Abstract:
An image forming apparatus including a sheet feed apparatus configured to sequentially separate sheets stacked on a sheet stacking member. The sheet feed apparatus includes a sheet feed roller configured to come in pressing contact with the uppermost sheet in order to feed the sheet. The sheet feed apparatus also includes a tilt member arranged to oppose the sheet feed roller. The sheet feed apparatus includes a contact face arranged to press against the sheet feed roller. The sheet feed apparatus also includes a tilt face arranged to contact an edge of the uppermost sheet. The tilt face and the contact face are formed from one of polybutylene terephthalate (PBT), polyethylene (PE), metal, poly-ether-ether-ketone (PEEK), and polyimide (PI) to provide superior wear resistance.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present document claims priority to Japanese Patent Application No. 2002-291810 filed in the Japanese Patent Office on Oct. 4, 2001, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet feed apparatus and an image forming apparatus such as a copying machine, a facsimile machine, a printer, or other similar image forming apparatus. 
   2. Discussion of the Background 
   Japanese Patent Laid-Open No. 10-139197 bulletin discloses a sheet feed apparatus that can separate one sheet of a plurality of stacking sheets by contacting each sheet with a tilt face of a tilt member. The sheet feed apparatus includes a separation means. The separation means includes a separation guide as the tilt member, and a high friction member. A coefficient of friction between the high friction member and the sheet is bigger than both a coefficient of friction between the sheet and the separation guide and a coefficient of friction between the sheet and the next sheet in the plurality of sheets. Therefore, one sheet can be conveyed by the separation means from stacking sheets. 
   In conventional systems, a sheet feed apparatus includes a feed roller contacting a tilt member with a separation means. However, in the conventional sheet feed apparatus there is problem in that the surface of the tilt member is easily worn or otherwise damaged when receiving a load by friction caused through contact with the feed roller. Once worn, the sheets are not consistently fed from the sheet feed apparatus, leading to missed pages, jammed pages, or other operational deficiencies. What is desirable, as discovered by the present inventors, is a sheet feed apparatus where the surface of the tilt member is not easily damaged from the friction associated with feeding sheets. 
   SUMMARY OF THE INVENTION 
   An image forming apparatus configured to form an image on a sheet fed from a sheet feeder. The image forming apparatus includes a sheet feed apparatus configured to separate sheets stacked on a sheet stacking member. The sheet feeding apparatus includes a sheet feed roller arranged to come in contact with the uppermost sheet in the sheet stacking member, and a tilt member arranged to oppose the sheet feed roller. The tilt member includes a contact face configured to press against the sheet feed roller, and a tilt face arranged to make contact with an edge of the uppermost sheet. The tilt face and the contact face are formed from at least one of polybutylene perephthalate (PBT), polyethylene (PE), metal, poly-ether-ether-ketone (PEEK), and polyimide (PI). 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  is a diagram of an image forming apparatus including a sheet feed apparatus; 
       FIG. 2  is a diagram of the sheet feed apparatus of  FIG. 1 ; 
       FIG. 3  is a diagram showing the internal construction of the sheet feed apparatus of  FIG. 2 ; 
       FIG. 4  is a diagram showing an enlarged view of  FIG. 3 ; 
       FIG. 5  is a chart of experiment results when different materials are used in the sheet feed apparatus of  FIG. 2 ; 
       FIG. 6  is a diagram of an image forming apparatus including a large paper feed apparatus; 
       FIG. 7  is a diagram a tilt member of the large paper feed apparatus of  FIG. 6 ; 
       FIG. 8  is a diagram showing the internal construction of the large paper feed apparatus of  FIG. 7 ; and 
       FIG. 9  is a chart of experiment results when different materials are used in the tilt member of  FIG. 7 . 
   

   Embodiments of the present invention are described in detail with reference to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is an image forming apparatus of the first embodiment. In this embodiment, a latent image is formed on a photo conductor  35  of an image forming part  34  by a writing device  33  based on an image data read by a reading device  32  above a main body  31 . A toner goes onto the latent image from a developing device  36 , and then a visible image is formed. 
   Below the main body  31 , a sheet feed apparatus  1  is disposed. A sheet feed roller  54  and conveying rollers  7  convey a sheet P through a passage  37  to the photo conductor  35 , and then the visible image transfers the sheet P. 
   The sheet P goes toward a fixing device  38 , and then the fixing device  38  fixes the visible image on the sheet P. Further, output rollers  39  output the sheet P to an output storing tray  40 . On the other hand, in the duplex mode, the sheet P passes a passage  41  to a duplex tray  43  of a duplex device  42 , and then the paper S is switched back. The paper S passes a passage  44  to the image forming part  34  and the fixing device  38 , and then the image is formed on the other side of the sheet S. 
   As shown in  FIG. 2 , the sheet feed apparatus  1  includes a bottom board  51  stacking sheets as a sheet stacking member, a sheet feed roller  54  feeding the sheet on the bottom board  51 , a tilt member  56  having a tilt face  56   a  arranged to touch the edge of the sheet. The sheets are separated in the tilt face  56   a.    
   In this embodiment, the whole tilt member  56  is formed from polybutylene terephthalate (PBT) or polyethylene (PE). It is possible that only the tilt face  56   a  and a contact face  56   b  contacting the sheet feed roller  54  may be formed from PBT or PE. 
   As shown in  FIG. 3 , sheets are received on the bottom board  51  in a sheet feed cassette  61 . The sheet feed cassette  61  is held in a main body  60  of the sheet feed apparatus  1  through a hole  60   b . The bottom board  51  is supported by a compression spring  53  and rotates in the axis  51   a  in the counterclockwise direction as shown in  FIG. 2 . The sheet feed roller  54  contacts the contact face  56   a  pressed by a compression spring  55 . 
   As shown in  FIG. 4 , the tilt member  56  of the first embodiment includes two ribs  56   d  in order to be guided by guiding rails  58  formed in the main body  60 . Therefore, the tilt member  56  can move toward the sheet feed roller  54  straightly. Further, the tilt member  56  includes two hooks  56   f  for limiting the range of the movement. 
     FIG. 5  is a chart of experimental results of different materials used in the sheet feed apparatus of  FIG. 2 . Experiment conditions were as follows:
         Materials of the tilt member—polycarbonate (PC), polybutylene terephthalate (PBT), polyethylene (PE)   A pressing force of the tilt member pushing the sheet feed roller—2.99N   Speed when the sheet feed roller is separating sheets—133.5 mm/sec   Speed after the sheet feed roller is separating the sheets—66.75 mm/sec   A pressing force when the sheet feed roller is feeding sheet—Minimum 3.90N, Max 5.90N   An angle of the tilt side to the sheet—60°   Timing of measuring a wear of the tilt side—0-60000 sheets; every 5000 sheets; 60000-180,000 sheets; 10,000 sheets   Kind of paper—LT size   Interval of experiment—5000 sheets per day   Distance between the contact face  56   a  and a plane face  56   g— 1.36 mm       
   In  FIG. 5 , the line A (1.16 mm) is designated as a non-feed line. The non-feed line is determined empirically as the point where significant non-feeds occur if the material is formed from PC. This line corresponds to 0.2 mm wear from an initial thickness of material. 
   The experiment showed that a tilt member formed from PE or PBT demonstrated superior wear resistance because tilt members made of these materials did not fall bellow the non-feed line L until about 110,000 sheets have been printed. In contrast, a tilt member formed from PC did not demonstrate good wear resistance as the tilt member fell below the non-feed line when about 10,000 sheets were printed. Therefore, experimental results showed that superior performance is achieved if at least the tilt face  56   a  and the contact face  56   b  are formed from PE or PBT. Further analysis showed that the entire tilt member  56  may be formed from either PE or PBT will reduce manufacturing costs. 
     FIG. 6  is a diagram of a second embodiment of an image forming apparatus. The image forming apparatus of the second embodiment includes a large sheet feed apparatus  10  in the right side lower part. The large sheet feed apparatus  10  includes a loading board  23  configured to stack a large number of sheets, a tilt member  56  having a tilt face and a contact face, a sheet feed roller  54  feeding a sheet on the stacking board  23 . The sheets are separated in the tilt face of the tilt member  56 . 
   The image forming apparatus also includes a main body  2 , an automatic document feeder (ADF)  20 , and a finisher  30  having a stapler device  21 . In the lower part of the main body  2 , a paper feed apparatus  22  including plural sheet feed cassettes is disposed. 
   When an image is formed on a one side of a sheet, a sheet is fed from the large sheet feed apparatus  10  or a sheet feed cassette of a sheet feed apparatus  22 . The sheet is conveyed by rollers, and then the sheet reaches a registration roller  3 . Then, an image on a photo conductor  18  is transferred to the sheet by a transfer belt  4 , and then a fixing device  5  fixes the image on the sheet. 
   In one simplex mode of operations (i.e., single-sided copying), the image side of the sheet is input face-up. In this mode of operations, the sheet is conveyed to the left shown in the  FIG. 6 . An entrance sensor  11  detects the image side of the sheet, and an upper divergence nail  19  and a lower divergence nail  8  are not engaged. Then, the sheet is output to the output tray  25  through the finisher  30 . 
   In another simplex mode of operations, the image side of the sheet is input facedown. In this mode of operations, the upper divergence nail  19  and the lower divergence nail  8  each rotate so that the sheet is led to an upper turning-over path  32  or a lower turning-over path  29 . In this mode of operation, either the upper divergence nail  19  or the lower divergence nail  8  may move first. However, the upper divergence nail  19  and the lower divergence nail  8  may move alternately to prevent the sheets from interfering with each other. 
   If the upper divergence nail  19  moves first, the sheet is sent to the upper turning-over path  32 . Then, a switchback roller  13  conveys the sheet. When a turning-over sensor  12  detects an end of the sheet, the switchback roller  13  turns in reverse. Then, the sheet returns to a divergence position and then the sheet is output to the output tray  25  through the finisher  30 . 
   When a second sheet is conveyed immediately behind the first sheet, the lower divergence nail  8  moves. Then, the sheet is sent to the lower turning-over path  29 . Then, the second sheet returns to a divergence position again and the second sheet is output to the output tray  25  through the finisher  30 . In this way, even if sheets are conveyed continually, the sheets do not interfere with each other. 
   In a duplex mode of operations (i.e., two-sided copying), the image forming process is the same as the simplex mode of operations. When a sensor  26  detects a sheet, however, the sensor  26  moves a both-sides divergence nail  6 . After that, the sheet is conveyed to conveyance rollers  15   a  and  15   b . The conveyance rollers  15   a  and  15   b  are connected to motor and the conveyance rollers  15   a  and  15   b  are rotated in reverse. Then, conveyance roller  16  conveys the registration rollers  2 , and an image is formed on the other side of the sheet 
   As shown in  FIGS. 7 and 8 , the tilt member  66  of the second embodiment includes a tilt part  67  and a support part  68 . The tilt part  67  includes a tilt face  67   a  where the sheet contacts the tilt part  67  and a contact face  67   b  contacting the sheet feed roller  54 . The tilt part  67  is formed from a metal or other high durability material. For example, the tilt part  67  is formed from aluminum (Al), poly-ether-ether-ketone (PEEK), polyimide (PI), or an alloy that includes polyimide (PAI). The tilt member  66  also includes a support member  68  that may be formed of the same material as the tilt part  67  or may be formed from a lower-cost material, for example, ABS resin, polyacetal (POM), polybutylene terephthalate (PBT), or polycarbonate (PC). The tilt member  66  includes two ribs  68   a  in order for the tilt member  66  to be guided by guiding rails formed in a main body. Further, the tilt member  66  includes two hooks  68   b  for limiting the range of the movement of the tilt member  66 . 
     FIG. 9  is chart of experimental results of different materials used in the large sheet feed apparatus of  FIG. 6 . In these experiments, conditions were similar to the conditions of the previous experiment except that the tilt member is now formed from one of aluminum (Al), poly-ether-ether-ketone (PEEK), polyimide (PI), or an alloy that includes polyimide (PAI). In  FIG. 9 , the line B is the empirically determined non-feed line corresponding to 0.2 mm wear from the initial thickness. 
   These experiments showed that a tilt member formed from the above-listed material has excellent wear resistance because the tilt member doesn&#39;t fall bellow the non-feed line until about 1,000,000 sheets. Therefore, these experiments show that the second embodiment has better wear resistant than the first embodiment and may be more cost-effective for use in tilt members in high-duty cycle, large sheet feed apparatus. 
   In other embodiments demonstrating excellent wear resistance, a glass fiber or another material can be added to the PBT, PE, Metal, PEEK, or PI. In yet other embodiments, alloys that include PBT, PE, Metal, PEEK, or PI can also be used. 
   It will be obvious to those having skill in the art that many changes may be made in the above-described details of the preferred embodiments of the present invention. The scope of the present invention, therefore, should be determined by the following claims.