JP3960294B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus capable of duplex printing and multiple printing.

  As such an image forming apparatus, an image carrier on which a toner image is formed on the surface, a transfer rotator that is disposed in contact with the image carrier to form a transfer nip portion, and a transfer bias is applied to the transfer rotator. A transfer bias applying means, and transferring the toner image on the surface of the image bearing member to the surface of the recording material by applying the transfer bias to the transfer rotator by the transfer bias applying means while sandwiching and transporting the recording material to the transfer nip portion. In the image forming apparatus, there are a constant current control method and a constant voltage control method as a control method of the transfer bias applying means, and the resistance value of the transfer rotator is switched between the constant current control method and the constant voltage control method of the transfer bias applying means. There is an image forming apparatus that is adapted to meet the requirements (for example, see Patent Document 1).

Further, in this image forming apparatus, switching between the constant current control method and the constant voltage control method of the transfer bias applying means is performed at the time of passing the first side and at the time of passing the second side in double-sided printing. .
JP 2000-221810A

  By the way, in the case of double-sided / multiple printing, the resistance value of the first surface (front) printed paper increases because moisture content is evaporated by heating by the fixing means. When printing on the second side (back side) of the first side printed paper whose resistance value has been increased, transfer to a transfer rotator (transfer roller) is required to perform high-quality transfer without causing transfer defects. It is necessary to perform bias optimization.

  In the image forming apparatus described in the above publication, switching between the constant current control method and the constant voltage control method of the transfer bias application unit is performed based on the resistance value of the transfer rotator, but the ambient environment conditions such as temperature and humidity, It is required to set the transfer bias more appropriately according to conditions such as the size and thickness of the paper.

  The present invention has been made paying attention to such a situation, and an object thereof is to provide an image forming apparatus capable of setting a more optimal transfer bias in accordance with conditions such as ambient environmental conditions and paper size. And

In order to achieve the above object, an image forming apparatus according to the present invention is capable of double-sided and multiple printing, and nips a sheet together with an image carrier and the image carrier to form an image of the image carrier on the paper. A transfer means for transferring; a current value detecting means for detecting a current value flowing into the transfer means; a transfer bias applying means for applying a transfer voltage to the transfer means; and a paper during transfer in printing on the first surface of the paper. A storage means for storing an average inflow current value to the transfer means in the nip, a temperature sensor for detecting the temperature inside the apparatus, and / or a humidity sensor for detecting the humidity inside the apparatus ,
The transfer bias applying means is detected by the temperature sensor and a current value flowing into the transfer means detected by the current value detecting means by applying a test voltage to the transfer means before printing on the first surface. The transfer voltage is determined based on temperature and / or humidity detected by the humidity sensor, and the determined transfer voltage is applied to the transfer means during printing on the first surface. Controlling the current value while detecting the current value flowing into the transfer means by the current value detecting means so as to maintain the voltage,
Further, the transfer bias applying means applies the same current value as the average inflow current value stored in the storage means while applying the determined transfer voltage to the transfer means during printing of the second surface. The voltage value applied to the transfer unit is controlled so as to be maintained .

When the transfer means is a transfer roller in contact with the image carrier, the volume resistance value of the transfer roller is preferably 2 × 10 ⁸ Ωcm or more.

  According to the present invention, the transfer bias can be set more optimally according to the ambient environment conditions such as temperature and humidity, and the conditions such as the paper size and thickness, thereby further improving the print image quality. Can be made.

Further, by adopting the configuration of claim 2 (increasing the volume resistance value of the transfer roller), the lateral flow of charges from the sheet to the image carrier can be prevented even when the resistance value of the sheet increases during the second surface transfer. Can be prevented.

  Hereinafter, the present invention will be described in more detail with reference to embodiments.

  FIG. 1 shows a block diagram of a configuration example of a facsimile machine as an example of an image forming apparatus according to the embodiment. This facsimile apparatus is configured as a multifunction machine having both a facsimile function and a copy function.

  The facsimile apparatus includes an MPU (control unit) 1, an NCU (Network Control Unit) 2, a MODEM 3, a ROM 4, a RAM 5, an image memory (DRAM) 6, and a CODEC (encoder / decoder). : Coder and Decoder) 7, an operation unit 8, a scanner 9, a printer interface 10, and a printer controller 12.

  The MPU 1 controls each part constituting this facsimile apparatus according to a program stored in the ROM 4. The NCU 2 controls the connection with the telephone line network (PSTN), and has a function of sending a dial signal corresponding to the telephone number (including the FAX number) of the other party and a function for detecting an incoming call. . MODEM3 is an ITU (International Telecommunication Union) -T recommendation T.264. 30 based on the facsimile transmission control procedure according to 17, V. 27ter, V.I. The transmission data is modulated and the received data is demodulated in accordance with 29. Alternatively, in addition to these, V.P. 34, modulation of transmission data and demodulation of reception data are performed.

  The ROM 4 stores a program for controlling the entire facsimile apparatus. The RAM 5 temporarily stores data and the like. The image memory 6 temporarily stores received image data and image data read by the scanner 9. The CODEC 7 encodes (encodes) the read image data by the MH, MR, MMR method, etc., and decodes the received image data.

  The operation unit 8 is used by the user to give instructions such as FAX transmission / reception and printing, and includes a numeric keypad, a one-touch key, a start key, and other keys. The scanner 9 reads image data of a document when performing copying or FAX transmission. The printer interface 10 receives print commands and data from a personal computer and sends them to the printer controller 12.

  The printer controller 12 controls the printer unit configured as shown in FIG. 2 (block diagram). The printer controller 12 has memory means (storage means) 12a for storing an average inflow current value to the transfer roller 29 in the paper nip during transfer in printing on the first surface of the paper.

  In the printer unit, a photosensitive drum (image carrier) 21 that is rotationally driven by a main motor 41 is disposed. Around the photosensitive drum 21, a scorotron charger 22 is disposed as a charging unit, and a predetermined positive charging voltage HVC is applied to the scorotron charger 22 by a charging voltage application circuit 23. The outer peripheral surface of the photosensitive drum 21 is uniformly charged to about +800 V by the scorotron charger 22 to which the positive charging voltage HVC is applied. In this embodiment, a scorotron charger 22 is provided as a charging means for charging the surface of the photosensitive drum 21 in a non-contact manner. Instead, a charging brush, sponge roller, solid roller for charging the surface of the photosensitive drum 21 in a contact state. Such a charging roller may be used.

  An LSU (laser scan unit) 24 as an exposure unit is disposed around the photosensitive drum 21 and downstream of the scorotron charger 22. In this LSU 24, image information is inputted, and in response to this, the scan laser beam output from the laser oscillation source is scattered by a polygon mirror rotated by a polygon motor, so that the outer peripheral surface of the photosensitive drum 21 corresponds to the image information. An electrostatic latent image is formed.

  The developing device disposed around the photosensitive drum 21 on the downstream side of the scorotron charger 22 includes a supply roller 25, a developing roller 26, and a blade 27. The supply roller 25 supplies toner to the developing roller 26 while charging the toner from a toner case containing positively charged toner. A predetermined supply voltage (+ 300V to + 700V) is supplied to the supply roller 25 by a development voltage application circuit 28. ) Is applied. The developing roller 26 which is in contact with the supply roller 25 and the photosensitive drum 21 and forms a developing nip portion between the photosensitive drum 21 is supplied with a predetermined developing voltage (+ 300V to + 700V, preferably about + 400V) is applied.

  The blade 27 elastically contacts the outer peripheral surface of the developing roller 26 and makes the layer thickness of the toner adhering to the outer peripheral surface of the developing roller 26 uniform. A bias voltage (+ 300V to + 700V) is applied.

Further, a transfer roller 29 serving as a transfer unit disposed around the photosensitive drum 21 on the downstream side of the developing unit is disposed so as to form a transfer nip portion with the outer peripheral surface of the photosensitive drum 21 with the sheet conveyance path F interposed therebetween. The main motor 41 is rotationally driven. A transfer voltage HVT is applied to the transfer roller 29 by a transfer voltage applying circuit (transfer bias applying means) 30. The current value flowing into the transfer roller 29 is detected by a current value detection circuit 51. The volume resistance value of the transfer roller 29 is preferably 2 × 10 ⁸ Ωcm or more, which will be described later.

  The transfer voltage application circuit 30 is based on the temperature inside the apparatus detected by the temperature sensor 34 and / or the humidity inside the apparatus detected by the humidity sensor 52 at the time of transfer in printing on the first surface of the paper. A transfer bias for the first surface is applied. Further, the transfer voltage application circuit 30 sets the transfer bias for the second surface to the transfer roller 29 at a constant current based on the average inflow current value stored in the memory means 12a during the transfer in printing on the second surface of the paper. Control.

  Fixing means disposed on the paper feed side of the transfer nip portion of the paper transport path F includes a heating roller 31 having a heater lamp 31a, a press roller 33, and the like. The heater lamp 31a of the heating roller 31 is heated by the heater driving circuit 32 so that the outer peripheral surface of the heating roller 31 has a predetermined temperature. The ambient temperature inside the apparatus is detected by the temperature sensor 34. The humidity inside the apparatus is detected by a humidity sensor 52. The heating roller 31 and the press roller 33 fix the toner image on the paper by heating and pressurizing the paper after the transfer process.

  On the other hand, a brush 35 that rotates about its own axis is provided between the scorotron charger 22 and the transfer roller 29 along the periphery of the photosensitive drum 21, and a predetermined diffusion is applied to the rotating brush 35 by a diffusion voltage application circuit 35a. A voltage HVCL is applied.

  A pickup roller 36, a PSS (paper feed sensor) 37, a registration roller 38, a PDS (paper discharge sensor) 39, and a paper discharge roller 91 are provided along the paper conveyance path F. The pickup roller 36 picks up the sheets one by one from the sheet cassette. The registration roller 38 aligns the leading edge of the paper and sends it to the transfer nip portion. The PSS 37 is a sensor for detecting the paper picked up from the paper feed cassette and the paper conveyed from the reverse conveyance path (not shown), and the PDS 39 carries out the paper recorded by the transfer / fixing. In this case, the sensor detects the paper. The paper discharge roller 91 is for discharging the recorded paper to the paper discharge tray. In addition to the main motor 41, a sub motor 42 for rotating the paper discharge roller 91 forward or backward, an intake FAN 44 for taking outside air into the apparatus, and an exhaust FAN 43 for exhausting the inside of the apparatus are provided. .

Next, the point that the volume resistance value of the transfer roller 29 is preferably 2 × 10 ⁸ Ωcm or more (increasing the volume resistance value) will be described. FIG. 3 is a partial enlarged cross-sectional view of a transfer nip portion between the photosensitive drum 21 and the transfer roller 29.

  In FIG. 3, if the volume resistance value of the transfer roller 29 is small, there arises a problem that the charge that should normally act as indicated by the arrow A flows laterally from the end of the paper 60 as indicated by the arrow B. In order to prevent this, the volume resistance value of the transfer roller 29 may be increased. This is because increasing the volume resistance value makes it easier for charges to pass through the paper 60 relatively.

Here, when the width of the transfer nip portion is 2 mm and the thickness t of the transfer roller 29 is 4 mm, the volume resistance value of the transfer roller 29 is preferably 2 × 10 ⁸ Ωcm or more.

That is: Transfer roller outer diameter: φ16.0
・ Outer diameter of transfer core metal: φ8.0
-Transfer nip width: 2.0 mm
・ Transfer roller width: 220.9mm
Transfer roller resistance value: 3.0 × 10 ^{7 + -0.25} Ω
... Minimum value at current level
Since the volume resistance value = (resistance value × cross-sectional area) / conductor length,
1. When the transfer roller is 3.0 × 10 ^6.75 Ω Volume resistance value = {(3.0 × 10 ^6.75 ) × 22.09 × 0.2} /0.4
= 1.86 × 10 ⁸ Ω · cm
2. When the transfer roller is 1.0 × 10 ^7.25 Ω Volume resistance value = {(1.0 × 10 ^7.25 ) × 22.09 × 0.2} /0.4
= 1.96 × 10 ⁸ Ω · cm
Accordingly, it is appropriate that the volume resistance value is 2.0 × 10 ⁸ Ωcm or more in a room temperature environment.

  As described above, in this facsimile apparatus, the transfer voltage application circuit 30 transfers the first surface to the transfer roller 29 based on the temperature and / or humidity inside the device when transferring the first surface of the paper. A bias is applied, and the transfer bias for the second surface to the transfer roller 29 is determined based on the average inflow current value to the transfer roller 29 at the time of transfer in the first surface printing at the time of transfer in the second surface printing. It is characterized by current control.

  Next, the printing operation of this facsimile apparatus, particularly the operation in the case of continuously performing double-sided printing of two sheets from the standby mode will be described with reference to the time chart of FIG. The time chart of FIG. 4 shows the fixing temperature, the charging voltage (HVC), the developing voltage (HVB), the transfer voltage (HVT), and the diffusion voltage (HVCL), but the other waveforms are omitted.

  Before starting the printing operation, voltage control for pre-printing processing is started. This pre-processing voltage control will be described in detail. When the temperature of the fixing device reaches the motor driving start temperature, the charging voltage application circuit 23 applies a positive charging voltage HVC to the scorotron charger 22, and the surface of the photosensitive drum 21. Are uniformly charged.

  When a predetermined time elapses after the fixing device temperature reaches the motor driving start temperature, the developing voltage HVB has the same polarity (positive polarity) as the developing voltage applied during the developing process, and a step voltage lower than that (positive polarity). As an example, about + 10V) is applied. This is to improve toner recovery efficiency.

  Eventually, when the rotation of the polygon mirror of the LSU 24 becomes stable, the developing voltage HVB is switched to a positive strong voltage (for example, about +400 V) necessary for the developing process. While a positive strong voltage is applied as the development voltage HVB, the electrostatic latent image on the photosensitive drum 21 is developed as a toner image.

  Further, when the region of the photosensitive drum 21 charged when the temperature of the fixing device reaches the motor driving start temperature reaches the transfer nip portion, the transfer voltage HVT is a positive voltage having a polarity opposite to that in the transfer process. Is applied for a period required for the transfer roller 29 to rotate. As a result, the residual toner adhering to the transfer roller 29 is returned to the photosensitive drum 21.

  Thereafter, a weak test voltage (for example, about −1 kV) having the same polarity as that during the transfer process is applied as the transfer voltage HVT. While the test voltage is applied to the transfer roller 29 (symbol a), the current value flowing into the transfer roller 29 is detected by the current value detection circuit 51, and the detected current value and the temperature sensor 34 are detected. The transfer voltage value is determined according to the temperature inside the apparatus and / or the humidity inside the apparatus detected by the humidity sensor 52. The determined transfer voltage value is an optimum transfer voltage value for transferring the toner image onto the paper under the environmental temperature and humidity conditions in which the apparatus is placed, and is a voltage value applied to the transfer roller 29. It is.

  Note that, after a predetermined time has elapsed since reaching the motor driving start temperature, a positive diffusion voltage HVCL is applied to the rotating brush 35 to weaken the adhesive force of the residual toner on the photosensitive drum 21, and the developing roller 26 Toner recovery is easy.

  When a predetermined time elapses after the PSS 37 is turned on (when the leading edge of the first sheet from the sheet feeding cassette is detected), the leading edge of the sheet reaches the transfer nip portion. In order to perform printing on the first surface (front surface) of the first sheet, the transfer voltage HVT is a negative strong voltage for transferring the toner image on the photosensitive drum 21 to the sheet, and the test voltage described above. The voltage determined in the application process is applied to the transfer roller 29. While the strong voltage is applied to the transfer roller 29 (symbol b), the current value is controlled while detecting the current value flowing into the transfer roller 29 by the current value detection circuit 51 so that the determined voltage is maintained. To do.

  In the period c included in the period indicated by the symbol b, the current value flowing into the transfer roller 29 is sampled by the current value detection circuit 51, the average value is calculated, and stored in the memory means 12a of the printer controller 12. To do.

  The end of the period c coincides with the time when the PSS 37 is turned off (the time when the trailing edge of the first sheet has passed the PSS 37), and there is no sheet in the transfer nip portion after a predetermined time has elapsed from this time. When the state is reached, the transfer voltage HVT is returned to a weak test voltage (for example, about −1 kV) having the same polarity as that during the transfer process.

  Then, when the first surface printed paper is conveyed on the reverse conveyance path, and the second surface (back surface) of the paper is opposed to the photosensitive drum 21, the paper reaches the transfer nip portion. For printing the second side (back side) of the eye paper, the transfer voltage HVT is a negative strong voltage for transferring the toner image on the photosensitive drum 21 to the paper, and the above test voltage application processing The voltage determined in step 1 is applied to the transfer roller 29. When the strong voltage is applied (symbol d), a voltage is applied by the transfer voltage application circuit 30 so as to maintain the same current value as the average value of the inflow current to the transfer roller 29 stored in the memory means 12a of the printer controller 12. Control the value.

  When the sheet is further conveyed and the sheet is removed from the transfer nip portion when a strong voltage is applied, the transfer voltage HVT is returned to a weak test voltage (for example, about −1 kV) having the same polarity as that during the transfer process.

  When the weak test voltage is applied, when the second sheet is conveyed from the paper feed cassette to the transfer nip portion, the transfer voltage HVT is set to a strong negative polarity for printing the first side of the second sheet. Return to voltage. When this strong voltage is applied (symbol e), the current value flowing into the transfer roller 29 by the current value detection circuit 51 is maintained so as to maintain the determined voltage, as in the first-side printing of the first sheet. The current value is controlled while detecting.

  When a strong voltage is applied, when the sheet is further conveyed and the sheet is removed from the transfer nip portion, the transfer voltage HVT is returned to a weak test voltage (for example, about −1 kV) having the same polarity as that during the transfer process.

  Then, as described above, when the second sheet has been conveyed on the reverse conveyance path and the second surface of the sheet is opposed to the photosensitive drum 21, the sheet reaches the transfer nip portion. The transfer voltage HVT is returned to the negative strong voltage for printing the second side of the first sheet. When this strong voltage is applied (symbol f), the current value is the same as the average value of the inflow current flowing into the transfer roller 29 stored in the memory means 12a of the printer controller 12, as in the second side printing of the first sheet. The voltage value is controlled by the transfer voltage application circuit 30 so as to maintain the above.

  After the transfer process related to the second surface printing of the second sheet, the transfer voltage HVT is switched based on various timers, whereby the transfer roller 29 and the photosensitive drum 21 are cleaned (post-rotation process).

  Next, the printing operation of this facsimile apparatus will be outlined with reference to the flowchart of FIG. However, details have been described with reference to the time chart of FIG. First, in step ST1, transfer FB (feedback) is performed. As described with reference to the time chart of FIG. 4, the current that flows into the transfer roller 29 while the test voltage having the same polarity as that during the transfer process is applied to the transfer roller 29 (reference a) as the transfer voltage HVT. The transfer voltage value is detected according to the detected current value and the internal temperature detected by the temperature sensor 34 and / or the internal humidity detected by the humidity sensor 52. It is a process to decide.

  Next, in step ST2, the first surface (front surface) printing is performed. In the first side printing (ST2a), the current value flowing into the transfer roller 29 by the current value detection circuit 51 is maintained so that the determined voltage is maintained when a strong voltage is applied to the transfer roller 29 (symbol b). The current value is controlled while detecting (ST2b). At the same time, the value of the current flowing into the transfer roller 29 is sampled by the current value detection circuit 51, and the average value is calculated and stored in the memory means 12a of the printer controller 12 (ST2c).

  In step ST3, it is determined whether or not the second side (back side) printing is performed for the paper. If not, the printing operation is terminated.

  If the determination in step ST3 is YES, the second side printing is performed in step ST4. In the second side printing (ST4a), when a strong voltage is applied (symbol d), the same current value as the average value of the current flowing into the transfer roller 29 stored in the memory means 12a of the printer controller 12 is maintained. Then, the voltage value is controlled by the transfer voltage application circuit 30 (ST4b). Thereafter, the printing operation is terminated.

1 is a block diagram illustrating a configuration example of a facsimile machine (a multifunction machine having both a facsimile function and a copy function) as an image forming apparatus according to an embodiment. FIG. 2 is a block diagram illustrating a configuration example of a printer unit of the facsimile apparatus. FIG. 3 is a partial enlarged cross-sectional view of a transfer nip portion between a photosensitive drum and a transfer roller in the facsimile apparatus. 4 is a time chart showing waveforms of respective parts when two-sided printing of two sheets is continuously performed from the standby mode after power-on of the facsimile apparatus. It is a flowchart explaining the printing operation of the facsimile apparatus.

Explanation of symbols

12 Printer controller 12a Memory means (storage means)
21 Photosensitive drum (image carrier)
24 LSU
25 Supply roller 26 Developing roller 29 Transfer roller (transfer means)
30 Transfer voltage application circuit (transfer bias application means)
31 Heating roller (fixing means)
33 Press roller (fixing means)
34 Temperature sensor 37 PSS
39 PDS
51 Current value detection circuit 52 Humidity sensor

Claims (2)

An image forming apparatus capable of duplex printing and multiple printing,
An image carrier;
Transfer means for nipping the paper together with the image carrier and transferring the image of the image carrier to the paper;
Current value detection means for detecting a current value flowing into the transfer means;
A transfer bias applying means for applying a transfer voltage to the transfer means;
Storage means for storing an average inflow current value to the transfer means in the paper nip at the time of transfer in printing on the first surface of the paper;
And a humidity sensor for detecting humidity of a temperature sensor and / or the apparatus interior for detecting the temperature inside the apparatus,
The transfer bias applying means is detected by the temperature sensor and a current value flowing into the transfer means detected by the current value detecting means by applying a test voltage to the transfer means before printing on the first surface. The transfer voltage is determined based on temperature and / or humidity detected by the humidity sensor, and the determined transfer voltage is applied to the transfer means during printing on the first surface. Controlling the current value while detecting the current value flowing into the transfer means by the current value detecting means so as to maintain the voltage,
Further, the transfer bias applying means applies the same current value as the average inflow current value stored in the storage means while applying the determined transfer voltage to the transfer means during printing of the second surface. An image forming apparatus , wherein a voltage value applied to the transfer unit is controlled so as to be maintained . It said transfer means is a transfer roller in contact with the image bearing member, an image forming apparatus according to claim 1, wherein the volume resistivity of the transfer roller is 2 × 10 ⁸ Ωcm or more.

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