JP2952009B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a printer, and more particularly, to an image forming apparatus including a charging member that contacts an image carrier and charges the image carrier. The present invention relates to an image forming apparatus.

(Background technology)

As a so-called contact charging method in which a roller or the like is brought into contact with an image carrier such as a photoconductor to perform charging, a voltage obtained by superimposing a DC voltage and an AC voltage is externally applied to a conductive member, and the conductive member is charged with an object to be charged. The present applicant has proposed a contact charging method in which charging is effected by contacting the contact member with, for example, JP-A-63-149669.

In this method, for example, as shown in FIG. 2, the conductive roller 1 is contact-rotated on the photosensitive drum 2 and a voltage (Vac + Vdc) obtained by superimposing an AC voltage Vac and a Vdc having a peak-to-peak voltage Vpp that is twice or more the charging start voltage is applied. ) Is applied to the conductive roller 1 to uniformly charge the photosensitive drum 2.

In the figure, 3 is a power supply on which AC and DC voltages are superimposed, 4 is a contact leaf spring used to apply a voltage to the charging roller core 1a,
Reference numeral 5 denotes a spring for pressing the charging roller 1 against the photosensitive drum 2.

On the other hand, as a developing method for developing the photosensitive drum on which the latent image is formed, the toner layer is formed into a uniform thin layer on the developing roller, brought close to the latent image surface on the image carrier, and a DC voltage and an AC voltage are superimposed. A so-called jumping development method in which the developed bias voltage is applied to a developing roller to perform development is known.

[Problems to be solved by the invention]

However, as a result of our research experiments, when using a voltage obtained by superimposing a DC voltage and an AC voltage on the charging bias voltage and the developing bias voltage as described above,
The following problems occurred.

That is, the AC frequency of the charging bias voltage is equal to the AC frequency of the developing bias voltage and an integral multiple or a fraction of the AC frequency of the developing bias voltage.
In the case of a frequency close to any one of the above, periodic development unevenness has occurred. The mechanism by which this periodic development unevenness occurs is not completely elucidated, but is presumed as follows.

When the photosensitive drum is charged by applying a charging bias voltage in which a DC voltage and an AC voltage are superimposed on a charging roller that is in contact with the photosensitive drum, which is a member to be charged, the approximate surface potential is substantially uniform in accordance with the DC voltage. become. However, since the surface of the photosensitive drum moves with respect to the charging roller, microscopically, a periodic change of the surface potential corresponding to the frequency of the AC voltage, that is, a pitch unevenness occurs due to the influence of the AC voltage. PMM / sec peripheral speed of the photosensitive drum, and the frequency of the AC voltage of the charging bias voltage and f _p Hz, periodic changes in surface potential on the photosensitive drum surface is repeated at p / f _p mm pitch .

On the other hand, since the AC voltage is also superimposed on the developing bias voltage applied to the developing sleeve, it is considered that the developing characteristics microscopically change periodically with respect to the moving photosensitive drum surface. Assuming that the frequency of the AC voltage of the developing bias voltage is f _d Hz, the periodic change of the developing characteristics on the surface of the photosensitive drum is repeated at a pitch of p / f _d mm.

The above p / f _p mm pitch and p / f _d mm pitch are each independently,
The surface potential, which is a periodic change at intervals that cannot be identified on a normal image, changes periodically with the p / f _p mm pitch is p / f _d mm
Since the development is performed by the development characteristic that changes periodically with pitch, there is a case where development unevenness occurs at a longer cycle than that of the both, that is, the development unevenness can be identified on the image. For example, in the case of a sound wave, a beat occurs due to interference between two waves having slightly different frequencies, and if the respective frequencies are f ₁ and f ₂ , the beat frequency becomes | f ₁ −f ₂ |.

Similarly, according to research experiments performed by the present inventors, not only when the AC frequency of the charging bias voltage is a frequency close to the AC frequency of the developing bias voltage but also when the AC frequency of the charging bias voltage is a frequency close to an integral multiple or a fraction of an integer. It was also confirmed that development unevenness was caused by interference. Development unevenness due to interference occurs when the AC frequency of the charging bias voltage is within a few percent before and after the AC frequency of the developing bias voltage and a frequency that is an integral multiple or a fraction of that of the developing bias voltage. It was not noticeable and had no effect on the image. Also, no development unevenness occurred when the value was exactly an integral multiple or a fraction of an integer. However, it is very difficult to match them exactly because the AC frequency has some fluctuation.

[Object of the invention]

The present invention has been made in view of the above points, and has as its object to provide an image forming apparatus that prevents uneven development and forms a good image.

[Configuration of the invention]

In order to achieve the above object, according to the present invention, in order to form a latent image on an image carrier, the image carrier is charged by applying a voltage having an AC component in contact with the image carrier. And a developing member to which a voltage having an AC component is applied to develop the latent image, the charging voltage has an AC frequency of ± 3% of the AC frequency of the developing voltage. Within a range of ± 3% of a frequency that is an integral multiple of the AC frequency of the developing voltage, and ± 3% of a frequency that is a fraction of the AC frequency of the developing voltage.
The range is set to a range excluding the range within.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a drawing showing the features of the present invention best, and is a schematic sectional view of an electrophotographic copying machine which is an image forming apparatus. Around the photosensitive drum 2, a charging roller 1, an image exposure unit 12, a developing unit 13, a transfer charging unit 14, and a cleaner 15 are arranged.

The charging roller 1 serving as a charging member has a high voltage power supply 21 for charging.
And a charging bias voltage obtained by superimposing a negative DC voltage and an AC voltage formed of a sine wave. To the developing sleeve 13a of the developing device 13, a developing bias voltage in which a DC voltage and an AC voltage formed of a rectangular wave are superimposed is applied from the developing high voltage power supply 22. The photosensitive drum 2 rotates in the direction of arrow A in the figure, and an image is formed. The photosensitive drum 2 has a grounded conductive substrate 2a made of aluminum, iron, or the like, and a photosensitive layer 2b made of an organic photoconductor provided on the surface thereof. The charging member is not limited to the roller, but may be a brush or a blade.

After the photosensitive drum 2 is negatively charged by the charging roller 1, the image is exposed by a laser scanner or the like (not shown) based on image information in an image exposure section 12, and the latent image formed thereby is exposed to a portion where the potential is attenuated. The reversal development is performed by the developing device 13 so that the negative toner adheres. A thin layer of toner as a developer is formed on a developing sleeve 13a of the developing device 13, and a minute gap is provided between the toner layer and the photosensitive drum 2. As described above, by applying the developing bias voltage from the power supply 22 to the developing sleeve 13a, an alternating electrolysis is formed between the photosensitive drum 2 and the developing sleeve 13a. Here, the waveform of the developing bias voltage obtained by superimposing the DC voltage and the AC voltage is a rectangular wave.

The developed toner image is transferred onto the transfer paper by a transfer charger 14 so that the transfer paper supplied from the right side in the figure is positively charged, further fixed by a fixing device 16, and discharged outside the apparatus. The developer remaining on the photosensitive drum 2 without being transferred is cleaned by the cleaner 15, the photosensitive drum 2 is charged again by the charging roller, and the above process is repeated.

Here, in this embodiment, the AC voltage of the charging bias voltage has a sine waveform, the maximum amplitude Vp-p is 1800 V, and the frequency is 400
Hz ± 20Hz and superimpose DC voltage -700V.

The developing bias voltage has a rectangular waveform, and has a maximum amplitude.
Vp-p is 1200V, frequency 1800Hz ± 90Hz, DC voltage -5
0V to -450V is superimposed. The DC voltage is set variably to make the image density a desired value. The peripheral speed of the photosensitive drum is 47
mm / sec.

The intersections ± 20 Hz and ± 90 Hz of the AC frequency of the charging bias voltage and the developing bias voltage are errors caused by variations in the high-voltage power supply. AC frequency of development bias voltage
FIG. 3 shows the range of 1800 Hz ± 90 Hz and a frequency that is a fraction of that integer. When the AC frequency of the charging bias voltage approaches the frequency in this range, development unevenness occurs.

When the respective frequencies of the developing bias voltage and the charging bias voltage were variously changed within the tolerance range by a high-frequency power supply having a variable frequency, for example, the lower limit of the AC frequency of the developing bias voltage was 1710 Hz and the upper limit of the charging bias voltage was 420 Hz. In the case of the combination and the combination of the upper limit of the AC frequency of the developing bias voltage of 1890 Hz and the lower limit of the AC frequency of the charging bias voltage of 380 Hz, uneven development was observed. Incidentally, the AC frequency of the charging bias voltage is 1 / 4.07 in the case of the former combination and 4.97 in the case of the latter combination with respect to the AC frequency of the developing bias voltage. The frequency is within ± 3% of 1. Here, when the AC frequency of the developing bias is 1710 Hz, the AC frequency of the charging bias is set to be smaller than 1710 × (1−0.03) × 1/4 ≒ 415 Hz, that is, 380 to 4
When set to 15 Hz, no development unevenness occurred. Also, when the AC frequency of the developing bias voltage is 1890 Hz, 1890 ×
Even when the AC frequency of the charging bias was set so as to be larger than (1 + 0.03) × 1/5 ≒ 389 Hz, that is, 389 to 420 Hz, no development unevenness occurred.

In FIG. 3, the AC frequency of the developing bias voltage is 18
The range of the frequency of the charging bias voltage at which development unevenness occurs when the charging bias voltage is changed to 00 ± 90 Hz is indicated by a dotted arrow.

As a result of research conducted by the present inventors, the AC frequency of the charging bias voltage is within a range of ± 3% of the AC frequency of the developing bias voltage, and within a range of ± 3% of a frequency that is an integral multiple of the AC frequency of the developing bias voltage. It has been found that by setting the range to a range excluding a range of ± 3% of the integral frequency of the AC frequency of the developing bias voltage, development unevenness due to interference can be prevented.

Next, a case where the AC frequency of the charging bias voltage is higher than the AC frequency of the developing bias voltage will be described.

Here, the AC frequency of the developing bias voltage is 1200 Hz ± 12
0 Hz, 1.5 times the AC frequency of charging bias voltage
It was set to 1800Hz ± 180Hz. The frequency at which the AC frequency of the developing bias voltage is an integral multiple of 1200 Hz ± 120 Hz falls within the range shown in FIG.

Even when the AC frequency of the bias voltage for each of charging and development was changed within the range of intersection, no development unevenness occurred.

Further, in FIG. 4, the range of the charging bias voltage frequency at which development unevenness occurs when the charging bias voltage is changed when the AC frequency of the developing bias voltage is set to 1200 Hz ± 120 Hz is indicated by a dotted arrow.

Here, the AC frequency of the charging bias voltage is set within a range of ± 3% of the AC frequency of the developing bias voltage, a range of ± 3% of a frequency that is an integral multiple of the AC frequency of the developing bias voltage, and the AC of the developing bias voltage. By setting the frequency to a range excluding a range within ± 3% of a frequency that is a fraction of the frequency, development unevenness due to interference can be prevented.

FIG. 5 is a circuit diagram of an AC high-voltage power supply according to another embodiment.
The oscillator 31 generates a frequency of 3600 Hz ± 360 Hz. Oscillator 3
Bisect the voltage generated by 1. One is divided by 9 by the charging frequency divider 32, and the charging AC frequency a is 400 Hz.
After that, the maximum amplitude Vp-p is 1800
The voltage is boosted to AC of V, and the AC voltage of the charging bias voltage is set. A charging DC voltage power supply 36 superimposes a DC voltage of −700 V on this, and supplies it to the charging roller 1. The other is a frequency divider for development 33
After the frequency is changed to 1800 Hz, which is the developing AC frequency b, the boosting transformer 35 boosts the AC to a maximum amplitude Vp-p of 1200 V to obtain an AC voltage of the developing bias voltage. A DC voltage of −50 V to −450 V is superimposed on the DC voltage by the developing DC voltage power supply 37 and supplied to the developing sleeve 13 a.

In the embodiment described with reference to FIGS. 3 and 4, since the charging and developing AC frequencies are supplied from separate high-voltage power supplies, the variations in the respective frequencies are independent. Therefore, as in the embodiment shown in FIG. 3, if one of the combinations is within the tolerance and the other is the upper limit and the other is the lower limit, the condition may easily cause development unevenness. Therefore, it is necessary to design a high-voltage power supply so as to reduce the variation tolerance of the frequencies of charging and developing. Thus, as shown in the present embodiment, a configuration is employed in which the relationship between the frequencies of charging and developing is kept constant, thereby stabilizing the image. That is, according to the above-described configuration, the AC frequency a of the charging bias voltage and the AC frequency b of the developing bias voltage are always constant a: b = 2: 9 for each oscillator even if there is a tolerance in the frequency of the oscillator 31. Keep the relationship. Therefore, the AC frequency of the charging bias voltage does not fall within ± 3% of the AC frequency of the developing bias voltage or an integer multiple thereof or 1 / integer, and development unevenness does not occur.

In the present embodiment, the AC voltage generated from one oscillator is divided into two, and each frequency is divided and used for charging and development, so that the relationship between the AC frequency of the charging bias voltage and the AC frequency of the developing bias voltage is constant. Therefore, the variation in the frequency generated by each oscillator may be large. Also,
By changing the values of the oscillation frequency and the frequency division, the optimum frequency is set for charging and developing, respectively, that is, the AC frequency of the charging bias voltage is ± 3 of the AC frequency of the developing bias voltage or an integral multiple or 1 / integral thereof. It can be set in the range excluding%.

The waveform of the AC voltage shown above is a sine wave or a rectangular wave, but may be a triangular wave as long as the voltage value changes periodically with time.

Further, in the above description, the example of so-called jumping development in which the toner layer of the developing sleeve and the photosensitive drum have a gap has been described. However, it is of course possible to provide the developing device so that the toner layer of the developing sleeve and the photosensitive drum are in contact with each other. is there.

〔The invention's effect〕

As described above, the AC frequency of the charging bias voltage is set to a range within ± 3% of the AC frequency of the developing bias voltage, a range of ± 3% of a frequency that is an integral multiple of the AC frequency of the developing bias voltage, and By setting the voltage to a range excluding a range within ± 3% of a frequency that is a fraction of the AC frequency of the voltage, development unevenness due to interference can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an electrophotographic copying machine embodying the present invention, FIG. 2 is a cross-sectional view showing a configuration of a charging roller, and FIG. 3 is a graph showing a range of AC frequencies of bias voltages for charging and developing. FIG. 4 is a graph showing the range of the AC frequency of the second embodiment, and FIG. 5 is a circuit diagram of the third embodiment. DESCRIPTION OF SYMBOLS 1 ... Charging roller 2 ... Photosensitive drum 3 ... High voltage power supply 4 ... Contact plate spring 5 ... Pressure contact spring 13 ... Developing device 21 ... High voltage power supply 22 ... High voltage power supply 31 ... Oscillator 32, 33 ... Divider 34, 35 …… Step-up transformer 36, 37 …… DC power supply

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuo Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Koichi Tanigawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-60-154271 (JP, A) JP-A-61-159678 (JP, A) JP-A-4-13164 (JP, A) JP-A-63-200168 (JP, A) A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G03G 15/02 G03G 15/06 101 G03G 15/00 303

Claims (1)

(57) [Claims] A charging member for charging the image carrier by applying a voltage having an AC component to the image carrier in order to form a latent image on the image carrier; An image forming apparatus having a developing member to which a voltage having an AC component is applied for developing, wherein the AC frequency of the charging voltage is within a range of ± 3% of the AC frequency of the developing voltage, An image forming apparatus characterized by being set to a range excluding a range within ± 3% of a frequency that is an integral multiple of the frequency and a range within ± 3% of a frequency that is a fraction of an AC frequency of the developing voltage. .