ELECTROSTATIC COPYING APPARATUS

Abstract: An electrostatic copying apparatus comprises a hous­ ing (2) having a photosensitive member disposed there­ within for free movement througt an endless moving path defined within the housing. An original-support mechanism (4) is disposed on the top surface of the housing (2) and includes a transparent plate (8) for receiving an original document to be copied. A charging corona-discharge device (22) applies corona discharge to the photosensitive member in a latent electrostatic image-forming zone (16) located along the moving path of the photosensitive member. An optical unit (32) projects the image of the original document placed on the transparent plate (8) onto the photosensitive member in the latent electrostatic image-­ forming zone (16), and a paper transfer unit (46) transfers a copying paper through a predetermined transfer passage extending through a transfer zone (20) located along the moving path of the photosensitive member and downstream of the latent electrostatic image-forming zone (16) in the moving direction of the photosensitive member. The apparatus further includes a detecting means for detecting the longitudinal size of the copying paper being transferred by the transfer unit (46) and a control means for operating the charging corona-discharge device (22) only for a time period corresponding to the detected longitudinal size of the copying paper.

Description: This invention relates to an electrostatic copying apparatus and its constituent elements. Recently, electrostatic copying apparatuses of the visible image-transfer type have gained wide-spread commercial acceptance. This type of electrostatic copying apparatus performs a copying process which comprises forming on a photosensitive member a latent electrostatic image corresponding to the image of an original document to be copied, applying toner particles to the latent image to develop it to a visible image, and transferring the visible image to a receptor sheet. The apparatus is provided with a photosensitive member which is disposed on the surface of a rotary drum or an endless belt-like member mounted within a housing and is adapted to be moved through a predetermined endless moving path (i.e., a circular or otherwise-shaped endless moving path defined by the surface of the rotary drum or endless belt-like member) according to the movement of the rotary drum or endless belt-like material, and along the moving path of the photosensitive member are located a latent electrostatic image-forming zone, a developing zone and a transfer zone in this order in the moving direction of the photosensitive member. In the latent electrostatic image-forming zone, corona discharge is generally applied to the surface of the photosensitive member by a charging corona-discharge device thereby charging the photosensitive member to a specified polarity. Then, by the action of an optical unit, the image of an original document placed on a transparent plate of an original-support mechanism disposed on the top surface of the housing is projected onto the photosensitive member. Consequently, the charge on the photosensitive member is selectively caused to disappear, and a latent electrostatic image corresponding to the image of the original document to be copied is formed on it. In the developing zone, toner particles are applied to the latent electrostatic image on the photosensitive member by the action of a developing device according to the charge of the latent image, thereby developing the latent image to a visible image (toner image). Then, in the transfer zone, the visible image on the photosensitive member is transferred to a receptor sheet transferred through the transfer zone, thereby forming the visible image corresponding to the image of the original document on the receptor sheet. In order to form the desired visible image of good quality repeatedly on receptor sheets in the above-mentioned electrostatic copying apparatus of the visible image-transfer type, it is important, as well known to those skilled in the art, that the electric charge and the toner particles remaining on the photosensitive member after the transfer of the visible image in the transfer zone should be fully removed so as to avoid any adverse effects of the residual charge and toner particles on the next copying cycle. Removal of the residual charge is generally effected by exposing the entire surface of the photosensitive member to light by means of a charge-eliminating lamp, and/or by applying corona discharge to the photosensitive member by a charge-eliminating corona discharge device, after the transfer of the visible image in the transfer zone. On the other hand, the removal of the residual toner is accomplished by causing a cleaning means such as a cleaning blade or a magnetic brush mechanism to act on the surface of the photosensitive member after the transfer of the visible image in the transfer zone. When the aforesaid developing device is comprised of a magnetic brush mechanism, the developing device can be caused to function both as developing means and cleaning means. A disadvantage with the conventional visible image-transfer type electrostatic copying apparatus is that because the longitudinal size of a visible image formed on the photosensitive member does not always correspond to that of a receptor sheet, a visible image having a larger longitudinal size than the receptor sheet transferred through the transfer zone is frequently formed on the photosensitive member and makes it difficult to remove the residual charge and toner particles fully from the photosensitive member after the transfer of the visible image in the transfer zone. When the longitudinal size of the visible image formed on the photosensitive member is larger than that of a receptor sheet transferred through the transfer zone, a part of the visible image on the photosensitive member naturally remains on the photosensitive member without being transferred to the receptor sheet after the transfer of the visible image in the transfer zone. The amount of the toner particles remaining on the photosensitive member after the transfer is relatively small in that area of the visible image on the photosensitive member which has been transferred to the receptor sheet, and therefore, in this area, the residual charge and toner particles on the photosensitive member can be fully removed by the action of the suitable charge-eliminating means and cleaning means of the types mentioned hereinabove. In that area of the visible image on the photosensitive member which remains untransferred to the receptor sheet, however, a relatively large amount of the toner particles remains on the photosensitive member after the transferring operation. In this case, the light irradiated onto the surface of the photosensitive member from a charge-eliminating lamp and/or the corona discharge applied to the surface of the photosensitive member from a charge-eliminating corona discharge device is intercepted by the toner particles remaining in a relatively large amount, and cannot act fully on the surface of the photosensitive member, resulting in insufficient removal of the residual charge. In addition, since the remaining toner particles in this area adhere relatively firmly to the photosensitive member owing to the insufficient removal of the charge as stated above, the remaining toner particles cannot be fully removed by the aforesaid cleaning means. In a conventional electrostatic copying apparatus of the latent electrostatic image-transfer type which differs from the aforesaid visible image-transfer type copying apparatus in that a latent electrostatic image formed on the photosensitive member is directly transferred to a copying paper without development and is developed to a visible image by application of toner particles, again, the longitudinal size of the latent electrostatic image formed on the photosensitive member does not always correspond to that of the copying paper transferred through the transfer zone, and a latent electrostatic image having a larger longitudinal size than the copying paper transferred through the transfer zone is frequently formed. In such a case, a part of the latent electrostatic image on the photosensitive member remains there without being transferred to the copying paper after the transfer of the latent electrostatic image to the copying paper, and therefore, even after the transfer of the latent electrostatic image in the transfer zone, a relatively large amount of charge remains in some area of the photosensitive member. It is not necessarily easy to remove such a relatively large amount of charge completely. It is known that when a corona discharge device for charging a photosensitive member to a specified polarity in a latent electrostatic image-forming area is controlled so as to be operated only for a time period corresponding to the longitudinal size of a copying paper transferred through a transfer zone, thereby making the longitudinal size of a latent electrostatic image formed on the photosensitive member or developed image obtained by developing the latent image substantially equal to, or smaller than, the longitudinal size of a copying paper transferred through a transfer zone, relatively large amounts of electric charge and/or toner particles are prevented from remaining on the photosensitive member without being transferred to the copying paper after the transfer of the visible image or latent image, and therefore that the charge and/or toner particles remaining on the photosensitive member after the transfer can be fully removed. Control of the corona discharge device in known arrangements has been achieved by incorporating in the copying apparatus a means which establishes the length of the copying paper by detecting its leading and trailing edges and computing the length accordingly. In U.S. Patent No. 3 944 356, the base plate which receives a stack of copying paper contains an array of mechanical switches which are selectively actuated in dependence upon the size of the copying sheets of the stack. In DE-A1-2729591, there is provided a pair of switch means adapted to respond to the leading and trailing edges respectively of each sheet of copying paper as it approaches a transfer station whereby the length of that sheet can be calculated and the corona discharge device controlled accordingly. It is an object of the present invention to improve the control arrangement of the known control systems in such electrostatic copying apparatuses. In accordance with the present invention, there is provided an electrostatic copying apparatus comprising a housing,a photosensitive member disposed within the housing for free movement through an endless moving path defined within the housing, an original-support mechanism disposed on the top surface of the housing and including a transparent plate on which to place an original document to be copied, a charging corona-discharge device for applying corona discharge to the photosensitive member in a latent electrostatic image-forming zone located along the moving path of the photosensitive member, an optical system for projecting the image of the original document placed on the transparent plate onto the photosensitive member in the latent electrostatic image-forming zone, one of the original-support mechanism and at least a part of the optical system being arranged, in operation, to be scanningly moved toward the other whereby the image of the original document placed on the transparent plate is scanned and projected onto the photosensitive member, and a copying paper transfer unit for transferring a copying paper through a predetermined transfer passage extending through a transfer zone located along the moving path of the photosensitive member and downstream of the latent electrostatic image-forming zone in the moving direction of the photosensitive member, a transfer corona-discharge device for applying, during the period of image transfer, corona discharge to the back surface of the copying paper passing through the transfer zone, and a fixing mechanism which has an electric heater and is disposed downstream of the transfer zone in the transfer passage for the copying paper, said copying paper transfer unit including a cassette-receiving section for detachably receiving a copying paper cassette containing a plurality of copying paper sheets of predetermined size in the stacked state and a feed mechanism for feeding the copying paper sheets one by one from the copying paper cassette when mounted to the cassette-receiving section, the apparatus further comprising a detecting means for determining the longitudinal size of the copying paper being transferred by the transfer unit and a control means for operating the charging corona-discharge device only for a period of time which corresponds to the detected longitudinal size of the copying paper,the copying paper size detecting means comprising a copying paper size indicating means which provides an indication of the paper size to be used with a given cassette, and a sensing means mounted in the cassette-receiving section of the apparatus and adapted to sense the copying paper size, indicating means for indicating the longitudinal size of the copying paper associated with that cassette, and the control means for the charging corona-discharge device comprising an actuation starting means for starting the actuation of the charging corona-discharge device simultaneously with, immediately before, or immediately after, the starting of the scanning movement of one of the original-support mechanism and said at least a part of the optical unit from a scanning movement starting position, and an actuation stopping means which, when one of the original-support mechanism and said at least a part of the optical unit has made a scanning movement from the scanning movement-starting position by a distance substantially corresponding to the longitudinal size of the copying paper detected by the copying paper size detecting means, detects it and stops the actuation of the charging corona-discharge device, the apparatus further comprising, for controlling the period of actuation of the transfer corona discharge device and the current supply to the heater of the fixing mechanism, an actuation starting timer for starting the actuation of the transfer corona-discharge device after the lapse of a predetermined period of time from the starting of the actuation of the charging corona-discharge device, an actuation stopping timer for stopping the actuation of the transfer corona-discharge device after the lapse of a predetermined period of time from the stopping of the actuation of the charging corona-discharge device,a temperature control means for varying current supply to the electric heater according to the temperature of the fixing mechanism, and a current supply variation inhibiting means for inhibiting variations of the current supply to the electric heater by the temperature control means while at least one of the charging corona-discharge device and the transfer corona-discharge device is in operation. The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a perspective view showing one embodiment of the electrostatic copying apparatus constructed in accordance with this invention; Figure 2 is a simplified sectional view of the electrostatic copying apparatus shown in Figure 1; Figure 3 is a perspective view showing the method of mounting a rotary drum and a developing device in the electrostatic copying apparatus shown in Figures 1 and 2. Figure 4 is a perspective view showing a first fan and a second fan used in the electrostatic copying apparatus shown in Figures 1 and 2; Figure 5 is a perspective view showing a manual paper-positioning mechanism applied to the electrostatic copying apparatus shown in Figures 1 and 2; Figure 6 is a sectional view showing the manual paper-positioning mechanism shown in Figure 5 applied to the electrostatic copying apparatus shown in Figures 1 and 2; Figures 7-A to 7-D are diagrammatic views schematically showing a paper cassette size displaying means provided in various copying paper cassettes applied to the electrostatic copying apparatus shown in Figures 1 and 2; Figure 8 is a perspective view showing a detecting switch mechanism used in the electrostatic copying apparatus shown in Figures 1 and 2; Figures 9-A to 9-D are simplified views showing the operation of a detecting switch mechanism used in Figures 1 and 2; Figure 10 is a simplified view showing actuators and a driven member used in the electrostatic copying apparatus shown in Figures 1 and 2; Figure 11 is a block diagram showing a part of an electrical control circuit used in the electrostatic copying apparatus shown in Figures 1 and 2; and Figure 12 is a time chart showing the states of the operations of various constituent elements used in the electrostatic copying apparatus shown in Figures 1 and 2. First of all, the general construction of the illustrated electrostatic copying apparatus is described in outline with reference to Figures 1 and 2. The illustrated electrostatic copying apparatus has a substantially rectangular housing shown generally at 2. On the top surface of the housing 2 is disposed an original-support mechanism 4 for supporting an original document to be copied. The original-support mechanism 4 is constructed of a support frame 6 mounted movably for scanning of the original document by a suitable method (in the left and right directions in Figure 2), a transparent plate 8 (Figure 2) fixed to the support frame 6 and adapted to place the original document thereon, and an original-holding member 10 which has one edge portion (the edge portion located in the upper part in Figure 1) connected pivotably to the support frame 6 and which is to be turned by a manual operation between a closed position at which it covers the transparent plate 8 and the original document placed on it (the position shown in Figures 1 and 2) and an open position at which the transparent plate 8 and the original document on it are brought to view. The original-support mechanism 4 is preferably of such a type that when the electrostatic copying apparatus is in an inoperative state, it stops at a stop position shown by a solid line in Figures 1 and 2, but when the copying apparatus sets in operation and the copying process is performed, it makes a preparatory movement from the stop position to a scanning movement starting position shown by a two-dot chain line 4A in Figure 2 in the right direction, then makes a scanning movement from this start position to a scanning movement-ending position shown by a two-dot chain line 4B in Figure 2 in the left direction, and thereafter, returns to the stop position in the right direction in Figure 2. On the upper part of the front surface of the housing 2 are provided operating elements such as a main switch, a knob for setting the number of copies required, and a knob for adjusting the intensity of exposure and display elements such as a display lamp, which are all known per se . As Figure 2 shows in a simplified manner, a cylindrical rotary drum 12 is rotatably mounted within the housing 2, and a photosensitive member is disposed on at least a part of the peripheral surface of the rotary drum 12. Accordingly, the photosensitive member is moved by the rotation of the rotary drum 12 through a circular endless moving path defined by the peripheral surface of the rotary drum 12. Instead of the rotary drum 12, an endless belt-like material known well to those skilled in the art may be mounted within the housing 2, and a photosensitive member may be disposed on at least a part of the surface of the endless belt-like member. In this alternative construction, the photosensitive member is moved through an endless moving path defined by the surface of the endless belt-like member. Along the peripheral surface of the rotary drum 12 rotated in the direction of an arrow 14, therefore along the moving path of the photosensitive member on the rotary drum 12, are disposed a latent electrostatic image-forming zone 16, a developing zone 18 and a transfer zone 20 in this order viewed in the moving direction of the photosensitive member. In the latent electrostatic image-forming zone 16 is disposed a charging corona-discharge device 22 for applying corona discharge to the surface of the photosensitive member to charge it to a specified polarity. A developing device 24 is provided within the developing zone 18, which function both as a developing means for applying toner particles to a latent electrostatic image formed on the photosensitive member to develop it and as a cleaning means for removing residual toner particles from the photosensitive member after the transfer of a developed image to a copying paper in the transfer zone 20 in the illustrated embodiment. The transfer zone 20 includes therein a transfer corona-discharge device 26 for applying corona discharge to the back surface of the copying paper at the time of transferring a developed image on the photosensitive member to the copying paper. A charge-eliminating corona-discharge device 28 and a charge-eliminating lamp 30 for removing residual charges on the photosensitive member after the transfer of a developed image on the photosensitive member to a copying paper in the transfer zone 20 are disposed downstream of the transfer zone 20 and upstream of the latent electrostatic image-forming zone 16 viewed in the rotating direction of the rotary drum 12 shown by the arrow 14, and therefore in the moving direction of the photosensitive member. The charge-eliminating corona-discharge device 28 applies corona discharge to the photosensitive member for charge elimination, and the charge-eliminating lamp 30 exposes the entire surface of the photosensitive member to light. An optical unit 32 for projecting the image of an original document placed on the transparent plate 8 of the original-support mechanism 4 onto the photosensitive member is provided above the rotary drum 12 within the housing 2. The optical unit 32 includes an illuminating lamp 36 for illuminating the original document through an exposure opening 34 formed on the top surface of the housing 2, and a first reflecting mirror 38, an in-mirror lens 40, a second reflecting mirror 42 and a third reflecting mirror 44 for projecting the light reflected from the original document onto the photosensitive member. As shown by a broken arrow in Figure 2, the optical unit 32 projects the image of the original document placed on the transparent plate 8 onto the photosensitive member at a position immediately downstream of the charging corona-discharge device 22 in the rotating direction of the rotating drum 12 in the latent electrostatic image-forming zone 16. In the illustrated embodiment, the image of the original document is scanned and optically projected on the photosensitive member by moving the original-support mechanism 4 in a scanning manner. Instead of this, the image of the original document can also be scanned and optically projected on the photosensitive member by scanningly moving at least a part of the optical unit. A paper transfer unit shown generally at 46 is also provided in the illustrated electrostatic copying apparatus. The paper transfer unit 46 includes a paper-feed mechanism 54 consisting of a paper cassette 50 whose end is inserted into a cassette-receiving section 48 within the housing 2 through an opening formed in the right end wall of the housing 2 and a paper feed roller 52 for feeding copying paper sheets one by one from the paper cassette 50 by being rotationally driven while being in engagement with the topmost sheet of a stack of paper sheets in the paper cassette 50 through an opening formed on the top surface of the paper cassette 50. The paper transfer unit 46 also comprises a pair of transfer rollers 55 for transferring the paper sheet delivered by the action of the paper feed roller 52 to the transfer zone 20 and a separator roller 56 for separating the copying paper adhering closely to the surface of the photosensitive member on the rotary drum 12 in the transfer zone 20 from the photosensitive member and carrying it away from the transfer zone 20. The copying paper carried away from the transfer zone 20 moves through a fixing mechanism shown generally at 58 for fixing the developed image on the copying paper and is discharged into a receiver tray 60 from a discharge opening formed in the left end wall of the housing 2. In the illustrated embodiment, the paper transfer unit 46 is of the type provided with the paper feed mechanism 54 utilizing the paper cassette 50. In place of, or in addition to, the paper feed mechanism 54, a paper feed mechanism of the type adapted to unwind a roll of copying paper, cut it to a required length and deliver it may be provided in the paper transfer unit 46. The operation of the electrostatic copying apparatus described above is described briefly. While the rotary drum 12 is being rotated in the direction of the arrow 14, a latent electrostatic image is formed on the surface of the photosensitive member in the latent electrostatic image-forming zone 16. Specifically, the latent electrostatic image is formed by applying corona discharge to the photosensitive member by means of the charging corona-discharge device 22 to charge it to a specified polarity, and then projecting the image of an original document placed on the transparent plate 8 onto the charged photosensitive member by means of the optical unit 32. In projecting the image of the original document onto the photosensitive member by the optical unit 32, the original-support mechanism 4 is caused to make a scanning movement from the scanning movement starting position shown by the two-dot chain line 4A to the scanning movement ending position shown by the two-dot chain line 4B in the left direction in Figure 2. Then, in the developing zone 18, toner particles are applied to the latent electrostatic image on the photosensitive member by the action of the developing device 24 thereby developing the latent electrostatic image on the photosensitive member. In the meantime, the paper transfer unit 46 transfers a copying paper to the transfer zone 20 in synchronism with the rotation of the rotary drum 12, and in the transfer zone 20, the developed image on the photosensitive member is transferred to the copying paper. The copying paper having the developed image transferred thereto is fixed by the fixing mechanism 58 and then discharged into the receiver tray 60. On the other hand, the rotary drum 12 continues to rotate through at least one turn, preferably through two or more turns, after the developed image on the photosensitive member has been transferred to the copying paper, and during this period, the residual charge on the photosensitive member is removed by the action of the charge-eliminating corona-discharge device 28 and the charge-eliminating lamp 30. Furthermore, by the functioning of the developing device 24 as a cleaning means, the residual toner on the photosensitive member is removed. In the present apparatus the operations of various constituent elements of the electrostatic copying apparatus are controlled on the basis of the longitudinal size of a copying paper transferred through the transfer zone 20 by the transfer unit 46, particularly the size of a copying paper contained in the cassette 50 mounted to the cassette-receiving section 48 (therefore, the paper fed by the action of the feed roller 52 and transferred through the transfer zone 20). In order to perform such an operational control, the illustrated electrostatic copying apparatus includes a paper size indicating means on the cassette 50 (Figure 2) mounted to the cassette-receiving section 48, and a sensing means for sensing the paper size indicating means is provided in the cassette-receiving section 48. The paper size indicating means and the sensing means constitute means for detecting the size of paper. In the illustrated electrostatic copying apparatus, one of four types of paper cassettes 50 including copying paper sheets of sizes A5, B5, A4 and B4 according to JIS is selectively mounted to the cassette-receiving section 48 provided at the lower part of the right end portion of the housing 2, as shown in Figure 2. Since the illustrated electrostatic copying apparatus is constructed such that each of the various types of paper cassettes 50 can be mounted selectively to one cassette-receiving section 48, it is convenient that irrespective of the sizes of the copying papers in the cassettes, at least the front end portion of the cassettes are formed in the same contour so that they can be mounted as required in the same configuration substantially on the cassette-receiving section 48. The various copying paper cassettes 50 to be selectively mounted on the cassette-receiving section 48 are provided each with a paper size indicating means for indicating the size of papers accommodated therein. One example of the paper size indicating means is described below when the electrostatic copying apparatus includes four types of cassettes (A5, B5, A4 and B4 sizes) as described above. Referring to Figures 7-A to 7-D, two indicating positions 266a, 266b are defined at predetermined parts of the front surface of each copying paper cassette 50. In the A5 paper cassette 50 (A5) shown in Figure 7-A, no magnet exists at either of the two indicating positions 266a and 266b. In the B5 paper cassette 50 (B5) shown in Figure 7-B, a magnet exists at the indicating position 266a, and no magnet exists at the indicating position 266b. In the A4 paper cassette 50 (A4) shown in Figure 7-C, no magnet exists at the indicating position 266a and a magnet exists at the indicating position 266b. In the B4 paper cassette 50 (B4) shown in Figure 7-D, a magnet exists both at the indicating positions 266a and 266b. The presence of a magnet in Figures 7-A to 7-D is indicated by blackening of the indicating positions. The sensing means for sensing the paper size indicating means described above is provided at the cassette-receiving section 48. The sensing means in the illustrated embodiment comprises reed switches 268a and 268b (only 268b is shown in Figures 2 and 6, and both are shown in the block diagrams to be described hereinbelow) which are located opposite to the indicating positions 266a and 266b respectively and are adapted to be closed by the action of a magnetic field which may be generated by the magnets at the indicating positions 266a and 266b. In the paper size detecting means comprised by the paper size indicating means and the sensing means, the reed switches 268a and 268b remain open when an A5 paper cassette 50 (A5) has been mounted to the cassette-receiving section 43. When the B5 paper cassette 50 (B5) is mounted in the cassette-receiving section 48, the reed switch 268a is closed, and when the cassette-receiving section 48 receives the A4 paper cassette 50 (A4), the reed switch 268b is closed. When the B4 paper cassette 50 (B4) is mounted to the cassette-receiving section 48, both the reed switches 268a and 268b are closed. Now, let the open condition of each of the reed switches 268a and 268b be "0", its closed condition be "1", the condition of the reed switch 268a be indicated at the first place and the condition of the reed switch 268b be indicated at the second place, then the sizes of the individual copying papers can be expressed by a binary system as shown in Table 1 below. Since in the illustrated embodiment, four types of the copying paper cassettes 50 are used selectively, the two indicating positions 266b are defined at the front surface of the cassette 50 and the two reed switches 268a and 268b are disposed at the cassette-receiving section 48. However, when only two types of paper cassettes 50 are used selectively, it is sufficient to provide one indicating position and one reed switch. Conversely, when five or more types of copying paper cassettes are used, three or more indicating positions and reed switches can respectively be provided. If desired, instead of the combination of a magnet and a reed switch at the indicating position, other suitable combinations, for example a combination of a protrusion and a limit switch, may also be used. As already stated with reference to Figure 2, in the illustrated electrostatic copying apparatus, scanning movement of the original-support mechanism 4 causes the image of an original document placed on the transparent plate 8 of the original-support mechanism 4 to be scanned and projected upon the photosensitive member 70 (Figure 3). As will be described in more detail hereinbelow, the operations of the various elements of the electrostatic copying apparatus are controlled on the basis of the movement of the original-support mechanism 4 (or instead of the movement of the original-support mechanism 4, movement of at least a part of the optical unit 32 when the electrostatic copying apparatus is of the type wherein by moving at least a part of the optical unit 32 instead of the original-support mechanism 4, the image of the original document on the transparent plate 8 of the original-support mechanism 4 is scanned and projected upon the photosensitive member 70) as well as the size of the copying paper as described above. In order to perform this operational control, the illustrated electrostatic copying apparatus uses the following construction for detecting the movement of the original-support mechanism 4 (or at least a part of the optical unit 32). Referring to Figures 8 and Figures 9-A to 9-D in conjunction with Figure 2, the illustrated electrostatic copying apparatus, as shown by the two-dot chain line in Figure 2, and partly shown in Figures 9-A to 9-D, includes a known chain mechanism 272 as a power transmitting element for drivingly connecting the original-support mechanism 4 to the main electric motor 232 (Figure 4). The chain mechanism 272 consists of a pair of sprocket wheels 274a and 274b rotatably mounted in spaced-apart relationship in the moving direction of the original-support mechanism 4 and an endless chain 276 wrapped about the sprocket wheels 274a and 274b. One of the sprocket wheels of the chain mechanism 272, for example the sprocket wheel 274a, is drivingly connected to the main electric motor 232 (Figure 4) through a suitable power transmitting element (not shown), and the endless chain 276 is driven in the direction shown by an arrow 278 by the power transmitted from the main electric motor 232 to the sprocket wheel 274a. On the other hand, a follower plate 280 extending perpendicularly downwardly is fixed to the support frame 6 of the original-support mechanism 4. In the follower plate 280 is formed an elongate slot 282 which extends in the perpendicular direction along a length corresponding to the distance between the upper travelling section and the lower travelling section of the endless chain 276. A cam roller 284 mounted on, and adapted to move with, the endless chain 276 is engaged with the slot 282. The chain mechanism 272, the follower plate 280 and the cam roller 284 are known elements, and the detailed structures and operations of these elements are described, for example, in Japanese Laid-Open Patent Publication No. 136336/1979, and a description thereof is therefore omitted in the present application. It is to be noted however that the follower plate 280 constitutes an actuating element which acts on a pivotable member to be described below. Within the housing 2, a mounting bracket 286 (Figure 8) is disposed at a fixed position with respect to the moving path of the follower plate 280, whose lower part constitutes the actuating element. To the mounting bracket 286 are mounted a pivotable member 288, two normally open switches 290 and 292 (as will be explained hereinbelow, the switch 290 constitutes a normally open switch for lamp illumination and is used to turn on an illuminating lamp 36 of the optical unit 32, and the switch 292 constitutes a normally open switch for initiation of actuation, for example to initiate the operation of the charging corona-discharge device 22, etc.), and a locking means 294. The pivotable member 288 is pivotably mounted on the mounting bracket 286 by means of a pin 296. Normally, the pivotable member 288 is resiliently biased to an inoperative position shown in Figures 8 and 9-A by the action of a suitable spring and a stop member (not shown). However, as will be described in detail below, it can be turned in the direction of arrow 298 by the lower portion (i.e., the actuating element) of the follower plate 280 and brought to the operative position shown in Figures 9-C and 9-D. The locking means 294, comprising a lever-like member mounted pivotably on the bracket 286 by means of a pin 300 is normally biased resiliently to the position shown in Figures 8, 9-A, 9-C and 9-D by the action of a suitable spring and stop member (not shown), but can be caused to pivot in the direction shown by an arrow 304 by the pivotable member 288 and a lock releasing member 302 secured to the endless chain 276 as will be described in detail hereinbelow. There will be described below the operation of the detecting switch mechanism comprised of the actuating element (the lower portion of the follower plate 280), the pivotable member 288, the normally open switches 290 and 292, the locking means 294 and the lock releasing member 302. When the original-support mechanism 4 makes a preparatory movement from the stop position shown by a solid line in Figure 2 to the right in Figure 2 (to the left in Figures 9-A to 9-D) toward a scan movement-starting position shown by a two-dot chain line 4A in Figure 2 and approaches the scan movement-starting position, one edge of the follower plate 280 abuts a receiving portion 306 of the pivotable member 288 as shown in Figure 9-A. As the original-support mechanism 4 continues with its preparatory movement, the one edge and lower edge of the follower plate 280 act on the receiving portion 306 of the pivotable member 288 to turn the pivotable member 288 in the direction of arrow 298 against the resilient biasing action of the spring (not shown), as can be understood from Figures 9-A and 9-B. When the pivotable member 288 is turned in the direction shown by arrow 298, a projection 308 formed on the pivotable member 288 abuts the locking means 294 as shown in Figure 9-B thereby pivoting the locking means 294 in the direction shown by arrow 304 against the resilient biasing action of a spring (not shown). As the original-support mechanism 4 continues to make its preparatory movement, that region of the lower edge of the follower plate 280 which projects downwardly acts on the receiving portion 306 of the pivotable member 288 as shown in Figure 9-C to pivot the pivotable member 288 to its critical position shown in Figure 9-C. When the pivotable member 288 has been turned to the critical position, the projection 308 of the pivotable member 288 enters a recess 310 formed in the locking means 294, whereupon the locking means 294 is returned to its initial position (the position shown in Figures 8, 9-A, 9-C and 9-D) by the resilient biasing action of the spring (not shown). As a result, the recess 310 of the locking means 294 comes into engagement with the projection 308 of the pivotable member 288 to lock the pivotable member 288 at the critical position illustrated in Figure 9-C. Accordingly, the pivotable member 288 is kept in the critical position illustrated in Figure 9-C by the locking action of the locking means 294 even when, after the preparatory movement, the original-support mechanism 4 moves to the scanning movement-starting position shown by the two-dot chain line 4A in Figure 2 and further makes a scanning movement to the left in Figure 2 (to the right in Figures 9-A to 9-D) toward a scanning movement-ending position shown by the two-dot chain line 4B in Figure 2, wherein the follower plate 280 is caused to move away from the pivotable member 288. When the original-support mechanism 4 continues to make a scanning movement and approaches the scanning movement-ending position, the lock releasing member 302, mounted on the endless chain 276 of the chain mechanism 272, approaches the locking means 294 as shown in Figure 9-D. As the original-support mechanism 4 continues to make the scanning movement, the lock releasing member 302 acts on the locking means 294 to pivot the locking means 294 in the direction of arrow 304 against the resilient biasing action of the spring (not shown). As a result, the recess 310 of the locking means 294 comes out of engagement with the projection 308 of the pivotable member 288, and therefore, the locking action of the locking means 294 is released. Thus, the pivotable member 288 is returned to the inoperative position, i.e. the inoperative position shown in Figures 8 and 9-A, by the resilient biasing action of the spring (not shown). The locking means 294 itself is returned to the aforesaid initial position by the resilient biasing action of its spring (not shown) when the lock releasing member 302 comes out of engagement with the locking means 294 as a result of continued scanning movement of the original-support mechanism 4. When the pivotable member 288 is caused to pivot from the inoperative position shown in Figure 9-A to the critical position shown in Figures 9-C in the direction shown by the arrow 298, and therefore when the original-support mechanism 4, after approaching the scanning movement-starting position shown by the two-dot chain line 4A in Figure 2, continues to make a preparatory movement and reaches the scan movement-starting position, the two normally open switches 290 and 292 are successively closed by the action of the pivotable member 288. As can be easily appreciated from Figures 9-A and 9-B, when the pivotable member 288 has pivoted from the inoperative position shown in Figure 9-A in the direction shown by the arrow 298, a first cam surface 312 of a nearly 180° arcuate shape, acts on an actuator 314 of the normally open switch 290 to close the normally open switch 290. When the pivotable member 288 is further turned from the position shown in Figure 9-B to the critical position shown in Figure 9-C, a second cam surface 316 of a nearly 100° arcuate shape acts on an actuator 318 of the normally open switch 292 to close the normally open switch 292. In other words, in turning from the inoperative position shown in Figure 9-A to the critical position shown in Figure 9-C in the direction of the arrow 298, the pivotable member 288 first closes the normally open switch 290, and then after some time interval, closes the normally open switch 292. The closed normally open switches 290 and 292, closed by the action of the pivotable member 288 return to the open state when the pivotable member 288 is returned to the inoperative position in the manner described above (therefore when the original-support mechanism 4 has made a scanning movement and approached or reached the scanning movement ending position shown by the two-dot chain line 4B in Figure 2). The illustrated electrostatic copying apparatus further includes the following construction in order to detect the movement of the original-support mechanism 4. As schematically shown in Figure 10, the under-surface of the origial-support mechanism 4 has provided thereon a plurality of actuators (first, second, third and fourth actuators 320a, 320b, 320c and 320d in the illustrated embodiment) at predetermined intervals in the moving direction of the original-support mechanism 4. At a predetermined position within the housing 2 is disposed a driven member 322 which responds to the actuators 320a, 320b, 320c and 320d. The actuators 320a, 320b, 320c and 320d, which can be formed of, for example, magnets, successively act on the driven member 322, which can be formed, for example, of a reed switch, when the original-support mechanism 4 makes a scanning movement from the scan movement-starting position shown by the two-dot chain line 4A to the right in Figure 10 to the scan movement-ending position shown by the two-dot chain line 4B. The driven member 322 produces a signal every time it is acted upon by the actuators 320a, 320b, 320c and 320d successively. In the illustrated embodiment, the first, second, third and fourth actuators 320a, 320b, 320c and 320d and the driven member 322 are positioned in such a manner that the first actuator 320a acts on the driven member 322 when the original-support mechanism 4 makes a scanning movement from the scan movement-starting position shown by the two-dot chain line 4A by a distance corresponding to the longitudinal size of an A5-size copying sheet in accordance with JIS standards (the size of the copying paper in the moving direction, which paper is fed from the paper cassette 50); the second actuator 320b acts on it when the original-support mechanism 4 makes a scanning movement and advances by a distance corresponding to the longitudinal size of a B5-size copying paper in accordance with JIS standards from the scan movement-starting position; the third actuator 320c acts on it when the original-support mechanism 4 moves from the scan movement-starting position by a distance corresponding to the longitudinal size of an A4-size copying paper in accordance with JIS standards; and the fourth actuators 320d acts on it when the original-support mechanism 4 moves from the scan movement-starting position by a distance corresponding to the longitudinal size of a B4-size copying paper in accordance with JIS standards. Now, with reference to Figure 11 which is a block diagram showing in a simplified manner a part of a control electrical circuit used in the illustrated electrostatic copying apparatus, a visible paper size displaying means shown generally at 324 for performing visible display of the paper cassette 50 (see Figure 2) mounted to the cassette-receiving section 48 described above is connected to the reed switches 268a and 268b (see Figures 5 and 6) which constitute the sensing means in the paper size detecting means. The visible paper size displaying means 324 includes an A5-size displayer, a B5-size displayer, an A4-size displayer and a B4-size displayer (not shown) which may be composed of suitable lamps, for example, and an A5-size displayer energizing circuit 326 (A5), a B5-size displayer energizing circuit 326 (B5), an A4-size displayer energizing circuit 326 (A4) and a B4-size displayer energizing circuit 326 (B4) associated respectively with these displayers. In the state shown in Figure 11, both of the reed switches 268a and 268b are closed by the mounting of the B-4 size paper cassette 50 (B4) shown in Figure 7-D to the cassette-receiving section 48. As can be readily appreciated from Figure 11, in such a state, the B4-size displayer energizing circuit 326 (B4) is actuated whereby the B4-size displayer (not shown) visibly indicates that the B4-size paper cassette 50 (B4) is mounted to the cassette-receiving section 48. When in place of the cassette 50 (B4), the A5-size paper cassette 50 (A5) shown in Figure 7-A is mounted in the cassette-receiving section 48, both the reed switches 268a and 268b are opened to actuate the A5-size displayer energizing circuit 326 (A5) whereby the A5-size displayer (not shown) visibly indicates that the A5-size paper cassette 50 (A5) is mounted in the cassette-receiving section 48. Furthermore, when the B5-size paper cassette 50 (B5) shown in Figure 7-B is mounted in the cassette-receiving section 48, the reed switch 268a is closed and the reed switch 268b remains open to actuate the B5-size displayer energizing circuit 326 (B5) whereby the B5-size displayer (not shown) visibly indicates that the B5-size paper cassette 50 (B5) is set at the cassette-receiving section 48. Likewise, upon mounting of the A4-size paper cassette 50 (A4) shown in Figure 7-C in the cassette-receiving section 48, the read switch 268a is opened and the reed switch 268b is closed to actuate the A4-size displayer energizing circuit 326 (A4) whereby the A4-size displayer (not shown) visibly indicates that the A4-size paper cassette 50 (A4) is mounted to the cassette-receiving section 48. Now, referring to Figure 12 which is a time chart showing the state of operation of various constituent elements of the illustrated electrostatic copying apparatus in conjunction with Figures 2 and 11, controlling of the operations of the original-illuminating lamp 36 of the optical unit 32, the charging corona-discharge device 22 and the transfer corona-discharge device 26, will be described in turn. As already stated with reference to Figures 8 and 9-A to 9-D, when in the illustrated electrostatic copying apparatus the main switch (not shown) is closed and the copy starting switch (not shown) is closed to cause the original-support mechanism 4 to make a preparatory movement from the stop position shown by the solid line in Figure 2 to the scan movement-starting position shown by the two-dot chain line 4A in Figure 2, the actuator element formed by the lower portion of the follower plate 280 moving together with the original-support mechanism 4 causes the pivotable member 288 to pivot, whereby the normally open switch 290 and the normally open switch 292 are successively closed with some time interval. When the normally open switch 290 is closed, the original-illuminating lamp 36 of the optical unit 32 is turned on, as can be appreciated from Figure 12. Since some period of time (the so-called rise time) is generally required from the lighting of the lamp to the time when the lamp is ready for performing the required operation, it is convenient to turn on the original illuminating lamp 36 a predetermined time before the original-support mechanism 4 starts to make a scanning movement from the scan movement starting position, namely before the scanning and exposing of an original document is started. When, on the other hand, the normally open switch 292 is closed after the lapse of a certain period of time from the closing of the switch 290, an input signal is supplied to a timer (or a delay circuit) 328 connected to the normally open switch 292 as can be understood from Figure 11, and the timer 328 produces an output signal after the lapse of an adjustable delay time dt (Figure 12) from the receipt of the input signal. When the timer 328 produces the output signal, the following actions occur. (1) Actuation of a counter 330 is started to actuate a circuit 332 for energizing the charging corona-discharge device whereby the actuation of the corona discharge device 22 is started. At the same time, signals from the reed switches 268a and 268b constituting the sensing means in the paper size detecting means are read into the counter 330. As already stated, in the state shown in Figure 11, the B4-size paper cassette 50 (B4) is mounted to the cassette-receiving section 48 and the reed switches 268a and 268b are closed. Hence, as can be readily understood from Table 1, the numeral "3" in the binary notation is read into the counter 330. On the other hand, when the A5-size paper cassette 50 (A5) is mounted to the cassette-receiving section 48, the numeral "0" in the binary notation is read into the counter 330. Likewise, the numeral "1" and the numeral "2" in the binary notation are read into the counter respectively when the cassette 50 at the cassette-receiving section 48 is the B5-size paper cassette 50 (B5) and the A4-size paper cassette 50 (A5), respectively. (2) Simultaneously, an actuation starting timer 334 for starting the actuation of the transfer corona-discharge device 26 is actuated. The actuation starting timer 334 produces an output signal after the lapse of a predetermined time t₁ and supplies the output signal to a circuit 336 for energizing the transfer corona-discharge device 26. As a result, the energization circuit 336 is actuated to start the actuation of the transfer corona discharge device 26. The actuation initiating means comprised of the normally open switch 292 and the timer 328 and capable of starting the actuation of the charging corona-discharge device 22 after the adjustable delay time dt from the closing of the normally open switch 292 can be set or adjusted so that it starts the actuation of the charging corona-discharge device 22 simultaneously with, immediately before, or immediately after, the starting of the scanning movement of the original-support mechanism 4 and therefore the starting of the scanning and exposing of the original document. Conveniently, it is set or adjusted in the following manner with respect to a copying paper transferred from the cassette 50 mounted to the cassette-receiving section 48 through the transfer zone 20. Specifically, it is convenient to set or adjust the delay time dt by the actuation starting means, especially the timer 328, such that the charging action of the corona discharge device 22 is started slightly upstream of that site of the photosensitive member 70 (Figure 3) on the rotary drum 12 with which is mated in the transfer zone 20 the leading end of the copying paper which is transferred from the cassette 50 to the transfer zone 20 in synchronism with the scanning and exposing of the original document (or the rotation of the rotary drum 12) by means known to those skilled in the art. If such setting or adjustment is effected, when a developed image formed on the photosensitive member 70 is transferred to the copying paper in the transfer zone 20, some length of the leading end of the copying paper remains in the original state without the developed image transferred thereto. This can effectively prevent the firm adhesion of the leading end of the copying paper to the surface of the fixing roller 200 in the fixing mechanism 58, which causes extreme difficulty of paper separation (for details of the occurrence of such a phenomenon, reference may be had to Japanese Patent Publication No. 36502/1979, for example). On the other hand, the time from the starting of the actuation of the charging corona-discharge device 22 to the starting of the actuation of the transfer corona-discharge device 26, i.e. the time t₁ defined by the actuation starting timer 334, can be set or adjusted so that it corresponds to the time required for a predetermined site on the photosensitive member 70 (Figure 3) to move from a region where it undergoes the action of the charging corona-discharge device 22 to a region where it undergoes the action of the transfer corona-discharge device 26 by the rotation of the rotary drum 12. When the original-illuminating lamp 36, the corona-discharge device 22 and the transfer corona-discharge device 26 are started, and the original-support mechanism 4 makes a scanning movement, a latent electrostatic image is formed on the photosensitive member 70 (Figure 3) on the rotary drum 12, and then by the action of the developing device 24, the latent electrostatic image is developed to a visible image which is then transferred to a copying paper, as is well known to those skilled in the art. As already described with reference to Figure 10, in the scanning movement of the original-support mechanism 4 from the scanning movement starting position, the actuators 320a, 320b, 320c and 320d provided on the original-support mechanism 4 successively act on the driven member 322 disposed in the housing 2, and the driven member 322 produces a pulse signal every time it is acted upon the actuators 320a, 320b, 320c and 320d as shown in Figure 12. Specifically, in the illustrated embodiment, when the original-support mechanism 4 makes a scanning movement from the scanning movement starting position by a distance corresponding to the longitudinal size of an A5-size copying paper, a first pulse signal is produced. A second pulse signal is produced when it makes a scanning movement by a distance corresponding to the longitudinal size of a B5-size copying paper. When it makes a scanning movement by a distance corresponding to the longitudinal size of an A4-size copying paper, a third pulse signal is produced. Furthermore, a fourth pulse signal is produced when the original-support mechanism 4 makes a scanning movement by a distance corresponding to the longitudinal size of a B4-size copying paper. On the other hand, as can be readily understood from Figure 11, the pulse signals produced by the driven member 322 are fed into the counter 330. Every time the counter 330 receives the pulse signal, its binary notation number read thereinto is decreased by one. When the counter 330 receives the pulse signal with the binary notation being "0", it produces an output signal. Accordingly, when a signal supplied to the counter 330 from the reed switches 268a and 268b constituting the sensing means of the paper size detecting means is "0" in the binary notation (that is, when the A5-size paper cassette 50 (A5) is mounted to the cassette-receiving section 48), the counter 330 produces an output signal upon receipt of the first pulse signal. When a signal supplied to the counter 330 from the reed switches 268a and 268b is "1" in the binary notation [that is, when the B5-size paper cassette 50 (B5) is mounted to the cassette-receiving section 48], the counter 330 produces an output signal upon receipt of the second pulse signal subsequent to the first pulse signal. When a signal supplied to the counter 330 from the reed switches 268a and 268b is "2" in the binary notation [that is, when the cassette A5-size paper cassette 50 (A4) is mounted to the cassette-receiving section 48], the counter 330 produces an output signal upon receipt of the third pulse signal subsequent to the first and second pulse signals. As illustrated in Figures 11 and 12, when a signal supplied to the counter 330 from the reed switches 268a and 268b is "3" in the binary notation, the counter 330 produces an output signal upon receipt of the fourth pulse signal subsequent to the first, second and third pulse signals. When the counter 330 produces the output signal, the following actions occur as will be understood from Figures 11 and 12. (1) The actuation of the circuit 332 for energizing the charging corona-discharge device is stopped and the actuation of the corona discharge device 22 is stopped (accordingly, the actuators 320, 320b, 320c and 320d, the driven member 322 and the counter 330 constitute means for stopping the actuation of the charging corona-discharge device 22). (2) Simultaneously, an actuation stopping timer 338 for stopping the actuation of the transfer corona-discharge device 26 is actuated. After the lapse of a predetermined period of time t₂, the timer 338 produces an output signal thereby to stop the actuation of the circuit 336 for energizing the transfer corona-discharge device 260. The time from the stopping of the actuation of the charging corona-discharge device 22 to the stopping of the actuation of the transfer corona discharge device 26, that is the time t₂ defined by the actuation stopping timer 338, can be set at or adjusted to a value substantially equal to, or slightly longer than, the time t₁ defined by the actuation starting timer 334. On the other hand, as can be understood from Figure 12, the original-illuminating lamp 36 turned on by the closing of the normally open switch 290 is turned off when the original-support mechanism 4 further makes a scanning movement and the lock releasing piece 302 (Figure 9-D) acts on the locking means 294 to return the pivoting piece 288 to the inoperative position (i.e., the position shown in Figures 8 and 9-A) and bring the normally open switch 290 to the open state. If desired, it is possible to employ additionally such a construction that the illuminating lamp 36 is turned off, for example immediately after the stopping of the actuation of the charging corona-discharge device 22. In the electrostatic copying apparatus including the aforesaid control system, the charging corona-discharge device 22 for charging purposes is actuated only for a period of time which corresponds to the longitudinal size of a copying paper which is contained in the cassette 50 set at the cassette-receiving section 48 and is transferred through the transfer zone 20. Hence, the longitudinal size (the size in the rotating direction of the rotary drum 12) of a latent electrostatic image formed on the photosensitive member 70 (Figure 3) on the rotary drum 12 and of a visible image obtained by developing the latent electrostatic image correspond respectively to the longitudinal size of the copying paper transferred through the transfer zone 20. Thus, in the transferring operation in the transfer zone 20, substantially the entire region of the visible image on the photosensitive member 70 is transferred to the copying paper. This is in contrast to a conventional electrostatic copying apparatus in which a part of the visible image on the photosensitive member 70 may not be transferred to the copying paper but remains there. For this reason, the residual charge and toner particles remaining on the photosensitive member 70 after the transfer operation can be reliably removed by suitable means such as the charge eliminating corona-discharge device 28, the charge-eliminating lamp 30 and the developing device 24 which also function as a cleaning means. For example, when the copying process is carried out successively through a plurality of cycles in the illustrated electrostatic copying apparatus (that is, when multiple copies are to be obtained from a single original document), the rotary drum 12 is rotated through two turns in each copying cycle (after rotating the rotary drum 12 through two turns in the final copying cycle, it is possible, if deired, to rotate the rotary drum 12 further through at least one turn, thereby exerting an additional action of removing the residual charge and toner particles). At this time, it is possible to cause the charge-eliminating corona-discharge device 28 and the charge-eliminating lamp 30 to act once on the photosensitive member 70 and simultaneously to cause the developing device 24 to act once as a cleaning means. By causing these means to act only once, the residual charge and toner particles can be fully removed from the photosensitive member 70 after the transfer operation. Furthermore, in the electrostatic copying apparatus including the aforesaid control system, the transfer corona-discharge device 26 is also actuated only for a period of time corresponding to the longitudinal size of a copying paper transferred through the transfer zone 20, and therefore it is possible to avoid any adverse effect on the photosensitive member 70 of direct corona-discharge which may be applied by the transfer corona-discharge device 26 when no copying paper exists in the transfer zone 20. Furthermore, the illustrated electrostatic copying apparatus is of the so-called visible image transfer type in which a latent electrostatic image formed on the photosensitive member 70 is developed and the developed image is transferred to a copying paper. However, the technical concept that the charging corona-discharge device 22 is actuated only for a period of time corresponding to the longitudinal size of a copying paper transferred through the transfer zone 20 can also be applied to an electrostatic copying apparatus of a so-called latent electrostatic image transfer type in which the latent electrostatic image formed on the photosensitive member 70 is transferred to a copying paper without development. The illustrated electrostatic copying apparatus is provided with the fixing mechanism 58 (Fig. 2) which includes a conventional hollow cylindrical fixing roller having an electric heater therein formed of electrical resistance wires. It is well known to those skilled in the art that in such a fixing mechanism 58, the supply of electric current to the heater which is started by the closing of the main switch (not shown) of the electrostatic copying apparatus is generally controlled properly according to the temperature of the fixing mechanism 58 in order to maintain the temperature of the fixing mechanism 58 within a required range. For example, this control is effected such that the current supply - is interrupted when the temperature of the fixing mechanism 58 rises above a certain limit, and is resumed when the temperature of the fixing mechanism 58 decreases below the limit. Alternatively, the current is supplied in the alternating-current half-wave state when the temperature of the fixing mechanism 58 exceeds the limit, and is supplied in the alternating-current full-wave state when the temperature of the fixing mechanism 58 falls below the limit. When a change occurs in the state of the current supply to the heater of the fixing mechanism 58 during the formation of a latent electrostatic image on the photosensitive member 70 or during the transfer of a visible image on the photosensitive member 70 to a copying paper, the power supply source of the electrostatic copying apparatus undergoes influences and some variations occur in the operations of electrical elements such as the original-illuminating lamp 36 of the optical unit 32 or the charging corona-discharge device 22 and the transfer corona-discharge device 26. This is likely to result in non-uniformity in the formation of the latent electrostatic image or the transfer of the visible image. In order to prevent occurrence of such a trouble, the apparatus of this invention, in one aspect thereof, includes a current supply change inhibiting means which maintains the state of current supply to the heater of the fixing mechanism 58 in a certain predetermined state while at least one of the corona-discharge devices 22 and 26 is in operation and therefore from the starting of formation of the latent electrostatic image until the end of the transfer of the developed image. As can be appreciated easily from Figures 11 and 12, when at least one of the corona-discharge devices 22 and 26 is actuated in the illustrated electrostatic copying apparatus, a signal is put into a temperature control means 340 which properly controls the state of current supply to the heater of the fixing mechanism 58 according to the temperature of the fixing mechanism 58. This input signal causes the temperature control means 340 to interrupt current supply to the heater, and this state in maintained while the input signal exists. Instead of causing the temperature control means 340 to interrupt current supply to the heater and be maintained in this state by the input signal, it is also possible, if desired, to cause the temperature control means 340 to continue current supply to the heater (in the alternating-current full-wave state or the alternating-current half-wave state) and be maintained in this state by the input signal. Alternatively, the state of the temperature control means 340 at the time of production of the input signal may be maintaned without particlarly changing it. The illustrated electrostatic copying apparatus further includes a toner particle dispensing control means shown generally at 342 in Figure 11 which actuates a conventional toner particle dispenser forming part of the developing apparatus 24 only for a time period which corresponds to the longitudinal size of a copying paper transferred through the transfer zone 20 (Figure 2). Referring to Figure 11, the toner particle dispensing control means 342 includes a counter 344, a first clock pulse oscillator 346, a second clock pulse oscillator 348 and a circuit 350 for energizing a toner particle dispensing electric motor (not shown). The first clock pulse oscillator 346 and the second clock pulse oscillator 348 are connected to the counter 344 through a gate element controlled by a signal from the reed switch 268a. As can be easily understood from Figure 11, when the reed switch 268a is open [and therefore when the A5-size paper cassette 50 (A5) shown in Figure 7-A or the A4-size paper cassete 50 (A4) shown in Figure 7-C is mounted in the cassette-receiving section 48 (Figure 2)], a clock pulse produced by the first clock pulse oscillator 346 is fed to the counter 344. Conversely, when the reed switch 268a is closed and therefore the B5-size paper cassette 50 (B5) shown in Figure 7-B or the B4-size paper cassette 50 (B4) shown in Figure 7-D is mounted to the cassette-receiving section 48 (Figure 2), a clock pulse generated by the second clock pulse oscillator 348 is fed into the counter 344. The period of the clock pulse generated by the first clock pulse oscillator 346 is set at the time required to dispense an amount of toner particles which corresponds to the amount of toner particles consumed in developing a latent electostatic image according to a standard A5-size original document (that is, the time of rotation required for the paper feed roller 126 to dispense the aforesaid amount of toner particles from the toner particle dispenser to a developer receptacle 94 in the developing device 24). The period of the clock pulse generated by the second clock pulse oscillator 348 is set at the time required to dispense an amount of the toner particles which corresponds to the amount of the toner particles consumed in developing a latent electrostatic image according to a standard B5-size original document. The reed switch 268b is connected further to the counter 344. When the reed switch 268b is open and therefore the A5-size paper cassette 50 (A5) shown in Figure 7-A or the B5-size paper cassette 50 (B5) is mounted to the cassette-receiving section 48 (Figure 2), once the counter 344 is actuated as described below, it is maintained in the actuated state only for one period of the clock pulse fed from the first or second clock pulse oscillator 346 or 348. Conversely, when the reed switch 268b is closed and therefore the A4-size paper cassette 50 (A4) shown in Figure 7-C or the B4-size paper cassette 50(B4) shown in Figure 7-D is mounted to the cassette-receiving section 48 (Figure 2), once the counter 344 is actuated as described below, the counter 344 is maintained in the actuated state for two periods of the clock pulse fed from the first or second clock pulse oscillator 346 or 348. Because of the above construction, it will be apparent that once the counter 344 is set into operation, it is maintained in the actuated state for one period of the clock pulse generated by the first clock pulse oscillator 346 (therefore, for the time required to dispense an amount of the toner particles which corresponds to the amount of the toner particles consumed in developing a latent electrostatic image according to a standard A5-size original document) when the A5-size paper cassette 50 (A5) is mounted to the cassette-receiving section 48; for one period of the clock pulse generated by the second clock pulse oscillator 348 (therefore, for the time required to dispense an amount of the toner particles which corresponds to the amount of the toner particles consumed in developing a latent electrostatic image according to a standard B5-size original document) when the B5-size paper cassette 50 (B5) is mounted to the cassette-receiving section 48; for 2 periods of the clock pulse generated by the first clock pulse oscillator 346 (therefore, for the time required to dispense an amount of the toner particles which corresponds to the amount of the toner particles consumed in developing a latent electrostatic image corresponding to a standard A4-size original document) when the A4-size paper cassette 50 (A4) is mounted to the cassette-receiving section 48; and for two periods of the clock pulse generated by the second clock pulse oscillator 348 (therefore, for the time required to dispense an amount of the toner particles which corresponds to the amount of the toner particles consumed in developing a latent electrostatic image according to a standard B4-size original document) when the B4-size paper cassette 50 (B4) is mounted to the cassette-receiving section 48. As can be easily understood from Figures 11 and 12, the counter 344 shown in Figure 11 is started during the rise time of the clock pulse supplied from the first or second clock pulse oscillator 346 or 348 after the lapse of the delay time dt defined by the timer 328 (in the state shown in Figures 11 and 12, during the rise time of the clock pulse fed from the second clock pulse oscillator 348 because the B4-size paper cassette 50 (B4) is mounted) and is maintained in the actuated state for the period of time described hereinabove (for two periods of the clock pulse generated by the second clock pulse oscillator 348 in the state shown in Figures 11 and 12). While such counter 344 is maintained in the actuated state, the circuit 350 for energizing the electric motor for toner particle dispensing is maintained in the actuated state, and the electric motor is energized to rotationally drive a feed roller for the period defined by the counter 344 whereby to dispense the toner particles to the developer receptacle. Because of the aforesaid construction, in the illustrated electrostatic copying apparatus including the toner particle dispensing control means 342, an amount of the toner particles which corresponds substantially to the size of a copying paper transferred through the transfer zone 20 (Figure 2) and therefore the size of a latent electrostatic image formed on the photo-sensitive member 70 (Figure 3), that is, the amount of the toner particles consumed by the development, is dispensed to the developer receptacle every time the copying process is performed.

Claims: 1. An electrostatic copying apparatus comprising a housing (2), a photosensitive member (12) disposed within the housing for free movement through an endless moving path defined within the housing, an original-support mechanism (4) disposed on the top surface of the housing (2) and including a transparent plate (8) on which to place an original document to be copied, a charging corona-discharge device (22) for applying corona discharge to the photosensitive member in a latent electrostatic image-forming zone (16) located along the moving path of the photosensitive member (12), an optical system (32) for projecting the image of the original document placed on the transparent plate onto the photosensitive member in the latent electrostatic image-forming zone (16), one of the original-support mechanism and at least a part of the optical system being arranged, in operation, to be scanningly moved toward the other whereby the image of the original document placed on the transparent plate is scanned and projected onto the photosensitive member, and a copying paper transfer unit (46) for transferring a copying paper through a predetermined transfer passage extending through a transfer zone (20) located along the moving path of the photosensitive member and downstream of the latent electrostatic image-forming zone (16) in the moving direction of the photosensitive member, a transfer corona-discharge device (26) for applying, during the period of image transfer, corona discharge to the back surface of the copying paper passing through the transfer zone, and a fixing mechanism (58) which has an electric heater and is disposed downstream of the transfer zone in the transfer passage for the copying paper, said copying paper transfer unit including a cassette-receiving section (48) for detachably receiving a copying paper cassette (50; 252) containing a plurality of copying paper sheets of predetermined size in the stacked state and a feed mechanism for feeding the copying paper sheets one by one from the copying paper cassette when mounted to the cassette-receiving section, the apparatus further comprising a detecting means for determining the longitudinal size of the copying paper being transferred by the transfer unit (46) and a control means for operating the charging corona-discharge device (22) only for a period of time which corresponds to the detected longitudinal size of the copying paper,the copying paper size detecting means comprising a copying paper size indicating means (266; 270) which provides an indication of the paper size to be used with a given cassette, and a sensing means (268) mounted in the cassette-receiving section of the apparatus and adapted to sense the copying paper size, indicating means (266; 270) for indicating the longitudinal size of the copying paper associated with that cassette, and the control means for the charging corona-discharge device comprising an actuation starting means for starting the actuation of the charging corona-discharge device simultaneously with, immediately before, or immediately after, the starting of the scanning movement of one of the original-support mechanism and said at least a part of the optical unit from a scanning movement starting position, and an actuation stopping means which, when one of the original-support mechanism and said at least a part of the optical unit has made a scanning movement from the scanning movement-starting position by a distance substantially corresponding to the longitudinal size of the copying paper detected by the copying paper size detecting means, detects it and stops the actuation of the charging corona-discharge device (22), the apparatus further comprising, for controlling the period of actuation of the transfer corona discharge device and the current supply to the heater of the fixing mechanism, an actuation starting timer (334) for starting the actuation of the transfer corona-discharge device after the lapse of a predetermined period of time from the starting of the actuation of the charging corona-discharge device, an actuation stopping timer (338) for stopping the actuation of the transfer corona-discharge device after the lapse of a predetermined period of time from the stopping of the actuation of the charging corona-discharge device, a temperature control means (340) for varying the current supply to the electric heater according to the temperature of the fixing mechanism, and a current supply variation inhibiting means for inhibiting variations of the current supply to the electric heater by the temperature control means (340) while at least one of the charging corona-discharge device and the transfer corona-discharge device is in operation. 2. An apparatus as claimed in claim 1, wherein the copying paper size indicating means is arranged to indicate the size of the copying paper in accordance with whether a magnet (270) is fixed to at least one predetermined site on the copying paper cassette, and the sensing means comprises at least one reed switch (268a, 268b) which is disposed in the cassette-receiving section (48) such that upon mounting of the copying paper cassette (50) to the cassette-receiving section (48), it senses whether the magnet (270) is fixed to said predetermined site. 3. An apparatus as claimed in claim 1 or 2 wherein, upon starting the copying process, the original-support mechanism is preparatorily moved from a predetermind initial position to the scanning movement-starting position in a predetermined direction, then moved scanningly from the scanning movement-starting position in a direction opposite to said predetermined direction, and further returned to the initial position in said predetermined direction, and wherein the actuation starting means comprises a detecting switch mechanism for detecting the approach or arrival of the original-support mechanism to or at the scanning movement starting position as a result of the preparatory movement, and a timer for actuating the charging corona-discharge device after the lapse of an adjustable period of time from the time when the detecting switch mechanism has detected the approach or arrival of the original-support mechanism to or at the scanning movement starting position. 4. An apparatus as claimed in claim 3 wherein the detecting switch mechanism of the actuation starting means comprises an actuating element (280) carried by the original-support mechanism, a pivotable member (288) mounted pivotably within the housing and biased resiliently to an inoperative position by a spring, the pivotable member (288) being turned by a predetermined angle from the inoperative position by abutment of the actuating element (280) thereagainst when the original support mechanism makes said preparatory movement, and a normally open switch (292) for initiating actuation, the switch (292) being closed by the pivotable member (288) when the pivotable member (288) is caused to pivot by said predetermined angle. 5. An apparatus as claimed in claim 4 wherein the detecting switch mechanism further comprises a locking means (294) which when the pivotable member (288) has been turned by the predetermined angle from the inoperative position, locks the pivotable member (288) at this angular position, and a lock releasing member (302) which moves in correspondence with the movement of the original-support mechanism and, when the original-support mechanism has made a scanning movement by a predetermined distance from the scanning movement-starting position, acts on the locking means (294) to release its locking action and thereby return the pivotable member (288) to its inoperative position under the biasing action of the spring. 6. An apparatus as claimed in claim 5 wherein, when the pivotable member (288) of the detecting switch mechanism is caused to pivot from the inoperative position by said predetermined angle, it first closes a normally open switch (290) adapted to turn on the original-illuminating lamp of the optical unit and then after the lapse of a period of time, closes the actuation initiating switch (292). 7. An apparatus as claimed in any of claims 1 to 6 wherein the actuation stopping means comprises a plurality of actuators (320a, 320b, 320c, 320d) aligned at a plurality of predetermined positions on the original-support mechanism at spaced intervals in the moving direction of the original-support mechanism, a driven member (322) disposed at a predetermined fixed position within the housing and adapted to be successively actuated by the actuators (320) when the original-support mechanism makes the scanning movement, and a counter (330) for counting the number of times the driven member (322) is actuated, and wherein the scanning movement distance of the original-support mechanism from the scanning movement-starting position is detected by a value counted by the counter (330), and said stopping means stops the actuation of the charging corona-discharge device when the scanning movement distance of the original-support mechanism so detected corresponds to the longitudinal size of the copying paper detected by the copying paper size detecting means. 8. An apparatus as claimed in any of claims 1 to 7 which further comprises means (324) for visibly displaying paper sizes, said means being adapted to display visibly the size of copying paper contained in the paper cassette mounted to the cassette-receiving section according to the size of the copying paper which is detected by the paper size detecting means. 9. An apparatus as claimed in claim 1 wherein the current supply variation inhibiting means causes failure of the current supply to the electric heater when at least one of the charging corona-discharge device and the transfer corona-discharge device is in operation. 10. An apparatus as claimed in claim 9 wherein the temperature control means (340) varies the current supply to the electric heater between an alternating-current full-wave supply state and an alternating-current half-way supply state, and the current supply variation inhibiting means maintains the current supply to the electric heater in the alternating-current halfwave supply state when at least one of the charging corona-discharge device and the transfer corona-discharge device is in operation. 11. An apparatus as claimed in any of claims 1 to 10 which further comprises a developing device for developing a latent electrostatic image formed on the photosensitive member by applying toner particles thereto in a developing zone located along the moving path of the photosensitive member, said developing device including a developer receptacle, and a toner particle dispenser mechanism for dispensing toner particles contained therein to the developer receptacle by being selectively actuated; and which further comprises a toner particle dispensing control means (342) for actuating the toner particle dispenser only for a period of time which corresponds to the longitudinal size of the copying paper detected by the copying paper size detecting means when the copying process is carried out.

Inventors: AOKI, TAKASHI, MIYOSHI, HIDEO, UMEDA, TADASHI
Applicants: MITA INDUSTRIAL CO. LTD.
Application year: 1981
Main classification: G03G15
IPC codes: B65H1, G03G15, G03G21