rus
Issue #5/2023
B.G.Turukhano, N.Turukhano, S.N.Khanov, V.V.Dobyrn, Yu.M.Lavrov, O.G.Ermolenko
NANOHOLOGRAPHIC LENGTH METERS AND LINEAR ENCODERS
NANOHOLOGRAPHIC LENGTH METERS AND LINEAR ENCODERS
DOI: https://doi.org/10.22184/1993-8578.2023.16.5.310.318
In this paper, the authors highlight the current state of measurement technology when measuring the linear dimensions of objects with nano-horizontal holographic encoders (LHE) and vertical nano-holographic length encoders (VEH) based on linear holographic diffraction gratings (LHDG).
In this paper, the authors highlight the current state of measurement technology when measuring the linear dimensions of objects with nano-horizontal holographic encoders (LHE) and vertical nano-holographic length encoders (VEH) based on linear holographic diffraction gratings (LHDG).
Теги: horizontal nano-holographic encoders linear holographic diffraction grating vertical nano-holographic length encoders вертикальный нанодлиномер голографический горизонтальный нано голографический датчик линейная голографическая дифракционная решетка
INTRODUCTION
Humanity has been creative throughout its existence and it is thanks to its enormous brain. Scientists believe that the human brain is the most voluminous object in the Universe. Moreover, the human being rises both up in the Universe and down to its beginning. In this paper, we will touch upon the second part of his activity related to the field of high technologies, more precisely, nano-measuring systems of linear movements.
If measuring systems in the 20th century have steadily reached the micron level and approached the nanometre, then in the 21st century man definitely wants to achieve more. In this case, the authors of this paper have already steadily reached 1 nanometre in their development of linear motion measurement systems.
Previously, one of the methods that scientists used to measure the geometric parameters of objects – length and angle – was a method using bar scales obtained mechanically, but it was almost impossible to achieve values of less than a micron on their basis, especially for large lengths of the objects under study.
The coherent radiation sources (lasers) development in the early 60s of the last century and, thanks to them, a new science – holography – opened up new possibilities for transition from micro to nanosystems.
This allowed us to make a new non-contact method of recording linear and radial holographic diffraction gratings (LHDG and RHDG) using interference of coherent wave beams [1]. It is well known, that waves are coherent if their phase difference remains constant in time. Only coherent waves can give a stable interference pattern. However, there appeared a need, on the one hand, to obtain gratings with high uniformity of stroke arrangement, and on the other hand, to write down gratings of large aperture. Such gratings were obtained by the authors of this paper, who managed to record a 1m 200 mm long LHDR (Fig.1a, b).
To develop the high-precision LHDGs of large lengths up to a metre and more it is necessary to use the method of synthesis of the holographic field aperture and an appropriate device for its implementation.
THE EQUIPMENT
Metre gratings with a step of 1 micron were certified in All-Russian Research Institute of Metrology named after D.I.Mendeleev. Certification of metrological linear holographic diffraction grating MLHDG with length L = 1000 mm (1988) was performed at the State primary length standard of All-Russian Research Institute of Metrology named after D.I.Mendeleev.
Linear holographic diffraction gratings (LHDGs) are necessary for design of sensors and systems for measuring linear dimensions of objects [2]. For this purpose, the principle of measurement based on photoelectric scanning of LHDG strokes is used.
The high-precision linear measuring LHDG is a glass substrate with a high-resolution photographic emulsion applied to it. On the photoemulsion the grating image is recorded in the form of parallel strokes, sinusoidal in intensity. The accuracy of the strokes has an irregularity not exceeding 0.01λ, where λ is the wavelength of the laser emitter of the diffraction grating recording setup.
Linear holographic sensors (LHS) are measurement devices based on precision linear holographic diffraction gratings.
LHD devices are based on two precision diffraction gratings – a measuring grating (Fig.2) and an indicator (auxiliary). By moving one grating relative to the other and shining a laser light source, it is possible to make reading of information on length measurement or displacement value. When two crossed gratings are shined simultaneously by a laser beam, interference patterns are formed: moiré (Fig.3) or obturation fringes (Fig.4), which move across the field with a step of one fringe when the grating is displaced by one step. The width of the interference moiré fringe depends on the crossing angle of the gratings, while width of the interference skirt fringe depends on the difference in their period. The smaller the crossing angle of the gratings or the difference in their period, the wider the moiré or skirt fringe. Thus it is possible to fix the movement of gratings relative to each other by a photodetector with a working aperture much larger than the pitch of the grating itself. The photodetector is a matrix of photodiodes. The lattice pitch, chosen as 1 µm, is convenient for counting lattice steps, However, there are very few individual photodetectors with such an input aperture. To read the information it is necessary to place in the field of interference fringes a photodetector, for example, a photodiode and a DC amplifier, at the output of which we will receive sinusoidal signals (Fig.4) in accordance with the movement of gratings relative to each other.
To determine the direction of gratings movement one relative to the other, it is necessary to use two photodetectors of phase-shifted strips [3]. With the help of shapers it is possible to obtain rectangular signals necessary for the counters operation. The use of data interpolation within one step leads to an increase in measurement resolution by at least two orders of magnitude.
The circuit diagram of the reader is shown in Fig.5, where the main measuring holographic diffraction grating (MLHDG):
high-resolution emulsion is applied to the glass substrate and the grating itself is directly recorded thereon;
the auxiliary grating 2 is such with the corresponding stroke frequency. Both gratings are arranged emulsion to each other with a small gap (80–100 µm);
a laser emitter 3, together with an optical lens 5 forming an illuminator;
mirror 4, allowing to direct the laser beam on the gratings under the Bragg angle and further on the photodetector 6.
The elements 2, 3, 4, 5 and 6 are rigidly fastened together and form the readhead. By moving the reading head relative to the main measuring grating (1) or vice versa, the main MLHDG relative to a reading head, displacement is measured. In real devices one of these variants is used.
At the output of the photomatrix we receive two signals shifted relative to each other by 90 degrees in the phase of interference fringes, which allow both counting of grating strokes and interpolation within the grating step. The electronics unit allows to operate both in stand-alone mode and together with a computer, which allows the measured information to be used for more complex measurement systems.
The obturatoria strokes, similar to moiré, are parallel with respect to the bars of the lattice.
Holographic length encoders are measuring devices based on precision holographic diffraction gratings (HDGs). For developing of high-precision HDGs of large lengths up to a metre and more it is necessary to use the method of synthesis of the holographic field aperture and the corresponding device for its implementation.
Holographic length gauges DG-30, DG-100 and DG-200 are shown in Fig.7. The devices are designed for measurements within 30 mm, 100 mm and 200 mm, respectively, with a resolution of 0.01 µm. These length encoders are designed and manufactured by the Laboratory of Holographic Information Measurement Systems (LHIMS) of the St. Petersburg Institute of Nuclear Physics, SIC "Kurchatov Institute". The devices can be checked and calibrated by special "end measures" both autonomously and when connected (on line) to a personal computer. Fig.8 shows a length gauge with a measuring limit of 300 mm [4], with automatic mode of operation, with a touch probe built on an additional grating that allows to determine with high accuracy the moment of touch of the stylus to the measured part. The touch probe of the measuring rod is organised by means of a third miniature grating of the same frequency as the main counting grating. The touch probe is mechanically connected to the auxiliary grating (the third one) and when the probe touches the measured object, the movement of the auxiliary grating starts in the opposite direction to the main grating and the count of this auxiliary grating is subtracted from the main count.
METHODS OF MEASURING
At the start of the count, the auxiliary grating is commanded to stop the drive motor, thus compensating for motor runaway and minimising stylus force. The measurement readings are captured by the computer and recorded for further processing, followed by a command to raise the probe array. The length of the gauges naturally depends on the length of the main MLHDG. Grids with lengths of 300 mm, 400 mm, 500–1300 mm have been produced.
Figure 9 shows a linear holographic nanosensor with a length of 500 mm [4–6].
On any measuring ruler there is a "zero reference" and all measurement references are made from zero. A label ("0-tag", NM) has been developed for the holographic ruler.
NM is a single, opaque stroke (Fig.10) outside the area of the working part of the measuring diffraction grating. The information is captured by means of 4 photodiodes located sequentially along the reading head movement direction combined in two groups of two photodiodes, connected in counter-parallel and included in a differential way to the inputs of two DC amplifiers, which allows to obtain two balanced signals, shifted relative to each other and independent of external illumination and in-phase interference.
When the shadow of a stroke passes over the photo matrix, sinusoidal-like signals are produced. Three-axis measurement of linear objects is in constant need of improvement. The first requirement is to improve accuracy, then to reduce measurement time, to automate measurements and to optimise operator performance.
Equipping with nano-holographic high-precision sensors and computerisation of microscopes significantly improves their metrological and operational characteristics. 3D nano UIM (Fig.11) is designed for precision measurements of three coordinates in orthogonal system with output of results to a computer.
The device is equipped with high-precision linear sensors on holographic diffraction gratings. The accuracy of measurements on such modernised devices is increased by at least an order of magnitude. The 3-axis measuring machine is shown in Fig.11. The software allows simultaneous tracking of 3 coordinates (Fig.12).
Figure 13 shows a 4-axis automatic measuring machine. Since in this machine for precise measurement in X coordinate two Y sensors are used, located on opposite guides, on which a bridge with a measuring grid in Y coordinate moves, and on this bridge moves a measuring head for measurement in Z coordinate. The two Y-coordinate grids are used to compensate for the bending of the bridge, more precisely to compensate for the backlash of the one-way Y-coordinate drive and to calculate the exact position of the X-coordinate measuring head.
The stand for testing of linear holographic sensors LHG (Fig.14) has a possibility to test 3 sensors simultaneously. The platform allows to move 3 sensors simultaneously, while using one sensor as a reference and digitising the other two sensors at the same time. The digitised data allows to obtain the characteristics of the other two sensors in digital and graphical form in 1 pass.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Humanity has been creative throughout its existence and it is thanks to its enormous brain. Scientists believe that the human brain is the most voluminous object in the Universe. Moreover, the human being rises both up in the Universe and down to its beginning. In this paper, we will touch upon the second part of his activity related to the field of high technologies, more precisely, nano-measuring systems of linear movements.
If measuring systems in the 20th century have steadily reached the micron level and approached the nanometre, then in the 21st century man definitely wants to achieve more. In this case, the authors of this paper have already steadily reached 1 nanometre in their development of linear motion measurement systems.
Previously, one of the methods that scientists used to measure the geometric parameters of objects – length and angle – was a method using bar scales obtained mechanically, but it was almost impossible to achieve values of less than a micron on their basis, especially for large lengths of the objects under study.
The coherent radiation sources (lasers) development in the early 60s of the last century and, thanks to them, a new science – holography – opened up new possibilities for transition from micro to nanosystems.
This allowed us to make a new non-contact method of recording linear and radial holographic diffraction gratings (LHDG and RHDG) using interference of coherent wave beams [1]. It is well known, that waves are coherent if their phase difference remains constant in time. Only coherent waves can give a stable interference pattern. However, there appeared a need, on the one hand, to obtain gratings with high uniformity of stroke arrangement, and on the other hand, to write down gratings of large aperture. Such gratings were obtained by the authors of this paper, who managed to record a 1m 200 mm long LHDR (Fig.1a, b).
To develop the high-precision LHDGs of large lengths up to a metre and more it is necessary to use the method of synthesis of the holographic field aperture and an appropriate device for its implementation.
THE EQUIPMENT
Metre gratings with a step of 1 micron were certified in All-Russian Research Institute of Metrology named after D.I.Mendeleev. Certification of metrological linear holographic diffraction grating MLHDG with length L = 1000 mm (1988) was performed at the State primary length standard of All-Russian Research Institute of Metrology named after D.I.Mendeleev.
Linear holographic diffraction gratings (LHDGs) are necessary for design of sensors and systems for measuring linear dimensions of objects [2]. For this purpose, the principle of measurement based on photoelectric scanning of LHDG strokes is used.
The high-precision linear measuring LHDG is a glass substrate with a high-resolution photographic emulsion applied to it. On the photoemulsion the grating image is recorded in the form of parallel strokes, sinusoidal in intensity. The accuracy of the strokes has an irregularity not exceeding 0.01λ, where λ is the wavelength of the laser emitter of the diffraction grating recording setup.
Linear holographic sensors (LHS) are measurement devices based on precision linear holographic diffraction gratings.
LHD devices are based on two precision diffraction gratings – a measuring grating (Fig.2) and an indicator (auxiliary). By moving one grating relative to the other and shining a laser light source, it is possible to make reading of information on length measurement or displacement value. When two crossed gratings are shined simultaneously by a laser beam, interference patterns are formed: moiré (Fig.3) or obturation fringes (Fig.4), which move across the field with a step of one fringe when the grating is displaced by one step. The width of the interference moiré fringe depends on the crossing angle of the gratings, while width of the interference skirt fringe depends on the difference in their period. The smaller the crossing angle of the gratings or the difference in their period, the wider the moiré or skirt fringe. Thus it is possible to fix the movement of gratings relative to each other by a photodetector with a working aperture much larger than the pitch of the grating itself. The photodetector is a matrix of photodiodes. The lattice pitch, chosen as 1 µm, is convenient for counting lattice steps, However, there are very few individual photodetectors with such an input aperture. To read the information it is necessary to place in the field of interference fringes a photodetector, for example, a photodiode and a DC amplifier, at the output of which we will receive sinusoidal signals (Fig.4) in accordance with the movement of gratings relative to each other.
To determine the direction of gratings movement one relative to the other, it is necessary to use two photodetectors of phase-shifted strips [3]. With the help of shapers it is possible to obtain rectangular signals necessary for the counters operation. The use of data interpolation within one step leads to an increase in measurement resolution by at least two orders of magnitude.
The circuit diagram of the reader is shown in Fig.5, where the main measuring holographic diffraction grating (MLHDG):
high-resolution emulsion is applied to the glass substrate and the grating itself is directly recorded thereon;
the auxiliary grating 2 is such with the corresponding stroke frequency. Both gratings are arranged emulsion to each other with a small gap (80–100 µm);
a laser emitter 3, together with an optical lens 5 forming an illuminator;
mirror 4, allowing to direct the laser beam on the gratings under the Bragg angle and further on the photodetector 6.
The elements 2, 3, 4, 5 and 6 are rigidly fastened together and form the readhead. By moving the reading head relative to the main measuring grating (1) or vice versa, the main MLHDG relative to a reading head, displacement is measured. In real devices one of these variants is used.
At the output of the photomatrix we receive two signals shifted relative to each other by 90 degrees in the phase of interference fringes, which allow both counting of grating strokes and interpolation within the grating step. The electronics unit allows to operate both in stand-alone mode and together with a computer, which allows the measured information to be used for more complex measurement systems.
The obturatoria strokes, similar to moiré, are parallel with respect to the bars of the lattice.
Holographic length encoders are measuring devices based on precision holographic diffraction gratings (HDGs). For developing of high-precision HDGs of large lengths up to a metre and more it is necessary to use the method of synthesis of the holographic field aperture and the corresponding device for its implementation.
Holographic length gauges DG-30, DG-100 and DG-200 are shown in Fig.7. The devices are designed for measurements within 30 mm, 100 mm and 200 mm, respectively, with a resolution of 0.01 µm. These length encoders are designed and manufactured by the Laboratory of Holographic Information Measurement Systems (LHIMS) of the St. Petersburg Institute of Nuclear Physics, SIC "Kurchatov Institute". The devices can be checked and calibrated by special "end measures" both autonomously and when connected (on line) to a personal computer. Fig.8 shows a length gauge with a measuring limit of 300 mm [4], with automatic mode of operation, with a touch probe built on an additional grating that allows to determine with high accuracy the moment of touch of the stylus to the measured part. The touch probe of the measuring rod is organised by means of a third miniature grating of the same frequency as the main counting grating. The touch probe is mechanically connected to the auxiliary grating (the third one) and when the probe touches the measured object, the movement of the auxiliary grating starts in the opposite direction to the main grating and the count of this auxiliary grating is subtracted from the main count.
METHODS OF MEASURING
At the start of the count, the auxiliary grating is commanded to stop the drive motor, thus compensating for motor runaway and minimising stylus force. The measurement readings are captured by the computer and recorded for further processing, followed by a command to raise the probe array. The length of the gauges naturally depends on the length of the main MLHDG. Grids with lengths of 300 mm, 400 mm, 500–1300 mm have been produced.
Figure 9 shows a linear holographic nanosensor with a length of 500 mm [4–6].
On any measuring ruler there is a "zero reference" and all measurement references are made from zero. A label ("0-tag", NM) has been developed for the holographic ruler.
NM is a single, opaque stroke (Fig.10) outside the area of the working part of the measuring diffraction grating. The information is captured by means of 4 photodiodes located sequentially along the reading head movement direction combined in two groups of two photodiodes, connected in counter-parallel and included in a differential way to the inputs of two DC amplifiers, which allows to obtain two balanced signals, shifted relative to each other and independent of external illumination and in-phase interference.
When the shadow of a stroke passes over the photo matrix, sinusoidal-like signals are produced. Three-axis measurement of linear objects is in constant need of improvement. The first requirement is to improve accuracy, then to reduce measurement time, to automate measurements and to optimise operator performance.
Equipping with nano-holographic high-precision sensors and computerisation of microscopes significantly improves their metrological and operational characteristics. 3D nano UIM (Fig.11) is designed for precision measurements of three coordinates in orthogonal system with output of results to a computer.
The device is equipped with high-precision linear sensors on holographic diffraction gratings. The accuracy of measurements on such modernised devices is increased by at least an order of magnitude. The 3-axis measuring machine is shown in Fig.11. The software allows simultaneous tracking of 3 coordinates (Fig.12).
Figure 13 shows a 4-axis automatic measuring machine. Since in this machine for precise measurement in X coordinate two Y sensors are used, located on opposite guides, on which a bridge with a measuring grid in Y coordinate moves, and on this bridge moves a measuring head for measurement in Z coordinate. The two Y-coordinate grids are used to compensate for the bending of the bridge, more precisely to compensate for the backlash of the one-way Y-coordinate drive and to calculate the exact position of the X-coordinate measuring head.
The stand for testing of linear holographic sensors LHG (Fig.14) has a possibility to test 3 sensors simultaneously. The platform allows to move 3 sensors simultaneously, while using one sensor as a reference and digitising the other two sensors at the same time. The digitised data allows to obtain the characteristics of the other two sensors in digital and graphical form in 1 pass.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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