Clamping device for strength and life testing of aircraft engine discs

Abstract

The present invention discloses a clamping device for testing the strength and life of an aircraft engine disc. The clamping device is connected to the upper and lower end faces of a test piece respectively through a connecting shaft and a pressure block, and the connecting structure is locked by a central pull rod and a locking nut, thereby ensuring the stability and reliability of the clamping structure. Moreover, during assembly, the central pull rod is axially pre-stretched, and the contraction force of the central pull rod is utilized to axially compress the pressure block, the test piece and the connecting shaft as a whole, so that the pressure block, the test piece and the connecting shaft form a stable clamping structure. During the disc strength and life test, the pressure block and the connecting shaft can always firmly clamp the test piece without loosening, thereby ensuring the reliability and accuracy of the disc strength and life test results.

Description

Technical Field

[0001] The invention relates to the technical field of strength and life testing of aircraft engine discs, and in particular to a clamping device used for strength and life testing of aircraft engine discs. Background Art

[0002] As a crucial component of modern aviation gas turbine engine rotors, the impeller typically operates under high temperature, high pressure, and high speed conditions. Its structural strength and lifespan reliability are directly linked to engine safety. Therefore, during aircraft engine development, the structural strength and lifespan of the impeller must be systematically tested and verified. Impeller strength and lifespan tests are typically conducted on a vertical impeller rotating tester. Prior to testing, the impeller must be assembled with a clamping device and then installed as a whole on the tester. During the test, the vertical impeller rotating tester outputs power, rotating the impeller. When the load exceeds the impeller's load limit, or the number of test cycles exceeds the impeller's fatigue life, the impeller will burst.

[0003] However, existing clamping devices typically use two clamping parts to clamp and lock the test piece before installing it on the tester. The clamping structure has poor stability. Although the wheel disc test piece can be firmly clamped before the test, after the test begins, as the clamping device and the wheel disc test piece continue to rotate, under the influence of factors such as centrifugal force and gravity, the clamping device and the wheel disc test piece gradually become loose, resulting in poor accuracy and reliability of the test results. The wheel disc test piece may even break away from the clamping device and fly away before reaching the load limit or fatigue life of the wheel disc. In addition, after the wheel disc explodes, the clamping device will also swing violently due to structural instability and break at the power output end of the equipment. The clamping device then falls into the explosion-proof chamber. In this process, not only will the tester be damaged, the clamping device will be destroyed and cannot be used anymore, and the debris of the exploded test piece may also suffer secondary damage, thereby affecting the analysis of the test results. Summary of the Invention

[0004] The present invention provides a clamping device for aero-engine wheel disc strength and life test, so as to solve the technical problem that the existing clamping device cannot firmly clamp the test piece during the wheel disc strength and life test.

[0005] According to one aspect of the present invention, there is provided a clamping device for strength and life testing of aircraft engine discs, comprising a connecting shaft, a pressure block, a center pull rod and a locking nut, wherein the top end of the connecting shaft is fixedly connected to the power output end of the equipment, the bottom end of the connecting shaft is connected to the top end of the test piece, the top end of the pressure block is connected to the bottom end of the test piece, the top end of the center pull rod passes through the pressure block and the test piece in sequence and is locked on the connecting shaft, the locking nut is mounted on the bottom end of the center pull rod and tightened on the bottom end face of the pressure block, and during assembly, the center pull rod is axially pre-stretched, and the pressure block, the test piece and the connecting shaft are axially compressed by the contraction force of the center pull rod.

[0006] Furthermore, it also includes a support rod with a long cylindrical structure, which is sleeved on the central pull rod and located between the boss on the central pull rod and the pressure block. The top end of the support rod is fixedly connected to the central pull rod, and the top end face of the support rod is pressed against the boss positioning surface of the central pull rod. The bottom end of the support rod and the central pull rod are clearance-fitted, and a preset gap is retained between the bottom end face of the support rod and the pressure block. When the test piece bursts, the pressure block loses its axial positioning, the central pull rod shrinks rapidly and drives the pressure block to move axially through the locking nut until the pressure block is supported by the support rod, and the support rod provides support and positioning for the pressure block again.

[0007] Furthermore, the top end of the inner hole of the support rod and the outer circle of the central pull rod are positioned by interference fit or connected by a positioning pin.

[0008] Furthermore, a radial gap between the bottom end of the inner hole of the support rod and the outer circle of the central pull rod is 0.01 mm to 0.02 mm.

[0009] Furthermore, the preset axial gap between the bottom end surface of the support rod and the pressing block needs to be greater than the axial deformation of the test piece and less than the axial stretching of the central pull rod.

[0010] Furthermore, a boss is provided in the middle portion of the central pull rod, and a small clearance is formed between the middle boss and the support rod, which plays a role in limiting the vibration amplitude when the support rod resonates.

[0011] Furthermore, a through hole is provided on the pressing block, and a threaded hole is provided inside the connecting shaft. The through hole on the pressing block, the threaded hole on the connecting shaft, and the center through hole of the test piece are coaxially arranged. A thread is provided on the outer circle of the top end of the center pull rod. The top end of the center pull rod passes through the through hole on the pressing block and the center through hole of the test piece in turn and is then locked in the threaded hole of the connecting shaft through threaded engagement.

[0012] Furthermore, a positioning boss and a screw hole are provided on the top end face of the connecting shaft. The connecting shaft is positioned and centered by cooperating with the positioning groove on the power output end of the equipment through the positioning boss, and is connected to the power output end of the equipment through screws or bolts.

[0013] Furthermore, the connecting shaft and the pressing block are both provided with a circle of evenly distributed threaded holes, and correction mass is applied in the form of screws added to the threaded holes during dynamic balancing.

[0014] Furthermore, before the test, the clamping device needs to be dynamically balanced separately and the relative positions of each part must be marked. Then, when the clamping device is assembled with the test piece, the clamping device should be assembled according to the marks. After the assembly is completed, the entire device should be dynamically balanced, and this dynamic balancing should not destroy the original balance state of the clamping device.

[0015] The present invention has the following effects:

[0016] The clamping device for aircraft engine disc strength and life test of the present invention is connected to the upper and lower end faces of the test piece respectively through a connecting shaft and a pressure block, and the connection structure is locked by a center pull rod and a locking nut, thereby ensuring the stability and reliability of the clamping structure. Moreover, during assembly, the center pull rod is axially pre-stretched and the contraction force of the center pull rod is utilized to axially compress the pressure block, the test piece and the connecting shaft as a whole, so that the pressure block, the test piece and the connecting shaft form a stable clamping structure. During the disc strength and life test, the pressure block and the connecting shaft can always firmly clamp the test piece without loosening, thereby ensuring the reliability and accuracy of the disc strength and life test results.

[0017] In addition, since the center pull rod is pre-stretched when assembling the test piece and the clamping device, when the test piece bursts and the pressure block loses its axial positioning, the center pull rod will shrink rapidly, driving the pressure block to move axially through the locking nut until the pressure block is supported by the support rod and regains its axial positioning, forming a new stable structure, so that the clamping device can quickly restore stability and ensure that the clamping device will not fall due to instability. After the test piece bursts, the clamping device can still decelerate smoothly from a high speed to stop rotation, thereby protecting the clamping device, the tester, and the wreckage of the test piece, saving the maintenance cost of the tester. The clamping device can be reused many times, saving the manufacturing cost of the clamping device, preventing the wreckage of the test piece from being damaged again, and ensuring the accuracy and reliability of the wheel strength and life test results.

[0018] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0020] Figure 1 The figure is a schematic structural diagram of a clamping device for strength and life testing of an aircraft engine disc according to a preferred embodiment of the present invention.

[0021] Figure 2 It is a structural schematic diagram of a clamping device for strength and life testing of an aircraft engine disc according to another embodiment of the present invention.

[0022] Figure 3 It is a schematic structural diagram of the interference fit between the top end of the inner hole of the support rod and the outer circle of the central pull rod in another embodiment of the present invention.

[0023] Figure 4 This is a structural diagram of another embodiment of the present invention in which the bottom end of the inner hole of the support rod is clearance-matched with the outer circle of the central pull rod and a small gap is reserved between the bottom end surface of the support rod and the pressing block.

[0024] Description of Reference Numerals

[0025] 1. Connecting shaft; 2. Pressure block; 3. Center pull rod; 4. Locking nut; 5. Support rod; 100. Equipment power output end; 200. Test piece. DETAILED DESCRIPTION

[0026] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0027] like Figure 1As shown, a preferred embodiment of the present invention provides a clamping device for testing the strength and life of an aircraft engine disc, comprising a connecting shaft 1, a pressure block 2, a central tie rod 3, and a locking nut 4. The top end of the connecting shaft 1 is fixedly connected to the power output end 100 of the equipment, the bottom end of the connecting shaft 1 is connected to the top end of a test piece 200, and the top end of the pressure block 2 is connected to the bottom end of the test piece 200. The bottom end surface of the connecting shaft 1 and the top end surface of the pressure block 2 are designed with end teeth or other connecting structures based on the actual connection method of the test piece 200 to connect with the test piece 200. The top end of the central tie rod 3 passes through the pressure block 2 and the test piece 200 in sequence and is then locked to the connecting shaft 1. The locking nut 4 is mounted on the bottom end of the central tie rod 3 and tightened against the bottom end surface of the pressure block 2, thereby compressing the pressure block 2, the test piece 200, and the connecting shaft 1 to achieve a secure clamping of the test piece 200. In addition, during assembly, the center tie rod 3 is axially pre-stretched, and the compression block 2, the test piece 200 and the connecting shaft 1 are axially compressed by the contraction force of the center tie rod 3. Specifically, during assembly, the top end of the center tie rod 3 is first locked on the connecting shaft 1, and then the connecting shaft 1 and the compression block 2 are connected to the test piece 200. The bottom end of the center tie rod 3 then passes through the test piece 200 and the compression block 2 in sequence and extends out. Then, the bottom end of the center tie rod 3 is fixed by a stretching device and the center tie rod 3 is axially pre-stretched. The locking nut 4 is tightened. Under the action of the contraction force of the center tie rod 3, the locking nut 4 is pressed on the bottom end of the compression block 2, thereby axially compressing the compression block 2, the test piece 200 and the connecting shaft 1. Finally, the top end of the connecting shaft 1 is installed on the power output end 100 of the equipment to perform a wheel disc strength and life test.

[0028] It can be understood that the clamping device for the strength and life test of an aircraft engine disc of this embodiment is connected to the upper and lower end faces of the test piece 200 respectively through the connecting shaft 1 and the pressure block 2, and the connection structure is locked by the center pull rod 3 and the locking nut 4, thereby ensuring the stability and reliability of the clamping structure. Moreover, during assembly, the center pull rod 3 is axially pre-stretched, and the contraction force of the center pull rod 3 is utilized to axially compress the pressure block 2, the test piece 200 and the connecting shaft 1 as a whole, so that the pressure block 2, the test piece 200 and the connecting shaft 1 form a stable clamping structure. During the disc strength and life test, the pressure block 2 and the connecting shaft 1 can always firmly clamp the test piece 200 without loosening, thereby ensuring the reliability and accuracy of the disc strength and life test results.

[0029] It will be understood that the top end surface of the connecting shaft 1 is provided with a positioning boss and a screw hole. The positioning boss cooperates with the positioning groove on the device power output terminal 100 for positioning and centering, and the connecting shaft 1 is connected to the device power output terminal 100 via screws or bolts. The number and position of the screw holes are designed based on the structure of the device power output terminal 100. In addition, a circle of evenly distributed threaded holes is provided in the middle of the connecting shaft 1 for dynamic balancing. During dynamic balancing, correction mass is applied by adding screws to the threaded holes.

[0030] In addition, a through hole is provided at the center of the pressure block 2, and a threaded hole is provided inside the connecting shaft 1. The through hole on the pressure block 2, the threaded hole on the connecting shaft 1, and the center through hole of the test piece 200 are coaxially arranged. A thread is provided on the outer circle of the top end of the center pull rod 3. The top end of the center pull rod 3 passes through the through hole on the pressure block 2 and the center through hole of the test piece 200 in turn and is locked in the threaded hole of the connecting shaft 1 through threaded engagement. At this time, the upper surface of the boss of the center pull rod 3 is in close contact with the connecting shaft 1. A circle of evenly distributed threaded holes is also provided in the middle position of the pressure block 2 for dynamic balancing. When performing dynamic balancing, correction mass is applied in the form of screws in the threaded holes. Optionally, the bottom end face of the pressure block 2 is flat to facilitate tightening of the locking nut 4.

[0031] It is understandable that when the test piece 200 explodes, the clamping device will swing violently due to the loss of axial positioning of the pressure block 2, and will break at the power output end 100 of the equipment. The clamping device will fall from the tester into the explosion-proof chamber. In this process, the clamping device will be damaged and cannot be used anymore. The tester will also be damaged and need repair. In addition, the debris after the test piece 200 explodes may also suffer secondary damage, affecting the analysis of the test results. Therefore, as a preferred method, Figures 2 to 4As shown, the clamping device for the strength and life test of the aircraft engine wheel disc also includes a strut 5 with a long cylindrical structure, which is used to quickly re-support and position the pressure block 2 after it loses its axial positioning. Specifically, the strut 5 is sleeved on the center tie rod 3 and is located between the boss on the center tie rod 3 and the pressure block 2. The top end of the strut 5 is fixedly connected to the center tie rod 3, and the top end face of the strut 5 is pressed against the lower surface of the boss of the center tie rod 3. The top end of the inner hole of the strut 5 and the outer circle of the center tie rod 3 are positioned by interference fit or connected by a locating pin to achieve positioning between the top end of the strut 5 and the center tie rod 3. The bottom end of the strut 5 and the center tie rod 3 are clearance fit, and a preset gap is retained between the bottom end face of the strut 5 and the pressure block 2. The top end of the strut 5 forms an interference fit with the center rod 3, while the bottom end of the strut 5 forms a clearance fit with the center rod 3. The interference fit provides highly stable support and positioning for the strut 5, while the clearance fit allows relative displacement between the center rod 3 and the strut 5. When the test piece 200 explodes, the compression block 2 loses its axial positioning. The center rod 3 rapidly contracts and drives the compression block 2 axially through the locking nut 4 until the compression block 2 is supported by the strut 5, and the strut 5 regains support and positioning for the compression block 2.

[0032] It can be understood that since the center pull rod 3 is pre-stretched when assembling the test piece 200 and the clamping device, when the test piece 200 bursts and the pressure block 2 loses its axial positioning, the center pull rod 3 will shrink rapidly and drive the pressure block 2 to move axially through the locking nut 4 until the pressure block 2 is supported by the support rod 5. The pressure block 2 regains its axial positioning and re-forms a new stable structure, so that the clamping device quickly recovers its stability and ensures that the clamping device will not fall due to instability. After the test piece 200 bursts, the clamping device can still decelerate smoothly from a high speed to stop rotation, thereby protecting the clamping device, the tester, and the wreckage of the test piece 200, saving the maintenance cost of the tester. The clamping device can be reused many times, saving the manufacturing cost of the clamping device, preventing the wreckage of the test piece 200 from secondary damage, and ensuring the accuracy and reliability of the wheel strength and life test results.

[0033] Optionally, a small clearance fit is formed between the bottom end of the inner hole of the support rod 5 and the outer circle of the central pull rod 3 , and a specific radial clearance is 0.01 mm to 0.02 mm.

[0034] Optionally, the preset axial gap between the bottom end face of the support rod 5 and the pressure block 2 needs to be greater than the axial deformation of the test piece 200 to ensure that during the test, the support rod 5 will not support the pressure block 2 and offset the preload force applied to the test piece 200, causing the clamping structure to become unstable during the test. At the same time, the preset axial gap between the bottom end face of the support rod 5 and the pressure block 2 needs to be smaller than the axial stretching of the center pull rod 3. When the test piece 200 bursts, the center pull rod 3 shrinks rapidly and drives the pressure block 2 to move through the locking nut 4. After the pressure block 2 is supported by the support rod 5, it is ensured that there is still a certain amount of residual preload force to compress the pressure block 2 and the support rod 5, so that the newly formed stable system can quickly form a stable state to avoid instability and falling from the tester due to excessive vibration.

[0035] It can be understood that since the axial deformation of the test piece 200 and the axial stretching of the center pull rod 3 are very small, and there are certain tolerances in the processing of each part, the gap between the support rod 5 and the pressure block 2 needs to be designed according to the actual size of the parts, and the length dimension of the support rod 5 requires high processing accuracy.

[0036] It is understandable that when the clamping device rotates at high speed, it may cause resonance of the strut 5 and lead to test failure. Therefore, when designing the strut 5, its natural frequency in the installed state should be checked to ensure that it does not resonate during the test. Preferably, a boss is provided in the middle portion of the center pull rod 3, and a small gap is formed between the middle boss and the strut 5. When the strut 5 resonates during high-speed rotation, it can limit its vibration amplitude. There can be multiple middle bosses, and the multiple bosses are spaced apart along the axial direction of the center pull rod 3.

[0037] It can be understood that after the test piece 200 bursts, the clamping device will quickly form a new stable system. In order to ensure that this new stable system can smoothly decelerate from a high speed to a stopped rotating state, dynamic balancing is required. Specifically, before the test, the clamping device needs to be dynamically balanced separately and the relative positions of each part need to be marked. That is, after the connecting shaft 1, the pressure block 2, the center pull rod 3, the locking nut 4 and the support rod 5 are assembled, the relative positions of each part are marked, and then the clamping device as a whole is dynamically balanced. After dynamic balancing, the clamping device is disassembled and then assembled with the test piece 200. During assembly, the various parts of the clamping device should be assembled according to the markings. After assembly is completed, the entire device is dynamically balanced, and this dynamic balancing should not destroy the original balance state of the clamping device. Among them, when dynamically balancing the clamping device and the test piece 200 as a whole, the method of applying a correction mass or removing material on the test piece 200 should be used for dynamic balancing.

[0038] It can be understood that the working process of the clamping device for the strength and life test of an aircraft engine disc of the present invention is as follows:

[0039] After assembling the connecting shaft 1, pressure block 2, center pull rod 3, locking nut 4 and support rod 5, mark the relative positions of each part, and then dynamically balance the clamping device as a whole. Disassemble the clamping device and then assemble it together with the test piece 200. During assembly, the various parts of the clamping device should be assembled according to the marks. After assembly, the entire device should be dynamically balanced, and this dynamic balancing should not destroy the original balance state of the clamping device. In addition, during assembly, the center pull rod 3 needs to be pre-stretched to apply a pre-tightening force to the test piece 200 to ensure the reliability and stability of the clamping structure and prevent the clamping structure from becoming unstable during the test. Then, install the clamping device with the test piece 200 installed to the power output end of the tester.

[0040] When the tester is turned on, it outputs power to drive the clamping device and test piece 200 to rotate at high speed. When the load exceeds the bearing limit of the test piece 200, or the number of test cycles exceeds the fatigue life of the test piece 200, the test piece 200 will burst, and the pressure piece 2 will lose its axial positioning. Because the center rod 3 is pre-stretched when assembling the test piece 200 and the clamping device, when the pressure piece 2 loses its axial positioning, the center rod 3 will rapidly contract, driving the pressure piece 2 in axial motion through the locking nut 4 until the pressure piece 2 is supported by the support rod 5. The pressure piece 2 is repositioned and the clamping device will quickly form a new stable system. Furthermore, since the gap between the bottom end face of the support rod 5 and the pressure block 2 is smaller than the axial stretch of the center pull rod 3, the locking nut 4 can still exert a certain residual preload on the pressure block 2, thereby compressing the pressure block 2 and the support rod 5, so that the newly formed stabilization system can quickly reach a stable state, avoiding the clamping device from swinging violently and causing the power output end 100 of the equipment to break, thereby causing the clamping device to fall from the tester, thus protecting the wreckage of the tester and the test piece 200, and the clamping device can also be reused multiple times. After the test piece 200 explodes, the clamping device can still smoothly decelerate from a high speed to a stopped state.

[0041] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A clamping device for strength and life testing of aircraft engine discs, characterized in that: It comprises a connecting shaft (1), a pressure block (2), a central pull rod (3) and a locking nut (4), wherein the top end of the connecting shaft (1) is fixedly connected to the power output end (100) of the equipment, the bottom end of the connecting shaft (1) is connected to the top end of the test piece (200), the top end of the pressure block (2) is connected to the bottom end of the test piece (200), the top end of the central pull rod (3) passes through the pressure block (2) and the test piece (200) in sequence and is then locked on the connecting shaft (1), the locking nut (4) is installed on the bottom end of the central pull rod (3) and is pressed against the bottom end face of the pressure block (2), and during assembly, the central pull rod (3) is axially pre-stretched, and the pressure block (2), the test piece (200) and the connecting shaft (1) are axially compressed by the contraction force of the central pull rod (3); The test piece (200) further comprises a support rod (5) in the form of an elongated cylindrical structure, the support rod (5) being sleeved on the central pull rod (3) and being located between the boss on the central pull rod (3) and the pressure block (2), the top end of the support rod (5) being fixedly connected to the central pull rod (3), and the top end face of the support rod (5) being pressed against the boss positioning face of the central pull rod (3), the bottom end of the support rod (5) being clearance-fitted with the central pull rod (3), and a preset clearance being retained between the bottom end face of the support rod (5) and the pressure block (2), when the test piece (200) bursts, the pressure block (2) loses its axial positioning, the central pull rod (3) rapidly contracts and drives the pressure block (2) to move axially through the locking nut (4), until the pressure block (2) is supported by the support rod (5), and the support rod (5) provides support and positioning for the pressure block (2) again.

2. The clamping device for aircraft engine disc strength and life test according to claim 1, characterized in that: The top end of the inner hole of the support rod (5) and the outer circle of the central pull rod (3) are positioned by interference fit or connected by a positioning pin.

3. The clamping device for aircraft engine disc strength and life test according to claim 1, characterized in that: The radial clearance between the bottom end of the inner hole of the support rod (5) and the outer circle of the central pull rod (3) is 0.01 mm to 0.02 mm.

4. The clamping device for aircraft engine disc strength and life test according to claim 1, characterized in that: The preset axial gap between the bottom end surface of the support rod (5) and the pressing block (2) needs to be greater than the axial deformation of the test piece (200) and less than the axial stretching of the central pull rod (3).

5. The clamping device for aircraft engine disc strength and life test according to claim 1, characterized in that: A boss is provided in the middle portion of the central pull rod (3), and a small clearance is formed between the middle boss and the support rod (5), which plays a role in limiting the vibration amplitude when the support rod (5) resonates.

6. The clamping device for aircraft engine disc strength and life test according to claim 1, characterized in that: A through hole is provided on the pressing block (2), and a threaded hole is provided inside the connecting shaft (1). The through hole on the pressing block (2), the threaded hole on the connecting shaft (1), and the central through hole of the test piece (200) are coaxially arranged. A thread is provided on the outer circle of the top end of the central pull rod (3). The top end of the central pull rod (3) passes through the through hole on the pressing block (2) and the central through hole of the test piece (200) in turn, and is then locked in the threaded hole of the connecting shaft (1) through threaded engagement.

7. The clamping device for aircraft engine disc strength and life test according to claim 1, characterized in that: A positioning boss and a screw hole are provided on the top end surface of the connecting shaft (1); the connecting shaft (1) is positioned and centered by cooperating with the positioning groove on the power output end (100) of the device through the positioning boss, and is connected to the power output end (100) of the device through screws or bolts.

8. The clamping device for aircraft engine disc strength and life test according to claim 1, characterized in that: The connecting shaft (1) and the pressing block (2) are both provided with a circle of evenly distributed threaded holes, and correction mass is applied in the form of screws added to the threaded holes during dynamic balancing.

9. The clamping device for aircraft engine disc strength and life test according to claim 8, characterized in that: Before the test, the clamping device must be dynamically balanced individually and the relative positions of the parts must be marked. Then, when the clamping device is assembled with the test piece (200), the clamping device must be assembled according to the markings. After the assembly is completed, the entire device must be dynamically balanced, and this dynamic balancing must not destroy the original balance state of the clamping device.

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