RU2505783C2 - Method of measuring small dimensions objects with unequal ends and interferograms based on photoelectric receiver - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: object image is recorded on slide and magnified by projecting to screen by slide projector. Size of obtained image is defined in relative units, ie electric pulses with preliminary calibration and subsequent conversion of the pulse train into metric units of length. Train of pulses is generated by switching counters ON and OFF. Signal to actuate said counters is fed regularly by photodiode displacing over the screen depending upon crossing white and black shades thereat. Obtained info is transmitted to computer for processing.

EFFECT: higher precision.

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Description

The invention relates to methods for measuring objects with small sizes, of the order of tens and hundreds of microns, with uneven edges, followed by computer processing of the measurement results. The purpose of the invention is the determination of the size of objects with uneven edges and bandwidths of interferograms.

The proposed method allows to increase the accuracy of measurement of the object and automatically determine the reference point with a blurry edge of the measurement object with subsequent computer processing of the measurement results. The principle of the technique is that the measured object is photographed with a microscope and the image of the measured object printed on the photo slide is projected using a slide projector onto the screen. Moreover, the ratio of the true size of an object to its image on a slide is easily determined by the magnification scale of the microscope. To determine the magnification scale of an object when projecting it onto the screen, the image is calibrated using a slide with an image of an object with previously known dimensions, for example, a strip with even edges 1 mm wide.

One of the particular solutions to this problem is to measure the width of the interference fringes obtained as a result of optical experiments. In this case, all interference fringes being the object of measurement have blurry edges. The installation includes:

1. A slide projector where a slide with a photographic frame of the developed image is inserted.

2. The screen where this frame is projected.

3. A photodiode that moves uniformly across the screen, meeting on its way an alternation of light and dark tones.

4. Two electric pulse counters with digital printing, one of which turns on and counts electric pulses when the LED moves, for example, in light tone and turns off when the photodiode enters the dark tone region. The other counter, on the contrary, turns on and counts electrical pulses when the photodiode enters the dark tone region and turns off when the photodiode enters the light tone region, as well as the elements shown in Fig. 1.

The preset is calibrated, i.e. a certain unit of length on a photographic slide must correspond to a certain number of pulses.

The block diagram of the installation is shown in Fig. 1.

One of the features of this technique is that the width of the measured object, in this case the interference band, is measured in relative units-pulses recorded on the screen of the recounting device when the device turns on and starts to read pulses by the signal from the photodiode.

Thus, the accuracy of measuring the width of the bands is significantly increased due to the fact that the pulse repetition rate and the passage time of the light and dark bands by the photodiode can be varied over a wide range.

After that, the result of measuring the bandwidth in the number of pulses is converted, in accordance with the calibration, into length units - mm or μm.

Another feature of this technique is that the photodiode automatically responds to the degree of darkening of the strip, i.e. he himself selects the reference point of the bandwidth, sending a signal to the recounting device. Thus, the problem of blurring the strip when the transition of a dark tone to a light one and vice versa is solved. After processing the measurement results using a computer on the monitor, an image of the interference pattern with sharp boundaries of the transition of light and dark tones is obtained.

Figure 2 shows the electrical schematic diagram of the device for starting and stopping the recalculation devices with PSO signals from the PD-1 photodiode when it passes through the dark and light bands of the interference pattern obtained on the photo slide.

The method is illustrated by an example.

Take a photo slide with the image of interference fringes. The borders of the bands when switching from light to dark have an unclear, blurry structure. The slide is inserted into the slide projector and projected onto the screen. For calibration, a slide with an image of a 1 mm wide strip with a clear transition from light to dark is inserted into the slide projector for calibration. Photodiode FD-1 moves uniformly on the screen, alternately crossing the boundaries of dark and light tones. When passing through the dark region, there is no signal from the photodiode; when passing through the bright region, an electrical signal is received from the photodiode.

The signal from the PD-1 photodiode is amplified by operational amplifiers 140 UD 6 and is fed to the input of the 155 TL 3 chip, which includes two Schmitt triggers with an element at input 4 AND-NOT. The signals from the two outputs of the MS goes directly to the inputs of the pulse counters of the PSO, previously amplified by amplifiers assembled on transistors K 361. The signals from the other two outputs of the MS 155 TL 3 are fed to the inputs of the MS 155 LA 3, which includes four AND 2 NOT elements and after that they arrive, preliminary amplifying, at the inputs of the pulse counter counters. This is done so that in the presence of a signal from the photodiode, the first PSO is turned on and starts to count pulses, and the second is turned off. And vice versa - in the absence of a signal from the photodiode, the first PSO turned off and finished counting pulses, and the second turned on and began to count pulses. When the calibration slide is projected onto the screen and the pulse counter is turned on when the photodiode passes the border of dark and light tones, the number of pulses corresponding to the bandwidth of 1 mm on the photographic slide is set. Thus, the coefficient for the recount is determined - the number of pulses per unit length. In accordance with the block diagram shown in Fig. 1, information from the PSO conversion devices enters the computer, where it is processed and, in accordance with the program, a signal is sent from the computer to reset the displays of the conversion devices for a new pulse count when the photodiode passes the next dark and light border tones. Thus, as the photodiode moves uniformly across the screen, the computer receives information about the width of the interference fringes projected onto the screen.

BIBLIOGRAPHY

1. P. Horowitz, W. Hill. The art of circuitry // Moscow, "Mir", 1986.

2. B.I. Yudin. Calculation of the gradient profile of the distribution of the refractive index of a given shape in optical elements made of glass to improve their optical parameters. // Devices and systems. Management, control, diagnostics. B.2, 2008, S. 27-29.

3. S.F. Griliches, V.G. Ilyin, M.N. Polyansky. Interactive change of parameters of gradient optics elements. // Sat scientific tr Tula: Tula Polytechnic Institute. 1980. S. 3-6.

Claims (1)

A method of measuring small objects with uneven edges and interferograms based on photoelectric radiation detectors, characterized in that, in order to increase the accuracy of measurements of these objects, their image obtained on a photo slide and projected onto a screen is measured in relative units - electrical pulses with preliminary calibration and the subsequent conversion of the number of pulses into metric units of length.

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