Ball screw contact load extraction method

Abstract

The invention provides a ball screw contact load extraction method, which comprises the following steps of: firstly determining the position of a first steel ball, then establishing a spiral line equation at the center of the steel ball of a screw so as to determine the coordinates of other steel balls, and then establishing a reference point at the determined coordinates for placing the steel ball, and finally, establishing a finite element model of the ball screw, defining a contact pair, an applied load and a boundary condition according to an actual contact relationship among parts, and extracting a contact load of a ball screw raceway and a steel ball in post-processing.

Description

Technical Field

[0001] The invention relates to a contact load extraction method, and more particularly to a ball screw contact load extraction method. Background Art

[0002] As a mechanical transmission element, ball screws are widely used in the field of mechanical manufacturing. In ball screw mechanisms, steel balls, as part of the carrier, not only directly bear the load, but also serve as an intermediate transmission element to transmit motion in a rolling manner. When the screw shaft rotates, the steel balls roll forward driven by the screw shaft thread raceway, and then drive the nut to make a linear motion. After rolling a circle on the screw shaft, the steel balls return one by one to the thread raceway between the screw shaft and the nut through the reverser, forming a complete closed-loop raceway.

[0003] After the screw is subjected to axial load, the steel balls will be pressed against the screw raceways and nut raceways, thereby generating contact loads. If the load is too large, the excessive contact stress between the raceways and the steel balls will cause plastic deformation of the raceways, which will in turn cause the ball screw to fail prematurely due to fatigue peeling. Therefore, it is necessary to calculate the contact stress of the ball screw raceways in advance in the early stages of product design, provided that the contact load can be accurately extracted, and then the contact stress of the raceways can be calculated based on the Hertz contact theory. At present, the extraction of ball screws is either done by using the mean value method, that is, all load-bearing steel balls are assumed to be uniformly loaded, or the contact load between the steel ball and the raceway is obtained by compiling a formula based on the elastic deformation theory and the force balance relationship, but the influence of the reverser groove in the nut and the position of the steel ball are not considered. There are also finite element analysis methods to extract the contact load, but they are limited by the processing of three-dimensional digital models. If the matching relationship between the steel ball and the screw raceway and the steel ball and the nut raceway is not handled well in the three-dimensional software, some steel balls and raceways will interfere with each other, and some will be in a gap state. The consequence is that the contact load distribution between the steel ball and the raceway is irregular. The above analysis methods all have shortcomings. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for extracting the contact load of a ball screw, which is used to extract the contact load between the steel ball and the raceway of the ball screw after it is subjected to an axial load, so as to calculate the contact stress of the raceway according to the Hertz contact theory, thereby avoiding the contact stress exceeding the operating value and causing failure.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for extracting contact load of a ball screw, comprising the following steps: Step 1, determine the position of the first steel ball; Step 2: Establish the helix equation at the center of the screw steel ball according to the position of the first steel ball determined in step 1, then determine the coordinates of other steel balls through the helix equation at the center of the screw steel ball, and then establish a reference point at the determined coordinates for placing the steel balls; Step three, establish a finite element model of the ball screw, define the contact pair according to the actual contact relationship between the components based on the finite element model, apply loads and boundary conditions, and then extract the contact load between the ball screw raceway and the steel ball in post-processing.

[0006] As a further improvement of the patent of the present invention, the method for determining the position of the first steel ball in the step one is to determine a steel ball that is close to the inverter side, located near the intersection of the inverter rotating raceway curve and the spiral line, and is tangent to the raceway as the first steel ball.

[0007] As a further improvement of the present invention, the helix equation at the center of the screw steel ball is established in step 2 as follows: Among them, R is the pitch diameter of the steel ball; P is the pitch.

[0008] As a further improvement of the present invention, the coordinates of other steel balls are determined in step 2 as follows: Step 2.1: Find the distance between the center of the first steel ball and the starting point of the spiral line. , at this time, the initial value of variable t can be determined. ; Step 22: Assume that the number of balls in each row of the ball screw is N, the number of balls placed in the reverser is a, and determine that in the static analysis, the number of balls in each row is Na. The increment n of the variable z can be expressed as ; Step 2 and 3, finally obtain the coordinates of other steel balls through the following formula: Among them, i is the steel ball number.

[0009] As a further improvement of the patent of the present invention, the specific method of establishing a reference point at the determined coordinates for placing the steel ball in step 2 is: establishing a reference point in the finite element analysis software ABAQUS according to the coordinates of the center of the steel ball at each position determined, and moving the center of the steel ball to the corresponding position reference point in the ABAQUS software modeling to ensure that each steel ball and the raceway are in a tangent state.

[0010] As a further improvement of the present invention, the finite element model of the ball screw established in step 3 is a complete model including the screw shaft, nut, and steel ball. The model defines the contact pair, applies axial load and boundary conditions according to the actual contact relationship between the components. The model extracts the contact load between the steel ball and the raceway in post-processing through calculation, and then calculates the contact stress according to the Hertz contact theory. The beneficial effect of the present invention is that it can avoid the errors caused by gaps or interferences between the steel balls and the screw shaft raceways and between the steel balls and the nut raceways due to poor or unreasonable assembly in the three-dimensional modeling software, and it can also take into account the influence of the reverser groove in the nut and the influence of the steel ball position due to the existence of the reverser. It is very practical to obtain satisfactory results without compiling a complex set of equations. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram of determining the position of the first steel ball. DETAILED DESCRIPTION

[0012] The present invention will be further described below in detail with reference to the embodiments shown in the accompanying drawings.

[0013] Reference Figure 1 As shown, a method for extracting contact load of a ball screw in this embodiment includes the following steps: first, determining the position of the first steel ball, then establishing the helix equation at the center of the screw steel ball, thereby determining the coordinates of other steel balls, and then establishing a reference point at the determined coordinates for placing the steel balls, and finally establishing a finite element model of the ball screw, defining the contact pair according to the actual contact relationship between the components, applying loads and boundary conditions, and extracting the contact load between the ball screw raceway and the steel ball in post-processing.

[0014] Furthermore, the position of the first steel ball is determined to be close to the inverter side, near the intersection of the inverter rotating raceway curve and the spiral line, ensuring that the steel ball and the raceway are in a tangent state. The advantage of this is that it facilitates rapid positioning.

[0015] Furthermore, the helix equation at the center of the lead screw steel ball is established, and the helix equation is: Among them, R is the pitch diameter of the steel ball; P is the pitch.

[0016] Furthermore, the coordinates of the other steel balls can be determined by first finding the distance between the center of the first steel ball and the starting point of the spiral line. , at this time, the initial value of variable t can be determined. , if the number of steel balls in each row of the ball screw is N, and the number of steel balls placed in the deflector is a, since the steel balls in the deflector do not bear any load, the steel balls in the deflector can be ignored in the static analysis. At this time, the number of steel balls in each row is Na, so the increment n of the variable z can be expressed as , so the coordinates of other steel balls can be expressed as: Among them, i is the steel ball number.

[0017] Furthermore, the reference points are established at the determined coordinates for placing the steel balls, and the reference points are established in the finite element analysis software ABAQUS according to the determined coordinates of the centers of the steel balls at each position, and the centers of the steel balls are moved to the corresponding reference points in the ABAQUS software modeling to ensure that each steel ball is in a tangent state with the raceway.

[0018] Furthermore, the finite element model of the ball screw is a complete model including the screw shaft, nut, and steel ball. The contact pair is defined according to the actual contact relationship between the components, and the axial load and boundary conditions are applied before submission for calculation. The contact load between the steel ball and the raceway is extracted in post-processing, and then the contact stress is calculated according to the Hertz contact theory, so that risks can be avoided in advance.

[0019] To sum up, the ball screw contact load extraction method of this embodiment, through the setting of steps one to three, can effectively extract the contact load between the steel ball and the raceway of the ball screw after it is subjected to axial load, so as to facilitate the calculation of the contact stress of the raceway according to the Hertz contact theory, and avoid the contact stress exceeding the operating value and causing failure.

[0020] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for extracting contact load of a ball screw, characterized in that: The steps include: Step 1, determine the position of the first steel ball; Step 2: Establish the helix equation at the center of the screw steel ball according to the position of the first steel ball determined in step 1, then determine the coordinates of other steel balls through the helix equation at the center of the screw steel ball, and then establish a reference point at the determined coordinates for placing the steel balls; Step three, establish a finite element model of the ball screw, define the contact pair according to the actual contact relationship between the components based on the finite element model, apply loads and boundary conditions, and then extract the contact load between the ball screw raceway and the steel ball in post-processing.

2. The ball screw contact load extraction method according to claim 1, characterized in that: The method for determining the position of the first steel ball in step one is to determine a steel ball that is close to the inverter side, located near the intersection of the inverter rotating raceway curve and the spiral line, and is tangent to the raceway as the first steel ball.

3. The ball screw contact load extraction method according to claim 1 or 2, characterized in that: The helix equation at the center of the screw steel ball established in step 2 is as follows: Among them, R is the pitch diameter of the steel ball; P is the pitch.

4. The ball screw contact load extraction method according to claim 1 or 2, characterized in that: The coordinates of other steel balls are determined in step 2 as follows: Step 2.1: Find the distance between the center of the first steel ball and the starting point of the spiral line. , at this time, the initial value of variable t can be determined. ; Step 22: Assume that the number of balls in each row of the ball screw is N, the number of balls placed in the reverser is a, and determine that in the static analysis, the number of balls in each row is Na. The increment n of the variable z can be expressed as ; Step 2 and 3, finally obtain the coordinates of other steel balls through the following formula: Among them, i is the steel ball number.

5. The ball screw contact load extraction method according to claim 1 or 2, characterized in that: The specific method of establishing a reference point at the determined coordinates for placing the steel ball in step 2 is: establishing a reference point in the finite element analysis software ABAQUS according to the coordinates of the center of the steel ball at each position, and moving the center of the steel ball to the corresponding position reference point in the ABAQUS software modeling to ensure that each steel ball and the raceway are in a tangent state.

6. The ball screw contact load extraction method according to claim 1 or 2, characterized in that: The finite element model of the ball screw established in step three is a complete model including the screw shaft, nut, and steel ball. The model defines the contact pair, applies axial load and boundary conditions according to the actual contact relationship between the components. The model extracts the contact load between the steel ball and the raceway through calculation in post-processing, and then calculates the contact stress according to the Hertz contact theory.

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