US 3892962 A
An apparatus in which the developability of an electrophotographic printing machine is regulated. Errors induced by temperature fluctuations are minimized by controlling the thermal environment.
Description (OCR text may contain errors)
United States Patent 11 1 Whited 1 July 1, 1975 THERMAL CHAMBER FOR A DEVELOPABILITY REGULATING APPARATUS  Inventor: Charles A. Whited, Rochester, NY.
 Assignee: Xerox Corporation, Stamford,
 Filed: Jan. 30, 1974  App]. No.1 438,126
Related US. Application Data  Division of Ser. No. 295,775, Oct. 6, 1972, Pat. No,
 US. Cl. 250/227; 250/238; 250/239  Int. Cl. G02b 5/14  Field of Search 250/227, 238, 239; 355/10, 355/3 DD; 356/201, 202, 203
 References Cited UNITED STATES PATENTS 3,327,126 Shannon 250/238 3,558,895 1/1971 Harlmann 250/227 3,737,629 6/1973 See 250/227 3,790,791 2/1974 Anderson 250/238 3,792,284 211974 Kaelin 250/227 3,800,147 3/1974 Shea 260/238 Primary Examinerlames W. Lawrence Assistant ExaminerD. C. Nelms Attorney, Agent, or FirmH. Fleischer; .1. .1. Ralabate; C. A. Green  ABSTRACT An apparatus in which the developability of an electrophotographic printing machine is regulated. Errors induced by temperature fluctuations are minimized by c0ntr01ling the thermal environment.
4 Claims, 5 Drawing Figures ISTS W JUL 1 SHEET THERMAL CHAMBER FOR A DEVELOPABILITY REGULATING APPARATUS This is a division. of application Ser. No. 295,775, filed Oct. 6, I972. now U.S. Pat. No. 3.817.6l6 issued to Whited in I974v BACKGROUND OF THE INVENTION This invention relates generally to an clectrophotographic printing machine, and more particularly concerns means for maintaining the thermal environment of a photosensor utilized in a developability regulating apparatus substantially at a predetermined temperature in order to minimize system errors.
In the process of electrophotographic printing a developer mix of carrier granules and toner particles is used to form a toner powder image of an original document on sheet material. The developability regulating apparatus adjusts the characteristics of the developer mix to produce toner powder images having suitable density and color balance, i.e. developability. Developability is related to the concentration of toner particles in the developer mix, i.ev the ratio of toner particles to carrier granules. Environmental conditions such as temperature and humidity conditions effect developability. The physical parameters of the development system also effect developablitlty, e.g. spacing. electrical bias, mass flow rate and the magnetic field, amongst others. Furthermore, the electrical attraction between the toner particles and carrier granules influences developability. Toner particle concentration within the developer mix is controlled to maintain image density and color balance at an appropriate levelv A system utilizing the developability apparatus of the present invention is described, in detail, in U.S. Pat. No. 3,754,821 issued to Whited in I973 and assigned to the assignee of the present invention.
The thermal environment surrounding the photosensor is subject to temperature transients. This is due, in part. to localized heating by such sub-components as the fuser which is incorporated in the printing machine to permanently fix the powder image to the support material. Moreover. heat from scan lamps and electrical power supplies, as well as the air flow generated by the blowers produce thermal transients which may rapidly change the temperature in the region surrounding the photosensor. Photosensors utilized in developability regulating apparatus are frequently sensitive to temperature variations. For example, at 4C change in the photosensor temperature causes the developability regulating mechanism to indicate that there is an incorrect concentration of toner particles in the developer mix.
It is, therefore, a primary object of the present invention to improve the thermal environment of the photosensor incorporated in the developability regulating apparatus of electrophotographic printing machine.
SUMMARY OF THE INVENTION Briefly stated, and in accordance with the present invention, there is provided an apparatus for maintaining the thermal environment of a photosensor substantially at a predetermined temperature.
This is accomplished in the present instance by an open ended container defining an internal chamber for housing the photosensor therein. One of the features of the present invention is to transmit light rays to the photosensor by means of a fiber optic light pipe. Hence, in the preferred ebodiment, provision is made in an end cap of the container to accommodate the light pipe. The end cap forms, in conjunction with the light pipe, a substantially heat-tight joint. Means are provided for heating the container to a predetermined temperature, and for controlling the heating means such that the container remains substantially at the predetermined temperature.
The present invention is also concerned with minimizing errors due to thermal variations in the photosen sor used in the developability regulating apparatus of an electrophotographic printing machine. In performing this function, the photosensor detects modulated light rays to indicate the density of toner particles electrostatically adhering to transparent electrode means. This corresponds to the density of toner particles being deposited on an electrostatic latent image recorded on a photoconductive member. In order to minimize errors in the regulating apparatus, the photosensor is disposed in a thermally controlled environment. Hence, the photosensor is housed in the previously discussed container and is maintained substantially at a predetermined temperature.
BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:
FIG. 1 is a schematic perspective view of an electrophotographic printing machine embodying the features of the present invention therein;
FIG. 2 is a sectional elevational view of a photoconductive drum used in the FIG. 1 printing machine, and showing, in detail, the apparatus of the present invention;
FIG. 3 is a sectional elevational view of the apparatus of the present invention;
FIG. 4 is an enlarged, exploded perspective view of the photosensor mounting arrangement incorporated in the FIG. 3 apparatus; and
FIG. 5 is an enlarged, perspective view of the FIG. 4 mounting arrangement.
While the present invention will be described in con nection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that ebodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings wherein like reference numerals have been used throughout to designate like elements, FIG. I schematically illustrates an electrophotographic printing machine adapted to reproduce muIti-color copies from a colored original document. The printing machine depicted in FIG. 1 utilizes a photoconductive member having a rotatably mounted drum 10 with a photoconductive surface 12. Drum I0 is arranged to rotate in the direction of arrow 14 and moves photoconductive surface 12 sequentially through processing stations A through E, inclusive.
Drum I0 initially rotates photoconductive surface I2 through charging station A. A corona generating device. depicted generally at I6, extends tranvfersely across photoconductive surface 12. By being positioned in this orientation, corona generating device 16 is capable of charging photoconductive surface 12 to a relatively high uniform potential. A suitable corona generating device 16 is described in U.S. Pat. No. 1778,9 46 issued to Mayo in l957.
Thereafter, charged photoconductive surface 12 rotates to exposure station B which includes thereat a moving lens system, designated generally by the reference numeral 18, and a color filter mechanism, indicated generally at 20. Original document 22 is stationarily supported face down upon transparent platen 24. Lamp assembly 26 and lens system 18 are moved in timed relation with photoconductive surface 12 to produce a flowing light image of the original document on photoconductive surface 12. During exposure. filter mechanism interposes selective color filters into the optical light path of lens 18. The color filter operates on the light passing therethrough to record an electrostatic latent image on photoconductive surface 12 corresponding to a spectral region of the electromagnetic wave spectrum i.e. a color separated latent image.
After the electrostatic latent image has been recorded on photoconductive l2. drum 10 rotates to development station C. Development station C includes three individual developer units generally indicated by the reference numeral 28, 30 and 32, respectively. Each developer unit contains toner particles of a specified color. The developer unit having toner particles appropriate for the filter utilized develops the clectrostatic latent image recorded on photoconductive sur' face 12. Preferably. developer units 28, 30 and 32 are all of a type generally referred to in the art as magnetic brush development units." In a typical magnetic brush development system, a magnetizable developer mix having carrier granules and toner particles is con tinually brought through a directional flux field forming a brush of developer mix. Development is achieved by bringing the brush of developer mix into contact with photoconductive surface l2. Each of the respective developer units 28. 30 and 32 apply toner particles corresponding to the complement of the color separated electrostatic latent image recorded on photoconductive surface 12.
Having been developed, the powder image electroitatically adhering to photoconductive surface 12 is advanced to transfer station D. At transfer station D. the aowder image is transferred to a sheet of final support naterial 34, e.g. plain paper or a thermoplastic trans- )arency amongst others, by means of a biased transfer 'oll, shown generally at 36. Transfer roll 36 is biased electrically to a potential of sufficient magnitude and aolarity to electrostatically attract toner particles from ahotoconductive surface 12 to support sheet 34. A single sheet of final support material 34 is supported on .ransfer roll 36. Roll 36 is arranged to move in synchroiism with photoconductive surface 12 and is adapted o recirculate support material 34 for a plurality of cyrles. i.e. 3 cycles. In this manner successive toner powier images, each corresponding to a specific color in he electromagnetic wave spectrum. are placed in su )erimposed registration upon support material 34. -lence. it is apparent, that in this way a multi-color :opy is reproduced from the colored original.
Support material 34 is stripped from roll 36 and Jassed to a fusing station (not shown) where the pow ler image is coalesced thereto.
The final processing station in the direction of rotation of drum It), as indicated by arrow 14, is cleaning station E. A rotatably mounted fibrous brush 38 is positioned at cleaning station E, and is maintained in engagement with photoconductive surface 12 of rotating drum 10. In this way, residual toner particles remaining on photoconductive surface 12 are removed therefrom.
Additional toner particles are added to the respective developer unit when developability, as hereinbefore described. is no longer satisfactory. The developability regulating apparatus, indicated generally at 40, includes transparent electrode means 42, illuminating means or light source 44, and sensing means or photosensor 46. During development, toner particles are deposited on electrode 42 and the intensity of the light rays transmitted therethrough is indicative of the density thereof. Fiber optic light pipe 48 directs the modulated light rays to photosensor 46. Photosensor 46 is mounted within heating apparatus 50 to minimize ther mal fluctuations due to temperature variations. Suitable logic circuitry compares the electrical output signal from photosensor 46 with a reference to determine whether or not toner particles should be dispensed to the appropriate developer unit, i.e. yellow toner parti cles to developer unit 28, magenta toner particles to developer unit 30, cyan toner particles to developer unit 32.
Turning now to FIG. 2, there is shown the detailed construction of regulating apparatus 40. Transparent electrode 42 is mounted on photoconductive surface 12 in the non-image portion thereof. Electrode 42 in cludes a glass window 52 having a transparent tin oxide coating thereon. Electrically conductive glass of this nature is made by Pittsburgh Plate Glass under the trademark NESA or by Corning Glass Company under the trademark Electro-Conductive. A generally tubular member threadedly engages an aperture in the circumferential surface of drum l0 and is arranged to align light source 44 mounted therein with glass 52. As shown in FIG. 2, light source 44 is mounted on plate 56 which, in turn. is mounted slidingly in tubular member 54. Plate 56 engages undercut 58 in tubular member 54 and is positioned thereby, Lock screw 60 secures plate 56 in the aforementioned position. Suitable lead wires 62 extend from light source 44 and are interconnected with lead wires 64 which pass through the hollow core of shaft member 66. Shaft member 66 is adapted to support drum l0 rotatably. Lead wires 66 are interconnected to slip ring assembly 68 which transmits a regulated current from voltage regulator 70. Voltage regulator 70 receives an unregulated input of between 8 and [0 volts and adjusts the aforementioned input to a regulated output preferably. of about 5 volts for exciting lamp 44.
Referring once again to FIG. 2, an electrical biasing voltage is applied to transparent electrode 42 through slip ring 68. Preferably. this voltage simulates the electrostatic latent image recorded on photoconductive surface [2. The voltage is automatically applied to transparent electrode 42 via the position of drum 10 with respect to slip ring assembly 68. Hence, prior to entering the development zone a voltage of about 200 volts above developer bias, which is preferably about 500 volts. is applied to transparent electrode 42. As drum 10 rotates into the development zone. the magnetic brush assembly of the respective developer unit applies toner particles to transparent electrode 42.
Toner particles are attracted to transparent electrode 42 by the voltage differential of approximately 200 volts between electrode 42 and the corresponding developer unit. The biasing voltage is removed from electrode 42 as it reaches cleaning station E permitting brush 38 to remove the remaining toner particles therefrom. The light rays transmitted through electrode 42 are guided by fiber optic light pipe 48 to photosensor, or photocell 46, disposed within heating apparatus 50. Preferably, glass fiber optics are used to obtain good transmittance in the near infrared region. Glass fiber optics do not attenuate radiant energy in the most sensitive region of the silicon phototransistor. which is the preferred photocell.
Fiber optic light pipe 48 is mounted in plenum chamber 72 by suitable mounting means, e.g. a clamp. Positive lamina flow is directed into the chamber to purge the system and reduce particle contamination therein. As shown in FIG. 2, fiber optic light pipe 48 extends into heating apparatus 50 through a heat-tight aperture therein to conduct modulated light rays transmitted through electrode 42 to photosensor 46 mounted therein. Photosensor 46 and the associate circuit elements are all mounted within heating apparatus 50. In this manner, both photosensor 46 and the associate circuit elements are maintained at a temperature ranging from about 50C to about 60C, the temperature preferably being about 55C. This arrangement minimizes thermal fluctuations in the surrounding environment and substantially reduces the system errors due to the temperature sensitivity of photocell 46.
Preferably, photocell 46 is a suitable silicon phototransistor such as that produced by the General Electric Co. Model No. LI4B. It should be noted that this type of photocell requires a controlled thermal environment to minimize errors. For example, a 4C change in temperature in the surrounding environment of photocell 46 will produce an error signal indicating an incorrect concentration of toner particles within the developer mix. Thus, it is highly desirable to maintain the thermal environment of photocell 46 substantially constant. This is accomplished. in the present instance by heating apparatus 50 of the present invention. The foregoing heating apparatus 50 will be described in greater detail with reference to FIGS. 3 through 5, inclusive.
Turning now to FIG. 3, there is shown, in detail heating apparatus 50. Temperature maintaining means or heating apparatus 50 includes an open ended container 74. Container 74 defines an internal chamber 80 for housing photosensor 46 therein. Container 74 is insulated and includes suitable circuitry and heating elements for maintaining interior chamber 80 at a suitable temperature. Control circuitry and heating elements 76 are disposed within container 74. By way of example, a thermistor functioning as one leg of a Wheatstone bridge may be used to detect temperature variations. This type of Wheatstone bridge arrangement may control wire wound resistance heating elements. Wall 78, interposed between the control circuitry and heating elements disposed in internal chamber 80, has a slot 82 therein for receiving a generally planar support member or printed circuit board 84. Disc member 86 is intermeshed with printed circuit board 84 to align lens 88 therein with photosensor 46 mounted on printed circuit board 84. The detailed assembly of disc member 86 with printed circuit board 84 will be described hereinafter with reference to FIGS. 4 and 5.
Referring once again to FIG. 3, end cap 90 is secured to container 74 on the open end thereof. End cap 90 is permanently affixed by suitable means, eg cement, to the open end of container 74 to form a heat'tight joint therebetween. A plurality of substantially equally spaced protuberances 92 (in this case 8 pins) extend from end cap 90 in a direction substantially parallel to the longitudinal axis thereof. In addition, thereto, end cap 90 includes aperture 94 which is substantially circular to receive end portion 96 of fiber optic light pipe 48. Flanged member 98 includes an aperture 100 therein permitting the fiber optic light pipe 48 to pass therethrough such that end portion 96 extends therebe' yond. Moreover, flanged member 98 includes a plurality of equally spaced apertures (in this case 8 holes extending partially therethrough substantially parallel to the longitudinal axis thereof) for receiving pins 92 of end cap 90. Thus, in operation fiber optic light pipe 48 is secured in a heat-tight fashion to flanged member 98 by passing through aperture I00 therein. Fiber optic light pipe 48 is, thereafter, assembled to container 74 by passing end portion 96 slidingly into aperture 94 of end cap 90. Pins 92 mate with holes 94 to form a substantially heat-tight joint therebetween, Hence, in this fashion modulated light rays are guided from transparent electrode 42 to lens 88 which focuses the aforementioned modulated light rays onto photocell 46 for measuring the intensity thereof.
Turning now to FIG. 4, there is shown an exploded perspective view of disc member 86 being assembled to circuit board 84. As depicted therein, disc member 86 includes substantially circular opening 104 for securing thereto lens 88. Furthermore, disc member 86 includes a slot 106 extending from the circumferential surface thereof partially therethrough being positioned transversely a radius chord thereof. Disc member 86 is adapted to intermesh with printed circuit board 84. In order to accomplish this, printed circuit board 84 also includes a slot 108 extending from one surface thereof partially therethrough.
Disc member 86 is assembled to board 84, as shown in FIG. 5, by intermeshing slot 106 therein with slot 108 in printed circuit board 84. In this manner, the composite assembly of disc member 86 and board 84 forms an integral support with aperture 104 properly aligned such that when lens 88 is disposed therein light rays passing therethrough are focused on photocell 46.
By way of example, the aforementioned heating apparatus 50 is arranged to raise the temperature of the internal chamber thereof, wherein photosensor 46 is positioned, from about 60F to about 55C within about three minutes. Heating apparatus 50 is excited by a suitable 24 volt DC input. The aforementioned control apparatus, hereinbefore described as being proportional, may also be of a suitable on-off type.
Thus, in recapitulation, heating apparatus 50 of the present invention maintains photosensor 46 in a substantially constant thermal environment to substantially minimize temperature fluctuations thereof. In this way, thermal errors induced in the development regulating apparatus are substantially reduced. Moreover. heating apparatus 50 is adapted to permit fiber optic light pipe 48 to pass therethrough and guide the modulated light rays from transparent electrode 42 to photosensor 46. The aforementioned fiber optic light pipe 48 7 is automatically aligned in heating apparatus 50 with lens 88 to focus the light rays passing thercthrough onto photosensor 46.
it is. therefore, apparent that there has been provided in accordance with this invention, an apparatus for minimizing thermally induced errors in a developability regulating apparatus that fully satisfies the objects. aims and advantages set forth above. While this invention has been described in conjunction with specific embodiments thereof. it is evident that many alernatives. modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives. modifications and variations that fall within the spirit and broad scope of the appended claims.
What is claimed is:
I. An apparatus for controlling the thermal environment of a photosensor adapted to detect light rays emitted from a light source, including:
a fiber optic light pipe for transmitting light rays to the photosensor;
an open ended container defining an internal chamber for housing the photosensor;
an end cap having an aperture therein adapted to receive one end portion of said fiber optic light pipe to form therewith a substantially light-tight joint, said end cap being mounted on the open end of said container to form therewith a substantially heat-tight joint;
means for heating said container to a predetermined temperature; and
means for controlling said heating means such that said container remains substantially at the predetermined temperature.
2. An apparatus as recited in claim I, wherein:
said end cap includes a plurality of substantially equally spaced protuberances extending therefrom in a direction substantially parallel to the longitudinal axis thereof; and
said fiber optic light pipe includes a flanged member having an aperture therein permitting the other end portion of said fiber optic light pipe to pass therethrough and extend therefrom forming a substan tially heat-tight joint therewith, said flanged memher having a plurality of substantially equally spaced openings therein arranged to receive said protuberances extending from said end cap.
3. An apparatus as recited in claim 1 further including:
a disc member having an aperture therein and an open ended slot extending over a portion of said disc member substantially transverse to a radius thereof spaced from the aperture therein;
a generally planar support member having mounted thereon said photosensor said support member having an open ended slot therein adapted to intermesh with the corresponding slot in said assembly. member to form a unitary assembly said disc member being positioned substantially normal to said support member; and
a lens member mounted in the aperture of said disc member and arranged to focus the light rays transmitted through said fiber optic light pipe onto said photosensor for measuring the intensity thereof.
4. An apparatus as recited in claim 3, wherein the predetermined temperature ranges from about 50C to about 60C preferably being about 55C.