JP2000284640A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten time from starting copying till finishing it or to reduce copying cost. SOLUTION: A joint detecting sensor 340 detects the joint of an endless belt. By controlling a retreat clutch 405, a retreat mechanism control part 404 switches a retreat mechanism to a basic position and a retreat position. The basic position is a position for supplying paper to all of cyan, magenta, yellow and black image forming units, and the retreat position is a position for supplying the paper only to the black image forming unit. The retreat mechanism control part switches the retreat mechanism from the basic position to the retreat position only when specified time elapses after the sensor 340 detects the joint of the endless belt and when a monochrome image forming mode is set.

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, and more particularly, to an image forming apparatus having a plurality of image forming units, which can make a path for conveying a recording medium different between a monochrome image forming mode and a color image forming mode. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art A digital copying machine that forms a full-color image by carrying a recording medium for forming an image on an endless belt and sequentially forming images with toners of different colors while conveying the recording medium is known. Are known. This digital copying machine forms an image using four color toners of cyan (C), magenta (M), yellow (Y), and black (K). One image is formed for each color. An image forming unit for forming is provided. Each time the recording medium passes through the image forming unit, an image of each color is formed, and when the recording medium passes through the four image forming units, the four color images are formed in a superimposed manner. as a result,
A full-color image is formed on the recording medium.

[0003] The image forming unit has a photosensitive drum for forming a toner image to be transferred to a recording medium.
When the photosensitive drum contacts the recording medium, the toner image formed on the photosensitive drum is transferred to the recording medium. Therefore, the endless belt carries the recording medium so that the carried recording medium can contact the photosensitive drum. Therefore, the endless belt comes into contact with the photosensitive drum even when the recording medium is not carried.

On the other hand, when a monochrome image is formed, only the black image forming unit for forming a black image is used, and it is not necessary to drive the image forming units for forming cyan, magenta and yellow images. However, as described above, since the endless belt is in contact with the photoconductor drum of the image forming unit, if these image forming units are not driven, the stopped photoconductor drum is worn at a portion where it comes into contact with the endless belt. Would. In addition, if the photoconductor drum is idled at the speed of the endless belt, wear due to contact with the endless belt can be prevented, but the photoconductor drum is made of a resin blade to remove excess toner. Is constantly in contact with the blade, and is worn by friction caused by contact with the blade.

In order to avoid this problem, there is a digital copying machine having a retraction mechanism for changing the trajectory of the endless belt between when forming an image in monochrome and when forming an image in full color. This retraction mechanism changes the trajectory that contacts all the image forming units with the photosensitive drums to the trajectory that contacts only the photosensitive drums of the black image forming units. Therefore, when forming an image in monochrome, the retraction mechanism changes the trajectory of the endless belt, so that the endless belt retreats from the photosensitive drum of the image forming unit that forms cyan, magenta, and yellow images.

Further, the endless belt has a seam because it is endless. Since the seam portion of the endless belt has different characteristics from other portions, there is a problem that an image is not formed well at the seam portion when the recording medium is conveyed at the seam portion of the endless belt. In order to avoid this, the recording medium is supplied to the endless belt so that the recording medium does not ride on the seam of the endless belt. For this reason, the position of the seam of the endless belt is detected, and control is performed so that the recording medium is not supplied to the endless belt when the endless belt is at a predetermined position.

[0007]

However, since the retracting operation of the endless belt by the retracting mechanism is performed mechanically, a predetermined time is required. Therefore, if the evacuation operation is frequently performed by the evacuation mechanism during the copy operation, the copy time becomes longer due to the time required for the evacuation operation. In particular, when a color original and a monochrome original are alternately copied, the copy operation and the operation of changing the trajectory of the endless belt by the standby mechanism are performed alternately, and the copy time becomes longer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has an image forming apparatus provided with a mechanism for switching a paper transport path between when a monochrome image is formed and when a color image is formed. An object of the present invention is to provide an image forming apparatus capable of shortening the time from the start of copying to the end of copying.

Another object of the present invention is to provide an image forming apparatus capable of reducing copy costs.

[0010]

According to one aspect of the present invention, there is provided an image forming apparatus, comprising: a plurality of image forming units for forming an image on a recording medium; A transport unit for transporting the recording medium in any of the second states, a switching unit for switching between the first state and the second state, and a detecting unit for detecting a reference point of the transport unit. Wherein the transport unit transports the recording medium to at least one of the plurality of image forming units in the first state, and transmits the recording medium to all of the plurality of image forming units in the second state. And the switching means is capable of switching from the second state to the first state only when the reference point is within a predetermined range.

According to the present invention, it is possible to provide an image forming apparatus capable of shortening the time from the start of copying to the end of copying.

Preferably, the switching means of the image forming apparatus is capable of switching from the second state to the first state even when the reference point is not within a predetermined range in the cost priority mode. And

According to the present invention, it is possible to provide an image forming apparatus capable of reducing a copy cost.

More preferably, the transport section of the image forming apparatus is a rotatable belt formed endlessly.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, one embodiment of the present invention will be described.
A digital copier will be described with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding members.

FIG. 1 is a schematic sectional view showing a schematic configuration of a digital copying machine according to one embodiment of the present invention. Referring to FIG. 1, digital copier 100 includes an automatic document feeder 101 for automatically transporting a document to an image reading position, an image reading unit 200 for reading image data from the document, and an image on paper. And an image forming unit 300 for forming the image.

The automatic document feeder 101 automatically conveys a document set on a document set tray 102 to an image reading position of the document reading section 200 when a print instruction is given from an operation panel described later. When the reading of the document is completed by the image reading apparatus 200, the document is discharged from the image reading position to the document discharge tray 103. When a plurality of documents are set on the document set tray 101, a series of operations of document conveyance, image reading, and document discharge are efficiently performed in order from the lowest document.

The image reading section 200 exposes an image of a document set on a document glass 208 by an exposure lamp 201 attached to a scanner that moves below the document. Light reflected from the document is guided to a lens 203 by a first mirror 206 and two reflection mirrors 202, and forms an image on a CCD sensor 204. The exposure lamp 201 and the first mirror 206 are attached to a scanner, and the scanner is moved by a scanner motor 209 in a direction indicated by an arrow (sub-scanning direction) at a speed V according to a copy magnification.
Thereby, the original set on the original glass 208 can be scanned over the entire surface. Further, with the movement of the exposure lamp 201 and the first mirror 206, the two reflecting mirrors 202 move in the direction of the arrow at the speed V / 2. As a result, the optical path length from the time when the light illuminated on the original by the exposure lamp 201 is reflected by the original until the image is formed on the CCD sensor 204 is always constant.

The scanner home sensor 210 detects the home position of the scanner on which the exposure lamp 201 and the first mirror 206 are mounted. The amount of movement of the scanner is detected based on the number of steps of the scanner motor 209. Thus, the amount of movement of the scanner from the home position is detected, and the position of the scanner is detected.

The reflected light imaged on the CCD sensor 204 is
The signal is converted into an electric signal in the CCD sensor 224 and sent to the image processing circuit 205. The image processing circuit 205 performs analog processing, A / D conversion processing, digital image processing, and the like on the received electric signal, and stores it in a memory in the image processing circuit 205. The same data as the data stored in the memory is output to the interface unit 207.

The image processing circuit 205 prints the image data stored in the memory or the image data input from the interface unit 207 in cyan (C), magenta (M), yellow (Y), and black (K). The data is converted into data for use in the image forming unit 300 and transmitted to the image forming unit 300.

In the image forming section 300, the received print data is sent to the respective exposure heads for cyan, magenta, yellow and black. Each exposure head emits a laser beam according to the received printing data (electric signal). The emitted laser light is one-dimensionally scanned by the polygon mirror 301, and the image forming units 307c, 307m, and 3 of cyan, magenta, yellow, and black, respectively.
Photoconductor drums 304c and 304 in 07y and 307k
Expose m, 304y and 304k. Since the image forming units 307c, 307m, 307y, and 307k differ only in the color of the toner to be handled, the operation of the image forming unit 307c for forming a cyan image will be described.

After being charged by the charging charger 305c, the photosensitive drum 304c is irradiated with laser light emitted by the yellow exposure head. As a result, an electrostatic latent image is formed on the photosensitive drum 304c. Subsequently, the toner is placed on the electrostatic latent image by the developing device 302c to form a toner image. The toner image formed on the photosensitive drum 304c is transferred onto a recording medium carried on the endless belt 320 by a transfer charger 303c.

The photosensitive drum 304c is always in contact with a resin blade 306c, and the blade 306c removes excess toner adhering to the photosensitive drum 304c.

As described above, the photosensitive drum 304c rotates clockwise in the drawing, so that the image forming process is continuously performed. The image forming unit 307
The components c, 307m, 307y, and 307k are integrally formed, and are detachable from the digital copying machine 100.

Sheet cassettes 310a, 310b, 310
In c, sheets of different sizes are set. Sheets of a desired size are supplied to the sheet cassettes 310a and 310a.
Paper feed roller 312 attached to 10b, 310c
a, 312b, and 312c, are supplied to the transport path.
The sheet supplied to the transport path is sent to a timing roller 315 by a transport roller pair 314.

On the other hand, the endless belt 320 is
22a and fixed rollers 322b, 322c, 322d,
It is suspended by the movable roller 321 so as not to be loosened. When the drive roller 322a rotates counterclockwise in the figure, the endless belt 320 rotates counterclockwise in the figure at a predetermined speed. With the rotation of the endless belt 320, the rollers 322b, 322c, 322d, 321 rotate counterclockwise.

Since the endless belt 320 is endless, it has a seam, and this seam is used as a reference mark of the endless belt. Timing sensor 323 and seam detection sensor 3
Reference numeral 40 denotes a sensor for detecting a joint of the endless belt. These sensors are non-contact sensors, which detect light at the endless belt 320 by irradiating the endless belt 320 with light and measuring the amount of light received.

The timing sensor 323 is connected to the endless belt 3
20 is provided at a position where paper is supplied. The length of the endless belt 320 from the position where the seam detection sensor 340 detects the seam of the endless belt to the position where the paper is supplied to the endless belt 320 is determined by the seam detection sensor 340.
It is set at a position that is the same as the length of the paper to be supplied. Timing sensor 323 and seam detection sensor 34
The timing roller 315 supplies the sheet to the endless belt 320 in synchronization with the detection signal outputted from the endless belt 320. Therefore, the sheet is not supplied from the timing roller 315 between the time when the seam detection sensor 340 detects the seam of the endless belt 320 and the time when the timing sensor 323 detects the seam of the endless belt 320. As a result, the paper is supplied so as not to get on the seam of the endless belt 320. Further, a guide 316 is provided to facilitate supply of the sheet from the timing roller 315 to the endless belt 320.

The sheet supplied to the endless belt 320 is carried on the endless belt 320 and is conveyed leftward in the figure. This allows the paper to be cyan, magenta, yellow,
The photosensitive drum 304 of the image forming unit in the order of black
c, 304m, 304y, and 304k. The recording medium is the respective photosensitive drums 304c, 304m, 30
4y and 304k, the transfer chargers 303c, 303m, 303y and 3 paired with the photosensitive drum.
At 03k, the toner image on the photosensitive drum is transferred to the paper.

Each of the image forming units 307c, 307m,
Registration correction sensor 3 built in 307y, 307k
08c, 308m, 308y, and 308k detect the reference marks on the endless belt 320. Registration correction sensor 3
The timings detected at 08c, 308m, 308y, and 308k are transmitted to the image processing circuit 205, so that the image forming units 307c, 307m, 307y, and
At 307k, the timing of forming an image is finely adjusted.
This prevents color shift due to resist shift.

The sheet on which the toner image has been transferred is conveyed to a pair of fixing rollers 325 and heated by the pair of fixing rollers 325. Thus, the toner is melted and fixed on the sheet. Thereafter, the paper is discharged to the paper discharge tray 327.

In the case of double-sided copying, the sheet on which the toner image has been fixed by the fixing roller pair 325 is inverted by the sheet reversing unit 326 and conveyed to the double-sided unit 328. Then, the sheet inverted from the duplex unit 328 is supplied again to the transport path by the sheet feeding roller 313. The image is formed on the back surface of the sheet by conveying the sheet along the above-described path.

The humidity sensor S1 is connected to the digital copier 100
The temperature sensor S2 is a sensor for detecting humidity in the inside,
This is a sensor for detecting the temperature inside the digital copying machine 100. The paper moisture absorption sensor S3 is a sensor for measuring the amount of moisture contained in the paper, and usually measures the moisture absorption of the paper by detecting a current value flowing through the paper in contact with the paper. The paper moisture absorption sensor S3 is provided immediately before the timing roller 315.

A registration pattern detection sensor 324 is mounted at the most downstream of the path along which the endless belt 320 conveys the sheet. Resist pattern detection sensor 324
Are image forming units 307c, 307m, 307y,
At 307k, the resist pattern formed on the endless belt 320 is read. The read data is the image processing circuit 2
05. The resist pattern detection sensor has a light emitting unit and a light receiving unit, irradiates light with the light emitting unit, and receives light reflected by the endless belt 320 at the light receiving unit. The level of the light received by the light receiving unit indicates the presence or absence of a resist pattern on the endless belt 320 or the color of the resist pattern formed by the toner. The position of the resist pattern formed on the endless belt 320 is detected from the timing of the signal output from the resist pattern detection sensor 324. This will be described in detail later.

The toner collecting device 329 includes an endless belt 320
The resist pattern formed above is collected. The toner collecting device 329 has a brush inside, and the brush rubs the endless belt 320 to remove a resist pattern formed of toner on the endless belt 320. The removed toner is stored in the toner collecting device 328.

FIG. 2 is a plan view of an operation panel provided on the upper surface of the digital copying machine 100. Referring to the figure, operation panel 500 includes a liquid crystal display device 501 and a touch panel 506 provided thereon and made of a transparent member. The liquid crystal display device 501 displays a print operation mode and an internal state of the digital copying machine 100. The touch panel 506 is a switch, and when used in combination with the liquid crystal display device 501, a user can input a predetermined operation such as setting of a print operation mode. The operation panel 500 further includes a numeric keypad 502 for inputting numerical values such as the number of copies and a print magnification, a start key 505 for instructing the start of a print operation, and a print operation mode set by a user input. Key 503 for clearing the digital copier 10
Stop key 50 for temporarily stopping print operation 0
4 and a cost priority button 507 for setting the digital copying machine 100 to the cost priority mode.

The above-described digital copying machine 100 is controlled by a control unit shown in FIG. FIG. 3 is a block diagram showing a schematic configuration of the control unit of the digital copying machine 100. Referring to the figure, a control unit includes a control CPU 400 for controlling the entire digital copying machine 100 and an endless belt 320.
A retreat mechanism control unit 404 for controlling a retreat mechanism for retreating the image, an image processing circuit 205 described above, and a resist correction unit 406 for calculating a resist correction value based on data output from the resist pattern detection sensor 324. Including.

The control CPU 400 includes an operation panel 500
, A seam detection sensor 340, a humidity sensor S1, a temperature sensor S2, a paper moisture absorption sensor S3, a JAM sensor S4, a paper empty sensor S5, a fixing temperature sensor S6, and a toner empty sensor S7. ing.

A print operation mode and the like input by the user from the operation panel 500 are sent from the operation panel 500, and data to be displayed on the liquid crystal display device 501 of the operation panel is sent from the control CPU 400.

The JAM sensor S4 is a sensor for detecting that a sheet is jammed in the transport path, and is provided at a plurality of positions in the transport path. Paper empty sensor S5
Are provided in each of the paper feed cassettes 310a, 310b, 310c, and are provided in the paper feed cassettes 310a, 310b, 3c.
This is a sensor for detecting the presence or absence of a sheet stored in 10c. The fixing temperature sensor S6 includes a fixing roller pair 3
25 is a sensor for measuring the temperature. The toner empty sensor S7 is connected to the developing device 302 of the image forming unit.
Sensors for detecting the presence / absence of toner set in c, 302m, 302y, and 302k, respectively.

The control CPU 400 has a backup RAM
402. Backup RAM 402
Stores data such as the number of prints and the number of operations of an element such as an image forming unit in the digital copying machine 100. The backup RAM 402 is backed up by a battery, and the main power of the digital copying machine 100 is turned off.
Even in the case of the FF state, the backup RAM 402
Can be stored.

The image processing circuit 205 includes the CCD sensor 20
4, an exposure head 410c for cyan, an exposure head 410m for magenta, and an exposure head 410 for yellow
y and the exposure head 410k for black. The R, G, B image data photoelectrically converted by the CCD sensor 204 is converted into C, M, Y,
It is converted to K printing data. The converted C, M,
The Y and K print data are subjected to registration correction processing based on the registration correction values received from the registration correction unit 406, and then the corresponding exposure heads 410c,
Output to 410m, 410y, 410k.

Each exposure head 410c, 410
m, 410y and 410k, upon receiving the registration-corrected data, irradiate the corresponding photosensitive drum with a laser beam based on the received data. As a result, an electrostatic latent image is formed on the photosensitive drum.

The registration correction unit 406 includes image forming units 307c, 307m, 307y, and 307k.
Calculates a registration correction value used to prevent color misregistration due to misregistration when an image is superimposed on a sheet.

The registration correction process includes a step of forming a predetermined resist pattern on the endless belt 320 in each of the image forming units 307c, 307m, 307y, and 307k, and a step of detecting a resist pattern formed on the endless belt by a resist pattern detection sensor. Reading at 324; calculating a resist correction value for print position correction, magnification correction and spatial distortion correction based on the data read by the resist pattern detection sensor; Based on the correction value, C, M, Y,
Performing registration correction on the K print data.

The registration correction unit 406 stores a predetermined registration pattern in advance, and transmits the registration pattern to the image processing circuit 205 so that each of the image forming units 307c, 307m, 307y,
At 307k, a resist pattern is formed on the endless belt 320.

FIG. 4 is a diagram showing an example of a resist pattern. Referring to the drawing, a resist pattern is formed at a predetermined position on endless belt 320 based on seam 601 of endless belt 320 by each image forming unit. The resist pattern is a pattern in which three squares are arranged at equal intervals in a direction perpendicular to the direction in which the endless belt 320 advances (the direction of the arrow in the drawing) for each image forming unit. Here, an example in which the resist pattern is a square has been described, but for example, a cross shape or a character shape of “Z” can be used.

The resist pattern formed by the image forming unit is formed in a predetermined shape at a predetermined position from the reference mark 601, but is not formed in a predetermined shape at a predetermined position when there is a registration deviation. The resist correction value is obtained from the deviation amount of the actually formed resist pattern.

The resist patterns 603a, 603b, 603c formed by the image forming unit 307c are formed at predetermined positions determined from the reference marks 601.

Of the resist patterns 605a, 605b, 605c formed by the image forming unit 307m,
Although the resist patterns 605a and 605c are formed at predetermined positions, the resist patterns 605a and 605c
b deviates from the determined position in the direction opposite to the direction in which the endless belt 320 advances (the direction of the arrow in the figure). In the drawing, a predetermined position where a resist pattern is to be formed is indicated by a dotted line. When the three resist patterns are relatively displaced in this way, spatial distortion is detected from the relative displacement, and a resist correction value for correcting the spatial distortion is obtained.

The resist patterns 607a, 607b, and 607c formed by the image forming unit 307y are formed such that the center of gravity of each pattern overlaps the center of gravity of a predetermined reference position. The size is reduced.
A resist correction value to be used for the magnification correction is obtained from the deviation amount of the magnitude.

The resist patterns 609a, 609b, 609c formed by the image forming unit 307k are shifted from the reference position by the same amount in the direction opposite to the direction in which the endless belt 320 advances (the direction of the arrow in the figure). A registration correction value for correcting the printing position is obtained from the positional deviation amount.

As described above, in the registration correction process,
By transmitting the resist pattern from the resist correction unit 406 to the image processing circuit 205, a predetermined resist pattern is formed on the endless belt 320 in each of the image forming units 307c, 307m, 307y, and 307k. Then, by reading the resist pattern with the resist pattern detection sensor 324, a deviation between the read resist pattern and the reference position is detected.
A registration correction value used for printing position correction, magnification correction, and spatial distortion correction is obtained. The registration correction value obtained by the registration correction unit 406 is stored in a memory in the image processing circuit 205.

Referring to FIG. 3, retraction mechanism control section 404
Is connected to the evacuation clutch. Evacuation mechanism controller 4
04 operates the evacuation clutch 405,
Switch the position of the evacuation mechanism. When the retraction mechanism moves, the movable roller 321 and the transfer charger 303y,
303m, 303c, the timing sensor 323, the guide 316, and the timing roller 315 move.
In addition, the endless belt is
Photoconductor drums 304c, 3 of all image forming units
The trajectory is switched to two positions: a trajectory that contacts the photoconductor drums 04m, 304y, and 304k, and a trajectory that contacts only the photoconductor drum 304k of the black image forming unit 307k. The endless belt is the photosensitive drum 30 of all the image forming units.
4c, 304m, 304y, and 304k, the position of the retracting mechanism when the track is in contact with the photosensitive drum 304k of the black image forming unit 307k. The position of the mechanism is referred to as a “parking position”.

FIG. 5 is a schematic sectional view of the digital copying machine 100 when the retracting mechanism has moved to the retracting position. FIG.
, The movable roller 321, the transfer chargers 303 y, 303 m, and 303 c, the timing sensor 323, the guide 316, and the timing roller 315 are moved downward by the retraction mechanism. As a result, the endless belt 320 comes into contact only with the photosensitive drum 304k of the black image forming unit 307k. In other words, the photosensitive drum 304c of the cyan image forming unit 307c, the photosensitive drum 304m of the magenta image forming unit 307m, and the yellow image forming unit 30
The 7y photosensitive drum 304y is not in contact with the endless belt 320. Therefore, when the endless belt 320 is retracted by the retracting mechanism, the driving of the image forming units for cyan, magenta, and yellow can be stopped. Therefore, the photosensitive drum 304
c, 304m, 304k and developing machines 302c, 302
It is possible to reduce wear caused by driving of the m and 302y.

Next, the flow of processing performed by the control unit of digital copier 100 will be described. FIG. 6 is a flowchart showing the flow of processing performed by the control unit of digital copier 100. Referring to the figure, the control unit initializes digital copying machine 100 (S11).
, A step of setting a mode for copying in the digital copying machine 100 (S12), a step of controlling the retraction mechanism (S13), and a step of performing copy processing (S14).
And

In the initial setting performed in step S11, when the main power supply of the digital copying machine 100 is turned on, for example, processing for increasing the temperature of the fixing roller pair 325 is performed. The initial setting is a preparation operation necessary for performing a copy process in the digital copying machine 100.

In step S12, a copy mode is set. The copy mode is set by the user from the operation panel 500 according to the menu displayed on the liquid crystal display device 501 by using the touch panel 506 or the numeric keypad 5.
02 is set by inputting. In the copy mode, for example, the number of copies, the copy magnification, the image forming mode, and the like are set. Here, the setting of the image forming mode refers to switching between the monochrome image forming mode and the color image forming mode. The monochrome image forming mode is a mode in which copy processing is performed using only the image forming unit 307k for black, and the color image forming mode is a mode in which copying processing is performed using all the image forming units 307c, 307m, 307y, and 307k. The mode to perform. For example, when the monochrome image forming mode is selected, the copy process is performed using only the black image forming unit 307k even if the original is in color.

In step S13, control of the retraction mechanism is performed. This will be described in detail later.

In step S14, copy processing is performed. Image formation is performed based on the copy mode set in step S12.

Next, control processing of the retraction mechanism will be described. FIG. 7 is a flowchart illustrating the flow of the evacuation mechanism control process performed in step S13 of FIG. Referring to the drawing, in the evacuation mechanism control processing, first, it is determined whether or not the evacuation mechanism is at the evacuation position (step S21). When the evacuation mechanism is not at the evacuation position but at the basic position, that is, all the image forming units 307c, 307m, and 307
If y, 307k is in contact with the endless belt 320, it is determined whether the image forming mode is the monochrome image forming mode (S22). Whether or not the mode is the monochrome image forming mode is determined based on whether or not the image forming mode is set to the monochrome image forming mode in the copy mode setting process in step S21 in FIG. The digital copier 100
Has an automatic color selection (ACS) function,
This may be used to switch between the monochrome image forming mode and the color image forming mode. The automatic color selection (ACS) function detects whether a document is monochrome or color by pre-scanning the document. The monochrome image formation mode is set when monochrome is detected, and the color printing mode is set when color is detected. The image mode is set.

If it is determined in step S22 that the mode is not the monochrome image forming mode, the process proceeds to step S26, and the retracting mechanism is not operated. If the mode is the monochrome image forming mode, it is determined in the next step S23 whether or not the mode is the cost priority mode. The setting of the cost priority mode is set when the user presses the cost priority button 507 on the operation panel 500. In addition, by displaying a setting menu on the liquid crystal display device 501 of the operation panel 500,
The user may select the displayed menu by pressing the touch panel 506. further,
The cost priority mode may be set by a dip switch provided on the side of the digital copying machine 100.

In the case of the cost priority mode, step S
The process advances to step S25, and if the mode is not the cost priority mode, the process advances to step S24. In step S24, the time until the joint of the endless belt 320 reaches the position where the sheet can be transported (the position where the sheet is supplied) is compared with the operation time for moving the retraction mechanism.

This will be described with reference to FIG. FIG.
FIG. 4 is a diagram for explaining a relationship between a position of a joint of an endless belt 320 and an operation time of a retraction mechanism. Referring to the figure, the position of seam detection sensor 340 is position A, and the position at which paper can be transported is position B. Further, the moving speed of the endless belt 320 is x [mm / s], and the seam detection sensor 340 is used.
Is the time elapsed since the seam was detected at t1 [sec],
The time required for the evacuation mechanism to move is t2 [mm / s],
Let the length of the endless belt 320 from the position A to the position B be y
[Mm].

With the timing roller 315, the endless belt 32
The paper cannot be fed to 0 when t1 is within the range of the following equation (1).

0 <t1 <y / x (1) From equation (1), the time required for the joint to reach position B is:
It is expressed by the following equation (2).

Y / x-t1 (2) On the other hand, when paper cannot be supplied to the endless belt 320,
If the retraction mechanism completes its operation, there is no time loss caused by the operation of the retraction mechanism. Therefore, in order to satisfy the condition for completing the operation of the retraction mechanism when the paper cannot be supplied to the endless belt 320, the following expression (3) is satisfied.
Should be satisfied.

T1 <y / x−t2 (where t1> 0, t2> 0) (3) If the evacuation mechanism is moved to the evacuation position only at t1 that satisfies the expression (3), the evacuation is performed. There is no time loss caused by the operation of the mechanism.

Returning to FIG. 7, in step S24,
If the elapsed time t1 from the detection of the seam by the seam detection sensor 340 does not satisfy the condition of the above equation (3), the process proceeds to step S26, and the evacuation mechanism is not operated.

If the elapsed time t1 satisfies the condition of the above equation (3), the operation proceeds to step S25, where the retracting clutch is operated and the retracting mechanism is moved to the retracting position (S2).
5). As a result, the endless belt 320 is retracted from the image forming units 307c, 307m, and 307y.

On the other hand, when the retracting mechanism is at the retracting position in step S21 (YES in S21), it is determined in next step S27 whether the image forming mode is the monochrome image forming mode. In the case of the monochrome image forming mode, there is no need to operate the evacuation mechanism, and thus the process is terminated. If the mode is not the monochrome image forming mode, the escape clutch is operated to move the escape mechanism to the basic position (S28). Thereby, the endless belt 320 is connected to all the image forming units 307c, 307m, and 307.
y, 307k.

As described above, the digital copying machine according to the present embodiment operates only when the elapsed time t1 from the detection of the seam by the seam detection sensor 340 satisfies the condition of the above equation (3). Is operated to move the evacuation mechanism to the evacuation position. Therefore,
Since the time loss caused by the operation of the evacuation mechanism is eliminated, the time required for copying by the digital copying machine 100 can be reduced. The digital copier 100
Image forming apparatuses 307c, 307m, 307y, 307
The operation rate of k can be improved. In particular, when a color document and a monochrome document are alternately copied, the copying operation and the movement of the standby mechanism are not performed alternately, and the time required for copying can be greatly reduced.

In the copy priority mode, the retract mechanism is moved regardless of the position of the endless belt seam, so that the copy cost for monochrome copying due to the move of the retract mechanism can be reduced. Becomes possible.

It should be noted that the embodiment disclosed this time is an example in all respects and is not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of a digital copying machine according to one of the embodiments.

FIG. 2 is a plan view of an operation panel 500 provided on an upper surface of the digital copying machine 100.

FIG. 3 is a block diagram illustrating a configuration of a control unit of the digital copying machine 100.

FIG. 4 is a diagram for explaining a resist pattern.

FIG. 5 is a schematic cross-sectional view of the digital copying machine 100 when the retracting mechanism has moved to a retracting position.

FIG. 6 is a flowchart showing a flow of a process performed by a control unit of the digital copying machine 100.

FIG. 7 is a flowchart illustrating a flow of a retracting mechanism control process performed in step S13 of FIG. 6;

FIG. 8 is a diagram for explaining the relationship between the position of the seam of the endless belt 320 and the operation time of the retraction mechanism.

[Explanation of symbols]

 204 CCD sensor 205 Image processing circuit 324 Registration pattern detection sensor 340 Joint detection sensor 400 Control CPU 404 Evacuation mechanism control unit 406 Registration correction unit 500 Operation panel S1 Humidity sensor S2 Temperature sensor S3 Paper moisture absorption sensor S4 JAM sensor S5 Paper empty sensor S6 Fixing temperature sensor S7 Toner empty sensor

Continued on the front page (72) Inventor Kazuyuki Kawabata 2-3-113 Azuchicho, Chuo-ku, Osaka City Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Shoji Imaizumi 2-3-13 Azuchicho, Chuo-ku, Osaka City No. Osaka International Building Minolta Co., Ltd. F-term (reference) 2H027 DA21 DE07 DE10 EB04 EC06 EC09 ED16 ED24 EE05 FA28 FA30 FA35 FB07 FB18 2H030 AB02 AD05 AD17 BB02 BB23 BB44 BB46 BB53 BB56

Claims (3)

[Claims] 1. A plurality of image forming units for forming an image on a recording medium, a conveyance unit for conveying the recording medium in one of a first state and a second state, and the first state A switching unit for switching between the first state and the second state; and a detecting unit for detecting a reference point of the transport unit. Transporting a recording medium to at least one of the plurality of image forming units;
The recording medium is conveyed to all of the plurality of image forming units in the state described above, and the switching unit can switch from the second state to the first state only when the reference point is within a predetermined range. An image forming apparatus, characterized in that: 2. The switching device according to claim 1, wherein in the cost priority mode, the switching from the second state to the first state is possible even if the reference point is not in the predetermined range. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the transport unit is a rotatable belt formed in an endless shape.