MEDIUM DETECTION MECHANISM AND IMAGE FORMING DEVICE

The image forming device includes a recording paper setting plate on which media are set, a paper end sensor lever, and a print control section that controls the whole of the device. The paper end sensor lever includes a paper contact part for detecting a first condition in which there are no media set on the recording paper setting plate and an arm contact part for detecting a second condition in which the amount of the media set on the recording paper setting plate is smaller than a prescribed amount.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a medium detection mechanism that detects the amount of media set in a medium setting part, and to an image forming device including the medium detection mechanism.

2. Description of the Related Art

Conventionally, there are devices that convey a medium that has been set in a medium setting part and perform image formation on the conveyed medium. Among such devices, there exist devices that enhance the user convenience by displaying a condition such as the amount of media set in the medium setting part. Japanese Patent Application Publication No. 2015-127250 describes a medium conveyance device including a paper detection section.

However, there are cases where it is required to detect the amount of the media set in the medium setting part with a simple structure.

SUMMARY OF THE INVENTION

The object of the present invention, which has been made to resolve the above-described problem, is to detect the amount of the media set in the medium setting part with a simple structure.

A medium detection mechanism according to an aspect of the present invention includes a medium setting part in which media are set; a rotating member having a rotational central shaft, the rotating member being configured to rotate around the rotational central shaft depending on an amount of the media set in the medium setting part; a detection sensor that detects the rotation of the rotating member; a display section that displays a condition of the medium detection mechanism; and a control section that controls the display section. The rotating member includes a first arm part for detecting a first condition in which there are no media set in the medium setting part and a second arm part for detecting a second condition in which the amount of the media set in the medium setting part is smaller than a prescribed amount, and the control section makes a first display indicating that there are no media set in the medium setting part on the display section when the media are judged to be in the first condition based on result of the detection by the detection sensor and makes a second display indicating that the amount of the media set in the medium setting part is smaller than the prescribed amount on the display section when the media are judged to be in the second condition based on the result of the detection by the detection sensor.

An image forming device according to another aspect of the present invention includes the above-described medium detection mechanism.

According to the present invention, the amount of the media set in the medium setting part can be detected with a simple structure.

DETAILED DESCRIPTION OF THE INVENTION

An image forming device according to an embodiment of the present invention will be described below with reference to the accompanying drawings. The image forming device according to the embodiment is a device including a medium detection mechanism that detects the amount of media that have been set in the image forming device. In the following description, a configuration that detects the amount of the media that have been set in the image forming device will be referred to as the medium detection mechanism.

An xyz orthogonal coordinate system is shown in the drawings to facilitate the understanding of the relationship among the drawings. An x-axis in the drawings is shown as a coordinate axis in an axial direction parallel to a width direction of the image forming device. A y-axis in the drawings is shown as a coordinate axis in an axial direction parallel to a depth direction of the image forming device. A z-axis in the drawings is shown as a coordinate axis orthogonal to both the x-axis and the y-axis and parallel to a vertical direction of the image forming device.

In the following description, a paper end condition as a first condition means a condition in which the remaining amount of paper is zero, a near end condition as a second condition means a condition in which the remaining amount of the paper is small (smaller than a prescribed amount), and a paper sufficiency condition as a third condition means a condition in which the remaining amount of the paper is sufficient (larger than or equal to the prescribed amount).

(1) First Embodiment

The configuration of an image forming device100according to a first embodiment of the present invention will be described below with reference toFIG. 1toFIG. 5.FIG. 1is a side view showing the general configuration of the image forming device100according to the first embodiment.FIG. 2is a perspective view showing the general configuration of the image forming device100according to the first embodiment.

The image forming device100conveys recording paper (sheet of paper) along a sheet conveyance path formed substantially in an S-shape and extending from a sheet feed storage cassette230as a starting point to a recording paper stack part210as an end point. As shown inFIG. 1, the image forming device100includes a recording paper setting plate104as a medium setting part, a recording paper setting plate fulcrum105, a spring106as an elastic part, recording paper201, a recording paper feed roller202as a medium conveyance part, first registration rollers203, second registration rollers204, an image forming section205, a fixation unit206, first ejection rollers207, second ejection rollers208, ejected recording paper209, the recording paper stack part210, a sheet feed tray211, a paper end sensor212, an IN sensor213, a WR sensor214, a recording paper conveyance roller215, a recording paper separation roller216, and the sheet feed storage cassette230.

The sheet feed storage cassette230, storing multiple sheets of recording paper201therein in a stacked state, is attached to a lower part of the image forming device100in a detachable manner. Provided over the sheet feed storage cassette230is the recording paper feed roller202that comes in contact with a sheet of recording paper201in the uppermost part of the stack of recording paper201stored in the sheet feed storage cassette230and sends out the recording paper201from the uppermost part. The recording paper201sent out by the recording paper feed roller202is separated from the stack by the recording paper conveyance roller215and the recording paper separation roller216provided as a pair of rollers and is conveyed as an individual sheet along the sheet conveyance path in a conveyance direction.

The recording paper setting plate104is a setting plate arranged in the sheet feed storage cassette230to set the stacked recording paper201. Arranged under the recording paper setting plate104is the spring106, by which the recording paper setting plate104is biased upward. The recording paper setting plate104is capable of tilting depending on the number of sheets of the recording paper201set on the recording paper setting plate104by using the recording paper setting plate fulcrum105as the fulcrum.

The recording paper setting plate104remains in a substantially horizontal state when the number of sheets of the recording paper201set on the recording paper setting plate104is large, and the tilt angle of the recording paper setting plate104increases with the decrease in the number of sheets of the recording paper201set on the recording paper setting plate104. The tilting of the recording paper setting plate104enables the uppermost part of the stacked recording paper201to come in contact with the recording paper feed roller202even when the number of sheets of the recording paper201set on the recording paper setting plate104has decreased. Accordingly, the sheet conveyance is carried out appropriately.

As shown inFIG. 1, the paper end sensor212that detects the position of top layer recording paper201in the stacked recording paper201is placed at the top of the recording paper201stacked in the sheet feed storage cassette230. The paper end sensor212detects the condition in which there is no recording paper201stacked in the sheet feed storage cassette230(paper end condition). As well as detecting the paper end condition of the recording paper201, the paper end sensor212in the first embodiment is capable of detecting the condition in which the amount of the recording paper201stacked in the sheet feed storage cassette230is small (near end condition) and the condition in which the amount of the recording paper201is larger than or equal to the prescribed amount (paper sufficiency condition).

The first registration rollers203are roller members formed of rubber material such as ethylene propylene diene rubber or urethane rubber, for example, and supported by rotary shafts that are not illustrated. The first registration rollers203correct the skew of the recording paper201(oblique feeding of the sheet) by using collision of the recording paper201with the rollers in the stopped state.

The second registration rollers204are roller members formed of rubber material such as ethylene propylene diene rubber or urethane rubber, for example, and supported by rotary shafts that is not illustrated. The second registration rollers204convey the recording paper201after the skew correction by the first registration rollers203to a transfer belt of the image forming section205.

As shown inFIG. 1, the IN sensor213is arranged between the first registration rollers203and the second registration rollers204along the sheet conveyance path. Further, the WR sensor214is arranged between the second registration rollers204and the image forming section205. The IN sensor213is a sensor that detects conveyance of the recording paper201thereto through the conveyance path. The WR sensor214is a sensor that detects the conveyed recording paper201at a position in front of the image forming section205in order to determine write timing of the image forming section205.

In the image forming section205, yellow, magenta, cyan and black image forming units are arranged in series along the conveyance path of the recording paper201. Each of the image forming units includes a photosensitive drum as an electrostatic latent image bearing body for forming an image, a development device as a development section for developing an electrostatic latent image formed on the photosensitive drum by use of toner and thereby forming a toner image, and a toner cartridge for supplying the toner to the development device.

Each of the image forming units further includes a charging roller as a charging section for supplying electric charge to the surface of the photosensitive drum and thereby uniformly charging the surface. Moreover, each of the image forming units includes an LED head as an exposure device for irradiating the uniformly charged surface of the photosensitive drum with light according to image data and thereby forming the electrostatic latent image.

The image forming section205further includes a transfer belt that conveys the recording paper201and transfer rollers as transfer sections. Each of the transfer rollers transfers the toner image, formed on the photosensitive drum by visualizing (developing) the electrostatic latent image with the toner, onto the recording paper201. Each of the transfer rollers is arranged to face the corresponding photosensitive drum so that the transfer belt is sandwiched between the transfer roller and the photosensitive drum at a transfer position.

Further, in the image forming section205, a cleaning blade for removing (scraping off) the toner remaining on the surface of the photosensitive drum after the transfer of the toner image onto the recording paper201is arranged in contact with the photosensitive drum.

As shown inFIG. 1, the fixation unit206is arranged in the sheet conveyance path on the downstream side of the image forming section205and includes a heat roller, a backup roller, and a thermistor or the like, for example. The heat roller is formed by, for example, coating a cylindrical hollow cored bar made of aluminum or the like with a heat-resistant elastic layer of silicone rubber and further coating the heat-resistant elastic layer with another member. In the cored bar, a heater such as a halogen lamp is provided, for example.

The backup roller is formed by, for example, coating a cored bar made of aluminum or the like with a heat-resistant elastic layer of silicone rubber and further coating the heat-resistant elastic layer with a PFA (polytetrafluoroethylene) tube, and is arranged so that a pressing part is formed between the backup roller and the heat roller. The heat roller and the backup roller rotate according to control by a fixation control section. The thermistor is a surface temperature detecting means for the heat roller and is arranged in the vicinity of the surface of the heat roller.

The recording paper201to which the toner images have been transferred passes through the pressing part formed by the backup roller and the heat roller maintained at a prescribed temperature, and thereby heat and pressure are applied to the toners on the recording paper201, the toners are fused and the toner images are fixed on the recording paper201.

The first ejection rollers207and the second ejection rollers208convey the recording paper201after passing through the fixation unit206along the sheet conveyance path and eject the recording paper201onto the recording paper stack part210formed by using the outer housing of the image forming device100. As shown inFIG. 1, multiple sheets of the ejected recording paper209are loaded on the recording paper stack part210.

As shown inFIG. 2, the image forming device100includes an operation panel217as an operation section of the image forming device, a display panel218for displaying operating status to a user, and operation keys219for receiving operations performed by the user. The operation panel217, the display panel218and the operation keys219are formed at the top of the image forming device100as shown inFIG. 2.

FIG. 3is a functional block diagram showing the general configuration of the image forming device100according to the first embodiment. As shown inFIG. 3, the image forming device100includes a print control section222as a control section. As shown inFIG. 3, the print control section222is connected to a sheet feed conveyance motor232as a drive source for the recording paper201, a main motor233as a drive source for the image forming section205, and a fixation motor234as a drive source for the fixation unit206.

The print control section222controls the sheet feed conveyance motor232and thereby controls the rotation of the recording paper feed roller202, the recording paper conveyance roller215, the recording paper separation roller216, the first registration rollers203, the second registration rollers204, the first ejection rollers207and the second ejection rollers208. The print control section222controls the main motor233and thereby controls the print process. The print control section222controls the fixation motor234and thereby controls the fixation unit206.

As shown inFIG. 3, the print control section222includes a print number counter223as a print number measurement section, a time counter224as a time measurement section, a medium setting storage section225, and a paper remaining amount judgment section226. A network (or external device)231is connected to the print control section222. Further, various sensors (the IN sensor213, the WR sensor214and the paper end sensor212) and the operation panel217are connected to the print control section222. The operation panel217includes the display panel218and the operation keys219. The print control section222controls a display on the display panel218.

The print number counter223counts the number of sheets on which the printing is performed in a prescribed time measured by the time counter224. The medium setting storage section225stores information on the recording paper201stored in the sheet feed storage cassette230(e.g., thickness information on the recording paper201). The paper remaining amount judgment section226makes a judgment on the remaining amount of the loaded recording paper201.

Next, detailed structure of a paper remaining amount detection section200in the first embodiment will be described below with reference toFIGS. 4A and 4BandFIGS. 5A and 5B. The paper remaining amount detection section200is a mechanism for detecting the remaining amount of the recording paper201by using the paper end sensor212and other members.FIG. 4Ais an exploded perspective view showing the general configuration of the sheet feed storage cassette230in the first embodiment, andFIG. 4Bis a partially enlarged view ofFIG. 4A.FIGS. 4A and 4Billustrate a state in which the sheet feed storage cassette230has not been inserted into the image forming device100yet (i.e., the sheet feed storage cassette230has been drawn out from the image forming device100).

FIG. 5Ais a side view showing the general configuration of the sheet feed storage cassette230in the first embodiment, wherein the sheet feed storage cassette230in a state before insertion is shown.FIG. 5Bis a partially enlarged view of the paper remaining amount detection section200in the sheet feed storage cassette230shown inFIG. 5A.

As shown inFIGS. 4A and 4B, the sheet feed storage cassette230includes a recording paper side guide227that comes in contact with a side face of the recording paper201. The sheet feed storage cassette230is inserted to a part under a base plate228of the image forming device100and the insertion of the sheet feed storage cassette230into the image forming device100is detected by a cassette presence/absence detection section229. The recording paper setting plate104, on which multiple sheets of recording paper201are stacked and set, is installed on the sheet feed storage cassette230. As shown inFIG. 4A, an opening125is formed through the recording paper setting plate104.

As shown inFIG. 5A, the sheet feed storage cassette230includes a drive mechanism that drives the recording paper setting plate104up and down. The drive mechanism includes a sun gear107as a gear part, a planet gear108, an internal gear rack109, a shaft110, a torque damper111, a ratchet gear112, a lock lever113, a lock spring114, a one-way gear115, a gear part cover116, a detection projection part117, and a detection arm part119as an intermediating member.

As shown inFIG. 5A, the recording paper setting plate104is connected to the shaft110, and the planet gear108is fixed to each end of the shaft110in the x-axis direction. Further, the internal gear rack109is formed to engage with the planet gear108. The planet gear108is capable of moving up and down along the internal gear rack109.

As shown inFIG. 5A, the sun gear107is installed in the sheet feed storage cassette230to engage with the planet gear108. Further, the ratchet gear112is installed on the same shaft as the sun gear107. Furthermore, the one-way gear115is installed to engage with both the sun gear107and the ratchet gear112. The torque damper111is installed to engage with the one-way gear115.

As shown inFIG. 5A, the detection arm part (intermediating member)119is provided inside the sheet feed storage cassette230. The detection arm part119is formed integrally with the gear part cover116shown inFIG. 4B. The sun gear107having the detection projection part117formed thereon rotates along with the rotation of the planet gear108, and thereby the detection projection part117and the detection arm part119are brought into a contact state or a non-contact state.

As shown inFIG. 5A, the lock lever113that sets the ratchet gear112in a locked state by engaging with the ratchet gear112and the lock spring114that applies pressing force to the lock lever113are installed on the upper side of the ratchet gear112. In the locked state, the left-hand side of the lock lever113is biased upward by the lock spring114, while the right-hand side of the lock lever113is biased downward and thereby engaged with the ratchet gear112to keep the ratchet gear112in the locked state in which the ratchet gear112is prevented from rotating.

As shown inFIGS. 4A and 4B, the base plate228of the image forming device100is provided with a paper end sensor holder126. The paper end sensor holder126is a holder that covers the whole of the paper end sensor212. A photosensor103and a paper end sensor lever102as a rotating member are fixed inside the paper end sensor holder126. The photosensor103as a detection sensor includes a light emission part and a light reception part and emits light from the light emission part in the x-axis direction inFIGS. 4A and 4B. The photosensor103has a function of detecting the rotation of the paper end sensor lever102.

As shown inFIG. 5B, the paper end sensor lever102includes a shaft102aas a rotary central shaft, a paper contact part124as a first arm part that comes in contact with the top layer recording paper201in the sheet feed storage cassette230, an arm contact part123as a second arm part that comes in contact with the detection arm part119of the sheet feed storage cassette230, and a photosensor light blocking part120.

The photosensor light blocking part120is a projecting part provided on the shaft102aof the paper end sensor lever102. The photosensor light blocking part120rotates around the shaft102aof the paper end sensor lever102according to the remaining amount of the recording paper201set on the recording paper setting plate104detected by the paper end sensor lever102and thereby blocks or transmits the light from the photosensor103.

As shown inFIG. 5B, the photosensor light blocking part120includes a photosensor transmissive part120aas a light transmissive part, and a first photosensor light blocking part120band a second photosensor light blocking part120cas light blocking parts. The photosensor transmissive part120ais a void part of the photosensor light blocking part120and has a function of transmitting the light emitted from the photosensor103by coinciding with a photosensor optical axis133when the paper contact part124comes in contact with the recording paper201. In a state in which the light emitted from the photosensor103passes through the photosensor transmissive part120a, the photosensor103is on and the paper sufficiency condition of the recording paper201is detected.

The first photosensor light blocking part120bis arranged to the left of the photosensor transmissive part120ainFIG. 5Band has a function of blocking the light emitted from the photosensor103when the contact of the paper contact part124and the recording paper201is released. By the blockage of the light emitted from the photosensor103by the first photosensor light blocking part120b, the photosensor103is turned off and the paper end condition of the recording paper201is detected.

The second photosensor light blocking part120cis arranged to the right of the photosensor transmissive part120ainFIG. 5Band has a function of blocking the light emitted from the photosensor103by rotating to a position coinciding with the photosensor optical axis133when the arm contact part123comes in contact with the detection arm part119. By the blockage of the light emitted from the photosensor103by the second photosensor light blocking part120c, the photosensor103is turned off and the near end condition of the recording paper201is detected.

As shown inFIG. 5B, the base plate228is provided with a lock lever releasing part134that comes in contact with the lock lever113due to the insertion of the sheet feed storage cassette230into the image forming device100and thereby releases the locked state of the lock lever113.

Next, the flow of the print operation performed by the image forming device100according to the first embodiment will be described below. After a print command from the network (or external device)231is received by the print control section222, the recording paper201set in the sheet feed storage cassette230is conveyed by making the sheet feed conveyance motor232rotate the recording paper feed roller202.

The recording paper201after reaching the recording paper conveyance roller215is separated from the stack by the recording paper separation roller216and detected by the IN sensor213, and thereafter the sheet feed conveyance motor232is stopped temporarily by a command from the print control section222in the state in which the recording paper201has collided with the second registration rollers204.

Subsequently, the conveyance of the recording paper201is restarted by making the sheet feed conveyance motor232rotate the second registration rollers204. The front end position of the recording paper201is detected by the print control section222by using the WR sensor214, and the toners are transferred to the recording paper201by the image forming section205driven by the main motor233and performing the toner/latent image formation and the image transfer.

Subsequently, the toners are thermally fused and fixed on the recording paper201by the fixation unit206driven by the fixation motor234. The recording paper201is conveyed by the first ejection rollers207and the second ejection rollers208and ejected onto the recording paper stack part210, so that the print operation is ended.

Next, the operation of the paper remaining amount detection performed by the image forming device100according to the first embodiment will be described below with reference toFIGS. 5A and 5BtoFIGS. 8A and 8B. The operation described below is an operation for making a condition check in regard to the number of sheets of the recording paper201stored in the sheet feed storage cassette230after the sheet feed storage cassette230is set in the image forming device100.

FIG. 6Ais a side view showing the general configuration of the sheet feed storage cassette230in the first embodiment, wherein the sheet feed storage cassette230in an inserted state is shown.FIG. 6Bis a partially enlarged view of the paper remaining amount detection section200in the sheet feed storage cassette230shown inFIG. 6A.FIGS. 6A and 6Billustrate a case where a large amount of recording paper201has been loaded on the recording paper setting plate104.

FIG. 7Ais a side view showing the general configuration of the sheet feed storage cassette230in the first embodiment, showing a state at a time when the near end condition of the recording paper201is detected.FIG. 7Bis a partially enlarged view of the paper remaining amount detection section200in the sheet feed storage cassette230shown inFIG. 7A.FIGS. 7A and 7Billustrate a case where the amount of the recording paper201loaded on the recording paper setting plate104is smaller than or equal to the prescribed amount.

FIG. 8Ais a side view showing the general configuration of the sheet feed storage cassette230in the first embodiment, showing a state at a time when the paper end condition of the recording paper201is detected.FIG. 8Bis a partially enlarged view of the paper remaining amount detection section200in the sheet feed storage cassette230shown inFIG. 8A.FIGS. 8A and 8Billustrate a case where the number of sheets of the recording paper201loaded on the recording paper setting plate104is zero.

As shown inFIGS. 5A and 5B, in the state before the sheet feed storage cassette230is inserted into the image forming device100, the planet gear108, the sun gear107, the one-way gear115and the ratchet gear112are engaged with each other. Further, since the ratchet gear112and the lock lever113pressed by the lock spring114are engaged with each other, each of the connected gears is inhibited from rotating and is stopped at the illustrated position.

Further, as shown inFIGS. 5A and 5B, although the recording paper setting plate104in the sheet feed storage cassette230is pressed upward by the spring106, the recording paper setting plate104connected to the planet gear108is locked up at its lowermost position since the gears are in the locked state. In this case, the photosensor103is in the off state since the photosensor transmissive part120aand the photosensor optical axis133do not coincide with each other and the light emitted from the photosensor103is blocked by the first photosensor light blocking part120b.

From the state shown inFIGS. 5A and 5B, the recording paper201is set on the recording paper setting plate104and the sheet feed storage cassette230is inserted into the image forming device100in a direction A. Then, the cassette presence/absence detection section229comes in contact with a non-illustrated detection switch in the image forming device100and detects the completion of the insertion of the sheet feed storage cassette230. This state is shown inFIGS. 6A and 6B.

When the sheet feed storage cassette230is inserted in the image forming device100as shown inFIGS. 6A and 6B, the lock lever releasing part134and the lock lever113come in contact with each other, the lock lever113is depressed in a direction B, and the engagement with the ratchet gear112is released. Thereby, the recording paper setting plate104starts ascending together with the recording paper201due to pressing force applied from the spring106.

The recording paper setting plate104stops ascending when the top layer of the recording paper201stacked on the recording paper setting plate104comes in contact with the recording paper feed roller202. In this case, the top layer recording paper201and the paper contact part124come in contact with each other and the paper end sensor lever102rotates counterclockwise. At that time, the paper end sensor lever102has rotated to a third rotational position. In this case, the photosensor transmissive part120aand the photosensor optical axis133coincide with each other and the photosensor103turns on.

Here, the time from the start of the ascending of the recording paper setting plate104to the turning-on of the photosensor103is measured by the time counter224of the print control section222. A time measured until the photosensor103turns on is defined as a time (measurement time) T. The time T is a rotation time of the planet gear108from the start of the ascending of the recording paper setting plate104to the stoppage of the ascending.

In a case where the time T is within a time T1 as a predetermined first time, it can be identified that the recording paper201and the paper contact part124have come in contact with each other and the paper end sensor lever102has rotated, and thus the paper remaining amount judgment section226of the print control section222judges that the recording paper201exists, and a display indicating that the printing is possible is made on the display panel218.

When the amount of the recording paper201loaded on the recording paper setting plate104is smaller than or equal to the prescribed amount (near end condition) as shown inFIGS. 7A and 7B, the recording paper setting plate104has ascended further since the planet gear108rotationally moves further clockwise from the state shown inFIGS. 6A and 6B. In this case, first, the photosensor103turns on due to the contact of the paper contact part124and the recording paper201. Subsequently, the sun gear107rotates together with the planet gear108, and the detection projection part117formed on the sun gear107comes in contact with a projection part119aof the detection arm part119and thereby raises the detection arm part119.

By the raising of the detection arm part119, the arm contact part123of the paper end sensor lever102comes in contact with the detection arm part119. The contact causes the paper end sensor lever102to rotate further counterclockwise from the state shown inFIGS. 6A and 6B. At that time, the paper end sensor lever102has rotated to a second rotational position. Due to the counterclockwise rotation of the paper end sensor lever102, the photosensor transmissive part120amoves to a position not coinciding with the photosensor optical axis133and the photosensor103turns off. Therefore, the photosensor103temporarily turns on and thereafter turns off.

In this case, since a relationship T1<T<T2 holds among the measured time T, the aforementioned time T1 and a time T2 as a second time longer than the time T1 and the photosensor103temporarily turned on and thereafter turned off, the paper remaining amount judgment section226of the print control section222judges that the condition of the stacked recording paper201is the near end condition (in which the remaining amount of the paper is small) and a near end display is made on the display panel218.

When the number of sheets of the recording paper201loaded on the recording paper setting plate104is zero (paper end condition) as shown inFIGS. 8A and 8B, the planet gear108has rotationally moved further upward from the state shown in FIGS.7A and7B. In this case, the sun gear107rotates further from the state shown inFIGS. 7A and 7B, the contact of the detection projection part117formed on the sun gear107with the projection part119aof the detection arm part119is lost, and the detection arm part119descends.

By the descending of the detection arm part119, the contact of the arm contact part123and the detection arm part119is lost and the paper end sensor lever102rotates clockwise from the state shown inFIGS. 7A and 7Bin this case. Here, the opening125is formed through the recording paper setting plate104at a position corresponding to the paper contact part124. When the paper end sensor lever102in the state shown inFIGS. 7A and 7Bhas rotated clockwise to the state shown inFIGS. 8A and 8B, the recording paper201shielding the opening125has run out.

In this case, the paper contact part124never comes in contact with the recording paper setting plate104due to the opening125, and thus the paper end sensor lever102rotates further clockwise compared to a case where there remains the recording paper201, and rotates to a position where the first photosensor light blocking part120bblocks the light from the photosensor103as shown inFIG. 8B. In this case, the paper end sensor lever102is situated at a first rotational position and the photosensor103is off.

As above, since no recording paper201is set on the recording paper setting plate104in the paper end condition, the paper contact part124never comes in contact with the recording paper201and the photosensor103never turns on within the time T1 or the time T2 as in the aforementioned paper sufficiency condition or near end condition. Therefore, the photosensor103does not turn on within the time T2.

As above, based on the fact that the photosensor103does not turn on within the time T2, the paper remaining amount judgment section226of the print control section222judges that the condition of the stacked recording paper201is the paper end condition (in which the remaining amount of the paper is zero) and a paper end display is made on the display panel218.

Next, an operation of paper remaining amount display performed by the image forming device100according to the first embodiment will be described below with reference toFIG. 9.FIG. 9is a flowchart showing an operation for making the condition check in regard to the remaining amount of the recording paper201in the first embodiment. As shown inFIG. 9, the insertion of the sheet feed storage cassette230is detected by the cassette presence/absence detection section229in step S1.

In the next step S2, a judgment is made on whether or not the time T until the photosensor103turns on is within the predetermined time T1. In a case where the time T is within the time T1 (YES in the step S2), it can be identified that the recording paper201and the paper contact part124have come in contact with each other and the paper end sensor lever102has rotated, and thus the process advances to step S5, the paper remaining amount judgment section226of the print control section222judges that the recording paper201exists, and the display indicating that the printing is possible is made on the display panel218.

In a case where the time T is longer than the time T1 in the step S2(NO in the step S2), the process advances to the next step S3and a judgment is made on whether or not the photosensor103temporarily turned on within the time T2 and thereafter turned off since there is possibility that the photosensor103temporarily turned on within the time T2 and thereafter turned off.

In a case where the photosensor103temporarily turned on within the time T2 and thereafter turned off in the step S3(YES in the step S3), it can be identified that the paper end sensor lever102has rotated counterclockwise due to the contact of the detection arm part119with the arm contact part123of the paper end sensor lever102and the photosensor103has turned off, and thus the process advances to step S6, the paper remaining amount judgment section226of the print control section222judges that the condition of the stacked recording paper201is the near end condition (in which the remaining amount of the paper is small), and the near end display is made on the display panel218.

In a case where the photosensor103did not temporarily turn on within the time T2 in the step S3(NO in the step S3), it can be identified that there remains no recording paper201set on the recording paper setting plate104, and thus the process advances to step S4, the paper remaining amount judgment section226of the print control section222judges that the condition of the stacked recording paper201is the paper end condition (in which the remaining amount of the paper is zero), and the paper end display is made on the display panel218. The operation for making the condition check in regard to the insertion of the sheet feed storage cassette230and the remaining amount of the recording paper201is completed as above.

Next, processing after the start of the printing will be described briefly. In a case where the condition of the recording paper201was judged to be the paper sufficiency condition because of the turning on of the photosensor103within the time T1, thereafter the printing was started, and subsequently the photosensor103turned off, it can be identified that the turning-off of the photosensor103was caused by the contact of the detection arm part119and the arm contact part123as shown inFIGS. 7A and 7B. Thus, based on such a change in the output of the photosensor103, the paper remaining amount judgment section226of the print control section222judges that the condition of the recording paper201has changed from the paper sufficiency condition to the near end condition, and the near end display is made on the display panel218.

In a case where the photosensor103turned on and thereafter turned off again due to further continuation of the printing, it can be identified that the condition of the recording paper201is the paper end condition as shown inFIGS. 8A and 8B. Thus, based on such a change in the output of the photosensor103, the paper remaining amount judgment section226of the print control section222judges that the condition of the recording paper201has shifted to the paper end condition, and the paper end display is made on the display panel218. By the above processing, the display indicating the condition of the recording paper201can be made based on the change in the output of the photosensor103even when the condition of the recording paper201changes due to continuation of the printing.

Incidentally, the detection condition for the near end display is designed so that the near end display is made at 60 sheets when thick paper (corresponding to 88-104 gsm (g/m2)) is used, for example. In contrast, in a case where the stored recording paper201is regular paper (corresponding to 64-74 gsm), making the near end display on the same condition as the thick paper at the time of the contact of the detection arm part119and the arm contact part123results in the near end display made when the remaining number of sheets of the recording paper201in the sheet feed storage cassette230is larger than 60 sheets due to the smaller thickness of the paper.

Since such variations in the remaining number of sheets can occur as above depending on the thickness of the recording paper201stored in the sheet feed storage cassette230, it is necessary to correct the timing of the near end display depending on the thickness of the recording paper201.FIG. 10is a diagram showing the relationship between the thickness of the recording paper201and a corrective number of sheets used for correcting the timing of the near end display in the first embodiment.

In the first embodiment, the correction of the near end display timing is made by using the corrective numbers of sheets shown inFIG. 10. For example, the corrective number of sheets for the “regular paper” with respect to the “thick paper” is calculated as “24 sheets” based on the following conditions (1) to (3):

near end detection sheet number difference: 84 sheets regarding regular paper−60 sheets regarding thick paper=24 sheets  (3)

Thus, the paper remaining amount judgment section226of the print control section222has the near end display made on the display panel218after the print number counter223has counted24printed sheets since the reception of a notification that the photosensor103is off. Incidentally, also when a setting of a different paper type (relatively thick paper, thin paper) is made, the near end display timing is corrected similarly based on the corrective numbers of sheets shown inFIG. 10.

As described above, in the image forming device100according to the first embodiment, combining the photosensor103and the rotating paper end sensor lever102makes it possible to detect both the paper end condition and the near end condition with only a conventionally existing sensor for the paper end detection, without the need of specially providing a sensor for the near end detection. Accordingly, the production cost of the mechanism for detecting the paper end condition and the near end condition can be reduced.

In the image forming device100according to the first embodiment, the timing of the near end display is corrected depending on the thickness of one sheet of the recording paper201being used. Accordingly, the near end display can be made at approximately the same remaining number of sheets even when the thickness of the used recording paper201is different, and the variations in the remaining number of sheets of the recording paper201in the sheet feed storage cassette230at the time of making the near end display can be restrained. Consequently, precise near end display can be implemented irrespective of the thickness of the used recording paper201.

(2) Second Embodiment

A description of an image forming device100aaccording to a second embodiment will be given below exclusively of parts different from those of the image forming device100according to the first embodiment.FIG. 11Ais a side view showing the general configuration of a sheet feed storage cassette230ain the second embodiment, and shows a state where preliminary detection explained later is made.FIG. 11Bis a partially enlarged view of a paper remaining amount detection section200ain the sheet feed storage cassette230ashown inFIG. 11A.

FIG. 12Ais a partially enlarged view of the paper remaining amount detection section200ain the second embodiment.FIG. 12Ashows a state after the preliminary detection and before the near end condition is detected.FIG. 12Bis a partially enlarged view of the paper remaining amount detection section200ain the second embodiment.FIG. 12Bshows a state at a time when the near end condition is detected.FIG. 12Cis a partially enlarged view of the paper remaining amount detection section200ain the second embodiment.FIG. 12Cshows a state at a time when the paper end condition is detected.

As shown inFIGS. 11A and 11B, the image forming device100aaccording to the second embodiment differs from the image forming device100according to the first embodiment in having a preliminary detection projection part118on the sun gear107. The preliminary detection projection part118is used for correcting the timing of the near end display by estimating the thickness of one sheet of the recording paper201stored in the sheet feed storage cassette230from the number of sheets of the recording paper201on which the printing is performed in a time period of the preliminary detection.

As shown inFIGS. 11A and 11B, the preliminary detection projection part118is arranged to the right of the detection projection part117of the sun gear107in the figures. The preliminary detection projection part118has a length around the sun gear107corresponding to an angle θ1. In the second embodiment, the height of the projection of the preliminary detection projection part118is equal to the height of the projection of the detection projection part117.

The operation of the image forming device100aaccording to the second embodiment will be described below. The operation from the insertion of the sheet feed storage cassette230ainto the image forming device100ato the ascending of the recording paper setting plate104is the same as that of the image forming device100according to the first embodiment.

After a certain amount of the printing, as shown inFIGS. 11A and 11B, the preliminary detection projection part118comes in contact with the detection arm part119due to the rotation of the sun gear107, the detection arm part119and the arm contact part123come in contact with each other, and the photosensor103turns off. At the same time, the print number counter223of the print control section222starts the count of the number of printed sheets. At that time, the paper end sensor lever102has rotated to a fourth rotational position.

The count of the number of printed sheets is made in the time period in which the sun gear107rotates clockwise by the angle θ1. After the sun gear107rotates by the angle θ1, the contact of the preliminary detection projection part118and the detection arm part119is released and the contact of the detection arm part119and the arm contact part123is also released as shown inFIG. 12A. Since the paper contact part124and the recording paper201are in contact with each other at that time, the paper end sensor lever102rotates by a prescribed angle and the photosensor103turns on. The number of printed sheets counted in the aforementioned time is sent to and stored in the paper remaining amount judgment section226of the print control section222.

As the printing is continued further, the detection arm part119is raised due to the contact of the detection projection part117with the detection arm part119as shown inFIG. 12B, the detection arm part119and the arm contact part123come in contact with each other again, and the photosensor103turns off. At that time, the paper remaining amount judgment section226of the print control section222determines the timing of the near end display based on the number of printed sheets counted earlier.

As the printing is continued further, the contact of the detection projection part117and the detection arm part119is released as shown inFIG. 12Cand the contact of the detection arm part119and the arm contact part123is also released, and thus the photosensor103remains off.

FIG. 13Ais a time chart showing an example of the near end detection in the second embodiment andFIG. 13Bis a time chart showing another example of the near end detection in the second embodiment.FIGS. 13A and 13Bshow the timing of the on/off switching of the photosensor103corresponding to the timing of the paper end display and the near end display.FIG. 13Ashows an example of the time chart in a case where the thickness of the recording paper201is 104 gsm, whileFIG. 13Bshows an example of the time chart in a case where the thickness of the recording paper201is 64 gsm.

As mentioned earlier, in the time period of the preliminary detection, the photosensor103remains off and thus the number of printed sheets in the time period is counted. As shown inFIG. 13A, if the number C of sheets counted in the time period of the preliminary detection is 60 sheets which is equal to a design value, for example, the near end display is made at the same time as the turning-off of the photosensor103. Accordingly, the near end display is made when the remaining number of sheets of the recording paper201is 60 sheets as shown inFIG. 13A.

In contrast, in a case where the number D of sheets counted in the time period of the preliminary detection is 84 sheets as shown inFIG. 13B, the near end display is made after the printing is performed on 24 sheets (prescribed number of sheets) as the difference between 84 sheets and 60 sheets since the turning-off of the photosensor103. Accordingly, even in a case where the recording paper201is thin (64 gsm), the near end display is made when the remaining number of sheets of the recording paper201is 60 sheets as shown inFIG. 13B. As above, by making the above-described correction, it becomes possible to make the near end display when the remaining number of sheets of the recording paper201is a constant number (e.g., 60 sheets) irrespective of the thickness of the recording paper201.

As described above, in the image forming device100aaccording to the second embodiment, a correction value calculated from the difference between the actual number of sheets on which the printing is performed in a certain fixed period (in the time period of the preliminary detection) and the design value is used for determining the timing of the near end display. By making the correction by use of an actual measurement value as above, the preciseness is greatly increased compared to correction made by use of a correction value previously set for each of several paper types, and it becomes possible to make a precise near end display with smaller variations in the remaining number of sheets.

Further, with the image forming device100aaccording to the second embodiment, effects similar to those of the image forming device100according to the first embodiment can be achieved.

A description of an image forming device100baccording to a third embodiment will be given below exclusively of parts different from those of the image forming device100aaccording to the second embodiment.FIG. 14Ais an enlarged view showing the general configuration of a paper remaining amount detection section200bin the third embodiment, and shows a state at a time when the paper sufficiency condition is detected.FIG. 14Bis an enlarged view showing the general configuration of the paper remaining amount detection section200bin the third embodiment, and shows a state at a time of the preliminary detection.

FIG. 14Cis an enlarged view showing the general configuration of the paper remaining amount detection section200bin the third embodiment, and shows a state after the preliminary detection and before detecting the near end condition.FIG. 14Dis an enlarged view showing the general configuration of the paper remaining amount detection section200bin the third embodiment, and shows a state at a time when the near end condition is detected.FIG. 14Eis an enlarged view showing the general configuration of the paper remaining amount detection section200bin the third embodiment, and shows a state at a time when the paper end condition is detected.

FIG. 15is a flowchart showing an operation for near end detection restoration in the third embodiment.FIG. 16is a table showing the relationship between an output of a density sensor135and a display on the display panel218in the third embodiment.

The image forming device100baccording to the third embodiment differs from the image forming device100aaccording to the second embodiment in including the density sensor135instead of the photosensor103. Further, the image forming device100baccording to the third embodiment differs from the image forming device100aaccording to the second embodiment in including a first density sensor reflective part130as a second reflective part, a second density sensor reflective part131as a first reflective part, a third density sensor reflective part132as a third reflective part and a fourth density sensor reflective part137instead of the photosensor transmissive part120a, the first photosensor light blocking part120band the second photosensor light blocking part120c.

Furthermore, the image forming device100baccording to the third embodiment differs from the image forming device100aaccording to the second embodiment in that the height of the preliminary detection projection part118of the sun gear107in the sheet feed storage cassette230is smaller than the height of the detection projection part117by hl and the photosensor optical axis133is replaced with a density sensor detecting position136.

As shown inFIG. 14AtoFIG. 14E, the paper end sensor lever102of the image forming device100baccording to the third embodiment has the first to fourth density sensor reflective parts130,131,132and137. Further, the density sensor135has the density sensor detecting position136. The paper end sensor lever102rotates around the shaft102aand thereby reflects light emitted from the density sensor135at the positions of the first to fourth density sensor reflective parts. The intensity of the reflected light is detected at the density sensor detecting position136.

The first density sensor reflective part130is arranged at the rightmost position among the density sensor reflective parts. The intensity of the reflected light reflected by the first density sensor reflective part130is the second highest among the first to fourth density sensor reflective parts and is detected at the density sensor detecting position136. Then Middle-High (Mid-H) is outputted by the density sensor135(seeFIG. 16). The first density sensor reflective part130is used to detect the near end condition.

The second density sensor reflective part131is arranged at the leftmost position among the density sensor reflective parts. The intensity of the reflected light reflected by the second density sensor reflective part131is the lowest among the density sensor reflective parts and Low is outputted by the density sensor135(seeFIG. 16). The second density sensor reflective part131is used to detect the paper end condition.

The third density sensor reflective part132is arranged at the third position from the right among the density sensor reflective parts. The intensity of the reflected light reflected by the third density sensor reflective part132is the highest among the density sensor reflective parts and High is outputted by the density sensor135(seeFIG. 16). The third density sensor reflective part132is used to detect the paper sufficiency condition.

The fourth density sensor reflective part137is arranged at the second position from the right among the density sensor reflective parts. The intensity of the reflected light reflected by the fourth density sensor reflective part137is the third highest among the density sensor reflective parts and Middle-Low (Mid-L) is outputted by the density sensor135(seeFIG. 16). The fourth density sensor reflective part137is used to make the preliminary detection.

(3-2) Detecting Operation in Normal Times

The operation of the image forming device100baccording to the third embodiment will be described below with reference toFIGS. 14A to 14E. The operation from the insertion of the sheet feed storage cassette230into the image forming device100bto the ascending of the recording paper setting plate104is the same as that of the image forming device100aaccording to the second embodiment and starts from the state shown inFIG. 14A.

As shown inFIG. 14B, after a certain amount of the printing, the preliminary detection projection part118comes in contact with the detection arm part119due to the rotation of the sun gear107, the detection arm part119also comes in contact with the arm contact part123, and the fourth density sensor reflective part137of the paper end sensor lever102moves to a position coinciding with the density sensor detecting position136.

At that time, the density sensor135receives the reflected light from the density sensor reflective part137at the density sensor detecting position136and the output Middle-Low (Mid-L) is acquired, while the print number counter223of the print control section222starts the count of the number of printed sheets at the same time.

As shown inFIG. 14C, as the sun gear107rotates further, the contact of the detection arm part119and the arm contact part123is released and the third density sensor reflective part132of the paper end sensor lever102moves to the position coinciding with the density sensor detecting position136.

At that time, the density sensor135receives the reflected light from the third density sensor reflective part132at the density sensor detecting position136, the count of the number of printed sheets is stopped due to the acquisition of the output High, and the counted number of printed sheets is sent to and stored in the paper remaining amount judgment section226of the print control section222.

As shown inFIG. 14D, as the printing is continued further, the detection projection part117and the detection arm part119come in contact with each other and the first density sensor reflective part130of the paper end sensor lever102moves to the position coinciding with the density sensor detecting position136.

At that time, the density sensor135receives the reflected light from the first density sensor reflective part130at the density sensor detecting position136and the output Middle-High (Mid-H) is acquired, while a paper near end notification is issued from the paper remaining amount judgment section226of the print control section222at the same time and the near end display is made on the display panel218.

As shown inFIG. 14E, as the printing is continued further, the contact is lost between the recording paper201and the paper contact part124, and the second density sensor reflective part131of the paper end sensor lever102moves to the position coinciding with the density sensor detecting position136.

At that time, the density sensor135receives the reflected light from the second density sensor reflective part131at the density sensor detecting position136, the output Low is acquired, the paper remaining amount judgment section226of the print control section222judges that the paper is in the paper end condition, and the paper end display is made on the display panel218. The flow from the setting of the recording paper201to the paper end display in normal printing is as described above.

(3-3) Operation at Power Shutdown

Next, an operation for recognizing again the amount of the recording paper201in the sheet feed storage cassette230and the position of the paper end sensor lever102, in a case where the power of the image forming device100bwith some recording paper201remaining therein is shut down due to some trouble and thereafter turned on again and the information stored in the paper remaining amount judgment section226of the print control section222is lost, will be described below with reference toFIG. 15.

As shown inFIG. 15, in step S11, an output check of the density sensor135“Is sensor output Low?” is made by the print control section222. If the sensor output is Low (YES in the step S11), it is judged that the density sensor detecting position136and the second density sensor reflective part131have coincided with each other, the process advances to a next step S12, and the paper end display is made on the display panel218.

If the sensor output is not Low (NO in the step S11), the process advances to a next step S13and an output check of the density sensor135“Is sensor output High?” is made.

If the output is High (YES in the step S13), it is judged that the density sensor detecting position136and the third density sensor reflective part132have coincided with each other, the process advances to a next step S14, and the paper remaining amount judgment section226has the paper sufficiency (printable) display made on the display panel218. Subsequently, the process advances to step S15and the recording paper201is fed without change. Thereafter, in the next step S16, whether or not the sensor output is still High also after a time T3 is checked.

If the sensor output is still High also after the time T3 (YES in the step S16), the process advances to a next step S17and the paper sufficiency display on the display panel218is continued since the density sensor detecting position136and the third density sensor reflective part132are coinciding with each other.

If the sensor output is not High after the time T3 (NO in the step S16), the process advances to a next step S18and an output check of the density sensor135“Is sensor output Mid-L?” is made. If the sensor output is Mid-L (YES in the step S18), it is judged that the density sensor detecting position136and the fourth density sensor reflective part137have coincided with each other, the operation mode shifts to a preliminary detection mode in which the preliminary detection is made in a next step S19, and the count of the number of printed sheets is started by the print number counter223.

If the sensor output is not Mid-L (NO in the step S18), it is judged that the density sensor detecting position136and the first density sensor reflective part130have coincided with each other and the near end display is made on the display panel218in a next step S20.

Returning to the step S13“Is sensor output High?”, if the output is not High (NO in the step S13), the process advances to a next step S21and a check “Is sensor output Mid-L?” is made. If the sensor output is Mid-L (YES in the step S21), it is judged that the density sensor detecting position136and the fourth density sensor reflective part137have coincided with each other, the operation mode shifts to the preliminary detection mode in which the preliminary detection is made in a next step S22, and the count of the number of printed sheets is started by the print number counter223.

If the sensor output is not Mid-L (NO in the step S21), the process advances to a next step S23, it is judged that the density sensor detecting position136and the first density sensor reflective part130have coincided with each other, and the near end display is made on the display panel218.

In the image forming devices100and100aaccording to the first and second embodiments described earlier, the remaining amount of the paper is judged based on two types of indication, on and off, by the photosensor103and there are two conditions, the paper end condition and the near end condition, when the photosensor103is off, and thus physical discrimination between the paper end condition and the near end condition cannot be made in a case where an unexpected shutdown of the device power occurred and the power is restored. Therefore, in such a case where an unexpected device power shutdown occurred and the power is restored, a problem arises in that the near end detection function cannot be restored unless the sheet feed storage cassette230is once drawn out from the device and reinserted into the device.

In contrast, with the image forming device100baccording to the third embodiment, it becomes possible to physically and instantaneously judge whether the remaining amount of paper is in the paper end condition, in the near end condition, in the paper sufficiency condition or in the preliminary detection condition in which the preliminary detection is made based on the output of the density sensor135. Accordingly, effect is achieved in that the user is relieved of the work of reinserting the sheet feed storage cassette230into the device and the near end detection function can be restarted automatically.

Further, with the image forming device100baccording to the third embodiment, effects similar to those of the image forming devices100and100aaccording to the first and second embodiments can be achieved.

(4) Description of Forms of Use

While examples of applying the present invention to a paper feed device of an electrophotographic printer have been described in the above embodiments, the present invention is applicable to any type of image forming devices that include a sheet feed storage cassette and a paper end sensor, and form an image on recording paper by using various printing methods, such as copiers, facsimile machines, printers and MFPs (multifunction printers).

In the above embodiments, messages regarding the paper end condition and the near end condition of the recording paper201are displayed by using the display panel218as a display section. However, the method of indication is not limited to such examples and it is possible, for example, to provide the device with an LED or the like as the display section and to indicate the paper end condition and the near end condition by using the color, the pattern or the like of light emitted from the LED.