Patent Application
20050117939
1. Field of the Invention
The present invention relates to an image forming apparatus using electrophotographic technology.
2. Description of the Related Art
Recently, image forming apparatuses such as copying machines which form images from image data, a facsimile machine or an image scanner used as a computer output device are being more widely used.
Many types of image forming means, including thermal fusion, thermal sublimation, thermal transfer, ink-jet, and electrophotographic, have been developed in response to user demands. Among others, a full-color electrophotographic image forming apparatus using four colors, including cyan, yellow, magenta and black, by arranging four process stations 1a, 1b, 1c and 1d that serve as image forming sections of different colors, as shown in
In
The individual process stations 1a to 1d serving as process cartridges are detachable from the image forming apparatus main body. The individual process cartridge integrally combines the photosensitive drums 2a to 2d, the primary chargers 3a to 3d, the developing units 5a to 5d, and cleaning means 6a to 6d.
A transfer medium S serving as a recording medium housed in a paper feed cassette 15 is fed into the image forming apparatus main body by a paper feed roller 16, and conveyed by a resist roller pair 17. Then, the transfer medium S is electrostatically attracted by a transfer conveyor belt 7, serving as a transfer medium carrier, by an attracting roller 12 to which a positive attracting bias voltage is applied by an attracting bias power source 13.
The transfer conveyor belt 7 is attracted and supported by four rollers including a driving roller 8, an attraction opposing roller 9, and tension rollers 10 and 11. The process stations 1a, 1b, 1c and 1d of the individual colors, including cyan, yellow, magenta and black, are arranged substantially perpendicular to the surface of the transfer conveyor belt 7 and sequentially from an upstream side along the moving direction of the transfer conveyor belt 7 (as shown by arrow a).
The transfer medium S, attracted by the transfer conveyor belt 7, passes sequentially through the process stations 1a to 1d of the individual colors. The toner images of the individual colors carried on the photosensitive drums 2a to 2d are electrostatically transferred in sequence. Subsequently, these toner images are heated and pressurized by a fixing unit 18, whereby the toner images are fixed on the transfer medium S to form permanent images.
At this point in time, the transfer medium S, which is a dielectric such as paper or a synthetic resin, carries a large amount of charge since the transfer medium undergoes four runs of the transfer process while passing through the four process stations 1a to 1d.
As a result, a peeling-discharge phenomenon takes place, at a peeling-separation section, from the transfer conveyor belt 7 provided on the circumference of the driving roller 8, and the toner images, transferred onto the transfer medium S, are disturbed along the discharge pattern.
To solve this problem, it is the usual practice to arrange a neutralizer (neutralizing member) between the transfer conveyor belt 7 and the fixing unit 18, as shown in
However, use of a neutralizer having the above-mentioned configuration has the following problems.
Use of a wire-type corona charger as a neutralizer is characterized by stabilization of discharge and availability of a neutralizing effect. On the other hand, when cleaning stains off of the discharge wire 52, or when removing transfer medium jam, the discharge wire 52 tends to be easily broken or it is difficult to maintain a sufficient life or ensure safety.
There is available a neutralizing member using a sharp electrode as a neutralizing mechanism posing no risk of breakage of the discharge wire 52, as in a corona charger 51. Use of a sharp electrode can, however, pose other problems.
The neutralizing mechanism using a sharp electrode (needle electrode or the like) has conventionally been arranged near the object of neutralization, since the neutralizing effect becomes more remarkable as the distance between the object of neutralization and the sharp electrode becomes smaller. However, in the neutralizing member using the sharp electrode, the rise in discharge current from the proximity of the discharge threshold value (electric field condition for start of discharge) is steep, making it difficult to stabilize the neutralizing effect because of the unstable discharge.
That is, it has generally been recognized that, if the object of discharge may flap as the transfer medium, a neutralizing member using a sharp electrode did not achieve uniform neutralization. When the distance between the neutralizing member and the object of neutralization is small, an increase in the number of transfers of the object of neutralization in the proximity of the neutralizing member causes adhesion of dust resulting from the object of neutralization itself, to the neutralizing member and an abnormal discharge at this adhesion, thus causing a problem in that the expected neutralizing effect cannot be achieved.
The present invention is directed to an image forming apparatus having a sharp neutralizing member.
The sharp neutralizing member ensures a uniform neutralizing effect for a long period of time on an object of neutralization. For example, for neutralization of an image carrier carrying a toner image, uniform neutralization of the entire image carrier can be achieved, and a high-quality toner image can be obtained.
In one aspect of the present invention, an image forming apparatus is operable to form images on a transfer medium. The apparatus includes a carrier configured to carry the transfer medium along a moving path and a neutralizing member which is configured to neutralize the transfer medium. The neutralizing member includes a first projection and a second projection adjacent to the first projection, wherein the first and second projections have first and second tip portions, respectively, and configured to neutralize the transfer medium. A minimum distance D1 between the first tip portion and the moving path of the transfer medium, a minimum distance D2 between the second tip portion and the moving path of the transfer medium, and a perpendicular distance P between the first tip portion and the second tip portion satisfy the following formulas:
D1≧4.0 mm, 0.8*D1≦P≦1.5*D1
D2≧4.0 mm, 0.8*D2≦P≦1.5*D2.
In another aspect of the present invention, an image forming apparatus includes a toner image carrier configured to carry a toner image; and a neutralizing member configured to neutralize the toner image carrier. The neutralizing member has a first projection and a second projection adjacent to the first projection, wherein the first and second projections have first and second tip portions, respectively. A minimum distance D1 between the first tip portion and the toner image carrier, a minimum distance D2 between the second tip portion and the toner image carrier, and a perpendicular distance P between the first tip portion and the second tip portion satisfy the following formulae:
D1≧4.0 mm, 0.8*D1≦P≦1.5*D1
D2≧4.0 mm, 0.8*D2≦P≦1.5*D2.
In still another aspect of the present invention, an image forming apparatus includes a conveyor configured to convey toner images; and a neutralizing member configured to neutralize the conveyor. The neutralizing member has a first projection and a second projection adjacent to the first projection. The first and second projections have first and second tip portions, respectively. A minimum distance D1 between the first tip portion and the conveyor, a minimum distance D2 between the second tip portion and the conveyor, and a perpendicular distance P between the first tip portion and the second tip portion satisfy the following formulae:
D1≧4.0 mm, 0.8*D1≦P≦1.5*D11,
D2≧4.0 mm, 0.8*D2≦P≦1.5*D2.
Further features and advantages of the present invention will become apparent from the following description of the embodiments (with reference to the attached drawings).
The image forming apparatus of the present invention will now be described in detail with reference to the drawings.
Outline of Image Forming Apparatus
An embodiment of the image forming apparatus using the full-color electrophotographic method will be described in detail as an example of the neutralizing unit of the present invention and the image forming apparatus having such a neutralizing unit with reference to the drawings.
The whole configuration of the image forming apparatus having the neutralizing member of the present invention will first be described with reference to
The process stations 32a to 32d have photosensitive drums 2a, 2b, 2c and 2d serving as image carriers. The surfaces of the photosensitive drums 2a to 2d are uniformly charged by primary chargers 3a, 3b, 3c and 3d arranged around the respective photosensitive drums 2a to 2d, and are then subjected to exposure based on image information by exposure units 4a, 4b, 4c and 4d, such as LEDs (light emitting diodes) or lasers, whereby electrostatic latent images are formed. The resultant electrostatic latent image to which different kinds of toner of the individual colors are deposited by developing units 5a, 5b, 5c and 5d are developed as toner images.
The individual process stations 32a to 32d are detachable from the image forming apparatus main body as process cartridges. The individual process cartridges are composed of integrally combined respective photosensitive drums 2a to 2d, primary chargers 3a to 3d, developing units 5a to 5d, and cleaning means 6a, 6b, 6c and 6d.
The transfer medium S serving as a recording medium housed in a paper feed cassette 15 is fed into the image forming apparatus main body, and is conveyed by a resist roller pair 17.
An intermediate transfer belt 31 is stretched by three rollers including a driving roller 8, a transfer counter roller 34, and a tension roller 10. The process stations 32a to 32d of the individual colors including cyan, yellow, magenta and black are arranged sequentially from an upstream side along the moving direction of the intermediate transfer belt 31 (the arrow a direction in
Transfer rollers 14a, 14b, 14c and 14d, serving as a transfer mechanism, are arranged on the inside of the intermediate transfer belt 31, opposite to the corresponding photosensitive drums 2a to 2d. Upon sequentially passing through the process stations 32a to 32d of the individual colors, the toner images of the individual colors carried on the respective photosensitive drums 2a to 2d are sequentially transferred electrostatically onto the surface of the intermediate transfer belt 31 by means of the individual transfer rollers 14a to 14d.
The transfer medium S is conveyed from the resist roller at a prescribed timing, and at the nip portions of the intermediate transfer belt 31 and a transfer roller 35, the toner images on the intermediate transfer belt 31 are transferred onto the transfer medium S.
A fixing unit 18, serving as a fixing device, is arranged downstream of the transfer roller 35 in the conveying direction of the recording medium. Through heating and pressurizing in the fixing unit 18, the toner images are fixed onto the transfer medium S to form a permanent image.
Residual toner remaining on the individual photosensitive drums 2a to 2d is collected by respective cleaning unit 6a to 6d so that the surfaces of the photosensitive drums are cleaned. Residual toner remaining on the intermediate transfer belt 31 is collected by a cleaning unit 33, thus cleaning the surface of the intermediate transfer belt 31.
Configuration of Neutralizing Member in this Embodiment
A neutralizing member 23 includes a plurality of saw-toothed electrodes 231, as shown in
In the image forming apparatus shown in
If the neutralizing member 23 is not provided, the transfer medium S becomes highly charged to a large extent since the transfer medium S is subjected to the transfer process during passage through the nip portion of the intermediate transfer belt 31 and the transfer roller 35, whereby a high potential of about −3,000 V is applied to maintain the charge. When the unfixed toner images on the transfer medium S are conveyed to the fixing unit 18 while maintaining the charge, the transfer medium S undergoes an abnormal discharge occurring on a conveying guide and on the back of the transfer medium S during the period until fixing thereof, and the toner images transferred onto the transfer medium S are disturbed along the discharge pattern. Particularly when the transfer medium S is dry as when forming images in a low-temperature low-humidity environment, or when forming images on a second surface in two-sided images, the transfer medium S has a high resistance, tends to be easily charged and the charge is hard to attenuate, thus easily causing the above-mentioned abnormal discharge.
In the present embodiment, the neutralizing member 23 is arranged between the transfer roller 35 on the recording medium conveying path and the fixing unit 18 as shown in
The neutralizing member 23 and the transfer roller 35 are arranged at positions such that the smallest distance therebetween is about 5 mm. This is for preventing leakage between the neutralizing member 23 and the transfer roller 35.
Experiments for Installation of Neutralizing Member
Upon installing the neutralizing member, the present inventors correlated the defective image with the shape of the neutralizing member and recognized an important effect on the image quality of the distance between tips of projections of the neutralizing member and the distance between the tip of the neutralizing member and the object of neutralization. The inventors found that these parameters were predominant by providing many kinds of neutralizing member and repeatedly passing the transfer media S therethrough. The present inventors further carried out the following experiments to see what influence these parameters had, and finally found an optimum relationship. The settings in the above-mentioned embodiments reflect the result of the following experiments. The experiments will now be described in detail.
Experiment 1
The distance (clearance D) between the tip of the neutralizing member (231 in
According to the result, when the clearance D is fixed, the appropriate pitch P (mm) is within a certain range, and to prevent occurrence of a defective image at a larger clearance D, the pitch P (mm) must also be larger.
Experiment 2
The reason for occurrence of a defective image with a fixed pitch P of the neutralizing member and a smaller distance of the object of neutralization was verified by outputting half-tone images. As a result, image defects of image were found to occur at a certain pitch. In addition, the output image was collated with the image conveying path to confirm the relationship between points of occurrence and the shape of the saw-toothed neutralizing member. It was confirmed that the pitch corresponds to the distance between the tip portions of the saw-toothed neutralizing member (see
Experiment 3
The result of an experiment providing clues for clarification of the mechanism of occurrence of a defective image when the pitch of the neutralizing member is one-sidedly reduced will now be presented.
At uniform pitch P, a larger clearance D (mm) between the neutralizing member 23 and the metal plate is suggested to lead to a smaller discharge current (μA). In other words, at a uniform pitch P, a large clearance D between the neutralizing member 23 and the transfer medium S results in a smaller neutralizing effect on the transfer medium S, and this may cause the occurrence of a defective image. When the clearance D between the neutralizing member 23 and the metal plate is fixed, the result of this experiment suggests that a larger pitch leads to a lager neutralizing effect of the transfer medium S, thus inhibiting the occurrence of a defective image.
This is attributable to the following fact. When the clearance D between the neutralizing member 23 and the metal plate is fixed, a larger pitch mm (an expected pitch) leads to concentration of electric field at the tips 231 of neighboring teeth, and interference between the tips 231 of the teeth is prevented.
Under the effect of the mechanism assumed above and from the result shown in
Experiment 4
The above-mentioned experiments are based on the result of single image forming runs. The following description concerns confirmation of the image quality of an image outputted after image forming on 50,000 A4-size pages. The result is shown in
According to the result, when durability is taken into account, it is necessary to separate the object of neutralization from the neutralizing member to some extent. The presence of the transfer medium, which is the object of neutralization, near the neutralizing member causes adhesion of dust and debris, such as toner or paper powder, to the neutralizing member, and this may cause uniformity of neutralization to be lost.
In a neutralizing member which carries out neutralization by discharging the object of neutralization by causing a discharge by the use of the potential difference between the neutralizing member and the transfer medium, a strong electric field is formed between the neutralizing member and the object of neutralization. If there is any dust in the proximity in this case, charged dust is attracted by the neutralizing member and adheres thereto. This is confirmed from the fact that a large neutralizing current flows according as the distance between the object of neutralization and the neutralizing member becomes smaller. Flow of neutralizing current in a larger amount leads to collection of much more dust. When dust adheres to the neutralizing member, abnormal discharge takes place at points of such adhesion (unexpected positions), and the expected neutralizing effect is not achieved. Particularly, the present embodiment achieves a uniform neutralizing effect from neutralization with the projections of the neutralizing member. It is therefore necessary to ensure a sufficient distance between the neutralizing member and the transfer medium so as to prevent dust from adhering to the neutralizing member and non-uniformity of discharge, as evaluated with various distances between the neutralizing member and the transfer medium, as shown in
The increase in the distance between the neutralizing member and the transfer medium S further makes it possible to avoid a jam caused by the transfer medium S catching on the neutralizing member, thus further preventing paper powder from adhering to the neutralizing member in jams.
For these reasons, the distance D between the neutralizing member and the object of neutralization is set at D≧4.0.
From the results of the first to third experiments, the condition 0.8D≦P≦1.5D must be satisfied with a large D value.
From the Result of Experiments
As is clear from the above-mentioned results of the experiments, a uniform and higher-quality image can be obtained, regarding the neutralizing member, by satisfying the conditions 0.8D≦P≦1.5D and D≧4.
In the above-mentioned experiments in this embodiment, an image forming apparatus using an intermediate transfer medium has been described. Also, in an image forming apparatus using transfer means carrying out a transfer directly from the photosensitive member, it is of course possible to obtain similar effects by arranging the neutralizing unit of this embodiment at the portion opposite to the transfer medium S.
The case where the transfer medium S is neutralized has been described above. There are similar problems also for the image forming apparatus using the transfer drum or the intermediate transfer medium as an object of neutralization.
The present embodiment has covered a case where the projections of the neutralizing member are equally spaced from each other. As is conceivable from the above-mentioned experiments, it is not always necessary to arrange them at equal intervals as long as the conditions given in the present invention are satisfied.
The second embodiment is characterized, as in the first embodiment, in that the transfer roller 35 is driven. According to the above-mentioned configuration, the transfer medium S passes through the nip portion of the intermediate transfer belt 31 and the transfer roller 35, and the behavior of the transfer medium during conveyance is stabilized. Particularly even when the weight of the transfer medium S changes, the behavior of the transfer medium S is harder to change, since the transfer medium S passes along the nip portion formed by the intermediate transfer belt 31 and the transfer roller 35. After passage through the nip portion of the intermediate transfer belt 31 and the transfer roller 35, the conveying direction becomes harder to vary.
When the pitch P of the neutralizing member 23 is fixed, as described above, in order to prevent occurrence of a defective image, it is necessary that the clearance D between the transfer medium S and the neutralizing member 23 be within a prescribed range.
As a result, as in the first embodiment, when the neutralizing member 23 is arranged between the transfer roller 35 and the fixing unit 18 on the conveyance path of the recording medium, and if the transfer roller 35 is driven as in this embodiment, the distance between the transfer medium S and the neutralizing member 23 is further stabilized.
In the present embodiment, therefore, even upon a change in the weight of the transfer medium, it is possible to expect a more stable neutralization of the transfer medium S, and to keep the image quality on a high level.
A third embodiment of the image forming apparatus using the full-color electrophotographic method will be described in detail as an example of the neutralizing unit of the present invention and the image forming apparatus having such a neutralizing unit with reference to the drawings.
When passing through the four process stations 32a to 32d, the intermediate transfer belt 31 is subjected to a large amount of charge while undergoing the four transfer steps by the individual transfer rollers 14a to 14d. As a result, unless the charge on the back of the intermediate transfer belt 31 is neutralized, a defective transfer is caused at the process stations arranged in the downstream. The potential difference between the surface of the toner on the surface of the intermediate transfer belt 31 and the photosensitive drums grows lager, thus causing abnormal discharge. Upon occurrence of the abnormal discharge, the toner images on the intermediate transfer belt not fixed splashes, leading to occurrence of a defective image.
For the purpose of neutralizing the back of the intermediate transfer belt 31, therefore, as shown in
The individual neutralizing members 23a to 23d are arranged at positions such that the shortest distance to the respective transfer rollers 14a to 14d is about 5 mm. The value of 5 mm is adopted to prevent leakage between the neutralizing members 23a to 23d and the transfer rollers 14a to 14d.
According to the above-mentioned configuration, it is possible to carry out neutralization of the back of the intermediate transfer belt 31 by means of the neutralizing member 23, and thus to prevent occurrence of a defective transfer or a defective image caused by the abnormal discharge.
A fourth embodiment of an image forming apparatus based on the full-color electrophotographic method will now be described in detail with reference to the drawings as an example of the neutralizing unit of the present invention and an image forming apparatus having such a neutralizing unit.
The process stations 1a to 1d have photosensitive drums 2a, 2b, 2c and 2d, serving as image carriers. The surfaces of the photosensitive drums 2a to 2d are uniformly charged by primary chargers 3a, 3b, 3c and 3d arranged around the individual photosensitive drums 2a, to 2d, and then, electrostatic latent images are formed through exposure based on image information by exposure units 4a, 4b, 4c and 4d such as LEDs (light emitting diodes) or lasers. These electrostatic latent images are developed to form toner images as a result of deposition of different kinds of toner of the individual colors by developing units 5a, 5b, 5c and 5d.
The individual process stations 1a to 1d, serving as process cartridges, are detachable from the image forming apparatus main body. These process cartridge have a configuration in which the individual photosensitive drums 2a to 2d, the primary chargers 3a to 3d, the developing units 5a to 5d and cleaning means 6a, 6b, 6c and 6d are integrally combined.
On the other hand, the transfer medium S, serving as a recording medium housed in a paper feed cassette 15, is sent into the image forming apparatus main body by a feeding roller 16, conveyed by resist roller pair 17, and then, electrostatically attracted by a transfer conveyor belt 7, serving as a transfer medium carrier by an attracting roller 12, to which a positive-pole attractive bias voltage is impressed by an attractive bias power source 13, to be carried and conveyed.
The transfer conveyer belt 7 is stretched by four rollers including a driving roller 8, an attracting counter roller 9, and tension rollers 10 and 11. Process stations 1a, 1b, 1c, and 1d of colors including cyan, yellow, magenta and black are substantially perpendicularly arranged to the surface of the transfer conveyor belt 7 and sequentially from an upstream side in the moving direction of the transfer conveyor belt 7 (the arrow “a” direction in
Transfer rollers 14a, 14b, 14c and 14d, serving as transfer means, are arranged on the inside of the transfer conveyor belt 7 opposite to the respective photosensitive drums 2a to 2d. When the transfer medium S, attracted by the transfer conveyor belt 7, passes sequentially through the process stations 1a to 1d of the respective colors, toner images of the respective colors carried on the photosensitive drums 2A to 2d by means of the respective transfer rollers 14a to 14d are sequentially transferred electrostatically onto the surface of the transfer medium S.
A fixing unit 18, serving as fixing means, is arranged in the downstream in the recording medium conveying direction of the transfer roller 14d on the most downstream side, serving as transfer means.
The transfer medium S onto which the toner images have been transferred from the photosensitive drums 2a to 2d by the transfer rollers 14a to 14d is conveyed to the fixing unit 18 after separation from the peripheral surface of the driving roller 8. Through heating and pressurizing in the fixing unit 18, the toner images are fixed onto the transfer medium S. After a permanent image is thus formed, the fixed image is discharged onto a discharge tray 19 provided outside the apparatus.
Residual toner remaining on the photosensitive drums 2a to 2d is collected by respective cleaning means 6a to 6d, thus cleaning the surface of the photosensitive drums 2a to 2d.
When images are formed on two sides of the transfer medium S, the transfer medium S discharged onto the discharge tray 19 is fed again by a re-feed guide 20 and a re-feed roller 21 and reversed. In the same manner as above, the transfer medium S is electrostatically attracted by the transfer conveyor belt 7 and carried and conveyed. After forming the toner images on the second side by means of the process stations 1a, 1b, 1c and 1d and the transfer rollers 14a to 14d, and after separation from the peripheral surface of the driving roller 8, the toner images are fixed on the transfer medium S in the fixing unit 18, and discharged onto the discharge tray 19 provided outside the apparatus.
In the image forming apparatus shown in
When passing through the four process stations 1a to 1d, the transfer medium S is subjected to a large amount of charge while undergoing four transfer steps by the transfer rollers 14a to 14d, and for example, a high potential of about −3,000V is impressed to keep the charge. When the transfer medium S is separated from the transfer conveyor belt 7, a potential difference between the transfer medium S and the surface of the transfer conveyor belt 7 causes peeling discharge. A charge is therefore imparted onto the surface of the transfer conveyor belt 7. Usually, the charge on the surface of the transfer conveyor belt 7 escapes through the tension rollers upon passing through the tension rollers 10 and 11, and decreases. Upon arrival at the attracting roller 12, the amount of charge on the surface of the transfer conveyor belt 7 is on such a level that there occurs no defective attraction of the transfer medium S or no defective transfer. However, particularly when the transfer medium S has a high resistance, and upon image forming or two-sided image forming in a low-temperature low-humidity environment tending to permit easy charging, paper is once continuously fed while forming an image on the second side of a transfer medium dried through the fixing step during image forming on the first side, a larger amount of charge is imparted when the transfer medium S passes through the four process stations 1a to 1d. When separating the transfer medium S from the transfer conveyor belt 7, therefore, the potential difference between the transfer medium S and the surface of the transfer conveyor belt 7 becomes larger, leading to a larger amount of charge imparted to the surface of the transfer conveyor belt 7. In a low-temperature, low-humidity environment, furthermore, resistance of the transfer conveyor belt 7 becomes higher. Therefore, during passage through the tension rollers 10 and 11, a smaller amount of charge of the surface of the transfer conveyor belt 7 escapes through the tension roller. The amount of charge on the surface of the transfer conveyor belt 7 at the moment of arrival at the attracting roller 12 reaches such a level that a defective attraction or a defective transfer of the transfer medium S can occur.
For the purpose of preventing the charge-up of the transfer conveyor belt 7, the neutralizing member 23 is arranged at a position opposite to the driving roller 8; the mutual clearance P (mm) of the tips 231 of the teeth of the toothed electrode 23 is set to about 5 (mm), and the clearance D (mm) between the tips 231 of teeth of the toothed electrode 23 of the charger 22 and the transfer conveyor belt 7 is set to about 5 (mm).
According to the above-mentioned configuration, it is possible to efficiently conduct neutralization of the surface of the transfer conveyor belt 7 by means of the neutralizing member 23, and prevent occurrence of a defective attraction or a defective transfer of the transfer medium S.
The image forming apparatus in this embodiment of the present invention utilizes an intermediate transfer medium, and carries out neutralization of the transfer medium S prior to transfer of toner images from the intermediate transfer medium. When the transfer medium S itself is charged, the neutralizing means 23 is arranged as shown in
The image forming apparatus of this embodiment carries out neutralization by means of the neutralizing member 23 prior to the advance of the transfer medium S to a position where the toner image are transferred from the intermediate transfer medium. The neutralizing member is arranged at a position in the upstream by about 10 mm from the nip position formed between the transfer roller 35 and the intermediate transfer medium in the moving direction of the transfer medium S. Even if it is probable that the transfer medium S is charged on the conveyance path of the transfer medium S, this position eliminates the probability, thus ensuring satisfactory transfer performance. The mutual clearance (pitch) P between the tips 231 of the teeth of the toothed electrode 23 for which the neutralizing member is set to about 5 (mm), and the clearance D (mm) between the tips 231 of the teeth of the toothed electrode 23 of the charger 22 and the transfer medium S is set to about 5 (mm).
The neutralizing mechanism based on this neutralizing member eliminates the necessity of setting a transfer bias by taking into account the charging condition of the transfer medium S. This effect is useful particularly when forming images on the second side while conducting two-sided image forming, or when, in a low-humidity environment, a high resistance value of the transfer medium S tends to easily cause charging.
In this embodiment, a case of neutralizing the transfer medium S, other than in the step of forming toner images on the transfer medium, will be presented. The image forming apparatus of this embodiment has basically the same configuration as that of the image forming apparatus presented in the third embodiment as shown in
In the image forming apparatus before arranging this neutralizing member 23, a jam has often been caused in the conveyance path of the transfer medium after passage through the fixing unit. In the fixing unit of this embodiment, a bias is applied between the fixing roller and the pressurizing roller to prevent electrostatic offsetting of the toner images. In this configuration, therefore, the transfer medium S having passed through the fixing unit is temporarily charged. Since the transfer medium S having once passed through the fixing unit is dried and curls, a strong adhering force acts when a metal plate is installed in the paths having curved portions from among the conveyance paths of the transfer medium S. Particularly, a curl of the transfer medium S depends upon the toner images formed on the transfer medium S. When heated, there is a considerable difference in the contracting rate between the transfer medium S itself and the toner.
In this embodiment of the present invention, therefore, occurrence of a jam is prevented by neutralizing in advance the transfer medium S which has to enter the conveyance path of the transfer medium again after passage through the fixing unit. Since it is on the conveyance path and the toner images have already been fixed onto the transfer medium S, it is possible for the neutralizing member 23 to utilize those in contact with the transfer medium S, but actually, the transfer medium may be damaged; the transfer medium S may be caught by the neutralizing member, thereby causing a jam; or the neutralizing member 23 may be partially broken and debris scatters on the conveyance path in all probabilities. It is therefore desirable that the transfer medium be kept non-contact, and a non-contact neutralizing configuration as in this embodiment is adopted.
Toothed neutralization members have been presented as neutralizing members in the above-mentioned first to sixth embodiments. In order to obtain advantages of the present invention, however, the only requirement is to have sharp members. A neutralizing member having needle-shaped projections was therefore used in place of the saw-toothed neutralizing member in these embodiments. Similar effects were obtained in all cases. This needle-shaped neutralizing member is illustrated in
The above-mentioned third embodiment has presented a configuration in which, by use of an intermediate transfer belt 31, neutralization is performed from the back of the intermediate transfer belt 31 while passing through the individual process stations 32a to 32d. This embodiment presents a configuration in which neutralization is conducted from the back of the transfer medium conveyor belt 7. This configuration is illustrated in
In the individual process stations, transfer rollers 14a to 14d carry out four transfer steps. As a result, charging is repeated upon every passage of the transfer medium S and the transfer medium conveyor belt 7 through the respective process stations. In this manner, when applying a charge to the transfer medium in the transfer step, the transfer bias at the process stations in the downstream must sequentially be increased.
This may sometimes cause an inconvenience in that it is necessary to increase the capacity of the power source which supplies the transfer bias. An abnormal discharge may take place with metal plates near the course of passage of the transfer medium conveyor belt 7 and the transfer medium S.
In this embodiment, therefore, the neutralizing member is arranged in the downstream of the transfer mechanism in each process station to permit neutralization of the transfer medium conveyor belt 7 and the transfer medium S after the completion of the transfer step.
In the above-mentioned first to eighth embodiments, the distance between the tips 231 of the neutralizing member and the member to be neutralized has been treated as the same D in all cases. In order to obtain the advantages of the present invention, however, it is not always necessary to use the same distance between the tip of the neutralizing member and the member to be neutralized in all cases. As shown in
D1≧4.0, 0.8*D1≦P≦1.5*D1, and
D2≧4.0, 0.8*D2≦P≦1.5*D2,
And the result showed that the advantages of the present invention were available under these conditions.
In the above-mentioned embodiments, the printer was presented as an example of the image forming apparatus. However, the present invention is not limited to this, but is applicable to other image forming apparatuses including copying machines and facsimile machines, and other image forming apparatuses such as a composite machine built by combining these functions. Similar effects can be obtained by applying the present invention to any of these image forming apparatuses.
While various embodiments of the present invention have been described above, the intent and the scope of the present invention are not limited to specific description and drawings within this specification.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims priority from Japanese Patent Application No. 2003-39883 filed Nov. 28, 2003, which is hereby incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-399883 | Nov 2003 | JP | national |
