The present exemplary embodiment relates to multiple beam raster output scanning devices (ROSs) and printers, copiers, and other document processing systems using one or more ROSs providing multiple scanned beam lines. Xerographic printing systems use one or more ROSs to project the laser scan line onto a photoreceptor such as a photosensitive plate, belt, or drum, for xerographic printing. The ROS provides a laser beam which switches on and off as it moves or scans across the photoreceptor to form a desired image thereon. The beam is selectively interrupted according to image data in order to create a latent image on the precharged photoreceptor surface, and a developer deposits toner onto the latent image to create a toner image that is thereafter transferred and fused to a final print medium, such as a printed sheet. Multiple beam ROSs concurrently scan multiple light beams onto the photoreceptor, using an array of lasers or other light sources to provide multiple beam lines to a rotating polygon having mirrored facets that create a set of parallel scan lines, sometimes referred to as a swath. Advanced printing systems have been proposed in which 32 individual scan lines are formed in each swath scanned across a photoreceptor belt in a fast scan direction as the photoreceptor moves in a perpendicular process direction. This wide swath of scan lines leads to various difficulties in controlling image quality, due to required synchronization and coordination between the process direction speed of the photoreceptor (e.g., belt or drum speed), the rotational velocity of the polygon, and the spacing between individual scan lines provided by the ROS.
In order to mitigate visually perceptible errors, it is desirable to control the scan line well as swath-to-swath spacing in the process direction at the photoreceptor, which are a function of the photoreceptor and polygon speeds. In certain ROS systems, moreover, scan line overwriting is used, in which consecutive swaths of scan lines are partially overwritten, for example, where line one of scan N+1 overlaps line 17 of scan n. Such overwriting may advantageously allow balancing of laser power and overall smoothing of a scanned image. However, interactions between scan line spacing and swath-to-swath spacing may lead to stitch error, causing undesirable image artifacts. In particular, both scan line spacing (as a function of swath width) and swath-to-swath spacing (as a function of photoreceptor velocity and polygon speed) contribute to stitch error. Too little spacing between swaths will cause bunching, while too much spacing will result in excess non-imaged area between the swaths. Either of these conditions can lead to image artifacts such as banding and beating.
Conventionally, the spacing issues could be addressed in the initial manufacturing setup steps, as well as in field calibration at runtime, by adjustment of photoreceptor process direction speed and/or with adjustments to the speed of the rotating polygon. However, many systems do not provide for adjustability in photoreceptor speed, particularly after a printer has been commissioned in the field (no runtime adjustment). Thus, a need remains for improved ROS systems and printers by which runtime compensation for swath to swath and scan line spacing can be achieved.
Stowe U.S. Pat. No. 7,542,200, issued Jun. 2, 2009 describes an agile beam steering mirror for active raster scan error correction, in which bow affects are corrected by periodic rotation of a beam steering mirror assembly in synchronization with the motion of a polygon mirror scanner, the entirety of which is hereby incorporated by reference. Appel U.S. Pat. No. 6,232,991, issued May 15, 2001 and assigned to the Assignee of the present application, describes a ROS adjustment technique using a tiltable scan lens for correcting bow errors by tilting a second scan lens along a fast scan axis using a threaded adjustment screw, the entirety of which is hereby incorporated by reference. Genovese U.S. Pat. No. 5,153,608, issued Oct. 6, 1992 and assigned to the Assignee of the present application, discloses an electrophotographic printer or image scanner in which a translucent Lucite or Plexiglas optical element is positioned along a line of beam scanning and is twisted for skew and bow correction, the entirety of which is hereby incorporated by reference.
The disclosure provides improved printing systems and multiple beam raster output scanners (ROSs) therefor, in which one or more beam path optical elements such as mirrors or lenses are adjustable at runtime to set the spacing between adjacent scan lines. This allows runtime variation in the scan swath width and line spacing by which stitching error and other problems can be mitigated or eliminated without requiring adjustment of the photoreceptor velocity.
One or more aspects of the disclosure relate to a ROS having a multibeam light source which concurrently provides a plurality of light beams to a first optical system that collimates the light beams. The ROS further includes a rotating polygon with mirrored facets that concurrently deflect the collimated light beams received from the first optical system. A second optical system then focuses the deflected light beams from the polygon into a plurality of moving spots and directs the spots towards a photoreceptor traveling in a process direction. An adjustable mirror is provided, having a reflective surface that is positioned in the optical system to deflect the light beams, along with an electronic adjustment input to change the position and/or shape of the reflective surface so as to increase or decrease the spacing between adjacent light beams in the process direction at the photoreceptor. The ROS or the system generally includes a controller to provide an electronic signal or value to the electronic adjustment input at runtime, and the controller holds the signal or value constant while the polygon rotates in order to set the beam spacing.
In certain embodiments, the adjustable mirror is situated in the first optical system along the beam path between the light source and the polygon. The reflective surface in certain embodiments is bowed, such as a convex reflective surface in some implementations, and the electronic adjustment input modifies the bowed shape or position in order to change the beam spacing, thereby allowing adjustment of line-to-line, and swath-to-swath spacing.
In accordance with further aspects of the disclosure, a multiple beam ROS is provided in which the first optical system between the light source and the polygon includes an adjustable lens with an electronic adjustment input to change the position of the lens in order to increase or decrease the spacing between adjacent light beams in the process direction at the photoreceptor. In some embodiments, the adjustable lens includes a motor operatively coupled with the lens to change an incident angle at which the light beams arrive at the lens from the light source. In other embodiments, the adjustable lens includes a linear actuator to change the distance between the lens and the light source along the path of the light beams in order to change the spacing between adjacent beams in the process direction at the photoreceptor.
Further aspects of the disclosure are directed to a printing system, which includes a photoreceptor moving in a process direction at a fixed speed, as well as a charging station which charges an exterior surface of an image area of the photoreceptor. The system also includes one or more raster output scanners to produce scan lines in a fast scan direction that is substantially perpendicular to the process direction. The raster output scanner includes a light source that concurrently emits a plurality of light beams, along with an optical system and a controller. The optics includes a first optical system to collimate the light beams received from the light source. The first optical system includes an adjustable optical element operative to increase or decrease the spacing between adjacent light beams in the process direction at the photoreceptor. In some embodiments, the adjustable optical element is a mirror with a reflective surface positioned in the first optical system to deflect the light beams, and an electronic adjustment input to change the position and/or shape of the reflective surface to increase or decrease the light beam spacing. In other embodiments, the adjustable optical element is an adjustable lens with an input to change the position of the lens to modify the deflected light beam spacing in the process direction at the photoreceptor.
The present subject matter may take form in various components and arrangements of components, as well as 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 the subject matter.
Referring now to the drawing figures, several embodiments or implementations of the present disclosure are hereinafter described in conjunction with the drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the various features, structures, and graphical renderings are not necessarily drawn to scale. The disclosure relates to provision of adjustable optical elements in a multibeam ROS allowing run-time adjustment of beam line to beam line spacing to avoid or mitigate stitching and related problems, where the disclosed systems and techniques are particularly advantageous in systems in which a process direction photoreceptor translation speed is fixed. The adjustment mechanisms disclosed herein can be used to reduce such errors in both manufacturing situations, as well as those calibration or configuration steps undertaken in the field. Moreover, the adjustment apparatus is electronically set, whereby such adjustment may be undertaken automatically under direction of a machine controller.
A transfer station 50 is located along the path 4p downstream of the ROSs 22, 28, 34, 40, 46 (at the bottom in
The system 2 also includes a ROS master clock 101 providing a clock output signal 101a to the ROSs 22, 28, 34, 40 and 46, where the clock output signal 101a can be an analog value or a digital value indicating a frequency or clock speed or other signals or values by which the ROS motor polygon assembly (MPA) operational speed can be set or adjusted, either dynamically using a controller 100 during operation, or which can be preset, for example, during system calibration or initial manufacturing. The controller 100 may be any suitable form of hardware, processor-executed software, firmware, programmable logic, or combinations thereof, whether unitary or implemented in distributed fashion in a plurality of components, wherein all such implementations are contemplated as falling within the scope of the present disclosure and the appended claims. The controller 100 provides data and one or more control signal(s) or command(s) to the individual ROSs 22, 28, 34, 40 and 46 based on image data to be provided thereto. In particular, the controller 100 provides at least one electronic signal or value 104 to each ROS to set the line-to-line spacing in the process direction 4p as detailed further below.
The photoreceptor 4 passes through a first charging station 10 that includes a charging device such as a corona generator 20 that charges the exterior surface of the belt 4 to a relatively high, and substantially uniform potential. The charged portion of the belt 4 advances to a first ROS 22 which image-wise illuminates the charged belt surface to generate a first electrostatic latent image thereon, where
The photoreceptor 4 then continues along the path 4p to a third image generating station 14 that includes a charging device 32 to recharge the photoreceptor 4 and a ROS exposure device 34 which illuminates the charged portion to generate a third latent image. The photoreceptor 4 proceeds to the corresponding third developer unit 36 which deposits toner particles of a corresponding third color on the photoreceptor 4 to develop a toner powder image, after which the photoreceptor 4 continues on to a fourth image station 16. The fourth station 16 includes a charging device 38 and a ROS exposure device 40 at which the photoreceptor 4 is again recharged and a fourth latent image is generated, respectively, and the photoreceptor 4 advances to the corresponding fourth developer unit 42 which deposits toner of a fourth color on the fourth latent image. The photoreceptor 4 then proceeds to a fifth station 18 that includes a charging device 44 and a ROS 46, followed by a fifth developer 48 for recharging, generation of a fifth latent image, and development thereof with toner of a fifth color.
Thereafter, the photoconductive belt 4 advances the multi-color toner powder image to the transfer station 50 at which a printable medium or substrate, such as paper sheet 52 in one example is advanced from a stack or other supply via suitable sheet feeders (not shown) and is guided along a first substrate media path P1. A corona device 54 sprays ions onto the back side of the substrate 52 that attracts the developed multi-color toner image away from the belt 4 and toward the top side of the substrate 52, with a stripping axis roller 60 contacting the interior belt surface and providing a sharp bend such that the beam strength of the advancing substrate 52 strips from the belt 4. A vacuum transport or other suitable transport mechanism (not shown) then moves the substrate 52 along the first media path P1 toward the fusing station (fuser) 58. The fusing station 58 includes a heated fuser roller 64 and a back-up roller 62 that is resiliently urged into engagement with the fuser roller 64 to form a nip through which the substrate 52 passes. In the fusing operation at the station 58, the toner particles coalesce with one another and bond to the substrate to affix a multi-color image onto the upper (first) side thereof.
While the multi-color developed image has been disclosed as being transferred from the photoreceptor belt 4 to the substrate 52, in other possible embodiments, the toner may be transferred to an intermediate member, such as another belt or a drum, and then subsequently transferred and fused to the substrate 52. Moreover, while toner powder images and toner particles have been disclosed herein, one skilled in the art will appreciate that a liquid developer material employing toner particles in a liquid carrier may also be used, and that other forms of marking materials may be employed, wherein all such alternate embodiments are contemplated as falling within the scope of the present disclosure.
For single-side printing, the fused substrate 52 continues on the first path P1 to be discharged to a finishing station (not shown) where the sheets are compiled and formed into sets which may be bound to one another and can then be advanced to a catch tray for subsequent removal therefrom by an operator or user. For two-sided printing, the system 2 includes a duplex router 82 that selectively diverts the printed substrate medium 52 along a second (e.g., duplex bypass) path P2 to a media inverter 84 in which the substrate 52 is physically inverted such that a second side of the substrate 52 is presented for transfer of marking material in the transfer station 50.
Referring also to
Referring also to
The light beams 122 are reflected from the facet 126 through a second optical system 130 to form a swath of scanned spots on the photosensitive image plane of the passing photoreceptor 4. The rotation of the facet 126 causes the spots to sweep across the image plane forming a succession of scan lines 400 oriented in a “fast scan” direction (e.g., generally perpendicular to a “slow scan” or process direction 4p along which the belt 4 travels). Movement of the belt 4 in the slow scan direction 4p is such that successive rotating facets 126 of the polygon 128 form successive scan lines 400 (or groups thereof) that are offset from each other (and from preceding and succeeding groups) in the slow scan (process) direction. Each such scan line 400 in this example consists of a row of pixels produced by the modulation of the corresponding laser beam 122 as the laser spot scans across the image plane, where the spot is either illuminated or not at various points as the beam scans across the scan line 400 so as to selectively illuminate or refrain from illuminating individual locations on the belt 4 in accordance with the input image.
Referring to
The first and second optical systems 124 and 130, respectively, may each include one or more optical elements for modifying paths of the beams 122 and the relative spacing thereof, including without limitation mirrors and/or lenses. In the illustrated embodiment, the first optical system 124 (the pre-polygon system) includes a collimator lens L0 followed by an aperture and another lens L1, after which the beams are deflected by a first mirror M1 through a lens L2 to a second mirror M2. In this implementation, the second mirror M2 is adjustable, although other embodiments are possible in which the first mirror M1 is adjustable. The system 124 also includes three more focusing mirrors L3-L5 disposed between the second mirror M2 and the rotating polygon 128. After the light beams 122 are deflected by the polygon facets 126, they pass through a second optical system 130 including lens L6, lens L7, and mirrors M3-M6 as shown in the
Referring also to
In one embodiment, the controller 100 provides a single voltage signal 104a to the adjustable mirror M2 to set the line-to-line spacing 404, and holds this electrical signal 104a constant while the polygon 128 is rotated in operation. In an alternative implementation, the adjustable mirror M2 is provided with a digital value or command from the controller 100, by which the position and/or location of the mirrored surface 530 is set, and is maintained at this value while the polygon 128 rotates. The controller 100, in this regard, can programmatically adjust the spacing 402, 404, W, etc. based on measured characteristics of the printing operation of the system 2, and/or the controller 100 may be instructed to provide the adjustment control 104a by a user.
Referring also to
In operation, the first drive electrode 538 is electrically connected to the upper layer 550 of the bending actuator 532 by an electrical lead 552, and the bending actuator 532 can be used by provision of a suitable electronic signal (e.g., voltage) to change the bow angle of the mirror 530 and/or its position relative to the beams 122. In particular, a voltage is applied by the controller 100 to the upper layer 550 via the second drive electrode 538 and the electrical lead 552, which causes a differential strain between the layers of the bending actuator 532. This strain causes the bending actuator 532 to deflect or rotate around its proximal end which is attached to the substrate 534 by the solder pad 544. This causes a change in the distance between the lower layer 548 of the bending actuator 532 and the capacitive sensing electrode 540. Thus, as further shown in
The above examples are merely illustrative of several possible embodiments of the present disclosure, wherein equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, systems, circuits, and the like), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component, such as hardware, processor-executed software, or combinations thereof, which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the illustrated implementations of the disclosure. In addition, although a particular feature of the disclosure may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Also, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications, and further that 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.