CN105014503A - Precise grinding method for large-caliber axisymmetric aspheric surfaces - Google Patents

Abstract

A precision grinding method for a large-diameter axisymmetric aspheric surface, comprising: a workpiece to be ground with an aspherical top surface fixed on a rotary table, and mounted on a y-feeding slide connected to an x-feeding slide The grinding wheel spindle and the grinding wheel abrasive tool fixed on the grinding wheel spindle are characterized in that: a three-axis linkage control model is used to control the rotation center line of the grinding wheel spindle and the normal line of the grinding point on the aspherical generatrix to keep coincident, so that Avoid the principle error caused by the grinding feed movement track and ensure the motion accuracy; use the end face of the grinding wheel to grind the aspheric surface to improve the grinding ratio; at the same time, use real-time detection methods to compensate for the grinding wheel. Loss to improve grinding efficiency. The invention has a simple movement mechanism, improves the grinding efficiency, and ensures the grinding precision, and is suitable for grinding large axisymmetric aspheric surfaces such as rotating paraboloids, rotating hyperboloids, and rotating elliptical surfaces.

Description

Precision Grinding Method of Axisymmetric Aspheric Surface with Large Diameter

technical field

The invention relates to a precision grinding method in the technical field of machine tools, in particular to a precision grinding method for a large-diameter axisymmetric aspheric surface.

Background technique

Aspherical optical elements such as paraboloids, hyperboloids, and ellipsoids are the core components of large telescopes, space cameras, laser fusion, and space exploration systems, and are widely used in aviation, aerospace, national defense, and astronomical observation industries. At present, the diameter of aspheric optical elements has reached several meters, so the precision manufacturing technology of aspheric optical elements is the key technology.

For the processing of non-ferrous metals and some crystal aspheric optical components, diamond ultra-precision turning can be used to complete; while for the aspheric processing of hard and brittle materials such as optical glass, glass ceramics and SiC, CNC grinding and forming methods and ion beam polishing are often used. method and other processing methods. Among them, the numerical control grinding forming method has higher requirements on the processing technology; the equipment investment and processing cost of the ion beam polishing method are high, and the efficiency is low. The processing technology of aspheric optical elements usually firstly performs rough milling on the element blank, then performs semi-finishing and fine grinding, and finally completes it by precision polishing.

Semi-finishing and fine grinding are important technological means for processing aspheric optical elements. Through precision grinding, the surface accuracy of aspheric elements is close to the final processing requirements, reducing the machining allowance of subsequent polishing processes, thereby improving polishing accuracy and efficiency. . At present, most of the precision grinding methods for aspheric optical elements use part of the end faces of ball-end grinding wheels, cylindrical grinding wheels or cup-shaped grinding wheels for grinding.

After searching the existing technical literature, it is found that the Chinese patent application number is: CN201010229423, and the name is: tangential method of numerical control aspheric surface processing method and machine tool, which discloses a tangential method of numerical control processing aspheric surface grinding method. Axisymmetric aspheric or spherical surface is processed by tangent method to obtain a theoretically continuous and smooth high-precision surface without ripples; the processing principle is to first coincide the point M on the grinding wheel axis with the z-axis of the rotation axis, and the workpiece axis only drives the workpiece to rotate. The grinding wheel rotates on the grinding wheel shaft, and the grinding wheel shaft takes the M point as the reference point, and moves in the direction of the X axis and the Y axis while rotating around the Z axis; the movement of the grinding wheel shaft is realized by the numerical control method based on the principle of speed interpolation. Three-axis linkage. This method of grinding with a point on the grinding wheel can obtain higher motion track accuracy, but grinding with a point on the grinding wheel will cause a lot of loss of the grinding wheel, and the wear compensation of the grinding wheel becomes the key, so it is necessary to repeatedly adjust the workpiece. Surface accuracy is detected, which will reduce grinding accuracy and grinding efficiency.

Contents of the invention

Aiming at the defects in the prior art, the present invention provides an intelligent precision grinding method for large-diameter axisymmetric aspheric surfaces, by realizing real-time detection of the workpiece to be ground and monitoring the wear of the grinding wheel and abrasive tool during the grinding process. Real-time compensation to achieve the purpose of improving grinding efficiency and ensuring grinding accuracy.

The present invention is achieved through the following technical solutions:

A precision grinding method for a large-diameter axisymmetric aspheric surface, comprising: a workpiece to be ground with an aspherical top surface fixed on a rotary table, and mounted on a y-feeding slide connected to an x-feeding slide The grinding wheel spindle and the grinding wheel abrasive tool fixed on the grinding wheel spindle are characterized in that: a three-axis linkage control model is used to control the rotation center line of the grinding wheel spindle and the normal line of the grinding point on the aspherical generatrix to keep coincident, so that Avoid the principle error caused by the grinding feed movement track and ensure the motion accuracy; use the end face of the grinding wheel to grind the aspheric surface to improve the grinding ratio; at the same time, use the real-time detection method to compensate the grinding wheel Loss to improve grinding efficiency.

Further, the vertex of the aspheric surface is defined as the coordinate origin O of the workpiece coordinate system Oxyz, the rotation axis of the aspheric surface coincides with the y-axis of the workpiece coordinate system Oxyz, and the rotation axis of the aspheric surface is aligned with the rotation axis The rotation center line of the worktable coincides, that is, the rotation center line of the rotary worktable coincides with the y-axis of the workpiece coordinate system Oxyz, and the rotary table performs low-speed rotational motion around the y-axis at a speed n ₁ , that is, the aspheric generatrix Rotate at a low speed around the y-axis; the rotation center line of the grinding wheel spindle intersects the coordinate origin O' of the processing coordinate system O'x'y'z' and the coordinates around the processing coordinate system O'x'y'z' The origin O' reciprocates in the O'x'y'plane; the machining coordinate system O'x'y'z' passes through the y feed slide and the x feed slide respectively in the Oxy plane of the workpiece coordinate system Oxyz Make up and down and left and right linear translation, so that the center line of rotation of the grinding wheel spindle and the normal line of the grinding point on the aspheric generatrix always keep coincident, and the grinding wheel spindle performs high-speed rotating motion at a speed _n2 ; through the The processing coordinate system O'x'y'z' is in the Oxy plane of the workpiece coordinate system Oxyz' up and down and left and right linear translation, the rotation center line of the grinding wheel spindle is around the processing coordinate system O'x'y'z' The reciprocating swinging motion of the coordinate origin O' in the O'x'y' plane, the low-speed rotational motion of the aspherical generatrix around the y-axis and the high-speed rotational motion of the grinding wheel spindle realize the precision grinding of the aspheric surface.

Further, the real-time detection method includes: the grinding wheel spindle is a hollow shaft; a detection device capable of linearly moving along the rotation centerline of the grinding wheel spindle is installed in the inner cavity of the grinding wheel spindle, and the detection device includes A displacement sensor whose detection point is on the rotation center of the grinding wheel spindle. During the grinding process, when the displacement sensor moves and touches the surface of the workpiece to be ground, the coordinate value of the grinding point is collected , and compare the data of the collected grinding point coordinates with the standard coordinate data of the aspheric surface through the control system, and if an error occurs, the three-axis linkage control model is corrected in real time to ensure that the The trajectory of the grinding point is always kept on the aspheric generatrix.

Further, the said grinding wheel is a cylindrical grinding wheel.

Further, the aspheric surface is an axisymmetric aspheric surface.

The beneficial effects of the present invention are:

The three-axis linkage control model is used to control the rotation center line of the grinding wheel spindle and the normal line of the grinding point of the aspheric generatrix to keep coincident, thereby avoiding the principle error caused by the grinding feed motion track, and the motion accuracy is guaranteed; the application circle The end face of the cylindrical grinding wheel grinds the aspheric surface, which improves the grinding ratio; at the same time, the loss of the grinding wheel is compensated by the real-time detection method, which improves the grinding efficiency. The invention is an intelligent grinding method, the motion mechanism is simple, the grinding efficiency is improved, and the grinding precision is guaranteed.

Description of drawings

The technical features, objects and advantages of the present invention will become more apparent by reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

Fig. 1 is a schematic diagram of a grinding device of the present invention.

Figure 2 is a three-dimensional schematic diagram of the method of the present invention.

Fig. 3 is a grinding schematic diagram of the present invention.

In the figure,

1—base, 2—rotary table, 3—workpiece to be ground, 4—grinding wheel, 5—spindle of grinding wheel, 6—column, 7—y feed slide, 8—x feed slide, 9— detection device.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Please refer to Figure 1, the rotary table 2 of the CNC precision grinding machine is rotatably installed on the base 1, and the workpiece 3 to be ground is fixedly installed on the rotary table 2 through the fixture, and the top surface of the workpiece 3 to be ground is a large diameter Axisymmetric aspherical surface, x feed slide 8 is connected to column 6 of CNC precision grinding machine, y feed slide 7 is connected to x feed slide 8, grinding wheel spindle 5 is installed on x feed slide 8 On the connected y feed slide seat 7, the grinding wheel grinding tool 4 is fixed on the top of the grinding wheel main shaft 5.

The present invention adopts the spherical surface grinding method to grind aspheric surfaces. Since the radius of curvature of the axisymmetric aspheric surface with large diameter is relatively large, if the swing center O' of the grinding wheel spindle 5 is positioned on the y-axis, the swing radius will become larger and affect the rigidity of the structure. For this reason, the present invention adopts the swing center O ' of emery wheel main shaft 5 to carry out the method for translation to realize the precision grinding of large-diameter axisymmetric aspheric surface, and this can make the end face of emery wheel grinding tool 4 to the pendulum center O ' of emery wheel main shaft 5 The distance is shortened.

The precision grinding method of the large-diameter axisymmetric aspheric surface adopts a three-axis linkage control model to control the rotation center line of the grinding wheel spindle 5 and the normal line of the grinding point on the generatrix of the aspheric surface to keep coincident, so as to avoid grinding progress. The principle error brought to the motion trajectory and ensure the motion accuracy; the end face of the application grinding wheel abrasive 4 is used to grind the aspheric surface to improve the grinding ratio; simultaneously, the real-time detection method is used to compensate the loss of the grinding wheel abrasive 4 to Improve grinding efficiency.

The vertex of the aspheric surface is defined as the coordinate origin O of the workpiece coordinate system Oxyz, and the rotation axis of the aspheric surface coincides with the y-axis of the workpiece coordinate system Oxyz, and the rotation axis of the aspheric surface is aligned with the rotary table 2 coincides with the center line of rotation, that is, the center line of rotation of the rotary table 2 coincides with the y-axis of the workpiece coordinate system Oxyz, and the rotary table 2 rotates at a low speed around the y-axis at a speed n ₁ , that is, the non- The spherical generatrix rotates at a low speed around the y-axis.

The center line of rotation of the grinding wheel spindle 5 intersects the coordinate origin O' of the processing coordinate system O'x'y'z', and the center line of rotation of the grinding wheel spindle 5 revolves around the processing coordinate system O'x'y'z' The origin O' of the coordinates swings back and forth in the O'x'y' plane. The processing coordinate system O'x'y'z' makes vertical linear translation through the y feed slide 7 in the Oxy plane of the workpiece coordinate system Oxyz, and through the x feed slide 8 in the workpiece coordinate system Oxyz Perform left and right linear translation in the Oxy plane, so that the rotation center line of the grinding wheel spindle 5 and the normal line of the grinding point on the aspherical generatrix always keep coincident; the grinding wheel spindle 5 rotates at a high speed at speed _n2 .

Through the above two linear motions: the vertical and left-right linear translation of the processing coordinate system O'x'y'z' in the Oxy plane of the workpiece coordinate system Oxyz, and a swing motion: the rotation centerline of the grinding wheel spindle 5 The reciprocating swing motion around the coordinate origin O' of the processing coordinate system O'x'y'z' in the O'x'y' plane, and two rotational motions: the low-speed rotational motion of the aspheric generatrix around the y-axis and The high-speed rotation of the grinding wheel spindle 5 realizes the precise grinding of the aspheric surface.

The rotating paraboloid is a typical axisymmetric aspheric surface. The present invention will be specifically described below with the precision grinding of the rotating paraboloid as an example. The grinding wheel and abrasive tool 4 described in this embodiment adopt a cylindrical grinding wheel, and the grinding wheel spindle 5 is hollow. axis.

Please refer to Figure 3, assuming that the generatrix equation of the paraboloid of revolution is formula (1), the coordinates of the center of curvature P(x ₂ , y ₂ ) of point M(x ₀ , y ₀ ) on the generatrix of the paraboloid of revolution can be obtained as formula (2 ) shown. PM is the radius of curvature of point M(x ₀ ,y ₀ ) on the generatrix of the paraboloid of revolution, and PM intersects the y-axis at P′(0,y ₁ ), obviously P′M<PM.

y=px ² -----------------------------(1)

$\left.\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; px</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; )</span>}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\end{array}\right\}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Grinding starts from the point M(x ₀ , y ₀ ) on the generatrix of the rotating paraboloid close to the coordinate origin O of the workpiece coordinate system Oxyz, x ₀ gradually increases, and controls the grinding wheel spindle 5 according to formulas (3), (4), and (5) The reciprocating swing angle α of the rotation center line around the coordinate origin O' of the processing coordinate system O'x'y'z' in the O'x'y' plane and the coordinate origin of the processing coordinate system O'x'y'z' The x and y coordinate positions of O′ keep the rotation center line of the grinding wheel spindle 5 and the normal line of the point M(x ₀ , y ₀ ) of the rotating paraboloid generatrix always coincident, so that the end face of the cylindrical grinding wheel grinding tool 4 rotates Parabolic grinding.

$\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; px</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; px</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

x＝x ₀ -|O′M|sinα----------------------(4)

$\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; px</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; o</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

According to the spherical grinding principle of the generative method, the surface ground out during the time when x ₀ does not change (that is, between two grinding feeds) is a cylindrical grinding wheel with a circumference around the y-axis and a width equal to that of a cylindrical grinding wheel. 4 An annular spherical belt with the same diameter, the center of the annular spherical belt is the point P′(0,y ₁ ) on the y-axis, and the spherical radius of the annular spherical belt is P′M. Because P′M<PM, that is, with the point P′(0,y ₁ ) as the center of the sphere, the radius of curvature of the spherical surface formed by P′M as the radius at M(x ₀ ,y ₀ ) is smaller than that of the rotating paraboloid at M(x ₀ ,y ₀ ) radius of curvature. The point M(x ₀ , y ₀ ) is the tangent point between the spherical surface and the rotating paraboloid, and a circle is formed when the point rotates around the y coordinate axis for one circle. As x ₀ increases, the diameter of the circle increases, that is, the rotating paraboloid It is composed of circles whose diameters are constantly changing, and the smoothness of the paraboloid of revolution is related to the amount of change of x ₀ each time.

In fact, the end face of the grinding wheel abrasive 4 is lossy during the grinding process, and the loss of the grinding wheel abrasive 4 affects the value of O'M in formulas (4) and (5), and the trajectory of motion also changes .

In order to realize precision grinding, the present invention further proposes a real-time detection method. The real-time detection method includes: a set of detection device 9 comprising a displacement sensor is installed in the inner cavity of the grinding wheel spindle 5, and the detection device 9 can move linearly along the rotation center line of the grinding wheel spindle 5. The detection device The detection point of the displacement sensor of 9 is on the rotation center of described grinding wheel main shaft 5; In grinding process, when described displacement sensor moves and touches the aspheric surface surface of described workpiece 3 to be ground, this grinding point The coordinate value of M is collected and recorded, and the data of the M coordinate value of the collected grinding point is compared with the standard coordinate data of the aspheric surface by the control system. If an error occurs, the formula (4), The three-axis linkage control model represented by (5) is corrected to ensure that the motion track of the grinding point M(x ₀ , y ₀ ) is always kept on the aspheric generatrix.

The method of the present invention can also grind large axisymmetric aspheric surfaces such as hyperboloids of rotation and ellipsoids of rotation.

Claims (5)

1. the precise grinding process of a heavy caliber axisymmetric aspheric surface, comprise the end face be fixedly mounted on rotary table be aspheric grinding workpiece, be arranged on the y feeding slide that is connected with x feeding slide on grinding wheel spindle and the emery wheel grinding tool that is fixed on this grinding wheel spindle, it is characterized in that: the rotation centerline adopting three-shaft linkage Controlling model to control described grinding wheel spindle remains with the normal of grinding points on aspheric surface bus and overlaps, and the errors of principles brought to avoid grinding and feeding movement locus also ensures kinematic accuracy; The end face of application wheel grinding tool carries out grinding to improve grinding ratio to described aspheric surface; Adopt real-time detection method to compensate the loss of described emery wheel grinding tool to improve grinding efficiency simultaneously.

2. the precise grinding process of heavy caliber axisymmetric aspheric surface according to claim 1, it is characterized in that: described aspheric summit is defined as the origin of coordinates O of workpiece coordinate system Oxyz, described aspheric rotating shaft overlaps with the y-axis of workpiece coordinate system Oxyz, and this aspheric rotating shaft is overlapped with the rotation centerline of described rotary table, namely the rotation centerline of described rotary table overlaps with the y-axis of workpiece coordinate system Oxyz, and this rotary table is with speed n ₁do low-speed rotation around y-axis, namely described aspheric surface bus does low-speed rotation around y-axis; The rotation centerline of described grinding wheel spindle is crossing with the origin of coordinates O ' of Cutter coordinate system O ' x ' y ' z ' and in O ' x ' y ' plane, do reciprocally swinging around the origin of coordinates O ' of this Cutter coordinate system O ' x ' y ' z '; Cutter coordinate system O ' x ' y ' z ' does up and down and left and right linear translation respectively by described y feeding slide and x feeding slide in the Oxy plane of workpiece coordinate system Oxyz, the rotation centerline of described grinding wheel spindle is remained with the normal of grinding points on described aspheric surface bus overlap, described grinding wheel spindle is with speed n ₂do high speed rotary motion; By described Cutter coordinate system O ' x ' y ' z ' in the Oxy plane of workpiece coordinate system Oxyz up and down and left and right linear translation, the oscillating traverse motion in O ' x ' y ' plane of the origin of coordinates O ' of pivot wire-wound Cutter coordinate system O ' x ' y ' z ' of described grinding wheel spindle and described aspheric surface bus realize described aspheric accurate grinding around the low-speed rotation of y-axis and the high speed rotary motion of described grinding wheel spindle.

3. the precise grinding process of heavy caliber axisymmetric aspheric surface according to claim 1, is characterized in that: described real-time detection method comprises: described grinding wheel spindle is hollow shaft, be provided with in the inner chamber of this grinding wheel spindle and can do along the rotation centerline of this grinding wheel spindle the checkout gear moved linearly, this checkout gear comprises the displacement transducer of test point on the pivot of described grinding wheel spindle, in grinding process, when institute's displacement sensors moves and touches described grinding workpiece surperficial, the coordinate value of this grinding points is collected to get off, and by control system, the data of gathered grinding points coordinate value and described aspheric standard coordinate data are compared, if generation error, just in real time described three-shaft linkage Controlling model is revised, to ensure that the movement locus of described grinding points remains on described aspheric surface bus.

4. the precise grinding process of the heavy caliber axisymmetric aspheric surface according to claim 1,2 or 3, is characterized in that: described emery wheel grinding tool is cylindrical shape emery wheel.

5. the precise grinding process of the heavy caliber axisymmetric aspheric surface according to claim 1,2 or 3, is characterized in that: described aspheric surface is axisymmetric aspheric surface.