Patent Grant
7298993
Aspects of the disclosure relate to imaging methods, image engines, and photoconductor charging systems.
A multi-step electrophotographic (EP) process is the basis for numerous laser printers, copiers, multiple function devices, and other configurations. In a first step, a photoconductor is electrically charged for the subsequent formation of latent images. The photoconductor may be charged using one or more charge roller, corona or scorotron in some implementations. In but one example, the Indigo 3000 press available from The Hewlett-Packard Company has three sets of double scorotrons for charging the photoconductor.
A charge roller may include a metal shaft with a conductive elastomer surrounding it. The outer portion has been constructed in two ways in some arrangements. A first example includes a single layer with a moderately conductive material, usually an ionic conductive agent, mixed inside. A single-layer charge roller may also have a thin (e.g., thickness of a few microns) insulating layer outwardly of the conductive material or layer.
Another example of a charge roller has plural layers including an insulating outer sleeve of increased thickness (e.g., greater than a few microns) and an inner elastomeric region which may be loaded with a highly conductive network such as carbon. A double-layer charge roller generally charges less uniformly compared with a single layer charge roller due to the difficulty in providing a constant sleeve thickness. Accordingly, a single-layer charge roller system may provide images of increased quality and may be preferred for high-quality color image applications.
A core of a charge roller may be supplied with direct current (DC) electrical energy and possibly an additional alternating current (AC) voltage during use. If DC energy is used alone, the shaft voltage may be roughly 600 V higher than a desired voltage to be provided at a surface of the photoconductor. The extra 600 V is provided to generate ions in the air as dictated by the Paschen curve. With usage of AC energy, the voltage of the DC energy may be close to a desired photoconductor voltage with an AC amplitude of 600 V peak or more. The addition of AC usually creates a more uniform charge layer on the photoconductor adding or subtracting the photoconductor surface charge as needed.
The conduction mechanism of a single-layer charge roller is mobile ion movement in response to an applied electric field. If material (e.g., elastomer) is sandwiched between the two electrodes (e.g., charge roller shaft and photoconductor) and a voltage is applied, a current flows, generally falling with time. This is consistent with ions moving and accumulating at one side and leaving behind a charged layer of the opposite polarity on the other side which decreases the electric field available for moving current within the layer. Some charge injection may also occur at the electrodes which could neutralize some of the ions, thus decreasing the ion concentration over time.
For printers of relatively reduced speed, the charge roller may be engineered to last the life of a replaceable cartridge. For relatively high-speed machines, the charge roller may be expected to have extended use before needing replacement.
Over time, a charge voltage of a photoconductor may fall or drop. For example, referring to
The non-recovery of
The above-described situation may worsen if high-speed printing is implemented in non-stop applications because the charge roller may not be allowed to sufficiently recover. In this case, additional problems may be present. For example, the charge roller may physically degrade due to high ionic concentration at an interface for most desired charge roller formulations. The high concentration may alter a local environment within the charge roller causing polymeric bonds of the charge roller to break. The result is that the elastomeric portions of the charge roller may return to a liquid state in the local region. The environment may be catalytic because the deterioration has been observed to continue long after the voltage is removed and the charge roller may continue to disintegrate. Affected regions of the charge roller may have a surface defect or a sticky surface stain which may negatively impact electrophotographic processes.
Rollers of similar composition used to donate charge or bias a surface may suffer the same drawbacks (e.g., if run at high speed in non-stop applications). An example is a transfer roller used in some electrophotographic applications which helps move toner from the photoconductor to the printing media wherein a voltage is applied between the transfer roller and the photoconductor to attract toner from the imaged photoconductor.
At least some aspects of the disclosure include methods and apparatus for providing improved generation of hard images upon media.
According to some aspects, imaging methods, image engines, and photoconductor charging systems are described.
According to one embodiment, an imaging method comprises providing a charge device configured to provide an electrical charge to a surface of an imaging member which is usable for imaging, moving a surface of the charge device adjacent to the imaging member and a bias member, during the moving, first charging a discharged portion of the surface of the charge device using the bias member providing a charged portion of the surface of the charge device, during the moving, second charging a portion of the surface of the imaging member using the charged portion of the charge device, the second charging providing the discharged portion of the surface of the charge device;, and repeating the first charging and the second charging during the moving.
According to another embodiment, an image engine comprises an imaging member configured to receive an electrical charge during imaging operations of the image engine, a discharge device configured to discharge selected portions of the imaging member to form latent images during the imaging operations of the image engine, a charge device positioned adjacent to the imaging member and having a surface comprising a plurality of portions, a bias member positioned adjacent to the charge device, and wherein individual ones of the surface portions of the charge device are rotated adjacent to the bias member to receive an electrical charge from the bias member and are rotated adjacent to the imaging member to impart the electrical charge to the imaging member during the imaging operations of the image engine.
Referring initially to
The depicted exemplary hard imaging device 10 includes a user/communications interface 12, processing circuitry 14, and an image engine 16. Additional components may be utilized to provide generation of hard images (e.g., media handling equipment, storage circuitry or memory configured to store image data, software, firmware, or other programming, etc.).
User/communications interface 12 is configured to interact with a user and/or implement external communications with respect to device 10. For example, interface 12 may include an input device such as a keyboard as well as a display (e.g., graphical user interface). Interface 12 may include an electrical interface such as a network interface card (NIC) in one embodiment to implement electrical data communications (input and/or output) externally of device 10.
Processing circuitry 14 is configured to process received user input, process image data, implement external communications, monitor imaging operations of device 10 and/or control imaging operations of device 10. Processing circuitry 14 may comprise circuitry configured to implement desired programming provided by appropriate media (e.g., hard disk, memory, etc.) in at least one embodiment. For example, the processing circuitry 14 may be implemented as one or more of a processor and/or other structure configured to execute executable instructions including, for example, software and/or firmware instructions, and/or hardware circuitry. Exemplary embodiments of processing circuitry 14 include hardware logic, PGA, FPGA, ASIC, state machines, and/or other structures alone or in combination with a processor. These examples of processing circuitry 14 are for illustration and other configurations are possible.
Image engine 16 is configured to form hard images upon media. For example, processing circuitry 14 may perform image processing operations upon data (e.g., rasterization) and provide the image data to image engine 16 for hard imaging upon media. An exemplary image engine 16 is configured to generate hard images upon media according to the received image data.
Referring to
In one embodiment, imaging member 20 may comprise a photoconductor implemented as a photoconductor drum 40 (
Charge system 22 includes a charge device 42 which is embodied as a charge roller 49 in the described exemplary embodiment shown in
In the exemplary described embodiment, discharge device 24 is configured to discharge the electrical charge on the imaging member 20 at selected locations corresponding to a desired image to be formed. The discharging of the electrical charge provides a latent image upon the imaging region of the imaging member 20. In one embodiment, discharge device 24 may be implemented as a light source 44 (
Development station 26 is configured to provide a marking agent, such as dry toner in a dry configuration or liquid ink in a liquid configuration. The marking agent may be electrically charged and attracted to the discharged locations of the imaging region of the imaging member 20 corresponding to the latent image to develop the latent image. Development station 26 may include a plurality of development rollers 46 (
The marking agent of the developed image formed upon the imaging region of the imaging member 20 may be transferred to media 30 such as paper 52 using a transfer member 28. In one embodiment, transfer member 28 is configured as a transfer drum 48 (
A cleaning station 54 shown in
At least some aspects of this disclosure are related to increasing the longevity of charge devices 42. Some aspects are discussed with respect to the exemplary embodiments of charge systems 22, 22a, 22b, 22c shown in
Referring to
Bias member 64 may be implemented as a metal roller configured to contact charge device 42 at a nip location 47 in one embodiment. Bias member 64 may rotate with charge device 42 in one exemplary arrangement. Other current-carrying configurations of bias member 64 are possible including metal brushes or blades for example. In addition, bias member 64 may comprise carbon-loaded materials or other conductors other than metallic structures.
Portions of charge device 42 which have supplied charge carriers to charge imaging member 20 become discharged portions of charge device 42 after the charging. The discharged portions of charge device 42 are then rotated to contact bias member 64 whereby they are again charged for subsequent charging of the imaging member 20. At a given moment in time, bias member 64 charges the portion of the outer surface of charge device 42 approximate nip location 47. Accordingly, less than an entirety of an outer surface of charge device 42 is charged by the bias member 64 at a given moment in time. In other embodiments, bias member 64 and charge device 42 may be spaced at nip location 47 wherein charging of charge device 42 occurs.
Charge device 42 includes a core 70 and an outer layer 72 about core 70 in the exemplary illustrated arrangement. In one implementation, core 70 is a metal shaft and outer layer 72 may be embodied as a conductive elastomer layer which may be constructed as described above in possible single layer and double layer embodiments. Outer layer 72 is configured to store charge carriers in one embodiment. For example, the charge carriers may be donated by bias member 64 and passed to imaging member 20.
It is believed that DC current flow within outer layer 72 (e.g., between core 70 and outer layer 72) during imaging operations may lead to degradation of outer layer 72. Some results suggest that the process of disintegration may be initiated after a certain total net DC charge has passed through the material of the outer layer 72. According to one aspect of charge system 22, net DC current flow within layer 72 (e.g., into or out of core 70) is reduced, minimized or eliminated to reduce degradation of charge device 42.
Still referring to
In one embodiment, charge system 22 is arranged to provide a charge of approximately −1000 V upon the outer surface of imaging member 20 rotated adjacent to charge device 42. Second power supply 62 is configured to provide electrical energy having a sufficient voltage magnitude to overcome losses while providing the desired voltage upon the outer surface of imaging member 20. For example, power supply 62 may provide a voltage of approximately −1600 V to core 70 to provide the desired voltage to the outer surface (e.g., −1000 V).
As mentioned above, power supply 60 may charge bias member 64 to a proper voltage to reduce the net DC current or charge flowing in outer layer 72 during charging of imaging member 20. In the above-described example wherein the surface of imaging member 20 is charged to approximately −1000 V, power supply 60 may provide a bias voltage of approximately −1800 V to bias member 64. Accordingly, power supplies 60, 62 provide voltages of the same polarity to charge device 42 and bias member 64 in at least one embodiment.
It is believed that DC current passing through outer layer 72 (either into core 70 or from core 70) may be related to disintegration of charge device 42 and/or voltage drops of charge received by the outer surface of imaging member 20 during charging of imaging member 20. More specifically, the continuous passage of DC current in a single direction (e.g., either radially into or out of core 70) may lead to the negative operational aspects described above. Bias member 64 applies current to charge device 42 to provide current passing in different directions (e.g., different radial directions) through outer layer 72 during imaging operations to reduce DC current flow in a single direction through layer 72 (e.g., into or out of core 70) during imaging.
Consider a surface patch on the outer surface of charge device 42 and a region of outer layer 72 inward of the surface patch. When the patch contacts imaging member 20, charge carriers (e.g., depending upon the biasing polarities involved exemplary charge carriers include electrons, negatively charged ions, positively charged ions, etc.) from the patch and the underlying region are donated or transported in a substantially radial direction of charge device 42 to the discharged surface of imaging member 20 to charge the surface from −50 V to approximately −1000 V. After the charge device 42 rotates 180 degrees in the illustrative example, the patch contacts bias member 64 which donates charge carriers which are transported in a substantially radial direction of charge device 42 to the patch and underlying region for restoration to a rest state. The charging of charge device 42 may be imparted from an area and a direction external of the outer surface of the charge device 42 in at least one embodiment. As shown, different portions of charge device 42 may be simultaneously donating and receiving charge carriers during imaging operations.
Accordingly, in one embodiment, during charging of imaging member 20, charge carriers of one sign flow in one direction with respect to the outer surface of charge device 42 while charge carriers of the same sign flow in an opposite direction with respect to the outer surface of charge device 42 during charging of charge device 42 by bias member 64. It follows that the DC current flow relative to the outer surface of charge device 42 is substantially b-directional or AC in nature and the net DC current flow through material of outer layer 72 is substantially zero in the exemplary embodiments of
According to the described example wherein the imaging member 20 is negatively charged, negative charge carriers flow from the charge device 42 to the imaging member 20 when the imaging member 20 is being charged and negative charge carriers flow from the bias member 64 to the charge device 42 when the charge device 42 is being charged. With respect to the outer surface of charge device 42, the directions of the above-described charge carrier flow are opposite for the charging of the imaging member 20 and the charge device 42.
Referring to the embodiments of
Referring to
In embodiments wherein the imaging member 20 is charged to −1000 V, DC power supply 80 may provide a DC voltage of about −1300 V and AC power supply 82 may provide electrical energy of 1400 V peak-to-peak and having a frequency of 6 kHz in one implementation. Transformer 84 adds the AC voltage to the output of the DC power supply 80 to produce the drive voltage for bias member 64. Coupling capacitor 86 passes the AC voltage to core 70 of charge device 42. Application of the AC voltage to charge device 42 and bias member 64 induces Paschen breakdown in the air gaps adjacent to contact nip 45 of imaging member 20 and charge device 42 providing imaging member 20 with a more uniform voltage compared with the embodiment of
A value of coupling capacitor 86 may be chosen so the AC reactance of the coupling capacitor 86 is relatively small compared to the AC reactance of the charge device 42. In one embodiment, a value of coupling capacitor 86 may be 0.01 uF or larger for an embodiment wherein a capacitance of the core 70 to imaging member 20 is approximately 600 pF.
Referring to
As shown, first and second DC power supplies 90, 92 are coupled with first and second secondary windings of transformer 84a, respectively. First DC power supply 90 may provide a DC voltage of approximately −1200 V and second DC power supply 92 may provide a DC voltage of approximately −1300 V to charge the outer surface of imaging member 20 to −1000 V according to the exemplary disclosed embodiment. AC power supply 94 may provide an AC voltage of 600 V peak-to-peak at a frequency of 6 kHz in one embodiment.
As discussed above with respect to
The embodiments described herein are applicable to Indigo digital presses available from The Hewlett-Packard Company. The voltage values of the above-described embodiments may be tailored for application to other digital press configurations. For example, the described charge systems 22, 22a, 22b may be used to charge a positive-charging imaging member 20 wherein positive charge carriers would be conducted reversing all of the above-described DC voltages (i.e., the charge carriers include electrons or negative ions in the above-described embodiments having a negative-charging imaging member 20). If negative charges are also involved, they move in a direction opposite to that of positive charges. The values of the generated DC voltages may also be adjusted to achieve other desired charged voltages of the imaging member 20. In addition, the frequency of the AC voltage may be tailored to a minimum value to reduce or avoid visible banding plus a small safety margin reducing the current and power provided by the AC supply to a minimum value. In general, lower frequencies may be used for hard imaging devices 10 having slower process speeds. In the above-described embodiments, AC voltage having a frequency of 6 kHz may be used for process speeds of hard imaging devices 10 of 1.2 meters/second.
Referring to
AC voltage was not used during the tests illustrated using the arrangement of
After a semi-continuous run of 200 K impressions (60 K impressions per day) middle section 108 of charge roller 100 started showing surface damage while the outer sections showed no surface damage. Some of the rubber material of the middle section 108 liquefied and portions of the outer layer became detached in these areas. Simple application of finger pressure produced wrinkles on the charge roller surface coating in the middle section 108 and the liquefied charge roller material leaked out through breaks in a coating. The outer sections of charge device 100 showed no visible damage or change compared with the beginning of the experiment.
Referring to
The depicted image engine 16a includes transfer member 28a including a transfer drum 48. Charge system 22c is implemented using transfer drum 48 and bias member 64 in the depicted embodiment. Transfer drum 48 defines a nip 53 with photoconductor drum 40 in the illustrated embodiment. Media 30 is configured to pass through nip 53 to receive developed images from photoconductor drum 40. Transfer drum 48 and bias member 64 of charge system 22c may be coupled with respective power supplies (not shown). For example, transfer drum 48 may be referred to as a charge device 42a electrically biased to assist with the attraction of the developed image from the photoconductor drum 40. More specifically; charge device 42a implemented as transfer drum 48 may charge the imaging member 20a comprising media 30 in the depicted example to assist with the transfer of developed images. Outer surface portions of charge device 42a which charge media 30 may be discharged during imaging. Bias member 64 may rotate with charge device 42a and be used to charge discharged portions of the outer surface of charge device 42a to reduce degradation of charge device 42a as described above. The embodiments herein illustrate exemplary aspects of the disclosure and other configurations of charge systems, charge devices and bias members are possible.
The protection sought is not to be limited to the disclosed embodiments, which are given by way of example only, but instead is to be limited only by the scope of the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5943533 | Ogata et al. | Aug 1999 | A |
| 6721523 | Sugiura et al. | Apr 2004 | B2 |
| 6751427 | Sugiara | Jun 2004 | B2 |
| 20030228172 | Nakamura et al. | Dec 2003 | A1 |
| 20050008396 | Nakamura et al. | Jan 2005 | A1 |
| 20050135839 | Inoue | Jun 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 06222649 | Aug 1994 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20060147227 A1 | Jul 2006 | US |
