Coaxiality Evaluation of Coaxial Imaging System with Concentric Silicon–Glass Hybrid Lens for Thermal and Color Imaging

Abstract

Thermal imaging is useful for tasks such as detecting the presence of humans and recognizing surrounding objects in the operation of several types of robots, including service robots and personal mobility robots, which assist humans. Because the number of pixels on a thermal imager is generally smaller than that on a color imager, thermal images are more useful when combined with color images, assuming that the correspondence between points in the images captured by the two sensors is known. In the literature, several types of coaxial imaging systems have been reported that can capture thermal and color images, simultaneously, from the same point of view with the same optical axis. Among them, a coaxial imaging system using a concentric silicon–glass hybrid lens was devised. Long-wavelength infrared and visible light was focused using the hybrid lens. The focused light was subsequently split using a silicon plate. Separate thermal and color images were then captured using thermal and color imagers, respectively. However, a coaxiality evaluation of the hybrid lens has not been shown. This report proposes an implementation and coaxiality evaluation for a compact coaxial imaging system incorporating the hybrid lens. The coaxiality of the system was experimentally demonstrated by estimating the intrinsic and extrinsic parameters of the thermal and color imagers and performing 2D mapping between the thermal images and color images.

Determination of Transmittance of IR Windows made of CaF2 within Operational Temperatures of Electric Devices

“…Then a metal box was put onto the radiator and the rationale for the simplification presented in the formula (12) was verified. For this purpose, the distance between the radiator and the IR window, the distance between the IR window and the thermographic camera lens was measured.…”

“…Additionally, the measurement result depends on a number of factors. The most important factors determining the value of the thermographic temperature measurement include: emissivity coefficient value [7], reflected temperature [8], distance between the thermographic camera lens and the surface under observation [9], ambient temperature [10], temperature of the external optical system [11], transmission of the external optical system [12], air humidity [13] and registered thermogram sharpness [14].…”

Infrared and Visible Image Registration for Airborne Camera Systems

“…When sensors do not share the same optical centre, some parallax is present in the images and the registration becomes scene dependant. Parallax-free designs are presented in [12], [14], [15].…”

The Solution for the Thermographic Measurement of the Temperature of a Small Object

“…In order to correctly assess temperature distribution on the housing of electronic components, it is necessary to take into account all factors that can influence the measurement [6][7][8]. The most important of them include the value of the emissivity coefficient ε [9], the reflected temperature ϑ r [10], the distance between the lens and the observed object d [11], the ambient temperature ϑ a [12], the temperature of the external optical system [13], the transmittance of the external optical system [14,15], the relative humidity ω [16], the viewing angle β [7], and the sharpness of the recorded thermogram [17][18][19]. An assessment of the influence of the abovementioned factors on the accuracy of the thermographic temperature measurement of small-sized electronic components is possible thanks to the use of a microscopic thermography stand.…”

“…The lower the value of τ a , the less IR radiation reaches the IR detector array of the thermographic camera. Consequently, due to the lower power of IR radiation absorbed by the array of IR detectors, the amplitude value of the output detector signal is lower [14][15][16][17]. In the case of microscopic thermography, due to the small values of d, the values of τ a and ω have little influence on the indication of the thermographic camera [19].…”