JP2008242026A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which does not control a transfer condition by the electric resistance of a recording medium while transferring to the recording medium on the more optimum transfer condition. <P>SOLUTION: In the image forming apparatus, a toner image formed on an image carrier can be preferably transferred onto the recording medium without causing transfer defect of any recording medium by applying transfer voltage to be applied to each transfer roller decided based on dielectric thickness and relaxation time calculated by a transfer control part from a transfer voltage applying part to a transfer part. Thus, the high-quality image is formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image by transferring a toner image formed on an image carrier to a recording medium.

  2. Description of the Related Art Conventionally, image forming apparatuses such as color electrophotographic printers are arranged in the form of a photoconductor on which an electrostatic latent image is formed using a photoconductive phenomenon, charging means for uniformly charging the photoconductor. A plurality of process units comprising LED (Light Emitting Diode) elements and comprising exposure means for exposing in accordance with image data and developing means for developing the electrostatic latent image written on the photoreceptor by the exposure means with toner. Used.

  The tandem color image forming apparatus has four process units corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively, and is electrostatically adsorbed on the conveyance belt. The toner images developed in the respective process units are sequentially transferred onto the conveyed recording medium. At this time, the toner images are arranged at positions facing the process unit with the recording medium interposed therebetween, and are sequentially transferred to the recording medium by electrostatic force generated between the transfer means to which a voltage having a polarity opposite to that of the toner particles is applied. Is done. As this type of apparatus, there is an apparatus that measures an electrical resistance of a recording medium and controls a transfer condition of a transfer unit based on the measurement information (for example, see Patent Document 1).

JP 7-175350 A

  In the image forming apparatus described in Patent Document 1, the transfer condition is determined from the electric resistance of the recording medium. However, even if transfer is performed on the recording medium having the same electric resistance under the same transfer condition, the recording medium There is a problem that a good transfer result cannot be obtained depending on the type.

  SUMMARY OF THE INVENTION Accordingly, in view of the above circumstances, an object of the present invention is to provide an image forming apparatus that can transfer to a recording medium under a more optimal transfer condition instead of controlling the transfer condition with the electric resistance of the recording medium. To do.

  The image forming apparatus of the present invention includes a transfer unit that transfers a toner image formed on an image carrier onto a recording medium with electrostatic force, a transfer voltage application unit that applies a transfer voltage to the transfer unit in an adjustable manner, Measured by a dielectric constant measuring unit that measures the dielectric constant of the recording medium, a resistance measuring unit that measures the resistance value of the recording medium, a thickness measuring unit that measures the thickness of the recording medium, and the dielectric constant measuring unit. Further, the applied voltage of the transfer voltage applying unit is controlled based on the dielectric constant of the recording medium, the resistance value of the recording medium measured by the resistance measuring unit, and the thickness of the recording medium measured by the thickness measuring unit. And a transfer control unit that performs the transfer control.

  According to the image forming apparatus of the present invention, the thickness measuring unit measures the thickness of the recording medium, the dielectric constant measuring unit measures the dielectric constant of the recording medium, and the resistance measuring unit measures the resistance value of the recording medium. The transfer control unit calculates the dielectric thickness and relaxation time of the recording medium from the measured thickness, dielectric constant, and resistance value of the recording medium, and applies the transfer to each transfer roller based on the dielectric thickness and relaxation time. Determine the voltage.

  The image forming apparatus of the present invention also includes a transfer unit that transfers a toner image formed on an image carrier onto a recording medium with electrostatic force, and a transfer voltage application unit that applies a transfer voltage to the transfer unit in an adjustable manner. A dielectric thickness measuring unit for measuring the dielectric thickness of the recording medium, a resistance measuring unit for measuring a resistance value of the recording medium, and the dielectric thickness and the resistance measurement of the recording medium measured by the dielectric thickness measuring unit. And a transfer control unit that controls an applied voltage of the transfer voltage applying unit based on a resistance value of the recording medium measured by the printing unit.

  According to the image forming apparatus of the present invention, the dielectric thickness measurement unit measures the dielectric thickness of the recording medium, and the resistance measurement unit measures the resistance value of the recording medium. Then, the transfer control unit determines the transfer voltage to be applied to each transfer roller based on the measured dielectric thickness of the recording medium and the relaxation time of the recording medium calculated from the resistance value.

  Furthermore, an image forming apparatus of the present invention includes a transfer unit that transfers a toner image formed on an image carrier onto a recording medium with electrostatic force, and a transfer voltage application unit that applies a transfer voltage to the transfer unit in an adjustable manner. A capacitance measuring unit that measures a capacitance of the recording medium, a resistance measuring unit that measures a resistance value of the recording medium, and a capacitance of the recording medium measured by the capacitance measuring unit And a transfer control unit that controls an applied voltage of the transfer voltage applying unit based on a resistance value of the recording medium measured by the resistance measuring unit.

  According to the image forming apparatus of the present invention, the capacitance measuring unit measures the capacitance of the recording medium, and the resistance measuring unit measures the resistance value of the recording medium. The transfer control unit calculates the dielectric thickness and relaxation time of the recording medium from the measured capacitance and resistance value of the recording medium, and the transfer voltage applied to each transfer roller based on the dielectric thickness and relaxation time. To decide.

  The image forming apparatus of the present invention applies a transfer voltage to be applied to each transfer roller determined based on the dielectric thickness and relaxation time calculated by the transfer control unit from the transfer voltage application unit to the transfer unit. In any recording medium, the toner image formed on the image carrier can be transferred onto the recording medium without causing a transfer defect. Thereby, a high-quality image can be formed.

  The image forming apparatus of the present invention will be described below with reference to the drawings. The image forming apparatus of the present invention is not limited to the following description, and can be appropriately changed without departing from the gist of the present invention.

[Embodiment 1]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 1 according to the present invention, and FIG. 2 is a diagram illustrating a structure of the image forming apparatus 1 described in the first embodiment. The image forming apparatus 1 includes a host interface unit 50 that performs a physical layer interface with a host computer and performs communication, and a command / image processing unit 51 that interprets commands and image data from the host computer or develops them into bitmap data. And an LED head interface unit 52 that processes the image data from the command / image processing unit 51 in accordance with the interface of the LED head 3 and processes the data according to a command from the command / image processing unit 51 to perform motor control and printing. It comprises a mechanism control unit 53 as a transfer control unit for performing control and the like.

  Further, the image forming apparatus 1 includes a group of sensors for detecting various situations and a plurality of actuators for control output, which are connected to the mechanism control unit 53 and are comprehensively controlled by the mechanism control unit 53. The sensor group includes sensors 21 and 22 for detecting the recording medium P, a sensor 23 for detecting the recording medium P separated from the conveyance belt 12 described later, a color shift detection sensor 24 for detecting color shift, and a later-described sensor group. A discharge sensor 27 for monitoring the jam in the fixing mechanism and the winding of the recording medium P around the heat roller 25, a thermistor 28 for monitoring the temperature of the heat roller 25, and an environmental temperature sensor for measuring the ambient temperature and relative humidity of the apparatus. 34.

  As actuators, a hopping motor 54 that drives the hopping roller 16, a registration motor 55 that drives the registration roller 17, a belt motor 56 that drives the driving roller 13 to move the conveyor belt 12, and a heat roller 25 are driven. The heater motor 57 for driving, the drum motor 58 for driving the photosensitive drum, the heater 59 disposed in the heat roller 25, and a microprocessor or a custom LSI (large scale integrated), and a charge supplied to each printing mechanism A high voltage control unit 60 that generates a control signal for generating a (charging) voltage, a development bias, a transfer voltage, and the like, a CH generation unit 61 that supplies a charge voltage to each printing mechanism, and development to each printing mechanism DB generator 6 for supplying a bias 2 and a TR generator 63 as a transfer voltage application unit for supplying a transfer voltage to the transfer roller of each printing mechanism.

  The mechanism control unit 53 is connected to the measurement unit 101 that measures the relative dielectric constant of the recording medium P, and performs control in the same manner as the sensor group and the actuator described above. The measurement unit 101 serves as both a thickness measurement unit that measures the thickness of the recording medium P and a resistance measurement unit that measures the resistance value of the recording medium P.

  Further, the image forming apparatus 1 includes a storage unit 80. The storage unit 80 stores the volume resistivity that can be derived from the thickness, relative dielectric constant, and resistance value of the recording medium P measured by the measurement unit 101.

  The image forming apparatus 1 includes four printing mechanisms 2K, 2Y, 2M, and 2C corresponding to toners as four color developers of cyan (C), magenta (M), yellow (Y), and black (K), respectively. Are arranged side by side along the transport path from the insertion side of the recording medium P to the discharge side in this order. The printing mechanisms 2K, 2Y, 2M, and 2C are electrophotographic LED print units for recording a color image using toner of each color on the recording medium P that is transported to the transport path.

  Specifically, the printing mechanisms 2K, 2Y, 2M, and 2C respectively include photosensitive drums 6K, 6Y, 6M, and 6C as electrostatic latent image carriers, and surfaces of the photosensitive drums 6K, 6Y, 6M, and 6C. Charging heads 5K, 5Y, 5M, and 5C that are to be charged, and LED heads 3K and 3Y that form electrostatic latent images by exposing the photosensitive drums 6K, 6Y, 6M, and 6C based on the input image data. 3M, 3C, developing rollers 7K, 7Y, 7M, 7C for developing the electrostatic latent images formed on the surfaces of the photosensitive drums 6K, 6Y, 6M, 6C with toner, and developing rollers 7K, 7Y, 7M, Developing blades 8K, 8Y, 8M, and 8C that uniformly regulate the toner layer formed on the surface of 7C, and sponge rollers 9K and 9 that supply toner to developing rollers 7K, 7Y, 7M, and 7C Has 9M, and 9C, the toner cartridge 10K for containing toner of each color, 10Y, 10M, and 10C.

  Below the photosensitive drums 6K, 6Y, 6M, and 6C of the printing mechanisms 2K, 2Y, 2M, and 2C, the toner images developed on the photosensitive drums 6K, 6Y, 6M, and 6C are recorded and conveyed by the conveyance belt 12, respectively. Transfer rollers 4K, 4Y, 4M, and 4C are provided as transfer portions that transfer to the medium P. A conveyor belt 12 is movably disposed between the transfer rollers 4K, 4Y, 4M, and 4C and the photosensitive drums 6K, 6Y, 6M, and 6C. The conveyor belt 12 is formed in a belt-like structure without a seam, and is stretched between a driving roller 13 and a driven roller 14. The material is a high resistance semiconductive plastic film. The drive roller 13 is connected to a belt motor 56, and the belt motor 56 causes the drive roller 13 to rotate in the arrow g direction. The driven roller 14 pulls the conveyor belt 12 in the direction of arrow f so that the conveyor belt does not slack.

  Further, the image forming apparatus 1 is provided with a paper feed mechanism for supplying paper to the transport path. This paper feed mechanism is composed of a hopping roller 16, a registration roller 17, a recording medium cassette 19, and a guide 20. The recording media P accommodated in the recording media cassette 19 are selected one by one by a discriminating means (not shown), fed out by the hopping roller 16, guided by the guide 20, and reach the registration roller 17.

  When the recording medium P is fed out in an incorrect posture, for example, when the recording medium P is fed obliquely, the posture of the recording medium P is corrected by the registration roller 17 and the pinch roller 18 facing the registration roller 17. Thereafter, the recording medium P is guided from the registration roller 17 to between the suction roller 15 and the conveyance belt 12. The suction roller 15 presses the recording medium P against the driven roller 14 and charges it. The conveying belt 12 electrostatically attracts the charged recording medium P on the upper surface thereof.

  The sensors 21 and 22 are respectively arranged before and after the registration roller 17 and detect the recording medium P. A sensor 23 is provided on the downstream side of the conveyance belt 12 in the conveyance direction of the recording medium P. The sensor 23 is for detecting the separated recording medium P from the conveyor belt 12 and detects the rear end position of the recording medium P.

  The recording medium P separated from the conveyance belt 12 is guided to the fixing mechanism. The fixing mechanism includes a heat roller 25 and a pressure roller 26 that presses the recording medium P. The heat roller 25 is driven by a heater motor 57, and the pressure roller 26 rotates around the heat roller 25.

  The fixing mechanism is disposed further downstream in the conveyance direction of the recording medium P of the sensor 23, and heats and melts the toner on the recording medium P to fix the toner image on the recording medium P. A thermistor 28 is provided in the vicinity of the surface of the heat roller 25 and a discharge sensor 27 is provided further downstream in the conveyance direction of the recording medium P of the heat roller 25, so that a jam in the fixing mechanism or the recording medium P is wound around the heat roller 25. Is monitoring. The thermistor 28 monitors the temperature of the heat roller 25. A guide 29 for conveying the recording medium P to the discharge stacker 30 is provided downstream of the discharge sensor 27 in the conveying direction of the recording medium P, and guides the printed recording medium P to be discharged to the discharge stacker 30.

  A cleaning mechanism including a cleaning blade 32 and a waste toner tank 33 is provided below the conveyor belt 12. The cleaning blade 32 is provided at a position facing the driven roller 14 via the lower half 12b of the conveyor belt 12, and is made of a flexible rubber material or plastic material. The cleaning blade 32 scrapes off toner remaining on the surface as waste toner in the upper half 12a of the conveyor belt 12. The waste toner tank 33 is provided in the vicinity of the cleaning blade 32, and can store the waste toner scraped off by the cleaning blade 32.

  In the image forming apparatus 1, the measurement unit 101 is installed in the medium conveyance path by the guide 20. FIG. 3 is a schematic diagram showing the configuration of this measurement unit. The measurement unit 101 includes an electrode 121 and an electrode 122 as contact members, and is disposed at a position where the recording medium P conveyed along the guide 20 is sandwiched between the electrode 121 and the electrode 122.

  The electrode 121 is connected to one end of a lever 124 that is rotatably installed around a joint 125. A tension spring 123 is provided on one end side of the lever 124 to which the electrode 121 is connected, and the tension spring 123 presses the electrode 121 to the method of the electrode 122 with a predetermined pressure.

  A cam 127 is provided on the other end side of the lever 124. By rotating the cam 127, the lever 124 is integrated with the electrode 121 and is movable in the vertical direction. The cam 127 rotates in accordance with the conveyance of the recording medium P so that the electrode 121 is lifted when the recording medium P reaches the measuring unit 101, and sandwiches the recording medium P between the electrode 121 and the electrode 122. Can do.

  A displacement sensor 126 is provided near the other end of the lever 124 opposite to the end provided with the tension spring 123. The displacement sensor 126 is configured by a reflection type photosensor, and measures the distance from the other end of the lever 124. The voltage output is A / D converted and detected by the mechanism control unit 53. The measuring unit 101 can measure the thickness of the recording medium P from the distance between the displacement sensor 126 and the other end of the lever 124.

  In the measurement unit 101, in addition to the thickness of the recording medium P, the relative dielectric constant and resistance value of the recording medium P can be measured. FIG. 4 is a circuit connection diagram for measuring the relative dielectric constant and the resistance value by the measurement unit. A switch 135 is connected to the electrode 122 of the measurement unit 101, and the switch 135 can be selectively connected to a grounded AC power supply 131 or a grounded DC power supply 132.

  A switch 136 is connected to the electrode 121, and the switch 136 can be selectively connected to the load resistor 133 or the variable load resistor 134. The AC power supply 131 and the DC power supply 132 are connected to the ground together with the load resistor 133 and the variable load resistor 134. The switch 135 and the switch 136 operate in conjunction with each other. When the electrode 122 is connected to the AC power supply 131, the load resistor 133 and the electrode 121 are connected, and when the electrode 122 is connected to the DC power supply 132, the switch 135 and the switch 136 are variable. The load resistor 134 and the electrode 121 are connected. Control of the switches 135 and 136 is controlled by the mechanism control unit 53.

  The measuring unit 101 has a terminal 137 between the electrode 121 and the switch 136, and a terminal 138 between the electrode 122 and the switch 135. Outputs from the terminals 137 and 138 can be monitored by the mechanism control unit 53.

  The mechanism control unit 53 can calculate the capacitance of the capacitor formed by the electrodes 121 and 122 and the recording medium P from the voltage difference between the AC power supply 131 and the load resistor 133 from the output voltages of the terminals 137 and 138. it can. Based on this capacity, the dielectric constant of the recording medium P can be derived.

  Further, the mechanism control unit 53 can calculate the value of the current flowing through the recording medium P from the resistance value of the variable load resistor 134 and the output of the DC power source 132. From the calculated current value and the voltage drop of the recording medium P, the resistance value of the recording medium P can be derived, and the volume resistivity can be calculated.

  Thus, the measurement unit 101 functions as a thickness measurement unit, a dielectric constant measurement unit, and a resistance measurement unit, but the electrode 121 and the electrode 122 that are in contact with the recording medium P are common. This eliminates the need to stop the recording medium P many times on the conveyance path in order to measure the thickness, relative dielectric constant, and resistance value of the recording medium P.

  The image forming apparatus 1 of the present invention having such a configuration operates as follows. When the image forming apparatus 1 receives print data transmitted from a host apparatus, that is, a host computer, via the host interface unit 50, the command / image processing unit 51 issues a print instruction to the mechanism control unit 53. When the mechanism control unit 53 receives a print instruction, the mechanism control unit 53 starts control to warm the heater 59. At this time, the mechanism control unit 53 refers to the environmental temperature sensor 34 and reads the optimum fixing temperature stored in the storage unit 80. Then, while monitoring the temperature detection value of the thermistor 28, the heater 59 is ON / OFF controlled so as to maintain the optimum fixing temperature. One page of image data to be printed on the recording medium P is stored in the memory built in the image processing unit 51, and the printing process is started when the temperature detection value of the thermistor 28 reaches the optimum temperature.

  Next, processing for printing print data on the recording medium P stored in the recording medium cassette 19 will be described. After the conditions for enabling the printing process are satisfied, the command / image processing unit 51 issues a print start command to the mechanism control unit 53. When the mechanism control unit 53 receives a print start command, the mechanism control unit 53 drives the belt motor 56 and the drum motor 58 to rotate the drive roller 13 to drive the transport belt 12. Then, each printing mechanism 2K, 2Y, 2M, 2C is driven. The toner in the printing mechanism 2K is rubbed strongly by the sponge roller 9K and the developing roller 7K and is frictionally charged. Thereafter, the mechanism control unit 53 drives the hopping motor 54 and rotates the hopping roller 16 to send only one recording medium P of the recording medium cassette 19 to the guide 20. When the leading edge of the recording medium P reaches between the registration roller 17 and the pinch roller 18, the hopping motor 54 stops.

  Then, each of the registration roller 17 and the heat roller 25 is rotated. At the same time, the mechanism control unit 53 turns on a suction charging power source (not shown) and supplies power to the suction roller 15. The recording medium P is conveyed by the registration roller 17, and the leading end reaches between the suction roller 15 and the conveyance belt 12. At this time, the leading edge of the recording medium P is attracted to the transport belt 12 by the electrostatic force between the attracting roller 15 and the driven roller 14. Further, when the registration roller 17 rotates, the recording medium P is conveyed in the direction of arrow e in the figure while being sucked by the conveyance belt 12.

  In order to supply power to the charging roller 5K and the developing roller 7K, the mechanism control unit 53 issues a command to the high voltage control unit 60, and the charging power source (CH generating unit 61) and the DB bias power source (DB generating unit 62). Set to ON. Thereby, the surface of the photosensitive drum 6K of the printing mechanism 2K is uniformly charged by the charging of the charging roller 5K. The developing roller 7K is also charged to a predetermined high voltage, and the charged toner adheres to the surface of the developing roller 7K with a uniform thickness by the developing blade 8K. The printing mechanisms 2Y, 2M, and 2C operate in the same manner, and each color toner adheres to the surfaces of the developing rollers 7Y, 7M, and 7C with a uniform thickness.

  When notified from the mechanism control unit 53 that the recording medium P has reached a predetermined position, the image processing unit 51 transmits black image data for one line from the memory storing the black image data. Transmit to the head interface unit 52. The LED head interface unit 52 converts the received image data into a format that can be transmitted to the LED head 3K, and then transmits it to the LED head 3K. The LED head 3K turns on the LED element based on the transmitted image data, and forms an electrostatic latent image for one line corresponding to the image data on the surface of the charged photosensitive drum 6K.

  Similarly, the black image data sent from the memory for each line is formed into an electrostatic latent image on the surface of the photosensitive drum 6K that rotates one after another until the page is filled. Black toner adheres from the charged developing roller 7K to the surface of the photosensitive drum 6K on which the electrostatic latent image is formed. By rotating the photosensitive drum 6K, electrostatic latent images are successively developed with black toner. When the leading edge of the recording medium P reaches between the photosensitive drum 6K and the transfer roller 4K, the mechanism control unit 53 issues a command to the high-pressure control unit 60 and turns on the black transfer power supply (TR generating unit 63). To do. As a result, the toner image on the surface of the photosensitive drum 6K is electrically transferred onto the recording medium P by the transfer roller 4K. By rotating the photosensitive drum 6K, the toner images are successively transferred onto the recording medium P, and a black image for one page is transferred onto the recording medium P. Thus, the transfer of the black toner image onto the recording medium P by the printing mechanism 2K is completed.

  The conveyance belt 12 continues to move, the recording medium P moves from the printing mechanism 2K to the printing mechanism 2Y, and the yellow toner image is transferred by the printing mechanism 2Y. The yellow toner image forming operation is the same as the black toner image forming operation. Subsequently, the toner images are transferred to the recording medium P in succession with magenta and cyan, and the toner images of the respective colors are transferred onto the recording medium P in an overlapping manner. Thereafter, the recording medium P is transported by the transport belt 12 to a fixing mechanism including a heat roller 25 and a pressure roller 26.

  When the recording medium P reaches the fixing mechanism, the toner image is thermally fixed to the recording medium P by the heat roller 25 that has already reached a fixing temperature and the pressure roller 26 that is in pressure contact with the heat roller 25. When the fixing is completed, the recording medium P is discharged to the discharge stacker 30. In this discharge process, the discharge sensor 27 detects the rear end of the recording medium P and notifies the mechanism control unit 53 of the detection. When the notification of the end of discharge is received, the mechanism control unit 53 stops all the motors. In each of the printing mechanisms 2K, 2Y, 2M, and 2C, when the toner transfer is completed, the transfer power supply (TR generating unit 63) is turned off, and the charging power supply (CH generating unit 61) and DB bias power supply ( The DB generator 62) is turned off when the rotation of the photosensitive drums 6K, 6Y, 6M, and 6C is stopped. As described above, a color image is recorded on the recording medium P fed out from the recording medium cassette 19.

  Next, a transfer voltage control operation as a transfer condition when the toner image is transferred to the recording medium P by the image forming apparatus 1 will be described.

The measurement unit 101 of the image forming apparatus 1 can measure the thickness d, the relative dielectric constant ε _r , and the resistance value R ₁ of the recording medium P. First, measurement of the thickness d of the recording medium P in the measurement unit 101 will be described.

  The mechanism control unit 53 controls the hopping motor 54 to drive the hopping roller 16 and sends the recording medium P to the measurement unit 101. At this time, the mechanism control unit 53 rotates the cam 127 to move the electrode 121 upward via the lever 124 to move away from the electrode 122, and is conveyed along the guide 20 between the electrode 121 and the electrode 122. It is assumed that the recording medium P can be sandwiched.

  The hopping roller 16 is driven by a hopping motor 54 controlled by the mechanism control unit 53 and stops when the recording medium P reaches the measurement unit 101. The feed amount of the recording medium P is controlled by the mechanism control unit 53 monitoring the rotation amount of the hopping motor 54. When the recording medium P reaches the measuring unit 101 and stops, the mechanism control unit 53 rotates the cam 127 to sandwich the recording medium P between the electrode 121 and the electrode 122.

  When the recording medium P is sandwiched between the electrode 121 and the electrode 122, the mechanism control unit 53 receives the output from the displacement sensor 126 composed of a photo sensor and the other side opposite to the end where the tension spring 123 of the lever 124 is provided. The displacement of the end is detected, and the distance between the displacement sensor 126 and the lever 124 is measured. Thereby, the displacement amount of the electrode 121, that is, the thickness d of the recording medium P can be measured from the distance between the displacement sensor 126 and the lever 124 and the dimension of the lever 124. Thus, the thickness d of the recording medium P measured by the measurement unit 101 is stored in the storage unit 80.

Next, measurement of the relative dielectric constant ε _r of the recording medium P in the measurement unit 101 will be described. When the recording medium P is sandwiched between the electrode 121 and the electrode 122 by the rotation of the cam 127, the mechanism control unit 53 drives the switch 135 and the switch 136 at the same time, connects the electrode 122 to the AC power supply 131, and the electrode 121. Is connected to the load resistor 133. As a result, the supply of the AC voltage from the AC power supply 131 is started, and the mechanism control unit 53 detects the voltage values of the terminal 137 and the terminal 138 by an AD converter (not shown) provided in the mechanism control unit 53.

The amplitude and frequency of the AC voltage output from the AC power supply 131 are determined in consideration of the areas of the electrodes 121 and 122, for example, the amplitude V ₀ = 5 [V] and the frequency f = 1000 [Hz]. . The detection of the voltage of the terminal 137 and the terminal 138 is performed at a frequency 10 ⁵ [Hz] which is sufficiently faster than the frequency of the AC power supply 131, for example, 100 times 1000 [Hz], and the detected voltage value is at least The data is stored in the storage unit 80 over one AC power supply cycle.

  In the circuit shown in FIG. 4, the electrode 121 and electrode 122 of the measurement unit 101 and the recording medium P play a role of a capacitor. Therefore, when measuring the relative permittivity, the measurement unit 101 is a series AC circuit including a load resistor 133 and a capacitor. A phase difference φ as shown in the following formula (1) is generated between the AC power supply 131 and the current flowing through the circuit.

In the above formula (1), R is the resistance value of the load resistor 133, for example, 10 ⁷ [Ω], C is the capacitance of the capacitor composed of the electrodes 121 and 122 and the recording medium P, and ω is The angular frequency corresponding to the output frequency f of the AC power supply 131 is represented by ω [rad / s] = 2πf.

  When the mechanism control unit 53 detects the output voltage values of the terminals 137 and 138, for example, as shown in FIG. From the circuit of the measurement unit 101 in FIG. 4, the output of the terminal 137 corresponds to the voltage of the load resistor 133, and the output of the terminal 138 corresponds to the voltage of the AC power supply 131. Since the phase of the current flowing through this circuit is the same as the voltage of the load resistor 133, the time Δt at which the output peak value of the terminal 137 and the output peak value of the terminal 138 are shifted as shown in FIG. The phase difference φ can be calculated from the following equation (2).

  In the circuit shown in FIG. 4, since the inductance is almost zero, the phase of the terminal 137 corresponding to the phase of the current is always ahead of the phase of the terminal 138 that is the phase of the voltage of the AC power supply 131. According to the above equation (1), since the phase difference φ is always positive in the direction in which the phase of the current is delayed, in this circuit, the phase difference φ is always negative.

  Since the phase difference φ is calculated from the output voltages of the terminal 137 and the terminal 138, the capacitance C of the capacitor can be calculated from the following equation (3) that can be derived from the above equation (1).

The capacitance C of the capacitor composed of the electrode 121 and the electrode 122 and the recording medium P has a relative dielectric constant ε _r , a thickness d of the recording medium P, an area S of the electrode 121 and the electrode 122, and a vacuum dielectric constant ε ₀ (8.88541872 × 10 ¹² [F / m]) can also be used to express the following equation (4).

Using the capacitance C of the capacitor calculated from the equation (3), the relative dielectric constant ε _r of the recording medium P can be derived from the following equation (5) that can be derived from the above equation (4).

The relative dielectric constant ε _r is the ratio between the vacuum dielectric constant ε ₀ and the dielectric constant ε, and can be expressed by the following equation (6). Then, obtaining the relative dielectric constant ε _r is equivalent to obtaining the dielectric constant ε.

The area S of the electrode 121 and the electrode 122 in the above formula (5) is known, and is 0.0004 [m] as an example. For example, when the thickness d of the recording medium P is 0.0001 [m] in the measurement unit 101 and the phase difference φ calculated by the above equation (2) is −π / 4 radians, the relative dielectric constant ε of the recording medium P _From the formula (5), _r becomes ε _r = dC / ε ₀ S = 2.27. Thus, the relative dielectric constant ε _r measured by the measurement unit 101 is stored in the storage unit 80.

Then, measurement of the resistance value of the recording medium P in the measurement unit 101 will be described. After measuring the relative dielectric constant ε _r by the measurement unit 101, the mechanism control unit 53 drives the switch 135 and the switch 136 at the same time, connects the electrode 122 to the DC power source 132, and connects the electrode 121 to the variable load resistor 134. Connect. As a result, a predetermined voltage V _DC is applied from the DC power source 132, and the mechanism control unit 53 controls the variable load resistor 134 so that the voltage of the terminal 137 falls within a predetermined range, and the variable load resistor 134. And the potential of the terminal 137 is measured. Current _{I DC} flowing from the potential _{V RV} variable load resistor 134 of a resistance value _{R V} and terminal 137 of the variable load resistor 134 can be calculated by the following equation (7).

By Kirchhoff's law, it is equal to the current flowing through the recording medium P is sandwiched between the electrode 121 and the electrode 122 of the measuring unit 101 and the current I _DC flowing through the variable load resistor 134. Therefore, the resistance value R ₁ per area of the recording medium P can be derived from the current value flowing through the variable load resistor 134 and the voltage value of the terminal 137 using the following equation (8).

In the above formula (8), the areas S of the electrodes 121 and 122 are known. Thus, by the thickness d of the measured recording medium P and the resistance value R ₁ at the measurement part 101, the volume resistivity of the recording medium P [rho can be calculated by the following equation (9).

For example, when the applied voltage V _DC from the DC power supply 132 is 5 [V], the potential V _{RV of the} terminal 137 is 1 [V], and the resistance value R _V of the variable load resistor 134 is 5 × 10 ⁷ [Ω]. From the above equations (7), (8), and (9), ρ = 8 × 10 ⁸ [Ω · m]. Thus, the volume resistivity ρ of the recording medium P calculated by the measurement unit 101 is stored in the storage unit 80.

The transfer conditions are controlled based on the thickness d, relative dielectric constant ε _r , and volume resistivity ρ of the recording medium P stored in the storage unit 80. The mechanism control unit 53 calculates the dielectric thickness D from the thickness d of the recording medium P stored in the storage unit 80 and the relative dielectric constant ε _r . The dielectric thickness D can be expressed as the thickness d of the recording medium P divided by the relative dielectric constant ε _r of the recording medium P as shown in the following formula (10).

At this time, the mechanism control unit 53 calculates the relaxation time τ from the relative dielectric constant ε _r and the volume resistivity ρ of the recording medium P stored in the storage unit 80. The relaxation time τ can be expressed by the product of the relative dielectric constant ε _r , the vacuum dielectric constant ε _0, and the volume resistivity ρ, as shown in the following formula (11).

  The calculated dielectric thickness D and relaxation time τ of the recording medium P are stored in the storage unit 80.

  As described above, after the dielectric thickness D and the relaxation time τ are calculated, the mechanism control unit 53 refers to the transfer voltage control table. The transfer voltage control table is a table indicating voltages applied to the transfer rollers 4K, 4Y, 4M, and 4C by the TR generation unit 63, and is stored in the storage unit 80. As shown in FIG. 6, the transfer voltage control table includes a first color transfer voltage control table, a difference table between the first color transfer voltage and the second color transfer voltage, a difference table between the second color transfer voltage and the third color transfer voltage, It is composed of a difference table between the third color transfer voltage and the fourth color transfer voltage.

  The first color transfer voltage control table of the transfer voltage control table is determined depending on the dielectric thickness D. FIG. 7 is a diagram for explaining the relationship between the dielectric thickness of the recording medium and the transfer voltage. During the transfer operation of the first color toner image, the voltage drop of the transfer voltage increases as the dielectric thickness D of the recording medium P increases. In order for the voltage in the gap between the recording medium having a large dielectric thickness D and the photosensitive drum 6 to be the same as the voltage in the gap between the recording medium having a small dielectric thickness D and the photosensitive drum 6, the dielectric thickness It is necessary to apply a transfer voltage setting value 1 larger than the transfer voltage setting value 2 applied to the shaft of the transfer roller 4 when the recording medium is thin D. Accordingly, the electric field strength in the gap between the photosensitive drum 6 and the recording medium P on which the transfer is performed does not depend on the recording medium P having a different dielectric constant and thickness, so that the voltage on the surface of the recording medium P becomes constant. Therefore, the mechanism control unit 53 controls the voltage to be applied to the shaft of the transfer roller 4 in consideration of the voltage drop difference due to the dielectric thickness D.

  The difference table between the first color transfer voltage and the second color transfer voltage, the difference table between the second color transfer voltage and the third color transfer voltage, and the difference table between the third color transfer voltage and the fourth color transfer voltage are the dielectric thickness D and the relaxation time. It depends on τ. When the toner image of the first color is transferred, the surface of the recording medium P is not charged, but when the toner image of the first color is transferred, charges are attached to the front and back surfaces of the recording medium. Therefore, for the second and subsequent colors, this adhesion of charges must be taken into account. FIG. 8 is a diagram for explaining the relationship between the charging of the recording medium and the transfer voltage. The negatively charged toner developed on the photosensitive drum 6 is copied onto the recording medium P by applying a positive voltage to the transfer roller 4. However, negative charges accumulate on the surface of the recording medium P on the photosensitive drum 6 side due to the contact between the recording medium P and the photosensitive drum 6, the current flowing in the conveyance belt 12, etc. Charge accumulates. That is, the voltage in the gap between the recording medium P and the photosensitive drum 6 at the time of transfer of the toner image of the first color or later is the gap between the recording medium P and the photosensitive drum 6 at the time of transfer of the toner image of the first color. In order to be the same as the internal voltage, it is necessary to apply a voltage higher than the voltage applied to the shaft of the transfer roller 4 when the first color toner image is transferred. This is because the amount of charge remaining on the surface of the recording medium P increases in accordance with the number of times of transfer. Therefore, it is necessary to increase the transfer voltage of the transfer roller 4 on the downstream side of the recording medium P.

  The relaxation time τ of the recording medium calculated as described above is a standard indicating the time for the charge charged on the substance to disappear. When the relaxation time τ elapses, the charge charged on the substance becomes approximately 1/3. That is, the amount of charge consumed on the surface of the recording medium P is proportional to the relaxation time τ of the recording medium P. Therefore, particularly when transferring the toner image of the second and subsequent colors, the electric field strength in the gap between the photosensitive drum 6 and the recording medium P on which the transfer is performed is recorded without depending on the recording medium P having a different dielectric constant and thickness. In order to make the voltage on the surface of the medium P constant, the mechanism control unit 53 controls not only the dielectric thickness D but also the relaxation time τ to apply a voltage to the shaft of the transfer roller 4. .

  When the transfer operation of the toner image onto the recording medium P is started, the mechanism control unit 53 reads the dielectric thickness D of the recording medium P stored in the storage unit 80, the relaxation time, and τ. Based on the relaxation time τ, the transfer voltage control table is referred to. Thereby, the mechanism control unit 53 determines the transfer voltages of the first color, the second color, the third color, and the fourth color from the upstream side in the conveyance direction of the recording medium P. At this time, the transfer voltage for the second and subsequent colors in the transfer voltage control table is shown as a difference from the voltage applied to the transfer roller on the upstream side thereof. A value obtained by adding the difference shown in the table to the voltage applied to the transfer roller is defined as a transfer voltage. Then, the mechanism control unit 53 applies the determined transfer voltage to each transfer roller 4.

In the image forming apparatus 1 of the present invention as described above, the thickness d, the relative dielectric constant ε _r , and the volume resistivity ρ of the recording medium P are measured by the measuring unit 101, and the dielectric thickness D and the relaxation time τ are determined from the measured results. calculate. By determining the transfer voltage to be applied to the transfer roller 4 based on the dielectric thickness D and the relaxation time τ, more optimal transfer conditions are determined in consideration of the voltage drop of the recording medium P and the amount of charge attenuation. be able to. As a result, the toner image can be transferred more optimally and a high-quality image can be formed.

In the image forming apparatus 1 described in the first embodiment, the measurement unit 101 measures the thickness d, the relative permittivity ε _r, and the volume resistivity ρ of the recording medium P, and determines the dielectric thickness D and the relaxation time τ from these values. Although calculated, the present invention is not limited to this. The dielectric thickness D of the recording medium P can also be calculated from the following formula (12) that can be derived from the above formula (5).

Since the dielectric constant ε _{0 of the} vacuum and the area S of the electrode 121 and the electrode 122 are known, the measurement unit 101 can measure the capacitance C of the capacitor composed of the electrode 121, the electrode 122, and the recording medium P. The dielectric thickness D can be derived without measuring the thickness d of the recording medium P.

  The relaxation time τ can also be calculated from the following equation (13) that can be derived from the above equations (4), (9), and (11).

By measuring the capacitance C of the capacitor and obtaining the resistance value R ₁ per electrode area of the recording medium P, the relaxation time can be obtained without measuring the relative dielectric constant ε _r of the recording medium P by the measuring unit 101. τ can be calculated. Therefore, as described above, optimal transfer conditions can be determined.

  At this time, the measurement unit 101 functions as a dielectric thickness measurement unit that measures the dielectric thickness D of the recording medium P and a resistance measurement unit that measures the resistance value of the recording medium P. In this case, the measurement unit 101 that is also a dielectric thickness measurement unit can actually measure the capacitance C of the capacitor formed of the electrode 121, the electrode 122, and the recording medium P from the equation (3) as described above.

[Embodiment 2]
The image forming apparatus described in the second embodiment is different in the circuit configuration of the measurement unit of the image forming apparatus described in the first embodiment. Hereinafter, although it demonstrates with reference to FIG. 9, the member which overlaps with description of Embodiment 1 attaches | subjects the same number, and abbreviate | omits description.

  As in the first embodiment, the measurement unit 101 includes an electrode 121 and an electrode 122 that sandwich the recording medium P. The electrode 122 is grounded and connected to the DC power source 132. In addition, a variable load resistor 134 is connected to the electrode 121. The variable load resistor 134 is connected to the switch 145, and the switch 145 can select whether to connect to the DC power source 132 or to short-circuit the electrode 122.

  The measuring unit 101 has a terminal 147 between the electrode 121 and the variable load resistor 134. The output from the terminal 147 can be monitored by the mechanism control unit 53.

  The measuring unit 101 having such a circuit configuration has a function as a capacitance measuring unit that measures the capacitance of the recording medium P and a function as a resistance measuring unit that measures the resistance value of the recording medium P. is doing. First, measurement of the capacitance C of the recording medium P will be described.

  First, the mechanism control unit 53 controls the hopping motor 54 to drive the hopping roller 16 and sends the recording medium P to the measurement unit 101. At this time, the mechanism control unit 53 rotates the cam 127 to move the electrode 121 upward via the lever 124 to move away from the electrode 122, and is conveyed along the guide 20 between the electrode 121 and the electrode 122. It is assumed that the recording medium P can be sandwiched.

  The hopping roller 16 is driven by a hopping motor 54 controlled by the mechanism control unit 53 and stops when the recording medium P reaches the measurement unit 101. The feed amount of the recording medium P is controlled by the mechanism control unit 53 monitoring the rotation amount of the hopping motor 54. When the recording medium P reaches the measuring unit 101 and stops, the mechanism control unit 53 rotates the cam 127 to sandwich the recording medium P between the electrode 121 and the electrode 122.

  When the recording medium P is sandwiched between the electrode 121 and the electrode 122 by the rotation of the cam 127, the mechanism control unit 53 drives the switch 145 to connect the variable load resistor 134 to the DC power source 132. As a result, supply of a DC voltage of, for example, 5 [V] from the DC power supply 132 is started, and the mechanism control unit 53 sets the voltage value of the terminal 147 by an AD converter (not shown) provided in the mechanism control unit 53. To detect.

After a predetermined time has elapsed since the DC power supply 132 and the variable load resistor 134 are connected, the mechanism control unit 53 drives the switch 145 to connect the switch 145 to the ground side, and the electrode 121, the electrode 122, and the recording medium The capacitor composed of P is discharged. At this time, the mechanism control unit 53 measures the voltage value of the terminal 147, connects the switch 145 to the ground side, and then 1 / e times the voltage value of the terminal 147 immediately before connecting the switch 145 to the ground side. Measure the time τ ₂ until This e is the base of the natural logarithm, and 1 / e is about 0.37.

This time τ ₂ is a relaxation time of a circuit formed by the capacitor constituted by the electrodes 121 and 122 and the recording medium P, and the variable load resistor 134. Therefore, the capacitance C of the capacitor constituted with the electrodes 121 and the electrode 122 by the recording medium P, the resistance value of the variable load resistor 134 when the _{R V,} derivable by the following formula (14).

For example, the relaxation time tau ₂ is 0.0001 [sec], the resistance value _{R V} of the variable load resistor 134, 1 if it is [M.OMEGA.], The capacitor formed between the electrode 121 and the electrode 122 by the recording medium P static The electric capacity C is C = 0.0001 / 1000,000 = 10 ⁻¹⁰ [F] from the above formula (14).

  Thus, the capacitance C of the capacitor constituted by the electrode 121 and the electrode 122 and the recording medium P can be measured. Thus, the capacitance C measured by the measurement unit 101 is stored in the storage unit 80.

It will now be described the measurement of the resistance value R ₁ per area of the recording medium P. Resistance _{R 1} per area of the recording medium P includes a voltage _{V 147} of the terminal 147, the voltage _{V DC} of DC power source 132, by the resistance value _{R V} of the variable load resistor 134, as in the first embodiment And can be derived from the above formulas (7) and (8). Thus, the resistance value R ₁ measured by the measurement unit 101 is stored in the storage unit 80.

Based on the capacitance C and the resistance R ₁ of the stored recording medium P in the storage unit 80, the control of the transfer condition is performed. The mechanism control unit 53 calculates the dielectric thickness D from the capacitance C of the recording medium P stored in the storage unit 80. Since the vacuum dielectric constant ε ₀ and the area S of the electrodes 121 and 122 are known, the dielectric thickness D of the recording medium P can be calculated according to the above equation (12). The calculated dielectric thickness D of the recording medium P is stored in the storage unit 80.

Further, the mechanism control unit 53 calculates the relaxation time τ of the recording medium P from the electrostatic capacity C and the resistance value R _{1 of} the recording medium P stored in the storage unit 80 according to the above equation (13). Can do. For example, when the resistance value R ₁ is 10 ¹⁰ [Ω], τ = 10 ⁻¹⁰ × 10 ¹⁰ = 1 [sec] from the equation (12). The calculated relaxation time τ of the recording medium P is stored in the storage unit 80.

  When the transfer operation of the toner image onto the recording medium P is started, the mechanism control unit 53 is the same as in the first embodiment based on the dielectric thickness D of the recording medium P stored in the storage unit 80 and the relaxation time τ. In addition, the transfer voltage control table is referred to. As a result, the mechanism control unit 53 determines the transfer voltages for the first, second, third, and fourth colors from the upstream side in the transport direction of the recording medium P, as in the first embodiment.

Thus, the measurement unit 101, and the electrostatic capacitance C of the capacitor constituted with the electrodes 121 and the electrode 122 by the recording medium P, by measuring the resistance value R ₁ of the recording medium P, the dielectric thickness of the recording medium P D and relaxation time τ can be calculated. By determining the transfer voltage to be applied to the transfer roller 4 based on the calculated dielectric thickness D of the recording medium P and the relaxation time τ, the voltage drop of the recording medium P and the charge attenuation amount are taken into consideration. Optimal transfer conditions can be determined. As a result, the toner image can be transferred more optimally and a high-quality image can be formed. In addition, compared with the circuit configuration of the measurement unit 101 described in the first embodiment, the circuit configuration is simpler and lower cost, and transfer control suitable for the recording medium P can be performed.

  In the image forming apparatus of the present invention, an LED head is used to form an electrostatic latent image, but a laser light source may be used. In the image forming apparatus of the present invention, the medium on which the electrostatic latent image is formed is a photosensitive drum. However, a photosensitive belt in which a photosensitive agent is applied to a belt-like member may be used. Further, the image forming apparatus according to the present invention has been described with respect to the case where black, yellow, magenta, and cyan are arranged in order from the upstream side of the conveyance state of the print medium. The order in which the printing mechanisms are arranged side by side is not limited. For example, it may be provided so that cyan is the most upstream. Further, the example in which the number of printing mechanisms is four has been described, but the number of printing mechanisms is not limited, and the present invention can be applied to a large number or a single printing mechanism. For example, the present invention can be applied only to a printing mechanism having black toner. Furthermore, although the image forming apparatus of the present invention is applied to a direct transfer type electrophotographic image forming apparatus, it is needless to say that it can also be applied to an indirect transfer type image forming apparatus.

1 is a diagram illustrating a configuration of an image forming apparatus of the present invention. 1 is a block diagram illustrating a structure of an image forming apparatus of the present invention. It is a schematic diagram which shows the structure of the measurement part of the image forming apparatus of this invention. 2 is a diagram illustrating a configuration circuit of a measurement unit of the image forming apparatus described in Embodiment 1. FIG. It is a figure which shows the output voltage of the measurement part shown in FIG. It is a figure which shows an example of the transfer voltage control table referred when controlling by the mechanism control part of the image picture formation apparatus of this invention. It is a figure explaining the relationship between the dielectric thickness of a recording medium, and a transfer voltage. FIG. 6 is a diagram for explaining a relationship between charging of a recording medium and a transfer voltage. FIG. 4 is a diagram illustrating a configuration circuit of a measurement unit of an image forming apparatus described in a second embodiment.

Explanation of symbols

1 Image forming apparatus 2K, 2Y, 2M, 2C Printing mechanism 3K, 3Y, 3M, 3C LED head 4K, 4Y, 4M, 4C Transfer roller 5K, 5Y, 5M, 5C Charge roller 6K, 6Y, 6M, 6C Photosensitive drum 7K , 7Y, 7M, 7C Developing roller 8K, 8Y, 8M, 8C Developing blade 9K, 9Y, 9M, 9C Sponge roller 10K, 10Y, 10M, 10C Toner cartridge 12 Conveying belt 13 Driving roller 14 Drive roller 15 Adsorption roller 16 Hopping roller 17 Registration roller 18 Pinch roller 19 Recording medium cassette 20, 29 Guide 21, 22, 23, 27 Sensor 24 Color misregistration detection sensor 25 Heat roller 26 Pressure roller 28 Thermistor 29 Guide 30 Discharge stacker 32 Cleaning blade 33 Waste toner tank 34 Environment Temperature sensor 50 Host interface unit 51 Command / image processing unit 52 Head interface unit 53 Mechanism control unit 54 Hopping motor 55 Registration motor 56 Belt motor 57 Heater motor 58 Drum motor 59 Heater 60 High pressure control unit 61 CH generation unit 62 DB generation unit 63 TR generation Unit 80 storage unit 101 measuring unit 121, 122 electrode 123 tension spring 124 lever 125 joint 126 displacement sensor 127 cam 131 AC power source 132 DC power source 133 load resistance 134 variable load resistance 135, 136, 145 switch 137, 138, 147 terminal P recoding media

Claims (4)

A transfer unit that transfers the toner image formed on the image carrier onto the recording medium with electrostatic force;
A transfer voltage application unit that adjustably applies a transfer voltage to the transfer unit;
A dielectric constant measuring unit for measuring the dielectric constant of the recording medium;
A resistance measuring unit for measuring a resistance value of the recording medium;
A thickness measuring unit for measuring the thickness of the recording medium;
Based on the dielectric constant of the recording medium measured by the dielectric constant measuring unit, the resistance value of the recording medium measured by the resistance measuring unit, and the thickness of the recording medium measured by the thickness measuring unit. An image forming apparatus comprising: a transfer control unit that controls an applied voltage of the voltage application unit.   The image forming apparatus according to claim 1, wherein the dielectric constant measurement unit, the resistance measurement unit, and the thickness measurement unit have a common contact unit that contacts the recording medium. A transfer unit that transfers the toner image formed on the image carrier onto the recording medium with electrostatic force;
A transfer voltage application unit that adjustably applies a transfer voltage to the transfer unit;
A dielectric thickness measuring unit for measuring the dielectric thickness of the recording medium;
A resistance measuring unit for measuring a resistance value of the recording medium;
A transfer control unit that controls an applied voltage of the transfer voltage applying unit based on a dielectric thickness of the recording medium measured by the dielectric thickness measuring unit and a resistance value of the recording medium measured by the resistance measuring unit; An image forming apparatus. A transfer unit that transfers the toner image formed on the image carrier onto the recording medium with electrostatic force;
A transfer voltage application unit that adjustably applies a transfer voltage to the transfer unit;
A capacitance measuring unit for measuring the capacitance of the recording medium;
A resistance measuring unit for measuring a resistance value of the recording medium;
A transfer control unit that controls the applied voltage of the transfer voltage applying unit based on the capacitance of the recording medium measured by the capacitance measuring unit and the resistance value of the recording medium measured by the resistance measuring unit. An image forming apparatus comprising: