JP4480680B2 - Charging device for image forming apparatus - Google Patents

Description

  The present invention includes a charging member arranged in contact with or close to an image carrier and charging the image carrier, and a high voltage generation circuit that generates an oscillating voltage applied to the charging member and superimposed with a DC voltage and an AC voltage. Further, the present invention relates to a charging device for an image forming apparatus that includes a voltage control unit that controls a peak-to-peak voltage value Vpp of the AC voltage.

  In recent years, from the viewpoint of low pressure process, low ozone generation, low cost, etc., a charging member such as a roller type or a blade type is arranged in contact with or close to the surface of the image carrier, and a DC voltage and an AC voltage are applied to the charging member. A contact charging method in which the surface of an image carrier is uniformly charged by applying a superposed vibration voltage is becoming mainstream. Here, the vibration voltage is not limited to a sine wave, but may be any vibration waveform that changes periodically, such as a rectangular wave, a triangular wave, and a pulse wave.

  As a charging device that employs such a contact charging method, Patent Document 1 discloses that when the voltage value Vpp between peaks of an alternating voltage among vibration voltages is increased, the charging voltage of the image carrier increases in proportion thereto, In order to secure the uniformity of charging, the charging potential is saturated when the peak-to-peak voltage value Vpp reaches about twice the charging start voltage due to the DC voltage, and the charging potential does not change even if the voltage is increased further. It is necessary to apply an oscillating voltage having a peak-to-peak voltage more than twice the charging start voltage when applying a DC voltage determined by various characteristics of the image carrier, and the resulting charging voltage is the DC component of the applied voltage. Are disclosed.

  Therefore, Patent Document 2 discloses that there is no problem such as deterioration of the image carrier, toner fusion, image flow, etc. by always generating a constant amount of discharge regardless of variations in the resistance value of the charging member due to the environment and manufacturing. Discharge to the image carrier when a DC voltage is applied to the charging member, provided with means for measuring the AC current value flowing to the charging means via the image carrier for the purpose of achieving uniform charging. When the starting voltage is Vth, at the time of non-image formation, the current value when a peak-to-peak voltage less than twice the Vth of at least one point is applied to the charging means, and at least twice the Vth of at least two points A charging control method is disclosed in which the current value when the above peak-to-peak voltage is applied is measured, and the peak-to-peak voltage of the alternating voltage applied to the charging means during image formation is determined based on the measured alternating current value.

  More specifically, the peak-to-peak voltage-alternating current obtained by connecting 0 to the current value when a peak-to-peak voltage less than twice the Vth of one point is applied to the charging means with D being a predetermined constant. By comparing the function fI1 (Vpp) with the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when the peak-to-peak voltage more than twice the Vth of at least two points is applied, fI2 The peak-to-peak voltage value at which (Vpp) −fI1 (Vpp) = D is determined as a desired discharge current amount, and the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is determined based on the determined peak-to-peak voltage value. Constant voltage control is performed.

JP-A 63-149668 JP 2001-201921 A

  However, the above-described technique described in Patent Document 2 is applied to a charging member formed of an epichlorohydrin rubber charging roller that is brought into contact with an image carrier having a thickness of 20 μm and having a photosensitive layer of amorphous silicon having a thickness of 20 μm with a pressing force of 1 Kgf. As shown in FIG. 8, in a high-temperature and high-humidity environment where the electric resistance value of the charging member is low, a desired discharge current value D is obtained from the measured alternating current value characteristics. However, in a normal temperature and normal humidity environment and a low temperature and low humidity environment, it was found that it is difficult to obtain a desired discharge current value D based on the measured AC current value characteristics.

  Such a situation is considered to depend on various fluctuation factors depending on variations in characteristics of the members constituting the charging device, fluctuations in the surrounding environment, and the type of the image carrier, and in various usage environments of the image forming apparatus. In order to appropriately set the peak-to-peak voltage value, the need for further improvement has been desired.

  In view of the above-described conventional problems, an object of the present invention is an image forming apparatus capable of setting an accurate peak-to-peak voltage value with high accuracy regardless of environmental fluctuations such as temperature and humidity, and secular changes of an image carrier or a charging member. The charging device is provided.

In order to achieve the above object, the first characteristic configuration of the charging device of the image forming apparatus according to the present invention is arranged in contact with or in close proximity to the image carrier as described in claim 1 of the claims. A charging member that charges the image carrier; a high-voltage generating circuit that generates an oscillating voltage in which a DC voltage and an AC voltage are superimposed; and a voltage that controls a peak-to-peak voltage value Vpp of the AC voltage. A charging device for an image forming apparatus including a control unit, wherein the peak-to-peak voltage value Vpp and a DC current value Idc between the charging member and the image carrier are expressed on a two-dimensional coordinate system. Two different low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) that are assumed to be lower than the voltage value at the inflection point that appears when the peak-to-peak voltage value Vpp is boosted with respect to the assumed characteristic curve. And said strange The high-voltage side peak-to-peak voltage value Vpp (C) that is assumed to be higher than the voltage value at the point includes preset table data based on the variation factor of the charging characteristics by the charging member, and the voltage control means , it said selected according to the table data low pressure side peak voltage value Vpp (a), Vpp DC current value Idc is measured upon application of the (B) (a), the coordinate a obtained on the basis of Idc (B) (Vpp (a), Idc ( a)), B and the straight line L1 passing through the (Vpp (B), Idc ( B)), was applied to selected the high pressure side peak voltage value Vpp (C) according to said table data At the intersection of a straight line L2 that passes through the coordinates C (Vpp (C), Idc (C)) obtained on the basis of the DC current value Idc (C) that is sometimes measured and is parallel to the coordinate axis representing the peak-to-peak voltage value Vpp. It lies in selecting controlling the peak-to-peak voltage value Vpp to respond as appropriate peak-to-peak voltage value Vpp (O).

  While examining the setting of the appropriate peak-to-peak voltage value Vpp (O), the present inventors have conducted various experiments and the charging member and the image generated by the vibration voltage applied to the charging member by the high-voltage generation circuit. When the DC current value Idc between the carriers was measured, as shown in FIG. 2, when the peak-to-peak voltage value Vpp was gradually increased from a low level, the DC current value Idc increased with a substantially constant slope, and thereafter Transition at a slope lower than the constant slope or zero slope, the surface potential of the image carrier when the peak-to-peak voltage value Vpp is changed, and the direct current value Idc are in a proportional relationship; and Assuming that an inflection point is an inflection point, the position of the inflection point varies depending on environmental conditions, but the peak-to-peak voltage value Vpp is higher than the inflection point. Potential has been confirmed to be stable.

  Accordingly, the peak-to-peak voltage value Vpp is adjusted to an inflection point or a value slightly higher than the inflection point while monitoring the DC current value Idc, so that the desired surface potential can be stably adjusted. Assuming that the relationship between the peak-to-peak voltage value Vpp and the direct current value Idc is an assumed characteristic curve as shown by the solid line in FIG. 3, two different peak-to-peak voltage values Vpp assumed to be lower than the inflection point P are obtained. Detected when a straight line L1 passing through two points A and B indicating a DC current value Idc detected when applied and one peak-to-peak voltage value Vpp assumed to be higher than the inflection point P are applied. An intersection point with a straight line L2 that passes through one point C indicating the direct current value Idc and is parallel to the horizontal axis (zero tilt) can be obtained as the approximate inflection point P ′. That is, by approximating the characteristic on the high voltage side from the inflection point P as the straight line L2, the approximate inflection point P ′ is obtained by applying a voltage at only one point on the high voltage side. By selecting the peak-to-peak voltage value Vpp corresponding to the approximate inflection point P ′ as the appropriate peak-to-peak voltage value Vpp (O), the subsequent surface potential can be stably controlled. is there. Here, when the assumed characteristic curve has a positive slope on the high voltage side from the inflection point P, the appropriate peak-to-peak voltage value Vpp (O) obtained is a value slightly higher than the voltage value at the inflection point P. As a result, stability is increased.

When the appropriate peak-to-peak voltage value Vpp (O) is obtained in this way, only one sampling point is required on the high voltage side from the inflection point P. The appropriate peak-to-peak voltage value Vpp (O) can be obtained more quickly than when obtaining a straight line, and the peak-to-peak voltage value Vpp applied at this time is also determined from the inflection point P of the assumed characteristic curve. Since a slightly higher value can be selected, it is possible to avoid the deterioration of the image carrier and the charging member due to the generation of discharge products caused by applying an unnecessarily high voltage .

Virtual constant characteristics even when the position of the inflection point on the curve is a case that varies by various fluctuation factors, it corresponds set in advance table data the low pressure side peak voltage value Vpp (A), Vpp (B ) And the high-voltage side peak-to-peak voltage value Vpp (C), the appropriate peak-to-peak voltage value Vpp (O) can be obtained appropriately.

In the second feature configuration, as described in claim 2, in addition to the first feature configuration described above, the table data includes an environmental temperature, an environmental humidity, or a cumulative use time of the charging member, or those The table data is set based on any combination of the above.

  According to the above configuration, the table data set based on each of the environmental temperature, the environmental humidity, or the cumulative usage time of the charging member, which is a main factor of the variation factor of the inflection point, or any combination thereof. Thus, even when the assumed characteristic curve fluctuates due to them, the appropriate peak-to-peak voltage value Vpp (O) can be obtained appropriately.

The third feature structure, as described in the claim 3, in addition to the first or second feature configuration described above, the voltage control means, the image forming processing period out by the image forming apparatus The point is that the appropriate peak-to-peak voltage value Vpp (O) is selected and controlled.

  According to the configuration described above, the selection control of the appropriate peak-to-peak voltage value Vpp (O) is performed outside the image forming process period, so that a good image can be always formed and the processing time of the image forming process is affected. Therefore, the productivity of the image forming apparatus is not reduced.

  As described above, according to the present invention, it is possible to provide a charging device for an image forming apparatus capable of setting an appropriate peak-to-peak voltage value regardless of environmental fluctuations such as temperature and humidity, and aging of an image carrier or a charging member. I was able to do that.

  Hereinafter, the charging device 1 of the image forming apparatus according to the present invention will be described. As shown in FIG. 1, the charging device 1 is incorporated in an image forming apparatus that employs an electrophotographic system, and is placed in contact with an image carrier 2 to charge the image carrier 2 and the charging member 3. A high voltage generating circuit 4 that generates an oscillating voltage that is applied to the member 3 and has a DC voltage and an AC voltage superimposed thereon, and a voltage control means 5 that controls the peak-to-peak voltage value Vpp of the AC voltage.

  The image carrier 2 is composed of a photoreceptor drum having a photoreceptor in which an amorphous silicon layer, which is a positively chargeable photoconductor, is deposited on the surface of an aluminum cylinder, and is fixed around a center support shaft by a driving device (not shown). It is configured to be driven at high speed.

  The charging member 3 is constituted by a charging roller 3 in which a cored bar 31 is covered with an chlorohydrin rubber layer 32 that is a conductive elastic material.

  The high voltage generation circuit 4 includes an AC constant voltage power supply 41 that generates a predetermined sine wave AC voltage from a low voltage DC voltage modulated in a pulse form using a step-up transformer, and a low voltage direct current modulated in a pulse form using a step-up transformer. A DC constant voltage power source 42 that rectifies a sinusoidal AC voltage generated from the voltage by a rectifier and generates a predetermined DC voltage, and a DC current that detects a DC current value Idc between the charging member 3 and the image carrier 2. The current detection means 43 is provided.

  As shown in FIG. 4, the voltage control means 5 performs an assumption characteristic curve on a two-dimensional coordinate representing a relationship between the peak-to-peak voltage value Vpp and the direct current value Idc between the charging member and the image carrier. When two different low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) that are assumed to be lower than the voltage value at the inflection point that appears when boosting the peak-to-peak voltage value Vpp are applied. A straight line L1 passing through coordinates A (Vpp (A), Idc (A)), B (Vpp (B), Idc (B)) obtained based on the measured DC current values Idc (A), Idc (B). And a coordinate C (Vpp obtained based on a DC current value Idc (C) measured when a high-voltage-side peak-to-peak voltage value Vpp (C) assumed to be higher than the voltage value at the inflection point is applied. (C), Idc (C)) through the peak-to-peak voltage Selectively controlling the peak-to-peak voltage value Vpp corresponding to the intersection of the parallel line L2 coordinate axes representing the Vpp as the appropriate peak-to-peak voltage value Vpp (O).

  The two different low voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) and the high voltage side peak-to-peak voltage value Vpp (C) are based on the variation factors of the charging characteristics of the charging member 3. Is set in advance in the table data 71 stored in the storage unit 7, and in the table data 71 in the present embodiment, as shown in FIG. 5, the environmental temperature which is a variation factor of the charging characteristics of the charging member 3 is used. And the peak-to-peak voltages Vpp (A), Vpp (B), and Vpp (C) are set in advance based on the environmental humidity.

The voltage control means 5 is based on the environmental temperature and environmental humidity of the charging member 3 output from the temperature sensor 60 and the humidity sensor 61 provided in the image forming apparatus outside the image forming process period of the image forming apparatus. The peak-to-peak voltage values Vpp (A), Vpp (B), and Vpp (C) are selected according to the table data 71, and the peak-to-peak voltage value Vpp corresponding to the intersection of the straight lines L1 and L2 is selected as the appropriate peak-to-peak voltage value. Selection control is performed as Vpp (O).

  Here, the table data 71 in the present embodiment is obtained by presetting the peak-to-peak voltage values Vpp (A), Vpp (B), and Vpp (C) based on the environmental temperature and the environmental humidity. However, the present invention is not limited to this, and the peak-to-peak voltage values Vpp (A), Vpp (B), and Vpp are based on the environmental temperature, environmental humidity or cumulative usage time of the charging member 3 or any combination thereof. (C) may be set in advance, and the voltage control means 5 is set based on the environmental temperature, the environmental humidity or the accumulated usage time of the charging member 3, or any combination thereof. The peak-to-peak voltage values Vpp (A), Vpp (B), and Vpp (C) may be selected from the table data.

  Hereinafter, the selection procedure of the appropriate peak-to-peak voltage value Vpp (O) of the vibration voltage applied to the charging member 3 will be described with reference to the flowchart shown in FIG.

  The voltage control means 5 has two low voltage side peak voltage values Vpp (A) and Vpp (B) different from the environmental temperature and the environmental humidity according to the table data 71, and a high voltage side peak voltage value Vpp (C ) Is determined (S1).

  The high voltage generation circuit 4 applies a vibration voltage of [Vdc + Vpp (A)] to the charging member 3 (S2), and a DC current value Idc (A) between the charging member 3 and the image carrier 2 is converted to the DC current. The detection means 43 detects (S3).

  Similarly, the high voltage generation circuit 4 applies a vibration voltage of [Vdc + Vpp (B)] to the charging member 3 (S4), and generates a DC current value Idc (B) between the charging member 3 and the image carrier 2. The DC current detection means 43 detects (S5), and assumes an assumed characteristic curve on a two-dimensional coordinate representing the relationship between the peak-to-peak voltage value Vpp and the DC current value Idc between the charging member 3 and the image carrier 2. On the other hand, the voltage control means 5 has a lower voltage than the voltage value at the inflection point from the coordinate A (Vpp (A), Idc (A)) and the coordinate B (Vpp (B), Idc (B)). A straight line L1 indicating the characteristic is derived (S6).

  Subsequently, the high voltage generation circuit 4 applies a vibration voltage of [Vdc + Vpp (C)] to the charging member 3 (S7), and generates a DC current value Idc (C) between the charging member 3 and the image carrier 2. The DC current detection means 43 detects (S8), and the voltage control means 5 passes through the coordinates C (Vpp (C), Idc (C)) and is parallel to the coordinate axis representing the peak-to-peak voltage value Vpp, and A straight line L2 indicating characteristics on the high voltage side from the voltage value at the inflection point is derived (S9), and the peak-to-peak voltage value Vpp corresponding to the intersection of the straight lines L1 and L2 is selected as the appropriate peak-to-peak voltage Vpp (O). (S10).

Hereinafter, the procedure of image formation in the image forming apparatus will be described with reference to the flowchart shown in FIG.

  When the image forming apparatus is started up (S1), the voltage control unit 5 acquires the environmental temperature and the environmental humidity from the temperature sensor 60 and the humidity sensor 61 (S2), and the appropriate peak voltage value Vpp (O). Is selected (S3).

  Here, the time of starting indicates when the image forming apparatus is powered on, when returning from the sleep state, and when the cover door of the image forming apparatus is changed from the open state to the closed state.

  When a predetermined time has elapsed after the selection of the appropriate peak-to-peak voltage value Vpp (O) (S4), the voltage control means 5 calculates the environmental temperature and the environmental humidity from the temperature sensor 60 and the humidity sensor 61. Obtain (S2) and select the appropriate peak voltage value Vpp (O) again (S3).

  When the operator presses a print switch from an operation unit (not shown) of the image forming apparatus (S5), the voltage control unit 5 acquires the environmental temperature and the environmental humidity from the temperature sensor 60 and the humidity sensor 61. Then (S6), it is confirmed whether or not there is a change in the environmental temperature and the environmental humidity when the appropriate peak voltage value Vpp (O) is selected (S7).

  If there is a change in the environmental temperature and the environmental humidity (S7), the voltage control means 5 again selects the appropriate peak-to-peak voltage value Vpp (O) (S8), and the high voltage generation circuit 4 is [Vdc + Vpp (O )] Is applied to the charging member 3 (S9), and an image forming operation is executed (S10).

  When calibration such as toner density adjustment is performed during execution of the image forming operation (S11), the voltage control unit 5 acquires the environmental temperature and the environmental humidity from the temperature sensor 60 and the humidity sensor 61. Then, the appropriate peak voltage value Vpp (O) is selected again (S8).

  Another embodiment will be described below.

  In the configuration described above, a photosensitive drum having a photosensitive body in which an amorphous silicon layer, which is a positively chargeable photoconductor, is deposited on the surface of an aluminum cylinder is used as the image carrier 2. An OPC drum that is a photoconductor or another type of photoconductive semiconductor drum in which the photoconductor is selenium or the like may be employed. In this case, depending on the charging characteristics of the photoconductor, You may change suitably the positive / negative polarity of the oscillating voltage applied to the charging member 3. FIG.

  In the above-described configuration, the charging member 3 is configured as a charging roller in which the core metal 31 is coated with the chlorohydrin rubber layer 32 that is a conductive elastic material. However, the charging member 3 may be a fur brush, a felt, a cloth, or the like. It may be composed of a shape / material.

  In the above-described configuration, the charging member 3 is arranged in contact with the image carrier 2, but may be arranged in close proximity.

  In the above configuration, the DC current detecting means 43 is incorporated in the high voltage generation circuit 4, but the DC current value Idc between the charging member 3 and the image carrier 2 can be detected at a location where the DC current value Idc can be detected. What is necessary is just to install the detection means 43. FIG.

  In the above-described configuration, the peak-to-peak voltage value with respect to an assumed characteristic curve on a two-dimensional coordinate representing the relationship between the peak-to-peak voltage value Vpp and the DC current value Idc between the charging member 3 and the image carrier 2. DC current value Idc measured when two different low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) assumed to be lower than the voltage value of the inflection point appearing when Vpp is boosted (A), a straight line L1 passing through coordinates A (Vpp (A), Idc (A)), B (Vpp (B), Idc (B)) obtained based on Idc (B), and the inflection point Coordinates C (Vpp (C), Idc (C) obtained based on a DC current value Idc (C) measured when a high-voltage side peak-to-peak voltage value Vpp (C) that is assumed to be higher than the voltage value is applied. )) Through the coordinate axis representing the peak-to-peak voltage value Vpp The peak-to-peak voltage value Vpp corresponding to the intersection with the parallel straight line L2 is selectively controlled as the appropriate peak-to-peak voltage value Vpp (O). However, an error is corrected to the peak-to-peak voltage value Vpp corresponding to the intersection. A configuration in which a product of a coefficient is selectively controlled as the appropriate peak-to-peak voltage value Vpp (O).

  In the above-described configuration, the waveform of the alternating voltage component of the oscillating voltage has been described as being a sine wave, but may be a rectangular wave, a triangular wave, a pulse wave, or the like.

  The charging device 1 provided in the image forming apparatus having the above-described configuration can be applied to any image forming apparatus of a color machine or a monochrome machine, and in a plurality of charging apparatuses used in a tandem type image forming apparatus or the like. A configuration in which the present invention is applied to each of the charging devices may be employed.

  The above-described embodiments are merely examples of the present invention, and the scope of the present invention is not limited by the description, and the specific configuration of each part is appropriately changed within the scope of the effects of the present invention. It goes without saying that it can be done.

1 is a block diagram of a partial configuration of an image forming apparatus according to an embodiment of the present invention. (A) A graph showing the relationship between the peak-to-peak voltage value at a DC voltage value of 400 [V] and the surface potential of the image carrier, (b) the peak-to-peak voltage value of the vibration voltage at the DC voltage value of 400 [V], and charging Graph showing the relationship of the DC current value between the member and the image carrier The figure explaining the relationship between the peak-to-peak voltage value Vpp of the oscillating voltage at the inflection point and the peak-to-peak voltage value Vpp at the intersection obtained by the present invention. Explanatory drawing of straight line L1, L2 calculated | required by this invention, coordinate A, B, C, and said appropriate peak-to-peak voltage value Vpp (O). Illustration of table data Flow chart used to explain selection procedure of appropriate peak-to-peak voltage value Vpp (O). Flowchart used to explain image formation execution procedure Graph showing peak-to-peak voltage value and change in alternating current value between the charging member and the image carrier when the peak-to-peak voltage value is changed

1: Charging device 2: Image carrier (photosensitive drum)
3: Charging member (charging roller)
4: High voltage generation circuit 5: Voltage control means 7: Storage unit 41: AC constant voltage power supply 42: DC constant voltage power supply 43: DC current detection means 60: Temperature sensor 61: Humidity sensor 71: Table data

Claims (3)

A charging member arranged in contact with or close to the image carrier to charge the image carrier; a high-voltage generating circuit that generates an oscillating voltage applied to the charging member and superimposed with a DC voltage and an AC voltage; and the AC voltage A charging device of an image forming apparatus comprising a voltage control means for controlling a peak-to-peak voltage value Vpp of
Appears when the peak-to-peak voltage value Vpp is boosted with respect to an assumed characteristic curve on a two-dimensional coordinate representing the relationship between the peak-to-peak voltage value Vpp and the DC current value Idc between the charging member and the image carrier. Two different low-voltage-side peak voltage values Vpp (A) and Vpp (B) that are assumed to be lower than the voltage value at the inflection point, and the high-voltage-side peak that is assumed to be higher than the voltage value at the inflection point. The inter-voltage value Vpp (C) includes preset table data based on a variation factor of charging characteristics by the charging member,
Said voltage control means, said selected according to the table data low pressure side peak voltage value Vpp (A), Vpp DC current value Idc is measured upon application of the (B) (A), based on the Idc (B) resulting Te coordinates a (Vpp (a), Idc (a)), B (Vpp (B), Idc (B)) and the straight line L1 passing through said selected according to the table data the high pressure side peak voltage value Vpp ( C) A straight line parallel to the coordinate axis representing the peak-to-peak voltage value Vpp through the coordinates C (Vpp (C), Idc (C)) obtained on the basis of the DC current value Idc (C) measured when applied. A charging device of an image forming apparatus that selectively controls a peak-to-peak voltage value Vpp corresponding to an intersection with L2 as an appropriate peak-to-peak voltage value Vpp (O). The table data, the environmental temperature of the charging member, the humidity or the cumulative usage time or a charging device according to claim 1 Symbol placement of the image forming apparatus is a table data that is set on the basis of their any combination. 3. The charging device for an image forming apparatus according to claim 1, wherein the voltage control unit selectively controls the appropriate peak-to-peak voltage value Vpp (O) outside an image forming process period by the image forming apparatus.

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