Method of determining irregularity of thermal expansion coefficient

FIELD: measuring engineering.

SUBSTANCE: method comprises manufacturing articles from various parts of the blanc, measuring their temperature elongation with the use of the interferometric dilatometer, and determining characteristics of irregularity of temperature coefficient of linear expansion. The characteristics of irregularity are determined by comparing the results of measurements for individual objects. The bottom reflecting member of the interferometer is made of the blank to be studied so that it has bearing face, reflecting surface, and height less than that of the blank. The bottom reflecting member and blank bear on the single plane by their bearing faces.

EFFECT: enhanced accuracy.

3 cl, 3 dwg

 

The invention relates to the field of study of the physical properties of materials, in particular for determining the inhomogeneity of the temperature coefficient of linear expansion (TCLE) billets of solid materials. The invention can be used to determine the heterogeneity of thermal expansion of optical workpieces, including blanks from Malorossiya optical materials (such as sically), intended for the production of large mirrors for astronomical telescopes.

There is a method of determining the heterogeneity of thermal expansion of the optical workpiece, in which several different parts of the investigated billet made samples, measure the absolute value of the linear thermal expansion coefficient of these samples and determine the characteristics of heterogeneity TCLE by comparing the measurement results obtained for individual samples, according to the method of the absolute value of the linear thermal expansion coefficient of the samples was measured using a quartz Electromechanical dilatometer. (A review of measurement systems for evaluating thermal expansion homogeneity of Corning Code 7971 ULETM/Proc. SPIE Vol.1533, 1991, p.201-202.)

The main drawback of this method is the low accuracy of the measurement because of the significant dependence of the readings from the temperature regime of the quartz rod used in the dilatometer.

Known interference measurement method absolute TCLE specimen is, when using a dilatometer containing the interferometer is a Fizeau type, formed by two surfaces of the reflective elements placed together with the sample in a furnace thermostat, with this dilatometer contains the sample holder from a material with known TCP, and the lower reflecting surface of the interferometer is rigidly connected with the holder, and the top has contact with the holder and with the sample mounted in the holder and resting on a wedge-shaped adjustment plate (Patent RF №2089890, CL G 02 In 25/16, G 01 B 9/02, epubl).

The accuracy of measurement with the use of such a device is insufficient, because the measurement is based on the change of the angle between the reflecting surfaces of the Fizeau interferometer that does not provide high sensitivity to the linear expansion of the sample, in addition, implemented in it the principle of interference measurement based on determining the change in the period of interference fringes, the accuracy of which depends substantially on the quality of manufacture of the reflecting surfaces of the interferometer.

There is a method of determining the heterogeneity of thermal expansion of the optical preform, selected as a prototype, in which several different parts of the investigated billet made samples, each of which has two supporting end, placed in a thermostat sample and two neg is gateljnykh element (top and bottom) to the reflective surface of these elements formed the interferometer is a Fizeau type, contacting with the corresponding reference sides of the sample, cover these elements parallel beam of coherent monochromatic radiation, the changes of temperature in thermostat, register picture of the interference bands, simultaneously measure the temperature in thermostat, determine the change of coordinates of interference fringes depending on temperature changes, repeat consistently all the described measurement procedure for each of the samples and determine the characteristics of heterogeneity TCLE by comparing the measurement results obtained for individual samples. (A review of measurement systems for evaluating thermal expansion homogeneity of Corning Code 7971 ULETM/Proc. SPIE Vol.1533, 1991 pp.199-201.)

The main disadvantage of this method is not sufficiently high measurement accuracy. The main components of the error are the error in the determination of length change of the sample (elongation), which is greater, the greater the optical path difference of the interfering beams, and the measurement error of the temperature, the contribution of which to the total measurement error is proportional to the change in the stroke difference of the interfering beams. In the specified way, the path difference of the interfering beams is determined by the length of the sample, which should be sufficient what about the large to provide the necessary sensitivity control.

The purpose of this invention is to provide such a method for determining the heterogeneity of thermal expansion of the optical workpiece, having a high sensitivity, would increase the accuracy of the measurement.

The technical result due to such aim is achieved in that in the known interference method for determining the heterogeneity of thermal expansion of the optical workpiece, in which several different parts of the investigated billet made samples, each of which has two supporting end, placed in a thermostat sample and two reflective elements (top and bottom) so that the reflective surface of these elements formed the interferometer is a Fizeau type, and the reflecting surface of the upper reflective element rested on the top bearing face of the sample, cover these elements parallel beam of coherent monochromatic radiation, the changes of temperature in thermostat, register picture of the interference bands, simultaneously measure the temperature in thermostat, determine the change of coordinates of interference fringes depending on temperature change, consistently repeat all the above procedure for each of the samples and determine the characteristics and heterogeneity of thermal expansion of the workpiece by comparing the measurement results obtained daudelin samples according to the invention the lower reflective element is made directly from the study of the workpiece so that it had a lower support end and an upper reflective surface and a height slightly less than the height of the sample, with the specified reflective element and the sample set of the lower support ends on a single base flat surface.

It is advisable TCLE lower reflective element pre-measured one of the known methods.

It is advisable to make a few lower reflective elements from several different sites investigated workpiece and the entire measurement procedure is repeated sequentially for each of the reflective element, while thermal expansion of the sample pre-measured one of the known methods.

Suitable lower reflective element and the sample is placed coaxially one inside the other.

The manufacture of the lower reflective element directly from the study of the workpiece so that it had a lower support end and an upper reflective surface and a height slightly less than the height of the sample, and setting the specified reflective element and sample the lower support ends on a single base flat surface allow, without reducing the sensitivity of the control to increase the measurement accuracy due to reduce the possible error of measurement of elongation and reduction of influence of the error of temperature measurement.

A preliminary measurement of the linear thermal expansion coefficient of the lower reflective element allows you to adjust for the difference of the lengths of the samples in the measurement result, which provides an opportunity to expand the tolerance on the length of the sample and to increase the accuracy of the measurement.

The production of several lower reflective elements from several different sites investigated workpiece and repeat the entire measurement procedure sequentially for each reflective element, and a preliminary measurement at this TCLE sample one of the famous ways you can simplify the measurement procedure by reducing the number of additional measuring devices.

The coaxial arrangement of the lower reflective element and sample one inside the other can reduce the likelihood of the measurement system unbalanced temperature gradients, leading to less accurate measurements.

Figure 1 depicts the scheme of the device used (interference dilatometer) and an option of placing it lower reflective element and the sample according to the invention.

Figure 2 depicts a parallel mutual arrangement of the lower reflective element and sample.

Figure 3 depicts a possible variant coaxial relative position of the lower reflective cell battery (included) is that of the sample.

To implement the proposed method uses the well-known interference dilatometer (Fig 1), including thermostat 1, the control device and temperature control 2, laser 3, the optical system 4, a bottom 5 and the top 6 of the reflective elements and a device for the recording of the interference pattern 7. At the bottom of thermostat installed quartz plate for placement on its base flat surface 8 of the lower reflective element 5 and the sample 9. Instead of the base plate surface can serve as the bottom of thermostat, manufactured with the required flatness.

The main variant of the proposed method for determining heterogeneity (TCLE) optical preform is carried out as follows. From several different areas of the investigated optical preform is made samples, each of which has two supporting end (flat or with three tabs). Directly from the inspected workpiece also produce the item, which is the lower reflector of the interferometer type Fizeau and has a lower bearing face (flat or with three projections) and the upper reflecting surface. The parts of the blank of which make these items should be distributed more evenly over the volume of the studied workpiece and, as a rule, are located within the dimensional allowances material is Ki; thus, in particular, for the manufacture of these parts can be used pieces of material remaining at hole drilling facilitate large astronomcal. Then mentioned the lower reflective element, and the upper reflective element of the Fizeau interferometer and one of the samples is placed in a thermostat, having them on a single polished flat base surface as shown in figure 2. The lower reflective element 5 install the lower bearing end on the polished flat base surface 8. Near this element on the same surface (lower anchor end) set the sample 9. On the top bearing face of the sample set top reflective element 6. Mutual arrangement of elements is such that the lower (reflecting) surface of the upper reflective element supported on the upper supporting face of the sample 9, and the upper (reflecting) surface of the lower reflective element form an interferometer type Fizeau, that is, the reflective surface is flat and wedge-shaped gap between them. The height of the lower reflective element is made just below the height of the support element, the minimum gap between them must be greater than the maximum possible difference between the movements of the lower reflective and supporting elements. To ensure klinovidnoj the gap enough to one of the elements 5 or 6 was made wedge-shaped, and the other plane. The reflective surface parallel light beam of coherent monochromatic radiation and get a picture of the interference fringes of equal thickness. Usually a wedge between reflectors in the interferometer type Fizeau do so within the field of interference was observed 5-10 interference fringes. The obtained interference pattern recorded one of the known methods and determine the coordinates of the interference fringes (for example, by way of visual observation, film or photographic recording or television reception with subsequent digitization and transmission of digital video images in the computer). To determine the desired characteristics of thermal expansion, the temperature in thermostat change within a given range and produce simultaneous measurement of temperature in thermostat and determining the change in the coordinates of interference fringes depending on the temperature. Such measurements are performed sequentially for each of the samples. The measured change the coordinates of the interference fringes ΔN, expressed in fractions interferentsionnoi strip in the temperature range ΔT is equal to:

where λ is the wavelength of the used radiation;

l is the length of the were acquired;

Δα=α-α0the difference TCLE α sample 3 and TCLE α0the lower reflective element 1;

Δl is the dierence between the lengths of the sample 3 and the reflective element 1.

For example, if all samples have the same length l, and the assessment of heterogeneity TCLE, characterized by a difference of thermal expansion in different parts of the investigated workpiece is defined as:

where δ(α) - the difference in thermal expansion of two different sections of the investigated workpiece;

δ(ΔN) is the dierence between the changes of coordinates of interference fringes obtained for the two corresponding samples in the temperature range ΔT;

l is the length of the sample.

According to the measurements can be calculated main values, which are indicators of heterogeneity, such as the maximum difference between the linear thermal expansion coefficient within the workpiece, the maximum deviation of the linear thermal expansion coefficient of the average procurement, standard deviation TCLE etc.

Technical effects of the invention consists in the following. In the method of determining the heterogeneity of thermal expansion of the optical preform, selected as a prototype, the measurement error of the difference of the linear thermal expansion coefficient at two points of the workpiece is determined by the measurement error TCLE single sample. In the proposed method the difference of thermal expansion in two different areas of the workpiece is determined by the results sravnenie the difference of the movements of the samples and the lower reflective element. Since the maximum difference between the linear thermal expansion coefficient within the workpiece, typically has a value one order of magnitude smaller than the average value of thermal expansion of the workpiece, the proposed method achieved a significant decrease in the influence of the error of temperature measurement in comparison with the method of the prototype. Another advantage of the proposed method lies in the possibility to significantly reduce the gap between the plates of the Fizeau interferometer, thereby reducing the difference of optical paths of the interfering beams beams without reducing the length of the specimen. This allows, without reducing the sensitivity of the control, significantly reduce the impact on the measurement accuracy of a number of factors leading to the decrease of measurement accuracy and increase the error of elongation. When the interference measurement plays a significant role the error caused by the instability wavelength, the sources of which are the instability of the frequency of radiation used in radiation source (laser), and changes the refractive index of the medium in which the radiation propagates. If the measurements are performed in air or in a shallow vacuum, when the temperature inside thermostat will change the refractive index of air. This change is extremely difficult to consider, because the refractive index is Suha is a function not only of temperature, but also pressure, humidity, percentage of different gases and other impurities. The range of dispersion of counts elongation due to the instability wavelength is directly proportional to the difference of progress of the interfering beams of rays (the distance between the mirrors of the interferometer is a Fizeau). In the method, selected as a prototype, this distance is determined by the length of the sample, but reducing the length of the sample leads to a reduction of sensitivity control, it increases the influence of the error of measurement of the elongation on the accuracy of the measurements. In the proposed method can be provided with extremely small values of the magnitude of the difference of the stroke of the interfering beams (up to hundredths of a millimeter) regardless of the length of the sample (it only needs to be greater than the maximum possible difference between the movements of the lower reflective element and the sample), which can significantly reduce the impact of the instability wavelength. In addition, in the interferometer of the type Fizeau possible deformation of the light wave light beam lead to the curvature of the fringes of an interference pattern that is recorded on the accuracy of the coordinates of the bands. This curvature is also proportional to the difference of progress of the interfering beams of rays. Thus, reducing this difference, reduce the impact of possible curvature of the bands caused by aberrations and rasfokusirovka the optical system.

In the proposed method TCLE lower reflective element pre-measured one of the known methods. This measurement can be performed, for example, by means of quartz dilatometer.

Technical effects of the invention consists in the following. If the samples (due to technological limitations) have different lengths, the difference in thermal expansion of two different sections of the investigated workpiece, which correspond to the two sample difference of lengths δl, can be expressed by the formula:

where δ(α) - the difference in thermal expansion of two different sections of the investigated workpiece;

δ(ΔN) is the dierence between the changes of coordinates of interference fringes obtained for the two corresponding samples in the temperature range ΔT;

λ is the wavelength of the used radiation;

l is the nominal length of the sample;

δl is the dierence between the lengths of samples;

α0- TCLE lower reflective element.

If the value of δl is large enough compared with the nominal sample length l, then it is necessary to consider its contribution in accordance with formula (3), for which it is necessary to know the value α0. Measuring pre α0may make the appropriate amendment to the measurement result, which provides the possibility of expanding the tolerance on the length of the sample.

Additional the technical effect consists in the possibility of determining the absolute value of the linear thermal expansion coefficient in each controlled point blank.

For the amendment can, on the contrary, pre-measure the linear thermal expansion coefficient of the sample (enough to produce and control only one sample), and to study the difference of thermal expansion in different areas of the workpiece should be made for each of these parts of the lower reflective element and sequentially execute the procedure of measuring the differential movements of the sample and the lower reflective element for each custom reflective element.

The technical effect of the invention is that to determine the linear thermal expansion coefficient of the sample does not require additional device because its configuration allows you to determine the linear thermal expansion coefficient of the interference method.

In the proposed method the sample 9 and the lower reflective element 5 have coaxially one inside the other. In one of these elements is made through the Central hole for the location therein of another element. Variants of this location are illustrated in figure 3, where the lower reflective element 5 is located inside the sample 9 and in figure 1, where the sample 9 is located within the reflective element 5.

The technical effect of the invention is that the coaxial mutual arrangement of these elements can reduce the likelihood of these elements unbalanced temperature is different gradients, leading to uncontrolled distortion of the reflecting surfaces of the Fizeau interferometer associated with these elements, which causes a noise change of coordinates of the interference fringes, which reduces the measurement accuracy.

Practical use of the method confirmed its reliability, efficiency and high accuracy of measurement.

1. The way to determine the inhomogeneity of the temperature coefficient of linear expansion of the optical workpiece, in which several different parts of the investigated billet made samples, each of which has two supporting end, placed in a thermostat sample and two reflective elements (top and bottom) so that the reflective surface of these elements formed the interferometer is a Fizeau type, and the reflecting surface of the upper reflective element rested on the top bearing face of the sample, cover these elements parallel beam of coherent monochromatic radiation, the changes of temperature in thermostat, register picture of the interference bands, simultaneously measure the temperature in thermostat, determine the change of coordinates of interference fringes based from temperature changes, consistently repeat all the above procedure for each of the samples and determine the characteristics podnar is gnosti temperature coefficient of linear expansion of the workpiece by comparing the measurement results, obtained for individual samples, wherein the lower reflective element is made directly from the study of the workpiece so that it had a lower support end and an upper reflective surface and a height slightly less than the height of the sample, with the specified reflective element and the sample set of the lower support ends on a single base flat surface.

2. The method according to claim 1, characterized in that the temperature coefficient of linear expansion lower reflective element pre-measured one of the known methods.

3. The method according to claim 1, characterized in that made several of the lower reflective elements from several different sites investigated workpiece and the entire measurement procedure is repeated sequentially for each of the reflective element, the temperature coefficient of linear expansion of the sample pre-measured one of the known methods.

4. The method according to any one of claims 1 to 3, characterized in that the lower reflective element and the sample feature coaxially one inside the other.



 

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FIELD: measuring engineering.

SUBSTANCE: method comprises manufacturing articles from various parts of the blanc, measuring their temperature elongation with the use of the interferometric dilatometer, and determining characteristics of irregularity of temperature coefficient of linear expansion. The characteristics of irregularity are determined by comparing the results of measurements for individual objects. The bottom reflecting member of the interferometer is made of the blank to be studied so that it has bearing face, reflecting surface, and height less than that of the blank. The bottom reflecting member and blank bear on the single plane by their bearing faces.

EFFECT: enhanced accuracy.

3 cl, 3 dwg

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EFFECT: provides creation of a new portable microscope.

2 cl, 2 dwg

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15 cl, 2 dwg

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EFFECT: possibility to measure coefficient of thermal expansion of film specimens.

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