Image-forming machine

Abstract: An image-forming machine comprising an image-­ bearing means having a photosensitive material on its surface, a latent electrostatic image-forming means for forming a latent electrostatic image corresponding to image information on the photosensitive material, a developing device for developing the latent electrostatic image, a transfer means for transferring the toner image from the photosensitive material to a sheet material, a conveying mechanism (72) for conveying the sheet material through a transfer zone, and a receiving section for receiving the sheet material conveyed through the transfer zone. Improvements have been made for size reduction of the machine with regard to the optical means (56) and the receiving section and to the optical means (56) and the developing device (46). An improvement is also made for maintaining a process unit having the image-bearing means and an optical unit having the optical means in a predetermined positional relationship. An improvement is also made for facilitating mounting and detachment of the image-­ bearing means on and from a process unit frame.

Description: The invention relates to an image-forming machine, such as a laser beam printer, comprising a main body including an upper wall, image-bearing means in the form of a rotating drum, including a surface having a photosensitive material thereon, optical means for projecting light having image information onto the photosensitive material on the surface, a developing device for developing a latent electrostatic image formed on the surface, transfer means for transferring a toner image formed on the surface in a transfer zone to a sheet material, a conveying mechanism for conveying the sheet material through the transfer zone, and a receiving section for receiving the sheet material conveyed by the conveying mechanism. Such an image-forming machine is known, for example, from JP-A-62-95 552. Such a conventional image-forming machine, however, is not entirely satisfactory, and there are still problems to be solved. Firstly, in such a conventional image-forming machine of the type in which a receiving section for receiving the discharged sheet material is defined by an upper wall of the main body of the machine, a main part of a light path in the optical means extends substantially horizontally, whereas the receiving surface of the receiving section defined by the upper surface of the upper wall in the main body of the machine extends horizontally while being inclined at a predetermined angle. Accordingly it will easily be understood that a relatively large, nearly triangular space is present between the optical means and the receiving section, wherein this wasteful space makes the entire machine large in size. Secondly, in a conventional image-forming machine of the type described above, the main part of the light path in the optical means extends substantially horizontally. Therefore, there is not sufficient space below the optical means and on one side of the image-bearing means. When the developing device is disposed in this very space, it is not possible to increase a toner-holding chamber in its size, even though the toner should be supplied relatively incessantly. In principle it is possible to increase the space by providing the entire optical means further upwardly. Such a structure, however, would also need wasteful space and would increase the size of the machine as a whole. Accordingly, the object underlying the present invention is to provide an image-forming machine which has a compact structure without wasting any space in the interior of the machine. According to the invention, this object is solved by an image-forming machine of the type specified above, wherein the machine is characterized in that the receiving section is disposed above the optical means and includes a receiving surface defined by an upper surface of the upper wall of the main body, the receiving surface being inclined upwardly at a predetermined angle to the horizontal; in that the optical means are disposed in a box-like optical unit frame, wherein the optical unit frame is disposed within the main body at a location above the rotating drum and extending substantially parallel to the receiving surface of the receiving section and inclined upwardly from a lower first end on a first side of the rotating drum to an upper second end on a second side of the rotating drum, thereby defining an enlarged space below the optical unit frame on the second side of the rotating drum; in that a main portion of a light path of the optical means is inclined to the horizontal substantially parallel to the receiving surface of the receiving section in a straight line from one end portion to another end portion of the optical unit frame; and in that the developing device is positioned in the enlarged space below the optical unit frame at a location on the second side of the rotating drum. A further development of the machine according to the invention is characterized in that the optical unit frame is mounted on an inside surface of the upper wall of the main body. In a specific embodiment of the machine according to the invention, the predetermined angle of inclination of the receiving surface is about 45°. A still further development of the machine according to the invention is characterized in that the developing device includes toner applicator means for applying toner to the surface of photosensitive material and a toner holding chamber for holding the toner, wherein the toner applicator means is positioned adjacent the rotating drum, and the toner holding chamber is disposed outwardly of the toner applicator means. According to the invention, the object is solved in an advantageous manner. In particular, the waste of space is minimized. The invention will be explained in further detail below with reference to preferred embodiments of the invention and with reference to the accompanying drawings showing various details of the invention. Figure 1 is a perspective view showing one embodiment of a laser beam printer as one example of the image-forming machine constructed in accordance with this invention. Figure 2 is a front view showing the laser beam printer of Figure 1 in its cut section partly broken away. Figure 3 is a sectional view showing the laser beam printer of Figure 1 in a simplified manner. Figure 4 is a sectional view showing a process unit in the laser beam printer of Figure 1. Figure 5 is a top plan view showing partly a first frame member of the process unit of Figure 4 and various constituent elements mounted on the frame member. Figure 6 is a sectional view for illustrating the operation of mounting a rotating drum on the unit frame of the process unit shown in Figure 4. Figure 7 is a partly broken-away sectional view for illustrating the state of supporting the rotating drum. Figure 8 is a partial sectional view showing a modified example of the process unit in which a second frame member is at an operative position. Figure 9 is a partial sectional view showing the process unit of Figure 8 in the state in which the second frame member is held in a non-operative position. Figure 10 is a sectional view showing an optical unit and its vicinity in the laser beam printer of Figure 1. Figure 11 is a top plan view showing the optical unit in the laser beam printer of Figure 1. Figure 12 is a sectional view for illustrating the positional relationship between the optical unit and the process unit in the laser beam printer of Figure 1. Figure 13 is a sectional view of the process unit and its vicinity, as viewed from above, in the laser beam printer of Figure 1. Figure 14 is a simplified view for illustrating the manner of mounting the process unit. Detailed Description of the Preferred Embodiments The preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that while these embodiments will be described as applied to a laser beam printer, they are equally applicable to other image-forming machines such as an electrostatic copying machine. Outline of the Laser Beam Printer With reference to Figures 1 to 3, the illustrated laser beam printer has a main body shown by reference numeral 2. The main body 2 is provided with a lower section 4 whose left portion 4a in Figures 1 and 2 projects upwardly. An opening-closing housing 6 is disposed in the right upper portion of the lower section 4. An operating panel 8 is provided in the front surface of the left portion 4a of the lower section 4. The housing 6 is mounted on the lower section 4 in the following manner. With reference mainly to Figure 2, a supporting shaft 14 extending in the front-rear direction (in the direction from left bottom to right top in Figure 1, in the direction perpendicular to the sheet surface in Figure 2 and in the left-right direction in Figure 3) is mounted on the inside of an upper wall 12 of the left portion 4a in the lower section 4. A pair of fixing projections 16 (only one of which is shown in Figure 2) are provided in the upper end portion of the housing 6 with a space therebetween in the front-rear direction. A linking member 18 is attached to each of the fixing projections 16. The linking member 18 is nearly U-shaped as a whole and a partly open, nearly circular hole is formed in its center. In an intermediate portion are provided a pair of protrusions 20, and by threadably securing a fixing screw 22 to the fixing projections 16 through the protrusion 20, the linking member 18 is attached as is required. The opening-closing housing 6 and the lower section 4 of the main body are linked to each other pivotally via the supporting shaft 14 and the linking member 18 by positioning the supporting shaft 14 within the hole of each linking member 18 and then threadingly securing a bolt 24 and a nut 26 through both end portions of the linking member 18. A locking means 28 is interposed between the lower section 4 of the main body and the opening-closing housing 6. The illustrated locking means 28 is comprised of an engaging member 30 mounted for free pivoting movement between a locked position in the right bottom of the housing 6 (the position shown by a solid line in Figure 2) and a non-locked position (the position shown by a two-dot chain line in Figure 2) and an engaging opening 34 formed in a wall 32 of the lower section 4 of the main body. When the engaging member 30 is at the locked position, its claw portion engages the engaging opening 34. Thus, when the housing 6 is at the closed position shown by the solid line in Figure 2, the claw portion of the engaging member 30 engages the engaging opening 34 to lock the housing 6 releasably at the closed position. On the other hand, when an operating portion 30a of the engaging member 30 is pivoted upwardly through an opening formed in the right bottom part of the housing 6, the engaging member 30 is held at the non-locked position, whereby the claw portion of the engaging member 30 comes out of engagement with the engaging opening 34 and the locking means 28 becomes nonlocked. A protrusion 32a is provided integrally in part of the wall 32 of the lower section 4 of the main body. When the engaging member 30 abuts with this protrusion 32a, the pivoting mevement of the engaging member 30 beyond the non-locked position is accurately hampered. When thereafter the housing 6 is pivoted in the direction shown by an arrow 35, it moves crosswise about the supporting shaft 14, i.e. about a central pivot axis extending in the front-rear direction, and is held at the open position shown by a two-dot chain line in Figure 2. It will be easily understood from Figure 2 that when both end portions of the linking member 18 are clamped relatively strongly by the bolt 24 and the nut 26, the frictional force between the inner surface of the linking member 18 and the peripheral surface of the supporting shaft 14 becomes relatively large and the opening and closing power for opening and closing the housing 6 becomes high. On the other hand, when both end portions of the linking member 18 are clamped relatively weakly by the bolt 24 and the nut 26, the frictional force between the inner surface of the linking member 18 and the peripheral surface of the supporting shaft 14 becomes relatively small, and consequently, the opening and closing power for opening and closing the housing 6 becomes low. A process unit shown generally at 36 is mounted on the main body 2. With reference mainly to Figure 3, the illustrated process unit 36 has a process unit frame 38 on which a rotating drum 40 constituting an image-bearing means is mounted rotatably. An electrographic photosensitive plate is disposed on the peripheral surface of the rotating drum 40. Around the rotating drum 40 rotating in the direction shown by an arrow 42 are disposed a charging corona discharger 44, a developing device 46, a transfer corona discharger 48 and a cleaning device 50. The charging corona discharger 44, the developing device 46 and the cleaning device 50 are mounted on the unit frame 38. The process unit 36 will be described in more detail hereinafter. In the upper portion of the main body 2, and above the process unit 36, is disposed an optical unit 56. The optical unit 56 includes a laser beam source 58 (Figure 11), a rotating polygon mirror 60, an fϑ lens 62, a first reflecting mirror 64, a second reflecting mirror 66 and a cylindrical lens 68. The laser beam source 58 irradiates a laser beam based on image information outputted from, for example, a computer toward the polygon mirror 60. The laser beam reflected from the rotating polygon mirror 60 passes through the fϑ lens 62 and reaches the first reflecting mirror 64, is reflected by the first and second reflecting mirrors 64 and 66, further passes through the cylindrical lens 68, and is projected onto the surface of the rotating drum 40 in a projecting zone 70 as shown by one-dot chain line. A conveying mechanism shown generally at 72 is disposed in the lower portion of the main body 2 and below the process unit 36. The conveying mechanism 72 defines a conveying passage for conveying a sheet material such as a recording paper through a transfer zone, and includes a conveyor roller pair 76, a guide plate 78, a guide plate 80, a fixing roller pair 82 and a lower discharge roller pair 84. In the illustrated embodiment, the upstream end of the conveying passage is bifurcated. One part extends in a straight line to the right in Figure 3 and a handinsertion feed means 86 is provided in its upstream end. The other part curves and extends downwardly. and an automatic feed means 88 is provided at its upstream end (specifically, below the conveying mechanism 72 and at the bottom part of the lower section 4). The hand-insertion feed means 86 includes a table 90 which is free to pivot between a feed position shown in Figure 3 and a storage position (not shown) displaced upwardly. When the hand-insertion feed means 86 is to be utilized, the table 90 is held at the feed position. When a sheet material is positioned on the table 90 and inserted into the main body 2 through an opening 92 defined in the right surface (Figure 3) of the lower section 4 of the main body, the sheet material is conducted to the conveyor roller pair 76 through a space between the under surface of a guide piece 94 and the upper end edge of a guiding protrusion 96 provided on the inner surface of a wall 95 of the lower section 4 of the main body. The illustrated automatic feed means 88 includes a cassette 98 in which sheet materials are stacked. The cassette 98 is detachably loaded into a cassette receiving section 102 defined in the lower section 4 of the main body through an opening 100 formed in the front surface (left surface in Figure 3) of the lower section 4 (see Figures 1 and 2 also). A feed roller 104 is disposed above the cassette-receiving section 102. By rotating the feed roller 104 in the direction shown by an arrow 106, the sheet materials in the cassette 98 are delivered one by one. The delivered sheet material is guided by a guiding protrusion 110 provided in an upstanding wall portion 108 of the lower section 4 of the main body and the above guiding protrusion 96 and conducted to the conveyor roller pair 76. The downstream end of the conveying passage is also bifurcated, and in regard to this structure, a rectangular opening-closing portion 112 in the front surface of the housing 6 is adapted to be selectively held at a first position shown by a two-dot chain line in Figure 3 and a second position shown by a solid line in Figure 3 (the positions also shown in Figures 1 and 2). When the opening-closing portion 112 of the housing 6 is at the first position, the sheet material delivered from the lower discharge roller pair 84 is discharged directly out of the housing 6 and received in the inside surface (the upper surface in the state shown by a two-dot chain line) of the opening-closing portion 112. Hence, at the first position, the opening-closing portion 112 functions as a first receiving section. On the other hand, when the opening-closing portion 112 is at the second position, the sheet material delivered from the lower discharge roller pair 84 is further conveyed upwardly passing between the opening-closing portion 112 and a part 113 of the housing 6 and by the action of an upper discharge roller pair 114, is discharged into a receiving section 116 (functioning as a second receiving section) defined in the upper surface of the housing 6. In the illustrated embodiment, the receiving section 116 is defined by an upwardly inclined wall 118 in the housing 6, and on the upper end portion of the upwardly inclined wall 118 is mounted an auxiliary receiving member 122 which is free to pivot between a receiving position shown in Figures 1 to 3 and a storage position pivoted about 180 degrees from the receiving position in the direction shown by an arrow 120. The operation of the laser beam printer described above will be described below briefly. While the rotating drum 40 is rotated in the direction of arrow 42, the charging corona discharger 44 charges the photosensitive material of the rotating drum 40. Then, a laser beam from the laser beam source 58 of the optical unit 56 is projected onto the photosensitive material in the projecting zone 70. Consequently, a latent electrostatic image corresponding to the image information is formed on the surface of the photosensitive material by the action of a latent electrostatic image forming means composed of the charging corona discharger 44 and the optical unit 56. Then, a toner is applied to the latent electrostatic image on the photosensitive material by the action of the developing device 46 to develop it into a toner image. A sheet material fed into the conveying passage from the hand insertion feed means 86 or the automatic feed means 88 is brought into contact with the photosensitive material in the transfer zone, and by the action of the transfer corona discharger 48, the toner image on the photosensitive material is transferred to the sheet material. The sheet material having the toner image transferred thereto is peeled from the rotating drum 40, and the toner image is fixed to the surface of the sheet material by the action of the fixing roller pair 82. The sheet material having the fixed toner image is conveyed to the lower discharge roller pair 84, and when the opening-closing portion 112 is at the first position, directly discharged onto the opening-closing portion 112. It will be understood from Figure 3 that in this case, the sheet material is discharged with its image-bearing surface directed upwardly. On the other hand, when the opening-closing portion 112 is at the second position, the sheet material conveyed to the lower discharge roller pair 84 is further conveyed upwardly, and discharged into the receiving section 116 by the action of the upper discharge roller pair 114. In this case, the sheet material is discharged with the image-bearing surface directed downwardly, as can be seen from Figure 1, and no page arrangement of the discharged sheet materials is necessary. In the meantime, the rotating drum 40 continues to rotate, and by the action of the cleaning device 50, the residual toner is removed from the surface of the photosensitive material. Process Unit With reference to Figures 4 and 5 as well as Figure 3, mainly to Figure 4, the process unit 36 will be described. The illustrated process unit 38 is provided with a first frame member 124 disposed in the right portion in Figure 4, and a second frame member 126 disposed in the left portion in Figure 4. The first frame member 124 has a pair of end walls 128 and 130 (Figure 5 shows one end wall 128 and Figures 3 and 4, the other end wall 130) spaced from each other in a direction (the vertical direction in Figure 5) perpendicular to the sheet surface in Figures 3 and 4, and an upper wall 132 is provided between the end walls 128 and 130. As will be described later, the rotating drum 40 and the developing device 46 are mounted on the first frame member 124, and a toner recovery chamber 134 in the cleaning device 50 is provided. The second frame member 126 has a pair of end walls 136 and 138 (Figure 7 shows one end wall 136, and Figures 3 and 4, the other end wall 138) spaced from each other in a direction perpendicular to the sheet surface in Figures 3 and 4, and an upper wall 140 is disposed between the end walls 136 and 138. The charging corona discharger 44 and the toner removing means 142 in the cleaning device 50 are mounted on the second frame member 126. The first frame member 124 and the second frame member 126 are mounted so as to be free to pivot in the directions shown by arrows 144 and 146 (Figure 6). The end walls 136 and 138 in the second frame member 126 are positioned outwardly of the end walls 128 and 130 in the first frame member 124, and the left end portion of the end wall 128 in the first frame member 124 is pivotally connected to a lower projecting portion 136a formed in the end wall 136 of the second frame member 126 via a linking pin (not shown). Furthermore, the left end portion of the end wall 130 of the first frame member 124 is pivotally connected to a lower projecting portion 138a formed in the end wall 138 of the second frame member 126 via a linking pin 148. When the second frame member 126 is pivoted in the closing direction shown by an arrow 144 and held at an operative position, the second frame member 126 and the first frame member 124 are maintained in the positional relationship shown in Figure 4. On the other hand, when the process unit 36 is placed on a surface S such as a table surface and pivoted in the opening direction shown by an arrow 146 from the operative position, the left end of the second frame member 126 abuts with the surface S, and the second frame member 126 and the first frame member 124 are maintained in the positional relationship shown in Figure 6. In the illustrated embodiment, an operative position locking means 150 is provided which releasably locks the second frame member 126 at the operative position. The locking means 150 is comprised of a protruding portion 152 provided in the left end portion in Figures 4 and 5 of the upper wall 132 of the first frame member 124 and a receiving portion 156 defined in an elastically deformable portion 154 provided in the right end portion in Figure 4 of the upper wall 140 of the second frame member 126. Accordingly, when the second frame member 126 is held at the operative position, the protruding portion 152 of the upper wall 132 is detachably received by the receiving portion 156 in the elastically deformable portion 154, and thus locked in the operative position by the locking means 150, and this locked state is maintained by the recovering force of the elastically deformable portion 154. The rotating drum 40 is mounted on the unit frame 38 in the following manner. With reference to Figures 4 to 6, the rotating drum 40 has a cylindrical portion 158 having a photosensitive material disposed on its peripheral surface and shaft portion 160 provided at opposite end surfaces of the cylindrical portion 158. A bearing member 162 is mounted on each of the shaft portions 160. On the other hand, receiving portions 164 and 166 (Figure 5 shows one receiving portion 164, and Figures 4 and 6, the other receiving portion 166) are provided nearly centrally in the left-right direction in Figures 4 and 5 in the end walls 128 and 130, respectively, of the first frame member 124. The receiving portions 164 and 166 are nearly circular with an open top, and are defined by the upper edges of the end walls 128 and 130. A first guide portion 168 and a second guide portion 170 are provided in the first frame member 124 to facilitate the mounting of the rotating drum. In the illustrated embodiment, inner walls 172 and 174 (Figure 5 shows one inner wall 172, and Figures 4 and 6, the other inner wall 174) are disposed inwardly of the left portions of the end walls 128 and 130 respectively, of the first frame member 124. These inner walls 172 and 174 function as the first guide portion 168. The inner walls 172 and 174 are disposed corresponding to both end parts of the cylindrical portion 158 of the rotating drum 40 on which no photosensitive material substantially exists, or an image is not substantially formed even when the photosensitive material exists. The upper surfaces of these inner walls are comparatively greatly inclined downwardly in a straight line toward the receiving portions 164 and 166. The left portions of the end walls 128 and 130 function as the second guide portion 170. The left portions of the end walls 128 and 130 are positioned correspondingly to the shaft portions 160 of the rotating drum 40 (in the illustrated embodiment, the bearing members 162 mounted on them), and their upper surfaces are comparatively gently inclined downwardly in a straight line from the left end of the unit frame 38 to the receiving portions 164 and 166. In mounting the rotating drum 40, both end parts of the cylindrical portion 158 of the rotating drum 40 are first positioned on the first guide member 168 (the inner walls 172 and 174) as shown in Figure 6, and moved downwardly to the lower end portion of the first guide portion 168 along the guiding surface of the first guide portion 168. Then, the rotating drum 40 is allowed to fall further downwardly and its shaft portions 160 (the bearing members 162) are positioned on the second guide portion 170 (the left portions of the end walls 128 and 130) and the rotating drum is moved slightly downwardly along the guiding surface of the second guide portion 170. Thereafter, the shaft portions 160 are allowed to fall into the receiving portions 164 and 166 defined by the end walls 128 and 130. Thus, the shaft portions 160 of the rotating drum 40 are detachably received in the receiving portions 164 and 166 of the end walls 128 and 130. To detach the rotating drum 40 from the unit frame 38, it is lifted in such a manner as to detach the shaft portions 160 from the receiving portions 164 and 166. In regard to the receiving portions 164 and 166, it is preferred to employ the structure shown in Figure 7. Firstly, it is preferred to provide an enlarged portion 178 in the upper parts of the receiving portions 164 and 166 (for the receiving portion 166, see Figures 4 and 6), more specifically in the upper side of that part of the receiving portions 164 and 166 which make contact with the bearing members 162, by forming a depressed portion, for example. By this structure, the introducing parts of the receiving portions 164 and 166 become slightly large, and the shaft portions 160 of the rotating drum 40 can be easily mounted on, and detached from, the receiving portions 164 and 166. Secondly, the receiving portions 164 and 166 are constructed such that they fully support the force acting on the rotating drum 40. Generally, to mount the shaft portions 160 of the rotating drum 40 detachably on the receiving portions 164 and 166, it is necessary to adjust the angle of contact between the shaft portion 160 and the receiving portion 164 or 166 not to be more than 180 degree. On the other hand, if the angle of contact is maintained relatively low, it is difficult to support the shaft portions 160 sufficiently accurately. In the illustrated embodiment, by employing the structure shown in Figure 7, the shaft portions 160 can be accurately supported despite the fact that the angle of contact between each shaft portion 160 and the receiving portions 164 or 166 is not more than 180 degrees. Specifically, a gear 180 provided in the rotating drum 40 is mesh with a driving gear 182 provided in the main body 2 of the machine as shown in Figure 7. When the driving gear 182 rotates in the direction shown by an arrow 184, the direction of an acting force F on the rotating drum 40 is displaced by an angle of 90 + α which is the sum of 90 degrees displaced clockwise from an axis line P connecting the center of rotation of the driving gear 182 and the center of rotation of the rotating drum 40 and the pressure angle α of the gear 180. If the pressure angle α is 20 degrees, this direction is the one shown in Figure 5. On the other hand, in the illustrated embodiment, the receiving portions 164 and 166 extends clockwise in an arcuate shape from right bottom in the horizontal direction to left top in the horizontal direction and make contact with the bearing members 162 to support the rotating drum 40, as shown in Figure 7. Accordingly, the arcuate parts of the receiving portions 164 and 166 extend further upwardly beyond the acting direction of the acting force F, and the acting force F exerted on the rotating drum 40 via the driving gear 182 and the gear 180 is transmitted to the end walls 128 and 130 via the bearing members 162 and the receiving portions 164 and 166. Consequently, the receiving portions 164 and 166 accurately support the shaft portions 160. The developing device 46 is mounted on the unit frame 38 in the following manner. Again, with reference to Figures 3 to 5, the illustrated developing device 46 includes a main body 188 having a lower housing 190 and an upper housing 192. An opening is defined in the lower part of the left surface (that surface which faces the rotating drum 40) of the main body 188 of the developing device, and a magnetic brush mechanism 194 is disposed in the opening portion. The magnetic brush mechanism 194 is comprised of a hollow sleeve 198 to be rotated in the direction shown by an arrow 196 and a stationary permanent magnet 200 disposed within the hollow sleeve 198, and holds a developer composed of a toner magnetically and applies it to the surface of the photosensitive material on the rotating drum 40. A doctor blade 202 which may be formed of, for example, a thin plastic film is disposed in the opening portion. The doctor blade 202 extends downwardly from a securing member 204 fixed to the upper housing 192 and its free end portion is kept in press contact with the peripheral surface of the hollow sleeve 198. The doctor blade 202 acts to remove the excess of the developer held on the magnetic brush mechanism 194. A toner is held in a toner holding chamber 206 defined by the lower housing 190, the upper housing 192 and the doctor blade 202, and an agitating feed roller 208 is disposed at the bottom of the toner holding chamber 206. The agitating feed roller 208 is rotated in the direction shown by an arrow 210 and mixes a toner in the toner holding chamber 206 with a toner which is recovered in a toner recovery chamber 134 and fed into the toner holding chamber 206 by the action of a toner transfer means (to be described) with agitation, and feeds the mixed toner to the magnetic brush mechanism 194. Supporting pins 216 (only one of which is shown in Figures 4 and 6) are fixed to the left upper parts of walls 212 and 214, and by attaching the supporting pins 216 pivotally to the inside surfaces of the end walls 128 and 130 of the unit frame 38, the developing device 46 is mounted on the unit frame 38. Pins 218 are fixed respectively to the lower parts of the outside surfaces of the end walls 212 and 214 in the main body 188 of the developing device, and corresponding to these pins 218, pins 220 are fixed also to the outside surfaces of the end walls 128 and 130 in the unit frame 38. Biasing coil springs 222 (one of them is shown in Figure 5, and the other, in Figures 4 and 6) are interposed between the pins 218 and pins 220 respectively. Thus, when the rotating drum 40 is detached from the unit frame 38, the developing device 46 is held at an angular position shown partly by a two-dot chain line in Figure 6 by the contraction of the biasing coil springs 222. On the other hand, when the rotating drum 40 is detachably mounted on the unit frame 38, both end parts of its cylindrical portion 158 acts on a roll 224 (Figure 7) mounted rotatably on the shaft portion of the hollow sleeve 198 in the magnetic brush mechanism 194 to pivot the developing device 46 slightly counterclockwise against the biasing force of the biasing coil springs 222. As a result, the developing device 46 is held at the angular position shown in Figure 4 and by a solid line in Figure 6. In this state, the developing device 46 is elastically biased in a direction approaching the rotating drum 40 with the supporting pins 216 as a center. Hence, the distance between the peripheral surface of the cylindrical portion 158 of the rotating drum 40 and the peripheral surface of the hollow sleeve 198 is adjusted to a fixed value determined by the roll 224. The cleaning device 50 is mounted on the unit frame 38 in the following manner. With reference to Figures 4 and 6, an elastic blade 226 constituting a toner removing means 142 is mounted on the second frame member 126. In the illustrated embodiment, linking portions 230 (only one of which is shown in Figures 4 and 6) provided at both ends of a swinging support member 228 are pivotally linked to the end walls 128 and 130 of the first frame member 124 via linking pins 148. A blade securing member 232 is fixed to the swinging support member 228, and the elastic blade 226 is fixed to the free end of the blade securing member 232 by an adhesive or otherwise. In the swinging support member 228, a pair of upper protrusions 234 (only one of which is shown in the drawings) spaced from each other in a direction perpendicular to the sheet surface in Figures 4 and 6 are provided integrally. A biasing coil spring 238 is interposed between each of the upper protrusions 234 and a linking wall 236 connected between the end walls 136 and 138 of the second frame member 126. The biasing coil spring 238 biases the swinging support member 228, and therefore the elastic blade 226, clockwise in Figures 4 and 6 about the linking pin 148 as a center. Suspending pieces 240 which can abut with the upper protrusions are provided at predetermined sites in the inner surface of the upper wall 140 of the second frame member 126. With this arrangement, the swinging support member 228 can pivot relative to the second frame member 126 between an angular position at which its left end abuts with the linking wall 236 and an angular position at which the upper protrusions abut with the suspending pieces 240 of the upper wall 140 in Figures 4 and 6. Usually, the swinging support member 228 is held by the action of the biasing coil spring 238 at the angular position at which the upper protrusions 234 abut with the suspending pieces 240. On the other hand, the toner recovery chamber 134 for recovering the toner removed from the rotating drum 40 is defined between the inner walls 172 and 174 of the first frame member 124. With reference to Figure 5 also, a nearly arcuate curved linking wall 242 is provided between the inner walls 172 and 174, and the toner recovery chamber 134 is defined by the inner surface of the linking wall 242. A film-like sealing member 244 extending toward the rotating drum 40 is provided at one end (upper end) of the linking wall 242, and a film-like sealing member 246 extending toward the rotating drum 40 and contacting or approaching the peripheral surface of the drum 40, at the other end portion (lower end portion). When the second frame member 126 is held at the operative position, the sealing member 244 makes contact with the under surface of the elastic blade 226 and seals up the space between the linking wall 242 and the elastic blade 226. The sealing member 246 prevents falling of the toner through the space between the rotating drum 40 and the linking wall 246, and conducts the toner removed from the rotating drum 40 to the toner recovery chamber 134. In the illustrated embodiment, a helical toner transfer member 248 extends from the toner recovery chamber 134 to the toner holding chamber 206 of the developing device 46, and feeds the toner recovered in the toner recovery chamber 134 to the toner holding chamber 206 through a hollow cylindrical member 250 (see Figure 3 also). With this structure, when the second frame member 126 is pivoted in the opening direction shown by arrow 146 (Figure 6), the upper protrusions 234 of the swinging support member 228 abut with the suspending pieces 240 of the upper wall 140. As a result, the swinging support member 228 is likewise pivoted, and the elastic blade 226 moves in a direction away from the rotating drum 40 and leaves the surface of the photosensitive material relatively greatly (see Figure 6). When the second frame member 126 is pivoted in the closing direction shown by arrow 144 (Figure 6) and held at the operative position, the forward end portion of the elastic blade 226 acts on the surface of the photosensitive material on the rotating drum 40 and is kept in press contact with its surface at a predetermined pressure by the biasing force of the biasing coil spring 238. In this press-contacting state, the biasing coil spring 238 is slightly contracted by the abutting of the elastic blade 226 with the surface of the photosensitive material, and the upper protrusions 234 of the swinging support member 228 are apart from the suspending pieces 240 of the upper wall 140, as shown in Figure 4. The mounting and detaching operations of the rotating drum 40 in the above process unit 36 will be described. With reference to Figures 4 and 6, the operation of detaching the rotating drum 40 starts with the detachment of the process unit 36 from the main body 2 of the machine in the manner to be described and the placing of the detached process unit 36 on the surface S (Figure 6) such as a table surface. Then, the elastically deformable portion 154 of the second frame member 126 is slightly deformed elastically and the engagement between the protruding portion 152 in the first frame member 124 with the receiving portion 156 defined in the elastically deformable portion 154 is cancelled. The second frame member 126 is pivoted in the opening direction shown by arrow 146 and brought to the position shown in Figure 6 (held at this position by the abutting of the left end of the second frame member 126 with the surface S. As a result, the swinging support member 228 pivots likewise, and the elastic blade 226 moves in a direction away from the rotating drum 40, whereby the elastic blade 226 comes out of contact with the photosensitive material of the rotating drum 40. Furthermore, the second frame member 126 moves substantially to the left of the first frame member 124 whereby the top of the rotating drum 40, the top of the left portions of the end walls 128 and 130 (the second guide portion 170) and the top of the inside walls 172 and 174 (the first guide portion 168) ate open to view, and the first guide portion 168 and the second guide portion 170 are exposed outside. Then, the rotating drum 40 is lifted and the bearing member 162 is detached from the receiving portions 164 and 166 defined in the end walls 128 and 130. The rotating drum 40 can thus be detached easily without injuring the photosensitive material on its surface because its top is relatively greatly open to view and the elastic blade 226 is spaced from the rotating drum 40. To mount the rotating drum 40 after the detachment in the above manner (mount the detached rotating drum 40 again, or mount a new rotating drum 40 in place of the detached rotating drum 40), both end portions of its cylindrical portion 158 are positioned from above onto the first guide portion 168, and moved as shown by the two-dot chain line in Figure 6 along the first guide portion 168. Then, the bearing members 162 on the shaft portions 160 are positioned in the second guide portion 170 as shown by the broken line in Figure 6 and slightly moved along it, and then allowed to fall into the receiving portions 164 and 166. As a result, the shaft portions 160 of the rotating drum 40 are detachably received by the receiving portions 164 and 166. At the time, too, the rotating drum 40 can be easily mounted without injuring the photosensitive material because the elastic blade 226 is in a retracted position. Furthermore, it is sufficient at the time of mounting to move the cylindrical portion 158 of the rotating drum 40 along the first guide portion 168 and then move the bearing members 162 in its shaft portion 160 along the second guide portion 170. Thus, the rotating drum 40 can be mounted easily without injuring the photosensitive material. When thereafter, the second frame member 126 is pivoted in the closing direction shown by arrow 144 and held at the operative position shown in Figure 4, the protruding portion 152 of the upper wall 132 is received in the receiving portion 156 of the elastically deformable portion 154 and thus the second frame member 126 is held at the operative position. In this state, the forward end portion of the elastic blade 226 is brought into press-contact with the surface of the photosensitive material in the rotating drum 40 by the action of the biasing coil spring 238, and the toner on the photosensitive material of the rotating drum 40 is removed by the action of the elastic blade 226. Furthermore, in this state, the movement of the bearing members 162 mounted on the rotating drum 40 in a downward direction and a crosswise direction (the left-right direction in Figure 4) is restrained by the receiving portions 164 and 166. The lower edges of the end walls 136 and 138 of the second frame member 126 held at the operative position abut with the upper edges of the bearing members 162 mounted on the rotating drum 40 to restrain the upward movement of the bearing members 162 and support the rotating drum 40 accurately on the unit frame 38. Modified Embodiment of the Process Unit In the illustrated embodiment, the second frame member is adapted to be releasably locked at the operative position. If desired, it is also possible to construct the second frame member such that it can also be releasably locked at a non-operative position displaced slightly in the opening direction from the operative position. With reference to Figures 8 and 9 showing such a modified embodiment of the process unit, a nonoperative position locking means 254′ is provided in addition to the operative position locking means 158′. The operative position locking means 150′ is provided with a receiving portion 156′ defined in the elastic deformable portion 154′ of the second frame member 126′, and by holding the second frame member 126′ at the operative position shown in Figure 8, the protruding portion 152′ provided in the upper wall 132′ of the first frame member 124′ is received detachably in the receiving portion 156′. When the second frame member 126′ is held at the operative position, the elastic blade 226′ acts on the surface of the photosensitive material on the rotating drum 40′, and its forward end portion is brought into press-contact with the surface of the photosensitive material by the action of the biasing coil spring 238′. The non-operative position locking means 254′ is provided with a receiving portion 256′ defined in the forward end portion of the elastically deformable portion 154′ (further forwardly of the site at which the receiving portion 156′ is defined), and by pivoting the second frame member 126′ slightly in the opening direction shown by arrow 146′ from the operative position, the protruding portion 152′ of the first frame member 124′ is detached from the receiving portion 156′ and received detachably in the receiving portion 256′, as shown in Figure 9. As a result, the non-operative position locking means 254′ is in the locking state, and the second frame member 126′ is held at the non-operative position shown in Figure 9. In this state, the elastic blade 226′ moves in a direction away from the rotating drum 40′ and its forward end portion does not substantially act on the surface of the photosensitive material but is slightly apart from the surface because the second frame member 126′ is slightly pivoted in the opening direction. With this process unit 36′ of the modified embodiment, the same effect as above can be achieved. In addition, by holding the second frame member 126′ at the non-operative position during conveying, storage, etc. of the process unit 36′, the press-contact of the photosensitive material on the rotating drum 40′ with the elastic blade 226′ can be cancelled. As a result, degradation of the photosensitive material and the deformation of the elastic blade 256′ can be prevented. In place of the above structure, the operative position locking means 150′ and the non-operative position locking means 254′ may be provided separately for exclusive use. Optical Unit and Manner of Mounting With reference to Figure 10 and 11 as well as Figure 3, the optical unit 56 will be described in detail. The optical Unit 56 is provided with a box-like optical unit frame 260, and the optical means 69 is disposed within the optical unit frame 260. The optical unit frame 260 is composed of various walls 262, 264, 266, 268, 270, 272 and 274 to do fine a substantially sealed space. The laser beam source 58 is mounted on the wall 264, and the rotating polygon mirror 60, the fϑ lens 62, the first reflecting mirror 64, the second reflecting mirror 66 and the cylindrical lens 68 are mounted on the optical unit frame 260. Specifically, parts 272a and 274a of the walls 272 and 274 project downwardly, and an elongate rectangular projecting opening 276 is defined by these projecting portions 272a and 274a. The opening 276 is covered with a transparent glass sheet 278, and a laser beam from the laser beam source 58 is projected onto the surface of the photosensitive material of the rotating drum 40 through the transparent glass sheet 278. The optical unit frame 260 is mounted on the inner surface of the upwardly inclined wall 118 of the housing 6 in the following manner. With reference to Figure 12, too, three inwardly projecting boss portions 282 are formed integrally in the inner surface of the upwardly inclined wall 118 of the housing 6 in the illustrated embodiment. As can be seen from Figure 12, one boss portion 282 is formed in the right end portion in Figure 12 of the upper wall 282, and two boss portions 282, in the left end portion in Figure 10 of the upwardly inclined wall 118 (the boss portions are spaced from each other in a direction perpendicular to the sheet surface in Figure 10). Internally threaded holes are formed in these boss portions 282. Four protrusions 284 protruding outwardly are formed in the peripheral surface of each boss portion 282, and a stepped part is provided in each of the protrusions 284. On the other hand, supporting outwardly projecting portions 286 and 288 are formed integrally in the walls 266 and 268 of the optical unit frame 260. One hole 290 corresponding to the boss portion 282 is formed in one supporting projecting portion 286, and two holes 292 corresponding to the two boss portions 282, in the other supporting projecting portion 288. As shown in Figures 10 and 12, the optical unit frame 260 is mounted on the inner surface of the upwardly inclined wall 118 by threadedly securing fixing screws 294 to the boss portions 282 of the upwardly inclined wall 118 throughout the holes 290 and 292 formed in the optical unit frame 260. In this mounted state, the optical unit frame 260 is free to move in the vertical direction in Figures 10 and 12, or in other words, in a direction moving toward and away from the process unit 36 between a position at which the supporting projecting portions 286 and 288 abut with the forward ends of the boss portions 282 and a position at which they abut with the head parts of the fixing screws 294 secured to the boss portions 282. Furthermore, in the illustrated embodiment, the outside diameter of the shaft portion of each fixing screw 294 is smaller than the inside diameter of the hole 290 or 292 formed in the optical unit frame 260. Hence, the optical unit frame 260 can move in the left-right direction in Figure 10 (the direction perpendicular to the sheet surface in Figure 12) and in a direction perpendicular to the sheet surface in Figure 10 (the left-right direction in Figure 12), or in other words in a horizontal direction substantially parallel to the process unit 36, within a range in which the shaft portions of the fixing screws 194 can move within the corresponding holes 190 and 192. Biasing coil springs 296 constituting a biasing means are also provided in the optical unit frame 260. The biasing coil springs 296 are fitted over the boss portions 282 and interposed between the stepped parts of the protrusions 284 and the supporting projecting portions 286 and 288. These biasing coil springs 296 elastically bias the optical unit frame 260 downwardly in Figures 10 and 12, or in other words, in a direction approaching the process unit 36. Thus, the optical unit frame 260 is usually (for example, when the housing 6 is held at the open position) held at a predetermined position by the abutting of the supporting projecting portions 286 and 288 with the head parts of the fixing screws 294. In the illustrated embodiment, a charge eliminating lamp (not shown) is mounted on the optical unit frame 260. With reference mainly to Figure 10, a lamp housing 298 is mounted by a fixing screw 300 to the under surface of the supporting protruding portion 288 of the optical unit frame 260, and the charge eliminating lamp is disposed in the lamp housing 298. The charge eliminating lamp illuminates the rotating drum 40 through a charge eliminating opening 304 (Figures 10 and 13) formed in the upper wall 140 of the second frame member 126 in the process unit 36 to erase the residual charge on the photosensitive material. Manner of Mounting the Process Unit The process unit 36 is mounted detachably on the lower section 4 of the main body 2 of the machine in the following manner. With reference to Figures 13 and 14, a pair of vertical base plates 310 and 312 are disposed in spaced-apart relationship in the aforesaid crosswise direction in the lower section 4 of the main body. The vertical base plate 310 is divided in the front-rear direction (the left-right direction in Figure 13), and an inwardly projecting supporting pin 314 is set up in the inner surface of its one side 310a. An inwardly projecting supporting pin 316 is also set up in the inner surface of its other side 310b. A pair of supporting pins 318 and 320 projecting inwardly and spaced from each other in the front-rear direction are also set up in the inside inner surface of the vertical base plate 312. A support projecting portion 322 corresponding to the supporting pin 314 is provided in the outer surface of the end wall 136 of the second frame member 126 of the process unit 36, and a support projecting portion 326 corresponding to supporting pin 318 is provided in the outer surface of the other end wall 138. A support projecting portion 324 corresponding to the supporting pin 316 is provided in the outer surface of the end wall 128 of the first frame member 124 of the process unit 36, and a support projecting portion 328 corresponding to the supporting pin 320, in the outer surface of the other end wall 130. The under surfaces of the support projecting portions 322 and 326 are substantially flat, and a pair of upwardly projecting knob protrusions 330 are provided in the upper surface of these support projection portions. Arcuate receiving portions are defined in the under surfaces of the support projecting portions 324 and 328. With this construction, the unit frame 38 is detachably mounted across the vertical base plates 310 and 312 by placing it on the supporting pins 314, 316, 318, and 320 from above, or more specifically, positioning the receiving portions defined in the support projecting portions 324 and 328 (at one end portion of the unit frame 38) in the supporting pins 316 and 320 (constituting one supporting means) and at the same time, positioning the support projecting portions 322 and 326 at the other end portion in the supporting pins 314 and 318 (constituting the other supporting means). In this mounted state, the movement of the unit frame 38 in the left-right direction in Figures 13 and 14 with respect to the vertical base plates 310 and 312 is accurately restrained because the cylindrical supporting pins 316 and 320 are positioned in the arcuate receiving portions of the support projecting portions 324 and 328. Furthermore, in the illustrated embodiment, an elastic piece 332 such as a plate spring is provided at that site of the first frame member 124 of the unit frame 38 on which the tip of the supporting pin 320 acts. Accordingly, in the above mounted state, the elastic piece 332 acts on the unit frame 38 to bias it elastically downwardly. The tip of the supporting pin 316 abuts with the end wall 128 of the first frame member 124, and the unit frame 38 is held at the position shown by a solid line in Figure 13. Furthermore, in this mounted state, the unit frame 38 is free to pivot about the supporting pins 316 and 320 (constituting an axis of the center of pivoting) as a center. Hence, by holding the knob portions 330 of the support projecting portions 332 and/or 326 and lifting them, the unit frame 38 can be pivoted in the direction shown by an arrow 334 to the position shown by a two-dot chain line in Figure 14. Positioning of the Optical Unit with respect to the Process Unit A positioning means and a rotation hampering means are provided to maintain the process unit 36 and the optical unit 56 at a predetermined positional relationship. With reference to Figures 10, 12 and 13, the illustrated positioning means is comprised of a combination of a positioning projection and a receiving portion for detachably receiving the positioning projection. In the illustrated embodiment, the positioning projection is comprised of a cylindrical positioning pin 346 set up integrally in the under surface of the wall 272 of the optical unit frame 260, and the receiving portion is comprised of a receiving hole 342 defined by a circular protrusion 338 provided integrally on the upper surface of the upper wall 140 of the second frame member 126 in the process unit 36. By providing the positioning pin 346 and the circular protrusion 338 defining the receiving hole 342 integrally in the optical unit frame 260 and the second frame member 126, the positioning to be described of the optical unit frame 260 and the process unit frame 38 can be effected accurately. The receiving hole 342 is of a circular shape having an inside diameter corresponding to the outside diameter of the positioning pin 346. When the opening-closing housing 6 is held at the closed position as will be described below, the positioning pin 346 is positioned in place in the receiving hole 342. As a result, that site of the process unit frame 38 at which the receiving hole 342 is provided is kept substantially in alignment in the vertical direction with that site of the optical unit frame 260 at which the positioning pin 346 is set up. To facilitate positioning of the positioning pin 346 in the receiving hole 342, it is preferred to taper the tip portion of the positioning pin 346 and to incline the opening part of the receiving hole 342 downwardly inwardly. Preferably, the receiving hole 342 defining the receiving portion is provided in the neighborhood of an exposure opening 347 defined between the upper wall 132 of the first frame member 124 and the upper wall 140 of the second frame member 126 as shown in Figure 13. This arrangement enables the projecting opening 226 in the optical unit 56 and the exposure opening 347 to be maintained at a predetermined positional relationship more accurately. The rotation hampering means is comprised of a rotation hampering protrusion and a receiving portion for detachably receiving the rotation hampering protrusion. In the illustrated embodiment, the rotation hampering protrusion is comprised of a cylindrical rotation hampering pin 348 integrally provided in the under surface of the wall 272 of the optical unit frame 260, and the receiving portion is comprised of an elongate receiving hole 344 defined in the protrusion 340 formed integrally on the upper surface of the upper wall 140 of the second frame member 126 in the process unit 36. The receiving hole 344 has a width corresponding to the outside diameter of the rotation hampering pin 348, and extends in a direction substantially perpendicular to the axis of the center of pivoting of the housing 6 (left-right direction in Figure 12). When the housing 6 is held at the closed position in the manner to be described, the rotation hampering pin 348 is positioned in place in the elongate receiving hole 344. As a result, the relative pivoting movement of the process unit frame 38 and the optical unit frame 260 about the positioning pin 346 as a center can be accurately hampered. To facilitate the positioning of the rotation hampering pin 348 in the receiving hole 344, it is preferred as shown in Figure 12 to taper the tip portion of the rotation hampering pin 348 and at the same time incline the opening portion of the receiving hole 344 downwardly inwardly. With regard to the positioning means, it is possible to provide the positioning protrusion in the process unit frame 38 and the receiving portion in the optical unit 260 contrary to the above-described feature. Furthermore, with regard to the rotation hampering means, too, it is possible to provide the rotation hampering protrusion in the process unit frame 38 and the receiving portion in the optical unit frame 260 contrary to the above feature. In the illustrated embodiment, three actuating pieces 350 are provided in the optical unit frame 260 in order to maintain a predetermined vertical distance between the process unit frame 38 and the optical unit frame 260. One actuating piece 350 is nearly triangular, and is provided at the end portion of the wall 274. It acts on the right end portion in Figure 10 of the upper wall 132 of the first frame member 124. The other two actuating pieces 350 are cylindrical pins and are provided on the supporting projection 288 in spaced-apart relationship in the lateral direction (the left-right direction in Figure 12 and in a direction perpendicular to the sheet surface in Figure 10). They act on the left end portion in Figure 10 of the upper wall 140 of the second frame member 126. With this construction, when the housing 6 is held at the closed position in the manner to be described, the actuating pieces 350 act on the process unit 36, and the distance between the process unit frame 38 and the optical unit frame 260 is maintained at a predetermined value by the action of these actuating pieces 350. By providing these actuating pieces 350 integrally in the optical unit frame 260, the distance between the optical unit frame 260 and the process unit frame 38 can be accurately maintained at a desired value. Mounting and Detaching Operations of the Process Unit With reference mainly to Figures 2 and 3, the operations of mounting and detaching the process unit 36 will be described. To detach the process unit 36, the openingclosing housing 6 is first opened. Specifically, the locking in the locking means 28 is released, and the housing 6 is pivoted in the direction of arrow 35. When the engaging member 30 in the locking means 28 is held at the non-locking position shown by the two-dot chain line in Figure 2, the engaging member 30 is disengaged from the engaging opening 34 formed in the lower section 4 of the main body. When the housing 6 is lifted thereafter, the housing 6 pivots in the direction of arrow 35 about the supporting shaft 14 as a center and held at the open position shown by the two-dot chain line in Figure 2. When the housing 6 is held at the open position, the top of the process unit 36 is open to view. Consequently, part of the conveying passage is opened, and the process unit 36 is in condition for detachment. With reference to Figures 13 and 14, part of the conveying passage (specifically that part of the conveying passage which is below the rotating drum 40) is opened by holding the knob portions 330 of the support portions 322 (and/or 326) provided in the unit frame 38 and lifting them. As a result, the unit frame 38 is pivoted in the direction of arrow 334 (Figure 14) about the supporting pins 316 and 320 as a center. For example, by pivoting the unit frame 38 to the position shown by the two-dot chain line in Figure 14, part of the conveying passage is opened as is required. Thus, should a sheet material be jammmed up in the above part of the conveying passage, especially in a region from a site below the rotating drum 40 to the fixing roller pair 82, the sheet material can be easily removed by opening the conveying passage as described above. To detach the process unit 36, the unit frame 38 is taken out through the space formed by holding the housing 6 in the open position. When the unit frame 38 is lifted, the support portions 322, 324, 326 and 328 are detached respectively from the supporting pins 314, 316, 318 and 320, and the gear 180 is disconnected from the driving gear 182 (Figure 7). As a result, the process unit 36 can be detached as is required. On the other hand, to mount the process unit 36, the unit frame 38 is positioned on the supporting pins 314, 316, 318 and 320 through the aforesaid space while the housing 6 is held at the open position. Consequently, as shown in Figure 13 and by a solid line in Figure 14, the support portions 322, 324, 326 and 328 provided in the unit frame 38 are positioned respectively on the corresponding supporting pins 314, 316, 318 and 320, whereby the process unit 36 is detachably mounted on the lower section 4 of the main body. Thereafter, the housing 6 is pivoted in a direction opposite to the direction of arrow 35 from the open position and held at the closed position shown in Figures 1 and 3 and by the solid line in Figure 2. At the closed position, the engaging member 30 engages the engaging opening 34, and the housing 6 is held releasably at the closed position by the action of the locking means 28. When the bousing 6 is held at the closed position, the positioning pin 346 and the rotation hampering pin 348 provided in the optical unit frame 260 are positioned in the receiving portion (the receiving hole 342) and the receiving portion (the receiving hole 344) defined in the unit frame 38 mounted across the vertical base plates 310 and 312 (Figure 13) as shown in Figures 10 and 12. Since the outside diameter of the positioning pin 346 is substantially equal to the inside diameter of the receiving hole 342, the specific sites of the unit frame 38 and the optical unit frame 260 (in the illustrated embodiment, that site of the optical unit frame 260 which is near the projecting opening 276 and that site of the unit frame 38 which is near the exposure opening 347) are kept in alignment vertically with each other. Furthermore, since the outside diameter of the rotation hampering pin 348 is substantially equal to the width of the receiving portion (receiving hole 344). The relative turning of the optical unit frame 260 about the positioning pin 346 as a center with respect to the unit frame 38 can be hampered. As a result, the optical unit 56 is positioned as is required above the process unit 36. The receiving portion 116 and the upper inclined wall 118 of the housing 6 are positioned above the optical unit 56, and the process unit 36 and the optical unit 56 are maintained accurately in a predetermined positional relationship via the positioning means and the rotation hampering means. When the opening-closing housing 6 is held at the closed position, the actuating pieces 350 formed in the optical unit frame 260 act on the upper surface of the unit frame 38 (one actuating piece 350 acting on the upper wall 132 of the first frame member 124, and the two actuating pieces 350, on the upper wall 140 of the second frame member 126), and the optical unit frame 260 is slightly elevated against the biasing force of the biasing coil spring 296 with respect to the unit frame 38, as shown in Figures 10 and 12. Accordingly, the optical unit frame 260 is maintained at a predetermined distance from the unit frame 38 by the action of the actuating pieces 350 and elastically pressed and held by the action of the biasing coil spring 296. Thus, the vertical distance between the unit frame 38 and the optical unit frame 260 is accurately maintained at a predetermined value. In an image-forming condition in which the opening-closing housing 6 is held at the closed position, the upwardly inclined wall 118 (the site defining the receiving portion 166) of the housing 6 extends upwardly at a first angle to the horizontal from left to right in Figures 3 and 10, that is, downstream in the discharging direction of the sheet material. In this regard, the optical unit frame 260 disposed in the inner wall of the upwardly inclined wall 118, also inclined to the horizontal, extends substantially parallel to the upwardly inclined wall 118. In the optical unit frame 260, a laser beam from the laser beam source 58 is reflected by the rotating polygon mirror 60, and the conducted toward left bottom in Figure 3 and downwardly in Figure 11. It is reflected by the first reflecting mirror 64 and reaches the second reflecting mirror 66. Then, it passes through the transparent glass 278 and reaches the rotating drum 40. The longest straight-line portion of the light path of the optical means 69, i.e. the part from the rotating polygon mirror 60 to the first reflecting mirror 64 in the illustrated embodiment, extends substantially parallel along the optical unit frame 260 or in other words, the upwardly inclined wall 118, from right end portion of the optical unit 260 in Figures 3 and 10 to its left end portion in Figures 3 and 10. Accordingly, no wasteful space substantially exists between the upwardly inclined wall 118 of the housing 6 and the optical unit frame 260, and the machine as a whole can be reduced in size. Furthermore, since the main part of the optical path of the optical means 69 is inclined as above described to the horizontal. The length in the left-right direction (horizontal) of the optical unit frame 260 in Figures 3 and 10 becomes small. While part of the machine slightly becomes higher, but the size of the machine as a whole in the left-right direction in Figure 3 can be greatly decreased. The first angle ϑ (Figure 3) can be preset at about 45 degrees in view of the dischargeability of the sheet material received by the receiving portion 116 and the size reduction of the machine as a whole. Furthermore, since the main portion of the light path of the optical means 69 is so inclined, a relatively large space is produced on the right side of the rotating drum 40 in Figures 3 and 10. In this space, the developing device 46 is disposed as shown in Figure 3, and the toner holding chamber 206 of the developing device 46 is apart from the rotating drum 40 and is positioned outwardly of the magnetic brush mechanism 104. Hence, the space existing below the right end portion of the optical unit frame 260 in Figures 3 and 10 in which the toner holding chamber 206 exists is relatively high and sufficiently large despite the smaller size of the machine as a whole. By effectively utilizing this space as the toner holding chamber 206. A toner in an amount sufficient for consumption until the photosensitive material of the rotating drum 40 substantially comes to the end of its life can be held. The above description has been directed mainly to the reduction of the space between the receiving portion 116 into which the sheet material is discharged and the optical means 69. To produce a relatively large space on one surface of the rotating drum 40, it is sufficient only to incline the main part of the light path of the optical means 69. At this time, the inclination angle (to the horizontal) of the main part of the light path may be a second angle which differs from the first angle. By enlarging the second angle, a large space for the developing device 46 is produced. The second angle is preferably about 45 degrees which is the same as the first angle when the receiving portion 116 is provided substantially parallel to the main part of the light path in the optical means 69.

Claims: An image-forming machine comprising a main body (2) including an upper wall (118), image-bearing means in the form of a rotating drum (40), including a surface having a photosensitive material thereon, optical means (56) for projecting light having image information onto the photosensitive material on the surface, a developing device (46) for developing a latent electrostatic image formed on the surface, transfer means (48) for transferring a toner image formed on the surface in a transfer zone to a sheet material, a conveying mechanism (72) for conveying the sheet material through the transfer zone, and a receiving section (116) for receiving the sheet material conveyed by the conveying mechanism (72), characterized in that the receiving section (116) is disposed above the optical means (56) and includes a receiving surface defined by an upper surface of the upper wall (118) of the main body (2), the receiving surface being inclined upwardly at a predetermined angle (ϑ) to the horizontal; in that the optical means (56) are disposed in a box-like optical unit frame (260), wherein the optical unit frame (260) is disposed within the main body (2) at a location above the rotating drum (40) and extending substantially parallel to the receiving surface of the receiving section (116) and inclined upwardly from a lower first end on a first side of the rotating drum (40) to an upper second end on a second side of the rotating drum (40), thereby defining an enlarged space below the optical unit frame (260) on the second side of the rotating drum (40); in that a main portion of a light path of the optical means (56) is inclined to the horizontal substantially parallel to the receiving surface of the receiving section (116) in a straight line from one end portion to another end portion of the optical unit frame (260); and in that the developing device (46) is positioned in the enlarged space below the optical unit frame (260) at a location on the second side of the rotating drum (40). The machine according to claim 1, characterized in that the optical unit frame (260) is mounted on an inside surface of the upper wall (118) of the main body (2). The machine according to claim 1 or 2, characterized in that the predetermined angle (ϑ) of inclination of the receiving surface is about 45°. The machine according to any of claims 1 to 3, characterized in that the developing device (46) includes toner applicator means (194) for applying toner to the surface of photosensitive material and a toner holding chamber (188) for holding the toner, wherein the toner applicator means (194) is positioned adjacent the rotating drum (40), and the toner holding chamber (188) is disposed outwardly of the toner applicator means (194).

Inventors: HORIHATA KATSUSHI, KOBAYASHI KAZUHIRO, KOYAMA SHIGEO, TANAKA HIROYUKI, TSUTSUI EIJI, HORIHATA, KATSUSHI, KOBAYASHI, KAZUHIRO, KOYAMA, SHIGEO, TANAKA, HIROYUKI, TSUTSUI, EIJI
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO. LTD.
Application year: 1988
Main classification: B41J29
IPC codes: G03G21, G06K15, B41J29, H04N1