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

Abstract

The application discloses a compact frame shaft end friction torque measurement system and method based on strain gauges, which comprises the following steps: 1) the compact shaft end structure comprises a shaft end cover, a shaft end seat, motor elements, a pair of rolling bearings and other components, and has the characteristics of compact structure and miniaturization; 2) based on the strain gauge pasting mode on the elastic body and the size characteristics of the elastic body; 3) based on the zero calibration method of the elastic body + strain gauge combination body with a specific shape; 4) based on the multi-position installation mode of the elastic body + strain gauge combination body between the contact interfaces, the contact surface strain and stress method is solved by coupling the multi-position measurement results; 5) the data collected by each strain gauge is processed by using a data processing method, and the tangential and normal mechanical characteristics between the contact surfaces are sequentially obtained; and 6) the shaft end friction torque is solved based on the tangential mechanical characteristics at each position, so that the electromagnetic interference torque and the friction torque generated by the shaft end torque motor assembly are excluded, and the friction torque between the dynamic rotor and the static rotor of the shaft end is obtained.

Description

Technical Field

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

[0002] The frame shaft system of a platform-type inertial navigation system is a key component for isolating the angular motion of the platform and carrier and ensuring stability in inertial space. In practical engineering applications, the frame shaft system typically rotates at extremely low speeds, and the bearings are in a state of frequent transition between dry friction, boundary lubrication, and mixed lubrication. This easily leads to fluctuations in frictional torque, which is the main source of interference torque at the frame shaft end. This affects the precise control of the shaft end torque motor, and thus restricts the navigation and guidance accuracy of the platform-type inertial navigation system. At the same time, due to the compact structure of the frame shaft end, the bearing frictional torque is difficult to measure directly, and the common method of measuring frictional torque using the torque motor current output is subject to electromagnetic interference and the influence of components such as the shaft end slip ring. Summary of the Invention

[0003] This invention provides a method for measuring the frictional torque at the shaft end of a compact frame based on strain gauges. The purpose is to overcome the structural limitations of the shaft end of a compact frame, obtain the frictional torque between the moving and stationary rotors at the shaft end using a direct measurement method, and eliminate the electromagnetic interference torque and frictional torque generated by the shaft end torque motor assembly, thus providing a basis for accurate analysis of 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, including an elastomer + 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 the data from the data acquisition module.

[0005] The elastomer + strain gauge combination device includes one rectangular elastomer and four thin-film resistance strain gauges. The elastomer includes a front and a back. The four thin-film resistance strain gauges are respectively named strain gauge 1, strain gauge 2, strain gauge 3, and strain gauge 4. Strain gauges 1 and 2 are attached to the back of the elastomer, and strain gauges 3 and 4 are attached to the front of the elastomer. Strain gauges 1 and 3 measure the strain in the Y direction, and strain gauges 2 and 4 measure the strain in the X direction.

[0006] During measurement, the rolling bearing is installed in the race, and the rolling bearing and the race are clearance fit; the shaft end system and the shaft end race rotate relative to each other through the rolling bearing; the number of elastic body + strain gauge combination devices installed on the shaft end race is 4, evenly distributed along the circumference, and the positions are marked as A1 to A4 respectively; the front and rear of the elastic body are perpendicular to the axial direction; the elastic body is in contact with the outer ring of the rolling bearing.

[0007] In conjunction with the first aspect, in some 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 and bottom surfaces of the elastomer are perpendicular to the radial direction of the ring at the location of the mounting hole and are positioned by the shoulder in the mounting hole. The side surfaces 1 and 2 of the elastomer are perpendicular to the tangential direction of the ring at the location of the mounting hole and are clamped by the mounting surface.

[0008] In conjunction with the first aspect, in some implementations of the first aspect, the elastic body is a cuboid with a curved bottom surface; the ratio of the length 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.

[0009] Secondly, a method for measuring the frictional torque at the shaft end of a compact frame based on strain gauges is provided. The method applies a system as described in any implementation of the first aspect above, and the method includes:

[0010] Calibration is performed after the elastomer + strain gauge combination device is installed on the collar;

[0011] Rotate the shaft end system to collect the output data of each strain gauge as time changes, and then perform post-processing on the data.

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

[0013] A uniformly distributed load P1 is applied to the top surface of the elastic body. P1 is gradually increased from small to large, and the output of each strain gauge is recorded. While keeping the pressure P1 on the top surface of the elastic body constant, a clamping force P2 is gradually applied to both sides from small to large, and the output of each strain gauge is recorded. The recorded data is post-processed to create a load-strain calibration diagram. The relationship between the applied load and strain is summarized using curve fitting, denoted as ε=f(P).

[0014] The calibration performed after the elastomer + strain gauge assembly is installed on the raceway includes:

[0015] After assembly at the shaft end, the strain output 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 conjunction with the second aspect, in some implementations of the second aspect, when the elastomer + strain gauge combination device is calibrated after being installed on the collar, the strain output by the strain gauge is denoted as... The superscript Ai indicates the installation position of the elastomer + strain gauge combination device, i = 1 to 4, the first subscript 2 indicates the free state of the strain gauge + elastomer combination in the collar, and the second subscript * indicates the strain gauge number.

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

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

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

[0020] In the y-direction, the normal force transmitted from the contact interface to the elastic body at position Ai. S represents 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 some implementations of the second aspect, the tangential force in the circumferential direction Radial contact surface normal force

[0022] In conjunction with the second aspect, in some implementations of the second aspect, the frictional 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 some 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 gauges were attached, they were calibrated in a free state. The outputs of the strain gauges were ε. 11 ε13 ε 12 ε 14 The first subscript 1 indicates that the strain gauge + elastomer combination is in a free state after being pasted, and the second subscript 1 to 4 indicate the strain gauge number;

[0026] When the elastomer + strain gauge combination device is calibrated after being installed on the collar, the strain output by the strain gauge is denoted as ε. 21 ε 23 ε 22 ε 24 The first subscript 2 indicates the free state of the strain gauge + elastomer combination in the collar, and the second subscript 1 to 4 indicate 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 has 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 frame, 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 the accurate compensation and control of friction torque;

[0032] (3) The shaft end friction torque measurement system and method of the present invention characterizes the stress state by measuring the strain changes at multiple points, and finally calculates the tangential force and normal force to characterize the friction torque change. This method attaches strain gauges between two contact surfaces, resulting in high comprehensive load; it fully analyzes the stress and deformation state of the strain gauges; the method designs a circumferential surface strain state measurement, fully considering the influence of circumferential curvature on the strain gauge measurement; the method uses the actual strain state measured by the strain gauges to solve the shaft end friction torque through a series of derivations, resulting in more accurate data processing. Attached Figure Description

[0033] Figure 1This is a schematic 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 This is a schematic diagram of a load-strain relationship calibration.

[0037] Figure 5 This is a schematic diagram of the stress state of an elastic body. Detailed Implementation

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

[0039] like Figure 1 The diagram shows a compact frame shaft friction torque measurement system based on strain gauges. The system includes an elastomer + 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 a computer via the computer interface, thus establishing the entire strain gauge + elastomer measurement system.

[0040] like Figure 2 The diagram shows a schematic of an elastomer and strain gauge assembly. The assembly includes one rectangular elastomer and four thin-film resistance strain gauges. The elastomer has a front and a back section. The four thin-film resistance strain gauges are designated as strain gauge 1, strain gauge 2, strain gauge 3, and strain gauge 4. Strain gauges 1 and 2 are attached to the back of the elastomer. Strain gauges 3 and 4 are attached to the front of the elastomer. Strain gauges 1 and 3 measure strain in the Y-direction (long side of the elastomer), and strain gauges 2 and 4 measure strain in the X-direction (short side of the elastomer). In other words, strain gauge 1 is sensitive along the long side (Y-direction) of the elastomer, strain gauge 2 is sensitive along the short side (X-direction), strain gauge 3 is sensitive along the long side (Y-direction), and strain gauge 4 is sensitive along the short side (X-direction).

[0041] In some embodiments, the elastomer is a regularly shaped cuboid with a certain curvature on its bottom surface, and the size of the elastomer needs to encompass the size of the strain gauge. In the elastomer + strain gauge combination device, 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.

[0042] like Figure 3The diagram shows the installation position of the elastomer + strain gauge combination device at the shaft end. There are four elastomer + strain gauge combination devices, evenly distributed along the circumference of the shaft end, with one set installed every 90 degrees along the circumference, and the positions are marked as A1 to A4 respectively.

[0043] The elastomer and strain gauge assembly is installed in the stepped area formed by the square mounting hole 6 of the shaft end ring 1. The top and bottom surfaces of the elastomer are perpendicular to the radial direction of the ring 1 at the location of the mounting hole 6, and are positioned by a shoulder within the mounting hole 6. The side surfaces 1 and 2 of the elastomer are perpendicular to the tangent direction of the ring 1 at the location of the mounting hole 6, and are clamped by the mounting surfaces. The front and rear surfaces of the elastomer are perpendicular to the axial direction. Then, the rolling bearing 5 is installed in the ring 1, with a small clearance fit between the rolling bearing 5 and the ring 1. The outer ring 4 of the rolling bearing 5 is adjusted to ensure good contact between the contact surface 7 of the elastomer and strain gauge assembly and the outer ring 4 of the rolling bearing 5. In other words, the contact interface of the compact frame shaft end is the mating surface between the shaft end ring 1 and the outer ring 4 of the rolling bearing 5, with a small clearance fit; the rotating shaft end cap and the shaft end ring 1 can achieve 360° relative rotation in the circumferential direction, and the torque transmission between them is through the rolling bearing 5.

[0044] The present invention also provides a method for measuring the frictional torque at the shaft end of a compact frame based on strain gauges, which is described in detail below.

[0045] Step 1: Connect each strain gauge to the full-bridge Wheatstone measurement circuit, and connect the circuit to the computer via the computer interface to build a measurement system with all strain gauges and the elastomer device.

[0046] Step 2: Before attaching the strain gauges, calibrate the resistance, dimensions, and strain output of the strain gauges in a free state, and record the output of each strain gauge in this state, denoted as: ε 01 ε 02 ε 03 ε 04 The first subscript 0 indicates that the strain gauge is in a free state, and the second subscript 1 to 4 indicates the strain gauge number.

[0047] Step 3, in the elastomer + strain gauge combination device, the strain gauges are arranged according to... Figure 2 The strain gauge is attached to the surface of the elastomer at the indicated position and orientation. After the adhesive has hardened, the resistance, dimensions, and strain output of the strain gauge + elastomer device are measured in its free state. At this point, the strain is ε. 11 ε 13 ε 12 ε 14 The first subscript 1 indicates the free state of the strain gauge + elastomer combination, and the second subscript 1 to 4 indicate the strain gauge number.

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

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

[0050] Step 6, as follows Figure 5 The stress analysis of the elastic body shown shows that the strain in the x and y directions at the mid-surface of the front and rear sides of the elastic body can be expressed as follows: or The first subscript * indicates the test state corresponding to the strain gauge and the elastic body, and the second subscript 1 to 4 indicates the strain gauge number; according to the stress-strain constitutive relation 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 derived 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, thereby determining the initial stress state at the mid-surface of the elastomer in the x and y directions after installation.

[0051] Step 7, refer to Figure 3 Rotating the shaft end system causes the inner ring of rolling bearing 5 to rotate accordingly, allowing the output data of each strain gauge to change over time to be collected. The superscript Ai indicates Figure 3The installation positions of the medium strain gauge + elastomer device are i = 1 to 4. The subscript 3 indicates the strain gauge data collected under the condition of the inner ring of the rotating bearing, and the subscript * indicates the strain gauge number 1 to 4.

[0052] Step 8, post-process the data: 1) such as Figure 5 As shown, the true strain at each strain gauge can be expressed as the difference between the measured value of each strain gauge under dynamic measurement conditions and the initial calibration value, i.e. 2) The y-direction stress in the section S2 of the elastic body can be expressed as: The x-direction stress in the section S1 of the elastic body can be expressed as: 3) By further integrating the stress in the x-direction at the mid-section S1, the tangential force transmitted from the contact interface to the elastic body at position Ai can be obtained, i.e. 4) By further integrating the stress in the y-direction at the mid-section S2, the normal force transmitted from the contact interface to the elastic body at position Ai can be obtained, i.e. 5) Due to the influence of the circular structure, the force in the x or y direction obtained from the strain gauges at the contact surfaces A1 to A4 is affected. They are not consistent; the tangential force in the circumferential direction is taken as... The radial contact surface normal force can be expressed as: 5) Solve for the frictional torque M at this contact point. f =F τ ·(R+h / 2), where h is the height of the elastic body in the Y direction, R is the distance from the contact interface to the center of rotation, and the static friction coefficient between the contact interfaces can be expressed as f=F N / F τ .

[0053] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can 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 should be determined by the scope defined in the claims of the present invention.

Claims

1. A method for measuring the frictional torque at the shaft end of a compact frame based on strain gauges, characterized in that, The method employs a compact frame shaft end friction torque measurement system based on strain gauges. The system includes an elastomer + 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 the data from the data acquisition module. The elastomer + strain gauge combination device includes one rectangular elastomer and four thin-film resistance strain gauges. The elastomer includes a front and a back. The four thin-film resistance strain gauges are respectively named strain gauge 1, strain gauge 2, strain gauge 3, and strain gauge 4. Strain gauges 1 and 2 are attached to the back of the elastomer, and strain gauges 3 and 4 are attached to the front of the elastomer. Strain gauges 1 and 3 measure the strain in the Y direction, and strain gauges 2 and 4 measure the strain in the X direction. During the measurement, the rolling bearing (5) is installed in the ring (1), and the rolling bearing (5) and the ring (1) are in clearance fit; the shaft end 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 circumference and are marked as A1 to A4 respectively; the front and rear of the elastic body are perpendicular to the axial direction; the elastic body is in contact with the outer ring (4) of the rolling bearing (5); The method includes: Calibration is performed after the elastomer + strain gauge assembly is installed on the collar (1); Rotate the shaft end system, collect the output data of each strain gauge changing over time, and perform post-processing on the data; When the elastomer + strain gauge assembly is calibrated after being installed on the collar (1), the strain output of the strain gauge is recorded as follows: 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 collar (1), and the second subscript * indicates the strain gauge number. Rotate the shaft end system and collect the output data of each strain gauge over time. The superscript Ai indicates the installation position of the elastomer + strain gauge combination device, i = 1 to 4; the subscript 3 indicates the strain gauge data collected under the condition of the inner ring of the rotating bearing; the subscript * indicates the strain gauge number. True strain at each strain gauge The y-direction stress of the elastic body is The stress in the x-direction of the elastic body is E represents the elastic modulus of a high-elasticity body; In the x-direction, the tangential force transmitted from the contact interface to the elastic body at position Ai. S represents the area, and S1 represents the cross-section of the elastic body perpendicular to the y-direction. In the y-direction, the normal force transmitted from the contact interface to the elastic body at position Ai. S represents the area, and S2 represents the cross-section of the elastic body perpendicular to the z-direction.

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

3. The method according to claim 1, characterized in that, The elastomer is a cuboid with a curved bottom surface; the ratio of the length 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.

4. The method according to claim 1, characterized in that, The method further includes: A uniformly distributed load P1 is applied to the top surface of the elastic body. P1 is gradually increased from small to large, and the output of each strain gauge is recorded. While keeping the pressure P1 on the top surface of the elastic body constant, a clamping force P2 is gradually applied to both sides from small to large, and the output of each strain gauge is recorded. The recorded data is post-processed to create a load-strain calibration diagram. The relationship between the applied load and strain is summarized using curve fitting, denoted as ε=f(P). The calibration performed after the elastomer + strain gauge assembly is installed on the collar (1) includes: After assembly at the shaft end, the strain output of each strain gauge is measured, and the stress state of the elastic body in each direction is calculated based on ε=f(P).

5. The method according to claim 1, characterized in that, Circumferential tangential force Radial contact surface normal force 6. The method according to claim 5, characterized in that, Frictional 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.

7. The method according to claim 5, characterized in that, The static friction coefficient between the contact interfaces is f = F N / F τ .

8. The method according to claim 1, characterized in that, The method further includes: After the strain gauges were attached, they were calibrated in a free state. The outputs of the strain gauges were ε. 11 ε 13 ε 12 ε 14 The first subscript 1 indicates that the strain gauge + elastomer combination is in a free state after being pasted, and the second subscript 1 to 4 indicate the strain gauge number; When the elastomer + strain gauge combination device is calibrated after being installed on the collar (1), the strain output by the strain gauge is denoted as ε. 21 ε 23 ε 22 ε 24 The first subscript 2 indicates the free state of the strain gauge + elastomer combination in the collar (1), and the second subscript 1 to 4 indicate 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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