Method for compensating radius of arc surface of turning tool of diffractive optical element

Abstract

The invention relates to the technical field of optical part precision machining, in particular to a turning tool arc surface radius compensation method for a diffractive optical element, which comprises the following steps of: establishing a machining curve according to an optical surface shape equation of the diffractive optical element; discrete processing is conducted on the equation of the machining curve, a machining contact point track is obtained, and the track is a surface contact point of the tool and the diffractive optical element in actual machining; according to the surface contact point, the cutter arc surface radius and a preset slope, performing normal offset compensation on the cutter arc surface radius at the continuous curved surface of the diffractive optical element; and performing linear compensation on the cutter arc surface radius at the step position of the diffractive optical element. The method for compensating the radius of the arc surface of the turning tool of the diffractive optical element aims at solving the problem that the turning precision of the diffractive optical element is low.

Description

Technical Field

[0001] The invention relates to the technical field of precision machining of optical parts, and in particular to a method for compensating the radius of an arc surface of a turning tool for a diffractive optical element. Background Art

[0002] Diffractive optical elements combine the principles of refraction and diffraction, and have special dispersion and thermal characteristics. The achromatic and athermal design of the diffractive element can improve the quality of the imaging system while reducing the weight and volume of the optical system, meeting the lightweight and compact design concept of modern optical systems. Diffractive optical elements made of infrared crystal materials are widely used in infrared optical systems, but because they have micro-scale step-shaped microstructures on aspherical substrates in order to achieve diffraction characteristics, their surfaces are discontinuous and require high surface accuracy and roughness requirements. Traditional grinding and polishing processes are difficult to meet their processing requirements.

[0003] Single-point diamond turning is a processing technology widely used in the field of infrared optical element processing. It uses diamond tools to achieve nano-level material removal and can obtain sub-micron surface accuracy and nano-level surface roughness in one processing. It is considered to be the best processing method for diffractive optical elements. In order to obtain higher surface quality, diamond tools are usually in the shape of arcs, which has a good processing effect for continuous surface processing. However, for non-continuous surfaces with microstructure characteristics such as diffractive optical elements, arc diamond tools will cause overcutting of step structures. There is a certain gap between the actual height and radial position and the ideal design, which affects the diffraction efficiency. Therefore, a good tool arc surface radius compensation method is needed to achieve high-precision processing of diffractive element microstructures.

[0004] Therefore, the inventor provides a method for compensating the radius of the arc surface of a turning tool for a diffractive optical element. Summary of the invention

[0005] (1) Technical issues to be solved

[0006] The embodiment of the present invention provides a method for compensating the radius of the arc surface of a turning tool for a diffractive optical element, which solves the technical problem of low turning precision of the diffractive optical element.

[0007] (2) Technical solution

[0008] The present invention provides a method for compensating the radius of an arc surface of a turning tool of a diffractive optical element, comprising the following steps:

[0009] Establishing a processing curve according to the optical surface equation of the diffractive optical element;

[0010] Discretizing the equation of the processing curve to obtain a processing contact point trajectory, where the trajectory is the surface contact point between the tool and the diffractive optical element during actual processing;

[0011] According to the surface contact point, the tool arc surface radius and the preset slope, the tool arc surface radius at the continuous curved surface of the diffractive optical element is compensated for normal offset; and the tool arc surface radius at the step position of the diffractive optical element is linearly compensated.

[0012] Furthermore, the preset slope is the slope of the equation of a straight line passing through the surface contact point and tangent to the processing curve.

[0013] Furthermore, the method of performing normal offset compensation on the tool arc surface radius at the continuous curved surface of the diffractive optical element according to the surface contact point, the tool arc surface radius and the preset slope specifically includes the following steps:

[0014] When turning the continuous curved surface of the diffractive optical element, the tool arc is always tangent to the processed curved surface, the tangent point is P, and the center point O of a circle with the tool arc surface radius r as the arc radius and passing through the point P and tangent to the processed curve is determined as the tool control point;

[0015] According to the coordinates P (x0, z0) of the surface contact point, determine the equation of a straight line passing through point P and tangent to the processing curve;

[0016] According to the straight line equation, the coordinates of the tool control point are calculated.

[0017] Furthermore, the horizontal coordinate of the tool control point is inversely correlated with the radius of the tool arc surface.

[0018] Furthermore, the ordinate of the tool control point is positively correlated with the radius of the tool arc surface, and is negatively correlated with the preset slope.

[0019] Furthermore, the linear compensation of the radius of the tool arc surface at the step position of the diffractive optical element is specifically performed as follows:

[0020] The intersection of an arc of a set radius with the surface contact point as the center and the step vertex of the processing curve is determined as the critical point. The tool moves vertically upward from the critical point for a first set distance and then moves horizontally for a second set distance to process a step-shaped microstructure.

[0021] Further, the point where the tool is compensated along the critical point P1(x1, z1) is determined to be O1(x t1 , z t1 ), the point of normal compensation along the step vertex is O2(x t2 , zt2 ), the motion trajectory of the tool is from point O1(x t1 , z t1 ) moves along the Z direction to the transition point (x t1 , z t2 ), and then move along the X direction to point O2(x t2 , z t2 ), forming the step-like microstructure.

[0022] Furthermore, the critical point is located in the interval [x2-r, x2], wherein x2 is the horizontal coordinate of the step vertex and r is the radius of the tool arc surface.

[0023] Furthermore, each location where the curvature suddenly changes in the processing curve is the step-shaped microstructure.

[0024] Furthermore, the diffractive optical element is a rotationally symmetric element, and the processing curve is a generatrix of the rotationally symmetric element.

[0025] (3) Beneficial effects

[0026] In summary, the present invention performs normal compensation at the continuous curved surface position of the diffractive optical element, performs precise position compensation at the step position, generates a single-point diamond turning machining trajectory point of the diffractive optical element, and realizes ultra-precision turning machining of the diffractive optical element. In addition, the step position is identified, and a trajectory that conforms to the step position is used for movement to replace the original trajectory offset along the normal direction in the interval to generate a machining trajectory. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0028] Figure 1 It is a schematic flow chart of a method for compensating the arc surface radius of a turning tool for a diffractive optical element provided by an embodiment of the present invention;

[0029] Figure 2 is a schematic diagram of a normal radius compensation provided by an embodiment of the present invention;

[0030] Figure 3 It is a schematic diagram of calculating the position of a critical point of a step provided by an embodiment of the present invention;

[0031] Figure 4 is a schematic structural diagram of a diffractive optical element provided in Example 1 of the present invention;

[0032] Figure 5 yes Figure 4 AA section view in;

[0033] Figure 6 is a trajectory diagram of a turning processing curve of a diffractive optical element provided in Example 1 of the present invention;

[0034] Figure 7 It is a schematic diagram for identifying the step position of a diffractive optical element provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The following is a further detailed description of the embodiments of the present invention in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the described embodiments, and covers any modification, replacement and improvement of parts, components and connection modes without departing from the spirit of the present invention.

[0036] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] Figure 1 FIG. 1 is a flow chart of a method for compensating the arc surface radius of a turning tool of a diffractive optical element provided by an embodiment of the present invention. Figure 1 , the method may include the following steps:

[0038] S100, establishing a processing curve according to an optical surface equation of the diffractive optical element.

[0039] Specifically, a processing curve is established according to the optical surface equation of the diffractive optical element. The processing element of this method is a rotationally symmetrical element, the processing method is single-point diamond turning, and the processing trajectory is the generatrix of the surface. The generatrix equation is:

[0040]

[0041] Where c is the vertex curvature, k is the cone coefficient, A, B, C are the aspheric higher-order coefficients, HOR is the diffraction order, n is the material refractive index, n0 is the air refractive index 1, λ0 is the central wavelength, Int is rounded, and C1, C2, C3 are the diffraction surface coefficients.

[0042] S200, discretizing the equation of the processing curve to obtain a processing contact point trajectory, where the trajectory is the surface contact point between the tool and the diffractive optical element in actual processing.

[0043] Specifically, in the actual machining process, the final trajectory is generated by the interpolation trajectory of the machining machine, so it is necessary to discretize the machining curve based on the continuous machining curve equation.

[0044] S300, performing normal offset compensation on the tool arc surface radius at the continuous curved surface of the diffractive optical element according to the surface contact point, the tool arc surface radius and the preset slope; and performing linear compensation on the tool arc surface radius at the step position of the diffractive optical element.

[0045] Specifically, the trajectory is the contact point between the diamond tool and the surface of the processed optical part in actual processing. Since a circular arc diamond tool is used, the arc radius of the tool needs to be compensated. There are two specific methods for compensation: one is normal offset compensation for the continuous part of the diffraction surface, and the other is compensation within the step range.

[0046] 1) Normal compensation of continuous surfaces:

[0047] When turning a continuous surface, the tool arc is always tangent to the ideal surface, and the tangent point is P. At the same time, P is the discrete point generated by the diffraction surface optical equation and the tool contact point. The center point O of the circle with the tool radius r as the arc radius and tangent to the diffraction optical equation through point P is the tool control point, that is, the moving trajectory point of the program during the actual processing. If the coordinates of the tool contact point are P (x0, z0), the equation of the straight line passing through point P and tangent to the diffraction surface equation curve is:

[0048] Z = kX + b;

[0049] In the formula, k is the slope, b is the x-axis intercept, and the values ​​of k and b are determined according to the diffraction surface equation curve of the specific diffractive optical element and are not fixed values.

[0050] According to the normal offset principle, the control point O(x t , z t ) can be calculated as follows:

[0051]

[0052] 2) Compensation of step position:

[0053] When the tool moves close to the step position, the slope of the tangent point of the diffraction equation changes close to infinity, and the normal compensation will cause repeated processing of the already processed surface. Therefore, in order to avoid this situation, special processing is required for the points close to the step position. The coordinates of the step vertex of the diffraction equation curve are P2(x2, z2). When the X-direction position of the tool contact point P1 moves to the range of [x2-r, x2], there must be a point P1(x1, z1) that makes the arc with a radius of r intersect with the step vertex P2(x2, z2) of the diffraction surface. This is the critical point for judgment, that is, the tool is compensated to this position along the normal radius of the continuous surface. At this time, the tool should move vertically upward to process the step-shaped microstructure of the diffraction surface, where the point where the tool is compensated along the normal of point P1(x1, z1) is O1(x2-r). t1 , z t1 ), the point along the step vertex normal compensation is O2(x t2 , z t2 ), the motion trajectory of the arc diamond tool in this range is from O1(x t1 , z t1 ) moves along the Z direction to the transition point (x t1 , z t2 ), and then move along the X direction to O2(x t2 , z t2 ), forming a step microstructure, and then continuing to use the normal compensation of the continuous surface. Since there are often multiple diffraction microstructures along the radial direction of the same surface, it is necessary to perform the same treatment on each step of the processing program.

[0054] Example 1

[0055] As Figure 4-5 Taking a certain type of microstructure diffractive optical element as an example, its generatrix equation is:

[0056]

[0057] In the formula, c is the vertex curvature, which is 0.01663; k is the cone coefficient, which is 0; A, B, and C are the aspheric higher-order coefficients, A=1.292647e-5, B=-6.371249e-9, C=-1.006326e-10; the diffraction order HOR=1; n=2.7781 is the material refractive index; n0=1 is the air refractive index; λ0=10μm is the center wavelength; Int is rounded to the integer; C1, C2, and C3 are the diffraction surface systems; C1=-6.3613e-4, C2=-1.42090796e-6, and C3=0. In the actual processing process, the final trajectory is generated by the interpolation trajectory of the processing machine tool. Therefore, it is necessary to discretize the curve based on the continuous generatrix equation. By subdividing the X-direction with equal step length, taking the X-direction step length as 0.001mm and the X-direction processing range as [-13.2,13.2], the processing contact point trajectory is obtained, such as Figure 6 shown.

[0058] The calculation formula for the step position is:

[0059]

[0060] The curve is shown in Figure 7. The location of each sudden change in curvature is the location of the step-shaped microstructure. The step position is identified by calculating the local peak point E of the curve, and the location of the peak point E is the step position point F.

[0061] It should be clear that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. In addition, for the sake of brevity, a detailed description of known methods and technologies is omitted here.

[0062] The above are only embodiments of the present application and are not limited to the present application. For those skilled in the art, the present application may have various changes and variations without departing from the scope of the present invention. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for compensating the radius of the arc surface of a turning tool for a diffractive optical element, characterized in that: The method comprises the following steps: Establishing a processing curve according to the optical surface equation of the diffractive optical element; Discretizing the equation of the processing curve to obtain a processing contact point trajectory, where the trajectory is the surface contact point between the tool and the diffractive optical element during actual processing; According to the surface contact point, the tool arc surface radius and the preset slope, the tool arc surface radius at the continuous curved surface of the diffractive optical element is compensated for normal offset; and the tool arc surface radius at the step position of the diffractive optical element is linearly compensated.

2. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 1, characterized in that: The preset slope is the slope of the equation of a straight line passing through the surface contact point and tangent to the processing curve.

3. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 2, characterized in that: The method of performing normal offset compensation on the tool arc surface radius at the continuous curved surface of the diffractive optical element according to the surface contact point, the tool arc surface radius and the preset slope specifically comprises the steps of: When turning the continuous curved surface of the diffractive optical element, the tool arc is always tangent to the processed curved surface, the tangent point is P, and the center point O of a circle with the tool arc surface radius r as the arc radius and passing through the point P and tangent to the processed curve is determined as the tool control point; According to the coordinates P (x0, z0) of the surface contact point, determine the equation of a straight line passing through point P and tangent to the processing curve; According to the straight line equation, the coordinates of the tool control point are calculated.

4. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 3, characterized in that: The horizontal coordinate of the tool control point is inversely correlated with the radius of the tool arc surface.

5. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 3, characterized in that: The ordinate of the tool control point is positively correlated with the radius of the tool arc surface, and is negatively correlated with the preset slope.

6. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 1, characterized in that: The linear compensation of the radius of the tool arc surface at the step position of the diffractive optical element is specifically: The intersection of an arc of a set radius with the surface contact point as the center and the step vertex of the processing curve is determined as the critical point. The tool moves vertically upward from the critical point for a first set distance and then moves horizontally for a second set distance to process a step-shaped microstructure.

7. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 6, characterized in that: Determine the point where the tool is compensated along the critical point P1(x1, z1) as O1(x t1 , z t1 ), the point of normal compensation along the step vertex is O2(x t2 , z t2 ), the motion trajectory of the tool is from point O1(x t1 , z t1 ) moves along the Z direction to the transition point (x t1 , z t2 ), and then move along the X direction to point O2(x t2 , z t2 ), forming the step-like microstructure.

8. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 6, characterized in that: The critical point is located in the interval [x2-r, x2], where x2 is the horizontal coordinate of the step vertex and r is the radius of the tool arc surface.

9. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 6, characterized in that: Each location where the curvature changes suddenly in the processing curve is the step-shaped microstructure.

10. The method for compensating the arc surface radius of a turning tool for a diffractive optical element according to claim 1, characterized in that: The diffractive optical element is a rotationally symmetric element, and the processing curve is a generatrix of the rotationally symmetric element.

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