Patent Grant
8488986
This invention relates to an electrophotographic print engine. In particular, this invention relates to reducing artifacts when fusing a receiver bearing a dry toner image.
In a dry electrophotographic print engine, a photoreceptive element is initially charged uniformly using known methods such as employing a grid controlled corona charger, or a roller charger. An electrostatic latent image is then formed on the photoreceptive element by image-wise exposing the photoreceptive element using known methods such as a light emitting diode (LED) array, a laser scanner, or an optical exposure system. The electrostatic latent image is then converted into a visible image by bringing the photoreceptive element into close proximity to marking or toner particles contained in a development station and biasing the development station so that the marking particles would be preferentially attracted to the latent-image bearing portions of the photoreceptive element and repelled by the portions of the photoreceptive element that do not bear latent image information. The toner is then transferred to a receiver such as paper, generally by pressing the paper into contact with the toned photoreceptive element while exerting an electrostatic field to urge the toner to the receiver. Alternatively, the toner can first be transferred to a transfer intermediate member and then from the intermediate member to the receiver.
Color images are made by making electrostatic latent images corresponding to the subtractive primary colors, cyan, magenta, yellow, and black, converting the electrostatic latent images into color images corresponding to those subtractive colors, and transferring the images, in register, either directly to a receiver or to an intermediate transfer member and then onto a receiver.
The toner or marking particles typically consist of dry particles comprising a polymer binder such as polyester or polystyrene, pigment or other colorant, surface treatment addenda such as nanometer-size clusters of silica, titania, or charge agents. Toner particles typically are between 4 μm and 8 μm in diameter, but may be larger (up to approximately 30 μm in diameter) or between approximately 1 μm and 4 μm. For the purpose of this invention, toner diameter refers to the volume weighted median diameter, as measured with a commercially available device such as a Coulter Multisizer or equivalent. The toner particles typically have a glass transition temperature Tg between approximately 45° C. and 65° C., more typically between 50° C. and 60° C. For the purpose of this invention, toner or marking particles refer to the particles used to transform the electrostatic latent image into a toner image, often referred to as a visible image. The toner particles may contain a colorant such as a pigment or dye. Alternatively, the toner particles can be clear or absent any added colorant.
While monocomponent developers that do not comprise so-called carrier particles are used in dry electrophotographic print engines, it is more common to employ so called two-component developers. In this instance, the toner particles are mixed with magnetic particles, often referred to as carrier particles. The carrier particles are generally larger than the toner particles and are triboelectrically dissimilar to the toner particles so that the toner particles become electrically charged when contacting the carrier particles. The mixture of toner and carrier particles is often referred to as a two-component developer.
Two-component developers are used to transform the electrostatic latent image into a visible image by bringing the charged toner particles into close proximity to the electrostatic latent image bearing photoreceptive element, where the charged toner particles are attracted to the charge pattern making up the electrostatic latent image. The carrier particles are contained and transported by a development station comprising a so-called magnetic brush, as is known in the literature.
After transfer to the receiver, the toner image is fixed to the receiver by fusing. This is generally accomplished by subjecting the toner image bearing receiver to heat and pressure so that the toner is heated to a temperature above its Tg while subjecting the toner image to pressure. This allows the toner to flow and to become permanently fixed to the receiver. In addition, if a color image has been printed, the subtractive primary colored toners flow together to create the full-color print. Application of heat and pressure to the toner image bearing receiver is generally accomplished by passing the receiver between two heated compliant rollers. The durameters of the rollers can vary significantly or be near equal to one another. Load applied between these two compliant rollers results in a fusing nip width that provides the dwell time for melting the toner. As the receiver enters the fusing nip, an increased load to the fuser drive system is created. This can cause the fuser rollers to slow down, thereby slowing the speed of the receiver. This causes the lead edge of the receiver to travel more slowly. If the trail edge of the receiver is driven at a higher speed with a force greater than the beam strength of the receiver, the receiver will buckle. This can cause physical print artifacts or degrade image quality. Moreover, the print engine speed may be altered by the mismatched fuser speed through the receiver coupling between them. These variations can result in nonuniform image gloss, streaks, incomplete fusing, hot or cold offset whereby toner that is either heated too much or too little transfers from the receiver to the fuser roller or color-to color misregistration. These effects can cause print artifacts and can result in damage or increased maintenance to the print engine.
In accordance with the present invention there is provided a method for reducing artifacts on a toned sheet caused by buckling during fusing, comprising:
An advantage of the present invention is the reduction of sheet buckling by controlling the roller speed. This will reduce artifacts. A feature of the invention is that it can be achieved by simple use of roller speed control without involving the complexity of additional structure. This invention can be practiced without increasing the size of the electrophotographic print engine in order to accommodate different length receivers.
Color images are made by making electrostatic latent images corresponding to the subtractive primary colors, cyan, magenta, yellow, and black, converting the electrostatic latent images into color images corresponding to those subtractive colors, and transferring the images, in register, either directly to a receiver or to an intermediate transfer member and then onto a receiver. In a preferred embodiment, the receiver is transported between the imaging units on an electrostatic transport web 50 and delivered to the fusing subsystem, although other transport arrangements such as drums, vacuum, or grippers, may be employed. Alternatively, the receiver may be transported directly into the fuser by a transfer nip.
The toner or marking particles typically consist of dry particles comprising a polymer binder such as polyester or polystyrene, pigment or other colorant, surface treatment addenda such as nanometer-size clusters of silica, titania, or charge agents. Toner particles typically are between 4 μm and 8 μm in diameter, but may be larger (up to approximately 30 μm in diameter) or between approximately 1 μm and 4 μm. For the purpose of this invention, toner diameter refers to the volume weighted median diameter, as measured with a commercially available device such as a Coulter Multisizer or equivalent. The toner particles typically have a glass transition temperature Tg between approximately 45° C. and 65° C., more typically between 50° C. and 60° C. For the purpose of this invention, toner or marking particles refer to the particles used to transform the electrostatic latent image into a toner image, often referred to as a visible image. The toner particles may contain a colorant such as a pigment or dye. Alternatively, the toner particles can be clear or absent any added colorant.
While monocomponent developers that do not comprise so-called carrier particles are used in dry electrophotographic print engines, it is more common to employ so called two-component developers. In this instance, the toner particles are mixed with magnetic particles, often referred to as carrier particles. The carrier particles are generally larger than the toner particles and are triboelectrically dissimilar to the toner particles so that the toner particles become electrically charged when contacting the carrier particles. The mixture of toner and carrier particles is often referred to as a two-component developer.
Two-component developers are used to transform the electrostatic latent image into a visible image by bringing the charged toner particles into close proximity to the electrostatic latent image bearing photoreceptive element, where the charged toner particles are attracted to the charge pattern making up the electrostatic latent image. The carrier particles are contained and transported by a development station comprising a so-called magnetic brush, as is known in the literature.
After transfer to the receiver, the toner image is fixed to the receiver by fusing. This is generally accomplished by subjecting the toner image bearing receiver to heat and pressure so that the toner is heated to a temperature above its Tg while subjecting the toner image to pressure. This allows the toner to flow and to become permanently fixed to the receiver. In addition, if a color image has been printed, the subtractive primary colored toners flow together to create the full-color print. This is generally accomplished by sandwiching the toner image bearing receiver between a pair of rollers that are pressed together, know as a fusing nip. A typical fuser system 42 is depicted in
Generally, there is limited control transport 102 such as a low pressure vacuum transport between the electrostatic transport web 50 and the fuser 42. If this transport is longer than the maximum receiver length, the fuser 42 is decoupled from the electrostatic transport web 50. This configuration greatly decreases the necessity to match speeds of the subsystems, but increases the overall size of the print engine. If the receiver is long enough such that it is still in control of the electrostatic transport web 50 when it enters the fuser 42 and the speed of the receiver in the fuser 42 is not exactly the same as the imaging unit transport speed at all times, the lead edge and trail edge of the receiver will be driven at different speeds. If the speed of the receiver in the fuser 42 is slower than the portion on the electrostatic transport web 50 the receiver will buckle between the fuser 42 and the electrostatic transport web 50, if both are able to supply a drive force sufficient to buckle the receiver. If the speed of the receiver in the fuser 42 is greater than that on the electrostatic transport web 50, the lead edge will be driven faster than the trail edge. If this differential drive is larger than the slack or buckle in the receiver, the receiver will be in tension and there will be a force transmitted by the fuser 42 on electrostatic transport web 50. Either speed variation can result in variations of image gloss, streaks, incomplete fusing, hot or cold offset whereby toner that is either heated too much or too little transfers from the receiver to the fuser roller 100, or cause color-to color misregistration. These effects can cause print artifacts and can result in damage to the print engine.
Increasing the inertia of the fuser system 42, drive motor torque, or drive system stiffness may decrease the swallowing loss 203. These modifications generally increase cost or power consumption. Another countermeasure is depicted in
Since the fuser motor and controller 104 is unable to fully attain the high commanded speed 207, the motor controller calculates a large position error, resulting a larger overshoot 204 and position compensation portion 205. If this occurs while the receiver is still adhered to the electrostatic transport web 50, the fuser 42 will pull the imaging unit transport after the remaining buckle in the receiver is consumed. A countermeasure for this is depicted in
The torque and responsiveness of the drive system limit the amount the swallowing loss 203 can be reduced without increasing the overshoot 204 excessively. For this reason, it is important to balance the improvement in swallowing loss 203 with the increase in overshoot 204. Since the swallowing loss 203 is a function of the paper parameters and fuser configuration, it is desirable to modify the compensation based on these parameters.
In a preferred embodiment, the amplitude or duration of the high fuser speed command 207, will be increased for receivers having greater thickness, or caliper. For instance, no high speed command may be necessary for receivers with a caliper less than a certain caliper in the range of 150 to 300 microns. The actual caliper threshold will be dependent on the fuser system configuration and setpoints. The adjustments may be made based on receiver weight rather than caliper if the relationship is known. Similarly, the magnitude of the swallowing loss 203 is proportional to the width of the receiver, so the magnitude of the high speed command may be increased for wider receivers. The swallowing loss 203 is also affected by the timing of the sheet arrival relative to the release of the previous sheet. This timing is a function of the fuser speed, fuser nip width, and interframe spacing between the sheets, which is affected by the sheet length (parallel to feed direction). For this reason, the high speed command 207 may be modified depending on these parameters. The first sheet in the set is a special case in which the interframe is essentially infinite and may be treated differently from the other sheets in the run.
The swallowing loss 203 is a function of the force in the fusing nip. The higher the force for a given configuration, the greater the swallowing loss will be. To compensate for this in variable force systems, the control unit 120 may modify the fuser motor speed adjustments 310 based on the fuser nip force, with greater compensation preferred for higher fuser nip forces. Similarly, the compensation may be adjusted for different fuser roller 100 and pressure roller 103 designs, as well as different drive systems.
Since the magnitude of the overshoot 204 increases as the swallowing loss 203 increases, the low fuser speed command 208 may be adjusted when the high speed command 207 is modified. This may or may not be done proportionally, depending on the configuration.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention
| Number | Name | Date | Kind |
|---|---|---|---|
| 6381422 | Tanaka | Apr 2002 | B1 |
| 6892047 | Giannetti et al. | May 2005 | B1 |
| 20050220473 | Bott et al. | Oct 2005 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20120107001 A1 | May 2012 | US |
