JPS61272166A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image with uniform quality by controlling recording behavior to be able to obtain dots of a fixed density on an image supporting drum, regardless of differences in distances between the line of respective dot recording elements and the drum surface of the recording head of the image supporting drum. CONSTITUTION:Due to the fact the the recording head 12 is flat, but the drum 11 has a cylindrical shape, an image build-up actions are differentiated correspondingly to the positions of dot recording element line. The recording head 12 is provided with line electrodes 31-1, 31-2...31-20 in the axial direction; and finger electrodes 32-1, 32-2...32-124 that cross obliquely and have small holes facing the above electrodes; and screen electrodes 33 that have small holes 33a provided in the positions facing the above small holes. For instance, if a voltage is applied between the line electrode 31-1 and the finger electrode 32-1, an ion current is created at the small hole 32a at the crossing, and the ion current is discharged through the small hole 32 and the small hole 33a of the screen electrode 33. By selectively energizing a line electrode and a finger electrode, a static electricity charged image consisting of many dot lines are formed on a static electricity body drum 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus used in printing machines, copying machines, facsimile machines, and the like.

[Conventional technology]

Conventionally, various types of image forming apparatuses have been proposed. For example, an electrostatic latent image consisting of a large number of dots is formed on an image bearing drum having a dielectric surface using an ion flow electrode. This was developed with toner to create a toner image, which was then transferred and fixed onto recording paper.
It is disclosed in Japanese Patent No. 7-501348. In such a conventional image forming apparatus, in order to obtain high resolution, the ion flow electrode has a plurality of dot recording element rows 2-1°2- spaced apart in the rotational direction of the drum 1, as shown in FIG. A recording head 3 having 2...-2-n is used.

That is, it has a considerably large effective recording width W when viewed in the rotational direction of the drum T. Therefore, each dot recording element row 2
-1, 2-2-2-n and the distance to the surface of the drum 1 are different. As shown in FIG. 11, a toner developing device 4, a transfer/fixing roller 5, a static eliminating/cleaning device 6 are arranged around the drum 1, and a recording paper 7
The toner image is transferred and fixed onto the recording paper when the toner image is conveyed between the drum 1 and the roller 5.

[Problem that the invention seeks to solve]

In the conventional image forming apparatus described above, since the distances between the plurality of dot recording element arrays 2 to 1, 2-2-, 2-n and the image carrier drum l are different, these dot recording If the recording operation is the same for each dot recording element array, the amount of electrostatic charge of the dots formed on the drum 1 will differ depending on the dot recording element array.

In other words, in the central dot recording element array where the distance to the image bearing drum 1 is short, the amount of ions reaching the drum increases, the amount of electrostatic charge charged on the drum increases, and a large amount of toner adheres to the drum. However, in the peripheral dot recording element rows where the distance to the drum 1 is long, the amount of ions reaching the drum is small, and the amount of electrostatic charge charged on the drum is small, and the toner is Since the amount of adhesion is reduced, the concentration is low. As described above, conventional image forming apparatuses have the disadvantage that the image density is not uniform and the image quality is deteriorated. In order to eliminate these defects, the surface of the recording head is curved along and parallel to the drum surface, so that the distance between each dot recording element row and the drum surface is the same. However, it is extremely difficult to manufacture such a curved recording head. Furthermore, the above-mentioned problem is not limited to recording heads having ion flow electrodes, but also occurs in other types of recording heads having a plurality of dot recording element rows.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide an image with uniform image quality on the image carrier drum even if the distances between the plurality of dot recording element arrays and the surface of the image carrier drum are different. An object of the present invention is to provide an image forming apparatus capable of forming images.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention includes a rotating image bearing drum, a recording head disposed opposite to the drum and having a plurality of dot recording element arrays distributed in the rotational direction of the drum, and and means for controlling the recording operation in each dot recording element array so that dots of a constant density can be formed on the drum regardless of the difference in distance between the dot recording element array and the drum surface. This is a characteristic feature.

[Effect]

In the image forming apparatus of the present invention described above, for example, when using an ion flow electrode, the ion flow time is adjusted or the density of the ion flow is adjusted in proportion to the distance from each dot recording element row to the surface of the image bearing drum. By adjusting this, the amount of charge of the electrostatic charge dots formed on the surface of the image bearing drum can be made uniform, and the image quality can therefore be improved.

〔Example〕

FIG. 1 shows the overall configuration of an embodiment of an image forming apparatus according to the present invention. This example is configured as a printer using an ion flow type recording head. An electrostatic charge image is formed by projecting an ion flow modulated in accordance with an image signal to be recorded in a dot shape by a recording head 12 equipped with an ion flow generation device onto a dielectric drum 11 rotating in the direction of the arrow. , this is developed with toner in the developing device 13 to form a toner image, and this toner image is placed under the conveying path of the recording paper and is rotated by a pressure that follows the rotation of the dielectric drum 11. The image is transferred and fixed onto the recording paper by the pressure of the transfer roller 14. Further, toner remaining on the dielectric drum 11 without being transferred to the recording paper in the transfer section is removed by a toner removing device 15 including a cleaning blade, and furthermore, the static charge on the dielectric drum 11 is removed by a static eliminator 16. It is removed and prepared for the formation of a new electrostatic charge image.

On the other hand, the recording papers 17 are stacked and stored in a paper feed tray 18, separated one by one by a separation roller 19, and transferred to a paper feed roller 18.
0, the toner image is transferred and fixed. The recording sheets to which this toner image has been transferred and fixed are sequentially stacked on a paper ejection tray 22 by a paper ejection roller 21. The pressure transfer roller 14 is driven by a spring and a cam, e.g.
It is pressed against the dielectric drum 11 with a large pressure of tons.

FIG. 2 is a diagrammatic plan view showing the configuration of the recording head 12 of the ion flow type. The recording heads are separated from each other by three
Equipped with different types of electrodes. That is, 20 line electrodes 3'l-1, 3 extending in the axial direction of the recording head 12
1-2-31-20, and 124 finger electrodes 32-1, 3 arranged diagonally across these line electrodes and having small holes in the portions facing the line electrodes.
2-2-32-124, and a screen electrode 33 which is arranged above these finger electrodes and has a small hole 33a at a position facing the small hole formed in the finger electrode. For example, when a voltage is applied between the first line electrode 31-1 and the leftmost finger electrode 32-1, an ion flow is generated at the small hole 32a where these intersect,
This small hole 32a and the screen electrode 3 facing it
An ion current is emitted through the small hole 33a formed in the dielectric drum 11, and a dot-shaped electrostatic charge is formed on the dielectric drum 11. Therefore, by selectively energizing the line electrodes 31-1 to 31-20 and the finger electrodes 32-1 to 32-124 as explained below, an electrostatic charge image consisting of a large number of dot lines can be formed. .

FIG. 3 shows the relationship between the ion current emission position formed on the recording head 12 and the dot pattern formed on the recording paper 17. One dot line is composed of 2480 dots, and one screen line is made up of 2480 dots. Although the number depends on the length of the recording paper 17, the configuration is such that ten or more Tonto lines are formed per IH. The interval between the small holes formed in each finger electrode 32, that is, the interval between the line electrodes 31, is equal to a four-dot line. FIG. 4 shows signals applied to the line electrode 31 and finger electrode 32. As will be described later, in one example of the present invention, the voltage applied to the line electrode 31 is changed depending on the position of the line electrode, and this voltage has a peak-to-peak value of, for example, 2.
The voltage applied to the finger electrode 32 is an AC voltage of 600 to 2800V and a frequency of IMHz, and the voltage applied to the finger electrode 32 is a DC voltage of 200V. Also, the application time of these voltages is approximately 6μ
Seconds.

First, a voltage is applied to the first line electrode 31-1, and a voltage corresponding to the image data on the first dot line is applied to the first to 124th line electrodes.
It is simultaneously applied to finger electrodes 32-1 to 32-124. Since each finger electrode is responsible for recording 20 dots when viewed in the line direction, the first . 21st. Image information of the 41st to 2461st dots are recorded simultaneously. That is, in the case of a black dot, a DC voltage of 200 V is applied to the corresponding finger electrode, and in the case of a white dot, no voltage is applied. Next 6.8
An alternating current voltage is applied to the second line electrode 31-2 after a period of μ seconds, and the finger electrodes 32-1 to 32-1
24, the second dot on the fifth dot line. 22nd--A DC voltage is applied corresponding to the image information of the 2462nd dot. The first dot on this fifth dot line. 21st-2nd
The image of the 461st dot is 4 where the line corresponding to the tontoline on the recording paper faces the first line electrode 31-1.
Already recorded before the cycle. Below, the same operation is performed in the second
The process is performed up to the 0 line electrode 31-20. When applying an AC voltage to the 20th line electrode 31-20, the 20th line electrode 31-20 is applied on the 77th dot line. Finger electrodes 32-1 to 32-3 correspond to the image information of the 40th to 2480th dots.
A DC voltage is applied to 2-124, and all the dots in the line on the recording paper corresponding to this dot line are formed.

The time required to scan from the first line electrode 31-1 to the twentieth line electrode 31-20 in this way is (6+6.
8) X 20 = 256 μsec. Next, the above-described operation is repeated again after a period of 254 μsec. Therefore, one cycle T is 256+254·510 μsec, and during this period the recording paper 17 travels downward by one ton trine as shown by the arrow in FIG. Therefore 1
The time it takes for the Tontline to be completely formed is 510'
X77=39, 270 μsec. In the next period T, an AC voltage is applied to the first line electrode 31-1, and the first, 21st and 21st dots on the newly recorded dot line are
- 1st to 12th dots according to the image information of the 2461st dot.
A DC voltage is selectively applied to the four finger electrodes 32-1 to 32-124. Next, an AC voltage is applied to the second line electrode 31-2, and the finger electrodes 32-1 to 32-124 are applied to the second line electrode 31-2 on the fourth dot line. A DC voltage is applied according to the image data of the 22nd to 2462nd dots.

Thereafter, similar recording is performed, and when applying a DC voltage to the 20th line electrode 31-20, the 20th, 41st, and 41st line electrodes on the 76th don't line. -., applying a DC voltage to the finger electrodes 32-1 to 32-124 according to the image information of the 2480th dot. In this way, an image consisting of a large number of dot lines can be formed by repeating the sequential operations.

In such an image forming apparatus, the recording head 12 has 20 dot recording element arrays (as shown in FIG. 2, line electrodes 31-1 to 31).
-20), but since the recording head 12 is flat while the drum 11 is cylindrical, the distance between the dot recording element array at the center and the drum surface is The distance between the dot recording element array and the drum surface at the periphery is longer. Because of this difference in distance, the amount of electrostatic charge on the dots recorded by the central recording element is greater than the amount of electrostatic charge on the dots recorded by the peripheral elements, and as a result, the toner The density of the developed dot image recorded by the central element is also higher than that recorded by the peripheral element. Therefore, the density of the recorded image is not uniform (and the image quality deteriorates).Therefore, in the present invention, the image forming operation in the dot recording element array is controlled depending on the position of the dot recording element array. To do this, the amplitude of the high frequency voltage applied to the line electrodes 31-1 to 31-20 can be made different for each line electrode, or The duration of the applied high frequency voltage can be varied.

FIG. 5 shows an embodiment of the means for adjusting the recording operation of the dot recording element in the image forming apparatus of the present invention as described above, and in this example, the amplitude of the high frequency voltage applied to the line electrode is changed. This is how it was done. The line electrodes 31-1 to 31-20 are each connected to a high frequency power source 51-1.
~51-20 to connect to line 52. Further, each of the finger electrodes 32-1 to 32-124 has a resistor 53-1.
53-124 and 54-1 to 54-124. The connection points of these resistors are connected to finger electrode drive FETs 55-1 to 55-124, respectively.
is connected to line 56 through line 56, and line 56 and line 5
A 240v fixed DC power supply 57 is connected between the two. Further, a variable DC power supply 58 is connected between the line 52 and the ground. The voltage of this variable DC power supply 58 is, for example, 500v.
By adjusting this, the concentration can be changed. When a high frequency voltage is now applied to the line electrode 31-1, the FETs 55-1 to 55-12
4 is in the off state, finger electrodes 32-1 to 32-3
For example, -500 is supplied to 2-124 by the variable DC power supply 58.
A voltage of V is applied. In this state no ion flow is generated. On the other hand, for example, when the FET 55-1 is driven and turned on, a voltage of 240V is applied from the fixed DC power supply 57, and a voltage of -740V is applied to the finger electrode 32-1. An ion current is generated at the intersection with the finger electrode 32-1, making it possible to record dots. However, since the voltages of the other finger electrodes 32-2 to 32-124 remain at -500 ν, no dots are recorded. In this way, depending on the image information to be recorded, the FETs 55-1 to 55-
By selectively driving 124, dots can be selectively formed. In this case, line electrode 31-1
The high frequency voltages to 31-20 are generated sequentially at a period of 12.8 μs as described above in FIG.

In this embodiment, the peak value of the high frequency voltage generated by the high frequency power supplies 51-1 to 51-20 is set to 26 as shown in FIG.
Change it between 20V and 2800V.

In this case, since the amount of charge on the drum is approximately proportional to the above-mentioned distance, the peak value of the high frequency voltage may be continuously changed by 20V. That is, the line electrode 31-1 has 2
A voltage of 800V is applied, and a voltage of 27V is applied to the line electrode 31-2.
A voltage of 80V is applied, and the voltage is gradually lowered by 20V.
A voltage of 20V is applied, and a voltage of 26V is applied to the line electrode 31-12.
A voltage of 40 V is applied, and the voltage is increased sequentially by 2 OV, so that a voltage of 2800 V is applied to the line electrodes 31-20. In this way, line electrode 31-1
By changing the voltage applied to the dots 31-20 according to the distance between the dot recording element array and the drum surface, the amount of charge on each dot becomes uniform, and nine high-quality images can be recorded.

In the embodiment described above, the peak value of the high frequency voltage applied to the line electrodes 31-1 to 31-20 was changed, but for this purpose, the peak value of the voltage generated by each high frequency power source 51-1 to 51-20 was adjusted. It is necessary to do this, and it can be troublesome.

Furthermore, since the peak value of the high frequency voltage applied to the line electrodes in the peripheral area is increased, there is a problem in that undesirable discharge occurs in the recording head. In another embodiment of the present invention that can solve this problem, as described below, the peak value of the high-frequency voltage applied to the line electrodes is constant, and its duration is varied for each line electrode. .

FIG. 7 is a circuit diagram showing the overall configuration of a line driver in such an embodiment. The line driver is composed of an enable signal generating section 61 that generates an enable signal ENA of variable duration, and a voltage generating section 62 that generates a high frequency voltage in response to this enable signal. The input terminal 63 is supplied with 5-bit line selection code signals LSEL0 to LSEL4 from the controller. This code signal is an input terminal of the ROM 64 of the enable signal generating section 61. ~A4 is supplied with binary data as shown in Table 1.
The code is read out to its output terminals 0°-04. This binary code is placed in counter 65 in response to the activation signal. The counter 65 receives 3 clocks from the clock generator 66.
MHz clock pulses are applied through an AND gate 67 and counted. AND gate 67 has counter 6
5 is supplied via an OR gate 68. Therefore, after placing the binary code in the counter 65, the clock is subtracted and counted, and when the counted value becomes zero, the ND gate 6
7 does not pass the clock pulse. In this way O
The output of the R gate 68 is the lO base number of the binary code placed in the counter 65, which is approximately 0.3 which is the clock period.
An H level output is generated for a time equal to the value multiplied by μs. By applying this output to NOTOR gate 68, enable signal ENA is obtained.

Table 1 In this way, an enable signal (2) whose duration changes gradually over a range of 4.8 to 7.5 μs is obtained. This enable signal ■ is used as the line selection code signal LSEL O-L
It is supplied to the voltage generator 62 along with SEL 4. In the voltage generator 62, the line selection code SEL O-
LSEL 4 is applied to a decoder 70, one of the 20 outputs is selected, and a line drive pulse equal to the duration of the enable signal ■ is generated at the selected output as shown in FIG. Ru.

This line drive pulse is supplied to 20 oscillators 71, and from each oscillator, an I
MI (generates a high frequency voltage of z).

FIG. 9 is a circuit diagram showing the configuration of an example of the oscillator 71.

A parallel circuit of a transistor T r 1 which is switched from an off state to an on state by a line drive pulse + a capacitor C1 and a resistor R1 connected to its collector, a transistor T r 2 + a transformer forming an automatic oscillator,
Feedback capacitor C2, variable resistor VR that adjusts the oscillation voltage
, l- It is constituted by a diode D and the like that apply a reverse bias to the transistor Tr2 to ensure that the transistor Tr2 is turned off when the transistor Trl is turned off. When an L level line drive pulse is applied to the base of the transistor Tri, this transistor turns on,
A large amount of current flows into the capacitor C1, reducing the rise time of the transistor Tr2 to 2 μs or less. The transistor Tr2 constitutes an automatic oscillator having a tuned circuit at its collector, and the output is fed back to the emitter via the primary winding of the transformer and the capacitor C2, and oscillation is maintained. This output is boosted by a transformer and a high frequency voltage is output to the output terminal. The peak value of this voltage can be adjusted within the range of 2650V±150ν by adjusting the variable resistor VR. Therefore, the variable resistor VR of each oscillator 71 is adjusted to correct output fluctuations due to variations in each component, so that all oscillators 71 output a high frequency voltage having a predetermined peak value.

By applying the high frequency voltage output from each oscillator 71 to the line electrodes 31-1 to 31-20 in this manner, the ion emission time in each dot recording element row can be changed, and uniform charging can be performed. be able to.

FIG. 10 shows another example of the configuration of the enable signal generating section. In this example, the line selection code LSEL O~L
Upper 4 bits b2 of 5 bits b1 to bS of SHL 4
~bs is supplied to a subtracter 85 via EXOR gates 81 to 83 and a NOT gate 84. In the subtractor, E
A 2-bit signal A'' is output from NOT gate 84 from 3-bit signals A, B, and C supplied from XOR gates 81-83.

B'' and the signal C'', which is always logic "0", are subtracted. Therefore, as shown in Table 2, when the most significant bit bs is "0", the output of this subtracter 85 becomes the inverted signal of b4bsbz, b3b2. , the most significant bit b is "1", it becomes b4bibz. This output is placed in a counter 86. At this time, since "1" is always given to the most significant bit D of the counter 86, the signal placed in the counter 86 changes symmetrically around the value at the center as shown in the right column of Table 2. Become something to do. Thereafter, the same operation as the embodiment shown in FIG. 7 will be performed using the clock generator 87. AND gate88. An enable signal is provided by OR gate 89 and NOT gate 90 and has a duration depending on the position of the line electrode selected at the output of NOT gate 90.
will be output.

The invention is limited only to the embodiments described above.

(Many modifications and changes are possible. For example, in the embodiment shown in Figure 7 and after, the duration of the high frequency voltage applied to the line electrode is changed, but the recording head is Since it is composed of a matrix, it is possible to change the duration of the DC voltage applied to the finger electrodes.Also, it is possible to change the peak value of the high frequency voltage and the duration of the voltage applied to the line electrode or finger electrode. The present invention is not limited to the embodiment described above, and various configurations can be adopted.Furthermore, the present invention is not limited to a recording head using the ion flow electrode configured as described above, The present invention can be applied to any type of recording head having at least two rows of dot recording elements.

〔Effect of the invention〕

As described above, according to the image forming apparatus of the present invention, the recording operation in each dot recording element array is changed in accordance with the distance between the dot recording element array and the surface of the image carrier drum, so that the recording operation is uniform over the entire area. It is possible to form high-quality images with high density.

[Brief explanation of drawings]

FIG. 1 is a side view schematically showing the overall configuration of an embodiment of the image forming apparatus of the present invention, FIG. 2 is a plan view showing the configuration of the recording head, and FIG. 3 is the same recording head. FIG. 4 is a waveform diagram for explaining its operation, FIG. 5 is a circuit diagram showing the configuration of the recording head drive circuit of the image forming apparatus according to the present invention, and FIG. 6 is a line diagram showing the distribution of the line electrode. A graph showing the peak value of the high-frequency voltage applied to the line electrode in response to the position of the line electrode, FIG. 7 is a circuit diagram showing an example of a circuit that changes the duration of the high-frequency voltage applied to the line electrode, and FIG. A signal waveform diagram for explaining the operation, Figure 9 is a circuit diagram showing the configuration of an example of the oscillator, and Figure 10 shows another example of a circuit that changes the duration of the high frequency voltage applied to the line electrode. The circuit diagram shown in FIG. 11 is a diagram showing the configuration of a conventional image recording apparatus. DESCRIPTION OF SYMBOLS 11... Image carrier drum 12... Recording head 13... Developing device 14... Pressure transfer roller 17... Recording paper 31-1 to 31-20... Line electrodes 32 to 1 to 32
-124...Finger electrodes 51-1 to 51-20...
・High frequency power supply 55-1 to 55-124...Finger electrode driving FET 61...Enable signal generating section 62...Voltage generating section 64...ROM 65...Counter 66...Clock generator 70 ... Decoder 71 ... Oscillator 85 ... Subtractor 8
6... Counter 87... Clock generator Figure 2 Figure 9 Figure 10

Claims (1)

[Claims] 1. A rotating image carrier drum, a recording head disposed opposite to the drum and having a plurality of dot recording element rows distributed in the rotational direction of the drum, and a connection between each dot recording element row and the drum surface. An image forming apparatus comprising: means for controlling a recording operation in each dot recording element array so that dots of a constant density can be formed on a drum regardless of a difference in distance.