Applicants hereby claim priority under 35 U.S.C. 119 based on European Patent Application No. 05105712.3 filed in Europe on Jun. 27, 2005.
The present invention relates to an image-forming element including a hollow drum body rotatable about an axis and having an outer wall surface, a, plurality of circumferentially extending electrodes supported on an electrically insulating layer arranged on the outer wall surface of the drum body, an electronic control unit containing a drivers circuit for energizing the electrodes, a support structure for supporting the drivers circuit, and contact means for electrically connecting each of the electrodes individually to the electronic control unit.
Image-forming elements are known from EP 0803 783 A1. In the known image-forming elements, the electronic control unit comprises a printed circuit board on which driver circuitry is mounted and which carries a pattern of electrical conductors which lead to a terminal array. The electronic control unit is shaped as an elongate body and is mounted inside a hollow drum body such that the terminal array formed at a longitudinal edge of the elongate body adjoins the internal wall surface of the drum body. Each of the conductors which lead to the terminal array is electrically connected to a corresponding one of the electrodes by contact means which pass through the wall of the hollow drum body.
A problem of the known drum body is the complicated manufacturing thereof. Through-holes have to be formed through the wall of the drum body, and have to be filled in with conductive material in order to provide contact of the electronic control unit with the electrodes placed on the outer surface of the drum body. The present invention seeks to provide an image-forming element for a printing apparatus in which the complications of the prior art are mitigated.
In accordance with the present invention, this object is accomplished in an image-forming element of the above mentioned kind, wherein the electronic control unit is arranged on the outer wall surface of the drum body. The manufacturing of the image-forming element is simplified and the production costs are thus reduced compared to the known image-forming elements. In particular, connecting the electrodes to the drivers circuitry can be realized in a much more simple and direct way.
According to an embodiment of the present invention, a recess for accommodating the drivers circuitry is formed in the outer wall surface of the drum body, the drivers circuitry being fixed in the recess. In this embodiment, the drivers circuitry is advantageously well protected from negative external influences such as temperature changes and high mechanical pressures during printing.
According to another embodiment of the present invention, the contact means includes a number of electrically-conducting projections extending upwardly from the drivers circuitry and having a dimension in a direction substantially parallel to the axis of the drum body of at least twice the pitch of the electrodes. The advantage of this embodiment is that the positioning of the electrodes with respect to the electronic control unit does not have to be realized with a very high degree of precision.
The present invention will now be explained with reference to the following exemplified embodiments of the present invention, and illustrated by reference to the drawings. The present embodiments serve to illustrate the present invention and should not be regarded as a limitation of the scope thereof.
The printing apparatus is provided with an automatic document feeder 8 for automatically feeding to a scanner unit 10 an original sheet or a stack of original sheets placed in the feeder. The scanner unit 10 is suited for optically scanning an original sheet fed thereto and for converting the optical information into electrical image signals by means of photoelectric sensors such as CCDs.
The printing apparatus also comprises a user interface panel 18, provided with a display screen and a key panel. The user interface panel is connected to the image processing unit 6 and to the print server 4 and is suited for selecting a user, setting queuing parameters, changing job attributes etc.
The print engine includes a number of image-forming elements 16. Each image-forming element comprises a rotating drum which can be driven in the direction of the arrow A by suitable driver means (not shown). For printing color images, a plurality of image-forming elements is used, each of said elements being supplied with toner in a specific color like cyan, magenta, yellow, red, blue, green or black for forming a separation image. Each image-forming element 16 is provided with a number of energizable image-forming electrodes placed beneath a dielectric layer. The electrodes are placed at a given distance from each other which determines the axial resolution of the print system, for example 600 dpi. A magnetic roll 14 and a developing unit 15 are provided. Conductive and magnetically attractive toner powder is supplied to the magnetic roll 14. By applying a predefined bias voltage to the magnetic roll 14, a uniform layer of toner powder is applied to the outer surface of the image-forming element 16. A soft-iron knife is disposed inside of the developing unit 15 and is placed between two magnets for generating a magnetic field in a gap. In order to develop a toner image on the image-forming element 16, the electrodes placed on the outer circumferential surface of the drum are activated image-wise by means of an electronic control unit having a drivers circuitry for energizing the electrodes individually. In an image-forming zone defined by the magnetic field in the gap, the toner powder is selectively removed from the surface of the image-forming element 16, depending on the activation pattern on the ring electrodes.
A toner powder image, being a separation image, is thus formed on the surface of each image-forming element 16. Each separation image is then transferred successively by means of pressure contact with an image receiving medium, for example a transfer drum 12 having a rubber surface. The complete color image is thus formed on said rubber surface and can be transferred and fused onto a print medium (for example a sheet of paper) by a suitable combination of pressure and temperature. The sheet of paper is conveyed from any of the paper trays 20 to the transfer drum by the guide track 26 and is then pressed between the heated transfer drum 12 and the pressure roll 28. The sheet of paper is then conveyed by the guide track 24 to the post fuser unit 30 and can undergo a duplex loop for printing on the reverse side, or can be directly output to the receiving tray 22.
An image-forming element 16 according to an embodiment of the present invention is shown in
Solder balls 42 and electrically conductive material 36 filling holes through the insulating layer 38 serve as contact means for electrically connecting each of the electrodes individually to the electronic control unit. Instead of solder balls, conductive epoxy pillars, copper pillars or electrically-conducting projections with a suitable shape can be used.
Each output of each driver of the drivers circuitry 44 is connected to a solder ball 42 deposited on the drivers circuitry. In order to obtain the desired solder balls pattern above the drivers circuitry, well-known structuring techniques are used, such as screen printing, photolithography in combination with electroplating or sputtering or the like. For a 600 dpi drum, wherein the pitch of the image-forming electrodes is 42.3 μm, the diameter of the solder balls is preferably chosen to be 120 μm. Generally, it is of great advantage that the diameter d of the solder balls (or of the conductive pillars or the like) is chosen to be at least two times the pitch p between the electrodes (see
Each electrode is electrically connected to the associated driver output via a through-hole which penetrates the insulating layer 38 and which is filled with an electrically conductive material 36 such as a metallic material, an electrically conductive epoxy resin, solder paste, electrically conductive polymer or the like. The trough-holes can be manufactured by laser drilling through the insulating layer 38. The through-holes are then filled with conductive materials to form contact means 36a, 36b, 36c, 36d for connecting, respectively, the electrodes 34a, 34b, 34c and 34d to the associated driver, each provided with a solder ball 42 for ensuring electrical contact.
The drivers circuitry 44 is fixed in the recess 40, for example by gluing the second side of the support structure 46 onto the bottom surface 45 of the recess 40. Preferably, the adhesion between the support structure 46 and the bottom surface 45 is such that a good thermal contact is achieved between the electronic control unit with the drivers circuitry 44 and the drum body 32.
In use, the transfer drum 12 is heated and consequently, heat is transferred to all parts of the image-forming element 16. The temperature of the electronic control unit raises. With a good thermal contact between the electronic control unit and the drum body, heat can be evacuated by the drum body which is cooled by air flow circulating in its hollow. The drum body is preferably made out of a metallic material, such as aluminium, and is provided with heat sinks placed in its hollow. Since the hollow of the drum body is free of any electronic component, the shape of the heat sinks can be freely chosen. Their shape can be optimized for very efficient cooling. Compared to the known image-forming element, wherein the design of the heat sink had to take into account the presence of the electronic control unit, the image-forming element of the present invention is more reliable due to a more efficient cooling, and accordingly, high speed print processes are enabled. Compared to the image-forming element known from
The volume of the recess not occupied by the electronic control unit can be filled with an electrically insulating material such as an epoxy resin. This material has the advantage that it can be chosen to have a suitable hardness in order to endure the forces exerted in use on the external surface the image-forming element.
As shown in
During manufacture, the solder balls or conductive pillars 142 can be positioned with a high degree of precision on ASICs (Application-Specific Integrated Circuit) 144, 244, making use of photolithography structuring techniques. The boards 146, 246 supporting the ASICs are then fixed on the outer wall surface 33. On a given ASIC, the pitch between solder balls is essentially constant and once the board with its ASIC is fixed on the outer wall surface 33 of the drum body, and the electrodes deposited, the shift between the array of solder balls and the array of electrodes is very small. As a consequence, there is always an electrode which is well positioned above a solder ball (or conductive pillar) provided that the diameter d thereof is chosen to be at least twice the electrode pitch p. After deposition of the insulating layer 38, the layer is structured in order to form small grooves wherein conductive material is to be deposited later to create the electrodes 134. After structuring of the insulating layer 38, through-holes are made through the layer 38 in order to form the interconnections 136 between the electrodes and the solder balls or conductive pillars 142. In
With the arrangement shown in
To solve this problem, the support structure 146 with ASIC 144, and the support structure 246 with ASIC 244 are placed in the axial direction AX of the hollow drum with an overlap. Placing the ASICs with such an overlap creates redundancy in the interconnections between the electrodes and the drivers. As a consequence thereof, a number of electrodes in the redundant areas are connected to two different drivers, each belonging to a different ASIC. This can be measured using appropriate circuits within the ASICs and corrected by tuning one of both drivers' outputs off. Electrodes 134b, 134c, 134d, 134e and 134f are each physically connected to two solder balls 142, each belonging to a different driver placed on a different ASIC, respectively ASIC 144 and ASIC 244. It is sufficient that the overlap is for one electrode only. With the arrangement of
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
Number | Date | Country | Kind |
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05105712.3 | Jun 2005 | EP | regional |