Compact frame shaft end friction torque measuring system and method based on strain gauges

Abstract

The invention discloses a strain gauge-based compact frame shaft end friction torque measurement system and method, 1) a compact shaft end structure comprises a shaft end cover, a shaft end seat, a motor element, paired rolling bearings and other parts, and has the characteristics of compact structure and miniaturization; 2) based on an elastomer upper strain gauge pasting mode and elastomer size characteristics; 3) a zero calibration method based on a specific-shape elastomer and strain gauge assembly; 4) based on a multi-position installation mode of an elastomer and strain gauge assembly between contact interfaces, coupling multi-position measurement results, and solving strain and stress methods between the contact surfaces; 5) acquiring data through the strain gauges, processing the data acquired by the plurality of strain gauges by using a data processing method, and sequentially acquiring tangential and normal mechanical characteristics between the contact surfaces; and 6) solving a shaft end friction torque based on tangential mechanical characteristic coupling at each position, thereby eliminating an electromagnetic interference torque and a friction torque generated by a shaft end torque motor assembly to obtain a friction torque between the shaft end dynamic and static rotors.

Description

Technical Field

[0001] The invention relates to the technical field of platform type inertial navigation system frame shaft system friction torque measurement, in particular to a compact frame shaft end friction torque measurement system and method based on strain gauges. Background Art

[0002] The frame axis system of the platform inertial navigation system is a key component that isolates the angular motion of the platform and the carrier and ensures the stability of the inertial space. In actual engineering applications, the frame axis system usually reciprocates at an extremely low speed, and the bearings are in a state of frequent conversion between dry friction, boundary lubrication and mixed lubrication, which can easily lead to fluctuations in the friction torque, which is the main source of interference torque at the frame shaft end, affecting the precise control of the shaft end torque motor, and thus restricting the navigation and guidance accuracy of the platform inertial navigation system. At the same time, due to the compact structure of the frame shaft end, the bearing friction torque is difficult to measure directly, and the common method of measuring friction torque using the current output of the torque motor will include the influence of electromagnetic interference and components such as the shaft end slip ring. Summary of the invention

[0003] The present invention provides a compact frame shaft end friction torque measurement method based on strain gauges, the purpose of which is to overcome the structural limitations of the compact frame shaft end, obtain the friction torque between the dynamic and static rotors at the shaft end by a direct measurement method, and eliminate the electromagnetic interference torque and friction torque generated by the shaft end torque motor assembly, thereby providing a basis for accurately analyzing the shaft end interference torque.

[0004] In the first aspect, a compact frame shaft end friction torque measurement system based on strain gauges is provided, comprising an elastic body + strain gauge combination device, a circuit measurement module, a computer interface, a data acquisition module and a data post-processing module; each strain gauge is connected to the circuit measurement module, and the circuit measurement module is connected to the data acquisition module of the computer through the computer interface, and the data post-processing module is used to process data of the data acquisition module;

[0005] The elastic body + strain gauge combination device includes a rectangular elastic body and 4 thin-sheet resistance strain gauges; the elastic body includes a front and a back; the 4 thin-sheet resistance strain gauges include strain gauge No. 1, strain gauge No. 2, strain gauge No. 3, and strain gauge No. 4 respectively; strain gauge No. 1 and strain gauge No. 2 are attached to the back of the elastic body; strain gauge No. 3 and strain gauge No. 4 are attached to the front of the elastic body; strain gauge No. 1 and strain gauge No. 3 measure strain in the Y direction, and strain gauge No. 2 and strain gauge No. 4 measure strain in the X direction;

[0006] When the system is measuring, the rolling bearing is installed in the ring, and the rolling bearing and the ring are clearance fit; the shaft end shaft system and the shaft end ring rotate relatively through the rolling bearing, and the number of installed elastomer + strain gauge combination devices on the shaft end ring is 4, evenly distributed along the circumferential direction, and the positions are marked as A1 to A4 respectively; the front and rear of the elastomer are perpendicular to the axial direction; the elastomer is in contact with the outer ring of the rolling bearing.

[0007] In combination with the first aspect, in certain implementations of the first aspect, the elastomer + strain gauge combination device is installed in the square mounting hole step of the shaft end ring, the top surface and the bottom surface of the elastomer are perpendicular to the radial direction of the ring at the mounting hole, and are positioned by the shoulder in the mounting hole; the side surface 1 and the side surface 2 of the elastomer are perpendicular to the tangential direction of the ring at the mounting hole, and the two side surfaces are clamped by the mounting surface.

[0008] In combination with the first aspect, in certain implementations of the first aspect, the elastomer is a rectangular parallelepiped with a curvature on the bottom; the ratio of the long side to the short side of the elastomer is greater than 2, the size of the elastomer is greater than 50% of the size of the strain gauge, and the curvature of the bottom surface of the elastomer is consistent with the curvature at the contact surface.

[0009] In a second aspect, a method for measuring the friction torque of a compact frame shaft end based on a strain gauge is provided, wherein the method applies a system as described in any one of the implementations of the first aspect, and the method comprises:

[0010] Calibrate after the elastomer + strain gauge assembly is installed on the ferrule;

[0011] Rotate the shaft end shaft system, collect the output data of each strain gauge changing with time, and post-process the data.

[0012] In conjunction with the second aspect, in some implementations of the second aspect, the method further includes:

[0013] Apply a uniformly distributed load P1 on the top surface of the elastic body, and gradually increase P1 from small to large, and record the output of each strain gauge; keep the pressure P1 on the top surface of the elastic body constant, and gradually apply the clamping force P2 on the two sides from small to large, and record the output of each strain gauge; post-process the recorded data, make a load-strain calibration diagram, and use the curve fitting method to summarize the relationship between the applied load and the strain, which is recorded as ε=f(P);

[0014] The calibration is performed after the elastic body + strain gauge combination device is installed on the ferrule, including:

[0015] After assembly at the shaft end, the output strain of each strain gauge is measured, and the stress state of the elastic body in each direction is calculated based on ε=f(P).

[0016] In combination with the second aspect, in certain implementations of the second aspect, when the elastic body + strain gauge combination device is installed on the ring and calibrated, the strain gauge output strain is recorded as The superscript Ai indicates the installation position of the elastic body + strain gauge combination device, i = 1 to 4, the first subscript 2 indicates the free state of the strain gauge + elastic body combination in the ring, and the second subscript * indicates the strain gauge number;

[0017] Rotate the shaft end shaft system and collect the output data of each strain gauge changing with time. The superscript Ai indicates the installation position of the elastic body + strain gauge combination device, i = 1 to 4, the subscript 3 indicates the strain gauge data collected when the inner ring of the bearing is rotating, and the subscript * indicates the strain gauge number;

[0018] True strain at each strain gauge The y-direction stress of the elastic body is The x-direction stress of the elastic body is E is the elastic modulus of the high elastomer;

[0019] In the x direction, the tangential force on the elastic body at the Ai position transmitted from the contact interface is S is the area, S1 represents the cross section of the elastic body perpendicular to the y direction;

[0020] In the y direction, the normal force on the elastic body at the Ai position transmitted from the contact interface is S is the area, and S2 represents the cross section of the elastic body perpendicular to the z direction.

[0021] In conjunction with the second aspect, in certain implementations of the second aspect, the circumferential tangential force Normal pressure of contact surface along radial direction

[0022] In conjunction with the second aspect, in certain implementations of the second aspect, the friction torque M f =F τ (R+h / 2), where h is the height of the elastic body in the y direction and R is the distance from the contact interface to the center of rotation.

[0023] In conjunction with the second aspect, in certain implementations of the second aspect, the static friction coefficient between the contact interfaces is f=F N / F τ .

[0024] In conjunction with the second aspect, in some implementations of the second aspect, the method further includes:

[0025] After the strain gauge is pasted, the strain gauge is calibrated in the free state. The output of the strain gauge is ε 11 , ε13 , ε 12 , ε 14 , where the first subscript 1 indicates that the strain gauge + elastic body combination is in a free state after bonding, and the second subscript 1 to 4 indicates the strain gauge number;

[0026] When the elastic body + strain gauge combination device is installed on the ring and calibrated, the output strain of the strain gauge is recorded as ε 21 , ε 23 , ε 22 , ε 24 , where the first subscript 2 indicates the free state of the strain gauge + elastic body combination in the ring, and the second subscript 1 to 4 indicates the strain gauge number;

[0027] The initial stress state of the elastic body in the x and y directions during calibration satisfies:

[0028] σ 2cenx =E[(ε 22 -ε 12 )+(ε 24 -ε 14 )] / 2 and σ 2ceny =E[(ε 21 -ε 11 )+(ε 23 -ε 13 )] / 2.

[0029] Compared with the prior art, the solution provided by the present invention includes at least the following beneficial technical effects:

[0030] (1) The shaft end friction torque measurement system and method of the present invention overcomes the limitations of special shaft end structures, realizes the measurement of shaft end friction torque of compact frames, and greatly reduces the structural requirements;

[0031] (2) The shaft end friction torque measurement system and method of the present invention effectively separates the friction torque caused by mechanical motion from the shaft end electromagnetic interference torque, providing a basis for accurate compensation and control of the friction torque;

[0032] (3) The shaft end friction torque measurement system and method of the present invention characterizes the stress state by measuring the multi-point strain change, and finally calculates the tangential force and normal force to characterize the friction torque change. This method pastes the strain gauge between the two contact surfaces, and the load is highly comprehensive; the stress and deformation state of the strain gauge are fully analyzed; this method designs the measurement of the circumferential surface strain state, and fully considers the influence of the circumferential curvature on the strain gauge measurement; this method uses the real strain state measured by the strain gauge to solve the shaft end friction torque through a series of derivations, and the data processing is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1Schematic diagram of a compact frame shaft end friction torque measurement system based on strain gauges.

[0034] Figure 2 This is a schematic diagram of an elastomer + strain gauge combination device.

[0035] Figure 3 This is a schematic diagram of the installation position of an elastomer + strain gauge combination device.

[0036] Figure 4 A schematic diagram of load-strain relationship calibration.

[0037] Figure 5 A schematic diagram of the stress state of an elastic body. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] like Figure 1 A schematic diagram of a compact frame shaft end friction torque measurement system based on strain gauges is shown. The measurement system includes an elastic body + strain gauge combination device, a circuit measurement module, a computer interface, a data acquisition module, and a data post-processing module. Each strain gauge is connected to a full-bridge Wheatstone measurement circuit, and the circuit is connected to the computer through a computer interface, thereby building a measurement system of all strain gauges + elastic body devices.

[0040] like Figure 2 The schematic diagram of the elastic body + strain gauge combination device is shown. The elastic body + strain gauge combination device includes a rectangular elastic body and four thin-sheet resistance strain gauges. The elastic body includes a front and a back. The four thin-sheet resistance strain gauges include strain gauge No. 1, strain gauge No. 2, strain gauge No. 3, and strain gauge No. 4 respectively. Strain gauge No. 1 and strain gauge No. 2 are attached to the back of the elastic body. Strain gauge No. 3 and strain gauge No. 4 are attached to the front of the elastic body. Strain gauge No. 1 and strain gauge No. 3 measure the strain in the Y direction (the direction of the long side of the elastic body), and strain gauge No. 2 and strain gauge No. 4 measure the strain in the X direction (the direction of the short side of the elastic body). In other words, the sensitive direction of strain gauge No. 1 is along the long side of the elastic body (Y direction), and the sensitive direction of strain gauge No. 2 is along the short side of the elastic body (X direction); the sensitive direction of strain gauge No. 3 is along the long side of the elastic body (Y direction), and the sensitive direction of strain gauge No. 4 is along the short side of the elastic body (X direction).

[0041] In some embodiments, the elastic body is a rectangular parallelepiped with a regular shape, and the bottom surface has a certain curvature, and the size of the elastic body needs to envelop the size of the strain gauge. In the elastic body + strain gauge combination device, the ratio of the long side to the short side of the elastic body is greater than 2, the size of the elastic body is greater than 50% of the size of the strain gauge, and the curvature of the bottom surface of the elastic body is consistent with the curvature at the contact surface.

[0042] like Figure 3The schematic diagram of the installation position of the elastic body + strain gauge combination device at the shaft end is shown. There are 4 elastic body + strain gauge combination devices, which are evenly distributed along the circumference of the shaft end, and one group is installed every 90 degrees along the circumference, and the positions are marked as A1 to A4.

[0043] The elastomer + strain gauge combination device is installed in the step formed by the square mounting hole 6 of the shaft end ferrule 1. The top and bottom surfaces of the elastomer are perpendicular to the radial direction of the ferrule 1 at the location of the mounting hole 6, and are positioned by the shoulder in the mounting hole 6. The side surface 1 and side surface 2 of the elastomer are perpendicular to the tangent direction of the ferrule 1 at the location of the mounting hole 6, and the two side surfaces are clamped by the mounting surface. The front and back of the elastomer are perpendicular to the axial direction. Then the rolling bearing 5 is installed in the ferrule 1, and the rolling bearing 5 and the ferrule 1 are matched with a small clearance. Adjust the outer ring 4 of the rolling bearing 5 to ensure that the contact surface 7 of the elastomer + strain gauge combination device and the outer ring 4 of the rolling bearing 5 are in good contact. In other words, the contact interface of the compact frame shaft end is the matching surface between the shaft end ferrule 1 and the outer ring 4 of the rolling bearing 5, and the two are matched with a small clearance; the rotary configuration shaft end cover and the shaft end ferrule 1 can realize 360° relative rotation in the circumferential direction, and the torque between the two passes through the rolling bearing 5.

[0044] The present invention also provides a method for measuring the friction torque of a compact frame shaft end based on a strain gauge, which is described in detail as follows.

[0045] Step 1: Connect each strain gauge to a full-bridge Wheatstone measurement circuit, and connect the circuit to a computer through a computer interface, thereby building a measurement system of all strain gauges + elastomer devices.

[0046] Step 2: Before gluing the strain gauge, calibrate the resistance, size, and strain output of the strain gauge in the free state, and record the output of each strain gauge in this state, which are respectively recorded as: ε 01 , ε 02 , ε 03 , ε 04 , where the first subscript 0 indicates the free state of the strain gauge, and the second subscript 1 to 4 indicates the strain gauge number.

[0047] Step 3: In the elastic body + strain gauge assembly, press the strain gauge Figure 2 The position and direction shown are pasted on the surface of the elastic body. After the adhesive is hardened, the resistance, size and strain output of the strain gauge in the free state of the strain gauge + elastic body device are measured. At this time, the strain is ε 11 , ε 13 , ε 12 , ε 14 , where the first subscript 1 represents the free state of the strain gauge + elastic body combination, and the second subscript 1 to 4 represents the strain gauge number.

[0048] Step 4: Place the elastic body on a high-rigidity curved surface block and apply a uniformly distributed load P1 on the top surface of the elastic body. P1 is gradually increased from small to large and the output of each strain gauge is recorded. Keep the pressure P1 on the top surface of the elastic body constant, apply clamping forces P2 and P3 on both sides from small to large, and record the output of each strain gauge. Post-process the recorded data to make the following Figure 4 The load-strain calibration diagram shown uses a curve fitting method to summarize the relationship between the applied load and the strain, which is recorded as ε=f(P).

[0049] Step 5, refer to Figure 3 After the compact frame shaft end friction torque measurement system is assembled on the shaft end, the strain gauges are calibrated again to measure the resistance and output of each strain gauge in the free state. The output strain of each strain gauge in this state is recorded as ε 21 , ε 23 , ε 22 , ε 24 , where the first subscript 2 indicates the free state of the strain gauge + elastic body combination, and the second subscript 1 to 4 indicates the strain gauge number. Figure 4 The calibration relationship shown in the figure is based on the output strain of each strain gauge to calculate the stress state of the elastic body in each direction, that is, P = f -1 (ε), denoted as P1, P3, P2, and P4 respectively.

[0050] Step 6, such as Figure 5 The stress analysis of the elastic body shown in the figure, the strains in the x and y directions at the mid-surfaces of the front and rear sides of the elastic body can be expressed as or The first subscript * indicates the state of strain gauge + elastic body corresponding to the test, and the second subscript 1 to 4 indicates the strain gauge number; according to the stress-strain constitutive relationship of the elastic body σ=Eε, Where E is the elastic modulus of the elastic body, the stress in the x and y directions at the central axis can be deduced as σ 2cenx =E[(ε 22 -ε 12 )+(ε 24 -ε 14 )] / 2 and σ 2ceny =E[(ε 21 -ε 11 )+(ε 23 -ε 13 )] / 2, and the initial stress state at the mid-surface of the elastic body in the x and y directions after installation is calibrated accordingly.

[0051] Step 7, refer to Figure 3 , rotate the shaft end shaft system, the inner ring of the rolling bearing 5 rotates accordingly, and collect the output data of each strain gauge changing with time The superscript Ai indicates Figure 3The installation position of the middle strain gauge + elastic body device is i=1~4, the subscript 3 represents the strain gauge data collected when the inner ring of the bearing is rotating, and the subscript * represents the strain gauge number 1~4.

[0052] Step 8, post-process the data: 1) Figure 5 As shown in the figure, the true strain at each strain gauge can be expressed as the difference between the measured value of each strain gauge and the initial calibration value under the dynamic measurement state, that is, 2) The y-direction stress in the elastic body section S2 can be expressed as The x-direction stress in the elastic body section S1 can be expressed as 3) Further integrating the stress in the x direction at the mid-surface section S1, we can obtain the tangential force transmitted from the contact interface to the elastic body at the Ai position, that is, 4) Further integrating the stress in the y direction at the mid-surface section S2, we can obtain the normal force transmitted from the contact interface to the elastic body at the Ai position, that is, 5) Affected by the circumferential structure, the force in the x-direction or y-direction solved by the strain gauges at positions A1 to A4 on the contact surface is Not consistent, the tangential force in the circumferential direction is The normal pressure of the contact surface along the radial direction can be expressed as 5) Solve the friction torque M on this contact f =F τ (R+h / 2), where h is the height of the elastic body in the Y direction, R is the distance between the contact interface and the rotation center, and the static friction coefficient between the contact interfaces can be expressed as f=F N / F τ .

[0053] Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined by the claims of the present invention.

Claims

1. A compact frame shaft end friction torque measurement system based on strain gauges, characterized in that: It includes an elastic body + strain gauge combination device, a circuit measurement module, a computer interface, a data acquisition module and a data post-processing module; each strain gauge is connected to the circuit measurement module, and the circuit measurement module is connected to the computer's data acquisition module through the computer interface. The data post-processing module is used to process data from the data acquisition module; The elastic body + strain gauge combination device includes a rectangular elastic body and 4 thin-sheet resistance strain gauges; the elastic body includes a front and a back; the 4 thin-sheet resistance strain gauges include strain gauge No. 1, strain gauge No. 2, strain gauge No. 3, and strain gauge No. 4 respectively; strain gauge No. 1 and strain gauge No. 2 are attached to the back of the elastic body; strain gauge No. 3 and strain gauge No. 4 are attached to the front of the elastic body; strain gauge No. 1 and strain gauge No. 3 measure strain in the Y direction, and strain gauge No. 2 and strain gauge No. 4 measure strain in the X direction; When the system is measuring, the rolling bearing (5) is installed in the ring (1), and the rolling bearing (5) and the ring (1) are clearance-fitted; the shaft end shaft system and the shaft end ring (1) rotate relative to each other through the rolling bearing (5); the number of elastic body + strain gauge combination devices installed on the shaft end ring (1) is 4, which are evenly distributed along the circumferential direction and the positions are marked as A1 to A4 respectively; the front and rear of the elastic body are perpendicular to the axial direction; and the elastic body is in contact with the outer ring (4) of the rolling bearing (5).

2. The system according to claim 1, characterized in that The elastic body + strain gauge combination device is installed in the step of the square mounting hole (6) of the shaft end ring (1), the top surface and the bottom surface of the elastic body are perpendicular to the radial direction of the ring (1) at the location of the mounting hole (6), and are positioned by the shoulder in the mounting hole (6); the side surface 1 and the side surface 2 of the elastic body are perpendicular to the tangential direction of the ring (1) at the location of the mounting hole (6), and the two side surfaces are clamped by the mounting surface.

3. The system according to claim 1, characterized in that The elastic body is a rectangular parallelepiped with a curvature on the bottom surface; the ratio of the long side to the short side of the elastic body is greater than 2, the size of the elastic body is greater than 50% of the size of the strain gauge, and the curvature of the bottom surface of the elastic body is consistent with the curvature at the contact surface.

4. A method for measuring the friction torque of a compact frame shaft end based on a strain gauge, characterized in that: The method applies the system according to any one of claims 1 to 3, and the method comprises: Calibration is performed after the elastic body + strain gauge assembly is installed on the ferrule (1); Rotate the shaft end shaft system, collect the output data of each strain gauge changing with time, and post-process the data.

5. The method according to claim 4, characterized in that The method further comprises: Apply a uniformly distributed load P1 on the top surface of the elastic body, and gradually increase P1 from small to large, and record the output of each strain gauge; keep the pressure P1 on the top surface of the elastic body constant, and gradually apply the clamping force P2 on the two sides from small to large, and record the output of each strain gauge; post-process the recorded data, make a load-strain calibration diagram, and use the curve fitting method to summarize the relationship between the applied load and the strain, which is recorded as ε=f(P); The calibration is performed after the elastic body + strain gauge combination device is installed on the ring (1), comprising: After assembly at the shaft end, the output strain of each strain gauge is measured, and the stress state of the elastic body in each direction is calculated based on ε=f(P).

6. The method according to claim 4, characterized in that When the elastic body + strain gauge assembly is installed on the ring (1) and calibrated, the strain gauge output strain is recorded as The superscript Ai indicates the installation position of the elastic body + strain gauge combination device, i = 1 to 4, the first subscript 2 indicates the free state of the strain gauge + elastic body combination in the ring (1), and the second subscript * indicates the strain gauge number; Rotate the shaft end shaft system and collect the output data of each strain gauge changing with time. The superscript Ai indicates the installation position of the elastic body + strain gauge combination device, i = 1 to 4, the subscript 3 indicates the strain gauge data collected when the inner ring of the bearing is rotating, and the subscript * indicates the strain gauge number; True strain at each strain gauge The y-direction stress of the elastic body is The x-direction stress of the elastic body is E is the elastic modulus of the high elastomer; In the x direction, the tangential force on the elastic body at the Ai position transmitted from the contact interface is S is the area, S1 represents the cross section of the elastic body perpendicular to the y direction; In the y direction, the normal force on the elastic body at the Ai position transmitted from the contact interface is S is the area, and S2 represents the cross section of the elastic body perpendicular to the z direction.

7. The method according to claim 6, characterized in that Tangential force in the circumferential direction Normal pressure of contact surface along radial direction 8. The method according to claim 7, characterized in that Friction torque M f =Fτ·(R+h / 2), where h is the height of the elastic body in y direction and R is the distance from the contact interface to the center of rotation.

9. The method according to claim 7, characterized in that: Static friction coefficient between contact interfaces f = F N / F τ .

10. The method according to claim 6, characterized in that The method further comprises: After the strain gauge is pasted, the strain gauge is calibrated in the free state. The output of the strain gauge is ε 11 , ε 13 , ε 12 , ε 14 , where the first subscript 1 indicates that the strain gauge + elastic body combination is in a free state after bonding, and the second subscript 1 to 4 indicates the strain gauge number; When the elastic body + strain gauge assembly is installed on the ring (1) and calibrated, the output strain of the strain gauge is recorded as ε 21 , ε 23 , ε 22 , ε 24 , wherein the first subscript 2 indicates the free state of the strain gauge + elastic body combination in the ring (1), and the second subscript 1 to 4 indicates the strain gauge number; The initial stress state of the elastic body in the x and y directions during calibration satisfies: s 2cenx =E[(e 22 -e 12 )+(e 24 -e 14 )] / 2 and σ 2ceny =E[(e 21 -e 11 )+(e 23 -e 13 )] / 2.

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