fig. 9 Schematic diagram of the tightening tooling structure

[0039] Among them, the reference numerals in the figure are:

[0040] A. The first manipulator;

[0041] B. The second manipulator;

[0042] 1. Clamping device;

[0043] 2. Gluing device; 2.1. First mounting plate; 2.2. Mounting clamp; 2.3. Gluing head;

[0044] 3. High-precision visual system; 3.1. Support frame;

[0045] 4. Positioning tooling; 4.1. First driving device; 4.2. V-block; 4.3. Guide rail assembly; 4.4. Fixing plate;

[0046] 5. Tightening device; 5.1. Tightening tool; 5.1.1. Tightening pin; 5.1.2. Spring; 5.2. Quick-change assembly; 5.3. Second mounting plate; 5.4. Third mounting plate; 5.5. Second driving device

[0047] 6. Control system;

[0048] 7. Piston rod;

[0049] 8. Piston;

[0050] 9. Tighten the holes. DETAILED DESCRIPTION

[0051] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0052] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present application.

[0053] See also Figure 2-10 , the utility model provides the embodiment:

[0054] Example 1

[0055] like Figure 2 As shown, a device for automatically assembling a piston rod and a piston of a hydraulic cylinder includes a clamping device 1 for clamping a piston 8. The piston 8 is clamped by the clamping claws of the clamping device 1. The clamping device 1 is installed on the movable end of a first manipulator A. The first manipulator A has a multi-degree-of-freedom adjustment function to ensure that the piston 8 can be accurately clamped and placed. A glue device 2 is installed on the side wall of the clamping device 1;

[0056] A positioning fixture 4, wherein the positioning fixture 4 is fixedly mounted with a piston rod 7, the clamping device 1 clamps the piston 8 and places it on the top of the piston rod 7 through the movement of the first manipulator A, and the glue application end of the glue application device 2 is located at the threaded portion of the end of the piston rod 7;

[0057] Specifically, Figure 4As shown, the positioning fixture 4 includes a first driving device 4.1, a V-block 4.2, a guide rail assembly 4.3 and a fixed plate 4.4, the fixed plate 4.4 is fixedly mounted on the table top of the processing table, the guide rail assembly 4.3 and the first driving device 4.1 are both mounted on the side wall of the fixed plate 4.4, the V-block 4.2 is provided in two groups, one of the V-blocks 4.2 of the two groups is fixedly mounted on the side wall of the fixed plate 4.4, the other V-block 4.2 is fixedly mounted on the side wall of the slide of the guide rail assembly 4.3, and the side wall of the V-block 4.2 mounted on the guide rail assembly 4.3 is fixedly mounted on the output shaft of the first driving device 4.1, the first driving device 4.1 can be an electric or pneumatic torque tool, as long as it can drive the V-block 4.2 to slide on the guide rail assembly 4.3, so that the two V-blocks 4.2 can clamp and fix the side wall of the piston rod 7;

[0058] The first driving device 4.1 drives the V-block 4.2 to slide on the guide rail assembly 4.3 to change the distance between the first driving device 4.1 and the other V-block 4.2, so as to clamp and fix the side wall of the piston rod 7.

[0059] By controlling the first driving device 4.1, one of the V-blocks 4.2 can move on one side of the fixed plate 4.4 under the sliding action of the guide rail assembly 4.3, while the other V-block 4.2 is fixedly installed on the side wall of the fixed plate 4.4, thereby changing the distance between the two V-blocks 4.2 to adjust according to different sizes and specifications of the piston rod 7 to ensure applicability, so that the piston rod 7 can be fixedly clamped to prevent the piston rod 7 from shaking and displacement during the process of installing the piston 8 on the piston rod 7.

[0060] Furthermore, two groups of positioning tools 4 can be provided, and the two groups of positioning tools 4 are mirror-mounted on the workbench surface, so that after the piston rod 7 on the first group of positioning tools 4 is assembled with the piston 8, the device for automatically assembling the piston rod 7 and the piston of the hydraulic cylinder can be assembled with the piston 8 on the piston rod 7 on another positioning tool 4 without stopping, and the piston rod 7 assembled on this positioning tool 4 is unloaded manually or by a robot to ensure assembly efficiency.

[0061] like Figure 3 As shown, the glue-spraying device 2 comprises a first mounting plate 2.1, a mounting clamp 2.2 and a glue injection head 2.3. The first mounting plate 2.1 is fixedly mounted on the side wall of the clamping device 1. The side wall of the first mounting plate 2.1 is fixedly mounted with the mounting clamp 2.2. The glue injection head 2.3 is clamped and mounted inside the mounting clamp 2.2.

[0062] After the first manipulator A places the top of the piston rod 7 through the clamping device 1, the glue outlet of the glue injection head 2.3 applies a proper amount of thread glue to the thread of the end of the piston rod 7, replacing manual glue application.

[0063] like Figure 5 As shown, the tightening device 5 comprises a tightening tool 5.1, a second driving device 5.5 and a mounting assembly, wherein the output shaft of the second driving device 5.5 is fixedly mounted on the tightening tool 5.1, and the second driving device 5.5 is fixedly mounted on the movable end of the second manipulator B through the mounting assembly;

[0064] Among them, the tightening device 5 rotates and tightens the piston 8 installed on the piston rod 7 through the movement of the second manipulator B. The second driving device 5.5 can be a servo motor or a stepping motor, as well as a driving device that can drive the tightening tool 5.1 to rotate and provide torque. The mounting assembly includes a second mounting plate 5.3, a third mounting plate 5.4 and a quick-change assembly 5.2. The second mounting plate 5.3 is fixedly mounted on the movable end of the second manipulator B, and the top surface of the third mounting plate 5.4 is fixedly mounted on the second driving device 5.5. The second mounting plate 5.3 is fixedly mounted on the first mounting plate 2.1 through the quick-change assembly 5.2.

[0065] After the first manipulator A places the piston 8 on the end of the piston rod 7, the second manipulator B drives the tightening device 5 to move to the top of the piston 8, and then descends, so that the tightening pin 5.1.1 on the tightening tool 5.1 is aligned with the tightening hole 9 opened on the piston 8, and the tightening pin 5.1.1 is inserted into the tightening hole 9, and then the tightening tool 5.1 is driven to rotate by the second driving device 5.5, and the piston 8 is installed on the end of the piston rod 7, thereby completing the assembly process of the piston rod 7 and the piston 8.

[0066] In order to enable the automatic assembly process of the piston rod 7 piston of the hydraulic cylinder to be completed, a control system 6 for controlling the coordinated work of various components and a high-precision visual system 3 for real-time monitoring of the placement position and state of the piston to ensure assembly accuracy are also provided;

[0067] like Figure 6 As shown, a high-precision visual system 3 is installed on one side of the second mounting plate 5.3. The visual system includes a high-definition camera and image processing software, which can identify the specific position and state of the piston 8 and the piston rod 7. The control system 6 is used to coordinate the workflow of each component to ensure the automation and precise control of the entire assembly process. The control system 6 includes a programmable logic controller (PLC) and a human-machine interface (HMI) for easy operation and monitoring:

[0068] like Figure 7 As shown, the specific workflow is as follows:

[0069] 1. Preliminary preparation: Fix the piston rod 7 on the positioning fixture 44, and apply a proper amount of thread glue on the thread position through the glue applying device 2.

[0070] 2. The first manipulator A clamps and places the piston: the first manipulator A drives the clamping device 1 to clamp the piston 8 and accurately places it on the top of the piston rod 7 on the positioning tooling 4.

[0071] 3. Visual system calibration: The high-precision visual system 3 accurately records the alignment of the piston 8 and the piston rod 7 and the position of the tightening hole 9 of the piston 8, and transmits it to the second manipulator B that installs the tightening device 5 through the communication protocol. The second manipulator B adjusts the tightening device 5 according to the visual data to complete the precise alignment of the tightening pin 5.1.1 of the tightening tool 5.1 and the tightening hole 9.

[0072] 4. Positioning of the tightening device 5: The second manipulator B carries the tightening device 5 and automatically positions the tightening pin 5.1.1 of the tightening tool 5.1 to the tightening hole 9 on the piston 8 according to the instruction of the control system 6.

[0073] 5. Automatically tighten the piston 8: By inserting the tightening tool 5.1, the tightening work of the piston 8 is automatically completed to ensure that the assembly torque reaches the preset standard.

[0074] Quality inspection: After assembly is completed, the system automatically detects the assembly quality.

[0075] Example 2

[0076] like Figure 8 As shown, in this embodiment 2, the first manipulator A, the second manipulator B, the clamping device 1, the glue-applying device 2, and the positioning tool 4 are all arranged in the same manner as in embodiment 1, except that the installation position of the high-precision visual system 3 is different from that in embodiment 1;

[0077] Specifically, a support frame 3.1 is fixedly installed on the table top of the processing table and on one side of the positioning tool 4. A high-precision visual system 3 is installed on the top of the support frame 3.1. The high-precision visual system 3 is placed in a fixed position, and the positions of the positioning piston rod 7, the piston 8 and the tightening hole 9 are analyzed by taking photos, and accurate feedback is given to the second manipulator B to drive the tightening device 5 to accurately insert the two tightening pins 5.1.1 of the tightening tool 5.1 into the tightening hole 9 to complete the tightening action.

[0078] Example 3

[0079] like Figure 9-10As shown, in this embodiment 3, the first manipulator A, the second manipulator B, the clamping device 1, the glue device 2, the positioning tool 4 and the tightening device 5 are the same as those in the embodiment 1, wherein the difference from the embodiment 1 is that the tightening pin 5.1.1 of the tightening tool 5.1 is set differently. The tightening pin 5.1.1 in the embodiment 1 can be fixed on the tightening tool 5.1, and the alignment of the tightening pin 5.1.1 and the tightening hole 9 is determined by the high-precision visual system 3, while in this embodiment 3, the tightening tool 5.1 includes the tightening pin 5.1.1 and the elastic spring 5.1.1. Spring 5.1.2, the tightening tool 5.1 is provided with a cavity 5.1.5 for accommodating the spring 5.1.2, the tightening tool 5.1 is also provided with a sliding hole 5.1.4, the tightening pin 5.1.1 is slidably connected in the sliding hole 5.1.4, the tightening pin 5.1.1 is located on the side wall of the cavity 5.1.5 and is fixedly connected to a limit block 5.1.3, the top surface of the limit block 5.1.3 is in contact with the spring 5.1.2, and the spring 5.1.2 is sleeved on the side wall of the tightening pin 5.1.1;

[0080] After the second manipulator B drives the tightening device 5 to the position of the piston 8, the tightening tool 5.1 contacts the end surface of the piston 8. At this time, the spring 5.1.2 is in a compressed state. The second driving device 5.5 drives the tightening tool 5.1 to rotate slowly under the control of the control system 6 until it reaches a certain position. The tightening pin 5.1.1 is inserted into the tightening hole 9 under the elastic force of the spring 5.1.2, and the second driving device 5.5 starts to rotate at a high speed to perform an automatic tightening action.

[0081] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A device for automatically assembling a piston rod and a piston of a hydraulic cylinder, characterized in that: It comprises a clamping device (1) for clamping a piston (8), the clamping device (1) being mounted on the movable end of a first manipulator (A), and a glue-applying device (2) being mounted on the side wall of the clamping device (1); A positioning tool (4), wherein the positioning tool (4) is fixedly mounted with a piston rod (7), the clamping device (1) clamps the piston (8) and places it on the top of the piston rod (7) through the movement of the first manipulator (A), and the glue application end of the glue application device (2) is located at the end thread of the piston rod (7); A tightening device (5), the tightening device (5) comprising a tightening tool (5.1), a second drive device and a mounting assembly, the output shaft of the second drive device being fixedly mounted on the tightening tool (5.1), and the second drive device being fixedly mounted on the movable end of the second manipulator (B) via the mounting assembly; The tightening device (5) performs a rotational tightening movement on the piston (8) mounted on the piston rod (7) through the movement of the second manipulator (B).

2. The device for automatically assembling a piston rod and a piston of a hydraulic cylinder according to claim 1, characterized in that: The glue-spraying device (2) comprises a first mounting plate (2.1), a mounting clamp seat (2.2) and a glue injection head (2.3); the first mounting plate (2.1) is fixedly mounted on a side wall of the clamping device (1); the mounting clamp seat (2.2) is fixedly mounted on the side wall of the first mounting plate (2.1); and the glue injection head (2.3) is clamped and mounted inside the mounting clamp seat (2.2).

3. The device for automatically assembling a piston rod and a piston of a hydraulic cylinder according to claim 1, characterized in that: The positioning tool (4) comprises a first driving device (4.1), a V-shaped block (4.2), a guide rail assembly (4.3) and a fixed plate (4.4); the fixed plate (4.4) is fixedly mounted on the table surface of the processing table; the guide rail assembly (4.3) and the first driving device (4.1) are both mounted on the side wall of the fixed plate (4.4); two groups of the V-shaped blocks (4.2) are provided; one of the V-shaped blocks (4.2) of the two groups of the V-shaped blocks (4.2) is fixedly mounted on the side wall of the fixed plate (4.4); the other V-shaped block (4.2) is fixedly mounted on the side wall of the slide of the guide rail assembly (4.3); and the side wall of the V-shaped block (4.2) mounted on the guide rail assembly (4.3) is fixedly mounted on the output shaft of the first driving device (4.1); The first driving device (4.1) drives the V-shaped block (4.2) to slide on the guide rail assembly (4.3) to change the distance between the first driving device (4.1) and another V-shaped block (4.2), so as to clamp and fix the side wall of the piston rod (7).

4. The device for automatically assembling a piston rod and a piston of a hydraulic cylinder according to claim 1, characterized in that: The mounting assembly comprises a second mounting plate (5.3), a third mounting plate (5.4) and a quick-change assembly (5.2); the second mounting plate (5.3) is fixedly mounted on the movable end of the second manipulator (B); the top surface of the third mounting plate (5.4) is fixedly mounted on the second drive device; and the second mounting plate (5.3) is fixedly mounted on the first mounting plate (2.1) via the quick-change assembly (5.2).

5. The device for automatically assembling a piston rod and a piston of a hydraulic cylinder according to claim 4, characterized in that: A high-precision visual system (3) is installed on one side of the second mounting plate (5.3).

6. The device for automatically assembling a piston rod and a piston of a hydraulic cylinder according to claim 3, characterized in that: A support frame (3.1) is fixedly installed on the tabletop of the processing table and located on one side of the positioning tool (4), and a high-precision visual system (3) is installed on the top of the support frame (3.1).

7. The device for automatically assembling a piston rod and a piston of a hydraulic cylinder according to claim 4, characterized in that: The tightening tool (5.1) comprises a tightening pin (5.1.1) and a spring (5.1.2). A cavity (5.1.5) for accommodating the spring (5.1.2) is provided inside the tightening tool (5.1). A sliding hole (5.1.4) is also provided inside the tightening tool (5.1). The tightening pin (5.1.1) is slidably connected in the sliding hole (5.1.4). The tightening pin (5.1.1) is fixedly connected to a limit block (5.1.5) on the side wall of the cavity (5.1.5). 5.1.3), the top surface of the limit block (5.1.3) contacts the spring (5.1.2), and the spring (5.1.2) is sleeved on the side wall of the tightening pin (5.1.1).

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