JPH01265278A - Image forming device - Google Patents

Abstract

PURPOSE:To lower the risk of toner dropping from a development sleeve by switching the rate of the on time and the off time of a recovery bias power source if image forming operation is not continuously performed after developing operation is finished. CONSTITUTION:A developing bias voltage Vb and a recovery bias voltage Vss, which are the reversed polarity to the electrostatic charge polarity of toner are impressed on the development sleeve 23 and on a toner supplying roller 30 by power sources 41 and 42. When the recovery bias power source is turned on and off and the developing operation is finished, if the image forming operation is not started although specific time passed after the developing operation, the rate of the on and the off time of the power source 42 is changed, and the on time is extended. Besides, the recovery bias voltage Vss is made higher than the developing bias voltage Vb. Thus, the toner dropping from the development sleeve 23 can be prevented by enlarging the recovery bias voltage Vss.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to image forming devices such as copying machines and printers that are equipped with a developing device that prepares a developer by mixing toner and carrier on the outer periphery of a developing sleeve. Regarding equipment.

(Prior Art) Conventionally, in an image forming apparatus, a two-component developer is prepared by mixing toner and carrier on the outer periphery of a developing sleeve, and at the same time, a toner supply roller supplies an amount of toner corresponding to the amount consumed by development. A device equipped with a developing device is provided.

In the developing device, a DC developing bias voltage having a polarity opposite to the charging polarity of the toner is applied to the developing sleeve and the toner supply roller.
By applying respective collection bias voltages and adjusting these values, it is possible to change the toner concentration (mixing ratio of toner to carrier) on the developing sleeve.

In addition, if this characteristic is used, the toner density on the developing sleeve is maintained at a high density state during development to improve image reproduction performance, and when development is completed, the toner density is switched to a low density state to prevent overtoning. It is possible to prevent toner from spilling.

(Problems to be Solved by the Invention) However, conventionally, the bias voltage has been adjusted using a variable resistor, which is easily affected by temperature and the like, and the output is unstable. Furthermore, since it takes a long time for the toner concentration on the developing sleeve to reach a predetermined value after changing the voltage, there is a problem in that the responsiveness to operation commands is poor.

By the way, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 2003-11101 that when an alternating current of several hundred volts is superimposed on a direct current as a recovery bias, the toner supply/collection performance can be dramatically improved, and the toner concentration on the developing sleeve can be quickly changed. 62-28
This is proposed in Publication No. 3369.

However, in order to obtain an AC voltage of several hundred volts, an AC transformer is required to transform the 100V AC voltage supplied to general consumers.

Therefore, an AC transformer must be provided in addition to the DC transformer, which has the drawback of increasing the size and cost of the image forming apparatus.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and will be described with reference to the accompanying drawings showing one embodiment. As shown in Figure 4, 1. A developing sleeve (23) holding a developer consisting of toner and carrier on its outer periphery;
a developing device (4) having a toner supply roller (30) facing the; and (iii) the developing sleeve (23).
The developing sleeve (2) is connected to the toner supply roller (30), and the toner supply roller (30) is connected to the toner supply roller (30) so that the toner is charged with the opposite polarity.
3) Power supply means for applying a DC voltage (Vss) higher than that [developing bias power supply (41), recovery bias power supply (
42)) and the output from the power supply means (power supply (42) in this embodiment) to the toner supply roller (30) are turned on and off, and after the development operation is completed, for example, in a copying machine, scanning is performed. If the image forming operation is not started even after a predetermined period of time has passed after the operation is completed, the exposure lamp is turned off, or the charging charger is stopped, the on-time of the output (τon
) a control means C microcomputer (MC)) for making the ratio of the image forming apparatus larger than that during development;

(effect) In the image forming apparatus, a power supply means C (41).

(42)] is applied to the developing sleeve (23), ) toner supply roller (30) with voltages of opposite polarity to the charged polarity of the toner, that is, the developing bias voltage (vb), the collection bias voltage (Vs
s) is applied.

and the recovery bias power supply (42) c12'.

If the image forming operation does not start even after a predetermined period of time has passed after the power source (42) is turned on and off as shown in Figure 3 and the developing operation is completed, the on time (τon) and off time (τo) of the power source (42) are changed.
The ratio of f f) time is changed and the on time (τon
) is set to a large ratio.

Here, the recovery bias voltage (Vss), which is the effective value of the voltage [(42)], is determined by the following equation.

τOn Vp: Peak voltage Also, the recovery bias voltage (Vss) is set to a higher voltage than the development bias voltage (vb). Therefore, as shown in Table 1 below, as the ratio of on-time (τon) increases, the collection bias voltage (Vss) increases, and the potential difference between the developing bias voltage (vb) and the collection bias voltage (Vss) increases. Become. Then, the toner concentration of the developer prepared on the outer periphery of the developing sleeve (23) decreases, the amount of toner held on the developing sleeve (23) decreases, and the toner may fall and contaminate peripheral devices. It becomes less.

[Below, remainder white] Table-1 (Example) Next, one embodiment of the present invention will be described with reference to the accompanying drawings.

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FIG. 1 is a schematic cross-sectional view of a copying machine, in which a photosensitive drum (2), which is an electrostatic latent image carrier, is installed approximately in the middle of the copying machine main body (1) so as to be rotatable in the direction of arrow (a). Around it, along the direction of rotation, are a charging charger (3), a developing device (4), a transfer charger (5>, and a separation charger (6).
), a cleaning device (7), and a main eraser (8).

Further, a document table glass (10) covered with a document cover (9) is provided at the top of the copying machine main body (1), and a slider having an exposure lamp (12) is provided in the optical system (11) below. (13) is provided so as to perform a scanning operation in the direction of arrow (b).

Further, a paper feed section (14) and a paper discharge section (16) are provided on the left and right sides of the Pg photocopier, respectively.

The general operation of the copying machine having the above configuration will be explained with reference to the timing chart of FIG.

When the print key (101)C (see Figure 7) is pressed and its on-edge is detected, the main motor (not shown)
starts, and the developing device (4) starts driving.

Next, the main eraser (8), the transfer charger (5),
The separation charger (6), the charging charger (3), and the exposure lamp (12) are turned on in sequence to set the photosensitive drum (2) in an image-formable state, and the copy paper is placed in the paper feed section (
14) to the front of the transfer charger (5).

Subsequently, the slider (13) scans in the direction of arrow (b) based on the scan signal, and the reflected light illuminates the document (not shown) on the document platen glass (10), which is reflected by the mirror,
The surface of the photoreceptor drum (2) is exposed to light through a lens or the like, and an electrostatic latent image corresponding to the original image is formed.

This electrostatic latent image is supplied with toner at an opposing portion of the developing device (4) and is visualized as a toner image.

On the other hand, the copy paper is conveyed from the paper feed section (14) in synchronization with the toner image, and the toner image is transferred at a section facing the transfer charger (5), and then transferred to the separation charger (6).
After being separated from the surface of the photoreceptor drum (2), the toner image is conveyed to a fixing device (15), where the toner image is fused and fixed, and then discharged to a paper discharge section (16).

A cleaning device (7) removes residual toner from the surface of the photosensitive drum (2) where the toner image has been lost in the transfer area, and a main eraser (8) removes residual charge.

When the original exposure is completed, the exposure lamp (12) is turned off, and then the slider (12) is turned off by turning off the scan signal.
3) stops its operation and returns to the starting position shown in FIG.

In the case of a single copy in which only - sheets are copied, the charger (3) stops after a time (τa) after the scan signal is turned off. Also, transfer charger (5), separation charger (6), main eraser (8)
Then, when the main motor stops, the developing device (4) also stops to complete the image forming operation.

On the other hand, when performing continuous copying to copy multiple sheets of the same original, for example, as shown in the timing chart of FIG. 14) is turned on, the scanning operation for the second sheet is resumed, and thereafter, the image forming operation is performed in the same manner as the single copy.

j! , , , , , 4. (Lll direct installation, structure of developing device) Fig. 4 shows a cross section of the developing device (4) used in a copying machine.

The developing device (4) is disposed on the side of the photoreceptor drum (2) and supplies toner to the electrostatic latent image formed on the photoreceptor drum (2). ) is a developing sleeve (23) adjacent to the photoreceptor drum (2).
), and the toner is supplied from a toner storage tank (38) formed on the back side of the developing sleeve (23) to the surface of the developing sleeve (23) via a toner supply roller (30). be.

The developing sleeve (23) is a cylindrical body made of a conductive non-magnetic material, to which a DC developing bias voltage (VB) is applied from a developing bias power source (41), and a magnetic roller (24) having a plurality of magnets inside. It is housed coaxially and fixedly.

The main developer stirring plate (25) is fixed to the photosensitive drum (2) side of the cover (22), and the auxiliary developer stirring plate (27) is fixed to the cover (22) via the support member (26). Both of them are made of non-magnetic material, and their tips face the circumferential surface of the developing sleeve (23).

The auxiliary developer stirring plate (27) has an opening (28) in the axial direction of the developing sleeve (23), and has an opening (28) in the axial direction of the developing sleeve (23).
), a blade (33) and a powder smoke prevention film (35), which will be explained later, form a space (36).

The toner supply roller (30) is a cylindrical body made of a conductive non-magnetic material such as aluminum, and the surface of the toner supply roller (30) is made of a conductive nonmagnetic material such as aluminum.
It is formed with four minute parts of about 0 μm, and is placed close to the back side of the developing sleeve (23).
23) can be rotated in the direction of arrow (c). Further, a recovery bias voltage (Vss) is applied to the toner supply roller (30) by a DC power supply (42), and its value is determined by checking the operation panel (100).
It is adjusted by the output of a microcomputer (MC) based on key operations, and the adjustment will be explained later.

A partition wall (31) is installed above the toner supply roller (30) so as to be rotatable around a support shaft (32), and one end of the partition wall (31) is attached to the rear end of the upper part of the developer tank (21) above the partition wall (31). The other end of the spring (34) is attached and always points in the direction of the arrow (d
) direction, and the lower end of the fuselage (33) provided at the lower part of the partition wall (31) is brought into pressure contact with the surface of the toner supply roller (30) in the direction of rotation thereof. Further, below the toner supply roller (30), a developer 1fj (2+
) is provided with a sealing member (37), the tip of which is brought into pressure contact with the outer periphery of the toner supply roller (30).

The toner storage tank (38) is formed by partitioning the rear part of the developer tank (21) with the partition wall (31), the blade (33), the toner supply roller (30), and the seal member (37). , this toner storage tank (38) is equipped with a stirring blade (
39) is installed so as to be rotatably driven in the direction of arrow (e). A positive polarity toner is contained in the toner storage tank (38), and is mixed and stirred by the stirring blade (39).

In addition, a spill prevention plate (40) is provided on the developing tank (21) and the cover (22) at the portions facing the photoreceptor drum (2), respectively.
, Mylar (41) to prevent powder smoke is provided, and the developing tank (21)
) to prevent developer and toner from scattering.

b. Operation of developing device Next, the operation of the developing device (4) will be explained.

A starter made of a mixture of a negatively charged magnetic carrier and a positively charged insulating toner is loaded into the space (36), and a positively charged insulating toner is loaded into the toner storage tank (38). . At this time, only a magnetic carrier may be loaded in the space (36) instead of the starter. Then, with the insulating toner loaded, the electrostatic latent image can be developed by the developing device (4).

Here, the toner stored in the toner storage f'J (38) enters the minute recess on the circumferential surface of the toner supply roller (30), and is conveyed in the same direction based on the rotation in the direction of the arrow (C). , excess toner is scraped off by the blade (33), and the part (B) facing the developing sleeve (23) is pre-charged due to friction with the blade (33).
The magnetic carrier on the developing sleeve (23) is scraped off by the magnetic brush formed by the toner supply roller (30).
and onto the developing sleeve (23).

Excess toner supplied onto the developing sleeve (23)
A developing sleeve (to which a developing bias voltage (vb) is applied)
23) and the toner collection roller (30) to which a collection bias voltage (Vss) is applied, due to the electrostatic attraction force based on the potential difference (ΔV), the toner supply roller (30) collects the toner. As a result, the developer containing toner is adjusted on the developing sleeve (23) to the extent that image reproduction is possible.

Note that the potential difference (ΔV) between the developing bias voltage (v b) and the collection bias voltage (V ss) and the developing sleeve (23
) The relationship between the toner concentration of the developer above and the relationship between the toner concentration and image reproducibility will be described later.

The toner supplied to the developing sleeve (23) is conveyed along with the carrier held on the circumferential surface of the developing sleeve (23) in the direction of the arrow (b) based on the rotation thereof, and is conveyed to the auxiliary developer stirring plate (27). ), most of the developer is blocked and pushed by the magnetic developer that is transported later.
It curves up along the auxiliary developer stirring plate (27), passes through the slit-shaped opening (28), and reaches the space (29) on the downstream side. The remaining developer passes through the gap between the auxiliary developer agitation plate (27) and the developing sleeve (23) and enters the downstream space (
29).

Most of the developer thus conveyed to the space (29) is blocked by the main developer stirring plate (25), and is mixed and stirred by rotating clockwise. A part of the developer passes through the gap between the main developer stirring plate (25) and the developing sleeve (23), and the brush height is regulated to form a magnetic brush, and the magnetic brush is exposed to light in the developing area (A). The surface of the body drum (2) is rubbed, and the electrostatic latent image on the surface is developed and visualized.

After being subjected to development, the magnetic developer remaining on the circumferential surface of the developing sleeve (23) reaches the part (B) facing the toner supply roller (30), where new toner is supplied, and then it is recycled again. Subjected to development.

Characteristics of C3 Developing Device Next, as characteristics of the developing device (4), the relationship between the potential difference (Δ■) and toner concentration, and the relationship between toner concentration and image reproducibility will be described.

FIG. 5 shows the developing bias voltage (
A developing sleeve (23) to which Vb) is applied and a toner supply roller (30) to which a recovery bias voltage (Vss) is applied.
) when changing the potential difference (ΔV) with the developing sleeve (2
3) It shows the change in toner concentration of the above developer.

In the figure, when the potential difference (ΔV) increases, the toner concentration decreases, and when the potential difference (ΔV) decreases (the toner concentration increases. This means that the toner supply from the toner supply roller (30) to the developing sleeve (23) is As mentioned above, this is done mechanically by scraping the developing sleeve (23) with a magnetic brush, and does not depend on the potential difference (ΔV) between the developing sleeve (23) and the toner supply roller (30). , from the developing sleeve (23) to the toner supply roller (3).
0) is performed by the action of electrostatic attraction based on the potential difference (ΔV), and naturally depends on the potential difference (ΔV). Then, the potential difference (ΔV
) is high, the electrostatic attraction force becomes large and the amount of toner collected increases.As a result, the toner concentration of the developer on the developing sleeve (23) is balanced at a low value, and the potential difference (Δ■)
This is because when is low, the electrostatic attraction force becomes small and the amount of toner collected decreases, so that on the contrary, the toner concentration is balanced at a high value.

FIG. 6 shows the image reproduction characteristics of the copying machine as a change in copy density with respect to original density. In the figure, (Q
, ) is the toner of the developer on the developing sleeve (23); the n degree is 7w% (weight %), and represents standard reproduction characteristics suitable for relatively line images with large gradients, and (a,) is when the toner concentration is 3.5 w%, and represents reproduction characteristics suitable for photographic images with a small gradient and good gradation reproducibility.

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The figure shows a part of the operation panel (100), which includes a print key (101), a display section (102) for displaying the number of copies, etc., and a numeric keypad for setting the number of copies. (lO3), clear/stop key (104) to initialize the number of copies and cancel copying.
, a volume (105) for adjusting the light intensity of the exposure lamp (12) that illuminates the original, a group of LEDs (106) that indicates the image mode, which is an indicator of the image quality of the copy to be created, A mode that emphasizes sexuality.

A soft key (107) for switching the image quality to a harder mode (a mode emphasizing fine line reproducibility) and a hard key (108) are provided.

The image mode changed by the soft key (107) and hard key (+08) can be selected in "5" steps, and the selected image mode is displayed by an LED with a corresponding number. There is.

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! FIG. 8 is a diagram showing the control configuration of the 1Q copying machine according to the present invention. Control of the copying machine is mainly carried out by a microcomputer (MC), and the operation panel (100) 17) Various types of cows (10)
1), (103).

In addition to (104), (107), (+08) and Rano signals, it is designed to accept signals from various sensors and other large sword keys. The microcomputer (MC) also has soft keys (107), 1 hard key (
Processes the input signal from IQ8) and outputs a remote signal to the recovery bias power supply (42) based on the result to adjust the recovery bias voltage (VsS),
The LED corresponding to the set image mode is turned on from among the LED group (106). Furthermore, numeric keypad (103)
In addition to displaying the number of copies on the display section (102) based on the signal from the control panel, the control signal and other necessary data are output to the exposure fluorescent lamp of the optical system (not shown).

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The output of the recovery bias power supply (42) is set in accordance with the image mode switched by the soft key (107) and hard key (108).

Here, the recovery bias voltage (Vss) is adjusted as follows.

That is, by alternately outputting an on signal and an off signal from a microcomputer (MC), the recovery bias power source (
42) is periodically turned on and off, and by changing the ratio of on time and off time, the effective voltage of the power supply (42) [corresponding to recovery bias voltage (VsS)] is adjusted to a value corresponding to the image mode. .

Specifically, the signal and developing bias voltage (Vss) output according to the image mode are determined as follows.

When the image mode is "l", which is the softest, as shown in FIG. f=38: is set to 22. Note that the on time (ran) and off time (ro
ff) is determined by a timer value set depending on the image mode.

The output of the recovery bias III (42) is periodically turned on and off according to the on time (ran) + off time (roff), and its effective voltage, the recovery bias voltage (Vss), is V S S = X V p τon + τoff = 38 + 22° (-600) --380 [V] Vp; electric, * (42) peak voltage.

Similarly, as shown in Figure 1o, the image mode is "
3”, on time ffJ (ron) and off time (ro
The ratio of fT) is ran:roff=32:2
Recovery bias voltage (Vss) −320
(V).

Furthermore, as shown in FIG. 11, when the image mode is "5", which is the hardest, the on time (ran) and off time (ro
The ratio of ff) is ran:roff=? 6 : set to 34, recovery bias voltage (V 5s) −260 (
V).

Furthermore, irrespective of the above-mentioned image modes 1'', . .

In this collection mode, the on time (ton) and off time (
The ratio of ron:roff) is set to ron:roff-48:12, and the recovery bias voltage (VsS) −480r
V).

Collection bias voltages (Vss) etc. set corresponding to each image mode and collection mode are shown in the table below.

Table-2 Image van: rorf Vss (V'J VbCV)
△V mode 1 38:22 -380 -150 230
2 35:25 -350 12003
32:28 -320' 1704
29:31 -290 11405 2
8:34 -260 1 110 (recovery)
48:12 -4go l360■, Control Operation of Copying Machine The operation control of this copying machine will be explained below with reference to FIGS. 13 to 15.

(1) Main routine In the main routine shown in FIG.
When the vi source (not shown) is turned on, step (Sl)
In this step, the RAM of the microcomputer (MC) is cleared, the temperature is adjusted, the display on the display section (102), the drive system, etc. are set to the initial state.

In the following step (S2), an internal timer is set to set one routine time for performing the following control, and in step (S3) it is determined whether the copying machine is in a copyable state.

If the copying machine is in a state where copying is possible, in step (S4), signals inputted from various keys on the operation panel (100) are accepted, and in step (S5), the signals selected in the above-mentioned step (S4) are accepted. outputs a collection bias voltage (Vss) corresponding to the selected image mode. On the other hand, if it is in a state where copying is not possible, abnormality processing such as displaying, correcting, and canceling the abnormality location is performed in step (S6).

Next, in step (S7), other processes such as temperature adjustment, display data setting, etc. are executed, and then in step (S8), the end of the internal timer is waited for, and step (S2) is executed.
Return to.

(11) Key manual processing routine FIG. 14 shows the contents of the key manual processing (S4) shown in FIG.
1) is pressed, and print key (IO) is pressed.
If 1) is pressed, the process moves to step (S12) to perform control for copying the number of copies set with the numeric keypad (103), and if the print key (101) is not pressed, the process moves to step (S13). Proceed to.

In step (Sl3), it is determined whether or not the numeric keypad (103) has been pressed. If it has been pressed, the number of multi-copies etc. are set in step (S14), and if it has not been pressed, the process advances to step (S15).

In step (S15), clear/stop cow-(104
) is pressed, and if it is pressed, the multi-copy is canceled or the number of multi-copies is initialized at stop (S16), and if it is not pressed, the Ste knob (S,
Proceed to I7).

In step (S17), it is determined whether the soft key (107) or the hard key (108) has been pressed to switch the image mode, and if it has been pressed, step (S18) is performed.
Set the recovery bias voltage (Vss) to a value according to the image mode set in , and if it is not pressed, step (S
In step 19), other key input processing is performed. Note that other manual processing includes, for example, magnification setting processing and developing device selection processing.

(iii) Recovery bias output routine FIG. 15 shows the contents of the recovery bias output step (S5) of the main routine shown in FIG. 13.

In this routine, it is determined in step (S21) whether or not the main motor of the copying machine is in the on state, and if it is in the off state, in step (S22) the microcomputer (
MC) to the recovery bias power supply (42) is turned off. As a result, the recovery bias was 71J (4
2) is turned off and the recovery bias voltage (VSS) is “OV
” is set.

On the other hand, if the main motor is in the on state, the step (S
In step 23), it is determined whether or not a multi-copy operation is in progress, in which a plurality of copies are made successively from the same original document, and if the multi-copy operation is in progress, the process advances to step (S25). If the multi-copy operation is not in progress, the process proceeds to step (S24), where it is determined whether or not the development operation has been completed.If the development operation is in progress, the process proceeds to Stella 7' (S25), and it is determined whether or not the development operation has ended. If so, proceed to step (S26).

Specifically, as shown in FIGS. 2 and 3, after the scan operation for the last copy sheet is completed under the drive of the main motor and the charger (3) is turned off, step (b) is elapsed. 326), and in other cases, that is, when the slider (13) and exposure lamp (12) are off during development or between image formations in multi-copying (see Figure 3), proceed to step 326). Proceed to (S25).

Note that (τb) is set to be longer than the time it takes for one point on the photosensitive drum (2) to move from the opposing portion of the charger (3) to the opposing portion of the developing device (4).

In step (S25), the duty data during development according to the image mode, that is, the data in Table 2 regarding the ratio of (τon) and (τoff), is read, and in step (S27), the recovery bias power supply (42) is read in. ) output is adjusted.

For example, when image mode “3” is selected, (τ
on) and (τofT) is set to 32:28, the collection bias voltage (Vss) is set to -320V, and the developing bias voltage (Vb) is set to -150V.

In step (326), the above (τon) and (τoH)
The ratio of is set in the recovery mode, and the recovery bias voltage (VSS) is adjusted in step (S27) according to the value. Therefore, as shown in FIGS. 2 and 3, the ratio of the (τon) time becomes higher than that during development, and the recovery bias voltage (Vss) is transformed to -48QV.

Further, the potential difference (△V) between the collection bias voltage (Vss) and the development bias voltage (vb) becomes larger than during development, and some of the toner on the development sleeve (23) is collected by the toner supply roller (30). , the toner density on the developing sleeve (23) is balanced at a low value.

Further, since the recovery bias power supply (42) is turned on and off, the same effect as applying alternating current can be obtained, and the switching of the toner concentration is instantaneously performed.

Therefore, even if vibrations are applied to the developing device (4), copying machine, etc. during non-development, the amount of toner that peels off and falls from the surface of the developing sleeve (23) is significantly reduced, and there is less chance of contaminating the surrounding area. .

, ■, 561. ．． In the above embodiment, the output of the recovery bias power supply (42) is switched to the recovery mode after ([b) time] after the charger (3) is turned off, but the switching timing is For example, the main motor (8), the transfer charger (5), and the separate charger (5) are not limited to the above embodiments.

The recovery bias voltage (Vss) may be switched based on the off timing of (6), or the paper discharge section (
The collection bias voltage (Vss) may be switched after detecting that the last sheet has been discharged in step 16).

Further, in the above embodiment, the present invention is applied to a copying machine, but it is of course applicable to other image forming apparatuses such as reader printers, printers, etc.

Furthermore, in the embodiment described above, a developing bias power source (4I) and a recovery bias power source (42) are provided to adjust the output of the recovery bias power source (42), but it is not necessary to provide separate power sources.

(Effects of the Invention) As is clear from the above description, in the present invention, when the image forming operation is not performed after the development operation is completed,
The ratio of on time and off time of the recovery bias power supply is changed to transform the recovery bias voltage to a high voltage, thereby reducing the toner concentration on the developing sleeve.

Therefore, even if vibration is applied to the developing device during non-development,
There is less risk of toner falling from the developing sleeve, and the interior of the image forming apparatus can be kept more clean.

Furthermore, in the present invention, the above operation is made to exhibit the same effect as AC by turning DC on and off, so an AC high-voltage transformer is not required, and the image forming apparatus is inexpensive, small, and compact. can be provided.

[Brief explanation of the drawing]

Figure 1 is a schematic sectional view of the image forming apparatus, Figure 2 is a timing chart for single copying, Figure 3 is a timing chart for continuous copying, Figure 4 is a sectional view of the developing device, and Figure 5 is a developing sleeve and toner. FIG. 6 is a diagram showing changes in toner density with respect to the potential difference between the toner and the supply roller, FIG. 6 is a diagram showing changes in copy density with respect to original density, FIG. 7 is a partial plan view of the operation panel, and FIG. 8 is a control block. 9 to 11 are waveform diagrams of the recovery bias voltage output from the recovery bias power supply corresponding to the image mode, and FIG. 9 is the image mode "1".
", Fig. 10 shows image mode "3", Fig. 11 shows image mode "5", and Fig. 12 shows a waveform diagram of the recovery bias voltage output from the recovery bias 1! source corresponding to the recovery mode. , FIGS. 13 to 15 are flowcharts showing the control contents. FIG. 13 is the main routine, FIG. 14 is the key manual processing routine, and FIG. 15 is the recovery bias output routine. 2... Photoreceptor drum (static) latent image carrier), 4... developing device, 23... developing sleeve, 30... toner supply roller, 41... developing bias power supply, 42... collection bias power supply, 100... operation panel , 107...
Soft key, 108...Hard key, MC...Microcomputer, vb...Development bias voltage, Vs
s...Recovery bias voltage, Vp...Peak voltage, Δ
V...Potential difference. Patent applicant Minolta Camera Co., Ltd. Agent
Patent attorney, above, and 1 other copyist Figure 7 Figure 8 Figure 9 Prisoner's picture image F1 10th drawing I Emore 3 11th drawing A I#7-d5 5th +2nd drawing L7-d ”won TOff τOn:τ0ffl148
=12 Figure 13

Claims (1)

[Claims] (1) A developing device having a developing sleeve holding a developer made of toner and carrier on its outer periphery, and a toner supply roller facing the developing sleeve, and charging polarity of toner in each of the developing sleeve and the toner supply roller. power supply means for applying a DC voltage of opposite polarity to the toner supply roller and higher than that of the developing sleeve; and power supply means for turning on and off the output from the power supply means to the toner supply roller, and for a predetermined period of time after the development operation is completed. An image forming apparatus characterized by comprising: a control unit that makes a ratio of the on-time of the output larger than that during development if an image forming operation is not started even after a lapse of time.