JP3529964B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a laser scanning optical system having a laser diode array (hereinafter referred to as an LDA), and more particularly, to a beam pitch depending on a pixel density. The present invention relates to improvement of a technique for converting (light emitting unit interval). 2. Description of the Related Art In recent years, image forming apparatuses having a laser scanning optical system such as a laser printer have been increasingly required to have higher density and higher speed. In order to realize this high density and high speed, it is necessary to increase the rotation speed of the polygon scanner. Normally, polygon scanners that can handle rotation speeds up to about 25,000 rpm are relatively inexpensive and small ones are available. However, if the rotation speed is higher than that, the cost and size of the polygon scanners are limited due to bearings and life. And rise sharply. Furthermore, even if you try to get one that supports high-speed rotation, it may be undeveloped and unavailable. In order to avoid such an increase in the cost of the polygon scanner, a method using an LDA is being studied. This is intended to realize high speed and high density without increasing the rotational speed of the polygon scanner using an LDA which generates at least two laser beams in the sub-scanning direction. According to this method, the number of rotations of the polygon scanner is ２ in the case of two arrays and シ ン グ ル in the case of two arrays compared to the case of a single beam diode, so that an inexpensive and small polygon scanner can be used. Become. There is also a demand for an image forming apparatus to support a plurality of pixel densities. In the case of a single beam diode, a plurality of pixel densities have been realized by changing the rotation speed of the polygon scanner, the pixel clock frequency, and the like. In the case of LDA, since the beam pitch in the sub-scanning direction is fixed, it has been proposed to realize a plurality of pixel densities by changing the pitch. For example, Japanese Patent Application Laid-Open No. 6-991 discloses that in a laser beam printer using a plurality of beams, the distance in the sub-scanning direction between beam spots on a photosensitive member can be reduced without increasing optical accuracy or control accuracy. The technology to do this is described. However, an LD that generates at least two or more laser beams in the sub-scanning direction
In the case where a conventional image forming apparatus using A is used to support a plurality of pixel densities, a certain time is required for changing the rotation speed of the polygon scanner and converting the beam pitch, so that the throughput may be reduced. Note that the above-mentioned Japanese Patent Application Laid-Open No.
The technique described in Japanese Patent Publication No. 91 relates to facilitation of control of a beam pitch, and does not attempt to improve throughput. The present invention has been made in view of such a background, and an image forming apparatus capable of high-speed image formation without lowering the throughput even when a plurality of pixel densities are supported by using an LDA. The purpose is to provide. In order to achieve the above object, according to the first aspect of the present invention, a printer controller having an interface with a host computer and at least two or more laser beams are generated. A laser scanning optical system including a laser diode array, a beam pitch conversion mechanism that converts a beam pitch of the laser diode array in the sub-scanning direction, and a polygon scanner that scans a laser beam generated from the laser diode array in the main scanning direction. And a printer engine unit for performing an actual image forming operation. The image forming apparatus performs beam pitch conversion according to the pixel density as required. When making changes, make sure that the printer The troller unit informs the printer engine unit by a notification unit that the pixel density is to be changed at the time of forming the (n + 1) th image, and when the beam pitch conversion is necessary for the (n + 1) th image formation, Immediately after the n-th sub-scanning direction effective image area signal is negated, the beam pitch conversion of the laser diode array in the sub-scanning direction and the change of the polygon scanner rotation speed are started without waiting for the completion of the ejection. The n-th sheet is controlled to operate for a predetermined time and to complete the discharge of the n-th sheet within the predetermined time. [0010] Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a laser scanning optical system of the image forming apparatus. The laser scanning optical system shown in FIG. 1 includes an LDA 11, a collimating lens 12, an aperture 13, a first cylinder lens 14, a polygon scanner 1,
6, polygon mirror 17, a pair of fθ lenses 18a, 1
8b, a first mirror 19, and a second cylinder lens 20. In order to determine the timing of writing on the photoconductor 15, a mirror 21, a cylinder lens 22, and a beam sensor 23 are arranged outside the effective image area (the area indicated by a dashed line 15a on the photoconductor 15). The write timing is determined based on the output of the beam sensor 23. In the laser scanning optical system configured as described above, the laser beam emitted from the LDA 11 is collimated by the collimator lens 12 and has an aperture 13 having a slit portion corresponding to the size of a dot to be formed.
As a result, an extra laser beam is cut. The laser beam is condensed by the first cylinder lens 14 so as to have a predetermined size on the photoreceptor 15, and is rotated by a polygon mirror 17 in a direction indicated by an arrow A by a polygon scanner 16. Are scanned in the main scanning direction (long axis direction of the photoconductor 15). Then, the pair of fθ lenses 18 converts the equiangular motion into the uniform motion, and corrects the curvature of field. Next, the angle of the laser beam is changed by the first mirror 19, and the laser beam is condensed by the second cylinder lens 20 in the sub-scanning direction indicated by the arrow y (the rotation direction of the photosensitive member 15 indicated by the arrow B). Then, the laser beam is irradiated onto the photoconductor 15. Here, the rotation speed of the polygon scanner 16 is Rm (rpm), and the pixel density is DPI (Dots Pes).
r Inch), the linear velocity of the photoconductor 15 is v (mm / s),
Assuming that the number of surfaces of the polygon mirror 17 is n (surface), Rm = (DPI × v × 60) · (25.4 × n). From the above equation, it can be seen that in order to increase the pixel density and the photoconductor linear velocity, it is necessary to increase the rotation speed of the polygon motor 16 (not shown). However, in the case of the LDA 11, the rotation speed of the polygon scanner 16 is as follows: Rm (2) = Rm / 2 in the case of two arrays Rm (4) = Rm / 4 in the case of four arrays FIG. 2 is a block diagram of a laser printer according to an embodiment of the present invention. The laser printer shown in FIG. 2 is connected to a host computer 31 and includes a printer controller 32, a communication unit 33, and a printer engine 34. The printer engine 34 includes a CPU 35,
It has a data storage ROM 36 and a laser scanning optical system 37 shown in FIG. As described above, the laser scanning optical system 37 is an LDA [LDA having LDA (1) to LDA (n)].
Unit] 11, a beam pitch conversion mechanism 38 in addition to the polygon scanner 16. The CPU 35 issues a start-up / rotation command to the polygon scanner 16, issues a beam pitch conversion command to the beam pitch conversion mechanism 38, and outputs a lighting signal to the LDA unit 11. Also, the polygon scanner 16 sends the CPU 3
5, a ready signal is output and the data storage ROM 3
6 outputs a stored data read signal to the CPU 35. The printer controller 32 develops print data transferred from the host computer 31 into bit information. Also, information such as the pixel density is notified to the printer engine 34 by the notification means 33. The printer engine 34 forms an image by a known electrophotographic process based on the bit information and the information of the communication means 33. When the pixel density is changed on the (n + 1) th sheet, the printer controller 32 notifies the printer engine 34 of the fact by the notifying unit 33 at the latest at the time of forming the nth sheet. The printer engine 34 follows this information,
The pixel density changing operation is performed before the image formation of the (n + 1) th sheet. Before the end of the n-th image formation, the printer engine 34 has already recognized that the pixel density change is necessary for the next image formation. Formation is possible. FIG. 3 is a flowchart showing a control example according to the first embodiment of the present invention. This flow represents the contents described above, and corresponds to the first aspect of the present invention. In step S1, a start (print request) is performed.
In step S2, it is determined whether or not the pixel density has changed. If there is a pixel density change request, the beam pitch is converted by the beam pitch conversion mechanism 38 in step S3. Next, an image forming operation is performed in step S4, and the process ends in step S5. FIG. 4 is an explanatory diagram showing a first example of the notification means. This example corresponds to the invention described in claim 2.
The notification means 33 is constituted by a serial I / F (interface). The printer controller 32 sends information such as pixel density to the printer engine 34 by a command. FIG. 5 is an explanatory view showing a second example of the notification means. This example corresponds to the invention described in claim 3.
The notification means 33 is composed of two hard wires using a parallel I / F. The printer controller 32 sends information such as pixel density to the printer engine 34 by a combination of “H” and “L” of the hard line. FIG. 6 shows an example of this combination. FIG. 7 is a timing chart of the image forming operation when the pixel density is not changed. The image formation by the polygon scanner and the LDA scanning is performed while FGATE (sub-scanning direction effective image area signal) is active. FIG. 8 is a timing chart of the image forming operation in the case where the pixel density is changed after the ejection of the nth sheet is completed. Since changing the pixel density requires changing the rotation speed of the polygon scanner and changing the beam pitch, a predetermined time “t” is required.
Need. FIG. 9 is an image forming operation timing chart when the pixel density is changed immediately after n-th FGATE negation. The present invention executes the pixel density change timing shown in FIG. 9, and starts the pixel density change operation immediately after the n-th FGATE is negated without waiting for the completion of the discharge of the n-th sheet. In this case, the throughput does not change from the case where the pixel density change shown in FIG. 7 is not performed. In other words, the throughput of image formation when the pixel density is changed is improved as compared with the case where the pixel density is changed after the nth sheet is discharged as shown in FIG. 7 and 8,
All signals in FIG. 9 are "L" active. FIG. 10 is a flowchart showing a control example according to the second embodiment of the present invention. This flow relates to the image forming operation timing shown in FIG. 9, and corresponds to the invention described in claim 4. After the start (print request) is performed in step S1, it is determined in step S2 whether there is a pixel density change request for the (n + 1) th sheet. If there is a change request, it is determined in step S3 whether the n-th FGATE has been negated after being activated. If negated, the beam pitch is converted by the beam pitch conversion mechanism 38 in step S4. Then, the number of rotations of the polygon scanner is changed. Thereafter, the process proceeds to the image forming operation in step S5, and ends in step S6. If there is no pixel density change request in step S2, the process directly proceeds to the image forming operation in step S5. According to the first aspect of the present invention, when the number of prints is set to n and the pixel density is changed for the (n + 1) th image formation, at the latest at the time of the nth image formation, The printer controller performs control to notify the printer engine by notification means that the pixel density is to be changed at the time of forming the (n + 1) th image, and the control means of the printer engine performs beam control to form the (n + 1) th image. When the pitch conversion is necessary, the control for starting the operation necessary for changing the pixel density is performed immediately after the n-th sub-scanning direction effective image area signal is negated without waiting for the completion of the discharge of the n-th sheet. ,
It is possible to provide an image forming apparatus capable of high-speed image formation without lowering the throughput even when a plurality of pixel densities are supported. ## EQU1 ##

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a laser scanning optical system of an image forming apparatus. FIG. 2 is a block diagram of the laser printer according to the embodiment of the present invention. FIG. 3 is a flowchart illustrating a control example according to the first embodiment of this invention. FIG. 4 is an explanatory diagram showing a first example of a notification unit. FIG. 5 is an explanatory diagram showing a second example of the notification means. FIG. 6 is a chart showing an example of a pixel density notification combination by the hard line shown in FIG. 5; FIG. 7 is an image forming operation timing chart when the pixel density is not changed. FIG. 8 is a timing chart of an image forming operation in a case where the pixel density is changed after the discharge of the n-th sheet is completed. FIG. 9 is an image forming operation timing chart when a pixel density is changed immediately after n-th FGATE negation. FIG. 10 is a flowchart illustrating a control example according to the second embodiment of this invention. [Description of Signs] 11 LDA section 16 Polygon scanner 31 Host computer 32 Printer controller 33 Notification means 34 Printer engine 35 CPU 36 Data storage ROM 37 Laser scanning optical system 38 Beam pitch conversion mechanism

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/44 B41J 2/51 B41J 29/38 G02B 26/10

Claims (1)

(57) [Claim 1] A printer controller having an interface with a host computer, a laser diode array for generating at least two or more laser beams, and a beam in the sub-scanning direction of the laser diode array A beam pitch conversion mechanism for converting a pitch, and the laser die
Laser beam generated from auto array in main scanning direction
A laser scanning optical system having a polygon scanner for scanning, a printer engine unit for performing an actual image forming operation, and an image forming apparatus for performing beam pitch conversion according to a pixel density as required; age,
To change the pixel density for the (n + 1) th image formation,
When n-th image forming at the latest printer controller, at the time n + 1 th image forming and notify to the printer engine unit by notification means that for performing pixel density changes
In both cases, beam pitch conversion is necessary for forming the (n + 1) th image.
If necessary, without waiting for the completion of the discharge of the n-th sheet,
Immediately after the scanning direction effective image area signal is negated,
Beam pitch in the sub-scanning direction of laser diode array
Start conversion and change of the polygon scanner rotation speed
Operate for a predetermined time, and within the predetermined time,
An image forming apparatus, wherein the discharge is controlled to be completed .