Abstract:
An image forming apparatus with an image reading apparatus that may suppress the intensity level of radiated noise from the image reading apparatus in an appropriate manner, without disrupting other functions, etc. The movable image reading apparatus comprises a carriage having a light source adapted to expose an original to light, a photoelectric conversion element, and a drive circuit unit adapted to drive the photoelectric conversion element; and a plurality of guide members adapted to movably guide the carriage. The plurality of guide members are individually earthed to a housing of the image forming apparatus through a plurality of earth contacts.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus with an image reading apparatus, and more particularly, to an image forming apparatus that suppresses noise radiating from an image reading apparatus. 
     2. Description of the Related Art 
     Image reading apparatuses are often connected to a printer or the like and used as one of the components of image forming apparatuses such as copiers or multi-function peripherals (MFPs), although they may be used standalone. 
       FIG. 7  is a top view of an image forming apparatus with an image reading apparatus, wherein components of a movable image reading apparatus  201  are mainly illustrated. In  FIG. 7 , the movable image reading apparatus  201  has a carriage  210 , and the carriage  210  has a lamp  211 , an image sensor  212 , and an image sensor substrate  213 . 
     The lamp  211  serves as a light source that emits light to an original. The emitted light is reflected by the original. Then, the reflected light is incident on the image sensor  212  through a lens or the like (not illustrated). The image sensor  212  includes a photoelectric conversion element such as a line CCD, and it is mounted on the image sensor substrate  213 . The image sensor  212  is driven by an image sensor driving circuit  215  formed in the image sensor substrate  213  (see  FIG. 8 ). 
     The carriage  210  is coupled to a timing belt  221 . The timing belt  221  is rotatably supported by a driving pulley  222  and a driven pulley  223 . The driving pulley  222  is connected via a gear or the like to a rotating shaft of a stepping motor  220 . In addition, the carriage  210  is slidably fitted into a guide shaft  310  and slidably engaged with a guide rail  311 . Further, the guide shaft  310  and the guide rail  311  are mounted on a side surface of the image reading apparatus  201  at a predetermined spaced-apart distance from, and in parallel to, a platen glass formed on the ceiling surface of the image reading apparatus  201 . 
     According to this configuration, the carriage  210  is moved in right and left directions in  FIG. 7  reciprocally along the bottom surface of the platen glass by forward/reverse rotations of the stepping motor  220 , by which the original (information on the original) is exposed and scanned accordingly. In this case, a position sensor  224  senses that the carriage  210  is moved to its home position. Upon sensing, the rotational direction of the stepping motor  220  is reversed. 
       FIG. 8  is a block diagram schematically showing a configuration of the control system of the movable image reading apparatus  201 . The carriage  210  has not only the above-mentioned lamp  211 , image sensor  212 , and image sensor substrate  213 , but also a lamp inverter  217  to turn on the lamp  211 . In addition, an A/D conversion circuit  216  and an image sensor driving circuit  215  (a drive circuit unit) are mounted on the image sensor substrate  213  together with the image sensor  212 . The image sensor  212  photoelectrically converts the image light associated with the original under a drive control of the image sensor driving circuit  215  and outputs as an analog image signal. The analog image signal is converted to a digital image signal by the A/D conversion circuit  216 . 
     The digital image signal is transferred to an image processing substrate  102  (an image processing unit within the image reading apparatus) through a video cable  214 . The video cable  214  includes a flexible flat cable (harness). The image processing substrate  102  is provided with a CPU  151  that controls the image reading apparatus  201 , a RAM  153 , and a ROM  152  that stores program for controlling the image reading apparatus  201 . Between the image processing substrate  102  and the image sensor substrate  213 , for example, signals are transmitted and received through the video cable  214 . In this case, for example, the image processing substrate  102  supplies power from the power source and driving signals for the image sensor  212  to the image sensor substrate  213 . On the other hand, the image sensor substrate  213  outputs, e.g., digitized image signals to the image processing substrate  102 . 
     The image sensor driving circuit  215  supplies to the image sensor  212  a driving clock signal with a high frequency of on the order of 10 MHz to read a signal charge (an image signal) from the image sensor  212 . Supplying such a high-frequency driving clock signal generates noise. The generated noise is radiated from the image sensor substrate  213  or the video cable  214 . The radiated noise has a negative impact on, e.g., electric appliances. 
     Measures for alleviating such radiated noise from the above harness (the video cable  214 ) include a method using a flexible flat video cable with an electrostatic shield (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 02-308667). As described above, providing an electrostatic shield to the video cable  214  could reduce the radiated noise to some extent. 
     However, there has not been achieved sufficient reduction in such radiated noise, because feeble radiated noise leaked from the harness or the substrate provided with such an electrostatic shield is combined with the electrically instable conductive members in vicinity and those conductive members become antennas accordingly, so that radiation efficiency increases. 
     In the image forming apparatus with the above-mentioned image reading apparatus  201 , the guide shaft  310  and the guide rail  311  of the image reading apparatus  201  may serve as the above-mentioned antennas. 
     That is, the guide shaft  310  and the guide rail  311  of the image reading apparatus  201  are earthed by conductive members such as earth lines or sheet metals with a side surface of the housing of the image reading apparatus  201  used as an earth path. The purpose of using a side surface of the housing of the image reading apparatus  201  as an earth path is to allow the carriage  210  to move successfully in an image reading operation. In addition, the housing of the image reading apparatus  201  and the housing of the image forming apparatus  101  are earthed at the rear-end portion of the side surface. 
     However, in such earth connection, as an earth path involves a large number of members, the length of the earth path becomes longer and contains impedance accordingly. As a result, this leads to electrical instability, particularly in higher frequency regions, and increases an intensity level of the radiated noise. 
     Further, in the above-mentioned earth connection, a GND (ground) loop R 101  is formed by the guide shaft  310 , the guide rail  311 , and the conductive members through which the guide shaft  310  and the guide rail  311  are connected to each other (see  FIG. 9 ). The GND loop R 101  serves as a loop antenna so that the intensity level of radiated noise increases at a wavelength corresponding to N and 1/N times the loop length. 
     It is considered, as an approach for reducing the intensity level of radiated noise, to reduce the loop area or the loop current of a GND loop. However, the reduced loop area would lead to reduction in size of readable originals, etc., which would not be considered feasible. In addition, the reduced loop current would lead to decrease in quality of the read images or the like, which would not be considered feasible. 
     SUMMARY OF THE INVENTION 
     The present invention provides an image forming apparatus with an image reading apparatus that may suppress the intensity level of radiated noise from the image reading apparatus in an appropriate manner, without disrupting other functions, etc. 
     In a first aspect of the present invention, there is provided an image forming apparatus with a movable image reading apparatus, the movable image reading apparatus comprising a carriage having a light source adapted to expose an original to light, a photoelectric conversion element, and a drive circuit unit adapted to drive the photoelectric conversion element; and a plurality of guide members adapted to movably guide the carriage, wherein the plurality of guide members are individually earthed to a housing of the image forming apparatus through a plurality of earth contacts. 
     According to the present invention, it is possible to reduce impedance in each earth path associated with each of the guide members and inhibit any loop in earth paths, by providing a plurality of earth contacts adapted to earth a plurality of guide members to the image forming apparatus individually. Accordingly, this allows the intensity level of radiated noise from the image reading apparatus to be reduced in an appropriate manner, without disrupting other functions, etc. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the present invention and, together with the description, serve to explain the principles of the present invention. 
         FIG. 1  is a view schematically showing a configuration of an image forming apparatus according to an embodiment of the present invention, with its image reading apparatus in its closed position. 
         FIG. 2  is a view schematically showing a configuration of the image forming apparatus of  FIG. 1 , with the image reading apparatus in its open position. 
         FIG. 3  is a top view of the image forming apparatus (and image reading apparatus) of  FIG. 1 . 
         FIG. 4  is a conceptual view illustrating the radiated noise from one end of the conductive members. 
         FIG. 5  is a view illustrating an exemplary connection between the guide member of the carriage and one of the conductive members (earth contacts). 
         FIG. 6A  is a view illustrating the length of the guide shaft of the carriage and the length of the conductive members (earth contacts), and  FIG. 6B  is a view illustrating the length of the guide rail of the carriage and the length of the conductive members (earth contacts). 
         FIG. 7  is a top view schematically showing a configuration of a conventional image reading apparatus (and image forming apparatus). 
         FIG. 8  is a block diagram schematically showing a configuration of the control system of the image reading apparatus of  FIG. 7 . 
         FIG. 9  is a view illustrating a GND loop formed on the image reading apparatus of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be now described in detail with reference to the drawings. 
       FIG. 1  is a view schematically showing a configuration of an image forming apparatus according to an embodiment of the present invention, with its image reading apparatus in its closed position.  FIG. 2  is a view schematically showing a configuration of the image forming apparatus of  FIG. 1 , with the image reading apparatus in its opened position.  FIG. 3  is a top view of the image forming apparatus (and image reading apparatus) of  FIG. 1 . 
     As illustrated in  FIGS. 1 and 2 , the image reading apparatus  201  is mounted on the top of the image forming apparatus  101  in an openable and closable manner with a hinge mechanism. Each configuration of the image forming apparatus  101  and the image reading apparatus  201  is basically the same as that conventionally practiced as described earlier ( FIGS. 7 to 9 ). Herein, like reference numerals refer to like elements, and a description will mainly be made to the differences therebetween. 
     The image forming apparatus  101  according to an embodiment of the present invention is different from that conventionally practiced in how the guide shaft  310  and the guide rail  311  of the image reading apparatus  201  is connected to the ground (or earthed). That is, in this embodiment, the guide shaft  310  and the guide rail  311  as guide members are earthed to the image forming apparatus  101  individually, instead of electrically connecting these through conductive members. In this earth connection, conductive members  303   a ,  303   b ,  303   c ,  303   d  are provided on both ends of each of the guide shaft  310  and the guide rail  311 , i.e., the guide members, as earth contacts at the image reading apparatus  201 . 
     Besides, since the guide shaft  310  and the guide rail  311  are slidably moved with the carriage  210  in image reading operations, they include durable metallic members (conductive members) as conventionally practiced. On the contrary, in this embodiment, the housing of the image reading apparatus  201  include non-conductive members for, e.g., reduced costs and weight saving. 
     The purposes of providing the conductive members  303   a ,  303   b ,  303   c ,  303   d  will now be described below. In this embodiment, as described above, since the housing of the image reading apparatus  201  include non-conductive members, the ends of the guide shaft  310  and the guide rail  311  become electrical open ends, respectively. As such, when the ends of the guide shaft  310  and the guide rail  311  corresponding to the conductive members become electrical open ends, as illustrated in  FIG. 4 , a region with a lineal length L 101  serves as a monopole antenna. That is, magnetic lines of force D 101  are generated with respect to the open ends of the guide shaft  310  and the guide rail  311  and radiated noise N 101  in vertical direction is propagated. 
     To this extent, in this embodiment, as earth contacts that prevent the ends of the guide shaft  310  and the guide rail  311  from serving as antennas, the conductive members  303   a ,  303   b ,  303   c ,  303   d  are provided on those ends, respectively. 
     Besides, in this embodiment, each of the conductive members  303   a ,  303   b ,  303   c ,  303   d  include such members in which blade spring  304  is integrally formed therewith and are electrically connected to the ends of the guide shaft  310  and the guide rail  311  through the blade spring  304  (see  FIG. 5 ). However, by way of an example,  FIG. 5  illustrates only a part of the conductive member  303   a.    
     The earth contacts at the image forming apparatus  101  will now be described below. Wire springs  301   a  and  301   b  as earth contacts are arranged at a position, opposed to the conductive members  303   a ,  303   b  connected to the guide shaft  310 , on the side sheet metals that constitute the housing of the image forming apparatus  101 . In addition, coil springs  302   a  and  302   b  as earth contacts are arranged at a position, opposed to the conductive members  303   c  and  303   d  connected to the guide rail  311 , on the upper sheet metal that constitute the housing of the image forming apparatus  101 . The wire springs  301   a ,  301   b  and the coil springs  302   a ,  302   b  are configured as metallic or conductive spring members. 
     That is, in this embodiment, one end of the guide shaft  310  is earthed to the image forming apparatus  101  following a route form the conductive member  303   a  to the wire spring  301   a , while the other end earthed to the image forming apparatus  101  following a route from the conductive member  303   b  to the wire spring  301   b . In addition, one end of the guide rail  311  is earthed to the image forming apparatus  101  following a route from the conductive member  303   c  to the coil spring  302   a , while the other end earthed to the image forming apparatus  101  following a route from the conductive member  303   d  to the coil spring  302   b.    
     In other words, the guide shaft  310  and the guide rail  311  are earthed to the image forming apparatus  101  individually, without being electrically connected through conductive members. This may achieve reduced impedance due to the shorter earth paths associated with the guide shaft  310  and the guide rail  311 , and it may avoid formation of any GND loop including the guide shaft  310  and the guide rail  311 . 
     Accordingly, such reduced impedance in each earth path associated with the guide shaft  310  and the guide rail  311  will also reduce noise currents flowing into the guide shaft  310  and the guide rail  311  as well as the intensity level of any radiated noise. Besides, the coil springs  302   a  and  302   b  may provide a larger contact area with respect to the other members in comparison to the wire springs  301   a  and  301   b . Accordingly, there are provided larger effects of the above-mentioned impedance reduction, i.e., the reduction in the intensity level of the radiated noise, in an earth path associated with the guide rail  311  than in another associated with the guide shaft  310 . 
     In addition, given that formation of any GND loop including the guide shaft  310  and the guide rail  311  may be avoided, the intensity level of the radiated noise may also be reduced. 
     Besides, as described above, in this embodiment, the wire springs  301   a  and  301   b  as earth contacts are mounted on the side sheet metals of the image forming apparatus  101 . Therefore, a user may easily perform such tasks as removing a jammed sheet of recording paper associated from a paper output tray  110  or attaching/removing a fuser, without contact on the earth contacts. In addition, to facilitate these tasks, it is not necessary to provide a larger horizontal width of the image forming apparatus  101  (the width in right and left directions in  FIGS. 1 and 2 ). 
     Referring now to  FIGS. 6A and 6B , each length of the conductive members  303   a ,  303   b ,  303   c ,  303   d  as earth contacts at the image reading apparatus  201  will be described below. 
       FIG. 6A  is a view schematically showing the connection length between the guide shaft  310  and the conductive members  303   a ,  303   b , and  FIG. 6B  is a view schematically showing the connection length between the guide rail  311  and the conductive members  303   c ,  303   d.    
     In the earth path associated with the guide shaft  310 , such a resonance is caused with a frequency with the length L 310  of the guide shaft  310  being a one-half wavelength (λ/2) thereof. Similarly, in the earth path associated with the guide shaft  310 , such a resonance is caused with a frequency with each of the length L 303   a  of the conductive member  303   a  and the length L 303   b  of the conductive member  303   b  being λ/2. Further, in the earth path associated with the guide shaft  310 , a resonance is caused with a frequency with L 310 +L 303   a +L 303   b =length of L 30 , i.e., the entire length of the earth path associated with the guide shaft  310  being λ/2. 
     In addition, in the earth path associated with the guide rail  311 , a resonance is also generated. That is, in the earth path associated with the guide rail  311 , a resonance is caused with a frequency with the length L 311  of the guide rail  311  being one-half wavelength (λ/2). In addition, in the earth path associated with the guide rail  311 , a resonance is caused with a frequency with each of the length L 303   c  of the conductive member  303   c  and the length L 303   d  of the conductive member  303   d  being λ/2. Further, in the earth path associated with the guide rail  311 , a resonance is caused with a frequency with L 311 +L 303   c +L 303   d =length of L 31 , i.e., the entire length of the earth path associated with the guide rail  311  being λ/2. Upon generation of these resonances, there is provided improved antenna efficiency and higher intension levels of the radiated noise. 
     Since the guide shaft  310  and the guide rail  311  are generally supported by side surfaces of the housing of the image reading apparatus  201 , the length of the guide shaft  310  and the guide rail  311  are consistent with the horizontal width of the housing of the image reading apparatus  201 . 
     Consequently, if the length of each of the conductive members is L 303   a =L 303   b =L 303   c =L 303   d =L 303 , then resonances are caused in four positions at the image reading apparatus  201  with a frequency with the length of L 303  being λ/2, which would result in increase in the intensity level of the radiated noise for that frequency. Further, if L 30 =L 31  holds, then resonances are caused at two positions at the image reading apparatus  201  with a frequency with the length being λ/2, which would result in increase in the intensity level of the radiated noise for that frequency. 
     Therefore, in this embodiment, letting L 303   a ≠L 303   b ≠L 303   c ≠L 303   d  and L 30 ≠L 31  enables resonant frequencies to be shifted depending on the length of an earth path of each of the conductive members. Accordingly, shifting the resonant frequencies may avoid generation of resonances with the same frequency in a superimposed manner and reduce the intension level of the radiated noise. 
     In addition, the present invention is not intended to be limited to the above-mentioned embodiments, and the earth contacts according to the embodiments may be applied to other embodiments with, e.g., three and more guide members adapted to guide the travel direction of the carriage  210 . In this case, only one of the spring members may be a coil spring that contacts one of the conductive members associated with one of the guide members near the hinge mechanism to open/close the image reading apparatus, and the other spring members may be wire springs that contact the other conductive members associated with the other guide members. 
     In addition, the earth contacts according to the above-mentioned embodiments may be applied to the case where all guide members are any one of guide shafts or guide rails. 
     Further, other forms of connection than that illustrated in  FIG. 5  may be employed between the conductive members as the earth contacts and the guide members. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions. 
     This application claims priority from Japanese Patent Application No. 2007-154402 filed Jun. 11, 2007, which is hereby incorporated by reference herein in its entirety.