Field of the Invention
The present invention relates to an image forming apparatus and an image forming method for forming an image on a recording medium.
Description of the Related Art
In general, an image forming apparatus includes a transfer section that transfers a toner image as a developer image onto a recording medium. For example, the image forming apparatus determines a transfer voltage value on the basis of a transfer current value in a state where a recording medium is absent in a transfer section. See Patent reference 1, Japanese patent application publication No. 2014-066919, for example.
It is desired for the image forming apparatus that image quality of the developer image transferred on the recording medium (image quality of an image fixed on the recording medium) is high, and the image forming apparatus is expected to be further enhanced in image quality.
An object of the present invention is to provide an image forming apparatus and an image forming method which are capable of enhancing image quality of the image formed on the recording medium.
According to an aspect of the present invention, an image forming apparatus includes: an transfer section including a transfer roller and a rotatable member facing the transfer roller, the transfer section performing transfer processing in which the transfer section transfers a developer to a recording medium passing between the transfer roller and the rotatable member; a power source controller that applies a voltage to the transfer roller, and measures a current value of a current that flows through the transfer roller and the rotatable member when the voltage is applied to the transfer roller; and a main controller that calculates a first electrical resistance value between the transfer roller and the rotatable member in a state where the recording medium is absent between the transfer roller and the rotatable member and a second electrical resistance value between the transfer roller and the rotatable member in a state where the recording medium is present between the transfer roller and the rotatable member on a basis of the current value measured by the power source controller, and determines a transfer voltage value for the transfer processing on a basis of the first electrical resistance value and the second electrical resistance value.
According to another aspect of the present invention, an image forming method for determining a transfer voltage value in a transfer section, the transfer section including a transfer roller and a rotatable member facing the transfer roller and performing transfer processing, in which the transfer section transfers a developer to a recording medium passing between the transfer roller and the rotatable member, includes: applying a voltage to the transfer roller, and measuring a current value of a current that flows through the transfer roller and the rotatable member when the voltage is applied to the transfer roller; calculating a first electrical resistance value between the transfer roller and the rotatable member in a state where the recording medium is absent between the transfer roller and the rotatable member on a basis of the measured current value of the current that flows through the transfer roller and the rotatable member; calculating a second electrical resistance value between the transfer roller and the rotatable member in a state where the recording medium is present between the transfer roller and the rotatable member; and determining a transfer voltage value for the transfer processing on a basis of the first electrical resistance value and the second electrical resistance value.
According to the image forming apparatus and the image forming method of the present invention, the transfer voltage is determined on the basis of the first electrical resistance value in a state where the recording medium is absent between the transfer roller and the rotatable member, and the second electrical resistance value in a state where the recording medium is present between the transfer roller and the rotatable member. Therefore, the image quality of the developer image transferred on the recording medium can be enhanced.
In the drawings:
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications will become apparent to those skilled in the art from the detailed description.
Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
The image forming apparatus 1 includes five image drum (ID) units 4 (4Y, 4M, 4C, 4K, and 4W) as image forming units, five exposure units 6 (6Y, 6M, 6C, 6K, and 6W) as light sources, five primary transfer rollers 7 (7Y, 7M, 7C, 7K, and 7W), a transfer belt (intermediate transfer belt) 11, a drive roller 12, an idle roller 13, a secondary transfer backup roller 31 as a rotatable member, and a reversely bending roller 15. Furthermore, the image forming apparatus 1 includes a conveyance roller pair 23, a cutting unit (cutter) 24, a conveyance roller pair 26, a secondary transfer roller 32, a fixing unit 60, and a discharge roller 29. In addition, the image forming apparatus 1 includes a medium detecting sensor 22, a writing sensor 25, and discharge sensors 27 and 28. The secondary transfer roller 22 and the secondary transfer backup roller 31 are disposed to face each other with the transfer belt 11 therebetween, and constitutes the transfer section 30. Further, the number of the ID units 4 is not limited to five, and may be four or less and may be six or more. The number of the exposure units 6 is not limited to five, and may be four or less and may be six or more.
Each of the five ID units 4 forms a toner image. To be specific, the ID unit 4Y forms the toner image having a yellow color (Y), the ID unit 4M forms the toner image having a magenta color (M), the ID unit 4C forms the toner image having a cyan color (C), the ID unit 4K forms the toner image having a black color (K), and the ID unit 4W forms the toner image having a white color (W). The ID units 4Y, 4M, 4C, 4K, and 4W are disposed so as to face the transfer belt 11, and are arranged in tandem in this order in a moving direction F. The moving direction F is a direction in which part of the transfer belt 11 facing the ID units 4Y, 4M, 4C, 4K, and 4W moves.
The photosensitive body 41 is capable of carrying an electrostatic latent image on a surface thereof (surface layer portion). The photosensitive body 41 is rotated counterclockwise in
In each ID unit, the charging roller 42 charges the surface (surface layer portion) of the photosensitive body 41 to negative polarity, for example. The charging roller 42 is disposed so as to contact with the surface (peripheral surface) of the photosensitive body 41, and is rotated clockwise in
In each ID unit, the developing roller 43 carries the toner charged to negative polarity. The developing roller 43 is disposed so as to contact with the surface (peripheral surface) of the photosensitive body 41, and is rotated clockwise in
The supply roller 44 charges the toner stored in the toner container 45 to negative polarity, and supplies the negatively charged toner to the developing roller 43. The supply roller 44 is disposed so as to contact with the surface (peripheral surface) of the developing roller 43, and is rotated clockwise in
The toner container 45 stores the toner therein. To be specific, the toner container 45 in the ID unit 4Y stores the yellow (Y) toner therein, the toner container 45 in the ID unit 4M stores the magenta (M) toner therein, the toner container 45 in the ID unit 4C stores the cyan (C) toner therein, the toner container 45 in the ID unit 4K stores the black (K) toner therein, and the toner container 45 in the ID unit 4W stores the white (W) toner therein.
In each ID unit, the toner blade 46 forms a layer (toner layer) made of the toner on the surface of the developing roller 43 by touching the surface of the developing roller 43, and regulates (control or adjust) a thickness of the toner layer. The toner blade 46 is a plate-like elastic member (plate spring) made of, for example, stainless or the like, and is disposed so that a tip of the toner blade 46 touches the surface of the developing roller 43. As will be described later, a predetermined voltage is applied to the toner blade 46 by the high-voltage power source section 56.
The five exposure units 6 (
The five primary transfer rollers 7 electrostatically transfer the toner images formed by the five ID units 4, respectively, onto an outer surface (a surface to be transferred) of the transfer belt 11. The primary transfer roller 7Y is disposed to face the photosensitive body 41 of the ID unit 4Y through the transfer belt 11, the primary transfer roller 7M is disposed to face the photosensitive body 41 of the ID unit 4M through the transfer belt 11, the primary transfer roller 7C is disposed to face the photosensitive body 41 of the ID unit 4C through the transfer belt 11, the primary transfer roller 7K is disposed to face the photosensitive body 41 of the ID unit 4K through the transfer belt 11, and the primary transfer roller 7W is disposed to face the photosensitive body 41 of the ID unit 4W through the transfer belt 11. As will be described later, predetermined voltages are applied to the primary transfer rollers 7 by the high-voltage power source section 56. Thereby, in the image forming apparatus 1, the toner images which have been formed by the ID units 4, respectively, are transferred (primary transfer) onto the outer surface of the transfer belt 11.
The transfer belt 11 is an endless elastic belt which includes, for example, a high-resistance semiconductor plastic film. The transfer belt 11 is tensioned (stretched) by the drive roller 12, the idle roller 13, the secondary transfer backup roller 31, and the reversely bending roller 15. Furthermore, the transfer belt 11 is stretched so as to move or rotate in the moving direction F in a circulating manner by rotation of the drive roller 12. In this case, the transfer belt 11 is stretched so as to move between the ID unit 4Y and the primary transfer roller 7Y, between the ID unit 4M and the primary transfer roller 7M, between the ID unit 4C and the primary transfer roller 7C, between the ID unit 4K and the primary transfer roller 7K, and between the ID unit 4W and the primary transfer roller 7W.
The drive roller 12 rotates the transfer belt 11 in a circulating manner. In the present embodiment, the drive roller 12 is disposed on an upstream side with respect to the five ID units 4 in the moving direction F, and is rotated clockwise in
The idle roller 13 rotates clockwise in
The secondary transfer backup roller 31 rotates clockwise in
The reversely bending roller 15 rotates counterclockwise in
Moreover, the rolled paper feeder 21, the medium detecting sensor 22, the conveyance roller pair 23, the cutting unit 24, the writing sensor 25, the conveyance roller pair 26, the secondary transfer roller 32, the discharge sensors 27 and 28, the fixing unit 60, and the discharge roller 29 are disposed along the conveyance path 20 along which the recording medium 9 is conveyed.
In the rolled paper feeder 21, the recording medium 9 as the rolled paper is set. The medium detecting sensor 22 is a sensor which detects the recording medium 9 supplied from the rolled paper feeder 21. The conveyance roller pair 23 includes a pair of rollers with the conveyance path 20 put between the rollers, and conveys the recording medium 9 so that the recording medium 9 supplied from the rolled paper feeder 21 reaches a suitable position at a suitable timing. The cutting unit 24 cuts the recording medium 9 as the rolled paper. The cutting unit 24, for example, cuts the recording medium 9 when a power source of the image forming apparatus 1 is turned ON, and when a user operates the image forming apparatus 1. The writing sensor 25 is a sensor which detects that the recording medium 9 has passed therethrough. The conveyance roller pair 26 includes a pair of rollers with the conveyance path 20 put between the rollers, and conveys the recording medium 9 along the conveyance path 20.
The secondary transfer roller 32 transfers the toner image on the outer surface of the transfer belt 11 onto the outer surface of the recording medium 9 passing between the secondary transfer roller 32 and the secondary transfer backup roller 31. The secondary transfer roller 32 includes a shaft 32a made of, for example, a metal, and a semiconductive urethane rubber layer 32b which covers an outer periphery (surface) of the shaft 32a. The secondary transfer roller 32 is disposed to face the secondary transfer backup roller 31 through the transfer belt 11 and the conveyance path 20. As will be described later, a positive transfer voltage (transfer voltage value Vtr for transfer processing) is supplied to the shaft 32a of the secondary transfer roller 32 through a resistance element 39 by a voltage generator (power supply) 56a, for example. Thereby, in the image forming apparatus 1, the toner image on the surface (outer surface) to be transferred of the transfer belt 11 is transferred (secondary transfer) onto a surface (an upper surface in
The discharge sensor 27 is a sensor which detects that the recoding medium 9 has passed through the transfer section 30.
The fixing unit 60 fixes the toner image transferred onto the recoding medium 9 by applying heat and pressure. The fixing unit 60 includes a heat roller 61, a pressure roller 62, and a temperature sensor 63. The heat roller 61 includes, for example, a heater such as a halogen lamp therein, and applies heat to the toner on the recording medium 9. The pressure roller 62 is disposed so as to form a pressure portion between itself and the heat roller 61, and applies the pressure to the toner on the recording medium 9. The temperature sensor 63 detects surface temperatures of the heat roller 61 and the pressure roller 62, for example. Thus, in the fixing unit 60, the toner on the recording medium 9 is heated, melted, and pressed. As a result, the toner image is fixed on the recording medium 9.
The discharge sensor 28 is a sensor which detects that the recording medium 9 has passed through the fixing unit 60.
The discharge sensor 29 includes a pair of rollers with the conveyance path 20 put between the rollers, and discharges the recording medium 9 to outside of the image forming apparatus 1.
The interface section 51 receives print data from a host computer as a host device and exchanges various kinds of control signals between itself and the host computer, for example. The environmental detector 52 (specifically, environmental temperature sensor 52a) detects an environmental temperature Ta of the image forming apparatus 1. The environmental detector 52 (specifically, environmental humidity sensor 52b) detects an environmental humidity Ha of the image forming apparatus 1. The environmental temperature sensor 52a and the environmental humidity sensor 52b are disposed inside or outside a housing of the image forming unit 1, for example. It is preferable that the environmental detector 52 detects at least one of the environmental temperature and the environmental humidity in the transfer section 30. The motor driving section 54 controls operation of the motors as power generating devices in the image forming apparatus 1. Thus, the motor driving section 54 controls the operation of each motor, thereby rotating the photosensitive bodies 41, the drive roller 12, the conveyance roller pair 23, the conveyance roller pair 26, the heat roller 61, and the discharge roller 29. The exposure controller 55 controls exposure operation in the exposure units 6.
The high-voltage power source section 56 supplies the voltages to the charging roller 42, the developing roller 43, the supply roller 44, and the toner blade 46 of each ID unit 4, each transfer roller 7, and the secondary transfer roller 32 of the transfer section 30. The high-voltage power source section 56 includes the voltage generator 56a and a current measuring section 56b. The high-voltage power source section 56 generates the transfer voltage of the transfer voltage value Vtr, and supplies (applies) the transfer voltage to the shaft 32a of the secondary transfer roller 32 through the resistance element 39 (which will be described later). To be specific, the voltage generator 56a generates the transfer voltage of the transfer voltage value Vtr, and applies the transfer voltage to the shaft 32a of the secondary transfer roller 32. The high-voltage power source section 56 measures a value (transfer current value) Itr of a transfer current in the transfer section 30. To be specific, the current measuring section 56b measures the current value (transfer current value) Itr of the transfer current that flows through the secondary transfer roller 32 and the secondary transfer backup roller 31 when the voltage is applied to the secondary transfer roller 32.
The resistance element 39 has a resistance value R of, for example, several MΩ (megaohms), and limits a current which flows through the transfer section 30. A ground terminal of the voltage generator 56a is grounded through the current measuring section 56b.
When the transfer section 30 intends to transfer the toner image on the transfer belt 11 to the recording medium 9, the voltage generator 56a generates the transfer voltage of the transfer voltage value Vtr. The generated transfer voltage is supplied to the secondary transfer roller 32 through the resistance element 39. Thereby, the transfer current of the transfer current value Itr flows through the resistance element 39, the shaft 32a, the urethane rubber layer 32b, the recording medium 9, the transfer belt 11, and the secondary transfer backup roller 31 in this order, for example. In this case, since the resistance values of these elements are changed depending on, for example, the environmental temperature and the environmental humidity, the transfer current value Itr may be changed, so that the transfer characteristics of the toner image in the transfer section 30 may be changed. In the image forming apparatus 1, as will be described later, the transfer voltage value Vtr is determined by the main controller 50 so that a current density of the current that flows through the recording medium 9, and an electric potential difference between a voltage value (electric potential) of a front surface and a voltage value (electric potential) of a back surface in the recording medium 9 are kept approximately constant irrespective of the temperature and the humidity (for example, corresponding to the environmental temperature Ta and the environmental humidity Ha) of the transfer section 30. As a result, in the image forming apparatus 1, the satisfactory transfer characteristics are obtained irrespective of the temperature and the humidity (for example, corresponding to the environmental temperature Ta and the environmental humidity Ha).
The main controller 50 (specifically, calculating section 57) calculates the transfer voltage value Vtr. For example, it is preferable that the calculating section 57, as will be described later, obtain the transfer voltage value Vtr on the basis of the environmental temperature Ta, the environmental humidity Ha, and the transfer current value Itr that flows through the transfer section 30.
For example, the storage section 58 is a nonvolatile memory, and stores a target current density table 58a and a target voltage table 58b.
Further,
The driving controller 59 controls each block (each configuration) shown in
Further, the calculating section 57 and the driving controller 59, for example, can be configured so as to include a microprocessor, a Read Only Memory (ROM), a Random Access Memory (RAM), an Input/Output (input and output) port, a timer, and so on.
Here, the secondary transfer roller 32 corresponds to a concrete example of “a transfer roller”. The secondary transfer backup roller 31 corresponds to a concrete example of “a rotatable member”. The toner corresponds to a concrete example of “a developer”. The five ID units 4, the five exposure units 6, the five primary transfer rollers 7, the transfer belt 11, and the transfer section 30 correspond to a concrete example of “an image forming section”. The calculating section 57 and the driving controller 59 correspond to a concrete example of “a main controller”. The environmental temperature sensor 52a and the environmental humidity sensor 52b correspond to a concrete example of “an environmental detecting section”.
Next, operation and function of the image forming apparatus 1 of the present embodiment will be described.
Image Forming Operation
Firstly, an outline of the whole operation of the image forming apparatus 1 will be described with reference to
When a temperature of the fixing unit 60 detected by the temperature sensor 63 has reached a temperature suitable for the fixing operation, the driving controller 59 controls the motor driving section 54, thereby rotating the photosensitive bodies 41 of the ID units 4. Furthermore, the driving controller 59 controls the motor driving section 54 so that a moving speed (linear speed) of outer surfaces of each photosensitive body 41 in a circumferential direction becomes the same level (substantially the same) as the conveyance speed of the recording medium 9 at printing. Concurrently therewith, the driving controller 59 controls the motor driving section 54, thereby rotating the drive roller 12, the conveyance roller pair 23, the conveyance roller pair 26, the heat roller 61, and the discharge roller 29. Furthermore, the driving controller 59 performs the control so that the conveyance speed becomes the same level (substantially the same) as the conveyance speed of the recording medium 9 at the printing.
In addition, the driving controller 59 controls the high-voltage power source section 56, thereby starting to rotate the photosensitive body 41 in such a way, and causes the high-voltage power source section 56 to apply a negative voltage (for example, −1150 V) to the charging roller 42. As a result, the photosensitive body 41 is uniformly charged to the negative voltage (for example, −700 V). In addition, the driving controller 59 causes the high-voltage power source section 56 to apply a negative voltage (for example, −300 V) to the developing roller 43 by controlling the high-voltage power source section 56. Furthermore, when the photosensitive body 41 is rotated in the ID unit 4 and a part which is negatively charged of the photosensitive body 41 has reached a nip portion between the photosensitive body 41 and the primary transfer roller 7, the ID unit 4 becomes a state of being able to perform the printing.
Next, the driving controller 59 causes the motor driving section 54 to convey the recording medium 9 from the rolled paper feeder 21 to a predetermined position along the conveyance path 20 on the basis of the detection result by the medium detecting sensor 22 by controlling the motor driving section 54. Furthermore, the driving controller 59 obtains a timing at which a front end of the recording medium 9 reaches a nip portion between the secondary transfer backup roller 31 and the secondary transfer roller 32 in the transfer section 30 on the basis of a detection result by the writing sensor 25.
Next, the driving controller 59 generates the image data the pieces of which the ID unit 4 should form on the basis of the print data. Furthermore, the driving controller 59 causes the exposure controller 55 to expose the photosensitive bodies 41 of the ID units 4 by using the exposure units 6 (causing the exposure units 6 to emit light) by controlling the exposure controller 55 at a timing (timing based on a recording-medium reaching timing) in consideration of the timing (recording-medium reaching timing) at which the front end of the recording medium 9 reaches the nip portion. Thereby, in each ID unit 4, an electric potential of the exposed portion of the surface of the photoreceptor 41 becomes about 0 V, and the electrostatic latent image is formed.
The driving controller 59 causes the high-voltage power source section 56 to apply a negative voltage (for example, −400 V) to the supply roller 44, and to apply a negative voltage (for example, −400 V) to the toner blade 46 by controlling the high-voltage power source section 56. Thereby, the supply roller 44 charges the toner to negative polarity, and supplies the charged toner to the developing roller 43. The toner supplied to the developing roller 43 is carried on the surface of the developing roller 43, and the thickness of the toner carried on the surface of the developing roller 43 is regulated by the toner blade 46, and the toner is charged to negative polarity. Since the electric potential of the exposed part of the surface of the photosensitive body 41 is about 0 V, the toner charged to negative polarity on the developing roller 43 is moved from the developing roller 43 to the exposed part of the surface of the photosensitive body 41 by Coulomb's force. Thereby, in the photosensitive body 41, a visible image which is the toner image is formed from the electrostatic latent image (that is, developing).
The driving controller 59 causes the high-voltage power source section 56 to apply the positive voltage (for example, +1,500 V) to each transfer roller 7 by controlling the high-voltage power source section 56. Thereby, the toner charged to negative polarity on the photosensitive body 41 is moved to the transfer belt 11 from the photosensitive body 41 by the Coulomb's force.
The driving controller 59 causes the high-voltage power source section 56 to supply the positive transfer voltage value Vtr (positive transfer voltage) determined by the calculating section 57 to the secondary transfer roller 32 through the resistance element 39 by controlling the high-voltage power source section 56. Thereby, the toner charged to negative polarity on the transfer belt 11 is moved to the recording medium 9 from the transfer belt 11 by the Coulomb's force.
The toner on the recording medium 9 is melted by being heated, and pressed by the fixing unit 60. As a result, the toner image is fixed on the recording medium 9.
Determining Operation of Transfer Voltage Value
Next, a determining operation of the transfer voltage value Vtr which is to be applied to the secondary transfer roller 32 will be described in detail.
Firstly, when the power source of the image forming apparatus 1 has been turned ON, the image forming apparatus 1 acquires the electrical characteristics of the transfer section 30 (step S1).
Acquisition of Electrical Characteristics of Transfer Section 30
Firstly, the driving controller 59 of the image forming apparatus 1 causes the cutting unit 24 to cut the recording medium 9 by controlling the cutting unit 24 (step S21). Furthermore, the image forming apparatus 1 starts to perform a conveying operation (step S22). To be specific, the driving controller 59 rotates the drive roller 12, the conveyance roller pair 26, the heat roller 61, and the discharge roller 29 by controlling the motor driving section 54. The transfer section 30 is in a state where the recording medium 9 is absent therein at the time of starting of the conveying operation.
Next, the image forming apparatus 1 supplies (applies) a voltage V1 to the secondary transfer roller 32 through the resistance element 39 to detect a current I1 (step S23). To be specific, the voltage generator 56a of the high-voltage power source section 56 generates the voltage V1 on the basis of an instruction sent from the driving controller 59. Furthermore, the current measuring section 56b detects the current I1, and supplies the detection result to the driving controller 59.
Next, the image forming apparatus 1 supplies (applies) a voltage V2 different from the voltage V1 to the secondary transfer roller 32 through the resistance element 39 to detect a current I2 (step S24). To be specific, the voltage generator 56a generates the voltage V2 on the basis of an instruction issued from the driving controller 59. Furthermore, the current measuring section 56b detects the current I2, and supplies the detection result to the driving controller 59.
Further, although in this example, the currents I1 and I2 are detected one time each, a detecting method for detecting the currents I1 and I2 is not limited thereto. For example, it may also be adopted that the current I1 is detected multiple times to obtain an average value thereof, and the current I2 is also detected multiple times to obtain an average value thereof.
Next, the calculating section 57 of the image forming apparatus 1 calculates a value of shaft voltage (shaft voltage value) Vs (for example, shaft voltage values Vs1 and Vs2) in the shaft 32a at the time of supply of the voltages in the steps S23 and S24 (step S25). That is to say, the voltage generator 56a supplies the voltage to the secondary transfer roller 32 through the resistance element 39. Therefore, the shaft voltage values Vs1 and Vs2 in the shaft 32a is different from the voltages V1 and V2 which the voltage generating portion 56a generates, for example. The shaft voltage values Vs1 and Vs2 can be expressed as follows by using the resistance value R of the resistance element 39:
Vs1=V1−R×I1 (1a)
Vs2=V2−R×I2 (1b)
The calculating section 57 calculates the shaft voltage values Vs1 and Vs2 by using expressions (1a) and (1b).
Next, the calculating section 57 calculates a current density J (for example, current density J1 and J2) in the transfer section 30 at the time of supply of the voltages in steps S23 and S24 (step S26). Here, the current densities J1 and J2 are each the current value per unit length in a length direction (a depth direction in
J1=I1/L (2a)
J2=I2/L (2b)
The calculating section 57 calculates the current densities J1 and J2 by using expressions (2a) and (2b).
Next, the calculating section 57 obtains a relational expression between the current density J and the shaft voltage value Vs by linear approximation, for example (step S27). The current density J can be expressed as follows by using the shaft voltage value Vs, and coefficients a and b:
J=a×Vs+b (3a)
a=(J2−J1)/(Vs2−Vs1) (3b)
b=(J1×Vs2−J2×Vs1)/(Vs2−Vs1) (3c)
The calculating section 57 calculates the coefficients a and b by using the shaft voltage values Vs1 and Vs2 calculated in step S25 (expressions (1a) and (1b)), the current densities J1 and J2 calculated in step S26 (expressions (2a) and (2b)), and expressions (3a), (3b), and (3c).
Further, the operation for acquiring the electrical characteristics of the transfer section 30 (steps S21 to S27) may be performed at least once after turn-ON of the power source, and before start of the printing.
As stated above, the processing flow (step S1 in
Next, as shown in
Furthermore, when the print data has been received (“Yes” in step S2), the image forming apparatus 1 calculates the transfer voltage value (initial value) Vtr (step S3).
Calculation of Transfer Voltage Value (Initial Value) Vtr
Firstly, the driving controller 59 of the image forming apparatus 1 acquires information concerning a width W (for example, a unit of the width W is mm) of the recording medium 9, contained in the print data, and also acquires the environmental temperature Ta (for example, a unit of the environmental temperature Ta is ° C.) detected by the environmental temperature sensor 52a, and the environmental humidity Ha (for example, relative humidity [%]) detected by the environmental humidity sensor 52b (step S31). Further, although in this example, the width W of the recording medium 9 is acquired on the basis of the print data, the acquiring method of the information concerning the width W is by no means limited thereto. For example, in a case where the image forming apparatus 1 includes a medium-width detector which detects the width W of the recording medium 9 set in the rolled paper feeder 21, the driving controller 59 may acquire the information concerning the width W from the medium-width detector.
Next, the calculating section 57 of the image forming apparatus 1 obtains the target medium current density Jp and the target medium voltage value Vp (step S32). To be specific, the calculating section 57 obtains the target medium current density Jp and the target medium voltage value Vp from the target current density table 58a and the target voltage table 58b by using the environmental temperature Ta and the environmental humidity Ha which were acquired in step S31.
Next, the calculating section 57 calculates a shaft voltage value Vs0 with which the target medium current density Jp and the target medium voltage value Vp which were obtained in step S32 can be realized (step S33).
We will now focus on the region R1. The shaft voltage value Vs0 can be expressed as follows:
Vs0=Vin+Vp (4)
where a voltage value Vin is a voltage component (electric potential difference) resulting from the existence of the transfer belt 11 and the urethane rubber layer 32b in the shaft voltage value Vs0. That is to say, a first term of the right side of expression (4) shows the voltage component (electric potential difference) caused by a contribution of the transfer belt 11 and the urethane rubber layer 32b. A second term of the right side of expression (4) is the voltage component (electric potential difference) generated by the existence of the recording medium 9 in the shaft voltage value Vs0. In the region R1, a current density in the transfer belt 11 and the urethane rubber layer 32b is substantially the same as the current density (target medium current density Jp) of the current that flows through the recording medium 9. Therefore, the voltage value Vin can be expressed as follows by using expression (3a):
Vin=(Jp−b)/a (5)
Therefore, the shaft voltage value Vs0 can be expressed as follows by using expressions (4) and (5):
Vs0=(Jp−b)/a+Vp (6)
The calculating section 57 calculates the shaft voltage value Vs0 by using expression (6).
Next, the calculating section 57 calculates the transfer current value Itr (step S34). Firstly, we will now focus on the region R2. Since both of the secondary transfer backup roller 31 and the shaft 32a are made of metal, the shaft voltage value Vs0 which was obtained by focusing on the region R1 in step S33 can be used even in the region R2. Since the recording medium 9 is absent in the region R2, the relational expression (expression (3a)) concerning the current density J and the shaft voltage value Vs in the case where the recording medium 9 is absent in the recording medium 9, which was obtained in step S27 can be used for the region R2. A current density Jout of a current that flows through the region R2 can be expressed as follows by using expression (3a):
Jout=a×Vs0+b (7)
The transfer current value Itr can be expressed as follows by using expression (7):
Here, a first term of the right side of expression (8) represents a component contributed by the region R1 in the transfer current value Itr, and a second term of the right side of expression (8) represents a component contributed by the region R2 in the transfer current value Itr. The calculating section 57 calculates the transfer current value Itr by using expression (8).
Next, the calculating section 57 calculates the transfer voltage value (initial value) Vtr which the voltage generator 56a should generate (step S35). As shown in
Vtr=Vs0+R×Itr (9)
Here, a first term of the right side of expression (9) represents a component contributed by the transfer section 30 in the transfer voltage value Vtr, and a second term of the right side of expression (9) represents a contribution by the resistance element 39 in the transfer voltage value Vtr. The calculating section 57 calculates the transfer voltage value Vtr by using the shaft voltage value Vs0 calculated in step S33 (expression (4)), the transfer current value Itr calculated in step S34 (expression (8)), and expression (9).
As stated above, the processing flow (step S3 in
Next, as shown in
Next, the image forming apparatus 1 calculates a medium resistance value Rb (step S5).
Calculation of Medium Resistance Value Rb
Firstly, the medium detecting sensor 22 detects the recording medium 9 (step S41).
Next, the current measuring section 56b of the image forming apparatus 1 detects a current value Itr1 before the recording medium 9 reaches the transfer section 30 (step S42). That is to say, the image forming apparatus 1 has already started to perform the printing operation in step S4, and the voltage generator 56a supplies (applies) the transfer voltage of the transfer voltage value Vtr to the secondary transfer roller 32 through the resistance element 39. Therefore, the current measuring section 56b detects the current value Itr1 of the transfer current which flows by the transfer voltage value Vtr before the recording medium 9 reaches the transfer section 30. Furthermore, the current measuring section 56b supplies the detection result to the driving controller 59.
Next, the current measuring section 56b detects a current Itr2 of the transfer current after the recording medium 9 has reached the transfer section 30 (step S43). Furthermore, the current measuring section 56b supplies the detection result to the driving controller 59.
Next, the calculating section 57 calculates a resistance value (first electrical resistance value) Rt1 of the transfer section 30 in the state where the recording medium 9 is absent in the transfer section 30 (specifically, between the secondary transfer roller 32 and the secondary transfer backup roller 31), and a resistance value (third electrical resistance value) Rt2 of the transfer section 30 in the state where the recording medium 9 is present in the transfer section 30 (step S44). To be specific, the resistance values Rt1 and Rt2 of the transfer section 30 can be expressed as follows:
Rt1=(Vtr/Itr1)−R (10a)
Rt2=(Vtr/Itr2)−R (10b)
The calculating section 57 calculates the resistance values Rt1 and Rt2 in the transfer section 30 by using expressions (10a) and (10b).
Next, the calculating section 57 calculates the medium resistance value Rb (step S45). Firstly, we will now focus on the region R1. A resistance value Rt3 of the transfer section 30 in the region R1 can be expressed as follows by using the medium resistance value Rb, and the resistance value Rt1 of the transfer section 30 in the state where the recording medium 9 is absent in the transfer section 30:
Rt3=Rb+Rt1×L/W (11)
Here, a second term of the right side of expression (11) is a total resistance value of a resistance value of the transfer belt 11, and a resistance value of the urethane rubber layer 32b in the region R1. Next, we will now focus on the region R2. A resistance value Rt4 of the transfer section 30 in the region R2 can be expressed as follows by using the resistance value Rt3 of the transfer section 30 in the region R1, and the resistance value Rt2 of the transfer section 30 in the state where the recording medium 9 is present in the transfer section 30:
The medium resistance value Rb can be expressed as follows by expressions (11) and (12).
The calculating section 57 calculates the medium resistance value Rb by using the resistance values Rt1 and Rt2 calculated in step S44 (expression (10)), the resistance value Rt4 calculated in step S45 (expression (12)), and expression (13).
From the above, the processing flow (step S5 in
Next, as shown in
When the printing distance M is larger than the predetermined reference distance Mth (“Yes” in step S6), the driving controller 59 confirms whether or not the image forming apparatus 1 is in a state of forming the image (step S7). Furthermore, at this time, the printing distance M is set to 0 as an initial value.
Furthermore, when the transfer section 30 stops the transfer processing (for example, when the area 92 reaches the nip portion between the secondary transfer backup roller 31 and the secondary transfer roller 32) (“NO” in step S7), the image forming apparatus 1 calculates the transfer voltage value Vtr again (step S8).
Calculation of Transfer Voltage Value (Update Value) Vtr
Firstly, the current measuring section 56b of the image forming apparatus 1 detects a current value Itr3 (step S51). That is to say, at this time, the voltage generator 56a supplies the transfer voltage value Vtr to the secondary transfer roller 32 through the resistance element 39, and the recording medium 9 has already reached the transfer section 30. Therefore, the current measuring section 56b detects the current value Itr3 in the state where the recording medium 9 is present in the transfer section 30. Furthermore, the current measuring section 56b supplies the detection result to the driving controller 59.
Next, the calculating section 57 calculates a resistance value (second electrical resistance value) Rt5 of the transfer section 30 in the state where the recording medium 9 is present in the transfer section 30 (specifically, between the secondary transfer roller 32 and the secondary transfer backup roller 31) (step S52). To be specific, the resistance value Rt5 of the transfer section 30 can be expressed as follows:
Rt5=(Vtr/Itr3)−R (14)
The calculating section 57 calculates the resistance value Rt5 of the transfer section 30 by using expression (14).
Next, the calculating section 57 calculates a resistance value Rt6 of the transfer section 30 in the state where the recording medium 9 is absent in the transfer section 30 (step S53). The resistance value Rt5 of the transfer section 30 in the state where the recording medium 9 is present in the transfer section 30, and the resistance value Rt6 of the transfer section 30 in the state where the recording medium 9 is absent in the transfer section 30 have the following relationship:
Here, a first term of the right side of expression (15) shows a conductance in the region R1, while a second term of the right side of expression (15) shows a conductance in the region R2. expression (15) is arranged with respect to the resistance value Rt6, thereby expression (16) is obtained:
L2×Rt62−(L2×Rt5−W×L×Rb)×Rt6+W×(L−W)×Rb×Rt5=0 (16)
Expression (16) is solved with respect to the resistance value Rt6, thereby expression (17) is obtained:
Of two values obtained by using expression (17), the positive one is the resistance value Rt6. The calculating section 57 calculates the resistance value Rt6 of the transfer section 30 in the state where the recording medium 9 is absent in the transfer section 30 by using the medium resistance value Rb calculated in step S5 (expression (13)), the resistance value Rt5 calculated in step S52 (expression (14)), and expression (17).
Next, the calculating section 57 calculates the shaft voltage value Vs0 (step S54). When we will now focus on the region R1, the shaft voltage value Vs0 can be expressed like expression (4). When we will now focus on the region R2, the voltage Vin can be expressed as follows:
Therefore, the shaft voltage value Vs0 can be expressed as follows by using expressions (4) and (18):
The calculating section 57 calculates the shaft voltage value Vs0 by using the resistance value Rt6 calculated in step S53, the target medium current density Jp and the target medium voltage value Vp calculated in step S32, the medium resistance value Rb, and expression (19).
Next, the calculating section 57 calculates the transfer current value Itr (step S55). Firstly, we will now focus on the region R2. Since both the secondary transfer backup roller 31 and the shaft 32a are made of metal, the shaft voltage value Vs0 obtained by focusing on the region R1 in step S54 can also be used in the region R2. A current Iout that flows through the region R2 can be expressed as follows:
Therefore, the transfer current value Itr can be expressed as follows by using expression (20):
Here, a first term of the right side of expression (21) shows a component contributed by the region R1 in the transfer current value Itr, while a second term of the right side of expression (21) shows a component contributed by the region R2 in the transfer current value Itr. The calculating section 57 calculates the transfer current value Itr by using the resistance value Rt6 calculated in step S53 (expression (17)), the shaft voltage value Vs0 calculated in step S54 (expression (19)), and expression (21).
Next, the calculating section 57 calculates the transfer voltage value (update value) Vtr which the voltage generator 56a should generate (step S56). The transfer voltage value (update value) Vtr which the voltage generator 56a should generate can be expressed as follows:
Vtr=Vs0+R×Itr (22)
The calculating section 57 calculates the transfer voltage value (update value) Vtr by using the shaft voltage value Vs0 calculated in step S54 (expression (19)), the transfer current value Itr calculated in step S55 (expression (21)), and expression (22).
From the above, the processing flow (step in
In a period of time for which no image is formed onto the recording medium 9 (non-transfer period which is a period of time other than a period of time for which the transfer section 30 transfers the developer (toner) image onto the recording medium 9), the voltage generator 56a generates the transfer voltage of the transfer voltage value Vtr obtained in step S8 on the basis of the instruction issued from the driving controller 59, and supplies (applies) the transfer voltage to the secondary transfer roller 32 through the resistance element 39. Therefore, the transfer voltage value Vtr is updated for the period of time for which no image is formed. Furthermore, the image forming apparatus 1 continues the printing operation even after updating the transfer voltage value Vtr. As a result, the current density of the current that flows through the recording medium 9 can be made to be about the same as the target medium current density Jp, and the electric potential difference between the voltage value (electric potential) of the front surface and the voltage value (electric potential) of the back surface in the recording medium 9 can be made to be about the same as the target medium voltage value Vp. Therefore, the satisfactory transfer characteristics can be obtained.
In such a way, in the image forming apparatus 1, in a case where the printing distance M is longer than the predetermined reference distance Mth, the resistance value Rt5 of the transfer section 30 is obtained in the state where the recording medium 9 is present in the transfer section 30. Furthermore, the resistance value Rt6 of the transfer section 30 in the state where the recording medium 9 is absent in the transfer section 30 is obtained on the basis of the resistance value Rt5, and the transfer voltage value Vtr is obtained on the basis of the resistance value Rt6. As a result, in the image forming apparatus 1, the image quality can be enhanced. In other words, in a case where the printing is performed continuously for a long time, the resistance value of the transfer section 30 may be changed due to heat, for example. In this case, for example, the current density in the recording medium 9 may deviate from the desired target medium current density Jp, or the electric potential difference between the voltage value (electric potential) of the front surface and the voltage value (electric potential) of the back surface in the recording medium 9 may deviate from the desired target medium voltage value Vp. As a result, the transfer characteristics in the transfer section 30 become worse and, for example, the defective printing such as the blurring of characters is caused. In particular, in a case where the recording medium 9 is the rolled paper, if once the printing is started, the printing is performed continuously for a long time. Therefore, the defective printing caused by the changes of the transfer characteristics is easy to generate. In the image forming apparatus 1, in the case where (each time) the printing distance M is longer than the predetermined reference distance Mth, the resistance value Rt5 of the transfer section 30 is obtained, and the transfer voltage value Vtr for the transfer processing is obtained on the basis of the resistance value Rt5. In other words, the main controller 50 calculates the resistance value Rt5 on the basis of the current value measured by the high-voltage power source section 56 each time the transfer section 30 transfers the developer to the recording medium 9 over the predetermined reference length Mth in the conveyance direction G of the recording medium 9, and obtains the transfer voltage value Vtr on the basis of the resistance value Rt5. As a result, even when the printing is performed continuously for a long time, the current density of the current that flows through the recording medium 9 can be made to be equal or nearly equal to the target medium current density Jp, and the electric potential difference between the voltage value (electric potential) of the front surface and the voltage value (electric potential) of the back surface in the recording medium 9 can be made to be equal or nearly equal to the target medium voltage value Vp. As a result, in the image forming apparatus 1, the satisfactory transfer characteristics can be kept for a long time, and thus the image quality can be enhanced.
In addition, in the image forming apparatus 1, since for the period of time for which no image is formed, the resistance value Rt5 of the transfer section 30 is obtained, the transfer voltage value Vtr can be obtained with high accuracy. For example, when the image forming apparatus 1 is forming the image, since the toner is present in the transfer section 30, the resistance value Rt5 may be influenced by the toner. Therefore, for example, when the transfer voltage value Vtr is obtained on the basis of the resistance value Rt5, the current density in the recording medium 9 may deviate from the desired target medium current density Jp, or the electric potential difference between the voltage value (electric potential) of the front surface and the voltage value (electric potential) of the back surface in the recording medium 9 may deviate from the desired target medium voltage value Vp. In the image forming apparatus 1, the resistance value Rt5 of the transfer section 30 is obtained for the period of time for which no image is formed, and the transfer voltage value Vtr is obtained on the basis of the resistance value Rt5. In other words, the main controller 50 calculates the resistance value Rt5 on the basis of the current value measured by the high-voltage power source section 56 in the non-transfer period that is a period of time other than a period of time in which the transfer section 30 transfers the developer to the recording medium 9, and obtains the transfer voltage value Vtr on the basis of the resistance value Rt5. Therefore, the transfer voltage value Vtr can be obtained with high accuracy without being influenced by the toner. Further, the main controller 50 sets the transfer voltage value Vtr as a new voltage value for the transfer processing within the non-transfer period. As a result, in the image forming apparatus 1, the satisfactory transfer characteristics can be obtained, and thus the image quality can be enhanced.
In addition, in the image forming apparatus 1, since for the period of time for which no image is formed, the transfer voltage value Vtr is updated, the image quality can be enhanced. For example, in a case where the transfer voltage value Vtr is updated when the image forming apparatus 1 is forming the image, since the transfer characteristics are largely changed within one image, the image quality may be reduced. In the image forming apparatus 1, since for the period of time for which no image is formed, the transfer voltage value Vtr is updated, the transfer characteristics are not largely changed within one image. Therefore, the possibility that the image quality is reduced can be reduced.
As set forth hereinabove, in the present embodiment, the resistance value in the state where the recording medium 9 is present in the transfer section 30, and the transfer voltage value Vtr is obtained on the basis of that resistance value. Therefore, even when the printing is performed continuously for a long time, the image quality can be enhanced.
In addition, in the present embodiment, for the period of time for which no image is formed, the resistance value is obtained in the state where the recording medium 9 is present in the transfer section 30. Therefore, the transfer voltage value Vtr can be obtained with high accuracy, so that the image quality can be enhanced.
In addition, in the present embodiment, since for the period of time for which no image is formed, the transfer voltage value Vtr is updated, the image quality can be enhanced.
Although in the above embodiment, the toner images formed by the ID units 4, respectively, are transferred (primary transfer) onto the surface to be transferred of the transfer belt 11, and thereafter, the toner images on the surface to be transferred of the transfer belt 11 are transferred (secondary transfer) onto the surface to be transferred of the recording medium 9, the present invention is by no means limited thereto. Instead thereof, the toner images formed by the ID units 4, respectively, may be directly transferred on the surface to be transferred of the recording medium 9. In this case, the calculating section 57 may calculate the transfer voltage values in the five transfer rollers facing the five ID units 4, respectively. Further, the present invention is by no means limited thereto, and thus, for example, with respect to only a part of the five transfer rollers, the transfer voltage value(s) may be calculated by using the above method, and the transfer voltage values in the remaining transfer rollers may be roughly estimated by using the calculation results. To be specific, for example, the transfer voltage value in the transfer roller disposed on the most upstream side in the conveyance direction of the recording medium 9, and the transfer voltage value in the transfer roller disposed on the most downstream side of the five transfer rollers may be calculated by using the above described method.
Although the predetermined reference distance Mth is made to be, for example, 1 meter in the above embodiment, the present invention is by no means limited thereto. For example, the value of the predetermined reference distance Mth is changed depending on, for example, the print speed, the quality of the material of the secondary transfer roller 32, and so on. Therefore, for example, it is preferable that the value of the predetermined distance Mth be set every kind of the image forming apparatus 1.
Although the calculating section 57 obtains the transfer voltage value Vtr in the case where the printing distance M is longer than the predetermined reference distance Mth in the above embodiment, the present invention is by no means limited thereto. Instead thereof, for example, the transfer voltage value Vtr may also be obtained in the case where the temperature of the transfer section 30 (environmental temperature) is higher than a predetermined temperature. In this case, if the main controller 50 determines that the environmental temperature of the transfer section 30 detected by the environmental detector 52 is not lower than the predetermined temperature, the main controller 50 calculates the resistance value Rt5 on the basis of the current value measured by the high-voltage power source section 56. The temperature of the transfer section 30 may be estimated or detected on the basis of a detection value detected by a temperature sensor such as the environmental temperature sensor 52a, for example. For example, in a case where the printing is performed continuously for a long time and the temperature of the transfer section 30 becomes higher than the predetermined temperature, the calculating section 57 obtains (updates) the transfer voltage value Vtr. As a result, the image quality can be enhanced similarly to the case of the above embodiment.
Although in the above embodiment, the cutting unit 24 cuts the recording medium 9 to put the transfer section 30 in the state where the recording medium 9 is absent in the transfer section 30, the present invention is by no means limited thereto. For example, even when the recording medium 9 is used up in the rolled paper feeder 21, and thus rolled paper is replenished, the transfer section 30 is put in the state where the recording medium 9 is absent therein. Therefore, even in this case, the above technique may be applied (updating the transfer voltage value Vtr).
In the steps S31 and S 32 in
For example, although in the above embodiment and the above modified examples, the printing is performed on the rolled paper as the recording medium 9, the present invention is by no means limited thereto, and thus the printing may be performed on any type of medium as long as a recording medium. To be specific, for example, a so-called continuous-form paper (continuous paper) or the like in which a small-hole line is provided every predetermined length may be used as the recording medium 9.
In addition, for example, in the above embodiment and the above modified examples, the present invention is applied to a color printer. However, the present invention is by no means limited thereto, and thus instead thereof, the present invention may be applied to a monochrome printer, for example. Further, the above embodiment and the above modified examples may be applied to an image forming apparatus that transfer section (including the primary transfer rollers 7, for example) directly transfers the developer on the photosensitive body 41 onto the recording medium 9.
In addition, for example, in the above embodiment and the above modified examples, the present invention is applied to the printer. However, the present invention is by no means limited thereto, and thus instead thereof, the present invention may be applied to a Multi Function Peripheral (MFP) having functions such as a printer, a facsimile, and a scanner and so on, for example.
Although the present invention has been described so far by giving the embodiment and the modified examples thereof, the present invention is by no means limited to the embodiment and the modified examples, and various changes can be made.
Number | Date | Country | Kind |
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2015-054254 | Mar 2015 | JP | national |
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Entry |
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English translation of JP-2015055672. |
English translation of JP 2009047833. |
Number | Date | Country | |
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20160274502 A1 | Sep 2016 | US |