Image reading device and image forming apparatus including the image reading device

In an image reading device having a sheet-through mechanism, a controller controls a stepping motor to decelerate an image reading system when the image reading system is moved to a reference white plate reading position, and controls a stepping motor drive electric current to decrease when the image reading system reads a reference white plate. When the image reading system finishes reading the reference white plate, the controller controls the stepping motor drive electric current to increase so as to rapidly decelerate the image reading system. The controller further controls the stepping motor such that a moving speed of the image reading system to an original document reading position is lower than a moving speed of the image reading system to the reference white plate reading position.

CROSS REFERENCE TO RELATED APPLICATIONS

This application contains subject matter related to and claims priority, under 35 U.S.C. §119, from Japanese Patent Application No. 2001-150446, filed in the Japanese Patent Office on May 21, 2001, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an image reading device that reads image data of an original document with an image sensor and an image forming apparatus, such as a digital copying machine, a laser beam printer, a facsimile machine, etc., that forms an image based on the image data output from the image reading device and more particularly, to a control of reading operation of a reference white plate for obtaining shading data in the image reading device having a sheet-through mechanism.

2. Discussion of Background

An image reading device used in a widespread digital copying machine, a scanner, or other similar image forming apparatus, may employ a method of reading an image of an original document by a two-dimensional scanning in which a charge-coupled device (CCD) line sensor is moved in a sub-scanning direction perpendicular to a main scanning line relatively to an original document illuminated by a lamp.

The image reading device employing such an image reading method in which the CCD line sensor is moved relatively to the original document, generally uses two types of image reading mechanisms. One type of image reading mechanism may be referred to as an image reading system moving mechanism in which an image of an original document set on an original document setting table (e.g., a contact glass) in a stationary state is read by moving an image reading system. Another type of image reading mechanism may be referred to as a sheet-through mechanism in which an original document is fed by an original document feeding device (hereinafter simply referred to as a “document feeder”) so as to pass through a stationary image reading system including a CCD line sensor. An image of an original document is read by the stationary image reading system while moving the original document relative to the image reading system.

Recently, an image reading device often has both of the above-described two types of image reading mechanisms. Hereinafter, a description will be made to an image reading device that reads an image of an original document by both of the two types of image reading mechanisms.

The image reading device having both of the two types of image reading mechanisms reads an image of an original document by a common image reading system. When performing an image reading operation in the sheet-through mechanism, the image reading operation is performed in a condition that a movable image reading system is held stationary at a predetermined image reading position provided at a part of an original document conveying path in a document feeder. In the image reading device having both of the two types of image reading mechanisms, it is not desirable that an output of image read by the image reading system moving mechanism is different from that of image read by the sheet-through mechanism or an output of image read by either of the two image reading mechanisms changes with time. Therefore, in order to stabilize outputs of read images, an image reading system reads a reference white plate before reading an image of an original document to obtain a reference white level or shading data based on the data of read reference white plate. A white level of image data of a read original document is corrected using the shading data.

In the image reading system moving mechanism, following a reading operation of a reference white plate arranged between a home position of an image reading system and a position where an original document is set on a contact glass, an image reading operation of the original document is performed.

In the sheet-through mechanism, as described above, an image reading system reads an image of a moving original document fed by a document feeder in a condition that the image reading system is held stationary at a predetermined image reading position. Therefore, when reading the same reference white plate also used in the image reading system moving mechanism, the image reading system needs to be moved to the position where the reference white plate is arranged. This results in adding a step of moving the image reading system contrary to the aim of eliminating the necessity of moving the image reading system in the sheet-through mechanism. Accordingly, in order not to reduce the advantage of high throughput in the sheet-through mechanism allowing an image reading device to read original documents consecutively, it may be desired to reduce a whole period of time required for performing the reading operation of the reference white plate as much as possible.

In the above-described image reading device, a carriage carrying the image reading system is driven to move by a stepping motor. Generally, an image reading operation is controlled to be performed when the movement of the carriage changes to a constant velocity movement after being accelerated from a stop position of the carriage. Subsequently, the movement of the carriage is controlled to be decelerated after the image reading operation. Such a control operation is performed in both of an image reading operation of an original document and a reading operation of a reference white plate.

FIG. 7is a velocity chart illustrating a control of movement of a carriage and a control of reading operation of a reference white plate according to a background art. With regard to a timing of reading a reference white plate according to a background art, a reading operation of the reference white plate is performed in an area indicated by a reference character “A” inFIG. 7in which the carriage moves at a constant velocity and vibrations of an image reading system carried by the carriage are the weakest after the carriage is driven to move by a stepping motor and is accelerated. Alternatively, in order to reduce a time of reading the reference white plate as much as possible, the reading operation of the reference white plate is performed in an area indicated by a reference character “B” inFIG. 7in which the carriage is accelerated, with some disadvantages such as vibrations of the image reading system.

Recently, demands have been increasing for an image reading performance satisfying both high speed and high image quality such as an image reading speed of 40 sheets/minute and a resolution of 1200 dpi, for example, in a color image reading device. In such a color image reading device, if a reading operation of a reference white plate is performed in the area “A” inFIG. 7, it takes time until vibrations of an image reading system become weak, and a start of the reading operation is delayed, thereby increasing a whole period of time required for performing the reading operation.

If the reading operation of the reference white plate is performed in the area “B” inFIG. 7, the reading operation can be started earlier than in the area “A”. However, there may be a high possibility of occurrence of error in data of the read reference white plate due to the vibrations generated when the carriage is driven to move from a stop position. As a result, it may be hard to obtain appropriate shading data.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an image reading device includes an image reading system configured to read an image of an original document, a stepping motor configured to apply a drive force to the image reading system so as to move the image reading system, a controller configured to control the stepping motor to drive in accordance with speed patterns of the stepping motor set for each operation of acceleration, moving at constant velocity, and deceleration of the image reading system, an original document feeder configured to feed an original document to a predetermined original document reading position where the image reading system is held stationary to read an image of the original document fed by the original document feeder, and a reference white plate configured to be read by the image reading system at a reference white plate reading position spaced apart from the original document reading position in a moving direction of the image reading system before reading the image of the original document using the image reading system to form a read image so as to correct a white level of the read image of the original document. The controller controls the stepping motor to drive the image reading system to move to the reference white plate reading position for reading the reference white plate while moving, and then controls the stepping motor to decelerate the image reading system when the image reading system is moved to the reference white plate reading position.

Objects, features, and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described in detail referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.

FIG. 1is a schematic perspective view of a carriage driving system of an image reading device according to an embodiment of the present invention.FIG. 2is a side view of a part of the image reading device illustrating a schematic construction of an image reading system.

Referring toFIGS. 1 and 2, an image reading device50includes a first carriage1that carries an exposure lamp14that irradiates an image surface of an original document with light and a first mirror15that reflects the light reflected from the image surface of the original document, and a second carriage2that carries a second mirror16and a third mirror17that reflect the light reflected from the first mirror15. The light reflected from the third mirror17, corresponding to the image of the original document, is imaged on a charge-coupled device19(hereinafter referred to as a CCD19) serving as an image sensor through an imaging lens18. In this embodiment, the first carriage1and the second carriage2and the above-described elements carried by the first and second carriages1,2are defined as an “image reading system” as a whole.

Referring toFIG. 1, the image reading device50further includes a pair of wires3, a drive shaft4, a pair of wire pulleys5integrally provided on the drive shaft4, idle pulleys6a,6b,6c, and6d, a timing belt7, a stepping motor8, timing belt pulleys9and10, a detection part11provided on the first carriage1, and a home position sensor12that detects the detection part11of the first carriage1.

Referring further toFIG. 2, the image reading device50further includes a contact glass13serving as an original document setting table, a stepping motor drive control board21that controls the stepping motor8to drive, a scanner control board20that controls image processing and the stepping motor drive control board21, and a reference white plate22used for obtaining shading data.

A brief description will be made to an operation of a carriage driving system referring toFIG. 1. The drive force of the stepping motor8is transmitted to the first carriage1and the second carriage2via the pair of wires3opposing each other and being extended at both respective sides of the first carriage1and the second carriage2in a main scanning direction indicated by arrow inFIG. 1. The wires3are driven by the pair of wire pulleys5integrally provided on both sides of the drive shaft4in the main scanning direction. The wire pulleys5are driven by the timing belt pulley10integrally provided on a shaft of the stepping motor8via the timing belt pulley9provided on one end of the drive shaft4and via the timing belt7spanned around the timing belt pulleys9and10.

When turning on a power supply switch (not shown), in order to accurately locate the first carriage1and the second carriage2at respective home positions, the stepping motor8starts to drive the drive shaft4. Then, the drive force of the stepping motor8is transmitted to the first carriage1and the second carriage2via the wires3, thereby causing the first carriage1and the second carriage2to move in a forward direction indicated by the arrow inFIG. 1. After moving a predetermined distance in the forward direction, the first carriage1and the second carriage2start moving in a return direction indicated by arrow inFIG. 1. When the home position sensor12detects the detection part11provided on a lower part of the first carriage1, the first carriage1and the second carriage2move further in the return direction by a predetermined distance corresponding to predetermined pulses, and stop moving at respective stopping positions. These respective stopping positions of the first carriage1and the second carriage2correspond to their home positions. The first carriage1and the second carriage2are in a standby condition at the respective home positions, and start reading operations from the respective home positions upon receiving a reading instruction.

In this embodiment, the image reading device50has two types of image reading mechanisms such as an image reading system moving mechanism and a sheet-through mechanism. Therefore, a document feeder30(illustrated inFIG. 5A) integrally formed with a platen plate (not shown) is provided above the contact glass13so as to cover and uncover the contact glass13. The platen plate serves to cover an original document set on the contact glass13and press the original document against the surface of the contact glass13.

The image reading device50, according to the embodiment of the present invention, includes a construction similar to that of a background image reading device that reads an image of an original document by two types of image reading mechanisms. InFIG. 2, a construction of the image reading device50above the contact glass13is omitted, so that the document feeder30is not shown. The image reading device50having the two types of image reading mechanisms reads an image of an original document by use of a common image reading system. When performing an image reading operation in the sheet-through mechanism, the image reading operation is performed in a condition that a movable image reading system is held stationary at a predetermined image reading position provided at a part of an original document conveying path in the document feeder30. The details of the image reading operation in the sheet-through mechanism will be described in more detail below referring toFIG. 5B.

Next, a description will be made of a control of the stepping motor8for driving the first carriage1and the second carriage2.

FIG. 3is a block diagram illustrating a structure of a stepping motor drive control system in the image reading device50. The stepping motor8is controlled to be driven by the stepping motor drive control board21. The scanner control board20, including a central processing unit (CPU) that controls the whole image reading device50, generates control signals, such as a stepping motor drive clock, forward/reverse signals, drive electric current switching signals, etc., based on control data, such as speed patterns of the stepping motor8set for each operation of the image reading system of the image reading device50. The above-described control signals, such as the stepping motor drive clock, the forward/reverse signals, the drive electric current switching signals, etc., are input to the stepping motor drive control board21. The stepping motor drive control board21controls the stepping motor8to drive by changing the drive electric current passing through each phase of the stepping motor8in accordance with the above-described control signals.

The speed of the stepping motor8is determined by the frequency of drive clock or the number of drive pulses per unit of time (pulse per second). The phase switching timing of the stepping motor8is controlled based on the frequency of drive clock. As the frequency of drive clock increases, the speed of the stepping motor8increases, and as the frequency of drive clock decreases, the speed of the stepping motor8decreases. Therefore, various kinds of acceleration and deceleration of the stepping motor8are achieved by controlling the frequency of drive clock. The drive electric current for the stepping motor8is controlled to be switched depending on the operations of the first and second carriages1,2, such as acceleration, deceleration, reading operation, return, wait, etc.

Next, a description will be made of a drive control of the first carriage1and the second carriage2at the time of a reading operation of the image reading device50.FIG. 5Ais a schematic view of the main elements of the image reading device50.FIG. 5Bis a velocity chart illustrating a movement control of the carriage in a reading mode by the sheet-through mechanism.FIG. 5Cis a velocity chart illustrating a movement control of the carriage in a reading mode by an image reading system moving mechanism.

Hereinafter, the reading mode by the sheet-through mechanism may be simply referred to as a “sheet-through mode”, and the reading mode by the image reading system moving mechanism may be simply referred to as an “image reading system moving mode”.

In this embodiment, the second carriage2moves together with the first carriage1in the sub-scanning direction at about one-half of the moving speed of the first carriage1. Therefore, hereinafter, the drive control of the first carriage1and the second carriage2at the time of the reading operation of the image reading device50may be described referring to the first carriage1as a whole.

Referring toFIG. 5A, the first carriage1carrying the exposure lamp14and the first mirror15is in a standby condition at a home position. The first carriage1moves from the home position to three different reading positions. Specifically, the first reading position is located at a position most close to the home position of the three reading positions. Further, the first reading position is located in a part of an original document conveying path in the document feeder30provided above the contact glass13. The first reading position is indicated as an “image reading position in a sheet-through mode” inFIG. 5A. At the first reading position, the first carriage1held in a stationary state reads an image of an original document being conveyed in the original document conveying path in the document feeder30.

The second reading position is located at some midpoint of movement of the first carriage1in the forward direction indicated by the arrow inFIG. 5Afrom the home position. At the second reading position, the first carriage1reads the reference white plate22provided at a part of the contact glass13while moving.

The third reading position is located at a position farthest away from the home position in the forward direction. The third reading position is indicated as an “image reading position in an image reading system moving mode” inFIG. 5A. The third reading position corresponds to a reference position of an original document where a leading edge of an original document is set on the contact glass13. At the third reading position, the first carriage1reads an image of an original document set on the contact glass13in a stationary condition while moving.

Hereinafter is described an operation of the image reading device50in an image reading system moving mode. When a start key (not shown) is pressed after setting an original document on the contact glass13and closing the platen plate, a drive clock is output from the scanner control board20to the stepping motor drive control board21at a predetermined timing, thereby driving the stepping motor8. The drive controls of the first and second carriages1,2, are performed based on the speed patterns of the stepping motor8set for each operation of the image reading system of the image reading device50.FIG. 4is a chart illustrating an example of a speed pattern of the stepping motor8for the movement control of the first and second carriages1,2, in the image reading system moving mode.

As illustrated inFIG. 4, the stepping motor8causes the first carriage1to move from an accelerated condition to a constant velocity condition. Because the first carriage1reads an image of an original document from the leading edge (i.e., a reading start position) to the trailing edge in a constant velocity period, the velocity of the first carriage1should be stabilized in the constant velocity period. Before reading an image of an original document, the first carriage1needs to read the reference white plate22so as to obtain shading data.

The timing of reading the reference white plate22will be described referring toFIG. 5C. As illustrated inFIG. 5C, the first carriage1starts to move in the forward direction by driving the stepping motor8, and moves from an accelerated condition to a constant velocity condition. The reading operation of the reference white plate22is performed in a stable constant velocity period after an unstable variable velocity period immediately after a velocity transitionary period. In the image reading system moving mode, an image reading operation of an original document is performed following the reading operation of the reference white plate22. Therefore, the reading operation of the reference white plate22is also performed in a part of the stable constant velocity period for reading an image of an original document.

The reflected light from the reference white plate22is led to the CCD19through the imaging lens18. The reflected light is converted into an electric signal by the CCD19. The data of the reference white plate22obtained by the CCD19is transmitted to the scanner control board20and is subjected to image processing. Consequently, a reference white level or shading data is obtained.

Following the reading operation of the reference white plate22, an image of an original document set on the contact glass13is read by the first carriage1and the second carriage2like the reference white plate22. The data of the read image of the original document is transmitted to the scanner control board20and is subjected to image processing. At this time, a white level of image data of the read original document is corrected using the shading data obtained by reading the reference white plate22. Thereby, an image output can be stabilized regardless of whether there are variations in image output levels caused by the decrease of the light amount of the exposure lamp14with time, etc.

Referring toFIG. 4, upon completion of image reading operation, the stepping motor8starts rotating in the reverse direction so as to return the first carriage1and the second carriage2to the respective home positions. In order to return the first carriage1and the second carriage2to their respective home positions, as much as possible, in the short time, the first carriage1and the second carriage2are moved in a high speed. As described above, the second carriage2moves in the sub-scanning direction at about one-half of the moving speed of the first carriage1.

When the home position sensor12detects the detection part11provided on the lower part of the first carriage1, the first carriage1and the second carriage2move by a predetermined distance corresponding to predetermined pulses, and the stepping motor8stops at the home position (i.e., the first and second carriages1,2stop at their respective home positions). The stepping motor8waits at the home position until the stepping motor8is driven for a next image reading operation of the image reading device50.

Next, an operation of the image reading device50in the sheet-through mode will be described.

Referring toFIGS. 5A and 5B, in the sheet-through mode, a stack of original documents are set on an original document tray (not shown) of the document feeder30. Upon pressing the start key (not shown), the original document starts to be fed out from the original document tray by a group of rollers provided in the document feeder30. Simultaneously, the drive clock is output from the scanner control board20to the stepping motor drive control board21at a predetermined timing so as to drive the stepping motor8. Subsequently, the first carriage1and the second carriage2start moving in the forward direction from their respective home positions by driving the stepping motor8. As illustrated inFIG. 5B, the first carriage1is accelerated to a predetermined velocity.

Immediately after the first carriage1is accelerated to a predetermined velocity, the motor drive electric current of the stepping motor8is decreased such that the first carriage1moves to a position where the reference white plate22is provided, thereby decelerating the first carriage1.

That is, the deceleration of the first carriage1is started in a velocity transitionary period from an acceleration to a constant velocity period.

After a predetermined time has passed since the decrease of the motor drive electric current of the stepping motor8, the vibrations of the first carriage1and the second carriage2decrease. That is, the friction loads of the first carriage1and the second carriage2function as a brake when the carriages are decelerated, thereby decreasing the load on the stepping motor8. Therefore, if the motor drive electric current is decreased when reading the reference white plate22, the vibrations of the first carriage1and the second carriage2decrease.

When the vibrations of the first carriage1and the second carriage2decrease, the reading operation of the reference white plate22is started. Due to the decrease of the vibrations of the first carriage1and the second carriage2, the reference white plate reading operation can be performed stably. Specifically, the surface of the reference white plate22is irradiated with a light of the exposure lamp14. The first mirror15reflects the light reflected from the surface of the reference white plate22. Further, the second mirror16and the third mirror17sequentially reflect the light reflected from the first mirror15. The light reflected from the third mirror17is led to the CCD19through the imaging lens18, and the reflected light is converted into an electric signal by the CCD19.

The data of the reference white plate22obtained by the CCD19is transmitted to the scanner control board20and is subjected to image processing. Consequently, a reference white level or shading data is obtained. The shading data is used for correcting a white level of image data of a read original document. By such a correction of the white level of image data of the read original document, an image output can be stabilized regardless of whether there are variations in image output levels caused by the decrease of the light amount of the exposure lamp14with time.

As illustrated inFIG. 5B, when the reading operation of the reference white plate22is completed, the first carriage1still moves in a decelerated condition. In order to stop the first carriage1and the second carriage2in the short time, the drive electric current for driving the stepping motor8is increased immediately after the completion of the reference white plate reading operation, and the first carriage1and the second carriage2are controlled to be rapidly decelerated and stopped. In this deceleration control operation, because the reference white plate reading operation is already completed, there is no serious influence even if the first carriage1and the second carriage2vibrate to some extent. Further, the first carriage1and the second carriage2can be stopped in the short time, so that the whole period of time required for performing the reading operation of the reference white plate22can be reduced.

Immediately after the first carriage1and the second carriage2have stopped, the first carriage1and the second carriage2are driven to move in the return direction indicated by the arrow inFIG. 5A. When the first carriage1moves to the “image reading position in the sheet-through mode,” the first carriage1and the second carriage2stop moving. With regard to the return speed of the first carriage1toward the “image reading position in the sheet-through mode,” in order to reduce the vibrations of the first carriage1as much as possible until the start of an image reading operation of an original document which is performed immediately after the stop of the first carriage1, the first carriage1is driven to move at a lower speed than the moving speed of the first carriage1when the first carriage1moves to the reference white plate22for reading.

At the “image reading position in the sheet-through mode,” an image of an original document fed out from the original document tray by a group of rollers provided in the document feeder30is read by the first carriage1and the second carriage2. Similarly in the image reading system moving mode, the reflected light from the image surface of the original document is led to the CCD19through the imaging lens18. The reflected light is converted into an electric signal by the CCD19. The data of the read image of the original document obtained by the CCD19is transmitted to the scanner control board20and is subjected to image processing. At this time, a white level of image data of the read original document is corrected using the shading data obtained by reading the reference white plate22. Thereby, an adequate image output can be obtained.

Because the image reading operation of the original document is performed in a condition that the vibrations of the first carriage1are reduced as much as possible, an inferior image reading at the tip portion of the image of the original document due to vibrations of the first carriage1is typically prevented. Therefore, an image of an original document can be read with accuracy in the image reading device50.

As described above, in the image reading device50according to the embodiment of the present invention, the deceleration of the first carriage1is started in a velocity transitionary period from an acceleration to a constant velocity period, and the reading operation of the reference white plate22is performed in the decelerated condition of the first carriage1. As compared to the reading operation of the reference white plate performed in the area “A” inFIG. 7according to the background art, the reading operation of the reference white plate22starts earlier in the image reading device50. As a result, the whole period of time required for performing the reading operation of the reference white plate can be reduced.

Further, as compared to the reading operation of the reference white plate performed in the area “B” inFIG. 7in which the carriage is accelerated according to the background art, the reading operation of the reference white plate22can be performed stably in a decelerated condition in which vibrations of the carriage are less than those in an accelerated condition. Therefore, the reference white plate22can be read with accuracy in the image reading device50.

Next, another embodiment of the present invention will be described referring toFIG. 6, in which the above-described image reading device50is used in an image forming apparatus, such as a copying machine.

FIG. 6is a schematic vertical longitudinal sectional side view of a copying machine according to another embodiment of the present invention. A copying machine60includes the above-described image reading device50serving as an image scanner at an upper part thereof, and a printer device61that forms an image of an original document read by the image reading device50on a sheet. In the printer device61, a sheet is fed to an electrophotographic printer engine64through a sheet conveying path67from one of a sheet feeding tray62that accommodates a stack of sheets therein and a manual sheet feeding tray63that manually feeds sheets. The sheet fed to the electrophotographic printer engine64is further conveyed to a sheet discharging stacker section66via a fixing unit65through the sheet conveying path67.

In this embodiment, the electrophotographic printer engine64includes an organic photoreceptor68, and a charging device (not shown), an optical writing device70, a developing device71, and a transfer device72arranged around the photoreceptor68. The printer device61further includes a sheet reversing mechanism73that reverses a sheet having an image on one side of the sheet.

An image is formed by the printer device61by an electrophotographic image forming process. A brief description will be made to an exemplary electrophotographic image forming process of the printer device61.

The image data of an original document read by the image reading device50are sent to the printer device61. The optical writing device70converts the image data from the image reading device50into optical signals, and exposes a surface of the photoreceptor68uniformly charged by the charging device with the optical signals to form an electrostatic latent image corresponding to the image of the original document. The electrostatic latent image on the photoreceptor68is developed with toner by the developing device71.

A toner image on the photoreceptor68is transferred to a sheet fed from one of the sheet feeding trays62and the manual sheet feeding tray63. Subsequently, the toner image on the sheet is fixed thereonto by the fixing device65. The sheet having the toner image is discharged to the sheet discharging stacker section66as a copy print.

The image forming apparatus such as the copying machine60can achieve high performance such as high speed, high image quality, etc., by employing the above-described image reading device50.

In the above embodiment of the present invention, the image reading device50is used in the copying machine60as an example of an image forming apparatus. Alternatively, the image reading device50may be used in other similar image forming apparatus, such as a facsimile machine.