JPH02144573A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the contamination of an image in the case of successively forming the images by gating an image signal with the aid of an image effective signal obtained by detecting the trailing edge of a transfer paper and stopping the image from being written on a drum in the trailing edge of the image. CONSTITUTION:The title device is so constituted that at least either of a 1st CPU 22 and a 2nd CPU 11 generates the image effective signal whose range is smaller than the length of the transfer paper in a drum rotating direction based on the detected results by a trailing edge sensor 9 and read or exposure is performed within the range controlled with the image effective signal. Therefore, since toner does not adhere to the part of the drum where write is not performed, the toner does not adhere to the edge part of the transfer paper and there is no trouble that the upper fixing roller of a fixation part is contaminated by the toner. Thus, the contamination of the image is prevented at the time of successively forming the images.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus such as a copying machine, and more particularly to an image forming apparatus that forms good images when continuously forming images. .

(Prior Art) For example, an electrophotographic copying machine includes an image reading means for scanning an image on a document and reading an image, a writing means for writing an image signal from the image reading means onto a photoreceptor drum, and a writing means for writing an image signal from the image reading means onto a photoreceptor drum. an image forming means for forming an image from an electrostatic latent image;
It is composed of many elements, such as a paper feeding means for supplying transfer paper, a transfer means for transferring an image onto the transfer paper, and a fixing means for fixing the transferred image with heat and pressure. Generally, each of these elements is controlled by a CPU.

(Problems to be Solved by the Invention) When performing fixing in the conventional image forming apparatus configured as described above, as shown in FIG.
14 and the upper fixing roller R1 apply heat and pressure to fix the toner T on the transfer paper.

By the way, the toner transferred to the edge of the transfer paper P is
As shown in the figure, when the transfer paper P passes, it adheres to the upper fixing roller Ru. The toner adhering to the upper fixing roller Ru in this way is removed by the cleaning roller Rc.

At this time, if the upper fixing roller Ru rotates twice and contacts the cleaning roller RC twice, the toner is almost completely removed.

However, when forming images continuously, when the upper fixing roller Ru makes one revolution (the upper fixing roller Ru and the cleaning roller Re contact each other only once), the next transfer sheet is placed on the fixing section. Sometimes they are sent. In such a case, the toner adhering to the upper fixing roller Ru will re-adhere to the next transferred transfer paper, resulting in image stains. This occurs when the transfer paper gap during continuous image formation is shorter than the outer circumference of the upper fixing rollers R, u.

The present invention was made in view of these problems, and
The purpose is to realize an image forming apparatus with a simple configuration that does not cause image staining during continuous image formation.

(Means for Solving the Problems) The present invention for solving the second problem is based on a first CPU that centrally controls the entire device and also performs process sequence control.
a second CPU coupled to the first CPU and controlling the image reading optical system; a reading/exposure means that reads the original image and exposes the photosensitive drum with laser light to form a latent image; a developing device that reversely develops the latent image formed on the photosensitive drum to form a toner image; a paper feeding device that supplies transfer paper in accordance with the rotation of the photosensitive drum; An image forming apparatus including a trailing edge sensor that detects a trailing edge of a transfer sheet, and a transfer unit that transfers a toner image on a photoreceptor drum to the transfer sheet, wherein the first CPU
Alternatively, at least one of the second CPUs generates an image valid signal in a range smaller than the transfer paper length in the drum rotation direction based on the detection result of the trailing edge sensor, and reads in the range limited by this image valid signal. Alternatively, it is characterized in that it is configured so that exposure is performed.

(Function) At least one of the first CPU and the second CPU generates an image valid signal in a range smaller than the transfer paper length in the drum rotation direction based on the detection result of the trailing edge sensor, and uses this image valid signal to Reading or exposure is performed within a limited range.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the main parts of the electrical configuration of an embodiment of the present invention. In this figure, 1 is a printer unit that forms an image on transfer paper.

2 is a first CPU that performs overall control of the entire device and also performs process sequence control; 3 is a video interface that receives image-processed image data; the output image data is sent via a second gate section 4 to a laser-driven CPU; It is output to circuit 5. Then, the laser light source 6 is driven by the output of the laser drive circuit 5, and an image is written. Note that the gate section 4 is controlled by an image valid signal V-VAL ID1 in the sub-scanning direction output from the first CPU 2. Image valid signal V-VA output from the first CPU 2
LIDI is for gating the image signal so that the area to be written on the transfer paper fits within the rough outline of the transfer paper. 7
is a motor drive circuit controlled by the first CPU 2,
A main motor 8 is driven by the motor drive circuit 7 and rotates the photosensitive drum and the like. Reference numeral 9 denotes a trailing edge sensor that detects the trailing edge of the transfer paper when the transfer paper is conveyed by the paper feeding means.

10 is a scanner unit for reading an original image. A second CPU 11 is connected to the first CPU 2 and controls an image reading optical system, and an image sensor 12 is a CCD line sensor that converts an original image into an analog image signal. Here, a case is shown in which reading is performed using two colors, red and blue.

13 is an A/D conversion circuit that converts an analog image signal into digital data. Here, a case is shown where each is converted to 6-bit data. 14 is an image processing circuit that performs color separation, scaling in the main scanning direction, and the like. Here, red data, which is image data read by the image sensor 12,
An example is shown in which blue data (6 bits each) is manually input, separated into red, blue, and black, and image data (3 bits each) of the colors specified by the second CPU 1 is output. 16 is a home position sensor that detects whether the optical system such as the image sensor 12 is at the home position; 17 is a second C
An optical system drive circuit 18 controlled by the PUII is an optical system motor driven by the optical system drive circuit 17 to move the optical system in the sub-scanning direction.

Note that the gate section 15 is controlled by an image valid signal V-VAL I D2 in the sub-scanning direction output from the second CPU 1. The image valid signal V-VALI02 output from the second CPU II is inverted when the number of drive pulses (number of steps) to the optical system motor 18 reaches a predetermined value, and only the image signal obtained by reading the document area is valid. This is for the purpose of

Figure 2 shows the first and second CPUs 2 and 11 and the image processing circuit 1.
FIG. 4 is a block diagram of a serial interface portion in the 4. Serial data sent from the other party's CPU is applied to the serial register SRI via the receiving terminal RxD and receiver RE.

The serial data stored here is converted to parallel data and sent to internal bus B via receive buffer register RxB.
Transferred to S. The data to be transferred to the other party's CPU is sent to the serial register SR via the transmission buffer register TxB.
Here, the parallel data is converted into serial data and outputted to the transmission terminal TxD by the driver DR.

RCTL is a reception control circuit, TCTL is a transmission control circuit,
In both cases, the clock is input to the serial register SR.
I and SR2 are controlled. SMR is connected to internal bus BS by a serial mode register.

Here, the data required to be transferred from the first CPU 2 to the second CPU 11, which centrally controls the entire device, is as follows.
Scan code (color code), threshold value 1 novel, scaling data in main scanning and sub-scanning directions.

There is scanning stop data, paper size data, transfer paper trailing edge detection data, etc.

These data from the first CPU2 to the second CPUII
Transfer to is performed using a serial communication method via serial communication dedicated terminals TxD and RxD. 2nd CPU II
data transfer from to the first CPU2, and the second CPU
Data transfer between the UII and the image processing circuit 14 is also performed using a similar serial communication method. Note that the second CPU 11 outputs a signal indicating that the reading section of the reading optical system is at the home position based on the output of the home position sensor 16 to the first CPU 2, and the first CPU 2 receives this signal. , transfers the data necessary for scanning to the second CPUI 1. This data transfer is performed during a period when the optical system motor 18 is stopped, when the operating rate of the second CPU II is low.

FIG. 3 is a structural sectional view showing the main parts of the mechanical structure of an embodiment of the invention, in which a color image forming apparatus is shown. Note that parts corresponding to those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted. In the figure, 10 is a scanner unit, and a movable mirror unit 22.2 moves on a slide rail 21.
3. A lens reading unit 25 that forms an optical image of the original 24 through these movable mirror units 22 and 23, and an image sensor consisting of two line sensors that read the optical image of the original 24 introduced through the lens reading unit 25. 12 and the movable mirror units 22 and 23 with the wire 2
The above-mentioned optical system motor 18 moves the optical system at a predetermined speed via the optical system 7.

In the printer unit 1, 31 is a motor, and 32 is a polygon mirror rotated by the motor 31, which rotates and scans the laser beam from the laser light source 6, and displays image data read by the image sensor 12 on the surface of the photoreceptor drum 33. Data that has been subjected to predetermined signal processing by the image processing circuit 14 described above is written. The surface of the photosensitive drum 33 is first coated with the first color (
For example, a latent image corresponding to red) is formed. In addition, here, images of parts such as characters are written with a laser beam,
Form a latent image. This latent image is developed by a first color developer 34, and a first color toner image is formed on the drum surface. Therefore, the toner adheres to the area written by the laser. While holding the toner image thus obtained on the drum surface, the photosensitive drum 33 passes under the cleaning section 37 that has been separated from the surface thereof, and enters the next copy cycle. That is, the photoreceptor drum 33 is charged again by the charging electrode 38, and a latent image corresponding to the second color (for example, blue) is formed in the same way, and is developed by the second color developer 35, and a latent image is formed on the drum surface. A second color toner image is formed. Similarly, a toner image corresponding to a third color (for example, black) is formed by the third color developer 36.

The superimposed image of the three-color toner images thus formed is transferred by the transfer pole 29a onto the transfer paper P sent from the paper feed section 40, and is conveyed to the determining section 41. Here, it is fixed and a color hard copy is obtained. A cleaning section 3 is installed on the photosensitive drum 33 after the transfer.
7 comes into contact and cleaning is performed.

Next, the overall operation will be explained.

After the first CPU 2 is powered on, it performs initialization processing and warm-up processing.

Thereafter, when the copy switch is turned on, the scanned data is transferred to the second CPU II. In the case of three-color copying, the color image forming apparatus shown in FIG. 3 performs three optical scans to overlap images of each color.
The changed scan data is sent to the first CPU 2 before starting optical scanning.
It is necessary to transfer it from there to the second CPU 11. Also, in the case of continuous monochrome copying, since the threshold level etc. may change, it is necessary to transfer data from the first CPU 2 to the second CPU 11 before starting optical scanning.

For example, in the case of three-color copying, this data transfer is performed at the following timing. That is, the first CPU 2 reads the scan data from the memory and transfers the data of the first optical scan to the second CPU II (serial communication 1
). Then, when it comes time to start optical scanning, the first
The CPU 2 receives a signal (READYR) from the second CPU 1.1 indicating that the exposure, light amount monitor, etc. are normal.
) and serial communication 2), send the optical scanning start (scan start) signal (S-START) to the second CP.
An input is made to U i 1 by interrupt. Second C
The PU 11 receives this interruption and starts optical scanning. When the first optical scan is completed and the scanner unit 10 returns to the home position and the optical system motor 18 stops, the second
The CPU 11 outputs a signal (
HOMER) is output to the first CPU 2. 1st CP
When U receives this home position signal, it reads the data of the next optical scan from the memory and sends it to the second CPU 1l.
Perform the next data transfer. Then, at the timing to start optical scanning, the first CPU 2
Check the signal indicating that the exposure, light amount monitor, etc. from 1 are normal, and send the optical scanning start signal to the 2nd CPU
For 1, manual intervention is performed. The second CPU II receives this interruption and starts optical scanning again. Thereafter, a third optical scan is also performed in the same manner.

The scanner unit 10 is driven in each optical scan by the second CPU II by driving the optical system motor 18 after lighting the halogen lamp 22a in the movable mirror unit 22. The image valid signal V-VALID2.2 in the sub-scanning direction is output from cputi-2. The image valid signal V-VAL IDI in the sub-scanning direction output from the first CPU 2 is, for example, as shown in FIG.

The number of driving pulses sent to the optical system motor 18 until the reading section (movable mirror unit 22) of the reading optical system reaches the leading edge of the document from the home position is S1, and the number of driving pulses corresponding to the blank space at the leading edge of the image is ΔSt. The number of drive pulses sent to the optical system motor 18 until the reading section of the reading optical system reaches the rear end from the home position is 82, and the number of drive pulses corresponding to the blank space at the rear end of the image is ΔS2.

The trailing edge sensor 9 outputs a high-level signal while the transfer paper fed by the paper feed section 40 passes.

Here, the image valid signal V-VALID2 in the sub-scanning direction output from the second CPU II (read V-VAL
ID) turns on when the number of drive pulses exceeds 81 and turns off just before the number of drive pulses reaches 52, as shown in FIG.

Also, the sub-scanning direction (f)' output from the first CPU 2
As shown in Figure 4, the MIF image valid (M number V-VALID 1 (write V-VALID) is turned on when the number of drive pulses reaches 81+ΔS1, and the number of drive pulses reaches 82-ΔS2. V-VALIDI turns off when the trailing edge sensor 9 detects the trailing edge of the transfer paper. This t can be expressed as follows. Can be done.

t-(L2-Ll-L3)/υ Ll; Distance L2 from writing position to transfer position; Distance L3 from trailing edge sensor to transfer position; Trailing edge erase amount υ ; Drum circumferential speed Therefore, t≧0 It is necessary to select the position of the rear end sensor 9 so that

Therefore, the laser drive signal is applied to the gate section 15 only during the high level period shown in FIG. It will finally pass through the gate section 4.

As an example, if the writing speed in the sub-scanning direction (scanning speed of the reading optical system) is 70 mm/s, ΔS1 is 3.0 m.
m (43a+s), ΔS2 is 2.5mm (36ss
), 2. from the leading edge of the transfer paper to the rise of V-VAL ID2 (7). 0+u (29ss), V-VAL
2.0mm from the trailing edge of ID2 to the rear edge of the transfer paper
(29ss), good results were obtained.

The size of this margin can be adjusted as necessary. Note that the margin at the leading edge is for improving the separation performance of the transfer paper.

Since the optical system motor 18 has a fixed rotation angle per pulse, the amount of movement of the reading section of the reading optical system can be determined from the number of drive pulses regardless of the scanning speed. In the above configuration, this fact is utilized to cause the CPU to generate an accurate image valid signal v-VALID in the sub-scanning direction.

By the way, here is V-VAL ID 17! l'V-VA
Since it is smaller than L ID2, the final result is V-
Although gated by VALIDI, it is not limited to this. For example, change V-VALID2 to V-
A similar effect can be obtained by performing gating with the value smaller than VALIDI. Furthermore, the same effect can be obtained by outputting only one V-VALID from either CPU and performing gating.

As described above, since the image signal is gated using the image valid signal V-VAL ID obtained by detecting the trailing edge of the transfer paper, writing on the drum is not performed at the trailing edge of the image. In the case of a copying machine that performs reversal development, toner does not adhere to the parts of the drum where writing is not performed, so toner does not adhere to the edges of the transfer paper. Therefore, there is no need to worry about staining the upper fixing roller Ru of the fixing section with toner. As a result, even when images are formed continuously, no image stains occur.

(Effects of the Invention) As described in detail above, in the present invention, the image signal is gated using the image valid signal obtained by detecting the trailing edge of the transfer paper, and the image is written on the drum at the trailing edge of the image. I decided not to do this. Therefore, since toner does not adhere to the portion corresponding to the edge of the image on the drum, toner does not adhere to the trailing edge of the transfer paper, and toner does not adhere to the fixing roller of the fixing section. Therefore, an image forming apparatus that does not cause image staining during continuous image formation can be realized with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of the electrical configuration of an embodiment of the present invention, and FIG.
and a block diagram of the serial interface part in the image processing circuit, FIG. 3 is a configuration sectional view showing the main parts of the mechanical configuration of the embodiment of the invention, and FIG. A time chart showing an example of an image valid signal in the scanning direction, and FIGS. 5 and 6 are explanatory diagrams showing how toner adheres to the fixing section. 1... Printer unit 2... First CPU3
...Video interface 4...Gate part 5...Laser drive circuit 6...Laser light source 7...Motor drive circuit 8...Main motor 9...Rear end sensor 10
... Scanner unit 11 ... Second CPU 12
...Image sensor 13...A/D conversion circuit 1
4... Image processing circuit 15... Gate section 16.
...Home position sensor 17...Optical system drive circuit 18...Optical system motor Fig. 2

Claims (1)

[Scope of Claims] A first CPU that performs overall control of the entire apparatus and process sequence control; A second CPU that is coupled to the first CPU and controls an image reading optical system; A document image. a reading/exposure means that reads and exposes the photoreceptor drum with laser light to form a latent image; a developing means that reversely develops the latent image formed by exposure on the photoreceptor drum to form a toner image; and a photoreceptor drum. a paper feeding device that feeds the transfer paper according to the rotation of the paper, a trailing edge sensor that detects the trailing edge of the transfer paper fed by the paper feeding device, and a transfer device that transfers the toner image on the photoreceptor drum to the transfer paper. an image forming apparatus having means, wherein at least one of the first CPU and the second CPU determines that an image is valid in a range smaller than the transfer paper length in the drum rotation direction based on the detection result of the trailing edge sensor. An image forming apparatus characterized in that it is configured to generate a signal and perform reading or exposure within a range limited by the image valid signal.