SU794373A2 - Apparatus for measuring twisting angles - Google Patents

Description

one

The invention relates to geodetic instrumentation, in particular to geodetic instruments for measuring torsion angles.

According to the main author. St. No. 5,69849, a device for measuring torsion angles is known, comprising a pickup transceiver consisting of an illuminator, an autocollimation telescopic system, an optical divider for spatial separation of the transmitting and receiving channels, the analyzer-modulator and the photodetector. An angular measuring sensor, located coaxially with the transceiver and mounted on the object, consists of a phase plate and a mirror-lens reflector. The electronic unit includes a narrowband amplifier, a generator, a phase detector and an indicator.

However, the absence of a compensating unit in the circuit of the device leads to a pestable operation of the device, to amplitude-phase errors, to nonlinearity and instability of the output characteristic and to an increase in the systematic error and, therefore, reduces the accuracy of measurement.

The aim of the invention is to increase the accuracy of the measurement of the twist angles.

This is achieved by introducing a modulator-compensator, a matching transformer, a constant voltage source and a bias regulator into the device, with a modulator-compensator consisting of an electro-optical crystal and two quarter-wave plates located between the radiator and the optical divider. connected through a matching transformer to the generator and through the winding of the transformer to a constant voltage source, the output of which is connected to the indicator, and the input connected to the bias regulator, connected to the phase detector.

FIG. 1 depicts functional

device layout; pas figs. 2 shows the angular dependences of the rotation of the vector of preferential polarization on the rotation of the angle-measuring sensor and the compensation rotation.

The device contains a transceiver 1 and an angle-measuring sensor 2 mounted on the object to be measured 3. The transceiver contains an illuminator 4 (for example, a laser), a compensator-to-compensator modulator, including a quarter-wave plate 5, the main axis of which is located at an angle of 45 ° to the X axis, an electro-optical crystal 6 (for example, ADP, KDP, LN) and a quarter-wave plate 7, the main axis of which is angled

-45 ° to the X axis, an optical divider 8 dividing the transmitting and receiving channels, and a telescopic system 9. The angle measuring sensor receiving and transmitting radiation contains a quarter-wave plate 10, the main axis of which is located at an angle of 45 ° to the X axis , a lens 11 and a reflective mirror 12, rigidly fixed in one case.

The receiving channel of the transceiver is formed by an analyzer 13 analyzing the polarization plane of the incoming radiation and the photoreceiver 14. The photoreceiver is connected via a narrowband amplifier 15 to the signal input of the phase detector 16, the output of which is connected to a bias regulator 17 connected to a constant voltage source 18, one of the outputs of which is connected to the indicator 19, and the other through the secondary winding of the transformer 20 is connected to an electro-optical crystal. The secondary winding of the transformer 20 is connected to one of the outputs of the generator 21, the other output of which is connected to the reference input of the phase detector.

The device works as follows.

The radiation source 4 sends a beam of linearly polarized light with a polarization azimuth of 6 0 (i.e., the vector of preferential oscillations E is directed along the X axis). A beam of light falls on the phase quarter-wave plate 5. After its passage, the light becomes circularly polarized and, passing through the electro-optical crystal b, is converted by the phase quarter-wave plate 7 into linearly polarized light with azimuth. Having passed the optical divider 8, the light beam is collimated by the telescopic system 9 and after passing the distance L falls on the phase quarter-wave plate 10 of the angle measuring sensor 2. Pass the objective 11 and reflected from the mirror 12, the secondary beam goes back through the objective and the phase quarter-wave plate in reverse. The beam coming out of the sensor will be linearly polarized with an azimuth of Y 90 ° (i.e., the vector of preferential oscillations p is directed along the Y axis), since the sum of two quarter-wave phase plates with the same direction of the main axes works as a half-wave phase plate. Passing the distance L in the reverse direction, the light beam is transformed by the telescopic system and, reflected from the optical divider, enters the analyzer 13, the azimuth of the plane of maximum transmission of which is angled, i.e. its plane of maximum transmission is perpendicular to the plane of oscillation of the incoming linearly field light. Therefore, the intensity of the incoming to the photodetector

14 light is zero. If the object to be measured 3, together with the angle measuring sensor 2, is rotated by an angle ± P (see Fig. 2), the azimuth of the linearly polarized light will change, and hence the intensity of the light incident on the photodetector. Based on the condition that, for a half-wave plate, the angles between the main axis of the plate and the input and output

vectors are equal, the angle of rotation of azimuth p is determined as follows:

R ± P + + 45 ° -90 ° ± p + (1)

R ± 2p. (2)

The operation of the device can be described by the following expression;

/ | / o l-COs 24 / -. a ° 7 X

CL ± 4,

(3)

light intensity on the photodetector;

light intensity of the radiation source;

9-Зг (oSin ± к) / - U

- phase difference between ordinary and extraordinary rays;

Po is the index of refraction of the ordinary ray;

22 is the electro-optical coefficient; d is the thickness of the crystal along the applied electric field; / is the optical path length of the light in the crystal;

t / o is the amplitude of the applied modulated voltage; W is the modulation frequency; UK is the compensating voltage. In the device, the modulation and compensation of the angle of rotation of the sensor are performed using an electro-optical crystal. When an alternating sinusoidal voltage is applied to it from the generator 21 through the matching transformer 20, it will change, which will change the light with circular polarization to the electro-optical crystal 6 after the quarter-wave plate 5, into the elliptical polarization after the crystal. At the same time, depending on the half-wave of the sinusoidal voltage, the large axis of the ellipse will oscillate, occupying the position + 45 ° or -45 °. After passing through the phase quarter-wave plate 7, the elliptical polarization light turns into linearly polarized light, since the azimuths of the main axes of the quarter-wave phase plate 7 fully correspond to the azimuths of the axes of the ellipse. Consequently, at the output of the modulator-compensator, there will be a linearly polarized light, the azimuth of which will oscillate synchronously with the alternating voltage relative to the zero (7 0) position. In this case, if the angle of rotation of the angle sensor, a signal is removed from the photodetector at frequency 2 (o. If the signal is removed at frequency ω, the phase of which depends on the direction of rotation of the angle measuring sensor, and the signal amplitude depends on the angle ip. The signal from the photoreceiver is applied to a narrowband amplifier 15 amplifying and transmitting oscillation at a frequency ω to the phase detector 16. A constant alternating signal from the output of the phase detector is fed to the bias regulator 17, which controls the input of the constant-voltage source 18. From one of the outputs of the constant bias source, the voltage UK, proportional to the angle of rotation of the angle measuring sensor, is applied to the electro-optical crystal and the phase difference b is changed so that the vector of linearly polarized light coming out of the compensator modulator is rotated angle and compensates for the angle of rotation of the angle sensor. Thus, a signal appears on the photodetector

frequency 2y), and on the indicator connected to the other output of the constant bias source, the voltage value is equal to UK, the sign of which will depend on the direction of rotation of the angle measuring sensor. The pre-measured value of the voltage t / k will be proportional to the angle of rotation of the angle-measuring sensor, and therefore the angle of rotation of the object.

Claims (1)

Invention Formula Device for measuring torsion angles by ed. St. No. 569849, characterized in that, in order to improve measurement accuracy, a modulator-compensator, a matching transformer, a constant voltage source and a bias regulator are introduced into it, with a modulator-compensator consisting of an electro-optical crystal and two phase quarter-wave plates and located between the emitter and the optical divider, connected through a matching transformer to the generator and through the transformer winding to a constant voltage source, the output of which is connected to the indicator, and the input is connected to the bias regulator connected to the phase detector. St Jn Phage. g