JP2000289861A - Picture image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To steplessly detect residual quantity of sheets accumulated on a paper feeding part without increasing the number of parts, complicating a mechanism and complicating a control circuit. SOLUTION: This device checks a state of a paper surface position detection detection sensor 4 when a paper feeding cassette is set and raises a bottom plate 1 until the paper surface position detection sensor 4 is put on when it is off (not detected), Time to reach a state where the paper surface position detection sensor 4 is put on from starting to rise is counted in a rising process of the bottom plate 1. Thereafter, sheet accumulated quantity (n) is assumed from this counted value (t) and rising speed of the bottom plate 1, and it is recorded in a non-volatile memory. When picture image forming motion is started, the sheet accumulated quantity (n) is decreased for each of the paper feeding motion, and recording value of the non-volatile memory is renewed. This newest recording value is regarded as sheet residual quantity at the current point of time. The motion is repeated in the case when the paper feeding cassette is removed when an electric power source is on.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine having these functions, and more particularly, to an image forming apparatus having an improved function of detecting a remaining amount of paper. is there. Is what you do.

[0002]

2. Description of the Related Art A plurality of personal computers (hereinafter, referred to as personal computers).
It is referred to as a host device. ) Operates in an office environment, these plurality of host devices and image forming apparatuses such as printers are interconnected by a network such as a LAN, and one or a small number of image forming apparatuses are shared by a larger number of users. Cases are increasing. As a result, the amount of paper consumption per image forming apparatus has increased, so that the number of sheets that can be accommodated in the paper feeding unit of the image forming apparatus has been further increased, and the remaining amount has been finely detected in multiple steps. It has become required. Techniques for detecting the remaining amount of paper in multiple stages have been known. As an example, a mechanism that raises the shielding plate in conjunction with the upward movement of the paper stacked in the paper feeding unit, and a plurality of sensors for detecting the position of the shielding plate are provided. Is detected in multiple stages according to the number of sensors shielded by the shielding plate. In addition, an encoder is provided in the rotating part of the motor for raising the bottom plate of the paper cassette, and a sensor for detecting the slit of the encoder is arranged, and the number of pulses emitted from the sensor every time the slit passes is counted. By using a stepping motor as the motor,
In some cases, the remaining amount of paper can be detected in multiple stages based on the number of motor drive pulses.

[0003]

However, in each of the above-mentioned prior arts, the number of parts is greatly increased and the mechanism is complicated as compared with the case where the remaining amount of paper is detected in one step, that is, only the presence or absence of paper is detected. However, the complexity of the control circuit is increased, and this is a factor that increases the manufacturing cost of the device.
The problem to be solved by the present invention is to solve the drawbacks of the conventional technology, and increase the number of parts, the complexity of the mechanism, and the paper stacked in the paper feeding unit without complicating the control circuit. An object of the present invention is to provide an image forming apparatus capable of continuously detecting the remaining amount of an image.

[0004]

According to another aspect of the present invention, there is provided an image forming apparatus comprising: a driving unit configured to raise a bottom plate of a sheet cassette on which sheets are stacked;
Paper detection means for detecting that the uppermost part of the paper has reached a predetermined position at the start of paper feeding by raising the bottom plate; and cassette mounting detection for detecting whether or not the paper feeding cassette is mounted in the apparatus main body. A sheet feeding unit having a mechanism and a mechanism for opening a connection between the bottom plate and the driving means and returning the bottom plate to a lower limit position when the sheet feeding cassette is pulled out of the apparatus main body; An engine unit having a drawing unit that forms an image on the fed sheet; and a control unit that controls driving of the engine unit and monitors the remaining amount of sheets in the sheet cassette. When the cassette mounting detecting means detects that the state of the sheet cassette has shifted from the non-mounting state to the mounting state, the uppermost part of the paper is detected by the paper detecting means. The drive means raises the bottom plate, counts the time from the start of the rise to the time when the sheet is detected, estimates the amount of sheets loaded on the bottom plate from the count value, and stores the value in a nonvolatile manner. After recording in the memory, the apparatus is shifted to a standby state, and thereafter, when the apparatus starts an image forming operation, the value is decremented every time paper is fed from the paper feed cassette, and the updated value is updated. Is recorded in the nonvolatile memory, and the updated value is regarded as the current remaining amount of paper and the remaining amount of paper is monitored. According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the control unit checks a state of the sheet detecting unit when the power of the apparatus is turned on, and detects no sheet. In the case of, the bottom plate is raised by the drive unit until the top of the paper is detected by the paper detection unit, and the time from the start of the rising until the paper is detected is counted, and the bottom plate is counted from the count value. After estimating the stacking amount of the sheets stacked in the non-volatile memory and recording the value in the non-volatile memory, the apparatus shifts to a standby state. Each time a sheet is fed, the value is decremented, the updated value is recorded in the nonvolatile memory, and the updated value is regarded as the current remaining amount of paper, and a function of monitoring the remaining amount of paper is further provided. It is characterized in that. The invention according to claim 3 is:
3. The image forming apparatus according to claim 1, wherein the control unit checks a state of the sheet detection unit when the apparatus is turned on, and stores the sheet in the nonvolatile memory when a sheet is detected. 4. After reading the value of the recorded paper remaining amount, the apparatus shifts to a standby state, and thereafter, when the apparatus starts an image forming operation, the value is set each time paper is fed from the paper feed cassette. Is decremented, the updated value is recorded in the non-volatile memory, and the updated value is regarded as the current remaining amount of paper and the function of monitoring the remaining amount of paper is further provided.

[0005]

Embodiments of the present invention will be described below. An image forming apparatus according to the present invention includes: a sheet feeding unit in which a sheet cassette in which sheets are stacked and stored is set; an engine unit including a drawing unit that forms an image on sheets fed from the sheet feeding unit; A control unit that controls the driving of the engine unit and monitors the remaining amount of sheets in the sheet cassette. 1A to 1E are diagrams illustrating the configuration and operation of a sheet feeding unit of the image forming apparatus according to the present invention. In the drawing, reference numeral 1 denotes a bottom plate of a sheet cassette. One end of the bottom plate 1 is fixed to a horizontally extending rotary shaft 2 provided in the paper feed cassette, and is supported rotatably up and down (in the direction of arrow A). The paper feed cassette is set in the image forming apparatus. Sometimes, it is mechanically connected to a drive mechanism (not shown) provided in the apparatus main body. The drive mechanism is driven by a motor 18 (FIG. 2), and pushes up and rotates the bottom plate 1, thereby rotating the paper 3 stacked on the bottom plate 1 upward. When the paper cassette is pulled out of the machine,
The mechanical connection between the drive mechanism and the bottom plate 1 is broken,
Is lowered to the lower limit position by its own weight and the weight of the paper 3 loaded thereon. The paper feed cassette is provided with a paper surface detection sensor 4 as a paper detection means, which is located above the vicinity of the free end of the bottom plate 1. The paper surface detection sensor 4
It is a detecting means for detecting whether or not the uppermost sheet among the sheets 3 stacked on the bottom plate 1 is at the upper limit position (sheet feeding position). This paper surface detection sensor 4 is provided with a light source (LE
D) and a light receiver (PD) that receives light from the light source. The light source and the light receiver of the paper surface detection sensor 4 are fixed to the opposing side plates of the sheet cassette with the light emitting unit and the light receiving unit facing each other in the horizontal direction (the direction perpendicular to the paper surface). When the paper 3 loaded on the bottom plate 1 reaches the upper limit position, light from the light source of the paper surface detection sensor 4 is blocked by the paper 3 and does not enter the light receiver.
The signal from the light receiver is sent to the CPU 11 on the engine board 10 (FIG. 2), as will be described later. When the light reception signal from the light receiver is stopped, the paper loaded on the bottom plate 1 of the sheet cassette is stopped. 3 is detected to have reached the upper limit position.

FIG. 2 is a block diagram showing a circuit configuration of a portion relating to the detection of the remaining amount of paper in the image forming apparatus according to the present invention. Among the components shown in FIG. 2, only the paper surface detection sensor 4 is provided in the paper feed cassette, and the other components are provided in the apparatus main body of the image forming apparatus. A power supply and a signal terminal of a circuit including the paper surface detection sensor 4 are electrically connected to a terminal connected to the engine board 10 provided in the apparatus main body when the sheet cassette is set in the image forming apparatus. ing. The engine board 10 is an engine control unit that controls driving of the engine unit. The engine board 10 includes a CPU 1
1, ROM 12, RAM 13, various I / Os 14, motor driver 15, cassette set detection SW (switch) 1
6, a controller I / F (interface) 17 and a motor 18 are provided. The CPU 11 uses the RO
According to the program stored in M12, the photosensitive drum and the developing roller of the drawing unit, the belt and the roller of the paper transport system,
A motor, a clutch, a solenoid, and the like for driving a mechanical element such as a drive mechanism for rotating the bottom plate 1 are generally controlled. The CPU 11 controls writing of a latent image on the photosensitive drum of the drawing unit in accordance with a print command from the controller board 20. The CPU 11 performs various processes using the ROM 12 as a work area. The ROM 12 stores a control program for detecting the remaining amount of paper according to the present invention.

The various I / Os 14 comprise various circuits for the CPU 11 to output control signals to motors, clutches, solenoids and the like provided in the apparatus main body, and to input signals from sensors and the like. Motor driver 15
A motor (hereinafter, referred to as a bottom plate drive motor) 18 of a drive mechanism for raising and lowering the bottom plate 1 of the sheet cassette,
1 is a circuit driven in accordance with a control signal from the control unit 1. The cassette set detection switch 16 is a detection unit for detecting whether or not the sheet cassette is set in the apparatus main body, and is turned on when the sheet cassette is set in the apparatus body, and is turned off when the sheet cassette is pulled out. It is supposed to. The controller I / F 17 is an interface circuit for the CPU 11 to communicate with the controller board 20. The controller board 20 receives a print command and print data from the host device, develops image data based on the print command and print data, and issues a print command corresponding to the developed data to the CPU via the controller I / F 17.
11 is a printer control unit. The controller board 20 includes a CPU, a ROM, a RAM,
And a communication interface for performing communication with a host device connected via a non-volatile memory (NVRAM).

Next, the operation of detecting the remaining amount of paper of the image forming apparatus according to this embodiment configured as described above will be described with reference to FIGS.
A description will be given according to (E). FIG. 1A shows a state in which sheets 3 are stacked on the bottom plate 1 of the paper feed cassette and the bottom plate 1 is at the lower limit position. At this time, the paper surface position detection sensor 4 is off. When the paper feed cassette is set in the apparatus main body while the power of the image forming apparatus is turned on, the CPU 11 detects this by changing the state of the cassette set detection SW 16 from off to on, and a paper surface position detection sensor Check the status of 4. At this time, if the state of the paper surface position detection sensor 4 is ON, it is determined that the state is not normal, and error processing is performed. This is because it is detected that the sheet 3 has reached the upper limit position even though the bottom plate 1 has not been raised yet.
If the state of the paper surface position detection sensor 4 is off, the CP
U11 determines that it is in a normal state, drives the bottom plate drive motor 18 through the motor driver 15 while monitoring the state of the paper surface position detection sensor 4, and raises the bottom plate 1 until the paper surface position detection sensor 4 is turned on.

In a process of raising the bottom plate 1, the CPU 11 starts the ascent and then turns on the paper surface position detection sensor 4.
That is, the time until the state of FIG. 1B is reached is counted. Then, the CPU 11 estimates the sheet stacking amount n from the count value (t) and the rising speed of the bottom plate 1. Here, the CPU 11 transmits the data of the above-described paper stacking amount n to the controller board 20 via the controller I / F 17. In the controller board 20,
The received data is recorded in the nonvolatile memory. In this state (the state of FIG. 1B), the image forming apparatus waits until a print command is received from the host device. Upon receiving a print command from the host device and starting an image forming operation, the CPU 11
Decrements the above-mentioned paper stacking amount n (substitute n-1 for n at that time) every time the paper feeding operation is performed, and transmits the value to the controller board 20 via the controller I / F 17. In the controller board 20, data recorded in the non-volatile memory is sequentially rewritten with data received later. That is, the latest value is always recorded in the nonvolatile memory. The latest recording value n is regarded as the current paper remaining amount. The state of the paper feed cassette is maintained in the state shown in FIG. 1C unless the paper 3 is removed or the paper 3 is replenished halfway until the paper 3 runs out, but the power of the image forming apparatus is turned on. If the paper cassette is removed during the operation, the above operation is repeated. In other words, when the sheet cassette is detached in the middle, the state shown in FIG. 1A or 1D (the state in which the bottom plate 1 is lowered) is reached. From this state, the rising of the bottom plate 1 starts and the paper surface position is detected. A series of operations including detection of the sheet 3 by the sensor 4, counting of the time from the start of the ascent to the turning-on of the sensor, and estimation of the sheet stacking amount from the count value and the ascending speed of the bottom plate 1 are performed. FIG. 1A shows a state after the paper cassette is detached when the paper 3 is replenished and full or a large amount is stacked, and FIG. 1D shows a state after the paper cassette is detached when the paper 3 is not replenished. It is a state of. 1A, the CPU 11 counts the time from the state shown in FIG. 1A to the state shown in FIG. 1B while the bottom plate 1 is being lifted. Figure 1
In the case of (D), the CPU 11 moves up the bottom plate 1 while
The time from the state of (D) to the state of FIG. 1 (E) is counted.

When the power supply of the apparatus is turned on, the CPU 11 confirms that the state of the cassette set detection SW 16 is on,
The state of the paper surface position detection sensor 4 is checked. When the state of the paper position detection sensor is off, the bottom plate driving motor 18 is driven through the motor driver 15 while monitoring the state of the paper surface position detection sensor 4, and the bottom plate 1 is raised until the paper surface position detection sensor 4 is turned on. Let it. The CPU 11 includes the bottom plate 1
During the rising process, the time from when the rising is started to when the paper surface position detection sensor 4 is turned on, that is, until the state shown in FIG. 1B is reached is counted. Then, the CPU 11 estimates the sheet stacking amount n from the count value (t) and the rising speed of the bottom plate 1. Here, the CPU 11 transmits the data of the above-described paper stacking amount n to the controller board 20 via the controller I / F 17. In the controller board 20, the received data is recorded in the nonvolatile memory. In this state (the state of FIG. 1B), the image forming apparatus waits until a print command is received from the host device. Subsequent operations are the same as in claim 1.

When the power supply of the apparatus is turned on, the CPU 11 confirms that the state of the cassette set detection SW 16 is on,
The state of the paper surface position detection sensor 4 is checked. The ON state of the paper surface position detection sensor means that the paper cassette is not attached or detached and the bottom plate 1 is not lowered when the apparatus is not powered on. In this case, the CPU 11
Controller board 2 via controller I / F17
After receiving the recorded value of the remaining amount of paper recorded in the non-volatile memory of 0, that is, the value immediately before the power of the apparatus is turned off, and recognizing the value as the current remaining amount of paper, the apparatus waits until a print command is received. . In other words, when the device is not powered on,
If the sheet cassette is not attached or detached and the bottom plate 1 is not lowered, the remaining amount of sheets in the sheet cassette should be the same as before the power supply of the apparatus is turned off. Therefore, in the non-volatile memory of the controller board 20, the value in the state immediately before the power of the apparatus is turned off or the state very close to it should be recorded. Therefore, the CPU 11
Estimates the value of the remaining amount of paper recorded in the non-volatile memory of the controller board 20 as the current remaining amount of paper, and enters a print standby state. Subsequent operations are the same as in claim 1. Next, the operation of this embodiment will be described with reference to the flowcharts shown in FIGS. This flow shows the content of the paper remaining amount detection process executed by the CPU 11 mounted on the engine board 10, that is, the content of the portion related to the paper remaining amount detection operation of the control program stored in the ROM 12.

The routine shown in FIG. 3 starts from a state where the power of the apparatus has already been turned on (S1). CPU11
When it is detected that the state of the cassette set detection switch 16 has changed from off to on, that is, that the sheet cassette has changed from the non-set state to the set state (S2), the state of the paper surface position detection sensor 4 is first determined. Confirm (S3).
Here, if the state of the paper surface position detection sensor 4 is not OFF (No in S3), the paper surface position detection sensor 4 is turned on even though the paper 3 in the paper feed cassette should not have reached the upper limit position. Since it is an abnormal state that is ON, error processing is performed. If the state of the paper surface position detection sensor 4 is off, the value t of the time counter and the value n of the number counter are set to 0 (clear) (S4). Next, the ascent of the bottom plate 1 is started (S5), and the time is counted until the paper surface position detection sensor 4 is turned on (S6). When it is confirmed that the paper surface position detection sensor 4 is turned on (S7), the stacking amount of the paper 3 is calculated from the count value t of the time counter (S8), and the result n is transmitted to the controller board 20 via the controller I / F17. After the transmission (S9), the ascent of the bottom plate 1 is immediately stopped (S10). Thereafter, the process stands by until a print command comes (S11). When a print command is received, a paper feeding operation is started (S12). Since the remaining amount of paper decreases as the paper is fed, and the bulkiness of the paper 3 decreases, the CPU 11 constantly monitors the state of the paper surface position detection sensor 4 (S13).
If it is off (paper is not detected) (No in S13), the bottom plate 1
Is raised (S14), and if ON (paper detection) (S14).
13 (Yes), the lifting of the bottom plate 1 is stopped (S15). That is, the ascending movement of the bottom plate 1 is controlled so that the paper 3 is detected by the paper surface position detection sensor 4. At that time, the CPU 11 increments the value n of the number counter (substitutes n-1 for n) every time sheet feeding is performed, and then transmits the value to the controller board 20 via the controller I / F 17 (S17). ). Thus, claim 1
Corresponding to.

The routine shown in FIG. 4 starts when the power of the apparatus is turned on (S21), and the CPU 11 first checks the state of the paper surface position detection sensor 4 (S22).
If the state of the paper surface position detection sensor 4 is off (S
22; No), the paper cassette is detached while the apparatus is turned off, and it is determined that the bottom plate 1 of the paper cassette is at the lower limit position, and the process proceeds to step S4 and subsequent steps in FIG. . The above corresponds to claim 2. Paper position detection sensor 4
Is ON (Yes in S22), the paper cassette is not attached or detached while the power of the apparatus is turned off, and the power of the apparatus is turned off in the state of the bottom plate 1 of the paper cassette. It is determined that the loaded amount of paper 3 has not changed, and the value of the remaining paper recorded in the non-volatile memory is received from the controller board 20 via the controller I / F 17 in the same manner as immediately before. (S23), FIG.
The process proceeds to step S11 and subsequent steps. The above corresponds to claim 3. As described above, in this embodiment, when the power of the image forming apparatus is already turned on, the cassette set detection SW 16 monitors the attachment / detachment of the sheet cassette, and detects that the sheet cassette has been set. In this case, the bottom plate 1 of the paper feed cassette is raised until the top of the paper 3 is detected by the paper surface position detection sensor 4, and the time from the start of the rise to the detection of the paper 3 is counted. After estimating the amount of paper 3 loaded on the bottom plate 1 and recording the value in a non-volatile memory, the apparatus is shifted to a standby state. Each time paper is fed from the cassette, the value is decremented, the updated value is recorded in the non-volatile memory, and the updated value is regarded as the current remaining amount of paper, and the remaining amount of paper is calculated. Since so as to view, increases the number of parts, complicating the mechanism, without complicating the control circuit, it is possible to detect the remaining amount of sheets stacked in the sheet cassette continuously.

Further, even when the sheet cassette is detached while the power of the image forming apparatus is turned off, the bottom plate 1 is raised until the top of the sheet 3 is detected by the sheet position detecting sensor 4. Paper 3
Is counted, and the amount of paper 3 loaded on the bottom plate 1 is estimated from the count value.
Since the value is regarded as the remaining amount of paper when the power is turned on, the remaining amount of paper is monitored, so that the remaining amount of paper 3 loaded in the paper feed cassette can be similarly detected steplessly. . If the paper cassette is not attached or detached while the power of the image forming apparatus is turned off, a recording value of the remaining amount of paper recorded in the nonvolatile memory is received, and the value is supplied to the power supply. Since the remaining amount of paper is monitored by considering it as the remaining amount of paper at the time of insertion, similarly, the remaining amount of paper 3 loaded on the paper feed cassette can be continuously detected. In the above-described embodiment, a photo-interrupter-type sensor including a light source and a light-receiving device that receives light from the light source is used as the paper-surface position detection sensor 4. However, instead of this, a photo-reflector type sensor, A light source, a reflector that reflects light from the light source, and a light receiver that receives light reflected from the reflector may be used. Further, a sensor that is turned on (or turned off) when it is in contact with or close to the upper surface of the paper 3 loaded on the paper feed cassette, a sensor that detects a distance from the upper surface of the paper 3, or the like may be used.

[0015]

As described above, according to the first aspect of the present invention, the uppermost part of the sheet is detected by utilizing the sheet detecting means for detecting whether or not the uppermost part of the sheet is at the sheet feeding position. The bottom plate of the paper feed cassette is raised until the paper is detected, the time from the start of the rise until the paper is detected is counted, the amount of paper loaded on the bottom plate is estimated from the count value, and the Since the remaining amount of paper is monitored based on the amount of used paper, the remaining amount of paper loaded in the paper cassette can be reduced without increasing the number of parts, complicating the mechanism, and complicating the control circuit. It is possible to provide an image forming apparatus having a sheet remaining amount detecting function capable of detecting at a stage. According to the second and third aspects of the present invention, whether the paper cassette is inserted or removed while the power of the apparatus is turned off or not, when the power of the apparatus is turned on and when the apparatus is not inserted or removed. It is possible to provide an image forming apparatus having a paper remaining amount detecting function capable of continuously detecting the remaining amount of paper in accordance with the printing operation.

[Brief description of the drawings]

FIGS. 1A to 1E are diagrams illustrating the configuration and operation of a sheet feeding unit of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram illustrating a circuit configuration of a part related to remaining paper amount detection of the image forming apparatus according to the present invention.

FIG. 3 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 4 is a flowchart showing another operation of the embodiment of the present invention.

[Explanation of symbols]

1: bottom plate, 4: paper surface detection sensor (paper detection means), 3:
Paper, 10: Engine board (control unit), 11: CP
U, 12: ROM, 13: RAM, 15: motor driver (driving means), 16: cassette set detection SW, 1
7: controller I / F (interface), 18: motor (driving means), 20: controller board (control unit).

Claims (3)

[Claims] A drive means for raising a bottom plate of a paper feed cassette loaded with paper; a paper detection means for detecting that the top of the paper has reached a predetermined position at the start of paper feeding by raising the bottom plate; Cassette mounting detecting means for detecting whether or not the paper cassette is mounted on the apparatus main body; and opening the connection between the bottom plate and the driving means when the paper cassette is pulled out of the apparatus main body. A sheet feeding unit having a mechanism for returning the bottom plate to the lower limit position, an engine unit including a drawing unit for forming an image on a sheet fed from the sheet feeding unit, and controlling driving of the engine unit A control unit that monitors a remaining amount of paper in the paper cassette, wherein the control unit changes a state of the paper cassette from a non-mounting state to a mounting state by the cassette mounting detection unit. If it is detected, the bottom plate is raised by the driving unit until the top of the paper is detected by the paper detection unit, and the time from the start of the rising until the paper is detected is counted, and After estimating the amount of paper loaded on the bottom plate, recording the value in a non-volatile memory, shifting the apparatus to a standby state, and thereafter, when the apparatus starts an image forming operation, Each time paper is fed from the cassette, the value is decremented, the updated value is recorded in the nonvolatile memory, and the updated value is regarded as the current remaining amount of paper, and the remaining amount of paper is monitored. An image forming apparatus comprising: 2. The control section checks the state of the sheet detecting means when the apparatus is turned on, and detects an uppermost portion of the sheet by the sheet detecting means when no sheet is detected. The bottom plate is raised by the drive unit until the time is elapsed, the time from the start of the lifting until the sheet is detected is counted, the amount of paper loaded on the bottom plate is estimated from the count value, and the value is calculated. After recording in the non-volatile memory, the apparatus is shifted to a standby state, and thereafter, when the apparatus starts an image forming operation, the value is decremented each time paper is fed from the paper feed cassette, 2. The image forming apparatus according to claim 1, wherein the updated value is recorded in the non-volatile memory, and the updated value is regarded as the current remaining amount of paper and the remaining amount of paper is monitored. 3. The control unit checks the state of the sheet detection unit when the apparatus is turned on, and when the sheet is detected, the remaining amount of the sheet recorded in the nonvolatile memory. After reading the value of
Thereafter, when the apparatus starts an image forming operation, each time paper is fed from the paper feed cassette, the value is decremented, and the updated value is recorded in the nonvolatile memory,
3. The image forming apparatus according to claim 1, wherein the updated value is regarded as the current remaining amount of paper and the remaining amount of paper is monitored.