JPH07325467A - Image-forming device - Google Patents

Abstract

PURPOSE:To provide a copying device which reduces copying time and greatly extends the life of the device by preventing attachment of unnecessary toner to a photoreceptor even in the case of applying voltages to the photoreceptor and a developing sleeve at the same timing. CONSTITUTION:The copying device is equipped with a potential difference producing means which produces a potential difference between the photoreceptor 9 and the developing sleeve, the potential difference being used for generating an electric field so that toner moves from the photoreceptor 9 to the developing sleeve when high-voltage-resistant relays 49a and b are switched from the ground of the photoreceptor 9 to the application of a voltage to the photoreceptor in order to calibrate an electrometer. This means consists of a constant-voltage element 43 connected between the output terminal of a DC circuit 48 and the AC circuits 44-47.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile and a printer, and more specifically, to a latent image forming means for forming a latent image on an image carrier and a developer carrier. Developing means for supplying the developed developer to the latent image to form a visible image, voltage applying means for applying a voltage to the image carrier and the developing carrier, and application of a voltage to the image carrier. The present invention relates to an image forming apparatus provided with a switching unit that switches grounding of an image carrier as necessary.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus of this type, the surface potential of an image carrier charged to a predetermined potential is detected by a surface potential detecting means, and the setting of image forming process conditions is changed based on the detection result. What is known is. The output of the surface potential detecting means used for such a purpose varies depending on the distance between the surface potential detecting means and the image carrier, so that the output error due to this distance dependency is corrected at a predetermined timing. There was a need. Traditionally, this calibration
The surface potentials of the known surface potentials of at least two image carriers are detected by the surface potential detecting means, and the calibration curve is created based on the output at this time and the known surface potentials. After that, the surface potential of the image carrier is calculated from the output of the surface potential detecting means using the calibration curve, and the setting of the image forming process conditions is changed based on the calculated surface potential. Here, in order to obtain the surface potentials of at least two known image carriers at the time of the above calibration, conventionally, a developing bias power source has been used. Specifically, the image carrier is separated from the ground, the DC voltage output terminal of the developing bias power supply circuit is connected to the image carrier, and a predetermined DC voltage is applied to the image carrier.

[0003]

However, in the above-described conventional calibration method, the DC voltage is applied from the developing bias power source to the image carrier while the developing bias power source is still connected to the developer carrier. However, the image carrying member and the developer carrying member have the same electric potential in terms of direct current, and there is a phenomenon in which the developer is developed on the image carrying member, albeit slightly. Therefore, after the calibration of the surface potential detecting means is completed, a cleaning step for cleaning the surface of the image carrier must be performed without fail, which causes a time hindrance in the subsequent copying operation and an extra cleaning step. Not only the image carrier but also parts around the image carrier (motor,
The fur brush, the static elimination light source, etc.) are fatigued or the life of the image forming apparatus is shortened, and the life of the image forming apparatus is finally shortened.

The problem that unnecessary developer adheres to the image carrier when the surface potential detecting means is calibrated is a problem even if the image forming apparatus is not equipped with the surface potential detecting means. This may occur when the DC voltage of the developing bias power source is used to apply the DC voltage to the image carrier with the power source still connected to the developer carrier.

The present invention has been made in view of the above problems, and an object of the present invention is to obtain an image even when a voltage is applied to the image carrier and the developer carrier at the same timing. An object of the present invention is to provide an image forming apparatus capable of shortening the time of the image forming operation and extending the life of the apparatus by preventing unnecessary adhesion of the developer to the carrier.

[0006]

In order to achieve the above-mentioned object, the invention of claim 1 provides a latent image forming means for forming a latent image on an image carrier, and a developer carried on a developer carrier. Developing means for supplying a latent image to the latent image to form a visible image, voltage applying means for applying a voltage to the image carrier and the developing carrier, and application of a voltage to the image carrier and the image carrier. In an image forming apparatus provided with a switching means for switching the grounding of the image carrier as necessary, a developer is moved from the image carrier to the developer carrier when a voltage is applied to the image carrier. It is characterized in that a potential difference generating means for generating a potential difference for generating an electric field is provided between the image bearing member and the developer bearing member.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, which is provided with a surface potential detecting means for detecting a surface potential of the image carrier, the image carrier is calibrated when the surface potential detecting means is calibrated. It is characterized in that the switching means is configured to apply the voltage.

According to a third aspect of the invention, in the image forming apparatus according to the first aspect, a constant voltage element is used as the potential difference generating means.

According to a fourth aspect of the invention, in the image forming apparatus according to the first aspect, the voltage applying means is constituted by a single power source.

According to a fifth aspect of the invention, in the image forming apparatus according to the first aspect, when a negative-positive developing system is used in the developing means, the absolute value of the voltage applied to the image carrier is applied to the developer carrier. The potential difference is smaller than the absolute value of the applied voltage, and when the positive-positive development method is used, the potential difference is set so that the absolute value of the voltage applied to the image carrier is larger than the absolute value of the voltage applied to the developer carrier. It is characterized in that it constitutes a generating means.

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, a high breakdown voltage relay is used as the switching means.

[0012]

According to the invention of claim 1, when the switching of the voltage application to the image carrier by the switching means,
A potential difference that generates an electric field so that the developer moves from the image bearing member to the developer bearing member by the potential difference generating means,
By generating between the image bearing member and the developer bearing member, unnecessary developer moves from the developing bearing member to the image bearing member and does not adhere thereto.

In particular, according to the second aspect of the invention, in order to calibrate the surface potential detecting means, even when a predetermined calibration voltage is applied to the image carrier by switching the switching means, the image carrier is carried from the developing carrier. Unnecessary developer moves and does not adhere to the body.

In particular, in the invention of claim 3, a constant voltage element is used for the potential difference generating means, and the constant voltage element is connected to a predetermined position of the voltage applying means, whereby the image carrier and the developer are connected. The potential difference can be stably generated between the carrier and the carrier.

In particular, in the invention of claim 4, since the voltage applying means is composed of a single power source, the structure of the voltage applying means can be simplified.

In particular, in the invention of claim 5, when the developing means uses a negative-positive developing system, the absolute value of the voltage applied to the image carrier is the absolute value of the voltage applied to the developer carrier. By making it smaller, unnecessary developer moves from the development carrier to the image carrier and does not adhere to it regardless of whether the developer has positive or negative polarity. Similarly, positive
When the positive developing method is used, by making the absolute value of the voltage applied to the image bearing member larger than the absolute value of the voltage applied to the developer bearing member, the developer bearing property is positive or negative. Unnecessary developer moves from the body to the image carrier and does not adhere.

Particularly, in the invention of claim 6, by using a high withstand voltage relay for the switching means, a transient current is generated when the voltage is switched to the image carrier, which is a capacitive load having high impedance and unstable. The current cutoff function can be maintained even though the current flows easily. (Hereafter, margin)

[0018]

First, an example of a color copying apparatus which is an image forming apparatus to which the present invention can be applied will be described. FIG. 1 is a schematic configuration diagram of a color copying apparatus, and FIG. 2 is an enlarged view around a photoconductor / intermediate transfer belt. This color copying apparatus is a color image reading apparatus (hereinafter, referred to as a color image reading apparatus that reads a color image of a document.
A color scanner) 1 and a color image recording device (hereinafter, referred to as a color printer) 2 for recording the read color image on a transfer paper. The color scanner 1 forms an image of the original 3 on the color sensor 7 via the illumination lamp 4, the mirror groups 5b and 5c, and the lens 6, and outputs the color image information of the original 3 to, for example, blue (B
Lue, hereinafter referred to as B), green (hereinafter referred to as G), and red (red, referred to as R) are read for each color-separated light and converted into electrical image signals. The color sensor 7 is composed of a photoelectric conversion element such as a CCD for separating an image into three colors of B, G, and R to detect an image, and simultaneously reads an image of the three colors. Then, on the basis of the B, G, and R color-separated image signal intensity levels obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter referred to as Bk) and cyan (Cy
Color image data of an (hereinafter referred to as C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) are obtained. This is visualized with Bk, C, M, and Y by the color printer 2 described below, and the toner images thus obtained are superimposed to form a four-color image.

The writing optical unit 8 as the latent image forming means of the color printer 2 includes a laser 8a and its light emission drive control section (not shown), a polygon mirror 8b and its rotation motor 8c, an f / θ lens 8d, and a reflection. Mirror 8e
The color image data from the color scanner 1 is converted into an optical signal to perform optical writing corresponding to the original image, and an electrostatic latent image is formed on the photoconductor 9 as an image carrier. The photoconductor 9 rotates counterclockwise as indicated by an arrow, and around it, a photoconductor cleaning unit (including a pre-cleaning static eliminator) 10, a static eliminator 11, a charger 12, and an electrometer as a surface potential detecting means. 13, Bk developing device 14, C developing device 15, M developing device 1 as developing means
6, a Y developing device 17, an optical sensor 18 for detecting a development density pattern, an intermediate transfer belt 19, and the like are arranged.

Each of the developing units is a developing sleeve (14a, 15a, 16) as a developer carrying member that rotates by bringing the brush of the developer into contact with the surface of the photoconductor 9 to develop the electrostatic latent image.
a, 17a) and the developing paddles (14b, 15b, 16b, 17) that rotate to draw up and agitate the developer.
b), and a toner concentration sensor (14c, 15) for the developer.
c, 16c, 17c) and the like. In the standby state, the developing sleeves (14a, 15
Agents on a, 16a, 17a) are spikes (development inoperative)
It is in a state.

The outline of the copying operation will be described below by taking the example of the developing operation order (color image forming order) as Bk, C, M, and Y (however, the image forming order is not limited to this). . When the copying operation is started, the color scanner 1 starts reading Bk image data from a predetermined timing, and optical writing by a laser beam and latent image formation start based on the image data (hereinafter, electrostatic image by Bk image data is used. The latent image is referred to as a Bk latent image. C, M, and Y are referred to as a C latent image, an M latent image, and a Y latent image, respectively). The Bk developing device 14 is provided to enable development from the tip of this Bk latent image.
Before the leading edge of the latent image reaches the developing position, the developing sleeve 14a is started to rotate so that the agent is spiked and the Bk latent image is developed with Bk toner. After that, the developing operation of the Bk latent image area is continued, and when the trailing edge of the latent image passes the Bk developing position, the developer on the Bk developing sleeve 14a is quickly cut off to make the developing inoperative state. This is at least
The process is completed before the leading edge of the C latent image by the next C image data arrives. In addition, the cutting off of the agent is performed by the developing sleeve 14
The rotation direction of a is switched to the opposite direction to that during the developing operation.

The Bk toner image formed on the photosensitive member 9 is transferred onto the surface of the intermediate transfer belt 19 which is driven at the same speed as the photosensitive member (hereinafter, the toner image transfer from the photosensitive member to the intermediate transfer belt is called belt transfer). ). The belt transfer is performed by applying a predetermined bias voltage to the transfer bias rollers 20a and 20b while the photoconductor 9 and the intermediate transfer belt 19 are in contact with each other. The intermediate transfer belt 19 has a photosensitive member 9
The Bk, C, M, and Y toner images sequentially formed on are sequentially aligned on the same surface to form a 4-color superposed belt transfer image, and then bulk transfer is performed on the transfer paper. This intermediate transfer belt unit will be described later.

On the side of the photosensitive member 9, the Bk process is followed by the C process, but the C image data reading by the color scanner 1 is started at a predetermined timing, and the C latent image is formed by writing the laser light by the image data. C developing device 1
The reference numeral 5 starts rotation of the developing sleeve 15a to raise the agent after the trailing edge of the previous Bk latent image has passed and before the leading edge of the C latent image has reached the developing position. Develop the latent image with C toner. After that, the development of the C latent image area is continued,
At the time when the trailing edge of the latent image passes, as in the case of the previous Bk developing device, the C-developing sleeve 15a is cut off to put it in the non-developing state. This is also completed before the leading edge of the next M latent image arrives. In each of the steps M and Y, the operations of reading image data, forming a latent image, and developing are performed in the same manner as the steps Bk and C described above.

In the intermediate transfer belt unit, the intermediate transfer belt 19 is stretched around the driving roller 21, the transfer bias rollers 20a and 20b, and the driven roller group.
The drive is controlled by a drive motor (not shown). The belt cleaning unit 22 that cleans the intermediate transfer belt 19 includes a brush roller 22a, a rubber blade 22b, and a contact / separation mechanism 22c from the belt. After the belt transfer of the Bk image of the first color,
While transferring the second, third, and fourth colors on the belt, the contact / separation mechanism 2
It is separated from the belt surface by 2c.

The paper transfer unit 23 includes a paper transfer bias roller 23a, a roller cleaning blade 23b,
And a belt contact / separation mechanism 23c. The paper transfer bias roller 23a is normally the belt 1
Although separated from the 9th surface, the four-color superposed image formed on the surface of the intermediate transfer belt 19 is pressed by the contact / separation mechanism 23c at a timing when collectively transferring to the transfer paper, and the roller 23a is predetermined. Is applied to transfer onto the transfer paper 24.

The transfer paper 24 is composed of a paper feed roller 25,
The registration roller 26 feeds the leading end portion of the four-color superimposed image on the surface of the intermediate transfer belt at the timing when it reaches the paper transfer position. The transfer paper 24 on which the four-color superposed toner images are collectively transferred from the surface of the intermediate transfer belt 19 is conveyed to the fixing device 28 by the paper conveying unit 27, and the toner is fixed by the fixing roller 28a and the pressure roller 28b controlled at a predetermined temperature. The image is fused and fixed, and is carried out to the copy tray 29,
Get a full color copy.

The photosensitive member 9 after the belt transfer is the photosensitive member cleaning unit 10 (pre-cleaning static eliminator 10).
The surface is cleaned with a, the brush roller 10b, the rubber blade 10c), and the charge is removed uniformly by the charge removing lamp 11. Further, the surface of the intermediate transfer belt 19 after the toner image is transferred onto the transfer paper 24 is cleaned by pressing the cleaning unit 22 again by the contact / separation mechanism 22c.

At the time of repeat copying, the color scanner 1
The operation and the image formation on the photosensitive member 9 proceed to the second Bk (first color) image process at a predetermined timing after the first Y (fourth color) image process. Further, in the intermediate transfer belt 19, the second Bk toner image is formed in the area where the surface is cleaned by the cleaning unit 22, following the batch transfer process of the first four-color superimposed image onto the transfer paper. Allow the belt to be transferred. After that, the same operation as the first sheet is performed. The transfer paper cassettes 30, 31, 32,
The reference numeral 33 stores transfer sheets of various sizes, which are fed and conveyed in the direction of the registration rollers 26 at a timing from a storage cassette of size sheets designated by an operation panel (not shown). Reference numeral 34 in the drawing denotes a manual paper feed tray for OHP paper, thick paper, or the like.

The above is the description of the copy mode in which four full colors are obtained, but in the case of the three-color copy mode and the two-color copy mode, the same operation as above is performed for the designated color and the number of times. It will be. In the single-color copy mode, until the predetermined number of sheets are finished, only the developing device of that color is in a developing operation (agent standing) state, and the intermediate transfer belt 19 remains in contact with the surface of the photoreceptor 9. Drives in the forward direction at a constant speed, and the belt cleaner 22 also drives the belt 19
The copy operation is performed in the state where the contact is kept.

By the way, in the color copying machine, the power is turned on.
After that, the photoconductor 9 is charged to a predetermined charging potential (for example, a plurality of 16-step charging potentials) by the charger 12, and the surface potential of the photoconductor 9 is detected by the electrometer 13 and based on the detection result. Control is performed so as to change the setting of the image forming process conditions (grid voltage of the charger 12, exposure amount by the laser 8a, etc.) during copying.
The main control unit that performs this control is, for example, a CPU or RA.
It can be configured by an M, a ROM, an I / O interface and the like.

Since the output of the electrometer 13 used for the above control changes depending on the distance to the surface of the photosensitive member 9,
It is necessary to calibrate once a day, every specified number of copy transfer sheets, or every maintenance such as replacement of the photoconductor 9. When the electrometer 13 is calibrated, a predetermined voltage is applied to the photoconductor 9 which is normally in the grounded state from a bias power source as a voltage applying means as described later. Then, as shown in FIG. 3, a predetermined calibration voltage V
Electrometer 13 when dr1 and Vdr2 are applied to the photoconductor 9
The respective outputs Odr1 and Odr2 are read, and the values of the slope Adr and the Y intercept Bdr of a straight line (Y = Adr · X + Bdr) obtained by linearly approximating the read result are obtained. Calculated slopes Adr and Y
The value of the intercept Bdr is stored in the RAM or the like of the main control unit, and when the surface potential of the photoconductor 9 is detected thereafter, the electrometer 1
The calibrated potential output (Y) can be obtained by substituting the output of 3 for X in the above linear approximation formula, and the calibrated value is used for the setting change control of the image forming process conditions. To be Here, the calibration voltages Vdr1 and Vdr2
As shown in FIG. 3, a value near the lower limit and the upper limit of the variable range of the bias power supply, which will be described later, and a value that maintains linearity may be selected. For example, when 0V to -1000V is the variable range of the bias power supply, Vdr1 = -200
If V and Vdr2 = -1000V, the linearity is maintained. At both ends in FIG. 3, the solid line indicates the actual electrometer 13
Of the linear approximation formula, and the broken line shows the extension of the above linear approximation formula.

Further, at the time of developing in the copying operation, each developing device (14, 15, 16, 1) is controlled by a bias power source.
7) developing sleeves (14a, 15a, 16a, 17)
Although a predetermined developing bias voltage is applied to the power supply portion (not shown) in a), a DC voltage on which a predetermined AC voltage is superimposed is applied as the developing bias voltage in this embodiment.
FIG. 4 is a schematic configuration diagram of a circuit of the bias power supply 35 used in this embodiment. Note that, in FIG. 4, for convenience of description, only a circuit for applying a developing bias voltage to one developing sleeve 14a is illustrated. At the power supply terminal Vpp of the bias power supply 35, the primary coil 3 that constitutes the first transformer 36 is provided.
6a and the primary coil 37 of the second transformer 37
One ends of a are connected to each other.

Primary coil 36 of the first transformer 36
The other end of a is connected to the collector of an npn-type transistor 38, and the base of this transistor 38 is connected to an AC oscillation circuit 39. The control signal 1 is supplied to the AC oscillation circuit 39 from the main controller. The other end of the primary coil 37a of the second transformer 37 is connected to the collector of an npn-type transistor 40, and the base of the transistor 40 has D
The oscillator circuit 41 for C is connected. A PWM circuit 42 is connected to the DC oscillating circuit 41, and the control signal 2 and the PWM signal are supplied from the main control section. The transistors 38 and 40 are
The emitters of are each grounded.

On the other hand, both ends of the secondary coil 36b of the first transformer 36 are connected to a bias terminal to the developing sleeve 14a and the photosensitive member 9 via a resistor R1 and constant voltage elements 43 and R2 described later, respectively. It is connected to the ground terminal. Both ends of the secondary coil 37b of the second transformer 37 are connected to both ends of the resistor R2 via a rectifying / smoothing circuit including a diode D and a capacitor C. This rectifying / smoothing circuit converts the AC voltage generated in the secondary coil 37b of the second transformer 37 into a DC voltage.

The control signal 1 and the control signal 2 are trigger level signals, and are respectively the AC oscillation circuit 39 and the DC oscillation circuit 39.
Is a signal for ON / OFF control of the oscillating circuit 41 and the PWM circuit 42. Further, the PWM circuit 42 changes the duty ratio of the oscillation waveform oscillated at the predetermined frequency (1 kHz or 2 kHz) of the DC oscillation circuit 41 based on the PWM signal from the main control unit to perform the rectification and smoothing. It is a circuit for changing the value of the DC voltage obtained by the circuit.

In the bias power supply 35 having the above structure, A
Depending on the oscillation frequency of the C oscillation circuit 39, the first transformer 3
The DC voltage generated in the secondary coil 36b of No. 6 is rectified and smoothed in the secondary coil 37a of the second transformer 37 according to the oscillation frequency of the DC oscillation circuit 41.
It is superimposed on the voltage. Then, the DC voltage on which the AC voltage is superposed is used as the developing bias voltage, and the bias (BIA
S) is applied to the developing sleeve 14a from the terminal.

FIG. 5 shows the developing sleeves (14a, 15).
FIG. 5 is a schematic configuration diagram of a bias power supply in which the circuit of FIG. 4 is combined so that a developing bias voltage can be applied to the power feeding unit of a, 16a, 17a). Here, AC1 to AC1 in FIG.
The four circuits 44, 45, 46, 47 correspond to the AC oscillation circuit 39, the first transformer 36, the transistor 38, and the resistor R1 in FIG. In addition, the DC circuit 48 in FIG.
Corresponds to the PWM circuit 42, the DC oscillation circuit 41, the transistor 40, the second transformer 37, the diode D, the capacitor C, and the resistor R2 in FIG.

Also, the bias power supply is equipped with an electrometer 13
A circuit switching means for applying predetermined calibration voltages Vdr1 and Vdr2 to the photoconductor 9 for calibration, and a predetermined circuit between the photoconductor 9 and the developing sleeve when the calibration voltage is applied to the photoconductor 9. A potential difference generating means for generating a potential difference is provided.

As the switching means, the drive coil 4 is used.
A high breakdown voltage reed relay 49 composed of 9a and a relay contact 49b is used. This reed relay 49 has a maximum of 1
It has a switching voltage function of 000 Vdc. A current is applied to the drive coil 49a based on the relay switching signal sent from the main control section, and when the electrometer 13 is calibrated, the output voltage of the DC circuit 48 is applied to the photoconductor 9 during calibration. In other cases, the relay contact 49b is switched so that the photoconductor 9 is grounded at other times.

The voltage generating means is composed of a constant voltage element 43 connected between the output terminal of the DC circuit 48 and each of the AC circuits 44 to 47. As the constant voltage element 43, for example, a Zener diode which is a kind of varistor can be used. By connecting the constant voltage element 43, the output voltage of the DC circuit 48 is controlled by the constant voltage element 43.
And is applied to each developing sleeve via each AC circuit 44 to 47. Here, since the photoreceptor 9 and the developing sleeve both have high impedance, the applied voltage is -600V.
The current is −30 to −60 μA with respect to dc. When viewed in terms of DC from the bias power source, since the constant voltage element 43 and the developing sleeve are directly connected to each other, the photoconductor 9 and the developing sleeve apparently have a potential difference corresponding to the voltage across the constant voltage element 43. The voltage across the constant voltage element 43 is preferably set to 50 V or higher. In this case, the toner on the developing sleeve does not start developing so as to move to the photosensitive member 9 side. In order to set it more accurately, it is determined in consideration of individual image forming conditions. Further, since the color copying apparatus of the present embodiment employs the negative-positive developing system, the circuit is constructed so that the absolute value of the voltage applied to the photoconductor 9 is larger than the absolute value of the voltage applied to the developing sleeve. However, when the positive-positive developing method is adopted, the circuit is configured so that the absolute value of the voltage applied to the photoconductor 9 is smaller than the absolute value of the voltage applied to the developing sleeve.

Further, if a bidirectional constant voltage element in which two Zener diodes are connected in series in opposite directions is used as the constant voltage element 43, it is possible to cope with the positive and negative developing bias voltages. Become.

As described above, according to this embodiment, even when the reed relay 49 is switched to apply a predetermined calibration voltage from the DC circuit 48 of the bias power source when the electrometer 13 is calibrated, each constant voltage element 43 is used. By generating a predetermined potential difference between the developing sleeve and the photoconductor 9, unnecessary cleaning of the toner on the photoconductor 9 is omitted, and the subsequent cleaning step is omitted. Therefore, the copying operation time is shortened. Therefore, it is possible to reduce fatigue of the photoconductor 9 and extend the life of the parts around the photoconductor 9.

Further, according to this embodiment, in order to generate a predetermined potential difference between each developing sleeve and the photosensitive member 9,
Since only the constant voltage element 43 is used, it is not necessary to add a special potential difference generating circuit or separately provide a dedicated power source for generating the potential difference.

Further, since the high withstand voltage reed relay 49 is used as a circuit switching means for applying the predetermined calibration voltages Vdr1 and Vdr2 to the photoconductor 9 for calibrating the electrometer 13, the high withstand voltage is not used. The current cutoff function can be maintained and the relay contact 49b can be protected even though the transient current is apt to flow when the voltage is switched to the stable capacitive load (developing sleeve, photoconductor 9). can do.

In the above embodiment, a color copying machine having a plurality of developing devices has been described. However, the present invention is not limited to the number of developing devices and can be applied to, for example, a copying device having a single developing device. Is also applicable.

[0046]

According to the invention of claims 1 to 6, when the voltage is switched to the image carrier by the switching means, the potential difference generating means causes a predetermined potential difference to be applied to the image carrier and the developer. Since the unnecessary developer moves from the development carrier to the image carrier and does not adhere to the image carrier due to the generation between the developer carrier and the image carrier, the subsequent cleaning step is also unnecessary, so that the time of the image forming operation is shortened and the apparatus is reduced. The effect is that the life of the can be extended.

In particular, according to the second aspect of the present invention, when the surface potential detecting means is calibrated, unnecessary developer moves from the developing carrier to the image carrier and does not adhere, and a subsequent cleaning step is also required. Therefore, there is an effect that the time for the image forming operation can be shortened and the life of the apparatus can be extended.

In particular, according to the invention of claim 3, by using a constant voltage element for the potential difference generating means, the constant voltage element is connected to a predetermined position of the voltage applying means to develop the image bearing member and the developing device. Since the above potential difference can be stably generated between the agent carrier and the agent carrier, it is not necessary to load a special circuit or separately provide a power source for generating the potential difference.

In particular, according to the fourth aspect of the invention, since the voltage applying means is composed of a single power source, the structure of the voltage applying means can be simplified, so that the space saving and cost reduction of the apparatus can be achieved. There is an effect that can be achieved.

In particular, according to the invention of claim 5, even when the negative-positive developing system or the positive-positive developing system is used in the developing means, regardless of the polarity of the developer,
There is an effect that it is possible to reliably prevent the unnecessary movement of the developer from the developing carrier to the image carrier and the adhesion to the image carrier.

In particular, according to the invention of claim 6, by using a high breakdown voltage relay for the switching means, it is possible to make a transition at the time of switching the voltage to the image carrier which is a capacitive load which is unstable with high impedance. Since the current cutoff function can be maintained even though the current easily flows, there is an effect that the switching by the switching means can be reliably performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color copying apparatus according to an embodiment.

FIG. 2 is an enlarged view around the photoconductor / intermediate belt in FIG.

FIG. 3 is a characteristic diagram showing a relationship between an output voltage and an applied bias voltage when calibrating an electrometer.

FIG. 4 is a block diagram of a circuit showing a part of a bias power supply.

FIG. 5 is a block diagram of a circuit of the entire bias power supply.

[Explanation of symbols]

 8 optical unit 9 photoconductor 13 electrometer 14 Bk developing device 15 C developing device 16 M developing device 17 Y developing device 14a Bk developing sleeve 15a C developing sleeve 16a M developing sleeve 17a Y developing sleeve 35 bias power source 43 constant voltage element 49a high Withstanding voltage reed relay drive coil 49b High withstand voltage reed relay contact

Claims (6)

[Claims] 1. A latent image forming means for forming a latent image on an image carrier, a developing means for supplying a developer carried on a developer carrier to the latent image to form a visible image, and the image carrier. An image forming apparatus comprising: a voltage applying unit that applies a voltage to the image carrier and the developing carrier; and a switching unit that switches the application of the voltage to the image carrier and the grounding of the image carrier as necessary. When a voltage is applied to the image carrier, a potential difference is generated between the image carrier and the developer carrier so that a potential difference is generated which causes an electric field so that the developer moves from the image carrier to the developer carrier. An image forming apparatus characterized in that a potential difference generating means for generating a voltage is provided. 2. The image forming apparatus according to claim 1, further comprising a surface potential detecting means for detecting a surface potential of the image carrier, wherein a voltage is applied to the image carrier when the surface potential detecting means is calibrated. An image forming apparatus, characterized in that the switching means is configured to perform. 3. The image forming apparatus according to claim 1, wherein a constant voltage element is used for the potential difference generating means. 4. The image forming apparatus according to claim 1, wherein the voltage applying means is composed of a single power source. 5. When the developing means uses a negative-positive developing system, the absolute value of the voltage applied to the image carrier is smaller than the absolute value of the voltage applied to the developer carrier, and the positive-positive developing system is used. In the case of using, the potential difference generating means is configured such that the absolute value of the voltage applied to the image carrier is larger than the absolute value of the voltage applied to the developer carrier. Image forming apparatus. 6. The image forming apparatus according to claim 1, wherein a high voltage relay is used as the switching means.