JPH0284675A - Image forming device - Google Patents

Abstract

PURPOSE:To shorten the lighting time of a light source by controlling the lighting starting timing of the light source so that the light source of an optical system is lighted after a certain time elapses from the start of scanning. CONSTITUTION:The light source 11a is lighted by a lighting control means 201 when a certain delay time elapses after starting the scanning of the optical system 10 for detecting the size of an original. The delay time is set so that the emitting light quantity of the light source 11a can rise to a specified value by the time when the light source 11a reaches the position of the trailing edge of the original D in the minimum size which can be detected. An optical sensor means 51 receives reflected light from the original D which is the light emitting from the light source of the optical system 10 and outputs a signal in accordance with the intensity of light. The size of the original can be detected by detecting the presence or absence of the original according to the receiving light quantity by the optical sensor means 51 and judging that a place where the absence of the original is detected finally is the position of the trailing edge of the original by an original size detection means 31. Thus, the lighting time of the light source can be reduced as much as possible and the rising temperature of an original platen and power consumption can be decreased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an i! Size (length) of the placed original
The present invention relates to an image forming apparatus having a document size detection device for detecting document size.

[Conventional technology and its problems]

Conventionally, image forming devices such as copying machines and image readers have been equipped with document size detection devices that automatically detect the size of the document placed on the document table. An appropriate size of copy paper is selected, and the lens is moved according to the document size and copy magnification.

Conventional document size detection equipment consists of an optical system that scans the document, an optical sensor that receives reflected light from the document and outputs a signal according to the light intensity, and an optical sensor that outputs a signal that is independent of the document size. The device is equipped with a comparator that outputs a signal indicating the presence or absence of a document by comparing it with a fixed reference value without a document, and the document size is determined at the time when the comparator first outputs a signal indicating the presence or absence of a document ( Special Publication No. 60-4974)
.

In such a conventional document size detection device, if scanning is started when the light source for illuminating the document is off or in a state where the amount of light is insufficient, sufficient reflected light cannot be obtained even though there is a document. I conclude that there is none.

Therefore, scanning for detecting the document size (preliminary scanning) cannot be started unless the light source is turned on and the amount of light reaches a specified value and becomes stable.

That is, when detecting the document size, the light source is turned on for at least the time required for the light source to stabilize and the time required for the light source to reach the trailing edge of the document after scanning.

Therefore, the temperature of the document table increases significantly due to radiant heat from the light source, and in particular, the temperature increase near the tip of the document table, which is the home position (standby position) of the light source, has become a problem.

Since the document table is a part that is directly touched by the operator, the temperature must be kept below a specified value for safety reasons, which poses problems such as difficulty in designing the temperature of the image forming device, such as setting the capacity of the cooling fan.

Further, as a matter of course, there is also the problem that power consumption is large because the lighting time of the light source is long.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide an image forming apparatus in which the lighting time of a light source for detecting the document size is shortened as much as possible.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a yj4 document table for placing a document on the R, an optical system for scanning the document on the document table, and an optical system for scanning the document from the optical system. an optical sensor means for receiving reflected light from the original and outputting a signal according to the light intensity, and detecting the presence or absence of an original based on the amount of light received by the optical sensor means, the image forming apparatus comprising: a document size detecting means that determines that the position where the blank is last detected is the trailing edge position of the document; and a light source of the optical system after a certain period of time has elapsed from the start of scanning by the optical system for detecting the document size. and a lighting control means for controlling the lighting start timing of the light source so that the light source is turned on.

The document size detection means for determining the trailing edge position of the document and the lighting control means for controlling the lighting start timing are realized by, for example, an appropriately programmed microcomputer and/or logic circuit.

[Function] The lighting control means turns on the light source after a certain delay time has elapsed after the scanning of the optical system for detecting the document size is started.

The delay time is set so that the amount of light emitted by the light source rises to a specified value by the time the light source reaches the rear end position of the document of the smallest size that can be detected.

The optical sensor means receives light reflected from the document by the light from the light source of the optical system, and outputs a signal corresponding to the intensity of the light.

The presence or absence of a document is detected based on the amount of light received by the optical sensor means, and the document size detection means determines that the position where the absence of a document is detected after J1 is the trailing edge position of the document, thereby detecting the document size.

〔Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front sectional view showing the general structure of a copying machine.

Approximately at the center of the copying machine body, a photosensitive drum l that can be driven to rotate in a counterclockwise direction is arranged, and around it are a main eraser lamp 2, an LED array 4, an electrostatic charger 5, a developing device 6a, 6b6c, a transfer charger 7, a separation charger 8, and a blade type cleaning device 9 are provided. The photoreceptor drum 1 has a photoreceptor layer provided on its surface, and its surface is uniformly charged by passing through an eraser lamp 2 and a charger 5, and receives image exposure from an optical system IO.

The optical system 10 is installed below a document glass 16 serving as a document table so that the image on the document tray can be scanned, and includes an exposure lamp lla serving as a light source, movable mirrors 11, 12, 13,
It is composed of a lens 14 and a mirror 15. Scanner 3 equipped with an exposure lamp Ila and a movable mirror 11
1 moves at a speed of v/n (n is the copying magnification) with respect to the circumferential speed V of the angry light body drum l, and the slider 32 equipped with a movable mirror 12.13 moves at a speed of V/2n. It is driven by a scan motor.

Note that the lower surface of the document cover 17, that is, the surface that presses the document holder, is colored yellow to facilitate optical detection of the presence or absence of the document holder.

A group of switches (not shown) are provided below the document glass 16, together with a document leading edge switch 50 that is turned on and off as the scanner 31 moves, and a home position switch 54 that detects the home position of the scanner 31.
The document leading edge switch 50 detects the leading edge position of the document tray when scanning the document tray or reading the document size, and outputs a reference signal.

Further, in the vicinity of the lens 14, a light emitted from the exposure lamp 11a and reflected by the document tray is received, and the presence or absence of the document at a specific position in the length direction of the document tray (scanning direction of the scanner 31) is detected. A light sensor 51 is provided for the purpose of the document glass 16, and is arranged to receive light reflected from the document plate during preliminary scanning by the scanner 31 for all standard-sized documents placed on the document glass 16. There is.

In other words, if the copying machine is of a type in which the document tray is set at the center position in the width direction of the document glass 16, the optical sensor 5
1 is disposed toward the center in the width direction of the document glass 16, and receives reflected light from near the center of the document glass 16 through preliminary scanning by the scanner 31.

The optical sensor 51 is provided with a blue transmission filter, which reduces the intensity of reflected light from the yellow-colored document cover 17, making it easier to optically detect document defects. There is.

On the other hand, there are paper feed rollers 21 on the left side of the copying machine body.
.
Timing roller pair 26, conveyance heald 27, fixing device 2
8 and a pair of discharge rollers 29, during which the image on the photosensitive drum 1 is transferred, fixed by the fixing device 28, and discharged onto the discharge tray 30.

FIG. 2 is a plan view of the operation panel 70 provided on the top surface of the copying machine.

The operation panel 70 includes a print start key 7117 for starting the copying operation, and a display section 72, O, which displays the number of copies and other information.
It consists of 10 numeric keys (from 9 to 9), including a numeric keypad 80 for inputting the number of copies, an interrupt key 90 for specifying interrupt copying, a clear/stop key 91, and a copy paper (paper ) by size, a paper display section 92a that displays the size of the selected copy paper, and a mode switching key 93 that sequentially switches between automatic paper selection mode, automatic magnification selection mode, and manual mode. , a mode display section 93axc for displaying the switched mode, and, although not shown, an up key and a down key for changing and setting the copy image density in steps,
A density display section for displaying the set density, a magnification setting key for manually setting the copy magnification, a magnification display section for displaying the set magnification, and the like are arranged.

FIG. 3 is a circuit diagram showing the control section of the copying machine.

201 is a CPU (central processing unit) consisting of a micro combinator, and the analog input terminal ANO of this CPU 201 is connected to an amplifying section 2 for amplifying the output of the optical sensor 51.
03 is connected, and other input terminals are connected to the various keys mentioned above, the display section, and drive circuits for the motor and clutch.

Further, an exposure lamp drive circuit that turns on or off the exposure lamp lla is connected to the output terminal PA4.

In this embodiment, before the scanner 31 performs exposure scanning for copying, a preliminary scan is performed in which the scanner 31 is moved while illuminating the document tray in order to detect the size of the document tray.

During preliminary scanning, reflected light from the document enters the optical sensor 51. The optical sensor 51 outputs a signal corresponding to the intensity of the received light, and the signal is amplified by the amplifying section 203 and then input to the CPU 201.

The CPU 201 digitally converts the signal input from the amplifying section 203, and based on the data obtained thereby, converts the signal into a C
A program stored in the PU 201 detects the size of the document and executes control according to the document size.

The document leading edge switch 50 is used to detect the leading edge of an image during a copying operation, and is used to obtain a reference signal that becomes a reference point for measuring the document length during preliminary scanning for detecting the document size. used for.

FIG. 4 is a timing chart showing signal states when detecting the document size by preliminary scanning. The document size detection operation will be explained with reference to this figure.

When the print start key 71 is turned on, a preliminary scan is started, and the scanner 31 starts moving at a constant speed from the home position in the scanning direction.

When the scanner 31 reaches the position directly below the leading edge of the document tray after the time TO has elapsed from the start of scanning, the scanner 31 operates the document leading edge switch 50 and switches the document leading edge switch 5.
A reference signal is output from 0.

At the timing when the reference signal is output, the CPU 201
A first timer for determining the scanning time (Tl) of the scanner 31 and a second timer for determining the lighting start timing of the exposure lamp lla are started. The first timer is set to a time T1 required to scan a document of the maximum size that can be detected. At this point, the exposure lamp
A is off.

The first timer and the second timer exist inside the CPU 201, and after starting, perform count amplification at regular intervals to update a state value representing the passage of time.

The CPU 201 determines that the state value of the second timer is the delay time T2.
When the value becomes equal to , the count-up of the second timer is stopped, and the exposure lamp 11a is turned on.

Note that the delay time T2 is set in consideration of the rise time T3 from when the exposure lamp lla is turned on until the prescribed light amount is reached.

In other words, the delay time T2 is set so that the time obtained by adding the rise time T3 to the delay time T2 is shorter than the time T4 required for the scanner 31 to scan between the front and rear edges of the minimum size document that can be detected. has been done.

Specifically, the rise time T3 of the exposure lamp lla is 0.5 seconds, and the scanning speed of the scanner 31 is 110 m/
If the smallest document size that can be detected is the size of a government postcard (100m x 148cm) vertically, the delay time T2
is within about 0.8 seconds.

Regardless of the state of the exposure lamp lla whose lighting start timing is controlled in this way, the CPU 201 controls the light sensor.
The signal from 51 is sampled and digitally converted to provide detection data, and this detection data is compared with a fixed reference value X. When this data is larger than the reference (Itx), it is determined that there is no document, and when the opposite is true, it is determined that there is a document.

When the judgment of the CPU 201 changes from there being a document to not having a document, the state value of the first timer at that time is sent to the CPU 201.
It is stored in the memory Δ which is the internal memory of 01. Memory A
The contents are written in literary terms that change from having a manuscript to not having a manuscript, and only the latest value is stored.

In other words, if the amount of light emitted from the exposure lamp lla does not reach the specified value, or if the signal from the optical sensor 51 changes or distorts due to the pattern or density of the original, etc. Even if it is once determined that there is no original, the state value of the first timer when the next time the state changes to no original is stored in the memory A.

When the first timer finishes counting time T1, the CPU2
01 instructs each drive circuit to turn off the exposure lamp lla and return the scanner 31 to the home position, and also determines the length of the document based on the state value finally stored in the memory A. do.

At this time, as mentioned above, the document length is determined based on the state value of the first timer when it was determined that there was no document last, and the document length is detected to be shorter than the actual length. Correct document size (A6, B5,
A4, B4, A3, etc.) are detected.

In this way, scanning by the scanner 31 starts immediately when the print start key 71 is turned on, without having to wait for the exposure lamp lla to start up (i.e., when the print start key 71 is turned on, the time required to detect the document size is shortened, and the start-up speed of the copying machine (fast (copy speed) can be increased.

Next, based on the flowcharts of FIGS. 5 to 8, the document size detection means and the lighting side i! The operation of the CPU 201, which functions as an If means, will be explained.

FIG. 5 is a main flowchart showing the overall operation of the copying machine.

In step #1, the CPU 201 is initialized after the power is turned on, and initial settings are made to put the copying machine into the initial mode.

In step #2, (1) an internal timer is set to define the length of the routine; This will result in steps #3~
Processing No. 12 is performed at regular intervals.

In step #3, it is checked whether or not a document size detection flag indicating whether or not document size detection is necessary is set in input processing (step #5) to be described later.

If the document size detection flag is reset to "0", the mode is manual mode, which will be described later, and the process proceeds to step #5 without detecting the document size.

If the document size detection flag is set to ``rl'', a document size detection routine based on the present invention is executed in step #4. This subroutine will be explained later.

In step #5, a manual routine is executed to input signals from various keys on the operation panel 70, the document leading edge switch 50, the optical sensor 51, the home position switch 54, and other switches and sensors (not shown).

In step #6, the operating state of the copying machine, such as the presence or absence of trouble or jamming, is detected based on the input result of step #5. Based on the result, it is determined in step #7 whether a copying operation is possible.

If the copying operation is possible, a copying operation routine is executed in step #8, and if not, an abnormality handling routine is executed in step #9.

At step #10, data to be displayed on each display section of the operation panel 70 is processed, and at step #11, the data is displayed and signals for controlling each section of the copying machine are output.

After performing these processes, in step #12, the previously set internal timer is waited for, and the process returns to step #2. This keeps the length of one routine constant.

While the power is on, step #2 to step #
12 processes are repeated.

FIG. 6 is a flowchart of the document size detection routine of step #4 described above.

First, in step #100, the detection state is determined. This detection state indicates the progress status of the document size detection process, and a value of "0" to "2" is sent, and depending on the value, the step #1 is
01.106.118.

When the detection state is "O" indicating the initial state in the document size detection routine, the process advances to step #101.

In step #101, in the preliminary scan started by keying in the print start key 71, it is determined whether the scanner 31 has moved to the document leading edge position and the document leading edge switch 50 has been turned on, that is, whether the reference signal has been output. is checked.

If the answer in step #101 is NO, the process returns and waits for the document leading edge switch 50 to be turned on.

If YES in step #101, step #102
~#105. Execute #200 in sequence.

In step #102, the detection state is set to "l", and then in step #103, a first timer for determining the end timing of the preliminary scan is cleared.

In step #104, the second timer for determining the lighting timing of the exposure lamp lla is cleared, and in step #1
At 05, the memory A storing the state value of the first timer is cleared. Also, in step #200, set the edge flag to “
0".

Steps #103 to #105. #200 is an initialization process for the original size detection operation.

In step #100, if the detection state is "1", processing from step #106 onwards is performed.

In step #106, the first timer is incremented.In step #107, it is determined whether the state value of the first timer has reached a predetermined value representing time Tl, that is, whether the first timer has ended. If the answer is NO, proceed to step #108.

The time T1 is 5. as described above. This determines the scanning time for detecting the document size, and is usually set to a value that provides some margin for the time required to scan between the front and back edges of the largest standard-sized document. Therefore, a negative determination in step #107 means that the scanner 31 is in the middle of scanning.

In step #108, a process is executed in which the signal from the optical sensor 51 input to the analog input port ANO of the CPU 201 is read and converted into digital data to obtain detection data.

In step #109, the presence or absence of a document is determined by comparing the detection data with the reference value X.

If YES in step #109, that is, if it is determined that there is no manuscript, it is determined in step #201 whether or not the edge flag is "l", and if it is "1",
It is not a process from having a manuscript to not having it, so step #1
Jump to 11. If it is "0", set the edge flag to "1" in step #202, and then in step #110, the CPU 20 sets the current state value of the first timer.
1. Store it in memory A inside 1. If no in step #109, set the edge flag to “
O” and jump to step #111.

Therefore, memory A is rewritten every time step #110 is executed, and the first timer is stored in memory A when it is determined that there is a document most recently and that there is no document during one preliminary scan. Only the value is stored.

In step #111, it is determined whether or not the second timer has expired. If no, the second timer is incremented in step #112, and the process returns.

If YES in step #111, step #111
At step 113, the exposure lamp lla is turned on, and then the process returns.

On the other hand, if the answer is YES in step #107, the process moves to step #114, where the content of memory A is read out, the document size is calculated from that value, and a process of displaying the document size is executed.

Subsequently, in step #115, the detection state is set to "2", in step #116, the exposure lamp 11a is turned off, and in step #117, the scan request flag is reset to "0", and the process returns.

In step #100 above, the detection state is “2”.
”, steps 6118 to #120 are performed.

That is, in step #118, it is checked whether the scanner 31 has returned to the home position based on the signal from the home position switch 54, and if it has not returned to the home position, the scanner 31 returns and returns. wait.

When returning to the home position, the detection state is set to "0" in step #119, the document size detection flag is set to "0" in step #120, the document size detection routine is ended, and the process returns to the main routine.

FIG. 7 is a flowchart of the above-mentioned step #5 person routine.

In step #21, it is determined whether the mode switching key 93 has been pressed or not, and if the key has been pressed, the processing from step #22 onwards is performed.

In step #22, the content of the document size detection mode counter is checked, and a detection mode is selected according to the content.

Detection mode is automatic paper selection mode (automatic paper selection mode) that detects the original size and selects paper of the same size based on the result.
APS mode), automatic magnification selection mode (AMS mode) that detects the document size and sets the copy magnification based on the result and the preselected paper size, and automatic magnification selection mode (AMS mode) that detects the document size and sets the copy magnification based on the paper size selected in advance. There are three types of manual modes in which the copy magnification is manually set, and when each detection mode is selected, a message to that effect is displayed on the mode display sections 93a-c.

In APS mode, set the flag FAPS indicating APS mode to "1" and reset the flag FAMSSFMANUAL indicating other detection modes (Step #23). Set the detection flag to "1" (step #24), and set the contents of the document size detection mode counter to "1".
” (Step #25).

In the AMS mode, set the flag FAMS indicating the AMS mode to "1", reset the flags indicating other detection modes (step #26), and set the document size detection flag to "1" (step #27). ), set the content of the document size detection mode counter to "2" (Step #28) In manual mode, set the flag FMANUAL indicating manual mode to "1" and reset the flags indicating other detection modes. Then, the document size detection flag is reset to "0" (step #30), and the content of the document size detection mode counter is set to "0" (step #31).

Through the above processing, each time the mode switching key 93 is pressed, the mode is switched in the following order: APS mode→ΔMS mode→manual mode→APS mode...

In step #32, it is determined whether or not the print start key 71 has been pressed, and if it has been pressed, the scan request flag is set to "1" and control n corresponding to the above-mentioned detection mode is started.

In step #34, signals from other keys on the operation panel 70, sensors arranged in various parts of the copying machine, etc. are input.

FIGS. 8a and 8b are flowcharts of the copying operation routine of step #8 described above.

First, in step #400, in order to determine whether the mode is for detecting the document size, the flag F M
Check whether A N tJ A L is "1".

If the flag FMANUAL is rlJ, it is manual mode and there is no need to detect the document size, so the processes from step #401 onwards are executed to perform normal copy control.

Steps #401 to #404 represent the steps from when the print start key 71 is pressed to when image forming preprocessing is performed.

First, after confirming that the scan request flag is set, the scan request flag is reset and the copy flag is set. Next, for preprocessing, the main motor, developing motor, charging charger 5, transfer charger 7, and separation charger 8 are turned on, respectively, and a timer A is used to determine the preprocessing time, a timer A is used to determine the on time of the paper feed roller, In order to wait for the exposure lamp lla to start up, a timer B that determines the time until the start of scanning is set, and the copy flag is reset.

When the timer E ends in step #405, the paper feed roller of the top picture paper section 20 or the bottom picture paper section 22 is turned on and timers A and timers 8 are set in step #406.

When the set time of timer A ends in step #407, the paper feed roller is turned off (step 4408), and the exposure lamp lla is turned on (step #409).

When the set time of timer B ends in step knob #410, the scan motor is rotated forward in step #411.
), thereby starting scanning of the optical system 10 including the scanner 31.

If the timing signal becomes "l" in step #412, the clutch of the timing roller pair 26 is turned on, a timer 0 that determines the on time is set, and a jam timer is set in step #413.

If the set time of the timer 〇 has elapsed in step #414, the charger 5,
The exposure lamp lla and the clutch of the timing roller pair 26 are turned off, the scan motor is reversed, and a return flag indicating that the optical system 10 has entered the return operation is set.

Next, if the return flag is 'lj' in step #416, the optical system 10 is in the return operation, so the process waits until the optical system 10 returns to the home position in step #417.

When the optical system 10 returns to the home position, the home position switch 54 is turned on and the home position signal becomes "rl", so in step #418, the return flag is reset, the scan motor is stopped, and the developing motor,
The transfer charger 7 and the separation charger 8 are turned off, and a timer D is set to stop the main motor.

When the set time of timer D ends in step #419, the main motor is stopped in step #420, and the copying operation ends.

On the other hand, if the answer in step #400 is NO, that is, if the flag FMANUAL is "0", the process from step #431 is executed to detect the document size.

In step #431, it is determined whether the document size detection flag is "l".

If the answer is yes in step #431, step #431
At 432, the presence or absence of a scan request is checked. If there is a scan request, the scan motor is rotated forward in step #433, and the main motor, developing motor, charger 5, transfer charger 7, and separation charger 8 are turned on in step #434.

At this point, the scanner 31 of the optical system 1O begins to move while the exposure lamp lla remains off, but by the time the scanner 31 reaches the rear edge position of the document of the smallest detectable document size (for example, A6 size). Since this takes time, if the exposure lamp lla has finished starting up by then, there will be no problem in the document size detection operation.

At the same time, the charging charger 5, the transfer charger 7, and the separation charger 8 are turned on, thereby performing preprocessing for the copying operation.

If there is no scan request in step #432,
At step #435, the scan motor is reversed, and at step #436, the copy request is set to "1".

On the other hand, if it is determined no in step #431 above,
Since the scanner 31 has returned to the home position, it is checked in step #440 that the copy request is "1", and then in step #441 the scan motor is stopped and the paper feed roller is turned on. Timer A&
and timer B, and set the copy request to "0".

This causes continuous copying operations to begin.

In other words, in steps #432 to 436, processing equivalent to the preprocessing in steps #401 to 404 described above has already been executed, so steps #401 to 436 are performed again.
The copying operation is started immediately by the process of step #441 without executing the process of step #44. by this,
The time required for copying operations is reduced.

According to the embodiment described above, the length of the document can be detected by the optical sensor 51, and the light intensity varies depending on the pattern and density of the document, so that it is determined that there is no document once while the document size is being detected. Even if this happens, this is ignored and the last position where no document was detected is determined to be the rear edge of the document, so the correct document size is detected without the document length being detected as short. .

Furthermore, since the exposure lamp lla can be turned on later than the start of scanning by the scanner 31, there is no need to wait for the exposure lamp 11a to start up before moving the scanner 31, and the first copy speed becomes faster.

Since the exposure lamp lla is turned off when scanning the leading edge of the document, which is always irradiated during copying and tends to accumulate heat, the rise in temperature of the document table is suppressed.

In the embodiment described above, the optical sensor 51 is connected to the lens 14.
The scanner 31 provided with the exposure lamp lla is moved to scan the document in the length direction, and the light sensor 51 may be attached to the scanner 31. Further, the optical sensor 51 may be scanned by a driving means separate from the scanner 31. The scanner 31, optical sensor 51, etc. may be fixed, and the original glass 16 may be moved together with the original.

In the above-mentioned embodiment, the first and second timers for detecting the document size, the document size detection means, and the lighting control means were realized in software by the program of the CPU 201, but they could also be realized by hard logic or the like. It's okay.

Further, in the above-described embodiment, in order to delay the lighting of the exposure lamp 11a, the second timer is operated based on the on-timing of the document leading edge switch 50. A timer may be activated.

〔Effect of the invention〕

According to the present invention, the document size can be accurately detected, and the lighting time of the light source during the document size detection operation can be shortened as much as possible, so that the temperature rise of the document table and the power consumption can be reduced. .

[Brief explanation of the drawing]

The drawings show embodiments of the present invention; FIG. 1 is a front cross-sectional view showing the general configuration of a copying machine, FIG. 2 is a plan view of an operation panel provided on the top of the copying machine, and FIG. 4 is a timing chart showing the signal state when detecting the document size by preliminary scanning, and FIGS. 5 to 8 are the processing of copying operation and document size detection operation in the CPU 20. It is a flowchart which shows. 10...Optical system, lla...Exposure lamp (light source),
16... Original glass (original platen), 31... Scanner 50... Original edge scan, 51... Optical sensor.
(Photosensor means), 201...CPIJ. Applicant Minolta Camera Co., Ltd.

Claims (1)

[Claims] (1) A document table on which a document is placed, an optical system that scans the document on the document table, and an optical sensor that receives light reflected by the document from the optical system and outputs a signal according to the light intensity. and an image forming apparatus configured to detect the presence or absence of a document based on the amount of light received by the optical sensor means, the document determining that the position where the absence of the document is last detected is the trailing edge position of the document. size detection means; and lighting control means for controlling the lighting start timing of the light source so that the light source of the optical system is turned on after a certain period of time has elapsed from the start of scanning by the optical system for detecting the document size. An image forming device characterized by: