JP2005077968A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is not influenced by change of environment. <P>SOLUTION: In the image forming apparatus which develops an electrostatic latent image carried by an electrostatic latent image carrier with a developer supplied from a developer carrier, an AC voltage is applied between the electrostatic latent image carrier and developer carrier. The waveform of the AC voltage has a 1st waveform part which energizes a developer being carried from the developer carried to the electrostatic latent image carrier and a 2nd waveform part which energizes a developer being carried from the electrostatic latent image carrier to the developer carrier. Then, a voltage elevation part atop of the 1st waveform part approximates a tip voltage elevation part of a rectangular waveform. Further, a voltage elevation part atop of the 2nd waveform part approximates a tip voltage elevation part of an exponetial waveform. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer.

Conventionally, an AC voltage is applied between an electrostatic latent image carrier that carries an electrostatic latent image and a developer carrier that carries a developer, and the developer carried on the developer carrier is changed to an AC voltage. An image forming apparatus that visualizes (develops) an electrostatic latent image by supplying it to an electrostatic latent image carrier is provided. However, in such an image forming apparatus, when the AC voltage is increased, the developer supply performance is improved. However, a discharge occurs between the electrostatic latent image carrier and the developer carrier, thereby causing an image on the image. There is a problem that a discharge trace (appears as a black spot trace on the image) occurs. On the other hand, when the AC voltage is reduced, there is a problem in that the supply capability of the developer is lowered and a desired image density cannot be obtained. Therefore, in an image forming apparatus that applies an AC voltage between the electrostatic latent image carrier and the developer carrier, the magnitude of the AC voltage (generally, a peak-to-peak value is expressed). The voltage is adjusted within a voltage range (hereinafter, this range is referred to as “appropriate development range”) in which a discharge phenomenon does not occur and a desired image density is obtained (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 4-136959

  However, the members constituting the electrostatic latent image carrier and the developer carrier (for example, the photosensitive member, the developing roller, the member that regulates the transport amount of the developer, and the member that supports them) change the environment (for example, Deformation) due to changes in temperature, and the appropriate development range may be narrowed due to the deformation. Therefore, it is desirable that the image forming apparatus can set the appropriate development range as wide as possible.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus in which an appropriate development range can be set as large as possible.

  An image forming apparatus that achieves this object is to develop an electrostatic latent image carried on an electrostatic latent image carrier by a developer supplied from the developer carrier, and the electrostatic latent image carrier and developer An AC voltage is applied between the carrier and the carrier. The waveform of the AC voltage includes a first waveform portion for urging the developer from the developer carrier to the electrostatic latent image carrier and the developer from the electrostatic latent image carrier to the developer carrier. The second waveform portions to be energized are alternately provided. And the voltage rise part in the front-end | tip of the 1st waveform part approximates the front-end | tip voltage rise part of a rectangular waveform. Further, the voltage increase portion at the tip of the second waveform portion approximates the tip voltage increase portion of the exponential waveform.

また、数１で示される式中の時定数τは、下記の数２の関係で表される。

さらに、数２で示される関係内のキャリブレーション値Ｃは２ｌｎ１０≦Ｃ≦３ｌｎ１０（ｌｎ：自然対数）の範囲にある。 An image forming apparatus according to another aspect of the present invention develops an electrostatic latent image carried on an electrostatic latent image carrier with a developer supplied from the developer carrier, and the electrostatic latent image carrier. An AC voltage is applied between the body and the developer carrying body. The waveform of the AC voltage includes a first waveform portion for urging the developer from the developer carrier to the electrostatic latent image carrier and the developer from the electrostatic latent image carrier to the developer carrier. Are alternately provided with second waveform portions for energizing. And the voltage rise part in the front-end | tip of the 1st waveform part approximates the front-end | tip voltage rise part of a rectangular waveform. Further, the frequency of the AC voltage is f [Hz], the duty ratio of the second waveform portion is D [%], the maximum voltage of the second waveform portion is Vmax [volts], and the voltage rising portion of the second waveform portion is When the voltage is V [volts], the frequency f [Hz] is in the range of 1500 ≦ f ≦ 3000, the duty ratio D [%] is in the range of 40 ≦ D ≦ 80, and the voltage V [ Bolt] is expressed by the following formula 1.

In addition, the time constant τ in the equation expressed by Equation 1 is expressed by the following Equation 2.

Further, the calibration value C within the relationship represented by Equation 2 is in the range of 2ln10 ≦ C ≦ 3ln10 (ln: natural logarithm).

  In an image forming apparatus according to another aspect of the present invention, it is particularly desirable that the calibration value C is 3ln10.

  According to the image forming apparatus employing such a configuration, the appropriate development range can be expanded as compared with the conventional case. Therefore, even if the constituent members of the electrostatic latent image carrier and the developer carrier are deformed due to environmental changes, the setting in the image forming apparatus after the deformation is still in a state where the proper development range can be maintained. Therefore, an image with black spots or low density due to discharge is not formed.

  FIG. 1 is a diagram illustrating a schematic configuration of the image forming apparatus 10. In this figure, a photoreceptor 12 that functions as an electrostatic latent image carrier that carries an electrostatic latent image is supported so as to be rotatable in the direction of an arrow 14. The photoconductor 12 need not be a cylindrical body, and may be an endless belt type photoconductor. Around the photosensitive member 12, a charging device 16 that charges the outer peripheral surface of the photosensitive member 12 to a predetermined potential, and exposure that forms an electrostatic latent image by exposing an image (light) to the outer peripheral surface of the charged photosensitive member 12. A developing device 20 that develops an electrostatic latent image using toner as a developer to form a toner image; a transfer device 24 that transfers a toner image to a sheet 22 conveyed along a one-dot chain line; A cleaning device 26 that collects toner remaining on the outer periphery of the photoreceptor 12 without being transferred is disposed. Since the configuration of such an electrophotographic image forming apparatus is well known, detailed description thereof will be omitted.

  The developing device 20 includes a housing 30, and a toner 34 that is a powder developer is stored in a toner storage portion 32 formed inside the housing 30. A pumping roller 36, which is a developer pumping unit that pumps up the toner 34 in the toner storage unit 32, is in contact with the toner 34 stored in the toner storage unit 32 and is supported so as to be rotatable in the direction of the arrow 38.

  A developing roller 40 that functions as a developer carrying member for developing the electrostatic latent image by supplying the toner 34 pumped up by the pumping roller 36 to the photoreceptor 12 is supported so as to be rotatable in the direction of arrow 42. It is accommodated in the housing 30 so as to face the pumping roller 36 in the supply area 44. The developing roller 40 is disposed to face the photoconductor 12 with a predetermined developing gap in the developing region 46 in a state where the developing device 20 is incorporated in the image forming apparatus 10. A blade 48 as a charged toner layer forming means fixed to the housing 30 is in contact with the outer peripheral surface of the developing roller 40, and the toner supplied to the developing roller 40 is regulated in the toner supply region 44 to develop the developing region 46. The amount of toner conveyed to the developing region 46 is made constant, and the toner conveyed to the developing region 46 is brought into contact with the toner to be charged to a predetermined polarity.

  In such a configuration, the developing roller 40 does not need to be a cylindrical body like the photoconductor 12, but may be an endless belt type developing body carrier. The developer pumping means is not limited to a roller, and is not necessarily required. For example, the developing roller 40 is configured such that the outer peripheral surface of the developing roller 40 contacts the toner 34 of the toner storage portion 32 and holds the toner. You can also.

  In order to keep the amount of toner 34 supplied from the developing roller 40 to the photosensitive member 12 appropriate, the photosensitive member 12 and the developing roller 40 are connected to a power supply device 50, and the photosensitive member 12 and the developing roller 40 are connected by the power supply device 50. The AC voltage Vac having the waveform shown in FIG. The AC voltage Vac is expressed as a relative potential of the developing roller 40 with respect to the photoconductor 12 when the photoconductor 12 is grounded.

  The AC voltage Vac will be described in detail. First, the AC voltage Vac is the first waveform portion of a typical rectangular wave (hereinafter referred to as “hereinafter”) that electrically energizes the toner 34 from the developing roller 40 toward the photosensitive member 12. And a second waveform portion (hereinafter, referred to as “development waveform portion”) having an exponential waveform portion at the front end portion of the rectangular wave for electrically energizing the toner 34 from the photosensitive member 12 toward the development roller 40. 54 are periodically and alternately provided. Hereinafter, a waveform in which the development waveform portion 52 is configured by a rectangular wave and the recovery waveform portion 54 is configured by a waveform having an exponential waveform portion at the tip thereof is referred to as an “exponential rectangular wave”.

  As a typical example, the peak voltage Vp1 of the development waveform portion 52 is set to −1650 V [volt], and the peak voltage Vp2 of the recovery waveform portion 54 having an exponential waveform portion is set to + 750V. Further, the tip voltage rise portion 56 of the development waveform portion 52 that shifts from the recovery waveform portion 54 to the development waveform portion 52 approximates the tip voltage rise portion of the typical rectangular waveform shown in FIG. The tip voltage rise portion (hereinafter referred to as “exponential waveform portion”) 58 of the recovery waveform portion 54 that shifts from 52 to the recovery waveform portion 54 approximates the tip voltage rise portion of the general exponent waveform shown in FIG. ing. The surface of the photosensitive member 12 charged by the charging device 16 has a potential of Vpc = −450 V, and the portion where the image is exposed by the exposure device 18 (electrostatic latent image portion) is Vi = −50 to 0V. (Hereinafter, for the sake of simplicity, it is assumed that Vi = 0V).

  According to the developing device 20 having such a configuration, the toner 34 stored in the toner storage portion 32 of the developing device 20 is pumped up by the pumping roller 36 and supplied to the developing roller 40 in the toner supply region 44. The toner 34 held on the developing roller 40 is transported to a contact area between the developing roller 40 and the blade 48 based on the rotation of the developing roller 40, where excess toner 34 is scraped off from the developing roller 40. Further, the toner 34 passing between the developing roller 40 and the blade 48 is charged with a predetermined polarity (in this embodiment, a negative polarity) by contact with the blade 48. Therefore, a thin layer of charged toner is formed on the outer peripheral surface of the developing roller 40 that has passed through the blade contact area.

  Next, the charged toner is conveyed to the development area 46 where the electrostatic latent image on the photoreceptor 12 is developed. The developing roller portion that is consumed for development in the development region 46 and does not carry the toner 34 is conveyed again to the toner supply region 44 based on the rotation of the development roller 40, where an amount of toner corresponding to the amount consumed for development is present. Is replenished.

  The development in the development region 46 is performed based on the potential difference between the AC voltage Vac and the electrostatic latent image, as shown in FIG. More specifically, the peak of the development waveform portion 52 has Vp1 = −1650V. Therefore, the electrostatic latent image portion (Vi = 0V) passing through the developing region 46 is at a high potential by + 1650V with respect to the developing roller 40. On the other hand, the surface portion of the photoreceptor where the image is not exposed (electrostatic latent image non-image portion) has a charging potential Vpc = −450V and is a high potential by + 1200V with respect to the developing roller 40. Accordingly, the negatively charged toner 34 adheres to the electrostatic latent image portion having a higher potential with respect to the toner, and the electrostatic latent image is developed by the attached toner 34.

  As described above, although the potential difference between the electrostatic latent image portion and the developing roller 40 is smaller than that between the electrostatic latent image non-image portion and the developing roller 40, charged toner is statically discharged. The electrostatic force attracted to the non-image portion of the electrostatic latent image is acting. Therefore, the charged toner may adhere to the electrostatic latent image non-image portion based on the electrostatic force. These are usually referred to as fogging. Such defective toner (toner indicated by reference numeral 60 in FIG. 2) is recovered from the photoreceptor 12 to the developing roller 40 by the action of the subsequent recovery waveform section 54.

  More specifically, the peak Vp2 of the recovery waveform portion 54 of the AC voltage Vac is + 750V. Therefore, the developing roller 40 when the recovery waveform portion 54 is applied is at a high potential by +1200 V with respect to the electrostatic latent image non-image portion (Vpc = −450 V) in the developing region 46, and the potential difference is static. It is larger than the potential + 750V with respect to the electrostatic latent image portion (Vpc = 0V). Therefore, the defective toner 60 adhering to the electrostatic latent image non-image portion is applied with a larger electrostatic force toward the developing roller 40 than the normal toner adhering to the electrostatic latent image portion, and the static electricity Collected by the developing roller 40 by force. At this time, a weak electrostatic force also acts on the normal toner adhering to the electrostatic latent image portion toward the developing roller 40, and the electrostatic force acts on the physical adhesion force between the normal toner and the photoconductor 12 and the electric force. Therefore, the normal toner is not collected by the developing roller 40 and is held in the electrostatic latent image portion.

  In the above description, in order to facilitate the understanding of the invention, specific values of the voltage of each part and the photosensitive member potential (electrostatic latent image image part and non-image part potential) in the AC waveform are given. These numerical values are merely examples, and the scope of the invention should not be construed as being limited to specific numerical values.

Experiment 1

  The conditions of the waveform of the AC voltage Vac necessary for obtaining an image having an appropriate density without generating a discharge between the photosensitive member 12 and the developing roller 40 were obtained by experiments. The contents of the experiment will be specifically described below.

(1) Equipment used:
The image forming apparatus used in the experiment is a magicolor 2300DL manufactured by Minolta Co., Ltd. In the image forming apparatus, a cylindrical photosensitive member having a diameter of 30 mm was used as the photosensitive member, and a cylindrical roller having a diameter of 16 mm was used as the developing roller. The moving speed (system speed) of the photoconductor was set to 100 mm / sec, and the moving speed of the developing roller was set to 1.5 times that of the photoconductor. These conditions are common to all experiments described later.

(2) Setting conditions:
The development gap between the photoreceptor and the developing roller was set to 220 μm. As shown in FIG. 2, the waveform of the AC voltage applied between the photosensitive member and the developing roller is an exponential rectangular wave having an exponential waveform portion at the tip voltage rising portion of the recovery waveform portion. The peak-to-peak voltage Vpp of this AC voltage was changed in the range of about 1500 to 3000V. At this time, the peak voltage Vp1 of the development waveform portion and the peak voltage Vp2 of the recovery waveform portion were set so that the average of these two voltages became substantially constant even when the peak-to-peak voltage Vpp changed. The frequency f was switched stepwise every 500 Hz in the range of 1000 to 3500 Hz. The duty ratio D [%] of the recovery waveform portion was switched stepwise every 10% in the range of 40 to 80%. The exponential waveform of the recovery waveform portion can be expressed by Equation 3 and Equation 4, and the coefficient M of Equation 4 that defines the time constant τ of Equation 3 is 1/6, 1/5, 1/4, 1/3, 1 Switched to 6 levels of / 2, 1. The calibration value C was 3ln10 (ln: natural logarithm).

  For comparison, a typical rectangular wave AC voltage shown in FIG. 3 was applied between the photosensitive member and the developing roller, and an experiment similar to the exponential rectangular wave was performed. This rectangular wave is different from the above-described exponential rectangular wave in terms of the waveform, and the peak-to-peak voltage, peak voltage relationship, frequency, and duty ratio are the same as those described above.

(3) Measurement and evaluation:
An image is created under the above conditions, and the maximum limit peak-to-peak voltage Vpp (max) at which no discharge trace is generated on the image and the minimum limit peak-to-peak voltage Vpp (min) that can ensure an appropriate image density Difference (voltage range corresponding to the appropriate development range) was measured. In addition, the degree of fog generated in the image was also examined.

  The experimental results are shown in the table of FIG. In the table, for the proper development range, “◯” means that the proper development range obtained when the exponential rectangular wave was applied was larger than the proper development range obtained when the rectangular wave was applied. “×” means that the former proper development range was smaller than the latter proper development range. For fog, “O” means that the degree of fog generated when an exponential rectangular wave was applied was smaller than the degree of fog generated when a square wave was applied, and “X” was the former. This means that the degree of fogging was greater than that of the latter. Needless to say, the smaller the degree of fog, the better the image.

Therefore, it can be understood from the results in the table that when an exponential rectangular wave AC voltage is used, it is preferable to set the conditions within the following range.
Frequency f [Hz]: 1500 ≦ f ≦ 3000
Duty ratio D [%]: 40 ≦ D ≦ 80
M: 1/5 ≦ M ≦ 1/2
Calibration value C: 3ln10

Experiment 2

  The developing gap between the photosensitive member and the developing roller is set to 135 μm (Example 1), 180 μm (Example 2), and 220 μm (Example 3) so that the same image density can be obtained for each condition. Further, the duty ratio D [%] of the recovery waveform portion in the exponential rectangular wave was adjusted to 62%, 60%, and 56%. For all conditions, the coefficient M was set to 1/3, the AC voltage frequency f was set to 2000 Hz, and the calibration value C was set to 3ln10. Then, as in Experiment 1, the maximum limit peak-to-peak voltage Vpp (max) at which no discharge trace is generated on the image and the minimum limit peak-to-peak voltage Vpp (min) that can ensure an appropriate image density are obtained. Asked. The results are shown in FIG. For comparison, peak-to-peak voltages Vpp (max) and Vpp (min) were also obtained for the three rectangular waves under the same conditions (same development gap, duty ratio, frequency) (Comparative Examples 1 and 2). 3). The results of this experiment are also shown in FIG.

  As shown in FIG. 6, the minimum limit peak-to-peak voltage Vpp (min) of the example and the comparative example was equal for each development gap. On the other hand, with respect to the maximum limit peak-to-peak voltage Vpp (max), the example exceeded that of the comparative example. As a result, an appropriate development range [Vpp (max) −Vpp (min)] larger than that of the comparative example was obtained in the examples.

Experiment 3

  The AC voltage of the exponential rectangular wave (Example 4) and the rectangular wave (Comparative Example 4), and as shown in FIG. 7, the development waveform portion and the recovery waveform portion both have an exponential waveform portion at their tip voltage rising portions. (Hereinafter, this waveform is referred to as “pseudo exponential wave”.) Using the AC voltage of (Comparative Example 5), the appropriate development ranges were compared. The development gap was 220 μm, the AC voltage frequency f was 2000 Hz, and the duty ratio D of the recovery waveform portion was 62%. For the exponential rectangular wave and the pseudo exponential wave, the coefficient M was set to 1/3 and the calibration value C was set to 3ln10.

  The result of the experiment is shown in FIG. As shown in the figure, in the same manner as in Experiment 2 described above, a larger appropriate development range was obtained for Example 4 than for Comparative Example 4. Further, in the case of the comparative example 5 using the pseudo exponential wave, the maximum peak-to-peak voltage Vpp (max) is larger than the comparative example 4 using the simple rectangular wave and is equivalent to the embodiment 4 using the exponential rectangular wave. was gotten. However, the minimum peak-to-peak voltage Vpp (min) of Comparative Example 5 increased more than Comparative Example 4 and Example 4. Therefore, the result that the proper development range of Comparative Example 5 is not only narrower than that of Example 4 but also narrower than the proper development range of Comparative Example 4 was obtained.

Finally, a time constant τ indicating the shape of the exponential waveform portion will be described with reference to FIG. In the figure, the AC voltage recovery waveform portion 62 is shown with the voltage rising portion at the tip thereof being a rectangular waveform portion 64 (dotted line) and those having exponent waveform portions 66 and 68. The exponent waveform portions 66 and 68 have different time constants, and the time constant of the exponent waveform portion 66 is smaller than that of the exponent waveform portion 68. The time constant τ includes a dimensionless coefficient M and a calibration value C, as shown in the following formula 5. By adjusting these two values M and C, the waveform of the exponent waveform portion is adjusted. More specifically, the exponent waveform portion does not approximate the rectangular waveform portion 64 (the time constant τ does not become too small), and the time to reach the maximum voltage Vp2 does not become long (time constant τ The exponent waveform portion is set by adjusting M and C within a range in which the value does not become too large. This is because when the exponent waveform portion approximates the rectangular waveform portion 64, it becomes the same as the rectangular wave of the comparative example in the experiment, and when the time to reach the maximum voltage Vp2 increases, the operation time of the maximum voltage Vp2 increases. This is because the toner becomes shorter and the defective toner 60 shown in FIG. 2 cannot be sufficiently collected. In a more preferred embodiment of the present invention, the calibration value C is fixed at 3ln10. Thereby, the setting of the time constant τ is simplified.

1 is a schematic view of an image forming apparatus according to the present invention. It is a figure which shows the exponential rectangular wave which concerns on this invention. It is a figure which shows a rectangular waveform. It is a figure which shows an exponential waveform. 6 is a chart showing the results of Experiment 1. It is a figure which shows the result of Experiment 2. It is a figure which shows a pseudo exponential wave. It is a figure which shows the result of the experiment 3. FIG. It is a figure of the collection | recovery waveform part explaining a time constant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus, 12 Photoconductor, 14 directions, 16 Charging apparatus, 18 Exposure apparatus, 20 Developing apparatus, 22 Sheet, 24 Transfer apparatus, 26 Cleaning apparatus, 30 Housing, 32 Toner accommodating part, 34 Toner, 36 Pumping roller, 38 direction, 40 developing roller, 42 direction, 44 toner supply area, 46 developing area, 48 blade, 50 power supply, 52 first waveform part, 54 second waveform part, 56 tip voltage rise part, 58 tip voltage rise Part, 60 defective toner, 62 recovery waveform part, 64 rectangular waveform part, 66 exponential waveform part, 68 exponential waveform part

Claims (3)

In an image forming apparatus for developing an electrostatic latent image carried on an electrostatic latent image carrier with a developer supplied from the developer carrier,
An AC voltage is applied between the electrostatic latent image carrier and the developer carrier,
The waveform of the AC voltage includes a first waveform portion for urging the developer from the developer carrier to the electrostatic latent image carrier and the developer from the electrostatic latent image carrier to the developer carrier. Alternating second waveform portions to be energized,
The voltage rise at the tip of the first waveform portion approximates a rectangular waveform tip voltage rise,
2. An image forming apparatus according to claim 1, wherein a voltage rising portion at a tip of the second waveform portion approximates a tip voltage rising portion having an exponential waveform. In an image forming apparatus for developing an electrostatic latent image carried on an electrostatic latent image carrier with a developer supplied from the developer carrier,
An AC voltage is applied between the electrostatic latent image carrier and the developer carrier,
The waveform of the AC voltage includes a first waveform portion for urging the developer from the developer carrier to the electrostatic latent image carrier and the developer from the electrostatic latent image carrier to the developer carrier. Alternating second waveform portions to be energized,
The voltage rise at the tip of the first waveform portion approximates a rectangular waveform tip voltage rise,
The frequency of the AC voltage is f [Hz],
The duty ratio of the second waveform portion is D [%],
The maximum voltage of the second waveform portion is Vmax [volt],
When the voltage of the voltage rising portion in the second waveform portion is V (volts),
The frequency f [Hz] is in a range of 1500 ≦ f ≦ 3000,
The duty ratio D [%] is in the range of 40 ≦ D ≦ 80,
The voltage V [volts] of the voltage rise part is expressed by the following equation:

The time constant τ in the above equation is expressed by the relationship of the following equation:

The calibration value C in the above formula is in the range of the following formula,

An image forming apparatus satisfying the requirements. The image forming apparatus according to claim 2, wherein the calibration value C is 3ln10.

Images