JP5167656B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In the electrophotographic image forming apparatus, various inventions have been devised in order to prevent various defects from occurring in the formed image. Among them, there is an invention disclosed in Patent Documents 1 and 2 as an invention for preventing a so-called defect called a banding (a defect in which a regular shading pattern is generated in an image to be formed). . The image forming apparatus disclosed in Patent Document 1 measures periodic fluctuations in the rotational speed of the photosensitive member due to the eccentricity (shift of the central axis) of the photosensitive member using an optical rotary encoder. Then, the driving means of the photosensitive member is controlled so as to cancel out this periodic variation, and the rotational speed of the photosensitive member is made constant, thereby preventing banding. The image forming apparatus disclosed in Patent Document 2 reads a formed image with an optical sensor, detects a change in the density of the read image, and controls various physical quantities related to development according to the detected change. To correct regular changes in concentration.

JP 2005-176467 A JP 2005-338836 A

  Incidentally, there are various factors that cause banding. Banding also occurs due to the eccentricity of the developing roll for supplying the developer to the photosensitive member and the eccentricity of the photosensitive member. Specifically, when the photoconductor and the developing roll are eccentric, a long portion and a short portion are generated in the distance from the central axis to the peripheral surface in the photoconductor and the developing roll. If the long distance portions from the central axis to the peripheral surface face each other when the opposing photoconductor and the developing roll rotate, the distance between the photoconductor and the developing roll becomes short. When the distance between the photoconductor and the developing roll is shortened, the developing electric field is increased, the amount of toner flying from the developing roll to the photoconductor is increased, and the image density is increased. On the other hand, when the portions having a short distance from the central axis to the peripheral surface face each other, the distance between the photoconductor and the developing roll becomes long. When the distance between the photoconductor and the developing roll is increased, the developing electric field is lowered, the amount of toner flying from the developing roll to the photoconductor is reduced, and the image density is lowered.

The image forming apparatus disclosed in Patent Document 1 prevents banding by suppressing periodic fluctuations in the rotational speed of the photoconductor due to eccentricity. However, even if the rotational speed is controlled, the developing roll and the photoconductor Since the distance between the two does not change, the developing electric field does not change, and banding caused by the distance between the photosensitive member and the developing roll as described above cannot be prevented.
In the image forming apparatus disclosed in Patent Document 2, a change in density of a formed image is detected, and control is performed so as to cancel the detected density change. However, in the image forming apparatus disclosed in Patent Document 2, a sensor having the same width as the width of the image is required to read the formed image, and a space for arranging the sensor is required, which increases the volume of the apparatus. And the problem that the number of parts increases and the manufacturing cost increases.

  The present invention has been made under the above-described background, and an object of the present invention is to provide a technique for preventing banding that occurs due to a change in the distance between the photosensitive member and the developing roll.

  In order to solve the above-described problems, the present invention provides an image holding member on which a latent image is formed, a rotating member that faces the image holding member and supplies developer to the image holding member, and rotates the rotating member. A motor in which a current flowing when rotating at a constant speed changes according to a load torque, current measuring means for measuring a current value of a current flowing through the motor, and image holding according to image information representing an image Provided is an image forming apparatus comprising: a latent image forming unit configured to form a latent image on a body, wherein the latent image forming unit controls a potential of the latent image formed on the image holding member according to a current value measured by the current measuring unit. To do.

  In the present invention, the image carrier has a latent image formed by changing the surface potential when irradiated with light, and includes an angle measuring unit that measures a rotation angle of the rotating body, and the angle measuring unit. From the measured rotation angle and the measurement result of the current value measured by the current measuring means, the relationship between the interval between the rotating body circumferential surface and the image holding body circumferential surface and the rotation angle of the rotating body is specified. The latent image forming means forms a latent image by controlling an irradiation position of light applied to the image holding body according to image information, and the latent image formed on the image holding body is exposed. The rotation angle of the rotating body when moved from the position to the developing position is obtained from the rotation angle obtained by the angle measuring means, and the distance between the peripheral surface of the image carrier and the rotating body at the obtained rotation angle is determined by the specifying means. Identified from the relationship found in It may be controlled in accordance with the intervals identifying the amount of light irradiated to the image carrier.

The present invention also provides an image carrier that forms a latent image by changing the surface potential when irradiated with light , and a rotation that faces the image carrier and supplies developer to the image carrier. A motor that rotates the image holding body, and a current that flows when rotating at a constant speed according to a load torque; and a current measuring unit that measures a current value of the current flowing through the motor; A latent image forming unit that forms a latent image on the image carrier in accordance with image information representing an image, and controls a potential of the latent image formed on the image carrier according to a current value measured by the current measuring unit. Means , an angle measuring means for measuring a rotation angle of the image carrier, a rotation angle measured by the angle measuring means, and a current value measured by the current measuring means, and A distance from the peripheral surface of the image carrier; Have a specifying means for specifying a relationship between the rotation angle of the image carrier, said latent image forming means, controlled to form a latent image in accordance with image information the irradiation position of the light irradiated to the image carrier The rotation angle of the image carrier when the latent image formed on the image carrier moves from the exposure position to the development position is obtained from the rotation angle obtained by the angle measuring means, and the image holding at the obtained rotation angle is obtained. An image forming apparatus characterized in that an interval between a body circumferential surface and the rotating body is specified from the relationship obtained by the specifying means, and the amount of light irradiated to the image holding body is controlled according to the specified interval. I will provide a.

In a preferred embodiment, when the motor is rotated at a constant speed, the relationship between the current flowing through the motor and the load torque is a linear value in which the increase amount of the current becomes a constant value when the load torque increases by a certain amount. Relationship may be.
In another preferred embodiment, the motor may be a brushless motor.

  According to the present invention, it is possible to prevent banding caused by a change in the distance between the photosensitive member and the developing roll.

[First Embodiment]
[Configuration of the embodiment]
FIG. 1 is a diagram schematically showing a configuration of a photosensitive member and each part around the photosensitive member in an electrophotographic image forming apparatus according to an embodiment of the present invention.

  The control unit 10 includes a ROM (Read Only Memory) storing a control program, a CPU (Central Processing Unit) that executes the control program, a RAM (Random Access Memory), a storage unit including a nonvolatile memory, and the like. The control unit 10 controls each unit described above according to the control program, thereby realizing an image forming function in the image forming apparatus according to the present embodiment. When the control program is executed, the image forming apparatus realizes a function of correcting a density change due to banding.

  A photoconductor (image carrier) 11 having a cylindrical shape has a photoconductive layer made of OPC (Organic Photo Conductor) as a charge acceptor formed on the surface, and is illustrated by a motor (not shown). It is rotated in the direction of arrow A inside. The charging device 12 is a corotron, for example, and uniformly charges the surface of the photoconductor 11 by corona discharge. The exposure device 13 includes a laser diode or the like, and changes the potential of the irradiated region by irradiating the surface of the photoconductor 11 with laser light in accordance with image information representing the image to be formed and the density of the image. An electrostatic latent image is formed.

  The sheet conveying belt 15 is a belt that conveys a sheet onto which the toner image formed on the photoconductor 11 is transferred, and is driven in the direction of arrow C in the drawing to convey the sheet. The transfer roll 16 facing the photoconductor 11 with the paper transport belt 15 interposed therebetween is charged to a predetermined potential, and the toner image developed on the surface of the photoconductor 11 is electrostatically charged at a position facing the photoconductor 11. Transfer to paper by force. The fixing device 17 includes a pair of rollers facing each other with the paper transport belt 15 interposed therebetween, and the toner image transferred onto the paper is fixed by heating and pressurizing the paper using the rollers. The cleaning device 18 is a device that removes toner remaining on the surface of the photoconductor 11 without being transferred onto a sheet. The neutralization device 19 is a device that irradiates the surface of the photoconductor 11 from which the toner has been removed by the cleaning device 18 with light to remove residual charges on the photoconductor 11.

  The developing device 14 is a device that supplies toner to the surface of the photoconductor 11, and includes a developing roll 14A including a magnet roll and a sleeve, a driving unit 150 that rotates the sleeve, a rotary encoder 160, and a trimmer 142. FIG. 2 is a diagram schematically showing the developing roller 14A, the photoconductor 11, and the toner T and the trimmer 142 attached to the developing roller 14A. As shown in the figure, in the developing roll 14A, the magnet roll 140 is disposed inside the sleeve (rotating body) 141, and a trimmer (restricting member) 142 is provided in the vicinity of the sleeve 141 to which the toner T adheres. Has been placed.

  The magnet roll 140 is a roll in which a powder of a magnetic material such as ferrite or a rare earth magnet alloy is formed into a cylindrical shape or a cylindrical shape, and is formed by arranging N poles and S poles in a predetermined pattern. The trimmer 142 limits the amount of toner T supplied to the photoconductor 11 by the sleeve 141, and scrapes off the toner adhering to the sleeve 141.

  The sleeve 141 is made of aluminum and is formed in a cylindrical shape, and is rotated in the direction of arrow B in FIG. The toner T adheres to the sleeve 141 due to the magnetic force of the magnet roll 140, and when the sleeve 141 rotates, the toner T attached to the sleeve 141 is supplied to the photoconductor 11, but the toner T supplied to the photoconductor 11 is Since the toner T is charged so as to have a polarity opposite to that of the electrostatic latent image, the toner T adheres to the electrostatic latent image due to a potential difference from the surface of the photoreceptor 11 and the electrostatic latent image is developed (visualized).

  The magnet roll 140 is disposed inside the cylindrical sleeve 141. As shown in FIG. 2, the central axis of the magnet roll 140 and the central axis of rotation of the sleeve 141 are completely in terms of assembly accuracy. (In FIG. 2, the shift of the central axis is emphasized for easy understanding that the central axes do not match.) If the central axis of the magnet roll 140 and the central axis of rotation of the sleeve 141 are deviated, the interval between the photoconductor 11 and the sleeve 141 varies during the rotation of the sleeve 141. As a result, the potential difference between the toner T and the photoconductor 11 varies, and the density of the toner image formed on the photoconductor 11 varies. Specifically, as shown in FIG. 3B, when the distance between the photosensitive member 11 and the peripheral surface of the sleeve 141 becomes narrower, the potential difference between the surface of the photosensitive member 11 and the toner increases, so that an electrostatic latent image is generated. The amount of adhering toner increases and the density of the developed toner image increases. Further, as shown in FIG. 3D, when the distance between the photosensitive member 11 and the circumferential surface of the sleeve 141 is increased, the potential difference between the surface of the photosensitive member 11 and the toner is reduced, so that the toner adhered to the electrostatic latent image. And the density of the developed toner image is lowered.

  The rotary encoder 160 detects the rotation angle of the sleeve 141, and outputs an angle signal indicating the rotation angle of the sleeve to the control unit 10. In the present embodiment, when the position P having the longest distance from the central axis of the magnet roll 140 to the circumferential surface of the sleeve 141 is at a position facing the trimmer 142, an angle signal indicating “0 degree” is output, As the sleeve 141 rotates in the direction of arrow B, the angle represented by the angle signal increases.

  Next, the configuration of the drive unit 150 that rotates the sleeve 141 will be described. FIG. 4 is a block diagram showing the configuration of the drive unit 150. The power supply unit 152 supplies power to the motor 151 that rotates the sleeve 141, and is connected to the current control unit 153. The detection unit 154 detects the rotation speed of the motor 151, obtains the rotation speed of the motor 151 by the Hall IC, and outputs a rotation speed signal indicating the obtained rotation speed.

  The setting unit 155 is connected to the control unit 10 and receives a speed instruction signal that is output from the control unit 10 and that indicates the rotation speed of the motor 151. Further, the rotation speed signal output from the detection unit 154 is input to the setting unit 155. The setting unit 155 controls the current control unit 153, and outputs a current control signal that instructs the motor 151 to flow a current to the current control unit 153 when a speed instruction signal is input. The setting unit 155 also includes a rotation speed (rotation speed instructed from the control unit 10) represented by the input speed instruction signal and a measured rotation speed (measured rotation) represented by the rotation speed signal input from the detection unit 154. Speed). When the measured rotation speed is slower than the instructed rotation speed, a current control signal instructing to flow more current than the current flowing to the motor 151 is output to the current control unit 153 and measured. If the rotation speed is higher than the instructed rotation speed, a current control signal instructing to flow a current smaller than the current flowing to the motor 151 is output to the current control unit 153.

  The current control unit 153 controls the current that flows to the motor 151, receives power supplied from the power supply unit 152, and causes the current to flow to the motor 151 in accordance with an instruction represented by the current control signal. Further, the current control unit 153 measures the current value flowing through the motor 151 and outputs a current value signal representing the measured current value to the control unit 10.

  The motor 151 is a brushless DC (Direct Current) motor, and rotates the sleeve 141 via a gear (not shown). The rotational speed of the motor 151 is controlled by the current flowing from the current control unit 153. FIG. 5 is a graph illustrating the relationship between the load torque of the motor 151 and the current flowing through the motor 151. As shown in FIG. 5, when the motor 151 is rotated at a constant rotational speed, the relationship between the load torque of the motor 151 and the current flowing through the motor 151 is linear. For this reason, if the current flowing through the motor 151 is measured, the load torque applied to the motor 151 can be measured.

[Operation of the embodiment]
Next, the operation of this embodiment will be described. In the following description, first, an operation for measuring a change in the current flowing through the motor 151 when the sleeve 141 is rotated will be described. Next, a change in image density caused by the rotation of the sleeve 141 will be described. The operation when suppressing the above will be described.

(Operation when measuring the current flowing through the motor 151)
First, when the power of the image forming apparatus is turned on and a control program stored in the ROM of the control unit 10 is executed by the CPU, the control unit 10 sends a speed instruction signal indicating a predetermined rotation speed to the setting unit 155. Output. When this speed instruction signal is input, setting unit 155 outputs a current control signal for instructing motor 151 to flow a current to current control unit 153. When this current control signal is input, the current control unit 153 causes a current to flow through the motor 151. As a result, the sleeve 141 to which the toner T adheres starts to rotate in the direction of arrow B in FIG.
When the sleeve 141 starts to rotate, the rotation angle of the sleeve 141 is detected by the rotary encoder 160, and an angle signal is output from the rotary encoder 160 to the control unit 10. Upon receiving the angle signal output from the rotary encoder 160, the control unit 10 analyzes the received angle signal and detects the rotation angle of the sleeve 141.

  Further, when the sleeve 141 rotates, the toner T adhering to the sleeve 141 is scraped off by the trimmer 142 and the amount adhering to the sleeve 141 is limited. The thickness of the toner T adhering to the sleeve 141 is substantially constant regardless of the distance from the central axis of the magnet roll 140 to the peripheral surface of the sleeve 141 before contact with the trimmer 142, but for example, FIG. 3) from the state of FIG. 3A to the state of FIG. 3A, the distance between the trimmer 142 and the peripheral surface of the sleeve 141 gradually decreases, and the amount of toner T that is scraped off in contact with the trimmer is reduced. Since it gradually increases, the load torque of the motor 151 that rotates the sleeve 141 also gradually increases. Here, when the position P reaches the position of the trimmer 142, an angle signal representing 0 degree is input to the control unit 10. The controller 10 starts measuring the current flowing to the motor 151 when the angle represented by the angle signal becomes 0 degrees.

  When the load torque of the motor 151 increases, the rotational speed of the motor 151 decreases, and the decreased rotational speed is measured by the detection unit 154. When a signal indicating the measured rotation speed is output from the detection unit 154 to the setting unit 155, the setting unit 155 indicates the rotation speed (instructed rotation speed) indicated by the speed instruction signal input from the control unit 10, and The measured rotational speed (measured rotational speed) represented by the rotational speed signal input from the detection unit 154 is compared. Here, since the rotational speed of the motor 151 is decreasing as described above, the measured rotational speed is slower than the instructed rotational speed. The setting unit 155 outputs, to the current control unit 153, a current control signal that instructs to flow more current than the current flowing to the motor 151 when the measured rotation speed is slower than the instructed rotation speed. To do.

When this current control signal is input, the current control unit 153 increases the current flowing through the motor 151. As a result, the rotation speed of the motor 151 approaches the rotation speed represented by the speed instruction signal. In the current control unit 153, a current value signal representing the value (I ₁₁ [A]) of the current flowing through the motor 151 at this time is output to the control unit 10. When receiving the current value signal, the control unit 10 stores the rotation angle of the sleeve 141 detected by the rotary encoder 160 and the current value represented by the current value signal in the storage unit in association with each other.

(Operation when the interval between the sleeve and trimmer is narrow → wide)
When the motor 151 continues to rotate, the sleeve 141 rotates from the state shown in FIG. 3A, and the state shown in FIG. 3B is passed to reach the state shown in FIG. During this time, at the position of the trimmer 142, as the sleeve 141 rotates, the interval between the trimmer 142 and the sleeve 141 becomes wider than in FIG. 3A, and the amount of toner scraped off by the trimmer 142 decreases. Therefore, the load torque of the motor 151 becomes smaller than that in FIG.

  When the load torque of the motor 151 decreases, the rotation speed of the motor 151 also increases, and a rotation speed signal representing the increased rotation speed is output from the detection unit 154. Here, since the rotational speed of the motor 151 is faster as described above, the measured rotational speed is faster than the instructed rotational speed, and the setting unit 155 decreases the rotational speed of the motor 151. A current control signal for instructing to flow a current smaller than the current flowing to the motor 151 is output to the current control unit 153.

  When this current control signal is input, the current control unit 153 reduces the current flowing through the motor 151. As a result, the rotation speed of the motor 151 approaches the rotation speed represented by the speed instruction signal. In the current control unit 153, a current value signal representing the value of the current flowing through the motor 151 at this time is output to the control unit 10. When receiving the current value signal, the control unit 10 stores the rotation angle of the sleeve 141 and the current value represented by the current value signal in the storage unit in association with each other.

For example, in the state shown in FIG. 3B, when the current flowing to the motor 151 is suppressed and the current value represented by the current value signal is I ₁₂ [A], the rotation angle (90 degrees) of the sleeve 141 at this time ) And the current value I ₁₂ [A] are associated with each other and stored in the storage unit. Further, in the state shown in FIG. 3C, when the current flowing to the motor 151 is suppressed and the current value represented by the current value signal is I ₁₃ [A], the rotation angle (180 degrees) of the sleeve 141 at this time ) And the current value I ₁₃ [A] are stored in the storage unit in association with each other.

(Operation when the distance between the sleeve and the trimmer is wide → narrow)
When the motor 151 continues to rotate from the state shown in FIG. 3C, the sleeve 141 rotates, and the state shown in FIG. 3D is passed to reach the state shown in FIG. 3A again. During this time, at the position of the trimmer 142, the interval between the trimmer 142 and the sleeve 141 becomes narrower than that in FIG. 3C, and the amount of toner scraped off by the trimmer 142 increases. The load torque also becomes larger than in the case of FIG.

When the load torque of the motor 151 increases and the rotation speed decreases, the setting unit 155 outputs a current control signal instructing to flow more current than the current flowing to the motor 151 to the current control unit 153. As a result, the rotational speed of the motor 151 approaches the rotational speed represented by the speed instruction signal. In the current control unit 153, a current value signal representing the value of the current flowing through the motor 151 at this time is output to the control unit 10. In the state shown in FIG. 3D, when the current value represented by the current value signal is I ₁₄ [A], the rotation angle (270 degrees) of the sleeve 141 and the current value I ₁₄ [A] are Correspondingly stored in the storage unit.

  As described above, when the power of the image forming apparatus is turned on, in the image forming apparatus, the sleeve 141 is rotated, and the rotation angle of the sleeve 141 corresponds to the current value flowing through the motor 151 at this rotation angle. It is memorized. The waveform of the current value measured when the sleeve 141 makes one revolution is as illustrated in FIG.

Here, the current flowing through the motor 151 increases and decreases according to the increase and decrease of the load torque. Since the load torque changes according to the interval between the circumferential surface of the sleeve 141 and the trimmer 142 (hereinafter, this interval is referred to as a first gap), the current value at a certain rotation angle in FIG. It can be said that it corresponds to the value of 1 gap (current value large → first gap small, current value small → first gap large). In FIG. 6, the interval between the first gaps is the narrowest when the current value is the largest, and the interval between the first gaps is the widest when the current value is the smallest.
Further, since the sleeve 141 rotates in the direction of arrow B in FIG. 2, the same change as the change in the first gap also occurs between the circumferential surface of the sleeve 141 and the photoconductor 11 after a certain time. That is, the phase of the waveform shown in FIG. 6 is set at a predetermined angle (a line connecting the central axis of rotation of the sleeve 141 and the trimmer 142, and a line connecting the central axis of rotation of the sleeve 141 and the central axis of the photosensitive member 11). The waveform delayed by an angle formed by (ie, 90 degrees in this case) represents a change in the interval between the sleeve 141 peripheral surface and the photoreceptor 11 peripheral surface (hereinafter, this interval is referred to as a second gap). The control unit 10 generates a waveform obtained by delaying the angle of the waveform illustrated in FIG. 6 by a predetermined angle (FIG. 7), and stores the generated second gap change waveform in the storage unit.
Further, when storing the change in the current value when the sleeve 141 makes one rotation, the control unit 10 obtains the average value of the stored current values and stores the obtained average value Iave in the storage unit.

(Operation when forming an electrostatic latent image)
Next, an operation for correcting a density change caused by the rotation of the sleeve 141 will be described.

  When the image forming apparatus forms an image, the photosensitive member 11 and the sleeve 141 are rotated under the control of the control unit 10, and the rotated photosensitive member 11 is charged by the charging device 12. Next, the control unit 10 determines that the electrostatic latent image formed by exposure is located on a line connecting the central axis of rotation of the sleeve 141 and the central axis of the photoconductor 11 from the exposure position (point Q in FIG. 1) (FIG. 1). Point R: hereinafter, this position will be referred to as a development position). Then, the control unit 10 obtains the rotation angle of the sleeve 141 that rotates during the obtained time based on the rotation speed of the motor 151.

Next, the control unit 10 monitors the angle signal output from the rotary encoder 160 while rotating the motor 151, and when the angle of the angle signal becomes 0 degrees, the value corresponding to the obtained rotation angle is shown in FIG. Obtain from the waveform shown. For example, when the sleeve 141 rotates 90 degrees while the electrostatic latent image moves from the exposure position to the development position, the current value I ₁₁ corresponding to 90 degrees is obtained from the graph shown in FIG.
Since I ₁₁ is greater than the average value Iave of the current value at the time when the sleeve 141 is rotated 90 degrees with an electrostatic latent image is moved to the development position from the exposure position, the second gap is narrower than the average of the second gap I understand that
When forming an electrostatic latent image, the amount of laser light is set according to information included in the image information of the image to be formed and representing the density of the image. Since the density is high, in order to prevent the density from becoming high, in this embodiment, the quantity of laser light is reduced from the quantity of light set according to the information representing the density of the image to form an electrostatic latent image.

  Thereafter, when the photosensitive member 11 and the sleeve 141 are rotated, when the electrostatic latent image reaches the developing position, the sleeve 141 is rotated by 90 degrees to be in the state shown in FIG. In the state shown in FIG. 3B, the interval between the photoreceptor 11 and the peripheral surface of the sleeve 141 is narrowed, and the density of the toner image to be formed increases if no correction is made to the exposure amount. As described above, since the amount of light when forming the electrostatic latent image at the development position is controlled so as not to increase in density, it is formed even if the distance between the photoreceptor 11 and the peripheral surface of the sleeve 141 is narrow. The density of the toner image does not increase.

Further, when the angle of the angle signal reaches 180 degrees (the state shown in FIG. 3C), the control unit 10 obtains I ₁₃ that is a current value corresponding to 270 degrees from the graph shown in FIG. Since I ₁₃ is smaller than the average value Iave of the current value at the time when the electrostatic latent image is sleeve 141 with moves to the development position from the exposure position rotated state from 90 ° in FIG. 3 (c), the second gap It can be seen that it is wider than the average of the second gap. Since the image density decreases as the second gap increases, the electrostatic latent image is formed by increasing the light amount of the laser light from the light amount set according to the information indicating the image density in order to prevent the density from decreasing.

  Thereafter, when the photoconductor 11 and the sleeve 141 rotate, the sleeve 141 is in the state shown in FIG. 3D when the electrostatic latent image reaches the developing position. In the state shown in FIG. 3D, the interval between the photosensitive member 11 and the peripheral surface of the sleeve 141 becomes wide, and the density of the toner image to be formed becomes light unless the exposure amount is corrected. As described above, since the amount of light when forming the electrostatic latent image at the development position is controlled so as not to reduce the density, it is formed even when the interval between the photoreceptor 11 and the sleeve 141 is wide. The toner image density does not become thin.

  As described above, according to the present embodiment, the exposure amount when forming the electrostatic latent image is controlled in accordance with the change in the interval between the photoreceptor 11 and the sleeve 141 circumferential surface. Occurrence of banding can be suppressed even if the distance between the sleeve and the circumferential surface of the sleeve 141 changes.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the image forming apparatus according to the present embodiment, the configuration of the drive unit 150A that drives the photoreceptor 11 is the same as that of the drive unit 150 of the first embodiment as shown in FIG. In FIG. 8, “A” is added to the end of the reference numeral for each component to distinguish it from the drive portion of the sleeve 141. A motor 151A shown in FIG. 8 is a brushless DC motor for rotating the photoconductor 11.

  FIG. 9 is a diagram schematically showing the developing roll 14 </ b> A and the photoreceptor 11. Also in the photoconductor 11, the central axis of the photoconductor 11 and the central axis of rotation when the photoconductor 11 rotates do not completely coincide with each other for accuracy when the photoconductor 11 is arranged. ), The second gap is narrowed, or the second gap is widened, as shown in FIG. 9C (in FIG. 9, in order to make the change in the interval easy to understand, The center axis deviation is highlighted).

  In this way, if the distance between the photoconductor 11 and the sleeve 141 changes during one rotation of the photoconductor 11, the potential difference between the toner on the developing roll 14 </ b> A and the photoconductor 11 changes, and the photoconductor 11 is formed. The density of the toner image will fluctuate. Specifically, as shown in FIG. 9A, when the second gap is narrowed, the potential difference between the surface of the photoconductor 11 and the toner is increased, so that the amount of toner adhering to the electrostatic latent image is increased and the toner is increased. The image density is high. Further, as shown in FIG. 9C, when the second gap is widened, the potential difference between the surface of the photoconductor 11 and the toner is reduced, so that the amount of toner adhering to the electrostatic latent image is reduced, and the toner image The concentration becomes lighter.

  In addition, the image forming apparatus according to the present embodiment includes a rotary encoder (not shown) that detects the rotation angle of the photoconductor 11. In the present embodiment, when the position P1 having the longest distance from the rotation axis of the photoconductor 11 to the circumferential surface of the photoconductor 11 is at the development position, an angle signal indicating 0 degree is output, and the photoconductor 11 is moved to an arrow. The angle represented by the angle signal increases as it rotates in the A direction.

[Operation of Second Embodiment]
Next, the operation of this embodiment will be described. In the following description, first, an operation for measuring a change in the current flowing through the motor 151A when the photoconductor 11 is rotated will be described. Next, an image generated with the rotation of the photoconductor 11 will be described. An operation for suppressing a change in density will be described.
(Operation when measuring the current flowing through the motor 151A)
First, when the power of the image forming apparatus is turned on and the control program stored in the ROM of the control unit 10 is executed by the CPU, the control unit 10 sends a speed instruction signal indicating a predetermined rotation speed to the setting unit 155A. Output. When this speed instruction signal is input, setting unit 155A outputs a current control signal that instructs current to flow to motor 151A to current control unit 153A. When this current control signal is input, the current control unit 153A causes a current to flow through the motor 151A. As a result, the photoconductor 11 starts rotating.
When the photoconductor 11 starts to rotate, the rotation angle of the photoconductor 11 is detected by the rotary encoder, and an angle signal is output from the rotary encoder to the control unit 10. Upon receiving the angle signal output from the rotary encoder, the control unit 10 analyzes the received angle signal and detects the rotation angle of the photoconductor 11.

  Now, for example, when the photoconductor 11 rotates from the state shown in FIG. 9D to the state shown in FIG. 9A, the distance between the photoconductor 11 and the peripheral surface of the sleeve 141 gradually decreases. The load torque of the motor 151A that drives the body 11 also gradually increases. Here, when the angle represented by the angle signal becomes 0 degree, measurement of the current flowing to the motor 151 is started.

  When the load torque of the photoconductor 11 increases, the rotation speed of the motor 151A that rotates the photoconductor 11 decreases, and this reduced rotation speed is measured by the detection unit 154A. When a signal representing the measured rotational speed is output from the detection unit 154A to the setting unit 155A, the setting unit 155A causes the rotational speed (instructed rotational speed) represented by the speed instruction signal input from the control unit 10 to be set. And the measured rotational speed (measured rotational speed) represented by the rotational speed signal input from the detection unit 154 is compared. Here, since the rotational speed of the photoconductor 11 is decreased as described above, the measured rotational speed is slower than the instructed rotational speed. When the measured rotational speed is slower than the instructed rotational speed, the setting unit 155A outputs a current control signal that instructs the current control unit 153A to flow more current than the current that is flowing to the motor 151A. To do.

When this current control signal is input, current control unit 153A increases the current that flows to motor 151A. As a result, the rotation speed of the motor 151A approaches the rotation speed represented by the speed instruction signal. In the current control unit 153A, a current value signal representing the value of the current (I ₂₁ [A]) flowing to the motor 151A at this time is output to the control unit 10. When receiving the current value signal, the control unit 10 stores the rotation angle of the photoconductor 11 detected by the rotary encoder and the current value represented by the current value signal in the storage unit in association with each other.

(Operation when the distance between the photoconductor and the sleeve is narrow → wide)
When the motor 151A continues to rotate, the photoconductor 11 rotates from the state shown in FIG. 9A, and the state of FIG. 9B is passed to reach the state of FIG. 9C. During this time, at the development position, the second gap becomes wider than that in FIG. 9A as the photoconductor 11 rotates, and the load torque of the motor 151A also becomes smaller than that in FIG. 9A.

When the load torque of the motor 151A is reduced, the rotation speed of the motor 151A is also increased, and a rotation speed signal representing the increased rotation speed is output from the detection unit 154A.
Here, since the rotation speed of the photoconductor 11 is higher as described above, the measured rotation speed is faster than the instructed rotation speed, and the setting unit 155A decreases the rotation speed of the motor 151A. A current control signal for instructing to flow a current smaller than the current that is currently flowing to the motor 151A is output to the current control unit 153A.

  When this current control signal is input, the current control unit 153A reduces the current flowing to the motor 151A. As a result, the rotation speed of the motor 151A approaches the rotation speed represented by the speed instruction signal. In the current control unit 153A, a current value signal representing the value of the current flowing through the motor 151A at this time is output to the control unit 10. Upon receiving the current value signal, the control unit 10 stores the rotation angle of the photoconductor 11 and the current value represented by the current value signal in the storage unit in association with each other.

For example, in the state shown in FIG. 9B, when the current flowing to the motor 151A is suppressed and the current value represented by the current value signal is I ₂₂ [A], the rotation angle (90 of the photoconductor 11 at this time (90 Degree) and the current value I ₂₂ [A] are associated with each other and stored in the storage unit. Further, in the state shown in FIG. 9C, when the current flowing to the motor 151A is suppressed and the current value represented by the current value signal is I ₂₃ [A], the rotation angle (180 of the photosensitive member 11 at this time (180). Degree) and the current value I ₂₃ [A] are stored in the storage unit in association with each other.

(Operation when the distance between the photosensitive member and the sleeve peripheral surface is wide → narrow)
When the motor 151A continues to rotate further from the state shown in FIG. 9C, the photoconductor 11 rotates, and the state shown in FIG. 9D is passed to reach the state shown in FIG. 9A again. Meanwhile, at the developing position, the second gap becomes narrower than that in FIG. 9C, and the load torque of the motor 151A also becomes larger than that in FIG. 9C.

When the load torque of the motor 151A increases and the rotation speed decreases, the setting unit 155A outputs a current control signal instructing to flow more current than the current flowing to the motor 151A to the current control unit 153A. As a result, the rotation speed of the motor 151A approaches the rotation speed represented by the speed instruction signal. In addition, the control unit 10 receives the current value signal, and stores the rotation angle of the photoconductor 11 and the current value represented by the current value signal in the storage unit in association with each other. For example, in the state shown in FIG. 9D, when the current flowing to the motor 151A increases and the current value represented by the current value signal is I ₂₄ [A], the rotation angle (270 degrees) of the photoconductor 11 is The current value I ₂₄ [A] is associated and stored in the storage unit.

  Thus, in the image forming apparatus, the photoconductor 11 is rotated, and the rotation angle of the photoconductor 11 and the current value flowing through the motor 151A at this rotation angle are stored in association with each other. Then, when the photoconductor 11 rotates once, the waveform of the measured current value is as illustrated in FIG.

  Here, since the current flowing through the motor 151A changes according to the second gap, it can be said that the current value at a certain rotation angle in FIG. 10 corresponds to the value of the second gap at a certain rotation angle. In FIG. 10, the second gap interval is the narrowest when the current value is the largest, and the second gap interval is the widest when the current value is the smallest. Further, when storing the change in current value when the photoconductor 11 makes one rotation, the control unit 10 obtains an average value of the stored current values, and stores the obtained average value in the storage unit.

(Operation when forming an electrostatic latent image)
Next, an operation for correcting a density change caused by the rotation of the photoconductor 11 will be described.

  When the image forming apparatus forms an image, the photoconductor 11 and the sleeve 141 are rotated under the control of the control unit 10, and the rotated photoconductor 11 is charged by the charging device 12. The control unit 10 monitors the angle signal output from the rotary encoder 160 while rotating the motor 151, and when the angle of the angle signal becomes 0 degrees, the angle is the angle stored in advance in the ROM, and the exposure position ( The angle formed by the line connecting the point Q) in FIG. 1 and the central axis of the photoconductor 11 and the line connecting the developing position and the central axis of the photoconductor 11 is added to the angle signal angle.

  And the electric current value corresponding to the calculated | required rotation angle is calculated | required from the waveform shown in FIG. For example, when the angle formed by the exposure position, the central axis of the photoconductor 11 and the development position is 45 degrees, a current value corresponding to 45 degrees is obtained from the graph shown in FIG. Since the waveform shown in FIG. 10 corresponds to the second gap, the amount of laser light output from the exposure apparatus 13 is controlled according to the obtained current value. Specifically, the current value corresponding to 45 degrees is larger than the average current value Iave with reference to FIG. The fact that the current value is larger than the average value indicates that the second gap is narrower than the average of the second gap when the photoconductor 11 rotates 45 degrees from the present time. When the second gap is narrowed, the image density becomes high. Therefore, in order to prevent the density from becoming high, an electrostatic latent image is formed by reducing the light quantity of the laser light from the light quantity set according to the information representing the density of the image.

  Thereafter, when the photoconductor 11 rotates 45 degrees, the electrostatic latent image reaches the developing position. If no control is performed with respect to the amount of exposure light, the density of the toner image to be formed increases when the second gap is narrow, but as described above, the amount of light when forming the electrostatic latent image at the development position. Since the density is controlled so as not to increase, the density of the formed toner image does not increase even if the second gap is narrowed.

  Further, in a state where the angle of the photoconductor 11 is 180 degrees, a current value corresponding to 225 degrees is obtained from the graph shown in FIG. Here, referring to FIG. 10, the current value corresponding to 225 degrees is smaller than the average current value Iave. The fact that the current value is smaller than the average value indicates that the second gap is wider than the average of the second gap when the photoconductor 11 rotates 45 degrees from the present time. Since the image density decreases as the second gap becomes wider, an electrostatic latent image is formed by increasing the light quantity of the laser light from the light quantity set according to the information representing the density of the image in order to prevent the density from being reduced.

  Thereafter, when the photoconductor 11 rotates 45 degrees, the electrostatic latent image reaches the developing position. If no control is performed with respect to the amount of exposure light, the density of the toner image formed becomes light when the second gap is wide, but as described above, the amount of light when forming the electrostatic latent image at the development position. Since the density is controlled so as not to decrease, the density of the formed toner image does not decrease even when the second gap is widened.

  As described above, according to the present embodiment, the exposure amount when forming the electrostatic latent image is controlled in accordance with the change in the interval between the photoreceptor 11 and the sleeve 141 circumferential surface. Occurrence of banding can be suppressed even if the distance between the sleeve and the circumferential surface of the sleeve 141 changes.

[Modification]
As mentioned above, although embodiment of this invention was described, embodiment mentioned above is an example of embodiment which concerns on this invention, This invention is not limited to embodiment mentioned above, It can implement with other various forms. It is. For example, the present invention may be implemented by modifying the above-described embodiment as follows.

  In the embodiment described above, the density is corrected by controlling the amount of laser light that forms the electrostatic latent image. However, in addition to the exposure amount, for example, the development potential may be controlled to control the density. .

  The image forming apparatus is provided with both the configuration of the first embodiment and the configuration of the second embodiment, and controls the amount of light when an electrostatic latent image is formed using the current value flowing to the motor 151 and flows to the motor 151A. You may make it control the light quantity when forming an electrostatic latent image using an electric current value.

In the embodiment described above, the time when the position P on the circumferential surface of the sleeve 141 moves from the position of the trimmer 142 to the development position is the same as the time when the electrostatic latent image moves from the exposure position to the development position. In this case, the current value represented by the current control signal output from the current control unit 153 may be obtained, and the light amount of the exposure apparatus 12 may be immediately controlled according to the obtained current value.
Further, if the time when the position P on the peripheral surface of the sleeve 141 moves from the position of the trimmer 142 to the development position is shorter than the time when the electrostatic latent image moves from the exposure position to the development position, the current is The current value of the current control signal output from the control unit 153 is obtained, and the light amount of the exposure apparatus 12 is not immediately controlled according to this current value, but the light amount of the exposure apparatus 12 according to this current value after a predetermined time. May be controlled.

The present invention is an image forming apparatus that forms a latent image by a method other than the above-described embodiment as long as it forms a latent image on an image carrier rotated by a motor and develops the latent image to form an image. It can also be applied to devices.
For example, in the above-described embodiment, the latent image is formed by irradiating the photoconductor 11 with light, but the method of forming the latent image is not limited to the method of the above-described embodiment. For example, when forming a latent image by ionography, the ions that form the latent image are controlled according to the current flowing through the motor that rotates the drum on which the latent image is formed and the motor that rotates the sleeve that supplies toner. The potential of the latent image may be controlled.

FIG. 2 is a schematic diagram of a photoreceptor and an area around the photoreceptor according to an embodiment of the present invention. It is a schematic diagram of the periphery of the developing roll 14A according to the embodiment. It is a figure for demonstrating the change of the space | interval between the sleeve 141 and the trimmer 142. FIG. It is the block diagram which showed the structure of the drive part which concerns on the same embodiment. 6 is a graph showing a relationship between a load torque applied to a motor 151 and a current value. FIG. 6 is a diagram showing a relationship between a rotation angle of a sleeve 141 and a current value of a motor 151. FIG. 6 is a diagram showing a relationship between a second gap and a rotation angle of a sleeve 141. It is the block diagram which showed the structure of 150 A of drive parts which concern on 2nd Embodiment of this invention. FIG. 6 is a diagram for explaining a change in a distance between a photoconductor 11 and a sleeve 141. FIG. 6 is a diagram illustrating a relationship between a rotation angle of a photoconductor 11 and a current value of a motor 151A.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Control part, 11 ... Photoconductor, 12 ... Charging device, 13 ... Exposure device, 14 ... Developing device, 15 ... Paper conveyance belt, 16 ... Transfer roll, DESCRIPTION OF SYMBOLS 17 ... Fixing device, 18 ... Cleaning device, 19 ... Static elimination device, 140 ... Magnet roll, 141 ... Sleeve 141 ... Trimmer, 150, 150A ... Drive part, 151 151A: Motor, 152, 152A ... Power supply unit, 153, 153A ... Current control unit, 154, 154A ... Detection unit, 155, 155A ... Setting unit, 160 ... Rotary encoder

Claims (5)

An image carrier on which a latent image is formed;
A rotating body facing the image carrier and supplying a developer to the image carrier;
A motor that rotates the rotating body, and a current that flows when rotating at a constant speed according to a load torque;
Current measuring means for measuring a current value of a current flowing through the motor;
A latent image forming unit that forms a latent image on the image carrier in accordance with image information representing an image, and controls a potential of the latent image formed on the image carrier according to a current value measured by the current measuring unit. And an image forming apparatus. When the image carrier is irradiated with light, the surface potential changes to form a latent image,
Angle measuring means for measuring the rotation angle of the rotating body;
From the rotation angle measured by the angle measuring means and the measurement result of the current value measured by the current measuring means, the distance between the peripheral surface of the rotating body and the peripheral surface of the image carrier, the rotational angle of the rotating body, And means for identifying the relationship between
The latent image forming unit forms a latent image by controlling an irradiation position of light applied to the image holding member according to image information, and the latent image formed on the image holding member moves from an exposure position to a developing position. The rotation angle of the rotating body at the time is obtained from the rotation angle obtained by the angle measuring means, and the interval between the peripheral surface of the image holding body and the rotating body at the obtained rotation angle is specified from the relationship obtained by the specifying means. The image forming apparatus according to claim 1, wherein the amount of light applied to the image holding body is controlled according to the specified interval. An image carrier on which a latent image is formed by changing the surface potential by irradiation with light ; and
A rotating body facing the image carrier and supplying a developer to the image carrier;
A motor that rotates the image carrier, and a current that flows when rotating at a constant speed according to a load torque;
Current measuring means for measuring a current value of a current flowing through the motor;
A latent image forming unit that forms a latent image on the image carrier in accordance with image information representing an image, and controls a potential of the latent image formed on the image carrier according to a current value measured by the current measuring unit. Means ,
Angle measuring means for measuring the rotation angle of the image carrier;
From the rotation angle measured by the angle measuring means and the measurement result of the current value measured by the current measuring means, the distance between the circumferential surface of the rotating body and the circumferential surface of the image holding body, and the rotation angle of the image holding body. have a specifying means for specifying a relationship with,
The latent image forming unit forms a latent image by controlling an irradiation position of light applied to the image holding member according to image information, and the latent image formed on the image holding member moves from an exposure position to a developing position. The rotation angle of the image carrier at the time is obtained from the rotation angle obtained by the angle measuring means, and the interval between the peripheral surface of the image carrier and the rotary body at the obtained rotation angle is obtained from the relationship obtained by the specifying means. Identify and control the amount of light applied to the image carrier according to the identified interval
An image forming apparatus comprising.   When rotating the motor at a constant speed, the relationship between the current flowing through the motor and the load torque is a linear relationship in which the increase amount of the current becomes a constant value when the load torque increases by a certain amount. The image forming apparatus according to claim 1 or 3. The image forming apparatus according to any one of claims 1 to 4, wherein the motor is a brushless motor.

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