JPH01186970A - Image forming device - Google Patents

Abstract

PURPOSE:To shorten a time for forming an image by controlling a timing setting means so that it can work in either a 2nd mode or a 1st mode according to the length of a paper supply path which is selectively used in case of forming the image. CONSTITUTION:The timing setting means is made to work in the 2nd mode or the 1st mode according to the length of the paper supply path. Namely, in the 1st mode, the supplied paper is fed out after it is stopped on a specified position before a transfer part for a specified time and its leading edge is adjusted to that of the image formed on a photosensitive body 1 in an exposing timing based on the detection of the paper on the specified position, so that the leading edges of the paper and the image can be adjusted regardless of the length of the paper supply paths 23a-23c. In the 2nd mode, the leading edges of the paper and the image formed on the photosensitive body 1 can be adjusted in the exposing timing based on the detection of the paper in earilier stage than the specified position without stopping the paper on the specified position. Thus, exposure is performed by utilizing the time when the paper is fed through the paper supply paths 23a-23c and also the leading edges of the paper and the image can be adjusted without stopping the paper.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus such as a copying machine or a printing apparatus.

(Prior Art) In conventional image forming apparatuses, the leading edge of the paper fed to the transfer unit and the leading edge position of the image formed by exposure on the moving photosensitive surface of the photoreceptor always have a predetermined correspondence relationship. A registration roller is provided in front of the transfer unit for adjusting the paper feeding timing common to each paper feeding path, and the timing at which this roller is turned on to feed the paper to the transfer unit is determined by detecting the leading edge of the paper just before the registration roller. It is set so that the leading edge of the paper is immediately at the leading edge of the image formed when exposure to the photoreceptor is started.

With this timing setting method, even if the paper feeding path is short and the paper reaches the transfer unit immediately after being fed,
Exposure is performed after the paper reaches a predetermined position in front of the transfer section,
Since the paper is sent to the transfer section at a timing such that when the leading edge of the resulting image reaches the transfer section, the leading edge of the paper also reaches the transfer section, so that the leading and end alignment at the transfer section is reliably achieved.

(Problem to be solved by the invention) However, when paper on which an image has been formed is fed again for selective feeding from multiple paper feed cassettes or manual feed slots, or for double-sided copying or image composition, Even if the paper feeding path becomes longer due to the above, exposure is not performed until the paper reaches just before the registration roller, and after the start of exposure, the paper takes a predetermined amount of time to align the leading edge with the latent image. Since the image forming apparatus is always temporarily stopped, the time required for image formation becomes longer and the image forming speed is significantly reduced even though the preparation of exposure data is completed.

In addition, the registration roller is driven and stopped by turning on and off the clutch for easy drive control, so turning the registration roller on and off for each sheet of paper fed will shorten the life of the clutch. Become.

Therefore, the present invention provides an image forming apparatus that can solve the above-mentioned problems by switching the timing setting mode for aligning the leading edges of paper and one image formed on a photoreceptor according to the length of the paper feed path. The purpose is to provide

(Means for Solving the Problems) In order to achieve the above objects, the present invention exposes a moving photosensitive surface of a photoreceptor to form a latent image, and develops this latent image to make it visible. In an image forming apparatus that transfers the image to a sheet of paper fed through one of a plurality of paper feeding paths passing through a timing roller in a transfer section and forms an image on this paper, the fed paper is placed at a predetermined position in front of the transfer section. In the first mode, the paper is stopped for a predetermined period of time and the leading edge of the paper is aligned with the image formed on the photoreceptor at the exposure timing given by detecting the paper at a predetermined position, and the paper being fed is stopped by a timing roller. a timing setting means having a second mode in which the leading edge of the paper is aligned with the image formed on the photoreceptor at an exposure timing given by detecting the paper at an earlier stage than a predetermined position; The timing setting means can be set to either the second mode or the first mode depending on the length of the paper feeding path.
The invention is characterized by comprising a control means that operates in one of two modes.

(Function) There are multiple paper feed paths, which are selectively used to feed paper from the paper cassette or manual feed slot, or to refeed paper for double-sided image formation or image composition. A sheet of paper can be sent to a transfer section via a timing roller and used for transferring an image from a photoreceptor.

At this time, the timing setting means is controlled by the control means to operate in either the second mode or the 1d mode depending on the length of the paper feeding path to be selectively used. In the first mode, the fed paper is stopped at a predetermined position in front of the transfer unit for a predetermined time, and then fed out, and the leading edge is aligned with the image formed on the photoreceptor at the exposure timing given by paper detection at the predetermined position. Therefore, alignment of the edges of the paper and the image can be guaranteed regardless of the length of the paper feeding path.

In the second mode, the paper is not stopped at a predetermined position, but the paper is detected at an earlier stage than the predetermined position, and the leading edge of the paper is aligned with the image formed on the photoreceptor at the exposure timing given, so that the paper can pass through a long paper feeding path. It is possible to perform exposure using the time while the paper is being fed, and to ensure that the edges of the paper and the image are aligned without stopping the paper.

(Example) Hereinafter, an example in which the present invention is applied to a laser beam printer will be described with reference to the drawings.

First, the overall configuration of a laser beam printer will be explained based on FIG. 3. Reference numeral 1.1 indicates a photoreceptor drum, and the surface of the photoreceptor drum 1 is irradiated with a laser beam 2 from an exposure device 3 to expose an image. Do it, 4a to 4C are on each hole,
These paper feed rollers correspond to the paper feed cassettes 22a to 22c provided in the middle and lower three stages, and these paper feed rollers 4a to 4
The paper fed from the paper feed cassettes 228 to 22c by c is transferred to the first paper sensor 5, the registration roller 6, and the second
The paper is fed through the vapor sensor 7 to a transfer section between the photoconductor drum 1 and the transfer/separation charger 10, and the image on the photoconductor drum 1 is transferred to the paper. The transferred image is a toner image in which a latent image formed on the photoreceptor drum 1 by exposure is developed into a desired color by the developing devices 24a and 24b. The paper onto which the image has been transferred is transferred to the fixing device 1.
1, the paper is guided to the composite/double-sided image unit 12, and during normal image formation, it is ejected as it is to the paper output tray 15 using the switching claw 13a, and during image composition, the switching claw 13a
, 13b to the paper refeed path 14, pass through the paper refeed roller 8, the third paper sensor 9, and the registration roller 6 again, where a second transfer is performed to form a composite image.

Furthermore, in the case of double-sided copying, the paper is once guided to the switchback path 22 by the switching claws 13a and 13b, then transported back and sent to the paper refeeding path 14 in a reversed state under the guidance of the switching claw 13b. and refeed roller 8,
It passes through the third paper sensor 9 and passes through the registration roller 6 again, and an image is formed on the back side.

Here, from the paper feed cassettes 22a and 22b to the paper feed path 23
As for the paper fed through a and 23b, the photosensitive drum 1 is exposed to light when the first paper sensor 5 immediately before the registration roller 6 detects the leading edge of the paper, and the paper is stopped by the registration roller 6 for a predetermined time. By sending it out after the exposure, the leading edge is aligned with the image formed on the photoreceptor drum 1 by the exposure, and the image is transferred. As a result, the paper fed by the short paper feeding paths 23a and 23b tries to reach the transfer section immediately, but the timing adjustment by the registration roller 6 allows the paper to be fed quickly from the photosensitive drum 1.
It is guaranteed that the leading edge will always be aligned with the image formed above by exposure and reach the transfer section.

On the other hand, for paper fed through the paper feed path 23c from the paper feed cassette 22c and paper refeed path 14, the third paper sensor 9 provided immediately after the paper feed roller 8 in this path detects the leading edge of the paper. At this point, the photosensitive drum 1 is exposed to light, and the paper is not stopped by the registration rollers 6, but the leading edges of the paper and the image on the photosensitive drum 1 are aligned, and the image is transferred.

As a result, although the paper feed path 23c takes longer time for the paper that is fed to reach the transfer section, the third paper sensor 9
Exposure is started in accordance with the early detection of the leading edge of the paper, and the paper can be sent to the transfer section without timing adjustment by the registration rollers 6, and the leading edge of the paper can be aligned with the image formed by the exposure. Therefore, delays in exposure due to the long paper feed path 23c and time loss due to timing adjustment of the paper by the registration rollers 6 are avoided.

Further, the registration roller 6 is not turned on or off due to unnecessary timing adjustment, and fatigue of the clutch or the like that turns on and off can be reduced.

However, when paper is fed through the paper feeding path 23c, even though the leading edge of the paper is detected by the third paper sensor 9, the preparation of exposure data may not be completed. In this case, if the exposure is delayed until the completion of the exposure and the feeding of the paper to the transfer unit is delayed by the delay time using the registration rollers 6, the delay caused by the exposure on the paper and the photoreceptor drum 1 can be completed without any time loss. It is possible to ensure tip alignment with the image. Note that in order for the control to be simple, the paper feed path 23
It is advantageous to switch to a timing scheme for paper feeding through a, 23b.

By the way, in the case of image composition, during the first image formation, the paper is supplied from the paper feed rollers 4a to 4c to the transfer unit 10 via the registration roller 6, but during the second and subsequent image formation, the paper is fed again via the paper refeed path 14. Since the paper is fed to the registration rollers 6 by the paper feed roller 8, the entry angle of the paper to the registration rollers 6 is completely different, and the position of the leading edge of the paper stopping on the registration rollers 6 is as shown in FIGS. 4(a) and 4(b). As shown in the figure, they are shifted from each other, and after the first and second time, the fifth
As shown in FIGS. (a) and (b), a shift occurs in the image position.

On the other hand, in order to eliminate the discrepancy between the leading edge of the paper and the image, for example,
In Publication No. 2, a registration roller is turned on or exposure is started based on a reference signal, and a timer is provided for timing an arbitrarily settable time after the reference signal is generated, and the output from this timer is used to A method has been disclosed in which the positions of the paper and the image are made to correspond by starting exposure or turning on the registration roller and adjusting the set value of the timer.

However, the apparatuses disclosed in these publications cannot effectively deal with misalignment of the leading edge of the paper during the first and second image formation in image composition.

On the other hand, it is conceivable to deal with the misalignment of the leading edge of the paper during the first and second image formations by not temporarily stopping the paper with the registration rollers 6 during the second and subsequent image formations. However, in this case, there is a risk that the composite image will be misaligned due to variations in the stopping position of the leading edge of the paper on the registration rollers 6 during the first image formation.

Therefore, in this embodiment, in order to avoid such a problem, the photosensitive drum 41 is exposed to light to form a latent image, this latent image is developed, and the image is synchronously fed by the registration roller 6 in the transfer section. When forming an image on a sheet of paper by transferring it to a sheet of paper, and forming multiple images by passing the same sheet of paper multiple times through the paper refeeding path 14 to the transfer section, when forming the image for the first time. A state in which the error in the relative position of the paper and the image is detected by actually measuring the time it takes for the paper to reach the second paper sensor 7 from the registration roller 6, and the paper is not stopped by the registration roller 6 during the second and subsequent image formations. The exposure timing is set in accordance with the error.

The configuration will be explained. In FIG. 1, CPU 21
Various input ports 22 and output ports 23 are provided for controlling various information. Also, CPU
The submemory 24 and main memory 25 can be directly accessed from the submemory 21. As shown in FIG. 2, the sub-memory 24 is provided with an area for a counter An area is provided for data storage. The main memory 25 is backed up by a battery 26, and the stored data is retained even when the power is turned off and then turned on again.

Next, the operation of the above configuration will be explained with reference to the flowcharts shown in FIGS. 6 to 10.

FIG. 6 schematically shows the main routine. First, CP[
Initial settings related to I are performed (6-1). At this point, the counter X is cleared to zero and the registration mode is set to the initial mode of "O". After that, a processing step that loops for a certain period of time begins. Performs input processing (6-2), output processing (6-3), and print request determination (6-
4) executes the sequence processing (6-5) or branches to bypass it. Furthermore, one loop is completed via loop management (6-6) for performing one loop at a fixed time, and the process returns to input processing (6-2).

The above sequence processing is shown in FIG. On/off timing processing of various rollers (7-1), exposure processing (7
-2), processing of other sensors, etc. (7-3) is performed,
Furthermore, a registration process (7-4) is executed. That is,
Registration correction processing is performed during printing.

To explain the processing of various rollers with reference to FIG. 8, the timing data area (not shown) set for each roller determines whether it is "0#" (8-1) (8-5), and sequentially counts down. Turn on (8-4) or turn off (8-8) each roller at “O” (8-3) (8-7). do.

Next, the exposure process will be explained with reference to FIG. 9. First, the mode is determined (9-1), and if it is "0", normal exposure processing is performed. In this normal exposure process, it is determined whether or not an exposure request has been received (9-3), and when it is received, the exposure is turned on (9-3).
-4) and at the same timing, set the registration roller on timer (9-5).

In the mode determination (9-1), if the determination of "3" is passed, it is determined whether the exposure-on timer is "0" or not, and if it is not "0", this timer is subtracted. (9-7), and determines whether the timer power (llQ#) is reached (9-8). If the timer is not "0", return as is. With this determination, the timer becomes "O". At that point, turn on the exposure (9-9) and set the registration roller off timer. (The registration roller is turned on in advance during the registration process.) Furthermore, the mode is returned to "01" which means the end of a series of correction processes.Thus, the process returns to the process of correcting the next sheet.

Next, the resist processing will be explained with reference to FIG.

First, the mode is determined (10-1 to 1O-4). If the mode is determined to be "0" according to the initial settings, it is determined whether the print request is in the composite mode (1O-5), and if the print request is in the normal mode rather than the composite mode, the process returns directly.

In the composite mode, by first determining the initial registration roller, the counter X measures the time it takes for the leading edge of the paper to reach the second paper sensor 7 from the registration roller 6 in the first image formation. Therefore, 1 is added to the counter X and the mode is set to (10-7
) Return.

Next, based on the determination of mode "1", it is determined whether or not the second paper sensor 7 is on (10-8), and the counter X is incremented until the second vapor sensor is on (10-11).
). At the timing when the second paper sensor turns on, the addition of counter
10-10) Return.

Next, it is determined whether or not the third paper sensor 9 is turned on based on the determination of mode '2'' (10-12).

That is, in order to feed the paper fed through the paper refeed path 14 and the paper feed path 23c to the transfer section without being temporarily stopped by the timing roller 6, the leading edge of the paper is detected by the third paper sensor 9. The timing for the second image formation is determined. This process is the same when paper is fed from the paper feed cassette 22c. Therefore, in order to turn on the registration roller 6 in advance, the registration roller on timer is set to 1 (10-13). This turns on the registration roller in the roller processing in the next loop.

Also, calculates the exposure-on timing for the second image formation based on the value of counter X, and sets the exposure-on timer (
10-13). Furthermore, set the mode to “3” (10
-13). As a result, exposure is turned on for the second image formation in the exposure process, and the process returns without processing in the resist process.

Next, the above processing will be explained from the actual positional relationship of sheets with reference to FIG. In (a), the counter X starts counting at the timing when the registration roller 6 is turned on, and the mode changes from "0" to "1". In (b), the time taken to reach the second paper sensor 7 is actually measured. That is, the counter X is set by turning on the second paper sensor 7, and the mode shifts from mode "1" to 2#. In (c), the paper on which the first image formation has been completed passes through the paper refeed path 14. In (d), when the third paper sensor 9 detects the leading edge of the paper, the exposure-on timer for the second image formation is set based on the value of the counter X, and the mode shifts from "2" to "3".

Then, in (e), a second image is formed on the sheet of paper, and the combined image is discharged.

Next, the relationship between the value of the counter X, which is sampling data, and the value of the exposure on timer will be explained with reference to FIG.

If the system speed is X (mo+/5ec), the arrival time from the registration roller 6 to the second paper sensor 7 is theoretically given by d/X (sec). However, the actually measured sampling data differs between the case where the leading edge of the paper stops protruding from the registration roller 6 (Pl) and the case where the leading end of the paper stops before the registration roller 6 (P2).

Pi < d / be.

PA-d/X-Pi, PB-P2-d/X On the other hand, timing data from detection by the third paper sensor 9 to exposure ON is given by (f+c+d'+e-a)/X.

In the case of Pl, since the paper is ahead in the first image formation, the image is formed inside the leading edge of the paper, and the exposure-on timing for the second image formation is based on the theoretical exposure-on timing. PA (sec) from the timing of
need to be delayed by a minute. Therefore, the exposure-on timing T1 is Tr+= (f +c +d +e −a
)/X0PA= (f +c +e -a)/X+2d
In the case of /X-PIP2, considering the same as above, image formation will be performed on the leading edge side as the paper is delayed, so it is necessary to turn on the exposure earlier. Therefore, the exposure-on timing T0 is T,! = (f + c + d + e - a)/X + PB
= (f + c + e - a)/X+2d/X
From P2 and above, it can be seen that the second exposure-on timing Tp can be set based on the sampling data P during the first image formation using the following equation.

TP −(f +c +e −a)/X+2d/X−P
(Effects of the Invention) According to the image forming apparatus of the present invention, the timing setting means is set to operate in either the second mode or the first mode by the control means depending on the length of the paper feeding path selected and used during image formation. In the first mode, the fed paper is stopped at a predetermined position in front of the transfer unit for a predetermined period of time and then sent out, and the image is formed on the photoreceptor at the exposure timing given by detecting the paper at the predetermined position. Since the leading edges of the paper are aligned, it is possible to ensure that the leading edges of the paper and the image are aligned regardless of the length of the paper feeding path, thereby avoiding inconveniences caused by the short paper feeding path. In addition, in the second mode, the paper is not stopped at a predetermined position, but the leading edge of the paper is aligned with the image formed on the photoreceptor at the exposure timing given by paper detection at an earlier stage than the predetermined position. By using the time while the paper is being fed through the paper path to perform exposure, it is possible to ensure that the edges of the paper and the image are aligned without stopping the paper, and because the paper feed path is long, the image It is possible to eliminate the problem of long forming time. Moreover, since it is not necessary to stop the paper at a predetermined position each time, it is possible to reduce the fatigue caused by repeatedly turning on and off the stopping means.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a control block diagram, FIG. 2 is an explanatory diagram of a memory space, FIG. 3 is a vertical cross-sectional view of a laser printer, and FIGS. 4(a) and (b). is an explanatory diagram of the state in which the leading edge of the paper is stopped by the timing roller, Fig. 5 (a)
, (b) is an explanatory diagram of the state of the composite image, Figures 6 to 10
11 is a flowchart of the control procedure, FIG. 11 is an explanatory diagram of the operation, and FIG. 12 is an explanatory diagram of the relationship between sampling data and the set value of the exposure-on timer.

Claims (1)

[Claims] (1) The moving photosensitive surface of the photoreceptor is exposed to light to form a latent image, this latent image is developed to become a visible image, and the image is sent to the transfer section through one of multiple paper feeding paths passing through a timing roller. In an image forming apparatus that transfers an image to a sheet of paper and forms an image on the sheet, the fed sheet is stopped at a predetermined position in front of the transfer unit for a predetermined period of time, and the photoreceptor is exposed at the exposure timing given by detecting the paper at the predetermined position. In the first mode, the leading edge of the paper is aligned with the image to be formed on the photoconductor, and the exposure timing given by detecting the paper at an earlier stage than the predetermined position without stopping the fed paper with a timing roller. A timing setting means having a second mode for aligning the leading edge of the image formed on the paper with the paper, and a second timing setting means having a second mode for aligning the leading edge of the paper with the image formed thereon;
An image forming apparatus comprising: a control means that operates in either the first mode or the first mode.