Portable scanning spectrophotometer

The specification discloses a portable spectrophotometer (10) providing improved movement and control of the sample (S) during analysis. The unit (10) includes a base (12) and an upper assembly (14) supported on the base (12) for floating movement. Both a spectral measurement engine (20) and drive rollers (104) are contained within the upper assembly. The base (12) includes independently suspended idler rollers (16), and the drive rollers (104) engage the idler wheels (16), so that at least a portion of the weight of the upper assembly (14) is borne by the engaging drive rollers (104) and idler rollers (16). The upper assembly (14) therefore floats up and down with samples (S) of varying thickness moving between the rollers (104 and 16). Additional upstream idler rollers (18 and 24) on the base and the upper assembly engage one another and bear a portion of the weight of the upper assembly (14) to create tension in opposition to the drive rollers (104) to hold the sample (S) taut. A planar media guide (130) is located on the underside of the upper assembly (14) and surrounds the spectral engine (20) to engage the sample (S) and reduce flexing and bowing of the sample (S). A manually actuated backer (30) is supported by the base (12) to selectively present to the spectral engine (20) one of two areas (32a and 52b) with different reflective properties. The unit (10) may include a fast light source (21) in the spectral engine and a second light source (60) in the backer (30) so that the spectrophotometer (10) is capable of both reflective and transmissive analysis.

TECHNICAL FIELD

The present invention relates to color measurement instruments, and more particularly, to spectrophotometers.

BACKGROUND ART

Color measurement instruments for many and varied applications are well known. Them instruments are used, for example, to determine color consistency in primed material, photographic material, textiles, and plastics. The most comprehensive color measurements are obtained by instruments known as spectrophotometers, which measure the spectral distribution of light and give a percentage reflection or transmission at many segments in the visible color spectrum.

The field of desk top publishing has expanded greatly in recent years, and color output devices such as color printers, plotters, proofers have become widely used. The color output devices are often controlled by computer software, which transmits control signals to the printer defining color to be produced. To assure color quality, it is desirable to be able to calibrate color printers to produce a selected quality of color for printed material produced by a number of different printers. Additionally, data defining a color product may be transmitted to remote locations to be printed by a variety of printers. In order to be able to provide a product of consistent color characteristics, a comparison to a color standard is requited. All of them functions requite the accurate measurement of many samples of different colors, produced on the device. These colors are produced using only a few colorants-usually cyan (C), magenta (M), yellow (Y), and black (K).

A color measurement instrument, such as a spectrophotometer, includes a color measurement engine having an optical pick-up. Additionally, many instruments include a drive mechanism for moving either the sample or the engine to effect relative movement between the two. The registration of the sample with respect to the engine and the controlled movement of the sample or the engine are critical components in obtaining consistent and accurate measurements. Only mail changes in the distance between the sample and the measurement engine can create significant errors and inconsistencies in the color measurement.

Prior color measurement instruments are illustrated in U.S. Pat. No. 5,369,494 issued Nov. 29, 1994 and entitled “Portable Scanning Colorimeter”; U.S. Pat. No. 5,118,183 issued Jun. 2, 1992 and entitled “Automated Strip Reader Densitometer” and U.S. Pat. No. 5,062,714 issued Nov. 5, 1991 and entitled “Apparatus and Method for Patter Recognition.” In these units, the sample drive mechanism is located in the base, while the color measurement engine is located in an assembly above the base. Because these two primary components are located in different housings, there is the possibility that sample registration and movement is not as precisely controlled as required for present day measurement. Accordingly, artisans continue to seek improved structures for maintaining improved consistency and accuracy in sample registration and movement.

DISCLOSURE OF INVENTION

The aforementioned issues are addressed in the present invention providing improved sample registration and movement within a portable spectrophotometer. The instrument contains a mechanical drive system that transports the sample past the measurement engine to a precise fashion.

First, the spectrophotometer includes a base and an upper assembly supported for floating movement on the base. Both the color measurement engine and the sample drive mechanism are located within the upper assembly. As the sample is drawn between the base and the upper assembly, the upper assembly can float with samples of various and varying thickness. This approach reduces or even eliminates the need for separate tensioning devices within the drive system, such as springs and/or close tolerances.

Second, the drive mechanism includes a plurality of drive wheels, and the base includes a plurality of independently suspended idler rollers, each of which engages and supports one of the drive wheels. The independently suspended rollers flex to accommodate samples of varying and various thicknesses.

In a third embodiment of the invention, the drive rollers are located “downstream” (in the direction of sample travel) from the color measurement engine. Tension rollers are provided upstream of the color measurement engine to at least partially resist movement of the sample in response to the drive rollers. The tension created within the sample improves its consistent maintenance in a uniform plane and therefore its consistent registration with the color measurement engine.

In a fourth embodiment of the invention, a planar, low-friction media guide is located on the underside of the upper assembly to engage the top surface of the sample. The thickness of the media is approximately the same as the distance that the drive wheels extend from the upper assembly, so that the media guide consistently engages the top surface of the sample. Therefore, the media guide improves the registration of the sample with respect to the color measurement engine; and the media guide assists the upper assembly in riding the top surface of the sample.

In a fifth embodiment, a two-position backer is provided in the base. The backer includes two separate areas with different reflective properties. The backer is readily manually movable so that either of the two areas can be aligned with the optical pickup of the color measurement engine. For example, the two areas may be white light diffusing opal and stable uniform black. In an alternative embodiment, the light diffusing opal may be illuminated for transmissive analysis.

In a sixth aspect of the invention, the spectrophotometer is capable of both reflective and transmissive analysis. A first light source is included within the color measurement engine and is activated only when reflective analysis is desired. A second tight source is included within the base, is aligned with the color measurement engine, and is activated only when transmissive analysis is desired.

MODE FOR CARRYING OUT THE INVENTION

A spectrophotometer constructed in accordance with a preferred embodiment of the present invention is illustrated in the drawings and generally designated10. As perhaps best illustrated in FIGS. 3 and 10, the spectrophotometer includes a base12and an upper assembly14supported on the base. The base includes two sets16and18of idler rollers. The upper assembly14includes a spectral analysis engine20, a drive assembly22, and tension rollers24. The engine20includes an optical pick-up75. The drive rollers22of the upper assembly engage the idler rollers16of the base, and the tension rollers24of the upper assembly engage the idler rollers18of the base all to partially support the upper assembly14on the base12. The drive rollers22pull or draw the sample S (see FIG. 1) through the spectrophotometer10and past the optical pick-up75. The tension rollers24create a tension on the sample S to maintain the sample in a consistent plane.

The base is perhaps beat illustrated in FIGS. 3-8. Generally, the base12includes a body26, idler rollers16and18, and a backer30.

The body26is plastic and includes a connector portion32and a sample portion34. The connector portion32includes a platform36, a pair of alignment pins35a and35b, and a pair of integrally molded spring clips38. The platform36provides so engagement surface for the upper numbly14. The pins35a and35b interfit with apertures97a and97b (see FIG. 10) respectively to prevent relative rotation of the upper assembly14on the base12in a horizontal plane. The spring clips38include catches39(see FIG. 4) above the platform36and actuating portions40(see FIGS. 7 and 9) that extend through and below the platform. The actuating portions may be manually actuated from the underside of the but12to release the upper assembly14from the base12.

The sample portion34of the base12is generally planar and supports the idler rollers16and18and the backer assembly30. The forward edge41of the platform is rounded to facilitate insertion of the sample S between the base12and the upper assembly14. A 35 mm groove or guide43in the forward edge41facilitates insertion and alignment of a strip of 35 mm film (not shown). A race-track shaped window39is defined is a central portion of the sample portion34.

The body base includes integral fingers47a,47b, and47c on its underside. The finger47a is opposed to the fingers47b and47c, and the fingers slidingly receive the backer assembly30as will be described. A foot45is mounted at each of the four corners of the base body. Preferably, the feet are fabricated of a relatively high-friction material to assist in securely support the unit10on a smooth surface.

All of the idler rollers16and18are generally identical to one another. In the preferred embodiment, each is fabricated on plastic. As seen in FIG. 3, each includes a roller body16a or18a and a pair of stub shafts16b or18b extending therefrom.

Each of the rollers16is supported by a suspension arm40. Each of the suspension arms40terminates in a bearing portion42which receives the stub shafts16b and rotatably supports the associated roller16. Each of the suspension arms40is integral with the remainder of the base body26. The base26is fabricated of a resiliently flexible plastic, and therefore each of the arms40is resiliently deflectable downwardly under the weight of the upper assembly14.

Similarly, each of the idler rollers18is supported for independent suspension on a suspension arm46. Each of the suspension arms terminates in a bearing portion46for which receives the stub shafts18b and rotatably supports the associated roller18. As with arms40, suspension arms44are resiliently deflectable in the downward direction under the weight of the upper assembly14. When not deflected, the rollers16and18lie within and define a plane. The rollers16and17are retained in the bearing portions42and46because the stub shafts16b and18b extend under the sample portion34. Any of the rollers16and17can be removed by pressing the supporting arm downwardly and lifting the roller from the bearing portion.

The backer assembly30is illustrated in FIGS. 3 and 7-8 and includes a body49, a spring plunger50, and an opal glass51. The body49is held between fingers47a on one side and47b and47c on the other side for sliding movement. The spring plunger50cooperates with deters (not visible) in the underside of the base body26to releasably catch the assembly in either of two opposite positions. The backer body49includes a recessed area34that facilitates removal of the backer assembly30from the base body26when the recessed area54is aligned with the finger47a.

The body49includes a platform portion52extending upwardly from the remainder of the body49and into the window39of the base body26. The platform provides two separate areas with different reflective properties. The first area57a is stable uniform black. The second area52b supports the white fight diffusing opal glass51. The white opal glass51is secured in position on the platform52using a solvent adhesive or other suitable interconnection means.

An alternative backer assembly30′ is illustrated in FIG. 9. The alternative backer assembly30′ is capable of providing illumination for operation of the spectrophotometer10in a transmissive mode of analysis. In the alternative backer30′, an illumination source60is positioned within the cavity37directly below the opal glass51(see FIG. 8). A power cord62extends from the backer assembly30′ and terminates in a plug64mounted within the backer base26. The cord62is secured under wire management fingers66, which are integral with the base body26. The plug or connector64is held in position by the base body26for automatic correction with the upper assembly14when the upper assembly14is installed on the base12.

II. Upper Assembly

The upper assembly14is illustrated in FIGS. 10-14. The upper assembly10includes a housing70, a spectral measurement engine20, a drive assembly22, and a lower plate72.

The housing70is injection molded of plastic to house the remaining upper assembly components. The housing includes an integral alignment mark71centered above the film strip guide43and linearly aligned with the spectral engine20to artist a user with properly aligning the sample S for scanning by the engine.

The spectral measurement engine20of the preferred embodiment is generally well known to those skilled in the all. For example, one suitable spectral engine is illustrated co-pending application Ser. No. 08/714,969 filed Sep. 17, 1996 by Berg et al and entitled “Compact Spectrophotometer,” the disclosure of which is incorporated by reference. Other measurement engines, such as those for calorimeters and densitometers, can be used depending on the application. Generally speaking, the engine20includes an optics assembly74, a printed circuit board (PCB) assembly76, and a control board shield78. The optics assembly74includes an optical pick-up75(see FIG. 14). The PCB assembly76and the shield78are secured to the optics assembly74using screws80and star lock washers82. The optics assembly74is secured to the aluminum stand-offs on the bottom plate72using screws81and star lock washers83. Additionally, the bottom plate72is secured to the optics assembly74using screws85. The aluminum bottom plate72and the aluminum standoffs98dissipate heat generated by the optics assembly and most notably by the illuminators77. A wire tie87is included for wire management

A plurality of illuminators77(see FIG. 14) are included within the spectral engine20to illuminate the sample S when the unit10is operated in the reflective analysis mode. The illuminators77an actuated only in the reflective mode (i.e. not in the transmissive mode).

The bottom plate72is generally planar, is fabricated of aluminum and provides an underside to the upper assembly14. The perimeter of the bottom plate72is dimensioned to closely fit within the bottom of the housing70. The plate72is secured to the housing70using screws73.

The plate define two rectangular apertures96that receive the locking arms38of the base12. When the upper assembly14is attached to the base12, the catches39of the locking arms38engage the upper surface of the bottom plate to lock the upper assembly on the base; and the bottom plate72rests upon the platform36of the base12to at least partially support the weight of the upper assembly. The plate further defines two alignment apertures97a and976that receive the alignment pins35a and35b respectively of the base12. The interest of the locking arms38within the apertures96and the interest of the alignment pins33within the apertures97prevents the upper assembly from rotating in a generally horizontal plane, but permits the upper assembly to float or pivot in a generally vertical plane.

The plate72defines a series of elongated apertures90through which drive milers extend, a pair of elongated apertures92through which idler rollers extend, and an optics aperture94aligned with the optical pick-up73(see FIG. 14).

The drive assembly22(see FIGS. 10-11) includes a drive shell assembly100and a motor assembly102. The drive shaft is secured to the motor assembly using set screws103. The drive shaft assembly100includes five drive wheels104of uniform diameter with the wheels being evenly spaced from one another. Because the upper assembly is free to float in a vertical plane, the drive shaft assembly is also free to float in a vertical plane. The individual suspension of the idler rollers16under the drive rollers104accommodates such angular floatation.

Each of the wheels104defines a circumferential groove106(see FIG. 11). An O-ring108, which acts as a tire, is fitted within each of the grooves106. Each of the O-rings is fabricated of a relatively high-friction material for gripping the sample to be analyzed. The material of the preferred embodiment is precision silicone. The motor assembly102is generally well known in the art. The motor of the preferred embodiment is a high-torque gear motor or a stepper motor. The drive rollers104extend through apertures90to extend approximately 0.3 millimeter (mm) from the lower surface of the bottom plate72(see FIG. 14). As currently implemented, the drive assembly moves or pulls the sample S at a speed of approximately 3 centimeters (cm) per second.

The drive assembly22is severed to the bottom plate72by the drive bearings110illustrated in greatest detail in FIG. 12. Each of the drive bearings110is generally U-shaped, defining an interior having a circular portion112and a pair of opposed flat portions114. The distance between the flat portions114is less than the diameter of the circular portion112. The drive bearings110are fabricated of bearing-quality plastic or other resiliently deformable material. Accordingly, the legs can be spread slightly to fit the bearing over the drive shaft100. The drive shaft then dicks into the circular portion112. Screws116(FIG. 10) are inserted through holes118in the bearing110to lock the drive shaft within the circular portion112and to secure the bearing to the bottom plate72. Lubricant preferably is included within the bearing110to facilitate rotation of the drive shaft100.

Idler rollers24(see FIG. 10) are rotatably supported on the bottom plate72by way of bearings120and screws122. The idler rollers24extend through apertures92to extend approximately0.3millimeter (mm) from the lower surface of the bottom plate72(see FIG. 14).

The media guide130is illustrated in FIGS. 3 and 13-14 and is a generally planar piece of relatively low-friction material. The preferred material of the present embodiment is a bearing-quality material that is soft enough to avoid damage of the sample S. As currently implemented, the material is a high-density polypropylene. As viewed in FIG. 3, the media guide is milkman shaped having a relatively narrow forward portion132to fit between the idler rollers24. The rearward portion134defines a central aperture136aligned with the optics aperture94in the base plate72and with the optical pickup75of the color measurement engine20. The media guide130is adhered to the bottom plate72using a pressure-sensitive adhesive or other suitable attachment means. The thickness of the media guide is approximately 0.3 mm so that it projects from the lower plate72approximately the same distance that the idler rollers24and the drive rollers104project from the lower plate72. Consequently, the rollers24and104mad the media guide130all lie within and define a plane.

As seen in FIG. 1, the upper assembly further includes a 12-volt power connection132for powering the unit10, an RS-232 port134for serial communication with a personal computer (PC) or other digital device, and a push-button136for actuating and operating the unit

The operation of the spectrophotometer10is perhaps best illustrated in FIGS. 1 and 14. For purposes of reference, the area above the backer assembly30and below the optical pick-up75is referred to as the scanning station140. The backer assembly30is aligned with the optical pick-up across the scanning station.

If necessary, the reflectance of the backer assembly30is selected by manually sliding the backer assembly to either of its two selectable positions. In the fast position, the stable uniform black portion52a of the platform52is presented to the cola measurement engine20. In the second position, the white light diffusing opal glassy51in portion52b is presented to the engine20.

A sample S (FIG. 1), having color patches S′, to be analyzed is aligned with the alignment mart71on the upper assembly and fed or pushed between the base12and the upper assembly14. The leading edge of the sample S passes between the tension rollers24on the upper assembly and the idler rollers18on the base. The sample continues through the scanning station140until the forward edge of the sample S is gripped by the drive wheels104, whereupon the sample is pulled between the drive rollers and the associated idle, rollers16. Spectral analysis or other color measurement operations are conducted on the sample S as it is drawn past the color measurement engine20and specifically the optical pickup73.

As the sample moves between the idler rollers18and24, the suspension arms44flex to permit the individual rollers18to move downwardly. Similarly, as the sample is drawn between the drive rollers104and the idler rollers16, the individual suspension arms40flex to permit the rollers16to move downwardly. Also, the tension rollers24and the drive rollers108engage and ride along the top surface of the sample S to assist in registration of the sample with respect to the optical pick-up73. The free floating ability of the upper assembly14and the individual suspension of the idler rollers18facilitate the accurate color measurement of samples of varying thickness. The upper assembly14rides along the top surface of the sample S to maintain a desired physical registration or relationship between the top surface of the simple and the engine20.

As noted above, the tension rollers24, the drive rollers104, and the media guide130all project a substantially equal distance from the bottom plate72. Accordingly, the media guide130also engages the top surface of the sample S to further assist in registration. The media guide130prevents flexing or bowing of the sample within the scanning station as may occur, for example, if the trailing edge of the sample is dropped below or is lifted above the level of the scanning station140.

The spectrophotometer may be operated in either the reflective or the transmissive mode. When operated in the reflective mode, only the illuminators77are actuated so that the top surface of the sample S is illuminated in accordance with the ANSI standard 45°/0° reflection measurement. When operated in the transmissive mode, only the base illuminator60within the backer assembly30is actuated to illuminate the sample from beneath in accordance with the ANSI standard 180°/0° transmissive measurement.

The above descriptions are those of preferred embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, including the Doctrine of Equivalents.