JPH08112930A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To provide an image forming apparatus capable of forming an image of high quality free from a silk mesh pattern. CONSTITUTION: A control voltage applying circuit 22 is constituted of a data input part 34, a data processing part 36, a shift register 38, a latch circuit 40, a counter 42, a timing control circuit 44, a comparator group 46 consisting of comparators CMP1-CMPm, a switching element group 48 consisting of switching elements SW1-SWm and a smoothing circuit group consisting of smoothing circuits RC1-RCm. A pulse signal having the pulse width corresponding to pixel data is converted to drive voltage by the switching elements SW 1-SWm and this drive voltage is converted to the DC voltage between 0 to +50V corresponding to the pulse width by the smoothing circuits RC1-RCm to be applied to respective control electrodes 6. As a result, toner is uniformly accumulated on a pixel forming area to enable variable density expression free from silk mesh pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a printer,
The present invention relates to an image forming apparatus that can be used for plotters, facsimiles, and the like.

[0002]

2. Description of the Related Art Conventionally, as one of image forming apparatuses,
For example, as disclosed in Japanese Patent Application Laid-Open No. 6-155798, an aperture electrode having a plurality of small holes (hereinafter referred to as apertures) for passing toner, and a control electrode provided for each aperture. The aperture electrode body is provided with an image recording medium such as printing paper by controlling the passage of the toner aperture by applying a drive signal corresponding to an image signal input from the outside to each control electrode of the aperture electrode body. A so-called toner jet type image forming apparatus for forming a toner image thereon is known.

In this type of apparatus, as one method of controlling the shading of a formed image, for example, as disclosed in Japanese Patent Application No. 3-43405, according to shading data of an image signal. A method of expressing the shading of a pixel is applied by applying a pulse signal having a pulse width (duty ratio) to the control electrode and controlling the voltage application time to the control electrode to control the amount of toner passing through the aperture. ing. According to this method, a drive circuit that applies a voltage to the control electrode can be configured relatively easily.

[0004]

However, since the image recording medium on which the toner image is formed is conveyed at a constant speed, the voltage pulse is applied to the control electrode within the pixel forming time for one pixel. If the toner flies only while the toner is flying, the toner will be accumulated at a certain position in the pixel formation area for one pixel, and each pixel formed on the image recording medium will be applied to the control electrode. Voltage pulse width (ie,
It has a specific pattern depending on the pixel density). As a result, there is a problem in that the formed image has a silk pattern based on the pattern of the pixels.

The present invention has been made to solve the above problems, and an image forming apparatus capable of forming a high quality image by uniformly depositing toner in a pixel forming area with a simple drive circuit configuration. Is intended to provide.

[0006]

In order to achieve the above object, the invention according to claim 1 is provided with a plurality of apertures through which toner passes, and control electrodes are provided at the peripheral edges of the apertures. An aperture electrode body having a toner supply means for supplying charged toner to the vicinity of the aperture, and a toner supply means pulse-width-modulated according to grayscale data of an image signal input from the outside. A drive signal generation unit that generates a drive voltage signal for controlling the amount of toner passing through the aperture in the vicinity of the aperture, and a pulse width modulated drive voltage signal generated by the drive signal generation unit are smoothed. The signal smoothing means applied to the control electrode is disposed on the opposite side of the aperture electrode body across the image recording medium, and is used for transporting the image recording medium. A back electrode for applying a predetermined voltage for forming a predetermined electric field between the toner supply means and the toner that has passed through the aperture to further fly and adhere and deposit the toner on the image recording medium to form a toner image. The gist is an image forming apparatus characterized by including:

The invention described in claim 2 is the same as claim 1
In the image forming apparatus described in the paragraph 1, the signal smoothing means is formed in a print pattern on the aperture electrode body.

[0008]

In the image forming apparatus according to the first aspect of the present invention configured as described above, the toner supply means supplies the charged toner to the vicinity of the aperture while
The drive signal generation means generates a drive voltage signal whose pulse width is modulated in accordance with the grayscale data of the image signal input from the outside, and the signal smoothing means smoothes the drive voltage signal to generate the drive voltage. The signal is converted into a DC voltage according to the duty ratio and applied to the control electrode.

Then, an electric field of a predetermined intensity is formed in each aperture and on the toner supply means in the vicinity of the aperture according to the voltage level applied to the control electrode, and the toner supplied in the vicinity of the aperture generates electrostatic force. It flies toward the receiving control electrode. At this time, the amount of toner corresponding to the strength of the electric field passes through the aperture.

That is, the amount of toner passing through the aperture is controlled not by the voltage application time to the control electrode but by the magnitude of the applied voltage. Further, the toner that has passed through the aperture is further ejected by receiving an electrostatic force due to an electric field formed between the back electrode to which a predetermined voltage is applied and the toner supply means, and is distributed between the back electrode and the aperture electrode body. A toner image is formed by adhering and depositing on the provided image recording medium.

Therefore, according to the image forming apparatus of the present invention,
A predetermined voltage corresponding to the grayscale data is continuously applied to the control electrode during the pixel formation time for one pixel, and during that time, the toner passes through the aperture substantially uniformly, so that the pixel formation area on the image recording medium. Toner can be evenly deposited on the
It is possible to form a high-quality image without a silk pattern.

Moreover, according to the present invention, a conventional apparatus for generating a signal whose pulse width is modulated according to grayscale data is provided.
This is a configuration in which only a smoothing means for smoothing the pulse width modulated signal is added, and the image quality can be easily improved. Further, in the image forming apparatus according to the second aspect, the signal smoothing means is formed on the aperture electrode body in a print pattern.

Therefore, since it is not necessary to retrofit the element, the number of assembling steps can be reduced. Further, since the space for mounting the element is not required, the device can be downsized.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an explanatory diagram showing a schematic configuration of the image forming apparatus 2 of the embodiment. As shown in FIG. 2, the image forming apparatus 2 according to the present exemplary embodiment includes a plurality of apertures 4 for passing the toner T and control electrodes provided in the vicinity of each aperture 4 for controlling the aperture passing of the toner T. An aperture electrode body 8 having 6 and a toner T for forming an image on an image recording medium P such as recording paper or OHP paper, which is provided below the aperture electrode body 8 and stores the toner T. 8 and a toner supply device 10 for supplying the lower part of the aperture electrode 8 and an upper part of the aperture electrode body 8
On the other hand, a cylindrical back electrode roller 12 that is rotatably supported at a predetermined interval (1 mm in this embodiment) and that conveys the image recording medium P inserted between the aperture electrode body 8 and the cylindrical back electrode roller 12.
And a heat roller that is provided in the conveyance path of the image recording medium P passing between the back electrode roller 12 and the aperture electrode body 8 and has a heater inside to heat the image recording medium P to a predetermined temperature. 14 and a pressure roller 16 which is provided at a position facing the heat roller 14 with the image recording medium P interposed therebetween, and which conveys the image recording medium P while pressingly contacting the heat roller 14.
And a DC power source 20 for applying a predetermined high voltage (1 kV in this embodiment) to the back electrode roller 12 to form a predetermined electric field between the back electrode roller 12 and the control electrode 6. The control voltage applying circuit 22 controls the passage of the toner T through the aperture by applying a predetermined voltage to the control electrode 6 according to image data input from the outside.

The back electrode roller 12, the heat roller 14 and the pressure roller 16 constituting the fixing device 18 are rotationally driven at a predetermined speed by a drive circuit (not shown), and the image recording medium P is moved at a predetermined speed. Left direction in the figure (arrow X
Direction). In addition, the control voltage application circuit 22
Is connected to an external computer, an image reading device, an image communication device, or the like, and image data is input from these devices.

Here, the toner supply device 10 includes a toner case 24 which also serves as a housing of the toner supply device 10.
A cylindrical toner carrying roller 26 that is rotatably supported in the toner case 24, is also rotatably supported in the toner case 24, and is arranged in parallel while being in contact with the toner carrying roller 26. Cylindrical supply roller 28
And a flat-plate-shaped toner layer regulating blade 30 which is disposed above the supply roller 28 so that one end thereof presses the roller surface of the toner carrying roller 26.

The toner carrying roller 26 and the supply roller 28 are rotationally driven at a predetermined speed in the clockwise direction (arrow Y direction) in the figure by a drive circuit (not shown). The surface of the toner carrying roller 26 is covered with an electrode body and is electrically grounded so that the potential thereof becomes 0V.

Toner supply device 10 thus configured
In the above, the toner T accumulated in the toner case 24 is rotated by the rotation of the supply roller 28, and
6 is conveyed. Then, the toner T conveyed to the contact surface between the supply roller 28 and the toner carrying roller 26
Is rubbed against the toner carrying roller 26 to be negatively charged, and also carried by the toner carrying roller 26.
The toner T carried on the toner carrying roller 26 in this manner
Is conveyed toward the aperture electrode body 8 by the rotation of the toner carrying roller 26, and in the middle thereof, is thinned by the toner layer regulating blade 30 so that the toner is evenly distributed on the roller surface. After the charge amount of each toner T is made uniform, it is supplied to the aperture electrode body 8.

Next, as shown in FIG. 3, the aperture electrode body 8 is composed of an insulating sheet 32 made of polyimide and having a thickness of 25 μm.
A plurality of circular apertures 4 having a diameter of 00 μm are formed in a line along the longitudinal direction, and a control electrode 6 made of a copper foil having a thickness of 8 μm is formed for each aperture 4 on the peripheral edge of the opening of the aperture 4. Has been done.

Aperture electrode body 8 constructed in this way
2 is disposed so as to contact the upper portion of the toner carrying roller 26 in a state where the surface on which the control electrode 6 is formed faces the back electrode roller 12, as shown in FIG. Next, the control voltage applying circuit 22, as shown in FIG. 1, receives a data input section 34 for inputting an image signal having grayscale data from the outside.
And a data processing unit 36 for converting the image signal input to the data input unit 34 into pixel data of 8 bits per pixel (shading data is expressed in 256 gradations), and the data processing unit 3
Pixel data input from 6 is taken in according to a predetermined shift timing signal ST, and one column, that is, all apertures 4
Shift register 38 for sequentially accumulating only the number (m) of
A latch circuit 40 that latches the pixel data for one line output from the shift register 38 according to a predetermined latch timing signal LT, and an 8-bit value that repeatedly counts the value of 0 to 255 according to a predetermined count clock CK. Of the counter 42, a timing control circuit 44 for extracting various timing signals included in the image signal, and generating various timing signals such as a shift timing signal ST, a latch timing signal LT, a count clock CK, and the like. Value of each pixel data and counter 4
The comparators CMP1 to CMPm that compare the count value of 2 respectively and output a High level when the latched value is greater than the count value and a Low level when the latched value is less than or equal to the count value. The comparator group 46 and the outputs of the comparators CMP1 to CMPm are 50V when the output is at the high level and 0V when the output is at the low level.
A switching element group 48 including switching elements SW1 to SWm for outputting
A well-known smoothing circuit R which is provided for smoothing the outputs of 1 to SWm and includes a resistor R (1 MΩ in this embodiment) and a capacitor C (1000 pF in this embodiment).
The smoothing circuit group 50 includes C1 to RCm.

The latch timing signal LT for causing the latch circuit 40 to latch the pixel data for one column is output at a period (1 msec in this embodiment) required for forming pixels for one column. Further, the counter 42 is incremented by a count clock CK (2.56 MHz in this embodiment), counts 0 to 255 every 0.1 msec, and ten times during the pixel formation time for one column. Count repeatedly.

The control voltage application circuit 2 configured as described above
2, the image signal having the grayscale data input to the data input unit 34 is output by the data processing unit 36 to 2 pixels per pixel.
It is converted into 8-bit pixel data capable of displaying 56 gradations and sequentially sent to the shift register 38. The pixel data taken into the shift register 38 in accordance with the shift timing signal ST is latched by the latch timing signal L output from the timing control circuit 44 every time one column (m pieces) is prepared.
It is latched in the latch circuit 40 by T.

The pixel data latched by the latch circuit 40 is compared with the count value of the counter 42 by the comparators CMP1 to CMPm, respectively. This time,
Each of the comparators CMP1 to CMPm outputs a high level until the count value of the counter 42 reaches the latched pixel data value, and then outputs a low level until the count value reaches 255.

The pixel formation time for one column (1 mse
During c), the same pixel data is held in the latch circuit 40, while the counter 42 repeats counting 0 to 255 ten times during this period. As a result, 10 pulse signals each having a pulse width (duty ratio) according to the pixel data are output from each of the comparators CMP1 to CMPm during the pixel formation time for one column.

As described above, the pulse signals having the pulse width corresponding to the pixel data are the switching elements SW1 to SW.
At m, the high level is a predetermined drive voltage (in this embodiment, +
50V), and further smoothing circuit RC1
Is converted into a DC voltage between 0 V and +50 V according to the pulse width at RCm, and then applied to each control electrode 6.

Now, referring to FIG. 4, the comparator CM
The relationship between the output of Pi (i = 1 to m) and the output of the smoothing circuit RCi will be described. As shown in FIG. 4, first, the comparator C is based on the pixel data latched by the latch circuit 40.
When, for example, a pulse signal having a duty ratio of 0.7 is output from MPi (period 1), the output of the smoothing circuit RCi becomes a DC voltage of approximately 35V (50V × 0.7).

Then, the latch circuit 40 latches the next pixel data, and 10 pulse signals having a duty ratio of 0.2 are output from the comparator CMPi based on the newly latched pixel data (period 2). Smoothing circuit RCi
Output gradually changes to a DC voltage value of about 10 V (50 V × 0.2) corresponding to the duty ratio during the period 2 (that is, the pixel formation time for one column).

Similarly, every time the latch circuit 40 latches new pixel data, the comparator CMPi outputs a pulse signal having a predetermined duty ratio based on the latched pixel data. As a result, The smoothing circuit RCi outputs a DC voltage corresponding to this duty ratio.

As described above, the smoothing circuits RC1 to RCm are
By smoothing a pulse signal having a duty ratio according to pixel data and outputting a DC voltage according to the duty ratio (and thus pixel data), each control electrode 6 has a pixel formation time for one column. During this period, a substantially constant voltage corresponding to the pixel data is applied.

It should be noted that, in FIG. 4, the smoothed signal is drawn so as to change smoothly for the sake of clarity, but in reality, a predetermined signal is generated while pulsating according to ON / OFF of the pulse signal. It approaches the voltage. However, this pulsation can be reduced by setting the time constant (1 msec in this embodiment) of the smoothing circuit RCi sufficiently larger than one pulse period (0.1 msec).

In the image forming apparatus 2 configured as described above, when an image signal is input from the outside, the control voltage application circuit 22 causes the control electrode 6 of each aperture 4 to respond to the grayscale data of the image signal. Then, a predetermined DC voltage between 0V and + 50V is applied. Then, due to the potential difference between the control electrode 6 to which the predetermined DC voltage is applied and the toner carrying roller 26 which is grounded and set to 0V, the voltage applied to the control electrode 6 is changed in each aperture 4. A corresponding electric field is formed, and the negatively charged toner T is subjected to an electrostatic force toward the side of higher potential.

That is, in the aperture 4 to which the voltage of 0 V is applied to the control electrode 6, the potential of the control electrode 6 and the potential of the toner carrying roller 26 become the same, so that the electrostatic force does not work,
The toner T carried on the toner carrying roller 26 remains in place. On the other hand, in the aperture 4 to which a direct current voltage other than 0V is applied to the control electrode 6, the potential on the control electrode 6 side becomes high, so that the toner T receives an electrostatic force toward the control electrode 6. As a result, the toner T carried on the toner carrying roller 26 flies from the surface of the toner carrying roller 26 and passes through the aperture 4. At this time, the amount of toner T passing through the aperture 4 increases as the applied voltage increases.

The toner T that has passed through the aperture 4 and is drawn to the side of the aperture electrode body 8 on which the control electrode 6 is formed is the back electrode roller 12 to which a voltage of +1 kV is applied by the DC power source 20 and the control electrode. 6 is subjected to electrostatic force by an electric field formed by a potential difference between the image recording medium and the back electrode roller 12 having a high potential, and further fly to the image recording medium disposed between the aperture electrode body 8 and the back electrode roller 12. Deposit and deposit on P.

As a result, on the image recording medium P, a pixel having a density corresponding to the voltage applied to the control electrode 6 of the aperture 4 is formed at a position facing each aperture 4, thereby forming one column. Toner image is formed. In this way, when one row of toner images is formed on the image recording medium P, the image recording medium P is rotated in the vertical direction with respect to the four rows of apertures by the rotational driving of the back electrode roller 12 and the heat roller 14. Only one pixel is transferred to. Then, the toner image for one screen is formed on the image recording medium P by repeating the process of forming the toner image for one column.

After that, the image recording medium P on which the toner image is formed is transferred to the position where the fixing device 18 is arranged,
The pressure roller 16 presses the image recording medium P against the heat roller 14, presses the image recording medium P, and the heat roller 14 heated to a predetermined temperature applies heat to the image recording medium P, whereby a toner image is obtained. Is fixed on the image recording medium P,
A series of operations for forming an image on the image recording medium P is completed.

As described above in detail, in the image forming apparatus 2 of this embodiment, the smoothing circuits RC1 to RCm smooth pulse signals having a predetermined pulse width (duty ratio) according to the grayscale data of the image signal. The DC voltage corresponding to the duty ratio of the pulse signal (that is, the grayscale data) is generated, and the DC voltage is applied to the control electrode 6 to control the aperture passing amount of the toner T.

That is, the aperture passing amount of the toner T is controlled not by the voltage application time but by the magnitude of the applied voltage. Therefore, according to this embodiment, a substantially constant voltage corresponding to the grayscale data is continuously applied to the control electrode 6 during the pixel formation time for one column, and the toner T has an approximately uniform aperture during that time. Since the toner passes through, the toner can be uniformly deposited in the pixel formation region on the image recording medium P, and a high-quality image without a silk pattern can be formed.

Moreover, according to the present embodiment, the resistor R for smoothing the pulse signal is added to the conventional device for generating the pulse signal having the predetermined pulse width according to the grayscale data.
And smoothing circuits RC1 to RC including a capacitor C
Since only m is provided, the image quality can be easily improved.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments.
Various changes can be made without departing from the spirit of the invention. For example, in the above embodiment, the resistance R
Although the smoothing circuits RC1 to RCm are configured with the capacitor C and the capacitor C, if a pulse signal having a predetermined duty ratio can be converted into a DC voltage according to the duty ratio,
Any smoothing circuit may be used, for example, the coil L and the resistor R
May be connected in series.

Further, in the above embodiment, the smoothing circuits RC1 to RCm are formed at the outputs of the switching elements SW1 to SWm of the control voltage application circuit 22, but the extraction pattern 6a of the control electrode 6 on the aperture electrode body 8 (see FIG. 3) and the capacitance generated between the drawing pattern 6a and the toner carrying roller 26 with the insulating sheet 32 sandwiched therebetween, these are regarded as resistors and capacitors to form the smoothing circuits RC1 to RCm. Good. As a method for adjusting the resistance of the extraction pattern 6a, the extraction pattern 6a
In addition to adjusting the thickness width of a, a part of the extraction pattern 6a may be carbon-printed.

In this case, since it is not necessary to add the smoothing circuits RC1 to RCm afterwards, the number of assembling steps can be reduced and
The device can be downsized. Further, in the above embodiment, the toner T that has passed through the aperture 4 is directly transferred to the image recording medium P such as paper.
An image is formed by adhering and depositing the toner on the intermediate recording medium between the aperture electrode body 8 and the back electrode roller 12, and the toner image formed on this intermediate recording medium is further transferred to the image recording medium P. You may do it.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a control voltage applying circuit 22 used in an image forming apparatus 2 of an embodiment.

FIG. 2 is an explanatory diagram showing a schematic configuration of an image forming apparatus 2 according to an embodiment.

FIG. 3 is a perspective view showing a configuration of an aperture electrode body 8 used in the image forming apparatus 2 of the embodiment.

FIG. 4 is an explanatory diagram showing the operation of the control voltage application circuit 22.

[Explanation of symbols]

2 ... Image forming apparatus 4 ... Aperture 6 ... Control electrode 8 ... Aperture electrode body 10 ... Toner supply device 18
... Fixing device 20 ... DC power supply 22 ... Control voltage application circuit 26 ...
Toner carrying roller 34 ... Data input section 36 ... Data processing section 38 ...
Shift register 40 ... Latch circuit 42 ... Counter 44 ... Timing control circuit 46 ... Comparator group (comparators CMP1 to CMP
m) 48 ... Switching element group (switching elements SW1 to SW1
SWm) 50 ... Smoothing circuit group (smoothing circuits RC1 to RCm)

Claims (2)

[Claims] 1. An aperture electrode body having a plurality of apertures for allowing toner to pass therethrough, and an aperture electrode body having control electrodes on the periphery of an aperture of the aperture, and a toner carrying a charged toner and supplying the toner in the vicinity of the aperture. And a drive voltage signal, which is pulse-width modulated in accordance with the density data of the image signal input from the outside, for controlling the aperture passing amount of the toner supplied in the vicinity of the aperture by the toner supply unit. Drive signal generating means for generating, a signal smoothing means for smoothing the pulse-width-modulated drive voltage signal generated by the drive signal generating means and applying it to the control electrode, and the aperture electrode body with an image recording medium sandwiched therebetween. And a predetermined voltage for forming a predetermined electric field between the toner supply unit and the toner supply unit. Is, the image forming apparatus characterized by comprising a back electrode to form a toner image by further caused to fly deposited deposited on said image recording medium the toner passed through the aperture. 2. The image forming apparatus according to claim 1, wherein the signal smoothing means is formed in a print pattern on the aperture electrode body.