JPH05257366A - Image forming device - Google Patents

Abstract

PURPOSE:To execute the off control of an erasing LED for erasing the leading edge of an image at a specified position without being influenced by the change of rising response. CONSTITUTION:The erasing LED 44 erasing the leading edge of the image is turned on at the detecting timing of a brake sensor BRS at the time of returning scanning. On the other hand, the erasing LED 44 is turned off at the time of going scanning after a specified time Ti from the detecting timing. At this time, the specified time Ti is corrected based on the rising response time Tr at the time of going scanning at the time of copying action of previous time on the second and later consecutive copies.

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 a technique for stably erasing the leading edge of an image even during continuous copying.

[0002]

2. Description of the Related Art When copying is performed by a copying machine, a margin is intentionally provided at the leading end of the transfer paper.
This is because if there is an image up to the leading edge, there is a high probability that the transfer paper will be wrapped around a part of the machine during the fixing process to cause a jam, and this is prevented. In particular, in a small-sized and low-cost copying machine such as a front-loading (whole sheet feeding) type, a white plate is installed at a position corresponding to the leading edge of the original on the lower surface of the original placing table to create a margin. As another technique for creating a margin, a sensor detects the movement of the optical system after the start of scanning, and the detection signal is used as a trigger to operate the erasing LED to erase the charge on the surface of the photoconductor to create a margin. (Japanese Patent Laid-Open No. 57-38482)
No.

[0003]

However, the above-described technique for providing a blank by providing a white plate has a problem that the erasing rate changes depending on the copy magnification and a mechanical shadow is formed. Further, the technique of forming a blank space by using the erasing LED has a problem that it is difficult to grasp the position of the optical system and it is difficult to stabilize the leading edge of the image in a device which pursues miniaturization. That is, in a small-sized image forming apparatus, it is possible to minimize the lateral width (width in the optical system scanning direction) in order to reduce the installation space, and to speed up the start-up in optical system scanning for higher performance. Required. In this case, the gliding time from the start of scanning by the optical system to the leading edge of the document is short, and it may not be enough if the sensor detects the position to determine the operation timing of the erase LED. In addition, even if the operation timing is obtained, the position of the optical system at that time may vary due to the effects of undershoot and overshoot at the time of rising, and a margin may not be stably created.

In such a case, it is conceivable that the operation of the optical system is precisely controlled by using a large number of ICs and the like to eliminate the variation, but this complicates the device and increases the cost, and the demand for the low cost device. Will be contrary to. In view of the problems of the prior art, the present applicant has previously proposed a device for controlling the operation of the erasing LED for erasing the image leading edge as described below (see Japanese Patent Application No. 3-6969).

That is, using the detection signal of the brake sensor for obtaining the brake timing during the return scan from the position after the original scan to the position during the copy standby (return scan after the preliminary scan for automatic density reading), While the erasing LED is turned on at the detection timing of the brake sensor, the erasing LED is turned off at a predetermined time after the detection timing of the brake sensor.

However, when continuous copying is performed, the temperature of the optical system motor may rise, and the rising response performance of the optical system scan may change (see FIG. 8). For this reason,
As described above, with the configuration in which the erasing LED is turned off after a predetermined time from the detection timing of the brake sensor, there is a possibility that the erasing position may shift due to the change in the rising characteristic.

The response time T in FIG. 8 indicates the time required from the start of the forward scan until the optical system leaves the standby position, and the elapsed time is the continuous copy start. Indicates the elapsed time from. The present invention has been made in view of the above problems, and in an apparatus that controls an erasing LED for erasing an image front end portion by time measurement triggered by a detection timing of a brake sensor at the time of a return scan, an optical system is provided by continuous copying. It is an object of the present invention to provide a device that can avoid the occurrence of a shift in the erase position even if the rising response of the system changes.

[0008]

Therefore, in the image forming apparatus according to the present invention, the optical system reciprocates between the first position during standby for copying and the second position after scanning the original, and the optical system is obtained during this reciprocation. A device for forming an electrostatic latent image by applying light reflected from the document to a photoconductor and transferring an image corresponding to the electrostatic latent image onto a transfer paper. The device includes the items shown in FIG. It

In FIG. 1, a position sensor is for obtaining a control timing during the return scan of the optical system from the second position to the first position, and the charge erasing means is composed of a charging section and an exposing section. It is provided between the two to erase the charge on the surface of the photoconductor. Then, after a lapse of a predetermined time from the detection timing by the position sensor during the return scan, the erasing timing control means brings the operation of the charging erasing means, which has been in the operating state until that timing, to a predetermined operating state including stop.

Here, the rising timing means counts the rising response time during the forward scan of the optical system from the first position to the second position, and the erasing timing correction means
During continuous copying, the predetermined time in the erasing timing control means is corrected according to the rising response time measured by the rising time measuring means in the previous copying.

[0011]

According to this structure, the operation of the charge erasing means is brought into a predetermined operation state including stop after a predetermined time from the detection timing of the position sensor in the return scan, but when the rising response time changes, a predetermined time is elapsed from the detection timing. The position of the erasure stop timing after the start of the forward scan will be shifted later. Therefore, during continuous copying, the charge erasing is stopped at a timing corrected by the variation of the response time based on the previous data of the response time of the rising edge, and even if there is variation in the response time of the rising edge, the charge is erased at a constant position. Elimination of static charge is completed.

[0012]

EXAMPLES Examples of the present invention will be described below. In the image forming apparatus of this embodiment, as shown in FIG. 2, an optical system (not shown) composed of a mirror, an illumination lamp, and the like has a first position during standby for copying and a second position after scanning a document. And the reflected light from the original obtained during this reciprocation is applied to the surface of the photosensitive drum 42 in a slit shape to form an electrostatic latent image, and an image corresponding to this electrostatic latent image is transferred onto the transfer paper. This is a known mirror moving type optical system copying apparatus for copying the contents of an original by transferring the same to the above.

Around the photoconductor drum 42, a general structure such as a strip electrode (charging portion) 43, an erasing LED 44, a developing device, a transfer electrode, a separating electrode, a discharging electrode, and a cleaning device is arranged along the rotation direction. It is provided so that exposure is performed between the erasing LED 44 and the developing device as an exposure unit. In FIG. 2, only the strip electrode 43 and the erasing LED 44 are shown as characteristic parts of the present invention, and other developing devices and the like are omitted.

Here, when a predetermined margin is created at the position corresponding to the leading edge of the document, the erase L as the charge eraser is used.
The ED 44 is turned on to erase the electric charge of the photoconductor drum 42 charged by the belt electrode 43, and the erase LED 44 is turned off to stop the charge erasing by a predetermined time before the exposure (image front end) timing. It is necessary to start the exposure when is advanced by a predetermined amount. In the present embodiment, such control is performed in the procedure shown in FIG. 3 to realize stable image erasing.

That is, during the return scanning operation of the optical system 50 for the EE scan (preliminary scan for automatic density reading), when the brake sensor BRS is passed at time t1 (in the figure, the time is written in parentheses), the erase LED 44 Is turned on to start charge erasing (point A of the photosensitive drum 42). After that, the optical system 50 stops at the end after passing the home position sensor HP, and the forward scan is started at time t5. Further, at time t6, the erasing LED 44 is turned off (point B of the photosensitive drum 42), and when it reaches the leading edge of the document at time t7, exposure is started. With such control, the transfer paper 60
A blank space corresponding to points A and B of the photosensitive drum 42 is formed at the tip of the.

As described above, the margin is created according to the time from the time t1 to the time t6, and when it is desired to change the size of the margin depending on the condition such as the magnification selection, the time t
The time-up time from 1 may be variably controlled. The brake sensor BRS is an optical system 50 for obtaining a brake timing (control timing) during the scan from the position (second position) after scanning the original of the optical system 50 to the position (first position) during standby for copying. Position sensor.
The home position sensor HP detects the position of the tip of the optical system near the position (first position) of the optical system in the standby state for copying.

The specific contents of the above control are shown in the time chart of FIG. In other words, during the return scan after the preliminary scan, the optical system 50 makes the brake sensor BRS at time t1.
After passing through, the timers 1, 3 and 4 start to operate, and the reverse brake is applied by the control of the start signal (signal for controlling the operation / stop of the optical system) and the direction signal,
The return speed of the optical system 50 is sharply reduced. Further, at the time t1 which is the detection timing of the brake sensor BRS, the erase LED 44 which has been turned off until then is turned on (lighted).

When the timer 1 times out at time t2, the optical system 50 is switched to the low speed constant speed control (H1 portion). Further, when the optical system 50 passes the home position sensor HP, the timer 2 starts operating at time t3. When the timer 2 times up at time t4, the reversal brake is applied and the optical system 50 stops. After that, when the timer 3 times out at time t5, the forward scan (main scan for copying) starts, and when the timer 4 times out at time t6, the erase L
The ED44 is turned off (turned off). Furthermore, exposure is started at time t7.

By such control, the brake sensor B
Consistency (coincidence) between the position of the optical system with the passage of time based on the RS detection timing and the control timing can be enhanced, and stable erasing and start of the image front end can be realized. That is, in the above-described control, the stop control of the return scan and the start control of the forward scan are performed by the time measurement based on the detection timing of the brake sensor BRS during the return scan, and further, the erase LED 44 is set a predetermined time after the reference. By turning it off, the erasing LED 44 can be turned off at a certain position after the start of scanning.

Further, since the control is performed by using the EE scan, it is convenient that there is no need to perform an extra scan. FIG. 5 shows an example of the configuration of a copying machine that performs such an operation. The control unit 30 includes four timers 1, 2, 3, and 4, an erasure area calculation unit 31, a drum control unit 32, an optical system / main lens control unit 33, an exposure timing control unit 34, and a paper feed control. Department
35, each control unit starts the control when the copy magnification is set by the magnification selection key 20 and the copy button 10 is pressed.

The optical system 50 is scanned by the optical system scanning section 48, the illumination lamp 52 is driven by the exposure control section 49, and the main lens 51 is controlled by the main lens adjusting section 47. The rotation of the photosensitive drum 42 is controlled at a constant speed by the drum control unit 32 described above. The roller 46 of the paper feeding system is a roller driving unit.
The sheet feeding timing is adjusted by the roller 46 (using a shutter, for example).

The erasing LED 44 is an erasing LED drive section.
The driving timing is based on a control signal from the erasing area calculation unit 31, a signal TP indicating the rotational phase of the photosensitive drum 42 obtained from the encoder 45, a signal RP indicating the sheet feeding timing, and the like. Will be decided. The erase area calculation unit 31 as the erase timing control means,
Based on the signal from the timer 4 and the margin size required from conditions such as magnification selection, the image leading edge is erased (creating a margin at the leading edge of the transfer paper) as described above, and the magnification selection key 20 is used. Based on the copy magnification signal and the transfer paper size signal, the area to be charged should be erased according to the area other than the effective image area and the shift amount of the relative positional relationship between the original and the transfer paper during copying ( Frame-shaped area)
Based on the rotation phase signal TP and the paper feed timing signal RP, the erasing LED 44 is operated during exposure in addition to erasing the image leading edge. The erasure control during exposure is disclosed in detail in Japanese Patent Laid-Open No. 3-48875.

As described above, each timer is triggered by the detection signals from the brake sensor BRS and the home position sensor HP. The configuration of the control unit 30 can be easily realized by using computer hardware or software technology. By the way, as described above, the erasing LED 44 is turned on at the detection timing of the brake sensor BRS, and after a predetermined time (time from time t1 to time t6) timed up by the timer 4 from the detection timing of the brake sensor BRS. By being turned off, erasing is stopped at a predetermined position after the forward scan is started, and a constant margin portion is formed at the leading end portion of the transfer paper.

However, during continuous copying, the rise response of the forward scan changes due to the temperature rise of the optical system motor (see FIG. 8). Therefore, if the erasing LED 44 is turned off after a certain time from the detection timing of the brake sensor BRS, the rise occurs. The erase position will be displaced by the variation of the response. Therefore, in the present embodiment, the rising response time is detected for each forward scan during continuous copying, and the erasing time Ti from the detection timing of the brake sensor BRS until the erasing LED 44 is turned off (time-up time of the timer 4, time t1). To the time t6) is corrected based on the detected rising response time.

The details will be described with reference to the flowcharts of FIGS. 6 and 7. The software functions shown in the flow charts of FIGS. 6 and 7 correspond to the erasing timing control means, the erasing timing correcting means, and the rising time measuring means, but in FIG. 5, the timer 5 corresponds to the rising time measuring means, and The rising delay correction unit 36 corresponds to the erase timing correction unit, and the erase region calculation unit 31 corresponds to the erase timing control unit.

In the flowchart of FIG. 6, first, it is judged whether or not the current copy is a continuous copy in which the copying operation is repeated a plurality of times continuously (S1), and when it is the first copy of the continuous copy (S2). ), The basic time To determined by the required margin size is set to the erase time Ti (S3). Then, the erase LED is detected at the detection timing (S6) of the brake sensor BRS during the return scan.
44 is turned on (S7), the operation of the timer 4 is started (S8), and the time measured by the timer 4 is the erase time T
When the time is up to i (S9), the erase LED 44 is turned off (S10).

On the other hand, in the case of the second and subsequent sheets of continuous copying,
The rising scan response time Tr of the forward scan at the time of the previous copying timed in the flowchart of FIG. 7 described later is read (S4), and then the time obtained by correcting the basic time To based on the response time Tr is Finally, the erase time Ti is set (S5), and similarly to the control of the first sheet, the erase LED 44 is turned on only during the erase time Ti from the detection timing of the brake sensor BRS.

That is, from the rising response time Tr in the previous copying operation, the correction time necessary to stop the image leading edge deletion at a fixed position in the current copying is calculated, and the basic time To is corrected by this. Even if the rise response time Tr changes, erasing is stopped at a fixed position. The flowchart of FIG. 7 shows the timing control of the rising response time Tr. First, whether or not the forward scan is started is determined by whether or not the timer 3 is up (S11), and the forward scan is performed. When is started, it is then determined whether or not the home position sensor HP has switched from the on state to the off state (S12).

When the home position sensor HP is switched from ON to OFF, the operation of the timer 5 is started (S13), and the time measurement is continued until the optical system is further scanned and detected by the brake sensor BRS. (S1
Four). Here, after the home position sensor HP is switched from ON to OFF, when the detection timing of the brake sensor BRS comes, the time measured by the timer 5 is stopped at that time, and the time measured up to that point is set as the rising response time Tr. Set (S15).

In the above embodiment, the time from the home position sensor HP to the brake sensor BRS is set as the rising response time, but the home position sensor H is started from the start of the forward scan due to the time up by the timer 3.
It is also possible to measure the time until P is switched from ON to OFF, or from the start of the forward scan to the detection timing of the brake sensor BRS, and use this result as the rising response time Tr.

[0031]

As described above, according to the image forming apparatus of the present invention, when the operation of the charge erasing means is stopped after a predetermined time from the time when the optical system reaches the predetermined position during the return scanning, the operation is continuously performed. Even if a delay occurs in the rising response of the forward scan due to copying, the predetermined time is corrected in response to the occurrence of such a response delay, so that it is possible to prevent the erase position from being displaced due to the occurrence of the rising response delay, and to perform continuous copying. Even if the above is performed, there is an effect that a certain margin can be created at the leading end of the transfer paper.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a basic relationship between on / off timing of an erasing LED for forming a blank space at a leading end of a transfer paper and movement of an optical system.

FIG. 3 is a diagram showing a specific operation of on / off timing of an erasing LED for forming a blank space at a front end portion of a transfer paper.

[Fig. 4] Reciprocal scanning of the optical system and turning on the erasing LED
The time chart which shows off timing.

FIG. 5 is a block diagram showing an example of a copying machine that performs erase LED control according to the embodiment.

FIG. 6 is a flowchart showing correction control of off timing of an erasing LED during continuous copying.

FIG. 7 is a flow chart showing a timing control of a rising response time used for correcting the off timing of the erase LED.

FIG. 8 is a diagram showing a change in rising response characteristic during continuous copying.

[Explanation of symbols]

 42 Photoconductor drum 43 Band electrode 44 Erase LED 50 Optical system 60 Transfer paper BRS Brake sensor HP Home position sensor

Claims (1)

[Claims] 1. An optical system reciprocates between a first position during standby for copying and a second position after scanning a document, and reflected light from the document obtained during this reciprocation is passed through the optical system. An image forming apparatus for forming an electrostatic latent image on a surface of a photoconductor, transferring an image corresponding to the electrostatic latent image onto a transfer paper, and copying the content of an original. A position sensor for obtaining a control timing during the return scan from the position to the first position, a charge erasing unit provided between the charging unit and the exposure unit to erase the charge on the surface of the photoconductor, and during the return scan After a lapse of a predetermined time from the detection timing by the position sensor, the erasing timing control means that brings the operation of the charging erasing means, which has been in the operating state up to that timing, into a predetermined operating state including stop, To the second position Rising timing means for measuring the rising response time during scanning, and erasing timing for correcting the predetermined time in the erasing timing control means in accordance with the rising response time measured by the rising timing means at the time of the previous copying during continuous copying. An image forming apparatus comprising: a correction unit.