1. Field of the Invention
The present invention relates to a goniometric spectrophotometer for measuring, in different illuminating or viewing directions, a special effect paint such as a metallic paint or a pearlescent paint appearing differently depending on an illuminating direction or a viewing direction.
2. Description of the Related Art
In a metallic paint or a pearlescent paint used for an exterior coating of automobile or the like, aluminum flakes or mica flakes called a special effect pigment is contained in a paint film, which provides a metallic effect or a pearlescent effect. Such an effect is provided because contribution of the special effect pigment to reflection characteristics is varied depending on an illuminating direction and a viewing direction. For color evaluation or colorimetric measurement of the metallic paint or the pearlescent paint, the following measuring apparatuses are used.
(1) a multi-angle spectrophotometer provided with a multi-angle geometry of illuminating from multiple directions and receiving from a single direction (multi angle illumination—directional receiving), or illuminating from a single direction and receiving from multiple directions (directional illumination—multi angle receiving); and
(2) a goniometric spectrophotometer capable of arbitrarily setting an illuminating direction or a receiving direction.
FIG. 14 is a schematic illustration showing an optical system S11 of a conventional multi-angle spectrophotometer of multi-angle illumination-directional receiving geometry. The optical system S11 has three illuminators 110, 120, and 130 arranged at three different angular positions with respect to a surface 1 of a sample, and a light receiver 140 arranged at a specified angular position. The illuminators 110, 120, and 130 are respectively set at 20 degrees, 0 degree, and −30 degrees with respect to a normal 1n to the surface 1 of the sample placed in a sample aperture (not shown), and the light receiver 140 is set at −45 degrees with respect to the normal 1n. The illuminators 110, 120, and 130 respectively include light sources 111, 121, and 131, and collimating lenses 112, 122, and 132 for collimating light fluxes emitted from the respective light sources 111, 121, and 131 into collimated light fluxes 113, 123, and 133 in the respective illuminating directions. The light receiver 140 has a spectral analyzer 141, and a collimating lens 142 for converging reflected light fluxes from the sample surface 1 to an incident aperture 141a of the spectral analyzer 141.
An operation of the multi-angle spectrophotometer provided with the optical system S11 is described. First, the light sources 111, 121, and 131 of the illuminators 110, 120, and 130 are sequentially turned on by an unillustrated control calculating unit. Light fluxes emitted from the light sources 111, 121, and 131 are respectively collimated into collimated light fluxes by the collimating lenses 112, 122, and 132, so that the collimated light fluxes from the respective illuminating directions are projected onto the sample surface 1. Then, a reflected light flux 143 from the sample surface 1 with an anormal angle of −45 degrees is converged to the incident aperture 141a of the spectral analyzer 141 by the collimating lens 142. The spectral analyzer 141 is provided with an unillustrated diffraction grating and a photo sensor array. The light flux through the incident aperture 141a is dispersed by the diffraction grating in the spectral analyzer 141 with respect to each wavelength component for calculating the spectral intensity of the dispersed light flux. Also, spectral reflectance factors of the sample surface 1 in the respective illuminating directions are calculated based on the spectral intensities of the reflected light fluxes 143 of the illumination light fluxes emitted from the illuminators 110, 120, and 130 at the different angular positions to the sample surface 1. The thus obtained spectral reflectance factors are converted into colorimetric values or the like. In this way, a color evaluation value for the sample surface 1 is acquired.
FIG. 15 is a schematic illustration of an optical system S12 of a goniometric spectrophotometer of directional illumination—gonio receiving geometry. The optical system S12 has an illuminator 150 arranged at an anormal angle of 45 degrees with respect to a normal in to a surface 1 of a sample placed in a sample aperture (not shown), and a light receiver 140 which is rotationally movable around an axis 1c on a measurement area of the sample surface 1 in the directions shown by the arrows 144. The light receiver 140 is loaded on an arm pivoted on the axis 1c, and is controllably moved by controlling the pivot angle of the arm by a driving means.
An operation of the goniometric spectrophotometer provided with the optical system S12 is described. First, when the light receiver 140 is moved to a position capable of receiving a reflected light flux in a certain receiving direction by an unillustrated control calculating unit, a light source 151 of the illuminator 150 is turned on. A light flux emitted from the light source 151 is collimated by a collimating lens 152 so that the collimated light flux is projected onto the sample surface 1. Then, a reflected light flux 143 from the sample surface 1 in a receiving direction depending on the position of the light receiver 140 is converged to an incident aperture 141a of a spectral analyzer 141 by a collimating lens 142 for calculating the spectral intensity of the reflected light flux 143. Then, the light receiver 140 is moved to a succeeding receiving position to calculate a spectral intensity of the reflected light flux 143 in the succeeding receiving direction in a similar manner as mentioned above. The control calculating unit calculates spectral reflectance factors of the sample surface 1 in the respective receiving directions based on the spectral intensities of the reflected light fluxes 143 from the sample surface 1 in the respective receiving directions. The thus obtained spectral reflectance factors are converted into colorimetric values or the like. In this way, a color evaluation value for the sample surface 1 is acquired.
In the goniometric spectrophotometer provided with the optical system S12, the receiving angle can be arbitrarily set with respect to the illuminating direction. Accordingly, more detailed spectral intensity information in terms of angles can be acquired, as compared with the conventional multi-angle spectrophotometer. For instance, colorimetric values of a metallic paint can be sufficiently precisely measured by the multi-angle spectrophotometer. However, the goniometric spectrophotometer capable of flexibly setting the receiving angle is advantageous in color evaluation of a pearlescent paint whose spectral reflectance is varied greatly depending on a viewing direction corresponding to a reflecting angle. Also, paints having special reflection effects have been yearly developed for an exterior coating of automobile or the like. The goniometric spectrophotometer is superior in the aspect that an optimal geometry can be established depending on reflection characteristics of the special effects paints.
As mentioned above, the goniometric spectrophotometer has flexibility in setting a geometry because it can arbitrarily set a receiving angle with respect to an illuminating direction. However, size increase and weight increase of the goniometric spectrometer is unavoidable because a mechanism for rotationally moving the light receiver 140 including the spectral analyzer 141 is indispensable. Also, it takes a considerable time to move the light receiver 140 as a whole with a necessary precision. In view of the above, it is mechanically difficult to make the size of the conventional goniometric spectrophotometer as shown in FIG. 15 more compact to such an extent that the spectrophotometer can be handled with one hand by an operator for color control of automobile bodies, for instance.