JPH01186924A - Original size detector for image forming device - Google Patents

Abstract

PURPOSE:To accurately detect the size of an original by storing the counted value of a first counter means at the time of switching of the discrimination result of a comparing means from the presence to the absence of the original and performing counting in a second counter means during the absence of the original and discriminating the size of the original in accordance with the last counted value in a storage means which is obtained when the counted value of the second counter means exceeds a prescribed value. CONSTITUTION:A comparing means compares the signal from an optical sensor means 51 with a reference value, and the counted value of the first counter means is stored in the storage means when the discrimination result of the comparing means is switched from the presence to the absence of an original D. That is, the counted value of the first counter means is rewritten with the latest value and is stored in the storage means every time when the discrimination result of the comparing means is switched from the presence to the absence of the original D. The second counter means performs counting while the discrimination result of the comparing means is the absence of the original D; and when its counted value exceeds a prescribed value, a discriminating means detects the size of the original in accordance with the counted value stored in the storage means at last. Thus, the correct original size is detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a document size detection method for detecting the size (length) of a document placed on a document table in an image forming device such as a copying machine or an image reader. Regarding equipment.

[Conventional technology and its problems]

In an image forming device, such as a copying machine, which includes a document table on which a document is placed and an optical system that scans the document on the document table,
Some copy machines select the size of copy paper according to the size of the original placed on the document table, and the lens moves according to the original size and copying magnification. is provided with a document size detection device for automatically detecting the size of the document.

Conventional document size detection devices use an optical sensor that receives reflected light from the document and outputs a signal according to the light intensity, and compares the output signal of the optical sensor with a fixed reference value that is unrelated to the document size. and a comparator that outputs a signal indicating the presence or absence of a document, and the document size is determined at the time when the comparator outputs a signal indicating the presence or absence of a document (Special Publications No. 6).
0-4974).

However, original documents have various densities and patterns, and the intensity of reflected light from the original varies greatly. For this reason, it is extremely difficult to set a standard value for the presence or absence of various originals, and the intensity of reflected light exceeds the standard value even if there is an original, resulting in the occurrence of no originals. Therefore, it has been difficult to reliably detect the presence or absence of a document.

Therefore, in the conventional document size detection device described above, there is a possibility that the length of the document is determined to be shorter than the actual length, and the document size is determined to be smaller.

Further, in the conventional document size detection device, a preliminary scan for detecting the document size is performed over the entire length of the document table, so there is a problem that it takes time to detect the document size.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to accurately detect the document size and to detect the document size in as short a time as possible depending on the document size.

[Means to solve the problem]

The present invention provides an image forming apparatus that includes a document table on which a document is placed and an optical system that scans the document on the document table. A light sensor means for outputting light, a scanning drive means for moving the light received by the light sensor means relative to the document, and a reference point detection means for detecting a reference point of the scanning drive means;
a first counter means that starts counting upon detection by the reference point detection means; a comparison means that compares a signal from the optical sensor means with a reference value to determine the presence or absence of a document;
a storage means for storing the count value of the first counter means when the judgment of the comparison means changes from document presence to document absence; counter means; and the second
The present invention is characterized in that the apparatus further comprises determining means for determining the document size from the count value last stored in the storage means when the counter means exceeds a predetermined value.

[For production]

The optical sensor means receives the light from the optical system or the light reflected from the document by the light from the dedicated light projector, and outputs a signal corresponding to the intensity of the light. The reference point detection means detects a reference point between the optical sensor means and the document, and the counting operation of the first counter means starts from the point in time when the reference point is detected.

The comparison means compares the signal from the optical sensor means with a reference value to determine whether there is a document or not, and when the determination result changes from the presence of a document to the absence of a document, the count value of the first counter means is stored. Memorize in the means. In other words, each time the judgment result of the comparison means changes from document present to document absent, the count value of the first counter means at that time is stored in the storage means by being sequentially rewritten or updated to the latest value. Ru.

The second counting means performs counting while the judgment result of the comparison means is that there is no original document, and when the count value exceeds a predetermined value, the judgment means calculates the original document from the count value last stored in the storage means. Detect size.

Therefore, even if the light intensity fluctuates depending on the pattern or density of the original, and the signal from the optical sensor exceeds the reference value, which may result in a no-original signal being output while the original is being detected, this will be ignored. The correct document size will be detected.

Note that in the present invention, the document size refers to A4, A5, B
It may be a standard size such as S, or it may be the length of the document itself.

〔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.

A photosensitive drum 1 that can be rotated counterclockwise is disposed approximately in the center of the copying machine body, and around it are a main eraser lamp 2, an LED array 4, a charger 5, a developing device 6a, 6b.

A 6C1 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 10.

The optical system 10 is installed below the original glass 16 so as to be able to scan the image on the original, and is composed of a light source 11a, movable mirrors 11, 12, 13, a lens 14, and a mirror 15. A scanner 31 equipped with a light source 11a and a movable mirror 11 moves at a speed of v/n (n is a copying magnification) with respect to the circumferential velocity V of the photoreceptor drum 1, and a slider 32 equipped with a movable mirror 12.13. is driven by a scan motor to move at a speed of V/2n.

Note that 17 is a document cover, and the lower surface of the document cover 17, that is, the surface on the side that presses the document tray, is colored yellow to facilitate optical detection of the document tray.

FIG. 2 shows the light if! of the optical path of the optical system 10. 11a is a schematic diagram showing a linear development of light emitted from a document printer and reflected by a document printer until it reaches a lens 14, a first sensor 5, and a second sensor 52. FIG.

Referring also to the figure, a reference position sensor 50 is provided below the tip of the original glass 16, which is turned on and off as the scanner 31 moves. Detects the position of the tip and outputs a reference signal. Further, in the vicinity of the lens 14, a first sensor 51 is provided for receiving the light emitted from the light RHa and reflected by the document tray, and detecting the presence or absence of the document at a specific position in the length and width direction of the document tray. and a second sensor 52 are provided.

The first sensor 51 is connected in the length direction of the original document (scanner 3
This is to detect the size of the scan direction (1).
It is arranged so as to receive the reflected light from the document plate during preliminary scanning by the scanner 31 for all standard size documents placed on the document glass 16 . 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 first sensor 5
1 is disposed toward the center of the document glass 160 in the width direction, and receives reflected light from near the center of the document glass 160 by preliminary scanning by the scanner 31.

Further, the second sensor 52 receives reflected light from a position different from that of the first sensor 51, and the second sensor 52 receives reflected light from a position different from that of the first sensor 51.
This is for detecting the setting direction, whether it is placed vertically or horizontally on top. For example, for an A4 size or B5 size document, it is placed in a position where it does not receive the reflected light from the document placed vertically, but only the reflected light from the document placed horizontally. ing.

The first sensor 51 and the second sensor 52 are provided with blue transmission filters, which, together with the fact that the document cover is colored yellow, facilitates optical detection of document defects. In addition, 53 performs automatic exposure adjustment,
This is an AE sensor that detects the density of the document.

On the other hand, there are paper feed rollers 21 on the left side of the copying machine body.
．． An upper collar paper section 20 and a sketch paper section 22 are provided, and the copy paper fed from either of them is passed through a pair of rollers 24,
Timing roller pair 26, conveyor belt 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. 3 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 71.7 for starting the copying operation, and a display section 72.0 that includes a seven-segment LED and 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 ) for specifying copy paper by size and vertical/horizontal direction, paper display section 92a for displaying the size and vertical/horizontal direction of the selected copy paper, automatic paper selection mode, automatic magnification selection mode, and manual mode. A mode switching key 93 for sequentially switching the mode, a mode display section 93a to 93c for displaying the switched mode, etc. are arranged, and although not shown, there are also mode display sections 93a to 93c for sequentially changing and setting the copy image density. An up key, a down key, a density display section for displaying the set density, a magnification setting key for manually setting the copying magnification, a magnification display section for displaying the set magnification, etc. are arranged.

FIG. 4 is a circuit diagram showing a control circuit of the copying machine.

201 is a CPU (central processing unit) consisting of a microcomputer, and the analog input terminal of 200 P U2O5 is connected to amplification units 203 and 204 that amplify the outputs of the first sensor 51 and the second sensor 52, In addition, the various keys mentioned above, the display section, and drive circuits for the motor and clutch are connected.

In this embodiment, before the scanner 31 performs exposure scanning for copying, in order to detect the size of the document paper,
During a preliminary scan in which the scanner 31 performs a preliminary scan in which the document tray is irradiated and moved, reflected light from the document tray is transmitted to the first sensor 51 and the second sensor 52.
incident on . The first sensor 51 and the second sensor 52 output a signal according to the intensity of the received light, and after the signal is amplified by the amplification sections 203 and 204, it is sent to the first CP.
Input to U2O5.

The CPU 205 digitally converts the signals input from the amplifiers 203 and 204, and based on the data obtained, determines the size of the original paper and its setting direction (or horizontal direction) according to a program stored inside the CPU 201. )
It detects the document size and executes control according to the document size and setting direction.

The reference position sensor 50 is used to detect the leading edge of an image during a copying operation, and obtains a reference signal that serves as a reference point for measuring the document length during a preliminary scan for detecting the document size. used for

FIG. 5 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 in the scanning direction.

When the scanner 31 reaches near the leading edge of the document tray, the scanner 31 activates the reference position sensor 50.
A reference signal is output from the reference position sensor 50.

A first counter inside the CPU 201 is started at the timing when the reference signal is output. Thereafter, the first counter counts up at regular intervals.

The CPU 2 O 5 samples the signal from the first sensor 51 and digitally converts it into detection data, and compares this detection data with a certain reference value. When this data is larger than the reference value, 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 CPU U2O5 changes from document present to document absent, the count value of the first counter at that time is
The length memory is stored in the internal memory of the PU 201.

The contents of the length memory are rewritten every time there is a change from the presence of a document to the absence of a document, so that only the latest count value is stored.

Also, at the same time as the document changes from having a manuscript to not having a manuscript, the CP
A second counter inside U201 starts. The second counter that has started stops when there is a change from no document to a document present, and then when the state changes again to no document, the count value is cleared and the count is started again.

If the count value of the second counter exceeds a predetermined value (predetermined time), it is assumed that there is no document residue in the position of the scanner 31 at that time, and the preliminary scan is terminated, and the scanner 31 is returned to its original position (home position).

The document length is determined by the count value finally stored in the length memory.

In other words, even if the signal from the first sensor 51 fluctuates depending on the pattern or density of the document, or if it is determined that there is no document even though there is a document, the second counter is still counting. When the document status changes during a predetermined period of time, only the count value when the status changes to the document status next time is stored in the length memory, and the document length is ultimately determined by the final count value.

Therefore, the light intensity fluctuates depending on the pattern and density of the original, and even if it is determined that there is no original while the original is being detected, this will be ignored and the original length will not be detected as short. The correct document length is detected.

The second sensor 52 is for detecting the setting direction of the document tray as described above, and is for measuring the presence or absence of the document in the width direction. After the above-mentioned reference signal is output, the CPU 2O5 Signal of sensor 52 (amplifier 2
04 output) at a constant period, converts it into digital data, and compares the obtained data with a constant reference value. When this data is larger than the reference value, it is determined that there is no document, and when the opposite is true, it is determined that there is a document. If the number of times it is determined that there is a document out of the predetermined number of data is greater than or equal to a predetermined number, it is determined that the document tray is set in the horizontal direction.

Based on the results of determining the document length and setting direction, the document size such as A4, A5, BS, etc. and the setting direction are correctly detected. Moreover, since the length of the document in the document tray can be detected after scanning the length of the document tray for a certain period of time, if the length of the document tray is short, the scanner 31 can detect the length of the document on the document glass. It is not necessary to perform a full scan over the entire length of 16 pages, the document size can be detected in a short time, and it is possible to suppress a decrease in the start-up speed (first copy speed) of the copying machine as much as possible.

Next, based on the flowcharts in FIGS. 7 to 10,
The copying operation and original size detection operation of the copying machine will be explained.

FIG. 7 is a main flowchart of the copying machine.

In step #1, the CPU 2O5 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, an internal timer is set to define the length of one routine. This will result in steps #3~
Processing No. 10 is performed at regular intervals.

In step #3, various keys on the operation panel 70, the reference position sensor 50, the first sensor 51, and the second sensor 52 are used.
, and other input routines for inputting signals from switches and sensors (not shown).

In step #4, based on the input result of step #3,
Detects the operating status of the copying machine, such as the occurrence of trouble or jams. Based on the result, it is determined in step #5 whether a copying operation is possible.

If the copying operation is possible, a copying operation routine is executed in step #6, and if not, an abnormality handling routine is executed in step #7.

In step #8, a document size detection routine for detecting the document size is executed.

In step #9, data to be displayed on each display section of the operation panel 70 is processed, and in step #10, the data is displayed and signals for controlling each section of the copying machine are outputted.

After performing these processes, in step #11, the previously set internal timer is waited for, and the length of one routine is controlled to be constant.

FIG. 8 is a flowchart of the input routine of step #3 described above.

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 paper selection without detecting the document size. There are three types of detection modes: a manual mode in which the detection mode and the copy magnification are manually set, and when each detection mode is selected, a message to that effect is displayed on the mode display sections 93a to 93C.

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

In AMS mode, set the flag FAMS indicating AMS mode to "1", reset the flags indicating other detection modes (step #26), and set the length state and width state to "1" (step #26). 27) Set the content of the original 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 (step #29).
, in order to not perform document size detection, reset the length state and width state to "O" Step #30
), 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 a rotational manner: APS mode→AMS 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 according to the above-described 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.

FIG. 9 is a flowchart of the copy operation routine of step #6 described above.

The length state and the width state are states that control document size detection, and during detection, they hold values of "1" to "4" depending on the state at that time.

These states become "0" in two cases: in a manual mode in which document size detection is not performed, and in a case in which the optical system 10 returns to the home position after completion of document size detection.

First, in steps #41 and #42, it is determined whether or not the document size detection process is in progress depending on whether the length state and the width state are not rQJ. If it is determined that the document size detection process is not in progress, the process proceeds to step #46 to create a copy. Execute the processing (including processing in the standby state) to do so. If it is determined that the process is in progress, the process from step #43 onwards is executed.

In step #43, the presence or absence of a scan request is checked. If there is a scan request, the scanner 31 is caused to scan in step #44. If there is no scan request,
In step #45, processing for returning the scanner 31 is performed.

FIGS. 10a to 10c are flowcharts of the document size detection routine of step #8 described above.

In step #50, the contents of the length state are checked, and if the length state is between "1" and "4", the process branches to steps #51, 61, 71, and 81, respectively.

When the length state is "1" and "2", the document length is detected, and when the length state is "3", the document size is detected based on the document length and the document setting direction. will be held.

When APS mode or AMS mode is selected, the length state is "1" in steps #24 and #27.
, the process starts from step #51.

When the manual mode is selected, the length state is "O", so these steps are not executed and the process proceeds to step #90.

When the length state is "1", first step #5
1, it is determined whether or not a reference signal is output from the reference position sensor 50 located in the middle of the moving route of the scanner 31. When the reference signal is being output, the first counter is cleared in order to measure the document length, and the length memory that stores the content of the first counter at the time when the document changes from document present to document absent, and document length memory. Each document flag indicating the presence or absence is initialized.

In step #53, the length state is set to "2".

Thereafter, the process proceeds to step #90 in which a process for detecting the setting direction is performed, but the process for detecting the document length will be described first.

When the state is "2", the first counter is incremented in step #61, and in step #62,
The output of the first sensor 51 is checked to determine the presence or absence of document paper in the length direction. If it is determined that there is a manuscript (
If the answer to step #62 is NO), the document flag is set to "0" (document present).

As the scanning by the scanner 31 progresses and it is determined that there is no document (YES in step #62), the document flag is checked (step #63). The content of the document flag checked here is the document presence/absence state one routine before, so the document flag is r□.

In the case of (manuscript present), the process advances to step #64, and a process is performed when the document changes from the document present to the document absent.

That is, in step #64, the original flag is set to "1".
(no original), and the contents of the first counter at that time are stored in the length memory. Next, in step #65, the second counter is cleared and counting is started in order to determine whether or not there continues to be no document. .

From now on, each time this routine is executed, the process proceeds in the order of step #61 -> step #62 -> step #63 -> step #66.

In step #66, the second counter is incremented, and in step #67, it is determined whether the second counter has reached a predetermined value. If the second counter has reached the predetermined value, the length state is set to "3" (step #68 ).

The flow described so far is used to process a document with almost no density contrast. However, documents that are actually used have various density patterns. For example, in a document with solid black, the intensity of reflected light decreases extremely when scanning the solid black portion, and the first sensor 5
The signal of 1 will be at the level of no document. Even in such a case, the document length can be detected correctly by the process described below.

Hereinafter, the document length detection operation will be explained with reference to FIG. 6, which shows an example of data fluctuations.

When the scanner 31 is in the section 81 in FIG. 6, that is, when the first sensor 51 is detecting the section B1 in FIG. 6, it is determined that there is a document, so step #6
The determination in step #2 is no, and the process proceeds to step #69.

When the first sensor 51 reaches point 82 in the figure,
The process changes from having a manuscript to not having a manuscript, and the determination at step #62 becomes YES, and the process proceeds to step #63. Since the manuscript flag is still "0," the determination at step #63 becomes YES, and the process proceeds to step #64. Here, the original flag becomes "1".

When the first sensor 51 detects section 33 (for example, the solid black part) in the figure, it is determined that there is no document, and the document flag is "1", so step #6
Perform the processing from step 6 onwards.

If the interval of B3 is within the length corresponding to the predetermined value of step #67, by reaching the point of B4, step #6 is executed before the determination of yes is made in step #67.
2 is judged as no. Then, in step #69, the document flag becomes rQJ, and the next time there is no document, the second counter is reset in step #65. Therefore, the length state update process in step #68 is not executed, and the document length detection continues.

As a result, an erroneous determination that there is no original due to a solid black part in the middle of the original is ignored.

When the first sensor 51 detects the section B5 and the point B6, the same processing as the above-mentioned section 81 and point B2 is performed, and the contents of the length memory are detected at the point 86. The count value of the first counter is updated at .

If the length of the section B7 is longer than the predetermined value in step #67, it is assumed that there is actually no document left when the point B8 is reached, and the length state is set to "3" in step #68. , and finishes detecting the document length.

When the length state is "3", it is determined in step #71 whether the width state is "4", that is, whether the detection in the width direction of the document has been completed. The processing after gaff 2 is bypassed, and the processing here waits until the width state becomes "4".

When the width state becomes "4", in step #72, the document size and cent direction of the document are determined from the detection result of the document length and the document width direction.

In this example, among the sizes A3 to A5 and 84 to B6, the dimensions in the length direction are different except for the cases of A4 width and A5 length, and B5 width and 86 length. Since the setting direction can be determined only from the detection result of the document length, only in the above case, the setting direction is determined based on the detection result of the width direction of the document. Therefore, in the above case, if the detection result in the width direction is that there is a document, the setting direction is horizontal (A4 or B5), and if there is no document, the setting direction is vertical (A5 or B6).

Then, in step #73, the scan request is set to "0" in order to return the scanner 31, and in step #74, the length state is updated to "4".

When the length state is "4", it is determined in step #81 whether the scanner 31 has returned to the home position, and if it has returned, both the length state and the width state are set to "O" in step #82. ” and return to the main routine.

Next, the processing from step #90 onwards will be described regarding detection in the width direction of the document.

In step #90, the content of the width state is checked, and if the width state is between "1" and "3", step #91. Branch to either Lot, 111.

When the APS mode or AMS mode is selected, the width state is "1", so the process is executed from step #91.

When the manual mode is selected, the width state is rQ, so these steps are not executed and the process returns to the main routine.

When the width state is "l", first step #91
In this step, it is determined whether or not a reference signal is output by the operation of the reference position sensor 50. When the reference signal is output, step # is activated to detect the document width direction.
92, a third counter for defining the measurement interval, a fourth counter for counting the number of measurements, and a fifth counter for counting the number of times when the measurement result indicates that a document is present.
Clear each counter.

In step #93, the width memory for storing the detection result in the width direction is cleared, and in step #94, the width state is updated to "2".

When the width state is "2", in step #101,
incrementing a third counter defining a measurement interval;
In step #102, it is checked whether the contents of the third counter have reached a predetermined value.

If the number has not been reached, the process returns to the main routine, and if the number has been reached, step #103 and subsequent steps are executed.

In step #103, the fourth counter is incremented and the third counter is cleared. As a result, the processes after step #102 are performed at regular intervals.

In step #104, the count value of the fourth counter, ie, whether or not the measurement has been performed a predetermined number of times, is checked. If the measurement is within a predetermined number of times, the process advances to step #105, and the presence or absence of a document is checked based on the signal from the second sensor 52. If there is a document, the fifth counter is incremented in step #106, and if there is no document, step #106 is bypassed.

As a result, the fifth counter counts the number of times there is a document present.

If measurements have been made a predetermined number of times (step #104)
(No), the width state is updated to "3" in step #107, and the process returns to the main routine.

When the width state is "3", the fifth counter is checked in step #111 to determine whether or not the number of times there is a document is greater than or equal to a predetermined number, and if it is greater than or equal to the predetermined number, step #112 is performed. The width memory is set to "1" (original present) in , and if the predetermined number of times is not reached, step #112 is bypassed. Finally, step #11
3 updates the width state to "4" and returns to the main routine.

When the width state is "4", the process immediately returns to the main routine.

According to the embodiment described above, the length of the document can be detected by the first 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 while the document size is being detected. Even if this happens, this is ignored and the correct document length is detected without the document being detected as short.

Furthermore, the second sensor 52 measures the presence or absence of the document in the width direction, making it possible to easily detect the direction in which the document is set.

Based on these determination results of the document length and setting direction, the document size and setting direction are correctly detected.

Moreover, since the length of the document in the document tray can be detected after scanning the length of the document tray for a certain period of time, if the length of the document tray is short, the scanner 31 can detect the length of the document on the document glass. It is not necessary to perform a full scan over the entire length of 16 pages, the document size can be detected in a short time, and it is possible to suppress a decrease in the start-up speed of the copying machine as much as possible.

In the above-described embodiment, the first sensor 51 and the second sensor 52 are provided near the lens 14 to receive the light reflected by the original document from the light source 11a.
Although the document tray is scanned in the length direction by moving the scanner 31 provided with It may be attached to 31. Further, the first sensor 51 and the second sensor 52 may be scanned by a driving means different from the scanner 31. The scanner 31, the first sensor 51, the second sensor 52, etc. may be fixed, and the original glass 16 may be moved together with the original.

In the above embodiment, the first to fifth counters, comparison means, and judgment means for detecting the document size are
This was realized in software by the U2O5 program, but
These may be realized by hard logic or the like.

〔Effect of the invention〕

According to the present invention, the light intensity varies depending on the pattern and density of the original, and even if it is determined that there is no original while detecting the original size, this is ignored and the original length is detected to be short. The correct document length can be detected without any errors, and therefore the document size can be detected correctly.

Moreover, the document length size can be detected after a certain period of scanning has been completed after the document length has been scanned, so if the document length is short, a full scan that spans the entire length of the document table is possible. This makes it possible to detect the document size in a short time and to minimize the decline in the start-up speed of the copying machine.

[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 schematic diagram showing the optical path of the optical system developed in a straight line, and FIG. 4 is a circuit diagram showing the control circuit of the copying machine; FIG. 5 is a timing chart showing the signal state when detecting the document size by preliminary scanning; FIG. Figure 6 is a timing chart showing an example of fluctuations in detection data to explain the document length detection operation, and Figures 7-
FIG. 10 is a flowchart showing the processing of the copying operation and document size detection operation in the CPU 2O5. 10...Optical system, 16... Original glass (original platen),
31... Scanner (scanning drive means), 50... Reference position sensor (reference point detection means), 51... First sensor (light sensor means), 201... CPU. Applicant Minolta Camera Co., Ltd. Agent Patent Attorney Yukio Kubo Figure 4 Figure 7 Figure 9

Claims (1)

[Claims] An optical sensor that receives reflected light from the original and outputs a signal according to the light intensity in an image forming device that includes a document table on which a document is placed and an optical system that scans the document on the document table. means, a scanning driving means for moving the light received by the optical sensor means relative to the document, a reference point detecting means for detecting a reference point of the scanning driving means, and a detection means for detecting a reference point by the reference point detecting means. a first counter means for starting counting; a comparison means for comparing the signal from the optical sensor means with a reference value to determine the presence or absence of a document; and when the determination of the comparison means changes from the presence of a document to the absence of a document. storage means for storing the count value of the first counter means, a second counter means for counting while the comparison means determines that there is no document; 1. A document size detecting device for an image forming apparatus, further comprising determining means for determining the document size from the count value last stored in the storage means when the document size is detected.