Patent Description:
Various image forming apparatuses handling a sheet roll are known to include a sheet feeding mechanism that performs a sheet feeding operation, after a user manually has inserted the leading end of a sheet roll into a sheet feeder and after the image forming apparatus has detected the leading end of the sheet roll.

When a known image forming apparatus performs a sheet feeding operation, a user takes time to insert the leading end of a sheet roll manually into the sheet feeder. When feeding the sheet roll, the leading end of the sheet roll that was inserted obliquely into the sheet feeder causes skew of the orientation of the sheet roll, resulting in making a service call.

Further, for example, PTL (<CIT>) discloses a technique that an image forming apparatus includes a sensor that changes the output value according to the distance to the sheet. The image forming apparatus causes a sheet roll to rotate in a sheet winding direction to separate a sheet from the sheet roll, so that the sensor then detects the leading end of the sheet stripped off or separated from the sheet roll. However, since the separation state of the sheet changes due to the thickness, stiffness, and the curling state of the sheet, the inconvenience that the output value of the sensor becomes unstable is not eliminated. Documents <CIT> and <CIT> are also relevant prior art documents which disclose printing apparatuses comprising means to detect the leading edge.

A sheet feeding device that reliably detects and conveys the leading end of a sheet of a sheet roll to a sheet feeder is disclosed in claim <NUM>, and an image forming apparatus incorporating the sheet feeding device is disclosed in claim <NUM>.

According to an aspect of the present disclosure, a sheet feeding device includes a sensor, a roller, and a support on which the sensor and the roller are disposed. The support supports the sensor and the roller so that the sensor and the roller contact a surface of the sheet roll The sensor and the roller face toward an axial center of the sheet roll. The roller is spaced apart from the sensor in a circumferential direction of the sheet roll. The sensor has a detection accuracy capable of detecting a step at a leading end of the sheet roll.

According to the present disclosure, the leading end of a sheet of a sheet roll is detected reliably and is conveyed to a sheet feeder.

The accompanying drawings are intended to depict example embodiments of the present disclosure and should not be interpreted to limit the scope thereof.

Now, a description is given of a sheet feeding device according to the present disclosure and an image forming apparatus according to the present disclosure, with reference to the drawings.

Further, in the drawings, the same reference numerals are given to same components and corresponding parts having the same configurations or functions, and redundant description thereof will be omitted.

A sheet feeding device according to an embodiment of the present disclosure feeds a sheet from a sheet roll. The sheet roll is a recording medium around which a long sheet (also referred to as a "sheet") is wound in a roll shape.

A description is given of an example of the configuration of an image forming apparatus to which a sheet feeding device according to an embodiment of the present disclosure is applied, with reference to <FIG> and <FIG>.

The image forming apparatus that is an aspect of an embodiment of the present disclosure is an inkjet printer that prints on a recording medium by discharging ink droplets corresponding to the image data but the configuration of the image forming apparatus is not limited to the inkjet printer. For example, the present disclosure may be applied to an image forming apparatus employing an electrophotographic method to convey and print a recording medium such as a copier and a printing machine.

<FIG> is a perspective view illustrating an example of the schematic configuration of an image forming apparatus <NUM> according to an embodiment of the present disclosure. <FIG> is a cross-sectional side view illustrating the configuration of the image forming apparatus of <FIG>. A description is given of the overall configuration and operations of the image forming apparatus <NUM> according to an embodiment of the present disclosure, with reference to <FIG> and <FIG>. In <FIG>, arrow X indicates the depth direction (front-back direction) of the image forming apparatus <NUM> (hereinafter, X direction), arrow Y indicates the width direction (main scanning direction) of the image forming apparatus <NUM> (hereinafter, Y direction), and arrow Z indicates the vertical direction (up-down direction) of the image forming apparatus <NUM> (hereinafter, Z direction).

In <FIG>, the image forming apparatus <NUM> is a serial-type image forming apparatus of a liquid discharge method (ink discharge method) and has a housing <NUM> and a housing frame <NUM>. The housing <NUM> is mounted on the housing frame <NUM>. In the image forming apparatus <NUM>, a main guide rod <NUM> and a sub guide rod <NUM> are bridged over in the housing <NUM>, in the main scanning direction corresponding to the Y direction indicated by bidirectional arrow in <FIG>. The main guide rod <NUM> movably supports a carriage <NUM> that includes a connection piece 66a that engages with the sub guide rod <NUM> to stabilize the posture of the carriage <NUM>.

The image forming apparatus <NUM> includes a timing belt <NUM> along the main guide rod <NUM>. The timing belt <NUM> is an endless belt that is stretched between a drive pulley <NUM> and a driven pulley <NUM>. The drive pulley <NUM> is driven and rotated by a main scanning motor <NUM>. The driven pulley <NUM> is disposed in a state in which the driven pulley <NUM> applies a predetermined stretching amount to stretch the timing belt <NUM> taut. As the main scanning motor <NUM> drives to rotate the drive pulley <NUM>, the drive pulley <NUM> rotates the timing belt <NUM> in the main scanning direction according to the rotational direction of the drive pulley <NUM>.

The carriage <NUM> is coupled to the timing belt <NUM>. As the drive pulley <NUM> rotates to move the timing belt <NUM> in the main scanning direction, the carriage <NUM> reciprocally moves in the main scanning direction along the main guide rod <NUM>.

The image forming apparatus <NUM> further includes a cartridge holder <NUM> and a maintenance unit <NUM>. The cartridge holder <NUM> and the maintenance unit <NUM> are detachably attached (stored) to one end of the housing <NUM> in the main scanning direction (Y direction). The cartridge holder.

<NUM> holds cartridges <NUM> that contain inks of respective colors, which are yellow (Y), magenta (M), cyan (C), and black (K). Each cartridge <NUM> is replaceably stored in the cartridge holder <NUM>. The carriage <NUM> has recording heads of respective colors, which are yellow (Y), magenta (M), cyan (C), and black (K). Each cartridge <NUM> of the cartridge holder <NUM> is coupled with the recording head of the corresponding color, via a pipe. According to this configuration, ink is supplied from the cartridges <NUM> of the cartridge holder <NUM> to the recording heads of the respective colors via the pipe.

In the image forming apparatus <NUM>, while the carriage <NUM> moves in the main scanning direction, the recording heads provided in the carriage <NUM> discharge ink droplets of respective colors onto the sheet P that is conveyed intermittently on a platen (plate) <NUM> (see <FIG>) in a sub-scanning direction (X direction indicated by arrow in <FIG>) orthogonal to the main scanning direction. By so doing, the image forming apparatus <NUM> records an image on a sheet P.

The sheet P is not limited to a paper sheet but may be various types of sheets such as a roll-type film. In order to clarify the description, hereinafter, a sheet during sheet conveyance is referred to as the sheet P, the sheet P in a roll shape is referred to as a sheet roll Pr (Pa, Pb), and a core tube (core portion) of the sheet roll Pr is referred to as a core tube Ps.

As illustrated in <FIG>, the image forming apparatus <NUM> further includes a chamber <NUM> provided with a fan. The chamber <NUM> is disposed below the platen <NUM>. As the fan of the chamber <NUM> is driven, the sheet P is conveyed on the platen <NUM> while the sheet P is closely contacting the platen <NUM>.

The image forming apparatus <NUM> intermittently conveys the sheet P in the sub-scanning direction. Then, while the conveyance of the sheet P in the sub-scanning direction is stopped, as the carriage <NUM> moves in the main scanning direction, ink droplets are discharged from the nozzle row of each recording head provided on the carriage <NUM> onto the sheet P on platen <NUM>. By so doing, an image is formed (recorded) on the sheet P in a roll shape.

The maintenance unit <NUM> performs maintenance of the recording head, such as cleaning of the ink discharging face of the recording head, capping the recording head, and discharging (removing) ink that is not used. By so doing, the maintenance unit <NUM> discharges (removes) unnecessary ink from the recording head and maintains the reliability of the recording head.

The image forming apparatus <NUM> further includes an encoder sheet over at least the moving range of the carriage <NUM> in parallel to the timing belt <NUM> and the main guide rod <NUM>. The carriage <NUM> includes an encoder sensor that reads the encoder sheet. The image forming apparatus <NUM> controls the driving of the main scanning motor <NUM> based on the sensing result of the encoder sensor obtained by reading the encoder sheet, so as to control the movement of the carriage <NUM> in the main scanning direction.

Further, a reflective sensor (e.g., an encoder sensor and a sheet leading end detection sensor) mounted on the carriage <NUM> detects both lateral side ends of the sheet P conveyed to an image forming device <NUM>. At that time, the size of the sheet P is detected according to the positions of the lateral side ends of the sheet P in the main scanning direction that is read by the sheet leading end detection sensor.

As illustrated in <FIG> and <FIG>, the image forming apparatus <NUM> further includes two spool bearing bases 5a and 5b on the housing frame <NUM> supported by the housing <NUM> of the image forming apparatus <NUM>. The spool bearing bases 5a and 5b are disposed vertically, that is, in the vertical direction (Z direction) of <FIG> and <FIG>.

As illustrated in <FIG> and <FIG>, the sheet rolls Pr are set on the spool bearing bases 5a and 5b. To be more specific, as illustrated in <FIG>, the sheet roll Pa is set on the spool bearing base 5a and the sheet roller Pb is set on the spool bearing base 5b. As the sheet P (in a roll shape) is drawn from the leading end of the sheet rolls Pa set on the spool bearing base 5a or the leading end of the sheet roller Pb set on the spool bearing base 5b, the sheet P is conveyed by pairs of sheet conveying rollers 6a and 6b, a registration roller <NUM>, and a registration pressure roller <NUM> in a corresponding one of sheet conveyance passages <NUM>, as indicated by arrows in <FIG>.

A controller <NUM> controls drive devices 7a and 7b to rotate the pairs of sheet conveying rollers 6a and 6b, the registration roller <NUM>, and the registration pressure roller <NUM>.

Sheet roll receiving bases 8a and 8b are disposed below the sheet roll Pr (i.e., the sheet rolls Pa and Pb) to prevent the sheet roll Pr from falling from the spool bearing bases 5a and 5b.

The sheet P passes through the corresponding one of the sheet conveyance passages <NUM> that are supported and partly defined by respective medium conveyance guides 18a and 18b. Then, the sheet P is conveyed to the platen <NUM> in the image forming device <NUM>. Note that, in a case in which a duplex printing is performed to form images on both faces (both sides) of the sheet P, the sheet P is reversed in a sheet reverse unit <NUM> to reverse the front face to the back face of the sheet P.

In the image forming device <NUM>, the recording heads that contain respective colors of inks discharge the ink droplets (liquid) of respective colors onto the sheet P according to image data, so that the image forming device <NUM> forms an image on the sheet P. A cutter <NUM> is disposed at the sheet ejection portion in the normal direction T of the sheet conveyance direction (positive X direction in <FIG>) of the sheet P on which an image is formed. The cutter <NUM> extends in the sub-scanning direction (i.e., sheet width direction and Y direction) to cut the continuous sheet P to the predetermined length of the sheet P.

In order to align the leading end of the sheet P that is a continuous sheet fed from the sheet roll Pr, the cutter <NUM> is fixed to a wire or a timing belt wound around or stretched between a plurality of pulleys. One of the plurality of pulleys is coupled with the drive motor. As the drive motor drives and conveys the continuous sheet P in the main scanning direction (i.e., Y direction), the sheet P is cut to the predetermined length. The cut sheet P is ejected to the sheet ejection portion.

Note that <FIG> and <FIG> depict the configuration example of the image forming apparatus having the configuration in which the sheet rolls Pa and Pb are set to the two spool bearing bases 5a and 5b. However, the configuration of the image forming apparatus to which the present disclosure is applicable is not limited to the above-described configuration. For example, the image forming apparatus may be provided with one spool bearing base. Further, in the above description, the parts and components related to the two sheet rolls Pa and Pb are distinguished by describing with the suffixes "a" and "b" (for example, the spool bearing bases 5a and 5b). Hereinafter, the suffixes "a" and "b" are omitted, except when the parts and components may need to be distinguished.

Here, a description is given of a comparative method of setting a sheet roll.

<FIG> are diagrams each for explaining a comparative method of setting a sheet roll.

A flange (flange member) <NUM> is set at both ends in the width direction of the sheet roll Pr, so that each spool <NUM> (spools 1a and 1b) is set to the flange <NUM>. A user sets the sheet roll to which the spool <NUM> (or spools 1a and 1b) is set, to a sheet feeder receiver (spool bearing base) of the image forming apparatus (see <FIG>). After finding the leading end of the sheet roll, the user holds the sheet roll while keeping (without losing) the leading end of the sheet roll by both hands, as illustrated in <FIG>. Then, the user rotates the sheet roll to cause the leading end of the sheet to come to face the user (in other words, to the front side of the image forming apparatus <NUM>. Then, the user places the leading end of the sheet at the position between the guide plates disposed behind the sheet roll and inserts the leading end of the sheet while rotating the sheet roll (see <FIG>). The guide plates include an upper guide plate and a lower guide plate, each made of a transparent material, so that the sheet can be seen through the guide plates. The user rotates the sheet roll toward the far side of the image forming apparatus <NUM> to cause the leading end of the sheet roll to come to the upper part of the lower guide plate. As the user inserts the sheet roll into the far side behind the lower guide plate, the sheet roll is fixed inside the housing of the image forming apparatus and drawn to the inside of the image forming apparatus.

As illustrated in <FIG>, since the guide plate into which the leading end of the sheet is inserted is located behind the sheet roll, the guide plate is hidden by the sheet roll and is difficult to see from the front side of the image forming apparatus. Further, since the guide plates are made of a transparent material, even when the user thinks the sheet is inserted between the two guide plates, the sheet may be actually placed on the top of the upper guide plate, which may cause the user to place the sheet on the correct position again. Further, when the guide plates are not made of a transparent material, it is difficult to confirm whether the sheet is inserted between the two guide plates.

In addition, the leading end of the sheet roll needs to be inserted evenly as possible, and therefore the user has to be careful. Furthermore, in a case in which the leading end of the sheet is not inserted evenly, the sheet in this uneven state may be fed obliquely, resulting in skew. Therefore, the operation may be performed again to prevent occurrence of a paper jam.

Further, as illustrated in <FIG>, in the image forming apparatus in which the sheet rolls are disposed vertically in two steps, there may be a case that a sheet roll is to be set on the lower step while another sheet roll has already been set on the upper step. In such a case, even when the leading end of the sheet roll is to be inserted between the guide plates, due to the sheet roll that has already been set on the upper step, it is further difficult to see the guide plates, and therefore may increase the difficulty in setting the sheet roll and the chances of the oblique insertion of the sheet.

In order to address this inconvenience, the sheet feeding device according to an embodiment of the present disclosure has a configuration in which the leading end of the sheet of the sheet roll is detected. By detecting the difference of step (height) of the leading end of the sheet, the leading end of the sheet P is detected, and therefore the sheet is fed to the sheet feeder (sheet feeding portion). The sheet feeder is a unit to supply the sheet of the sheet roll to a supplying target. For example, the sheet feeder is the pair of sheet conveying rollers <NUM> or the sheet conveyance passage <NUM> illustrated in <FIG>.

<FIG> is a side view illustrating the main part of a configuration example of a sheet feeding device according to an embodiment of the present disclosure, included in the image forming apparatus <NUM> of <FIG>.

The sheet feeding device <NUM> includes at least an arm <NUM>, a roller <NUM>, a sensor <NUM>, and the pair of sheet conveying rollers <NUM> that functions as a sheet conveyor. It is more preferable that the sheet feeding device <NUM> further includes an entrance guide plate <NUM>.

In <FIG>, the broken line indicates the position of the sheet roll Pr when the user sets the sheet roll Pr in the sheet feeding device <NUM>. The sheet roll Pr is rotatably held by a module component, based on the center (shaft) of the sheet roll Pr.

The arm (guide plate) <NUM> functions as a support of the sheet roll Pr and is rotatable about the rotation center <NUM>. The arm <NUM> is pressed against one end of the axis of the rotation center <NUM> toward the sheet roll Pr by a biasing member such as a spring. Accordingly, the arm <NUM> contacts the outer diameter of the sheet roll Pr even when the diameter of the sheet roll Pr changes. The white arrows indicate the moving direction of the arm <NUM>, to be more specific, the rotational direction of the arm <NUM>.

Further, the arm <NUM> has a roller <NUM> and a sensor <NUM> on the opposite end of the axis of the rotation center <NUM>. Since the arm <NUM> is pressed toward the sheet roll Pr, the roller <NUM> and the sensor <NUM> are supported to come into contact with the surface of the sheet roll Pr.

The arm <NUM> acts as a guide plate to guide the sheet P stripped off or separated from the sheet roll Pr in the sheet conveyance direction. The arm <NUM> may have a shape along the outer diameter of the sheet roll Pr (e.g., arc shape) at the portion (end portion) to which the sheet roll Pr is set. According to the shape of the arm <NUM>, when the sheet roll Pr is set, the sheet roll Pr is reliably held (without falling). The arm <NUM> also functions as the sheet roll receiving table <NUM> illustrated in <FIG>.

The arm <NUM> as a support also functions as a guide plate to guide the sheet roll Pr, so that the number of parts and components is reduced, thereby restraining the cost.

The roller <NUM> and the sensor <NUM> are disposed facing substantially the center of the sheet roll Pr, in other words, toward the axial center of the sheet roll Pr, regardless of the diameter of the sheet roll Pr.

The roller <NUM> is spaced apart from the sensor <NUM> in the circumferential direction of the sheet roll Pr, so that the roller <NUM> and the sensor <NUM> are disposed at offset positions (different positions) from each other in the circumferential direction of the sheet roll Pr.

The sensor <NUM> has the detection accuracy capable of detecting a step (thickness) at the leading end of the sheet roll Pr.

The entrance guide plate <NUM> guides the sheet P that has been stripped off or separated from the sheet roll Pr, in the sheet conveyance direction. In the configuration example of <FIG>, when the sheet P is fed in the sheet feeding operation (with the normal rotation of the sheet roll Pr), the arm <NUM> that functions as a guide plate guides the sheet P on the upstream side in the sheet conveyance direction and the entrance guide plate <NUM> guides the sheet P on the downstream side in the sheet conveyance direction. In other words, the arm <NUM> is disposed upstream from the entrance guide plate <NUM> in the rotational direction of the sheet roll in the sheet feeding operation.

Next, a description is given of the control of the function of the sheet feeding device <NUM>.

<FIG> is a functional block diagram illustrating an example of the functions of the sheet feeding device according to an embodiment of the present disclosure.

A controller <NUM> executes the overall control of the sheet feeding device <NUM>. Note that <FIG> illustrates the functional block in which the controller <NUM> controls the sensor <NUM> and motor drive circuits <NUM> and <NUM> and the other function blocks are omitted. The functions of the controller <NUM> may be executed by the controller <NUM> (see <FIG>) that controls the overall control of the image forming apparatus <NUM>.

The controller <NUM> includes, for example, a central processing unit (CPU), a random access memory (RAM), and a read only memory (ROM).

The CPU executes various programs and controls the entire image forming apparatus <NUM> based on arithmetic processing and control programs.

The RAM is a volatile storage medium to read and write information at high speed and functions as a work area when the CPU executes a program.

The ROM is a read-only nonvolatile storage medium in which various programs and control programs are stored.

The motor drive circuit <NUM> drives the motor under the control by the controller <NUM> to drive a sheet roll driver <NUM>.

The sheet roll driver <NUM> rotates the sheet roll Pr in the normal direction or the reverse direction. The sheet roll driver <NUM> includes a sheet roll rotation motor, for example.

The motor drive circuit <NUM> drives the motor under the control by the controller <NUM> to drive a sheet conveyance driver <NUM>.

The sheet conveyance driver <NUM> drives a sheet conveyor <NUM>.

The sheet conveyor <NUM> is a sheet conveyor that conveys the sheet P, for example, the pair of sheet conveying rollers <NUM>.

Next, a description is given of the operation example to set the sheet roll Pr. <FIG> is a flowchart illustrating an operation example to set the sheet roll in the sheet feeding device according to an embodiment of the present disclosure.

When the controller <NUM> detects that the sheet roll Pr is set to the sheet feeding device <NUM>, for example, based on the detection result of the sensor <NUM> (step S11), the controller <NUM> controls the motor drive circuit <NUM> to cause the sheet roll driver <NUM> to rotate the sheet roll Pr in the reverse direction. The controller <NUM> turns on the sheet roll rotation motor (sheet roll driver <NUM>) to rotate the sheet roll Pr in a direction to wind the sheet in the sheet reverse operation, in other words, to perform a reverse rotation (step S12). Then, the sensor <NUM> starts to perform detection of the leading end of the sheet roll Pr (step S13). As the sensor <NUM> detects the leading end of the sheet roll Pr, the controller <NUM> turns off the motor drive circuit <NUM> to stop the sheet roll rotation motor at the sheet leading end stop position (step S14), and then turns on the sheet roll rotation motor to rotate the sheet roll Pr in the normal direction (normal rotation) in the sheet conveyance direction to feed the leading end of the sheet roll Pr in the sheet conveyance direction (step S15). The motor drive circuit <NUM> rotates the sheet conveyor <NUM> to convey the leading end of the sheet P into the inside of the motor drive circuit <NUM> (step S16).

Next, a description is given of the configuration example of the arm <NUM> as a support and an operation example of detection of the leading end of the sheet roll.

<FIG> are diagrams each illustrating a configuration example of the arm <NUM> according to an embodiment of the present disclosure. Specifically, <FIG> is a perspective view illustrating an example of the arm <NUM>, <FIG> is a schematic diagram illustrating the external appearance of the sensor <NUM>, and <FIG> is a side view illustrating an example of an actuator and a side plate, each included in the sensor <NUM>.

In the operation in which the sensor <NUM> detects the leading end of the sheet roll (reverse rotation), the roller <NUM> is disposed on the upstream side of the arm <NUM> in the sheet conveyance direction and the sensor <NUM> is disposed on the downstream side of the arm <NUM> in the sheet conveyance direction. In other words, the sensor <NUM> is disposed downstream from the roller <NUM> in the sheet conveyance direction, i.e., the rotational direction of the sheet roll Pr.

The sensor <NUM> includes an encoder sensor that includes, for example, an actuator <NUM> and a slit <NUM> in the actuator <NUM>. The actuator <NUM> is disposed between two side plates <NUM> that construct the sensor housing. A shaft <NUM> is fitted into a bearing of the side plates <NUM> and rotates about the shaft <NUM>. The actuator <NUM> has an asymmetrical shape centered on the shaft <NUM>, for example, as illustrated in <FIG>.

The sensor <NUM> has a light emitting portion and a light receiving portion. The number of lights passing from the light emitting portion to the light receiving portion through the slits <NUM> of the actuator <NUM> is counted, in other words, the number of signal waveforms are counted, so that the leading end of the sheet roll Pr is detected.

In the configuration example of <FIG>, there are two rollers <NUM> and the sensor <NUM> is disposed between the two rollers <NUM>. By disposing the sensor <NUM> between the rollers <NUM>, the lifting of the leading end of the sheet roll Pr is pressed reliably. By so doing, the output of the sensor <NUM> is not varied according to the state of the thickness, stiffness, and curling of the sheet, and therefore the leading end of the sheet is detected reliably. Further, since each roller <NUM> and the sensor <NUM> are disposed offset from each other in the circumferential direction of the sheet roll, even if there is a partial scratch, for example, it is less likely that the scratch is extended on both the roller <NUM> and the sensor <NUM>. Therefore, it is difficult to generate misdetection of the leading end of the sheet P.

In the following description, two or more rollers <NUM>, in other words, the plurality of rollers, are also referred to as roller portions.

<FIG> are diagrams each illustrating an embodiment of an operation of detecting the leading end of the sheet roll Pr. <FIG> are diagrams each for explaining a difference due to the position of the roller <NUM> relative to the sensor <NUM>.

<FIG> illustrate states in which the leading end of the sheet roll Pr passes the roller <NUM> and the sensor <NUM>. To be more specific, <FIG> is the state before the leading end of the sheet roll Pr passes the rollers <NUM>, <FIG> is the state after the leading end of the sheet roll Pr has passed the rollers <NUM> and before the leading end of the sheet roll Pr passes the sensor <NUM>, and <FIG> is the state after the leading end of the sheet roll Pr has passed the sensor <NUM>.

<FIG> illustrate states in the detection of the leading end of the sheet roll Pr to indicate the difference in occurrence of slack of the sheet roll Pr. To be more specific, <FIG> is the state in which the rollers <NUM> are disposed downstream from the sensor <NUM> in the sheet conveyance direction, and <FIG> is the state in which the rollers <NUM> are disposed upstream from the sensor <NUM> in the sheet conveyance direction.

The sensor <NUM> and the rollers <NUM> are disposed close to each other and offset from each other, in other words, disposed offset in the circumferential direction of the sheet roll Pr. According to this configuration, since the rollers <NUM> are disposed upstream from the sensor <NUM> in the sheet conveyance direction, the roller <NUM> presses the leading end of the roll sheet Pr immediately before the sensor <NUM> detects the leading end of the sheet roll Pr (<FIG>). According to this configuration, while the tip end of the sensor <NUM> is in close contact with the surface of the sheet roll Pr, as illustrated in <FIG>, the sensor <NUM> detects the step (thickness) of the surface of the sheet roll Pr as the leading end of the sheet roll Pr. Accordingly, the output of the sensor <NUM> (i.e., the detection result of the sensor <NUM>) is not varied according to the state of the thickness, stiffness, and curling of the sheet, and therefore the sensor <NUM> detects the leading end of the sheet roll Pr reliably.

Note that the roller <NUM> (or the rollers <NUM>) is disposed upstream from the sensor <NUM> in the sheet conveyance direction in the example of the present embodiment but the leading end of the sheet roll Pr may be detected with a configuration in which the rollers <NUM> and the sensor <NUM> are disposed in the opposite positions, as illustrated in <FIG>. However, it is preferable that the roller <NUM> is disposed upstream from the sensor <NUM> so that the lifting of the leading end of the sheet roll Pr is pressed more reliably until immediately before the detection of the leading end of the sheet roll Pr.

Further, since two rollers <NUM> are provided and the sensor <NUM> is disposed between the rollers <NUM> as illustrated in <FIG>, when compared to the configuration having one roller <NUM>, the lifting of the leading end of the sheet roll Pr is pressed more reliably.

Further, since the sheet feeding device <NUM> according to an embodiment of the present disclosure has the configuration in which each roller <NUM> and the sensor <NUM> are disposed offset (shifted) from each other in the circumferential direction of the sheet roll Pr, even if there is a partial scratch, for example, it is less likely that the scratch is extended on both the roller <NUM> and the sensor <NUM>. <FIG> are diagrams each illustrating an example of a signal waveform detected by the sensor. To be more specific, <FIG> illustrates an example of a signal waveform when the leading end of the sheet roll is detected and <FIG> illustrates an example of a signal waveform when a projecting streak or scratch is detected.

In a case of the arrangement of the roller <NUM> and the sensor <NUM> as illustrated in <FIG>, in a regular detection of the leading end of the sheet roll Pr (in a case in which the leading end of the sheet P passes), the signal waveform illustrated in <FIG> is formed.

On the other hand, when a strip-shaped projecting streak (scratch) is formed on the surface of the sheet roll Pr, the signal waveform illustrated in <FIG> has a rise and a fall different from the signal waveform of the detection of the leading end of the sheet roll Pr. Therefore, the controller <NUM> distinguishes the detection result of the sensor <NUM> between the signal waveform of the regular detection of the leading end of the sheet roll and the signal waveform of the detection of the scratch, so that the projecting streak (scratch) is rejected as a foreign material (is not the leading end of the sheet roll). Accordingly, detection of the leading end of the sheet roll and the projecting streak (scratch) is hardly performed with error.

Next, a description is given of detection of a recessed streak (concave-shaped scratch). <FIG> is a diagram for explaining a case in which the sheet roll has a recessed streak (scratch) on the surface of the sheet roll.

In a case of a recessed streak (scratch), the shape of the tip end of the sensor <NUM> is generally greater than the recessed streak (scratch) and the edge of the scratch does not have the acute angle as the angle of the leading end of the sheet roll. Therefore, the streak or scratch is not detected. By making the shape of the actuator greater than the recessed streak (scratch), the sensor <NUM> does not detect the recessed streak (scratch), and therefore the detection is not made with error. Accordingly, the detection accuracy is achieved.

According to the configuration illustrated in <FIG>, the leading end of the sheet roll is directly detected. Therefore, the output of the sensor <NUM> (detection result) does not vary according to the state of the thickness, stiffness, or curling of the sheet, and therefore the sensor <NUM> detects the leading end of the sheet roll Pr reliably with the detection accuracy. Further, with a simple operation that a user places the sheet roll placed on the sheet feeding device <NUM>, the setting of the sheet roll is automatically finished. This configuration reduces the manual effort and prevents skew and paper jam caused by a guiding failure.

As described above, the configuration example of the sheet feeding device according to an embodiment of the present disclosure is explained. However, it is preferable that the sensor <NUM> is configured as described below.

<FIG> are diagrams each illustrating a frictional load applied to the surface of the sheet roll when the actuator of the sensor contacts the surface of the sheet roll. When the actuator <NUM> of the sensor <NUM> contacts the surface of the sheet roll, as the sheet roll rotates, the frictional load is generated on the contact portion.

The "normal" direction (normal rotation) illustrated in <FIG> indicates the rotational direction in the sheet feeding operation when the sheet roll Pr is conveyed in the sheet conveyance direction. The "reverse" direction (reverse rotation) illustrated in <FIG> indicates the rotational direction in the detection of the leading end of the sheet roll Pr.

In the "reverse rotation" direction, the "load at the reverse rotation" is generated to the actuator <NUM>, so that a force is applied in a direction in which the actuator <NUM> bites the sheet roll Pr.

On the other hand, in the "normal rotation" direction, when the "load at the normal rotation" is generated to the actuator <NUM>, the actuator <NUM> rotates about a shaft <NUM> as a rotation fulcrum to reduce the load. In other words, the actuator moves in a direction to reduce the load applied to the actuator when the load is generated to the actuator on the contact portion of the actuator and the sheet roll Pr as the sheet roll Pr rotates in the sheet feeding operation.

Here, the detection of the leading end of the sheet roll Pr in the "reverse rotation" direction is an operation when the sheet roll Pr is set to the sheet feeder of the sheet feeding device. When compared with the rotational direction of the sheet roll Pr along with the operations (e.g., the sheet feeding operation and the printing operation) in the "normal rotation" direction, the "normal rotation" direction takes a substantially longer time to perform the operation. When the large force is applied to the actuator <NUM> in the "normal rotation" direction, it is more likely that the operation failure occurs due to damage of the sensor <NUM> and wear of the actuator <NUM>. Therefore, the sheet feeding device has the configuration in which the load is avoided (eliminated) when the sheet roll is rotated in the "normal rotation" direction, so as to prevent the damage and operation failure.

<FIG> is a diagram for explaining an example that the actuator has a tip end that contacts the sheet roll and that is provided with a rotatable roller functioning as a rotary body.

Even when the actuator <NUM> of the sensor <NUM> has the frictional load with the sheet roll Pr, a roller <NUM> rotates to reduce the load to the actuator <NUM>, thereby preventing damage and the operation failure.

Note that this configuration example describes the configuration in which the actuator rotates, but the configuration is not limited to this configuration example. For example, the configuration in which the actuator moves vertically and has the tip end provided with a rotatable roller may be applied to the present disclosure.

Next, a description is given of a variation of a support having the sensor and the roller. While the configuration example illustrated in <FIG> includes the arm <NUM> that functions as a support, the configuration example illustrated in <FIG> includes another support that is different from the arm <NUM> (or the guide plate).

<FIG> is a diagram for explaining an example that the sensor <NUM> and the roller <NUM> are provided near the entrance guide plate <NUM> for sheet conveyance performed by a sheet feeding device 90A.

The sheet feeding device 90A basically has the configuration identical to the configuration of the sheet feeding device <NUM>, except that the sheet feeding device 90A includes an arm 91A instead of the arm <NUM> of <FIG>, and a support <NUM> that holds the sensor <NUM> and the roller <NUM> (or rollers <NUM>). The support <NUM> is disposed near the entrance guide plate <NUM> and upstream from the entrance guide plate <NUM> in the "reverse rotation" direction, in other words, in the direction when the sheet roll Pr rotates in the reverse rotation operation. The arm 91A basically has the structure identical to the structure of the arm <NUM> illustrated in <FIG>, except that the arm 91A does not include the sensor <NUM>.

According to this configuration, immediately after the roller <NUM> (or the rollers <NUM>) and the sensor <NUM>, which are held by the support <NUM>, have detected the leading end of the sheet roll Pr, the leading end of the sheet roll Pr is stopped at the position between the entrance guide plate <NUM> and the arm 91A, so that the leading end of the sheet roll Pr is fed to the pair of sheet conveying rollers <NUM> in the "normal rotation" operation. Accordingly, the normal rotation operation starts in the shortest time from the detection of the leading end of the sheet roll. The support <NUM> is disposed to face toward the substantially center of the sheet roll Pr. According to this configuration, even as the diameter of the sheet roll Pr changes, the support <NUM> is continuously in contact with the surface of the sheet roll Pr.

As described above, since the image forming apparatus that feeds the sheet in a roll shape includes the sheet feeding device according to an embodiment of the present disclosure, with a simple operation that a user sets the sheet roll to the image forming apparatus, the sheet thickness sensor such as the encoder sensor automatically detects the leading end of the sheet roll to convey the leading end of the sheet roll to the sheet feeder of the sheet feeding device. Accordingly, the manual effort taken for setting the sheet roll is omitted and the sheet is inserted into the sheet feeder reliably, and therefore the sheet is prevented from being inserted obliquely or at an angle, into the sheet feeder.

Further, since the sheet feeding device according to an embodiment of the present disclosure detects the leading end of the sheet roll while the leading end of the sheet roll is closely contact with the surface of the sheet roll, the leading end of the sheet roll is detect reliably regardless of the state of the thickness, stiffness, and curling of the sheet. Further, variation in manual insertion of the sheet is eliminated when setting the sheet roll, and therefore the leading end of the sheet roll is inserted into the sheet feeder reliably.

This patent application is based on and claims priority to <CIT> in the Japan Patent Office.

Claim 1:
A sheet feeding device (<NUM>) configured to feed a sheet (P) from a sheet roll (Pr), the sheet feeding device comprising:
a sensor (<NUM>);
a roller (<NUM>); and
a support (<NUM>, <NUM>) on which the sensor and the roller are disposed,
characterized in that:
the support is configured to support the sensor and the roller so that the sensor and the roller contact a surface of the sheet roll,
the sensor and the roller face toward an axial center of the sheet roll,
the roller is spaced apart from the sensor in a circumferential direction of the sheet roll,
the sensor has a detection accuracy capable of detecting a step at a leading end of the sheet roll.