Harmonic gear with continuous meshing tooth profile and tooth profile design method thereof
阅读说明：本技术 具有连续啮合齿形的谐波齿轮及其齿形设计方法 (Harmonic gear with continuous meshing tooth profile and tooth profile design method thereof ) 是由 袁高峰 于振江 于 2020-06-05 设计创作，主要内容包括：本发明提供了一种具有连续啮合齿形的谐波齿轮,它由刚轮、柔轮、波发生器组成,刚轮为刚性内齿轮,柔轮为杯形圆柱直齿外齿轮,刚轮齿数与柔轮齿数之差为二,刚轮齿形由旋转变换法描述的柔轮变形端中线上点的运动轨迹通过偏移和等距生成,柔轮齿形由设计刚轮齿形的等距距离为半径的圆弧齿顶和与圆弧齿顶光滑过渡的曲线组成；本发明同时提供了一种应用旋转变换法而形成的具有连续啮合齿形的谐波齿轮的齿形设计方法,该设计方法具有齿形设计简便,设计的谐波齿轮具有啮合齿数多,承载能力大、疲劳寿命长、柔轮发生畸变小,啮入深度大,传动精度高,平稳性好和耐磨等特点,非常适合谐波齿轮传动的齿形设计。(The invention provides a harmonic gear with continuous meshing tooth form, which consists of a rigid gear, a flexible gear and a wave generator, wherein the rigid gear is a rigid internal gear, the flexible gear is a cup-shaped cylindrical straight-tooth external gear, the difference between the tooth number of the rigid gear and the tooth number of the flexible gear is two, the tooth form of the rigid gear is generated by the motion track of the point on the central line of the deformation end of the flexible gear described by a rotation transformation method through deviation and equidistance, and the tooth form of the flexible gear consists of an arc tooth top and a curve which is smoothly transited with the arc tooth top, wherein the equidistance distance of the tooth form of the rigid gear; the invention also provides a method for designing the tooth profile of the harmonic gear with continuous meshing tooth profile formed by applying a rotation transformation method, and the method has the characteristics of simple and convenient tooth profile design, more meshing tooth number of the designed harmonic gear, high bearing capacity, long fatigue life, small deformation of a flexible gear, large meshing depth, high transmission precision, good stability, wear resistance and the like, and is very suitable for the tooth profile design of the harmonic gear transmission.)
1. A harmonic gear with a continuous meshing tooth form comprises a rigid gear, a flexible gear and a wave generator, wherein the rigid gear is a rigid inner gear, the flexible gear is a cup-shaped cylindrical straight-tooth outer gear, the difference between the number of the rigid gear teeth and the number of the flexible gear teeth is two, the tooth form of the rigid gear is generated by shifting and equidistance of the motion track of an upper point on the central line of a deformation end of the flexible gear described by a rotation transformation method, and the tooth form of the flexible gear is formed by designing an arc tooth top with the equidistant distance of the tooth form of the rigid gear as a radius and a curve smoothly transiting to the arc tooth top.
2. A tooth profile design method of a harmonic gear having a continuous meshing tooth profile suitable for use in claim 1, characterized by: the method comprises the following steps:
the first step is as follows: the harmonic gear drives the first type of movement, at the moment, the wave generator is in a fixed state, and the flexible gear and the rigid gear are in a moving state; obtaining the form that any point on the midline of the flexible gear deformation end is represented by K:
wherein K represents the K section that the arc length of the central line of the flexible gear deformation end is equally divided into e sections, and e is a positive integer; phi1(K-1) represents an abscissa value; phi2(K-1) represents a longitudinal coordinate value;
the second step is that: the harmonic gear drives the first type of motion to be converted into a second type of motion when the rigid wheel is in a static state, the flexible wheel and the wave generator are in a rotating state, and the rigid wheel is in a fixed state;
in the first step, the formula (1) is multiplied by a coordinate transformation matrix to obtain a second motion state, and a motion track expression of any point on the center line of the flexible gear deformation end under the rigid gear motionless coordinate system is as follows:
phi' represents the angle of the first motion of the harmonic gear transmission converted into the second motion;
the third step: determining a deviation curve of a point track at a deformed end of the flexible gear; the offset distance of the locus of the midpoint of the deformed end of the flexspline is given by:
wherein d represents the offset distance of the midpoint track of the flexible gear deformation end;
then, in the second type of motion of harmonic gear transmission, the offset curve of the midpoint track of the flexible gear deformation end under the rigid gear fixed coordinate system can be obtained according to the formula (2) and the formula (3), and the curve equation is as follows:
according to the equation (4), the tangential tilt angle of the deviation curve of the locus of the midpoint of the deformed end of the flexible gear is obtained as follows:
the fourth step: determining the tooth form of the rigid wheel; the tooth profile of the rigid gear is generated by an equidistant curve of a deviation curve of a point track at the deformed end of the flexible gear, so that the theoretical tooth profile of the rigid gear can be obtained according to the formula (4); the tooth form equation is as follows:
orWherein R represents an equidistant distance;
the flexible gear tooth form consists of an arc tooth top and a curve which is smoothly transited with the arc tooth top, wherein the equidistant distance R of the rigid gear tooth form is designed to be the radius, and the curve in the region which is wrapped by the straight line which is smoothly transited with the arc tooth top can be theoretically used as the transition curve of the flexible gear.
3. The tooth profile design method of a harmonic gear with a continuously meshing tooth profile according to claim 2, wherein the first-step medium wave generator is in the form of one of an elliptical cam, a cosine cam, or a double eccentric circular arc cam.
Technical Field
The invention belongs to the technical field of harmonic gear transmission, and particularly relates to a harmonic gear with a continuous meshing tooth form and a tooth form design method thereof.
Background
With the rapid development of the industrial robot industry, the use requirements of the harmonic gear transmission device become more extensive, and especially, the use amount of the harmonic gear transmission with high precision, small volume and high reliability is increased rapidly, which has a great challenge to Chinese researchers who research the later harmonic gear transmission. There are many institutions and enterprises which research and manufacture harmonic gear transmissions nationwide, and the main research range of the institutions and the enterprises is various, and one of the institutions and the enterprises is the research on meshing tooth profiles.
As regards the studies on the tooth profile, the first harmonic gear drive used a straight tooth profile, which was proposed by american scholars c.w. After the advent of harmonic gear transmission, c.w.musser had insufficient knowledge of its meshing principle and did not consider that changes in the curvature of the flex spline centerline would cause rotation of the axis of symmetry of the flex spline teeth. Therefore, the proposed linear tooth profile makes it difficult to ensure that the teeth are conjugate when the gears are engaged. With the research of the meshing theory, researchers prove the feasibility of applying the involute tooth profile to the harmonic gear transmission and put the involute tooth profile into practice. Besides, the involute tooth profile has a mature process, so that the involute tooth profile becomes the tooth profile which is most widely applied in harmonic gear transmission. However, strictly speaking, the correct meshing angle of the involute tooth profile is small, only a few degrees, and the involute tooth profile belongs to cusp meshing at other meshing angles, so that the problems of low transmission precision, low load capacity, poor reliability and the like of the harmonic gear are caused. These disadvantages are clearly unacceptable for mechanical devices with high transmission requirements.
In recent years, various tooth profiles have been designed in order to design a harmonic gear that satisfies the requirement of high accuracy. The S-shaped tooth profile designed by Japanese researchers theoretically realizes the continuous meshing of harmonic gear transmission. Because the design of the tooth profile is based on the assumption of infinite tooth number, some harmonic gear transmission devices with less tooth number do not conform to conjugate meshing, and the optimal meshing performance cannot be ensured. Domestic scholars have designed double-circular-arc conjugate tooth shapes based on an envelope method, an improved motion method, an instant center method, a rotation transformation method (patent document 1), and the like. The design idea of the tooth profile is to firstly give the tooth profile parameters of a kind of gear to obtain the conjugate tooth profile. Then adjusting initial parameters according to the meshing performance indexes of analysis and evaluation to enable the mutually conjugated tooth profiles to achieve the best meshing performance. And finally, fitting the conjugate tooth profile to realize the design of the transmission tooth profile of the harmonic gear. The double-circular-arc tooth profile is formed by splicing multiple sections of curves, and the analysis and evaluation of the conjugate tooth profile of each section of tooth profile and the fitting of the conjugate tooth profile are required, so the realization is more complicated. Moreover, the selection of the fitting error and the fitting function is difficult, and if the fitting function is selected improperly, the design of harmonic gear transmission is greatly problematic. Usually, the fit curve needs to be evaluated for backlash, and the quality and calculation error of the backlash evaluation method also have an influence on the design of the conjugate tooth profile.
Patent document
Patent document 1: chinese patent publication No. CN110688716A
Disclosure of Invention
In order to solve the problems, the invention provides a harmonic gear with continuous meshing tooth profiles, which can improve the transmission precision and the bearing capacity and reduce the noise.
Another object of the present invention is to provide a method for designing a tooth profile of a harmonic gear having a continuous meshing tooth profile.
The technical solution of the invention is as follows: the utility model provides a harmonic gear with continuous meshing profile of tooth, includes rigid gear, flexbile gear, wave generator, the rigid gear is the rigidity internal gear, the flexbile gear is cup-shaped cylinder straight-tooth external gear, the rigid gear number of teeth with the difference of flexbile gear number of teeth is two, the wave generator comprises cam and flexible bearing, and the cam is one of ellipse cam, cosine cam or two eccentric circular arc cams, the motion orbit of flexbile gear deformation end central line upper point that the rigid gear profile of tooth was described by the rotation transformation method is through skew and equidistance generation, the flexbile gear profile of tooth is by the equidistance distance of design rigid gear profile of tooth for the circular arc addendum of radius and with the curve that the circular arc addendum smooth transition constitutes, the flexible gear teeth and rigid gear are at harmonic gear drive in-process continuous meshing.
A method for designing the tooth profile of a harmonic gear having a continuous meshing tooth profile formed by applying a rotational transformation method, comprising the steps of:
the first step is as follows: the harmonic gear drives the first type of movement, at the moment, the wave generator is in a fixed state, and the flexible gear and the rigid gear are in a moving state; in the first type of motion, the parametric equation of the midline of the deformation end of the known flexible wheel in a rectangular coordinate system is as follows:
wherein if the outer contour of the wave generator is an elliptical cam contour, the parameters of the formula (1) are correspondedRepresents the elliptical centrifugal angle; if the profile of the cam is other, the parameters of the corresponding formula (1)An angle of eccentricity representing the cam profile;
according to the formula (1), the arbitrary arc length of the central line of the flexible gear deformation end starting from the positive direction of the transverse axis is represented as follows:
wherein e represents a positive integer; k represents the K-th section that the arc length of the central line of the flexible gear deformation end is evenly divided into e sections;representing a centrifugal angle corresponding to the K-th arc length;in the formula (1)To pairA derivative of (a);in the formula (1)
the full arc length S (i.e., circumference) of the flexspline deformed end centerline can be expressed as:
S＝e·ΔS (3)
wherein, Delta S represents that the full arc length S of the midline of the flexible gear deformation end is evenly divided into any one arc length of e sections;
substituting formula (2) for formula (3) to obtain:
equation (4) can be written as follows:
wherein formula (5) is an inverse functional form of formula (4);
substituting formula (5) into formula (1) to obtain the form that any point on the midline of the flexible gear deformation end is represented by K:
wherein, the formula (6) represents the form that the point on the center line of the flexible gear deformation end is represented by K, and K corresponds to
the second step is that: the flexible gear and the wave generator are regulated to rotate, and when the rigid gear is fixed, the flexible gear and the wave generator are in a second type of motion driven by the harmonic gear; according to the principle of relative motion, if a rotary motion opposite to the angular velocity of a rigid wheel is added to the whole gear train for transmitting the first type of motion to the harmonic gear, the relative motion relationship among all components is still kept unchanged; however, the whole gear train is added with the rotary motion with the angular speed opposite to that of the rigid wheel, so that the rigid wheel is in a static state, and the harmonic gear transmission first-class motion is converted into the second-class motion, namely the harmonic gear transmission second-class motion is obtained by the rotation of the harmonic gear transmission first-class motion; therefore, a coordinate transformation matrix is multiplied by the formula (6) to obtain a motion trajectory expression of any point on the center line of the deformed end of the flexible gear under the rigid gear motionless coordinate system in the second motion state:
wherein phi' represents the angle through which the harmonic gear drives the first type of motion to be converted into the second type of motion.
In the formula (7), K corresponds to
according to the equation (8), the inclination angle of the normal line of the corresponding point on the midline of the deformed end of the flexible gear corresponding to the K value is obtained as follows:
as shown in the formula (9), phi is a variable phi' and
similarly, from formula (7), X3And Y3Is also the variable φ' anda function of, pair
and phi' and
wherein z is1Indicating number of flexspline teeth, z2Representing the number of teeth of the ring gear, rmA radius representing a flexspline centerline in an undeformed state;
in formula (12), aAnd (5) obtaining a derivative:
the third step: determining a deviation curve of a point track at a deformed end of the flexible gear; the offset distance of the locus of the midpoint of the deformed end of the flexspline is given by:
wherein d represents the offset distance of the midpoint track of the flexible gear deformation end;
then, in a second motion type of harmonic gear transmission, a deviation curve of the locus of the midpoint of the flexible gear deformation end under the rigid gear fixed coordinate system can be obtained according to the formula (7) and the formula (14), and the curve equation is as follows:
pair of equation (15)The derivative of (c) is obtained:
from equation (16), the inclination angle of the tangent line of the offset curve of the locus of the midpoint of the deformed end of the flexspline is obtained as:
the fourth step: determining the tooth form of the rigid wheel; the tooth profile of the rigid wheel is generated by the movement track of a point on the center line of the deformed end of the flexible wheel through deviation and equidistance, so the theoretical tooth profile of the rigid wheel can be obtained according to the formula (15); the tooth form equation is as follows:
wherein R represents an equidistant distance;
the method for designing the tooth profile of the rigid wheel comprises four steps, wherein in the first step, a formula (6) is derived according to a given wave generator shape function (one of an elliptic cam, a cosine cam or a double-eccentric arc cam); secondly, determining a motion trail expression (7) of any point on the center line of the deformed end of the flexible gear under the rigid gear fixed coordinate system according to the expression (6); thirdly, obtaining an offset curve expression (15) of a point track on the central line of the flexible gear deformation end and an inclination angle expression (17) of a tangent line of the offset curve expression under the rigid gear fixed coordinate system according to the expressions (7) and (14); finally, the fourth step, substituting the formula (15) and the formula (17) into a rigid wheel tooth form expression (18), and obtaining the tooth form of the rigid wheel; and the other formulas are expressions which need to be solved in the process of solving the formulas.
In order to avoid interference in the harmonic transmission process, the flexible gear tooth form consists of an arc tooth top and a curve in smooth transition with the arc tooth top, wherein the equidistant distance R of the rigid gear tooth form is designed to be the radius, the transition curve can be a curve wrapped by a straight line in smooth transition with the arc tooth top, the curves in the area can be used as the transition curve of the flexible gear, and the transition curve is designed to be a straight line in order to improve the bearing capacity of the flexible gear.
Compared with the prior art, the technical scheme can lead the tooth shape of the rigid wheel driven by the harmonic gear to be a midline offset equidistant tooth shape; the tooth form is designed based on the motion rule of the central line of the deformed end of the flexible gear, so that all the tooth pairs of the flexible gear and the rigid gear are theoretically continuously meshed, the transmission precision, the bearing capacity and the meshing performance of the harmonic gear are improved, the characteristics of stable transmission and wear resistance are achieved, and the possibility of noise reduction and flexible gear distortion reduction is reduced.
The invention has the beneficial effects that: because the tooth form of the harmonic gear rigid gear is designed according to the elastic deformation motion rule of the flexible gear ring, the shape of the harmonic gear rigid gear is only related to the basic design parameters (modulus and tooth number) of the harmonic gear transmission, the outline of a wave generator, the offset distance and the equidistant distance; when basic design parameters (modulus and tooth number) of harmonic gear transmission, the shape, offset distance and equidistant distance of a wave generator are known, the tooth shape parts of the rigid gear and the flexible gear are also determined; the harmonic gear transmission designed according to the tooth profile can realize continuous meshing, and theoretically has the characteristic that all tooth pairs are meshed simultaneously; the tooth shape design method has the characteristics of simple tooth shape design, more meshing tooth numbers of the designed harmonic gear, high bearing capacity, long fatigue life, low possibility of deformation of the flexible gear, high meshing depth, high transmission precision, good stability, wear resistance and the like, and is very suitable for the tooth shape design of high-precision harmonic gear transmission.
Drawings
The present invention will be specifically described below with reference to the accompanying drawings in conjunction with examples. The advantages and realisation of the invention will be more apparent from the following description, given for the purpose of illustration only, without being limitative in any way, of the invention, in which:
FIG. 1 is an elevational view of the assembly of a harmonic gear of the present invention having a continuously meshing tooth form;
FIG. 2 is a left side view of a harmonic gear assembly of the present invention having a continuously meshing tooth profile;
FIG. 3 is a schematic illustration of a centerline offset equidistant tooth profile design employed by the rigid wheels in a harmonic gear of the present invention having a continuously meshing tooth profile; the tooth profile is obtained by firstly shifting the motion trail of a point on the central line of the deformed end of the flexible gear by a distance d to obtain a shifting curve and then equidistantly obtaining the shifting curve;
FIG. 4 is a schematic diagram of a tooth form design method for a harmonic gear with a continuously meshing tooth form according to the present invention, wherein K represents any point on the centerline of the deformed end of the flexible gear that the harmonic gear drives the first type of motion;
FIG. 5 is a schematic diagram of a motion trajectory of a rigid gear in a stationary coordinate system, wherein the harmonic gear drives any point on a center line of a deformed end of a flexible gear of a second type of motion in the gear design method of the harmonic gear with a continuous meshing tooth profile according to the present invention;
FIG. 6A is a schematic diagram of a method for designing a tooth profile of a harmonic gear having a continuous meshing tooth profile according to the present invention, in which a rigid gear tooth profile is calculated when a tangential tilt angle θ < π/2 of a shift curve of a motion trajectory of a point on a center line of a deformed end of a flexspline;
FIG. 6B is a schematic diagram of the calculation of the tooth profile of a rigid gear when the tangential tilt angle theta of the offset curve of the motion trajectory of the point on the center line of the deformed end of the flexible gear is not less than pi/2 in the tooth profile design method of the harmonic gear with the continuous meshing tooth profile of the invention;
FIG. 7 is a schematic view of a tooth profile design method for a harmonic gear with a continuous meshing tooth profile according to the present invention, wherein a flexible gear has a circular arc tooth top with a radius R and a tooth profile with a smooth transition curve of a straight line;
FIG. 8 is a schematic diagram of the motion trajectory of a flexible gear tooth relative to a rigid gear tooth in the method for designing the tooth profile of a harmonic gear with a continuously meshing tooth profile according to the present invention.
In the drawings:
1. rigid gear 2, flexible gear 3, wave generator 4, elliptical cam 5, flexible bearing 6, rigid gear tooth form 7, offset curve 8, motion track 9 of point on center line of flexible gear deformation end, flexible gear tooth form
Detailed Description
In order to make the technical means for implementing the present invention easily understood, the technical solutions provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments.
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