Description:
BACKGROUND OF THE INVENTION
This invention relates generally to an electrophotographic printing machine, and more particularly concerns an illuminating apparatus having the spectral energy distribution of the light rays being disseminated therefrom substantially constant.
In the process of electrophotographic printing, a photoconductive surface is uniformly charged and exposed to a light image of an original document. Exposure of the photoconductive surface records thereon an electrostatic latent image corresponding to the original document. The electrostatic latent image is then rendered visible by depositing thereon toner particles which adhere electrostatically thereto in image configuration. Subsequently, the toner powder image is transferred to a sheet of support material which may be plain paper or a transparent thermoplastic material, amongst others. The toner powder image is, then, permanently affixed to the support material, thereby providing a copy of the original document.
Multi-color electrophotographic printing is substantially the same as the heretofore discussed process with the following distinctions. Rather than forming a total light image of the original, the light image is filtered producing a single color light image which is a partial light image of the original. The foregoing single color light image exposes the charged photoconductive surface recording thereon a single color electrostatic latent image. This single color latent image is developed with toner particles of a color complementary to the single color light image. Thereafter, the single color toner powder image is transferred to the support material. The foregoing process is repeated a plurality of cycles with differently colored light images and the respective complementary colored toner particles. Each single colored toner powder image is transferred to the support material in superimposed registration with the prior toner powder image to form a composite multi-powder image thereon. This multi-color powder image is coalesced and permanently affixed to the support material.
It is apparent that in a multi-color electrophotographic printing machine, the spectral characteristics of the illuminating apparatus are critical. Preferably, the spectral energy distribution of the light source in the illuminating apparatus remains substantially constant. This is desirable to insure that the filtered light image has the specified bandwidth and amplitude. In turn, the photoconductive member is designed to be responsive to the bandwidth and amplitude of the light image being transmitted through the filter. Variations in bandwidth and/or amplitude will create variations in the color balance of the reproduction.
A typical light source may be a tri-phosphor fluorescent lamp. This type of lamp is arranged to have peak energy outputs at the blue, green and red wavelengths. The corresponding filters are arranged to permit a single color light image to pass therethrough. Hence, a blue filter only permits the blue light image to be transmitted therethrough, a red filter only a red light image and a green filter only a green light image. It is apparent that if the spectral energy distribution of the lamp should vary, the amplitude and/or bandwidth of the filtered light image may be changed. For example, if the spectral energy distribution of the lamp varies such that the blue light image is of a too narrow a bandwidth and/or of a low amplitude, a weak blue light image will be formed. This weak blue image will, in turn, record a weak electrostatic latent image on the photoconductive member, and the complementary toner powder image will be course be weak. However, the toner powder images complementary to the red and green filtered light images will be of normal strength resulting in the copy having a distorted color balance.
Fluorescent lamps generally are sensitive to thermal variations in the surrounding environment. Typical fluorescent lamps have a discrete amount of liquid mercury deposited within a phosphor coated lamp bulb. During lamp operation, the mercury is vaporized to a very low pressure generating a mercury line radiation at a wavelength of 253.7 nm. This radiation is absorbed by the phosphor coating producing radiation in the visible spectrum. The spectral energy distribution of the lamp is a function of the 253.7 nm mercury line radiation, which, in turn, is a function of the mercury vapor pressure within the lamp bulb. However, the mercury vapor pressure is dependent upon the lamp bulb temperature. Thus, amplitude and/or the bandwidth of the respective spectral energy outputs from the lamp are dependent upon temperature gradients.
In an electrophotographic printing machine, particularly a multi-color machine, heat is continually being dissipated by the exposure mechanism, and the fusing apparatus adapted to coalesce and fix the powder image to the support material. It is evident that thermal gradients of this nature may adversely effect the spectral energy distribution of the illuminating apparatus.
Accordingly, it is a primary object of the present invention to improve the temperature control system of an illuminating apparatus maintaining the spectral energy distribution therefrom substantially constant.
SUMMARY OF THE INVENTION
Briefly stated, and in accordance with the present invention, there is provided an illuminating apparatus in which the spectral energy distribution therefrom is maintained substantially constant.
This is accomplished in the present instance by a light source having heating means entrained about a portion of the exterior peripheral surface thereof. In addition, cooling means, spaced from the light source, are provided. Regulating means control the cooling and heating means to maintain the light source substantially at a predetermined temperature. In this manner, the spectral energy distribution of the light rays emitted from the light source are unaffected by thermal disturbances and remains substantially constant.
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 having the present invention therein;
FIG. 2 is a schematic illustration of the illuminating apparatus incorporated in the FIG. 1 printing machine; and
FIG. 3 is a perspective view of the light source utilized in the FIG. 2 illuminating apparatus.
While the present invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. 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 INVENTION
Whith continued reference to the drawings wherein like reference numerals have been used throughout to indicate like elements, FIG. 1 schematically illustrates the components of an electrophotographic printing machine for producing multi-color copies from a colored original.
As shown schematically in FIG. 1, the electrophotographic printing machine, particularly adapted to utilize the present invention, includes a rotatably mounted drum 10 having a photoconductive surface 12 thereon. Drum 10 is mounted on a shaft journaled in the printing machine frame to rotate in the direction indicated by arrow 14 causing photoconductive surface 12 to pass sequentially through processing stations A through E, inclusive.
Initially, drum 10 rotates in the direction of arrow 14 to move photoconductive surface 12 through charging station A. Charging station A has positioned thereat a corona generating device indicated generally at 16. As illustrated in FIG. 1, corona generating device 16 is arranged to extend in a generally transverse direction across photoconductive surface 12. Corona generating device 16 charges photoconductive surface 12 to a relatively high substantially uniform potential. U.S. Pat. No. 2,778,946 issued to Mayo in 1957 describes a typical corona generating device which may be suitable for use in a multi-color electrophotographic printing machine.
After photoconductive surface 12 is charged to a substantially uniform potential, drum 10 rotates to exposure station B. At exposure station B, photoconductive surface 12 is exposed to a single color light image of the original document. A moving lens system, generally designated by the reference numeral 18, and a color filter mechanism, shown generally at 20 are positioned at exposure station B. One type of moving lens system suitable for the electrostatographic printing machine of FIG. 1 is disclosed in U.S. Pat. No. 3,062,108 issued to Mayo in 1962. Original document 22 is supported stationarily upon transparent viewing platen 24. The lamp assembly, indicated generally at 25, includes a pair of lamps 26, associated with lens system 18. Lamps 26 move in a timed relation with drum 10 scanning successive incremental areas of original document 22 positioned upon platen 24. This creates a flowing light image of original 22 which is recorded on photoconductive surface 12. During the exposure process, filter mechanism 20 interposes selected colored filters into the optical light path of lens 18. The color filter operates on the light rays transmitted through lens 18 to record a single color electrostatic latent image on photoconductive surface 12 corresponding to a preselected spectral region of the electromagnetic wave spectrum.
After the single color electrostatic latent image is recorded on photoconductive surface 12, drum 10 rotates to development station C. Development station C includes three individual developer units, generally indicated by the reference numerals 28, 30 and 32, respectively. A suitable development system utilizing a plurality of developer units is disclosed in copending application Ser. No. 255,259 filed in 1972. As disclosed in the foregoing patent application, the developer units are all magnetic brush development units. Typical magnetic brush developer units utilize a magnetizable developer mix including carrier granules and toner particles. This developer mix is brought continually through a directional flux field to form a brush thereof. Development is achieved by bringing the single color electrostatic latent image recorded on photoconductive surface 12 into contact with the brush of developer mix. Differently colored toner particles corresponding to the complement of the spectral region of the wavelength of light transmitted through filter 20 are contained within each of the respective developer units. For example, a green filtered electrostatic image is made visible by depositing green absorbing magneta toner particles thereon. Similarly, blue and red latent images are developed with yellow and cyan toner particles respectively,
Subsequent to the formation of the toner powder image on photoconductive surface 12, drum 10 is rotated to transfer station D. At transfer station D, the powder image adhering electrostatically to photoconductive surface 12 is transferred to a sheet of final support material 34. Final support material 34 may be plain paper or, in the formation of transparencies, a thermoplastic transparent material. A bias transfer roll, shown generally at 36, recirculates support material 34 in the direction of arrow 38. Roll 36 is electrically biased to a potential of sufficient magnitude and polarity to electrostatically attract toner particles from photoconductive surface 12 to sheet 34. U.S. Pat. No. 3,612,677 issued to Langdon in 1972 discloses a suitable electrically biased transfer roll. Transfer roll 36 is arranged to rotate in synchronism with photoconductive surface 12, i.e. transfer roll 36 and drum 10 rotate substantially at the same speed and have substantially the same outer diameter. Inasmuch as support material 34 is secured releasably to transfer roll 36 for movement therewith in a recirculating path, successive toner powder images may be transferred thereto. Hence, successively colored toner particles are transferred from photoconductive surface 12 to support material 34 in superimposed registration with one another. In this way, a multi-colored toner powder image corresponding to the colors found in the original document is formed on support material 34.
With continued reference to FIG. 1, the paper path for advancing support material 34 to transfer roll 36 will hereinafter be described. Stack 40 of support material 34 is supported on tray 42. Feed roll 44 operatively associated with retard roll 46 separates and advances the uppermost sheet from stack 40. The advancing sheet moves into paper chute 48 and is directed into the nip of register rolls 50. Next, gripper fingers 42, mounted on transfer roll 36, releasably secure thereto support material 34 for movement therewith in a recirculating path.
After all of the discretely colored powder images have been transferred to support material 34, support material 34 is stripped from transfer roll 36 and moved on endless belt conveyor 54 to fixing station E, where a fuser indicated generally at 56, coalesces and permanently affixes the transferred powder image to sheet 34. A typical fuser is described in U.S. Pat. No. 3,498,592 issued to Moser et al. in 1970. After the powder image is fused, support material 34 is advanced by endless belt conveyors 58 and 60 to catch tray 62. At catch tray 62, an operator may remove the final multi-color copy from the machine.
As indicated by arrow 14, the final process in the direction of rotation of drum 10 is cleaning station F. Preferably, brush cleaning device 64 positioned at cleaning station F, is of the type described in U.S. Pat. No. 3,590,412 issued to Gerbasi in 1971. As disclosed therein, a rotatably mounted fibrous brush is maintained in contact with photoconductive surface 12 to remove residual toner particles remaining thereon after each transfer operation.
The apparatus of the present invention is associated with maintaining the spectral energy output of lamp 26 substantially constant and will be discussed, hereinafter, in detail, in association with FIGS. 2 and 3. As heretofore indicated, lamp 26, preferably, is of the type conventionally referred to as a fluorescent lamp. Typical fluorescent lamps are sensitive to variations in the surrounding thermal environment. It is, therefore, evident that it would be desirable to maintain the thermal environment surrounding lamp 26 substantially constant.
Turning now to FIG. 2, there is shown lamp carriage 56 supporting a pair of light sources or lamps 26 therein. Lamp carriage 66 is arranged to traverse platen 24 illuminating incremental widths of original 22. Heating means or sleeve heater 68 is arranged to supply energy to light source 26. Sleeve heater 68 has an arcuate portion arranged to be mounted slidably on lamp 26 extending about the entire longitudinal length thereof, and in substantial contact with a portion of the exterior circumferential surface thereof. The arcuate portion extends over a 270° arc with a slot extending the entire length of lamp 26 permitting light rays to pass therethrough. Heater 68, preferably, has a 20 watt output and operates at a voltage ranging from about 98 volts to 127 volts at about 60 hertz. The wire resistance elements incorporated in heater 68 have a resistance of about 685 ohms. The laminated structure surrounding the wire resistant elements is a polyester impregnated glass cloth laminated over a nomex substrate or, in lieu thereof, a nichrome wire grid laminated in an insulation of teflon and epoxy coated glass cloth. The exterior surface of the heater is coated with a flat black paint arranged to withstand an operating temperature of about 175° F. Sleeve heater 68 engages the exterior surface of lamp 26 with a pull-out force ranging from about 1 pound to about 5 pounds, and preferably is about 3 pounds. Cooling means or blower 70 is secured to lamp carriage 66. Blower 70 creates a flow of air, in the direction of arrow 72, upon lamp 26 for reducing the temperature thereof. In this way, heater 68 may raise the temperature of lamp 26 when it is beneath a predetermined temperature, and blower 70 may reduce the temperature of lamp 26 when it exceeds a predetermined temperature. Blower 70 is a centrifugal blower having a two-pole permanent split capacitor motor, and operates at about 117 volts, 60 hertz with about a 53 CFM capacity at a sea level static pressure of about 0 inches of water. Air filter 71 is secured to the intake of blower 70. The density of the air filter is critical in establishing the flow characteristics of the system. Preferably, filter 71 is made from a foam material having a density of 45 pores per linear inch. Regulating means, operatively associated with heater 68 and blower 70 maintain lamp 26 substantially at about the predetermined temperature, preferably, 100° F. The predetermined temperature may range from about 90° F to about 115° F.
Referring now to FIG. 3, there is shown a single lamp 26 having a sleeve heater 68 wrapped thereabout. As shown in FIG. 3, sleeve heater 68 extends the entire length of lamp 26 about 270° arc. The exterior circumferential surface of lamp 26 is opaque with a clear region 74 extending over a 45° arc therein. Region 74 extends substantially the entire length of tubularly configured lamp 26. Lamp 26 operates at about 30 watts, 37 volts and 1.5 amps RMS. The spectral energy distribution of the red output is about 44 micro watts per centimeter squared, the green output about 82 micro watts per centimeter squared, and the blue output about 25 micro watts per centimeter squared. The lamp includes three phosphors having a color balance such that the blue/green ratio is 0.3 and the red/green is about 0.53.
As depicted in FIG. 3, the regulating means includes suitable circuit means (not shown) and/or a thermally responsive member 76. Thermally responsive member 76 is, preferably, a hermatically sealed bi-metal snap action disc type thermostat. The contacts of thermostat 76 are rated at about 0.5 amps, 117 volts AC at 60 hertz. The contacts open at about 110° F and close at about 100° F. Preferably, thermostat 76 is positioned on the wall of lamp 26 substantially at the center of the slot in sleeve heater 68. Thermostat 76 is an on-off type of device. In operation, when lamp 26 is heated to a temperature greater than 110° F, the contacts of thermostat 76 open de-energizing sleeve heater 68. Since blower is continually operative, the flow of air therefrom reduces the temperature of lamp 26. When the temperature of lamp 26 is beneath 100° F, the contacts of thermostat 76 close energizing sleeve heater 68. In this way, lamp 26 is maintained within a temperature ranging from about 100° F to about 110° F.
While the invention has been described in connection with an on-off type of thermostat, one skilled in the art will appreciate that the invention is not necessarily so limited and that a proportional thermistor is conjunction with suitable circuit means may be utilized to control the temperature of lamp 26. For example, a proportional thermistor may be connected as one leg of a conventional Wheatstone bridge circuit. The resulting error signal is indicative of the deviation in lamp temperature from the predetermined temperature. This error signal may be utilized to de-energize sleeve heater 68 when the predetermined temperature is exceeded. Similarly, the error signal energizes sleeve heater 68 when the lamp temperature is beneath the predetermined temperature.
The foregoing types of control schemes maintain the temperature surrounding lamp 26 substantially constant. This insures that the light rays emitted from lamp 26 have a substantially constant spectral energy distribution. Thus, the various electrostatic images recorded on photoconductive surface 12 have the color content thereof properly balanced with one another.
In recapitulation, it is evident that the thermal environment surrounding the light source utilized in the electrophotographic printing machine heretofore described is maintained substantially constant. Hence, thermal fluctuations in the surrounding environment are minimized and the spectral energy output thereform is maintained substantially constant. This is achieved by sleeve heater 68, blower 70, and thermostat 76. In operation, a thermal control range is developed by the interaction of heater 68, blower 70 and thermostat 76. When the upper temperature limit of this control range is approached, thermostat 76 de-energizes heater 68. Cooling air from blower 70 reduces the temperature of lamp 26 beneath the upper temperature limit. When the lower temperature limit of the control range is approached, thermostat 76 energizes heater 68 transferring thermal energy to lamp 26. The resulting interaction of cooling air from blower 70, self heating from lamp 26, and thermal energy from lamp 26 maintain lamp 26 at a temperature equilibrium within the specified temperature control range. Therefore, the present invention improves the temperature control of the illuminating apparatus utilized in multi-color electrophotographic printing machines, thereby maintaining the spectral energy distribution therefrom substantially constant. This, in turn, insures that the color balance of the copy compares favorably with the original.
It is, therefore evident that there has been provided, in accordance with the present invention, an illuminating 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 alternatives, 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.