Image forming apparatus

Abstract: When an original (D) is carried onto a supporting means (2) by a carrying means (12) in accordance with a designation of a designating means (3a), a decreasing means (34; 35; 36) decreases a density of an image formed on a transferred medium (P). Formation of an unnecessary image IS caused by an opening portion (4a) of a covering means (4) can be prevented, and a good image can be formed.

Description: The present invention relates to an image forming apparatus for recording an image corresponding to an original image on a recording medium. Such apparatus is defined by the features of the preamble of Claim 1. An automatic original feeder is arranged in an image forming apparatus such as an electronic copying apparatus to automatically feed an original to an original table or to feed it from the original table. An opening portion is formed in, e.g., an original table cover in the automatic original feeder. A carrying roller for carrying an original is arranged on the table in the location corresponding to the opening portion. When an original is to be copied by an electronic copying apparatus having the automatic original feeder, an original fed to the original table in the automatic original feeder is exposed and scanned by an exposure/ scanning unit while the original is kept in contact with the original table by means of the original table cover. When a thin original is to be copied by the electronic copying apparatus having the automatic original feeder, light emitted from the exposure/scanning unit is reflected by the original and is also transmitted through it and reflected by the original table cover. These light components reflected by the original and the original table cover are radiated on a photosensitive drum through an optical system. Since a contact surface of the original table cover is white or has a light color, a portion in contact with the original table cover is copied to accurately reproduce an original image because an electric charge of the corresponding portion of the photosensitive drum is removed by the light reflected by the original table cover. A portion corresponding to the opening portion of the original table cover has a small amount of reflected light because light emitted from the exposure/scanning unit and transmitted through the original is attenuated, and the electric charge of the photosensitive drum is not sufficiently removed. Therefore, an unnecessary image corresponding to the opening portion is formed in the copied image, thus posing a serious problem. From US-A-4 505 575, which forms the basis for the preamble of claim 1, there is known a non-image erase system for an image forming apparatus in which rollers for carrying the original to the original table are provided on the rear surface of the original cover. The apertures through which the rollers are exposed are provided on the rear surface of the original cover. A mechanically slidable shutter is provided between the apertures and the rollers. When the original is exposed, the shutter is moved to shut the apertures in order to prevent the apertures from being formed on the copied image. Another document, JP-60-22148, relates to a method by which an electrostatic latent image of an original is prevented from being influenced by punched holes formed on the original by means of lighting a discharge lamp in register with the locations of the punched holes in order to erase the image of the punched holes from the latent image. It is an object of the present invention to provide an image forming apparatus capable of preventing formation of an unnecessary image corresponding to an opening portion of an original table cover. In order to achieve the above object, according to the invention, there is provided an image forming apparatus comprising an original table for supporting an original thereon, an original cover provided to be opened and closed between a first, closed position for covering said original table and a second, open position in which said original table is uncovered, means for exposing said original supported on said original table by scanning said original while radiating light onto said original, an image carrying member to which said light radiated by said exposing means and reflected from said original is guided to form an electrostatic latent image of said original thereon, at least one carrying roller provided on said original table for carrying said original, and said original cover comprises at least one opening portion as a first portion which receives said carrying roller when said original cover is in said first position, and a second portion except for said first portion, characterized in that said apparatus comprises means for decreasing a density of said image formed on said image carrying member in those portions of said image which correspond to one portion of said original supported on said original table which is opposed to said first portion of said original cover in case said original cover is positioned in said first position. Preferred embodiments of the image forming apparatus of the invention are defined in the subclaims. According to the present invention, when the original is fed onto the supporting means by the carrying means in accordance with the designation of the designating means, the density of the image to be formed on the transferred means is corrected by the correcting means, and an unnecessary image caused by the opening portion of the covering means is prevented, thereby obtaining a good image. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a partially cutaway perspective view showing an embodiment of an image forming apparatus according to the present invention; Fig. 2 is a block diagram showing an arrangement of a control system of the image forming apparatus shown in Fig. 1; Fig. 3 is a plan view showing a main part of an operation panel 3 in Fig. 1; Fig. 4A is a plan view showing an unnecessary image on a copy sheet; Fig. 4B is a graph explaining a correction value for an exposure amount or a developing bias voltage of the unnecessary image IS according to a first or second embodiment of the present invention; Figs. 5A and 5B are flow charts explaining a copying operation of the image forming apparatus when taken together; Fig. 6 is a plan view showing a positional relationship between a set position of an original and an opening portion; Fig. 7 is a graph explaining a correction value for a charge amount of an unnecessary image IS according to a third embodiment of the image forming apparatus of the present invention; Fig. 8 is a perspective view showing a main part according to a fourth embodiment of the image forming apparatus of the present invention; Fig. 9A is a plan view showing an unnecessary image on a copy sheet in Fig. 8; Fig. 9B is a graph explaining a correction value for an exposure amount or a developing bias voltage of the unnecessary image IS in Fig. 9A; and Fig. 9C is a graph explaining a correction value for a charge amount of the unnecessary image IS in Fig. 9A. An embodiment of an image forming apparatus of the present invention will be described hereinafter with reference to the accompanying drawings. Fig. 1 is a perspective view showing an embodiment of the image forming apparatus according to the present invention. An original table 2 is arranged in an upper surface portion of a main body 1 of an electronic copying apparatus. An operation panel 3 for setting the number of the copies, various operation modes and the like is arranged in front of the original table 2. An original table cover 4 which can be opened and closed, for covering the original table 2 is arranged in the rear portion of the original table 2. The original table cover 4 is used to bring an original into tight contact with the original table 2 during a copying operation of the original. The surface of the original table cover 4 which is brought into contact with the original table 2 is white or has a light color. When a thick original such as a book is set on the original table 2, hinge portions 5 and 6 of the original table cover 4 can be vertically moved in accordance with the thickness of the original. An opening/closing detecting switch 7 is arranged inside the main body 1 to detect opening/closing of the original table cover 4. A scale 8 serving as a reference for manually setting an original is provided at one end portion of the original table 2 along its longitudinal direction. An automatic original feeder 9 is arranged at the other end portion of the original table 2 along its longitudinal direction. The automatic original feeder 9 comprises a pickup roller (not shown) for picking up each original D set on an original tray 10 provided on the main body 1 and feeding it onto the original table 2, an original detecting switch 11, a carrying roller 12, and a plurality of discharging rollers 13. The original detecting switch 11 detects the presence/absence of an original on the original tray 10. The carrying roller 12 sets each original picked up from the original tray 10 by the pickup roller with reference to the other end portion of the original table 2 along its longitudinal direction, as shown in Fig. 1. In addition, upon completion of the copying operation of the original, the carrying roller 12 removes the original from the original table 2 and feeds it to the automatic original feeder 9. The plurality of discharging rollers 13 discharge the original fed by the carrying roller 12 into the automatic original feeder 9 onto the upper surface of the original table cover 4 which covers the original table 2 upon completion of the copying operation. An opening portion 4a is formed in the original table cover 4. When the original table cover 4 is kept closed, the carrying roller 12 is fitted in the opening portion 4a. An exposure/scanning unit 14 having an exposure lamp 14a is arranged inside the main body 1. The exposure/scanning unit 14 radiates light emitted from the exposure lamp 14a onto the original and exposes and scans the original. A photosensitive drum 15 is arranged near the exposure/scanning unit 14. A charger 16, a developer 17, a transferring charger 18, a separating charger 19, a cleaner 20, and a discharge lamp 21 are arranged around the photosensitive drum 15 along the direction of its rotation. The charger 16 applies a predetermined charge to the photosensitive drum 15. The developer 17 applies a toner to an electrostatic latent image formed on the surface of the photosensitive drum 15 upon exposure and scanning of the original, thereby forming a toner image. The transferring charger 18 transfers the toner image developed by the developer 17 onto a copy sheet P carried by the carrying means (not shown). The separating charger 19 separates the copy sheet P from the photosensitive drum 15. Upon completion of a separation, the cleaner 20 removes toner particles left on the surface of the photosensitive drum 15. The discharge lamp 21 discharges a residual charge from the photosensitive drum 15. The copy sheet separated from the photosensitive drum 15 by the separating charger 19 is carried to a fixing unit 23 along a carrying belt 22. After the toner image is fixed on the copy sheet by the fixing unit 23, the copy sheet is discharged outside the main body 1 from a discharging port 24. Fig. 2 is a block diagram showing an arrangement of a control system in the image forming apparatus shown in Fig. 1. A controller 31 comprises, e.g., a microcomputer and controls the operations of the overall electronic copying apparatus. The controller 31 is connected to a memory 32, various switches (e.g., the opening/closing detecting switch 7 and the original detecting switch 11), the operation panel 3, a motor driving portion 33, a charge control portion 34, a developing bias voltage control portion 35, and a lamp regulator 36. The memory 32 stores programs for controlling the operations of the controller 31 and a correction value for an exposure amount (to be described later). The motor driving portion 33 drives a motor 33a for driving the exposure/scanning unit 14 arranged inside the main body 1, a motor 33b for driving the photosensitive drum 15, and a motor 33c for driving a carrying system for carrying the copy sheet as a transferred medium. The charge control portion 34 controls the charger 16. The charge control portion 34 controls an ON/OFF operation of the charger 16 and a charge amount of the photosensitive drum 15. The developing bias voltage control portion 35 controls a bias voltage applied to a developing roller (not shown) arranged in the developer 17 and controls an amount of toner supplied to the photosensitive drum 15. The lamp regulator 36 controls the ON operation and light amount, i.e., an exposure amount of the original, of the exposure lamp 14a arranged in the exposure/scanning unit 14. Fig. 3 is a plan view showing the main part of the operation panel 3 in Fig. 1. The operation panel 3 includes a copy key 3a for designating a start of the copying operation, a ten-key pad 3b for setting the number of copies, various modes such as a correction amount change mode (to be described later), a magnification key 3c for setting a copying magnification, a copying density key 3d for setting a copying density, a correction mode key 3e for setting an image density correction mode (to be described later), and a display portion 3f for displaying information corresponding to each key input operation and paper jam. A first embodiment of the image forming apparatus of the present invention will be described below. Fig. 4A is a plan view showing an unnecessary image IS on the copy sheet, and Fig. 4B is a graph explaining a correction value for an exposure amount or a developing bias voltage of the unnecessary image IS in the first or second embodiment of the present invention. As shown in Fig. 4A, when the unnecessary image IS is formed on the copy sheet P, a reference exposure amount Ea corresponding to an image except for the unnecessary image IS is set, and an exposure amount Eb larger than the reference value is set as a correction value in correspondence with the unnecessary image IS. The exposure amount Eb is set in correspondence with an amount of light reflected from the opening portion 4a. The exposure amounts Ea and Eb are stored in the memory 32. When the copying portion is started, the exposure amounts Ea and Eb are read out from the memory 32 upon movement of the exposure/scanning unit 14. Since the position of the opening portion 4a of the original table cover 4 is fixed in the copying apparatus, the exposure amounts Ea and Eb are read out in accordance with the position of the opening portion 4a. More specifically, when the exposure/scanning unit 14 scans an original portion except for the opening portion 4a, the exposure amount Ea is read out. However, when the exposure/scanning unit 14 scans an original portion corresponding to the opening portion 4a, the exposure amount Eb is read out. In the first embodiment, the exposure amount of the exposure lamp 14a is therefore corrected. Operations of the image forming apparatus of this embodiment will be described hereinafter with reference to Figs. 5A and 5B. Figs. 5A and 5B are flow charts explaining the copy operation of the image forming apparatus. Referring to Fig. 5A, the controller 31 determines whether the copy key 3a in the operation panel 3 is depressed (step ST1). If NO in the step ST1, the controller 31 determines whether a correction value change mode is set (step ST2). This correction value change mode can be set upon simultaneous depression of, e.g., "0" and "1" keys constituting the ten-key pad 3b on the operation panel 3. If NO in the step ST2, the flow returns to the step ST1. If YES in the step ST1, i.e., if the controller 31 determines that the copy key 3a is depressed, the controller 31 detects an operating state of the opening/closing detecting switch 7 (step ST3). If the controller 31 determines that the opening/closing detecting switch 7 is ON and that the original table cover 4 is kept closed, the controller 31 determines whether the correction mode key 3e on the operation panel 3 is operated to set the image density correction mode (step ST4). If YES in the step ST4, the controller 31 determines whether the original detecting switch 11 of the automatic original feeder 9 is ON, i.e., whether an original is set on the original tray 10 (step ST5). As a result, when the controller 31 determines that the original is set on the original tray 10, the copying operation is performed in the image density correction mode (step ST6). More specifically, each original is picked up from the original tray 10 by the automatic original feeder 9 and is set on the original table 2, as shown in Fig. 1. In this state, the exposure/scanning unit 14 is moved along the original. Upon movement of the exposure/scanning unit 14, the correction values are sequentially read out from the memory 32. The exposure lamp 14a is turned on by the lamp regulator 36 in accordance with the readout correction values. That is, the original portion except for the opening portion 4a of the original table cover 4 is exposed with the reference exposure amount Ea, and the original portion corresponding to the opening portion 4a is exposed with the exposure amount Eb larger than the reference exposure amount Ea. An amount of light reflected from the opening portion 4a is set to be almost equal to that from the portion except for the opening portion 4a, and an unnecessary latent image corresponding to the opening portion 4a is not formed on the photosensitive drum 15. Therefore, when the latent image is transferred to the copy sheet, the unnecessary image is not formed on the copy sheet. If the controller 31 determines in the step ST3 that the original cover 4 is open, if the controller 31 determines in the step ST4 that the image density correction mode is not set, and if the controller 31 determines in the step ST5 that the original is not set on the original tray 10, the correction values stored in the memory 32 are not used, and a normal copying operation is performed (step ST7). When the controller 31 determines in the step ST3 that the original cover 4 is open, a thick original is set on the original table 2, and no correction is required. When the controller 31 determines in the step ST4 that the image density correction mode is not set, processing is performed in the currently set mode. When the controller 31 determines in the step ST5 that the original is not set on the original tray 10, the original is manually set. When the original is manually set, the original is set along the scale 8 on the original table 2, as shown in Fig. 6. Since the size of the original table 2 is larger than a maximum size of the original, even if the original having a maximum size is set, the end of the original does not close the opening portion 4a of the original cover 4. Therefore, no correction is required. An operation in the correction amount change mode set in the step ST2 will be described with reference to Fig. 5B. A current correction value stored in the memory 32 is read out, and the readout correction value is displayed on the display portion 3f on the operation panel 3 (step ST8). In this state, the controller 31 determines whether a key for changing a desired correction value, e.g., a "clear key C" is operated (step ST9). If NO in the step ST9, the flow returns to the step ST1 in Fig. 5A. However, if YES in the step ST9, a message for instructing an operator to input a correction value is displayed on the display portion 3f (step ST10). Thereafter, when a correction value is input with the ten-key pad 3b (step ST11), the input correction value is displayed on the display portion 3f (step ST12). When the "clear key C" which represents confirmation of key depression is operated (step ST13), the input correction value is stored in the memory 32 (step ST14), and the normal mode is restored (step ST1). According to the first embodiment, since the exposure amount of the exposure lamp 14a is set to be large in correspondence with the opening portion 4a of the original table cover 4, even if a thin original is to be copied, an unnecessary image formed in correspondence with the opening portion 4a can be eliminated. When the opening/closing detecting switch 7 detects that the original table cover 4 is kept open, the exposure amount is not corrected. When a thick original is to be copied, an original image corresponding to the opening portion 4a of the original table cover 4 will not have a low density. When an original is manually set on the original table 2, when the correction mode is not set with the correction mode key 3e, or when the automatic original feeder 9 is not used, the exposure amount is not corrected. Therefore, wasteful operations can be eliminated. In addition, when the correction value change mode is designated from the operation panel 3, the exposure amount of the exposure lamp can be changed, so that an optimal exposure amount corresponding to an amount of light from the opening portion 4a can be set. A second embodiment of the image forming apparatus of the present invention will be described below. The correction value of the exposure amount of the exposure lamp 14a is corrected in the first embodiment. In the second embodiment, however, a developing bias voltage of the developer 17 shown in Fig. 2 is changed in accordance with a correction value to obtain the same effect as described above. In this case, the developing bias voltage corresponding to the opening portion 4a of the original table cover 4 is set to be higher than the developing bias voltage corresponding to the portion except for the opening portion 4a. The same effect as in the first embodiment can be obtained in this arrangement of the second embodiment. A third embodiment of the image forming apparatus of the present invention will be described below. The unnecessary image IS corresponding to the opening portion 4a of the original table cover 4 can be eliminated by changing a charge amount of the photosensitive drum 15 by means of the charger 16. In this case, as shown in Fig. 7, a charge amount Cb of the portion corresponding to the opening portion 4a is set to be smaller than a charge amount Ca of the portion except for the opening portion 4a, and these amounts are stored in the memory 32 as correction values. With this arrangement, when the latent image formed on the photosensitive drum is to be developed by the developer, an amount of toner attached to the portion corresponding to the opening portion 4a can be reduced, and formation of the unnecessary image IS can be prevented. A fourth embodiment of the image forming apparatus of the present invention will be described with reference to Figs. 8 and 9. The same reference numerals as in Fig. 1 denote the same parts in Fig. 8, and only different parts will be described below. The image forming apparatus according to the fourth embodiment of the present invention shown in Fig. 8 has an automatic original feeder different from that in Fig. 1. An automatic original feeder 41 comprises a pickup unit 41a and a carrying unit 41b. The pickup unit 41a carries the original D picked up from the original tray 10 and carries it to the original table 2. The original D carried on the original table 2 is carried to one end of the original table 2 along its longitudinal direction by the carrying unit 41b. The carrying unit 41b comprises a plurality of carrying rollers 43 arranged on a surface of an original table cover 42 which opposes the original table 2. The carrying rollers 43 are stored in an opening portion 42a formed in the original table cover 42. The original D carried by the carrying unit 41b is brought into contact with the scale 8 and is then set. In this state, the copying operation is performed. Upon completion of the copying operation, the original D on the original table 2 is carried by the carrying unit 41b to an external discharging tray 44 outside the main body 1. When a thin original is copied using the automatic original feeder 41, unnecessary images IS may be formed in a copied image in correspondence with the carrying rollers 43 mounted in the original table cover 42 and the opening portion 42a formed therein, as shown in Fig. 9A. These unnecessary images IS can be similarly eliminated as described with reference to the above embodiments. When an exposure amount of the exposure lamp 14a or a bias voltage of the developer 17 is changed to eliminate the unnecessary images IS, exposure amounts or developing bias voltages may be set in correspondence with the unnecessary images IS and may be stored in the memory 32, as shown in Fig. 9B. When a charge amount of the photosensitive drum 15 is changed by the charger 16, a charge amount corresponding to the unnecessary images IS may be set and stored in the memory 32, as shown in Fig. 9C. According to the fourth embodiment of the present invention, even if the plurality of carrying rollers 43 are arranged in the original table cover 42, the unnecessary images formed in correspondence with the carrying rollers 43 and the opening portions 42a for storing these rollers can be easily eliminated.

Claims: An image forming apparatus comprising: an original table (2) for supporting an original (D) thereon; an original cover (4) provided to be opened and closed between a first, closed position for covering said original table (2) and a second, open position in which said original table (2) is uncovered; means (14) for exposing said original (D) supported on said original table (2) by scanning said original (D) while radiating light onto said original (D); an image carrying member (15) to which said light radiated by said exposing means (14) and reflected from said original (D) is guided to form an electrostatic latent image of said original (D) thereon; at least one carrying roller (12) provided on said original table (2) for carrying said original (D); and said original cover comprises at least one opening portion as a first portion which receives said carrying roller (12) when said original cover (4) is in said first position, and a second portion except for said first portion; characterized in that said apparatus comprises means (34,35,36) for decreasing a density of said image formed on said image carrying member (15) in those portions of said image which correspond to one portion of said original (D) supported on said original table (2) which is opposed to said first portion of said original cover (4) in case said original cover (4) is positioned in said first position. The apparatus according to claim 1, characterized in that said decreasing means comprises means (36) for changing an exposure amount by which said exposing means (14) exposes said original (D) in an exposure and scanning operation so that it exposes one portion of said original (D) supported on said original table (2) which is opposed to said first portion of said original cover (4) at an exposure amount which is larger than an exposure amount at which it exposes another portion of said original (D) supported on said original table (2) which is opposed to said second portion of said original cover (4) in case said original cover (4) is positioned in said first position. The apparatus according to claim 1, characterized in that said apparatus further comprises means (17) for developing said electrostatic latent image formed on said image carrying member (15); and said decreasing means comprises means (35) for changing a developing bias voltage at which said developing means (17) develops said electrostatic latent image so that it develops one portion of said electrostatic latent image corresponding to one portion of said original (D) supported on said original table (2) which is opposed to said first portion of said original cover (4) at a developing bias voltage which is higher than a developing bias voltage at which it develops another portion of said electrostatic latent image corresponding to another portion of said original (D) supported on said original table (2) which is opposed to said second portion of said original cover (4) in case said original cover (4) is positioned in said first position. The apparatus according to claim 1, characterized in that said apparatus further comprises charging means (16) for applying an electric charge to said image carrying member (15); and said decreasing means comprises means (35) for changing a charge amount of said charging means (16) so that it charges one portion of said image carrying member (15) corresponding to one portion of said original (D) supported on said original table (2) which is opposed to said first portion of said original cover (4) at a charge amount (cb) which is smaller than a charge amount (ca) at which it charges another portion of said image carrying member (15) corresponding to another portion of said original (D) supported on said original table (2) which is opposed to said second portion of said original cover (4) in case said original cover (4) is positioned in said first position. The apparatus according to any one of the preceding claims, characterized by further comprising means (7) for detecting opening/closing of said original cover (4), and wherein said decreasing means (34,35,36) decreases a density of said image when said detecting means (7) determines that said original cover (4) is closed. The apparatus according to any one of the preceding claims, characterized by further comprising means (3,31,32) for setting a decreasing amount of said decreasing means (34,35,36). The apparatus according to claim 6, characterized by further comprising means (3b,3f,31,32) for accessing a decreasing amount of said decreasing means (34,35,36) which is set by said setting means (3,31,32). The apparatus according to any one of the preceding claims, characterized in that said means (34,35,36) for decreasing a density of said image formed on a transferred medium (P) decreases the density at a timing corresponding to those portions of said image which correspond to said one portion of said original (D) supported on said original table (2) which is opposed to said first portion of said original cover (4) in case said original cover (4) is positioned in said first position.

Inventors: IWATA YASUHIRO C O INTELLECTUA, KUBO KOJI C O INTELLECTUAL PRO, IWATA, YASUHIRO, C/O INTELLECTUAL PROPERTY DIV., KUBO, KOJI, C/O INTELLECTUAL PROPERTY DIV.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1990
Main classification: G03G15
IPC codes: G03G15, G03G21