JPH02134258A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To always efficiently execute stable image recording processing regardless of the indication of high and low scanning densities by mounting a previous rotation control means making variable a preset previous rotation processing complete time with respect to a photosensitive body and an optical scanning system on the basis of indicated scanning density. CONSTITUTION:In the case of 400 DPI, a main motor, a scanner motor and a primary charger 4 begin to operate at time P simultaneously and the number of rotations of the scanner motor reach a predetermined number of rotations up to (time Q) starting image writing. In the case of 600 DPI, at first, the scanner motor begins to rotate at time P1 and, subsequently, the main motor and the primary charger 4 start operation at the same time P as the 400 DPI. The number of rotations of the scanner motor reach the predetermined number of rotations indicated to the 600 DPI up to a position Q beginning to write an image. As mentioned above, an image pre-processing time (previous rotation processing time) is made variable at every scanning density (as a result, an image pre-processing complete time is made variable) to make it possible to shorten a fast printing time in the 400 DPI.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus that scans and exposes a recording medium with a high-definition light beam by switching the scanning density to form an image.

(Prior Art) Conventionally, in laser beam printers using semiconductor lasers, scanning densities (240, 300, 4
00DPI). but,
With recent improvements in image processing technology, scanning densities have increased to 500, 600, and 80 in order to print image data, etc. in high definition.
There is also a growing demand for 0DPI.

On the other hand, one laser beam printer can have multiple scanning densities (e.g. 300DPI and 400DPI or 400DPI).
There has also been proposed an apparatus that executes printing processing by switching between 1 and 600 DPI.

This is so that one laser beam printer can be connected to a plurality of host computers, and an appropriate scanning density can be selected depending on the desired image sample.

Note that as the scanning density increases (scanning becomes more precise)
Although the image quality is high, specific problems arise such as it takes a long time to develop the image information into dots, and it takes a considerable amount of time to transfer the image information.

In particular, for character information such as kanji, it is possible to print sufficiently finely at around 400DPI, but for photographic images, etc., a scan density of around 400DPI does not necessarily result in good image quality; There will be cases where you will be required to specify the scanning density.

(Problem to be Solved by the Invention) In general, when changing the scanning density in the sub-scanning direction, especially in laser beam printers, the optical scanning system (scanner motor, polygon mirror, imaging lens, folding mirror, etc.) This is achieved by increasing and decreasing the rotational speed of the scanner motor, etc., up to a constant speed.

However, a relatively non-negligible time lag occurs between the time it takes to start up to the reference rotation speed set at, for example, 400 DPI and the time to start up to the reference rotation speed set at 600 DPI.

Therefore, in conventional low-density laser beam printers,
If the scanner motor is started up in synchronization with the start-up timing of the main motor (the motor that drives the photosensitive drum, etc.), the specified rotation speed will be reached before image printing starts, and stable exposure scanning will be possible. When specifying scanning density, with the scanner motor start-up control as described above, even if the main motor start-up is completed, the scanner motor rotation speed may not reach the specified rotation speed, which may affect the quality of the reproduced image. There were serious problems that caused significant damage.

This invention was made to solve the above problems, and by varying the starting timing of the optical scanning system driving means according to the scanning density and varying the preprocessing end time, it is possible to control the scanning density specification. To provide an image recording device that can always form high-definition images from low resolution to high resolution from the first print regardless of the situation.

[Means to solve the problem]

The image forming apparatus according to the present invention is provided with a pre-rotation control means for varying the pre-rotation processing completion time set in advance for the photoreceptor and the optical scanning system based on a designated scanning density designation. Further, the pre-rotation control means varies the start-up timing of the optical scanning system based on the designated scanning density.

[Effect]

In this invention, the pre-rotation control means determines the designated scanning density, and varies the start-up timing of the optical scanning system based on the designated scanning density. The scanning system and the photoconductor are driven at the same time, and when high scanning density is used, the optical scanning system is driven in advance of the photoconductor drive timing, and the preprocessing rotation completion time is variably adjusted to achieve fast Stabilize the speed of the optical scanning system before starting printing.

(Embodiment) FIG. 1 is a sectional view illustrating the configuration of an image forming apparatus showing an embodiment of the present invention, and 1 is composed of a semiconductor laser, a polygon mirror, a precision motor for driving the polygon mirror, etc. It is a scanner unit (optical scanning system),
The laser beam emitted from the semiconductor laser passes through a collimator lens to become parallel light, and then enters a polygon mirror, and the laser beam scans the photosensitive drum 3 by the polygon mirror that rotates at high speed. 2 is fθ
It is an optical system consisting of lenses, folding mirrors, etc.

This optical system 2 causes the laser beam to enter the photosensitive drum 3 . The wavelength of the semiconductor laser in this embodiment is 770 to 800 nm, and the photosensitive drum 3 uses a photosensitive member sensitive to this wavelength, such as a phthalocyanine-based organic photoconductor or a selenium-based photoconductor.

A primary charger 4 uniformly charges the photosensitive drum 3 made of an organic photoconductor.

In this embodiment, a grid 17 is provided at a constant distance from the photosensitive drum 3 in order to perform primary charging more uniformly and to stabilize the potential on the photosensitive drum 3. This grid 17 is grounded via a self-voltage generating member, and when a corona discharge current flows, the grid 17
A constant voltage is generated at 7 to control the surface potential of the photosensitive drum 3. The photosensitive drum 3 charged by the charger 4 is transferred to the scanner unit 1 described above. It is scanned by a laser beam guided by the optical system 2, and an electrostatic latent image is formed.

In this embodiment, the portion to be visualized is scanned with a laser beam. In other words, a so-called image scanning method is used in which a portion irradiated with a laser beam is developed. This is because the image scan method has clearer image quality than the background method, requires less laser light emission time, and is advantageous for the lifespan of the semiconductor laser.

This electrostatic latent image is visualized by the next developing device 5.

In this embodiment, a one-component magnetic development method is adopted as a developing method, which makes it possible to simplify and downsize the developing device 5, and to construct a developing device with less contamination by toner. An AC voltage on which a DC voltage is superimposed is applied to the sleeve 5 by a power source (not shown).

On the other hand, the sheet P on the stacking table S is fed onto the photosensitive drum 3 by a feeding roller 6 and a registration roller 7 that rotates in synchronization with the image on the photosensitive drum 3. Then, the toner image on the photosensitive drum 3 is transferred onto the sheet P by the transfer charger 8. Thereafter, the sheet P separated from the photosensitive drum 3 by the separating means 9a
is guided to the fixing device 10 by the guide 9, and the sheet P
After the upper toner image is fixed, it is discharged onto a tray 12 by a discharge roller 11. Note that 13 indicates a cleaner.

Note that in this embodiment, the photosensitive drum 3. -Charger 4. Developing device5. The cleaner 13 constitutes an integrated process cartridge 14. The process cartridge 14 is detachably attached to the main body, and when loaded into the main body, the sliding portion 14b of the frame 14a of the process cartridge 14 engages with the main body guide 15 and is guided. . Reference numeral 16 denotes a pre-exposure means for irradiating light onto the photosensitive drum 3 before primary charging, and a halogen lamp, incandescent bulb, LED, etc. may be used as the light source. This pre-exposure light passes through the opening of the process cartridge 14 and is irradiated onto the surface of the photosensitive drum 3.

Reference numeral 18 denotes a controller unit that controls the pre-rotation completion time in accordance with the scan density designation according to a flowchart to be described later.

FIG. 2 is a timing chart explaining the operation of FIG. 1. T1 to TIO indicate the startup timing or voltage application timing, characteristics, etc. of each part. Note that T1 indicates the start timing of the main motor, T2 indicates the start timing of the scanner motor, T3 indicates the rotation speed of the scanner motor, T4 indicates the start timing of the pre-exposure means 16, and T5 indicates the start timing of the primary charger 4. T6
indicates the starting timing of the transfer charger 8, T7 indicates the laser beam exposure timing, T8 indicates the surface potential characteristics of the photosensitive member, T9 indicates the starting timing of the DC component developing bias, and TIO indicates the starting timing of the AC component developing bias. Indicates start timing.

Hereinafter, a case will be described in which the scanning density is switched between 400 DPI (and lower scanning density) and 600 DPI.

First, in the case of 400 DPI, the main motor, scanner motor, charger 4, etc. start operating simultaneously at time P (timings Tl, T2, T5). The number of revolutions of the scanner motor reaches a predetermined number of revolutions by the time image writing is started (time Q).

However, in the case of 600 DPI, the scanner motor first starts rotating at time P1, and then the main motor and charger 4 start operating at the same time P as 400 DPI. The number of revolutions of the scanner motor reaches a predetermined number of revolutions designated as 600 DPI by the time Q at which image writing begins.

In this way, the image preprocessing time (pre-rotation processing time) can be varied for each scanning density (as a result, the image preprocessing completion time can be varied)
Therefore, at 400DPI, the first print time can be shortened. Further, when printing a photographic image using 600 DPI, it takes time to transfer the image data, so even if the first print time becomes slightly longer, it does not cause any major problem. Note that Table 1 below shows examples of scanner motor start-up times for different scanning densities.

Table 1 Note that the laser beam printer shown in Table 1 above uses six polygon mirrors.

In addition, in this embodiment, it takes about 5 seconds from when the main motor starts operating to when the image signal is printed, so 400
At DP1 or less, the scanner motor can be started up during the pre-rotation.

The following other image forming sequence will be explained.

In the pre-rotation, first, the pre-exposure means 16 lights up at the same time as the rotation of the photosensitive drum 3 starts (see timing T4), and the primary charger 4 starts discharging at the same time or with a slight delay (see timing T4).
(See timing T5). This is because the polarity of the transfer charger 8 is positive, so when the photosensitive drum 3 is charged with a positive charge of opposite polarity to the negative charger 4, charging memory remains on the photosensitive drum 3.
This is because it is not preferable for the photosensitive drum 3. Therefore, after the photosensitive drum 3 has been primary charged, transfer charging is started so as to overlap the portion that has received this secondary charging. In this way, the potential on the photosensitive drum 3 is not charged to a high potential with a polarity opposite to that of the -order charging, and no charging memory is left on the drum.

After image exposure with a laser is performed, the transfer charger stops discharging during post-rotation, and then the primary charger 4 continues discharging for the time required for the photosensitive drum 3 to rotate between the transfer and primary charger 4, and transfer. After the potential on the photosensitive drum 3 that has received the charger 8 is brought to a potential close to the -degree charging potential VD, in order to attenuate this charging potential, the photosensitive drum 3 is rotated approximately one revolution to uniformly apply pre-exposure to the entire circumference of the photosensitive drum 3. irradiate. In this way, by once setting the potential of the photosensitive drum 3 to a negative potential and then irradiating it with light, the potential on the photosensitive drum 3 can be uniformly and almost attenuated. At this timing, the transfer charger 8 must stop discharging after the transfer material passes through the transfer charger 8.

Furthermore, the negative charger 4 must stop discharging after overlapping the discharged portion of the transfer charger 8.

Furthermore, since the pre-exposure requires irradiation of all the areas that have received primary charge, it is necessary to rotate at least one rotation after the -order charge stops discharging.

In this way, after the potential on the photosensitive drum 3 becomes uniform, the rotation of the photosensitive drum 3 is stopped and the pre-exposure is turned off.

If the above timing is adopted, the photosensitive drum 3 is primarily charged and then irradiated with light, so that almost no charging memory or optical memory remains.

Next, a voltage is applied to the transfer charger 8 (timing T6 shown in FIG. 2), whereby corona ions move toward the photosensitive drum 3, and the surface potential becomes approximately dark potential (potential at point A shown in FIG. 2). (timing T8). Immediately after this charged region reaches the development position, a DC component of the development bias (potential at point B shown in FIG. 2) is applied to the development electrode (timing T9 shown in FIG. 2). After the potential of the photosensitive drum 3 uniformly becomes a dark potential, image exposure is started, and just before the image area reaches the development position, an alternating current component of the development bias (
0 point potential shown in Figure 2) is applied (timing T
10). After the image exposure is completed and the rear end of the image area passes the development position, the AC component of the development bias is cut off at point D shown in FIG. It is phrased after passing through. Then, the -order charging is turned off. Subsequently, the surface potential of the photosensitive drum 3 drops to near zero due to pre-exposure, and just before the leading edge of that area reaches the development position, the DC component of the developing bias is cut off, and the pre-exposure is also cut off.

FIG. 3 is a control block diagram illustrating the configuration of the controller unit 18 shown in FIG. 1. Reference numeral 30 is a controller on the printer side, which is connected to a host computer 39 on the host side via a connector.

On the other hand, a signal from the controller 30 is sent to the main motor 32 via the main motor driver 31 or to the scanner motor 34 via the scanner motor driver 33, and the respective motors 32 and 34 are driven.

On the other hand, the laser 35 is driven by a laser driver included in the controller 30 according to the image signal. 36
is a high voltage power supply, which applies high voltage to a charger such as a primary charger based on a control signal from the controller 3°. A pre-exposure unit 37 performs pre-exposure processing based on a control signal from the controller 30. A developing bias power supply 38 applies a predetermined developing bias to the developing sleeve based on a control signal from the controller 30.

The controller 3o adjusts the scanning density according to a command from the host side or a scanning density designation provided in the printer device.
For example, it is possible to selectively switch between 600DPI and 400DPI, and when a high scanning density such as 600DPI is specified, the scanner motor driver 33
On the other hand, a drive command is issued prior to the time of 400 DPI, substantially extending the pre-rotation processing completion period, and the rotation of the scanner motor 34 is started and stabilized before the start of image recording. As a result, the time until the first print is substantially extended when 600 DPI is specified, but the time until the first print is shortened when 400 DPI is specified.

Although the above embodiments have been described using a laser beam printer that performs pre-exposure as an example, the present invention can also be applied to a laser beam printer that does not perform pre-exposure.

Furthermore, in the above embodiment, a case has been described in which only the scanner motor 34 is started before the other drive systems, but the main motor 32 is simultaneously driven at the same time as the scanner motor 34 rotates, and idle rotation processing is performed for a predetermined period of time. You may run it.

Furthermore, in the case of a printer in which the scanner motor 34 is rotated at a low speed when the printer is in standby mode, and then ramped up to a predetermined rotation speed when printing, pay attention to the startup time from low speed rotation to the predetermined rotation speed. hand,
This invention can be applied.

FIG. 4 is a timing chart for explaining the control operation of an image forming apparatus showing another embodiment of the present invention, and the same parts as in FIG. 2 are given the same reference numerals. In addition, 400DP
In the case of I designation, the explanation is omitted since the control is between the control shown in FIG.

When 600 DPI is specified as the scanning density, the scan motor 34 first starts rotating, and when it reaches 4000 rpm, which is lower than the specified rotation speed (point R in the diagram).
, pre-exposure means 16. -Charger 4. Main motor 32 is started. This is to start the printing operation with the expectation that when the rotation speed reaches 4000 rpm, the image will be written out and the specified rotation speed will be reached by point Q in the figure).

As a result, even if 600 DPI is specified as the scanning density, a printed image can be obtained in the minimum time (shorter than the control time shown in FIG. 2). Note that although 600 DPI has been described as an example here, it is of course possible to use 800 DPI, 1000 DPI, etc.

(Effects of the Invention) As described above, the present invention provides a pre-rotation control means for varying the pre-rotation processing completion time set in advance for the photoreceptor and optical scanning system based on a designated scanning density designation. Since the rotation control means is configured to vary the start-up timing of the optical scanning system based on the specified scanning density, even if high density is specified as the scanning density, the optical scanning is completed before the start of image recording. The scanning speed of the system can be stably started up to the specified speed, and when a low scanning density is specified, the time to obtain the first print can be shortened. This provides excellent effects such as efficient execution of image recording processing.

[Brief explanation of drawings]

FIG. 1 is a sectional view illustrating the configuration of an image forming apparatus showing an embodiment of the present invention, FIG. 2 is a timing chart illustrating the operation of FIG. 1, and FIG. FIG. 4 is a control block diagram illustrating the configuration of the controller section, and a timing chart illustrating the control operation of an image forming apparatus showing another embodiment of the present invention. In the figure, 1 is a scanner unit, 3 is a photosensitive drum, 4 is a primary charger, 5 is a developer, 8 is a transfer charger, 10 is a fixing device, 16 is a pre-exposure means, and 18 is a controller unit. Diagram

Claims (2)

[Claims] (1) A beam generating means that emits a light beam that modulates an input image signal at a specified frequency, and an optical system that deflects and scans the light beam emitted from the beam generating means to form an image on a photoreceptor. An image forming apparatus having a scanning system and a rotating means for rotating the optical scanning system at a predetermined speed, and recording an image by switching the frequency and the rotational speed of the optical scanning system based on a specified scanning density, An image forming apparatus comprising a pre-rotation control means for varying a pre-rotation processing completion time set in advance for the photoreceptor and optical scanning system based on a specified scanning density designation. (2) The image forming apparatus according to claim 1, wherein the pre-rotation control means varies the start-up timing of the optical scanning system based on a specified scanning density.