RU2111106C1 - Method of shape-forming of surfaces of large-sized optical parts by means of small tool - Google Patents

Abstract

FIELD: machining of parts; technology of shape-forming optical surfaces by means of small tools and automated control of shape-forming process. SUBSTANCE: optical surface is analyzed by indication of local curvature and machining allowance is determined only for convex sections whose curvature exceeds permissible limits. Then topographic mat of new surface is plotted through subtraction of allowances obtained from initial topographic map. The above-mentioned operations are repeated "n" times. Machining allowances are determined through summing up the allowances obtained in each cycle. Then required sections are subjected to machining. EFFECT: enhanced efficiency. 14 dwg

Description

 The invention relates to a technology for processing optical parts, in particular to a technology for automated shaping of optical surfaces with a small tool and automated control of the shaping process.

 A known method of automated shaping of optical surfaces "Zebra-3", which consists in constructing a topographic map of the surface, determine the residence time of the tool in the surface areas requiring processing, move the tool so that the center of the tool is within each area for the required time. The tool moving speed is constant, and the tool dwell time within each section is controlled by the number of elementary processing cycles. The tool rotates forcibly around its axis and describes a trajectory resembling a figure eight.

 The disadvantage of this method is the relatively low accuracy and productivity of forming, due to the fact that the tool rotates around its axis. This makes it difficult to eliminate local errors, since they need to be produced with the edge of the tool, but at the same time its opposite edge can be in the area that does not require processing. The disadvantage is the discrete regulation of the residence time of the tool, which leads to a decrease in accuracy and an increase in the fine-structure error (m.s.o.).

 Closest to the proposed method is a method of forming surfaces of optical parts.

 In this method, the tool makes a plane-parallel circular motion with a certain eccentricity relative to the tool spindle. The processing time in each section ij is determined in proportion to the size of the allowance in the specified section and inversely proportional to pressure, processing speed and technological factors; the processing time is controlled by the speed of the tool. The specified method allows you to simultaneously eliminate all kinds of errors in the shape of the optical surface.

 The disadvantage of this method is that if the initial surface had a significant m.so., then its elimination by this method is very difficult. As a result of such processing, the optical surface, possessing high accuracy according to the criteria for the range of deviations and standard deviation (r.m.s.), does not satisfy the requirements for the magnitude of m.s.

 The aim of the invention is to increase the accuracy of the formation of optical surfaces by reducing the magnitude of MSO by automated processing with a small tool.

The goal is achieved by building a topographic map about. , for which they determine the convex sections ij of the surface, the values of the local curvature G _{ij of} which satisfy the condition:
[0-0.3] G _min ≥G _ij ≥G _min ,
Where
G _min - the minimum local surface curvature, determine for the mentioned sections the value of the intermediate allowance I _ij according to the formula:
I _ij = d _ij - (d _i-lj + d _{i + lj} + d _{ij + 1} + d _ij-1 ) / 4
Where
d _ij is the value of the deviation of the surface from the required at the site ij, and taking into account the obtained intermediate allowances, a topographic map of the expected surface is built; these operations are carried out in a cycle to satisfy the condition
(G _min (old) - G _min (now)) / G _min (now) ≤ [0,1-0,3],
Where
G _min (old) and G _min (now) are the minimum values of the local surface curvature in the previous and current cycles, and the final allowance is chosen equal to the sum of the intermediate allowances, according to which the processing is performed.

Comparative analysis with the prototype shows that the inventive method of forming surfaces of large optical parts with a small tool is different in that they construct a topographic map of a fine-structure error, for which the surface topography is analyzed by the local curvature G _ij and the intermediate processing allowance is determined only for convex sections with respect to their immediate environment, build a topographic map of the expected surface, these operations are repeated in a cycle, and the final starting intermediate is selected equal to the sum of allowances, whereupon processing required portions.

 Thus, the claimed method of forming surfaces of large optical parts with a small tool meets the criteria of the invention of "novelty."

 Comparison of the proposed solution not only with the prototype, but also with other technical solutions in the art does not allow them to identify signs that differ the claimed solution from the prototype, which allows us to conclude that the criterion of "significant differences".

In FIG. 1 shows the dependence of the number of sections selected for calculating the intermediate allowance, on the value of the coefficient on the left side of the condition [0-0.3] G _min ≥G _ij ≥G _min ; in FIG. 2 - change in the minimum curvature of the expected surface depending on the number of cycles of operations; in FIG. 3 - change in amplitude and s.c.o. the expected surface (in fractions of a wavelength of 0.6328 microns) depending on the number of cycles of operations; in FIG. 4 - change in amplitude and s.k. about. the resulting allowance (in fractions of the wavelength) depending on the number of cycles of operations; in FIG. 5 is a topographic map of the original surface; in FIG. 6 - volumetric image of the topography of the original surface; in FIG. 7 - volumetric image of the topography of the intermediate stock after the first selection cycle m. about. ; in FIG. 8 is a three-dimensional image of the topography of the expected surface after the first selection cycle of ms. about.; in FIG. 9 is a three-dimensional image of the intermediate allowance after the sixth cycle of allocation of m.s.o .; in FIG. 10 is a three-dimensional image of the expected topography of the surface after the sixth cycle of allocation of MSO .; in FIG. 11 - topographic map of the final total allowance (topographic map m.s.o.); in FIG. 12 is a three-dimensional image of a topographic map of the total allowance; in FIG. 13 is a topographic map of the surface processed by the proposed method; in FIG. 14 - topographic map of m.so. surface after processing.

где
C и D - эмпирически подобранные коэффициенты, а d_ij - величина отклонения поверхности на участке ij.The method is implemented as follows. A topographic map of the surface of the optical part is constructed (see FIG. 5) and a topographic map of the fine structure surface error is formed on it. For this, a topographic map of the surface is analyzed by the sign of local curvature. For each section ij, the value of the local curvature of the surface G _{ij is} calculated:

Where
C and D are empirically selected coefficients, and d _ij is the value of the surface deviation in section ij.

Local curvature is characterized by the sign and value of the parameter G _ij . If G _ij = 0, then this means that the surface of section ij is flat, positive G _ij indicate concave sections, negative ones indicate convex ones, and the smaller (larger) the value of G _ij , the more abruptly (concave) the surface section is.

The selection of sections, the curvature of which G _ij satisfies the condition:
[0 - 0.3] G _min ≥G _ij ≥G _min ,
Where
G _min - the minimum value of all of them G _ij for a given topographic map. This allows you to select for processing only convex surface areas with negative curvature (zero left side) that are available for polishing, or to select the most steeply curved ones (left side is 0.3 G _min ), which make the largest contribution to . Increasing the left side in the positive direction will include in the number of sections to be processed, a number of concave sections that cannot be polished. On the other hand, choosing the left side less than 0.3G _min greatly reduces the number of sections, which makes the procedure ineffective, leading to an increase in the number of cycles. For the example of FIG. Figure 1 shows the dependence of the number of sites (N) selected for processing on the value of the left side of the condition. As can be seen from the graph, changing the value of the left side from 0 to 0.3 reduces the number of selected sections by almost 10 times.

For the selected sections, the value of the intermediate allowance is determined with respect to the areas of the nearest environment using the formula:
I _ij = d _ij - (d _i-lj + d _{i + lj} + d _{ij + l} + d _ij-l ) / 4.

 Then the topographic map of the expected surface (now) is calculated as the difference between the analyzed topographic map (old) and the obtained values of the intermediate allowances.

After that, the above operations are repeated in a cycle until the condition is met:
(G _min (old) - G _min (now)) / G _min (now) ≤ [0,1-0,3],
The choice of the value of the right side of more than 0.3 terminates the cycle prematurely, leaving unrealized the possibility of better surface smoothing. On the other hand, a decrease of this value to less than 0.1 increases the number of cycles, despite the fact that in the last cycles no significant surface improvement is observed. In FIG. 2 shows a characteristic change in the minimum curvature of the expected surface as a function of the number of cycles; FIG. 3 - change in scope and s.c.o. the topography of the expected surface, depending on the number of cycles, and in Fig. 4, a similar change in magnitude and r.c.c. topographies of intermediate stocks. The graphs show that the most effective choice is observed for cycles in which, accordingly, there is a sharp decrease in the absolute value of the minimum local curvature.

 Next, the final allowance is calculated as the sum of the intermediate allowances and the technological processing sessions are calculated, after which the surface is processed on automated machines. After processing, the surface is monitored and a topographic map of the surface is built with the selection of a topographic map of the fine-structure error and an estimation of its parameters. If the resulting surface does not meet the required criteria for m.s.o., the entire technological cycle is repeated.

 The specified method was implemented in practice when processing optical parts on machines of the AD series. In FIG. 5 shows a topographic map of the original optical surface, span and r.h. deviations of which are 0.0880 and 0.0143 μm, respectively. In FIG. 6, for clarity, a three-dimensional image of the topography of this surface is shown. It can be seen that the surface topography is constructed by broken lines and is not smooth.

 The initial topography was analyzed on the basis of local curvature, and for the selected convex sections, a topographic map of the intermediate stock was constructed after the first cycle, the volumetric image of which (the vertical scale for clarity is increased) is shown in FIG. 7. Its magnitude is 0.0088 microns, and s.ko. 0.0016 microns. It is clearly seen that the selected sites are confined not only to the peaks, but also to the slopes of the original topography. A topographic map of the expected surface after the first cycle, a three-dimensional image of which is shown in FIG. 8, does not show significant smoothing of the surface — its span is 0.0836 μm, and the s.c.o. 0.0139 μm.

 The above operation was carried out in a cycle of 6 times. In FIG. 9 shows a three-dimensional image of a topographic map of the intermediate stock after the sixth cycle. It can be seen that a larger number of surface areas began to satisfy the selection criterion, but their contribution became smaller - the range of the topography of the intermediate allowance was 0.0031 μm, and the scrit 0,0007 μm.

 A 3D image of the expected topographic map of the surface after the sixth cycle is shown in FIG. 10, its span is 0.0741 microns, and s.c. about. 0.0128 μm. Compared to the original topography, the surface began to look much smoother, although its span and r.h.p. changed slightly.

 Interim allowances were added up. A topographic map of the final stock is shown in FIG. 11, and its volumetric image is in FIG. 12. The scope of the final allowance of 0.0197 microns, s.k.o. 0.0056 μm. It is seen that the allowance is broken in nature and has a fine structure.

 According to the topographic map of the final allowance, a session of automated processing was carried out. The obtained surface was checked; its topographic map is shown in FIG. 13. The range of topography is 0.0755 microns, and s.k.o. 0.0129 μm.

 The analysis performed on the basis of local curvature and the construction of a topographic map of the fine-structure error shown in FIG. 14, showed that the value of m.s. after processing, it is 0.0038 μm in scope and 0.0013 μm in s.c.o. less m.s. the initial surface is 5 times in scope and 4 times in s.c.o. The obtained result confirms the effectiveness of the proposed method to reduce the fine-structure error.

 A positive effect when using the proposed method is to increase the accuracy of optical surfaces by reducing the MSO without deterioration of other surface parameters - scope and RMS, and for the implementation of the method does not require additional equipment and tooling.

Claims (1)

A method for shaping the surfaces of large-sized optical parts with a small tool, in which the processing is performed taking into account the required surface parameters in terms of span and standard deviation, characterized in that after the said processing, a topographic map of the fine-structure error is constructed, for which convex sections ij of the surface are determined, values of local curvature G _{i j} which satisfy the condition
[0 - 0.3] G _{m i n} > = G _{i j} > = G _{m i n} ,
where G _{m i n} is the minimum local curvature of the surface,
determine for these sections the value of the intermediate allowance I _{i j} according to the formula
I _{i j} = d _{i j} - (d _i - l _j + d _i + l _j + d _{i j + 1} + d _{i j - 1} ) / 4,
where d _{i j} is the value of the deviation of the surface from the required at the site ij,
and taking into account the obtained intermediate allowances, a topographic map of the expected surface is built, these operations are performed in a cycle until the condition is satisfied
(G _{m i n} (old) - G _{m i n} (now)) / G _{m i n} ) (now) <= [0.1 - 0.3],
where G _{m i n} (old) and G _{m i n} (now) are the minimum values of the local surface curvature in the previous and current cycles,
and the final allowance is chosen equal to the sum of the intermediate allowances, according to which the processing is performed.

Images