The way to increase the measurement accuracy of the laser interferometer
The invention relates to methods of measurement, in particular measurements of the distance produced by using a laser interferometer (1, 2). The method according to this invention is the determination of the temperature along the entire path of the laser beam 3 emitted from the laser interferometer by measuring the speed of sound 5, passing through the same path, and use these values to calculate the dependent temperature correction to the measured value, in particular the measured distance. The technical result is to increase the accuracy of measurements. 8 C.p. f-crystals, 3 ill.
The object of this invention is a method of increasing the measurement accuracy, in particular measurements of the distance produced by using a laser interferometer.
In cases where the required high accuracy of measurements, for example in mechanical engineering, for measuring the distance of the applied laser interferometers, as they provide greater accuracy than other methods. However, the accuracy of the laser interferometer depends on various factors such as the dependence of the wavelength of the laser beam from the coefficient rotten the Ana on the wavelength of light, knowledge of the refractive index of the medium is crucial to achieve sufficiently accurate results. In practice, the environment for such measurements is air, the refractive index of which is a function of pressure, temperature and humidity, and concentrations of gases such as carbon dioxide, in the air. The temperature varies significantly due to the rapid and continuous movement of air masses caused by temperature differences between the different points of measurement, as well as due to aerodynamic effects. Due to changes in air temperature integrated value of instantaneous temperature along the path of the laser beam of the laser interferometer can not be accurately measured using thermometers, currently used in laser interferometry.
In laser interferometers available on the market, the refractive index of air is determined by measuring the above quantities in the air and then evaluated their influence on the wavelength. For this purpose, the laser interferometers currently in use, are equipped with sensors for measuring temperature and air pressure, and sometimes also and humidity sensors. Usually ustanavlivaetsya time based on the fact that the sensor receives ambient air temperature. These thermometers measure the temperature at specific points near the beam. These thermometers can measure temperature at each point of the space along the entire path of the laser beam as required in reality. Another disadvantage is that due to the inertia of the currently known temperature sensors, laser interferometers, the measurement results are always behind the instantaneous values of the temperature at each point where the measurement is carried out. As a consequence, such measuring devices can only measure temperature, integrated in a particular time period and only at certain points; they are not able to measure the ever-changing instant temperatures. The use of such a measurement method, which is able to measure the temperature at specific points and also with high inertia, and the adoption of the measured thus temperature values as the integral of the instantaneous temperature of the entire trajectory of the laser beam that is causing the most significant error of all errors that affect precision the Oia measurement accuracy of the laser interferometer, allowing inexpensive means to ensure the effective accounting of the instantaneous temperature changes of the air along the path of the laser beam of the laser interferometer.
The problem is solved in that way improve the accuracy of distance measurements with a laser interferometer, to determine the influence of temperature on the laser beam emitted by the laser interferometer, the path of the laser beam between the interferometer and retroreflector laser interferometer by measuring the speed of sound at the specified path of the laser beam, the speed of sound is measured simultaneously with the measurement of the distance, and calculate the temperature-dependent air amendment to the distance value using the measured values of the speed of sound.
It is advisable to determine the speed of sound to do with the application used for this calculation the values of the distance, which is measured by a laser interferometer.
To further enhance the accuracy of determining the distance should be taken into account in computing the corrections to the measured value of the distance effect, at least one of the following factors: air pressure, relative humidity, gas concentration, temperature gradi is the speed of sound waves, when they pass in both opposite directions along the path of the laser beam between the interferometer and retroreflector a laser interferometer.
Reasonable speed of sound measured with at least one pair of emitters/receivers, sound waves, are installed respectively on the interferometer and retroreflector a laser interferometer, each emitter/receiver can alternately emit and receive sound waves. While the emitters/receivers sound waves of the pair are set so that the path of propagation of sound waves between them is parallel to the defined path of the laser beam and as close as possible to the emitters/receivers do not interfere with the normal functioning of a laser interferometer, and the path length of sound waves varies identically with the path length of the laser beam by the mutual displacement of the interferometer and retroreflector.
It is advisable to account for the influence of temperature deviations in the direction perpendicular to the specified path of the laser beam, the speed of sound to measure using at least two pairs of emitters/receivers and emitters/receivers of each pair ustanavlivaetsya the specified path of the laser beam.
It is advisable the use of directional emitters/receivers sound with the corner solution of the beam 5-8 degrees to provide noise immunity when measuring large distances.
Also to improve noise immunity, it is advisable to use the emitters/receivers of ultrasonic frequency range.
The method according to the present invention includes the determination of the values of the temperature of the air path of the laser beam of the laser interferometer by measuring the speed of sound passing through the same path, and use the resulting values to calculate the temperature-dependent corrections to the measured distance value. The expression "the same way" means in this case that the sound waves and waves of laser light emanate from the same point, or in practice, from closely spaced points and arrive at the same point, or in practice, in closely spaced points, and that these waves propagate at the same time. The amendment to the measurements made by the laser interferometer can be calculated by the value of the air temperature. This method gives accurate representation of the instantaneous values of air temperature, integrated along the entire paragraph is In the preferred implementation, the speed of sound is determined using the values of the distance measured by the laser interferometer simultaneously with the measurement of the speed of sound. When applying the method according to this invention, the accuracy of measurements made with a laser interferometer is significantly increased. The described method can be applied to commercially available laser interferometers without changes or modifications, and equipment that implements this invention can also be installed on them. Moreover, the method and the equipment is simple and inexpensive to implement, and the cost of production and use of small equipment.
The invention is based on the phenomenon that, as known from the wave theory of light, the refractive index of the medium (in practice, air), which affects the wavelength of the laser beam and the speed of sound in air, is known from theory of acoustics, depend on the same properties of air, namely pressure, temperature, humidity and the concentration of carbon dioxide, and therefore known to relate to each other. Another advantage of the invention is that the sound waves do not interfere with the light beam of the laser emitted from a laser interferometer that makes it possible for sound waves and the laser beam to pass through the same path at the same time. Thus, the instantaneous changes of properties vozle the impact of changes temperature more than 1000 times stronger effect on the speed of sound, than the refractive index of air, it is possible to achieve very accurate measurements.
The method according to this invention provides that the determination of the corrections to the measurement results of the distance-dependent temperature on the entire path of the laser beam, which is obtained by using a laser interferometer, based on the fact that when sound waves pass through the air on the same path with the laser beam, the instantaneous temperature at each point of this path affect the velocity of the sound wave. The time required by the sound wave to pass through the air is inversely proportional to the integral of the instantaneous temperature in the path of the sound wave. In addition to air temperature, the speed of sound depends on other factors, which influence in the tens or hundreds of times smaller than the influence of temperature. These factors have a relatively uniform effect on the properties of air throughout the space, in contrast to air temperature, which differs significantly from point to point and varies over time. These factors include humidity, air pressure, and concentrations of various gases, such as carbon dioxide.
Another advantage of the invented method of measuring actorii laser beam is only a time want sound waves to pass this way. This is a significant difference and outstanding principal advantage of the proposed method in comparison with currently used in laser interferometers slow thermometers.
In the preferred implementation of this invention, the emitters and receivers of acoustic waves are arranged on a laser interferometer or near to it so that the trajectory and the axis of the laser beam and the acoustic waves are as close as possible to each other, and the sound waves are propagated in parallel and symmetrically located relative to the laser beam paths. To reduce measurement errors.
Hereinafter the invention will be described in more detail with reference to the accompanying drawings, in which
Fig.1 shows a block diagram of the measuring device that implements the method of the present invention;
Fig.2 and 3 illustrate some of the embodiments of the method in the form of diagrams.
Fig.1 depicts the optical nodes 1 and 2, a laser interferometer, where the first node 1 (on the side of the laser interferometer combines the light source and the interferometer/beam splitter and the second node 2 contains the retroreflector. Fixed Each emitter/receiver can radiate or receive sound waves. The part also contains a moisture sensors 6, the air pressure sensor 7, the gas analyzer 8, and the control unit and calculations 9. Laser interferometer 1 emits a laser beam 3 and the emitters 4 emit sound waves 5.
The emitters/receivers 4 are grouped in pairs so that the axis 5 of the sound waves emitted by the emitters/receivers are placed symmetrically around the laser beam 3; axis can be, for example, above and below the beam, and the right and left of the beam. Symmetric pair placement simplifies calculations performed later according to the method. The number of pairs of emitters/receivers may be changed in accordance with the needs of the various applications of this invention. For example, in Fig.2 and 3 show 4 and 6 pairs respectively.
The implementation of the invention does not require any special properties of orientation for emitters/receivers. However, modern emitters/receivers, with the width of the pattern of only a few degrees (for example, from 5 to 8 degrees), provide greater noise immunity and can be applied over large distances. This is important in practical measurements, for example, in the factory.
Sound frequency is not limited by any of opredelennymi greater noise immunity. When the measured distance (i.e. the distance between the interferometer 1 and retroreflection 2) is changed accordingly and the distance between each of the emitters/receivers 4. The control unit and computing 9 takes the exact value of the measured distance from the laser interferometer 1.
The speed of sound is measured simultaneously produced by a laser interferometer measurements. The speed of sound can be measured in various ways; one of the possible options are described below.
The speed of sound is measured in continuously repeating cycles, which consist of the following steps:
The control unit and computing 9 sends sound waves through the emitter 4A on a laser interferometer (this invention does not limit the number of oscillations in each package; for example, adequate is 5-20 fluctuations). These sound waves 5 pass over the laser beam 3. After the timeout, the receiver 4b on the opposite from the laser interferometer side (on the side of retroreflector) accepts arriving sound waves, and the time taken for the passage of sound waves, is registered by the control unit and calculations. The control unit and calculations sends sound waves through) the donkey certain delay, the receiver 4A receives the arriving sound wave and the time spent on the passage of sound waves, is registered by the control unit and calculations. The time dimension in both directions is required for the complete elimination of the effect of wind when calculating the speed of sound. After the measurement described above is performed a similar measurement using located symmetrically with respect to the laser beam 3 opposite the emitters/receivers. In other words, now measure the time of propagation of sound waves from the transmitter 4 to the receiver 4d and back from the emitter 4d to the receiver 4C, and thus the sound waves pass through the axis, located under the laser beam 3. Symmetric measurements made immediately on opposite sides of the laser beam ensures that the measured transit time of sound waves along the laser beam 3 represents the greatest extent real time, and eliminates the temperature variation in the direction perpendicular to the laser beam.
After measuring the travel time of sound waves by the method described above using located opposite each other pairs of emitters/receivers, such measurements are made on other pairs of emitters and receivers. If used in the right of the laser beam. The block diagram shows the four emitter/receiver, or two pairs, but the number of emitters/receivers can be selected according to needs in various applications of the present invention.
After the time of sound propagation in both directions measured for all pairs of emitters/receivers, the cycle repeats.
During the measurement unit 9 of the control and computing receives in real time the following information:
- the distance reported by a laser interferometer 1,
- air pressure reported by an air pressure sensor 7,
- relative humidity reported by the humidity sensor 6,
- information about the concentration of gases in the air when performing highly accurate measurements, in this case, the gas analyzer 8 measures the concentration of carbon dioxide and, if necessary, the concentration of other gases in the air.
Based on the information listed above, unit 9 of the control and computing first calculates the velocity of the air along the entire laser beam 3, making the necessary correction to account for the influence of air pressure, relative humidity, gas concentration, wind and temperature gradient, and then calculates the adjustment to the initial indication of the distance measured hodiau statistical processing.
Fig.2 and 3 show examples of how the emitters/receivers sound waves 4 can be symmetrically arranged around the laser beam. In the center of the housing 10 has a hole 11 for accommodating the optical nodes of the laser interferometer. Hole 11 has such a size that there was no interference with the normal functioning of the optics of the laser interferometer.
The invention is not limited to the preferred example of implementation described above, which are given for example only, and various changes and modifications are possible without departure from the scope of this invention as defined in the attached claims.
1. The way to improve the accuracy of distance measurements with a laser interferometer, including the determination of the effect of temperature on the laser beam emitted by the laser interferometer, the path of the laser beam between the interferometer and retroreflector laser interferometer by measuring the speed of sound at the specified path of the laser beam, the speed of sound is measured simultaneously with the measurement of the distance, and the calculation of temperature-dependent air, amendments to the distance value using metering is used for computing the values of the distance, that is measured by a laser interferometer.
3. The method according to p. 1, in which the calculation of the correction values to the measured distance value consider the influence of at least one of the following factors: air pressure, relative humidity, gas concentration, temperature gradient, wind.
4. The method according to p. 1, in which the sound velocity measurement includes determining the speed of sound waves as they travel in both opposite directions along a specified path of the laser beam.
5. The method according to p. 1, in which the speed of sound is measured using at least one pair of emitters/receivers, sound waves, are installed respectively on the interferometer and retroreflector a laser interferometer, each emitter/receiver can radiate or receive sound wave emitters/receivers sound waves of the pair are set so that the path of propagation of sound waves between them is parallel to the defined path of the laser beam and as close as possible to the emitters/receivers do not interfere with the normal functioning of a laser interferometer, and the length of the path of propagation of sound waves varies identically with the length of the specified path of Lasea deviations of temperature in the direction perpendicular to the specified path of the laser beam, the speed of sound is measured using at least two pairs of emitters/receivers, and the method includes the installation of emitters/receivers of each pair so that the path of propagation of sound waves in pairs of emitters/receivers are located symmetrically with respect to the specified path of the laser beam.
7. The method according to PP.5 and 6, including the use of directional emitters/receivers sound with the corner solution of the beam 5-8°.
8. The method according to PP.5-7, in which the emitters/receivers sound operate at ultrasonic frequencies.