Patent Publication Number: US-8126363-B2

Title: Belt feed apparatus and image forming apparatus using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2008-008967 filed Jan. 18, 2008. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a belt feed apparatus and an image forming apparatus using the belt feed apparatus. 
     2. Related Art 
     In an image forming apparatus of an electro photographic type or a similar type, there is incorporated a belt feed apparatus of a type using a feed belt for electrostatically sucking and feeding a recording member or an intermediate transfer belt for temporarily holding and feeding a toner image. In this type of belt feed apparatus, on the back surface side of a belt member such as the feed belt and intermediate transfer belt, there is provided a belt back surface member serving as a support member for supporting a member such as a transfer member. Especially when reducing the size of the apparatus, the belt back surface member is disposed such that a portion thereof is situated close to the inner peripheral surface of the belt member. 
     SUMMARY 
     According to an aspect of the invention, there is provided a belt feed apparatus, including: 
     an endless belt member that is carried on a plurality of carry members and capable of circulatory motion thereon; 
     a belt back surface member that is disposed on a back surface side of the endless belt member, the belt back surface member including a close portion disposed close to the endless belt member to such a degree that, when the endless belt member stands stationary, the close portion is prevented from touching the endless belt member, and while the endless belt member is circulating, the close portion can be contacted with the endless belt member irregularly; and 
     a non-sticking portion that includes a non-sucking surface contactable with the endless belt member to prevent the endless belt member from being electrostatically sucked to the close portion, the non-sucking surface being provided in an entire portion or part of a surface of the close portion opposed to the endless belt member, and due to the existence of the non-sucking surface, the non-sticking portion being able to prevent the endless belt member from sticking to the close portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1A  is an explanatory view of the outline of an image forming apparatus to which a belt feed apparatus according to a first exemplary embodiment of the present embodiment model of the invention is applied, and  FIG. 1B  is a partially enlarged view of a non-sticking portion formed in a belt back surface member; 
         FIG. 2A  is an explanatory view of the outline of an image forming apparatus to which a belt feed apparatus according to a second exemplary embodiment of the present embodiment model of the invention is applied,  FIG. 2B  is a partially enlarged view of a non-sticking portion and an attitude correcting portion respectively formed in a belt back surface member, and  FIG. 2C  is an explanatory view of the waving movement of a belt member; 
         FIG. 3  is an explanatory view of the outline of an image forming apparatus according to an exemplary embodiment 1; 
         FIG. 4  is an explanatory view of a belt feed apparatus according to the exemplary embodiment 1; 
         FIG. 5A  is a partially enlarged view of the belt feed apparatus, and  FIGS. 5B to 5D  are respectively explanatory views of the specific examples of a non-sticking portion; 
         FIG. 6A  is an explanatory view of a process cartridge replacing method, and  FIG. 6B  is an explanatory view of a method for supplying a recording member, respectively in the image forming apparatus according to the exemplary embodiment 1; 
         FIG. 7  is an explanatory view of a belt feed apparatus according to an exemplary embodiment 2; 
         FIG. 8  is a typical view of a shift mechanism employed in the belt feed apparatus according to the exemplary embodiment 2; 
         FIG. 9A  is a partially enlarged view of the belt feed apparatus according to the exemplary embodiment 2, and  FIGS. 9B to 9D  are respectively explanatory views of the specific examples of a non-sticking portion and an attitude correcting portion; 
         FIG. 10A  is an explanatory view of the circulation operation of a belt in the exemplary embodiment 2, while  FIGS. 10B and 10C  are respectively explanatory views of comparison models; more specifically,  FIG. 10B  shows a case in which a belt member does not wave and  FIG. 10C  shows a case in which the belt member waves; 
         FIG. 11  is an explanatory view of the outline of an image forming apparatus according to an exemplary embodiment 3; 
         FIG. 12  is an explanatory view of a belt feed apparatus according to the exemplary embodiment 3; 
         FIGS. 13A to 13C  are respectively explanatory views of the specific examples of a non-sticking portion according to the exemplary embodiment 3; 
         FIG. 14  is an explanatory view of a belt feed apparatus according to an exemplary embodiment 4; 
         FIG. 15A  shows a specific example of a non-sticking portion used in the exemplary embodiment 4, and  FIG. 15B  is an explanatory view of the position relationship between the non-sticking portion and a detect device; 
         FIG. 16  is a table to show the results of Example 1; and 
         FIG. 17  is a table to show the results of Example 2. 
     
    
    
     DETAILED DESCRIPTION 
     Firstly, description will be given roughly of an embodiment model to which the invention is applied. 
     Summary of the Embodiment Model 
       FIGS. 1A and 1B  show the outline of an image forming apparatus to which there is applied a belt feed apparatus according to a first exemplary embodiment of the embodiment model for embodying the invention. In  FIGS. 1A and 1B , according to the structure of an image forming apparatus according to the present embodiment model, an image hold member  8  (in the present embodiment, two hold members  8   a  and  8   b ) is disposed such that it is opposed to the surface side of a belt member  1  used in the present belt feed apparatus, and, on the back surface side of the belt member  1 , there is disposed a transfer member  9  (in the present embodiment, two transfer members  9   a  and  9   b ) for transferring a toner image on the image hold member  8  at a position opposed to the image hold member  8 . 
     A typical belt feed apparatus applied to the above-structured image forming apparatus, as shown in  FIGS. 1A and 1B , includes: an endless belt member  1  carried on a plurality of carry members  2  ( 2   a ,  2   b ) and capable of circulating thereon; a belt back surface member  3  disposed on the back surface side of the belt member  1  and including a close portion  3 A disposed so close to the belt member  1  that it is prevented from touching the belt member  1  when the belt member  1  stands stationary and can be irregularly contacted with the belt member  1  while it is circulating; and, a non-sticking portion  4  disposed on the back surface side of the belt member  1  and including a non-sucking surface  5  formed in the entire or partial portion of the close portion  3 A of the belt back surfaced member  3  opposed to the belt member  1  and contactable with the belt member  1  to thereby prevent the belt member  1  from being electrostatically sucked to the close portion  3 A, while, owing to the existence of the non-sucking surface  5 , the non-sticking portion  4  is able to prevent the belt member  1  from sticking to the close portion  3 A. Here,  FIG. 1A  shows the schematic structure of the image forming apparatus and  FIG. 1B  is a partially enlarged view of the surface of the close portion  3 A when the close portion  3 A shown in  FIG. 1A  is viewed from the arrow mark E direction. 
     Here, the belt back surface member  3  is disposed on the back surface side of the belt member  1 , for example, in such a manner that it supports a built-in member such as the transfer member  9 . Thus, from the viewpoint of shape stability, mass production and the like, preferably, the belt back surface member  3  may be made of synthetic resin. Also, the term “close position that allows the close portion  3 A to touch the belt member  1  irregularly” means that the belt back surface member  3  includes the close portion  3 A disposed at such distance that allows the belt member  1  to touch the belt back surface member  3  when the circulating belt member  1  flutters or is pressed toward the back surface side thereof. 
     Further, the belt member  1  may be a member which is carried on a plurality of carry members  2  and is able to circulate thereon. Specifically, it may be a feed belt which holds and feeds a recording member, or it may be an intermediate transfer member which holds toner images temporarily and transfers them to a recording member all at once. 
     And, as the non-sticking portion  4 , in order to prevent the belt member  1  and close portion  3 A from sticking to each other, there may be used a portion which include the non-sucking surface  5 . As the non-sucking surface  5  is used to prevent the belt member  1  from sticking to the close portion  3 A of the belt back surface member  3 . Thus, as the non-sucking surface  5 , for example, in order to be able to reduce an electrostatic sucking force with respect to the belt member  1  while circulating, for example, there may be stuck a sheet which provides a small amount of frictional electrification with respect to the belt member  1 , or the surface of the belt back surface member  3  itself may be formed such that the contact area thereof with the belt member  1  is reduced so as to be able to reduce the electrostatic sucking force. 
     In order to reduce an electrostatic sticking force depending on the amount of frictional electrification generated when the belt member  1  rubs against the non-sticking portion  4 , the non-sticking portion  4  may preferably structured in the following manner. 
     That is, the non-sticking portion  4  may be formed integrally with or separately from the close portion  3 A of the belt back surface member  3  and, in the range thereof where it functions as the non-sucking surface  5 , the non-sticking portion  4  may be made of such material that can reduce the frictional electrification amount generated between the belt member  1  and the non-sucking surface  5 . This structure can control the frictional electrification amount itself generated down to a low level. Specifically, when the belt member  1  is made of polyamide-imide system resin, the non-sucking surface  5  may be structured such that a polyurethane system resin sheet member is disposed on the belt back surface member  3 . Here, as the polyurethane system resin sheet member, there may be used a rubber member and a foaming member. 
     Also, in order that the non-sticking portion  4  can reduce its contact area with the belt member  1 , there may be employed the following structure. 
     That is, the non-sucking surface  5  of the non-sticking portion  4  may preferably structured such that it can be contacted with the belt member  1  as a line-shaped contact surface. Owing to this, even when the belt member  1  and belt back surface member  3  are contacted with each other, the contact area thereof can be reduced, thereby being able to reduce an electrostatic sucking force generated between them. 
     Here, according to a typical embodiment which includes a line-shaped contact surface, a plurality of ribs may be provided in the close portion  3 A which respectively project toward the belt member  1 . In this case, the rib may preferably have such a curve-shaped section that the contact portion of the rib with the belt member  1  provides the top portion of the rib. 
     On the other hand, according to a typical embodiment which includes a point-shaped contact surface, in the close portion  3 A, as the non-sucking surface  5 , there may be formed a granulated surface which is formed according to a granulation working such that it has arithmetic mean roughness Ra of 5 μm or more and a ten point mean roughness Rz of 20 μm or more. When the arithmetic mean roughness Ra of the granulated surface is less than 5 μm or when the ten point mean roughness Rz is less than 20 μm, the average spaced distance between the belt member  1  and granulated surface is also small, thereby raising a fear that the belt member  1  can be stuck to the close portion  3 A due to an electrostatic sucking force generated when the belt member  1  rubs against the belt back surface member  3 . Also, when the roughness of the granulated surface is increased, the contact area thereof can be reduced but, in order to reduce the damage of the belt member  1  and facilitate the working of the granulated surface, the arithmetic mean roughness Ra may preferably be 20 μm or less. Here, the arithmetic means roughness Ra and ten point mean roughness Rz are based on JIS B 0601-1994. 
     Generally, the belt member  1  carried on the carry member  2  receives a force in a direction where the belt itself is extended by the carry member  2 , and the waving movements of the belt member  1  are easy to increase on the two end sides thereof in the width direction thereof perpendicular to the circulating direction of the belt member  1 . Thus, in an image forming apparatus to which a belt feed apparatus according to a second exemplary embodiment of the present embodiment model is applied, the waving movement of the belt member  1  is taken into consideration. 
     That is, as shown in  FIGS. 2A and 2B , the image forming apparatus includes an image hold member  8  ( 8   a ,  8   b ) for holding a toner image and a belt feed apparatus in which an endless belt member  1  is disposed opposed to the image hold member  8  and is allowed to circulate. Specifically, the present belt feed apparatus includes: the endless belt member  1  carried on a plurality of carry members  2  ( 2   a ,  2   b ) and capable of circulating thereon; a belt back surface member  3  disposed on the back surface side of the belt member  1  and including a close portion  3 A, the close portion  3 A being disposed such that, when the belt member  1  stands stationary, it is prevented from touching the belt member  1  and also such that, while the belt member  1  is circulating, it exists so close to the belt member  1  as to be contactable with the belt member  1  irregularly; a non-sticking portion  4  including a non-sucking surface  5  formed in a portion of such surface of the close portion  3 A of the belt back surface member  3  as opposed to the belt member  1 , the non-sucking surface  5  being contactable with the belt member  1  to thereby prevent the belt member  1  against its electrostatic suction to the close portion  3 A, and the non-sticking portion  4 , owing to the existence of the non-sucking surface  5 , capable of preventing the belt member  1  from sticking to the close portion  3 A; and, an attitude correcting portion  6  including two sucking surfaces  7  respectively formed in the other portions of the non-sticking portion  4  than the non-sucking surface  5  on the two sides thereof in the width direction perpendicular to the circulating direction of the belt member  1  and easier to suck electrostatically the belt member  1  than the non-sucking surface  5 , while the attitude correcting portion  6 , owing to existence of the sucking surfaces  7 , is capable of electrostatically sucking and moving the width-direction two side portions of the belt member  1  in a direction to move away from the image hold member  8  in a state where the width-direction two side portions are not electrostatically sucked to the sucking surfaces  7 , thereby correcting the circulatory feed attitude of the belt member  1 . Here,  FIG. 2A  shows the schematic structure of the image forming apparatus to which the belt feed apparatus according to the second exemplary embodiment is applied, and  FIG. 2B  is a partially enlarged view of the surface of the close portion  3 A shown in  FIG. 2A  when the close portion  3 A is viewed from the arrow mark F direction. 
     Especially, the belt feed apparatus according to the second exemplary embodiment is suitable for use in an image forming apparatus including a shift mechanism capable of shifting the belt member  1  between a contact position where the belt member  1  is contacted with all of the image hold members ( 8   a ,  8   b ) and a spaced position where the belt member  1  is contacted with one image hold member  8   a  and is spaced from the other remaining image hold member  8   b.    
     In other words, as shown in  FIG. 2C , when the thin belt member  1  is carried on the carry members  2  and is allowed to circulate thereon, in some cases, the width-direction two end portions of the thus carried belt member  1  can be waved. In a structure in which the image hold member  8  is disposed opposed to the belt member  1  and, especially, in a structure in which the image hold member  8  is disposed close to the belt member  1  (for example, in a structure in which the image hold member  8  is disposed close to the transfer portion; or, in a structure in which the image hold member  8  includes a plurality of image hold members  8 , with respect to an image holder  8  which is disposed spaced from the belt member  1 ), such waving motion of the belt member  1  raises a possibility that, while the belt member  1  is circulating, the waved portion of the belt member  1  can be contacted with the image hold member  8 . In order to prevent such unnecessary contact of the belt member  1  with the image hold member  8 , preferably, the belt member  1  may be prevented from sticking to the close portion  3 A of the belt back surface member  3  and the attitude of the belt member  1  may be corrected to thereby prevent the waving motion of the belt member  1 . 
     Specifically, in a portion of the close portion  3 A of the belt back surface member  3 , there may be provided a non-sticking portion  4  having a non-sucking surface  5  which is prevented from being sucked electrostatically to the belt member  1 ; and, in the portions of the belt back surface member  3  that exist outside the non-sucking surface  5  of the non-sticking portion  4 , there may be provided two attitude correcting portions  6  each including a sucking portion  7  capable of electrostatically sucking and moving the belt member  1  in a state where the belt member  1  is not sucked electrostatically to the close portion  3 A. That is, owing to the operations of these two portions, there can be realized an image forming apparatus which not only can prevent the waving motion of the belt member  1  but also can prevent the belt member  1  from sticking to the close portion  3 A. Here,  FIG. 2C  is a section view taken along the c-c line shown in  FIG. 2A . 
     And, as a typical embodiment of the above-structured image forming apparatus, there can be provided an image forming apparatus which, when forming images such as a monochrome image and a color image different in mode from each other, can switch the mode by shifting the belt member  1  using a shift mechanism. 
     Next, description will be given below in more detail of the influence of the belt member  1  when switching the mode in this manner. Here, it is assumed that, as shown in  FIG. 2C , the belt member  1  is waving in the width-direction two end portions thereof, while a non-sucking surface  5  is provided in a portion of the close portion  3 A of the belt back surface member  3  and a sucking surface  7  is provided outside the non-sucking surface  5 . As shown in  FIG. 2A , when, as an image forming apparatus, the belt member  1  is contacted with a plurality of image hold members  8  ( 8   a ,  8   b ), the belt member  1  is held by the image hold members  8 ; or, when, as the transfer members  9  ( 9   a ,  9   b ), there are used roller-shaped members, the belt member  1  is held by and between the image hold members  8  and transfer members  9  disposed opposed to the image hold members  8  from the back surface side of the belt member  1 . Therefore, generation of poor images does not provide any special big problem. 
     However, when there exists an image hold member  8  (in the present embodiment,  8   b ) which is spaced from the belt member  1 , depending on the spaced distance thereof, there is a possibility that the waved portion of the belt member  1  can be contacted with the image hold member  8   b . Especially, when there is employed a system which, when shifting the belt member  1  carried on the carry members  2  ( 2   a ,  2   b ) using a shift mechanism, the belt member  1  is moved away from the image hold member  8   b  while the belt member  1  remains in contact with one of the image hold member  8   a , the shift mechanism for shifting the belt member  1  can be itself simplified but it is difficult to secure a large spaced distance, thereby raising a fear that the waved portion of the belt member  1  can be contacted with the image hold member  8   b  to cause a defective image. 
     On the other hand, according to the present embodiment model, since such portion of the close portion  3 A of the belt back surface member  3  as corresponds to the waved portion of the belt member  1  provides the sucking surface  7 , the belt back surface  3  and belt member  1  can be electrified due to their mutual friction; and, when the belt member  1  is frictionally electrified once, an electrostatic sucking force is applied to the belt back surface member  3  side of the belt member  1 , whereby the waved portion of the belt member  1  is pulled toward the belt back surface member  3 . As a result of this, the waving motion of the belt member  1  is controlled and thus the attitude of the belt member  1  is corrected, whereby, even when the spaced distance between the belt member  1  and image holder  8   b  is small, the belt member  1  can be prevented against contact with the image hold member  8   b.    
     In this embodiment, the non-sucking surface  5  may only be structured such that the belt member  1  can be prevented from sticking to the close portion  3 A as a whole. For example, the non-sucking surface  5  may also be disposed near to the width-direction center of the close portion  3 A. 
     Also, although the sucking surface  7  is not limited to any specific surface, from the viewpoint of simplifying the structure, as the sucking surface  7 , preferably, there may be used a flat and smooth surface which is flat and smooth to such a degree that, due to an electrostatic sucking force generated due to friction between the belt member  1  and sucking surface  7 , the belt member  1  can be sucked and moved electrostatically in a state where the belt member  1  is not electrostatically sucked to the image hold member  8   b . Here, in the image forming apparatus to which the belt feed apparatus according to the second exemplary embodiment is applied, the non-sucking surface  5  of the non-sticking portion  4  is similar to the first exemplary embodiment and thus the description thereof is omitted here. 
     And, in an embodiment in which the belt member  1  is an intermediate transfer member, when there is provided a detect member which is used to detect the density of a toner image on the intermediate transfer member, preferably, the detect member may be disposed such that it corresponds to the area of the non-sucking surface  5 . According to this structure, the toner image on the belt member  1  can be detected in the less fluttering portion of the belt member  1 , thereby being able to enhance the accuracy of the image detection. 
     Now, description will be given below in more detail of the invention with reference to the embodiments thereof respectively shown in the accompanying drawings. 
     Exemplary Embodiment 1 
       FIG. 3  shows an image forming apparatus according to an exemplary embodiment 1 to which the belt feed apparatus according to the first exemplary embodiment of the present embodiment model. In  FIG. 3 , the image forming apparatus according to the present embodiment is structured in the following manner: that is, in the lower portion of an apparatus casing  10 , there is disposed a recording member supply unit  11  for supplying a recording member in such a manner that the unit  11  can be pulled out; and, upwardly of the recording member supply unit  11 , there are arranged image forming engines  20  ( 20   a ˜ 20   d ) respectively for forming four colors, namely, yellow (Y), magenta (M), cyan (C) and black (K) toner images on the recording member in such a manner that the respective engines  20  extend linearly in the vertical direction. 
     Also, upwardly of these image forming engines  20 , there is disposed a fixing device  14  for fixing toner images formed on the recording member by the image forming engines  20 . Further, the apparatus casing  10  includes, in a portion of the upper surface thereof, a recording member storage portion  10   a  into which the recording member fixed by the fixing device  14  is discharged and stored from the apparatus casing  10 . 
     Further, in a position which exists between the recording member supply unit  11  and fixing device  14  within the apparatus casing  10  and is opposed to the four image forming engines  20   a ˜ 20   d , there is disposed a belt feed apparatus  30  which is structured such that it electrostatically sucks and feeds the recording member and can detach it in a given detach portion. 
     The image forming engine  20  according to the present embodiment includes a process cartridge  21  capable of forming the respective colors toner images, a laser exposure device  24  for forming an electrostatic latent image on a sensitive member  22  disposed in the rear of the process cartridge  21  for holding therein the toner images formed by the process cartridge  21 , and a transfer roller  27  disposed at a position existing within the process cartridge  21  and opposed to the sensitive member  22 . Here, at positions which exist within the process cartridge  21  and in the periphery of the sensitive member  22 , there are disposed a charging roller  23  for charging the sensitive member  22 , a toner supply roller  26  for supplying a toner to developing rollers  25  and  26  which are used to develop electrostatic latent images formed on the sensitive member  22  into visible images, and the like. 
     Also, the recording member supply unit  11  according to the present embodiment includes a supply cassette  11   a  in which there can be stored recording members that can be supplied therefrom. And, in the vicinity of the recording member feed direction downstream side end portion of the supply cassette  11   a , there is provided a handling mechanism  12  which is used to handle and send out the recording members one by one from the supply cassette  11   a . According to the handling mechanism  12 , the recording members sent out from the supply cassette  11   a  using a pickup roller  12  are handled through the cooperative operations of the feed roller  12   b  and retard roller  12   c , and only the top one of the recording members is sent out to the downstream side. 
     And, on the upstream side of the belt feed apparatus  30 , there is disposed a registration roller  13  which registers the positioning of the recording member being fed once and, after then, feeds the thus position-registered recording member to the belt feed apparatus  30  at a given timing. 
     On the other hand, the fixing device  14  includes, for example, a heating roller  14   a  and a pressurizing roller  14   b  and is structured such that it can carry out the fixation of the toner images sufficiently. Also, on the recording medium feed direction downstream side of the fixing device  14 , there is provided a discharge roller  15  which is disposed opposed to the opening of the apparatus casing  10  and is used to discharge the recording members onto the recording member storage portion  10   a . Here, the discharge roller  15  is to be reversed as the need arises in order to be able to form images on both sides of the recording member. 
     Also, a recording member feed passage according to the present embodiment includes: a normal feed passage  41  in which the recording member supplied from the supply cassette  11   a  is fed through the registration roller  13 , belt feed apparatus  30  and fixing device  30  to the discharge roller  15 ; and, a reversal feed passage  42  in which the recording member reversed by the discharge roller  15  is fed from the discharge roller  15  through a different passage from the normal feed passage  41  to the registration roller  13 . 
     Also, according to the present embodiment, a portion of the reversal feed passage  42  is formed in the inside of the recording member supply unit  11  as well. Here, in both of the normal feed passage  41  and reversal feed passage  42 , there are properly provided feed members (such as a feed roller and a feed guide) which are used to secure the feeding operation of the recording member. 
     Next, description will be given below of the belt feed apparatus  30  according to the present embodiment. 
     As shown in  FIG. 4 , the belt feed apparatus  30 , which is disposed opposed to the sensitive members  22  ( 22   a ˜ 22   d ), includes: a feed belt  31  carried on two carry rollers  32  and  33  and capable of circulating thereon in such a manner that it is driven by, for example, the carry roller  33  which is disposed upwardly, that is, disposed on the downstream side in the feed direction of the recording member, the feed belt  31  being made of, for example, polyamide-imide system resin and serving as an endless belt member; a support frame member  35  serving as a synthetic-resin-made belt back surface member provided on the back surface side of the feed belt  31  for supporting, for example, transfer rollers  27  ( 27   a ˜ 27   d ); a charging device  34  disposed opposed to the carry roller  32  with the feed belt  31  between them for electrostatically sucking the recording member onto the feed belt  31 , the carry roller  32  being disposed on the recording member feeding surface of the feed belt  31  on the upstream side in the recording member feed direction; and, a cleaning member  36  which is provided on the recording member non-feeding surface of the feed belt  31  at a position more downstream in the circulating direction of the feed belt  31  than the carry roller  33  so as to press the feed belt  31  toward the support member  35  and is also used to clean the surface of the feed belt  31 . Also, according to the present embodiment, the belt feed apparatus  30  further includes the transfer rollers  27 . 
     Here, the charging device  34  is structured such that a given charging bias can be applied from a bias power supply (not shown) into between the charging device  34  and the carry roller  32  grounded as a backup roller to provide a proper electrostatic sucking property for the feed belt  31 , thereby allowing the feed belt  31  to start its recording member feeding operation. 
     On the other hand, the support frame member  35 , which is provided on the back surface side of the feed belt  31 , is made of a member produced by injection molding a polymer alloy of, for example, polycarbonate resin and ABS resin. And, the support frame member  35  includes, in its downstream side portion adjoining the transfer rollers  27 , a surface side projecting surface  35 A projecting close to the inner peripheral surface of the recording member feed surface of the feed belt  31  and, in its portion corresponding to the transfer rollers  27  and in its upstream side portion adjoining the transfer rollers  27 , a back surface side projecting surface  35 B (which corresponds to the close portion) projecting toward the recording member non-feed surface side of the feed belt  31 . Here, on the upstream side of the most-upstream transfer roller  27   a  and on the downstream side of the most-downstream side transfer roller  27   d , in order to reduce the size of the belt feed apparatus  30 , there are not provided such projecting surfaces. 
     And, especially, according to the present embodiment, as shown in  FIG. 5A , of the back surface side projecting surface  35 B of the support frame member  35 , at the close position (in  FIG. 5A , an area shown by α) of the cleaning member  36 , the belt member  31  is made to be closest to the back surface side projecting surface  35 B by the cleaning member  36 . Owing to this, over the entire feed belt width direction area of the back surface side projecting surface  35 B, there is formed a non-sticking portion which can prevent the feed belt  31  from sticking to the support frame member  35  due to an electrostatic sucking force generated between the support frame member  35  and feed belt  31  when the feed belt  31  is contacted with and rubbed against the support frame member  35 ; and, as the non-sucking surface of the non-sticking portion, there is attached a sheet  37  which is made of polyurethane system resin (see  FIG. 5B ). Here, the lower portion of  FIG. 5B  is a front view of the back surface side projecting portion  35 B when it is viewed from the arrow mark D direction, while the upper portion of  FIG. 5B  is a plan view thereof. 
     In other words, according to the present embodiment, the support frame member  35  corresponds to a belt back surface member; and, in order to reduce the size of the belt feed apparatus  30 , the feed belt  31  and a portion of the support frame member  35  are disposed close to each other, and the distance between them is set such that they can be contacted with each other while the feed belt  31  is circulating. 
     Next, description will be given below of the operations of the support frame member  35  and feed belt  31  in the thus structured belt feed apparatus  30 . In the belt feed apparatus  30  shown in  FIG. 5A , since the cleaning member  36  presses the feed belt  31  toward the support frame member  35 , the feed belt  31  is further easier to come into contact with the support frame member  35 . Especially, such phenomenon is easy to occur after the feed belt  31  has been used for a long period of time, or depending on the precision of parts, the assembling precision of the apparatus and the environmental condition thereof. In this case, when the support frame member  35  and feed belt  31  rub against each other and a difference between their mutual charging systems is large, both of them are easy to be charged frictionally, thereby generating a large electrostatic sucking force between them. Especially, as in the present embodiment, when the support frame member  35  is made of synthetic resin, the part precision and mass production performance are both excellent but the influences of the frictional electrification are outstandingly large when compared with the support frame member  35  is made of metal. 
     And, when such electrostatic sucking force is generated, the feed belt  31  is easy to stick to the support frame member  35 . When the feed belt  31  sticks to the support frame member  15  at a position once, the portion of the feed belt  31  existing in the vicinity of such position is also pulled toward the support frame member  35  and thus such sticking tends to increase. As a result of this, the circulatory movement of the feed belt  31  can be made unstable, which can end up stopping the circulatory movement of the feed belt  31 . 
     In view of this, as in the present embodiment, when the sheet  37  is stuck to the portion of the support frame member  35  corresponding to the easy-to-stick portion of the feed belt  31 , in this portion, the feed belt  31  is prevented against direct contact with the support frame member  35  and the feed belt  31  can be selectively contacted with the sheet  37 . In this case, the amount of frictional electrification generated between the feed belt  31  made of polyamide-imide system resin and the sheet  37  made of polyurethane resin is small (which results from the fact that their mutual electrifying systems are close to each other). This can reduce a force which electrostatically sucks the feed belt  31  toward the sheet  37 , thereby being able to prevent the sticking of the feed belt  31 . That is, since the sheet  37  stuck portion of the support frame member  35  functions as a non-sucking surface, the above effect can be provided. This can secure the stabilized circulatory motion of the feed belt  31 . In other words, according to the present embodiment, the portion where the sheet  37  is stuck can function as the non-sticking portion of the support frame member  35 . 
     Also, according to the present embodiment, as shown in  FIG. 5B , the sheet  37  is stuck over the entire area of the support frame member  35  in the width direction thereof perpendicular to the circulating direction of the feed belt  31 . However, the sheet  37  may also be stuck selectively to other portion of the support frame member  35  that can be contacted with the feed belt  31 . Also, the sheet  37  may also be stuck over the entire area of the back surface side projecting surface  35 B. Further, when there is a possibility that the surface side projecting surface  35 A can be contacted with the feed belt  31 , the sheet  37  may also be stuck to the surface side projecting surface  35 A. Here, as the sheet  37 , there may be selected a material which has an electrifying system close to the material of the feed belt  31 , and the selected material may be stuck to the support frame  35 . Also, when the material of the sheet  37  is the same as the material of the support frame member  35 , since the frictional electrification need not be taken into account, the support frame member  35  itself may be disposed further closer to the feed belt  31 . 
     In the above embodiment, as a non-sticking portion, there is illustrated an example in which the sheet  37  is stuck to the support frame member  35 . However, the non-sticking portion is not limited to this but other means may also be employed. That is, even when the feed belt  31  comes to rub against the support frame member  35 , if the contact area thereof is reduced, the amount of frictional electrification itself can be reduced, thereby being able to prevent the sticking of the feed belt  31 . 
       FIGS. 5C and 5D  respectively show the examples of the above-mentioned non-sticking portions. Specifically, in an example shown in  FIG. 5C , as the non-sucking surface, there are provided a plurality of ribs  38  which are respectively formed on the back surface side projecting surface  35 B respectively extending along the circulating direction of the feed belt  31  simultaneously when the support frame member  35  is produced. In this example, the ribs  38  are respectively made of projections which extend in the feed belt circulating direction and each of which has a substantially semicircular-shaped section. In this case, even when the feed belt  31  comes to touch the support frame member  35 , the feed belt  31  are actually contacted with the top portions of these ribs  38  and thus the contact surfaces thereof provide linear contact surfaces, so that the contact area thereof itself is very small. Therefore, even when the ribs  38  and feed belt  31  rub against each other, the amount of frictional electrification generated in the mutual rubbing portions can be controlled to a very small amount, which can prevent the feedbelt  31  from sticking to the support frame member  35 . Here, the shape of the rib  38  is not limited to this, but, in order to keep the circulatory movement of the feed belt  31  in a good condition, preferably, the rib  38  may have a component which extends along the feed belt circulating direction. Also, according to the present example, there is used a rib which has a height of 1 mm. However, this is not limitative but, normally, there may be used a rib having a height of 0.2 mm or more. 
     Also,  FIG. 5D  shows an example in which as a non-sucking surface, a granulated surface  39 , which can be produced by granulation working, is provided on the back surface side projecting surface  35 B. The granulation working is a working in which, normally, a blasting processing for blasting blast material is enforced on a forming mold or a chemical etching processing is enforced on a forming mold to thereby form an uneven surface, and the uneven surface is used to provide a large number of micro projections. Owing to this, the contact surfaces of the support frame member  35  to be contacted with the feed belt  31  provide dot-like contact surfaces, whereby the contact area thereof is very small. This can reduce the frictional electrification amount between these two members, thereby being able to prevent the feed belt  31  from sticking to the support frame member  35 . Here, in the present example, as the granulation surface  39 , there is used a granulation surface which has an arithmetic mean roughness Ra of 8 μm. However, this is not limitative but there may also be used a granulation surface which has an arithmetic mean roughness Ra of 5 μm or more or a ten point mean roughness Rz of 20 μm or more. 
     In other words, according to these examples, the area of the support frame member  35 , where the ribs  38  or granulation surface  39  are formed, function as the non-sucking surface of the support frame member  35 . 
     Next, description will be given below of a method for replacing the process cartridge  21  and a method for supplying the recording member to the recording member supply unit  11  in the above-structured image forming apparatus. 
       FIG. 6A  shows a state in which the main body cover  10   b  provided on the apparatus casing  10  is opened from the apparatus casing  10 . On the main body cover  10   b , there are integrally mounted a portion of a reversal feed passage  42  and the belt feed apparatus  30  respectively by their associated brackets (not shown) or the like and, when the main body cover  10   b  is opened, they are moved with the opening movement of the main body cover  10   b . Also, the main body cover  10   b  is structured such that it can be opened in the arrow mark “A” direction with a support shaft  50 , which is provided on the lower portion of the apparatus casing  10 , as a pivot thereof. Owing to this structure, when the main body cover  10   b  is opened, for example, as shown in  FIG. 6A , the process cartridge  21  (which, in the present embodiment, corresponds to the process cartridge of the image forming engine  20   c ) can be pulled out easily in the arrow mark “B” direction. 
     Also,  FIG. 6B  shows a state in which the recording member supply unit  11  provided on the lower portion of the apparatus casing  10  is pulled out from the apparatus casing  10  in the arrow mark “C” direction. Normally, in a state where the recording member supply unit  11  is pulled out from the apparatus casing  10 , the recording member is supplied. Owing to this, it is possible to realize an image forming apparatus which is excellent in maintenance and is reduced in size. 
     Exemplary Embodiment 2 
       FIG. 7  shows an image forming apparatus according to a second exemplary embodiment to which the belt feed apparatus according to the second exemplary embodiment is applied. The image forming apparatus according to the present embodiment is structured substantially similarly to the exemplary embodiment 1 and the belt feed apparatus  30  is also structured substantially similarly. However, the belt feed apparatus  30  according to the exemplary embodiment 2 is different from the belt feed apparatus  30  according to the exemplary embodiment 1 in that it has a so called retractable structure in which the feed belt  31  is shifted in position between the monochrome image forming time and the color image forming time. 
     The belt feed apparatus  30  in the color image forming time according to the present embodiment is similar in structure to the exemplary embodiment 1 (see  FIG. 4 ). Thus, description thereof is omitted here and description will be given below of the operation of the belt feed apparatus  30  in the monochrome image forming time. In the monochrome image forming time, as shown in  FIG. 7 , the feed belt  31  is spaced from three sensitive members  22   a ˜ 22   c . In other words, the feed belt  31  according to the present embodiment, in the monochrome image forming time, is contacted with only the most-downstream side sensitive member  22   d  and is spaced from the remaining sensitive members  22   a ˜ 22   c.    
     According to the present embodiment, a shift mechanism for shifting the feed belt  31  is structured as shown in  FIG. 8 . Here,  FIG. 8  is a typical view of the structure of the shift mechanism of the belt feed apparatus  30  and, for easy understanding, in  FIG. 8 , a shift amount is expressed in an enlarged manner. 
     In  FIG. 8 , the belt feed apparatus  30  according to the present embodiment is structured such that, for example, the upstream side carry roller  32  can be wholly rotated in the arrow mark “G” direction, which is a direction where the roller  32  moves away from the sensitive members  22 , about the rotation shaft  33   a  of the most-downstream side (in  FIG. 8 , the upwardly situated side) carry roller  33 . When the carry roller  32  is rotated in this manner, together with this rotation, the respective transfer rollers  27   a ˜ 27   d  are also moved together with a support frame member (not shown); however, since the transfer rollers  27  respectively include energizing members  28  which energize the transfer rollers  27  toward the feed belt  31 , to the transfer rollers  27 , there are applied forces which press them outwardly with respect to the feed belt  31 . Therefore, the position of the transfer roller  27   d , which has a small shift amount, is held substantially at the same position thereof before it is spaced. As a result of this, the transfer portions of the three upstream side transfer rollers  27   a ˜ 27   c  are held at positions spaced from their corresponding sensitive members  22  ( 22   a ˜ 22   c ), whereas the most-downstream side transfer roller  27   d  can be held in a state where it is disposed opposed to the sensitive member  22   d . This makes it possible to form a monochrome image on the recording member. 
     In the image forming apparatus of this type, when the feed belt  31  is spaced from the three upstream side sensitive members  22   a ˜ 22   c , the sensitive member  22   c , which is situated on the most downstream side of the three sensitive members  22   a ˜ 22   c , provides the narrowest spacing distance with respect to the feed belt  31 . In this case, when the feed belt  31  itself waves in the width-direction two end portions thereof, the waving end portions are easiest to come into contact with the sensitive member  22  having the narrowest spacing distance. 
     Such contact raises no problem when the feed belt  31  is spaced greatly from the sensitive members  22 . However, in order to reduce the size of the apparatus and simplify the shift mechanism, the spacing distance must be controlled to a small distance, which makes it necessary to take measures with respect to the waving movement of the feed belt  31 . 
     According to the present embodiment, as the measures against the waving movement of the feed belt  31 , there is employed the following structure. That is, as shown in  FIGS. 9A and 9B , the surface side projecting surface  35 A of the support frame member  35  provided on the back surface side of the feed belt  31  is disposed close to the inner peripheral surface of the feed belt  31  with a clearance of approx. 1 mm or less between them. To a portion of the surface side projecting surface  35 A (in the present example, a portion which exists near to the width-direction center thereof), there is stuck a sheet  37  which is similar to the embodiment 1; and, the surfaces of other areas of the surface side projecting surface  35 A than the sheet sticking area are respectively formed as a flat and smooth surface  40  the surface of which is flat and smooth. In other words, the area with the sheet  37  stuck thereto provides a non-sticking portion having a non-sucking surface thereon, while the two flat and smooth surfaces  40  on both sides of the non-sticking portion respectively provide an attitude correcting portion which has a sucking surface. Here, the lower section of  FIG. 9B  is a front view of the support frame member  35  when it is viewed from the arrow mark “H” direction, whereas the upper section of  FIG. 9B  is a plan view of the support frame member  35 . Also, the flat and smooth surface  40  is set to have an arithmetic mean roughness Ra of less than 5 μm. 
     Next, description will be given below of the circulation locus of the feed belt  31  according to the present embodiment. 
       FIG. 10A  shows the attitude of the feed belt  31  in the width direction thereof according to the present embodiment. In  FIG. 10A , to the surface side projecting surface  35 A of the support frame member  35 , there is stuck a sheet  37  at a position near to the center of the projecting surface  35 A; and, on both sides of the sheet  37 , there are formed flat and smooth surfaces  40  respectively. 
     According to this structure, when the feed belt  31  is contacted with the surface side projecting surface  35 A to rub against it, since this portion provides a small frictional electrification amount, in the near-to-center portion of the projecting surface  35 A, a force for electrostatically sucking the feed belt  31  toward the surface side projecting surface  35  is small, so that the circulation locus of the feed belt  31  becomes stable. Also, in the flat and smooth surfaces  40 , even when it rubs against the feed belt  31  due to the waving movement of the feed belt  31 , the amount of frictional electrification generated here remains in the flat and smooth surfaces  40  and thus it acts as a force for electrostatically sucking the feed belt  31  passing here in such a manner that the feed belt  31  is not sucked to the surface side projecting surface  35 A electrostatically, thereby electrostatically sucking and moving the feed belt  31  toward the flat and smooth surfaces  40 . This can control the waving movement of the feed belt  31  and, even when the spacing distance between the feed belt  31  and sensitive members  22  is narrow, the feed belt  31  can be prevented against contact with the surfaces of the sensitive members  22 . 
     In other words, according to the present embodiment, the sheet  37  stuck portion of the surface side projecting surface  35 A near to the feed belt  31  acts as the non-sucking surface to thereby reduce the electrostatic sucking force and thus secure the performance of the non-sticking portion. On the other hand, since the flat and smooth surfaces  40  act as a sucking surface, it acts as the attitude correcting portion to apply a force in a direction to control the waving movement of the feed belt  31 . As a result of this, the circulation locus of the feed belt  31  can be stabilized and ill influences due to the waving movement of the feed belt  31  can also be reduced. 
     Assuming that, as shown in  FIG. 10B , the feed belt  31  does not wave, there is not caused a problem that the feed belt  31  is contacted with the sensitive members  22 . However, when the non-sucking surface is not provided on the surface side projecting surface  35 A, there is raised a problem that the feed belt  31  can stick to the surface side projecting surface  35 A. On the other hand, as shown in  FIG. 10C , when the feed belt  31  waves, the waving portion of the feed belt  31  can be contacted with the sensitive members  22 . Also, if the non-sucking surface is not provided on the surface side projecting surface  35 A, when the feed belt  31  rubs against the surface side projecting surface  35 A, the amount of frictional electrification caused by such rubbing action is excessively large, so that, although there is applied a force for restricting the waving movement of the feed belt  31 , the circulation locus of the feed belt  31  is impaired. 
     According to the present embodiment, as shown in  FIG. 10A , the sheet  37  is stuck to the near-to-center portion of the surface side projecting surface  35 A to provide the non-sucking surface, and both sides of the sheet  37  are formed as the flat and smooth surfaces  40  which function as the sucking surface, thereby being able to satisfy the conflicting actions: that is, not only the circulation locus of the feed belt  31  is not impaired, but also the waving movement of the feed belt  31  can be controlled. 
     Here, as the non-sucking surface, there is shown an example in which the sheet  37  is stuck to the surface side projecting surface  35 A. However, instead of sticking the sheet  37 , similarly to the exemplary embodiment 1, there may also be provided such ribs  38  as shown in  FIG. 9C . Also, when there is formed such granulated surface  39  as shown in  FIG. 9D , there can be provided a similar effect. However, when the ribs  38  or granulated surface  39  are used, of course, both sides of them must be formed as the flat and smooth surfaces  40 . 
     Exemplary Embodiment 3 
       FIG. 11  shows an exemplary embodiment 3 of an image forming apparatus which employs a belt feed apparatus different from those used in the exemplary embodiments 1 and 2. 
     A belt feed apparatus  300  according to the present embodiment is different from the belt feed apparatus  30  according to the exemplary embodiment 1 (see, for example,  FIG. 3 ) in that, instead of the feed belt, it uses an intermediate transfer belt  310  for holding a toner image temporarily and then feeding it. Here, in the exemplary embodiment 3, the same composing elements thereof as those used in the exemplary embodiment 1 are given the same designations and thus the detailed description thereof is omitted here. 
     In  FIG. 11 , an image forming apparatus according to the present embodiment is structured in the following manner: that is, the belt feed apparatus  300  is not formed to suck and feed a recording member but it includes an intermediate transfer belt  310  which is carried on a plurality of (in the present embodiment, three) carry rollers  320 ,  330 ,  340  and is allowed to circulate in the arrow mark direction. In this case, at a position that is opposed to the carry roller  340  with the intermediate transfer belt  310  between them, there is provided a secondary transfer roller  360  with the carry roller  340  as its backup roller; and, when a given secondary transfer bias is applied between them, toner images on the intermediate transfer belt  310  can be transferred all at once onto a recording member. 
     A recording member feed passage according to the present embodiment includes: a normal feed passage  410  in which a recording member sent out from the supply cassette  11   a  moves through the registration roller  13  and secondary transfer portion (a portion where the secondary transfer roller  360  and carry roller  340  are disposed opposed to each other) and reaches the fixing device  14  and discharge roller  15 ; and, a reversal feed passage  420  in which the recording member reversed by the discharge roller  15  is fed through a different passage from the normal feed passage  410  to the registration roller  13 . Here, in these normal feed passage  410  and reversal feed passage  420 , there may be provided properly a feed member (such as a feed roller or a feed guide) which is used to secure the feeding performance of the recording member. 
     And, a belt feed apparatus  300  according to the present embodiment, as shown in  FIG. 12 , includes: an intermediate transfer belt  310  which is made of, for example, polyamide-imide system resin and also which can be driven by, for example, a carry roller  330  and is thereby allowed to circulate; a support frame member  350  which is disposed on the back surface side (inner peripheral surface side) of the intermediate transfer belt  310 , is made of a polymer alloy composed of, for example, polycarbonate resin and ABS resin, and is used to support transfer rollers  27 ; and, a cleaning member  36  which is used to clean remaining toners on the intermediate transfer belt  310  on the upstream side of the intermediate transfer belt circulating direction in the vicinity of the carry roller  330 . 
     Especially, according to the present embodiment, of the back surface side projecting surface  350 B of the support frame member  350 , a portion thereof existing near to the cleaning member  36  is modified. The lower section of  FIG. 13A  is a front view of the support frame member  350  when it is viewed from the arrow mark J direction shown in  FIG. 12 , while the upper section of  FIG. 13A  is a plan view thereof. To the entire area of this portion of the support frame member  350 , there is stuck a sheet made of polyurethane system resin in the width direction of the intermediate transfer belt  310 . 
     Next, description will be given below mainly of the feeding operation of the recording member to be fed through the normal feed passage  410  according to the image forming apparatus of the present embodiment with reference to  FIG. 11 . In  FIG. 11 , recording members, which are sent out from the supply cassette  11   a  by a pickup roller  12   a , are handled by the cooperative operation of a feed roller  12   b  and a retard roller  12   c , whereby only the top one of the recording members is sent out toward the downstream side. The thus-sent-out recording member is regulated in position by the registration roller  13  and, after then, it is fed to the downstream side secondary transfer portion at a given timing. 
     On the other hand, on the side of the image forming engine  20 , given toner images are respectively formed on their associated sensitive members  22 , and, to the circulation of the intermediate transfer belt  310 , the respective color toner images are transferred sequentially from the image forming engine  20   d  onto the intermediate transfer belt  310 . On the intermediate transfer belt  310 , which has passed through the image forming engine  20   a  situated most-downstream in the intermediate transfer belt circulating direction, there are formed four color multiplexed toner images. These multiplexed toner images are, as they are, transferred to the secondary transfer portion according to the circulation of the intermediate transfer belt  310 . 
     In the secondary transfer portion, the multiplexed toner images on the intermediate transfer belt  310  are transferred all at once onto the recording member sent out from the supply cassette  11   a . After the transfer of the toner images onto the recording member is finished, the recording member is as it is fed to the fixing device  14 , where the transferred toner images are fixed. After then, the recording member is discharged from the discharge roller  15  to the recording member storage portion  10   a.    
     In connection with the above operations, description will be given below of the operations of the support frame member  350  and intermediate transfer belt  310  in the belt feed apparatus  300 . As shown in  FIG. 12 , in the back surface side projecting surface  350 B of the support frame member  350 , especially, since the intermediate transfer belt  310  is pressed toward the support frame member  350  by the cleaning member  36 , at a position near to the cleaning member  36 , the intermediate transfer belt  310  is easy to come into contact with the support frame member  350 . When the support frame member  350  and intermediate transfer belt  310  rub against each other, there is generated frictional electrification between them. When the amount of this frictional electricity becomes excessively large, there is applied an electrostatic sucking force between the intermediate transfer belt  310  and support frame member  350 , which impairs the circulation locus of the intermediate transfer belt  310  and finally causes a phenomenon that the intermediate transfer belt  310  sticks to the support frame member  350 . 
     When the circulation locus of the intermediate transfer belt  310  is impaired in this manner, the multiplexing of the toner images on the intermediate transfer belt  310  is ill influenced, which gives rise to image defects such as color shift, or causes the intermediate transfer belt  310  to stick to the support frame member  350 , thereby stopping the image forming operation itself. 
     In order to avoid the above-mentioned inconveniences, according to the present embodiment, as shown in  FIG. 13A , the sheet  37  made of polyurethane system resin is stuck onto the corresponding back surface side projecting surface  350 B of the support frame member  350 . That is, as a non-sucking surface, there is used the sheet  37 . The intermediate transfer belt  310  and sheet  37  made of polyurethane system resin are near to each other in the electrification system and thus an amount of frictional electrification between them is small. Therefore, even when the intermediate transfer belt  310  rubs against the support frame member  350 , an electrostatic sucking force between the intermediate transfer belt  310  and sheet  37  is small. This can reduce the ill influences on the circulation locus of the intermediate transfer belt  310  and thus can secure the stable circulation of the intermediate transfer belt  310 . 
     According to the present embodiment, as shown in  FIG. 13A , the sheet  37  is stuck over the entire area of the support frame member  350  in the width direction thereof perpendicular to the intermediate transfer belt circulating direction. However, the sheet  37  may also be selectively stuck to such portions of the support frame member  350  as can be contacted with the intermediate transfer belt  310 . Also, the sheet  37  may also be stuck to the entire area of the back surface side projecting surface  350 B. 
     In the above embodiment, there is shown an example of a non-sticking portion which uses the sheet  37  as the non-sucking surface. However, the non-sticking portion is not limited to this but there may also be employed other type of non-sticking portion. That is, as shown in  FIG. 13B , as the non-sucking surface of the non-sticking portion, there may also be provided a plurality of ribs  38  on the back surface side projecting surface  350 B at the same time when the support frame member  350  is produced. Each rib  38 , in the present example, includes a projection, the section of which is substantially semicircular, in a direction along the intermediate transfer belt circulating direction. Owing to this structure, even when the intermediate transfer belt  310  comes into contact with the support frame member  350 , since the intermediate transfer belt  310  comes into contact only with the top portion of the rib  38 , the contact area between them is very small. Thus, even when the ribs  38  and intermediate transfer belt  310  rub against each other, the amount of frictional electrification generated in these portions is very small, thereby being able to prevent the intermediate transfer belt  310  from sticking to the support frame member  350 . 
     Also, as shown in  FIG. 13C , as the non-sucking surface of the non-sticking portion, there may also be formed a granulated surface  39  on the back surface side projecting surface  350 B according to a granulation working operation. In this case, there are formed a large number of micro projections on the back surface side projecting surface  350 B. Accordingly, when the intermediate transfer belt  310  and support frame member  35  are contacted with each other, the contact area thereof is very small, thereby being able to reduce the amount of frictional electrification generated between them. 
     Further, according to the present embodiment, not only on the back surface side projecting surface  350 B of the support frame member  350 , but also on the surface side projecting surface thereof, there may also be formed a similar non-sticking portion. 
     Exemplary Embodiment 4 
       FIG. 14  shows a belt feed apparatus used in an image forming apparatus according to an exemplary embodiment 4 of the invention. In the present embodiment, the image forming apparatus is structured substantially similarly to the image forming apparatus according to the exemplary embodiment 3 but is difference from the image forming apparatus according to the exemplary embodiment 3 in that it includes a detect device for detecting the image densities of toner images on an intermediate transfer belt. Here, the composing elements of the exemplary embodiment 4 similar to those of the exemplary embodiment 3 are given the same designations and thus the detailed description thereof is omitted here. 
     In  FIG. 14 , a belt feed apparatus  300  is structured similarly to the belt feed apparatus  300  according to the exemplary embodiment 3 (see  FIG. 12 ) but is different in the following aspect: that is, at a position near to a carry roller  320  and existing upstream in the intermediate transfer belt circulating direction, there is provided a detect device  370  in such a manner that it is opposed to the outer peripheral surface of the intermediate transfer belt  310  and is capable of detecting the image density. Also, on the support frame member  350  side as well, at a position opposed to the detect device  370  with the intermediate transfer belt  310  between them, there is provided a surface side projecting surface  350 A; and, the relationship between the structure of the surface side projecting surface  350 A and the installation position of the detect device  70  is modified. 
     In the surface side projecting surface  350 A according to the present embodiment, as shown in  FIG. 15A , in such portion thereof that is near to the center thereof in the intermediate transfer belt circulating direction, there is stuck a sheet  37  functioning as the non-sucking surface of a non-sticking portion. 
     Also, as shown in  FIG. 15B , correspondingly to the position where the sheet  37  is stuck, there is provided the detect device  370  which is used to detect the densities of images on the intermediate transfer belt  310 . In other words, at the position where the detect device  370  is disposed, the distance between the intermediate transfer belt  310  and support frame member  350  is narrower than distances between them at other positions by an amount equivalent to the sticking of the sheet  37 . 
     When detecting the densities of images on the intermediate transfer belt  310  using the detect device  370 , the detect accuracy varies due to the fluttering movement of the intermediate transfer belt  310 . In view of this, the installation portion of the detect device  370  must be a portion where the intermediate transfer belt  310  flutters little and also which can provide a space capable of installation of the detect device  370 . 
     According to the present embodiment, since the detect device  370  is disposed so as to correspond to the portion of the surface side projecting surface  350 A where the sheet  37  is stuck, even when the intermediate transfer belt  310  happens to flutter, in the sheet  37  stuck portion of the surface side projecting surface  350 A, the amount of fluttering of the intermediate transfer belt  310  can be reduced over its peripheral portions. When compared with a structure in which the detect device  370  is disposed at a position not corresponding to the portion where the sheet  37  is stuck, the detect accuracy of the detect device  370  can be enhanced. Here, it goes without saying that, even when the intermediate transfer belt  310  is contacted with the sheet  37 , the circulating locus of the intermediate transfer belt  310  can be maintained stably. 
     According to the present embodiment, there is shown an example in which the sheet  37  is stuck as the non-sucking surface of the non-sticking portion. However, this is not limitative but, similarly to the exemplary embodiment 3, as the non-sucking surface of the non-sticking portion, there may be provided a plurality of ribs on the surface side projecting surface  350 A, or there may be provided a granulated surface. This structure can also provide a similar effect to a structure using the sheet  37 . 
     EXAMPLES 
     Example 1 
     The present example is conducted on the belt member such as the feed belt and intermediate transfer belt in order to confirm the sheet member suitable for the non-sucking surface of the non-sticking portion; and, specifically, the surface potential of the sheet member is measured after the belt member (polyamide-imide system resin) is made to rub against the surface of the sheet member. 
     The measurement is carried out under the low temperature low humidity environment (specifically, 10° C. 15% RH) where the frictional electrification amount is large. As the sheet member, there are used a sheet made of polyurethane system resin, a sheet of polyester system resin, and a sheet of polypropylene system sheet. The belt member is put on the sheet member fixed and, while applying a given load to the belt member, the belt member is pulled substantially in the horizontal direction to thereby cause the belt member to rub against the surface of the sheet member. 
     The measurement is carried out five times and the results of the five measurements are as shown in  FIG. 16 . Specifically, the polyurethane, polyester and polypropylene sheets all showed large measuring errors; and, polyurethane sheet showed plus and minus values, whereas the remaining sheets showed plus values. Also, in the median values of these materials, the polyurethane sheet showed the smallest surface potential. 
     In the measurement of the surface potential, it is very difficult to obtain stable measurement values and the measured values vary greatly. Above all, the fact that the polyurethane sheet provides plus and minus values shows that the electrifying system of the polyurethane sheet is near to that of the belt member (polyamide-imide system resin) when compared with the remaining sheets made of different material. 
     Example 2 
     The present example is conducted to evaluate the relationship between the surface property of the support frame member and the amount of frictional electrification. 
     In this example, while applying a given load to the belt member (polyamide-imide system resin, the belt member is pulled substantially in the horizontal direction to thereby rub it against the surface of the granulation worked resin (an alloy of polycarbonate resin and ABS resin). Here, the environmental conditions of this example are set similarly to Example 1. 
     The test is conducted five times repeatedly and the results of the five measurement tests are as shown in  FIG. 17 . Here, Ra and Rz respectively designate the arithmetic mean roughness Ra and ten points mean roughness Rz that have been obtained after the measurements are conducted based on JIS B 0601-1994. 
       FIG. 17  shows that, as the arithmetic mean roughness Ra increases, the median values decrease gradually probably because the contact area of the sheet member with the belt member decreases. The measured values do not always show this tendency. However, this is partly because the measurement of the surface potential itself contains unstable factors to thereby make it difficult to obtain stable measured values. Here, for reference, a polyurethane sheet is also stated in  FIG. 17 . Since the polyurethane sheet provides plus and minus values as the measured values, it tells that the polyurethane sheet has a property different from the granulation worked sheet member. 
     Also, using support frame members having the above-mentioned surface properties, in the belt feed apparatus according to the exemplary embodiment 1, a test is conducted to evaluate the circulation performance of the actual feed belt (belt member). The results of this test shows that, as the arithmetic mean roughness Ra decreases, the circulation performance of the feed belt is degraded. Specifically, it is confirmed that, when Ra is 3.5 μm or less, the circulation performance of the feed belt is degraded. Also, this tendency is also confirmed similarly in the ten points mean roughness Rz. 
     Based on the above-mentioned results, the present inventors et al. have made a further study and, as a result, have confirmed that, when the arithmetic mean roughness Ra is 5 μm or more or when the ten points mean roughness Rz is 20 μm or more, the circulation performance of the feed belt (belt member) is not degraded. This shows that the flat and smooth surface used in the exemplary embodiment 2 may be less than 5 μm. Here, as regards the roughness, in order to prevent the belt member against damage while circulating, it is also found that the upper limit value of the arithmetic mean roughness Ra may preferably be 20 μm. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments are chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various exemplary embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.