The present exemplary embodiments relate to printing systems and to techniques and apparatus for increasing depth of focus of an LED printhead. LED arrays and other light sources are commonly used for selective exposure of a photoreceptor belt or drum in xerographic printing systems. Raster Output Scanning (ROS) exposure systems involve rotating polygon mirror assemblies to scan the light output in a cross-process or fast scan direction through an optical system onto the photoreceptor moving along a process direction. ROS systems advantageously use a small number of light sources to scan across the cross-process direction of the photoreceptor, thereby creating images with potentially high dots per inch count, but occupy a large amount of physical space including a fairly large amount of process-direction area proximate the photoreceptor, sometimes referred to as waterfront. Many printing systems employ more than one xerographic imaging station, with a photoreceptor traveling along a path past the imaging stations for sequential transfer of different toner colors, such as cyan (c), magenta (m), yellow (y) and black (k) to build a color image on the photoreceptor prior to image transfer to a printed medium, such as a sheet of paper, after which the transferred image is thermally fused in a fusing station. In certain applications, moreover, it is desirable to provide a further imaging station along the path of the photoreceptor, for example, to add a further color for gamut extension and/or for providing a specific customer-requested Pantone color or for other special-purpose printing capabilities. However, many printing system designs do not accommodate the addition of a fifth ROS type imaging station, largely due to the total space and waterfront considerations. LED printheads may be used in such situations, as they occupy less physical space than ROS type systems. LED printhead assemblies for printbars typically include an LED array with a large number of LEDs corresponding to or exceeding the desired pixel resolution across the cross-process direction, along with a focusing lens. The use of such a print bar to provide a fifth imaging station in a conventional CMYK printing system, however, requires careful tailoring of the focal distance or depth of focus of the focusing lens of the print bar. Accordingly, improved LED printhead apparatus and printing systems are desirable to provide a tailored depth of focus while reducing waterfront and tolerance issues near the photoreceptor.
The present disclosure relates to LED printhead apparatus and printing systems including an LED array and two lens arrays, such as self-focusing lens arrays to provide a compact, low waterfront imaging apparatus which can be tailored to a variety of different applications by changing the angle or depth of focus of the second lens array. A first high angle lens array can be provided in an LED printbar assembly with the LED array, and a second low angle lens array is provided between the first lens array and a photoreceptor, such as a belt or drum, to relay the output of the first lens array to the photoreceptor, thereby providing a larger depth of focus and reducing waterfront and mitigating tolerance issues near the photoreceptor.
Printing systems and printhead apparatus therefor are disclosed, which include an LED array with a plurality of LEDs, and a first self-focusing lens array with multiple lens elements. A second self-focusing lens array is provided, and is disposed between the first lens array and a photoreceptor in use in a given application. In certain embodiments, the first and second lens arrays are spaced from one another by a distance approximately equal to the sum of the image conjugate distance of the first lens array and the object conjugate distance of the second lens array along a first direction between the LED array and the photoreceptor location. In certain embodiments, moreover, the depth of focus of the second lens array is greater than that of the first lens array, and the second lens array is spaced along the first direction from the photoreceptor by a distance approximately equal to the image conjugate distance of the second lens array. In certain implementations, moreover, the LED array and the first lens array are housed in an LED printbar assembly, and the width of the second lens array in a direction parallel to the photoreceptor path direction is less than the corresponding width of the LED printbar assembly, thereby reducing the overall waterfront area occupied by the printhead apparatus near the photoreceptor. One or both of the lens arrays may include gradient index lens elements in certain embodiments. Furthermore, the first lens array in certain embodiments has a first angle and the second lens array has a lower angle, thereby providing a larger depth of focus and corresponding larger spacing distance between the second lens array and the photoreceptor. The various concepts of the present disclosure thus advantageously facilitate use of the second lens array as a relay lens without modification of the depth of focus of the first lens array, and different relay lenses can be employed in different printing systems to accommodate any desired depth of focus and lens/photoreceptor spacing.
The present subject matter may take form in various components and arrangements of components, and 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.
Several embodiments or implementations of the different aspects 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 apparatus and techniques for enhancing the depth of focus of an LED printbar assembly using a relay lens array, and will be described in the context of a multi-color printing system having multiple ROS-based primary imaging stations or print engines, although the printhead apparatus of the present disclosure finds utility in other printing and imaging applications.
In addition, as described further below, an additional marking station 102 is provided having an LED printhead apparatus 200 upstream of the remaining marking devices 102 along the path of the ITB photoreceptor 104 using an LED array and two or more lens arrays without a ROS (e.g., non-scanning). In other possible implementations, the additional marking station 102 may be provided downstream of the other marking devices 102 along the photoreceptor path. A transfer station 106 is situated downstream of the marking devices 200, 102 along a lower portion of the ITB path to transfer marking material from the ITB 104 to an upper side of a final print medium 108 traveling along a path P1 from a media supply. After transfer of toner to the print medium 108 at the transfer station 106, the final print medium 108 is provided to a fuser type affixing apparatus 110 along the path P1 where the transferred marking material is thermally fused to the print medium 108.
As further shown in
In the multi-color example of
Referring also to
As further seen in
The first lens array 214 is a “high angle” array, for example, having an associated half-angle of 17° in one embodiment, or 20° in another non-limiting embodiment. The half-angle of the second lens array 220, in contrast, is lower, such as about 9° in one non-limiting example. In the illustrated embodiments, the angle of the first lens array 214 is greater than about 1.8 times the lower angle of the second lens array 220, although other angle ratios may be used. The angle of the second lens array 220, moreover, is preferably significantly lower than that of the first lens array 214 such that the subsequent spacing 206 between the lower end 220-2 of the second lens array 220 and the photoreceptor 104 is approximately equal to the image conjugate distance (OCD2) of the second lens array 220. Since this lens arrays 214 and 220 provide one to one imaging, and since the image and object conjugate distances of the second lens array 220 are significantly larger than the corresponding image and object conjugate distances of the first lens array 214, use of the second lens array 220 as an optical relay to transfer light output by the first lens array 214 to the photoreceptor 104 advantageously allows a higher gap distance 206 relative to the intermediate transfer belt 104 than if the first lens array 214 were used alone. In addition, the depth of focus of the first lens array 214 is less than the depth of focus of the second lens array 220, and use of the second lens array 220 with a corresponding larger depth of focus at the output of the printhead apparatus 220 advantageously facilitates manufacturing and adjustment of the spacing distance 206 to facilitate improved focusing for imaging onto the photoreceptor 104, whereas the smaller depth of focus of the first lens array 214 would require tighter tolerances during manufacturing in positioning the apparatus 200 with respect to the photoreceptor 104.
Referring also to
The lens elements 230, moreover, are enclosed in an enclosure 222, such as plastic in one example, having open first and second ends to allow ingress and egress of light rays via the lens elements 230. In practice, the lens arrays 214 and 220 will generally have more lens elements 230 than depicted in
In operation, the gradient index elements 230 preferably employ a radial index gradient where the index of refraction is highest in the center of the generally cylindrical lens element 230 and decreases with radial distance from the center axis, wherein certain implementations provide a quadratic reduction in the index of refraction as a function of radial distance. In operation, rays entering the first end 214-1, 220-1 follow sinusoidal paths within the lens elements 230 until reaching the second ends 214-2, 220-2, and the provision of multiple lens elements 230 in the respective arrays 214, 220 effectively provides one-to-one erect imaging from input to output, where the number of lens elements 230 need not be the same as the number of LED elements in the LED array 212, and the number and arrangement of lens elements 230 in the first and second lens arrays 214 and 220 may, but need not be the same in all embodiments.
Also, the second side 220-2 of the second lens array 220 is spaced along the −Z direction from the photoreceptor 104 by a second distance 206 approximately equal to the second image conjugate distance ICD2. Furthermore, the first lens array 214 has a first depth of focus and the second lens array 220 has a second depth of focus DOF2, and wherein the first depth of focus DOF1 is less than the second depth of focus DOF2. Thus, while high angle, short depth of focus lens arrays such as the first array 214 are advantageous in certain situations requiring short optical path length, the use of the second (e.g., relay) lens array 220 advantageously increases the optical path length of the overall apparatus 200, thereby facilitating proper focusing of the incident light at the photoreceptor 104, while providing a significantly longer spacing distance 206 between the second lens array and the photoreceptor 104.
The second light output is received at the first side 220-1 of the second lens array 220, where the low angle received light entering the second lens array 220 is indicated in dashed form as 220a, and is only a portion of the high angle light 214b. The second lens array 220 provides a third light output at a second end 220-2 which faces the photoreceptor 104, illustrated in dashed form as 220b in the drawing. As previously mentioned, the depth of focus (DOF1) of the first lens array 214 in this example is much smaller than the depth of focus (DOF2) of the second lens array 220, and the spacing distance 204 between the second end 214-2 of the first lens array 214 and the first end 220-1 of the second lens array 220 is approximately the sum of the first image conjugate distance and the second object conjugate distance (e.g., distance 204 in
As previously mentioned, provision of the relay lens array 220 between the first lens array 214 and the photoreceptor 104 provides advantages in increasing the spacing distance 206 from the photoreceptor 104 to the apparatus 200. In printing system applications, this increases the working distance from the lens 220 to the ITB photoreceptor 104, thereby facilitating efforts to keep the lens 220 clean, and facilitates provision of a sliding cleaner or other means for cleaning the second side 220-2 of the lens array 220 in the gap 206. Furthermore, the increase in the spacing distance 206 advantageously saves the cost of mechanical machining or manual or automatic focus adjustment in assembling a printing system or other host system (e.g., printing system 100 in
In addition, use of the relay lens array 220 provides for reduction in the waterfront dimension occupied by the apparatus 200. As seen 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.
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3658407 | Kitano et al. | Apr 1972 | A |
5166999 | Rees et al. | Nov 1992 | A |
6384918 | Hubble et al. | May 2002 | B1 |
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Entry |
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“Amorphous Silicon (a-Si) Photoreceptor Drums”, Kyocera Corporation, http://global.kyocera.com/prdct/printing-devices/electrophotography/index.html, retrieved from the Internet Nov. 25, 2013, 3 pgs. |
“Printing Devices”, General Brochure, Kyocera Corporation, Jul. 2013, pp. 1-16. |
Number | Date | Country | |
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20150168864 A1 | Jun 2015 | US |