Color electronphotographic apparatus

Abstract: A plurality of image forming units (1BK, 1C, 1M, 1Y) composed of a developing means having different electrostatic carriers and toners different in color are used. Each of the image forming units (1Bk), 1C, 1M, 1Y) can be moved to the same image forming position. The image forming unit is light exposed in image by the light exposing means (3) in the image forming position so as to effect an image forming operation, so that the toner images are transferred on the transfer material by the opposite transfer carrying means (31). In the color electrophotographic apparatus, the image forming units (1Bk, 1C, 1M, 1Y) of the image forming position are sequentially replaced and also, the transfer material is reciprocated by the transfer carrying means (31) so that the toner images of each color are put together, superposed in position and transferred on the same transfer material.

Description: BACKGROUND OF THE INVENTION The present invention generally relates to a color electronic photographic apparatus which can be applied to a color duplicating machine, a color printer and so on. In order to form color images with an electronic photograph, a method of superposing the toner images of the respective colors of yellow, magenta, cyanide, black on a transfer material so as to form color images is provided. As methods of effecting the superposition of the toner images on the transfer material, there are a transfer drum system of rotating a transfer material wound around the transfer drum so as to repeatedly bring it to the same image forming position, where the sequentially formed toner images of each color are transferred in piles, and a continuous superposing system of arranging a plurality of image forming portions side by side so as to let the transfer material to be carried with belts or the like pass in the positions of the respective image forming portions so that the toner images of each color are transferred sequentially and are superposed. There is an example of a color image forming apparatus shown in JP-A-1-252982, which uses the transfer drum system of the former. Fig. 7 shows the summary of the whole construction in the conventional embodiment, which will be described easily hereinafter in construction and operation. In Fig. 7, reference numeral 101 is a photosensitive material. A charger 102, a developer portion 103, a transfer drum 104, a cleaner 105 are positioned oppositely to it. The developer portion 103 is composed of a Y developer 106 for making the toner image of a yellow color, a M developer 107 for making a magenta color, a C developer 108 for making a cyanide color, a K developer 109 for a black color. The respective developers are oppositely positioned in sequence to the photosensitive material 101 so that the developing operation can be effected through the rotation of the whole. The transfer drum 112 and the photosensitive material are being rotated at a constant speed in an arrow direction respectively while being opposite during the operation. When the operation starts, the photosensitive material 101 is rotated in the arrow direction, the surfaces are charged evenly by the charger 102. A laser beam 110 modulated with a signal for forming the yellow image of a first color is illuminated upon the surfaces of the photosensitive material so as to form latent images. The latent images are developed by a developer 106 of yellow opposite at first to the photosensitive material so as to form the toner image of the yellow. One sheet of paper as a transfer material fed from the paper feeding portion 111 is at its tip end caught with a pawl portion 112 and is already wound on the outer periphery of the transfer drum 104 by time the toner image of formed yellow comes to a position opposite to the transfer drum 104. Timing is set so that the toner image of the yellow on the photosensitive material may meet oppositely in the given position of the paper so as to form the toner images. The toner images of the yellow on the photosensitive material is transferred on the paper by the function of the transfer charger 113, and thereafter, the photosensitive material surfaces are cleaned by a cleaner 105 so as to prepare the image formation of the next color. Continuously the toner images of magenta, cyanide, black are also formed similarly. At this time, each developer 103 positions each developer used in accordance with the color oppositely to the photosensitive material to put the condition into a development possible one. The diameter of the transfer drum has a sufficient size so that the longest paper may be wound and the developer may be exchanged in time among the images of the respective colors. The illumination of the laser beam 110 for image forming operation of each color is set at timing so that the toner images of each color and the toner images transferred already on the paper on the transfer drum may be opposed in positional conformity. In this manner, four colors of toner images are transferred superposedly on paper on the transfer drum 104 so that the color images are formed on the paper. After the toner images of all the colors have been transferred, the paper is peeled off from the transfer drum 104 with the peeling pawl 114. The above toner images are fixed with a fixer 116 through the carrying portion 115 so as to discharge the paper out of the apparatus. The above description is the brief description of the construction and the operation in the conventional embodiment. JP-A-1-250970 discloses an example of the color image forming apparatus using the continuous transferring system. Four colors of image forming stations each including a photosensitive material, a light scanning means and so on are arranged side by side for four colors of image formation in the example. Paper carried with the belt passes under the lower portion of the respective photosensitive material so as to superpose the toner images. A method of reciprocating the transfer material with respect to the photosensitive material so as to repeat the transferring operation, superposing the toner images is disclosed in US-A-4905048 as the other method for superposing toner images of different colors on the transfer material so as to form color images. In the transfer drum system of such conventional embodiments as described hereinabove, a transfer drum is used so as to put the position of the toner image of a different color in conformity so as to superpose it. The transfer drum is rotated at the same speed with the photosensitive material, and further the timing of the tip end of the image is set so that the mutual positions of the toner images of each color when color images are formed are put into conformity. As the paper is required to be wound around the transfer drum in such construction as described hereinabove, the diameter of the transfer drum is necessary to make the constant size larger and the construction is very complicated in construction so that the apparatus becomes larger on scale. Paper, which was strong in the knees, such as postcard, thick paper or the like was impossible to use, because it could not be wound around the transfer drum. The continuous transfer system has image forming positions corresponding to the number of colors. The transfer drum is not necessary as the paper has only to pass there one after another. But in this case, the latent image forming means of the laser optical system and so on for forming latent images on the photosensitive material are necessary in accordance with the number of the colors, thus resulting in very complicated construction in this portion. As the image forming position is plural in number, the relative positional relation of the image forming portions of the respective colors has large influences upon the color divergences. Especially, the positional alignment among the respective colors of the latent images by the latent image forming means is necessary to be correctly effected, with a problem that the considerable contrivance and the complicated construction of the image light exposing system as the latent image forming means are necessary as shown in the example of Japanese Laid-Open Patent Application No. 1-250970. In the example disclosed in the US-A-4905048 for reciprocating the transfer material, the shape of the photosensitive material becomes large as the toner image of each color is formed in order on one photosensitive material, and the construction and control for combining the sensitive body with the developer of each color become very complicated with a problem that the maintenance for exchange of them is hard to effect. SUMMARY OF THE INVENTION Accordingly, the present invention has been developed with a view to substantially eliminating the above discussed drawbacks inherent in the prior art, and has for its essential object to provide an improved color electronic photographic apparatus. Another important object of the present invention is to provide a color electronic photographic apparatus which requires neither complicated transfer drums nor complicated construction for positioning alignment of the image light exposing system, and is capable of correct positional alignment of the colors with small-sized and simple construction. A further important object of the present invention is to provide a color electronic photographic apparatus where the construction of the toner image forming portion including the photosensitive material and the developer is simple, and the maintenance property is better. In accomplishing these objects, according to the present invention, there is provided a color electronic photographic apparatus comprising a movable image forming unit group composed of a plurality of image forming units, each including an electrostatic image carrier, a developing means and a toner of a respective color, wherein the respective image forming units are capable of forming toner images of colors each being different on the respective electrostatic image carriers, a transfer carrying means capable of placing a transfer material so as to reciprocate it, and provided with a transferring means for transferring on the transfer material the toner images provided on the electrostatic image carriers in a single transfer position, a light exposing means for effecting an image light exposing operation in a single light exposing position corresponding to the transfer position, a moving means for sequentially moving each of the plurality of image forming units to the image forming position corresponding to the light exposing position and to the transfer position, so that the toner images of different colors are put together in position and superposed on the transfer material so as to form color images. Further advantageous embodiments are defined in the sub-claims. As the image forming operation of each color can be all effected in the same image forming position without the use of a transfer drum of complicated construction, the positional alignment of correct colors can be effected with a simple construction. As the image forming means is complete as one image forming means each being independent for each color, the construction is simple and the image forming means for each color can be exchanged, thus resulting in superior maintenance property. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment hereof with reference to the accompanying drawings, in which; Fig. 1 is a block diagram of a color electronic photographic apparatus in a first embodiment of the present invention; Fig. 2 is a block diagram of an image forming unit to be used in the color electronic photographic apparatus in the first embodiment of the present invention; Fig. 3 is an illustrating view showing a condition where an image forming unit of a color electronic photographic apparatus in the first embodiment of the present invention is drawn out from an apparatus; Fig. 4 is a block diagram of a color electronic photographic apparatus in a second embodiment of the present invention; Fig. 5 is a block diagram of an image forming unit to be used in the color electronic photographic apparatus of the second embodiment of the present invention; Fig. 6 is an illustrating view showing a position of the image forming unit on one condition of the color electronic photographic apparatus in the second embodiment of the present invention; and Fig. 7 is a block diagram of the conventional color electronic photographic apparatus. DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. Concrete Embodiment 1 A color electronic photographic apparatus in a first embodiment of the present invention will be described hereinafter with reference to the drawings. Fig. 1 shows a printer portion where the image formation of the color electronic photographic apparatus of the present invention is drawn. Image forming units 1Bk, 1C, 1M, 1Y are disposed side by side as four units of image forming means for the respective black, cyanide, magenta, yellow colors. As the respective image forming units are respectively the same component members except for developers to be put into them, an image forming unit for magenta use will be described for simplification of the description, with the other colors being omitted. The same parts are designated by the same reference numerals for each color use. When the difference among each color construction is necessary, letters showing the respective colors are given to the reference numerals. An image forming unit 1M for magenta use is shown in detail in Fig. 2. In Fig. 2, reference numeral 9 is a drum shaped organic photosensitive material as electrostatic image carrier with futarocyanine being dispersed in polyester binder resin, reference numeral 10 is a magnet fixed to a rigid shaft coaxial to the axial center to the photosensitive material 9, reference numeral 11 is a corona charger for charging the photosensitive material to minus, reference numeral 12 is a grid electrode for controlling the charging potential of the photosensitive material, reference numeral 13 is a laser beam scanning light, reference numeral 14 is a toner hopper. Two component developers 26M where iron powder carrier 24M, of 100 µm in grain diameter, whose surface are coated with silicone resin, and a toner 25M are blended, are put into a toner hopper 14, and are adhered on the surfaces of the photosensitive material 9 with magnetic force. Reference numeral 16 is a toner amount controlling blade made of nickel which is a magnetic material, reference numeral 17 is a toner recovering electrode roller made of aluminum, reference numeral 18 is an alternating current high voltage power supply for applying a voltage to a toner recovering electrode roller, reference numeral 19 is a scraper made of polyester film for scraping down the toner on the toner recovering electrode roller. Magnetic flux density on the surface of the photosensitive material 9 is 800 gausses in a maximum position. The photosensitive material 9 is 30 mm in diameter and is rotated 120 mm/s in peripheral speed. Reference numeral 27 is a cleaner for cleaning the toner remaining on the photosensitive material surface after the transfer operation. The image forming unit constructed as described hereinabove will be described in its operation with the use of Fig. 2. A photosensitive material 9 is charged to -500V with a corona charger 11 (application voltage -5 kV, voltage -50OV of grid 12). Laser beam scanning light 13 is illuminated upon the photosensitive material 9 so as to form electrostatic latent images. At this time, the light exposure potential of the photosensitive material is -100V. When the photosensitive material 9 with electrostatic latent images formed on it in this manner on the developer 26M is allowed to pass, the carrier 24M is adhered on the magnet and does not move. Only the toner 25M moves together with the photosensitive material 9. After the toner amount controlling blade passes, uniform toner layer of approximately 30 µm is obtained on the photosensitive material 9. At this time, the voltage of -500V is applied upon the toner amount controlling blade 16. At this time, the toner was charged to approximately -3µC/g. Then, the photosensitive material 9 with the toner layer being adhered on it was made to pass before the toner recovering electrode roller 17. An AC voltage (frequency 300Hz) of 400Vo-p (peak · to · peak 800V) with a DC voltage of -300V being piled upon it was applied upon the toner recovery electrode roller 17 by a high voltage power supply 18. The toner layer on the photosensitive material 9 is reciprocated between the photosensitive material 9 and the toner recovering electrode roller 17. Gradually the toner of the non-image portion was moved onto the toner recovering electrode roller 17 side. The toner images inverted in negative, positive onto the image portion remained on the photosensitive material 9. The toner adhered on the toner recovering electrode roller 17 was scraped by the scraper 19, was returned into the toner hopper 14 again so as to be used for the next image formation. The toner images of magenta color are obtained on the photosensitive material 9 in this manner. The other developing apparatuses 1BK, 1C, 1Y except for the magenta are similar in construction and operation. The construction of a printer portion will be described hereinafter again with the use of Fig. 1. The image forming units 1BK, 1C, 1M, 1Y to be arranged side by side are collectively driven by a moving motor 30 which is a moving means and can move in a horizontal direction. The respective image forming units can be sequentially positioned in an image forming position 50 opposite to the transfer portion 33 slightly raised by a belt controlling material 32 of the transfer carrying belt 31. Reference numeral 3 is a laser light exposing apparatus which generates a laser beam scanning light 13 modulated with signals inputted into a printer portion. The laser beam scanning lights are reflected by mirrors 4, 5 and are illuminated upon the photosensitive material of the image forming units located in the first image forming position 50 so as to form latent images. In the condition of Fig. 1, an operation is effected upon the image forming unit 1BK for black use. Reference numeral 8 is a eraser lamp secured to a main body, which is in a position for illuminating the surface after the cleaning operation of the sensitive body of the image forming unit provided in an image forming position 50. Reference numeral 31 is a transfer carrying belt, which is composed of an endless belt shaped polyester film of 100µm in thickness, is wound around a driving roller 34 and a roller 35. Paper is adhered on the surfaces thereof so that it can be reciprocated. In the present embodiment, the distance between the driving roller 34 and the roller 35 is set slightly longer than the length twice as long in the shorter direction of the A4 form. An adhering charger 37 for adhering the paper to be fed from a paper feeding portion 36 on the polyester film is provided at the right hand end of the transfer carrying belt. A transfer charger 38 is disposed at a transfer potion 33. A discharger 39 for discharging the paper separated from the transfer carrying belt, and fed to the left hand, and the transfer carrying belt is disposed at the left hand end. In the present embodiment, the transfer carrying belt is composed of an insulating polyester film. In addition, it may be composed of films made of semiconductive material with carbon and so on being dispersed in, for example, polyester, urethane and so on. As the electric charge at the charging time is hard to gather in the transfer carrying belt in this case, superposed transferring operation is further simplified. Reference numeral 40 is a toner receiver for receiving a drainage toner to be discharged from a cleaner portion 27 where each image forming unit operates in an image forming position. Reference numeral 41 is belt cleaner portion including a belt cleaner for cleaning the transfer carrying belt. The toner receiver 40 is coupled to a belt cleaner portion 41. The drainage toner to be discharged from each image forming unit in the image forming position 50 is gathered in the belt cleaner portion 41. The transfer carrying belt 31, the transfer discharger 38, a belt cleaner portion 41 and so on are adapted to move to positions of dotted lines collectively when clogged with paper. Reference numeral 44 is a fixing unit for fixing toner images on the form after the transferring operation, reference numeral 45 is a discharge roller for discharging the paper after the fixing operation. The driving operation of the driving roller 34 and the fixing unit 44 of the transfer carrying belt is respectively controlled by the carrying control means 46. The above description is the description of the major construction of the electronic photographic apparatus of the present invention. The operation of the apparatus will be described hereinafter when the color image of the A4 size is formed. A4 paper (not shown) is fed from the paper feeding portion 36 in a shorter direction. The paper is moved in the left hand direction (hereinafter referred to as forward direction) at a fixed speed on a transfer carrying belt while the paper is adhered on the transfer carrying belt 31 with the operation of the absorbent charger 37. At this time, the paper is positively adhered on the transfer carrying belt 31, so that the transfer carrying belt and the paper are not deviated in position from each other if the transfer carrying belt is reciprocated as described later, so that the paper is easier to arrange in position when the toner images of each color are superposed. At first, the image forming unit is in such a position as shown in Fig. 1, and an image forming unit 1BK for black use is in an image forming position 50, being confronted with the transfer portion 33. A black signal light is inputted to the image forming unit 1BK by the laser light exposing apparatus 3, setting at timing when the paper is carried on the transfer carrying belt from the right so that the images are formed by the black toner. At this time, a image forming speed (which is equal to the peripheral speed of the sensitive body) of the image forming unit 1BK is set to become the same as the moving speed of the transfer carrying belt. The black toner images are being transferred on the paper by the operation of the transfer charger 38 through the movement of the paper at the same time when the images are formed. Immediately after the trailing end of the paper has passed the transfer portion after the completion of all the transferring operations of the black toner images, the movement of the transfer carrying belt is once stopped and then, is moved at a speed larger than the previous moving speed in the forward direction in a direction (hereinafter a reverse direction) reverse to the previous direction. At this time, the leading end of the paper is near the driving roller and cannot be peeled off from the transfer carrying belt as the length of the transfer carrying belt is sufficiently long. At the approximately same time with the reverse direction moving start of the transfer carrying belt, all the image forming unit group 1BK, 1C, 1M, 1Y are driven by the moving motor 30 and move integrally in the left hand direction of Fig. 1. The reverse direction moving speed of the transfer carrying belt and the moving time of the image forming unit are set so that the image forming unit 1C may reach the image forming position 50 immediately after the paper moves in the reverse direction and the trailing end thereof has almost passed the transfer portion. As the bottom portion of the toner hopper 14 (see Fig. 2) except for the photosensitive material of the image forming unit is positioned on the side above the photosensitive material during this time, the black images on the paper are not disturbed by the contact against the image forming unit. The paper trailing end passes the transfer portion 33 in the right-hand direction, and the image forming unit 1C arrives at the image forming position 50. Thereafter, the transfer carrying belt is moved again at a constant speed in the forward direction. In the same manner as before, the laser light exposing apparatus inputs the signal lights into the image forming unit 1C with a signal of cyanide so as to form and transfer the toner images of the cyanide. At this time, the moving start of the transfer carrying belt is controlled at timing so that the next cyanide toner images may be conformed in position with the black toner images on the paper with respect to the storing start of the signal light. The same operation as described hereinabove is effected even about the magenta and the yellow and the color images are formed with four toner images being superposed in positional conformity on the paper. After the transfer operation of the last yellow toner images, the transfer carrying belt keeps moving as it is in the forward direction. The paper with color images being formed on it is separated from the transfer carrying belt, being discharged by the operation of the discharger 39, and is discharged from the apparatus, with the toner images being fixed by the fixing unit, through the discharging roller. The distance between the driving roller 34 of the transfer carrying belt and the roller 35 is set slightly larger than the seven fourth of the total length in the horizontal direction of Fig. 1 of the image forming unit group. If the image forming unit group moves integrally till each of the image forming units reaches the image forming position, it does not hit the adhering charger 37 and the discharger 39. As the charge is sufficiently removed when the paper is separated from the transfer carrying belt, the toners on the paper are not scattered away so that pretty color images are obtained. As the leading end of the paper does not reach the fixing unit yet immediately after the transfer of the last toner images has been completed, the forward direction moving speed of the transfer moving belt and the speed of the fixing unit is lowered at speed by the operation of the carrying control means 46 through the change in the operation mode at this time so that the low speed fixing operation can be effected. Therefore, glossy color images and pretty OHP superior in transmission property can be made. The photosensitive material during the operation in the image forming position is cleaned with the cleaner 27 (see Fig. 2) on the surface after the transfer operation. Toners to be discharged at this time are collected at the belt cleaner portion 41 through the toner receiver 40, the coupling portion 42. Also, the toners scattered onto the transfer carrying belt are cleaned during the operation in the belt cleaner portion. The above description is the description of the operation at the A4 color mode of the electronic photographic apparatus in the present invention. The operation at a single color mode will be described hereinafter. At the single mode time, the image forming unit of a given color is moved to the image forming position before the paper reaches the transfer position at first. Then, the image formation of a given color and the transferring operation are effected in the same manner as before. After the transferring operation, the transfer carrying belt moves continuously as it is in the forward direction so as to an fixing operation and the discharging operation of the paper. Therefore, at the single color mode time, A4 size or more, for example, A3 paper can be also used. The drainage toner to be discharged from the cleaner at this time is toed at the belt cleaner portion 41 through the coupling portion 42 on occasion. The construction, for exchange of the image forming unit, of the apparatus will be described hereinafter. Fig. 3 shows a condition where one image forming unit 1Y of the image forming unit is drawn out from the apparatus. A first supporter for supporting the image forming unit group 1BK through 1Y is adapted to move in the apparatus depth direction with respect to a second supporter 48 for support it. Further, the second supporter 48 is engaged with a portion of the belt 29 to be driven by a moving motor 30 so as to be able to move in the lateral width direction of the apparatus along rails 49 fixed to the main body. At the image forming unit exchange time, the image forming unit group are all drawn out integrally onto this side of the apparatus as shown in Fig. 4. Further, the respective image forming units are adapted to be independently drawn out upwards from it. The above description is the description of the construction and the operation in the first embodiment. By the above described construction, all the respective colors of image forming operations can be effected in the small image forming position without the use of the transfer drum of complicated construction so that the positional alignment of correct colors can be effected by the simple construction. As the image forming means is complete as one image forming means independently respective for each of colors, the construction is simple with superior maintenance property that the image forming means can be exchanged for each color. The image forming and transferring operations are sequentially effected by each color of image forming unit during the reciprocating movement of the transfer paper on the transfer carrying belt so as to effect a superposing operation. The carrying speed of the transfer paper is lowered at a particular mode at the making time of the OHP or the like so as to effect the sufficient fixing operation so that the pretty color images can be made with simple, small sized construction. An image forming unit group is adapted to be integrally drawn out of the apparatus and the respective image forming units are adapted to be exchanged singly so that an apparatus which is superior in maintenance property such as exchange, maintenance and so on of the image forming units is provided. As the respective image forming units including the photosensitive material can be singly adjusted externally in the present construction, the units adjusted already at, for example, a factory shipment time can be easily exchanged on the spot. At the single color mode time, the transfer carrying belt can be moved continuously only in the forward direction so as to effect an image formation so that the single color of image formation can be effected fast and the image forming operation can be effected even on the paper of A4 or longer. The maintenance property can be improved with simple construction by the treatment of the drainage toner from the image forming unit and the drainage toner from the transfer carrying belt at the same drainage toner sink. Further, in the present construction, stable picture images without electrostatic fatigue can be obtained as the respective photosensitive materials are at rest every time while the other colors are formed even when the color images are continuously formed. A second embodiment of the present invention will be described in construction and operation hereinafter. An electronic photographic apparatus in a second embodiment of the present invention will be described hereinafter with reference to the drawings. Fig. 4 shows only a printer portion for forming the images of the color electronic photographic apparatus in the second embodiment of the present invention. The same reference numerals as those of the embodiment 1 are given to the same construction as that of the embodiment 1. Further, the same construction and operation as those in the embodiment 1 are omitted in description. The difference from the embodiment 1 is the portion of some operations related to the portion of the image forming unit and the maintenance. In the present embodiment, four units of image forming units for the respective colors of black, cyanide, magenta, yellow are shown with 51Bk, 51C, 51M, 51Y. As the respective image forming units are respectively the same component members except for developers to be put into them, an image forming unit for magenta use will be described for simplification of the description, with the other colors being omitted. An image forming unit 51M for magenta use will be described in detail in Fig. 5. In Fig. 5, reference numeral 59 is an organic photosensitive material with futarocyanine being dispersed in polycarbonate system binder resin, reference numeral 60 is a non-rotating magnet fixed coaxial to a photosensitive material 59, reference numeral 61 is a corona charger for charging the photosensitive material to minus, reference numeral 62 is a grid electrode for controlling the charging potential of the photosensitive material, reference numeral 13 is a laser beam scanning light, reference numeral 64 is a developer hopper. Two component developers 76M where felite carrier 74M of 50 µm in grain diameter, whose surface is coated with silicone resin, and a toner 75M are blended are put into a developer hopper 64, and are adhered on the surfaces of the photosensitive material 59 with magnetic force. The toner to be used has pigment dispersed in polyester resin, with an addition agent being added to it. Reference numeral 67 is a rotatable recovering electrode roller made of aluminum, reference numeral 66 is a non-rotatable magnet fixed coaxially within it, reference numeral 68 is an AC high voltage power supply for applying the voltage upon the recovering electrode roller, reference numeral 69 is a scraper made of polyester film for scraping down the toner on the recovering electrode roller. Magnetic flux density on the surface of the photosensitive material 59 and on the recovering electrode roller surface are respectively 800 gausses in a maximum position. The photosensitive material 59 is 30mm in diameter and is rotated 120mm/s at peripheral speed in the arrow direction. The recovering electrode roller 67 is 16mm in diameter and is rotated 100mm/s at peripheral speed in the arrow direction. Reference numeral 27 is a cleaner for cleaning the toner remaining on the photosensitive material surface after the transfer operation. Reference numeral 78 is a discharger which operates to discharge the paper immediately under it at the timing to be described later and the transfer carrying belt. The image forming unit constructed as described hereinabove will be described hereinafter in its operation with the use of Fig. 5. A photosensitive material 59 is charged to -500V with a corona charger 61 (application voltage -5 kV, voltage -500V of grid 62). Laser beam scanning light 13 is illuminated upon the photosensitive material 59 so as to form electrostatic latent images. At this time, the light exposure potential of the photosensitive material is -100V. Two component developers 76M were adhered with magnetic force, on the surfaces of the photosensitive material 59, within the developer hopper 64. Then, the photosensitive material 59 was made to pass before the electrode roller 67. At the passing time of the photosensitive material 59 through the uncharged region, the alternating current voltage (frequency 1kHz) of 750 Vo-p (peak · to · peak 1.5kV) with the direct current voltage of the OV being piled up on it was applied on the electrode roller 67 by the alternating current high voltage power supply 68. Thereafter, at the passing time of the photosensitive material 59 charged to -500V and stored in electrostatic latent image, the alternating current voltage (frequency 1kHz) of 750 Vo-p (peak · to · peak 1.5 kV) with the direct current voltage of -350 V being piled up on it was applied upon the electrode roller 67 by the alternating power high voltage power supply 68. A carrier, a carrier on the photosensitive material 59 and a toner attached on the charged portion are recovered on the electrode roller 67, and toner images inverted negative, positive only to the picture image portion remain on the photosensitive material 59. The carrier and the toner attached onto the electrode roller 67 to be rotated in the arrow direction are scraped by the scraper 69, and are returned again into the developer hopper 64. They are used for the next image forming operation. In this manner, toner images of magenta color are obtained on the photosensitive material 59. The similar construction is provided even about the other developers 51BK, 51C, 51Y except for the magenta. The similar operation is effected. The construction and the operation of the printer operation are described again with the use of Fig. 4. As the construction is almost similar to that of the embodiment 1, the description will be omitted. In the present embodiment, the transfer portion of the transfer carrying belt 31 is slightly raised from the other portion and is brought into the contact against the photosensitive material of the image forming unit existing in the light exposing position. The other construction is possible in which the transfer carrying belt may be flat, and the image forming unit to be operated may be slightly lowered only at the image forming time. The operation of the apparatus at the color image forming time of the size of A4 will be described hereafter. The A4 form (not shown) is fed from a paper feeding portion 36 in the shorter direction, is placed on the transfer carrying belt, while being absorbed on the transfer carrying belt 31 by the operation of the adhering charger 37, and is moved in the left hand direction at a constant speed. At first, the image forming unit is in such a position as shown in Fig. 1, and the image forming unit 51BK for black use is in an image forming position 50, being opposite to the transfer portion 33. A black signal light is inputted into the image forming unit 51BK by a laser light exposing apparatus 3 at timing when the paper is being carried on the transfer carrying belt from the right. Image forming operation with the black toner is effected. At this time, the speed (peripheral speed of photosensitive material) of the image formation of the image forming unit 51BK is set to become the same as the moving speed of the transfer carrying belt. The black toner images are transferred on the paper form by the function of the transfer charger 38 through the movement of the paper at the same time with the image formation. Immediately after the trailing end of the paper has passed on the transfer portion after the completion of the transferring operation of all the black toner images, the movement of the transfer carrying belt is once stopped. The paper is moved, at a speed larger than the previous forward moving speed, in a direction reverse to the previous direction (referred to as reverse direction). At this time, the tip end of the paper is close to the driving roller as the length of the transfer carrying belt is sufficiently long. The tip end thereof does not tear off from the transfer carrying belt. At the approximately same time with the reverse direction moving start of the transfer carrying belt, the image forming unit group 51BK, 51C, 51M, 51Y are driven to the moving motor 30, and are all moved integrally at a high speed in the left hand direction of Fig. 4. They are stopped in such positions as shown in Fig. 6. At this time, the high voltage of the alternating current is applied upon the discharger 78 and the transfer charger 38 attached to the image forming unit 51BK so as to remove the power while the paper having the toner images and the transfer carrying belt are moving, passing in the opposite direction. As the bottom portion (see Fig. 2) except for the photosensitive material of the image forming unit is positioned on the upper side from the photosensitive material during this period, the black toner images on the paper are not disturbed in contact with the image forming unit. The image forming unit 51C is moved to come to the image forming position immediately after the rear end of the paper has passed. The subsequent operation is to superpose the toner images, fix them so as to make color images in the same manner as in the embodiment 1. The operation at the single color mode is completely the same as the embodiment 1. The construction for exchange of the image forming unit of the apparatus will be described hereinafter. For example, at the waiting time and the stopping time of the apparatus except for at the image forming time, the image forming unit is set by the moving motor 30 so as to be positioned as shown in Fig. 6. Therefore, the image forming unit is positioned as shown in Fig. 6 even at the exchange of the image forming unit, and the image transfer carrying belt and the image forming unit are separated from each other. When the image forming unit group is drawn out from the apparatus in the same manner explained in Fig. 3 of the embodiment 1, they are not rubbed against each other. The construction and the operation of the color electronic photographic apparatus in the second embodiment are described hereinabove. The transfer carrying belt is adapted not to come into contact against a portion except for the photosensitive material drum of the image forming unit which is located in the light exposing position in the present construction as described hereinabove so that any image forming unit is not provided in the light exposing position except for at the apparatus operation time. The image forming units can be integrally drawn out of the apparatus without influences be applied upon the other parts with the simple construction. The apparatus which is superior in maintenance property such as exchange, maintenance of the image forming unit. As each image forming unit including the photosensitive material can be externally adjusted singly, for example, the unit already adjusted at the factory shipment time can be exchanged with ease on the spot. A superior color electronic photographic apparatus capable of pretty superposed transferring operation can be provided, because a discharging means which is attached to the image forming unit group is provided so as to discharge the paper and the belt for each transferring operation of the respective colors, and to effect beautiful superposing transfer operation. In the above described embodiment, specified one as the construction of the image forming unit was used. The essential quality and the operational effect remain unchanged even in the case of the image forming unit of the construction using the conventional developing method in addition to it.

Claims: A color electronic photographic apparatus comprising a movable image forming unit group composed of a plurality of image forming units (1BK, 1C, 1M, 1Y; 51BK, 51C, 51M, 51Y), each including an electrostatic image carrier (9;59), a developing means and a toner (25M; 75M) of a respective color, wherein the respective image forming units (1BK, 1C, 1M, 1Y, 51BK, 51C, 51M, 51Y) are capable of forming toner images of colors each being different on the respective electrostatic image carriers (9;59), a transfer carrying means (31, 34, 35) capable of placing a transfer material so as to reciprocate it, and provided with a transferring means for transferring on the transfer material the toner images provided on the electrostatic image carriers (9;59) in a single transfer position, a light exposing means (3) for effecting an image light exposing operation in a single light exposing position corresponding to the transfer position, a moving means (30) for sequentially moving each of the plurality of image forming units (1BK, 1C, 1M, 1Y, 51K, 51C, 51M, 51Y) to the image forming position corresponding to the light exposing position and to the transfer position, so that the toner images of different colors are put together in position and superposed on the transfer material so as to form color images. A color electronic photographic apparatus as defined in claim 1, wherein the transfer carrying means (31, 34, 35) comprises a reciprocating belt (31) having an approximately flat portion including the transfer position of the belt (31) and being approximately twice or more as long as the length in the progressive direction of the maximum color image, and seven fourth or more of the total length in the transfer paper progressive direction of the plurality of image forming units (1BK, 1C, 1M, 1Y; 51BK, 51C, 51M, 51Y). A color electronic photographic apparatus as defined in claim 1, wherein the pluraltiy of image forming units (1BK, 1C, 1M, 1Y; 51BK, 51C, 51M, 51Y) is composed of units capable of possible independent exchange. A color electronic photographic apparatus as defined in claim 1, wherein the plurality of image forming units (1BK, 1C, 1M, 1Y; 51BK, 51C, 51M, 51Y) is adapted to be drawn out integrally from the apparatus. A color electronic photographic apparatus as defined in claim 1, wherein the transfer carrying means (31, 34, 35) is provided with a carrying control means (46) for moving the transfer material in one direction in a single color mode, and for reciprocating it in a color mode. A color electronic photographic apparatus as defined in claim 1, wherein the length in the progressive direction of the maximum single color picture image is larger than the length in the progressive direction of the maximum color picture image. A color electronic photographic apparatus as defined in claim 1, further comprising a fixing means (44) disposed rearwards of the transfer carrying means (31, 34, 35) so as to fix the toner images on the transfer material after the transferring operation of the toner image of the last color, and a carrying control means (46) for changing the transfer material moving speed of the transfer carrying means and the speed of the fixing means (44) after the transferring operation of the toner image of the last color, such that these respective speeds differ from the corresponding speeds at the image forming time. A color electronic photographic apparatus as defined in claim 1, wherein each of the plurality of movable image forming units (1BK, 1C, 1M, 1Y; 51BK, 51C, 51M, 51Y) additionally includes a cleaning means (27) for cleaning the respective electrostatic image carrier surfaces, the transfer carrying means (31, 34, 35) is provided with a cleaning means (41), and a coupling means (42) is provided for coupling the cleaning means (27) of the image forming unit (1BK, 1C, 1M, 1Y; 51BK, 51C, 51M, 51Y) provided in the image forming position and the cleaning means (41) of the transfer carrying means to the same drainage reservoir. A color electronic photographic apparatus as defined in claim 1, wherein a discharging means (78) is attached to the image forming unit (51BK, 51C, 51M, 51Y) or the image forming unit group and is provided in a position opposite to the transfer carrying means (31, 34, 35). A color electronic photographic apparatus as defined in claim 1, wherein the moving means is controlled so that either of the image forming units (1BK, 1C, 1M, 1Y; 51BK, 51C, 51M, 51Y) is not positioned in the light exposing position except at the image forming time, and the belt (31) is disposed in position of non-contact with the image forming unit group except in that portion wherein the electrostatic image carrier (24M; 74M) of one of the image forming units (1BK, 1C, 1M, 1Y; 51BK, 51C, 51M, 51Y) is provided in the light exposing position.

Inventors: TERADA HIROSHI, YAMAMOTO HAJIME, TERADA, HIROSHI, YAMAMOTO, HAJIME
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1992
Main classification: G03G15
IPC codes: G03G15