RU2687172C1 - Method of elastic deformation of an optical workpiece for production of off-axis thin aspherical mirror of telescope and mechanism for its implementation (versions) - Google Patents

Abstract

FIELD: instrument engineering.SUBSTANCE: group of inventions is used in production of off-axis aspherical elements of a composite telescope mirror. Method is used for elastic deformation of thin optical workpiece from glass ceramics by directed attraction to thickened slightly deformed glass-ceramic substrate by means of tightening elements. In edge zone of billet and substrate or only substrate there made are holes for tightening elements, on these places bonding bushings with smooth holes are glued to substrate or with threaded holes – to billet. In the middle zone of the substrate or workpiece also bonding sleeves without holes are glued. Billet is installed on bushings of substrate or directly on substrate, if billet with glued bushings. In the edge holes there fixed are tightening elements of the deformation mechanism, each of which is made in the form of a rod with a nut on the lower end and with a spring fixed in bushings on it and with a nut and a conical washer on the upper end, or with a threaded upper end.EFFECT: technical result consists in simplification of mechanism and method of elastic deformation of optical workpieces of mirrors of telescopes.5 cl, 9 dwg

Description

The invention relates to the production of aspherical optical products and can be used in the manufacture of off-axis elements (segments) of large composite telescope mirrors.

Mirrors of modern telescopes, for example, ELT with a diameter of 39 m or TMT with a diameter of 30 m consist of six-sided off-axis segments made of glass-ceramic material (Zerodur or Astrositall) with an aspherical surface, 1.5 m in size, in an amount of 800 and 500 pieces. respectively. For the accelerated and mass production of such mirrors, a method of aspherization of the workpiece in an elastically deformed state was proposed and implemented (Proc. Of SPIE, vol. 7733 773328 - 3, 05.08.2010). According to this method (see Fig. 3.2.), It is required to bend a round polished billet at specified design points in such a way as to obtain the shape of a mirror that is the opposite of the required one. In this case, the area of the surface of the mirror, where it is necessary to carry out the removal of material, will rise in the form of mounds. Then the surface is polished with a full-sized tool to get a spherical shape of a given radius. After removing the deformations, an aspherical off-axis surface close to the required one will be obtained, which must then be brought to the requirements of the specification by program-controlled grinding and then polishing with a small tool or ion beam. Internal equivalent stresses in such a bend should be no more than 5 MPa, which allows to avoid the occurrence of plastic deformations in the material. After processing, a hexagonal segment of the composite mirror is cut from the blank, for example.

A known method of bending (elastic deformation) of thin 1.5-meter blanks for segments of the ELT M1 telescope using a deforming coupling device (Proc. Of SPIE vol. 9145, 914539-4, 914539-5, 2014, Emm. Hugot "Stress polishing demonstrator for ELT M1 segment ”). The hitch is made in the form of 24 metal handles, glued either to the workpiece around the circumference, or to a thick ring-substrate. For bending of the workpiece in given places, forces are applied to the ends of some handles, which allows transferring pure shear forces and bending moments to an optical meniscus. In addition, a uniform load (pressure) is applied to the back side of the workpiece to compensate for the spherical aberration. After removing all the loads and processing the workpiece, it was found that the residual voltage was at a satisfactory level - no more than 4 MPa.

The closest to the present invention to the technical essence will be a method and mechanism for the elastic deformation of an optical workpiece for the subsequent manufacture of a thin off-axis aspherical telescope mirror, described in the publication “CELT Report Number 34. Conceptual Design for a TMT, June 2002, Section 5.3.4, Fig 5- 9 and 5-10. The method of elastic deformation consists in the directional attraction of a circular optical blank to a thickened low-deformable substrate with the help of tightening elements fixed vertically to the circumference of the blank. To do this, a complex robotized mechanism is constructed above the billet, the lower end of the binder is glued to the billet, and two spring thrusts are fixed to the upper end, one directed radially inward, the other upward and working from hydraulic devices. When connecting the corresponding bracing elements to the glue zones of the workpiece, they are mutually perpendicular to the efforts and, as a result, the workpiece is flexibly directed. After dismantling the mechanism, aspherization of the workpiece is carried out in a known way, as in the first analogue (Proc. Of SPIE, vol. 7733 773328 - 3, 08/05/2010).

The specified mechanism and method as a whole is very complicated and time consuming both during setup and during implementation.

The objective of the invention is to simplify the mechanism and method of elastic deformation of the optical blanks of telescope mirrors for their subsequent aspherization.

The technical result due to the task is achieved by the fact that in the method of elastic deformation of an optical workpiece for the manufacture of an off-axis thin telescope aspherical mirror by directional attraction to a thick low-deformable substrate using tightening elements fixed around the perimeter of the workpiece, in contrast to the known,

Option 1: coaxial holes for tightening elements are made in the edge area of the substrate and the optical preform, gluing unloading sleeves with apertures are installed on the edge openings of the substrate, and sleeves without holes are installed in the middle area of the substrate, an optical ground flat workpiece is installed on the sleeves the openings let through tightening elements in the form of rods with nuts at the ends and with a spring fixed in the sleeves on the lower nut, with a conical washer under the upper nut, nuts attract the tongue to the substrate, perform on the workpiece by grinding the sphere closest to the aspherical surface, unwind the nuts, install different-height calibrated gaskets on the discharge bushings, again attract the workpiece to the substrate before touching it with the gaskets and bending the workpiece, and then controlling the deformed workpiece, produce a spherical surface given radius, dismount the tightening elements and direct the workpiece to the final finishing of the aspherical surface;

option 2: in the marginal zone of the substrate, holes for tightening elements are made, unloading sleeves with threaded holes are glued to the workpiece with them, and discharge holes without holes are glued in the middle zone of the workpiece, tightening elements in the form of rods are threaded onto the holes in the substrate the upper end and the nut on the lower end, on which the spring is located in the bushes, screw the rods into the threaded holes of the relief sleeves by tightening the nuts and thereby attract the workpiece the substrate, polished onto the workpiece, the sphere closest to the aspherical surface, unscrew the nuts; on the substrate, at different locations of the discharge sleeves, calibrated spacers of different heights are installed; the workpiece, the grinding of a spherical surface of a given radius is performed, the tightening elements are removed and the workpiece is directed to the final development aspherical surface,

as well as the fact that:

in the mechanism for the elastic deformation of an optical preform, which includes tightening elements fixed along the perimeter of the preform, in contrast to the known:

for option 1: tightening elements made in the form of rods with nuts at the ends, with a spring over the lower nut with its fastening between two bushings, while the upper nut is fixed with a conical washer, tightening elements are installed in coaxial holes in the marginal zone of the workpiece and the substrate with a discharge sleeve with coaxial bore and calibrated gaskets between them;

Option 2: tightening elements made in the form of threaded rods at the upper end and a nut at the lower end, on which a spring is located in the bushes, tightening elements installed in the holes in the substrate's edge zone, with the possibility of screwing them into the threaded holes of the discharge sleeves glued to the workpiece and aligned with the holes in the edge area of the substrate.

The proposed system of tightening elements in the form of thin rods passing through the edge holes in the workpiece and the substrate, allows you to deform (bend) the workpiece simply by tightening the nuts at the ends of the rods. The system of multi-height spacers between the substrate and the workpiece ensures the deformation of the workpiece in the right places. The system of discharge sleeves ensures uniform unloading of the workpiece on the substrate during all operations of its deformation and processing. Simple assembly and disassembly of the entire deformation mechanism allows you to quickly carry out successive technological operations until the final aspherization of the workpiece (deformation, grinding, surface monitoring, its finishing).

The invention is illustrated in the drawing, where:

FIG. 1 - type of optical preform;

FIG. 2 - a cut along the edge of the hole;

FIG. 3 is a view of the substrate;

FIG. 4 - cut along the edge of the hole;

FIG. 5 - the general scheme of the deformation process;

FIG. 6 - workpiece in conjunction with the substrate;

FIG. 7 - the mechanism for the deformation assembly (option 1);

FIG. 8 is a diagram of multi-height gaskets;

FIG. 9 - the mechanism for the deformation assembly (option 2).

As examples of the implementation of the proposed method of deformation of the optical preform and a tightening mechanism for the implementation of the deformation, two variants of their execution will be given for producing an off-axis thin aspherical segment of the ELT M1 mirror with a 1520 mm billet diameter of glass-ceramic CO-115 M.

Option 1 - for the case when it is acceptable to drill small technological holes in the optical zone. The blank (Fig. 1) is a round thin disc 1 with a diameter of 1520 mm and a thickness of 54 mm with polished flat surfaces. In the marginal zone of the workpiece drilled holes 2 (Fig. 2), for example, 12 pieces for tightening elements. To perform the workpiece deformation procedure, a special glass-ceramic substrate is manufactured. Its thickness is calculated in such a way that its deformations are an order of magnitude smaller than the deformation of the workpiece and are minimal. A flat surface is ground on the substrate with a deviation from the plane of less than 1 micron. The surface should have a roughness that meets the requirements of gluing auxiliary metal elements to glass ceramics. The substrate (Fig. 3) is a thick disk 3 made of glass-ceramic with a diameter of 1520 mm and a thickness of 240 mm. In it, as well as in the workpiece, 12 holes 4 (Fig. 3, 4) for tightening elements and three holes 80 with a diameter of 80 mm in the middle zone are drilled in the marginal zone to accommodate three jacks for raising and lowering the workpiece.

The general scheme of the deformation process is shown in FIG. 5 and 6, and the mechanism for strain assembly is shown in FIG. 7. Optical preform 1 is located above the substrate 3 so that the holes 2 and 4 coincide, but not directly, but on the discharge metal bushes 6 and 7, glued to the substrate. Of these, a part of the sleeves with holes 6 is aligned with the holes 4, and a part of the sleeves without holes 7 are glued in the calculated places in the middle zone of the substrate (in Fig. 3 on the dash-dotted circle).

At the glueing points of the sleeves 6 and 7, glue is applied (in particular, DP-190), and in order to ensure the necessary and uniform thickness of the adhesive layer, it is recommended to install three temporary technological sleeves with an increased (for example, 0.15) on the peripheral circumference of the substrate at an angle of approximately 120 °. mm) tall. On these three bushings set the workpiece. Excess glue is squeezed out. After 4 hours of incubation at room temperature, the glue acquires the necessary viscosity and three temporary sleeves are removed. This technique will ensure uniform unloading of the workpiece on the sleeves 6 and 7.

The deformation of the workpiece is carried out using a mechanism consisting of 12 identical tightening elements located in the combined holes 2 and 4 of the marginal zone of the workpiece and the substrate. Each tightening element (Fig. 7) consists of a thin rod (stud) 8 with a nut 9 at the lower end (the nut can be welded to the stud) and a nut 10 with a conical washer 11 under the nut 10. On the lower nut 9 is installed between the stepped sleeve 12 and a conical sleeve 13 spring 14.

The method of deformation is carried out in the following sequence. On the work table with three jacks install the substrate 3 so that the jacks entered into the holes 5. On the substrate 3 are glued in the specified positions of the sleeve 6 and 7 (they must be the same height). After the glue polymerization process is completed, optical billet 1 is installed on the grommets by aligning the holes 2 and 4 in the marginal zones of the billet and substrate. The studs are inserted into these openings from the bottom by tightening the elements and tightening both or only the upper nuts press the workpiece against the substrate (Fig. 6). A spherical surface with a radius equal to the nearest radius of an off-axis aspheric surface with a 1 µm deflection from the sphere is ground on the workpiece. Unscrew the nuts and on discharge sleeves 6 and 7 install raznovisotnye calibrated gasket 15 (Fig. 8). Again attract the workpiece to the substrate until it touches the pads 15 and bending the workpiece. The degree of tightening is ensured by the stiffness of the springs 14. The measurement of the surface obtained is carried out on a coordinate measuring machine, namely its deviations from the calculated one. The spherical surface of a given radius is polished again, after which the tightening elements are removed and the workpiece is directed to the final finishing of the aspherical surface. In all these operations, raising and lowering the workpiece is carried out using three jacks. Subsequently, the desired hexagon is cut out of the polished workpiece, and thus the edge segments with technological holes are cut off.

Option 2 - for the case when the presence of holes in the edge zone of the workpiece is unacceptable. The method will be different modifications of some operations, and the mechanism - another constructive solution.

In this case, the substrate will be made absolutely in the same way as in option 1 (Fig. 3 and 4), and the workpiece - in the form of a disk, only without holes in the marginal zone. 12 unloading metal sleeves 16 with threaded holes along the axis are glued to the bottom surface of the workpiece so that these holes are then aligned with the holes in the edge area of the substrate (Fig. 9), as well as several, for example, 8 sleeves 7 without holes - in the middle the workpiece zone 1. Each tightening element of the deformation mechanism is made similarly as a stud 17 with a welded nut 9 at the lower end with a spring 14 placed on the nut in sleeves 12 and 13, while the stud 17 is threaded at the upper end (analog of a bolt) POSSIBILITY screwing it into threaded hole 16. The sleeve deformation Procedures carried out as follows. The workpiece 1 is installed on the substrate so that the threaded holes in the glued relief sleeves 16 are aligned with the holes 4 in the edge area of the substrate. Studs (bolts) 17 of the tightening elements assembled (Fig. 9) are inserted into the holes 4, tightening the nuts (bolt heads) 9, screw them into sleeves 16, thereby attracting the workpiece 1 to the substrate 3. On the workpiece they grind a spherical surface with a radius equal to the nearest radius of an off-axis aspheric surface. Unscrew the nuts and on the substrate establish calibrated gaskets 15 with different heights aligned with the edge holes (Fig. 9). Again attract the workpiece to the substrate until it touches the pads 15 and bending the workpiece. Further operations (grinding the sphere, control, fine-tuning) are performed similarly to option 1.

In both cases, the deformation mechanism is an analogue of a conventional bolted joint, and the deformation process is carried out with a simple tightening, i.e. they are industrially applicable.

Claims (5)

1. The method of elastic deformation of an optical preform for the manufacture of an off-axis thin aspherical mirror of a telescope by directional attraction to a thick non-deformable substrate by means of tightening elements fixed along the perimeter of the preform, characterized in that in the edge area of the substrate and the optical preform are aligned edge holes of the substrate are installed by gluing the discharge sleeves with holes, and in the middle zone of the substrate - sleeves without holes, for watts Streets establish an optical ground flat billet, pass through the edge holes tightening elements in the form of rods with nuts at the ends and with a spring fixed in the sleeves on the lower nut, with a conical washer under the upper nut, nuts attract the billet to the substrate, perform a sphere on the billet by grinding, close to the aspherical surface, unscrew the nuts, install different-height calibrated gaskets on the discharge sleeves, again attract the workpiece to the substrate until it touches the gaskets and the gaskets The bending of the workpiece, after which the deformed workpiece is monitored, the spherical surface of a given radius is polished, the tightening elements are removed and the workpiece is directed to the final finishing of the aspheric surface. 2. The method of elastic deformation of an optical preform for the manufacture of an off-axis thin aspherical mirror of a telescope by directional attraction to a thick low-deformable substrate with the help of tightening elements fixed along the perimeter of the workpiece, which are glued to the preform in the edge area of the substrate discharge sleeves with threaded holes, and in the middle zone of the workpiece, discharge sleeves without holes are glued through the edge holes in the In the attachment, tightening elements are inserted in the form of threaded rods at the upper end and a nut at the lower end, on which the spring is located in the bushes, screw the rods into the threaded holes of the unloading bushings by tightening the nuts, and then grind the sphere closest to the workpiece. aspherical surface, unscrew the nuts, on the substrate at the locations of the discharge sleeves set calibrated razors of different heights, on them set the workpiece, again attract the workpiece to odlozhke to touch with calibrated spacers and bending the workpiece and then monitored the deformed preform produce grinding a spherical surface of given radius, tightening elements dismantled and sent to the final finishing of the workpiece aspherical surface. 3. The method of elastic deformation of the optical preform according to claim 1 and 2, characterized in that after dismantling the tightening elements, the workpiece is lifted with the help of jacks installed in three holes in the middle zone of the substrate. 4. Mechanism for elastic deformation of an optical workpiece for manufacturing an off-axis thin telescope aspherical mirror, including tightening elements fixed along the perimeter of the workpiece, characterized in that the tightening elements are made in the form of rods with nuts at the ends, with a spring above the bottom nut with its fastening between two bushings, while the top nut is fixed with a conical washer, tightening elements are installed in coaxial holes in the marginal zone of the workpiece and the substrate with a discharge sleeve with a coaxial hole calibrated shims between them. 5. Mechanism for elastic deformation of the optical billet for the manufacture of off-axis thin telescope aspherical mirror, including tightening elements fixed along the perimeter of the optical billet, characterized in that the tightening elements are made in the form of rods with a thread on the upper end and a nut on the lower end on which in the sleeves spring, tightening elements are installed in the holes in the edge area of the substrate with the possibility of screwing them into the threaded holes of the discharge sleeves glued to the workpiece and aligned with the holes in the edge area of the substrate.

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