Developability sensor with diffuse and specular optics array

Details Developability sensor with diffuse and specular optics array Developability sensor with diffuse and specular optics array

2000-04-20

2002-10-08

Ben, Loha (Department: 2873)

Optics: measuring and testing

Of light reflection

With diffusion

C356S445000, C356S072000, C250S353000, C250S341800, C250S358100, C399S049000

Reexamination Certificate

active

06462821

ABSTRACT:

Disclosed in the embodiments herein is an improved system and sensor for optically analyzing or measuring the development of imaging material in a printer, for control thereof. In particular, an improved developability sensor for more accurately sensing the development of imaging materials that may have at least partially specular optical properties instead of, or in addition to, diffusely reflective optical properties.
It has been found that some newer types of imaging material, in particular certain color toners for xerographic printers, give partially specular “false diffuse” signals in prior developability sensors. The disclosed embodiment of an improved developability sensor has a low cost and simple optical and sensor system improvement for detecting the diffuse reflections from the control patches of such new toners at an angle and configuration which will not “see” these “false diffuse” specular reflections from such new toners.
By way of background, various types of developability sensors are known in the art for measuring and controlling image development. In particular, it is well known in the art to provide developability sensors for regularly automatically optically analyzing toner-developed test patch areas regularly automatically generated on the surface of the photoreceptor of a xerographic printer, to provide image quality control signals for the controller of that printer. The following Xerox Corp. U.S. patent disclosures are noted by way of providing some known examples and known details which need not be repeated herein: U.S. Pat. Nos. 4,989,985; 4,553,033; 5,083,161; 5,519,497; 5,666,194; and 5,078,497. The latter U.S. Pat. No. 5,078,497 will be referred to by way of background below in connection with explaining problems with such prior systems which the present system addresses. Said U.S. Pat. Nos. 5,083,161, 5,666,194, etc., are also of particular interest for illustration in their FIGS. 2-4, etc., of the general physical configuration of such developability sensors. As so shown, an outer case may have integral molded-in lens elements and the photoemitter and photosensor may be on a circuit board mounted therein.
For reader clarity, the following definitions of terms used in the description of technical background and specific embodiments herein is provided. The terms “printer” or “reproduction apparatus” as used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise defined in a claim. Likewise, the type of “developability sensor” in the embodiment herein is a reflective “densitometer” or “toner mass sensor” measuring “DMA” (developed mass per unit area, typically in milligrams per square centimeter). It is more specifically referred to herein as an “ETAC”, which is an acronym of “Enhanced Toner Area Coverage” sensor. That is, an “ETAC” may be thought of as one type of “DMA sensor” and also as one type of “developability sensor”. An ETAC sensor is an optical, non-contact, sensor and could be used as reflective or transmissive sensor, but is illustrated in the embodiment below as a reflective sensor.
Typically such an ETAC sensor is a small integral unit with a small LED or other, infra-red (IR) light source and lens to illuminate, at a suitable angle (such as 19 degrees), a small area of the imaged surface, and an oppositely angled and positioned sensor lens and photosensor, to provide a variable voltage output proportional to the reflected illumination from a toner test patch on the closely adjacent imaged surface passing by the ETAC. The photosensors may be standard, commercially available, PIN photodiodes or PN photodiodes, mounted in defined locations and areas.
“Developability”, in the broad sense, is the end result of the various variable parameters of a printer, which affect the development of an image (including a test patch) on an imaging surface, especially, a toner-developed image area on a xerographic photoreceptor, or on an intermediate transfer belt to which a developed image is transferred before its final transfer to a paper sheet, web, or other final printed substrate. In view of the latter, the “imaged surface”, (bearing a “test patch”) referred to herein as being examined by the subject developability sensor, will be understood to encompass a photoreceptor, an intermediate transfer surface, or a final substrate surface, unless otherwise indicated. The specific illustrated example herein is a ETAC sensor for sensing colored toner test patches developed on a xerographic photoreceptor of a full color printer.
Such developability sensors for the measurement of toner or other imaging development materials density in a control patch are common elements in mid to high volume copier and printer products. The accuracy of such sensors is particularly important for full color machines. It is also desirable to provide such developability sensing systems with the flexibility and capability for controlling machines with faster process speeds, different photoreceptors, overlaid layers of several different color imaging materials, and/or a variety of image development materials packages.
In that regard, although as noted, devices which optically sense the amount of toner developed on (deposited on) a control patch on a photoreceptor have been commonly used in xerographic machine controls, the reflective properties of the toners being sensed are changing with changes and improvements in developer materials technology. It has been found that toner size, toner composition, the types and sizes of toner material pigments and additives, and the methods of applying them, can all affect the response of a conventional developability sensor. That is, a major current barrier to accurate optical developability sensing is the constantly evolving materials set (toners and their associated constituents of base polymers, pigments, additives, and processing). The optical properties of each part of the new toner can have a dramatic effect on the way a particular developability sensor configuration will react to it.
In particular, the introduction of “flushed pigment” toners has led to a peculiar and misleading response of the above-cited and other types of TAC sensor (a current color DMA sensor). U.S. issued U.S. Pat. Nos. 6,004,714; 5,885,739; 5,866,288; 5,837,409; 5,736,291; 5,723,245; 5,719,002; 5,712,068 and 5,658,704, etc., by Xerox Corp. describe some examples of what are called “flushed pigment” toners, especially those for full color, high speed, printers. A major difference in these toners from predecessor toners is the manner in which the pigments are applied to the base resins. These toners may have a nominal size of about 7 microns, but have dispersed pigment particles which are on the order of only about 0.2 microns. Yet the wavelength of the infrared (IR) light source desirably used in developability sensors is about 0.9 microns.
In previous toners, the pigments were typically applied to the base resins in such a manner that small pigment particles ended up stuck to the outside of the base resin in “clumps”. These made the overall surface texture of the toner particles rough and very diffusely reflective. The prior TAC color process control sensor was designed to work with this almost completely diffusely reflective toner material.
In contrast, in flushed pigment toners the pigment disperses across the surface of the base resin particles more evenly so that no large clumps are present, basically forming a monolayer of isolated pigment particles on the surface of the base resin particles. This allows some of the optical properties of the base resin to remain visible through the very thin, semi-transparent surface layer of pigment. Also, the base resin particles may have the form of very small flat platelets or flakes. These resin platelets, even covered by pigment, can provide specular reflections from the platelets which are aligned at the Bragg angle to the TAC illumination source and an area of the TAC photodetector which heretofore was only accessible to diffuse reflectio

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