Apparatus for measuring goniometric reflection property of sample

An apparatus for measuring a goniometric reflection property of a sample has: one or more illuminators; a toroidal mirror which is rotationally symmetrical around a center axis effectively contacting with a surface of the sample; a light receiver having an incident aperture on the center axis; a rotating optics which rotates around a rotation axis which effectively coincides with the center axis; and a controller for controlling operations of the illuminators, the light receiver, and the rotating optics, wherein the toroidal mirror reflects light fluxes emitted from the surface of the sample illuminated by the one or more illuminators in emitting directions perpendicular to the center axis and directs each of the light fluxes to the center axis, and wherein the rotating optics specifies one of the light fluxes reflected by the toroidal mirror and directs the specified light flux to the incident aperture of the light receiver.

This application is based on Japanese Patent Application No. 2005-185387 filed on Jun. 24, 2005, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

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. 14is a schematic illustration showing an optical system S11of a conventional multi-angle spectrophotometer of multi-angle illumination-directional receiving geometry. The optical system S11has three illuminators110,120, and130arranged at three different angular positions with respect to a surface1of a sample, and a light receiver140arranged at a specified angular position. The illuminators110,120, and130are respectively set at 20 degrees, 0 degree, and −30 degrees with respect to a normal1nto the surface1of the sample placed in a sample aperture (not shown), and the light receiver140is set at −45 degrees with respect to the normal1n. The illuminators110,120, and130respectively include light sources111,121, and131, and collimating lenses112,122, and132for collimating light fluxes emitted from the respective light sources111,121, and131into collimated light fluxes113,123, and133in the respective illuminating directions. The light receiver140has a spectral analyzer141, and a collimating lens142for converging reflected light fluxes from the sample surface1to an incident aperture141aof the spectral analyzer141.

An operation of the multi-angle spectrophotometer provided with the optical system S11is described. First, the light sources111,121, and131of the illuminators110,120, and130are sequentially turned on by an unillustrated control calculating unit. Light fluxes emitted from the light sources111,121, and131are respectively collimated into collimated light fluxes by the collimating lenses112,122, and132, so that the collimated light fluxes from the respective illuminating directions are projected onto the sample surface1. Then, a reflected light flux143from the sample surface1with an anormal angle of −45 degrees is converged to the incident aperture141aof the spectral analyzer141by the collimating lens142. The spectral analyzer141is provided with an unillustrated diffraction grating and a photo sensor array. The light flux through the incident aperture141ais dispersed by the diffraction grating in the spectral analyzer141with respect to each wavelength component for calculating the spectral intensity of the dispersed light flux. Also, spectral reflectance factors of the sample surface1in the respective illuminating directions are calculated based on the spectral intensities of the reflected light fluxes143of the illumination light fluxes emitted from the illuminators110,120, and130at the different angular positions to the sample surface1. The thus obtained spectral reflectance factors are converted into colorimetric values or the like. In this way, a color evaluation value for the sample surface1is acquired.

FIG. 15is a schematic illustration of an optical system S12of a goniometric spectrophotometer of directional illumination—gonio receiving geometry. The optical system S12has an illuminator150arranged at an anormal angle of 45 degrees with respect to a normal in to a surface1of a sample placed in a sample aperture (not shown), and a light receiver140which is rotationally movable around an axis1con a measurement area of the sample surface1in the directions shown by the arrows144. The light receiver140is loaded on an arm pivoted on the axis1c, 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 S12is described. First, when the light receiver140is moved to a position capable of receiving a reflected light flux in a certain receiving direction by an unillustrated control calculating unit, a light source151of the illuminator150is turned on. A light flux emitted from the light source151is collimated by a collimating lens152so that the collimated light flux is projected onto the sample surface1. Then, a reflected light flux143from the sample surface1in a receiving direction depending on the position of the light receiver140is converged to an incident aperture141aof a spectral analyzer141by a collimating lens142for calculating the spectral intensity of the reflected light flux143. Then, the light receiver140is moved to a succeeding receiving position to calculate a spectral intensity of the reflected light flux143in the succeeding receiving direction in a similar manner as mentioned above. The control calculating unit calculates spectral reflectance factors of the sample surface1in the respective receiving directions based on the spectral intensities of the reflected light fluxes143from the sample surface1in 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 surface1is 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 receiver140including the spectral analyzer141is indispensable. Also, it takes a considerable time to move the light receiver140as 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 inFIG. 15more 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.

SUMMARY OF THE INVENTION

In view of the above problems residing in the prior art, it is an object of the present invention to provide a compact, lightweight, portability-oriented goniometric spectrophotometer that enables to easily and arbitrarily set a receiving angle with respect to an illuminating direction in a short period.

To accomplish the object, an apparatus of the present invention for measuring a goniometric reflection property of a sample comprises: one or more illuminators; a toroidal mirror which is rotationally symmetrical around a center axis effectively contacting with a surface of a sample; a light receiver having an incident aperture on the center axis; a rotating optics which rotates around a rotation axis which effectively coincides with the center axis; and a controller for controlling operations of the illuminators, the light receiver, and the rotating optics, wherein the toroidal mirror reflects a light flux emitted from the surface of the sample illuminated by the one or more illuminators in emitting directions perpendicular to the center axis and directs each of the light fluxes to the center axis, and wherein the rotating optics specifies one of the light fluxes reflected by the toroidal mirror and directs the specified light flux to the incident aperture of the light receiver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the invention are described. The terminology in the following explanation is substantially based on ASTM E2175-01 “Standard Practice for Specifying the Geometry of Multi-angle Spectrophotometer”.

First Embodiment

FIG. 1is a front view showing an arrangement of a principle optical system S1of a goniometric spectrophotometer i.e. an apparatus for measuring goniometric reflection characteristics of a sample according to a first embodiment.FIG. 2is a cross-sectional side view of the optical system S1in a plane perpendicular toFIG. 1and including a normal1nto a surface1of a sample placed in a sample aperture (not shown).FIG. 3is a perspective view of the principle optical system. As shown inFIGS. 1 through 3, the optical system S1includes: a toroidal mirror2rotationally symmetrical around a center axis2xsubstantially contacting with the sample surface1(or the sample aperture) coated with a pearlescent paint or the like; an illumination system10for illuminating the sample surface1with an illumination light flux: a receiving optics20for receiving a reflected light flux from the sample surface1; and a spectral analyzer40for measuring a spectral intensity of the reflected light flux received by the receiving optics20. In the case of an apparatus for measuring goniometric reflection characteristics of a sample, a receiving optics for measuring an intensity of a reflected light flux is provided in place of the spectral analyzer40. The receiving optics20includes a plane mirror31serving as a rotating optics, and a relay lens24serving as a relay optics. The relay lens24is a fixed optics that does not rotate.

The toroidal mirror2is a concave mirror having different cross sections from each other in two perpendicular planes. The toroidal mirror2of this embodiment is a part of a ring shaped concave mirror symmetrical around the center axis2xcontacting with the sample aperture.

Specifically, the toroidal mirror2has a circular cross section201in a plane2a(hereinafter, referred to as “measurement plane2a”) (seeFIG. 3) perpendicular to the center axis2xand including the normal in to the sample surface1at a center1c, and parabolic cross sections202in planes including the center axis2x. The focus point of each of the parabolic cross sections202is located on a circle2f(hereinafter, referred to as “focus point circle2f”) in the plane parallel to and apart by a predetermined distance from the measurement plane2acentered at the center axis2xwhose radius is around half of that of the toroidal mirror2. The axis of symmetry of each of the parabolic cross sections202perpendicularly crosses the center axis2xand includes the focus point.

With the thus shaped toroidal mirror2, reflected light fluxes from the sample surface1in the respective illuminating directions around the center axis2xparallel to the measurement plane2aperpendicular to the center axis2xare reflected on the toroidal mirror2. The reflected light fluxes reflected on the toroidal mirror2are converged at respective focus points on the focus point circle2fof the toroidal mirror2corresponding to the respective illuminating directions around the center axis2x.

The illumination system10includes a light source11which is disposed on the focus point circle2fof the toroidal mirror2with an anormal angle of 45 degrees with respect to the normal1n. An illumination light flux emitted from the light source11does not directly illuminate the sample surface1, but is projected onto the sample surface1after being collimated by reflection on the toroidal mirror2, as shown inFIG. 1. The illumination system10of the abovementioned arrangement is made more compact than the arrangement linearly provided with the light sources and the collimating lenses as shown inFIGS. 14 and 15.

The plane mirror31of the receiving optics20is an oval shaped plane reflector (seeFIG. 3) having a high reflectance and rotates around a rotational axis30xcoinciding with the center axis2xof the toroidal mirror2. Specifically, the plane mirror31is mounted obliquely with respect to the rotational axis30x, and is driven rotationally around the rotational axis30xin the directions shown by the arrows30ainFIGS. 1 and 3by an unillustrated driving means. The plane mirror31is rotated around the rotational axis30xby about 180 degrees to cover substantially the whole area of the circular cross section201of the toroidal mirror2.

Specifically, the plane mirror31is rotatably provided at such a position as to allow substantially all the light fluxes that have been reflected on the toroidal mirror2and converged on the focus point circle2fto be incident thereon, and with such a tilt angle as to reflect the light fluxes incident onto the plane mirror31in the direction of the center axis2xi.e. the rotational axis30x. The converging position of each light flux on the focus point circle2fis specified by the rotation angle of the plane mirror31so that the light flux in a specified direction is directed to an incident aperture41aof the spectral analyzer40.

FIG. 4is an illustration showing a function of the plane mirror31, specifically showing a cross section in a plane passing the intersecting point “A” of a reflection surface of the plane mirror31shown inFIG. 3with the center axis2x, and perpendicular to the center axis2x. As shown by the solid line inFIG. 4, in the case where the cross section of the plane mirror31is set parallel to the sample surface1, out of the light reflected on the sample surface1, a light flux parallel to a radius RP1coinciding with the normal in is reflected on a reflection area A1of the toroidal mirror2facing the plane mirror31. After the reflected light flux is converged on the point F1of the focus point circle2f, the converged light flux is selectively converged to the incident aperture41a.

On the other hand, as shown by the dotted line inFIG. 4, in the case where the cross section of the plane mirror31is rotated by a certain angle θ from the parallel position, out of the light reflected on the sample surface1, a light flux parallel to a radius RP2, which is angularly displaced from the radius RP1by the angle θ, is reflected on a reflection area A2of the toroidal mirror2facing the plane mirror31. After the reflected light flux is converged on the point F2on the focus point circle2f, the converged light flux is selectively converged to the incident aperture41a. In this way, the plane mirror31serves as a selector for selectively allowing a reflected light flux to be incident to the incident aperture41ain accordance with the rotation angle of the plane mirror31. In other words, the optical system S1is configured to variably set the receiving angle with respect to the illuminating direction in accordance with the rotation angle of the plane mirror31.

The relay lens24comprises one or more lens elements having a positive optical power, and converges the light flux reflected along the center axis2xby the plane mirror31into the incident aperture41a. Thus, the light flux converged at the selected position on the focus point circle2fby the rotation angle of the plane mirror31is re-converged into the incident aperture41a.

The spectral analyzer40measures spectral intensities of the light fluxes incident into the incident aperture41a.FIG. 5is a schematic illustration showing an example of the spectral analyzer40. The spectral analyzer40includes a collimating lens41, a diffraction grating42, and a photo sensor array43.

The collimating lens41transmits the light flux passing through the incident aperture41ato the diffraction grating42as a collimated light flux and produces a dispersed image of the incident aperture41aon the surface of the photo sensor array43. The diffraction grating42reflects and disperses the collimated light flux into the wavelength components. The photo sensor array43comprises a plurality of photosensitive pixels (silicon photodiodes for example) arrayed in line at even interval. The dispersed light incident in each pixel of the photo sensor array43is converted to a corresponding photocurrent by the photodiodes of the channel.

An analog light signal indicative of the received light component is outputted from each pixel of the photo sensor array43, and is processed by a signal processor501and a calculator502. Thus, spectral intensities of the light fluxes are obtained, as well as reflectance factors and colorimetric values based on the spectral intensities of the light fluxes. Specifically, the signal processor501performs amplification and digital conversion with respect to the analog light signals. The calculator502calculates spectral intensities, reflectance factors, and colorimetric values based on digital signals outputted from the signal processor501.

An operation or a process of the optical system S1having the above arrangement in the first embodiment is described. A light flux11aemitted toward the toroidal mirror2from the light source11arranged at an anormal angle of 45 degrees with respect to the normal in is reflected on the toroidal mirror2, and the reflected light flux is projected onto the sample surface1as a collimated light flux11bwith the anormal angle of 45 degrees. The collimated light flux11bis reflected on the sample surface1in accordance with the reflection characteristics of the sample surface1.

A light flux11cwhich is a part of the light reflected from the sample surface1and is parallel to the measurement plane2ais reflected on the toroidal mirror2as a reflected light flux11d.FIGS. 1 and 2illustrate merely the reflected light flux11cin the direction of the normal1n. The reflected light flux11dis converged at a point11eon the focus point circle2fcorresponding to the reflecting directions around the center axis2x, because each of the parabolic cross sections202of the toroidal mirror2has a parabolic profile with a vertical line2has the symmetrical axis (seeFIG. 2). The converging point11eis changed depending on the reflecting direction from the toroidal mirror2.

As mentioned above, the respective converging points11eon the focus point circle2fare points where images of the incident aperture41aof the spectral analyzer40are produced by combined operation of the plane mirror31and the relay lens24. Also, the focus point circle2fhas such a configuration that the light flux converged on the respective converging points lie of the focus point circle2fis selected in accordance with the rotation of the plane mirror31. With this arrangement, an optical path from the toroidal mirror2to the incident aperture41ais defined in accordance with the rotation angle of the plane mirror31. Specifically, a divergent light flux11fout of the converging point11eselected by the rotation of the plane mirror31is reflected on the plane mirror31, and is incident along the center axis2xor the rotational axis30xonto the relay lens24, which, in turn, allows the divergent light flux11fto be incident to the incident aperture41a, as a converged light flux11g.

When the converged light flux11gis incident to the incident aperture41a, the spectral analyzer40measures a spectral intensity of the converged light flux119, as a spectral intensity of the reflected light flux from the sample surface1in the direction defined by the rotation angle of the plane mirror31. In the example ofFIG. 1, the illumination light flux with the anormal angle of 45 degrees is projected onto the sample surface1, and the plane mirror31is set at such a rotation angle as to selectively reflect the reflected light flux along the normal1n. Accordingly, the spectral intensity of the reflected light flux with an anormal angle of 0 degree with respect to the illumination light flux is measured.

The goniometric spectrophotometer provided with the optical system S1is particularly useful in evaluating the color of a pearlescent paint.FIGS. 6A to 6Care graphs showing reflection characteristics of a generally available solid paint, a metallic paint, and a pearlescent mica paint, wherein the illumination angle is set at −45 degrees, and the receiving angle is changed in the range of −25 degrees to 65 degrees. In the graph ofFIG. 6Aconcerning colorimetric measurement of the solid paint, the magnitudes and the ratio of tri-stimulus values (X, Y, Z) are substantially constant except for specular reflection. This shows that the solid paint exhibits substantially the same color to any viewing direction. In the graph ofFIG. 6Bconcerning colorimetric measurement of the metallic paint, although the magnitudes of tri-stimulus values (X, Y, Z) are varied depending on the receiving angle, the ratio of the tri-stimulus values (X, Y, Z) is stable. This means that the hue of the metallic paint appears substantially the same to any viewing direction. On the other hand, in the graph ofFIG. 6Cconcerning colorimetric measurement of the pearlescent mica paint, not only the magnitudes of tri-stimulus values (X, Y, Z) but also the ratio thereof are changed depending on the receiving angle. This means that the hue of the pearlescent mica paint changes depending on the viewing direction.

A goniometric spectrophotometer capable of flexibly setting the receiving angle is particularly suitable for accessing the pearlescent color represented by a pearlescent paint such as the paint containing mica flakes which has the appearance highly dependent on the observing angle and require to measure the spectral intensities of light fluxes from consecutively different directions with a small interval. Further, in the goniometric spectrophotometer in the first embodiment, the observing direction is flexibly set by combined operation of the toroidal mirror2and the plane mirror31having the rotational axis30xin agreement with the center axis2xof the toroidal mirror2so as to extract a reflected light flux in any direction parallel to the measurement plane2aout of the reflected light fluxes from the sample surface1, whereby a spectral intensity of the extracted reflected light flux is measured by the spectral analyzer40. Unlike the conventional goniometric spectrophotometer designed such that the entire light receiver is rotationally moved, the arrangement in the embodiment enables to produce a compact goniometric spectrophotometer because the plane mirror31is the only member to be rotated. Also, since the plane mirror31is the only member to be driven, a load to the driving means can be reduced, which enables to perform angular positioning of the plane mirror31within a relatively short period, thereby enabling speedy measurement.

Second Embodiment

In the following, a second embodiment as an example of a more practical goniometric spectrophotometer is described. It is desirable to solve the following drawbacks (1) to (3) of the principle optical system S1shown inFIGS. 1 to 3for practical application.

(1) Since the rotational axis30xof the plane mirror31, the optical axis of the relay lens24, and the incident aperture41aof the spectral analyzer40are in agreement with the center axis2xof the toroidal mirror2substantially contacting with the sample surface1, a part of the plane mirror31, the relay lens24, and the spectral analyzer40locate below the sample surface1. Thus, the interference of the sample surface1with the part of the measuring apparatus may obstruct measurement of a large sample.

(2) After the light flux reflected on the toroidal mirror2is converged at the respective converging points of the focus point circle2f. The divergent light flux is incident onto the plane mirror31and the relay lens24after the convergence. In view of this, a plane mirror and a relay optics each having a large effective diameter are required, which may increase the size and cost of the measuring apparatus.

(3) It is necessary to incorporate a reference optics for monitoring an output fluctuation of the light source11.

FIG. 7is a front view showing an arrangement of an optical system S2of a goniometric spectrophotometer as the second embodiment, taking into consideration of the aforementioned drawbacks (1) to (3).FIG. 8is a cross-sectional side view of the optical system S2in a plane perpendicular toFIG. 7and including a normal to a surface5of a sample placed in a sample aperture (not shown). The optical system52is different from the optical system S1in that the optical system S2is provided with a reflective mirror3between a toroidal mirror2and the surface5of the sample disposed at a certain angle with respect to a center axis2xof the toroidal mirror2for folding a measurement plane2a(seeFIGS. 1 and 3). With this arrangement, the aforementioned drawback (1) can be solved, and a colorimetric value of the surface5of a sample having a large size such as an automobile body can be measured. Also, the optical system S2is different from the optical system S1in that a second relay lens32comprising a relay optics is additionally provided between a plane mirror31and a focus point circle2f, and that a reference optics60is provided. With these arrangements, the drawbacks (2) and (3) are solved. In the following, the second embodiment is described primarily on the differences.

The reflective mirror3is a plane mirror of an elongated rectangular shape, and is fixed between the center axis2xof the toroidal mirror2and a reflection surface of the toroidal mirror2with such a tilt angle as to fold the measurement plane2aby 90 degrees. The sample surface5is arranged at a position equivalent to a position substantially in contact with the center axis2xof the toroidal mirror2, although the optical path is folded by the reflective mirror3. The positional relation between the toroidal mirror and the sample surface in the embodiments of the invention may include a case that the sample surface1is actually contacted by the center axis2xof the toroidal mirror2, as in the arrangement of the optical system S1, and a case that the sample surface5is not actually contacted but effectively contacted by the center axis2xvia the reflective mirror3, as in the arrangement of the optical system S2.

The relay optics includes a first relay lens (first lens element)24provided between the plane mirror31and an incident aperture41a, and the second relay lens32(second lens element) provided between the plane mirror31and the focus point circle2f. Although the illustration of the second relay lens32is simplified, the second relay lens32is integrated with the plane mirror31and rotates therewith. Additionally providing the second relay lens32enables to suppress divergence of light fluxes converged at the respective converging points on the focus point circle2f, thereby enabling to narrow the light fluxes onto the plane mirror31and the first relay lens24. This enables to suppress the effective diameter of the plane mirror31and of the first relay lens24, which contributes to realize a compact optics.

The reference optics60includes a diffuser61and a reference optical fiber62. The reference optics60is arranged at such a position as to allow incidence of a reference light flux13r, i.e. a part of a light flux that has been emitted from a light source11and reflected on an extension2bextending along the center axis2xof the toroidal mirror2. The diffuser61is located on an incident plane of the reference optics60. The diffuser61is an optical component having a property of diffusively transmitting a light flux incident thereon, and is provided on the center axis2xof the toroidal mirror2. The diffuser61is, as shown inFIG. 8, located at such a position that does not interfere with the reflective mirror3. The reference optical fiber62has an incident end62aon the back side of the diffuser61to allow a light flux61ri.e. a part of the reference light flux13rthat has been incident onto the diffuser61and diffusively transmitted through the diffuser61to be incident into the incident end62aas a reference light flux.

Alternatively, the incident end62aof the reference optical fiber62may be directly disposed on the center axis2xof the toroidal mirror2so that the reference light flux is incident to the incident end62aof the reference optical fiber62without passing the diffuser61. Allowing the reference light flux to be incident to the incident end62aof the reference optical fiber62via the diffuser61, as proposed in the embodiment, is advantageous as follows. For instance, in the case where plural light sources are arranged on the focus point circle2f, this arrangement allows reference light fluxes originated from the light sources in the respective illuminating directions to be incident into the incident end62aof the reference optical fiber62, because a part of each reference light flux13rthat has been diffusively transmitted through the diffuser61is incident into the incident end62a.

In the second embodiment, the spectral analyzer40is a dual-channel analyzer provided with two incident apertures. One of the incident apertures is an incident aperture41ainto which reflected light fluxes from the sample surface are incident via the relay optics, and the other is a reference aperture41binto which reference light fluxes are incident. The incident aperture41ais arranged along the center axis2x. The reference aperture41bis connected to an exit end62bof the reference optical fiber62.

An operation or a process of the optical system S2having the above arrangement in the second embodiment is described. A light flux13aemitted from the light source11arranged substantially at an anormal angle of 45 degrees is reflected on the toroidal mirror2, and the reflected light flux is incident onto the reflective mirror3as a collimated light flux13bsubstantially with an anormal angle of 45 degrees so that the sample surface5is illuminated with a collimated light flux13creflected on the reflective mirror3. The collimated light flux13cis reflected on the sample surface5in accordance with the reflection characteristics of the sample surface5, as a reflected light flux13d, which, in turn, is incident onto the reflective mirror3for reflection.

A part of the reflected light flux13dparallel to the measurement plane2a(seeFIG. 3) perpendicular to the center axis2xis reflected on the toroidal mirror2, as a reflected light flux13f. The reflected light flux13fis converged at a converging point13gof the focus point circle2fdepending on the respective reflecting directions around the center axis2x, because each of parabolic cross sections202of the toroidal mirror2has a parabolic profile with a vertical line2has the symmetrical axis. The converging point13gis selected in accordance with the rotation angle of the plane mirror31. Thereafter, a diffused light flux13hout of the converging point13gselected by the rotational position of the plane mirror31is narrowed by the second relay lens32. And the narrowed light flux is reflected on the plane mirror31along the direction of the center axis2xfor incidence onto the first relay lens24to be a converged light flux13j, which in turn is incident into the incident aperture41a.

A part of the light flux emitted from the light source11is reflected on the extension2bof the toroidal mirror2as the reference light flux13rso that the reference light flux13ris projected onto the diffuser61. A part of the reference light flux13rthat has been diffusively transmitted through the diffuser61is incident into the incident end62aof the reference optical fiber62as a reference light flux, which in turn is transmitted to the reference aperture41bvia the reference optical fiber62.

In the second embodiment, a stepping motor33and a stepping motor driver34are used as an example of a driving means for rotating the plane mirror31(seeFIG. 8). An output shaft of the stepping motor33is directly connected to a rotary shaft331of the plane mirror31. The plane mirror31is driven rotationally around an axis of the rotary shaft331when the stepping motor driver34outputs a predetermined number of driving pulses to the stepping motor33. The light source11is controllably turned on by a light source driver115. The light source driver115, the stepping motor driver34, and the spectral analyzer40are controlled by a control calculating unit50.

FIG. 9is a block diagram showing functional elements of the control calculating unit50. The control calculating unit50includes a central processing unit (CPU), a read only memory (ROM) storing a control program and the like, and a random access memory (RAM) for temporarily saving data for computation processing or control processing. The control calculating unit50functionally includes a measurement controller51for controlling the light source11and the stepping motor33, and a calculator52for performing processing of a measurement signal outputted from the spectral analyzer40. Also, the control calculating unit50receives an operation command signal from an operator by way of an operating unit53.

The measurement controller51has a light source controller511, a stepping motor controller512, and a pulse count setter513. The light source controller511generates a lighting control signal for controlling emission of the light source11in accordance with the operation command signal sent from the operating unit53, a measurement sequence, or the like to control the emission of the light source11via the light source driver115.

The stepping motor controller512generates a stepping motor driving signal for driving the stepping motor33. Specifically, the stepping motor controller512obtains the necessary pulse count for rotating the plane mirror31to a predetermined angle from the pulse count setter513, which will be described later, and supplies as many pulses as the necessary pulse count to the stepping motor driver34as a driving pulse signal. The stepping motor driver34generates a driving pulse based on the driving pulse signal, and supplies the generated driving pulse to the stepping motor33.

The pulse count setter513correlates the number of pulses to a rotation angle of the plane mirror31, and sets the pulse count data for rotating the plane mirror31by the predetermined angle from the initial position. When the plane mirror31is rotated at every 5 degree position from the initial position, for example, the pulse count data for rotating the plane mirror31at every 5 degree position is set for each 5 degree position. The pulse count data set by the pulse count setter513is read, and the read pulse count data is sent to the stepping motor controller512in accordance with the measurement sequence as a driving pulse signal.

The initial position of the plane mirror31can be the direction of specular reflection by the sample positioned at the predetermined position and illuminated by the light source11, which is detected by the spectral analyzer40as the position of the maximum reflection intensity. Alternatively, the initial position of the plane mirror31can be detected by an additional initial position sensor such as a photo-interrupter, which is arranged at a suitable position on the plane mirror31. However, when the sample is inclined from the right position, the measurement will be erroneous if the initial position is detected by the additional initial position sensor, unlike a case that the initial position is detected as the specular reflection by the sample.

The calculator52has a spectral intensity calculator521, and a reflectance factor and colorimetric value calculator522. The spectral intensity calculator521calculates a spectral intensity of a reflected light flux with respect to each of the rotation angles of the plane mirror31i.e. each of the predetermined receiving angles, using the spectral intensity signal which has been outputted from the sensor array43of the spectral analyzer40and processed by a signal processor44. At the time of the calculation, a predetermined correction calculation is performed in accordance with intensity fluctuations of the reference light fluxes.

The reflectance factor and colorimetric value calculator522calculates a spectral reflectance factor acquired from the intensity obtained by the spectral intensity calculator521and converts it to colorimetric values of the sample in the respective receiving directions selected by the rotation of the plane mirror31by applying a predetermined color system to the spectral reflectance factors. Examples of the color system are XYZ color system, L*a*b* color system, and L*C*h* color system. Alternatively, a color difference may be obtained by applying a predetermined color difference equation to the colorimetric values. Examples of the color difference equation are L*a*b* color difference, CIE 94 color difference, and CIE 2000 color difference recommended by the International Commission on Illumination (CIE) and CMC (l:c) color difference.

An operation of the goniometric spectrophotometer in accordance with the second embodiment is described referring to a flowchart shown inFIG. 10. When a surface5of a sample is set in a predetermined sample aperture to start measurement, the light source11is turned on by the light source controller511(Step S1). Then, the stepping motor controller512sequentially generates a driving pulse for detecting specular reflection to detect the initial position of the plane mirror31, in other words, the specular reflection position of the sample surface5, and the stepping motor33is driven rotationally by every predetermined angular interval based on the driving pulse (Step S2). Thereby, the plane mirror31is driven rotationally around the rotary shaft331(seeFIG. 8). At the time of the rotation of the plane mirror31, the spectral intensity calculator521calculates a spectral intensity of a reflected light flux by the certain angular interval of the stepping motor33.

Subsequently, it is judged whether the current angular position of the plane mirror31is the specular reflection position (Step S3). Specifically, comparison is made to judge whether the spectral intensity of the reflected light flux calculated by the spectral intensity calculator521reaches the maximum value. The comparison is cyclically repeated until the maximal value of the spectral intensity of the reflected light flux is detected to define the angular position of the plane mirror31where the spectral intensity of the reflected light flux is maximal, as the initial position of the plane mirror31(Step S4).

After the initial position is defined, the pulse count setter513sets a drive pulse number in accordance with the rotation angle of the plane mirror31based on the initial position (Step S5). Specifically, since the rotation angle of the stepping motor33can be precisely controlled by the drive pulse number, and a relation between the drive pulse number and the rotation angle can be defined in advance, the drive pulse number in accordance with the angular interval of the plane mirror31, e.g. the drive pulse number necessary for rotating the plane mirror31at every 5 degree position is set. Then, the stepping motor controller512reads the drive pulse number for rotating the plane mirror31by the first rotation angle set at first in the measurement sequence, and the read drive pulse number is outputted to the stepping motor driver34. Thereby, the stepping motor33rotates the plane mirror31by the first rotation angle (Step S6).

Then, the converged light flux at the converging point on the focus point circle2fselected by the rotation angle of the plane mirror31is incident into the incident aperture41aof the spectral analyzer40, and the reference light flux incident into the incident end62aof the reference optical fiber62via the diffuser61is incident into the reference aperture41b. Next, the spectral intensity calculator521calculates the spectral intensity of the reflected light flux from the sample surface5and the spectral intensity of the reference light flux, as spectral intensity data (Step S7). Subsequently, the reflectance factor and colorimetric value calculator522calculates a spectral reflectance factor based on the spectral intensity data (Step58). The calculated spectral reflectance factor is temporarily saved in the RAM of the control calculating unit50.

Thereafter, it is judged whether there remains measurement to be conducted in the predetermined receiving angle (Step S9). If it is judged that there remains measurement to be conducted (NO in Step S9), the flow returns to Step S5to cyclically repeat the measurement. For instance, the stepping motor controller512reads the drive pulse number for rotating the plane mirror31by the second rotation angle set at second in the measurement sequence. If, on the other hand, it is judged that the measurement in the predetermined receiving angle is completed (YES in Step S9), the light source11is turned off (Step S10). Then, the reflectance factor and colorimetric value calculator522calculates the colorimetric values (or color differences) in the respective receiving angles (Step811). Thus, the processing is completed.

The above operation flow is described for the case that the stepping motor33is used as a driving means for rotating the plane mirror31. In the case where the stepping motor33is not used, a similar measurement as mentioned above may be performed by reading rotation angle information of the plane mirror31detected by an initial position sensor, a position sensor, and the like.

(1) Modified Illumination System Incorporated with an Aperture Plate

In the first and second embodiments, the light source11of the illumination system10is arranged on the focus point circle2f. Alternatively, an illumination system10′ as shown inFIG. 11may be used in place of the illumination system10. The illumination system10′ has a light source11, a light source reflective mirror12M, a condensing lens14, and an aperture plate15.

The light source reflective mirror12M is arranged on a focus point circle2fof a toroidal mirror2with a predetermined angle to reflect a light flux12athat has been emitted from the light source11and converged by the condensing lens14so that the reflected light flux is incident onto a reflecting surface of the toroidal mirror2as a divergent light flux12b. The divergent light flux12bis collimated into a collimated light flux12cby reflection on the toroidal mirror2so that the collimated light flux12cis projected onto a sample surface1or a sample surface5via a reflective mirror3. A part of the reflected light flux12athat has been reflected on an extension2bof the toroidal mirror2is projected onto a surface of a diffuser61as a reference light flux12r.

The aperture plate15is provided between the light source11and the condensing lens14. The aperture plate15is formed with a sample aperture15aand a reference aperture15b. The aperture plate15is positioned at the position equivalent to the position of the sample surface1to form the image on the sample surface1and the diffuser61by combined operation of the toroidal mirror2and the condensing lens14. With this arrangement, a light image15a′ of the sample aperture15ais formed on the sample surface1, and a light image15b′ of the reference aperture15bis formed on the surface of the diffuser61.

In the thus constructed illumination system10′, with use of the aperture plate15formed with the sample aperture15aand the reference aperture15b, a measurement area on the sample surface1i.e. an illumination area on the sample surface1with the illumination light is confined within the area of the light image15a′ and an illumination area on the surface of the diffuser61with the reference light is confined within the area of the light image15b′. This enables to suppress stray light to thereby perform more accurate colorimetric measurement.

(2) Modified Embodiment Provided with Plural Illuminators

In the first and second embodiments, the light source11of the illumination system10is arranged at an anormal angle of 45 degrees on the focus point circle2f. Alternatively, a plurality of light sources may be arranged on a focus point circle2f.FIG. 12is a front view showing an arrangement of an optical system S3provided with plural illuminators. The optical system S3has a first illuminator110arranged at an anormal angle of 45 degrees, a second illuminator120arranged at an anormal angle of 65 degrees, and a third illuminator130arrange at an anormal angle of 15 degrees.

The first illuminator110has a light source111arranged on the focus point circle2fwith an anormal angle of 45 degrees to project a collimated light flux112onto a sample surface via a toroidal mirror2. Similarly, the second illuminator120has a light source121arranged on the focus point circle2fwith an anormal angle of 65 degrees to project a collimated light flux122onto the sample surface via the toroidal mirror2. Likewise, the third illuminator130has a light source131arranged on the focus point circle2fwith an anormal angle of 15 degrees to project a collimated light flux132onto the sample surface via the toroidal mirror2. In this way, arranging the illuminators110,120, and130at the respective angular positions enables to speedily perform color evaluation of a pearlescent paint whose spectral reflectance factor is varied depending on an illuminating direction.

In the case of a goniometric spectrophotometer provided with the optical system S3, a control calculating unit may have a function of selectively turning on the light source111,121,131of the first, second, third illuminator110,120,130, in addition to the functional elements as shown inFIG. 9. Also, a stepping motor33may be controllably driven in association with light emission of the light source111,121,131to drivingly rotate a plane mirror31so that a light flux in an intended receiving angle defined by the angular position of the plane mirror31is incident to an incident aperture41a.

Further alternatively, an optical system may be configured in such a manner that a single light source is arranged on a focus point circle2f, and the light source is made movable along the focus point circle2f, in place of providing the first to third illuminators110,120, and130. The altered optical system enables to realize an operation substantially equivalent to the operation of the optical system provided with the plural illuminators.

(3) Modified Embodiment with a Retractable Shutter at the Sample Aperture

It is desirable to provide a retractable shutter capable of openably closing a sample aperture except for a condition that a sample faces a sample aperture formed in the housing of a goniometric spectrophotometer. In the case where the retractable shutter is provided, it is desirable that the retractable shutter is driven by the power of the stepping motor33in the second embodiment.

FIG. 13is a cross-sectional side view showing essential parts of a goniometric spectrophotometer provided with a retractable shutter. As illustrated inFIG. 13, the goniometric spectrophotometer is housed in a housing701. A sample aperture702is formed on the housing701at a position facing a sample surface5. A gear332is combined to an output shaft of a stepping motor33, and the gear332engages a large size gear341connected to a rotation shaft34. With this arrangement, when the stepping motor33is driven, the rotation shaft34is driven rotationally in the directions shown by the arrows inFIG. 13.

The rotation shaft34has one end thereof fixed to a plane mirror31, and the other end thereof fixed to an end of a plate of the retractable shutter7having such dimensions as to cover the sample aperture702. Specifically, the rotation shaft34serves as an axis of rotation of the plane mirror31and as a driving axis of the retractable shutter7. The plane mirror31and the retractable shutter7are mounted on the rotation shaft34with such a positional relation that the shutter7does not close the sample aperture702when the plane mirror31is rotated in a rotation angle range of about 180 degrees required for goniometric spectrophotometry. In other words, when the rotation shaft34is rotated to such an angular position that the rotation angle of the plane mirror31exceeds the rotation angle range of 180 degrees, the shutter7is moved to the position of closing the sample aperture702, as shown by the dotted line inFIG. 13. Namely, the shutter7is selectively movable to a closed position where the shutter7closes the sample aperture702, and a retracted position where the shutter7is retracted away from the sample aperture702to open the sample aperture702by the stepping motor33for drivingly rotating the plane mirror31.

In the goniometric spectrophotometer provided with the shatter7, when measurement is not performed, the sample aperture702can be closed by the shutter7by moving the shutter7to the closed position with use of the stepping motor33for rotating the plane mirror31. This enables to protect the measuring optics and to suppress intrusion of external foreign matters such as dusts. This arrangement eliminates additional provision of a driving means for the shutter7or the like, thereby eliminating cost increase.

SUMMARY OF EMBODIMENTS

(1) A goniometric spectrophotometer for measuring a goniometric reflection characteristic of a sample comprises: one or more illuminators; a toroidal mirror which is rotationally symmetrical with respect to a center axis substantially contacting with a surface of a sample; a light receiver including a spectral analyzer provided with an incident aperture on the center axis; a rotating optics provided with a rotation axis substantially in agreement with the center axis; and a controller for controlling operations of the illuminator, the light receiver, and the rotating optics, wherein the toroidal mirror reflects a light flux that has been emitted from the one or more illuminators and reflected on the sample surface in respective reflecting directions around the center axis and parallel to a measurement plane perpendicular to the center axis, and converges the light flux at respective converging points on a focus point circle of the toroidal mirror corresponding to the respective reflecting directions around the center axis, and wherein the light flux converged at the respective converging point on the focus point circle is selectively incident to the incident aperture of the light receiver in accordance with a rotation angle of the rotating optics around the rotation axis.

In this arrangement, arbitrarily setting the rotation angle of the rotating optics around the rotation axis by combined operation of the toroidal mirror and the rotating optics enables to extract the reflected light flux from the sample surface in a selected reflecting direction parallel to the measurement plane for measurement of a spectral intensity of the extracted light flux by the spectral analyzer. In other words, functioning the rotating optics as a selector for selecting the light flux converged at the respective converging point on the focus point circle of the toroidal mirror corresponding to the respective reflecting directions enables to extract the reflected light flux in the selected reflecting direction. This arrangement enables to make the goniometric spectrophotometer more compact, as compared with the conventional goniometric spectrophotometer designed such that the light receiver as a whole is rotationally moved, because the rotating optics with the rotation axis substantially in agreement with the center axis is the only member to be driven. Also, since measurement can be performed by merely rotating the rotating optics, a load to a driving means for rotating the rotating optics can be reduced, which enables to perform angular positioning of the rotating optics in a relatively short period.

With the goniometric spectrophotometer (1), in addition to the merit inherent to the goniometric spectrophotometer capable of flexibly measuring reflection light in an arbitrary reflecting direction merely by changing a control software controlling the rotation angle of the rotating optics or an equivalent technique, this arrangement enables to make the goniometric spectrophotometer compact and lightweight, thereby providing a portable goniometric spectrophotometer, because the rotating optics is the sole member to be driven, unlike the conventional goniometric spectrophotometer. Also, since a relatively inexpensive driver can be used and the angular positioning of the rotating optics can be performed in a relatively short period due to a reduced load to the driving means for rotating the rotating optics, this arrangement contributes to production cost reduction, and measurement time reduction.

(2) the goniometric spectrometer (1) further comprises a relay optics for converging the light flux converged at the respective converging points into the incident aperture of the light receiver, wherein the rotating optics has a plane mirror arranged obliquely relative to the rotation axis, the plane mirror being rotatable around the rotation axis by the controller, and wherein the converging point of the light flux on the focus point circle is selectively defined in accordance with a rotation angle of the plane mirror so that the light flux converged at the selected converging point is converged into the incident aperture of the light receiver by the relay optics.

In this arrangement, the light flux converged at the converging point on the focus point circle selected in accordance with the rotation angle of the plane mirror arranged obliquely relative to the rotation axis is incident into the incident aperture of the light receiver via the relay optics.

With the goniometric spectrophotometer (2), since the plane mirror is the sole member to be actually driven, a compact driving means for rotating the rotating optics can be produced, which contributes to size reduction and production cost reduction of the goniometric spectrophotometer.

(3) The relay optics, or a part of the relay optics of the goniometric spectrophotometer (2) is a fixed optics having an optical axis substantially in agreement with the center axis.

In this arrangement, since the relay optics, or the part of the relay optics is the fixed optics, the plane mirror, or the plane mirror and the part of the relay optics is the member to be actually driven. This contributes to reduction of the load to the driving means for rotating the rotating optics.

With the goniometric spectrophotometer (3), since the rotating optics is substantially constituted of the plane mirror, or the plane mirror and the part of the relay optics, the goniometric spectrometer can be realized with a simplified arrangement.

(4) The relay optics of the goniometric spectrophotometer (2) includes a first lens element having an optical axis substantially in agreement with the center axis, and a second lens element which is provided between the plane mirror and the focus point circle and is rotated with the plane mirror.

In this arrangement, since the light flux incident onto the plane mirror and the first lens element is narrowed by the second lens element, a plane mirror and a first lens element with a smaller effective diameter can be used.

With the goniometric spectrophotometer (4), since the plane mirror and the first lens element with the smaller effective diameter can be used with the help of the second lens element, a more compact and lightweight goniometric spectrophotometer can be realized.

(5) The illuminator in any one of the goniometric spectrophotometers (1) through (4) has a light source arranged substantially on the focus point circle, and the light flux emitted from the light source is collimated into a collimated light flux by reflection on the toroidal mirror for illuminating the sample surface.

In this arrangement, the collimated light flux generated with use of the toroidal mirror is projected onto the sample surface. Also, providing one or more light sources at appropriate positions on the focus point circle enables to easily change or increase the illuminating directions.

With the goniometric spectrophotometer (5), since the illuminating direction can be added or changed easily, and various geometries can be realized easily, a geometry of multi angle illumination-multi angle receiving, which is required for color evaluation of a pearlescent paint for instance, can be realized without the need of unduly cost increase.

(6) Any one of the goniometric spectrophotometers (1) through (5) further comprises a reflective mirror arranged between the toroidal mirror and the sample at a certain angle with respect to the center axis for folding the measurement plane.

In this arrangement, since the reflective mirror for folding the measurement plane is provided, the sample can be placed at such a position as to avoid an interference with the constituent elements of the goniometric spectrophotometer such as the rotating optics or the relay optics.

With the goniometric spectrometer (6), providing the reflective mirror for folding the measurement plane enables to dispose the sample at such a position as to avoid an interference with the constituent elements of the goniometric spectrophotometer. This enables to evaluate the color of a large sample such as an automobile body, for instance.

(7) In the goniometric spectrophotometer (6), the light flux which has been emitted from the light source arranged substantially on the focus point circle and reflected on the toroidal mirror is reflected on the reflective mirror to project the reflected light flux onto the sample surface, and a part of the light flux is allowed to be incident onto a reference optics arranged on the center axis without being reflected by the reflective mirror.

In this arrangement, it is possible to extract the illumination light substantially analogous to the illumination light illuminating the sample surface, as reference light.

With the goniometric spectrophotometer (7), since the illumination light substantially analogous to the illumination light illuminating the sample surface can be extracted as the reference light, precise measurement correction can be performed to compensate an output fluctuation of the illumination light or the like.

(8) The reference optics of the goniometric spectrophotometer (7) includes a diffuser arranged at an incident aperture of the reference optics on the center axis.

In this arrangement, a part of the illumination light that has diffusively transmitted through the diffuser is incident onto the reference optics. This enables to allow the reference light originated from each of plural light sources arranged on the focus point circle in respective illuminating directions to be incident onto the reference optics.

With the goniometric spectrophotometer (8), the reference light originated from each of the plural light sources arranged on the focus point circle in the respective illuminating directions is allowed to be incident onto the reference optics. This enables to simplify the construction of the reference optics.

(9) Any one of the goniometric spectrophotometers (1) through (8) has a housing formed with a sample aperture so that the sample is placed facing the sample aperture, and a retractable shutter for closing the sample aperture, the Retractable shutter being controllably movable to a closed position or a retracted position by a driving means for rotating the rotating optics.

In this arrangement, the shutter is driven by the driving means for rotating the rotating optics to close the sample aperture when measurement is not performed.

With the goniometric spectrophotometer (9), since the retractable shutter is driven by the driving means for rotating the rotating optics to close the sample aperture, this arrangement enables to suppress intrusion of external foreign matters such as dusts and protect the measuring optics. Further, this arrangement eliminates additional provision of a driving means for driving the shutter, which suppresses cost increase.

(10) An apparatus for measuring a goniometric reflection characteristic of a sample comprises: one or more illuminators; a toroidal mirror which is rotationally symmetrical with respect to a center axis substantially contacting with a surface of a sample; a light receiver provided with an incident aperture on the center axis: a rotating optics provided with a rotation axis substantially in agreement with the center axis; and a controller for controlling operations of the illuminator, the light receiver, and the rotating optics, wherein the toroidal mirror reflects a light flux that has been emitted from the one or more illuminators and reflected on the sample surface in respective reflecting directions around the center axis parallel to a measurement plane perpendicular to the center axis, and converges the light flux at respective converging points on a focus point circle of the toroidal mirror corresponding to the respective reflecting directions around the center axis, and wherein the light flux converged at the respective converging points on the focus point circle is selectively incident into the incident aperture of the light receiver in accordance with a rotation angle of the rotating optics around the rotation axis.

With the measuring apparatus (10), unlike the conventional measuring apparatus, the rotating optics is the sole member to be driven. This contributes to realize a compact and lightweight measuring apparatus, thereby providing a portable goniometric reflection characteristic measuring apparatus. Also, since the load to the driving means for rotating the rotating optics is reduced, a relatively inexpensive driving means can be used, and the angular positioning of the rotating optics can be performed in a relatively short period, which contributes to production cost reduction and measurement time reduction.