Abstract:
An electrode unit capable of printing images with an excellent quality and a printing device provided with this electrode unit. Rows of apertures (L 1 , L 2 ) formed by disposing apertures ( 11 ) in s preset direction of a base material consisting of a resin film or a resin sheet are provided, non-image forming sections ( 15, 15 ) not used for forming images are defined along a length at least 50 times, preferably at least 200 times, the thickness of the base material extending from the opposite ends of the base material in the rows of apertures (L 1 , L 2 ) lengthwise direction, and an image forming section ( 16 ) is formed in the remaining portion. Apertures ( 11 ) and control electrodes ( 12 ) surrounding the apertures ( 11 ) are used to control the transfer of toner particles to form images.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to an electrostatic printing device for forming an image using toner particles in printers, facsimiles, copying machines and so on, and parts therefor. 
     2. Description of the Prior Art 
     Printing devices, by which electric signals output from computers, word processors, facsimiles, or the like are formed as visible images on a recording medium such as paper or the like, include an electrostatic printing device  1  shown in FIG. 5, in which an electrode unit is arranged between a particle carrier and a back electrode. 
     The electrostatic printing device  1  generates an electric potential difference between the particle carrier  20  and the back electrode  30  to create an electric field, by which toner particles are conveyed toward the back electrode  30  from the particle carrier  20 , and the electrode unit  10  arranged between the particle carrier  20  and the back electrode  30  controls conveyance of toner toward the back electrode  30  from the particle carrier  20  to enable forming of a desired image on a recording medium  50 , such as paper or the like, or an intermediate recording medium, such as a transfer belt or the like, disposed between the particle carrier  20  and the back electrode  30 . 
     The above-mentioned electrode unit  10  comprises apertures  11  and control electrodes  12  surrounding the apertures  11  at least partially (see FIG.  6 ), and voltage applied on the control electrodes  12  has an influence on an electric field, by which toner particles are conveyed toward the back electrode  30 , so that toner particles conveyed toward the back electrode  30  from the particle carrier  20  determine positions, sizes and the like of dots formed on the recording medium  50 . 
     The electrode unit  10  is formed from a base material of a resin film or resin sheet composed of, for example, a resin material such as polyimide or the like and having a thickness of around 25 to 200 μm, the base material being formed with a plurality of apertures  11  aligned in a predetermined direction, and the apertures  11  being formed to be at least partially surrounded by, for example, mutually intersecting control electrodes or the control electrodes  12  formed in a ring-shaped fashion. 
     When being assembled into the printing device  1 , the electrode unit  10  is disposed between the particle carrier  20  and the back electrode  30  such that rows of the apertures (L 1  to L 4 ) of the unit  10  are made in parallel to an axis of the particle carrier  20 , which is formed as a column or cylinder-shaped rotating body. 
     In the example shown in FIG. 5, the electrode unit  10  is formed with four rows of apertures (L 1  to L 4 ) disposed in parallel. In the case where the plural rows of apertures (L 1  to L 4 ) are provided in the electrode unit  10 , a distance between the surface of the particle carrier  20  and the apertures  11  formed on the electrode unit  10  varies depending upon, for example, to which of the rows of apertures (L 1  to L 4 ) the apertures  11  belong, when the electrode unit  10  is positioned in a planar manner. 
     In the specification of the present application, assuming that Lk denotes a distance between the respective apertures  11  of the electrode unit  10  and the surface of the particle carrier  20 , Lk is large between the apertures  11  belonging to the right and left rows (L 1 , L 4 ) in FIG.  5  and the surface of the particle carrier  20  and small between the apertures  11  belonging to the central rows (L 2 , L 3 ) and the surface of the particle carrier  20 . Also, since even with an electrode unit  10  comprising one or two rows of apertures, it is difficult to arrange the row or rows of apertures in completely parallel to the axis of the particle carrier, Lk is in some cases varied in the apertures  11  belonging to the same row. Therefore, as Lk is varied, the control electrodes  12  have different influences on an electric field formed between the particle carrier  20  and the back electrode  30  even in the case where the same voltage is applied to the control electrodes  12  surrounding the apertures  11  in the respective rows (L 1  to L 4 ) of apertures, so that dots formed on the recording medium  50 , such as paper or the like, vary in size and density depending upon which of the control electrodes  12  surrounding the apertures  11  has controlled the forming of the dots. 
     By way of example, in the case where dots are formed on the recording medium  50  assuming that all the control electrodes  12  surrounding the apertures  11  (L 1  to L 4 ) formed on the electrode unit  10  in the printing device  1  shown in FIG. 5 are the same in electric potential, when the apertures  11  belonging to the rows L 2 , L 3  and having a relatively small distance Lk between them and the surface of the particle carrier  20  form relatively deep and large dots, and the apertures  11  belonging to the rows L 1 , L 4  and having a relatively small distance Lk between them and the surface of the particle carrier  20  form light and small dots, quantity of toner particles adhered to a printed surface finished and sizes of dots formed differ depending upon, through which of the apertures  11  adherence of toner particles and formation of dots are made, when dots are consecutively shown in, for example, FIG. 6, so that there are produced areas being uneven in density and not printed, such unevenness and non-printed areas being visually recognized as lines. 
     Such phenomenon is called “white line noise”, which causes degradation in printing quality, and removal of which is contemplated. In order to prevent generation of such “white line noise”, distances Lk between the surface of the particle carrier  20  and the apertures  11  formed on the electrode unit  10  are made constant to eliminate variation ΔLk in the distances, thereby solving the problem of “white line noise”. Therefore, there has been proposed a printing device (see FIG. 7) constructed such that distances Lk between the apertures  11  of the electrode unit  10  and the surface of the particle carrier  20  are made uniform in all the rows (L 1  to L 4 ) by bending that area of the electrode unit  10 , in which the apertures  11  are formed, so that all the apertures  11  are adjusted to be disposed on a circle concentric with an outer periphery of the particle carrier  20 . 
     As described above, with the printing device  1 , in which the area of the electrode unit  10  formed with the apertures  11  is bent in compliance with the surface configuration of the particle carrier  20 , all the distances Lk between the surface of the particle carrier  20  and the respective rows (L 1  to L 4 ) of the apertures of the electrode unit  10  are uniform, and therefore it is possible to prevent that degradation in printing quality, which is attributed to unevenness in such distances. 
     When the electrode unit  10  formed from a base material of a resin film or resin sheet is bent in a certain direction, the cross section of the bent portion itself undergoes deformation in its inner surface with the result that such deformation causes the electrode unit  10  to change in shape. 
     For example, when an X—X axis of an electrode unit  10  put in a state of being disposed in a planar position shown in FIG. 8 is bent into a shape shown by a broken line X′—X′ as shown in FIG. 9, the electrode unit  10  generates warp ρ at both ends in the direction along a Z—Z axis perpendicular to the X—X axis thus bent (see FIG.  9 ). 
     FIG. 10 shows a state of a minute space containing an origin O and cut from the bent portion of the electrode unit  10  put in the state shown in FIG.  9 . When the electrode unit  10  is bent in a widthwise direction in a square column above the origin O (above the broken line) in FIG. 10, normal stress acts to compress the electrode unit  10  in the direction along the X—X axis, thereby generating longitudinal strain ε x  and lateral strain ε x (=−νε x ) in the direction along the Z—Z axis since the electrode unit  10  compressed by the normal stress tends to expand in a lateral direction. 
     Also, stress and strain in a state opposite to the above are generated in a square column below the origin O (below the broken line) in FIG.  10 . Therefore, when the electrode unit  10  is bent in the direction along the X—X axis, stress is generated in the direction along the Z—Z axis to tend to bend the electrode unit  10 . This stress is liable to be released at ends of the substrate, so that “warp” which affects the print quality is caused in both end portions of the substrate in the direction along the Z—Z axis (see FIG.  11 ). 
     Thus, when the electrode unit  10  is bent in the direction perpendicular to the rows of apertures, “warp” is produced in both longitudinal end portions of the rows of apertures, so that degradation in printing quality is caused in the case where apertures  11  are formed up to end portions of the electrode unit  10  and all the apertures  11  are used for formation of an image. That is, the apertures  11  formed in both end portions of the electrode unit  10  are displaced in directions away from the surface of the particle carrier  20  to make distances Lk large to generate dispersion between the apertures  11  in the same rows. Therefore, in the case where such displacement is generated to a degree having an influence on printing quality, that is, beyond an error in an allowable range, dots formed are different in size and density between the respective apertures  11  to cause degradation in printing quality. 
     However, there have not been conventionally proposed any method and device for dissolving that degradation in image quality, which is caused by “warp” generated in both longitudinal end portions of an electrode unit  10 . 
     Accordingly, the present invention has been made with a view to overcoming the above disadvantages of the prior art and has its object to provide an electrode unit capable of forming an image of excellent quality by eliminating variations in distances between apertures formed on an electrode unit and the surface of a particle carrier as far as possible even if “warp” is generated at both end portions of rows of apertures in a longitudinal direction of rows of apertures when the electrode unit is bent in the direction perpendicular to the rows of apertures. 
     SUMMARY OF THE INVENTION 
     In order to attain the above object, an electrostatic printing device  1  and an electrode unit  10  used for the electrostatic printing device  1  according to the present invention are provided, the electrostatic printing device comprising a column-shaped or cylinder-shaped particle carrier  20  carrying toner particles on the surface thereof, a back electrode  30  disposed opposite the particle carrier  20  and an electrode unit  10  arranged between the particle carrier  20  and the back electrode  30  and formed with a plurality of apertures  11 , which are at least partially surrounded by control electrodes  12 , and wherein electric voltage producing an electric potential difference between the particle carrier  20  and the back electrode  30  and applied to the control electrodes  12  of the electrode unit  10  controls conveyance of toner particles toward the back electrode  30  from the particle carrier  20  to form a desired image on a recording medium  50  disposed between the particle carrier  20  and the back electrode  30 , and the electrode unit  10  comprises a substrate formed from a resin film or resin sheet, the apertures  11  being arranged in a predetermined direction of the substrate to provide rows of apertures (L 1 , L 2 ), the rows of apertures (L 1 , L 2 ) on the electrode unit  10  being arranged in the direction parallel to an axis of the particle carrier  20 , the electrode unit  10  being arranged to be curved in the direction perpendicular to the longitudinal direction of the rows of apertures (L 1 , L 2 ), and the respective rows of apertures (L 1 , L 2 ) being positioned equidistantly from an outer periphery of the particle carrier  20 , and wherein when the substrate is bent in the direction perpendicular to the rows of apertures (L 1 , L 2 ), the substrate curves in the longitudinal direction of the rows of apertures (L 1 , L 2 ) to create an image forming area  16  defined by that portion on the substrate, in which displacements (variations ΔLk) produced in directions away from the surface of the particle carrier  20  are in a predetermined range of allowable error, and image unforming areas  15 ,  15  being not used for formation of an image and defined by those areas, which extend from both ends of the image forming area to both ends of the substrate. 
     In addition, the image unforming areas  15 ,  15  may comprise areas, in which the apertures  11  are not formed, and the apertures  11  may be formed. However, the apertures  11  formed in the image unforming areas  15 ,  15  are not used for formation of an image. 
     The image unforming areas  15 ,  15 , respectively, are provided to extend over a length fifty times or more, more preferably, two hundred times or more a thickness of the substrate in the longitudinal direction of the rows of apertures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and advantages of the invention will become understood from the following detailed description of preferred embodiments thereof in connection with the accompanying drawings in which like numerals designate like elements, and in which; 
     FIG. 1 is a plan view showing an electrode unit according to the present invention; 
     FIG. 2 is a schematic view illustrating a printing device according to the present invention; 
     FIG. 3 is an explanatory view showing holding means, to which the electrode unit is mounted; 
     FIG. 4 is an explanatory view showing an example, in which the electrode unit is mounted to the holding means; 
     FIG. 5 is a schematic view illustrating a conventional printing device; 
     FIG. 6 is a view illustrating the generation of white line noise; 
     FIG. 7 is a schematic view illustrating a conventional printing device with an electrode unit curved; 
     FIG. 8 is a view illustrating an electrode unit; 
     FIG. 9 is a view illustrating an electrode unit in a curved state; 
     FIG. 10 is a view illustrating how strain is generated in an electrode unit in a curved state; and 
     FIG. 11 is a view illustrating “warp” in a longitudinal direction of the electrode unit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described below with reference to the accompanying drawings. 
     In FIG. 1, the reference numeral  10  denotes an electrode unit according to the present invention. The electrode unit  10  is called a flexible printed board (FPC) and is formed from a base material of a resin film or resin sheet composed of, for example, a resin material such as polyimide or the like and having a thickness of around 25 to 200 μm, and formed with a multiplicity of apertures  11  extending through the base material, the apertures  11  being formed to be at least partially surrounded by a control electrodes  12 . In the present embodiment, the many apertures  11  having a diameter of around 160 μm are formed in the base material having a diameter of 100 μm to form the electrode unit  10 . 
     The control electrodes  12  are shown as comprising ring-shaped portions  12   a  surrounding the respective apertures  11  and lead portions  12   b  for connecting the ring-shaped portions  12   a  of the respective control electrodes  12  to an electric voltage source (not shown) in the embodiment shown in FIG.  1 . The control electrodes  12  is not limited to a configuration shown in FIG. 1 but may be one, in which a plurality of intersecting control electrodes surround the apertures at least partially, and one, in which control electrodes are provided to surround a plurality of apertures  11  at a time, and can use various known configurations. 
     Also, the control electrodes  12  may be formed on either of front and back surfaces of the above base material composed of a resin film or resin sheet, or may be formed on both surfaces of the base material, or further may be embedded in and disposed on the base material, and is not limited to arrangement, configuration and the like provided that conveyance of toner particles toward the back electrode  30  can be controlled. 
     In the embodiment shown in FIG. 1, the apertures  11  are arranged in the direction along the line Z—Z to define rows (L 1 , L 2 ) of apertures, and a plurality of rows (L 1 , L 2 ) of apertures are arranged in parallel in the direction along the line X—X, so that two rows. (L 1 , L 2 ) of apertures are formed in the embodiment shown in FIG.  1 . 
     It should be noted that these rows (L 1 , L 2 ) of apertures are not limited to two-row arrangement but may be arranged in two or more rows and can also be applied to one row arrangement. 
     With the electrode unit  10  constituted in the above manner, an image is formed through the apertures  11  formed in an image forming area  16 , and image unforming areas  15 ,  15  being not used for formation of an image are formed on both ends of the image forming area  16 . 
     The image forming area  16  used for formation of an image comprises that portion on the substrate, in which displacements (variations ΔLk) produced in directions away from the surface of the particle carrier  20  are in a predetermined range of allowable error when the substrate of the electrode unit curves in a longitudinal direction (direction along the line Z—Z in FIG. 1) of the rows (L 1 , L 2 ) of apertures after the substrate is bent in the direction (direction along the line X—X in FIG. 1) perpendicular to the rows (L 1 , L 2 ) of apertures, and the apertures  11  formed in the image forming area  16  and the control electrodes  12  surrounding the apertures  11  control conveyance of toner particles to control positions, sizes and densities of dots formed. Also, the image unforming areas  15 ,  15  being not used for formation of an image are formed on those areas of the substrate, which extend from both ends of the image forming area  16  to both ends of the substrate. 
     In what extent the image unforming areas  15 ,  15  should be provided, that is, what extent from both ends of the electrode unit  10  correspond to those portions, in which large variations ΔLk are generated, is determined by a thickness of the substrate of the electrode unit  10  such that large variations ΔLk are generated in portions at a distance fifty times or less the thickness of the substrate, more surely a distance two hundred times or less the thickness of the substrate, from both ends of the electrode unit  10 . Therefore, those portions define the image unforming areas  15 ,  15  and the remaining portion defines the image forming area  16 , in which the apertures  11  and the control electrodes  12  surrounding the apertures  11  control conveyance of toner particles to form an image, thereby enabling prevention of degradation in printing quality. 
     In the present embodiment, the resin substrate of the electrode unit  10  has a thickness of about 100 μm, so that the image unforming areas  15 ,  15  are provided over lengths of 5 mm, more surely 2 cm or more from both ends of the electrode unit  10  whereby degradation in printing quality can be prevented even if “warp” of the substrate occurs at both longitudinal ends thereof. 
     In addition, while the apertures  11  are also formed in the image unforming areas  15 ,  15  in the present embodiment shown in FIG. 1, the apertures  11  may not be formed in the image non-forming areas  15 ,  15 . In the case where the apertures  11  are formed in the image unforming areas  15 ,  15 , the apertures  11  formed in the image unforming areas  15 ,  15  should not be used for formation of an image by not connecting to the control electrodes  12  surrounding those apertures to a voltage source (not shown). Thus, in the case where the apertures  11  are formed not only in the image forming area  16  but also in the image unforming areas  15 ,  15 , there is no need of any complex work for forming (or not forming) the apertures  11  partially in manufacture of the electrode unit  10 , so that the electrode unit  10  can be manufactured easily. 
     In this manner, the image unforming areas  15 ,  15  being not used for formation of an image are provided over a distance fifty times or less the thickness of the substrate of the electrode unit  10 , more surely a distance two hundred times or less the thickness of the substrate in both ends of the electrode unit  10  in the longitudinal direction of the rows of apertures, whereby it is possible to prevent that dispersion in distances Lk between the apertures  11  and the surface of the particle carrier  20 , which is caused by “warp” produced at both longitudinal ends of the rows of apertures when the electrode unit  10  is bent in the direction perpendicular to the rows of apertures as described later. 
     The electrode unit  10  constituted in the above manner is arranged between the particle carrier  20  and the back electrode  30  to form a printing device  1  shown in FIG. 2 while that area, in which the apertures  11  are formed, is bent in compliance with a circle concentric with the outer peripheral shape of the particle carrier  20 . 
     In FIG. 2, the electrostatic printing device  1  comprises the particle carrier  20  formed in a cylindrical-shape, the back electrode  30 , and the electrode unit  10  arranged between the particle carrier  20  and the back electrode  30 . 
     In the electrostatic printing device  1 , the particle carrier  20  is in the form of a column-shaped or cylinder-shaped rotating body, and constructed such that upon rotation of the particle carrier  20 , toner particles T filled in a container  60  adhere to the surface of the particle carrier  20  to be conveyed thereby. 
     In the case where, for example, toner of magnetic substance is used as toner particles, the particle carrier  20  may be formed in the form of a cylinder, in which magnets are arranged, and may be constructed to be able to electrically adhere toner particles to the surface thereof, and can adopt various known configurations. 
     In this manner, upon rotation of the particle carrier  20 , toner particles having adhered to the surface of the particle carrier  20  are conveyed to a position, in which the apertures  11  of the electrode unit  10  are formed, and toner particles can be conveyed toward the back electrode  30  by an electric field formed by electric potential difference given between the particle carrier  20  and the back electrode  30 . 
     In the electrostatic printing device  1 , the electrode unit  10  arranged between the particle carrier  20  and the back electrode  30  is constructed to be held in a curved state so that distances Lk between the apertures  11  in the rows (L 1 , L 2 ) of apertures formed on the electrode unit  10  and the surface of the particle carrier  20  are made uniform. 
     In order to hold the electrode unit  10  in a curved state, the printing device  1  in the present embodiment comprises holding means  40  for the electrode unit  10 . An example of the holding means  40  is shown in FIG. 3, and the holding means  40  for holding the electrode unit  10  of the present invention in a curved state is not limited to a configuration shown in FIG.  3 . 
     In FIG. 3, the holding means  40  comprises a frame formed to be substantially rectangular-shaped, and the electrode unit  10  formed to be rectangular-shaped is arranged in the frame. A side of the electrode unit  10  is, for example, interposed between holding portions  41  provided on a side of the holding means  40  to be fixed at its one end, and a side facing the above side is made a free end which is not fixed to the holding means  40 . 
     Further, the holding means  40  comprises pressing means  42  provided on a side thereof opposite to the side, on which the holding portions  41  are formed, and for pushing a free end side of the electrode unit  10  upward and bending the same in FIG. 3, the pressing means  42  in the present embodiment comprising a push pin inserted into a hole  43  formed in a side of the frame of the holding means  40  to be able to advance or retract and extending through the frame in FIG.  3 . 
     When a side of the electrode unit  10  is interposed between the holding portions  41  of the holding means  40  constructed in the above manner and the free end side of the electrode unit  10  is pushed up by the above pushing pin  42 , the electrode unit  10  formed from a resin material such as polyimide or the like to posses flexibility is curved as shown in FIG. 4. A position, in which the electrode unit  10  is bent, can be adjusted by advancing and retracting the pushing pin  42  such that bending of the electrode unit  10  can be generated near and toward the holding portions  41  by moving the pushing pin  42  toward the holding portions  41  and bending of the electrode unit  10  can be shifted away from the holding portions  41  by moving the pushing pin  42  in the direction away from the holding portions  41 , such adjustment enabling bending of the electrode unit  10  to correspond to a position, in which the apertures  11  are formed. 
     The curved electrode unit  10  is arranged to conform to the outer periphery of the particle carrier  20  in the form of a columnar or cylindrical configuration, and the respective apertures  11  are made equidistant from the outer periphery of the particle carrier  20 . 
     In addition, the electrode unit  10  may be arranged in such a manner that either or both of portions disposed right and left of that area, in which the apertures  11  are formed, contact the surface of the particle carrier  20  in FIG. 4, in which case a material involving less frictional resistance may be adhered to the contact portion between the electrode unit and the particle carrier  20 . 
     In this manner, the electrode unit  10  arranged between the particle carrier  20  and the back electrode  30  is constructed such that the control electrodes  12  surrounding the apertures  11  are connected to a voltage source (not shown) and when a predetermined voltage is applied to the control electrodes  12  through a control device (not shown) or the like, conveyance of toner particles toward the back electrode  30  from the particle carrier  20  is controlled to form a desired image on a recording medium  50 , such as paper or the like, disposed between the particle carrier  20  and the back electrode  30 . 
     The electrode unit constituted in the above manner and the printing device provided with the electrode unit are arranged in a state, in which the image forming area of the electrode unit is curved to be able to be disposed on a circle concentric with the outer periphery of the particle carrier which is formed into a columnar or cylindrical shape, so that all distances between the respective apertures formed on the electrode unit and the surface of the particle carrier become the same whereby unevenness in printing among the apertures in the respective rows is eliminated, dots printed through the respective apertures are of the same size and the same density, and printing quality is improved without generation of “white line noise” as shown in FIG.  6 . 
     Also, when the electrode unit is bent in the direction perpendicular to the rows of apertures, the substrate of the electrode unit curves in a longitudinal direction of the rows of apertures to create an image forming area defined by that portion on the substrate, in which displacements produced in directions away from the surface of the particle carrier are in a predetermined range of allowable error, and image unforming areas being not used for formation of an image and defined by those portions, which extend from both ends of the image forming area to both ends of the electrode unit, whereby it is possible to provide an electrostatic printing device and an electrode unit used for the same, in which no conspicuous error is generated in distances between the apertures and the particle carrier due to the warp generated in the longitudinal direction of the rows of apertures of the electrode unit caused by bending of the electrode unit, and dots formed can be made as uniform as possible in size and density. 
     Thus the broadest claims that follow are not directed to a machine that is configure in a specific way. Instead, said broadest claims are intended to protect the heart or essence of this breakthrough invention. This invention is clearly new and useful. Moreover, it was not obvious to those of ordinary skill in the art at the time it was made, in view of the prior art when considered as a whole. 
     Moreover, in view of the revolutionary nature of this invention, it is clearly a pioneering invention. As such, the claims that follow are entitled to very broad interpretation so as to protect the heart of this invention, as a matter of law. 
     It will thus be seen that the objects set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrated and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.