Patent Application
20060165424
The present inventive subject matter relates to the art of photoreceptor thickness measurement. It finds particular application in conjunction with xerographic machines, and will be described with particular-reference thereto. However, one of ordinary skill in the art will appreciate that it is also amenable to other like applications.
As is known in xerography, a xerographic machine employs a photoreceptor (PR) to produce or reproduce an image on an output media such as paper. The photoreceptor (PR) is typically constructed of a photoconductive layer (PCL) arranged over an electrically conductive substrate. In response to light exposure, the photoconductive layer acts as an electrical conductor or as an electrical insulator. The photoreceptor commonly takes the form of a cylindrical drum, belt or other suitable form.
The photoreceptor is prepared to receive a latent image thereon by a charging process wherein a substantially uniform electrical charge is induced on the photoreceptor surface by a charging device, e.g., a corotron, scorotron, dicorotron, bias charge roll (BCR), etc. The latent image is formed on the charged photoreceptor by projecting onto it a pattern of light corresponding to the desired image being formed. In accordance with the light pattern to which the photoreceptor was exposed, the charge on the surface of the photoreceptor is selectively discharged or altered such that the latent image is formed and/or represented by the electrostatic difference or variation across the surface of the photoreceptor.
Typically, an electrically charged toner is applied to the photoreceptor containing the latent electrostatic image, thereby developing a visible toner image on the surface of the photoreceptor. The toner image is eventually transferred and fused to the output media. Commonly, after the transferring and fusing processes, any excess toner remaining on the photoreceptor is removed so that the photoreceptor is again ready for charging.
Variations in the thickness of the photoconductive layer can be experienced for a variety of reasons. For example, in a given photoreceptor, the thickness of the photoconductive layer may be reduced over time due to standard wear-and-tear. In another example, the thicknesses of photoconductive layers from photoreceptor to photoreceptor may vary due to inexact manufacturing tolerances.
The charging and/or discharging response of the photoreceptor and/or other photoreceptor characteristics can be affected by the thickness of the photoconductive layer. Therefore, unpredictable changes in the photoconductive layer thickness may ultimately effect the image quality of the xerographic machine absent any corrective measures. However, by knowing the thickness of the photoconductive layer at any given time, some degree of compensation can be achieved.
Accordingly, a new and improved apparatus and/or method for determining the thickness or thickness changes of a xerographic photoreceptor is disclosed that overcomes the above-referenced problems and others.
In accordance with one exemplary embodiment, a method for detecting a thickness of a photoconductive layer is provided in a xerographic machine having, a photoreceptor including the photoconductive layer arranged over an electrically conductive substrate, and a charging station for applying a substantially uniform electrostatic charge to a surface of the photoconductive layer. The method includes: measuring an electrical property of the charging station; and, determining the thickness of the photoconductive layer from the measured electrical property.
In accordance with another exemplary embodiment, a xerographic machine includes: a photoreceptor including a photoconductive layer arranged over an electrically conductive substrate, said photoconductive layer having a thickness; a charging station that applies a substantially uniform electrostatic charge to a surface of the photoconductive layer; and, a detection system that detects the thickness of the photoconductive layer by measuring an electrical property.
Numerous advantages and benefits of the inventive subject matter disclosed herein will become apparent to those of ordinary skill in the art upon reading and understanding the present specification.
The present inventive subject matter may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting. Further, it is to be appreciated that the drawings are not to scale.
With reference to
The xerographic machine 10 is also equipped with a thickness detection system 400. The thickness detection system 400 detects the thickness of the photoconductive layer 112. A processor 402 or other similar controller suitably regulates the operation of the respective components of the xerographic machine 10 to conduct a thickness detection process. Optionally, a user interface 404 including input and/or output devices permits a user to manually initiate the thickness detection process and/or obtain the results. Alternately or in addition to manual operation, the thickness detection process is optionally run automatically on a determined schedule or at specified times. Optionally, in response to the obtained thickness results, imaging, charging and/or other operating parameters of the xerographic machine 10 are automatically adjusted by the processor 402 to compensate for a detected change in the thickness t.
In a suitable embodiment (as shown in
Referring now, more particularly, to the illustrated BCR system,210, an electrically conductive roll member 212 is provided in contacting engagement with the photoconductive surface 116 of the photoreceptor 110. The roll member 212 is axially supported on an electrically conductive core or shaft 214, situated transverse to the direction of relative movement of the photoreceptor 110. Suitably, the roll member 212 is provided in the form of a deformable, elongated roller supported for rotation about an axis 216 and is optionally comprised of a polymer material such as, for example, Neoprene, F.P.D.M. rubber, Hypalon rubber, Nitrile rubber, Polyurethane rubber (polyester type), Polyurethane rubber (polyether type), Silicone rubber, Viton/Fluorel Rubber, Epichlorohydrin rubber, or other similar materials having a D.C. volume resistivity in the range of 103 to 107 ohm-cm after suitable compounding with carbon particles, graphite or other conductive additives. These materials are chosen for the characteristic of providing a deformable structure while in engagement contact with the photoreceptor 110, as well as wearability; manufacturability and economy. Suitably, the deformability of the roll member 212 provides a nip having a substantially measurable width while being engaged with the photoreceptor 110. It is to be appreciated that alternative BCR arrangements can have the conductive roll member 212 slightly out of contact with the photoconductor surface 116 at a substantially fixed spacing. In such BCR arrangements, deformability properties of the roll member 212 are not as important. For convenience, the following discussions shall refer to contacting BCR arrangements, but it will be apparent to those skilled in the art that discussions can be readily extended to non-contacting BCR arrangements.
As illustrated, a high voltage power supply 220 is connected to the roll member 212 via shaft 214 for supplying a suitable input drive voltage to the roll member 212, e.g., such as an oscillating input drive voltage, a DC voltage, an AC voltage optionally with or with out a DC offset, etc. Suitably, as known in the art, the oscillating input drive voltage is selected to have a peak-to-peak voltage typically chosen to be high enough to cause air breakdown at small air gap regions between the roll member 212 and the photoreceptor surface 116 very near the contact zone therebetween. The DC offset voltage is suitably chosen based on the desired charge potential to be induced on the photoconductive surface 116. At operating AC voltage conditions, the charge potential induced on the photoconductive surface 116 will typically be near or equal to the DC offset voltage. While it is possible to use a standard line voltage, other voltage levels or voltage signal frequencies may be desirable in accordance with other factors dependent on individual machine design, such as the desired charge level to be induced on the photoreceptor 110, or the speed of copying and/or printing operations desired. Accordingly, a charging operation involves the application of a voltage signal from the BCR system 210 to the photoconductive surface 116 of photoreceptor 110 in the usual manner, which creates a voltage potential across the photoreceptor 110 to ground 300.
In the current embodiment, the thickness detection system 400 (
C=e0[Anip/(tK+dair0)]+CS (1);
where C is the measured capacity. In equation (1), it should be noted that the capacity of the roll member (i.e., the layer between the shaft 214 and the outer photoconductor contacting surface of the roll member 212) has been neglected, and this is generally a good approximation for practical arrangements. The right hand side of equation (1) includes: a first term for the capacity related to the contacting nip area between the roll member 212 and the photoconductor surface 116; and, a second term CS representing the capacity between the roll member 212 and the photoconductor substrate 114 in the air gap regions between the roll member 212 and photoconductor 110 that are beyond the contacting nip. In equation (1), Anip is the contact area between the roll member 212 and the surface 116 of the photoreceptor 110, dair0 represents a very small air gap that can be present between the contacting roll member 212 and the photoconductive layer 112 in the nip, e0 is the permittivity of free space, and K is the dielectric constant of the photoconductive layer 112, such that e0×K=ε, where ε is the permittivity of the photoconductive layer 112. While not explicitly identified herein, it suffices to note that specific expressions for the CS term, while potentially complex, are derivable by those skilled in the art. For a typical BCR system, the CS term is generally significantly smaller than the first term of equation (1), and it is weakly dependant on the photoconductive layer thickness, if at all. For a contacting BCR system (such as the exemplary illustrated BCR system 210), the dair0 term is often small compared to the t/K term. Notably, for most BCR systems, dair0 is relatively constant.
For simple-cases where CS is suitably small compared to the first term in equation (1), solving equation (1) for t gives:
t=ε(AnipC)−Kdair0 (2).
In this simple case, there is a linear dependence of t on the measured capacity C. In more general cases where the CS term is not sufficiently negligible, the dependence of the thickness t on the measured capacity C may more complex than equation (2) suggests. Also, in some very general cases, the photoconductor 110 may have some level of conductivity or can have somewhat complex dielectric properties, and this may further affect the relationship between the thickness t and the measured capacity C. Also, while equation (1) would suitably maintain a similar form, it is modified somewhat for a BCR arrangement having a roll member that is spaced from the photoconductor. In any event, there remains a defined relationship between the measured capacity C and the thickness of the photoconductive layer, that is suitably derivable.
As an alternative to analytical determination, the relationship between C and t is determined experimentally for the actual BCR configuration and photoconductor employed in a particular application. This is done, for example, by purposely varying the thickness t (e.g., via deliberate wearing or another representative means) in one or more models or test machines, and measuring the resultant capacity C at a plurality of different thicknesses (e.g., which are known or otherwise accurately determined or measured using standard techniques). Accordingly, a look-up table or the like is generated relating capacity to thickness. Advantageously, the experimental approach readily accounts for possible sources of complexity that might affect the relationship between t and C. Once the specific relationship between t and C is established and available, e.g., in a look-up table, subsequent measurements of C, in a machine having the same or similar configuration as the models or test machines, can be used to readily determine t or changes thereto.
Suitably, a capacitance-bridge (CB) 410 (optionally part of the detection system 400) is employed to measure the capacity C between the BCR system 210 and the photoreceptor 110. Alternately, another capacity measuring device is employed. In the illustrated embodiment, the CB 410 is operatively connected between the shaft 214 of the roll member 212 and the conductive substrate 114 of the photoreceptor 110. Optionally, the processor 402 (
As described above, measurements of capacitance in the BCR system 210 are used to determine the thickness t or changes in the thickness t. Another suitable embodiment uses measurement of the AC current flow between the BCR system 210 and the photoconductor substrate 114 instead of measured capacitance. Notably, this AC current is related to the capacitance. Actually, the AC current flow between the roll member 212 and the photoconductor 110 has a “corona current” component in addition to the capacitive component, but this does not create any issues related to using AC current as a surrogate, instead of a capacitance measurement, to determine photoconductor thickness. As is known in the art, a controlled air breakdown or ionization generally referred to as “corona” occurs in small air gap regions between the roll member 212 and the photoconductor 110 due to the application of suitably high AC potentials. The corona current component of the AC current flow between the roll member 212 and the photoconductor 110 is out of phase with the capacitive current flow component therebetween, but it still adds to the total current. Also, the corona current component of the total current increases or decreases as the photoconductive layer 112 increases or decreases in thickness. Therefore, an increase in total current corresponds to a decrease in t, and thus a relationship between the AC current and t can be established. Suitably, the specific relationship is established by using similar analytical and/or experimental techniques such as those previously described. As in the capacitance case, experimental determination has similar advantageous. Suitably, the experimentally determined correspondence between measured AC current and t is supplied to a look up table. Later measurements of the AC current between the BCR system 210 and the photoconductor 110 are then used to readily determine the thickness t and/or changes therein.
Optionally, the AC current between the BCR system 210 and the photoconductor 110 is measured directly with a current meter 412 (or other AC current detector, sensor or monitor system) placed between the photoconductor 110 and ground connection 300. This arrangement is particularly suitable, e.g., if the AC current flow to the photoconductor substrate 114 from the BCR system 210 is sufficiently higher than the AC current flow to the substrate 114 from other charging sources delivering current to the photoconductor 110 in the xerographic module 100, such as the development system, etc. If other AC current sources to the photoconductor 110 are relatively high in magnitude (i.e., sufficiently close to that of the BCR system 210), but are of a sufficiently different operating frequency than the BCR system 210, a phase detection sensor or circuitry is optionally employed to separate the AC BCR current from these other sources. Alternatively, the AC BCR current is monitored at the power supply 220. Measurement of the current at the supply is, however, potentially disadvantageous to the extent that it may include a high level of AC leakage current, e.g., due to stray capacitance to ground between the high voltage power supply output lead and the roll member connection contact, which effect is depicted generally in
In another suitable embodiment (as shown in
The scorotron 250 is suitably configured and/or arranged as any conventional scorotron. The exemplary scorotron illustrated includes a coronode 252, a shield 254, and a grid 256. Suitably, the coronode 252 is a fine electrically conductive wire or thin rod elongated substantially parallel with the photoreceptor 110. Alternately, the coronode 252 is formed from an electrically conductive sheet of material with a sawtooth cut edge or comb-shaped pin arrangement facing the photoreceptor 110, the sawtooth points or comb-shaped pins forming what is known as scorotron pins. Suitably, the shield 254 is a typically a u-shaped or other suitably shaped electrically conductive member extending the length of and surrounding the coronode 252 with its open side facing the photoreceptor 110. The grid 256 is suitably positioned across the open side of the shield 254 between the coronode 252 and the photoreceptor 110. During charging of the photoconductor 110, the grid 256 helps control the strength and uniformity of the charge placed on the photoreceptor 110. Suitably, the grid 256 is formed from an electrically conductive, perforated material, e.g., from a thin metal film having a pattern of spaced perforations opened therein. Alternately, the grid 256 is formed from a weave or lattice of electrically conductive wires with openings therebetween.
While not shown, in yet another suitable embodiment, the grid and shield may be optionally combined with the grid forming a u-shape or other suitable shape. This alternate embodiment is particularly applicable to a scoroton employing a pin style coronode.
Returning attention now to
Suitably, for the charging process, the grid 256 is maintained at a high D.C. voltage potential VG and the coronode 252 is supplied a high D.C. voltage potential VC that is optionally varied to maintain a substantially constant current flow IC to the coronode 252. Typically, the potential of the first high voltage source 260 is in the range of approximately 1 to 10 kilovolts (kV), often about 6 kV. Typically, with a well designed scorotron, the resulting photoconductor potential after passage through the device is near the value of the potential supplied to the grid VG. For example, during the charging process, the coronode is supplied a potential VC of around 6 kV and the grid 254 is maintained at a potential VG in the range of approximately 0.3 kV to 1.5 kV, suitably at about 0.6 kV. In certain cases, optionally, the shield 254 may also be biased, e.g., to the same potential as the grid 256 or to some other potential depending on the type of corona device being used. Accordingly, in the usual manner, the charging process involves ionization of the surrounding air or generation of a corona by appropriately energizing the various components of the scorotron 250, thereby a charge is transferred and/or applied to the photoconductive surface 116 which creates a voltage potential VPR across the photoreceptor 110 to ground 300.
In the current embodiment, the thickness detection system 400 (
With added reference to
Notably, the thickness t of the photoconductive layer 112 is related to the photoreceptor's surface charge density and voltage in accordance with the following equation:
t/K=e0(VPR/CD) (3);
where CD is the charge density or charge per area on the surface 116 of the photoconductor 110. Note the term t/K represents the so called dielectric thickness.
With particular reference to
t/K=e0×n×VELPR×L (4);
where VELPR is the photoreceptor velocity, and L is the charging process length. Note that the length term converts from current to current per length, and the velocity term converts from current per length to charge per area, i.e., CD. Note also that any constant non-surface charge residual voltage will only contribute to the intercept 270 and not the slope n.
Turning attention now to
t=e0×K×G×m×VELPR×L (5);
where G is a factor of proportionality such that:
VPR=G×VG+C (6);
where C is a constant. Suitably, G is constant or varies in a well defined way with changes in IC.
Suitably, a current meter 420 or other current sensing device (optionally part of the detection system 400) is operatively connected to the circuit depicted in
The discussions thus far have utilized simple relationships between the thickness t and the dynamic currents and grid voltages that suitably apply for most photoconductor systems. However, these relationships potentially become somewhat more complex in other more complex systems having photoconductors where the charging characteristics are more complex than that described. Nevertheless, for both simple and more complex systems, there is a relationship between changes in the dynamic current vs. grid voltage curve and changes in the thickness t. Suitably, this relationship is established experimentally (e.g., during development of the particular system) and a look up table is created that may, for example, not depend on linearity of the curves to determine the corresponding thickness t or changes therein associated with a particular measured change, e.g., in the shape of the dynamic current vs. grid potential curve.
In connection with the particular exemplary embodiments presented herein, certain structural and/or function features are described as being incorporated in particular embodiments. It is to be appreciated that different aspects of the exemplary embodiments may be selectively employed as appropriate to achieve other alternate embodiments suited for desired applications, the other alternate embodiments thereby realizing the respective advantages of the aspects incorporated therein.
Additionally, it is to be appreciated that certain elements described herein as incorporated together may under suitable circumstances be stand-alone elements or otherwise divided. Similarly, a plurality of particular functions described as being carried out by one particular element may be carried out by a plurality of distinct elements acting independently to carry out individual functions, or certain individual functions may be split-up and carried out by a plurality of distinct elements acting in concert. Alternately, some elements or components otherwise described and/or shown herein as distinct from one another may be physically or functionally combined where appropriate.
In short, the present specification has been set forth with reference to exemplary embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the present specification. It is intended that the inventive subject matter be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
