Abstract:
A color measurement instrument such as a reflection densitometer or a spectral reflectometer is fitted with an asymmetric tapered sample area optical enclosure to allow an improved operator sight line to the sample target area and allow ease of placement on the sample target, while allowing for the standard 45° illumination/90° measurement geometry. The disclosed structure is particularly suitable for use as a hand-held instrument.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of instruments used to measure the reflective color of an object, such as a reflection densitometer or a spectral reflectometer. These types of instruments are used extensively in measuring printed ink colors, paint colors, or the colors of any other object for which a numerical color value is desired. In the case of printing devices, the measured values are often used to calibrate the printing device in a feedback loop so as to reproduce a desired color. In other cases, the measured value is used to specify a desired color in a digital image or document, often for the purpose of matching the color of the measured object. 
     Instruments of this type are well known in the prior art and are generally comprised of one or more light sources and one or more light sensitive detectors arranged in specific geometry. Under common standards (such as ANSI/ISO May 4, 1995  Density Measurements—Part  4 : Geometric Conditions for Reflection Density , or DIN 16536  Color Density Measurements on Prints: Requirements on Measuring Apparatus for Reflection Densitometers ), the measurement geometry is specified to consist of an annular ring of illumination projected onto the center of a sample target area at an angle of between 40 and 50 degrees. The light reflected off the sample is sensed by a detector positioned at an angle of between 85 and 90 degrees from the target sample. Alternatively, the positions of the light source and detector may be interchanged. 
     Detailed discussions relating to the background of color measurement instruments may be found in prior art such as U.S. Pat. Nos. 5,015,098 and 5,073,028. 
     Such measuring devices may also be configured as hand-held devices. Hand-held measuring devices used to measure the reflective color of an object are generally manually aimed by positioning a small (3 to 7 mm diameter) sampling aperture in contact with and over the area of the sample for which the color is to be measured. The manual aiming process can be tedious and error-prone due to the inability of the operator to accurately see where the sampling aperture of the measuring device is about to be placed on the sample. The enclosure of the measuring device is generally constrained by the measurement geometry requirements to taper away from the sampling aperture at an angle no greater than 40 degrees. Such a configuration significantly obstructs the operator&#39;s sight line during aiming and positioning of the sampling aperture over an area to be sampled. 
     For example, a typical prior art hand-held measuring device is illustrated in FIG.  1 . FIG. 1 shows a prior art measuring device  100  having a sample area optical enclosure  101 . The optical enclosure  101  includes light sources  120  and  121  arranged such that light is projected towards a sampling aperture  110  at an angle of 45 degrees. The detector  130  is arranged to detect light reflected at a surface normal to the sampling aperture  110 . FIG. 1 shows the measuring device  100  positioned over a sample area  210  of a sample  200 . The portion of the optical enclosure  101  which tapers down to form a sampling aperture  110  is formed by the optical enclosure walls  140  which narrow toward the sampling aperture in the shape of a cone. The cone shaped walls  140  are symmetrically arranged and angled at approximately 45 degrees. This angle of the walls  140  is constrained both by the placement of the light sources  120  and  121  so as to project light toward the sampling aperture  110  at an angle of 45 degrees and by the placement of the detector  130  so as to detect light reflected at a surface normal to the sampling aperture  110 . 
     The geometry of the prior art measuring device  100  conforms to standard measurement geometry relating to placement of the light source and detector. As can be seen from FIG. 1, such a configuration results in the optical enclosure obstructing the view of the area to be sampled. The operator sight line, shown in FIG. 1 as  300 , is angled at approximately 45 degrees from the targeted sample area. Such an obstructed sight line makes it extremely difficult for an operator to accurately position the measuring device  100  over the sample area, resulting in erroneous measurements. 
     A slight improvement over the prior art is illustrated by FIG. 2, which shows a hand-held measuring device such as that disclosed in U.S. Pat. No. 5,963,333. FIG. 2 shows the same elements as disclosed in FIG.  1  and all reference numbers correspond. 
     The prior art measuring device of FIG. 2 allows for a different configuration of the light sources  120  and  121 , which results in a slightly improved operator sight line  300 . The light sources  120  and  121  are positioned such that the light is projected onto reflective surfaces  142  of walls  140  proximal to the sampling aperture, which reflective surfaces reflect the light towards the sampling aperture at an angle of approximately 45 degrees. Such a configuration maintains the standard measurement geometry, while allowing the optical enclosure walls  140  to be arranged symmetrically and angled at approximately 60 degrees. As shown in FIG. 2, such an arrangement of the optical enclosure walls  140  allows for a slightly improved operator sight line  300  of approximately 60 degrees. 
     While the sight line of the measuring device illustrated in FIG. 2 is an improvement over that of FIG. 1, such a configuration still results in an obstructed view of the area to be sampled and results in difficulty in accurately positioning the sampling aperture over the sample area. The sight line of approximately 60 degrees is less than optimal. 
     An operator sight line approaching the optimal 90 degrees is desired and is accomplished by the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to eliminate the problems associated with the restricted sight line of the prior art color measurement instruments such as reflection densitometers or spectral reflectometers. The object of the present invention is accomplished by arranging the light source and detector in a manner which allows the sample area optical enclosure walls to taper away from the sampling aperture in an asymmetrical manner. The taper angle of the optical enclosure is higher at the front of the optical enclosure where the operator requires a better sight line, while the taper angle of the optical enclosure walls at the portions towards the rear of the optical enclosure is approximately 40 degrees. Such a configuration allows for the standard measurement geometry between the detector and sample of approximately 90 degrees and between the light source and sample of approximately 45 degrees. The asymmetrical configuration of the optical enclosure allows for an operator sight line of approximately 80 degrees. 
     The light source can comprise, for example, one or more incandescent light sources, one or more infrared light sources, one or more light emitting diodes, or the like. Similarly, the detector can comprise, for example, one or more detectors or series of detectors, a detector with a multitude of detection elements, or the like. 
     In one embodiment of the present invention, the light source is positioned only towards the rear of the optical enclosure. As light is projected into the sampling aperture from only one position, such a configuration provides illumination of the sample area that is not completely in adherence with standard measurement techniques, such as the American National Standards Institute (ANSI) standard (ANSI/ISO May 4, 1995). However, the measurements achieved are sufficiently accurate for most applications. Only in the case of heavily textured sample surfaces would the orientation of illumination become significant, and only where the textured sample is significantly directional in its arrangement. 
     In another embodiment of the invention, a first light source is positioned towards the rear of the optical enclosure and illuminates the sampling aperture directly at an angle of projection of approximately 45 degrees. A second light source is positioned toward the rear of the optical enclosure and projects light onto a reflective surface proximal to the front of the sampling aperture, which reflecting surface is arranged such that the light from the light source is projected into the sampling aperture at an angle of approximately 45 degrees. Such a configuration maintains the standard measurement geometry and conforms to measurement standards, while allowing the operator an improved sight line for placement of the sampling aperture over the area to be sampled. As with the previously described embodiment, the operator sight line in such a configuration is approximately 80 degrees. 
     Alternatively, a single light source can be positioned at the rear of the optical enclosure such that it directs light both directly into the sampling aperture at an angle of 45 degrees and at the reflective surface proximal to the front of the sampling aperture, from which the light is reflected into the sampling aperture at approximately 45 degrees. 
     In another embodiment of the invention, the optical enclosure comprises an outer cone and an inner cone. The inner cone acts to maximize the transmission of light reflected off of a sample to the detector. The interior surface of the inner cone may comprise a non-reflective surface for maximizing light transferred from the sample to the detector. 
     In a preferred embodiment the optical enclosure forms part of a hand-held measuring device such as a hand-held reflection densitometer or a hand-held spectral reflectometer which can be manually positioned over the object to be sampled. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a reflective color measuring device known in the prior art having a symmetrical optical enclosure configuration and a light source and detector arranged in conventional measuring geometry. 
     FIG. 2 is a cross-sectional view of a reflective color measuring device known in the prior art having a symmetrical optical enclosure configuration and using a reflective surface proximal to the sampling aperture to obtain conventional measuring geometry. 
     FIG. 3 is a cross-sectional view of an exemplary embodiment of the present invention having an asymmetrical optical enclosure configuration. 
     FIG. 4 is a cross-sectional view of a second exemplary embodiment of the present invention having an asymmetrical optical enclosure configuration. 
     FIG. 5 is a cross-sectional view of a third exemplary embodiment of the present invention having an asymmetrical optical enclosure configuration. 
     FIG. 6 is a side view of the sampling aperture and the respective angles of illumination and detection. 
     FIG. 7 is a bottom view of the sampling aperture with positioning of the light source and detector. 
     FIG. 8 is a side view exterior illustration of a hand-held measuring device. 
     FIG. 9 is a bottom view of the optical enclosure for a particular embodiment. 
     FIG. 10 is a side view of the optical enclosure shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 discloses an embodiment of the invention in which a color measuring instrument  100  has a sample area optical enclosure  101 . The optical enclosure  101  has a rear portion  114  and a front portion  115 . The optical enclosure  101  includes a light source  120  arranged only toward a rear portion  114  of the optical enclosure. 
     A circular sampling aperture  110  is shown positioned over a sample area  210  of a sample  200 . It is noted that in all of the embodiments of the invention, sampling apertures of other shapes can be used instead of the circular aperture depicted in the drawings. The light source  120  is arranged such that light is projected towards the sampling aperture  110  at an angle α of 45 degrees. A detector  130  is positioned to measure light reflected from the sample  200  at an angle β of 90 degrees. 
     The portion of the optical enclosure  101  which tapers down to form the sampling aperture  110  is formed by an optical enclosure rear wall  140  and an optical enclosure front wall  141  which narrow asymmetrically toward the sampling aperture in the general shape of a cone. The walls  140  and  141  taper towards the sampling aperture and are asymmetrically arranged such that the rear wall  140  is angled at approximately 40 degrees and the front wall  141  is angled at approximately 80 degrees. Thus the taper angle of the optical enclosure is greater at the front portion  115  of the optical enclosure where the operator requires a better sight line. Such a configuration of the optical enclosure walls  140  and  141  provide a relatively unobstructed view of the targeted sample area  210 . The operator sight line  300  is approximately 80 degrees from the targeted sample area  210 . 
     In this embodiment, the light source  120  is positioned only towards the rear portion  114  of the optical enclosure and projects light into the sampling aperture at an angle α of 45 degrees. As light is projected into the sampling aperture from only one position, such a configuration provides illumination of the sample area  210  that does not completely adhere to standard measurement techniques, such as the ANSI standard. However, the measurements achieved are sufficiently accurate for most applications. Only in the case of heavily textured sample surfaces would the orientation of illumination become significant, and only where the textured sample is significantly directional in its arrangement. 
     FIG. 6 illustrates the relative positioning of the light source  120  and the detector  130  with respect to the sampling aperture  110 . In the foregoing embodiment, the light source  120  is positioned only toward the rear portion  114  of the optical enclosure and projects light toward the sampling area  110  at an angle α of 45 degrees. The detector  130  is positioned to detect light reflected off a sample at an angle β of 90 degrees. 
     FIG. 7 shows the sampling aperture  110  from a bottom view, with the positioning of the light source  120  and detector  130  in perspective. The sampling aperture  110  is shown with a center line  150  dividing the front portion  115  and rear portion  114  of the optical enclosure. 
     FIGS. 6 and 7 are intended only to show the relative relationship between the angle of illumination α and angle of detection α with respect to the sampling aperture  110 . The exact positioning of the light source and detector can vary in a particular embodiment of the invention. In addition, the positions of the detector and light source may be interchanged in any given embodiment. 
     Additionally, the light source  120  can comprise, for example, one or more incandescent light sources, one or more infrared light sources, one or more light emitting diodes, or the like. 
     Similarly, the detector  130  can comprise, for example, one or more detectors or series of detectors, a detector with a multitude of detection elements, or the like. 
     In another embodiment of the invention as shown in FIG. 4, the optical enclosure  101  includes a light source  120  arranged toward a rear portion  114  of the optical enclosure  101 . The light source  120  is positioned so that it illuminates a sampling aperture  110  directly at an angle of projection α of approximately 45 degrees. The light source  120  also projects light onto a reflective surface  142  proximal to the front of the sampling aperture, which reflecting surface  142  is arranged such that the light from the light source  120  is projected by the reflecting surface  142  into the sampling aperture  110  at an angle α of approximately 45 degrees. A detector  130  is positioned to detect light reflected normal to the sampling aperture  110 . 
     The sampling aperture  110  is shown positioned over a sample area  210  of a sample  200 . The portion of the optical enclosure  101  which tapers down to form the sampling aperture  110  is formed by an optical enclosure rear wall  140  and an optical enclosure front wall  141  which narrow asymmetrically toward the sampling aperture in the general shape of a cone. The walls  140  and  141  taper towards the sampling aperture and are asymmetrically arranged such that the rear wall  140  is angled at approximately 40 degrees and the front wall  141  is angled at approximately 80 degrees. Thus the taper angle of the optical enclosure is greater at the front portion  115  of the optical enclosure where the operator requires a better sight line. Such a configuration of the optical enclosure walls  140  and  141  provide a relatively unobstructed view of the targeted sample area  210 . 
     Such a configuration maintains the standard measurement geometry and conforms to measurement standards, while allowing the operator an improved sight line for placement of the sampling aperture over the area to be sampled. The operator sight line  300  in such a configuration is approximately 80 degrees from the targeted sample area  210 . 
     In another embodiment of the invention as shown in FIG. 5, the optical enclosure  101  includes a first light source  120  arranged toward a rear portion  114  of the optical enclosure  101 . The light source  120  is positioned so that it illuminates a sampling aperture  110  directly at an angle of projection α of approximately 45 degrees. A second light source  121  arranged toward the rear portion  114  of the optical enclosure projects light onto a reflective surface  142  proximal to the front of the sampling aperture, which reflecting surface  142  is arranged such that the light from the light source  121  is projected by the reflecting surface  142  into the sampling aperture  110  at an angle of approximately 45 degrees. A detector  130  is positioned to detect light reflected normal to the sampling aperture  110 . 
     Such a configuration maintains the standard measurement geometry and conforms to measurement standards, while allowing the operator an improved sight line for placement of the sampling aperture over the area to be sampled. The operator sight line in such a configuration is approximately 80 degrees. 
     In another embodiment of the invention, the optical enclosure forms part of a hand-held measuring device such as a hand-held reflection densitometer or a hand-held spectral reflectometer which can be manually positioned over the object to be sampled. FIG. 8 shows a side view exterior illustration of such a hand-held measuring device  100 . The optical enclosure  101  of the hand-held measuring device is configured as in the previously discussed embodiments. In particular, the optical enclosure  101  has an optical enclosure front wall  141  and an optical enclosure rear wall  140  which taper towards the sampling aperture  110  in the general shape of a cone. The walls  140  and  141  are asymmetrically arranged such that the rear wall  140  is angled at approximately 40 degrees and the front wall  141  is angled at approximately 80 degrees. The asymmetrical configuration of the walls can be seen in FIG. 8 as providing a operator sight line toward the sample area of approximately 80 degrees. 
     The arrangement of the light source and detector as described in any embodiment of the invention may be used in such a hand-held configuration. 
     Additionally, the exterior of the optical enclosure proximal to the sampling aperture may be configured to function as a guide to aid the placement of the sampling aperture over the object to be measured. 
     A further embodiment of the present invention as shown in FIG. 9 uses a series of light emitting diodes (LEDs) as the light source  120  arranged toward the rear portion  114  of the optical enclosure. FIG. 9 shows a bottom view of the optical enclosure  101  with the optical enclosure rear wall  140  and optical enclosure front wall  141 . In this embodiment, the series of LEDs  120   a ,  120   b ,  120   c ,  120   d ,  120   e ,  120   f  and  120   g  are a combination of red, green, and blue LEDs which are focused to provide a white spectrum for illumination of the sampling aperture  110 . The number, type, size and arrangement of the LEDs may vary in a particular embodiment. As in the previous embodiments, the optical enclosure walls  140  and  141  taper asymmetrically to allow a substantially improved operator sight line. 
     FIG. 10 is a cross-sectional view of a further embodiment. Light source  120  arranged toward the rear  114  of the optical enclosure  101  projects light into the sampling aperture  110  at an angle of 45 degrees. In this view the detector  130  is shown affixed to a printed circuit board  150  directly above the sampling aperture  110 . The detector  130  in this particular embodiment comprises a series of detection elements (such as the TSL1402 256×1 Linear Sensor Array with Hold made by Texas Advanced Optoelectronic Solutions, Inc. of Plano, Tex.) positioned behind a linear variable filter  135  which separately filters light impinging upon each detector element to enable different detector elements to detect different wavelengths. Such filters are available, for example, as the LVF400-700 or LVF400-700NB Selectraband Linear Variable Filters made by OCLI of Santa Rosa, Calif. The linear variable filter  135  is shown behind an infrared filter  136  and a light shield  137 . 
     In this particular embodiment, the optical enclosure rear wall  140  and the optical enclosure front wall  141  form an outer cone  145 . An inner cone  146  is provided to maximize the transmission of the light reflected off of a sample to the detector  130 . The interior of the inner cone  146  consists preferably of a non-reflective surface  147  for maximizing light transmitted from the sample to the detector  130 . 
     Also shown in FIG. 10 is a button  155  for activation of a switch  156 , which operates the measuring device  100 . A busy light  157  is provided which signals when the measuring device is in operation. 
     As shown in FIG. 10, such a configuration allows for the optical enclosure walls  140  and  141  to taper asymmetrically away from the sampling aperture, thereby providing the operator with an improved sight line toward the area to be sampled of approximately 80 degrees. 
     It will now be appreciated that the present invention provides an improved optical enclosure for use in measuring the reflective qualities of samples, wherein the operator sight line toward the area to be sampled is greatly improved by providing an asymmetrically shaped sample area optical enclosure. 
     Although the invention has been described in connection with preferred embodiments thereof, those skilled in the art will appreciate that numerous adaptations and modifications may be made thereto without departing from the spirit and scope of the invention, as set forth in the following claims.