Sheet detecting apparatus and image forming apparatus

A sheet detecting apparatus includes a sheet supporting surface, a first sensor flag including a first flag portion, a first contact portion, and a third contact portion, a second sensor flag including a second flag portion, and a second contact portion, a first detection sensor configured to transit to a first state of outputting a first detection signal and to a second state of outputting a second detection signal, the first detection sensor transiting to one of the first state and the second state in response to a position of the first flag portion, and a second detection sensor configured to transit to a third state of outputting a third detection signal and to a fourth state of outputting a fourth detection signal, the second detection sensor transiting to one of the third state and the fourth state in response to a position of the second flag portion.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a sheet detecting apparatus configured to detect a sheet and an image forming apparatus including the same.

Description of the Related Art

Hitherto, a copier including a cassette capable of loading A3, A4 and A5 size sheets is proposed as disclosed in Japanese Patent Application Laid-open No. H07-112844 for example. This copier includes a side guide configured to regulate a widthwise position of a sheet within the cassette, a sheet presence detecting lever, a first sheet width detecting lever, a second sheet width detecting lever, a first photo-sensor and a second photo-sensor. The first sheet width detecting lever is provided at a position permitting to interfere with the side guide being in contact with an end portion of an A5 size sheet and is capable of shading the first photo-sensor. The second sheet width detecting lever is provided at a position permitting to interfere with the side guide being in contact with an end portion of an A4 size sheet and is capable of shading the second photo-sensor. The sheet presence detecting lever is provided at a position permitting to contact with any size sheets of A3 to A5.

In a state in which no sheet is loaded in the cassette, the sheet presence detecting lever presses down detection portions of the first and second sheet width detecting levers and the first and second photo-sensors are both turned ON. When the cassette is inserted into a body of the copier, the sheet presence detecting lever separates from the first and second sheet width detecting levers and the first and second photo-sensors are turned OFF by the sheet loaded on the cassette. Then, in the state in which the cassette is inserted into the copier and in a case where an A5 size sheet is stored in the cassette, the first sheet width detecting lever is pushed up by the side guide and the first photo-sensor turns ON. At this time, the second photo-sensor is still kept OFF.

In a case where an A4 size sheet is stored in the cassette, the second sheet width detecting lever is pushed up by the side guide and the second photo-sensor turns ON. At this time, the first photo-sensor is still kept OFF. In a case where an A3 size sheet is stored in the cassette, the first and second photo-sensors are kept OFF because the first and second sheet width detecting levers are not pushed up by the side guide. Thus, the first and second photo-sensors are turned ON or OFF as the side guide presses up the first sheet width detecting lever or the second sheet width detecting lever at positions corresponding to the sheet sizes.

However, Japanese Patent Application Laid-open No. H07-112844 has a problem that because the respective sheet width detecting levers pivot in response to the positions of the side guide, the photo-sensors may erroneously detect in a case where a user has not moved the side guide to an appropriate position for example.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a sheet detecting apparatus includes a sheet supporting surface configured to support a sheet, a first sensor flag including a first flag portion configured to pivot around a first pivot shaft extending in an axial direction, a first contact portion configured to pivot integrally with the first flag portion and configured to contact, at a first position in the axial direction, with the sheet supported by the supporting surface, and a third contact portion configured to pivot integrally with the first flag portion and configured to contact, at a third position, with the sheet supported by the supporting surface, the third position being located on a side opposite from the first position across a second position in the axial direction, a second sensor flag including a second flag portion configured to pivot around a second pivot shaft, and a second contact portion configured to pivot integrally with the second flag portion and configured to contact, at the second position, with the sheet supported by the supporting surface, a first detection sensor configured to transit to a first state of outputting a first detection signal and to a second state of outputting a second detection signal different from the first detection signal, the first detection sensor transiting to either one of the first state and the second state in response to a position of the first flag portion, and a second detection sensor configured to transit to a third state of outputting a third detection signal and to a fourth state of outputting a fourth detection signal different from the third detection signal, the second detection sensor transiting to either one of the third state and the fourth state in response to a position of the second flag portion, wherein in a case where no sheet is disposed at the first, second and third positions, the first detection sensor is brought to the first state and the second detection sensor is brought to the third state, wherein in a case where a sheet is disposed at the first position and no sheet is disposed at the second and third positions, the first detection sensor is brought to the second state and the second detection sensor is brought to the third state, wherein in a case where a sheet is disposed at the first and second positions and no sheet is disposed at the third position, the first detection sensor is brought to the second state and the second detection sensor is brought to the fourth state, and wherein a sheet is disposed at the first, second and third positions, the first detection sensor is brought to the first state and the second detection sensor is brought to the fourth state.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

Overall Configuration

A printer100serving as an image forming apparatus of a first embodiment is an electro-photographic laser beam printer configured to form a monochrome toner image. As illustrated inFIG. 1, the printer100includes a sheet feeding unit30configured to feed a sheet, an image forming unit20configured to form an image on the sheet being fed and a sheet discharge roller pair not illustrated capable of discharging the sheet to a discharge tray15.

When an instruction of forming an image is issued to the printer100, the image forming unit20starts an image forming process based on image information inputted from an external computer or the like connected to the printer100. The image forming unit20includes a process cartridge9, a laser scanner14, a transfer roller10and a fixing unit40. The process cartridge9includes a rotatable photosensitive drum5and a charging roller6, a developing sleeve7and toner8disposed along the photosensitive drum5. The transfer roller10defines a transfer nip T1together with the photosensitive drum5. Note that while the printer100is a monochrome laser printer in the present embodiment, the present disclosure is not limited to that. For instance, the printer100may be a full-color laser beam printer.

The laser scanner14irradiates the photosensitive drum5with a laser beam13based on the inputted image information. Because the photosensitive drum5has been charged in advance by the charging roller6at this time, an electrostatic latent image is formed on the photosensitive drum5by the irradiation of the laser beam13. After that, the electrostatic latent image is developed by the developing sleeve7by using the toner8and a monochrome toner image is formed on the photosensitive drum5.

The sheet is fed from the sheet feeding unit30in parallel with the abovementioned image forming process. The sheet feeding unit30includes a sheet feed tray50disposed at a lower part of the printer100, and the sheet feed tray50includes a supporting surface50acapable of supporting the sheet S. The sheet feeding unit30also includes a pickup roller2and a conveyance roller pair3. In response to the instruction of forming the image, the sheet S supported by the supporting surface50ais fed by the pickup roller2and is conveyed to the transfer nip T1by the conveyance roller pair3.

At the transfer nip T1, the toner image on the photosensitive drum5is transferred onto the sheet S conveyed by the conveyance roller pair3to the transfer nip T1by applying an electrostatic negative bias to the transfer roller10. Residual toner left on the photosensitive drum5is collected by a cleaning blade not illustrated.

Predetermined heat and pressure are applied to the sheet S onto which the toner image has been transferred by a fixing roller11and a pressure roller12of the fixing unit40such that the toner image is melted and is adhered, i.e., is fixed, to the sheet S. The sheet that has passed through the fixing unit40is discharged to the discharge tray15by a discharge roller pair not illustrated.

Comparative Example

Next, a sheet feeding unit130of a comparative example will be described. As illustrated inFIGS. 2A and 2B, the sheet feeding unit130includes a sheet feed tray150, a detection unit160and a pair of side regulating plates51and52. The pair of side regulating plates51and52serving as first and second regulating members are movable in a width W direction orthogonal to a sheet feeding direction D and are interlocked in a direction of approaching with each other and in a direction of separating from each other by an interlock portion55composed of a rack and a pinion. That is, the side regulating plates51and52are disposed symmetrically about a center line50C between the side regulating plates51and52to regulate widthwise positions of one and the other ends of the sheet loaded in the sheet feed tray150.

Notches181,182and183are defined on a downstream end side in the sheet feed direction D of the sheet feed tray150in order at positions closer to the center line50C. The detection unit160includes sensor flags171,172and173disposed respectively at the notches181,182and183and photo-interrupters161,162and163disposed at positions corresponding to these sensor flags171,172and173.

The sensor flag171includes a pivot shaft171aconfigured to pivot and a contact portion171band a flag portion171cfixed respectively to the pivot shaft171a. The contact portion171bis configured to contact with a sheet loaded in the sheet feed tray150and the flag portion171cis capable of shading or opening an optical path of the photo-interrupter161. The sensor flag172includes a pivot shaft172aand a contact portion172band a sensor flag172cfixed respectively to the pivot shaft172a. The contact portion172bis configured to contact with a sheet loaded in the sheet feed tray150and the flag portion172cis capable of shading or opening an optical path of the photo-interrupter162.

The sensor flag173includes a pivot shaft173aconfigured to pivot and a contact portion173band a flag portion173cfixed respectively to the pivot shaft173a. The contact portion173bis configured to contact with a sheet loaded in the sheet feed tray150and the sensor flag173cis capable of shading or opening an optical path of the photo-interrupter163.

These sensor flags171,172and173are constructed respectively in the same manner and are in-phase in a natural condition. The photo-interrupters161,162and163are also constructed in the same manner and are optical elements each including a light emitting element and a light receiving element provided so as to face the light emitting element. The light receiving element outputs different detection signals depending on whether the light receiving element receives a light from a light source. The light receiving element is set to output a signal of L level in a case where the light receiving element receives no light as described in Tables simply as “L” and to output a signal of H level in a case where the light receiving element receives light as described in Table simply as “H”. Note that in the case where the light receiving element outputs the L level signal, a low level voltage is detected in a circuit connected to the light receiving element and in the case where the light receiving element outputs the H level signal, a high level voltage is detected in a circuit connected to the light receiving element.

As illustrated inFIG. 2C, in a state in which no sheet is loaded in the sheet feed tray150and no sheet is in contact with the contact portions of the sensor flags171,172and173, the flag portions do not shade the photo-interrupters161,162and163. Therefore, the photo-interrupters161,162and163output the L level signal.

When a sheet is inserted into a leading edge butting portion53of the sheet feed tray150as illustrated inFIG. 2D, the contact portions of the sensor flags171,172and173are pressed by the sheet and the sensor flags171,172and173pivot. Thereby, the flag portions shade the optical path of the photo-interrupters161,162and163and the photo-interrupters161,162and163output H level signals. In a case where the sheet is drawn out or runs out of sheets in the sheet feed tray150, the sensor flags171,172and173return to their original positions, i.e., to the positions as indicated inFIG. 2C, by their own weight or by an urging member such as a spring.

While there are various sizes of sheets, the following description will be made by roughly dividing such sheets into three kinds of sheets of a small size sheet, a medium size sheet and a large size sheet for convenience. As illustrated inFIG. 3, the small size, the middle size and the large size sheets are aligned by the side regulating plates51and52such that a widthwise center of the sheets coincide with the center line50C. Then, the sensor flag171is disposed at a position where the sensor flag171can come into contact with the small size, the middle size and the large size sheets. The sensor flag172is disposed at a position where the sensor flag172can come into contact with the middle size and the large size sheets and is unable to come into contact with the small size sheet. The sensor flag173is disposed at a position where the sensor flag173can come into contact with the large size sheet and is unable to come into contact with the small size and the middle size sheets.

By arranging the sensor flags171,172and173and the photo-interrupters161,162and163as described above, the photo-interrupters161,162and163output signals in four states as indicated in Table inFIG. 4. That is, in a state in which no sheet is loaded in the sheet feed tray150, the photo-interrupters161,162and163output the L level signal, respectively. In a state in which the small size sheet is loaded in the sheet feed tray150, the photo-interrupter161outputs an H level signal and the photo-interrupters162and163output L level signals.

In a state in which the middle size sheet is loaded in the sheet feed tray150, the photo-interrupters161and162output H level signals and the photo-interrupter163outputs an L level signal. In a state in which the large size sheet is loaded in the sheet feed tray150, the photo-interrupters161,162and163output H level signals. It is possible to detect the size of the sheet loaded in the sheet feed tray150from the signals from the photo-interrupters161,162and163as described above.

Sheet Feeding Unit

Next, the sheet feeding unit30of the present embodiment will be described. Note that components of the present embodiment similar to those of the comparative example described above will be denoted by the same reference signs and their description will be omitted here. As illustrated inFIGS. 5A and 5B, the sheet feeding unit30serving as a sheet detecting apparatus includes a sheet feed tray50, a detection unit60and a pair of side regulating plates51and52.

Notches81,82and83are defined on a downstream end side in the sheet feed direction D of the sheet feed tray50in order at positions closer to the center line50C. The notch81serving as a first notch, the notch82serving as a second notch and the notch83serving as a third notch include contact portions71b,72band73brespectively penetrating through the notches. The notch83is formed to be longer than the notches81and82in the sheet feed direction D, i.e., in the insert direction of the sheet inserted toward the supporting surface50a. The detection unit60includes sensor flags71and72and the photo-interrupters61and62and is capable of detecting the sheet supported by the sheet feed tray50. The detection unit60is disposed in a printer body100A (seeFIG. 1) serving as an apparatus body in which the image forming unit20is provided. The supporting surface50ais disposed in the printer body100A.

The sensor flag71serving as a first sensor flag includes a pivot shaft71aserving as a first pivot shaft extending in the width direction W, i.e., an axial direction, contact portions71band73b, and a flag portion71c. The contact portions71band73band the flag portion71care fixed to the pivot shaft71aand are configured to pivot integrally with the pivot shaft71a. The contact portion71bserving as a first contact portion projects out of the notch81toward the supporting surface50aside and is configured to contact with the sheet at the first position. The contact portion73bserving as a third contact portion projects out of the notch83toward the supporting surface50aside and is configured to contact with the sheet S at the third position. The third position is a position on a side opposite from the first position across a second position in terms of the width direction W. The first, second and third positions are located on a downstream end side of the supporting surface50ain the sheet feed direction D, i.e., in the insert direction of the sheet inserted toward the supporting surface50a. The flag portion71cserving as a first flag portion is capable of shading or opening an optical path of the photo-interrupter61.

The sensor flag72serving as a second sensor flag includes a pivot shaft72aserving as a second pivot shaft extending in the width direction W and a contact portion72band a flag portion72cfixed respectively to the pivot shaft72aand pivoting integrally with the pivot shaft72a. The contact portion72bserving as a second contact portion projects out of the notch82toward the supporting surface50aand is configured to contact with the sheet S at the second position. The flag portion72cserving as a second flag portion is capable of shading or opening an optical path of the photo-interrupter62serving as a second detection sensor. The pivot shaft72aextends in parallel with the pivot shaft71a, and the contact portion72band the flag portion72care disposed on sides opposite from each other across the pivot shaft71awhen viewed from the width direction W. Note that the pivot shaft72amay extend in a direction intersecting with the pivot shaft71a.

The photo-interrupters61and62are constructed in the same manner and are optical elements respectively including a light emitting element and a light receiving element provided so as to face the light emitting element. The light receiving element outputs different detection signals depending on whether the light receiving element has received light from a light source. Specifically, the photo-interrupter61includes a light emitting element61aand a light receiving element61b, and the photo-interrupter62includes a light emitting element62aand a light receiving element62b. In the present embodiment, a state in which the optical path of the photo-interrupter61is not shaded and an L level signal is outputted as a first detection signal is set to be a first state. A state in which the optical path of the photo-interrupter61is shaded and an H level signal is outputted as a second detection signal is set to be a second state. That is, the photo-interrupter61is capable of transiting from the first state to the second state and vice versa and is brought to either one of the first state and the second state in response to a position of the flag portion71cof the sensor flag71.

Still further, a state in which the optical path of the photo-interrupter62is not shaded and an L level signal is outputted as a third detection signal is set to be a third state. A state in which the optical path of the photo-interrupter62is shaded and an H level signal is outputted as a fourth detection signal is set to be a fourth state. That is, the photo-interrupter62is capable of transiting from the third state to the fourth state and vice versa and is brought to either one of the third state and the fourth state in response to a position of the flag portion72cof the sensor flag72.

As illustrated inFIG. 6A, an angle of the contact portion73bmounted to the pivot shaft71ais different from that of the contact portion71b, and the contact portion73bextends with an angle closer to horizontal as compared to that of the contact portion71b. Therefore, the contact portion73bcontacts with the sheet upstream more than the contact portion71bin the sheet feed direction D. In other words, the contact portion73bprojects upstream more than the contact portion71bin the insert direction of the sheet inserted in the sheet feed direction D, i.e., toward the supporting surface50a, in a state in which the flag portion71cis positioned at a standby position. In a state in which no sheet is loaded in the sheet feed tray50and the contact portions71band73bcontact with no sheet, the flag portion71cis positioned at the standby position and does not shade the optical path of the photo-interrupter61. Due to that, the photo-interrupter61outputs an L level signal.

When the sheet is inserted into the leading edge butting portion53of the sheet feed tray150(seeFIG. 5A) and the contact portion71bis pressed by the sheet as illustrated in FIG.6B, the flag portion71cpivots by a first pivot angle from the standby position. At this time, the flag portion71cshades the optical path of the photo-interrupter61, and the photo-interrupter61outputs an H level signal.

When the contact portion73bis pressed by a sheet as illustrated inFIG. 6C, the flag portion71cpivots from the standby position by a second pivot angle which is greater than the first pivot angle. At this time, because the flag portion71cpivots by exceeding the position of shading the optical path of the photo-interrupter61, i.e., the position as indicated inFIG. 6B, the photo-interrupter61outputs an L level signal. That is, the photo-interrupter61transits in order of the first state, the second state and the third state as the flag portion71cpivots as described above. In a case where all sheets are drawn out of the sheet feed tray50or no sheet is left in the sheet feed tray50, the sensor flags71and72return to their original positions as indicated inFIG. 5Bby their own weights or by an urging member such as a spring.

Detection of Sheet Size

Next, a method for detecting the small size, middle size and large size sheets, like the comparative example described above, will be described. As illustrated inFIG. 7, the small size, middle size and large size sheets are aligned by the side regulating plates51and52such that a widthwise center of the sheets coincides with the center line50C. The middle size sheet serving as a second size sheet is longer, in terms of the width direction W, than the small size sheet serving as a first size sheet. The large size sheet serving as a third size sheet is longer, in terms of the width direction W, than the middle size sheet.

Then, the contact portion71bis disposed at the first position where the contact portion71bcan contact with the small size, middle size and large size sheets. That is, the first position where the contact portion71bis positioned is distant from the center line50C by a first distance d1which is a distance of a half or less of a width of the small size sheet. The contact portion72bis disposed at a second position where the contact portion72bcan contact with the middle size and large size sheets and is unable to contact with the small size sheet. That is, the contact portion72bis disposed at a position distant from the center line50C by a second distance d2which is a distance more than a half of the width of the small size sheet and a half or less of a width of the middle size sheet. The second distance d2is greater than the first distance d1.

The contact portion73bis disposed at a third position where the contact portion73bcan contact with the large size and is unable to contact with the small size and middle size sheets. That is, the contact portion73bis disposed at a position distant from the center line50C by a third distance d3which is a distance more than a half of the width of the middle size sheet and a half or less of a width of the large size sheet. The third distance d3is greater than the second distance d2.

By arranging the sensor flags71and72and the photo-interrupters61and62as described above, the photo-interrupters61and62output signals in four states described later as indicated in Table inFIG. 8. That is, in a non-sheet state in which no sheet is loaded in the sheet feed tray50and no sheet is disposed at the first, second and third positions, the photo-interrupters61and62output L level signals, respectively.

In a state in which the small size sheet is loaded in the sheet feed tray50and in which the sheet is disposed at the first position and no sheet is disposed at the second and third positions, the photo-interrupter61outputs an H level signal and the photo-interrupter62outputs an L level signal. In a state in which the middle size sheet is loaded in the sheet feed tray50and in which the sheet is disposed at the first and second positions and no sheet is disposed at the third position, the photo-interrupters61and62output H level signals.

In a state in which the large size sheet is loaded in the sheet feed tray50and in which the sheet is disposed at the first, second and third positions, the photo-interrupter61outputs an L level signal and the photo-interrupter62outputs an H level signal. As compared to the comparative example described with reference toFIG. 4and in the case where the large size sheet is loaded, while the photo-interrupter161outputs the H level signal, the photo-interrupter61of the present embodiment outputs the L level signal. It is because the flag portion71cpivots exceeding the optical path of the photo-interrupter61in a case where the sheet is inserted into the leading edge butting portion53and the contact portion73bis pressed by the leading edge of the sheet.

In the four states as described above, it is possible to detect the size of the sheet loaded in the sheet feed tray50and the non-sheet state by outputting the signals outputted from the photo-interrupters61and62to the control unit200(seeFIG. 1). Still further, because the contact portions71b,72band73bcontact directly with the sheet loaded in the sheet feed tray50and pivot the flag portions71cand72c, the sheet will not be erroneously detected even if the user forgets to operate the side regulating plates51and52. Still further, the two photo-interrupters61and62are used in the present embodiment in detecting the four states described above, so that it is possible to reduce by one photo-interrupter, thus cutting costs as compared to the comparative example described above. Still further, as compared to a case where the pivot shaft, the contact portion and the flag portion are provided respectively for one photo-interrupter, this arrangement makes it possible to omit the pivot shaft, the bearing and the flag portion, thus cutting costs.

Note that while the contact portions71b,72band73bare all disposed at one widthwise side of the center line50C in the present embodiment, the present disclosure is not limited to such arrangement. For instance, as illustrated inFIG. 9, the contact portions71band72bmay be disposed at one widthwise side of the center line50C and the contact portion73bmay be disposed at another widthwise side of the center line50C. Still further, as illustrated inFIG. 10, the contact portions71band73bmay be disposed at one widthwise side of the center line50C and the contact portion72bmay be disposed at another widthwise side of the center line50C.

Second Embodiment

Next, a second embodiment of the present disclosure will be described. The second embodiment is different from the first embodiment in that sheet aligning positions are different in terms of the sheet widthwise direction. Therefore, the same components with those of the first embodiment will not be illustrated or will be described by denoting the same reference numerals.

As illustrated inFIG. 11, a sheet feeding unit230serving as a sheet detecting apparatus of the present embodiment includes a sheet feed tray90, a detection unit60, a side regulating plate91and a reference wall92. The reference wall92serving as a second regulating member is a fixed member provided on a frame of the sheet feed tray90or the printer100. The reference wall92includes a butting surface92aagainst which one widthwise end portion of a sheet butts. The side regulating plate91serving as a first regulating member is supported movably in the width direction W and regulates a position of another widthwise end portion of the sheet whose one end portion is butting against the butting surface92a. That is, the side regulating plate91is provided to be movable in the width direction W with respect to a supporting surface of the sheet feed tray90, and the reference wall92is provided to be unmovable with respect to the supporting surface of the sheet feed tray90.

As illustrated inFIG. 12, small size, middle size and large size sheets are aligned in a condition in which the one widthwise end portion of the sheet butts against the reference wall92by the reference wall92and the side regulating plate91.

Then, the contact portion71bis disposed at a first position where the contact portion71bis configured to contact with the small size, middle size and large size sheets. That is, the first position where the contact portion71bis positioned is a position distant from the reference wall92by a fourth distance d4which is a distance less than a width of the small size sheet. The contact portion72bis disposed at a second position where the contact portion72bis configured to contact with the middle size and large size sheets and is uncontactable with the small size sheet. That is, the second position where the contact portion72bis positioned is a position distant from the reference wall92by a fifth distance d5which is a distance more than the width of the small size sheet and less than a width of the middle size sheet. The fifth distance d5is greater than the fourth distance d4.

The contact portion73bis disposed at a third position where the contact portion73bis configured to contact with the large size sheet and is uncontactable with the small size and middle size sheets. That is, the third position where the contact portion73bis positioned is a position distant from the reference wall92by a sixth distance d6which is a distance more than the width of the middle size sheet and less than the width of the large size sheet. The sixth distance d6is greater than the fifth distance d5. Since the method for detecting the sheet size is the same with that of the first embodiment, its description will be omitted here.

As described above, it is possible to directly detect the sheet and to reduce erroneous detection also in a mode of loading the sheet while butting against the reference wall92. It is also possible to cut costs because the three types of sheet sizes and the non-sheet state by the two photo-interrupters.

Note that although the contact portions71b,72band73bhave been disposed at widthwise different positions to detect the sheet size based on the width of the sheet in any embodiments described above, the present disclosure is not limited to such arrangement. That is, the contact portions71b,72band73bmay be disposed at positions different from each other in a direction along a plane direction of the supporting surface50aof the sheet feed tray50as long as they are contactable respectively with different size sheets. For instance, the contact portions71b,72band73bmay be disposed at positions different in the sheet feed direction D to detect the sheet sizes based on lengths in the sheet feed direction D of the sheets. Still further, the insert direction of the sheet inserted toward the supporting surface50aand the sheet feed direction D may not be parallel from each other and may intersect with each other. For instance, the sheet insert direction may be orthogonal to the sheet feed direction D.

Still further, while the flag portions71cand72chave been disposed such that the photo-interrupters61and62are not shaded in a state in which the contact portions of the sensor flags71and72are not pressed by the sheet in any of the embodiments described above, the present disclosure is not limited to such arrangement. That is, it is also possible to arrange such the flag portions71cand72cshade the photo-interrupters61and62in a natural state. At this time, it is preferable to provide the flag portions capable of shading the photo-interrupter61at two circumferentially different positions.

Still further, while the sensor flags71and72have included the pivot shafts71aand72arespectively in any embodiments described above, the present disclosure is not limited to such arrangement. For instance, the sensor flags71and72may respectively include bearings capable of pivotally supporting a pivot shaft extending from the frame of the printer100or the sheet feed tray50, and the contact portion and the flag portion may be fixed to the bearing.

While the interrupter which is a transmission type photo-sensor has been used in any of the embodiments described above, the present disclosure is not limited to such arrangement. For instance, a reflection type photo-sensor including a light receiving element receiving light reflected by a flag portion may be used, and a magnet sensor or a contact type sensor may be used instead of the optical sensor.

Still further, while the sheet feed tray50of a type not drawn out of the printer100has been used in any of the embodiments described above, the present disclosure is not limited to such arrangement. For instance, the present disclosure is also applicable to a cassette that can be drawn out of and attachable to the printer100, to a large volume deck connected to a side surface of the printer100and others. In this case, the detection unit60is disposed within the printer body100A (seeFIG. 1).

Still further, while the description has been made by exemplifying the detection unit detecting the respective states in which the thee size sheets are loaded and the non-sheet state in any of the embodiments described above, the present disclosure is not limited to such arrangement. For instance, the present disclosure is applicable to any arrangement in which n−1 photo-sensors are provided to detect n kinds (n>0) of sizes of sheets.

Still further, while the description has been made by using the electro-photographic printer100in any of the embodiments described above, the present disclosure is not limited to such arrangement. For instance, the present disclosure is applicable also to an ink jet type image forming apparatus configured to form an image on a sheet by discharging ink droplet from a nozzle.

OTHER EMBODIMENTS

This application claims the benefit of Japanese Patent Application No. 2018-231966, filed Dec. 11, 2018, which is hereby incorporated by reference herein in its entirety.