Recording Medium Carrier System

Abstract: A recording medium carrier system of an image forming apparatus is constituted by independent units as a paper supply cassette (20), a paper feed unit (24, 31, 33), a transfer unit (12, 13), a fixing unit (50), and a paper ejecting unit (60). An intermediate transfer unit in the transfer unit is provided with an intermediate transfer belt (360) to which a toner image formed on a photoconductive drum (110) is primarily transferred at a primary transfer position and which secondarily transfers the toner image on a recording medium (S) at a secondary transfer position, and a driving roller (310) for circulating the intermediate transfer belt (360). The primary transfer position is arranged close to the driving roller (310).

Description: The present invention relates to a recording medium carrier system used in an image formation apparatus using an electrophotographic method, such as a copying machine, a printer and a facsimile. As for a copying machine, a printer, a facsimile and other image formation apparatuses respectively using electrophotography, above all, an image formation apparatus using a laser beam writing device, a function for transferring and fixing a toner image while carrying a recording medium at high speed is required to make good use of the function of the writing device, and operability for allowing a simple measure for paper jam and others caused by the provision of such a function is also required. US 5,510,886 which discloses the features defined in the preamble portion of appended claim 1, shows a conventional recording medium carrier system having a paper feed mechanism, including pairs of rollers for carrying a recording medium to a transfer part. It has been found that the conventional recording medium carrier system is somewhat insufficient in reliably carrying the recording medium. Therefore, it is an object of the present invention to provide a recording medium carrier system having an increased performance in carrying the recording medium. This object is solved by providing a recording medium carrier system as defined in appended claim 1. Further details and advantages of the invention will be apparent from the following description when taken in conjunction with the drawings, in which: Fig. 1 is a block diagram of an apparatus showing an embodiment of the present invention. Fig. 2 is a timing chart showing the operation of the above apparatus. Preferred embodiments of the present invention will now be described below. Fig. 1 shows the outline of a color image formation apparatus provided with a recording medium carrier system of an embodiment of the present invention. First, the whole system of the apparatus will be described. Around a photoconductive drum 2 in Fig. 1, in the order from the upstream side in the rotational direction, there are provided a charging roller 3, a laser beam scanning type latent image formation unit 4, developing units of yellow, magenta, cyan and black 5, 6, 7 and 8, and a cleaning unit 10 opposite to a first transfer part 9. The above apparatus is constructed so that a toner image according to recording information is formed on the photoconductive drum 2 by repeating each imaging process of yellow, magenta, cyan and black every rotation of the photoconductive drum 2. In the meantime, an intermediate transfer belt 11 without an end touched or detached to/from the photoconductive drum 2 in the transfer part 9 is constructed so that a color toner image formed on the peripheral surface of the photoconductive drum 2 is transferred onto the intermediate transfer belt by a primary transfer roller 12 and is secondarily transferred onto a recording medium S by a backup roller 13. Recording paper S piled on a paper supply cassette 20 reaches a secondary transfer part via a pickup roller 24 and pairs of paper carriage rollers 31 and 33, and in the secondary transfer part, a color toner image is transferred onto the recording paper. Further, after the transferred color toner image is fixed by a fixing unit 50, the recording paper is ejected onto a paper ejection tray 66 via pairs of paper ejecting rollers 62 and 64. Next, a recording paper carrier mechanism will be described in detail. The paper supply cassette 20 is constructed so that it can be installed in the lower part at the front of the frame 1 of the apparatus, that is, in the lower part in Fig. 1, and the fixing unit 50 can be turned forward so that recording paper S can be readily supplied and measures for paper jam can be taken. A paper pushing-up plate 21 provided to the above paper supply cassette 20 is coupled to a driving motor via a stepping clutch not shown and stopped at 120° and 240° so that the paper pushing-up plate is driven by the single driving motor not shown for driving a cam 45 for touching or detaching a secondary transfer roller 41 and all the pair of paper separating rollers 26 and the pairs of paper carriage rollers 31 and 33 between the pickup roller 24 and the pair of gate rollers 35, and can be vertically moved. The paper pushing-up plate is constituted so that it is lifted when the whole apparatus starts operation and lowered after printing operation is finished. Further, a pressing roller 22 made of resin for pressing an envelope and others is provided to the paper supply cassette 20 at the back of the pickup roller 24 so that slanting at paper supply, which may be caused because the edge of the uppermost envelope of piled ones is lifted and is slantwise touched to the pickup roller 24, can be prevented. In the meantime, the pickup roller 24 for feeding recording paper S pushed up by the paper pushing-up plate 21 is formed as a roller approximately 40 mm long which is made of rubber the hardness of which is 25 to 40° and is constituted so that the pickup roller comes in contact with the center in width of paper, and is driven via a first clutch not shown so that the pickup roller is interlocked with the pair of paper separating rollers 26. The pair of paper separating rollers 26 arranged close on the downstream side in a direction in which paper is fed of the pickup roller 24, consist of an upper separating roller 27 rotated in the carriage direction of paper and a lower separating roller 28 normally rotated and reversely rotated via a torque limiter, and both are respectively formed as a roller approximately 40 mm long so that each roller comes in contact with the center in width of recording paper S and plural sheets are prevented from being fed. In the meantime, a paper carriage path between the pair of paper separating rollers 26 and the secondary transfer part functions as a paper reversing carriage path 30 for reversing recording paper S. In this portion, first and second pairs of carriage rollers 31 and 33 and a pair of gate rollers 35 are arranged at an interval at which a postal card can be fed longitudinally or according to circumstances, are arranged at an interval at which an envelope can be fed sideways, and are constituted so that driving force is transmitted via a second clutch. The first pair of carriage rollers 31 are arranged close on the downstream side of the pair of paper separating rollers 26 and are constituted as rollers of the length equal to the width of recording paper S to supplement the unstable feeding of the pair of paper separating rollers 26 which hold only the center in width of paper and carry it. The pair of gate rollers 35 are supported by a plain bearing, whereas these first and second pairs of carriage rollers 31 and 33 are supported by a ball bearing. The above rollers are constituted so that the free rotation torque of these pairs of carriage rollers is smaller than that of the pair of gate rollers 35 and even if recording paper S fed at high speed collides with the pair of gate rollers 35, the pair of gate rollers 35 are prevented from being moved by the force of the collision. Further, in the paper reversing carriage path 30, tensile force is prevented from being applied to recording paper S in the carriage process by setting the peripheral speed of each pair of rollers 26, 31 and 33 between the pickup roller 24 and the pair of gate rollers 35 so that it is slower in order and furthermore, recording paper S is prevented from being slipped in the secondary transfer part by setting the peripheral speed of the pair of gate rollers 35 so that it is faster than that of the transfer belt 11. The peripheral speed of each pair of rollers 26, 31 and 33 has only to be set in an extent that the peripheral speed of the roller on the upstream side when the tolerance of the diameter of the roller on the downstream side is maximum, is equal to or slower than the peripheral speed of the roller on the upstream side when the tolerance of the diameter of the roller on the upstream side is maximum. Also, the peripheral speed of the pair of gate rollers 35 has only to be set in an extent that the peripheral speed of the gate roller when the tolerance of the diameter of the gate roller is minimum, is equal to or faster than the speed of the transfer belt 11. In the paper reversing carriage path 30, first and second paper sensors 32 and 34 are arranged close on the downstream side of the first pair of carriage rollers 31 and close on the upstream side of the pair of gate rollers 35. If recording paper does not reach the first paper sensor 32 after predetermined time elapses since the pickup roller 24 starts the feed of the recording paper, it is supposed that the second paper sensor 34 detects abnormality independent of whether the second paper sensor 34 detects the recording paper or not, and a signal is output to control means. Therefore, the quantity of information to be sent to the control means is reduced by the quantity of the signal. The pickup roller 24, the pair of paper separating rollers 26, the first and second pairs of carriage rollers 31 and 33, and the pair of gate rollers 35 described above are assembled as one paper feed unit 37 as shown by a broken line in Fig. 1. The paper feed unit is attached to the body 1 of the apparatus so that it can be detached from the body, and is constituted so that it can be also connected to a paper supply cassette with large capacity. In the meantime, reference number 40 denotes a secondary transfer roller unit arranged on the downstream side of the pair of gate rollers 35 via a paper guide member 38. The unit 40 is constituted by a swing lever 41 which can be swung around a supporting point 43 with the swing lever pressed by the spring 43 so that the secondary transfer roller 42 supported by the swing lever is always in contact with the transfer belt 11, and the cam 45 for swinging the swing lever 41 so that the secondary transfer roller 42 is detached from the transfer belt 11 via a cam follower 44. The cam 45 for touching or detaching is coupled to the driving motor via the stepping clutch 4 not shown so that the cam is stopped in plural positions in one rotation, at 120° and 240° in this embodiment, and the lead of the cam is formed to have an extremely small sine curve so that the secondary transfer roller is detached from the transfer belt 11 in a range in which atmospheric discharge may occur by applying voltage to the transfer belt 11, for example, approximately 1 mm. Shock when the secondary transfer roller 42 comes in contact with the transfer belt 11 is reduced and the deterioration of the quality of an image due to the shock is prevented by constituting as described above. The application of voltage to the secondary transfer roller 42 is controlled so that after the secondary transfer roller 42 comes in contact with the transfer belt 11, current application is started and before the secondary transfer roller 42 is detached, current application is stopped to prevent atmospheric discharge from occurring actually. Reference number 50 denotes a fixing unit for fixing a transferred toner image on recording paper S. The fixing unit 50 is attached so that it can be turned outside with a supporting part 51 provided at the inner lower end as a supporting point and is constructed so that paper jam caused on paper ejecting path can be easily handled and each developing unit 5 to 9 can be easily replaced. The fixing unit 50 is constituted by a heat roller 52, first and second pressurizing rollers 54 and 56 pressed on the heat roller 52, and a heat insulating member 55 arranged among them. Toner can be more securely fixed at higher speed by providing large nip length and large contact pressure to the first pressurizing roller 54 to provide a function for melting toner, in the meantime, providing large curvature to the second pressurizing roller 56 to provide a function for fixing toner, and further, providing a function for guiding recording paper and a function for controlling heat radiation from the heat roller 52 to the heat insulating member 56. A group of pairs of paper ejecting rollers following the fixing unit 50, that is, two pairs of paper ejecting rollers 62 and 64 in this embodiment are attached to the front side of the apparatus 1 as one paper ejecting roller unit. These pairs of paper ejecting rollers 62 and 64 are constructed so that recording paper can be ejected on the paper ejection tray 66 with the recording paper S tense by setting the paper carriage speed of these pairs of paper ejecting rollers 62 and 64 so that it is faster than that of the fixing unit 50 and setting the paper carriage speed of the pair of paper ejecting rollers 64 on the downstream side in the paper carriage direction so that it is faster than that of the pair of paper ejecting rollers 62 on the upstream side. The peripheral speed of each pair of paper ejecting rollers 62 and 64 has only to be set in an extent that the peripheral speed of the roller on the downstream side when the diameter of the roller is maximum, is equal to or not slower than the peripheral speed of the roller on the upstream side when the diameter of the roller is minimum according to the same thought as in the case of the above rollers on the paper feed path. Reference numbers 61 and 63 denote each paper detecting sensor arranged on the paper ejecting path. Next, the recording paper carriage operation of the apparatus constructed as described above will be described referring to Fig. 2. When the operation of the whole apparatus is started at time "a" after a period for initialization for supplying paper, the paper pushing-up plate 21 pushes up loaded recording paper S and touches the center in width of the uppermost paper to the pickup roller 24. When a paper feed/separating roller clutch is connected at time "b" in relation to an imaging process, and the pickup roller 24 the rotation of which is started, feeds first recording paper S, the pair of paper separating rollers 26 arranged close on the downstream side of the pickup roller prevent plural sheets from being fed by rotating the lower separating roller 28 reversely. A paper carriage roller clutch connected together with the paper feed/separating roller clutch transmits rotation to each first and second pair of carriage rollers 31 and 33 for time equivalent to the length of a paper path between the paper supply tray 20 and the pair of gate rollers 35, that is, till time c, and is touched to the full width of recording paper S from the pair of paper separating rollers 26 to carry it to the pair of gate rollers 35 in a stable state. At time "d" after fixed time elapses after primary transfer is started, a gate roller clutch transmits driving force to the pair of gate rollers 35 for time equivalent to the length of a path between the pair of gate rollers 35 and the secondary transfer roller 42, that is, till time e, and at the same time, carries recording paper S to a transfer part in cooperation with the first and second pairs of carriage rollers 31 and 33 to which the driving force is transmitted via the paper carriage roller clutch, then executes required transfer processing on it. Though different according to the length in the carriage direction of recording paper S, the paper feed/separating roller clutch for carrying second recording paper S is connected at time "f" before or after the operation of the gate roller clutch, at the following time "g", the paper carriage roller clutch transmits driving force to the first and second pairs of carriage rollers 31 and 33 for time equivalent to the length of a path between the first pair of carriage rollers 31 and the pair of gate rollers 35, that is, till time "h", and carries second recording paper S to the pair of gate rollers 35. In the meantime, in such an apparatus in which recording paper is continuously carried, high durability and advanced paper carriage control means are provided. However, the wear and tear of parts and the occurrence of paper jam and others cannot be avoided. If such a situation occurs, a target unit of units respectively independently attached as the paper feed unit 37, a transfer unit 40, the fixing unit 50, and a paper ejecting unit 60 is detached from the body 1 of the apparatus by a user, or is replaced. As described above, according to the present invention, since a paper feed mechanism, a transfer mechanism, a fixing mechanism, and a paper ejecting mechanism constituting a recording medium carrier system are constructed as an independent unit, a user can handle such a situation, by detaching or replacing a unit, that paper jam or the wear and tear of parts occurs in this type of image formation apparatus which continuously carries a recording medium at high speed. Thus, the cost required for maintenance can be reduced and the operation rate of the apparatus can be greatly enhanced.

Claims: A recording medium carrier system used for an image formation apparatus of a type in which a toner image formed according to an electrophotographic method is transferred and fixed onto a recording medium (S), comprising: a paper feed mechanism (24, 31, 33) for carrying a recording medium (S) to a transfer part, said paper feed mechanism (24, 31, 33) including pairs of rollers (31, 33); a transferring mechanism (12, 13) for transferring a toner image onto a recording medium; a fixing mechanism (50) for fixing the transferred toner image on the recording medium; and an ejecting mechanism (62, 64) for ejecting the recording medium from a fixing part, wherein said paper feed mechanism (24, 31, 33), said transferring mechanism (12, 13), said fixing mechanism (50), and said ejecting mechanism (62, 64) are respectively constructed as an independent unit, characterized in that a carriage speed of each of said pairs of rollers (31, 33) is set so that the closer said pair of rollers are to a pair of gate rollers (35), the slower the carriage speed of said pair of rollers (31, 33) is. A recording medium carrier system according to claim 1, wherein said paper feed mechanism includes pairs of rollers (31, 33), and a free rotation torque of each of said pairs of rollers (31, 33) is smaller than that of a pair of gate rollers (35). A recording medium carrier system according to claim 1 or 2, wherein a carriage speed of said paper ejecting mechanism (62, 64) is faster than that of said fixing mechanism (50); and a carriage speed of a pair of paper ejecting rollers on a downstream side in a carriage direction in said paper ejecting mechanism (62, 64) is faster than that of a pair of paper ejecting rollers on an upstream side. A recording medium carrier system according to any one of claims 1 to 3, wherein said paper feed unit (24, 31, 33) includes pairs of rollers (31, 33), and a carrying capacity of each of said pairs of rollers (31, 33) is set so that the closer a pair of carrier rollers (31, 33) are to a downstream side in a carriage direction, the larger the carrying capacity of said pair of rollers (31, 33) is.

Inventors: ABE NOBUMASA, ABE, NOBUMASA
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1998
Main classification: G03G21
IPC codes: G03G21, G03G9, G03G15