Patent Grant
7877050
This invention relates to an electrophotographic marking system and, more specifically, to the transfer station in such a system.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material is made from toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. Heat is applied to the toner particles to permanently affix the powder image to the copy sheet.
High speed commercial printing machines of the foregoing type handle a wide range of differing weight copy sheets. The beam strength of the copy sheet is a function of the weight of the sheet. Heavier weight copy sheets have greater beam strength than lighter weight copy sheets so additional wear may be put on components in the transfer station. This is called tolerance stack-up. At the transfer station, the copy sheet adheres to the photoconductive member. In the electrostatic transfer of the toner powder image to the copy sheet, it is necessary for the copy sheet to be in uniform, intimate contact with the toner powder image developed on the photoconductive surface. Failure to do so results in variable transfer efficiency and, in the extreme, areas of low or no transfer resulting in image deletions. Clearly, an image deletion is very undesirable in that useful information and indicia are not reproduced on the copy sheet. Various methods have been used to minimize the incidence of image deletions. Hereinbefore, mechanical devices such as rollers have been used to press the copy sheet against the toner powder image on the photoconductive surface.
In another embodiment, a blade is used as a pressing member, adapted to move from a non-operative position spaced from the copy sheet to an operative position contacting the copy sheet and presses the copy sheet into contact with at least the developed image on the photoconductive surface in the transfer station to substantially eliminate any spaces between the copy sheet and the developed image.
The method of transfer includes the steps of establishing, at the transfer station, a transfer field that is effective to attract the developed image from the photoconductive surface to the copy sheet. A blade is moved from a non-operative position, spaced from the copy sheet, to an operative position, contacting the copy sheet, to press the copy sheet into contact with at least the developed image on the photoconductive surface in the transfer station. This substantially eliminates any spaces between the copy sheet and the developed image.
In some prior art systems, the transfer subsystem utilizes a Transfer Assist Blade (TAB) that applies force against the backside of the media that enter the transfer zone. This force is required to hold the paper against the photoreceptor so proper transfer of the image can be achieved to the front side of the media. The TAB has to be able to activate as the media enters the transfer zone and apply force just inside of the lead edge of the media, normally about 3 mm. The TAB will continue to apply force on the media until about 3 mm before reaching the trail edge. The TAB must then deactivate away from the photoreceptor belt in order not to swipe through the toner laden control patches within the interdocument zone. This high-speed activation and deactivation requirement repeats for each subsequent sheet and is timed on the order of milliseconds, otherwise either transfer defects or toner contamination on the backside of the prints result. The drive for this mechanism is generally a stepper motor linked to the TAB assembly. The stepper motor translates between the deactivated position, referred to as the “home” position and the activated position of “home” plus 17 motor steps”. The home position is set in manufacturing by pinning the TAB in its home position which is linked to the stepper motor. The stepper motor has an actuator mounted onto its “D” shaft. To set the home position, an adjustable bracket mounting an optical sensor is positioned such that the actuator that is on the stepper motor just trips the optical sensor. However, because of the large tolerance stack-up due to the multitude of parts affecting the linkage, over time the setting of the sensor to the actuator cannot be achieved. This occurs, even though the optical sensor bracket was designed with the maximum allowable adjustment limited by the space constraint within the transfer deck cavity. The inability to adjust the home position has resulted in problems. First, the manufacturing operator may inadvertently improperly set the optical sensor bracket to its limit. In doing so, often the stepper motor over torques when operating at this stressful home position. When the motor over torques, it will skip steps during subsequent operation causing the TAB assembly extrusion to contact the photoreceptor belt and trip a fault. This scenario costs a great deal of money with high spare rates on the transfer deck. Second, when this problem occurs, a rapid re-centered actuator has to be made (rework tool cost) and part shortage to the line. Re-centering the actuator within the sensor position has been shown to be only a short term fix since this had been done before, only to be done again later when the stack-up condition repeats.
This invention provides a reversible actuator that is physically similar to the existing actuator (and can easily be retrofitted) yet nearly doubles the range of adjustment within the same space constraints by the simple means of reverse mount capability. The actuator is intentionally designed eccentric in terms of the working edges. Depending on the direction of the tolerance stack-up within the system will determine which side of the actuator is used or installed. The use of this reversible eccentric actuator allows for the setting of start actuation for nearly double the tolerance stack-up. By “tolerance stack-up” is meant, wear of the plurality of components in the transfer station caused by extended usage and, or variation in initial manufacture. Once one or more component is worn, the actuator gate must be adjusted to take into consideration this tolerance or wear.
In the prior art, once the home position needed readjustment and could not be adjusted to a useful position, then a complete new transfer station (deck) unit was required. This was very costly and required reinstalling a new unit each time the variation in internal components rendered the sensor bracket inadequate, having gone beyond its useful adjustment limit.
Embodiments of this invention provide an adjustable motor homing system for increased transfer assist blade (TAB) adjustment latitude. The Transfer deck incorporates an adjustable bracket that allows for fine adjustment of the TAB mechanism for optimized transfer. In the prior art, the fine adjustment has limited travel and, due to wear over time, may need to be repeatedly adjusted past its limits for proper operation. The motor drive system that positions the TAB has a homing mechanism incorporating an optical sensor and a flag-actuator. Typically, in the prior art, the flag is symmetrical. This invention provides an asymmetrical flag that can be mounted on the motor shaft with either side of the flag-actuator facing the motor. The combination of the asymmetry and the reversible mounting provides two course adjustment positions for the TAB assembly and can effectively double the adjustment latitude when combined with the fine adjust. The advantages of the present invention are a low cost means of increasing the home position adjustment capability and ease of manufacturing or field repair.
In the present system, it is only required to remove the non-reversible, symmetrical actuator and replace it with a reversible asymmetrical flag-actuator of this invention. The flag-actuator fits over a D-flat on the actuator shaft; in the prior art, the D-flat is perfectly horizontal so that the axis of the flag-actuator is perpendicular to the D-flat. In the present invention, the D-flat is positioned so that the axis of the flag-actuator is not centered or perpendicular to the D-flat but rather is asymmetrical or at an angle not perpendicular to the D-flat. This provides a wider range of adjustment of the flag-actuator and thus therefore the TAB blade. On a top portion of the support for the flag-actuator is an adjustable plate (shown in the drawings as element 5 in
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To summarize, embodiments of the present invention provide a transfer station for an electrophotographic marking system comprising a blade assembly, a motor, a flag-actuator and a sensor. This blade assembly comprises a blade configured to press a copy sheet into contact with a developed image on a photoconductive surface. The blade assembly is adapted to move the blade from an inoperative position where the blade is spaced and out of contact from the copy sheet to an operative position where the blade presses the copy sheet into contact with the toned-developed image on the photoconductive surface. The blade assembly is operatively, movably connected to the flag-actuator and the flag-actuator is configured to be activated by the sensor. The flag-actuator has an asymmetrical and reversible configuration and has a reverse mount capability.
The flag-actuator is reversible and has a side 1 and a side 2, each having a different skewed start position when mounted on a D-flat in the actuator shaft. This reversible, asymmetrical flag-actuator provides a substantially larger range of adjustment within the same space constraints of prior art flag-actuators. The flag-actuator is mounted at an angle on the D-flat other than at a right angle. The side 1 of the reversible flag-actuator is configured to be mounted on the D-flat at a different angle than that on side 2 of the flag-actuator. The flag-actuator of this invention is physically similar to prior art actuators and is adapted to be easily retrofitted into existing transfer stations.
The flag-actuator is in operative electrical contact with the sensor and is configured to be repositioned in contact after prolonged use and is useful for an extended period longer than prior art actuators.
It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4341456 | Iyer et al. | Jul 1982 | A |
| 5923921 | OuYang et al. | Jul 1999 | A |
| 6078777 | Imumi et al. | Jun 2000 | A |
| 6687480 | Obrien et al. | Feb 2004 | B2 |
| 6766138 | Obrien et al. | Jul 2004 | B2 |
| 6845224 | Gross et al. | Jan 2005 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20100046992 A1 | Feb 2010 | US |
