A platen cover assembly for reproduction machines

Abstract: An electrostatographic reproduction machine (10; Fig.1A) including a cover assembly (20) for holding an original document onto a glass platen (22), and for dissipating heat build up from the top of the glass platen. The cover assembly includes a heat conductive white film layer (60) for contacting the original document, and a layer of foam (62) with air flow passages (66) therethrough mounted over the white film layer. The cover assembly also includes a rigid frame (70) having a top panel (72) including air flow openings (74) formed therethrough, mounted over the layer of foam, for dissipating heat from the layer of foam and white film layer to the ambient.

Description: This invention relates to a cover assembly for a transparent glass platen of an electrostatographic reproduction machine which provides cooling of the glass platen. In conventional light lens or scanner type electrostatographic reproduction machines, an original document to be reproduced is manually placed or automatically conveyed onto a glass platen. The original document on the platen is illuminated by an elongate lamp assembly located in an optics cavity, either by moving the platen while the lamp is held stationary, or by moving the lamp assembly beneath a stationary platen. Alternatively, both the scan lamp and the platen can be held fixed and the document moved across the platen surface in a continuous velocity transport (CVT) mode. In any of these cases, a problem to be anticipated is a buildup of heat at the platen from operation of the document illuminating lamps. The lamps used for document scanning, for example, are typically mercury fluorescent or tungsten halogen lamps. With either source, but particularly with the tungsten halogen type of lamp, the heat buildup at the platen can become a source of concern. For example, with continued usage, such a platen may become so hot as to present a safety concern for the machine operator or cause defects in the glass platen. Various approaches therefore have been devised and disclosed, for example, in the following patents for glass platen cooling in electrostatographic reproduction machines. US-A-4,945,383 discloses an image forming apparatus which includes a temperature control device to control the temperature of light on a photosensitive medium. The apparatus is comprised of a pair of cooling fans and a heat ray reflecting shutter. The heat ray reflecting shutter aids in the ventilation created by the fans. US-A-4,632,539 discloses an apparatus for cooling a fluorescent lamp by causing a flow of cooling air to pass along a conduit extending along the length of the lamp. US-A-5,136,328 discloses a contoured scanning lamp reflector which entrains air flow underneath a platen glass and around the scanning lamp assembly for disturbing a boundary layer of heat thereof and coolipg the lamp and platen. JP 61160737 discloses using a layer of aluminum foil in a cover for a platen in order to effectively diffuse any accumulated heat. Unfortunately, airflow devices which are located underneath the glass platen, are only partially effective because much of the heat from the document illuminating lamps reaches the glass platen through empty space as radiation. Radiant heat as such will pass through moving air which appear transparent to heat waves in the infrared range. Therefore, despite the use of air flow devices underneath the glass platen. The glass platen still builds up heat, particularly during long copy runs of a single original document when the cover of the machine is stationary and down over the document. The stationary cover which, in the down position, serves to conform the document to the platen, traps heat over the platen, thus t heating the platen and raising its temperature. Accordingly, one aspect of the present invention is to provide a cover assembly for a reproduction machine which holds an original document onto a transparent platen and dissipates heat therefrom. In an embodiment of the invention, the cover assembly includes a heat conductive white film layer for contacting the original document, and a layer of material with air flow passages therein mounted over the white film layer. The cover assembly also includes a frame having a top panel including air flow openings formed therethrough, mounted over the layer of material, for dissipating heat from the layer of material and white film layer to the ambient. The present invention will now be described by way of example with reference to the accompanying drawings, in which like reference numerals refer to like elements, and wherein: FIGS. 1A and 1B are perspective views of an exemplary electrostatographic reproduction machine showing the cover assembly according to the present invention in a closed and an open position, respectively; FIG. 2 is a side schematic view of the machine of FIGS. 1A and 1B incorporating the cover assembly of the present invention; FIG. 3 is an exploded view of the platen assembly, and of a first embodiment of the cover assembly of FIG. 2; FIG. 4 is a detail of the cover assembly of FIG. 3; FIG. 5 is an exploded view of the platen assembly, and of a second embodiment of the cover assembly of FIG. 2; and FIG. 6 is a detail of the cover assembly of FIG. 5. Referring to FIGS. 1A and 1B, an electrostatographic reproduction machine 10 is shown which includes a stand or base portion 12 and a main body 14. The main body 14 includes a paper supply 16, for example, and an output tray 18. Importantly, the main body 14 includes the cover assembly 20 of the present invention (described below) which as shown is mounted pivotably over a glass platen 22. As is well known, individual original documents to be reproduced can be placed manually on the glass platen 22 according to registration indicia, or, as also illustrated, they can be fed automatically in a registered manner onto the glass platen 22. For feeding sheets automatically, the cover assembly 22 of the present invention can include a single sheet feeding device section 24 for feeding one original document at a time, as well as a multi-sheet feeding device section 26 for feeding seriatim, one or more original documents automatically. In either the manual or automatic document feeding cases, as many copies of each original document can be made with the document on the platen glass 22 with the cover assembly 20 resting over it. In Figure 2, various elements of the reproduction machine 10 are schematically depicted. Inasmuch as the art of electrostatographic reproduction is well known, the various processing stations shown in the Figure 2 will be only briefly described. As illustrated, Figure 2 is a side schematic view of a light lens document reproduction machine incorporating a tungsten halogen lamp as the document illuminator. However, other types of illumination lamps may be used consistent with the principles of the present invention. An original document 30 to be copied is placed on the surface of the transparent glass platen 22. A scanning assembly 32 located within an optics cavity 33, consists of a tungsten halogen lamp 34, an associated reflector 36, and a scan mirror 38. Scanning assembly 32 is mounted for parallel movement along a scan path beneath and parallel to platen 22 on a scan carriage 40. A half-rate mirror assembly 42, adapted to travel on a 1/2 rate scan carriage (not shown) at 1/2 the rate of mirror 38, reflects line images of the document 30 into projection lens 44. Lens 44 projects a flowing image of the document 30 onto the surface of photoreceptive image bearing member drum 46 via drum mirror 48. Arranged around the photoreceptive drum 46 are conventional electrostatographic processing stations, namely: a charging station 58 for applying a uniform charge to the photoreceptive drum surface, an exposure station 59 where a latent image of the original document is formed on the drum 46, a developing station 50 for applying a toner of suitable polarity to the latent image thus forming a toner image; a transfer station 52 for transferring the toner image to an output sheet; a fusing station 54 for fixing the transferred toner image to the copy sheet; and a cleaning station 56 for removing residual particles from the drum surface. In a document scanning mode, carriage 40 is driven on guide rails by conventional drive means, from left to right to incrementally scan document 30. At the end of one scan, the carriage is returned to the start of another scan position, and repeats. The entire document 30 can thus be imaged onto the charged surface of the photoreceptive drum 46. As is also known, the entire document 30 may also be imaged in a non-scanning optical machine embodiment merely by stationary repeated lamp flashes illuminating and exposing the surface of the drum 46 to the entire document 30 with each flash. During such repeated illumination of the document 30, heat generated by the lamp 34, in the absence of any heat reduction mechanism, ordinarily will result in heat build up in, and even in an overheating of the glass platen 22 through which the document 30 is repeatedly being illuminated for multiple copies. Such overheating might result in an unsafe condition for an operator, or possibly subject the glass platen 22 to stresses and eventual fractures. It has been found that such overheating can still result from heat trapped on the top of the glass platen 22 even when an airflow mechanism such as an air blower (not shown), is provided underneath the glass platen 22 for exhausting air from the optics cavity 33. Referring to FIGS. 3 and 4, the optics cavity 33, the glass platen 22, and the cover assembly 20 of the present invention are illustrated in an exploded view. The purpose of the present invention is reducing the platen temperature by reducing the overall heat transfer resistance of the cover assembly 20, thereby increasing the heat flow from the top of the platen 22 to the ambient. Ordinarily, the cover assembly 20 on the platen 22 when down, acts to block the heat flux on the top surface of the platen. Heat is thus continuously accumulated or built up in the platen during long copy runs. Such heat build up is due in part to the high thermal resistance of thick conventional polyurethane foam that is attached within conventional cover assemblies for firmly supporting and conforming documents onto the platen 22. A forced air flow mechanism (not shown), for example, associated with the optics cavity 33 may help to reduce the platen temperature by moving some heat from the bottom surface or underneath side of the platen 22. However, radiant heat reaches the glass platen through radiation even though the air is moving and continues to heat the platen. Thus, undesirable heat is built up on the top side of the glass platen 22. The cover assembly 20 of the present invention is designed to effectively dissipate heat build up from the top of the platen 22. A first embodiment of the present invention is illustrated in FIG. 3, wherein the cover assembly 20 includes a heat conductive white film layer 60 for contacting and providing backing for a document positioned on the platen 22 to be illuminated. Preferably, the white film layer 60 is about 0.5mm (0.020") thick, and is comprised of a polycarbonate film for enabling acceptable heat conductivity therethrough, while still maintaining sufficient film stiffness in order to avoid warpping of the film. As illustrated in this embodiment, the cover assembly 20 does not include single or multi-sheet automatic feeding devices. However, it is understood that the heat dissipating features of the illustrated cover assembly 20 are equally applicable in an embodiment thereof including automatic sheet feeding devices. In such cases, the white film layer 60 will be provided in the shape of a continuous driven belt with suitable drive means. The cover assembly 20 also includes a layer of foam 62. Conventional cover assemblies typically have a high insulation value due to the use of thick foam layers for the purpose of conforming documents to the shape of the platen 22. Such thick layers of foam however have been found to act as insulation, thus trapping heat on top of the platen and undesirably resulting in high glass platen temperatures. According to the present invention however, the layer of foam 62 is relatively thinner, and is intended to reduce the platen temperature by increasing the heat transfer resistance thereof. The layer of foam 62 is attached as by gluing on top of the white film layer 60. The layer of foam 62 of the present invention includes heat dissipating means such as air flow passages 64 machined therethrough. The air flow passages 64 in the first embodiment of the cover assembly 20 are, for example, holes 66 (FIG. 4). The holes 66 are formed as a repeated pattern, and are rectangular but may also be circular. They are produced, for example, by punching, thus leaving the piece of foam to be attached or mounted over the white film layer 60, as an integral piece. The holes 66 are formed so that heat conducted by the white film layer 60 away from the top of the platen 22, will be dissipated upwards principally by convection through such holes. The heat dissipating ability of the layer of foam 62 is preferably enhanced by making the layer 62 out of a thermally conductive foam such as silicone sponge foam. As also shown, the cover assembly 20 further includes a rigid frame 70 that has a top generally solid panel 72. The top panel 72 is mounted on top of the layer of foam 62, and an edge of the rigid frame 70 is ordinarily mounted to a top edge of the reproduction machine (FIG. 1B) for pivotable movement relative to the top of the platen 22. Although shown as a simple manual cover, the rigid frame 70 and top panel 72 could equally be those including automatic sheet feeding devices (FIG. 1A). In either case, the top panel 72 of the rigid frame 70 includes heat dissipating means formed therein as vents or air flow openings 74. The vents or air flow passages 74 which open from the bottom surface of the top panel 72 to the ambient serve to release, by convection, hot air and heat from the layer of foam 62. The vents or air flow openings 74 are formed facing front to back, and have a size each so as to prevent an operator from accidentally getting a finger, for example, caught in one of the openings. However, the openings 74 are suitable for effecting air exchange between the ambient and the layer of foam 62 as mounted beneath the top panel 72. As disclosed in FIGS. 3 and 4, the cover assembly 20 is suitable for dissipating heat naturally by conduction and convection from the top of the platen 22 to the ambient. The idea is to transport the accummulated heat in the platen 22 by conduction through the white film layer, by natural convection through the layer of foam using the passages 66, and finally by convection again through the air flow openings 74 in the top panel 72, into the ambient. Referring now to FIGS. 5 and 6, a second embodiment of the cover assembly 20 of the present invention is illustrated for use in conjunction with a forced air flow mechanism within the reproduction machine. In this illustration, like numerals represent like elements as in the first embodiment of FIGS. 3 and 4. As shown, the white film layer 60 is the same as in this embodiment as it is in the first embodiment. However, the heat dissipating features of the layer of foam 62 and of the rigid frame 70 have been modified to cooperate with the forced air flow system of the reproduction machine 10. As shown, the forced air flow system of the reproduction machine 10 includes a blower mechanism (not shown). It also includes a series of air outlet openings 78 that are formed and air sealed through a top edge of the reproduction machine 10, adjacent the platen 22. The outlet openings 78 are formed so as to be in communication with a forced airstream 80 moving underneath the platen 22 due to the blower mechanism. As such, hot air from the region above the platen 22 including the cover assembly 20 of the present invention can be pulled through the outlet openings 78 into the airstream 80, thereby cooling to top of the platen 22. As further shown, rigid frame 70 of the second embodiment of cover assembly 20 includes a series of air flow openings in the form of air inlet openings 82 that are formed along an edge thereof so as to correspond and communicate through the layer of foam 62 with the outlet openings 78. The layer of foam 62 has formed partially into its upper surface, facing the top panel 72 of rigid frame 70 and inlet openings 82 therein, a series of horse-shoe shaped air flow channels 84, each with first and second open ends 86, 88, respectively. Additionally, the foam layer 62 may consist of one entire piece of foam with such two dimensional horse-shoe shaped channels formed therein, along with a series of through openings (not shown) for bottom to top surface convective heat flow. In order to cause ambient air pulled through the inlet openings 82 to circulate through a major area of the layer of foam 62, the first open end 86 of each horse-shoe channel is aligned with an inlet opening 82, and the second open end 88 is aligned with an outlet opening 78. In operation, heat build up underneath the platen 22 is removed conventionally by an air blower. In addition, heat build up on the top of the platen 22 is dissipated by conduction through the white film layer 60 and through the layer of foam 62. Such heat is then dissipated from the top part of the layer of foam 62 by forced air drawn therethrough by the blower mechanism into and out the outlet openings 78. In other words, fresh air from the ambient is caused to circulate on the platen top surface thereby taking heat with it by convection. In the embodiments above foam has been described as the material mounted on top of the white film layer. It will be appreciated that other light weight resistant material, for example plastics material, can be utilized.

Claims: A cover assembly (20) for use on an electrostatographic reproduction machine (10) including a transparent platen (22) for holding an original document being reproduced and an original document illuminating means (32) mounted in an optics cavity (33) underneath the platen, the cover assembly comprising: a white film layer (60); a layer of material (62) mounted on top of said white film layer (60); and a frame (70) including a top panel (72) attached to said layer of material (62); characterized in that, heat dissipating means (64,74) are formed in said layer of material and in said frame for dissipating heat from on top of the platen, thereby enabling a cooling of the platen of the electrostatographic reproduction machine. A cover assembly as claimed in claim 1, wherein said white film layer (60) is thermally conductive. A cover assembly as claimed in claims 1 or 2, wherein said heat dissipating means formed in said layer of material (62) compises air flow passages (64,66) machined therethrough. A cover assembly as claimed in claims 1 to 3, wherein said heat dissipating means formed in said frame comprises air flow openings (74) formed through said top panel (72) thereof for air exchange between the ambient air and said layer of material (62) beneath said top panel. A cover assembly as claimed in claims 1 to 4, wherein said white film layer (60) is comprised of a polycarbonate film. A cover assembly as claimed in claims 3 to 5, wherein said air flow passages (64, 66) machined through said layer of material (62) comprise a repeated pattern of holes for air to flow from said white film layer (60) to said frame (70). A cover assembly as claimed in claims 3 to 6, wherein said air flow passages (64, 66) machined through said layer of material (62) are comprised of a series of horse-shoe shaped channels (84) machined partially into a surface of said layer of material (62). A cover assembly as claimed in claim 7, wherein each said horse-shoe shaped channel (84) includes an open first end (86) aligned with one said air flow opening (82) formed in said top panel (72); and wherein each said horse-shoe shaped channel (84) includes an open second end (88) aligned with an air outlet opening formed through an edge of the platen (78). The cover assembly as claimed in any one of claims 1 to 8, wherein the layer of material (62) comprises foam. The cover assembly as claimed in claim 9, wherein said layer of foam (62) comprises silicone sponge foam for increasing heat dissipation therethrough by conduction. An electrostatographic reproduction machine (10) including: an optics cavity (33); a platen (22) mounted over said optics cavity for holding an original document being reproduced; and document illuminating lamps (34) located within said optics cavity for illuminating an original document on said platen (22); the machine further including a cover assembly (20) for holding an original document on said glass platen is as claimed in any of the claims 1 to 10.

Inventors: VELAZQUEZ CARLOS A, VELAZQUEZ, CARLOS A.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1995
Main classification: G03G15
IPC codes: G03G15, G03B27