Measurement principle and method of spectral confocal sensor

Spectral confocal sensor measurement principle and measurement methods believe that many people do not know what is, today I will tell you about the spectral confocal sensor knowledge, I hope to be useful to you.

Principle of spectral confocal measurement

As we all know, sunlight in nature belongs to white light. White light is not pure light, but consists of many monochromatic lights. The wavelength range of visible light is 700 nm. When light propagates in different media, there may be angle deviation, but under the actual white light irradiation, the single line light will refract many times in different media.

Optical material (lens) has different refractive index for different monochromatic light, that is, different refraction angle. The shorter the wavelength, the smaller the refractive index. The same thin lens has different focal length for different monochromatic light, and each monochromatic light has different focal length. According to the wavelength of color light, their image points are arranged on the optical axis from near to far, far away from the lens (different monochromatic light has different wavelengths), so the so-called chromatic aberration lens error is produced in imaging. The error of chromatic aberration lens results in color spot or halo. In photographic equipment, special treatment should be carried out to minimize the imaging problems caused by chromatic aberration lens error. Common elimination methods include double gluing system and double separation system.

However, the spectral confocal measurement method takes advantage of this physical phenomenon. By using a special lens, the focus halo range of light with different colors is expanded, and the special amplified chromatic aberration is formed. Thus, according to the distance between the measured object and the lens, the light with accurate wavelength can be focused on the object to be measured. By measuring the wavelength of the reflected light, the precise distance between the measured object and the lens can be obtained. This process is the opposite of the process in which the photographic equipment reduces the chromatic aberration in various ways.

In order to obtain the above special color difference, several special lenses are needed in the sensor probe to decompose the light according to the required range. Then a convex lens is used to gather the light from the sensor probe on an axis to form the so-called focusing axis. If the convex lens is not used, the light from the sensor probe will be scattered and cannot be measured.

White light passes through the surface of the half lens and reaches the convex lens. This is where the above special color difference occurs. When the light irradiates the object to be measured, it will reflect and return to the half lens in the sensor probe after passing through the convex lens. The half lens refracts the reflected light to the perforated cover plate, and only the well focused reflected light can pass through the hole. The light passing through the porous cover plate is a group of fuzzy spectra, that is, light of several different wavelengths can pass through the hole and irradiate the CCD photosensitive matrix cell.

However, only the reflected light focused on the object to be measured has enough light intensity to produce an obvious peak value on the CCD photosensitive matrix. Behind the perforated cover plate, a spectrometer is needed to measure the color information of the reflected light. The splitter is similar to a special grating, which can increase or decrease the refractive index according to the wavelength of the reflected light. Therefore, each position on the CCD matrix corresponds to the distance from the measured object to the probe.

Measurement method of spectral confocal sensor

The spectral confocal measurement method takes advantage of the physical phenomenon of aberration lens deviation. By using a special lens, the focus halo range of light with different colors is extended to form a special amplification chromatic aberration. According to the distance between the measured object and the lens, the light of a precise wavelength will be focused on the object to be measured.

By measuring the wavelength of the reflected light, the precise distance between the measured object and the lens can be obtained. This process is the opposite of the process of subtracting chromatic aberration of photographic equipment by various methods.

In order to obtain the above special color difference, it is necessary to use some special lenses in the sensor probe to decompose the light according to the required range. Finally, a convex lens is used to gather the light emitted by the sensor probe on an axis to form the so-called focus axis. If the convex lens is not used, the light emitted by the sensor probe will be scattered, and the measurement can not be carried out.