JPH02293877A - Image forming device - Google Patents

Abstract

PURPOSE:To highly accurately adjust the image-forming condition of a spot on a photosensitive body in the short time by changing the image-forming condition of a image-forming system plural times while output image information is formed on the photosensitive body once through the use of a luminous flux. CONSTITUTION:A focusing means or a means changing the image-forming condition of the image forming system is constituted of a holder 207 which is the holder of a correcting lens 3 and moves in the direction of an arrow A by the rotation of a pole screw 206 in parallel and a motor 205 driven by a prescribed amount according to an instruction from a control part 201, etc. When an image for focal adjustment is obtained, the image-forming condition of the image-forming system is changed plural times at a prescribed interval while one stroke of latent images, etc., ie., one sheet of the latent images is formed once. Consequently, strip-like output parts corresponding to the various image-forming consitions are formed in an image output for the focul adjustment. Thus, by manually or automatically adjusting the image-forming system, etc., the image-forming condition can be adjusted in the short time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming apparatus, particularly an optical scanning image forming apparatus that forms an image by focusing a light beam from a light source such as a laser or an LED on a photoreceptor. Regarding.

[Background Art] In recent years, optical scanning image forming devices (optical printers) have become widely used as output devices for digital images, computer output documents, etc. These optical printers scan a photoreceptor with a light beam modulated in accordance with an image signal, give an exposure distribution there, and form a latent image.Then, this latent image is transferred to an output medium such as paper or film. The well-known electrophotographic method is often used to visualize the latent image.Many methods have been proposed and implemented for forming the exposure distribution on the photoreceptor. It has been done. In most systems, an imaging system is used, and the image of a light source such as a laser or LED is formed onto a photosensitive book by this imaging system, and the light source is controlled to control the amount of exposure on the photosensitive member, the exposure time, etc. By controlling the power and modulating the shutter ON/OFF, an exposure distribution corresponding to the image signal is formed on the photoreceptor. On the other hand, one of the recent trends in optical printers is the increasing resolution of images, such as 400 pixels/inch (Cdpi), 6
There is a growing demand for high-density printing such as 00 dpi. Furthermore, in the PWM (pulse width modulation) method, halftone output is achieved by dividing each pixel into smaller sections and changing the size and thickness of the printed dots. In high-definition optical printers that meet these demands, the size of the light source image (hereinafter referred to as a spot) formed on the photoreceptor must be miniaturized to correspond to the fineness of the printed dots. .

For example, an optical printer with an output density of 800 dpi, or
In a PWM type optical printer with an output of 00 dpi, the spot size must be suppressed to about 40 μm (diameter from the peak value to a value of l/e'' in a Gaussian intensity distribution) in the scanning direction.

Imaging systems that produce spots with such minute diameters on the photoreceptor generally have a shallow depth of focus (therefore, it is necessary to improve the imaging relationship between the light source and the photoreceptor over the entire printing or image forming range). This requires some kind of adjustment means for the imaging system or the like.

[Problem to be Solved by the Invention] However, even with an optical printer having such adjustment means, in order to monitor the image formation state of a spot on the photoreceptor, a television camera or the like must be placed at the photoreceptor position during adjustment. In addition, the entire adjustment device becomes large-scale, and the adjustment at the time of assembling the optical printer requires time and cost. Furthermore, in the market, it is almost impossible to adjust the image formation state that is deviated due to vibrations applied to the optical printer or other causes.

In addition, with the imaging state measuring device, it is difficult to observe the entire printing area at once, and measurements must be repeated at several locations within the printing area, which takes a long time in terms of adjustment time and accuracy. It becomes a problem.

SUMMARY OF THE INVENTION Therefore, in order to solve the above-mentioned problems, it is an object of the present invention to easily measure the imaged image in the entire printing or image forming area, and to adjust the imaged state of the spot on the photoreceptor in a short time and with high precision. The objective is to provide an image forming device that can perform [Means for Solving the Problems] In the present invention to achieve the above object, a light beam from a light source is focused on a photoreceptor through an imaging system, and this light beam is used to output onto the photoreceptor. Means is provided for changing the imaging state of the imaging system multiple times during the formation of image information (latent image, etc.) once. In the above, if distinguishable markings are made at positions corresponding to different imaging states in the output image, the output image becomes easier to see. [Function] According to the configuration of the present invention, the focus adjustment image C To obtain an image, the imaging system is activated multiple times at predetermined intervals while forming a latent image such as T on the photoreceptor once, that is, for one stroke (for example, forming a latent image for one sheet of paper). Since the imaging state is changed, the image output for focus adjustment will have, for example, output parts corresponding to different imaging states in a band shape, and the parts corresponding to good imaging states will be visible at a glance. This can be determined and the corresponding state of the imaging system can also be easily recognized.

[Embodiment] FIG. 1 shows a schematic configuration of a first embodiment of an image forming apparatus according to the present invention. In the figure, ■ is a semiconductor laser device that is a light source, 2 is a silimeter lens system that converts the laser beam emitted from the semiconductor laser device 1 into approximately parallel light, and 3 is a lens system for adjusting the focal position of the entire imaging system. This is a correction lens, and is movable within a predetermined range in eight directions indicated by arrows, which are the optical axis directions of the laser beam, by a focus adjusting means to be described later.

Furthermore, 4 is a rotating polygon mirror that reflects and scans the laser beam from the correction lens 3 by rotating at a constant speed in the direction of arrow B, and 5 is an f/θ lens group placed after the rotating polygon mirror 4, which is a polygonal mirror. The laser beam deflected by the mirror 4 forms an image on the surface to be scanned, and the scanning speed is kept constant on the surface to be scanned.

Further, 6 is a photosensitive drum which is a surface to be scanned,
During exposure, it rotates in the direction of arrow C.

Incidentally, a developing device, primary and transfer chargers, a cleaner, etc. (not shown) are provided around the photosensitive drum 6, and the latent image formed on the surface of the photosensitive drum 6 is visualized by a known electrophotographic process. It is designed to be transferred to a transfer material such as paper or film. Figure 2 shows a block diagram regarding control of the first embodiment. In the figure, 201 is a CPU. A control unit 202 composed of a memory and the like is a pattern generator 20 that creates a predetermined image signal sequence according to instructions from the control unit 201.
3 is a laser driver that converts the image signal from the pattern generator 202 into a drive signal for the semiconductor laser element 1 and controls the blinking of the semiconductor laser l; 204 drives the motor 205 by a predetermined amount in accordance with a command from the control unit 201; A motor driver 206 is a ball screw rotated by the motor 205, and 207 is a holder for the correction lens 3, which is moved in parallel in eight directions indicated by arrows in FIG. 1 by rotation of the ball screw 206. The holder 207, the motor 205, etc. constitute focus adjustment means or means for changing the imaging state of the imaging system.

Furthermore, 208 is a driver for each process on the side of the electrophotographic machine, including a high-voltage driver for charging, transfer, etc., a motor driver for rotating the polygon (rotating polygon mirror 4), rotating the photosensitive drum 6, etc. Reference numeral 209 indicates various sensors, and based on signals from these sensors, the control unit 201 sends commands to each unit or changes the mode of control. For example, when a temperature sensor sends a signal indicating that the temperature of the device has exceeded a predetermined value,
The control unit 20l starts an AF (autofocus) mechanism and adjusts and moves the correction lens 3 based on the image formation state of the spot. Further, the control unit 201 may start an operation for obtaining an image output for focus adjustment, which will be described below, based on a signal from a sensor indicating a spot imaging state. In the above configuration, focus adjustment of the imaging system is performed as follows. First, the control unit 201 instructs the motor driver 204 to
The motor 205 is driven and the correction lens holder 207 is instructed to be placed in the standard position. Here, if the minimum amount of movement of the lens holder 207 due to the rotation of the motor 205 is defined as a "step", the step is selected such that the amount of movement of the image plane of the imaging system is smaller than its depth of focus. For example, if the depth of focus of the imaging system is 1 mm, the steps should be set in advance so that the amount of image plane movement corresponding to step (1) is approximately 0.3 to 0.5 mm. Next, the control unit 201 similarly instructs the motor driver 204 to move the correction lens holder 207 by a predetermined number of steps. At this time, the image surface of the imaging system moves according to the number of steps, and the number of steps is selected so that the amount of movement is equal to or greater than the amount of bint shift expected at that time. For example, if the bint shift is expected to be about ±2 mm, and if the image plane moves by 0-5 mm in steps, then move the correction lens 3 by 4 steps or more from 2 mm 70.5 mm = 4. Next, the control unit 201 gives an instruction to each process driver 208 of the electrophotographic mechanism to start an output operation. At the same time, the pattern generator 202 is made to output an image pattern for focus adjustment. The mode drivers 20 and 4 are provided with a correction lens holder 20 while outputting an image pattern for focus adjustment.
7 is instructed to move by a predetermined number of M (one step) a predetermined number of times.

At this time, most of the focus adjustment image signal generated by the pattern generator 202 is in the scanning direction.
It is desirable that the halftone output be a fine pattern in which a semiconductor laser l flickers every few pixels or in each pixel using a PWM method. As described above, an image output for focus adjustment formed by changing the imaging state in several steps is obtained, and from this it is possible to determine the position of the correction lens 3 to obtain a good imaging state.

FIG. 3 shows an example of the image output for focus adjustment output in this way, and the image formation state is changed multiple times while recording an image on one sheet of paper. In the figure, 301 is a halftone output section, and 302 is a halftone output section 30.
This is a marker that divides 1 into several stages. The marker 302 is formed by the pattern generator 202 by turning on all the lasers 1 or turning off all the lasers 1 at a predetermined timing over several scans of the image area in synchronization with the movement of the correction lens holder 207 in several steps. be done. The marker 302 may be formed by causing a pixel shift by mechanical vibration due to movement of the correction lens holder 207 or the like.

The eight-tone image 30l between each marker 302 corresponds to a predetermined position of the correction lens 3, and in FIG.
This corresponds to the position of the correction lens 3 moved by -4 steps from the standard position, the next stage is -3 steps, etc., and the final stage is the output corresponding to the position of +4 steps. Then, halftone images 301 corresponding to a total of nine positions of the correction lens 3 can be compared and observed at one time. Figures 4 and 5 show output images when the semiconductor laser 1 flickers, and Figure 4 shows the output when the spot on the photoreceptor 6 is out of focus and the imaging condition of the spot on the photoreceptor 6 deteriorates. , and FIG. 5 shows the output when the spot is in focus and the image formation state of the spot on the photoreceptor 6 is good. If the imaging condition is poor, microscopically the line L becomes thicker and the blank space S becomes smaller, resulting in a macroscopically dense halftone image. When the imaging condition is good, the gaps between the lines L are improved, resulting in a halftone image with low density.

With these things in mind, looking at the image output as shown in Figure 3, in order to obtain a good spot imaging condition with the correction lens 3 in the standard position, for example, adjust the tilt equivalent to ±1 step at the left and right edges of the image. The operator clearly determines that it is necessary to adjust the optical path length corresponding to -1 step. The inclination may be adjusted by adjusting the inclination of the photosensitive drum 6 or by integrally adjusting the rotation of the semiconductor lens 1, collimator lens system 2, correction lens 3, polygon lens 4, and f.0 lens group 5 as a whole.

The optical path length can be adjusted by moving the photosensitive drum 6 in parallel. However, when adjusting the optical path length, this is not done, but instead a function is provided in the control unit 201 to register and store the standard position of the correction lens 3. In the example shown in Fig. 3, the current +1 step position is changed to the new standard position. The correcting lens 3 may be registered as a new standard position, and in subsequent normal image output, the correction lens 3 may be moved to this new standard position to perform image formation. A normal image output operation is performed by making the semiconductor laser 1 scan the rotating photosensitive drum 6 while emitting a modulated light beam according to the image signal after the above-mentioned adjustments, and forming a latent image thereon. It will be done. In this normal operation, the AF
Adjustment operations may be performed. Next, the second embodiment will be explained with reference to FIG. The first embodiment is an example in which the present invention is applied to a laser beam printer, while the second embodiment is an example in which the present invention is applied to an LED printer.

In the figure, 21 is an LED array in which a large number of LED elements 22 are arranged in a line, and 23 is a SELFOC lens array (manufactured by Japanese glass) that forms an image of each LED element 22 on the LED array 2l on the photosensitive drum 6. , hereinafter referred to as SLA), 24 and 25 are flanges that hold the SLA 23 and move together, and 26 and 27 are arranged between the base 28 and the flanges 24 and 25, and each flange 24, 25 and the base 2
This is a Viezo piezoelectric element that adjusts the distance between the two.

The focus adjustment operation is almost the same as that in the first embodiment, and the light beam that forms the image for focus adjustment on the photosensitive drum 6 is
Viezo piezoelectric elements 26, 2 while being emitted from the D array 21
7 to move the SLA 23 by a predetermined amount in the optical axis direction by several steps to obtain an image output for focus adjustment. Since the amount of movement of the SLA 23 is determined by the voltage applied to the piezoelectric elements 26 and 27, the inclination of the SLA 23 is adjusted by applying a difference in the voltage applied to each piezoelectric element 26 and 27, and the optical path length is adjusted by applying a voltage to each piezoelectric element 26 and 27. This can be done by increasing or decreasing the applied voltage by the same amount. In the above, a uniform halftone image was used as the image output for focus adjustment, but other images or character data may be used as long as changes in the imaging state can be clearly recognized. Furthermore, in addition to the lines between the halftone images shown in FIG. 3, characters or the like may be used as markers. In this case, in order to clarify which step of the imaging state each part of the output image corresponds to, information regarding each imaging state, such as the correction lens position, adjustment amount, etc., may be output. [Effects of the Invention] As explained above, since the image forming apparatus of the present invention has the function of changing the focusing state multiple times during outputting a single focus-adjusted image, 4. It is also possible to monitor the current imaging state of the device without special measuring equipment, and based on this result, it is possible to adjust the imaging system etc. manually or automatically to adjust the imaging state. Become. Therefore, a product that can always obtain general image output with simple operations can be realized.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of the first embodiment of the present invention, Fig. 2 is a control block diagram of the first embodiment, Fig. 3 is a diagram showing an output example of an image for focus adjustment, and Fig. 4 is an image formation diagram. FIG. 5 is a diagram showing an enlarged print image when the condition is bad, FIG. 5 is a diagram showing the same when the condition is good, and FIG. 6 is an explanatory diagram of a second embodiment of the present invention. 1... Semiconductor laser, 2... Collimator lens system, 3... Correction lens, 4... Rotating polygon mirror, 5... f/θ lens group, 6...Photosensitive drum, 2l...LED array, 22...
LED element, 23... Self-cleaning lens array, 24, 25... Flange, 26, 27...
・Viezo element

Claims (1)

[Claims] 1. In an image forming apparatus that forms an image by condensing a light beam from a light source onto a photoreceptor via an imaging system, output image information is outputted onto the photoreceptor using the light beam. An image forming apparatus comprising means for changing the imaging state of the imaging system multiple times during one formation. 2. The image forming apparatus according to claim 1, wherein distinguishable markings are made at positions corresponding to different imaging states in the output image. 3. The image forming apparatus according to claim 1, wherein the means for changing the imaging state moves a correction lens of the imaging system by a plurality of steps. 4. The image forming apparatus according to claim 1, wherein the imaging system is a Selfoc lens array, and the means for changing the imaging state moves the Selfoc lens array in multiple steps.