Image forming apparatus, recording medium detecting apparatus and recording medium detecting method

An image forming apparatus according to an embodiment includes an image forming unit which forms an image on a recording medium, and a carrying unit which guides the recording medium to the image forming unit via a first carrying path or a second carrying path. A media sensor is arranged at a part where the first carrying path and the second carrying path merge together, to discriminate the type of the recording medium. The media sensor is movable toward the first carrying path or toward the second carrying path where the recording medium passes.

FIELD

Embodiments described herein relate generally to an image forming apparatus in which a recording medium such as a sheet is carried via plural carrying paths. Embodiments described herein also relate generally to a recording medium detecting apparatus and a recording medium detecting method.

BACKGROUND

Conventionally, an image forming apparatus such as a copy machine or printer can form an image on plural types of recording media with different sizes and thicknesses. As the recording media, paper sheets and OHP sheets and the like are used. In the following description, a sheet is used as an example of the recording media.

A sheet can be supplied to an image forming unit by manual insertion as well as from a paper supply cassette. In the image forming apparatus, an image forming unit including a photoconductive drum is provided. An image is formed on a sheet supplied from a paper supply cassette or a sheet supplied by manual insertion.

By the way, since a sheet is carried to the image forming unit via plural carrying path, a media sensor is installed on each carrying path within the image forming apparatus. Thus, the media sensor discriminates the thickness and type of the sheet passing through each carrying path.

However, there is an inconvenience that the arrangement of the media sensor on each carrying path increases the cost.

DETAILED DESCRIPTION

In general, according to one embodiment, an image forming apparatus includes:

an image forming unit which forms an image on a recording medium;

a carrying unit which guides the recording medium to the image forming unit via a first carrying path or a second carrying path;

a media sensor which is arranged at apart where the first carrying path and the second carrying path merge together, and which discriminates a type of the recording medium; and

a moving mechanism which moves the media sensor toward the first carrying path or toward the second carrying path where the recording medium passes.

Hereinafter, an image forming apparatus according to a first embodiment will be described with reference to the drawings. The same parts in the drawings are denoted by the same reference numerals.

FIG. 1shows the internal configuration of the image forming apparatus according to the first embodiment. In the following description, an MFP (multi-function peripheral) which is a multi-functional machine is described as an example. However, other image forming apparatuses such as a printer can also be used.

InFIG. 1, an image forming apparatus10has an image forming unit11at the center of the apparatus. An automatic document feeder (ADF)12, an image reading unit (scanner)13and a paper discharge unit14are provided in an upper part of the image forming apparatus10. A paper supply unit15is provided below the image forming unit11. An operation panel16including an operation unit and a display unit is provided in an upper part of the image forming apparatus10.

The automatic document feeder (ADF)12feeds a document to the image reading unit13. The image reading unit13reads the document and generates image data. The image forming unit11is formed, for example, by a tandem color laser printer and scans a photoconductive member with a laser beam from a laser exposure device17and thus generates an image.

The image forming unit11includes image forming sections20Y,20M,20C and20K for the colors of yellow (Y), magenta (M), cyan (C) and black (K). The image forming sections20Y,20M,20C and20K are arranged in parallel along the lower side of an intermediate transfer belt21as an intermediate transfer medium, from upstream toward downstream.

In the following description, components constituting the image forming sections20Y,20M,20C and20K are denoted by reference numerals with symbols Y, M, C and K. However, in some cases, the components may be described without the symbols Y, M, C and K.

Since the image forming sections20Y,20M,20C and20K have the same configuration, the image forming section20Y will be described as a representative example. The image forming section20Y has a photoconductive drum22Y. A charger23Y, a developing device24Y, a transfer roller25Y, a cleaner26Y and the like are arranged around the photoconductive drum22Y.

The intermediate transfer belt21moves circularly. For example, semi-conducting polyimide is used in view of heat resistance and wear resistance. The intermediate transfer belt21is extended over a driving roller27and driven rollers28,29and30. The intermediate transfer belt21faces and can contact the photoconductive drum22Y. At a position on the intermediate transfer belt21facing the photoconductive drum22Y, a primary transfer voltage is applied by the transfer roller25Y and a toner image on the photoconductive drum22Y is primary-transferred to the intermediate transfer belt21.

A secondary transfer roller31is arranged facing the driving roller27over which the intermediate transfer belt21is extended. When a sheet S passes between the driving roller27and the secondary transfer roller31, a secondary transfer voltage is applied by the secondary transfer roller31and the toner image on the intermediate transfer belt21is secondary-transferred to the sheet S. A belt cleaner32is provided near the driven roller30on the intermediate transfer belt21.

An exposure position on the photoconductive drum22Y is irradiated with a yellow laser beam from the laser exposure device17and a latent image is thus formed on the photoconductive drum22Y. The charger23Y uniformly charges the entire surface of the photoconductive drum22Y, for example, to approximately −700 V. The developing device24Y supplies a two-component developer including toner and carrier of each color to the photoconductive drum22Y, with a developing roller to which a developing bias of approximately −500 V is applied. The cleaner26Y removes residual toner on the surface of the photoconductive drum22Y using a blade.

Meanwhile, the laser exposure device17scans the photoconductive drum22Y in the axial direction with a laser beam emitted from a semiconductor laser element. The laser exposure device17includes a polygon mirror17A, an imaging lens system17B, a mirror17C and the like.

The paper supply unit15has plural paper supply cassettes15A and15B accommodating recording media (sheets or the like) of various sizes. Moreover, the image forming apparatus10is provided with a manual insertion tray33through which a recording medium is supplied by manual insertion. In the following description, an example of forming an image on a sheet S as a recording medium will be described.

In a path from the paper supply cassettes15A and15B to the secondary transfer roller31, pickup rollers34A and34B to take out the sheet S from the paper supply cassettes15A and15B, separation rollers35A and35B, carrying rollers36and37and a registration roller38are provided. In a path from the manual insertion tray33to the registration roller38, a pickup roller39to take out the sheet S and a manual insertion paper supply roller40are provided.

Moreover, a fixing device41is provided downstream of the secondary transfer roller31. A paper discharge carrying path42is provided from the fixing device41to the paper discharge unit14. A reverse carrying path43is further provided. In the reverse carrying path43, a gate44is provided to sort the sheet toward the paper discharge unit14or toward the reverse carrying path43. The reverse carrying path43reverses the sheet S and then guides the sheet S in the direction of the secondary transfer roller31. The reverse carrying path43is used in double-side print or the like.

Next, the operation of the image forming apparatus10will be briefly described. When image information is inputted from a scanner, personal computer terminal or the like, toner images of yellow (Y), magenta (M), cyan (C) and black (K) are formed by the image forming sections20Y to20K and the toner images of magenta (M), cyan (C) and black (K) are multiple-transferred to the same position where the toner image of yellow (Y) is formed, on the intermediate transfer belt21. Thus, a full-color toner image is provided.

The full-color toner image on the intermediate transfer belt21is collectively secondary-transferred onto the sheet S by the secondary transfer roller31. The sheet S is supplied to the position of the secondary transfer roller31from the paper supply cassette15A or15B or the manual insertion tray33. The sheet S to which the toner image is secondary-transferred is sent to the fixing device41and the toner image is fixed to the sheet S.

The sheet S to which the toner image is fixed is sorted to the paper discharge unit14by the gate44when the sheet S has the image on one side. In the case of performing double-side print or multiple prints, the sheet S is sorted toward the reverse carrying path43by the gate44and is carried again to the secondary transfer roller31.

Meanwhile, after the secondary transfer is finished, the residual toner on the intermediate transfer belt21is cleaned by the belt cleaner32. The residual toner on the photoconductive drum22is removed by the cleaner26after the primary transfer of the toner image to the intermediate transfer belt21, and the photoconductive drum22thus becomes available for the next image forming.

The image forming apparatus10has plural carrying paths to carry sheets toward the image forming unit11. The sheet S is supplied, for example, via a carrying path toward the image forming unit11from the paper supply cassettes15A and15B, a carrying path toward the image forming unit11from the manual insertion tray33, or a carrying path toward the image forming unit11from the reverse carrying path43. Since sheets with different sizes and thicknesses are supplied from each carrying path, the type of the sheet (for example, thickness) is detected by a media sensor.

The media sensor is expensive. Therefore, arranging the media sensor in each carrying path raises the cost and also increases the installation space.

Thus, in the first embodiment, an image forming apparatus is provided in which sheets passing through plural carrying paths are detected by a common media sensor. The media sensor is arranged at a merging point where the plural carrying paths merge together. The media sensor is also made movable in the direction of each carrying path. The position of the media sensor is controlled every time the supply source of the supplied sheet changes.

Hereinafter, the media sensor and a moving mechanism of the media sensor will be described.

FIG. 2AandFIG. 2Bare explanatory views showing a media sensor50and the operation of the media sensor. As shown inFIG. 2A, the media sensor50has a roller52provided on the outer circumference of a bearing51, and a supporting part53supporting the roller52. The supporting part53is rotatable about a fulcrum55provided in a body part54of the sensor. A magnet is provided at the base of the supporting part53. A magnetic sensor is provided in the body part54.

As shown inFIG. 2B, the roller52of the media sensor50can contact the sheet. When sheet S is carried in contact with the roller52, the roller52rotates around the bearing51because of the friction with the sheet S. When the thickness of the sheet S is changed, the supporting part53rotates about the fulcrum55as indicated by angle α. As the angle of inclination of the supporting part53changes, the magnetic force changes. The magnetic sensor in the body part54detects magnetic resistance due to the change in the magnetic force and detects the thickness of the sheet S.

FIG. 3shows the position of arrangement of the media sensor50and the configuration of the moving mechanism. In the example ofFIG. 3, the media sensor50is arranged at a merging point where a sheet carrying path61toward the image forming unit11from the paper supply cassette15A (or15B) and a sheet carrying path62toward the image forming unit11from the manual insertion tray33merge together.

Hereinafter, the sheet carrying path from the paper supply cassette15A (or15B) is called a first carrying path61. The sheet carrying path from the manual insertion tray33is called a second carrying path62. The sheet carrying path toward the secondary transfer roller31in the image forming unit11after the merging point is called a third carrying path63. Besides, the first carrying path61, the second carrying path62and the third carrying path63configure the carrying unit.

A moving mechanism70to move the media sensor50is provided. The moving mechanism70moves the media sensor50toward the first carrying path61(in the direction of arrow A) or toward the second carrying path62(in the direction of arrow B) according to the carrying of the sheet S.

FIG. 4shows the configuration of an example of the moving mechanism70of the media sensor50. InFIG. 4, it is assumed that the media sensor50moves in left-right directions, so that the movement of the media sensor50by the moving mechanism70can be easy to understand. The description also assumes that the first carrying path61and the second carrying path62are symmetrical about the third carrying path63.

The moving mechanism70has a moving member71supporting the media sensor50. A rack72is formed on the moving member71. A gear73is provided to mesh with the rack72. The gear73is driven by a motor. As the motor rotates the gear73forward and backward, the moving member71can move in the direction of arrow A or B.

As shown inFIG. 5, when the sheet S passes through the first carrying path61, the moving mechanism70moves the media sensor50in the direction of the first carrying path61(the direction of arrow A) and presses the roller52against the sheet S. Therefore, the media sensor50can detect the thickness of the sheet S passing through the first carrying path61.

When the sheet S passes through the second carrying path62, the moving mechanism70moves the media sensor50in the direction of the second carrying path62(the direction of arrow B) and presses the roller52against the sheet S. Therefore, the media sensor50can detect the thickness of the sheet S passing through the second carrying path62.

Usually, there are many cases where the image forming apparatus10forms an image on the sheet S carried form the paper supply cassettes15. Therefore, the media sensor50may be situated usually toward the first carrying path61and may be moved toward the second carrying path62when the sheet S is supplied by manual insertion.

As for the timing of detecting the thickness of the sheet S, the thickness is detected in response to an operation on the operation panel16. For example, when the user operates the operation panel16to set the sheet size and the number of sheets and then presses the copy button, the media sensor50is moved in the direction of the first carrying path61. Then, every time sheets are sequentially carried, the thickness of each sheet is detected.

A sheet sensor56is provided on the manual insertion tray33(FIG. 1). When the sheet S is placed on the manual insertion tray33, the sensor56detects the sheet S and the moving mechanism70moves the media sensor50in the direction of the second carrying path62. Then, as the user operates the operation panel16to set the sheet size and the number of sheets and then presses the copy button, the media sensor50detects the thickness of each sheet carried sequentially via the second carrying path62.

FIG. 6shows the configuration of another example of the moving mechanism70. InFIG. 6, the moving member71supports the media sensor50. A cam74is in contact with the moving member71. A spring75energizes the moving member71so that the moving member71is constantly in contact with the cam74. The cam74is, for example, an elliptic eccentric cam and rotates about a shaft76. A motor rotates the shaft76, causing the moving member71to move in the direction of arrow A or arrow B.

The moving member71is not limited to the above example and various modifications can be employed.

FIG. 7is a block diagram showing a control system of the image forming apparatus according to the embodiment. InFIG. 7, a system control unit80includes a CPU and ROM, and controls the image forming unit11, the ADF12, the image reading unit13and the like of the image forming apparatus10according to a control program stored in the ROM.

The operation panel16is connected to the system control unit80. As the user operates the operation panel16, the system control unit80controls the image forming unit11and the image reading unit13, executing operations such as print, copy, and scan.

The system control unit80is also supplied with the result of detection from the media sensor50. The system control unit80controls the image forming unit11according to the thickness of the sheet detected by the media sensor50and thus adjusts the image forming state. For example, when the sheet S is thick, the amount of toner transferred to the sheet S is increased or the fixing temperature of the fixing device41is set to a relatively high temperature. Meanwhile, when the sheet S is thin, the amount of toner transferred to the sheet S is reduced or the fixing temperature of the fixing device41is set to a relatively low temperature.

The result of detection from the sensor56provided on the manual insertion tray33is also inputted to the system control unit80. The system control unit80drives a driving unit77according to the result of detection from the sensor56. The driving unit77is provided with a motor. The motor rotates to rotate the gear73or the cam74of the moving mechanism70.

For example, when a sheet is set on the manual insertion tray33, the system control unit80determines that the apparatus is in the manual insertion mode, and the media sensor50is moved in the direction of the second carrying path62. When no sheets are set on the manual insertion tray33, the system control unit80determines that the apparatus is in the normal mode, and the media sensor50is moved in the direction of the first carrying path61.

In the above example, the media sensor50is arranged on the sheet carrying path from the paper supply cassettes15or the manual insertion tray33. However, the media sensor50may also be provided at a merging point between the carrying path toward the registration roller38from the paper supply cassettes15and the carrying path toward the registration roller38from the reverse carrying path43shown inFIG. 1.

The reverse carrying path43is used for double-side print. The thickness of the sheet varies depending on the amount of toner adhering to both sides of the sheet. Therefore, for example, the amount of the adhering toner transferred to the sheet S can be controlled according to the result of detection from the media sensor50.

Sheets can also be supplied from an external large-capacity paper supply tray in addition to the paper supply cassettes15. Therefore, the media sensor50may be arranged at a part where the sheet carrying path from the paper supply cassettes15and the sheet carrying path from the large-capacity paper supply tray merge together, and the media sensor50may detect the thickness of the sheet in each carrying path.

In the embodiment, the technique which is applied to the image forming apparatus is described. However, the technique may also be applied to a recording medium detecting apparatus that does not include the image forming unit11but includes the parts downstream of the paper supply unit15in terms of the sheet carrying direction and up to the third carrying path63, as an independent unit.

According to such embodiments, the moving mechanism moves the media sensor50, enabling common use of the media sensor50in plural carrying paths. Therefore, the installation space for the media sensor50need not be increased and the rise in the cost can be restrained.

Various modifications can be implemented without being limited to the embodiments. For example, an image can be formed on other recording media than the sheet S, such as OHP sheets. Therefore, the difference in thickness between a paper sheet and an OHP sheet may be discriminate and the image forming state may be controlled. The media sensor50may detect light transmittance to discriminate the type of paper, other than detecting the thickness of the sheet S.