An assembly device and implementation method for double hinge joint-fork ear structure docking

Abstract

The present invention discloses an assembly device and an implementation method for the docking of a double-hinge joint-fork ear structure, belonging to the field of aviation assembly manufacturing technology. The device includes a posture adjustment platform, a transmission mechanism, a clamping tool, a sensor component, a connecting structure, a control panel, and a display. The posture adjustment platform is used to support an actuator to implement posture adjustment; the sensor component is used to measure and provide feedback on the relative position relationship between the joint and the fork ear; the transmission mechanism is used to complete the docking of the joint when the joint is aligned with the fork ear; the clamping tool is used to fix and support the actuator, and is connected to the transmission mechanism through a connecting structure, and the other side of the connecting structure is connected to the sensor component. The control panel and the display are used to process the signals uploaded by the sensor component and provide a human-computer interaction interface, which solves the problems of difficult operation, heavy labor load, low efficiency and high risk of structural damage when manually assembling the actuator in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of aviation assembly manufacturing, and in particular to an assembly device and an implementation method for butt-jointing a double-hinge joint-fork ear structure. Background Art

[0002] Aircraft control surfaces are primarily driven by hydraulic actuators. The actuators, control surfaces, and fuselage structure are connected using a joint-fork-ear arrangement, connected by a rotating pin, creating a double-hinged connection. To install the actuator, the joints on both sides must first be precisely aligned with the fork-ear structures, and then the actuator must be moved to allow the joints to enter the fork-ears.

[0003] In the existing technology, installation is generally carried out manually through lifting or mechanical tooling assistance, and assembly and docking are performed by manually controlling the posture adjustment. This has problems such as difficult operation, heavy labor load, low efficiency and high risk of structural damage. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems and propose an assembly device and implementation method for the docking of a double-hinge joint-fork ear structure. The device has alignment state measurement and feedback functions, which can realize efficient and accurate docking of the double-hinge joint-fork ear structure.

[0005] The present invention is achieved through the following technical solutions:

[0006] An assembly device for the docking of a double-hinge joint and a fork ear structure includes a posture adjustment platform, a transmission mechanism, a clamping tool, a sensor component, a connection structure, a control panel, and a display.

[0007] The posture adjustment platform is used to support the actuator to implement posture adjustment; the sensor component is used to measure and feedback the relative position relationship between the joint and the fork ear; the transmission mechanism is used to complete the docking of the joint when the joint is aligned with the fork ear; the clamping tool is used to fix and support the actuator, and the front of the clamping tool is provided with an auxiliary positioning component for positioning and fixing the actuator; the back of the clamping tool is connected to the transmission mechanism through a connecting structure, and the other side of the connecting structure is connected to the sensor component. The control panel and display are used to process the signals uploaded by the sensor component and provide a human-computer interaction interface.

[0008] Furthermore, the posture adjustment platform adopts a pneumatic power-assisting arm as the posture adjustment platform.

[0009] Furthermore, the transmission mechanism includes a fixed end, a guide rod, a screw rod, a pressure plate, and a turntable. The fixed end is connected to the end of the posture adjustment platform. The guide rod and the fixed end cooperate through a sliding pair I, so that the guide rod performs linear translation motion relative to the fixed end.

[0010] The screw rod is matched with the fixed end through a screw pair I. One side of the screw rod is a boss structure, and the screw rod is pressed and fixed to the fixed end through a pressure plate; the other side of the screw rod is fixedly connected to the turntable.

[0011] Furthermore, the back side of the clamping fixture is connected to the guide rod of the transmission mechanism, fits with the boss structure of the screw rod, and is fixed by two pressing plates.

[0012] Furthermore, the axes of the guide rod and the screw rod are perpendicular to the back side of the clamping tool.

[0013] Furthermore, the sensing assembly includes a center plate, two pressure sensors, a guide column, two coil springs, contacts, and thrust nuts. The two pressure sensors are respectively arranged on both sides of the center plate, the two coil springs are respectively connected to the pressure sensors, and the inner sides of the two contacts are respectively connected to the two coil springs. The guide column passes through the center of the center plate, pressure sensor, coil spring and contact, and the above-mentioned components are limited to the middle of the guide column by two thrust nuts.

[0014] Furthermore, the outer side of the contact is spherical and the inner side is flat. The guide post is cylindrical, and both ends of the guide post are processed with thread structures.

[0015] Furthermore, one side of the connection structure is connected to the clamping fixture; and the other side cooperates with the center plate of the sensor assembly.

[0016] Furthermore, the position where the connection structure cooperates with the center plate adopts a double-plate structure, and the center plane of the double-plate structure coincides with the center plane of the actuator joint.

[0017] Furthermore, the controller includes a sensor connection interface, an analog / digital conversion module, a force data processing module, and a display driver module. The sensor connection interface is used to power the sensor component and collect analog signals; the analog / digital conversion module is used to convert the analog signals into digital signals, the force data processing module is used to calculate the position status of the joint and the fork ear based on the digital signal, and the display driver module is connected to the display, and the position status of the joint and the fork ear is visually displayed on the display.

[0018] A method for docking a double-hinge joint-fork ear structure, based on the aforementioned device, includes the following steps:

[0019] A. Rough positioning steps

[0020] Manually operate the attitude adjustment platform to move the actuator joint close to the fork ear and roughly align it with the fork ear to achieve rough alignment of the joint relative to the fork ear;

[0021] B. Sensor component installation

[0022] First, manually pinch the two contacts together, place the center plate, two pressure sensors, two coil springs, and the two contacts between the two fork ears, and push the contacts to slide into the fork ear holes. Then, insert the guide post from the outside of one fork ear. Finally, connect the thrust nuts to the guide post on the outside of the two fork ears and tighten the fork ears.

[0023] C. Connection of sensor components

[0024] Connect the connecting structure to the center plate of the sensor assembly, manually adjust the connecting structure to fit the corresponding position of the clamping fixture, and finally use screws to fix the connecting structure and the clamping fixture;

[0025] D. Precision positioning

[0026] Observe the position status of the joint and the fork ear through the display, and manually operate the attitude adjustment platform to adjust the position of the actuator;

[0027] E. Butt feed and pin connection

[0028] Ⅰ. Manually remove the connection structure and sensor assembly, manually rotate the turntable to control the joint feed, and after the joint hole on the fuselage side is close to the fork ear hole, manually operate the attitude adjustment platform to make the joint hole coincide with the fork ear hole, and install the pin;

[0029] Ⅱ. Then rotate the rudder surface so that the side fork ear hole of the rudder surface coincides with the joint hole, and install the pin.

[0030] Furthermore, in step B, the deviation of the center plate relative to the equilibrium position of the two coil springs is obtained by dividing the difference between the measured values of the two pressure sensors by the elastic modulus of the coil spring.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] 1. In the present invention, in order to meet the measurement requirements of the relative position between the joint and the fork ear, a measuring assembly composed of components such as a spring and a pressure sensor is used. The position deviation is fed back through the deformation of the spring, which has the characteristics of simple construction and convenient implementation.

[0033] 2. In the present invention, in response to the matching requirements of the joint and the fork ear positions, the positional relationship between the center plane of the joint and the center plane of the fork ear is transmitted through the cooperation of structures such as the clamping tooling, the connection structure and the center plate of the measuring component, which has the characteristics of simple implementation and efficient operation.

[0034] 3. In the present invention, a posture state measurement component based on a spring and a pressure sensor is designed. Based on the obtained measurement data, intuitive position adjustment data is generated to guide personnel to accurately align the joint with the fork ear, thereby significantly improving operational efficiency and reducing the risk of structural damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural diagram of the actuator.

[0036] Figure 2 This is a schematic diagram of the joint and fork ear posture status after completing the rough positioning step.

[0037] Figure 3 It is a structural diagram of the measurement component.

[0038] Figure 4 It is a structural diagram of the installation status of the measuring component and the fork ear.

[0039] Figure 5 It is a structural diagram of the transmission mechanism.

[0040] Figure 6 It is a structural diagram of the pressure plate.

[0041] Figure 7 It is a structural diagram of the screw rod.

[0042] Figure 8 It is a structural diagram of the connection structure and the installation status of the measurement component.

[0043] Figure 9 is a side view of the connection structure.

[0044] Figure 10 This is the control connection block diagram of the control panel and display.

[0045] Among them, 1. actuator; 2. transmission mechanism; 3. clamping tool; 4. sensing component; 5. connection structure; 6. fork ear; 7. fork ear hole; 101. cylinder; 102. push rod; 103. joint; 201. fixed end; 202. guide rod; 203. screw rod; 204. pressure plate; 205. turntable; 301. auxiliary positioning component; 401. center plate; 402. pressure sensor; 403. guide column; 404. contact; 405. thrust nut. DETAILED DESCRIPTION

[0046] In order to more clearly illustrate the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with specific implementation methods and drawings. It should be understood that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, and therefore should not be regarded as limiting the scope of protection. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technical personnel in this field without making creative work are within the scope of protection of the present invention.

[0047] Example 1

[0048] This embodiment takes the installation of the aileron actuator as an example to illustrate the present invention. The aileron actuator is located below the aileron of the wing, and the installation path is moving from bottom to top. Figure 1 、 2 As shown, when installing the aileron actuator, the connectors 103 on both sides of the actuator 1 need to be moved between the fork ears 6 on both sides, and the holes of the connectors 103 are aligned with the fork ear holes 7 to facilitate the installation of the pins.

[0049] In this embodiment, a specific structure of an assembly device for a double hinge joint-fork ear structure docking is used, including a posture adjustment platform, a transmission mechanism 2, a clamping tool 3, a sensor component 4, a connection structure 5, a control panel and a display. Figure 2-9 .

[0050] In this embodiment, the posture adjustment platform is used to support the actuator 1 for posture adjustment. A commercially available pneumatically powered robotic arm serves as the posture adjustment platform. The sensor assembly 4 measures and provides feedback on the relative position of the connector 103 and the fork lug 6. The transmission mechanism 2 aligns the connector 103 with the fork lug 6 to achieve docking of the connector 103. The clamping fixture 3 secures and supports the actuator 1. The front of the clamping fixture 3 is equipped with an auxiliary positioning assembly 301 for positioning and securing the actuator 1. The back of the clamping fixture 3 is connected to the transmission mechanism 2 via a connecting structure 5. The other side of the connecting structure 5 is connected to the sensor assembly 4. The control panel and display process the signals transmitted by the sensor assembly 4 and provide a human-machine interface.

[0051] In this embodiment, reference Figure 5-7 The transmission mechanism 2 includes a fixed end 201, a guide rod 202, a screw rod 203, a pressure plate 204, and a turntable 205. The fixed end 201 is connected to the end of the posture adjustment platform. The guide rod 202 cooperates with the fixed end 201 through a sliding pair, so that the guide rod 202 performs linear translation motion relative to the fixed end 201.

[0052] The screw rod 203 is matched with the fixed end 201 through a spiral pair. One side of the screw rod 203 is a boss structure. The screw rod 203 is pressed and fixed to the fixed end 201 through a pressure plate 204; the other side of the screw rod 203 is fixedly connected to the turntable 205.

[0053] In this embodiment, the back side of the clamping fixture 3 is connected to the guide rod 202 of the transmission mechanism 2 , fits with the boss structure of the screw rod 203 , and is fixed by two pressing plates 204 .

[0054] In this embodiment, the axes of the guide rod 202 and the screw rod 203 are perpendicular to the back side of the clamping tool 3 .

[0055] In this embodiment, the sensing assembly 4 includes a center plate 401, two pressure sensors 402, a guide column 403, two coil springs, a contact 404, and a thrust nut 405. Referring to 3, 6, and 8, the two pressure sensors 402 are respectively arranged on both sides of the center plate 401, the two coil springs are respectively connected to the pressure sensors 402, and the inner sides of the two contacts 404 are respectively connected to the two coil springs. The guide column 403 passes through the center of the center plate 401, the pressure sensor 402, the coil spring and the contact 404, and the above-mentioned components are limited to the middle of the guide column 403 by two thrust nuts 405.

[0056] In this embodiment, the outer side of the contact 404 is spherical and the inner side is flat. The guide post 403 is cylindrical, and both ends of the guide post 403 are processed with thread structures.

[0057] In this embodiment, one side of the connecting structure 5 is connected to the clamping fixture 3 ; and the other side cooperates with the central plate 401 of the sensor assembly 4 .

[0058] In this embodiment, the position where the connecting structure 5 cooperates with the center plate 401 adopts a double-plate structure, and the center plane of the double-plate structure coincides with the center plane of the joint 103 of the actuator 1.

[0059] In this embodiment, reference Figure 10 The controller includes a sensor connection interface, an analog / digital conversion module, a force data processing module, and a display driver module. The sensor connection interface is used to power the sensor component 4 and collect analog signals; the analog / digital conversion module is used to convert the analog signals into digital signals; the force data processing module is used to calculate the position status of the joint 103 and the fork ear 6 based on the digital signals; the display driver module is connected to the display, and the position status of the joint 103 and the fork ear 6 is visually displayed on the display.

[0060] A method for docking a double-hinge joint-fork ear structure, based on the aforementioned device, includes the following steps:

[0061] A. Rough positioning steps

[0062] Manually operate the posture adjustment platform to move the joint 103 of the actuator 1 close to the fork ear 6 and roughly align it with the fork ear 6 to achieve rough alignment of the joint 103 relative to the fork ear 6;

[0063] B. Installation of sensor component 4

[0064] First, manually pinch the contacts 404 on both sides to compress the coil springs, place the center plate 401, two pressure sensors 402, two coil springs and the contacts 404 on both sides between the fork ears 6 on both sides, and push the contacts 404 to slide into the fork ear holes 7; then insert the guide column 403 from the outside of one side of the fork ear 6, and finally connect the thrust nuts 405 to the guide column 403 on the outside of the two fork ears 6, and tighten the fork ears 6.

[0065] Furthermore, the deviation of the center plate 401 relative to the equilibrium position of the two coil springs is obtained by dividing the difference between the measurement values of the two pressure sensors 402 by the elastic modulus of the coil spring.

[0066] In order to achieve a better effect, further, the diameter of the spherical outer side of the contact 404 is a specific value, and after being installed on the fork ear hole 7, the outer surface of the two contacts 404 should be on the same sphere.

[0067] C. Connection of sensor component 4

[0068] Connect the connecting structure 5 to the center plate 401 of the sensor assembly 4, manually adjust the connecting structure 5 to fit the corresponding position of the clamping fixture 3, and finally use screws to fix the connecting structure 5 and the clamping fixture 3;

[0069] D. Precision positioning

[0070] Observe the position status of the joint 103 and the fork ear 6 through the display, and manually operate the posture adjustment platform to adjust the position of the actuator 1;

[0071] E. Butt feed and pin connection

[0072] I. Manually remove the connecting structure 5 and the sensor assembly 4. Manually rotate the dial 205 to control the feed of the joint 103. After the hole of the joint 103 on the fuselage side is close to the fork ear hole 7, manually operate the attitude adjustment platform to make the hole of the joint 103 coincide with the fork ear hole 7, and install the pin.

[0073] II. Then rotate the rudder surface so that the rudder surface side fork ear hole 7 coincides with the joint 103 hole and install the pin.

[0074] Based on the above implementation method, the detailed process of installing the aileron actuator 1 in this embodiment is as follows:

[0075] 1. Manually move the actuator 1 onto the clamping fixture 3 and position it;

[0076] 2. Manually operate the power-assisted robotic arm to move the actuator 1 to the bottom of the fork ear 6 and preliminarily align the joint 103 with the fork ear 6;

[0077] 3. Manually install the center plate 401, pressure sensor 402, coil spring, contact 404 and other components on the fork ear hole 7. The specific method is as follows: first, manually pinch the contact 404 to compress the coil spring, place it between the two fork ears 6, and then push the contact 404 to slide it into the fork ear hole 7;

[0078] 4. Manually insert the guide post 403 from the outside of the fork ear hole 7 into the center plate 401, pressure sensor 402, coil spring, and contact 404. Install the thrust nuts 405 on both sides of the guide post 403 and tighten the fork ear 6.

[0079] 5. Manually clamp the double-plate structure of the connecting structure 5 to the center plate 401, and match the other side with the clamping tool 3 to securely connect;

[0080] 6. The manual control controller starts working. The pressure sensor 402 is connected to the interface to collect the analog signal of the force sensor. The analog / digital conversion module converts the analog signal into a digital signal. The force data processing module calculates the position deviation of the center plate 401 between the two fork ears 6 based on the deviation of the output values of the two pressure sensors 402 divided by the elastic modulus of the coil spring. The display driver module visually displays the position status of the joint 103 and the fork ears 6 based on this position deviation.

[0081] 7. Manually operate the power-assisting manipulator arm to adjust the posture of the actuator 1 according to the position of the joint 103 and the fork ear 6, so that the joint 103 and the fork ear 6 are aligned, and then use the built-in brake device to fix the posture of the power-assisting manipulator arm;

[0082] 8. Manually remove the connecting structure 5 and the sensor assembly 4 including the thrust nut 405, the guide post 403, the center plate 401, the pressure sensor 402, the coil spring, the contact 404 and other components in order;

[0083] 9. Manually rotate dial 205 to control the feed of actuator 1 connector 103 toward fork lug 6. After the connectors 103 on both sides of actuator 1 enter the fork lug 6, release the brake device of the power-assisting mechanical arm. Then manually operate the power-assisting mechanical arm to align the connector 103 hole on the fuselage side with the fork lug hole 7. After installing the pin, manually adjust the aileron rotation to align the connector 103 hole on the aileron side with the fork lug hole 7, and install the pin.

[0084] In this embodiment, in order to meet the measurement requirements of the relative positions of the joint 103 and the fork ear 6, a measuring assembly composed of components such as a spring and a pressure sensor 402 is used. The position deviation is fed back through the deformation of the spring, which has the characteristics of simple construction and convenient implementation. In order to meet the matching requirements of the positions of the joint 103 and the fork ear 6, the position relationship between the center plane of the joint 103 and the center plane of the fork ear 6 is realized through the cooperation of structures such as the clamping tool 3, the connecting structure 5 and the center plate 401 of the measuring assembly, which has the characteristics of simple implementation and efficient operation.

[0085] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. An assembly device for docking a double-hinge joint-fork ear structure, characterized by: It includes a posture adjustment platform, a transmission mechanism (2), a clamping tool (3), a sensor component (4), a connection structure (5), a control panel, and a display. The posture adjustment platform is used to support the actuator (1) to implement posture adjustment; the sensor component (4) is used to measure and feedback the relative position relationship between the joint (103) and the fork ear (6); the transmission mechanism (2) is used to complete the docking of the joint (103) when the joint (103) is aligned with the fork ear (6); the clamping tool (3) is used to fix and support the actuator (1), and the front of the clamping tool (3) is provided with an auxiliary positioning component for positioning and fixing the actuator (1); the back of the clamping tool (3) is connected to the transmission mechanism (2) through the connecting structure (5), and the other side of the connecting structure (5) is connected to the sensor component (4), and the control panel and the display are used to process the signal uploaded by the sensor component (4) and provide a human-computer interaction interface.

2. The assembly device for docking a double hinge joint-fork ear structure according to claim 1, characterized in that: The posture adjustment platform adopts a pneumatic power-assisting arm as the posture adjustment platform.

3. The assembly device for docking a double hinge joint-fork ear structure according to claim 1, characterized in that: The transmission mechanism (2) comprises a fixed end (201), a guide rod (202), a screw rod (203), a pressure plate (204), and a turntable (205); the fixed end (201) is connected to the end of the posture adjustment platform; the guide rod (202) and the fixed end (201) cooperate with each other through a sliding pair I, so that the guide rod (202) performs linear translation motion relative to the fixed end (201); The screw rod (203) is matched with the fixed end (201) through a screw pair I. One side of the screw rod (203) is a boss structure. The screw rod (203) is pressed and fixed to the fixed end (201) through a pressure plate (204); the other side of the screw rod (203) is fixedly connected to the turntable (205).

4. The assembly device for docking a double hinge joint-fork ear structure according to claim 3, characterized in that: The back side of the clamping tool (3) is connected to the guide rod (202) of the transmission mechanism (2), fits with the boss structure of the screw rod (203), and is fixed by two pressing plates (204).

5. The assembly device for docking a double hinge joint-fork ear structure according to claim 4, characterized in that: The axes of the guide rod (202) and the screw rod (203) are perpendicular to the back side of the clamping tool (3).

6. The assembly device for docking a double hinge joint-fork ear structure according to claim 5, characterized in that: The sensing assembly (4) comprises a center plate (401), two pressure sensors (402), a guide post (403), two coil springs, a contact (404), and a thrust nut (405). The two pressure sensors (402) are respectively arranged on both sides of the center plate (401). The two coil springs are respectively connected to the pressure sensors (402). The inner sides of the two contacts (404) are respectively connected to the two coil springs. The guide post (403) passes through the center of the center plate (401), the pressure sensor (402), the coil spring, and the contact (404), and the aforementioned components are limited to the middle of the guide post (403) by the two thrust nuts (405).

7. The assembly device for docking a double hinge joint-fork ear structure according to claim 6, characterized in that: The outer side of the contact (404) is spherical; the inner side is flat; the guide post (403) is cylindrical; and both ends of the guide post (403) are machined with thread structures.

8. The assembly device for docking a double hinge joint-fork ear structure according to claim 7, characterized in that: One side of the connection structure (5) is connected to the clamping fixture (3); the other side cooperates with the center plate (401) of the sensor assembly (4).

9. The assembly device for docking a double hinge joint-fork ear structure according to claim 8, characterized in that: The position where the connection structure (5) cooperates with the center plate (401) adopts a double-plate structure, and the center plane of the double-plate structure coincides with the center plane of the actuator (1) joint (103).

10. The assembly device for docking a double hinge joint-fork ear structure according to claim 1, characterized in that: The controller includes a sensor connection interface, an analog / digital conversion module, a force data processing module, and a display drive module. The sensor connection interface is used to power the sensor component (4) and collect analog signals. The analog / digital conversion module is used to convert the analog signal into a digital signal, the force data processing module is used to calculate the position state of the joint (103) and the fork ear (6) based on the digital signal, and the display drive module is connected to the display, and the position state of the joint (103) and the fork ear (6) is visually displayed on the display.

11. A method for docking a double hinge joint-fork ear structure, characterized in that: The assembly device according to claim 9 comprises the following steps: A. Rough positioning steps Manually operate the posture adjustment platform to move the joint (103) of the actuator (1) close to the fork ear (6) and roughly align it with the fork ear (6), thereby achieving rough alignment of the joint (103) relative to the fork ear (6); B. Sensor assembly (4) installation First, manually pinch the contacts (404) on both sides, place the center plate (401), two pressure sensors (402), two coil springs and the contacts (404) on both sides between the fork ears (6), and push the contacts (404) to slide into the fork ear holes (7); then, insert the guide column (403) from the outside of one fork ear (6), and finally connect the thrust nuts (405) to the guide column (403) on the outside of the two fork ears (6), and press the fork ears (6); C. Connection of sensor components (4) Connect the connecting structure (5) to the center plate (401) of the sensor assembly (4), manually adjust the connecting structure (5) so that it fits the corresponding position of the clamping fixture (3), and finally fix the connecting structure (5) and the clamping fixture (3) with screws; D. Precision positioning The position of the joint (103) and the fork ear (6) is observed through a display, and the position of the actuator (1) is adjusted by manually operating the posture adjustment platform; E. Butt feed and pin connection Ⅰ. Manually dismantle the connecting structure (5) and the sensor assembly (4), control the feed of the joint (103) by manually rotating the turntable (205), and after the hole of the joint (103) on the fuselage side approaches the fork ear hole (7), manually operate the attitude adjustment platform to make the hole of the joint (103) coincide with the fork ear hole (7), and install the pin; Ⅱ. Then rotate the rudder surface so that the rudder surface side fork ear hole (7) and the joint (103) hole coincide with each other and install the pin.

12. The method for docking a double hinge joint-fork ear structure according to claim 11, characterized in that: In step B, the deviation of the center plate (401) relative to the equilibrium position of the two coil springs is obtained by dividing the difference between the measured values of the two pressure sensors (402) by the elastic modulus of the coil spring.

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