Mounting method astronomical mirrors in the telescope

 

(57) Abstract:

The invention relates to the field of astronomical instrumentation and can be used in serial small telescopes for fastening the main mirror having a Central hole. The invention allows to unload the mirror of its own weight without any complicated handling devices, to exclude the decentering of the mirror to compensate for the influence of temperature during observations on the shape of its surface. This is ensured by the fact that in the process of fixing astronomical mirror with a Central hole in the tube of the telescope is a mirror glued to the rim of the Central hole to the support sites of the elastic petals split sleeve. Features gluing to produce heat-resistant adhesive with a degree of shrinkage of not more than 3%, and a split bushing to perform carbon steel with subsequent thermal treatment. 1 C.p. f-crystals, 4 Il.

The present invention relates to the field of astronomical instruments and can be used in serial small telescopes for fastening the main mirror having a Central hole.

The literature describes ways of fastening astronomicas is the mirror frame [1].

Known methods of fastening astronomical mirrors in frames lead to structurally complex, massive and overall attachment points of the main mirror, requiring, in addition, a significant amount of time on his atstone when the temperature of the telescope environment.

Mounting method astronomical mirrors in the frame without thermal compensation gap [2] , used in serial telescopes small current openings (up to 300 mm), requires hard massive steel structure with elements unloading mirror on the back of its own weight, allowing you to save the exact shape of the mirror in all its provisions (or without, if the mirror thickness is sufficient). Between the mirror and the frame is left a small thermal gap within which the main mirror is free to roll at reruns of the tool in the observations, which is a serious drawback of this method of fastening the mirror.

Unrestricted movement of the main mirror within thermal gap and elasticity discharge devices result in significant and unacceptable, especially in the case of high-aperture systems, decenterable mirror, what about, ultimately, leads to loss of image quality and the need for frequent pereustanovki tool. Attempts to lock the mirror in the frame, introducing, for example, the sealant into the gap at several points of the diameter of the mirror, will inevitably lead to a distortion of the shape of its surface when the temperature of the telescope environment.

The proposed method of attaching the mirror gives you the opportunity to get rid of the massive structure and to relieve the mirror of its own weight without any complicated handling fixtures, completely eliminate the decentering of the mirror and to compensate the influence of temperature changes in the process of observation on the shape of its surface.

This is achieved by gluing the mirror to the rim of the Central hole to the support sites of the elastic petals split sleeve, which assumes the function of the element unloading mirror of its own weight and at the same time is a temperature compensator.

The author is not known fastening astronomical mirrors Central hole, through rigidly glued it to the split sleeve, so the proposed method of attaching the mirror has novelty.

The proposed invention illustratesthe in the telescope tube, way to stick it to the rim of the Central hole to the reference sites petals split sleeve;

Fig.2 - interferogram mirror before pasting it split sleeve;

Fig.3 - interferogram mirror after pasting it split sleeve;

Fig. 4 - interferogram mirror glued it split sleeve after local thermal shock in the center.

In Fig.1 shows a structural variant of the fastening astronomical mirror with a Central hole in the tube of the telescope by the proposed method. Mirror 1 is rigidly glued on the rim of the Central hole to the support sites of the elastic petals split sleeve 2, which is connected to the rear flange of the telescope tube 3 through the elements of the spherical hinge 4, 5, serving to align the mirrors.

Explain the possibility of achieving the stated effects on the sample mounting 200 mm main spherical mirror mirror-lens telescope of the proposed method.

The deflection mirror surface, is fixed to the Central hole, from the action of its own weight can be analyzed using the methods described in the literature [3], which discussed the different cases of fixing all of this literature for deflection plane-parallel plate in case it is hard crushing the diameter of the Central hole, you can come to the conclusion that when the hole in the center of the mirror 1/4-1/3 of its diameter deflections of the surface under its own weight will be significantly less than when unloading the rear side of the mirror in a frame [1] six or nine anchor points (with the same thickness of the mirror and its diameter) and, moreover, will be axisymmetric. Ceteris paribus, this reduces the thickness and therefore the weight of the mirror.

If a sufficiently large number of blades and the small gaps between the split sleeve 2, glued reference sites petals to the rim of the Central hole, almost the equivalent of a solid, therefore, can assume the function of unloading the mirror from the action of its own weight, therefore, a need in the casing and discharge devices is eliminated, which simplifies the attachment of the main mirror and reduces its weight.

The rear flange of the telescope 3 Fig.1, on which the mirror Assembly is based spherical joint 4, 5, which serves for alignment, can be made from aluminum alloys (for structure(1) is totally unacceptable due to the large thermal gaps). It also significantly reduces the weight of the attachment point of the main mirror.

the inner diameter of the telescope. This will reduce the pipe diameter to the minimum established by the current aperture and field of view, which again reduces the dimensions and weight of the telescope.

For the totality of all the factors can be considered obosnovannym as an opportunity to offload mirrors rigidly blocked by the adhesive on the split sleeve from its own weight, and is associated with significant structural simplification of the mount mirrors and reducing the weight of the telescope.

Split sleeve also performs the important role of thermal compensator radial forces acting on the mirror when the temperature changes during the observations at the telescope and turning in practically rigid structure after polymerization of the adhesive, stably keeps the mirror from any movement under the influence of transport vibrations or reruns of the pipe.

When the temperature of the environment, as well as in the process of shrinkage of the adhesive in the direction normal to the surface of the pads, elastic petals split sleeve is moved in the radial direction, thereby compensating forces acting on the mirror. It should be emphasized the fact that if Bush was splashing mirrors so practically watch with such a mirror would be impossible. That is why the sleeve is slotted carbon steel (grade 45-60), followed by heat treatment to improve its elasticity.

In order elastic petals bushings themselves had no harmful effects on the shape of the mirror surface, between the surface area of the reference sites, the length and number of blades and the thickness of cross section should be certain ratio, which in complex ways related to the properties of the adhesive and finally established empirically.

If a sufficiently large number of blades bushings (10-12) their cross-section in a plane perpendicular to the axis of the mirror, close to rectangular. Analysis of deflection of the individual petal-rectangular beams [4] allows to conclude that the magnitude of the radial forces transmitted reference area of the petal mirror, is proportional to the cube of the thickness of the cross section of the petal in the radial direction in the bend and inversely proportional to the cube of its length and number of blades. Therefore, the larger the number of blades of the sleeve and their length and less than the thickness of the cross-section of a petal, the less effort petal passes the mirror when radial shrinkage kisou, otherwise possible deformation of the mirror surface due to shrinkage of the adhesive towards the surface of the supporting pad. The contact area of the supporting point of the petal depends mainly on the magnitude of the shrinkage of the adhesive and the thickness of the mirrors in place of the center hole. Therefore, the adhesive must be applied with less shrinkage, at least, as research has shown that less than 3%. Because the mirror must operate in a wide temperature interval without failure of the adhesive, it is necessary to use heat-resistant adhesives, not destroyed at temperatures of up to -60 degrees.

The variation of the surface shape of the mirror is a practical criterion for the applicability of the proposed method of attachment. At all stages of the selection parameters of the split sleeve and glue these changes were controlled by interferometer type Fizeau from the center of curvature of the mirror.

Interferometric testing of mirrors allowed us to establish the optimal combination of parameters of the split sleeve, including heat treatment, and to select suitable brand of glue. The tests were carried out with the main spherical mirror of astromical (SO-M) to 200 mm lens / mirror telescope. The external diameter of the mirror 206 mm Thickness according to cent with quenching to HRC 45-50 kgf/mm

Interferometric measurements of the surface shape determined that in this case the area of the contact pads of the petal split sleeve must not exceed values of the order of one square centimeter when using temperature resistant from -60 to +50 degrees C) adhesives with a degree of shrinkage of about 2%-3% (glue K-300-61 [5], which was tested mirror has a 2% shrinkage). With this mirror, this corresponds to a split sleeve with ten petals.

The rigidity of astronomical mirrors in the radial direction is usually excessive and is such that the permissible radial force applied on the frame of the petal to the rim of the Central hole, comparable with the weight of the mirror, yet does not cause significant deformation of its surface. The latter also tested empirically: the study of form loaded mirror from the center of curvature of the interferometer. The shape of the surface of the mirror with a loaded within its weight center, and suspended on a cylindrical sleeve Central hole, practically does not change.

Thus, by determining the allowable magnitude of the effort on the petal of the split sleeve [4], it is possible to calculate other parameters: the length and thickness of seceratary from -30 to +40 degrees size, obviously not a danger to the surface shape of the mirror. The final parameters of the split sleeve, as discussed above, adjusted on the basis of interferometric testing and found the following: the average length of the petals from the center of the pad to the end of the slot in the sleeve (see Fig.1) is 22 mm, the thickness of the cross section of the petal - 1 mm, number of blades - 10. The gap in the opening between the mirror and the petals of the sleeve not more than 50 μm. Brand glue To 300-61 [5].

In Fig. 2 shows the interferogram mirror in mutually perpendicular directions before pasting it split sleeve. Almost straight shape of interference fringes, and the standard deviation of the wave front from the nearest areas of comparison does not exceed 0,03 (shown in the upper right-hand corner of Fig.2) indicates the high quality mirror surface. In Fig.3 shows the interferogram of the same mirror after pasting it split sleeve and complete polymerization of the adhesive. The standard deviation of the wave front from the nearest areas of comparison in this case amounted to no more than 0.04. This suggests that due to shrinkage of the adhesive surface shape of the mirror has not changed. In Fig.4 shows the interferogram that is so local thermal temperature gradient center-edge about 40-60 degrees. However, the interferogram shows that the shape of the mirror surface practically does not change. From the bottom of the interferogram of Fig. 4 (rings) you can clearly see the absence of astigmatism surface (o-ring). The flow of warm air ahead of the mirror is clearly visible in all the interferograms of Fig.4 and has no relation to the shape of the surface of the mirror.

If inserted into the Central hole of the mirror split sleeve with elastic petals compensates for such apparently large and unrealistic in practical operating conditions, the temperature gradient in a pair of steel-Sitall (when the difference between the coefficients of linear expansion 0,000011), then a relatively small fluid temperature fluctuations occurring in the real observation conditions, moreover, should not affect the shape of the surface of the mirror.

Thus, the above material (see Fig.2, 3, 4) confirms that the inset in the Central hole of the mirror split sleeve when the above ratio between its structural elements does not distort the shape of the mirror surface, including a very significant gradient pace is dialing stress arising at the site of contact of its petals with mirror from temperature changes in the telescope environment.

The rigidity of the mount mirror, locked in the tube of the telescope proposed method was verified indirectly. Carefully aligned the telescope locked on split sleeve mirror (tolerance on rotation of the mirror in the telescope system 40") were subjected to vibrations on the stand with the accelerations of the order of 2g (transport shaking) in a rigid container without absorbers for one hour (for comparison: pipe telescopes of the same class of the American firm "MEADE" transported in containers with dual depreciation and vertical position to reduce harmful transverse components of the vibrations). Quality control image of a point source of light with this telescope after three cycles of vibrations showed that it practically does not change. This suggests that the proposed method of attachment has, among other things, sufficient rigidity and allows you to securely lock the mirror with tolerances on the rotation axis at least 30 to 40 seconds of arc.

Thus, it can be considered proven that the proposed method of attachment allows you to unload SEPA, and to ensure low sensitivity of the instrument to fluctuations in the ambient temperature and vibrations, to which the telescope is exposed during transport and during operation.

LITERATURE

1. Maksutov D. D. Fabrication and study of astronomical optics. - M.: Nauka. CH. nat. Ed.-Mat. lit., 1984, S. 63-87.

2. Michelson N. N. Optical telescopes. Theory and design. - M.: Nauka. CH. nat. Ed.-Mat. lit., 1976, S. 384-401.

3. Timoshenko S. P., voinovski-Krieger S. Plates and shells. - M.: Nauka., 1966, S. 73-79.

4. Yuriev Century. And. Guide designer-mechanical engineer: 3 so, T. 1, 6th ed., revised and enlarged extra - M.: Mashinostroenie, 1982. - S. 64-85.

5. OST B6-5-5100-77 Glue-300-61".

1. Mounting method astronomical mirror with a Central hole in the tube of the telescope, namely, that allows to unload the mirror without complicated handling devices, characterized in that the mirror is glued to the rim of the Central hole to the support sites of the elastic petals split sleeve.

2. Mounting method under item 1, characterized in that the gluing produce heat-resistant adhesive with a degree of shrinkage of not more than 3%, and a split sleeve made of coal

 

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