Image reading apparatus and method of controlling the same

An image reading apparatus capable of changing a main reading unit at an appropriate time point such that a plurality of reading units can be equally used, and a method of controlling the same. The image reading apparatus includes an automatic document feeder, a first reading unit to read a first side of a document fed by the automatic document feeder and to function as a main reading unit, a second reading unit to read a second side of the document fed by the automatic document feeder; and a control unit to change the main reading unit from the first reading unit to the second reading unit if the number of times La of usage of the first reading unit reaches a reference value. The control unit compares the number of times La of usage of the first reading unit with a predicted lifetime Lt of the first reading unit and changes the main reading unit to the second reading unit if it is determined that the number of times La of usage of the first reading unit reaches a predetermined percentage of the predicted lifetime of the first reading unit. The control unit determines whether the main reading unit is changed or not, based on frequencies of use of the first reading unit and the second reading unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2007-74168, filed on Jul. 24, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to an image reading apparatus, and, more particularly, to an image reading apparatus capable of equally using a plurality of reading units to read image information from a document, and a method of controlling the same.

2. Description of the Related Art

An image reading apparatus reads image information recorded on a document and is mounted in a machine such as a scanner, a digital copier or a multi-function machine.

A method of reading both sides of a document in an image reading apparatus may be classified into two methods. One is a method of reading a first side of a transported document via a reading unit, changing a transport direction of the document via a document direction changing device, reversing the first side and a Second side of the document via a duplex path, and reading the second side of the document. Such a method is advantageous in that both sides of the document can be read using one reading unit, but is disadvantageous in that it takes significant time to read the both sides of the document.

A second method is reading both sides of a document by mounting a first reading unit to read a first side of the document and opposite a second reading unit to read a second side of the document. Such a method is advantageous in that the both sides of the document can be simultaneously read without unnecessarily circulating the document and thus a two-sided reading operation can be performed with high speed.

An example of the image reading apparatus employing the latter method is disclosed in Japanese Unexamined Patent Application Publication No. 2004-187144. The disclosed image reading apparatus includes first and second reading units respectively to read an upper side and a lower side of a document fed by an automatic document feeder. In a one-sided reading mode in which only one side of the document is read, the first reading unit reads the document and, in a two-sided reading mode in which both sides of the document are read, the first reading unit and the second reading unit read the document. Since the first reading unit is used in both the one-side reading mode and the two-sided reading mode, the first reading unit may be called a main reading unit which performs a main function when the document is read. Although the lifetime of the first reading unit is set to be equal to that of the second reading unit, the first reading unit140expires earlier than the second reading unit150because of the difference in work load.

However, since the conventional image reading apparatus is not built to take into account that the effective lifetime of the first reading unit is shorter than that of the second reading unit, the following problems may be caused. First, since the lifetimes of the first reading unit and the second reading unit expire at different points in time, it is cumbersome for a user to repair each reading unit whenever the replacement of such is necessary. Thus, the user may distrust the quality of the product.

If the document is read using the second reading unit which has been used less frequently than the first reading unit, better reading quality can be obtained. However, since the document is read using the first reading unit which has been used more frequently than the second reading unit, reading quality may deteriorate. In addition, when both sides of the document are read, an image read by the first reading unit is different from an image read by the second reading unit in quality.

SUMMARY OF THE INVENTION

The present general inventive concept provides an image reading apparatus capable of changing a main reading unit at an appropriate time such that a plurality of reading units can be used with substantially similar expiration times, and a method of controlling the same.

The foregoing and/or other aspects and utilities of the present general inventive concept can be achieved by providing an image reading apparatus including: an automatic document feeder; a first reading unit to read a first side of a document fed by the automatic document feeder and to function initially as a main reading unit; a second reading unit to read a second side of the document fed by the automatic document feeder; and a control unit to change the main reading unit from the first reading unit to the second reading unit if the number of times Laof usage of the first reading unit reaches a reference value.

The control unit may compare the number of times Laof usage of the first reading unit with a predicted number of lifetime usages Ltof the first reading unit and change the main reading unit to the second reading unit if it is determined that the number of times Laof usage of the first reading unit reaches at least a predetermined percentage of the predicted lifetime usages of the first reading unit.

The control unit may determine whether the main reading unit is changed, taking into account the frequencies of the first reading unit and the second reading unit.

The control unit may include an ADF two-sided reading mode to read the first side and the second side of the document fed by the automatic document feeder using the first reading unit and the second reading unit, respectively, and the control unit may change the main reading unit to the second reading unit if the number of times Laof usage of the first reading unit satisfies the following equation in a relationship between the predicted lifetime usages Ltof the first reading unit and a frequency Fdin use of the ADF two-sided reading mode.
La≧Lt[1−(Fd+α)], (α is a constant and 0<Fd+α<1)

The image reading apparatus may further include a flat panel on which a document to be read is laid, the control unit may include an ADF two-sided reading mode to read the first side and the second side of the document using the first reading unit and the second reading unit and a flat-panel reading mode to read the document laid on the flat panel using the first reading unit, and the control unit may change the main reading unit to the second reading unit if the number of times Laof usage of the first reading unit satisfies the following equation in a relationship among the predicted lifetime usages Ltof the first reading unit, a frequency Fdin use of the ADF two-sided reading mode and a frequency Ffin use of the flat-panel reading mode.
La≧Lt[1−(Fd+Ff)],(0<Fd+Ff<1)

The image reading apparatus may further include a display unit to display an operation state of the image reading apparatus, and the control unit may display information on the change of the main reading unit on the display unit before the main reading unit is changed to the second reading unit.

The image reading apparatus may further include an input unit having a main reading unit changing unit to allow a user to input a command to change the main reading unit.

The image reading apparatus may further include a display unit to display an operation state of the image reading apparatus. A document feed tray on which the document fed by the automatic document feeder is laid, and the control unit may display information on a direction of a side to be read in the document laid on the document feed tray when the main reading unit is changed to the second reading unit.

The foregoing and/or other aspects and utilities of the present general inventive concept can also be achieved by providing a method of controlling an image reading apparatus including a first reading unit to read a first side of a transported document and to function as a main reading unit and a second reading unit to read a second side of the transported document, the method including: determining whether the number of times Laof usage of the first reading unit reaches a reference value and determining whether the main reading unit is changed to the second reading unit according to the determined result.

At this time, the number of times Laof usage of the first reading unit may be compared with a predicted lifetime usage Ltof the first reading unit and the main reading unit may be changed to the second reading unit if it is determined that the number of times Laof usage of the first reading unit reaches at least a predetermined percentage of the predicted lifetime usages of the first reading unit.

When the main reading unit is changed may be determined taking into account frequencies in use of the first reading unit and the second reading unit.

A frequency Fdin use of an ADF two-sided reading mode to read the first side and the second side of the document using the first reading unit and the second reading unit may be computed, and the main reading unit may be changed to the second reading unit if the number of times Laof usage of the first reading unit satisfies the following equation in a relationship between the predicted lifetime usage Ltof the first reading unit and the frequency Fdof using the ADF two-sided reading mode.
La≧Lt[1−(Fd+α)], (α is a constant and 0<Fd+α<1)

The frequency Fdused in an ADF two-sided reading mode to read the first side and the second side of the document using the first reading unit and the second reading unit and a frequency Ffusing a flat-panel reading mode to read the document laid on a flat panel using the first reading unit may be computed, and the main reading unit may be changed to the second reading unit if the number of times Laof usage of the first reading unit satisfies the following Equation in a relationship among the predetermined lifetime Ltof the first reading unit, the frequency Fdin use of the ADF two-sided reading mode and the frequency Ffused in the flat-panel reading mode.
La≧Lt[1−(Fd+Ff)],(0<Fd+Ff<1)

Information on the change of the main reading unit may be displayed on a display unit before the main reading unit is changed to the second reading unit.

The main reading unit may be changed to the second reading unit when a command of a user is inputted.

Information indicating which of an upper side and a lower side of the document laid on a document feed tray becomes a side to be read may be displayed on a display unit when the main reading unit is changed to the second reading unit.

The foregoing and/or other aspects and utilities of the present general inventive concept can also be achieved by providing a method of controlling an image reading apparatus including a first reading unit to read a first side of a transported document and to function initially as a main reading unit, and a second reading unit to read a second side of the transported document. The method includes predetermining a predicted total usage value Ltfor the first reading unit, electronically calculating a frequency Fdof use for an ADF two-sided reading mode to read the first side and the second side of the document using the first reading unit and the second reading unit, respectively, electronically calculating a frequency Ffof use for a flat panel reading mode to read the first side of the document using the first reading unit, determining whether the total usage Laof the first reading unit has exceeded a threshold value according to the formula
La≧Lt[1−(Fd+Ff)],(0<Fd+Ff<1)

The second reading unit may also have a predicted total usage value Lt, so that if the main reading unit is changed to the second reading unit when the first reading unit has only slightly exceeded the threshold value, the first and second reading units will expire at substantially similar times.

The foregoing and/or other aspects and utilities of the present general inventive concept can also be achieved by providing a method of controlling an image reading apparatus including a first reading unit to read a first side of a transported document and to function initially as a main reading unit and a second reading unit to read a second side of the transported document, is provided. The method includes predetermining a predicted total usage value Ltfor the first reading unit, electronically calculating a frequency Fdof use for an ADF two-sided reading mode to read the first side and the second side of the document using the first reading unit and the second reading unit, respectively, predetermining a constant α for use in electronic calculations with Fd, and determining whether the total usage Laof the first reading unit has exceeded a threshold value according to the formula
La≧Lt[1−(Fd+α)], (0<Fd+α<1).

The apparatus may have a flat-panel reading function performed by the first reading unit, regardless of the total usage value, La. The predetermination of α also takes into account such flat-panel reading function.

The foregoing and/or other aspects and utilities of the present general inventive concept can also be achieved by providing an image reading apparatus, including: an automatic document feeder, at least two reading units and a control unit to control which of the at least two reading units will be used during each document loading operation based on previous usages of each of the at least two reading units.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a view illustrating the configuration of a multi-function machine having an image reading apparatus according to an embodiment of the present general inventive concept,FIG. 2is a view illustrating the configuration of the image reading apparatus according to the general inventive concept, andFIG. 3is a block diagram illustrating the image reading apparatus according to the general inventive concept.

As illustrated inFIG. 1, the multi-function machine includes an image reading apparatus100to read an image recorded on a document D and a printing apparatus200to print an image on a document S.

The printing apparatus200prints an image according to a signal inputted from the image reading apparatus100or inputted from an external apparatus such as a personal computer (PC). The printing apparatus200includes a document feed unit210to feed a document S which is a printable medium, a development unit220to develop an image on the document S, a fixing unit230to apply heat and pressure to the document S and fix the developed image to the document S, and an ejection unit240to eject the document on which the image is printed.

The document S loaded on a document tray211is picked up by a pickup roller212and is transported to the development unit220. An electrostatic latent image is formed on the surface of a photosensitive drum221, which is charged with a predetermined potential by a charging roller222. The electrostatic latent image is developed to a toner image by a development roller223and is transferred onto document S by a transfer roller224. The toner image transferred onto the document is fixed to the document S by heat and pressure when passing between a heating roller231and a pressurization roller232of the fixing unit230, and the document passing through the fixing unit230is transported and ejected by an ejection roller241.

As illustrated inFIGS. 2 and 3, the image reading apparatus100according to an embodiment of the present general inventive concept includes a reading apparatus main body101including a reading frame110and a cover120, an automatic document feeder130which automatically feeds a document D such that a reading operation can be continuously performed, first and second reading units140and150to irradiate light onto a document D and read image information, and a control unit160to control the whole operation of the image reading apparatus100according to an input signal of a user and a predetermined program.

The first reading unit140and the second reading unit150irradiate light onto the document D, detect the light reflected from the document D, convert the amount of light into an electrical signal, and send the electrical signal to the control unit160. The first reading unit140and the second reading unit150face each other with a document transporting path133interposed therebetween. More particularly, the first reading unit140is located below the document D fed by the automatic document feeder130to read image information from a first side of the document D, and the second reading unit150is located above the document D fed by the automatic document feeder130to read image information from a second side of the document D.

The cover120is rotatably coupled to the reading frame110so as to open and close the upper surface of the reading frame110. The second reading unit150and the automatic document feeder130are mounted inside the cover120.

The first reading unit140is mounted inside the reading frame110, and a flat panel111and a first ADF glass171are mounted on the upper surface of the reading frame110. The user can lay the documents D on the flat panel111one by one in order to read the documents D. The first reading unit140is moved along the flat panel111below the flat panel111to read the document D laid on the flat panel111, and is located below the first ADF glass171to read the first side of the document D transported by the automatic document feeder130.

The automatic document feeder130includes a document insertion port131through which a document D to be read is inserted, a document ejection port132through which the read document is ejected, the document transporting path133which is formed inside the cover120so as to transport the document, and rollers which are mounted on the document transporting path133so as to transport the document D.

The document insertion port131is formed at one side of the cover120and the document ejection port132is formed below the document insertion port131. A document feed tray131aand a document insertion detection sensor131b, which detects whether a document D is inserted and outputs the detected result to the control unit160, are provided in the vicinity of the document insertion port131. Automatic document feeder130transports documents D on the document feed tray131a. A document ejection tray132a, on which the documents D ejected after the reading operation is completed are loaded, is provided in the vicinity of the document ejection port132.

The document transporting path133has a C-shape. One end of the document transporting path133is connected to the document feed tray131avia the document insertion port131and the other end thereof is connected to the document ejection tray132avia the document ejection port132. The first ADF glass171and a second ADF glass172are sequentially arranged on the reading path133asuch that the first reading unit140and the second reading unit150can read the image information recorded on the document D passing through the document transporting path133. The first ADF glass171is mounted on the reading frame110at a position corresponding to the first reading unit140and the second ADF glass172is mounted on the cover120at a position corresponding to the second reading unit150.

The document transporting rollers include a document pickup roller134to pick up the document D loaded on the document feed tray131a, first to third transporting rollers135,136and137to transport the document picked up by the document pickup roller134on the document transporting path133, and an ejection roller138to eject the read document to the document ejection tray132a. The first transporting roller135, which is provided closest to the document pickup roller134, separates the documents picked up by the document pickup roller134one by one. In order to separate the documents, a friction pad135ais provided so as to be opposed to the first transporting roller135.

The control unit160may operate both the first reading unit140and the second reading unit150to perform an ADF two-sided reading mode in which both sides of a document fed by the automatic document feeder130are read. The control unit160may operate either the first reading unit140or the second reading unit150to perform an ADF one-sided reading mode in which one side of document D fed by the automatic document feeder130is read. At this time, since both the two reading units140and150are used in the ADF two-sided reading mode, the reading unit used in the ADF one-sided reading mode becomes the main reading unit.

Here, the main reading unit is defined as the reading unit which is more frequently used when reading a document D. In general, the first reading unit140which is mounted below a document D to read a first side of document D becomes the main reading unit.

The control unit160may perform in a flat-panel reading mode in which a document D laid on the flat panel111is read using the first reading unit140which is the main reading unit. While the second reading unit150is used in only the ADF two-sided reading mode, the first reading unit140is used in the ADF two-sided reading mode, the ADF one-side reading mode and the flat-panel reading mode. Accordingly, the lifetime of the first reading unit140expires earlier than the second reading unit150.

The control unit160determines whether the main reading unit is changed on the basis of the number of times, La, of usage of the first reading unit140(i.e. the number of documents read using the first reading unit) and changes the main reading unit to the second reading unit according to the determined result such that the first reading unit140and the second reading unit150are substantially equally used throughout the lifetime of the reading units. In other words, both reading units140and150should expire at substantially the same time provided second reading unit150becomes the main reading unit at the appropriate time. More particularly, the control unit160reads the number of times of usage of the first reading unit140, which is the main reading unit, from a memory183(seeFIG. 3) and changes the main reading unit to the second reading unit150if the number of times of usage reaches a predetermined reference value.

At this time, the control unit160compares the number of times Laof usage of the first reading unit140with a predetermined lifetime Ltof the first reading unit140and changes the main reading unit to the second reading unit if it is determined that the number of times Laof usage of the first reading unit140reaches at least a predetermined percentage of the predicted lifetime usages Ltof the first reading unit140. For example, if the predicted lifetime Ltof the first reading unit140is 50,000 sheets, the control unit160may change the main reading unit to the second reading unit150if the first reading unit140reads at least 25,000 documents which correspond to 50% (this percentage may be appropriately changed if necessary in design) of 50,000 documents.

By the above-described method, the first reading unit140and the second reading unit150can be equally used by changing the main reading unit at an appropriate point in time. However, in this method, since the point in time when the main reading unit is changed is determined according to the predetermined reference value without considering which reading mode is more frequently used by the user, there is a limitation. For example, any user may frequently use the ADF two-sided reading mode. In this case, even when the main reading unit is changed to the second reading unit150, the first reading unit140is frequently used. In contrast, any user may infrequently use the ADF two-sided reading mode. In this case, when the main reading unit is changed to the second reading unit150, the first reading unit140is not frequently used. Therefore, in the case where the ADF two-sided reading mode is frequently used, the main reading unit needs to be changed to the second reading unit150at an earlier point in time, compared with the case where the ADF two-sided reading mode is infrequently used.

Accordingly, the point in time when the main reading unit is changed can be determined in consideration of the frequencies in using the first reading unit140and the second reading unit150.

Considering that the first reading unit140is used in both the ADF two-sided reading mode and the flat-panel reading mode when the main reading unit is changed to the second reading unit150, the control unit160may change the main reading unit to the second reading unit150if the number of times Laof usage of the first reading unit140satisfies Equation 1 in a relationship among the predicted lifetime usage Ltof the first reading unit140, a frequency Fdused in the ADF two-sided reading mode and a frequency Ffused in the flat-panel reading mode.
La≧Lt[1−(Fd+Ff)],(0<Fd+Ff<1)  Equation 1

where, the frequency Fdin use of the ADF two-sided reading mode and the frequency Ffused in the flat-panel reading mode are defined as follows:

Fd=(the number of documents read in the ADF two-sided reading mode)/(the total number of read documents)

Ff=(the number of documents read in the flat-panel reading mode)/(the total number of read documents)

For example, suppose that the first reading unit140is the main reading unit, Fd=0.2, and Ff=0.1 (in this case, a frequency Fsused in the ADF one-sided reading mode becomes 0.7). According to Equation 1, when the number of times Laof usage of the first reading unit140becomes [1−(0.2+0.1)]Lt(=0.7Lt), the main reading unit is changed to the second reading unit150. Since the second reading unit150is used in only the ADF two-sided reading mode, the number of times Lbof usage of the second reading unit150becomes La*0.2, that is, 0.14Lt(assume that the predicted and actual lifetime usage of the second reading unit150is substantially equal to that of the first reading unit140), at the time when the main reading unit is changed. In a state in which the main reading unit is changed to the second reading unit150, the remaining lifetime usage of the first reading unit140becomes 0.3Ltand the remaining lifetime usage of the second reading unit150becomes 0.86Lt.

When the main reading unit is changed to the second reading unit150, the second reading unit150is used in the ADF one-sided reading mode and the ADF two-sided reading mode and the first reading unit140is used in the ADF two-sided reading mode and the flat-panel reading mode. When the frequency of each mode is considered, the remaining lifetime usage of the first reading unit140becomes 0.86Lt[(0.1+0.2)/(0.7+0.2)], that is, about 0.29Ltwhile the remaining lifetime usage of the second reading unit150, that is, 0.86Lt, is consumed. Thus, the lifetime usages of the first reading unit140and the second reading unit150expire at substantially the same time.

The control unit160may change the main reading unit to the second reading unit if the number of times Laof usage of the first reading unit satisfies Equation 2 in a relationship between the predicted lifetime usage Ltof the first reading unit and the frequency Fdin use of the ADF two-sided reading mode.
La≧Lt[1−(Fd+α)]  Equation 2
where, α denotes a constant (0<Fd+α<1). Considering the frequency of each reading mode may vary after the main reading unit is changed to the second reading unit150, α may be appropriately selected according to design requirements. Equation 2 may be applied when the image reading apparatus100does not perform the flat-panel reading function. Even when the image reading apparatus100performs the flat-panel reading function, Equation 2 may still be applied. In this case, α should be determined taking into consideration that the first reading unit140is still used in the one-sided reading mode even after the main reading unit is changed to the second reading unit150.

As illustrated inFIG. 3, the image reading apparatus100according to the present general inventive concept includes an input unit181, a display unit182, the memory183, and the driving unit184.

The input unit181inputs information on the operation of the image reading apparatus selected by the user to the control unit160. The user can select a reading mode such as a one-sided reading operation or a two-sided reading operation using the input unit181. A main reading unit changing unit181awhich allows the user to input a command to change the main reading unit may be provided in the input unit181.

The display unit182displays the operation state of the image reading apparatus100to the user. In the present general inventive concept, the control unit160may inform the user that the main reading unit needs to be changed and inquire of the user whether the user wants to change the main reading unit, via the display unit182. The control unit160displays information on which side to be read via the display unit182in the ADF one-sided reading mode, after the main reading unit is changed to the second reading unit150. The information indicates whether the side to be read is directed upward or downward when the document is laid on the document feed tray131a.

The memory183stores a variety of data necessary to control the image reading apparatus. More particularly, the memory183stores information on the predicted lifetime usage Ltof the first reading unit140and the total number of read documents D and data related to the number of times Laof usage of the first reading unit140counted in the control unit160. That is, the memory183stores data necessary to compute the frequency in use of each of the reading modes, i.e., the number of documents D read in each of the reading modes (the flat-panel reading mode, the ADF one-sided reading mode and the ADF two-sided reading mode).

The driving unit184includes at least one motor to drive the rollers134,135,136,137and138provided in the automatic document feeder130. The driving unit184drives the motor under the control of the control unit160, rotates the rollers134,135,136,137and138, and transports the document D on the document transporting path133.

Hereinafter, a method of controlling the image reading apparatus according to the present general inventive concept will be described with reference toFIGS. 2 to 5.FIGS. 4 and 5are flowcharts illustrating a method of controlling the image reading apparatus100according to the present general inventive concept.

As illustrated inFIGS. 2,3and4, the control unit160determines whether a document D is inserted into the document insertion port131via a signal inputted from the document insertion detection sensor131b(operation S300).

If it is determined that the document D is inserted, the control unit160checks whether the first reading unit140is the main reading unit (operation S310). If it is determined that the first reading unit140is the main reading unit, the control unit160reads the number of times Laof usage of the first reading unit140, which is stored in the memory183, and the predicted lifetime usage Ltof the first reading unit140(operation S320).

The control unit160determines whether the point when the main reading unit is changed has been reached on the basis of the number of times Laof usage of the first reading unit140and the predicted lifetime usage Ltof the first reading unit140(operation S330). At this time, the control unit160compares the number of times Laof usage of the first reading unit140with the predicted lifetime Ltof the first reading unit140and determines that the point in time when the main reading unit should be changed has been reached if the number of times Laof usage of the first reading unit140reaches at least the predetermined percentage of the predicted lifetime usage of the first reading unit140.

As illustrated inFIG. 5, the point when the main reading unit is changed may be determined by factoring in the frequencies of the first reading unit140and the second reading unit150. The control unit160computes the frequencies Ffand Fdin the flat-panel reading mode and the ADF two-sided reading mode on the basis of data stored in the memory183(operation S331). Subsequently, the control unit160may determine that the point in time when the main reading unit is to be changed when the number of times Laof usage of the first reading unit140satisfies Equation 1 with respect to the predicted lifetime usage Ltof the first reading unit140(operation S332). Similarly, the point in time when the main reading unit is changed may be determined using Equation 2.

If it is determined that the point in time when the main reading unit is changed has been reached in Operation S330(operation S332), then the control unit160informs the user that the main reading unit needs to be changed and inquires of the user whether the user wants to change the main reading unit to the second reading unit150, via the display unit182(operation S340).

Subsequently, the control unit160determines whether a command to change the main reading unit has been inputted (operation S350). If it is determined that the command to change the main reading unit has been inputted, then the main reading unit is changed to the second reading unit150(operation S360).

Alternatively, the control unit160may inform the user that the main reading unit has been changed automatically in Operation S340and then change the main reading unit to the second reading unit150without performing Operation S350.

If the main reading unit is changed in Operation S360, or if it is determined that the first reading unit140is not the main reading unit in Operation310, or if it is determined that the point when the main reading unit is to be changed has not yet been reached in Operation330, or if it is determined that the command to change the main reading unit is not inputted in Operation S350, then the control unit160determines a reading mode selected by the user (operation S370).

If it is determined that the user selects the one-sided reading mode, then the control unit160displays information on the direction of the side of the document D to be read, that is, information indicating whether the side to be read is directed upward or downward when the document D is laid on the document feed tray131a(seeFIG. 1), and controls the first reading unit140or the second reading unit150to read one side of the document (operations S380and S390).

More particularly, if it is determined that the main reading unit is changed to the second reading unit150in Operation S360, or if it is determined that the first reading unit140is not the main reading unit in Operation S310, the second reading unit150is the main reading unit and thus the second reading unit150reads one side of the document D in Operation S390. In this case, the control unit160instructs the user to lay the document D on the document feed tray131ain a state to allow the second reading unit150to read the document D, that is, in a state in which a side to be read is directed downward.

In contrast, if it is determined that the point in time when the main reading unit is changed is not reached in Operation S330, or if it is determined that the command to change the main reading unit is not inputted in Operation S350, then the first reading unit140is the main reading unit and thus the first reading unit140reads one side of the document D in Operation S390. In this case, the control unit160instructs the user to lay the document D on the document feed tray131ain a state to allow the first reading unit140to read the document, that is, in a state in which the side to be read is directed upward.

Meanwhile, if it is determined that the one-sided reading mode is not selected in Operation S370, then the control unit160controls the first reading unit140to read a first side of the document D and controls the second reading unit150to read a second side of the document D, thereby reading both sides of the document D (operation S400).

As described above, according to the general inventive concept, it is possible to equally use two reading units until the lifetime usages of the two reading units are expired, by changing a main reading unit at an appropriate point in time. Accordingly, it is possible to prevent reading quality from deteriorating when only one reading unit of a plurality of reading units is frequently used, initially. In addition, it is possible to improve convenience by allowing the user to replace the two reading units with new reading units at substantially the same point in time.