JPH02245347A - Electrophotographic printer - Google Patents

Abstract

PURPOSE:To maintain the constant recording density of a recorded picture even if a recording sheet feeding speed exceeds a required speed by constituting such that the top edge of a recording sheet reaches a fixing device to speed up the conveyance of the recording sheet when a first image forming density is switched to a second one to lead an image forming position to a transfer position. CONSTITUTION:A horizontal synchronizing signal generating circuit 20 is a means to switch an image forming density in a sub-scan direction, and is composed of set switches 22 and 23, a data selector 24, and a down counter 25. When the recording sheet conveying speed of a fixing device is one-percent higher, for instance, the set switches 22 and 23 are set at 100 and 99, respectively. If image formation starts, the cycle of the set switch 22 is selected, whereas if the top edge of the recording sheet reaches the fixing device, the cycle of the set switch 23 is selected. The data selector 24 switches data transmitted to the down counter 25 according to a timing changeover signal (b). If the timing changeover signal (b) is off, the set switch 22 is selected, whereas if the signal (b) is on, the set switch 23 is selected.

Description

[Detailed Description of the Invention] [Summary] This invention relates to electrophotographic printer devices, particularly printers in which the recording paper conveyance speed of the fixing device is set slightly faster than the specified conveyance speed, when the leading edge of the recording paper reaches the fixing device. The purpose of this printer is to provide a printer in which the recording density of the recorded image transferred to the recording paper does not change even if the recording paper transport speed becomes faster than the specified speed. A detection means predicts the image forming density of the photoreceptor in the sub-scanning direction, a first density corresponding to a prescribed recording paper conveyance speed of the image forming means;
or a switching means for switching to a second density corresponding to the recording paper conveyance speed of the fixing means, and the image forming position when switching the image forming density from the first density to the second density reaches the transfer position. The configuration is such that when the leading edge of the recording paper reaches the fixing device, the conveyance speed of the recording paper becomes faster.

[Industrial application field]

The present invention relates to an electrophotographic printer, and particularly to a printer in which the recording paper conveyance speed of a fixing device is set slightly faster than a specified conveyance speed.

Printers are used as output devices for electronic computers and the like, and in recent years, electrophotographic printers that are capable of high-speed, high-resolution recording have been widely used. Electrophotographic printers are becoming faster, smaller, and less expensive, and are now being used as output devices for word processors. In order for electrophotographic printers to become widely used as output devices for word processors in the future, it is desired to achieve lower prices without lowering recording quality.

[Conventional technology] FIG. 5 shows a configuration diagram of an electrophotographic LED printer.

The image forming means 60 includes a cleaning device 61 and a static eliminating device 62.
, a charging device 63, an exposure device 64, a developing device 65, a transfer device 66, a photoreceptor 67, and the like.

The charging device 63 is a device that uniformly charges the surface of the photoreceptor 67. The exposure device 64 includes an LED array head, and selectively causes each LED array to emit light to expose the photoconductor 6.
This device forms a latent image at a desired position of 7. The developing device 65 is a device that applies a developer to the latent image to form a visible image. The transfer device 66 is a device that transfers the developer on the photoreceptor 67 onto recording paper. The cleaning device 61 is a device that removes developer that has not been transferred to the recording paper.

The charge eliminator 62 removes the charge remaining on the photoreceptor 67.

The fixing bag f70 includes a fixing roller 71 having a heat source and a pressure roller 72. The mainstream of popular laser printers and LED printers is a thermal fixing method, in which the developer is fixed to the recording paper using heat and pressure.

The recording paper transport mechanism 40 includes a recording paper transport belt 41, a recording paper pickup roller (not shown), and the like, and transports the recording paper 90 by rotation of the recording paper transport belt 41 and the photoreceptor 67. Further, the paper human force sensor 11 detects that the recording paper 90 has reached a predetermined position and detects the timing of starting image formation.

The paper output sensor 12 detects when the recording paper 90 is ejected from the fixing device 90 and detects the occurrence of a trouble such as a paper jam.

Conventionally, in some electrophotographic printers, in order to prevent the recording paper 90 from being bent in the recording paper conveyance path 91 between the transfer device 66 and the fixing roller 71, the recording paper conveyance speed of the fixing roller 71 is controlled by the recording paper conveyance belt. The speed is set to be slightly faster than the conveyance speed, for example, about 1% faster. Ideally, the recording paper conveyance speeds of the recording conveyance belt 66 and the fixing roller 71 should be the same, but in reality they vary somewhat depending on mechanical precision. If the conveyance speed of the fixing roller 71 is even slightly slower than the conveyance speed of the recording paper conveyance belt 41, the recording paper may be bent between the transfer device 66 and the fixing roller 71, causing problems such as jams.

In order to solve this problem, a method has been adopted in which the recording paper conveyance speed of the fixing device is set slightly faster than the prescribed conveyance speed of the recording conveyance mechanism.

[Problem to be solved by the invention]

However, the recording paper transport speed of the fixing device is faster than the specified speed (
If this is set, when the leading edge of the recording paper reaches the fixing roller of the fixing device, the recording paper conveyance force of the fixing roller will cause the recording paper conveyance speed to become faster than the specified speed. For example, assume that the recording paper conveyance speed of the fixing device is set 1% faster than the specified speed. When the leading edge of the recording paper reaches the fixing device, the conveyance speed of the recording paper becomes 1% faster (this is 1% faster than the recorded image transferred when it is conveyed at the specified speed).
The image becomes elongated. A delay of about 1% is hardly a problem during normal printing, but it becomes a problem if higher quality recorded images are desired in the future. Furthermore, in a color printer that has image forming means for a plurality of colors and obtains a color image by superimposing images of each color, if the conveyance speed of the recording paper changes, the images of each color do not overlap accurately and the image quality deteriorates.

Therefore, an object of the present invention is to provide a printer in which the recording density of the recorded image transferred to the recording paper does not change even if the leading edge of the recording paper reaches the fixing device and the recording paper conveyance speed becomes faster than the specified speed. do.

[Means to solve the problem]

In order to achieve the above object, in a printer in which the recording paper conveyance speed of the fixing device is set slightly faster than the specified speed, a detection means for predicting the timing when the leading edge of the recording paper reaches the fixing device, and a detection means for predicting the timing when the leading edge of the recording paper reaches the fixing device, and The image forming density in the sub-scanning direction is set to a first density corresponding to a specified recording paper conveyance speed of the image forming means, or a second density corresponding to the recording paper conveyance speed of the fixing means.
1. a switching means for switching to a density of 1. When the image forming position reaches the transfer position when the image forming density is switched from the first density to the second density, the leading edge of the recording paper reaches the fixing device so that the conveyance speed of the recording paper becomes faster. Configure.

[Effect]

The detection means predicts the timing at which the conveyance speed of the recording paper increases, and the switching means switches the image forming density from the first density to the second density in accordance with the predicted timing. The second image forming density is set higher than the first density according to the increment of the recording paper conveyance speed. When the image forming density switching position reaches the transfer position, the leading edge of the recording paper reaches the fixing device and the conveyance speed becomes faster than the specified speed, and when the recording paper conveyance speed becomes faster, the second image forming density is reached. Since the image is transferred, the recording density of the recorded image does not change.

〔Example〕

FIG. 1 shows a block diagram of the configuration of an embodiment of the present invention. In the figure, 11 is a paper human force sensor, 80 is a switching timing generation circuit, 20 is a horizontal synchronization signal generation circuit, 50 is a bitmap memory, and 30 is an LED array.

The paper manpower sensor 11 detects the presence or absence of recording paper, and the output a of the paper manpower sensor turns on when the leading edge of the recording paper passes the sensor position, as shown in FIG. It turns off when it passes the sensor position. The sensor 11 is installed so that the distance between the sensor 11 and the transfer position corresponds to the distance between the exposure position and the transfer position, and the output a of the paper human force sensor is used as a timing signal for starting image formation. When the image that is formed at the same time as the sensor output a is turned on reaches the transfer position, the leading edge of the recording paper also reaches the transfer position and is transferred to the leading edge of the recording paper.

Similarly, the image formed immediately before the sensor output a is turned off is transferred to the rear of the recording paper when the transfer position reaches the edge position, the rear end of the recording paper reaches the transfer position.

The switching timing generation circuit 80 is a detection means that predicts the timing when the leading edge of the recording paper reaches the fixing device. The output a of the paper manual force sensor is input to the switching timing generating circuit 80, and as shown in FIG. 2, a certain period of time T has elapsed since the sensor output a was turned on.

Turn on the rear switching timing signal and also turn on the sensor output a.
is turned off, and the switching timing signal is also turned off. T+ is the time required for the recording paper to reach the fixing device from the transfer position. The switching timing generation circuit 80 includes an internal timer, and the timer is set to a time Tt and is operated by the clock C sent from the clock generation circuit 70.

The horizontal synchronizing signal generation circuit 20 is means for switching the image forming density in the sub-scanning direction. The horizontal synchronization signal is synchronized with image formation of one line, and by changing the period of the horizontal synchronization signal, the image formation density in the sub-scanning direction can be changed. The horizontal synchronization signal generation circuit 20 is composed of setting switches 22 and 23, a data selector 24, and a down counter 25.

The setting switches 22 and 22 are used to set the period of the horizontal synchronization signal. For example, if the recording paper transport speed of the fixing device is 1% faster, set the setting switch 22 to 100, and set the setting switch 23 to 100.
is set to 99, and the period is selected in the setting switch 22 when starting image formation, and the period is selected in the setting switch 23 when the leading edge of the recording paper reaches the fixing device. Data selector 24
switches the data sent to the down counter 25 in response to the switching timing signal. When the switching timing signal is off, the setting switch 22 is selected, and when it is on, the setting switch 23 is selected.

The down counter 25 is a down counter that loads the data sent from the data selector 24 when the load signal (horizontal synchronization signal d) is input, and performs down counting according to the clock C sent from the clock generation circuit 70. 25 outputs a carry when the count value becomes zero. The carry is used as a horizontal synchronization signal and is also input as a load signal to the load terminal. As shown in Fig. 3, the horizontal signal d has a cycle of 1 when the switching timing signal is off.
00, and the cycle is 99 when it is on.

The horizontal synchronization signal d is sent to the focus map memory 50 and the LED array 30. The bitmap memory 50 is located in the printer device or host device and stores image data, that is, the lighting pattern of each LED. Image data stored in bitmap memory 50 is sent to LED array 30 in response to data transfer lock f. As shown in FIG. 4, the data transfer lock r occurs for the number of dots in one line after a time T2 from the timing of the horizontal synchronization signal d, and stops occurring after a time T3 from the timing of the horizontal synchronization signal d. The time T3 is set taking into account that the period of the horizontal synchronization signal d changes.

Image data sent from the bitmap memory 50 to the LED array 30 is input to the shift register 33 and sequentially shifted in accordance with the data transfer lock f. When one line of image data, that is, the LED lighting pattern is stored in the shift register 33, the latch circuit and driver circuit 3
2 latches the LED lighting pattern stored in the shift register 33, and causes each LED element to emit light according to the lighting pattern.

Although the above embodiments are for LED printers, the invention can be implemented in other electrophotographic printers such as laser printers. In a laser printer, the image forming density in the sub-scanning direction can be changed by increasing the rotation speed of the polygon mirror and the transfer time of image data. Further, in a liquid crystal printer, the image forming density can be changed as in this embodiment.

Furthermore, even in a multi-photoconductor type color printer having a plurality of photoconductors, each photoconductor is equipped with an image forming density switching means and a switching timing generation means, so that it is possible to prevent the recording density of each color image from changing. be.

(Effects of the Invention) According to the present invention, a high-quality recorded image with no change in recording density can be provided in a printer in which the recording paper conveyance speed of the fixing device is set faster than a specified speed. Further, by setting the recording paper conveyance speed of the fixing device faster than the specified speed, a highly accurate and complicated recording paper conveyance mechanism is not required, and the printer can be made smaller and lower in price.

50・・・Bitmap memory 80...Switching timing generation circuit

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is a diagram showing a switching timing signal, Fig. 3 is a diagram showing a horizontal synchronization signal, Fig. 4 is an explanatory diagram of the operation of an LED array, and Fig. 5 is a diagram showing a switching timing signal. FIG. 1 is a configuration diagram of an electrophotographic printer. In the figure, 20...Horizontal synchronization signal generation circuit 30...LE
D array invention. -A 1.7 Punishing Enemy Timing A1-TE Chapter 27 3F IED Array 4 O 4 Lower Diaphragm H8 Empress A''vI

Claims (1)

[Scope of Claims] Includes means (64) for forming a latent image on a photoreceptor, means (65) for developing the latent image into a visible image, and means (66) for transferring the visible image onto recording paper. It includes an image forming means (60) and a fixing means (70) for fixing the transferred image on a recording paper, and the recording paper conveyance speed of the fixing means (70) is set according to the regulation of the image forming means (60). In an electrophotographic printer whose speed is set faster than the recording paper conveyance speed, there is provided a detection means (11, 80) for predicting the timing at which the leading edge of the recording paper reaches the fixing means, and a detection means (11, 80) for predicting the timing at which the leading edge of the recording paper reaches the fixing means, and a detection means (11, 80) for predicting the image forming density in the sub-scanning direction. Depending on the prediction of the detection means (11, 80),
a switching means (2) for switching between a first density corresponding to a prescribed recording paper conveyance speed of the image forming means (60) or a second density corresponding to a recording paper conveyance speed of the fixing means (70);
0), such that when the image forming position reaches the transfer position when the image forming density is switched from the first density to the second density, the leading edge of the recording paper reaches the fixing means (70). An electrophotographic printer consisting of