rus
Issue #8/2024
M. A. Zavyalova, P. S. Zavyalov, A. V. Soldatenko
Confocal Hyperchromatic Optical System with the Enhanced Energy Characteristics
Confocal Hyperchromatic Optical System with the Enhanced Energy Characteristics
DOI: 10.22184/1993-7296.FRos.2024.18.8.622.628
A new concept of a confocal sensor designed to measure the displacements and surface
microprofiles of the optical transparent media is proposed. The sensor is based on a superluminescent diode and a hyperchromatic lens. The sensor uses a multimode fiber-optic
coupler and a radiation source with a spectral width of 40 nm. The displacement and elevation
difference of the object are determined by measuring the spectrum of radiation reflected from the surface, with isolation of the dominant wavelength using the special software algorithms and implementation of the confocality principle of the sensor’s optical scheme.
A new concept of a confocal sensor designed to measure the displacements and surface
microprofiles of the optical transparent media is proposed. The sensor is based on a superluminescent diode and a hyperchromatic lens. The sensor uses a multimode fiber-optic
coupler and a radiation source with a spectral width of 40 nm. The displacement and elevation
difference of the object are determined by measuring the spectrum of radiation reflected from the surface, with isolation of the dominant wavelength using the special software algorithms and implementation of the confocality principle of the sensor’s optical scheme.
Теги: chromatic encoding method confocal method hyperchromatic systems non-contact optical measurements бесконтактные оптические измерения гиперхроматические системы конфокальный метод метод хроматического кодирования
Confocal Hyperchromatic Optical System With the Enhanced Energy Characteristics
M. A. Zavyalova, P. S. Zavyalov, A. V. Soldatenko
Technological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences (TDI SIE SB RAS), Novosibirsk, Russia
A new concept of a confocal sensor designed to measure the displacements and surface microprofiles of the optical transparent media is proposed. The sensor is based on a superluminescent diode and a hyperchromatic lens. The sensor uses a multimode fiber-optic coupler and a radiation source with a spectral width of 40 nm. The displacement and elevation difference of the object are determined by measuring the spectrum of radiation reflected from the surface, with isolation of the dominant wavelength using the special software algorithms and implementation of the confocality principle of the sensor’s optical scheme.
Key words: non-contact optical measurements, hyperchromatic systems, confocal method, chromatic encoding method
Article received: October 22, 2024
Article accepted: November 20, 2024
Introduction
The industrial production processes and unique research in the scientific field require the development and advancement of available technologies for the high-precision three-dimensional measurements to ensure the specified accuracy of critical product manufacturing [1–3]. The optical measurement principles have some significant advantages since they provide the high-precision non-contact high-speed control [4, 5]. The non-contact properties are of primary concern when measuring the profile of optical components and microstructured surfaces, as well as during operation in the difficult conditions, such as vacuum, high temperatures or industrial conditions [6]. The confocal methods based on chromatic encoding stand out among the high-precision methods for the surface profile measurement since they provide high axial resolution up to 10 nm, and their ease of implementation allows them to be used in the industrial workshops and research centers [7, 8].
The confocal hyperchromatic optical systems represent the contactless devices for high-precision measurements. The key feature of such systems is the application of dispersion or diffraction properties of the optical elements, when the light is focused not at one point, but with division by the wavelength at various distances. Thus, when using a diffractive optical element (hereinafter referred to as the DOE), the light with shorter wavelengths is focused at a greater distance from the element than the light from the long-wave spectral portion. This principle allows encoding various distances with different colors. A chromatic confocal sensor does not require any scanning along the optical axis due to the increased measurement range compared to the depth of focus. To spatially limit the focus in the image region, a confocal method is applied according to which the reflected light is filtered by a small-diameter diaphragm, and in the case of a fiber sensor – by the end of the fiber.
A concept of confocal hyperchromatic optical system with the enhanced
energy characteristics
The conceptual design of the confocal sensor systems using a multimode fiber-optic coupler, various radiation sources and hyperchromatic elements is considered quite often in the scientific literature [8, 9]. In addition, in the authors’ earlier articles [10, 11], various modifications of such systems were described and their accuracy specifications were investigated. The aim of this paper is to develop the confocal hyperchromatic system for measuring displacements and microprofiling the surface of optical transparent media with a low reflectivity.
To convert this opportunity, it is proposed to use a fiber superluminescent LED as a light source [12] that allows for a significant increase in the signal level compared to the normally used halogen lamp. For such a source, a hyperchromatic lens (HCL) is designed, where a DOE is applied as a spectral element. The superluminescent LEDs have a spectral width of about Δλ = 20–40 nm, so the use of diffractive optics for such light sources is almost the only option for the HCL development with an extended chromatic section Δz.
In [13], as a result of a numerical experiment, it is shown that in a fiber confocal sensor based on the chromatic encoding principles, the error of the wave front generated by the HCL shall not exceed ΔW ≤ λ / 10 when using a light source with a spectral width of less than 40 nm. It iss also theoretically and experimentally demonstrated that when using the lenses with various focal lengths in the HCL, it is possible to compensate for spherical aberration by changing the distance between the DOE and a single lens.
Based on the studies performed [14], a fiber confocal sensor (FCS) has been developed. The FCS is an optical module (Fig. 1) consisting of a multimode fiber to provide the probing radiation from a superluminescent diode, a special diffractive optical element, and a lens, the distance between which can vary. The FCS resolution depends on the length of the chromatic segment. The sensor is compatible with the spectrometers having the fiber-optic radiation coupling and can be integrated into the automated production lines. The special software has been developed for operation of this sensor that allows working with various types of connected equipment, such as the spectrometers, three-coordinate positioners, and color video cameras.
The illuminator used in the FCS is a superluminescent diode SLD‑790-14BF (Nolatech, Russia) with the output power of 5 mW and a spectral width of 40 nm (760–800 nm); as well as a multimode coupler with a core diameter of 50 µm (Core Graded-Index Fibers Available with 50:50, Thorlabs, Germany). The optical module consists of a replaceable diffractive optical element made on a circular laser write system (Novosibirsk Instrument-Making Plant JSC) and a single lens with a focal length of 36 mm. The displacement of object under study is provided using a movable platform that includes a three-axis table ZSS 33.200.1.2 (Phytron, Germany). The spectrum of reflected radiation is introduced through the fiber-optic splitter into the Qwave VIS spectrometer (RGB Lasersystems, Germany) and then analyzed by the special software. The experimental results have showed that when using a superluminescent diode to measure the distance to the low-reflecting surfaces, the reflected signal is 106 times higher than when using a halogen lamp (680 μW/ nm and 408 pW/nm, respectively).
Fig. 2 shows one of the options of the FCS optical scheme. The lengths of the chromatic segments can vary when using various DOEs. The spherical aberration is minimized by changing the distance l between the lens and the DOE.
Technical specifications of the FCS:
length of the chromatic segment: 300, 500 and 800 µm;
error: it depends on the length of the chromatic segment and resolution capacity of the spectrometer or color video camera and is less than 0.1 µm;
synchronization with the peripheral equipment: USB interface, RS‑232;
light source: a superluminescent diode SLD‑790-14BF (Nolatech, Russia);
multimode fiber optical connector E 2000;
operating temperature from +5 °C to +50 °C;
weight of the optical module: 0.2 kg.
The FCS allows the following measurements to be taken: surface profile height, surface roughness, coating thickness, shape of the objects, optical properties of the materials. When measuring the surface profile height, the FCS provides an acceptable measurement error of up to several nanometers. This allows the surface quality to be controlled and its geometric parameters to be determined.
When measuring the surface roughness being an important parameter for many engineering applications, the FCS allows monitoring the surface treatment process to achieve a specified surface quality. Having considered the ability to measure the coating thickness, the FCS can be used to control the coating application process on the object surfaces. The FCS can be used to measure the shape of objects such as the machinery parts, electronic components, medical implants, etc. This allows monitoring the object production process and determining their geometric parameters. When using the FCS to measure the optical properties of materials, such as transparency or refractive index, it is possible to control any changes in the optical properties of materials on a lot-to-lot basis supplied for the serial industrial production.
The increased energy characteristics of these sensors allow them to measure the surface parameters of materials that are difficult to be measured by the conventional sensors. For example, they can be used to measure the surface parameters of highly reflective materials or transparent materials such as glass or ceramics.
In general, the confocal chromatic sensors with the enhanced energy characteristics represent a powerful tool for measuring surface parameters of a wide range of materials for various applications.
Conclusion
A result has been obtained available for practical application: the design documentation has been developed and a fiber confocal sensor (FCS) has been produced based on the chromatic encoding method for quality control of the low-reflective surfaces for critical products on an industrial production scale.
As a result of the studies performed it has been established that when measuring distance to the low-reflecting surfaces, the application of a superluminescent diode in the FCS optical system instead of a halogen lamp provides a reflected signal that is 106 times higher (680 μW/nm and 408 pW/nm, respectively). For a narrow-spectrum radiation source (the spectral width is 760–800 nm), the special diffractive optical elements have been designed, allowing focusing the light into the segments with various lengths.
The practical result obtained is the basis for integration of the fiber confocal sensor based on chromatic encoding into the automated optical-electronic systems and surface microprofiling set-ups. Due to its advantages (non-contact measurement mode, small focal spot, high accuracy, high speed), it ensures the precise positioning and high-precision digitization of the three-dimensional low-reflective surfaces. This sensor is specified by its low cost, high stability, accuracy and portability.
Acknowledgments
The financial support for the work has been provided by the Ministry of Science and Higher Education of the Russian Federation.
AUTHORS
Marina Andreevna Zavyalova, PhD in technical sciences, senior researcher, Technological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia; e-mail: mzav@tdisie.nsc.ru; region of interest: optical and electronic devices and systems, laser technologies.
ORCID: 0000-0003-2000-6226
Pyotr Sergeevich Zavyalov, PhD in technical sciences, director, Technological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia; e-mail: zavyalov@tdisie.nsc.ru; region of interest: optical and electronic devices and systems, machine vision systems, diffractive optics.
ORCID: 0000-0001-6222-5000
Aleksey Vladimirovich Soldatenko, 1st grade developer, Technological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia; e-mail: tok9_11@mail.ru; region of interest: 3D-design.
RSCI ID: 1156988
M. A. Zavyalova, P. S. Zavyalov, A. V. Soldatenko
Technological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences (TDI SIE SB RAS), Novosibirsk, Russia
A new concept of a confocal sensor designed to measure the displacements and surface microprofiles of the optical transparent media is proposed. The sensor is based on a superluminescent diode and a hyperchromatic lens. The sensor uses a multimode fiber-optic coupler and a radiation source with a spectral width of 40 nm. The displacement and elevation difference of the object are determined by measuring the spectrum of radiation reflected from the surface, with isolation of the dominant wavelength using the special software algorithms and implementation of the confocality principle of the sensor’s optical scheme.
Key words: non-contact optical measurements, hyperchromatic systems, confocal method, chromatic encoding method
Article received: October 22, 2024
Article accepted: November 20, 2024
Introduction
The industrial production processes and unique research in the scientific field require the development and advancement of available technologies for the high-precision three-dimensional measurements to ensure the specified accuracy of critical product manufacturing [1–3]. The optical measurement principles have some significant advantages since they provide the high-precision non-contact high-speed control [4, 5]. The non-contact properties are of primary concern when measuring the profile of optical components and microstructured surfaces, as well as during operation in the difficult conditions, such as vacuum, high temperatures or industrial conditions [6]. The confocal methods based on chromatic encoding stand out among the high-precision methods for the surface profile measurement since they provide high axial resolution up to 10 nm, and their ease of implementation allows them to be used in the industrial workshops and research centers [7, 8].
The confocal hyperchromatic optical systems represent the contactless devices for high-precision measurements. The key feature of such systems is the application of dispersion or diffraction properties of the optical elements, when the light is focused not at one point, but with division by the wavelength at various distances. Thus, when using a diffractive optical element (hereinafter referred to as the DOE), the light with shorter wavelengths is focused at a greater distance from the element than the light from the long-wave spectral portion. This principle allows encoding various distances with different colors. A chromatic confocal sensor does not require any scanning along the optical axis due to the increased measurement range compared to the depth of focus. To spatially limit the focus in the image region, a confocal method is applied according to which the reflected light is filtered by a small-diameter diaphragm, and in the case of a fiber sensor – by the end of the fiber.
A concept of confocal hyperchromatic optical system with the enhanced
energy characteristics
The conceptual design of the confocal sensor systems using a multimode fiber-optic coupler, various radiation sources and hyperchromatic elements is considered quite often in the scientific literature [8, 9]. In addition, in the authors’ earlier articles [10, 11], various modifications of such systems were described and their accuracy specifications were investigated. The aim of this paper is to develop the confocal hyperchromatic system for measuring displacements and microprofiling the surface of optical transparent media with a low reflectivity.
To convert this opportunity, it is proposed to use a fiber superluminescent LED as a light source [12] that allows for a significant increase in the signal level compared to the normally used halogen lamp. For such a source, a hyperchromatic lens (HCL) is designed, where a DOE is applied as a spectral element. The superluminescent LEDs have a spectral width of about Δλ = 20–40 nm, so the use of diffractive optics for such light sources is almost the only option for the HCL development with an extended chromatic section Δz.
In [13], as a result of a numerical experiment, it is shown that in a fiber confocal sensor based on the chromatic encoding principles, the error of the wave front generated by the HCL shall not exceed ΔW ≤ λ / 10 when using a light source with a spectral width of less than 40 nm. It iss also theoretically and experimentally demonstrated that when using the lenses with various focal lengths in the HCL, it is possible to compensate for spherical aberration by changing the distance between the DOE and a single lens.
Based on the studies performed [14], a fiber confocal sensor (FCS) has been developed. The FCS is an optical module (Fig. 1) consisting of a multimode fiber to provide the probing radiation from a superluminescent diode, a special diffractive optical element, and a lens, the distance between which can vary. The FCS resolution depends on the length of the chromatic segment. The sensor is compatible with the spectrometers having the fiber-optic radiation coupling and can be integrated into the automated production lines. The special software has been developed for operation of this sensor that allows working with various types of connected equipment, such as the spectrometers, three-coordinate positioners, and color video cameras.
The illuminator used in the FCS is a superluminescent diode SLD‑790-14BF (Nolatech, Russia) with the output power of 5 mW and a spectral width of 40 nm (760–800 nm); as well as a multimode coupler with a core diameter of 50 µm (Core Graded-Index Fibers Available with 50:50, Thorlabs, Germany). The optical module consists of a replaceable diffractive optical element made on a circular laser write system (Novosibirsk Instrument-Making Plant JSC) and a single lens with a focal length of 36 mm. The displacement of object under study is provided using a movable platform that includes a three-axis table ZSS 33.200.1.2 (Phytron, Germany). The spectrum of reflected radiation is introduced through the fiber-optic splitter into the Qwave VIS spectrometer (RGB Lasersystems, Germany) and then analyzed by the special software. The experimental results have showed that when using a superluminescent diode to measure the distance to the low-reflecting surfaces, the reflected signal is 106 times higher than when using a halogen lamp (680 μW/ nm and 408 pW/nm, respectively).
Fig. 2 shows one of the options of the FCS optical scheme. The lengths of the chromatic segments can vary when using various DOEs. The spherical aberration is minimized by changing the distance l between the lens and the DOE.
Technical specifications of the FCS:
length of the chromatic segment: 300, 500 and 800 µm;
error: it depends on the length of the chromatic segment and resolution capacity of the spectrometer or color video camera and is less than 0.1 µm;
synchronization with the peripheral equipment: USB interface, RS‑232;
light source: a superluminescent diode SLD‑790-14BF (Nolatech, Russia);
multimode fiber optical connector E 2000;
operating temperature from +5 °C to +50 °C;
weight of the optical module: 0.2 kg.
The FCS allows the following measurements to be taken: surface profile height, surface roughness, coating thickness, shape of the objects, optical properties of the materials. When measuring the surface profile height, the FCS provides an acceptable measurement error of up to several nanometers. This allows the surface quality to be controlled and its geometric parameters to be determined.
When measuring the surface roughness being an important parameter for many engineering applications, the FCS allows monitoring the surface treatment process to achieve a specified surface quality. Having considered the ability to measure the coating thickness, the FCS can be used to control the coating application process on the object surfaces. The FCS can be used to measure the shape of objects such as the machinery parts, electronic components, medical implants, etc. This allows monitoring the object production process and determining their geometric parameters. When using the FCS to measure the optical properties of materials, such as transparency or refractive index, it is possible to control any changes in the optical properties of materials on a lot-to-lot basis supplied for the serial industrial production.
The increased energy characteristics of these sensors allow them to measure the surface parameters of materials that are difficult to be measured by the conventional sensors. For example, they can be used to measure the surface parameters of highly reflective materials or transparent materials such as glass or ceramics.
In general, the confocal chromatic sensors with the enhanced energy characteristics represent a powerful tool for measuring surface parameters of a wide range of materials for various applications.
Conclusion
A result has been obtained available for practical application: the design documentation has been developed and a fiber confocal sensor (FCS) has been produced based on the chromatic encoding method for quality control of the low-reflective surfaces for critical products on an industrial production scale.
As a result of the studies performed it has been established that when measuring distance to the low-reflecting surfaces, the application of a superluminescent diode in the FCS optical system instead of a halogen lamp provides a reflected signal that is 106 times higher (680 μW/nm and 408 pW/nm, respectively). For a narrow-spectrum radiation source (the spectral width is 760–800 nm), the special diffractive optical elements have been designed, allowing focusing the light into the segments with various lengths.
The practical result obtained is the basis for integration of the fiber confocal sensor based on chromatic encoding into the automated optical-electronic systems and surface microprofiling set-ups. Due to its advantages (non-contact measurement mode, small focal spot, high accuracy, high speed), it ensures the precise positioning and high-precision digitization of the three-dimensional low-reflective surfaces. This sensor is specified by its low cost, high stability, accuracy and portability.
Acknowledgments
The financial support for the work has been provided by the Ministry of Science and Higher Education of the Russian Federation.
AUTHORS
Marina Andreevna Zavyalova, PhD in technical sciences, senior researcher, Technological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia; e-mail: mzav@tdisie.nsc.ru; region of interest: optical and electronic devices and systems, laser technologies.
ORCID: 0000-0003-2000-6226
Pyotr Sergeevich Zavyalov, PhD in technical sciences, director, Technological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia; e-mail: zavyalov@tdisie.nsc.ru; region of interest: optical and electronic devices and systems, machine vision systems, diffractive optics.
ORCID: 0000-0001-6222-5000
Aleksey Vladimirovich Soldatenko, 1st grade developer, Technological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia; e-mail: tok9_11@mail.ru; region of interest: 3D-design.
RSCI ID: 1156988
Readers feedback
