A method for accelerating the life test of high-speed precision gear transmission

Abstract

The invention relates to the field of high-speed precision gear transmission, and discloses an accelerated life test method for a high-speed precision gear transmission device, which breaks through the limitations of traditional gear transmission life test methods, designs and guides the accelerated life test of a gear transmission device based on the performance degradation caused by friction and wear on the gear transmission interface, and starts from the meshing mechanism and transmission performance of the gear transmission device. The fatigue life and failure degradation of the gear transmission device are evaluated based on the consistency of the failure mechanism and failure mode to formulate its accelerated life test method.

Description

Technical Field

[0001] The invention relates to the field of high-speed precision gear transmission, and in particular to an accelerated life test method for a high-speed precision gear transmission device. Background Art

[0002] Conventional harmonic reducer life test methods (see national standard GB / T30819-2014 Harmonic gear reducer for robots) usually run for no less than 500 hours under rated load and rated speed conditions, and regularly check the degradation of reducer temperature, transmission efficiency, transmission error and other indicators during operation. This test method is time-consuming and greatly affected by uncertain factors in the external environment.

[0003] The existing robot reducers use the accelerated life test method (see national standard GB / T35089-2018 Test method for precision gear transmission devices for robots), set the reducer loading curve, and ensure that the maximum output torque does not exceed 2.5 times the rated output torque, and the maximum speed is not greater than the rated speed. Most of these test methods are based on actual engineering experience, lack theoretical support, and are not universal.

[0004] The existing calculation of the fatigue life of harmonic gear reducers is based on the failure of flexible bearings. However, when the robot's accuracy drops beyond its accuracy requirements, the transmission accuracy and transmission efficiency of the robot reducer are only in the degradation stage, and have not yet reached the fatigue failure of the reducer's flexible bearings. Therefore, the fatigue life of the harmonic reducer obtained based on the flexible bearing fatigue life test is unreasonable and cannot effectively reflect the failure of the reducer's internal components. Summary of the invention

[0005] The present invention aims to provide an accelerated life test method for a high-speed precision gear transmission device, so as to break through the limitations of the traditional gear transmission life test method, and to design and guide the accelerated life test of the gear transmission device based on the performance degradation caused by friction and wear at the gear transmission interface, from the meshing mechanism and transmission performance of the gear transmission device, and to formulate its accelerated life test method by evaluating the fatigue life and failure degradation of the gear transmission device based on the consistency of failure mechanism and failure mode.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for accelerating the life test of a high-speed precision gear transmission device, comprising the following steps:

[0007] A. Determine the acceleration: Without changing the failure mechanism of the gear transmission device before and after the test, determine whether there is a regular acceleration process based on the structural characteristics and transmission principle of the gear transmission device. If there is a regular acceleration process, there is acceleration, and proceed to the next step;

[0008] B. Select acceleration stress: determine the film thickness ratio through the equivalent radius of curvature, entrainment speed, equivalent elastic modulus, dimensionless entrainment speed, dimensionless elastic modulus, and dimensionless load, determine the lubrication state through the film thickness ratio, determine the film thickness ratio under different working conditions through different multiples of load and speed, obtain the corresponding relationship curve of film thickness ratio with respect to load and speed, and determine the load and speed that meet the conditions as the acceleration stress according to the film thickness ratio;

[0009] C. Select the acceleration factor: get the acceleration factor by accelerating stress;

[0010] D. Establish an acceleration model: Calculate the test time of the gear transmission device under acceleration conditions based on the acceleration stress and acceleration factor, that is, the life under acceleration conditions.

[0011] Preferably, as an improvement, in step B, the equivalent radius of curvature is determined by the following formula:

[0012] R=(1 / r1+1 / r2) -1

[0013] Where R is the equivalent radius of curvature, r1 and r2 are the radii of curvature of the two contact surfaces at the meshing point, respectively, in meters;

[0014] The entrainment speed is determined by the following formula:

[0015] U=(u1+u2) / 2

[0016] Where U is the entrainment velocity, u1 and u2 are the tangential velocities of the two surfaces, respectively, in meters per second;

[0017] The equivalent elastic modulus is determined by the following formula:

[0018]

[0019] Where E' is the equivalent elastic modulus, v1 and v2 are the Poisson's ratios of the two surfaces, and E1 and E2 are the elastic moduli of the two surfaces, respectively, in Pascals.

[0020] Preferably, as an improvement, in step B, the dimensionless entrainment velocity is determined by the following formula:

[0021] U * =η0U / (E'R)

[0022] Where U * is the dimensionless entrainment velocity at the gear meshing point, η0 is the ambient viscosity of the lubricant, in Pas;

[0023] The dimensionless elastic modulus is determined by the following formula:

[0024] G * =αE'

[0025] Where G * is the dimensionless elastic modulus of the gear tooth contact surface, α is the viscosity coefficient, the unit is one part of Pa;

[0026] The dimensionless load is determined by the following formula:

[0027] W * =w / (E'R)

[0028] Where W * is the dimensionless load at the meshing point of the gear teeth, and w is the load on the gear teeth at the meshing point, in Newtons.

[0029] Preferably, as an improvement, the film thickness ratio in step B is determined by the following formula:

[0030] λ=h / σ

[0031] Where λ is the film thickness ratio, h is the contact pair oil film thickness, unit is micrometer, and σ is the composite root mean square roughness value;

[0032] The composite RMS roughness value is determined by the following formula:

[0033]

[0034] Where σ1 and σ2 are the root mean square values ​​of the roughness of the two contact surfaces, in micrometers;

[0035] The contact pair oil film thickness is determined by the following formula:

[0036] H=h / R=3.06U *0.69 G *0.56 W *-0.1

[0037] Where h is the contact oil film thickness.

[0038] Preferably, as an improvement, the lubrication state in step B includes boundary lubrication λ<1.0, mixed lubrication 1.0<λ<3, and full film lubrication λ>3.

[0039] Preferably, as an improvement, in step B, the rated speed is set to n0, the rated load is w0, the film thickness ratio of the meshing position under the rated working condition is λ0, the speed and load are divided into orthogonal grids, and the acceleration stress under different multiples of the rated load working conditions and the rated speed is calculated respectively, and recorded in a table, and the speed and load curve under the same interface lubrication state is drawn according to the calculated numerical points, and the speed and load are selected on the curve to guide the acceleration experiment of the gear transmission device, then w1, w2…w n It is the acceleration stress at the corresponding speed.

[0040] Preferably, as an improvement, in step C, the recorded values ​​of the speed and load obtained in step B are curve-fitted to obtain a continuous curve of the load with respect to the speed. The speed and load corresponding to each point on the curve can be used as a reference to guide the acceleration experiment of the gear transmission device, and the acceleration factor is determined by the following formula:

[0041]

[0042] Where n i The speed corresponding to each point on the curve, w i is the load corresponding to each point on the curve.

[0043] Preferably, as an improvement, in step D, the test time of the gear transmission device under the accelerated condition, that is, the life under the accelerated condition, is determined according to the accelerated stress and the accelerated factor:

[0044]

[0045] Where L is the test time in hours, and L0 is the rated life of the gear transmission device in hours.

[0046] The beneficial effects of the present invention include:

[0047] First: The accelerated life test evaluation method for a gear transmission device proposed in the present invention can accelerate the performance degradation process of the internal components of the gear transmission device to a certain extent, thereby shortening the test time of the gear transmission device life test and reducing the test cost. Second: The accelerated life test evaluation method for a gear transmission device proposed in the present invention starts from the meshing mechanism and transmission performance of the gear transmission device, and uses the friction and wear process of the gear transmission interface to reveal the performance degradation mechanism of the gear transmission device, thereby guiding the accelerated life test of the gear transmission device, and evaluating the life and failure degradation of the gear transmission device based on the consistency of the failure mechanism and failure mode. It is a gear transmission device accelerated life test evaluation method based on forward design, has sufficient theoretical basis, and can be used to guide the accelerated life test of the gear transmission device.

[0048] Third: The accelerated life test evaluation method for gear transmission proposed in the present invention starts from the friction and wear conditions of the meshing interface of the gear transmission parts, and comprehensively considers the interaction between the transmission interface oil film thickness and the microscopic interface roughness of the moving surface, so as to obtain the real meshing conditions and lubrication conditions between the gear transmission parts. Therefore, according to the friction and wear conditions of the parts reflected by the meshing conditions and lubrication conditions, the real failure and degradation conditions of the gear transmission can be directly and effectively judged, and the fatigue life of the gear transmission obtained thereby is also closer to the real fatigue life of the gear transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1Schematic diagram of a flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The following is further described in detail through specific implementation methods:

[0051] Embodiment: A method for accelerating the life test of a high-speed precision gear transmission device, the process is as follows Figure 1 As shown, including:

[0052] The first part is to judge the acceleration: the failure mechanism of the gear transmission device before and after the test is unchanged, which is a prerequisite for the accelerated life test. It is necessary to judge whether there is a regular acceleration process based on the structural characteristics and transmission principle of the gear transmission device, that is, whether there is acceleration. If there is acceleration, proceed to the next step;

[0053] The second part is to select the accelerating stress: The correct selection of the accelerating stress has a great influence on the acceleration efficiency of the test. Usually, the accelerating stress needs to be selected according to the failure mechanism and working conditions of the gear transmission device;

[0054] (1) Calculation of film thickness ratio

[0055] For the accelerated wear performance degradation test of gear transmission, in order to ensure the consistency of the accelerated failure mode and failure mechanism, the test is repeated by ensuring the consistency of the oil film thickness ratio until the accelerated stress level is determined. Taking ordinary spur gear transmission as an example, its gear meshing belongs to the line contact type, and the film thickness ratio calculation formula is shown in formula (1):

[0056] λ=h / σ (1)

[0057] Where:

[0058] λ——film thickness ratio;

[0059] h——contact oil film thickness, usually calculated in the center of the contact area within half the Hertz radius, in micrometers (μm);

[0060] σ——composite root mean square roughness value, Unit: micrometer (μm);

[0061] σ1, σ2——the root mean square value of the roughness of the two contact surfaces, respectively, in micrometers (μm).

[0062] The calculation formula of contact pair oil film thickness is as follows:

[0063] H=h / R=3.06U *0.69 G *0.56 W *-0.1 (2)

[0064] Where:

[0065] U* ——dimensionless entrainment velocity at the meshing point of the gear teeth;

[0066] G * ——Dimensionless elastic modulus of the material of the gear tooth contact surface;

[0067] W * ——dimensionless load at the meshing point of gear teeth;

[0068] R——equivalent radius of curvature, R=(1 / r1+1 / r2) -1 , r1, r2 are the radii of curvature of the two contact surfaces at the meshing point, respectively, in meters (m);

[0069] The dimensionless entrainment velocity calculation formula is as follows:

[0070] U * =η0U / (E'R) (3)

[0071] In the formula,

[0072] η0——lubricant environmental viscosity, in Pascal seconds (Pa*s);

[0073] U——Entrainment velocity, U=(u1+u2) / 2, u1 and u2 are the tangential velocities of the two surfaces respectively, in meters per second (m / s); E'——Equivalent elastic modulus, ν1, ν2 are the Poisson's ratios of the two surfaces, E1, E2 are the elastic moduli of the two surfaces, in Pascals (P a );

[0074] The dimensionless material elastic modulus is calculated as follows:

[0075] G * =αE' (4)

[0076] In the formula,

[0077] α——viscosity pressure coefficient, unit is one part of Pa (1 / P a );

[0078] The dimensionless load calculation formula is as follows:

[0079] W * =w / (E'R) (5)

[0080] In the formula,

[0081] w is the load on the gear teeth at the meshing point, in Newtons (N).

[0082] (2) Determine the lubrication status

[0083] According to the presence of lubricants between the parts interface and the thickness of the fluid film, the lubrication state can be divided into boundary lubrication, mixed lubrication, and full film lubrication. The mechanism of fluid lubrication can be described by the well-known Stribeck curve. It is generally believed that: λ<1.0, boundary lubrication; 1.0<λ<3, mixed lubrication; λ>3, full film lubrication.

[0084] (3) Determine the accelerated stress

[0085] In order to ensure the consistency of the failure mode and failure mechanism of the gear transmission under accelerated conditions with those under normal conditions, it is necessary to ensure that the lubrication state of the gear tooth interface under accelerated conditions is the same as that under normal conditions, that is, the film thickness ratio is in the same lubrication state range. Therefore, in order to conduct the accelerated degradation life test of the gear transmission, it is necessary to appropriately adjust the film thickness ratio without changing the lubrication state, and then find the accelerated stress that satisfies the consistency of the lubrication state. The accelerated stress confirmation method is as follows:

[0086] Assume the rated speed is n0, the rated load is w0, and the film thickness ratio of the meshing position under the rated working condition is λ0. First, the speed and load are divided into orthogonal grids. Calculate the acceleration stress under different multiples of the rated load conditions and rated speed, record them in the table, and draw the speed and load curve under the same interface lubrication state according to the calculated numerical points. Select the appropriate speed and load on the curve to guide the acceleration experiment of the gear transmission device. Then w1, w2…w n That is the acceleration stress at the corresponding speed:

[0087] Table 1 Accelerated stress value record table

[0088]

[0089] The third part is to select the acceleration factor: the acceleration factor is the ratio of the characteristic value of the life of the gear transmission under accelerated stress conditions to the characteristic value of the life under normal stress conditions. It reflects the effect of the accelerated stress level and is a function of the accelerated stress.

[0090] The speed obtained in the second part is subjected to curve fitting with the recorded value of the load to obtain a continuous curve of the load and the speed. The speed n corresponding to each point on the curve is i With load w i It can be used as a reference to guide the acceleration test of gear transmission devices. The acceleration factor can be calculated by the following formula:

[0091]

[0092] The fourth part is to establish an accelerated model: establish the changing relationship between life characteristics and accelerated stress levels, and linearize the model through mathematical transformation to clarify the law of changes in the tribological properties of each contact part with working conditions.

[0093] Calculate the test time of the gear transmission under accelerated conditions according to the accelerated stress and acceleration factor, that is, the life under accelerated conditions:

[0094]

[0095] In the formula,

[0096] L——test time, in hours (h);

[0097] L0——Rated life of gear transmission device, in hours (h);

[0098] k – acceleration factor.

[0099] The present invention proposes an accelerated life test evaluation method for a gear transmission device. The method can obtain the acceleration factor and acceleration force of the gear transmission device under the premise of ensuring the consistency between the failure mode and the failure mechanism of the gear transmission device, thereby guiding the gear transmission device to perform an accelerated life test, which can effectively shorten the test time and reduce the influence of external uncertain factors.

[0100] According to the interface lubrication theory, the lubrication condition of the gear transmission gear teeth meshing is analyzed, and the acceleration factor expression is derived from the interaction law between the oil film thickness at the meshing point and the contact interface roughness, and then the acceleration factor that meets the consistency of the interface lubrication condition is obtained, thereby guiding the gear transmission acceleration test and providing a sufficient theoretical basis for the gear transmission acceleration test. The gear transmission device accelerated life test evaluation method proposed in the present invention starts from the meshing mechanism and transmission performance, and is designed to guide the gear transmission device accelerated life test based on the performance degradation caused by the friction and wear of the gear transmission interface. This method can truly reflect the meshing transmission and friction and wear conditions of the transmission interface, and the predicted life of the gear transmission device obtained based on this is more reliable and informative than the bearing service life.

[0101] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for accelerating the life test of a high-speed precision gear transmission device, characterized in that: The following steps are involved: A. Determine the acceleration: Without changing the failure mechanism of the gear transmission device before and after the test, determine whether there is a regular acceleration process based on the structural characteristics and transmission principle of the gear transmission device. If there is a regular acceleration process, there is acceleration, and proceed to the next step; B. Select acceleration stress: determine the film thickness ratio through the equivalent radius of curvature, entrainment speed, equivalent elastic modulus, dimensionless entrainment speed, dimensionless elastic modulus, and dimensionless load, determine the lubrication state through the film thickness ratio, determine the film thickness ratio under different working conditions through different multiples of load and speed, obtain the corresponding relationship curve of film thickness ratio with respect to load and speed, and determine the load and speed that meet the conditions as the acceleration stress according to the film thickness ratio; The equivalent radius of curvature is determined by the following formula: R＝(1 / r1+1 / r2) -1 Where R is the equivalent radius of curvature, r1 and r2 are the radii of curvature of the two contact surfaces at the meshing point, respectively, in meters; The entrainment speed is determined by the following formula: U=(u1+u2) / 2 Where U is the entrainment velocity, u1 and u2 are the tangential velocities of the two surfaces, respectively, in meters per second; the equivalent elastic modulus is determined by the following formula: Where E' is the equivalent elastic modulus, v1 and v2 are the Poisson's ratios of the two surfaces, and E1 and E2 are the elastic moduli of the two surfaces, in Pascals; The dimensionless entrainment velocity is determined by the following formula: U * =η0U / (E'R) Where U * is the dimensionless entrainment velocity at the gear meshing point, η0 is the ambient viscosity of the lubricant, in Pas; The dimensionless elastic modulus is determined by the following formula: G * =αE' Where G * is the dimensionless elastic modulus of the gear tooth contact surface, α is the viscosity coefficient, the unit is one part of Pa; The dimensionless load is determined by the following formula: W * =w / (E'R) Where W * is the dimensionless load at the meshing point of the gear teeth, w is the load on the gear teeth at the meshing point, in Newtons; The film thickness ratio is determined by the following formula: λ=h / σ Where λ is the film thickness ratio, h is the contact pair oil film thickness, unit is micrometer, and σ is the composite root mean square roughness value; The composite RMS roughness value is determined by the following formula: Where σ1 and σ2 are the root mean square values ​​of the roughness of the two contact surfaces, in micrometers; The contact pair oil film thickness is determined by the following formula: H=h / R=3.06U *0.69 G *0.56 W *-0.1 Where h is the contact oil film thickness; Lubrication states include boundary lubrication λ<1.0, mixed lubrication 1.0<λ<3, and full film lubrication λ>3; Assume that the rated speed is n0, the rated load is w0, and the film thickness ratio of the meshing position under the rated working condition is λ0. The speed and load are divided into orthogonal grids, and the acceleration stress under different multiples of the rated load conditions and the rated speed is calculated respectively, and recorded in the table. According to the calculated numerical points, the speed and load curve under the same interface lubrication state is drawn. The speed and load are selected on the curve to guide the acceleration experiment of the gear transmission device. Then w1, w2…w n That is the acceleration stress at the corresponding speed; C. Select the acceleration factor: The acceleration factor is obtained by accelerating stress; the recorded values ​​of speed and load obtained in step B are curve fitted to obtain a continuous curve of load with respect to speed. The speed and load corresponding to each point on the curve can be used as a reference to guide the acceleration experiment of the gear transmission device. The acceleration factor is determined by the following formula: Where n i The speed corresponding to each point on the curve, w i is the load corresponding to each point on the curve; D. Establish an acceleration model: Calculate the test time of the gear transmission device under acceleration conditions, that is, the life under acceleration conditions, based on the acceleration stress and acceleration factor; Determine the test time of the gear transmission device under acceleration conditions, that is, the life under acceleration conditions, based on the acceleration stress and acceleration factor: Where L is the test time in hours, and L0 is the rated life of the gear transmission device in hours.

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