Generally, the present invention relates to electrophotographic (EP) devices, such as laser printers or copy machines. Particularly, it relates to adjusting print speed of the EP device by scaling imaging data. In one aspect, bitmap resolution is stretched, such as by insertion of lines of bitmap data or by other processing. An EP device incorporating the image scaling has a fixed scan rate and utilizes either bi-directional scanning or traditional unidirectional scanning.
Traditional EP devices have a spinning polygon mirror that directs a laser beam to a photoconductor, such as a drum, to create one or more scan lines of a latent to-be-printed image. Recently, however, it has been suggested that torsion oscillator or resonant galvanometer structures can replace the traditional spinning polygon mirror and create scan lines in both the forward and reverse directions (e.g., bi-directionally), thereby increasing efficiency of the EP device. Because of their MEMS scale size and fabrication techniques, the structures reduce the relative cost of manufacturing. Unfortunately, the structures are tuned to a fixed, resonant frequency of oscillation, unlike their polygon mirror counterparts, which tends to limit printing at media output speeds of full speed or half speed modes, only (e.g., 50 pages per minute (ppm) or 25 ppm). In that robust, modern EP devices require all sorts of media output speeds, especially per different media types, e.g., transparencies, vinyl labels, envelopes, etc., two speeds is quite insufficient.
Accordingly, a need exists in the art to enable a variety of media output speeds, despite fixation of the rate of scanning of latent images brought about by the advent of oscillator or galvanometer type scanning mechanisms. Ultimately, the need extends to any scanning mechanism, regardless of type, having a relatively fixed scan rate. Naturally, any improvements along such lines should further contemplate good engineering practices, such as relative inexpensiveness, stability, low complexity, ease of implementation, etc.
The above-mentioned and other problems become solved by applying the principles and teachings associated with the hereinafter described image scaling for an electrophotographic (EP) device, such as a laser printer or copy machine, to obtain various media output speeds, especially in pages per minute (ppm).
In a basic sense, an EP device with a substantially fixed scan rate scans multiple scan lines on a photoconductor to create a latent image at a first resolution, as is typical. A media is advanced into contact with the latent image at a predetermined process speed to obtain a printed image output of the latent image. Beforehand, however, a controller alters image input data used to create the latent image by changing a bitmap at a second resolution into a bitmap at the first resolution. Certain techniques for altering the resolution include conducting pre- and/or post-processing regarding a raster image processor (RIP). In one embodiment, the resolution dimension of an input bitmap is stretched into a larger resolution dimension, such as that which occurs by stretching a 600×600 resolution into a 600×685 resolution or other. Repeating scan lines and inserting them into the bitmap is one such technique to stretch the bitmap as is visual processing whereby scan lines are created and inserted to make the hard copy image appear correct.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in the description which follows, and in part will become apparent to those of ordinary skill in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.
The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings:
In the following detailed description of the illustrated embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention and like numerals represent like details in the various figures. Also, it is to be understood that other embodiments may be utilized and that process, mechanical, electrical, software, and/or other changes may be made without departing from the scope of the present invention. In accordance with the present invention, image scaling for an electrophotographic (EP) device, such as a laser printer or copy machine, to obtain various media output speeds is hereafter described.
With reference to
With more specificity, the output, video signal 28 energizes a laser 30 to produce a beam 32 directed at a scanning unit 39, such as a torsion oscillator, e.g., resonant galvanometer, or spinning polygon mirror. As the scanning unit moves (indicated by the movement or oscillation wave lines 35) the beam 32 is reflectively cast to create beam lines 34a, 34b on either side of a central position 34. As a result, multiple scan lines in alternate directions (or similar directions for the mirror embodiment) are formed on a photoconductor 36, such as a drum, and together represent a latent image 38 of the image data supplied from the controller.
Optically, certain lenses, mirrors or other structures 40 exist between the photoconductor and the scanning unit and transform the laser beam into a substantially linear scan of a beam at the photoconductor 36, including a substantially uniform linear scan velocity with substantially uniform laser beam spot size along the imaging area of the drum. To provide common reference for the beam lines, various sensors are employed. Preferably, a forward sensor 42a and a reverse sensor 42b, called horizontal synchronization (hsync) sensors, are positioned near opposite ends of the photoconductor to provide a common reference for all forward scanning beam lines and all reverse scanning beam lines, respectively. In addition to, or in lieu of the sensors 42a, 42b, forward and reverse hsync sensors may be positioned at 44a and 44b, upstream of the representative optics 40. Alternatively still, a single hsync sensor might be used with one or more mirrors emplaced variously to act as a second hsync sensor. Regardless, the outputs of these sensors are supplied to the controller 24 for referencing correct locations of the scan line(s) of the latent images.
With reference to
Regardless of type, the printed image in
As before, however, the printed image 29 is not always an accurate representation of the image data input 22 and various operations are employed to tightly calibrate the EP device. In this regard, a variety of sensors for temperature, pressure, etc. are used to learn ambient operating conditions and/or an observation and correction feedback loop 46, of sorts, is employed to fix image nuances. In one instance, this corresponds to an end-user making a visual observation of the printed image and informing the EP device, such as by way of a user interface of an attendant computer (not shown) or an operator panel directly on the EP device, of a preferred correction. In another, a reading of the printed image occurs and an automated selection is made and conveyed to the EP device. Reading, as is well known, can occur by way of optical scanners or other devices. In still another instance, the observation and correction occurs internal to the EP device such as by observing a printed image still in the EP device or by observing the latent image 38 on the photoconductor. Observation and correction can also occur relative to a specially made calibration page that manufacturers, service technicians or end-user operators employ as part of a manufacturing, servicing or end-user act for aligning print. Corrections C then occur by way of the controller 24 and its attendant output signal 28.
In that polygon mirrors are better known in the art as a scanning unit 39, reference to
With reference to
However, by stretching the bitmap of the image input data into a bitmap 410,
As should be appreciated by skilled artisans, this now enables various media output speeds. That is, having a fixed scan rate in a scanning unit, such as by tuning an oscillator or fixing a rotation speed of a polygon mirror, and only slowing down the printing process speed, the effective resolution is increased by a known scalar. If the print job is then processed to account for this scalar, i.e. creating an oversized bitmap vertically, then the resultant printed image output will be properly resized as the controller creates the latent image at the higher resolution. As has been shown in theory, and expected to be released soon in actual products by the assignee of this invention, an otherwise fixed scan rate oscillator in a laser printer operable at 600 or 1200 dpi only (full speed and half speed modes) will now be able to achieve the following operational points of media output speeds: 50 ppm to some maximum rated speed; 45 ppm to support legacy input option trays and output options that cannot go faster than 45 ppm; 40 ppm to support an envelop feeder option that cannot go faster than 40 ppm; and 35 ppm to support vinyl labels that cannot be fed and fused reliably at faster speeds. Also, typical scanning rates of oscillators fixed in EP devices that yield 35 ppm around 600 dpi operate per the following: 35 ppm*(1 l+1.8 in)/page*1 m/60 sec=7.467 in/sec*600 dpi=4,480 scans/sec. Now, such EP devices will yield more media output speeds than just full and half speed modes.
Intuitively, it should also be appreciated that the invention intermediately scales images so that the ultimate printed image output appears in size to the user exactly like the size of image input data. The import of this relates to prior art scaling techniques whereby hard-copy outputs appear different in size (and or shape) than the image input data, such as found with a single input image having two, three, four or more replicas of the single input on a single hard-copy. Also, the prior art has variable rate scanning devices at its disposal to accomplish this, unlike the present invention utilizing essentially fixed rate scanning units 39 (
To actually achieve the foregoing-described altered bitmaps in a controller of an EP device, to obtain the desired various media output speeds, reference is taken to
As an example of both, consider the bitmap 610 in
In
Appreciating distortion or print artifacts may exist in the final printed image output if the original image input data is “overstretched,” it may be desirable to avoid or limit inserting redundant lines to stretch the bitmap resolution. In turn,
Finally, one of ordinary skill in the art will recognize that additional embodiments of the invention are also possible without departing from the teachings herein. This detailed description, and particularly the specific details of the exemplary embodiments, is given primarily for clarity of understanding, and no unnecessary limitations are to be imported, for modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit or scope of the invention. Relatively apparent modifications, of course, include combining the various features of one or more figures with the features of one or more of other figures.