Robot rotary joint zeroing device and method

Abstract

The invention discloses a robot rotary joint zeroing device and method, a large arm assembly comprises a J1 shaft rotationally connected with a base, the J1 shaft is driven by a J1 motor, a small arm assembly comprises a J2 shaft rotationally connected with the large arm assembly, and the J2 shaft is driven by a J2 motor; the base is provided with a base limiting piece, the large arm assembly is provided with a large arm limiting piece and a large arm fixing piece, the small arm assembly is provided with a small arm limiting piece, the large arm limiting piece abuts against the base limiting piece when the large arm assembly is located at the positive limiting position, and the small arm limiting piece abuts against the large arm fixing piece when the small arm assembly is located at the negative limiting position. The inherent mechanical structure of the robot is utilized, and the limiting piece is additionally arranged, so that the problems that a traditional scribing or grooving mode depends on human eye judgment, subjective errors are large, and precision is low are solved. Inconsistency of manual operation is eliminated, maintenance cost and requirements for skills of operators are reduced, and rapid and accurate zeroing is realized.

Description

Technical Field

[0001] This application belongs to the field of robot zeroing technology, specifically relating to a robot rotary joint zeroing device and method. Background Technology

[0002] SCARA robots typically have two rotary joints and two prismatic joints. During robot transport or operation, the rotary joints may lose their encoder zero point due to collisions, vibrations, or long-term use, affecting positioning accuracy and operational reliability. Therefore, performing a zero-point homing operation periodically or when necessary is a crucial step in ensuring robot accuracy.

[0003] Currently, common zero-return methods mainly rely on mechanical alignment, such as setting grooves or markings on two relatively moving parts of a rotary joint, and manually aligning the grooves or inserting calibration blocks to achieve zero return. However, these methods have significant drawbacks: first, they depend on manual operation, leading to large differences in alignment accuracy between different operators and poor repeatability; second, the machining precision of the grooves or markings is limited, making them susceptible to wear, contamination, and other factors, resulting in inaccurate alignment; and third, the operation process is cumbersome, inefficient, and hinders rapid production recovery. Especially in high-precision applications, the zero-return accuracy and reliability of existing methods are insufficient to meet requirements.

[0004] Therefore, it is necessary to improve the existing zeroing method to overcome the problems of reliance on manual labor and unstable accuracy in the existing technology, and improve the maintenance efficiency and performance of SCARA robots. Summary of the Invention

[0005] This application provides a robot rotary joint zeroing device and method, which solves at least one of the above-mentioned technical problems.

[0006] The technical solution adopted in this application is as follows:

[0007] A robot rotary joint zeroing device is disclosed. The robot includes a large arm assembly rotatably connected to a base and a small arm assembly rotatably connected to the large arm assembly. The large arm assembly includes a J1 axis rotatably connected to the base and driven by a J1 motor. The small arm assembly includes a J2 axis rotatably connected to the large arm assembly and driven by a J2 motor. The base is provided with a base limiting member, the large arm assembly is provided with a large arm limiting member and a large arm fixing member, and the small arm assembly is provided with a small arm limiting member. The large arm limiting member abuts against the base limiting member when the large arm assembly is in a positive limiting position, and the small arm limiting member abuts against the large arm fixing member when the small arm assembly is in a negative limiting position.

[0008] As an optional embodiment, the base limiting member includes a first limiting block fixed to the top surface of the base; the boom assembly includes a boom body; the boom limiting member includes a second limiting block disposed at the bottom of the boom body, the second limiting block rotating with the boom body; the boom fixing member includes a third limiting block disposed at the top of the boom; the forearm assembly includes a forearm body; the forearm limiting member includes a fourth limiting block disposed at the bottom of the forearm body, the fourth limiting block rotating with the forearm body.

[0009] As an optional embodiment, the base is provided with a forward rotation limit block and a negative rotation limit block to limit the rotation angle of the boom assembly, and the forward rotation limit block is set as the base limit component.

[0010] This application also includes a method for returning a robot rotary joint to zero, applied to the zero-return device as described in any of the preceding claims, the method comprising:

[0011] Move the boom assembly until the boom limiting member abuts against the base limiting member, obtain the current positive limiting joint angle of the J1 axis when the boom assembly is in the positive limiting position, and obtain the corresponding J1 motor zero angle based on the current positive limiting joint angle.

[0012] Move the forearm assembly until the forearm limiting member abuts against the upper arm fixing member, obtain the current negative limiting joint angle of the J2 axis of the forearm assembly, and obtain the corresponding J2 motor zero angle of the J2 motor based on the current negative limiting joint angle.

[0013] Preferably, the method further includes: recording the initial zero angle of the J1 motor and the initial zero angle of the J2 motor calibrated before leaving the factory, and recording the initial positive limit joint angle of the J1 axis and the initial negative limit joint angle of the J2 axis corresponding to them.

[0014] The system determines the difference between the current positive limit joint angle and the initial positive limit joint angle. If the difference is less than a preset positive limit threshold, the system outputs the zero angle of the J1 motor as the current zero angle of the J1 motor. If the difference is greater than the preset positive limit threshold, the system issues a warning signal.

[0015] The system determines the difference between the current negative limit joint angle and the initial negative limit joint angle. If the difference is less than a preset negative limit threshold, the system outputs the zero angle of the J2 motor as the current zero angle of the J2 motor. If the difference is greater than the preset negative limit threshold, the system issues a warning signal.

[0016] Preferably, both the preset positive limit threshold and the preset negative limit threshold are set to 0.1°.

[0017] Preferably, the method includes: determining whether the rotation direction of the upper arm assembly and / or the lower arm assembly is correct when returning to zero based on the difference; if the difference is greater than a preset direction threshold, the rotation direction is determined to be incorrect, and the system issues a warning signal.

[0018] As an optional embodiment, the method further includes limiting and fixing the boom assembly when the boom limiting member abuts against the base limiting member; and limiting and fixing the forearm assembly when the forearm limiting member abuts against the boom fixing member.

[0019] Preferably, the base is provided with a fixing plate, the fixing plate is provided with a first tension spring pin, and the boom assembly is provided with a second tension spring pin. When the base limiting member abuts against the boom limiting member, the two ends of the tension spring are respectively connected to the first tension spring pin and the second tension spring pin.

[0020] Preferably, the forearm assembly is provided with a third tension spring pin, which connects the two ends of the tension spring to the second tension spring pin and the third tension spring pin respectively when the forearm limiting member abuts against the upper arm fixing member.

[0021] Due to the adoption of the above technical solution, the beneficial effects achieved by this application are as follows:

[0022] (1) The robot's inherent mechanical structure (base, upper arm assembly, lower arm assembly) and drive system (J1 motor, J2 motor) are utilized, and by adding limiting components (base limiting component, upper arm limiting component, upper arm fixing component, lower arm limiting component), the zero point is strongly correlated with specific, repeatable mechanical hard limiting positions. This solves the problems of traditional scribing or groove methods that rely on human judgment, have large subjective errors, and low precision. By moving the boom assembly to the "positive limit" (the boom limiter abuts against the base limiter) and the forearm assembly to the "negative limit" (the forearm limiter abuts against the boom fixing member), physical reference positions are defined for the two rotary joints respectively. These positions will not change due to power outages or other reasons, providing a constant reference point for recalibrating the motor's zero point. This not only improves the repeatability of the zero-return operation and eliminates inconsistencies caused by human operation, but also eliminates the need for additional, easily lost calibration blocks as in traditional methods. This simplifies the operation process, reduces maintenance costs and the skill requirements for operators, and achieves fast and accurate zero-return, thereby improving equipment maintenance efficiency and production restart speed.

[0023] (2) By moving the robotic arm to the mechanical hard limit and reading the motor encoder value (current joint angle) at this time, the new motor zero angle is calculated, standardizing the operation steps and eliminating the subjective arbitrariness of manual alignment of the marking lines. The zero-return accuracy is further improved from relying on the human eye. By using reliable mechanical limit contact, the positioning accuracy of the robot's zero-point recovery is guaranteed, solving the problem of "large errors caused by different people operating" in the background technology, and realizing high-precision and repeatable zero-return operation. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 This is a front view of the robot in one embodiment of the present invention;

[0026] Figure 2 This is a top view of the robot in one embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the boom assembly structure in one embodiment of the present invention;

[0028] Figure 4 This is a schematic diagram of the assembly of a tension spring in one embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1-Base, 2-Up boom assembly, 3-Forearm assembly, 4-J1 axis, 5-J2 axis, 6-Base limiting block, 7-Up boom limiting block, 8-Up boom fixing block, 9-Forearm limiting block, 10-Fixing plate, 11-First tension spring pin, 12-Second tension spring pin, 13-Tension spring. Detailed Implementation

[0031] To more clearly illustrate the overall concept of this application, a detailed explanation is provided below with reference to the accompanying drawings.

[0032] Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below. It should be noted that, unless otherwise specified, the embodiments of this application and the features thereof can be combined with each other.

[0033] Furthermore, it should be understood in the description of this application that the terms "top", "bottom", "inner", "outer", "axial", "radial", "circumferential", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0034] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0035] In this application, unless otherwise expressly specified and limited, the "above" or "below" of the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In the description of this specification, references to terms such as "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples.

[0036] This application provides a robot rotary joint return-to-zero device, such as... Figures 1 to 4 As shown, the robot includes a large arm assembly 2 rotatably connected to a base 1 and a small arm assembly 3 rotatably connected to the large arm assembly 2. The large arm assembly 2 includes a J1 axis 4 rotatably connected to the base 1 and driven by a J1 motor. The small arm assembly 3 includes a J2 axis 5 rotatably connected to the large arm assembly 2 and driven by a J2 motor. The base 1 is provided with a base limiting member, the large arm assembly 2 is provided with a large arm limiting member and a large arm fixing member, and the small arm assembly 3 is provided with a small arm limiting member. When the large arm assembly 2 is in the positive limiting position, the large arm limiting member abuts against the base limiting member. When the small arm assembly 3 is in the negative limiting position, the small arm limiting member abuts against the large arm fixing member.

[0037] This application utilizes the robot's inherent mechanical structure (base 1, upper arm assembly 2, lower arm assembly 3) and drive system (J1 motor, J2 motor), and by adding limiting components (base limiting component, upper arm limiting component, upper arm fixing component, lower arm limiting component), strongly correlates the zero point with specific, repeatable mechanical hard limiting positions. This solves the problems of traditional engraving or groove methods relying on human judgment, resulting in large subjective errors and low precision. By moving the boom assembly 2 to the "positive limit" (the boom limiter abuts against the base limiter) and the forearm assembly 3 to the "negative limit" (the forearm limiter abuts against the boom fixing member), physical reference positions are defined for the two rotary joints respectively. These positions will not change due to power outages or other reasons, providing a constant reference point for recalibrating the motor's zero point. This not only improves the repeatability of the zeroing operation and eliminates inconsistencies caused by human operation, but also eliminates the need for additional, easily lost calibration blocks as in traditional methods. This simplifies the operation process, reduces maintenance costs and the skill requirements for operators, and achieves fast and accurate zeroing, thereby improving equipment maintenance efficiency and production restart speed.

[0038] In one embodiment, the base limiting member includes a first limiting block fixed to the top surface of the base 1, the upper arm assembly 2 includes an upper arm body, the upper arm limiting member includes a second limiting block disposed at the bottom of the upper arm body, the second limiting block rotates with the upper arm body; the upper arm fixing member includes a third limiting block disposed at the top of the upper arm, the forearm assembly 3 includes a forearm body, the forearm limiting member includes a fourth limiting block disposed at the bottom of the forearm body, the fourth limiting block rotates with the forearm body.

[0039] As standard mechanical parts, limit blocks are simple in structure, robust and durable, low in cost, and easy to process and install, ensuring the reliability and economy of the device. The positions of each limit block and the fixing block ensure that when the joint rotates to its limit position, the contact (abutment) between the limit blocks is a direct or near-direct contact, and the force flow is directly transmitted, avoiding complex torque and potential jamming problems. This ensures the stability and consistency of the contact state, thus laying the mechanical foundation for further angle reading and ensuring zero-return accuracy.

[0040] Preferably, the base 1 is provided with a forward rotation limit block and a negative rotation limit block to limit the rotation angle of the boom assembly 2, and the forward rotation limit block is set as a base limit component.

[0041] By directly utilizing the existing forward rotation limit block on base 1, which is used to prevent mechanical overshoot, as a "base limit component," functional integration is achieved. This eliminates the need to design and install a new, independent limit block on base 1 for the zero-return function, maximizing the simplification of the mechanical structure and saving installation space and material costs. This minimizes modifications to the robot body, making it easy to retrofit and add to existing robot models, thus improving the technology's versatility and applicability.

[0042] This application also includes a method for returning a robot rotary joint to zero, applied to the zero-return device as described in any of the above claims, the method comprising:

[0043] Move the boom assembly 2 until the boom limiter abuts against the base limiter, obtain the current positive limit joint angle of the J1 axis 4 when the boom assembly 2 is in the positive limit position, and obtain the corresponding J1 motor zero angle based on the current positive limit joint angle.

[0044] Move the forearm assembly 3 until the forearm limiter abuts against the upper arm fixing member, obtain the current negative limit joint angle of the J2 axis 5 of the forearm assembly 3, and obtain the corresponding J2 motor zero angle based on the current negative limit joint angle.

[0045] By moving the robotic arm to its mechanical hard limit and reading the motor encoder value (current joint angle) at that moment, the new motor zero-position angle is calculated. This standardizes the operation steps and eliminates the subjective arbitrariness of manual alignment. The zero-return accuracy is further improved from relying on the human eye. Reliable mechanical limit contact ensures the positioning accuracy of the robot's zero-point recovery, solving the problem of "large errors caused by different operators" in the background technology, and achieving high-precision, repeatable zero-return operation.

[0046] Preferably, the method further includes: recording the initial zero angle of the J1 motor and the initial zero angle of the J2 motor calibrated before leaving the factory, and recording the initial positive limit joint angle of the J1 axis 4 and the initial negative limit joint angle of the J2 axis 5 corresponding to them.

[0047] The system determines the difference between the current positive limit joint angle and the initial positive limit joint angle. If the difference is less than the preset positive limit threshold, the system outputs the zero angle of motor J1 as the current zero angle of motor J1. If the difference is greater than the preset positive limit threshold, the system issues a warning signal.

[0048] The system determines the difference between the current negative limit joint angle and the initial negative limit joint angle. If the difference is less than the preset negative limit threshold, the system outputs the zero angle of the J2 motor as the current zero angle of the J2 motor. If the difference is greater than the preset negative limit threshold, the system issues a warning signal.

[0049] By calling and comparing the initial angle data calibrated at the factory, the system can automatically determine whether the current zeroing operation is within the expected reasonable range (judged by a preset threshold). It can effectively detect operational errors. For example, if the operator turns the joint to the wrong extreme direction (a positive limit operation mistakenly becomes a negative limit operation), the resulting angle difference will far exceed the threshold. The system will issue a warning to prevent the recording of an incorrect zero point and avoid the risk of collisions in subsequent operations due to misoperation. At the same time, it can monitor major abnormalities in the mechanical structure. If the mechanical limit block or the mounting base is severely deformed or displaced due to a violent collision, it will also cause abnormal angle differences. The system alarm can prompt the user to perform a deeper mechanical inspection, playing a role in fault diagnosis and preventive maintenance.

[0050] Preferably, both the preset positive limit threshold and the preset negative limit threshold are set to 0.1°.

[0051] By quantifying the positive and negative limit thresholds to 0.1°, the method allows for minute mechanical gaps, elastic deformation, and sensor noise, avoiding unnecessary frequent alarms caused by extremely small deviations and ensuring its practicality. Simultaneously, it ensures that the zero-return accuracy is far higher than traditional manual methods (typically greater than 1°). This effectively filters out non-critical deviations while capturing meaningful anomalies, making the self-test function sensitive and reliable.

[0052] Preferably, the method includes: determining whether the rotation direction of the upper arm assembly 2 and / or the lower arm assembly 3 is correct when returning to zero based on the difference; if the difference is greater than a preset direction threshold, it is determined that the rotation direction is incorrect and the system issues a warning signal.

[0053] In complex equipment maintenance scenarios, operators may misremember or misread the zeroing direction. This method's judgment logic can instantly and automatically identify such directional errors and immediately alert the operator with a warning signal. This completely avoids serious problems such as zero-point setting failure or even coordinate system chaos caused by directional errors, greatly enhancing operational safety and the method's error-proofing capabilities.

[0054] As an optional embodiment, the method further includes limiting and fixing the boom assembly 2 when the boom limiting member abuts against the base limiting member; and limiting and fixing the forearm assembly 3 when the forearm limiting member abuts against the boom fixing member.

[0055] This method ensures that the robotic arm is in a stable, undisturbed state when reading critical angle data. During manual pushing of the robotic arm, slight overshoot or rebound is inevitable, causing the limit blocks to not be in optimal contact. By using limit fixing (tension spring 13 or other clamping mechanisms), this elastic deformation and gap can be actively eliminated, forcing the limit surfaces into tight contact. This ensures that the read current joint angle more accurately corresponds to the set mechanical zero position, further improving the accuracy and consistency of angle data acquisition and providing another layer of protection for improving the final zero-return accuracy.

[0056] Preferably, the base 1 is provided with a fixing plate 10, the fixing plate 10 is provided with a first tension spring pin 11, and the boom assembly 2 is provided with a second tension spring pin 12. When the base limiting member abuts against the boom limiting member, the two ends of the tension spring 13 are respectively connected to the first tension spring pin 11 and the second tension spring pin 12.

[0057] The tension spring 13 provides a flexible, unidirectional tension force that continuously pulls the boom assembly 2 towards the base limiting block 6, automatically compensating for any minor gaps or rebounds to ensure reliable contact without requiring manual effort. The structure is simple, requiring only the addition of a fixing plate 10 and a tension spring pin to the existing structure, resulting in extremely low cost and easy installation without adding extra complexity. It should be noted that the tension force of the tension spring 13, after proper selection, is sufficient to overcome the internal resistance of the reducer, allowing the boom to smoothly enter position, without being excessively heavy or impactful to the mechanical structure, ensuring safety and reliability.

[0058] Preferably, the forearm assembly 3 is provided with a third tension spring pin, which connects the two ends of the tension spring 13 to the second tension spring pin 12 and the third tension spring pin respectively when the forearm limiting member abuts against the upper arm fixing member.

[0059] Similarly, this method also provides a stable limiting guarantee for the forearm's zero-return operation. By using the second tension spring pin 12 on the shared upper arm assembly 2, in conjunction with the third tension spring pin, it is ensured that the forearm limiting block 9 and the upper arm fixing component can also fit tightly and stably under the action of the tension spring 13, thereby ensuring the accuracy of the angle reading when the J2 axis 5 returns to zero. It is understood that the third tension spring pin is not shown in the figure, but its setting is similar to that of the second tension spring pin 12, and can be set by those skilled in the art by analogy to the second tension spring pin 12.

[0060] For any parts not mentioned in this application, existing technologies may be used or referenced.

[0061] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0062] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A robot rotary joint zeroing device, the robot including a large arm assembly rotatably connected to a base and a small arm assembly rotatably connected to the large arm assembly, the device comprising: The large arm assembly comprises a J1 shaft rotationally connected with the base, the J1 shaft being driven by a J1 motor, the small arm assembly comprises a J2 shaft rotationally connected with the large arm assembly, the J2 shaft being driven by a J2 motor; the base is provided with a base limiting piece, the large arm assembly is provided with a large arm limiting piece and a large arm fixing piece, and the small arm assembly is provided with a small arm limiting piece; the large arm limiting piece abuts against the base limiting piece when the large arm assembly is in positive limiting, and the small arm limiting piece abuts against the large arm fixing piece when the small arm assembly is in negative limiting.

2. The zeroing device of claim 1, wherein The base limiting piece comprises a first limiting block fixed to the top surface of the base, the large arm assembly comprises a large arm body, the large arm limiting piece comprises a second limiting block arranged at the bottom of the large arm body, and the second limiting block rotates with the large arm body; the large arm fixing piece comprises a third limiting block arranged at the top of the large arm body, the small arm assembly comprises a small arm body, and the small arm limiting piece comprises a fourth limiting block arranged at the bottom of the small arm body, and the fourth limiting block rotates with the small arm body.

3. The zeroing device of claim 1, wherein The base is provided with a positive rotation limiting block and a negative rotation limiting block for limiting the rotation angle of the large arm assembly, and the positive rotation limiting block is arranged as the base limiting piece.

4. A robot rotary joint zeroing method, characterized by, The method is applied to the zero resetting device of any one of claims 1-3, and the method comprises: moving the large arm assembly to the large arm limiting piece abutting against the base limiting piece, obtaining the current positive limiting joint angle of the J1 shaft when the large arm assembly is in positive limiting, and obtaining the J1 motor zero angle corresponding to the J1 motor according to the current positive limiting joint angle; moving the small arm assembly to the small arm limiting piece abutting against the large arm fixing piece, obtaining the current negative limiting joint angle of the J2 shaft of the small arm assembly, and obtaining the J2 motor zero angle corresponding to the J2 motor according to the current negative limiting joint angle.

5. The zeroing method of claim 4, wherein, The method further comprises: recording the initial J1 motor zero angle and the initial J2 motor zero angle of pre-factory calibration, and recording the initial positive limiting joint angle of the J1 shaft and the initial negative limiting joint angle of the J2 shaft corresponding thereto; judging the difference between the obtained current positive limiting joint angle and the initial positive limiting joint angle, if the difference is less than a preset positive limiting threshold, outputting the J1 motor zero angle as the current J1 motor zero angle, and if the difference is greater than the preset positive limiting threshold, the system sends an alarm signal; judging the difference between the obtained current negative limiting joint angle and the initial negative limiting joint angle, if the difference is less than a preset negative limiting threshold, outputting the J2 motor zero angle as the current J2 motor zero angle, and if the difference is greater than the preset negative limiting threshold, the system sends an alarm signal.

6. The zeroing method of claim 5, wherein, The preset positive limiting threshold and the preset negative limiting threshold are both set to 0.1°.

7. The zeroing method of claim 5, wherein, The method comprises: judging whether the rotation direction of the large arm assembly and / or the small arm assembly is correct during zero resetting according to the difference, if the difference is greater than a preset direction threshold, it is judged that the rotation direction is incorrect, and the system sends an alarm signal.

8. The zeroing method of claim 5, wherein, The method further comprises, when the large arm limiting piece abuts against the base limiting piece, limiting and fixing the large arm assembly; and when the small arm limiting piece abuts against the large arm fixing piece, limiting and fixing the small arm assembly.

9. The zeroing method of claim 8, wherein, The base is provided with a fixing plate, the fixing plate is provided with a first tension spring pin, the large arm assembly is provided with a second tension spring pin, and when the base limiting piece and the large arm limiting piece abut against each other, the two ends of the tension spring are connected to the first tension spring pin and the second tension spring pin respectively.

10. The zeroing method of claim 9, wherein, The small arm assembly is provided with a third tension spring pin, and when the small arm limiting piece and the large arm fixing piece abut against each other, the two ends of the tension spring are connected to the second tension spring pin and the third tension spring pin respectively.

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